May 1998 arXiv papers — page 13

Katherine M. Blundell, Anthony J. Beasley

Two rival hypotheses have been proposed for the origin of the compact radio flux observed in radio-quiet quasars (RQQs). It has been suggested that the radio emission in these objects, typically some two or three orders of magnitude less powerful than in radio-loud quasars (RLQs), represents either emission from a circumnuclear starburst or is produced by ra

Yasuhiro Miura, Kazuhiro Yamamoto, Kenta Miyauchi, Masayasu Hosonuma

Large-angle fluctuations in the cosmic X-ray background are investigated by a new formalism with a simple model of the X-ray sources. Our method is formulated from the Boltzmann equation and a simple extension of the work by Lahav et al. to be applicable to a hyperbolic (open) universe. The low multipole fluctuations due to the source clustering are analyzed

P. J. E. Peebles

I argue that the weight of the available evidence favours the conclusions that galaxies are unbiased tracers of mass, the mean mass density (excluding a cosmological constant or its equivalent) is less than the critical Einstein-de Sitter value, and an isocurvature model for structure formation offers a viable and arguably attractive model for the early asse

Annette M. N. Ferguson, Jay Gallagher, Rosemary F. G. Wyse

We present the first results of an ongoing project to investigate the present-day chemical abundances of the extreme outer parts of galactic disks, as probed by the emission line spectra of a new sample of HII regions. The galaxies studied here, NGC628, NGC1058 and NGC6946, are all late-type spiral galaxies, characterized by larger than average HI-to-optical

N. Magnussen

Selected results from the HEGRA experiment on charged Cosmic Rays and on very high energy gamma-rays are presented. The MAGIC Telescope is presented as an outlook to the future of Gamma-Ray astronomy.

Unal Ertan, M. Ali Alpar

We note that the solution of accretion disk dynamics for an initial delta-function mass distribution gives a light curve that fits both the rise and the decay pattern of the outburst light curves of black-hole soft X-ray transients (BSXTs) until the onset of the first mini outburst quite well. The Green's function solution of Lynden-Bell & Pringle (1974)

B. M. Gaensler, A. J. Green, R. N. Manchester

We present Australia Telescope Compact Array observations of the supernova remnant (SNR) G309.2-00.6. In a 1.3-GHz continuum image the remnant appears as a near-circular shell, but with two brightened and distorted arcs of emission on opposite sides. HI absorption against the SNR yields a distance in the range 5.4 to 14.1 kpc, corresponding to an age (1-20)x

A. L. Kagan, M. Neubert

We present an updated next-to-leading order analysis of the B -> X_s gamma branching ratio and photon spectrum, including consistently the effects of Fermi motion in the heavy-quark expansion. For the Standard Model, we obtain B(B -> X_s gamma) = (2.57+-0.26^{+0.31}_{-0.36}) * 10^{-4} for the integral over the high-energy part of the photon spectrum with E_g

Karen O'Neil, G. D. Bothun, C. D. Impey, S. McGaugh

Utilizing the F814W and F300W filters, short exposure HST WFPC-2 images were taken of UGC 12695 a nearby (z ~ 0.021) low surface brightness disk galaxy. UGC 12695 has an unusual morphology, consisting of a Y-shaped nucleus surrounded by a faint spiral arm with a number of bright H II regions interspersed throughout the galaxy. Surface photometry indicates th

A. Restuccian, J. Stephany

The generating functional of two dimensional $BF$ field theories coupled to fermionic fields and conserved currents is computed in the general case when the base manifold is a genus g compact Riemann surface. The lagrangian density $L=dB{\wedge}A$ is written in terms of a globally defined 1-form $A$ and a multi-valued scalar field $B$. Consistency conditions

K. Kifonidis, T. Plewa, E. Mueller

In recent years the technique of Adaptive Mesh Refinement (AMR) has been successfully applied to several astrophysical problems. This method should also allow a consistent multi-dimensional modelling of supernova explosions. In this contribution we address some of the computational difficulties encountered when trying to apply the AMR method to explosive nuc

A. M. Poskanzer, S. A. Voloshin

The strategy and techniques for analyzing anisotropic flow (directed, elliptic, etc.) in relativistic nuclear collisions are presented. The emphasis is on the use of the Fourier expansion of azimuthal distributions. We present formulae relevant for this approach, and in particular, show how the event multiplicity enters into the event plane resolution. We al

