June 1997 arXiv papers — page 13

S. Raghavan

We extend our analysis of the effects of the interplay of quantum phases and nonlinearity to address saturation effects in small quantum systems. We find that initial phases dramatically control the dependence of self-trapping on initial asymmetry of quasiparticle population and can compete or act with nonlinearity as well as saturation effects. We find that

A. Zawadowski, G. Zarand, P. Nozieres, K. Vladar

The role of the electron-hole symmetry breaking is investigated for a symmetrical commutative two-level system in a metal using the multiplicative renormalization group in a straightforward way. The role of the symmetries of the model and the path integral technique are also discussed in detail. It is shown that the electron-hole symmetry breaking may make t

G. Zarand, K. Vladar

The article reviews recent results for the low energy physics of fast tunneling centers in metallic environments. For strong enough couplings to the environment these tunneling centers display an orbital Kondo effect and give rise to a non-Fermi-liquid behavior. This latter property is explained by establishing a mapping of the tunneling center model to the

O. Pilla, G. Viliani, R. DellAnna, G. Ruocco

The Raman coupling coefficients of site- and bond-percolators at concentration higher than percolation threshold are computed for two scattering mechanisms: Bond Polarizability (BPOL) and Dipole-Induced-Dipole (DID). The results show that DID does not follow a scaling law at low frequency, while in the case of BPOL the situation is less clear. The numericall

Athanassios Bardas, Dmitri V. Averin

We have generalized the scattering-matrix theory of multiple Andreev reflections in mesoscopic Josephson junctions to the multi-mode case, and applied it to short superconductor/normal metal/superconductor junctions with diffusive electron transport. Both the dc and ac current-voltage characteristics are analyzed for a wide range of bias voltages $V$. For vo

Masaki Oshikawa, Ian Affleck

In a recent neutron-scattering experiment on the quasi-one-dimensional $S=1/2$ antiferromagnet Cu Benzoate, a gap was induced by an applied magnetic field. We argue that the primary mechanism of the gap formation is an effective staggered field due to both the alternating $g$-tensor and the Dzyaloshinskii-Moriya interaction. We explain the dependence of the

Ellen Riloff, Jessica Shepherd

Semantic knowledge can be a great asset to natural language processing systems, but it is usually hand-coded for each application. Although some semantic information is available in general-purpose knowledge bases such as WordNet and Cyc, many applications require domain-specific lexicons that represent words and categories for a particular topic. In this pa

Andrew Kehler

Certain applications require that the output of an information extraction system be probabilistic, so that a downstream system can reliably fuse the output with possibly contradictory information from other sources. In this paper we consider the problem of assigning a probability distribution to alternative sets of coreference relationships among entity desc

Rebecca J. Passonneau

Studies of the contextual and linguistic factors that constrain discourse phenomena such as reference are coming to depend increasingly on annotated language corpora. In preparing the corpora, it is important to evaluate the reliability of the annotation, but methods for doing so have not been readily available. In this report, I present a method for computi

Hwee Tou Ng

In this paper, we report recent improvements to the exemplar-based learning approach for word sense disambiguation that have achieved higher disambiguation accuracy. By using a larger value of $k$, the number of nearest neighbors to use for determining the class of a test example, and through 10-fold cross validation to automatically determine the best $k$,

Eric Sven Ristad, Peter N. Yianilos

The library of practical abstractions (LIBPA) provides efficient implementations of conceptually simple abstractions, in the C programming language. We believe that the best library code is conceptually simple so that it will be easily understood by the application programmer; parameterized by type so that it enjoys wide applicability; and at least as effici

J. -P. Eckmann, J. Rougemont

We study slowly moving solutions of the real Ginzburg-Landau equation on the line, by a method due to J. Carr and R.L. Pego. These are functions taking alternately positive or negative values on large intervals. A consequence of our approach is that we can propose a rigorous derivation of a stochastic model of coarsening by successive elimination of the smal

Vishal Mehra, Ramakrishna Ramaswamy

We calculate the maximal Lyapunov exponent in constant-energy molecular dynamics simulations at the melting transition for finite clusters of 6 to 13 particles (model rare-gas and metallic systems) as well as for bulk rare-gas solid. For clusters, the Lyapunov exponent generally varies linearly with the total energy, but the slope changes sharply at the melt

Wolung Lee, Li-Zhi Fang

We study thermally induced density perturbations during inflation. This scenario is characterized by two thermodynamical conditions: (1) The primordial perturbations originate in the epoch when the inflationary universe contains a thermalized heat bath. (2) The perturbations of the inflationary scalar field are given by the fluctuation-dissipation relation.

