November 1998 arXiv papers — page 22

D. Garfinkle, C. Gundlach, J. M. Martin-Garcia

For the formation of a black hole in the gravitational collapse of a massless scalar field, we calculate a critical exponent that governs the black hole angular momentum for slightly non-spherical initial data near the black hole threshold. We calculate the scaling law by second-order perturbation theory. We then use the numerical results of a previous first

J. B. Griffiths, S. Micciche

We analyse vacuum gravitational "soliton" solutions with real poles in the cosmological context. It is well known that these solutions contain singularities on certain null hypersurfaces. Using a Kasner seed solution, we demonstrate that these may contain thin sheets of null matter or may be simple coordinate singularities, and we describe a number o

Jacob D. Bekenstein

I discuss the no hair principle, the recently found hairy solutions, generic properties of nonvacuum spherical static black holes, and the new no scalar hair theorems. I go into the generic phenomenon of superradiance, first uniform linear motion superradiance, then Kerr black hole superradiance, and finally general rotational superradiance and its possible

Philip Edmonds

This paper presents a partial solution to a component of the problem of lexical choice: choosing the synonym most typical, or expected, in context. We apply a new statistical approach to representing the context of a word through lexical co-occurrence networks. The implementation was trained and evaluated on a large corpus, and results show that the inclusio

Philip Edmonds

This paper argues that an interlingual representation must explicitly represent some parts of the meaning of a situation as possibilities (or preferences), not as necessary or definite components of meaning (or constraints). Possibilities enable the analysis and generation of nuance, something required for faithful translation. Furthermore, the representatio

L. Bass, G. Chastek, P. Clements, L. Northrop

The second Software Engineering Institute Product Line Practice Workshop was a hands-on meeting held in November 1997 to share industry practices in software product lines and to explore the technical and non-technical issues involved. This report synthesizes the workshop presentations and discussions, which identified factors involved in product line practi

Inderjeet Mani, Eric Bloedorn

A key problem in text summarization is finding a salience function which determines what information in the source should be included in the summary. This paper describes the use of machine learning on a training corpus of documents and their abstracts to discover salience functions which describe what combination of features is optimal for a given summariza

Todd L. Veldhuizen

This paper explores the relationship between C++ templates and partial evaluation. Templates were designed to support generic programming, but unintentionally provided the ability to perform compile-time computations and code generation. These features are completely accidental, and as a result their syntax is awkward. By recasting these features in terms of

J. Mesot, M. R. Norman, H. Ding, J. C. Campuzano

In a recent paper Saini et al. have reported evidence for a pseudogap around (pi,0) at room temperature in the optimally doped superconductor Bi2212. This result is in contradiction with previous ARPES measurements. Furthermore they observed at certain points on the Fermi surface hot spots of high spectral intensity which they relate to the existence of stri

S. A. Artamonov, Yu. G. Pogorelov, V. R. Shaginyan

We analyze stability of a fermion system with model repulsive pair interaction potential. The possibility for different types of restructuring of the Fermi ground state (at sufficiently great coupling constant) is related to the analytic properties of such potential. In particular, for the screened Coulomb law it is shown that the restructuring cannot be of

Isabelle Kraus, Robert B. Meyer

We report on a new experimental procedure for forming and studying polar smectic liquid crystal films. A free standing smectic film is put in contact with a liquid drop, so that the film has one liquid crystal/liquid interface and one liquid crystal/air interface. This polar environment results in changes in the textures observed in the film, including a boo

Eldon Emberly, George Kirczenow

Quantum descriptions of many complex systems are formulated most naturally in bases of states that are not mutually orthogonal. We introduce a general and powerful yet simple approach that facilitates solving such models exactly by embedding the non-orthogonal states in a new Hilbert space in which they are by definition mutually orthogonal. This novel appro

Oleg Derzhko, Taras Krokhmalskii

Using a numerical approach we examine the dynamics of $zz$ correlations for the spin-$1\over2$ isotropic XY chain with random Lorentzian intersite coupling and transverse field at sites that depends linearly on the neighbouring couplings. We study in detail the wave vector- and frequency-dependent $zz$ structure factor at different values of Hamiltonian para

