February 2000 arXiv papers — page 20

Yu. M. Shukrinov, A. Namiranian, A. Najafi

The tunneling density of states of HTSC is calculated taking into account tight binding band structure, group velocity, and tunneling directionality for s-wave and d-wave gap symmetry. The characteristic density of states has quasiparticle peaks' asymmetry, flat s-wave and cusplike d-wave case subgap behavior, and asymmetric background. We consider that

Nisha Mathias, Venkatesh Gopal

We investigate small-world networks from the point of view of their origin. While the characteristics of small-world networks are now fairly well understood, there is as yet no work on what drives the emergence of such a network architecture. In situations such as neural or transportation networks, where a physical distance between the nodes of the network e

Mher M. Aghasyan, Samvel M. Badalyan, Garnett W. Bryant

A theory for the relaxation rates of a test electron and electron temperature in quantum wires due to deformation, piezoelectric acoustical and polar optical phonon scattering is presented. We represent intra- and inter-subband relaxation rates as an average of rate kernels weighted by electron wave functions across a wire. We exploit these expressions to ca

Gregory A. Shields

Some QSOs show an abrupt, strong rise in polarization near rest wavelength 750 A. If this arises in the atmosphere of an accretion disk around a supermassive black hole, it may have diagnostic value. In PG 1222+228, the polarization rise occurs at the wavelength of a sharp drop in flux. We examine and reject interpretations of this feature involving a high v

Luciano Pietronero, Francesco Sylos Labini

Galaxy structures are certainly fractal up to a certain crossover scale λ_0. A clear determination of such a scale is still missing. Usually, the conceptual and practical implications of this property are neglected and the structures are only discussed in terms of their global amplitude. Here we present a compact summary of these implications. First, we disc

Sofia Feltzing, Gerard Gilmore

The Galactic Bulge has long been assumed to be a largely old stellar population. However, some recent studies based on observations with the HST WF/PC-1 and WFPC2 of stars in the Galactic Bulge have concluded that the old population may not make up more then 30% of the total. Other studies using HST/WFPC2 differential studies of `Bulge' globular clusters

Francois Ochsenbein, Patricia Bauer, James Marcout

VizieR is a database grouping in an homogeneous way thousands of astronomical catalogues gathered since decades by the Centre de Donnees de Strasbourg (CDS) and participating institutes. The history and current status of this large collection is briefly presented, and the way these catalogues are being standardized to fit in the VizieR system is described. T

W. N. Brandt, A. E. Hornschemeier, D. P. Schneider, G. P. Garmire

We present results from a study of 2-8 keV X-ray sources detected by the Advanced CCD Imaging Spectrometer (ACIS) instrument on the Chandra X-ray Observatory in the field of the z=0.516 cluster CRSS J0030.5+2618. In our 63.5 arcmin^2 search area, we detect 10 sources with 2-8 keV fluxes down to approximately 4x10^{-15} erg cm^{-2} s$^{-1}; our lowest flux so

Manuel Peimbert Antonio Peimbert

A new determination of the pregalactic helium abundance based on the Magellanic Clouds H II regions is discussed. This determination amounts to Yp = 0.2345 +- 0.0030 and is compared with those derived from giant extragalactic H II regions in systems with extremely low heavy elements content. It is suggested that the higher primordial value derived by other a

Max Tegmark, Matias Zaldarriaga

We compute the constraints on a ``standard'' 10 parameter cold dark matter (CDM) model from the most recent CMB and data and other observations, exploring 30 million discrete models and two continuous parameters. Our parameters are the densities of CDM, baryons, neutrinos, vacuum energy and curvature, the reionization optical depth, and the normaliza

Michael R. Douglas, Bartomeu Fiol, Christian Römelsberger

We define the concept of Pi-stability, a generalization of mu-stability of vector bundles, and argue that it characterizes N=1 supersymmetric brane configurations and BPS states in very general string theory compactifications with N=2 supersymmetry in four dimensions.

