December 1998 arXiv papers — page 19

O. Narayan, B. S. Shastry

The statistical mechanics of a two dimensional Coulomb gas confined to one dimension is studied, wherein hard core particles move on a ring. Exact self-duality is shown for a version of the sine-Gordon model arising in this context, thereby locating the transition temperature exactly. We present asymptotically exact results for the correlations in the model

N. Furukawa

This article gives a comprehensive review on the recent studies of the double exchange systems using non-perturbative approaches; the dynamical mean-field theory and the Monte Carlo method. Investigations beyond mean-field type treatments are described. Taking into account strong spin fluctuations which create large changes in conduction electron structure,

Keith Slevin, Tomi Ohtsuki

We report a numerical analysis of corrections to finite size scaling at the Anderson transition due to irrelevant scaling variables and non-linearities of the scaling variables. By taking proper account of these corrections, the universality of the critical exponent for the orthogonal universality class for three different distributions of the random potenti

A. Sawada, Z. F. Ezawa, H. Ohno, Y. Horikoshi

We have measured the Hall-plateau width and the activation energy of the bilayer quantum Hall (BLQH) states at the Landau-level filling factor $ν=1$ and 2 by tilting the sample and simultaneously changing the electron density in each quantum well. The phase transition between the commensurate and incommensurate states are confirmed at $ν=1$ and discovered at

Holger Waalkens, Jan Wiersig, Holger R. Dullin

The classical mechanics, exact quantum mechanics and semiclassical quantum mechanics of the billiard in the triaxial ellipsoid is investigated. The system is separable in ellipsoidal coordinates. A smooth description of the motion is given in terms of a geodesic flow on a solid torus, which is a fourfold cover of the interior of the ellipsoid. Two crossing s

Victor M. Eguiluz, Emilio Hernandez-Garcia, Oreste Piro

The effect of a finite geometry on the two-dimensional complex Ginzburg-Landau equation is addressed. Boundary effects induce the formation of novel states. For example target like-solutions appear as robust solutions under Dirichlet boundary conditions. Synchronization of plane waves emitted by boundaries, entrainment by corner emission, and anchoring of de

D. Saumon, S. B. Jacobson

Microlensing events observed in the line of sight toward the LMC indicate that a significant fraction of the mass of the dark halo of the Galaxy is probably composed of white dwarfs. In addition, white dwarf sequences have now be observed in the HR diagrams of several globular clusters. Because of the unavailability of white dwarf atmospheres for Teff < 4000

L. da Costa, M. Nonino, R. Rengelink, S. Zaggia

This paper presents ground-based data obtained from deep optical and infrared observations of the HST Hubble Deep Field South (HDF-S) field carried out at the ESO 3.5 New Technology Telescope (NTT). These data were taken as part of the ESO Imaging Survey (EIS) program, a public survey coordinated by ESO and member states, in preparation for the first year of

R. J. Brunner, A. J. Connolly, A. S. Szalay

Studies of the distribution and evolution of galaxies are of fundamental importance to modern cosmology; these studies, however, are hampered by the complexity of the competing effects of spectral and density evolution. Constructing a spectroscopic sample that is able to unambiguously disentangle these processes is currently excessively prohibitive due to th

J. M. Solanes, E. Salvador-Sole, G. Gonzalez-Casado

Subclustering is investigated in a set of 67 rich cluster galaxy samples extracted from the ESO Nearby Abell Cluster Survey (ENACS) catalog. We apply four well-known statistical techniques to evaluate the frequency with which substructure occurs. These diagnostics are sensitive to different aspects of the spatial and velocity distribution of galaxies and exp

M. Stiavelli, T. Treu, C. M. Carollo, P. Rosati

The combined use of the ESO Very Large Telescope (VLT) UT1 Science Verification (SV) images and of the Hubble Space Telescope (HST) Hubble Deep Field South observations allows us to strengthen the identification as a candidate elliptical galaxy of the Extremely Red Object HDFS 223251-603910 previously identified by us on the basis of NICMOS and Cerro Tololo

J. LaSala, P. A. Charles, R. A. D. Smith, M. Balucinska-Church

We present epoch 1996, high-quality radial velocity data for HDE 226868, the optical counterpart of Cygnus X-1. Combining our results with all published historical data, we have derived a new ephemeris for the system of HJD2450235.29 + n x 5.5998, which allows accurate orbital phase calculations to be made for any X-ray observations over the last 30 years. W

