January 1999 arXiv papers — page 8

D. T. Frayer, R. J. Ivison, N. Z. Scoville, A. S. Evans

We report the detection of CO(3-2) emission from the submillimeter-selected luminous galaxy SMM J14011+0252. The optical counterpart of the submillimeter source has been identified as a merger system with spectral characteristics consistent with a starburst at z=2.565. The CO emission confirms the optical identification of the submillimeter source and implie

B. Otte, R. -J. Dettmar

Spectroscopic measurements of emission line ratios and velocities are presented for ionized gas across the central plane of NGC 55, a late-type galaxy in the Sculptor group. The low metallicity in NGC 55 leads to relatively low line ratios of [S II]/H$α$ and [N II]/H$α$ for H II regions as well as the diffuse ionized gas. These are the first spectroscopical

Philip T. Komljenovic, Shantanu Basu, Doug Johnstone

Recent high resolution observations of Galactic superbubbles have motivated us to re-examine several classes of superbubble models. We compare three classes of hydrodynamic models (the Kompaneets approximation, the thin shell model, and numerical simulations) in order to understand the structure of superbubbles and to gain insight into observations. In parti

Laura E. Kay, A. M. Magalhaes, F. Elizalde, C. Rodrigues

We observed the narrow-line Seyfert 1 galaxies IRAS 20181-2244 and IRAS 13324-3809 with a new spectropolarimeter on the RC spectrograph at the CTIO 4m telescope. Previously it had been suggested that IRAS 20181-2244 was a Type 2 QSO and thus might contain an obscured broad-line region which could be detected by the presence of broad Balmer lines in the polar

Leo Blitz, David N. Spergel, Peter J. Teuben, Dap Hartman

Hierarchical structure formation models predict the existence of large numbers of low velocity dispersion dark halos. Galaxy surveys find far fewer galaxies than predicted by analytical estimates and numerical simulations. In this paper, we suggest that these dark halos are not missing, but have been merely misplaced in the galactic astronomy section of the

Kim Venn

New abundances of N, O, Na, Mg, Si, Ca, Sc, Ti, Cr, Fe, Sr, Zr, and Ba are presented for 10 A-type supergiants in the SMC, plus upper limits for C. In interpreting the CNO results for constraints on stellar evolution theories, careful attention has been paid to the comparison abundances, i.e., the present day abundances of SMC nebulae and B-dwarf stars. Thes

Wlodzimierz Kluzniak, William H. Lee

We used a newtonian SPH (smooth-particle hydrodynamics) code to follow the final stages of evolution of a coalescing binary system of a neutron star and a black hole. We find that the outcome of the "merger" is very sensitive to the equation of state describing the neutron star. A neutron star with a soft equation of state (polytrope with index Gamma

A. N. Lasenby, S. L. Bridle, M. P. Hobson

Observations of the Cosmic Microwave Background (CMB), large scale structure (LSS) and standard candles such as Type 1a Supernovae (SN) each place different constraints on the values of cosmological parameters. We assume an inflationary Cold Dark Matter model with a cosmological constant, in which the initial density perturbations in the universe are adiabat

L. Morales-Rueda, M. D. Still, P. Roche

We detect the likely optical counterpart to previously reported X-ray QPOs in spectrophotometry of the intermediate polar GK Persei during the 1996 dwarf nova outburst. The characteristic timescales range between 4000--6000 s. Although the QPOs are an order of magnitude longer than those detected in the other dwarf novae we show that a new QPO model is not r

A. J. Connolly, A. S. Szalay

Over the next few years new spectroscopic surveys (from the optical surveys of the Sloan Digital Sky Survey and the 2 degree Field survey through to space-based ultraviolet satellites such as GALEX) will provide the opportunity and challenge of understanding how galaxies of different spectral type evolve with redshift. Techniques have been developed to class

Boudewijn F. Roukema, David Valls-Gabaud, Bahram Mobasher, Stanislaw Bajtlik

The amplitude of the angular two-point galaxy correlation function w(θ) for galaxies at z~2 is estimated for galaxies in the Hubble Deep Field by using a U < 27 complete sub-sample. (i) It is confirmed that the amplitude of the correlation can be corrected for the integral constraint without having to make assumptions about the shape of the correlation funct

Nikolai Chugai, Sergei Blinnikov, Peter Lundqvist

A hydro code coupled with radiation transfer was applied to produce monochromatic light curves of two models of type II supernovae (SN II) simulating SN II-P and SN IIb (SN 1993J-like). We then used these template light curves to evaluate the possibility of detecting SNe II at different redshifts. With a 5 hour exposure at VLT/FORS the SN II-P model may be d

Jean-Pierre Lasota

I present a short review of irradiation processes in close binary systems.

