February 1998 arXiv papers — page 9

Kazuyuki Fujii, Tatsuo Suzuki

We treat in this paper non-linear sigma models such as $CP^1$-model, $QP^1$-model and etc, in 1+2 dimensions. For submodels of such ones we definitely construct an infinite number of nontrivial conserved currents. Our result is a generalization of that of authors (Alvarez, Ferreira and Guillen).

J. P. B. C de Melo, J. H. O. Sales, T. Frederico, P. U. Sauer

The electromagnetic current of bound systems in the light-front is constructed in the Breit-Frame, in the limit of momentum transfer $q^+=(q^0+q^3)$ vanishing. In this limit, the pair creation term survives and it is responsible for the covariance of the current. The pair creation term is computed for the $j^+$ current of a spin one composite particle in the

D. Indumathi, H. S. Mani, Anubha Rastogi

The production of the octet of baryons and mesons in e^+ e^- collisions is analysed, based on considerations of SU(3) symmetry and a simple model for SU(3) symmetry breaking in fragmentation functions. All fragmentation functions, D_q^h(x, Q^2), describing the fragmentation of quarks into a member of the baryon octet (and similarly for fragmentation into mem

Kiwoon Choi, Kyuwan Hwang, Jae Sik Lee

We consider the proton decay involving a light gravitino or axino in gauge-mediated supersymmetry breaking models to derive constraints on the $R$ parity and baryon number violating Yukawa couplings. Bounds on all nine coupling constants are obtained by considering the decay amplitudes at one-loop order.

Shi-Lin Zhu, W. -Y. P. Hwang, Ze-sen Yang

The method of QCD sum rules in the presence of external elctromagnetic fields is used to calculate the $Ω$ magnetic moment $μ_{Ω^-}$ and $Σ^0$-$Λ$ transition magnetic moment $μ_{Σ^0Λ}$, with the susceptibilities obtained previously from the study of octet baryon magnetic moments. The results $μ_{Ω^-}=-1.92μ_N$ and $μ_{Σ^0Λ}=1.5μ_N$ are in good agreement with

Shi-Lin Zhu, W. -Y. P. Hwang, Ze-sen Yang

We calculate the on-shell $Σ^0$-$Λ$ mixing parameter $θ$ with the method of QCD sum rule. Our result is $θ(m^2_{Σ^0}) =(-)(0.5\pm 0.1)$MeV. The electromagnetic interaction is not included.

Hae-Young Kee, I. L. Aleiner, B. L. Altshuler

We study the tunneling density of states (DoS) in the superconducting systems driven by Zeeman splitting $E_Z$ into the paramagnetic phase. We show that, even though the BCS gap disappears, superconducting fluctuations cause a strong DoS singularity in the vicinity of energies $-E^*$ for electrons polarized along the magnetic field and $E^*$ for the opposite

A. Kaminski, I. L. Aleiner, L. I. Glazman

We study mesoscopic fluctuations of the differential capacitance of a dot connected to a lead by a single-mode quantum channel with adjustable conductance G. We show that the amplitude of the fluctuations reaches maximum at a partially opened channel, G\lesssim e^2/π\hbar. Parametric correlations of fluctuations at different values of the applied voltage and

Shigeru Koikegami, Kosaku Yamada

We study the superconducting transition temperature $T_c$ of the bilayer d-p model with $d_{x^2-y^2}$-wavelike attractive interaction based on the formalism first employed by Nozières and Schmitt-Rink. In the strong coupling regime, $T_c$ obtained through this formalism are much suppressed, compared with those through Thouless criterion only. We also find th

Robert Link, Michael J. Pierce

We describe a new approach for the determination of cosmological parameters using gravitational lensing systems with multiple arcs, exploiting the fact that a given cluster can produce multiple arcs from sources over a broad range in redshift. The coupling between the critical radius of a single arc and the projected mass density of the lensing cluster can b

N. D. Ramesh Bhat, Yashwant Gupta, A. Pramesh Rao

We present here the results from an extensive scintillation study of twenty pulsars in the dispersion measure (DM) range 3 - 35 pc cm^-3 carried out using the Ooty Radio Telescope, to investigate the distribution of ionized material in the local interstellar medium (LISM). Our analysis reveals several anomalies in the scattering strength, which suggest that