M. Hernanz, J. Gomez-Gomar, J. Jose, A. Coc

A lot of information concerning the mechanism of nova explosions will be extracted from the possible future observations with INTEGRAL. In order to be prepared for this task, we are performing detailed models of the gamma-ray emission of classical novae, for a wide range of possible initial conditions. Spectra at different epochs after the explosion and ligh

M. K. van Aalst, P. C. H. Martens, A. J. C. Beliën

Coronal Mass Ejections continuously drag closed magnetic field lines away from the Sun, adding new flux to the interplanetary magnetic field (IMF). We propose that the outward-moving blobs that have been observed in helmet streamers are evidence of ongoing, small-scale reconnection in streamer current sheets, which may play an important role in the preventio

Xavier Luri, J. Torra, F. Figueras, A. E. Gomez

The distance modulus of the Large Magellanic Cloud (LMC) is the first step on the determination of the cosmic distance scale. In this paper it is obtained from a new calibration of the classical Cepheid Period-Luminosity (PL) relation. Our new calibration is obtained by applying the LM method -- a parametric method designed to obtain luminosity calibrations

Brian Chaboyer, Elizabeth M. Green, James Liebert

An extensive grid of metal-rich isochrones utilizing the latest available input physics has been calculated for comparison with the old, metal-rich open cluster NGC 6791. The isochrones have been simultaneously fit to BV and VI color magnitude diagrams, with the same composition, reddening and distance modulus required for both colors. Our best fitting isoch

M. Tavani, G. Barbiellini, P. Caraveo, S. Di Pippo

AGILE is an innovative, cost-effective gamma-ray mission proposed to the ASI Program of Small Scientific Missions. It is planned to detect gamma-rays in the 30 MeV - 50 GeV energy band and operate as an {\bf Observatory} open to the international community. Primary scientific goals include the study of AGNs, gamma-ray bursts, Galactic sources, unidentified g

Eugenio Carretta, Raffaele Gratton, Chris Sneden, Angela Bragaglia

In this research we use a large sample of field metal-poor stars ([Fe/H]<-1) in different evolutionary phases to prove observationally that (small mass) subgiants (stars brighter than the first dredge-up and fainter than the RGB bump) have abundances of light elements in agreement with predictions from classical evolutionary models. A further mixing episode

F. Arenou, X. Luri

We first review the current knowledge of Hipparcos systematic and random errors, in particular small-scale correlations. Then, assuming Gaussian parallax errors and using examples from the recent Hipparcos literature, we show how random errors may be misinterpreted as systematic errors, or transformed into systematic errors. Finally we summarise how to get u

E. Oliva, D. Lutz, S. Drapatz, A. F. M. Moorwood

ISO-SWS spectral observations of the supernova remnant IC443 are presented. Like other radiative SNRs, this object is characterized by prominent line-emitting filaments and relatively strong IRAS 12 and 25 micron emission which is commonly interpreted as thermal radiation from very small grains stochastically heated by collisions with the hot plasma behind t

D. Lynden-Bell

We outline reasoning that led to the current theory of quasars and look at George Contopoulos&#39;s place in the long history of the N-body problem. Following Newton we find new exactly soluble N-body problems with multibody forces and give a strange eternally pulsating system that in its other degrees of freedom reaches statistical equilibrium.

Ben R. Oppenheimer, S. R. Kulkarni, John R. Stauffer

After a discussion of the physical processes in brown dwarfs, we present a complete, precise definition of brown dwarfs and of planets inspired by the internal physics of objects between 0.1 and 0.001 M_sun. We discuss observational techniques for characterizing low-luminosity objects as brown dwarfs, including the use of the lithium test and cooling curves.

