May 1998 arXiv papers — page 3

Daniel Schaerer, Duilia de Mello, Claus Leitherer, Jennifer Heldmann

We present a study of the gaseous and stellar emission in I Zw18, the most metal-poor star-forming galaxy known. Archival HST WFPC2 and FOS data have been used to analyze the spatial distribution of [OIII], Halpha, and HeII 4686. The latter is used to identify Wolf-Rayet stars found by ground-based spectroscopy and to locate nebular HeII emission. Most of th

S. J. Watkins, A. S. Bhattal, H. M. J. Boffin, N. Francis

It is expected that an average protostar will undergo at least one impulsive interaction with a neighbouring protostar whilst a large fraction of its mass is still in a massive, extended disc. If protostars are formed individually within a cluster before falling together and interacting, there should be no preferred orientation for such interactions. As star

S. J. Watkins, A. S. Bhattal, H. M. J. Boffin, N. Francis

It is expected that an average protostar will undergo at least one impulsive interaction with a neighbouring protostar whilst a large fraction of its mass is still in a massive, extended disc. Such interactions must have a significant impact upon the evolution of the protostars and their discs. We have carried out a series of simulations of coplanar encounte

H. M. J. Boffin, S. J. Watkins, A. S. Bhattal, N. Francis

It appears that most stars are born in clusters, and that at birth most stars have circumstellar discs which are comparable in size to the separations between the stars. Interactions between neighbouring stars and discs are therefore likely to play a key role in determining disc lifetimes, stellar masses, and the separations and eccentricities of binary orbi

F. Verbunt, G. Hasinger

We analyze ROSAT HRI observations obtained from 1992 to 1996 of the globular cluster 47 Tuc. Identifications of two X-ray sources with HD 2072 and with a galaxy, respectively, are used to obtain accurate (<2&#39;&#39;) positions of the X-ray sources in the cluster. We find possible optical counterparts, including the blue objects V1 and V2, for three X-ray s

T. Di Matteo

A magnetically-structured accretion disk corona, generated by buoyancy instability in the disk, can account for observations of flare--like events in Active Galactic Nuclei. We examine how Petschek magnetic reconnection, associated with MHD turbulence, can result in a violent release of energy and heat the magnetically closed regions of the corona up to cano

T. Di Matteo, A. Celotti, A. C. Fabian

We present a model for the different X-ray spectral states displayed by Galactic Black Hole Candidates (GBHC). We discuss the physical and spectral implications for a magnetically structured corona in which magnetic flares result from reconnection of flux tubes rising from the accretion disk by the magnetic buoyancy instability. Using observations of one of

S. J. Aarseth, D. C. Heggie

We consider the use of N-body simulations for studying the evolution of rich star clusters (i.e. globular clusters). The dynamical processes included in this study are restricted to gravitational (point-mass) interactions, the steady tidal field of a galaxy, and instantaneous mass loss resulting from stellar evolution. With evolution driven by these mechanis

Eiji Shima, Takuya Matsuda, Ulrich Anzer, Gerhard Borner

A new numerical algorithm for calculating isothermal wind accretion flows has been developed and is applied here to the analysis of the hydrodynamics of two-dimensional plane symmetric accretion flows in wind-fed sources. Polar coordinates are used to ensure fine resolution near the object. It is found that a thin accretion column is formed which shows wave-

Duilia de Mello, Daniel Schaerer, Jennifer Heldmann, Claus Leitherer

I Zw 18 is the most metal poor star-forming galaxy known and is an ideal laboratory to probe stellar evolution theory at low metallicities. Using archival HST WFPC2 imaging and FOS spectroscopy we were able to improve previous studies. We constructed a continuum free HeII map, which was used to identify Wolf-Rayet (WR) stars recently found by ground-based sp

Ben O&#39;Shaughnessy, Dimitrios Vavylonis

We study kinetics of single species reactions (&#34;A+A -> 0&#34;) for general local reactivity Q and dynamical exponent z (rms displacement x_t ~ t^{1/z}.) For small molecules z=2, whilst z=4,8 for certain polymer systems. For dimensions d above the critical value d_c=z, kinetics are always mean field (MF). Below d_c, the density n_t initially follows MF de

