January 1999 arXiv papers — page 2

Grazyna Siemieniec-Ozieblo, Andrzej Woszczyna

We investigate the Robertson-Walker cosmology with Lagrangian $R+α_1\hbar R^2+α_2\hbar R^{μν}R_{μν} +L_{rad}$ where $L_{rad}$ means classical source with traceless energy-momentum tensor. We weaken the self-consistence condition (L. Parker, J. Z. Simon, Phys. Rev. {D47}(1993),{1339}). Quantum corrections are expressed as contributions to the effective equati

Claudia Winge, David J. Axon, F. D. Macchetto, A. Capetti

We present the results from a detailed kinematic analysis of both ground-based, and Hubble Space Telescope/Faint Object Camera long-slit spectroscopy at sub-arcsec spatial resolution, of the narrow-line region of NGC 4151. In agreement with previous work, the extended emission gas (R > 4") is found to be in normal rotation in the galactic plane, a behavi

F. -X. D'esert, A. Benoit

We describe here the important astrophysical results that could be obtained by using large format (say 32 by 32) bolometric detectors at 1 and 2 mm with the IRAM 30m telescope: having a confusion-limited 1 mm extragalactic survey containing a large fraction of high redshift objects, mapping star formation regions in our galaxy at 1 mm, and mapping the Sunyae

P. Ubertini, A. Bazzano, M. Cocchi, L. Natalucci

The transient X-ray source GS 1826-238 was monitored during five different observing periods between August 1996 and October 1998 with the BeppoSAX Wide Field Camera instrument in the framework of a deep observation of the Galactic Center region. A first detection of X-ray bursts from this source occurred, ruling out its previously suggested black hole candi

I. Vauglin, G. Paturel, J. Borsenberger, P. Fouqué

This paper presents the first I-band photometric catalog of the brightest galaxies extracted from the Deep Near Infrared Survey of the Southern Sky (DENIS) An automatic galaxy recognition program has been developed to build this provisional catalog. The method is based on a discriminating analysis. The most discriminant parameter to separate galaxies from st

David Montes, Lawrence W. Ramsey, Alan D. Welty

We present a library of Penn State Fiber Optic Echelle (FOE) observations of a sample of field stars with spectral types F to M and luminosity classes V to I. The spectral coverage is from 3800 AA to 10000 AA with nominal a resolving power 12000. These spectra include many of the spectral lines most widely used as optical and near-infrared indicators of chro

L. K. Hunt, M. A. Malkan

We have compared the morphological characteristics of the 891 galaxies in the Extended 12-micron Sample (E12GS), and assessed the effect of the 12-micron selection criterion on galaxy properties. The normal spirals in the E12GS have the same axial ratios, morphological types, and bar and ring fractions as other normal spirals. The HII/starburst galaxies have

Tim de Zeeuw, John Norris

This summary discribes the highlights of the Third Stromlo Symposium, on the nature of the stellar, gaseous, and dark components of the Galactic Halo.

Edward A. Baltz, Joseph Silk

It has been shown that a flux--weighted full width at half maximum timescale of a microlensing event can be used in an unbiased estimator of the optical depth. For the first time, this allows a physical parameter to be easily estimated from pixel microlensing data. We derive analytic expressions for the observed rate of pixel lensing events as a function of

Philippe Fischer

Galaxy cluster mass distributions are useful probes of Omega_0 and the nature of the dark matter. Large clusters will distort the observed shapes of background galaxies through gravitational lensing allowing the measurement of the cluster mass distributions. For most cases, the agreement between weak lensing and radial velocity mass measurements of clusters

Jimmy A. Irwin, Joel N. Bregman, August E. Evrard

Previous analyses of ASCA data of clusters of galaxies have found conflicting results regarding the slope of the temperature profile of the hot X-ray gas within clusters, mainly because of the large, energy-dependent point spread function (PSF) of the ASCA mirrors. We present a summary of all ASCA-determined cluster temperature profiles found in the literatu

Pasquale Blasi

Superheavy (SH) quasistable particles generated in the Early Universe could be responsable for Ultra High Energy Cosmic Rays (UHECR) and be a component of Cold Dark Matter (CDM) in the universe. These particles are likely to cluster in the galactic halo, so that the main part of UHECR are gamma rays produced in the decay of neutral pions. Charged pions are a