R. Chary, B. Zuckerman, E. E. Becklin

We present ISOCAM 7 micron and 15 micron observations of 12 nearby white dwarfs, 6 of which have been found to have metals such as Ca, Mg and Fe in their photospheres. Our purpose was to search for an excess of infrared emission above the stellar photospheres. We find that none of the white dwarfs other than G29-38 shows a detectable infrared excess and this

S. D. Bloom, A. P. Marscher, E. M. Moore, W. K. Gear

We present multiwaveband observations of a well selected sample of 28 quasars and two radio galaxies with flat radio spectra and strong millimeter wave emission (referred to here as FSRQ&#39;s). The observations include multifrequency VLBI measurements, X-ray observations with ROSAT and submillimeter observations with the JCMT. Particularly interesting among

Piero Madau

I review recent observational and theoretical progress in our understanding of the cosmic evolution of luminous sources. Through a combination of deep imaging, Keck spectroscopy, and COBE background measurements, important constraints have emerged on the emission history of the galaxy population as a whole. A simple stellar evolution model, defined by a star

D. Ruffolo

We have developed a numerical simulation code that treats the transport and acceleration of charged particles crossing an idealized oblique, non-relativistic shock within the framework of pitch angle transport using a finite-difference method. We consider two applications: 1) to study the steady-state acceleration of energetic particles at an oblique shock,

Patrick Godon, Mario Livio

The non-linear hydrodynamic stability of thin, compressible, Keplerian disks is studied on the large two-dimensional compressible scale, using a high-order accuracy spectral method. We show that purely hydrodynamic perturbations, while developing initially into sheared disturbances or coherent vortices, do not evolve into a self-sustained turbulence. This is

G. W. Gibbons, P. K. Townsend

We argue that the large $n$ limit of the $n$-particle $SU(1,1|2)$ superconformal Calogero model provides a microscopic description of the extreme Reissner-Nordstr{ö}m black hole in the near-horizon limit.

Michal Chodorowski

I derive a second-order local relation between the REDSHIFT-space mass density field and the REAL-space velocity field. This relation can be useful for comparisons between the cosmic density and peculiar velocity fields, for a number of reasons. First, relating the real-space velocity directly to the redshift-space density enables one to avoid the Omega-depe

A. Abada, J. Matias, R. Pittau

We investigate in this work the leading contributions of the MSSM with R-parity violation and of Left-Right models to the low-energy five-leg photon-neutrino processes. We discuss the results and compare them to the Standard Model ones.

F. V. Gubarev, M. I. Polikarpov, V. I. Zakharov

We consider the monopole-antimonopole static potential in the confining phase of the Abelian Higgs model and in particular the corrections to the Coulomb-like potential at small distances r. By minimizing numerically the classical energy functional we observe a linear in r, stringy correction even at distances much smaller than the apparent physical scales.

David H. Adams

An explicit, detailed evaluation of the classical continuum limit of the axial anomaly/index density of the overlap Dirac operator is carried out in the infinite volume setting, and in a certain finite volume setting where the continuum limit involves an infinite volume limit. Our approach is based on a novel power series expansion of the overlap Dirac opera

Kazusumi Ino

We consider the general abelian background configurations for the Haldane-Rezayi quantum Hall state. We determine the stable configurations to be the ones with the spontaneous flux of $(\Z+1/2) ϕ_0$ with $ϕ_0 = hc/e$. This gives the physical mechanism by which the edge theory of the state becomes identical to the one for the 331 state. It also provides a new

Ashoke Sen

In certain regions of the moduli space of K3 and Calabi-Yau manifolds, D-branes wrapped on non-supersymmetric cycles may give rise to stable configurations. We show that in the orbifold limit, some of these stable configurations can be described by solvable boundary conformal field theories. The world-volume theory of N coincident branes of this type is desc

A. Cuccoli, V. Tognetti, R. Giachetti, R. Maciocco

The pure-quantum self-consistent harmonic approximation (PQSCHA) permits to study a quantum system by means of an effective classical Hamiltonian - depending on quantum coupling and temperature - and classical-like expressions for the averages of observables. In this work the PQSCHA is derived in terms of the holomorphic variables connected to a set of boson

E. Schiller, H. Müther, P. Czerski

Brueckner-Hartree-Fock calculations are performed for nuclear matter with an exact treatment of the Pauli exclusion operator in the Bethe-Goldstone equation. The differences in the calculated binding energy, compared to the angle-average approximation, which is commonly used, are non-negligible. These difference exhibits a specific density dependence, which

Bing Hurl

Based on the principle of relativity, we find that the sufficient and necessary condition for the general covariance of a field theory actually requires more than the invariance of its local Langrangian density. If the spacetime is not a flat one, its derivative requirement from the analysis of the parallel transportation of tensor fields over spacetime rest