Grigory Rybnikov

We construct two combinatorially equivalent line arrangements in the complex projective plane such that the fundamental groups of their complements are not isomorphic. The proof uses a new invariant of the fundamental group of the complement to a line arrangement of a given combinatorial type with respect to isomorphisms inducing the canonical isomorphism of

BS Acharya, JM Figueroa-O'Farrill, B Spence

This is the first of a series of papers devoted to the group-theoretical analysis of the conditions which must be satisfied for a configuration of intersecting M5-branes to be supersymmetric. In this paper we treat the case of static branes. We start by associating (a maximal torus of) a different subgroup of Spin(10) with each of the equivalence classes of

G. Bonelli, L. Bonora, F. Nesti

Extending a recent result of S.B. Giddings, F. Hacquebord and H. Verlinde, we show that in the U(N) SYM Matrix theory there exist classical BPS instantons which interpolate between different closed string configurations via joining/splitting interactions similar to those of string field theory. We construct them starting from branched coverings of Riemann su

J. Goryo, K. Ishikawa

We analyze time reversal violating processes of the p-wave superconductor. The Landau-Ginzuburg effective action has an induced T-violating term of electromagnetic potentials which resembles the Chern-Simons term and causes a mixing between the electric field and the magnetic field. Several T-violating electromagnetic phenomena caused by this term, such as u

M. Gilfanov, M. Revnivtsev, R. Sunyaev, E. Churazov

The X-ray light curve and broad band spectral properties of the millisecond X-ray pulsar/burster SAX J1808.4-3658 are reported. In the course of RXTE observations in April--May 1998 the 3--150 keV luminosity of the source decreased by a factor of ~100 from the peak value of ~9E36 erg/s (for a 4 kpc distance). However, the spectrum was remarkably stable and m

R. A. Litherland

Let N be a regular branched cover of a homology 3-sphere M with deck group G isomorphic to Z_2^d and branch set a trivalent graph Gamma; such a cover is determined by a coloring of the edges of Gamma with elements of G. For each index-2 subgroup H of G, M_H = N/H is a double branched cover of M. Sakuma has proved that the first homology of N is isomorphic, m

Adel Bilal

We investigate whether DLCQ of M-theory can be defined as a limit of M-theory compactified on an almost light-like circle. This is of particular interest since the proofs of the matrix description of M-theory by Seiberg and Sen rely on this assumption. By the standard relation between M-theory on $S^1$ and IIA string theory, we translate this question into t

V. B. Kopeliovich

The binding energies of baryonic systems (BS) with baryon number $B=2, 3$ and 4 possessing heavy flavor, charm and bottom, are estimated within the rigid oscillator version of the bound state approach to chiral soliton models. Two tendencies are noted: the binding energy increases with increasing mass of the flavor and with increasing $B$. Therefore, the cha

Pradip Roy, Sourav Sarkar, Jan-e Alam, Binayak Dutt-Roy

Changes in the properties of the vector mesons in hot and dense hadronic matter, as produced in heavy ion collisions, lead to the intriguing possibility of the opening of the decay channel $ω\ra ρπ$, for the omega meson, which is impossible in free space. This along with the channel $ωπ\ra ππ$ would result in a decrease in its effective life-time enabling it

I. P. Lokhtin, A. M. Snigirev

Angular structure of radiative and collisional energy losses of a hard parton jet propagating through dense QCD-matter is investigated. For small angular jet cone sizes, $θ_0 < 5^0$, the radiative energy loss is shown to dominate over the collisional energy loss due to final state elastic rescattering of the hard projectile on thermal particles in the medium

Jose F. Nieves, Palash B. Pal

In a medium that contains electrons but not the other charged leptons, such as normal matter, the gravitational interactions of neutrinos are not the same for all the neutrino flavors. We calculate the leading order matter-induced corrections to the neutrino gravitational interactions in such a medium and consider some of their physical implications.

