May 1998 arXiv papers — page 12

C. V. Rodrigues, D. Cieslinski, J. E. Steiner

We present the first optical polarimetric measurements of RX J1141.3-6410 which confirm that star as a polar. The circular polarization varies between 0 and 13% with the orbital period. Halpha spectroscopy shows that this line is formed by, at least, two components: a broad and a narrow one. The phase of maximum redshift of the broad component is shifted by

S. Engineer, K. Srinivasan, T. Padmanabhan

Several investigations in the study of cosmological structure formation use numerical simulations in both two and three dimensions. In this paper we address the subtle question of ambiguities in the nature of two dimensional gravity in an expanding background. We take a detailed and formal approach by deriving the equations describing gravity in (D+1) dimens

J. D. Landstreet

I have carried out spectrum synthesis of R = 120,000 spectra of several A and B stars having v sin i less than about 6 km/s. The following conclusions emerge: (1) As T_e descends from 12,000 to 8,000 K, microturbulent velocity xi deduced from abundance analysis rises steadily from 0 to about 5 km/s. (2) Stars with xi >= 1 km/s show direct evidence in their l

A. P. Hatzes, A. Kanaan

We present recent results from our radial velocity (RV) studies of rapidly oscillating Ap (roAp) stars. Our measurements reveal that the pulsational amplitude of these stars depends on the spectral region that is examined. For one star, gamma Equ, the pulsational RV amplitude depends on both line strength and atomic species. The elemental difference is most

S. Hubrig, F. Castelli, G. Mathys

Preliminary results from a study of the isotopic compositions of the elements Hg and Pt in a number of HgMn stars are presented. This work represents an improvement over previous studies thanks to the very high spectral resolution available (R = 118 000) and to the new information on wavelengths and atomic structure of Hg II and Pt II.

M. M. Dworetsky, C. M. Jomaron, C. A. Smith

There is a widespread assertion in the literature that the optical Ga lines give much higher abundances than the UV lines. We have determined Ga abundances in HgMn stars taking the observed hyperfine structure of the optical Ga II lines into account. This reduces these abundances to within 0.2 dex of the values from the resonance lines.

T. N. Dorokhova, N. I. Dorokhov

Since 1992, observations of roAp stars have been carried out using the dual-channel photometer attached to the 0.8m telescope, which is situated in Central Asia, at the Mt. Dushak-Erekdag station of Odessa Astronomical Observatory. Some results of observations of gamma Equ and of HD 134214 are presented. 5 stars were investigated as roAp candidates. The Four

Milan S. Dimitrijevic, Dragana Tankosic

In order to find out if regularities and systematic trends found to be apparent among experimental Stark line shifts allow the accurate interpolation of new data and critical evaluation of experimental results, the exceptions to the established regularities are analysed on the basis of critical reviews of experimental data, and reasons for such exceptions ar

I. V. Chernyshova, S. M. Andrievsky, V. V. Kovtyukh, D. E. Mkrtichian

Seven high-resolution and high S/N CCD spectra were used to derive elemental abundances in the atmosphere of VW Ari A (T_eff=7200, log g=3.7) which is the primary component of a visual binary system. The synthetic spectrum technique applied in the analysis allowed to reveal the following feature: the atmosphere of this star is strongly deficient in some meta

N. Magnussen

A project to construct a 17 m diameter imaging air Cherenkov telescope, called the MAGIC Telescope, is described. The aim of the project is to close the observation gap in the gamma-ray sky extending from 10 GeV as the highest energy measurable by space-borne experiments to 300 GeV, the lowest energy measurable by the current generation of ground-based Chere

Rodrigo A. Ibata, Harvey B. Richer, Gregory G. Fahlman, Michael Bolte

This paper presents a detailed description of the acquisition and processing of a large body of imaging data for three fields in the globular cluster M4 taken with the Wide Field and Planetary Camera 2 aboard the Hubble Space Telescope. Analysis with the ALLFRAME package yielded the deepest photometry yet obtained for this cluster. The resulting data-set for

Martin M. Sirk, Steve B. Howell

We have developed a model of the high-energy accretion region for magnetic cataclysmic variables and applied it to {\it Extreme Ultraviolet Explorer} observations of 10 AM Herculis type systems. The major features of the EUV light curves are well described by the model. The light curves exhibit a large variety of features such as eclipses of the accretion re

