July 1998 arXiv papers — page 6

E. Pehlke, P. Kratzer

Relaxed atomic geometries and chemisorption energies have been calculated for the dissociative adsorption of molecular hydrogen on vicinal Si(001) surfaces. We employ density-functional theory, together with a pseudopotential for Si, and apply the generalized gradient approximation by Perdew and Wang to the exchange-correlation functional. We find the double

H. J. Schulz

The doping-induced metal-insulator transition in two-chain systems of correlated fermions is studied using a solvable limit of the t-J model and the fact that various strong- and weak-coupling limits of the two-chain model are in the same phase, i.e. have the same low-energy properties. It is shown that the Luttinger-liquid parameter K_ρtakes the universal v

O. Z. Alekperov

Free carrier capture by a screened Coulomb potential in semiconductors are considered. It is established that with decreasing screening radius the capture cross section decreases drastically, and it goes to zero when $% r_s=a_B^{*}$. On the basis of this result a new mechanism of shallow impurity electric field break down in semiconductors is suggested.

Yukito Iba, Macoto Kikuchi, Kei Tokita

A novel approach to heteropolymer design is proposed. It is based on the criterion by Kurosky and Deutsch, with which the probability of a target conformation in a conformation space is maximized at low but finite temperature. The key feature of the proposed approach is the use of soft spins (fuzzy monomers) that leads to a design equation, which is an analo

O. Z. Alekperov

It is established experimentally that the low temperature photoelectric spectra line width of shallow impurities depends not only on charged impurity concentration $N_i=2KN_A$ and degree of samples compensation $% K=N_A/N_D$, as it was believed earlier.To a great extent it depends on the impurity distribution inhomogeneity also.For samples with homogeneous a

M. V. Zverev, M. Baldo

The structure of the ground state beyond the instability point of the quasiparticle system with Fermi-step momentum distribution is studied within the model of a Fermi liquid with a strong repulsive interaction. A ground state rearrangement occurs as the interaction strength is increased beyond a definite critical value. Numerical investigation of the initia

Jianjun Xie, Stefano de Gironcoli, Stefano Baroni, Matthias Scheffler

The thermal properties of silver are calculated within the quasi-harmonic approximation, by using phonon dispersions from density-functional perturbation theory, and the pseudopotential plane-wave method. The resulting free energy provides predictions for the temperature dependence of various quantities such as the equilibrium lattice parameter, the bulk mod

Norbert Broeker

This paper explores commonalities and differences between \dachs, a variant of Dependency Grammar, and Lexical-Functional Grammar. \dachs\ is based on traditional linguistic insights, but on modern mathematical tools, aiming to integrate different knowledge systems (from syntax and semantics) via their coupling to an abstract syntactic primitive, the depende

Simon Lilly, Steven Eales, Walter Gear, Dick Bond

Deep surveys in the far-infrared and sub-millimeter wavebands are revealing a new phase of galactic evolution hidden by dust. Observations with SCUBA on the JCMT show that 25% of the COBE/FIRAS background at 850 microns is being produced by high luminosity sources (L ~ 3x10^12 L_sun) at high redshifts 0.5 < z < 3+. These sources have an estimated redshift di

A. L. Zezas, I. Georgantopoulos, M. J. Ward

We present ROSAT (HRI and PSPC) and ASCA observations of the two luminous (L_x ~10^{41-42} erg s^{-1}) star-forming galaxies NGC3310 and NGC3690. The HRI shows clearly that the sources are extended with the X-ray emission in NGC3690 coming from at least three regions. The combined 0.1-10 keV spectrum of NGC3310 can be described by two components, a Raymond-S

S. K. Leggett, F. Allard, P. H. Hauschildt

We present new infrared photometry for 61 halo and disk stars around the stellar/substellar boundary. These data are combined with available optical photometry and astrometric data to produce color--color and absolute magnitude--color diagrams. The disk and halo sequences are compared to the predictions of the latest model atmospheres and structural models.