K. Hurley, T. Cline, E. Mazets, R. Aptekar

The extremely energetic (~10^-4 erg/cm^2) gamma-ray burst (GRB) of 1999 December 8 was triangulated to a ~14 sq. arcmin. error box ~1.8 d after its arrival at Earth with the 3rd interplanetary network (IPN), consisting of the Ulysses, Near Earth Asteroid Rendezvous (NEAR), and WIND spacecraft. Radio observations with the Very Large Array ~2.7 d after the bur

A. A. Barrientos Bendezu, K. -P. O. Diener, B. A. Kniehl

We study the quantum effects on vector-boson pair production in e^+e^- annihilation induced by the sleptons and squarks of the minimal supersymmetric extension of the standard model (MSSM) in the one-loop approximation. We list full analytic results, and quantitatively analyze the resulting deviation from the standard-model prediction of e^+e^- -> W^+W^- for

Johan Jonasson, Oded Schramm

The cover time of a finite connected graph is the expected number of steps needed for a simple random walk on the graph to visit all the vertices. It is known that the cover time on any n-vertex, connected graph is at least (1+o(1)) n log(n) and at most (1+o(1))(4/27)n^3. This paper proves that for bounded-degree planar graphs the cover time is at least c n(

N. Andersson, D. I. Jones, K. D. Kokkotas, N. Stergioulas

We present a simple spin evolution model that predicts that rapidly rotating accreting neutron stars will mainly be confined to a narrow range of spin-frequencies; P= 1.5-5 ms. This is in agreement with current observations of both neutron stars in the Low-Mass X-ray Binaries and millisecond radiopulsars. The main ingredients in the model are; i) the instabi

J. G. Contreras, R. Peschanski, C. Royon

A method allowing for a direct comparison of data with theoretical predictions is proposed for forward jet production at HERA. It avoids the reconstruction of multi-parton contributions by expressing the experimental data directly as correction factors on the QCD forward jet cross-section. An application to the determination of the effective Pomeron intercep

TheJLAB t20 collaboration, D. Abbott

A rigorous extraction of the deuteron charge form factors from tensor polarization data in elastic electron-deuteron scattering, at given values of the 4-momentum transfer, is presented. Then the world data for elastic electron-deuteron scattering is used to parameterize, in three different ways, the three electromagnetic form factors of the deuteron in the

Merced Montesinos, Carlo Rovelli

We study the possibility of applying statistical mechanics to generally covariant quantum theories with a vanishing Hamiltonian. We show that (under certain appropiate conditions) this makes sense, in spite of the absence of a notion of energy and external time. We consider a composite system formed by a large number of identical components, and apply Boltzm

Merced Montesinos

We study the classical and quantum dynamics of generally covariant theories with vanishing a Hamiltonian and with a finite number of degrees of freedom. In particular, the geometric meaning of the full solution of the relational evolution of the degrees of freedom is displayed, which means the determination of the total number of evolving constants of motion

Frederick Hamann, Hagai Netzer, Joseph Shields

We discuss new Hubble Space Telescope spectroscopy of the radio-loud quasar, 3C 288.1. The data cover ~590 A to ~1610 A in the quasar rest frame. They reveal a wealth of associated absorption lines (AALs) with no accompanying Lyman-limit absorption. The metallic AALs range in ionization from C III and N III to Ne VIII and Mg X. We use these data and photoion

T. R. Govindarajan, V. Suneeta, S. Vaidya

We study the time-independent modes of a massless scalar field in various black hole backgrounds, and show that for these black holes, the time-independent mode is localised at the horizon. A similar analysis is done for time-independent equilibrium modes of the five dimensional plane AdS black hole. A self-adjointness analysis of this problem reveals that i

E. Lisi, A. Marrone, D. Montanino

It is shown that the results of the Super-Kamiokande atmospheric neutrino experiment, interpreted in terms of nu_mu<--->nu_tau flavor transitions, can probe possible decoherence effects induced by new physics (e.g., by quantum gravity) with high sensitivity, supplementing current laboratory tests based on kaon oscillations and on neutron interferometry. By v

