May 1999 arXiv papers — page 5

David B. Cline, Christina Matthey, Stanislaw Otwinowski

We have carried out a detailed study of the morphology of gamma-ray bursts (GRBs) with time duration less than 100 ms that includes: (1) a fast-Fourier spectrum analysis, (2) a comparison with the Stern analysis of longer bursts, (3) an inner comparison of the properties of the short bursts, and (4) a comparison of the short burst properties with the bulk of

T. X. Thuan, Y. I. Izotov, C. B. Foltz

We use Multiple Mirror Telescope (MMT) spectrophotometry and Hubble Space Telescope (HST) Faint Object Spectrograph (FOS) spectra and Wide Field and Planetary Camera 2 (WFPC2) V and I images to study the properties and evolutionary status of the nearby (D = 11.4 Mpc) extremely metal-deficient blue compact dwarf (BCD) galaxy SBS 1415+437=CG 389. The oxygen ab

M. Ribo, P. Reig, J. Marti, J. M. Paredes

RX J1826.2-1450/LS 5039 has been recently proposed to be a radio emitting high mass X-ray binary. In this paper, we present an analysis of its X-ray timing and spectroscopic properties using different instruments on board the RXTE satellite. The timing analysis indicates the absence of pulsed or periodic emission on time scales of 0.02-2000 s and 2-200 d, re

Kenneth R. Sembach, Blair D. Savage, Mark Hurwitz

We present Goddard High Resolution Spectrograph and ORFEUS-II measurements of Si IV, CIV, N V, and O VI absorption in the interstellar medium of the Galactic disk and halo toward the nucleus of the Seyfert galaxy ESO141-055. The high ionization absorption is strong, with line strengths consistent with the spectral signature expected for hot (log T = 5-6) col

J. P. Halpern, T. J. Turner, I. M. George

The X-ray source AXJ0341.4-4453 was described by Boyle et al. as a Type 2 AGN at z = 0.672 based on the absence of broad emission lines in the observed wavelength range 4000-7000 Angstroms. We obtained a new spectrum of AXJ0341.4-4453 extending to 9600 Angstroms which reveals broad Balmer lines and other characteristics of Seyfert 1 galaxies. The FWHM of bro

G. Fiorentini, B. Ricci

We review recent advances concerning helioseismology, solar models and solar neutrinos. Particularly we shall address the following points: i) helioseismic tests of recent SSMs; ii)the accuracy of the helioseismic determination of the sound speed near the solar center; iii)predictions of neutrino fluxes based on helioseismology, (almost) independent of SSMs;

P. Cinzano, F. Falchi, C. D. Elvidge, K. E. Baugh

We present a project to map the artificial sky brightness in Europe in the main astronomical photometrical bands with a resolution better than 3 km. The aim is to understand the state of night sky pollution in Europe, to quantify the present situation and to allow future monitoring of trends. The artificial sky brightness in each site at a given position on

D. L. Khokhlov

Generation of adiabatic density perturbations from fluctuations caused by the birth of baryons is considered. This is based on the scenario of baryogenesis in which the birth of protons takes place at the temperature equal to the mass of electron.

E. A. Barsukova, S. N. Fabrika, S. A. Pustilnik, A. V. Ugryumov

Results of optical spectral monitoring of CI Cam just after its a unusual bright and rapidly evolving X-ray burst are reported. This star is a symbiotic-type X-ray binary. The X-ray-radio-optical burst and the appearance of relativistic S-shaped SS433-like jets make CI Cam to be a very interesting star. We observed emergence of a high excitation and variable

G. E. Brown, R. A. M. J. Wijers, C. -H. Lee, H. -K. Lee

We use recent results in binary stellar evolution to argue that binaries with at least one black hole dominate the rate of compact-object mergers. Two phenomena generally attributable to such mergers, gamma-ray bursts and gravity-wave bursts, are therefore likely to originate from near the event horizon of a black hole. In addition to sheer numbers, black ho

T. Lejeune, R. Buser

In view of the important contributions of red giants to the integrated light in evolutionary synthesis calculations of old stellar populations in clusters and galaxies, we provide a comparison of theoretical isochrones computed from the Padova, Geneva, and Yale evolutionary tracks, respectively. Using the most recent version of the color-calibrated library o