Eric C. Ford, Philip Kaaret, Kaiyou Chen, Marco Tavani

We investigate the behavior of the high frequency quasi-periodic oscillations (QPOs) in 4U 0614+091, combining timing and spectral analysis of RXTE observations. The energy spectra of the source can be described by a power law (alpha ~ 2.8) and a blackbody (kT ~ 1.5), with the blackbody accounting for 10 - 20% of the total energy flux. We find a robust corre

E. F. Borra

I review the present status of liquid mirror telescopes. In a nutshell: LMTs do work and several have been built and used. Extensive interferometric tests of liquid mirrors (the largest one having a diameter of 2.5 meters) show diffraction limited performance. A large quantity of astronomical data have been taken at the NASA 3- m LMT and are currently being

M. W. Feast, P. A. Whitelock

A summary is given of an analysis of the Hipparcos trigonometrical parallaxes and proper motions of classical Cepheids. It is possible for the first time to derive zero-points for the period-luminosity and period-luminosity-colour relations from parallaxes alone, avoiding the problems of less direct methods. The results imply an increase of 8 to 10 percent i

P. A. Whitelock, F. van Leeuwen, M. W. Feast

Hipparcos trigonometrical parallaxes of Mira-type variables have been combined with ground-based angular diameter measurements to derive linear diameters. Of eight stars with ground-based data, six have diameters indicating overtone pulsation whilst two, both with periods over 400 day, are pulsating in the fundamental. Hipparcos parallaxes of 11 Miras have b

John J. Broderick, Eugene T. Herrin, Timothy P. Krisher, David L. Morgan

One of the most important questions in the study of compact objects is the nature of pulsars, including whether they consist of neutron matter or strange quark matter (SQM). However, few mechanisms for distinguishing between these two possibilities have been proposed. The purpose of this paper is to show that a strange star (one made of SQM) will have a vibr

A. Schroeder, R. C. Kraan-Korteweg, G. A. Mamon, S. Ruphy

We investigated the potential of using DENIS for studies of galaxies behind the obscuration layer of our Milky Way, and mapping the Galactic extinction. As a pilot study, we examined DENIS I-, J-, and K-band images of heavily obscured galaxies from a deep optical (B_J-band) galaxy survey in the Zone of Avoidance. We tried to uncover additional galaxies at la

A. Burkert, M. Bate, P. Bodenheimer

Hydrodynamical calculations in three space dimensions of the collapse of an isothermal, rotating 1 M\sol protostellar cloud are presented. The initial density stratification is a power law with density $ρ\propto r^{-p}$, with $p=1$. The case of the singular isothermal sphere ($p=2$) is not considered; however $p=1$ has been shown observationally to be a good

S. Cassisi, S. Degl'Innocenti, M. Salaris

This paper investigates the effect of microscopic diffusion of helium and heavy elements on the location of the Red Giant Branch Luminosity Function Bump in Population II stellar models. To this aim updated evolutionary models taking into account diffusion from the Main Sequence until the Zero Age Horizontal Branch have been computed. The observational lumin

Simon F. Portegies Zwart, Piet Hut, Stephen L. W. McMillan, Frank Verbunt

Three-body effects greatly complicate stellar evolution. We model the effects of encounters of binaries with single stars, based on parameters chosen from conditions prevalent in the cores of globular clusters. For our three-body encounters, we start with a population of primordial binaries, and choose incoming stars from the evolving single star populations

William G. Mathews, Fabrizio Brighenti

Interstellar magnetic fields in elliptical galaxies are assumed to have their origin in stellar fields that accompany normal mass loss from an evolving population of old stars. The seed fields are amplified by interstellar turbulence driven by stellar mass loss and supernova events. These disordered fields are further amplified by time-dependent compression

Yu Zhang, Avery Meiksin, Peter Anninos, Michael L. Norman

We discuss the origin and physical nature of the Lya forest absorption systems as found in hydrodynamical simulations of the Intergalactic Medium in a standard Cold Dark Matter cosmology (Omega=1, H0=50 km/s/Mpc, sigma_8=0.7). The structures of the systems that give rise to the Lya forest span a wide range in morphologies, depending on the density contrast.