Antal Jevicki, Tamiaki Yoneya

Motivated by the space-time uncertainty principle, we establish a conformal symmetry in the dynamics of D-particles. The conformal symmetry, combined with the supersymmetric non-renormalization theorem, uniquely determines the classical form of the effective action for a probe D-particle in the background of a heavy D-particle source, previously constructed

Katsunori Kitano, Toshio Aoyagi

It is well known that a sparsely coded network in which the activity level is extremely low has intriguing equilibrium properties. In the present work, we study the dynamical properties of a neural network designed to store sparsely coded sequential patterns rather than static ones. Applying the theory of statistical neurodynamics, we derive the dynamical eq

Takuya Hayashi, Yoshihisa Ohshima, Kiyoshi Okuyama, Hiroshi Suzuki

By undertaking additional analyses postponed in a previous paper, we complete our construction of a manifestly supersymmetric gauge-covariant regularization of supersymmetric chiral gauge theories. We present the following: An evaluation of the covariant gauge anomaly; a proof of the integrability of the covariant gauge current in anomaly-free cases; a calcu

Shinji Mukohyama

A new interpretation of entanglement entropy is proposed: entanglement entropy of a pure state with respect to a division of a Hilbert space into two subspaces 1 and 2 is an amount of information, which can be transmitted through 1 and 2 from a system interacting with 1 to another system interacting with 2. The transmission medium is quantum entanglement bet

H. Hatanaka, T. Inami, C. S. Lim

We report on an attempt to solve the gauge hierarchy problem in the framework of higher dimensional gauge theories. Both classical Higgs mass and quadratically divergent quantum correction to the mass are argued to vanish. Hence the hierarchy problem in its original sense is solved. The remaining finite mass correction is shown to depend crucially on the cho

B. G. Sidharth

It is pointed out that very recent results based on supernovae observations that the universe will accelerate and expand for ever with ever decreasing density have been predicted in a recent cosmological model which also deduces hitherto purely empirical features like the mysterious relation between the pion mass and the Hubble Constant.

John N. Bahcall, Sarbani Basu, M. H. Pinsonneault

Solar neutrino fluxes and sound speeds are calculated using a systematic reevaluation of nuclear fusion rates. The largest uncertainties are identified and their effects on the solar neutrino fluxes are estimated.

Abraham Loeb, Rosalba Perna

Gamma-Ray Bursts (GRBs) are thought to originate at cosmological distances from the most powerful explosions in the Universe. If GRBs are not beamed then the distribution of their number as a function of Gamma-ray flux implies that they occur once per (0.3-40) million years per bright galaxy and that they deposit >10^{53} ergs into their surrounding interste

S B Leble, A V Yurov

Supersymmetrical quantum--mechanical system is consider in the case of d=2. The problem of addition of the lower level to spectrums of matrix and scalar components of d=2 SUSY Hamiltonian is investigated. It is shown that in the case, the level E=0 may be degenerate. The multi--dimensional scalar Hamiltonians with energy spectra coinciding up to finite numbe

J. P. Palao, J. G. Muga, R. Sala

The multiple scattering interferences due to the addition of several contiguous potential units are used to construct composite absorbing potentials that absorb at an arbitrary set of incident momenta or for a broad momentum interval.

Masanao Ozawa

Every measurement leaves the object in a family of states indexed by the possible outcomes. This family, called the posterior states, is usually a family of the eigenstates of the measured observable, but it can be an arbitrary family of states by controlling the object-apparatus interaction. A potentially realizable object-apparatus interaction measures pos

Michael E. Fisher, Daniel M. Zuckerman

It can be fruitful to view two-component physical systems of attractive monomers, A and B, ``chemically&#39;&#39; in terms of a reaction A + B <-> C, where C = AB is an associated pair or complex. We show how to construct free energies in the three-component or chemical picture which, under mass-action equilibration, exactly reproduce any given two-component

S. Fujita, N. Sugiyama

We have fabricated light emitting diodes (LEDs) with Schottky contacts on Si-nanocrystals formed by simple techniques as used for standard Si devices. Orange electroluminescence (EL) from these LEDs could be seen with the naked eye at room temperature when a reverse bias voltage was applied. The EL spectrum has a major peak with a photon energy of 1.9 eV and

St. Hollinger, M. Luecke, H. W. Mueller

A minimal, analytically manageable Galerkin type model for convection in binary mixtures subject to realistic boundary conditions is presented. The model elucidates and reproduces the typical bifurcation topology of extended stationary and oscillatory convective states seen for negative Soret coupling: backwards stationary and Hopf bifurcations, saddle node

Masako Bando, Katsuya Hasebe, Ken Nakanishi, Akihiro Nakayama

We analyze Optimal Velocity Model (OVM) with explicit delay. The properties of congestion and the delay time of car motion are investigated by analytical and numerical methods. It is shown that the small explicit delay time has almost no effects. In the case of the large explicit delay time, a new phase of congestion pattern of OVM seems to appear.