Barry C. Sanders, Dien A. Rice

We demonstrate several new results for the nonlinear interferometer, which emerge from a formalism which describes in an elegant way the output field of the nonlinear interferometer as two-mode entangled coherent states. We clarify the relationship between squeezing and entangled coherent states, since a weak nonlinear evolution produces a squeezed output, w

M. Adler, T. Shiota, P. van Moerbeke

What is the connection of random matrices with integrable systems? Is this connection really useful? The answer to these questions leads to a new and unifying approach to the theory of random matrices. Introducing an appropriate time t-dependence in the probability distribution of the matrix ensemble, leads to vertex operator expressions for the n-point corr

C. Gonera, M. Majewski, P. Maślanka

The Calogero model with negative harmonic term is shown to be equivalent to the set of negative harmonic oscillators. Two time-independent canonical transformations relating both models are constructed: one based on the recent results concerning quantum Calogero model and one obtained from dynamical $sL(2,\rr)$ algebra. The two-particle case is discussed in

C. Gonera, P. Kosiński, M. Majewski, P. Maślanka

Two properties of Calogero wave functions for rational Calogero models are studied: (i) the representation of the wave functions in terms of the exponential of Lassalle operators, (ii) the $sL(2,\rr)$ structure of the Calogero--Moser wave functions.

T. Tsuchida, M. Wadati

Generalization of the modified KdV equation to a multi-component system, that is expressed by $(\partial u_i)/(\partial t) + 6 (\sum_{j,k=0}^{M-1} C_{jk} u_j u_k) (\partial u_i)/(\partial x) + (\partial^3 u_{i})/(\partial x^3) = 0, i=0, 1, ..., M-1 $, is studied. We apply a new extended version of the inverse scattering method to this system. It is shown tha

I. T. Habibullin, A. N. Vil&#39;danov

Integrable boundary conditions in 1+1 and 2+1 dimensions are discussed from the higher symmetries point of view. Boundary conditions consistent with the discrete Landau-Lifshitz model and infinite 2D Toda lattice are represented.

Joseph Kapusta, Agnes Mocsy

The number of hydrogen-like atoms produced when heavy nuclei collide is estimated for central collisions at the Relativistic Heavy Ion Collider using the sudden approximation of Baym et al. As first suggested by Schwartz, a simultaneous measurement of the hydrogen and hadron spectra will allow an inference of the electron or muon spectra at low momentum wher

J. Brian Conrey, Xian-Jin Li

L. de Branges proposed an approach to the Riemann hypothesis using certain positivity conditions. In this paper, the authors examine this approach and indicate its difficulty.

G. Lassmann, E. Sparla

In this paper our main result states that there exist exactly three combinatorially distinct centrally-symmetric 12-vertex-triangulations of the product of two 2-spheres with a cyclic symmetry. We also compute the automorphism groups of the triangulations. These instances suggest that there is a triangulation of $S^2 \times S^2$ with 11 vertices -- the minim

Andreas Cap, Jan Slovak, Vladimir Soucek

This paper demonstrates the power of the calculus developed in the two previous parts of the series for all real forms of the almost Hermitian symmetric structures on smooth manifolds, including e.g. conformal Riemannian and almost quaternionic geometries. Exploiting some finite dimensional representation theory of simple Lie algebras, we give explicit formu

M. Kapranov

We give an interpretation of the double affine Hecke algebra of Cherednik as the (suitably regularized) algebra of double cosets of a group G by a subgroup J, extending the well known interpretations of finite and affine Hecke algebras. In this interpretation, G consists of K-points of a split reductive group where K is a 2-dimensional local field such as Q_

Francesco Antonuccio

A representation of the Lorentz group is given in terms of 4 X 4 matrices defined over the hyperbolic number system. The transformation properties of the corresponding four component spinor are studied, and shown to be equivalent to the transformation properties of the complex Dirac spinor. As an application, we show that there exists an algebra of automorph

A. Khavaev, K. Pilch, N. P. Warner

We analyze a particular SU(2) invariant sector of the scalar manifold of gauged N=8 supergravity in five dimensions, and find all the critical points of the potential within this sector. The critical points give rise to Anti-de Sitter vacua, and preserve at least an SU(2) gauge symmetry. Consistent truncation implies that these solutions correspond to Anti-d

Jean-Pierre Ader, Franck Biet, Yves Noirot

We derive the supersymmetric structure present in W-gravities which has been already observed in various contexts as Yang-Mills theory, topological field theories, bosonic string and chiral W_{3}-gravity. This derivation which is made in the geometrical framework of Zucchini, necessitates the introduction of an appropriate new basis of variables which replac

Mans Henningson, Kostas Skenderis

We review our calculation of the Weyl anomaly for d-dimensional conformal field theories that have a description in terms of a (d + 1)-dimensional gravity theory.