Birkett Huber, Frank Sottile, Bernd Sturmfels

We develop numerical homotopy algorithms for solving systems of polynomial equations arising from the classical Schubert calculus. These homotopies are optimal in that generically no paths diverge. For problems defined by hypersurface Schubert conditions we give two algorithms based on extrinsic deformations of the Grassmannian: one is derived from a Gröbner

Stefan Forste, Debashis Ghoshal, Sudhakar Panda

We study an orientifold of the solitonic fivebrane of type II string theory. The consideration is restricted to a space-time domain which can be described by an exact conformal field theory. There are no IR divergent contributions to tadpole diagrams and thus no consistency conditions arise. However, extrapolating the results to spatial infinity leads to con

N. B. Kopnin, G. E. Volovik

Effects of fermionic zero modes (bound states in a vortex core) on the rotational dynamics of vortices with sponaneously broken axisymmetry are considered. The results are compared with the Helsinki experiments where the vortex cores were driven to a fast rotation and torsional oscillations by an NMR r.f. field (Kondo et al, Phys. Rev. Lett. 67, 81 (1991)).

Duiliu-Emanuel Diaconescu, Rami Entin

Sigma models describing low energy effective actions on D0-brane probes with N=8 supercharges are studied in detail using a manifestly d=1, N=4 super-space formalism. Two 0+1 dimensional N=4 multiplets together with their general actions are constructed. We derive the condition for these actions to be N=8 supersymmetric and apply these techniques to various

D. Falcone, O. Pisanti, L. Rosa

A parameter free, model independent analysis of quark mass matrices is carried out. We find a representation in terms of a diagonal mass matrix for the down (up) quarks and a suitable matrix for the up (down) quarks, such that the mass parameters only depend on the six quark masses and the three angles and phase appearing in the Cabibbo-Kobayashi-Maskawa mat

M. Klasen

We review the theoretical framework of jet photoproduction at HERA discussing the conceptual ideas, phenomenological models, and higher order perturbative calculations. Numerically, we study the physically interesting distribution of transverse energy within the observed jet, the real and virtual photon structure, and the proton structure at large x.

Leonardo Giusti, Alessandro Strumia

We show that the two scenarios able to explain the HERA anomaly --- a new leptoquark coupling or a new contact interaction --- predict new contributions to atomic parity violation. These corrections are sufficiently large and different that a feasible reduction in the dominant atomic theory uncertainty could give some hint in favour of one of the two scenari

J. M. Campbell, E. W. N. Glover, D. J. Miller

We compute the one-loop QCD amplitudes for the decay of an off-shell vector boson with vector couplings into a quark-antiquark pair accompanied by two gluons keeping, for the first time, all orders in the number of colours. Together with previous work this completes the calculation of the necessary one-loop amplitudes needed for the calculation of the next-t

Giuseppe Castagnoli

Computation is currently seen as a forward propagator that evolves (retards) a completely defined initial vector into a corresponding final vector. Initial and final vectors map the (logical) input and output of a reversible Boolean network respectively, whereas forward propagation maps a one-way propagation of logical implication, from input to output. Conv

Feng Yuan, Kuang-Ta Chao

We present an analysis of the ψψproduction from double parton (DP) sacttering and single parton (SP) scattering in the large p_T region via color-octet gluon fragmentation. We find that at the Tevatron the DP ψψproduction is at the edge of the detectability at present, and at the LHC the DP cross section will dominate over the SP cross section in the lower p

P. Hajicek, J. Bicak

The dynamics of a spherically symmetric thin shell with arbitrary rest mass and surface tension interacting with a central black hole is studied. A careful investigation of all classical solutions reveals that the value of the radius of the shell and of the radial velocity as an initial datum does not determine the motion of the shell; another configuration

G. X. Peng, P. Z. Ning

We have derived the popularly used parametrization formulae for quark masses at low densities and modified them at high densities within the mass-density-dependent model. The results are applied to investigate the lowest density for the possible existence of strange quark matter at zero temperature.

