August 1998 arXiv papers — page 9

S. Baroni, S. Moroni

We present an elementary and self-contained account of the analogies existing between classical diffusion and the imaginary-time evolution of quantum systems. These analogies are used to develop a new quantum simulation method which allows to calculate the ground-state expectation values of local observables without any mixed estimates nor population-control

Alex Travesset

We discuss the properties of Skyrmions in the Fractional Quantum Hall effect (FQHE). We begin with a brief description of the Chern-Simons-Landau-Ginzburg description of the FQHE, which provides the framework in which to understand a new derivation of the properties of FQHE Skyrmions (S. Baez, A.P. Balachandran, A. Stern and A. Travesset cond-mat/9712151) fr

J. Schiøtz, T. Vegge, F. D. Di Tolla, K. W. Jacobsen

We discuss how simulations of mechanical properties of materials require descriptions at many different length scales --- from the nanoscale where an atomic description is appropriate, through a mesoscale where dislocation based descriptions may be useful, to macroscopic length scales. In some materials, such as nanocrystalline metals, the range of length sc

T. Dahm, D. Manske, L. Tewordt

The role of collective modes in various experiments on the cuprates is investigated. We calculate the neutron scattering, photoemission (ARPES), and Raman scattering intensities below $T_c$ within the fluctuation-exchange (FLEX) approximation for the two-dimensional Hubbard model. It is shown that the large peak in the dynamical spin susceptibility arises fr

Lei-Han Tang

The coarsening dynamics of three-dimensional islands on a growing film is discussed. It is assumed that the origin of the initial instability of a planar surface is the Ehrlich-Schwoebel step-edge barrier for adatom diffusion. Two mechanisms of coarsening are identified: (i) surface diffusion driven by an uneven distribution of bonding energies, and (ii) mou

Guang-Shan Tian, Lei-Han Tang

The parity effect in an ultra-small superconducting grain is examined. By applying a generalized version of Lieb's spin-reflection positivity technique, we show rigorously that the parity parameter $Δ_P$ is nonvanishing in such a system. A positive lower bound for $Δ_P$ is derived.

Jean-Philippe Bouchaud, Marc Potters

We reconsider the problem of option pricing using historical probability distributions. We first discuss how the risk-minimisation scheme proposed recently is an adequate starting point under the realistic assumption that price increments are uncorrelated (but not necessarily independent) and of arbitrary probability density. We discuss in particular how, in

M. I. Salkola, J. R. Schrieffer

Properties of low-energy excitations in one-dimensional superconductors and density-wave systems are examined by the bosonization technique. In addition to the usual spin and charge quantum numbers, a new, independently measurable attribute is introduced to describe elementary, low-energy excitations. It can be defined as a number w which determines, in mult

Gang Su, Masuo Suzuki

This paper has been withdrawn.

Sitabhra Sinha

Chaotic systems can be synchronized by linking them to a common signal, subject to certain conditions. However, the presence of multiple driving signals coming from different systems, give rise to novel behavior. The particular case of Lorenz systems, with two independent systems driving another system through drive-response coupling has been studied in this

C. Greiveldinger, B. Aschenbach

We have analyzed five ROSAT HRI images of the Crab Nebula spanning the years 1991 to 1997 and have found significant changes in the emission structure of the X-ray torus surrounding the pulsar. Certain regions increase in brightness by about 20% over the six years, while others show decreases in surface brightness. The origin of these changes is unclear, but

Michael R. Meyer, Suzan Edwards, Kenneth H. Hinkle, Stephen E. Strom

We present a catalogue of H-band spectra for 85 stars of approximately solar abundance observed at a resolving power of 3000 with the KPNO Mayall 4m FTS. The atlas covers spectral types O7-M5 and luminosity classes I-V as defined on the MK system. We identify both atomic and molecular indices and line-ratios which are temperature and luminosity sensitive all

Stefanie Komossa, Henner Fink

We present a study of the nature of warm absorbers on the basis of ROSAT X-ray observations and photoionization calculations carried out with the code Cloudy. We focus on `non-standard' warm absorbers: (i) the proposed dusty warm absorbers in IRAS 13349+2438 and IRAS 17020+4544, and possibly in 4C +74.26; (ii) we explore several scenarios to account for