D. Raboud, M. Grenon, L. Martinet, R. Fux

Using available kinematical data for a subsample of NLTT stars from the HIPPARCOS mission we confirm the existence of a previously reported local anomaly in the (u,v) plane: the mean motion u for old disc stars, with v < -30 km/s, is largely positive (+19 +/- 9 km/s w.r.t. the Galactic Center). With the use of the newest global self-consistent numerical mode

B. Grzadkowski, Z. Hioki

The energy spectrum of the lepton(s) in e^+e^- --> tt-bar --> l^{+-} ...../l^+l^-..... at next linear colliders (NLC) is studied for arbitrary longitudinal beam polarizations as a possible test of new physics in top-quark couplings. The most general non-standard couplings for gamma-tt-bar, Ztt-bar and Wtb vertices are considered. Expected precision of the no

Bernd A. Berg, Ulrich H. E. Hansmann

Applied to statistical physics models, the random cost algorithm enforces a Random Walk (RW) in energy (or possibly other thermodynamic quantities). The dynamics of this procedure is distinct from fixed weight updates. The probability for a configuration to be sampled depends on a number of unusual quantities, which are explained in this paper. This has been

In-Saeng Suh, G. J. Mathews

We have studied finite temperature corrections to the baryon transport cross sections and diffusion coefficients. These corrections are based upon the recently computed renormalized electron mass and the modified state density due to the background thermal bath in the early universe. It is found that the optimum nucleosynthesis yields computed using our diff

T. V. Shahbazyan, I. E. Perakis, J. -Y. Bigot

We study the effect of Coulomb correlations on the ultrafast optical dynamics of small metal particles. We demonstrate that a surface-induced dynamical screening of the electron-electron interactions leads to quasiparticle scattering with collective surface excitations. In noble-metal nanoparticles, it results in an interband resonant scattering of d-holes w

Felix Finster, Joel Smoller, Shing-Tung Yau

It is shown analytically that the Dirac equation has no normalizable, time-periodic solutions in a Reissner-Nordstrom black hole background; in particular, there are no static solutions of the Dirac equation in such a background field. The physical interpretation is that Dirac particles can either disappear into the black hole or escape to infinity, but they

G. E. Volovik

We show that the clean superconductor with line of gap nodes is not in conflict with the Nernst theorem. The answer to the question in the title of the Schopohl-Dolgov paper in Phys. Rev. Lett. 80 (1998) 4761 (cond-mat/9802264) is yes.

T. Gaitanos, C. Fuchs, H. H. Wolter

The influence of realistic interactions on the reaction dynamics in intermediate energy heavy ion collisions is investigated. The mean field in relativistic transport calculations is derived from microscopic Dirac-Brueckner (DB) self-energies, taking non-equilibrium effects, in particular the anisotropy of the local phase space configurations, into account.

U. Nowak, K. D. Usadel

We study the dynamics of a driven interface in a two-dimensional random-field Ising model close to the depinning transition at small but finite temperatures T using Glauber dynamics. A square lattice is considered with an interface initially in (11)-direction. The drift velocity v is analyzed for the first time using finite size scaling at T = 0 and addition

M. Alimohammadi, V. Karimipour, M. Khorrami

A two--parameter family of asymmetric exclusion processes for particles on a one-dimensional lattice is defined. The two parameters of the model control the driving force and an effect which we call pushing, due to the fact that particles can push each other in this model. We show that this model is exactly solvable via the coordinate Bethe Ansatz and show t

Tommy Ohlsson, Hakan Snellman

We analyze recent measurements of the nucleon quark sea isospin asymmetry in terms of the chiral quark model. The new measurements indicate that the SU(3) model with modest symmetry breaking and no $η&#39;$ Goldstone boson gives a satisfactory description of data. We also discuss the matching parameter for the axial-vector current. Finally, we analyze the nu

A. B. Arbuzov, E. A. Kuraev, B. G. Shaikhatdenov

The lowest order QED radiative corrections to the radiative large angle Bhabha scattering process in the region where all kinematic invariants are large compared to the electron mass are considered. We show that the leading logarithmic corrections do not factorize before the Born cross section, contrary to the picture assumed in the renormalization group app

Mohammad R. Garousi

We derive fully covariant expressions for disk scattering amplitudes of any two massless closed strings in which mixed Neumann and Dirichlet world-sheet boundary conditions are included. From the two-point amplitudes, we derive the long range background fields and verify that they correspond to D$p$-brane bound state. Also, from the scattering amplitudes, we

Avraham E. Mayo

Some examples in support of the conjecture that the horizon area of a near equilibrium black hole is an adiabatic invariant are described. These clarify somewhat the conditions under which the conjecture would be true.