A. R. King, U. Kolb

We show that neither accretion nor angular momentum extraction are likely to lead to significant changes in the mass M_1 or angular momentum parameter a_* of a black hole in a binary system with realistic parameters. Current values of M_1 and a_* therefore probably reflect those at formation. We show further that sufficiently energetic jet ejection powered b

Jean-Pierre Lasota, Erik Kuulkers, Phil Charles

We argue that quiescent WZ Sge is a rapidly spinning magnetic rotator in which most of the matter transfered from the secondary is ejected from the system. Assuming that the observed 27.87 s oscillation period is due to the spinning white dwarf we propose that the other observed principal period of 28.96 s is a beat due to reprocessing of the rotating white

Y. Alibert, I. Baraffe, P. Hauschildt, F. Allard

Based on consistent evolutionary and pulsation calculations, we analyse the effect of metallicity and of different convection treatments in the stellar models on period - magnitude, - color and - radius relationships. In order to perform an accurate comparison with observations, we have computed grids of atmosphere models and synthetic spectra for different

K. Jedamzik, J. C. Niemeyer

Primordial black holes (PBHs) may form in the early universe when pre-existing adiabatic density fluctuations enter into the cosmological horizon and recollapse. It has been suggested that PBH formation may be facilitated when fluctuations enter into the horizon during a strongly first-order phase transition which proceeds in approximate equilibrium. We empl

J. C. Niemeyer, K. Jedamzik

We present a numerical investigation of the gravitational collapse of horizon-size density fluctuations to primordial black holes (PBHs) during the radiation-dominated phase of the Early Universe. The collapse dynamics of three different families of initial perturbation shapes, imposed at the time of horizon crossing, is computed. The perturbation threshold

M. Joyce, M. Montuori, F. Sylos Labini

We report our analysis of the properties of galaxy clustering for a new redshift sample of galaxies, the CfA2-South catalog, using statistical methods which do not rely on the assumption of homogeneity. We find that, up to ~ 20 Mpc/h, which is the largest scale to which correlation properties can be reliably inferred, the galaxy clustering is scale-invariant

O. Semerak, V. Karas

Several topics are discussed regarding the pseudo-Newtonian models of the gravitational field around rotating black holes

Paolo Padoan, AAke Nordlund

Supersonic random motions are observed in dark clouds and are traditionally interpreted as Alfven waves, but the possibility that these motions are super-Alfvenic has not been ruled out. In this work we report the results of numerical experiments in two opposite regimes; M_a ~ 1 and M_a >> 1, where M_a is the initial Alfvenic Mach number --the ratio of the r

Bhuvnesh Jain, Uros Seljak, Simon White

Selected results on estimating cosmological parameters from simulated weak lensing data with noise are presented. Numerical simulations of ray tracing through N-body simulations have been used to generate shear and convergence maps due to lensing by large-scale structure. Noise due to the intrinsic ellipticities of a finite number of galaxies is added. In th

Hee Il Kim, Bum-Hoon Lee, Chul H. Lee

We propose that the amplified density fluctuations by the vanishing sound velocity effect during the cosmological quark-hadron phase transition lead to quark-gluon plasma lumps decoupled from the expansion of the universe, which may evolve to quark nuggets (QNs). Assuming power-law spectrum of density fluctuations, we investigate the parameter ranges for the

Lewis Ball, Andrew Melatos, Simon Johnston, Olaf Skjaeraasen

We discuss the interpretation of transient, unpulsed radio emission detected from the unique pulsar/Be-star binary system PSR B1259-63. Extensive monitoring of the 1994 and 1997 periastron passages has shown that the source flares over a 100-day interval around periastron, varying on time-scales as short as a day and peaking at 60 mJy (~100 times the apastro

