May 2000 arXiv papers — page 17

Jean-Christophe Desplat, Ignacio Pagonabarraga, Peter Bladon

This paper describes `Ludwig', a versatile code for the simulation of Lattice-Boltzmann (LB) models in 3-D on cubic lattices. In fact `Ludwig' is not a single code, but a set of codes that share certain common routines, such as I/O and communications. If `Ludwig' is used as intended, a variety of complex fluid models with different equilibrium fr

Leor Barack

Recently, we proposed a method for calculating the ``radiation reaction'' self-force exerted on a charged particle moving in a strong field orbit in a black hole spacetime. In this approach, one first calculates the contribution to the ``tail'' part of the self force due to each multipole mode of the particle's self field. A certain analy

Victor S. L'vov, Itamar Procaccia

The main difficulty of statistical theories of fluid turbulence is the lack of an obvious small parameter. In this paper we show that the formerly established fusion rules can be employed to develop a theory in which Kolmogorov's statistics of 1941 acts as the zero order, or background statistics, and the anomalous corrections to the K41 scaling exponent

I. A. Nekrasov, K. Held, N. Blümer, A. I. Poteryaev

The spectral properties of La$_{1-x}$Sr$_{x}$TiO$_{3}$, a doped Mott insulator with strong Coulomb correlations, are calculated with the ab initio computational scheme LDA+DMFT(QMC). It starts from the non-interacting electronic band structure as calculated by the local density approximation (LDA), and introduces the missing correlations by the dynamical mea

J. Maharana, S. S. Pal

We consider open strings ending on D-branes in the presence of constant metric, G, antisymmetric tensor, B and gauge field, A. The Hamiltonian is manifestly invariant under a global noncompact group; strikingly similar to toroidally compactified closed string Hamiltonian. The evolution equations for the string coordinates, $\{X^i \}$ and their dual partners,

Bert Schroer

I show that a particle structure in conformal field theory is incompatible with interactions. As a substitute one has particle-like exitations whose interpolating fields have in addition to their canonical dimension an anomalous contribution. The spectra of anomalous dimension is given in terms of the Lorentz invariant quadratic invariant (compact mass opera

D. Tansley, M. Birkinshaw, M. J. Hardcastle, D. M. Worrall

We present images of infrared emission from the radio jet in 3C66B. Data at three wavelengths (4.5, 6.75 and 14.5 microns) were obtained using the Infrared Space Observatory. The 6.75 micron image clearly shows an extension aligned with the radio structure. The jet was also detected in the 14.5 micron image, but not at 4.5 micron. The radio-infrared-optical

Weiqiang Wang, Jian Zhou

We prove that the wreath product orbifolds studied earlier by the first author provide a large class of higher dimensional examples of orbifolds whose orbifold Hodge numbers coincide with the ordinary ones of suitable resolutions of singularities. We also make explicit conjectures on elliptic genera for the wreath product orbifolds.

Alan Heavens, Alexandre Refregier, Catherine Heymans

Weak gravitational lensing is now established as a powerful method to measure mass fluctuations in the universe. It relies on the measurement of small coherent distortions of the images of background galaxies. Even low-level correlations in the intrinsic shapes of galaxies could however produce a significant spurious lensing signal. These correlations are al

B. Huke, M. Lücke

For ferrofluids that are described by a system of hard spheres interacting via dipolar forces we evaluate the magnetization as a function of the internal magnetic field with a Born--Mayer technique and an expansion in the dipolar coupling strength. Two different approximations are presented for the magnetization considering different contributions to a serie

Eri Asakawa, S. Y. Choi, Jae Sik Lee

We perform a systematic study of the production of a third-generation fermion-pair, $μ^+μ^-\to f\bar{f}$ for $f=τ^-,b$, and t in the minimal supersymmetric standard model (MSSM) with explicit CP violation, which is induced radiatively by soft trilinear interactions related to squarks of the third generation. We classify all the observables for probing the CP

Hiroyuki Fuji, Yutaka Matsuo

We develop some basic properties of the open string on the symmetric product which is supposed to describe the open string field theory in discrete lightcone quantization (DLCQ). After preparing the consistency conditions of the twisted boundary conditions for Annulus/Möbius/Klein Bottle amplitudes in generic non-abelian orbifold, we classify the most genera

Jay D. Salmonson

This paper presents an interpretation based on gamma-ray burst source kinematics for the relationship found by Norris et al. between peak luminosity and energy-dependent pulse lag. I argue that the correlation should instead be between "number" luminosity and pulse lag. This interpretation improves the least-squares fit of this correlation for the kn

