July 2000 arXiv papers — page 5

Sudha, A. V. Gopala Rao

The Classification of Polarization elements, the polarization affecting optical devices which have a Jones matrix representation, according to the types of eigenvectors they possess, is given a new visit through the Group-theoretical connection of polarization elements. The diattenuators and retarders are recognized as the elements corresponding to boosts an

D. B. Leinweber, A. W. Thomas

New data from parity-violating experiments on the deuteron now allow isolation of the strange-quark contribution to the nucleon magnetic moment, G_M^s(0), without the uncertainty surrounding the anapole moment of the nucleon. Still, best estimates place G_M^s(0) > 0. It is illustrated how this experimental result challenges the very cornerstone of the consti

J. C. Flores, R. Beltran

Gause's principle of competition between two species is studied when one of them is sterile. We study the condition for total extinction in the niche, namely, when the sterile population exterminates the native one by an optimal use of resources. A mathematical Lotka-Volterra non linear model of interaction between a native and sterile species is propose

Piotr Sniady

In this paper we investigate a quantum stochastic calculus build of creation, annihilation and number of particles operators which fulfill some deformed commutation relations. Namely, we introduce a deformation of a number of particles operator which has simple commutation relations with well known q-deformed creation and annihilation operators. Since all op

E. V. Ferapontov, A. P. Veselov

The factorisation method for Schrödinger operators with magnetic fields on a two-dimensional surface $M^2$ with non-trivial metric is investigated. This leads to the new integrable examples of such operators and brings a new look at some classical problems such as Dirac magnetic monopole and Landau problem. The global geometric aspects and related spectral p

J. T. Stafford, M. Van den Bergh

In this survey article we describe some geometric results in the theory of noncommutative rings and, more generally, in the theory of abelian categories. Roughly speaking and by analogy with the commutative situation, the category of graded modules modulo torsion over a noncommutative graded ring of quadratic, respectively cubic growth should be thought of a

Victor Guillemin, Catalin Zara

The one-skeleton of a G-manifold M is the set of points p in M where $\dim G_p \geq \dim G -1$; and M is a GKM manifold if the dimension of this one-skeleton is 2. Goresky, Kottwitz and MacPherson show that for such a manifold this one-skeleton has the structure of a ``labeled" graph, $(Γ, α)$, and that the equivariant cohomology ring of M is isomorphic

Joel Merker

We introduce S-nondegenerate formal CR maps and establish their convergence (revision of a preliminary version).

Pavel Etingof, Robert Guralnick, Alexander Soloviev

In this paper we show that all indecomposable nondegenerate set-theoretical solutions to the Quantum Yang-Baxter equation on a set of prime order are affine, which allows us to give a complete and very simple classification of such solutions. This result is a natural application of the general theory of set-theoretical solutions to the quantum Yang-Baxter eq

Atsushi Matsuo

Formulae expressing the trace of the composition of several (up to five) adjoint actions of elements of the Griess algebra of a vertex operator algebra are derived under certain assumptions on the action of the automorphism group. They coincide, when applied to the moonshine module $V^\natural$, with the trace formulae obtained in a different way by S.Norton

R. Ordonez, K. M. Passino

In this paper we present a direct adaptive control method for a class of uncertain nonlinear systems with a time-varying structure. We view the nonlinear systems as composed of a finite number of ``pieces,'' which are interpolated by functions that depend on a possibly exogenous scheduling variable. We assume that each piece is in strict feedback for

Victor Guillemin, Catalin Zara

Let G be a torus of dimension n > 1 and M a compact Hamiltonian G-manifold with $M^G$ finite. A circle, $S^1$, in G is generic if $M^G = M^{S^1}$. For such a circle the moment map associated with its action on M is a perfect Morse function. Let $\{ W_p^+ ; p \in M^G\}$ be the Morse-Whitney stratification of M associated with this function, and let $τ_p^+$ be

Victor Guillemin, Catalin Zara

Let G be an n-dimensional torus and $τ$ a Hamiltonian action of G on a compact symplectic manifold, M. If M is pre-quantizable one can associate with $τ$ a representation of G on a virtual vector space, Q(M), by $\spin^{\CC}$-quantization. If M is a symplectic GKM manifold we will show that several well-known theorems about this ``quantum action'' of