Miao Li

We discuss the ten dimensional black holes made of D0-branes in the regime where the effective coupling is large, and yet the 11D geometry is unimportant. We suggest that these black holes can be interpreted as excitations over the threshold bound state. Thus, the entropy formula for the former is used to predict a scaling region of the wave function of the

Francisco J. Solis, Monica Olvera de la Cruz

We study the attractive interactions between rod-like charged polymers in solution that appear in the presence of multi-valence counterions. The counterions condensed to the rods exhibit both a strong transversal polarization and a longitudinal crystalline arrangement. At short distances between the rods, the fraction of condensed counterions increases, and

G. Debregeas, C. Josserand

We propose a model to describe the quasistatic shearing of dry granular materials, which notably captures the differences in velocity profiles recently observed in 2 and 3-D Couette flow experiments. In our scheme, the steady-state flow is due to the intermittent motion of particle clusters moving together with the wall. The motion of a cluster is associated

M. B. Voloshin

The dependence of inclusive weak decay rates of heavy hadrons on the flavors of spectator light quarks is revisited with application to decays of charmed and b hyperons. It is pointed out that the differences in the semileptonic decay rates, the differences in the Cabibbo suppressed decay rates of the charmed hyperons, and the splitting of the total decay ra

Richard Shurtleff

The beta-decay of a tritium nucleus produces an entangled quantum system, a beta electron, a helium nucleus, and an antineutrino. For finite collapse times, the post-collapse beta electron energy can originate from a range of pre-collapse energies due to the uncertainty principle. Long collapse times give negligible uncertainty, so the pre-collapse spectrum

Fyodor V. Tkachov

A systematic framework for jet definition is developed from first principles of physical measurement, quantum field theory, and QCD. A jet definition is found which: is theoretically optimal in regard of both minimization of detector errors and inversion of hadronization; is similar to a cone algorithm with dynamically negotiated jet shapes and positions fou

L. Ya. Glozman, K. Varga

It is shown that the instanton-induced interaction in qq pairs, iterated in t-channel, leads to a meson-exchange interactions between quarks. In this way one can achieve a simultaneous understanding of low-lying mesons, baryons and the nuclear force. The discussion is general and does not necessarily rely on the instanton-induced interaction. Any nonperturba

A. Donini, S. Rigolin

We discuss the structure of general Anisotropic Compactification in Type I D=4, N=1 string theory. It is emphasized that, in this context, a possible interpretation of M_{Planck} as ``dual'' to (at least) one of the Kaluza-Klein or Windings Modes could provide interesting interpretations of the ``physical scales'' and the GUT coupling. Some o

Takahiro Tanaka

The so-called negative mode problem in the path integral approach to the false vacuum decay with the effect of gravity has been an unsolved problem. Several years ago, we proposed a conjecture which is to be proved in order to give a consistent solution to the negative mode problem. We called it the ``no-negative mode conjecture''. In the present pap

Mauro Anselmino, Maria Boglione, Francesco Murgia

A phenomenological description of single transverse spin effects in hadron-hadron inclusive processes is proposed, assuming a generalized factorization scheme and pQCD hard interactions. The transverse momentum, k_T, of the quarks inside the hadrons and of the hadrons relatively to the fragmenting quark, is taken into account in distribution and fragmentatio

John Scalo, David Chappell

The relation between the star formation rate and the kinetic energy increase in a region containing a large number of stellar sources is investigated as a possible prescription for star formation feedback in larger scale galaxy evolution simulations, and in connection with observed scaling relations for molecular clouds, extragalactic giant H II regions, and

Yu Shi

We present a so-called adaptive Ising model (AIM) to provide a unifying explanation for sensitivity and perfect adaptation in bacterial chemotactic signalling, based on coupling among receptor dimers. In an AIM, an external field, representing ligand binding, is randomly applied to a fraction of spins, representing the states of the receptor dimers, and ther

Vladimir V. Tchernov

Recently Arnold's $\St$ and $J^{\pm}$ invariants of generic planar curves have been generalized to the case of generic planar wave fronts. We generalize these invariants to the case of wave fronts on an arbitrary surface $F$. All invariants satisfying the axioms which naturally generalize the axioms used by Arnold are explicitly described. We also give a

Weinan E, Eric Vanden Eijnden

The power law range for the velocity gradient probability density function in forced Burgers turbulence has been an issue of discussion recently. It is shown in [chao-dyn/9901006] that the negative exponent in the assumed power law range has to be strictly larger than 3. Here we give another direct argument for that result, working with finite viscosity. At

