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1305.0417
|
transfer - ionization in fast collisions between a bare ion and an atom , in which one of the atomic electrons is captured by the ion whereas another one is emitted , crucially depends on dynamic electron - electron correlations . we show that in collisions with a highly charged ion a strong field of the ion has a very profound effect on the correlated channels of transfer - ionization . in particular , this field weakens electron emission into the direction opposite to the motion of the ion and strongly suppresses the emission perpendicular to this motion . instead , electron emission is redirected into those parts of the momentum space which are very weakly populated in fast collisions with low charged ions .
| 125
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cond-mat9901197
|
the diffusive properties in velocity fields whose small scales are parameterized by non @xmath0-correlated noise is investigated using multiscale technique . the analytical expression of the eddy diffusivity tensor is found for a @xmath1d steady shear flow and it is an increasing function of the characteristic noise decorrelation time @xmath2 . in order to study a generic flow @xmath3 , a small-@xmath2 expansion is performed and the first correction @xmath4 to the effective diffusion coefficients is evaluated . this is done using two different approaches and it results that at the order @xmath2 the problem with a colored noise is equivalent to the white - in - time case provided by a renormalization of the velocity field @xmath5 depending on @xmath2 . two examples of @xmath1d closed - streamlines velocity field are considered and in both the cases an enhancement of the diffusion is found . pacs number(s ) : ; +
| 152
|
1405.3468
|
computational kernel of the three - dimensional variational data assimilation ( 3d - var ) problem is a linear system , generally solved by means of an iterative method . the most costly part of each iterative step is a matrix - vector product with a very large covariance matrix having gaussian correlation structure . this operation may be interpreted as a gaussian convolution , that is a very expensive numerical kernel . recursive filters ( rfs ) are a well known way to approximate the gaussian convolution and are intensively applied in the meteorology , in the oceanography and in forecast models . in this paper , we deal with an oceanographic 3d - var data assimilation scheme , named oceanvar , where the linear system is solved by using the conjugate gradient ( gc ) method by replacing , at each step , the gaussian convolution with rfs . here we give theoretical issues on the discrete convolution approximation with a first order ( 1st - rf ) and a third order ( 3rd - rf ) recursive filters . numerical experiments confirm given error bounds and show the benefits , in terms of accuracy and performance , of the 3-rd rf .
| 205
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hep-ph0004105
|
we propose a simple ansatz for the three generation neutrino mass matrix @xmath0 which is motivated from an so(10 ) grand unified theory . the ansatz can be combined with information from neutrino oscillation experiments and bounds on neutrinoless double beta decay to determine the neutrino masses themselves and to reconstruct , with some assumptions , the matrix @xmath1 . = 17pt # 1=#1pt = by -by -makecaption#1#2 tempboxa tempboxa > = = # 1 # 2 to = 13pt su-4240 - 719 + hep - ph/0004105 + * complementary ansatz for the neutrino mass matrix * = 12pt deirdre black amir h. fariborz + 0.5 cm salah nasri joseph schechter + _ department of physics , syracuse university , syracuse , ny 13244 - 1130 , usa . _ + 0.5 cm * abstract *
| 136
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physics0507166
|
in the conventional quantum mechanics ( i.e. , hermitian qm ) the adiabatic theorem for systems subjected to time periodic fields holds only for bound systems and not for open ones ( where ionization and dissociation take place ) [ d. w. hone , r. ketzmerik , and w. kohn , phys . rev . a * 56 * , 4045 ( 1997 ) ] . here with the help of the ( t , t ) formalism combined with the complex scaling method we derive an adiabatic theorem for open systems and provide an analytical criteria for the validity of the adiabatic limit . the use of the complex scaling transformation plays a key role in our derivation . as a numerical example we apply the adiabatic theorem we derived to a 1d model hamiltonian of xe atom which interacts with strong , monochromatic sine - square laser pulses . we show that the generation of odd - order harmonics and the absence of hyper - raman lines , even when the pulses are extremely short , can be explained with the help of the adiabatic theorem we derived . department of chemistry and minerva center of nonlinear physics in complex systems technion israel institute of technology haifa 32000 , israel . + 03.65.-w , 42.50.hz , 42.65.-ky , 32.80.rm
| 221
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gr-qc0209074
|
we formulate the nonlinear isovector model in a curved background , and calculate the spherically symmetric solutions for weak and strong coupling regimes . the usual belief that gravity does not have appreciable effects on the structure of solitons will be examined , in the framework of the calculated solutions , by comparing the flat - space and curved - space solutions . it turns out that in the strong coupling regime , gravity has essential effects on the solutions . masses of the self - gravitating solitons are calculated numerically using the tolman expression , and its behavior as a function of the coupling constant of the model is studied .
| 112
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astro-ph9712158
|
the chemical structure of neutral clouds in low metallicity environments is examined with particular emphasis on the h to and c@xmath0 to co transitions . we observed near - ir , , and lines and the @xmath1co line from 30 doradus and n159/n160 in the large magellanic cloud and from dem s 16 , dem s 37 , and li - smc 36 in the small magellanic cloud . we find that the emission is uv - excited and that ( weak ) emission always exists ( in our surveyed regions ) toward positions where and [ ] emission have been detected . using a pdr code and a radiative transfer code , we simulate the emission of line radiation from spherical clouds and from large planar clouds . because the [ ] emission and emission arise on the surface of the cloud and the lines are optically thin , these lines are not affected by changes in the relative sizes of the neutral cloud and the bearing core , while the optically thick emission can be strongly affected . the sizes of clouds are estimated by measuring the deviation of co emission strength from that predicted by a planar cloud model of a given size . the average cloud column density and therefore size increases as the metallicity decreases . our result agrees with the photoionization regulated star formation theory by mckee ( 1989 ) .
| 237
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1608.03551
|
we study a family of graphs related to the @xmath0-cube . the middle cube graph of parameter @xmath1 is the subgraph of @xmath2 induced by the set of vertices whose binary representation has either @xmath3 or @xmath1 number of ones . the middle cube graphs can be obtained from the well - known odd graphs by doubling their vertex set . here we study some of the properties of the middle cube graphs in the light of the theory of distance - regular graphs . in particular , we completely determine their spectra ( eigenvalues and their multiplicities , and associated eigenvectors ) .
| 104
|
1503.05703
|
our paper presents new methods for finding and testing of weak periodic variability of stellar objects developed for the purpose of detecting expected regular light variations of magnetic chemically peculiar ( mcp ) candidates in the large magellanic cloud . we introduce two new periodograms of the mcp star , bs cir ( hd 125630 ) , appropriate for rotating spotted variables and compare the results with those obtained by the well - known lomb - scargle periodogram . the usage of periodograms and the testing of the significance of the found period candidates are demonstrated with two examples : the observed and simulated observations of the magnetic field of the mcp star cq uma ( hd 119213 ) and the mcp candidate ogle lmc136.7 16501 . three newly developed tests of the periodic variability the shuffling , bootstrap and subsidiary ones , are presented . we demonstrate that the found periodic variations known with signal - to - noise ratio larger than 6 can be approved as real .
| 170
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1102.3784
|
it is argued that whereas the shatskiy single rings produced by the gravitational inner field of a spherically symmetric wormhole and the concentric double einstein rings generated by a toroidal ringhole could not be used without some uncertainty to identify the presence of such tunnelings in the universe or the existence of a parallel universe , the image which the inner gravitational field of a non orientable klein - bottle hole tunneling would leave by lensing a single luminous source is that of a truncated double spiral , which is a signature that can not be attributed to any other single or composite astronomical object in whichever universe it may be placed . in this report we argue some more reasons to predict that such a signature would imply the discovery of one such non orientable tunneling in our or other universe . after all , a nonorientable klein - bottle hole is also a perfectly valid solution to the einstein equations and the stuff which would make it feasible is becoming more and more familiar in cosmology .
| 179
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1403.6970
|
we describe dynamics of spin and valley transitions driven by alternating electric fields in quantum dots defined electrostatically within semiconducting carbon nanotubes ( cnt ) . we use the tight - binding approach to describe the states localized within a quantum dot taking into account the circumferential spin - orbit interaction due to the s - p hybridization and external fields . the basis of eigenstates localized in the quantum dot is used in the solution of the time - dependent schrdinger equation for description of spin flips and inter - valley transitions that are driven by periodic perturbation in the presence of coupling between the spin , valley and orbital degrees of freedom . besides the first order transitions we find also fractional resonances . we discuss the transition rates with selection rules that are lifted by atomic disorder and the bend of the tube . we demonstrate that the electric field component perpendicular to the axis of the cnt activates spin transitions which are otherwise absent and that the resonant spin - flip time scales with the inverse of the electric field .
| 185
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cond-mat0605604
|
the bcs - like pairing in ultracold fermionic atomic ( @xmath0 ) gases is studied in the model of `` isotopic - spin '' pairing proposed in 1991 ku - hof - ssc . this model assumes a mismatch ( @xmath1 ) in chemical potentials of pairing fermionic atoms . it is shown that a @xmath2-josephson junction can be realized in @xmath0 systems , where the left and right banks @xmath3 are the @xmath0 superfluids . the weak link @xmath4 consists from the normal @xmath5 with the finite mismatch @xmath1 . if the @xmath2-junction is a part of a closed ring the superfluid mass - current flows spontaneously in the ring , i.e. , the time - reversal symmetry is broken spontaneously . this is realized if the radius of the ring @xmath6 is larger than the critical one @xmath7 . all these effects exist also in the case when @xmath8 , where @xmath9 is the superfluid gap , but with the reduced thickness of the weak link . it is also discussed , that if junctions @xmath10 and trilayers @xmath11 from @xmath0 are realizable this renders a possibility for a novel electronics - _ hypertronics_.
| 196
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1308.5678
|
the transmission dynamics of some infectious diseases is related to the contact structure between individuals in a network . we used five algorithms to generate contact networks with different topological structure but with the same scale - free degree distribution . we simulated the spread of acute and chronic infectious diseases on these networks , using si ( susceptible infected ) and sis ( susceptible infected susceptible ) epidemic models . in the simulations , our objective was to observe the effects of the topological structure of the networks on the dynamics and prevalence of the simulated diseases . we found that the dynamics of spread of an infectious disease on different networks with the same degree distribution may be considerably different . * adv . studies theor . phys . , vol . 7 , 2013 , no . 16 , 759 - 771 * * hikari ltd , www.m-hikari.com * * http://dx.doi.org/10.12988/astp.2013.3674 * * raul ossada , jos h. h. grisi - filho , * * fernando ferreira and marcos amaku * faculdade de medicina veterinria e zootecnia universidade de so paulo so paulo , sp , 05508 - 270 , brazil copyright @xmath0 2013 raul ossada et al . this is an open access article distributed under the creative commons attribution license , which permits unrestricted use , distribution , and reproduction in any medium , provided the original work is properly cited . * keywords : * scale - free network , power - law degree distribution , dynamics of infectious diseases
| 256
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1403.8066
|
we present results about the effect of the use of a stiffer equation of state , namely the ideal - fluid @xmath0 ones , on the dynamical bar - mode instability in rapidly rotating polytropic models of neutron stars in full general relativity . we determine the change on the critical value of the instability parameter @xmath1 for the emergence of the instability when the adiabatic index @xmath2 is changed from 2 to 2.75 in order to mimic the behavior of a realistic equation of state . in particular , we show that the threshold for the onset of the bar - mode instability is reduced by this change in the stiffness and give a precise quantification of the change in value of the critical parameter @xmath3 . we also extend the analysis to lower values of @xmath1 and show that low - beta shear instabilities are present also in the case of matter described by a simple polytropic equation of state .