Amy E. Ksir

Given a tame Galois branched cover of curves pi: X -> Y with any finite Galois group G whose representations are rational, we compute the dimension of the (generalized) Prym variety corresponding to any irreducible representation ρof G. This formula can be applied to the study of algebraic integrable systems using Lax pairs, in particular systems associated

Nils R. Scheithauer

We construct 2 families of automorphic forms related to twisted fake monster algebras and calculate their Fourier expansions. This gives a new proof of their denominator identities and shows that they define automorphic forms of singular weight. We also obtain new infinite product identities which are the denominator identities of generalized Kac-Moody super

Michele Mulazzani

We show that every p-fold strictly-cyclic branched covering of a b-bridge link in $S^3$ admits a p-symmetric Heegaard splitting - in the sense of Birman and Hilden - of genus $g=(b-1)(p-1)$. This gives a complete converse of one of the results of the two authors. Moreover, we introduce the concept of weakly p-symmetric Heegaard splittings and prove similar r

Victor Guillemin, Catalin Zara

Let $Γ$ be a finite d-valent graph and G an n-dimensional torus. An ``action'' of G on $Γ$ is defined by a map, $α$, which assigns to each oriented edge e of $Γ$ a one-dimensional representation of G (or, alternatively, a weight, $α_e$, in the weight lattice of G). For the assignment, $e \to α_e$, to be a schematic description of a ``G-action'&#3

A. Bovier, M. Eckhoff, V. Gayrard, M. Klein

We study a large class of reversible Markov chains with discrete state space and transition matrix $P_N$. We define the notion of a set of {\it metastable points} as a subset of the state space $\G_N$ such that (i) this set is reached from any point $x\in \G_N$ without return to x with probability at least $b_N$, while (ii) for any two point x,y in the metas

Piotr Sniady

We construct a family of random matrix models for the q-deformed Gaussian random variables G_μ=a_μ+a^\star_μwhere the annihilation operators a_μand creation operators a^\star_νfulfil the q-deformed commutation relation a_μa^\star_ν-q a^\star_νa_μ=Γ_{μν}, Γ_{μν} is the covariance and 0<q<1 is a given number. Important feature of considered random matrices is

Masa-Hiko Saito, Hiroshi Umemura

In this paper, we show that the Bäcklund transformations of Painlevé equations come from birational maps of rational surfaces constructed by Okamoto as the spaces of initial conditions. The simultaneous resolutions of rational double points of the families of rational surfaces give rise to flops which are origins of symmetry groups of Painlevé equation. More

L. Dorcak, I. Petras, I. Kostial

In this paper we present the mathematical description and analysis of a fractional-order regulated system in the state space. A little historical background of our results in the analysis and synthesis of the fractional-order dynamical regulated systems is given. The methods and results of simulations of the fractional-order system described by a state space

Nils R. Scheithauer

We calculate twisted denominator identities of the fake monster superalgebra and use them to construct new examples of supersymmetric generalized Kac-Moody superalgebras. Their denominator identities give new infinite product identities.

M. Ablikim, E. Corrigan

The supersymmetric sinh-Gordon model on a half-line with integrable boundary conditions is considered perturbatively to verify conjectured exact reflection factors to one loop order. Propagators for the boson and fermion fields restricted to a half-line contain several novel features and are developed as prerequisites for the calculations.

C. Chiou-Lahanas, G. A. Diamandis, B. C. Georgalas, A. Kapella-Ekonomou

We study backreaction effects in two-dimensional dilaton gravity. The backreaction comes from an $R^2$ term which is a part of the one-loop effective action arising from massive scalar field quantization in a certain approximation. The peculiarity of this term is that it does not contribute to the Hawking radiation of the classical black hole solution of the

Tom Banks, Michael Dine, Lubos Motl

Motivated by recent work of Bousso and Polchinski (BP), we study theories which explain the small value of the cosmological constant using the anthropic principle. We argue that simultaneous solution of the gauge hierarchy problem is a strong constraint on any such theory. We exhibit three classes of models which satisfy these constraints. The first is a ver

Aristophanes Dimakis, Folkert Muller-Hoissen

A covariant formalism for Moyal deformations of gauge theory and differential equations which determine Seiberg-Witten maps is presented. Replacing the ordinary product of functions by the noncommutative Moyal product, noncommutative versions of integrable models can be constructed. We explore how a Seiberg-Witten map acts in such a framework. As a specific

John H. Schwarz

Lenny Susskind has made many important contributions to theoretical physics during the past 35 years. In this talk I will discuss the early history of string theory (1968-72) emphasizing Susskind&#39;s contributions.

