November 1998 arXiv papers — page 5

A. Bovier, M. Eckhoff, V. Gayrard, M. Klein

We study a class of Markov chains that describe reversible stochastic dynamics of a large class of disordered mean field models at low temperatures. Our main purpose is to give a precise relation between the metastable time scales in the problem to the properties of the rate functions of the corresponding Gibbs measures. We derive the analog of the Wentzell-

M. A. Jafarizadeh, F. Darabi, A. Rezaei-Aghdam, A. R. Rastegar

The tunneling rate, with exact prefactor, is calculated to first order in $\hbar$ for an empty closed Friedmann-Robertson-Walker (FRW) universe with decaying cosmological term $Λ\sim R^{-m}$ ($R$ is the scale factor and $m$ is a parameter $0\leq m \leq 2$). This model is equivalent to a cosmology with the equation of state $p_χ=(m/3 -1)ρ_χ$. The calculations

R. Pandharipande

Degenerate contributions to higher genus Gromov-Witten invariants of Calabi-Yau 3-folds are computed via Hodge integrals. The vanishing of contributions of covers of elliptic curves conjectured by Gopakumar and Vafa is proven. A formula for degree 1 covers for all genus pairs is computed in agreement with M-theoretic calculations of Gopakumar and Vafa. Final

H. Okamura, J. Naitoh, N. Nanba, M. Matoba

Optical reflectivity study has been made on the hexagonal (NiAs-type) Ni_{1-d}S in order to probe its electronic properties, in particular those associated with the metal-nonmetal transition in this compound. Samples with d=0.005 and 0.02 are studied, which have transition temperatures Tt=246 K and 161 K, respectively. A pronounced dip appears in the reflect

Shi-Lin Zhu, Yuan-Ben Dai

We study the effect of $Bπ$ continuum in the QCD sum rule analysis of the heavy meson doublet $(0^+, 1^+)$ in the leading order of heavy quark effective theory. New sum rules are derived for the leading order binding energy ${\bar Λ_{+,{1\over 2}}}$ and pionic coupling constant $g'$.

D. B. Leinweber, J. I. Skullerud, A. G. Williams, C. Parrinello

The Landau gauge gluon propagator for the pure gauge theory is evaluated on a 32^3x64 lattice with a physical volume of (3.35^3x6.7)fm^4. Comparison with two smaller lattices at different lattice spacings allows an assessment of finite volume and finite lattice spacing errors. Cuts on the data are imposed to minimize these errors. Scaling of the gluon propag

S. Scheel, L. Knoll, D. -G. Welsch, S. M. Barnett

A recently developed scheme [S. Scheel, L. Knoll, and D.-G. Welsch, Phys. Rev. A 58, 700 (1998)] for quantizing the macroscopic electromagnetic field in linear dispersive and absorbing dielectrics satisfying the Kramers-Kronig relations is used to derive the quantum local-field correction for the standard virtual-sphere-cavity model. The electric and magneti

N. V. Vitanov

This paper presents analytic formulas for various transition times in the Landau-Zener model. Considerable differences are found between the transition times in the diabatic and adiabatic bases, and between the jump time (the time for which the transition probability rises to the region of its asymptotic value) and the relaxation time (the characteristic dam

N. V. Vitanov, K. -A. Suominen

We examine the effect of nonlinearity at a level crossing on the probability for nonadiabatic transitions $P$. By using the Dykhne-Davis-Pechukas formula, we derive simple analytic estimates for $P$ for two types of nonlinear crossings. In the first type, the nonlinearity in the detuning appears as a {\it perturbative} correction to the dominant linear time

J. Andries, F. Benatti, M. De Cock, M. Fannes

In this paper, we consider the long time asymptotics of multi-time correlation functions for quantum dynamical systems that are sufficiently random to relax to a ``reference state''. In particular, the evolution of such systems must have a continuous spectrum. Special attention is paid to general dynamical clustering conditions and their consequences

J. Clausen, M. Dakna, L. Knoll, D. -G. Welsch

Using conditional measurement on a beam splitter, we study the transformation of the quantum state of the signal mode within the concept of two-port non-unitary transformation. Allowing for arbitrary quantum states of both the input reference mode and the output reference mode on which the measurement is performed, we show that the non-unitary transformation