Dean E. McLaughlin

(Abridged): The total populations of globular cluster systems (GCSs) are discussed in terms of their connection to the efficiency of globular cluster formation---the mass fraction of star-forming gas that was able to form bound stellar clusters rather than isolated stars or unbound associations---in galaxy halos. Observed variations in GCS specific frequenci

Antonio Riotto, Mark Trodden

We provide an up to date account of progress in understanding the origin of the observed baryon asymmetry of the universe. While our primary goal is to be current, we have attempted to give a pedagogical introduction to the primary areas of research in this field, giving a detailed description of the different scenarios. The very recent developments in GUT b

W. Losert, D. G. W. Cooper, J. Delour, A. Kudrolli

We present an experimental study of velocity statistics for a partial layer of inelastic colliding beads driven by a vertically oscillating boundary. Over a wide range of parameters (accelerations 3-8 times the gravitational acceleration), the probability distribution P(v) deviates measurably from a Gaussian for the two horizontal velocity components. It can

G. Bonelli, L. Bonora, F. Nesti, A. Tomasiello

The correspondence between Matrix String Theory in the strong coupling limit and IIA superstring theory can be shown by means of the instanton solutions of the former. We construct the general instanton solutions of Matrix String Theory which interpolate between given initial and final string configurations. Each instanton is characterized by a Riemann surfa

D. Amati, J. G. Russo

We show that the decay spectrum of massive excitations in perturbative string theories is thermal when averaged over the (many) initial degenerate states. We first compute the inclusive photon spectrum for open strings at the tree level showing that a black body spectrum with the Hagedorn temperature emerges in the averaging. A similar calculation for a mass

Rikard von Unge

We use toric geometry to investigate the recently proposed relation between a set of D3 branes at a generalized conifold singularity and type IIA configurations of D4 branes stretched between a number of relatively rotated NS5 branes. In particular we investigate how various resolutions of the singularity corresponds to moving the NS branes and how Seiberg&#

B. Geyer, M. Lazar, D. Robaschik

Bilocal light-ray operators which are Lorentz scalars, vectors or antisymmetric tensors, and which appear in various hard scattering QCD processes, are decomposed into operators of definite twist. These operators are harmonic tensor functions and their Taylor expansion consists of (traceless) local light-cone operators with span irreducible representations o

G. Ricco, S. Simula, M. Battaglieri

Power corrections to the Q**2 behaviour of the low-order moments of both the longitudinal and transverse structure functions of proton and deuteron have been investigated using available phenomenological fits of existing data in the Q**2 range between 1 and 20 (GeV/c)**2. The Natchmann definition of the moments has been adopted for disentangling properly tar

A. Gorsky, N. Nekrasov, V. Rubtsov

We explain Sklyanin&#39;s separation of variables in geometrical terms and construct it for Hitchin and Mukai integrable systems. We construct Hilbert schemes of points on $T^{*}Σ$ for $Σ= {\IC}, {\IC}^{*}$ or elliptic curve, and on ${\bf C}^{2}/Γ$ and show that their complex deformations are integrable systems of Calogero-Sutherland-Moser type. We present t

P. F. L. Maxted, T. R. Marsh

We present the results of a radial velocity survey designed to measure the fraction of double degenerates among DA white dwarfs. The narrow core of the H-alpha line was observed twice or more for 46 white dwarfs yielding radial velocities accurate to a few km/s. This makes our survey the most sensitive to the detection of double degenerates undertaken to dat

Yaron Oz, Donam Youm

We construct the supergravity solution for the intersecting D1-D5 brane system in Type I String Theory. The solution encodes the dependence on all the electric charges of the SO(32) gauge group. We discuss the near horizon geometry of the solution and a proposed dual (0,4) superconformal field theory.