Tsvi Piran

Gamma-ray bursts GRBs are among the most mysterious astronomical phenomenon ever discovered. Unlike most astronomical discoveries which were explained within weeks or months after their initial discovery, GRBs remain a puzzle for more than thirty years. During the last decade our understanding of GRBs has undergone two major revolutions. First, BATSE discove

A. Celotti, M. J. Rees

We discuss the role that magnetic fields in low luminosity accretion flows can play in creating and maintaining a multi-phase medium, and show that small magnetically-confined clouds or filaments of dense cold gas can dramatically reprocess the `primary&#39; radiation from tori. In particular, radio emission would be suppressed by free-free absorption, and a

Sergio Molinari, Leonardo Testi, Jan Brand, Riccardo Cesaroni

IRAS 23385+6053 is a Young Stellar Object with luminosity 16,000 solar luminosities at a kinematic distance of 4.9 kpc. This candidate precursor of an ultracompact HII region is associated with a millimeter source detected at the JCMT but is undetected at centimeter wavelengths with the VLA. We observed this source with the OVRO millimeter array at 3.4 mm in

G. Cleaver, M. Cvetic, J. R. Espinosa, L. Everett

From the &#34;top-down&#34; approach we investigate physics implications of the class of D- and F- flat directions formed from non-Abelian singlets which are proven flat to all orders in the nonrenormalizable superpotential, for a prototype quasi-realistic free fermionic string model with the standard model gauge group and three families (CHL5). These flat d

Evgueni K. Sklyanin, Takashi Takebe

For the elliptic Gaudin model (a degenerate case of XYZ integrable spin chain) a separation of variables is constructed in the classical case. The corresponding separated coordinates are obtained as the poles of a suitably normalized Baker-Akhiezer function. The classical results are generalized to the quantum case where the kernel of separating integral ope

Fei Zhou, Yong Baek Kim

Motivated by the recent Coulomb drag experiment of M. P. Lilly et. al, we study the Coulomb drag in a two-layer system with Landau level filling factor $ν=1/2$. We find that the drag conductivity in the incompressible paired quantum Hall state at zero temperature can be finite. The drag conductivity is also greatly enhanced above $T_c$, at which the transiti

John Ellis, Nemanja Kaloper, Keith A. Olive, Jun&#39;ichi Yokoyama

We consider the possibility that higher-curvature corrections could drive inflation after the compactification to four dimensions. Assuming that the low-energy limit of the fundamental theory is eleven-dimensional supergravity to the lowest order, including curvature corrections and taking the descent from eleven dimensions to four via an intermediate five-d

Alejandro Ayala, Sangyong Jeon, Joseph Kapusta

We compute the Coulomb effects produced by an expanding, highly charged fireball on the momentum distribution of pions. We compare our results to data on Au+Au at 11.6 A GeV from E866 at the BNL AGS and to data on Pb+Pb at 158 A GeV from NA44 at the CERN SPS. We conclude that the distortion of the spectra at low transverse momentum and mid-rapidity can be ex

Kathryn V. Johnston, HongSheng Zhao, David N. Spergel, Lars Hernquist

We explore the use of tidal streams from Galactic satellites to recover the potential of the Milky Way. Our study is motivated both by the discovery of the first lengthy stellar stream in the halo (\cite{it98}) and by the prospect of measuring proper motions of stars brighter than 20th magnitude in such a stream with an accuracy of $\sim 4μas/$yr, as will be

Tomasz Plewa, Ewald Mueller

Simple modifications for higher-order Godunov-type difference schemes are presented which allow for accurate advection of multi-fluid flows in hydrodynamic simulations. The constraint that the sum of all mass fractions has to be equal to one in every computational zone throughout the simulation is fulfilled by renormalizing the mass fractions during the adve

Scott T. Kay, Richard G. Bower

In this paper, we have extended the entropy-driven model of cluster evolution developed by Bower (1997) in order to be able to predict the evolution of galaxy clusters for a range of cosmological scenarios. We have applied this model to recent measurements of the evolution of the L_x-T normalisation and X-ray luminosity function in order to place constraints

L. N. Lipatov

The duality symmetry of the hamiltonian and integrals of motion for reggeon interactions in the multi-colour QCD is formulated as an integral equation for the wave function of compound states of reggeized gluons, which together with the property of holomorphic factorization allows one to reduce the Odderon problem in QCD to the solution of the one-dimensiona

Helmut Schlattl, Achim Weiss, Georg Raffelt

Helioseismological sound-speed profiles severely constrain possible deviations from standard solar models, allowing us to derive new limits on anomalous solar energy losses by the Primakoff emission of axions. For an axion-photon coupling $g_{aγ} < 5 x 10^(-10) GeV^(-1)$ the solar model is almost indistinguishable from the standard case, while $g_{aγ} > 10 x