Jean-Michel Courty, Francesca Grassia, Serge Reynaud

We consider a model of quantum measurement built on an ideal operational amplifier operating in the limit of infinite gain, infinite input impedance and null output impedance and with a feddback loop. We evaluate the intensity and voltage noises which have to be added to the classical amplification equations in order to fulfill the requirements of quantum me

T. A. Osborn, M. F. Kondrat'eva, G. C. Tabisz, B. R. McQuarrie

A new and computationally viable full quantum version of line shape theory is obtained in terms of a mixed Weyl symbol calculus. The basic ingredient in the collision--broadened line shape theory is the time dependent dipole autocorrelation function of the radiator-perturber system. The observed spectral intensity is the Fourier transform of this correlation

G. D'Agostini

The intuitive reasoning of physicists in conditions of uncertainty is closer to the Bayesian approach than to the frequentist ideas taught at University and which are considered the reference framework for handling statistical problems. The combination of intuition and conventional statistics allows practitioners to get results which are very close, both in

Shi-Lin Zhu

The light cone QCD sum rules are derived for the $K^\ast Kπ$ coupling $g_{K^\ast Kπ} $ and the $ρππ$ coupling $g_{ρππ}$. The contribution from the excited states and the continuum is subtracted cleanly through the double Borel transform with respect to the two external momenta, $p_1^2$, $p_2^2=(p-q)^2$. Our result $g_{K^\ast Kπ}=(8.7\pm 0.5)$ and $g_{ρππ}=(1

R. Bellwied, S. Gavin, T. Humanic

By using a dynamical transport code we show that chirally disoriented domains might survive the hadronization phase in a central relativistic heavy ion collision. A successful measurement of such domains after freeze-out will depend on the domain size and the manifestation of the disorientation in the low part of the charged pion momentum spectrum. We invest

S. L. Yakovlev

Three-body Faddeev equations are considered as a spectral problem for nonsymmetrical matrix operator. Invariant subspaces related to physical and spurious solutions to Faddeev equations and its adjoint are described. Respective eigenvectors corresponding to invariant subspaces are constructed for Faddeev operator and its adjoint. Extensions of the formalism

C. Volpe, Ph. Chomaz, M. V. Andres, F. Catara

We apply boson expansion methods to an extended Lipkin-Meshkov-Glick model including anharmonicities in analogy with previous microscopic calculations. We study the effects of different approximations present in these calculations, among which the truncation of the hamiltonian and of the space, in connection with the study of the properties of two-phonon and

J. A. Christley, E. G. Lanza, S. M. Lenzi, M. A. Nagarajan

The excitation of the isovector giant dipole resonance (GDR) by alpha scattering is investigated as a method of probing the neutron excess in exotic nuclei. DWBA calculations are presented for 28O and 70Ca and the interplay of Coulomb and nuclear excitation is discussed. Since the magnitude of the Coulomb excitation amplitude is strongly influenced by the Q-

M. Coraddu, G. Kaniadakis, A. Lavagno, M. Lissia

The physics of nuclear reactions in stellar plasma is reviewed with special emphasis on the importance of the velocity distribution of ions. Then the properties (density and temperature) of the weak-coupled solar plasma are analysed, showing that the ion velocities should deviate from the Maxwellian distribution and could be better described by a weakly-none

J. Smejkal, E. Truhlik

It has recently been claimed by Cheon and Cheoun that the discrepancy between the experimental value of the induced pseudoscalar g_P, obtained at TRIUMF from a measurement of the radiative muon capture by proton, and its value predicted by using PCAC and pion pole dominance can be explained by a contact term generated from a simple pion-nucleon Lagrangian. W

Mark Andrea A. de Cataldo

A proof based on reduction to finite fields of Esnault-Viehweg's stronger version of Sommese Vanishing Theorem for $k$-ample line bundles is given. This result is used to give different proofs of isotriviality results of A. Parshin and L. Migliorini.

Mark Andrea A. de Cataldo

We use basic algebraic topology and Ellingsrud-Stromme results on the Betti numbers of punctual Hilbert schemes of surfaces to compute a generating function for the Euler characteristic numbers of the Douady spaces of "n-points" associated with a complex surface. The projective case was first proved by L. Göttsche.

Peter G. Casazza

We characterize Riesz frames and frames with the subframe property and use this to answer most of the questions from the literature concerning these properties and their relationships to the projection methods etc.