Moshe Moshe

This is a short summary of the phase structure of vector O(N) symmetric quantum field theories in a singular limit, the double scaling limit.It is motivated by the fact that summing up dynamically triangulated random surfaces using Feynman graphs of the O(N) matrix model results in a genus expansion and it provides,in some sense, a nonperturbative treatment

S. J. Brodsky, J. Rathsman

Commensurate scale relations are perturbative QCD predictions which relate observable to observable at fixed relative scale, such as the ``generalized Crewther relation&#34;, which connects the Bjorken and Gross-Llewellyn Smith deep inelastic scattering sum rules to measurements of the $e^+ e^-$ annihilation cross section. All non-conformal effects are absor

Amol Dighe, Sergio Pastor, Alexei Smirnov

We report on the main results presented at the workshop on The Physics of Relic Neutrinos. The study of relic neutrinos involves a broad spectrum of problems in particle physics, astrophysics and cosmology. Features of baryogenesis and leptogenesis could be imprinted in the properties of the relic neutrino sea. Relic neutrinos played a crucial role in the bi

Nathan Isgur

The neutron&#39;s electric form factor contains vital information on nucleon structure, but its interpretation within many models has been obscured by relativistic effects. I demonstrate that, to leading order in the relativistic expansion of a constituent quark model, the Foldy term cancels exactly against a contribution to the Dirac form factor F_1 to leav

M. J. Herrero

These lectures provide an introduction to the basic aspects of the Standard Model, $SU(3)_{C} \times SU(2)_{L} \times U(1)_{Y}$.

T. D. Blokhintseva, M. Nagy, Yu. S. Surovtsev

The process $πN\to e^+e^- N$ (IPE), being a natural and unique laboratory for studying the hadron electromagnetic structure in the sub-$N\bar{N}$-threshold time-like region of the virtual-photon ``mass&#39;&#39; $λ^2$, turns out to be also very useful for investigating the nucleon weak structure. A theoretical basis of the methods for extracting practically

Fiorenza Donato

We report the main results of a paper where recent data of low-energy cosmic-ray $\bar p$ spectrum have been analyzed in terms of newly calculated fluxes for secondary antiprotons and for a possible contribution of an exotic signal due to neutralino annihilation in the galactic halo. We also present the results of a paper in which we have proved that a sizea

Riccardo Barbieri, Leonardo Giusti, Lawrence J. Hall, Andrea Romanino

We show how a specific sequential breaking pattern of a U(2) flavour symmetry occurs automatically in a broad framework. The relative orientation in U(2) space of the spurion fields that breaks the U(2) symmetry is uniquely fixed, thus determining the form of the fermion mass matrices in a predictive way.

V. A. Petrov

This is a brief survey of the present state of ideas concerning the parton content of the nucleon spin after their ten-years evolution since the discovery of the EMC.

S. Y. Choi, A. Djouadi, H. S. Song, P. M. Zerwas

In most supersymmetric theories, charginos $\tildeχ^\pm_{1,2}$, mixtures of charged color-neutral gauginos and higgsinos, belong to the class of the lightest supersymmetric particles. They are easy to observe at $e^+e^-$ colliders. By measuring the total cross sections and the left-right asymmetries with polarized electron beams in $e^+e^-\to\tildeχ_i^-\tild

John Ellis

In the first lecture, the Standard Model is reviewed, with the aim of seeing how its successes constrain possible extensions, the significance of the apparently low Higgs mass indicated by precision electroweak experiments is discussed, and defects of the Standard Model are examined. The second lecture includes a general discussion of the electroweak vacuum

Stephen R. Sharpe

I summarize recent progress in lattice gauge theory, with particular emphasis on results from numerical simulations. A major success has been the determination of the light hadron spectrum in the quenched approximation with sufficient accuracy to expose statistically significant disagreements with the experimental spectrum. The differences are, however, fair