Matthias Vojta, Klaus W. Becker

The two-layer square lattice quantum antiferromagnet with spins 1/2 shows a magnetic order-disorder transition at a critical ratio of the interplane to intraplane couplings. We investigate the dynamics of a single hole in a bilayer antiferromagnet described by a t-J Hamiltonian. To model the spin background we propose a ground-state wave function for the und

Y. -B. Zhang, Y. -H. Nie, S. -P. Kou, J. -Q. Liang

The quantum-classical transitions of the escape rates in a uniaxial spin model relevant to the molecular magnet Mn$_{12}$Ac and a biaxial anisotropic ferromagnetic particle are investigated by applying the periodic instanton method. The effective free energies are expanded around the top of the potential barrier in analogy to Landau theory of phase transitio

D. Samsoen, P. Quentin, I. N. Mikhailov

It has been previously proposed to explain gamma-ray staggerings in the deexcitation of some superdeformed bands in the $^{150}$Gd region in terms of a coupling between global rotation and intrinsic vortical modes. The observed 4$\hbar$ period for the phenomenon is suggested from our microscopic Routhian calculations using the Skyrme SkM* effective interacti

P. Desgrolard, L. Jenkovszky, B. Struminsky

By using realistic models for elastic hadron scattering we demonstrate that at present accelerator energies the $s$-channel unitarity bound is safe, not to be reached until $10^5$ GeV, while the black disc limit is saturated around 1 TeV. It will be followed by a larger transparency of the scattered particles near the center.

S. Hosono, M. -H. Saito, A. Takahashi

We consider the generating function (prepotential) for Gromov-Witten invariants of rational elliptic surface. We apply the local mirror principle to calculate the prepotential and prove a certain recursion relation, holomorphic anomaly equation, for genus 0 and 1. We propose the holomorphic anomaly equation for all genera and apply it to determine higher gen

Xuelei Chen, Marc Kamionkowski

Three-body final states are included in the calculation of cross section and neutrino production in neutralino annihilations. In some regions of the parameter space, three-body channels maybe important and can enhance the neutrino flux by a few times.

M. J. Duff, James T. Liu

We present new anti-de Sitter black hole solutions of gauged N=8, SO(8) supergravity, which is the massless sector of the AdS_4\times S^7 vacuum of M-theory. By focusing on the U(1)^4 Cartan subgroup, we find non-extremal 1, 2, 3 and 4 charge solutions. In the extremal limit, they may preserve up to 1/2, 1/4, 1/8 and 1/8 of the supersymmetry, respectively. I

Maximo Banados

We review some aspects of three-dimensional quantum gravity with emphasis in the `CFT -> Geometry' map that follows from the Brown-Henneaux conformal algebra. The general solution to the classical equations of motion with anti-de Sitter boundary conditions is displayed. This solution is parametrized by two functions which become Virasoro operators after quan

Bernd Burghardt, Joachim Stolze

We study the application of the coherent-state path integral as a numerical tool for wave-packet propagation. The numerical evaluation of path integrals is reduced to a matrix-vector multiplication scheme. Together with a split-operator technique we apply our method to a time-dependent double-well potential.

M. Patra, C. W. J. Beenakker

A general theory is presented for the photodetection statistics of coherent radiation that has been amplified by a disordered medium. The beating of the coherent radiation with the spontaneous emission increases the noise above the shot-noise level. The excess noise is expressed in terms of the transmission and reflection matrices of the medium, and evaluate

Jan-Åke Larsson

A local-variable model yielding the statistics from the singlet state is presented for the case of inefficient detectors and/or lowered visibility. It has independent errors and the highest efficiency at perfect visibility is 77.80%, while the highest visibility at perfect detector-efficiency is 63.66%. Thus, the model cannot be refuted by measurements made

D. Cai, C. M. Snell, K. M. Beardmore, N. Gronbech-Jensen

We simulate dopant profiles for phosphorus implantation into silicon using a new model for electronic stopping power. In this model, the electronic stopping power is factorized into a globally averaged effective charge Z1*, and a local charge density dependent electronic stopping power for a proton. There is only a single adjustable parameter in the model, n

