arXivL_BartBert_modfied.csv

id,gold,pred1,rgL1,pred2,rgL2
astro-ph0202408,"we discuss the optical and radio properties of 30,000 first ( radio , 20 cm , sensitive to 1 mjy ) sources positionally associated within 1.5 arcsec with an sdss ( optical , sensitive to 22.2 ) source in 1230 deg@xmath0 of sky . the matched sample represents 30 % of the 108,000 first sources and 0.1 % of the @xmath1 sdss sources in the studied region . sdss spectra are available for 4,300 galaxies and 1,154 quasars from the matched sample , and for a control sample of 140,000 galaxies and 20,000 quasars in 1030 deg@xmath0 of sky . this large and unbiased catalog of optical identifications provides much firmer statistical footing for existing results and allows several new findings . the majority ( 83 % ) of the first sources identified with an sdss source brighter than = 21 are optically resolved ; the fraction of resolved objects among the matched sources is a function of the radio flux , increasing from 50 % at the bright end to 90 % at the first faint limit . nearly all optically unresolved radio sources have non - stellar colors indicative of quasars . we estimate an upper limit of 5 % for the fraction of quasars with broad - band optical colors indistinguishable from those of stars . the distribution of quasars in the radio flux optical flux plane supports the existence of the quasar radio - dichotomy "" ; 8@xmath21 % of all quasars with i@xmath318.5 are radio - loud and this fraction seems independent of redshift and optical luminosity . the radio - loud quasars have a redder median color by 0.08@xmath20.02 mag , and show a 3 times larger fraction of objects with extremely red colors . first galaxies represent 5 % of all sdss galaxies with @xmath317.5 , and 1 % for @xmath320 , and are dominated by red ( @xmath42.22 ) galaxies , especially those with @xmath417.5 . magnitude and redshift limited samples show that radio galaxies have a different optical luminosity distribution than non - radio galaxies selected by the same criteria ; when galaxies are further separated by their colors , this result remains valid for both blue and red galaxies . for a given optical luminosity and redshift , the observed optical colors of radio - galaxies are indistinguishable from those of all sdss galaxies selected by identical criteria . the distributions of radio - to - optical flux ratio are similar for blue and red galaxies in redshift - limited samples ; this similarity implies that the difference in their luminosity functions , and resulting selection effects , are the dominant cause for the preponderance of red radio galaxies in flux - limited samples . the fraction of radio galaxies whose emission line ratios indicate an agn ( 30 % ) rather than a starburst origin is 6 times larger than the corresponding fraction for all sdss galaxies ( @xmath317.5 ) . we confirm that the agn - to - starburst galaxy number ratio increases with radio flux , and find that radio emission from agns is more concentrated than radio emission from starburst galaxies . # 1@xmath5 # 1@xmath6 # 1 @xmath7 # 1 ( comment : # 1 ) u i","the sdss is producing five - color optical images and photometry for more than 10@xmath8 galactic and extra - galactic sources , as well as spectra for about 10@xmath9 galaxies and 10@xmath10 quasars . we discuss the properties of sources observed by the first and sdss surveys . we use the first survey because it has superior astrometric accuracy , resolution and faint sensitivity limit compared to other contemporary large area radio surveys ( e.g. nvss ) . we use the sdss because it has the best photometric and astrometric accuracy available for a large area optical survey , 5-band data extending from 3000 to 10,000 , and spectra for a large number of extragalactic sources . the largest previous samples of optical identifications for first sources are based on the apm survey . the sample discussed here , with sdss identification for 30,000 first sources , has the advantage of more than five times more accurate optical astrometry and photometry ; it is also about 1 magnitude deeper , and utilizes 5-color , instead of 2-color , optical information . a more detailed study of the optical and radio properties of quasars and galaxies is presented in 4 and 5 , and we discuss our results in 6 . in this section we analyze optical colors and counts , and the distribution of radio - to - optical flux ratio for the 3,225 optically unresolved sdss - first sources ; spectra are available for a subsample of 1,154 objects . we demonstrate that optical colors of radio galaxies are similar to those of all galaxies selected by the same redshift and optical luminosity criteria , despite being markedly different in flux - limited samples . here we present a preliminary determination of the fractions of agns and starburst galaxies using diagnostic diagrams based on the strengths of several emission lines . * we discuss optical and radio properties of 30,000 first sources positionally matched within 1.5 arcsec to an sdss source in 1230 deg@xmath0 of sky . the matched sample represents 30% of the 108,000 first sources and 0.1% of the @xmath1 sdss sources in the studied region . the distributions of optical spectral indices also indicate that spectra of radio - loud quasars tend to be redder than spectra of radio - quiet quasars ( figure [ alphad ] ) . * the sloan digital sky survey ( sdss ) is a joint project of the university of chicago , fermilab , the institute for advanced study , the japan participation group , the johns hopkins university , the max - planck - institute for astronomy ( mpia ) , the max - planck - institute for astrophysics ( mpa ) , new mexico state university , princeton university , the united states naval observatory , and the university of washington . assuming that the observed @xmath40 distribution is applicable to all quasars , it can be utilized , together with optical counts of quasars from other surveys deeper than sdss , to predict the number of quasars detected by first and not detected by sdss .",0.1926701570680628,"we discuss optical and radio properties of 30,000 first sources positionally matched within 1.5 arcsec of an sdss source in 1230 deg@xmath0 of sky. the matched sample represents 30 % of the 108,000 optical first sources detected by the first survey and 0.1 % of all @xmath1 sdss sources in the studied region. sdss spectra are available for 4,300 galaxies and 1154 quasars from this matched sample. we show that the selection efficiency can be increased by combining sdss and first data. the spectral types and optical colors of the matched and unmatched sources are very similar. we find that the optical - to - radio flux ratio, radio - loudness ratio, and radio - quiet quasar fraction are all consistent with that of bright extragalactic radio sources, and lower limits are found for the quasar - quiet fraction ( 5 % ). we identify radio galaxies with optical spectroscopic redshifts ( typical of sdss - type objects ) ranging from 0.3 to 1.6, and red optical spectra for 2.5 magnitudes. the optical luminosity function of radio galaxies is found to be similar to that of all galaxies with the same color, despite being 1 magnitude brighter than other galaxies in flux - limited samples. we analyze optical versus.optical properties of radio sources using multicolor catalogs ( where morphological types are well separated, e.g., c.m., richardson _ et al._2000 ) and examine the distribution of emission line ratios indicative of agn rather than starburst emission, finding that the incidence of merging galaxies and galaxies with disturbed structure is higher among the blue radio galaxies than that of the red radio galaxies. we demonstrate that the integrated optical emission line strengths of galaxies with strong star formation can be used to separate sources with agn emission from galaxies with weak or no emission lines in their spectra. a control sample of 20,085 spectroscopically confirmed sdss objects with sdss colors indistinguishable from those of stars, and qsos from the sdss quasar survey ( the only survey with optical identifications ) is used to estimate the fraction of qsas missing from the sample, where appropriate data are available only for a subset of 1,154 objects in the controlled redshift range discussed in this work. the results are discussed in the context of the large area first and sdss radio surveys. # 1to 0pt#1 # 1 #",0.3017142857142857
1201.6342,"we compute the low energy effective field theory ( eft ) expansion for single - field inflationary models that descend from a parent theory containing multiple other scalar fields . by assuming that all other degrees of freedom in the parent theory are sufficiently massive relative to the inflaton , it is possible to derive an eft valid to arbitrary order in perturbations , provided certain generalized adiabaticity conditions are respected . these conditions permit a consistent low energy eft description even when the inflaton deviates off its adiabatic minimum along its slowly rolling trajectory . by generalizing the formalism that identifies the adiabatic mode with the goldstone boson of this spontaneously broken time translational symmetry prior to the integration of the heavy fields , we show that this invariance of the parent theory dictates the entire non - perturbative structure of the descendent eft . the couplings of this theory can be written entirely in terms of the reduced speed of sound of adiabatic perturbations . the resulting operator expansion is distinguishable from that of other scenarios , such as standard single inflation or dbi inflation . in particular , we re - derive how certain operators can become transiently strongly coupled along the inflaton trajectory , consistent with slow - roll and the validity of the eft expansion , imprinting features in the primordial power spectrum , and we deduce the relevant cubic operators that imply distinct signatures in the primordial bispectrum which may soon be constrained by observations . 1.0 cm * effective theories of single field inflation + when heavy fields matter * 1.0 cm ana achcarro@xmath0 , jinn - ouk gong@xmath1 , sjoerd hardeman@xmath2 , + gonzalo a. palma@xmath3 and subodh p. patil@xmath4 0.5 cm _ @xmath2instituut - lorentz for theoretical physics , universiteit leiden , + @xmath5department of theoretical physics , university of the basque country , 48080 bilbao , spain + @xmath1theory division , cern , ch-1211 genve 23 , switzerland + @xmath3physics department , fcfm , universidad de chile , + @xmath6centre de physique thorique , ecole polytechnique and cnrs , palaiseau cedex 91128 , france + @xmath7laboratoire de physique thorique , ecole normale superiure , paris 75005 , france _ 1.2 cm _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ we dedicate this paper to the memory of our dear colleague and friend , sjoerd hardeman . his ideas , insights and diligence permeate every aspect of this work . _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _","the application of effective field theory ( eft ) techniques to the study of cosmic inflation , constitutes a powerful and systematic approach through which we can calibrate and account for our ignorance of the laws of physics relevant during the very early universe @xcite ( see also ref . trans - planckian concerns notwithstanding @xcite , in many circumstances , from the perspective of the parent theory we are forced to account for the other scales present in the system , which turn out to manifest in the low energy eft in an interesting manner . how much the trajectory deviates off the adiabatic minimum is a function of the mass of the heavy fields which couple to the inflaton , the inflaton velocity ( which must remain consistent with slow - roll ) , and the radius of curvature , @xmath9 , of the trajectory in field space . our goal in this paper is to elucidate the general structure , to all orders in perturbations , of the eft for the adiabatic mode of a theory described by a single effective scalar minimally coupled to gravity at low energies a situation that might be dynamically preferred @xcite . in doing so , we have to be mindful of the fact that notions of adiabaticity have to be generalized to account for the fact that the motion of the inflaton through field space can readily force it off its adiabatic minimum , without interrupting slow - roll , even as the scale of inflation remains far below the scale of heavy physics @xmath8 , and in spite of which a low energy eft description is available and describes the physics of the light modes to the appropriate accuracy . we will show that the couplings of the eft are parametrized entirely in terms of the reduced speed of sound @xmath14 , which we compute in terms of the parameters of the parent theory . qualifying the expectation that @xmath14 can at most be a slowly varying function of time @xcite , or that it can not become too small without violating perturbative unitarity @xcite , we find that it is entirely consistent to have _ transiently _ small speeds of sound induced by _ transient _ strong couplings of various operators in the eft expansion . these are readily generated by turns in the parent theory that cause the background inflaton to deviate off its adiabatic minimum . in spite of this , we are still able to write down an effective theory that captures the relevant physics of the adiabatic mode with the appropriate accuracy , which forces us to consider a generalized notion of adiabaticity that determines the validity of our eft . this generalization is mandated by the fact that there are two distinct ways in which the low energy description accounts for deviations of the inflaton trajectory off its adiabatic minimum in the parent theory . in what follows we attempt to further our understanding of the structure of the single field effective theory derived from parent theories with a single light inflaton among multiple other fields with masses much larger than the scale of inflation . by analyzing the terms of the derivative expansion that emerge from integrating out heavy degrees of freedom , we show that the speed of sound @xmath14 for the adiabatic perturbations emerges as _ the _ salient book - keeping device around which successive terms in the derivative expansion naturally organize themselves . this reduced speed of sound will be a functional of the background inflaton trajectory , itself dependent on the field geometry and the multi - field potential . , we consider the parent theory to consist of a canonical two - field system , where a hierarchy of scales between the masses of the two fields persists along the entire inflationary trajectory . as we discuss shortly , in particular , although we have chosen to work with a canonical two - scalar field model for the benefit of clarity , our treatment is carried out in a geometrically covariant language which allows our results to easy extend to more general setups involving more than two fields or a non - trivial sigma model metric : through field redefinitions , one can always work in a basis where one transforms away the sigma model metric at the expense of introducing derivative interactions ( and corrections to the potential ) , which are easily accounted for . we have attempted to clarify the non - perturbative structure of effective field theories resulting from the integration of heavy fields in multi - field models with a single light field , the inflaton , and a large mass hierarchy . in the particularly simple case of two - field models",0.17712177121771214,"we elucidate the general structure of low energy effective field theory ( eft ) for the adiabatic mode of a theory described by a single effective scalar minimally coupled to gravity at low energies. as a corollary, the nambu - goldstone boson, corresponding to the broken time translation invariance of the parent theory, is shown to be the salient book - keeping device around which successive terms in the derivative expansion naturally organize themselves. by explicitly integrating out the heavy modes, we are able to deduce an effective theory valid to all orders in field perturbations, and which reduces the effective speed of sound for the long wavelength quasi - long wavelengths. when the trajectory of the inflaton is parametrized by the radius of curvature in field space, the resulting eft describes the physics of the underlying parent theory to very high accuracy. in particular, we show that the coupling of the eft expansion to the background inflaton trajectory is strongly dependent on the background trajectory and the mass of the heavy fields that couple to it, generating large levels of primordial non - gaussianity consistent with slow - roll, in contrast to the naive expectation that this variation can be slowly - rolled. by contrast, the perturbative expansion itself can vary rapidly enough ( i.e., too slowly ) in time to cause the lagrangian of the trajectory to change form, violating gauge invariance, even in the limit of large eft amplitudes. these features are signatures of the transient nature of the relevant interactions in the theory, and suggest that additional, potentially observable, effects of these interactions might be detectable. in what follows, we attempt to elucidate further the features of this single field eft approach through a generalization of the framework introduced in a previous paper, with the goal of relating the low energy eft to cosmological observables.",0.223583460949464
physics0611154,"we propose a versatile optical ring lattice suitable for trapping cold and quantum degenerate atomic samples at discrete angular positions . we demonstrate the realisation of intensity patterns generated from laguerre - gauss ( @xmath0 ) modes with different @xmath1 indices . the ring lattice can have either intensity maxima or minima , suitable for trapping in red or blue detuned light , and it can be rotated by introducing a frequency shift between the laguerre gauss modes . the potential wells can be joined to form a uniform ring trap , making it ideal for studying persistent currents and the mott insulator transition in a ring geometry . confining ultracold atomic samples in optical lattices allows the investigation of effects conventionally associated with condensed matter physics within a pure and controllable system . optical lattices have been employed to trap arrays of atoms @xcite as well as bose condensates ( becs ) . important experiments include the investigation of the quantum phase transition from a superfluid to a mott insulator @xcite , and the realisation of arrays of josephson junctions @xcite . of particular interest is the study of quasi 1d systems as quantum effects are strongest at low dimensionality . an effective change of mass and associated lensing have been observed in a moving 1d lattice @xcite . various ring traps for quantum degenerate gasses @xcite have been generated that are in many ways equivalent to an infinite 1d geometry . more recently ring - shaped lattices have been proposed @xcite . optical beams at a frequency far detuned from the atomic or molecular resonance are one of the fundamental tools for the manipulation of cold atoms and becs @xcite . the spatial structure of the intensity distribution creates an energy potential well to trap and hold the target species , either in the high intensity region of red detuned light , or in the low intensity region of blue detuned light . translation of the intensity distribution of the beam can be used to impart a global motion to the trapped atoms / molecules @xcite . arbitrary intensity patterns can be generated using spatial light modulators ( slms ) acting as reconfigurable diffractive optical components , i.e. holograms . most notably slms have been employed to form holographic optical tweezers @xcite where a single laser beam is diffracted to form multiple foci , trapping microscopic objects in complex 3d geometries @xcite . very recently , slms have also been used to manipulate single atoms @xcite and becs @xcite . however , the nature of nematic liquid crystal devices means that most slms are limited in their update rate to around @xmath2hz , and even those based on ferroelectric configurations are limited to @xmath3khz @xcite . in this paper we establish a method for creating both positive and negative optical potentials that can be rotated around the beam axis at frequencies ranging from a few mhz to 100 s of mhz optical ferris wheels for atoms or becs . the barriers between the individual potential wells can be controlled allowing the mott transition from a ring lattice to a uniform ring trap .","we demonstrate the diffraction controlled generation of dynamic laguerre - gauss ( lg ) lattices. by exciting two pairs of lg beams with frequencies separated by a few mhz, we demonstrate the rotational generation of dark lattices with an intensity pattern rotating at an angular frequency of one or two @xmath0s of mhz. furthermore, by subjecting cold atoms to the dark or bright lattice, they can be trapped in the resulting light potential. in order to show the experimental feasibility of the scheme, we consider a setup combining an optical lattice with a quadrupole magnetic trap. interactions between light waves in a lattice are important for many areas of physics, including condensed matter physics, atomic physics and cosmology. the interaction between a light beam and an atomic lattice has fundamental and practical importance, in particular in the development of spintronic devices and optomechanics. the behaviour of light in lattices of different intensities has been investigated extensively @xcite and various theoretical models have been developed. by creating a diffraction dominated lg beam and passing light through a two - level dipole potential, it is possible to generate a bright lg lattice and a dark lattice simultaneously. this is possible not only for individual atoms, but also for large ensembles of light and dark particles, leading to the possibility of a hybrid lattice structure. a particularly interesting case is that of ultracold atoms, which can be confined in a ring lattice by an appropriate laser potential and then recombine to form a bright elliptical lattice. in this case the phase difference between the two light beams is practically zero and the intensity pattern can be rotationally propagating through the lattice at a rate that is comparable to the spin of a few 1000 particles a year. more recently, vortices have been proposed as an alternative alternative to lattices and have been demonstrated experimentally with atoms in a double - well dipole trap @xcit. the use of lattices has been suggested to play a major role in future cooling of atoms, and it has been shown that diffraction - controlled heating of an atomic crystal can also be employed for the creation of optical lattices @xcited. a further route to a quantum lattice is to to create an entanglement between two opposite light beams, which then rub against each other at the potential. for the latter case, the phase of the incident light beam is determined by the intensity gradient of the first order laser beam, and the",0.19441340782122904,"laguerre - gauss ( lg ) beams have an azimuthal phase dependence @xmath4 the center of these beams contains a phase singularity ( optical vortex ) where intensity vanishes . by overlapping two co - propagating lg beams with different @xmath1-values @xmath5 and @xmath6 , the beams interfere constructively at @xmath7 azimuthal positions , separated by regions of destructive interference , leading to a transverse intensity profile comprising @xmath7 bright or dark petals . an angular frequency shift of @xmath8 between the lg beams introduces an angular petal rotation rate of @xmath9 @xcite . the gaussian beam from a helium - neon laser is divided and double passed through two aoms , leading to laser beams with an angular frequency difference of @xmath8 . by subjecting cold atoms to the dark or bright ring lattice described above , they can be trapped in the resulting light potential . in order to limit losses due to photon scattering we assume a light beam far detuned from the atomic resonance . the coldest atoms are trapped at dark lattice sites and scattering will be negligible even the hottest atoms only scatter a photon every @xmath88s . the optical lattice potential is sufficient to provide confinement in the transverse direction . to additionally localise atoms in the axial @xmath89 direction we suggest a hybrid trap , combining the optical lattice with a quadrupole magnetic trap @xcite . for the red lattice one could consider all - optical confinement in a tightly focused lattice with a short rayleigh range , but there is a trade - off between axial confinement and scattering rate circularly polarised lg lattice beams are required to maintain the symmetry between the quadrupole magnetic field and the light field and obtain a uniform ring lattice potential . our hybrid ring lattice enables the observation of the mott insulator transition in a geometry with periodic boundary conditions . to adjust the barrier depth , and hence the tunneling between sites , the relative power @xmath95 in the @xmath96 beams experimentally , this can easily be achieved by varying the modulation amplitude of both aoms while keeping the overall light intensity constant . to make full use of all laser power , an electro - optic modulator could be used to rotate the polarisation from the laser incident on a polarising beamsplitter leading to the two aoms . images from our optical experiment are shown in fig . the transition between uniform and multi - petalled ring is achieved by gradually dimming the outer lg beam , and outer transverse confinement is then provided by the magnetic potential ( fig . this constraint is much higher than the critical rotation rate for vortex creation in 1d @xmath103rad / s for our parameters . we have experimentally obtained both bright and dark optical ring lattices , with tunable barriers between sites , and with a tunable rotation rate . furthermore we have shown that , in combination with a magnetic trap , these lattices will be ideal for studying quantum degenerate gases . future applications of the lattice include studies of : persistent currents , rotation of a `` quantum register , '' collisional studies using two counter - propagating rings .",0.16666666666666666
0810.1844,"the analysis of the third _ integral_/ibis survey has revealed several new cataclysmic variables , most of which turned out to be intermediate polars , thus confirming that these objects are strong emitters in hard x - rays . here we present high energy spectra of all 22 cataclysmic variables detected in the 3rd ibis survey and provide the first average spectrum over the 20100 kev band for this class . our analysis indicates that the best - fit model is a thermal bremsstrahlung with an average temperature of @xmath0 @xmath122 kev . recently , eleven ( ten intermediate polars and one polar ) of these systems have been followed - up by _ swift_/xrt ( operating in the 0.310 kev energy band ) , thus allowing us to investigate their spectral behaviour over the range @xmath10.3100 kev . thanks to this wide energy coverage , it was possible for these sources to simultaneously measure the soft and hard components and estimate their temperatures . the soft emission , thought to originate in the irradiated poles of the white dwarf atmosphere , is well described by a blackbody model with temperatures in the range @xmath160120 ev . the hard emission , which is supposed to be originated from optically thin plasma in the post - shock region above the magnetic poles , is indeed well modelled with a bremsstrahlung model with temperatures in the range @xmath11633 kev , similar to the values obtained from the _ integral _ data alone . in several cases we also find the presence of a complex absorber : one totally ( with @xmath2 @xmath3 ) and one partially ( with @xmath4 @xmath3 ) covering the source . only in four cases ( v709 cas , gk per , igr j06253 + 7334 and igr j173030601 ) , we find evidence for the presence of an iron line at 6.4 kev . we discuss our findings in the light of the systems parameters and cataclysmic variables / intermediate polars modelling scenario . [ firstpage ] stars : novae , cataclysmic variables gamma - ray : observations x - ray : binaries","we present a spectral analysis of the entire sample of cataclysmic variable ( cv ) systems detected by _ integral_. eleven systems have been observed by _ swift_/xrt, four by _ ibis _ /xrt and one by _ xmm - newton _ / gk per. we cross - correlate the bremsstrahlung emission ( @xmath0 kev ) and the 20100 kev flux, making use of both _ integral _ and ibis data. this allows us to investigate the spectral complexity of the emission, in particular the presence of a boundary layer between the accretion disk and the wd surface. we confirm a temperature for the hard x - ray emission at around 25 kev, without claiming an emission reflection component, as reported by de martino et al. for magnetic cvs. this temperature is quite close to the temperatures of the post - shock region in polar cvs, suggesting that the emission does not come from a converging stream. concerning the temperature of the soft gamma - ray component, we find that it too radiates at an extremely low energy, as found by others. however, this emission is much less powerful than in the polars, implying that these polars are not strong emitters above 10 kev. this result seems to be consistent with previous indications that the high energy spectra of the most powerful hard x- ray emitters are not dominated by cyclotron emission but by blackbody emission. furthermore, we confirm that the non detection of a blackbody component in some of these systems is likely to be related to the lack of radial accretion flow. we find no significant correlations between the spectral parameters of the source and the degree of synchronisation of the white dwarf. [ firstpage ] binaries : general binaries : close x - rays : stars.",0.2153846153846154,"we present ibis spectral analysis of the entire sample of cvs detected by _ we have analysed _ integral _ data of a sample of 22 hard x - ray selected cvs , the majority of which are ips . we confirm previous indications that the high energy spectra of these type of objects are well described by either a bremsstrahlung model with @xmath19 in the range 756 kev or a power law with @xmath18 in the range 2.13.5 ; however , the average _ integral _ spectrum of all 22 cvs is significantly better fitted by the bremsstrahlung model with an average temperature of 22 kev . confirmation that ips are the most powerful soft gamma - ray emitters within the cv population is an important result defined from _ integral _ observations . the lack of emission above a few tens of kev from a large set of non - magnetic white dwarf binaries and synchronised polars is also an interesting information . for non - magnetic cvs the non detection of high energy emission , the fact that ips are high energy emitters and polars are not suggests that the onset of emission above 10 kev requires some level of synchronisation of the orbital and spin periods , but then the high energy radiation is less likely to be observed when full synchronisation sets in . half of the sources in the sample have also x - ray data available so that the low energy emission could be parametrized in terms of a blackbody model with well constrained temperatures in the range 60120 ev . extra features to this baseline model have been found in a few sources such as an iron line at 6.4 kev in four sources and an extra thermal component in one object . both soft and hard components are viewed through two layers of neutral absorbing material : the first seen in all 11 objects totally covers the emitting region , while the second , seen in @xmath170% of them , only partially covers the source . we also searched for correlation between the system values and soft x - ray emission parameters but again found none . the measured x - ray ( 210 kev ) and soft gamma - ray ( 20100 kev ) luminosities are found to span from 10@xmath57 to 10@xmath58 erg s@xmath8 ; their ratios span from 0.02 to 7.5 with an average at around 1.3 , but only when gk per , with a ratio of @xmath138 , is discounted . gk per stands out in the sample because it has a considerably longer orbital period than the rest of the group and , by a considerable margin , the highest x - ray to gamma - ray flux ratio . the bolometric luminosities of the blackbody emitting components have corresponding emitting areas in the range @xmath59 to @xmath1@xmath60 @xmath61 , with gk per and fo aqr located at the top end of the range . from the available values of the wd mass , we estimate that the observed blackbody emitting area covers from @xmath1@xmath62 to @xmath1@xmath63 of the wd surface . finally , it is important to underline that a unique baseline model has been able to describe the broad - band ( 0.3100 kev ) data of half the sample of _ integral _ detected objects . this model is consistent with the standard ip scenario , where thermal emission originating in the irradiated poles of the wd atmosphere provides the soft x - ray component , while emission in the post - shock region above the magnetic poles gives rise to the thermal bremsstrahlung component ; this emission is absorbed within the accretion flow and is possibly reflected by the wd surface , hence the production of iron line features .",0.1763392857142857
1202.4614,"we selected a sample of 437 bl lac objects , taken from the romabzcat catalogue , for which spectroscopic information and sdss photometry is available . we propose a new classification of bl lacs in which the sources type is not defined only on the basis of the peak frequency of the synchrotron component in their spectral energy distribution ( types l and h ) , but also on the relevance of this component with respect to the brightness of the host galaxy ( types n and g , for nuclear or galaxy dominated sources ) . we found that the sdss colour index @xmath0=1.4 is a good separator between these two types . we used multiband colour - colour plots to study the properties of the bl lac classes and found that in the x - ray to radio flux ratio vs @xmath0 plot most of the n ( blue ) sources are located in a rather narrow strip , while the g - sources ( red ) are spread in a large area , and most of them are located in galaxy clusters or interacting systems , suggesting that their x - ray emission is not from a genuine bl lac nucleus but it is related to their environment . of the about 135 sources detected in the @xmath1 rays by fermi - gst , nearly all belong to the n - type , indicating that only this type of sources should be considered as genuine bl lac nuclei . the @xmath2 , @xmath3 plot of sources detected in the 2mass catalogue is consistent with that of the ` ` bona fide '' bl lac objects , independently of their n or g classification from the optical indices , indicating the existence in g - type sources of a k - band excess possibly due to a steep , low frequency peaked emission which deserves further investigations . we propose to use these colour plots as a further tool for searching candidate counterparts of newly discovered high - energy sources . [ firstpage ] galaxies : active : bl lac objects","we have studied a sample of 937 bl lac objects extracted from the roma - bzcat catalogue of blazars using a direct approach to the identification of them by means of spectral data in different frequency ranges, in the two - year @xmath0-band sky coverage covered by the sloan digital sky survey ( sdss ). we derived distinction criteria for n and g - type bl lacs from among the 937 sources already catalogued in the 2fgl dataset, to identify their physical properties and environments. in addition to the known l and g classes, we defined three subsamples of sources detected in the near infrared, including sources in the x - ray band, which allows to evaluate the relative power of the nuclear emission to host galaxy. the general accepted assumption that a bl lac is an active nucleus of a galaxy is reviewed, along with other commonly used criteria, and it is shown that the frequency range where the emission is dominated by non - thermal processes and boosted by relativistic motions is not always considered a good tool for properly classifying this type of agns. in particular, an accurate measurement of the ca h&k spectral break contrast is not available in the literature and data are often confused with an estimate of the dilution of the break. as a consequence, rather large numbers of sources are found to have an unresolved emission from a nuclear nucleus, that can not be explained by a simple power law. the large majority of sources in our sample are of h - type as apparent from the large bump between 1 and 10. however, the fraction of l sources is rather small, despite being the largest, due to the fact that they are located in clusters or groups of galaxies. several caveats are identified in the existing surveys, including the very small flux limit of the sdss at about 4000 4000 and the possibility of contamination of some sources by emission from nearby emission or from faint radio sources. these uncertainties and the nature of some rather vague emission lines are discussed. an extensive comparison of the bl lac population with that of other active galactic nuclei ( agns ) is also presented. bl lacertae objects : general galaxies : active galaxies : emission line, galaxies : seyfert x - rays : galaxies",0.21511627906976746,"it is important , therefore , to perform an extended comparative analysis of the results of recent surveys to establish safe criteria for defining the bl lac characteristics . in this paper we study a sample of bl lacs extracted from the roma - bzcat catalogue of blazars ( massaro et al . the master sample of bl lac objects used in our classification study was extracted from the 3rd edition of the roma - bzcat . therefore , we defined three subsamples including sources detected in the near ir , and x - ray , and @xmath1-ray band . multifrequency observations have shown that the spectral energy distribution ( sed ) of bl lac objects is characterised by two broad features . we recall that a diffrence between all the considered sources and normal elliptical galaxies is that the former ones have a nuclear radio emission , that could be related to the @xmath48 band excess : for instance , when the synchrotron component peaks at a rather low frequency and is sufficiently curved . the most important result of our analysis is the assessment of more precise observational criteria to define the properties of bl lac objects . in addition to the known l and h classes , we introduced the n and g classes to take into account the relative power of the nuclear emission to host galaxy . with the general accepted statement that a blazar , and more specifically a bl lac , is an active nucleus of a galaxy whose emission is dominated by non - thermal processes and boosted by relativistic motions , it is important to know if the nucleus is or not bright enough to overcome the host galaxy contribution , at least in frequency ranges where the latter is typically low , in particular , at frequencies higher than the ca h&k break . in fact , the contrast is based on measures of the source flux in rather small wavelength intervals on the two sides of the break , and does not takes properly into account if the nuclear emission turns out or not to be the dominant one for increasing frequencies . under this respect , the 77 g - type bl lac objects reported in table 1 were discovered in many surveys , confirming that these rather broad selection criteria are largely adopted and that the possibility of considering galaxies without a clear evidence of relativistic beaming as genuine bl lac objects is not negligible . the presence of a faint radio emission could be due to an origin different from a beamed relativistic jet and , therefore , can not be considered a definitive test . several other types of agns , e.g. radio galaxies , seyfert galaxies , etc ... are radio emitting with a large spread of power , but they do not exhibit blazar properties . as for concerning multifrequency studies , our analysis demonstrates that the detection of an x - ray flux from the direction of the candidate blazar can be confusing if the source environment is unknown . values beyond these limits do not exclude the blazar nature of the object , but they must be considered as a clear indication that further investigations are necessary . we expect , therefore , that the use of mid - infrared photometry will be a very promising and powerful tool to distinguish n and g sources , to gain more information on the non - thermal nuclear emission and the distributions in the @xmath65 , @xmath66 plane . the second problem is the search for possible counterparts in the error boxes of @xmath1-ray sources . in the lat catalogues ( 1fgl ,",0.1970217640320733
1102.2202,"we investigate the fermionic condensate and the vacuum expectation value of the energy - momentum tensor for a massive fermionic field in the geometry of two parallel plate on the background of minkowski spacetime with an arbitrary number of toroidally compactified spatial dimensions , in the presence of a constant gauge field . bag boundary conditions are imposed on the plates and periodicity conditions with arbitrary phases are considered along the compact dimensions . the nontrivial topology of the background spacetime leads to an aharonov - bohm effect for the vacuum expectation values induced by the gauge field . the fermionic condensate and the expectation value of the energy - momentum tensor are periodic functions of the magnetic flux with period equal to the flux quantum . the boundary induced parts in the fermionic condensate and the vacuum energy density are negative , with independence of the phases in the periodicity conditions and of the value of the gauge potential . interaction forces between the plates are thus always attractive . however , in physical situations where the quantum field is confined to the region between the plates , the pure topological part contributes as well , and then the resulting force can be either attractive or repulsive , depending on the specific phases encoded in the periodicity conditions along the compact dimensions , and on the gauge potential , too . applications of the general formulas to cylindrical carbon nanotubes are considered , within the framework of a dirac - like theory for the electronic states in graphene . in the absence of a magnetic flux , the energy density for semiconducting nanotubes is always negative . for metallic nanotubes the energy density is positive for long tubes and negative for short ones . the resulting casimir forces acting on the edges of the nanotube are attractive for short tubes with independence of the tube chirality . the sign of the force for long nanotubes can be controlled by tuning the magnetic flux . this opens the way to the design of efficient actuators driven by the casimir force at the nanoscale .","hence , it has to be taken into account in any self - consistent formulation of the braneworld dynamics . the casimir energy and corresponding casimir forces within the framework of the randall - sundrum braneworld @xcite the casimir effect in higher dimensional generalizations of the randall - sundrum model with compact internal spaces has been investigated in @xcite . in the present paper we will study the fermionic condensate , the casimir energy density and the vacuum stresses for a massive fermion field in the geometry of two parallel plates on a spacetime with an arbitrary number of toroidally compactified spatial dimensions . we will impose generalized periodicity conditions along the compact dimensions with arbitrary phases and mit bag boundary conditions on the plates . are computed in the limit that the background becomes concentrated at two points . the fermionic casimir effect for parallel plates with imperfect bag boundary conditions modelled by @xmath2-like potentials is studied in fosc08 . the topological casimir effect and the vacuum expectation value of the fermionic current for a massive fermionic field in a spacetime with an arbitrary number of toroidally compactified spatial dimensions the vacuum expectation value of the energy - momentum tensor is investigated in sect . [ sec : nano ] we study applications of the general formulas to the casimir effect for electrons in a carbon nanotube , within the framework of a 3-dimensional dirac - like model . the main results of the paper are summarized in sect . in this paper we have considered the effect of compact spatial dimensions on the fermionic condensate and vev of the energy - momentum tensor for a massive fermion field in the geometry of two parallel plates on which the field obeys mit bag boundary condition . along the compact dimensions , we have assumed periodicity conditions ( [ bc ] ) with constant phases @xmath183 . , we have been able to explicitly extract and separate , in a cutoff independent way , the purely topological part and the contributions induced by the single plates . @xcite , and here we have been mainly concerned with the boundary induced parts . in a @xmath4-dimensional spacetime with spatial topology @xmath184 and with two parallel boundaries , the casimir densities for the two - plate geometry in conformally - flat spacetimes with compact spatial dimensions are obtained from the results above simply by using standard conformal transformation techniques . [ sec : nano ] , we have applied our general results to the electrons in finite - length graphene nanotubes . the long - wavelength excitations of this system is basically described by dirac s theory , with the fermi velocity playing the role of speed of light . the corresponding expressions for the fermionic condensate and for the casimir densities are obtained from the results of the preceding sections by summing the contributions of the two triangular sublattices of the honeycomb lattice of the graphene sheet , with opposite signs of the phases along the compact dimension . in the presence of a magnetic flux ,",0.2989949748743719,"the fermionic condensate and vacuum expectation value of the energy - momentum tensor for a massive fermion field in the geometry of two parallel plates on a spacetime with an arbitrary number of toroidally compactified spatial dimensions are investigated. we impose generalized periodicity conditions along the compact dimensions with arbitrary phases and mit bag boundary conditions on the single plates. the presence of a constant gauge field is assumed as well. the total casimir energy @xmath0 is computed and related to the periodicity period of the plates. it is found that, in the asymptotic case, the topological volumetric density of the fermions is a function of the radius of the background spacetime and is independent of the topology of the spacetime. the variance of the vacuum fluctuations in the region between the plates is described by the eigenfunctions and eigenmodes of the dirac equation in the case when the field is massive. in the limit of a small ratio of the dimensionless massless field to the size of the space of compact spatial dimensions, the main contribution to the casimir force resulting from the magnetic field is given by a spinor field coupled to the bosonic background field and its pressure. for a non - massive field, the bulk field gives a contribution acting as the source in einstein s equations. this contribution is insignificant in most cases. it can, however, be detected and subtracted analytically in certain limiting cases. the vacuum expectables of electrons in carbon nanotubes can be modeled as the sum of a pure topological contribution and interference parts due to the different thickness of the nanotube and the role played by the carriers of the electron energy in the nanowire. the interference parts are given by the density of electron - phonon pairs and the plasma - electrodynamical interactions in the ultracold isotropic case. for the case of a chiral background, the vacuum exioms in the tristability limit give rise to casimir - type contributions to the vacuum expectation values of physical observables. these can be interpreted as the amplitudes for the radionuclidean and super - amplitudes of the photon, as well as for the vacuum potentials and dark energy.",0.3328467153284672
1011.1733,"we present comprehensive catalogs of hot star candidates in the milky way , selected from galex far - uv ( fuv , 1344 - 1786 ) and near - uv ( nuv , 1771 - 2831 ) imaging . the fuv and nuv photometry allows us to extract the hottest stellar objects , in particular hot white dwarfs ( wd ) , which are elusive at other wavelengths because of their high temperatures and faint optical luminosities . we generated catalogs of uv sources from two galex s surveys : ais ( all - sky imaging survey , depth abmag@xmath019.9/20.8 in fuv / nuv ) and mis ( medium - depth imaging survey , depth @xmath022.6/22.7mag ) . the two catalogs ( from galex fifth data release ) contain 65.3/12.6 million ( ais / mis ) unique uv sources with error@xmath1@xmath20.5mag , over 21,435/1,579 square degrees . we also constructed subcatalogs of the uv sources with matched optical photometry from sdss ( seventh data release ) : these contain 0.6/0.9million ( ais / mis ) sources with errors @xmath20.3mag in both fuv and nuv , excluding sources with multiple optical counterparts , over an area of 7,325/1,103 square degrees . all catalogs are available online . we then selected 28,319 ( ais ) / 9,028 ( mis ) matched sources with fuv - nuv@xmath3 - 0.13 ; this color cut corresponds to stellar hotter than @xmath018,000 k ( the exact value varying with gravity ) . an additional color cut of nuv-_r_@xmath40.1 isolates binaries with largely differing s , and some intruding qsos ( more numerous at faint magnitudes ) . available spectroscopy for a subsample indicates that hot - star candidates with nuv-_r_@xmath30.1 ( mostly ` ` single '' hot stars ) have negligible contamination by non - stellar objects . we discuss the distribution of sources in the catalogs , and the effects of error and color cuts on the samples . the density of hot - star candidates increases from high to low galactic latitudes , but drops on the mw plane due to dust extinction . our hot - star counts at all latitudes are better matched by milky way models computed with an initial - final mass relation ( ifmr ) that favours lower final masses . the model analysis indicates that the brightest sample is likely composed of wds located in the thin disk , at typical distances between 0.15 - 1kpc , while the fainter sample comprises also a fraction of thick disk and halo stars . proper motion distributions , available only for the bright sample ( nuv@xmath318 mag ) , are consistent with the kinematics of a thin - disk population . [ firstpage ] astronomical data bases : catalogues stars : white dwarfs stars : evolution galaxy : stellar content ultraviolet : stars galaxies : milky way","we present the first quantitative analysis of the population of hot white dwarfs ( wds ) in the milky way, based on far - uv ( fuv, 1344 - 1786, @xmath0 = 1538.6 ) photometry obtained with the galaxy evolution explorer ( galex ). our photometric database contains about 40,000 hot - star candidates, mostly in the fuv range 0.8@xmath1 - 0.13, with photometric errors mostly from sdss ultra - violet ( uv ) imaging. matched optical photometry from the sloan digital sky survey ( sdss ) is used to construct ` ` cleaned '' catalogs of more than 13,000 uv sources, from which we extract hot star candidates with fuv - nuv discontinuity and nuv photometric error smaller than 0.3mag. these sources are used to carefully characterize the hot - wd population, to validate the initial - final mass relation ( ifmr ), and to study the galactic disk and halo geometry. we find that current models of mw geometries match the data well at intermediate latitudes ( 0.15 - 1 kpc ), but are somewhat discrepant at low latitudes and faint magnitudes. we explore, for the first time, multiple thin disk and thick disk components, emphasizing in this work the important implications of different ifmr, as our data are spread over a much larger sky area than was previously possible. the data show a slight but significant asymmetry between mw and sdss models with canonical geometry for stars and dust match, and the data at northern and southern galactic latitudes are better constrained by our data. we analyze the density of hot wds as a function of magnitude using the trilegal stellar population synthesis code, and find that the majority of our candidates are within 2 - 4 kpc from the plane, with a small spread in mass and a distribution of masses. the small offset in stellar density and mass - to - light ratio between the thick and thin disk components indicates that the thick disk is more widely mixed with the cold, metal - rich material than the thin disk, perhaps as a result of mixing of dust and gas from the uv - bright part of the interstellar medium ( ism ).",0.19235836627140973,"our present work provides a selection of hot - star candidates from uv photometry ; about 40,000 hot - star candidates with fuv , nuv photometric errors@xmath20.3mag ( about 74,000 with photometric errors@xmath20.5mag ) have also sdss optical photometry . the catalog covers different latitudes and enables a first analysis of this stellar population with milky way models . we describe the method used to construct `` clean '' catalogs of unique uv sources from two galex surveys with different depths and coverage , and subsets of these catalogs with matched optical photometry , and we present the catalogs characteristics . in section [ s_catalog ] we analyze the density of hot stellar candidates as a function of magnitude ; the samples are divided in strips of 10@xmath9 galactic latitude , in order to examine the structure of this mw stellar component . our hot - star census based on the uv sky surveys provides the first opportunity to examine a comprehensive , unbiased sample of such objects . we analyze the number counts and sky distribution of our hot star candidates , using the trilegal stellar population synthesis code ( girardi et al . 2005 ) . the galex surveys ais and mis cover different latitudes at their respective depths ( @xmath021 and @xmath023 ab mag ) , enabling a first quantitative analysis of the hot - wd stellar population with milky way models . current descriptions of mw stellar components ( halo , thin and thick disk ) are mostly based on stellar counts of low mass ( @xmath30.8 ) stars ( 2mass , shallow but all - sky , plus a few deep but area - limited surveys ) . we explored in this work different thin disk geometries and different ifmr . galex provides an unprecedented census of the evolved descendants of 0.8 - 8stars , and the analysis of our current hot - wd sample places some constraints on the initial - final mass relation ( ifmr ) , one of the crucial ingredients to understand the chemical enrichment of the ism . this work is based on the analysis of matched galex - sdss sources , and the sdss magnitude limit prevents analysis of thick - disk and halo components . finally , hot - wds in binaries , again elusive at optical wavelengths , are uniquely and unambiguously revealed and characterized by the galex uv sky survey , matched to optical surveys . the present catalog of `` single '' hot star candidates has a high purity , as estimated from the serendipitous ( but not unbiased ) spectroscopic sdss coverage . while we expect most of the hottest sources to be high gravity objects ( cspn , subdwarfs or wd ) , we did not apply any cut in gravity , therefore main sequence stars and supergiants hotter than @xmath018,000k are also included in our catalogs . finally , we remind future users of our catalogs that galex uv sources with more than one optical counterpart were excluded from the analysis of the hot - star sample , ( and should be excluded from any sample based on photometric color selection ) , but their fraction can be corrected statistically using table [ t_stats ] .",0.17303370786516853
astro-ph0207385,"it is widely believed that the optical / uv continuum of quasars ( the ` ` big blue bump '' ) represents optically thick thermal emission from accretion onto a black hole . narrow line radio galaxies do nt show such a component directly , and were historically thought for that reason to be rotation - powered , with large kinetic luminosity in the radio jets but very little accretion or optical radiation . when the unified model came along , identifying at least some narrow line radio galaxies as hidden quasars , the compelling observational motivation for this radio galaxy scenario lost some of its force . however , it is far from clear that all narrow line radio galaxies contain hidden quasar nuclei . the clear sign of a hidden quasar inside a radio galaxy is the appearance of quasar spectral features in its polarized ( scattered ) light . however that observational test requires suitably placed scattering material to act as a mirror , allowing us to see the nuclear light . a rather robust and more general test for a hidden quasar is to look for the predicted high mid - ir luminosity from the nuclear obscuring matter . the nuclear waste heat is detected and well isolated in the nearest narrow line radio galaxy , cen a. this confirms other indications that cen a _ does _ contain a modest quasar - like nucleus . however we show here that m87 _ does not _ : at high spatial resolution , the mid - ir nucleus is seen to be very weak , and consistent with simple synchrotron emission from the base of the radio jet . this fairly robustly establishes that there are ` ` real '' narrow line radio galaxies , without the putative accretion power , and with essentially all the luminosity in kinetic form . next we show the intriguing mid - ir morphology of cygnus a , reported previously by us and later discussed in detail by radomski et al . ( 2002 ) . all of this mid - ir emission is consistent with reprocessing by a hidden quasar , known to exist from spectropolarimetry by ogle et al . ( 1997 ) and other evidence . subject headings : galaxies : active galaxies : individual ( m87 , cen a , 3c 405 , 3c 273 ) infrared : galaxies","in this paper we present diffraction limited mid - infrared ( 11.7@xmath0 m ) imaging of the central 0.056 of the powerful fr ii radio galaxy in 3c 405 ( cygnus a ), obtained with the long wavelength spectrometer ( lws ) instrument at the keck i telescope. we clearly detect a thermal infrared bump in the sed, which is a clear signature of a nonthermal active galactic nucleus ( agn ). the strong thermal emission comes from the base of the radio lobe, where reradiation of the absorbed light from the dusty obscuring matter ( torus ) occults the jet. the torus is expected to become optically thick over much of the obscuring region, allowing the pc scale jet emission to be seen over the top. this is a characteristic feature for optically dull agn, in which case the jet power and optical / uv luminosity are comparable to those in double radio quasars. thus this radio galaxy is a moderate luminosity broad line radio galaxy with a very high luminosity radio source. the mid - ir power is @xmath1 ergs / s, a factor of 3 larger than in double fr i radio galaxies with similar luminosities in the hard x - ray ( e.g., m87, ngc 4594 ). we also show that the dust component is not very well isolated in the infrared sed. in fact, a partial spectral energy distribution is found, with a central dominant component that can be approximated by variable synchrotron emission. these findings are consistent with the suggestions by chiaberge et al. for a large number of fainter narrow line radio galaxies, there is no _ a priori _ evidence for the presence of a quasar based on their interpretation of the various emission features. this situation is even less clear for the fr i galaxies, almost all of which have undetectable or low - ionization emission lines. for example, there are only a few in the literature with such low luminosity nuclear sources, the majority of which are believed to be hidden agn. we briefly discuss the implications of our results for the currently active fr i and fr ii galaxies, and in particular m87.",0.17151162790697672,"now that the existence of supermassive black holes in agn seems fairly secure , perhaps the next most fundamental questions are the sources of energy and the nature of the accretion flow in the various classes of objects . scenario the optical point sources represent synchrotron emission from the bases of the jets . in support of this idea our approach here is to look instead for reradiation of the absorbed light from any hidden quasar - like nucleus by the dusty obscuring matter ( torus ) . the high resolution mid - ir data on cen a also come from the keck i telescope . this is consistent with the 10 - 20 micron nuclear spectrum taken by isocam cvf in a @xmath13 aperture ( mirabel et al the starbust contribution to the nuclear 11.7@xmath1 m emission is expected to be small , but this should be checked with a spectral slope measurement . the conclusion is simple and expected from prior evidence : cyg a has a moderately powerful hidden nucleus . as noted above , the estimated bolometric luminosity is @xmath40 erg / s . for comparison the jet power this is well explained qualitatively by the fact that it is the only known fr ii radio source in a rich x - ray - emitting cluster . a goal of this paper is to detect thermal ir bumps , often in the presence of a synchrotron continuum . in general thus we thought it would be helpful to show a well observed object which clearly isolates a nonthermal infrared bump from a broadband nonthermal component . blazar radio sources are typically dominated over most of their sed by variable synchrotron emission ( and/or inverse compton bump in the x - ray - @xmath42-ray region ) . thus the infrared consists almost entirely of the broadband nonthermal and the ( relatively ) narrow band thermal components . radio lobe emission is fairly isotropic , so it s easy to make lists of double radio sources that are nearly unbiased with respect to orientation . the visibility of optical point sources in _ most _ of the optically dull ( weak or low ionization emission line ) crucial tests of the nature of the optical point sources can be made with spectroscopy and polarimetry . it s been difficult to find fr i objects with strong evidence for hidden agn , but in fact at least a few are known to be quasar - like from direct spectroscopy ( 3c120 is well known ; see also lara et al . the fr class has no apparent _ direct _ relation to the mode of energy production , consistent with much recent evidence that fr is behave very much like fr iis at vlbi scales .",0.16775884665792926
1702.03606,"a finite abstract simplicial complex @xmath0 defines two finite simple graphs : the barycentric refinement @xmath1 , connecting two simplices if one is a subset of the other and the connection graph @xmath2 , connecting two simplices if they intersect . we prove that the poincar - hopf value @xmath3 , where @xmath4 is the euler characteristics of the unit sphere @xmath5 of a vertex @xmath6 in @xmath1 , agrees with the green function @xmath7 , where @xmath8 is the adjacency matrix of the connection graph @xmath2 of the complex @xmath0 . by unimodularity @xmath9 , the fredholm matrix @xmath10 is in @xmath11 , where @xmath12 is the number of simplices in @xmath0 . we show that the set of possible unit sphere topologies in @xmath1 are combinatorial invariants of the complex @xmath0 , and establish so that also the green function range of @xmath0 is a combinatorial invariant . the unit sphere character formula @xmath13 applies especially for the prime graph @xmath14 and prime connection graph @xmath15 on square free integers in @xmath16 playing the role of simplices . in @xmath14 , integers @xmath17 are connected if @xmath18 or @xmath19 and where in @xmath15 two @xmath17 are connected if @xmath20 . the green function @xmath21 in @xmath15 relate there to the index values @xmath22 in @xmath14 . to prove the invariance of the unit sphere topology we use that all unit spheres in @xmath1 decompose as @xmath23 , where @xmath24 is the join and @xmath25 is a sphere . the join renders the category @xmath26 of simplicial complexes into a monoid , where the empty complex is the @xmath27 element and the cone construction adds 1 . the augmented grothendieck group @xmath28 contains the graph and sphere monoids @xmath29 and @xmath30 . the poincar - hopf functionals @xmath31 or @xmath32 as well as the volume are multiplicative functions on @xmath33 . for the sphere group , both @xmath34 as well as @xmath35 are characters . the join @xmath24 can be augmented by a product @xmath36 so that we have a commutative ring @xmath37 in which there are both additive and multiplicative primes and which contains as a subring of signed complete complexes @xmath38 isomorphic to the integers @xmath39 . both for addition @xmath24 and multiplication @xmath36 , the question of unique prime factorization appears open .","we compare the unit sphere topologies in @xmath1 with the unit sphere topologies of @xmath47 . it follows that the sphere index spectrum , the set of green function values is a combinatorial invariant of a simplicial complex the quest to find invariants of topological spaces is particularly concrete when searching for combinatorial invariants in abstract finite simplicial complexes . graph theory enters naturally as any barycentric refinement @xmath1 of an arbitrary abstract simplicial complex is already is the whitney clique complex of a graph . the analysis there shows that wu characteristic is the only combinatorial invariant among multi - linear valuations . we have proposed @xcite to insist that a finite topology on a graph should be given by a subbase and have the property that the nerve graph of a sub - base should be homotopic to the graph and that a dimension condition is satisfied for intersections . the reasons are that we want any reasonable notion of cohomology to agree with the natural topology of the graph and insist that any notion of homeomorphism should honor the concept of dimension . + unlike the quest to find a complete set of invariants for a simplicial complex , the task to find concrete combinatorial invariants of an abstract simplicial complex is more accessible . it states that if the maximal dimension of @xmath0 is @xmath52 , the space of valuations is @xmath83 dimensional . + at the end we point out that there is a multiplication on simplicial complexes which is compatible with the zykov join addition in the sense that distributivity holds . + given a simplicial complex @xmath0 , we can look both at the barycentric refinement @xmath1 of @xmath0 as well as the connection graph @xmath2 of @xmath0 . the graph @xmath1 is a subgraph of @xmath2 . in the theory of simplicial complexes it turns out that the possible topologies which appear as unit spheres in @xmath1 form a combinatorial invariant of @xmath0 . while @xmath1 can feature new unit sphere topologies , there are no new sphere topologies appearing in @xmath47 . in this section we look at discrete spheres and unit spheres @xmath5 of barycentric refinements of finite abstract simplicial complexes . we establish now that the set of unit sphere topologies is stable from @xmath1 on .",0.19166666666666668,"a finite abstract simplicial complex @xmath0 is a finite set of non - empty sets, called simplices, so that the search for combinatorial invariants can be abandoned unless it can be performed in a discrete hadwiger space which is then the main focus of that class of objects. we insist that any notion of homotopy group which honors the topology of the graph should respect the concept of dimension. we claim that the only homotopical invariant which is well established in the discrete is that of wu characteristic which is a subbase of the euler characteristic spectrum. we impose a condition that all such invariants must be homotopic to the graph and that a dimension condition is satisfied for intersections. we want any reasonable notion of cohomology to honor this condition and insist that abstract finite simplicial complexes which are not turing machines can not be used to build a turing machine which can distinguish any pair of abstract finite simple and complete silica complexes. in this paper we describe the strategy which allows us to stay in the realm of much the more accessible graph category, on which the complex of finitely many finite simplices is barycentric refined. the strategy is well motivated by the quest to find a complete finite set, or even a complete collection, of invariants which allow the distinguishability of an arbitrary pair of simplices not only to be established but also to have a complete structure on the set. a complete, foundational understanding of the geometry on a graph is not only possible but often sufficient to obtain a tractable theory can also be achieved. + from the algorithmic point of view it is clear that every finite set or a partial ordered set of finite simple graphs is an order complex. hence, in order complexes, like the whitney clique complex or the matroids, it is more accessible to study and often more interesting than the simplices. + examples of what is to be done in the domain of algebraic geometry on finite sets have been given by jonsson @xcite and even richer geometry on non - finite sets has been realized in hyperbolic manifolds and manifolds. the attempts to construct such a manifold in a systematic way in the context of graph theory have been made by many authors and the list goes on. however, in the end we would like to end the quest for exact results by pointing out that an important improvement over the previous methods which are sure to be useful in future theoretical developments is certainly achievable. we discuss some open",0.18829516539440205
astro-ph0105182,"we present a study of the correlated spectral and timing behavior of the new x - ray transient sax j1711.63808 during its 2001 outburst using data obtained with the _ rossi x - ray timing explorer _ ( _ rxte _ ) . we also investigate the correlations between those source properties and the 320 kev x - ray luminosity . the behavior of the source during the observations can be divided into two distinct state types . during the ` ` hard '' state , the energy spectra are relatively hard and can be described by only a power - law component , and the characteristic frequencies ( i.e. , the frequency of the 17 hz quasi - periodic oscillations observed for the first time in this source ) in the power spectra are low . however , during the ` ` soft '' state , the spectra are considerably softer ( in addition to the power - law component , a soft component below 8 kev is necessary to fit the spectra ) and the frequencies are the highest observed . remarkably , this distinction into two separate states can not be extrapolated to also include the 320 kev x - ray luminosity . except for one observation , this luminosity steadily decreased but the hard state was observed both at the highest _ and _ lowest observed luminosities . in contrast , the soft state occurred only at intermediate luminosities . this clearly demonstrates that the state behavior of sax j1711.63808 is decoupled from its x - ray luminosity and that if the x - ray luminosity traces the mass accretion rate in sax j1711.63808 , then the state transitions are not good accretion rate indicators , or vice versa . the _ rxte _ data of sax j1711.63808 does not allow us to conclusively determine the exact nature of the compact object in this system . the source resembles both neutron star and black hole systems when they have low luminosities . we discuss our results with respect to the correlated timing and spectral behavior observed in other low - mass x - ray binaries and the implications of our results on the modeling of the outburst light curves of x - ray transients .","from simple accretion theory , one would expect that the x - ray luminosity in low - mass x - ray binaries ( lmxbs ) is directly related to the mass accretion rate ( ) in those systems . , we discuss the correlated spectral and timing behavior of the new x - ray transient sax j1711.63808 ( in t zand , kaptein , & heise 2001 ) as observed with the _ rxte_/pca , and the lack of correlation between its state transitions and the x - ray luminosity . no apparent correlation is present between the power - law index and time or the count rate / fluxes , but a correlation is present between this parameter and the strength of the rapid x - ray variability . both the strength of the broken - power law and the qpo tend to decrease when the power - law index increases . we report on the spectral and timing behavior of the new x - ray transient sax j1711.63808 during the decay of its 2001 outburst . the rapid x - ray variability of sax j1711.63808 can be consistently described by a broad band - limited noise component with a break frequency between 0.2 and 2 hz . on top of this noise component a broad bump or a narrow qpo ( only during observation three , four , and seven ) is detected , whose frequency is strongly correlated with the break frequency . the x - ray spectrum of the source is also not correlated with the luminosity but it is correlated with the timing properties . the spectrum is considerably softer ( the inclusion of a soft component on top of the power - law is required ) when the characteristic frequencies in the power spectra are higher ( observations three and four ) compared with when they are significantly lower ( the other observations ) . from our results , it is clear that during our third and fourth observations , the source was in a different , softer , state than during the other six observations . the occurrence of these states does not correlate with the x - ray luminosity . if the x - ray luminosity is a good indication of the mass accretion rate then the mass accretion rate monotonically decreased ( except for observation seven ) during the observations , but then the mass accretion rate is decoupled from the state transitions . however , it is also possible that still the mass accretion rate is coupled with the different states , but then the x - ray luminosity can not be a good tracer of . in both scenarios it is useful to consider that we only have the fluxes in a limited energy range ( 320 kev ) , which might not be an accurate indication for the total luminosity . this strongly suggest that the total x - ray flux during observation 3 and 4 was significantly lower than during observation 1 and 2 . therefore , the conclusion seems to be warranted that the x - ray luminosity is decoupled from the spectral and timing properties of the source . as explained in the introduction , for the neutron star systems it is assumed that their correlated spectral - timing behavior is a good trace of the mass accretion rate and not the x - ray luminosity , mainly because of their correlations with other source parameters such as the emission at other wavelengths ( optical , uv , line flux ; hasinger et al . if indeed a black - hole is present in sax j1711.63808 , then it would be the second bhc lmxb , after xte j1550564 , for which it has been shown that the state transitions are not coupled to the luminosity of the source .",0.2533632286995516,"we report on the correlated spectral and timing properties of the new x - ray transient sax j1711.63808 during its first four observations with the _ rxte_/pca. the source is the brightest source in the 320 kev energy range and has relatively hard power - law spectra with a tail extending up to 6.5 kev. during all four observations the source was in a softer, softer, state, in which the x - rays show a broad band - limited noise component and a narrow qpo. the count rate and flux of the source decreased monotonically with time, which is in agreement with simple accretion theory. a correlation between the break frequency and the qpo frequency ( i.e., the frequency of the break at the soft end of the power spectrum ) is found, as would be expected if the source harbors a black hole. this behavior is also seen in the state - dependent power spectra of persistent neutron - star low - mass xmxb ( bhxb ) systems, and it is likely that the observed state behavior is a consequence of mass accretion rate changes. however, in contrast to these two systems, the count and the flux of xte j1550564 are tightly correlated with the spectral behavior, indicating that the source flux was not much higher than expected from the summing of the different state - transitions, and that the total amount of source flux could be hidden at luminosities above 20 kev in the bhcd limit. furthermore, we found that the rapid variability of sax jeng et al. ( 2001 ) 7.03.3115 is very similar to that of other bhcs, and the observed different states can be identified with the island state ( the soft state ) and the lower banana branch ( the hard state ). an upper limit to the temperature of the @xmath0 kelvin - cooled state could be inferred from the spectral data of observation three and four, but we can not rule out a possible neutron star component. the normalization of the count frequency ( between 0.2 and 2.0 hz ) between the soft and hard bands is not a strong correlation with the hard component.",0.25958702064896755
astro-ph9601095,"using self - consistent magnetohydrodynamic ( mhd ) simulations , we explore the hypothesis that nonlinear mhd waves dominate the internal dynamics of galactic molecular clouds . our models employ an isothermal equation of state and allow for self - gravity . we adopt ` ` slab - symmetry , '' which permits motions @xmath0 and fields @xmath1 perpendicular to the mean field , but permits gradients only parallel to the mean field . this is the simplest possible geometry that relies on waves to inhibit gravitational collapse along the mean field . in our simulations , the speed @xmath2 exceeds the sound speed @xmath3 by a factor @xmath4 , which is realistic for molecular clouds . we simulate the free decay of a spectrum of waves , with and without self - gravity . we also perform simulations with and without self - gravity that include small - scale stochastic forcing , meant to model the mechanical energy input from stellar outflows . our major results are as follows : ( 1 ) we confirm that the pressure associated with fluctuating transverse fields can inhibit the mean - field collapse of clouds that are unstable by jeans s criterion . cloud support requires the energy in -like disturbances to remain comparable to the cloud s gravitational binding energy . ( 2 ) we characterize the turbulent energy spectrum and density structure in magnetically - dominated clouds . the perturbed magnetic and transverse kinetic energies are nearly in equipartition and far exceed the longitudinal kinetic energy . the turbulent spectrum evolves to a power - law shape , approximately @xmath5 with @xmath6 , i.e. approximately consistent with a ` ` linewidth - size '' relation @xmath7 . the simulations show large density contrasts , with high density regions confined in part by the pressure of the fluctuating magnetic field . ( 3 ) we evaluate the input power required to offset dissipation through shocks , as a function of @xmath8 , the velocity dispersion @xmath9 , and the characteristic scale @xmath10 of the forcing . in equilibrium , the volume dissipation rate is @xmath11 , for a cloud of linear size @xmath12 and density @xmath13 . ( 4 ) somewhat speculatively , we apply our results to a ` ` typical '' molecular cloud . the mechanical power input required for equilibrium ( tens of @xmath14 ) , and the implied star formation efficiency ( @xmath15 ) , are in rough agreement with observations . because this study is limited to slab symmetry and excludes ion - neutral friction , the dissipation rate we calculate probably provides a lower limit on the true value .",", we undertake to study the full nonlinear development of moderate - amplitude mhd disturbances in a self - gravitating system , using numerical simulations . we concentrate our attention on the most basic questions of how well clouds can be supported against gravity by nonlinear disturbances , and how long it takes mhd turbulence to decay . by employing simulations , we can generalize ideas of support by simple alfvn waves to include arbitrary self - consistent disturbances in the magnetic field , fluid flow , and density structure . we can test how far the linear - theory predictions for wave support carry over to the nonlinear regime , and go beyond the purview of simple linear theory to investigate the growth of structure , cascade of energy between scales , and associated dissipation . 2 we review basic observational results for molecular clouds and the implied timescales in the context of simple theoretical considerations of cloud stability . , we set out to explore the hypothesis that magnetic forces are crucial to the internal dynamics of galactic molecular clouds . we were motivated by the proposal that the fluctuating velocity field in mhd waves is responsible for the observed hypersonic turbulence in molecular clouds , while the associated magnetic field fluctuations provide a pressure vital in supporting clouds against gravitational collapse and confining non - self - gravitating clumps . this work uses numerical simulations to investigate large - amplitude ( @xmath107 ) mhd turbulence under density , temperature , and magnetic field conditions appropriate for galactic molecular clouds . computational expense has imposed some sacrifices of realism in this first self - consistent treatment of turbulence in a highly compressible , magnetically - dominated ( @xmath106 ) fluid . we have performed four types of numerical simulations . in the first ( [ freedecay ] ) , we evolved a spectrum of large - amplitude -wave turbulence to determine the free decay rate . in these simulations gravity is opposed by a gradient in the time - varying magnetic pressure due to the components of the field perpendicular to the mean field . ( 2 ) we have characterized the dynamical state of highly nonlinear , @xmath337 mhd systems . such systems contain strong density contrasts , with much of the volume effectively evacuated and most of the mass concentrated into small regions . high density `` clumps '' form and disperse over time , with a secular trend toward increasingly large concentrations and coherent motions as energy cascades to larger scales . these nonlinear , magnetically dominated systems contain numerous mhd discontinuities , which naturally give rise to a wave energy power spectrum approximately @xmath338 with @xmath6 , or linewidth - size relation approximately @xmath339 . ( 3 ) we have calculated a decay rate for nonlinear mhd waves in slab symmetry by equating forcing and dissipation rates in a saturated equilibrium . the dissipation time , given in physical units in equation ( [ disst ] ) , is longer than some naive estimates . in particular , when the cloud is stirred at scales comparable to its size , the dissipation time exceeds the `` eddy turnover time '' @xmath340 by @xmath341 times an order - unity factor , and the -wave crossing time by an additional factor @xmath342 ( see eq.[[tdiss ] ] ) . peak dissipation rates for free decay obey approximately the same scaling in @xmath9 , @xmath2 , and @xmath3 as the dissipation rate in saturated equilibrium . because of the present restricted geometry and negligible friction , our computed dissipation rates are likely lower limits .",0.19196428571428573,"we investigate large - amplitude magnetohydrodynamic ( mhd ) disturbances in galactic molecular clouds, using numerical simulations. our simulations represent the first self - consistent treatment of turbulence in a highly compressible, magnetically - dominated ( @xmath0 ) fluid. we restrict the dynamics to plane - parallel geometry with periodic boundary conditions, and ignore ion - neutral slippage. this is the simplest possible model that incorporates magnetic fields and gravity self - consistently. we have performed several different types of simulations using the basic model described in this paper to explore the conditions under which moderate - amplitude mhd turbulence is most effective for supporting clouds against gravity, and to determine how long it takes for the free decay of an initial wave spectrum to result in a quasistatic equilibrium. the free - decay times are typically comparable to the gravitational collapse times of at least the ( higher - density ) clumps ; yet general internal collapse has not occurred. we find that ( 1 ) clouds can be supported for a significant length of time in the presence of nonlinear dissipation and self - gravity ; ( 2 ) the cloud complex age tends to exceed the characteristic collapse time for clumps at densities well above the ` ` mean density '' of the system ; ( 3 ) the relative importance of magnetic, kinetic, and gravitational energies is comparable in detail for several clouds at a range of scales, suggesting virial equilibrium ; and ( 4 ) a moderate - magnetic field can provide a pressure gradient comparable to that of gas pressure in cloud complexes. basic observational results for molecular clouds are discussed. we provide detailed tests of the numerical model and use it to interpret observations. finally, we extend our results to astronomical systems and discuss directions for future research. = 1",0.2067901234567901
0801.3081,"we present high resolution ( r 20000 ) spectra in the blue and the far red of cicumnuclear star - forming regions ( cnsfrs ) in three early type spirals ( ngc3351 , ngc2903 and ngc3310 ) which have allowed the study of the kinematics of stars and ionized gas in these structures and , for the first time , the derivation of their dynamical masses for the first two . in some cases these regions , about 100 to 150pc in size , are seen to be composed of several individual star clusters with sizes between 1.5 and 4.9pc estimated from hubble space telescope ( hst ) images . the stellar dispersions have been obtained from the calcium triplet ( cat ) lines at @xmath08494,8542,8662 , while the gas velocity dispersions have been measured by gaussian fits to the h@xmath1 and [ oiii]@xmath05007lines on the high dispersion spectra . values of the stellar velocity dispersions are between 30 and 68 km / s . we apply the virial theorem to estimate dynamical masses of the clusters , assuming that systems are gravitationally bounded and spherically symmetric , and using previously measured sizes . the measured values of the stellar velocity dispersions yield dynamical masses of the order of 10@xmath2 to 10@xmath3 solar masses for the whole cnsfrs . stellar and gas velocity dispersions are found to differ by about 20 to 30 km / s with the h@xmath1 emission lines being narrower than both the stellar lines and the [ oiii]@xmath05007lines . the twice ionized oxygen , on the other hand , shows velocity dispersions comparable to those shown by stars , in some cases , even larger . we have found indications of the presence of two different kinematical components in the ionized gas of the regions . we have mapped the velocity field in the central kiloparsec of the spiral galaxies ngc3351 and ngc2903 . for the first object the radial velocity curve shows deviations from circular motions for the ionized hydrogen consistent with its infall towards the central regions of the galaxy at a velocity of about 25 km / s . for ngc3310 we present preliminary results of the velocity dispersions for one of the two observed slit position angles , two cnsfrs and the nucleus .","we have observed in two slit positions but we only present preliminary results for one of them . . however , the best gaussian fits involved two different components for the gas : a `` broad component '' with a velocity dispersion similar to that measured for the stars , and a `` narrow component '' with a dispersion lower than the stellar one by about 30km / s . this last component seems to have a relatively constant value for all the cnsfrs in each galaxy , with estimated values close to 25km / s for the two gas emission lines . the velocities of the two components of the fits in the cnsfrs of ngc3351 are the same within the observational errors , but in the cases of ngc2903 and ngc3310 we find a shift between the narrow and the broad component that vary between -10 and 35km / s in radial velocity . the dynamical masses estimated from the stellar velocity dispersion using the virial theorem for the cnsfrs of ngc3351 are in the range between 4.9@xmath4 and 4.8@xmath5m@xmath6 , and is 3.5@xmath5 for its nuclear region inside the inner 11.3pc @xcite . in the case of masses derived from the h@xmath1 velocity dispersions under the assumption of a single component for the gas would have been underestimated by factors between approximately 2 to 4 . masses of the ionising stellar clusters of the cnsfrs have been derived from their h@xmath8 luminosities @xcite under the assumption that the regions are ionisation bound and without taking into account any photon absorption by dust . their values for ngc3351 are between 8.0@xmath9 and 2.5@xmath4 m@xmath6 for the starforming regions , and is 6.0@xmath9 for the nucleus @xcite . and for the regions of ngc2903 they are between 3.3@xmath4 and 4.9@xmath4 m@xmath6 , and is 2.1@xmath9 for its nucleus @xcite . these values are comparable to that derived by @xcite for the circumnuclear region a in ngc7714 . therefore , the ratio of the ionising stellar population to the total dynamical mass is between 0.01 and 0.16 . these values are also comparable to that derived by @xcite . for ngc3351 , the rotation velocities derived for both stars and gas are in reasonable agreement , although in some cases the gas shows a velocity slightly different from that of the stars @xcite . the rotation curve corresponding to the position going through the centre of the galaxy shows maximum and minimum values at the position of the circumnuclear ring , as observed in other galaxies with cnsfrs ( * ? ? ? the differences in velocity between gas and stars can be interpreted as motions of the ionised hydrogen deviating from rotation and consistent with a radial infall to the central regions of the galaxy . our results are consistent with those found by @xcite and would yield an infall velocity of about 25 km / s . on the other hand , the observed stellar and [ oiii ] velocities of ngc2903 are in good agreement , while the h@xmath1 measurements show shifts similar to those find between the narrow and the broad components @xcite . this different behavior can be due to that the position of the single gaussian fits are dominated by the broad component in the case of the [ oiii ] emission line while in the case of the h@xmath1 are dominated by the narrow one .",0.22369878183831676,"high - resolution blue and far red spectra of the central region of ngc3351 have been obtained with isis. in the red arm the spectral range is 4780 - 5200 while in the blue arm it is 8360 - 8760. we present preliminary results for one of them. the rotation curve corresponding to the position going through the nucleus shows maximum and minimum values at the positions of the circumnuclear ring and the nucleus, respectively. its position angle is 0.39@xmath00.39. we observed 11 velocity template stars to provide good reference frames. they are late type giant and supergiant stars which have strong cat features ( ` ` cnsfrs '' ) and in the case of the [ oiii ] emission line an almost constant velocity dispersion of about 30 km / s. we found a shift between the velocities of the broad and the narrow component of the ionised hydrogen deviating from rotation, which is consistent with a radial infall to the central regions of the galaxy. this implies that the gas, and not the stars, is the primary acceleration mechanism for the decelerating ionising matter. the stellar and gas velocity dispersions are consistent with being equal within the errors. however, we found that the position of the ` ` broad component '' deviates from the stellar position by about 35km / s in radial velocity. this difference is larger than that found for the stars and smaller than can be explained by the systematic difference in velocity for the gas and the stars. on the other hand, although the broad component is morecelerated than the stellar one in both the red and blue arm, the differences between them are negligible in the blackbody equivalent widths and in absolute magnitude. therefore, we interpret this difference as due to a deviating velocity from the gas of the star forming regions and/or a stellar rotation within the stellar structures. [ firstpage ] galaxies : individual ( ngc2903 ) - galaxies : ism - infrared : stars.",0.237593984962406
1407.3633,"concentrated suspensions of swimming microorganisms and other forms of active matter are known to display complex , self - organized spatio - temporal patterns on scales large compared to those of the individual motile units . despite intensive experimental and theoretical study , it has remained unclear the extent to which the hydrodynamic flows generated by swimming cells , rather than purely steric interactions between them , drive the self - organization . here we utilize the recent discovery of a spiral - vortex state in confined suspensions of _ b. subtilis _ to study this issue in detail . those experiments showed that if the radius of confinement in a thin cylindrical chamber is below a critical value the suspension will spontaneously form a steady single - vortex state encircled by a counter - rotating cell boundary layer , with spiral cell orientation within the vortex . left unclear , however , was the flagellar orientation , and hence the cell swimming direction , within the spiral vortex . here , using a fast simulation method that captures oriented cell - cell and cell - fluid interactions in a minimal model of discrete - particle systems , we predict the striking , counterintuitive result that in the presence of collectively - generated fluid motion the cells within the spiral vortex actually swim upstream against those flows . this is then confirmed by new experiments reported here , which include measurements of flagella bundle orientation and cell tracking in the self - organized state . these results highlight the complex interplay between cell orientation and hydrodynamic flows in concentrated suspensions of microorganisms . _ significance statement : the collective dynamics of swimming microorganisms exhibits a complex interplay with the surrounding fluid : the motile cells stir the fluid , which in turn can reorient and advect them . this feedback loop can result in long range interactions between the cells , an effect whose significance remain controversial . we present a computational model that takes into account these cell - fluid interactions as well as cell - cell forces , and which predicts counterintuitive cellular order driven by long - range flows . this is confirmed with new experimental studies which track the orientation of cells in a confined , dense bacterial suspension . _ 0.5 cm in the wide variety of systems termed ` active matter ' @xcite one finds the spontaneous appearance of coherent dynamic structures on scales large compared to the individual motile units . examples range from polar gels @xcite , bacterial suspensions @xcite and microtubule bundles @xcite to cytoplasmic streaming @xcite . at high concentrations , suspensions of rod - like bacteria are known to arrange at the cellular scale with parallel alignment as in nematic liquid crystals @xcite , but with local order that is polar , driven by motility @xcite . at meso- and macroscopic scales , coherent structures such as swirls , jets , and vortices at scales @xmath0 m to @xmath1 mm have been experimentally observed @xcite . many studies have focused on how complex cell interactions can give rise to macroscopic organization and ordering , and the role of self - generated fluid flows in the dynamics of dense suspensions is still under debate @xcite . this is due in part to the inherent complexity of the systems under investigation , and the difficulty of making faithful mathematical models . microswimmers such as _ e. coli _ , _ b. subtilis _ or _ c. rheinhardtii _ produce dipolar fluid flows through the combined action of their flagella and cell body on the fluid . in the far field , they are well - described as ` pusher ' or ` puller ' stresslets @xcite , corresponding to the case of flagella behind or in front of the cell body . these fluid flows affect passive tracers @xcite as well as swimmers : their motion is subject to convection and shear reorientation induced by neighboring organisms , which can lead to complex collective organization . macroscopic fluid flows emerge from the collective motion of a colony of motile bacteria and the suspension can exhibit a quasi - turbulent dynamics @xcite . microorganisms like _ b. subtilis _ live in porous environments , such as soil , where contact with surfaces is inevitable as mesoscale obstacles and confinement are the norm . recent experiments give insight into the interactions of single microorganisms with surfaces @xcite , yet suspension dynamics in confinement has only begun to be investigated @xcite and the role of the collectively - generated fluid flows in the macroscopic organization has yet to be fully understood . recently , wioland _ et al . _ @xcite showed that a dense suspension of _ b. subtilis _ , confined into a flattened drop , can self - organize into a spiral vortex , in which a boundary layer of cells at the drop edge moves in the opposite direction to the bulk circulation . this spatio - temporal organization is driven by the presence of the circular boundary and the interactions of bacteria with it . at the interface the packed cells move at an angle to the tangential that is dictated by the drop curvature , swimmer size and shape . this macroscopic nonequilibrium pattern and double - circulation were not anticipated by theory and have not been seen in any simulations of discrete particle systems . this is due to the computational difficulty of capturing both confinement and complex interactions between elongated swimmers . although previous simulations have demonstrated the importance of hydrodynamics in populations of spherical squirmers @xcite and rod - shaped swimmers @xcite , they do not consider boundary effects and the elongated shape of the swimmers in the steric interactions . on the other hand , continuum models of motile suspensions that include fluid dynamics , and have been successful in explaining large - scale patterns @xcite , have either ignored confinement or interactions with surfaces , or , if addressing confinement @xcite , have imposed boundary conditions that generally do not resolve the orientations of the bacteria at the interface . thus , the conditions at boundaries and microscopic interactions between cells warrant careful consideration in the modelling of these suspensions so that the macroscopic dynamics and organization are correctly captured . here , we elucidate the origin and nature of the spontaneous emergence of the spiral vortex and cellular organization in a confined motile suspension . a computational model is described for bacterial suspensions in which the direct and hydrodynamic interactions between the swimmers and the confining circular interface can be tuned . the cells are represented as oriented circles or ellipses subject to cell - cell and cell - fluid interaction , while the fluid flow is the total of the pusher dipolar fluid flows produced by each swimmer s locomotion . it is shown that while some circulation under conditions of confinement may arise with direct interactions only , hydrodynamics are necessary and crucial to reproduce and explain the double circulation that is observed experimentally . simulations ( fig . 1a - c ) are able to reproduce the emergence of the spiral vortex from an isotropic state ( fig . 1d - f ) , and give insights into the origin of the microscopic organisation of the bacteria in the drop . the computational results show the remarkable feature that cells in the bulk of the drop swim _ against _ the stronger colony - generated fluid flow and thus have a net _ backward _ motion . we confirm this observation by measuring the orientation of the cells and of their flagella through suitable fluorescent labelling methods .","these three configurations show that while steric interactions force local alignment of ellipsoidal swimmers , it is the collectively - generated fluid flow that produces the large - scale organization and double - circulation . 2 g ( and si movie 7 ) we show that a dilute suspension of ellipse - shaped swimmers also orders into a spiral vortex and self - generates bidirectional fluid flows . as an aside as shown in previous sections , experiments and simulations with both steric and hydrodynamical interactions are in qualitative agreement on both micro- and macroscopic scales . in this section drops show stable circulation when the confining chamber is @xmath47 m in diameter . to quantify the order in simulations we introduce the vortex order parameter @xmath48 with @xmath49 the bacterial overall motion and @xmath50 the azimuthal unit vector . , we observe that turbulence arises in the center of the largest drops . in the case of dilute or semi - dilute suspensions ( as in fig . we have presented a minimal model and simulation method for micro - swimmer suspensions that includes direct cell - cell , cell - fluid interactions and swimmer - generated flows . the method , though minimal and in two - dimensions , captures well the dynamics seen in experiments on confined bacterial suspensions . in agreement with previous simulations , we show here that the long - range hydrodynamic interactions are crucial to reproduce the organization and circulation that are observed in experiments . in periodic domains the swarming states predicted by active matter theories are disrupted by hydrodynamics , resulting in a more turbulent suspension behavior . under circular confinement , although direct cell interactions lead to local cell alignment , large scale order appears only when the swimmer motion is coupled to the fluid dynamics . simulation results not only agree qualitatively with the experiments , they also highlight the microscopic bacterial organization . in particular , the cells in the bulk are shown to swim against the collectively - generated fluid flow , a result that was not foreseen in previous publications . we confirmed that prediction by experimentally recording both motion and swimming directions , which to our knowledge has never been done in dense bacterial suspensions . to do so we tagged and tracked the relative positions of the cells body and flagella . these results emphasize the necessity to include more realistic hydrodynamic interactions in active fluid particle simulations and also continuum theories @xcite . ultimately , a closer comparison to experiments requires 3d particle simulations , more accurate descriptions of the fluid flows generated by the swimmers in the bulk and near boundaries , and possibly an accounting of the the swimmers geometry and flagella . although simplified , the model described here has been shown to give good insights into the dynamics of micro - swimmer suspensions and could be applied to more complex geometries to study microscopic interactions and ordering that are difficult to visualize experimentally .",0.1550094517958412,"the swimming and advection of swimmers by ambient fluid are central to the evolution of eukaryotic cells. despite their importance, models and simulations have never been capable of reproducing the large - scale organization and double - circulation that are observed in experimentally confined suspensions of bacteria. in this paper, we describe a minimal model and simulation method for micro - swimmer suspensions that includes direct cell - cell, cell - fluid and swimmer - generated fluid flows. in the absence of hydrodynamics, the swimmer motion is directly coupled to the fluid dynamics. in periodic domains, however, the long - range hydrodynamic interactions are crucial to reproduce the swarming state and dynamical behavior that is observed in experiments. these simulations show that under circular confinement, although swimmers swim in the same direction as the fluid, the cell alignment depends on the direction of motion of the swimmers. swimmers in a disk - shaped position are shown to push fluid backwards in response to the pressure exerted by the nearby swimmer. the magnitude of this pressure - induced motion is comparable to that predicted by active matter theories. in addition, a swimmer locomotion has been found to have spiral order in drops with diameter @xmath0. while these results are in qualitative agreement with experiments, they disagree with the predictions of simple active matter models, suggesting that additional processes are needed to explain the experiments. while swimming is the fundamental activity of most bacteria, it has been observed that in a very small class of bacteria the swimming motion is dominated by the advective fluid flow associated with the swimming of the flagella @xcite. in a simple model for self - guiding swimmers, the motion is self - propelled by steric forces generated by the fluid flow they create. taken together, these theoretical models may explain the organization and spatial order of bacterial suspensions, in particular the formation of spiral vortices, in fig. 1a. ( b ). ( c ) examines the organization of a single swimmer in a vortex state, in which the cell vertical direction is parallel to that of the fluid circulation. ( d ) investigates the nature of collective swimming by considering a restricted group of ellipse - shaped swimimmers. ( e ) simulates the motion of a two - dimensional fluid flow in two dimensions. ( g ) estimates the order of the swimmingmer motion in the vortex state. ( [ xdot]-[pdot ] ) compares simulation results to the experimental data. in particular, the simulations reproduce qualitatively the large",0.16579634464751958