R. M. Cavalcanti, C. A. A. de Carvalho

We examine Gamow's method for calculating the decay rate of a wave function initially located within a potential well. Using elementary techniques, we examine a very simple, exactly solvable model, in order to show why it is so reliable for calculating decay rates, in spite of its conceptual problems. We also discuss the regime of validity of the exponen

A. N. F. Aleixo, A. B. Balantekin, M. A. Candido Ribeiro

We study the intensity-dependent and nonresonant Jaynes-Cummings Hamiltonian when the field is described by an arbitrary shape-invariant system. We determine the eigenstates, eigenvalues, time evolution matrix and the population inversion matrix factor.

A. N. F. Aleixo, A. B. Balantekin, M. A. Candido Ribeiro

A class of shape-invariant bound-state problems which represent transitions in a two-level system introduced earlier are generalized to include arbitrary energy splittings between the two levels. We show that the coupled-channel Hamiltonians obtained correspond to the generalization of the non-resonant Jaynes-Cummings Hamiltonian, widely used in quantized th

N. J. Cerf, S. Iblisdir

The cloning of continuous quantum variables is analyzed based on the concept of Gaussian cloning machines, i.e., transformations that yield copies that are Gaussian mixtures centered on the state to be copied. The optimality of Gaussian cloning machines that transform N identical input states into M output states is investigated, and bounds on the fidelity o

M. Gyulassy, P. Levai, I. Vitev

A systematic expansion in opacity, $L/λ$, is used to clarify the non-linear behavior of induced gluon radiation in quark-gluon plasmas. The inclusive differential gluon distribution is calculated up to second order in opacity and compared to the zeroth order (factorization) limit. The opacity expansion makes it possible to take finite kinematic constraints i

M. Beyer

Starting from a suitably modified three-body equation to include dominant medium effects such as self energy corrections and Pauli blocking I present results on several observables relevant for the formation of light clusters in a heavy ion collision at moderate energies. Properly taking into account the medium leads to the Mott effect, larger reaction rates

Pierre Collet, Jean-Pierre Eckmann

We prove that if the initial condition of the Swift-Hohenberg equation $\partial_t u(x,t)=\bigl(ε^2-(1+\partial_ x^2)^2\bigr) u(x,t) -u^3(x,t)$ is bounded in modulus by $Ce^{-βx}$ as $x\to+\infty $, the solution cannot propagate to the right with a speed greater than $\sup_{0<γ\leβ}γ^{-1}(ε^2+4γ^2+8γ^4).$ This settles a long-standing conjecture about the pos

David Damanik, Günter Stolz

We prove a criterion for absence of eigenvalues for one-dimensional Schrödinger operators. This criterion can be regarded as an $L^1$-version of Gordon&#39;s theorem and it has a broader range of application. Absence of eigenvalues is then established for quasiperiodic potentials generated by Liouville frequencies and various types of functions such as step

V. Hnizdo

The self-force of classical electrodynamics on a charged &#34;rigid&#34; body of radius R is evaluated analytically for the body undergoing a slow (i.e., with a speed v<<c), slight (i.e., small compared to R), and temporary displacement from an initial position of rest. The results are relevant to the Bohr-Rosenfeld analysis of the measurability of the elect

P. Basarab-Horwath, V. Lahno, R. Zhdanov

The present paper solves completely the problem of the group classification of nonlinear heat-conductivity equations of the form\ $u_{t}=F(t,x,u,u_{x})u_{xx} + G(t,x,u,u_{x})$. We have proved, in particular, that the above class contains no nonlinear equations whose invariance algebra has dimension more than five. Furthermore, we have proved that there are t

Jason Fulman

Type A affine shuffles are compared with riffle shuffles followed by a cut. Although these probability measures on the symmetric group S_n are different, they both satisfy a convolution property. Strong evidence is given that when the underlying parameter $q$ satisfies $gcd(n,q-1)=1$, the induced measures on conjugacy classes of the symmetric group coincide.