T. Lejeune, E. Lastennet, P. Westera, R. Buser

In view of the importance of accurate fundamental stellar parameters for `Spectro-photometric dating of stars and galaxies", we present simultaneous effective temperature and metallicity determinations for a sample of 40 stars from Stromgren synthetic photometry with an empirically calibrated grid of model atmosphere spectra (BaSeL models). Comparisons w

E. Lastennet, D. Valls-Gabaud, T. Lejeune, E. Oblak

Three binary systems in the Hyades open cluster, with known metallicity and good Johnson photometric data are used to test the validity of three independent sets of stellar evolutionary tracks. A statistical method is described and applied to the colour-magnitude diagram of the six selected components, giving rise to $χ^2$-contours in the age-metallicity pla

Katherine M. Blundell, Steve Rawlings

Radio galaxies can be seen out to very high redshifts, where in principle they can serve as probes of the early evolution of the Universe. Here we show that for any model of radio-galaxy evolution in which the luminosity decreases with time after an initial rapid increase (that is, essentially all reasonable models), all observable high-redshift radio-galaxi

M. H. Montgomery, E. W. Klumpe, D. E. Winget, M. A. Wood

We present an exploration of the significance of Carbon/Oxygen phase separation in white dwarf stars in the context of self-consistent evolutionary calculations. Because phase separation can potentially increase the calculated ages of the oldest white dwarfs, it can affect the age of the Galactic disk as derived from the downturn in the white dwarf luminosit

N. Wex, V. Kalogera, M. Kramer

We use recent information on geodetic precession of the binary pulsar B1913+16 along with measurements of its orbital parameters and proper motion to derive new constraints on the immediate progenitor of this double neutron star system. As part of our analysis we model the motion of the binary in the Galaxy after the second supernova explosion, and we derive

Roser Pello

Clusters of galaxies as gravitational lenses allow to study the stellar content and properties of high-z galaxies much fainter than the usual spectroscopic field surveys. We review the recent results obtained on the identification and study of very distant galaxies seen through lensing clusters. Using the gravitational amplification effect in lenses with wel

Luciano Mantegazza, Ennio Poretti

The line profile variations of the Delta Scuti star HD 2724=BB Phe were studied on the basis of new 189 high-resolution spectrograms covering 52 hours of observations on a baseline of 8.3 days. By combining these results with those of a previous campaign 13 pulsation modes were identified: 5 of them are both photometric and spectroscopic, 3 are purely spectr

Sungsoo S. Kim, Mark Morris, Hyung Mok Lee

We investigate the dynamical evolution of compact young clusters (CYCs) near the Galactic center (GC) using Fokker-Planck models. CYCs are very young (< 5 Myr), compact (< 1 pc), and only a few tens of pc away from the GC, while they appear to be as massive as the smallest Galactic globular clusters (~10^4 Msun). A survey of cluster lifetimes for various ini

W. Kluzniak

If Lorentz invariance is broken at an energy scale Eq, as has recently been suggested in the context of attempts to quantize gravity, the kinematics of photon-photon collisions would be profoundly affected at lower energies. Specifically, electron-positron pair creation on soft photons may be forbidden at photon energies as low as 30 TeV times square root of

F. Falchi, P. Cinzano

We obtained the map of the zenith brightness of the night sky in Italy. The artificial sky brightness in each site is computed by integration of the contributions by each unitary area of surface obtained by applying a propagation function to the upward emission of the area as obtained from DMSP satellite night-time images. We also evaluated the emission vers

Aaron Bertram

A new proof of the mirror conjecture for Fano and Calabi-Yau complete intersections in P^n is given, using only the circle action on the graph space. The proof applies to projective bundles as well, with applications to "linear" relative Calabi-Yau's and to Schubert calculus.