J. R. Hiller

The method of discrete light-cone quantization (DLCQ) and useful refinements are summarized. Applications to various field theories are reviewed.

J. R. Hiller

Methods are described for the nonperturbative calculation of wave functions and scattering amplitudes in light-cone quantization. Form factors are computed from the boost-invariant wave functions, which appear as coefficients in a Fock-state expansion of the field-theoretic eigenstate. A technique is proposed for calculating scattering amplitudes from matrix

S. Heinemeyer, G. Weiglein

Higher-order results for electroweak precision observables in the Standard Model are analyzed in view of the experimental accuracies achievable at the present and the next generation of colliders, and the indirect prediction of the Higgs-boson mass from the precision data is discussed. Within the MSSM, two-loop results for the lightest CP-even Higgs-boson ma

A. Doff, F. Pisano

We show the specific unusual features on chiral gauge anomalies cancellation in the minimal, necessarily 3-3-1, and the largest 3-4-1 weak isospin chiral gauge semisimple group leptoquark-bilepton extensions of the 3-2-1 conventional standard model of nuclear and electromagnetic interactions. In such models a natural explanation for the fundamental question

Kenneth Lane

This review is based on lectures on technicolor and extended technicolor presented at the Frascati Spring School in May 2000. I summarize the motivation and structure of this theory of dynamical breaking of electroweak and flavor symmetries. Particular attention is paid to the main phenomenological obstacles to this picture-flavor-changing neutral currents,

A. Makhlin, E. Surdutovich

Using the framework of wedge dynamics, we compute the effective transverse mass of a soft quark mode propagating in the expanding background of hard quarks and gluons created at the earliest time of the collision. We discover that the wedge dynamics does not require any external infrared or collinear cut-off. The effective mass is produced mainly due to the

A. Makhlin

We derive expressions for various correlators of the gauge field and find the propagators in Hamiltonian dynamics which employs a new gauge $A^τ=0$. This gauge is a part of the wedge form of relativistic dynamics suggested earlier as a tool for the study of quantum dynamics in ultra-relativistic heavy ion collisions. We prove that the gauge is completely fix

A. Makhlin

We suggest that the ultrarelativistic collisions of heavy ions provide the simplest situation for the study of strong interactions which can be understood from first principles and without any model assumptions about the microscopic structure of the colliding nuclei. We argue that the boost-invariant geometry of the collision, and the existence of hard parto

Volker D. Burkert

The physics of electromagnetic excitation of nucleon resonances and of their relevance in nucleon structure studies are discussed. Preliminary data from the CLAS detector on the N-Delta(1232) transition multipoles, the helicity amplitudes of the N*(1535), and the search for so-called &#34;missing resonances&#34; at Jefferson Lab are presented.

T. Barnes

In this talk I summarize the status of exotic mesons, including both theoretical expectations and experimental candidates. The current experimental candidates are ``spin-parity exotics&#39;&#39;; since these are most often considered possible hybrid mesons, the theoretical discussion will be mainly concerned with hybrids. The exotic meson candidates discusse

Gennaro Corcella

We discuss vector boson production at hadron colliders and the treatment of the initial-state radiation according to Monte Carlo parton shower simulations and resummed calculations. In particular, we investigate the effect of matrix-element corrections to the HERWIG event generator on W/Z transverse momentum distributions.

Steven D. Bass, Stefan Wetzel, Wolfram Weise

We discuss the sensitivity of eta and eta&#39; photoproduction near threshold to the gluonic OZI breaking parameters in the U_A(1)-extended effective chiral Lagrangian for low-energy QCD. Our coupled-channels analysis hints at a strong correlation between the gluon-induced contributions to the eta&#39; mass and the low-energy pp -> pp eta&#39; reaction and t

Bernd A. Kniehl, Jungil Lee

We calculate the partonic cross sections for the hadroproduction of polarized chi_{cJ} mesons using the factorization formalism of nonrelativistic QCD. We also describe how the polarization is passed on to the J/psi mesons in the radiative feed-down chi_{cJ} -> J/psi + gamma and in the double-cascade decays of psi&#39; mesons via chi_{cJ} intermediate states