B. Scott Gaudi, Andrew Gould

Microlensing is a powerful tool for studying stellar atmospheres because as the source crosses regions of formally infinite magnification (caustics) the surfaceof the star is resolved, thereby allowing one to measure the radial intensity profile, both photometrically and spectroscopically. However, caustic crossing events are relatively rare, and monitoring

Heidi Jo Newberg, Brian Yanny

Using high precision parallaxes from the Hipparcos catalog, we construct H-R diagrams for two samples of bright stars. The first is a magnitude-limited sample that is over 90% complete and uses uniform photometry from the Catalog of WBVR Magnitudes of Northern Sky Bright Stars (declination above -14 deg). This sample shows a smooth distribution of stars alon

N. D. Ramesh Bhat, Yashwant Gupta, A. Pramesh Rao

We present here the results from an extensive scintillation study of twenty pulsars in the dispersion measure (DM) range 3 - 35 pc cm^-3 caried out using the Ooty Radio Telescope (ORT) at 327 MHz, to investigate the distribution of ionized material in the local interstellar medium. Observations were made during the period January 1993 to August 1995, in whic

V. R. Chitnis, P. N. Bhat

The details of Cerenkov light produced by a gamma ray or a cosmic ray incident at the top of the atmosphere is best studied through systematic simulations of the extensive air showers. Recently such studies have become all the more important in view of the various techniques resulting from such studies, to distinguish gamma ray initiated showers from those g

Ted von Hippel

I present a literature search through 31 July 1997 of white dwarfs (WDs) in open and globular clusters. There are 36 single WDs and 5 WDs in binaries known among 13 open clusters, and 340 single WDs and 11 WDs in binaries known among 11 globular clusters. From these data I have calculated WD mass fractions for four open clusters (the Pleiades, NGC 2168, NGC

Arun V. Thampan, Bhaskar Datta

We calculate the disk and boundary layer luminosities for accreting rapidly rotating neutron stars with low magnetic fields in a fully general relativistic manner. Rotation increases the disk luminosity and decreases the boundary layer luminosity. A rapid rotation of the neutron star substantially modifies these quantities as compared to the static limit. Fo

Maxim Lyutikov, George Machabeli, Roger Blandford

Electromagnetic processes associated with a charged particle moving in a strong circular magnetic field is considered in cylindrical coordinates. We investigate the relation between the vacuum curvature emission and Cherenkov emission and argue, that for the superluminal motion of a particle in the inhomogeneous magnetic field in a dielectric, the combined e

Serguei B. Isakov

We propose a phenomenological approach to quantum liquids of particles obeying generalized statistics of a fermionic type, in the spirit of the Landau Fermi liquid theory. The approach is developed for fractional exclusion statistics. We discuss both equilibrium (specific heat, compressibility, and Pauli spin susceptibility) and nonequilibrium (current and t

Joel E. Moore

The radiation force on a single electron in an ultraintense plane wave ($a = eE/mcω\sim 1$) is calculated and shown to be proportional to $a^4$ in the high-$a$ limit for arbitrary waveform and polarization. The cyclotron motion of an electron in a constant magnetic field and an ultraintense plane wave is numerically found to be quasiperiodic even in the high

Ian I. Kogan, Alex Lewis

A new relation between two-dimensional conformal field theories and three-dimensional topologically massive gauge theories is found, where the dynamical nature of the 3d theory is ultimately important. It is shown that the those primary states in CFT which have non-unitary descendants correspond in the 3d theory to supercritical charges and cause vacuum inst

Taichi Itoh, Hiroshi Kato

We study dynamical symmetry breaking in three-dimensional QED with a Chern-Simons (CS) term, considering the screening effect of $N$ flavor fermions. We find a new phase of the vacuum, in which both the fermion mass and a magnetic field are dynamically generated, when the coefficient of the CS term $κ$ equals $N e^2/4 π$. The resultant vacuum becomes the fin

A. Cavaliere, N. Menci, P. Tozzi

To predict the X-ray observables associated to the diffuse baryons in clusters of galaxies, we develop a new physical approach to model such a hot intra-cluster plasma. Such approach is based on punctuated equilibria. and comprises the following blocks: Monte Carlo ``merging histories'' of dark matter potential wells; the central hydrostatic disposit

