January 2000 arXiv papers — page 15

M. Pleimling, W. Selke

The two-dimensional Ising model with fixed magnetization is studied using Monte Carlo techniques. At the coexistence line, the macroscopic, extensive droplet of minority spins becomes thermally unstable by breaking up into microscopic clusters. Intriguing finite--size effects as well as singularities of thermal and cluster properties associated with the tran

A. B. Kuz'menko, D. van der Marel, P. J. M. van Bentum, E. A. Tishchenko

Optical properties of single-crystal monoclinic CuO in the range 70 - 6000 \cm were studied at temperatures from 7 to 300 K. Normal reflection spectra were obtained from the (001) and (010) crystal faces thus giving for the first time separate data for the $A_{u}$ and $B_{u}$ phonon modes excited in the purely transverse way (TO modes). Mode parameters, incl

Jae Dong Noh, Deok-Sun Lee, Doochul Kim

We investigate symmetry properties of the Bethe ansatz wave functions for the Heisenberg $XXZ$ spin chain. The $XXZ$ Hamiltonian commutes simultaneously with the shift operator $T$ and the lattice inversion operator $V$ in the space of $Ω=\pm 1$ with $Ω$ the eigenvalue of $T$. We show that the Bethe ansatz solutions with normalizable wave functions cannot be

O. Kiriyama, M. Maruyama, F. Takagi

The chiral phase transition at finite temperature T and/or chemical potential $μ$ is studied using the QCD-like theory with a variational approach. The ``QCD-like theory'' means the improved ladder approximation with an infrared cutoff in terms of a modified running coupling. The form of Cornwall-Jackiw-Tomboulis effective potential is modified by th

M. Jimbo, H. Konno, S. Odake, Y. Pugai

The Wakimoto construction for the quantum affine algebra U_q(\hat{sl}_2) admits a reduction to the q-deformed parafermion algebras. We interpret the latter theory as a free field realization of the Andrews-Baxter-Forrester models in regime II. We give multi-particle form factors of some local operators on the lattice and compute their scaling limit, where th

De-Min Li, Hong Yu, Qi-Xing Shen

Based on a $3\times3$ mass matrix describing the mixing of the scalar states $f_0(1370)$, $f_0(1500)$ and $f_0(1710)$, the hadronic decays of the three states are investigated. Taking into account the two possible assumptions concerning the mass level order of the bare states $|N>=|u\bar{u}+d\bar{d}>/\sqrt{2}$, $|S>=|s\bar{s}>$ and $|G>=|gg>$ in the scalar s

C. Firmani, V. Avila-Reese

We predict the structure and dynamics of disc galaxies using galaxy evolution models within a hierarchical formation scenario The halo mass aggregation histories, for a Lambda CDM model, were generated and used to calculate the virialization of dark matter (DM) haloes. A diversity of halo density profiles were obtained, the most typical one being close to th

Y. F. Zhou, Y. L. Wu

New physics effects on the $B^0-\bar{B}^0$ mixing and B-decay amplitudes are discussed. By a combined analysis, the model of new physics can be partially distinguished.It is emphasized that the extraction of unitarity angles $β$ and $γ$ through rare decay $K\to πν\tildeν$ and charged B decay $B^{\pm}\to DK^{\pm}$ respectively is not likely to be affected by

Demosthenes Ellinas, Magnus Johansson, Peter L Christiansen

Quantized nonlinear lattice models are considered for two different classes, boson and fermionic ones. The quantum discrete nonlinear Schroedinger model (DNLS) is our main objective, but its so called modified discrete nonlinear (MDNLS) version is also included, together with the fermionic polaron (FP) model. Based on the respective dynamical symmetries of t

A. N. F. Aleixo, A. B. Balantekin, M. A. Candido Ribeiro

A class of shape-invariant bound-state problems which represent two-level systems are introduced. It is shown that the coupled-channel Hamiltonians obtained correspond to the generalization of the Jaynes-Cummings Hamiltonian.