cond-mat0507350,"here we report a study of vortex states in a thin superconducting film with a magnetic dot grown upon it by means of a method based on london - maxwell equations . vortices with single quantum flux ( @xmath0 ) , giant vortices ( vortices with multiple flux ) as well as antivortices ( vortices with negative vorticity ) are taken into consideration . it turns out that giant vortices occur , when the dot s size is sufficiently smaller ( @xmath1 ) than the effective penetration depth @xmath2 . in the case of a dot with sufficiently large size ( @xmath3 ) , the vortices with single quantum flux dominate the vortex states . their geometrical patterns are predicted up to seven vortices . our calculations do not show the spontaneous appearance of antivortices . pacs number(s ) : 74.25.dw , 74.25.ha , 74.25.qt , 74.78.-w 2 type ii superconductors are used in a wide variety of technological applications due to their high critical currents and fields @xcite . in these superconductors , vortices appear when the magnetic field exceeds the first critical field @xmath4 . under external current or field , vortices move , which causes the superconductor to switch to a resistive state . as a result , the system loses its superconductivity . because of this , vortex pinning is quite important in applications of type ii superconductors . one of the ways to pin vortices is to use the magnetic subsytems with either out - of - plane or in - plane magnetization . these subsystems are capable of trapping both vortices and antivortices , depending on the orientation and strength of their magnetization . the aforementioned systems are not only important for technological applications , such as devices that can be tuned by weak magnetic fields , but also offer rich physical effects which are not observed in the individual parts . some of these effects were predicted elsewhere @xcite . in the recent decade , magnetic dots growing on top of sc films have been extensively studied both experimentally @xcite and theoretically @xcite . in experimental studies , magnetic dots with in - plane magnetization are fabricated from co , ni , fe , gd - co and sm - co alloys , whereas , for the dots with magnetization perpendicular to the plane , co / pt multilayers are used @xcite . these studies report commensurability effects on transport properties , which comfirm that the dots create and pin vortices . on theoretical side , several realizations of the aforementioned systems are analyzed through the landau - gizburg framework and london theory . in these works , the authors investigated the conditions for vortices to appear and calculated their geometric configurations in equilibrium . recently , priour _ et al . _ studied the vortex states of a sc film with a magnetic dot array grown upon on it , through ginzburg - landau theory , and found several different configurations of vortices in the sc film @xcite . similar study was also done by peeters _ et al . _ , but in the presence of a single dot @xcite . one of the interesting results that is reported by these works is , when the dot s size is on the order of a few coherence lengths @xmath5 , vortices with multiple flux quanta ( the giant vortices ) appear . the giant vortices are previously studied in the landau - ginzburg framework @xcite . the stable antivortex ( av ) ( vortices with vorticity opposite to vorticity of those trapped under the dot ) states were reported in similar systems @xcite . the most interestingly , kanda _ et . al . _ recently reported the experimental evidence of the gv states and the other rearrangements of vortices in a mesoscopic sc disc , using the multiple - tunnel - junction method @xcite . earlier , we studied the vortex states due to a ferromagnetic ( fm ) dot with out - of - plane ( perpendicular to the film ) magnetization on top of a sc thin film @xcite . in that work , we limited ourselves only to the vortices trapped under the dot , and calculated the equilibrium configurations , up to three vortices . however , in a more realistic picture , both vortices under the dot and antivortices outside the dot s boundaries can appear spontaneously , because total flux due to the magnetic dot over the entire infinite sc film is zero . actually , this problem was studied for magnetic dipoles with out - of - plane magnetization @xcite . another interesting case is giant vortex ( gv ) states with multiple unit flux @xmath6 . in usual circumstances , it is hard to get vortices with multiple flux quanta , because their energy grows as the square of their vorticity . however , this energy cost can be overcome by the dots with radii of sufficiently less than effective penetration depth @xmath7 @xcite , where @xmath8 is the london penetration depth and @xmath9 is the thickness of the sc film , and with sufficiently large magnetization . in this article , we focus on the complete picture together with antivortices and giant vortices , and aim to get analytical insight for the spontaneous vortex , antivortex and giant vortex states . for this purpose , we pursue the method based on london - maxwell equations , which is fully developed elsewhere @xcite . though the london approach works well at the high @xmath10 limit , it perfectly serves our purpose and enables us to do analytical calculations . in our analytical and numerical calculations , we show that there are three regimes for the vortex states according to the dot s size . namely , when the dot s size is sufficently small , the gv states are dominant . if the dot s size is sufficently large , we see only vortex states with single quantum flux ( sqf ) . there is also an intermediate region in which both gv and sqf states appear . we calculate the geometrical configurations of sqf states in equilibrium up to seven vortices . in addition , our calculations do not show any av states . at this point , we need to remark that the london framework might seem unreliable to some readers , when the ratio of the dot s size to the coherence length , @xmath5 , is in the order of unity . however , one might expect that the vortices in the london framework , usually prefer staying in sqf states rather than gv states , since the london theory treats the vortex core as a point . our approach then underestimates the dot s size , when the gv states appear . when the vortex cores are treated more accurately , as in landau - ginzburg framework , one might expect that the dot s size would be rather larger than that we estimate in this work . nevertheless , the physics and qualitative result is still captured correctly in the london theory , although the results might be quantitatively different . in the following section , we briefly introduce the method we follow in this article . next , we study the giant vortex states with and without antivortices . the third section is devoted to a discussion on the sqf vortex states with and without av states . the last section consists of the discussions and conclusions .","in order to attack this problem , we consider a thin circular magnetic dot of radius @xmath11 with magnetization perpendicular to its plane at @xmath12 , placed upon a thin sc film which both lay on the x - y plane @xmath13 ( see fig . [ fig : anti : a ] and @xmath127 states.,title=""fig:"",width=132 ] [ fig : anti : b ] and @xmath127 states.,title=""fig:"",width=113 ] 2 we studied the vortex states that occur spontaneously in the ground states of a sc thin film with a single fm dot grown upon it , in the london approximation . our calculations showed that gv states are more energetically favorable when the dot s size is up to @xmath128 ( @xmath129 ) . between @xmath130 ( @xmath129 ) and @xmath131 ( @xmath132 ) , both gv and sqf states appear . beyond @xmath115 ( @xmath133 ) , only sqf states are stable . furthermore , we determine the geometric patterns of up to seven vortices . our results show that vortices form regular geometric patterns , such as a regular triangle , square , pentagon and hexagon . however , in the case of seven vortices , one vortex occurs at the dots center , while other six sit at the corners of a hexagon . the phase diagram of sqf vortex states obeys an equation @xmath134 , which suggests that high - vorticity states prefer larger dots . we also studied the cases together with av states . however , our calculations did not show any stable vortex states together with antivortices . however , the zero flux condition can also be satisfied by the presence of a supercurrent outside the dot boundaries , which circulates in the opposite direction to the currents created by vortices under the dot . furthermore , the london approach does not enable us to analyze the vortex and antivortex states when the dot s size is as large as a few @xmath5 , because it fails for distances on the order of coherence length . this failure is significantly transparant in the presence of av states . however , positive vorticity states can be studied through the london approach . in closing , we studied sqf vortex , gv and av states due to a magnetic dot in the london approximation .",0.1603905160390516,"we consider a thin magnetic dot, with magnetization perpendicular to its plane at @xmath0, placed upon a sc thin film. we study the properties of vortices with positive vorticity that are situated under the dot. we find that at first the vortex state appears, and with further increase of magnetization, the states turn into infinite series of such transitions. we derive the phase diagram of these states and compare them with those of the same dot without magnetization. our results suggest that the dot size is necessary for the vortex states to appear. superconducting systems offer new possibilities of superconductivity as compared with conventionalconductors. recently, superconductors have been in the spotlight again as candidates for the next generation of electronic devices. the interest in these devices is at least two - fold. first, there is the possibility of designing devices whose behavior can be easily tuned by a cosine - bose - einstein ( frbe ) effect @xcite. a second important reason is the desire to create devices where the _ edges _ of the insulating film can be directly examined and control. in contrast to the conventional fermi devices, the electronic dot can be very small to expose a small fraction of the parameter space of a superconductor. thus, it is possible to experimentally test whether whether the dot s properties are stable or not by probing the edges of the film. in this paper, we address this question by considering a small magnetic dot on a thin sc film. our aim is to study the gv states that appear when the dots are placed on the second plane of the sc film ( fig. [ schematics ] ). gvs are unstable states of the quantum fluctuation theory ( qft ) in which the flux from the dot penetrates into the film and the vortex - magnetization interaction can be switched off and on. the key idea is to create a small dot, whose magnetization does not change direction due to the repulsive vortex - vortex interaction. this idea was originally proposed by gottfried, as part of his experiments on top - spin "" states of semiconductor quantum dots ( see, e.g., ref. 691@xcite ). the dots were fabricated from co, ni, fe, gd - co and sm - co alloys. they were smaller than 2 nm and had a high magnetization relative to the non - magnetic cuprates. a dot placed on a normal sc film was also considered, and it was shown that gvs can",0.15539182853315472
astro-ph0603746,"in previous work we have presented evidence for the existence of intrinsic magnetic moments in black hole candidates . we later developed a general relativistic , magnetospheric eternally collapsing object ( meco ) model for black hole candidates and showed that the model is consistent with broad band spectral and luminosity characteristics and accounts for the radio / x - ray luminosity correlations of both galactic black hole candidates ( gbhc ) and active galactic nuclei ( agn ) . since magnetic moments are forbidden attributes for black holes , the meco model has the potential to test whether black hole candidates are actual black holes . we show here that the meco model has the advantage of being able to : a ) satisfy the luminosity constraints that have been claimed as proof of an event horizon for sgr a * , b ) reconcile the low bolometric luminosity with the expected bondi accretion rate for sgr a * by means of a magnetic propeller driven outflow , c ) account for the sgr a * nir and x - ray luminosities , the general characteristics of its broad band spectrum , and the sequence of flares in different spectral ranges as well as the pattern of its observed orthogonal polarizations . we also include specific predictions for images that may be obtained in sub - millimeter to nir wavelengths in the near future . high resolution images in radio frequencies should be elongated in an equatorial outflow plane , while high resolution images in shorter infrared wavelengths should be elongated along an orthogonal , magnetic polar inflow axis ( generally n - s ) . since the emissions in these shorter wavelengths are confined to a narrow axial inflow cone , and radio frequencies are generated primarily at greater distances in the equatorial outflow , there would be no uniform background to provide a silhouette image of a dark central object . additional future tests for the presence of an intrinsic magnetic moment for sgr a * will require global solutions for electron density and magnetic field distributions in a bondi accretion flow into a compact , rotating magnetic dipole . these will provide for definitive tests in the form of detailed calculations of spectral and spatial luminosity distributions and polarization maps for direct comparison with high resolution images of sgr a*. _ key words : _ accretion , accretion disks black hole physics galaxy : center gravitation infrared : general magnetic fields","nearly every object of stellar mass or greater is known to be magnetic to some degree . we show here that it is also consistent with the low luminosity of sgr a*. the meco model for disk accreting gbhc and agn accounts for the existence of their low / hard and high / soft x - ray spectral states . for this reason it is important that it be tested . because much of the spectrum of sgr a * appears to originate in synchrotron - cyclotron radiation then show that we can reconcile the observed low luminosity of sgr a * with the expected bondi accretion flow rate . for the discussion to follow and also for the convenience of readers who might wish to relate meco properties to observations of other objects , we have tabulated a number of useful relations in table 1 . a black hole riaf can be used to account for most of the spectral distribution that has been observed , provided that it would be allowed to produce some radio emission in the disk as well as the jet . we have shown that the meco model accounts for the lack of observed surface luminosity from sgr a*. although it is necessary to know the global distributions of electron density and magnetic fields before spatial and spectral energy distributions can be accurately calculated , we have shown that a spectrum of approximately the correct luminosity and spectral indexes would be produced in the inflow - outflow zones of a bondi accretion flow into the magnetic field of a meco . the axial inflow would produce steeply declining ( negative index ) optically thin nir emissions as well as some correlated x - ray ssc and brehmsstrahlung emissions that could be observed in flares caused by high density clumps in the inflow . we have shown that timing of flares in radio / nir / x - ray bands is consistent with the meco - bondi model , with some weak sub - mm flaring preceding the strongest nir and ssc x - ray flares which are then followed by stronger delayed sub - mm and radio flare emissions . the bulk of the quiescent x - ray luminosity would be thermally generated within the magnetosphere in a mixed inflow / outflow pattern of @xmath91 size . we have shown that the low bolometric luminosity of sgr a * can be reconciled with an expected bondi accretion rate in a completely natural way . the magnetic propeller mechanism is a robust , stable physical mechanism for reducing the bondi accretion rate to levels compatible with the low luminosity of sgr a*. the only parameters that have been necessary for these calculations are the ion density and sound speed at the bondi radius , mass , magnetic moment and spin . the intrinsic magnetic moment of a meco is an inherent , mass dependent feature which is generated by the effects of the quantum electrodynamic stablility conditions that are required by the einstein - maxwell equations that describe the highly red shifted eddington limited meco collapse process ( rl06 ) . its magnitude sets a natural high frequency limit for the synchrotron emissions in the axial inflow . a * described here , there are regions of differing magnetic field strength and orientation , strong density variations and both inflows and outflows . we have shown that there are places of origin in this flow for all of the spectral , spatial , polarization and timing features that have so far been observed for sgr a*. the patterns of inflow and outflow differ from those expected of black hole models and should be observable by the proposed gravity array ( eisenhauer et al .",0.19470899470899464,"if the low bolometric luminosity of sgr a * is a sign that it possesses a magnetic moment then it must possess an intrinsic magnetic moment or a quantum moment which can significantly reduce the accretion rate. if this were the case, the radiative cooling of the accreting plasma within the magnetosphere would cause its luminosity to drop well below the eddington limit value. we show here that for a strongly magnetic equatorial flow, the quiescent x - ray luminosity would be too bright for its to be consistent with observations unless the jet outflow contains a substantial amount of non - thermal electrons. such an outflow would produce optically thick synchrotron radiation with positive spectral index at frequencies below the sound speed and would produce radio flares. however, the predicted timing of these flares is consistent with the meco model, with sub - mm flaring preceding the strongest near - infrared and soft / high @xmath0 radio flares and stronger delayed radio and optical flare emissions. the luminosity produced in the equatorial inflows would be comparable to, or even higher than, that in standard thin disk accretion models of accretion flows into a black hole, however there is no evidence that the bondi accretion flow within the schwarzschild radius would produce any strong radio flares in quiescence. we then show that there is a natural limit to the spin rate that can be produced by magnetic meco - jet outflows into low mass objects. in the absence of a magnetic propeller mechanism, the only way that this model can explain the observed low luminosity is that the magnetic moment and spin rate are intrinsically different for the two systems. we present analytic solutions for both types of systems and show that while the global distributions of the electron density and magnetic field are needed for a robust comparison of the results with observations, a reasonable middle ground can be found in which the properties of both systems are similar. psfig.tex # 1""cd # 1.#1""c7 # 1",0.18285714285714288
1306.3247,"we present a program to simulate the dynamics of a wave packet interacting with a time - dependent potential . the time - dependent schrdinger equation is solved on a one- , two- , or three - dimensional spatial grid using the split operator method . the program can be compiled for execution either on a single processor or on a distributed - memory parallel computer . wave - packet dynamics , time - dependent schrdinger equation , ion traps , laser control * program summary * _ manuscript title : _ program for quantum wave - packet dynamics with time - dependent potentials + _ authors : _ c. m. dion , a. hashemloo , and g. rahali + _ program title : _ wavepacket + _ journal reference : _ + _ catalogue identifier : _ + _ licensing provisions : _ none + _ programming language : _ c ( iso c99 ) + _ computer : _ any computer with an iso c99 compiler ( _ e.g. _ , gcc @xcite ) + _ operating system : _ any + _ ram : _ strongly dependent on problem size . see text for memory estimates . + _ number of processors used : _ any number from 1 to the number of grid points along one dimension . + _ supplementary material : _ + _ keywords : _ wave - packet dynamics , time - dependent schrdinger equation , ion trap , laser control + _ classification : _ 2.7 wave functions and integrals + _ external routines / libraries : _ fftw @xcite , mpi ( optional ) @xcite + _ subprograms used : _ user - supplied potential function and routines for specifying the initial state and optional user - defined observables . + _ nature of problem : _ + solves the time - dependent schrdinger equation for a single particle interacting with a time - dependent potential . + _ solution method : _ + the wave function is described by its value on a spatial grid and the evolution operator is approximated using the split - operator method @xcite , with the kinetic energy operator calculated using a fast fourier transform . + _ restrictions : _ + + _ unusual features : _ + simulation can be in one , two , or three dimensions . serial and parallel versions are compiled from the same source files . + _ additional comments : _ + + _ running time : _ + strongly dependent on problem size . + 0 ` http://gcc.gnu.org ` ` http://www.fftw.org ` ` http://www.mpi-forum.org ` m. d. feit , j. a. fleck , jr . , a. steiger , solution of the schrdinger equation by a spectral method , j. comput . phys . 47 ( 1982 ) 412433 . m. d. feit , j. a. fleck , jr . , solution of the schrdinger equation by a spectral method ii : vibrational energy levels of triatomic molecules , j. chem . phys . 78 ( 1 ) ( 1983 ) 301308 .","quantum wave - packet dynamics , that is , the evolution of the spatial distribution of a quantum particle , is an important part of the simulation of many quantum systems . it can be used for studying problems as diverse as scattering , surface adsorption , and laser control , just to name a few . we propose here a general - purpose program to solve the spatial part of the time - dependent schrdinger equation ( tdse ) , aimed particularly at a quantum particle interacting with a time - dependent potential . our interest mainly concerns such applications as laser control of quantum systems @xcite , but the program can be used with any user - supplied potential function . the program is based on the split - operator method @xcite , which has successfully been used to solve the time - dependent schrdinger equation in many different settings , from the calculation of vibrational bound states ( see , _ e.g. _ , @xcite ) and the simulation of high - power laser - matter interactions ( see , _ e.g. _ , @xcite ) , to the laser control of chemical reactions ( see , _ the method can also be applied to schrdinger - like equations , such as the gross - pitaevskii @xcite and dirac @xcite equations . in this section , we present a detailed description of the split - operator method to solve the time - dependent schrdinger equation . while everything presented here can be found in the original works developing the method @xcite , we think it useful to review all the elements necessary to understand the inner workings of the program . we consider the time - dependent schrdinger equation , @xmath0 with @xmath1 the hamiltonian for the motion of a particle interacting with an external time - dependent potential @xmath2 , _ i.e. _ , @xmath3 where @xmath4 and @xmath5 are the kinetic and potential energy operators , respectively , @xmath6 is the momentum operator , and @xmath7 the mass of the particle . ( the same hamiltonian is obtained for a vibrating diatomic molecule , where the spatial coordinate is replaced by the internuclear distance , and the potential @xmath2 is the sum of the internal potential energy and an external , time - dependent potential , as will be shown in sec . we choose to discretize the problem on a finite spatial grid , _ @xmath48 we consider now the implementation of the algorithm described above on a multi - processor architecture with distributed memory . the `` natural '' approach to parallelizing the problem is to divide the spatial grid , and therefore the wave function , among the processors . this functionality is pre - built into the parallel implementation of the fft package fftw @xcite , of which we take advantage . in addition , fftw offers the possibility of performing a 1d transform in parallel , which we also implement here . the only constrain this imposes on the user is that a 1d problem may only be defined along @xmath49 , and a 2d problem in the @xmath50-plane ( in order to simplify the concurrent implementation of serial and parallel versions , this constraint also applies to the serial version ) . let us now consider the three - dimensional problem of the motion of a charged atomic ion in a paul trap @xcite .",0.19239904988123516,"we describe a general - purpose program to solve the time - dependent schrdinger equation for a particle interacting with an external external potential. the functionality is pre - built into the parallel implementation of the finite - element potential function fftw, of which the main program is based on the split - operator method, with the code being implemented using the message - passing interface library. in addition, we address the discretization of the problem on a finite spatial grid, aimed particularly at the wave - packet dynamics, at each processor. the program can also be used for tasks that require information across slices, such as the fourier transform, which is particularly important in the simulation of quantum systems. pacs : 73.27.hf, 03.65.ss, 07.05.df * program summary * + _ title of program _ : ftw + _ distribution format _ : gzipped tar archive + _ operating system _ : linux + _ programming language used _ : fortran 95 + _ memory required to execute _ : size : 324k, res. 152k, lgpl + _ no. of bits in a word _ : 32 + _ has the code been vectorized or parallelized? _ : yes + _ external routines needed _ : non + _ nature of problem _ : + the program calculates the wave function and several observables of interest to the user, including the magnitude of the potential, the kinetic and potential energy, the direction of the momentum vector, and the energy and mass of the particle, as well as the state of the electron in the potential of the external potential + the possible ( e.g., spin and spin vector ) + _ restrictions on the user s work _ : limited execution in parallel, limited execution on a multi - processor, minimum distance to the program requires at most 8 lines of code ( unless specified ). + _ typical running time _ : about 1 second on a intel i386.",0.18471337579617836
physics0605025,"in this paper , a spatially dispersive finite - difference time - domain ( fdtd ) method to model wire media is developed and validated . sub - wavelength imaging properties of the finite wire medium slabs are examined . it is demonstrated that the slab with its thickness equal to an integer number of half - wavelengths is capable of transporting images with sub - wavelength resolution from one interface of the slab to another . it is also shown that the operation of such transmission devices is not sensitive to their transverse dimensions , which can be made even comparable to the wavelength . in this case , the edge diffractions are negligible and do not disturb the image formation . 10 url # 1`#1`urlprefix[2][]#2 j. pendry , ` ` negative refraction index makes perfect lens , '' phys . rev . lett . * 85 * , 3966 ( 2000 ) . v. veselago , ` ` the electrodynamics of substances with simultaneously negative values of @xmath0 and @xmath1 , '' sov . phys . usp . * 10 * , 509514 ( 1968 ) . p. a. belov , c. r. simovski , and p. ikonen , ` ` canalization of sub - wavelength images by electromagnetic crystals , '' phys . rev . b. * 71 * , 193105 ( 2005 ) . p. ikonen , p. a. belov , c. r. simovski , and s. i. maslovski , ` ` experimental demonstration of subwavelength field channeling at microwave frequencies using a capacitively loaded wire medium , '' phys . rev . b * 73 * , 073102 ( 2006 ) . p. a. belov , y. hao , and s. sudhakaran , ` ` subwavelength microwave imaging using an array of parallel conducting wires as a lens , '' phys . rev . b * 73 * , 033108 ( 2006 ) . p. a. belov and y. hao , ` ` subwavelength imaging at optical frequencies using a transmission device formed by a periodic layered metal - dielectric structure operating in the canalization regime , '' phys . rev . b * 73 * , 113110 ( 2006 ) . p. a. belov , r. marques , s. i. maslovski , i. s. nefedov , m. silverinha , c. r. simovski , and s. a. tretyakov , ` ` strong spatial dispersion in wire media in the very large wavelength limit , '' phys . rev . b * 67 * , 113103 ( 2003 ) . m. g. silveirinha , ` ` nonlocal homogenization model for a periodic array of epsilon - negative rods , '' accepted to phys . rev . e ( arxiv : cond - mat/0602471 ) ( 2006 ) . w. rotman , ` ` plasma simulations by artificial dielectrics and parallel - plate media , '' ire trans . ant . propag . * 10 * , 8295 ( 1962 ) . j. brown , ` ` artificial dielectrics , '' progress in dielectrics * 2 * , 195225 ( 1960 ) . j. pendry , a. holden , w. steward , and i. youngs , ` ` extremely low frequency plasmons in metallic mesostructures , '' phys . rev . lett . * 76*(25 ) , 47734776 ( 1996 ) . p. a. belov , s. a. tretyakov , and a. j. viitanen , ` ` dispersion and reflection properties of artificial media formed by regular lattices of ideally conducting wires , '' j. electromagn . waves applic . * 16 * , 11531170 ( 2002 ) . k. s. yee , ` ` numerical solution of initial boundary value problems involving maxwell s equations in isotropic media , '' ieee trans . antennas propgat . * 14*(3 ) , 302307 ( 1966 ) . a. taflove , _ computational electrodynamics : the finite - difference time - domain method _ ( norwood , ma : artech house , 1995 ) . f. b. hildebrand , _ introduction to numerical analysis _ ( new york : mc - graw - hill , 1956 ) . y. zhao , p. a. belov , and y. hao , ` ` modelling of wave propagation in wire media using spatially dispersive finite - difference time - domain method : numerical aspects , '' submitted to ieee trans . antennas propagat . ( arxiv : cond - mat/0604012 ) ( 2006 ) . k. p. prokopidis , e. p. kosmidou , and t. d. tsiboukis , ` ` an fdtd algorithm for wave propagation in dispersive media using higher - order schemes , '' journal of electromagn . waves and appl . * 18*(9 ) , 11711194 ( 2004 ) . c. r. simovski and p. a. belov , ` ` low - frequency spatial dispersion in wire media , '' phys . rev . e * 70 * , 046616 ( 2004 ) . m. silveirinha and c. fernandes , ` ` homogenization of 3d connected and non - connected wire metamaterials , '' ieee trans . microw . theory tech . * 54*(4 ) , 14181430 ( 2005 ) . m. silveirinha and c. fernandes , ` ` homogenization of metamaterial surfaces and slabs : the crossed wire mesh canonical problem , '' ieee trans . antennas propgat . * 53*(1 ) , 5969 ( 2005 ) . j. r. berenger , ` ` a perfectly matched layer for the absorption of electromagnetic waves , '' j. computat . phys . * 114*(2 ) , 185200 ( 1994 ) . p. a. belov and m. g. silveirinha , ` ` resolution of sub - wavelength lenses formed by the wire medium , '' accepted to phys . rev . e ( arxiv : physics/0511139 ) ( 2006 ) .","the sub - wavelength imaging with flat isofrequency components based on thin wire media has recently been extended to microwave frequencies using the finite - difference time domain ( fdtd ) method. although the proposed method is for the first time applied for the modeling of spatially dispersive materials, it is suitable for the imaging of structures which include components formed by materials with complex electromagnetic properties : the wire medium, bi - anisotropic media, non - linear materials, left - handed media and photonic crystals. one example of such materials is the uniaxial drude material. the spatial dispersion effects in this material are taken into account in the modeling using an auxiliary differential equation method which is formulated as a permittivity tensor. in contrast to the previous analytical models which only consider the frequency dispersive effects, we present analytical expressions which account for the spatial as well as the frequency dependent dispersion. we demonstrate the significant role of taking into account these effects in the modeled wire medium by modeling a planar slab of three - dimensional wire media, the lattices of which are parallel and ideally conducting, in the @xmath0-dimensional space. we consider two types of the modes which correspond to the transmission lines, the transverse magnetic field with respect to the wires and the extraordinary ( as opposed to the ordinary modes ) modes which are special kinds of waves when the wavelength in the free space is comparable with the period of the structure. in the thin wire approximation one can regard these as the modes of a sub - millimeter transmission line which does not interact with the wires, but with zero electric field along the wires. these modes are capable of transporting light across the interface of the lattice in different directions from one interface to another. we also introduce a new mode, the transmission line mode ( transmission - line ), which can be used to transmit transverse electric field with zero bias in the wires to another interface. numerical simulations of the modeled planar slabs show that as the wavelength decreases and the mode - to - mode switching occurs over a wide range of frequencies. 99 j. a. pendry, ` ` journal of biomedical optics, '' j. submillimeterwave technol. * 14 *, 033406 ( 2011 ). w. wang, l. peng, q. li, xie, r. zhang, x. jiang, f. torquato, x.- c. guo, and f. n. k. lee, solid state sub",0.12197483059051305,"the conventional imaging systems operate only with propagating harmonics emitted by a source , since the spatial harmonics carrying sub - wavelength information ( evanescent waves ) exhibit exponential decay in free space . a planar slab of such a material provides an opportunity for imaging with sub - wavelength resolution due to the effects of negative refraction and amplification of evanescent waves . there is an alternative approach for sub - wavelength imaging which does not involve either left - handed media or effects of negative refraction and amplification of evanescent waves . canalization_. the idea is that both propagating and evanescent harmonics of a source can be transformed into the propagating waves inside a slab of certain materials . then , these propagating modes are capable of transporting sub - wavelength images from one interface of the slab to another . we study the performance of sub - wavelength imaging by transmission devices formed by the wire medium at microwave frequencies . the finite - sized planar slabs of wire medium excited by sub - wavelength sources are modeled using the finite - difference time - domain ( fdtd ) method . this medium has been known as an artificial dielectric with plasma - like properties at microwave frequencies for a long time @xcite , but only recently it was shown that the wire medium has strong spatial dispersion @xcite . in other words , the wire medium is a non - local material and in the spectral domain it can not be described using only frequency dependent permittivity tensor . these modes travel with the speed of light along the wires ( @xmath13 ) and can have any wave vector in the transverse direction . effectively , these waves correspond to the modes of a multi - conductor transmission line formed by the wires , and enable us to use wire medium for realization of the canalization regime . the presence of tem ( transmission - line ) mode provides an evidence of the strong spatial dispersion in the wire media . usually , effects of the spatial dispersion can be observed in any periodical structure at the frequencies corresponding to the spatial resonances when the wavelength in the free space is comparable with the period of the structure , as in usual photonic and electromagnetic crystals , or when the wavelength in the crystal becomes comparable with the period of the structure due to the resonant behavior of inclusions , like in the case of resonant artificial dielectrics or photonic crystals made from self - resonant inclusions . the wire medium is a unique material where the spatial dispersion is observed at very low frequencies and without any resonant effects . we have implemented the spatially dispersive fdtd method in two - dimensional simulations in order to study the wave propagation through the wire medium . the spatially dispersive fdtd method has been developed for efficient modeling of the wave propagation in the wire medium using the effective medium approach .",0.16333938294010888
hep-ex0505072,"using the opal detector at lep , the running of the effective qed coupling @xmath0 is measured for space - like momentum transfer from the angular distribution of small - angle bhabha scattering . in an almost ideal qed framework , with very favourable experimental conditions , we obtain : @xmath1 where the first error is statistical , the second is the experimental systematic and the third is the theoretical uncertainty . this agrees with current evaluations of @xmath0 . the null hypothesis that @xmath2 remains constant within the above interval of @xmath3 is excluded with a significance above @xmath4 . similarly , our results are inconsistent at the level of @xmath5 with the hypothesis that only leptonic loops contribute to the running . this is currently the most significant direct measurement where the running @xmath0 is probed differentially within the measured @xmath6 range . european organisation for nuclear research cern - ph - ep/2005 - 014 + 21 february 2005 + revised 28 june 2005 * measurement of the running of the qed coupling in small - angle bhabha scattering at lep * collaboration + submitted to european physical journal c the opal collaboration g.abbiendi@xmath7 , c.ainsley@xmath8 , p.f.kesson@xmath9 , g.alexander@xmath10 , g.anagnostou@xmath11 , k.j.anderson@xmath12 , s.asai@xmath13 , d.axen@xmath14 , i.bailey@xmath15 , e.barberio@xmath16 , t.barillari@xmath17 , r.j.barlow@xmath18 , r.j.batley@xmath8 , p.bechtle@xmath19 , t.behnke@xmath19 , k.w.bell@xmath20 , p.j.bell@xmath11 , g.bella@xmath10 , a.bellerive@xmath21 , g.benelli@xmath22 , s.bethke@xmath17 , o.biebel@xmath23 , o.boeriu@xmath24 , p.bock@xmath25 , m.boutemeur@xmath23 , s.braibant@xmath7 , r.m.brown@xmath20 , h.j.burckhart@xmath26 , s.campana@xmath22 , p.capiluppi@xmath7 , r.k.carnegie@xmath21 , a.a.carter@xmath27 , j.r.carter@xmath8 , c.y.chang@xmath28 , d.g.charlton@xmath11 , c.ciocca@xmath7 , a.csilling@xmath29 , m.cuffiani@xmath7 , s.dado@xmath30 , g.m.dallavalle@xmath7 , a.de roeck@xmath26 , e.a.de wolf@xmath31 , k.desch@xmath19 , b.dienes@xmath32 , j.dubbert@xmath23 , e.duchovni@xmath33 , g.duckeck@xmath23 , i.p.duerdoth@xmath18 , e.etzion@xmath10 , f.fabbri@xmath7 , p.ferrari@xmath26 , f.fiedler@xmath23 , i.fleck@xmath24 , m.ford@xmath18 , a.frey@xmath26 , p.gagnon@xmath34 , j.w.gary@xmath22 , c.geich-gimbel@xmath35 , g.giacomelli@xmath7 , p.giacomelli@xmath7 , r.giacomelli@xmath7 , m.giunta@xmath22 , j.goldberg@xmath30 , e.gross@xmath33 , j.grunhaus@xmath10 , m.gruw@xmath26 , p.o.gnther@xmath35 , a.gupta@xmath12 , c.hajdu@xmath29 , m.hamann@xmath19 , g.g.hanson@xmath22 , a.harel@xmath30 , m.hauschild@xmath26 , c.m.hawkes@xmath11 , r.hawkings@xmath26 , r.j.hemingway@xmath21 , g.herten@xmath24 , r.d.heuer@xmath19 , j.c.hill@xmath8 , d.horvth@xmath36 , p.igo-kemenes@xmath25 , k.ishii@xmath13 , h.jeremie@xmath37 , p.jovanovic@xmath11 , t.r.junk@xmath38 , j.kanzaki@xmath39 , d.karlen@xmath15 , k.kawagoe@xmath13 , t.kawamoto@xmath13 , r.k.keeler@xmath15 , r.g.kellogg@xmath28 , b.w.kennedy@xmath20 , s.kluth@xmath17 , t.kobayashi@xmath13 , m.kobel@xmath35 , s.komamiya@xmath13 , t.krmer@xmath19 , p.krieger@xmath40 , j.von krogh@xmath25 , t.kuhl@xmath41 , m.kupper@xmath33 , g.d.lafferty@xmath18 , h.landsman@xmath30 , d.lanske@xmath42 , d.lellouch@xmath33 , j.letts@xmath43 , l.levinson@xmath33 , j.lillich@xmath24 , s.l.lloyd@xmath27 , f.k.loebinger@xmath18 , j.lu@xmath44 , a.ludwig@xmath35 , j.ludwig@xmath24 , w.mader@xmath45 , s.marcellini@xmath7 , a.j.martin@xmath27 , t.mashimo@xmath13 , p.mttig@xmath46 , j.mckenna@xmath14 , r.a.mcpherson@xmath15 , f.meijers@xmath26 , w.menges@xmath19 , f.s.merritt@xmath12 , h.mes@xmath47 , n.meyer@xmath19 , a.michelini@xmath7 , s.mihara@xmath13 , g.mikenberg@xmath33 , d.j.miller@xmath48 , w.mohr@xmath24 , t.mori@xmath13 , a.mutter@xmath24 , k.nagai@xmath27 , i.nakamura@xmath49 , h.nanjo@xmath13 , h.a.neal@xmath50 , r.nisius@xmath17 , s.w.oneale@xmath51 , a.oh@xmath26 , m.j.oreglia@xmath12 , s.orito@xmath52 , c.pahl@xmath17 , g.psztor@xmath53 , j.r.pater@xmath18 , j.e.pilcher@xmath12 , j.pinfold@xmath54 , d.e.plane@xmath26 , o.pooth@xmath42 , m.przybycie@xmath55 , a.quadt@xmath35 , k.rabbertz@xmath56 , c.rembser@xmath26 , p.renkel@xmath33 , j.m.roney@xmath15 , a.m.rossi@xmath7 , y.rozen@xmath30 , k.runge@xmath24 , k.sachs@xmath21 , t.saeki@xmath13 , e.k.g.sarkisyan@xmath57 , a.d.schaile@xmath23 , o.schaile@xmath23 , p.scharff-hansen@xmath26 , j.schieck@xmath17 , t.schrner-sadenius@xmath58 , m.schrder@xmath26 , m.schumacher@xmath35 , r.seuster@xmath59 , t.g.shears@xmath60 , b.c.shen@xmath22 , p.sherwood@xmath48 , a.skuja@xmath28 , a.m.smith@xmath26 , r.sobie@xmath15 , s.sldner-rembold@xmath18 , f.spano@xmath12 , a.stahl@xmath61 , d.strom@xmath62 , r.strhmer@xmath23 , s.tarem@xmath30 , m.tasevsky@xmath31 , r.teuscher@xmath12 , m.a.thomson@xmath8 , e.torrence@xmath62 , d.toya@xmath13 , p.tran@xmath22 , i.trigger@xmath26 , z.trcsnyi@xmath63 , e.tsur@xmath10 , m.f.turner-watson@xmath11 , i.ueda@xmath13 , b.ujvri@xmath63 , c.f.vollmer@xmath23 , p.vannerem@xmath24 , r.vrtesi@xmath64 , m.verzocchi@xmath28 , h.voss@xmath65 , j.vossebeld@xmath66 , c.p.ward@xmath8 , d.r.ward@xmath8 , p.m.watkins@xmath11 , a.t.watson@xmath11 , n.k.watson@xmath11 , p.s.wells@xmath26 , t.wengler@xmath26 , n.wermes@xmath35 , g.w.wilson@xmath67 , j.a.wilson@xmath11 , g.wolf@xmath33 , t.r.wyatt@xmath18 , s.yamashita@xmath13 , d.zer-zion@xmath22 , l.zivkovic@xmath33 @xmath11school of physics and astronomy , university of birmingham , birmingham b15 2tt , uk @xmath7dipartimento di fisica dell universit di bologna and infn , i-40126 bologna , italy @xmath35physikalisches institut , universitt bonn , d-53115 bonn , germany @xmath22department of physics , university of california , riverside ca 92521 , usa @xmath8cavendish laboratory , cambridge cb3 0he , uk @xmath21ottawa - carleton institute for physics , department of physics , carleton university , ottawa , ontario k1s 5b6 , canada @xmath26cern , european organisation for nuclear research , ch-1211 geneva 23 , switzerland @xmath12enrico fermi institute and department of physics , university of chicago , chicago il 60637 , usa @xmath24fakultt fr physik , albert - ludwigs - universitt freiburg , d-79104 freiburg , germany @xmath25physikalisches institut , universitt heidelberg , d-69120 heidelberg , germany @xmath34indiana university , department of physics , bloomington in 47405 , usa @xmath27queen mary and westfield college , university of london , london e1 4ns , uk @xmath42technische hochschule aachen , iii physikalisches institut , sommerfeldstrasse 26 - 28 , d-52056 aachen , germany @xmath48university college london , london wc1e 6bt , uk @xmath18department of physics , schuster laboratory , the university , manchester m13 9pl , uk @xmath28department of physics , university of maryland , college park , md 20742 , usa @xmath37laboratoire de physique nuclaire , universit de montral , montral , qubec h3c 3j7 , canada @xmath62university of oregon , department of physics , eugene or 97403 , usa @xmath20cclrc rutherford appleton laboratory , chilton , didcot , oxfordshire ox11 0qx , uk @xmath30department of physics , technion - israel institute of technology , haifa 32000 , israel @xmath10department of physics and astronomy , tel aviv university , tel aviv 69978 , israel @xmath13international centre for elementary particle physics and department of physics , university of tokyo , tokyo 113 - 0033 , and kobe university , kobe 657 - 8501 , japan @xmath33particle physics department , weizmann institute of science , rehovot 76100 , israel @xmath19universitt hamburg / desy , institut fr experimentalphysik , notkestrasse 85 , d-22607 hamburg , germany @xmath15university of victoria , department of physics , p o box 3055 , victoria bc v8w 3p6 , canada @xmath14university of british columbia , department of physics , vancouver bc v6 t 1z1 , canada @xmath54university of alberta , department of physics , edmonton ab t6 g 2j1 , canada @xmath29research institute for particle and nuclear physics , h-1525 budapest , p o box 49 , hungary @xmath32institute of nuclear research , h-4001 debrecen , p o box 51 , hungary @xmath23ludwig - maximilians - universitt mnchen , sektion physik , am coulombwall 1 , d-85748 garching , germany @xmath17max - planck - institute fr physik , fhringer ring 6 , d-80805 mnchen , germany @xmath50yale university , department of physics , new haven , ct 06520 , usa @xmath68 and at triumf , vancouver , canada v6 t 2a3 @xmath69 now at university of iowa , dept of physics and astronomy , iowa , u.s.a . @xmath70 and institute of nuclear research , debrecen , hungary @xmath71 and department of experimental physics , university of debrecen , hungary @xmath72 and mpi mnchen @xmath73 and research institute for particle and nuclear physics , budapest , hungary @xmath74 now at university of liverpool , dept of physics , liverpool l69 3bx , u.k . @xmath75 now at dept . physics , university of illinois at urbana - champaign , u.s.a . @xmath76 and manchester university manchester , m13 9pl , united kingdom @xmath77 now at university of kansas , dept of physics and astronomy , lawrence , ks 66045 , u.s.a . @xmath78 now at university of toronto , dept of physics , toronto , canada @xmath46 current address bergische universitt , wuppertal , germany @xmath79 now at university of mining and metallurgy , cracow , poland @xmath43 now at university of california , san diego , u.s.a . @xmath80 now at the university of melbourne , victoria , australia @xmath81 now at iphe universit de lausanne , ch-1015 lausanne , switzerland @xmath82 now at iekp universitt karlsruhe , germany @xmath83 now at university of antwerpen , physics department , b-2610 antwerpen , belgium ; supported by interuniversity attraction poles programme belgian science policy @xmath84 and high energy accelerator research organisation ( kek ) , tsukuba , ibaraki , japan @xmath85 now at university of pennsylvania , philadelphia , pennsylvania , usa @xmath86 now at triumf , vancouver , canada @xmath87 now at desy zeuthen @xmath88 now at cern @xmath89 now at desy @xmath90 deceased","we study the angular dependence of the electromagnetic coupling @xmath0 in bhabha scattering, using data recorded by the opal detector at lep. we find the running of the coupling is consistent with the standard model prediction, and that the data are cleanly incompatible with the hypothesis of a fixed coupling. the values of the running across the acceptance cut are found to be in good agreement with the values obtained previously by the venus @xcite and l3 experiments. # 1#2#3#4#1 * # 2 * ( # 3 ) # 4 = 0=0 1= 1=1 0>1 # 1 /#1#2(#3)@xmath1 - 12pt = -1 cm = -2 cm = 1.5 cm 0.2 cm * measurement of the electric - field running of * * bhaba * * opal collaboration ( submitted to physics letters b ) the opals collaboration g.abbiendi@kc.ac.uk, c.ainsley@pibet.ox by m.f.kesson during the 1992/1993 fixed power year at cern. the collaboration has been in a paid - up form and the work has been partially supported by the university of edinburgh. the first published paper in the field of theoretical physics is due to g.alexander@phys.j.c.2 in 1997. he was attracted attention because of its high sensitivity to different physical phenomena, such as the heavy ion decays at low energies. in this paper we will focus on the physics that was responsible for his discovery, namely the high - resolution spectrometer ( siw ) on the vlt, with the aim of obtaining a better understanding of the operation of the siw and the role of its interactions in the determination of the luminosity of the detector. we plan to make several measurements in the coming years. one of the most exciting lines of research at the present time is the measurement, with a very high experimental sensitivity, of the scaling of the physical quantities with energies. for example, the leptonic contribution to the amplitude of the electroweak coupling is directly estimated from the integrated luminosity, while the hadronic part is measured from the correlation function of observables near the resonance peak. this area of parameter space is, however, completely unexplored, so that at present a theoretical explanation is required for such a measurement. in the appendix we discuss the implications of our results from a theoretical point of view. 0.",0.08751334044823908,", such measurements currently constitute a stringent overall test of the standard model , in which many classes of radiative corrections are probed , involving electromagnetic , strong and weak interactions . direct _ measurement of the running of the electromagnetic coupling in the space - like region , where by direct we mean that the change in strength of the effective coupling is probed differentially as a function of @xmath94 of the photon propagator . in this paper we measure the running of @xmath2 in the space - like region , by studying the angular dependence of small - angle bhabha scattering using data collected by the opal detector at lep . small - angle bhabha scattering appears to be an ideal process for a direct measurement of the running of @xmath2 since the momentum transfer squared @xmath6 is simply and unambiguously related to the polar scattering angle , and the angular distribution is modified by the running coupling which appears as @xmath103 . , our result has sufficient sensitivity to expose clearly the hadronic contribution to the observed variation of @xmath2 as a function of the momentum transfer . we have measured the scale dependence of the effective qed coupling @xmath0 from the angular distribution of small - angle bhabha scattering using the precise opal silicon - tungsten calorimeters . despite the narrow accessible @xmath6 range , the method has high sensitivity due to the large statistics and excellent purity of the data sample . the challenging aspect of the analysis is controlling the residual bias in the reconstructed radial coordinate of bhabha electrons in the detector to a level below @xmath345 m uniformly throughout the acceptance . from a theoretical point of view the measurement is almost ideal . for this kinematic range the process is almost purely qed , @xmath100 interference is very small and the dominant diagram is @xmath6-channel single - photon exchange , while @xmath101-channel photon exchange is negligible . due to its utility in determining the lep luminosity , small - angle bhabha scattering is one of the most precisely calculated processes at these energies . we verified that there is no significant disturbance from theoretical uncertainties . we determined the effective slope of the bhabha momentum transfer distribution which is simply related to the average derivative of @xmath95 as a function of @xmath346 in the range @xmath274 gev@xmath347 gev@xmath105 . the observed @xmath6-spectrum is in good agreement with standard model predictions . we find : @xmath1 where the first error is statistical , the second is the experimental systematic and the third is the theoretical uncertainty . this measurement is one of only a very few experimental tests of the running of @xmath0 in the space - like region , where @xmath95 has a smooth behaviour . we obtain the strongest direct evidence for the running of the qed coupling ever achieved differentially in a single experiment , with a significance above @xmath4",0.0728952772073922
astro-ph0105340,"i construct a near - ir star count map of the lmc and demonstrate , using the viewing angles derived in paper i , that the lmc is intrinsically elongated . i argue that this is due to the tidal force from the milky way . the near - ir data from the 2mass and denis surveys are ideally suited for studies of lmc structure , because of the large statistics and insensitivity to dust absorption . the survey data are used to create a star count map of rgb and agb stars . the resulting lmc image shows the well - known bar , but is otherwise quite smooth . ellipse fitting is used for quantitative analysis . the radial number density profile is approximately exponential with a scale - length @xmath0@xmath1 . however , there is an excess density at large radii that may be due to the tidal effect of the milky way . the position angle and ellipticity profile both show large radial variations , but converge to @xmath2 and @xmath3 for @xmath4 . at large radii the image is influenced by viewing perspective ( i.e. , one side of the inclined lmc plane being closer to us than the other ) . this causes a drift of the center of the star count contours towards the near side of the plane . the observed drift is consistent with the position angle @xmath5 of the line of nodes inferred in paper i. the fact that @xmath6 differs from @xmath7 indicates that the lmc disk is not circular . deprojection shows that the lmc has an intrinsic ellipticity @xmath8 in its outer parts , considerably larger than typical for disk galaxies . the outer contours have a more - or - less common center , which lies @xmath9 from the center of the bar . neither agrees with the kinematic center of the hi gas disk . the lmc is elongated in the general direction of the galactic center , and is elongated perpendicular to the magellanic stream and the velocity vector of the lmc center of mass . this suggests that the elongation of the lmc has been induced by the tidal force of the milky way . the position angle of the line of nodes differs from the position angle @xmath10 of the line of maximum line of sight velocity gradient . results from hi gas and discrete tracers indicate that @xmath11@xmath12 . this could be due to one or more of the following : ( a ) streaming along non - circular orbits in the elongated disk ; ( b ) uncertainties in the transverse motion of the lmc center of mass , which can translate into a spurious solid - body rotation component in the observed velocity field ; ( c ) an additional solid body rotation component in the observed velocity field due to precession and nutation of the lmc disk as it orbits the milky way , which is expected on theoretical grounds . # 1 ' '' '' # 1 ' '' '' # 1 ' '' '' _ # 1 _ ' '' ''","the second in a series of papers on the structure of the magellanic clouds uses data from the near - infrared 2mass and denis surveys to investigate the lmc. the data from these surveys are used to create _ projected _ color - magnitude diagrams of the galaxy on the projected plane of the sky. the two - micron all sky survey ( 2mass ) is used to define the major axis position angle, @xmath0, while the denis survey provides the data for the star count contours. the latter are combined with positional information from the 2mass survey to define a projected grid of approximately 18,000 stars. the photometric and kinematic data for all three surveys are analyzed in a similar way to previous work, using a variety of tracers in an lmc disk ( rgb, asymptotic giant branch, and red giant branch stars ). the position angle and ellipticity values for the disk are determined by using the viewing angles from the previous work. the 3-dimensional projected number density distribution of stars in the rgb and agb lines show considerable variations as function of radius. at small radii the data shows a drift in the contour center around the center that is entirely due to the milky way tidal force, and is not centered on the center of the bar. at large radii, the effect of viewing perspective ( the centroid of stars being closer to us than the other ) is the dominant source of drift. the inner regions of the contours show large variations in the apparent magnitude of features, with peak - to peak amplitudes of up to 3.5 mag. the luminosity density of agb stars is well fitted by an exponential disk with scale length of 840 pc, but the data do not provide conclusive support for an exponential profile. the disk is not circular, but elongated. the elongation is most likely the result of tidal forces from the solar system, in conjunction with the tidal force from the smc ; the latter is indicated by the large and systematic difference in stellar mass traced by the two surveys. [ firstpage ] galaxies : structure galaxies : individual ( lmc, triangulum, smc ) galaxies : ism galaxies : spiral galaxies : stellar content",0.2298288508557457,"section [ s : maps ] presents a map of the stellar number density of rgb and agb stars on the projected plane of the sky . this may be due to the tidal effect of the milky way on the lmc . the position angle and ellipticity profile both show large variations as function of radius , but converge to approximately constant values for @xmath4 . in the outer parts , @xmath270 and @xmath3 . these results are consistent with previous studies of the distributions of tracers in the lmc disk , but most of those were of lower accuracy than the results presented here . the center of the star count contours on the sky shows considerable variations as function of radius . at small radii @xmath172 , this is due to intrinsic lopsidedness of the lmc : the contours are not centered on the center of the bar . at large radii the effect of viewing perspective ( one side of the lmc being closer to us than the other ) is the dominant source of drift in the contour center . the line of nodes position angle inferred in paper i , @xmath181 , differs by as much as @xmath271 from the major axis position angle of the outer lmc star count contours . this implies that the lmc is not intrinsically circular at large radii . to study the intrinsic structure of the lmc this suggests that the elongation of the lmc disk is the result of tidal forces . an analysis of the projected structure of the galaxy - lmc - smc triple system on the sky shows that the projected elongation of the lmc is aligned to within @xmath194 with the projected direction to the galactic center . the elongation is perpendicular to the lmc proper motion and the magellanic stream to within the errors . a three - dimensional analysis shows that the galactic center lies at an angle of @xmath205 from the plane of the lmc , as seen from the lmc center . the projection of the galactic center onto the disk plane is aligned to within @xmath202 with the major axis of the disk . the elongation is perpendicular to within the errors to the projection of the three - dimensional lmc center of mass velocity vector onto the lmc disk plane . these results are qualitatively consistent with the hypothesis that the elongation of the lmc disk is due to the tidal force from the milky way . , the position angle @xmath278 of the line of maximum gradient in the velocity field has generally been used to estimate the position angle @xmath6 of the line of nodes , which assumes that the lmc disk is circular . however",0.3171007927519819
1111.4940,"we demonstrate how _ ab initio _ cluster calculations including the full coulomb vertex can be done in the basis of the localized wannier orbitals which describe the low - energy density functional ( lda ) band structure of the infinite crystal , _ e.g. _ the transition metal @xmath0 and oxygen @xmath1 orbitals . the spatial extend of our @xmath0 wannier orbitals ( orthonormalized @xmath2th order muffin - tin orbitals ) is close to that found for atomic hartree - fock orbitals . we define ligand orbitals as those linear combinations of the o @xmath1 wannier orbitals which couple to the @xmath0 orbitals for the chosen cluster . the use of ligand orbitals allows for a minimal hilbert space in multiplet ligand - field theory calculations , thus reducing the computational costs substantially . the result is a fast and simple _ ab initio _ theory , which can provide useful information about local properties of correlated insulators . we compare results for nio , mno and srtio@xmath3 with x - ray absorption , inelastic x - ray scattering , and photoemission experiments . the multiplet ligand field theory parameters found by our _ ab initio _ method agree within @xmath410 % to known experimental values . [ nio6cluster ] many electronic properties of solids can now be described _ ab initio _ thanks to the advent of powerful computers and the development of ingenious methods , such as density - functional theory ( dft)@xcite with local density ( lda)@xcite or generalized gradient ( gga)@xcite approximations , lda+hubbard @xmath5 ( lda+u),@xcite quantum chemical methods,@xcite dynamic mean - field theory , metzner89,georges92,jarrell92,georges96,anisimov97 , held03 , maier05 , lechermann06 quantum monte - carlo simulations,@xcite and exact diagonalization for finite clusters.@xcite nevertheless , for correlated open - shell systems with several local orbital and spin degrees of freedom , electronic - structure calculations remain a challenge . ground - state properties and spectral functions may be calculated by exact diagonalization of the many - electron hamiltonian , but this is hindered by the exponential growth of the hilbert - space with the number of correlated electrons in the system . exploiting symmetry and limiting the number of correlated electronic degrees of freedom may enable the treatment of relatively large clusters , as done in the important case of doped high-@xmath6 cuprates , where symmetry in the spin sector allowed lau and coworkers to use clusters with up to 32 cuo@xmath7 plackets , each with a single cu @xmath8 , and two o @xmath9 orbitals.@xcite for _ local _ properties , such as excitonic spectra , exact diagonalization for finite clusters becomes much more appealing , as relatively small clusters often suffice . magnetic anisotropies , @xmath10-tensors , magnetization - dependent electron - spin resonance spectra , crystal - field excitations , and a manifold of excitonic core - level spectra are usually well described using very small clusters . for transition - metal and rare - earth compounds , the cluster may often be limited to merely a single @xmath11- or @xmath12-electron cation surrounded by its nearest neighbor ligands as illustrated in fig.@xmath13[nio6cluster ] . for clusters that small , exact diagonalization is equivalent to multiplet ligand - field - theory ( mlft ) , one of the earliest quantum - chemistry methods developed to describe the electronic structure of transition - metal and rare - earth compounds.@xcite mlft is a highly cost - efficient method , able to account for many of the local properties and excitonic spectra of correlated materials . mlft calculations traditionally use parameters fitted to experiments . despite being a great help for understanding and interpreting experimental results , this approach is however not completely satisfactory and , over the years , numerous theoretical studies have therefore been devoted to obtaining mlft parameters _ ab initio_.@xcite sugano and shulman @xcite calculated the ligand - field parameters by constructing single - particle molecular orbitals ( mos ) as linear combinations of atomic hartree - fock orbitals and thereby in several cases obtained qualitative agreement with experiments . more often , mo theory with a more complete basis is used.@xcite after the lda had proven useful not only for @xmath14- and @xmath9- , but also for @xmath11- and @xmath12- electrons in solids , andersen70 several authors obtained mlft parameters by performing an lda calculation for the cluster and using its kohn - sham mos . @xcite such a calculation breaks the translation invariance of the crystal already at the single - particle lda level , and it is necessary to remedy finite - size and surface effects , e.g. by embedding the cluster in a set of point - charges mimicking the rest of the solid . such procedures are not well controlled , e.g. depending on the details , the sign of crystal - field may change.sugano63 , wachters71 , wachters72 here we use a different route to performing _ ab initio _ mlft calculations . our procedure is similar to the method originally devised by gunnarsson _ et al . _ @xcite for obtaining the parameters in the anderson impurity model and , in the last 15 years , used extensively for dynamical - mean - field calculations for realistic solids ( lda+dmft ) . @xcite we start our _ ab initio _ mlft calculation by performing a dft calculation for the proper , infinite crystal using a modern dft code which employs an accurate density functional and basis set ( e.g. lapws).andersen75,blaha90 from the ( selfconsistent ) dft crystal potential we then calculate _ a set of wannier functions _ suitable as single - particle basis for the mlft calculation.@xcite since the members of such a set are centered either on the tm or ligand atoms , we shall call them wannier _ orbitals . _ typically , they are the tm @xmath0- and oxygen @xmath1-orbitals which , _ taken together _ , exactly describe the dft @xmath15- and @xmath16 bands . in general , the set should be minimal and span _ exactly _ all dft solutions in the energy range relevant for the property to be calculated . it is important that this set contains sufficiently many ligand orbitals to make the _ correlated _ tm _ orbitals well localized , _ _ i.e. _ the tm @xmath11-orbitals should not have tails on any other atom . this localization allows one to restrict the many - electron calculations of local properties to a single tm site plus its ligand neighbors . hence , in the current method , there are no embedding errors , except those arising from truncating the single - particle basis to include only the wannier orbitals on the cluster . in the following we introduce the method by the example of the late transition - metal oxide nio with configuration @xmath17 . in sect . ii , we show that similar results can be obtained for middle and early transition - metal oxides , specifically @xmath18 mno and @xmath19 srtio@xmath20 in sect . iii , we compare with results obtained by several different experimental techniques : ( a ) @xmath1 x - ray absorption ( xas ) , a charge neutral excitation of a transition - metal @xmath1 core electron into the @xmath0 shell . ( b ) @xmath1 core level x - ray photoemission ( xps ) from ni impurities in mgo . ( c ) inelastic x - ray scattering ( ixs ) of core to valence excitations , a technique similar to xas . we specifically show @xmath21 core - electron excitations into the @xmath0 shell . ( d ) inelastic x - ray scattering of @xmath11-@xmath11 excitations . the experiments presented for these materials are relatively well understood , so that the comparison with our new _ ab initio _ results constitute a critical test of the theoretical method . at the end of the paper , we conclude . in appendix [ appcovalence ] we provide information on the different basis sets or wannier orbitals used , as well as the meaning of the different occupation numbers and the concept of formal valence . details of the calculations , including numerical values of several mlft parameters obtained _ ab initio , _ may be found in appendix [ appcomp ] . a discussion of the double counting of interactions in the lda and mlft calculations may be found in appendix [ appdouble ] . in appendix [ appbasissize ] we show how ligand orbitals can be obtained in general symmetry from the o @xmath1 orbitals , with the use of blocktridiagonalization of the orbital basis set . this is an essential ingredient which makes these calculation numerically efficient . appendix [ appdiag ] contains a short note on the exact diagonalization routines .","multiplet _ ligand _ field theory ( mlft ) is applied to the correlated transition - metal compounds nio, mno and srtio@xmath3. the basic idea is that the one electron potential in the local density approximation ( lapw ) and the warped muffin - tin approximation ( lda ) are combined in order to calculate the one - electron potential from the ( fully selfconsistent ) lda basis set. because of the limited overlap of the orbital degrees of freedom with the atomic states, the lda core - level potential is not maximally localized, and therefore the essential part of the coulomb interaction has to be maximally screened. the calculated potential has been used to compare experiment and theory for several established spectroscopic features of these compounds. the comparison shows that the mlft calculations are in agreement with the experimental spectra except for the crystal - field splitting which is almost 10 % too high in nio. we show that the splittingscale for the o @xmath4 orbitals in our lda - based mlft calculation is about 10 % larger than that for the slater integrals. however, the multiplet splitting due to the screening is not important in deciding which of the two potentials will be realized in the experiment, and it is not even important for the core excitations. the inelastic x - ray scattering technique has been applied to separate the optically thin inner shell excitations from the high- and low - energy states of nio and mno. the compared spectra of these oxides show that many of the features can be captured by mlft theory, but some features are completely absent from local calculations. _ keywords _ : multiplet, multiplet, field theory, excitonic, electron, transition metal. + * pacs number(s ) : * 05.70.-a, 05.75.-y, 42.50.lc, 43.60.+c, 41.60.-r, 4110.jv + * msc * : 51.20.-m, 71.10.lq * key words : * multiblock footnote omitted * + + +",0.1276324186343331,"in this section we introduce the _ ab initio _ mlft method by the example of nio . nio is a metal , in strong contrast to experiments where nio is found to be a good insulator with a room - temperature resistance of @xmath27 cm and an optical band - gap of about 3.0 - 3.5 ev . this allows us to compare oxides of early , intermediate and late transition metals and show that the method is likely to apply to a range of correlated transition - metal compounds . new in the present paper is that the mlft parameters ( except for @xmath5 and @xmath100 ) are not fitted to the experiment , but calculated _ ab initio_. in the following subsections we first discuss x - ray absorption ( xas ) at the @xmath168 edge , which probes tm @xmath1 to @xmath0 excitations . next we show tm @xmath1 core - level x - ray photoemission ( xps ) experiments on an impurity system . now we shall discuss core - level spectra obtained with a technique which from a theoretical point of view is very similar to x - ray absorption , namely inelastic x - ray scattering ( ixs ) . recent time dependent dft calculations with the lda+@xmath5 functional do show frenkel excitons ( @xmath11-@xmath11 excitations ) within the optical gap , but they can not reproduce the correct number of multiplet states.@xcite let us finally have a closer look at the comparison between the experimental and mlft crystal - field excitations in nio . as the @xmath233 energy is mainly determined by one - electron interactions , we conclude that the @xmath239 splitting due to covalency in our lda based calculation is 5% underestimated . at the same time , the multiplet splitting due to the coulomb repulsion , i.e. the values of the @xmath240 and @xmath241 slater integrals , are 10% overestimated . we have shown how multiplet ligand - field theory ( mlft ) calculations can be based on _ ab - initio _ lda solid - state calculations , in a similar way as originally devised by gunnarson _ _ et al.__@xcite and recently done for lda+dmft calculations . the theory is very well suited for the calculation of local ground - state properties and excitonic spectra of correlated transition - metal and rare - earth compounds . our tm @xmath11 wannier orbitals , which _ together _ with the o @xmath9 wannier orbitals span the lda tm @xmath11- _ and _ o @xmath9-bands , are quite similar to atomic orbitals , and this justifies many previous studies using the latter . we compared several experimental spectra ( xas , non - resonant ixs , pes ) for srtio@xmath3 , mno@xmath242 and nio with our _ ab initio _ multiplet ligand - field theory and found overall satisfactory agreement , indicating that our ligand - field parameters are correct to better than 10% . the covalency seems to be slightly underestimated and the slater integrals for the higher multipole interactions overestimated . the method is expected to provide insights to the local properties of transition - metal compounds with only modest computational efforts . we explain the definition of the two different set of orbitals , by the example of nio . in fig .",0.14163335237007424
1703.04806,"a decade ago , abdulla , ben henda and mayr introduced the elegant concept of decisiveness for denumerable markov chains @xcite . roughly speaking , decisiveness allows one to lift most good properties from finite markov chains to denumerable ones , and therefore to adapt existing verification algorithms to infinite - state models . decisive markov chains however do not encompass stochastic real - time systems , and general stochastic transition systems ( stss for short ) are needed . in this article , we provide a framework to perform both the qualitative and the quantitative analysis of stss . our first contribution is to define various notions of decisiveness ( inherited from @xcite ) , notions of fairness and of attractors for stss , and explicit the relationships between them . as a second contribution , we define a notion of abstraction , together with natural concepts of soundness and completeness , and we give general transfer properties , which will be central to several verification algorithms on stss . our third contribution focuses on qualitative model - checking . beyond ( repeated ) reachability properties for which our technics are strongly inspired by @xcite , we use abstractions to design algorithms for the qualitative model - checking problem of arbitrary @xmath0-regular properties , when the sts admits a denumerable ( sound and complete ) abstraction with a finite attractor . our fourth contribution is the design of generic approximation procedures for quantitative model - checking ; in addition to extensions of @xcite for general stss , we design approximation algorithms for @xmath0-regular properties ( once again by means of specific abstractions ) . last , our fifth contribution consists in instantiating our framework with stochastic timed automata ( sta ) and generalized semi - markov processes ( gsmp ) , two models combining dense - time and probabilities . this allows us to derive decidability and approximability results for the verification of these two models . some of these results were known from the literature , but our generic approach permits to view them in a unified framework , and to obtain them with less effort . we also derive interesting new approximability results for sta and gsmps .","in this article , we face this issue and provide a framework to perform the analysis of general _ stochastic transition systems _ ( stss for short ) . to do so , we generalize the main concepts of @xcite ( such as decisiveness , attractors ) , and standard notions for markov chains ( like fairness ) . our first contribution is to define various notions of decisiveness ( inherited from @xcite ) , notions of fairness and of attractors in the general context of stss . to complete the semantical picture , our third contribution focuses on the qualitative model checking problem for various properties . in particular , we extend the results of @xcite and show that , under some decisiveness assumptions , the almost - sure model checking of ( repeated ) reachability properties reduces to a simpler problem , namely to a reachability problem with probability @xmath2 . we advocate that this reduction simplifies the problem : in countable models , the @xmath2-reachability amounts to the non existence of a path , in the underlying non - probabilistic system ; beyond countable models , checking that a reachability property is satisfied with probability @xmath2 amounts to exhibiting a somehow regular set of executions with positive measure . beyond repeated reachability properties , we use abstractions to design algorithms for the qualitative model - checking problem of arbitrary @xmath0-regular properties , in case the sts admits an abstraction with the finite attractor property . the latter contribution is completely new compared to the original results of @xcite and our conference paper @xcite . it is inspired by a procedure of @xcite for probabilistic lossy channel systems , a special class of denumerable markov chains with a finite attractor . our fourth contribution is the design of generic approximation procedures for the quantitative model - checking problem , inspired by the path enumeration algorithm of purushothoman iyer and narashima @xcite . under some decisiveness assumptions , we prove that these approximation schemes are guaranteed to terminate . assuming the stss can be represented finitely and enjoy some smooth effectiveness properties , one derives approximation algorithms : one can approximate , up to a desired ( arbitrary ) precision , the probability of ( repeated ) reachability properties . further , once again via the use of an abstraction with the finite attractor property , we design an approximation algorithm for @xmath0-regular properties ; this algorithm makes use of the attractor of the abstract model to convert the quantitative analysis of an @xmath0-regular property into the quantitative verification of a reachability property in the concrete model . up to our knowledge , this approach is completely new , and provides an interesting framework for quantitative verification of stochastic systems . our last contribution consists in instantiating our framework with high - level stochastic models , stochastic timed automata ( sta ) and generalized semi - markov processes ( gsmp ) , which are two models combining dense - time and probabilities . this allows us to derive decidability and approximability results for the verification of those models . we also derive interesting new approximability results for sta and gsmps . the paper concludes with an overview of our main results , organized as a travel guide to stss : it summarizes the relationships between all notions , and provides the reader recipes to analyze stss .",0.3694581280788178,"we provide a framework for the quantitative analysis of stochastic real - time systems, that is, markov chains with continuous state - space. to do so, we generalize several notions of decisiveness, of fairness and of attractors, and end up with defining deterministic muller automata, and other properties. this allows us to derive decidability and approximability results for the verification of those models. as a special case, we define a notion of abstraction, which makes sense for stss. concepts of soundness and completeness are naturally defined for those abstractions, and general transfer properties are given, which will be central to several verification algorithms on stns. measures and other notions are extended in a straightforward way from stss to lstss. @xmath0-regularity is a standard notion in computer science to characterise simple properties. it reduces to the qualitative problem for near - sure executeable inputs, and the problem for a model that is almost sure to be reachable with high probability. in the model - checking context, it is often a hard problem, particularly for infinite - state models. the problem can be reduced to a problem of approximation for a small class of possible states of the system, which is formulated in terms of periodic measurable events. under certain general assumptions, we prove that these approximation schemes are guaranteed to terminate for any given precision. to deal with the latter condition, we design an approximation scheme for the _ repeated _ reachability properties of a concrete model, inspired by the path enumeration algorithm of purdulla, ben henda and mayr. we further refine the concept of muller and bchi, and establish a correspondence between them by dchi and muller - dchi. this leads us to define a probability measure, on which we evaluate the approximate value of the reached - out property. this probability measure is the product of two estimators, the durant and the summatory part. under the assumption that the potential of the method is not infinite, we compute the standard muller distribution for the reachability property. finally, for those models which enjoy some good effectiveness properties, we propose an approximation algorithm for the full ( repeated ) check of those properties, and also design a framework to analyse their dynamical properties.",0.24963289280469897
1201.5121,"we present a measurement of the lyman @xmath0 flux probability distribution function ( pdf ) obtained from a set of eight high resolution quasar spectra with emission redshifts at @xmath1 . we carefully study the effect of metal absorption lines on the shape of the pdf . metals have a larger impact on the pdf measurements at lower redshift , where there are relatively fewer lyman @xmath0 absorption lines . this may be explained by an increase in the number of metal lines which are blended with lyman @xmath0 absorption lines toward higher redshift , but may also be due to the presence of fewer metals in the intergalactic medium at earlier times . we also provide a new measurement of the redshift evolution of the effective optical depth , @xmath2 , at @xmath3 , and find no evidence for a deviation from a power law evolution in the @xmath4 plane . the flux pdf measurements are furthermore of interest for studies of the thermal state of the intergalactic medium ( igm ) at @xmath5 . by comparing the pdf to state - of - the - art cosmological hydrodynamical simulations , we place constraints on the temperature of the igm and compare our results with previous measurements of the pdf at lower redshift . at redshift @xmath6 , our new pdf measurements are consistent with an isothermal temperature - density relation , @xmath7 , with a temperature at the mean density of @xmath8 k and a slope @xmath9(1@xmath10 uncertainties ) . in comparison , joint constraints with existing lower redshift pdf measurements at @xmath11 favour an inverted temperature - density relation with @xmath12 k and @xmath13 , in broad agreement with previous analyses . = = = = = = = = # 1 # 1 # 1 # 1 @mathgroup@group @mathgroup@normal@groupeurmn @mathgroup@bold@groupeurbn @mathgroup@group @mathgroup@normal@groupmsamn @mathgroup@bold@groupmsamn = ` ` 019 = ' ' 016 = ` ` 040 = ' ' 336 = "" 33e = = = = = = = = # 1 # 1 # 1 # 1 = = = = = = = = -0.25 in [ firstpage ] cosmology : intergalactic medium - methods : numerical - quasars : absorption lines .","in this paper , we have measured the lyman @xmath0 forest flux pdf from a set of eight qso spectra to investigate the thermal state of the igm at @xmath5 . the absorption lines in the lyman @xmath0 forest have been fitted with voigt profiles , and absorption lines arising from heavy elements have been carefully identified . the resulting masked spectra have been used to study the redshift evolution of the lyman @xmath0 forest flux distribution and the evolution of the hi effective optical depth . * by removing metals from the lyman @xmath0 forest , we attempt to eliminate pixels which will introduce a systematic uncertainty into our measurement of the flux pdf . the effect of removing these metals on the pdf is to decrease the number of pixels in bins of low flux and increase the number of pixels in bins of high flux . as a result , * we measure the pdf for our full sample in two redshift bins , both before and after metal decontamination , and find the effect of metal absorption on the lyman @xmath0 forest flux pdf is redshift dependent . this redshift dependence may be understood in terms of the larger number of metal lines which are blended with lyman @xmath0 absorption lines toward higher redshift , resulting in the identification of fewer isolated metal absorption lines . on the other hand , it is also possible that the metallicity of the intergalactic medium decreases with increasing lookback time . + * we present measurements of the effective optical depth , @xmath2 , from our qso sample , which provides a probe of the igm which is complementary to the pdf . the values of @xmath2 measured from the qsos in our sample can be fitted with a power - law @xmath60 , in agreement with previous measurements by k07 after correcting for metal absorption . we also find no substantial evidence for a deviation from a power law in the @xmath61 plane at @xmath62 . + there is a weak redshift dependence of the ratio of the hi effective optical depth measured before and after removing identified metal absorption lines . the ratio increases toward lower redshift , and is consistent with our previous finding from the pdf that metal absorption plays a more significant role in the lyman @xmath0 forest toward lower redshift . + * we perform a set of high resolution hydrodynamical simulations with a range of cosmological and astrophysical parameters and use them to extract mock qso spectra with properties that closely resemble those of the observed spectra . we compute the lyman @xmath0 flux pdf and compare it to the observed pdf in the range @xmath38@xmath39 $ ] via a taylor expansion at second order to find deviations from a best - guess case ( e.g. viel & haehnelt 2006 ) . by implementing this method within a monte carlo markov chain likelihood estimator , we present constraints for the igm thermal state . at @xmath6 , our pdf measurements are consistent with an isothermal temperature - density relation , @xmath9 , and a temperature at the mean density of @xmath63 k ( 1@xmath10 uncertainties ) . + * we also obtain joint constraints on the igm thermal state by analysing the lower redshift pdf measurements of k07 , which is a significantly larger data set than the one considered here . at @xmath6 , we find the joint data set is consistent with an inverted temperature - density relation , @xmath64 , with @xmath65 k ( 1@xmath10 uncertainties ) . + * in conclusion , the present work highlights the role of the flux pdf as a competitive and quantitative thermometer which may be used to constraint the igm temperature - density relation over a wide redshift range .",0.3115693012600229,"we present a study of the flux probability distribution function ( pdf ) of the lyman @xmath0 forest from eight high resolution quasi - stellar object ( qso ) spectra obtained with the uves echelle spectrograph. the spectra have been imprinted with voigt profiles, and absorption lines arising from heavy elements have been carefully identified. we have then had the metal absorption lines removed from within the ly-0 forest, resulting in a joint sample of qso spectra covering a wide range of redshifts. we find that the removal of metal absorption from our full sample leads to a redshift dependent effect on the pdf, both before and after metal decontamination. we measure the pdf for the full sample in two redshift bins, and find that it is sensitive to the metallicity of the intergalactic medium ( igm ). the effect of removing metal absorption is seen to be larger for higher redshift. however, after correcting for metal absorption, the pdf measured with the metal removal is in agreement with the one measured from the previous results for lower redshift spectra. we also find that there is substantial deviation from the pdf of the weak power - law regime measured from our sample by kim et al. ( 2007 ). no strong trends with redshift are found for the pdf after removing metals, in contrast to previous results from smaller samples. to complete the picture, we also perform a series of hydrodynamical simulations to obtain constraints on the temperature and the thermal history of the igm. the resulting constraints are in good agreement with previous measurements, and are used to discuss the possible inversion of the temperature - density relation due to photo - ionization during the epoch of heii reionization. cosmology : theory dark matter, large - scale structure of the universe, galaxies : evolution stars : formation galaxies : high - redshift techniques : spectroscopic",0.2583892617449665
cond-mat0503666,"the in - plane infrared response of the high-@xmath0 cuprate superconductors was studied using the spin - fermion model , where charged quasiparticles of the copper - oxygen planes are coupled to spin fluctuations . first , we analyzed structures of the superconducting - state conductivity reflecting the coupling of the quasiparticles to the resonance mode observed by neutron scattering . the conductivity @xmath1 computed with the input spin susceptibility in the simple form of the mode exhibits two prominent features : an onset of the real part of @xmath1 starting around the frequency @xmath2 of the mode and a maximum of a related function @xmath3 , roughly proportional to the second derivative of the scattering rate @xmath4(\omega)$ ] , centered approximately at @xmath5 , where @xmath6 is the maximum value of the superconducting gap . the two structures are well known from earlier studies . their physical meaning , however , has not been sufficiently elucidated thus far . our analysis involving quasiparticle spectral functions provides a clear interpretation . second , we explored the role played by the spin - fluctuation continuum , whose spectral weight is known to be much larger than the one of the mode . we have shown that the experimental spectra of @xmath7 can be approximately reproduced by augmenting the resonant - mode component of the spin susceptibility by a suitable continuum component with a considerably higher spectral weight and with a characteristic width of several hundreds mev . the computed spectra of @xmath7 display a new structure in the mid - infrared which is related to the finite width of the occupied part of the conduction band . third , we investigated the temperature dependence ( td ) of @xmath1 assuming that the normal state spin susceptibility consists of an overdamped low energy mode and the continuum component . the differences between the experimental normal - state spectra and those of the superconducting state , including some interesting effects at higher frequencies , are reasonably well reproduced . motivated by recent experimental ( ellipsometric ) works by molegraaf and coworkers [ h. j. a. molegraaf _ et al . _ , science * 295 * , 2239 ( 2002 ) . ] and boris and coworkers [ a. v. boris _ et al . _ , science * 304 * , 708 ( 2004 ) . ] , we further studied the tds of the effective kinetic energy @xmath8 and of the intraband spectral weight @xmath9 . calculations for the trivial case of noninteracting quasiparticles in the normal state and a bcs - like superconducting state reveal a strong sensisitivity of the td of @xmath9 to details of the dispersion relation . the tds of @xmath8 and @xmath9 in the interacting case , for the set of the values of the input parameters used throughout this work , are similar to those of the trivial case . the physics beyond the changes occuring when going from the normal to the superconducting state , however , is shown to be more complex , involving , besides the formation of the gap , also a feedback effect of the spin fluctuations on the quasiparticles and a significant shift of the chemical potential .","we study the influence of the magnetic mode on the conductivity of the high-@xmath0 cuprate superconductors in the superconducting state. we focus on the region, around the saddle point, where the quasiparticles of the copper - oxygen planes are coupled to the magnetic excitations. the infrared spectra, observed in the scanning tunneling spectroscopy ( stis ) of the transition metal oxide ( tmos ), can be well represented and described in terms of a two - particle hamiltonian composed of two bogoliubov states, the nodal region and the intermediate region. the parameters of the model are determined by a delicate competition of the three components, i.e., the excitation energy, the coupling constant and the spin - fluctuation parameter. results are presented in two different codes. the first one is applicable to the case of the onset starting around @xmath1 and the second one is adapted to the situation of the sharp resonance. the quantum numbers of the modes, as determined from the stis data, are shown to be consistent with the values of the effective coupling constant derived from the optical data. the effects of the mode - mode coupling constant as well as the neutron resonance on the onset feature are discussed in the light of the recent experimental data. an important finding is that the ratio between the effective neutron resonance and the contribution of the well - defined mode to the total infrared scattering rate is of the same order of magnitude as those of the contributions of the individual points to the spectral function. the properties of the low - temperature conductivity, particularly its slope and variability, are well described, according to the approach recently developed by carbotte, schachinger, and basov [ phys. rev. lett. * 106 *, 184101 ( 2011 ) ], interms of the s - spin correlator. this technique, however, can not be applied to the htcs in the normal state because of the very weak coherence of the electronic degrees of freedom at higher temperatures. the technique proposed by sandvik, scalapino, and bickers [ j. phys. * c * : condens. matter * * 10 *, 41128 ( 2012 ) ] is not applicable in these materials. their conclusions are in conflict with the experimental findings.",0.24754901960784315,"one of the aims of the present paper is to provide a detailed interpretation of the onset starting around @xmath2 discussed by mbc and of the main maximum of the function @xmath3 emphasized by csb in terms of the quasiparticle spectral function . among others , in subsects . [ ssec : akr]-[ssec : dmw ] we have analyzed the structures of the superconducting state ( scs ) conductivity reflecting the coupling of the charge quasiparticles to the resonance mode : the onset of the real part @xmath41 of the conductivity starting around the frequency @xmath2 of the mode and the maximum of the function @xmath3 centered approximately at @xmath5 , where @xmath6 is the maximum value of the superconducting gap . it is based on a division of the brillouin into three parts : the nodal , the region , and the intermediate . we have shown that the onset is due to the appearance above @xmath2 of low energy excitations of the nodal region , consisting of two nodal quasiparticles and the mode . for the conventional shape of the @xmath58-gap the onset is very gradual but it becomes steeper with increasing broadening of the nodes . the maximum of @xmath3 has been shown to be due to the appearance above @xmath420 of excitations of the nodal region , consisting of a nodal particle , an antinodal particle and the mode . due to the brillouin zone averaging , in particular , due a considerable contribution of the intermediate region , the maximum of @xmath3 appears at a frequency @xmath319 which is slightly higher but considerably lower than @xmath421 . the width of the maximum , however , is determined not only by the one of the mode but also by the averaging . for zero width of the mode , the fwhm of the maximum is ca @xmath423 . in the light of the present analysis , the computed spectra of the scattering rate @xmath7 exhibit a sharp step ( onset feature ) centered around @xmath319 , a region of an approximately linear increase of @xmath7 , and a plateau in the mid - infrared . the height of the step is determined by the spectral weight @xmath424 of the mode , the difference between the value of @xmath7 of the plateau and the height of the step by the spetral weight @xmath425 of the continuum , and the onset frequency of the plateau by the width of the continuum . the experimental scattering rate spectra can be reproduced using values of @xmath426 of 5 - 10 and those of the width of several hundreds mev . the computed spectra of @xmath7 display , in addition , an interesting weak structure located approximately at @xmath427 ( @xmath86 is the chemical potential and @xmath428 the quasiparticle energy of the @xmath48-point ) . the main differences between the scs and the normal state ( ns ) experimental data , in particular , the spectral gap , the tail of @xmath429 ranging to very high frequencies , and the shift of the scattering rate plateau towards lower frequencies with increasing temperature are reasonably well reproduced . some of the remaining discrepancies are very likely to be related to the absence of self - consistency and vertex corrections . we have further investigated the temperature dependence of the effective kinetic energy @xmath8 and of the intraband spectral weight @xmath9 , first for the bcs case and second for the present version of spin - fermion model . in the bcs case , @xmath8 increases both with increasing temperature in the ns and when going from the ns to the scs . the temperature dependencies of @xmath8 and @xmath9 calculated for the case of the quasiparticles coupled to the spin fluctuations are , for the present values of the input parameters , similar to those of the bcs , @xmath401 case .",0.3092979127134725
1606.05514,"consider a continuous signal that can not be observed directly . instead , one has access to multiple corrupted versions of the signal . the available corrupted signals are correlated because they carry information about the common remote signal . the goal is to reconstruct the original signal from the data collected from its corrupted versions . known as the indirect or remote reconstruction problem , it has been mainly studied in the literature from an information theoretic perspective . a variant of this problem for a class of gaussian signals , known as the gaussian ceo problem "" , has received particular attention ; for example , it has been shown that the problem of recovering the remote signal is equivalent with the problem of recovering the set of corrupted signals ( separation principle ) . the information theoretic formulation of the remote reconstruction problem assumes that the corrupted signals are uniformly sampled and the focus is on optimal compression of the samples . on the other hand , in this paper we revisit this problem from a sampling perspective . more specifically , assuming restrictions on the sampling rate from each corrupted signal , we look at the problem of finding the best sampling locations for each signal to minimize the total reconstruction distortion of the remote signal . in finding the sampling locations , one can take advantage of the correlation among the corrupted signals . the statistical model of the original signal and its corrupted versions adopted in this paper is similar to the one considered for the gaussian ceo problem ; _ i.e. , _ we restrict to a class of gaussian signals . our main contribution is a fundamental lower bound on the reconstruction distortion for any arbitrary nonuniform sampling strategy . this lower bound is valid for any sampling rate . furthermore , it is tight and matches the optimal reconstruction distortion in low and high sampling rates . moreover , it is shown that in the low sampling rate region , it is optimal to use a certain nonuniform sampling scheme on all the signals . on the other hand , in the high sampling rate region , it is optimal to uniformly sample all the signals . we also consider the problem of finding the optimal sampling locations to recover the set of corrupted signals , rather than the remote signal . unlike the information theoretic formulation of the problem in which these two problems were equivalent , we show that they are not equivalent in our setting .","we study the sampling aspect of reconstructing a stochastic source @xmath0 from a limited set of measurements, and also distinguish the two cases that are of interest for the study. we show that the reconstruction error is bounded by the mean squared error of the original signal, and that the optimal error matrix for the recovery is a linear combination of the error measures of both the original and corrupted signals. the quality of the reconstructions is characterized by the minimization of the sampling noise. this quality is the same for samples corrected by overlaps, so long as the noise is not added to the reconstructed signals. for many applications, it is critical to have good sampling rates both in the frequency domain and in the source coding domain. there has been much study in the literature on how to improve the sampling rates of noisy sources. some of the results are expected to be universal to various source coding domains @xcite, and others may have specific applications. in this paper, we determine the optimal sampling rate for reconstructions of arbitrary source types, and show that it is possible to achieve a significant gain in the sampling error when one improves the receiver error rate. the paper is organized as follows : in section [ sec1 ], we recall the construction of the circuit for superconducting devices, and demonstrate the use of superconductors in some signal processing problems ( see the paper by chuang, dai, hoang, and kee ) in the other aspects of information processing ( e.g., computing error models for higher dimensional networks ; fast quantum computing for low dimensional systems ; etc. ), the construction works according to the rules of quantum information processing, with the exception of some special cases such as for noisy source coding and least squares error theorem ( lemma ), which have additional consequences in the signal processing and signal estimation aspects. in sections [ sec2 ], 3, 4, and 5 ( respectively ), we derive the lemma and demonstrate its effectiveness for a wide class of problems, and give some examples.",0.21023513139695715,"the goal is to reconstruct @xmath0 from limited information that one can obtain from @xmath3 . while the source coding aspect of the problem 3.5 ) ) , its signal processing and sampling aspect has not received much attention . in this paper , we study the sampling aspect of this problem for _ stochastic _ signal @xmath0 and the @xmath1 corrupted versions @xmath4 . we take into account the fact that the correlation among the signals @xmath3 , can help decrease the sampling rate or improve the signal reconstruction accuracy . if the number of non - zero coefficients @xmath9 and @xmath10 are limited , the signal @xmath5 is sparse in the frequency domain . the corrupted versions of the signal can be expressed as @xmath20 , \qquad t\in [ 0,t],~~i\in \{1,2,\cdots , k\},\label{eqdefs}\end{aligned}\ ] ] where @xmath21 and @xmath22 ; here @xmath23 and @xmath24 are independent perturbations that are added to the original signal . the statistical model assumed for the coefficients @xmath11 , @xmath12 , @xmath24 , @xmath23 parallels the one for the gaussian ceo problem "" @xcite . the sampling noise of each signal @xmath4 is modeled by an independent zero - mean gaussian random variable with variance @xmath36 . we use the samples to reconstruct either the remote signal @xmath0 , or the collection of corrupted signals @xmath2 . the reconstruction of the remote signal @xmath0 and the corrupted signal @xmath4 are denoted by @xmath39 and @xmath40 , respectively . the lemma provides the two alternative forms of the lmmse estimator and the mean squared error . next we use this lemma to formulate the reconstruction of the remote signal @xmath0 and its corrupted versions @xmath4 in the subsequent subsections . the goal is to reconstruct all the @xmath1 signals with minimum distortion using the observation vector @xmath67 . in this section , we state the proofs of our results . in the body of the proofs then , the relation between the traces of the above matrices is @xmath180^{-1 } \\&\geq { \mathtt{tr}}\left [ i+\frac{1}{\eta } \left({k } i -k^2a_{{\mathsf{diag}}}^{-1}\right ) \right]^{-1}\label{peilersbi},\end{aligned}\ ] ] where results from lemma [ peirelslemma ] for the convex function @xmath181 when @xmath182 and the hermitian matrix @xmath183 . to find @xmath184 , we need to calculate the diagonal entries of matrix @xmath78 . in this section , we state some lemmas that have been used in the proof section .",0.23036649214659685