Luis Quiroga, Neil F. Johnson

We show that excitons in coupled quantum dots are ideal candidates for reliable preparation of entangled states in solid-state systems. An optically controlled exciton transfer process is shown to lead to the generation of Bell and GHZ states in systems comprising two and three coupled dots, respectively. The strength and duration of selective light-pulses f

Anne M Green, Andrew R Liddle

It has normally been assumed that primordial black holes (PBHs) always form with mass approximately equal to the mass contained within the horizon at that time. Recent work studying the application of critical phenomena in gravitational collapse to PBH formation has shown that in fact, at a fixed time, PBHs with a range of masses are formed. When calculating

Iver Brevik, Valery Marachevsky

The Casimir surface force density F on a dielectric dilute spherical ball of radius a, surrounded by a vacuum, is calculated at zero temperature. We treat (n-1) (n being the refractive index) as a small parameter. The dispersive properties of the material are taken into account by adopting a simple dispersion relation, involving a sharp high frequency cutoff

Mohammad R. Garousi

We derive fully covariant expressions for all two-point scattering amplitudes involving closed string tachyon and massless strings from Dirichlet brane in type 0 theories. The amplitude for two massless D-brane fluctuations to produce closed string tachyon is also evaluated. We then examine in detail these string scattering amplitudes in order to extract wor

S. Fujii, R. Okamoto, K. Suzuki

A method is formulated for the description of lambda hypernuclei in the framework of the unitary-model-operator approach (UMOA). The method is applied to $_{\Lambda}^{17}$O. A lambda-nucleon effective interaction is derived, taking the coupling of the sigma-nucleon channel into account. The lambda single-particle energies are calculated for the 0s_{1/2}, 0p_

Curtis V. Manning

A satisfactory theory for the formation of globular star clusters (GCs) has long been elusive, perhaps because their true progenitors had not yet been guessed. In this paper I propose a causal relationship between the strongly decreasing densities of Lyman alpha (LyA) clouds at high redshift and the formation of GCs - namely that GCs were created by the accr

Maciej Lewenstein, Kazimierz Rzazewski

We demonstrate that near threshold decay processes may be accelerated by repeated measurements. Examples include near threshold photodetachment of an electron from a negative ion, and spontaneous emission in a cavity close to the cutoff frequency, or in a photon band gap material.

Shoju Kudaka, Shuichi Matsumoto

When we quantize a system consisting of a single particle, the proper time $τ$ and the rest mass $m$ are usually dealt with as parameters. In the present article, however, we introduce a new quantization rule by which these quantities are regarded as operators in addition to the position and the momentum. Applying this new rule to a scalar particle and to a

Svetlana Sytova

The objective of this article is to study the behavior of electromagnetic field under X-ray diffraction by time-dependent deformed crystals. Derived system of differential equations looks like the Takagi equations in the case of non-stationary crystals. This is a system of multidimensional first-order hyperbolic equations with complex time-dependent coeffici

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

We investigate the impact parameter dependence of the specific entropy S/A in relativistic heavy ion collisions. Especially the anti-Lambda/anti-proton ratio is found to be a useful tool to distinguish between chemical equilibrium assumptions assumed in hydrodynamics (here: the 3-fluid model) and the chemical non-equilibrium scenario like in microscopic mode

S. Scherer

These lectures give a pedagogical introduction to real and virtual Compton scattering at low energies. We will first discuss real Compton scattering off a point particle as well as a composite system in the framework of nonrelativistic quantum mechanics. The concept of electromagnetic polarizabilities is introduced. We then address a description of the Compt

S. B. Gerasimov

The reaction $pp \to pp2γ$, proposed earlier to probe for the NN--decoupled dibaryon resonances, has been studied by the DIB$2γ$ Collaboration (JINR) and their preliminary data seem to give evidence for the resonance effect at about 1920 MeV. We discuss some other two-photon processes: the double radiative capture reaction in pionic deuterium, photoabsorptio

Michael Baake

This introductory survey deals with mathematical and physical properties of discrete structures such as point sets and tilings. The emphasis is on proper generalizations of concepts and ideas from classical crystallography. In particular, we focus on their interplay with various physically motivated equivalence concepts such as local indistinguishability and

S. P. Hrabak

A geometric multisymplectic formulation of the classical BRST symmetry of constrained first-order classical field theories is described. To effect this we introduce graded analogues of the bundles and manifolds of the multisymplectic formulation of first-order field theories. The Lagrange-d&#39;Alembert formalism is also developed in terms of the multisymple

S. P. Hrabak

We describe a new algebraic multisymplectic formulation of the classical BRST symmetry. The analogue of Marsden-Weinstein reduction for multisymplectic manifolds is described. We then give a homological description of Multisymplectic Marsden-Weinstein reduction.