Demosthenes Ellinas, Ioannis Tsohantjis

Brownian motion on a smash line algebra (a smash or braided version of the algebra resulting by tensoring the real line and the generalized paragrassmann line algebras), is constructed by means of its Hopf algebraic structure. Further, statistical moments, non stationary generalizations and its diffusion limit are also studied. The ensuing diffusion equation

Demosthenes Ellinas

Within the algebraic framework of Hopf algebras, random walks and associated diffusion equations (master equations) are constructed and studied for two basic operator algebras of Quantum Mechanics i.e the Heisenberg-Weyl algebra (hw) and its q-deformed version hw_q. This is done by means of functionals determined by the associated coherent state density oper

Guihua Zeng, Guangcan Guo

In this letter, we proposed a quantum authentication protocol. The authentication process is implemented by the symmetric cryptographic scheme with quantum effects.

Guihua Zeng, Zhongyang Wang, Xinmei Wang

Quantum correlation between two particles and among three particles show nonclassic properties that can be used for providing secure transmission of information. In this paper, we propose two quantum key distribution schemes for quantum cryptographic network, which use the correlation properties of two and three particles. One is implemented by the Greenberg

Guihua Zeng

An unsymmetrical quantum key distribution scheme is proposed, its security is guaranteed by the correlation of the Greenberger-Horne-Zeilinger triplet state. In the proposed protocol, the distribution of quantum states are unsymmetrical. This unsymmetrical characteristic makes the transmission qubits (except the loss qubits) be useful. Sequentially the propo

Demosthenes Ellinas, Elena P. Papadopoulou, Yiannis G. Saridakis

A method of quantization of classical soliton cellular automata (QSCA) is put forward that provides a description of their time evolution operator by means of quantum circuits that involve quantum gates from which the associated Hamiltonian describing a quantum chain model is constructed. The intrinsic parallelism of QSCA, a phenomenon first known from quant

M. Capdequi-Peyranere

Supersymmetry applied to quantum mechanics has given new insights in various topics of theoretical physics like analytically solvable potentials, WKB approximation or KdV solitons. Duality plays a central role in many supersymmetric theories such as Yang-Mills theories or strings models. We investigate the possible existence of some duality within supersymme

J. L. McCauley

Deterministic chaos, and even maximum computational complexity, have been discovered within Newtonian dynamics. Economists assume that prices and price changes can also obey abstract mathematical laws of motion. Sociologists and other postmodernists advertise that physics and chemistry have outgrown their former limitations, that chaos and complexity provide

Ulrich H. E. Hansmann

A modified version of stochastic tunneling, a recently introduced global optimization technique, is introduced as a new generalized-ensemble technique and tested for a benchmark peptide, Met-enkephalin. It is demonstrated that the new technique allows to evaluate folding properties of this peptide

J. L. McCauley

Well-known to specialists but little-known to the wider audience is that Newtonian gravity can be understood as geodesic motion in space-time, where time is absolute and space is Euclidean. Newtonian cosmology formulated by Heckmann agrees implicitly with Cartan's formulation of Newtonian mechanics as geodesic motion in space-time, but does not unfold th

V. B. Belyaev, M. B. Miller, A. K. Motovilov, A. V. Sermyagin

Experimental search for molecular-nuclear transitions H_2O\to^{18}Ne^*(4.522,1^-)\to^{18}F\to^{18}O in water molecules was carried out. The measurements were performed in a low-background laboratory at the Baksan Neutrino Observatory. Under the assumption that the above transitions take place, the estimate for the half-life time of water molecule was found t

I. V. Kolokolov

For the Burgers equation driven by thermal noise leading asymptotics of pair and high-order correlators of the velocity field are found for finite times and large distances. It is shown that the intermittency takes place: some correlators are much larger than their reducible parts.

Ziemowit Popowicz

The general method of the cojmplex supersymmetrization (supercomplexifications) of the soliton equations with the odd (bi) hamiltoninan structure is established. New version of the supercomplexified Kadomtsev-Petvishvili hierarchy is given. The second odd Hamiltonina operator of the SUSY KdV equation generates the odd N=2 SUSY Virasoro like algebra.

