December 1999 arXiv papers — page 6

Alan Weinstein

In this survey, we discuss a series of linearization problems--for Poisson structures, Lie algebroids, and Lie groupoids. The last problem involves a conjecture on the structure of proper groupoids. Attempting to prove this by the method of averaging leads to problems concerning almost actions of compact groups and almost invariant submanifolds for compact g

Zoltan Furedi, Dhruv Mubayi, Douglas B. West

Given graphs H_1,...,H_k, we study the minimum order of a graph G such that for each i, the induced copies of H_i in G cover V(G). We prove a general upper bound of twice the sum of the numbers m_i, where m_i is one less than the order of H_i. When k=2 and one graph is an independent set of size n, we determine the optimum within a constant. When k=2 and the

D. Kastler, T. Krajewski, P. Seibt, K. Valavane

In this paper, we study finite dimensional quotients of the Hopf algebra U_{q}(sl_{2}) at fourth root of unity. We give explicitly all the corresponding automorphisms, real forms and idempotents.

David Blanc

We show how a certain type of CW simplicial resolutions of space by wedges of spheres may be constructed for any topological space, and how such resolutions yield an obstruction theory for a given space X to be a loop space.

David Blanc

We describe algebraic obstruction theories for realizing an abstract coalgebra K_* over the mod p Steenrod algebra as the homology of a topological space, and for distinguishing between the p-homotopy types of different realizations. The theories are expressed in terms of the Quillen cohomology of K_*.

M. Cahen, S. Gutt, J. Rawnsley

We determine the isomorphism classes of symmetric symplectic manifolds of dimension at least 4 which are connected, simply-connected and have a curvature tensor which has only one non-vanishing irreducible component -- the Ricci tensor.

Greg Trayling

A geometric approach to the standard model in terms of the Clifford algebra $% C\ell_{7}$ is advanced. The gauge symmetries and charge assignments of the fundamental fermions are seen to arise from a simple geometric model involving extra space-like dimensions. The bare coupling constants are found to obey $g_{s}/g=1$ and $g^{\prime}/g=\sqrt{3/5}$, consisten

M. Sakamoto, M. Tachibana, K. Takenaga

We propose a new mechanism of spontaneous supersymmetry breaking. The existence of extra dimensions with nontrivial topology plays an important role. We investigate new features resulted from the mechanism in two simple supersymmetric Z_2 and U(1) models. One of remarkable features is that there exists a phase in which the translational invariance for the co

Arno R. Bohm, N. L. Harshman, M. J. Mithaiwala

The foundations of time asymmetric quantum theory are reviewed and are applied to the construction of relativistic Gamow vectors. Relativistic Gamow vectors are obtained from the resonance pole of the S-matrix and furnish an irreducible representation of the Poincare' semigroup. They have all the properties needed to represent relativistic quasistable pa

O. Baerwald, P. West

We show that the fully covariant equations of motion for the M-theory fivebrane can be interpreted as charge conservation equations. The associated charges induce `shift'-symmetries of the scalar, spinor and gauge-fields of the fivebrane, so allowing an interpretation of all these fields as Goldstone fields. We also find that the fivebrane possesses a ne

Bernard de Wit, Dieter Lust

We study BPS dominated loop amplitudes in M-theory on T^2. For this purpose we generalize the concept of helicity supertraces to nine spacetime dimensions. These traces distinguish between various massive supermultiplets and appear as coefficients in their one-loop contributions to n-graviton scattering amplitudes. This can be used to show that only ultrasho

Israel Klich, August Romeo

The Casimir energy of a dilute dielectric cylinder, with the same light-velocity as in its surrounding medium, is evaluated exactly to first order in $ξ^2$ and numerically to higher orders in $ξ^2$. The first part is carried out using addition formulas for Bessel functions, and no Debye expansions are required.

F. Delduc, E. Ivanov, S. Krivonos

We construct the worldline superfield massive superparticle actions which preserve 1/4 portion of the underlying higher-dimensional supersymmetry. The rest of supersymmetry is spontaneously broken and realized by nonlinear transformations. We consider the cases of N=4 to N=1 and N=8 to N=2 partial breaking. In the first case we present the corresponding Gree

Raimar Wulkenhaar

We review the appearance of Hopf algebras in the renormalization of quantum field theories and in the study of diffeomorphisms of the frame bundle important for index computations in noncommutative geometry.

