Datasets:

Hazem91

/

Arxive_PUBMED

like 0

katz and vafa @xcite showed how charged matter can arise geometrically by the deformation of ade - type orbifold singularities in type iia , m - theory , and f - theory compactifications . in this paper we use those same basic ingredients , used there to geometrically engineer specific matter representations , here to deform the compactification manifold itself in a way which naturally compliments many features of unified model building . we realize this idea explicitly by deforming a manifold engineered to give rise to an @xmath0 grand unified model into a one giving rise to the standard model . in this framework , the relative local positions of the singularities giving rise to standard model fields are specified in terms of the values of a small number of complex structure moduli which deform the original manifold , greatly reducing the arbitrariness of their relative positions .

the recently updated data of the twin kilohertz quasi - periodic oscillations ( khz qpos ) in the neutron star low - mass x - ray binaries are analyzed . the power - law fitting @xmath0 and linear fitting @xmath1 are applied , individually , to the data points of four z sources ( gx 17 + 2 , gx 340 + 0 , gx 5 - 1 and sco x-1 ) and four atoll sources ( 4u 0614 + 09 , 4u 1608 - 52 , 4u 1636 - 53 and 4u 1728 - 34 ) . the @xmath2-tests show that the power - law correlation and linear correlation both can fit data well . moreover , the comparisons between the data and the theoretical models for khz qpos are discussed . qpos ; accretion disks ; neutron stars ; x - rays binaries .

this paper develops a contention - based opportunistic feedback technique towards relay selection in a dense wireless network . this technique enables the forwarding of additional parity information from the selected relay to the destination . for a given network , the effects of varying key parameters such as the feedback probability are presented and discussed . a primary advantage of the proposed technique is that relay selection can be performed in a distributed way . simulation results find its performance to closely match that of centralized schemes that utilize gps information , unlike the proposed method . the proposed relay selection method is also found to achieve throughput gains over a point - to - point transmission strategy . automatic repeat request , relays , convolutional codes .

we propose a hodge field theory construction that captures algebraic properties of the reduction of zwiebach invariants to gromov - witten invariants . it generalizes the barannikov - kontsevich construction to the case of higher genera correlators with gravitational descendants . we prove the main theorem stating that algebraically defined hodge field theory correlators satisfy all tautological relations . from this perspective the statement that barannikov - kontsevich construction provides a solution of the wdvv equation looks as the simplest particular case of our theorem . also it generalizes the particular cases of other low - genera tautological relations proven in our earlier works ; we replace the old technical proofs by a novel conceptual proof .

entangling and disentangling capacities are the key manifestation of the nonlocal content of a quantum operation . a lot of effort has been put recently into investigating ( dis)entangling capacities of unitary operations , but very little is known about capacities of non - unitary operations . here we investigate ( dis)entangling capacities of unital cptp maps acting on two qubits .

during the last three decades , evidence has mounted that star and planet formation is not an isolated process , but is influenced by current and previous generations of stars . although cool stars form in a range of environments , from isolated globules to rich embedded clusters , the influences of other stars on cool star and planet formation may be most significant in embedded clusters , where hundreds to thousands of cool stars form in close proximity to ob stars . at the cool stars 14 meeting , a splinter session was convened to discuss the role of environment in the formation of cool stars and planetary systems ; with an emphasis on the `` hot '' environment found in rich clusters . we review here the basic results , ideas and questions presented at the session . we have organized this contribution into five basic questions : what is the typical environment of cool star formation , what role do hot star play in cool star formation , what role does environment play in planet formation , what is the role of hot star winds and supernovae , and what was the formation environment of the sun ? the intention is to review progress made in addressing each question , and to underscore areas of agreement and contention .

in the previous study ( hiremath 2006a ) , the solar cycle is modeled as a forced and damped harmonic oscillator and from all the 22 cycles ( 1755 - 1996 ) , long - term amplitudes , frequencies , phases and decay factor are obtained . using these physical parameters of the previous 22 solar cycles and by an _ autoregressive model _ , we predict the amplitude and period of the future fifteen solar cycles . predicted amplitude of the present solar cycle ( 23 ) matches very well with the observations . the period of the present cycle is found to be 11.73 years . with these encouraging results , we also predict the profiles of future 15 solar cycles . important predictions are : ( i ) the period and amplitude of the cycle 24 are 9.34 years and 110 ( @xmath0 ) , ( ii ) the period and amplitude of the cycle 25 are 12.49 years and 110 ( @xmath1 11 ) , ( iii ) during the cycles 26 ( 2030 - 2042 ad ) , 27 ( 2042 - 2054 ad ) , 34 ( 2118 - 2127 ad ) , 37 ( 2152 - 2163 ad ) and 38 ( 2163 - 2176 ad ) , the sun might experience a very high sunspot activity , ( iv ) the sun might also experience a very low ( around 60 ) sunspot activity during cycle 31 ( 2089 - 2100 ad ) and , ( v ) length of the solar cycles vary from 8.65 yrs for the cycle 33 to maximum of 13.07 yrs for the cycle 35 .

kinetically constrained spin models are known to exhibit dynamical behavior mimicking that of glass forming systems . they are often understood as coarse - grained models of glass formers , in terms of some `` mobility '' field . the identity of this `` mobility '' field has remained elusive due to the lack of coarse - graining procedures to obtain these models from a more microscopic point of view . here we exhibit a scheme to map the dynamics of a two - dimensional soft disc glass former onto a kinetically constrained spin model , providing an attempt at bridging these two approaches .

spectral diagnostic features formed in the solar chromosphere are few and difficult to interpret they are neither formed in the optically thin regime nor in local thermodynamic equilibrium ( lte ) . to probe the state of the chromosphere , both from observations and theory , it is therefore necessary with modeling . i discuss both traditional semi - empirical modeling , numerical experiments illustrating important ingredients necessary for a self - consistent theoretical modeling of the solar chromosphere and the first results of such models .

cosmological shock waves result from supersonic flow motions induced by hierarchical clustering of nonlinear structures in the universe . these shocks govern the nature of cosmic plasma through thermalization of gas and acceleration of nonthermal , cosmic - ray ( cr ) particles . we study the statistics and energetics of shocks formed in cosmological simulations of a concordance @xmath0cdm universe , with a special emphasis on the effects of non - gravitational processes such as radiative cooling , photoionization / heating , and galactic superwind feedbacks . adopting an improved model for gas thermalization and cr acceleration efficiencies based on nonlinear diffusive shock acceleration calculations , we then estimate the gas thermal energy and the cr energy dissipated at shocks through the history of the universe . since shocks can serve as sites for generation of vorticity , we also examine the vorticity that should have been generated mostly at curved shocks in cosmological simulations . we find that the dynamics and energetics of shocks are governed primarily by the gravity of matter , so other non - gravitational processes do not affect significantly the global energy dissipation and vorticity generation at cosmological shocks . our results reinforce scenarios in which the intracluster medium and warm - hot intergalactic medium contain energetically significant populations of nonthermal particles and turbulent flow motions .

density - functional theory has been applied to investigate systematics of sodium clusters na@xmath0 in the size range of @xmath1= 39 - 55 . a clear evolutionary trend in the growth of their ground - state geometries emerges . the clusters at the beginning of the series ( @xmath1=39 - 43 ) are symmetric and have partial icosahedral ( two - shell ) structure . the growth then goes through a series of disordered clusters ( @xmath1=44 - 52 ) where the icosahedral core is lost . however , for @xmath253 a three shell icosahedral structure emerges . this change in the nature of the geometry is abrupt . in addition , density - functional molecular dynamics has been used to calculate the specific heat curves for the representative sizes @xmath1= 43 , 45 , 48 and 52 . these results along with already available thermodynamic calculations for @xmath1= 40 , 50 , and 55 enable us to carry out a detailed comparison of the heat capacity curves with their respective geometries for the entire series . our results clearly bring out strong correlation between the evolution of the geometries and the nature of the shape of the heat capacities . the results also firmly establish the size - sensitive nature of the heat capacities in sodium clusters .

the approximate atomic self - interaction corrections ( asic ) method to density functional theory is put to the test by calculating the exchange interaction for a number of prototypical materials , critical to local exchange and correlation functionals . asic total energy calculations are mapped onto an heisenberg pair - wise interaction and the exchange constants @xmath0 are compared to those obtained with other methods . in general the asic scheme drastically improves the bandstructure , which for almost all the cases investigated resemble closely available photo - emission data . in contrast the results for the exchange parameters are less satisfactory . although asic performs reasonably well for systems where the magnetism originates from half - filled bands , it suffers from similar problems than those of lda for other situations . in particular the exchange constants are still overestimated . this reflects a subtle interplay between exchange and correlation energy , not captured by the asic .

we present observations of a solar quiet region obtained by the ground - based dutch open telescope ( dot ) , and by instruments on the spacecraft soho and trace . the observations were obtained during a coordinated observing campaign on october 2005 . the aim of this work is to present the rich diversity of fine - scale structures that are found at the network boundaries and their appearance in different instruments and different spectral lines that span the photosphere to the corona . detailed studies of these structures are crucial to understanding their dynamics in different solar layers , as well as the role such structures play in the mass balance and heating of the solar atmosphere .