J. F. Feinstein, D. W. B. Somerset

This paper continues the study of spectral synthesis and the topologies $τ_{\infty}$ and $τ_r$ on the ideal space of a Banach algebra, concentrating particularly on the class of Haagerup tensor products of C$^*$-algebras. For this class, it is shown that spectral synthesis is equivalent to the Hausdorffness of $τ_{\infty}$. Under a weak extra condition, spec

Teodor Banica

We construct inclusions of the form $(B_0\otimes P)^G\subset (B_1\otimes P)^G$, where $G$ is a compact quantum group of Kac type acting on an inclusion of finite dimensional $\c^*$-algebras $B_0\subset B_1$ and on a $II_1$ factor $P$. Under suitable assumptions on the actions of $G$, this is a subfactor, whose Jones to er and standard invariant can be comput

Marzia Polito

We give a complete description of the tautological subgroup of the fourth cohomology group of the moduli space of pointed stable curves, and prove that for g \geq 8 it coincides with the cohomology group itself. We further give a conjectural upper bound depending on the genus for the degree of new tautological relations.

Rui Pedro Carpentier

In \cite{4} Kauffman and Vogel constructed a rigid vertex regular isotopy invariant for unoriented four-valent graphs embedded in three dimensional space. It assigns to each embedded graph $G$ a polynomial, denoted $[G]$, in three variables, $A$, $B$ and $a$, satisfies the skein relation: $$ [\psdiag{2}{6}{overcross}]=A [\psdiag{2}{6}{horlines}]+B [\psdiag{2

Anders Kock

We put together some of the efforts by several people of making aspects of fibre bundle theory into algebra. The initiator of these efforts was Charles Ehresmann, who put the notion of groupoid and groupoid action in the focus of fibre bundle theory in general, and in connection theory in particular.

S. Ole Warnaar

A refinement of the q-trinomial coefficients is introduced, which has a very powerful iterative property. This ``T-invariance&#39;&#39; is applied to derive new Virasoro character identities related to the exceptional simply-laced Lie algebras E_6,E_7 and E_8.

Nguyen Anh Ky

The two-parametric quantum superalgebra $U_{p,q}[gl(2/2)]$ and its induced representations are considered. A method for constructing all finite-dimensional irreducible representations of this quantum superalgebra is also described in detail. It turns out that finite-dimensional representations of the two-parametric $U_{p,q}[gl(2/2)]$, even at generic deforma

J. Kahn, J. H. Kim, L. Lovasz, V. H. Vu

The cover time C of a graph G is the expected time for a random walk starting from the worst vertex to cover all vertices in G. Similarly, the blanket time B is the expected time to visit all vertices within a constant factor of number of times suggested by the stationary distribution. (Our definition will be slightly stronger than this.) Obviously, all vert

Marshall W. Buck, Clara S. Chan, David P. Robbins

The minimum k-assignment of an m by n matrix X is the minimum sum of k entries of X, no two of which belong to the same row or column. If X is generated by choosing each entry independently from the exponential distribution with mean 1, then Coppersmith and Sorkin conjectured that the expected value of its minimum k-assignment is \sum_{i,j \ge 0, i+j<k} 1/((

S. James Gates,, Sergei Gukov, Edward Witten

We consider two-dimensional supergravity theories with four supercharges constructed from compactification of Type II string theory on a generic Calabi-Yau four-fold. In Type IIA and Type IIB cases, respectively, new superspace formulations of N=(2,2) and N=(0,4) dilaton supergravities are found and their coupling to matter multiplets is discussed.

J. A. Nieto, M. C. Marin

It is shown that matroid theory may provide a natural mathematical framework for a duality symmetries not only for quantum Yang-Mills physics, but also for M-theory. Our discussion is focused in an action consisting purely of the Chern-Simons term, but in principle the main ideas can be applied beyond such an action. In our treatment the theorem due to Thist

Andrea Cappelli, Giuseppe D&#39;Appollonio

Recent conjectures of the c-theorem in four and higher dimensions have suggested that the coefficient of the Euler characteristic in the trace anomaly could measure the degrees of freedom in field theory and decrease along the renormalization-group flow. We compute this quantity for free massless scalar, fermion and antisymmetric tensor fields in any dimensi

Michihiro Naka, Tadashi Takayanagi, Tadaoki Uesugi

We construct the explicit boundary state description of the vortex-type (codimension two) tachyon condensation in brane-antibrane systems generalizing the known result of the kink-type (Frau et al. hep-th/9903123). In this description we show how the RR-charge of the lower dimensional D-branes emerges. We also investigate the tachyon condensation in T^4/Z_2

J. Lukierski, P. C. Stichel, W. J. Zakrzewski

We consider a nonstandard $D=2+1$ gravity described by a translational Chern--Simons action, and couple it to the nonrelativistic point particles. We fix the asymptotic coordinate transformations in such a way that the space part of the metric becomes asymptotically Euclidean. The residual symmetries are (local in time) translations and rigid rotations. The