| 163
|
1103.1419
|
we study the self - gravitational effect on the equation of state ( eos ) of bose and fermi gases in thermal equilibrium at the end of reheating , the period after quark - hadron transition and before big bang nucleosynthesis ( bbn ) . after introducing new grand canonical partition functions based on the work of uhlenbeck and gropper , we notice some interesting features of the newly developed eoss with distinct behaviors of relativistic and non - relativistic gases under self - gravity . the usual negligence of the self - gravitational effect when solving the background expansion of the early universe is justified with numerical results , showing the magnitude of the self - gravitational modification of the state constant to be less than @xmath0 . this helps us to clarify the background thermal evolution of the primordial patch . such clarification is crucial in testing gravity theories , evaluating inflation models and determining element abundances in bbn .
| 162
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1405.7564
|
we calculate the free energy , entropy and pressure of the quark gluon plasma ( qgp ) at finite temperature and density with a given fraction of spin - up and spin - down quarks using a mit bag model with corrections up to @xmath0 . the expressions for the specific heat and the spin susceptibility are derived in terms of fermi momentum and temperature . the effects of interaction between the quarks on the properties of the qgp phase are also investigated . within our phenomenological model , we estimate the transition temperature @xmath1 by constructing the phase boundary between the hadronic phase and the qgp phase . finally , we compute the equation of state of the qgp and its dependence on the temperature and the density .
| 130
|
1011.0694
|
is it possible to trap a quantum particle in an open geometry ? in this work we deal with the boundary value problem of the stationary schroedinger ( or helmholtz ) equation within a waveguide with straight segments and a rectangular bending . the problem can be reduced to a one dimensional matrix schroedinger equation using two descriptions : oblique modes and conformal coordinates . we use a corner - corrected wkb formalism to find the energies of the one - dimensional problem . it is shown that the presence of bound states is an effect due to the boundary alone , with no classical counterpart for this geometry . the conformal description proves to be simpler , as the coupling of transversal modes is not essential in this case . + * pacs : * 37.10.gh , 42.25.gy , 03.65.ge + * keywords : * bent waveguides , bound states , corners , dirichlet conditions .
| 157
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1403.1176
|
for a projective curve @xmath0 and the canonical divisor @xmath1 on @xmath0 , it is classically known that the canonical ring @xmath2 is finitely generated in degree at most three . in this article , we study whether analogous statements hold for finite graphs and tropical curves . for any finite graph @xmath3 , we show that the canonical semi - ring @xmath4 is finitely generated but that the degree of generators are not bounded by a universal constant . for any hyperelliptic tropical curve @xmath5 with integer edge - length , we show that the canonical semi - ring @xmath6 is not finitely generated , and , for tropical curves with integer edge - length in general , we give a sufficient condition for non - finite generation . # 1
| 132
|
astro-ph0403082
|
we discuss the propagation of electromagnetic waves on a rectangular lattice of polarizable point dipoles . for wavelengths long compared to the lattice spacing , we obtain the dispersion relation in terms of the lattice spacing and the dipole polarizabilities . we also obtain the dipole polarizabilities required for the lattice to have the same dispersion relation as a continuum medium of given refractive index @xmath0 ; our result differs from previous work by draine & goodman ( 1993 ) . our new prescription can be used to assign dipole polarizabilities when the discrete dipole approximation is used to study scattering by finite targets . results are shown for selected cases .
| 112
|
0805.1318
|
necessary and sufficient conditions for bipartite entanglement are derived , which apply to arbitrary hilbert spaces . motivated by the concept of witnesses , optimized entanglement inequalities are formulated solely in terms of arbitrary hermitian operators , which makes them useful for applications in experiments . the needed optimization procedure is based on a separability eigenvalue problem , whose analytical solutions are derived for a special class of projection operators . for general hermitian operators , a numerical implementation of entanglement tests is proposed . it is also shown how to identify bound entangled states with positive partial transposition .
| 100
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1006.1325
|
let @xmath0 be an irreducible shift of finite type ( sft ) of positive entropy , and let @xmath1 be its set of words of length @xmath2 . define a random subset @xmath3 of @xmath1 by independently choosing each word from @xmath1 with some probability @xmath4 . let @xmath5 be the ( random ) sft built from the set @xmath3 . for each @xmath6 and @xmath2 tending to infinity , we compute the limit of the likelihood that @xmath5 is empty , as well as the limiting distribution of entropy for @xmath5 . for @xmath4 near @xmath7 and @xmath2 tending to infinity , we show that the likelihood that @xmath5 contains a unique irreducible component of positive entropy converges exponentially to @xmath7 . these results are obtained by studying certain sequences of random directed graphs . this version of `` random sft '' differs significantly from a previous notion by the same name , which has appeared in the context of random dynamical systems and bundled dynamical systems . .
| 170
|
cond-mat0402343
|
many molecular theories of nematic liquid crystals consider the constituent molecules as cylindrically symmetric . in many cases , this approximation may be useful . however the molecules of real nematics have lower symmetry . therefore a theory was developed ( mol . phys . 30 ( 1975 ) 1345 ) for an ensemble of such particles based upon a general expansion of the pairwise intermolecular potential together with the molecular field approximation . in this study , we would like to handle this molecular field theory by using tsallis thermostatistics which has been commonly used for a decade to study the physical systems . with this aim , we would like to investigate the dependence of the order parameters on temperature and would like to report the variation of the critical values of the order parameters at the transition temperature with the entropic index . pacs number(s ) : 05.20.-y , 05.70.-a , 61.30.cz , 61.30 . gd . keywords : tsallis thermostatistics , maier - saupe theory , nematic liquid crystals , non - cylindrically symmetrical molecules .
| 180
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0712.1239
|
we have studied the abundance of oxygen in the igm by analyzing , , , and pixel optical depths derived from a set of high - quality vlt and keck spectra of 17 qsos at @xmath0 . comparing ratios @xmath1 to those in realistic , synthetic spectra drawn from a hydrodynamical simulation and comparing to existing constraints on [ si / c ] places strong constraints on the ultraviolet background ( uvb ) model using weak priors on allowed values of [ si / o ] : for example , a quasar - only background yields [ si / o ] @xmath2 , highly inconsistent with the [ si / o ] @xmath3 expected from nucleosynthetic yields and with observations of metal - poor stars . assuming a fiducial quasar+galaxy uvb consistent with these constraints yields a primary result that [ o / c ] = 0.66 @xmath4 0.06 @xmath4 0.2 ; this result is sensitive to gas with overdensity @xmath5 . consistent results are obtained by similarly comparing @xmath6 and @xmath7 to simulation values , and also by directly ionization - correcting @xmath8 as function of @xmath9 into [ o / h ] as a function of density . subdividing the sample reveals no evidence for evolution , but low- and high-@xmath9 samples are inconsistent , suggesting either density - dependence of [ o / c ] or more likely prevalence of collisionally - ionized gas at high density .
| 241
|
1501.04241
|
this paper establishes the continuity of the path delay operators for _ dynamic network loading _ ( dnl ) problems based on the lighthill - whitham - richards model , which explicitly capture vehicle spillback . the dnl describes and predicts the spatial - temporal evolution of traffic flow and congestion on a network that is consistent with established route and departure time choices of travelers . the lwr - based dnl model is first formulated as a system of _ partial differential algebraic equations _ ( pdaes ) . we then investigate the continuous dependence of merge and diverge junction models with respect to their initial / boundary conditions , which leads to the continuity of the path delay operator through the _ wave - front tracking _ methodology and the _ generalized tangent vector _ technique . as part of our analysis leading up to the main continuity result , we also provide an estimation of the minimum network supply without resort to any numerical computation . in particular , it is shown that gridlock can never occur in a finite time horizon in the dnl model . ( 1,0)469 path delay operator , continuity , dynamic network loading , lwr model , spillback , gridlock
| 208
|
astro-ph9510060
|
we demonstrate how measuring orbital period derivatives can lead to more accurate distance estimates and transverse velocities for some nearby binary pulsars . in many cases this method will estimate distances more accurately than is possible by annual parallax , as the relative error decreases as @xmath0 . unfortunately , distance uncertainties limit the degree to which nearby relativistic binary pulsars can be used for testing the general relativistic prediction of orbital period decay to a few percent . nevertheless , the measured orbital period derivative of psr b1534 + 12 agrees within the observational uncertainties with that predicted by general relativity if the proper - motion contribution is accounted for .
| 112
|
cond-mat0107253
|
we consider interacting spinless fermions in one dimension embedded in self - similar quasiperiodic potentials . we examine generalizations of the fibonacci potential known as precious mean potentials . using a bosonization technique and a renormalization group analysis , we study the low - energy physics of the system . we show that it undergoes a metal - insulator transition for any filling factor , with a critical interaction that strongly depends on the position of the fermi level in the fourier spectrum of the potential . for some positions of the fermi level the metal - insulator transition occurs at the non interacting point . the repulsive side is an insulator with a gapped spectrum whereas in the attractive side the spectrum is gapless and the properties of the system are described by a luttinger liquid . we compute the transport properties and give the characteristic exponents associated to the frequency and temperature dependence of the conductivity .
| 159
|
astro-ph0109252
|
we study the luminosity function and the correlation function of about 1200 z@xmath04 lyman break galaxies ( lbgs ) with @xmath1 that are photometrically selected from deep @xmath2 imaging data of a 618 arcmin@xmath3 area in the subaru / xmm - newton deep field taken with subaru prime focus camera . the contamination and completeness of our lbg sample are evaluated , on the basis of the hubble deep field - north ( hdf - n ) objects , to be 17% and 45% , respectively . we derive the uv ( rest 1700 ) luminosity functions ( lfs ) and find a large population of uv - luminous galaxies at @xmath4 . the lfs of the red and blue subsamples imply that the bright lbgs are redder in the uv continuum than the average color of the lbgs . then we calculate the correlation function over @xmath5 and find that it is fitted fairly well by a power law , @xmath6 , with @xmath7 . we estimate the correlation length @xmath8 ( in comoving units ) of the two - point spatial correlation function @xmath9 to be @xmath10 @xmath11mpc ( @xmath12 and @xmath13 ) . the correlation function shows an excess of @xmath14 on small scales ( @xmath15 ) , departing from the power - law fit at @xmath16 significance level . interpreting this as being due to galaxy mergers , we evaluate the fraction of galaxies undergoing mergers to be @xmath17 , which is significantly smaller than those of galaxies at intermediate redshifts .