we study ground state properties and excitation spectra for hard - core bosons on square and triangular lattices , at half filling , using series expansion methods . nearest - neighbor repulsion between the bosons leads to the development of short - range density order at the antiferromagnetic wavevector , and simultaneously a roton minima in the density excitation spectra . on the square - lattice , the model maps on to the well studied xxz model , and the roton gap collapses to zero precisely at the heisenberg symmetry point , leading to the well known spectra for the heisenberg antiferromagnet . on the triangular - lattice , the collapse of the roton gap signals the onset of the supersolid phase . our results suggest that the transition from the superfluid to the supersolid phase maybe weakly first order . we also find several features in the density of states , including two - peaks and a sharp discontinuity , which maybe observable in experimental realization of such systems .

a gravitating global k - monopole produces a tiny gravitational field outside the core in addition to a solid angular deficit in the k - field theory . as a new feature , the gravitational field can be attractive or repulsive depending on the non - canonical kinetic term .

vimos is a wide - field imager and spectrograph mounted on ut3 at the vlt , whose fov consists of four 7x8 quadrants . here we present the measurements of total transmission profiles i.e. the throughput of telescope + instrument for the broad band filters u , b , v , r , i , and z for each of its four quadrants . those measurements can also be downloaded from the public vimos web - page . the transmission profiles are compared with previous estimates from the vimos consortium .

the lifshitz - type formulas describing the free energy and the force of the van der waals interaction between an atom ( molecule ) and a single - wall carbon nanotube are obtained . the single - wall nanotube is considered as a cylindrical sheet carrying a two - dimensional free electron gas with appropriate boundary conditions on the electromagnetic field . the obtained formulas are used to calculate the van der waals free energy and force between a hydrogen atom ( molecule ) and single - wall carbon nanotubes of different radia . comparison studies of the van der waals interaction of hydrogen atoms with single- and multi - wall carbon nanotubes show that depending on atom - nanotube separation distance the idealization of graphite dielectric permittivity is already applicable to nanotubes with only two or three walls .

a new _ xmm - newton _ observation has made possible a detailed study of both lobes of the radio galaxy pictor a. their x - ray emission is of non thermal origin and due to inverse compton scattering of the microwave background photons by relativistic electrons in the lobes , as previously found . in both lobes , the equipartition magnetic field ( _ b@xmath0 _ ) is bigger than the inverse compton value ( _ b@xmath1 _ ) , calculated from the radio and x - ray flux ratio . the _ b@xmath0 _ /_b@xmath1 _ ratio never gets below 2 , in spite of the large number of reasonable assumptions tested to calculate _ b@xmath0 _ , suggesting a lobe energetic dominated by particles . the x - ray data quality is good enough to allow a spatially resolved analysis . our study shows that _ b@xmath1 _ varies through the lobes . it appears to increase behind the hot spots . on the contrary , a rather uniform distribution of the particles is observed . as a consequence , the radio flux density variation along the lobes appears to be mainly driven by magnetic field changes .

the problem of characterizing complexity of quantum dynamics - in particular of locally interacting chains of quantum particles - will be reviewed and discussed from several different perspectives : ( i ) stability of motion against external perturbations and decoherence , ( ii ) efficiency of quantum simulation in terms of classical computation and entanglement production in operator spaces , ( iii ) quantum transport , relaxation to equilibrium and quantum mixing , and ( iv ) computation of quantum dynamical entropies . discussions of all these criteria will be confronted with the established criteria of integrability or quantum chaos , and sometimes quite surprising conclusions are found . some conjectures and interesting open problems in ergodic theory of the quantum many problem are suggested . _ invited review article for special issue of journal of physics a on quantum information _

if dark matter decays to electromagnetically - interacting particles , it can inject energy into the baryonic gas and thus affect the processes of recombination and reionization . this leaves an imprint on the cosmic microwave background ( cmb ) : the large - scale polarization is enhanced , and the small - scale temperature fluctuation is damped . we use the wmap three - year data combined with galaxy surveys to constrain radiatively decaying dark matter . our new limits to the dark - matter decay width are about ten times stronger than previous limits . for dark - matter lifetimes that exceed the age of the universe , a limit of @xmath0 ( 95% cl ) is derived , where @xmath1 is the efficiency of converting decay energy into ionization energy . limits for lifetimes short compared with the age of the universe are also derived . we forecast improvements expected from the planck satellite .

recently @xmath0 data obtained from differential ages of galaxies have been proposed as a new geometrical probe of dark energy . in this paper we use those data , combined with other background tests ( cmb shift and snia data ) , to constrain a set of general relativistic dark energy models together with some other models motivated by extra dimensions . our analysis rests mostly on bayesian statistics , and we conclude that lcdm is at least substantially favoured , and that extradimensional models are less favoured than general relativistic ones .

if predictions for species extinctions hold , then the ` tree of life ' today may be quite different to that in ( say ) 100 years . we describe a technique to quantify how much each species is likely to contribute to future biodiversity , as measured by its expected contribution to phylogenetic diversity . our approach considers all possible scenarios for the set of species that will be extant at some future time , and weights them according to their likelihood under an independent ( but not identical ) distribution on species extinctions . although the number of extinction scenarios can typically be very large , we show that there is a simple algorithm that will quickly compute this index . the method is implemented and applied to the prosimian primates as a test case , and the associated species ranking is compared to a related measure ( the ` shapley index ' ) . we describe indices for rooted and unrooted trees , and a modification that also includes the focal taxon s probability of extinction , making it directly comparable to some new conservation metrics . _ keywords : _ phylogenetic diversity , extinction , biodiversity conservation , shapley index _ short title : _ taxon - specific indices of expected future biodiversity

we wish to transmit messages to and from a hypersonic vehicle around which a plasma sheath has formed . for long distance transmission , the signal carrying these messages must be necessarily low frequency , typically 2 ghz , to which the plasma sheath is opaque . the idea is to use the plasma properties to make the plasma sheath appear transparent .

based on the results of numerical modeling , it is shown that dipole - dipole interactions among atoms in the active medium influences strongly the character of the associated superradiation . the main effect is to make the nuclear subsystem behave chaotically . its strength increases with the atom density , and leads to the suppression of distant collective correlations and superradiation . near correlations between the atoms are established , causing a confinement effect : a shielding of radiation in the active medium . _ keywords_:superradiation , superfluorescence , dipole - dipole interaction , coherent radiation

we update the analytical estimate of the final spin of a coalescing black - hole binary derived within the effective - one - body ( eob ) approach . we consider unequal - mass non - spinning black - hole binaries . it is found that a more complete account of relevant physical effects ( higher post - newtonian accuracy , ringdown losses ) allows the _ analytical _ eob estimate to `` converge towards '' the recently obtained _ numerical _ results within @xmath0 . this agreement illustrates the ability of the eob approach to capture the essential physics of coalescing black - hole binaries . our analytical approach allows one to estimate the final spin of the black hole formed by coalescing binaries in a mass range ( @xmath1 ) which is not presently covered by numerical simulations .

we perform a time - dependent study of the driven dynamics of overdamped particles which are placed in a one - dimensional , piecewise linear random potential . this set - up of spatially quenched disorder then exerts a dichotomous varying random force on the particles . we derive the path integral representation of the resulting probability density function for the position of the particles and transform this quantity of interest into the form of a fourier integral . in doing so , the evolution of the probability density can be investigated analytically for finite times . it is demonstrated that the probability density contains both a @xmath0-singular contribution and a regular part . while the former part plays a dominant role at short times , the latter rules the behavior at large evolution times . the slow approach of the probability density to a limiting gaussian form as time tends to infinity is elucidated in detail .

this paper includes a reflection on the role of networks in the study of english language acquisition , as well as a collection of practical criteria to annotate free - speech corpora from children utterances . at the theoretical level , the main claim of this paper is that syntactic networks should be interpreted as the outcome of the use of the syntactic machinery . thus , the intrinsic features of such machinery are not accessible directly from ( known ) network properties . rather , what one can see are the global patterns of its use and , thus , a global view of the power and organization of the underlying grammar . taking a look into more practical issues , the paper examines how to build a net from the projection of syntactic relations . recall that , as opposed to adult grammars , early - child language has not a well - defined concept of structure . to overcome such difficulty , we develop a set of systematic criteria assuming constituency hierarchy and a grammar based on lexico - thematic relations . at the end , what we obtain is a well defined corpora annotation that enables us i ) to perform statistics on the size of structures and ii ) to build a network from syntactic relations over which we can perform the standard measures of complexity . we also provide a detailed example .. keywords : syntax , complex networks , learning , computation

we present time - resolved photoluminescence measurements on two series of oligo-_p_-phenylenevinylene materials that self - assemble into supramolecular nanostructures with thermotropic reversibility in dodecane . one set of derivatives form chiral , helical stacks while the second set form less organised , ` frustrated ' stacks . here we study the effects of supramolecular organisation on the resonance energy transfer rates . we measure these rates in nanoassemblies formed with mixed blends of oligomers and compare them with the rates predicted by frster theory . our results and analysis show that control of supramolecular order in the nanometre lengthscale has a dominant effect on the efficiency and dimensionality of resonance energy transfer .

high resolution molecular line observations of , , , and were obtained toward the starless globule in order to investigate its kinematics and chemistry . the hco@xmath0 and cs spectra show clear self - reversed and asymmetric profiles across the face of the globule . the sense of the observed asymmetry is indicative of the global presence of expansion motions in the outer layers of the globule . these motions appear to be subsonic and significantly below the escape velocity of the globule . comparison of our observations with near - infrared extinction data indicate that the globule is gravitationally bound . taken together these considerations lead us to suggest that the observed expansion has its origin in an oscillatory motion of the outer layers of the globule which itself is likely in a quasi - stable state near hydrostatic equilibrium . analysis of the observed linewidths of c@xmath1o and confirm that thermal pressure is the dominant component of the cloud s internal support . a simple calculation suggests that the dominant mode of pulsation would be an l = 2 mode with a period of @xmath2 @xmath3 yrs . deformation of the globule due to the large amplitude l = 2 oscillation may be responsible for the double - peaked structure of the core detected in high resolution extinction maps . detailed comparison of the molecular - line observations and extinction data provides evidence for significant depletion of c@xmath1o and perhaps hco@xmath0 while may be undepleted to a cloud depth of @xmath2 40 magnitudes of visual extinction .