Leonid Pechenik, Herbert Levine

The problem of velocity selection for reaction fronts has been intensively investigated, leading to the successful marginal stability approach for propagation into an unstable state. Because the front velocity is controlled by the leading edge which perforce has low density, it is interesting to study the role that finite particle number fluctuations have on

I. V. Stasyuk, A. M. Shvaika, K. V. Tabunschyk

Dynamics and thermodynamics of the model with local anharmonism in the case of absence of the electron (Hubbard) correlation is investigated in the present work. The correlation functions, mean values of pseudospin and particle number as well as the thermodynamical potential are calculated. The calculation is performed by diagrammatic method in the mean fiel

Eric Lutz, Hans A. Weidenmueller

Are Markovian master equations for quantum Brownian motion independent of model assumptions used in the derivation and, thus, universal? With the aim of answering this question, we use a random band-matrix model for the system-bath interaction to derive Markovian master equations for the time evolution of one-dimensional quantum systems weakly coupled to a h

E. Il'ichev, V. Zakosarenko, R. P. J. IJsselsteijn, H. E. Hoenig

The current-phase relation (CPR) for asymmetric 45 degree Josephson junctions between two d-wave superconductors has been predicted to exhibit an anomalous periodicity. We have used the single-junction interferometer to investigate the CPR for this kind of junctions in YBCO thin films. Half-fluxon periodicity has been experimentally found, providing a novel

Pavel Smilauer, Martin Rost, Joachim Krug

Homoepitaxial growth is unstable towards the formation of pyramidal mounds when interlayer transport is reduced due to activation barriers to hopping at step edges. Simulations of a lattice model and a continuum equation show that a small amount of desorption dramatically speeds up the coarsening of the mound array, leading to coarsening exponents between 1/

M. C. Marques, J. F. F. Mendes

We propose and study a model where, for the first time, two aspects are present: parity conservation and infinitely many absorbing states. Whereas steady-state simulations show that the static critical behaviour is not affected by the presence of multiple absorbing configurations, the influence of the initial state associated with the presence of slowly deca

A. J. Manninen, R. S. Poikolainen, T. V. Ryynanen, J. P. Pekola

We have performed the first experiments in a superconductor - normal metal - superconductor single electron transistor in which there is an extra superconducting strip partially overlapping the normal metal island in good metal-to-metal contact. Superconducting proximity effect gives rise to current peaks at voltages below the quasiparticle threshold. We int

X. Zotos

Using the Bethe ansatz method, the zero frequency contribution (Drude weight) to the spin current correlations is analyzed for the easy plane antiferromagnetic Heisenberg model. The Drude weight is a monotonically decreasing function of temperature for all 0<Delta< 1, it approaches the zero temperature value with a power law and it appears to vanish for all

J. Reidl, A. Csordás, R. Graham, P. Szépfalusy

The mode frequencies of a weakly interacting Bose gas in a magnetic trap are studied as a function of the anisotropy of the trap. As in earlier works the generalized Hartree-Fock-Bogoliubov equations within the Popov approximation (HFB-Popov) are used for our calculations. The new feature of our work is the combined use of a mode expansion in a finite basis

P. Durganandini, Sumathi Rao

We study transport through two Luttinger liquids (one-dimensional electrons interacting through a Coulomb repulsion in a metal) coupled together at {\it two} points. External voltage biases are incorporated through boundary conditions. We include density-density couplings as well as single-particle hops at the contacts. For weak repulsive interactions, trans

Abhik Basu, Jayanta K Bhattacharjee, Sriram Ramaswamy

We show that a recently proposed [J. Fleischer and P.H. Diamond, {\em Phys. Rev. E}{\bf 58}, R2709 (1998)] one-dimensional Burgers-like model for magnetohydrodynamics (MHD) is in effect identical to existing models for drifting lines and sedimenting lattices. We use the model to demonstrate, contrary to claims in the literature, that the energy spectrum of M

Hyeong Rag Lee

A fractional quantization in a two dimensional space is proposed. The angular momenta of the two dimensional electrons are quantized in fractional numbers by the boundary conditions on a multi-layered Riemann surface. Extended wave functions for the incompressible quantum fluid states are presented and the cohesive and the excitation energies are given.