| 256
|
astro-ph9909441
|
results of two years of continuous monitoring of flux density variations at 8.3 and 2.3 ghz of the galactic center super - massive black hole candidate sgr a * are reported . the average rms modulation indices are 6% and 2.5% at 8.3 & 2.3 ghz respectively . there is a certain degree of correlation between both frequencies . the timescale of variability at 8.3 & 2.3 ghz is between 50 and 200 days . we can not confirm a @xmath0 dependence of the timescale . at 2.3 ghz a quasi - periodic behaviour with a period of 57 days was discovered which is reminiscent to , though longer than , those found in some compact extragalactic radio sources .
| 120
|
cond-mat9904402
|
raman spectra are reported for ba doped fullerides , @xmath0 ( x=3 , 4 , and 6 ) . the lowest frequency @xmath1 modes split into five components for @xmath2 and @xmath3 even at room temperature , allowing us a quantitative analysis based on the electron - phonon coupling theory . for the superconducting @xmath2 , the density of states at the fermi energy was derived as 7 @xmath4 , while the total value of electron - phonon coupling @xmath5 was found to be 1.0 , which is comparable to that of @xmath6 . the tangential @xmath7 mode , which is known as a sensitive probe for the degree of charge transfer on @xmath8 molecule , shows a remarkable shift depending on the ba concentration , being roughly consistent with the full charge transfer from ba to @xmath8 . an effect of hybridization between ba and @xmath8 @xmath9 orbitals is also discussed . = 10000 * pacs numbers : 78.30.-j , 72.80.rj , 74.70.-b *
| 165
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1405.4264
|
we investigate the evolution of the raman spectrum of defected graphene as a function of doping . polymer electrolyte gating allows us to move the fermi level up to 0.7ev , as monitored by _ in - situ _ hall - effect measurements . for a given number of defects , the intensities of the d and d peaks decrease with doping . we assign this to an increased total scattering rate of the photoexcited electrons and holes , due to the doping - dependent strength of electron - electron scattering . we present a general relation between d peak intensity and defects valid for any doping level .
| 109
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1511.01450
|
we numerically construct the bps and non - bps wavefunctions of an @xmath0 quiver quantum mechanics with two abelian nodes and a single arrow . this model captures the dynamics of a pair of wrapped d - branes interacting via a single light string mode . a dimensionless parameter @xmath1 , which is inversely proportional to the the fayet - iliopoulos parameter , controls whether the bulk of the wavefunctions are supported on the higgs branch or the coulomb branch . we demonstrate how the bps and excited states morph as @xmath1 is tuned . we also numerically compute the energy gap between the ground state and the first excited states as a function of @xmath1 . an expression for the the gap , computed on the coulomb branch , matches nicely with our numerics at large @xmath1 but deviates at small @xmath1 where the higgs branch becomes the relevant description of the physics . in the appendix , we provide the schrdinger equations fully reduced via symmetries which , in principle , allow for the numerical determination of the entire spectrum at any point in moduli space . for the ground states , this numerical determination of the spectrum can be thought of as the first _ in silico _ check of various witten index calculations . mit - ctp-4731 susy in silico : numerical d - brane bound state spectroscopy tarek anous _ center for theoretical physics , massachusetts institute of technology , cambridge , ma 02139 , usa _
| 252
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astro-ph0611129
|
we carry out a model independent study of resonant photon scattering off dark matter ( dm ) particles . the dm particle @xmath0 can feature an electric or magnetic transition dipole moment which couples it with photons and a heavier neutral particle @xmath1 . resonant photon scattering then takes place at a special energy @xmath2 set by the masses of @xmath0 and @xmath1 , with the width of the resonance set by the size of the transition dipole moment . we compute the constraints on the parameter space of the model from stellar energy losses , data from sn 1987a , the lyman-@xmath3 forest , big bang nucleosynthesis , electro - weak precision measurements and accelerator searches . we show that the velocity broadening of the resonance plays an essential role for the possibility of the detection of a spectral feature originating from resonant photon - dm scattering . depending upon the particle setup and the dm surface mass density , the favored range of dm particle masses lies between tens of kev and a few mev , while the resonant photon absorption energy is predicted to be between tens of kev and few gev .
| 196
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nucl-th0401031
|
we investigate hadron production and transverse hadron spectra in nucleus - nucleus collisions from 2 @xmath0gev to 21.3 @xmath0tev within two independent transport approaches ( urqmd and hsd ) based on quark , diquark , string and hadronic degrees of freedom . the enhancement of pion production in central au+au ( pb+pb ) collisions relative to scaled @xmath1 collisions ( the kink ) is described well by both approaches without involving a phase transition . however , the maximum in the @xmath2 ratio at 20 to 30 a@xmath3gev ( the horn ) is missed by @xmath4 40% . also , at energies above @xmath4 5 a@xmath3gev , the measured @xmath5 @xmath6-spectra have a larger inverse slope than expected from the models . thus the pressure generated by hadronic interactions in the transport models at high energies is too low . this finding suggests that the additional pressure - as expected from lattice qcd at finite quark chemical potential and temperature - might be generated by strong interactions in the early pre - hadronic / partonic phase of central heavy - ion collisions . finally , we discuss the emergence of density perturbations in a first - order phase transition and why they might affect relative hadron multiplicities , collective flow , and hadron mean - free paths at decoupling . a minimum in the collective flow @xmath7 excitation function was discovered experimentally at 40 a@xmath3gev - such a behavior has been predicted long ago as signature for a first order phase transition .
| 253
|
hep-ex0611051
|
high - statistics data on near - horizontal muons collected with russian - italian coordinate detector decor are analyzed . precise measurements of muon angular distributions in zenith angle interval from 60@xmath0 to 90@xmath0 have been performed . in total , more than 20 million muons are selected . dependences of the absolute integral muon intensity on zenith angle for several threshold energies ranging from 1.7 gev to 7.2 gev are derived . results for this region of zenith angles and threshold energies have been obtained for the first time . the dependence of integral intensity on zenith angle and threshold energy is well fitted by a simple analytical formula .
| 111
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physics0111136
|
the reference rdbms for bessy ii has been set up with a device oriented data model . this has proven adequate for e.g. template based rtdb generation , modelling etc . but since assigned i / o channels have been stored outside the database ( a ) numerous specific conditions had to be maintained within the scripts generating configuration files and ( b ) several generic applications could not be set up automatically by scripts . in a larger re - design effort the i / o channels are introduced into the rdbms . that modification allows to generate a larger set of rtdbs , map specific conditions into database relations and maintain application configurations by relatively simple extraction scripts .
| 121
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1202.5059
|
we examine the statics and dynamics of particles with repulsive yukawa interactions in the presence of a two - dimensional triangular substrate for fillings of up to twelve particles per potential minimum . we term the ordered states yukawa cluster crystals and show that they are distinct from the colloidal molecular crystal states found at low fillings . as a function of substrate and interaction strength at fixed particle density we find a series of novel crystalline states that we characterize using the structure factor . for fillings greater than four , shell and ring structures form at each potential minimum and can exhibit sample - wide orientational order . a disordered state can appear between ordered states as the substrate strength varies . under an external drive , the onsets of different orderings produce clear changes in the critical depinning force , including a peak effect phenomenon that has generally only previously been observed in systems with random substrates . we also find a rich variety of dynamic ordering transitions that can be observed via changes in the structure factor and features in the velocity - force curves . the dynamical states encompass a variety of moving structures including one - dimensional stripes , smectic ordering , polycrystalline states , triangular lattices , and symmetry locking states . despite the complexity of the system , we identify several generic features of the dynamical phase transitions which we map out in a series of phase diagrams . our results have implications for the structure and depinning of colloids on periodic substrates , vortices in superconductors and bose - einstein condensates , wigner crystals , and dusty plasmas .
| 278
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1305.6965
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a novel protocol , measurement - device - independent quantum key distribution ( mdi - qkd ) , removes all attacks from the detection system , the most vulnerable part in qkd implementations . in this paper , we present an analysis for practical aspects of mdi - qkd . to evaluate its performance , we study various error sources by developing a general system model . we find that mdi - qkd is highly practical and thus can be easily implemented with standard optical devices . moreover , we present a simple analytical method with only two ( general ) decoy states for the finite decoy - state analysis . this method can be used directly by experimentalists to demonstrate mdi - qkd . by combining the system model with the finite decoy - state method , we present a general framework for the optimal choice of the intensities of the signal and decoy states . furthermore , we consider a common situation , namely _ asymmetric _ mdi - qkd , in which the two quantum channels have different transmittances . we investigate its properties and discuss how to optimize its performance . our work is of interest not only to experiments demonstrating mdi - qkd but also to other non - qkd experiments involving quantum interference .
| 220
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1703.08811
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we study the single site dynamics in stochastic particle systems of misanthrope type with bounded rates on a complete graph . in the limit of diverging system size we establish convergence to a markovian non - linear birth death chain , described by a mean - field equation known also from exchange - driven growth processes . conservation of mass in the particle system leads to conservation of the first moment for the limit dynamics , and to non - uniqueness of stationary measures . the proof is based on a coupling to branching processes via the graphical construction , and establishing uniqueness of the solution for the limit dynamics . as particularly interesting examples we discuss the dynamics of two models that exhibit a condensation transition and their connection to exchange - driven growth processes . * keywords . * mean - field equations , misanthrope processes , non - linear birth death chain , condensation .
| 158
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1407.3376
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in this paper , we show that the time evolution of the bloch vector governed by the thermal jaynes - cummings model is equivalent to a compressible inviscid flow with zero vorticity . because of its quasiperiodicity , the dynamics of the bloch vector includes countably infinite angular momenta as integrals of motion . moreover , to derive the bloch vector , we trace out the hilbert space of the cavity field and remove entanglement between the single atom and the cavity mode . these facts indicate that the dynamics of the bloch vector can be described with a hidden - variable model that has local determinism and a countably infinite number of degrees of freedom . our results fit these considerations .