U. A. Yajnik, K. Narayan

We propose a scheme for quantizing a scalar field over the Schwarzschild manifold including the interior of the horizon. On the exterior, the timelike Killing vector and on the horizon the isometry corresponding to restricted Lorentz boosts can be used to enforce the spectral condition. For the interior we appeal to the need for CPT invariance to construct a

S. A. Gurvitz

We study dynamics of the measurement process in quantum dot systems, where a particular state out of coherent superposition is observed. The ballistic point-contact placed near one of the dots is taken as a noninvasive detector. We demonstrate that the measurement process is fully described by the Bloch-type equations applied to the whole system. These equat

Sang Pyo Kim

We present a nonperturbative field theoretic method based on the Liouville-Neumann (LN) equation. The LN approach provides a unified formulation of nonperturbative quantum fields and also nonequilibrium quantum fields, which makes use of mean-field type equations and whose results at the lowest level are identically the same as those of the Gaussian effectiv

Mark J. Hadley

For the first time it is shown that the logic of quantum mechanics can be derived from Classical Physics. An orthomodular lattice of propositions, characteristic of quantum logic, is constructed for manifolds in Einstein's theory of general relativity. A particle is modelled by a topologically non-trivial 4-manifold with closed timelike curves - a 4-geon

A. A. Davydov

The article is devoted to the describtion of quasitriangular structures (universal R-matrices) on cocommutative Hopf algebras. It is known that such structures are concentrated on finite dimensional Hopf subalgebras. In particular, quasitriangular structure on group algebra is defined by the pairs of normal inclusions of an finite abelian group and by invari

D. Hanstorp, G. Haeffler, A. E. Klinkmueller, U. Ljungblad

We present the results of experimental studies of photon-negative ion interactions involving the dynamics of two electrons. Resonances associated with doubly excited states of Li^- and He^- have been observed using laser photodetachment spectroscopy. Total and partial photodetachment cross sections have been investigated. In the former case, the residual ato

P. Papazoglou, S. Schramm, J. Schaffner-Bielich, H. Stöcker

A generalized Lagrangian for the description of hadronic matter based on the linear $SU(3)_L \times SU(3)_R$ $σ$-model is proposed. Besides the baryon octet, the spin-0 and spin-1 nonets, a gluon condensate associated with broken scale invariance is incorporated. The observed values for the vacuum masses of the baryons and mesons are reproduced. In mean-fiel

P. Mohr, H. Beer, H. Herndl, H. Oberhummer

Several neutron capture cross sections of light neutron-rich nuclei were measured in the astrophysically relevant energy region of 5 to 200 keV. The experimental data are compared to calculations using the direct capture model. The results are used for the calculation of neutron capture cross sections of unstable isotopes. Furthermore, neutron sources with e

Frank Sottile

We give an elementary proof of the Pieri-type formula in the cohomology of a Grassmannian of maximal isotropic subspaces of an odd orthogonal or symplectic vector space. This proof proceeds by explicitly computing a triple intersection of Schubert varieties. The decisive step is an exact description of the intersection of two Schubert varieties, from which t

Regis Le Du

The complete structure of curvature squared terms is analyzed in the context of chirally extended supergravity, with special emphasis on the gravitationally induced Fayet-Iliopoulos D--term. Coupling of (chiral) matter is discussed in relation with a possible extension to U(1) supergravity of the equivalence mechanism between $\cR+\al\cR^2$ and General Relat

V. F. Kovalev, V. V. Pustovalov, D. V. Shirkov

An original regular approach to constructing special type symmetries for boundary value problems, namely renormgroup symmetries, is presented. Different methods of calculating these symmetries, based on modern group analysis are described. Application of the approach to boundary value problems is demonstrated with the help of a simple mathematical model.

U. Trittmann

Numerical results on the positronium spectrum in the front form of QED at large coupling constant are presented. Emphasis is put on the question whether one can derive an effective interaction at all, and whether this effective interaction is rotationally invariant. (Proceedings of Les Houches 1997)

Takeshi Oota

The Lie algebraic structures of the S-matrices for the affine Toda field theories based on the dual pairs (X_N^{(1)}, Y_M^{(l)}) are discussed. For the non-simply-laced horizontal subalgebra X_N and the simply-laced horizontal subalgebra Y_M, we introduce a ``q-deformation'' of a Coxeter element and a ``p-deformation'' of a twisted Coxeter el

H. C. Pauli

The canonical front form Hamiltonian for non-Abelian SU(N) gauge theory in 3+1 dimensions is mapped non-perturbatively on an effective Hamiltonian which acts only in the Fock space of a quark and an antiquark. The approach is based on the novel method of iterated resolvents and on discretized light-cone quantization, driven to the continuum limit. It is free