P. Coleman, A. M. Tsvelik, N. Andrei, H. Y. Kee

We discuss the possibility of a co-operative Kondo effect driven by channel interference in a Kondo lattice where local moments are coupled to a single Fermi sea via two orthogonal scattering channels. In this situation, the channel quantum number is not conserved. We argue that the absence of channel conservation causes the Kondo effect in the two channels

Eduardo Fradkin, Chetan Nayak, Kareljan Schoutens

We construct Landau-Ginzburg effective field theories for fractional quantum Hall states -- such as the Pfaffian state -- which exhibit non-Abelian statistics. These theories rely on a Meissner construction which increases the level of a non-Abelian Chern-Simons theory while simultaneously projecting out the unwanted degrees of freedom of a concomitant envel

Margarita Voitikova

The stochastic discrete space-time model of an immune response on tumor spreading in a two-dimensional square lattice has been developed. The immunity-tumor interactions are described at the cellular level and then transferred into the setting of cellular automata (CA). The multistate CA model for system, in which all statesoflattice sites, composing of both

P. D. Ditlevsen, I. A. Mogensen

We study the GOY shell model simulating the cascade processes of turbulent flow. The model has two inviscid invariants governing the dynamical behavior. Depending on the choice of interaction coefficients, or coupling parameters, the two invariants are either both positive definite, analogous to energy and enstrophy of 2D flow, or only one is positive defini

S. Laine, J. H. Knapen, D. Pérez-Ramírez, R. Doyon

We report the discovery of trailing grand-design nuclear spiral structure in the spiral galaxy NGC 5248. Two tightly-wound red spiral arms, with widths less than 1 arcsec (~75 pc), emanate at 1 arcsec outside the quiescent nucleus of the galaxy, and can be followed for 3 arcsec, appearing to end before the radius of the circumnuclear starburst &#34;ring&#34;

Chris Mihos, Marco Spaans, Stacy McGaugh

We present models for the interstellar medium in disk galaxies. In particular, we investigate whether the ISM in low surface brightness galaxies can support a significant fraction of molecular gas given their low metallicity and surface density. It is found that the abundance and line brightness of CO in LSB galaxies is small and typically below current obse

Melinda L. Weil

The virial, projected and spherical Jeans equation galaxy mass estimators are compared. High-resolution models of elliptical galaxies from N-body simulations are used to compare predicted mass profiles. Averages over eight models and directions in the three intrinsic projections show that all the mass estimators are comparably poor for r<4 kpc but that, with

Q. Daniel Wang

We have investigated the structure and evolution of hot gas in the 30 Dor nebula, based on recent X-ray observations. Our deep ROSAT HRI image shows that diffuse X-ray emission arises in blister-shaped regions outlined by loops of HII gas. X-ray spectroscopic data from ASCA confirm the thermal nature of the emission and indicate that hot gas temperature decr

F. Nicastro, F. Fiore, G. Matt

A number of emission and absorption features are expected to be visible in high energy resolution X-ray spectra of type 1 AGN with ionized gas along the line of sight (so called &#34;warm absorbers&#34;). Emission strongly depends on the geometrical configuration of the gas, while absorption along the line of sight does not. Absorption features include photo

A. F. Boden, C. D. Koresko

We have determined the visual orbit for the spectroscopic binary iota~Pegasi with interferometric visibility data obtained by the Palomar Testbed Interferometer in 1997. iota~Pegasi is a double-lined binary system whose minimum masses and spectral typing suggests the possibility of eclipses. Our orbital and component diameter determinations do not favor the

Paolo Gondolo

We propose an estimator of the microlensing optical depth from pixel lensing data that involves only measurable quantities. In comparison to the only previously proposed estimator, it has the advantage of not being limited to events with large magnification at maximum, and it applies equally well to satellite and ground-based observations.