I. M. Suslov

According to Lipatov, the high orders of perturbation theory are determined by saddle-point configurations (instantons) of the corresponding functional integrals. According to t&#39;Hooft, some individual large diagrams, renormalons, are also significant and they are not contained in the Lipatov contribution. The history of the conception of renormalons is p

P. John, M. G. Schmidt

We compute the wall velocity in the MSSM. We therefore generalize the SM equations of motion for bubble walls moving through a hot plasma at the electroweak phase transition and calculate the friction terms which describe the viscosity of the plasma. We give the general expressions and apply them to a simple model where stops, tops and W bosons contribute to

C. Bagnuls, C. Bervillier

We critically review the use of the exact renormalization group equations (ERGE) in the framework of the scalar theory. We lay emphasis on the existence of different versions of the ERGE and on an approximation method to solve it: the derivative expansion. The leading order of this expansion appears as an excellent textbook example to underline the nonpertur

Pedro F. Gonzalez-Diaz

In order to reconcile the non conventional character of brane cosmology with standard Friedmann cosmology, we introduce in this paper a slowly-varying quintessence scalar field in the brane and analyse the cosmological solutions corresponding to some equations of state for the scalar field. Different compensation mechanisms between the cosmological constant

Uma Mahanta, Subhendu Rakshit

In this paper we study some low energy effects of a light stabilized radion in the Randall-Sundrum scenario. We find that the NLC 500 with its projected precision level will be able to probe the radion contribution to the anomalous magnetic moment and electric quadrupole moment of W boson for values of radion vev up to 500 Gev. On the other hand the BNL expe

Yong-Shi Wu, Yue Yu, Huan-Xiong Yang

We develop a bosonization approach to study the low temperature properties of one-dimensional gas of particles obeying fractional exclusion statistics (FES). It is shown that such ideal gas reproduces the low-energy excitations and asymptotic exponents of a one-component Luttinger liquid (with no internal degrees of freedom). The bosonized effective theory a

Jens O. Andersen, Eric Braaten, Michael Strickland

The &#34;basketball diagram&#34; is a three-loop vacuum diagram for a scalar field theory that cannot be expressed in terms of one-loop diagrams. We calculate this diagram for a massive scalar field at nonzero temperature, reducing it to expressions involving three-dimensional integrals that can be easily evaluated numerically. We use this result to calculat

M. Langham

String equations for the vertex operators of type IIB on $AdS_3\times S^3$ background with NS-NS flux are calculated using Berkovits-Vafa-Witten formalism. With suitable field definitions, the linearized field equations for six-dimensional supergravity and a tensor multiplet on $AdS_3\times S^3$ are recovered from these. We also discuss the massless degrees

Alexander R. Kessel, Vladimir L. Ermakov

Using virtual spin formalism it is shown that a quantum particle with eight energy levels can store three qubits. The formalism allows to realize a universal set of quantum gates. Feasible formalism implementation is suggested which uses nuclear spin-7/2 as a storage medium and radio frequency pulses as the gates. One pulse realization of all universal gates

B. E. Allman, A. Cimmino, A. G. Klein

We describe a force-free phase shift due only to temporal geometric boundary conditions placed on a neutron deBroglie wave packet.