Kirti Joshi

In this note we prove the non existence of certain irreducible two dimensional representations of the the absolute Galois group. Such results are predicted by Serre&#39;s conjecture and we use Fontaine&#39;s methods to verify these predictions in a small number of cases. We also use a methods of Faltings to study certain finiteness conjectures for Galois rep

Q. Ye

We first classify the possible configurations of fibrations which are not semi-stable on extremal elliptic K3 surfaces. Then we give a complete list of extremal elliptic K3 surfaces whose singular fibers are all not of type $I_n$.

M. Havlíček, A. U. Klimyk, S. Pošta

An algebra homomorphism $ψ$ from the q-deformed algebra $U_q({\rm iso}_2)$ with generating elements $I$, $T_1$, $T_2$ and defining relations $[I,T_2]_q=T_1$, $[T_1,I]_q=T_2$, $[T_2,T_1]_q=0$ (where $[A,B]_q=q^{1/2}AB-q^{-1/2}BA$) to the extension ${\hat U}_q({\rm m}_2)$ of the Hopf algebra $U_q({\rm m}_2)$ is constructed. The algebra $U_q({\rm iso}_2)$ at $q

Denis V. Juriev

Procedures of the short-term predictions for processes in general 2-person differential interactive games are proposed. Their effectiveness is discussed.

Dmitry Kleinbock

We prove an inhomogeneous analogue of W. M. Schmidt&#39;s (1969) theorem on Hausdorff dimension of the set of badly approximable systems of linear forms. The proof is based on ideas and methods from the theory of dynamical systems, in particular, on abundance of bounded orbits of mixing flows on homogeneous spaces of Lie groups.

Pierre Deligne, Daniel S. Freed

We develop classical globally supersymmetric theories. As much as possible, we treat various dimensions and various amounts of supersymmetry in a uniform manner. We discuss theories both in components and in superspace. Throughout we emphasize geometric aspects. The beginning chapters give a general discussion about supersymmetric field theories; then we mov

V. Frolov, D. Fursaev, J. Gegenberg, G. Kunstatter

In this paper we describe a Liouville gravity which is induced by a set of quantum fields (constituents) and represents a two-dimensional analog of Sakharov&#39;s induced gravity. The important feature of the considered theory is the presence of massless constituents which are responsible for the appearance of the induced Liouville field. The role of the mas

Eugene Perevalov

We explore a relation between four-dimensional N=2 heterotic vacua induced by Mirror Symmetry via Heterotic/Type II duality. It allows us to compute the α&#39; corrections to the hypermultiplet moduli space of heterotic compactifications on K3xT^2 in the limit of large base of the elliptic K3. We concentrate on the case of point-like instantons on orbifold s

C. Hamzaoui, M. Pospelov

The bounds on the neutron electric dipole moment and T-odd nucleon-nucleon interaction are used to extract the limits on the effective CP-odd four-fermion operators containing strange quark field. This completes the study of the dim=5,6 CP-odd operators built from the light-quark fields. The limits are very strong and comparable to those obtained previously

G. I. Gakh, V. Yu. Gonchar, N. P. Merenkov

Analitical calculations have been used to describe the calorimeter event selection in small-angle electron-positron scattering at LEP1. The first-order QED correction to the Born cross-section has been derived with leading log and the next-to-leading log approximations. The second- and the third-order corrections were computed with leading accuracy. The pres

H. Spiesberger, M. W. Krasny

Existing and missing calculations of standard model processes producing large transverse energy in electron-proton interactions at HERA are reviewed. The adequacy of the existing standard model Monte Carlo programs for generic searches of exotic processes is analyzed.

Roman Jackiw, Alan Kostelecky

In a nonperturbative formulation, radiative corrections arising from Lorentz and CPT violation in the fermion sector induce a definite and nonzero Chern-Simons addition to the electromagnetic action. If instead a perturbative formulation is used, an infinite class of theories characterized by the value of the Chern-Simons coefficient emerges at the quantum l

R. Jeannerot, X. Zhang, R. Brandenberger

We propose a mechanism of nonthermal production of a neutralino cold dark matter particle, $\chi$, from the decay of cosmic strings which form from the spontaneous breaking of a U(1) gauge symmetry, such as $U_{B-L}(1)$, in an extension of the minimal supersymmetric standard model (MSSM). By explicit calculation, we point out that with a symmetry breaking sc