| 123
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quant-ph0108037
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we investigate the problem of determining the parameters that describe a quantum channel . it is assumed that the users of the channel have at best only partial knowledge of it and make use of a finite amount of resources to estimate it . we discuss simple protocols for the estimation of the parameters of several classes of channels that are studied in the current literature . we define two different quantitative measures of the quality of the estimation schemes , one based on the standard deviation , the other one on the fidelity . the possibility of protocols that employ entangled particles is also considered . it turns out that the use of entangled particles as a new kind of nonclassical resource enhances the estimation quality of some classes of quantum channel . further , the investigated methods allow us to extend them to higher dimensional quantum systems . # 1|#1 # 1#1| # 1#2#1|#2 # 1#2#3#1|#2|#3
| 158
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astro-ph9705113
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any viable cosmological model must produce enough structure at early epochs to explain the amount of gas associated with high - redshift systems . we study the evolution of systems at redshifts @xmath0 in cold dark matter ( cdm ) and cold+hot dark matter ( cdm+hdm ) models using both @xmath1-body and hydrodynamic simulations . our approach incorporates the effects of gas dynamics , and we find that all earlier estimates which assumed that all the baryons in dark matter halos would contribute to absorption have overestimated the column density distribution @xmath2 and the fraction of neutral dense gas @xmath3 in systems . the differences are driven by ionization of hydrogen in the outskirts of galactic halos and by gaseous dissipation near the halo centers , and they tend to exacerbate the problem of late galaxy formation in cdm+hdm models . we only include systems up to the highest observed column density @xmath4 @xmath5 in the estimation of @xmath3 for a fair comparison with data . if the observed @xmath2 and @xmath3 inferred from a small number of confirmed and candidate absorbers are robust , the amount of gas in systems at high redshifts in the @xmath6 cdm+hdm model falls well below the observations . epsf.tex submitted to _ the astrophysical journal letters _
| 214
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1406.5733
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the production of all identified hadrons at the cern large hadron collider ( lhc ) is studied with emphasis on the @xmath0 distributions up to 20 gev / c in central collisions . in the framework of the recombination model we find that the shower partons ( due to the fragmentation of semihard partons ) play an important role in the formation of hadrons in the low- and intermediate-@xmath0 regions . parameters that control the energy loss of minijets are determined by fitting the upper half of the @xmath0 range of the pion distribution . the resultant soft shower partons are then found to dominate over the thermal partons in the non - strange sector , but not in the strange sector . since the data on the @xmath0 spectra of all observed hadrons are well reproduced , there is no way out of the implication that any alternative dynamical model on particle production would be incomplete if it does not consider the effects of minijets even at very low @xmath0 . hydrodynamics that relies on rapid equilibration without accounting for the delayed thermalization effects of the hard and semihard partons copiously produced at lhc is an example of such models . the difference between the densities of shower partons produced at lhc and at bnl relativistic heavy - ion collider ( rhic ) is quantified and discussed .
| 229
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1308.6478
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we present the first detection of n@xmath0h@xmath1 towards a low - mass protostellar outflow , namely the l1157-b1 shock , at @xmath2 0.1 pc from the protostellar cocoon . the detection was obtained with the iram 30-m antenna . we observed emission at 93 ghz due to the @xmath3 = 10 hyperfine lines . the analysis of the emission coupled with the hifi chess multiline co observations leads to the conclusion that the observed n@xmath0h@xmath1(10 ) line originates from the dense ( @xmath4 10@xmath5 @xmath6 ) gas associated with the large ( 20@xmath725@xmath7 ) cavities opened by the protostellar wind . we find a n@xmath0h@xmath1 column density of few 10@xmath8 @xmath9 corresponding to an abundance of ( 28 ) @xmath10 10@xmath11 . the n@xmath0h@xmath1 abundance can be matched by a model of quiescent gas evolved for more than 10@xmath12 yr , i.e. for more than the shock kinematical age ( @xmath13 2000 yr ) . modelling of c - shocks confirms that the abundance of n@xmath0h@xmath1 is not increased by the passage of the shock . in summary , n@xmath0h@xmath1 is a fossil record of the pre - shock gas , formed when the density of the gas was around 10@xmath12 @xmath6 , and then further compressed and accelerated by the shock .
| 213
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cond-mat0408243
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basis set convergence of the hartree - fock and the correlation energy is examined for the hydrogen bonded _ infinite _ bent chains ( hf)@xmath0 and ( hcl)@xmath0 . we employ series of correlation consistent basis sets up to quintuple @xmath1 quality together with a coupled cluster method ( ccsd ) to describe electron correlation on _ ab initio _ level . the hartree - fock energy converges rapidly with increasing basis set quality whereas the correlation energy is found to be slowly convergent for the same series of basis sets . we study basis set extrapolation for ( hf)@xmath0 and ( hcl)@xmath0 and show that it substantially enhances the accuracy of both the hartree - fock and the correlation energy in _ extended _ systems . , electron correlation , ab initio calculations , hydrogen fluoride , hydrogen chloride , infinite bent chains , basis set convergence , basis set extrapolation 31.15.ar , 31.25.qm , 71.15.nc , 71.20.ps
| 159
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1512.01599
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an established phenomenology and theoretical interpretation of @xmath0-@xmath0 collision data at lower collision energies should provide a reference for @xmath0-@xmath0 and other collision systems at higher energies , against which claims of novel physics may be tested . the description of @xmath0-@xmath0 collisions at the relativistic heavy ion collider ( rhic ) has remained incomplete even as claims for collectivity and other novelties in data from smaller systems at the large hadron collider ( lhc ) have emerged recently . in this study we report the charge - multiplicity dependence of two - dimensional ( 2d ) angular correlations and of single - particle ( sp ) densities on transverse rapidity @xmath1 and pseudorapidity @xmath2 from 200 gev @xmath0-@xmath0 collisions . we define a comprehensive and self - consistent two - component ( soft + hard ) model ( tcm ) for hadron production and report a significant @xmath0-@xmath0 nonjet ( nj ) quadrupole component as a third ( angular - correlation ) component . our results have implications for @xmath0-@xmath0 centrality , the underlying event ( ue ) , collectivity in small systems and the existence of flows in high - energy nuclear collisions .
| 196
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quant-ph0208175
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it is shown how any lindbladian evolution with selfadjoint lindblad operators , either markovian or nonmarkovian , can be understood as an averaged random unitary evolution . both mathematical and physical consequences are analyzed . first a simple and fast method to solve this kind of master equations is suggested and particularly illustrated with the phase - damped master equation for the multiphoton resonant jaynes - cummings model in the rotating - wave approximation . a generalization to some intrinsic decoherence models present in the literature is included . under the same philosophy a proposal to generalize the jaynes - cummings model is suggested whose predictions are in accordance with experimental results in cavity qed and in ion traps . a comparison with stochastic dynamical collapse models is also included .
| 131
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0901.4570
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we study the andreev edge states with different pairing symmetries and boundary topologies on semi - infinite triangular lattice of na@xmath0coo@xmath1@xmath2h@xmath1o . a general mapping from the two dimensional lattice to the one dimensional tight - binding model is developed . it is shown that the phase diagram of the andreev edge states depends on the pairing symmetry and also the boundary topology . surprisingly , the structure of the phase diagram crucially relies on the nodal points on the fermi surface and can be explained by an elegant gauge argument . we compute the momentum - resolved local density of states near the edge and predict the hot spots which are measurable in fourier - transformed scanning tunneling spectroscopy .
| 121
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1007.1147
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a simple effective model for a description of magnetically ordered insulators is analysed . the tight binding hamiltonian consists of the effective on - site interaction ( @xmath0 ) and intersite magnetic exchange interactions ( @xmath1 , @xmath2 ) between nearest - neighbours . the phase diagrams of this model have been determined within the variational approach , which treats the on - site interaction term exactly and the intersite interactions within the mean - field approximation . we show that , depending on the values of interaction parameters and the electron concentration , the system can exhibit not only homogeneous phases : ( anti-)ferromagnetic ( f@xmath3 ) and nonordered ( no ) , but also phase separated states ( ps@xmath3 : ) .
| 124
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1506.00297
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we have analyzed numerically the localization length of light @xmath0 for nearly periodic arrangements of homogeneous stacks ( formed exclusively by right - handed materials ) and mixed stacks ( with alternating right and left - handed metamaterials ) . layers with index of refraction @xmath1 and thickness @xmath2 alternate with layers of index of refraction @xmath3 and thickness @xmath4 . positional disorder has been considered by shifting randomly the positions of the layer boundaries with respect to periodic values . for homogeneous stacks , we have shown that the localization length is modulated by the corresponding bands and that @xmath0 is enhanced at the center of each allowed band . in the limit of long - wavelengths @xmath5 , the parabolic behavior previously found in purely disordered systems is recovered , whereas for @xmath6 a saturation is reached . in the case of nearly periodic mixed stacks with the condition @xmath7 , instead of bands there is a periodic arrangement of lorenztian resonances , which again reflects itself in the behavior of the localization length . for wavelengths of several orders of magnitude greater than @xmath8 , the localization length @xmath0 depends linearly on @xmath5 with a slope inversely proportional to the modulus of the reflection amplitude between alternating layers . when the condition @xmath9 is no longer satisfied , the transmission spectrum is very irregular and this considerably affects the localization length .
| 235
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1401.3108
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motivated by the physical relevance of a spectral singularity of interacting many - particle system , we explore the dynamics of two bosons as well as fermions in one - dimensional system with imaginary delta interaction strength . based on the exact solution , it shows that the two - particle collision leads to amplitude - reduction of the wave function . for fermion pair , the amplitude - reduction depends on the spin configuration of two particles . in both cases , the residual amplitude can vanish when the relative group velocity of two single - particle gaussian wave packets with equal width reaches the magnitude of the interaction strength , exhibiting complete particle - pair annihilation at the spectral singularity .
| 123
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1105.0333
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controlled generation of entangled states of two quantum bits is a fundamental step toward the implementation of a quantum information processor . in nano - devices this operation is counteracted by the solid - state environment , characterized by broadband and non - monotonic power spectrum often @xmath0 at low frequencies . for single qubit gates , incoherent processes due to fluctuations acting on different time scales result in peculiar short- and long - time behaviors . markovian noise originates exponential decay with relaxation and decoherence times , @xmath1 and @xmath2 , simply related to the symmetry of the qubit - environment coupling hamiltonian . noise with @xmath0 power spectrum at low frequencies is instead responsible for defocusing processes and algebraic short - times behavior . in this article we identify the relevant decoherence times of an entangling operation due to the different decoherence channels originated from solid state noise . entanglement is quantified by the concurrence , which we evaluate in analytic form employing a multi - stage approach . `` optimal '' operating conditions of reduced sensitivity to noise sources are identified . we apply this analysis to a superconducting @xmath3 gate for experimental noise spectra .