David Cai, Niels Gronbech-Jensen, Charles M. Snell, Keith M. Beardmore

It is crucial to have a good phenomenological model of electronic stopping power for modeling the physics of ion implantation into crystalline silicon. In the spirit of the Brandt-Kitagawa effective charge theory, we develop a model for electronic stopping power for an ion, which can be factorized into (i) a globally averaged effective charge taking into acc

C. Josserand, Y. Pomeau, S. Rica

The present article represents part of the PhD. dissertation by C. Josserand. We discuss the nucleation of quantized vortices in the nonlinear Schrödinger equation (NLS) for a flow around a disk in two spatial dimensions. It appears that the vortices are nucleated when the flow becomes locally (at the edge of the disk) supersonic. A detailed study of the pha

Keith M. Beardmore, Niels Gronbech-Jensen

We present a highly efficient molecular dynamics scheme for calculating the concentration depth profile of dopants in ion irradiated materials. The scheme incorporates several methods for reducing the computational overhead, plus a rare event algorithm that allows statistically reliable results to be obtained over a range of several orders of magnitude in th

Yu Shi, Thomas Duke

Bacterial chemotaxis is controlled by the signalling of a cluster of receptors. A cooperative model is presented, in which coupling between neighbouring receptor dimers enhances the sensitivity with which stimuli can be detected, without diminishing the range of chemoeffector concentration over which chemotaxis can operate. Individual receptor dimers have tw

K. Tsushima

Using the quark-meson coupling (QMC) model, we investigate whether $ω, η, η'$ and $D^-$ mesons form meson-nucleus bound states. Our results suggest that one should expect to find $η$- and $ω$-nucleus bound states in all the nuclei considered. Furthermore, it is shown that the $D^-$ meson will form quite narrow bound states with $^{208}$Pb.

Urs Achim Wiedemann, Ulrich Heinz

In this report we give a detailed account on Hanbury Brown/Twiss (HBT) particle interferometric methods for relativistic heavy-ion collisions. These exploit identical two-particle correlations to gain access to the space-time geometry and dynamics of the final freeze-out stage. The connection between the measured correlations in momentum space and the phase-

Peter Schneider, Jeremy Teitelbaum

We study in detail certain natural continuous representations of G = GL(n,K) in locally convex vector spaces over a locally compact, non-archimedean field K of characteristic zero. We construct boundary value maps, or integral transforms, between subquotients of the dual of a ``holomorphic'' representation coming from a p-adic symmetric space, and ``

Pierre Leroux, Etienne Rassart

Parallelogram polyominoes are a subclass of convex polyominoes in the square lattice that has been studied extensively in the literature. Recently congruence classes of convex polyominoes with respect to rotations and reflections have been enumerated by counting orbits under the action of the dihedral group D4, of symmetries of the square, on (translation-ty

Thomas A. Ivey, David A. Singer

The energy minimization problem associated to uniform, isotropic, linearly elastic rods leads to a geometric variational problem for the rod centerline, whose solutions include closed, knotted curves. We give a complete description of the space of closed and quasiperiodic solutions. The quasiperiodic curves are parametrized by a two-dimensional disc. The clo

Daniel S. Sage

Let $G$ be a group, $F$ a field, and $A$ a finite-dimensional central simple algebra over $F$ on which $G$ acts by $F$-algebra automorphisms. We study the ideals and subalgebras of $A$ which are preserved by the group action. Let $V$ be the unique simple module of $A$. We show that $V$ is a projective representation of $G$ and $A\cong\text{End}_D(V)$ makes $

Miklos Bona, Michel Bousquet, Gilbert Labelle, Pierre Leroux

The purpose of this paper is to enumerate various classes of cyclically colored m-gonal plane cacti, called m-ary cacti. This combinatorial problem is motivated by the topological classification of complex polynomials having at most m critical values, studied by Zvonkin and others. We obtain explicit formulae for both labelled and unlabelled m-ary cacti, acc

G. F. Chew

Massless elementary-particle propagation is represented historically (cosmologically) through 3-scale ``towers of quartet rings'' within a lattice of magneto-electrodynamically communicating ``pre-events''. The lightlike intervals within a ring of 4 pre-events (discrete ``closed string'') display transverse GUT-scale and longitudinal

J. F. Donoghue, T. Torma

The quantum effective theory of general relativity, independent of the eventual full theory at high energy, expresses graviton-graviton scattering at one loop order O(E^4) with only one parameter, Newton's constant. Dunbar and Norridge have calculated the one loop amplitude using string based techniques. We complete the calculation by showing that the 1/