Gregor Tanner

Quantum graphs have recently been introduced as model systems to study the spectral statistics of linear wave problems with chaotic classical limits. It is proposed here to generalise this approach by considering arbitrary, directed graphs with unitary transfer matrices. An exponentially increasing contribution to the form factor is identified when performin

Gregor Tanner

Periodic orbit action correlations are studied for the piecewise linear, area-preserving Baker map. Semiclassical periodic orbit formulae together with universal spectral statistics in the corresponding quantum Baker map suggest the existence of universal periodic orbit correlations. The calculation of periodic orbit sums for the Baker map can be performed w

Norbert Euler, Ove Lindblom

In the Painleve analysis of nonintegrable partial differential equations one obtains differential constraints describing the movable singularity manifold. We show, for a class of n-dimensional wave equations, that these constraints have a general structure which is related to the $n$-dimensional Bateman equation. In particular, we derive the exact expression

Giovanni Gallavotti

We analyze the physical meaning of fluctuations of the phase space contraction rate, that we also call entropy creation rate, and its observability in space-time intermittency phenomena. For concreteness we consider a Navier-Stokes fluid.

Alexander David Gottlieb

The propagation of molecular chaos, a tool of classical kinetic theory, is generalized to apply to quantum systems of distinguishable particles. We prove that the Curie-Weiss model of ferromagnetism propagates molecular chaos and derive the effective dynamics of a single-spin state in the mean-field limit. Our treatment differs from the traditional approach

A. Nakayashiki, F. A. Smirnov

We study the affine ring of the affine Jacobi variety of a hyper-elliptic curve. The matrix construction of the affine hyper-elliptic Jacobi varieties due to Mumford is used to calculate the character of the affine ring. By decomposing the character we make several conjectures on the cohomology groups of the affine hyper-elliptic Jacobi varieties. In the int

Alexander Fel'shtyn

We prove that the Nielsen zeta function is a rational function or a radical of a rational function for orientation preserving homeomorphisms on closed orientable 3-dimensional manifolds which are special Haken or Seifert manifolds. In the case of pseudo-Anosov homeomorphism of surface we compute an asymptotic for the number of twisted conjugacy classes or fo

Noson S. Yanofsky

This article tackles categorical coherence within a two-dimensional generalization of Lawvere's functorial semantics. 2-theories, a syntactical way of describing categories with structure, are presented. From the perspective here afforded, many coherence results become simple statements about the quasi-Yoneda lemma and 2-theory-morphisms. Given two 2-the

Alexander David Gottlieb

The propagation of chaos is a central concept of kinetic theory that serves to relate the equations of Boltzmann and Vlasov to the dynamics of many-particle systems. Propagation of chaos means that molecular chaos, i.e., the stochastic independence of two random particles in a many-particle system, persists in time, as the number of particles tends to infini

Eugene A. Ingerman, Helen Shvets

A model of unsteady filtration (seepage) in a porous medium with capillary retention is considered. It leads to a free boundary problem for a generalized porous medium equation where the location of the boundary of the water mound is determined as part of the solution. The numerical solution of the free boundary problem is shown to possess self-similar inter

Erik Guentner, Jerome Kaminker

We study the connection between the condition that the reduced C*-algebra of a finitely presented group is exact and the Novikov conjecture holding. The main result states that if the group is strongly exact in the sense that the inclusion of the group C*-algebra into the uniform Roe algebra of the group is a nuclear embedding then the Novikov conjecture hol

Guangfeng Jiang

We prove an algebraic formula for the Euler characteristic of the Milnor fibres of functions with critical locus a smooth curve on a space which is a weighted homogeneous complete intersection with isolated singularity.

R. Casadio, B. Harms

Starting from a WZWN action in the ISO(2,1) Poincare' group which describes a bosonized spinning string in 2+1 Minkowski space-time, we show that a sequence of non-trivial compactifications leads to the description of a spinless string which moves in a (linear dilaton) vacuum, AdS_3 or BTZ black hole background. Other solutions are also obtained and thei

R. L. Jaffe

A simple generalization of the Breit Interaction explains many qualitative features of the spectrum of hadrons.