Raimar Wulkenhaar

We review Kreimer's construction of a Hopf algebra associated to the Feynman graphs of a perturbative quantum field theory.

Dirk Schlingemann

The construction of the known interacting quantum field theory models is mostly based on euclidean techniques. The expectation values of interesting quantities are usually given in terms of euclidean correlation functions from which one should be able to extract information about the behavior of the correlation functions of the Minkowskian counterpart. We th

B. Iochum, T. Krajewski, P. Martinetti

Following the general principles of noncommutative geometry, it is possible to define a metric on the space of pure states of the noncommutative algebra generated by the coordinates. This metric generalizes the usual Riemannian one. We investigate some general properties of this metric in the finite commutative case which corresponds to a metric on a finite

B. Sazdovic

The gauged WZNW model has been derived as an effective action, whose Poisson bracket algebra of the constraints is isomorphic to the commutator algebra of operators in quantized fermionic theory. As a consequence, the hamiltonian as well as usual lagrangian non-abelian bosonization rules have been obtained, for the chiral currents and for the chiral densitie

Pei Wang, Ruihong Yue

Our motivation is to find the relationship between the commutator of coordinates and uncertainty relation involving only the coordinates. The boundary condition with constant background field is connected with the rotation of D-brane at general angle. And the mode expansions of D-brane we found is more reasonable than those appeared in literature. The partit

V. A. Gani, A. E. Kudryavtsev

We study the time evolution of configurations in the form of two parallel domain walls moving towards each other in a supersymmetric field model. The configurations involved are not BPS-saturated. It is found that for such collisions there exists some critical value $v_{cr}\approx0.9120$ of the initial velocity v_i of the walls. At v_i<v_{cr} we observed ref

Victor O. Rivelles

According to the holographic principle all information in the bulk of a space is coded at its border. We will check this statement in three situations involving the AdS/CFT correspondence. There is a well known equivalence between the Maxwell-Chern-Simons theory and the self-dual model in 3 dimensions when the parameters of both theories are related in a giv

Dirk Schlingemann

Recently D. Buchholz and R. Verch have proposed a method for implementing in algebraic quantum field theory ideas from renormalization group analysis of short-distance (high energy) behavior by passing to certain scaling limit theories. Buchholz and Verch distinguish between different types of theories where the limit is unique, degenerate, or classical, and

D. Cormier, R. Holman

We analyse the dynamics of spinodal decomposition in inflationary cosmology using the closed time path formalism of out of equilibrium quantum field theory combined with the non-perturbative Hartree approximation. In addition to a general analysis, we compute the detailed evolution of two inflationary models of particular importance: lambda Phi^4 new inflati

G. J. McCance

The analysis of event shape variables enable studies of QCD and determinations of alpha-s, but require predictions to next-to-leading order. The predictions of two next-to-leading order programs are compared for current jet thrust, current jet-broadening, C parameter and jet-mass in deep inelastic scattering.

Massimo Giovannini

Physical scenarios, leading to highly energetic stochastic gravitational waves backgrounds (for frequencies ranging from the $μ$Hz up to the GHz) are examined. In some cases the typical amplitude of the logarithmic energy spectrum can be even eight orders of magnitude larger than the ordinary inflationary prediction. Scaling violations in the frequency depen

J. J. M. Verbaarschot

The order parameter of the chiral phase transition is directly related to the infrared part of the spectrum of the QCD Dirac operator. This part of the spectrum follows from the low energy limit of QCD which is given by a partition function of weakly interacting Goldstone modes. We find that the slope of the Dirac spectrum is determined by the pion decay con

Stephane Pepin, Michael C. Birse, Judith A. McGovern, Niels R. Walet

We study the instabilities of quark matter in the framework of a generalized Nambu--Jona-Lasinio model, in order to explore possible competition between three-quark clustering to form nucleons and diquark formation leading to color superconductivity. Nucleon and $Δ$ solutions are obtained for the relativistic Faddeev equation at finite density and their bind