G. Fabbri, F. Matera

We study the effects of the Coulomb interaction on the growth of unstable modes in asymmetric nuclear matter. In order to compare with previous calculations we use a semiclassical approach based on the linearized Vlasov equation. Moreover, a quantum calculation is performed within the R.P.A.. The Coulomb effects are a slowing down of the growth and the occur

F. A. Smirnov

We consider the quantum Toda chain using the method of separation of variables. We show that the matrix elements of operators in the model are written in terms of finite number of ``deformed Abelian integrals&#39;&#39;. The properties of these integrals are discussed. We explain that these properties are necessary in order to provide the correct number of in

Alan L. Carey, Edwin Langmann

The positive energy representations of the loop group of U(1) are used to construct a boson-anyon correspondence. We compute all the correlation functions of our anyon fields and study an anyonic W-algebra of unbounded operators with a common dense domain. This algebra contains an operator with peculiar exchange relations with the anyon fields. This operator

H. Montani, R. Trinchero

We consider a twisted version of quantum groups corepresentations. This generalization amounts to include in the theory the case where quantum space coordinates and its endomorphism matrix entries belong to a non-commutative quadratic algebra.

D. B. A. Epstein, Paul J. Sanders

It is shown how to use a small finite state automaton in two variables in order to carry out part of the Knuth--Bendix process for rewriting words in a group. The main objective is to provide a substitute for the most space-demanding module of the existing software which attempts to find a shortlex-automatic structure for a group. The two-variable automaton

Wei-Ping Li, Zhenbo Qin

This is the second part of two papers. In this part, we establish closed formulae for the universal functions in the blowup formulae for virtual Hodge polynomials of Gieseker moduli spaces of rank-2 stable sheaves and Uhlenbeck compactification spaces over algebraic surfaces.

Wei-Ping Li, Zhenbo Qin

This is the first part of two papers. In this part, we prove the blowup formulae for virtual Hodge polynomials of Gieseker moduli spaces of rank-2 stable sheaves and Uhlenbeck compactification spaces over algebraic surfaces. In particular, we verify the blowup formulae for the S-duality conjecture of Vafa-Witten, i.e. the blowup formulae for the Euler number

Ivan Cherednik

The note is a continuation of the previous paper ``On q-analogues of Riemann&#39;s zeta&#39;&#39; (math.QA/980499). It contains an output of the computer program calculating the zeros of the ``sharp&#39;&#39; q-zeta function.

Tamas Hauer

We analyze string networks in 7-brane configurations in IIB string theory. We introduce a complex parameter M characterizing equivalence classes of networks on a fixed 7-brane background and specifying the BPS mass of the network as M_{BPS} = | M |. We show that M can be calculated without knowing the particular representative of the BPS state. Based on deta

Kasper Olsen, Ricardo Schiappa

We consider target space duality transformations for heterotic sigma models and strings away from renormalization group fixed points. By imposing certain consistency requirements between the T-duality symmetry and renormalization group flows, the one loop gauge beta function is uniquely determined, without any diagram calculations. Classical T-duality symmet

H. Gustafsson, S. E. Hjelmeland, U. Lindstrom

Starting from certain 3D non-abelian dual systems, we discuss a number of related dual systems in 2D, some of which are obtained by dimensional reduction. The dualities relate massive scalar and vector fields, and may be relevant for string theory in the context of massive type IIA supergravity. Supersymmetric extensions of the models are also presented.

David Hillman

I investigate a class of dynamical systems in which finite pieces of spacetime contain finite amounts of information. Most of the guiding principles for designing these systems are drawn from general relativity: the systems are deterministic; spacetime may be foliated into Cauchy surfaces; the law of evolution is local (there is a light-cone structure); and

Csaba Csaki, Hitoshi Murayama

We show how to extend the &#39;t Hooft anomaly matching conditions to discrete symmetries. We check these discrete anomaly matching conditions on several proposed low-energy spectra of certain strongly interacting gauge theories. The excluded examples include the proposed chirally symmetric vacuum of pure N=1 supersymmetric Yang-Mills theories, certain non-s