| 199
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0902.1712
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pour lastrophysicien qui aborde le puzzle de la matire noire , celle - ci apparat sous deux aspects diffrents : dune part en cosmologie , cest - - dire trs grandes chelles , o elle semble tre forme dun bain de particules , et dautre part lchelle des galaxies , o elle est dcrite par un ensemble de phnomnes trs particuliers , qui paraissent incompatibles avec sa description en termes de particules , et qui font dire certains que lon est en prsence dune modification de la loi de la gravitation . rconcilier ces deux aspects distincts de la matire noire dans un mme formalisme thorique reprsente un dfi important qui pourrait peut - tre conduire une physique nouvelle en action aux chelles astronomiques .
| 125
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astro-ph0310298
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we present results from the photometric and spectroscopic identification of 122 x - ray sources recently discovered by xmm - newton in the 2 - 10 kev band ( the hellas2xmm 1df sample ) . one of the most interesting results ( which is found also in deeper sourveys ) is that @xmath0 of the sources have an x - ray to optical flux ratio ( x / o ) ten times or more higher than that of optically selected agn . unlike the faint sources found in the ultra - deep chandra and xmm - newton surveys , which reach x - ray ( and optical ) fluxes @xmath1 times lower than in the hellas2xmm sample , many of the extreme x / o sources in our sample have r@xmath2 and are therefore accessible to optical spectroscopy . we report the identification of 13 sources with extreme x / o values . while four of these sources are broad line qso , eight of them are narrow line qso , seemingly the extension to very high luminosity of the type 2 seyfert galaxies . x - ray : background , x - ray : surveys , qso : evolution
| 200
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1610.00666
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double parton scattering ( dps ) is studied at the example of @xmath0 pair - production in the lhcb and atlas experiments of the large hadron collider ( lhc ) at centre - of - mass energies of @xmath1 , 8 , and 13 tev . we report theoretical predictions delivered to the lhcb and atlas collaborations adjusted for the fiducial volumes of the corresponding measurements during run i and provide new predictions at 13 tev collision energy . it is shown that dps can lead to noticeable contributions in the distributions of longitudinal variables of the di-@xmath0 system , especially at 13 tev . the increased dps rate in double @xmath0 production at high energies will open up more possibilities for the separation of single parton scattering ( sps ) and dps contributions in future studies . ms - tp-16 - 21 * double parton scattering in pair - production of @xmath0 mesons at the lhc revisited * + christoph borschensky@xmath2 and anna kulesza@xmath3 _ @xmath4 institute for theoretical physics , university of tbingen , auf der morgenstelle 14 , d-72076 tbingen , germany + @xmath5 institute for theoretical physics , wwu mnster , d-48149 mnster , germany _
| 200
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0812.4612
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i explore entanglement dynamics in a three qubit system comparing the ability of entanglement witnesses to detect tri - partite entanglement to the phenomenon of entanglement sudden death ( esd ) . using a system subject to dephasing i invoke entanglement witnesses to detect tri - partite ghz and w - type entanglement and compare the evolution of their detection capabilites with the evolution of the negativity , bi - partite concurrence , and tri - partite negativity . interestingly , i find a state in which there is no concurrence or tri - partite negativity but there is entanglement . finally , i utilize a three qubit quantum error correction ( qec ) code to address how esd affects the abilities of quantum error correction .
| 127
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cond-mat0509295
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we report detailed studies of the ac susceptibility butterfly hysteresis on the ru1222 ruthenocuprate compounds . two separate contributions to these hysteresis have been identified and studied . one contribution is ferromagnetic - like and is characterized by the coercive field maximum . another contribution , represented by the so called inverted maximum , is related to the unusual inverted loops , unique feature of ru1222 butterfly hysteresis . the different nature of the two identified magnetic contributions is proved by the different temperature dependences involved . by lowering the temperature the inverted peak gradually disappears while the coercive field slowly raises . if the maximum dc field for the hysteresis is increased , the size of the inverted part of the butterfly hysteresis monotonously grows while the position of the peak saturates . in reaching saturation exponential field dependence has been demonstrated to take place . at t = 78 k the saturation field is 42 oe .
| 159
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0801.2981
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we report and discuss case study simulations of the rayleigh - taylor instability in the boussinesq , incompressible regime developed to turbulence . our main focus is on a statistical analysis of density and velocity fluctuations inside of the already developed and growing in size mixing zone . novel observations reported in the article concern self - similarity of the velocity and density fluctuations spectra inside of the mixing zone snapshot , independence of the spectra of the horizontal slice level , and universality showing itself in a virtual independence of the internal structure of the mixing zone , measured in the re - scaled spatial units , of the initial interface perturbations . ,
| 115
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1508.06519
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diverse models of engines energised by quantum - coherent , hence non - thermal , baths allow the engine efficiency to transgress the standard thermodynamic carnot bound . these transgressions call for an elucidation of the underlying mechanisms . here we show that non - thermal baths may impart not only heat , but also mechanical work to a machine . the carnot bound is inapplicable to such a hybrid machine . intriguingly , it may exhibit dual action , concurrently as engine and refrigerator , with up to 100% efficiency . we conclude that even though a machine powered by a quantum bath may exhibit an unconventional performance , it still abides by the traditional principles of thermodynamics .
| 120
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cond-mat9503032
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we perform an exact enumeration study of polymers formed from a ( quenched ) random sequence of charged monomers @xmath0 . such polymers , known as polyampholytes , are compact when completely neutral and expanded when highly charged . our exhaustive search included all spatial conformations and quenched sequences for up to 12step ( 13site ) walks . we investigate the behavior of the polymer as a function of its overall excess charge @xmath1 , and temperature @xmath2 . at low temperatures there is a phase transition from compact to extended configurations when the charge exceeds @xmath3 . there are also indications of a transition for small @xmath1 between two compact states on varying temperature . numerical estimates are provided for the condensation energy , surface tension , and the critical exponent @xmath4 .
| 134
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nlin0702018
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the chaotic sea below the lowest energy spanning curve of the complete fermi - ulam model ( fum ) is numerically investigated when the amplitude of oscillation @xmath0 of the moving wall is small . we use scaling analysis near the integrable to non - integrable transition to describe the average energy as function of time @xmath1 and as function of iteration ( or collision ) number @xmath2 . if @xmath1 is employed as independent variable , the exponents related to the energy scaling properties of the fum are different from the ones of a well known simplification of this model ( sfum ) . however , if @xmath2 is employed as independent variable , the exponents are the same for both fum and sfum . in the collision number analysis , we present analytical arguments supporting that the exponents @xmath3 and @xmath4 related to the initial velocity and to @xmath0 are given by @xmath5 and @xmath6 . we derive also a relation connecting the scaling exponents related to the variables time and collision number . moreover , we show that , differently from the sfum , the average energy in the fum _ saturates _ for long times and we justify the physical origins for some differences and similarities observed between the fum and its simplification .
| 218
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gr-qc0109078
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the dynamical instability of new - born neutron stars is studied by evolving the linearized hydrodynamical equations . the neutron stars considered in this paper are those produced by the accretion induced collapse of rigidly rotating white dwarfs . a dynamical bar - mode ( @xmath0 ) instability is observed when the ratio of rotational kinetic energy to gravitational potential energy @xmath1 of the neutron star is greater than the critical value @xmath2 . this bar - mode instability leads to the emission of gravitational radiation that could be detected by gravitational wave detectors . however , these sources are unlikely to be detected by ligo ii interferometers if the event rate is less than @xmath3 per year per galaxy . nevertheless , if a significant fraction of the pre - supernova cores are rapidly rotating , there would be a substantial number of neutron stars produced by the core collapse undergoing bar - mode instability . this would greatly increase the chance of detecting the gravitational radiation . 0.5 cm pacs : 04.30.db , 95.30.sf , 97.60.jd 2
| 179
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cond-mat9710250
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an _ ab initio _ hartree - fock approach aimed at directly obtaining the localized orthogonal orbitals ( wannier functions ) of a crystalline insulator is described in detail . the method is used to perform all - electron calculations on the ground states of crystalline lithium fluoride and lithium chloride , without the use of any pseudo or model potentials . quantities such as total energy , x - ray structure factors and compton profiles obtained using the localized hartree - fock orbitals are shown to be in excellent agreement with the corresponding quantities calculated using the conventional bloch - orbital based hartree - fock approach . localization characteristics of these orbitals are also discussed in detail .
| 119
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1004.5511
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consider the celebrated lyness recurrence @xmath0 with @xmath1 . first we prove that there exist initial conditions and values of @xmath2 for which it generates periodic sequences of rational numbers with prime periods @xmath3 or @xmath4 and that these are the only periods that rational sequences @xmath5 can have . it is known that if we restrict our attention to positive rational values of @xmath2 and positive rational initial conditions the only possible periods are @xmath6 and @xmath7 . moreover 1-periodic and 5-periodic sequences are easily obtained . we prove that for infinitely many positive values of @xmath8 positive 9-period rational sequences occur . this last result is our main contribution and answers an open question left in previous works of bastien & rogalski and zeeman . we also prove that the level sets of the invariant associated to the lyness map is a two - parameter family of elliptic curves that is a universal family of the elliptic curves with a point of order @xmath9 including @xmath10 infinity . this fact implies that the lyness map is a universal normal form for most birrational maps on elliptic curves . _ 2000 mathematics subject classification : _ ` 39a20 , 39a11,14h52 . ` _ keywords : _ lyness difference equations , rational points over elliptic curves , periodic points , universal family of elliptic curves .
| 226
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1412.3932
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synchrotron radiation x - ray absorption and emission spectroscopy techniques , complemented by high - resolution transmission electron microscopy methods and density functional theory calculations are employed to investigate the effect of mn in al@xmath0ga@xmath1n : mn samples with an al content up to 100% . the atomic and electronic structure of mn is established together with its local environment and valence state . a dilute alloy without precipitation is obtained for al@xmath0ga@xmath1n : mn with al concentrations up to 82% , and the surfactant role of mn in the epitaxial process is confirmed . + = 0 = 0
| 100
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0806.0695
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these lecture notes provide an introduction to mm / submm extragalactic astronomy , focused on agn studies , with the final goal of preparing students to their future exploitation of the alma capabilities . i first provide an overview of the current results obtained through mm / submm observations of galaxies and agns , both local and at high redshift . then i summarize the main mm / submm facilities that are currently available . alma is then presented with a general description and by providing some details on its observing capabilities . finally , i discuss some of the scientific goals that will be achievable with alma in extragalactic astronomy , and for agn studies in particular . galaxies : active , evolution , formation , high - redshift , nuclei , quasars , seyfert , starburst , millimeter , submillimeter , instrumentation : high angular resolution , interferometers 95.85.fm , 95.85.bh , 98.54.-h , 98.54.cm , 98.54.ep , 98.54.kt
| 161
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astro-ph9907145
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high - accuracy astrometry permits the determination of not only stellar tangential motion , but also the component along the line - of - sight . such non - spectroscopic ( i.e. astrometric ) radial velocities are independent of stellar atmospheric dynamics , spectral complexity and variability , as well as of gravitational redshift . three methods are analysed : ( 1 ) changing annual parallax , ( 2 ) changing proper motion and ( 3 ) changing angular extent of a moving group of stars . all three have significant potential in planned astrometric projects . current accuracies are still inadequate for the first method , while the second is marginally feasible and is here applied to 16 stars . the third method reaches high accuracy ( @xmath0 km s@xmath1 ) already with present data , although for some clusters an accuracy limit is set by uncertainties in the cluster expansion rate .