Peter G. Casazza

We show that every frame for a Hilbert space H can be written as a (multiple of a) sum of three orthonormal bases for H. A result of N.J. Kalton is included which shows that this is best possible in that: A frame can be represented as a linear combination of two orthonormal bases if and only if it is a Riesz basis. We further show that every frame can be wri

Peter G. Casazza

We develope a local theory for frames on finite dimensional Hilbert spaces. In particular, a bounded frame on a finite dimensional Hilbert space contains a subset which is a good Riesz basis for a percentage (arbitrarily close to one) of the space. We also construct a normalized frame for a Hilbert space which contains a subset which is a Schauder basis for

Peter G. Casazza, Ole Christensen

We give sufficient conditions for translates and modulates of a function g in L^2(R) to be a frame for its closed linear span. Even in the case where this family spans all of L^2(R), wou conditions are significantly weaker than the previous known conditions.

Peter G. Casazza, Nigel J. Kalton

We give counterexamples to a conjecture of Bourgain, Casazza, Lindenstrauss and Tzafriri that if X has a unique unconditional basis (up to permutation) then so does c_0(X). In particular, we show that for Tsirelson's space T, every unconditional basis of c_0(T) must be equivalent to a subsequence of the canonical basis but c_0(T) still fails to have a un

Peter G. Casazza, Ole Christensen, Nigel J. Kalton

We give necessary and sufficient conditions for a subfamily of regularly spaced translates of a function to form a frame (resp. a Riesz basis) for its span. One consequence is that ifthetranslates are taken only from a subset of the natural numbers, then this family is a frame if and only if it is a Riesz basis. We also consider arbitrary sequences of transl

Vincenzo Marotta, Antonino Sciarrino

Crystal tensor operators, which tranform under U_q->0(sl(2)), in analogous way as the vectors of the crystal basis, are introduced. The Wigner-Eckart theorem for the crystal tensor is defined: the selection rules depend on the initial state and on the component of the tensor operator; the transition amplitudes to the states of the same final irreducible repr

P. Kosiński, P. Maślanka

A particular deformation of central extended Galilei group is considered. It is shown that the deformation influences the rules of constructing the composed systems while one particle states remain basically unaffected. In particular the mass appeared to be non additive.

Paul E. Gunnells, Mark McConnell

Let G be a reductive algebraic group associated to a self-adjoint homogeneous cone defined over Q, and let G' be an appropriate neat arithmetic subgroup of G. We present two algorithms to compute the action of the Hecke operators on the integral cohomology of G'. This simultaneously generalizes the modular algorithm of Ash-Rudolph to a larger class o

Andrew Dancer, Andrew Swann

Classification results are given for (i) compact quaternionic Kähler manifolds with a cohomogeneity-one action of a semi-simple group, (ii) certain complete hyperKähler manifolds with a cohomogeneity-two action of a semi-simple group preserving each complex structure, (iii) compact 3-Sasakian manifolds which are cohomogeneity one with respect to a group of 3

P. H. Damgaard, J. C. Osborn, D. Toublan, J. J. M. Verbaarschot

We derive the microscopic spectral density of the Dirac operator in $SU(N_c\geq 3)$ Yang-Mills theory coupled to $N_f$ fermions in the fundamental representation. An essential technical ingredient is an exact rewriting of this density in terms of integrations over the super Riemannian manifold $Gl(N_f+1|1)$. The result agrees exactly with earlier calculation

J. Fuchs, C. Schweigert

In two-dimensional conformal field theory, we analyze conformally invariant boundary conditions which break part of the bulk symmetries. When the subalgebra that is preserved by the boundary conditions is the fixed algebra under the action of a finite group G, orbifold techniques can be used to determine the structure of the space of such boundary conditions

G. Papadopoulos, J. Gutowski

We find the dyonic worldvolume solitons due to parallel (p,q) strings ending on a D-3-brane. These solutions preserve 1/4 of bulk supersymmetry. Then we investigate the scattering of well-separated dyons and find that their moduli space is a toric hyper-Kähler manifold. In addition, we present the worldvolume solitons of the D-3-brane which are related by du

Tomasz Radozycki

The fermion propagator and the 4-fermion Green function in the massless QED2 are explicitly found with topological effects taken into account. The corrections due to instanton sectors k=+1,-1, contributing to the propagator, are shown to be just the homogenous terms admitted by the Dyson-Schwinger equation for S. In the case of the 4-fermion function also se

M. Fabbrichesi

I briefly review recent work on the comparison between two and three graviton scattering in supergravity and matrix theory

R. M. Kashaev

In the quantum Teichmuller theory, based on Penner coordinates, the mapping class groups of punctured surfaces are represented projectively. The case of a genus three surface with one puncture is worked out explicitly. The projective factor is calculated. It is given by the exponential of the Liouville central charge.