Sanjaye Ramgoolam, Daniel Waldram

The non-commutative algebra which defines the theory of zero-branes on $T^4/Z_2$ allows a unified description of moduli spaces associated with zero-branes, two-branes and four-branes on the orbifold space. Bundles on a dual space $\hat T^4/Z_2$ play an important role in this description. We discuss these moduli spaces in the context of dualities of K3 compac

Dan Pirjol, Nikolai Uraltsev

We introduce and study the properties of the &#34;color-straight&#34; four-quark operators containing heavy and light quark fields. They are of the form (\bar bΓ_b b)(\bar qΓ_q q) where both brackets are color singlets. Their expectation values include the bulk of the nonfactorizable contributions to the nonleptonic decay widths of heavy hadrons. The expecta

John J. Portman, Shoji Takada, Peter G. Wolynes

We present a microscopic variational theory for the free energy surface of a fast folding protein that allows folding kinetics to be resolved to the residue level using Debye-Waller factors as local order parameters. We apply the method to lambda-repressor and compare with site directed mutagenesis experiments. The formation of native structure and the free

W. Lee, D. Weingarten

We evaluate the continuum limit of the valence (quenched) approximation to the mass of the lightest scalar quarkonium state, for a range of different quark masses, and to the mixing energy between these states and the lightest scalar glueball. Our results support the interpretation of $f_0(1710)$ as composed mainly of the lightest scalar glueball.

A. Bezryadin, R. M. Westervelt, M. Tinkham

Charge transport in electrorheological fluids is studied experimentally under strongly nonequlibrium conditions. By injecting an electrical current into a suspension of conducting nanoparticles we are able to initiate a process of self-organization which leads, in certain cases, to formation of a stable pattern which consists of continuous conducting chains

Daniel J. H. Chung, Edward W. Kolb, Antonio Riotto

We discuss several cosmological production mechanisms for nonthermal supermassive dark matter and argue that dark matter may be elementary particles of mass much greater than the weak scale. Searches for dark matter should not be limited to weakly interacting particles with mass of the order of the weak scale, but should extend into the supermassive range as

Antonio Campos, B. L. Hu

We introduce functional methods to study the non-equilibrium dynamics of a quantum massless scalar field at finite temperature in a gravitational field. We calculate the Close Time Path (CTP) effective action and, using its formal equivalence with the influence functional, derive the noise and dissipation kernels of the quantum open system in terms of quanti

D. A. Garanin, Benjamin Canals

Thermodynamic quantities and correlation functions (CFs) of the classical antiferromagnet on the kagomé lattice are studied for the exactly solvable infinite-component spin-vector model, D \to \infty. In this limit, the critical coupling of fluctuations dies out and the critical behavior simplifies, but the effect of would be Goldstone modes preventing order

A. A. Bytsenko, A. E. Goncalves, W. da Cruz

The invariant integration method for Chern-Simons theory for gauge group SU(2) and manifold Γ\H^3 is verified in the semiclassical approximation. The semiclassical limit for the partition function associated with a connected sum of hyperbolic 3-manifolds is presented. We discuss briefly L^2 - analytical and topological torsions of a manifold with boundary.

I. Jack, D. R. T. Jones, A. Pickering

We explore the relationship between the DRED and NSVZ schemes. Using certain exact results for the soft scalar mass $β$-function, we derive the transformation of $α^{\DRED}$ to $α^{\NSVZ}$ through terms of order $α^4$. We thus incidentally determine $β_α^{\DRED}$ through four loops, and we compare our result to a previous Padé Approximant prediction.

Muktish Acharyya, Dietrich Stauffer

The fractions of samples spanning a lattice at its percolation threshold are found by computer simulation of random site-percolation in two- and three-dimensional hypercubic lattices using different boundary conditions. As a byproduct we find $p_c = 0.311605(5)$ in the cubic lattice.

M. Di Pierro, C. T. Sachrajda

We compute the matrix elements of the operators which contribute to spectator effects in inclusive decays of $B$-mesons. The results agree well with estimates based on the vacuum saturation (factorization) hypothesis. For the ratio of lifetimes of charged and neutral mesons we find $τ(B^-)/τ(B_d)=1.03\pm 0.02\pm 0.03$, where the first error represents the un

H. Babujian, A. Fring, M. Karowski, A. Zapletal

We provide detailed arguments on how to derive properties of generalized form factors, originally proposed by one of the authors (M.K.) and Weisz twenty years ago, solely based on the assumption of &#34;minimal analyticity&#34; and the validity of the LSZ reduction formalism. These properties constitute consistency equations which allow the explicit evaluati