| 154
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physics0309032
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a proximity focusing ring imaging cherenkov detector using aerogel as the radiator has been studied for an upgrade of the belle detector at the kek - b - factory . we constructed a prototype cherenkov counter using a @xmath0 array of 64-channel flat - panel multi - anode pmts ( hamamatsu h8500 ) with a large effective area . the aerogel samples were made with a new technique to obtain a higher transmission length at a high refractive index ( @xmath1 ) . multi - channel pmts are read - out with analog memory chips . the detector was tested at the kek - ps @xmath2 beam line in november , 2002 . to evaluate systematically the performance of the detector , tests were carried out with various aerogel samples using pion beams with momenta between 0.5 gev/@xmath3 and 4 gev/@xmath3 . the typical angular resolution was around 14 mrad , and the average number of detected photoelectrons was around 6 . we expect that pions and kaons can be separated at a 4@xmath4 level at @xmath5 . aerogel , flat - panel pmt , ring imaging cherenkov counter , proximity focusing , particle identification , belle 29.40.ka
| 198
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1107.5118
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the problem of the nonequivalence of the sets of equilibrium points and energy - casimir extremal points , which occurs in the noncanonical hamiltonian formulation of equations describing ideal fluid and plasma dynamics , is addressed in the context of the euler equation for an incompressible inviscid fluid . the problem is traced to a casimir deficit , where casimir elements constitute the center of the poisson algebra underlying the hamiltonian formulation , and this leads to a study of singularities of the poisson operator defining the poisson bracket . the kernel of the poisson operator , for this typical example of an infinite - dimensional hamiltonian system for media in terms of eulerian variables , is analyzed . for two - dimensional flows , a rigorously solvable system is formulated . the nonlinearity of the euler equation makes the poisson operator inhomogeneous on phase space ( the function space of the state variable ) , and it is seen that this creates a singularity where the nullity of the poisson operator ( the `` dimension '' of the center ) changes . the problem is an infinite - dimension generalization of the theory of singular differential equations . singular casimir elements stemming from this singularity are unearthed using a generalization of the functional derivative that occurs in the poisson bracket .
| 222
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1607.02851
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we describe a method for calculating the probability with which the wall of a plasma absorbs an electron at low energy . the method , based on an invariant embedding principle , expresses the electron absorption probability as the probability for transmission through the wall s long - range surface potential times the probability to stay inside the wall despite of internal backscattering . to illustrate the approach we apply it to a sio@xmath0 surface . besides emission of optical phonons inside the wall we take elastic scattering at imperfections of the plasma - wall interface into account and obtain absorption probabilities significantly less than unity in accordance with available electron - beam scattering data but in disagreement with the widely used perfect absorber model .
| 126
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astro-ph0305513
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intermediate mass stars occupy the mass range between 0.8 - 8 . in this contribution , evolutionary models of these stars from numerous sources are compared in terms of their input physics and predicted yields . in particular , the results of renzini & voli , van den hoek & groenewegen , and marigo are discussed . generally speaking , it is shown that yields of 4 , , and 14 decrease with increasing metallicity , reduced mass loss rate , and increased rotation rate . integrated yields and recently published chemical evolution model studies are used to assess the relative importance of intermediate mass and massive stars in terms of their contributions to universal element buildup . intermediate mass stars appear to play a major role in the chemical evolution of 14 , a modest role in the case of , and a small role for 4 . furthermore , the time delay in their release of nuclear products appears to play an important part in explaining the apparent bimodality in the distribution of damped lyman-@xmath0 systems in the n/@xmath0@xmath0/h plane . [ 1996/06/01 ] a&a 4@xmath1he 14@xmath2n
| 189
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1604.05499
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many natural language processing ( nlp ) tasks can be generalized into segmentation problem . in this paper , we combine semi - crf with neural network to solve nlp segmentation tasks . our model represents a segment both by composing the input units and embedding the entire segment . we thoroughly study different composition functions and different segment embeddings . we conduct extensive experiments on two typical segmentation tasks : named entity recognition ( ner ) and chinese word segmentation ( cws ) . experimental results show that our neural semi - crf model benefits from representing the entire segment and achieves the state - of - the - art performance on cws benchmark dataset and competitive results on the conll03 dataset .
| 124
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1201.1750
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two - photon photoassociation of hot magnesium atoms by femtosecond laser pulses , creating electronically excited magnesium dimer molecules , is studied from first principles , combining _ ab initio _ quantum chemistry and molecular quantum dynamics . this theoretical framework allows for rationalizing the generation of molecular rovibrational coherence from thermally hot atoms [ l. rybak _ et al . _ , phys . rev . lett . * 107 * , 273001 ( 2011 ) ] . random phase thermal wave functions are employed to model the thermal ensemble of hot colliding atoms . comparing two different choices of basis functions , random phase wavefunctions built from eigenstates are found to have the fastest convergence for the photoassociation yield . the interaction of the colliding atoms with a femtosecond laser pulse is modeled non - perturbatively to account for strong - field effects .
| 146
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astro-ph0106163
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we derive a semi - analytic solution for the structure of conduction - mediated transition layers above an x - ray illuminated accretion disk , and calculate explicitly the x - ray line radiation resulting from both resonance line scattering and radiative recombination in these layers . the vertical thermal structure of the illuminated disk is found to depend on the illuminating continuum : for a hard power law continuum , there are two stable phases connected by a single transition layer ; while for a softer continuum , there may exist three stable phases connected by two separate transition layers , with an intermediate stable layer in between . we show that the structure can be written as a function of the electron scattering optical depth through these layers , which leads to unique predictions of the equivalent width of the resulting line radiation from both recombination cascades and resonance line scattering . we find that resonance line scattering plays an important role , especially for the case where there is no intermediate stable layer .
| 177
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1204.4181
|
we present the results of a machine - learning ( ml ) based search for new r coronae borealis ( rcb ) stars and dy persei - like stars ( dypers ) in the galaxy using cataloged light curves from the all - sky automated survey ( asas ) catalog of variable stars ( acvs ) . rcb stars a rare class of hydrogen - deficient carbon - rich supergiants are of great interest owing to the insights they can provide on the late stages of stellar evolution . dypers are possibly the low - temperature , low - luminosity analogs to the rcb phenomenon , though additional examples are needed to fully establish this connection . while rcb stars and dypers are traditionally identified by epochs of extreme dimming that occur without regularity , the ml search framework more fully captures the richness and diversity of their photometric behavior . we demonstrate that our ml method can use newly discovered rcb stars to identify additional candidates within the same data set . our search yields 15 candidates that we consider likely rcb stars / dypers : new spectroscopic observations confirm that four of these candidates are rcb stars and four are dypers . our discovery of four new dypers increases the number of known galactic dypers from two to six ; noteworthy is that one of the new dypers has a measured parallax and is @xmath0 mag , making it the brightest known dyper to date . future observations of these new dypers should prove instrumental in establishing the rcb connection . we consider these results , derived from a machine - learned probabilistic classification catalog , as an important proof - of - concept for the efficient discovery of rare sources with time - domain surveys .
| 299
|
astro-ph0701356
|
we present accurate @xmath0-band photometry for a planetary transit of ogle - tr-111 acquired with vimos at the eso very large telescope . the measurement of this transit allows to refine the planetary radius , obtaining @xmath1 . given the mass of @xmath2 previously measured from radial velocities , we confirm that the density is @xmath3 . we also revise the ephemeris for ogle - tr-111-b , obtaining an accurate orbital period @xmath4 days , and predicting that the next observable transits would occur around december 2006 , and after that only in mid-2008 . even though this period is different from previously published values , we can not yet rule out a constant period .
| 116
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astro-ph0103370
|
in this article i review the main theoretical problems that are posed by the highest energy end of the observed cosmic ray spectrum , stressing the importance of establishing their composition in order to decide between proposed scenarios . i then discuss the possibilities that are opened by the detection of inclined showers with extensive air shower arrays . recent progress in modelling magnetic deviations for these showers has allowed the analysis of inclined showers that were detected by the haverah park experiment . this analysis disfavours models that predict a large proportion of photons in the highest energy cosmic rays and open up new possibilities for future shower array detectors particularly those , like the pierre auger observatory , using water erenkov detectors .
| 125
|
astro-ph0006361
|
the late - type galaxy ngc 4303 ( m61 ) is one of the most intensively studied barred galaxies in the virgo cluster . its prominent enhanced star formation throughout large areas of the disk can be nicely studied due to its low inclination of about 27 . we present observations of ngc 4303 with the rosat pspc and hri in the soft x - ray ( 0.12.4 kev ) . the bulk of the x - ray emission is located at the nuclear region . it contributes more than 80% to the total observed soft x - ray flux . the extension of the central x - ray source and the @xmath0/@xmath1 ratio point to a low luminous agn ( liner ) with a circumnuclear star - forming region . several separate disk sources can be distinguished with the hri , coinciding spatially with some of the most luminous regions outside the nucleus of ngc 4303 . the total star formation rate amounts to 12 m@xmath2 yr@xmath3 . the x - ray structure follows the distribution of star formation with enhancement at the bar - typical patterns . the best spectral fit consists of a power - law component ( agn and hmxbs ) and a thermal plasma component of hot gas from supernova remnants and superbubbles . the total 0.12.4 kev luminosity of ngc 4303 amounts to 5 erg s@xmath3 , consistent with comparable galaxies , like e.g. ngc 4569 .