The ICARUS Collaboration

The 50 liter liquid Argon TPC is a detector built and successfully operated at CERN for R&D purposes within the ICARUS programme. In the year 1997 it has been exposed at the CERN neutrino beam for the entire SPS neutrino run period as proposed and approved at the SPSLC of January 1997. The detector, complemented with scintillators acting as veto, trigger cou

O. V. Bulekov, N. D. Galanina, V. S. Demidov, A. L. Endalov

The A-dependence is observed in $x_F$-distributions for the $ΛK^0$ system produced with the small transverse momentum in the neutron-nucleus interactions. For the $Λ$ hyperons similar dependence isn&#39;t seen. The result is interpreted as an effect from intermediate excitative nucleon state, which decays into strange particles. Such interpretation is confir

S. Deser

I review some ways in which spacetime dimensionality enters explicitly in gravitation. In particular, I recall some unusual geometrical gravity models that are constructible in dimensions different from four, especially in D=3 where even ordinary Einstein theory is "different", e.g., fully Machian.

Patricio S. Letelier

We give a physical interpretation to the multi-polar Erez-Rozen-Quevedo solution of the Einstein Equations in terms of bars. We find that each multi-pole correspond to the Newtonian potential of a bar with linear density proportional to a Legendre Polynomial. We use this fact to find an integral representation of the $γ$ function. These integral representati

Zoltán Perjés, Gyula Fodor, László Á. Gergely, Mattias Marklund

A rigidly rotating incompressible perfect fluid solution of Einstein&#39;s gravitational equations is discussed. The Petrov type is D, and the metric admits a four-parameter isometry group. The Gaussian curvature of the constant-pressure surfaces is positive and they have two ring-shaped cusps.

I. E. Lagaris, A. Likas, D. G. Papageorgiou

Partial differential equations (PDEs) with Dirichlet boundary conditions defined on boundaries with simple geometry have been succesfuly treated using sigmoidal multilayer perceptrons in previous works. This article deals with the case of complex boundary geometry, where the boundary is determined by a number of points that belong to it and are closely locat

A. Likas, I. E. Lagaris

A new training algorithm is presented for delayed reinforcement learning problems that does not assume the existence of a critic model and employs the polytope optimization algorithm to adjust the weights of the action network so that a simple direct measure of the training performance is maximized. Experimental results from the application of the method to

Hang LI

In this thesis, I address the problem of automatically acquiring lexical semantic knowledge, especially that of case frame patterns, from large corpus data and using the acquired knowledge in structural disambiguation. The approach I adopt has the following characteristics: (1) dividing the problem into three subproblems: case slot generalization, case depen

Philip W. Anderson

I derive equations of motion for quasiparticles near the nodes in the d-wave gap of high Tc superconductors. Previous versions have not properly taken into account the spatial dependence of the gap parameter phase. The results are compatible with magnetothermal conductivity measurements in the superconducting phase by Ong and Krishana.

M. -Carmen Miguel, J. M. Rubi

We study the behavior of an isolated field-oriented chain of dipolar particles in elongational fluid flow. Our main goal is to emphasize the effect of dipolar interactions on the chain&#39;s contribution to the pressure tensor and to the viscosities of a dilute suspension of these linear aggregates. In our model, despite the overall rigid appearance of the c

C. Stephen Hellberg, Steven C. Erwin

We demonstrate theoretically that the electronic ground state of the potassium-covered Si(111)-B surface is a Mott insulator, explicitly contradicting band theory but in good agreement with recent experiments. We determine the physical structure by standard density-functional methods, and obtain the electronic ground state by exact diagonalization of a many-

Sher Alam

Keeping in mind some salient features of quantum symmetry groups and in lieu of the interesting critique by Baskaran and Anderson of the hypothesis of the SO(5) model of Zhang and the related works of others such as Sachdev to describe superconductivity and antiferromagnetism we propose a conjecture to model these complex phenomenona by quantum groups, at le

S. Franz, T. Garel, H. Orland

We consider a model of two (fully) compact polymer chains, coupled through an attractive interaction. These compact chains are represented by Hamiltonian paths (HP), and the coupling favors the existence of common bonds between the chains. Using a ($n=0$ component) spin representation for these paths, we show the existence of a phase transition for strong co