Xerxes Tata

In these Lectures, we present a pedagogical introduction to weak scale supersymmetry phenomenology. A basic understanding of the Standard Model and of the ideas behind Grand Unification, but no prior knowledge of supersymmetry, is assumed. Topics covered include: What is supersymmetry and why do we bother with it? Working with a supersymmetric theory: A toy

P. Desgrolard, M. Giffon, E. S. Martynov

We reanalyse $\bar p p$ and $pp$ high energy data of the elastic scattering above $\sqrt{s}=5$ GeV on the total cross-section $σ_{tot}$ and on the forward $ρ$-ratio for various models of Pomeron, utilizing two methods. The first one is based on analytic amplitudes, the other one relies on assumptions for $σ_{tot}$ and on dispersion relation for $ρ$. We argue

Peter Arnold

I explain, as simply and pedagogically as I can, recent arguments that the high-temperature baryon number violation rate depends on the electroweak coupling as $Γ= # α_\w^5 T^4$ (up to higher order corrections). This is in contrast to the form $Γ= # α_\w^4 T^4$ that has historically been assumed in discussions of electroweak baryogenesis. I will give a gener

Gregory Mahlon, Stephen Parke

A comparison is made between the off-diagonal and helicity spin bases for top quark pair production at the FNAL Tevatron. In the off-diagonal basis, 92% of the top quark pairs are in the spin configuration up-down plus down-up, whereas in the helicity basis only 70% are left-right plus right-left. The off-diagonal basis maximizes the spin asymmetry and hence

A. Khodjamirian, R. Rückl, S. Weinzierl, O. Yakovlev

We report on the perturbative $O(α_s)$ correction to the light-cone QCD sum rule for the $B\to π$ transition form factor $f^+$. The correction to the product $f_Bf^+$ in leading twist approximation is found to be about 30%, that is similar in magnitude to the corresponding $O(α_s)$ correction in the two-point sum rule for $f_B$. The resulting cancellation of

J. R. Morris

It is pointed out that various types of cosmic string solutions that exist in nonsupersymmetric and globally supersymmetric theories, such as D-type gauge strings, F-type global and gauge strings, and superconducting Witten strings, also exist in supergravity models. When the D term and superpotential satisfy some simple conditions allowing the determination

She-Sheng Xue

We propose a novel theoretical understanding of neutrino masses and mixings, which is attributed to the intrinsic vector-like feature of the regularized Standard Model at short distances. We try to explain the smallness of Dirac neutrino masses and the decoupling of the right-handed neutrino as a free particle. Neutrino masses and mixing angles are completel

E. G. Ferreiro, C. Pajares

Recent experimental data on antibaryon production outside nucleon-nucleon kinematical limits have been obtained in Pb-Pb collisions at SPS energies. We present a possible explanation for this phenomenon based on the existence of collective effects. String Fusion Model results are compared to the data and predictions are also presented.

A. Riotto

In this talk the following question is addressed: are internal symmetries necessarily restored at high temperature in supersymmetric theories? Contrary to the general belief, we argue that the answer is no when systems possess a net background charge. Our findings are exemplified on abelian models, for both cases of global and local symmetries and possible c

D. Palle

We show that the correct perturbation theory for mixed fermion states leads to nonvanishing contributions of the dimension-four vertex operators for flavour-changing transitions. Their contributions to the amplitude are of the same order of magnitude as the dimension- five vertex operators. Considerations are valid irrespective of the electroweak model. A co

Feng Yuan, Kuang-Ta Chao

Color-octet mechanism for the decay B\to \eta^\prime X is proposed to explain the large branching ratio of Br(B\to \eta^\prime X)\sim 1\times 10^{-3} recently announced by CLEO. We argue that the inclusive \eta^\prime production in B decays may dominantly come from the Cabbibo favored b\to (\bar c c)_8s process where \bar c c pair is in a color-octet configu

M. F. McDermott

This talk concerns the production of open charm in diffractive deep inelastic scattering. This has been calculated recently in the context of the semi-classical approach to diffraction. A comparison is made to approaches in which the diffractive exchange is modelled by the exchange of two gluons in the $t$-channel. Two phenomenological test of the underlying

I. Royen

We show that the lowest-order QCD calculation in a simple model of elastic vector-meson production does reproduce correctly the ratios of cross sections for rho, phi and J/psi (measured by H1 and ZEUS), both in photoproduction and in high-Q^2 quasi-elastic scattering. The mass and Q^2 dependence of the cross sections is reproduced as well. We also examine th