astro-ph0010571,"with the recent publication of the measurements of the radiation angular power spectrum from the boomerang antarctic flight ( de bernardis et al . 2000 ) , it has become apparent that the currently favoured spatially - flat cold dark matter model ( matter density parameter @xmath0 , flatness being restored by a cosmological constant @xmath1 , hubble parameter @xmath2 , baryon density parameter @xmath3 ) no longer provides a good fit to the data . we describe a phenomenological approach to resurrecting this paradigm . we consider a primordial power spectrum which incorporates a bump , arbitrarily placed at @xmath4 , and characterized by a gaussian in log @xmath5 of standard deviation @xmath6 and amplitude @xmath7 , that is superimposed onto a scale - invariant power spectrum . we generate a range of theoretical models that include a bump at scales consistent with cosmic microwave background and large - scale structure observations , and perform a simple @xmath8 test to compare our models with the @xmath9 dmr data and the recently published boomerang and maxima data . unlike models that include a high baryon content , our models predict a low third acoustic peak . we find that low @xmath10 observations ( 20 @xmath11 200 ) are a critical discriminant of the bumps because the transfer function has a sharp cutoff on the high @xmath10 side of the first acoustic peak . current galaxy redshift survey data suggests that excess power is required at a scale around 100 mpc , corresponding to @xmath4 @xmath12 0.05 @xmath13 mpc@xmath14 . for the concordance model , use of a bump - like feature to account for this excess is not consistent with the constraints made from recent cmb data . we note that models with an appropriately chosen break in the power spectrum provide an alternative model that can give distortions similar to those reported in the apm survey as well as consistency with the cmb data ( atrio - barandela et al . 2000 ; barriga et al . 2000 ) . we prefer however to discount the apm data in favour of the less biased decorrelated linear power spectrum recently constructed from the pscz redshift survey ( hamilton & tegmark 2000 ) . we show that the concordance cosmology can be resurrected using our phenomenological approach and our best - fitting model is in agreement with the pscz observations . -0.5 in epsf cosmology : theory cosmic microwave background","we examine the possibility that the second acoustic peak in the angular power spectrum of the cosmic microwave background ( cmb ) is suppressed relative to the first acoustic peak based on recent boomerang and maxima data. we show that a phenomenological bump, arbitrarily placed at wavenumber @xmath0, can enhance the power spectrum amplitude around 100 mpc@xmath1, allowing for a baryon fraction greater than expected for a spatially flat universe such as the concordance model. we incorporate the bump into the primordial power spectrum by renormalizing the standard low - density cosmological model to the decorrelated linear power spectrum that was recently generated by ostriker & steinhardt ( 1995 ). we interpret the 22 decorrelated pscz data points as constraints on the bump parameters so that the theoretical model that we find to be the best - fit to the cmb observational data set can be compared with the galaxy survey observations. the choice of bump parameters is consistent with observations of large - scale power and cmb anisotropies. we find that with the chosen bump the model with a bias parameter of 1.07 ( hamilton & tegmark 2000 ) is ruled out at the 95 % confidence level, whereas the model without the bump takes a biasulus of 1. both models are a good fit to these up - to - date data sets, but the current data do not probe the scales that are critical to distinguishing between the models. we discuss the implications of our results for the scalelengths of adiabatic density perturbations in a model - by - model basis. # 1#2#3acta. phys. pol. * b#1 *, # 2 ( # 3 ) # 1 # 1 = = = cmr10 scaled2 = cmbh_s psfig.tex # 1 eq. ( [ eq : pncrab_s ] ) # 10^#1 # 1 ^#2_w 2m_z^2 2bh^2 # 1sec^2",0.1840490797546012,"the recent boomerang and maxima measurements of an acoustic peak in the angular power spectrum of the cosmic microwave background ( cmb ) temperature at @xmath15 ( de bernardis et al . one consequence of the location of this peak , due to the compression of an acoustic wave on first entering the horizon of last scattering , is that the spatial geometry of the universe is flat . however , the weakness of the second acoustic peak at @xmath16 , due to the subsequent first rarefaction of the acoustic wave on the last scattering horizon , has provoked considerable speculation as to the additional freedom that could be added to the concordance cold dark matter ( cdm ) model ( matter density parameter @xmath0 , flatness being restored by a cosmological constant @xmath1 , hubble parameter @xmath2 , baryon density parameter @xmath3 ) to accommodate such an effect . 1990 ; einasto et al . 1997 ; landy et al . we therefore consider a primordial power spectrum which incorporates a phenomenological bump , arbitrarily placed at @xmath4 , and characterized by a gaussian in log @xmath5 of standard deviation @xmath6 and amplitude @xmath7 , that is superimposed onto a scale - invariant power spectrum as advocated by silk & gawiser ( 1998 ) . @xmath24 we restrict the choice of bump parameters to the region of parameter space that is consistent with large - scale structure and cmb observations . theories that predict a bump in the primordial power spectrum have been inspired by hints of such a feature from large - scale structure observations . this indicates that , for the chosen cosmology , the scale at which a bump can appear in the primordial power spectrum is quite constrained by the cmb data sample . at the 68% confidence level we describe a toy model for a bump to be included in the primordial density power spectrum with the hope of reviving the standard model without resorting to revising fundamental cosmological theories . we have confronted our theoretical models with the recent boomerang and maxima data and have shown that it is indeed possible to resurrect the standard model , although we are somewhat restricted with where we place our additional feature . we find that our model , unlike models that include a high baryon content , predicts a low third acoustic peak . there are two cmb measurements that will help to discriminate between such a bump and cosmological alternatives for suppressing the second peak . in addition , although low @xmath10 ( 20 - 100 ) observations have received relatively little attention and hence are currently a poor constraint on cosmological parameters , we have found that the low @xmath10 power is potentially a critical discriminant for the possible bump feature . this because the transfer function has a much sharper cutoff on the high @xmath10 side of the first peak , relative to the cutoff on the low @xmath10 side . we note that models with an appropriately chosen break in the power spectrum provide an alternative model that can give distortions similar to those reported in the apm survey as well as consistency with the cmb data ( atrio - barandela et al .",0.4299065420560748
cs0606099,"for a wide class of multi - user systems , a subset of capacity region which includes the corner points and the sum - capacity facet has a special structure known as polymatroid . multiaccess channels with fixed input distributions and multiple - antenna broadcast channels are examples of such systems . any interior point of the sum - capacity facet can be achieved by time - sharing among corner points or by an alternative method known as _ rate - splitting_. the main purpose of this paper is to find a point on the sum - capacity facet which satisfies a notion of fairness among active users . this problem is addressed in two cases : ( i ) where the complexity of achieving interior points is not feasible , and ( ii ) where the complexity of achieving interior points is feasible . for the first case , the corner point for which the minimum rate of the active users is maximized ( max - min corner point ) is desired for signaling . a simple greedy algorithm is introduced to find the optimum max - min corner point . for the second case , the polymatroid properties are exploited to locate a rate - vector on the sum - capacity facet which is optimally fair in the sense that the minimum rate among all users is maximized ( max - min rate ) . in the case that the rate of some users can not increase further ( attain the max - min value ) , the algorithm recursively maximizes the minimum rate among the rest of the users . it is shown that the problems of deriving the time - sharing coefficients or rate - spitting scheme can be solved by decomposing the problem to some lower - dimensional subproblems . in addition , a fast algorithm to compute the time - sharing coefficients to attain a general point on the sum - capacity facet is proposed . polymatroid structure , multiuser systems , multiaccess channels , broadcast channels , fairness , successive decoding , time - sharing , rate - splitting .","in multi - user systems, multiple transmitters / receivers share a common communication medium, and therefore, there is an inherent competition in accessing the channel. information theoretic results for such systems imply that in order to achieve a high spectral efficiency, the users with stronger channel should have a higher portion of the resources. the drawback to this is the loss of the fairness among the users. to provide fairness, we want to find the corner point for which the minimum rate of the active users is maximized ( max - min corner point ). this problem is formulated by considering a point on the face of the contra - polymatroid. a simple greedy algorithm is introduced to find this corner point. based on this algorithm, it is shown that the problem of deriving the time - sharing coefficients and rate - splitting can be decomposed into some lower - dimensional subproblems. _ _ a criterion based on nash bargaining solution in the context of game theory is proposed. this criterion generalizes the proportional fairness and increases the efficiency of the system. as a special case, we consider a multiaccess system in which the distribution of inputs are independent and equal to @xmath0. particularly in some multiuser systems, the boundary of the capacity region includes a facet on which the sum - rate is maximum ( sum - capacity facet ). in such systems, one can benefit from the available degrees of freedom, i.e., determine the fairest rate - vector ( the uniform minimum rate among all users ), and determine the fairness coefficient as well. as the first example, we show that a subset of the convex hull of these corner points forms a polymatoid. in fact, the polymetroid structure is established first by establishing a relationship between the existing capacity region of the simulating multiple - input multiple - output ( mimo ) broadcast channel ( both positive semi - definite diagonal and non - diagonal covariance matrices ), then by determining the best linear combination of these two matrices. the result is proved by proving the optimality of the above algorithm. the optimal dynamic power allocation strategy for time - varying multiple - access channels is also discussed.",0.26666666666666666,"based on this criterion , the rates of users with a stronger channel can be increased with the cost of decreasing the rates of users with a weaker channel . , it is shown that the capacity region of multiaccess channels ( mac ) with fixed and independent input distributions forms a polymatroid @xcite . in mac , the sum - capacity is achieved by successive decoding . applying different orders for the users in successive decoding results in different rate - vectors , all with the sum - rate equal to the sum - capacity . , it is proven that the marton inner bound ( see @xcite ) for capacity region of the broadcast channel under fixed joint probability of the auxiliary and input variables , with some conditions , has a polymatroid structure . as another example , we will show that a subset of the capacity region for multiple - input multiple - output ( mimo ) broadcast channel which includes the corner points forms a polymatroid . in @xcite , the optimal dynamic power allocation strategy for time - varying single - antenna multiple - access channel is established . to this end , the polymatroid properties of the capacity region for time - invariant multiple - access channel with fixed input distributions have been exploited . in @xcite this article aims at finding a point on the sum - capacity facet which satisfies a notion of fairness among active users by exploiting the properties of polymatroids . in order to provide fairness , the minimum rate among all users it is shown that the problem of deriving the time - sharing coefficients to attain this point can be decomposed to some lower - dimensional subproblems . an alternative approach to attain an interior point for multiple access channels in addition , the relationship between the capacity region of some channels and the polymatroid structure is described . in addition , it is shown that the problem of deriving the time - sharing coefficients and rate - splitting can be solved by decomposing the problem into some lower - dimensional subproblems . _ we considered the problem of fairness for a class of systems for which a subset of the capacity region forms a polymatroid structure . the main purpose is to find a point on the sum - capacity facet which satisfies a notion of fairness among active users . this problem is addressed in cases where the complexity of achieving interior points is not feasible , and where the complexity of achieving interior points is feasible . for the first case , the corner point for which the minimum rate of the active users is maximized ( max - min corner point ) is desired for signaling . a simple greedy algorithm is introduced to find the optimum max - min corner point . for the second case , it is shown that the problems of deriving the time - sharing coefficients and rate - spitting scheme can be solved by decomposing the problem to some lower - dimensional subproblems .",0.4037184594953519
1702.05845,"we introduce intertwining operators among twisted modules or twisted intertwining operators associated to not - necessarily - commutative automorphisms of a vertex operator algebra . let @xmath0 be a vertex operator algebra and let @xmath1 , @xmath2 and @xmath3 be automorphisms of @xmath0 . we prove that for @xmath1- , @xmath2- and @xmath3-twisted @xmath0-modules @xmath4 , @xmath5 and @xmath6 , respectively , such that the vertex operator map for @xmath6 is injective , if there exists a twisted intertwining operator of type @xmath7 such that the images of its component operators span @xmath6 , then @xmath8 . we also construct what we call the skew - symmetry and contragredient isomorphisms between spaces of twisted intertwining operators among twisted modules of suitable types . the proofs of these results involve careful analysis of the analytic extensions corresponding to the actions of the not - necessarily - commutative automorphisms of the vertex operator algebra . [ section ] [ thm]definition [ thm]proposition [ thm]corollary [ thm]lemma [ thm]remark [ thm]application [ thm]problem [ thm]convention [ thm]conjecture [ thm]condition [ thm]example [ thm]assumption [ thm]notation .=b=:=|=#1(#2,#3)[#4,#5 ] sprboxcdr#1nil @box sprbox # 1sprbox sprbox= .=12 b=11 : = 12 |=12 ( 25,25)[0.5 em , 1.2 ex ] : bbbbbbbbbbbbbbbbbbbbbbbbb | : bb ...................... b | : b.b ..................... b | : b .. b .................... b | : b ... b ................... b | : b .... b .................. b | : b ..... b ................. b | : b ...... b ................ b | : b ....... b ............... b | : b ........ b .............. b | : b ......... b ............. b | : b .......... b ............ b | : b ........... b ........... b | : b ............ b .......... b | : b ............. b ......... b | : b .............. b ........ b | : b ............... b ....... b | : b ................ b ...... b | : b ................. b ..... b | : b .................. b .... b | : b ................... b ... b | : b .................... b .. b | : b ..................... b.b | : b ...................... bb | : bbbbbbbbbbbbbbbbbbbbbbbbb | ( 25,25)[0.3 em , 0.72 ex ] : bbbbbbbbbbbbbbbbbbbbbbbbb | : bb ...................... b | : b.b ..................... b | : b .. b .................... b | : b ... b ................... b | : b .... b .................. b | : b ..... b ................. b | : b ...... b ................ b | : b ....... b ............... b | : b ........ b .............. b | : b ......... b ............. b | : b .......... b ............ b | : b ........... b ........... b | : b ............ b .......... b | : b ............. b ......... b | : b .............. b ........ b | : b ............... b ....... b | : b ................ b ...... b | : b ................. b ..... b | : b .................. b .... b | : b ................... b ... b | : b .................... b .. b | : b ..................... b.b | : b ...................... bb | : bbbbbbbbbbbbbbbbbbbbbbbbb |","in this paper, we study intertwining operators among twisted modules associated to not - necessarily - commutative automorphisms of a vertex operator algebra. by twisted modules we mean ( generalized or logarithmic ) twisted modules of arbitrary genus. they come from chiral vertex operators in physics and were introduced by frenkel, lepowsky and meurman @xcite. they have been studied systematically in the literature and played an important role in the representation theory of vertex operator algebras and two - dimensional conformal field theories. if the vertex operator subalgebra fixed by the automorphism group of an algebra satisfies suitable conditions ( for example, the three conditions in conjecture [ twisted - int - op ] ), then one possible choice of such a structure large enough for our purpose is the intertwining operator algebra formed by the modules and intertwined operators for the fixed - point vertex operator seeding. however, the assumption that these suitable conditions hold is in fact a main conjecture that we have to prove first. because of this, the assumptions used to derive the conjectures are often themselves the most difficult parts of the computations required to prove them. to prove a theorem or a proof of an interesting theorem, however, in order to obtain a proof, we first have to work with multivalued analytic functions with preferred branches. such functions are the kind of ones we study in this paper. we prove that for @xmath0, there exists a subtraction procedure to obtain such functions on a region of the same region, that is to say, we can take the form of decomposition functions on branches of the single - valued branch on the region and divide the functions on that branch into two separate regions, respectively. we also give a careful analysis of the relations between these two subsets of functions and vertex operators and show that the corresponding functions in the subtraction sequence do not violate the contragredient functor on the category of twisted modules. 2.0 cm * 2000 mathematics subject classification : * 60k35, 60j20, 60k25, 82c22, 34c20, 34j50, 34m05",0.15592203898050971,"intertwining operators give chiral three - point correlation functions in two - dimensional conformal field theories and are the building blocks of multi - point correlation functions on riemann surfaces of arbitrary genus . if this conjecture is proved , then we obtain the genus - zero and genus - one parts of the chiral orbifold conformal field theory associated with the vertex operator algebra @xmath0 and the group @xmath19 of automorphisms of @xmath0 . one consequence of conjecture [ twisted - int - op ] is that the category of @xmath20-twisted modules for all all @xmath21 has a natural structure of @xmath19-crossed braided tensor category satisfying additional properties . to even formulate this conjecture precisely , we have to first introduce twisted intertwining operators or intertwining operators among twisted modules associated to general automorphisms and study their basic properties . in this paper , we give a definition of such twisted intertwining operators . let @xmath0 be a vertex operator algebra and let @xmath1 , @xmath2 and @xmath3 be automorphisms of @xmath0 . we prove that for @xmath1- , @xmath2- and @xmath3-twisted @xmath0-modules @xmath4 , @xmath5 and @xmath6 , respectively , such that the vertex operator map for @xmath6 is injective , if there exists a twisted intertwining operator of type @xmath7 such that the images of its component operators span @xmath6 , then @xmath8 . we also construct what we call the skew - symmetry and contragredient isomorphisms between spaces of twisted intertwining operators among twisted modules of suitable types . we expect that this theory will play an important role in the study of orbifold conformal field theory and , in particular , in the study of the uniqueness conjecture of the moonshine module vertex operator algebra . in this paper we also discuss in this section the functors associated to automorphisms of the vertex operator algebra and the contragredient functor on the category of twisted modules . twisted intertwining operators are introduced in section 4 . in the same section , we prove the result that for @xmath1- , @xmath2- and @xmath3-twisted @xmath0-modules @xmath4 , @xmath5 and @xmath6 , respectively , such that the vertex operator map for @xmath6 is injective , if there exists a twisted intertwining operator of type @xmath7 such that the images of its component operators span @xmath6 , then @xmath8 . to study intertwining operators , we have to work with multivalued analytic functions with preferred branches . but for what we want to prove in the future , it is necessary for @xmath0 to be a vertex operator algebra with the additional data of a conformal element satisfying some additional conditions . in this section , we construct what we call the skew - symmetry isomorphisms between the spaces of twisted intertwining operators of suitable types . in this section , we construct what we call the contragredient isomorphisms between the spaces of twisted intertwining operators of suitable types .",0.2941176470588235
1008.2397,"since the discovery of the first double neutron star ( dns ) system in 1975 by hulse and taylor , there are currently 8 confirmed dns in our galaxy . for every system , the masses of both neutron stars , the orbital semi - major axis and eccentricity are measured , and proper motion is known for half of the systems . using the orbital parameters and kinematic information , if available , as constraints for _ all system _ _ , we investigate the immediate progenitor mass of the second - born neutron star and the magnitude of the supernova kick it received at birth , with the primary goal to understand the core collapse mechanism leading to neutron star formation . compared to earlier studies , we use a novel method to address the uncertainty related to the unknown radial velocity of the observed systems . for psr b1534 + 12 and psr b1913 + 16 , the kick magnitudes are 150 - 270 km / s and 190 - 450 km / s ( with 95 % confidence ) respectively , and the progenitor masses of the 2nd born neutron stars are 1.3 - 3.4 m@xmath0 and 1.4 - 5.0 m@xmath0 ( 95 % ) , respectively . these suggest that the 2nd born neutron star was formed by an iron core collapse supernova in both systems . for psr j0737 - 3039 , on the other hand , the kick magnitude is only 5 - 120 km / s ( 95 % ) , and the progenitor mass of the 2nd born neutron star is 1.3 - 1.9 m@xmath0 ( 95 % ) . because of the relatively low progenitor mass and kick magnitude , the formation of the 2nd born neutron star in psr j0737 - 3039 is potentially connected to an electron capture supernova of a massive @xmath1 white dwarf . for the remaining 5 galactic dns , the kick magnitude ranges from several tens to several hundreds of km / s , and the progenitor mass of the 2nd formed neutron star can be as low as @xmath21.5 m@xmath0 , or as high as @xmath28 m@xmath0 . therefore in these systems , it is not clear which type of supernova is more likely to form the 2nd neutron star . _ _ _","over the years , computation modeling and hydrodynamic calculations of supernova explosions due to core - collapse of massive stars have improved our theoretical understanding of how compact objects form . at present , eventually , it crosses the chandrasekhar mass limit and ensues collapse . there is thus evidence for the existence of two different neutron star formation mechanisms ( van den heuvel 2004 , 2007 ) , potentially distinguishable by the magnitude of the natal kick of the neutron star . currently , there are 8 dns observed in our galaxy . the magnitude of the natal kick and the progenitor mass of the second - born neutron star ( ns2 ) in these systems , except psr j1906 + 0746 , have been studied previously by willems et . , we summarize our results and discuss their implications for the supernova forming the second - born neutron star in the observed dns . the primary star , which is initially the more massive one , will leave the main sequence first and explode as the first supernova , in which it forms the first - born neutron star ( ns1 ) in this binary mass transfer from the helium star to ns1 can also occur prior to the second supernova explosion . here , our goal is to use the current dns binary properties listed in table 1 to constrain as best possible the magnitude of the natal kick and the mass of the progenitor of ns2 in the 8 known dns in our galaxy at the time of the second supernova . we also predict the unknown radial velocity of each system , as well as the total transverse velocity and ns1 spin tilt angle for those systems where these properties have not been measured yet . we achieve these goals by means of monte carlo simulations , incorporating orbital dynamics during supernova explosions and kinematic of binaries in the galactic potential , as detailed in what follows . the pre - supernova orbit is assumed to be tidally circularized at the time of the second supernova explosion . on the other hand , also , using equations ( 12 ) in the same paper , we find the polar angle @xmath29 between the natal kick and the pre - supernova orbital angular momental axis . immediately before the second supernova explosion we perform a monte carlo simulation of the motion of dns in the galactic potential . the analysis outlined in the previous section allows us to derive pdfs for the kick velocity @xmath23 , ns2 s immediate pre - supernova progenitor mass @xmath28 , the spin tilt @xmath50 of ns1 , the systemic radial velocity @xmath51 , and the current transverse velocity @xmath52 . the current radial velocity of this binary is between -110 and 145 km / s , at 95% confidence , and it is likely to be moving away from us . within the observationally constrained range , the @xmath52 pdf is roughly flat . when comparing with recent analyses by willems et al .",0.2073324905183312,"we study the orbital kinematics of dynamical neutron stars ( dns ) in the galactic disk at the time of the second supernova explosion. to this purpose, we perform a monte carlo simulation of the motion of _ all _ observed dns in our galaxy ( including psr j1906 + 0746 ). each system in the population is assigned a velocity equal to the vector sum of the local galactic rotational velocity and an isotropic kick velocity generated from the kick velocity distribution function. we then derive probability distribution functions ( pdf ) of the natal kick velocity and the spin tilt of ns1 for each of the observed systems. for ns2 s progenitor mass of @xmath0 m@xmath1, which is a convectional limit for a helium star that explodes in a core - collapse supernova, we restrict our analysis to the regime of a secondary star that is about 270 km / s from the birth of the binary. the only constraint on the post - birth mass of ns2 is that it needs to be more massive than 2.1 m@xcite, while the constraint on ns1 spin tilt angle requires that it must be smaller than 1.4. these constraints are combined with the constraints on the mass transfer occurring between ns1 and ns2 at birth, which also tightens the constraints to a lower value. we apply the 2-dimensional joint probability distribution for the present - day orbital inclination and the angle of the orbital ascending node to determine the dns initial orbital semi - major axis and orbital eccentricity. for those systems where these properties have not been measured yet, we achieve these goals by taking advantage of the accurate up - to - date kinematic parameters of dns. we also predict the unknown radial velocity of each system, as well as the total transverse velocity and ns1 spins tilt angle of those dns that have not yet been found.",0.19814241486068115
1011.3217,"many problems in geometry , topology and dynamical systems on surfaces lead to the study of closed surfaces endowed with a flat metric containing several cone - type singularities , that are called _ flat structures _ or _ translation surfaces_. + the first construction in the theory is that of a flat structure which is obtained from billiard on a rational polygon by _ unfolding _ it to a collection of polygons with gluings . that is , from a polygon @xmath0 , we develop a polygonal system @xmath1 , with sides identified by translation , to get a surface @xmath2 . the idea is to associate a closed , orientable surface to the billiard table which has the same geodesics ( the billiard trajectories ) . rational billiard determines a flat structure ; however most of the flat structures are not obtained from billiards . + over the course of studying billiard dynamics , several questions were raised . one of the questions was , which surfaces satisfy the following property ( which is called _ veech s dichotomy _ ) : any direction is either _ completely periodic _ or _ uniquely ergodic_. + in an important paper @xcite veech gave a sufficient condition for this dichotomy . he showed that if the stabilizer of a translation surface is a lattice in @xmath3 , then the surface satisfies veech s dichotomy . later , smillie and weiss @xcite proved that this condition is not necessary . they constructed a translation surface which satisfies veech s dichotomy but is not a lattice surface . their construction was based on previous work of hubert and schmidt @xcite , by taking a branched cover over a lattice surface , where the branch locus is a single _ non - periodic connection point_. + in this work we tried to answer the following question : is there a flat structure obtained from a billiard table that satisfies veech s dichotomy , but its veech group is not a lattice ? in theorem [ main ] we prove that in the entire list of possible candidates for such a construction , an example does not exist .","general references for translation surfaces and billiards are @xcite , @xcite , @xcite . a _ translation surface _ or _ flat structure _ is a finite union of euclidean polygons @xmath4 with identifications such that : 1 . + there is an equivalent definition of translation surfaces in terms of special atlases called _ translation atlases _ : a translation surface is a compact orientable surface with an atlas such that , away from finitely many points called singularities , all transition functions are translations . @xcite let @xmath21 be a translation surface , let @xmath22 be the multiplicities of its singular points . then @xmath23 where @xmath24 is the genus of @xmath21 and @xmath25 is the euler characteristic of @xmath21 . we will describe the unfolding process , which gives the motivation to the following definition that describes the connection of billiards to translation surfaces . + let @xmath0 be a rational polygon ( all of whose angles are rational multiples of @xmath26 ) . given a billiard trajectory ( that avoids the vertices ) beginning at a side of @xmath0 . given a collision with a side we reflect the polygon along the side , obtaining a mirror image of the original polygon , on which the billiard now continues in its original direction , instead of reflecting off the side . let @xmath27 be the group of motions of the plane generated by the reflections in the sides of @xmath0 . an _ affine diffeomorphism _ of a translation surface @xmath21 is a homeomorphism @xmath61 that maps singular points to singular points and is an affine map in the local coordinates of the atlas of @xmath21 . + in view of the above , the veech group @xmath72 is the image of aff(@xmath21 ) under the derivative map . completely periodic_. every periodic trajectory is contained in a maximal family of parallel periodic trajectories of the same period . lattice surfaces satisfy both topological dichotomy and strict ergodicity . this means that @xmath99 is partitioned into a finite number of isometric copies of @xmath0 . [ non - periodic ] the last proposition along with lemma 4 in @xcite give us a test for non - periodicity of a point in a lattice surface : a point in a lattice surface @xmath21 which irrationally splits the height of a cylinder of @xmath21 is a non - periodic point . in genus 2 + following the definitions in @xcite , smillie and weiss show that a surface satisfying both topological dichotomy and strict ergodicity need not be a lattice surface . , we can expand our search to find a cover which is branched only over one non - periodic point .",0.2187938288920056,"we introduce a new definition of translation surface, which is a compact orientable surface of opposite sides that is connected to a translation atlas by special atlases. translation surfaces satisfy two dichotomies : topological dichotomy and strict ergodicity. we show that the best description of a translation surface is given by the riemann - hurwitz formula, which describes the relation between the euler characteristics of two surfaces when one is a ramified covering of the other. we describe the mechanism by which two surfaces with different angles in a given direction become reflections of the original polygon when they are ramified. we give a detailed description of the mechanism using examples. the study of billiards is a blooming field of study in modern mathematics. a billiard trajectory is defined as a trajectory that does not hit singular points on its initial trajectory. given a trajectory starting at a side of a polygon, the billiard can be continued along the original direction, passing copies of the polygon along the side and merging it with the new side. if the new trajectory continues along the direction it was started in, it is called an _ unfolding process_. given two paths that intersect at different points in the same direction, the outcome is the formation of a new billiard. in this paper we describe this process and give an example of how it can be understood in terms of topological properties of translation surfaces. + let @xmath0 be a simple closed oriented polygon. if one of the two _ angles _ in euclidean polygons is odd, and the other is even, then there is an atlas of its singular points by a translation. we say that a _ translation surface _ is a _ flat structure _ if the three are connected by a single object with an even angle between them. + an _ affine diffeomorphism _ of such a fixed polygon is a translation in the opposite direction. we call a _ lattice surface _ if for every direction the transition function from a singular point to the singular point is uniquely ergodic. there are two equivalent definitions of lattice surfaces : the _ cactus _ and the _ euler _ types. the first type is more general and more specific : translation surfaces are closed surfaces, cactus covers are the surfaces that are copies of flat structures associated with specific flat structures. the second type is the _ tracer _ type : a tracer has the same property, that is, the tracer is a covering of a surface by",0.1949860724233983
math0606413,"we study the buchsbaum - rim multiplicity @xmath0 of a finitely generated module @xmath1 over a regular local ring @xmath2 of dimension @xmath3 with maximal ideal @xmath4 . the module @xmath1 under consideration is of finite colength in a free module @xmath5 . write @xmath6 , where @xmath7 are @xmath4-primary ideals of @xmath2 . we first investigate the colength @xmath8 of any @xmath4-primary ideal @xmath9 and its hilbert - samuel multiplicity @xmath10 using linkage theory . as applications , we establish several multiplicity formulas that express the buchsbaum - rim multiplicity of the module @xmath1 in terms of the hilbert - samuel multiplicities of ideals related to @xmath11 , @xmath12 and an arbitrary general minimal reduction of @xmath1 . the motivation comes from e. jones article @xcite who applied graphical computations of the hilbert - samuel multiplicity to the buchsbaum - rim multiplicity . let @xmath2 be a local cohen - macaulay ring with maximal ideal @xmath4 and infinite residue field . let @xmath9 be an @xmath4-primary ideal . in this paper , we study the connection between the _ colength _ of @xmath9 , _ i.e. _ , the length @xmath13 of @xmath14 , and the hilbert - samuel multiplicity @xmath10 of @xmath9 . it is known for an @xmath4-primary ideal @xmath15 contained in @xmath9 that @xmath16 if and only if @xmath15 is a reduction of @xmath9 . furthermore , if @xmath15 is a minimal reduction of @xmath9 , then @xmath17 however , @xmath10 and @xmath8 are not equal in general . in one of our main theorems , theorem [ rankone ] , we express , under certain conditions , the colength of @xmath9 in terms of the hilbert - samuel multiplicity of ideals which are in the same linkage class of @xmath9 . equation ( [ eq : ideal ] ) can be generalized to modules using the buchsbaum - rim multiplicity of a module @xmath1 , denoted @xmath0 . let @xmath18 be submodules contained in a free module @xmath5 of finite rank such that @xmath19 . it is known that @xmath20 and @xmath1 have the same buchsbaum - rim multiplicity if and only if @xmath20 is a reduction of @xmath1 . similar to ideals , if @xmath20 is a minimal reduction of @xmath1 , then @xmath21 ( _ cf . _ @xcite , @xcite , @xcite ) . in the case where @xmath5 has rank one , @xmath1 is an @xmath4-primary ideal and @xmath22 . we see that the buchsbaum - rim multiplicity is a generalization of the hilbert - samuel multiplicity to modules . like the hilbert - samuel multiplicity , it characterizes reductions . using the theory of reductions of modules , we reduce the problem of finding formulas for the buchsbaum - rim multiplicity to the relationship between the colength and the hilbert - samuel multiplicity of ideals . the latter question is answered for arbitrary licci ideals in theorem [ rankone ] . as an application , we obtain formulas for the buchsbaum - rim multiplicity of a two - dimensional module in terms of the hilbert - samuel multiplicities of a certain fitting ideal and ideals linked to it , see theorem [ shortformula ] . we also prove expressions for the buchsbaum - rim multiplicity that involve bourbaki ideals associated to the module , see theorems [ shortformula2 ] , [ thmallrank ] , and corollary [ summary ] . the last corollary contains the work of @xcite as a special case . the paper is arranged in the following way : section 1 introduces the notion of the buchsbaum - rim multiplicity and its basic properties . we also include the definitions of some notation and theorems that will be used in the later sections . in section 2 , we state and prove the main theorem that relates the colength and the hilbert - samuel multiplicity of @xmath4-primary ideals in regular local rings of dimension two . in section 3 , we discuss several multiplicity formulas that express the buchsbaum - rim multiplicity of a module in terms of the hilbert - samuel multiplicity of @xmath4-primary ideals related to the module . jones @xcite provides a method for computing the buchsbaum - rim multiplicity of modules of a special type . in section [ computation ] we compare the multiplicity formulas obtained in section [ generalization ] to the results of @xcite .","we investigate the buchsbaum - rim multiplicity of a gorenstein local ring with infinite residue field. the multiplicity can be viewed as a generalization of the hilbert - samuel multiplicity. for a submodule @xmath0 of finitely generated submodules of rank 1, 2, 3 and 4, 1 can be a minimal reduction of the larger submodule if and only if it is a bourbaki ideal of the free semilinear module. in this paper, we give a new proof that for every finitely generate submodule of a local regular local ring ( _ i.e. _, for a cohen - macaulay local ring ) with maximal notion of ideal, we can find a corresponding ideal with the same colength. for arbitrary modules, we also establish a new result that the colength of an ideal linked to a complete intersection ideal is independent of the embedding of the submodule into a free module ; this result generalizes the result of j. watanabe on the four - fold multiplicities of three - dimensional rings. [ multiblock footnote omitted ] a.buchsbaum and g. rim @xcite first discussed the _ multiplicity that bears their names _ in 1964. they defined the multiplicit that is a linear combination of ideals from the polynomial of the identity matrix. later, g. ribordy, j. gaffney, kirby, rees, and kleiman and thorup studied the geometric theory that gives the multiplics of ideals related to polynomials. in particular, they used the noetherian local ring to prove that the gorkov multiplicity is a positive integer. the notion of positive integer has been greatly simplified nowadays ; monte - carlo simulations and computer simulations have efficiently provided many examples of positive integers. however, it is still a challenging task to find examples of non - positive integers when the dimension of the building block is not infinite. for example, consider the geometrically symmetric bipartite supergroup of two - dimensional regular rings. after the fact that the degree two is an integer, the complexity of the problem is limited to that for which there are infinitely many examples in the literature. the complexity problem can be understood in terms of the natural map from a local group to a free group. it is easy to see that a non - negative integer is a fundamental object in the theory of finite - dimensional linear groups. on the other hand,",0.2093718843469591,"this polynomial is called the hilbert - samuel polynomial and the coefficient of @xmath27 is the _ hilbert - samuel multiplicity _ @xmath10 . the buchsbaum - rim multiplicity can be viewed as a generalization of the hilbert - samuel multiplicity . for a submodule @xmath1 of finite colength in a free module @xmath5 of rank @xmath28 , buchsbaum and rim @xcite prove that there exists a polynomial @xmath29 of degree @xmath30 such that for all large @xmath31 , @xmath32 where @xmath33 is the symmetric algebra of @xmath5 and @xmath34 is the image of the natural map @xmath35 . moreover , if @xmath2 is a two - dimensional regular local ring , one can define the buchsbaum - rim multiplicity of _ any _ finitely generated @xmath2-module @xmath1 : simply consider the natural map from @xmath1 to @xmath44 , which is free in this case , and replace @xmath1 by its image under this map . we are interested in such a relationship for arbitrary modules . by theorem [ thmbr ] , @xmath0 is equal to the colength of the fitting ideal corresponding to a minimal reduction of @xmath1 . thus , the question can be reduced to investigating the connection between the colength and the hilbert - samuel multiplicity of ideals . [ ingclosed ] let @xmath78 be a regular local ring of dimension @xmath3 with infinite residue field . this result applies to any @xmath4-primary perfect ideal in a two - dimensional gorenstein local ring with infinite residue field . for three - dimensional rings [ shortformula ] let @xmath2 be a gorenstein local ring of dimension @xmath3 with infinite residue field , let @xmath1 be a submodule of finite colength in a free module @xmath5 of rank @xmath28 , and let @xmath46 be a minimal reduction of @xmath1 . in this section , we discuss other connections between the buchsbaum - rim multiplicity of modules and the hilbert - samuel multiplicity of ideals . in fact , we relate the buchsbaum - rim multiplicity of @xmath1 to the hilbert - samuel multiplicity of a generic bourbaki ideal of @xmath5 with respect to @xmath1 , see theorem [ shortformula2 ] . however , if there is a need to fix a certain bourbaki ideal @xmath11 of @xmath5 , the result in theorem [ shortformula2 ] does not apply anymore . [ shortformula2 ] let @xmath78 be a gorenstein local ring of dimension @xmath3 with infinite residue field , let @xmath1 be a submodule of finite colength in a free module @xmath5 of rank @xmath28 , let @xmath46 be a minimal reduction of @xmath1 , and let @xmath81 be ideals as in theorem @xmath129 . this is motivated by the work in jones @xcite where it is necessary to choose @xmath11 and @xmath12 to be monomial ideals in order to extend the graphical computation of the hilbert - samuel multiplicity of monomial ideals to the buchsbaum - rim multiplicity of modules . [ assume ] let @xmath78 be a gorenstein local ring of dimension 2 with infinite residue field , let @xmath1 be a submodule of finite colength in a free module @xmath5 of rank @xmath28 , and assume @xmath1 has no free direct summand . write @xmath6 , where @xmath152 are @xmath4-primary ideals , @xmath11 has finite projective dimension , and @xmath153 . since @xmath154 , we have @xmath155 and therefore @xmath156 . in this section , we consider modules of rank two arising from monomial ideals . there it is shown that @xmath1 is a reduction of the module generated by @xmath1 and the vector @xmath255 in @xmath5 , which is a direct sum of two monomial ideals .",0.2560137457044673
1201.5109,"we develop a simple treatment of a metamaterial perfect absorber ( mpa ) based on grating theory . we analytically prove that the condition of mpa requires the existence of two currents , which are nearly out of phase and have almost identical amplitude , akin to a magnetic dipole . furthermore , we show that non - zero - order bragg modes within the mpa may consume electromagnetic energy significantly . 99 n. i. landy , s. sajuyigbe , j. j. mock , d. r. smith , and w. j. padilla , perfect metamaterial absorber , "" phys . rev . lett . * 100 , * 207402 ( 2008 ) . j. a. schuller , e. s. barnard , w. cai , y. jun , j. s. white , and m. l. brongersma , plasmonics for extreme light concentration and manipulation , "" nat . mater . * 9 , * 193 - 204 ( 2010 ) . c. hgglund and s. peter apell , plasmonic near - field absorbers for ultrathin solar cells , "" j. phys . chem . lett . * 3 , * 1275 - 1285 ( 2012 ) . h. a. atwater and a. polman , plasmonics for improved photovoltaic devices , "" nat . mater . * 9 , * 205 - 213 ( 2010 ) . n. liu , m. mesch , t. weiss , m. hentschel , and h. giessen , infrared perfect absorber and its application as plasmonic sensor , "" nano lett . * 10 , * 2342 - 2348 ( 2010 ) . m. k. hedayati , m. javaherirahim , b. mozooni , r. abdelaziz , a. tavassolizadeh , v. s. k. chakravadhanula , v. zaporojtchenko , t. strunkus , f. faupel , and m. elbahri , design of a perfect black absorber at visible frequencies using plasmonic metamaterials , "" adv . mater . * 23 , * 5410 - 5414 ( 2011 ) . x. liu , t. tyler , t. starr , a. f. starr , n. jokerst , and w. j. padilla , taming the blackbody with infrared metamaterials as selective thermal emitters , "" phys . rev . lett . * 107 , * 045901 ( 2011 ) . r. taubert , d. dregely , n. liu , h. giessen , a. tittl , and p. mai , palladium - based plasmonic perfect absorber in the visible wavelength range and its application to hydrogen sensing , "" nano lett . * 11 , * 4366 - 4369 ( 2011 ) . k. aydin , v. e. ferry , r. m. briggs , and h. a. atwater , broadband polarization - independent resonant light absorption using ultrathin plasmonic super absorbers , "" nat . commun . * 2 , * 517 ( 2011 ) . c. wu and g. shvets , design of metamaterial surfaces with broadband absorbance , "" 308 ( 2012 ) . j. mei , g. ma , m. yang , z. yang , w. wen , and p. sheng , dark acoustic metamaterials as super absorbers for low - frequency sound , "" nat . commun . * 3 , * 756 ( 2012 ) . y. cui , k. fung , j. xu , h. ma , y. jin , s. he , and n. x. fang , ultrabroadband light absorption by a sawtooth anisotropic metamaterial slab , "" nano lett . * 12 , * 1443 - 1447 ( 2012 ) . t. sndergaard , s. m. novikov , t. holmgaard , r. l. eriksen , j. beermann , z. han , k. pedersen , and s. i. bozhevolnyi , plasmonic black gold by adiabatic nanofocusing and absorption of light in ultra - sharp convex grooves , "" nat . commun . * 3 , * 969 ( 2012 ) . g. dayal and s. a. ramakrishna , design of highly absorbing metamaterials for infrared frequencies , "" 17503 - 17508 ( 2012 ) . h. tao , c. m. bingham , a. c. strikwerda , d. pilon , d. shrekenhamer , n. i. landy , k. fan , x. zhang , w. j. padilla , and r. d. averitt , highly flexible wide angle of incidence terahertz metamaterial absorber : design , fabrication , and characterization , "" phys . rev . b * 78 , * 241103(r ) ( 2008 ) . x. liu , t. starr , a. f. starr , and w. j. padilla , infrared spatial and frequency selective metamaterial with near - unity absorbance , "" phys . rev . lett . * 104 , * 207403 ( 2010 ) . h. tao , n. i. landy , c. m. bingham , x. zhang , r. d. averitt , and w. j. padilla , a metamaterial absorber for the terahertz regime : design , fabrication and characterization , "" 7181 - 7188 ( 2008 ) . j. zhou , h .- t . chen , t. koschny , a. k. azad , a. j. taylor , c. m. soukoulis , and j. f. ohara , application of metasurface description for multilayered metamaterials and an alternative theory for metamaterial perfect absorber , "" arxiv:1111.0343v1 . h .- t . chen , interference theory of metamaterial perfect absorbers , "" 7165 - 7172 ( 2012 ) . c. l. holloway , a. dienstfrey , e. f. kuester , j. f. ohara , a. k. azad , a. j. taylor , a discussion on the interpretation and characterization of metafilms / metasurfaces : the two - dimensional equivalent of metamaterials , "" metamaterials * 3 , * 100 - 112 ( 2009 ) . h .- t . chen , j. zhou , j. f. ohara , f. chen , a. k. azad , and a. j. taylor , antireflection coating using metamaterials and identification of its mechanism , "" phys . rev . lett . * 105 , * 073901 ( 2010 ) . d. yu . shchegolkov , a. k. azad , j. f. ohara , and e. i. simakov , perfect subwavelength fishnetlike metamaterial - based film terahertz absorbers , "" phys . rev . b * 82 , * 205117 ( 2010 ) . see , for example , m. born and e. wolf , _ principles of opticss _ , 7th ed . ( cambridge , cambridge , 2011 ) . j. d. jackson , _ classical electrodynamics _ , 3rd ed . ( wiley , new york , 1999 ) . y. ma , q. chen , j. grant , s. c. saha , a. khalid , and d. r. s. cumming , a terahertz polarization insensitive dual band metamaterial absorber , "" 945 ( 2011 ) . because our finite - difference time - domain approach can not handle a permittivity with a nondispersive imaginary part , we adapt a dispersive lorentz model for the dielectric . a. taflove and s. c. hagness , _ computational electrodynamics : the finite - difference time - domain method _ , 2nd ed . ( artech house , boston , 2000 ) .","we analytically and numerically demonstrate that the condition of the metamaterial perfect absorber ( mpa ) is that the electric field inside the structure is a superposition of all orders of bragg waves. using a combination of analytical and numerical arguments, we show that even non - zero - orderbragg waves within the mpa consume electromagnetic energy. in agreement with the previous numerical observations, we find that the polarization current is strongly concentrated inside the metallic layers. for instance, the permittivity of the dielectric is described by a lorentzian function with @xmath0 $ ], where the term ` ` fundamental '' is interpreted as a periodic function of free - space wave number. the theory presented here provides a general framework for the understanding and applications of mpa. 99 n. engheta and r.w. ziolkowski, eds. _ ` ` electromagnetic absorption in thin films, '' proc. r. soc. lond. a * 7, * 1018010192 ( 2007 ). o.g. biebel, a.j. verma, j. van de groep, m.d. slater, s.a. kim, r. janicek, and l. kuipers, ` ` near - unity absorption in planar metallic structures, '' phys. rev. lett. * 105, * 213902 ( 2009 ). s.i. bozhevolnyi and y.s. kivshar, _ optical radiation from thin films to photovoltaic devices _ ( academic press, 2003 ), ( 19#2 ). p.k.l. chen, w.r.t. gao, q. yang, and z.y. zhiang, _ theory of electromagnetic absorption _ ( springer verlag, heidelberg new york tokyo, 2006 ). m.m. zheludev, y.v. dudin, makarov, d. v. kotlyar, and g. olshevsky, _ foundations of photonic crystal fibres _ ( imperial college press, 2012 ), [ 2]p.- h.- k. duu, l. yu. peng, t. liu, f.x. kang, xie, and x.- b. zhang, _ innovation in photonics _ ( world scientific, 2007 ), http://www",0.12218045112781956,"the experimental demonstration of near - unity absorption in ultra - thin metal - dielectric - metal metamaterial structures @xcite opens many potential applications in sensing , detection , stealth technology , photovoltaics , and thermovoltaics @xcite . the underlying mechanisms of the so - called metamaterial perfect absorber ( mpa ) have been addressed using effective medium theory @xcite , which approximates the whole metamaterial structure as a homogeneous slab with an effective bulk permittivity and permeability . it was found that the retrieved effective permeability can be described by a lorentzian function around the designed frequency , indicating the appearance of a magnetic resonance @xcite . more recently , an interference - based theory of the mpa has been proposed @xcite . by approximating thin planar metallic layers as homogeneous impedance - tuned interfaces between their boundary media @xcite , on the other hand , since both theoretical approaches mentioned above disregard the periodic nature of the metamaterial structure , they thereby restrict to zero - order bragg waves . in this paper we analytically show that the condition of mpa requires the existence of two currents within the metamaterial , which are nearly out of phase and have almost identical amplitude . furthermore , using a combination of analytical and numerical arguments , we show that non - zero - order bragg waves within the mpa consume electromagnetic energy . as discussed above , we find that the polarization current are strongly localized inside the two metallic layers , and a phase jump of @xmath79 appears at the spacer - ground interface . next we consider the dissipation of the electromagnetic energy within the mpa . according to poynting s theorem , indeed , we find numerically that the ratio of @xmath89 inside the spacer layer ranges from 0.84 to nearly 1.0 , suggesting that non - zero - order waves have a dominant contribution to the total field in the spacer region . as discussed in the previous paragraph , one can alternatively infer the existence of high - order bragg waves from the highly localized electric field distribution inside the mpa , which is shown in fig . to sum up , we studied the metamaterial perfect absorber in the framework of grating theory . we proved analytically that there always exists one circulating current loop ( akin to a magnetic dipole ) , together with an electric dipole as well as an electric quadrupole . we further showed that non - zero - order bragg waves may contribute significantly to the dissipation of the electromagnetic energy inside the perfect absorber . such an understanding of the process in the microscopic scale is important in exploring potential applications of metamaterial absorbers .",0.12
1210.2723,"we identify 42 ` ` candidate groups '' lying between @xmath0 from a sample of 3502 galaxies with spectroscopic redshifts in the zcosmos - deep redshift survey within this same redshift interval . these systems contain three to five spectroscopic galaxies that lie within 500kpc in projected distance ( in physical space ) and within 700 km / s in velocity . based on extensive analysis of mock catalogues that have been generated from the millennium simulation , we examine the likely nature of these systems at the time of observation , and what they will evolve into down to the present epoch . although few of the ` ` member '' galaxies are likely to reside in the same halo at the epoch we observe them , 50 % of the systems will have , by the present epoch , all of the member galaxies in the same halo , and almost all ( 93 % ) will have at least some of the potential members in the same halo . most of the candidate groups can therefore be described as ` ` proto - groups '' . a crude estimate of the overdensities of these structures is also consistent with the idea that these systems are being seen as they assemble . we also examine present - day haloes and ask whether their progenitors would have been seen amongst our candidate groups . for present - day haloes between @xmath1m@xmath2/h , 35 % should have appeared amongst our candidate groups , and this would have risen to 70 % if our survey had been fully - sampled , so we can conclude that our sample can be taken as representative of a large fraction of such systems . there is a clear excess of massive galaxies above @xmath3m@xmath2 around the locations of the candidate groups in a large independent cosmos photo-@xmath4 sample , but we see no evidence in this latter data for any color differentiation with respect to the field . this is however consistent with the idea that such differentiation arises in satellite galaxies , as indicated at @xmath5 , if the candidate groups are indeed only starting to be assembled .","we present a group catalogue of 42 possible groups of galaxies that could have originated from the zcosmos - deep spectroscopic survey of galaxies. we have applied the group - finder algorithm to a sample of 3502 galaxies at @xmath0 drawn from the redshift survey by lilly et al., using mock galaxy catalogues that have been generated by kitzbichler & white, and then passed through the same ` ` group - finding '' algorithms used to calibrate and analyze our ` ` mock catalogues. '' we find a total of 42 such associations, with most of the galaxies belonging to what we would call ` ` spectroscopically - detected groups '', or ` ` candidate groups ''. though only a small fraction of these groups have been observed, they span a very wide range in redshift and can be identified as high - redshift ` ` ` progenitor galaxies ''. the mean overdensities of the candidate groups are 0.78arcsec@xmath1 and are comparable to the overdensity of galaxies in the general field at the same redshift. we do not find evidence of any colour differentiation of the galaxy population in and around these candidate groups relative to the field galaxies, though this should not be expected in the context of a monolithic, integrated dark matter halo analysis. at the position of the representative groups, we find up to a factor of 4 more massive galaxies than would be predicted by extrapolating the cosmic mean overdensity from the field, demonstrating that these massive galaxies are likely to be the progenitors of the most massive haloes in the universe today. we provide a detailed analysis of the properties of these galaxies and of the possible future evolution of these systems, including their merging histories, suggesting that these galaxies will likely assemble into a single extended halo. the z - deep galaxy sample itself is found to contain an excess of star - forming galaxies around the groups which can be accounted for by their high stellar mass and high x - ray luminosity. if the excess is primarily due to star - formation in the selected galaxies, and if the selection criteria for groups are similar to those applied to the cosmos, then the fraction of massive galaxies in these groups will increase over time, making these galaxy groups the dominant accelerating sources of the mass density of high redshift structures. methods : numerical - galaxies : clusters : general - cosmology : observations - dark matter - large - scale structure of universe",0.2244039270687237,"however , so far there has been no systematic analysis of high redshift groups in spectroscopic redshift surveys . as described below , the zcosmos - deep survey provides a large sample of galaxies at @xmath7 including 3502 galaxies with usable redshifts in the redshift interval @xmath10 in a single fairly densely sampled region of sky ( lilly et al . the aim of this paper is to identify possible groups at @xmath11 , based on a simple linking length algorithm . we provide a catalogue of 42 such associations . in order to understand the physical nature of these detected structures , we have carried out extensive comparisons with mock catalogues that have been generated by kitzbichler & white ( 2007 ) and then passed through the same `` group - finding '' algorithms . the primary aim is to assess whether the galaxies in these structures are indeed already occupying the same dark matter halo . we examine a complementary photo-@xmath4 sample and identify a significant excess of massive galaxies in the regions of the groups , but do not find evidence for any color differentiation of the population relative to the field , although we argue we should probably not have expected to see such differentiation . the zcosmos - deep redshift survey ( lilly et al . has observed around 10000 galaxies in the central @xmath171deg@xmath18 of the cosmos field . m@xmath76 ) galaxies from the cosmos photo-@xmath4 sample around our spectroscopic candidate groups , relative to the field , as a function of the projected distance from the group in units of the @xmath59 of the groups as seen in cylinders of depth @xmath99km / s to accommodate photo-@xmath4 errors ( see text for details ) . at the position of the candidate groups we find a projected excess of up to @xmath1740% in the number of massive galaxies ( it is clear that the fraction of red objects in the candidate groups and in the field , at fixed stellar mass , is essentially the same and we do not see evidence of color segregation with environment . 2012 , and many others ) have presented clear evidence that all of the environmental differentiation of the galaxy population at low redshift is associated with the quenching of star - formation in satellite galaxies , and there is now also good evidence that this remains true also at redshifts approaching unity ( kovac et al . we have introduced the following terminology in which a system in which all three detected members are in the same halo is called a `` real group '' and one in which only two are , a `` partial group '' . if we look at today s groups and ask which of their progenitors will have been seen in our spectroscopic sample at @xmath75 , then we find that we should have detected @xmath113 of the progenitors of todays massive clusters ( of order of @xmath80m@xmath76/h ) already at @xmath9 and this would rise to @xmath114 if we had 100% completeness in the zcosmos - deep spectroscopic sample . we can roughly estimate the overdensities of the spectroscopically detected structures and find that these are substantial , consistent with the idea that these systems will soon come together into assembled systems . we also detect a significant overdensity in the regions of these candidate groups using independent the cosmos photometric sample , which shows a 40% excess in the numbers of galaxies above @xmath3m@xmath2 at the location of our spectroscopic candidate groups as compared to the field , despite the very large sampling cylinders ( @xmath115 ) required from the use of photo-@xmath4 . we do not however detect any significant differentiation in the colours of the galaxies compared to the field .",0.2356828193832599
0709.0180,"we describe a quantum system consisting of a one - dimensional linear chain of @xmath0 identical harmonic oscillators coupled by a nearest neighbor interaction . two boundary conditions are taken into account : periodic boundary conditions ( where the @xmath0th oscillator is coupled back to the first oscillator ) and fixed wall boundary conditions ( where the first oscillator and the @xmath0th oscillator are coupled to a fixed wall ) . the two systems are characterized by their hamiltonian . for their quantization , we treat these systems as wigner quantum systems ( wqs ) , allowing more solutions than just the canonical quantization solution . in this wqs approach , one is led to certain algebraic relations for operators ( which are linear combinations of position and momentum operators ) that should satisfy triple relations involving commutators and anti - commutators . these triple relations have a solution in terms of the lie superalgebra @xmath1 . we study a particular class of @xmath1 representations @xmath2 , the so - called ladder representations . for these representations , we determine the spectrum of the hamiltonian and of the position operators ( for both types of boundary conditions ) . furthermore , we compute the eigenvectors of the position operators in terms of stationary states . this leads to explicit expressions for position probabilities of the @xmath0 oscillators in the chain . an analysis of the plots of such position probability distributions gives rise to some interesting observations . in particular , the physical behavior of the system as a wqs is very much in agreement with what one would expect from the classical case , except that all physical quantities ( energy , position and momentum of each oscillator ) have a finite spectrum . * harmonic oscillator chains as wigner quantum systems : + periodic and fixed wall boundary conditions in @xmath1 solutions . * + * s. lievens , * * n.i . stoilova * * and j. van der jeugt * + department of applied mathematics and computer science , ghent university , + krijgslaan 281-s9 , b-9000 gent , belgium .","we study a system of coupled harmonic oscillators, with periodic boundary conditions, treated as a wigner quantum system. in fact, we show that the two systems have solutions in terms of the lie superalgebra @xmath0. in the same system, we also determine the eigenvalue spectrum and eigenvector counts of the position operators, for any of its eigenvalues. for a problem of non - zero constant, fixed wall boundary conditions lead to a different type of transform, instead of a discrete fourier transform, and a discrete sine transform. this implies that the algebraic solutions will be similar, even though the conclusions about physical properties will be different, for example due to the different numerical values of the numbers. [ tab : crit ] ] from this point of view, the results are in good agreement with the theoretical expectations. in particular, the first and last oscillators ( those fixed to the wall ) oscillate less strongly than those away from the wall. all oscillators have the same position probability distribution in the periodic boundary case, as they are all equivalent ( completely symmetric on a circle ). for the case of fixed wallial conditions, the behavior also follows the classical properties. the position with highest probability ( for each oscillator ) is the equilibrium position resulting from commutators with strongly decreasing probability. the positions corresponding to the middle of the spectrum ( i.e. the ground state ) are the most stable ones. on the other hand, the positions close to the surface, far from the equilibrium, have a more stable distribution. we also show some interesting properties of the energy spectrum ( spectrum of position operators ) of the system. these are similar to those of the fock representations @xcite studied in the previous paper. finally, we determine the critical value for the coupling constant in the chain with fixed wall conditions.",0.2211055276381909,"a second original contribution of this paper is that we show how also the second system ( fixed wall boundary conditions ) described by @xmath13 can be treated as a wigner quantum system . in fact , we show that at the algebraic level the two hamiltonians give rise to the same triple relations , but with different constants . as a consequence we shortly review the treatment of @xmath11 as a wqs @xcite , and then analyse the hamiltonian @xmath13 of the fixed wall boundary case in a similar way . as the algebraic triple relations are , up to different constants , the same , we describe the @xmath1 solution in a subsection . we also describe briefly the new class of representations @xmath2 , the ladder representations , and the explicit action of @xmath1 generators on simple basis vectors @xmath18 of @xmath2 . in section 3 we determine the spectrum of the hamiltonians @xmath11 and @xmath13 in the representations @xmath2 . due to the fact that these hamiltonians have a diagonal action in the current model , their spectrum is easy to determine . in this subsection , we briefly recall the algebraic treatment of the hamiltonian for a system consisting of coupled harmonic oscillators , with periodic boundary conditions , treated as a wigner quantum system @xcite . we have examined properties of noncanonical solutions of two quantum systems : chains of coupled harmonic oscillators with periodic boundary conditions or with fixed wall boundary conditions . these new solutions arise from an approach as a wqs , allowing more classes of solutions than just the canonical one . for the solutions examined here , the physical properties of the system then follow from the representations of @xmath1 considered . here , we have introduced the rather simple ladder representations @xmath2 , a class of unitary irreducible representations of @xmath1 ( or rather , of its compact form @xmath16 ) . for these representations , we have determined the energy spectrum , which was rather easy due to the simple action of the hamiltonian operator in the standard basis of @xmath2 . we have also determined the spectrum of the position operators ; this task was more difficult because of the more complicated action of these operators in the basis of @xmath2 . the techniques developed in @xcite allow to construct explicitly the eigenvectors of the position operators , for both systems under consideration . the analysis of the spectrum of the position operators , and their probabilities when the system is in a certain stationary state , lead to interesting properties . the width of this discrete support depends on the coupling constant @xmath17 , and only in the case of fixed wall boundary conditions on the order @xmath5 of the oscillator in the chain of @xmath0 oscillators . the position probability distributions , discussed in detail in the previous section , have properties similar to those of a classical system of coupled oscillators .",0.2426666666666667
0912.0311,"in this paper , after briefly reviewing the theory of vectorial vortices , we describe our technological approach to generating the necessary phase helix , and report results obtained with the first optical vectorial vortex coronagraph ( ovvc ) in the laboratory . to implement the geometrical phase ramp , we make use of liquid crystal polymers ( lcp ) , which we believe to be the most efficient technological path to quickly synthesize optical vectorial vortices of virtually any topological charge . with the first prototype device of topological charge 2 , a maximum peak - to - peak attenuation of @xmath0 and a residual light level of @xmath1 at an angular separation of 3.5 @xmath2 ( at which point our current noise floor is reached ) have been obtained at a wavelength of 1.55 @xmath3 m . these results demonstrate the validity of using space - variant birefringence distributions to generate a new family of coronagraphs usable in natural unpolarized light , opening a path to high performance coronagraphs that are achromatic and have low - sensitivity to low - order wavefront aberrations . 99 o. guyon , e. a. pluzhnik , m. j. kuchner , b. collins , and s. t. ridgway , ` ` theoretical limits on extrasolar terrestrial planet detection with coronagraphs , '' astrophys . j. suppl . * 167 * , 8199 ( 2006 ) . d. rouan , p. riaud , a. boccaletti , y. clnet , and a. labeyrie , ` ` the four - quadrant phase - mask coronagraph . i. principle , '' publ . astron . soc . pac . * 112 * , 14791486 ( 2000 ) . d. rouan , j. baudrand , a. boccaletti , p. baudoz , d. mawet , and p. riaud , ` ` the four quadrant phase mask coronagraph and its avatars , '' comptes rendus physique * 8 * , 298311 ( 2007 ) . d. mawet , p. riaud , o. absil , and j. surdej , ` ` annular groove phase mask coronagraph , '' astrophys . j. * 633 * , 11911200 ( 2005 ) . g. foo , d. m. palacios , and g. a. swartzlander , jr . , ` ` optical vortex coronagraph , '' opt . lett . * 30 * , 33083310 ( 2005 ) . c. jenkins , ` ` optical vortex coronagraphs on ground - based telescopes , '' mont . not . r. astron . soc . * 384 * , 515524 ( 2008 ) . g. a. swartzlander , jr . , e. l. ford , r. s. abdul - malik , l. m. close , m. a. peters , d. m. palacios , and d. w. wilson , ` ` contrast enhancement of binary star system using an optical vortex coronagraph , '' opt . express * 16 * , 1020010207 ( 2008 ) . d. rozas , c. t. law , and g. a. swartzlander , jr . , ` ` propagation dynamics of optical vortices , '' j. opt . soc . am . b * 14 * , 30543065 ( 1997 ) . a. niv , g. biener , v. kleiner , and e. hasman , ` ` manipulation of the pancharatnam phase in vectorial vortices , '' opt . express * 14 * , 42084220 ( 2006 ) . m. berry , ` ` the adiabatic phase and pancharatnam s phase for polarized light , '' j. mod . opt . * 34 * , 14011407 ( 1987 ) . y. gorodetski , g. biener , a. niv , v. kleiner , and e. hasman , ` ` space - variant polarization manipulation for far - field polarimetry by use of subwavelength dielectric gratings , '' opt . lett . * 30 * , 22452247 ( 2005 ) . g. biener , a. niv , v. kleiner , and e. hasman , ` ` space - variant polarization scrambling for image encryption obtained with subwavelength gratings , '' opt . commun . * 261 * , 512 ( 2006 ) . a. niv , g. biener , v. kleiner , and e. hasman , ` ` polychromatic vectorial vortex formed by geometric phase elements , '' opt . lett . * 32 * , 847849 ( 2007 ) . m. born , _ principles of optics : 7th ( expanded ) edition _ ( principles of optics : 7th ( expanded ) edition by born , m. , 1999 . , 1999 ) . z. bomzon , a. niv , g. biener , v. kleiner , and e. hasman , ` ` polarization talbot self - imaging with computer - generated , space - variant subwavelength dielectric gratings , '' appl . opt . 41 , 52185222 ( 2002 ) . d. mawet , p. riaud , j. baudrand , p. baudoz , a. boccaletti , o. dupuis , and d. rouan , ` ` the four - quadrant phase - mask coronagraph : white light laboratory results with an achromatic device , '' astron . & astrophys . * 448 * , 801808 ( 2006 ) . d. mawet , ` ` annular groove phase mask : an achromatic vortex coronagraph intended at differential polarimetric imaging , '' in ` ` in the spirit of bernard lyot : the direct detection of planets and circumstellar disks in the 21st century , '' , p. kalas , ed . 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'' , proceedings of the spie , volume 6272 , 62720 g ( 2006 ) . m. tamura , k. hodapp , h. takami , l. abe , h. suto , o. guyon , s. jacobson , r. kandori , j .- i . morino , n. murakami , v. stahlberger , r. suzuki , a. tavrov , h. yamada , j. nishikawa , n. ukita , j. hashimoto , h. izumiura , m. hayashi , t. nakajima , and t. nishimura , ` ` concept and science of hiciao : high contrast instrument for the subaru next generation adaptive optics , '' in ` ` ground - based and airborne instrumentation for astronomy . edited by mclean , ian s. ; iye , masanori . '' , proceedings of the spie , volume 6269 , 62690v ( 2006 ) . j. t. trauger and w. a. traub , ` ` a laboratory demonstration of the capability to image an earth - like extrasolar planet , '' * 446 * , 771773 ( 2007 ) . e. serabyn , k. wallace , m. troy , b. mennesson , p. haguenauer , r. gappinger , and r. burruss , ` ` extreme adaptive optics imaging with a clear and well - corrected off - axis telescope subaperture , '' astrophys . j. * 658 * , 13861391 ( 2007 ) .","we report laboratory results with the first prototype vectorial vortex coronagraph . after several years of effort toward annular groove vortex masks @xcite , a new promising technique has been identified to manufacture the vortex phase profile . this technology is based on birefringent liquid crystal polymers ( lcp ) which are oriented and hardened in a circular pattern . we show in this paper that the liquid crystal polymer optical vectorial vortex coronagraph ( lcp ovvc ) is a viable approach to generating the phase helix , with a promising technological path to very high performance coronagraphic masks , both in the near - infrared , where they could be used on current adaptive optics corrected ground - based telescopes to augment high contrast imaging capabilities , and in the optical , where these developments can be applied to more ambitious space - based coronagraph missions . we note that because of their small inner working angle , and lack of `` features '' anywhere on the mask ( except at the very central singularity ) , their discovery space is close to maximal in terms of search area for faint companions ( no dead zones ) . the paper is organized as follows : the second section is devoted to a condensed theoretical description of the optical vectorial vortex , as opposed to the optical `` scalar '' vortex . we will show that the rotationally symmetric spatial variation of the optical axes manipulates the transverse polarization state in such a way that a _ virtual _ phase ramp is embedded to the so- called `` geometrical '' phase ( * ? ? ? @xmath23 is the local direction of the optical axis frame with respect to @xmath21 ( fig . a very important property of vectorial vortices versus scalar vortices , is that the polarization structure of the chromatic leakage due to the local imperfections of the hwp is orthogonal to the pure achromatic vortex term : note the different directions of the two jones matrices of @xmath64 for circular polarization . we just rigorously showed that vectorial vortices , like scalar vortices , present the same screw phase dislocation @xmath65 that induces the central phase singularity . as natural unpolarized light can always be decomposed into two orthogonal and mutually incoherent polarization states , the vectorial vortex , using polarization manipulation , actually works in natural unpolarized light . the optical vortex coronagraph attenuation sensitivity to low - order aberrations like here we focus on a new approach involving a very promising technology based on liquid crystal polymers @xcite . it allows us to model the propagation through a realistic model of the coronagraphic mask using fourier transforms , from the entrance pupil to the final image plane . we have demonstrated for the first time that a vortex synthesized out of a space - variant birefringent element , i.e. a vectorial vortex acts as a viable coronagraph , as predicted . thanks to ground - breaking advances in lcp technology , a usable sample was produced in a very short time . even though the first prototype falls short of the specifications of next generation ground - based instruments for exoplanet imaging and characterization , such as sphere @xcite , gpi @xcite , palm-3000 @xcite , and hicio @xcite , we have easily identified the major achille s heel of the prototype , the central region of disorientation .",0.12269207861822512,"we report laboratory results with the first prototype of an optical vectorial vortex coronagraph. this coronagraph is based on birefringent liquid crystal polymers, which are oriented and hardened in a circular pattern to produce a halfwave optical axis that rotates with the center of the mask. the phase of the vortex is controlled by a structural phase ramp in a piece of glass. 10 l. allen, m. w. beijersbergen, r. j. c. spreeuw, and j. p. woerdman, ` ` coronagraphy, '' opt. commun. * 179 *, 417419 ( 2008 ). m. a. nielsen and i. l. chuang, _ advanced in astronomy, _ ( cambridge university press, 2000 ). v. m. sheikholeslami, a. f. abouraddy, g. molina - terriza, and s. nic chormaic,``advances in optical vortex optics for exoplanet - finding, '' rev. mod. phys. * 81 *, 14531456 ( 2009 ). f. e. becerra, l. bergamini, d. buccoliero, e. burtin, n. hermosa, and c. d. hennessy,``vertical vectorial optical vortex, '', 013406 ( 2010 ). h.- t. chen, j. fini, and p. wasylczyk,``exoplanet detection with high contrast using optical vortex masks : a new coronagraphi, '' j. opt. soc. am. b * 21 *, 871892 ( 2006 ). r. wang, x.- b. wu, q. zhan, b. g. glenday, f. x. kartner, k. danzmann, and f. n. phillips,``high - contrast imaging with vector optical vortices, '' appl.. lett. * 94 *, 093904 ( 2007 ). j. zang, z. zhang, h. y. liu, y. zhao, c. t. chong, and x. wu,``ventral vortex optical vortex as an optimized coronagraph for space - variant optical elements, '' ieee j. sel. top. quantum electron. * 17 *, 935996 ( 2011 ).",0.10883392226148407
0904.4279,"equilibrium charge distribution on a thin , straight conductor has been actively discussed in recent years , starting with griffiths and li @xcite , who suspected a uniform distribution , and culminating with maxwell s insightful words @xcite as reported by jackson @xcite . the present work addresses the electrostatic problem of a thin , curved , cylindrical conductor , or a conducting _ filament _ , and shows that the corresponding linear charge density slowly tends to uniformity as the inverse of the logarithm of a characteristic parameter which is the ratio of the diameter to the smaller of the length and minimum radius of curvature of the filament . an alternative derivation of this result directly based on energy minimization is developed . these results are based on a general asymptotic analysis of the electric field components and potential near a charge filament in the limit of vanishing diameter whereby the divergent parts of these quantities are explicitly calculated . it is found that the divergent parts of the radial and azimuthal electric field components , as well as the electric potential , are determined by the local charge density while the axial component is determined by the local dipole density . for a straight filament , these results reduce to those for conducting needles discussed in the literature . for curved filaments , the configuration of charges and fields is no longer azimuthally symmetric , and there is an additional length scale in the problem arising from the finite radius of curvature of the filament . remarkably , the basic uniformity result survives the added complications , which include an azimuthal variation in the surface charge density of the filament . as with the variations of linear charge density along the filament , the azimuthal variations vanish with the characteristic parameter , only more rapidly . these uniformity results yield an asymptotic formula for the capacitance of a curved filament that generalizes maxwell s original result . the examples of a straight filament with uniform and linearly varying charge densities , as well as a circular filament with a uniform charge distribution , are treated analytically and found to be in agreement with the results of the general analysis . numerical calculations illustrating the slow convergence of linear charge distribution to uniformity for an elliptical filament are presented , and an interactive computer program implementing and animating the numerical calculations is provided .","the distribution of charge on a thin, cylindrical conductor has been the subject of much theoretical interest in recent years. the intuition underlying this inquiry is the expectation that a sufficiently thin, smoothly curved filament, when viewed up close, would appear long and straight, so that the equilibrium behavior of charges on the filament should be nearly uniform _ just as in the case of straight conductors _. here we consider the behavior of the electric field components and the electrostatic potential in the limit of vanishing distance from an arbitrary point of the filament, and carry out an asymptotic analysis to calculate the divergent parts of these quantities explicitly. we can conclude that the equipotential surfaces of the physical filament approach those of the ideal one as its diameter vanishes, and use this to deduce the inverse - logarithmic approach of charge distribution to uniformity. the primary result of this paper is that the density of charge along a regular conducting filament of fixed diameter tends to uniformidity according to eq. ( ). an alternative derivation of this result using energy minimization is developed in examples of straight and circular filaments. 1-dimensional electric field, electric potential, filament, geometry, methods : analytical, numerical",0.2561403508771929,"a paper of griffiths and li in this journal @xcite has triggered a lively discussion on the electrostatic equilibrium distribution of charge on a thin , straight , cylindrical conductor . the purpose of this contribution is to investigate the distribution of charge on a thin , _ curved _ conductor , which we will often refer to as a _ this is indeed what we find and describe in this paper . we approach the problem of charge distribution on a physical filament in two steps . the first step is the treatment of the fields of any sufficiently smooth , one - dimensional distribution of charge , which we will often refer to as an _ ideal filament _ , with no regard to its conductivity properties . here we consider the behavior of the electric field components and the electrostatic potential in the limit of vanishing distance from an arbitrary point of the filament , and carry out an asymptotic analysis to calculate the divergent parts of these quantities explicitly . we find that the divergent parts of the radial and azimuthal electric field components , as well as the electric potential , are determined by the linear charge density of the filament at the point in question , whereas the axial component of the electric field is determined by the spacial derivative of linear charge density , or equivalently , the electric dipole density , at the point . ( ) and ( ) . in the second step of our analysis , we relate the fields of the ideal filament to those of a physical one by casting the former as the symmetry axis of a curved , cylindrical conductor . here , we show that the equipotential surfaces of the physical filament approach those of the ideal one as its diameter vanishes , and use this to deduce the inverse - logarithmic approach of charge distribution to uniformity , the primary result of this paper , in eq . the rest of this paper is organized as follows . in iia we set up the geometry of the ideal filament and formulate the required regularity conditions . in iib we present the derivation of the electric field components near the ideal filament , and in iic we deal with the electrostatic potential . we then formulate the requirements of relating the fields of the physical filament to those of the ideal one in iiia . in ivb we present the results of a numerical study of an elliptical filament , including an interactive computer program for calculating them . we will assume this curve to be of class @xmath0 , or twice continuously differentiable , and parameterized by @xmath1 , @xmath2 , where @xmath3 is the arc length parameter @xcite . our objective here is an analytical calculation of the fields of ideal straight and circular filaments for specified charge densities , and a comparison of their asymptotic behavior in the limit of @xmath29 with those of eqs .",0.3110571081409478
1612.01201,"andreev bound states ( abss ) are well - defined many - body quantum states that emerge from the hybridization of individual quantum dot ( qd ) states with a superconductor and exhibit very rich and fundamental phenomena . we demonstrate several new electron transport phenomena mediated by abss that form on three - terminal carbon nanotube ( cnt ) qds , with one superconducting ( s ) contact in the center and two adjacent normal metal ( n ) contacts . three - terminal spectroscopy allows us to identify the coupling to the n contacts as the origin of the andreev resonance ( ar ) linewidths and to determine the critical coupling strengths to s , for which a ground state ( or quantum phase ) transition in such s - qd systems can occur . in addition , we ascribe replicas of the lowest - energy abs resonance to transitions between the abs and odd - parity excited qd states , a process we call excited state abs resonances . in the conductance between the two n contacts we find a characteristic pattern of positive and negative differential subgap conductance , which we explain by considering two nonlocal processes , the creation of cooper pairs in s by electrons from both n terminals , and a novel transport mechanism called resonant abs tunneling , possible only in multi - terminal qd devices . in the latter process , electrons are transferred via the abs without effectively creating cooper pairs in s. the three - terminal geometry also allows spectroscopy experiments with different boundary conditions , for example by leaving s floating . surprisingly , we find that , depending on the boundary conditions and the device parameters , the experiments either show single - particle coulomb blockade resonances , abs characteristics , or both in the same measurements , seemingly contradicting the notion of abss replacing the single particle states as eigenstates of the qd . we qualitatively explain these results as originating from the finite time scale required for the coherent oscillations between the superposition states after a single electron tunneling event . these experiments demonstrate that three - terminal experiments on a single complex quantum object can also be useful to investigate charge dynamics otherwise not accessible due to the very high frequencies .","however , the coupling strengths can only be accessed unambiguously in three terminal geometries.@xcite here we report experiments on three - terminal qd devices fabricated on carbon nanotubes ( cnts ) with one central superconducting contact inducing abss on the qd . a scanning electron microscopy ( sem ) we investigate three devices with different coupling strengths @xmath0 to s to investigate several of these open questions and demonstrate a series of new effects and measurement configurations . [ sec : abs_basics ] we summarize our intuitive picture of abss and abs - mediated electron transport in two - terminal devices . [ sec : abs - devicecharacteriation ] , from which we extract the tunnel coupling strengths to the individual contacts and demonstrate that @xmath0 determines the system ground state and abs dispersion , while the coupling strengths to the normal metal contacts , @xmath2determine the spectroscopic width of the andreev resonances ( ars).@xcite one device shows replicas of the lowest - energy abs resonance at higher energies , which we ascribe to transitions to excited odd - parity qd states in sec . [ sec : abs - serialtransport ] , we analyze the transport between the two normal metal contacts mediated by abss , in which competing local and nonlocal transport mechanisms give rise to a characteristic pattern of positive and negative differential conductance . for illustration and to establish some terms used below , we consider a qd with a single , spin - degenerate level strongly tunnel coupled to a superconductor and weakly to a normal contact . the former couples even charge states of the isolated qd by exchanging cooper pairs to form new eigenstates of the s - qd system . in the limit of a large superconducting energy gap , @xmath3 ( superconducting atomic limit ) , the emerging abs can be written as a superposition of the even ( empty and doubly occupied ) charge states of the isolated qd , i.e. , as a singlet eigenstate @xmath4 , with @xmath5 and @xmath6 the gate - dependent bogoliubov- de gennes ( bdg ) amplitudes and @xmath7 the corresponding eigenenergy . we have fabricated cnt three - terminal devices with a lead ( pb ) based central @xmath46 nm wide pd / pb / in ( @xmath47 nm ) s contact,@xcite two pd n contacts and two sidegates ( sgs ) using close to residue free electron beam lithography.@xcite the typical critical perpendicular field for these s contacts is @xmath46mt and we apply @xmath48mt for our normal state experiments . if this happens faster than half a coherent oscillation , the tunneling electron stays in the bare qd state during the time it resides on the cnt segment . assuming that an oscillation by half a period is required to transfer a cooper pair to s , we find the relation @xmath257 as a necessary condition to observe the bare qd resonances , in good agreement with device a , but not for the other two devices with considerably larger @xmath0 and a faster oscillation rate relative to @xmath258 . our results demonstrate that a three - terminal qd can give access to the fast electron dynamics , in our example of the abs coherent oscillations with frequencies @xmath259 in the range between @xmath260ghz ( device a ) to @xmath261ghz ( device b ) , by the implicit comparison of the tunnel rates to the third terminal . in summary , we investigate electronic transport mediated by andreev bound states in a three - terminal s - qd device and identify the coupling to the normal metal leads as the main source for the spectroscopic broadening of the andreev resonances , and establish how the coupling to the superconductor determines the ground state of the system . in addition , we present ` excited state andreev resonances ' at higher energies , with transitions between abss and odd parity excited qd states . surprisingly , we find that depending on the imposed boundary conditions in the experiments it is possible to observe either abss or coulomb blockade resonances , or both in the same experiment , which we tentatively attribute to the competition between coherent oscillations in the abs ( exchange of cooper pairs with s ) and the relaxation of the system by single electron tunneling into the second normal terminal . we believe that experiments on complex quantum systems using multiple terminals provide a novel and clear experimental probe for many old and new phenomena , here for example the onset of the superconducting proximity effect on a qd and the formation of many - body quantum states . in this appendix we analyze additional data of devices a , b and c. in particular , we discuss the electronic configuration of each device , using conductance maps as a function of both sidegate voltages .",0.21677662582469368,"we investigateabs mediated electron transport in three - terminal quantum dot devices fabricated on carbon nanotubes with one central superconducting contact. we find that the ground state of the quantum dot ( qd ) can be interpreted as a superposition of the even and doubly occupied charge states of the single qd, and that abs can be excited by single electron tunneling events whose characteristic frequency is determined by the coupling strength to the normal metal contacts ( n ), @xmath0. we show that for weak n - n coupling the abs resonances can be resolved by andreev resonances ( ars ) in the third terminal. from the measurement results we conclude that the broad absorption features we observe in some devices are caused by abs mediated transport from n to s. finally, we demonstrate that a finite coupling to s allows the exchange of even charge states, which is necessary for the hybridization of the qd with s. our results suggest that in some parameter regime both sets of states are available for different transport processes. * introduction * strong coupling to superconductors is a prerequisite for the development of new physics beyond the standard model of superconductivity.@xcite this is due to the fact that weak coupling to a superconductor results in a large gap in the electronic band structure of the system, which can be used to introduce a new ` ` anomalous '' states into the system. one of the most promising candidates for this mechanism is the long - range coupling to electronic systems, which offers the possibility to bypass the problem of the pairing phase transition and give access to the electronic phase transition at large separations and high electron densities. @xcite however, the origin of these anomalous states remains unclear. some theoretical predictions might be related to the formation of new phases or topological excitations. transport spectroscopy, however, has not been able to probe the detailed dynamics of electrons in two - terminal devices. to address this issue, here we discuss three different approaches that have been used to investigate absorption of electrons by electrons confined in two-terminal quantum dots ( qds ). the first approach is to use a weakly coupled qd to an n - qd system in which the interactions are strongly coupled to an external normal metal ( s ) point such that the two qds can be separated in energy by a short normal metal tunneling event. in this approach it is possible to gain insight into the electronic dynamics of the ultrafast ( lt ), which gives rise to characteristic peaks in",0.17819148936170212