we present here a review of the fundamental topics of hartree - fock theory in quantum chemistry . from the molecular hamiltonian , using and discussing the born - oppenheimer approximation , we arrive to the hartree and hartree - fock equations for the electronic problem . special emphasis is placed in the most relevant mathematical aspects of the theoretical derivation of the final equations , as well as in the results regarding the existence and uniqueness of their solutions . all hartree - fock versions with different spin restrictions are systematically extracted from the general case , thus providing a unifying framework . then , the discretization of the one - electron orbitals space is reviewed and the roothaan - hall formalism introduced . this leads to a exposition of the basic underlying concepts related to the construction and selection of gaussian basis sets , focusing in algorithmic efficiency issues . finally , we close the review with a section in which the most relevant modern developments ( specially those related to the design of linear - scaling methods ) are commented and linked to the issues discussed . the whole work is intentionally introductory and rather self - contained , so that it may be useful for non experts that aim to use quantum chemical methods in interdisciplinary applications . moreover , much material that is found scattered in the literature has been put together here to facilitate comprehension and to serve as a handy reference . quantum chemistry ; introduction ; hartree - fock ; basis sets ; scf * table of contents * to

we present a scaling law that predicts the values of the stresses obtained in numerical simulations of saturated mri - driven turbulence in non - stratified shearing boxes . it relates the turbulent stresses to the strength of the vertical magnetic field , the sound speed , the vertical size of the box , and the numerical resolution and predicts accurately the results of 35 numerical simulations performed for a wide variety of physical conditions . we use our result to show that the saturated stresses in simulations with zero net magnetic flux depend linearly on the numerical resolution and would become negligible if the resolution were set equal to the natural dissipation scale in astrophysical disks . we conclude that , in order for mri - driven turbulent angular momentum transport to be able to account for the large value of the effective alpha viscosity inferred observationally , the disk must be threaded by a significant vertical magnetic field and the turbulent magnetic energy must be in near equipartition with the thermal energy . this result has important implications for the spectra of accretion disks and their stability .

in this paper , we propose a quantum field theoretical renormalization group approach to the vortex dynamics of magnetically coupled layered superconductors , to supplement our earlier investigations on the josephson - coupled case . we construct a two - dimensional multi - layer sine - gordon type model which we map onto a gas of topological excitations . with a special choice of the mass matrix for our field theoretical model , vortex dominated properties of magnetically coupled layered superconductors can be described . the well known interaction potentials of fractional flux vortices are consistently obtained from our field - theoretical analysis , and the physical parameters ( vortex fugacity and temperature parameter ) are also identified . we analyse the phase structure of the multi - layer sine gordon model by a differential renormalization group method for the magnetically coupled case from first principles . the dependence of the transition temperature on the number of layers is found to be in agreement with known results based on other methods .

in this paper the benefits provided by multi - cell processing of signals transmitted by mobile terminals which are received via dedicated relay terminals ( rts ) are assessed . unlike previous works , each rt is assumed here to be capable of full - duplex operation and receives the transmission of adjacent relay terminals . focusing on intra - cell tdma and non - fading channels , a simplified uplink cellular model introduced by wyner is considered . this framework facilitates analytical derivation of the per - cell sum - rate of multi - cell and conventional single - cell receivers . in particular , the analysis is based on the observation that the signal received at the base stations can be interpreted as the outcome of a two - dimensional linear time invariant system . numerical results are provided as well in order to provide further insight into the performance benefits of multi - cell processing with relaying .

following an old idea of fritz zwicky , we make an attempt to establish a `` universal '' mass function for astronomical objects on all scales . the object classes considered are : solar system planets and small bodies , exoplanets , brown dwarfs , stars and stellar remnants , open and globular clusters , molecular clouds , galaxies , groups and clusters of galaxies . for comparison we also include cdm halos taken from numerical simulations . we show that the mass functions of individual object classes , when properly normalized , can indeed be concatenated to build a surprisingly continuous mass function of the universe , from @xmath0 ( sub - kilometer size asteroids ) up to @xmath1 ( rich clusters of galaxies ) , covering 36 orders of magnitude in mass . most individual mass functions roughly follow a power law of the form @xmath2 . a notable exception are planets and small bodies which seem to obey a flatter distribution . cdm halos from high - resolution numerical simulations show a very similar relation , again of `` universal slope '' @xmath3 , from clusters of galaxies all the way down to the planetary mass scale . on the scale of stars and star clusters this is a remarkable coincidence , as the formation processes involved are thought to be totally different ( bottom - up gravitational clustering of dm halos versus top - down gravoturbulent fragmentation of gas clouds ) .

with the great success in simulating many intelligent behaviors using computing devices , there has been an ongoing debate whether all conscious activities are computational processes . in this paper , the answer to this question is shown to be no . a certain phenomenon of consciousness is demonstrated to be fully represented as a computational process using a quantum computer . based on the computability criterion discussed with turing machines , the model constructed is shown to necessarily involve a non - computable element . the concept that this is solely a quantum effect and does not work for a classical case is also discussed .

this contribution briefly reviews the reverberation mapping technique which leads to determination of black hole masses . i focus on the emerging relation between the broad - line region size and the active galactic nucleus ( agn ) luminosity , and on an overview of recent results of reverberation mapping studies which are starting to cover the full agn luminosity range . preliminary results and time lag determination from a reverberation mapping program of high - luminosity quasars are also presented .

we derive the exact solution for the optical conductivity @xmath0 of one hole in the holstein-@xmath1-@xmath2 model in the framework of dynamical mean - field theory ( dmft ) . we investigate the magnetic and phonon features associated with polaron formation as a function of the exchange coupling @xmath2 , of the electron - phonon interaction @xmath3 and of the temperature . our solution directly relates the features of the optical conductivity to the excitations in the single - particle spectral function , revealing two distinct mechanisms of closing and filling of the optical pseudogap that take place upon varying the microscopic parameters . we show that the optical absorption at the polaron crossover is characterized by a coexistence of a magnon peak at low frequency and a broad polaronic band at higher frequency . an analytical expression for @xmath0 valid in the polaronic regime is presented .

we investigate the effects of risk perception in a simple model of epidemic spreading . we assume that the perception of the risk of being infected depends on the fraction of neighbors that are ill . the effect of this factor is to decrease the infectivity , that therefore becomes a dynamical component of the model . we study the problem in the mean - field approximation and by numerical simulations for regular , random and scale - free networks . we show that for homogeneous and random networks , there is always a value of perception that stops the epidemics . in the `` worst - case '' scenario of a scale - free network with diverging input connectivity , a linear perception can not stop the epidemics ; however we show that a non - linear increase of the perception risk may lead to the extinction of the disease . this transition is discontinuous , and is not predicted by the mean - field analysis .

new radio observations of the counterpart of the ultraluminous x - ray source in ngc 5408 show for the first time that the radio emission is resolved with an angular size of @xmath0 to @xmath1 . this corresponds to a physical size of 3546 pc , and rules out interpretation of the radio emission as beamed emission from a relativistic jet . in addition , the radio spectral index of the counterpart is well determined from three frequencies and found to be @xmath2=@xmath30.8 @xmath40.2 . the radio emission is likely to be optically - thin synchrotron emission from a nebula surrounding the x - ray source . the radio luminosity of the counterpart is @xmath5 and the minimum energy required to power the nebula is @xmath6 . these values are two orders of magnitude larger than in any galactic nebula powered by an accreting compact object .

we report the detection of periodic ( @xmath0 hours ) bursts of extremely bright , 100% circularly polarized , coherent radio emission from the m9 dwarf tvlm 513 - 46546 . simultaneous photometric monitoring observations have established this periodicity to be the rotation period of the dwarf . these bursts , which were not present in previous observations of this target , confirm that ultracool dwarfs can generate persistent levels of broadband , coherent radio emission , associated with the presence of kg magnetic fields in a large - scale , stable configuration . compact sources located at the magnetic polar regions produce highly beamed emission generated by the electron cyclotron maser instability , the same mechanism known to generate planetary coherent radio emission in our solar system . the narrow beams of radiation pass our line of sight as the dwarf rotates , producing the associated periodic bursts . the resulting radio light curves are analogous to the periodic light curves associated with pulsar radio emission highlighting tvlm 513 - 46546 as the prototype of a new class of transient radio source .

we show that hard - scattering factorization is violated in the production of high-@xmath0 hadrons in hadron - hadron collisions , in the case that the hadrons are back - to - back , so that @xmath1 factorization is to be used . the explicit counterexample that we construct is for the single - spin asymmetry with one beam transversely polarized . the sivers function needed here has particular sensitivity to the wilson lines in the parton densities . we use a greatly simplified model theory to make the breakdown of factorization easy to check explicitly . but the counterexample implies that standard arguments for factorization fail not just for the single - spin asymmetry but for the unpolarized cross section for back - to - back hadron production in qcd in hadron - hadron collisions . this is unlike corresponding cases in @xmath2 annihilation , drell - yan , and deeply inelastic scattering . moreover , the result endangers factorization for more general hadroproduction processes .