Asim Gangopadhyayaa, Jeffry V. Mallow, Uday P. Sukhatme

Using the underlying algebraic structures of Natanzon potentials, we discuss conditions that generate shape invariant potentials. In fact, these conditions give all the known shape invariant potentials corresponding to a translational change of parameters. We also find that while the algebra for the general Natanzon potential is $SO(2,2)$, a subgroup $SO(2,1

G. C. Branco, D. Delepine, D. Emmanuel-Costa, R. Gonzalez Felipe

We consider the possibility of electroweak baryogenesis in a simple extension of the standard model with an extra singlet complex scalar and a vector-like down quark. We show that in the present model the first-order electroweak phase transition can be strong enough to avoid the baryon asymmetry washout by sphalerons and that the CP-violating effects can be

Bruce A. Campbell, Mary K. Gaillard, Hitoshi Murayama, Keith A. Olive

In supergravity models (such as standard superstring constructions) that possess a Heisenberg symmetry, supersymmetry breaking by the inflationary vacuum energy does not lift flat directions at tree level. One-loop corrections give small squared masses that are negative (about -g^2 H^2/(4π)^2) for all flat directions that do not involve the stop. After infla

R. S. Thorne

I present a calculation of structure functions at leading order which includes an unambiguous inclusion of the leading ln(1/x) terms for each power of alpha_s, and also the correct effects due to the mass of the charm and bottom quarks. I compare the results of fits to data to those obtained using conventional NLO in alpha_s calculations, noting a clear pref

R. S. Thorne

I present a method for calculating heavy quark production which extrapolates smoothly from the well understood limits of the fixed-flavour number scheme for Q^2 approx m_H^2 to the zero-mass scheme at Q^2/m_H^2 -> infinity. For all Q^2 > m_H^2 the evolution of the heavy quark distribution is precisely as in the massless MSbar scheme. The method is simple to

C. Balzereit, W. Kilian, T. Mannel

We compute the one-loop anomalous dimension for the light cone distribution function of a heavy quark and solve the corresponding evolution equation analytically. Some implications of the results for inclusive $B$ decays are discussed.

Werner Vogelsang

We discuss the NLO evolution of quark transversity densities and of the parton distribution function for linearly polarized gluons in a linearly polarized hadron. A supersymmetric relation between the NLO evolution kernels for transversity and for linear polarization is found. We also study the implications of NLO evolution for Soffer&#39;s inequality and th

Thorsten Feldmann, Peter Kroll

The new CLEO and LEP data on the eta-gamma and eta&#39;-gamma transition form factors have renewed the interest in simple interpolation formulas, valid at any value of momentum transfer. We are going to show that recent theoretical and phenomenological results on eta-eta&#39; mixing lead to two-pole forms, where each pole term resembles the Brodsky/Lepage in

B. Faid, G. L. Fogli, E. Lisi, D. Montanino

The vacuum oscillation solution to the solar neutrino problem predicts characteristics variations of the observable neutrinos rates, as a result of the L/E_nu dependence of the nu_e survival probability (L and E_nu being the neutrino pathlength and energy, respectively). The E_nu-dependence can be studied through distortions of the recoil electron spectrum i

Varun Sheel, Hiranmaya Mishra, Jitendra C. Parikh

We evaluate equal time point to point spatial correlation functions of mesonic currents at finite temperature. For this purpose we consider the QCD vacuum structure in terms of quark antiquark condensates and their fluctuations in terms of an irreducible four point structure of the vacuum. The temperature dependence of quark condensates is modeled using chir

Kevin Cahill, Gary Herling

We have applied a new noncompact, gauge-invariant, Monte Carlo method to simulate the U(1), SU(2), and SU(3) gauge theories on 8^4 and 12^4 lattices. For U(1) the Creutz ratios of the Wilson loops agree with the exact results for beta > 0.5 after a renormalization of the charge. The SU(2) and SU(3) Creutz ratios robustly display quark confinement at beta = 0

B. Abbott

The DZERO detector is used to study proton-antiproton collisions at the 1800 GeV and 630 GeV center-of-mass energies available at the Fermilab Tevatron. To measure jets, the detector uses a sampling calorimeter composed of uranium and liquid argon as the passive and active media respectively. Understanding the jet energy calibration is not only crucial for p

Steven L. Liebling

The gravitational collapse of a complex scalar field in the harmonic map is modeled in spherical symmetry. Previous work has shown that a change of stability of the attracting critical solution occurs in parameter space from the discretely self-similarity critical (DSS) solution originally found by Choptuik to the continuously self-similar (CSS) solution fou

Miguel Á. G. Bonilla

We obtain a family of first-order symmetric hyperbolic systems for the Bianchi equations. They have only physical characteristics: the light cone and timelike hypersurfaces. In the proof of the hyperbolicity, new positivity properties of the Bel tensor are used.