L. Stodolsky

The description of a measuring process, such as that which occurs when a quantum point contact (QPC) detector is influenced by a nearby external electron which can take up two possible positions, provides a interesting application of the method of quantum damping. We find a number of new effects, due to the complete treatment of phases afforded by the formal

Emil Lundh, C. J. Pethick, H. Smith

The properties of vortex states in a Bose-Einstein condensed cloud of atoms are considered at zero temperature. Using both analytical and numerical methods we solve the time-dependent Gross-Pitaevskii equation for the case when a cloud of atoms containing a vortex is released from a trap. In two dimensions we find the simple result that the time dependence o

Taejin Lee

The dual relationship between the supergravity in the anti-de Sitter(AdS) space and the superconformal field theory is discussed in the simplest form. We show that a topological Ward identity holds in the three dimensional Chern-Simons gravity. In this simple case the proposed dual relationship can be understood as the topological Ward identity. Extensions t

Anthony Challinor, Anthony Lasenby

We consider the Comptonization of an isotropic radiation field by a thermal distribution of electrons with non-vanishing bulk velocity. We include all relativistic effects, including induced scattering and electron recoil, in the derivation of a kinetic equation which is correct to O(theta^2, beta theta^2, beta^2 theta), where beta is the bulk velocity (in u

Seong-Youl Choi, Manuel Drees

We point out that oscillation between the two scalar tau (stau) mass eigenstates can give rise to CP-violation if some parameters appearing in the stau or chargino/neutralino mass matrices are complex. If stau^+ and stau^- decay into different charginos or neutralinos, rate asymmetries as large as 20% are possible. If both staus decay directly into tau + LSP

Paolo Aschieri

We review known real forms of the quantum orthogonal groups SO_q(N). New *-conjugations are then introduced and we contruct all real forms of quantum orthogonal groups. We thus give an RTT formulation of the *-conjugations on SO_q(N) that is complementary to the U_q(g) *-structure classification of Twietmeyer \cite{Twietmeyer}. In particular we easily find a

Charles H. Lineweaver

I use the most recent cosmic microwave background (CMB) anisotropy measurements to constrain the leading cold dark matter models in the Omega_m - Omega_lambda plane. A narrow triangular region is preferred. This triangle is elongated in such a way that its intersection with even conservative versions of recent supernovae, cluster mass-to-light ratios and dou

Gilles Brassard, Peter Hoyer, Alain Tapp

We study some extensions of Grover&#39;s quantum searching algorithm. First, we generalize the Grover iteration in the light of a concept called amplitude amplification. Then, we show that the quadratic speedup obtained by the quantum searching algorithm over classical brute force can still be obtained for a large family of search problems for which good cla

Leif Thomas, Werner Pesch, Guenter Ahlers

We report experimental results for convection near onset in a thin layer of a homeotropically aligned nematic liquid crystal heated from below as a function of the temperature difference $ΔT$ and the applied vertical magnetic field $H$ and compare them with theoretical calculations. The experiments cover the field range $8 \alt h \equiv H/ H_{F} \alt 80$ ($H

Marcus Linek, Guenter Ahlers

We report experimental results for a boundary-mediated wavenumber-adjustment mechanism and for a boundary-limited wavenumber-band of Taylor-vortex flow (TVF). The system consists of fluid contained between two concentric cylinders with the inner one rotating at an angular frequency $Ω$. As observed previously, the Eckhaus instability (a bulk instability) is

M. V. Stoitsov, W. Nazarewicz, S. Pittel

A complete discrete set of spherical single-particle wave functions for studies of weakly-bound many-body systems is proposed. The new basis is obtained by means of a local-scale point transformation of the spherical harmonic oscillator wave functions. Unlike the harmonic oscillator states, the new wave functions decay exponentially at large distances. Using

S. Ayik, O. Yilmaz, A. Gokalp, P. Schuck

A detailed derivation of the collisional widths of collective vibrations is presented in both quantal and semi-classical frameworks by considering the linearized limits of the extended TDHF and the BUU model with a non-Markovian binary collision term. Damping widths of giant dipole and giant quadrupole excitations are calculated by employing an effective Sky