M. Pleimling, W. Selke

Using Monte Carlo techniques, we show that the recently experimentally observed transitionlike phenomena in the transverse spin-ordering close to the anomalies in the antiferromagnetic phase of FeBr2 (Petracic et al. [Phys. Rev. B 57, R11051 (1998)]) may result from the quantum nature of the S=1 spins and an off-diagonal exchange between axial and planar spi

C. Livermore, D. S. Duncan, R. M. Westervelt, K. D. Maranowski

We present measurements of transport through two tunnel-coupled quantum dots of different sizes connected in series in a strong, variable, perpendicular magnetic field. Double dot conductance was measured both as a function of magnetic field, which was varied across the filling factor nu = 4 quantum Hall plateau, and as a function of charge induced evenly on

X. Leyronas, J. Tworzydlo, C. W. J. Beenakker

The decay of a quasiparticle in a confined geometry, resulting from electron-electron interactions, has been mapped onto the single-electron problem of diffusion on a Cayley tree by Altshuler et al. [Phys.Rev.Lett. 78, 2803 (1997)]. We study an alternative model, that captures the strong correlations between the self-energies of different excitations with th

Kamran Kaviani, Ali Dalafi Rezaie

We investigate the thermodynamic curvature resulting from a Riemannian geometry approach to thermodynamics for the Pauli paramagnetic gas which is a system of identical fermions each with spin 1/2. We observe that the absolute value of thermodynamic curvature can be interpreted as a measure of the stability of the considered system only in the classical and

S. Majumdar, R. Mallik, E. V. Sampathkumaran, P. L. Paulose

Results of low temperature magnetoresistance ($Δρ/ρ$) and isothermal magnetization (M) measurements on polycrystalline ferromagnetic (T_C close to 300 K) natural multilayers, LaMn_{2+x}Ge_{2-y}Si_y, are reported. It is found that the samples with large residual resistivity ratio, $ρ(300K)/ρ(4.2K)$, exhibit large positive magnetoresistance at high magnetic fi

M. A. Vesaghi, A. Shafiekhani

The Jahn-Teller effect used semi-theoretically to analyse UV-visible spectra of the diamond like-carbon films on Si substrates. By deconvolution of UV-visible absorption spectra of the typical films, different absorption lines found. For each sample, six lines which were related to $\V^\circ$ by Jahn-Teller effect are distinguished. Our theoretical approach

Biplab Chattopadhyay, A. N. Das

A modified version of the interlayer tunneling model, including interlayer single particle hopping (ISPH), is considered as a phenomenological model to describe cuprate superconductors. The effective ISPH (t_\perp^{eff}) is taken along with a probability factor P, that involves the normal state pseudogap (E_g). This makes t_\perp^{eff} to mimic experimental

X. R. Wang, S. C. Ma, X. C. Xie

We propose a new mechanism of negative magnetoresistance in non-magnetic granular materials in which electron transport is dominated by hopping between two nearest-neighbor clusters. We study the dependence of magnetoresistance on temperature and separation between neighboring clusters. At a small separation we find a negative magnetoresistance at low temper

L. Kaplan, E. J. Heller

The phenomenon of periodic orbit scarring of eigenstates of classically chaotic systems is attracting increasing attention. Scarring is one of the most important &#34;corrections&#34; to the ideal random eigenstates suggested by random matrix theory. This paper discusses measures of scars and in so doing also tries to clarify the concepts and effects of eige

R. Benzi, G. Amati, C. M. Casciola, F. Toschi

Well defined scaling laws clearly appear in wall bounded turbulence, even very close to the wall, where a distinct violation of the refined Kolmogorov similarity hypothesis (RKSH) occurs together with the simultaneous persistence of scaling laws. A new form of RKSH for the wall region is here proposed in terms of the structure functions of order two which, i

Eva K. Grebel, Puragra Guhathakurta

We have obtained Keck Low Resolution Imaging Spectrograph images in V and I of the newly discovered Local Group dwarf galaxies Pegasus dSph and Cassiopeia dSph and their surrounding field. The first stellar luminosity functions and color-magnitude diagrams are presented for stars with V <~ 25 and I <~ 24. The distances to the new dwarfs are estimated from th