Brien C. Nolan

Criteria which a space-time must satisfy to represent a point mass embedded in an open Robertson--Walker (RW) universe are given. It is shown that McVittie&#39;s solution in the case $k=0$ satisfies these criteria, but does not in the case $k=-1$. Existence of a solution for the case $k=-1$ is proven and its representation in terms of an elliptic integral is

Giampiero Esposito, Alexander Yu. Kamenshchik

Recent work in the literature has studied a new set of local boundary conditions for the quantized gravitational field, where the spatial components of metric perturbations, and ghost modes, are subject to Robin boundary conditions, whereas normal components of metric perturbations obey Dirichlet boundary conditions. Such boundary conditions are here applied

D. Bennett-Wood, J. L. Cardy, I. G. Enting, A. J. Guttmann

We have extended the enumeration of self-avoiding walks on the Manhattan lattice from 28 to 53 steps and for self-avoiding polygons from 48 to 84 steps. Analysis of this data suggests that the walk generating function exponent gamma = 1.3385 +- 0.003, which is different from the corresponding exponent on the square, triangular and honeycomb lattices. This pr

Dirk Helbing

Two complementary mathematical models for attitude formation are considered: Starting from the model of Weidlich and Haag (1983), which assumes indirect interactions that are mediated by a mean field, a new model is proposed, which is characterized by direct pair interactions. Three types of pair interactions leading to attitude changes can be found: First,

Oe. Elgaroey, C. J. Pethick

Possible fragmentation of a Bose-Einstein condensate with negative scattering length is investigated using a simple two-level model. Our results indicate that fragmentation does not take place for values of the coupling for which the system is metastable. We also comment on the possibility of realizing a fragmented condensate in trapping potentials other tha

Aninda Jiban Bhattacharyya, S. Tarafdar

In this paper we present a computer simulation of a random walk (RW) for diffusion on a rearranging lattice. The lattice consists of two types of sites -- one good conducting (type 1) and the other poor conducting (type 2), distributed at random. The two types of sites are assigned different waiting times ($τ_{1}$ for type 1 and $τ_{2}$ for type 2) . We assu

Miroslav Kotrla, Frantisek Slanina, Milan Predota

We studied scaling in kinetic roughening and phase ordering during growth of binary systems using 1+1 dimensional single-step solid-on-solid model with two components interacting via Ising-like interaction with the strength K. We found that the model exhibits crossover from the intermediate regime, with effective scaling exponents for kinetic roughening sign

S. Jain, K. J. Hammarling

The random-bond XY spin glass with ferromagnetic next-nearest-neighbour interactions is studied on a square lattice by Monte Carlo simulations. We find strong evidence for a finite-temperature spin glass transition at $T_c\approx 1.1$. We also give estimates for the spin glass critical exponents for different values of the strength of the nearest-neighbour i

E. N. M. Cirillo, G. Gonnella, M. Troccoli, A. Maritan

We consider the procedure for calculating the pair correlation function in the context of the Cluster Variation Methods. As specific cases, we study the pair correlation function in the paramagnetic phase of the Ising model with nearest neighbors, next to the nearest neighbors and plaquette interactions in two and three dimensions. In presence of competing i

Matthieu Micoulaut

In this article, we present a universal relationship between the glass transition temperature $T_g$ and the local glass structure. The derivation of the simplest expression of this relationship and some comparisons with experimental $T_g$ values have already been reported in a recent letter. We give here the analytical expression of the parameter $β$ of the

Reimer Kuehn, Yu-Cheng Lin, Gerhard Poeppel

A new approach to combinatorial optimization based on systematic move-class deflation is proposed. The algorithm combines heuristics of genetic algorithms and simulated annealing, and is mainly entropy-driven. It is tested on two problems known to be NP hard, namely the problem of finding ground states of the SK spin--glass and of the 3-$D$ $\pm J$ spin-glas