I. A. Smith, R. P. J. Tilanus, J. van Paradijs, T. J. Galama

We discuss the first results of our ongoing program of Target of Opportunity observations of gamma-ray bursts (GRBs) using the SCUBA instrument on the James Clerk Maxwell Telescope. We present the results for GRB 970508, 971214, 980326, 980329, 980519, and 980703. Our most important result to date is the detection of a fading counterpart to GRB 980329 at 850

R. P. van der Marel

HST observations show that the surface brightness profiles of early-type galaxies have central cusps. I summarize here the results of van der Marel (1999), which show that the observed characteristics of these cusps are consistent with the hypothesis that all early-type galaxies have central black holes (BHs) that grew adiabatically in homogeneous isothermal

A. C. Quillen

I summarize a series of studies where the underlying theme is to exploit non-axisymmetry disk structures such as bars and spiral arms. By measuring the strength of gravitational forces from these structures we can measure the mass in them. The advantage of this approach is that mass to light ratios can be constrained in a way independent of the dark matter p

Wei Cui, Wan Chen, S. N. Zhang

The X-ray observation of black hole candidates provides a valuable tool to probe regions very close to the central black hole, where strong-field relativistic effects become important. Recent studies have shown that these effects seem to manifest themselves in the observed X-ray spectrum, in terms of the shape of X-ray continuum and the profile of emission l

John D. Barrow

We analyse a generalisation of general relativity that incorporates a cosmic time-variation of the velocity of light in vacuum, $c,$ and the Newtonian gravitation &#39;constant&#39;, $G,$ proposed by Albrecht and Maguejo. We find exact solutions for Friedmann universes and determine the rate of variation of $c$ required to solve the flatness and classical co

S. L. Pistinner, P. H. Hauschildt, D. Eichler, E. A. Baron

We calculate a grid of spherically symmetric OB stellar atmospheres at low metallicities, including both non-local thermodynamic equilibrium (NLTE) and metal line blanketing effects. This is done to assess the uncertainties in helium abundance determination by nebular codes due to input stellar atmosphere models. The more sophisticated stellar atmosphere mod

M. R. S. Hawkins

The idea that dark matter in the form of small compact bodies (most plausibly planetary mass primordial black holes) betrays its presence by the microlensing of quasars, has been stimulated by statistical studies of quasar light curves and gravitationally lensed quasar systems. In this paper we review this evidence, and discuss the significance of the recent

T. Venturi, R. Morganti, S. Bardelli, D. Dallacasa

We present here the first results of a 22cm survey of the Shapley Concentration core. The observations were carried out with the Australia Telescope Compact Array. Our radio observations completely and uniformely cover the A3558 complex, allowing a thorough multifrequency study, by comparison of our results with the available optical spectroscopic and X-ray

S. Bardelli, E. Zucca, G. Zamorani

We present the results of a galaxy redshift survey in the central region of the Shapley Concentration. Our total sample contains ~2000 radial velocities of galaxies both in the clusters and in the intercluster field. We reconstruct the density profile of this supercluster, calculate its overdensity and total mass. Moreover we detect a massive structure behin

J. Kataoka, J. R. Mattox, J. Quinn, H. Kubo

We present the results of a multiwavelength campaign for Mrk 501 performed in March 1996 with ASCA, EGRET, Whipple, and optical telescopes. In the X-ray band, a spectral break was observed around 2 keV. We report here for the first time the detection of high-energy gamma-ray flux from Mrk 501 with EGRET with 3.5 sigma significance (E>100 MeV). Higher flux wa

Seungjoon Hyun, Won Tae Kim, Julian Lee

We study AdS/CFT correspondence in the case of AdS3. We obtain the statistical entropy of the BTZ black hole in terms of the correct central charge and the conformal dimensions for the states corresponding to the BTZ black hole. We point out the difference between our method and the old fashioned approaches based on SL(2,R) Wess-Zumino-Witten model or Liouvi

B. L. G. Bakker, M. N. Chernodub, M. I. Polikarpov, A. I. Veselov

We show that the extended Abelian magnetic monopoles in the Maximal Abelian projection of lattice SU(2) gluodynamics are locally correlated with the magnetic and the electric parts of the SU(2) action density. These correlations are observed in the confined and in the deconfined phases.