Rouzbeh Allahverdi, Bruce. A. Campbell, John Ellis

We re-examine Affleck-Dine baryo/leptogenesis from the oscillation of condensates along flat directions of the supersymmetric standard model, which attained large vevs at the end of inflationary epoque. The key observation is that superpotential interactions couple the flat directions to other fields, which acquire masses induced by the flat-direction vev th

E. Accomando, R. Arnowitt, B. Dutta

Supersymmetric CP violating phases are examined within the framework of gravity mediated supergravity grand unified models with R parity invariance for models with a light ($\stackrel{<}{\sim} 1$ TeV) particle spectrum. In the minimal model, the nearness of the t quark Landau pole naturally suppresses the t-quark cubic soft breaking parameter at the electrow

A. Pich

These lectures provide an overview of Quantum Chromodynamics (QCD), the SU(3) gauge theory of the strong interactions. The running of the strong coupling and the associated property of Asymptotic Freedom are analyzed. Some selected experimental tests and the present knowledge of $α_s$ and the quark masses are briefly summarized. A short description of the QC

A. M. Gago, H. Nunokawa, R. Zukanovich Funchal

We have found that long-wavelength neutrino oscillations induced by a tiny breakdown of the weak equivalence principle of general relativity can provide a viable solution to the solar neutrino problem.

Ling-Fong Li

In this introductory lecture, some basic features of the spontaneous symmetry breaking are discussed. More specifically, $σ$-model, non-linear realization, and some examples of spontaneous symmetry breaking in the non-relativistic system are discussed in details. The approach here is more pedagogical than rigorous and the purpose is to get some simple explan

Nicolao Fornengo

We discuss the effect induced on the neutralino-nucleon scalar cross-section by the present uncertainties in the values of the quark masses and of the quark scalar densities in the nucleon. We examine the implications of this aspect on the determination of the neutralino cosmological properties, as derived from measurements of WIMP direct detection. We show

Mark I. Gorenstein, Marek Gazdzicki, Walter Greiner

The statistical production of antibaryons is considered within the canonical ensemble formulation. We demonstrate that the antibaryon suppression in small systems due to the exact baryon number conservation is rather different in the baryon-free (B=0) and baryon-rich (B>1) systems. At constant values of temperature and baryon density in the baryon-rich syste

Nicolao Fornengo

The present status of some theoretical interpretations of the atmospheric neutrino deficit is briefly discussed. Specifically, we show the results for the FC mechanism and for the standard oscillation hypothesis, both in the active and in the sterile channels. All these mechanisms are able to fit the present data to a good statistical level. Among them, the

B. E. Cox, K. Goulianos, L. Lonnblad, J. J. Whitmore

This paper is a summary of the discussion within the Diffractive and Low-x Physics Working Group at the 1999 Durham Collider Workshop of the interpretation of the Tevatron and HERA measurements of inclusive hard diffraction.

Merab Gogberashvili

Brane-Universe model embedded in 6-dimensional space-time with the signature (2+4) is considered. A matter is gravitationally trapped in three space dimensions, but both time-like directions are open. Choosing of the dimension and the signature of the model is initiated with the conformal symmetry for massless particles and any point in our world can be (1+1

T. Blum, A. Soni

This paper has been withdrawn.

T. Blum, P. Chen, N. Christ, C. Dawson

This paper has been withdrawn.

UKQCD Collaboration, P. Pennanen, C. Michael

The crossing from a static quark-antiquark system to a system of two static-light mesons when the separation of the static quarks is increased is calculated in zero-temperature lattice QCD. The mixing of these two states is extracted from the lattice operators. We also discuss the breaking of an excited string of a hybrid meson.

David H. Adams

The fermionic topological charge of lattice gauge fields, given in terms of a spectral flow of the Hermitian Wilson--Dirac operator, or equivalently, as the index of Neuberger&#39;s lattice Dirac operator, is shown to have analogous properties to Lüscher&#39;s geometrical lattice topological charge. The main new result is that it reduces to the continuum top

R. G. Edwards, U. M. Heller, R. Narayanan

We review the spectral flow techniques for computing the index of the overlap Dirac operator including results relevant for SUSY Yang-Mills theories. We describe properties of the overlap Dirac operator, and methods to implement it numerically. We use the results from the spectral flow to illuminate the difficulties in numerical calculations involving domain

J. Bouchez

We show that the unified method recently proposed by Feldman and Cousins to put confidence intervals on bounded parameters cannot avoid the possibility of getting null results. A modified bayesian approach is also proposed (although not advocated) which ensures no null results and proper coverage.