A. Donini, M. B. Gavela, P. Hernandez, S. Rigolin

The prospects of measuring the leptonic angles and CP-odd phases at a {\em neutrino factory} are discussed in the scenario of three active plus one sterile neutrino, motivated by the $ν_μ\raw ν_e$ LSND signal. Sensitivity to the MNS mixing matrix angles at $O (10^{-3})$ is achieved with a 1 T detector at $\sim 1$ km from the source, whereas leptonic CP-viola

C. E. C. Lima, H. M. Portella

A detailed study of the solar neutrino vacuum oscillation was made taking into account three neutrino flavours and the seasonal effect. This analysis was established for a range of the mixing parameter sin^2(2ϕ), that is concerned with the electron-tau neutrino oscillations, from 0 to 1. We obtained the allowed mass regions versus mixing angles by fitting on

E. -M. Ilgenfritz, W. Kerler, M. Müller-Preussker, H. Stüben

The improvement of simulations of QCD with dynamical Wilson fermions by combining the Hybrid Monte Carlo algorithm with parallel tempering is studied on $10^4$ and $12^4$ lattices. As an indicator for decorrelation the topological charge is used.

G. Brooijmans

During their exposure, nuclear emulsion sheets detect both tracks from experiment-related particles, as well as a considerable amount of background tracks, mainly due to cosmic rays. Unless the exposure has been fairly short, it is therefore fairly likely that a fraction of the tracks that have been identified as belonging to the particles the experiment is

Marina Artuso, Jianchun Wang

A Monte Carlo simulation has been developed to predict the spatial resolution of silicon pixel detectors. The results discussed in this paper focus on the unit cell geometry of 50 $μ$m x 400 $μ$m, as chosen for BTeV. Effects taken into account include energy deposition fluctuations along the charged particle path, diffusion, magnetic field and response of th

The VCS, A1 collaboration

Absolute differential cross sections for the reaction (e+p -> e+p+gamma) have been measured at a four-momentum transfer with virtuality Q^2=0.33 GeV^2 and polarization ε= 0.62 in the range 33.6 to 111.5 MeV/c for the momentum of the outgoing photon in the photon-proton center of mass frame. The experiment has been performed with the high resolution spectrome

S. E. Perez Bergliaffa, K. E. Hibberd

We analyze the stress-energy tensor necessary to generate a general stationary and axisymmetric spacetime. The constraints on the geometry arising from considering a perfect fluid as a source are derived. For a fluid with a nonzero stress tensor, we obtain two necessary conditions on the metric. As an example, we show that the rotating wormhole presented in

Gianni Amati, Konstantinos Georgatos

The problem of Information Retrieval is, given a set of documents D and a query q, providing an algorithm for retrieving all documents in D relevant to q. However, retrieval should depend and be updated whenever the user is able to provide as an input a preferred set of relevant documents; this process is known as em relevance feedback. Recent work in IR has

Konstantinos Georgatos

We show that Gabbay&#39;s nonmonotonic consequence relations can be reduced to a new family of relations, called entrenchment relations. Entrenchment relations provide a direct generalization of epistemic entrenchment and expectation ordering introduced by Gardenfors and Makinson for the study of belief revision and expectation inference, respectively.

Konstantinos Georgatos

Rational inference relations were introduced by Lehmann and Magidor as the ideal systems for drawing conclusions from a conditional base. However, there has been no simple characterization of these relations, other than its original representation by preferential models. In this paper, we shall characterize them with a class of total preorders of formulas by

Konstantinos Georgatos

In this thesis we shall present two logical systems, MP and MP, for the purpose of reasoning about knowledge and effort. These logical systems will be interpreted in a spatial context and therefore, the abstract concepts of knowledge and effort will be defined by concrete mathematical concepts.

Konstantinos Georgatos

We study the topological models of a logic of knowledge for topological reasoning, introduced by Larry Moss and Rohit Parikh. Among our results is a solution of a conjecture by the formentioned authors, finite satisfiability property and decidability for the theory of topological models.