T. Jungwirth, A. H. MacDonald, L. Smrcka, S. M. Girvin

Recently reported giant anisotropy in the longitudinal resistivity of a 2D electron system with valence Landau level index $N \ge 2$ has been interpreted as a signal of unidirectional charge density wave (UCDW) ground states. We report on detailed Hartree-Fock calculations of the UCDW orientation energy induced by a tilted magnetic field. We find that for cu

Vitaly Vanchurin, Alexander Vilenkin, Serge Winitzki

Models of inflationary cosmology can lead to variation of observable parameters (&#34;constants of Nature&#34;) on extremely large scales. The question of making probabilistic predictions for today&#39;s observables in such models has been investigated in the literature. Because of the infinite thermalized volume resulting from eternal inflation, it has prov

H. R. Christiansen

We discuss the spontaneous breakdown of chiral symmetry in Quantum Chromodynamics by considering gluonic instanton configurations in the partition function. It is shown that in order to obtain nontrivial fermionic correlators in a two dimensional gauge theory for the strong interactions among quarks, a regular instanton background has to be taken into accoun

F. A. Harrison, J. S. Bloom, D. A. Frail, R. Sari

We present multi-color optical and two-frequency radio observations of the bright SAX event, GRB 990510. The well-sampled optical decay, together with the radio observations are inconsistent with simple spherical afterglow models. The achromatic optical steepening and the decay of the radio afterglow both occuring at $t \sim 1$ day are evidence for hydrodyna

Leonard S. Kisslinger, Wei-hsing Ma

It has long been believed that the Pomeron, which has been successful in phenomenological fits to high energy scattering data, is associated with gluonic exchange. By determining the Regge-nucleon vertex in terms of previously determined glueball-quark coupling we show that the Pomeron might be related to the Regge trajectory defined by a light scalar glueba

H. Ebeling, L. R. Jones, E. Perlman, C. Scharf

The WARPS team reviews the properties and history of discovery of ClJ0152.7-1357, an X-ray luminous, rich cluster of galaxies at z=0.833. At L_X = 8 x 10^44 h^(-2) erg/s (0.5-2.0 keV) ClJ0152.7-1357 is the most X-ray luminous cluster known at redshifts z>0.55. The high X-ray luminosity of the system suggests that massive clusters may begin to form at redshif

I. M. Dremin, J. W. Gary

Analytic predictions for the energy dependence of the mean multiplicities in gluon and quark jets are presented at the next-to-next-to-next-to-leading order (3NLO) of perturbative QCD and are compared to experiment. The 3NLO correction to the gluon jet multiplicity is found to be small. The corresponding theoretical expression provides a good description of

Jorgen Rasmussen

See hep-th/0002188

F. Leyvraz, R. A. Mendez-Sanchez, M. Lombardi, T. H. Seligman

The multichannel quantum defect theory (MQDT) can be reinterpreted as a quantum Poincare map in representation of angular momentum. This has two important implications: we have a paradigm of a true quantum Poincare map without semi-classical input and we get an entirely new insight into the significance of MQDT.

V. Barger, T. Han, C. Kao, R. -J. Zhang

In the Kaluza-Klein (KK) scenario with n large extra dimensions where gravity propagates in the 4+n dimensional bulk of spacetime while gauge and matter fields are confined to a four dimensional subspace, the light graviton KK modes can be produced in the Sun, red giants and supernovae. We study the energy-loss rates through photon-photon annihilation, elect

C. M. Ginsburg

Neutral-current and charged-current deep-inelastic scattering at very high four-momentum transfer squared (Q^2) have been studied in positron-proton collisions at center-of-mass energy 300 GeV using the ZEUS detector at HERA. An integrated luminosity of 47.7 $pb^{-1}$ was collected in the years 1994-1997. Differential cross sections are presented for $Q^2 >

G. Degrassi, P. Gambino

We present the evaluation of the two-loop O(g^4 mt^2) effects in the partial widths of the Z boson in the MSbar scheme and in two different implementations of the on-shell scheme. We observe a clear reduction of the scheme dependence of the predictions. The renormalization procedure and the Heavy Top Expansion employed in the O(g^4 mt^2) calculations are ill

K. -H. Rehren

A rigorous (and simple) proof is given that there is a one-to-one correspondence between causal anti-deSitter covariant quantum field theories on anti-deSitter space and causal conformally covariant quantum field theories on its conformal boundary. The correspondence is given by the explicit identification of observables localized in wedge regions in anti-de

H. Mehl, I. Furman, O. Biham, M. Karimi

We present a class of models that describe self diffusion on several fcc(001) metal substrates within a common framework. The models are found to apply well for Cu(001), Ag(001), Au(001), Ni(001) and Pd(001).For each of these metals the models can be used to estimate the activation energy of any diffusion process using a few basic parameters which may be obt

Ü. Parts, V. V. Avilov, J. H. Koivuniemi, N. B. Kopnin

We discuss the configurations in which singly and doubly quantized vortex lines may coexist in a rotating superfluid. General principles of energy minimization lead to the conclusion that in equilibrium the two vortex species segregate within a cylindrical vortex cluster in two coaxial domains where the singly quantized lines are in the outer annular region.