recent results from the hess gamma ray telescope have shown the presence of both a diffuse , extended , flux of gamma rays above @xmath00.4 tev and discrete sources in and near the galactic centre . here , we put forward a possible explanation in terms of the diffusion of cosmic ray protons from a succession of supernova remnants ( snr ) in the sgra * region of the galaxy plus a contribution from snr in the rest of the galactic centre region , to be called the galactic centre ridge ( gcr ) . protons are favoured over electrons because the @xmath1 magnetic fields in the region will attenuate energetic electrons severely . prominent features are the need for anomalous diffusion of the protons in the whole region and the adoption of low efficiency for snr acceleration in the high density regions . the latter is related by us to the well - known low cosmic ray gradient in the galaxy . a corroborating feature is the close correlation of inferred cosmic ray intensity with the smoothed intensity of 5 ghz radio radiation . we attribute this to the presence of the snr in the gcr . plus .1pt minus .1pt -2.0 cm -1.0 cm 1.0 cm a.d.erlykin @xmath2 , a.w.wolfendale @xmath3 \(1 ) p. n. lebedev physical institute , moscow , russia + ( 2 ) department of physics , university of durham , durham , uk

superluminal motion is a common feature of radio jets in powerful @xmath0-ray emitting active galactic nuclei . conventionally , the variable emission is assumed to originate near the central supermassive black - hole where the jet is launched on parsec scales or smaller . here , we report the discovery of superluminal radio features within a distinct flaring x - ray emitting region in the jet of the nearby radio galaxy m87 with the _ very long baseline array_. this shows that these two phenomenological hallmarks superluminal motion and high - energy variability are associated , and we place this activity much further ( @xmath1120 pc ) from the `` central engine '' in m87 than previously thought in relativistic jet sources . we argue that the recent excess very high - energy tev emission from m87 reported by the h.e.s.s . experiment originates from this variable superluminal structure , thus providing crucial insight into the production region of @xmath0-ray emission in more distant blazars .

synthetic bio - molecular spiders with `` legs '' made of single - stranded segments of dna can move on a surface which is also covered by single - stranded segments of dna complementary to the leg dna . in experimental realizations , when a leg detaches from a segment of the surface for the first time it alters that segment , and legs subsequently bound to these altered segments more weakly . inspired by these experiments we investigate spiders moving along a one - dimensional substrate , whose legs leave newly visited sites at a slower rate than revisited sites . for a random walk ( one - leg spider ) the slowdown does not effect the long time behavior . for a bipedal spider , however , the slowdown generates an effective bias towards unvisited sites , and the spider behaves similarly to the excited walk . surprisingly , the slowing down of the spider at new sites increases the diffusion coefficient and accelerates the growth of the number of visited sites .

i describe a bayesian method to account for measurement errors in linear regression of astronomical data . the method allows for heteroscedastic and possibly correlated measurement errors , and intrinsic scatter in the regression relationship . the method is based on deriving a likelihood function for the measured data , and i focus on the case when the intrinsic distribution of the independent variables can be approximated using a mixture of gaussians . i generalize the method to incorporate multiple independent variables , non - detections , and selection effects ( e.g. , malmquist bias ) . a gibbs sampler is described for simulating random draws from the probability distribution of the parameters , given the observed data . i use simulation to compare the method with other common estimators . the simulations illustrate that the gaussian mixture model outperforms other common estimators and can effectively give constraints on the regression parameters , even when the measurement errors dominate the observed scatter , source detection fraction is low , or the intrinsic distribution of the independent variables is not a mixture of gaussians . i conclude by using this method to fit the x - ray spectral slope as a function of eddington ratio using a sample of 39 @xmath0 radio - quiet quasars . i confirm the correlation seen by other authors between the radio - quiet quasar x - ray spectral slope and the eddington ratio , where the x - ray spectral slope softens as the eddington ratio increases . idl routines are made available for performing the regression .

the behavior of interacting populations typically displays irregular temporal and spatial patterns that are difficult to reconcile with an underlying deterministic dynamics . a classical example is the heterogeneous distribution of plankton communities , which has been observed to be patchy over a wide range of spatial and temporal scales . here , we use plankton communities as prototype systems to present theoretical approaches for the analysis of the combined effects of turbulent advection and stochastic growth in the spatiotemporal dynamics of the population . incorporation of these two factors into mathematical models brings an extra level of realism to the description and leads to better agreement with experimental data than that of previously proposed models based on reaction - diffusion equations .

in the present work , the non - spherical dust grain characteristics of comet hale - bopp are studied using the t - matrix method and the modified power law distribution function . it is found that the observed data fits very well with the power index ( @xmath0 . the best fit values of complex refractive index @xmath1 and the aspect ratio ( e ) at @xmath2 are calculated to be @xmath3 and @xmath4 at @xmath5 and @xmath6 respectively . kerola & larson ( k - l ) analysed the same comet using the t - matrix method and the power law distribution function ( @xmath7 ) , and found that the prolate grains can explain the observed polarization in a more satisfactory manner as compared to the other shapes . but their analysis could not reproduce the negative polarization branch beyond scattering angle @xmath8 . however , the results obtained from the present work successfully generate the expected negative polarization curve beyond @xmath8 and the fitting in this case is much better than k - l s work . so it is concluded from the present study that the use of modified power law distribution function ( with @xmath2 ) can fit the observed data in a better way , as compared to the power law distribution function used by previous authors . [ firstpage ] comets : general dust , extinction scattering polarization

the performance of telescope systems working at microwave or visible / ir wavelengths is typically described in terms of different parameters according to the wavelength range . most commercial ray tracing packages have been specifically designed for use with visible / ir systems and thus , though very flexible and sophisticated , do not provide the appropriate parameters to fully describe microwave antennas , and thus to compare with specifications . in this work we demonstrate that the strehl ratio is equal to the phase efficiency when the apodization factor is taken into account . the phase efficiency is the most critical contribution to the aperture efficiency of an antenna , and the most difficult parameter to optimize during the telescope design . the equivalence between the strehl ratio and the phase efficiency gives the designer / user of the telescope the opportunity to use the faster commercial ray - tracing software to optimize the design . we also discuss the results of several tests performed to check the validity of this relationship that we carried out using a ray - tracing software , zemax and a full physical optics software , grasp9.3 , applied to three different telescope designs that span a factor of @xmath0 in terms of @xmath1 . the maximum measured discrepancy between phase efficiency and strehl ratio varies between @xmath2% and 1.9% up to an offset angle of @xmath3 beams , depending on the optical configuration , but it is always less than 0.5% where the strehl ratio is @xmath4 .

the composite torsional ultrasonic oscillator , a versatile experimental system , can be used to investigate slip of newtonian fluid at a smooth surface . a rigorous analysis of slip - dependent damping for the oscillator is presented . initially , the phenomenon of finite surface slip and the slip length are considered for a half - space of newtonian fluid in contact with a smooth , oscillating solid surface . definitions are revisited and clarified in light of inconsistencies in the literature . we point out that , in general oscillating flows , navier s slip length @xmath0 is a complex number . an intuitive velocity discontinuity parameter of unrestricted phase is used to describe the effect of slip on measurement of viscous shear damping . the analysis is applied to the composite oscillator and preliminary experimental work for a 40 khz oscillator is presented . the non - slip boundary condition ( nsbc ) has been verified for a hydrophobic surface in water to within @xmath1 nm of @xmath2 nm . experiments were carried out at shear rate amplitudes between 230 and 6800 s@xmath3 , corresponding to linear displacement amplitudes between 3.2 and 96 nm . + + + + + + + receipt date : 6 september 2007 + pacs numbers : 83.50.lh , 47.80.-v , 68.08.-p +

we provide a comprehensive , up - to - date analysis of possible new physics contributions to the mass difference @xmath0 in @xmath1-@xmath2 mixing . we consider the most general low energy effective hamiltonian and include leading order qcd running of effective operators . we then explore an extensive list of possible new physics models that can generate these operators , which we organize as including extra fermions , extra gauge bosons , extra scalars , extra space dimensions and extra symmetries . for each model we place restrictions on the allowed parameter space using the recent evidence for observation of @xmath3 meson mixing . in many scenarios , we find strong constraints that surpass those from other search techniques and provide an important test of flavor changing neutral currents in the up - quark sector . we also review the recent babar and belle findings , and describe the current status of the standard model predictions of @xmath1-@xmath2 mixing .

the neutrinos detected from the next galactic core - collapse supernova will contain valuable information on the internal dynamics of the explosion . one mechanism leading to a temporal evolution of the neutrino signal is the variation of the induced neutrino flavor mixing driven by changes in the density profile . with one and two dimensional hydrodynamical simulations we identify the behavior and properties of prominent features of the explosion . using these results we demonstrate the time variation of the neutrino crossing probabilities due to changes in the msw neutrino transformations as the star explodes by using the s - matrix - monte carlo - approach to neutrino propagation . after adopting spectra for the neutrinos emitted from the proto - neutron star we calculate for a galactic supernova the evolution of the positron spectra within a water cerenkov detector and the ratio of charged current to neutral current event rates for a heavy water - sno like - detector and find that these detector signals are feasible probes of a number of explosion features .