Takuya Matsuda, Makoto Makita, Hiroshi Yukawa, Henri M. J. Boffin

The first convincing piece of evidence of spiral structure in the accretion disc in IP Pegasi was found by Steeghs et al. (1997). We performed two kinds of 2D hydrodynamic simulations, a SFS finite volume scheme and a SPH scheme, with a mass ratio of 0.5. Both results agreed well with each other. We constructed Doppler maps and line flux-binary phase relatio

J. L. Alonso, Ph. Boucaud, J. M. Carmona, J. L. Cortes

We propose a way of protecting a Dirac fermion interacting with a scalar field from acquiring a mass from the vacuum. It is obtained through an implementation of translational symmetry when the theory is formulated with a momentum cutoff, which forbids the usual Yukawa term. We consider that this mechanism can help to understand the smallness of neutrino mas

Kirill Tuchin

A study of the high angular momentum particles &#39;atmosphere&#39; near the Schwarzschild black hole horizon suggested that strong gravitational interactions occur at invariant distance of the order of $\sqrt[3]{M}$ (A. Casher et. al). We present a generalization of this result to the Kerr-Newman black hole case. It is shown that the larger charge and angul

P. Prelovsek, A. Ramsak, I. Sega

The c-axis optical conductivity and d.c. resistivity are calculated within the t-J model assuming that the interlayer hopping is incoherent. Use is made of numerical results for spectral functions recently obtained with the finite-temperature Lanczos method for finite two-dimensional systems. In the optimally doped regime we find an anomalous relaxation rate

Makoto Makita, Takuya Matsuda

We perform 2D and 3D numerical simulations of an accretion disc in a close binary system using the Simplified Flux vector Splitting (SFS) finite volume method. In our calculations, gas is assumed to be the ideal one, and we calculate the cases with gamma=1.01, 1.05, 1.1 and 1.2. The mass ratio of the mass losing star to the mass accreting star is unity. Our

Yosuke Imamura

We study supersymmetry breaking due to the presence of branes on anti-de Sitter space and obtain conditions for brane orientations not to break too many supersymmetries. Using the conditions, we construct a brane configuration corresponding to a baryon in large N gauge theory, and it is shown that the baryon is a marginal bound state of quarks as is expected

Mark A. Walker

If dark halos are composed of dense gas clouds, as has recently been inferred, then collisions between clouds lead to galaxy evolution. Collisions introduce a core in an initially singular dark matter distribution, and can thus help to reconcile scale-free initial conditions -- such as are found in simulations -- with observed halos, which have cores. A pseu

M. S. Brotherton, Wil van Breugel, R. J. Smith, B. J. Boyle

We report the discovery of five broad-absorption-line (BAL) QSOs in a complete sample of 111 ultraviolet excess (UVX) QSO candidates also detected in the NRAO VLA Sky Survey. All five BAL QSOs, which include two high-ionization BAL QSOs and three low-ionization BAL QSOs, are formally radio-loud. Of QSOs with z > 0.4, 3+/-2% show low-ionization BALs, and of Q

J. G. Muga, C. R. Leavens, J. P. Palao

The properties of the time-of-arrival operator for free motion introduced by Aharonov and Bohm and of its self-adjoint variants are studied. The domains of applicability of the different approaches are clarified. It is shown that the arrival time of the eigenstates is not sharply defined. However, strongly peaked real-space (normalized) wave packets construc

Werner Fischer, Hajo Leschke, Peter Mueller

Exact results are derived on the averaged dynamics of a class of random quantum-dynamical systems in continuous space. Each member of the class is characterized by a Hamiltonian which is the sum of two parts. While one part is deterministic, time-independent and quadratic, the Weyl-Wigner symbol of the other part is a homogeneous Gaussian random field which

V. Pleitez

Although we accept that Physics is, as a last resort, an experimental science, the relationship between theory and experiment is far away from being trivial. Any experiment is always explained within a determinate theoretical context and, at the same time, an experiment can give suggestions for theories or even can bring new theoretical challenges. Thus, we

N. Piovella, L. Serafini, M. Ferrario

We present the anticipated performances of a multi-cell RF injector operated either with a thermoionic cathode or with a gated photo-cathode. By means of a magnetic compression and a Coherent Spontaneous Emission seeded FEL radiating at 100 to 200 mm, the system produces a beam fully bunched with a 200 A peak current at 2 mm.mrad rms emittance. The electron