Yanqin Wu, Peter Goldreich

We report on numerical calculations of nonadiabatic eigenvalues and eigenfunctions for g-modes in ZZ Ceti variables. The spectrum of overstable $l=1$ modes delineates the instability strip. Its blue edge occurs where $ωτ_c \approx 1$ for the $n=1$ mode. Here $ω$ is radian frequency and $τ_c$ is about four times the thermal timescale at the bottom of the surf

Mario Hamuy, Philip A. Pinto

We use Monte Carlo simulations of the Calan/Tololo photographic supernova survey to show that a simple model of the survey&#39;s selection effects accounts for the observed distributions of recession velocity, apparent magnitude, angular offset, and projected radial distance between the supernova and the host galaxy nucleus for this sample of Type Ia superno

D. C. -J. Bock, M. I. Large, Elaine M. Sadler

The Molonglo Observatory Synthesis Telescope, operating at 843 MHz with a 5 square degree field of view, is carrying out a radio imaging survey of the sky south of declination -30 deg. This survey (the Sydney University Molonglo Sky Survey, or SUMSS) produces images with a resolution of 43&#34; x 43&#34; cosec(Dec.) and an rms noise level of about 1 mJy/beam

Neil Trentham, A. W. Blain, Jeff Goldader

A major recent development in extragalactic astronomy has been the discovery of a population of galaxies that are luminous at submillimetre wavelengths. Estimates of their spectral energy distributions suggest that these galaxies are the high-redshift analogues of the ultraluminous infrared galaxies (ULIGs) observed locally. We identify plausible (but non-un

Paul A. Crowther, S. C. Beck, Allan J. Willis, Peter S. Conti

ISO-SWS spectroscopy of the WR galaxy NGC5253 is presented, and analysed to provide estimates of its hot young star population. Our approach differs from previous investigations in that we are able to distinguish between the regions in which different infrared fine-structure lines form, using complementary ground-based observations. The high excitation nebul

G. Ghisellini, A. Celotti

Quasi-thermal Comptonization in internal shocks formed between relativistic shells can account for the high energy emission of gamma-ray bursts. This is in fact the dominant cooling mechanism if the typical energy of the emitting particles is achieved either through the balance between heating and cooling or as a result of electron-positron pair production.

T. J. Davidge, S. Courteau

The Canada-France-Hawaii Telescope (CFHT) Adaptive Optics Bonnette (AOB) has been used to obtain high angular resolution JHK images of the centers of the metal-poor globular clusters NGC5272 (M3), NGC6205 (M13), NGC6287, and NGC6341 (M92). The color-magnitude diagrams (CMDs) derived from these data include the upper main sequence and most of the red giant br

C. Brocksopp, A. E. Tarasov, V. M. Lyuty, P. Roche

By accumulating all available radial velocity data and combining it with our own spectroscopy we present a new and improved ephemeris for Cygnus X-1 (V1357 Cygni/HDE226868). We initially calculate an orbital period of 5.599847+/-0.000018.days and then, by including the more recent radial velocities of LaSala et al. (1998) and Sowers et al.(1998) we refine th

You-Hua Chu, Kerstin Weis, Donald R. Garnett

We have selected the seven most well-defined WR ring nebulae in the LMC (Br 2, Br 10, Br 13, Br 40a, Br 48, Br 52, and Br 100) to study their physical nature and evolutionary stages. New CCD imaging and echelle observations have been obtained for five of these nebulae; previous photographic imaging and echelle observations are available for the remaining two

Frederic Pont

More than two hundred classical cepheids were measured by the Hipparcos astrometric satellite, making possible a geometrical calibration of the cepheid distance scale. However, the large average distance of even the nearest cepheids measured by Hipparcos implies trigonometric parallaxes of at most a few mas. Determining unbiased distances and absolute magnit

G. I. Ogilvie

The dynamics of a viscous accretion disc subject to a slowly varying warp of large amplitude is considered. Attention is restricted to discs in which self-gravitation is negligible, and to the generic case in which the resonant wave propagation found in inviscid Keplerian discs does not occur. The equations of fluid dynamics are derived in a coordinate syste

D. A. Baiko, D. G. Yakovlev

The effect of the magnetic field on the energy loss rate in the direct Urca reactions is studied. The general expression for the neutrino emissivity at arbitrary magnetic field B is derived. The main emphasis is laid on a case, in which the field is not superstrong, and charged reacting particles (e and p) populate many Landau levels. The magnetic field keep