Huiqiu Yuan, Uwe Grimm, Przemyslaw Repetowicz, Michael Schreiber

We study energy spectra, eigenstates and quantum diffusion for one- and two-dimensional quasiperiodic tight-binding models. As our one-dimensional model system we choose the silver mean or `octonacci&#39; chain. The two-dimensional labyrinth tiling, which is related to the octagonal tiling, is derived from a product of two octonacci chains. This makes it pos

G. Balestrino, S. Lavanga, S. Martellucci, P. G. Medaglia

Pulsed Laser Deposition in molecular-beam epitaxy environment (Laser-MBE) has been used to grow high quality BaCuOx/CaCuO2 superlattices. In situ Reflection High Energy Electron Diffraction (RHEED) shows that the growth mechanism is 2-dimensional. Furthermore, weak but reproducible RHEED intensity oscillations have been monitored during the growth. Ex-situ x

I. L. Aleiner, B. L. Altshuler, Y. M. Galperin, T. A. Shutenko

The possibility for a two-channel Kondo ($2CK$) non Fermi liquid state to appear in a metal as a result of the interaction between electrons and movable structural defects is revisited. As usual, the defect is modeled by a heavy particle moving in an almost symmetric double-well potential (DWP). Taking into account only the two lowest states in DWP is known

A. R. Lima, M. Argollo de Menezes

In this paper we apply the multicanonical method of statistical physics on the number-partitioning problem (NPP). This problem is a basic NP-hard problem from computer science, and can be formulated as a spin-glass problem. We compute the spectral degeneracy, which gives us information about the number of solutions for a given cost $E$ and cardinality $m$. W

R. Pietri, K. Ingersent, B. Andraka

The specific heat C of Ce_{0.8}La_{0.2}Al_{3} has been measured as a function of temperature T in magnetic fields up to 14 T. A large peak in C at 2.3 K has recently been ascribed to an anisotropic Kondo effect in this compound. A 14-T field depresses the temperature of the peak by only 0.2 K, but strongly reduces its height. The corresponding peak in C/T sh

P. I. Tamborenea, H. Metiu

The localization of two interacting electrons in a coupled-quantum-dots semiconductor structure is demonstrated through numerical calculations of the time evolution of the two-electron wave function including the Coulomb interaction between the electrons. The transition from the ground state to a localized state is induced by an external, time-dependent, uni

M. Blaauboer

We theoretically study reflection and transmission of light in a one-dimensional disordered phase-conjugating medium. Using an invariant imbedding approach a Fokker-Planck equation for the distribution of the probe light reflectance and expressions for the average probabilities of reflection and transmission are derived. A new crossover length scale for loca

M. C. Gordillo, D. M. Ceperley

We have performed Path Integral Monte Carlo (PIMC) calculations to determine the effect of quenched disorder on the superfluid density of a dilute 3D hard sphere gas. The disorder was introduced by locating set of hard cylinders randomly inside the simulation cell. Our results indicate that the disorder leaves the superfluid critical temperature basically un

F. Celestini, J. M. Debierre

We present the results of non-equilibrium molecular dynamics simulations for the growth of a solid binary alloy from its liquid phase. The regime of high pulling velocities, $V$, for which there is a progressive transition from solute segregation to solute trapping, is considered. In the segregation regime, we recover the exponential form of the concentratio

Wiebe Geertsma, D. Khomskii

We present a study of the nearest--neighbor (nn) and next-nearest-neighbor (nnn) exchange constants between magnetic Cu centers of the spin-Peierls material CuGeO3. The dependence of these constants on the lattice parameters (modified e.g. by variation of temperature, pressure or doping) is calculated. Based on the observation that the bond angles are more s

T. Rejec, A. Ramsak, J. H. Jefferson

The conductance threshold of a clean nearly straight quantum wire in which a single electron is bound is studied. This exhibits spin-dependent conductance anomalies on the rising edge to the first conductance plateau, near G=0.25(2e^{2}/h) and G=0.7(2e^{2}/h), related to a singlet and triplet resonances respectively. We show that the problem may be mapped on

T. Rejec, A. Ramsak, J. H. Jefferson

We study the conductance threshold of clean nearly straight quantum wires in which an electron is bound. We show that such a system exhibits spin-dependent conductance structures on the rising edge to the first conductance plateau, one near 0.25(2e^2/h), related to a singlet resonance, and one near 0.75(2e^2/h), related to a triplet resonance. As a quantitat