A. Kievsky, M. Viviani, S. Rosati, D. Hueber

High precision benchmark calculations for phase-shifts and mixing parameters as well as observables in elastic neutron-deuteron scattering below the deuteron breakup threshold are presented using a realistic nucleon-nucleon potential. Two totally different methods, one using a variational principle in configuration space and the other solving the Faddeev equ

J. Helgesson, J. Randrup

Transport simulations including in-medium properties derived in a microscopic pi + nucleon-hole + delta-hole model in infinite nuclear matter are presented. In-medium pion dispersion relations, partial delta decay widths, pion absorption cross sections and delta cross sections are incorporated into the transport description by means of a local-density approx

M. Viviani, S. Rosati, A. Kievsky

The Kohn variational principle and the (correlated) Hyperspherical Harmonics technique are applied to study the n-3H and p-3He scattering at zero energy. Predictions for the singlet and triplet scattering lengths are obtained for non-relativistic nuclear Hamiltonians including two- and three-body potentials. The calculated n-3H total cross section agrees wel

F. Andreozzi, L. Coraggio, A. Covello, A. Gargano

The structure of the particle-hole nucleus 132Sb provides a direct source of information on the effective neutron-proton interaction in the 132Sn region. We have performed a shell-model calculation for this nucleus using a realistic effective interaction derived from the Bonn A nucleon-nucleon potential. The results are in very good agreement with the experi

Joachim Asch, Pierre Duclos, Pavel Exner

We consider a quantum particle in a periodic structure submitted to a constant external electromotive force. The periodic background is given by a smooth potential plus singular point interactions and has the property that the gaps between its bands are growing with the band index. We prove that the spectrum is pure point--i.e. trajectories of wave packets l

Oliver Rudolph, J. D. M. Wright

General history quantum theories are quantum theories without a globally defined notion of time. Decoherence functionals represent the states in the history approach and are defined as certain bivariate complex-valued functionals on the space of all histories. However, in practical situations -- for instance in the history formulation of standard quantum mec

Alexander Moroz, Adriaan Tip

The transition operator T for the scattering of a particle from N potentials V_j can be expanded into a series featuring the transition operators t_j associated with the individual potentials. For V_j(x) both absolutely and square integrable in x, we show, using an analytic continuation argument, that if T is on-shell, i.e. in < k|T(sigma^{2}+ i0)|k&#39; >,

Tevian Dray, Corinne A. Manogue

The eigenvalue problem for 3x3 octonionic Hermitian matrices contains some surprises, which we have reported elsewhere. In particular, the eigenvalues need not be real, there are 6 rather than 3 real eigenvalues, and the corresponding eigenvectors are not orthogonal in the usual sense. The nonassociativity of the octonions makes computations tricky, and all

Michael Tsatsomeros

The principal pivot transform (PPT) of a matrix A partitioned relative to an invertible leading principal submatrix is a matrix B such that A [x_1^T x_2^T]^T = [y_1^T y_2^T]^T if and only if B [y_1^T x_2^T]^T = [x_1^T y_2^T]^T, where all vectors are partitioned conformally to A. The purpose of this paper is to survey the properties and manifestations of PPTs

J. Avan, L. Frappat, M. Rossi, P. Sorba

The elliptic algebra A_{q,p}(sl(N)_{c}) at the critical level c=-N has an extended center containing trace-like operators t(z). Families of Poisson structures, defining q-deformations of the W_N algebra, are constructed. The operators t(z) also close an exchange algebra when (-p^{1/2})^{NM} = q^{-c-N} for M \in Z. It becomes Abelian when in addition p=q^{Nh}

Yanyan Li, Gilbert Weinstein

We prove a priori bounds for the trace of the second fundamental form of a $C^4$ isometric embedding into $R^{n+1}$ of a metric $g$ of non-negative sectional curvature on $S^n$, in terms of the scalar curvature, and the diameter of $g$. These estimates give a bound on the extrinsic geometry in terms of intrinsic quantities. They generalize estimates original

B. G. Konopelchenko

Generalized Weierstrass representations for generic surfaces conformally immersed into four-dimensional Euclidean and pseudo-Euclidean spaces of different signatures are presented. Integrable deformations of surfaces in these spaces generated by the Davey-Stewartson hierarchy of integrable equations are proposed. Willmore functional of a surface is invariant

David Eisenbud, Sorin Popescu

The Gale transform, an involution on sets of points in projective space, appears in a multitude of guises, in subjects as diverse as optimization, coding theory, theta-functions, and recently in our proof that certain general sets of points fail to satisfy the minimal free resolution conjecture. In this paper we reexamine the Gale transform in the light of m

Katrin Becker, Melanie Becker

The complete result for the effective potential for two graviton exchange at two loops in M(atrix) theory can be expressed in terms of a generalized hypergeometric function.