H. Ikemori, S. Kitakado, H. Nakatani, H. Otsu

Quantum mechanics on manifolds is not unique and in general infinite number of inequivalent quantizations can be considered. They are specified by the induced spin and the induced gauge structures on the manifold. The configuration space of collective mode in the Skyrme model can be identified with $S^{3}$ and thus the quantization is not unique. This leads

Aharon Levy

HERA, the electron-proton collider, enables to probe the proton with a high resolving power due to the deep inelastic scattering reactions at high $Q^2$ values. In the low $Q^2$ region, one can study the properties of the photon. The large fraction of diffractive events found both in the low and high $Q^2$ region allows the study of the Pomeron. A review of

C. D. Froggatt

We review some approaches to the quark-lepton mass problem. The ideas of mass-protection and approximate chiral flavour symmetries as a framework for resolving the mass hierarchy problem are presented. Dynamical calculations of the top quark and Higgs particle masses, based on infra-red fixed points and the so-called multiple point principle respectively, ar

Paul Langacker

The importance of non-zero neutrino mass as a probe of particle physics, astrophysics, and cosmology is emphasized. The present status and future prospects for the solar and atmospheric neutrinos are reviewed, and the implications for neutrino mass and mixing in 2, 3, and 4-neutrino schemes are discussed. The possibilities for significant mixing between ordi

M. Bleicher, M. Reiter, A. Dumitru, J. Brachmann

We propose to study the impact parameter dependence of the anti-Lambda/anti-Proton ratio in Pb(160AGeV)+Pb reactions. The anti-Lambda/anti-Proton ratio is a sensible tool to distinguish between hadronic cascade models and hydrodynamical models, which incorporate a QGP phase transition.

Taekoon Lee, Guo-Hong Wu

We show that the nonlinear supersymmetric effective lagrangian can be used for model-independent parameterization of the light gravitino scattering amplitude at energies up to and above the soft supersymmetry-breaking masses. This provides the most convenient framework for systematic studies of goldstino phenomenology both at low energies and in high energy

Gustavo Burdman

I discuss some theoretical aspects of rare $K$, $D$ and $B$ decays focusing mainly on their potential as tests of the one loop structure of the standard model. I concentrate on flavor changing neutral current processes and compare our ability to extract short distance physics in the three cases. Finally, I give some examples of the sensitivity of these decay

Guido Altarelli

This set of lectures provides an elementary introduction to the standard electroweak theory, followed by a detailed discussion of its experimental tests. We then consider the conceptual limitations of the Standard Model and briefly review the existing phenomenological indications of new physics. We summarize the case for a supersymmetric extension of the Sta

I. Vilja

The evaporation of the black holes during the very early universe is studied. Starting from black hole filled universe, the distiributions of particle species are calculated and showed, that they differ remarkably from the corresponding equilibrium distributions. This may have great impact to the physics of the very early universe. Also the evolution of the

T. Asaka, Masahiro Yamaguchi

Recently we have proposed a simple hadronic axion model within gauge-mediated supersymmetry breaking. In this paper we discuss various cosmological consequences of the model in great detail. A particular attention is paid to a saxion, a scalar partner of an axion, which is produced as a coherent oscillation in the early universe. We show that our model is co

S. V. Goloskokov

Large - distance effects in the hadron wave function for the hadron-Pomeron vertex in the QCD -model are discussed. It is shown that they lead to the spin-flip part of the Pomeron coupling which can reach $10 ÷20 %$ with respect to the non-flip part. The obtained structure of the Pomeron coupling modifies spin asymmetries in high--energy diffractive reaction

Nima Arkani-Hamed, Savas Dimopoulos, Gia Dvali, John March-Russell

Recently it was proposed that the standard model (SM) degrees of freedom reside on a $(3+1)$-dimensional wall or ``3-brane'' embedded in a higher-dimensional spacetime. Furthermore, in this picture it is possible for the fundamental Planck mass $\mst$ to be as small as the weak scale $\mst\simeq O(\tev)$ and the observed weakness of gravity at long d