V. R. Manfredi, J. M. G. Gomez, L. Salasnich

We perform large shell model calculations for Calcium isotopes in the full fp shell by using the realistic Kuo-Brown interaction. The Calcium isotopes are especially interesting because the nearest-neighbour spacing distribution P(s) of low-lying energy levels shows significant deviations from the predictions of the Gaussian Orthogonal Ensemble of random--ma

L. Mangiarotti, G. Sardanashvily

It is shown that any dynamic equation on a configuration bundle $Q\to R$ of non-relativistic time-dependent mechanics is associated with connections on the affine jet bundle $J^1Q\to Q$ and on the tangent bundle $TQ\to Q$. As a consequence, any non-relativistic dynamic equation can be seen as a geodesic equation with respect to a (non-linear) connection on t

Takashi Hara, Gordon Slade

We announce our recent proof that, for independent bond percolation in high dimensions, the scaling limits of the incipient infinite cluster&#39;s two-point and three-point functions are those of integrated super-Brownian excursion (ISE). The proof uses an extension of the lace expansion for percolation.

Carrie Eschenbrenner, Michael Falk

The $OS$ algebra $A$ of a matroid $M$ is a graded algebra related to the Whitney homology of the lattice of flats of $M$. In case $M$ is the underlying matroid of a hyperplane arrangement \A in $\C^r$, $A$ is isomorphic to the cohomology algebra of the complement $\C^r\setminus \bigcup \A.$ Few examples are known of pairs of arrangements with non-isomorphic

Doron Zeilberger

It is way too soon to teach our computers how to become full-fledged humans. It is even premature to teach them how to become mathematicians, it is even unwise, at present, to teach them how to become combinatorialists. But the time is ripe to teach them how to become experts in a suitably defined and narrowly focused subarea of combinatorics. In this articl

Michael Yampolsky

We demonstrate the existence of a global attractor A with a Cantor set structure for the renormalization of critical circle mappings. The set A is invariant under a generalized renormalization transformation, whose action on A is conjugate to the two-sided shift.

Vladimir G. Troitsky

Let T be the quasinilpotent operator on ell_1 without an invariant subspace constructed by C. J. Read in [R3]. We prove that the modulus of this operator has an invariant subspace (and even an eigenvector). This answers a question posed by Y. Abramovich, C. Aliprantis and O. Burkinshaw in [AAB1,AAB3]

Wladyslaw Marcinek

The concept of quantum commutativity with respect to an action or coaction of a given Hopf algebra is used for the algebraic description of a system of particles and their interaction with certain quantum field. Graded commutativity and particles in singular magnetic field are considered as a particular example of the general formalism. The corresponding sta

Everett W. Howe

We show how for every integer n one can explicitly construct n distinct plane quartics and one hyperelliptic curve over the complex numbers all of whose Jacobians are isomorphic to one another as abelian varieties without polarization. When we say that the curves can be constructed ``explicitly&#39;&#39;, we mean that the coefficients of the defining equatio

M. Kreuzer, H. Skarke

We present the last missing details of our algorithm for the classification of reflexive polyhedra in arbitrary dimensions. We also present the results of an application of this algorithm to the case of three dimensional reflexive polyhedra. We get 4319 such polyhedra that give rise to K3 surfaces embedded in toric varieties. 16 of these contain all others a

P. Berglund, A. Klemm, P. Mayr, S. Theisen

We describe type IIB compactifications with varying coupling constant in d=6,7,8,9 dimensions, where part of the ten-dimensional SL(2,Z) symmetry is broken by a background with Gamma_0(n) or Gamma(n) monodromy for n=2,3,4. This extends the known class of F-theory vacua to theories which are dual to heterotic compactifications with reduced rank. On compactify

F. Antonuccio, S. Pinsky

We consider SU(N) QCD_{1+1} coupled to massless adjoint Majorana fermions, where N is finite but arbitrary. We examine the spectrum for various values of N, paying particular attention to the formation of multi-particle states, which were recently identified by Gross, Hashimoto and Klebanov in the N -> infinity limit of the theory. It is believed that in the

J. J. McKenzie-Smith, D. J. Toms

We discuss the role of the multiplicative anomaly for a complex scalar field at finite temperature and density. It is argued that physical considerations must be applied to determine which of the many possible expressions for the effective action obtained by the functional integral method is correct. This is done by first studying the non-relativistic field

A. Keurentjes, A. Rosly, A. V. Smilga

An explicit proof of the existence of nontrivial vacua in the pure supersymmetric Yang-Mills theories with higher orthogonal SO(N), N>=7 or the G_2 gauge group defined on a 3-torus with periodic boundary conditions is given. Extra vacuum states are separated by an energy barrier from the perturbative vacuum A_i=0 and its gauge copies.