A. Yu. Ignatiev, R. R. Volkas

We have performed a detailed investigation of geophysical constraints on the possible admixture of mirror matter inside the Earth. On the basis of the Preliminary Reference Earth Model (PREM) -- the `Standard Model&#39; of the Earth&#39;s interior -- we have developed a method which allows one to compute changes in various quantities characterising the Earth

Adam K. Leibovich, Ian Low, I. Z. Rothstein

Following a strategy introduced earlier by the authors, we show that it is possible to extract |V_{ub}| from the cut hadronic mass spectrum of B decays without large systematic errors which usually arise from having to model the Fermi motion of the heavy quark. We present a closed form expression for |V_{ub}|/|V_{ts}| which is accurate up to corrections of o

J. Berges, N. Tetradis, C. Wetterich

We review the use of an exact renormalization group equation in quantum field theory and statistical physics. It describes the dependence of the free energy on an infrared cutoff for the quantum or thermal fluctuations. Non-perturbative solutions follow from approximations to the general form of the coarse-grained free energy or effective average action. The

G. Montagna, M. Moretti, O. Nicrosini, A. Pallavicini

Four-fermion processes with a particle lost in the beam pipe are studied at LEP to perform precision tests of the electroweak theory. Leading higher-order QED corrections to such processes are analyzed within the framework of the Structure Functions (SF) approach. The energy scale entering the QED SF is determined by inspection of the soft and collinear limi

Ingo Bojak

The complete details of our calculation of the NLO QCD corrections to heavy flavor photo- and hadroproduction with longitudinally polarized initial states are presented. The main motivation for investigating these processes is the determination of the polarized gluon density at the COMPASS and RHIC experiments, respectively, in the near future. All methods u

S. V. Chekanov

A method to measure the suppression of soft-gluon radiation by a heavy quark (&#34;dead cone&#34;) is discussed. We analyse this QCD phenomenon in the framework of the HERA experiment using Monte Carlo simulations.

S. Kumano

We report the polarized parton distributions proposed by the Asymmetry Analysis Collaboration (AAC). Using parametrized distributions at Q^2=1 GeV^2 and measured A_1 data, we determine optimum polarized distributions in the leading order (LO) and next-to-leading order (NLO). We find that the polarized antiquark distribution is not well determined particularl

Stephen P. Martin

The problem of the origin of the mu parameter in the Minimal Supersymmetric Standard Model can be solved by introducing singlet supermultiplets with non-renormalizable couplings to the ordinary Higgs supermultiplets. The Peccei-Quinn symmetry is broken at a scale which is the geometric mean between the weak scale and the Planck scale, yielding a mu term of t

M. Boglione, E. Leader

We discuss a possible explanation of the 25 year old mystery of the large transverse spin asymmetries found in many semi-inclusive hadron-hadron reactions. We obtain the first reliable information about the transverse polarized quark densities Delta_T q(x) and we find surprising implications for the usual, longitudinal, polarized DIS. The plan of the present

F. A. Berends, C. G. Papadopoulos, R. Pittau

We introduce a new, fully massive, Monte Carlo program to compute all four-fermion processes in electron-positron collisions, including Higgs production. We outline our strategy for the matrix element evaluation, the phase space generation and the implementation of the leading higher order effects, and show, where available, comparisons with existing results

Y. Meurice, M. B. Oktay

We probe the numerical errors made in renormalization group calculations by varying slightly the rescaling factor of the fields and rescaling back in order to get the same (if there were no round-off errors) zero momentum 2-point function (magnetic susceptibility). The actual calculations were performed with Dyson&#39;s hierarchical model and a simplified ve

A. Hart, B. Lucini, Z. Schram, M. Teper

We calculate the variation with temperature of the vortex free energy in D=2+1 SU(2) lattice gauge theories. We do so both above and below the deconfining transition at T=Tc. We find that this quantity is zero at all T for large enough volumes. For T<Tc this observation is consistent with the fact that the phase is linearly confining; while for T>Tc it is co

C. J. Hamer, M. Samaras, R. J. Bursill

A `forward walking&#39; Green&#39;s Function Monte Carlo algorithm is used to obtain expectation values for SU(3) lattice Yang-Mills theory in (3+1) dimensions. The ground state energy and Wilson loops are calculated, and the finite-size scaling behaviour is explored. Crude estimates of the string tension are derived, which agree with previous results at int