Daijiro Suematsu

We propose a neutrino mass matrix model in which five neutrino species remain light through the seesaw mechanism within a supersymmetric $3ν_L+3ν_R$ framework. We construct such a model based on the nonrenormalizable terms in the superpotential constrained by the discrete symmetry which may be expected in the models at the high energy scale such as superstri

Buell T. Jannuzi, John N. Bahcall, Jacqueline Bergeron, Alec Boksenberg

We present a catalogue of absorption lines obtained from the analysis of the ultra-violet spectra of 66 quasars. The data were acquired with the Faint Object Spectrograph of the HST as part of the Quasar Absorption Line Survey, a Key Project for the first four cycles of HST observations. This is the third of a series of catalogues of absorption lines produce

W. D. Heiss, M. Mueller, I. Rotter

Phase transitions in open quantum systems, which are associated with the formation of collective states of a large width and of trapped states with rather small widths, are related to exceptional points of the Hamiltonian. Exceptional points are the singularities of the spectrum and eigenfunctions, when they are considered as functions of a coupling paramete

Lucien Hardy, Wim van Dam

It is shown that with the use of entanglement a specific two party communication task can be done with a systematically smaller expected error than any possible classical protocol could do. The example utilises the very tight correlation between separate spin measurements on a singlet state for small differences in the angles of these two measurements. An ex

Dean Karlen

A method to approximate continuous multi-dimensional probability density functions (PDFs) using their projections and correlations is described. The method is particularly useful for event classification when estimates of systematic uncertainties are required and for the application of an unbinned maximum likelihood analysis when an analytic model is not ava

B. Dasgupta, P. Dasgupta, M. S. Janaki, T. Watanabe

Relaxed States of a slightly resistive and turbulent magnetized plasma is obtained by invoking the principle of minimum dissipation which leads to curl curl curl B = λB . A solution of the above equation is accomplished using the analytic continuation of the Chandrasekhar-Kendall eigenfunctions in the complex domain. The new features of this theory is to sho

Stefan Leupold, Ulrich Mosel

Vector mesons show up in the electromagnetic current-current correlator. QCD sum rules provide a constraint on hadronic models for this correlator. This constraint is discussed for the case of finite nuclear density concerning the longitudinal as well as the transverse part of the current-current correlator at finite three-momentum.

K. Jungmann, A. Grossmann, J. Merkel, V. Meyer

A new result from searching for muonium to antimuonium conversion is reported which sets an upper limit on the coupling constant in an assumed $(V-A) \times (V-A)$ type interaction of $G_{M\bar{M}} \leq 3\cdot 10^{-3} G_F$ ~ (90% C.L.). A particular Z_8 and a minimal 331 GUT model can be ruled out. Further new and stringent limits can be set for masses of bi

L. Beaulieu, L. Phair, L. G. Moretto, G. J. Wozniak

To make a statement about the nature and mechanism of fragmentation, it is necessary to probe directly any competition, or lack thereof, between the emission of various particle species as a function of excitation energy. The task is then to find a global observable that best follows the increase in excitation energy or dissipated energy. In the following, w

L. Beaulieu, L. Phair, L. G. Moretto, G. J. Wozniak

We explore the natural limit of binomial reducibility in nuclear multifragmentation by constructing excitation functions for intermediate mass fragments (IMF) of a given element Z. The resulting multiplicity distributions for each window of transverse energy are Poissonian. Thermal scaling is observed in the linear Arrhenius plots made from the average multi

Glenn G. Chappell

Let G be an n-vertex graph with list-chromatic number $χ_\ell$. Suppose each vertex of G is assigned a list of t colors. Albertson, Grossman, and Haas conjecture that at least $t n / {χ_\ell}$ vertices can be colored from these lists. We prove a lower bound for the number of colorable vertices. As a corollary, we show that at least 6/7 of the conjectured num