Paul H. Frampton, Masayasu Harada

In a model where CP is spontaneously broken, the aspon model, it is shown by extending previous arguments about B decay and the value of $Re(ε^{&#39;}/ε)$ in the kaon system, that the neutron electric dipole moment $D_n$ is bounded from below by $D_n \geq 10^{-29}$e.-cm.

Salam Tawfiq, Patrick J. O&#39;Donnell, J. G. Koerner

The $SU(2N_{f}) X O(3)$ constituent quark model symmetry of the light diquark system are used to analyze single pion transitions of S-wave to S-wave and P-wave to S-wave heavy baryons. We show that the Heavy Quark Symmetry (HQS) coupling factors are given in terms of the three independent couplings $g_{Σ_Q Λ_Q π}, f_{Λ_{Q1} Σ_Q π}$ and $f_{Λ^{*}_{Q1} Σ_Q π}$

Paul Langacker

Many extensions of the standard model, especially grand unified theories and superstring models, predict the existence of additional Z&#39; bosons and associated exotic chiral supermultiplets. It has recently been argued that for classes of string motivated models with supergravity mediated supersymmetry breaking there are two scenarios for the additional Z&

B. R. Webber

A simple parametrization of the QCD running coupling at low scales is introduced and used to illustrate various schemes for the estimation of non-perturbative power corrections. The `infrared matching' scheme proposed earlier gives satisfactory results when combined with next-to-leading (or higher) order perturbative predictions. Estimates based on renormalo

J. Hashida, T. Muta, K. Ohkura

The supersymmetric version of the Nambu-Jona-Lasinio model is investigated in connection with the chiral symmetry breaking induced by a soft SUSY breaking term. It is found that the broken chiral symmetry due to the soft breaking term is restored at suitably high temperature and the symmetry restoration occurs as first-order phase transitions. The critical t

E. W. N. Glover

I review the status of fixed order jet Monte Carlos and briefly discuss the prospects for next-to-next-to-leading order calculations. I present a general purpose next-to-leading order Monte Carlo program for four jet event shape observables in electron-positron annihilation and present some estimates of the light jet mass and narrow jet broadening distributi

E. Sassaroli

The Lagrangian that is normally associated with Dirac neutrinos is analyzed in a complete and simple way through field theory. It is found that the elements of the neutrino mass matrix are field strength renormalization constants and that the flavor fields can be directly applied to the one-particle energy states through these rescaling factors. Moreover thi

E. Sassaroli, Y. N. Srivastava, J. Swain, A. Widom

The dynamical Casimir effect for the ideal case of two perfectly conducting non-charged parallel plates, is discussed using the zero-point energy summation method to the first order in perturbation theory. We show that it is possible to create photon radiation when the two plates are modulated rapidly in time. Moreover we point out that the static Casimir en

R. Sekhar Chivukula, Howard Georgi

Topcolor and topcolor-assisted technicolor provide examples of dynamical electroweak symmetry breaking which include top-condensation, thereby naturally incorporating a heavy top quark. In this note we discuss the roles of the Nambu-Jona-Lasinio (NJL) and large-N approximations often used in phenomenological analyses of these models. We show that, in order t

F. Ferrer, J. A. Grifols

Using dispersion theoretic techniques, we consider coherent long range forces arising from double pseudoscalar exchange among fermions. We find that Yukawa type coupling leads to $1/r^3$ spin independent attractive potentials whereas derivative coupling renders $1/r^5$ spin independent repulsive potentials.

K. Fialkowski, R. Wit

The influence of the Bose - Einstein interference effect on the joint WW hadronic decay is discussed. It is shown that the weight method incorporating this effect into Monte Carlo generators produces in a natural way an excess of average multiplicity as compared to the independent decay of two W bosons. The quantitative results for the average multiplicity a

C. Pajares, D. Sousa, R. A. Vázquez

We discuss collective effects like percolation, quark gluon plasma, or string fusion and their effect on the longitudinal development of high energy showers in air. It is shown that iron-air showers could develop more slowly than expected and produce the observed change in the slope of $X_max$ at the highest energies.