we report on the development of a technique for precise radial - velocity measurements of cool stars and brown dwarfs in the near infrared . our technique is analogous to the iodine ( @xmath0 ) absorption cell method that has proven so successful in the optical regime . we rely on telluric ch@xmath1 absorption features to serve as a wavelength reference , relative to which we measure doppler shifts of the co and h@xmath2o features in the spectra of our targets . we apply this technique to high - resolution ( r@xmath350,000 ) spectra near 2.3@xmath4 of nine l dwarfs taken with the phoenix instrument on gemini - south and demonstrate a typical precision of 300 m s@xmath5 . we conduct simulations to estimate our expected precision and show our performance is currently limited by the signal - to - noise of our data . we present estimates of the rotational velocities and systemic velocities of our targets . with our current data , we are sensitive to companions with @xmath6 in orbits with periods less than three days . we identify no companions in our current data set . future observations with improved signal - to - noise should result in radial - velocity precision of 100 m s@xmath5 for l dwarfs .

we describe an expansion of the solution of the wave equation in the de sitter schwarzschild metric in terms of resonances . the main term in the expansion is due to a zero resonance . the error term decays polynomially if we permit a logarithmic derivative loss in the angular directions and exponentially if we permit an @xmath0 derivative loss in the angular directions .

results for the cross sections of the exclusive @xmath0o(e , e@xmath1pn)@xmath2n and @xmath0o(@xmath3,pn)@xmath2n knockout reactions are presented and discussed in different kinematics . in comparison with earlier work , a complete treatment of the center - of - mass ( cm ) effects in the nuclear one - body current is considered in connection with the problem of the lack of orthogonality between initial bound and final scattering states . the effects due to cm and orthogonalization are investigated in combination with different treatments of correlations in the two - nucleon overlap function and for different parametrizations of the two - body currents . the cm effects lead in super - parallel kinematics to a dramatic increase of the @xmath0o(e , e@xmath1pn ) cross section to the @xmath4 excited state ( 3.95 mev ) of @xmath2n . in all the situations considered the results are very sensitive to the treatment of correlations . a crucial role is played by tensor correlations , but also the contribution of long - range correlations is important .

we examine the question of whether the formal expressions of equilibrium statistical mechanics can be applied to time independent non - dissipative systems that are not in true thermodynamic equilibrium and are nonergodic . by assuming the phase space may be divided into time independent , locally ergodic domains , we argue that within such domains the relative probabilities of microstates are given by the standard boltzmann weights . in contrast to previous energy landscape treatments , that have been developed specifically for the glass transition , we do not impose an a priori knowledge of the inter - domain population distribution . assuming that these domains are robust with respect to small changes in thermodynamic state variables we derive a variety of fluctuation formulae for these systems . we verify our theoretical results using molecular dynamics simulations on a model glass forming system . non - equilibrium transient fluctuation relations are derived for the fluctuations resulting from a sudden finite change to the system s temperature or pressure and these are shown to be consistent with the simulation results . the necessary and sufficient conditions for these relations to be valid are that the domains are internally populated by boltzmann statistics and that the domains are robust . the transient fluctuation relations thus provide an independent quantitative justification for the assumptions used in our statistical mechanical treatment of these systems .

we analyze a recently proposed method to create fractional quantum hall ( fqh ) states of atoms confined in optical lattices [ a. srensen _ et al . _ , phys . rev . lett . * 94 * 086803 ( 2005 ) ] . extending the previous work , we investigate conditions under which the fqh effect can be achieved for bosons on a lattice with an effective magnetic field and finite onsite interaction . furthermore , we characterize the ground state in such systems by calculating chern numbers which can provide direct signatures of topological order and explore regimes where the characterization in terms of wavefunction overlap fails . we also discuss various issues which are relevant for the practical realization of such fqh states with ultra cold atoms in an optical lattice , including the presence of the long - range dipole interaction which can improve the energy gap and stabilize the ground state . we also investigate a new detection technique based on bragg spectroscopy to probe these system in an experimental realization .

we present the _ suzaku _ broad band observations of two agns detected by the _ swift_/bat hard x - ray ( @xmath015 kev ) survey that did not have previous x - ray data , swift j0601.98636 and swift j0138.64001 . the _ suzaku _ spectra reveals in both objects a heavily absorbed power law component with a column density of @xmath1 @xmath2 that dominates above 10 kev , and an intense reflection component with a solid angle @xmath3 from a cold , optically thick medium . we find that these agns have an extremely small fraction of scattered light from the nucleus , @xmath4 with respect to the intrinsic power law component . this indicates that they are buried in a very geometrically - thick torus with a small opening angle and/or have unusually small amount of gas responsible for scattering . in the former case , the geometry of swift j0601.98636 should be nearly face - on as inferred from the small absorption for the reflection component . the discovery of two such objects in this small sample implies that there must be a significant number of yet unrecognized , very compton thick agns viewed at larger inclination angles in the local universe , which are difficult to detect even in the currently most sensitive optical or hard x - ray surveys .

we study the single transverse - spin asymmetry for dijet production in hadronic collisions in both the collinear qcd factorization approach and the brodsky - hwang - schmidt model . we show that a nonvanishing asymmetry is generated by both initial - state and final - state interactions , and that the final - state interactions dominate . we find that in the leading kinematic region where the transverse momentum imbalance of the two jets , @xmath0 , is much less than the momentum of either jet , the contribution from the lowest non - trivial perturbative order to both the spin - averaged and the spin - dependent dijet cross sections can be factorized into a hard part that is a function only of the averaged jet momentum @xmath1 , and perturbatively generated transverse momentum dependent ( tmd ) parton distributions . we show that the spin asymmetry at this non - trivial perturbative order can be described by the tmd parton distributions defined in either semi - inclusive dis or the drell - yan process . we derive the same hard parts from both the collinear factorization approach and in the context of the brodsky - hwang - schmidt model , verifying that they are not sensitive to details of the factorized long distance physics .

we compute the coleman weinberg effective potential for the higgs field in rs gauge - higgs unification scenarios based on a bulk @xmath0 gauge symmetry , with gauge and fermion fields propagating in the bulk and a custodial symmetry protecting the generation of large corrections to the @xmath1 parameter and the coupling of the @xmath2 to the bottom quark . we demonstrate that electroweak symmetry breaking may be realized , with proper generation of the top and bottom quark masses for the same region of bulk mass parameters that lead to good agreement with precision electroweak data in the presence of a light higgs . we compute the higgs mass and demonstrate that for the range of parameters for which the higgs boson has standard model - like properties , the higgs mass is naturally in a range that varies between values close to the lep experimental limit and about 160 gev . this mass range may be probed at the tevatron and at the lhc . we analyze the kk spectrum and briefly discuss the phenomenology of the light resonances arising in our model .

in a quantizing magnetic field , the two - dimensional electron ( 2deg ) gas has a rich phase diagram with broken translational symmetry phases such as wigner , bubble , and stripe crystals . in this paper , we derive a method to get the dynamical matrix of these crystals from a calculation of the density response function performed in the generalized random phase approximation ( grpa ) . we discuss the validity of our method by comparing the dynamical matrix calculated from the grpa with that obtained from standard elasticity theory with the elastic coefficients obtained from a calculation of the deformation energy of the crystal .

vibrational energy transfer of the amide i mode of n - methylacetamide ( nma ) is studied theoretically using the vibrational configuration interaction method . a quartic force field of nma is constructed at the b3lyp/6 - 31g+(d ) level of theory and its accuarcy is checked by comparing the resulting anharmonic frequencies with available theoretical and experimental values . quantum dynamics calculations for the amide i mode excitation clarify the dominant energy transfer pathways , which sensitively depend on the anharmonic couplings among vibrational modes . a ratio of the anharmonic coupling to the frequency mismatch is employed to predict and interpret the dominant energy flow pathways . , , , and vibrational configuration interaction ( vci ) method , vibrational energy relaxation ( ver ) , n - methylacetamide ( nma ) , quartic force field ( qff )

models which accelerate the expansion of the universe through the addition of a function of the ricci scalar @xmath0 leave a characteristic signature in the large - scale structure of the universe at the compton wavelength scale of the extra scalar degree of freedom . we search for such a signature in current cosmological data sets : the wmap cosmic microwave background ( cmb ) power spectrum , snls supernovae distance measures , the sdss luminous red galaxy power spectrum , and galaxy - cmb angular correlations . due to theoretical uncertainties in the nonlinear evolution of @xmath0 models , the galaxy power spectrum conservatively yields only weak constraints on the models despite the strong predicted signature in the linear matter power spectrum . currently the tightest constraints involve the modification to the integrated sachs - wolfe effect from growth of gravitational potentials during the acceleration epoch . this effect is manifest for large compton wavelengths in enhanced low multipole power in the cmb and anti - correlation between the cmb and tracers of the potential . they place a bound on the compton wavelength of the field be less than of order the hubble scale .

we briefly recall the physical background of the transport of angular momentum and the mixing of chemicals inside stellar radiation zones and its importance for stellar evolution . then , we describe its present modeling , its successes and its weaknesses . next , we introduce the new theoretical developments that allow us to treat in a self - consistent way the effect of the coriolis force on the low - frequencies internal waves and its consequences for the transport processes . this research is aimed at improving the modeling of stellar interiors in the perspective of future astero and helioseismology missions such as corot and golf - ng .