Andreas Schadschneider

The modelling of traffic flow using methods and models from physics has a long history. In recent years especially cellular automata models have allowed for large-scale simulations of large traffic networks faster than real time. On the other hand, these systems are interesting for physicists since they allow to observe genuine nonequilibrium effects. Here t

Alessandro Campa

We study the propagation of very large amplitude localized excitations in a model of DNA that takes explicitly into account the helicoidal structure. These excitations represent the ``transcription bubble&#39;&#39;, where the hydrogen bonds between complementary bases are disrupted, allowing access to the genetic code. We propose these kind of excitations in

S. E. Korshunov

The structure and the degenracy of the ground state of a fully-frustrated XY-model are investigated for the case of a dice lattice geometry. The results are applicable for the description of Josephson junction arrays and thin superconducting wire networks in the external magnetic field providing half-integer number of flux quanta per plaquette. The mechanism

Sandeep K. Joshi, Debendranath Sahoo, A. M. Jayannavar

We present a detailed analysis of the Aharonov-Bohm interference oscillations manifested through transmission of an electron in a mesoscopic ring with a magnetic impurity atom inserted in one of its arms. The electron interacts with the impurity through the exchange interaction leading to exchange spin-flip scattering. Transmission in the spin-flipped and sp

Bodo Huckestein, Alexander Altland

We present a numerical study of the quasi-particle density of states (DoS) of two-dimensional d-wave superconductors in the presence of smooth disorder. We find power law scaling of the DoS with an exponent depending on the strength of the disorder and the superconducting order parameter in quantitative agreement with the theory of Nersesyan et al. (Phys.Rev

Sanjay Kumar, Yashwant Singh

We study the problem of adsorption and collapse transition of a linear polymer chain situated in a fractal container represented by a 4-simplex lattice and interacting with a surface adsorbed linear polymer chain. The adsorbed chain monomers act as pinning sites for the polymer chain. This problem has been solved exactly using real space renormalization grou

Karsten Kruse, Frank Julicher

We introduce a phenomenological model to study the properties of bundles of polar filaments which interact via active elements. The stability of the homogeneous state, the attractors of the dynamics in the unstable regime and the tensile stress generated in the bundle are discussed. We find that the interaction of parallel filaments can induce unstable behav

Yukitoshi Motome, Nobuo Furukawa

A new Monte Carlo method is proposed for fermion systems interacting with classical degrees of freedom. To obtain a weight for each Monte Carlo sample with a fixed configuration of classical variables, the moment expansion of the density of states by Chebyshev polynomials is applied instead of the direct diagonalization of the fermion Hamiltonian. This reduc

Gwang-Hee Kim

Quantum-classical escape-rate transition has been studied for two general forms of magnetic anisotropy in ferrimagnetic or antiferromagnetic particles. It is found that the range of the first-order transition is greatly reduced as the system becomes ferrimagnetic and there is no first-order transition in almost compensated antiferromagnetic particles. These

T. J. Inagaki, T. Iida, M. Aihara

We present a unified theory for pump-probe spectra in highly excited semiconductors, which is applicable throughout the whole density regime including the high-density electron-hole BCS state and the low-density excitonic Bose-Einstein condensate (BEC). The analysis is based on the BCS-like pairing theory combined with the Bethe-Salpeter (BS) equation, which

D. A. Rabson, B. J. Jonsson-Akerman, A. H. Romero, R. Escudero

Interest in magnetic-tunnel junctions has prompted a re-examination of tunneling measurements through thin insulating films. In any study of metal-insulator-metal trilayers, one tries to eliminate the possibility of pinholes (small areas over which the thickness of the insulator goes to zero so that the upper and lower metals of the trilayer make direct cont

Zhen Ye

In many body systems, constituents interact with each other, forming a recursive pattern of mutual interaction and giving rise to many interesting phenomena. Based upon concepts of the modern many body theory, a model for a generic many body system is developed. A novel approach is used to investigate the general features in such a system. An interesting pha

G. E. Romero, S. A. Cellone, J. A. Combi

We present results of two-colour photometry with high time resolution of the violently variable BL Lac object AO 0235+164. We have found extreme intranight variability with amplitudes of ~ 100 % over time scales of 24 hours. Changes of 0.5 magnitudes in both R and V bands were measured within a single night, and variations up to 1.2 magnitudes occurred from