F. Caravaglios

The four fermion contact interactions, required to explain the anomalous HERA result, could come from the exchange of new heavy (probably composite) resonances. Depending on their charges and quantum numbers, one gets different scenarios and finds that many of these configurations are unsuitable. For example, new neutral resonances seems to be disfavored by

Mayumi Aoki, Akio Sugamoto, Noriyuki Oshimo

We study baryogenesis at the electroweak phase transition of the universe within the framework of the supersymmetric standard model (SSM) based on N=1 supergravity. This model contains a new source of CP violation in the mass-squared matrices for squarks, which could enable $t$ squarks to mediate the charge transport mechanism for generating baryon asymmetry

J. Ambjorn, K. N. Anagnostopoulos, T. Ichihara, L. Jensen

We study the fractal structure of space-time of two-dimensional quantum gravity coupled to c=-2 conformal matter by means of computer simulations. We find that the intrinsic Hausdorff dimension d_H = 3.58 +/- 0.04. This result supports the conjecture d_H = -2 α_1/α_{-1}, where α_n is the gravitational dressing exponent of a spinless primary field of conforma

K-I. Ishikawa, H. Matsufuru, T. Onogi, N. Yamada

We calculate the heavy-light meson decay constant using lattice NRQCD action for the heavy quark and Wilson quark action for the light quark over a wide range in the heavy quark mass. Simulations are carried out on a 16^3 x 32 lattice with 120 quenched gauge configurations generated with the plaquette action at beta=5.8. For the heavy quark part of the calcu

B. Boisseau, B. Linet

We examine the dynamics of a self-gravitating string in the scalar-tensor theories of gravitation by considering a thin tube of matter to describe it. For a class of solutions, we obtain in the generic case that the extrinsic curvature of the world sheet of the central line is null in the limit where the radius of the string tends to zero. However, if we imp

Neven Bilic, Raoul Viollier

We study a system of self-gravitating massive fermions in the framework of the general-relativistic Thomas-Fermi model. We postulate the free energy functional and show that its extremization is equivalent to solving the Einstein's field equations. A self-gravitating fermion gas we then describe by a set of Thomas-Fermi type self-consistency equations.

Nora Menyhard, Geza Odor

One-dimensional non-equilibrium kinetic Ising models evolving under the competing effect of spin flips at zero temperature and nearest neighbour spin exchanges exhibiting a parity-conserving (PC) phase transition on the level of kinks are investigated here numerically from the point of view of the underlying spin system. The dynamical persistency exponent $Θ

Ryo Maezono, Sumio Ishihara, Naoto Nagaosa

We study the phase diagram of R_{1-x}A_xMnO_3 (R=La, Pr, Nd, Sm ; A=Ca, Sr, Ba) by taking into account the degeneracy of $e_g$ orbitals and the anisotropy of the transfer integral. The electron-electron interaction is treated in the mean field approximation with the optimization of the spin and orbital structures. The global phase diagram is understood in te

Anton Bovier, Veronique Gayrard

We study the finite dimensional marginals of the Gibbs measure in the Hopfield model at low temperature when the number of patterns, $M$, is proportional to the volume with a sufficiently small proportionality constant $\a>0$. It is shown that even when a single pattern is selected (by a magnetic field or by conditioning), the marginals do not converge almos

T. P. C. van Noije, M. H. Ernst, R. Brito, J. A. G. Orza

Using fluctuating hydrodynamics we describe the slow build-up of long range spatial correlations in a freely evolving fluid of inelastic hard spheres. In the incompressible limit, the behavior of spatial velocity correlations (including $r^{-d}$-behavior) is governed by vorticity fluctuations only and agrees well with two-dimensional simulations up to 50 to

P. Simon

We consider the 2D $J_1-J_2$ classical XY model on a square lattice. In the frustrated phase corresponding to $J_2>J_1/2$, an Ising order parameter emerges by an ``order due to disorder'' effect. This leads to a discrete symmetry plus the O(2) global one. We formulate the problem in a Coulomb gas language and show by a renormalization group analysis

J. M. Rubí, P. Mazur

A system of N Brownian particles suspended in a nonuniform heat bath is treated as a thermodynamic system whith internal degrees of freedom, in this case their velocities and coordinates. Applying the scheme of non-equilibrium thermodynamics, one then easily obtains the Fokker-Planck equation for simultaneous Brownian motion of N particles in a temperature g

G. Baskaran, P. W. Anderson

In this note we bring out several problems with the SO(5) unification attempt of Zhang [cond-mat/9610140].