Udo Seifert

Biological adhesion often involves several pairs of specific receptor-ligand molecules. Using rate equations, we study theoretically the rupture of such multiple parallel bonds under dynamic loading assisted by thermal activation. For a simple generic type of cooperativity, both the rupture time and force exhibit several different scaling regimes. The depend

F. Sattin

In this paper we study theoretically the process of electron capture between one-optical-electron atoms (e.g. hydrogenlike or alkali atoms) and ions at low-to-medium impact velocities (v/v_e <= 1) working on a modification of an already developed classical Over Barrier Model (OBM) [V. Ostrovsky, J. Phys. B: At. Mol. Opt. Phys. {\bf 28} 3901 (1995)], which al

Alexey K. Mazur

The macroscopic curvature induced in double helical B-DNA by regularly repeated adenine tracts (A-tracts) is a long known, but still unexplained phenomenon. This effect plays a key role in DNA studies because it is unique in the amount and the variety of the available experimental information and, therefore, is likely to serve as a gate to the unknown genera

A. Bianconi, G. Bonomi, M. P. Bussa, E. Lodi Rizzini

We present an optical potential analysis of the antiproton-proton interactions at low energies. Our optical potential is purely phenomenological, and has been parametrized on data recently obtained by the Obelix Collaboration at momenta below 180 MeV/c. It reasonably fits annihilation and elastic data below 600 MeV/c, and allows us for an evaluation of the e

Toshitaka Tatsumi

Spontaneous magnetization of quark liquid is examined. It is pointed out that quark liquid has potential to be ferromagnetic at rather low densities.

J. B. Elliott, L. G. Moretto, L. Phair, G. J. Wozniak

It is shown that the Fisher Droplet Model (FDM), percolation and nuclear multifragmentation share the common features of reducibility (stochasticity in multiplicity distributions) and thermal scaling (one-fragment production probabilities are Boltzmann factors). Barriers obtained, for cluster production on percolation lattices, from the Boltzmann factors sho

J. Bryssinck, L. Govor, V. Yu. Ponomarev F. Bauwens, O. Beck

The odd-mass $^{117}$Sn nucleus was investigated in nuclear resonance fluorescence experiments up to an endpoint energy of the incident photon spectrum of 4.1 MeV at the bremsstrahlung facility of the Stuttgart University. More than 50 mainly hitherto unknown levels were found. From the measurement of the scattering cross sections model independent absolute

D. Volchenkov, R. Lima

In the inertial range of fully developed turbulence, we model the vertex network dynamics by an iterated unimodular map having the universal behavior. Inertial range anomalous scaling for the pair correlation functions of the velocity and the local energy dissipation is established as a consequence of the chaotic behavior of the unimodular map when the Feige

V. E. Vekslerchik

The finite-genus solutions for the Hirota&#39;s bilinear difference equation are constructed using the Fay&#39;s identities for the theta-functions of compact Riemann surfaces.

Steve Zelditch

In this addendum we strengthen the results of math-ph/0002010 in the case of polynomial phases. We prove that Cesaro means of the pair correlation functions of certain integrable quantum maps on the 2-sphere at level N tend almost always to the Poisson (uniform limit). The quantum maps are exponentials of Hamiltonians which have the form a p(I) + b I, where

Steve Zelditch

We consider the eigenvalue pair correlation problem for certain integrable quantum maps on the 2-sphere. The classical maps are time one maps of Hamiltonian flows of perfect Morse functions. The quantizations are unitary operators on spaces of homogeneous holomorphic polynomials of degree N in two complex variables. There are N eigenphases on the unit circle

Siegfried Echterhoff, S. Kaliszewski, John Quigg, Iain Raeburn

We show that induction of covariant representations for C*-dynamical systems is natural in the sense that it gives a natural transformation between certain crossed-product functors. This involves setting up suitable categories of C*-algebras and dynamical systems, and extending the usual constructions of crossed products to define the appropriate functors. F

S. Kaliszewski, John Quigg

There are at least three imprimitivity bimodules naturally associated to a maximal coaction of a discrete group G on a C*-algebra and a normal subgroup of G: Mansfield&#39;s bimodule; the bimodule assembled by Ng from Green&#39;s imprimitivity bimodule and Katayama duality; and a bimodule assembled from Green&#39;s bimodule and a crossed-product Mansfield bi