Jonathan E. Baker, Marc Davis, Michael A. Strauss, Ofer Lahav

We have used the Optical Redshift Survey (ORS; Santiago et al. 1995) to construct the gravity field due to fluctuations in the galaxy density field out to distances of 8000 km/s. At large scales where linear theory applies, the comparison of this gravity field with the observed peculiar velocity field offers a powerful cosmological probe, because the predict

Kikuo Harigaya

Ring torsion effects on optical excitation properties in poly(para-phenylene) (PPP) and polyaniline (PAN) are investigated by extending the Shimoi-Abe model [Synth. Met. 78, 219 (1996)]. The model is solved by the intermediate exciton formalism. Long-range excitons are characterized, and the long-range component of the oscillator strengths is calculated. We

H. R. Christiansen, M. S. Cunha, J. A. Helayel-Neto, L. R. U. Manssur

An N=1--supersymmetric version of the Cremmer-Scherk-Kalb-Ramond model with non-minimal coupling to matter is built up both in terms of superfields and in a component-field formalism. By adopting a dimensional reduction procedure, the N=2--D=3 counterpart of the model comes out, with two main features: a genuine (diagonal) Chern-Simons term and an anomalous

William T. Reach, William F. Wall, Nils Odegard

We have created a map of the large-scale infrared surface brightness in excess of that associated with the atomic interstellar medium, using region-by-region correlations between the far-infrared and 21-cm line surface brightness. Our study updates and extends a previous attempt with IRAS and Berkeley/Parkes H I surveys. The far-infrared observations used he

Adam Doliwa

It is shown that quadratic constraints are compatible with the geometric integrability scheme of the multidimensional quadrilateral lattice equation. The corresponding Ribaucour reduction of the fundamental transformation of quadrilateral lattices is found as well, and superposition of the Ribaucour transformations is presented in the vectorial framework. Fi

Masanao Ozawa

Quantum mechanics predicts the joint probability distribution of the outcomes of simultaneous measurements of commuting observables, but, in the state of the art, has lacked the operational definition of simultaneous measurements. The question is answered as to when the consecutive applications of measuring apparatuses give a simultaneous measurement of thei

Jason Zimba, Rob Clifton

We apply the machinery of projection lattices and von Neumann algebras to analyze the question of how modal interpretations can (and do) circumvent von Neumann's infamous 'no-hidden-variables' theorem.

Maxim Lyutikov

Transverse quasilinear relaxation of the cyclotron-Cherenkov instability in the inhomogeneous magnetic field of pulsar magnetospheres is considered. We find quasilinear states in which the kinetic cyclotron-Cherenkov instability of a beam propagating through strongly magnetized pair plasma is saturated by the force arising in the inhomogeneous field due to t

R. Guardiola, M. Portesi

We calculate the ground-state energy for the nucleus 4He with V4 nucleon interactions, making use of a Jastrow description of the corresponding wavefunction with state-dependent correlation factors. The effect related to the state dependence of the correlation is quite important, lowering the upper bound for the ground-state energy by some 2 MeV.

T. Rauscher, F. -K. Thielemann

An improved code for the calculation of astrophysical reaction rates in the statistical model is presented. It includes the possibility to study isospin effects. Such effects heavily affect capture rates involving self-conjugate nuclei and may also be found in reactions on other intermediate and heavy targets.

L. Jaede

A unified description of NN and pi-N elastic scattering is presented in the framework of the one solitary boson exchange potential (OSBEP). This model already successfully applied to analyze NN scattering is now extended to describe pi-N scattering while also improving its accuracy in the NN domain. We demonstrate the importance of regularization of pi-N sca

J. Gegelia

It is shown that chiral perturbation theory (in its original form by Weinberg) can describe NN scattering with positive as well as negative effective range. Some issues connected with unnaturally large NN ^1S_0 scattering length are discussed.

W. S. Wilburn, J. D. Bowman

The recent measurement of the nuclear anapole moment of 133Cs has been interpreted to yield a value of the weak pion-nucleon coupling H_pi^1 which contradicts the upper limit from the 18F experiments. We argue that because of the sensitivity of the anapole moment to H_rho^0 in the odd proton nucleus 133Cs, there is a combination of weak meson-nucleon couplin

Arturo Magidin

We show that every nilpotent group of class at most two may be embedded in a central extension of abelian groups with bilinear cocycle. The embedding is shown to depend only on the base group. Some refinements are obtained by considering the cohomological situation explicitly.