Dirk Helbing

The gas-kinetic foundation of fluid-dynamic traffic equations suggested in previous papers [Physica A 219, 375 and 391 (1995)] is further refined by applying the theory of dense gases and granular materials to the Boltzmann-like traffic model by Paveri-Fontana. It is shown that, despite the phenomenologically similar behavior of ordinary and granular fluids,

Hikaru Kawamura

Recent theoretical and experimental studies on the critical properties of frustrated antiferromagnets with the noncollinear spin order, including stacked-triangular antiferromagnets and helimagnets, are reviewed. Particular emphasis is put on the novel critical and multicritical behaviors exhibited by these magnets, together with an important role played by

H. -B. Schüttler, C. Gröber, H. G. Evertz, W. Hanke

We show that doping-induced charge fluctuations in strongly correlated Hubbard electron systems near the 1/2-filled, insulating limit cause overscreening of the electron-electron Coulomb repulsion. The resulting attractive screened interaction potential supports d_{x^2-y^2}-pairing with a strongly peaked, doping dependent pairing strength at lower doping, fo

Yolande H. Szczech, Michael A. Tusch, David E. Logan

We study the collective excitation spectrum of a d=3 site-disordered Anderson-Hubbard model at half-filling, via a random-phase approximation (RPA) about broken-symmetry, inhomogeneous unrestricted Hartree-Fock (UHF) ground states. We focus in particular on the density and character of low-frequency collective excitations in the transverse spin channel. In t

Lauri Karttunen

This paper presents a novel formalization of optimality theory. Unlike previous treatments of optimality in computational linguistics, starting with Ellison (1994), the new approach does not require any explicit marking and counting of constraint violations. It is based on the notion of &#34;lenient composition,&#34; defined as the combination of ordinary co

Adam Frank, Dongsu Ryu, Kris Davidson

In this paper we address the issue of the origin of LBV bipolar bubbles. Previous studies have explained the shapes of LBV nebulae, such as $η$ Car, by invoking the interaction of an isotropic fast wind with a previously deposited, slow aspherical wind (a ``slow torus&#39;&#39;). In this paper we focus on the opposite scenario where an aspherical fast wind e

Michael S. Vogeley

I review some results of estimation of the power spectrum of density fluctuations from galaxy redshift surveys and discuss advances that may be possible with the Sloan Digital Sky Survey. I then examine the realities of power spectrum estimation in the presence of Galactic extinction, photometric errors, galaxy evolution, clustering evolution, and uncertaint

S. G. Djorgovski

Several arguments suggest that quasars at z > 4 may be in the cores of future giant ellipticals, and forming at the very highest peaks of the primordial density field. A strong bias-driven primordial clustering is then expected in these fields, which are naturally interpreted as the cores of future rich clusters. High-redshift quasars can thus be used as mar

H. Teplitz, M. Malkan, I. S. McLean

We report the cumulative results of an on-going near-infrared search for redshifted H-alpha emission from normal galaxies at z>2. An infrared search reduces the bias due to reddening. Using narrow-band imaging with the Near Infrared Camera on the Keck I 10-m telescope, a survey area of almost 12 square arcminutes has been covered. Target regions were selecte

Karsten Jedamzik

A brief overview of non-standard big bang nucleosynthesis (BBN) scenarios is presented. Trends and results of the light-element nucleosynthesis in BBN scenarios with small-scale or large-scale inhomogeneity, the presence of antimatter domains, stable or unstable massive neutrinos, neutrino oscillations, neutrino degeneracy, or massive decaying particles are

Marc Postman, Lori M. Lubin, J. B. Oke

We present an extensive photometric and spectroscopic study of two high-redshift clusters of galaxies based on data obtained from the Keck 10m telescopes and the Hubble Space Telescope. The clusters CL0023+0423 (z=0.84) and CL1604+4304 (z=0.90) are part of a multi-wavelength program to study nine candidate clusters at z > 0.6 (Oke, Postman & Lubin 1998). Bas

Przemyslaw R. Wozniak, Andrzej A. Zdziarski, David Smith, Greg M. Madejski

We study X-ray and soft gamma-ray spectral properties of BLRGs using data from Ginga, ASCA, OSSE and EXOSAT. The X-ray spectra are well fitted by an intrinsic power-law continuum with an energy index of alpha ~ 0.7, moderately absorbed by a cold medium. In addition, the Ginga spectra show Fe K-alpha lines with an average equivalent width of ~ 100 eV, and, in