Ted Pedersen, Rebecca Bruce

This paper describes an experimental comparison of three unsupervised learning algorithms that distinguish the sense of an ambiguous word in untagged text. The methods described in this paper, McQuitty's similarity analysis, Ward's minimum-variance method, and the EM algorithm, assign each instance of an ambiguous word to a known sense definition bas

Lawrence Saul, Fernando Pereira

We consider the use of language models whose size and accuracy are intermediate between different order n-gram models. Two types of models are studied in particular. Aggregate Markov models are class-based bigram models in which the mapping from words to classes is probabilistic. Mixed-order Markov models combine bigram models whose predictions are condition

Ido Dagan, Yael Karov, Dan Roth

Learning problems in the text processing domain often map the text to a space whose dimensions are the measured features of the text, e.g., its words. Three characteristic properties of this domain are (a) very high dimensionality, (b) both the learned concepts and the instances reside very sparsely in the feature space, and (c) a high variation in the numbe

Elliott D. Bloom, James D. Wells

Active Galactic Nuclei (AGN) may emit highly collimated and intense jets of relativistic electrons which upscatter ambient photons. These electrons can also scatter off the cold dark matter halo of the galaxy to produce high energy photons which have a more isotropic signature than the upscattered photons from QED processes. We propose to look for these high

Jeremy Goodman

Stars twinkle to the eye through atmospheric turbulence, but planets, because of their larger angular size, do not. Similarly, scintillation due to the local interstellar medium will modulate the radio flux of gamma-ray-burst afterglows and may permit indirect measurements of their angular sizes. The amplitude of refractive scintillation is of order ten perc

Alvio Renzini

Available X-ray data are collected and organized concerning the iron and gas content of galaxy clusters and groups, together with the optical luminosity, mass and iron abundance of cluster galaxies. Several astrophysical inferences are then drawn, including the evidence for rich clusters having evolved without much baryon exchange with their surrondings, and

Michiel R. Hogerheijde, Ewine F. van Dishoeck, Geoffrey A. Blake, Huib Jan van Langevelde

Interferometer observations of millimeter-continuum (OVRO) and single-dish observations of HCO+ and H13CO+ J=1-0, 3-2, and 4-3 (JCMT, IRAM 30m) are presented of nine embedded low-mass young stellar objects (YSOs) in Taurus. All nine objects are detected at 3.4 and 2.7 mm, with fluxes of 4-200 mJy, and consist of unresolved (<3 arcsec) point sources, plus, to

W. van Driel, R. C. Kraan-Korteweg, B. Binggeli, W. K. Huchtmeier

Sensitive 21cm HI line observations were performed for 23 dwarf members and possible members of the nearby M81 group of galaxies, including five objects of a clustering of extremely low-surface brightness objects of unknown nature. With the Nancay decimetric radio telescope the radial velocity range of -529 to 1826 km/s was searched to an rms noise of ~3-5 m

A. Burrows, D. Sudarsky, C. Sharp, M. Marley

We have developed a new non-gray theory of the evolution, spectra, and colors of extrasolar giant planets (EGPs) and brown dwarfs that reveals their exotic nature and uniqueness. We have discovered that the fluxes of such objects for T$_{eff}$s from 1300 K to 100 K can be spectacularly higher in the near infrared bands than black body values and that their i

S. Aiso, M. Chikawa, Y. Hayashi, N. Hayashida

The Telescope Array prototype detectors were installed at Akeno Observatory and at the Utah Fly&#39;s Eye site. Using these detectors, we have observed the Crab Nebula and AGN&#39;s since the end of 1995. The successful detections of TeV gamma rays from Crab Nebula and Mkn501 are reported.

Re&#39;em Sari

The detection of delayed emission at X-ray optical and radio wavelengths, ``after-glow&#39;&#39;, suggests that the relativistic shell which emitted the initial GRB due to internal shocks decelerates on encountering an external medium, giving rise to the after-glow. At a very early stage (few seconds), the observed bolometric luminosity increases as t^2. On

P. Kahabka, W. Pietsch

We present the result of a systematic search for spectrally hard and soft X-ray binary systems in the Small Magellanic Cloud (SMC). This search has been applied to ROSAT PSPC data (0.1-2.4 keV) collected during 9 pointed observations towards this galaxy covering a time span of 2 years from October 91 till October 93. Selection criteria have been defined in o

M. -L. Chabanol, V. Hakim

We analyze a random neighbor version of the OFC stick-slip model. We find that the mean avalanche size is finite as soon as dissipation exists in the bulk but that this size grows exponentially fast when dissipation tends to zero.