Michael Loewenstein

I review the results of recent analysis and interpretation of X-ray observations of elliptical galaxies, focusing on elemental abundances and dark matter. The hot ISM is characterized by subsolar Fe abundances and solar Si-to-Fe ratios; and, I compare these with stellar abundances and discuss implications of these measurements. From models constructed to exp

W. Raphael Hix, Friedrich-Karl Thielemann

Having examined the application of quasi-equilibrium to hydrostatic silicon burning in Paper I of this series, Hix & Thielemann (1996), we now turn our attention to explosive silicon burning. Previous authors have shown that for material which is heated to high temperature by a passing shock and then cooled by adiabatic expansion, the results can be divided

Brian Chaboyer

The present status of the distance scale to Galactic globular clusters is reviewed. Six distance determination techniques which are deemed to be most reliable are discussed in depth. These different techniques are used to calibrate the absolute magnitude of the RR Lyrae stars. The various calibrations fall into three groups. Main sequence fitting using Hippa

Carlo Contaldi, Mark Hindmarsh, Joao Magueijo

We compute the power spectra in the cosmic microwave background and cold dark matter (CDM) fluctuations seeded by strings, using the largest string simulations performed so far to evaluate the two-point functions of their stress energy tensor. We find that local strings differ from global defects in that the scalar components of the stress-energy tensor domi

Brian Chaboyer

A minimum age of the universe can be estimated directly by determining the age of the oldest objects in the our Galaxy. These objects are the metal-poor stars in the halo of the Milky Way. Recent work on nucleochronology finds that the oldest stars are 15.2+/-3.7 Gyr old. White dwarf cooling curves have found a minimum age for the oldest stars of 8 Gyr. Curr

Spiro K. Antiochos, Peter J. MacNeice, Daniel S. Spicer, James

We present simulations of a model for the formation of a prominence condensation in a coronal loop. The key idea behind the model is that the spatial localization of loop heating near the chromosphere leads to a catastrophic cooling in the corona (Antiochos & Klimchuk 1991). Using a new adaptive grid code, we simulate the complete growth of a condensation, a

Elisabete M. de Gouveia Dal Pino, Adriano H. Cerqueira

In this work, we sumarize the results of three-dimensional smooth particle magnetohydrodynamic numerical simulations of supermagnetosonic, radiatively cooling jets.

C. Pichon, E. Thiebaut

A general inversion technique for the recovery of the underlying distribution function for observed galactic disks is presented and illustrated. Under the assumption that these disks are axi-symmetric and thin, the proposed method yields the unique distribution compatible with all the observables available. The derivation may be carried out from the measurem

Adriano H. Cerqueira, Elisabete M. de Gouveia Dal Pino

We investigate the effect of magnetic fields on the propagation dynamics and morphology of overdense, radiatively cooling, supermagnetosonic jets, with the help of fully three-dimensional SPMHD simulations. Evaluated for a set of parameters which are mainly suitable for protostellar jets (with density ratios between the jet and the ambient medium 3-10, and a

Elisabete M. de Gouveia Dal Pino, Adriano H. Cerqueira

In the present work, with the help of fully 3-D smooth particle magnetohydodynamic (SPMHD) simulations, we explore the nonlinear effects of magnetic fields (in close equipartition with the gas) in the structure of radiatively cooling, overdense jets and test their importance on the dynamics of protostellar jets.

Francesco Sylos Labini

The fact that galaxy distribution exhibits fractal properties is well established since twenty years. Nowadays, the controversy concerns the range of the fractal regime, the value of the fractal dimension and the eventual presence of a cross-over to homogeneity. Fractal properties maybe studied with methods which do not assume homogeneity a priori as the sta

G. A. Richter, J. Greiner, P. Kroll

We have identified the ROSAT all-sky survey source RX J1953.1+2115 with a newly discovered dwarf novae (named S 10943 Vulpeculae) with a recurrence time of 83.6 days. With the expected period of ~2.8 hrs (based on the measured superhump period of 2.871 hrs) S 10943 Vul would be the SU Ursae Majoris star with the second largest superhump (and orbital) period

The MACHO Collaboration, C. Alcock, D. R. Alves, A. Becker

Using the novel data set of the MACHO project, we show that three ``Blazhko Effect'' RR Lyrae stars show nearly-pure amplitude modulation of a single pulsation mode. This is strong observational evidence that the ``Oblique Pulsator Model'' is the correct solution to this 90-year-old problem.