Xinming Liu, Douglas B. West

The concept of coreflexive set is introduced to study the structure of digraphs. New characterizations of line digraphs and nth-order line digraphs are given. Coreflexive sets also lead to another natural way of forming an intersection digraph from a given digraph.

J. Chadzynski, T. Krasinski

We show that for a polynomial mapping F = (f_1,...,f_m): C^n \to C^m the Lojasiewicz exponent at infinity of F is attained on the set {z \in C^n : f_1(z)...f_m(z) = 0}

Michel Brion

This text is an introduction to equivariant cohomology, a classical tool for topological transformation groups, and to equivariant intersection theory, a much more recent topic initiated by D. Edidin and W. Graham. It is based on lectures given at Montréal is Summer 1997. Our main aim is to obtain explicit descriptions of cohomology or Chow rings of certain

Raoul Bott, Alberto S. Cattaneo

This note is a sequel to our earlier paper of the same title [dg-ga/9710001] and describes invariants of rational homology 3-spheres associated to acyclic orthogonal local systems. Our work is in the spirit of the Axelrod-Singer papers, generalizes some of their results, and furnishes a new setting for the purely topological implications of their work.

Luis E. Ibanez

Supersymmetric N=1, D=4 string vacua are known to be finite in perturbation theory. However, the effective low energy D=4, N=1 field theory lagrangian does not yield in general finite theories. In this note we present the first (to our knowledge) such an example. It may be constructed in three dual ways: i) as a $Z_3$, SO(32) heterotic orbifold; ii) as a Typ

R. A. Janik, J. Wosiek

The intercept of the odderon trajectory is derived, by finding the spectrum of the second integral of motion of the three reggeon system in high energy QCD. When combined with earlier solution of the appropriate Baxter equation, this leads to the determination of the low lying states of that system. In particular, the energy of the lowest state gives the int

J. Manjavidze

To solve the quantum-mechanical problem the procedure of mapping onto linear space $W$ of generators of the (sub)group violated by given classical trajectory is formulated. The formalism is illustrated by the plane H-atom model. The problem is solved noting conservation of the Runge-Lentz vector $n$ and reducing the 4-dimensional incident phase space $T$ to

R. R. Metsaev

Arbitrary spin free massless fermionic fields corresponding to mixed symmetry representations of the \hbox{$SO(d-1)$} compact group and propagating in even $d$-dimensional anti-de Sitter spacetime are investigated. Free wave equations of motion, subsidiary conditions and the corresponding gauge transformations for such fields are proposed. The lowest eigenva

B. de Wit, K. Peeters, J. C. Plefka

We briefly review recent developments in the theory of supermembranes and supermatrix models. In a second part we discuss their interaction with background fields. In particular, we present the full background field coupling for the bosonic case. This is a short summary of the talk at the workshop. A more extended version will appear elsewhere.

Chris Quigg

To provide context for discussions of experiments at future muon colliders, I survey what is known and what will be known about the top quark and the Higgs boson from experiments at hadron colliders.

Maria Asprouli, Victor Galan-Gonzalez

We use a generalised real-time path formalism with properly regularised propagators based on Le Bellac and Mabilat \cite{belmab} and calculate the effective potential and the higher order derivative terms of the effective action in the case of real scalar fields at finite temperature. We consider time-dependent fields in thermal equilibrium and concentrate o

J. Manjavidze

The aim of the article is to discuss the S-matrix interpretation of perturbation theory for the Wigner functions generating functional at a finite temperature. For sake of definiteness, fruitful from pedagogical point of view, the concrete problem from particle physics of high-temperature initial states dissipation into cold one is considered from experiment

L. L. Jenkovszky, A. Lengyel, F. Paccanoni

We show that simple parametrisations at small x of the proton structure function work so well in limited regions of the $(x,Q^2)$ plane because they are approximately "self-consistent" solutions of the QCD evolution equation. For a class of them, we predict their $Q^2$ dependence and compare the result with experimental data.

H. Boettcher

This paper has been withdrawn by the author

Rajamani Narayanan

The fermionic determinant of a lattice Dirac operator that obeys the Ginsparg-Wilson relation factorizes into two factors that are complex conjugate of each other. Each factor is naturally associated with a single chiral fermion and can be realized as a overlap of two many body vacua.