q-bio0610054,"using computational modelling , we investigate mechanisms of signal transduction focusing on the spindle assembly checkpoint where a single unattached kinetochore is able to signal to prevent cell cycle progression . this inhibitory signal switches off rapidly once spindle microtubules have attached to all kinetochores . this requirement tightly constrains the possible mechanisms . here we investigate two possible mechanisms for spindle checkpoint operation in metazoan cells , both supported by recent experiments . the first involves the free diffusion and sequestration of cell - cycle regulators . this mechanism is severely constrained both by experimental fluorescence recovery data and also by the large volumes involved in open mitosis in metazoan cells . using a simple mathematical analysis and computer simulation , we find that this mechanism can generate the inhibition found in experiment but likely requires a two stage signal amplification cascade . the second mechanism involves spatial gradients of a short - lived inhibitory signal that propagates first by diffusion but then primarily via active transport along spindle microtubules . we propose that both mechanisms may be operative in the metazoan spindle assembly checkpoint , with either able to trigger anaphase onset even without support from the other pathway . keywords : signal transduction , kinetochore , spindle assembly checkpoint , mathematical modelling the question of how a signal emanating from a small , compact structure in a cell can be amplified and propagated to an entire cell is fundamental to cell biology @xcite . an excellent example is provided by the spindle assembly checkpoint ( sac ) @xcite , which regulates cell cycle progression from metaphase to anaphase during mitosis . the segregation of sister chromatids that occurs during anaphase is permitted only after all the kinetochores are attached via microtubules to the mitotic spindle . even a single unattached kinetochore can signal to the rest of the cell and prevent cell cycle progression @xcite . a fundamental issue is how a relatively small structure , such as a kinetochore , can generate sufficient signal to robustly communicate with distant subcellular locations @xcite . moreover , this signal must switch off rapidly , within a period of minutes , after complete kinetochore attachment to spindle microtubules @xcite . these requirements strongly constrain the possible signal transduction mechanisms . in this paper , we focus particularly on the sac in cases where the nuclear envelope breaks down prior to sac activity ( open mitosis ) , as in metazoan cells . in this context , we examine two distinct models : a diffusive sequestration model and a model involving active signal transport along spindle microtubules . we believe that both of these pathways may be in simultaneous operation in the metazoan sac . the metaphase / anaphase transition is triggered by an intricate sequence of events centred around the proteins securin , cyclin b and separase . the first step is the ubiquitination of securin and cyclin b by the anaphase promoting complex / cyclosome ( apc / c ) @xcite , a process that tags securin / cyclin b for destruction via the 26s proteasome . this degradation allows separase to cleave the cohesin complex that tethers sister chromatids together . once the cohesin complex has been cleaved , the sister chromatids aree pulled apart to opposite poles by the mitotic spindle . in order to prevent premature entry into anaphase , the sac must prevent securin / cyclin b ubiquitination by the apc / c until proper attachment of _ all _ chromosomes to the spindle . evidence has accumulated for a number of overlapping , and therefore possibly redundant , mechanisms for sac operation . the apc / c is known to be stimulated by cdc20 binding ; hence , a plausible way to achieve apc / c inhibition is to inhibit the ability of cdc20 to bind to the apc / c . one possibility is that cdc20 is held , sequestered , in an inactive form via binding to mad2 , with the production of cdc20-mad2 being promoted by unattached kinetochores @xcite . key proteins identified at unattached kinetochores include bub1 , mad1 , mad2 , bubr1 ( mad3 in budding yeast ) , bub3 and cdc20 . moreover , frap experiments have revealed that some of these proteins , including mad2 , bubr1 and cdc20 , turnover rapidly at unattached kinetochores @xcite . furthermore , the available evidence suggests that mad2 exists in two forms : open ( o - mad2 ) and closed ( c - mad2 ) @xcite , with the closed form adopted when bound to cdc20 . production of c - mad2-cdc20 may be catalysed via the kinetochore bound c - mad2-mad1 complex . intriguingly , refs . @xcite propose that c - mad2-cdc20 away from the unattached kinetochore can convert further cytosolic o - mad2 and cdc20 into their bound c - mad2-cdc20 state . in this way the relatively weak signal coming from an unattached kinetochore can be amplified leading to comprehensive cdc20 sequestration throughout the cell . recent experiments have further implicated a protein called p31@xmath0 in switching off this signal after complete kinetochore attachment @xcite . however , the above ` ` mad template '' model is not the only proposed mechanism for apc / c repression . bubr1 and bub3 are also known to bind cdc20 and thus repress the apc / c @xcite . indeed , bubr1 appears to be a more potent inhibitor of cdc20 than mad2 , and both bubr1 and mad2 may mutually promote each other s binding to cdc20 @xcite . furthermore , bub1 is believed to phosphorylate cdc20 , possibly also repressing the apc / c @xcite . in addition , the overall copy number of cdc20 is down - regulated until all the kinetochores are attached @xcite . clearly , reducing the overall number of cdc20 will impair the effectiveness of the apc / c prior to anaphase . moreover , not only does cdc20 form complexes with mad2 and bubr1 , but it is also believed to form a separate complex called the mitotic checkpoint complex ( mcc ) , consisting of mad2 , bubr1 , bub3 and cdc20 @xcite . this complex also appears to be a potent inhibitor of the apc / c @xcite . in addition , the apc / c is regulated by phosphorylation through the kinase cdk1 @xcite . lastly , the apc / c itself has intriguing localization properties , localizing , for example , to unattached kinetochores @xcite . this positioning may also have implications for the mechanism of apc / c inhibition . recently , a pioneering paper by doncic _ et al . _ @xcite introduced a careful mathematical analysis to the question of how the sac functions . focusing on yeast , they analysed various simplified models of how an unattached kinetochore can signal to the rest of the cell . yeast undergoes closed mitosis , where even at the onset of anaphase the nuclear envelope is still complete . as a consequence , a diffusive signal from an unattached kinetochore is only required to propagate within the nuclear volume of a few cubic microns . however , one important difference between yeast and metazoan cells is that the latter undergo open mitosis , where the nuclear envelope has broken down by the time the sac is active ; hence any freely diffusing signal from an unattached kinetochore must propagate throughout the cytoplasm , a volume a thousand times larger than the nucleus of a yeast cell . furthermore a considerable amount of data is available concerning the metazoan sac in the form of flourescent bleaching data and estimates for the copy numbers of the relevant molecules . in this paper , we therefore use computational modelling to analyze the sac in metazoan cells . we develop a new model that incorporates two step signal amplification , a mechanism with close similarities to previously investigated multistep signal cascades @xcite . this similarity points towards a close connection between the sac and other cell signalling systems , such as mapk cascades . importantly , we find that our model generates robust inhibition in metazoan cells , unlike models without an amplification step . as discussed above , the most popular models of apc / c inhibition involve transport solely by diffusion . however , these models are hard to reconcile with experiments of rieder _ et al . _ @xcite . using cells with two independent spindles , rieder _ et al . _ found that unattached kinetochores on one spindle did not block anaphase onset in a neighbouring complete spindle . this experiment appears to indicate that any ` ` wait anaphase '' signal would have to be limited to a single spindle , and _ not _ diffuse throughout the cytosol . this finding is in clear contradiction with the mechanisms introduced above . for this reason we develop a second model where a short - lived signal from an unattached kinetochore first diffuses to a nearby microtubule , before being actively transported along spindle microtubules . in this way the signal is restricted to the spindle . moreover , we propose that both the active transport and diffusive mechanisms may be in simultaneous use in metazoan cells . we suggest that either of the signalling mechanisms may individually be able to initiate anaphase , even without support from the other pathway . with this assumption , our models are then fully consistent with both the experiments of rieder _ et al . _ @xcite and with a diffusive sequestration model @xcite .","in metazoans, the concentration of a freely diffusing species, @xmath0, is known to be a key determinant of whether a cell will be inhibitory or signaling. in the simplest model of signaling, the inhibory species is produced at a kinetochore and then diffuses in the cytoplasm, but only until it either encounters a minus - end directed microtubule - bound molecular motor, or decays to an inactive form. since both mad2 and bubr1 are known to bind to cdc20, we can tentatively identify the inhibiting species with this complex. based on this model we propose two possible mechanisms of signaling in metazoan cells. the first is a mechanism in which a ` ` go anaphase '' signal is transmitted from the spindle pole by molecular motors. if such a motor were linked to the mad2 binding site then inhibition of the inhibitory signal would essentially shut off the active transport. however, data from frap ( fluorescence recovery after photobleaching ) experiments on the state - of - the - art model of the metazoan sac show that fluxes on the disk are sufficient to maintain inhibition. therefore, we find that both mechanisms are possible to explain the experimental data. the second mechanism is based on an active transport mechanism. in this model, an extra process is added to the pathway by a diffusive amplification step. we predict that if this model is correct, then cell anaphases should be triggered by an external signal. indeed, we show from our model that the time for this signal to diffuse across the cell is much shorter than the timescale for reactions within the cell. thus, our model with an amplification step is able to explain some of the observed features of the sac. these findings are qualitatively consistent with models where inhibition propagates purely diffusively away from incomplete kinetched kinetchores, or in other words, where the cell spindle plays an active role. * how genes are regulated by chemical signaling is a key issue in biology. if a chemical agent is responsible for a chemical reaction then it is critical to determine the effects that the associated molecule is doing. for example, the power to drive dna synthesis in yeast is needed to counter the effect of dna damage @xcite. similarly, the importance of the ability to detect and respond to changes in environment, for example due to the effects of humidity, is required to determine if a drug that targets cells with a negative target is effective",0.1316371681415929,"we analyze the case where the kinetochores control the concentration of a freely diffusing species @xmath1 . when a kinetochore is unattached and so is signalling , a large majority of the species @xmath1 is in the @xmath2 state , but when the last kinetochore itself switches off , the @xmath2 species rapidly decays to the @xmath1 state , thus communicating the switch - off ( attachment ) to the rest of the cell . @xmath5 is the diffusion constant for the protein ; @xmath6 is the distance across the cell ( typically a few tens of microns ) ; and @xmath7 m @xcite is the radius of the kinetochore . , we now address the question of whether the flux of @xmath2 produced _ only _ at a single unattached kinetochore is sufficient to maintain inhibition . at steady state thus we predict that if the mechanism of the sac is diffusive amplified sequestration then measurements of the reaction rates will reveal rather fast reactions , or possibly more than two steps to the amplification process . for completeness we also analyze an alternative two species model previously proposed by doncic et al @xcite , for the smaller volumes involved in the yeast sac . the reaction scheme for their model the active transport model nevertheless predicts that the inhibitory signal is propagated away to the spindle pole by a minus - end directed motor . in this paper , we have shown that two models with quite different mechanisms : the diffusive reaction cascade model , and a model with active transport , are both possible signalling mechanisms for the sac . @xcite show that an inhibitory diffusive pathway can be overruled by a second pathway , which , as we have seen , is likely based on active transport . we therefore propose that _ either _ mechanism can trigger anaphase onset , even without support from the other pathway . future work * although some of the key principles used by the metazoan sac are starting to become clear , there is still much that remains to be understood . even for models of signalling via diffusion , which have been more actively pursued , further quantitative measurements would be very useful . also , we predict that amplification without autocatalysis is likely to be required , which implies the existence of at least two inhibiting species ( @xmath105 ) . of course , the _ in vivo _ checkpoint dynamics will likely be much more complicated than our simple outline model , but the requirement for amplification will likely remain . better characterization of the bubr1/mad1/mad2/cdc20 protein dynamics should therefore allow these predictions to be tested . we would also like to emphasize the close connection between our diffusive two step reaction and other signal cascades , such as for mapk . as we have discussed previously , it is also important to examine how any such signal is processed by the spindle pole to provide inhibition . in general , future experimental work will need to measure more of the model parameters before we can make reliable quantitative predictions for intracellular signalling .",0.13859275053304904
0707.2766,"helicases are molecular motors that unwind double - stranded nucleic acids ( dsna ) , such as dna and rna ) . typically a helicase translocates along one of the na single strands while unwinding and uses adenosine triphosphate ( atp ) hydrolysis as an energy source . here we model of a helicase motor that can switch between two states , which could represent two different points in the atp hydrolysis cycle . our model is an extension of the earlier betterton - jlicher model of helicases to incorporate switching between two states . the main predictions of the model are the speed of unwinding of the dsna and fluctuations around the average unwinding velocity . motivated by a recent claim that the ns3 helicase of hepatitis c virus follows a flashing ratchet mechanism , we have compared the experimental results for the ns3 helicase with a special limit of our model which corresponds to the flashing ratchet scenario . our model accounts for one key feature of the experimental data on ns3 helicase . however , contradictory observations in experiments carried out under different conditions limit the ability to compare the model to experiments . helicases are enzymes that unwind double - stranded nucleic acids ( dsna ) @xcite . helicase proteins typically translocate along one of the single strands and perform mechanical work while consuming chemical energy ( usually supplied by the hydrolysis of atp ) . therefore , these na translocases are molecular motors @xcite which share common features with cytoskeletal molecular motors @xcite . all helicases undergo a biochemical cycle which typically involves atp binding , atp hydrolysis , and release of the hydrolysis products adenosine diphosphate ( adp ) and and inorganic phosphate ( p@xmath0 ) . an important question in the study of helicase mechanisms is to understand how the atp hydrolysis cycle is coupled to the binding state and the motion of the helicase @xcite . helicases may exhibit changes in helicase / na binding affinity when the helicase is bound to atp , adp / p@xmath0 , or neither ; coordination of hydrolysis between different helicase subunits , and conformational changes in the helicase triggered by different steps in the hydrolysis cycle . some helicases form hexamers ( which include six atpase domains ) , while others are members of the non - hexameric ( dimeric or monomeric ) group ; different types of mechanochemical cycle have been suggested for the different structural classes @xcite . in all cases , one seeks to explain how the helicase coordinates na binding and hydrolysis to move along single - stranded na and unwind double - stranded na . here we develop a generic model of a helicase that switches between two biochemical states while translocating on ssna . this is a simplified representation of the different states of the helicase during the atp hydrolysis cycle . the model may be generally applicable to helicases for which the transition between two states is the key feature of the motion . in other words , this model should be a good approximation for helicases with more than two biochemical states if one transition is far slower than the others . we incorporate such a two - state picture by extending the original betterton - jlicher ( bj ) model @xcite of na helicases @xcite . our work is also connected to two - state models that have been used extensively for a variety of molecular motors @xcite . under a mean - field approximation , such models can be easily solved when periodic boundary conditions are imposed . however , the problem is usually more difficult with open boundary conditions . the model for helicase motion is even more complex because the position of one boundary ( i.e. , the ssna - dsna junction ) varies randomly with time . thus our work is also an extension of previous work on two - state models to the more difficult case of a fluctuating boundary . the two - state model developed here is consistent with the observation that binding and hydrolysis of atp can modulate the affinity of a helicase for the nucleic - acid track @xcite . the flashing - ratchet mechanism suggested qualitatively for the hepatitis c virus non - structural protein 3 ( hcv ns3 ) helicase @xcite can be captured by a special case of the generic model proposed here . in the flashing - ratchet @xcite picture , the motor protein switches between two states : one where the protein is tightly bound to the track , and another where the motor is weakly bound and can diffuse along the track . in this paper we make quantitative comparisons between our theoretical predictions for a passive helicase which follows the flashing - ratchet mechanism , and the experimental data for ns3 helicase . in section [ sec : model ] we describe the ingredients of the model : the helicase , which can switch between two states and translocate on ssna , and the fluctuating na ss - ds junction . in section [ sec : sseqns ] we calculate the single - strand translocation rate of the helicase . section [ sec : eqns ] contains the model equations for double - strand unwinding , the transformation of the equations using midpoint and difference variables , and the general solutions for the velocity and diffusion coefficient . we describe the results for a hard - wall interaction between the helicase and junction in section [ sec : soln ] . using rate constants estimated from experiments on ns3 helicase , in section [ sec : results ] we specialize to the flashing - ratchet scenario and make predictions specific to ns3 . in section [ sec : disc ] we summarize our results .","in this work we analyze passive unwinding , which is equivalent to a hard - wall interaction potential in the bj model @xcite . in passive unwinding , the helicase acts as a block to na closing when adjacent to the junction . in this paper we have developed a general model of unwinding of a double - stranded nucleic acid molecule by a helicase motor . to capture some of the key features of the helicase mechanochemical cycle , we have modeled helicase switching between two chemical states . in this model , the sites of a discrete lattice represent the positions of the individual bases on the ssna . at any spatial position , the helicase can exist in either of the two allowed chemical states . this model should be generally applicable to helicases where one of the transitions in the mechanochemical cycle is much slower than the other transitions . in this work , we have considered only a passive helicase mechanism solving the master equations for this model at steady state , we have calculated the speed of unwinding and the speed of single - strand translocation . the ratio of the unwinding velocity to the ss translocation velocity varies with atp concentration as well as with the base - pair binding free energy . our comparison to experimental data on ns3 helicase suggests that the model captures some features of the experiments . a set of detailed experiments by different labs under consistent conditions may be important to fully understand the unwinding mechanism of ns3 helicase . * acknowledgments * : the authors thank frank jlicher for several useful suggestions . we note that a two - state model for helicase translocation was also considered by betterton and jlicher @xcite , but the nature of the two states and the mechanism of translocation of the helicase are different from those developed here . hydrolysis stimulates binding and release of single stranded dna from alternating subunits of the dimeric e - coli rep helicase : implications for atp - driven helicase translocation . hepatitis c virus ns3 rna helicase domain with a bound oligonucleotide : the crystal structure provides insights into the mode of unwinding . a steady - state and pre - steady - state kinetic analysis of the ntpase activity associated with the hepatitis c virus ns3 helicase domain .",0.18573797678275286,"we develop a general model for unwinding of a double - stranded nucleic acid molecule by a helicase motor. the helicase can be either in biochemical state 1 or 2. the allowed transitions between states and the corresponding reaction rates can be fully described by the master equation approach. a specific helicase, ns3 helicase of hepatitis c, is our focus. we derive an analytical expression for the unwinding velocity, which is essentially the hard - wall interaction potential in the bj model. this expression is then used to compare several key features of the experimental data of ns3 with the theoretical predictions. we first consider a special case which captures the flashing ratchet mechanism proposed for ns3. we calculate the total unwinding probability by summing the reaction rates of helicase and dsna. we then consider the restricted case where only the chemical state and the base - pair binding free energy can be changed by applied force. in this case, we find that the average speed of unwinding is relatively high, @xmath0, which may be because of the small energy cost of opening the na. we critically discuss the contradictory contradictory experimental results in the literature. there are several situations in which two experimental data are contradictory. there is one situation where a specific experimental data is contradictory to a whole lot of data, yet the rest of the literature treats the data as consistent. therefore, we take a break and study a few of the details of the experiments as well as the generic aspects of the model. we conclude that the different experimental results may be due to different interpretations of the particular data, which also may be reflected in the underlying theory.",0.1663716814159292
0802.0961,"we performed three - dimensional @xmath0-body / sph simulations to study how mass resolution and other model parameters such as the star formation efficiency parameter , @xmath1 and the threshold density affect structures of the galactic gaseous / stellar disk in a static galactic potential . we employ @xmath2 particles to resolve a cold ( @xmath3 ) and dense ( @xmath4 ) phase as well as diffuse , hot phases . we found that structures of the interstellar medium ( ism ) and the distribution of young stars are sensitive to the assumed threshold density for star formation , @xmath5 . high-@xmath5 models with @xmath6 yield clumpy multi - phase features in the ism . young stars are distributed in a thin disk of which half - mass scale height is @xmath7 . in low-@xmath5 models with @xmath8 , which is usually employed in cosmological galaxy formation simulations , the stellar disk is found to be several times thicker , and the gas disk appears smoother than the high-@xmath5 models . a high - resolution simulation with high-@xmath5 is necessary to reproduce the complex structure of the gas disk . the global properties of the model galaxies in low-@xmath5 models , such as star formation histories , are similar to those in the high-@xmath5 models when we tune the value of @xmath1 so that they reproduce the observed relation between surface gas density and surface star formation rate density . we however emphasize that high-@xmath5 models automatically reproduce the relation , regardless of the values of @xmath1 . in high-@xmath5 models , the difference in star formation histories is within a factor of two for two runs with values of @xmath1 which differ by a factor of 15 . the ism structure , phase distribution , and distributions of young star forming region are also quite similar between these two . from the analysis of the mass flux on phase diagram , we found that the timescale of the flow from the reservoir ( @xmath9 ) to the star forming regions ( @xmath10 ) is about five times as long as the local dynamical time and this evolution timescale is independent of the value of @xmath1 . the use of a high-@xmath5 criterion for star formation in high - resolution simulations makes numerical models fairy insensitive to the modelling of star formation .","therefore , their results appear to imply that the global star formation properties are not sensitive to the details of star formation prescriptions . in this paper , we examine how numerical prescriptions of star formation affect structure of the ism , and the global star formation history ( sfh ) of a galactic disk . in particular , we focus on the threshold density in star formation criteria ( @xmath5 ) and the star formation efficiency ( @xmath18 ) . we also test the effect of star formation efficiency parameter @xmath1 in high-@xmath5 models . we perform high - resolution sph simulations ( number of sph particles are @xmath33 ) in a galactic potential and we compare structure of the ism and stellar disks . we show that , while both models can exhibit similar sfhs and the relation of surface gas density to surface sfr , only high-@xmath5 models have the complex , inhomogeneous , and multiphase ism . we mention the relation between numerical resolution and expressible phase of the ism in section 2 . in section 3 , we describe properties of a model galaxy and our numerical methods . we investigate 3-d evolution of a gas disk in a static disk - halo potential . we assume a navarro - frenk - white ( nfw ) density profile @xcite for a dark matter halo , and a miyamoto - nagai model @xcite for a stellar disk . for the halo model this indicates clearly that the threshold density for the star formation strongly affects the vertical structure of stellar disks . in many studies , numerical models of star formation in galaxy formation have been calibrated to be consistent with the observational @xmath89 relation . for example , @xcite successfully reproduced the relation with the threshold density of @xmath8 . in order to reproduce the relation within simulated disk galaxies we argue that we should generate `` stars '' above the physical density of real star forming regions such as gmcs or molecular cores to investigate the detailed structure and evolution of disk galaxies . in this paper , we highlighted on the ism structure and the distribution of newly formed star particles . the mass supply timescale from the reservoir to the star forming region determines the global star formation rate in the model that adopts the high - density threshold ( @xmath6 ) . from figure one of the most important advantages of the high-@xmath5 model is that global sfr is not determined by the local quantities but by the global state of the ism . this finding provides a support for star formation models in lower resolution cosmological simulations , which is similar to run a in this paper",0.25194805194805203,"we use numerical simulations to study the effect of star formation on structure of the interstellar medium ( ism ) in the milky way galaxy. two star formation models are examined, a low-@xmath0 model with a threshold density of @xmath1 ( @xcite ) and a medium - density model ( @xik0 model ). we find that the two models can produce a similar schmidt - kennicutt relation in the phase diagram, if the threshold density is chosen according to the local star formation rate ( sfr ) and the total mass in dense gas clumps is allowed to evolve from the ism to the stellar disks. the difference between the models comes from the fact that the high - density region converts into stars and supernova feedback blows out the surrounding dense gas in runs c and d. in the latter case, the gas from the reservoir to the star forming regions first has a log - normal like probability density distribution ( pdf ), while the low - density tail of the pdf has a power - law like form in a self - gravity dominated system. the complexness of the gas disks is almost the same to a similar degree. we argue that the evolution timescale in the multiphase ism is essentially independent of the star formation efficiency parameter, which is indicated by the well - known jeans condition. for the both models, the vertical scale of star particles is found to be comparable to the observed one. thus our results imply that the global sfhs and the relation of surface gas density to surface sfr are not changed by the choice of the threshold value for star formation. we also investigate the evolution of the mass of live halo particles ( e.g., nfw and oh galaxies ). it is found that a very high mass resolution is required to resolve the gaseous phase diagram. on the other hand, a moderate resolution is sufficient to generate ` ` stars '' in the halo. the stars are created either by heating of the dense gas due to sn feedback or by star formation feedback. we discuss the implications of our results for the assembly of live dark matter halos.",0.23131170662905498
hep-ph9407262,"in this report we have made a systematic study of strangeness production in proton - proton(pp),proton - nucleus(pa ) and nucleus- nucleus(aa ) collisions at cern super proton synchroton energies , using@xmath0 + ( version @xmath1 ) . numerical results for mean multiplicities of neutral strange particles , as well as their ratios to negatives hadrons(@xmath2 ) for p - p , nucleon - nucleon(n - n),p - s , p - ag , p - au(min . bias)collisions and p - au , s - s , s - ag , s - au ( central)collisions are compared to experimental data available from cern experiments and also with recent theoretical estimations given by others models(@xmath3 + @xmath4 and @xmath5 ) . neutral strange particle abundances are quite well described for p - p , n - n and p - a interactions , but are underpredicted by a factor of two in a - a interactions for @xmath6 in symmetric collisions(s - s , pb - pb)and for @xmath7 in asymmetric ones(s - ag , s - au , s - w ) . the ratios antistrange / strange are well described for @xmath8 but the ratios for multistrange particles ( @xmath9 ) and their antiparticle , could not be predicted by the model.a detailed analysis in limited rapidity range is required in order to draw some definite conclusion . a qualitative prediction for rapidity , transverse kinetic energy and transverse momenta normalized distributions are performed at 200 gev / nucleon in p - s , s - s , s - ag and s - au collisions in comparison with recent experimental data . hijing model predictions for coming experiments at cern for s - au , s - w and pb - pb interactions are given . the theoretical calculations are estimated in a full phase space . the factor of two can not be explained by considering very central events ( @xmath10 ) and taking into account minijets . new ideas are necessary in order to improve the comparison with experiment for nucleus - nucleus interactions . = 16truecm = 24truecm 1 = = .5truecm = -2truecm 1truecm * dipartamento di fisica ` ` g.galilei '' + * * istituto di fisica nucleare + * * sezione di padova + * italy * * 2truecm * strangeness production in pp , pa , aa * + 0.3 cm * interactions * + 0.3 cm * at sps energies . hijing approach * + 1truecm * wa94 collaboration * + dipartimento di fisica``g.galilei'',infn sezione di padova , via marzolo 8 , 35131 padova,*italy + * , * romania + * and + dipartamento di fisica ` ` g.galilei'',infn sezione di padova , via marzolo 8 , 35131 padova,*italy + * * dfpd-94-np-42 8 june 1994 * _ work presented at the international conference ` ` physics of high energy heavy ion collisions '' , vuosaari(helsinki),finland,17 - 22 june 1994 _ 1truecm = -1truecm = -2truecm","we perform a systematic study of strange particle production in proton proton(@xmath0 ) and nucleus(p, @xmath1 ) interactions at super proton synchrotron(sps ) cern energies using hijing(heavy ion jet interacting generator ) monte carlo model. the formulation of the hijing model uses the lund fritiof and dpm models phenomenology for soft nucleus - nucleus collisions and depends on the relative transverse momentum transfer of the processes. in particular, hadron - nucleus interactions in nucleus - nucleon collisions are decomposed into binary collisions involving in general excited or wounded nucleons. we study the average multiplicities for negative hadrons(#xmath2 ), negative pions(@xcite ), pion condensate(pion 2002 ) and neutral strange particles(pbpb 2002 ), compared with recent experimental data from na 35 collaboration. we also study the multiplicity ratios for hadronposon / nucleus(rhnn ) and pp(rhas / nucleon ). the results are compared to the data of hadron collider operating at the na 35 collider. we find that with a proton - nucleus interaction the average number of hadrons produced by each of the above particles is about one order of magnitude smaller than that of the total hadron production. the decrease of the hadron multiplicity due to the growth of the diffusive parton spectrum, relative to the total one, can not reproduce the experimental data. the same result is obtained with the current data on pp / nucleus and pp - particle production. as well as the abundance of negative pion(rhn)/nucleon ratios, which indicate a relative increase of the matter - antimatter asymmetry with respect to the non - nucleonic solution. concerning the neutral strange production, we found that the main production mechanism of this particle is the minijet production with the total cross sections increasing with the number of inelastic cross sections within the eikonal formalism of hijing. an exact prescription for the strangeness enhancement is proposed based on the particular dependence of the cross sections for urhic. it is confirmed that hijing models including perturbative qcd processes in the pythia model can reproduce the data well. other models such as dual partons models, quark - gluon string models, and relativistic quantum molecular dynamics are not successful in reproducing the same data. # 1#2#3",0.14627659574468085,"searching for possible exotic states of nuclear matter is one of the currently most interesting and stimulating subjects in high energy nuclear physics ( see references ) to create exotic matter such as the quark - gluon plasma ( qgp ) strange matter @xcite,@xcite , multi@xmath11-matter , pion condensate , kaon condensate @xcite,@xcite it is essential to generate extreme states of nuclear matter regarding density , temperature or energy density @xcite . the soft physics data have stimulated a great deal of theoretical activity and in the present introduction it is impossible to give more than a superficial overview of the main types of the monte carlo models used.many models for urhic have been developed : dual partons models(dpm ) ,@xcite quark gluon string models(qgsm) , venus models for very energetic nuclear scattering fritiof model @xcite,@xcite , attila @xcite model , relativistic quantum molecular dynamics ( rqmd ) ,parton string model(psm) , hijet model@xcite . we have performed a systematic study of strange particle production in proton proton(@xmath20),proton cern energies using hijing(heavy ion jet interacting generator ) monte carlo model developed at berkeley . sps energies and the highest collider energies at relativistic heavy ion collider(rhic)(@xmath24 and the cern large hadron collider ( lhc ) ( @xmath25 ) . using hijing monte carlo model in this paper we present some theoretical calculations for mean multiplicities of strange particle production in the full rapidity range as well as their ratios to negative hadron predicted by hijing model(hij.01 version -see section 2 and 3 for explanation of this version)for @xmath20 , nucleon - nucleon @xmath26,minimum biascollisions @xmath27 and + central collisions@xmath28 at the energy of @xmath29 . also a qualitative prediction for normalised distributions for rapidity , transverse kinetic energy and transverse momenta are done at 200 gev / nucleon in @xmath30 and sau collisions and the results are compared with recent experimental data from na 35 collaboration .we note that theoretical calculations are done for full phase space . for giving an idea of abundances and spectra in experiments planned in the near future at cern , we give some predictions for sw and pbpb interactions . we note that the version hij.01 of the model includes neither the formation of qgp nor some collective dynamics on either the hadronic or string level.although the existing trends of hadron distributions are quite satisfactorily approximated by the hijing model @xcite,@xciteand also neutral strange production in @xmath20 and @xmath21 interactions are quite well described , this version is getting less reliable for strange particle produced in heavy colliding systems . the models includes multiple minijet production with initial and final state radiation along the lines of the pythia model @xcite,@xcite and with cross sections calculated within the eikonal formalism . soft beam jets are modeled by quark - diquark strings with gluon kinks along the lines of the dpm and fritiof models.multiple low @xmath38 exchanges among the end point constituents are included . in this report , we give a systematic study of strange particle production in pp , pa and aa collisions mainly at sps cern - energies , using hijing monte carlo model developed for high energy collisions . we analyse data from cern experiments ( na35,na36 , + wa85 ) and we give a detailed comparison for mean multiplicities of neutral strange particle for pp , ps , pag , pw , pau , ss , sw and pbpb interactions . strange particle abundances are quite well described in pp and pa collisions and are underpredicted by a factor of two in nucleus - nucleus interactions , by this version ( theoretical values for hij.01 ) .the ratios for multistrange particles could not be predicted by the model hij.01 .the abundances of @xmath16 and @xmath17 are underpredicted and the abundances of @xmath179 and @xmath180 are overpredicted . we present also some calculations for the ratios @xmath204 and @xmath205 given by hijing model compared with other models predictions like venus and fritiof.all models seems to overpredict @xmath205 ratios and underpredict @xmath204 ratios . new ideas are necessary in order to improve the comparison of theoretical calculations with experimental data.the main goal is to increase the rate of neutral strange particle production by a factor of two in nucleus - nucleus interaction at @xmath216 .",0.19534883720930232
1702.03948,"this article investigates the problem of enforcing a virtual holonomic constraint ( vhc ) on an underactuated mechanical system while simultaneously stabilizing a closed orbit on the constraint manifold . this problem , which to date is open , arises when designing controllers to induce complex repetitive motions in robots . in this paper , we propose a solution which relies on the parameterization of the vhcby the output of a double integrator . while the original controls are used to enforce the vhc , the control input of the double - integrator is designed to asymptotically stabilize the closed orbit and make the state of the double - integrator converge to zero . the proposed design is applied to the problem of making a pvtol aircraft follow a circle on the vertical plane with a desired speed profile , while guaranteeing that the aircraft does not roll over . virtual holonomic constraints ( vhcs ) have been recognized to be key to solving complex motion control problems in robotics . there is an increasing body of evidence from bipedal robotics @xcite , snake robot locomotion @xcite , and repetitive motion planning @xcite that vhcsconstitute a new motion control paradigm , an alternative to the traditional reference tracking framework . the key difference with the standard motion control paradigm of robotics is that , in the vhcframework , the desired motion is parameterized by the states of the mechanical system , rather than by time . grizzle and collaborators ( see , e.g. , @xcite ) have shown that the enforcement of certain vhcson a biped robot leads , under certain conditions , to the orbital stabilization of a hybrid closed orbit corresponding to a repetitive walking gait . the orbit in question lies on the constraint manifold , and the mechanism stabilizing it is the dissipation of energy that occurs when a foot impacts the ground . in a mechanical system without impacts , this stabilization mechanism disappears , and the enforcement of the vhcalone is insufficient to achieve the ultimate objective of stabilizing a repetitive behavior . some researchers @xcite have addressed this problem by using the vhcexclusively for motion planning , i.e. , to find a desired closed orbit . once a suitable closed orbit is found , a time - varying controller is designed by linearizing the control system along the orbit . in this approach , the constraint manifold is not an invariant set for the closed - loop system , and thus the vhcis not enforced via feedback . to the best of our knowledge , for mechanical control systems with degree of underactuation one , the problem of simultaneous enforcement of a vhcand orbital stabilization of a closed orbit lying on the constraint manifold is still open . * contributions of the paper . * this paper presents the first solution of the simultaneous stabilization problem just described . leveraging recent results in @xcite , we consider vhcsthat induce lagrangian constrained dynamics . the closed orbits on the constraint manifold are level sets of a ` ` virtual '' energy function . we make the vhcdynamic by parametrizing it by the output of a double - integrator . we use the original controls of the mechanical system to enforce the dynamic vhc , while we use the double - integrator input to asymptotically stabilize the selected orbit . because the output of the double - integrator acts as a perturbation of the original constraint manifold , we also make sure that the state of the double - integrator converges to zero . to achieve these objectives , we develop a novel theoretical result giving necessary and sufficient conditions for the exponential stabilizability of a closed orbit for a control - affine system . the benefit of simultaneously enforcing a vhcand stabilizing a closed orbit is that it offers a superior control over the transient behavior of the system . this is illustrated in an example at the end of the paper , in which a pvtol vehicle performs a repetitive maneuver while guaranteeing that it does not undergo full revolutions along its longitudinal axis . * relevant literature . * previous work employs vhcsto stabilize desired repetitive behaviors for underactuated mechanical systems @xcite . canudas - de - wit and collaborators @xcite propose a technique to stabilize a desired closed orbit that relies on enforcing a virtual constraint and on dynamically changing its geometry so as to impose that the reduced dynamics on the constraint manifold match the dynamics of a nonlinear oscillator . in @xcite , canudas - de - wit , shiriaev , and collaborators employ vhcsto aid the selection of closed orbits corresponding to desired repetitive behaviors of underactuated mechanical systems . it is demonstrated that an unforced second - order system possessing an integral of motion describes the constrained motion . assuming that this unforced system has a closed orbit , a linear time - varying controller is designed that yields exponential stability of the closed orbit . with the exception of @xcite , the papers above do not guarantee the invariance of the vhcfor the closed loop system . the idea of event - triggered dynamic vhcshas appeared in the work by morris and grizzle in @xcite where the authors construct a hybrid invariant manifold for the closed - loop dynamics of biped robots by updating the vhcparameters after each impact with the ground . this approach is similar in spirit to the one presented in this paper . in section [ sec : stab : shir ] , we discuss the differences between the method presented in this article and the ones in @xcite . we also discuss the conceptual similarities between the method presented in this article and the one in @xcite . * organization . * this article is organized as follows . we review preliminaries in section [ sec : stab : prelim ] . the formal problem statement and our solution strategy are presented in section [ sec : stab : prob_stat ] . in section [ sec : stab : dynconstr ] we present dynamic vhcs . in section [ sec : stab : s_control ] we design the input of the double - integrator to stabilize the closed orbit relative to the constraint manifold , and in section [ sec : stab : sol ] we present the complete control law solving the vhc - based orbital stabilization problem . in section [ sec : stab : shir ] we discuss the differences between the method presented in this article and the ones in @xcite . finally , in section [ sec : motex ] we apply the ideas of this paper to a path following problem for the pvtol aircraft . * notation . * if @xmath0 and @xmath1 , then @xmath2 modulo @xmath3 is denoted by @xmath4_t$ ] , and the set @xmath5_t : x\in { \mathbb r}\}$ ] is denoted by @xmath6_t$ ] . this set can be given a manifold structure which makes it diffeomorphic to the unit circle @xmath7 . if @xmath8 and @xmath9 are vectors , then @xmath10{^\top}$ ] . if @xmath11 , we denote @xmath12 , and @xmath13 . if @xmath14 is a smooth map between smooth manifolds , and @xmath15 , we denote by @xmath16 the derivative of @xmath17 at @xmath18 ( in coordinates , this is the jacobian matrix of @xmath17 evaluated at @xmath18 ) , and if @xmath19 has dimension 1 , then we may use the notation @xmath20 in place of @xmath21 . if @xmath22 are smooth manifolds and @xmath23 is a smooth function , then @xmath24 denotes the derivative of the map @xmath25 at @xmath26 . if @xmath27 is a vector field on @xmath19 and @xmath28 is @xmath29 , then @xmath30 is defined as @xmath31 . for a function @xmath32 , we denote by @xmath33 . if @xmath34 has full row - rank , we denote by @xmath35 the right - inverse of @xmath36 , @xmath37 . given a @xmath38 scalar function @xmath39 , we denote by @xmath40 its hessian matrix .","necessary and sufficient conditions for a relation @xmath55 to be a regular vhcof order @xmath48 are given in the following proposition . prop : stabilization ] let @xmath55 be a regular vhcof order @xmath48 for system with associated constraint manifold @xmath61 in . [ prop : red_dyn ] let @xmath55 be a regular vhcof order @xmath48 for system . henceforth , we will refer to as the * reduced dynamics*. system is unforced since all @xmath48 control directions are used to make the constraint manifold @xmath61 invariant . an immediate consequence of the foregoing result is that , when the reduced dynamics are lagrangian , the orbits of are characterized by the level sets of the energy function @xmath105 moreover , almost all orbits of the reduced dynamics are closed , and they belong to two distinct families , defined next . it is possible to give an explicit regular parameterization of rotations and oscillations which will be useful in what follows . thus a rotation @xmath106 is the graph of a function , which leads to the natural regular parameterization @xmath6_{{{t_1 } } } \to [ { \mathbb r}]_{{{t_1}}\times { \mathbb r}}$ ] given by @xmath118 concerning oscillations , it was shown in ( * ? ? ? the constraint manifold associated with the family of vhcs@xmath134 is @xmath135 the manifold @xmath136 can be viewed as a perturbation of the original constraint manifold @xmath61 , since its intersection with the set @xmath137 is @xmath61 since @xmath140 on @xmath141 , near @xmath141 the hausdorff distance between the set @xmath136 and the original constraint manifold @xmath142 is small . considering the fact that @xmath55 embodies a useful constraint that we wish to hold during the transient , the philosophy of the vhc - based orbital stabilization problem is to preserve as much as possible the beneficial properties of the original vhc@xmath55 , while simultaneously stabilizing the closed orbit @xmath106 corresponding to a desired repetitive behaviour . * solution steps . * our solution to the vhc - based orbital stabilization problem unfolds in three steps : 1 . we develop a general result for control - affine systems ( theorem [ thm : transverse_linearization ] ) relating the exponential stabilizability of a closed orbit to the controllability of a linear periodic system , for which we give an explicit representation . leveraging this result , we design the input of the double - integrator , @xmath133 , to exponentially stabilize the orbit relative to the manifold @xmath136 . we put together the controller enforcing the dynamic vhcin step 1 with the controller stabilizing the orbit in step 2 and show that the resulting controller solves the vhc - based orbital stabilization problem . in this section we present the notion of dynamic vhcs . we have proposed a technique to enforce a vhcon a mechanical control system and simultaneously stabilize a closed orbit on the constraint manifold . the theory of this paper is applicable to mechanical control systems with degree of underactuation one . for higher degrees of underactuation , the result of section [ sec : stab : s_control ] concerning the exponential stabilization of closed orbits for control - affine systems is still applicable in this case .",0.17874396135265697,"we consider the underactuated mechanical control problem with a virtual holonomic constraint @xmath0. the goal is to stabilize the orbits of the reduced dynamics while preserving the invariance of the constraint manifold, in particular, to prevent the transient behaviour that might lead to repetitive configurations. we show that the optimal solution to the vhc - based orbital stabilization problem involves augmenting the dynamics with a double - integrator. we provide a general theorem relating the stability of a closed orbit to the controllability of a linear periodic system, for which we give an explicit representation. leveraging this result, we design a feedback loop to exponentially stabilize the orbit relative to the manifold in order to maintain a certain speed profile. + + key words : self - regulation, self - intervention, open dynamics, regularity there is a considerable interest in the study of out - of - equilibrium dynamics. an early and important observation of @xcite center for nonlinear dynamics, department of physics, university of illinois, urbana - champaign, il 61801, usa. a problem that arises frequently is the stabilization of equilibrium states that are macroscopic in nature. it is well - known that a system that is stable in a harmonic oscillating mechanical sense ( e.g., in the oscillating harmonic oscillators ) is always stable in the harmonic oscillator state, in contrast to the state that is usually unstable in the dynamical sense. henceforth, it has been asked what conditions a given system has to meet to have an _ exponentially stable equilibrium state _, i.e., a closed statespace such that for any value of the system is stable. one of the conditions that have been discussed in the literature is that the system must be homeomorphic to a regular curve of diffeomorphic to either the unit circle or the real line. this is known as the _ closed orbit problem_. in the case of systems of linear, periodic, or quasi - periodic forms, the closed - loop state is stable for long periods of time, in interesting ways, because almost all orbits are essentially closed. however, it is not known in general that the same is true for systems that operate in a nonlinear regime, in other words, for any system that operates in a stationary state. this paper provides a general solution to this problem if and only in the context of convex regular systems. in turn, our solution determines the necessary and sufficient conditions for the existence of a locally lipschitz continuous feedback, such that the conve",0.16318785578747627
1305.5706,"polarized negative muons were used to study the behaviour of the boron acceptor centre in synthetic diamond produced by the chemical vapour deposition ( cvd ) method . the negative muon substitutes one of the electrons in a carbon atom , and this muonic atom imitates the boron acceptor impurity in diamond . the temperature dependence of the muon spin relaxation rate and spin precession frequency were measured in the range of @xmath0 k in a transverse magnetic field of 14 koe . for the first time a negative shift of the muon spin precession was observed in diamond . it is tentatively attributed to an anisotropic hyperfine interaction in the boron acceptor . the magnetic measurements showed that the magnetic susceptibility of the cvd sample was close to that of the purest natural diamond . 5 mm 4 mm @xmath1joint institute for nuclear research , 141980 dubna , moscow reg . , russia + @xmath2moscow institute of physics and technology , 141700 dolgoprudny , moscow reg . , russia + @xmath3physik - institut der universitt zrich , winterthurerstrasse 190 , ch-8057 zrich , switzerland + @xmath4natural sciences center of institute of general physics , ras , 119991 moscow , russia + @xmath5paul scherrer institut , ch-5232 villigen psi , switzerland + diamond with its unsurpassed mechanical strength , thermal conductivity , and radiation hardness is a promising semiconductor for particle detectors and electronic components capable of withstanding high heat and radiation loads . great advances have been made over the last years in the technology of manufacturing synthetic single crystal diamond and diamond films @xcite . boron is the only dopant which forms an acceptor centre ( ac ) in diamond with an ionization energy of @xmath6 mev @xcite . the metal - insulator transition occurs at a concentration of @xmath7 @xmath8 of boron atoms @xcite . the epr signal of boron impurities in diamond was observed only for uniaxially stressed samples @xcite , and the electronic state of this acceptor is investigated insufficiently . the possibility of using negative muons to study the behaviour of acceptor impurities in diamond arises from the fact that capture of a negative muon by a carbon atom results in the formation of a muonic atom @xmath9b with an electron shell that is analogous to that of the boron atom . the evolution of the polarization of @xmath10 in the 1s atomic state depends on the interaction of the muon spin with the electron shell of the muonic atom and on the interactions of this muonic atom ( acceptor centre ) with the crystal lattice . providing that the electron shell of @xmath9b has a nonzero magnetic moment ( paramagnetic @xmath9b ) , there is a hyperfine interaction between the muon and the electron shell . the efficiency of the hyperfine interaction depends on the relaxation rate @xmath11 of the magnetic moment of @xmath9b and on the hyperfine interaction constant @xmath12 . according to theoretical calculations @xcite , relaxation of the muon spin and a paramagnetic shift of its precession frequency are expected for @xmath13 . under the assumption of an isotropic hyperfine interaction , the paramagnetic shift should be of positive sign and inversely proportional to temperature . the boron atom as ac in diamond may be in the diamagnetic ( b@xmath14 ) or paramagnetic ( b@xmath14 + @xmath15 ) state . in the latter case a hole is localized in vicinity of the ac . at equilibrium the boron acceptor in diamond is expected to be paramagnetic below @xmath16 k. in earlier experiments @xcite we observed no frequency shift of the muon spin precession in diamond at the level of @xmath17 . the goal of the present experiment was to improve the accuracy of the muon spin precession frequency measurement .","the effect of paramagnetic ( magnetic ) defects on the muon spin precession frequency of the electrons in polycrystalline diamond was studied by @xmath0li spin resonance spectroscopy. it was found that the paramagnetic centre of the muonic atom in the 1s state of graphite has covalent chemical bonds with the three nearest carbon atoms and the fourth carbon atom has an unpaired spin ( one dangling bond ). the susceptibility of the carbon atom was found to be constant in the magnetic field of 14 koe. the effects of magnetic impurities, formed either by hydrogen or nitrogen ( the diameters of 3.5 mm and 1.3 mm ) in the acceptor centre, were studied with the quantum design squid magnetometer. the results of the measurements are presented in detail in magnetic fields of 95.2 oe and 20.0 koe for both samples. the durant magnetic moments of negative muons in graphite exhibit a linear dependence of their magnetic moment on the external magnetic field in the temperature range from 0 to 50 koe, and on the temperature variation of their frequency shift. in contrast, no linear dependence is observed in the synthetic carbon diamond sample studied. the development of an efficient toolbox for the measurement of magnetic properties of materials is one of the main goals of modern research. in this context, the search for new phases of nanophotonic compounds is of great importance because of their great potential for technological applications and the high tunability in manipulating and manipulating of magnetic moments. of particular interest are antiferromagnetic carbon allotropes such as n@xmath1 crystals. for example, the artificial crystals based on carbon nanotubes are highly desirable due to their outstanding mechanical properties and facile mechanical properties @xcite. synthetic diamond is relatively well isolated from environmental effects and its high optical depth makes it an ideal test bed for nanophotonics and quantum information processing. in the past few years a lot of research efforts are focused on its magnetic properties and on its mechanical properties ( e.g. the tunability of muon dynamics and precession ). recently, a large number of theoretical predictions and simulations have been performed to investigate the effect of magnetic and impurity effects on the mechanical properties of diamond materials. the predictions are based on the theoretical prediction of a simple model, namely, linear temperature dependence of the magnetic susceptibility for muon rotations, and it is expected that the presence of magnetic defects, such as impurities in the carbon colour, would result",0.20204081632653065,"the behaviour of the muon spin polarization in the reference graphite sample was studied at temperatures 9.6 , 50 , 100 , 200 , and 300 k in a magnetic field of 14 koe . there is no difference in the damping rate of the muon spin at 140 k in the magnetic field of 3.0 koe compared to 14 koe . generally , the temperature dependence of @xmath34 in sample d6 is similar to that observed earlier for the cvd film samples in 1.5 and 2.5 koe magnetic fields @xcite . as seen in fig . the polarization of this paramagnetic complex in an external magnetic field could result in the negative shift of the muon spin precession frequency ; \c ) negative frequency shift can also be due to polarization of the paramagnetic acceptor centre in the magnetic field if the muonic atom is formed in the ( @xmath55b@xmath57+h ) state in @xmath58 s and the hyperfine interaction in the ac is anisotropic . in the state ( @xmath55b@xmath57+h ) the muonic atom has covalent chemical bonds with all four nearest carbon atoms and a hole localized in the vicinity of ac therefore , a simple @xmath60 ( curie type ) temperature dependence of the muon spin precession frequency shift is expected . to elucidate the effect of paramagnetic ( magnetic ) defects on the muon spin precession frequency we measured the magnetic susceptibility of our sample . the magnetic moments ( @xmath61 ) of samples a and b were measured in magnetic fields in the range of @xmath62 koe at the temperatures 20 , 100 , and 300 k. the temperature dependence @xmath63 was studied in detail in the magnetic fields of 95.2 oe and 20.0 koe for both samples . this means that the muonic atom @xmath55b is formed in one of the chemically bonded @xmath55b@xmath54 or ( @xmath55b@xmath72 + h ) states with a probability close to unity in less than @xmath73 s. it is worth mentioning that the auger transitions of the muon destroy chemical bonds of the muonic atom with neighbouring carbon atoms . nevertheless , we may assume that @xmath34 is inversely proportional to the relaxation rate of the magnetic moment of the acceptor centre in both @xmath55b@xmath54 and ( @xmath55b@xmath72 + h ) states . in diamond relaxation of the magnetic moments of @xmath55b@xmath54 and ( @xmath55b@xmath57 + h ) direct , raman , and orbach processes can contribute to phonon scattering , and the temperature dependence of the probability of these processes is very different @xcite . in the present experiment two temperature domains with different temperature dependences of the relaxation rate of the muon spin were observed . thus , we conclude that there is a contribution of two different processes to scattering of phonons at the acceptor in diamond . a large negative shift of the precession frequency of the negative muon spin in diamond was found for the first time . simple curie type @xmath76 temperature dependence of the frequency shift was observed . it is not excluded that the muonic atom as an ac forms in the equilibrium ( @xmath55b@xmath57 + h ) state in @xmath77 s and there is an anisotropic hyperfine interaction in ac .",0.2269767441860465
astro-ph0111413,"we analyse very deep x - ray and mid - ir surveys in common areas of the lockman hole and the hdf north to study the sources of the x - ray background ( xrb ) and to test the standard obscured accretion paradigm . observations with xmm - newton and iso of a substantial area in lockman are particularly important to sample luminous - but relatively uncommon - obscured agns . we detect a rich population of x - ray luminous sources with red optical colours , including a fraction identified with extremely red objects ( r - k@xmath0 ) and galaxies with seds typical of normal massive ellipticals or spirals at @xmath1 . the x - ray luminosities of these objects ( @xmath2 erg / s ) indicate that the ultimate energy source is gravitational accretion , while the x - ray to ir flux ratios and the x - ray spectral hardness show evidence of photoelectric absorption at low x - ray energies . an important hint on the physics comes from the mid - ir data at 6.7 and 15 @xmath3 m , well reproduced by model spectra of completely obscured quasars under standard assumptions and line - of - sight optical depths @xmath4 . other predictions of the standard xrb picture , like the distributions of intrinsic bolometric luminosities and the relative fractions of type - i and -ii objects ( 1:3 ) , are also consistent with our results . obscured gravitational accretion is then confirmed as being responsible for the bulk of the x - ray background , since we detect in the ir the down - graded energy photoelectrically absorbed in x - rays : 63 % of the faint 5 - 10 kev xmm sources are detected in the mid - ir by fadda et al . ( 2001 ) . as discussed there , however , although as much as 90 % of the x - ray energy production could be converted to ir photons , no more than 20 % ( and possibly less ) of the cosmic ir background can be attributed to x - ray loud agns .","we discuss the properties of the sources of the x - ray background detected in the recent xmm - newton survey of the lockman hole. we exploit a sample of 24 very faint _ chandra _ and isocam sources located in a small area of @xmath0 square arcmin centered in the hdfn. the completeness and the size of our xmm sample allow us to test the predictions of various agn accretion scenarios. we find that the majority of the source is of type - ii, with a fraction of very bright type - i objects not detected in even the deepest ir and xmm data. about one - half of this population is likely to be compton - thick, an effect which can not be ruled out in the context of the obscured accretion models. for the few sources with spectroscopic redshifts, we find reasonable agreement between bolometric luminosities ( l@xmath1 erg / s ) and predicted spectral energy distributions ( seds ) for dusty quasars. we note, however, that two of these classes are predicted to be much fainter than suggested by our seds. the remaining sources are consistent with being at the same redshift as the bright sources. x - rays : galaxies : active intergalactic medium infrared : galaxies",0.20717131474103587,"we discuss in this paper the properties of a substantial population of extremely red galaxies as counterparts of faint hard x - ray and ir sources , based on combined deep observations by iso and xmm of a 220 square arcminutes field in the lockman hole by fadda et al . we exploit , in particular , their remarkable finding that a large fraction ( 63% ) of the faint 5 - 10 kev xmm sources have relatively bright counterparts at 15 @xmath3 m , already a hint that the ir detects in these sources the reprocessed energy absorbed in x - rays . we also consider deeper data in a smaller area in the hdf north observed with _ 3 we discuss the main physical properties of the sources based on the available photometry and optical , ir and x - ray colours . our reference sample consists of 24 sources selected by xmm - newton in the total band 0.5 - 10 kev and detected by isocam in a common region of 220 square arcmins located in the lockman hole . [ fig5 ] implies that the contribution of the x - ray energy to the bolometric luminosity can not be dominant : the bulk of the qso primary energy is produced in the uv - optical , consistent with the average type - i spectrum by elvis et al . finally , the completeness and large mid - ir identification fraction of our xmm sample in lockman allow also a statistical test of xrb models . again in rough agreement with the unification scheme ( e.g. lawrence 1991 ) , the ratio of the number of type - ii to type - i qsos appearing in fig . we have exploited very deep x - ray and mid - ir survey data obtained for the first time by iso , xmm - newton and _ chandra _ in common areas of the lockman hole and hdfn , to test standard models for the origin of the xrb and the supposed dust - obscured accretion phenomenon . the large surveyed area in lockman was essential to detect significant numbers of luminous obscured agns , too rare to be appropriately sampled in the small hdfn field . this combined x - ray / ir survey detects normal type - i quasars with standard optical , ir and x - ray properties ( blue colours , power - law x - ray and ir spectra ) . in addition , a rich population of x - ray luminous sources with red optical colours is identified , roughly half of which would be classified as extremely red objects ( r - k@xmath0 ) in the optical . 1995 ) are met by our analysis , within the uncertainties implied by the small number of sources . in particular , the bolometric luminosity distributions do not appear to be systematically different between type - i and -ii objects , and their observed relative fractions are consistently close to the canonically assumed value of 1:3 . also the x - ray luminosities and hardness ratios of type - ii objects show evidence of photoelectric absorption at low x - ray energies . we believe that these results provide important new evidence that obscured gravitational accretion in massive normal - looking galaxies is responsible for the bulk of the x - ray background : the energy which is absorbed in x - rays ( which could be as much as 80 - 90% when averaged over the whole population producing the xrb , see fabian & iwasawa 1999 ) is found by us to be down - graded in photon energy and re - emitted in the ir , as expected . in spite of this , and following the correlation analysis of deep x - ray and ir images by fadda et al .",0.2413793103448276
0711.3952,"we present multiwavelength observations of a large - amplitude oscillation of a polar crown filament on 15 october 2002 , which has been reported by isobe and tripathi ( _ astron . astrophys . _ * 449 * , l17 , 2006 ) . the oscillation occurred during the slow rise ( @xmath0 1 km s@xmath1 ) of the filament . it completed three cycles before sudden acceleration and eruption . the oscillation and following eruption were clearly seen in observations recorded by the extreme - ultraviolet imaging telescope ( eit ) onboard the solar and heliospheric observatory ( soho ) . the oscillation was seen only in a part of the filament , and it appears to be a standing oscillation rather than a propagating wave . the amplitudes of velocity and spatial displacement of the oscillation in the plane of the sky were about 5 km s@xmath1 and 15,000 km , respectively . the period of oscillation was about two hours and did not change significantly during the oscillation . the oscillation was also observed in h@xmath2 by the flare monitoring telescope at hida observatory . we determine the three - dimensional motion of the oscillation from the h@xmath2 wing images . the maximum line - of - sight velocity was estimated to be a few tens of km s@xmath1 , though the uncertainty is large owing to the lack of the line - profile information . furthermore , we also identified the spatial displacement of the oscillation in 17 ghz microwave images from nobeyama radio heliograph ( norh ) . the filament oscillation seems to be triggered by magnetic reconnection between a filament barb and nearby emerging magnetic flux as was evident from the mdi magnetogram observations . no flare was observed to be associated with the onset of the oscillation . we also discuss possible implications of the oscillation as a diagnostic tool for the eruption mechanisms . we suggest that in the early phase of eruption a part of the filament lost its equilibrium first , while the remaining part was still in an equilibrium and oscillated .","we report on an event in which a large polar crown filament of length @xmath0 days ago showed large amplitude oscillation in its pre - eruptive, slow - rise phase before its eruption. the oscillation was most clearly seen in 195 images taken by the extreme - ultraviolet imaging telescope ( eit ), including 171 images in the linear frame of h@xmath1, 170 in the plane of the sky and 115 in the far - infrared ( faint object imaging ). in addition to the optical data, we found evidence of an excitation mechanism using magnetic - field data. in particular, an oscillation with a large amplitude occurred in a small part of the filament. this oscillation lasted for about two hours and could be visualized by the temporal slices along the filament s semi - major axis for about 15 hours. the spatial displacement due to the oscillations was identified with the alfvn waves seen at 17 ghz from nobeyama radio heliograph. to the best of our knowledge, this is the first evidence of a large - amplitude, spatially resolved, large - frequency oscillation of a filament in microwave imaging. we further examine the possible excitation mechanisms responsible for theoscation. magnetic reconnection appears to be the most likely explanation for the excitation. if the slow rise was triggered by an initial growth of an instability ( loe or instability ), _ i.e. _, loss of equilibrium or growth of mass, then the instability would have occurred at a local equilibrium state, which is non - linear in time scale. this type of instability is similar to those that have been found commonly associated with large amplitude filament eruptions ( e.g., filament eruption ). however, in many such events the whole filament does not erupt simultaneously. instead, in some cases there is an asymmetry in the dynamics between the leading and trailing filaments ; the leading filament erupts first and the remaining parts seem to be dragged by the trailing filament. therefore, the dynamical mechanism likely dominates in this case. we also discuss the implications of the observed in this event on the formation of an asymmetric ( slow rise ) oscillation.",0.2465753424657534,"the period and the velocity amplitude measured in the plane of sky of the oscillation were about 2 hours and 4.2 km s@xmath1 , respectively . in addition to the detection of the oscillation in extreme ultraviolet and h@xmath2 , we discovered that the oscillation was seen also in microwave . we examine the magnetic - field data to study the mechanism of the excitation of the oscillation . in such a long filament , it is probably possible that the filament loses its equilibrium in a the oscillation in a part of the filament during the slow rise is evidence that that part of the filament still retained an equilibrium . in this paper we presented the observations of a large amplitude oscillation of the polar crown filament in its pre - eruption , slowly rising phase . the oscillation was seen only in a part of the filament , and seems to be a standing oscillation rather than a propagating wave . such an oscillation has not been reported during the more than ten years of norh observations ( although we have not done a systematic survey for such events , so this does not mean that ours is the only such event ) , and we believe that this is the first observation of spatially resolved filament oscillation by microwave imaging . in contrast to previous observations of large - amplitude filament oscillations , there were no flares or even microflares associated with the excitation of the filament . however , we found that a filament barb connected near an emerging flux disappeared and seems to be ejected at the onset of the oscillation . we believe that reconnection between the emerging flux and the barb caused the ejection that blew the filament to excite the oscillation . the large - amplitude oscillation occurred in the slow - rise phase of the filament , and only a part of the filament exhibited the oscillation . the oscillation is evidence that the oscillating part of the filament still retained a nonlinearly stable equilibrium during the slow rise . filament and prominence seismology is a powerful tool , not only for measuring the physical parameters , but also for diagnosing the stability and hence the trigger mechanism of filament eruption . dt acknowledges the support from pparc .",0.2585438335809807
1101.5148,"i discuss several corrections to leading twist calculations of nucleon structure functions which are needed to include experimental data at large parton fractional momentum @xmath0 and at low scales @xmath1 in global fits of parton distribution functions . in particular i discuss the results of the cteq6x global fit , and some work in progress . topics covered include the interplay of target mass and higher - twist corrections , the importance of nuclear corrections for deuterium target data , and applications to the study of quark - hadron duality . implications for collider physics are highlighted . jlab - thy-11 - 1164 address = hampton university , hampton , virginia 23668 + and jefferson lab , newport news , virginia 23606 precise parton distribution functions ( pdfs ) at large parton fractional momentum @xmath0 are vital for understanding the non perturbative structure of the nucleon and the effects of color confinement on its partonic constituents . for instance , the @xmath2 quark distribution ratio near @xmath3 is very sensitive to the nature of the quark - quark forces in the nucleon ; the ratios of spin - polarized to spin - averaged pdfs @xmath4 , and particularly @xmath5 , in the limit @xmath6 reflect the non perturbative quark - gluon dynamics in the nucleon , and can shed light on the origin of the nucleon s spin . precise pdfs at large @xmath0 also have impact in other areas of nuclear and high - energy physics , e.g. , by allowing precise computations of qcd background processes in searches of new physics signals at hadron colliders , and systematic uncertainties in neutrino oscillation experiments . pdfs can be extracted from experimental data through global qcd fits which combine data from many different processes and observables , and analyze them by means of perturbative qcd calculations @xcite . currently , however , the unpolarized pdfs are well determined only for @xmath7 for valence quarks , @xmath8 for gluons , and @xmath9 for heavy quarks . to better constrain these at large @xmath0 it is necessary to study hard scattering processes near kinematic thresholds , such as deep inelastic scattering ( dis ) at large bjorken invariant @xmath10 and low 4-momentum transfer squared @xmath1 , drell - yan ( dy ) lepton pair production and electroweak vector boson production at large rapidity . in these kinematic regimes several corrections to leading twist perturbative qcd calculations can become important because of the rapid fall - off of the cross section near the kinematic boundary . examples are target and jet mass corrections @xcite , threshold resummation @xcite , and higher - twists ( ht ) contributions @xcite . moreover , data taken on nuclear targets must be corrected for nuclear effects such as shadowing , binding , fermi motion and nucleon off - shellness , to access the partonic structure at the nucleon level . accessing the highest values of @xmath0 in dis also requires understanding quark - hadron duality @xcite in order to utilize data in the resonance region . all these effects need to be incorporated in a consistent framework , simultaneously computed for a wide range observables , and utilized in a global pdf fit . the cteq6x global fit published in ref . @xcite took a first step in this program by considering the combined effect of tmc and ht corrections , alongside nuclear corrections for dis data on deuterium targets needed for flavor separation of the up and down quark . in this talk , i discuss the results of this analysis and some recent work in progress which extends it . detailed references can be found in ref . @xcite .","it is also clear that nuclear smearing corrections do not disappear at large @xmath1 : in general , they are not a subleading effect , and can not be avoided by kinematics cuts such as those commonly used in global pdf fits . there is a substantial reduction in the uncertainty of these pdfs due to the increased data , with the cut3 errors reduced by 1020% for @xmath56 , and by up to 4060% at larger @xmath0 . a detailed investigation of the systematic pdf uncertainties induced by nuclear corrections modeling is underway , as reviewed by j. owens @xcite . quark - hadron duality in structure functions refers to the experimental observation that inclusive structure functions in the region dominated by low - lying nucleon resonances follow deep inelastic structure functions describing high energy data , to which the resonance structure functions average @xcite . the new large-@xmath0 cteq6x pdfs can be used to verify to what degree this holds true , which is important to understand the transition from the perturbative ( partonic ) to the non perturbative ( hadronic ) regime of qcd . the handbag diagram used in the pqcd computations assumes no interaction between the scattered quark and the target remnant . [ fig : qhd ] the ratios of jefferson lab data averaged over different resonance regions to computations using cteq6x are plotted @xcite . this opens the possibility of using resonance region data to extend the range of validity in @xmath0 of the fits . i have shown that a good control of global pdf fits can be achieved when including dis data in the pre - asymptotic region of large @xmath0 and small @xmath1 , if one considers tmc and ht corrections . this is very good for applications to collider and neutrino physics @xcite , and for comparing pdf moments to lattice calculations @xcite . theoretical nuclear corrections to deuteron target data are necessary for @xmath27 and @xmath26 quark separation at @xmath77 . the @xmath26-quark and , surprisingly , the gluon pdf turn out to be very sensitive to uncertainties in the modeling and calculation of nuclear effects . a careful study shows that the induced systematic @xmath26-quark pdf uncertainty is of the same order as the experimental uncertainty if the deuteron target data are removed from the fit @xcite . therefore , further progress in constraining the @xmath26 quark and the gluon pdfs at large @xmath0 requires a better theoretical understanding of nuclear corrections , combined with new data on free proton , but sensitive to @xmath26 , such as from parity violating dis or from neutrino dis on a hydrogen target @xcite . alternatively one can use data minimizing nuclear corrections , such as from proton - tagged dis on deuteron targets , for which the nuclear uncertainty is smaller than 2% @xcite . using quark - hadron duality to include resonance region data in the fits , thereby extending their @xmath0 range , seems also feasible . finally , data sensitive to large @xmath0 gluons , such as from the longitudinal and charm structure functions , @xmath78 and @xmath79 , are required to constrain the gluons independently of the jet data .",0.17916260954235638,"the possibility to use hadronic perturbative qcd structure functions as ` ` tracers '' of the underlying quark - hadron structure function to study low - lying nucleon resonances in the hadron spectrum is discussed. this hypothesis is supported by new large-@xmath0 parity - violating data on the structure function of the nucleon. the operator product expansion formalism is used to obtain a global fit to these data, which includes nuclear corrections, including the full set of higher - twist contributions, as well as variations of the dis kinematic cuts. the regularization parameters are fixed by the choice of cuts in the region @xmath1 and the range of jefferson lab data. results are compared to calculations using cteq6x, alekhin09 and ht corrections, which are all consistent with hadronic structure functions in the georgi - politzer formalism. in particular, we confirm that the presence of nuclear corrections limits the ranges of tmc, ht and deuteron corrections that can be considered. # 1#2#3#4#1 * # 2 * ( # 3 ) # 4 desy 10 - 043issn 0418 - 9833 + march 2010 * on the hadronic transition from qcd to qcd * * in the nonperturbative regime * * s. fukuzawa@ntc.nasa / goddard space flight center, greenbelt, md 20771, usa * * # 1 * [ cols=""<,>#1 >, < "", ] _ submitted to physics letters b _ c _ the deutsches elektronen - synchrotron ( dis ) collaboration _ m. fleischhauer@nta.physikalisches institut, d-85748 possible locations for the future cherenkov telescope at tbingen, germany _ the mit kavli institute for nuclear physics, + ul. radzikowskiego 152, 31 - 342 cracow, poland _ + _ the enrico fermi institute, the university of chicago, illinois, 60126, u.s.a. _ + e - mail : f.m.feldt@mit.edu _ keywords : deep inelastic structure functions, qcd, parton correlators, hadron duality, large - twist corrections, parity violation, transverse confinement.",0.1372549019607843
1010.0678,"we investigate the relationship between spiral arms and star formation in the grand - design spirals ngc 5194 and ngc 628 and in the flocculent spiral ngc 6946 . filtered maps of near - ir ( 3.6@xmath0 m ) emission allow us to identify arm regions "" that should correspond to regions of stellar mass density enhancements . the two grand - design spirals show a clear two - armed structure , while ngc 6946 is more complex . we examine these arm and interarm regions , looking at maps that trace recent star formation far - ultraviolet ( galex ngs ) and 24@xmath0 m emission ( _ spitzer _ sings ) and cold gas co ( heracles ) and hi ( things ) . we find the star formation tracers and co more concentrated in the spiral arms than the stellar 3.6@xmath0 m flux . if we define the spiral arms as the 25 % highest pixels in the filtered 3.6@xmath0 m images , we find that the majority ( 60 % ) of star formation tracers occurs in the interarm regions ; this result persists qualitatively even when considering the potential impact of finite data resolution and diffuse interarm 24@xmath0 m emission . even with a generous definition of the arms ( 45 % highest pixels ) , interarm regions still contribute at least 30 % to the integrated star formation rate tracers . we look for evidence that spiral arms trigger star or cloud formation using the ratios of star formation rate ( sfr , traced by a combination of fuv and 24@xmath0 m emission ) to h@xmath1 ( traced by co ) and h@xmath1 to hi . any enhancement of sfr / m(h@xmath1 ) in the arm region is very small ( less than 10 % ) and the grand design spirals show no enhancement compared to the flocculent target . arm regions do show a weak enhancement in h@xmath1/hi compared to the interarm regions , but at a fixed gas surface density there is little clear enhancement in the h@xmath1/hi ratio in the arm regions.thus , it seems that spiral arms may only act to concentrate the gas to higher densities in the arms .","to assess empirically how spiral arms affect star formation , we aim here to provide two key pieces of information : first , the fraction of star formation that occurs in the arms , as opposed to the interarm regions . looking at the nearby galaxies with prominent spiral arms , we first focus on observable tracers of star formation and gas and ask what fraction of them lies near spiral arms . we then use the tracers to estimate the sfr and sfe and examine if there are any differences in the arm and interarm regions . we also examine whether the fraction of molecular gas , ( m(h@xmath3)/m(hi ) ) , is enhanced in the arm and interarm regions in order to determine if the arms are triggering molecular gas formation . in 3 we examine how concentrated the star formation and gas tracers are in the spiral arms relative to the stellar mass density and infer the amount of interarm star formation . in , 1993 ) for a detailed discussion see schinnerer et al . arms may drive the formation of molecular gas by bringing the total cold gas to high surface densities , but we do not see clear evidence that spiral shocks are contributing to form either clouds or stars . however , we remind the reader that our study does not encompass the outer regions of these galaxies ( i.e. outside @xmath18 0.35 @xmath16 ) . we have used three spiral galaxies ( ngc 5194 , ngc 628 and ngc 6946 ) to determine the fraction of star formation and cold gas found in the interarm regions of spiral galaxies . we based our definition of the spiral arm areas on stellar mass density enhancements traced by 3.6@xmath0 m images . we find that at least 30% of the emission of star formation tracers ( far - uv and 24 @xmath0 m images ) must be located in the interarm region , showing that interarm star formation is significant even in grand design spirals . we examined the star formation efficiency based on h@xmath3 in the arm and interarm areas . we confirmed the results of l08 that this quantity is constant on average and any enhancement in the arm areas is less than 10% for the grand design spirals , ngc 628 and ngc 5194 . the flocculent spiral , ngc 6946 , does show an enhancement of the sfe in the arm region , but this may be caused by an underlying weak spiral density wave , which has caused our spiral definition to be associated with isolated regions of high sfr . we then explored whether the arms were triggering the formation of molecular gas by comparing the fraction of molecular gas in the arm and interarm regions . taken together these results show that interarm star formation is significant and that the spiral arms gather the gas into regions of higher surface densities , which leads to an enhanced molecular fraction , but they do not shock trigger "" star formation nor molecular gas formation .",0.2481572481572482,"we present a study of the effect of spiral arms on the formation of young stars. we use keck / lris and heracles / ccd as well as near - infrared and far - uv images to probe the extent to which spiral arms affect the underlying star formation process. we select three spiral galaxies, two grand design spirals ( ngc 628 and ngc 5194 ) and one flocculent spiral galaxy, ngc 6946, and study how the arm and interarm regions are defined, quantifying the amount of star formation that occurs in the arm regions and compared to the total gas surface density for the arms. we first compare what is observed in the arms with a previous study by leroy et al. ( 2008 ) and find that star formation efficiency ( sfe ), as measured from the h@xmath0 m emission, is enhanced in the spiral arms relative to the overall trend. we do not find any evidence for a triggering of molecular cloud formation, though a triggering may be implied based on the higher sfe. combined with our recent result that 30 % of resolved star formation tracers occur in the interarm region, we find no significant evidence for shock - triggered star formation. the triggering scenario would predict that higher arm strengths and hence shock strengths should lead to higher star formation rates and thus more young, blue stars. thus, despite a triggering scenario, the effect that spiral arms have on the net production of stars should still be small irrespective of triggering. we find that, even if triggering is invoked to explain the high sfe, the enhanced star formation occurs only for a relatively narrow range of arm pixel fractions. this is because the molecular gas, which provides the fuel for star formation, is poorly mixed with the ambient interstellar medium. [ firstpage ] galaxies : spiral galaxies : star formation galaxies : ism",0.23233908948194665
1607.01998,"in this work we have estimated 10 collisional ages of 9 families for which for different reasons our previous attempts failed . in general , these are difficult cases that required dedicated effort , such as a new family classifications for asteroids in mean motion resonances , in particular the @xmath0 and @xmath1 with jupiter , as well as a revision of the classification inside the @xmath2 resonance . of the families locked in mean motion resonances , by employing a numerical calibration to estimate the yarkovsky effect in proper eccentricity , we succeeded in determining ages of the families of ( 1911 ) schubart and of the ` ` super - hilda '' family , assuming this is actually a severely eroded original family of ( 153 ) hilda . in the trojan region we found families with almost no yarkovsky evolution , for which we could compute only physically implausible ages . hence , we interpreted their modest dispersions of proper eccentricities and inclinations as implying that the trojan asteroid families are fossil families , frozen at their proper elements determined by the original ejection velocity field . we have found a new family , among the griquas locked in the 2/1 resonance with jupiter , the family of ( 11097 ) 1994 ud1 . we have estimated the ages of 6 families affected by secular resonances : families of ( 5 ) astraea , ( 25 ) phocaea , ( 283 ) emma , ( 363 ) padua , ( 686 ) gersuind , and ( 945 ) barcelona . by using in all these cases a numerical calibration method , we have shown that the secular resonances do not affect significanly the secular change of proper a. for the family of ( 145 ) adeona we could estimate the age only after removal of a number of assumed interlopers . with the present paper we have concluded the series dedicated to the determination of asteroid ages with a uniform method . we computed the age(s ) for a total of 57 families with @xmath3 members . for the future work there remain families too small at present to provide reliable estimates , as well as some complex families ( 221 , 135 , 298 ) which may have more ages than we could currently estimate . future improvement of some already determined family ages is also possible by increasing family membership , revising the calibrations , and using more reliable physical data . * keywords * : asteroids , dynamics ; impact processes ; resonances , orbital ; trojan asteroids .","we discuss new family classifications for asteroids in mean motion resonances with jupiter, plus a revision and critical discussion of the classification for families in the hilda region. a v - shape in the plane with coordinates proper @xmath0 and proper elements of asteroids is used to estimate collisional ages, provided a yarkovsky factor is present in the proper elements. in the case of the trojan asteroids, the traditional family classification is replaced by the ( 153 ) hilda family, severely depleted in small size members and with a much larger number of members. also families with a strange shape ( apparently due to removal of the namesake asteroid ) are found, including the ( 624 ) hector family. instead there are five families with enough membership to be suitable for age estimation, but in significant way by secular resonances, in which either all or a good portion of the members are locked. for these families we either have not found a consistent collisional model, or we have found alternative collisional models but the results are not consistent. as a general rule, families which are locked in the mean motion resonance are considerably younger than those which are free of the resonance. this is not just a matter of observational selection, but also a consequence of the different dynamical properties of the families : their semimajor axis has a drift, while other elements can undergo a secular drift, thus giving rise to large, strongly eroded families. in several cases the family is significantly depleted in members, while in the remaining cases it has up to 508 members. these latter numbers are significantly larger than those found in previous investigations. before being able to interpret these results self - consistently, however, it is necessary to provide a theory of the long term dynamical evolution of these families, a theory which clearly needs to be calibrated with the new data presented in this paper. this work discusses the complex relationship between dynamical families and collisional families ( formed at a single time of collision ).",0.22668579626972746,"in our previous work ( @xcite , hereinafter referred to as paper i , and @xcite , paper ii ) , we have introduced new methods to classify asteroids into families , applicable to an extremely large dataset of proper elements , to update continuously this classification , and to estimate the collisional ages of large families . in later work ( @xcite , paper iii , and in @xcite , paper iv ) , we have systematically applied a uniform method ( an improvement of that proposed in paper i ) to estimate asteroid family collisional ages , and solved a number of problems of collisional models , including cases of complex relationship between dynamical families ( identified by clustering in the proper elements space ) and collisional families ( formed at a single time of collision ) . in this paper we discuss new family classifications for asteroids in mean motion resonances , in particular the @xmath0 and @xmath1 with jupiter , plus a revision and critical discussion of the classification inside the @xmath2 resonance . overall we have estimated @xmath6 additional ages for @xmath7 families . two examples : first , removal of interlopers has played a critical role in several cases , to the point that @xmath8 of the @xmath7 families used for age estimation have seen removal of the namesake asteroid as an interloper , resulting in change of the family name ; second , the interaction of the yarkovsky effect with resonances has very different outcomes : outside resonances , the semimajor axis undergoes a secular drift , while inside a mean motion resonance the semimajor axis is locked and other elements can undergo a secular drift . inside a secular resonance the paper is organized as follows : in section [ s : meanmot ] we deal with the specific problems of families formed by asteroids locked inside the strongest mean motion resonances with jupiter , namely @xmath2 ( hildas ) , @xmath0 ( trojans ) , and @xmath1 ( griquas ) . in section [ s : secres ] we discuss the families affected by secular resonances ( involving the perihelia and nodes of the asteroid and the planets jupiter and/or saturn ) . in section [ s : complex ] we present two successful interpretations of families with strange shapes and many interlopers . in section [ s : obstest ] we discuss the families for which we either have not found a consistent collisional model , or we have found a model ( and computed an age ) but there are still problems requiring dedicated observational efforts . in section [ there we found family 1911 with a good age determination and family 153 of the _ eroded _ type , that is which can be seen visually in the plots in the proper @xmath204 plane but can not be confirmed by the statistical tests of the hcm method . , we are presenting in this paper a new classification which identifies a number of families by using synthetic proper elements and a full hcm method . hcm is well established and has been succesfully applied to the main asteroid belt , but the results in the trojan swarms indicate that families there have a very different structure . this implies that all trojan families are _ fossil _ families , frozen with the original field of relative velocities , which are small for cratering families , for the fragmentation case somewhat larger , but still limited to the order of the escape velocity from the parent body . thus we find no way to estimate the ages of the families , while they can be a reliable source of information on the original velocity field immediately after the collision . we have found a new family among the griquas , locked in the 2/1 resonance with jupiter . we have analysed 6 large families affected by secular resonances , mostly the nonlinear ones . we have used a numerical calibration method , which has shown in all cases that the secular resonances do not affect significanly the secular change of proper @xmath4 , thus the v - shape method in the @xmath199 plane can be used to compute the age in the standard way ( as in paper iii ) .",0.2663975782038345
0805.1166,"one of the most surprising consequences of quantum mechanics is the nonlocal correlation of a multi - particle system observable in joint - detection of distant particle - detectors . ghost imaging is one of such phenomena . taking a photograph of an object , traditionally , we need to face a camera to the object . but with ghost imaging , we can image the object by pointing a ccd camera towards the light source , rather than towards the object . ghost imaging is reproduced at quantum level by a non - factorizable point - to - point image - forming correlation between two photons . two types of ghost imaging have been experimentally demonstrated since 1995 . type - one ghost imaging uses entangled photon pairs as the light source . the non - factorizable image - forming correlation is the result of a nonlocal constructive - destructive interference among a large number of biphoton amplitudes , a nonclassical entity corresponding to different yet indistinguishable alternative ways for the photon pair to produce a joint - detction event between distant photodetectors . type - two ghost imaging uses chaotic light . the type - two non - factorizable image - forming correlation is caused by the superposition between paired two - photon amplitudes , or the symmetrized effective two - photon wavefunction , corresponding to two different yet indistinguishable alternative ways of triggering a join - detection event by two independent photons . the multi - photon interference nature of ghost imaging determines its peculiar features : ( 1 ) it is nonlocal ; ( 2 ) its imaging resolution differs from that of classical ; and ( 3 ) the type - two ghost image is turbulence - free . ghost imaging has attracted a great deal of attention , perhaps due to these features for certain applications . achieving these features , the realization of nonlocal multi - photon interference is a necessary condition . classical simulations , such as the man - made factorizable speckle - speckle correlation , can never have such features . + yanhua shih + department of physics + university of maryland , baltimore county , + baltimore , md 21250 , u.s.a .","the concept of optical ghost imaging was introduced by einstein - podolsky - rosen in the language of nonlocal correlations of two independent photons. it is general in nature and applies to any radiation, including thermal light. the concept of two - photon interference "" was extended by hanbury brown and twiss in 1956. despite the successful application of this concept to thermal light, there are still many open questions concerning its classical nature. in this paper, we will discuss the three main questions : is the ghost imaging phenomenon due to constructive - destructive interference between chaotic sub - fields, is it a quantum interference or a classical intensity fluctuation correlation? we will then analyze the physical mechanisms underlying type - one and type - two ghost imaging in terms of the biphoton amplitudes of an entangled photon - pair using the equations of motion of a nonlinear crystal pumped by a continuous wave ( cw ) and the dynamics of spontaneous parametric down - conversion ( spdc ). the imaging lens is a focal length- and background - dependent lens which illuminates the light passing through the aperture. we envision the lensless ghost imaging setup as a lens that consists of a pair of independent nonlinear crystals of different thickness. the point - to - point correlation between the object and the image planes is considered as the result of a statistical correlation of intensity fluctuations. this is contrary to classical optics where markovian correlations dominate. however, despite the similarity in the nature of thermal light and the proposed theory of ghost imaging, the opposite may happen : it might be true that chaotic radiations propagate to any transverse plane in a random and chaotic manner. this then allows for a simple explanation of the experiment of pittman _ et al. _ [ phys. rev. lett. * 95 *, 194102 ( 1995 ) ] : any radiation starting from a point on the object plane will collapse "" to a unique pointon the image plane. similar to that of type - 1, it involves the nonlocal superposition of two- photon amplitudes. contrary to the case of physical optics, the ghost image is a reproduction, either magnified or demagnified, of the illuminated object. furthermore, unlike classical light, objects will experience unequal distance propagations to superpose destructively at all other points on the image surface. we will conclude that the concepts of quantum and classical ghost imaging are not equivalent and should not be considered to apply to each other.",0.18338108882521487,"[ fig : projection-1 ] that the point - to - point relationship is the result of _ constructive - destructive interference_. the radiation fields coming from a point on the object plane will experience equal distance propagation to superpose constructively at one unique point on the image plane , and experience unequal distance propagations to superpose destructively at all other points on the image plane . type - one and type - two ghost imaging , in certain aspects , exhibit a similar point - to - point imaging - forming function as that of classical except the ghost image is reproducible only in the joint - detection between two independent photodetectors , and the point - to - point imaging - forming function is in the form of second - order correlation , @xmath16 where @xmath17 is the joint - detection counting rate between photodetectors @xmath18 and @xmath19 . the signal photon passes through a convex lens of 400 mm focal length and illuminates a chosen aperture ( mask ) . these independent sub - intensities simply add together , yielding a constant total intensity in space and in time on any transverse plane . in the lensless ghost imaging setup we have concluded and will show that the partial point - to - point correlation between the object and image planes in type - two ghost imaging is the result of _ two - photon interference_. similar to that of type - one , it involves the nonlocal superposition of two - photon amplitudes , a nonclassical entity corresponding to different yet indistinguishable alternative ways of triggering a joint - detection event @xcite . different from that of type - one , the joint - detection events observed in type - two ghost imaging are triggered by two randomly distributed independent photons . it is interesting to see that the quantum mechanical concept of _ two - photon interference _ is applicable to classical "" thermal light .- function . ] in fact , this is not the first time in the history of physics we apply quantum mechanical concepts to thermal light . the partial point - to - point correlation of thermal radiation is not a new discovery either . it is then reasonable to ask : is the near - field type - two ghost imaging with thermal light a simple classical effect similar to that of hbt ? is it possible that the ghost imaging phenomenon itself , including the type - one ghost imaging of 1995 , is merely a simple classical effect of intensity fluctuation correlation?@xcite@xcite@xcite@xcite this article will address these important questions and explore the multi - photon interference nature of ghost imaging . to explore the two - photon interference nature , we will analyze the physics of type - one and type - two ghost imaging in five steps . ( 1 ) review the physics of coherent and incoherent light propagation ; ( 2 ) review classical imaging as the result of constructive - destructive interference among electromagnetic waves ; ( 3 ) analyze type - one ghost imaging in terms of constructive - destructive interference between the biphoton amplitudes of an entangled photon - pair ; ( 4 ) analyze type - two ghost imaging in terms of two - photon interference between chaotic sub - fields ; and ( 5 ) discuss the physics of the phenomenon : whether it is a quantum interference or a classical intensity fluctuation correlation . the observation of type - one ghost imaging has demonstrated a non - factorizable point - to - point epr correlation between the object and image planes . in this section we discuss the physics of type - two ghost imaging . we have shown that the partial point - to - point correlation of thermal radiation is the result of a constructive - destructive interference caused by the superposition of two two - photon amplitudes , corresponding to two alternative ways for a pair of jointly measured photons to produce a joint - detection event .",0.22347629796839727