Sungeun Kim, You-Hua Chu, Lister Staveley-Smith, R. Chris Smith

We have obtained high-resolution HI observations of N44, one of the largest HII complexes in the Large Magellanic Cloud. The distribution and internal motions of the HI gas show dynamic effects of fast stellar winds and supernova blasts. Numerous HI holes are detected, with the most prominent two corresponding to the optically identified superbubbles Shell 1

S. G. Djorgovski, S. R. Kulkarni, J. S. Bloom, R. Goodrich

We present spectroscopic observations of the host galaxy of the gamma-ray burst (GRB) 980703. Several emission and absorption features are detected, making the redshift, z = 0.966, completely unambiguous. This is only the third known redshift for a GRB host. The implied isotropic gamma-ray energy release from the burst is in excess of 10^{53} erg, for a reas

Priyamvada Natarajan, J. E. Pringle

The inner parts of an accretion disk around a spinning black hole are forced to align with the spin of the hole by the Bardeen-Petterson effect. Assuming that any jet produced by such a system is aligned with the angular momentum of either the hole or the inner disk, this can, in principle provide a mechanism for producing steady jets in AGN whose direction

I. A. Lubashevsky, V. V. Gafiychuk

We study the problem of how a ``living'' system complex in structure can respond perfectly to local changes in the environment. Such a system is assumed to consist of a distributed ``living'' medium and a hierarchical ``supplying'' network that provides this medium with ``nutritious'' products. Because of the hierarchical orga

M. de Koning, A. Antonelli, Martin Z. Bazant, Efthimios Kaxiras

We calculate the free energies of unstable stacking fault (USF) configurations on the glide and shuffle slip planes in silicon as a function of temperature, using the recently developed Environment Dependent Interatomic Potential (EDIP). We employ the molecular dynamics (MD) adiabatic switching method with appropriate periodic boundary conditions and restric

C. H. Bennett, D. P. DiVincenzo, T. Mor, P. W. Shor

An unextendible product basis (UPB) for a multipartite quantum system is an incomplete orthogonal product basis whose complementary subspace contains no product state. We give examples of UPBs, and show that the uniform mixed state over the subspace complementary to any UPB is a bound entangled state. We exhibit a tripartite 2x2x2 UPB whose complementary mix

William H. Lee, Wlodzimierz Kluzniak

We present a detailed study of the hydrodynamical interactions in a Newtonian black hole-neutron star binary during the last stages of inspiral. We consider close binaries which are tidally locked, use a stiff equation of state (with an adiabatic index Gamma=3) throughout, and explore the effect of different initial mass ratios on the evolution of the system

Yuval Grossman, Yosef Nir, Yael Shadmi

The experimental data on atmospheric and solar neutrinos suggest that there is near-maximal mixing between ν_μand ν_τbut that their masses are hierarchically separated. In models of Abelian horizontal symmetries, mixing of O(1) generically implies that the corresponding masses are of the same order of magnitude. We describe two new mechanisms by which a larg

A. S. Alexandrov, P. E. Kornilovitch

Extending the Froehlich polaron problem to a discrete ionic lattice we study a polaronic state with a small radius of the wave function but a large size of the lattice distortion. We calculate the energy dispersion and the effective mass of the polaron with the 1/λperturbation theory and with the exact Monte Carlo method in the nonadiabatic and adiabatic reg

Fernando C. Lombardo, Francisco D. Mazzitelli, Jorge G. Russo

We clarify some issues related to the evaluation of the mean value of the energy-momentum tensor for quantum scalar fields coupled to the dilaton field in two-dimensional gravity. Because of this coupling, the energy-momentum tensor for the matter is not conserved and therefore it is not determined by the trace anomaly. We discuss different approximations fo

Shoichi Sasaki, Osamu Miyamura

We study the topological feature in the QCD vacuum based on the hypothesis of abelian dominance. The topological charge $Q_{\rm SU(2)}$ can be explicitly represented in terms of the monopole current in the abelian dominated system. To appreciate its justification, we directly measure the corresponding topological charge $Q_{\rm Mono}$, which is reconstructed

A. J. Millis, Jun Hu, Sankar Das Sarma

We use the dynamical mean field method to study the high-temperature resistivity of electrons strongly coupled to phonons. The results reproduce the qualtiative behavior of the temperature and disorder dependence of the resistivity of the 'A-15' materials, which is commonly described in terms of saturation, but imply that the resistivity does not sat