Andrew R. Liddle, David H. Lyth, Karim A. Malik, David Wands

It has recently been claimed by Bassett et al that preheating after inflation may affect the amplitude of curvature perturbations on large scales, undermining the usual inflationary prediction. We analyze the simplest model, and confirm the results of Jedamzik and Sigl and of Ivanov that in linear perturbation theory the effect is negligible. However the dom

Scott Dodelson

I explain the origin and evolution of anisotropies in the Cosmic Microwave Background (CMB) and argue that upcoming experiments will measure cosmological and fundamental parameters very accurately. Most of the paper focuses on present data, which strongly suggest that the universe is flat. Several arguments are given to prove that present data sets are not c

Carlo Ewerz, Lynne H. Orr, W. James Stirling, Bryan R. Webber

Hadron colliders can provide important tests of BFKL `small-x&#39; dynamics. We discuss two examples of such tests, the inclusive dijet jet cross section at large rapidity separation and the number of associated `mini-jets&#39; in Higgs boson production.

A. E. Kudryavtsev

We give some remarks on the $\bar n p$-partial branching ratios in flight at low momenta of antineutron, measured by OBELIX collaboration. The comparison is made to the known branching ratios from the $p \bar p$-atomic states. The branching ratio for the reaction $\bar n p \to π^+π^0$ is found to be suppressed in comparison to what follows from the $ p \bar

Shaaban Khalil

We show that large SUSY phases have no significant effect on the relic density of the lightest supersymmetric particle (LSP). However, they are very significant for the detection rates. We emphasise that the phase of the trilinear coupling increase the direct and indirect detection rates.

H. Neufeld

I discuss a low-energy effective field theory which permits the full treatment of isospin-breaking effects in semileptonic weak interactions. In addition to the pseudoscalars and the photon, also the light leptons have to be included as dynamical degrees of freedom in an appropriate chiral Lagrangian. I describe the construction of the local action at next-t

V. Kuvshinov, R. Shulyakovsky

Factorial, cumulant and $H_q$-moments in dependence on their rank q for the instanton-induced deep inelastic scattering (DIS) in the frameworks of QCD are calculated and analysed. The obtained correlation moments behaviour has specific form, which can be considered as a new criterion of the QCD-instantons identification on experiment at HERA.

Tomas Blazek

We show that the best fits of the MSSM constrained by a simple SO(10) SUSY GUT are consistent with the present data on the muon anomalous magnetic moment. The best fits assume rather large values of tan$β\approx 50$, and in our analysis they are not {\em a priori} correlated in any way, directly or indirectly, with the experimental limit on $a_μ$. Regions in

Gregory Mahlon, Stephen Parke

We show that the single top quarks produced in the Wg-fusion channel at a proton-proton collider at a center-of-mass energy sqrt{s}=14 TeV posses a high degree of polarization in terms of a spin basis which decomposes the top quark spin in its rest frame along the direction of the spectator jet. A second useful spin basis is the eta-beamline basis, which dec

Alan Kostelecky

Possible signals for indirect CPT violation arising in experiments with neutral kaons are considered in the context of a general CPT- and Lorentz-violating standard-model extension. Certain CPT observables can depend on the meson momentum and exhibit sidereal variations in time. Any leading-order CPT violation would be controlled by four parameters that can

Keith R. Dienes, Emilian Dudas, Tony Gherghetta

We study some of the novel effects that arise when the QCD axion is placed in the ``bulk&#39;&#39; of large extra spacetime dimensions. First, we find that the mass of the axion can become independent of the energy scale associated with the breaking of the Peccei-Quinn symmetry. This implies that the mass of the axion can be adjusted independently of its cou

Eri Asakawa

Multi-Higgs doublet models include more than one neutral Higgs bosons, some of which have different properties under a CP transformation. We examine their productions at $γγ$ colliders. It is found that helicity observations of final top-pairs can be powerful tools to distinguish their CP properties, especially when masses of the Higgs bosons are almost dege