V. Berezinsky, G. Fiorentini, M. Lissia

The excess of solar-neutrino events above 13 MeV that has been recently observed by Superkamiokande can be explained by vacuum oscillations (VO). If the boron neutrino flux is 20% smaller than the standard solar model (SSM) prediction and the chlorine signal is assumed 30% (or 3.5 sigmas) higher than the measured one, there exists a VO solution that reproduc

Eric Braaten

The Bose-Einstein condensation of atoms can be conveniently formulated as a problem in thermal quantum field theory. There are many properties of the equilibrium system and its collective excitations that can be studied experimentally. The remarkable experimental control over all aspects of the system make it an ideal testing ground for the methods of therma

Stefan Leupold

A new method is proposed for the calculation of the free energy of an N-component Phi^4 theory at finite temperature. The method combines a perturbative treatment of the hard modes with a non-perturbative treatment in the effectively three-dimensional sector of the soft modes. The separation between hard and soft modes is achieved by the effective field theo

Robert G. Edwards, Urs M. Heller, Rajamani Narayanan

We compute fermionic observables relevant to the study of chiral symmetry in quenched QCD using the Overlap-Dirac operator for a wide range of the fermion mass. We use analytical results to disentangle the contribution from exact zero modes and simplify our numerical computations. Details concerning the numerical implementation of the Overlap-Dirac operator

Constantia Alexandrou, Artan Boriçi, Alessandra Feo, Philippe de Forcrand

We present a study of the deconfinement phase transition of one-flavour QCD, using the multiboson algorithm. The mass of the Wilson fermions relevant for this study is moderately large and the non-hermitian multiboson method is a superior simulation algorithm. Finite size scaling is studied on lattices of size $8^3\times 4$, $12^3\times 4$ and $16^3\times 4$

L. Baudis, G. Heusser, B. Majorovits, Y. Ramachers

The GENIUS project is a proposal for a new dark matter detector, with an increased sensitivity of three orders of magnitude relative to existing direct dark matter detection experiments. We performed a technical study and calculated the main background sources for the relevant energy region in a detailed detector geometry. The achieved overall background lev

R. Tanaka

Single W and single gamma productions which are sensitive to the trilinear gauge coupling WWgamma have been studied at LEP. It isshown that single W production has particular sensitivity to the "anomalous" magnetic moment Kgamma of the W boson, complementary to WW production at LEP and Wgamma production at hadron colliders. The invisible decay of W b

D. Ambrose

The most sensitive experiment to date to search for the muon and electron lepton number violating decay $K^0_L \to μ^\pm e^\mp$ has detected no events consistent with this process. Based on this result, the 90% confidence level upper limit on the branching fraction is $B(K^0_L \to μ^\pm e^\mp) < 4.7\times10^{-12}$.

H. Casini, R. Montemayor, P. Sisterna

In this work we generalize a previously developed semiclassical approach to inflation, devoted to the analysis of the effective dynamics of coarse-grained fields, which are essential to the stochastic approach to inflation. We consider general non-trivial momentum distributions when defining these fields. The use of smooth cutoffs in momentum space avoids hi

M. A. Jafarizadeh, F. Darabi, A. Rezaei-Aghdam, A. R. Rastegar

The tunneling rate, with exact prefactor, is calculated to first order in \hbar for a closed FRW universe filled with perfect fluid violating the strong energy condition. The calculations are performed by applying the dilute-instanton approximation on the corresponding Duru-Kleinert path integral. It is shown that a closed FRW universe filled with a perfect

M. A. Jafarizadeh, F. Darabi, A. R. Rastegar

We show that the Duru-Kleinert fixed energy amplitude leads to the path integral for the propagation amplitude in the closed FRW quantum cosmology with scale factor as one degree of freedom. Then, using the Duru-Kleinert equivalence of corresponding actions, we calculate the tunneling rate, with exact prefactor, through the dilute-instanton approximation to

Orhan Karaali, Gerald Corrigan, Ira Gerson, Noel Massey

This paper describes the design of a neural network that performs the phonetic-to-acoustic mapping in a speech synthesis system. The use of a time-domain neural network architecture limits discontinuities that occur at phone boundaries. Recurrent data input also helps smooth the output parameter tracks. Independent testing has demonstrated that the voice qua