Christian Baer

Consider a nontrivial solution to a semilinear elliptic system of first order with smooth coefficients defined over an $n$-dimensional manifold. Assume the operator has the strong unique continuation property. We show that the zero set of the solution is contained in a countable union of smooth $(n-2)$-dimensional submanifolds. Hence it is countably $(n-2)$-

Christian Baer

We derive upper eigenvalue bounds for the Dirac operator of a closed hypersurface in a manifold with Killing spinors such as Euclidean space, spheres or hyperbolic space. The bounds involve the Willmore functional. Relations with the Willmore inequality are briefly discussed. In higher codimension we obtain bounds on the eigenvalues of the Dirac operator of

E. Schrohe, M. Walze, J. -M. Warzecha

Let (A,H,F) be a p-summable Fredholm module where the algebra A= C Γis generated by a discrete group of unitaries in L(H) which is of polynomial growth r. Then we construct a spectral triple (A,H,D) with F= sign D which is q-summable for each q > p+r+1. In case (A,H,F) is (p,\infty)-summable we obtain (q,\infty)-summability of (A,H,D) for each q > p+r+1.

S L Kleiman

This is a report on some recent work by Gaffney, Massey, and the author, characterizing the conditions A_f and W_f for a family of ICIS germs equipped with a function. First we introduce the work informally. Then we review the formal definitions of A_f and W_f, and state the theorems that characterize them by the constancy of Milnor numbers. Next we review t

Grigori Rybnikov

Let us say that a map of arcwise connected topological spaces (having the homotopy type of CW-complexes) is a pseudo-homeomorphism if it induces an isomorphism of the first integer homology groups and an epimorphism of the second integer homology groups. We prove that any invariant of a topological space w.r.t. pseudo-homeomorphisms is an invariant of the fu

S. Ferrara, M. A. Lledó, A. Zaffaroni

We consider certain supersymmetric Born-Infeld couplings to the D3 brane action and show that they give rise to massless and massive KK excitations of type IIB on $AdS_5\times S_5$, in terms of singleton Yang-Mills superfields.

Raphael Bousso

I show that de Sitter space disintegrates into an infinite number of copies of itself. This occurs iteratively through a quantum process involving two types of topology change. First a handle is created semiclassically, on which multiple black hole horizons form. Then the black holes evaporate and disappear, splitting the spatial hypersurfaces into large par

G. M. Graf, J. Hoppe

We calculate the power law decay, and asymptotic form of a (unique) SO(9) and SU(2) invariant wave function satisfying, to leading and sub-leading order, $Q_{\hatβ} ψ= 0$ for all 16 supercharges of the matrix model corresponding to supermembranes in 11 space-time dimensions.

S. Bellucci, A. Galajinsky

We reconsider the issue of the existence of a complex structure in the Gupta-Bleuler quantization scheme. We prove an existence theorem for the complex structure associated with the $d=10$ Casalbuoni-Brink-Schwarz superparticle, based on an explicitly constructed Lagrangian that allows a holomorphic-antiholomorphic splitting of the fermionic constraints cons

Meinulf Goeckeler, Thomas Schuecker

We are unable to formulate lattice gauge theories in the framework of Connes&#39; spectral triples.

Stuart Raby, Kazuhiro Tobe

In this paper we present a dynamical model of SUSY breaking with a hybrid messenger sector. SUSY is broken dynamically at a scale of order $10^9$ GeV via strong SU(2) gauge interactions. SUSY breaking is then transmitted to the observable sector via two distinct sources: (1) messengers, carrying Standard Model gauge quantum numbers, with the messenger mass o

Steven D. Bass, Stanley J. Brodsky, Ivan Schmidt

We show that the first moment of the spin-dependent structure function $g_1^γ(x,Q^2)$ of a real photon vanishes independent of the momentum transfer $Q^2$ it is probed with. This result is non-perturbative: it holds to all orders in perturbation theory in abelian and non-abelian gauge theory and at every twist.

Richard D. Ball, Stefano Forte

We show that the all order summation of small x logarithms cannot be included in the Q^2 evolution of structure functions because the NLLx corrections overwhelm the LLx contribution.