Kurt Langfeld, Alexandra Schafke

A new gauge (m-gauge) condition is proposed by means of a generalization of the Maximal Abelian gauge (MAG). The new gauge admits a space time dependent embedding of the residual U(1) into the SU(2) gauge group. This embedding is characterized by a color vector $\vec{m}(x)$. It turns out that this vector only depends of gauge invariant parts of the link conf

R D St. Denis

Current issues in the studies of Heavy Flavours in colliders are described with particular emphasis on experiments in which the UK is involved. Results on charm production at HERA are examined and compared to those at the Tevatron. B production rates at the Tevatron as well as the status of B lifetimes and mixing in the LEP collaborations and at the Tevatron

A. S. Thompson

The W-boson mass has been measured using the ALEPH detector at LEP. Preliminary results from data taken in 1998 are added to previous measurements to give mW = 80.411 +- 0.064(stat.) +- 0.037(syst.) +- 0.022(BE-CR) +- 0.018(LEP) GeV/c2.

N. H. Brook

Results on the analysis of the hadronic final state in neutral current deep inelastic scattering at HERA are presented; recent results on inclusive single particle distributions, particle correlations and event shapes are highlighted.

N. H. Brook, T. Carli, E. Rodrigues, M. R. Sutton

The Monte Carlo models ARIADNE, HERWIG and LEPTO are compared to deep-inelastic scattering data measured at the ep-collider HERA.

H1 Collaboration, C. Adloff

Deep-inelastic ep scattering data, taken with the H1 detector at HERA, are used to study the event shape variables thrust, jet broadening, jet mass, C parameter and two kinds of differential two-jet rate. The data cover a large range of the four-momentum transfer Q, which is considered to be the relevant energy scale, between 7 GeV and 100 GeV. The Q depende

O. Biebel

The potential of the TESLA linear e+e- collider to determine the strong coupling constant, alpha_S, at 500 GeV is investigated. Experimental complications due to background from W- and Z-pairs, top-production, initial state photon radiation and from beamstrahlung are considered. The hadronic event selection procedures used by the experiments at LEP II are re

F. Boehm, J. Busenitz, B. Cook, G. Gratta

We report on the initial results from a measurement of the anti-neutrino flux and spectrum at a distance of about 800 m from the three reactors of the Palo Verde Nuclear Generating Station using a segmented gadolinium-loaded scintillation detector. We find that the anti-neutrino flux agrees with that predicted in the absence of oscillations to better than 5%

Uchida Gen, Misao Sasaki

We consider a wave-function approach to the false vacuum decay with gravity and present a new method to calculate the tunneling amplitude under the WKB approximation. The result agrees with the one obtained by the Euclidean path-integral method, but gives a much clearer interpretation of an instanton (Euclidean bounce solution) that dominates the path integr

G. L. Alberghi, R. Casadio, A. Gruppuso

The equations governing the evolution of non-minimally coupled scalar matter and the scale factor of a Robertson-Walker universe are derived from a minisuperspace action. As for the minimally coupled case, it is shown that the entire semiclassical dynamics can be retrieved from the Wheeler-DeWitt equation via the Born-Oppenheimer reduction, which properly yi

I. V. Kanatchikov

Recently proposed quantization in field theory based on an analogue of Hamiltonian formulation which treats space and time on equal footing (the so-called De Donder-Weyl theory) is applied to General Relativity in metric variables. We formulate a covariant analogue of the Schroedinger equation for the wave function of space-time and metric variables and a su

S. S. Xulu

We use the energy-momentum complexes of Landau and Lifshitz and Papapetrou to obtain the energy distribution in Melvin&#39;s magnetic universe. For this space-time we find that these definitions of energy give the same and convincing results. The energy distribution obtained here is the same as we obtained earlier for the same space-time using the energy-mom

Angela Bonifati, Stefano Ceri

XML is becoming the most relevant new standard for data representation and exchange on the WWW. Novel languages for extracting and restructuring the XML content have been proposed, some in the tradition of database query languages (i.e. SQL, OQL), others more closely inspired by XML. No standard for XML query language has yet been decided, but the discussion

David Eppstein

We develop data structures for dynamic closest pair problems with arbitrary distance functions, that do not necessarily come from any geometric structure on the objects. Based on a technique previously used by the author for Euclidean closest pairs, we show how to insert and delete objects from an n-object set, maintaining the closest pair, in O(n log^2 n) t

M. D. Lee, C. W. Gardiner

A detailed analysis of the growth of a BEC is given, based on quantum kinetic theory, in which we take account of the evolution of the occupations of lower trap levels, and of the full Bose-Einstein formula for the occupations of higher trap levels, as well as the Bose stimulated direct transfer of atoms to the condensate level introduced by Gardiner et al.