E. E. Zabrodin, L. V. Bravina, H. Stoecker, W. Greiner

Heavy ion collisions at ultrarelativistic energies offer the opportunity to study the irreversibility of multiparticle processes. Together with the many-body decays of resonances, the multiparticle processes cause the system to evolve according to Prigogine&#39;s steady states rather than towards statistical equilibrium. These results are general and can be

G. Giacomelli, M. Spurio

After some generalities on neutrino oscillations and on neutrinos, the recent experimental results presented by Soudan 2, MACRO and SuperKamiokande at the Neutrino&#39;98 conference are summarized and discussed.

Yongseok Oh, Wolfram Weise

We analyse the baryon mass spectrum in a framework which combines the 1/Nc expansion with chiral perturbation theory. Meson loop contributions involving the full SU(3) octet of pseudoscalar Goldstone bosons are evaluated, and the influence of explicit chiral and flavor symmetry breaking by non-zero and unequal quark masses is investigated. We also discuss si

Alexander Kusenko

Fragmentation of the Affleck-Dine condensate into Q-balls could fill the Universe with dark matter either in the form of stable baryonic balls, or LSP produced from the decay of unstable Q-balls. The dark matter and the ordinary matter in the Universe may share the same origin.

Yoav Achiman

Asymmetric mass matrices can induce large RH mixings. Those are non- measurable in the SM but are there and play an important role in its extensions. The RH rotations are in particular relevant for the proton decay, neutrino properties and baryon asymmetry. E.g. large RH mixings lead to kaon dominated proton decay even without SUSY and could be the reason fo

B. Bloch-Devaux

Preliminary but close to final results on the Z lineshape and Forward-Backward asymmetries from the four LEP experiments are presented. Combined values extracted from ALEPH. DELPHI, L3 and OPAL data recorded at energies around the Z pole are discussed.

N. T. Bishop, R. Gomez, L. Lehner, M. Maharaj

A code that implements Einstein equations in the characteristic formulation in 3D has been developed and thoroughly tested for the vacuum case. Here, we describe how to incorporate matter, in the form of a perfect fluid, into the code. The extended code has been written and validated in a number of cases. It is stable and capable of contributing towards an u

A. Barvinsky, A. Kamenshchik, C. Kiefer

We develop the formalism for the one-loop no-boundary state in a cosmological model with fermions. We use it to calculate the reduced density matrix for an inflaton field by tracing out the fermionic degrees of freedom, yielding both the fermionic effective action and the standard decoherence factor. We show that dimensional regularisation of ultraviolet div

Sukratu Barve, T. P. Singh, Cenalo Vaz, Louis Witten

We describe a simple method of determining whether the singularity that forms in the spherically symmetric collapse of inhomogeneous dust is naked or covered. This derivation considerably simplifies the analysis given in the earlier literature, while giving the same results as have been obtained before.

Tao Jiang, Ming Li, Paul Vitanyi

We prove a general lower bound on the average-case complexity of Shellsort: the average number of data-movements (and comparisons) made by a $p$-pass Shellsort for any incremental sequence is $Ω(pn^{1 + 1/p)$ for all $p \leq \log n$. Using similar arguments, we analyze the average-case complexity of several other sorting algorithms.

Andrew Odlyzko

The conversion of scholarly journals to digital format is proceeding rapidly, especially for those from large commercial and learned society publishers. This conversion offers the best hope for survival for such publishers. The infamous &#34;journal crisis&#34; is more of a library cost crisis than a publisher pricing problem, with internal library costs muc

Ramiro Pino, Victor M. Villalba

We compute the energy levels of a 2D Hydrogen atom when a constant magnetic field is applied. With the help of a mixed-basis variational method and a genera lization of virial theorem, which consists in scaling the wave function, we calculate the binding energies of the 1S, $2P^-$ and $3D^-$ levels. We compare the computed energy spectra with those obtained

J. F. Fernandez, Carlos Criado

We propose a simple algorithm for generating normally distributed pseudo random numbers. The algorithm simulates N molecules that exchange energy among themselves following a simple stochastic rule. We prove that the system is ergodic, and that a Maxwell like distribution that may be used as a source of normally distributed random deviates follows when N ten