C. W. Engelbracht, M. J. Rieke, G. H. Rieke, D. M. Kelly

We have obtained long-slit spectra of NGC 253 in the J, H, K, and N bands, broadband images in the J, H, and Ks bands, narrowband images centered at the wavelengths of BrGamma and H2(1,0)S(1), and imaging spectroscopy centered on [NeII](12.8um). We use these data and data from the literature in a comprehensive re-assessment of the starburst in this galaxy. W

L. M. Haffner, R. J. Reynolds, S. L. Tufte

During the initial data reduction of the Wisconsin H-Alpha Mapper (WHAM) H-Alpha Sky Survey, we have discovered several very long (~30--80 deg) filaments superimposed on the diffuse H-Alpha background. These features have no clear correspondence to the other phases of the interstellar medium revealed by 21 cm, X-ray, IR, or radio continuum surveys, and they

A. Aret, A. Sapar

We give concisely the formulae governing diffusion of chemical elements and their isotopes in quiescent stellar atmospheres, due to electrostatic, gravitational and radiation fields and to impacts between particles. Isotope segregation of heavy elements due to light-induced drift is emphasized.

N. A. Sokolov

A new method of T_eff determination for CP stars is proposed. The method is based on the fact that the slope of the energy distribution in the Balmer continuum near the Balmer jump is identical for &#34;normal&#34; main sequence stars and for CP stars with the same T_eff. It is shown that the T_eff of CP stars derived by this method are in good agreement wit

Karsten Jedamzik

Observations by the MACHO collaboration indicate that a significant fraction of the galactic halo dark matter may be in form of compact objects with masses $M\sim 0.5M_{\odot}$. Identification of these objects as red or white dwarfs is problematic due to stringent observational upper limits on such dwarf populations. Primordial black hole (PBH) formation fro

Anshu Gupta, Amruta Mishra, Hiranmaya Mishra, A. R. Prasanna

We consider here the structure of rotating compact objects endowed with a magnetic field in general relativity as models of pulsars. We discuss first the structure of rotating stars in the framework of Hartle taking different realistic equations of state and study their effects on bulk properties of the star. We consider the possibilty of rotating stars with

J. A. Sellwood, Robert W. Nelson, Scott Tremaine

We study the vertical heating and thickening of galaxy disks due to accretion of small satellites. Our simulations are restricted to axial symmetry, which largely eliminates numerical evolution of the target galaxy but requires the trajectory of the satellite to be along the symmetry axis of the target. We find that direct heating of disk stars by the satell

Gerard Gilmore, Rosemary F. G. Wyse

It is well-established that the vast majority of metal-poor Galactic halo stars shows evidence for enrichment by solely massive stars. Recent observations have identified more varied behavior in the pattern of elemental abundances measured for metal-rich, [Fe/H]=-1, halo stars, with both high and low values of the ratio of [alpha/Fe]. The low values are most

T. Ryabchikova, O. Kotchoukhov, G. Galazutdinov, F. Musaev

A careful investigation of a CCD spectrum of the SB1 system kappa Cnc in the spectral region 3800 A - 8000 A resulted in the discovery of the lines of the secondary star. We then analyzed several short-wavelength range Reticon spectra obtained at different orbital phases to find additional radial velocities. The mass ratio is m_A/m_B = 2.2 +- 0.1 and, from b

Samar Abbas, Afsar Abbas, Shukadev Mohanty

A few of the major mass extinctions of paleontology have recently been found to consist of two distinct extinction peaks at higher resolution. A viable explanation for this remains elusive. In this paper it is shown that the recently proposed volcanogenic dark matter model can explain this puzzling characteristic of these extinctions. The accumulation and an

J. Alves, C. Lada, E. Lada, S. Kenyon

We report results of a near--infrared imaging survey of L977, a dark cloud in Cygnus seen in projection against the plane of the Milky Way. We use measurements of the near--infrared color excess and positions of the 1628 brightest stars in our survey to measure directly dust extinction through the cloud following the method described by Lada et al. (1994). W

B. J. Boyle, S. M. Croom, R. J. Smith, T. Shanks

We review previous results on the clustering and environments of QSOs. We show that the correlation length for QSOs derived from existing surveys is r~5/h Mpc, similar to the observed correlation length for field galaxies at the present epoch. The galaxy environment for z<1 radio-quiet QSOs is also consistent with field galaxies. The evolution of the QSO cor