Lucia V. Mercaldo, Vladimir V. Talanov, Steven M. Anlage

The temperature dependence of the microwave surface impedance and conductivity are used to study the pairing symmetry and properties of cuprate superconductors. However, the superconducting properties can be hidden by the effects of paramagnetism and antiferromagnetic long-range order in the cuprates. To address this issue we have investigated the microwave

Valentina S. U. Fazio, S. T. Lagerwall, P. Busson, A. Hult

True phase-matched second-harmonic generation in a waveguide of crosslinkable ferroelectric liquid crystals is demonstrated. These materials allow the formation of macroscopically polar structures whose order can be frozen by photopolymerization. Homeotropic alignment was chosen which offers decisive advantages compared to other geometries. All parameters co

Valentina S. U. Fazio, S. T. Lagerwall, V. Zauls, S. Schrader

A binary mixture of ferroelectric liquid crystals (FLCs) was used for the design of a channel waveguide. The FLCs possess two important functionalities: a chromophore with a high hyperpolarizability $β$ and photoreactive groups. The smectic liquid crystal is aligned in layers parallel to the glass plates in a sandwich geometry. This alignment offers several

D. Villani, E. Lange, A. Avella, G. Kotliar

We show how to resolve coherent low-energy features embedded in a broad high-energy background by use of a fully self-consistent calculation for composite particle operators. The method generalizes the formulation of Roth, which linearizes the dynamics of composite operators at any energy scale. Self-consistent equations are derived and analyzed in the case

Irene D&#39;Amico, Giovanni Vignale

We introduce a distinctive feature of spin-polarized transport, the Spin Coulomb Drag: there is an intrinsic source of friction for spin currents due to the Coulomb interaction between spin ``up&#39;&#39; and spin ``down&#39;&#39; electrons. We calculate the associated ``spin transrestistivity&#39;&#39; in a generalized random phase approximation and discuss

Joachim Krug

The effect of quenched disorder in the one-dimensional asymmetric exclusion process is reviewed. Both particlewise and sitewise disorder generically induces phase separation in a range of densities. In the particlewise case the existence of stationary product measures in the homogeneous phase implies that the critical density can be computed exactly, while f

Joachim Krug, Paolo Politi, Thomas Michely

We develop a theory of nucleation on top of two-dimensional islands bordered by steps with an additional energy barrier $ΔE_S$ for descending atoms. The theory is based on the concept of the residence time of an adatom on the island,and yields an expression for the nucleation rate which becomes exact in the limit of strong step edge barriers. This expression

Jamal Berakdar

The emission of correlated electrons from an itinerant ferromagnet following the impact of a polarized electron beam is analyzed in terms of irreducible tensorial parameters that can be measured. Under favorable conditions, specified in this work, these parameters are related to the spin polarization in the ferromagnet. The formal results are illustrated by

A. Mourachkine

The in-plane resistivity and out-of-plane resistivity of non-superconducting RBCO (R = Y, Tm) and Fe-doped Bi2212 single crystals are discussed. The comparison of electrical transport properties of the cuprates and quasi-one dimensional (1D) (TMTSF)2PF6 organic conductor suggests that RBCO and Bi2212 exhibit 1D transport properties, and the step rise at low

T. Srokowski

We solve the generalized Langevin equation driven by a stochastic force with power-law autocorrelation function. A stationary Markov process has been applied as a model of the noise. However, the resulting velocity variance does not stabilizes but diminishes with time. It is shown that algebraic distributions can induce such non-stationary affects. Results a

Yuriy Makhlin, Gerd Schoen, Alexander Shnirman

Quantum computers could perform certain tasks which no classical computer can perform in acceptable times. Josephson junction circuits can serve as building blocks of quantum computers. We discuss and compare two designs, which employ charge or magnetic flux degrees of freedom to process quantum information. In both cases, elementary single-qubit and two-qub