Klaus Behrndt, Dieter Lust

The embedding of a Taub-NUT space in the directions transverse to the world volume of branes describes branes at (spherical) orbifold singularities. Similarly, the embedding of a pp-wave in the brane world volume yields an AdS orbifold. In case of the D1-D5--brane system, the AdS3 orbifolds yields a BTZ black hole; as we will show, the same holds for D3-bran

Detlev Buchholz, Martin Florig, Stephen J. Summers

If the vacuum is passive for uniformly accelerated observers in anti-de Sitter space-time (i.e. cannot be used by them to operate a &#34;perpetuum mobile&#34;), they will (a) register a universal value of the Hawking-Unruh temperature, (b) discover a TCP symmetry, and (c) find that observables in complementary wedge-shaped regions are commensurable (local) i

Federico Finkel, Artemio Gonzalez-Lopez, Miguel A. Rodriguez

We show that there are two different families of (weakly) orthogonal polynomials associated to the quasi-exactly solvable Razavy potential $V(x)=(\z \cosh 2x-M)^2$ ($\z>0$, $M\in\mathbf N$). One of these families encompasses the four sets of orthogonal polynomials recently found by Khare and Mandal, while the other one is new. These results are extended to t

Ayse Humeyra Bilge

We construct a recursion operator for the system $(u_t,v_t)=(u_4+v^2,1/5 v_4)$, for which only one local symmetry is known and we show that the action of the recursion operator on $(u_t,v_t)$ is a local function.

R. Marx, A. F. Fahmy, J. M. Myers, W. Bermel

We demonstrate a five-bit nuclear-magnetic-resonance quantum computer that distinguishes among various functions on four bits, making use of quantum parallelism. Its construction draws on the recognition of the sufficiency of linear coupling along a chain of nuclear spins, the synthesis of a suitably coupled molecule, and the use of a multi-channel spectrome

P. G. Kwiat, J. R. Mitchell, P. D. D. Schwindt, A. G. White

The essential operations of a quantum computer can be accomplished using solely optical elements, with different polarization or spatial modes representing the individual qubits. We present a simple all-optical implementation of Grover&#39;s algorithm for efficient searching, in which a database of four elements is searched with a single query. By `compiling

J. Clausen, M. Dakna, L. Knoell, D. -G. Welsch

The generation of arbitrary single-mode quantum states from the vacuum by alternate coherent displacement and photon adding as well as the measurement of the overlap of a signal with an arbitrarily chosen quantum state are studied. With regard to implementations, the transformation of the quantum state of a traveling optical field at an array of beam splitte

Asher Peres

Statistical tests are needed to determine experimentally whether a hypothetical theory based on local realism can be an acceptable alternative to quantum mechanics. It is impossible to rule out local realism by a single test, as often claimed erroneously. The ``strength&#39;&#39; of a particular Bell inequality is measured by the number of trials that are ne

Liping Fu, Jun Luo, Li Xiao, Xizhi Zeng

We report experimental implementation of discrete Fourier transformation(DFT) on a nuclear magnetic resonance(NMR) quantum computer. Experimental results agree with theoretical results. Using the pulse sequences we introduced, DFT can be realized on any L-bit quantum number in principle.

Alec Maassen van den Brink

We evaluate the finite-temperature Euclidean phase-space path integral for the generating functional of a scalar field inside a leaky cavity. Provided the source is confined to the cavity, one can first of all integrate out the fields on the outside to obtain an effective action for the cavity alone. Subsequently, one uses an expansion of the cavity field in

Bedrettin Subasilar

A new and simple method of blood bilirubin detection through light reflection from skin is developed. The basic improvement over the existing methods is in the design of the light emitter and detector geometry which facilitates a two-stream plane parallel homogenous medium solution to the emitting-scatterig radiative transfer equation. The forward peak in th

S. Kitsunezaki

We study a theoretical model of mud cracks, that is, the fracture patterns resulting from the contraction with drying in a thin layer of a mixture of granules and water. In this model, we consider the slip on the bottom of this layer and the relaxation of the elastic field that represents deformation of the layer. Analysis of the one-dimensional model gives