Dipali Pal, Munshi Golam Mustafa

We evaluate the bremsstrahlung production of low mass dileptons and soft photons from equilibrating and transversely expanding quark gluon plasma which may be created in the wake of relativistic heavy ion collisions. We use initial conditions obtained from the self screened parton cascade model. We consider a boost invariant longitudinal and cylindrically sy

J. W. van de Leur, R. Martini

Frobenius manifolds (solutions of WDVV equations) in canonical coordinates are determined by the system of Darboux-Egoroff equations. This system of partial differential equations appears as a specific subset of the $n$-component KP hierarchy. KP representation theory and the related Sato infinite Grassmannian are used to construct solutions of this Darboux-

Guang-jiong Ni, Weimin Zhou, Jun Yan

When a particle is in high speed or bound in the Coulomb potential of point nucleus, the variation of its mass can be ascribed to the variation of relative ratio of hiding antimatter to matter in the particle. At two limiting cases, the ratio approaches to 1.

Kai Druhl

We study the effects of higher order transversal modes in a model of a singly-resonant OPO, using both numerical solutions and mode expansions including up to two radial modes. The numerical and two-mode solutions predict lower threshold and higher conversion than the single-mode solution at negative dispersion. Relative power in the zero order radial mode r

J. Rougemont

We consider initial data for the real Ginzburg-Landau equation having two widely separated zeros. We require these initial conditions to be locally close to a stationary solution (the ``kink'' solution) except for a perturbation supported in a small interval between the two kinks. We show that such a perturbation vanishes on a time scale much shorter

Elena A. Ostrovskaya, Yuri S. Kivshar

We develop a nonlinear theory of soliton-induced waveguides that describes a finite-amplitude probe beam guided by a spatial dark soliton in a saturable nonlinear medium. We suggest an effective way to control the interaction of these soliton-induced waveguides and also show that, in sharp contrast with scalar dark solitons, the dark-soliton waveguides can a

Denes Molnar, Laszlo Pal Csernai, Zsolt Iosif Lazar

In energetic heavy ion collisions, if quark-gluon plasma is formed, its hadronization may lead to observable critical fluctuations, i.e., DCC formation. The strength and observability of these fluctuations depend on the initial state. Here we study the canonical ensemble of initial states of chiral fluctuations in heavy ion collisions and the probability to

L. A. Kondratyuk, Ye. S. Golubeva, M. Buescher

We investigate the reactions p n -> d omega and p n -> d phi close to threshold and at higher energies. Near threshold we calculate the S-wave amplitudes within the framework of the two-step model which is described by a triangle graph with pi-mesons in the intermediate state and find a ratio of the S-wave amplitudes squared of R =|A(phi)|^2/|A(omega)|^2 = (

Alexander Krasulin

This part of the series is devoted to the generalization of exterior differential calculus. I give definition to the integral of a five-vector form over a limited space-time volume of appropriate dimension; extend the notion of the exterior derivative to the case of five-vector forms; and formulate the corresponding analogs of the generalized Stokes theorem

Valeri V. Dvoeglazov

In the old articles of Ogievetskii and Polubarinov, Kalb and Ramond the notoph concept, the longitudinal field originated from the antisymmetric tensor (AST), has been proposed. In our work we analyze the theory of the AST field of the second rank from the viewpoint of the normalization problem. We obtain 4-potentials and strengths which coincide with those

Michael Kapovich

We show that for each aspherical compact complex surface $X$ whose fundamental group $π$ fits into a short exact sequence $$ 1\to K \to π\to π_1(S) \to 1 $$ where $S$ is a compact hyperbolic Riemann surface and the group $K$ is finitely-presentable, there is a complex structure on $S$ and a nonsingular holomorphic fibration $f: X\to S$ which induces the abov

Tom Graber

We recursively compute the Gromov-Witten invariants of the Hilbert scheme of two points in the plane. By studying the space of stable maps and computing virtual contributions, we use these invariants to enumerate hyperelliptic plane curves of degree d and genus g passing through 3d+1 general points.

Harm Derksen, Frank Kutzschebauch, Joerg Winkelmann

We investigate algebraic and analytic subvarieties of C^n with automorphisms which can not be extended to the ambient space.