Shigetaka Moriyama

An experimental method is introduced to search for almost monochromatic solar axions. In this method, we can search for solar axions by exploiting the axion-quark coupling, not relying on the axion-photon coupling at all. A recent experimental result of Kr\v cmar is presented.

N. H. Brook

A review of HERA measurements of structure functions, fragmentation functions and forward jet production is presented.

Remo Garattini

A one-loop correction of the quasilocal energy in the Schwarzschild background, with flat space as a reference metric, is performed by means of a variational procedure in the Hamiltonian framework. We examine the graviton sector in momentum space, in the lowest possible state. An application to the black hole pair creation via the Casimir energy is presented

Sukratu Barve, T. P. Singh, Cenalo Vaz, Louis Witten

We calculate the quantum stress tensor for a massless scalar field in the 2-d self-similar spherical dust collapse model which admits a naked singularity. We find that the outgoing radiation flux diverges on the Cauchy horizon. This may have two consequences. The resultant back reaction may prevent the naked singularity from forming, thus preserving cosmic c

J. A. Valiente Kroon

The existence of conserved quantities with a structure similar to the Newman-Penrose quantities in a polyhomogeneous space-time is addressed. The most general form for the initial data formally consistent with the polyhomogeneous setting is found. The subsequent study is done for those polyhomogeneous space-times where the leading term of the shear contains

B. Mashhoon, J. C. McClune, H. Quevedo

We study the pseudo-local gravitoelectromagnetic stress-energy tensor for an arbitrary gravitational field within the framework of general relativity. It is shown that there exists a current of gravitational energy around a rotating mass. This gravitational analog of the Poynting flux is evaluated for certain classes of observers in the Kerr field.

Branko P. Stojkovic, Z. G. Yu, A. R. Bishop, A. H. Castro Neto

We study the competition between long-range and short-range interactions among holes within the spin density wave picture of layered transition metal oxides. We focus on the problem of charge ordering and the charge phase diagram. We show that the main interactions are the long-range Coulomb interaction and a dipolar short-range interaction generated by the

Paul J. Petersan, Steven M. Anlage

Precise microwave measurements of sample conductivity, dielectric, and magnetic properties are routinely performed with cavity perturbation measurements. These methods require the accurate determination of quality factor and resonant frequency of microwave resonators. Seven different methods to determine the resonant frequency and quality factor from complex

G. Czycholl

Without a hybridization between the localized f- and the conduction (c-) electron states the spinless Falicov-Kimball model (FKM) is exactly solvable in the limit of high spatial dimension, as first shown by Brandt and Mielsch. Here I show that at least for sufficiently small c-f-interaction this exact inhomogeneous ground state is also obtained in Hartree-F

Dirk Helbing

This paper presents and derives the interrelations between survival analysis and master equation. Survival analysis deals with modeling the transitions between succeeding states of a system in terms of hazard rates. Questions related with this are the timing and sequencing of the states of a time series. The frequency and characteristics of time series can b

Gregory Brown, Per Arne Rikvold, Martin Grant

The universal form for the average scattering intensity from systems undergoing order-disorder transitions is found by numerical integration of the Langevin dynamics. The result is nearly identical for simulations involving two different forms of the local contribution to the free energy, supporting the idea that the Model A dynamical universality class incl

E. C. Marino

A continuous field theory which describes the process of doping in high-T$_c$ superconductors of the YBCO-type is presented. It is shown that the introduction of dopants produces the creation of skyrmion topological excitations on the antiferromagnetic background. The energy of these excitations is evaluated. Destruction of the Néel ground state occurs for a

N. V. Brilliantov

Accurate &#34;first-principle&#34; expressions for the excess free energy $F_{ex}$ and internal energy $U_{ex}$ of the classical one-component plasma (OCP) are obtained. We use the Hubbard-Schofield transformation that maps the OCP Hamiltonian onto the Ising-like Hamiltonian, with coefficients expressed in terms of equilibrium correlation functions of a refe

D. R. Leadley, R. J. Nicholas, D. K. Maude, A. N. Utjuzh

Energy gaps have been measured for the ferromagnetic quantum Hall effect states at v=1 and 3 in GaAs/GaAlAs heterojunctions as a function of Zeeman energy, which is reduced to zero by applying hydrostatic pressures of up to 20kbar. At large Zeeman energy the gaps are consistent with spin wave excitations. For a low density sample the gap at v=1 decreases wit