Francesca Borzumati, Glennys Farrar, Nir Polonsky, Scott Thomas

Radiatively generated fermion masses without tree level Yukawa couplings are re-analyzed within supersymmetric models. Special emphasis is given to the possible appearance of color and charge breaking vacua. Several scenarios in which the radiative mechanism can be accomodated for the first, second, and third generation fermion masses are presented. Some of

Stefano Rigolin

The one-loop weak-magnetic and weak-electric dipole form factors of heavy fermions in a generic model are derived. Numerical predictions for the $τ$ lepton and $b$ quark Weak Anomalous Magnetic and Electric Dipole Moments (AWMDM and WEDM) in the SM and MSSM are reviewed. The MSSM contribution to the $τ$ ($b$) AWMDM could be, in the high $\tanβ$ scenario, fou

A. F. Krutov, V. E. Troitsky

The asymptotics of pion charge form factor is obtained in the framework of relativistic Hamiltonian dynamics for the infinite value limit of momentum transfer and zero value limit of constituent--quark mass. It is shown that this asymptotics is the same as given by the perturbative QCD and is determined by relativistic kinematics only, being independent on t

Loretta M. Johnson, Douglas W. McKay

We develop a framework and unified, compact notation to include neutrino direct interaction effects with neutrino oscillations for a wide class of low-energy, effective four-Fermi interactions. Modest flavor-violating interaction strengths can make significant changes in the boundaries in $ΔM^2 \leftrightarrow sin^2 2θ$ and in $tan^2 θ_{13} \leftrightarrow t

JA Gracey

We review the computation of the anomalous dimensions of the twist-2 unpolarized operators in the large N_f expansion. Results are discussed for the predominantly gluonic singlet operator and the O(1/N_f) part of the 3-loop splitting function is given.

Y. Kiyo, T. Morozumi, M. Tanimoto

We investigate the rare decay processes of the K mesons, K_{L,S} -> π^0 ν\barν and K^{+} -> π^+ ν\barν in LR model with lepton family number being well conserved. In these processes, scalar operators (\bar{s}d)(\barν_τν_τ), which are derived from box diagram in LR model, play an important role due to an enhancement factor M_{K}/m_{s} in the matrix element $<

D. Jido, Y. Nemoto, M. Oka, A. Hosaka

Chiral properties of positive and negative parity nucleons, N and N*$, are studied from the viewpoint of chiral symmetry. Two possible ways to assign chiral transformations to the negative parity nucleon are considered. Using linear sigma models based on the two chiral realizations, theoretical as well as phenomenological consequences of the two different as

X. -H. Guo

The two-body nonleptonic weak decays of Λ_b \to Λ_c P(V) (P and V represent pseudoscalar and vector mesons respectively) are analyzed in two models, one is the Bethe-Salpeter (B-S) model and the other is the hadronic wave function model. The calculations are carried out in the factorization approach. The obtained results are compared with other model calcula

Xin-Heng Guo, Hong-Ying Jin, Xue-Qian Li

In the heavy quark limit a heavy baryon which contains two heavy quarks is believed to be composed of a heavy diquark and a light quark. Based on this picture, we evaluate the weak semileptonic decay rates of such baryons. The transition form factors between two heavy baryons are associated with those between two heavy mesons by applying the superflavor symm

Xiaotong Song

Using the unified scheme for describing both quark spin and orbital angular momenta in the chiral quark model developed in the previous work, the magnetic moments of octet and decuplet baryons are calculated. The numerical result shows that the overall agreement with data is improved by including the orbital contributions.

K. Rummukainen, M. Tsypin, K. Kajantie, M. Laine

We study the universality class and critical properties of the electroweak theory at finite temperature. Such critical behaviour is found near the endpoint m_H=m_{H,c} of the line of first order electroweak phase transitions in a wide class of theories, including the Standard Model (SM) and a part of the parameter space of the Minimal Sypersymmetric Standard

I T Drummond

A model for SU(n) string breaking on the lattice is formulated using strong coupling ideas. Although necessarily rather crude, the model gives an explicit picture of string breaking in the presence of dynamical quarks as a mixing phenomenon that involves the string state and a two-meson state. A careful analysis, within the model, of the Wilson loop shows th

D. Schuette, A. Wichmann, C. Weichmann

The coupled cluster method has been applied to the eigenvalue problem lattice Hamiltonian QCD (without quarks) for SU(2) gauge fields in two space dimensions. Using a recently presented new formulation and the truncation prescription of Guo et al. we were able to compute the ground state and the lowest $0^+$-glueball mass up to the sixth order of the coupled