C. Balteanu, Z. Fiedorowicz, R. Schwaenzl, R. Vogt

We develop a notion of iterated monoidal category and show that this notion corresponds in a precise way to the notion of iterated loop space. Specifically the group completion of the nerve of such a category is an iterated loop space and free iterated monoidal categories give rise to finite simplicial operads of the same homotopy type as the classical littl

O. W. Greenberg, Robert C. Hilborn

Quons are particles characterized by the parameter $q$, which permits smooth interpolation between Bose and Fermi statistics; $q=1$ gives bosons, $q=-1$ gives fermions. In this paper we give a heuristic argument for an extension of conservation of statistics to quons with trilinear couplings of the form $\bar{f}fb$, where $f$ is fermion-like and $b$ is boson

Y. Hosotani, K. Saririan, B. Tekin

Complex monopole solutions exist in the three dimensional Georgi-Glashow model with the Chern-Simons term. They dominate the path integral and disorder the Higgs vacuum. Gribov copies of the vacuum and monopole configurations are studied in detail.

R. Banerjee

The constrained structure of the duality invariant form of Maxwell theory is considered in the Hamiltonian formulation of Dirac as well as from the symplectic viewpoint. Compared to the former the latter approach is found to be more economical and elegant. Distinctions from the constrained analysis of the usual Maxwell theory are pointed out and their implic

Abdel Pérez-Lorenzana, William A. Ponce, Arnulfo Zepeda

We explore the possibility of achieving one--step unification of the standard model coupling constants within non supersymmetric and supersymmetric gauge models, which at low energies have only the standard particle content. The constraints are the experimental values of $α_{em}$, $α_s$ and $\sin^2θ_W$ at $10^2 GeV$, and the lower bounds for FCNC and proton

Carl E. Carlson, Christopher D. Carone

Recently we considered the electromagnetic decays of the orbitally-excited SU(6) 70-plet baryons in large-N_c QCD, fitting to the helicity amplitudes measured in photoproduction experiments. Using the results of this analysis, we predict the helicity amplitudes for the decays N^* \to Δγand Δ^* \to Δγ. These decays can be studied at a number of new experiment

V. Barger

The quest for the physics underlying the breaking of the electroweak symmetry and the generation of mass is surveyed.

V. Barger

Models with three active neutrinos and one sterile neutrino can naturally account for maximal oscillations of atmospheric neutrinos, explain the solar neutrino deficit, and accommodate the results of the LSND experiment. The models predict either $ν_e\toν_τ$ or $ν_e\toν_s$ oscillations in long-baseline experiments with the atmospheric $δm^2$ scale and amplit

C. Gale, S. Jeon, J. Kapusta

Precisely measured Drell-Yan cross sections for 800 GeV protons incident on a variety of nuclear targets exhibit a deviation from linear scaling in the atomic number A. We show that this deviation can be accounted for by energy degradation of the proton as it passes through the nucleus if account is taken of the time delay of particle production due to quant

T. Kinoshita

The method of NRQED is an adaptation of QED to bound systems. While it is fully equivalent to QED, it enables us to explore the QED bound states systematically as an expansion in the fine structure constant $α$ and velocity ($\sim Zα$) of the bound electron. I describe how to construct the NRQED Hamiltonian choosing recent works on the $α(Zα)$, $α^2 (Zα)$,$α

H. V. Klapdor-Kleingrothaus, H. Päs

The search for neutrinoless double beta decay and WIMP dark matter has a broad potential to test particle physics beyond the standard model. During the last years, the analysis of various contributions to the double beta decay rate by the Heidelberg group led, besides the most restrictive limit on the effective Majorana neutrino mass, to bounds on left-right

A. Jakovac

We show how the resummation for time dependent quantities at high temperature can be performed with an effective classical theory. As an application we demonstrate that the leading term in the shear viscosity, which is related to the $ρ_{Φ^2Φ^2}$ spectral function can be calculated classically, either using classical linear response theory or from the classi

Krishna Rajagopal

I first sketch recent developments concerning the phase diagram of strongly interacting matter as a function of temperature and baryon density, obtained using a model for two-flavor QCD in which the interaction between quarks is modelled on that induced by instantons. The phase diagram has a chiral symmetry breaking vacuum, a color superconductor phase at hi

John F. Wheater, Joao Correia

We show that the spectral dimension on non-generic branched polymers with positive susceptibility exponent is given by $d_s=2/(1+γ)$. For those models with $γ<0$ we find that $d_s=2$.