D. A. Gorokhov, G. Blatter

We consider the singularities of the zero temperature renormalization group flow for random elastic manifolds. When starting from small scales, this flow goes through two particular points $l^{*}$ and $l_{c}$, where the average value of the random squared potential $<U^{2}>$ turnes negative ($l^{*}$) and where the fourth derivative of the potential correlato

V. I. Yukalov

The occurrence of mesoscopic fluctuations in statistical systems implies, from the point of view of dynamical theory, the existence of local instabilities. However, the presence of such fluctuations can make a system, as a whole, more stable from the thermodynamic point of view. Thus, in many cases, a local dynamic instability is a requisite for the global t

T. Muller, W. Selke

Using kinetic Monte Carlo simulations and a bond-counting ansatz, thermal stability and diffusion of an adatom island on a crystal surface are studied. At low temperatures, the diffusion constant $D$ is found to decrease for a wide range of island sizes like $D \propto N^{-α}$, where $α$ is close to one, $N$ being the number of adatoms in the cluster. By hea

P. Castiglione, A. Crisanti

The diffusive properties in velocity fields whose small scales are parameterized by non $δ$-correlated noise is investigated using multiscale technique. The analytical expression of the eddy diffusivity tensor is found for a 2D steady shear flow and it is an increasing function of the characteristic noise decorrelation time $τ$. In order to study a generic f

Peiqing Tong, Baowen Li, Bambi Hu

We study the transmission coefficient of a plane wave through a 1D finite quasi-periodic system -- the Frenkel-Kontorova (FK) model -- embedding in an infinite uniform harmonic chain. By varying the mass of atoms in the infinite uniform chain, we obtain the transmission coefficients for {\it all} eigenfrequencies. The phonon localization of the incommensurat

Wei Chen, Kazuo Hida

The one dimensional S=1/2 XXZ model with dimerization (1-j) and quadrumerization δis studied by the numerical exact diagonalization of finite size systems. Using the conformal field theory and the level spectroscopy method, we calculate the ground state phase diagram with XY-like anisotropy Δ(0<Δ<1). The ground states of this model contain the Haldane state,

Mitake Miyazaki, Keita Kishigi, Yasumasa Hasegawa

We have investigated the transition temperature $T_{\rm c}(H)$ of superconductiv ity in quasi-two-dimensional (Q2D) tight-binding electrons in a strong magnetic field. When the magnetic field is parallel to 2D conducting plane, $T_{\rm c}(H) $ of the Q2D superconductor is shown to increase in an oscillatory manner as the magnetic field becomes large and to r

Dung-Hai Lee

The purpose of this paper is to identify an unsettled issue in the theory of the half-filled Landau level, and state our point of view.

B. Sriram Shastry, Diptiman Sen

We introduce and study an exactly solvable model of several species of fermions in which particles interact pairwise through a mutual magnetic field; the interaction operates only between particles belonging to different species. After an unitary transformation, the model reduces to one in which each particle sees a magnetic field which depends on the total

Revaz Ramazashvili

I study a quantum Lifshitz point in a three-dimensional itinerant antiferromagnet, in particular the scaling of the Néel temperature, the correlation length, the staggered susceptibility, the specific heat coefficient and the resistivity. At low temperatures, the model is shown to have the inverse staggered susceptibility and the resistivity varying as T$^{5

V. Fiorentini, F. Bernardini, F. Della Sala, A. DiCarlo

Huge built-in electric fields have been predicted to exist in wurtzite III-V nitrides thin films and multilayers. Such fields originate from heterointerface discontinuities of the macroscopic bulk polarization of the nitrides. Here we discuss the background theory, the role of spontaneous polarization in this context, and the practical implications of built-

David J. Christini, Daniel T. Kaplan

Dynamical control of excitable biological systems is often complicated by the difficult and unreliable task of pre-control identification of unstable periodic orbits (UPOs). Here we show that, for both chaotic and nonchaotic systems, UPOs can be located, and their dynamics characterized, during control. Tracking of system nonstationarities emerges naturally

L. P. Horwitz, Y. Ashkenazy

The basic work of Zaslavskii et al showed that the classical non-relativistic electromagnetically kicked oscillator can be cast into the form of an iterative map on the phase space; the resulting evolution contains a stochastic flow to unbounded energy. Subsequent studies have formulated the problem in terms of a relativistic charged particle in interaction