1108.4433,"during most stages of stellar evolution the nuclear burning of lighter to heavier elements results in a radial composition profile which is stabilizing against buoyant acceleration , with light material residing above heavier material . however , under some circumstances , such as off - center ignition , the composition profile resulting from nuclear burning can be destabilizing , and characterized by an outwardly increasing mean molecular weight . the potential for instabilities under these circumstances , and the consequences that they may have on stellar structural evolution , remain largely unexplored . in this paper we study the development and evolution of instabilities associated with unstable composition gradients in regions which are initially stable according to linear schwarzschild and ledoux criteria . in particular , we explore the mixing taking place under various conditions with multi - dimensional hydrodynamic convection models based on stellar evolutionary calculations of the core helium flash in a 1.25 star , the core carbon flash in a 9.3star , and of oxygen shell burning in a star with a mass of 23 . the results of our simulations reveal a mixing process associated with regions having outwardly increasing mean molecular weight that reside below convection zones . the mixing is not due to overshooting from the convection zone , nor is it due directly to thermohaline mixing which operates on a timescale several orders of magnitude larger than the simulated flows . instead , the mixing appears to be due to the presence of a wave field induced in the stable layers residing beneath the convection zone which enhances the mixing rate by many orders of magnitude and allows a thermohaline type mixing process to operate on a dynamical , rather than thermal , timescale . the mixing manifests itself in the form of overdense and cold blob - like structures originating from density fluctuations at the lower boundary of convective shell and ` ` shooting '' down into the core . they are enriched with nuclearly processed material , hence leaving behind traces of higher mean molecular weight . in these regions we find that initially smooth composition gradients steepen into stair - step like profiles in which homogeneous , mixed regions are separated by composition jumps . these step like profiles are then seen to evolve by a process of interface migration driven by turbulent entrainment . we discuss our results in terms of related laboratory phenomena and associated theoretical developments . we also discuss the degree to which the simulated mixing rates depend on the numerical resolution , and what future steps can be taken to capture the mixing rates accurately .","we present results from numerical simulations of off - center helium- and carbon - flash convection in two and three dimensions ( 2d and 3d ), respectively. these simulations include a detailed exploration of a mixing process that takes place below the temperature maximum immediately after convection starts. associated with the mixing is the redistribution of composition and entropy within the stable layers that reside beneath the shell convection zone. these layers form ` ` fingers '' of high mean molecular weight material which traverse the mixing region. these fingers are essentially tracer of material trasport taking place across the stable layer. the speed of mixing in these stable layers is comparable to the angular displacement speed across the unstable layer. we find that the mixing takes place against a background state which is initially stable, but as the convection rate increases and the background state disappears, the fingers trace the location of the unstable mixing region and the rate of mixing increases. this mixing process is not observed to operate below the burning shell in the oxygen burning case. we identify the new mixing process with a coupling between the kinetic energy of the convective shell and the layers which reside below it, a coupling which has potentially significant consequences for the star s structure and evolution. some salient features of the mixing process are not observed in the 3d simulations. the 2d model hefl.2d.1 contains small circular vortices which are unstable to thermohaline mixing on a dynamical timescale, and core helium flash simulations do not show significant temperature fluctuations. we discuss these results in the context of other processes commonly encountered in stellar interiors, including penetration and overshoot, semiconvection, and salt fingering. [ firstpage ] stars : evolution stars : abundances stars : winds, outflows hydrodynamics shock waves",0.18129496402877696,", we present calculations of both helium and carbon shell convection following off - center ignition . in both of these evolutionary phases this coupling leads to mixing below the burning shell that has potentially significant consequences for the star s structure and evolution . .some characteristic properties of our initial models : total stellar mass @xmath0 , stellar population , metal content @xmath1 , mass of the mapped model @xmath2 , outer ( inner ) radius @xmath3 of the mapped model , and nuclear energy production rate @xmath4 of the mapped model , respectively . abundance changes due to nuclear burning during the he - flash are described by a reaction network consisting of the four @xmath12-nuclei @xmath13he , @xmath14c , @xmath15o , and @xmath16ne coupled by seven reactions . in this paper we focus our analysis on a mixing process which operates within the stably stratified layers residing beneath the shell convection zones in both the carbon- and helium - flash simulations . we have identified a mixing process operating in our simulations of off - center helium- and carbon - flash convection . the mixing results in the redistribution of composition and entropy within the stable layers that reside beneath the shell convection zones . associated with the mixing process is the formation of `` fingers '' of high mean molecular weight material which traverse the mixing region . we find that this mixing takes place against a background state which is initially _ dynamically stable _ to linear perturbations . and while the mixing region is indeed unstable to thermohaline mixing on a secular timescale , the mixing process that we observe operates on a _ dynamical timescale _ our search for a counterpart to the mixing observed in our simulations among terrestrial experiments with qualitatively similar conditions led us to phenomena like viscous or density fingering driven by a rayleigh - taylor instability @xcite and buoyancy - driven instabilities resulting from differences in mass diffusion coefficients of chemically - reacting species sitting on top of each other @xcite . properties of these phenomena do not fit the mixing in our simulations . as an alternative explanation we describe a scenario in which mixing is instigated by the finite amplitude jostling motions of the stable layer by the turbulence present in the adjacent convective shell . the perturbations induced in the stable layer by the adjacent convection are primarily in the form of waves ( i.e. , g - modes ) . the jostling of the stable layer results in a diffusive mixing process therein which leads to a redistribution of the entropy and composition on a dynamical timescales . this scenario is qualitatively similar to the enhanced mixing discussed by @xcite and @xcite who found that thermal and mass transport is not only a function of temperature and composition gradients , but also a function of the fluid shearing motions setup by the presence of a passing wave field . indeed , the layer from which the mixing begins coincides with layers of strongest shear ( fig.[fig.fingall ] c ) . but the shear and the finite amplitude perturbations alone do not drive mixing and have to be preceded by the formation of sufficiently steep compositional gradients . in the case of our core helium and carbon flash models , one of the pressing goals for stellar evolution is the construction of algorithms for 1d codes that capture mixing processes such as that described in this paper , and which extend mixing due to hydrodynamic processes beyond the boundaries of convective regions and into stably stratified layers .",0.19685863874345552
astro-ph0209568,"we report the discovery of two spectroscopic binaries in the field of the old open cluster m67 s1063 and s1113 whose positions in the color - magnitude diagram place them @xmath0 1 mag below the subgiant branch . a rosat study of m67 independently discovered these stars to be x - ray sources . both have proper - motion membership probabilities greater than 97 % ; precise center - of - mass velocities are consistent with the cluster mean radial velocity . s1063 is also projected within one core radius of the cluster center . s1063 is a single - lined binary with a period of 18.396 days and an orbital eccentricity of 0.206 . s1113 is a double - lined system with a circular orbit having a period of 2.823094 days . the primary stars of both binaries are subgiants . the secondary of s1113 is likely a 0.9 @xmath1 main - sequence star , which implies a 1.3 @xmath1 primary star . we have been unable to explain securely the low apparent luminosities of the primary stars . the colors of s1063 suggest 0.15 mag higher reddening than found for either m67 or through the entire galaxy in the direction of m67 . s1063 could be explained as an extincted m67 subgiant , although the origin of such enhanced extinction is unknown . the photometric properties of s1113 are well modeled by a cluster binary with a 0.9 @xmath1 main - sequence secondary star . however , the low composite luminosity requires a small ( 2.0 @xmath2 ) primary star that would be supersynchronously rotating , in contrast to the short synchronization timescales , the circular orbit , and the periodic photometric variability with the orbital period . geometric arguments based on a tidally relaxed system suggest a larger ( 4.0 @xmath2 ) primary star in a background binary , but such a large star violates the observed flux ratio . thus we have not been able to find a compelling solution for the s1113 system . we speculate that s1063 and s1113 may be the products of close stellar encounters involving binaries in the cluster environment , and may define alternative stellar evolutionary tracks associated with mass - transfer episodes , mergers , and/or dynamical stellar exchanges .","the stars s1063 and s1113 in the field of the old open cluster m67 have attracted special attention due to their likely positions in the color - magnitude diagram. both stars are double - lined spectroscopic binaries with periods of 18.4 and 6.8 days, respectively, and a projected radial velocity of 33.45 km s@xmath0. while the precise proper motion of the primary star in m67 is debated, current existing measurements of the proper - motion properties of the binary are consistent with it being a cluster member. both binaries show photometric variability on timescales longer than 18 days, but with no clear period variability for periods greater than 20 days. in the context of this study, we recommend using the single field - star interloper model to account for the multiple radial - velocity measurements of both stars. this model requires that the uv flux from each star be balanced against the flux from the co - moving primary star, and that the ratio of primary to secondary v fluxes is set by the distance to the cluster center. the geometric argument strongly supports this interpretation, though the variability of the composite light with the orbital period can not be fully ruled out for the two stars. if the variability is caused by asymmetries in the photometric light distribution, then both stars should be highly reddened, with a mean reddening e(b - v ) = 0.14 - 0.18. in contrast to m67, the entire galactic reddening in the direction of our cluster is only 0.03 mag, thus the implied enhanced reddening of s1097 is likely centered on the primary. ground - based observations are not consistent with the existence of warm circumstellar dust in this system, and we suggest that the x - ray emission is due to rapid rotational motion. finally, we note that both stars show significant absorption in the ca ii h and k lines, and both are likely chromospherically active stars.",0.22686567164179106,"we have underway a multi - decade survey of the spectroscopic binary population in m67 ( mathieu et al . in this paper we present a comprehensive discussion of the orbital , spectroscopic , and photometric properties of s1063 and s1113 . regrettably , like the blue stragglers and s1072 , their interpretation remains a puzzle . s1113 is a double - lined spectroscopic binary with a period of 2.8 days , a circular orbit , and a mass ratio of 0.7 . the photometric properties of s1113 are well modeled by a binary with a 0.9 @xmath1 main - sequence secondary star and 1.3 @xmath1 a subgiant primary star ( 2.0 @xmath2 ) at a distance similar to m67 . however , this model does not easily explain the large projected rotation velocity ( 53 kms@xmath5 ) of the primary star . supersynchronous rotation of the primary is required , in contrast to the short synchronization timescales , the circular orbit , and the observed variability of the composite light with the orbital period . alternatively , mean densities for both stars are derived geometrically assuming a tidally relaxed system . these densities indicate a 0.9 @xmath1 main - sequence secondary star and a 1.3 @xmath1 , 4.0 @xmath2 primary star that very nearly fills its roche lobe . in this model however , the v flux ratio derived from this model differs by a factor 3 from the spectroscopically measured flux ratio . in addition , the observed light curve shows no evidence for asymmetry of the nearly - roche - filling primary star . this interpretation runs counter to the very close kinematic three - dimensional association of both binaries to the cluster . still , our statistical analyses indicate that the probability of one of the two being a background binary is not entirely negligible , although both being background stars is improbable . equally important , we have not been able to create model background binaries which reproduce all of the observed properties of either s1063 or s1113 . regrettably we have not yet been able to explain their low luminosities , although we conjecture that their evolutionary histories include mass - transfer episodes , mergers , and/or dynamical stellar exchanges . finally , the primaries of both s1063 and s1113 are candidates for future mass transfer .",0.3105413105413105
math0609552,"we revisit the problem of deciding whether a finitely generated subgroup @xmath0 is a free factor of a given free group @xmath1 . known algorithms solve this problem in time polynomial in the sum of the lengths of the generators of @xmath0 and exponential in the rank of @xmath1 . we show that the latter dependency can be made exponential in the rank difference @xmath2 , which often makes a significant change . nous revenons sur la question de dcider si un sous - groupe finiment engendr @xmath0 est facteur libre dun groupe libre donn @xmath1 . on trouve dans la littrature des algorithmes qui rsolvent ce problme en temps polynomial en la somme des longueurs des gnrateurs de @xmath0 , et exponentiel en le rang de @xmath1 . nous montrons que lon peut remplacer la dpendance exponentielle en @xmath3 par une dpendance exponentielle en la diffrence @xmath2 , ce qui change souvent les choses de faon considrable . the combinatorial aspects of group theory have attracted the attention of theoretical computer scientists for a long time , and for a variety of reasons . there is no need to recall the importance of the concept of monoid ( e.g. free , finite ) in the theory of automata since the foundational results of schtzenberger and eilenberg ( see the books @xcite ) , and groups form a special case of monoids that sometimes play an important role in purely language- and monoid - theoretic questions ( e.g. the type ii conjecture , see @xcite for a survey ) . algorithmic questions ( the word problem , the conjugacy problem , . ) have been very influential in group theory throughout the 20th century , starting from the work of dehn , and specialists of combinatorics on words find a particular interest in the challenges posed by the analogous combinatorics of the free group . recent work on important non - commutative groups like the thompson group and the so - called automata groups strongly relies on the formalism of finite state automata ( see @xcite for recent examples ) . it is already a classical result that these automata - theoretic and combinatorial points of view converge in the ( admittedly simpler ) study of the subgroups of free groups , this is central in the algorithmic problem tackled here and is discussed in detail in the first part of this paper . let us also mention another reason for the recent multiplication of research projects on the boundary between computer science and combinatorial group theory . public - key cryptography relies heavily on group theory : sometimes finite groups such as the groups of units in modular arithmetic , or the groups of rational points on elliptic curves over finite fields , sometimes infinite non - commutative groups like the braid groups ( see for instance @xcite and many others ) . at any rate , the design of more robust cryptographic schemes and the attack of such schemes rely on a deeper understanding of the combinatorial and algorithmic properties of non - commutative groups . as mentioned above , the combinatorial and algorithmic problems concerning free groups are of special interest . free groups are archetypal groups , whose structure is far from being totally elucidated , and the efficient solution of standard problems in their context can shed some light on the possible solution of the same problems in more complex groups . moreover , the solution of algorithmic problems in free groups may be more attainable since we can use the resources of combinatorics on words and automata theory . we now present the specific algorithmic problem addressed in this paper . for the classical facts about free groups recorded below without a reference , we refer the reader to the book by lyndon and schupp @xcite . it is well - known that the minimal sets of generators , or _ bases _ , of a free group @xmath1 all have the same cardinality , called the _ rank _ of @xmath1 . moreover , if @xmath1 has finite rank @xmath4 , every @xmath4-element generating set of @xmath1 is a basis , see ( * ? ? ? * prop . i.3.5 ) . in this paper , we consider only finite rank free groups . let @xmath0 be a subgroup of a free group @xmath1 , written @xmath5 . then @xmath0 itself is a free group whose rank may be greater than the rank of @xmath1 . we say that @xmath0 is a _ free factor _ of @xmath1 , written @xmath6 , if there exist bases @xmath7 of @xmath0 and @xmath8 of @xmath1 such that @xmath9 ( free factors can be defined in all groups by a universal property , but the operational definition given here is sufficient for the purpose of this study ) . it is well known that one can decide whether a given finite rank subgroup @xmath5 is a free factor of @xmath1 , but the known algorithms have a rather high time complexity . more precisely , the best of these algorithms require time that is polynomial in the size of @xmath0 and exponential in the rank of @xmath1 , see section [ whitehead ] below for the details . here , the size of @xmath0 is taken to be the sum of the lengths of a finite set of generators of @xmath0 in @xmath1 . we propose a new algorithm to decide whether a given finitely generated subgroup @xmath0 is a free factor of the free group @xmath1 , which is polynomial in the size of @xmath0 and exponential in the rank difference between @xmath1 and @xmath0 . in many instances , this represents a substantial advantage over exponential dependency in the rank of @xmath1 . our algorithm relies essentially on a careful analysis of the construction of the _ graph representation _ of @xmath0 . more precisely , once a basis @xmath8 of the ambient free group @xmath1 is fixed , there is a natural and elegant representation of the finitely generated subgroups of @xmath1 by @xmath8-labeled graphs ( or inverse automata ) . this construction a graphical representation of ideas that go back to the early part of the twentieth century ( * ? ? ? * chap . 11 ) was made explicit by serre @xcite and stallings @xcite . it has been used to great profit by many authors since the late 1970s , see @xcite for recent examples . given a finite set of generators of @xmath0 ( as reduced words over the alphabet @xmath10 ) , the graph representation of @xmath0 can be effectively constructed ( see @xcite , @xcite , ) . the number of vertices and edges of this graph is bounded above by @xmath11 , the sum of the lengths of a set of generators of @xmath0 , and the whole representation can be computed in time at most @xmath12 ( in fact , in time @xmath13 according to a recent announcement , @xmath14 is the least integer @xmath15 such that the @xmath15-th iterate of the @xmath16 function of @xmath17 is at most 1 . the growth of @xmath14 is so slow that it can be considered a constant for all practical purposes ] by touikan @xcite ) . we discuss this representation in more detail in section [ representation ] below , and we show in sections [ careful ] and [ sec deciding ] how to use it to decide more efficiently the free factor relation . it is interesting to note that our algorithm is the first to be expressed entirely in terms of the graph representation of @xmath0 . let us also emphasize that we do not claim that our algorithm is optimal . it is an open question whether one can decide the free factor relation @xmath18 in time polynomial both in the size of @xmath0 and in the size , or the rank of @xmath19 .","we consider automata which describe the subgroups of a finite rank free group of rank @xmath0, acting on an i - step expansion of a free group. automata are edge - labeled directed graphs which map a path in the free group towards a given automaton. we provide a description of the well - known algorithm to construct such automata for a given finitely generated subgroup using whitehead automorphisms. we also describe a generalization of this algorithm which achieves exponential cardinality ( in terms of the cost ) for sequences of non - negative integers, and provides a necessary condition for the automaton to be semisimple, i.e., to be ` ` dual ''. the notion of automata was introduced by whitehead @xcite, motivated by questions arising from the study of how to treat the relationship between the _ gaussimal complexity _ of finite - rank free groups and the ` ` computational complexity '' of approximation algorithms ( see, e.g., m. boileau and m. e. harris 2011 ). essentially, this is a characterization of the computational complexity of approximate linear automata. more precisely, _ implicit _ or explicit _, a _ semilinear _ automaton is an automaton which describes the functional dependence of certain structural properties of finite groups on _ computational complexity _, that is, the ability to factorize a problem into a subproblem which can be solved exactly. the first to analyze this approach were whitehead ( *??? * remark 5.4 ). for this purpose, we describe two techniques which we will review in more detail in section [ sec. 1. in the first section, we define automata and the above - mentioned methods for constructing them. the second section is devoted to a different approach towards automata, and we discuss the results obtained by monte carlo simulation of the reduction of sequences of i - steps in the combinatorics of reduced word - groups. this approach, which we call _ dual automaton _, is of a particular interest, in the sense that it provides an explicit algorithm for automata - or at least, an explicit bijection - based on a notion of ` ` free groups '' ( see section [ prop unique ] ).",0.1402116402116402,"if @xmath8 is a basis of a free group @xmath1 , we often write @xmath20 and we represent the elements of @xmath1 as reduced words over the alphabet @xmath8 . more precisely , we consider the set of all words on the symmetrized alphabet @xmath21 , where @xmath22 is a set that is disjoint from @xmath8 , equipped with an explicit bijection with @xmath8 , namely @xmath23 . a word in @xmath31 is _ reduced _ if it contains no factor of the form @xmath32 or @xmath33 with @xmath27 , and it is well known that @xmath1 can be identified with the set of reduced words over @xmath8 . we describe the main tool for the representation of subgroups of free groups in terms of automata ( see @xcite ) . an _ automaton _ on alphabet @xmath8 is a triple of the form @xmath37 where @xmath38 is a finite set called the _ state _ set , @xmath39 is the _ initial state _ , and @xmath40 is the set of _ edges _ , or _ transitions_. a transition @xmath41 is said to be from state @xmath42 , to state @xmath43 , with label @xmath44 . the _ label of a path _ in @xmath45 ( a finite sequence of consecutive transitions ) is the sequence of the labels of its transitions , a word on alphabet @xmath8 , that is , an element of the free monoid @xmath46 . moreover @xmath48 is a submonoid of @xmath63 and @xmath64 is a subgroup of @xmath65 . let @xmath51 be a trim dual automaton , let @xmath75 and let @xmath76 be a non - empty word . if @xmath77 is the expansion of @xmath45 by @xmath78 , then @xmath79 is the subgroup generated by @xmath0 and @xmath80 , that is , @xmath81 . the resulting factorization of @xmath35 makes it clear that @xmath35 is a product of elements of @xmath48 and @xmath86 . thus , @xmath87 is the submonoid generated by @xmath88 , and @xmath79 is the subgroup generated by @xmath64 and @xmath80 . we say that @xmath77 is obtained from @xmath45 by an _ elementary reduction of type 1_. [ reduction1 ] let @xmath45 be a dual automaton and let @xmath77 be obtained from @xmath45 by an elementary reduction of type 1 . this leads directly to the well - known algorithm to construct a reduced inverse automaton representing a given finitely generated subgroup @xmath0 . let @xmath0 be a finitely generated subgroup of a free group @xmath1 of rank @xmath4 , with basis @xmath8 . i.4 ) for the definition of these automorphisms , it suffices to note here that the set @xmath208 of whitehead automorphisms of @xmath1 which do not preserve length , has exponential cardinality ( in terms of @xmath4 ) . a result of whitehead ( it is routine to check that @xmath291 is a well - order on the set of finite sequences of non - negative integers , which is stable under the concatenation of sequences . if @xmath0 is indeed a free factor of the free group @xmath1 , the algorithm described in section [ sec algorithm ] also provides a sequence of rank - incrementing i - steps taking @xmath140 to @xmath418 , where @xmath399 is the set of letters of @xmath8 that occur in the generators of @xmath0 .",0.17495506291192334
1206.3597,"the vibrational excitations of crystalline solids corresponding to acoustic or optic one phonon modes appear as sharp features in measurements such as neutron spectroscopy . in contrast , many - phonon excitations generally produce a complicated , weak , and featureless response . here we present time - of - flight neutron scattering measurements for the binary solid uranium nitride ( un ) , showing well - defined , equally - spaced , high energy vibrational modes in addition to the usual phonons . the spectrum is that of a single atom , isotropic quantum harmonic oscillator and characterizes independent motions of light nitrogen atoms , each found in an octahedral cage of heavy uranium atoms . this is an unexpected and beautiful experimental realization of one of the fundamental , exactly - solvable problems in quantum mechanics . there are also practical implications , as the oscillator modes must be accounted for in the design of generation iv nuclear reactors that plan to use un as a fuel . the spectrum of elementary excitations in materials is one of the core concepts in modern condensed matter physics . the archetypical example is the set of quantized lattice vibrations in crystalline solids , or phonons@xcite . for crystals with more than one atom per unit cell , one expects both acoustic and optic phonon modes and if these are known one can calculate the lattice contribution to fundamental properties such as the heat capacity . the vibrational spectrum at energies above those of the highest optic phonon mode is generally a complicated many phonon continuum that is often weak and featureless . in sharp contrast , for the binary solid uranium nitride ( un)@xcite , where the nitrogen atoms are very light compared to the uranium atoms , our inelastic neutron scattering measurements reveal that the high energy spectrum is greatly simplified and consists of a set of equally - spaced , well - defined modes that can be measured to energies at least ten times as large as that of the optic phonon modes . this data is best explained by assuming that each nitrogen atom behaves as an independent quantum harmonic oscillator ( qho ) , and the nitrogen motion is therefore a rare experimental realization of an exactly soluble , three - dimensional model in quantum mechanics@xcite . the binary uranium systems of the form ux ( x = c , n , s , se , te , as , sb ) have relatively simple rocksalt crystal structures as illustrated in fig . [ structure ] . they have been extensively studied due to their vast array of puzzling physical and magnetic properties@xcite , including unusually high electronic specific heats and drastic suppression of ordered magnetic moments . among these systems , un has received significant attention@xcite recently due to its potential use as a high - temperature nuclear fuel@xcite . the primary magnetic and lattice excitations of un have been investigated previously via inelastic neutron scattering@xcite . despite these efforts , several intriguing open questions remain concerning the details of the experimental spectra . since the initial measurements , significant advances have been made in inelastic neutron scattering using time - of - flight methods . next generation chopper spectrometers allow for measurements over much broader energy ( @xmath0 ) and momentum ( @xmath1 ) transfer ranges than were previously accessible , with both improved intensity and resolution . for these reasons , the excitations in un were re - examined using the fermi chopper spectrometers sequoia@xcite and arcs@xcite at the spallation neutron source of oak ridge national laboratory . in addition to the expected magnon and phonon modes , this investigation resulted in the unexpected discovery of a series of excitations spaced equally in energy by intervals of approximately 50 mev , and extending up to at least 500 mev .","the well - defined peaks in the orientationally - averaged data imply that the modes are localized and isotropic . some enhanced response at an energy corresponding to twice that of the optic phonon was observed in previous neutron scattering studies of un and attributed to two - phonon processes@xcite . however , the observation of such an extended series of equally - spaced and well - defined modes is unprecedented . one can postulate that the extremely light mass of the n atom relative to the u atom leads to a situation where high frequency vibrations in the crystal essentially consist of motions of individual n atoms in a very isotropic and harmonic potential arising from a surrounding regular octahedron of u atoms . each n atom is then a nearly ideal realization of the qho in three dimensions , with a fundamental frequency corresponding to an energy @xmath12 @xmath13 50 mev , equivalent to a temperature of 580 k. the qho is one of the simplest and best understood theoretical models in quantum mechanics@xcite , and serves as the foundation for understanding diverse phenomena such as the vibrational modes of molecules , the motion of atoms in a lattice , and the theory of heat capacity . we show below that the qho model can quantitatively describe the high - energy vibrational features observed in the un data . the neutron scattering signal expected from the qho is well - known@xcite . the magnitude of the fitted parameters @xmath21 are found to be monotonically - decreasing with energy and dependent on the incident neutron energy . the background can arise from several sources , including overlap of the oscillator modes due to imperfect instrumental resolution , and contributions from acoustic - acoustic and acoustic - optic multiphonon excitations . nuclear reactor designs require a detailed knowledge of the neutron cross - sections and thermal behavior of the constituent atoms composing the nuclear fuel . most importantly , multiple scattering due to any combination of elastic scattering and inelastic scattering events from oscillator modes results in intensity at higher order oscillator mode positions . the @xmath26 parameter was found to be 2.76(2)x10@xmath28 @xmath31 and 2.64(2)x10@xmath28 @xmath31 for the @xmath4 @xmath3 500 mev and 800 mev data sets respectively . as discussed in the manuscript , theory@xcite predicts that the oscillator modes of a real binary crystal will be broadened and can be approximated by gaussian functions . in principle , the width of the peaks depends on several factors , including the temperature , wavevector , and the ratio of the fundamental oscillator mode energy to the zone boundary energy of the acoustic phonon modes . the width involves a convolution of the acoustic modes and harmonic oscillator response and therefore should be of the same order as the bandwidth of the acoustic modes . table i shows that the spacing of the modes agrees well with the estimates of @xmath23 obtained by the constrained fitting as described above . this deviation from the prediction of the binary solid model may be due to multiple scattering effects that have already been discussed in detail .",0.18113912231559293,"universities in high - energy heavy - ion collisions provide a unique forum for studying the collisional properties of heavy nuclei. the light weight of nitrogen atoms in the uranium lattice creates an environment where the fundamental vibrational modes of the nitrogen atoms oscillate far more efficiently than in lower energy systems. this has lead to novel spectroscopic signatures in the spectra of low - energy neutrons than previously observed in other systems, such as the quantum harmonic oscillator. we show that the high frequency vibrations in the un single crystal exhibit no fine structure within the instrumental energy resolution and are well - described by a model consisting of a collection of equally - spaced and evenly - spaced oscillator modes. we suggest that this model may be applied to the nuclear fuel - material un. nucl. phys. * b#1 *, # 2 ( # 3 ) [ cols=""<,^, < "", ] ( presented by *??? * p. fermi, f. h. kim, b. a. m. pietryga, and l. zhang, phys. rev. e * 81 *, 06111501 ( 2006 ) ]. h. t. mccusker, a. j. holden, m. atkin, d. bouwmeester, and a. k. ekert, ` ` x - ray scattering from tritons and phonons in metallic hydrides, '' phys.. lett. * 58 *, 154715495545 ( 1993 ). u. leonhardt, h. g. schaadt, r. ralph, j. c. mcphedran, v. s. yakovlev, and y. d. korolkova, solid state physics for binary systems using neutrons from an ultrathin al sample, "". r. b. p. ghosh and p. w. marangos, applied mathematics in applied physics, "" class. quantum electron. * 29 *, 13671369 ( 1985 ). a. n. poddubny, n. huse, s. bassler, l. betev, and w. tittel, a neutron collider for high energy nuclear power plants, "" j. phys. ref. * 12 *, 06301030 ( 2005 ). x. wang, g. baluschev, q. zhu, x. guo, b",0.1371158392434988
1004.3992,"the spontaneous onset of magnetic reconnection in thin collisionless current sheets is shown to result from a thermal - anisotropy driven magnetic weibel - mode , generating seed - magnetic field x - points in the centre of the current layer . the idea of magnetic reconnection as the main plasma process that converts stored magnetic energy into kinetic energy originates from the intuitive geometric picture of annihilating antiparallel magnetic field lines when approaching each other ( see , e.g. , * ? ? ? * ; * ? ? ? * ; * ? ? ? * ) . observations in space have unambiguously confirmed the presence of reconnection under collisionless conditions ( see , e.g. , * ? ? ? * ; * ? ? ? * ; * ? ? ? * ) when the fluid theoretical approaches break down . however , no convincing theoretical argument for the spontaneous occurrence of reconnection has so far been given . in collisionless numerical simulations reconnection is artificially ignited ( cf . , e.g. , * ? ? ? * ) , mostly by _ ad hoc _ imposing a seed x - point in the current sheet separating the anti - parallel fields . the ongoing search for the mechanism of spontaneous onset of collisionless reconnection points to the ` missing microphysics ' in thin current sheets . in the present letter we show that instability of the inner current layer gives rise to the self - consistent generation of local magnetic fields @xmath0 transverse to the current layer . such local fields are equivalent to the generation of microscopic seed x - points in the current sheet centre and are capable of spontaneously igniting reconnection as is known from two - dimensional pic particle simulations . since in an ideal current sheet ions and electrons become non - magnetic on their respective inertial scales @xmath1 , where @xmath2 are the plasma frequencies of ions and electrons , ( classical ) collisionless convective transport of magnetic fields into the current layer takes place up to a vertical distance @xmath3 from the centre of the current sheet . the region between @xmath4 is known as the ` hall - current ' @xcite or ( mistakenly , as there is no diffusion present ) ` ion - diffusion ' region . being a by - product of thinning of the current layer , the hall currents are presumably not involved in the reconnection process proper . they close along the magnetic field by electrons that are accelerated in the oblique lower - hybrid - drift / modified - two - stream instability driven by magnetised hall - electrons on the non - magnetic ion background thereby coupling the reconnection site to the auroral ionosphere @xcite . when speaking of a current sheet , we refer to ideal current sheets separating strictly antiparallel fields . the observational paradigm of a reconnecting current sheet is the magnetospheric tail - current sheet . this current sheet is not ideal in the above sense as it is embedded into a quasi - dipolar field which still might preserve a weak rudimentary ( normal ) magnetic field component @xmath5pointing northward . this @xmath5 component re - magnetises the central - sheet electrons and affects the evolution of ( collisionless ) tearing modes @xcite . nevertheless below , when using numbers , we will for reasons of resolution refer to conditions in the magnetotail even though our theory might better apply to the magnetopause , interplanetary space or astrophysics . in principle , observation of the electron - inertial ( ` electron - diffusion ' ) region is difficult because of its narrow width . unambiguous observations do not yet exist . at the magnetopause , in particular , very narrow electron layers have sometimes been reported assuming that they relate to the electron - inertial region during reconnection ( for a recent discussion of the experimental prospects of resolving the electron - inertial region cf . , * ? ? ? * ) .","this may happen when two magnetised collisionless plasmas of finite lateral extension collide . in the magnetotail current sheet ( known as electron and ion phase space holes ) which trap a substantial part of the electrons and heat them in the direction along the current drift velocity . this is the maximum angle the wavevector assumes in the weibel - field vertexes . for @xmath72 and @xmath73 this in order to infer how long it takes the instability to achieve substantial magnetic field amplitudes we need to estimate the magnetic thermal fluctuation level @xmath80 from where the weibel instability starts growing in the presence of the electron pressure anisotropy ( thermally fluctuating magnetic fields will be denoted by lower case letters ) . magnetic thermal levels have recently been estimated @xcite . from basic fluctuation theory @xcite the spectral energy density of the zero - frequency thermally - anisotropic weibel mode can be written @xmath81 ^ 2}%\nonumber\ ] ] the 0-subscript refers to vanishing real frequency . here the weibel instability in this case excites an entire spectrum of magnetic field structures in the current layer . in the geomagnetic tail the present approach has so far only implicitly taken into account the narrow width of the non - magnetic central current region which imposes boundary conditions on the evolution of the weibel mode . as demonstrated , this imposes limits on wave number and propagation angles of the weibel mode . clearly the parallel case is preferred as the antiparallel case generates small - scale current bifurcation . on the other hand , this is possible because the evolution of the weibel mode is completely independent of the presence of the external field . the inner current region decays into a ` magnetic vortex street ' consisting of ( electronic ) plasmoids and seed - x points . one may ask what structure of the field and current layer is expected in the direction parallel to the current flow . , it is the thermal - anisotropy driven weibel instability which provides the magnetic field to penetrate the inner region of the current layer , generates a local normal field component @xmath5 and , by producing short wavelength magnetic vortices and vertexes , it may ignite reconnection on a time scale of tens of seconds to few minutes in the magnetotail . this is in rough agreement with observations , e.g. in the magnetotail , and is sufficiently short for initiating magnetospheric substorms . this logically consistent chain of processes provides a satisfactory mechanism for the spontaneous self - ignited onset of fast magnetic reconnection in thin collisionless current layers .",0.19108280254777069,"the mechanism for spontaneous magnetospheric reconnection weibel instability is discussed here with emphasis on the small - scale ( @xmath0 m ) seed - x points that are expected to grow from thermal fluctuations in the magnetotail current sheet. weibel instabilities are low frequency ( about zero ) electromagnetic instabilities which are capable of generating large ( tens of khz ) magnetic field amplitudes without the need for any magnetic dynamo mechanism. the small size of the magnetic field component in this case provides seed x - points on geophysically reasonable spatial and temporal scales. in the antiparallel case these may evolve into large - scale vortex - like structures, and spontaneous reconnection between adjacent magnetic layers is likely to occur spontaneously. - magnetic fields are observed not only in condensed astrophysical plasmas, but also in the geomagnetic tail ( where they are believed to grow up to a level comparable to the external magnetic field ) and magnetohydrodynamic ( mhd ) systems @xcite. the origin of these magnetic fields is still unclear, although recent experimental evidence suggests their presence in planetary interiors. the main problem in modelling these large magnetic field systems is then to understand the connection between the emerging magnetic field structures and the already existing ( magnetic ) current flow. in this letter we explore this problem both analytically and with numerical simulations. we hypothesise that the growing instability is driven by an increase in the temperature anisotropy of the incoming electrons, i.e. when the electron pressure is anisotropic. the weibel field is generated in the plane parallel to both anisotropies, but perpendicular to the direction of higher thermal velocity, which in our case has been assumed as the parallel direction. thus the instability grows in a parallel plane without any external magnetic force. it is then possible to form a plasmoid - like current flow, or even a mott insulator, in the presence of magnetic fields along the current. this mechanism ( weibel self - organisation ) is of limited practical importance, as it will short - range ( e.g., within a few e - folding times ) dynamo effects which are likely to shut down existing magnetic bifurcation channels, thus limiting the ability to reconnect via weibel mode generation in the bi - maxwellian limit.",0.1743016759776536
1602.08112,"single crystals of the kitaev spin - liquid candidate @xmath0-rucl@xmath1 have been studied to determine low - temperature bulk properties , structure and the magnetic ground state . refinements of x - ray diffraction data show that the low temperature crystal structure is described by space group @xmath2 with a nearly - perfect honeycomb lattice exhibiting less than 0.2 % in - plane distortion . the as - grown single crystals exhibit only one sharp magnetic transition at @xmath3 = 7 k. the magnetic order below this temperature exhibits a propagation vector of @xmath4 = ( 0 , 1 , 1/3 ) , which coincides with a 3-layer stacking of the @xmath2 unit cells . magnetic transitions at higher temperatures up to 14 k can be introduced by deformations of the crystal that result in regions in the crystal with a 2-layer stacking sequence . the best fit symmetry allowed magnetic structure of the as - grown crystals shows that the spins lie in the @xmath5-plane , with a zigzag configuration in each honeycomb layer . the three layer repeat out - of - plane structure can be refined as a 120@xmath6 spiral order or a collinear structure with spin direction 35@xmath6 away from the @xmath7-axis . the collinear spin configuration yields a slightly better fit and also is physically preferred . the average ordered moment in either structure is less than 0.45(5 ) @xmath8 per ru@xmath9 ion . this manuscript has been authored by ut - battelle , llc under contract no . de - ac05 - 00or22725 with the u.s . department of energy . the united states government retains and the publisher , by accepting the article for publication , acknowledges that the united states government retains a non - exclusive , paidup , irrevocable , world - wide license to publish or reproduce the published form of this manuscript , or allow others to do so , for united states government purposes . the department of energy will provide public access to these results of federally sponsored research in accordance with the doe public access plan(http://energy.gov / downloads / doepublic - access - plan ) .","the honeycomb lattice candidate @xmath0-rucl@xmath1 is investigated using neutron diffraction on a sample of untwinned single crystals grown by vapor transport techniques at the hb-3a four - circle diffractometer at ornl. the materials order in - plane with a three - dimensional stacking structure exhibits a single sharp magnetic transition at 7 k with a periodicity that is strongly dependent on the details of the crystal. the crystals are characterized by a pseudo three - layer stacking sequence that consists of three stacked zigzag layers coupled antiferromagnetically and two layers of octahedrally coordinated ferromagnetic interactions. the micron - sized crystals exhibit a high density of stacking faults due to the low dimensionality of the honeycomb layers. the low - temperature structure displays a significant dependence on the stacking sequence, exhibiting a first order phase transition at 155 k which is sensitive to the local environment and the stacking strength. x - ray refinements of this structure yield a monoclinic space group with symmetrical symmetry within a finite number of layers. this space group is compatible with the arrangement of three rhombic sheets cobalt, silicon and phosphoreuclidean ice particles. the magnetic ordering in the crystals is consistent with a two - layered structure, with one layer ordered parallel to the higher planes and the other ordered perpendicular to the lower planes, suggesting that the two layered planes are the same and that there is no lateral separation of the magnetic ground state from the neighboring sheets. the three layered structure also exhibits a significant diffuse scattering arising primarily from the large - scale magnetization fluctuations. the heat capacity measurements reveal a nearly degenerate heat capacity below 100 k and a nearly uniform heat capacity above 100 k. inelastic neutron scattering and raman scattering. the very small diffuse scattering indicates that the ground state of the material at these low temperature levels is dominated by the kitaev - heisenberg model. theractractors are likely to be the quasi - two dimensional ( 2d ) case with strong van der waals interactions.",0.19571865443425074,"the kitaev quantum spin liquid ( qsl ) is an exotic state of matter that exhibits fractionalized excitations in the form of majorana fermions , and a realization of this physics has potential applications in the field of quantum information @xcite . neutron diffraction studies @xcite have shown that the materials order in - plane with a zigzag spin structure which can arise from the kitaev - heisenberg model @xcite as well as kitaev - dominated models with additional more complicated interactions@xcite . in the course of investigations of @xmath0-rucl@xmath1 , it has become clear that sample - dependent issues have led to some confusion . with hexagonal or honeycomb layers that are weakly coupled , given that the magnetic properties can be dependent on the stacking sequence , it is crucial to study and refine the structures on single crystals of @xmath0-rucl@xmath1 with minimal stacking faults . here we report the results of studies of such crystals . x - ray refinements of the low temperature structure yield a monoclinic @xmath17 space group with a symmetrical in - plane honeycomb lattice . consistently , bulk characterization shows that the as - grown crystals exhibit a single well - defined and sharp magnetic transition at 7 k , with no signature of order apparent at 14 k. mechanically deforming the crystals induces a magnetic transition at 14 k and the crystals subject to repeated deformations eventually exhibit only one broad transition at 14 k. the 14 k transition with its observed two - layer periodicity is likely associated with a high density of stacking faults . neutron diffraction on a large high - quality single crystal conforms to the same monoclinic structure and only one transition at 7 k corresponding to an in - plane zigzag structure with 3-layer periodic magnetic ground state . the ordered moment is found to be small with the spin direction confined to the @xmath5-plane . two symmetry - allowed magnetic models have been found to be consistent with the observed data : one is collinear and the other exhibits an out - of - plane spiral . the best overall refinement has been obtained with the collinear model and leads to moment directions pointing 35@xmath6 away from the @xmath7-axis . peak indexing and integration were done using d*trek in the crystalclear package @xcite . these room temperature trigonal crystals typically show a first order phase transition at 155 k , resulting in a low temperature @xmath2 structure . observations to date show that powders@xcite and crystals with significant diffuse scattering from stacking faults@xcite show a broad transition near 14 k with alternating layers coupled antiferromagnetically . the crystals measured in the present study exhibit a pseudo three layer stacking sequence with minimal stacking faults . diffraction alone can not determine the phase angle @xmath57 characterizing the exact modulation in the best fit collinear structure . to gain insight expects that quantum spin fluctuations are dominant , and the full spectrum of magnetic excitations will not be well - described by a classical spin - wave picture . single crystals of @xmath0-rucl@xmath1 with minimal stacking faults are seen to consistently exhibit a low temperature crystal structure described by the @xmath2 space group .",0.2184873949579832
1402.5289,"the spontaneous emergence of coherent behavior through synchronization plays a key role in neural function , and its anomalies often lie at the basis of pathologies . here we employ a parsimonious ( mesoscopic ) approach to study analytically and computationally the synchronization ( kuramoto ) dynamics on the actual human - brain connectome network . we elucidate the existence of a so - far - uncovered intermediate phase , placed between the standard synchronous and asynchronous phases , i.e. between order and disorder . this novel phase stems from the hierarchical modular organization of the connectome . where one would expect a hierarchical synchronization process , we show that the interplay between structural bottlenecks and quenched intrinsic frequency heterogeneities at many different scales , gives rise to frustrated synchronization , metastability , and chimera - like states , resulting in a very rich and complex phenomenology . we uncover the origin of the dynamic freezing behind these features by using spectral graph theory and discuss how the emerging complex synchronization patterns relate to the need for the brain to access in a robust though flexible way a large variety of functional attractors and dynamical repertoires without _ ad hoc _ fine - tuning to a critical point . neuro - imaging techniques have allowed the reconstruction of structural human brain networks , composed of hundreds of neural regions and thousands of white - matter fiber interconnections . the resulting ` ` human connectome '' ( hc ) @xcite turns out to be organized in moduli characterized by a much larger intra than inter connectivity structured in a hierarchical nested fashion across many scales @xcite . on the other hand , ` ` functional '' connections between nodes in these networks have been empirically inferred from correlations in neural activity as detected in electroencephalogram and functional magnetic resonance time series . unveiling how structural and functional networks influence and constrain each other is a task of outmost importance . a few pioneering works found that the hierarchical - modular organization of structural brain networks has profound implications for neural dynamics @xcite . for example , neural activity propagates in hierarchical networks in a rather distinctive way , not observed on simpler networks @xcite ; beside the usual two phases percolating and non - percolating commonly encountered in models of activity propagation , an intermediate ` ` griffiths phase '' @xcite emerges on the hierarchical hc network @xcite . such a griffiths phase stems from the existence of highly diverse relatively - isolated moduli or ` ` rare regions '' where neural activity remains mostly localized generating slow dynamics and very large responses to perturbations @xcite . brain function requires coordinated or coherent neural activity at a wide range of scales , thus , neural synchronization is a major theme in neuroscience @xcite . synchronization plays a key role in vision @xcite , memory @xcite , neural communication @xcite , and other cognitive functions @xcite . an excess of synchrony results in pathologies such as epilepsy or parkinsonian disease , while neurological deficit of synchronization has been related to autism and schizophrenia @xcite . our aim here is to scrutinize the special features of synchronization dynamics @xcite as exemplified by the canonical kuramoto model @xcite running on top of the best available human connectome mapping @xcite . this consists of a network of @xmath0 nodes , each of them representing a mesoscopic population of neurons able to produce self - sustained oscillations @xcite whose mutual connections are encoded by a symmetric weighted connectivity matrix @xmath1 @xcite . the validity of this admittedly simplistic kuramoto model as a convenient tool to explore the generic features of complex brain dynamics at a large scales has been recently emphasized in the literature @xcite . here , we uncover the existence of a novel intermediate phase for synchronization dynamics similar in spirit to the griffiths phases discussed above which stems from the hierarchical modular organization of the hc and which gives rise to very complex and rich synchronization dynamical patterns . we identify this novel phase as the optimal regime for the brain to harbor complex behavior , large dynamical repertoires , and optimal trade - offs between local segregation and global integration . the kuramoto dynamics on a generic network ( see @xcite for a nice and comprehensive review ) is defined by : @xmath2 , \label{eq : kuramoto}\ ] ] where @xmath3 is the phase at node @xmath4 at time @xmath5 . the intrinsic frequencies @xmath6 accounting for node heterogeneity are extracted from some arbitrary distribution function @xmath7 , @xmath8 are the elements of the @xmath9 connectivity matrix @xmath1 , and @xmath10 is the coupling strength . time delays , noise , and phase frustration could also be straightforwardly implemented . the kuramoto order parameter is defined as @xmath11 , where @xmath12 gauges the overall coherence and @xmath13 is the average global phase . in large populations of well - connected oscillators without frequency dispersion , perfect coherence ( @xmath14 ) emerges for any coupling strength ; on the other hand , frequency heterogeneity leads to a phase transition at some critical value of @xmath10 , separating a coherent steady state from an incoherent one @xcite . analytical insight onto this phase transition can be obtained using the celebrated ott - antonsen ( oa ) ansatz , allowing for a projection of the high - dimensional dynamics into an evolution equation for @xmath15 with remarkable accuracy in the large-@xmath16 limit @xcite . , for kuramoto dynamics on the hc network for a specific and fixed set of frequencies extracted from a @xmath17 gaussian distribution . a broad intermediate regime separates the incoherent phase ( low @xmath10 ) from the synchronous one ( high @xmath10 ) . in this regime , coherence increases with @xmath10 in an intermittent fashion , and with strong dependence on the frequency realization . b ) raster plot of individual phases ( vertical axis ) showing local rather than global synchrony and illustrating the coexistence of coherent and incoherent nodes ( @xmath18 ) as time runs . c ) @xmath19 for @xmath20 values of @xmath10 ( arrows in the main plot ) . d ) adjacency matrix of the hc network with nodes ordered to emphasize its modular structure as highlighted by a community detection algorithm ( main text ) , keeping the partition into the @xmath21 hemispheres ( dashed lines ) . intra - modular connections ( shown in color ) are dense while inter - modular ones ( grey ) are limited to tiny subsets , acting as interfaces between moduli . integration between hemispheres is mostly carried out by the @xmath22 central moduli . this plot visually illustrates the hierarchical modular organization of the human connectome network.,width=453 ]","we have performed a computational study of the kuramoto model running on top of the hc network ( details are given in the methods section ) . our results reveal the existence of an intermediate regime placed between the coherent and the incoherent phase ( see fig.1 ) . local coherence emerged for large enough values of the phase lag . our two - block model shows that the presence of `` structural bottlenecks '' between moduli combined with heterogeneous frequencies at their contact nodes ( interfaces ) are essential ingredients to generate a broad region of global oscillations in @xmath53 , even in the absence of phase lag . it was noted in the past that synchronization in a synthetic network with hubs could be limited to those hubs by tuning clustering properties , and global order could be attained in a monotonous step - like fashion upon increasing @xmath10 @xcite . the emergence of chimera - like states and anomalously slow dynamics we suggest to go beyond the single - level modular network model and study hierarchical modular networks ( hmn ) in which moduli exists within moduli in a nested way at various scales @xcite . this is obviously not the case for a regular lattice , where the spectral gap is always well defined . a fractal lattice or an ordered tree , simple models of synchronization dynamics exhibit an unexpectedly rich phenomenology when operating on top of empirical human brain networks . this complexity includes oscillatory behavior of the order parameter suggesting the existence of relatively isolated structural communities or moduli , that as a matter of fact can be identified by using standard community detection algorithms . aimed at unveiling this complex behavior we have introduced a family of hierarchical modular networks and studied them in order to assess what structural properties are required in order to reproduce the complex synchronization patterns observed in brain networks . in the absence of frequency dispersion , perfect coherence is achieved in synthetic hierarchical networks by following a bottom - up ordering dynamics in which progressively larger communities with inherently different timescales become coherent ( see @xcite ) . this structural complexity brings about anomalously - slow dynamics at very large timescales . observe that the hc , in spite of being a coarse - grained mapping of a brain network , already shows strong signals of this ideal hierarchical architecture as reflected in its anomalously slow synchronization dynamics as well as in the presence of non - degenerate eigenvalues in the lower edge of its laplacian spectrum , acting as a fingerprint of structural heterogeneity and complexity . we stress that such a complex phenomenology would be impossible to obtain in networks with stronger connectivity patterns ( e.g. with the small world property ) such as scale free - networks or high - degree random graphs . even the generic presence of simple communities may not be sufficient to grant the emergence of frustration : the uniqueness of the human connectome , and of hierarchical modular networks in general , resides in the strong separation into distinct levels , which the synchronization dynamics is able to resolve only at well - separated values of the coupling @xmath10 . accordingly , it has been suggested that the brain is routinely exploring different states or attractors @xcite and that in order to enhance spontaneous switching between attractors brain networks should operate close to a critical point , allowing for large intrinsic fluctuations which on their turn entail attractor `` surfing '' and give access to highly varied functional configurations @xcite and , in particular , to maximal variability of phase synchrony @xcite .",0.16258064516129034,"simple models of synchronization dynamics exhibit an unexpectedly rich phenomenology when operating on top of empirical human brain networks, hinting at the presence of a hidden structure which hinders collective coherence. what is more striking is that such a complex behavior would be impossible to obtain in networks with much stronger connectivity patterns, such as scale free - networks or high - degree random graphs, which already shows strong signals of the ideal hierarchical structure reflected in the human connectome. here we study a family of hierarchical modular networks describing the evolution of the attractor dynamics in the hubble network ( hc ), revealing the existence of an intermediate regime between the coherent and incoherent stretched - exponential asymptotic behavior. this is characterized by broad quasi - periodic temporal oscillations of @xmath0, whose onsets are located within well - separated levels ( which we call transition points ), that as a matter of fact can be identified by using standard community detection algorithms. two distinct transitions are found in the level of internal coherence : at low levels, local order emerges out of a bottom - up ordering process in which progressively larger communities with inherently different timescales are coherent. at higher levels, i.e. at the collective level, local coherences prevail over a broad range of inter - moduli bandwidths allowing the system to escape from metastable and chimera - like states with traits of local coherence at different hierarchical levels. a prominent feature of the hc hierarchical modular structure is the strong separation between two different levels of coherence a regime characterized by metastable coherence and an oscillatory pattern in which the system remains trapped between two levels due to the absence of a phase lag. this, together with the heterogeneous frequencies at the contact nodes ( interfaces ), suggests that the system is on the verge of achieving regime of complete global synchronization. the result is a complex synchronization landscape, which is especially rich and diverse in the intermediate regime put forward here. likely additional realistic ingredients such as explicit phase frustration and time delays to our simplistic approach should add complexity to the structural frustration effect reported here. it is also expected that more refined models including neuro - realistic ingredients including time delays would generate similar results.",0.12803532008830024
1105.2667,"the mesoscale model meso - nh is used to simulate the optical turbulence at mt graham ( arizona , us ) , site of the large binocular telescope . measurements of the @xmath0-profiles obtained with a generalized scidar from 41 nights are used to calibrate and quantify the model ability in reconstructing the optical turbulence above the site . the measurements are distributed over different periods of the year permitting us to study the model performance in different seasons . a statistical analysis of the simulations is performed for all the most important astroclimatic parameters : the @xmath0-profiles , the seeing @xmath1 , the isoplanatic angle @xmath2 and the wavefront coherence time @xmath3 . the model shows a general good ability in reconstructing the morphology of the optical turbulence ( shape of the vertical distribution of the @xmath0 ) as well as the strength of all the integrated astroclimatic parameters . the relative error ( with respect to measurements ) of the averaged seeing on the whole atmosphere for the whole sample of 41 nights is within 9.0 % . the median value of the relative error night by night is equal to 18.7 % so that the model still maintains very good performances . comparable percentages are observed in partial vertical slabs ( free atmosphere and boundary layer ) and in different seasons ( summer and winter ) . we prove that the most urgent problem , at present , is to increase the ability of the model in reconstructing very weak and very strong turbulence conditions in the high atmosphere . this evidence in the model mainly affects , at present , the model performances for the isoplanatic angle predictions for which the median value of the relative error night by night is equal to 35.1 % . no major problems are observed for the other astroclimatic parameters . a variant to the standard calibration method is tested but we find that it does not provide better results confirming the solid base of the standard method . [ firstpage ] site testing atmospheric effects turbulence methods : data analysis","we investigate the possibility to characterize and predict the optical turbulence ( vertical distribution and integrated values ) at mt graham using an atmospheric mesoscale model called meso - nh . in a previous paper @xcite we proved that the meso - nh model provides reliable estimates of the vertical distribution of the wind speed at all heights from the ground up to 20 km . we present the results of this study in four subsection dedicated respectively to the vertical distribution of the optical turbulence ( @xmath0-profiles ) , the seeing @xmath1 , the isoplanatic angle @xmath2 and the wavefront coherence time @xmath3 . in section [ sec : concl ] the conclusions of this study are presented . in this study we discussed the abilities of the meso - nh model in simulating the optical turbulence above mt graham , site of the large binocular telescope . simulated @xmath0-profiles are compared to a large statistical sample of measured @xmath0-profiles related to 41 nights obtained with a generalized scidar . this large sample of measurements allowed us to study the performances of the model calibration in great detail and to investigate the performance of the model in different seasons discussing statistically how well the model reconstruct the @xmath0 , the seeing in different regions of the atmosphere , the isoplanatic angle and the wavefront coherence time . two different methods of model calibrations have been investigated . the calibration is done on a sample of 34 nights and the model performances are discussed on the whole sample of 41 nights . the most important results obtained are:(i ) we have proved that the model calibration definitely improves the model performance . if we look at the model behaviour in different seasons , we show evidence of a model overestimate of @xmath0 in the high part of the atmosphere ( h @xmath25 8 km ) in summer . this bias is highly probable because the sample of the investigated nights is not completely uniformly distributed between summer and winter . with a reasonably richer sample ( of the order of 1 yr ) this small bias can be corrected . this is not surprising because it is the parameter that , more than others , is very sensitive to the turbulence in the high part of the atmosphere . we proved that the small bias in the high atmosphere on the @xmath0 produces a negligible effect on @xmath3 . the cumulative distribution of the relative error calculated night by night is still very good with a median value equal to 22.5% . the most urgent problem to be solved is the improvement of the model ability in reconstructing the very weak and very strong turbulent conditions in the high atmosphere , i.e. the ability in reconstructing isoplanatic angles in better agreement with measurements . finally we have put in evidence the importance to have a very rich statistical sample of @xmath0-profiles to efficiently calibrate the model . in the future we would like to access an even much richer samples of measurements done preferably with a gs in order to be able to consider a completely independent sample for the model validation . in the future",0.2885085574572127,"this is the fourth paper of a series in which we investigate the use of an atmospheric mesoscale model for the purpose of simulating the optical turbulence at mt graham. the model is a combination of an optical model ( meso - nh ) developed jointly by des recherches mtorologiques et laboratoire darologiques ( cnrm - mto - france ) and generalized scidar ( gs ). it is based on the observation of binaries with typical separations @xmath0 ( 3 - 10@xmath1 ), ( 5 - 6,m=0.5 - 0.8 mag ) and ( 1 - 5,m(m=1 ). a large statistical sample of observations is used to calibrate the model. the calibration is done on a sample of 34 nights corresponding to the whole dataset studied. the most important results obtained in this study are : ( i ) we have proved that the model calibration definitely improves the model performance. the vertical distribution of the internal optical turbulence ( i.e. the average of all observations, see, isoplanatic angle and wavefront coherence time ) matches very well with the corresponding measured @xma0-profile. if we look at the model behaviour in different seasons, we show evidence of a possible bias ( of the order of 1 - 3 yr ) between the best seeing and the worst seeing in the high part of the atmosphere ( h @xcite ) due to the saturation of the model in summer. this bias is removed / removed when we use a sub - sample of the observed data not used for the calibration. ( ii ) for the model we obtained a typical of the operational conditions ( very good and bad turbulence conditions ) reconstructed by the model with a correlation coefficient of ( c.c. ( v ) if we consider cumulative errors night by night for the seeing, we find extremely encouraging results. the median value of the relative errors is indeed extremely small with only a small deviation from the real conditions in the free atmosphere. ( iii ) the seeing is slightly deviates from the operational mode on the whole height from the ground to 20 km but it is always very good with a dispersion of only 0.1 %. ( iv ) the model provides excellent performances in reconstructing the shapes of the measured vertical wind speed profiles from measurements up to the highest heights ( 0.2 - 2 km ) and it is able to reconstruct the shape of the turbulent cell velocity distribution well correlated to the measurements with",0.2492917847025496
math0606413,"we study the buchsbaum - rim multiplicity @xmath0 of a finitely generated module @xmath1 over a regular local ring @xmath2 of dimension @xmath3 with maximal ideal @xmath4 . the module @xmath1 under consideration is of finite colength in a free module @xmath5 . write @xmath6 , where @xmath7 are @xmath4-primary ideals of @xmath2 . we first investigate the colength @xmath8 of any @xmath4-primary ideal @xmath9 and its hilbert - samuel multiplicity @xmath10 using linkage theory . as applications , we establish several multiplicity formulas that express the buchsbaum - rim multiplicity of the module @xmath1 in terms of the hilbert - samuel multiplicities of ideals related to @xmath11 , @xmath12 and an arbitrary general minimal reduction of @xmath1 . the motivation comes from e. jones article @xcite who applied graphical computations of the hilbert - samuel multiplicity to the buchsbaum - rim multiplicity . let @xmath2 be a local cohen - macaulay ring with maximal ideal @xmath4 and infinite residue field . let @xmath9 be an @xmath4-primary ideal . in this paper , we study the connection between the _ colength _ of @xmath9 , _ i.e. _ , the length @xmath13 of @xmath14 , and the hilbert - samuel multiplicity @xmath10 of @xmath9 . it is known for an @xmath4-primary ideal @xmath15 contained in @xmath9 that @xmath16 if and only if @xmath15 is a reduction of @xmath9 . furthermore , if @xmath15 is a minimal reduction of @xmath9 , then @xmath17 however , @xmath10 and @xmath8 are not equal in general . in one of our main theorems , theorem [ rankone ] , we express , under certain conditions , the colength of @xmath9 in terms of the hilbert - samuel multiplicity of ideals which are in the same linkage class of @xmath9 . equation ( [ eq : ideal ] ) can be generalized to modules using the buchsbaum - rim multiplicity of a module @xmath1 , denoted @xmath0 . let @xmath18 be submodules contained in a free module @xmath5 of finite rank such that @xmath19 . it is known that @xmath20 and @xmath1 have the same buchsbaum - rim multiplicity if and only if @xmath20 is a reduction of @xmath1 . similar to ideals , if @xmath20 is a minimal reduction of @xmath1 , then @xmath21 ( _ cf . _ @xcite , @xcite , @xcite ) . in the case where @xmath5 has rank one , @xmath1 is an @xmath4-primary ideal and @xmath22 . we see that the buchsbaum - rim multiplicity is a generalization of the hilbert - samuel multiplicity to modules . like the hilbert - samuel multiplicity , it characterizes reductions . using the theory of reductions of modules , we reduce the problem of finding formulas for the buchsbaum - rim multiplicity to the relationship between the colength and the hilbert - samuel multiplicity of ideals . the latter question is answered for arbitrary licci ideals in theorem [ rankone ] . as an application , we obtain formulas for the buchsbaum - rim multiplicity of a two - dimensional module in terms of the hilbert - samuel multiplicities of a certain fitting ideal and ideals linked to it , see theorem [ shortformula ] . we also prove expressions for the buchsbaum - rim multiplicity that involve bourbaki ideals associated to the module , see theorems [ shortformula2 ] , [ thmallrank ] , and corollary [ summary ] . the last corollary contains the work of @xcite as a special case . the paper is arranged in the following way : section 1 introduces the notion of the buchsbaum - rim multiplicity and its basic properties . we also include the definitions of some notation and theorems that will be used in the later sections . in section 2 , we state and prove the main theorem that relates the colength and the hilbert - samuel multiplicity of @xmath4-primary ideals in regular local rings of dimension two . in section 3 , we discuss several multiplicity formulas that express the buchsbaum - rim multiplicity of a module in terms of the hilbert - samuel multiplicity of @xmath4-primary ideals related to the module . jones @xcite provides a method for computing the buchsbaum - rim multiplicity of modules of a special type . in section [ computation ] we compare the multiplicity formulas obtained in section [ generalization ] to the results of @xcite .","we investigate the buchsbaum - rim multiplicity of a gorenstein local ring with infinite residue field. the multiplicity can be viewed as a generalization of the hilbert - samuel multiplicity. for a submodule @xmath0 of finitely generated submodules of rank 1, 2, 3 and 4, 1 can be a minimal reduction of the larger submodule if and only if it is a bourbaki ideal of the free semilinear module. in this paper, we give a new proof that for every finitely generate submodule of a local regular local ring ( _ i.e. _, for a cohen - macaulay local ring ) with maximal notion of ideal, we can find a corresponding ideal with the same colength. for arbitrary modules, we also establish a new result that the colength of an ideal linked to a complete intersection ideal is independent of the embedding of the submodule into a free module ; this result generalizes the result of j. watanabe on the four - fold multiplicities of three - dimensional rings. [ multiblock footnote omitted ] a.buchsbaum and g. rim @xcite first discussed the _ multiplicity that bears their names _ in 1964. they defined the multiplicit that is a linear combination of ideals from the polynomial of the identity matrix. later, g. ribordy, j. gaffney, kirby, rees, and kleiman and thorup studied the geometric theory that gives the multiplics of ideals related to polynomials. in particular, they used the noetherian local ring to prove that the gorkov multiplicity is a positive integer. the notion of positive integer has been greatly simplified nowadays ; monte - carlo simulations and computer simulations have efficiently provided many examples of positive integers. however, it is still a challenging task to find examples of non - positive integers when the dimension of the building block is not infinite. for example, consider the geometrically symmetric bipartite supergroup of two - dimensional regular rings. after the fact that the degree two is an integer, the complexity of the problem is limited to that for which there are infinitely many examples in the literature. the complexity problem can be understood in terms of the natural map from a local group to a free group. it is easy to see that a non - negative integer is a fundamental object in the theory of finite - dimensional linear groups. on the other hand,",0.2093718843469591,"this polynomial is called the hilbert - samuel polynomial and the coefficient of @xmath27 is the _ hilbert - samuel multiplicity _ @xmath10 . the buchsbaum - rim multiplicity can be viewed as a generalization of the hilbert - samuel multiplicity . for a submodule @xmath1 of finite colength in a free module @xmath5 of rank @xmath28 , buchsbaum and rim @xcite prove that there exists a polynomial @xmath29 of degree @xmath30 such that for all large @xmath31 , @xmath32 where @xmath33 is the symmetric algebra of @xmath5 and @xmath34 is the image of the natural map @xmath35 . moreover , if @xmath2 is a two - dimensional regular local ring , one can define the buchsbaum - rim multiplicity of _ any _ finitely generated @xmath2-module @xmath1 : simply consider the natural map from @xmath1 to @xmath44 , which is free in this case , and replace @xmath1 by its image under this map . we are interested in such a relationship for arbitrary modules . by theorem [ thmbr ] , @xmath0 is equal to the colength of the fitting ideal corresponding to a minimal reduction of @xmath1 . thus , the question can be reduced to investigating the connection between the colength and the hilbert - samuel multiplicity of ideals . [ ingclosed ] let @xmath78 be a regular local ring of dimension @xmath3 with infinite residue field . this result applies to any @xmath4-primary perfect ideal in a two - dimensional gorenstein local ring with infinite residue field . for three - dimensional rings [ shortformula ] let @xmath2 be a gorenstein local ring of dimension @xmath3 with infinite residue field , let @xmath1 be a submodule of finite colength in a free module @xmath5 of rank @xmath28 , and let @xmath46 be a minimal reduction of @xmath1 . in this section , we discuss other connections between the buchsbaum - rim multiplicity of modules and the hilbert - samuel multiplicity of ideals . in fact , we relate the buchsbaum - rim multiplicity of @xmath1 to the hilbert - samuel multiplicity of a generic bourbaki ideal of @xmath5 with respect to @xmath1 , see theorem [ shortformula2 ] . however , if there is a need to fix a certain bourbaki ideal @xmath11 of @xmath5 , the result in theorem [ shortformula2 ] does not apply anymore . [ shortformula2 ] let @xmath78 be a gorenstein local ring of dimension @xmath3 with infinite residue field , let @xmath1 be a submodule of finite colength in a free module @xmath5 of rank @xmath28 , let @xmath46 be a minimal reduction of @xmath1 , and let @xmath81 be ideals as in theorem @xmath129 . this is motivated by the work in jones @xcite where it is necessary to choose @xmath11 and @xmath12 to be monomial ideals in order to extend the graphical computation of the hilbert - samuel multiplicity of monomial ideals to the buchsbaum - rim multiplicity of modules . [ assume ] let @xmath78 be a gorenstein local ring of dimension 2 with infinite residue field , let @xmath1 be a submodule of finite colength in a free module @xmath5 of rank @xmath28 , and assume @xmath1 has no free direct summand . write @xmath6 , where @xmath152 are @xmath4-primary ideals , @xmath11 has finite projective dimension , and @xmath153 . since @xmath154 , we have @xmath155 and therefore @xmath156 . in this section , we consider modules of rank two arising from monomial ideals . there it is shown that @xmath1 is a reduction of the module generated by @xmath1 and the vector @xmath255 in @xmath5 , which is a direct sum of two monomial ideals .",0.2560137457044673
1403.3580,"nai(tl ) large crystals are applied in the search for galactic dark matter particles through their elastic scattering off the target nuclei in the detector by measuring the scintillation signal produced . however , energies deposited in the form of nuclear recoils are small , which added to the low efficiency to convert that energy into scintillation , makes that events at or very near the energy threshold , attributed either to radioactive backgrounds or to spurious noise ( non - bulk nai(tl ) scintillation events ) , can compromise the sensitivity goals of such an experiment . dama / libra experiment , using 250 kg nai(tl ) target , reported first evidence of the presence of an annual modulation in the detection rate compatible with that expected for a dark matter signal just in the region below 6kevee ( electron equivalent energy ) . in the frame of the anais ( annual modulation with nai scintillators ) dark matter search project a large and long effort has been carried out in order to understand the origin of events at very low energy in large sodium iodide detectors and develop convenient filters to reject those non attributable to scintillation in the bulk nai(tl ) crystal . @xmath0 is probably the most relevant radioactive contaminant in the bulk for nai(tl ) detectors because of its important contribution to the background at very low energy . anais goal is to achieve levels at or below 20ppb natural potassium . in this paper we will report on our effort to determine the @xmath1k contamination in several nai(tl ) crystals , by measuring in coincidence between two ( or more ) of them . results obtained for the @xmath0 content of crystals from different providers will be compared and prospects of the anais dark matter search experiment will be briefly reviewed . + + * keywords : * sodium iodide ; scintillation , potassium ; dark matter search , annual modulation . + * pacs numbers : * 29.40.mc ; 29.40.wk ; 95.35.+d laboratorio de fsica nuclear y astropartculas , universidad de zaragoza , c/ pedro cerbuna 12 , 50009 zaragoza , spain + laboratorio subterrneo de canfranc , paseo de los ayerbe s.n . , 22880 canfranc estacin , huesca , spain","the anais project aims at the study of the annual modulation signal attributed to galactic dark matter particles using 250 kg nai(tl ) scintillators at the canfranc underground laboratory. the problem of the detection of dark matter has been addressed through the direct measurement of the @xmath0 content in the scintillation detectors using these crystals. anais-0 and prototype iii set - ups were built using different prototypes, each equipped with a 10.7 kg bicron crystal, sharing the same energy threshold and built in collaboration with dama / libra. the anais setup used for the final design and performance of the experiment was the same as the prototype i, but with 250 kg more crystals, corresponding to 0.42 - 0.68ppm natural potassium content. this large number of crystals allowed us to significantly increase the detection rate, to levels comparable with those of dama, and thus, to extend the reach of the dark matter campains which have been searched so far using ultrapure nai powder. in this paper we will present some of the past and recent results obtained in an efforts to determine the importance and the background of anais low energy events. we will focus on the determination of the estimated total anais activity in different crystals and the techniques used to determine its content. # 1#2#3#4#1 * # 2 * ( # 3 ) # 4 = 0.65 cm * # 1 * anais collaboration * ivan v. kotov@xmath1, lian p. m. pietryjczr following @xcite + _ dipartimento di fisica teorica delluniversit e sezione di roma ` ` la sapienza '', + _ i.n.r.a.s. ; + _ institut fr theoretische physik _, universitt wrzburg, + am hubland, emil - fischer - str. 31, d-97074 wrzberg, germany _ + _ ifae, cnrs / in2p3 - universitat de valncia, + & paris sud, f-91406 orsay cedex, france _ + e - mail : m.k@fis.usb.vej.fr, v.m.krasznahorkos@zubi.ch, g.alexander@gmail.com",0.16666666666666669,"anais project aims at the study of the annual modulation signal attributed to galactic dark matter particles using 250 kg nai(tl ) scintillators at the canfranc underground laboratory ( lsc ) , in spain . dama experiment , at the laboratori nazionali del gran sasso , in italy , and using 100 kg nai(tl ) target , reported first evidence of the presence of an annual modulation in the detection rate compatible with that expected for a dark matter signal just in the region below 6 kevee ( electron equivalent energy ) with a high statistical significance @xcite . to achieve such a goal anais detectors should be as good ( or better ) as ( than ) those of dama / libra in terms of energy threshold and radioactive background below 10 kevee ( electron equivalent energy ) . in this paper we will present some of the past and recent efforts to determine and reduce the background related to @xmath0 contamination in several prototypes , as well as to determine the achievable threshold profiting from the low energy events population , conveniently tagged , that such a contamination provides . we will start by presenting the anais project and the different crystals and experimental set - ups studied ; then , we will move to understand the importance of the background due to @xmath0 contamination and the technique used to determine its content in the different crystals , in particular , in anais-25 modules , as well as the results derived . the anais collaboration started to look for new nai(tl ) crystals with very low content in potassium ( less than 20ppb ) . the anais experiment had then to be redefined and , in order to reach the experimental goals , the final proposal consisted of 250 kg of ultrapure nai(tl ) crystals to study the expected annual modulation in the galactic dark matter signal . an ultrapure powder provider and manufacturer of the ultra - low - background crystals had to be searched for . in this section , we will present the potassium bulk content results for all the studied crystals . this result is compatible with the activity derived from the coincidence measurement and implies that the anais-0 background is dominated by @xmath0 in the bulk , as confirmed the background model proposed and simulated in ref .. at last , the temporal distribution of @xmath0 events at low energy selected by the coincidence above the threshold is shown in fig . the low energy spectra in coincidence with the @xmath9 window around the 1460.8kev line in the other detector , are shown in fig . averaging the @xmath9 window results for the two crystals , we can conclude that anais-25 crystals have a @xmath0 content @xmath29mbq / kg ( @xmath30ppb of potassium ) much lower than that estimated for anais-0 crystal , see fig . nai(tl ) crystals from different manufacturers have been characterized in terms of their potassium bulk content by a measurement in coincidence , and improvement of one order of magnitude in the potassium content can be reported for the anais-25 detectors , built in collaboration with alpha spectra . however , the 20ppb goal has not yet been achieved and before ordering the additional 18 modules required to complete the anais total detection mass , careful analysis of the situation in collaboration with alpha spectra is undergoing , trying to further purify the starting nai powder . however , having a tagged population of bulk scintillation events at 3.2kev is very useful for many other purposes related to the dm search . just to show an example , in anais-25 setup we used this @xmath0 events to estimate the trigger efficiency of the experiment .",0.2165745856353591
astro-ph0104063,"in this study we cross - correlate many _ iue _ echellograms of a variety of well observed stars to evaluate systematic error sources in the wavelength zero - points ( velocities ) of all three cameras . we first evaluate differences between the final archived ( newsips "" ) and the originally processed ( iuesips "" ) echellograms . these show a marked time dependence in zero - point for the _ swp _ camera due to several revisions of wavelength calibration coefficients used for _ iuesips_. smaller offsets are present for the _ lwr _ camera between the two processings . we also evaluated small - amplitude fluctuations in the zero - points of the _ newsips _ wavelength calibration spectra themselves . in the case of the _ swp _ camera , these variations are too complicated to have been completely removed in the _ newsips _ wavelength calibration . we also examine wavelength zero - point disparities between data obtained both through the small and large entrance apertures as well as for observations made by different target acquisitions of faint and bright stars . we also find that statistical differences between these alternative observing modes are virtually nil . for large - aperture observations the dominant error source is the placement of the target in the aperture . these give rise to non - gaussian , extended tails "" in apparent velocity . we also searched for spurious trends with time . except for a possible trend for faint objects with _ swp _ camera data , we can not detect significant dependences with time . additionally , we discovered a trend with telescope focus for datasets derived from intensive monitoring campaigns of bright stars . these exhibit a repeatable , one - day radial velocity variation "" with a semi - amplitude of nearly 3 km s@xmath0 . this pattern appears to be a by - product of fluctuations in telescope focus caused by operational procedures to maintain the ambient instrument temperature . in the second part of the paper , we measure the mean zero - point errors of _ newsips _ echellogram data with respect to laboratory results by using the _ goddard high resolution spectrograph _ ( _ ghrs _ ) spectral atlas of the o9 v spectral standard 10 lacertae as an intermediary reference . we find that the derived apparent velocity difference for this star is essentially zero : -1 @xmath13.5 km s@xmath0 . several less precise comparisons lead to similar results , including cross - correlations of : ( 1 ) spectra of 10 lac and two stars with similar spectra , hd 93521 and hd 60753 , ( 2 ) lines in common with the _ swp _ camera and _ ghrs _ and _ stis _ atlases of arcturus and procyon , and ( 3 ) interstellar lines in the _ ghrs _ spectrum of the white dwarf g191-b2b . the zero - points of the _ newsips_-processed long - wavelength cameras are evaluated and are also found to be nearly zero ( @xmath15 km s@xmath0 ) relative to the arcturus and procyon atlas calibrations and relative to one another . in general , these results do not support the suggestion by gonzlez - riestra that corrections should be introduced to the wavelength scales of various _ newsips _ high - dispersion data products . despite our optimistic results , it is obvious that using small _ iue _ datasets from large - aperture observations of arbitrarily chosen stars can contain velocity errors of at least a few km s@xmath0 . @xmath2stsci / csc , space telescope science institute , 3700 san martin dr . baltimore , md 21218 ; email : msmith@stsci.edu","our purpose is to give a general evaluation of the robustness of the wavelength calibration of the _ newsips "" _ which , in contrast to its predecessor iuesips "" software , is not known to produce wavelength errors as a function of time or other relevant variables . unlike other wavelength comparisons of the _ iue _ calibration , our study relies on cross - correlations of like spectra , that is , of the same star . thus , a second goal will be to evaluate the absolute "" wavelength zero - point errors of the _ iue _ cameras in high - dispersion . we next cross - correlated 13 _ swp lgap _ spectra of the star with the mean _ ghrs _ spectrum in narrow wavelength regions centered on 12 interstellar features studied by these lemoine et al . cross - correlation tools have been used to determine whether systematic trends in wavelength zero - points exist with respect to camera aperture , time , focus , and thda for high - dispersion _ iue / newsips _ data for all three cameras . we have also found that dedicated time - series observations of bright stars can substantially reduce apparent velocity errors . yet , even for such data strings , changes in the spacecraft environment can produce spurious variations of @xmath28 km s@xmath0 over a timescale of a few hours . it is not clear that series of long - wavelength spectra exist in _ iue _ database to detect such effects , but we expect that they are present nonetheless . using the _ ghrs _ atlas of 10 lac as an secondary standard , we have found that the apparent radial velocity determined from high - dispersion images of the _ iue _ _ swp _ camera is zero , within the errors of measurement , with respect to the ultraviolet wavelength system defined by contemporary laboratory catalogs ( brandt et al . this result has been checked by lower - accuracy comparisons such as the difference between apparent radial velocities from _ swp _ echellograms of two other presumed constant early - type stars with similar spectral type , hd 93521 and hd 60753 , and also by comparing wavelengths of several interstellar lines with those measured by the _ ghrs_. additionally , and for all three _ iue _ cameras , we have confirmed the accuracy of the zero - points with more limited sets of lines with the _ ghrs _ and _ stis _ atlases of procyon and arcturus , respectively . we have compared the zero - points of the two _ iue _ long - wavelength cameras by means of the arcturus and procyon atlases and also by compared wavelengths within a common narrow wavelength order among the three cameras . neither of these comparisons led to a siginificant radial velocity offset between the _ iue _ and _ hst _ instruments . the long - wavelength camera results are also in agreement with the ground - based velocity of procyon , but less precisely so . our estimate of the accuracy of in the zero - point error for the _ lwp _ and _ lwr _ cameras is itself imprecise , but judging from its consistency with the _ arcturus _ and _ procyon _ atlas wavelengths , it is probably no worse than @xmath53 km s@xmath0 . their results led to shifts in the wavelength scales of the _ swp _ high - dispersion and _ lwp / lwr _ low - dispersion data for the _ ines _ ( _ iue newly extracted spectra _ ) data product produced by the _ finally , because the _ ghrs _ atlas of 10 lac has a broad wavelength coverage and shows good correspondence in its wavelengths compared to laboratory data , we recommend the use of this atlas as a reference standard for comparison of astronomical mid - uv wavelengths with data from other missions .",0.22139534883720927,"we have used the cross - correlation program _ newsips _ to evaluate the accuracy of the wavelength calibration of the _ international ultraviolet explorer _ ( _ iue _ ) cameras in high - dispersion. cross - correlations have a high internal accuracy and offer safeguards against systematic errors in the measurement process. we have found no significant trends in the zero - point shifts of interstellar lines as a function of time or other instrumental parameters. rather, the relative biases seem to arise from an implied inconsistency in the target - centering / guiding among the different cameras, some of which could arise from different thermal histories of the telescope and in fact could be from the _ goddard high resolution spectrograph _ itself. even over 1015 years the cameras exhibit apparent velocity errors of a few km s@xmath0. in particular the _ swp _ camera shows a significant velocity shift, of -1.3 @xmath1 km s_0, relative to the _ ghrs _ wavelength system. in contrast, the _ lwr _ and _ scocton _ cameras have velocity shifts of -2.1 and -0.7 km s*xxx0, respectively. our findings are in agreement with the predictions of the so - called hsb model, but they are at variance with the more general hsb prediction of -8.2 km sec ynt. in addition we have cross - correlated the wavelengths of seven interstellar lines measured by the _ wavecal _ instrument on board the _ hubble space telescope_. by taking the wavelength of the white dwarf g191-b2b as a proxy for the _ wavelength _ of the star, we find that the difference between the apparent radial velocities of the three stars is zero, within the errors of measurement, for the ranges of optical orders from the far - infrared to the ultraviolet. this result is consistent with earlier lower - accuracy comparisons made with the _ hamiltonian _ and with the absolute ( laboratory ) values compiled in the literature.",0.19244823386114493
0802.0958,"we discuss the spin - wave interaction in two - dimensional ( 2d ) heisenberg ferromagnet ( fm ) with dipolar forces at @xmath0 using @xmath1 expansion . a comprehensive analysis is carried out of the first @xmath1 corrections to the spin - wave spectrum . in particular , similar to 3d fm discussed in our previous paper a.v . syromyatnikov , prb * 74 * , 014435 ( 2006 ) , we obtain that the spin - wave interaction leads to the _ gap _ in the spectrum @xmath2 renormalizing greatly the bare gapless spectrum at small momenta @xmath3 . expressions for the spin - wave damping @xmath4 are derived self - consistently and it is concluded that magnons are well - defined quasi - particles in both quantum and classical 2d fms at small @xmath5 . we observe thermal enhancement of both @xmath4 and @xmath6 at small momenta . in particular , a peak appears in @xmath4 and @xmath6 at small @xmath3 and at any given direction of @xmath7 . if @xmath8 the height of the peak in @xmath6 is not larger than a value proportional to @xmath9 , where @xmath10 is the spin - wave stiffness . in the case of large spins @xmath11 the peak in @xmath6 can not be greater than that of the classical 2d fm found at @xmath12 which height is small only _ numerically _ : @xmath13 for the simple square lattice . frustrating next - nearest - neighbor exchange coupling increases @xmath14 in classical 2d fm only slightly . we find expressions for spin green s functions and the magnetization . the latter differs from the well - known result by s.v . maleev , sov . phys . jetp * 43 * , 1240 ( 1976 ) . the effect of the exchange anisotropy is also discussed briefly . higher order corrections to the spectrum are considered and it is concluded that they are small compared to the first corrections obtained . our results contradict to findings of the previous works ( ar . abanov , a. kashuba , v.l . pokrovsky , prl * 77 * , 2554 ( 1996 ) ; prb * 56 * , 3181 ( 1997 ) ) in which a diffusion spin - wave mode was obtained at small momenta . it is shown that the origin of this discrepancy is that the spin - wave gap was ignored in the previous studies .","we present a comprehensive analysis of the first @xmath0 corrections to the spin - wave spectrum in two - dimensional heisenberg magnet with dipolar interactions. we investigate the case of large spins that arises due to anisotropy in the total energy of the quantum 2d ferromagnet that makes directions along the edges of the square to be energetically favorable in the simple square lattice. we derive expressions for spin green s functions and the magnetization. the effect of the exchange anzotropy is also discussed. finally, the spectrum renormalization is carried out. * the results and implications of our analysis are widely applied to the study of magnetic properties of thin films. it is well known that in the ferromagnetic ( fm ) model, due to the dipolar interaction, short - range magnetic order at small temperature is suppressed considerably and the bare gapless spectrum can be greatly enhanced by gapless fluctuations at small momenta. in contrast, in the presence of the next - nearest - neighbor exchange coupling the gap in the spectrum is shown to be proportional to the inverse of the characteristic dipolar energy. the gap is formed due to a multi - orbital structure of the fermionic components and the longitudinal spin susceptibility is renormalized greatly even for large spins in 2d fm. then, according to the model predictions, the ground state is a hard target for finite - temperature fluctuations and consequently the long - range order is suppressed. this effect is called the ` ` dipolar gap '' and it was first observed in ref. @xcite. subsequent studies predicted the existence of such gap and other unusual features in the fm of 2d and 3d magnons, respectively. however, it was not observed till today that anisotropic effects also occur in these systems. in the present paper we present a consistent analysis of all the features that contribute to the damping of the open quantum gap at small momentsa. we demonstrate the relation between the gap and the anisolitude of the fluctuations that leads to finite temperature fluctuations. the possible underlying mechanism of this phenomenon is not understood at present.",0.22156573116691286,"@xcite that dipolar forces lead to strong long - wavelength fluctuations manifesting themselves in infrared divergence of the first perturbation corrections to the uniform longitudinal spin susceptibility : @xmath16 . it should be noted that appearance of the gap in 2d and 3d fms is quite expected because dipolar interaction due to its symmetry and long - range nature violates the goldstone theorem . besides , the spin - wave gap was observed in 2d antiferromagnet with dipolar interaction in the zeroth order of @xmath1 ( i.e. , in the spin - wave approximation ) . we confirmed this long - standing statement for 3d fm in our previous paper @xcite and demonstrated the relation between the gap and the anisotropy at @xmath22 . a four - fold in - plane anisotropy in square 2d fm caused by quantum fluctuations but it is well known that in classical systems with degenerate ground states some of these states can be selected via order - by - disorder mechanism at finite temperature . then , one expects also appearance of the spin - wave gap in classical 2d fm with dipolar forces . in the present paper we carry out a comprehensive analysis of the first @xmath1 corrections to the spin - wave spectrum in 2d fm with dipolar interaction . similar to 3d fm we obtain the spin - wave gap @xmath24 in the spectrum @xmath2 which appears to be proportional to @xmath25 for @xmath8 and @xmath26 for @xmath11 and @xmath27 . the limiting case of classical spins is also discussed at @xmath29 and the gap was found to be proportional to @xmath30 , where @xmath31 and @xmath32 are values of the exchange and the characteristic dipolar energy in the classical model , respectively . it is demonstrated below that the spin - wave gap that was ignored in refs . we derive the spin - wave damping @xmath4 self - consistently and find that spin waves are well - defined quasi - particles in both quantum and classical 2d fms at small @xmath5 . interestingly , we observe thermal enhancement of the damping at small momenta . in particular , in quantum 2d fm we obtain a peak in both @xmath4 and @xmath6 at @xmath33 , @xmath34 and at any given @xmath7 direction . if @xmath8 the height of the peak in @xmath6 can not axceed a value proportional to @xmath35 . in the case of large spins we derive the four - fold in - plain anisotropy in the total energy of quantum 2d fm that makes directions of the magnetization along edges of the square to be energetically favorable in the simple square lattice . [ disc ] we i ) demonstrate the relation between the anisotropic term in the total energy appearing due to the dipolar interaction and the spin - wave gap at @xmath22 , ( ii ) discuss the further order @xmath1 corrections to the spin - wave spectrum , ( iii ) calculate the magnetization taking into account the spin - wave spectrum renormalization , ( iv ) derive the spin green s functions in the first order of @xmath1 , and ( v ) discuss briefly the effect of the easy - plane anisotropy and consider the spectrum renormalization obtained in refs . meantime we show in the next section that the temperature correction to the spin - wave gap is large at such large @xmath5 and @xmath80 . as a result in the present paper we discuss two - dimensional heisenberg ferromagnet ( 2d fm ) with dipolar forces at @xmath328 described by the hamiltonian ( [ ham0 ] ) and consider renormalization of the bare spin - wave spectrum ( [ spec1 ] ) due to interaction between spin waves . for this purpose",0.3209876543209877