Alec Maassen van den Brink, K. Young

Dissipative systems can be described in terms of non-hermitian hamiltonians H, whose left eigenvectors f^j and right eigenvectors f_j form a bi-orthogonal system. Bi-orthogonal systems could suffer from two difficulties. (a) If the eigenvectors do not span the whole space, then H can only be diagonalized to blocks (the Jordan-block problem). (b) Normalizatio

Robert Carroll

We sketch some of the different roles played by Whitham times in connection with averaging, adiabatic invariants, soliton theory, Hamiltonian structures, Seiberg-Witten theory, isomonodromy problems, Hitchin systems, WDVV and Picard-Fuchs equations, renormalization, soft susy breaking, etc.

Mohammad Obiedat

Let $\widetilde{JO}(X)=\widetilde{KO}(X)/TO(X)$ be the J-group of a connected finite CW complex X. We Obtain two computable formulas of $TO(X)_{(p)}$, the localization of $TO(X)$ at a prime p. Then we show how to use these two formulas of $TO(X)_{(p)}$ to find the J-orders of elements of $\widetilde{KO}(CP^m)$, at least the 2 and 3 primary factors of the can

Craig Benham, Xiao-Song Lin, David Miller

The inclusion of the space of all knots of a prescribed writhe in a particular isotopy class into the space of all knots in that isotopy class is a weak homotopy equivalence.

A. N. Schellekens

A formula is derived for the fixed point resolution matrices of simple current extended WZW-models and coset conformal field theories. Unlike the analogous matrices for unextended WZW-models, these matrices are in general not symmetric, and they may have field-dependent twists. They thus provide non-trivial realizations of the general conditions presented in

Matthias Schwarz

An explicit isomorphism between Morse homology and singular homology is constructed via the technique of pseudo-cycles. Given a Morse cycle as a formal sum of critical points of a Morse function, the unstable manifolds for the negative gradient flow are compactified in a suitable way, such that gluing them appropriately leads to a pseudo-cycle and a well-def

Ashok Das, Gerald Dunne

We study an extreme non-static limit of 2+1-dimensional QED obtained by making a dimensional reduction so that all fields are spatially uniform but time dependent. This dimensional reduction leads to a 0+1-dimensional field theory that inherits many of the features of the 2+1-dimensional model, such as Chern-Simons terms, time-reversal violation, an analogue

Iosif Bena

In the Poincare patch of Minkovski AdS_5 we explicitly construct local bulk fields from the boundary operators, to leading order in 1/N. We also construct the Green&#39;s function implicitly defined by this procedure. We generalize the construction of local fields for near horizon geometries of Dp branes. We try to expand the procedure to the interacting cas

Paul Federbush

The bare bones of a theory of quantum gravity are exposed. It may have the potential to solve the cosmological constant problem. Less certain is its behavior in the Newtonian limit.

D. Bazeia

We investigate a model for a real scalar field in bidimensional space-time, described in terms of a positive semi-definite potential that presents no vacuum state. The system presents topological solutions of the BPS type, with energy density that follows a Lorentzian law. These BPS solutions differ from the standard $\tanh$-type kink, but they also support

R. Helling, J. Plefka, M. Serone, A. Waldron

The leading eikonal S-matrix for three graviton scattering in d=11 supergravity and Matrix Theory are shown to precisely agree. The result unifies the source-probe plus recoil approach of Okawa and Yoneya and relaxes the restriction imposed by those authors that all D-particle impact parameters and velocities are mutually perpendicular. Furthermore, the unif

Abhas Mitra

Supersymmetric String theories find occurrences of extremal Black Holes with gravitational mass M=Q where Q is the charge (G=c=1). Thus, for the chargeless cases, they predict M=0. We show that General Theory of Relativity, too, demands a unique BH mass M=0. And we do this by considering the problem from various angles, both mathematically and physically. Ou

Antonio Masiero, Francesca Rosati

Last year observations had a profound impact on our views on the amount and nature of dark matter in the universe. We give a brief review of the recent history of dark matter models beyond the pure cold dark matter universe. In view of the most recent cosmological data, we then go on to discuss models with a positive cosmological constant. Finally we explici