L. Klein, Y. Kats, A. F. Marshall, J. W. Reiner

$\rm SrRuO_3$ is an itinerant ferromagnet with $T_c \sim 150 \rm K$. When $\rm SrRuO_3$ is cooled through $T_c$ in zero applied magnetic field, a stripe domain structure appears whose orientation is uniquely determined by the large uniaxial magnetocrystalline anisotropy. We find that the ferromagnetic domain walls clearly enhance the resisitivity of $\rm SrR

S. Suellow, S. A. M. Mentink, T. E. Mason, R. Feyerherm

We present a study of annealing effects on the physical properties of tetragonal single--crystalline URh_2Ge_2. This system, which in as-grown form was recently established as the first metallic 3D random-bond heavy-fermion spin glass, is transformed by an annealing treatment into a long-range antiferromagnetically (AFM) ordered heavy-fermion compound. The t

Kristine Bourke Arnvig, Steen Pedersen, Kim Sneppen

Production of heat shock proteins are induced when a living cell is exposed to a rise in temperature. The heat shock response of protein DnaK synthesis in E.coli for temperature shifts from temperature T to T plus 7 degrees, respectively to T minus 7 degrees is measured as function of the initial temperature T. We observe a reversed heat shock at low T. The

H. Kimura, H. Matsushita, K. Hirota, Y. Endoh

We report magnetic neutron scattering measurements of incommensurate magnetic order in a superconducting single crystal of La1.88Sr0.12CuO4. We find that the incommensurate wavevectors which describe the static magnetism do not lie along high-symmetry directions of the underlying CuO2 lattice. The positions of the elastic magnetic peaks are consistent with t

S. Atzkern, S. V. Borisenko, M. Knupfer, M. S. Golden

We present a joint theoretical and experimental investigation of the electronic and optical properties of vanadium pentoxide. Electron energy-loss spectroscopy in transmission was employed to measure the momentum-dependent loss function. This in turn was used to derive the optical conductivity, which is compared to the results of band structure calculations.

H. A. Radovan, E. Behne, R. J. Zieve, J. S. Kim

We investigate the influence of columnar defects on the superconducting transition temperatures of pure and thoriated UBe13. The defects cause all the transitions to widen and to drop slightly in temperature. Quantitatively, the single UBe13 transition resembles the lower transition in a sample with 3% thorium more closely than the upper thoriated transition

Xin Wan, R. N. Bhatt

We investigate the effect of mass anisotropy on the Wigner crystallization transition in a two-dimensional (2D) electron gas. The static and dynamical properties of a 2D Wigner crystal have been calculated for arbitrary 2D Bravais lattices in the presence of anisotropic mass, as may be obtainable in Si MOSFETs with (110) surface. By studying the stability of

Oscar Iglesias, Amilcar Labarta

We present the results of a Monte Carlo simulation of the ground state and magnetic relaxation of a model of a thin film consisting on a two-dimensional square lattice of Heisenberg spins with perpendicular anisotropy K, exchange J and long-range dipolar interactions g. We have studied the ground state configurations of this system for a wide range of the in

R. Narayanan, Thomas Vojta, D. Belitz, T. R. Kirkpatrick

The Griffiths region that is due to rare regions and the resulting local moments in disordered itinerant quantum magnets, and its influence on the critical behavior, is considered within the framework of an effective field theory. It is shown that the local moments can be described in terms of static, annealed disorder, and the physical consequences of this

M. F. Carusela, H. Castellini, L. Romanelli

A system of N unidimensional global coupled maps (GCM), which support multiattractors is studied. We analize the phase diagram and some special features of the transitions (volume ratios and characteristic exponents), by controlling the number of elements of the initial partition that are in each basin of attraction. It was found important difference with wi

Tod E. Strohmayer

X-ray brightness oscillations with frequencies from 300 - 600 Hz have been observed in six low mass X-ray binary (LMXB) bursters with the Rossi X-ray Timing Explorer (RXTE). These oscillations likely result from spin modulation of a hot region on the stellar surface produced by thermonuclear burning. If this hypothesis is correct the rotational velocity of t

Hugo E. Schwarz

This paper gives a personal impression of the conference ``Asymmetrical PNe II: From Origins to Microstructures&#39;&#39;, flags some of the highlights, gathers together some facts and terminology, and indicates some promising future lines of work in this field.