S. Belin, K. Behnia, A. Deluzet

The first study of thermal conductivity, $κ$, in a quasi-two-dimensional organic superconductor of the $κ$-(BEDT-TTF)$_2$X family reveals features analogous to those already observed in the cuprates. The onset of superconductivity is associated with a sudden increase in $κ$ which can be suppressed by the application of a moderate magnetic field. At low tempe

Andrea De Martino, Andrea Giansanti

Lack of self-averaging originates in many disordered models from a fragmentation of the phase space where the sizes of the fragments remain sample-dependent in the thermodynamic limit. On the basis of new results in percolation theory, we give here an argument in favour of the conjecture that critical two dimensional percolation on the square lattice lacks o

Erika Hult, Henrik Rydberg, Bengt I. Lundqvist, David C. Langreth

In a framework for long-range density-functional theory we present a unified full-field treatment of the asymptotic van der Waals interaction for atoms, molecules, surfaces, and other objects. The only input needed consists of the electron densities of the interacting fragments and the static polarizability or the static image plane, which can be easily eval

B. Irmer, M. Kehrle, H. Lorenz, J. P. Kotthaus

We study local oxidation induced by dynamic atomic force microscopy (AFM), commonly called TappingMode AFM. This minimizes the field induced forces, which cause the tip to blunt, and enables us to use very fine tips. We are able to fabricate Ti/TiOx line grids with 18 nm period and well defined isolating barriers as small as 15 nm. These junctions show a non

B. Irmer, R. H. Blick, F. Simmel, W. Goedel

We define superconducting constrictions by ploughing a deposited Aluminum film with a scanning probe microscope. The microscope tip is modified by electron beam deposition to form a nano-plough of diamond-like hardness, what allows the definition of highly transparent Josephson junctions. Additionally a dc-SQUID is fabricated to verify appropriate functionin

Ranjan Kumar Ghosh, P. K. Mohanty, Sumathi Rao

Motivated by the problem of N coupled Hubbard chains, we investigate a generalisation of the Schulz-Shastry model containing two species of one-dimensional fermions interacting via a gauge field that depends on the positions of all the particles of the other species. The exact many body ground state of the model can be easily obtained through a unitary trans

Sergei Sergeenkov

The response of an intrinsic Josephson contact to externally applied stress is considered within the framework of the dislocation-induced atomic scale Josephson effect. The predicted quasi-periodic (Fraunhofer-like)stress-strain and stress-current patterns should manifest themselves for experimentally accessible values of applied stresses in intrinsically de

S. Nishimoto, Y. Ohta

An exact-diagonalization technique on small clusters is used to study the ground state of the dimerized t-J model at quarter filling. The equal-time charge and spin correlations, charge and spin gaps, and binding energy are calculated for the two-dimensional lattice with a spatial dimerization pattern corresponding to organic conductors $κ-(BEDT-TTF)_2X$. We

Deniz Yuret

This work has been motivated by two long term goals: to understand how humans learn language and to build programs that can understand language. Using a representation that makes the relevant features explicit is a prerequisite for successful learning and understanding. Therefore, I chose to represent relations between individual words explicitly in my model

Victor Yakhot

In the limit $d\to\infty$ the role of pressure gradients and that of the incompressibility constraint decreases, thus blurring the difference between transverse and longitudinal velocity correlation functions. Using Polyakov&#39;s expression for the dissipation anomaly the closed equation for the probability density function is obtained. This model for the d

Kirk Korista, Jack Baldwin, Gary Ferland

Using a realistic model for line emission from the broad emission line regions of quasars, we are able to reproduce the previously observed correlations of emission-line ratios with the shape of the spectral energy distribution (SED). In agreement with previous studies, we find that the primary driving force behind the Baldwin Effect (EW ~ L^beta, beta < 0)

J. Greiner

I have collected all available ROSAT observations of VY Scl stars including those during the all-sky survey to investigate the presence, strength and spectrum of soft X-ray emission (0.1-2.4 keV) of this group of nova-like variables. A total of 9 out of the 14 VY Scl stars are detected with ROSAT, mostly during optical high states. Interestingly, all detecti