Won Tae Kim, Yong-Wan Kim, Young-Jai Park

The second class constraints algebra of the abelian Chern-Simons theory is rigorously studied in terms of the Hamiltonian embedding in order to obtain the first class constraint system. The symplectic structure of fields due to the second class constraints disappears in the resulting system. Then we obtain a new type of Chern-Simons action which has an infin

Mitsuo Abe, Noboru Nakanishi

In previous work, the conformal-gauge two-dimensional quantum gravity in the BRS formalism has been solved completely in terms of Wightman functions. In the present paper, this result is extended to the closed and open bosonic strings of finite length; the open-string case is nothing but the Kato-Ogawa string theory. The field-equation anomaly found previous

Qiong-gui Lin

The theory of a spinor field interacting with a pure Chern-Simons gauge field in 2+1 dimensions is quantized. Dynamical and nondynamical variables are separated in a gauge-independent way. After the nondynamical variables are dropped, this theory reduces to a pure spinor field theory with nonlocal interaction. Several two-body scattering processes are studie

Qiong-gui Lin

The theory of a complex scalar interacting with a pure Chern-Simons gauge field is quantized canonically. Dynamical and nondynamical variables are separated in a gauge-independent way. In the physical subspace of the full Hilbert space, this theory reduces to a pure scalar theory with nonlocal interaction. Several scattering processes are studied and the cro

Kingman Cheung

In this talk, I summarize a global analysis on electron-quark contact interactions using the updated NC DIS data at HERA, Drell-yan production at the Tevatron, total hadronic cross sections at LEP, atomic parity violation measurement, low energy $e$-nucleon scattering data, and the $ν$-nucleon scattering data. The global data do not show any evidence for con

A. A. Barrientos Bendezu, B. A. Kniehl

We study the production of a charged Higgs boson in association with a W boson at the CERN Large Hadron Collider in the context of the minimal supersymmetric extension of the standard model. This production mechanism is particularly promising if the charged Higgs boson is too heavy to be generated by top-quark decay. We compare the contributions due to b b-b

S. Prelovsek, S. Fajfer, P. Singer

The decays $D\to Vl^+l^-$ present in principle the opportunity to observe the short distance FCNC transition $c\to ul^+l^-$, which is sensitive to the physics beyond the Standard Model. We analyze the $D \to V l^+ l^- $ decays within the Standard Model, where in addition to the short distance dynamics also the long distance dynamics is present. The short dis

Giuseppe Battistoni, Paolo Lipari

Measurements of atmospheric neutrinos by Super-Kamiokande an other detectors have given evidence for the existence of neutrino oscillations with large mixing and $Δm^2$ in the range 10^{-3}-10^{-2} eV^2. In this work we discuss critically some of the possible experimental strategies to confirm this result and determine more accurately the neutrino oscillatio

M. A. Ivanov, V. E. Lyubovitskij, E. Z. Lipartia, A. G. Rusetsky

We review the existing theoretical approaches to the study of the observables of hadronic atoms. In the relativistic perturbative approach based on the Bethe-Salpeter equation and Chiral Perturbation Theory we derive the general expression for the pi+pi- atom lifetime. The lowest-order correction to the relativistic Deser-type formula for the atom width is p

Dominik J. Schwarz

The different phases of QCD at finite temperature and density lead to interesting effects in cosmology and astrophysics. In this work I review some aspects of the cosmological QCD transition and of astrophysics at high baryon density.