D. A. Harris, A. Para

This report describes an apparatus that could be used to measure both the identity and charge of an outgoing lepton in a charged current neutrino interaction. This capability in a massive detector would allow the most comprehensive set of neutrino oscillation physics measurements. By measuring the six observable transitions between initial and final state ne

F. Andersson, S. B. Edgar

We give new simple direct proofs in all spacetimes for the existence of asymmetric $(n,m+1)$-spinor potentials for completely symmetric $(n+1,m)$-spinors and for the existence of symmetric $(n,1)$-spinor potentials for symmetric $(n+1,0)$-spinors. These proofs introduce a `superpotential&#39;, i.e., a potential of the potential, which also enables us to get

Simonetta Frittelli, Thomas P. Kling, Ezra T. Newman

We propose a definition of an exact lens equation without reference to a background spacetime, and construct the exact lens equation explicitly in the case of Schwarzschild spacetime. For the Schwarzschild case, we give exact expressions for the angular-diameter distance to the sources as well as for the magnification factor and time of arrival of the images

E. S. Rodrigues, E. V. Anda, P. Orellana

Time dependent phenomena associated to charge transport along a quantum dot in the charge quantization regime is studied. Superimposed to the Coulomb blockade behaviour the current has novel non-linear properties. Together with static multistabilities in the negative resistance region of the I-V characteristic curve, strong correlations at the dot give rise

F. Comas, Nelson Studart

We report calculations of high electric field transport for the case of a strained Si/GeSi double heterostructure (DHS) considering transport along the Si channel and by applying the analytical Fokker-Planck approach (FPA), where the process is modeled as drift-diffusion in energy space. We limit ourselves to electronic transport in the conduction band of th

J. L. McCauley

Two-dimensional driven dissipative flows are generally integrable via a conservation law that is singular at equilibria. Nonintegrable dynamical systems are confined to n*3 dimensions. Even driven-dissipative deterministic dynamical systems that are critical, chaotic or complex have n-1 local time-independent conservation laws that can be used to simplify th

J. L. McCauley

Extensive confusion exists and persists in the literature on dynamical systems theory, cosmology, and other fields over spectra of fractal dimensions. Entirely different generating functions have been treated as if they should yield identical spectra, or scaling exponents. An uncritical implicit assumption of universality of scaling exponents is made, even t

G. Diedrich, L. Santen, A. Schadschneider, J. Zittartz

We present results on the modeling of on- and off-ramps in cellular automata for traffic flow, especially the Nagel-Schreckenberg model. We study two different types of on-ramps that cause qualitatively the same effects. In a certain density regime one observes plateau formation in the fundamental diagram. The plateau value depends on the input-rate of cars

Nelson A. Alves, Ulrich H. E. Hansmann

The free-energy landscape of two peptides is evaluated at various temperatures and an estimate for its fractal dimension at these temperatures calculated. We show that monitoring this quantity as a function of temperature allows to determine the glass transition temperature.

John R. Melrose

Sheared concentrated colloids with short range polymer coats are examined via simulations. Distributions of force are found to be sums of exponentials. The &#39;hydrodynamic clustering&#39; underlying the shear thickening effect is shown, in this system, to be a network of percolating coat contacts, with coats both in compression and extension. The geometry

M. H. Kalos, Francesco Pederiva

We offer a new proposal for the Monte Carlo treatment of many-fermion systems in continuous space. It is based upon Diffusion Monte Carlo with significant modifications: correlated pairs of random walkers that carry opposite signs; different functions ``guide&#39;&#39; walkers of different signs; the Gaussians used for members of a pair are correlated; walke

Mao, Yong Warner, Mark

We present a continuum model for a nematic elastomer network formed in a chiral environment, for instance in the presence of a chiral solvent. When this environment is removed, the network can retain some memory of its chiral genesis. We predict the residual chiral order parameter for a number of possible scenarios, and go on to examine the robustness (stabi

Gianfranco Durin, Stefano Zapperi

We investigate the scaling properties of the Barkhausen effect, recording the noise in several soft ferromagnetic materials: polycrystals with different grain sizes and amorphous alloys. We measure the Barkhausen avalanche distributions and determine the scaling exponents. In the limit of vanishing external field rate, we can group the samples in two distinc