The OPAL Collaboration, K. Ackerstaff et al

A search for the resonant production of high mass photon pairs associated with a leptonic or hadronic system has been performed using a data sample of 57.7 pb-1 collected at an average center-of-mass energy of 182.6 GeV with the OPAL detector at LEP. No evidence for contributions from non-Standard Model physics processes was observed. The observed candidates

M. J. Reboucas, A. F. F. Teixeira

Causal anomalies in two Kaluza-Klein gravity theories are examined, particularly as to whether these theories permit solutions in which the causality principle is violated. It is found that similarly to general relativity the field equations of the space-time-mass Kaluza-Klein (STM-KK) gravity theory do not exclude violation of causality of Gödel type, where

K. S. Bedell, J. R. Engelbrecht, K. B. Blagoev

This is a response to a recent paper by van Dongen, Uhrig, and E. Müller-Hartmann. We clarify the issues, which the above authors apparently did not fully appreciate, by referring to the microscopic foundations of Landau&#39;s Fermi Liquid Theory, its general application to the theory of metals and the theory of local Fermi Liquids.

D. A. Lidar, D. Thirumalai, R. Elber, R. B. Gerber

The fractal properties of the total potential energy V as a function of time t are studied for a number of systems, including realistic models of proteins (PPT, BPTI and myoglobin). The fractal dimension of V(t), characterized by the exponent γ, is almost independent of temperature and increases with time, more slowly the larger the protein. Perhaps the most

E. Cappelluti, R. Zeyher

We study the phase diagram of the t-J model using a mean field type approximation within the Baym-Kadanoff perturbation expansion for Hubbard $X$-operators. The line separating the normal state from a d-wave flux or bond-order state starts near optimal doping at T=0 and rises quickly with decreasing doping. The transition temperature $T_c$ for d-wave superco

Ghyslain Boisvert, Laurent J. Lewis

We report the results of a density-functional study of the diffusion of Pt dimers on the (111) surface of Pt. The calculated activation energy of 0.37 eV is in {\em exact} agreement with the recent experiment of Kyuno {\em et al.} \protect{[}Surf. Sci. {\bf 397}, 191 (1998)\protect{]}. Our calculations establish that the dimers are mobile at temperatures of

P. Grassberger

We argue that the synchronization transition of stochastically coupled cellular automata, discovered recently by L.G. Morelli {\it et al.} (Phys. Rev. {\bf 58 E}, R8 (1998)), is generically in the directed percolation universality class. In particular, this holds numerically for the specific example studied by these authors, in contrast to their claim. For r

Alexander K. Hartmann

Large numbers of ground states of the three-dimensional $\pm J$ random-bond Ising model are calculated for sizes up to $14^3$ using a combination of a genetic algorithm and Cluster-Exact Approximation. Several quantities are calculated as function of the concentration $p$ of the antiferromagnetic bonds. The critical concentration where the ferromagnetic orde

A. N. Samukhin, V. N. Prigodin, L. Jastrabik, A. J. Epstein

We suggest treating a conducting network of oriented polymer chains as an anisotropic fractal whose dimensionality D=1+εis close to one. Percolation on such a fractal is studied within the real space renormalization group of Migdal and Kadanoff. We find that the threshold value and all the critical exponents are strongly nonanalytic functions of εas εtends t

Steven M. Anlage, C. P. Vlahacos, D. E. Steinhauer, S. K. Dutta

We briefly review some non-accelerator high-frequency applications of superconductors. These include the use of high-Tc superconductors in front-end band-pass filters in cellular telephone base stations, the High Temperature Superconductor Space Experiment, and high-speed digital electronics. We also present an overview of our work on a novel form of near-fi

Steven M. Anlage, Wensheng Hu, C. P. Vlahacos, David Steinhauer

This paper discusses some of the major experimental features of microwave nonlinearity in high temperature superconductors, both intrinsic and extrinsic. The case is made for solving the problem of extrinsic nonlinearity through the use of localized measurements of microwave surface impedance and electromagnetic fields. Along these lines, a brief introductio