V. S. Fadin, R. Fiore

The generalization of the BFKL equation for the case of non-forward scattering is considered. The kernel of the generalized equation in the next-to-leading approximation is expressed in terms of the gluon Regge trajectory and the effective vertices for particle production in Reggeon collisions. The ``bootstrap&#39;&#39; equations for the gluon Reggeization a

Peter Kroll

The present status of the diquark model for exclusive reactions at moderately large momentum transfer is reviewed. That model is a variant of the Brodsky-Lepage approach in which diquarks are considered as quasi-elementary constituents of baryons. Recent applications of the diquark model, relevant to high energy physics with electromagnetic probes, are discu

Peter Kroll

The role of higher Fock-state contributions to exclusive charmonium decays will be discussed. It will be argued that the J/Psi (Psi&#39;) decays into baryon-antibaryon pairs are dominated by the valence Fock-state contributions. P-wave charmonium decays, on the other hand, receive strong contributions from the c cbar g Fock states since the valence Fock-stat

R. Fiore, F. Gliozzi, P. Provero

According to the Svetitsky-Yaffe conjecture, a three-dimensional gauge theory undergoing a continuous deconfinement transition is in the same universality class as a two-dimensional statistical model with order parameter taking values in the center of the gauge group. This allows us to use conformal field theory techniques to evaluate exactly various correla

The CHORUS Collaboration

The present results on the $\numtonut$ oscillation search by the CHORUS experiment at CERN are summarised. A fraction of the neutrino interactions collected in 1994-1995-1996 by the CHORUS experiment has been analysed, searching for $ν_τ$ charged current interactions followed by the $τ$ lepton decay into a negative hadron or into a muon. A sample of 68,156 e

A. D. Dolgov, I. D. Novikov

It has been found in several papers that, because of quantum corrections, light front can propagate with superluminal velocity in gravitational fields and even in flat space-time across two conducting plates. We show that, if this is the case, closed time-like trajectories would be possible and, in particular, in certain reference frames photons could return

Valerio Faraoni

The non-minimal coupling of a scalar field to the Ricci curvature in a curved spacetime is unavoidable according to several authors. The coupling constant is not a free parameter: the prescriptions for the value of the coupling constant in specific scalar field and gravity theories (in particular in general relativity) are studied. The results are applied to

K. Srinivasan, T. Padmanabhan

This paper presents a critical review of particle production in an uniform electric field and Schwarzchild-like spacetimes. Both problems can be reduced to solving an effective one-dimensional Schrodinger equation with a potential barrier. In the electric field case, the potential is that of an inverted oscillator -x^2 while in the case of Schwarchild-like s

B. Mashhoon, N. O. Santos

We discuss gravitomagnetism in connection with rotating cylindrical systems. In particular, the gravitomagnetic clock effect is investigated for the exterior vacuum field of an infinite rotating cylinder. The dependence of the clock effect on the Weyl parameters of the stationary Lewis metric is determined. We illustrate our results by means of the van Stock

F. Zhou, C. Biagini

We show that above the critical temperature of superconductor - metal phase transitions, both the longitudinal and Hall conductivity exhibit strong temperature dependent mesoscopic fluctuations, with amplitudes much larger than the mesoscopic fluctuations in noninteracting normal metals. Such an enhancement of the mesoscopic fluctuations arises from pairing

Eugenia Corvera Poire, Martine Ben Amar

We make a theoretical study of the behavior of a simple fluid displacing a shear thinning fluid confined in a Hele-Shaw cell. To study the Saffman-Taylor instability when the displaced fluid is non Newtonian we face the problem of having a field which is non laplacian. By means of an hodographic transformation we are able to solve the problem in the case of

G. Hackenbroich, B. Rosenow, H. A. Weidenmueller

As a realization of the quantum Zeno effect, we consider electron tunneling between two quantum dots with one of the dots coupled to a quantum point contact detector. The coupling leads to decoherence and to the suppression of tunneling. When the detector is driven with an ac voltage, a parametric resonance occurs which strongly counteracts decoherence. We p

Kun Yang, R. N. Bhatt

We report results of numerical studies of the integer quantum Hall effect in a tight binding model on a two-dimensional square lattice with non-interacting electrons, in the presence of a random potential as well as a uniform magnetic field applied perpendicular to the lattice. We consider field magnitudes such that the area per flux quantum is commensurate

H. J. Kaufmann, O. V. Dolgov, E. K. H. Salje

We have analysed optical reflectivity data for Ba_{1-x}K_xBiO_3 in the far-infrared region using Migdal-Eliashberg theory and found it inconsistent with standard electron-phonon coupling: Whereas the superconducting state data could be explained using moderate coupling, λ=0.7, the normal state properties indicate λ\le 0.2. We have found that such behaviour c