Sukanta Dutta, Raj Gandhi, Biswarup Mukhopadhyaya

We study the possibilities offered by muon storage rings for tau-neutrino appearance experiments due to nu_mu to nu_tau and nu_e to nu_tau oscillations. Tau event rates for such experiments are first discussed with a view to examining their variation prior to the inclusion of experimental cuts, in order to better understand how baselines, beam energies, forw

G. Holzwarth

Localized static solutions of the 2D-O(3) model are investigated in a representation with the 3-vector field $\vec Phi$ split into the unit vector $\hat Phi$ and the modulus $Φ$. As in the nonlinear version of the model this allows for the definition of a topological winding number $B$, and for the separation of the complete configuration space into distinct

N. Tetradis

We summarize recent work on the consistent calculation of bubble-nucleation rates. Our approach is based on the notion of a real coarse-grained potential. The bubble-nucleation rate is calculated through an expansion around the semiclassical saddle point associated with tunnelling. We resolve outstanding problems related to the convexity of the potential, th

A. Di Giacomo, B. Lucini

The status of our understanding of confinement is reviewed. The evidence from lattice is that monopole condensation, or dual superconductivity, is at work. Confinement is an order-disorder transition. Different monopole species look equivalent, indicating that the symmetry of the disordered phase is more interesting that we understand.

LVD Collaboration

We analysed the arrival directions of single muons detected by the first LVD tower from November, 1994 till January, 1998. The moon shadowing effect has been observed. To search for point sources of high energy photons we have analysed muons crossing the rock thickness greater than 3, 5 and 7 km w.e., which corresponds to the mean muon energies 1.6, 3.9 and

LVD Collaboration

The flux of muon-produced neutrons far away from the muon track may constitute a background for the underground detectors searching for rare events. The muon events collected by the first LVD tower from March, 1996, to February, 1998, (1.56 years of live time) were used to estimate the neutron flux at various distances from the muon track or muon-produced ca

Daniel A. T. Vanzella, George E. A. Matsas

We discuss the possible influence of gravity in the neutronization process, $p^+ e^- \to n ν_e$, which is particularly important as a cooling mechanism of neutron stars. Our approach is semiclassical in the sense that leptonic fields are quantized on a classical background spacetime, while neutrons and protons are treated as excited and unexcited nucleon sta

R. Scipioni

We show how a Metric Affine theory of Dilaton gravity can be reduced to an effective Riemannian Dilaton gravity model. A simple generalization of the Obukhov-Tucker-Wang theorem to Dilaton gravity is then presented.

V. A. Rubakov, S. M. Sibiryakov

We suggest a technique that explicitly accounts for the structure of an initial state of quantum field in the semiclassical calculations of path integral in curved space-time, and consider decay of metastable state (conformal vacuum of scalar particles above false classical vacuum) in background de Sitter space-time as an example. Making use of this techniqu

Tetsuya Shiromizu, Uchida Gen

We define space-times which are asymptotic to radiation dominant Friedman-Robertson-Walker space-times at timelike infinity and study the asymptotic structure. We discuss the local asymptotic symmetry and give a definition of the total energy from the electric part of the Weyl tensor.

L. Ozyuzer, Z. Yusof, J. F. Zasadzinski, T. -W. Li

New results from tunneling spectroscopies on near optimally-doped single crystals of Tl_{2}Ba_{2}CuO_{6} (Tl-2201) junctions are presented. The superconductor-insulator-normal metal (SIN) tunnel junctions are obtained using the point-contact technique with a Au tip. The tunneling conductances reproducibly show a sharp cusp-like subgap, prominent quasiparticl

C. Rodríguez-Castellanos, M. T. Pérez-Maldonado

The effect of strong laser radiation on magnetic subbands in semiconductor superlattices is investigated. Due to the presence of a magnetic field perpendicular to the growth direction, non-linear effects such as band supression and electron localization become relevant at relatively lower intensities and for any polarization perpendicular to the magnetic fie

A. L. Efros

The distribution of electron density in the quantum Hall liquid is considered in the presence of macroscopic density gradient caused by side electrodes or inhomogeneous doping. In this case different Landau levels are occupied in different regions of a sample. These regions are separated by incompressible liquid. It is shown that the applicability of the app

Norbert Elstner, Hartmut Monien

In this paper we report results from a systematic strong-coupling expansion of the Bose-Hubbard model in one and two spatial dimensions. We obtain numerically exact results for the structure factor and the spectrum of single particle and single hole excitations in the Mott insulator. This enables the determination of the zero-temperature phase diagram and th