Kenji Hirose, Ned S. Wingreen

Using spin-density-functional theory, we study the electronic states of a two-dimensional parabolic quantum dot with up to N=58 electrons. We observe a shell structure for the filling of the dot with electrons. Hund&#39;s rule determines the spin configuration of the ground state, but only up to 22 electrons. At specific N, the ground state is degenerate, an

Andrzej Eilmes, Uwe Grimm, Rudolf A. Roemer, Michael Schreiber

To investigate the influence of electronic interaction on the metal-insulator transition (MIT), we consider the Aubry-André (or Harper) model which describes a quasiperiodic one-dimensional quantum system of non-interacting electrons and exhibits an MIT. For a two-particle system, we study the effect of a Hubbard interaction on the transition by means of the

Emmanuel Trizac

We propose a ballistic coalescence model (punctuated-Hamiltonian approach) mimicking the fusion of vortices in freely decaying two-dimensional turbulence. A temporal scaling behaviour is reached where the vortex density evolves like $t^{-ξ}$. A mean-field analytical argument yielding the approximation $ξ=4/5$ is shown to slightly overestimate the decay expon

H. Potempa, A. Bäker, L. Schweitzer

The crossover from the quantum Hall regime to the Hall-insulator is investigated by varying the strength of the diagonal disorder in a 2d tight-binding model. The Hall and longitudinal conductivities and the behavior of the critical states are calculated numerically. We find that with increasing disorder the current carrying states close to the band center d

J. Perez-Conde, F. Bouis, P. Pfeuty

We have analyzed the antiferromagnetic (J>0) Kondo-Hubbard lattice with the band at half-filling by means of a perturbative approach in the strong coupling limit, the small parameter is an arbitrary tight-binding band. The results are valid for any band shape and any dimension. We have obtained the energies of elementary charge and spin excitations as well a

Yukihiro Okuno, Kazumasa Miyake

UPt${}_{3}$ exhibits a paradoxical behavior in its antiferromagnetism. Namely, the neutron scattering experiments surely detect the antifferomagnetic ordering below the transition temperature ${\rm T}_{N}\sim 5K$, while no trace of the transition is seen in the NMR experiments and in the specific heat at ${\rm T}_{N}$. For resolution of this paradox, we prop

Marcus Kasner, J. J. Palacios, A. H. MacDonald

We report on a study of the temperature and Zeeman-coupling-strength dependence of the one-particle Green&#39;s function of a two-dimensional (2D) electron gas at Landau level filling factor $ν=1$ where the ground state is a strong ferromagnet. Our work places emphasis on the role played by the itinerancy of the electrons, which carry the spin magnetization

H. Kusunose, Y. Kuramoto

Peculiarity of the Kondo effect in Ce$_x$La$_{1-x}$B$_6$ is investigated on the basis of the scaling equations up to third order. For the case where the $f^1$-$f^2$ charge fluctuation enters in addition to the $f^1$-$f^0$ one, the effective exchange interaction becomes anisotropic with respect to the orbital pseudospins which represent the two different orbi

B. H. Miller, Branko P. Stojkovi&#39;c, E. D. Dahlberg

We measure the giant magnetoresistance (GMR) with the current both parallel and perpendicular to the direction of the magnetization in the ferromagnetic (FM) layers and thus probe the anisotropy of the effective mean free paths for the spin-up and spin-down electrons, seen in the anisotropic magnetoresistance. We find that the difference of the GMR in the tw

Masanori Yamanaka, Tohru Koma

We study the scattering of an electron by a ferromagnetic domain wall of the quantum Heisenberg-Ising model (XXZ model) with certain boundary conditions. The spin of the electron interacts with the spins of the XXZ model by the Hund coupling. Using the exact domain wall ground states of the XXZ model, we analytically obtain the exact effective Schrödinger eq

Asantha R. Cooray

It is well known that a combined analysis of the Sunyaev-Zel&#39;dovich (SZ) effect and the X-ray emission observations can be used to determine the angular diameter distance to galaxy clusters, from which the Hubble constant is derived. The present values of the Hubble constant derived through the SZ/X-ray route have a broad distribution ranging from 30 to

R. D. Preece, M. S. Briggs, R. S. Mallozzi, G. N. Pendleton

The synchrotron shock model (SSM) for gamma-ray burst emission makes a testable prediction: that the observed low-energy power-law photon number spectral index cannot exceed -2/3 (where the photon model is defined with a positive index: dN/dE is proportional to E^alpha). We have collected time-resolved spectral fit parameters for over 100 bright bursts obser