J. M. Aroca, Yu. Kubyshin

The vacuum expectation value of the Wilson loop functional in pure Yang-Mills theory on an arbitrary two-dimensional orientable manifold is studied. We consider the calculation of this quantity for the abelian theory in the continuum case and for the arbitrary gauge group and arbitrary lattice action in the lattice case. A classification of topological secto

Arjan Keurentjes

We propose a construction of non-trivial vacua for Yang-Mills theories on the 3-torus. Although we consider theories with periodic boundary conditions, twisted boundary conditions play an essential auxiliary role in our construction. In this article we will limit ourselves to the simplest case, based on twist in SU(2) subgroups. These reproduce the recently

P. Bozhilov

We consider a model for tensionless (null) p-branes with N=1 global supersymmetry in 10-dimensional Minkowski space-time. We give an action for the model and show that it is reparametrization and kappa-invariant. We also find some solutions of the classical equations of motion. In the case of null superstring (p=1), we obtain the general solution in arbitrar

Seungjoon Hyun, Youngjai Kiem, Hyeonjoon Shin

The classical probe dynamics of the eleven-dimensional massless superparticles in the background geometry produced by N source M-momenta is investigated in the framework of N-sector DLCQ supergravity. We expand the probe action up to the two fermion terms and find that the fermionic contributions are the spin-orbit couplings, which precisely agree with the m

Jifeng Yang

A new attempt is demonstrated that QFTs can be UV finite if they are viewed as the low energy effective theories of a fundamental underlying theory (that is complete and well-defined in all respects) according to the modern standard point of view. This approach works for any interaction model and space-time dimension. It is much simpler in principle and in t

G. A. Kozlov

The phenomenological model of an extra U(1) neutral gauge Z' boson coupled to heavy quarks is presented. In particular, we discuss the probability for a light $Z_{2}$ mass eigenstate decay into a bound state composed of heavy quarks via Higgs boson emission.

J Bordes, HM Chan, ST Tsou

We show that assuming fermion generations to be given by a gauge symmetry plus a certain Higgs mechanism for its breaking, the known empirical features of quark and lepton mixing can be largely explained, including in particular the fact that the mixing (CKM) matrix element $U_{\mu3}$ responsible for the muon anomaly in atmospheric neutrinos is near maximal

Stefano Moretti

At future electron-positron colliders, one of the largest irreducible backgrounds to top searches in the channel `4 jets + lepton + missing energy' comes from QCD events of order $α_s^2$. We compute here such processes exactly at the parton level by resorting to 2 -> 6 matrix elements exploiting helicity amplitude techniques. We adopt a typical selection

Yoonbai Kim, Seung Joo Lee, Kei-ichi Maeda, Nobuyuki Sakai

The decay of a metastable false vacuum by bubble nucleation is studied in the high temperature limit of the gauge theory in which an SO(3) gauge symmetry is spontaneously broken to an SO(2). The effects of internal symmetry are so drastic that, in addition to the known Euclidean bounce solution, there exists a new bubble solution involving a 't Hooft-Pol

Richard Easther, Matthew Parry

We discuss the interaction between perturbations in the inflaton and the background during the preheating phase in simple inflationary models. By numerically solving the Einstein field equations we are able to assess the impact of non-linear gravitational effects on preheating, and to assess the accuracy of perturbative discussions of the preheating epoch.

A. L. S. Angelis, J. Bartke, M. Yu. Bogolyubsky, S. N. Filippov

The physics motivation for a very forward detector for the ALICE heavy ion experiment at the CERN LHC is discussed. A phenomenological model describing the formation and decay of a Centauro fireball in nucleus-nucleus collisions is presented. The CASTOR detector which is aimed to measure the hadronic and photonic content of an interaction and to identify dee

SELEX collaboration, V. Kubarovsky

We present data on coherent production of the pi-pi-pi+ system by 600 GeV pion beam for the C, Cu and Pb targets. The Primakoff formalism was used for extracting the radiatve width of the a2 meson. We obtain a preliminary value Γ(a2->pi+gamma)=225+/-25(stat)+/-45(syst) keV.