The OPAL Collaboration, K. Ackerstaff et al

The inclusive production rates and differential cross-sections of photons and mesons with a final state containing photons have been measured with the OPAL detector at LEP. The light mesons covered by the measurements are the π^0, η, ρ(770)+-, ω(782), η&#39;(958) and a_0(980)+-. The particle multiplicities per hadronic Z^0 decay, extrapolated to the full ene

L. E. Sinclair

The cross section for producing three high transverse energy jets with a three-jet invariant mass of M_3J > 50 GeV has been measured in photoproduction at HERA. The angular distribution of the three jets is presented and found to be inconsistent with a uniform population of the available phase space. In contrast, parton shower models and O(alpha alpha_s^2) p

Stefan Soldner-Rembold

At high energies photon-photon interactions are dominated by quantum fluctuations of the photons into fermion-antifermion pairs and into vector mesons. This is called photon structure. Electron-positron collisions at LEP are an ideal laboratory for studying photon structure and for testing QCD.

Stefan Soldner-Rembold

The structure of the photon is studied in high energy photon-proton interactions at HERA and photon-photon interactions at LEP. The status of these measurements is reviewed.

M. A. Pelath, K. P. Tod, Robert M. Wald

We investigate existence and properties of trapped surfaces in two models of collapsing null dust shells within the Gibbons-Penrose construction. In the first model, the shell is initially a prolate spheroid, and the resulting singularity forms at the ends first (relative to a natural time slicing by flat hyperplanes), in analogy with behavior found in certa

R. Loll

The construction of a consistent theory of quantum gravity is a problem in theoretical physics that has so far defied all attempts at resolution. One ansatz to try to obtain a non-trivial quantum theory proceeds via a discretization of space-time and the Einstein action. I review here three major areas of research: gauge-theoretic approaches, both in a path-

S. Capozziello, G. Lambiase, G. Scarpetta

We consider scalar perturbations of energy-density for a class of cosmological models where an early phase of accelerated expansion evolves, without any fine-tuning for graceful exit, towards the standard Friedman eras of observed universe. The quantum geometric procedure which generates such models agrees with results for string cosmology since it works if

S. Capozziello, G. Lambiase, R. Capaldo

We investigate $(n+1)$-dimensional string-dilaton cosmology with effective dilaton potential in presence of perfect-fluid matter.We get exact solutions parametrized by the constant $\gam$ of the state equation $p=(\gam-1)ρ$, the spatial dimension number $n$, the bulk of matter, and the spatial curvature constant $k$. Several interesting cosmological behaviou

Jacob D. Bekenstein

I describe some examples in support of the conjecture that the horizon area of a near equilibrium black hole is an adiabatic invariant. These include a Schwarzschild black hole perturbed by quasistatic scalar fields (which may be minimally or nonminimally coupled to curvature), a Kerr black under the influence of scalar radiation at the superradiance treshol

David I. Santiago, Dimitri Kalligas, Robert V. Wagoner

We study the asymptotic behavior at late times of Friedmann-Robertson-Walker (uniform density) cosmological models within scalar-tensor theories of gravity. Particularly, we analyze the late time behavior in the present (matter dominated) epoch of the universe. The result of Damour and Nordtvedt that for a massless scalar in a flat cosmology the Universe evo

A. A. Odintsov, W. Smit, H. Yoshioka

The persistent current of interacting electrons in toroidal single-wall carbon nanotubes is evaluated within Haldane&#39;s concept of topological excitations. The overall pattern of the persistent current corresponds to the constant interaction model, whereas the fine structure stems from the electronic exchange correlations.

L. Alff, A. Beck, R. Gross, A. Marx

We have performed a detailed study of the tunneling spectra of bicrystal grain boundary junctions (GBJs) fabricated from the HTS YBCO, BSCCO, LSCO, and NCCO. In all experiments the tunneling direction was along the CuO planes. With the exception of NCCO, for all materials a pronounced zero bias conductance peak was observed which decreases with increasing te

Ya-Sha Yi, Zhi-Gang Yu, A. R. Bishop, J. Tinka Gammel

We study nickelate-centered and oxygen-centered stripe phases in doped La$_{2}$NiO$_{4}$ materials. We use an inhomogeneous Hartree-Fock and random-phase approximation approach including both electron-electron and electron-lattice(e-l) coupling for a layer of La$_{2}$NiO$_{4}$. We find that whether the ground state after commensurate hole doping comprises Ni