Steve Zelditch

This paper generalizes the methods and results of our article xxx.lanl.gov math.SP/0002036 from elliptic to general non-degenerate closed geodesics. The main purpose is to introduce a quantum Birkhoff normal form of the Laplacian at a general non-degenerate closed geodesic in the sense of V.Guillemin. Guillemin proved that the coefficients of the normal form

Steve Zelditch

This paper concerns spectral invariants of the Laplacian on a compact Riemannian manifold (M,g) known as wave invariants. If U(t) denotes the wave group of (M,g), then the trace Tr U(t) is singular when t = 0 or when ti is the length of a closed geodesic. It has a special type of singularity expansion at each length and the coefficients are known as the wave

Dmitriy S. Kalyuzhniy

We show that the factorization problem $θ(z)=θ_2(z)θ_1(z)$ is solvable in the class of Hilbert space operator-valued functions holomorphic on some neighbourhood of $z=0$ in $\nspace{C}{N}$ and having a zero at $z=0$ (here $θ(z)$ has a multiple zero at $z=0$). Such a factorization problem becomes more complicated if we demand for $θ(z), θ_1(z)$ and $θ_2(z)$ t

B. Enriquez

We construct quasi-Hopf algebras associated with a semisimple Lie algebra, a complex curve and a rational differential. This generalizes our previous joint work with V. Rubtsov (Israel J. Math. (1999) and q-alg/9608005).

Chien-Hao Liu, Shing-Tung Yau

From the work of Lian, Liu, and Yau on &#34;Mirror Principle&#34;, in the explicit computation of the Euler data $Q=\{Q_0, Q_1, ... \}$ for an equivariant concavex bundle ${\cal E}$ over a toric manifold, there are two places the structure of the bundle comes into play: (1) the multiplicative characteric class $Q_0$ of $V$ one starts with, and (2) the splitt

F. A. Belgun

We study complex 4-manifolds with holomorphic self-dual conformal structures, and we obtain an interpretation of the Weyl tensor of such a manifold as the projective curvature of a field of cones on the ambitwistor space. In particular, its vanishing is implied by the existence of some compact, simply-connected, null-geodesics. We also relate the Cotton-York

Rui Loja Fernandes

We discuss contravariant connections on Poisson manifolds. For vector bundles, the corresponding operational notion of a contravariant derivative had been introduced by Izu Vaisman. We show that these connections play an important role in the study of global properties of Poisson manifolds and we use them to define Poisson holonomy and new invariants of Pois

B. Julia

Hidden symmetries are the backbone of Integrable two-dimensional theories. They provide classical solutions of higher dimensional models as well, they seem to survive partially quantisation and their discrete remnants in M-theory called U-dualities, would provide a way to control infinities and nonperturbative effects in Supergravities and String theories. S

D. S. Berman, Maulik K. Parikh

We study the thermodynamics of the confined and unconfined phases of superconformal Yang-Mills in finite volume and at large N using the AdS/CFT correspondence. We discuss the necessary conditions for a smooth phase crossover and obtain an N-dependent curve for the phase boundary.

G. B. Cleaver, A. E. Faraggi, D. V. Nanopoulos, Joel W. Walker

Recently, by studying exact flat directions of non-Abelian singlet fields, we demonstrated the existence of free fermionic heterotic-string models in which the SU(3)_C x SU(2)_L x U(1)_Y-charged matter spectrum, just below the string scale, consists solely of the MSSM spectrum. In this paper we generalize the analysis to include VEVs of non-Abelian fields. W

V. Gupta

The CKM-matrix V is written as a linear combination of the unit matrix I and a matrix U which causes intergenerational-mixing. It is shown that such a V results from a class of quark-mass matrices. The matrix U has to be hermitian and unitary and therefore can depend at most on 4 real parameters. The available data on the CKM-matrix including CP-violation ca

B. Loiseau, T. E. O. Ericson, A. W. Thomas

The isovector GMO sum rule for zero energy forward pion-nucleon scattering is critically studied to obtain the charged pion-nucleon coupling constant using the precise negatively charged pion-proton and pion-deuteron scattering lengths deduced recently from pionic atom experiments. This direct determination leads to a pseudoscalar charged pion-nucleon coupli

Jonathan L. Feng

An overview of the physics motivations for e-e- colliders is presented.