David Toback

The CDF and DØcollaborations continue to search for new physics using more than 100~pb$^{-1}$ of \xxbar{p} collisions at $\sqrt{s}=1.8$ TeV collected at the Fermilab Tevatron. We present recent results from both experiments on R-parity violating Supersymmetry and $Z&#39;$/Technicolor production with $ee$ and \xxbar{t} final states. In addition we introduce S

V. Pierro, I. M. Pinto, A. D. Spallicci, E. Laserra

The relevance of orbital eccentricity in the detection of gravitational radiation from (steady state) binary stars is emphasized. Computationnally effective fast and accurate)tools for constructing gravitational wave templates from binary stars with any orbital eccentricity are introduced, including tight estimation criteria of the pertinent truncation and a

Robert Beig

A class of vacuum initial-data sets is described which are based on certain expressions for the extrinsic curvature first studied and employed by Bowen and York. These expressions play a role for the momentum constraint of general relativity which is analogous to the role played by the Coulomb solution for the Gauss-law constraint of electromagnetism.

R. N. Hansen, M. Christensen, A. L. Larsen

We show that in a pioneering paper by Polnarev and Zembowicz, some conclusions concerning the characteristics of the Turok-strings are generally not correct. In addition we show that the probability of string collapse given there, is off by a large prefactor (~1000).

Dragomir R. Radev, Hongyan Jing, Malgorzata Budzikowska

We present a multi-document summarizer, called MEAD, which generates summaries using cluster centroids produced by a topic detection and tracking system. We also describe two new techniques, based on sentence utility and subsumption, which we have applied to the evaluation of both single and multiple document summaries. Finally, we describe two user studies

Diego Moll&#39;a Aliod, Michael Hess

This paper reports on the scalability of the answer extraction system ExtrAns. An answer extraction system locates the exact phrases in the documents that contain the explicit answers to the user queries. Answer extraction systems are therefore more convenient than document retrieval systems in situations where the user wants to find specific information in

David B. Benson

Withdrawn since -order- was overlooked. First order reductions without order are much too weak to separate.

D. A. Tennant, C. Broholm, Daniel H. Reich, S. E. Nagler

We report measurements of the two-magnon states in a dimerized antiferromagnetic chain material, copper nitrate (\QTR{group}{Cu(NO$_{3}$)$_{2}\cdot 2.5$D$_{2}$O}). Using inelastic neutron scattering, we have studied the one- and two-magnon excitation spectra in a large single crystal of this material. We compare this new data with perturbative expansions of

F. Chevy, K. Madison, J. Dalibard

We study the quadrupole oscillation of a Bose-Einstein condensate of $^{87}$Rb atoms confined in an axisymmetric magnetic trap, after it has been stirred by an auxiliary laser beam. The stirring may lead to the nucleation of one or more vortices, whose presence is revealed unambiguously by the precession of the axes of the quadrupolar mode. For a stirring fr

T. Giamarchi, E. Orignac

Due to the peculiar non-fermi liquid of one dimensional systems, disorder has particularly strong effects. We show that such systems belong to the more general class of disordered quantum solids. We discuss the physics of such disordered interacting systems and the methods that allows to treat them. In addition to, by now standard renormalization group metho

I. E. Psarobas, N. Stefanou, A. Modinos

We study the effect of planar defects in phononic crystals of spherical scatterers. It is shown that a plane of impurity spheres introduces modes of vibration of the elastic field localized on this plane at frequencies within a frequency gap of a pure phononic crystal; these show up as sharp resonances in the transmittance of elastic waves incident on a slab

P. Paci, C. Grimaldi, L. Pietronero

The inclusion of nonadiabatic corrections to the electron-phonon interaction leads to a strong momentum dependence in the generalized Eliashberg equations beyond Migdal&#39;s limit. For a s-wave symmetry of the order parameter, this induced momentum dependence leads to an enhancement of Tc when small momentum transfer is dominant. Here we study how the d-wav

G. Malescio, G. Pellicane

We find that a system of particles interacting through a simple isotropic potential with a softened core is able to exhibit a rich phase behavior including: a liquid-liquid phase transition in the supercooled phase, as has been suggested for water; a gas-liquid-liquid triple point; a freezing line with anomalous reentrant behavior. The essential ingredient l