T. Boeker

Recent observations with the Hubble Space Telescope (HST) have revealed that a large fraction of late-type (Sc and later) spiral galaxies harbor a bright, compact stellar cluster in their dynamical centers. Statistics of the mass, age, and star formation history of these clusters as a function of their host galaxy&#39;s Hubble type can be used to constrain m

Stefanie Wachter, Alan P. Smale, Charles Bailyn

In April 1999 the transient low mass X-ray binary X1658-298 resumed its strong and persistent X-ray emission after a 21-year interval of quiescence. We present RXTE data obtained soon after the reappearance, including four eclipses with a mean duration of 901.9 +/- 0.8 sec and ingress/egress times of 6-13 sec. Our updated ephemeris for the source indicates t

T. Boeker

A short overview on aperture synthesis in space for the non-specialist

M. J. Vasconcelos, V. Jatenco-Pereira, R. Opher

We investigate the effects of heating generated by damping of Alfven waves on protostellar accretion disks. Two mechanisms of damping are investigated, nonlinear and turbulent, which were previously studied in stellar winds (Jatenco-Pereira & Opher 1989a, b). For the nominal values studied, f=delta v/v_{A}=0.002 and F=varpi/Omega_{i}=0.1, where delta v, v_{A

M. J. Hardcastle, D. M. Worrall

HST observations have shown that low-redshift 3CR radio galaxies often exhibit a point-like optical component positionally coincident with the GHz-frequency radio core. In this paper we discuss the correlation between the luminosities of the radio, optical and X-ray cores in these objects, and argue that all three components have a common origin at the base

N. Brosch, A. Brook, L. Wisotzki, E. Almoznino

We analyze UV observations with FAUST of four sky fields in the general direction of the fourth Galactic quadrant, in which we detect 777 UV sources. This is ~50% more than detected originally by Bowyer et al (1995). We discuss the source detection process and the identification of UV sources with optical counterparts. For the first time in this project we u

P. Meszaros

Steep X-ray spectral slopes, X-ray excesses and preferred spectral energy breaks in the 01-0.3 MeV range are discussed as the possible consequences of the photospheric component of the GRB relativistic outflow, and of pair breakdown in internal shocks leading to comptonization on semirelativistic electrons or MHD waves. We also discuss the X-ray and UV spect

P. Meszaros

Gamma-ray bursts are thought to be the outcome of a cataclysmic event leading to a relativistically expanding fireball, in which particles are accelerated at shocks and produce nonthermal radiation. We discuss the theoretical predictions of the fireball shock model and its general agreement with observations. Some of the recent work deals with the collimatio

G. Raimondo, E. Brocato, S. Cassisi, V. Castellani

We present preliminary results of an incoming theoretical work concerning the integrated properties of the Population III clusters of stars. On the basis of synthetic Color-Magnitude Diagrams, we provide a grid of optical and near-IR colors of Simple Stellar Populations with very low metallicity (Z=10$^{-10}$ and Z=10$^{-6}$) and age which spans from 10 Myr

L. Cayon, J. L. Sanz, R. B. Barreiro, E. Matinez-Gonzalez

It is the aim of this paper to introduce the use of isotropic wavelets to detect and determine the flux of point sources appearing in CMB maps. The most suited wavelet to detect point sources filtered with a Gaussian beam is the Mexican Hat. An analytical expression of the wavelet coefficient obtained in the presence of a point source is provided and used in

W. B. Burton, Robert Braun

A class of compact, isolated high-velocity clouds which plausibly represents a homogeneous subsample of the HVC phenomenon in a single physical state was objectively identified by Braun and Burton (1999). Six examples of the CHVCs, unresolved in single-dish data, have been imaged with the Westerbork Synthesis Radio Telescope. The high-resolution imaging reve

W. B. Burton, Robert Braun

Six examples of the compact, isolated high-velocity clouds catalogued by Braun & Burton (1999) and identified with a dynamically cold ensemble of primitive objects falling towards the barycenter of the Local Group have been imaged with the Westerbork Synthesis Radio Telescope; an additional ten have been imaged with the Arecibo telescope. The imaging reveals

E. Athanassoula

I first comment on some recent advances in computing equipment for CPU-intensive numerical simulations, and on possible developments in the near future. I then discuss some particularly important and yet unsolved problems in dynamics and evolution of galaxies, on which analytical, numerical and observational effort should be focused.