Ya-Sha Yi, A. R. Bishop

We study the spin-dependent geometric phase effect in mesoscopic rings of charge-density-wave(CDW) materials. When electron spin is explicitly taken into account, we show that the spin-dependent Aharonov-Casher phase can have a pronounced frustration effects on such CDW materials with appropriate electron filling. We show that this frustration has observable

Dirk Helbing, Joachim Keltsch, Peter Molnar

Many human social phenomena, such as cooperation, the growth of settlements, traffic dynamics and pedestrian movement, appear to be accessible to mathematical descriptions that invoke self-organization. Here we develop a model of pedestrian motion to explore the evolution of trails in urban green spaces such as parks. Our aim is to address such questions as

M. Lisowski, E. Zipper

We present some model calculations of persistent currents in disordered one- and two-dimensional mesoscopic systems. We use the tight-binding model and calculate numerically the currents in small systems for several values of disorder. Next we fit appropriate analytical formulae, and using them we find self- -sustaining currents and critical fields in larger

C. Riva, V. A. Schweigert, F. M. Peeters

We investigate the effect of the position of the donor in the quantum well on the energy spectrum and the oscillator strength of the D- system in the presence of a perpendicular magnetic field. As a function of the magnetic field we find that when the D- centers are placed sufficiently off-center they undergo singlet-triplet transitions which are similar to

Ken&#39;ichi Takano, Kazuhiro Sano

We examine experimental magnetic susceptibility $χ^{tot}(T)$ for CaV$_4$O$_9$ by fitting with fitting function $αχ^{mag}(T) + c$. The function $χ^{mag}(T)$ is a power series of 1/T and the lowest order term is fixed as $C/T$, where $C$ is the Curie constant as determined by the experimental $g$-value (g=1.96). Fitting parameters are $α$, $c$ and expansion co

Adriaan M. J. Schakel

Effective theories of quantum liquids (superconductors and superfluids of various types) are derived starting from microscopic models at the absolute zero of temperature. Special care is taken to assure Galilei invariance. The effective theories are employed to investigate the quantum numbers carried by the topological defects present in the phases with spon

J. Ranninger, A. Romano

Using a scenario of a hybridized mixture of localized bipolarons and conduction electrons, we demonstrate for the latter the simultaneous appearance of a pseudogap and of strong incoherent contributions to their quasi-particle spectrum which arise from phonon shake-off effects. This can be traced back to temporarily fluctuating local lattice deformations, gi

J. Heinonen, I. Bukharev, T. Ala-Nissila, J. M. Kosterlitz

We consider a simple model for the growth of isolated steps on a vicinal crystal surface. It incorporates diffusion and drift of adatoms on the terrace, and strong step and kink edge barriers. Using a combination of analytic methods and Monte Carlo simulations, we study the morphology of growing steps in detail. In particular, under typical Molecular Beam Ep

Yun Song, H. Q. Lin, Jue-Lian Shen

We improved the decoupling approximation of the double-time Green&#39;s function theory, and applied it to study the spin-${1\over 2}$ two-dimensional antiferromagnetic Heisenberg model with broken bonds at finite temperature. Our decoupling approximation is applicable to the spin systems with spatial inhomogeneity, introduced by the local defects, over the

M. T. Batchelor, D. Bennett-Wood, A. L. Owczarek

We provide general formulae for the configurational exponents of an arbitrary polymer network connected to the surface of an arbitrary wedge of the two-dimensional plane, where the surface is allowed to assume a general mixture of boundary conditions on either side of the wedge. We report on a comprehensive study of a linear chain by exact enumeration, with

Dirk Helbing

The behavior of pedestrians shows certain regularities, which can be described by quantitative (partly stochastic) models. The models are based on the behavior of individual pedestrians, which depends on the pedestrian intentions and on the aspects of movement. The pedestrian intentions concerning a sequence of destinations are influenced by the demand for c

Denis Feinberg

A phenomenological model is proposed for melting of a vortex lattice, based on screening of the elastic shear modulus by mobile or partially pinned dislocations. A first-order softening line is found and ends at a critical point beyond which the lattice crosses over to an hexatic vortex solid. The consequences of softening on vortex dynamics are explored, as

Thomas Schreiber, Andreas Schmitz

We propose a general scheme to create time sequences that fulfill given constraints but are random otherwise. Significance levels for nonlinearity tests are as usually obtained by Monte Carlo resampling. In a new scheme, constraints including multivariate, nonlinear, and nonstationary properties are implemented in the form of a cost function.