W. Gotze, Th. Voigtmann

It is demonstrated that the susceptibility spectra of supercooled propylene carbonate as measured by depolarized-light-scattering, dielectric-loss, and incoherent quasi-elastic neutron-scattering spectroscopy within the GHz window are simultaneously described by the solutions of a two-component schematic model of the mode-coupling theory (MCT) for the evolut

B. J. van Wees

In a recent Letter Hammar et al. claim the observation of injection of a spin-polarized current in a two-dimensional electron gas (2DEG). This is an important observation, since, despite considerable effort of several groups, all attempts to realize spin-injection into a 2DEG using purely electrical measurements have failed sofar. However, in my opinion the

A. S. Mel&#39;nikov, I. M. Nefedov, D. A. Ryzhov, I. A. Shereshevskii

The structure of a single flux line in (s+d)-wave superconductors has been analyzed within the Ginzburg-Landau (GL) model generalized for two order parameter components. The fourfold symmetric singular vortex solution is shown to be unstable in a certain range of the GL parameters with respect to the mutual shift of s- and d- wave unit vortices. The resultin

Ana Celia Mota, Elisabeth Dumont, James L. Smith

We have found a sharp transition at T_c2=350 mK in the vortex creep rate of a single crystal of (U_1-xTh_x)Be_13 with T_c=523 mK (x=0.0275). For T<<T_c2, no creep of vortices is observed in a time scale of 10^5 s, while for T_c2<T<T_c, vortices creep at very high rates (30 % of decay from a metastable configuration in the first 10^5 s at T=400 mK). The sharp

A. C. Mota, E. Dumont, A. Amann, Y. Maeno

We have found a sharp transition in the vortex creep rates at a temperature T^\ast=0.05 T_c in a single crystal of Sr_2RuO_4 (T_{c}=1.03 K) by means of magnetic relaxation measurements. For T<T^\ast, the initial creep rates drop to undetectable low levels. One explanation for this transition into a phase with such extremely low vortex creep is that the low-t

Inna M. Kaganova, Moisey I. Kaganov

The effective impedance of strongly anisotropic polycrystals has been investigated under the conditions of extremely anomalous skin effect. We were interested in finding out how the value of the effective impedance depends on the geometry of the Fermi surface of a single crystal grain. The previously obtained nonperturbative solution based on the application

Elisabeth Dumont, Ana Celia Mota, James L. Smith

We investigated low field vortex dynamics in a single crystal of U_.9725Th_.0275Be_13. We found a sharp transition in the vortex creep rate at the lower transition temperature T_c2, coincident with the second jump in the specific heat. In the high-temperature phase, rather strong creep rates are observed. In the low temperature phase, the rates drop to undet

S. S. A. Razee, J. B. Staunton, B. Ginatempo, F. J. Pinski

The cubic lattice symmetry of ferromagnetic homogeneously disordered alloys is when a compositional modulation is imposed. This can have a profound influence on the magnetocrystalline anisotropy energy (MAE). We describe our ab-initio theory of this effect and use the framework of concentration waves with the electronic structure described within the spin-po

Seiji Miyashita, Keiji Saito, Hiroto Kobayashi, Hans De Raedt

In discrete energy structure of nanoscale magnets, nonadiabatic transitions at avoided level crossings lead to fundamental processes of dynamics of magnetizations. The thermal environment causes dissipative effects on these processes. In this paper we review the features of the nonadiabatic transition and the influence of the thermal environment. In particul

D. J. Reilly, G. R. Facer, A. S. Dzurak, B. E. Kane

Zero length quantum wires (or point contacts) exhibit unexplained conductance structure close to 0.7 X 2e^2/h in the absence of an applied magnetic field. We have studied the density- and temperature-dependent conductance of ultra-low-disorder GaAs/AlGaAs quantum wires with nominal lengths l=0 and 2 mu m, fabricated from structures free of the disorder assoc