physics0512034,"am 14.dezember des jahres 1900 berichtete max planck der deutschen physikalischen gesellschaft ` ` uber seine physikalische interpretation einer harmlos aussehenden , von ihn selbst zuvor aufgestellten formel , die das spektrale verhalten der sogenannten w''armestrahlung beschreibt . ma``sgeblich durch das eingreifen albert einsteins entwickelte sich daraus i m folgenden vierteljahrhundert eine fundamentale krise der physik , die dann in einer wissenschaftlichen revolution gr''o``sten ausma''ses m""undete : der quantentheorie . die quantentheorie entwickelte sich von anfang an diametral gegen die intentionen ihrer sch``opfer . f''ur planck bedeutete sie trotz gr``o''ster ` ` au''serer anerkennungen das vollst``andige scheitern eines langj''ahrigen forschungsprogramms , f``ur einstein letztlich eine absage an seine wissenschaftlichen grund''uberzeugungen . wir schildern die hintergr``unde dieser seltsamen entwicklung und beleuchten damit die begriffliche seite physikalischer ( und allgemein naturwissenschaftlicher ) forschung , die gemeinhin stark untersch''atzt wird . um die rolle zu verstehen , die albert einstein bei der entwicklung der quantentheorie gespielt hat , m``ussen wir uns zun''achst die vorangegangenen leistungen plancks vergegenw``artigen , die ihn zur aufstellung seiner ber''uhmten strahlungsformel gef``uhrt haben . mit dieser gelang ihm die vollst''andige _ quantitative _ aufkl``arung des ph''anomens der _ w""armestrahlung _ , die ihm den nobelpreis des jahres 1918 einbrachte : ` ` als anerkennung des verdienstes , das er sich durch seine quantentheorie um die entwicklung der physik erworben hat '' . zu diesem zeitpunkt lag die eigentliche tat schon mehr als 17 jahre zur""uck . genauer ist sie auf den 14.dezember des jahres 1900 zu datieren . davon wird weiter unten die rede sein . etwas weniger bekannt ist die tatsache , da``s diese wissenschaftliche gro''stat plancks gleichzeitig auch die restlose zerschlagung seines langj``ahrigen , akribisch vorbereiteten und meisterhaft durchgef''uhrten forschungsprogramms bedeutete , das in einer tief anti - atomistischen , an absoluten gesetzm``a''sigkeiten sich orientierenden naturauffassung wurzelt . in der verfolgung dieser ideale legt planck den grundstein zur quantentheorie , die dem konsequenten atomismus zum endg``ultigen durchbruch verhilft und dem element des zufalls eine fundamentale bedeutung innerhalb des gef''uges physikalischer gesetzm``a''sigkeiten zuweist . hauptmotor dieser entwicklung , die den planckschen vorstellungen diametral entgegenlief , war albert einstein . und mitunter unverfroren bestand er auf der restlosen kl''arung der begrifflichen grundlagen und konsequenzen der planckschen theorie . mit seiner lichtquantenhypothese erkl``arte er nicht nur den photoelektrischen effekt , sondern legte den eigentlich revolution''aren kern dieser theorie frei und provozierte so ma``sgeblich eine tiefe krise , die 20 jahre sp''ater in der formulierung der quantenmechanik m``undete . etwas ' ' ubertreibend , aber i m kern doch zutreffend , kann man sagen , da``s einstein der einzige war , der die plancksche theorie wirklich ernst nahm so ernst , da ' 's die konsequenzen sich schlie``slich auch gegen seine grund''uberzeugungen richteten .","aus der thermodynamik lediglich statistische gesetz m``a''sigkeiten einer sonst regellosen bewegung sehr vieler molek``ule sehen wollten, wieviel energie in form von elektromagnetischen wellen der klassischen physik ( mechanik und elektrodynamik ) ist. er wird nach einiger zeit einzelnen resonators der schwingungsfrequenz @xmath0 aus den hohlraum aufbau und zum allem deren komplizierte wechselwirkung mit auftreffenden lichtstrahlen zum damaligen zeitpunkt noch ganz gan unverstanden waren. aus der selbstverst``andig zu erfassen ganz i m gegensatz zu einer realistischen wand zu dans la konfiguration dellinfurter energie. planck w``aus den hypothetischen mediums einstellt, dieselbe spektrale energieverteilung von w ` `armestrahlung '' einstellen. daraus entsteht nun die theoretische aufgabe, diese universelle funktion ist the result of der nochmals betont werden, da''s diese eine galilean physik zu bestimmen, so genaueren beschaffenheit der w``ande abh''angt, also nicht von ihrer form oder ihrem material. ein partierung zum allgemein g``ultigen thermodynamischen relation, nach the die ableitung der entropie nach der energie die inverse temperatur ist ( siehe gleichung ) i m anhang[universit ] ), w``s hier noch mikroskopische energie emittiert wie absorbiert, leitete planck die folgendest anteile davon ) in _ allen _ frequenzbereichen mit der strahlung wechlassionalinairement aus dem jahre 1905 ( @xcite, band2, dokument14 ) macht e",0.09076682316118936,"dies geschah aus einer opposition zu den vertretern des atomismus , die in den gesetzen der thermodynamik lediglich statistische gesetzm``a''sigkeiten einer sonst regellosen bewegung sehr vieler molek``ule sehen wollten , w''ahrend planck fest an eine strenge gesetzlichkeit ohne statistische ausnahmen glaubte . in einer jugendarbeit aus dem jahre @xmath3 , so wird sich nach einiger zeit i m hohlraum eine bestimmte konfiguration elektromagnetischer strahlung einstellen , die sogenannte w''armestrahlung . zwischen strahlung und der die w''ande bildenden materie wird nach einiger zeit ein thermodynamisches gleichgewicht bestehen . einzig wesentliche voraussetzung f``ur die existenz eines stabilen gleichgewichtszustandes ist die annahme , da ' 's die materie ( oder zumindest anteile davon ) in _ allen _ frequenzbereichen mit der strahlung wechselwirkt , also strahlung aller frequenzen emittieren und absorbieren kann . funktion @xmath4 f``ur die spektrale energieverteilung der strahlung . wand`` ist nun durch die damals bekannten gesetze der elektrodynamik und mechanik vollst''andig zu erfassen ganz i m gegensatz zu einer realistischen wand , deren mikroskopischer aufbau und vor allem deren komplizierte wechselwirkung mit auftreffenden lichtstrahlen zum damaligen zeitpunkt noch ganz unverstanden waren . aus der selbstverst``andlichen bedingung , da ' 's i m thermodynamischen gleichgewicht jeder dieser elementaren resonatoren genauso viel elektromagnetische energie emittiert wie absorbiert , leitete planck die folgende bedingung zwischen spektraler energiedichte @xmath4 und mittlerer energie @xmath14 eines einzelnen resonators der schwingungsfrequenz @xmath5 bei der temperatur @xmath3 ab : @xmath15 es mu``s hier nochmals betont werden , da ' 's diese gleichung eine unzweideutige folge der gesetze der klassischen physik ( mechanik und elektrodynamik ) ist . er w``are damit zum sogenannten rayleigh - jeans - gesetz gelangt : @xmath19 das obwohl eine ebenso unzweideutige folge der klassischen physik zum beispiel besagt es , da ' 's bei fester temperatur @xmath3 die in elektromagnetischen wellen der frequenz @xmath5 abgestrahlte energie quadratisch in @xmath5 w``achst , insgesamt also unendlich viel energie abgestrahlt wird , wenn man ' ' uber alle frequenzen summiert . so sehr sich planck aber auch abm``uhte , eine begr''undung des erforderlichen neuen ausdrucks zu liefern , es wollte ihm einfach nicht gelingen . in seinem ringen um das auffinden allgemeiner methoden , die es erlauben w``urden , die entropie eines resonators i m strahlungsfeld zu berechnen , verfiel er schlie''slich auf den verzweifelten ausweg , ausgerechnet die von ihm bisher vehement bek``ampfte methode der statistischen interpretation der entropie seines widersachers boltzmann zu verwenden . danach ist die entropie eine rein kombinatorische gr''o``se , die bekannt ist , wenn man die anzahl der m''oglichkeiten kennt , eine feste energiemenge auf eine feste anzahl von resonatoren zu verteilen . damit die entropie endlich herauskommt , mu``s planck annehmen , da ' 's die gesamtenergie nur in ganzzahligen vielfachen einer bestimmten grundeinheit `` uber die resonatoren verteilt werden kann . a quantum theory of the scattering of x - rays by light elements.`` physical review 21 ( 1923 ) pp.483 - 502 .",0.11434977578475335
1406.6366,"we propose a new method to estimate the bondi ( hot gas ) accretion rates , @xmath0 , onto the supermassive black holes ( smbhs ) at the centres of elliptical galaxies . it can be applied even if the bondi radius is not well - resolved in x - ray observations and it is difficult to measure the gas density and temperature there . this method is based on two simple assumptions : ( 1 ) hot gas outside the bondi radius is in nearly a hydrostatic equilibrium , and ( 2 ) the gas temperature near the galaxy centre is close to the virial temperature . we apply this method to 28 bright elliptical galaxies in nearby galaxy clusters ( 27 of them are the brightest cluster galaxies ; bcgs ) . we find a correlation between the bondi accretion rates and the power of jets associated with the smbhs over four orders of magnitude in @xmath0 . for most galaxies , the accretion rates are large enough to account for the jet powers , which is in contrast with previous studies . our results indicate that the feedback from the active galactic nuclei ( agn ) correlates with the properties of the hot gas surrounding the smbhs . we also find that more massive smbhs in bcgs tend to have larger specific growth rates . this may explain the hyper masses ( @xmath1 ) of some of the smbhs . comparison between the accretion rates and the x - ray luminosities of the agn suggests that the agn in the bcgs are extremely radiatively inefficient compared with x - ray binaries in the milky way , even when their eddington accretion ratio , @xmath2 , exceeds 0.01 . the corollary is that this ratio is not the only parameter which controls the radiative efficiency of the accretion flow . lastly , we find a tight correlation between the bondi accretion rates and the x - ray luminosities of cool cores . their relation is linear and the power generated by the bondi accretion is large enough to compensate the radiative cooling of the cool cores . although the ` classical ' bondi accretion model is a greatly oversimplified one , the correlations we find here demonstrate that the accretion onto the smbhs reflects broadly the properties of the bondi accretion in some time - averaged sense . [ firstpage ] accretion , accretion discs black hole physics galaxies : active galaxies : jets x - rays : galaxies .","finally , no correlation between agn jet power and total molecular gas mass is known to exist @xcite , which suggests that simple accretion of the molecular gas does not control the agn activities in bcgs at low redshifts . in this paper , we investigate whether accretion onto the smbhs in bcgs can be characterised by the bondi accretion in the broad sense , by studying the correlation between the accretion rate and the agn jet power . we also compare the power available through the bondi accretion with the x - ray agn and cool core luminosities to study the radiation efficiency of the accretion discs and suppression of the cooling flows . for these studies , we have investigated the bondi accretion onto the smbhs in bcgs . for that purpose , we devised a new method to estimate the bondi accretion rate even when the bondi radius is under - resolved in the x - ray observations . our method is based on two assumptions : ( 1 ) the gas is in nearly a hydrostatic equilibrium , and ( 2 ) the gas temperature is represented by the virial temperature of the galaxy near its centre . we have applied our method to 28 galaxies and have obtained the bondi accretion rates . we found a correlation between the bondi accretion power and the power of the jets associated with the smbhs . we also found that the jet power can be well supported by the bondi accretion , in contrast with previous studies . these results indicate that the agn feedback in the bcgs is controlled by the accretion of the surrounding hot gas , whose origin lies in a stable heating of the cluster cool cores . the specific growth rates of the smbhs increase as their mass increases , which may explain the existence of hypermassive smbhs ( @xmath207 ) . the eddington x - ray luminosities of the agn are very small compared to their eddington luminosities , even if the accretion rates are close to the eddington accretion rate . this may suggest that massive gas accretion with a low radiative efficiency is realised in bcgs . moreover , we have found that the bondi accretion power correlates linearly with the x - ray luminosities of the cluster cool cores . we have shown that the power is large enough to offset the radiative cooling of the cool core .",0.3631436314363144,"we investigate whether accretion onto the supermassive black holes ( smbhs ) in the centres of brightest cluster galaxies ( bcgs ) can be characterised by the bondi accretion rate, which is thought to be a promising route for the gas supply to the smbh in the near future. we have studied the agn activity in 9 nearby, x - ray luminous elliptical galaxies including eight bcgs with recent _ chandra x ray observatory _ observations. in all these systems, we find that the increase in the hot gas density and temperature at the innermost measurement radius ( @xmath0 kpc ) is accompanied by a decrease in the temperature of the surrounding hot gas. we assume a simple power - law for the temperature and density profiles, and derive a new technique to estimate the bonduiscat line - of - sight velocity dispersion, which does not depend on the gas mass and the gas density. except for the central part of the central region of perseus cluster, where the density profile might have been affected by the angular momentum and/or temporal agn heating, we assume that the hot accretion proceeds through a bondi flow in a nearly hydrostatic equilibrium with a sound crossing time of about 0.1 myr. the cold gas accretion is assumed to proceed through an adiabatic process in the core, which triggers a cold gas disk and may produce the observed cold gas discs. the estimated agn jet powers are compared with the observed agn accretion rates. it is found that the minimum power required to offset by the slow conduction timescale and the lack of radiative cooling in the cool cores in the bcgs is insufficient to compensate for the radiative energy loss of the cluster cool cores. we propose a model in which attributes the efficiency of the cold accretion discs on the black hole surface to their buoyancy timescale. this model provides a reasonable fit to the observed gas temperature profiles and reduces the need for a large cold gas disc. besides, it provides a good explanation for the observed temperature gradients in the central regions of the lowest redshifts. [ firstpage ] galaxies : clusters : general galaxies : active galaxies : evolution galaxies : individual : bcgs x - rays : galaxies methods : statistical",0.271604938271605
astro-ph0703600,"propagating star formation in a collisional ring galaxy arp 10 is investigated by a complex approach , which includes the broad- and narrow - band photometry , long - slit spectroscopy , and scanning fabry - perot spectroscopy . the ionized gas velocity field obtained with best spatial resolution to date indicates a non - isotropic expansion of the outer ring with a maximum velocity 110 km s@xmath0 . strong vertical and non - circular motions are also seen in the vicinity of the inner ring . our kinematic data suggest that arp 10 has a small inclination @xmath1 and high total ( luminous plus dark matter ) mass of about @xmath2 within a 50 kpc radius . the internal extinction in hii regions and extinction - corrected h@xmath3 fluxes are estimated from the emission lines . the abundance of oxygen 12 + log(o / h ) in both star - forming rings is about 8.6 . the analysis of spectral indices provides an estimate on the propagation velocities of both rings and metallicity of the pre - collision stellar population . a small ` ` knot '' near the nucleus of arp 10 , which was previously suspected as a possible candidate for collision , is now unambiguously identified as the ` ` intruder '' . the intruder spectrum suggests that it was a spiral galaxy before the collision and its present mass amounts to at least one - fourth of the total mass of arp 10 . a high value of the intruder velocity relative to arp 10 ( @xmath4 km s@xmath0 ) suggests that the intruder is either gravitationally unbound or marginally bound to the main galaxy . we use a simplified two - dimensional hydrodynamic modeling of galaxy collisions to test a collisional origin of arp 10 . we confirm that the sizes of the inner and outer rings , maximum expansion velocity of the outer ring , and radial profile of the gas circular velocity can be reproduced by a near - central collision with the intruder galaxy , which occurred approximately 85 myr ago . we acknowledge that an apparent crescent - shaped distribution of h@xmath3 emission in the outer ring is caused by a star formation threshold in the gas disk of arp 10 .","we present new kinematic, spectral, and hydrodynamic observations of the collisional ring galaxy arp 10. the new spectroscopic data formed using the 6-meter telescope at the russian academy of sciences presents unprecedented spatial resolution ( @xmath0 ). we find that the inner 0.7 kpc and the outer 1.8 kpc contain signatures of an extended low surface density exponential stellar disk ( scale length 7.2 kpc ), plus a prominent bulge and a massive dark matter halo. from the spectral index modeling, we infer that the radius of the present h@xmath3 ring is located at about half the stellar disk radius. this location is in agreement with recent photometry of northern ring galaxies by @xcite. the gas distribution in the inner ring is typical for a large spiral galaxy. the existence of large rings is probably the result of gaseous density waves that propagate in the gas disk of the galaxy. outside the outer ring, the gas surface density drops significantly below the star formation threshold and the inner and outer rings therefore form at the right radius of peak stellar activity. the kinematics of the total stellar mass in the galaxy can be approximated by a superposition of four components : a slowly rotating disk, the radial expansion of the disk around the center, a secular decrease in the rotation curve with radius, and a vertical motion of the ionized gas. the model rotation curves show that the stellar disks expand radially and that the rotation velocity at large radii is declining at an increasing rate until the present day. the stellar line - of - sight velocity at radii larger than 10 kpc is consistent with the observed rotation curve and hence can not be accounted for by the model absence of a stellar bulge. hydrodynamics simulations are used to set constraints on the total masses of the stellar and dark matter components. the high metallicities inferred from the model spectral indices are in good agreement with the available values. this suggests that the metallicity gradients in the center ofarp 10 are small. a sequential triggering of star formation by expanding density waves in the disk is likely to leave behind a remnant stellar population, which is characterized by a radial gradient in the color - magnitude diagram.",0.2033426183844011,"we apply kinematic , spectral , and numerical approaches to develop a self - consistent model of propagating star formation in a collisional ring galaxy arp 10 . our kinematic data have the best spatial resolution obtained for arp 10 to date . we found that the pre - collision arp 10 was a large ( sb ? ) disk galaxy with an extended low surface density exponential stellar disk ( scale length 7.2 kpc ) , substantial exponential bulge , and massive dark matter halo . the spiral arms that are traceable in our b - band and h@xmath3 images beyond the outer ring suggest that arp 10 has had a spiral structure before the collision . our spectral index modeling suggests the solar ( using all selected indices or mg , ca , and ti - related indices ) or slightly subsolar ( using iron - dominated spectral indices ) metallicity of the old stellar population in the center of arp 10 . the gradient of relative metallicity of the old population is @xmath194 dex kpc@xmath0 . the available measurements of the total hydrogen mass and the shape of the rotation curve suggest high values of the toomre @xmath124-parameter ( @xmath195 ) in the pre - collision gas disk of arp 10 , which implies that star formation was moderated or even totally suppressed before the collision the intruder is now seen as a small `` knot '' 5 arcsec to the south - west from the nucleus of arp 10 . the gravitational perturbation from the intruder generated two outwardly expanding density waves , which are presently seen in the b - band and h@xmath3 images as bright asymmetric rings . the expansion velocity of gas in the outer ring is a strong function of azimuth , with a maximum value of about @xmath162 km s@xmath0 in the brightest part of the ring and a minimum value of about @xmath197 km s@xmath0 . the inner ring has a more symmetric shape than the outer ring and expands with a velocity less than 50 km s@xmath0 . star formation is triggered at the crest of an expanding gas density wave , if the gas surface density exceeds a star formation threshold . an apparent crescent - like distribution of h@xmath3 emission in the outer ring is most probably caused by a variation of the toomre @xmath124-parameter along the ring . the current star formation rate is estimated from the far - infrared flux to be 10 . the expanding waves of star formation have created less than @xmath192 of the total stellar disk mass since the collision .",0.27651006711409404
1107.2936,"tiny grains such as polycyclic aromatic hydrocarbons ( pahs ) have been thought to dramatically reduce the coupling between gas and magnetic fields in weakly ionized gas such as in protoplanetary disks ( ppds ) because they provide tremendous surface area to recombine free electrons . the presence of tiny grains in ppds thus raises the question of whether the magnetorotational instability ( mri ) is able to drive rapid accretion to be consistent with observations . charged tiny grains have similar conduction properties as ions , whose presence leads to qualitatively new behaviors in the conductivity tensor , characterized by @xmath0 , where @xmath1 and @xmath2 denote the number densities of free electrons and all other charged species respectively . in particular , ohmic conductivity becomes dominated by charged grains rather than electrons when @xmath3 exceeds about @xmath4 , and hall and ambipolar diffusion ( ad ) coefficients are reduced by a factor of @xmath5 in the ad dominated regime relative to that in the ohmic regime . applying the methodology of bai ( 2011 ) , we find that in ppds , when pahs are sufficiently abundant ( @xmath6 per h@xmath7 molecule ) , there exists a transition radius @xmath8 of about @xmath9 au , beyond which the mri active layer extends to the disk midplane . at @xmath10 , the optimistically predicted mri - driven accretion rate @xmath11 is one to two orders of magnitude smaller than that in the grain - free case , which is too small compared with the observed rates , but is in general no smaller than the predicted @xmath11 with solar - abundance @xmath12 m grains . at @xmath13 , we find that remarkably , the predicted @xmath11 exceeds the grain - free case due to a net reduction of ad by charged tiny grains , and reaches a few times @xmath14 yr@xmath15 . this is sufficient to account for the observed @xmath11 in transitional disks . larger grains ( @xmath16 m ) are too massive to reach such high abundance as tiny grains and to facilitate the accretion process .","our result is directly applicable to protoplanetary disks ( ppds ) , where the ionization fraction resulting from major ionization sources such as x - rays and cosmic rays is generally orders of magnitude below unity , and it decreases from surface to the midplane because of the attenuation of ionizing particles @xcite . tiny grains are important charge carriers in weakly ionized gas and strongly affect the non - ideal mhd effects when their abundance is above the ionization fraction . we generalize the commonly used simple expressions for non - ideal mhd diffusion coefficients ( [ eq : diff0 ] ) to incorporate the effect of charged tiny grains . we show that at sufficiently small ionization level , tiny grains become the dominant charge carriers , and the non - ideal mhd diffusion coefficients behave very differently from the grain - free case . the ohmic conductivity is dominated by charged grains rather than electrons when @xmath2 exceeds about @xmath218 . in the ad regime ( strong magnetic field ) , hall and ad coefficients are strongly reduced by a factor of about @xmath5 relative to those in the ohmic regime ( weak magnetic field ) , and for sufficiently large @xmath3 , hall dominated regime diminishes . we study the role of tiny grains on the mri driven accretion in ppds , and find that novel behaviors occur when the tiny grains are sufficiently abundant with @xmath207 , regardless of whether larger grains are present or not . at the inner disk where accretion is layered , the predicted accretion rate in the presence of tiny grains is one to two orders of magnitude less than the grain - free case due to increased ohmic resistivity , but is similar to or higher than that with solar - abundance @xmath12 m grains . a sharp increase in the predicted @xmath11 occurs at the transition radius @xmath219 au ( in the fiducial model ) where the disk midplane becomes active , making ohmic resistivity irrelevant to the accretion rate . quite unexpectedly , we find that at @xmath205 , tiny grains make accretion even more rapid than the grain - free case . moreover , our predicted accretion rate increases with pah abundance . these results are due to that at large pah abundance , ionization - recombination balance makes @xmath2 orders of magnitude larger than @xmath1 , and even exceeds the grain - free electron density @xmath120 at disk midplane . these facts prevent ohmic resistivity from rapidly increasing as @xmath131 increases , reduce the dissipation by ad , thus facilitate the active layer to extend deeper into the disk midplane and permit stronger mri turbulence . our results highlight the importance of evaluating the full conductivity tensor in the calculation of the non - ideal mhd diffusion coefficients rather than using the simple grain - free formulae ( [ eq : diff0 ] ) . we emphasize that the effects studied in this paper mainly apply to tiny grains ( @xmath220 m ) , and when they are sufficiently abundant ( @xmath207 ) . for grains larger than @xmath12 m we discuss the activation of the midplane by the mri in this appendix and explain the sharp dependence of @xmath11 on disk radius near @xmath8 .",0.2756005056890013,"in weakly ionized gas, tiny grains are important charge carriers and affect the non - ideal magnetohydrodynamics ( mhd ) effects via ohmic conductivity, hall effect, and ambipolar diffusion. we study the role of tiny grains in driving magnetorotational instability ( mri ) driven accretion in protoplanetary disks ( ppds ), and find novel behaviors occur when agn grains are abundant ( despite whether larger grains are present or not ). at the inner disk where accretion is layered, the predicted @xmath0 is one to two orders of magnitude lower than in the grain - free case due to increased ohmic resistivity, but is similar to or higher than that with solar - abundance #xmath1 grains. the increase in the predicted accretion rate occurs at the transition radius where the disk midplane flares, and the ohmic resistor becomes active, making grain coagulation and fragmentation irrelevant to the mri. quite unexpectedly, we find that tiny grains make mri - induced accretion even more rapid than the case without tiny grains. our results highlight the importance of adsorption of pah grains on the disk. * according to the ad nature model, electrons and ions are the only charged species in a gas at a given temperature, and neutral particles are the main charge carriers. when the density of the neutral particles increases, the electron number density is reduced, resulting in the increase of the ionization fraction and the hall diffusivity. however, the amount of electron ionization depends strongly on the magnetic field strength, with positively charged species contributing more to the mass budget in the gas than negatively charged species. in tenuous regions, ohmic effect dominates even when the hall parameter lies in between. grains, which are well known for enhancing the electron recombination rate, strongly affect the mhd effects. in six out of ten regions with strong magnetic field, the distributed grains contribute to significantly increase the local ohmic resistance compared to the neutral grains, with the magnitude of the increase depending on the grain abundance. beyond the extent of this increase, ad - dominated regions are strongly damped. *",0.20496894409937888
astro-ph0308318,"we present the results from a survey for extremely red objects ( eros ) in deep , high resolution optical images taken from the _ hubble space telescope _ ( _ hst _ ) medium deep survey . we have surveyed 35 deep f814w _ hst_/wfpc2 fields in the near - infrared to a typical depth of @xmath0 . from a total area of 206 arcmin@xmath1 and to a limit of @xmath2 we identify 224 eros ( @xmath3 arcmin@xmath4 ) with @xmath5 and 83 ( @xmath6 arcmin@xmath4 ) with @xmath7 . we find that the slope of the number counts of the @xmath5 eros flattens beyond @xmath8 , in line with results from previous surveys , and the typical colours of the eros become redder beyond the break magnitude . we morphologically classify our ero sample using visual and quantitative schemes and find that 35 % of our sample exhibit clear disk components , 15 % are disturbed or irregular , a further 30 % are either spheroidal or compact and the remaining 20 % are unclassifiable . using a quantitative measure of morphology , we find that the ero morphological distribution evolves across the break in their counts , such that low concentration ( disk - like ) galaxies decline . we relate the morphological and colour information for our eros and conclude that those eros morphologically classified as bulges do indeed possess seds consistent with passive stellar populations ; while eros with dusty star - forming seds are mostly associated with disk - like and peculiar galaxies . however , @xmath9 of disk eros reside in the passive region of i / j / k colour - colour space . these could be either genuinely passive systems , lower redshift contaminants to the high - z ero population , or systems with composite star - forming and passive seds . we use photometric redshifts for our high s / n multicolour photometry and derive redshift distributions in good agreement with spectroscopic work of somewhat brighter ero examples . [ firstpage ] cosmology : observations , galaxies : bulges , galaxies : peculiar , galaxies : starburst , galaxies : evolution , infrared : galaxies","we have compiled a new catalogue of @xmath12-selected extremely red objects in regions with deep _ hst _ @xmath88-band observations . we apply a number of tests to examine the nature of the ero population and investigate the origin of the turnover in the ero number counts around @xmath89 . the main aim of our work is to study the morphologies of our eros using the exquisite resolution of the _ hst_. however , for a subsample of our dataset with multicolour data we can also utilise sed - fitting as a classification tool . hence , we were able to examine the commonly applied hypothesis that the passive population defined by multicolour photometry ( or equally spectral line diagnostics ) is associated with bulge - dominated morphologies ; and that eros with the colours of dusty star - forming galaxies have disk - like / irregular morphologies . we find a surface density of @xmath55 eros @xmath3 arcmin@xmath4 at @xmath2 . the number count slope flattens from @xmath90 for @xmath65 to @xmath91 for @xmath66 , in good agreement with other surveys in the literature . this turnover in the number counts is associated with a reddening of the faint ero population , from a median colour of @xmath92 at @xmath65 to @xmath93 at 19.0@xmath9420.0 . our visual morphological fractions at the bright end ( k@xmath9519.0 ) are in good agreement with @xcite , and we extend this sample to fainter depths , finding a mix of 35% disk - like , 15% disturbed / irregular , 30% spheroidal or compact and 20% unclassifiable . using quantitative measures , we find that the concentrations of eros evolves across the break in their number counts , such that the fraction of disk - like galaxies declines . \5 . we find on the basis of @xmath96 colours , using the scheme of @xcite , that most disk - like and amorphous galaxies are associated with dusty star - formation activity , and most bulge - like and compact sources have the colours of passive stellar populations . however , @xmath9730% of disks appear to have the colours of passive stellar populations . these are probably genuinely passive disks or at least have substantial evolved stellar populations . we also fit the seds of our eros finding slightly better agreement between the morphological classification and the expected star - formation activity of such morphological types , than the @xcite classification , i.e. most disk - like eros exhibit photometric signs of recent star - formation . \7 . for a subsample of our eros we derive sed - fitted photometric redshift distributions with a median of @xmath98 , in reasonable agreement with spectroscopic redshifts of small samples of somewhat brighter eros . we have highlighted the diversity of extremely red objects , comparing morphological and photometric classification schemes . we suggest that the apparent break in ero counts at k@xmath9719 is due to a rapid rise in bluer disk eros at bright magnitudes . the dominance of this population declines as it is joined around @xmath99 by a more modestly increasing population of galaxies comprising bulges , amorphous , merging and increasingly unclassifiable systems . we have shown that these blue disk eros have properties not inconsistent with them being at the same redshifts as the rest of the other ero sub - populations .",0.2622549019607843,"we present a new catalogue of extremely red objects ( eros ), selected from the _ hubble space telescope _ ( _ hst _ ) wfpc2 f814w-band imaging of @xmath0 fields in the hubble deep field north. our aim is to examine the nature of the ero population to determine whether it is dominated by galaxies with bulge - like or disk - like morphologies, as well as by evolved, passive systems. our approach incorporates deep multicolour imaging in addition to the optical and near - infrared coverage of the survey area, allowing us to break the age - metallicity degeneracy which plagues most existing colour - selected ero surveys. we find that the majority of our eros are not simple star - forming galaxies, rather they are composed of morphologically unclassified sources with a wide range of properties, with around 17 % of the objects showing signs of merger / interaction. we use photometric spectral energy distribution fitting to investigate the fraction of these unclassified eros. accounting for the colour turnover in our number counts leads to a number density for passive eros of around 19@xmath1, consistent with the median value in the literature. the normalization of this number density implies a turnover in the number of active eros with apparent magnitude of around 0.8. modelling the source morphologies with pure luminosity evolution models has difficulty in explaining the number counts, as a large fraction of eros at faint magnitudes are missed due to reddening. we compare our observed ero number counts with those of galaxies in the local universe that are believed to be dusty, yet have high redshifts, providing strong evidence that the latter is not a reliable indicator of the present day star formation history of the universe. the remarkably, our ero counts match well with those derived from radio surveys of very red galaxies, despite the fact that our survey probes distances which are much fainter than the centroid of the radio - selected population. [ firstpage ] galaxies : evolution galaxies : active galaxies : starburst dust, extinction radiative transfer radio lines : galaxies",0.21350078492935634
1011.2175,"the weyl tensor and the ricci tensor can be algebraically classified in a lorentzian spacetime of arbitrary dimensions using alignment theory . used in tandem with the boost weight decomposition and curvature operators , the algebraic classification of the weyl tensor and the ricci tensor in higher dimensions can then be refined utilizing their eigenbivector and eigenvalue structure , respectively . in particular , for a tensor of a particular algebraic type , the associated operator will have a restricted eigenvector structure , and this can then be used to determine necessary conditions for a particular algebraic type . in principle , this analysis can be used to study all of the various algebraic types ( and their subclasses ) in more detail . we shall present an analysis of the discriminants of the associated characteristic equation for the eigenvalues of an operator to determine the conditions on ( the associated ) curvature tensor for a given algebraic type . we will describe an algorithm which enables us to completely determine the eigenvalue structure of the curvature operator , up to degeneracies , in terms of a set of discriminants . since the characteristic equation has coefficients which can be expressed in terms of the scalar polynomial curvature invariants of the curvature tensor , we express these conditions ( discriminants ) in terms of these polynomial curvature invariants . in particular , we can use the techniques decribed to study the necessary conditions in arbitrary dimensions for the weyl and ricci curvature operators ( and hence the higher dimensional weyl and ricci tensors ) to be of algebraic type * ii * or * d * , and create syzygies which are necessary for the special algebraic type to be fulfilled . we are consequently able to determine the necessary conditions in terms of simple scalar polynomial curvature invariants in order for the higher dimensional weyl and ricci tensors to be of type * ii * or * d*. we explicitly determine the scalar polynomial curvature invariants for a weyl or ricci tensor to be of type * ii * or * d * in five dimensions . a number of simple examples are presented to illustrate the calculational method and the power of the approach . in particular , we will present a detailed analysis of the important example of a 5 dimensional rotating black ring .","we investigate the conditions on a tensor for a given algebraic type in higher dimensions. in particular, we use an analysis of the discriminants of the associated characteristic equation to determine the necessary conditions for the weyl and ricci tensors ( and hence the higher dimensional riemann curvature tensor ) to be of algebraic types * ii * or * d*. we are consequently able to determine necessary conditions in terms of simple scalar polynomial curvature invariants. in addition, the analysis can be used to determine conditions on the eigenvalue structure of the curvature operator up to degeneracies. the resulting syzygies can then be written as special scalar impurity solutions of the characteristic equation. we illustrate the usefulness of this approach by using a number of simple examples, including a four - dimensional rotating black ring, a five - dimensional pure einstein space, and a space with complex hyperbolic sections. # 1#2#3 _ ann. phys. ( ny ) _ * # 1 * ( # 2 ) # 3 # 1= msam10 scaled1 = msam7 = = = -1.5 cm = -2.0 cm = 23.9truecm = 16.7truecm 30 pt plus 1000pt minus 100pt # 1 # 1 = rm10 at 10pt = rm7 at 8.5pt citex[#1]#2@fileswauxout tempcntb@ne h@ldciteaciteforciteb:=#2#1 @nobreak esphack eqnlabel#1 # 1@y to # 1 @=11 to''' '' ( [ # 1])([#2 ] ) # 1eqncrtempaeqcitea#1#2q_#1@xmath0 = \mathrm{re}probability#1 } \def\ear{\end{aligned}\ ] ] # 1to 0pt#1 u#1u # 1u#1 [ firstpage ] relativity methods : data analysis methods : statistical cosmology : observations",0.2755102040816326,"it was proven that a four - dimensional lorentzian spacetime metric is either _ @xmath6-non - degenerate _ , and hence completely locally characterized by its scalar polynomial curvature invariants , or _ . it would be particularly useful to find necessary conditions in terms of simple scalar invariants in order for the weyl type ( or the ricci type ) to be * ii * or * d*. _ the main goal of this work is the determination of necessary conditions in higher dimensions for algebraic type , and particularly type * ii * ( or * d * ) , using scalar curvature invariants . a bivector formalism in higher dimensional lorentzian spacetimes has been developed to algebraically classify the weyl bivector operator . used in tandem with the boost weight decomposition , the algebraic classification of the weyl tensor and the ricci tensor ( based on their eigenbivector and eigenvalue structure , respectively ) can consequently be refined . the purpose of this paper is the determination of necessary conditions for the algebraic type of a higher dimensional weyl tensor or ricci tensor , and particularly type * ii * ( or * d * ) , using scalar curvature invariants . for a tensor of a particular algebraic type we will also present a detailed analysis of the important example of a 5d rotating black ring @xcite which is generally of type @xmath21 , but can also be of type @xmath22 or @xmath23 . in particular , we shall show that the rotating black ring is of type @xmath22 ( or type @xmath23 ) on the black hole horizon , by showing that a number of discriminants ( the @xmath24 invariants ) vanish there . in this paper we have used an analysis of the discriminants of the associated characteristic equation to determine the conditions on a tensor for a given algebraic type . since the characteristic equation has coefficients which can be expressed in terms of the scalar polynomial curvature invariants of the operator , we can give conditions , or syzygies , on the eigenvalue structure expressed manifestly in terms of these polynomial scalar curvature invariants . indeed , we have described an algorithm which enables us to completely determine the eigenvalue structure of the curvature , up to degeneracies , in terms of a set of _ discriminants _ @xmath20 , @xmath200 , etc .. the resulting syzygies ( discriminants ) can then be written as special scalar polynomial invariants . in particular , we have used the technique to study the necessary conditions in arbitrary dimensions for the weyl and ricci curvature operators ( and hence the higher dimensional weyl and ricci tensors ) to be of algebraic type * ii*/*d * , and created syzygies which are necessary for the special algebraic type to be fulfilled . we are consequently able to determine the necessary conditions in terms of simple scalar polynomial curvature invariant for the higher dimensional weyl and ricci tensors to be of type * ii * or * d*. we have explicitly determined the scalar polynomial curvature invariants for a weyl or ricci tensor to be of type * ii * ( or * d * ) in 5d . we also presented a detailed analysis of the important example of a 5d rotating black ring @xcite which is generally of type @xmath21 , but can also be of type @xmath22 or @xmath23 for particular values of the parameters . in particular , we showed that the rotating black ring is of type @xmath22 ( or type @xmath23 ) on the black hole horizon ( @xmath186 ) , by showing that @xmath202 on the horizon ( and studying some of the secondary discriminants ) . the example also illustrates the utility in practical computations of employing rather more simple discriminants like @xmath151 ( which is a 40th order syzygy in the weyl tensor ) . in lorentzian spacetimes , identical metrics the notion of an @xmath6-non - degenerate spacetime metric in the class of 4d lorentzian manifolds , which implies that the spacetime metric is locally determined by its scalar polynomial curvature invariants , was introduced . by determining an appropriate set of projection operators from the riemann tensor and its covariant derivatives ,",0.4615384615384616
1102.3430,"by cross - correlating akari all sky survey in 6 infrared ( ir ) bands ( 9 , 18 , 65 , 90 , 140 , and 160@xmath0 ) with the sdss galaxies , we identified 2357 infrared galaxies with a spectroscopic redshift . this is not just one of the largest samples of local ir galaxies , but akari provides crucial fir bands in accurately measuring galaxy sed across the peak of the dust emission at @xmath1 . by fitting modern ir sed models to the akari photometry , we measured the total infrared luminosity ( @xmath2 ) of individual galaxies . using this @xmath2 , we constructed the luminosity functions of infrared galaxies at a median redshift of z=0.031 . the lf agrees well with that at z=0.0082 ( the rbgs ) , showing smooth and continuous evolution toward higher redshift lfs measured in the akari nep deep field . by integrating the ir lf weighted by @xmath2 , we measured the local cosmic ir luminosity density of @xmath3= ( 3.8@xmath4 @xmath5mpc@xmath6 . we separate galaxies into agn ( active galactic nuclei ) , star - forming , and composite by using the @xmath7/h\alpha$ ] vs @xmath8/h\beta$ ] line ratios . the fraction of agn shows a continuous increase with increasing @xmath2 from 25 % to 90 % at 9@xmath912.5 . the sfr@xmath10 and @xmath11}$ ] show good correlations with @xmath2 for sfg ( star - forming galaxies ) and agn , respectively . the self - absorption corrected h@xmath12/h@xmath13 ratio shows a weak increase with @xmath2 with a substantial scatter . when we separate ir lfs into contributions from agn and star - forming galaxies ( sfg ) , the agn contribution becomes dominant at @xmath14 , coinciding the break of the both sfg and agn ir lfs . at @xmath15 , sfg dominates ir lfs . only 1.1@xmath16 % of @xmath3 is produced by lirg ( @xmath14 ) , and only 0.03@xmath170.01 % is by ulirg ( @xmath18 ) in the local universe . compared with high redshift results from the akari nep deep survey , we observed a strong evolution of @xmath19(1+z)@xmath20 and @xmath21(1+z)@xmath22 . our results show all of our measured quantities ( ir lfs , @xmath23 , @xmath24 , @xmath25 ) show smooth and steady increase from lower redshift ( the rbgs ) to higher redshift ( the akari nep deep survey ) . [ firstpage ] galaxies : evolution , galaxies : interactions , galaxies : starburst , galaxies : peculiar , galaxies : formation","to understand the cosmic history of star formation and agn ( active galactic nuclei ) , it is vital to understand infrared ( ir ) emission ; the more intense star formation , the more deeply it is embedded in the dust , hence , such star formation is not visible in uv but in the infrared . we have cross - correlated the akari fis bright source catalog with the sdss dr7 galaxy catalog @xcite , which is the largerst redshift survey in the local universe to date . in this work , since we have optical spectra of individual galaxies , we use @xmath7/h\alpha$ ] vs @xmath8/h\beta$ ] line ratios to classify galaxies into agn or sfg ( star - forming galaxies ) . in fig.[fig : bpt ] , we plot @xmath7/h\alpha$ ] against @xmath8/h\beta$ ] line ratios . , we can also investigate @xmath24 . by integrating ir lf@xmath113 in fig.[fig : agn_lf ] , we obtained @xmath24=(1.9@xmath114 @xmath5mpc@xmath6 . in fig.[fig : tld_agn_all ] , we show the evolution of @xmath24 , which shows a strong evolution with increasing redshift . at a first glance , both @xmath24 and @xmath25 show rapid evolution , suggesting that the correlation between star formation and black hole accretion rate continues to hold at higher redshifts , i.e. , galaxies and black holes seem to be evolving hand in hand . we have cross - correlated the akari ir all sky survey with the sdss to find 2357 ir galaxies with optical spectra . using akari s 6-band ir photometry in 9 , 18 , 65 , 90 , 140 , and 160@xmath0 , we have measured @xmath2 via sed model fitting . the akari s 6 bands cover the crucial far - ir wavelengths across the peak of the dust emission , providing us with more accurate @xmath2 measurements than iras . by separating sfg / agn using optical line ratios , we constructed local ir lfs separately for sfg and agn . we also computed local infrared luminosity density through the derived lfs , and compared @xmath25 and @xmath24 to those at higher redshifts . the local ir lf with the akari data at the median redshift of z=0.031 agrees well with that at z=0.0081 , and shows smooth and continuous evolution toward higher redshift results from the akari nep deep field . * by integrating the ir lf weighted by @xmath2 , we obtain the local cosmic ir luminosity density of @xmath3= ( 3.8@xmath4 @xmath5mpc@xmath6 . * the fraction of agn and composite galaxies show continuous incrase from 25% to 90% at @xmath11912.5 . * the @xmath11}$ ] correlates well with @xmath2 for agn . * the agn contribution to @xmath3 becomes dominant at @xmath14 , above the break of the both sfg and agn ir lfs . at @xmath15 , sfg dominates ir lfs . * lirg and ulirg contribute to @xmath3 a little ; only 1.1@xmath16% of @xmath3 is produced by lirg ( @xmath14 ) , and only 0.03@xmath170.01% is by ulirg ( @xmath18 ) in the local universe . *",0.3597122302158273,"we used the akari fis bright source catalog to construct the local infrared ( ir ) luminosity function ( lf ) of galaxies. this is the first attempt to use an ir lf, which is several times larger than previous work, to measure the peak of the dust emission in the fir wavelength and thus the @xmath0 luminosity of galaxies, and thereby to base our cosmological evolution studies at high redshift both by the current akari, spitzer, and herschel satellites and by next - generation ir satellites such as wise, jwst, and spica. we found cross - matches of 2357 galaxies, with which we will measure ir lfs. among these, 97, 98, and 87 % of sources the number of galaxies used are similar to iras, despite the twice increase in the optical ( sdss ) sample. from the spitzer survey and galex survey, we will also compare the agn fraction as a function of redshift. in our first paper, we measured the optical line - ratio of agn ( active galactic nuclei ) and star - forming galaxies ( sfg ). after adding the galaxies considered in this paper to the sdss agn sample, we cross - correlated the kron et al. ( 2002 ) extended survey with the wide - field infrared survey explorer ( wise ). the two samples have similar line - ratios and redshifts, suggesting there is no significant contamination from agn in the observations. in addition, we compared the fis and wise infrared luminosity functions with the galaxy spectral energy distributions fitted by different sed models. we find the best fit with a simple power - law, although the chel ( chemical evolution models without seds ) fits the data better. more detailed sed fits will be presented in a forthcoming paper. among the 1710,000 optically - selected agn based on the optical spectra, 905,000 show dominant agn emission, with agn fractions ranging from 4.9@xmath1/\alpha$ ] to 9.1@xfig.7/\beta$ ]. the results show the majority ( 96 % ) of the total ir luminosity is emitted by sfg, while only 4.8 % is produced by agn at z=0.031, in contrast to previous findings. considering the redshift evolution and uncertainties in the sed fitting, the present data still supports the fact that agn contribution is already negligible in the lirgs range.",0.19945355191256836
1101.5148,"i discuss several corrections to leading twist calculations of nucleon structure functions which are needed to include experimental data at large parton fractional momentum @xmath0 and at low scales @xmath1 in global fits of parton distribution functions . in particular i discuss the results of the cteq6x global fit , and some work in progress . topics covered include the interplay of target mass and higher - twist corrections , the importance of nuclear corrections for deuterium target data , and applications to the study of quark - hadron duality . implications for collider physics are highlighted . jlab - thy-11 - 1164 address = hampton university , hampton , virginia 23668 + and jefferson lab , newport news , virginia 23606 precise parton distribution functions ( pdfs ) at large parton fractional momentum @xmath0 are vital for understanding the non perturbative structure of the nucleon and the effects of color confinement on its partonic constituents . for instance , the @xmath2 quark distribution ratio near @xmath3 is very sensitive to the nature of the quark - quark forces in the nucleon ; the ratios of spin - polarized to spin - averaged pdfs @xmath4 , and particularly @xmath5 , in the limit @xmath6 reflect the non perturbative quark - gluon dynamics in the nucleon , and can shed light on the origin of the nucleon s spin . precise pdfs at large @xmath0 also have impact in other areas of nuclear and high - energy physics , e.g. , by allowing precise computations of qcd background processes in searches of new physics signals at hadron colliders , and systematic uncertainties in neutrino oscillation experiments . pdfs can be extracted from experimental data through global qcd fits which combine data from many different processes and observables , and analyze them by means of perturbative qcd calculations @xcite . currently , however , the unpolarized pdfs are well determined only for @xmath7 for valence quarks , @xmath8 for gluons , and @xmath9 for heavy quarks . to better constrain these at large @xmath0 it is necessary to study hard scattering processes near kinematic thresholds , such as deep inelastic scattering ( dis ) at large bjorken invariant @xmath10 and low 4-momentum transfer squared @xmath1 , drell - yan ( dy ) lepton pair production and electroweak vector boson production at large rapidity . in these kinematic regimes several corrections to leading twist perturbative qcd calculations can become important because of the rapid fall - off of the cross section near the kinematic boundary . examples are target and jet mass corrections @xcite , threshold resummation @xcite , and higher - twists ( ht ) contributions @xcite . moreover , data taken on nuclear targets must be corrected for nuclear effects such as shadowing , binding , fermi motion and nucleon off - shellness , to access the partonic structure at the nucleon level . accessing the highest values of @xmath0 in dis also requires understanding quark - hadron duality @xcite in order to utilize data in the resonance region . all these effects need to be incorporated in a consistent framework , simultaneously computed for a wide range observables , and utilized in a global pdf fit . the cteq6x global fit published in ref . @xcite took a first step in this program by considering the combined effect of tmc and ht corrections , alongside nuclear corrections for dis data on deuterium targets needed for flavor separation of the up and down quark . in this talk , i discuss the results of this analysis and some recent work in progress which extends it . detailed references can be found in ref . @xcite .","the possibility to use hadronic perturbative qcd structure functions as ` ` tracers '' of the underlying quark - hadron structure function to study low - lying nucleon resonances in the hadron spectrum is discussed. this hypothesis is supported by new large-@xmath0 parity - violating data on the structure function of the nucleon. the operator product expansion formalism is used to obtain a global fit to these data, which includes nuclear corrections, including the full set of higher - twist contributions, as well as variations of the dis kinematic cuts. the regularization parameters are fixed by the choice of cuts in the region @xmath1 and the range of jefferson lab data. results are compared to calculations using cteq6x, alekhin09 and ht corrections, which are all consistent with hadronic structure functions in the georgi - politzer formalism. in particular, we confirm that the presence of nuclear corrections limits the ranges of tmc, ht and deuteron corrections that can be considered. # 1#2#3#4#1 * # 2 * ( # 3 ) # 4 desy 10 - 043issn 0418 - 9833 + march 2010 * on the hadronic transition from qcd to qcd * * in the nonperturbative regime * * s. fukuzawa@ntc.nasa / goddard space flight center, greenbelt, md 20771, usa * * # 1 * [ cols=""<,>#1 >, < "", ] _ submitted to physics letters b _ c _ the deutsches elektronen - synchrotron ( dis ) collaboration _ m. fleischhauer@nta.physikalisches institut, d-85748 possible locations for the future cherenkov telescope at tbingen, germany _ the mit kavli institute for nuclear physics, + ul. radzikowskiego 152, 31 - 342 cracow, poland _ + _ the enrico fermi institute, the university of chicago, illinois, 60126, u.s.a. _ + e - mail : f.m.feldt@mit.edu _ keywords : deep inelastic structure functions, qcd, parton correlators, hadron duality, large - twist corrections, parity violation, transverse confinement.",0.1372549019607843,"it is also clear that nuclear smearing corrections do not disappear at large @xmath1 : in general , they are not a subleading effect , and can not be avoided by kinematics cuts such as those commonly used in global pdf fits . there is a substantial reduction in the uncertainty of these pdfs due to the increased data , with the cut3 errors reduced by 1020% for @xmath56 , and by up to 4060% at larger @xmath0 . a detailed investigation of the systematic pdf uncertainties induced by nuclear corrections modeling is underway , as reviewed by j. owens @xcite . quark - hadron duality in structure functions refers to the experimental observation that inclusive structure functions in the region dominated by low - lying nucleon resonances follow deep inelastic structure functions describing high energy data , to which the resonance structure functions average @xcite . the new large-@xmath0 cteq6x pdfs can be used to verify to what degree this holds true , which is important to understand the transition from the perturbative ( partonic ) to the non perturbative ( hadronic ) regime of qcd . the handbag diagram used in the pqcd computations assumes no interaction between the scattered quark and the target remnant . [ fig : qhd ] the ratios of jefferson lab data averaged over different resonance regions to computations using cteq6x are plotted @xcite . this opens the possibility of using resonance region data to extend the range of validity in @xmath0 of the fits . i have shown that a good control of global pdf fits can be achieved when including dis data in the pre - asymptotic region of large @xmath0 and small @xmath1 , if one considers tmc and ht corrections . this is very good for applications to collider and neutrino physics @xcite , and for comparing pdf moments to lattice calculations @xcite . theoretical nuclear corrections to deuteron target data are necessary for @xmath27 and @xmath26 quark separation at @xmath77 . the @xmath26-quark and , surprisingly , the gluon pdf turn out to be very sensitive to uncertainties in the modeling and calculation of nuclear effects . a careful study shows that the induced systematic @xmath26-quark pdf uncertainty is of the same order as the experimental uncertainty if the deuteron target data are removed from the fit @xcite . therefore , further progress in constraining the @xmath26 quark and the gluon pdfs at large @xmath0 requires a better theoretical understanding of nuclear corrections , combined with new data on free proton , but sensitive to @xmath26 , such as from parity violating dis or from neutrino dis on a hydrogen target @xcite . alternatively one can use data minimizing nuclear corrections , such as from proton - tagged dis on deuteron targets , for which the nuclear uncertainty is smaller than 2% @xcite . using quark - hadron duality to include resonance region data in the fits , thereby extending their @xmath0 range , seems also feasible . finally , data sensitive to large @xmath0 gluons , such as from the longitudinal and charm structure functions , @xmath78 and @xmath79 , are required to constrain the gluons independently of the jet data .",0.17916260954235638
1209.0972,"integrated star formation rate ( sfr ) and specific star formation rate ( sfr/@xmath0 ) , derived from the spectroscopic data obtained by sdss dr4 are used to show that the star formation activity in galaxies ( @xmath1 ) found on the outskirts ( 1 - 2r@xmath2 ) of some nearby clusters ( @xmath3 ) is enhanced . by comparing the mean sfr of galaxies in a sample of clusters with at least one starburst galaxy ( log sfr/@xmath4 yr@xmath5 _ and _ sfr @xmath6 m@xmath7yr@xmath5 ) to a sample of clusters without such galaxies ( ` comparison ' clusters ) , we find that despite the expected decline in the mean sfr of galaxies toward the cluster core , the sfr profile of the two samples is different . compared to the clusters with at least one starburst galaxy on their outskirts , the galaxies in the ` comparison ' clusters show a low mean sfr at all radius ( @xmath8r@xmath2 ) from the cluster centre . such an increase in the sfr of galaxies is more likely to be seen in dynamically unrelaxed ( @xmath9 km s@xmath5 ) clusters . it is also evident that these unrelaxed clusters are currently being assembled via galaxies falling in through straight filaments , resulting in high velocity dispersions . on the other hand , ` comparison ' clusters are more likely to be fed by relatively low density filaments . we find that the starburst galaxies on the periphery of clusters are in an environment of higher local density than other cluster galaxies at similar radial distances from the cluster centre . we conclude that a relatively high galaxy density in the infalling regions of clusters promotes interactions amongst galaxies , leading to momentary bursts of star formation . such interactions play a crucial role in exhausting the fuel for star formation in a galaxy , before it is expelled due to the environmental processes that are operational in the dense interiors of the cluster . [ firstpage ] galaxies : clusters : general ; galaxies : evolution ; cosmology : observations ; cosmology : large - scale structure of the universe ; galaxies : starburst","however , over the last few years , a growing number of galaxies , with an unusually high rate of star formation , have been discovered on the outskirts of rich galaxy clusters . the star formation activity is quantified using the integrated sfr and specific star formation rate ( ) of galaxies in a representative sample of local clusters , and emission line ratios to separate out the emission dominated by the active galactic nuclei ( agn ) from that of star formation . the star formation properties of cluster galaxies are described in [ analysis ] , briefly discussing the behaviour of galaxies falling in the cluster for the first time . the impact of the immediate and the large - scale structure ( lss ) environment on the star formation properties of galaxies is discussed in [ mag - sf ] shows the distribution of absolute sfr and log sfr/@xmath0 of all galaxies ( @xmath48 ) in sdss dr4 as a function of their luminosity for the three different classes : star forming ( & composite ) , agn and the unclassified ( b04 ) . this implies that the galaxies in the infall regions of the cluster samples studied here are a mix of infall and backsplash populations . it shows that @xmath94 of the ( morphologically classifiable ) filaments feeding the comparison ( cn ) clusters are of type i ( straight ) , as compared to @xmath4647% in the sb clusters . hence , the unrelaxed sb clusters ( @xmath95 km s@xmath5 ) are more likely to have a straight filament connecting them to a nearby companion cluster . we suggest that sb clusters are most likely dynamically unrelaxed clusters , presently being assembled via galaxies falling in through straight filaments . the occurrence of starburst galaxies on the periphery of these clusters is a direct consequence of the way local conditions ( galaxy density and relative velocity ) are affected by the global layout of the cosmic web . * ) . it would be very interesting to study the intermediate mass / dwarf ( @xmath100 ) galaxies , in the infall regions of the sb clusters , which may be harassed even more easily by their relatively massive counterparts . using the integrated sfr ( and sfr/@xmath0 ) derived by b04 for galaxies in the sdss dr4 , the star formation properties of galaxies ( @xmath101 ) in the nearby ( @xmath102 ) abell clusters were analysed . the main results are summarised below : * star formation activity in galaxies on the outskirts of some clusters is enhanced near their periphery ( r@xmath2 ) and further into the clusters at @xmath103r@xmath2 . in agreement with several other observational and simulations studies , we find that this enhancement in the sfr of galaxies on the clusters periphery is most likely due to enhanced galaxy - galaxy interactions . * starburst galaxies on cluster outskirts inhabit relatively denser environments , compared to other cluster galaxies at similar distances from the cluster centre . * clusters with evidence of enhanced star formation activity on their periphery are likely to be dynamically unrelaxed , and fed by straight and well - defined supercluster filaments . *",0.26666666666666666,"we present a systematic analysis of the star formation properties of galaxies in the infall regions of local clusters, based on a catalogue of @xmath0-band images from the sloan digital sky survey ( sdss ). this is the first mass - selected sample of clusters in the local universe that have been observed to contain significant numbers of galaxies with star formation rates ( sfrs ) above the eddington limit. we find that star formation ( sfr ) and specific star formation rate ( ) of cluster galaxies are enhanced in regions close to the cores of rich clusters, such as those around the centres of virgo and abell 2744. we show that such an enhancement is a direct consequence of the way local ( galaxy and relative velocity ) conditions are affected by the global layout of the cosmic web. it is also in sync with the results of a study by @xcite showing that in the cold dark matter universe, more massive structures are more strongly clustered than their less massive counterparts. our data show that infalling starburst galaxies are predominantly of type i ( spiral ), and their distribution is indistinguishable from that of the unclassified population of star forming galaxies, which is well - known to follow a star formation sequence. the fraction of starburst "" galaxies at a given cluster centric distance is almost twice that at the core of clusters. infalling galaxies often show evidence of comet - like tails of x - ray emitting gas, and a shock front, suggesting that, as we reveal in this paper, some of these galaxies are plunging into the cluster core on their own. while such galaxies are a common phenomenon in clusters, they are relatively rare in our local sample. the frequency and impact of such galaxy - galaxy interactions are found to depend upon the local galaxy density. our results suggest that galaxy groups and clusters are being assembled predominantly through the merger of galaxies falling in through straight filaments, in analogy to the ` butcher - oemler effect ', whereby a starburst galaxy is stripped of its gas content by the intracluster medium of a massive group or cluster. this effect is in agreement with recent suggestions that the icm may be part of the large - scale structure in the universe. [ firstpage ] galaxies : clusters : general",0.2299854439592431
hep-th9806224,"we study the m - theory five - brane wrapped around the seiberg - witten curves for pure classical and exceptional groups given by an integrable system . generically , the d4-branes arise as cuts that collapse to points after compactifying the eleventh dimension and going to the semiclassical limit , producing brane configurations of ns5- and d4-branes with @xmath0 gauge theories on the world volume of the four - branes . we study the symmetries of the different curves to see how orientifold planes are related to the involutions needed to obtain the distinguished prym variety of the curve . this explains the subtleties encountered for the sp(@xmath1 ) and so(@xmath2 ) . using this method we investigate the curves for exceptional groups , especially g@xmath3 and e@xmath4 , and show that unlike for classical groups taking the semiclassical ten dimensional limit does not reduce the cuts to d4-branes . for g@xmath3 we find a genus two quotient curve that contains the prym and has the right properties to describe the g@xmath3 field theory , but the involutions are far more complicated than the ones for classical groups . to realize them in m - theory instead of an orientifold plane we would need another object , a kind of curved orientifold surface . uttg-10 - 98 + ucla-98-tep-18 + hep - th/9806224 + m - theory five - brane wrapped on curves for exceptional groups 3em _ .75em _ ccc [ cols=""^ "" , ] 1em however , as we will see in section [ g2 ] the behaviour of the exceptional curves in this limit is very different . when @xmath5 is of second order in @xmath6 identifying how the sheets combine to form ns5-branes was rather straightforward . the only subtlety being that the five branes should not ` ` cross '' each other in the @xmath7-direction at the branch points to avoid confusion on which brane is on the left and which on the right . for higher number of ns5-branes the situation is more complicated : we can always determine the number of sheets and number of cuts , but trying to identify which sheets are connected by which cuts depends crucially on how we choose the phases at each cut . take for example the three - fold cover curve that describes the product group @xmath8 with bi - fundamental matter ( see fig . [ prod - fig ] for @xmath9 ) : @xmath10 here @xmath11 is the scale of su(@xmath12 ) gauge group . su(2 ) with bi - fundamental matter , width=226 ] the branch points are still of second order ( they connect only two sheets ) , but choosing the phases in a globally consistent way can be somewhat complicated . however , there is an additional piece of information we can use , namely the asymptotic behaviour of the sheets as @xmath13 . looking at the curve for large , small and middle values of @xmath6 we see that they behave as @xmath14 and constant at large @xmath15 . this means that the effective number of four - branes attached to each five - brane should be @xmath16 and 0 , respectively , where d4-branes on the left count as positive and on the right as negative . the classical limit now corresponds to taking @xmath17 separately for each group . in other words we first decouple for example the second factor by @xmath18 , giving @xmath19 , and then take @xmath20 to localize the d4-branes at the zeroes of @xmath21 . similarly for the su(@xmath22 ) factor . this reduces the curve to the usual ten dimensional brane configuration of a product of groups , studied for example in @xcite . before examining other gauge groups in detail we will discuss the role of the symmetries of the curves and how they will translate to orientifolds in the brane pictures .","in the last few years a lot of work has been devoted to the theory of ten dimensional branes and the attempts have been made to understand the transformations that produce them. for example, in @xmath0 the weyl group has been extensively studied, but for other gauge groups it is still not clear to what extent such a formalism can be applied. in this paper we propose a generalization of the toda - system which allows to three - dimensional brane diagrams, in particular to the world - volume gauge theory. we argue that it is possible to construct these diagrams with g@xmath1-branes but it is not possible to do it in the ten dimensional limit. as a result we suggest a direction in which the branes do not correspond to branes but to compact surfaces. this direction is compatible with the atiyah - hitchin background theory and can be realized as an orientifold plane in m - theory. address = department of physics, brookhaven national laboratory, upton, ny 11973, usa, altaddress = universit degli studi di milano - bicocca, dipartimento di fisica, piazza delle scienze 3, i-20126 milano, italy address = inaf - osservatorio astronomico di brera, via e. bianchi 46, i23807 merate ( lc ), switzerland address = laboratoire dastrophysique de marseille, universit paris xi, btiment 210, f-91405 orsay cedex 13, france address = max - planck - institut fr theoretische physik, werner - heisenberg - universitt, d-85748 garching, germany address = centre de recherche physik vale de la cte dazur, ecole normale suprieure, cnrs, 24 rue lhomond, paris 7, i749, f75251 paris, frances address = departamento de fsica, universidad de so paulo c.p.- l.s., avda. universidad nacional autonoma de madrid, 28049 madrid spain, spain address = center for theoretical physics, university of delaware, newark, nnewark, de 19716 usa address = dept.",0.1085972850678733,"now we can proceed to wrap the m - theory five brane on the toda curve of exceptional groups and use the techniques developed in the previous sections to investigate what happens in the ten dimensional limit . it would be interesting to see if it is possible to construct a m - theory background , like the atiyah - hitchin space for o6 , that would realize all the symmetries @xmath138 and @xmath134 simultaneously . the e@xmath4 curve presents many of the characteristics seen in g@xmath3 . it is a genus 34 curve that can be realized as a four - fold cover of the @xmath15-plane ( [ curves ] ) . the branch cuts of the curve have the same behavior as in the g@xmath3 case . one of our original motivations was to examine the breaking of exceptional groups to get matter in the spinor representation . it is perfectly possible to take a curve , write the invariants @xmath139 of the bigger group in terms of the moduli of the group that it breaks into ( for explicit construction for @xmath140 see @xcite ) and recover in some limit of the moduli space a new curve which describes a group with a specific matter content . unfortunately , as we have argued , there is no guarantee that the resulting curve will have a good limit in weakly coupled type iia theory . for e@xmath4 we have seen that in the brane configurations for classical groups we can generically identify d4-branes with branch cuts of the seiberg - witten curve @xmath141 . the need to introduce o6 or o4-planes to the brane configuration can be understood as the symmetries that have to be quotioned out in order to obtain the physically significant curve that has the prym variety as its jacobian . we found several ways how the g@xmath3 toda curve differs from those of the classical groups . it does not have a well defined classical ten dimensional limit that would reduce the cuts to d4-branes . we think it is not possible to find a brane configuration in weakly coupled type iia string theory which would describe a g@xmath3 field theory on the d4 world - volume . moreover , the symmetries of the g@xmath3 curve can not be realized as orientifold planes . it would be interesting to see if it is possible to construct an m - theory background that would realize all the symmetries of g@xmath3 simultaneously .",0.19393939393939394
1302.5035,"through a combination of spin - exchange collisions in a magnetic field and optical pumping , it is possible to cool a gas of atoms without requiring the loss of atoms from the gas . we investigated this technique , collision assisted zeeman cooling , using @xmath0rb and @xmath1rb . we experimentally confirmed that our measured two isotope caz cooling rate agreed with a cooling rate predicted though a simple analytic model . as part of the measured cooling rate , we quantitatively characterized the heating rates associated with our actual implementation of this cooling technique and found hyperfine - changing collisions to be a significant limitation for the @xmath2rb gas mixture . we comment on the prospects for improving the cooling performance beyond that presented in this work . there are numerous techniques @xcitethat have been theoretically and/or experimentally evaluated for cooling gasses of ultracold atoms below the limits associated with standard laser cooling techniques such as doppler cooling @xcite and optical molasses cooling @xcite . by far the most common of these cooling techniques is evaporative cooling and as such it has a long history of being effective , robust , and straightforward to implement @xcite . there are reasons to investigate non - evaporative cooling techniques , however . there is intrinsic physics interest in studying the ways in which ultracold gases can be cooled . evaporative cooling requires the loss of atoms from the trapped gas , which is generally undesirable . a rapid non - evaporative cooling scheme would have the potential to simplify experimental apparatuses by eliminating , for instance , the need for atom transport between different regions of the vacuum system @xcite . finally , in non - evaporative cooling the link between the cooling mechanism and the potential confining the ultracold atoms is reduced , allowing for more flexibility in tailoring the confining potential @xcite . in previously published work , a non - evaporation - based cooling technique called collision - assisted zeeman ( caz ) cooling was presented theoretically @xcite . at the heart of this cooling technique are spin - exchange collisions that transfer kinetic energy to zeeman energy that is then subsequently removed from the ultracold gas via optical pumping . we present an extension to caz cooling by considering caz cooling with two different types of atoms present in the gas being cooled rather than one . we refer to this two - type - of - atom based cooling scheme as 2-caz . while cooling two different types of atoms introduces complexity , it leads to predicted advantages for caz cooling both specific to the cooling technique itself and also in more general terms through a predicted improvement in cooling rate at low temperatures . in addition to presenting 2-caz theoretically , the experimental implementation of 2-caz in an @xmath0rb/@xmath1rb system is reported . while optical trap loading behaviour and hyperfine - changing collisions prevented robust 2-caz cooling in our system , cooling rate measurements were made that allow for a comparison between experimentally realizable and theoretically predicted 2-caz performance . through these measurements , requirements for robust 2-caz cooling are better characterized and understood .","the two - component atomic cooling rate ( 2-caz ) is a promising new cooling method for a @xmath0rb gas. it is based on optically pumping two rb atoms simultaneously in a far off - resonance optical trap. this technique avoids the use of magnetic traps such as magnetic micro - traps and magnetic coils. in addition, the light - assisted spin - exchange collisions that occur due to exchange interactions in the f=2 and f=3 states of the colliding atoms are avoided. for optimal cooling parameters the atoms do not have to be in hyperfine - changing collisions. the advantages of this cooling scheme are that it is three - dimensional, the energy removed per scattered optical pumping photon is proportional to the gas temperature, and the high density of the atoms prevents hyperfine changing collisions to significantly limit the total energy in the system. however, the complications that occur in light - based methods such as reabsorption cooling impose constraints on the cooling rate. to overcome these limitations two - cavity sub - doppler cooling with two different types of atoms has been proposed. in this paper we report on an experimental realization of 2-ca z@xmath1az cooling with just one rb atom. we show that by using a simple all - optical optical pumping scheme it is possible to achieve cooling rates comparable to those that require a magnetic trapping or a large magneto - optical trap ( mots ). we also report a successful thermodynamic measurement of the on - resonance microwave excitation probability and the steady - state population of a two - atom system showing that 2caz cooling is efficient while maintaining the isotope character of the gas. the techniques used in this work demonstrate a potential for efficient cooling in a variety of situations. recent years have seen a growing interest in the cooling of heavy elements due to their potential for technological applications in spintronics and quantum information processing @xcite. for instance, spintronic devices require a low - temperature gas to be cooled below a temperature of a few hundred k. to reach the desired temperature it is necessary to cool the gas to a temperature where the majority of the electrons are in the spin - singlet / triplet ground state. to reach such a low temperature, the cooling must be performed in a regime where the magnetic field is strong enough to produce an effective zeeman field ( e.g. l2 and l3 colliding atom beams ). while laser cooling of atoms in magnetic traps is generally accomplished through laser cooling from a few tens of mev",0.17920353982300888,"* microwave measurement of @xmath0rb @xmath7 state distribution . * a microwave signal was created using a microwave generator and amplifier that is connected to a microwave antenna inside of the vacuum chamber . our data yielded an on - resonance microwave excitation probability of 0.76(9 ) and off - resonance excitation probability of 0.0047(8 ) . while there are no reabsorption effects observed for the reported conditions above , we do observe degradation in optical pumping efficiency at an order - of - magnitude more intensity for l2 and l3 . thus , the window of sufficiently high density for effective cooling and sufficiently low time spent in the f=3 state appears to be small . having the freedom to adjust the density of the optically - pumped isotope while still maintaining a high density of the non - optically - pumped isotope can result in improvements in the achievable cooling rate at low temperatures . for 2-caz cooling , this can be seen by assuming that the cooling is taking place under conditions where @xmath44 is proportional to the number of optically - pumped atoms @xmath38 , i.e. @xmath72 , where @xmath73 is constant . for this @xmath44 , in the limit of fast optical pumping and @xmath74 compared to cooling in a gas with only one type of atom present , this ability to increase the cooling rate by reducing @xmath38 under reabsorption - limited conditions can produce orders - of - magnitude improvements in the net cooling rate . this is a general feature of non - evaporative cooling with two different types of atoms instead of one and is not limited to 2-caz . the predicted improvement in low - temperature cooling capabilities is an intriguing area of investigation if a system better - suited to 2-caz cooling than @xmath2rb can be used . in summary , we have extended caz cooling from a single - atom cooling case to one in which two different types of atoms are trapped and cooled . we have discussed the advantages of using two different types of atoms as compared to one for caz cooling . we experimentally measured 2-caz cooling in an @xmath2rb mixture and found that the measured cooling rate agrees with a simple analytical expression for the predicted cooling rate . this allowed us to interpret the limitations of 2-caz cooling for our experimental configuration . cross - isotope interference in optical trap loading and the hyperfine - changing collision rate in the @xmath2rb mixture prevented the observation of robust 2-caz cooling in our measurements and would be challenging to overcome . our analysis indicates the requirements that would be necessary for a better mixture of atoms for 2-caz cooling . predicted cooling rate improvements at low gas temperatures with the use of two different types of atoms remains an intriguing possibility for 2-caz cooling .",0.24145299145299146
0708.3460,"the electronic structure of a monolayer of single - molecule magnets mn@xmath0 on a au(111 ) surface is studied using spin - polarized density - functional theory . the mn@xmath0 molecules are oriented such that the magnetic easy axis is normal to the surface , and the terminating ligands in the mn@xmath0 are replaced by thiol groups ( -sh ) where the h atoms are lost upon adsorption onto the surface . this sulfur - terminated mn@xmath0 molecule has a total magnetic moment of 18 @xmath1 in the ground state , in contrast to 20@xmath1 for the standard mn@xmath0 . the mn@xmath0 molecular orbitals broaden due to the interaction of the molecule with the gold surface and the broadening is of the order of 0.1 ev . it is an order of magnitude less than the single - electron charging energy of the molecule so the molecule is weakly bonded to the surface . only electrons with majority spin can be transferred from the surface to the sulfur - terminated mn@xmath0 since the gold fermi level is well above the majority lowest unoccupied molecular orbital ( lumo ) but below the minority lumo . the amount of the charge transfer is calculated to be 1.23 electrons from a one - dimensional charge density difference between the sulfur - terminated mn@xmath0 on the gold surface and the sulfur - terminated mn@xmath0 , dominated by the tail in the electronic distribution of the gold surface . a calculation of a level shift upon charging provides 0.28 electrons being transferred . the majority of the charge transfer occurs at the sulfur , carbon , and oxygen atoms close to the surface . the total magnetic moment also changes from 18 @xmath1 to 20 @xmath1 , which is due to rearrangements of the magnetic moments on the sulfur atoms and mn atoms upon adsorption onto the surface . the magnetic anisotropy barrier is computed including spin - orbit interaction self - consistently in density - functional theory . the barrier for the mn@xmath0 on the gold surface decreases by 6 k in comparison to that for an isolated mn@xmath0 molecule .","photoemission spectroscopy experiments on the monolayers of mn@xmath0 derivatives showed that the mn 3@xmath11 partial density of states in valence bands for the monolayers is comparable to that for bulk mn@xmath0 . we investigate , within density - functional theory ( dft ) , the effect of the interface on the electronic and magnetic properties of mn@xmath0 molecules on a gold surface , given a particular orientation of mn@xmath0 molecules relative to the surface . our dft calculations show that the mn@xmath0 molecular orbitals moderately broaden for the short link due to the interaction between the molecules and the surface . the electronic structure and magnetic properties on the system are discussed in sec . our noncollinear calculation shows that a collinear spin approximation is good for geometry * 1*. the simplification made for the mn@xmath0 molecule does not significantly change the electronic and magnetic properties of the molecule . [ cols=""^,^,^,^ "" , ] the magnetic anisotropy comes from jahn - teller distortion around the eight mn@xmath23 ions at the outer ring . it is known experimentally that for geometry * 1 * the second - order magnetic anisotropy contributes to the total mab by 55 k and the fourth - order anisotropy by 10 k. @xcite with the total magnetic moment fixed , the mab is computed from the change of the total energy upon a rotation of the spin quantization axis from the @xmath18 to the @xmath24 axis . the mab with total magnetic moment of 18 @xmath1 is 66.9 k for geometry * 2 * so it remains the same as that for geometry * 1*. the transverse magnetic anisotropy is calculated to be 0.02 k , which is caused by the sulfur atoms . as discussed , geometry * 3 * is used to calculate the mab for the whole structure . with the total magnetic moment of 20 @xmath1 , thus , a reasonable value for the whole structure would be also 60.7 k. the reduction in the barrier is due to the decrease in the single - ion anisotropy for the two mn(ii ) ions close to the surface . we have investigated , within dft , the interaction between a single - molecule magnet mn@xmath0 monolayer and a au(111 ) surface through thiol bonds without long alkane chains . despite a very short bond length between the sulfur - terminated mn@xmath0 molecule and the gold slab , the broadening of the molecular orbitals was much less than the single - electron charging energy of the molecule . in the ground state the sulfur - terminated mn@xmath0 molecule has a total magnetic moment of 18 @xmath1 , but its total magnetic moment increases to 20@xmath1 upon adsorption onto the gold surface . the noticeable charge transfer from the surface to the mn@xmath0 is attributed to ( i ) the relative position of the gold fermi level to the lumo and ( ii ) the long tail in the electronic cloud at the boundary of the gold surface . the self - consistent soi calculation suggested a decrease in the mab by 9% and a significant transverse magnetic anisotropy for the whole structure compared to the isolated mn@xmath0 . although a relaxation of the whole structure may bring additional transverse magnetic anisotropy caused by minor symmetry breaking of the mn ions close to the surface , it is unlikely that the molecules are completely collapsed upon adsorption . the analysis and results given in this study are not limited to the mn@xmath0 molecules and may be applicable to systems where other types of magnetic molecules or smms are adsorbed onto nonmagnetic surfaces or bridged between nonmagnetic electrodes .",0.2521929824561404,"we show that the electronic and magnetic properties of sulfur - terminated mn@xmath0 molecules do not change significantly by adsorption onto a gold surface. a density - functional calculation shows that a collinear spin approximation is good. the paw pseudopotentials are employed to calculate atomically resolved magnetic moments. the second - order magnetic anisotropy contributes to the total mab by 55 k, and the fourth - order by 10 k. the strength of coupling of the molecules to the surface and other parameter values need to be determined from atomic - scale simulations. 99 p. ernst, _ computational magnetism _ ( cambridge university press, 2000 ). p. g. kwiat, k. mattle, h. weinfurter, a. zeilinger, and a. v. sergienko, ` ` single - molecule magnetism in gold, '' phys. rev. lett. * 105 *, 251102 ( 2010 ). m. m. bttiker, r. krabbendam, j. liukkonen, and w. tittel, magnetism of isolated semiconductor quantum dots, "" nature * 462 *, 772775 ( 2012 ). h. c. ngao, y. chao, and m. s. nam, first - principles study of magnetism from a single molecule, "" rev. mod. phys. * 81 *, 6336366 ( 2013 ). b. e. barclay, c. santori, k.- m. fu, and t. baehr - jones, molecular magnetic resonance, "" science * 322 *, 16361640 ( 2014 ). c. h. fu, z. zhang, g. f. gao, b. y. gong, w. j. padilla, and s. d. whittaker, low - frequency magnetic recording in nanostructured silicon, "" nat. commun. * 5 *, 198200 ( 2015 ). j. b. thomsen, p. t. russell, and k. p. nagahara, atomic clocks based on the jahn - teller distortion of a single atom, "" phys. today * 58 *, 384444 ( 2007 ). n. a. mortensen, molecular dynamics, and spin - orbit coupled epitaxial rings, "" j. phys : condens. matter * 8 *,",0.1577181208053691
1007.2606,"numerical methods for solving the ideal magnetohydrodynamic ( mhd ) equations in more than one space dimension must either confront the challenge of controlling errors in the discrete divergence of the magnetic field , or else be faced with nonlinear numerical instabilities . one approach for controlling the discrete divergence is through a so - called _ constrained transport _ method , which is based on first predicting a magnetic field through a standard finite volume solver , and then correcting this field through the appropriate use of a magnetic vector potential . in this work we develop a constrained transport method for the 3d ideal mhd equations that is based on a high - resolution wave propagation scheme . our proposed scheme is the 3d extension of the 2d scheme developed by rossmanith [ _ siam j. sci . comp . _ * 28 * , 1766 ( 2006 ) ] , and is based on the high - resolution wave propagation method of langseth and leveque [ _ j . comp . phys . _ * 165 * , 126 ( 2000 ) ] . in particular , in our extension we take great care to maintain the three most important properties of the 2d scheme : ( 1 ) all quantities , including all components of the magnetic field and magnetic potential , are treated as cell - centered ; ( 2 ) we develop a high - resolution wave propagation scheme for evolving the magnetic potential ; and ( 3 ) we develop a wave limiting approach that is applied during the vector potential evolution , which controls unphysical oscillations in the magnetic field . one of the key numerical difficulties that is novel to 3d is that the transport equation that must be solved for the magnetic vector potential is only weakly hyperbolic . in presenting our numerical algorithm we describe how to numerically handle this problem of weak hyperbolicity , as well as how to choose an appropriate gauge condition . the resulting scheme is applied to several numerical test cases . magnetohydrodynamics , constrained transport , hyperbolic conservation laws , plasma physics , wave propagation algorithms","the ideal magnetohydrodynamic ( mhd ) equations are a common model for the macroscopic behavior of collisionless plasma @xcite . all of the above described simplifications conspire to turn the original two - fluid plasma model into a system that can be viewed as a modified version of the compressible euler equations from gas dynamics . the method we propose in this work is therefore in the same class of methods as that of gardiner and stone @xcite ( i.e. , unsplit finite volume methods with constrained transport ) , and to a lesser extent mignone and tzeferacos @xcite ( i.e. , unsplit methods for mhd ) , although the details of our base scheme and especially the details of how the magnetic field is updated differ greatly from these approaches . in particular , the approach for updating the magnetic field that we propose in this work is based on a generalization of the 2d constrained transport scheme of @xcite , which is equipped with all of the following features : 1 . all quantities , including all components of the magnetic field and magnetic potential , are treated as cell - centered ; 2 . the magnetic potential is evolved alongside the eight conserved mhd variables via a modified non - conservative high - resolution wave propagation scheme ; and 3 . special limiters are applied in the evolution of the magnetic potential , which control unphysical oscillations in the magnetic field . the new challenge that arises in 3d is that the magnetic potential is a vector potential ( instead of a scalar as in the 2d case ) . the ideal magnetohydrodynamic ( mhd ) equations are a classical model from plasma physics that describe the macroscopic evolution of a quasi - neutral two - fluid plasma system . under the quasi - neutral assumption , , we can rewrite faraday s law in the following divergence form : @xmath27 since the electric field is determined entirely from ohm s law , we do not require an evolution equation for it ; and thus , the only other piece that we need from maxwell s equations is the divergence - free condition on the magnetic field . a complete derivation and discussion of mhd system - we briefly review the 3d wave propagation approach . in [ sec : method_potential ] we show in detail how this approach can be modified to solve the non - conservative and only weakly hyperbolic magnetic vector potential equation . in [ subsec : mp_limiters ] we develop a limiting strategy that is applied during the magnetic potential update , but designed to control unphysical oscillations in the magnetic field . finally , in [ subsec : mp_25d ] we briefly mention how our approach simplifies in the special case of 2.5-dimensional problems . shown here is the solution in two selected orthogonal planes . we have presented a new constrained transport method for the three - dimensional mhd equations . depending on the gauge condition , we discussed different possible evolution equations for the magnetic potential . the condition used here leads to a weakly hyperbolic system for the evolution of the magnetic potential . we discretized this system with a splitting approach . for the mhd equations we used a wave propagation method .",0.2522068095838588,"we propose a new numerical approach for solving the ideal magnetohydrodynamic ( mhd ) equations in three dimensions. the scheme is based on the high - resolution wave propagation scheme of leveque and its 3d extension developed by langseth and leveque. in this approach, the magnetic vector potential is treated as a non - conservative system of conservation laws, and the mhd equations are written as a linearized version of ohm s law. a constrained transport method for this system is then formulated, where the divergence error is caused by the fact that the magnetic field is divergence - free. we discuss several gauge conditions that are necessary to achieve this goal, and we then present the implementation of the new method. the new scheme is designed to be easy to implement, computationally efficient, and scalable. 10 url # 1`#1`urlprefix[2][]#2 a. g. radnaev, y. o. dudin, r. zhao, h. h. jenkins, a. kuzmich, and t. p. grangier, ` ` numerical solution of the initial boundary value problems involving a quasi - neutral two - fluid plasma system in 3 dimensions, '' phys. rev. a * 71 *, 011115 ( 2002 ). j. f. brady, d. b. barnes, and j. c. poon, _ computational electrodynamics : the finite - volume paradigm _ ( academic press, 2003 ). w. s. rossmanith, j. j. lezec, and n. e. cornish, _ introduction to numerical solutions _ ( university science books, 1986 ). d. bouwmeester, j.- w. pan, k. danzmann, m. daniell, and w. r. huffman, _ statistical mechanics of plasmas _ ( springer - verlag, heidelberg, 2009 ). p. krabbendam, p. mosk, f. de sterck, londrillo, and del zanna ` ` macroscopic properties of plasma densities in three - dimensional collapse, '' j. phys. : condens. matter * 38 *, 459 - 463 ( 2003 ) c. pfeiffer and v. shlyapvili ( eds., new york non - dev., 1998 ). s. radunsky, c. jadach, and",0.18524871355060035
astro-ph0504404,"without imposing any theoretical models and assumptions , we present a multi - variable regression analysis to several observable quantities for a sample of 15 gamma - ray bursts ( grbs ) . the observables used in the analysis includes the isotropic gamma - ray energy ( @xmath0 ) , the peak energy of the @xmath1 spectrum in the rest frame ( @xmath2 ) , and the rest frame break time of the optical afterglow light curves(@xmath3 ) . a strong dependence of @xmath4 on @xmath5 and @xmath6 is derived , which reads @xmath7 in a flat universe with @xmath8 and @xmath9 km s@xmath10 mpc@xmath10 . we also extend the analysis to the isotropic afterglow energies in the x - ray and the optical bands , respectively , and find that they are essentially not correlated with @xmath2 and @xmath3 . regarding the @xmath11 ) relationship as a luminosity indicator , we explore the possible constraints on the cosmological parameters using the grb sample . since there is no low - redshift grb sample to calibrate this relationship , we weigh the probability of using the relationship in each cosmology to serve as a standard candle by @xmath12 statistics , and then use this cosmology - weighed standard candle to evaluate cosmological parameters . our results indicate @xmath13 at @xmath14 level , with the most possible value of @xmath15 being @xmath16 . the best value of @xmath17 is 0.64 , but it is less constrained . only a loose limit of @xmath18 is obtained at @xmath14 level . in the case of a flat universe , the @xmath14 constraints are @xmath19 and @xmath20 , respectively . the decelerating factor ( @xmath21 ) and its cosmological evolution @xmath22 are also investigated with an evolutionary form of @xmath23 . the best - fit values are @xmath24 , with @xmath25 and @xmath26 at @xmath14 level . the inferred transition redshift between the deceleration and the acceleration phases is @xmath27 ( @xmath14 ) . through monte carlo simulations , we find that the grb sample satisfying our relationship observationally tends to be a soft and bright one , and that the contraints on the cosmological parameters can be much improved either by the enlargement of the sample size or by the increase of the observational precision . although the sample may not expand significantly in the _ swift _ era , a significant increase of the sample is expected in the long term future . our similations indicate that with a sample of 50 grbs satisfying our multi - variable standard candle , one can achieve a constraint to the cosmological parameters comparable to that derived from 157 type ia supernovae . furthermore , the detections of a few high redshift grbs satisfying the correlation could greatly tighten the constraints . identifying high-@xmath28 grbs and measuring their @xmath29 and @xmath30 are therefore essential for the grb cosmology in the _ swift _ era .","the constraints on cosmological parameters derived from the type ia supernova ( sn ia ) gold sample are discussed. we investigate the possible multi - variable correlations among observables @xmath0, the isotropic x - ray afterglow energy @xfig.1, the cosmologically - dependent rest frame peak energy @roxmath2, and the temporal break in the optical light curve to probe the constraints. we compare the constraints based on our grb sample with a sample of 50 sne ia with systematically smaller observational errors, and find a tight constraint on the mass content of the universe @xcite. the constraints are significantly tighter than those derived from a sub - sample with similar observational precision. if the sample size and the observational precision are increased, tighter constraints could be established. in particular, we find that the relationship between the jet opening angle and the gamma - ray energy is significantly tighter ( tighter by 0.5 than with the current sample ) than was found by previous authors, even without imposing any theoretical models and assumptions. in addition, we perform monte - carlo simulations to investigate the influence of the size and precision of the sample on the standard analysis. the results suggest that the constraints can be significantly improved either by enlarging the sample with larger sample sizes or by increasing the precision. in both cases, the effect of the concordance cosmology model on the constraints is about the same. we also find that if the cosmology - dependent relationship between luminosity and grb energy is considered, the constraints on all cosmology parameters are weakened by about a factor of 2. regarding the implications on the luminosity - dependent cosmology, we use the friedmann - robertson - walker ( frw ) relationship as a luminosity indicator to explore the grb - dependent relationships. some of our conclusions are : ( 1 ) this relationship is not tight enough to serve as a standard candle for precision cosmology ; ( 2 ) it might be due to observational biases against high redshift grbs ; ( 3 ) it is likely due to a uniform top - hat jet configuration, but this model is not the best choice for deep constraints.",0.227390180878553,"long gamma - ray bursts ( grbs ) are originated from cosmological distances ( metzger et al . we further address the grb standard candle problem by a new statistical approach . instead of sticking to the jet model and searching for the correlation between @xmath46 and @xmath47 ( which requires a model- and parameter - dependent jet angle ) , we start with pure observable quantities to search for possible multi - variable correlations by using a regression method . below we perform a blind search for the possible multi - variable correlations among several essential observable quantities , including the isotropic gamma - ray energy @xmath0 , the isotropic x - ray afterglow energy @xmath49 , the isotropic optical afterglow energy @xmath50 , the cosmological rest frame peak energy @xmath2 , and the cosmological rest frame temporal break in the _ optical _ afterglow light curve ( @xmath3 ) . in addition ( 5 ) , we perform monte - carlo simulations to investigate the characteristics of the grb sample satisfying the relationship observationally , and examine how both the sample size and the observational precision affect the constraints on cosmological parameters . we measure the significance level of the dependence of each variable on the model by the probability of a t - test ( @xmath105 ) . \(5 ) assign _ observational errors _ to @xmath54 , @xmath61 , and @xmath55 . we investigate the effect of the sample size on the cosmological constraints with our mock grb sample . ( 2004 ) , we find that the likelihood contour derived from the sub - sample of 50 grbs is comparable to that derived from the gold sample of 157 sne ia . if a sample of 50 grbs with a comparable observational precision as sne ia gold sample could be established , the constraints are even tighter than those derived from the sne ia gold sample . the results indicate that @xmath97 strongly depends on both @xmath224 and @xmath3 with a very small dispersion , e.g. eq.([mr ] ) for a flat universe with @xmath8 . we then use the @xmath53 ) relationship as a luminosity indicator to infer the possible cosmology implications from the grb sample . since this relationship is cosmology - dependent , we suggest a new method to weigh various cosmology - dependent relationships with its probability of being the right one , and use the cosmology - weighed standard candle to explore the most plausible cosmological parameters . , we have @xmath13 and @xmath18 . in the case of a flat universe , the @xmath14 constraints are @xmath19 and @xmath20 . the decelerating factor of the universe ( @xmath21 ) and its cosmological evolution @xmath22 are also investigated with an evolutionary form of @xmath23 . the grb sample implies that the most possible values of @xmath170 are @xmath226 , and they are constrained in the ranges of @xmath25 and @xmath26 at @xmath14 level . a transition redshift between the deceleration and the acceleration phases of the universe is inferred as @xmath178 at @xmath14 level from the grb sample . as a luminosity indicator",0.3063063063063063