we study the @xmath0 and @xmath1 signatures @xmath2 for different values of @xmath3 in the msugra model . with @xmath3 rising , we observe a characteristic change in the shape of dilepton mass spectra in @xmath4 versus @xmath5 final states reflecting the decrease of @xmath6 branching ratio . we also study the non msugra modifications of the cms test point lm1 with arbitrary relations among gaugino and higgsino masses . for such modifications of the msugra test point lm1 the number of lepton events depends rather strongly on the relations among gaugino and higgsino masses and in some modifications of the test point lm1 the signatures with leptons and @xmath7 do not lead to the susy discovery and the single susy discovery signature remains the signature with @xmath8 . # 1#2#3#4#1 * # 2 * ( # 4 ) # 3

we report the detection of 21-cm absorption at @xmath0 towards 1622 + 238 ( 3c336 ) . the line is very broad with a full - width half maximum ( fwhm ) of 235 , giving a velocity integrated optical depth of @xmath1 . the centroid of the line is offset from that of the known damped lyman-@xmath2 absorption ( dla ) system by @xmath3 , and _ if _ the lyman-@xmath2 and 21-cm absorption are due to the same gas , we derive a spin temperature of @xmath4 k , which would be the lowest yet in a dla . the wide profile , which is over four times wider than that of any other dla , supports the hypothesis that the hydrogen absorption is occurring either in the disk of a large underluminous spiral or a group of dim unidentified galaxies , associated with the single object which has been optically identified at this redshift . [ firstpage ] quasars : absorption lines cosmology : observations cosmology : early universe galaxies : ism galaxies : individual ( 3c336 )

we derive the proper motions , membership probabilities , and velocity dispersions of stars in the regions of the young ( @xmath0 myr - old ) open clusters ngc 2244 ( the central cluster in the monoceros r2 association ) and ngc 6530 ( the dominant cluster in the sgr ob1 association ) from photographic plate material obtained at shanghai astronomical observatory , with time baselines of 34 and 87 years , respectively . both clusters show clear evidence of mass segregation , but they do not exhibit any significant velocity - mass ( or , equivalently , a velocity - luminosity ) dependence . this provides strong support for the suggestion that the observed mass segregation is at least partially due to the way in which star formation has proceeded in these complex star - forming regions ( `` primordial '' mass segregation ) . based on arguments related to the clusters published initial mass functions , in conjunction with our new measurements of their internal velocity dispersions ( @xmath1 and 8 km s@xmath2 for ngc 2244 and ngc 6530 , respectively ) , we provide strong arguments in favor of the dissolution of ngc 2244 on very short time - scales , while we speculate that ngc 6530 may be more stable against the effects of internal two - body relaxation . however , this latter object may well be destroyed by the strong tidal field prevalent at its location in the galactic plane in the direction of the galactic center .

the possibility of an alternative way to formulate the hawking radiation in a static schwarzschild spacetime has been explored . to calculate the hawking radiation , there can be two possible choices of the spacetime wedge pairs in the krucal - szekeres coordinates . one is the wedge pair consists of exterior spacetime of a black hole and the exterior spacetime of a white hole , and the other is that of exterior and interior spacetimes of one black hole . the radiation from the former is the hawking s original one . though the the latter has been often regarded as the same phenomena as the former , the result here suggests it is not ; its radiation has a temperature twice as high as the hawking temperature . 04.62.+v , 04.70.dy

ferromagnetism in the @xmath0-@xmath1 hubbard model is investigated on a square lattice . correlation effects in the form of self - energy and vertex corrections are systematically incorporated within a spin - rotationally - symmetric scheme which explicitly preserves the goldstone mode and is therefore in accord with the mermin - wagner theorem . interplay of band dispersion and correlation effects on ferromagnetic - state stability are highlighted with respect to both long- and short - wavelength fluctuations , which are shown to have substantially different behaviour . our approach provides a novel understanding of the enhancement of ferromagnetism near van hove filling for @xmath2 in terms of strongly suppressed saddle - point contribution to the destabilizing exchange part of spin stiffness . finite - temperature electron spin dynamics is investigated directly in terms of spectral - weight transfer across the fermi energy due to electron - magnon coupling . relevant in the context of recent magnetization measurements on ultrathin films , the role of strong thermal spin fluctuations in low dimensions is highlighted , in the anisotropy - stabilized ordered state , by determining the thermal decay of magnetization and @xmath3 within a renormalized spin - fluctuation theory .

adaptive populations such as those in financial markets and distributed control can be modeled by the minority game . we consider how their dynamics depends on the agents initial preferences of strategies , when the agents use linear or quadratic payoff functions to evaluate their strategies . we find that the fluctuations of the population making certain decisions ( the volatility ) depends on the diversity of the distribution of the initial preferences of strategies . when the diversity decreases , more agents tend to adapt their strategies together . in systems with linear payoffs , this results in dynamical transitions from vanishing volatility to a non - vanishing one . for low signal dimensions , the dynamical transitions for the different signals do not take place at the same critical diversity . rather , a cascade of dynamical transitions takes place when the diversity is reduced . in contrast , no phase transitions are found in systems with the quadratic payoffs . instead , a basin boundary of attraction separates two groups of samples in the space of the agents decisions . initial states inside this boundary converge to small volatility , while those outside diverge to a large one . furthermore , when the preference distribution becomes more polarized , the dynamics becomes more erratic . all the above results are supported by good agreement between simulations and theory .

we propose a method to perform precision measurements of the interaction parameters in systems of @xmath0 ultra - cold spin @xmath1 atoms . the spectroscopy is realized by first creating a coherent spin superposition of the two relevant internal states of each atom and then letting the atoms evolve under a squeezing hamiltonian . the non - linear nature of the hamiltonian decreases the fundamental limit imposed by the heisenberg uncertainty principle to @xmath2 , a factor of @xmath0 smaller than the fundamental limit achievable with non - interacting atoms . we study the effect of decoherence and show that even with decoherence , entangled states can outperform the signal to noise limit of non - entangled states . we present two possible experimental implementations of the method using bose - einstein spinor condensates and fermionic atoms loaded in optical lattices and discuss their advantages and disadvantages .

building on work of barker , humpherys , lafitte , rudd , and zumbrun in the shock wave case , we study stability of compressive , or `` shock - like '' , boundary layers of the isentropic compressible navier stokes equations with @xmath0-law pressure by a combination of asymptotic ode estimates and numerical evans function computations . our results indicate stability for @xmath1 $ ] for all compressive boundary - layers , independent of amplitude , save for inflow layers in the characteristic limit ( not treated ) . expansive inflow boundary - layers have been shown to be stable for all amplitudes by matsumura and nishihara using energy estimates . besides the parameter of amplitude appearing in the shock case , the boundary - layer case features an additional parameter measuring displacement of the background profile , which greatly complicates the resulting case structure . moreover , inflow boundary layers turn out to have quite delicate stability in both large - displacement and large - amplitude limits , necessitating the additional use of a mod - two stability index studied earlier by serre and zumbrun in order to decide stability .

a model of dense plasmas relying on the superconfiguration approximation is presented . in each superconfiguration the nucleus is totally screened by the electrons in a wigner - seitz sphere ( ion - sphere model ) . superconfigurations of the same charge are grouped into ions . it is shown that boundary values of the wavefunctions play a crucial role in the form of the virial theorem from which the pressure formula is derived . finally , a condition is presented and discussed , which makes the ion - sphere model variational when bound electrons are treated quantum - mechanically and free electrons quasi - classically .

the ground state carrier dynamics in self - assembled ( in , ga)as / gaas quantum dots has been studied using time - resolved photoluminescence _ and _ transmission . by varying the dot design with respect to confinement and doping , the dynamics is shown to follow in general a non - exponential decay . only for specific conditions in regard to optical excitation and carrier population , for example , the decay can be well described by a mono - exponential form . for resonant excitation of the ground state transition a strong shortening of the luminescence decay time is observed as compared to the non - resonant case . the results are consistent with a microscopic theory that accounts for deviations from a simple two - level picture .

we present our new scheme for the classification of radial stellar surface brightness profiles for disk galaxies . we summarize the current theoretical attempts to understand their origin and give an example of an application by comparing local galaxies with their counterparts at high redshift ( @xmath0 ) . +

we propose a scenario in which the dark components of the universe are manifestations of a single bulk viscous fluid . using dynamical system methods , a qualitative study of the homogeneous , isotropic background scenario is performed in order to determine the phase space of all possible solutions . the specific model which we investigate shares similarities with a generalized chaplygin gas in the background but is characterized by non - adiabatic pressure perturbations . this model is tested against supernova type ia and matter power spectrum data . different from other unified descriptions of dark matter and dark energy , the matter power spectrum is well behaved , i.e. , there are no instabilities or oscillations on small perturbation scales . the model is competitive in comparison with the currently most popular proposals for the description of the cosmological dark sector .

angular momentum in protostellar discs can be transported either radially , through turbulence induced by the magnetorotational instability ( mri ) , or vertically , through the torque exerted by a large - scale magnetic field . we present a model of steady - state discs where these two mechanisms operate at the same radius and derive approximate criteria for their occurrence in an ambipolar diffusion dominated disc . we obtain `` weak field '' solutions which we associate with the mri channel modes in a stratified disc and transform them into accretion solutions with predominantly radial angular - momentum transport by implementing a turbulent - stress prescription based on published results of numerical simulations . we also analyze `` intermediate field strength '' solutions in which both radial and vertical transport operate at the same radial location . our results suggest , however , that this overlap is unlikely to occur in real discs .