Narinder Kaur, Navdeep Bajwa, K. Dharamvir, V. K. Jindal

Dimer C60 solids are monoclinic crystals with molecular longer axis aligned along the c-axis. A simple model based on atom-atom potential used to calculate various bulk, structural and thermodynamic properties of this fullerite, has also been used to investigate the pressure and temperature dependent properties such as bulk modulus, lattice and orientational

Gabor Fath, Andras Suto

We analyze the onset of incommensurabilities around the VBS point of the S=1 bilinear-biquadratic model. We propose a simple effective field theory which is capable of reproducing all known properties of the commensurate-incommensurate transition at the disorder point $θ_{\rm vbs}$. Moreover, the theory predicts another special point $θ_{\rm disp}$, distinct

U. Tirnakli, G. F. J. Garin, C. Tsallis

We numerically calculate, at the edge of chaos, the time evolution of the nonextensive entropic form $S_q \equiv [1-\sum_{i=1}^W p_i^q]/[q-1]$ (with $S_1=-\sum_{i=1}^Wp_i \ln p_i$) for two families of one-dimensional dissipative maps, namely a logistic- and a periodic-like with arbitrary inflexion $z$ at their maximum. At $t=0$ we choose $N$ initial conditio

Patrizia Monachesi, Maurizia Palummo, Rodolfo Del Sole, Rajeev Ahuja

We are able to disentagle the effects of the intraband and interband parts of the bulk dielectric function on the bare dielectric anisotropy of the surface. We show how the position, sign and amplitude of the structures observed in such spectra depend on the above quantities. The lineshape of all the calculated structures agree very well with the ones observ

Masanori Yumoto, Hidetoshi Fukuyama, Hiroshi Matsukawa, Naoto Nagaosa

We investigate quantum depinning of the one-dimensional (1D) commensurate charge-density wave (CDW) in the presence of one impurity theoretically. Quantum tunneling rate below but close to the threshold field is calculated at absolute zero temperature by use of the phase Hamiltonian within the WKB approximation. We show that the impurity can induce localized

F. millange, S. de Brion, G. Chouteau

In the manganite Nd0.5Ca0.5MnO3, charge ordering occurs at much higher temperature than the antiferromagnetic order (TCO=250K,TN=160K). The magnetic behavior of the phase TN<T<TCO is puzzling: its magnetization and susceptibility are typical of an antiferromagnet while no magnetic order is detected by neutron diffraction.We have undertaken an extensive study

Aleksey D. Drozdov

Governing equations are derived for the kinetics of physical aging in polymeric glasses. An amorphous polymer is treated as an ensemble of cooperatively rearranged regions (CRR). Any CRR is thought of as a string of elementary clusters (EC). Fragmentation of the string may occur at random time at any border between ECs. Two string can aggregate at random tim

G. Bilalbegovic

The room temperature structure of aluminum, copper and gold infinite nanowires is studied. The molecular dynamics simulation method and the same type of the embedded atom potentials made by Voter and coworkers are used. It was found that multi-shelled and various filled metallic nanowires exist depending on the metal and the initial configuration. The result

J. S. Qualls, J. S. Brooks, S. Uji, T. Terashima

Detailed studies of the magnetoresistance of alpha-(ET)2KHg(SCN)4 and alpha-(ET)2TlHg(SCN)4 as a function of temperature, magnetic field strength, and field orientation are reported. Below 15 K, the temperature dependence of the magnetoresistance is metallic (dR/dT > 0) for magnetic field orientation corresponding to an angular dependent magnetoresistance os

J. S. Qualls, L. Balicas, J. S. Brooks, N. Harrison

We present angular dependent magneto-transport and magnetization measurements on alpha-(ET)2MHg(SCN)4 compounds at high magnetic fields and low temperatures. We find that the low temperature ground state undergoes two subsequent field-induced density-wave type phase transitions above a critical angle of the magnetic field with respect to the crystallographic

R. Bruinsma, G. Gruner, M. R. D&#39;Orsogna, J. Rudnick

We propose a model Hamiltonian for charge transfer along the DNA double helix with temperature driven fluctuations in the base pair positions acting as the rate limiting factor for charge transfer between neighboring base pairs. We compare the predictions of the model with the recent work of J.K. Barton and A.H. Zewail (Proc.Natl.Acad.Sci.USA, {\bf 96}, 6014

G. Franzese, G. Malescio, A. Skibinsky, S. V. Buldyrev

To study the possibility of a fluid-fluid phase transition, we analyze a three-dimensional soft-core isotropic potential for a one-component system. We utilize two independent numerical approaches, (i) integral equation in the hypernetted-chain approximation and (ii) molecular dynamics simulations, and find for both approaches a fluid-fluid phase transition