F. Nicastro, F. Fiore, G. Matt

We present photoionization models accounting for both photoelectric and resonant absorption. We demonstrate that resonance absorption lines are detectable even in moderate resolution X-ray spectra of type 1 AGN. The spectra transmitted by gas illuminated by the ionizing continua typical of flat X-ray spectrum, broad optical emission line type 1 AGN, and stee

P. H. Hauschildt, E. Baron

In this paper we discuss numerical methods and algorithms for the solution of NLTE stellar atmosphere problems involving expanding atmospheres, e.g., found in novae, supernovae and stellar winds. We show how a scheme of nested iterations can be used to reduce the high dimension of the problem to a number of problems with smaller dimensions. As examples of th

Xiang-Ping Wu, Li-Zhi Fang, Wen Xu

The relationship between the X-ray determined temperature $T$ of the intracluster gas and the optical measured velocity dispersion $σ$ of the cluster galaxies is often believed to be not only a straightforward but also robust test for the dynamical properties of galaxy clusters. Here, we present the $σ$-$T$ relationship using the 94 clusters drawn from the l

Xiang-Ping Wu

I report the current status on the determinations of the baryon fractions and dynamical/lensing masses of galaxy clusters as well as the $σ$ - $T$ relationship, making use of all the published data in literature which include 304 measurements for baryon fractions, 320/21 data points for masses of intracluster gas/cluster galaxies, (152+228)/72 data points fo

Xiang-Ping Wu, Tzihong Chiueh, Li-Zhi Fang, Yan-Jie Xue

Rich and massive clusters of galaxies at intermediate redshift are capable of magnifying and distorting the images of background galaxies. A comparison of different mass estimators among these clusters can provide useful information about the distribution and composition of cluster matter and their dynamical evolution. Using a hitherto largest sample of lens

C. Charbonnel, J. A. Brown, G. Wallerstein

We discuss the observational evidences for the non-standard mixing that occurs in low mass stars while they are ascending the Red Giant Branch.

L. Maraschi, L. Chiappetti, F. Tavecchio, A. Celotti

PKS 2155-304 was observed with BeppoSAX in November 1997 for 64 ksec (total elapsed time 33.5 hours) and, for the first time, simultaneously in gamma-rays with EGRET on board the Compton Gamma Ray Observatory and with the ground based TeV telescope CANGAROO, during a phase of high brightness in the X-ray band. The LECS and MECS light curves show a pronounced

L. Eyer, P. Bartholdi

In the analysis of variable stars, the problem of sampling is central. This article focusses on the determination of the Nyquist frequency. It is well defined in the case of regular sampling. However, the time series of variable stars observations are generally unevenly sampled. Fourier analysis using the spectral window furnishes some clues about the equiva

Fabrizio Brighenti, William G. Mathews

We study the complete dynamical evolution of hot interstellar gas in massive elliptical galaxies born into a simple flat universe beginning with an overdense perturbation. Within the turn-around radius dark matter flows in a self-similar fashion into a stationary Navarro-Frenk-White halo and the baryonic gas shocks. After a few gigayears, when enough gas acc

Xavier Delfosse, Thierry Forveille, Michel Mayor, Christian Perrier

High precision radial velocity observations of the nearby M4 dwarf Gl 876 with the Observatoire de Haute Provence 1.93 m telescope and the new 1.20 m swiss telescope at la Silla indicate the presence of a jovian mass companion to this star. The orbital fit to the data gives a period of 60.8 days, a velocity amplitude of 246 m/s and an eccentricity of 0.34. A

M. Boettcher, E. P. Liang, I. A. Smith

We present a detailed study of the observable effects of photoionization and Comptonization of line and continuum radiation from a cold accretion disk with a thin, warm, photoionized transition layer in the framework of self-consistent accretion-disk corona models for Galactic black-hole candidates. We use an iterative method to treat the non-linear radiatio

Andre Lukas, Burt A. Ovrut, Daniel Waldram

We construct vacua of M-theory on S^1/Z_2 associated with Calabi-Yau three-folds. These vacua are appropriate for compactification to N=1 supersymmetry theories in both four and five dimensions. We allow for general E_8 x E_8 gauge bundles and for the presence of five-branes. The five-branes span the four-dimensional uncompactified space and are wrapped on h