A. Bernui, G. I. Gomero, M. J. Reboucas, A. F. F. Teixeira

We study the role played by the compactness and the degree of connectedness in the time evolution of the energy of a radiating system in the Friedmann-Robertson-Walker (FRW) space-times whose $t=const $ spacelike sections are the Euclidean 3-manifold ${\cal R}^3$ and six topologically non-equivalent flat orientable compact multiply connected Riemannian 3-man

Piotr Jaranowski, Gerhard Schaefer

It is shown that the recently found non-uniqueness of the third post-Newtonian binary point-mass ADM-Hamiltonian is related to the non-uniqueness at the third post-Newtonian approximation of the applied ADM-coordinate conditions.

Flavio G. Alvarenga, Nivaldo A. Lemos

By regarding the vacuum as a perfect fluid with equation of state p=-rho, de Sitter's cosmological model is quantized. Our treatment differs from previous ones in that it endows the vacuum with dynamical degrees of freedom. Instead of being postulated from the start, the cosmological constant arises from the degrees of freedom of the vacuum regarded as a

Shinji Mukohyama, Masafumi Seriu, Hideo Kodama

Entanglement entropy is a statistical entropy measuring information loss due to coarse-graining corresponding to a spatial division of a system. In this paper we construct a thermodynamics (entanglement thermodynamics) which includes the entanglement entropy as the entropy variable, for a massless scalar field in Minkowski, Schwarzschild and Reissner-Nordstr

C. Jarzynski

A recent result, relating the (irreversible) work performed on a system during a non-quasistatic process, to the Helmholtz free energy difference between two equilibrium states of the system, is discussed. A proof of this result is given for the special case when the evolution of the system in question is modelled by a Langevin equation in configuration spac

Yan Levin

A comparison between the Kosterlitz-Thouless theory of metal insulator transition in a two dimensional plasma and a counterion condensation in a polyelectrolyte solution is made. It is demonstrated that, unlike some of the recent suggestions, the counterion condensation and the Kosterlitz-Thouless transition are distinct.

Yan Levin

We study the interaction potential between two polyions inside a colloidal suspension. It is shown that at large separation the interaction potential is purely repulsive, with the induced attractive interactions being doubly screened. For short separations the condensed counterions become correlated, what leads to an effective attraction between the two macr

S. R. Dahmen, B. Wehefritz, G. Albertini

A new exponent characterizing the rounding of crystal facets is found by mapping a crystal surface onto the asymmetric six-vertex model (i.e. with external fields h and v) and using the Bethe Ansatz to obtain appropriate expansions of the free energy close to criticality. Leading order exponents in δh, δv are determined along the whole phase boundary and in

D. F. Agterberg

The vortex lattice structures of Sr$_2$RuO$_4$ for the odd parity representations of the superconducting state are examined for the magnetic field along the crystallographic directions. Particular emphasis is placed upon the two dimensional representation which is believed to be relevant to this material. It is shown that when the zero-field state breaks tim

J. M. Roman, G. Sierra, J. Dukelsky, M. A. Martin-Delgado

We present a manifestly rotational invariant formulation of the matrix product method valid for spin chains and ladders. We apply it to 2 legged spin ladders with spins 1/2, 1 and 3/2 and different magnetic structures labelled by the exchange coupling constants, which can be ferromagnetic or antiferromagnetic along the legs and the rungs of the ladder We com

Jukka A. Ketoja, Indubala I. Satija

The incommensurability of the supercritical Frenkel-Kontorova model is decomposed into a family of dimer type "defects" by appropriate decimations. Interestingly, this hidden dimer results in Bloch-wave type excitations of the renormalized chain which appear in the disguised form of multi-step phonon modes for the original system. We call these intri

D. E. Buergler, D. M. Schaller, C. M. Schmidt, F. Meisinger

By means of magneto-optical Kerr effect we observe for the first time antiferromagnetic coupling between ferromagnetic layers across an amorphous metallic spacer layer. Biquadratic coupling occurs at the transition from a ferromagnetically to an antiferromagnetically coupled region. Scanning tunneling microscopy images of all involved layers are used to extr