Eric W. Deutsch, Bruce Margon, Joss Bland-Hawthorn

We have used innovative features of the Taurus Tunable Filter instrument on the 3.9-m Anglo-Australian Telescope to obtain nearly-continuous, high-throughput, linear photometry of V2116 Oph in a 7 Angstrom bandpass at the center of the O I 8446 emission line. This instrumental technique shows promise for applications requiring precise, rapid, narrowband phot

S. Seager, D. D. Sasselov

We investigate the effects on extrasolar giant planets [EGPs] of intense irradiation by their parent stars, describing the issues involved in treating the model atmosphere problem correctly. We treat the radiative transfer in detail, allowing the flux from the parent star to interact with all relevant depths of the planetary atmosphere, with no need for a pr

Scott Tremaine

Resonant relaxation is a novel form of two-body relaxation that arises in nearly Keplerian disks such as protoplanetary disks. Resonant relaxation does not affect the semimajor axes of the particles, but enhances relaxation of particle eccentricities and inclinations. The equilibrium state after resonant relaxation is a Rayleigh distribution, with the mean-s

G. B. Taylor, D. A. Frail, S. R. Kulkarni, D. S. Shepherd

We report on the discovery of a variable radio source, VLA J070238.0+385044, associated with the proposed x-ray counterpart, 1SAX J0702.6+3850 of GRB 980329. The source was monitored from one day after the burst to one month later at centimeter wavelengths (1.4, 4.9, 8.3 and 15 GHz; Very Large Array -- VLA), and in the 3-mm band (90 GHz; Owen Valley Radio Ob

D. C. Hannikainen, R. W. Hunstead, D. Campbell-Wilson, R. K. Sood

The Molonglo Observatory Synthesis Telescope (MOST) has been monitoring the candidate Galactic black hole binary system GX 339-4 at 843 MHz since 1994 April. We present the results of this program up to 1997 February and show a possible correlation between radio and X-ray light curves.

M. Bossi, L. Mantegazza, N. S. Nunez

On the basis of our new simultaneous photometry and spectroscopy (885 uvby differential measurements in 11 nights and 154 spectrograms of the FeII 4508 A region in 5 nights), we can detect 12 probable periodicities in the variability pattern of this star, determining the frequencies of 7 without any ambiguity. Through a direct fit of pulsational models to ou

U. Fritze-v. Alvensleben, C. S. Möller, P. - A. Duc

Evolutionary synthesis models for Tidal Dwarf Galaxies (TDGs) are presented that allow to have varying proportions of young stars formed in the merger-induced starburst and of stars from the merging spirals&#39; disks. The specific metallicities as well as the gaseous emission of actively star forming TDGs are consistently accounted for. Comparison of models

A. Maciolek-Niedzwiecki, P. Magdziarz

This paper reviews the effects of general relativity in an X-ray spectrum reflected from a cold matter accreting onto a black hole. The spectrum consists of the iron K$α$ line and the Compton reflection. We sketch the overall picture of radiative processes in the central parts of the accretion flow with relation to the relativistic effects derived from the d

L. Cram, A. Hopkins, B. Mobasher, M. Rowan-Robinson

The decimetric radio continuum luminosity of a star-forming galaxy appears to be directly proportional to the rate of formation of supernovae in the galaxy. Since decimetric radiation does not suffer significant extinction and is not directive, radio luminosities may thus provide a particularly straightforward way to determine the current rate of star format

B L Feigin, A M Semikhatov, V A Sirota, I Yu Tipunin

We evaluate characters of irreducible representations of the N=2 supersymmetric extension of the Virasoro algebra. We do so by deriving the BGG-resolution of the admissible N=2 representations and also a new 3,5,7...-resolution in terms of twisted massive Verma modules. We analyse how the characters behave under the automorphisms of the algebra, whose most s

J. X. Lu, Shibaji Roy

U-duality p-branes in toroidally compactified type II superstring theories in space-time dimensions $10 > D \ge 4$ can be constructed explicitly based on the conjectured U-duality symmetries and the corresponding known single-charge super p-brane configurations. As concrete examples, we first construct explicitly the $SL(3, Z)$ superstrings and $SL(3, Z) \ti

Vijay Balasubramanian, Per Kraus, Albion Lawrence

We investigate the details of the bulk-boundary correspondence in Lorentzian signature anti-de Sitter space. Operators in the boundary theory couple to sources identified with the boundary values of non-normalizable bulk modes. Such modes do not fluctuate and provide classical backgrounds on which bulk excitations propagate. Normalizable modes in the bulk ar