Orhan Karaali, Gerald Corrigan, Ira Gerson

Text-to-speech conversion has traditionally been performed either by concatenating short samples of speech or by using rule-based systems to convert a phonetic representation of speech into an acoustic representation, which is then converted into speech. This paper describes a system that uses a time-delay neural network (TDNN) to perform this phonetic-to-ac

Gerald Corrigan, Noel Massey, Orhan Karaali

A combination of a neural network with rule firing information from a rule-based system is used to generate segment durations for a text-to-speech system. The system shows a slight improvement in performance over a neural network system without the rule firing information. Synthesized speech using segment durations was accepted by listeners as having about t

L. V. Mercaldo, Steven M. Anlage, L. Maritato

The surface impedance of Nb/CuMn (superconducting/spin-glass) bilayers has been measured at 10 GHz with the parallel plate resonator technique to obtain information about the exotic behavior of the order parameter in superconducting/magnetic proximity systems. The data strongly differs from the superconducting/normal-metal case, showing the magnetic nature o

B. I. Schnieder, D. L. Feder

The ground and excited states of a weakly interacting and dilute Bose-Einstein condensed gas, confined in a completely anisotropic harmonic oscillator potential, are determined at zero temperature within the Bogoliubov approximation. The numerical calculations employ a computationally efficient procedure based on a discrete variable representation (DVR) of t

H. G. Katzgraber, H. P. Büchler, G. Blatter

We present a new approach to calculate the attractive long range vortex-vortex interaction of the van der Waals type present in anisotropic and layered superconductors. The mapping of the statistical mechanics of vortex lines onto the imaginary time quantum mechanics of two dimensional charged bosons allows us to define a 2D Casimir problem: Two half-spaces

G. Kurz, S. Sarkar

A new theory of hydrodynamics of uniaxial nematic liquid crystal films in the presence of defects is developed. A gauge field incorporating screening is introduced, resulting in the static elastic free energy having the form of a two-dimensional Abelian-Higgs model. Hydrodynamic equations are derived via the standard methods of de~Groot and Mazur. By working

Yuri G. Pogorelov, J. M. B. Lopes dos Santos, J. M. V. P. Lopes

A model of strongly disordered lattice system with long-range Coulomb interactions between localized charge carriers has been considered. The total electronic energy is characterized by the presence of multiple metastable minima (including the true ground state), and different types of excitation spectra over these minima. A numeric procedure, accounting for

J. J. Garcia-Ripoll, J. I. Cirac, J. Anglin, V. Perez-Garcia

We study the feasibility of preparing a Bose-Einstein condensed sample of atoms in a 2D spin monopole. In this state, the atomic internal spins lie in the x-y plane, and point in the radial direction.

J. Soding, D. Guery-Odelin, P. Desbiolles, F. Chevy

We have measured the three-body decay of a Bose-Einstein condensate of rubidium ($^{87}$Rb) atoms prepared in the doubly polarized ground state $F=m_F=2$. Our data are taken for a peak atomic density in the condensate varying between $2\times 10^{14}$ cm$^{-3}$ at initial time and $7\times 10^{13}$ cm$^{-3}$, 16 seconds later. Taking into account the influen

Silvano De Franceschi, Francesco Giazotto, Fabio Beltram, Lucia Sorba

Andreev-reflection dominated transport is demonstrated in Al/n-In0.38Ga0.62As superconductor-semiconductor junctions grown by molecular beam epitaxy on GaAs(001). High junction transparency was achieved in low-doped devices by exploiting Si interface bilayers to suppress the native Schottky barrier. It is argued that this technique is ideally suited for the

M. J. Calderon, L. Brey, F. Guinea

The electronic structure and magnetic properties of La_{1-x}A_{x}MnO_3 are investigated. It is assumed that, at the outermost layer, the environment of the Mn ions does not have cubic symmetry. The e_g orbitals are split and the double exchange mechanism is weakened. The charge state of the Mn ions is modified, and the magnetic ordering of the spins tends to

O. J. O&#39;Loan, M. R. Evans

We study flocking in one dimension, introducing a lattice model in which particles can move either left or right. We find that the model exhibits a continuous nonequilibrium phase transition from a condensed phase, in which a single `flock&#39; contains a finite fraction of the particles, to a homogeneous phase; we study the transition using numerical finite