J. Richter, N. B. Ivanov, J. Schulenburg

We examine the ground state and the excitations of an one-dimensional Heisenberg spin 1/2 antiferromagnet with alternating dimers and four-spin plaquettes (dimer-plaquette chain). The properties of the system depend on the competing dimer and plaquette bonds. Several exact, exact-numerical and perturbational results are presented. We find that the system is

J. van den Brink, W. Stekelenburg, D. I. Khomskii, G. A. Sawatzky

The elementary excitations of a model Hamiltonian that captures the low energy behavior of a simple two-fold degenerate Hubbard Hamiltonian with Hund's rule coupling, is studied. The phase diagram in the mean-field limit and in a two-site approach reveals a rich variety of phases where both the orbital and the spin degrees of freedom are ordered. We show

J. Salas

We study the 3-state hexagonal-lattice Potts antiferromagnet by a Monte Carlo simulation using the Wang-Swendsen-Kotecky cluster algorithm. We study the staggered susceptibility and the correlation length, and we confirm that this model is disordered at all temperatures T>=0. We also measure the ground-state entropy density.

Kikuo Harigaya

Nonlinear optical properties in the fullerene C$_{60}$ and the extracted higher fullerenes -- C$_{70}$, C$_{76}$, C$_{78}$, and C$_{84}$ -- are theoretically investigated by using the exciton formalism and the sum-over-states method. We find that off-resonant third order susceptibilities of higher fullerenes are a few times larger than those of C$_{60}$. The

Bumsoo Kyung

We study the formation of a heavy-fermion state in the 2D periodic Anerson model. For U=2, the density of states, imaginary part of the self-energy and effective magnetic moment all indicate the Kondo screening of local f electrons, leading to a coherent heavy-fermion state. For U=3 and 4, the dominance of RKKY interaction over Kondo screening at low tempera

D. G. Sterling, J. D. Meiss

Chaotic dynamics can be effectively studied by continuation from an anti-integrable limit. Using the Henon map as an example, we obtain a simple analytical bound on the domain of existence of the horseshoe that is equivalent to the well-known bound of Devaney and Nitecki. We also reformulate the popular method for finding periodic orbits introduced by Biham

Maxim Lyutikov, George Machabeli, Roger Blandford

Emission of a charged particle propagating in a medium with a curved magnetic field is reconsidered stressing the analogy between this emission mechanism and collective Cherenkov-type plasma emission. It is explained how this mechanism differs from conventional Cherenkov, cyclotron or curvature emission and how it includes, to some extent, the features of ea

Maxim Lyutikov

It is shown that induced Raman scattering of electromagnetic waves in the strongly magnetized electron-positron plasma of pulsar magnetosphere may be important for wave propagation and as an effective saturation mechanism for electromagnetic instabilities. The frequencies, at which strong Raman scattering occurs in the outer parts of magnetosphere, fall into

A. F. Nelson, J. R. P. Angel

In this paper we develop an analytical expression relating the sensitivity to a periodic signal to the duration and accuracy of a given set of data. The effects of windowing are explored, and also the sensitivity to periods longer than the total length of observations. As specific examples, we outline the performance of our technique on large amplitude and l

Marco Tavani

We briefly discuss the theoretical implications of recent detections of gamma-ray bursts (GRBs) by BSAX. Relativistic shock wave theories of fireball expansion are challenged by the wealth of X-ray, optical and radio data obtained after the discovery of the first X-ray GRB afterglow. BSAX data contribute to address several issues concerning the initial and a

Marco Tavani

We classify gamma-ray bursts (GRBs) according to their observed durations and physical properties of their spectra. We find that long/hard bursts (of duration T_90 > 2.5 s, and typical photon energy E_p > 0.8 MeV corresponding to BATSE's energy fluence hardness H^e_{32} > 3) show the strongest deviation from the three-dimensional Euclidean brightness dis

Andrew F. Nelson, Willy Benz, Fred C. Adams, David Arnett

We present a series of 2-dimensional hydrodynamic simulations of massive disks around protostars. We simulate the same physical problem using both a `Piecewise Parabolic Method' (PPM) code and a `Smoothed Particle Hydrodynamic' (SPH) code, and analyze their differences. The disks studied here range in mass from $0.05 M_*$ to $1.0 M_*$ and in initial