F. M. Munteanu, Yongmin Kim, C. H. Perry, D. G. Rickel

We present here the results of polarized magneto-photoluminescence measurements on a high mobility single-heterojunction. The presence of a doublet structure over a large magnetic field range (2>nu>1/6) is interpreted as possible evidence for the existence of a magneto-roton minima of the charged density waves. This is understood as an indication of strong e

A. D. Mirlin, J. Wilke, F. Evers, D. G. Polyakov

We calculate the semiclassical magnetoresistivity $ρ_{xx}(B)$ of non-interacting fermions in two dimensions moving in a weak and smoothly varying random potential or random magnetic field. We demonstrate that in a broad range of magnetic fields the non-Markovian character of the transport leads to a strong positive magnetoresistance. The effect is especially

Sergei A. Sergeenkov

Low-frequency magnetic noise spectrum is calculated within the superconductive glass model. The model predicts the existence of both white noise and flicker-like noise f^{-z} with z strongly dependent on applied magnetic field and temperature. It is shown, in particular, that z increases with field from 0.5 to 1, and that in the critical region (near T_{c}(H

Sergei A. Sergeenkov

The oxygen defects induced phase transition from nonergodic to ergodic state in superconductors with intragrain granularity is considered within the superconductive glass model. The model predictions are found to be in a qualitative agreement with some experimental observations in deoxygenated high-T_c single crystals.

S. C. Bradley, R. Bulla, A. C. Hewson, G-M. Zhang

The O(3) symmetric Anderson model is an example of a system which has a stable low energy marginal Fermi liquid fixed point for a certain choice of parameters. It is also exactly equivalent, in the large U limit, to a localized model which describes the spin degrees of freedom of the linear dispersion two channel Kondo model. We first use an argument based o

G. J. Milburn

We show an equivalence between the approach of Buttiker and the Fermi quantum stochastic calculus for mesoscopic systems. To illustrate the method we derive the current fluctuations in a two terminal mesoscopic circuit with two tunnel barriers containing a single quasi bound state on the well. The method enables us to focus on either the incoming/outgoing Fe

Teruhisa S. Komatsu

This letter investigates the molecular dynamics of inelastic disks without external forcing. By introducing a new observation frame with a rescaled time, we observe the virtual steady states converted from asymptotic energy dissipation processes. System behavior in the thermodynamic limit is carefully investigated. It is found that a phase transition with sy

Alex Hansen, Mogens H. Jensen, Kim Sneppen, Giovanni Zocchi

Comments: 6 pages RevTeX, 6 Postscript figures. We review a statistical mechanics treatment of the stability of globular proteins based on a simple model Hamiltonian taking into account protein self interactions and protein-water interactions. The model contains both hot and cold folding transitions. In addition it predicts a critical point at a given temper

D. K. Klimov, D. Thirumalai

Single molecule force spectroscopy reveals unfolding of domains in titin upon stretching. We provide a theoretical framework for these experiments by computing the phase diagrams for force-induced unfolding of single domain proteins using lattice models. The results show that two-state folders (at zero force) unravel cooperatively whereas stretching of non-t

Barbara Drossel, Hemant Bokil, M. A. Moore, A. J. Bray

We study the link overlap between two replicas of an Ising spin glass in three dimensions using the Migdal-Kadanoff approximation and scaling arguments based on the droplet picture. For moderate system sizes, the distribution of the link overlap shows the asymmetric shape and large sample-to-sample variations found in Monte Carlo simulations and usually attr

T. Hikihara, A. Furusaki, M. Sigrist

We calculate the ground-state two-spin correlation functions of spin-1/2 quantum Heisenberg chains with random exchange couplings using the real-space renormalization group scheme. We extend the conventional scheme to take account of the contribution of local higher multiplet excitations in each decimation step. This extended scheme can provide highly accura

Erik Koch, Olle Gunnarsson, Richard M. Martin

Describing the doped Fullerenes using a generalized Hubbard model, we study the Mott transition for different integer fillings of the t_1u band. We use the opening of the energy-gap E_g as a criterion for the transition. E_g is calculated as a function of the on-site Coulomb interaction U using fixed-node diffusion Monte Carlo. We find that for systems with