H. T. Nieh, Ping Sheng, Xiao-Bing Wang

A Ward-Takahashi identity, as a consequence of gauge invariance and in a form that relates self-energy to the two-particle Bethe-Salpeter scattering kernel, was first derived by Vollhardt and Wölfle for a system of independent particles moving in a random medium. This is generalized to a class of interacting electronic systems in materials with or without ra

Prabhakar Pradhan

Several aspects of interplay between Anderson localization and coherent amplification/absorption, and aspect of mirrorless laser for a laser-active (amplifying) disordered dielectric medium have been addressed. We have calculated the statistics of the reflection coefficient and the associated phase for a light wave reflected from a coherently amplifying/abso

Eugene Pivovarov

In the model considered, the nonlocal interaction of the fermions in different sublattices of a bipartite lattice is introduced. It can also be regarded as local interaction of fermions with opposite ``hypercharge&#39;&#39;. The corresponding term in the Hamiltonian is SU(4)-invariant and appears to be the most tractable version of the SO(5)-invariant model

P. Giuliani, V. Carbone

We investigate the time evolution of two different (GOY-like) shell models which have been recently proposed to describe the gross features of MHD turbulence. We see that, even if they are formally of the same type sharing with MHD equations quadratic couplings and similar conserved quantities, fundamental differences exist which are related to the ideal inv

Lin Wan, Ruth A. Daly, Erick J. Guerra

Multi-frequency radio observations of the radio bridge of powerful classical double radio sources can be used to determine: the beam power of the jets emanating from the AGN; the total time the source will actively produce jets that power large-scale radio emission; the thermal pressure of the medium in the vicinity of the radio source; and the total mass, i

Erick J. Guerra, Ruth A. Daly, Lin Wan

A sample of 20 powerful extended radio galaxies with redshifts between zero and two were used to determine constraints on global cosmological parameters. Data for six radio sources were obtained from the VLA archive, analyzed, and combined with the sample of 14 radio galaxies used previously by Guerra & Daly to determine cosmological parameters. The new resu

Laura E. Kay, Edward C. Moran

We have detected a broad H alpha emission line in the polarized flux spectrum of the Seyfert 2 galaxy NGC 788, indicating that it contains an obscured Seyfert 1 nucleus. While such features have been observed in ~15 other Seyfert 2s, this example is unusual because it has a higher fraction of galaxy starlight in its spectrum, a lower average measured polariz

Andrew Gould

The Space Infrared Telescope Facility (SIRTF) will drift away from the Earth at about 0.1 AU/yr. Microlensing events will therefore have different characteristics as seen from the satellite and the Earth. From the difference, it is possible in principle to measure v-tilde, the transverse velocity of the lens projected onto the observer plane. Since v-tilde h

J. Michael Shull, Steven V. Penton, John T. Stocke, Mark L. Giroux

We report observations from the Hubble Space Telescope (HST) and the VLA on the galactic environment, metallicity, and D/H in strong low-redshift Lya absorption systems toward the bright BL Lac object PKS 2155-304. GHRS/G160M spectra at 20 km/s resolution show 14 Lya absorbers, 6 clustered at cz = 16,100-18,500 km/s. ORFEUS claimed LyC absorption at z = 0.05

T. Di Matteo, A. C. Fabian, M. J. Rees, C. L. Carilli

The growing evidence for supermassive black holes in the centres of nearby galaxies has brought into sharper focus the question of why elliptical galaxies, rich in hot gas, do not possess quasar-like luminosities. Recent studies suggest that advection-dominated accretion flows (ADAFs), with associated low radiative efficiency, might provide an explanation fo

Rene Oudmaijer, Daniel Proga, Janet Drew, Dolf de Winter

New high resolution spectroscopic and medium resolution spectropolarimetric data, complemented with optical broad and narrow band imaging, of the B[e] star HD 87643 are presented. The spectrum of HD 87643 exhibits the hybrid characteristics well known to be representative of the group of B[e] stars; a fast wind with an expansion velocity in excess of 1000 km

Pieter G. van Dokkum, Marijn Franx, Daniel D. Kelson, Garth D. Illingworth

We present deep spectroscopy with the Keck telescope of eight galaxies in the luminous X-ray cluster MS1054-03 at z=0.83. The data are combined with imaging observations from the Hubble Space Telescope (HST). The spectroscopic data are used to measure the internal kinematics of the galaxies, and the HST data to measure their structural parameters. Six galaxi