| 243
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nucl-th0507028
|
we discuss an exact analytical solution of a simplified version of the statistical multifragmentation model with the restriction that the largest fragment size can not exceed the finite volume of the system . a complete analysis of the isobaric partition singularities of this model is done for finite volumes . it is shown that the real part of any simple pole of the isobaric partition defines the free energy of the corresponding state , whereas its imaginary part , depending on the sign , defines the inverse decay / formation time of this state . the developed formalism allows us , for the first time , to exactly define the finite volume analogs of gaseous , liquid and mixed phases of this model from the first principles of statistical mechanics and demonstrate the pitfalls of earlier works . the finite size effects for large fragments and the role of metastable ( unstable ) states are discussed . numbers : 25.70 . pq , 21.65.+f , 24.10 . pa
| 168
|
1305.2474
|
a massive star can enter the blue supergiant region either evolving directly from the main - sequence , or evolving from a previous red supergiant stage . the fractions of the blue supergiants having different histories depend on the internal mixing and mass - loss during the red supergiant stage . we study the possibility to use diagnostics based on stellar pulsation to discriminate blue supergiants having different evolution histories . for this purpose we have studied the pulsation property of massive star models calculated with the geneva stellar evolution code for initial masses ranging from 8 to 50m@xmath0 with a solar metallicity of @xmath1 . we have found that radial pulsations are excited in the blue - supergiant region only in the models that had been red - supergiants before . this would provide us with a useful mean to diagnose the history of evolution of each blue - supergiant . at a given effective temperature , much more nonradial pulsations are excited in the model after the red - supergiant stage than in the model evolving towards the red - supergiant . the properties of radial and nonradial pulsations in blue supergiants are discussed . predicted periods are compared with period ranges observed in some @xmath2-cygni variables in the galaxy and ngc300 . we have found that blue supergiant models after the red - supergiant stage roughly agree with observed period ranges in most cases . however , we are left with the puzzle that the predicted surface n / c and n / o ratios seem to be too high compared with those of deneb and rigel . [ firstpage ] stars : evolution stars : early - type stars : mass - loss stars : oscillations stars : rotation stars : abundances
| 296
|
1305.4233
|
a clear understanding of body force densities due to external electromagnetic fields is necessary to study flow and deformation of materials exposed to the fields . in this paper , we derive an expression for stress in continua with viscous and elastic properties in presence of external , static electric or magnetic fluids . our derivation follows from fundamental thermodynamic principles . we demonstrate the soundness of our results by showing that they reduce to known expressions for newtonian fluids and elastic solids . we point out the extra care to be taken while applying these techniques to permanently polarized or magnetized materials and derive an expression for stress in a ferro - fluid . lastly , we derive expressions for ponderomotive forces in several situations of interest to fluid dynamics and rheology .
| 134
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0810.4363
|
laser cooling and trapping are now widely used in atomic physics laboratory . interestingly , cold atoms in optical lattices are now used in advanced research to mimic phenomena in condensed matter physics and also as a test laboratory for the models of these phenomena . it follows then that it is now possible and necessary to advance the atomic physics laboratory by including the use of ultracold atoms in optical lattices for instructional contents of phenomena in condensed matter physics . in this paper , we have proposed how to introduce into the atomic physics laboratory the study of quantum magnetism with cold atoms in a double well optical lattice . in particular , we demonstrates how to compare the theoretical parameters of a spin hamiltonian model with those extracted from spin ordering experiment .
| 136
|
cond-mat0401431
|
we present a continuum model for the propagation of cracks and fractures in brittle materials . the components of the strain tensor @xmath0 are the fundamental variables . the evolution equations are based on a free energy that reduces to that of linear elasticity for small @xmath0 , and accounts for cracks through energy saturation at large values of @xmath0 . we regularize the model by including terms dependent on gradients of @xmath0 in the free energy . no additional fields are introduced , and then the whole dynamics is perfectly defined . we show that the model is able to reproduce basic facts in fracture physics , like the griffith s dependence of the critical stress as a minus one half power of the crack length . in addition , regularization makes the results insensitive to the numerical mesh used , something not at all trivial in crack modeling . we present and example of the application of the model to predict the growth and curving of cracks in a non - trivial geometrical configuration .
| 177
|
0906.5048
|
using a markov chain monte carlo approach , we find the allowed parameter space of a mssm model with seven free parameters . in this model universality conditions at the gut scale are imposed on the gaugino sector . we require in particular that the relic density of dark matter saturates the value extracted from cosmological measurements assuming a standard cosmological scenario . we characterize the parameter space of the model that satisfies experimental constraints and illustrate the complementarity of the lhc searches , b - physics observables and direct dark matter searches for further probing the parameter space of the model . we also explore the different decay chains expected for the coloured particles that would be produced at lhc . _ _ date : * constraining the mssm with universal gaugino masses and implication for searches at the lhc * + g. blanger@xmath0 , f. boudjema@xmath0 , a. pukhov@xmath1 , r. k. singh@xmath2 + _ 1 ) lapth , univ . de savoie , cnrs , b.p.110 , f-74941 annecy - le - vieux , france + 2 ) skobeltsyn inst . of nuclear physics , moscow state univ . , moscow 119992 , russia + 3 ) institut fr theoretische physik und astrophysik , universitt wrzburg , + d-97074 wrzburg , germany _ +
| 217
|
astro-ph9909478
|
we perform a series of high resolution n - body simulations designed to examine the density profiles of dark matter halos . from 12 simulated halos ranging the mass of @xmath0 ( represented by @xmath1 million particles within the virial radius ) , we find a clear systematic correlation between the halo mass and the slope of the density profile at 1% of the virial radius , in addition to the variations of the slope among halos of the similar mass . more specifically , the slope is @xmath2 , @xmath3 , and @xmath4 for galaxy , group , and cluster mass halos , respectively . while we confirm the earlier simulation results that the inner slope is steeper than the _ universal _ profile originally proposed by navarro , frenk & white , this mass dependence is inconsistent with the several analytical arguments attempting to link the inner slope with the primordial index of the fluctuation spectrum . thus we conclude that the dark matter density profiles , especially in the inner region , are not universal .
| 179
|
1507.03886
|
sports are spontaneous generators of stories . through skill and chance , the script of each game is dynamically written in real time by players acting out possible trajectories allowed by a sport s rules . by properly characterizing a given sport s ecology of ` game stories ' , we are able to capture the sport s capacity for unfolding interesting narratives , in part by contrasting them with random walks . here , we explore the game story space afforded by a data set of 1,310 australian football league ( afl ) score lines . we find that afl games exhibit a continuous spectrum of stories rather than distinct clusters . we show how coarse - graining reveals identifiable motifs ranging from last minute comeback wins to one - sided blowouts . through an extensive comparison with biased random walks , we show that real afl games deliver a broader array of motifs than null models , and we provide consequent insights into the narrative appeal of real games .
| 172
|
astro-ph0510499
|
we have analysed the magnitudes , kinematics and positions of a complete sample of 320 pns in the elliptical galaxy ngc 4697 . we show ( i ) that the pns in ngc 4697 do not constitute a single population that is a fair tracer of the distribution of all stars . the radial velocity distributions , mean velocities , and dispersions of bright and faint subsamples differ with high statistical confidence . ( ii ) using the combined data for pns brighter than @xmath0 , we have identified a subpopulation of pns which is azimuthally unmixed and kinematically peculiar , and which thus neither traces the distribution of all stars nor can it be in dynamical equilibrium with the galaxy potential . ( iii ) the planetary nebula luminosity functions ( pnlf ) of two kinematic subsamples in ngc 4697 differ with 99.7% confidence , ruling out a universal pnlf . we estimate that the inferred secondary pn population introduces an uncertainty in the bright cutoff magnitude of @xmath1 mag for this galaxy . we argue that this secondary pn distribution may be associated with a younger , @xmath2 gyr old stellar population , perhaps formed in tidal structures that have now fallen back onto the galaxy , as has previously been suggested for the x - ray point sources in this galaxy , or coming from a more recent merger / accretion with a red galaxy . the use of pns for extragalactic distance determinations is not necessarily compromised , but their use as dynamical tracers of dark halos will require deep observations and careful analysis of large pn samples .
| 273
|
1506.02756
|
we study surface and bulk properties of porous films produced by a model in which particles incide perpendicularly to a substrate , interact with deposited neighbors in its trajectory , and aggregate laterally with probability of order @xmath0 at each position . the model generalizes ballistic - like models by allowing attachment to particles below the outer surface . for small values of @xmath0 , a crossover from uncorrelated deposition ( ud ) to correlated growth is observed . simulations are performed in @xmath1 and @xmath2 dimensions . extrapolation of effective exponents and comparison of roughness distributions confirm kardar - parisi - zhang roughening of the outer surface for @xmath3 . a scaling approach for small @xmath0 predicts crossover times as @xmath4 and local height fluctuations as @xmath5 at the crossover , independently of substrate dimension . these relations are different from all previously studied models with crossovers from ud to correlated growth due to subsurface aggregation , which reduces scaling exponents . the same approach predicts the porosity and average pore height scaling as @xmath6 and @xmath5 , respectively , in good agreement with simulation results in @xmath1 and @xmath2 dimensions . these results may be useful to modeling samples with desired porosity and long pores .
| 208
|
1101.3474
|
gene set enrichment analysis ( gsea ) and its variations aim to discover collections of genes that show moderate but coordinated differences in expression . however , such techniques may be ineffective if many individual genes in a phenotype - related gene set have weak discriminative power . a potential solution is to search for combinations of genes that are highly differentiating even when individual genes are not . although such techniques have been developed , these approaches have not been used with gsea to any significant degree because of the large number of potential gene combinations and the heterogeneity of measures that assess the differentiation provided by gene groups of different sizes . to integrate the search for differentiating gene combinations and gsea , we propose a general framework with two key components : ( a ) a procedure that reduces the number of scores to be handled by gsea to the number of genes by summarizing the scores of the gene combinations involving a particular gene in a single score , and ( b ) a procedure to integrate the heterogeneous scores from combinations of different sizes and from different gene combination measures by mapping the scores to p - values . experiments on four gene expression data sets demonstrate that the integration of gsea and gene combination search can enhance the power of traditional gsea by discovering gene sets that include genes with weak individual differentiation but strong joint discriminative power . also , gene sets discovered by the integrative framework share several common biological processes and improve the consistency of the results among three lung cancer data sets .
| 273
|
1202.1138
|
we present scaling relations between stellar - mass ( @xmath0 ) and the size of galaxies at @xmath1 for half- ( @xmath2 ) and 90 percent - light ( @xmath3 ) radii , using a deep @xmath4-band selected catalogue taken with the subaru telescope and moircs in the goods - north region . the logarithmic slope @xmath5 is independent of redshift in a wide mass range of @xmath6 m@xmath7 , irrespective of galaxy populations ( star - forming , quiescent ) . the offset change is @xmath8 percent . provided that optical light in the rest frame traces the stellar mass of galaxies , the universal relation demonstrates that the stellar mass was built up in galaxies over their cosmic histories in a similar manner on average irrelevant to galaxy mass . the small offset in each stellar mass bin from the universal relation shows weak size evolution at a given mass . there is a moderate increase of 3050 percent for @xmath2 and @xmath3 for less massive galaxies ( @xmath9 m@xmath7 ) from @xmath10 to @xmath11 , while the sizes remains unchanged or slightly decrease towards @xmath12 . for massive galaxies ( @xmath13 m@xmath7 ) , the evolution is @xmath14 % increase in @xmath3 from @xmath10 to @xmath12 , though that in @xmath2 is weaker . the evolution of compactness factor , @xmath15 , which becomes smaller at lower redshift , is suggestive of minor merging effect in the outer envelope of massive galaxies . [ firstpage ] galaxies : evolution galaxies : fundamental parameters galaxies : high - redshift infrared : galaxies .