Peter F. Arndt

To analyze phase transitions in a nonequilibrium system we study its grand canonical partition function as a function of complex fugacity. Real and positive roots of the partition function mark phase transitions. This behavior, first found by Yang and Lee under general conditions for equilibrium systems, can also be applied to nonequilibrium phase transition

Frederic A. Rasio, James C. Lombardi

Smoothed Particle Hydrodynamics is a multidimensional Lagrangian method of numerical hydrodynamics that has been used to tackle a wide variety of problems in astrophysics. Here we develop the basic equations of the SPH scheme, and we discuss some of its numerical properties and limitations. As an illustration of typical astrophysical applications, we discuss

K. K. Dyer, S. P. Reynolds, K. J. Borkowski

Galactic cosmic rays up to energies of around 10^15 eV are assumed to originate in supernova remnants (SNRs). The shock wave of a young SNR like SN 1006 AD can accelerate electrons to energies greater than 1 TeV, where they can produce synchrotron radiation in the X-ray band. A new model (SRESC) designed to model synchrotron X-rays from Type Ia supernovae ca

David B. Cline

We describe the liquid-xenon dark-matter detector program of the UCLA-Torino team. A two-phase detector, ZEPLIN II, for the Boulby Mine is a good match for the current search for WIMP dark matter.

Demosthenes Kazanas

We present a model for the aperiodic variablity of accreting Black Hole Candidates (BHC) along with model light curves. According to the model this variability is the combined outcome of random (Poisson) injection of soft photons near the center of an extended {\sl inhomogeneous} distribution of hot electrons (similar to those advocated by the ADAF or ADIOS

Mark Dragovan

Fundamentally new technology is described for constructing low areal mass density (1kg/m^2), high precision (< 10micron RMS) reflectors scalable to large apertures (10 to 20 meters) for use as the primary element of a telescope system. A large reduction in mass is achieved by minimizing the mass of the reflective surface using a high reflectivity metallic me

Dipak Munshi

Future weak lensing surveys will directly probe the density fluctuation in the universe. Recent studies have shown how the statistics of the weak lensing convergence field is related to the statistics of collapsed objects. Extending earlier analytical results on the probability distribution function of the convergence field we show that the bias associated w

Andrew J. Berkley, Demosthenes Kazanas, Jonathan Ozik

We model the correlated X-ray - UV observations of NGC 7469, for which well sampled data in both these bands have been obtained recently in a multiwavelength monitoring campaign. To this end we derive the transfer function in wavelength \ls and time lag \t, for reprocessing hard (X-ray) photons from a point source to softer ones (UV-optical) by an infinite p

L. P. Bassino, S. Waldhausen, R. E. Martinez

We present the results of BV(RI)_KC CCD photometry down to V=21 mag in the region of NGC 6994. To our knowledge, no photometry has previously been reported for this object and we find evidences that it is a poor and sparse old open cluster, with a minimum angular diameter of 9 arcmin, i.e. larger than the 3 arcmin originally assigned to it. We obtain a color

David B. Cline

We discuss the prospects for detecting nu_{mu,tau} and nu_{tau}neutrinos from Type II supernovas using the novel detector at the Supernova Burst Observatory (SNBO) or OMNIS that is being designed for an underground laboratory in the USA. This detector would collect ~2000 flavor selected events from a Galactic supernova and could probe neutrino mass down to a

J. L. McCauley

From the standpoint of theoretical physics we can treat Newtonian cosmology as a problem in nonlinear dynamics. The attempt to average the density, in search of a method of making contact between theory and observation, is replaced by the more systematic idea of coarsegraining. I also explain in this context why two previous attempts at the construction of h

Sean G. Ryan

Metal-poor stars provide information on the characteristics and chemical evolution of the halo population of the Galaxy, the first epoch of star formation and Galaxy formation (not just locally but with relevance to high-redshift objects), and big bang nucleosynthesis. This review looks at recent developments in this subject.