Romano L. M. Corradi, Mario Perinotto, Eva Villaver, Antonio Mampaso

We analyze optical images and high-resolution, long-slit spectra of three planetary nebulae which possess collimated, low-ionization features. NGC 3918 is composed of an inner, spindle-shaped shell mildly inclined with respect to the plane of the sky. Departing from the polar regions of this shell, we find a two-sided jet expanding with velocities which incr

Romano L. M. Corradi, Denise R. Goncalves, Eva Villaver, Antonio Mampaso

We have obtained narrow-band images and high-resolution spectra of the planetary nebulae NGC 6337, He 2-186, and K 4-47, with the aim of investigating the relation between their main morphological components and several low-ionization features present in these nebulae. The data suggest that NGC 6337 is a bipolar PN seen almost pole on, with polar velocities

Agnieszka Janiuk, Bozena Czerny

We study in detail the properties of the accreting corona model for active galactic nuclei and galactic black holes. In this model the fraction of the energy liberated in the corona at a given radius is calculated from the global parameters of the model (mass of the central object, accretion rate and viscosity parameter) and it appears to be a strong functio

Fabio Favata, G. Micela, F. Reale

We have studied the X-ray emission (both the quiescent component and the flares) of the dM3e star AD Leo, analyzing the Einstein IPC, ROSAT PSPC and ASCA SIS observations. Using a consistent method which explicitly considers sustained heating we have analyzed six flares with sufficient statistics, deriving constraints on the physical parameters of the flarin

Gabriele Ghisellini, Annalisa Celotti, Davide Lazzati

If the emission of gamma-ray bursts were due to the synchrotron process in the standard internal shock scenario, then the typical observed spectrum should have a slope F(nu) \propto nu^{-1/2}, which strongly conflicts with the much harder spectra observed. This directly follows from the cooling time being much shorter than the dynamical time. Particle re-acc

A. S. Evans, J. A. Surace, J. M. Mazzarella, D. B Sanders

Millimeter (CO) observations of 5 double-nucleus ultraluminous infrared galaxy (ULIG) mergers are presented. With nuclear separations of 3-5 kpc, these galaxies are in the ``intermediate&#39;&#39; stages of the merger process. A preliminary comparison of the distribution of molecular gas (the likely fuel source for both starbursts and active galactic nuclei:

Eric G. Blackman, George B. Field

We show that the presence of a steady $\ao$ dynamo in astrophysical rotators likely leads to an outflow of relative magnetic helicity and thus magnetic energy available for particle acceleration in a corona. The connection between energy and magnetic helicity arises because the generation of large scale field is linked to a generation of large scale magnetic

De-Hai Zhang

The evolution of the quintessence in various stages of the universe, the radiation-, matter-, and quintessence-dominated, is closely related with the tracking behavior and the deceleration parameter of the universe. We gave the explicit relation between the equation-of-state of the quintessence in the epoch of the matter-quintessence equality and the inverse

W. Hofstetter, R. Bulla, D. Vollhardt

We investigate the physics of a magnetic impurity with spin 1/2 in a correlated metallic host. Describing the band by a Hubbard Hamiltonian, the problem is analyzed using dynamical mean-field-theory in combination with Wilson&#39;s nonperturbative numerical renormalization group. We present results for the single-particle density of states and the dynamical

B. Bistrovic, D. Klabucar

The form factor for the anomalous process gamma pi^+ -> pi^+ pi^0, which is presently being measured at CEBAF, is calculated in the Schwinger-Dyson approach in conjunction with an impulse approximation. The form factors obtained by us are compared with the ones predicted by the simple constituent quark loop model, vector meson dominance and chiral perturbati