H. N. Nagashima, R. N. Onody, R. M. Faria

A statistical model of resistor network is proposed to describe a polymer structure and to simulate the real and imaginary components of its ac resistivity. It takes into account the polydispersiveness of the material as well as intrachain and interchain charge transport processes. By the application of a transfer matrix technique, it reproduces ac resistivi

Rosario Fazio, Carlo Lucheroni

In this Letter we discuss various properties of the local density of states (DOS) for a superconductor-ferromagnet hybrid system. The DOS is modified at small energies on both sides of the interface. Due to the interplay of superconductivity and ferromagnetism, the local DOS depends on the spin direction. The spin polarization effects extend over a long dist

R. Egger, A. O. Gogolin

We comment on the paper by H. Yoshioka and A. Odintsov, to appear in PRL, see cond-mat/9805106.

Diptiman Sen, Siddhartha Lal

We study the spectrum of fermions hopping on a chain with a weak incommensuration close to dimerization; both q, the deviation of the wave number from pi, and delta, the strength of the incommensuration, are small. For free fermions, we use a continuum Dirac theory to show that there are an infinite number of bands which meet at zero energy as q approaches z

Joachim Holzfuss, Matthias Ruggeberg, Andreas Billo

A single bubble in water is excited by a standing ultrasound wave. At high intensity the bubble starts to emit light. Together with the emitted light pulse, a shock wave is generated in the liquid at collapse time. The time-dependent velocity of the outward-travelling shock is measured with an imaging technique. The pressure in the shock and in the bubble is

David S. Graff, Lance T. Gardiner

We analyse an N-body simulation of the Small Magellanic Cloud (SMC), that of Gardiner & Noguchi (1996) to determine its microlensing statistics. We find that the optical depth due to self-lensing in the simulation is low, 0.4 x 10^{-7}, but still consistent (at the 90% level) with that observed by the EROS and MACHO collaborations. This low optical depth is

M. Goetz, J. P. Huchra, R. H. Brandenberger

Three popular algorithms (FOF, DENMAX, and SKID) to identify halos in cosmological N-body simulations are compared with each other and with the predicted mass function from Press-Schechter theory. It is shown that the resulting distribution of halo masses strongly depends upon the choice of free parameters in the three algorithms, and therefore much care in

D. D. Carpintero, J. C. Muzzio, F. C. Wachlin

As a first step towards a comprehensive investigation of stellar motions within globular clusters, we present here the results of a study of stellar orbits in a mildly triaxial globular cluster that follows a circular orbit inside a galaxy. The stellar orbits were classified using the frequency analysis code of Carpintero and Aguilar and, as a check, the Lia

J. Jimenez-Vicente, E. Battaner, M. Rozas, H. Castaneda

The nearly face-on spiral galaxy NGC 3938 has been observed in the $H_α$ line with the TAURUS II Fabry-Perot interferometer at the William Herschel Telescope in order to study the kinematics of the ionized gas. We are able to construct intensity, velocity and velocity dispersion maps for this galaxy. The rotation curve of the galaxy is calculated up to 4.5 r

Jan J. Blom, Timothy A. D. Paglione, Alberto Carraminana

We present a search for high energy gamma-ray emission from 9 nearby starburst galaxies and M31 with the EGRET instrument aboard CGRO. Though the diffuse gamma-ray emission from starburst galaxies was suspected to be detectable, we find no emission from NGC 253, M82 nor from the average of all 9 galaxies. The 2 sigma upper limit for the EGRET flux above 100

K. Hurley, P. Li, C. Kouveliotou, T. Murakami

We present a 2 - 10 keV ASCA observation of the field around the soft gamma repeater SGR1900+14. One quiescent X-ray source was detected in this observation, and it was in the SGR error box. In 2 - 10 keV X-rays, its spectrum may be fit by a power law with index -2.2, and its unabsorbed flux is 9.6 x 10^-12 erg cm^-2 s^-1. We also find a clear 5.16 s period.

Y. I. Izotov, T. X. Thuan

We present high-quality ground-based spectroscopic observations of 54 supergiant H II regions in 50 low-metallicity blue compact galaxies with oxygen abundances 12 + log O/H between 7.1 and 8.3. We use the data to determine abundances for the elements N, O, Ne, S, Ar and Fe. We also analyze Hubble Space Telescope (HST) Faint Object Spectrograph archival spec

Carlo Baccigalupi, Francesca Perrotta

Recently Peebles and Vilenkin proposed and quantitatively analyzed the fascinating idea that a substantial fraction of the present cosmic energy density could reside in the vacuum potential energy of the scalar field responsible for inflation (quintessential inflation). Here we compute the signature of this model in the cosmic microwave background polarizati

R. Fux

New constraints on the Milky Way&#39;s bar parameters are derived from the gaseous spiral structure within the Galactic bar, and in particular from the identification of the dustlanes leading the bar major axis.