Jolien D. E. Creighton

Of all the astronomical sources of gravitational radiation, the ringdown waveform arising from a small perturbation of a spinning black hole is perhaps the best understood: for the late stages of such a perturbation, the waveform is simply an exponentially-damped sinusoid. Searching interferometric gravitational wave antenna data for these should be relative

A. V. Toporensky

Friedmann-Robertson-Walker cosmological models with a massive scalar field are studied in the presence of hydrodynamical matter in the form of a perfect fluid. The ratio of the number of solutions without inflation to the total number of solutions is evaluated, depending on the fluid density. It is shown that in a closed model this ratio can reach 60%, by co

Naresh Dadhich, A. K. Raychaudhuri

A particular choice of the time function in the recently presented spherical solution by Dadhich [1] leads to a singularity free cosmological model which oscillates between two regular states. The energy-stress tensor involves anisotropic pressure and a heat flux term but is consistent with the usual energy conditions (strong, weak and dominant). By choosing

Sukratu Barve, T. P. Singh, Louis Witten

We derive an equation for the acceleration of a fluid element in the spherical gravitational collapse of a bounded compact object made up of an imperfect fluid. We show that non-singular as well as singular solutions arise in the collapse of a fluid initially at rest and having only a tangential pressure. We obtain an exact solution of Einstein equations, in

Victor Marek, Jan Treur, Miroslaw Truszczynski

Default logic can be regarded as a mechanism to represent families of belief sets of a reasoning agent. As such, it is inherently second-order. In this paper, we study the problem of representability of a family of theories as the set of extensions of a default theory. We give a complete solution to the representability by means of normal default theories. W

Keith M. Beardmore, Niels Gronbech-Jensen

We present a highly efficient molecular dynamics scheme for calculating the concentration profile of dopants implanted in group-IV alloy, and III-V zinc blende structure materials. Our program incorporates methods for reducing computational overhead, plus a rare event algorithm to give statistical accuracy over several orders of magnitude change in the dopan

R. M. C. de Almeida, S. Goncalves, I. J. R. Baumvol, F. C. Stedile

The thermal growth of silicon oxide films on Si in dry O2 is modelled as a dynamical system, assuming that it is basically a diffusion-reaction phenomenon. Relevant findings of the last decade are incorporated, as structure and composition of the oxide/Si interface and O2 transport and reaction at initial stages of growth. The present model departs from the

C. -R. Hu, X. -Z. Yan

It has been noted previously that the sizable areal density of midgap states which must exist on any non-{n0m} surface of a d-wave superconductor can lead to a giant magnetic moment. Here we show that this effect is observable, and discuss two precise ways to observe it: (i) by directly measuring magnetic moment in a system with a large density of internal {

Luca Bonci, Richard Berkovits

The addition spectrum of a disordered stadium is studied for up to 120 electrons using the self consistent Hartree-Fock approximation for different values of the dimensionless conductance and in the presence and absence of a neutralizing background. In all cases a Gaussian distribution of the addition spectrum is reached for $r_s \leq 1$. An empirical scalin

P. Fertey, M. Poirier, P. Batail

We report a microwave study of the longitudinal and transverse transport properties of the quasi-one-dimensional organic conductor (TMTSF)$_2$PF$_6$ in its normal phase. The contactless technique have provided a direct measurement of the temperature profile of the resistivity along the {\bf b'} direction and in magnetic fields up to 14 T. A characteristi

S. Das Sarma, P. Punyindu

A limited mobility nonequilibrium solid-on-solid dynamical model for kinetic surface growth is introduced as a simple description for the morphological evolution of a growing interface under random vapor deposition and surface diffusion bias conditions. Simulations using a local coordination dependent instantaneous relaxation of the deposited atoms produce c

J. P. Dewitz, W. Hübner

The nonlinear magneto-optical Kerr-effect (NOLIMOKE) is determined for freestanding Fe monolayers with several in-plane structures from first principles. Based on the theory of nonlinear magneto-optics by Hübner and Bennemann [Phys. Rev. B, {\bf 40}, 5973 (1989)] we calculate the nonlinear susceptibilities of the monolayers using the ab initio FLAPW-method W

Y. Avishai, Y. Band, D. Brown

Mesoscopic fluctuations of two-port conductance and four-port resistance between Hall plateaus are studied within a realistic model for a two-dimensional electron gas in a perpendicular magnetic field and a smooth disordered potential. The two-port conductance distribution $P(g)$ is concave between $g=0$ and $g=1$ and is nearly flat between $g=0.2$ and $g=0.