R. L. M. Corradi, M. Livio, H. E. Schwarz, U. Munari

Symbiotic Miras give a nice practical demonstration of the formation of bipolar and highly aspherical nebulae as a consequence of interaction in detached binaries. We believe that these binary systems are among the most promising candidates for the progenitors of bipolar planetary nebulae. We present a list of the optically extended nebulae known to date aro

Romano L. M. Corradi

Some of the correlations between morphological and other physical properties of planetary nebulae (PNe) are reviewed. In particular, the finding that bipolar (b) PNe have more massive progenitors than the other morphological classes is discussed in detail. Earlier results are confirmed; including all the various sources of uncertainty, the Galactic distribut

Sergio Molinari, Jan Brand, Riccardo Cesaroni, Francesco Palla

The James Clerk Maxwell Telescope has been used to obtain submillimeter and millimeter continuum photometry of a sample of 30 IRAS sources previously studied in molecular lines and centimeter radio continuum. All the sources have IRAS colours typical of very young stellar objects (YSOs) and are associated with dense gas. In spite of their high luminosities (

Sean G. Ryan

A highly homogeneous study of 23 halo field dwarf stars has achieved a Li abundance accuracy of 0.033 dex per star. The work shows that the intrinsic spread of the Li abundances of these stars at a given metallicity is <0.02 dex, and consistent with zero. That is, the Spite Li plateau for halo field dwarfs is incredibly thin. The thinness rules out depletion

J. R. Stauffer, R. D. Jeffries, E. L. Martin, D. M. Terndrup

We provide a review of the current status of several topics on the ages, distances, and mass functions of open clusters, with a particular emphasis on illuminating the areas of uncertainty. Hipparcos has obtained parallaxes for nearby open clusters that have expected accuracies much better than has been previously achievable. By using the lithium depletion b

Luc Dessart, Paul A. Crowther, D. John Hillier, Allan J. Willis

Neon abundances are derived in four Galactic WC stars -- gamma Vel (WR11, WC8+O7.5III), HD156385 (WR90, WC7), HD192103 (WR135, WC8), and WR146 (WC5+O8) - using mid-infrared fine structure lines obtained with ISO/SWS. Stellar parameters for each star are derived using a non-LTE model atmospheric code (Hillier & Miller 1998) together with ultraviolet (IUE), op

T. Shahbaz, P. Groot, S. N. Phillips, J. Casares

We have obtained intermediate resolution optical spectra of the black-hole candidate Nova Sco 1994 in June 1996, when the source was in an X-ray/optical active state (R~15.05). We measure the radial velocity curve of the secondary star and obtain a semi-amplitude of 279+/-10 km/s; a value which is 30 per cent larger than the value obtained when the source is

Paul A. Crowther

The stellar properties of Sk41 (AB4, WN5h), the only known single Wolf-Rayet star in the SMC, are derived from ultraviolet (IUE), optical (AAT) and near-IR (NTT) spectroscopy. Contrary to expectations, the stellar properties of Sk41 are typical of equivalent WN stars in the Galaxy and LMC, with T=42kK, log(L/Lo)=5.7, v_inf=1300 km/s, Mdot/sqrt(f)=3x10^-5 Mo/

D. Mehlert, S. Seitz, R. P. Saglia, T. L. Hoffmann

Using the Focal Reducer Spectrograph (FORS) at the Very Large Telescope (VLT) during the FORS commissioning time in December 1998 we took long slit spectra of the gravitational arc visible on images of the galaxy cluster 1E 0657 (z = 0.296). This cluster is one of the hottest (massive) cluster known so far and hence perfectly acts as a gravitational telescop

J. Moultaka, D. Pelat

Stellar population synthesis can be approached as an inverse problem. The physical information is extracted from the observations through an inverse model. The process requires the transformation of the observational errors into model errors. A description is given for the error analysis to obtain objectively the errors in the model. Finding a solution for o

J. V. Arnau, D. Saez

This paper is concerned with experiments which measure CMB anisotropies on small angular scales. A certain coverage, a beam structure and a level of uncorrelated noise define each experiment. We focus our atention on the reversion of the beam average. In each experiment, we look for the best pixelization for reversion, namely, for the pixelization that -afte

P. Kalas, J. Larwood, B. A. Smith, A. Schultz

The nearby main sequence star Beta Pictoris is surrounded by an edge-on disk of dust produced by the collisional erosion of larger planetesimals. Here we report the discovery of substructure within the northeast extension of the disk midplane that may represent an asymmetric ring system around Beta Pic. We present a dynamical model showing that a close stell