Hangmo Yi, H. A. Fertig

We investigate the microwave absorption of a pinned, two-dimensional Wigner crystal in a strong magnetic field at finite temperatures. Using a model of a uniform commensurate pinning potential, we analyze thermal broadening of the electromagnetic absorption resonance. Surprisingly, we find that the pinning resonance peak should remain sharp even when the tem

G. Tiana, R. A. Broglia, E. I. Shakhnovich

With the help of a simple 20 letters, lattice model of heteropolymers, we investigate the energy landscape in the space of designed good-folder sequences. Low-energy sequences form clusters, interconnected via neutral networks, in the space of sequences. Residues which play a key role in the foldability of the chain and in the stability of the native state a

Guillermo Tenorio-Tagle, Sergey A. Silich, Daniel Kunth, Elena Terlevich

The detection of Ly alpha emission in star-forming galaxies in different shapes and intensities (always smaller than predicted for case B recombination) has puzzled the astronomical community for more than a decade. Here we use two dimensional calculations to follow the evolution of superbubbles and of the H II regions generated by the output of UV photons f

S. Vaughan, J. Reeves, R. Warwick, R

We present a systematic analysis of the X-ray spectral properties of a sample of 22 ``narrow-line&#39;&#39; Seyfert 1 galaxies for which data are available from the ASCA public archive. Many of these sources, which were selected on the basis of their relatively narrow H-beta line width (FWHM <= 2000 km/s), show significant spectral complexity in the X-ray ba

Chun Xu, Mario Livio, Stefi A. Baum

We generated a sample of 409 AGNs for which both the radio luminosity at 5 GHz and the line luminosity in [OIII] 5007 have been measured. The radio luminosity spans a range of ten orders of magnitude, and the [OIII] line luminosity spans a range of eight orders of magnitude --- both considerably larger than the ranges in previous studies. We show that these

Keith A. Olive, Gary Steigman, Terry P. Walker

We review the Cosmology and Physics underlying Primordial Nucleosynthesis and survey current observational data in order to compare the predictions of Big Bang Nucleosynthesis with the inferred primordial abundances. From this comparison we report on the status of the consistency of the standard hot big bang model, we constrain the universal density of baryo

J. T. Bonnell, J. P. Norris

The inhomogeneous brightness distribution of BATSE detected gamma-ray bursts has been considered strong evidence for their cosmological origin. However, subclasses of gamma-ray bursts have been shown to have significantly more homogeneous brightness distributions. Pendleton et al. (1997) have found such a result for gamma-ray bursts with no detectable emissi

G. Fritz Benedict, Barbara McArthur, D. W. Chappell, E. Nelan

We report on a sub-stellar companion search utilizing interferometric fringe-tracking astrometry acquired with Fine Guidance Sensor 3 (FGS 3) on the Hubble Space Telescope. Our targets were Proxima Centauri and Barnard&#39;s Star. We obtain absolute parallax values for Proxima Cen pi_{abs} = 0.7687 arcsecond and for Barnard&#39;s Star pi_{abs} = 0.5454 arcse

H. Genreith

A simple model of a universe is presented composed of black holes and black branes. It uses the most simplest approximations and models of General Relativity and Quantum Dynamics to offer an idea of an unification and gives a possible answer to the quantization and entropy of Black Holes. It proposes a mass spectra for elementary particles and gives a vivid

Paul C. Hewett, Stephen J. Warren, Jon P. Willis, Joss Bland-Hawthorn

Most surveys for multiply-imaged gravitational lenses, outside of rich galaxy clusters, are based on sifting through large samples of distant sources to identify the rare examples of lensing. An alternative strategy, based on the selection of optimal lines-of-sight, offers a number of significant advantages. Utilising the multiplex capability of wide-area mu

Arnon Dar

Recent observations suggest that gamma ray bursts (GRBs) and their afterglows are produced in star formation regions in distant galaxies by highly relativistic jets that happen to point in our direction. Relativistic beaming collimates the emission from the highly relativistic jets into small solid angles along the jet direction. It implies that we are seein

S. Cristiani

Together with the CMB, the three sources of information that astronomers have at high redshift as probes of the formation and evolution of the LSS are QSOs, galaxies and absorbers observed in the spectrum of distant background objects. In this contribution I try to give a hint of historical perspective, following how the technological advances have driven th