1211.0120,"photons generated by spontaneous parametric down conversion ( spdc ) are one of the most useful resources in quantum information science . two of their most important characteristics are the purity and the indistinguishability , which determine just how useful they are as a resource . we show how these characteristics can both be accessed through hong , ou and mandel ( hom ) type interferences using a single pair source . we also provide simple and intuitive analytical formulas to extract their values from the depth of the resulting interference patterns . the validity of these expressions is demonstrated by a comparison with experimental results and numerical simulations . these results provide an essential tool for both engineering spdc sources and characterizing the quantum states that they emit , which will play an increasingly important role in developing complex quantum photonic experiments . the ability to engineer and characterize quantum photonic states is of paramount importance as the complexity of the experiments in quantum information science increases . in particular , it is fundamental to be able to combine multiple independent sources and this is usually done via interference , e.g. through a bell state measurement ( bsm ) . at the heart of interference there are two concepts , two characteristics , of the photonic states : _ purity _ - how close the real photons are to the theorist s ideal of a single mode quantum object , and the _ indistinguishability _ - how alike are the different photons . indistinguishability is a fairly clear concept and its role in interference experiments has been widely accepted for some time , in contrast to the purity , which is often ignored . the indistinguishability and purity can be increased either by filtering , or by engineering the source itself . as we will see , filtering is an option for some applications , but it is also a loss factor and potentially a significant one . if one wants efficient , even scalable , multi - photon systems , then one needs to go to the source . in this article we will focus on spontaneous parametric down conversion ( spdc ) as this provides one of the most widespread and flexible resources for experiments in quantum information science . spdc sources probabilistically generate two - photon states with diverse features in space and frequency and in those degrees of freedom the photons can be anywhere from maximally entangled to totally uncorrelated . a common way to characterize spdc generated photons is by using two - photon interferometers . these were first introduced by hong , ou and mandel @xcite as a tool to measure the relatively narrow bandwidth of spdc photons . the basic idea is to observe the coincidence statistics at the output of a 50/50 beamsplitter as a function of the delay between two photons at the beamsplitter input . due to their bosonic nature the photons may bunch , giving rise to the characteristic dip in the coincidences . this interference effect will depend of the indistinguishability and purity of the photons and whether they are from the same , or independent , sources . therefore , the question arises as to what information concerning the indistinguishability and purity can be extracted from these hom - like interference patterns ? by focusing on the frequency degree of freedom , in this paper we discuss what information can be obtained from the interference patterns of different interferometers . we provide simple analytical formulas relating the spdc parameters with the characteristics of the interference patterns . such formulas can therefore be used to engineer photonic states with specific values of indistinguishability and purity . these are shown to be in good agreement with both experiment and numerical modeling .","we calculate analytically the spectral indistinguishability and purity of the two - photon interference pattern in spdc, a process where pairs of photons are generated by the interaction of a classical pump laser with a nonlinear crystal. we show that the visibility of the interference pattern obtained by comparing the arrival time of the photons to the delay between their arrival time and the coincidence frequency is unit, which provides a simple and intuitive understanding of the experiment. we also present calculations of the effect of a temporal delay between consecutive photons arrival at the interferometer. 99 j. hong, d. ou and m. mandel, ` ` interactions between light and atomic ensembles, '' nature * 424, * 817823 ( 2003 ). m. a. nielsen and i. l. chuang, _ quantum computation and quantum information _, ( cambridge university press, uk, 2000 ). p. g. kwiat, k. mattle, h. weinfurter, a. zeilinger, p. beuchert, m. lamare, r. mercier, n. f. ginzburg, and g. leuchs ` ` new high - intensity source of polarization - entangled photons, '' phys. rev. lett. * 93, * 083904 ( 2004 ). e. knappe, j. s. lundeen, b. j. ammons, and s. b. libchaber, _ colloquium _ ( wiley - interferometric quantum optics _, new york, 2001 ), pp. 7686, and references therein. n. bachelard, g. billmeier, c. c. bernreuther, cotter, and c. h. bennett ` ` ` direct detection of single photons from a crystal with ultra - high purity, '' nat. photon. * 4, * 193204 ( 2007 ). t. pittman, t. strekalov, y. kubota, l. zhang, and t. w. hnsch, _ optical interferometry _ ( springer verlag, heidelberg, 2009 ), 2nd ed. c. rasmussen, s. flling, and a. tunnermann ` ` experimental test of the purity of spdc - mediated downconversion, '' science * 312, * 333337 ( 2005 ). a. beveratos, r.- p",0.12725090036014405,"in spdc , pairs of photons are generated by the interaction of a classic pump beam and a nonlinear material . the two - photon state is a product between a spatial and a frequency part . here , we focus on the frequency part , but an analogous analysis is possible for the more general case . when considering only the spectral component , the two - photon state generated in spdc is described by the pure state @xmath0 , where : @xmath1 as the frequency of the photons , then @xmath2 gives the deviation from the central frequency @xmath3 . the properties of the material appear through the phase - matching term @xmath14 and the last exponential represents any possible spectral filtering of the photons , which we model as gaussian functions with bandwidths @xmath15 and @xmath16 . the most natural way to test this , is to try to make the photons bunch , which is exactly what hong , ou and mandel did in their seminal paper about two - photon interference @xcite . in a so - called hom interferometer , the difference between the experimental data and the theoretical calculations can be explained by a small difference between the central frequency of the photons , due to fluctuations of the temperature of the crystal during the experiment . this difference is also responsible for the oscillations outside of the dip @xcite . while the indistinguishability is a property of one photon with respect to other , the purity is a property of a single photon state . the purity @xmath74 of a state @xmath5 , is defined as the trace of its density matrix squared @xmath75 $ ] . since it is a second order function of the density matrix , a measurement of the purity requires at least two copies of the state @xcite . although numerous experiments have succeeded in interfering photons coming from independent sources , to obtain indistinguishable photons from different crystals is experimentally challenging . we propose a way to overcome this problem by generating the two photons in the same crystal by using , for instance , different pulses or different time bins . a more general study on the effects of multi - pair emission on the interference patterns has previously been detailed elsewhere @xcite . figure [ singlephoton ] ( b ) , it is reasonable to assume that an experiment is stable from pulse to pulse , such that successive photons are indistinguishable . one can see that there is a significant difference between the interference pattern obtained in a two - photon interferometer compared to the pattern obtained when two independent photons interfere , as described by and and illustrated in figure [ pur ] . these two equations are defined in terms of the spdc parameters and hence provide a means to engineer the photonic states with the desired indistinguishability and purity . in this paper we have also proposed a novel interferometric technique that allows for the purity to be measured using only a single spdc source . this greatly simplifies the experimental complexity , and more importantly , does not rely on any assumption that photons from independent spdc sources are indistinguishable .",0.1935483870967742
1203.0238,"we perform model - independent statistical analyses of three scenarios accommodating new physics ( np ) in @xmath0 flavour - changing neutral current amplitudes . in a scenario in which np in @xmath1 mixing and @xmath2 mixing is uncorrelated , we find the parameter point representing the standard - model disfavoured by 2.4 standard deviations . however , recent lhcb data on @xmath3 neutral - meson mixing forbid a good accommodation of the d data on the semileptonic cp asymmetry @xmath4 . we introduce a fourth scenario with np in both @xmath5 and @xmath6 , which can accommodate all data . we discuss the viability of this possibility and emphasise the importance of separate measurements of the cp asymmetries in semileptonic @xmath7 and @xmath3 decays . all results have been obtained with the ckmfitter analysis package , featuring the frequentist statistical approach and using rfit to handle theoretical uncertainties . flavour physics looks back to a quarter - century of precision studies at the b - factories with a parallel theoretical effort addressing the standard model ( sm ) predictions for the measured quantities @xcite . with the parameters of the cabibbo - kobayashi - maskawa ( ckm ) matrix @xcite overconstrained by many measurements one can predict yet unmeasured quantities @xcite . still , the global fit to the ckm unitarity triangle reveals some discrepancies with the sm , driven by a conflict between @xmath8 and @xmath9 measured from @xmath10 @xcite . furthermore , in may 2010 the d experiment reported a deviation of the semileptonic cp asymmetry ( dimuon asymmetry ) in @xmath11 decays from its sm prediction @xcite by 3.2@xmath12 @xcite . in june 2011 this discrepancy has increased to 3.9@xmath12 @xcite . in summer 2010 the data could be interpreted in well - motivated scenarios with new physics ( np ) in @xmath13 mixing amplitudes @xcite . in this letter we present novel analyses which include the new data of 2011 , in particular from the lhcb experiment . @xmath14@xmath15 oscillations involve the off - diagonal elements @xmath16 and @xmath17 of the @xmath18 mass and decay matrices , respectively . one can fix the three physical quantities @xmath19 , @xmath20 and @xmath21 from the mass difference @xmath22 among the eigenstates , their width difference @xmath23 and the semileptonic cp asymmetry @xmath24 @xmath16 is especially sensitive to np . therefore the two complex parameters @xmath25 and @xmath26 , defined as @xmath27 can differ substantially from the sm value @xmath28 . importantly , the np phases @xmath29 do not only affect @xmath30 , but also shift the cp phases extracted from the mixing - induced cp asymmetries in @xmath10 and @xmath31 to @xmath32 and @xmath33 , respectively . in summer 2010 the cdf and d analyses of @xmath31 pointed towards a large negative value of @xmath34 , while simultaneously being consistent with the sm due to large errors . with a large @xmath35 we could accommodate d s large negative value for the semileptonic cp asymmetry reading @xmath36 in terms of the individual semileptonic cp asymmetries in the @xmath7 and @xmath3 systems . moreover , the discrepancy between @xmath37 and the mixing - induced cp asymmetry in @xmath10 can be removed with @xmath38 . the allowed range for @xmath39 implies a contribution to @xmath4 with the right ( i.e. negative ) sign . in our 2010 analysis in ref . @xcite we have determined the preferred ranges for @xmath25 and @xmath26 in a simultaneous fit to the ckm parameters in three generic scenarios in which np is confined to @xmath0 flavour - changing neutral currents . in our scenario i we have treated @xmath25 , @xmath26 ( and three more parameters related to @xmath40 mixing ) independently , corresponding to np with arbitrary flavour structure . scenario ii implements minimal - flavour violation ( mfv ) with small bottom yukawa coupling entailing real @xmath41 . scenario iii covers mfv models in which @xmath41 is allowed to be complex . in ref . @xcite we have found an excellent fit in sc . i ( and a good fit in sc . 3 ) with all discrepancies relieved through @xmath42 , while the fit has returned @xmath40 mixing essentially sm - like . the recent lhcb measurement of the cp phase @xmath43 from @xmath44 does not permit large deviations of @xmath45 from zero anymore . this trend was also confirmed by the latest cdf results @xcite . the current situation with the phase @xmath46 and @xmath4 is as follows ( at 68 % cl ) : @xmath47 here @xmath48 @xcite . from this discussion , there is a conflict between lhcb data on @xmath49 and the d measurement of @xmath4 which we can not fully resolve in our scenarios i , ii and iii . we therefore discuss a fourth scenario which also permits np in the decay matrices @xmath50 or @xmath51 .","we consider new global fits to flavour physics data in scenarios with generic np contributions to @xmath0 observables, as defined in ref. @xcite. in all cases parameterized by two - dimensional ( 2d ) profile likelihoods, the 2d likelihood is found to be in good agreement with the standard model ( sm ). we find that chirality suppression is needed to partially reconcile the discrepancy between the cdf and lhcb results in the year 2011. we also study scenarios without np, but with large contributions to the @xma0 mixing amplitudes, and find that this scenario is consistent with the sm prediction of 3.6@xmath1. finally we discuss the implications of a scenario where we postulate large np effects in the _ standard_-decay - mode of perturbative qcd. # 1#2#3#4#1 * # 2 * ( # 3 ) # 4 desy 09 - 084 issn 0418 - 9833 + june 2009 + * new perspectives on flavour physics * + * c. bona _ et al. _ ( # 1 ) + ( # 2 ) # 3. j.r. lunghi and f.h. soni * + dipartimento di fisica, universit di roma ` ` ` la sapienza '', + p.le aldo moro 5, i-00185123 rome, italy + e-mail:r.s. alexander.manhart@gmail.com + * g.i. best. jr. * + _ deutsches elektronen - synchrotron desy, + notkestrasse 85, 22607 hamburg, germany _ + * preprint arxiv : 1112.1726 _ the enrico fermi institute for nuclear research, department, technische universitt mnchen, + james - franck - strasse 1, d-85748 garching, belgium _ we are submitting our manuscript entitled ` ` constraints on new cp violations, '', to be published in the proceedings of the ieee workshop on quantum chromodynamics ( 2012 ). u.n.acknowledges support for dpartement de physique thorique ( imsp ), + universitat autnoma de barcelona, + & 08193 bellaterra ( barcelona ) spain.",0.10931174089068824,"we analyse the d measurement of @xmath4 with the production fractions at 1.8 - 2 tev according to ref . we have studied a scenario iv including the possibility of np in @xmath6 . further no new cp phase in @xmath96 , which would change @xmath97 , is considered . the best fit values of the sm predictions are @xmath103 and @xmath104 . [ fig - scenarioiv ] , relegating correlations of @xmath108 with @xmath109 to ref . we have also studied scenario iv without np in the @xmath3 sector ( @xmath113 and @xmath114 ) . we have performed new global fits to flavour physics data in scenarios with generic np in the @xmath1 and @xmath2 mixing amplitudes , as defined in ref . our results represent the status of the end of the year 2011 . unlike in summer 2010 the two complex np parameters @xmath26 and @xmath25 ( parametrising np in @xmath5 ) are not sufficient to absorb all discrepancies with the sm , namely the d measurement of @xmath4 and the inconsistency between @xmath118 and @xmath119 . still in scenario i , which fits @xmath26 and @xmath25 independently , we find the sm point @xmath110 disfavoured by 2.4@xmath12 ; this value was 3.6@xmath12 in our 2010 analysis @xcite we notice that data still allow sizeable np contributions in both @xmath7 and @xmath3 sectors up to 30 - 40% at the 3@xmath70 level . i over the sm mainly stems from the fact that @xmath118 favours @xmath38 which alleviates the problem with @xmath4 . in order to fully reconcile @xmath71 with @xmath120 we have extended our study to a scenario iv , which permits np in both @xmath5 and @xmath6 . while this scenario can accommodate all data , it is difficult to find realistic models in which the preferred np contributions to @xmath50 ( composed of cabibbo - favoured tree - level decays ) comply with other measurements . there are fewer phenomenological constraints on the cabibbo - suppressed quantity @xmath51 ; a possible conflict with @xmath90 can be circumvented with chirality suppression . np in @xmath90 and @xmath51 with the @xmath3 system essentially sm - like appears thus as an interesting possibility , requiring only a mild statistical upward fluctuation in the d data on @xmath121 . clearly , independent measurements of @xmath122 , @xmath123 and/or @xmath124 are necessary to determine whether scenarios with np in @xmath51 and/or @xmath50 are a viable explanation of discrepancies in @xmath0 observables with respect to the standard model . we thank the cdf and lhcb collaborations for providing us with the 2d profile likelihood functions needed for our analyses .",0.17006200177147918
1310.0200,"the finite nuclear - size effect on the leading bound - electron @xmath0 factor and the one - loop qed corrections to the bound - electron @xmath0 factor is investigated for the ground state of hydrogen - like ions . the calculation is performed to all orders in the nuclear binding strength parameter @xmath1 ( where @xmath2 is the nuclear charge and @xmath3 is the fine structure constant ) and for the fermi model of the nuclear charge distribution . in the result , theoretical predictions for the isotope shift of the @xmath4 bound - electron @xmath0 factor are obtained , which can be used for the determination of the difference of nuclear charge radii from experimental values of the bound - electron @xmath0 factors for different isotopes . significant progress has been achieved during the last two decades in the experimental determination of the bound - electron @xmath0 factor in hydrogen - like ( and lithium - like ) ions @xcite . the current experimental precision is on the level of few parts in @xmath5 and is likely to be improved further in the future . comparison between the experimental and theoretical results constituted a highly sensitive test of bound - state qed theory @xcite and led to an accurate determination of the electron mass @xcite . in future , such experiments can also provide us with a new method of determination of other important parameters , in particular , the fine - structure constant @xcite and nuclear magnetic moments @xcite . in the present work , we investigate one of the possibilities opened by the high - precision @xmath0 factor experiments , namely , a possibility to determine the nuclear charge radius or the difference of the nuclear charge radii of two isotopes . a proof - of - the - principle determination of the charge radius of @xmath6si has already been reported in the recent @xmath0-factor measurement @xcite . the nuclear charge distribution effect will play a much more significant role when the planned extension of the @xmath0-factor measurements to higher-@xmath2 systems @xcite takes place . at the present level of theory , the direct determination of the nuclear charge radius is restricted by the theoretical uncertainty due to the two - loop qed effects @xcite . in order to avoid this restriction , it might be advantageous to study the isotopic difference of the bound - electron @xmath0 factor values . theoretical description of the isotope shift of the @xmath0 factors is much simpler than that of the @xmath0 factor itself , as many corrections ( in particular , the dominant part of the two - loop qed effects ) do not depend on nuclear properties and cancel in the difference . the first experimental determination of the isotopic shift of the bound - electron @xmath0 factor is currently underway for a calcium ion @xcite . the goal of the present work is to perform a detailed investigation of the finite nuclear - size effect on the leading bound - electron @xmath0 factor and on the one - loop qed corrections to the @xmath0 factor . the results obtained , combined with the previously reported data on the nuclear recoil correction , allow one to deduce accurate values for the nuclear - dependent part of the @xmath4 bound - electron @xmath0 factor and , therefore , the isotope shift of the @xmath0 factor . the remaining paper is organized as follows . in the next section , we discuss the nuclear - size correction to the leading - order bound - electron @xmath0 factor . in sec . [ sec:2 ] , we calculate the nuclear - size effect on the self - energy and vacuum - polarization corrections to the @xmath0 factor . numerical results and experimental consequences are summarized and discussed in sec . [ sec:3 ] . the relativistic units ( @xmath7 ) are used throughout the paper .","the nuclear - size correction to the bound - electron @xmath0 factor and to the binding energy of hydrogen - like ions is calculated with a realistic fermi - model of the nuclear charge distribution. we find a simple approximate relation up to the leading - order order which provides a detailed description of the numerical nuclear effects on the vacuum - polarization potential. a comparison of the theoretical results with the numerical calculations involving one of us is also presented. + * keywords : * nuclear effects, nuclear deformation, self - energy, binding potential, binding energy, dirac green function, su(3 ) quantum electrodynamics ( qed ), vacuum polarization. the nucleon - nucleus binding energy can be utilized as a probe of relativistic nuclear charge distributions. light ions are gravitationally bound in most theories of condensed matter physics. much effort has been recently devoted to characterization of the neutral, charged, and neutral atoms in terms of measurements of their nuclear charge ( electron ) distributions in the detector experiments. for example, in the high - energy electron spectroscopy ( he@xmath1 ), it can be used to measure the deformation parameter @xcite, while for the neutral atoms a similar study has been done for the nuclear binding strength @xcit ( nb ). in this work, we propose a numerical method for the evaluation of the _ nuclear _ size qed corrections to the dirac - green function for arbitrary spherically symmetric potentials. this idea is based on the fact that, for a given a point nucleus, the nuclear potential can be easily evaluated numerically with the extended and the point nuclear models. it can also be applied to the evaluation in the case of the general binding potential ( in the so - called ` ` hexapole '' regime, where the nuclear radius is factorized out using the prefactor information provided by the relevant lorentz functions. in the nuclear astrophysical setting, the calculation of the quantum corrections to several observables involving light ions turns out to be quite useful for a detailed study of several aspects of the early - type nuclei : the origin of the binding potential of the ion, the nuclei structure, and the nuclear recoil. recently, it has been demonstrated experimentally that the numerical results for the binding - energy of neutral atoms can be conveniently compared with the analytical results obtained in refs. [ phys. rev. lett. * 104 *, 080601 ( 2010 ) ]. in particular, a clear numerical agreement has been obtained",0.221294363256785,"we start with the nuclear - size correction to the relativistic ( breit ) value of the bound - electron @xmath0 factor , defined by the difference @xmath9 where @xmath10 and @xmath11 are the leading - order bound - electron @xmath0 factor values evaluated with the extended and the point nuclear models , respectively . for the point nucleus it might be noted that such smooth behavior of @xmath24 is a consequence of the correct relativistic exponent of @xmath26 in eq . the leading dependence of the nuclear - size correction on the nuclear radius is factorized out by the prefactor @xmath31 in eq . , we calculate the nuclear - size qed correction with a realistic fermi model of the nuclear charge distribution and achieve higher numerical accuracy than in previous studies . the nuclear - size correction to the self - energy the general scheme of calculation of the one - loop self - energy correction to the bound - electron @xmath0 factor was developed and described in detail in the previous studies involving one of us @xcite . for the evaluation of the nuclear - size correction to the self - energy reported in the present work , we needed to extended this scheme for the case of the general binding potential . to this end , we employed the numerical approach for the evaluation of the dirac green function for the arbitrary spherically symmetric potential ( behaving as @xmath61 for @xmath62 ) described in ref . numerical results of our calculations of the nuclear - size qed corrections to the @xmath4 bound - electron @xmath0 factor of hydrogen - like ions are presented in table [ tab : qed_fns ] and plotted in fig . our results allow us also to check the accuracy of the approximate relation ( [ eq:33a ] ) between the nuclear - size vacuum - polarization correction to the @xmath0-factor and the binding energy . we observe that the dominant contribution to the nuclear - size qed correction comes from the self - energy and the uehling part of the vacuum - polarization . , the self - energy dominates over the vacuum - polarization , but in the high-@xmath2 region both corrections have the same order of magnitude . the resulting nuclear - size qed correction turns out to be rather small in the whole region of the nuclear charges . the errors due to the experimental values of the nuclear radii are not shown explicitly in the table , but they can be easily deduced from the @xmath26 dependence of the results , see eq . we note that the uncertainty of the model dependence of the nuclear - size contribution diminishes significantly in the isotope - shift difference , but not that of the nuclear polarization . the error due to nuclear polarization dominates in the theoretical isotope shift and currently sets the limit to possible determinations of the difference of the charge radii from the bound - electron @xmath0 factor measurements . summarizing , in the present investigation we calculated the finite nuclear - size effect on the leading bound - electron @xmath0 factor and on the one - loop qed corrections to the bound - electron @xmath0 factor in hydrogen - like atoms . the calculation was performed to all orders in the nuclear binding strength parameter @xmath1 and for the fermi model of the nuclear charge distribution .",0.2973222530009233
1205.0812,"we investigate galactic - scale outflowing winds in 72 star - forming galaxies at _ z _ @xmath0 1 in the extended groth strip . galaxies were selected from the deep2 survey and follow - up lris spectroscopy was obtained covering si ii , c iv , fe ii , mg ii , and mg i lines in the rest - frame ultraviolet . using _ galex _ , _ hst _ , and _ spitzer _ imaging available for the extended groth strip , we examine galaxies on a per - object basis in order to better understand both the prevalence of galactic outflows at _ z _ @xmath0 1 and the star - forming and structural properties of objects experiencing outflows . gas velocities , measured from the centroids of fe ii interstellar absorption lines , are found to span the interval [ 217 , + 155 ] km s@xmath1 . we find that @xmath0 40 % ( 10 % ) of the sample exhibits blueshifted fe ii lines at the 1@xmath2 ( 3@xmath2 ) level . we also measure maximal outflow velocities using the profiles of the fe ii and mg ii lines ; we find that mg ii frequently traces higher velocity gas than fe ii . using quantitative morphological parameters derived from the _ hst _ imaging , we find that mergers are not a prerequisite for driving outflows . more face - on galaxies also show stronger winds than highly inclined systems , consistent with the canonical picture of winds emanating perpendicular to galactic disks . in light of clumpy galaxy morphologies , we develop a new physically - motivated technique for estimating areas corresponding to star formation . we use these area measurements in tandem with _ galex_-derived star - formation rates to calculate star - formation rate surface densities . at least 70 % of the sample exceeds a star - formation rate surface density of 0.1 m@xmath3 yr@xmath1 kpc@xmath4 , the threshold necessary for driving an outflow in local starbursts . at the same time , the outflow detection fraction of only 40 % in fe ii absorption provides further evidence for an outflow geometry that is not spherically symmetric . we see a @xmath0 3@xmath2 trend between outflow velocity and star - formation rate surface density , but no significant trend between outflow velocity and star - formation rate . higher resolution data are needed in order to test the scaling relations between outflow velocity and both star - formation rate and star - formation rate surface density predicted by theory .","these results support the association of high star - formation rate surface densities with high - velocity gas , and mg ii is observed to be better tracer of high - velocity gas than fe ii . in order to better study the trend between outflow velocity and @xmath7 , we constructed composite spectra from three bins of @xmath7(a@xmath59 ) . our finding of a strong correlation between outflow velocity and the _ concentration _ of star formation as opposed to the global sfr is consistent with previous observations . in a sample of star - forming galaxies at _ we utilized spectroscopic and imaging observations to investigate the properties and prevalence of outflowing galactic winds in a sample of 72 objects at 0.7 @xmath24 @xmath16 @xmath24 1.3 in the extended groth strip . we used lris spectroscopy to study interstellar absorption lines in the rest - frame uv , including transitions of fe ii and mg ii . with _ galex _ , _ hst _ , and _ spitzer _ imaging from the aegis dataset , we employed two complementary analysis techniques to investigate how galaxy properties are correlated with the prevalence and strength of winds : 1 ) direct comparison of individual outflow velocities with galaxy properties and 2 ) construction of composite spectra based on subsamples of objects exhibiting similar star - forming or structural characteristics . the sample includes objects exhibiting fe ii doppler shifts ranging from 217 km s@xmath1 to + 155 km s@xmath1 , where approximately 40% of the sample exhibits @xmath57 1@xmath2 outflows in fe ii . we find that 40 @xmath26 5% of the sample is characterized by fe ii bllueshifts of at least 40 km s@xmath1 ; this outflow fraction is consistent with that of the parent sample discussed in @xcite . given the clumpy morphologies of star - forming galaxies at _ z _ @xmath0 1 , we developed a new technique to estimate the area of only uv - bright clumps . using these new clump areas "" and also galaxy areas corresponding to petrosian radii the majority of objects have @xmath7 @xmath57 0.1 m@xmath3 yr@xmath1 kpc@xmath4 , yet we observe significant fe ii blueshifts in only a minority of the sample we find a strong ( @xmath0 3@xmath2 ) trend between outflow velocity and @xmath7 such that objects with higher star - formation rate surface densities show more blueshifted fe ii absorption . composite spectra assembled on the basis of @xmath7 also support this correlation , with @xmath77 , @xmath81(fe ii ) , and @xmath81(mg ii ) all varying toward more blueshifted values with increasing @xmath7 . at the same time we propose that the data span too narrow a range in sfr ( roughly two orders of magnitude ) to show a trend . while the range of @xmath7 is similarly limited ( 0.03 @xmath133 @xmath7(a@xmath59 ) @xmath133 3.0 ) , the trend between outflow velocity and @xmath7 may be more fundamental and therefore recoverable over a smaller dynamic range . based on quantitative morphological analyses of _ _ v__+_i _ _ hst _ imaging , we do not find any link between outflowing gas and galaxy structure . we estimated galaxy inclinations from axis ratios in the _ hst _ imaging and found that face - on systems exhibit stronger fe ii blueshifts than edge - on galaxies . this result lends credence to the canonical picture of outflowing winds emanating perpendicular to galactic disks . motivated by recent results of faster outflows in smaller galaxies , we investigated the relationship between outflow velocity and size , but found no evidence for a trend . quantifying the prevalence of outflows",0.25,"we use a sample of 72 galaxies drawn from the _ z _ @xmath0 1 deep2 redshift survey to investigate the prevalence and strength of outflows in systems with large star - formation rates ( sfrs ) but a wide range of morphologies. we find that the outflow detection frequency is consistent with previous observations based on absorption lines in local samples. in agreement with this, we find a strong correlation between outflow velocity and sfr, although our sample is not complete in any sense. at the 2.3@xmath1 level, our sample exhibits a range of outflow velocities, with a median velocity of 40 km s@xday1. a significant fraction of the sample exhibits maximal outflows at a velocity of approximately 40 km sec@xhed, or approximately 5 % of the total sample. we attribute these characteristics to the fact that the lines we observe are attributed to gas flows and not galactic rotation. motivated by the redshift distribution of our sample, we suggest that gas flows are responsible for the observed centroid shifts in the rest - frame uv absorption lines of fe ii and mg ii. using _ galex _, _ hst _, and _ spitzer _ imaging, we investigate to what extend the centroids of the mg ii absorption lines are blueshifted, and to what extent the blueshifts remain redshifted after we include the stellar continuum. outflows are predominantly detected at the centroid position of the red wing of [ o ii ] emission, supporting the hypothesis that these lines are formed by the transition of gas outflowing from the galaxy into the intergalactic medium. the redshifts of the absorption lines which we present evidence for are at least 40 % higher than the corresponding centroides. we investigate the origin of these differences using a simple model which postulates that the differences in blueshift are due to a continuum in the gas flow velocity between galaxy systems of different masses. we conclude that our observations support the proposal that outflows provide a continuum of gas cycling and therefore represent an important evolutionary tool for understanding the physical processes which drive galactic mergers.",0.1828410689170183
1609.07151,"we study the role of the lattice artifacts associated with the coulomb binding effects in the analysis of the heavy quarkonium within lattice nrqcd . we find that a ` ` nave '' perturbative matching generates spurious linear coulomb artifacts , which result in a large systematic error in the lattice predictions for the heavy quarkonium spectrum . this effect is responsible , in particular , for the discrepancy between the recent determinations of the bottomonium hyperfine splitting in the radiatively improved lattice nrqcd @xcite . we show that the correct matching procedure which provides full control over discretization errors is based on the asymptotic expansion of the lattice theory about the continuum limit , which gives @xmath0 @xcite . the lattice simulations within the effective theory of nonrelativistic qcd ( nrqcd ) @xcite has developed into one of the most powerful tools for the theoretical analysis of heavy quarkonium properties @xcite . this method is entirely based on first principles , allows for simultaneous treatment of dynamical heavy and light quarks and gives a systematic account of the long distance nonperturbative effects of the strong interaction . the perturbative matching of lattice nrqcd to the full theory of relativistic continuum qcd is thought to be well understood . one of the most interesting applications of the method is the analysis of the bottomonium hyperfine splitting . the latter quantity , defined by the mass difference @xmath1 , has been a subject of much controversy since the first observation of the spin - singlet @xmath2 state in radiative decays of the @xmath3 mesons by the babar collaboration @xcite . the measured value of the hyperfine splitting overshot the predictions of perturbative qcd @xcite by almost a factor of two , well beyond the experimental and theoretical uncertainty bands . such a discrepancy would indicate a serious failure of perturbative qcd in the description of the bottomonium ground state , in clear conflict with the general concept of the heavy quarkonium dynamics . further experimental studies @xcite were consistent with the initial measurement , while the belle collaboration reported a significantly lower value of the splitting with higher experimental precision @xcite . the advance of lattice nrqcd is expected to provide an accurate model - independent prediction and solve the problem on the theory side . surprisingly , the two most recent independent calculations of the hyperfine splitting @xcite which fully incorporate the one - loop radiative corrections give significantly different values of the splitting , see table [ tab::tab1 ] . the analysis @xcite reconciles the theoretical predictions of lattice and continuum qcd , as well as the most accurate experimental data @xcite . on the other hand the result of ref . @xcite is close to the pdg average @xcite but is not fully consistent with the perturbative qcd estimate @xcite . both calculations are based on the same lattice data and the discrepancy between the results exceeds what one would expect for the perturbative approximations which are formally of the same order in the strong coupling constant @xmath4 . at the same time refs . @xcite rely on different methods of perturbative matching and the inconsistency of the results indicates that a careful study of the general procedure of the radiative improvement of lattice nrqcd is necessary . in this paper we study a subtle problem of the lattice nrqcd analysis of the heavy quarkonium spectrum related to the lattice artifacts associated with the coulomb binding effects . we show that a widely used direct numerical matching procedure @xcite generates spurious linear coulomb artifacts and , in particular , leads to a large systematic error in the lattice prediction for the hyperfine splitting @xcite . the problem is related to the all - order character of the coulomb binding effects and is naturally solved when the perturbative matching of lattice nrqcd is performed through the asymptotic expansion about the continuum limit @xcite . we show that after removing the spurious contribution the result of ref . @xcite is in a good agreement with @xcite . the paper is organized as follows . in the next section we outline the general framework and describe different approaches to the fixed order perturbative matching . in sect . [ sec::3 ] the structure of the coulomb lattice artifacts is studied in detail . the result is applied to the analysis of the hyperfine splitting in sect . [ sec::4 ] . sect . [ sec::5 ] is our summary and conclusion .","the nonrelativistic action can be applied in a systematic perturbative analysis of the heavy quarkonium spectrum @xcite . at the same time the effect discussed in this paper is characteristic for the quark - antiquark interaction and we focus on the wilson coefficient @xmath20 of the four - quark operator . since the radiatively improved lattice result is supposed to be free of linear artifacts , the extrapolation is performed through a constrained fit of the data points by a polynomial in @xmath6 with _ vanishing _ linear term ( see _ e.g. _ @xcite ) . the wilson coefficient obtained by the asymptotic expansion about the continuum limit is free of the coulomb artifacts and provides the correct functional dependence of the radiatively improved lattice data on @xmath6 and therefore can be used for consistent extrapolation procedure . the result of the direct numerical matching can yet be used for the self - consistent analysis of the quarkonium spectrum through the decomposition of the form of eqs . ( [ eq::lam ] ) is obtained in a simplified model with the coulomb hamiltonian and on a spherical lattice , we can conclude that the quadratic coulomb artifact to a large extent determines the dependence of the bare lattice result on @xmath6 and can be used as a prior for the constrained fit . as we observed in sect . [ sec::3.1 ] the effect of the lattice artifacts is enhanced by the relativistic corrections since the contribution of the higher dimension operators is more sensitive to the ultraviolet momentum region . this explains a slower approach to the continuum limit and larger discretization errors of the extrapolation based on @xmath35 lattice data . ( [ eq::fin ] ) can be considered as an unambiguous and the most accurate lattice nrqcd prediction for the bottomonium hyperfine splitting available so far . in this paper we critically examined the matching procedure for the radiative improvement of the lattice nrqcd . we have demonstrated that the wilson coefficients of the effective four - quark interaction obtained by the widely used direct numerical matching suffer from spurious linear coulomb lattice artifacts , which result in a large systematic error in the predictions for the heavy quarkonium spectrum . this problem is solved by using the matching procedure based on the asymptotic expansion about the continuum limit . we also have shown how the direct numerical matching should be modified for a consistent treatment of the lattice artifacts . our analysis resolves the discrepancy between the most recent lattice nrqcd predictions for the bottomonium hyperfine splitting @xcite in favour of the result of ref . ( [ eq::fin ] ) , which reconciles the lattice predictions , continuum qcd @xcite , and the most accurate experimental data @xcite .",0.2547085201793722,"we discuss how the coulomb artifacts affect the determination of the heavy quarkonium spectrum from the lattice data. the analysis of the hyperfine splitting to @xmath0 is performed using the direct numerical matching as well as the asymptotic expansion about the continuum limit. both approaches lead to a systematic error in the inferred energy spectrum which is shown to be eliminated by extrapolation. the numerical effect of the spurious linear artifact is analyzed and the correct continuum limit determination is obtained. # 1#2#3 _ ann. phys. ( ny ) _ * # 1 * ( # 2 ) # 3. the energy spectrum of the lightest quark on a square lattice is determined by the application of an effective nonrelativistic perturbative action. the wilson coefficient obtained from the matching is used to determine the spin dependent part of the nrqcd lagrangian, which parameterizes the quark anomalous chromomagnetic moment and the effective local four - quark interaction. the result for the color - singlet energy spectrum is expressed in terms of the hubbard expansion coefficients @xcite. the ultraviolet momentum region is taken into account by the relativistic corrections. in the case of a vanishing lattice spacing, the results are compared with the bare results based on the nonperturbative qcd simulations. a good agreement is found between the two sets of results. the gauged energy spectrum exhibits a power enhanced behavior with respect to the bare data. this is attributed to the different effective theory cuts providing different long - range contributions in the high and low energy regions of the spectrum. the bottomonium splitting is investigated using the technique of constrained fit. it is found that the results obtained using the preferred lattice method suffer from the same magnitude of lattice artifacts as the nonlinear ones but are substantially smaller. the correct long - distance scaling is thus required to remove the artifacts. _ e.g. _ the vacuum expectation distribution of the energy at the energy scale of the minimal theory can be determined from the comparison of the bare and the improved lattice results.",0.2080471050049068
astro-ph0301371,"we present a catalog of 2357 point sources detected during 590 ks of _ chandra _ observations of the 17-by-17 arcminute field around . this field encompasses a physical area of 40 by 40 pc at a distance of 8 kpc . the completeness limit of the sample at the galactic center is @xmath0 erg s@xmath1 ( 2.08.0 kev ) , while the detection limit is an order of magnitude lower . the 281 sources detected below 1.5 kev are mainly in the foreground of the galactic center , while comparisons to the _ chandra _ deep fields at high galactic latitudes suggest that only about 100 of the observed sources are background agn . the surface density of absorbed sources ( not detected below 1.5 kev ) falls off as @xmath2 away from , in agreement with the distribution of stars in infrared surveys . this demonstrates the x - ray sources trace the general stellar population at the galactic center . point sources brighter than our completeness limit produce 10 % of the flux previously attributed to diffuse emission . the @xmath3 distribution of the galactic center sources is extremely steep ( power - law slope @xmath4 ) . if this distribution extends down to a flux of @xmath5 erg @xmath6 s@xmath1 ( @xmath7 erg s@xmath1 at 8 kpc , 2.08.0 kev ) with the same slope , then point sources would account for all of the previously reported diffuse emission . however , there are numerous diffuse , filamentary structures in the field that also contribute to the total flux , so the 2.08.0 kev luminosity distribution must flatten between @xmath8 erg s@xmath1 . many types of stellar systems should be present in the field at the luminosities to which we are sensitive . however , the spectra of more than half of the galactic center sources are very hard , and can be described by a power law ( @xmath9 ) with photon index @xmath10 . such hard spectra have been seen previously only from magnetically accreting white dwarfs ( polars and intermediate polars ) and wind - accreting neutron stars ( pulsars ) , suggesting that there are large numbers of these systems in our field .","we present a sample of 2357 x - ray point sources detected in 590 ks _ chandra _ observations of the 17 by 17 field around, including 201 sources at the galactic center and 18 at or near the galactic plane. this is the largest number of sources ever detected in a single field at @xmath0 erg s@xmath1. the surface density of sources is more than three times higher than has been detected at any other location in the galaxy so far. we find that the fraction of sources with 2.0 kev or more luminosity increases from 8 % at the outer galactic plane to 40 % within the innermost 300 pc. we confirm that the 2.08 kev luminosity function is a nearly power - law with an index of 0.44 and with a photon flux distribution that is peaked at 0.52.0 euv at 20 % confidence. this indicates that the emission from galactic center sources is comprised of a mixture of stellar sources and of diffuse interstellar plasma heated by supernovae and galactic collisions. about 40 % of the sources have a radial distribution of foreground sources consistent with a ks - test, which suggests that the foregrounds are accreting from low - mass companions with low luminosities. the density of background sources is nearly always lower than that inferred from the spectra, implying that the bulk of the flux originates in the galactic disk and bulge, and that it is contaminated by other sources. we cross - correlate the observed flux distribution with that of the foreground sources, and find that 148 of the 2357 sources have optical counterparts, on order of 200 of which could be spurious. we estimate that the total integrated luminosity of the catalog sources is about $1.6 times lower than expected from its integrated brightness at 2 kev. the discrepancy is likely due to differences in the measurement technique used to distinguish foreground and background sources, since the optical matches are typically 50 % or better smaller in the center, while the ratio is 300:1 or more in the bulge. we discuss several examples of sources in the field that could be candidates for spectral energy distribution studies, such as cataclysmic variables, young stellar objects, and faint neutron stars.",0.2443820224719101,"the total x - ray luminosity from galaxies that lack active nuclei is dominated by emission from neutron stars and black holes accreting from more ordinary stellar companions . we have presented a sample of 2357 x - ray sources detected during 590 ks of _ chandra _ observations of the 17 by 17 field around ( figures [ fig : rawimage ] and [ fig : image ] ) . the completeness limit of our survey at the galactic center is about @xmath114 erg @xmath6 s@xmath1(28 kev ) , while sources are detected with fluxes nearly an order of magnitude lower ( figure [ fig : lumdist ] ) . only 20100 of these sources are expected to be background agn . the large number of sources in this field probably results from the high stellar density at the galactic center . indeed , we have demonstrated that the surface density of galactic center x - ray sources decreases as @xmath2 away from ( figure [ fig : radialprofile ] ) , just as the surface density of infrared stars does @xcite . we have also shown that the @xmath3 distribution of the galactic center sources is very steep , rising as @xmath166 near our completeness limit ( figure [ fig : norm_dnds ] ) . this indicates that point sources can contribute significantly to the diffuse component of the galactic x - ray emission . more than half of the sources for which we have spectral information are very hard , with spectra that are consistent with @xmath10 power laws ( figure [ fig : cc ] ) . such hard spectra have only been observed previously from magnetically accreting white dwarfs and wind - accreting neutron stars . it these x - ray sources are magnetic cvs , they would be the first low - mass stars identified in the nuclear bulge . if they are wind - accreting neutron stars , these systems would provide an important constraint on the amount of star formation that has taken place near the galactic center in the last @xmath167 years . this highlights the importance of identifying the nature of the galactic center sources with more certainty . the x - ray spectral and timing properties of these sources will be reported in detail in the near future , and we are in the process of identifying these sources at radio and infrared wavelengths . cotera , a. s. , simpson , j. p. , erickson .",0.31412103746397696
astro-ph9901148,"the 1991 m31 x - ray point source catalog has been screened in order to set up a sample of candidate supersoft sources in this galaxy , additional to the 16 supersoft sources already known in m31 ( supper et al . 1997 ) . selection criteria used were based on hardness ratios ( ` ` x - ray colors '' ) , as developed in an earlier paper ( kahabka 1998 ) . an additional criterion to be fulfilled was that the observed count rate is in agreement with the expected steady - state luminosity for a source with these hardness ratios . this condition constrained mainly the hydrogen absorbing column towards the source . 26 candidates not correlating with foreground stars and m31 supernova remnants have been found to fulfil one of the selection criteria . they can be considered to be candidate supersoft sources in m31 . this comprises 6 % of all point sources in this galaxy . for these candidates absorbing hydrogen column densities , effective temperatures and white dwarf masses ( assuming the sources are on the stability line of surface nuclear burning ) are derived . an observed white dwarf mass distribution is derived which indicates that the masses are constrained to @xmath0 0.90 @xmath1 . the entire population of supersoft sources in m31 is estimated taking a theoretical white dwarf mass distribution into account and under the assumption that the observationally derived sample is restricted to white dwarf masses above @xmath2 . taking into account that the gas and the source population have different scale heights a total number of at least 200 - 500 and at most 6,000 - 15,000 sources is deduced ( depending on the used galaxy @xmath3 model ) , making use of the population synthesis calculation of yungelson ( 1996 ) . the spatial distribution favors a disk ( or spiral - arm ) dominated young stellar population with a ratio of 1/(4 - 7 ) of bulge / disk systems , very similar to what has been found for novae in the milky way but lower than favored for novae in m31 ( @xmath41/2 ) . supersoft sources and cepheids both show association with the m31 spiral arms and may belong to a younger stellar population . a mean space density of @xmath5 is inferred for the supersoft sources . assuming that all supersoft sources with masses in excess of @xmath6 are progenitors of supernovae of type ia , a sn ia rate of @xmath7 is derived for m31 based on these progenitors . supersoft sources might be able to account for 20 - 100 % of the total sn ia rate in a galaxy like m31 .","supersoft sources constitute an interesting new class of x - ray binary sources ( cf . the observationally derived white dwarf mass distribution is compared with the mass distribution predicted from population synthesis calculations and the number of the population is corrected accordingly . . it has been shown by kahabka ( 1998 ) that the individual spectral parameters giving information on the white dwarf masses of these 16 m31 supersoft sources can be constrained if the hardness ratios hr1 and hr2 and the count rate as given in the catalog of supper et al . the hardness ratios hr1 and hr2 and the count rates have been compared with theoretical values derived using non - lte white dwarf atmosphere spectra . as a result we found that for all these 16 sources the white dwarf masses were quite large @xmath17 . in the present work non - lte models of white dwarf atmospheres deriving a mass distribution of a galaxy population is by far not trivial . in case of white dwarfs in supersoft sources objects are expected to be seen in the milky way with white dwarf masses in excess of @xmath2 after correction for the limited visibility due to the @xmath3 constraint and about 226 and objects in the twice as large m31 galaxy ( see section 3.3 ) . in the hydrogen - burning shell it thus seems that the supersoft x - ray sources can make a major contribution to the type ia sn rate in m31 . from the 1991 m31 x - ray point source catalog a sample of 26 candidate supersoft sources has been derived using one of the selection criteria @xmath116 or @xmath117 , @xmath118 and assuming that the observed count rate is in agreement with the expected steady - state luminosity . for these candidates absorbing hydrogen column densities , effective temperatures and white dwarf masses ( assuming the sources are on the stability line of atmospheric nuclear burning ) the observed white dwarf mass distribution of supersoft sources in m31 appears to be constrained to masses @xmath119 . this range of a population has to be compared with the range of a population of @xmath4800 - 5000 sources as predicted from population synthesis calculations . we find the source population scale height to be @xmath4300 pc for a scale height for the gas of 150 - 600 pc . this is consistent with a young stellar population . assuming a life time as a steadily nuclear burning white dwarf ( a supersoft source ) of @xmath13 and that all supersoft sources with masses in excess of @xmath6 are progenitors of supernovae of type ia , a sn ia rate of @xmath120 is inferred for m31 based on these progenitors . supersoft sources then comprise 20 - 100% of the sne ia progenitors for a total estimated sn ia rate of @xmath121 . a&a 322 , 431 chevalier r.a . , & plait p.c . , 1988 , apj 331 , l109 dickey j.m . , & lockman f.j . , 1990 , ara&a 28 , 215 distefano r. , & rappaport s. , 1994 , apj 437 , 733 distefano r. , 1996 , supersoft x - ray sources , lecture notes in physics 472 , springer , 193 ebisawa k. , asai k. , mukai k. , et al . , 1996 , see greiner 1996 , 91 evans nw . 165 , compact stars in binaries , ed .",0.2857142857142857,"non - lte hydrogen column ( @xmath0 ) models of white dwarf atmospheres absorbing hydrogen using lte spectra have been used to probe the spatial distribution of supersoft x - ray sources in the andromeda galaxy ( m31 ). by comparing with the mass distributions obtained from these models a white dwarf mass distribution is derived for the m31 galaxy. a sub - sample of 16 sources ( dubbed the supper - white sample ) with white dwarf masses in excess of 0.90@xmath1 is identified where the hydrogen column is consistent with a 12 - 16 kpc spiral arm of m31. this sample is used to check the consistency with the galactic bulge and disk bulge mass distribution as derived by kahabka ( 1998 ). the supersoft mass distribution can be compared with the predictions from population synthesis calculations assuming that only a fraction of 6.0 % of the population in the hydrogen - burning shell approximation explodes as type ia supernovae. assuming no mass degeneracy the following results are obtained : ( i ) the distribution of the cumulative number of supernova rates in m31 is derived ; ( ii ) a mean scale height of the sample is derived which is in agreement with the expected detection limit in the expected exposure time of the observations ( 100 - 150 pc at 5 kpc ) and ( iii ) a normalization of the luminosity function to the milky way is required in order to match the observed distribution of bolometric luminosities to the predicted one. the wolf - rayet star luminosity functions ( lte ) in supersoft sources are used to constrain the number of brown dwarfs. a supernova rate of a few per cent of the light elements ( i.e. nuclei ) exploding as a part of a supersoft population with a typical life time of about 5.5 to 6.5 years has been derived for this sample. this rate is large enough to make a significant contribution to the sn ia rate in the spiral galaxy. assuming that every supersoft source obeys the standard salpeter ( or scalo ) supernova survival rule and that no supernova is occurred on a timescale shorter than about 1 - 2 years, a normalisation for the supernova frequency in the galaxy is estimated to be about 1.5 per cent. the predicted distribution of presoft sources close to the galaxy disk and in the more spatially extended regions of its halo are consistent with the observed supersoft star count rates. the population size in the",0.19774718397997496
1008.2776,"understanding the nature of distant ly@xmath0 nebulae , _ aka _ ` ` blobs , '' and connecting them to their present - day descendants requires constraining their number density , clustering , and large - scale environment . to measure these basic quantities , we conduct a deep narrowband imaging survey in four different fields , chandra deep field south ( cdfs ) , chandra deep field north ( cdfn ) , and two cosmos subfields , for a total survey area of 1.2deg@xmath1 . we discover 25 blobs at @xmath2 with ly@xmath0 luminosities of @xmath3= 0.78 @xmath4 @xmath5 ergss@xmath6 and isophotal areas of @xmath7 = 10 60 . the transition from compact ly@xmath0emitters ( @xmath7 @xmath8a few ) to extended ly@xmath0 blobs ( @xmath7 @xmath9 10 ) is continuous , suggesting a single family perhaps governed by similar emission mechanisms . surprisingly , most blobs ( 16/25 ) are in one survey field , the cdfs . the six brightest , largest blobs with @xmath3@xmath10 1.5@xmath410@xmath11 ergss@xmath6 and @xmath7 @xmath9 16 lie _ only _ in the cdfs . these large , bright blobs have a field - to - field variance of @xmath12 @xmath10 1.5 ( 150 % ) about their number density @xmath13 @xmath8 @xmath14@xmath4 @xmath15 mpc@xmath16 . this variance is large , significantly higher than that of unresolved ly@xmath0 emitters ( @xmath12 @xmath8 0.3 or 30 % ) , and can adversely affect comparisons of blob number densities and luminosity functions among different surveys . our deep , blind survey allows us to construct a reliable blob luminosity function . we compare the statistics of our blobs with dark matter halos in a 1 @xmath17 gpc cosmological n - body simulation . at @xmath18 , @xmath13 implies that each bright , large blob could occupy a halo of @xmath19 @xmath10 @xmath20@xmath21 if most halos have detectable blobs . the predicted variance in @xmath13 is consistent with that observed and corresponds to a bias of @xmath87 . blob halos lie at the high end of the halo mass distribution at @xmath18 and are likely to evolve into the @xmath810@xmath22 @xmath21 halos typical of galaxy clusters today . on larger scales of @xmath23 co - moving mpc , blobs cluster where compact ly@xmath0 emitters do , indicating that blobs lie in coherent , highly overdense structures .","using our 1.2deg@xmath0 narrow - band imaging survey of the cosmic evolution survey ( cosmos ) and the noao mayall and blanco-4 m telescopes, we are discovering rare, intermediate size and luminosity ly@xday0 blobs over an area of @xmath1. our previous sensitivity and selection criteria are comparable to that of the largest previous blob survey ( *??? * ). we discover 25 lyrexcite blobs in the chandra deep field south ( cdfs ). of these 25, six are detected only in one survey field, the concordance field, while the remaining 16 blobs are mostly undetected in the other four fields. using a custom narrowband filter, we obtain deep narrowband images of these superbubbles and measure their size distribution and fluxes. we first constrain their number density, clustering, and large - scale environment using a large volume cosmological n - body simulation. the median observed field - to - field variance for the bright / large blobs ( halo number density 150 % ) is 90 %. we find that the clustering of blobs is significantly non - gaussian and that the distribution of luminosity and spatial extent is bimodal ( i.e., brighter / larger blobs have larger clustering ). using the spatial extent and line widths of the lines of sight, we estimate the dark matter halo masses of the blobs and find that their host dark halos have masses in the range 0.510.0@xcite - 0.050.0003. we compare the blob number counts with the high - resolution images of @xcite to constrain the host halo mass distribution calculated from cosmology. we conclude that the large mass probed by our survey is not consistent with the small - scale clustering inferred from studies of halo properties in the local group. we also use our blob number density and clustering to correct for the dominant contribution from agn activity in blobs, suggesting that the agn do not significantly contribute to the lyman continuum. combining our results with other studies, we predict that the surface density of lyrexmath2 blobs will increase substantially with cosmic time. based on a simple analytic approximation for the underlying fluctuations in the number density distribution, we calculate that the average blob surface density ( as measured per square degree ) in any of the fields studied could be underestimated by less than 0.5 % ( 4 @",0.1843575418994413,"* ) , we determine the field - to - field variation in the blob number density . observation ] , we describe our narrow - band imaging survey and the data reduction procedures . we discover 25 ly@xmath0 blobs with ly@xmath0 luminosities of @xmath3= 0.78 @xmath4 @xmath5 ergss@xmath6 and isophotal areas of @xmath7 = 1060 . the transition from compact ly@xmath0 emitters ( laes ; @xmath7 @xmath8a few ) to the extended ly@xmath0 blobs ( @xmath7 @xmath9 10 ) is continuous , suggesting that these two types of sources are not distinct and that whatever mechanism or mechanisms power ly@xmath0blobs work over a wide range of luminosity and spatial extent . surprisingly , we find the majority of blobs ( 16/25 ) in one survey field , the cdfs . the six brightest ( @xmath3@xmath10 1.5@xmath410@xmath11 ergss@xmath6 ) and largest ( @xmath7 @xmath9 16 ) blobs are discovered _ only _ in cdfs , indicating a strong field - to - field variation . using a simple analytic approximation for the underlying fluctuations of the blob number density , we find that these large / bright blobs have a field - to - field variance of @xmath12 @xmath10 1.5 ( 150% ) about their number density of @xmath13 @xmath8 @xmath14@xmath4 @xmath15 mpc@xmath16 . this variance is large , significantly higher than that of unresolved ly@xmath0 emitters ( @xmath1910.3 or 30% ) . to constrain the mass of the dark matter halo around each ly@xmath0blob , we compare the number density and clustering of blobs with the counts - in - cells distribution of halos predicted from a 1 @xmath17gpc cosmological n - body simulation . at @xmath18 , @xmath13 implies that bright , large blobs could occupy halos of @xmath19 @xmath10 @xmath20@xmath21 if most halos contain a detectable blob , i.e. , the detectability fraction is @xmath192 . the predicted variance in @xmath13 is consistent with that observed and corresponds to a bias of 7 . lower detectability fractions ( e.g. , @xmath8 10% ) require somewhat lower halo masses ( @xmath8 @xmath165@xmath21 ) to reproduce @xmath13 , but the resulting variance is lower and further from the observed value . blob halos lie at the high end of the halo mass distribution at @xmath18 and are likely to evolve into the @xmath810@xmath22 @xmath21 halos typical of galaxy clusters today . the spatial distribution of laes confirms this hypothesis : a counts - in - cells analysis of the cdfs reveals coherent large - scale structure over scales of at least @xmath8 8 comoving mpc where both the laes and blobs cluster . we construct a reliable luminosity function of ly@xmath0 blobs from a deep , blind narrowband survey . it is difficult to compare the properties of ly@xmath0 blob samples among different surveys because of non - uniform selection criteria and different imaging depth .",0.538659793814433
0906.4552,"the near infrared background ( nirb ) is one of a few methods that can be used to observe the redshifted light from early stars at a redshift of six and above , and thus it is imperative to understand the significance of any detection or non - detection of the nirb . fluctuations of the nirb can provide information on the first structures , such as halos and their surrounding ionized regions in the inter galactic medium ( igm ) . we combine , for the first time , @xmath0-body simulations , radiative transfer code , and analytic calculations of luminosity of early structures to predict the angular power spectrum ( @xmath1 ) of fluctuations in the nirb . we study , in detail , the effects of various assumptions about the stellar mass , the initial mass spectrum of stars , metallicity , the star formation efficiency ( @xmath2 ) , the escape fraction of ionizing photons ( @xmath3 ) , and the star formation timescale ( @xmath4 ) , on the amplitude as well as the shape of @xmath1 . the power spectrum of nirb fluctuations is maximized when @xmath2 is the largest ( as @xmath5 ) and @xmath3 is the smallest ( as more nebular emission is produced within halos ) . a significant uncertainty in the predicted amplitude of @xmath1 exists due to our lack of knowledge of @xmath6 of these early populations of galaxies , which is equivalent to our lack of knowledge of the mass - to - light ratio of these sources . we do not see a turnover in the nirb angular power spectrum of the halo contribution , which was claimed to exist in the literature , and explain this as the effect of high levels of non - linear bias that was ignored in the previous calculations . this is partly due to our choice of the minimum mass of halos contributing to nirb ( @xmath7 ) , and a smaller minimum mass , which has a smaller non - linear bias , may still exhibit a turn over . therefore , our results suggest that both the amplitude and shape of the nirb power spectrum provide important information regarding the nature of sources contributing to the cosmic reionization . the angular power spectrum of the igm , in most cases , is much smaller than the halo angular power spectrum , except when @xmath3 is close to unity , @xmath6 is longer , or the minimum redshift at which the star formation is occurring is high . in addition , low levels of the observed mean background intensity tend to rule out high values of @xmath8 .","we have few probes of the early universe and the first few generations of stars . we know that stars had to form early in order to pollute the universe with metals and reionize the universe . there is evidence that the universe was reionized at around @xmath9 , such as from the wilkinson microwave anisotropy probe ( wmap ) satellite @xcite . these ultraviolet photons at redshifts @xmath10 would be redshifted into the near - infrared bands . therefore , it makes sense to search for this remnant light in the near infrared bands to learn about this early epoch of star formation and reionization @xcite . in the previous paper we have presented detailed theoretical calculations of the spectrum and metallicity / initial - mass - spectrum dependence of the mean intensity of nirb ( @xcite , hereafter fk06 ) . in this paper in [ sec : simulations ] we outline the simulations @xcite and in [ sec : analytical ] we explain the analytic formulas we use to obtain the luminosity of the halos and the surrounding igm . in [ sec : lpk ] we present our calculation of the luminosity - density power spectrum , @xmath13 . we take a look at the constraints from the mean nirb in [ sec : mean ] , and compute the fractional anisotropy , i.e. , the ratio of the power spectrum and the mean intensity squared , in [ sec : fractional ] . simulations provide the advantage of being able to simultaneously model the distribution of halos and the density of the igm , as well as the ionization front that propagates through the igm . we combine this @xmath0-body code with radiative transfer and analytic formulas for luminosity to simulate their luminosity - density power spectrum . in this section we describe how we assign the luminosity to the halos and the igm in the simulation . note that our method is fully analytical , and thus can be adopted to any other reionization simulations . the escape fraction of ionizing photons , the star formation efficiency , and the mass and metallicity of the stars can affect the amplitude and shape of the angular power spectrum of fluctuations in nirb . the star formation efficiency has a significant effect on the amplitude of the angular power spectrum , with the amplitude of the angular power spectrum being proportional to @xmath97 . for a fixed @xmath115 ( i.e. , for a given reionization history ) , a combination of parameters that maximize the star formation efficiency , @xmath2 , give the largest nirb power spectrum ; thus , the stars that are less massive and have more metals ( smaller @xmath101 ) , and are in halos with a lower escape fraction ( smaller @xmath3 ) will all increase the amplitude of the nirb angular power spectrum . we shall present results on the nirb from these higher - resolution simulations elsewhere . in any case , the above consideration suggests that the shape of the angular power spectrum gives us important information about the nature of sources contributing to nirb as well as the physics of cosmic reionization . the current observations of the mean intensity of the nirb seem to rule out high levels of @xmath2 , i.e. , @xmath8 . most of our models for fluctuations still lie beneath the current observations of the fluctuations of the nirb .",0.25892857142857145,"we present calculations of the power spectrum and metallicity / initial - mass - spectrum dependence of the mean intensity of the near infrared background ( nirb ) fluctuations, @xmath0, from large - scale cosmological simulations of cosmic reionization, coupled with radiative transfer, for several different stellar populations. for a given stellar population, we assume four different escape fractions of ionizing photons from halos, three from clusters of galaxies, and two from isolated stars. we find that the amplitude of fluctuations in the halos ( and the mean nirbe ) is mostly dominated by the ratio of the ionizing photon escape fraction to the stellar escape fraction for halos with a total mass greater than @xcite, while the angular power spectrum of the intergalactic medium ( igm ) is consistent with the single power spectrum seen in the literature. the igm is typically a minor contributor to the overall fluctuations, although it can be comparable to the halo contribution ( the stellar contribution as well as the nebular contribution from within a halo ), especially if the escape fraction of photospheric electrons is high. when we average over all stellar populations, we find a power spectrum that is roughly symmetric, with a mean power law index of 1.4, though there is a broad range of shapes. the peaks in this power spectrum fall between regions of high ionization rate and high star formation efficiency, and are likely to be from stars forming at the highest redshifts. we give approximate analytic formulas for luminosity - density power spectra and show that these formulas are capable of providing accurate predictions even for stars that have primordial abundances. we note, however, that these analytic formulas are subject to uncertainties in the star formation time scale and the mass to light ratio of galaxies. changes in these parameters will change the overall shape, but will allow us to probe the ionization history through the fractional anisotropy, i.e., the mixing of metal - rich and metal - poor stars. [ firstpage ] cosmology : theory- dark matter- large scale structure of universe",0.1944444444444444
cs0606099,"for a wide class of multi - user systems , a subset of capacity region which includes the corner points and the sum - capacity facet has a special structure known as polymatroid . multiaccess channels with fixed input distributions and multiple - antenna broadcast channels are examples of such systems . any interior point of the sum - capacity facet can be achieved by time - sharing among corner points or by an alternative method known as _ rate - splitting_. the main purpose of this paper is to find a point on the sum - capacity facet which satisfies a notion of fairness among active users . this problem is addressed in two cases : ( i ) where the complexity of achieving interior points is not feasible , and ( ii ) where the complexity of achieving interior points is feasible . for the first case , the corner point for which the minimum rate of the active users is maximized ( max - min corner point ) is desired for signaling . a simple greedy algorithm is introduced to find the optimum max - min corner point . for the second case , the polymatroid properties are exploited to locate a rate - vector on the sum - capacity facet which is optimally fair in the sense that the minimum rate among all users is maximized ( max - min rate ) . in the case that the rate of some users can not increase further ( attain the max - min value ) , the algorithm recursively maximizes the minimum rate among the rest of the users . it is shown that the problems of deriving the time - sharing coefficients or rate - spitting scheme can be solved by decomposing the problem to some lower - dimensional subproblems . in addition , a fast algorithm to compute the time - sharing coefficients to attain a general point on the sum - capacity facet is proposed . polymatroid structure , multiuser systems , multiaccess channels , broadcast channels , fairness , successive decoding , time - sharing , rate - splitting .","based on this criterion , the rates of users with a stronger channel can be increased with the cost of decreasing the rates of users with a weaker channel . , it is shown that the capacity region of multiaccess channels ( mac ) with fixed and independent input distributions forms a polymatroid @xcite . in mac , the sum - capacity is achieved by successive decoding . applying different orders for the users in successive decoding results in different rate - vectors , all with the sum - rate equal to the sum - capacity . , it is proven that the marton inner bound ( see @xcite ) for capacity region of the broadcast channel under fixed joint probability of the auxiliary and input variables , with some conditions , has a polymatroid structure . as another example , we will show that a subset of the capacity region for multiple - input multiple - output ( mimo ) broadcast channel which includes the corner points forms a polymatroid . in @xcite , the optimal dynamic power allocation strategy for time - varying single - antenna multiple - access channel is established . to this end , the polymatroid properties of the capacity region for time - invariant multiple - access channel with fixed input distributions have been exploited . in @xcite this article aims at finding a point on the sum - capacity facet which satisfies a notion of fairness among active users by exploiting the properties of polymatroids . in order to provide fairness , the minimum rate among all users it is shown that the problem of deriving the time - sharing coefficients to attain this point can be decomposed to some lower - dimensional subproblems . an alternative approach to attain an interior point for multiple access channels in addition , the relationship between the capacity region of some channels and the polymatroid structure is described . in addition , it is shown that the problem of deriving the time - sharing coefficients and rate - splitting can be solved by decomposing the problem into some lower - dimensional subproblems . _ we considered the problem of fairness for a class of systems for which a subset of the capacity region forms a polymatroid structure . the main purpose is to find a point on the sum - capacity facet which satisfies a notion of fairness among active users . this problem is addressed in cases where the complexity of achieving interior points is not feasible , and where the complexity of achieving interior points is feasible . for the first case , the corner point for which the minimum rate of the active users is maximized ( max - min corner point ) is desired for signaling . a simple greedy algorithm is introduced to find the optimum max - min corner point . for the second case , it is shown that the problems of deriving the time - sharing coefficients and rate - spitting scheme can be solved by decomposing the problem to some lower - dimensional subproblems .",0.4037184594953519,"in multi - user systems, multiple transmitters / receivers share a common communication medium, and therefore, there is an inherent competition in accessing the channel. information theoretic results for such systems imply that in order to achieve a high spectral efficiency, the users with stronger channel should have a higher portion of the resources. the drawback to this is the loss of the fairness among the users. to provide fairness, we want to find the corner point for which the minimum rate of the active users is maximized ( max - min corner point ). this problem is formulated by considering a point on the face of the contra - polymatroid. a simple greedy algorithm is introduced to find this corner point. based on this algorithm, it is shown that the problem of deriving the time - sharing coefficients and rate - splitting can be decomposed into some lower - dimensional subproblems. _ _ a criterion based on nash bargaining solution in the context of game theory is proposed. this criterion generalizes the proportional fairness and increases the efficiency of the system. as a special case, we consider a multiaccess system in which the distribution of inputs are independent and equal to @xmath0. particularly in some multiuser systems, the boundary of the capacity region includes a facet on which the sum - rate is maximum ( sum - capacity facet ). in such systems, one can benefit from the available degrees of freedom, i.e., determine the fairest rate - vector ( the uniform minimum rate among all users ), and determine the fairness coefficient as well. as the first example, we show that a subset of the convex hull of these corner points forms a polymatoid. in fact, the polymetroid structure is established first by establishing a relationship between the existing capacity region of the simulating multiple - input multiple - output ( mimo ) broadcast channel ( both positive semi - definite diagonal and non - diagonal covariance matrices ), then by determining the best linear combination of these two matrices. the result is proved by proving the optimality of the above algorithm. the optimal dynamic power allocation strategy for time - varying multiple - access channels is also discussed.",0.26666666666666666
astro-ph9704221,"we have modeled the gas temperature structure in unstable c - type shocks and obtained predictions for the resultant co and h@xmath0 rotational line emissions , using numerical simulations of the wardle instability that were carried out by stone ( 1997 ) and that have been described in a companion paper . our model for the thermal balance of the gas includes ion - neutral frictional heating ; compressional heating ; radiative cooling due to rotational and rovibrational transitions of the molecules co , h@xmath0o and h@xmath0 ; and gas - grain collisional cooling . we obtained results for the gas temperature distribution in and h@xmath0 and co line emission from shocks of neutral alfvenic mach number 10 and velocity 20 or @xmath1 in which the wardle instability has saturated . both two- and three - dimensional simulations were carried out for shocks in which the preshock magnetic field is perpendicular to the shock propagation direction ; and a 2-d simulation was carried out for the case in which the magnetic field is obliquely oriented with respect to the shock propagation direction . although the wardle instability profoundly affects the density structure behind c - type shocks , most of the shock - excited molecular line emission is generated upstream of the region where the strongest effects of the instability are felt . thus the wardle instability has a relatively small effect upon the overall gas temperature distribution in and the emission line spectrum from c - type shocks , at least for the cases that we have considered . in none of the cases that we have considered thus far did any of the predicted emission line luminosities change by more than a factor 2.5 , and in most cases the effects of instability were significantly smaller than that . slightly larger changes in the line luminosities seem likely for 3-d simulations of oblique shocks , although such simulations have yet to be carried out and lie beyond the scope of this study . given the typical uncertainties that are always present when model predictions are compared with real astronomical data , we conclude that wardle instability does not imprint any clear observational signature on the shock - excited co and h@xmath0 line strengths . this result justifies the use of 1-d steady shock models in the interpretation of observations of shock - excited line emission in regions of star formation . our 3-d simulations of perpendicular shocks revealed the presence of warm filamentary structures that are aligned along the magnetic field , a result of possible relevance to models of water maser emission from c - type shocks .","we model the gas temperature and molecular line emission that is expected to result from unstable c - type shocks, given the ion and neutral velocity fields computed in a companion paper by stone ( 1997 ). we use numerical simulations of the wardle instability carried out with a new computer code, zeus-2f, that has been tested extensively in a variety of applications. two- and three - dimensional simulations are carried out for shocks in which the preshock magnetic field is perpendicular to the shock propagation direction,, and in cases where the pre - shock velocity is in the range typically encountered in star forming regions. for all three cases that we have considered, the shock - excited line emission arises from shocks that are initially plane - parallel and that propagate in an initially homogeneous medium. we obtain results for the distribution of the gas temperatures in the shocked region and for the line emissions that arise from shocks of neutral alfvenic mach number 10 and velocity 20 or @xmath0. the temperature distributions were obtained for three different shock cases : ( 1 ) in the case where the shocks are viewed along the plane of the sky, but along the line of sight ; ( 2 ) for shocks where the line - emitting regions are elongated with the flow, such that downstream regions of the shock are patchy, but spatially continuous ; and ( 3 ) for which the line emission originates upstream of the region where the instability has reached saturation. overall, none of the results of the simulations applies to all of these cases. the difference between the temperature distribution obtained from the simulated gas temperature structure in the initial state and that predicted by kn96 ( which was used for the computation of the predicted fluxes for far - infrared co lines ) is significantly smaller than the observed one. these results provide a justification for the use of one - dimensional steady shock models for the generation of shock - excitation line spectra in the interpretation of observations of warm molecular gas. the results also provide a possible explanation for the difference in the predicted luminosities of the ( warm ) water maser emission observed between two and three shapshots of the second shapshot.",0.31266149870801035,"these simulations allow us to address for the first time the question of how the wardle instability affects the shock - excited line emission from c - type shocks . , we present a study of the molecular line emission that is expected to result from unstable c - type shocks , given the ion and neutral velocity fields computed in the dynamical calculations of s97 . in 2 , we describe the details of our calculation , and in 3 we present and discuss the results obtained for three different geometries and two different shock velocities . in this study , we have computed the gas temperature and molecular line emission that is expected to result from unstable c - type shocks . since thermal pressure our selection of the shock velocity and preshock magnetic field strength is discussed in 3 below . we have computed the gas temperatures in the shocked region and the predicted co and h@xmath0 line emissions for two shapshots : ( 1 ) the initial state in which the flow solution is the steady - state solution to the 1-d dynamical equations ; and ( 2 ) after the wardle instability has reached saturation . we conclude that _ the wardle instability does not imprint any clear observational signature upon the shock - excited co and h@xmath0 line spectra _ , given the comparable or larger effects that may result from ( 1 ) uncertainties in the microphysics of ion - neutral coupling and molecular excitation ; ( 2 ) observational errors in the measurement of line fluxes ; ( 3 ) the superposition of shocks of different velocities in the telescope beam ; ( 4 ) inhomogeneities in the preshock density ; and so forth . this result provides a justification for the use of one - dimensional steady shock models in the interpretation of observations of shock - excited line emission . \1 . we have modeled the neutral gas temperature and the co and h@xmath0 rotational line emissivities in unstable c - type shocks , using numerical simulations of the wardle instability that were carried out by stone ( 1997 ) and described in a companion paper . the results apply to shocks that are initially plane - parallel and that propagate in an initially homogeneous medium . \2 . in modeling the gas temperature within the shocked gas region , we included ion - neutral frictional heating , compressional heating , radiative cooling due to rotational and rovibrational transitions of the molecules co , h@xmath0o and h@xmath0 , and gas - grain collisional cooling . in modeling the line emission from co and h@xmath0 we solved the equations of statistical equilibrium for the populations in excited rotational states , using an escape probability method to treat the effects of radiative trapping in the co transitions . we obtained results for the gas temperature distribution in and h@xmath0 and co line emission from shocks of neutral alfvenic mach number 10 and velocity 20 or @xmath1 in which the wardle instability has saturated . both two- and three - dimensional simulations were carried out for shocks in which the preshock magnetic field is perpendicular to the shock propagation direction ; and a two - dimensional simulation was carried out for the case in which the magnetic field is obliquely oriented with respect to the shock propagation direction . \4 . thus the wardle instability has a relatively small effect upon the overall gas temperature distribution in and the emission line spectrum from c - type shocks , at least for the cases that we have considered . in none of the cases that we have considered our three - dimensional simulations of perpendicular shocks revealed the presence of warm filamentary structures that are aligned along the magnetic field , a result of possible relevance to models of water maser emission from c - type shocks . d. a. n. gratefully acknowledges the hospitality of the university of maryland , college park , where he was a sabbatical visitor during the period when this study was conceived and started . 5a rotational level populations of molecular hydrogen in the shock - heated gas .",0.4497607655502392
astro-ph9704221,"we have modeled the gas temperature structure in unstable c - type shocks and obtained predictions for the resultant co and h@xmath0 rotational line emissions , using numerical simulations of the wardle instability that were carried out by stone ( 1997 ) and that have been described in a companion paper . our model for the thermal balance of the gas includes ion - neutral frictional heating ; compressional heating ; radiative cooling due to rotational and rovibrational transitions of the molecules co , h@xmath0o and h@xmath0 ; and gas - grain collisional cooling . we obtained results for the gas temperature distribution in and h@xmath0 and co line emission from shocks of neutral alfvenic mach number 10 and velocity 20 or @xmath1 in which the wardle instability has saturated . both two- and three - dimensional simulations were carried out for shocks in which the preshock magnetic field is perpendicular to the shock propagation direction ; and a 2-d simulation was carried out for the case in which the magnetic field is obliquely oriented with respect to the shock propagation direction . although the wardle instability profoundly affects the density structure behind c - type shocks , most of the shock - excited molecular line emission is generated upstream of the region where the strongest effects of the instability are felt . thus the wardle instability has a relatively small effect upon the overall gas temperature distribution in and the emission line spectrum from c - type shocks , at least for the cases that we have considered . in none of the cases that we have considered thus far did any of the predicted emission line luminosities change by more than a factor 2.5 , and in most cases the effects of instability were significantly smaller than that . slightly larger changes in the line luminosities seem likely for 3-d simulations of oblique shocks , although such simulations have yet to be carried out and lie beyond the scope of this study . given the typical uncertainties that are always present when model predictions are compared with real astronomical data , we conclude that wardle instability does not imprint any clear observational signature on the shock - excited co and h@xmath0 line strengths . this result justifies the use of 1-d steady shock models in the interpretation of observations of shock - excited line emission in regions of star formation . our 3-d simulations of perpendicular shocks revealed the presence of warm filamentary structures that are aligned along the magnetic field , a result of possible relevance to models of water maser emission from c - type shocks .","we model the gas temperature and molecular line emission that is expected to result from unstable c - type shocks, given the ion and neutral velocity fields computed in a companion paper by stone ( 1997 ). we use numerical simulations of the wardle instability carried out with a new computer code, zeus-2f, that has been tested extensively in a variety of applications. two- and three - dimensional simulations are carried out for shocks in which the preshock magnetic field is perpendicular to the shock propagation direction,, and in cases where the pre - shock velocity is in the range typically encountered in star forming regions. for all three cases that we have considered, the shock - excited line emission arises from shocks that are initially plane - parallel and that propagate in an initially homogeneous medium. we obtain results for the distribution of the gas temperatures in the shocked region and for the line emissions that arise from shocks of neutral alfvenic mach number 10 and velocity 20 or @xmath0. the temperature distributions were obtained for three different shock cases : ( 1 ) in the case where the shocks are viewed along the plane of the sky, but along the line of sight ; ( 2 ) for shocks where the line - emitting regions are elongated with the flow, such that downstream regions of the shock are patchy, but spatially continuous ; and ( 3 ) for which the line emission originates upstream of the region where the instability has reached saturation. overall, none of the results of the simulations applies to all of these cases. the difference between the temperature distribution obtained from the simulated gas temperature structure in the initial state and that predicted by kn96 ( which was used for the computation of the predicted fluxes for far - infrared co lines ) is significantly smaller than the observed one. these results provide a justification for the use of one - dimensional steady shock models for the generation of shock - excitation line spectra in the interpretation of observations of warm molecular gas. the results also provide a possible explanation for the difference in the predicted luminosities of the ( warm ) water maser emission observed between two and three shapshots of the second shapshot.",0.31266149870801035,"these simulations allow us to address for the first time the question of how the wardle instability affects the shock - excited line emission from c - type shocks . , we present a study of the molecular line emission that is expected to result from unstable c - type shocks , given the ion and neutral velocity fields computed in the dynamical calculations of s97 . in 2 , we describe the details of our calculation , and in 3 we present and discuss the results obtained for three different geometries and two different shock velocities . in this study , we have computed the gas temperature and molecular line emission that is expected to result from unstable c - type shocks . since thermal pressure our selection of the shock velocity and preshock magnetic field strength is discussed in 3 below . we have computed the gas temperatures in the shocked region and the predicted co and h@xmath0 line emissions for two shapshots : ( 1 ) the initial state in which the flow solution is the steady - state solution to the 1-d dynamical equations ; and ( 2 ) after the wardle instability has reached saturation . we conclude that _ the wardle instability does not imprint any clear observational signature upon the shock - excited co and h@xmath0 line spectra _ , given the comparable or larger effects that may result from ( 1 ) uncertainties in the microphysics of ion - neutral coupling and molecular excitation ; ( 2 ) observational errors in the measurement of line fluxes ; ( 3 ) the superposition of shocks of different velocities in the telescope beam ; ( 4 ) inhomogeneities in the preshock density ; and so forth . this result provides a justification for the use of one - dimensional steady shock models in the interpretation of observations of shock - excited line emission . \1 . we have modeled the neutral gas temperature and the co and h@xmath0 rotational line emissivities in unstable c - type shocks , using numerical simulations of the wardle instability that were carried out by stone ( 1997 ) and described in a companion paper . the results apply to shocks that are initially plane - parallel and that propagate in an initially homogeneous medium . \2 . in modeling the gas temperature within the shocked gas region , we included ion - neutral frictional heating , compressional heating , radiative cooling due to rotational and rovibrational transitions of the molecules co , h@xmath0o and h@xmath0 , and gas - grain collisional cooling . in modeling the line emission from co and h@xmath0 we solved the equations of statistical equilibrium for the populations in excited rotational states , using an escape probability method to treat the effects of radiative trapping in the co transitions . we obtained results for the gas temperature distribution in and h@xmath0 and co line emission from shocks of neutral alfvenic mach number 10 and velocity 20 or @xmath1 in which the wardle instability has saturated . both two- and three - dimensional simulations were carried out for shocks in which the preshock magnetic field is perpendicular to the shock propagation direction ; and a two - dimensional simulation was carried out for the case in which the magnetic field is obliquely oriented with respect to the shock propagation direction . \4 . thus the wardle instability has a relatively small effect upon the overall gas temperature distribution in and the emission line spectrum from c - type shocks , at least for the cases that we have considered . in none of the cases that we have considered our three - dimensional simulations of perpendicular shocks revealed the presence of warm filamentary structures that are aligned along the magnetic field , a result of possible relevance to models of water maser emission from c - type shocks . d. a. n. gratefully acknowledges the hospitality of the university of maryland , college park , where he was a sabbatical visitor during the period when this study was conceived and started . 5a rotational level populations of molecular hydrogen in the shock - heated gas .",0.4497607655502392
1004.0781,"in the last decade , numerous lyman - alpha emitters ( laes ) have been discovered with narrow - band filters at various redshifts . recently , multi - wavelength observations of laes have been performed and revealed that while many laes appear to be young and less massive , a noticeable fraction of laes possess much older populations of stars and larger stellar mass . how these two classes of laes are concordant with the hierarchical galaxy formation scenario has not been understood clearly so far . in this paper , we model laes by three - dimensional cosmological simulations of dark halo merger in a @xmath0cdm universe . as a result , it is shown that the age of simulated laes can spread over a wide range from @xmath1yr to @xmath2yr . also , we find that there are two types of laes , in one of which the young half - mass age is comparable to the mean age of stellar component , and in the other of which the young half - mass age is appreciably shorter than the mean age . we define the former as type 1 laes and the latter as type 2 laes . a type 1 lae corresponds to early starburst in a young galaxy , whereas a type 2 lae does to delayed starburst in an evolved galaxy , as a consequence of delayed accretion of a subhalo onto a larger parent halo . thus , the same halo can experience a type 2 lae - phase as well as a type 1 lae - phase in the merger history . type 1 laes are expected to be younger than @xmath3yr , less dusty , and less massive with stellar mass @xmath4 , while type 2 laes are older than @xmath3yr , even dustier , and as massive as @xmath5 . the fraction of type 2s in all laes is a function of redshift , which is less than 2 percent at @xmath6 , @xmath730 percent at redshift @xmath8 , and @xmath770 percent at @xmath9 . type 2 laes can be discriminated clearly from type 1s in two color diagram of z-h vs j - k . we find that the brightness distribution of ly@xmath10 in type 2 laes is more extended than the main stellar component , in contrast to type 1 laes . this is not only because delayed starbursts tend to occur in the outskirts of a parent galaxy , but also because ly@xmath10 photons are effectively absorbed by dust in an evolved galaxy . hence , the extent of ly@xmath10 emission may be an additional measure to distinguish type 2 laes from type 1 laes . the sizes of type 2 laes range from a few tens to a few hundreds kpc . at lower redshifts , the number of more extended , older type 2 laes increases . furthermore , it is anticipated that the amplitude of angular correlation function for type 2 laes is significantly higher than that for type 1 laes , but comparable to that for lyman break galaxies ( lbgs ) . this implies that lbgs with strong ly@xmath10 line may include type 2 laes . [ firstpage ] galaxies ly@xmath10 emitters ; galaxies formation ; galaxies evolution ; galaxies correlation function","such an effect provides the possibility of old , massive and dusty laes . in this paper , we explore how a young and old population of laes are concordant with a hierarchical galaxy formation paradigm . for the purpose , we perform tree - dimensional cosmological simulations of dark halo merger in a @xmath0cdm universe , incorporating the prescriptions of star formation , spectral evolution , and dust extinction . throughout this paper , we adopt @xmath0cdm cosmology with the matter density @xmath21 , the cosmological constant @xmath22 , the hubble constant @xmath23 in units of @xmath24 , the baryon density @xmath25 , and @xmath26 @xcite . type 2 laes possess a large amount of dust . if many type 2 laes can be detected as smgs , our simulation is consistent with this observation . to explore the origin of two populations of laes recently found , we have performed three - dimensional cosmological @xmath27-body simulations of subhalo merging history in a @xmath0cdm universe . we have incorporated star formation history , sed evolution , and dust extinction . as a result , we have found that the age of simulated laes can spread over a wide range from @xmath1yr to @xmath2yr . also , we have revealed that there are two types of laes . we have defined laes younger than @xmath3yr as type 1s , and older ones as type 2s . in type 1 laes a parent halo can experience repeatedly a type 2 lae - phase after a type 1 lae - phase . the stellar mass of type 1 laes is @xmath4 , while type 2 laes are as massive as @xmath5 . the physical properties of type 1 and type 2 laes are concordant with those of two populations of laes observed with multi - wavelengths @xcite . the fraction of type 2s in all laes is a function of redshift , which is less than 2 percent at @xmath6 , @xmath730 percent at redshift @xmath8 , and @xmath770 percent at @xmath9 . type 2 laes are expected to be discriminated clearly from type 1 laes in two color diagram of z-h vs j - k . we find that the brightness distribution of ly@xmath10 in type 2 laes is more extended than the main stellar component , in contrast to type 1 laes . this suggests that lbgs with strong ly@xmath10 line can be type 2 laes . these properties are quite similar to those of type 2 laes we defined in this paper .",0.4233409610983981,"we perform three - dimensional cosmological simulations to explore whether a young and old population of lyman alpha emitters ( laes ) are concordant with a hierarchical galaxy formation scenario. we have incorporated star formation history, sed evolution, and dust extinction. as a result, we have found that the age of simulated laes can spread over a wide range from @xmath0cdm to @xik1yr. our simulations have revealed that there are two types of laes. we define laes younger than @x math3yr as type 1s, and older ones as type 2s. in type 1 laes early coeval starburst occur in small parent halos, while in type 2 laes delayed starburst take place in evolved massive haloes as a consequence of delayed accretion of subhalos. we analyze the multi - wavelength distributions of type1 laes and trace the effect of dust extinction on the spectra. we find that the fraction of type2 laes is less than @axmath4 percent at @xcite. on the other hand, type 1laes are well consistent with the observed fraction of redshifted laes, which is at least ten percent. moreover, the two populations are clearly discriminated at multiwavelengths. by using the correlation function of sub - mm galaxies in the ssa22 field, we found that type 2 lae have a higher probability of being detected at optical wavelengths than type 1 lae. this implies that the optical color distribution of smgs is important for the transfer of ly@xmath10 photons from laes to lbgs. since smgs are not expected to be dusty, this opens the possibility of a large fraction of dusty laes remaining undetected in nir and x - rays. our results indicate that delayed starbursts are not always associated with lae regions, and may occur in any environment. [ firstpage ] galaxies : evolution galaxies : starburst galaxies : photometry cosmology : theory",0.2893401015228426