James M. Stone

Our understanding of the dynamical processes which control the structure and evolution of the interaction region between an accretion disk and the central star is reviewed. If the central star is unmagnetized, this interaction is in the form of a classical boundary layer. However, if the central star is strongly magnetized, it is expected that the inner disk

Limin Lu, Wallace L. W. Sargent, Thomas A. Barlow, Michael Rauch

We investigate the metal contents of Lyman-alpha clouds at 2.2<z<3.6 with 10^13.5<N(HI)<10^14 cm-2 using high resolution, high S/N spectra of 9 quasars obtained with the 10m Keck I telescope. Using an composite spectrum analysis technique, we deduce a mean metallicity of [C/H]<-3.5 for such clouds, which is a factor of more than 10 less than that inferred fo

J. H. Swank

RXTE has been operating for nearly 2 years and is planning the third. The spacecraft performance has been good and the three instruments are operating well. Observations have been made of the range of targets suitable for RXTE, including such different objects as accreting neutron stars and black holes, stellar flares, and supernova remnants. The goals of st

Beverley J. Wills, Dean C. Hines

Broad-band polarimetry and spectropolarimetry of a complete sample of 18 luminous AGNs (Lbol > 10^11.5 Lsun), selected in an orientation-independent way by warm infrared flux, shows that an orientation-dust-covering Unified Scheme like that successfully explored for the lower luminosity Seyfert galaxies applies to the luminous QSOs. Broad emission lines and

Alvio Renzini

Derived from first physical principles, a few simple rules are presented that can help in both the planning and interpretation of CCD and IR-array camera observations of resolvable stellar populations. These rules concern the overall size of the population sampled by a frame as measured by its total luminosity, and allow to estimate the number of stars (in a

H0 Key Project, :, Shaun M. G. Hughes, Mingsheng Han

The distance to NGC 7331 has been derived from Cepheid variables observed with HST/WFPC2, as part of the Extragalactic Distance Scale Key Project. Multi-epoch exposures in F555W (V) and F814W (I), with photometry derived independently from DoPHOT and DAOPHOT/ALLFRAME programs, were used to detect a total of 13 reliable Cepheids, with periods between 11 and 4

F. Durret, W. Forman, D. Gerbal, C. Jones

We present a combined X-ray and optical analysis of the ABCG 85/87/89 complex of clusters of galaxies, based on the ROSAT PSPC image, optical photometric catalogues (Slezak et al. 1998), and an optical redshift catalogue (Durret et al. 1998). From this combined data set, we find striking alignments at all scales at PA$\simeq$160°. At small scales, the cD gal

J. C. Niemeyer

In the framework of the Chandrasekhar mass white dwarf model for Type Ia supernovae, various stages of the explosion are described in terms of the burning regimes of the thermonuclear flame front. In the early flamelet regime following the ``smoldering&#39;&#39; phase prior to the explosion, the flame is sufficiently thin and fast to remain laminar on small

Stefanie Komossa, Norbert Bade

We present a study of the properties of dusty warm absorbers and point to some important consequences for the resulting X-ray absorption spectra of AGN. Pronounced effects of the presence of dust in warm material are (i) an apparent flattening of the observed X-ray spectrum in the ROSAT band due to a sequence of absorption edges and a shift to lower gas ioni

R. P. Fender, K. Southwell, A. K. Tzioumis

We present a radio survey of X-ray sources in the Large and Small Magellanic clouds with the Australia Telescope Compact Array at 6.3 and 3.5 cm. Specifically, we have observed the fields of five LMC and two SMC supersoft X-ray sources, the X-ray binaries LMC X-1, X-2, X-3 & X-4, the X-ray transient Nova SMC 1992, and the soft gamma-ray repeater SGR 0525-66.

A. F. Boden, M. Shao, D. Van Buren

Following previous suggestions of other researchers, this paper discusses the prospects for astrometric observation of MACHO gravitational microlensing events. We derive the expected astrometric observables for a simple microlensing event with either a dark or self-luminous lens, and demonstrate that accurate astrometry can determine the lens mass, distance,

A. Magazzu, R. Rebolo, M. R. Zapatero Osorio, E. L. Martin

We present optical and infrared observations of RPr1, a faint (I = 21.01) and very red object (I - K = 4.57) discovered in a deep CCD survey, covering an area of 800 square arcmin of the Praesepe open cluster. A low resolution spectrum shows that RPr1 is a very late object, the latest object in Praesepe for which a spectrum has been taken to date. Our estima