we examine aspects of primordial star formation in the presence of a molecular hydrogen - dissociating ultraviolet background . we compare a set of amr hydrodynamic cosmological simulations using a single cosmological realization but with a range of ultraviolet background strengths in the lyman - werner band . this allows us to study the effects of lyman - werner radiation on suppressing 2 cooling at low densities as well as the high - density evolution of the collapsing cloud core in a self - consistent cosmological framework . we find that the addition of a photodissociating background results in a delay of the collapse of high density gas at the center of the most massive halo in the simulation and , as a result , an increase in the virial mass of this halo at the onset of baryon collapse . we find that , contrary to previous results , population iii star formation is not suppressed for j@xmath0 , but occurs even with backgrounds as high as j@xmath1 . we find that 2 cooling leads to collapse despite the depressed core molecular hydrogen fractions due to the elevated 2 cooling rates at @xmath2 k. we observe a relationship between the strength of the photodissociating background and the rate of accretion onto the evolving protostellar cloud core , with higher lw background fluxes resulting in higher accretion rates . finally , we find that the collapsing cloud cores in our simulations do not fragment at densities below @xmath3 @xmath4 regardless of the strength of the lw background , suggesting that population iii stars forming in halos with t@xmath5 k may still form in isolation .

in this paper we explore a possibility that all transport turbulent models are contained in a coarse - grained kinetic equation . building on a recent work by h.chen et al ( 2004 ) , we account for fluctuations of a single -point probability density in turbulence , by introducing a``two - level '' ( @xmath0)-phase - space , separating microscopic ( @xmath1 ) and hydrodynamic ( @xmath2 ) modes . unlike traditional kinetic theories , with hydrodynamic approximations derived in terms of small deviations from thermodynamic equilibrium , the theory developed in this work , is based on a far- from -equilibrium isotropic and homogeneous turbulence as an unperturbed state . the expansion in dimensionless rate of strain leads to a new class of turbulent models , including the well - known @xmath3 , reynolds stress and all possible nonlinear models . the role of interaction of the fluxes in physical space with the energy flux across the scales , not present in standard modeling , is demonstrated on example of turbulent channel flow . to close the system , neither equation for turbulent kinetic energy nor information on pressure - velocity correlations , contained in the derived coarse - grained kinetic equation , are needed .

we examine the possibility of distinguishing a supersymmetric gluino from a kaluza - klein gluon of universal extra dimensions ( ued ) at the large hadron collider ( lhc ) . we focus on the case when all kinematically allowed tree - level decays of this particle are 3-body decays into two jets and a massive daughter ( typically weak gaugino or kaluza - klein weak gauge boson ) . we show that the shapes of the dijet invariant mass distributions differ significantly in the two models , as long as the mass of the decaying particle @xmath0 is substantially larger than the mass of the massive daughter @xmath1 . we present a simple analysis estimating the number of events needed to distinguish between the two models under idealized conditions . for example , for @xmath2 , we find the required number of events to be of order several thousand , which should be available at the lhc within a few years . this conclusion is confirmed by a parton level monte carlo study which includes the effects of experimental cuts and the combinatoric background . .5 cm * testing gluino spin with three - body decays * .2 cm * csaba cski , johannes heinonen and maxim perelstein * + _ institute for high energy phenomenology + newman laboratory of elementary particle physics , + cornell university , ithaca , ny 14853 , usa _ + 0.3truecm

distributional sources of matter on codimension - two and higher branes are only well - defined as regularized objects . nevertheless , intuition from effective field theory suggests that the low - energy physics on such branes should be independent of any high - energy regularization scheme . in this paper , we address this issue in the context of a scalar field model where matter fields ( the standard model ) living on such a brane interact with bulk fields ( gravity ) . the low - energy effective theory is shown to be consistent and independent of the regularization scheme , provided the brane couplings are renormalized appropriately at the classical level . we perform explicit computations of the classical renormalization group flows at tree and one - loop level , demonstrate that the theory is renormalizable against codimension - two divergences , and extend the analysis to several physical applications such as electrodynamics and brane localized kinetic terms .

the total entropy production generated by the dynamics of an externally driven systems exchanging energy and matter with multiple reservoirs and described by a master equation is expressed as the sum of three contributions , each corresponding to a distinct mechanism for bringing the system out of equilibrium : nonequilibrium initial conditions , external driving , and breaking of detailed balance . we derive three integral fluctuation theorems ( fts ) for these contributions and show that they lead to the following universal inequality : an arbitrary nonequilibrium transformation always produces a change in the total entropy production greater or equal than the one produced if the transformation is done very slowly ( adiabatically ) . previously derived fluctuation theorems can be recovered as special cases . we show how these fts can be experimentally tested by performing the counting statistics of the electrons crossing a single level quantum dot coupled to two reservoirs with externally varying chemical potentials . the entropy probability distributions are simulated for driving protocols ranging from the adiabatic to the sudden switching limit .

i utilize the petrov - galerkin formulation and develop a new method for solving the unsteady collisionless boltzmann equation in both the linear and nonlinear regimes . in the first order approximation , the method reduces to a linear eigenvalue problem which is solved using standard numerical methods . i apply the method to the dynamics of a model stellar disk which is embedded in the field of a soft - centered logarithmic potential . the outcome is the full spectrum of eigenfrequencies and their conjugate normal modes for prescribed azimuthal wavenumbers . the results show that the fundamental bar mode is isolated in the frequency space while spiral modes belong to discrete families that bifurcate from the continuous family of van kampen modes . the population of spiral modes in the bifurcating family increases by cooling the disk and declines by increasing the fraction of dark to luminous matter . it is shown that the variety of unstable modes is controlled by the shape of the dark matter density profile .

a comodule algebra @xmath0 over a hopf algebra @xmath1 with bijective antipode is called principal if the coaction of @xmath1 is galois and @xmath0 is @xmath1-equivariantly projective ( faithfully flat ) over the coaction - invariant subalgebra @xmath2 . we prove that principality is a piecewise property : given @xmath3 comodule - algebra surjections @xmath4 whose kernels intersect to zero , @xmath0 is principal if and only if all @xmath5 s are principal . furthermore , assuming the principality of @xmath0 , we show that the lattice these kernels generate is distributive if and only if so is the lattice obtained by intersection with @xmath2 . finally , assuming the above distributivity property , we obtain a flabby sheaf of principal comodule algebras over a certain space that is universal for all such @xmath3-families of surjections @xmath4 and such that the comodule algebra of global sections is @xmath0 .

there is a strong connection between the formation of a disk galaxy and the properties of the interstellar medium ( ism ) . theoretical work has typically either focused on the cosmological buildup of a galaxy with a relatively crude model for the gas physics , or examined local processes in the ism and ignored the global evolution of the galaxy itself . here , i briefly review what has been learned from both of these approaches , and what can be done to bridge the gap between them . i argue that cosmological simulations need to learn from observational and theoretical work on local ism properties and adopt more sophisticated models for the processes that they can not resolve . since the ism is still incompletely understood , there are a number of reasonable approaches for these subgrid " models , and i will discuss the strengths and limitations of each .

optical photometric and spectroscopic data are presented that show an association of an ultraluminous x - ray source in ngc 7331 with a young star cluster of mass @xmath0 m@xmath1 and age @xmath2 myr . if the ulx is part of the bright stellar cluster , then the mass of the progenitor of the compact accretor must have been @xmath340 - 50 m@xmath1 in order to already have evolved through the supernova stage to a compact object . the companion star is also likely an evolved massive star . the emission line spectrum of the nebula surrounding the cluster can be interpreted as a result of photoionization by the cluster ob stars with an additional source of shock excitation producing strong [ s ii ] , [ o i ] and n ii lines . this additional source appears to be as much as five times more powerful than the supernovae and stellar winds in the cluster can provide . additional mechanical energy input associated with the ulx itself can help explain the residual shock excited line luminosities of the emission region .

we present results from _ chandra _ and _ xmm - newton _ spectroscopic observations of the nuclei of @xmath0 radio galaxies and quasars from the 3crr catalog , and examine in detail the dichotomy in the properties of low- and high - excitation radio galaxies . the x - ray spectra of low - excitation sources ( those with weak or absent optical emission lines ) are dominated by unabsorbed emission from a parsec - scale jet , with no contribution from accretion - related emission . these sources show no evidence for an obscuring torus , and are likely to accrete in a radiatively inefficient manner . high - excitation sources ( those with prominent optical emission lines ) , on the other hand , show a significant contribution from a radiatively efficient accretion disk , which is heavily absorbed in the x - ray when they are oriented close to edge - on with respect to the observer . however , the low - excitation / high - excitation division does not correspond to the fri / frii division : thus the fanaroff - riley dichotomy remains a consequence of the interaction between the jet and the hot - gas environment through which it propagates . finally , we suggest that accretion of the hot phase of the igm is sufficient to power _ all _ low - excitation radio sources , while high - excitation sources require an additional contribution from cold gas that in turn forms the cold disk and torus . this model explains a number of properties of the radio - loud active galaxy population , and has important implications for agn feedback mechanisms .

collisions of antiprotons with he- , ne- , ni - like , bare , and neutral uranium are studied theoretically for scattering angles close to 180@xmath0 and antiproton energies with the interval 100 ev 10 kev . we investigate the coulomb glory effect which is caused by a screening of the coulomb potential of the nucleus and results in a prominent maximum of the differential cross section in the backward direction at some energies of the incident particle . we found that for larger numbers of electrons in the ion the effect becomes more pronounced and shifts to higher energies of the antiproton . on the other hand , a maximum of the differential cross section in the backward direction can also be found in the scattering of antiprotons on a bare uranium nucleus . the latter case can be regarded as a manifestation of the screening property of the vacuum - polarization potential in non - relativistic collisions of heavy particles .