Martina Hentschel, Manfred Bobeth, Gerhard Diener, Wolfgang Pompe

The short-time stability of concentration profiles in coherent periodic multilayers consisting of two components with large miscibility gap is investigated by analysing stationary solutions of the Cahn-Hilliard diffusion equation. The limits of the existence and stability of periodic concentration profiles are discussed as a function of the average compositi

Jian-Xin Li, Wei-Guo Yin, Chang-De Gong

The effects of nonmagnetic impurity on the spin excitation spectra in a $d_{x^2-y^2}$-wave superconductor are examined, using the self-consistent $t$-matrix approximation. It is shown that the impurity self-energy acts to shift the position of the resonance peak to low frequencies and broaden the peak. While the impurity vertex correction causes a broad spec

F. J. Jedema, B. J. van Wees, B. H. Hoving, A. T. Filip

We present a description of spin-polarized transport in mesoscopic ferromagnet-superconductor (F/S) systems, where the transport is diffusive, and the interfaces are transparent. It is shown that the spin reversal associated with Andreev reflection generates an excess spin density close to the F/S interface, which leads to a spin contact resistance. Expressi

Jian-Xin Li, W. C. Wu, T. K. Lee

Motivated by recent experimental measurements on the Fermi surface(FS) destruction in underdoped high-$T_{c}$ cuprates, we examine its effect on the transport properties based on the Boltzmann equation approach. The effect is modeled by simply taking the density of states for electrons in the gapped regions to be zero. Within the nearly antiferromagnetic Fer

A. P. Roberts, E. J. Garboczi

We statistically reconstruct a three-dimensional model of a tungsten-silver composite from an experimental two-dimensional image. The effective Young's modulus ($E$) of the model is computed in the temperature range 25-1060^o C using a finite element method. The results are in good agreement with experimental data. As a test case, we have reconstructed t

P. J. Martinez, L. M. Floria, F. Falo, J. J. Mazo

The phenomenon of intrinsic localization in discrete nonlinear extended systems, i.e. the (generic) existence of discrete breathers, is shown to be not restricted to periodic solutions but it also extends to more complex (chaotic) dynamical behaviour. We illustrate this with two different forced and damped systems exhibiting this type of solutions: In an ani

W. T. Vestrand, P. Sreekumar

We present x-ray observations of the nearby BL Lac PKS 2155-304 taken when it was undergoing a GeV/TeV gamma-ray outburst. During the outburst we measured x-ray fluxes in the 2-10 keV band that are the largest ever observed for PKS 2155-304. Comparison of these November 1997 measurements and other x-ray observations made contemporaneously with GeV or TeV gam

Edward B. Jenkins, Todd M. Tripp, Przemyslaw R. Wozniak, Ulysses J. Sofia

Studies of the abundances of deuterium in different astrophysical sites are of fundamental importance to answering the question about how much deuterium was produced during big bang nucleosynthesis and what fraction of it was destroyed later. With this in mind, we used the Interstellar Medium Absorption Profile Spectrograph (IMAPS) on the ORFEUS-SPAS II miss

K. M. Belotsky, Yu. A. Golubkov, M. Yu. Khlopov, R. V. Konoplich

The AMS--Shuttle experiment is shown to be sensitive to test the hypothesis on the existence of antimatter globular cluster in our Galaxy. The hypothesis follows from the analysis of possible tests for the mechanisms of baryosynthesis and uses antimatter domains in the matter dominated Universe as the probe for the physics underlying the origin of the matter

Philip James, Bahram Mobasher

Near-infrared spectra of 50 elliptical galaxies in the Pisces, A2199 and A2634 clusters, and in the general field, have been obtained. The strength of the CO (2.3 micron) absorption feature in these galaxies is used to explore the presence of an intermediate-age population (e.g. Asymptotic Giant Branch stars) in ellipticals in different environments. We find

M. Demianski, A. Doroshkevich

An approximate statistical description of the formation and evolution of structure of the universe based on the Zel'dovich theory of gravitational instability is proposed. It is found that the evolution of DM structure shows features of self-similarity and the main structure characteristics can be expressed through the parameters of initial power spectru

A. Dolgov, A. Doroshkevich, D. Novikov, I. Novikov

Geometrical and statistical properties of polarization of CMB are analyzed. Singular points of the vector field which describes CMB polarization are found and classified. Statistical distribution of the singularities is studied. A possible signature of tensor perturbations in CMB polarization is discussed. For a further analysis of CMB statistics Minkowski f