Jan van Paradijs

Galactic accretion driven stellar X-ray sources can be divided into groups in different ways. An important division, which covers almost all known X-ray binaries, can be made according to the mass of the donor star: high-mass X-ray binaries and low-mass X-ray binaries. Another distinction (partially overlapping with the previous one) can be made on the basis

I. F. Mirabel, L. Vigroux, V. Charmandaris, M. Sauvage

We compare mid-infrared images of the Antennae galaxies (NGC 4038/39) from the Infrared Space Observatory, with optical images from the Hubble Space Telescope. The mid-infrared observations show that the most intense starburst in this colliding system of galaxies takes place in an off-nucleus reg ion that is inconspicuous at optical wavelengths. The analyses

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

We present ROSAT PSPC observations of the twin-jet radio galaxy 3C449. The soft X-ray emission from this object is dominated by an extended halo with a scale comparable to that of the radio source. The asymmetry of the X-ray emission is reflected in that of the radio lobes, providing evidence that the behaviour of the jets is strongly influenced by the exter

Erik M. Leitch, Gautam Vasisht

The terrestrial fossil record shows that the exponential rise in biodiversity since the Precambrian period has been punctuated by large extinctions, at intervals of 40 to 140 Myr. These mass extinctions represent extremes over a background of smaller events and the natural process of species extinction. We point out that the non-terrestrial phenomena propose

Brad K. Gibson, Emma J. Woolaston

We examine the origin of heavy elements in the intracluster medium (ICM) of galaxy clusters, concentrating upon the roles played by supernovae (SNe) Types Ia and II. The most accurately determined elemental abundances, Si and Fe, imply a mild predominance of Type II SNe as the source of ICM Fe, contributing approximately 60-80% of its total (and approximatel

Dany Page

After a brief summary of neutron star cooling theory I present results which emphasize the importance of baryon pairing in the neutron star core. I show how the thermal evolution may be totally controlled by pairing for models which include only nucleons and models containing also hyperons. Finally, I consider the thermal evolution of ultramagnetized neutron

Bruce Margon, Eric W. Deutsch

We present spatially-resolved, moderate-resolution spectrophotometry of the recurrent nova T Pyx and a portion of the surrounding shell. The spectrum extracted from a strip of width 10&#39;&#39; centered on the star shows well-known, strong emission lines typical of old novae, plus a prominent, unfamiliar emission line at 6590 Angstroms. This line, and a wea

Piotr Popowski, Andrew Gould

In this paper we investigate whether a misestimate of proper motions could have been a source of substantial systematic errors in the statistical parallax determination of the absolute magnitude of RR Lyrae stars. In an earlier paper, we showed that the statistical parallax method is extremely robust and rather insensitive to various systematic effects. The

M. D. Gladders, O. Lopez-Cruz, H. K. C. Yee, T. Kodama

The current formation models for cluster elliptical galaxies which incorporate a mechanism for the metallicity enhancement of massive ellipticals predict a change in the observed slope of the red sequence of ellipticals as a function of redshift. This change occurs primarily because the metal-rich galaxies become redder faster than the metal-poorer galaxies

C. K. Young, M. J. Currie, .

In a recent paper, Binggeli & Jerjen (1998) question the value of the extra- galactic distance indicators presented by Young & Currie (1994 & 1995) and state that they have refuted `the claim that the Virgo dEs [dwarf-elliptical galaxies]...are distributed in a prolate structure stretching from 8 to 20 Mpc distance (Young & Currie 1995).&#39; even though no

Chikara Furusawa, Kunihiko Kaneko

A dynamic model for cell differentiation is studied, where cells with internal chemical reaction dynamics interact with each other and replicate. It leads to spontaneous differentiation of cells and determination, as is discussed in the isologous diversification. Following features of the differentiation are obtained: (1)Hierarchical differentiation from a `

Igor Halperin, Ariel Zhitnitsky

Recently a non-supersymmetric analog of Veneziano-Yankielowicz (VY) effective Lagrangian has been proposed and applied for the analysis of the theta dependence in pure Yang-Mills theory. This effective Lagrangian is similar in many respects to the VY construction and, in particular, exhibits a kind of low energy holomorphy which is absent in the full YM theo