Y. Ashkenazy, L. P. Horwitz

A charged particle circling in a uniform magnetic field and kicked by an electric field is considered. Under the assumption of small magnetic field, an iterative map is developed. Comparison between the (relativistic) non-radiative case and the (relativistic) radiative case shows that in both cases one can observe a stochastic web structure, and that both ca

The MACHO Collaboration, D. L. Welch, C. Alcock, R. A. Allsman

In this paper, we will review major new results regarding classical Cepheids, in the Large Magellanic Cloud (LMC) and Small Magellanic Cloud (SMC). Specifically, we discuss recent work regarding multimode Cepheids and describe new observations of a W Vir star (HV 5756) and a Cepheid which are each in eclipsing binary systems. An additional interesting pulsat

Joe Mohr, Ben Mathiesen, Gus Evrard

We present a systematic analysis of the intracluster medium (ICM) in an X-ray flux limited sample of 45 galaxy clusters. Using archival ROSAT PSPC data and published ICM temperatures, we present best fit double and single beta model profiles and extract ICM central densities and radial distributions. We use numerical cluster simulations to estimate uncertain

J. Michael Shull, Steven V. Penton, John T. Stocke

The low-redshift Ly-alpha forest of absorption lines provides a probe of large-scale baryonic structures in the intergalactic medium, some of which may be remnants of physical conditions set up during the epoch of galaxy formation. We discuss our recent Hubble Space Telescope (HST) observations and interpretation of low-z Ly-alpha clouds toward nearby Seyfer

Gary P. Zank, Priscilla C. Frisch

The interaction of the heliosphere with interstellar clouds has attracted interest since the late 1920&#39;s, both with a view to explaining apparent quasi-periodic climate &#34;catastrophes&#34; as well as periodic mass extinctions. Until recently, however, models describing the solar wind - local interstellar medium (LISM) interaction self-consistently had

J. Alvarez-Muñiz, R. A. Vázquez, E. Zas

We discuss the possibilities of detecting radio pulses from high energy showers in ice, such as those produced by PeV and EeV neutrino interactions. It is shown that the rich radiation pattern structure in the 100 MHz to few GHz allows the separation of electromagnetic showers induced by photons or electrons above 100 PeV from those induced by hadrons. This

P. Sreekumar, D. L. Bertsch, R. C. Hartman, P. L. Nolan

EGRET has detected 67 sources associated with active galactic nuclei. With the exception of radio galaxy Cen A, all are classified as belonging to the blazar class of active galactic nuclei. The cumulative exposure from multiple EGRET observations has provided the first clear detection of Centaurus A. Unlike the \gr blazars seen by EGRET which are believed t

E. Ros, J. M. Marcaide, J. C. Guirado, M. A. Perez-Torres

The VLBI technique can image compact radio sources with resolutions of the order of the milliarcsecond and can determine astrometrically relative positions with submilliarcsecond precisions. We determined the angular separations among the radio sources in the triangle 1803+784/1928+738/2007+777 with submilliarcsecond accuracy from a weighted least squares an

Smita Mathur, Martin Elvis, Belinda Wilkes

We have observed the much studied Seyfert 1 galaxy NGC5548 with the GHRS spectrometer on HST. Our 14ksec observation covers the CIV emission line at a resolution of >20,000. Our purpose was to study the absorption line found at lower resolution by IUE and HST/FOS. We found that the CIV absorption line resolves into 6 separate doublets with EWs of 0.07Å--0.38

Seb Oliver

The European Large Area ISO Survey (ELAIS) has surveyed ~12 square degrees of the sky at 15mu and 90mu and subsets of this area at 6.75mu and 175mu using the Infrared Space Observatory (ISO). This project was the largest single open time programme executed by ISO, taking 375 hours of data. A preliminary catalogue of more than 1000 galaxies has been produced.

Seb Oliver

Surveys with ISO (Kessler et al 1996), in particular with the CAM (Cesarsky et al 1996) and PHOT (Lemke et al 1996) instruments, will greatly extend our understanding of extra-galactic populations and their cosmological evolution. The main advantages that ISO surveys have over e.g IRAS are increased sensitivity/depth and wavelength coverage. Within the Guara