P. Valageas

Density fluctuations in the matter distribution lead to distortions of the images of distant galaxies through weak gravitational lensing effects. This provides an efficient probe of the cosmological parameters and of the density field. In this article, we investigate the statistical properties of the convergence due to weak gravitational lensing by non-linea

Joan Najita, Glenn Tiede, John Carr

We investigate the low-mass population of the young cluster IC348 down to the deuterium-burning limit, a fiducial boundary between brown dwarf and planetary mass objects, using a new and innovative method for the spectral classification of late-type objects. Using photometric indices, constructed from HST/NICMOS narrow-band imaging, that measure the strength

K. Grogan, S. F. Dermott, D. D. Durda

Recent observations of the size-frequency distribution of zodiacal cloud particles obtained from the cratering record on the LDEF satellite (Love and Brownlee 1993) reveal a significant large particle population (100 micron diameter or greater) near 1 AU. Our previous modeling of the Solar System dust bands (Grogan et al 1997), features of the zodiacal cloud

P. Lira, A. Lawrence, R. A. Johnson

We discuss ROSAT HRI X-ray observations of 33 very nearby galaxies, sensitive to X-ray sources down to a luminosity of approximately 10^38 erg/s. The galaxies are selected from a complete, volume limited sample of 46 galaxies with d<7 Mpc for which we have extensive multi-wavelength data. For an almost complete sub-sample with M_B<-14 (29/31 objects) we have

T. Kajino, T. -K. Suzuki, S. Kawanomoto, H. Ando

We discuss the primordial nucleosynthesis in lepton asymmetric Universe models. In order to better estimate the universal baryon-mass density parameter $Ω_b$, we try to remove the uncertainty from the theoretical prediction of primordial $^7$Li abundance. We propose a new method to determine the primordial $^7$Li by the use of isotopic abundance ratio $^7$Li

S. Nishiura, M. Shimada, Y. Ohyama, T. Murayama

In order to investigate dynamical properties of spiral galaxies in the Hickson compact groups (HCGs), we present rotation curves of 30 galaxies in 20 HCGs. We found as follows. 1) There is not significant relation between dynamical peculiarity and morphological peculiarity in HCG spirals. 2) There is no significant relation between the dynamical properties a

Corinne Charbonnel, Suchitra C. Balachandran

We present a critical analysis of the nature of the so-called Li-rich RGB stars. For a majority of the stars, we have used Hipparcos parallaxes to determine masses and evolutionary states by comparing their position on the Hertzsprung-Russell diagram with theoretical evolutionary tracks. Among the twenty Li-rich giants whose location on the HR diagram we wer

Seb Oliver, S. Serjeant, A. Efstathiou, H. Crockett

We present some recent results from the European Large Area ISO Survey (ELAIS). This survey was the largest non-serendipitous ISO field survey. A preliminary reduction has recently been completed and catalogues of sources released to the community. Early results show strongly evolving source counts. A comprehensive identification programme is underway and a

G. I. Ogilvie

The non-linear fluid dynamics of a warped accretion disc was investigated in an earlier paper by developing a theory of fully non-linear bending waves in a thin, viscous disc. That analysis is here extended to take proper account of thermal and radiative effects by solving an energy equation that includes viscous dissipation and radiative transport. The prob

A. A. Pamyatnykh

An updated theoretical instability domain of the Delta Scuti star models in the Hertzsprung-Russell diagram, in the log g - log Teff diagram and in diagrams for dereddened uvby-beta photometric indices is presented. The sensitivity of both the position of the evolutionary tracks and the Blue Edge of the instability domain to changes in the chemical compositi

R. A. E. Fosbury

There is considerable evidence that powerful radio quasars and radio galaxies are orientation-dependent manifestations of the same parent population: massive spheroids containing correspondingly massive black holes. Following the recognition of this unification, research is directed to the task of elucidating the structure and composition of the active nucle

M. Bertero, P. Boccacci, M. Robberto

Ground-based astronomical observations at thermal infrared wavelengths face the problem of extracting the weak astronomical signal from the large and rapidly variable background flux. The observing strategy most commonly used, the so-called ``chopping and nodding&#39;&#39; differential technique, provides reliable representations of the target uniquely in th