Coel Hellier

I collect emission line profiles for seven intermediate polars, phase-resolved over the spin cycles. I then present the first systematic application of Doppler tomography to the spin cycles, with the aim of investigating whether spin-cycle tomography is a useful diagnostic tool. Four stars show line emission from material falling onto both magnetic poles of

Z. Paragi, S. Frey, L. I. Gurvits, K. I. Kellermann

We present very long baseline interferometry (VLBI) images of ten very high redshift (z>3) quasars at 5 GHz. The sources 0004+139, 0830+101, 0906+041, 0938+119 and 1500+045 were observed in September 1992 using a global VLBI array, while 0046+063, 0243+181, 1338+381, 1428+423 and 1557+032 were observed in October 1996 with the European VLBI Network and Harte

Tim de Zeeuw, Leiden Observatory

This summary discusses new results on the stellar and gaseous luminous halo, and on the dark halo. It concludes with a look towards the future, with emphasis on the role of space astrometry missions.

Padeli. P. Papadopoulos, E. R. Seaquist

We present fully sampled ^{12}$CO, ^{13}CO J=2-1, 3-2 maps of the inner $\sim 1'\times 1'$ region of NGC 1068. We combine these measurements with an existing interferometric map of ^{12}CO J=1-0 that includes single dish data and thus contains all the flux present. This allows a reliable estimate of the ^{12}CO (J=3-2)/(J=1-0) ratio at the highest an

B. Novosyadlyj, Yu. Chornij

We examine the dependence of the spatial two-point correlation function of quasars $ξ_{qq}(r,z)$ at different redshifts on the initial power spectrum in flat cosmological models. Quasars and other elements of the large-scale structure of the universe are supposed to form in the peaks of the scalar Gaussian field of density fluctuations of appropriate scales.

P. Goldoni, A. Goldwurm, F. Lebrun, J. Paul

The Center of the Milky Way emits radiation through all the electromagnetic spectrum due to the presence of several astrophysical phenomena. Various scientifical questions remain unsolved in the picture that emerge from observations, the main one being the presence and activity of a supermassive black hole at the Galactic Center. Also in the X-ray band a str

Christopher M. Wright, Ewine F. van Dishoeck, Pierre Cox, Sunil D. Sidher

We report the first detection outside of the solar system of the lowest pure rotational J=1-0 transition of the HD molecule at 112 microns. The detection was made toward the Orion Bar using the Fabry-Perot of the Long Wavelength Spectrometer (LWS) on board the Infrared Space Observatory (ISO). The line appears in emission with an integrated flux of (0.93+/-0

Feng-Li Lin, Yong-Shi Wu

De Sitter spacetime is known to have a cosmological horizon that enjoys thermodynamic-like properties similar to those of a black hole horizon. In this note we show that a universal argument can be given for the entropy of de Sitter spacetime in arbitrary dimensions, by generalizing a recent near horizon symmetry plus conformal field theory argument of Carli

Keith M. Beardmore, Niels Gronbech-Jensen

Using molecular dynamics (MD) simulation, we investigate the mechanical response of silicon to high dose ion-irradiation. We employ a realistic and efficient model to directly simulate ion beam induced amorphization. Structural properties of the amorphized sample are compared with experimental data and results of other simulation studies. We find the behavio

Limin Wang, R. R. Caldwell, J. P. Ostriker, Paul J. Steinhardt

We present a comprehensive study of the observational constraints on spatially flat cosmological models containing a mixture of matter and quintessence --- a time varying, spatially inhomogeneous component of the energy density of the universe with negative pressure. Our study also includes the limiting case of a cosmological constant. Low red shift constrai

Neil Turok

Hawking and the author have proposed a class of singular, finite action instantons for defining the initial conditions for inflation. Vilenkin has argued they are unacceptable. He exhibited an analogous class of asymptotically flat instantons which on the face of it lead to an instability of Minkowski space. However, all these instantons must be defined by i

S. G. Chung

The thermodynamics of the 2D XY model is formulated by a transfer matrix method and analyzed by a density matrix renormalization group. The finite-size scaling and the beta function of the model are studied by the Roomany-Wyld renormalization group theory. It is found that the 2D XY model has an essential finite-size effect and the Berezinskii-Kosterlitz-Tho