astro-ph0310681,"we report interferometric radio co2 - 1 and hcn1 - 0 observations at resolutions of 0.7 and 2.0 respectively , and 0.085 resolution adaptive optics k - band spectroscopy , including h@xmath0 1 - 0s(1 ) line emission and co2 - 0 stellar absorption , of the inner few arcseconds of ngc7469 . the co2 - 1 map shows a ring of molecular clouds ( which in general lie outside the compact knots seen in k - band images ) and a bright extended nucleus , with a bar or pair of spiral arms between them . the dynamical structure of both the radio co2 - 1 and the k - band h@xmath0 1 - 0s(1 ) lines at their different resolutions can be reproduced using a single axisymmetric mass model comprising 3 components : a broad disk , a ring 45 across , and an extended nucleus which we interpret as an inner nuclear ring about 0.5 across . the velocity residuals between the model and the data have a standard deviation of 25 , and no non - circular motions faster than this are seen , although this may be because in some cases a secondary bar is not expected to cause gas inflow . from the dynamical mass and estimates of the stellar mass we find that the co - to - h@xmath0 conversion is 0.40.8 times that for the milky way , following the trend to small factors that has been previously reported for intense star forming environments . the central h@xmath0 1 - 0s(1 ) morphology has a strong peak at the nucleus , but this does not trace the mass distribution ; the rotation curves indicate that there is no strong nuclear mass concentration . the origins of the 1 - 0s(1 ) emission are instead likely to lie in x - ray and uv irradiation of gas by the agn rather than via processes associated with star formation . using the 2.3@xmath1 m stellar co2 - 0 bandhead absorption and the slope of the continuum we have directly resolved the nuclear star cluster to be 0.150.20 across , and find that it is asymmetric . this cluster has an age of less than about 60myr and contributes 2030 % of the nuclear k - band light , and about 10 % of the nuclear bolometric luminosity . within a radius of @xmath24 gas contributes more than half the total mass ; but in the nucleus , within a radius of 0.1 , it is likely that most of the mass is due instead to stars .",", we have constructed kinematic models which can explain the various features observed in the kinematic major and minor axis p - v maps , and which also estimate the rotation velocities inside a radius of 5 . as a starting point we have derived a single mass model which matches the kinematics from both the co radio data and the near infrared h@xmath0 spectroscopic data at their different resolutions . we have presented 0.7 radio co2 - 1 observations and 0.085 adaptive optics k - band spectroscopy of the central region of ngc7469 . using these data we have investigated the distribution and kinematics of the cold and warm molecular gas across nearly 2 orders of magnitude in spatial scale . additionally , we have studied the nuclear stellar cluster . the kinematics of the co2 - 1 and 1 - 0s(1 ) lines can be reproduced by an axisymmetric mass model consisting of a broad disk component , a circumnuclear ring at 2.3 , and a nuclear ring at 0.2 . the co2 - 1 morphology also suggests that there may be a bar or pair of spiral arms between the two rings , although there is no kinematical signature in the data . this may be because ngc7469 represents the case where straight shocks can not form along an inner bar , and hence there is no gas inflow . nevertheless , the increase in gas density in the bar / spiral may have triggered star formation and this is now seen as the knots of emission which lie inside the radius of the molecular ring . comparison of the dynamical and stellar masses indicates that molecular gas makes up more than half of the total mass within a radius of 1kpc , and that the remaining gas mass is at least several times that of recently formed stars in the ring . the co - to - h@xmath0 conversion factor is 0.40.8 times the galactic conversion factor . similar values have been seen a number of times in intense star forming environments . by mapping the stellar co absorption and considering the slope of the continuum , we have directly resolved the nuclear stellar cluster in ngc7469 . it is extended over 3060pc and contributes 2030% of the nuclear k - band continuum , and about 10% of the nuclear bolometric luminosity . the stellar mass counts for at least half , and probably more , of the total mass within 30pc ( 0.1 ) of the nucleus . the authors extend their thanks to the following people : jack gallimore and lowell tacconi - garman for considerable help with the co data , particularly calibrating and modelling the co1 - 0 data ; aaron evans and rodger thompson for providing reduced and calibrated _ hst _ images ; andrew baker for helpful discussions about disk dynamics ; the anonymous referee for several suggestions about how to improve the paper .",0.3118405627198124,"we present a study of the kinematic structure of the molecular gas in the luminous infrared galaxy ngc7469, based on a combination of high resolution radio co data and near infrared adaptive optics h@xmath0 1 - 0s(1 ) data. the high spatial resolution of the co data taken with the adaptive optics system on the canada - france - hawaii telescope allows us to study the distribution of the gas with respect to the central 0.5 in the plane of symmetry of the galaxy. we find that the gas is kinematically connected to the nuclear ring on scales of 3.2 - 5.5 from the nucleus, and that it is oriented in the same plane as the bar and spiral arms seen in hcn. we therefore reject the possibility that the co and hcn lines trace different parts of the circumnuclear ring, although the latter do show some evidence for an asymmetrical distribution. the difference in position angle between the co ring and the nucleus on the basis of the hcn data is consistent with a bar - driven dynamical instability in the gas, and suggests that the ring and its nuclear ring are not located in a unique position angle @xmath1. the mass distribution in the co radio data is close to spherically symmetric, with both the major and minor axes distinctly non - axisymmetric. we have been able to constrain the mass inside a radius of 0.52.5 of the ring to be less than 4 times the mass of recently formed stars. utilising the scaling of the stellar light component, and using a model for the evolution of the mass surface density as a function of radius which describes the observed in p - v maps of the nuclear region, we derive a total dynamical mass of 6.8mx - 0.7 for the ring. this value is more than a factor of two above the total mass of stars and several times more than the mass in the ring observed in a k - band image of ngc1068, the only galaxy in which has been found to contain a nuclear ring which is strongly detected. the radial mass distribution we find is best described by a model in which accounts for all kinematics features except for the asymmetrical ring. with such a model we can explain the mass - to - light ratio and pah pah inclination of 2.3 in terms of a superposition of stellar and gas components. in particular, it provides a good match to the values found for the 1 -",0.19756097560975608
astro-ph0403639,"we present new spectra of wr 140 ( hd 193793 ) in the @xmath0 bands with some covering the 1.083-@xmath1 m hei emission line at higher resolution , observed between 2000 october and 2003 may to cover its 2001 periastron passage and maximum colliding - wind activity . the wc7 + o4 - 5 spectroscopic binary wr 140 is the prototype of colliding - wind , episodic dust - making wolf - rayet systems which also show strong variations in radio and x - ray emission . the @xmath0 spectra showed changes in continuum and in the equivalent widths of the wc emission lines , consistent with formation of dust starting between 2001 january 3 and march 26 ( orbital phases 0.989 and 0.017 ) and its subsequent fading and cooling . the 1.083-@xmath1 m hei line has a p - cygni profile which showed variations in both absorption and emission components as wr 140 went through periastron passage . the variation of the absorption component of the profile yielded tight constraints on the geometry of the wind - collision region , giving @xmath2 for the opening semi - angle of the interaction region ` cone ' , indicating a wind - momentum ratio @xmath3 , about three times larger than previously believed . as the system approached periastron , the normally flat - topped emission component of 1.083-@xmath1 m line profile showed the appearance of a significant sub - peak . the movement of the sub - peak across the profile was seen to be consistent with its formation in wind material flowing along the contact discontinuity between the wc7 and o4 - 5 stellar winds and the changing orientation of the colliding wind region as the stars moved in their orbits . the flux carried in the sub - peak was significant , exceeding the x - ray fluxes measured at previous periastron passages . this additional source of radiative cooling of the shock - heated gas probably causes it to depart from being adiabatic around periastron passage , thereby accounting for the departure of the x - ray flux from its previously expected @xmath4-dependency . [ firstpage ] binaries : spectroscopic circumstellar matter stars : individual : wr 140 stars : wolf - rayet stars : winds","it is believed , now , that episodic dust making wc stars are massive binary systems in which the stellar winds of two massive stars interact . wr 140 ( hd 193793 ) is the prototype of colliding - wind , episodic dust forming wc stars ( williams 1995 ) . from the photometry of the infrared maxima in 1977 and 1985 and earlier data , this implies that the momentum of the o star wind had been underestimated or that of the wc star overestimated . if we are correct in interpreting this movement as a change of the orientation of the wind - collision region moving with the stars in their orbits , then quadrature and periastron passage must have occurred after january 2 . this is consistent with the predictions of t@xmath96 of 2001 february 20 ( w90 ) or february 6 ( from elements by marchenko et al . ) but rules out the 72-day shift to december 10 proposed by zhekov & skinner . relative to the elements of w90 , but with a relatively large uncertainty , 117 days , which does not constrain our solution . ) we propose instead that the x - ray flux departs from a @xmath4-dependence because the shocked wc wind is not totally adiabatic during periastron passage as a consequence of significant additional cooling in the hei sub - peak . infrared spectroscopy of wr 140 during and after its 2001 periastron passage showed dilution of the emission lines consistent with the formation of circumstellar dust between 2001 january 3 and march 26 , phases 0.989 and 0.017 . the hei 1.083-@xmath1 m line showed a strong p - cygni profile . variation of the strength of the absorption component measured from high - resolution spectra was interpreted in terms of the passage of different parts of the colliding wind structure in our line of sight to the two stars . this allowed us to set fairly tight limits on the opening half angle of the ` cone ' modelling the interaction region : @xmath99 . this , in turn , indicated a wind - momentum ratio @xmath67 , signifcantly higher than the @xmath100 found from the mass - loss rates and terminal velocities of the wc7 and o components . we suggested that the mass - loss rate of the wc7 star , @xmath62 derived from the 5-ghz flux density at radio minimum was overestimated because the wind is clumped . at phases ( @xmath101 ) close to periastron passage , the normally flat - topped emission component of the 1.083-@xmath1 m line showed the appearance of a sub - peak which moved from the blue to the red end of the profile during periastron . the evolution of the position and width of the sub - peak were found to be reasonably conistent with the flow of the emitting material along the surface of the interaction region modelled by a cone having @xmath68 . the maximum radiative flux in the sub - peaks is greater than the 110 kev x - ray flux at periastron and is a significant source of cooling of the shocked wc wind .",0.3195121951219512,"we have carried out a high - resolution observing of the pre - main sequence binary system wr 140 with the 3.8-m united kingdom infrared telescope ( ukirt ) using the hei line at 1.083 @xmath0 m. the star was placed in a near - contact orbit with an o star in a close orbit with a period of 7.9 years. the 2.2-mm orbital motion of the two stars was followed for 10 - 15 months after periastron passage in 2001 june, until 2003 february. in contrast to previous cycles, the flux in the far - infrared region of the binary system varied systematically with orbital separation less than 0.1 %. this flux was higher than in the past for the o star, but lower than for the wc star, which showed stronger emission lines at phases 0.83 - 0.96. the ob stars were on almost circular orbits. the spectra show strong hei absorption with a blue edge at phase 0.21.3, which is not seen in the x - ray images. this is inconsistent with the model predictions of the thin shell model of lhrs and hill, moffat & st - louis ( 2002 ) which attributes the emission to dust formed in the expanding shell of a single wolf - rayet star. we model the rms variation of the emission as arising from clumpy, expanding dust shell with radial velocities varying with orbital motion and find that the observed flux variations are consistent with large variations in the rv of the centre and extent of the dust shell. the radial profile of the absorption, which we interpret as a change in the wind - absorption, shows a steeply rising continuum below 2 kev and a gradual weakening at higher energies, consistent with the behaviour of the underlying stellar continuum. this pre - eclipse eclipse was not triggered by any inhomogeneous, p - cygni absorbed absorption profile as is the case for wr 140. [ firstpage ] stars : binaries : eclipsing stars : early - type stars : mass - loss stars : winds, outflows",0.20359281437125748
1208.6132,"the first complete submillimetre spectrum ( 190 - 670@xmath0 m ) of the seyfert 2 galaxy ngc1068 has been observed with the spire fourier transform spectrometer onboard the _ herschel _ space observatory . the sequence of co lines ( j@xmath1=4 - 13 ) , lines from h@xmath2o , the fundamental rotational transition of hf , two o - h@xmath2o@xmath3 lines and one line each from ch@xmath3 and oh@xmath3 have been detected , together with the two [ ci ] lines and the [ nii]205@xmath0 m line . the observations in both single pointing mode with sparse image sampling and in mapping mode with full image sampling allow us to disentangle two molecular emission components , one due to the compact circum - nuclear disk ( cnd ) and one from the extended region encompassing the star forming ring ( sf - ring ) . radiative transfer models show that the two co components are characterized by density of @xmath4=@xmath5 and @xmath6 @xmath7 and temperature of @xmath8 = 100k and 127k , respectively . the comparison of the co line intensities with photodissociation region ( pdr ) and x - ray dominated region ( xdr ) models , together with other observational constraints , such as the observed co surface brightness and the radiation field , indicate that the best explanation for the co excitation of the cnd is an xdr with density of n(h@xmath2 ) @xmath9 10@xmath10 @xmath7 and x - ray flux of 9 erg s@xmath11 @xmath12 , consistent with illumination by the active galactic nucleus , while the co lines in the sf - ring are better modeled by a pdr . the detected water transitions , together with those observed with the _ herschel _ pacs spectrometer , can be modeled by an lvg model with low temperature ( @xmath13 40k ) and high density ( @xmath4 in the range @xmath14 @xmath15 @xmath7 ) . the emission of h@xmath2o@xmath16 and oh@xmath16 are in agreement with pdr models with cosmic ray ionization . the diffuse ionized atomic component observed through the [ nii]205@xmath0 m line is consistent with previous photoionization models of the starburst .","we report the results of molecular line observations of ngc1068 with the spire and photodetector array camera and spectrometer, which have revealed the presence of a giant x - ray - dominated region ( xdr ) in this prototypical starburst galaxy. in particular we have detected for the first time the j = 1 - 0 transition of hydrogen fluoride in the local universe, characteristic of all the heavy element groups common to the milky way. in addition, three fine - structure lines, including the two lines from neutral carbon and the [ nii]205 @xmath0 m line, have been detected, in addition to the three atomic lines observed with the _ herschel_-spire fts in absorption in m82, the ulirg arp220, and the coverleaf quasar at z=2.56. we have analyzed the origin of the j=1 - 0 lines by fitting them with radiation transfer models which include a two - component component, associated with the circum - nuclear region ( cnd ) and a medium excitation component, which accounts for the water - like molecules and excitation region ( me ). the me component of the cnd is found to have a kinetic temperature of 40@xmath1 k, a mass of m(h@xday2 ) n(7 - 30 @xida ) @xiff2, and a density of n(9 - 10@xiff3 @xfig0 @xft4 @xld with a volume density n(n - 10)_up to 10(17 - 30 ) _, similar to the regions found in ulirgs mrk231 and m82. the radiation transfer model fits to the data do not exclude, but do not constrain, the two components responsible for the excitation of the co, as well as the contributions from other partially extended molecular lines, which should be detected with future submillimetre telescopes. a cnd contribution of 0.2 - 1 % is suggested by the observed and predicted co surface brightness, while a contribution from a pure rotational co component ( i.e., non - thermal excitation ) is also possible. the overall picture that emerges from our molecular line study is that of two or more components, with different contributions from the uv through xdr regions, in a process that can only be satisfactorily understood in the context of the large velocity gradient ( lvg ) model.",0.2103703703703704,"on the other hand , figure [ surface_xdr ] shows that the predicted co surface brightness in the cnd , for an xdr model with density of @xmath9 10@xmath75 @xmath7 and incident x - ray flux @xmath76 3 erg s@xmath11 @xmath12 , agrees well with the best fit value of 0.02 erg s@xmath11 @xmath12 sr@xmath11 . we found that the observations of water lines are consistent with lvg model predictions for an emission size of @xmath120 , a kinetic temperature of @xmath121 @xmath122 40@xmath12310 k , a density n(h@xmath2 ) from @xmath124 to @xmath125 @xmath7 , and a value of the @xmath126 varying between @xmath127 and @xmath128 @xmath12 . we conclude therefore that for ngc1068 collisions seem to be the dominant excitation mechanism for water and that radiative pumping can be neglected . , we analyze the origin of the three atomic fine - structure lines detected with the spire fts , namely , the two lines from neutral carbon and the [ nii]205 @xmath0 m line . we discuss here our results in the context of the various molecular observations of ngc1068 in the literature . we summarize here the results of this work . the first complete submillimetre ( 190670 @xmath0 m ) spectrum of the seyfert type 2 galaxy ngc1068 reveals the full sequence of co pure rotational lines from j@xmath1=4 to j@xmath1=13 . the radiation transfer analysis of these lines shows the presence of two physically distinct components : the first one originating from the circum - nuclear disk ( cnd ) of few arcseconds in diameter ( @xmath9 4@xmath24 ) and the second one excited in the star forming ring ( sf - ring ) with a diameter ten times larger ( @xmath9 40@xmath24 ) . these results indicate a kinetic temperature of co of @xmath8=100 k and 127 k , a gas density of @xmath4=@xmath5 and @xmath6 @xmath7 and a derived molecular hydrogen mass of m(h@xmath118 ) @xmath9 2.4@xmath2010@xmath191 m@xmath192 and m(h@xmath118 ) @xmath9 3.5@xmath2010@xmath194 m@xmath192 , for the compact and extended regions , respectively . the comparison of the observed co line intensities with predictions of photodissociation ( pdr ) and x - ray dominated regions ( xdr ) models shows that the circum - nuclear disk emission can be modeled equally well by both types of models , while the co lines in the star - forming ring can be modeled by a photodissociation region only . however some observational constraints , such as the total co surface brightness and the required radiation field , indicate that the most plausible explanation for the co excitation of the cnd is an xdr with density of n(h@xmath2 ) @xmath9 10@xmath10 @xmath7 and x - ray flux of 9 erg s@xmath11 @xmath12 , consistent with the agn illumination . in contrast , the excitation of the sf - ring component is due to pdr emission originating from the young stars / hii regions in the spiral arms . the water lines that we have detected with spire , together with those observed by pacs ( s. hailey - dunsheath 2012 , private comm . ) , have been modeled with an lvg model to constrain the physical conditions of the water excitation . we have found that the kinetic temperature is t@xmath39=40 k , the molecular hydrogen density is @xmath195 and the column density is of order n(h@xmath2o)=8 @xmath196 @xmath12 for both water forms . the molecular masses that we derived from our analysis are in good agreement with the masses estimated from both co interferometric measurements of low - j lines and mid - infrared h@xmath2 emission lines . finally we show that the intermediate - j co and [ ci ] lines in galaxies with l@xmath198 can be observed from planned and future ground - based and space telescopes up to redshift of z @xmath9 0.5 , making their diagnostic power an important tool to study galaxy evolution at intermediate redshift .",0.3241525423728813
1405.6084,"hybrid semiconductor - superconductor systems are interesting melting pots where various fundamental effects in condensed matter physics coexist . for example , when a quantum dot is coupled to a superconducting electrode two very distinct phenomena , superconductivity and the kondo effect , compete . as a result of this competition , the system undergoes a quantum phase transition when the superconducting gap @xmath0 is of the order of the kondo temperature @xmath1 . the underlying physics behind such transition ultimately relies on the physics of the anderson model where the standard metallic host is replaced by a superconducting one , namely the physics of a ( quantum ) magnetic impurity in a superconductor . a characteristic feature of this hybrid system is the emergence of sub - gap bound states , the so - called yu - shiba - rusinov ( ysr ) states , which cross zero energy across the quantum phase transition , signaling a switching of the fermion parity and spin ( doublet or singlet ) of the ground state . interestingly , similar hybrid devices based on semiconducting nanowires with spin - orbit coupling may host exotic zero - energy bound states with majorana character . both , parity crossings and majorana bound states ( mbs)s , are experimentally marked by zero bias anomalies in transport , which are detected by coupling the hybrid device with an extra normal contact . we here demonstrate theoretically that this extra contact , usually considered as a non - perturbing tunneling weak probe , leads to nontrivial effects . this conclusion is supported by numerical renormalization group calculations of the phase diagram of an anderson impurity coupled to both superconducting and normal - state leads . we obtain this phase diagram for an arbitrary ratio @xmath2 for the first time , which allows us to analyze relevant experimental scenarios , such as parity crossings as well as novel kondo features induced by the normal lead , as this ratio changes . spectral functions at finite temperatures and magnetic fields , which can be directly linked to experimental tunneling transport characteristics , show zero - energy anomalies irrespective of whether the system is in the doublet or singlet regime . we also derive the analytical condition for the occurrence of zeeman - induced fermion - parity switches in the presence of interactions which bears unexpected similarities with the condition for emergent mbss in nanowires .","the connection between the physics of magnetic impurities in superconductors and majorana bound states ( mbs ) in the presence of quantum fluctuations is investigated in detail. a recent theoretical work considers a linear chain of anderson impurities on a superconductor as the minimal model that might explain the phenomenon of yu - shiba - rusinov ( ysr ) bound states, that appear owing to pair - breaking effects that magnetic moments have on superconductivity. this mbs are predicted to appear as zero - energy bound states in effective spinless p - wave nanostructures, such as the ones resulting from the combined action of spin - orbit coupling and zeeman splitting in nanowire devices. we discuss how this picture is modified by the normal - state lead, which not only widens the sub - gap bound states into resonances of finite width, but also leads to additional kondo screening that generates an additional spectral peak pinned to zero frequency. this results in a significant change in the character of the zero - bias region in the phase diagram. using a diagonalization scheme, the critical temperature at which the zeeman energy of states above the gap @xmath0 for both normal and superconducting leads is determined. we find a condition for the system with a doublet - singlet cross - over between the ` ` singlet '' and ` ` doublet '' regimes that can be empirically distinguished from the case of a single site. we also provide an analytical expression for the condition for zeeman - induced parity crossings of states crossing the doublet at arbitrary ratio of the fermi energy, and provide a detailed derivation of the necessary for a non - bcs ground state, as well as for a topological phase transition to occur in this hybrid system. in addition, we study the effect of finite external magnetic field and external quantum fluctuations on the mbs and the mab parity system, and discuss the conditions for its existence and symmetry. the study of mbs proximized by proximizing quantum dots provides us with an important tool to understand the crossover from weakly interacting to strongly interacting systems. the complete phase diagram of this system is computed, which provides a complete picture of how the ysr bound states cross each other and can be reconciled with the shiba band picture of majorana states. the full set of results can be downloaded from the authors at http://www.sciencedirect.com/science/article/pii/s037015731400",0.18230563002680966,"a characteristic feature of these systems is the presence of sub - gap excitations , the so - called yu - shiba - rusinov ( ysr ) bound states or simply shiba states , that appear owing to the pair - breaking effects that magnetic moments have on superconductivity . for large enough @xmath4 , however , @xmath9 can cross zero energy such that the state with one unpaired quasiparticle , which is a non - bcs state , becomes the new ground state . zero energy crossings of the yrs state thus signal a quantum phase transition ( qpt ) where _ the fermionic parity of the ground state changes _ . quantum fluctuations lead to a very complex scenario since exchange is mediated by kondo processes . in a superconductor , this shiba band can support a topological phase with end mbs , which is yet another example where ysr bound states smoothly evolve towards mbs . the recent experimental observations reported in ref . using spatially resolved scanning tunneling spectroscopy reveal the existence of nearly zero - energy quasi - bound energy states that , however , are too localized to be reconciled with the shiba band picture of majorana end states . this state of affairs motivates a detailed study of the minimal anderson model incorporating both superconducting lead and normal - state tunneling probe , and fully taking into account quantum fluctuations for an arbitrary ratio of the gap to the kondo temperature . we describe different criteria for identifying the doublet - singlet cross - over region , the origin of the additional zero - bias anomalies , and provide numerical results for the @xmath24 dependence . for @xmath56 the role of the field is two - fold : ( a ) it leads to zeeman splitting of the doublet ysr states , and ( b ) it suppresses the bcs pairing parameter @xmath0 . up to now , we have presented results computed for varying @xmath22 at fixed @xmath0 . for completeness , we now provide some results computed as a function of both @xmath22 and @xmath0 : the actual experimental situation corresponds to some @xmath168 curve in this plane . in fig . we have calculated the phase diagram of an anderson impurity in contact with superconducting and normal - state leads by means of the numerical renormalization group , and established that even a very weak coupling to the normal lead perturbs the system . our results , valid for an arbitrary ratio @xmath2 , are analyzed in the context of experimental scenarios such as zero - bias anomalies induced by parity crossing transitions of yu - shiba - rusinov bound states and novel kondo features induced by the normal lead . in particular , we have discussed how spectral functions at finite temperatures and magnetic fields , which can be directly linked to experimental tunneling transport characteristics , can show zero - energy anomalies irrespective of whether the system is in the doublet or singlet regime . these results indicate that due caution is needed in interpreting experiments aiming to detect majorana bound states since in hybrid systems kondo physics and parity crossings may manifest in unanticipated ways . we have also derived the analytical condition for the occurrence of zeeman - induced fermion - parity switches in the presence of interactions , eq . , which bears unexpected similarities with the condition for emergent majorana bound states in nanowires , eq . this result suggests that the physics of zeeman - induced parity - crossings in the minimal anderson model in contact with a superconductor is connected with the condition for emergent majorana bound states . while we do not have a final answer for this , we note that the analogy persists for finite spin - orbit coupling in the non - interacting regime : it has been shown that zeeman - induced parity crossings in short non - interacting nanowires ( with finite spin - orbit coupling ) smoothly evolve towards true topological transitions as the wire becomes longer . whether our interacting results are also smoothly connected with mbs physics in the finite spin - orbit case and beyond the single quantum impurity limit remains an open question worth to be investigated .",0.3031536113936928
astro-ph0310681,"we report interferometric radio co2 - 1 and hcn1 - 0 observations at resolutions of 0.7 and 2.0 respectively , and 0.085 resolution adaptive optics k - band spectroscopy , including h@xmath0 1 - 0s(1 ) line emission and co2 - 0 stellar absorption , of the inner few arcseconds of ngc7469 . the co2 - 1 map shows a ring of molecular clouds ( which in general lie outside the compact knots seen in k - band images ) and a bright extended nucleus , with a bar or pair of spiral arms between them . the dynamical structure of both the radio co2 - 1 and the k - band h@xmath0 1 - 0s(1 ) lines at their different resolutions can be reproduced using a single axisymmetric mass model comprising 3 components : a broad disk , a ring 45 across , and an extended nucleus which we interpret as an inner nuclear ring about 0.5 across . the velocity residuals between the model and the data have a standard deviation of 25 , and no non - circular motions faster than this are seen , although this may be because in some cases a secondary bar is not expected to cause gas inflow . from the dynamical mass and estimates of the stellar mass we find that the co - to - h@xmath0 conversion is 0.40.8 times that for the milky way , following the trend to small factors that has been previously reported for intense star forming environments . the central h@xmath0 1 - 0s(1 ) morphology has a strong peak at the nucleus , but this does not trace the mass distribution ; the rotation curves indicate that there is no strong nuclear mass concentration . the origins of the 1 - 0s(1 ) emission are instead likely to lie in x - ray and uv irradiation of gas by the agn rather than via processes associated with star formation . using the 2.3@xmath1 m stellar co2 - 0 bandhead absorption and the slope of the continuum we have directly resolved the nuclear star cluster to be 0.150.20 across , and find that it is asymmetric . this cluster has an age of less than about 60myr and contributes 2030 % of the nuclear k - band light , and about 10 % of the nuclear bolometric luminosity . within a radius of @xmath24 gas contributes more than half the total mass ; but in the nucleus , within a radius of 0.1 , it is likely that most of the mass is due instead to stars .","we present a study of the kinematic structure of the molecular gas in the luminous infrared galaxy ngc7469, based on a combination of high resolution radio co data and near infrared adaptive optics h@xmath0 1 - 0s(1 ) data. the high spatial resolution of the co data taken with the adaptive optics system on the canada - france - hawaii telescope allows us to study the distribution of the gas with respect to the central 0.5 in the plane of symmetry of the galaxy. we find that the gas is kinematically connected to the nuclear ring on scales of 3.2 - 5.5 from the nucleus, and that it is oriented in the same plane as the bar and spiral arms seen in hcn. we therefore reject the possibility that the co and hcn lines trace different parts of the circumnuclear ring, although the latter do show some evidence for an asymmetrical distribution. the difference in position angle between the co ring and the nucleus on the basis of the hcn data is consistent with a bar - driven dynamical instability in the gas, and suggests that the ring and its nuclear ring are not located in a unique position angle @xmath1. the mass distribution in the co radio data is close to spherically symmetric, with both the major and minor axes distinctly non - axisymmetric. we have been able to constrain the mass inside a radius of 0.52.5 of the ring to be less than 4 times the mass of recently formed stars. utilising the scaling of the stellar light component, and using a model for the evolution of the mass surface density as a function of radius which describes the observed in p - v maps of the nuclear region, we derive a total dynamical mass of 6.8mx - 0.7 for the ring. this value is more than a factor of two above the total mass of stars and several times more than the mass in the ring observed in a k - band image of ngc1068, the only galaxy in which has been found to contain a nuclear ring which is strongly detected. the radial mass distribution we find is best described by a model in which accounts for all kinematics features except for the asymmetrical ring. with such a model we can explain the mass - to - light ratio and pah pah inclination of 2.3 in terms of a superposition of stellar and gas components. in particular, it provides a good match to the values found for the 1 -",0.19756097560975608,", we have constructed kinematic models which can explain the various features observed in the kinematic major and minor axis p - v maps , and which also estimate the rotation velocities inside a radius of 5 . as a starting point we have derived a single mass model which matches the kinematics from both the co radio data and the near infrared h@xmath0 spectroscopic data at their different resolutions . we have presented 0.7 radio co2 - 1 observations and 0.085 adaptive optics k - band spectroscopy of the central region of ngc7469 . using these data we have investigated the distribution and kinematics of the cold and warm molecular gas across nearly 2 orders of magnitude in spatial scale . additionally , we have studied the nuclear stellar cluster . the kinematics of the co2 - 1 and 1 - 0s(1 ) lines can be reproduced by an axisymmetric mass model consisting of a broad disk component , a circumnuclear ring at 2.3 , and a nuclear ring at 0.2 . the co2 - 1 morphology also suggests that there may be a bar or pair of spiral arms between the two rings , although there is no kinematical signature in the data . this may be because ngc7469 represents the case where straight shocks can not form along an inner bar , and hence there is no gas inflow . nevertheless , the increase in gas density in the bar / spiral may have triggered star formation and this is now seen as the knots of emission which lie inside the radius of the molecular ring . comparison of the dynamical and stellar masses indicates that molecular gas makes up more than half of the total mass within a radius of 1kpc , and that the remaining gas mass is at least several times that of recently formed stars in the ring . the co - to - h@xmath0 conversion factor is 0.40.8 times the galactic conversion factor . similar values have been seen a number of times in intense star forming environments . by mapping the stellar co absorption and considering the slope of the continuum , we have directly resolved the nuclear stellar cluster in ngc7469 . it is extended over 3060pc and contributes 2030% of the nuclear k - band continuum , and about 10% of the nuclear bolometric luminosity . the stellar mass counts for at least half , and probably more , of the total mass within 30pc ( 0.1 ) of the nucleus . the authors extend their thanks to the following people : jack gallimore and lowell tacconi - garman for considerable help with the co data , particularly calibrating and modelling the co1 - 0 data ; aaron evans and rodger thompson for providing reduced and calibrated _ hst _ images ; andrew baker for helpful discussions about disk dynamics ; the anonymous referee for several suggestions about how to improve the paper .",0.3118405627198124
astro-ph0301305,"we present here a new and homogeneous sample of 3340 galaxies selected from the sloan digital sky survey ( sdss ) based solely on the observed strength of their hydrogen balmer absorption line . the presence of a strong line within the spectrum of a galaxy indicates that the galaxy has under gone a significant change in its star formation history within the last gigayear . therefore , such galaxies have received considerable attention in recent years , as they provide an opportunity to study galaxy evolution _ in action_. these galaxies are commonly known as ` ` post starburst '' , ` ` e+a '' , ` ` k+a '' and strong galaxies , and the study of these galaxies has been severely hampered by the lack of a large , statistical sample of such galaxies . in this paper , we rectify this problem by selecting a sample of galaxies which possess an absorption equivalent width of @xmath0from 106682 galaxies in the sdss . we have performed extensive tests on our catalog including comparing different methodologies of measuring the absorption lines and studying the effects of stellar absorption , dust extinction and emission filling on our measurements . we have determined the external error on our measurements using duplicate observations of 11538 galaxies in the sdss . the measured abundance of our selected ( hds ) galaxies is @xmath1 % of all galaxies within a volume limited sample of @xmath2 and m(@xmath3 , which is consistent with previous studies of such galaxies in the literature . we find that only 25 of our hds galaxies in this volume limited sample ( @xmath4 % ) show no , or little , evidence for and emission lines , thus indicating that true e+a ( or k+a ) galaxies ( as originally defined by dressler & gunn ) are extremely rare objects at low redshift , _ i.e. _ , only @xmath5 % of all galaxies in this volume limited sample are true e+a galaxies . in contrast , @xmath6 % of our hds galaxies in the volume limited sample have significant detections of the and emission lines . of these , only 131 galaxies are robustly classified as active galactic nuclei ( agns ) and therefore , a majority of these emission line hds galaxies are star forming galaxies . we find that @xmath7 % ( 27/52 ) of galaxies in our volume limited hds sample that possess no detectable emission , do however possess detectable emission lines . these galaxies may be dusty star forming galaxies . we provide the community with this new catalog of selected galaxies to aid in the understanding of these galaxies , via detailed follow up observations , as well as providing a low redshift sample for comparison with higher redshift studies of hds galaxies . we will study the global properties of these galaxies in future papers .","we present a sample of selected galaxies that have been selected solely on the strength of an absorption line from the sloan digital sky survey ( sdss ). this sample of galaxies exhibits a diversity in both the morphologies and stellar populations, and it contains some of the sub classes of galaxies discussed in the literature, such as ` ` e+a '', k+a, and h@xmath0strong galaxies. to avoid confusion with other authors, we simply call this sample ` ` selected '' ( hds ) galaxies. in this paper, we present the details of our selection criteria and leave the investigation and interpretation of these galaxies to subsequent papers. we examine the frequency of emission lines (,, ) in the spectra of our sample of hds galaxies. using the measured equivalent width ( ew ) of the absorption line, we compare our measurements of the ew of this line against that of spectro1d for all sdss spectra regardless of their emission line strengths. we find that only @xmath1 % of our hds sample satisfies the strict criteria of ew ( ) / oii ) = @xcite, oii + \delta ew([oii ] ) + \geq0}$]to be strong, which indicates the presence of on going star formation activity, yet the non - detection of indicates that the galaxy has under gone a recent transformation in its star formation history. we compare the properties of our samples of galaxies with those of a shallower sample of high redshift galaxies, namely the 2dfgrs and the sdss luminosity function, as well as with higher redshift studies of such galaxies. although our sample is not complete in any sense, our findings provide a benchmark for the community to use these data to help the community construct a larger sample of strong galaxies, thus aiding in the interpretation of existing and future strong galaxy samples, _ e.g. _, the agn plus post starburst galaxy sample, and the sample of lrg galaxies and quasars.",0.2681258549931601,"therefore , many of the difficulties associated with understanding the physical nature of these galaxies could be solved through the study of a large , homogeneous sample of galaxies . in this paper , we present such a sample derived from the sloan digital sky survey ( sdss ; york et al . the advantage of this sample , over previous work , is the quality and quantity of both the photometric and spectroscopic data , as well as the homogeneous selection of sdss galaxies which covers a wide range of local environments . we present in this paper a sample of galaxies that have been selected based solely on the observed strength of their absorption line . we publish our sample of hds galaxies to help the community construct larger samples of such galaxies , which are critically needed to advance our understanding of these galaxies , as well as aiding in the planning of follow up observations and comparisons with higher redshift studies of such galaxies . in section [ data ] in this section , we discuss the measurement of the equivalent width ( ew ) of the absorption line in the sdss galaxy spectra described in section [ data ] . in this section , we compare our sample of hds galaxies against previous samples of such galaxies in the literature . further analysis of the global properties ( luminosity , environment , morphology , _ etc . _ ) of these galaxies will be presented in future papers . in this section , we present a preliminary comparison of our sdss hds galaxies with other samples of post starburst galaxies in the literature . we next examine the frequency of hds galaxies with emission , but no detectable emission . using the criteria of ew ( ) @xmath721 @xmath88 detection and ew ( ) @xmath69 1@xmath88 detection ( _ i.e. _ , @xmath89 ) + \delta ew([oii ] ) < 0}$] and @xmath90 ) , we find @xmath91% ( 21/717 ) of our hds galaxies in the volume limited sample satisfy these cuts . we present in this paper the largest , most homogeneous , search yet for strong galaxies ( _ i.e. _ , post starburst galaxies , e+a s , k+a s , a+k s _ etc . we provide the astronomical community with a new catalog of such galaxies selected from the sloan digital sky survey ( sdss ) based solely on the observed strength of the hydrogen balmer absorption line within the spectrum of the galaxy . we have carefully studied different methodologies of measuring this weak absorption line and conclude that a non parametric flux summing technique is most suited for an automated application to large datasets like the sdss , and more robust for the observed signal to noise ratios available in these sdss spectra . the measured abundance of our selected ( hds ) galaxies is @xmath960.1% of all galaxies within a volume limited sample of @xmath2 and m(@xmath97)@xmath98 , which is consistent with previous studies of post starburst galaxies in the literature . we find that only 25 galaxies ( @xmath4% ) of hds galaxies in this volume limited sample show no , or little , evidence for and emission lines , thus indicating that true e+a galaxies ( as originally defined by dressler & gunn ) are extremely rare objects , _ i.e. _ , only @xmath5% of all galaxies in our volume limited sample . , 131 galaxies are robustly classified as active galactic nuclei ( agns ) and therefore , a majority of these emission line hds galaxies are star forming galaxies , similar to the e(a ) and a+em galaxies discussed by poggianti et al .",0.3756449948400413
0802.0958,"we discuss the spin - wave interaction in two - dimensional ( 2d ) heisenberg ferromagnet ( fm ) with dipolar forces at @xmath0 using @xmath1 expansion . a comprehensive analysis is carried out of the first @xmath1 corrections to the spin - wave spectrum . in particular , similar to 3d fm discussed in our previous paper a.v . syromyatnikov , prb * 74 * , 014435 ( 2006 ) , we obtain that the spin - wave interaction leads to the _ gap _ in the spectrum @xmath2 renormalizing greatly the bare gapless spectrum at small momenta @xmath3 . expressions for the spin - wave damping @xmath4 are derived self - consistently and it is concluded that magnons are well - defined quasi - particles in both quantum and classical 2d fms at small @xmath5 . we observe thermal enhancement of both @xmath4 and @xmath6 at small momenta . in particular , a peak appears in @xmath4 and @xmath6 at small @xmath3 and at any given direction of @xmath7 . if @xmath8 the height of the peak in @xmath6 is not larger than a value proportional to @xmath9 , where @xmath10 is the spin - wave stiffness . in the case of large spins @xmath11 the peak in @xmath6 can not be greater than that of the classical 2d fm found at @xmath12 which height is small only _ numerically _ : @xmath13 for the simple square lattice . frustrating next - nearest - neighbor exchange coupling increases @xmath14 in classical 2d fm only slightly . we find expressions for spin green s functions and the magnetization . the latter differs from the well - known result by s.v . maleev , sov . phys . jetp * 43 * , 1240 ( 1976 ) . the effect of the exchange anisotropy is also discussed briefly . higher order corrections to the spectrum are considered and it is concluded that they are small compared to the first corrections obtained . our results contradict to findings of the previous works ( ar . abanov , a. kashuba , v.l . pokrovsky , prl * 77 * , 2554 ( 1996 ) ; prb * 56 * , 3181 ( 1997 ) ) in which a diffusion spin - wave mode was obtained at small momenta . it is shown that the origin of this discrepancy is that the spin - wave gap was ignored in the previous studies .","@xcite that dipolar forces lead to strong long - wavelength fluctuations manifesting themselves in infrared divergence of the first perturbation corrections to the uniform longitudinal spin susceptibility : @xmath16 . it should be noted that appearance of the gap in 2d and 3d fms is quite expected because dipolar interaction due to its symmetry and long - range nature violates the goldstone theorem . besides , the spin - wave gap was observed in 2d antiferromagnet with dipolar interaction in the zeroth order of @xmath1 ( i.e. , in the spin - wave approximation ) . we confirmed this long - standing statement for 3d fm in our previous paper @xcite and demonstrated the relation between the gap and the anisotropy at @xmath22 . a four - fold in - plane anisotropy in square 2d fm caused by quantum fluctuations but it is well known that in classical systems with degenerate ground states some of these states can be selected via order - by - disorder mechanism at finite temperature . then , one expects also appearance of the spin - wave gap in classical 2d fm with dipolar forces . in the present paper we carry out a comprehensive analysis of the first @xmath1 corrections to the spin - wave spectrum in 2d fm with dipolar interaction . similar to 3d fm we obtain the spin - wave gap @xmath24 in the spectrum @xmath2 which appears to be proportional to @xmath25 for @xmath8 and @xmath26 for @xmath11 and @xmath27 . the limiting case of classical spins is also discussed at @xmath29 and the gap was found to be proportional to @xmath30 , where @xmath31 and @xmath32 are values of the exchange and the characteristic dipolar energy in the classical model , respectively . it is demonstrated below that the spin - wave gap that was ignored in refs . we derive the spin - wave damping @xmath4 self - consistently and find that spin waves are well - defined quasi - particles in both quantum and classical 2d fms at small @xmath5 . interestingly , we observe thermal enhancement of the damping at small momenta . in particular , in quantum 2d fm we obtain a peak in both @xmath4 and @xmath6 at @xmath33 , @xmath34 and at any given @xmath7 direction . if @xmath8 the height of the peak in @xmath6 can not axceed a value proportional to @xmath35 . in the case of large spins we derive the four - fold in - plain anisotropy in the total energy of quantum 2d fm that makes directions of the magnetization along edges of the square to be energetically favorable in the simple square lattice . [ disc ] we i ) demonstrate the relation between the anisotropic term in the total energy appearing due to the dipolar interaction and the spin - wave gap at @xmath22 , ( ii ) discuss the further order @xmath1 corrections to the spin - wave spectrum , ( iii ) calculate the magnetization taking into account the spin - wave spectrum renormalization , ( iv ) derive the spin green s functions in the first order of @xmath1 , and ( v ) discuss briefly the effect of the easy - plane anisotropy and consider the spectrum renormalization obtained in refs . meantime we show in the next section that the temperature correction to the spin - wave gap is large at such large @xmath5 and @xmath80 . as a result in the present paper we discuss two - dimensional heisenberg ferromagnet ( 2d fm ) with dipolar forces at @xmath328 described by the hamiltonian ( [ ham0 ] ) and consider renormalization of the bare spin - wave spectrum ( [ spec1 ] ) due to interaction between spin waves . for this purpose",0.3209876543209877,"we present a comprehensive analysis of the first @xmath0 corrections to the spin - wave spectrum in two - dimensional heisenberg magnet with dipolar interactions. we investigate the case of large spins that arises due to anisotropy in the total energy of the quantum 2d ferromagnet that makes directions along the edges of the square to be energetically favorable in the simple square lattice. we derive expressions for spin green s functions and the magnetization. the effect of the exchange anzotropy is also discussed. finally, the spectrum renormalization is carried out. * the results and implications of our analysis are widely applied to the study of magnetic properties of thin films. it is well known that in the ferromagnetic ( fm ) model, due to the dipolar interaction, short - range magnetic order at small temperature is suppressed considerably and the bare gapless spectrum can be greatly enhanced by gapless fluctuations at small momenta. in contrast, in the presence of the next - nearest - neighbor exchange coupling the gap in the spectrum is shown to be proportional to the inverse of the characteristic dipolar energy. the gap is formed due to a multi - orbital structure of the fermionic components and the longitudinal spin susceptibility is renormalized greatly even for large spins in 2d fm. then, according to the model predictions, the ground state is a hard target for finite - temperature fluctuations and consequently the long - range order is suppressed. this effect is called the ` ` dipolar gap '' and it was first observed in ref. @xcite. subsequent studies predicted the existence of such gap and other unusual features in the fm of 2d and 3d magnons, respectively. however, it was not observed till today that anisotropic effects also occur in these systems. in the present paper we present a consistent analysis of all the features that contribute to the damping of the open quantum gap at small momentsa. we demonstrate the relation between the gap and the anisolitude of the fluctuations that leads to finite temperature fluctuations. the possible underlying mechanism of this phenomenon is not understood at present.",0.22156573116691286
astro-ph0612003,"we investigate the evolution over the last 6.3 gyr of cosmic time ( i.e. , since @xmath0 ) of the average properties of early - type galaxies within the extended deep field - south ( ) . our early - type galaxy sample includes 539 objects with red - sequence colors and srsic indices larger than @xmath1 , which were selected jointly from the combo-17 ( classifying objects by medium - band observations in 17 filters ) and gems ( galaxy evolution from morphologies and seds ) surveys . we utilize the deep observations over the and stacking analyses to constrain primarily the average emission from ` ` normal '' early - type galaxies ( i.e. , those that are not dominated by luminous active galactic nuclei [ agns ] ) . in our analyses , we study separately optically luminous ( @xmath2 ) and faint ( @xmath3 ) galaxy samples , which we expect to have soft ( ) emission dominated by hot ( @xmath41 kev ) interstellar gas and low mass binary ( lmxb ) populations , respectively . we detect individually 49 ( @xmath59 % ) of our galaxies in the band , and classify these sources as either normal early - type galaxies ( 17 galaxies ) or agn candidates ( 32 galaxies ) . the agn fraction of our optically luminous samples evolves with redshift in a manner consistent with the @xmath6 evolution observed in other investigations of -selected agns . after removing potential agns from our samples , we find that the mean luminosity ratio ( @xmath7 ) for optically luminous early - type galaxies does not evolve significantly over the redshift range . this lack of evolution implies a general balance between the heating and cooling of the hot interstellar gas . if transient agn activity is largely responsible for maintaining this balance , then we infer that mechanical power must be dominating the feedback out to @xmath0 . furthermore , in this scenario the average mechanical agn power must remain roughly constant over the last half of cosmic time despite significant evolution in the average agn radiative luminosity . for our optically faint early - type galaxies , we find suggestive evidence that @xmath7 increases with redshift over the range ; however , due to limited statistical constraints on both the local @xmath7 ratio and the agn contamination of our samples , we consider this result to be marginal .",", we utilize the m05 sample and a supplementary sample of 64 additional early - type galaxies located within the ( selected using the same techniques discussed in m05 ) to characterize the redshift evolution of the properties of early - type galaxies . we investigate separately the cosmic - time evolution of ( 1 ) the hot interstellar gas content through optically luminous galaxy samples and ( 2 ) the lmxb populations through optically faint galaxy samples . using stacking analyses , we have investigated the evolution of 539 , @xmath19 0.10.7 early - type galaxies located in the . these galaxies were selected using a combination of red - sequence colors and srsic indices as a part of the combo-17 and gems surveys ( m05 ) . we classified our original early - type galaxy sample as the `` general sample '' and generated an additional `` faded sample , '' which was corrected for the passive fading of old stellar populations . using these samples , we analyzed separately optically luminous ( @xmath2 ) and faint ( @xmath3 ) populations , which are expected to have soft spectra dominated by hot interstellar gas and lmxbs , respectively . we detected 49 early - type galaxies in the band and classified 32 of these as agn candidates based on their , optical , and radio properties ( see @xmath27 2.1.1 for details ) ; the remaining 17 -detected sources had multiwavelength properties consistent with normal galaxies . in addition to the 32 -detected agn candidates , we identified 13 galaxies with agn - like radio to optical flux ratios , which we characterized as potential agns . we found that the majority of the agn candidates were coincident with optically luminous early - type hosts . the inferred agn fraction for our optically luminous galaxies shows evidence for evolution with redshift in a manner consistent with the @xmath6 evolution expected from other studies of agn evolution . 2 . when stacking the counts from our normal optically luminous early - type galaxy samples , we found that the to optical mean luminosity ratio , @xmath7 , stays roughly constant over the redshift range , which indicates that the -emitting gas has not significantly evolved over the last @xmath56.3 gyr ( i.e. , since @xmath248 ) . using the data available we interpret the lack of evolution of optically luminous early - type galaxies to be due to an energy balance between the heating and cooling of the hot gas over each cooling time . when assuming that the heating is largely due to transient agn activity , we found that mechanical feedback dominates the heating out to @xmath0 versus radiative power , which we inferred to be very poorly coupled to the gas . , we found suggestive evidence that @xmath7 increases with redshift . by @xmath19 0.5 , @xmath7 is measured to be @xmath162 and @xmath163 times larger than that measured at @xmath251 for our general and faded samples , respectively ; however , due to poor statistical constraints on the local relation and the undetected agn population , we could not confidently rule out the null hypothesis . we hypothesized that evolution of the optically faint early - type galaxy emission may be due to the evolution of lmxbs in galaxies that have recently joined the red - sequence and/or the cooling of hot gas within these galaxies .",0.3478260869565217,"we have investigated the redshift evolution of 539, @xmath0 0.10.7 early - type galaxies using multiwavelength observations from the combo-17 and gems surveys. the sample was originally selected to be redshifted from the _ hubble space telescope _ ( ) optical bandpass to the _ great observatories origins deep survey _ ( goods ) bandpass. using stacking analyses, we identified 32 candidates of agn based on their radio, optical, and radio properties. the majority ( 29 out of 32 ) of these galaxies were not detected individually in the deep observations. however, the other 17 sources were detected in at least one of three bands ( and probably in all three bands ), providing evidence that these are heavily contaminated by hot interstellar gas and/or large - scale molecular clouds ( lmxbs ). the evolution of the average luminosity - weighted mean optical luminosity ratio,, steeply decreases with redshift out to. the inferred ratio is roughly constant compared to the optically luminous galaxy samples, which shows a shallower slope and a brighter tail at higher redshifts. from the best - fit linear relation between and the mean absolute magnitude and the effective temperature of the hot -emitting gas, we find that the average ( uncorrected for absorption and emission ) luminosity of the lmxb component scales linearly with the host galaxy luminosity, as expected from the passive fading of old stellar populations. the weak dependence of the on - going agn activity on redshift also suggests that the present - day luminosity function is largely controlled by feedback from transient active galactic nuclei ( agns ), which is consistent with observations of distant, low - redshift galaxies. using the properties of the majority of the agn candidates, we were able to classify and place constraints on the x - ray luminosity evolution of agns and normal, optically faint galaxies. the median redshift of the faded sample is 0.34 gyr, while the average agn fraction stays roughly constant over that redshift range. using measurements of the cosmic microwave background ( cmb ) emission, we found that the integrated ( or luminosity ) emission of the cmb in low - luminosity ( or -like sources ) galaxies increases significantly with cosmic time, suggesting that the main source of emission from these galaxies is likely to be the stellar mass of an as yet undisturbed fraction of stars.",0.2109704641350211
astro-ph0607609,"we calculate many different nova light curves for a variety of white dwarf masses and chemical compositions , with the assumption that free - free emission from optically thin ejecta dominates the continuum flux . we show that all these light curves are homologous and a universal law can be derived by introducing a ` ` time scaling factor . '' the template light curve for the universal law has a slope of the flux , @xmath0 , in the middle part ( from @xmath1 to @xmath2 mag below the optical maximum ) but it declines more steeply , @xmath3 , in the later part ( from @xmath2 to @xmath4 mag ) , where @xmath5 is the time from the outburst in units of days . this break on the light curve is due to a quick decrease in the wind mass loss rate . the nova evolutions are approximately scaled by the time of break . once the time of break is observationally determined , we can derive the period of a uv burst phase , the duration of optically thick wind phase , and the turnoff date of hydrogen shell - burning . an empirical observational formula , @xmath6 , is derived from the relation of @xmath0 , where @xmath7 and @xmath8 are the times in days during which a nova decays by 2 and 3 mag from the optical maximum , respectively . we have applied our template light curve model to the three well - observed novae , v1500 cyg , v1668 cyg , and v1974 cyg . our theoretical light curves show excellent agreement with the optical @xmath9 and infrared @xmath10 , @xmath11 , @xmath12 light curves . the continuum uv 1455 light curves observed with _ iue _ are well reproduced . the turn - on and turn - off of supersoft x - ray observed with _ rosat _ are also explained simultaneously by our model . the wd mass is estimated , from the light curve fitting , to be @xmath13 for v1500 cyg , @xmath14 for v1668 cyg , and @xmath15 for v1974 cyg , together with the appropriate chemical compositions of the ejecta .","thus we can follow the developments of the optical , uv , and supersoft x - ray light curves by a single modeled sequence of the steady wind solutions . we present new light curves for the optical and ir observations based on the free - free emission model . we propose a light curve model based on free - free emission and on the optically thick wind model , and have successfully applied it to three well observed novae , v1500 cyg , v1668 cyg , and v1974 cyg . our main results are summarized as follows : \(1 ) we have calculated light curves of novae in which free - free emission from optically thin ejecta dominates the continuum flux . the free - free luminosity is obtained from the density structures outside the photosphere , which are calculated using the optically thick wind model . \(2 ) the free - free emission light curves are homologous among various white dwarf ( wd ) masses , chemical compositions , and wavelengths ( in optical and infrared ) . therefore , we are able to represent a wide range of nova light curves by a single template light curve on the basis of one - parameter family , i.e. , a time scaling factor . \(3 ) the template light curve declines as @xmath0 in the middle part ( from @xmath1 to @xmath2 mag below the optical maximum ) and then as @xmath3 in the later part ( from @xmath2 to @xmath4 mag ) , where @xmath5 is the time from the outburst in units of days . this break on the light curve is caused by the sharp decrease in the wind mass loss rate . since the time of the break is proportional to the time scaling factor , we use this time of break to specify the timescale of a nova light curve in the one - parameter family instead of the time scaling factor . \(4 ) if we know , from observation , the time of break in the light curve , we can tell when the optically thick winds stop ( supersoft x - ray turn - on time ) and when hydrogen shell - burning ends ( supersoft x - ray turnoff time ) . \(6 ) our modeled light curves have been applied to three well - observed novae , v1500 cyg ( nova cygni 1975 ) , v1668 cyg ( nova cygni 1978 ) , and v1974 cyg ( nova cygni 1992 ) . direct fittings with our free - free light curves indicate the wd mass of @xmath13 for v1500 cyg and @xmath14 for v1668 cyg for the chemical compositions suggested . in v1974 cyg , @xmath333 is obtained for the hydrogen content of @xmath66 while @xmath14 is suggested for the different hydrogen content of @xmath71 . \(7 ) model light curves of the 1455 band nicely follow the observations both for v1668 cyg and v1974 cyg . fitting with the uv 1455 light curves , we estimate the distances of v1668 cyg to be @xmath334 kpc for @xmath232 and the distance of v1974 cyg to be @xmath294 kpc for @xmath280 . \(8 ) the supersoft x - ray flux was observed in v1974 cyg , which emerged on day @xmath335 and declined on day @xmath274 . this feature is explained consistently by our model . the photospheric temperature rises high enough to emit supersoft x - rays on day @xmath336 , which corresponds to the end of optically thick winds .",0.3556638246041413,"we present a theoretical model of nova light curves in which the optical ( @xmath0 ) and ultraviolet ( uv ) light curves are dominated by free - free emission from the optically thin, optically thick, ejecta. we extend our model to include the effects of the white dwarf mass, chemical composition of the envelope, and the companion star thermal condition, which is widely applicable to optical and ir light curves of novae. a sequence of steady - state solutions for nova outbursts is calculated by considering the nova envelope to be in a steady state, after which time the envelope mass is decreased by the winds and nuclear burning. because the winds are driven by the strong peak of opal opacity, the wind - blown flux drops very quickly after the optical peak. this is because the energy generation during the wind phase depends on the total amount of cno but hardly on the chemical composition. we assume that c or o ( or ne ) is dredged up from the wd interior during the very early phase of the outburst and then mixed into the entire envelope by convection. we calculate optical and uv light curves by using the same method and also by applying it to three well observed novae, v1500 cygni, v1668 cyg, and v1974 cyg. we find that the optical flux is a good indicator of wd mass if we assume a single white dwarf. the turn - on time is the earliest part of the x - ray / turn - off time and is particularly important in the optical / uv band, because it is the longest and most variable of all parameters. except for the early in the outburst, the uv 1455 light curve is well fitted by a single template light curve having a universal decline law. we also find that in the ultraviolet band, the flux at the optical and infrared wavelengths is a power law with a photon index of 1.0. this suggests that the ultraviolet light curve of a typical nova may be composed of many components, i.e., many mag brighter in the early phase and less dense in the late phase, which may be reflected in the later uv and optical fluxes. we compare our model light curves with the _ iue _ and _ rosat _ data of v1624 cyg and v1455. we confirm that the former is a best - fit model light curve and that its optical decay is due to the large variation of the luminosity with wavelength. we apply our method to",0.23724137931034486
astro-ph0010571,"with the recent publication of the measurements of the radiation angular power spectrum from the boomerang antarctic flight ( de bernardis et al . 2000 ) , it has become apparent that the currently favoured spatially - flat cold dark matter model ( matter density parameter @xmath0 , flatness being restored by a cosmological constant @xmath1 , hubble parameter @xmath2 , baryon density parameter @xmath3 ) no longer provides a good fit to the data . we describe a phenomenological approach to resurrecting this paradigm . we consider a primordial power spectrum which incorporates a bump , arbitrarily placed at @xmath4 , and characterized by a gaussian in log @xmath5 of standard deviation @xmath6 and amplitude @xmath7 , that is superimposed onto a scale - invariant power spectrum . we generate a range of theoretical models that include a bump at scales consistent with cosmic microwave background and large - scale structure observations , and perform a simple @xmath8 test to compare our models with the @xmath9 dmr data and the recently published boomerang and maxima data . unlike models that include a high baryon content , our models predict a low third acoustic peak . we find that low @xmath10 observations ( 20 @xmath11 200 ) are a critical discriminant of the bumps because the transfer function has a sharp cutoff on the high @xmath10 side of the first acoustic peak . current galaxy redshift survey data suggests that excess power is required at a scale around 100 mpc , corresponding to @xmath4 @xmath12 0.05 @xmath13 mpc@xmath14 . for the concordance model , use of a bump - like feature to account for this excess is not consistent with the constraints made from recent cmb data . we note that models with an appropriately chosen break in the power spectrum provide an alternative model that can give distortions similar to those reported in the apm survey as well as consistency with the cmb data ( atrio - barandela et al . 2000 ; barriga et al . 2000 ) . we prefer however to discount the apm data in favour of the less biased decorrelated linear power spectrum recently constructed from the pscz redshift survey ( hamilton & tegmark 2000 ) . we show that the concordance cosmology can be resurrected using our phenomenological approach and our best - fitting model is in agreement with the pscz observations . -0.5 in epsf cosmology : theory cosmic microwave background","we examine the possibility that the second acoustic peak in the angular power spectrum of the cosmic microwave background ( cmb ) is suppressed relative to the first acoustic peak based on recent boomerang and maxima data. we show that a phenomenological bump, arbitrarily placed at wavenumber @xmath0, can enhance the power spectrum amplitude around 100 mpc@xmath1, allowing for a baryon fraction greater than expected for a spatially flat universe such as the concordance model. we incorporate the bump into the primordial power spectrum by renormalizing the standard low - density cosmological model to the decorrelated linear power spectrum that was recently generated by ostriker & steinhardt ( 1995 ). we interpret the 22 decorrelated pscz data points as constraints on the bump parameters so that the theoretical model that we find to be the best - fit to the cmb observational data set can be compared with the galaxy survey observations. the choice of bump parameters is consistent with observations of large - scale power and cmb anisotropies. we find that with the chosen bump the model with a bias parameter of 1.07 ( hamilton & tegmark 2000 ) is ruled out at the 95 % confidence level, whereas the model without the bump takes a biasulus of 1. both models are a good fit to these up - to - date data sets, but the current data do not probe the scales that are critical to distinguishing between the models. we discuss the implications of our results for the scalelengths of adiabatic density perturbations in a model - by - model basis. # 1#2#3acta. phys. pol. * b#1 *, # 2 ( # 3 ) # 1 # 1 = = = cmr10 scaled2 = cmbh_s psfig.tex # 1 eq. ( [ eq : pncrab_s ] ) # 10^#1 # 1 ^#2_w 2m_z^2 2bh^2 # 1sec^2",0.1840490797546012,"the recent boomerang and maxima measurements of an acoustic peak in the angular power spectrum of the cosmic microwave background ( cmb ) temperature at @xmath15 ( de bernardis et al . one consequence of the location of this peak , due to the compression of an acoustic wave on first entering the horizon of last scattering , is that the spatial geometry of the universe is flat . however , the weakness of the second acoustic peak at @xmath16 , due to the subsequent first rarefaction of the acoustic wave on the last scattering horizon , has provoked considerable speculation as to the additional freedom that could be added to the concordance cold dark matter ( cdm ) model ( matter density parameter @xmath0 , flatness being restored by a cosmological constant @xmath1 , hubble parameter @xmath2 , baryon density parameter @xmath3 ) to accommodate such an effect . 1990 ; einasto et al . 1997 ; landy et al . we therefore consider a primordial power spectrum which incorporates a phenomenological bump , arbitrarily placed at @xmath4 , and characterized by a gaussian in log @xmath5 of standard deviation @xmath6 and amplitude @xmath7 , that is superimposed onto a scale - invariant power spectrum as advocated by silk & gawiser ( 1998 ) . @xmath24 we restrict the choice of bump parameters to the region of parameter space that is consistent with large - scale structure and cmb observations . theories that predict a bump in the primordial power spectrum have been inspired by hints of such a feature from large - scale structure observations . this indicates that , for the chosen cosmology , the scale at which a bump can appear in the primordial power spectrum is quite constrained by the cmb data sample . at the 68% confidence level we describe a toy model for a bump to be included in the primordial density power spectrum with the hope of reviving the standard model without resorting to revising fundamental cosmological theories . we have confronted our theoretical models with the recent boomerang and maxima data and have shown that it is indeed possible to resurrect the standard model , although we are somewhat restricted with where we place our additional feature . we find that our model , unlike models that include a high baryon content , predicts a low third acoustic peak . there are two cmb measurements that will help to discriminate between such a bump and cosmological alternatives for suppressing the second peak . in addition , although low @xmath10 ( 20 - 100 ) observations have received relatively little attention and hence are currently a poor constraint on cosmological parameters , we have found that the low @xmath10 power is potentially a critical discriminant for the possible bump feature . this because the transfer function has a much sharper cutoff on the high @xmath10 side of the first peak , relative to the cutoff on the low @xmath10 side . we note that models with an appropriately chosen break in the power spectrum provide an alternative model that can give distortions similar to those reported in the apm survey as well as consistency with the cmb data ( atrio - barandela et al .",0.4299065420560748
hep-ph0102265,"assuming three - neutrino mixing and massive majorana neutrinos , we study the implications of the neutrino oscillation solutions of the solar and atmospheric neutrino problems and of the results of the chooz experiment for the predictions of the effective majorana mass in neutrinoless double beta ( -)decay , . the general case of cp - nonconservation is investigated . the predicted values of , which determines the magnitude of the -decay rate , depend strongly on the type of the neutrino mass spectrum , on the solution of the solar neutrino problem , as well as on the values of the two majorana cp - violating phases , present in the lepton mixing matrix . we find that i ) @xmath0ev for a hierarchical neutrino mass spectrum , ii ) @xmath1ev if the spectrum is of the inverted hierarchy type , and iii ) @xmath2 in the case of three quasi - degenerate neutrinos , @xmath3 being the common neutrino mass scale which is limited by the bounds from the @xmath4h @xmath5decay experiments , @xmath6ev . the indicated maximal values of are reached in the cases i ) , ii ) and iii ) respectively , for the large mixing angle ( lma ) msw solution , the small mixing angle ( sma ) msw , and for all current solutions , of the solar neutrino problem . if cp - invariance holds , is very sensitive to the values of the relative cp - parities of the massive majorana neutrinos . the cases of neutrino mass spectra which interpolate between the hierarchical or inverted hierarchy type and the quasi - degenerate one are also studied . the observation of the -decay with a rate corresponding to @xmath7ev can provide unique information on the neutrino mass spectrum . combined with information on the lightest neutrino mass or the type of neutrino mass spectrum , it can give also information on the cp - violation in the lepton sector , and if cp - invariance holds - on the relative cp - parities of the massive majorana neutrinos . 0.6 cm * majorana neutrinos , neutrino mass spectrum , cp - violation and + neutrinoless double @xmath8-decay : i. the three - neutrino mixing case + * s. m. bilenky@xmath9 , s. pascoli@xmath10 and s. t. petcov@xmath10 0.4 cm","we consider the possible types of neutrino mass spectrum : hierarchical , with two quasi - degenerate in mass majorana neutrinos ( the third having a different mass ) , and with three quasi - degenerate majorana neutrinos . in the case of two quasi - degenerate massive neutrinos , we investigate the general case of cp - nonconservation and we use the results of the analyzes of the latest solar and atmospheric neutrino data . combined with data on the mass of the lightest neutrino or / and on the type of neutrino mass spectrum , it can give also information on the cp - violation in the lepton sector , and if cp - invariance holds - on the relative cp - parities of the massive majorana neutrinos . assuming three - neutrino mixing and massive majorana neutrinos , we have studied in detail the implications of the neutrino oscillation solutions of the solar and atmospheric neutrino problems and of the data of the reactor long baseline chooz and palo verde experiments @xcite , for the predictions of the effective majorana mass , which determines the -decay rate . we have investigated the general case of cp - nonconservation . the -decay effective majorana mass depends , in general , on two physical ( majorana ) cp - violating phases . for each of the five types of neutrino mass spectrum indicated above we have derived detailed predictions for the values of for the three solutions of the solar neutrino problem , favored by the current solar neutrino data : the lma msw , the sma msw and the low - qvo one . in each of these cases we have identified the `` just - cp - violation '' region of values of whenever it existed : a value of in this region would unambiguously signal the presence of cp - violation in the lepton sector . analyzing the case of cp - conservation , we have derived predictions for corresponding to all possible sets of values of the relative cp - parities of the three massive majorana neutrinos . this was done for all different types of neutrino mass spectrum we have considered . if the neutrino mass spectrum is hierarchical , only the contributions to due to the exchange of the two heavier majorana neutrinos @xmath64 can be relevant and depends only on one cp - violating phase , @xmath65 . in the case of the neutrino mass spectrum with inverted hierarchy , eqs . accordingly , the results for we have found in the case of neutrino mass spectrum with partial hierarchy ( partial inverted hierarchy ) `` interpolate '' between the results for the hierarchical ( inverted mass hierarchy ) and the quasi - degenerate neutrino mass spectra . most of these results are presented graphically in figs . , we have found that the observation of the -decay with a rate corresponding to @xmath7ev , which is in the range of sensitivity of the future -decay experiments , can provide unique information on the neutrino mass spectrum . combined with information on the lightest neutrino mass or the type of neutrino mass spectrum , it can give also information on the cp - violation in the lepton sector , and if cp - invariance holds - on the relative cp - parities of the massive majorana neutrinos . we have assumed that the -decay is induced by the ( v - a ) charged current weak interaction via the exchange of the massive majorana neutrinos between two neutrons in the initial nucleus .",0.41169590643274856,"we study in detail the implications of the neutrino oscillation solutions of the solar and atmospheric problems and of the results of the reactor long baseline chooz and palo verde experiments, for the predictions of the effective majorana mass parameter, which controls the -decay rate. we address the general case of cp - nonconservation and we obtain predictions for the values of the relative cp - parities of the three massive majorana neutrinos : the lma msw, the sma msw and the low - qvo one. in each of these cases we identify the ` ` just - cp - violation '' region of values of whenever it existed : a value of in this region would unambiguously signal the presence of chr - violation in the lepton sector. analyzing the case of clumping, we derive predictions for corresponding to all possible sets of values and we give the corresponding non - trivial lower bounds on. we find that a sufficiently accurate measurement of, @xmath0, can allow to get direct information on the value of the cp - violating phase. in particular, a measurement of the -dependence of with a rate comparable to that of the super - kamiokande experiment can lead to a unique determination of, i.e., to a substantial reduction of the signal - to - noise of the future high - sensitivity experiments. cern - ph - th/2005 - 241 + tum -t39 - 03 - ove + mpp-2005 - 156 + hep - ph/0512032 * andrzej j. buras,@xmath1 physik - department, technische universitt mnchen, d-85747 garching, germany pacs numbers : 14.60.jh, 12.38.bx, 14.80.cp @=11 -11 - reprinted figurations, provided with the permission of the authors, are as follows. the first four figures are shown in postscript form, which may be viewed as a black box. the last two images are of the final result, displayed in black - space, shown in red - light and shown in blue - shadowed form. + + + 1.5 cm i.z. uren, peter l. andreani, + _ and _ instituto de fsica, depto. fsica terica, + c.f., universidad andres bello, av. lisboa, chile _ + 2.5",0.27409638554216864
0705.4475,"we study the stokes - einstein ( se ) and the stokes - einstein - debye ( sed ) relations , @xmath0 and @xmath1 where @xmath2 and @xmath3 are translational and rotational diffusivity respectively , @xmath4 is the temperature , @xmath5 the viscosity , @xmath6 the boltzmann constant and @xmath7 is the ` ` molecular '' radius , using molecular dynamics simulations of the extended simple point charge model of water . we find that both the se and sed relations break down at low temperature . to explore the relationship between these breakdowns and dynamical heterogeneities ( dh ) , we also calculate the se and sed relations for subsets of the @xmath8 ` ` fastest '' and @xmath8 ` ` slowest '' molecules . we find that the se and sed relations break down in both subsets , and that the breakdowns occur on all scales of mobility . thus these breakdowns appear to be generalized phenomena , in contrast with the view where only the most mobile molecules are the origin of the breakdown of the se and sed relations , embedded in an inactive background where these relations hold . at low temperature , the se and sed relations in both subsets of molecules are replaced with ` ` fractional '' se and sed relations , @xmath9 and @xmath10 where @xmath11 and @xmath12 . we also find that there is a decoupling between rotational and translational motion , and that this decoupling occurs in both fastest and slowest subsets of molecules . we also find that when the decoupling increases , upon cooling , the probability of a molecule being classified as both translationally and rotationally fastest also increases . to study the effect of time scale for se and sed breakdown and decoupling , we introduce a time - dependent version of the se and sed relations , and a time - dependent function that measures the extent of decoupling . our results suggest that both the decoupling and se and sed breakdowns are originated at the time scale corresponding to the end of the cage regime , when diffusion starts . this is also the time scale when the dh are more relevant . our work also demonstrates that selecting dh on the basis of translational or rotational motion more strongly biases the calculation of diffusion constants than other dynamical properties such as relaxation times .","we test the validity of the stokes - einstein ( se ) relation and the decoupling of translational and rotational motion in the spc / e model of water. by performing molecular dynamics simulations, we find that at low temperatures there is a breakdown of both the se and sed relations and these relations can be replaced by fractional functional forms. the se breakdown is observed in every scale of rotational mobility. similarly, the sed breakdown is produced by a generalized breakdown, instead of a view where only the most mobile molecules are the origin of the breakdown. we also find that, upon cooling, the liquid does not become a glass in a spatially homogeneous fashion. finally, we include the effect of time scale in the study. = 1.5truecm = -0.3truecm 1truecm * c - v. diff. nucl. * b#1 *, # 3 ( # 2 ) # 1#2#3#4#5#6c. r. # 1 # 2 - # 3 - # 4#1#2 # 3 # 4 # 5#1| # # 1| # 1*#1 # 1 - # 1(#2,#3)_adv. chem. _ * # 1 * # 2 ( # 3 ) [ apj ] # 1,#2 ] apj. phys. lett. # 1 ( 19#3 ) [ m]#1 hep - th/9911158 + ens/99/17 + june 1999 + * breakdowns of stokes and einstein relations in molecular systems * + chung - lin shan + _ department of chemistry, national cheng kung university _ + no. 1, university road, tainan city 70101, taiwan, r.o.c. _ + e - mail : clshan@mail.ncku.edu.tw + @xmath0 center for emergent matter science, department of physics, tsing hua university, beijing 100084, china + electronic - chemistry department, national center for theoretical sciences, hsinchu city 30013, chia",0.2240802675585284,"we perform molecular dynamics ( md ) simulations of the spc / e model of water @xcite . the behavior of @xmath105 and @xmath108 indicates that the emergence of dh is correlated to the rotation / translation decoupling , just as it does for the breakdown of the se and sed relations . in this work , we tested in the spc / e model for water ( i ) the validity of the se and sed equations , ( ii ) the decoupling of rotational and translational motion , and ( iii ) the relation of ( i ) and ( ii ) to dh . we found that at low temperatures there is a breakdown of both the se and sed relations and that these relations can be replaced by fractional functional forms . the se breakdown is observed in every scale of translational mobility . thus our results support the view of a generalized breakdown , instead of a view where only the most mobile molecules are the origin of the breakdown of the se and sed relations , embedded in an inactive background where these relations hold . we also found that , upon cooling , there is a decoupling of translational and rotational motion . this decoupling is also observed in all scales of rotational and translational mobilities . in agreement with md simulations of an otp model @xcite , we find that an opposite decoupling is observed depending on whether one uses the rotational diffusivity , @xmath3 , or the rotational relaxation time , @xmath90 . in the first case , we also found that as the decoupling of @xmath81 increases , the number of molecules belonging simultaneously to both rh and th also increases . we also explored the role of time scales in the breakdown of the se and sed relations and decoupling . to do this we introduced time dependent versions of the se and sed expressions . our results suggest that both the decoupling and se and sed breakdowns are originated at the time scale corresponding to the end of the cage regime , when diffusion starts . this is also the time scale at which the dh are more relevant . our work also demonstrates that selecting dh on the basis of translational or rotational displacement more strongly biases the calculation of diffusion constants than the other dynamical properties . if appropriate care is taken , this should not be problematic , but it does make apparent that an alternative approach to identify dh would be valuable . this is especially true when contrasting behavior of diffusion constants and relaxation times , as is the case for the se and sed relations .",0.48010610079575605
1301.4051,"_ there is a growing consensus among physicists that the classical notion of spacetime has to be drastically revised in order to find a consistent formulation of quantum mechanics and gravity . one such nontrivial attempt comprises of replacing functions of continuous spacetime coordinates with functions over noncommutative algebra . dynamics on such noncommutative spacetimes ( noncommutative theories ) are of great interest for a variety of reasons among the physicists . additionally arguments combining quantum uncertainties with classical gravity provide an alternative motivation for their study , and it is hoped that these theories can provide a self - consistent deformation of ordinary quantum field theories at small distances , yielding non - locality , or create a framework for finite truncation of quantum field theories while preserving symmetries . in this thesis we study the gauge theories on noncommutative moyal space . we find new static solitons and instantons in terms of the so - called generalized bose operators ( gbo ) . gbos are constructed to describe reducible representation of the oscillator algebra . they create / annihilate @xmath0-quanta , @xmath0 being a positive integer . we start with giving an alternative description to the already found static magnetic flux tube solutions of the noncommutative gauge theories in terms of gbos . the nielsen - olesen vortex solutions found in terms of these operators also reduce to the ones known in the literature . on the other hand , we find a class of new instanton solutions which are unitarily inequivalent to the ones found from adhm construction on noncommutative space . the charge of the instanton has a description in terms of the index representing the reducibility of the fock space representation , i.e. , @xmath0 . after studying the static soliton solutions in noncommutative minkowski space and the instanton solutions in noncommutative euclidean space we go on to study the implications of the time - space noncommutativity in minkowski space . to understand it properly we study the time - dependent transitions of a forced harmonic oscillator in noncommutative 1 + 1 dimensional spacetime . we also provide an interpretation of our results in the context of non - linear quantum optics . we then shift to the so - called dsr theories which are related to a different kind of noncommutative ( @xmath1-minkowski ) space . dsr ( doubly / deformed special relativity ) aims to search for an alternate relativistic theory which keeps a length / energy scale ( the planck scale ) and a velocity scale ( the speed of light scale ) invariant . we study thermodynamics of an ideal gas in such a scenario . _ in first chapter we introduce the subjects of the noncommutative quantum theories and the dsr . chapter [ instanton ] starts with describing the gbos . they correspond to reducible representations of the harmonic oscillator algebra . we demonstrate their relevance in the construction of topologically non - trivial solutions in noncommutative gauge theories , focusing our attention to flux tubes , vortices , and instantons . our method provides a simple new relation between the topological charge and the number of times the basic irreducible representation occurs in the reducible representation underlying the gbo . when used in conjunction with the noncommutative adhm construction , we find that these new instantons are in general not unitarily equivalent to the ones currently known in literature . chapter [ qo ] studies the time dependent transitions of quantum forced harmonic oscillator ( qfho ) in noncommutative @xmath2 perturbatively to linear order in the noncommutativity @xmath3 . we show that the poisson distribution gets modified , and that the vacuum state evolves into a ` ` squeezed '' state rather than a coherent state . the time evolutions of uncertainties in position and momentum in vacuum are also studied and imply interesting consequences for modelling nonlinear phenomena in quantum optics . in chapter [ dsr ] we study thermodynamics of an ideal gas in doubly special relativity . we obtain a series solution for the partition function and derive thermodynamic quantities . we observe that dsr thermodynamics is non - perturbative in the sr and massless limits . a stiffer equation of state is found . we conclude our results in the last chapter . to + _ bhaiji ( shri dhiraj kumar mishra ) + and + _ pappaji ( shri karunakar dutt ) _ _ i hereby declare that the work presented in this thesis entitled ` ` topics in noncommutative gauge theories and deformed relativistic theories '' is the result of the investigations carried out by me under the supervision of prof . sachindeo vaidya at the centre for high energy physics , indian institute of science , bangalore , india , and that it has not been submitted elsewhere for the conferment of any degree or diploma of any institute or university . keeping with the general practice , due acknowledgements have been made wherever the work described is based on other investigations . + dated : nitin chandra + sachindeo vaidya + associate professor + centre for high energy physics , + indian institute of science , + bangalore - 560012 , + karnataka , india + first and foremost i thank my phd adviser sachindeo vaidya , whose guidance made my ph.d . possible . despite of my slow progress in research , he has been very patient , cooperative and helpful . timely completion of this thesis is a result of his support and encouragement . i also acknowledge my sincere thanks to manu paranjape of universit de montreal . i simply ca nt explain in words how wonderful person he is . his friendly behaviour is the prime reason for my stay in montreal being a wonderful and memorable one . i thank iisc and udem for giving me an opportunity to pursue my research and learn a lot in the process . i also thank canadian commonwealth scholarship program and iisc for providing the financial assistance . i thank all chep members , especially the student friends for all the fun including baba and chicken parties . thanks to all my friends who were also my collaborators . i learnt a lot about independent research while working with sandeep on the problem of dsr . thanks to all the friends from iisc including those in physics , bihari samiti , my rkm friends , integrated phd batch - mates , b - mess friends for making this 7 year - long stay enjoyable . i also want to thank all my friends outside iisc in bangalore for the memorable moments i spent with them . presence of my friend sp makes me forget all my worries . i am thankful to all my childhood friends who kept contact with me throughout these years . i thank pappu bhaiya and his family . they supported me as local guardians throughout my stay in bangalore . i dedicate my thesis to bhaiji and pappaji . bhaiji is the person with whom i discussed all my curiosities in science when i was a child . pappaji taught me english when i needed it most . finally and most importantly i am grateful to my parents and family . i am forever indebted to their love and support which gives me greatest satisfaction and happiness . 1 . _ time dependent transitions with time - space noncommutativity and its implications in quantum optics _ + n. chandra + j. phys . a a * 45 * , 015307 ( 2012 ) [ arxiv:1104.1059 [ hep - th ] ] . 2 . _ thermodynamics of ideal gas in doubly special relativity _ + n. chandra and s. chatterjee + phys . rev . d * 85 * , 045012 ( 2012 ) [ arxiv:1108.0896 [ gr - qc ] ] . 3 . _ noncommutative vortices and instantons from generalized bose operators _ + n. acharyya , n. chandra and s. vaidya + jhep * 1112 * , 110 ( 2011 ) [ arxiv:1109.3703 [ hep - th ] ] . the metric for @xmath4 minkowski space has been taken to be @xmath5 where the first element comes for time coordinate . the abbreviations used in the thesis are * gbo : _ generalized bose operator _ * uir : _ unitary irreducible representation _ * adhm : _ atiyah , drinfeld , hitchin and manin _ * sd : _ self dual _ * asd : _ anti self dual _ * sho : _ simple harmonic oscillator _ * fho : _ forced harmonic oscillator _ * qfho : _ quantum forced harmonic oscillator _ * sr : _ special relativity _ * dsr : _ doubly / deformed special relativity _","we study a model of forced harmonic oscillator embedded in a @xmath0 dimensional noncommutative spacetime in the special relativistic limit. the oscillator is assumed to be formed by elements of a doubly / deformed special relativity ( dsr ) theory. we show that the transformation of the dsr algebra into a lorentz algebra at the origin has a profound effect on the thermodynamics of the model. in particular, the modified dispersion relation and the dispersion corrections to the planck length and energy are found to be in contradiction with poincar invariance. we also study the consequences of the modification of the equation of state for a loop system which contains a black hole, a white dwarf and a pair of white dwarfs. the physics is appreciably richer in the latter case. -.6 in -0.8 in # 1#2#3 _ ann. phys. ( ny ) _ * # 1 * ( # 2 ) # 3 # 1= # 2= # 1=#1 # 1,#2(#3)phys. rev. _ * d#1 * ( 19#2 ) # 4 # 1gev^2_#1(#2)_g # 1hep. bl lac # 1*(20#1 ) # 2 hep - th/0209004 aue-02 - 02/11.5 in * program summary * _ title of program _ : # 1 _ catalogue identifier _ : adxx _ + _ program obtainable from _ : institute of theoretical physics, chinese academy of sciences, beijing 100190. + _ reference to original publication _ : + http://pibeta.ac.cn/@xmath1#1#2_instituto de fsica corpuscular c.s.i.c./universitat de valncia + edificio de institutos de paterna, apartado 22085 rovisco pais, p.le a. l. lpez mateos, and marco genovese + _ used of the department of physics _ : univ. paris - sud, laboratoire de physique thorique, + bt. 210, f-91405 orsay cedex, france + _ external files _ : e - mail : wliu@irsamc.univ-par-saclay.fr + _ licensing provisions _ : none + _ computers _ : all +",0.0955540809555408,"we start by studying the implications of the construction of so - called generalized bose operators ( gbo ) @xcite in noncommutative gauge theories . we study a simple quantum mechanical model of forced harmonic oscillator in @xmath28 dimensional noncommutative spacetime to get the essence of the effect of noncommutative time coordinate . for this we follow the unitary formulation of quantum mechanics with time - space noncommutativity discussed in @xcite . in particular , we study the thermodynamics in the so - called doubly / deformed special relativistic ( dsr ) theories which are related to a noncommutative space known as @xmath1-minkowski space @xcite . attempts to combine gravity with quantum mechanics in search of the theory for quantum gravity always seem to give rise to the planck length @xmath29 that provides the scale at which the quantum effects of gravity will show up @xcite . the effect of modified dispersion relations in loop - quantum - gravity on black hole thermodynamics was studied in @xcite . the same as a lorentz violating phenomena on the thermodynamics of macroscopic systems ( like white dwarfs ) @xcite and as a noncommutative phenomena on cosmology and astrophysical systems we study the thermodynamics of an ideal gas in the above described dsr scenario . they correspond to reducible representations of the harmonic oscillator algebra . we demonstrate their relevance in the construction of topologically non - trivial solutions in noncommutative gauge theories , focusing our attention to flux tubes , vortices , and instantons . our method provides a simple new relation between the topological charge and the number of times the basic irreducible representation occurs in the reducible representation underlying the gbo . when used in conjunction with the noncommutative adhm construction , we find that these new instantons are in general not unitarily equivalent to the ones currently known in literature . chapter [ qo ] studies the time dependent transitions of quantum forced harmonic oscillator ( qfho ) in noncommutative @xmath2 perturbatively to linear order in the noncommutativity @xmath3 . we show that the poisson distribution gets modified , and that the vacuum state evolves into a `` squeezed '' state rather than a coherent state . the time evolutions of uncertainties in position and momentum in vacuum are also studied and imply interesting consequences for modelling nonlinear phenomena in quantum optics . in chapter [ dsr ] we study thermodynamics of an ideal gas in doubly special relativity . new type of special functions ( which we call incomplete modified bessel functions ) emerge .",0.30445544554455445