in order to understand the first stages of the nucleation of carbon nanotubes in catalytic processes , we present a tight - binding monte carlo study of the stability and cohesive mechanisms of different carbon structures deposited on nickel ( 100 ) surfaces . depending on the geometry , we obtain contrasted results . on the one hand , the analysis of the local energy distributions of flat carbon sheets , demonstrate that dangling bonds remain unsaturated in spite of the presence of the metallic catalyst . their adhesion results from the energy gain of the surface ni atoms located below the carbon nanostructure . on the other hand , carbon caps are stabilized by the presence of carbon atoms occupying the hollow sites of the fcc nickel structure suggesting the saturation of the dangling bonds .

malin 1 has long been considered a prototype giant , dark matter dominated low surface brightness galaxy . two recent studies , one based on a re - analysis of vla hi observations and the other on an archival hubble i - band image , throw a new light on this enigmatic galaxy and on its dark / luminous matter properties .

we classify 329 late - type giants within 1 parsec of sgr a@xmath0 , using the adaptive optics integral field spectrometer sinfoni on the vlt . these observations represent the deepest spectroscopic data set so far obtained for the galactic center , reaching a 50% completeness threshold at the approximate magnitude of the helium - burning red clump ( @xmath1 mag . ) . combining our spectroscopic results with naco @xmath2 and @xmath3 photometry , we construct an observed hertzsprung - russell diagram , which we quantitatively compare to theoretical distributions of various star formation histories of the inner galaxy , using a @xmath4 analysis . our best - fit model corresponds to continuous star formation over the last 12 gyr with a top - heavy initial mass function ( imf ) . the similarity of this imf to the imf observed for the most recent epoch of star formation is intriguing and perhaps suggests a connection between recent star formation and the stars formed throughout the history of the galactic center .

the photoproduction of quarkonium in coherent hadron - hadron ( @xmath0 ) interactions for lhc energies is an important tool to investigate the qcd dynamics at high energies . in this paper we estimate the integrated cross section and rapidity distribution for @xmath1 and @xmath2 production using the color glass condensate ( cgc ) formalism . we predict large rates , implying that the experimental identification could be feasible at the lhc .

motivated by a proposal of daykin @xcite , we study the wave that propagates along an infinite chain of dominoes and find the limiting speed of the wave in an extreme case . + * keywords * : dominoes , waves , modelling , mechanics + * ams subject classification * : 70b99 , 70f35 , 97a90 + * doi * : 10.1137/s0036144504414505

we analyze the line radiative transfer in protoplanetary disks using several approximate methods and a well - tested accelerated monte carlo code . a low - mass flaring disk model with uniform as well as stratified molecular abundances is adopted . radiative transfer in low and high rotational lines of co , c@xmath0o , hco@xmath1 , dco@xmath1 , hcn , cs , and h@xmath2co is simulated . the corresponding excitation temperatures , synthetic spectra , and channel maps are derived and compared to the results of the monte carlo calculations . a simple scheme that describes the conditions of the line excitation for a chosen molecular transition is elaborated . we find that the simple lte approach can safely be applied for the low molecular transitions only , while it significantly overestimates the intensities of the upper lines . in contrast , the full escape probability ( fep ) approximation can safely be used for the upper transitions ( @xmath3 ) but it is not appropriate for the lowest transitions because of the maser effect . in general , the molecular lines in protoplanetary disks are partly subthermally excited and require more sophisticated approximate line radiative transfer methods . we analyze a number of approximate methods , namely , lvg , vep ( vertical escape probability ) and vor ( vertical one ray ) and discuss their algorithms in detail . in addition , two modifications to the canonical monte carlo algorithm that allow a significant speed up of the line radiative transfer modeling in rotating configurations by a factor of 1050 are described .

_ xmm - newton _ and _ chandra _ observations of the transient 7.8 s pulsar are used to characterize its pulse shape and spectrum , and to facilitate a search for an optical or infrared counterpart . in outburst , the absorbed , hard x - ray spectrum with @xmath0 and @xmath1 @xmath2 is typical of x - ray binary pulsars . the precise _ chandra_localization in a faint state leads to the identification of a probable infrared counterpart at r.a . = @xmath3 , decl . = @xmath4 ( j2000.0 ) with magnitudes @xmath5 , @xmath6 , @xmath7 , and @xmath8 . if this is a highly reddened o or b star , we estimate a distance of 10 kpc , at which the maximum observed x - ray luminosity is @xmath9 ergs s@xmath10 , typical of be x - ray transients or wind - fed systems . the minimum observed luminosity is @xmath11 ergs s@xmath10 . we can not rule out the possibility that the companion is a red giant . the two known x - ray outbursts of are separated by @xmath12 yr , which may be the orbital period or a multiple of it , with the neutron star in an eccentric orbit . we also studied a late m - giant long - period variable that we found only @xmath13 from the x - ray position . it has a pulsation period of @xmath14 yr , but is not the companion of the x - ray source .

the impact of hst photometry and european astronomy in studies concerning the star formation histories of resolved galaxies is described . our current knowledge of the star formation history of systems within 10 - 20 mpc , as derived from the colour - magnitude diagrams of their resolved stellar populations , is reviewed , as well as the impact of these results on our understanding of galaxy evolution .

in this article we develop quantum algorithms for learning and testing _ juntas _ , i.e. boolean functions which depend only on an unknown set of @xmath0 out of @xmath1 input variables . our aim is to develop efficient algorithms : whose sample complexity has no dependence on @xmath1 , the dimension of the domain the boolean functions are defined over ; with no access to any classical or quantum membership ( `` black - box '' ) queries . instead , our algorithms use only classical examples generated uniformly at random and fixed quantum superpositions of such classical examples ; which require only a few quantum examples but possibly many classical random examples ( which are considered quite `` cheap '' relative to quantum examples ) . our quantum algorithms are based on a subroutine @xmath2 which enables sampling according to the fourier spectrum of @xmath3 ; the @xmath2 subroutine was used in earlier work of bshouty and jackson on quantum learning . our results are as follows : we give an algorithm for testing @xmath0-juntas to accuracy @xmath4 that uses @xmath5 quantum examples . this improves on the number of examples used by the best known classical algorithm . we establish the following lower bound : any @xmath2-based @xmath0-junta testing algorithm requires @xmath6 queries . we give an algorithm for learning @xmath0-juntas to accuracy @xmath4 that uses @xmath7 quantum examples and @xmath8 random examples . we show that this learning algorithms is close to optimal by giving a related lower bound .

we study the properties and the molecular content of the host of a type - ia supernova ( sn1997ey ) . this @xmath0 host is the brightest submillimetre source of the sample of type - ia supernova hosts observed at 450@xmath1 m and 850@xmath1 m by @xcite . observations were performed at iram-30 m to search for co(2 - 1 ) and co(3 - 2 ) lines in good weather conditions but no signal was detected . the star formation rate can not exceed 50 @xmath2/yr . these negative results are confronted with an optical analysis of a keck spectrum and other data archives . we reach the conclusion that this galaxy is a late - type system ( 0.7 @xmath3 ) , with a small residual star - formation activity ( 0.2 m@xmath4yr@xmath5 ) detected in the optical . no source of heating ( agn or starburst ) is found to explain the submillimetre - continuum flux and the non - co detection excludes the presence of a large amount of cold gas . we thus suggest that either the star formation activity is hidden in the nucleus ( with @xmath6 ) or this galaxy is passive or anemic and this flux might be associated with a background galaxy . [ firstpage ] supernovae : individual : sn1997ey radio lines : galaxies submillimetre galaxies : general methods : observational

in earlier work , the abstract state machine thesis that arbitrary algorithms are behaviorally equivalent to abstract state machines was established for several classes of algorithms , including ordinary , interactive , small - step algorithms . this was accomplished on the basis of axiomatizations of these classes of algorithms . here we extend the axiomatization and , in a companion paper , the proof , to cover interactive small - step algorithms that are not necessarily ordinary . this means that the algorithms ( 1 ) can complete a step without necessarily waiting for replies to all queries from that step and ( 2 ) can use not only the environment s replies but also the order in which the replies were received .

we discuss fragmentation mechanisms and isospin transport occurring in central collisions between neutron rich systems at fermi energies . in particular , isospin effects are analyzed looking at the correlations between fragment isotopic content and kinematical properties . simulations are based on an approximate solution of the boltzmann - langevin ( bl ) equation . an attempt to solve the complete bl equation , by introducing full fluctuations in phase space is also discussed . multifragmentation , isospin transport , symmetry energy , fluctuations , many - body approaches 25.70.pq , 25.70.-z , 21.30.fe

the loop expansion is applied to a chiral effective hadronic lagrangian ; with the techniques of infrared regularization , it is possible to separate out the short - range contributions and to write them as local products of fields that are already present in our lagrangian . ( the appropriate field variables must be re - defined at each order in loops . ) the corresponding parameters implicitly include short - range effects to all orders in the interaction , so these effects need not be calculated explicitly . the remaining ( long - range ) contributions that must be calculated are nonlocal and resemble those in conventional nuclear - structure calculations . nonlinear isoscalar scalar @xmath0 and vector @xmath1 meson interactions are included , which incorporate many - nucleon forces and nucleon substructure . calculations are carried out at the two - loop level to illustrate these techniques at finite nuclear densities and to verify that the coupling parameters remain natural when fitted to the empirical properties of equilibrium nuclear matter . contributions from the @xmath2 tensor coupling are also discussed .