Nidhal Guessoum, Demosthenes Kazanas

We examine the processes which could lead to the observed enhancement of Li and possibly other light elements (Be, B) in the companions of a number of X-ray novae. We conclude that one of the most promising mechanisms is the spallation of CNO elements on the surface of the companion induced by the neutron flux produced in the hot accretion flow onto the comp

Alberto Buzzoni

Physical and numerical constraints in building up self-consistent population synthesis models are briefly analysed discussing their application to most of the current synthesis codes widely adopted in Galactic and extragalactic studies.

A. Capetti, D. J. Axon, F. D. Macchetto, A. Marconi

We have obtained HST FOC long-slit optical spectroscopy of the Narrow Line Region of the Seyfert 2 galaxy Mrk 3. In the region cospatial with the radio-jet the velocity field is highly perturbed and shows two velocity systems separated by as much as 1700 km/s. We interpret this to be the consequence of the rapid expansion of a cocoon of hot gas, shocked and

A. Różańska, B. Czerny, P. T. Życki, G. Pojmański

We study vertical structure of radiation pressure dominated disc with a hot corona. We include all the relevant processes like bound--free opacity and convection. We show that the presence of the corona modifies considerably the density and the opacity of the disc surface layers which are important from the point of view of spectrum formation. The surface of

PATRIZIA A. CARAVEO, ROBERTO MIGNANI

Owing to the dramatic evolution of telescopes as well as optical detectors in the last 20 yrs, we are now able to measure anew the proper motion of the Crab pulsar, after the classical result of Wyckoff and Murray (1977) in a time span 40 times shorter. The proper motion is aligned with the axis of symmetry of the inner Crab nebula and, presumably, with the

L. A. Anchordoqui, G. E. Romero, S. E. Perez Bergliaffa, J. A. Combi

In this letter we give an account of the possible acceleration of protons in the outer radio lobes of the active galaxy PKS 1333-33. We also make estimates of the arrival energy spectrum.

T. P. Roberts, R. S. Warwick, T. Ohashi

NGC 4736 is a nearby Sab spiral galaxy, hosting one of the closest examples of a LINER nucleus. We have utilized recent observations by ROSAT and ASCA to characterise the X-ray properties of this galaxy. Twelve discrete X-ray sources are detected within the region subtended by its optical disk, the majority of which are likely to be X-ray binaries associated

Jesper Storm, Bruce W. Carney, Anne M. Fry

We present results based on a Baade-Wesselink analysis of Cepheids in the Small Magellanic Cloud. The Baade-Wesselink analysis provides individual luminosities for these metal-poor Cepheids which combined with recent Baade-Wesselink results from Gieren et al. (1998) on solar metallicity Galactic Cepheids constrain the metallicity effect on the zero-point of

K. Y. Lo, Z. -Q. Shen, J. -H. Zhao, Paul~T. P. Ho

By means of near-simultaneous multi-wavelength VLBA measurements, we determine for the first time the intrinsic size of Sgr A* to be 3.6 AU by <1 AU with the major axis oriented essentially north-south. Contrary to previous expectation that the intrinsic structure of Sgr A* is observable only at wavelength shorter than 1 mm, we can discern the intrinsic sour

R. H. Sanders

Sticky particle calculations indicate that a coherent structure, a dispersion ring, forms when a cloud on a low angular momentum orbit passes close to the dynamical center of an isothermal sphere containing a central point mass. The cloud is tidally stretched and differentially wrapped, and dissipation in shocks organizes the gas into a precessing off-set el

Markus Kissler-Patig, Carl J. Grillmair, Georges Meylan, Jean P. Brodie

We investigate the kinematics of a combined sample of 74 globular clusters around NGC 1399. Their high velocity dispersion, increasing with radius, supports their association with the gravitational potential of the galaxy cluster rather than with that of NGC 1399 itself. We find no evidence for rotation in the full sample, although some indication for rotati