| 265
|
0811.1192
|
we study the relaxation dynamics of systems of straight , parallel crystal dislocations , starting from initially random and uncorrelated positions of the individual dislocations . a scaling model of the relaxation process is constructed by considering the gradual extinction of the initial density fluctuations present in the system . the model is validated by ensemble simulations of the discrete dynamics of dislocations . convincing agreement is found for systems of edge dislocations in single slip irrespective of the net burgers vector of the dislocation system . it is also demonstrated that the model does not work in multiple slip geometries . _ keywords _ : defects ( theory ) , fluctuations ( theory ) , plasticity ( theory )
| 120
|
0912.4700
|
a theoretical model for the calculation of the phonon - drag thermopower , @xmath0 , in degenerately doped semiconducting single - wall carbon nanotubes ( swcnts ) is proposed . detailed calculations of @xmath0 are performed as a function of temperature , tube radius and position of the fermi level . we derive a simple analytical expression for @xmath0 that can be utilized to determine the free carrier density in doped nanotubes . at low temperatures @xmath0 shows an activated behavior characteristic of the one - dimensional ( 1d ) character of carriers . screening effects are taken into account and it is found that they dramatically reduce the magnitude of @xmath0 . our results are compared with previous published experimental data in bulk p - doped swcnt materials . excellent agreement is obtained in the temperature range 10 - 200 k for a consistent set of parameters . this is a striking result in view of the complexity of these systems .
| 163
|
1010.3062
|
relationships between the x - ray and radio behavior of black hole x - ray binaries during outbursts have established a fundamental coupling between the accretion disks and radio jets in these systems . i begin by reviewing the prevailing paradigm for this disk - jet coupling , also highlighting what we know about similarities and differences with neutron star and white dwarf binaries . until recently , this paradigm had not been directly tested with dedicated high - angular resolution radio imaging over entire outbursts . moreover , such high - resolution monitoring campaigns had not previously targetted outbursts in which the compact object was either a neutron star or a white dwarf . to address this issue , we have embarked on the jet acceleration and collimation probe of transient x - ray binaries ( jacpot xrb ) project , which aims to use high angular resolution observations to compare disk - jet coupling across the stellar mass scale , with the goal of probing the importance of the depth of the gravitational potential well , the stellar surface and the stellar magnetic field , on jet formation . our team has recently concluded its first monitoring series , including ( e)vla , vlba , x - ray , optical , and near - infrared observations of entire outbursts of the black hole candidate h1743 - 322 , the neutron star system aquila x-1 , and the white dwarf system ss cyg . here i present preliminary results from this work , largely confirming the current paradigm , but highlighting some intriguing new behavior , and suggesting a possible difference in the jet formation process between neutron star and black hole systems .
| 285
|
1307.2146
|
we present a x - ray survey of the disrupted recycled pulsars ( drps ) , isolated radio pulsars with @xmath0 ms and @xmath1 g. these observations were motivated as a search for the immediate descendants of the @xmath2 central compact objects ( ccos ) in supernova remnants , three of which have similar timing and magnetic properties as the drps , but are bright , thermal x - ray sources consistent with minimal neutron star cooling curves . since none of the dprs were detected , there is no evidence that they are `` orphaned '' ccos , neutron stars whose supernova remnants has dissipated . upper limits on their thermal x - ray luminosities are in the range log @xmath3=31.8 - 32.8 $ ] , which implies cooling ages @xmath4 yr , roughly 10 times the ages of the @xmath5 known ccos in a similar volume of the galaxy . the order of a hundred cco descendants that could be detected by this method are thus either intrinsically radio quiet , or occupy a different region of ( @xmath6 ) parameter space from the drps . this motivates a new x - ray search for orphaned ccos among radio pulsars with larger @xmath7-fields , which could verify the theory that their fields are buried by fall - back of supernova ejecta , but quickly regrow to join the normal pulsar population .
| 234
|
astro-ph9907268
|
i review the constraints imposed by the observed extragalactic background light ( ebl ) on the history of the stellar birthrate in galaxies . at faint magnitudes , the logarithmic slope of the galaxy counts is flatter than @xmath0 in all seven @xmath1 optical bandpasses of the _ hubble deep field - south _ imaging survey . the integration of the number counts provides a lower limit to the surface brightness of the optical extragalactic sky of @xmath2 , comparable to the intensity of the far - ir background from _ cobe _ data . if the initial mass function has a salpeter slope with a lower mass cutoff consistent with observations of m subdwarf disk stars , a lower limit of @xmath3 ( at hubble constant @xmath4 ) is derived for the visible ( processed gas @xmath5 stars ) mass density needed to generate an extragalactic background light ( ebl ) at a level of @xmath6 . the current ` best - guess ' estimate to @xmath7 is @xmath8 , about 16% of the nucleosynthetic baryon density . the contribution of quasar activity to the observed ebl is unlikely to exceed 20% .
| 194
|
astro-ph0501370
|
we present a generalization of the multiphase chemical evolution model applied to a wide set of theoretical galaxies with different masses and evolutionary rates . this generalized set of models has been computed using the so - called _ universal rotation curve _ from @xcite to calculate the radial mass distribution of 44 _ theoretical _ protogalaxies . this distribution is a fundamental input which , besides its own effect on the galaxy evolution , defines the characteristic collapse time - scale or gas infall rate onto the disc . we have adopted 10 sets of values , between 0 and 1 , for the molecular cloud and star formation efficiencies , as corresponding to their probability nature , for each one of the radial distributions of total mass . thus , we have constructed a bi - parametric grid of models , depending on those efficiency sets and on the rotation velocity , whose results are valid in principle for any spiral or irregular galaxy . the model results provide the time evolution of different regions of the disc and the halo along galactocentric distance , measured by the gas ( atomic and molecular ) and stellar masses , the star formation rate and chemical abundances of 14 elements , for a total of 440 models . this grid may be used to estimate the evolution of a given galaxy for which only present time information such as radial distributions of elemental abundances , gas densities and/or star formation , which are the usual observational constraints of chemical evolution models is available . [ firstpage ] galaxies : abundances galaxies : evolution galaxies : spirals galaxies : stellar content
| 280
|
physics0008061
|
for short , high - intensity electron bunches , alkali - tellurides have proved to be a reliable photo - cathode material . measurements of lifetimes in an rf gun of the clic test facility ii at field strengths greater than 100 mv / m are presented . before and after using them in this gun , the spectral response of the cs - te and rb - te cathodes were determined with the help of an optical parametric oscillator . the behaviour of both materials can be described by spicer s 3-step model . whereas during the use the threshold for photo - emission in cs - te was shifted to higher photon energies , that of rb - te did not change . our latest investigations on the stoichiometric ratio of the components are shown . the preparation of the photo - cathodes was monitored with 320 nm wavelength light , with the aim of improving the measurement sensitivity . the latest results on the protection of cs - te cathode surfaces with csbr against pollution are summarized . new investigations on high mean current production are presented .
| 191
|
1407.0247
|
we present an inelastic neutron scattering study on single - crystalline lifeas devoted to the characterization of the incommensurate antiferromagnetic fluctuations at @xmath0 . time - of - flight measurements show the presence of these magnetic fluctuations up to an energy transfer of 60 mev , while polarized neutrons in combination with longitudinal polarization analysis on a triple - axis spectrometer prove the pure magnetic origin of this signal . the normalization of the magnetic scattering to an absolute scale yields that magnetic fluctuations in lifeas are by a factor eight weaker than the resonance signal in nearly optimally co - doped bafe@xmath1as@xmath1 , although a factor two is recovered due to the split peaks owing to the incommensurability . the longitudinal polarization analysis indicates weak spin space anisotropy with slightly stronger out - of - plane component between 6 and 12 mev . furthermore , our data suggest a fine structure of the magnetic signal most likely arising from superposing nesting vectors .
| 164
|
1602.05027
|
by means of one - step model calculations the strong in - plane anisotropy seen in angle - resolved photoemission of the well - known iron pnictide prototype compounds and in their low - temperature antiferromagnetic phases is investigated . the fully - relativistic calculations are based on the korringa - kohn - rostoker - green function approach combined with the coherent potential approximation alloy theory to account for the disorder induced by co substitution on fe sites in a reliable way . the results of the calculations can be compared directly to experimental spectra of detwinned single crystals . one finds very good agreement with experiment and can reveal all features of the electronic structure contributing to the in - plane anisotropy . in particular the local density approximation can capture most of the correlation effects for the investigated system without the need for more advanced techniques . in addition , the evolution of the anisotropy for increasing co concentration @xmath0 in can be tracked almost continuously . the results are also used to discuss surface effects and it is possible to identify clear signatures to conclude about different types of surface termination .
| 195
|
0712.1883
|
we give an exposition of the parametrization method of @xcite in the context of the multisymplectic approach to field theory , as presented in @xcite . the purpose of the formalism developed herein is to make any classical field theory , containing a metric as a sole background field , generally covariant ( that is , _ parametrized _ , with the spacetime diffeomorphism group as a symmetry group ) as well as fully dynamic . this is accomplished by introducing certain `` covariance fields '' as genuine dynamic fields . as we shall see , the multimomenta conjugate to these new fields form the piola kirchhoff version of the stress - energy - momentum tensor field , and their euler lagrange equations are vacuously satisfied . thus , these fields have no additional physical content ; they serve only to provide an efficient means of parametrizing the theory . our results are illustrated with two examples , namely an electromagnetic field and a klein gordon vector field , both on a background spacetime .
| 175
|
1406.4412
|
flagellated bacteria exploiting helical propulsion are known to swim along circular trajectories near surfaces . fluid dynamics predicts this circular motion to be clockwise ( cw ) above a rigid surface ( when viewed from inside the fluid ) and counter - clockwise ( ccw ) below a free surface . recent experimental investigations showed that complex physicochemical processes at the nearby surface could lead to a change in the direction of rotation , both at solid surfaces absorbing slip - inducing polymers and interfaces covered with surfactants . motivated by these results , we use a far - field hydrodynamic model to predict the kinematics of swimming near three types of interfaces : clean fluid - fluid interface , slipping rigid wall , and a fluid interface covered by incompressible surfactants . representing the helical swimmer by a superposition of hydrodynamic singularities , we first show that in all cases the surfaces reorient the swimmer parallel to the surface and attract it , both of which are a consequence of the stokes dipole component of the swimmer flow field . we then show that circular motion is induced by a higher - order singularity , namely a rotlet dipole , and that its rotation direction ( cw vs. ccw ) is strongly affected by the boundary conditions at the interface and the bacteria shape . our results suggest thus that the hydrodynamics of complex interfaces provide a mechanism to selectively stir bacteria .
| 244
|
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