A. R. Rao, S. Naik, S. V. Vadawale, S. K. Chakrabarti

We investigate the origin of the ubiquitous 0.5 - 10 Hz QPO in the Galactic microquasar GRS 1915+105. Using the archival X-ray data from RXTE, we make a wide band X-ray spectral fitting to the source during a low-hard state observed in 1999 June. We resolve the X-ray spectra into three components, namely a multi-color disk component, a Comptonised component

R. C. Nichol, A. J. Connolly, A. W. Moore, J. Schneider

We present initial results on the use of Mixture Models for density estimation in large astronomical databases. We provide herein both the theoretical and experimental background for using a mixture model of Gaussians based on the Expectation Maximization (EM) Algorithm. Applying these analyses to simulated data sets we show that the EM algorithm - using the

Jose M. Solanes, Alberto Manrique, Carlos Garcia-Gomez, Guillermo Gonzalez-Casado

We derive the atomic hydrogen content for a total of 1900 spirals in the fields of eighteen nearby clusters. By comparing the HI deficiency distributions of the galaxies inside of and outside of one Abell radius of each cluster, we find that two thirds of the clusters in our sample show a dearth of neutral gas in their interiors. Possible connections between

John Kormendy

Dynamical searches find central dark objects - candidate supermassive black holes (BHs) - in at least 34 galaxies. The demographics of these objects lead to the following conclusions: (1) BH mass correlates with the luminosity of the bulge component of the host galaxy, albeit with considerable scatter. The median BH mass fraction is 0.15 % of the mass of the

John Kormendy

Surveys with the Hubble Space Telescope find supermassive black holes (BHs) of 10**6 to 10**9.5 solar masses in every galaxy that has an elliptical-galaxy-like &#34;bulge&#34; component. BHs appear to be standard equipment in galaxy bulges. At the 2000 June meeting of the American Astronomical Society, two groups announced the discovery of a tight correlatio

C. P. Dullemond

The uniqueness and stability of irradiated flaring passive protostellar disks is investigated in the context of a simplified set of equations for the vertical height H as a function of radius R. It is found that the well-known flaring disk solution with H ~ R^{9/7} is not unique. Diverging solutions and asymptotically conical (H ~ R) solutions are also found

S. Ettori, A. C. Fabian

In this Letter, we use the recent Chandra observation of A2142 reported by Markevitch et al. to put constraints on thermal conduction in the intracluster plasma. We show that the observed sharp temperature gradient requires that classical conductivity has to be reduced at least by a factor of between 250 and 2500. The result provides a direct constraint on a

D. C. Homan, J. F. C. Wardle

We present five epochs of 15 GHz VLBA observations of 13 AGN. These observations were specially calibrated to detect parsec scale circular polarization and our calibration techniques are discussed and analyzed in detail. We obtained reliable detections of parsec scale circular polarization in the radio jets of 4 AGN: 3C84, PKS 0528+134, 3C273, and 3C279. For

A. Vallenari, G. Bertelli, L. Schmidtobreick

We present deep V and I photometry of stellar field in four previously unstudied low latitude regions of the Galactic disk. All observed fields are located at the western side of the Galactic Center in the direction of the Coalsack-Carina region. Two of them are suspected to cross the inner spiral arm. More than $10^5$ stars are detected in total, down to a

J. D. Monnier, W. C. Danchi, D. S. Hale, E. A. Lipman

The U. C. Berkeley Infrared Spatial Interferometer has measured the mid-infrared visibilities of the carbon star IRC+10216 and the red supergiant VY CMa. The dust shells around these sources have been previously shown to be time-variable, and these new data are used to probe the evolution of the dust shells on a decade time-scale, complementing contemporaneo

M. Cappi, G. Di Cocco, M. Dadina, G. Malaguti

IC 4329A is the brightest known Seyfert galaxy in hard (~2-30 keV) X-rays and is likely to be representative of Seyfert 1 galaxies as a class. A recent 100 ks BeppoSAX observation (Perola et al. 1999) clearly confirmed the presence of a warm absorber, a reflection component (R~0.6), and a high-energy cut-off in the power law at Ec~270 keV. Its richness in sp

V. I. Slysh, M. A. Voronkov, V. Migenes, K. M. Shibata

We report on the first space-VLBI observations of the OH34.26+0.15 maser in two main line OH transitions at 1665 and 1667 MHz. The observations involved the space radiotelescope on board the Japanese satellite HALCA and an array of ground radio telescopes. The map of the maser region and images of individual maser spots were produced with an angular resoluti