Daniel S. Reich, Jonathan D. Victor, Bruce W. Knight

We describe a new, computationally simple method for analyzing the dynamics of neuronal spike trains driven by external stimuli. The goal of our method is to test the predictions of simple spike-generating models against extracellularly recorded neuronal responses. Through a new statistic called the power ratio, we distinguish between two broad classes of re

A. S. Rinat, B. K. Jennings

We derive for a non-relativistic system an approximation for Final State Interactions in a form, resembling a DWIA which corrects the structure function computed in the PWIA. We then compare the Gersch-Rodriguez-Smith and the IA series for structure functions and prove that to order ${\cal O}(1/q^2)$ the above DWIA representation is contained in the GRS seri

Roberto Capote, Augusto Gonzalez

A new stochastic number projection method is proposed. The component of the BCS wave function corresponding to the right number of particles is obtained by means of a Metropolis algorithm in which the weight functions are constructed from the single-particle occupation probability. Either standard BCS or Lipkin-Nogami probability distributions can be used, t

Susana A. Salamanca-Riba, David A. Vogan

Suppose G is a real reductive Lie group in Harish-Chandra&#39;s class. We propose here a structure for the set Π_u(G) of equivalence classes of irreducible unitary representations of G. (The subscript u will be used throughout to indicate structures related to unitary representations.) We decompose Π_{u}(G) into disjoint subsets with a (very explicit) discre

Hing Sun Luk, Stephen S. -T. Yau

The purpose of this paper is to give a counterexample of Theorem 10.4 in [Ann. of Math. 102 (1975), 223-290]. In the Harvey-Lawson paper, a global result is claimed, but only a local result is proven. This theorem has had a big impact on CR geometry for almost a quarter of a century because one can use the theory of isolated singularities to study the theory

Harvey M. Friedman

We present a coherent collection of finite mathematical theorems some of which can only be proved by going well beyond the usual axioms for mathematics. The proofs of these theorems illustrate in clear terms how one uses the well studied higher infinities of abstract set theory called large cardinals in an essential way in order to derive results in the cont

John Friedlander, Henryk Iwaniec

This article develops a new sieve method which by adding an additional axiom to the classical formulation breaks the well-known parity problem and allows one to detect primes in thin, interesting integer sequences. In the accompanying paper [math.NT/9811184] the practicality of the axiom is demonstrated by verifying it (and the other axioms) to produce prime

John Friedlander, Henryk Iwaniec

This article proves that there are infinitely many primes of the form a^2 + b^4, in fact getting the asymptotic formula. The main result is that \sum_{a^2 + b^4\le x} Λ(a^2 + b^4) = 4π^{-1}κx^{3/4} (1 + O(\log\log x / \log x)) where a, b run over positive integers and κ= \int^1_0 (1 - t^4)^{1/2} dt = Γ(1/4)^2 /6\sqrt{2π}. Here of course, Λdenotes the von Man

Diego Cordoba

The problem we are concerned with is whether singularities form in finite time in incompressible fluid flows. It is well known that the answer is ``no&#39;&#39; in the case of Euler and Navier-Stokes equations in dimension two. In dimension three it is still an open problem for these equations. In this paper we focus on a two-dimensional active scalar model

William A. Veech

The goals of this paper are first to describe and then to apply an ergodic-theoretic generalization of the Siegel integral formula from the geometry of numbers. The general formula will be seen to serve both as a guide and as a tool for questions concerning the distribution, in senses to be made precise, of the set of closed leaves of measured foliations sub

Steven Boyer, Xingru Zhang

Consider the exterior M of a hyperbolic knot lying in a closed, connected, orientable 3-manifold. Culler and Shalen defined norm on H_1(dM;R) using the SL(2,C) character variety of pi_1(M). The Culler-Shalen norm encodes many topological properties of M; in particular it provides information about Dehn fillings of M. Their construction may be applied to arbi

Paul J. Sanders

A sharp bound is derived for the nilpotency class of a regular p-group in terms of its coexponent, and is used to show that the number of groups of order p^n with a given fixed coexponent, is independent of n, for p and n sufficiently large. Explicit formulae are calculated in the case of coexponent 3.

Julian Dontchev

This paper covers some recent progress in the study of sg-open sets, sg-compact spaces, N-scattered spaces and some related concepts. A subset $A$ of a topological space $(X,τ)$ is called sg-closed if the semi-closure of $A$ is included in every semi-open superset of $A$. Complements of sg-closed sets are called sg-open. A topological space $(X,τ)$ is called

Julian Dontchev

The aim of this paper is to introduce the class of ${\cal A}{\cal B}$-sets as the sets that are the intersection of an open and a semi-regular set. Several classes of well-known topological spaces are characterized via the new concept. A new decomposition of continuity is provided.