James Robinson, Eric Gawiser, Joseph Silk

We consider constraints on the amplitude of mass fluctuations in the universe, sigma_8, derived from two simple observations: the present number density of clusters and the amplitude of their correlation function. Allowing for the possibility that the primordial fluctuations are non-gaussian introduces a degeneracy in the value of sigma_8 preferred by each o

Gerry Gilmore, Michael Perryman, L Lindegren, F Favata

GAIA is a short-listed candidate for the ESA Cornerstone mission C5, meeting the ESA Survey Committee requirement for an observatory mission, dedicated to astrometry, providing 10 micro-arcsecond accuracy at 15th magnitude. The GAIA mission concept follows the dramatic success of the ESA HIPPARCOS mission, utilising a continuously scanning spacecraft, accura

D. M. Smith, D. Main, F. Marshall, J. Swank

A new x-ray transient, designated XTE J1739-302, was discovered with the Proportional Counter Array (PCA) on the Rossi X-ray Timing Explorer (RXTE) in data from 12 August 1997. Although it was the brightest source in the Galactic Center region while active (about 3.0 x 10^-9 ergs/cm2/s from 2 to 25 keV), it was only observed on that one day; it was not detec

J. B. Hutchings, S. A. Baum, D. Weistrop, C. Nelson

We present and discuss visible-wavelength long-slit spectra of four low redshift 3C galaxies obtained with the STIS instrument on the Hubble Space Telescope. The slit was aligned with near-nuclear jet-like structure seen in HST images of the galaxies, to give unprecedented spatial resolution of the galaxy inner regions. In 3C 135 and 3C 171, the spectra reve

Andrew Gould, Piotr Popowski

We sing the praises of the central limit theorem. Having previously removed all other possible causes of significant systematic error in the statistical parallax determination of RR Lyrae absolute magnitudes, we investigate systematic errors from two final sources of input data: apparent magnitudes and extinctions. We find corrections due to each of ~0.05 ma

Jeremy S. Heyl, Lars Hernquist

Recent ROSAT measurements show that the x-ray emission from isolated neutron stars is modulated at the stellar rotation period. To interpret these measurements, one needs precise calculations of the heat transfer through the thin insulating envelopes of neutron stars. We present nearly analytic models of the thermal structure of the envelopes of ultramagneti

Sally D. Hunsberger, Jane C. Charlton, Dennis Zaritsky

From R-band images of 39 Hickson compact groups (HCGs), we use galaxy counts to determine a luminosity function extending to M_R=-14.0, approximately two magnitudes deeper than previous compact group luminosity functions. We find that a single Schechter function is a poor fit to the data, so we fit a composite function consisting of separate Schechter functi

Arthur Kosowsky

Fast and accurate computations of the power spectrum of cosmic microwave background fluctuations are essential for comparing current and upcoming data sets with the large parameter space of viable cosmological models. The most efficient numerical algorithm for power spectrum calculation, recently implemented by Seljak and Zaldarriaga, involves integrating so

C. L. Carilli, K. S. Dwarakanath, W. M. Goss

We have detected HI 21cm line absorption by the Warm Neutral Medium (WNM) using the Westerbork Synthesis Radio Telescope. The absorption was detected toward Cygnus A at LSR velocities of -40 and -70 km s^{-1}. These two velocity ranges were previously identified as being relatively free of cold absorbing clouds. The measured optical depth for the WNM along t

Tsevi Mazeh, Dorit Goldberg, David W. Latham

We consider the mass distribution of the nine unseen companions orbiting solar-type stars with minimum possible masses in the planetary mass range reported as of March 1998. We compare the mass distribution of these nine extrasolar planet candidates with the distribution of low-mass secondaries in spectroscopic binaries. We choose to use a logarithmic scale

Adam Burrows

Recent observations of supernovae, supernova remnants, and radio pulsars suggest that there are correlations between pulsar kicks and spins, infrared and gamma-ray line profiles, supernova polarizations, and ejecta debris fields. A framework is emerging in which explosion asymmetries play a central role. The new perspective meshes recent multi-dimensional th