H. Feuchtgruber, F. P. Helmich, E. F. van Dishoeck, C. M. Wright

Observations with the Short Wavelength Spectrometer (SWS) onboard the {\it Infrared Space Observatory} (ISO) have led to the first detection of the methyl radical ${\rm CH_3}$ in the interstellar medium. The $ν_2$ $Q-$branch at 16.5 $μ$m and the $R$(0) line at 16.0 $μ$m have been unambiguously detected toward the Galactic center SgrA$^*$. The analysis of the

L. Jimenez-Benito, A. I. Diaz, R. Terlevich, E. Terlevich

We present spectra of 6 type 1 Seyfert galaxies, 2 Seyfert 2, a starburst galaxy and a compact narrow line radiogalaxy, taken in two spectral ranges centered around the near--IR CaII triplet (CaT) (at ~8600 Angstroms), and the Mgb stellar feature at 5180 Angstroms. We measured the equivalent width (EWs) of these features and the Fe52 and Fe53 spectral indice

A. Malizia, L. Bassani, I. Negueruela

In the present work we report the BeppoSAX serendipitous discovery of the type 2 AGN 1SAXJ2234.8-2541 in the MECS field of view when pointing at the Seyfert 2 galaxy NGC7314. The source is optical identified with the bright (m_B=14.40) galaxy ESO533-G50 at redshift z=0.026. The source is clearly detected at energies above 4 keV but barely visible below this

Piercarlo Bonifacio, Vanessa Hill, Paolo Molaro, Luca Pasquini

Two giants of the Sagittarius dwarf spheroidal have been observed with the UVES spectrograph on the ESO 8.2m Kueyen telescope, during the commissioning of the instrument. Sgr 139 has [Fe/H]=-0.28 and Sgr 143 [Fe/H]=-0.21, these values are considerably higher than photometric estimates of the metallicity of the main population of Sgr. We derived abundances fo

V. A. Kilborn, L. Staveley-Smith, M. Marquarding, R. L. Webster

We report the discovery, from the HI Parkes All-Sky Survey (HIPASS), of an isolated cloud of neutral hydrogen which we believe to be extragalactic. The HI mass of the cloud (HIPASS J1712-64) is very low, 1.7 x 10^7 Msun, using an estimated distance of ~3.2 Mpc. Most significantly, we have found no optical companion to this object to very faint limits (mu(B)~

Philipp Richter

More than 20 years after the Copernicus satellite, ORFEUS allows the investigation of molecular hydrogen (H_2) in the diffuse interstellar medium by way of FUV absorption spectroscopy once again. This time, targets in the Magellanic Clouds were also observed, allowing the first investigation of cold H_2 in a metal-poor environment outside the Milky Way disk.

Steven Weinberg

The old cosmological constant problem is to understand why the vacuum energy is so small; the new problem is to understand why it is comparable to the present mass density. Several approaches to these problems are reviewed. Quintessence does not help with either; anthropic considerations offer a possibility of solving both. In theories with a scalar field th

Richard E. Borcherds

The Gross-Kohnen-Zagier theorem describes Heegner points on a modular curve in terms of coefficients of modular forms. We give another proof of this theorem which generalizes to higher dimensions.

S. Peng Oh

The next generation of gamma-ray telescopes may be able to observe gamma-ray blazars at high redshift, possibly out to the epoch of reionization. The spectrum of such sources should exhibit an absorption edge due to pair-production against UV photons along the line of sight. One expects a sharp drop in the number density of UV photons at the Lyman edge E_{L}

S. Peng Oh

Observations of the Ly-alpha forest at z~3 reveal an average metallicity Z~0.01 Z_solar. The high-redshift supernovae that polluted the IGM also accelerated relativistic electrons. Since the energy density of the CMB scales as (1+z)^4, at high redshift these electrons cool via inverse Compton scattering. Thus, the first star clusters emit X-rays. Unlike stel

Neil J. Cornish

Recent measurements of the cosmic microwave background radiation by the Boomerang experiment indicate that the universe is spatially flat. Here some simple back-of-the-envelope calculations are used to explain their result. The main result is a simple formula for the angular scale of the acoustic peak in terms of the standard cosmological parameters: l=193*[

J. M. Colberg, S. D. M. White, N. Yoshida, T. J. MacFarland

We use very large cosmological N--body simulations to obtain accurate predictions for the two-point correlations and power spectra of mass-limited samples of galaxy clusters. We consider two currently popular cold dark matter (CDM) cosmogonies, a critical density model ($τ$CDM) and a flat low density model with a cosmological constant ($Λ$CDM). Our simulatio