Falk Herwig, Norbert Langer

(abridged) Observations clearly show that low-mass AGB stars can provide a nucleosynthesis site of the s-process. Recent stellar evolution models indicate that radiative burning of C13 between thermal pulses in low-mass AGB stars may indeed provide the needed neutrons. Some mixing between the proton-rich envelope and the carbon-rich core may lead to the prod

Paolo Salucci

From the kinematics of 137 spirals we find that the DM halo density profiles are self-similar at least out to R_opt and show core radii much larger that the corresponding disk scale-lenghts. The luminous regions of spirals consist of stellar disks embedded in dark halos with roughly constant density. With respect to previous work, the present evidence is obt

Bernardo Salasnich, Leo Girardi, Achim Weiss, Cesare Chiosi

We present four large sets of evolutionary tracks for stars with initial chemical compositions [Y=0.250, Z=0.008], [Y=0.273, Z=0.019], [Y=0.320, Z=0.040] and [Y=0.390, Z=0.070] and enhancement of alpha elements with respect to the solar pattern. The major improvement with respect to previous similar calculations is that we use consistent opacities - i.e. com

Ch. Fendt, D. Dravins

The influence of strong, large-scale magnetic fields on the structure and temperature distribution in white dwarf atmospheres is investigated. Magnetic fields may provide an additional component of pressure support, thus possibly inflating the atmosphere compared to the non-magnetic case. Since the magnetic forces are not isotropic, atmospheric properties ma

Robert A. Gruendl, You-Hua Chu, Bryan C. Dunne, Sean D. Points

We have observed H-alpha and [OIII] emission from eight of the most well defined Wolf-Rayet ring nebulae in the Galaxy. We find that in many cases the outermost edge of the [OIII] emission leads the H-alpha emission. We suggest that these offsets, when present, are due to the shock from the Wolf-Rayet bubble expanding into the circumstellar envelope. Thus, t

R. Casalegno, M. Orio, J. Mathis, C. Conselice

Through a program of narrow band imaging, we have observed the changing structure of the H alpha emission line around Nova Cyg 1992 (V1974 Cyg) at regular intervals from 1996 to 1999. Between 1994 and 1996, the nebular boundary advanced to the southwest at nearly the speed of light, implying that the nebula was created by an expanding wave of radiation origi

L. A. Anchordoqui, G. Cooperman, V. Grinberg, T. P. McCauley

We present an evaluation of a simulated cosmic ray shower, based on {\sc geant4} and {\sc top-c}, which tracks all the particles in the shower. {\sc top-c} (Task Oriented Parallel C) provides a framework for parallel algorithm development which makes tractable the problem of following each particle. This method is compared with a simulation program which emp

Michael M. Fogler, Frank Wilczek

We show that a quantum Hall bilayer with the total filling $ν= 1$ should exhibit a dynamical regime similar to the flux-flow in large Josephson junctions. This analogy may explain a conspicuous peak in the interlayer tunneling conductance [\prl {\bf 84}, 5808 (2000)]. The flux-flow is likely to be spatiotemporally chaotic at low bias voltage, which will mani

Tetsuya Shiromizu, Masaru Shibata

We numerically construct time-symmetric initial data sets of a black hole in the Randall-Sundrum brane world model, assuming that the black hole is spherical on the brane. We find that the apparent horizon is cigar-shaped in the 5D spacetime.

Kevin R. Lynch, Meenakshi Narain, Elizabeth H. Simmons, Stephen Mrenna

Z&#39; bosons that couple preferentially to the third generation fermions can arise in models with extended weak (SU(2)xSU(2)) or hypercharge (U(1)xU(1)) gauge groups. We show that existing limits on quark-lepton compositeness set by the LEP and Tevatron experiments translate into lower bounds of order a few hundred GeV on the masses of these Z&#39; bosons.

Martin B. Einhorn, Jose Wudka

We define the CP transformation properties of scalars, fermions and vectors in a gauge theory and show that only three types of interactions can lead to CP violation: scalar interactions, fermion-scalar interactions and $ F \tilde F $ associated with the strong CP problem and which involve only the gauge fields. For technicolor theories this implies the abse