I. I. Kogan, A. Momen, R. J. Szabo

We consider the conformally-invariant coupling of topologically massive gravity to a dynamical massless scalar field theory on a three-manifold with boundary. We show that, in the phase of spontaneously broken Lorentz and Weyl symmetries, this theory induces the target space zero mode of the vertex operator for the string dilaton field on the boundary of the

M. Wobisch

Various QCD studies based on jet observables in hadronic final states in deep-inelastic scattering and hadron-hadron collisions are presented. Measured quantities are event shape variables, jet rates and jet cross sections. QCD analyses have been performed to determine the value of the strong coupling constant $α_s(M_z)$, the gluon density in the proton and

Maria Teresa DOVA, John SWAIN, Lucas TAYLOR

We use recent experimental measurements of tau branching fractions to determine the weak charged current magnetic and electric dipole moments of the tau and the Michel parameter $η$ with unprecedented precision. These results are then used to constrain the tau compositeness scale and the allowed parameter space for Higgs doublet models. We also present new c

Stephan Narison

I report here on the (first) direct extraction of the running charm quark mass m_c(ν) from the D-meson sum rules, and on the implications of this result for the estimate of the leptonic decay constants f_{D_s}. The outputs: m_c(M_c)=(1.08\pm 0.11) GeV, f_{D}= (1.52\pm 0.16)f_π, f_{D_s}= (1.75\pm 0.18)f_πand f_B=(1.44\pm 0.07)f_πare in good agreement with the

Andrei Kondashov

A study of the $π^0π^0$ system produced in charge exchange $π^-p$ collisions at 38 and 100 GeV/c and in central $pp$ interactions at 450 GeV/c has been carried out. The $S$ wave has rather a complicated structure in both processes indicating the existence of several scalar resonances. The $f_0(980)$ and $f_0(1500)$ appear as dips at 1 and 1.5 GeV in the $S$

Andrei V. Frolov

This paper studies the non-spherical perturbations of the continuously self-similar critical solution of the gravitational collapse of a massless scalar field (the Roberts solution). The exact analysis of the perturbation equations reveals that there are no growing non-spherical perturbation modes.

Lane A. Hemaspaandra, Alan L. Selman

Each researcher should have a full shelf---physical or virtual---of books on writing and editing prose. Though we make no claim to any special degree of expertise, we recently edited a book of complexity theory surveys (Complexity Theory Retrospective II, Springer-Verlag, 1997), and in doing so we were brought into particularly close contact with the subject

Rob Swaters

Previous studies of dwarf irregular galaxies have mostly found that these systems have slowly rising rotation curves and that they are dominated by dark matter, even well within the optical disk. However, based on new observations and a different technique to derive rotation curves, we find that the rotation curves may be steeper and that dark matter may be

Robert A. Benjamin

Several authors have now suggested that some interstellar clouds above the plane of the Galaxy are interacting with the Reynolds&#39; layer, the warm ionized gas extending well above (H~910 pc) the Galactic plane (Reynolds 1993). Characterizing the interaction between these clouds and their surroundings should be useful in understanding one source of interst

Mordecai-Mark Mac Low

In this review I focus on how massive stars in the disks of galaxies determine the properties of the ionized, gaseous haloes of star-forming galaxies. I first examine the ionization state of the halo, and conclude that diluted radiation from massive stars, along with a possible secondary heating source such as shocks, appears sufficient to explain the observ

Henry A. Kobulnicky, Robert C. Kennicutt, James L. Pizagno

The advent of 8--10 meter class telescopes enables direct measurement of the chemical properties in the ionized gas of cosmologically--distant galaxies with the same nebular analysis techniques used in local H II regions. We show that spatially unresolved (i.e., global) emission line spectra can reliably indicate the chemical properties of distant star-formi

M. Bliton, E. Rizza, J. O. Burns, F. N. Owen

We have examined the ROSAT PSPC X-ray properties of a sample of 15 Abell clusters containing 23 narrow-angle tailed (NAT) radio galaxies. We find that clusters with NATs show a significantly higher level of substructure than a similar sample of radio-quiet clusters, indicating that NAT radio sources are preferentially located in dynamically complex systems.