Charles H. Lineweaver, Domingos Barbosa

We use a combination of the most recent cosmic microwave background (CMB) flat -band power measurements to place constraints on Hubble&#39;s constant h and the total density of the Universe Omega_o in the context of inflation-based cold dark matter (CDM) models with no cosmological constant. We use chisquared minimization to explore the 4-dimensional paramet

V. G. Kurt, V. V. Sokolov, S. V. Zharikov, G. G. Pavlov

We observed the middle-aged radio pulsar 0656+14 with a CCD detector at the 6-m telescope. Broadband BVRI images show the following magnitudes of the pulsar counterpart: B = 24.85 (+0.19, -0.16), V = 24.90 (+0.16, -0.14), R = 24.52 (+0.12, -0.11), I = 23.81 (+0.27, -0.21). We fitted the UV-optical (space + ground-based) data with a two-component model which

L. Dixon, A. Signer

We present the next-to-leading order (O(alpha_s^3)) perturbative QCD predictions for e^+e^- annihilation into four jets. A previous calculation omitted the O(alpha_s^3) terms suppressed by one or more powers of 1/N_c^2, where N_c is the number of colors, and the `light-by-glue scattering&#39; contributions. We find that all such terms are uniformly small, co

Paul Singer, Da-Xin Zhang

The exclusive decay modes $B \to K γγ$ and $B_s \to η(η&#39;) γγ$ are shown to have significant branching ratios of approximately $0.5\times 10^{-7}$. This first calculation of these modes employs a model based on a cascade transition $B\to Vγ\to Pγγ$ for estimating the long-distance contribution and the process $b\to sγγ$ for the short distance one.

Hitoshi Yamamoto

When a vector meson such as phi, J/Ψ(3S) or Upsilon(4S) decays to a particle-antiparticle pair of neutral mesons, the time distribution of inclusive decay to a given final state is naively expected to be the incoherent sum of those of the two mesons with opposite flavors. In this paper, we show that this is in general not the case for arbitrary coherent two-

U. P. Sukhatme, C. Rasinariu, A. Khare

We formulate and study the set of coupled nonlinear differential equations which define a series of shape invariant potentials which repeats after a cycle of $p$ iterations. These cyclic shape invariant potentials enlarge the limited reservoir of known analytically solvable quantum mechanical eigenvalue problems. At large values of $x$, cyclic superpotential

Walter Kob, Claudio Donati, Steven J. Plimpton, Peter H. Poole

We present the results of a large scale molecular dynamics computer simulation study in which we investigate whether a supercooled Lennard-Jones liquid exhibits dynamical heterogeneities. We evaluate the non-Gaussian parameter for the self part of the van Hove correlation function and use it to identify ``mobile&#39;&#39; particles. We find that these partic

R. M. Fye

We analytically calculate the ground state pairing symmetry and excitation spectra of two holes doped into the half-filled t-t&#39;-t&#39;&#39;-J_z model in the strong-coupling limit (J_z >> |t|, |t&#39;|, |t&#39;&#39;|). For the t&#39;-t&#39;&#39;-J_z model, there are regions of d-wave, s-wave, and p-wave symmetry. We find that the t-J_z model maps in lowes

Galina V. Lipunova, Vladimir M. Lipunov, Ivan E. Panchenko

The possible low-frequency radio emission from the progenitors of gamma ray bursts can experience a delay from tens of seconds to hours on the way to the observer due to the dispersion in galactic and extragalactic plasma, and thus reach the observer as a radio afterglow of the burst. This opens a unique possibility (peculiar &#34;Time Machine&#34;) of seein

Ka Chun Yu, John Bally, David Devine

We report the discovery of nearly a dozen collimated outflows from young stellar objects embedded in the molecular filament that extends north of the Orion Nebula towards the H II region NGC 1977. The large number of nearly co-eval outflows and embedded class-0 young stellar objects indicates that the OMC-2/3 region is one of the most active sites of on-goin