C. N. Tadhunter, R. Morganti, A. Robinson, R. Dickson

The nature of the optical--radio correlations for powerful radio galaxies is investigated using spectroscopic observations of a complete sample of southern 2Jy radio sources. In line with previous work, we find that significant correlations exist between the luminosities of the [OIII]5007, [OII]3727 and Hbeta emission lines and the radio luminosity. However,

Robert E. Rutledge, Walter H. G. Lewin, Michiel van der Klis, Jan van Paradijs

By comparing positions on a spectral color-color diagram from 10 black hole candidates (BHCs) observed with Ginga (1354-64, 1826-24, 1630-47, LMC X-1, LMC X-3, GS 2000+25, GS 2023+33, GS 1124-68, Cyg X-1, and GX 339-4) with the observed broad-band noise (0.001-64 Hz; BBN) and quasi-periodic oscillation (QPO) variability, we find that the so-called ``Very Hig

Nestor Sanchez, Antonio Parravano

The structure of cloud complexes appears to be well described by a &#34;tree structure&#34; representation when the image is partitioned into &#34;clouds&#34;. In this representation, the parent-child relationships are assigned according to containment. Based on this picture, a hierarchical model for the evolution of Cloud Complexes, including star formation

Makoto Taiji, Takashi Ikegami

A new approach for the study of social games and communications is proposed. Games are simulated between cognitive players who build the opponent&#39;s internal model and decide their next strategy from predictions based on the model. In this paper, internal models are constructed by the recurrent neural network (RNN), and the iterated prisoner&#39;s dilemma

Kok-Kiong Loh, Joseph Rudnick

Two-dimensional domains containing an XY-like order parameter exhibit non-trivial internal structure and take on shapes controlled by the configuration that the order parameter adopts. The textures exhibited by the order parameter in such domains are controlled by the interplay between bulk and surface contributions to the energy. We report calculations of t

Prem P Singh

This paper reports on the discovery of the B_c meson.

M. J. Duff, H. Lu, C. N. Pope

We consider type IIB configurations carrying both NS-NS and R-R electric and magnetic 3-form charges, and whose near horizon geometry contains AdS_3 x S^3. Noting that S^3 is a U(1) bundle over CP^1 \sim S^2, we construct the dual type IIA configurations by a Hopf T-duality along the U(1) fibre. In the case where there are only R-R charges, the S^3 is untwis

A. Gonzalez-Arroyo, C. Pena

By studying zero modes of the Dirac equation on the lattice, we explicitly construct the Nahm transform of some topologically non-trivial gauge field configurations.

K. C. Hwang

This paper has been withdrawn due to crucial errors.

Jamal Jalilian-Marian, Alex Kovner, Andrei Leonidov, Heribert Weigert

We analyze the general nonlinear evolution equations for multi gluon correlators derived in hep-ph/9709432 by restricting ourselves to a double logarithmic region. In this region our evolution equation becomes local in transverse momentum space and amenable to simple analysis. It provides a complete nonlinear generalization of the GLR equation. We find that

B. L. Cerchiai, R. Hinterding, J. Madore, J. Wess

The geometry of the $q$-deformed line is studied. A real differential calculus is introduced and the associated algebra of forms represented on a Hilbert space. It is found that there is a natural metric with an associated linear connection which is of zero curvature. The metric, which is formally defined in terms of differential forms, is in this simple cas

Stefan Davids

We explore the geometry and asymptotics of extended Racah coeffecients. The extension is shown to have a simple relationship to the Racah coefficients for the positive discrete unitary representation series of SU(1,1) which is explicitly defined. Moreover, it is found that this extension may be geometrically identified with two types of Lorentzian tetrahedra

Shinsuke Kawai, Jiro Soda

Non-singular Bianchi type I solutions are found from the effective action with a superstring-motivated Gauss-Bonnet term. These anisotropic non-singular solutions evolve from the asymptotic Minkowski region, subsequently super-inflate, and then smoothly continue either to Kasner-type (expanding in two directions and shrinking in one direction) or to Friedman

Andreas Jaster

We investigate the positional order of the two-dimensional hard disk model with short-time dynamics and equilibrium simulations. The melting density and the critical exponents z and eta are determined. Our results rule out a phase transition as predicted by the Kosterlitz-Thouless-Halperin-Nelson-Young theory as well as a first-order transition.