Stephen Godfrey, Pat Kalyniak, Basim Kamal, Arnd Leike

We investigate the sensitivity of e- gamma ---> nu_e nu_mu(bar) mu- to extra charged gauge bosons. The sensitivity is much below that of e-e+ ---> nu nu(bar) gamma. We conclude that e- gamma ---> d u(bar) nu_e and e- gamma ---> f f(bar) e- are also inferior to e+e- collisions in setting bounds on extra charged and neutral gauge bosons and on four fermion con

D. B. Blaschke, G. R. G. Burau, M. A. Ivanov, Yu. L. Kalinovsky

We consider an extension of the finite-temperature Dyson-Schwinger equation (DSE) approach to heavy mesons and quarkonia and apply it to calculate the cross section for the J/Psi breakup reaction J/Psi + pi --> D + D. We study the effects of chiral symmetry restoration in the light quark sector on this process and obtain a critical enhancement of the reactio

Thomas Coan

The CLEO detector at the Cornell Electron Storage Ring (CESR) is completing a major upgrade that significantly extends its physics reach in the study of heavy quarks and leptons. The major elements of this detector upgrade are the installation of a ``fast&#39;&#39; ring imaging Cherenkov detector, a new central drift chamber and a new barrel-style silicon st

M. Ouchrif

In this paper we present some features of Q-balls and we discuss their interactions with matter, and their energy losses in the Earth, for a large range of velocities. These calculations are used to compute the fractional geometrical acceptance of the MACRO detector. Furthermore a systematic analysis of the energy losses of Q-balls in three types of detector

U. S. Nilsson, C. Uggla

In this paper, the gravitational field equations for static spherically symmetric perfect fluid models with a polytropic equation of state, $p=kρ^{1+1/n}$, are recast into two complementary 3-dimensional {\it regular} systems of ordinary differential equations on compact state spaces. The systems are analyzed numerically and qualitatively, using the theory o

U. S. Nilsson, C. Uggla

In this paper Einstein&#39;s field equations, for static spherically symmetric perfect fluid models with a linear barotropic equation of state, are recast into a 3-dimensional regular system of ordinary differential equations on a compact state space. The system is analyzed qualitatively, using the theory of dynamical systems, and numerically. It is shown th

Akira Tomimatsu, Hiroko Koyama

We study vacuum polarization of quantized massive scalar fields $ϕ$ in equilibrium at black-hole temperature in Reissner-Nordström background. By means of the Euclidean space Green&#39;s function we analytically derive the renormalized expression $<ϕ^{2}>_{H}$ at the event horizon with the area $4πr_{+}^{2}$. It is confirmed that the polarization amplitude $

Jeremy Bryans, Howard Bowman, John Derrick

Modern distributed systems include a class of applications in which non-functional requirements are important. In particular, these applications include multimedia facilities where real time constraints are crucial to their correct functioning. In order to specify such systems it is necessary to describe that events occur at times given by probability distri

Deborah East, Miroslaw Truszczynski

Randomized algorithms for deciding satisfiability were shown to be effective in solving problems with thousands of variables. However, these algorithms are not complete. That is, they provide no guarantee that a satisfying assignment, if one exists, will be found. Thus, when studying randomized algorithms, there are two important characteristics that need to

Federico Ricci-Tersenghi, Daniel A. Stariolo, Jeferson J. Arenzon

We study the breakdown of fluctuation-dissipation relations between time dependent density-density correlations and associated responses following a quench in chemical potential in the Frustrated Ising Lattice Gas. The corresponding slow dynamics is characterized by two well separated time scales which are characterized by a constant value of the fluctuation

Gergely Zarand, Daniel L. Cox, Avraham Schiller

We present a procedure to calculate 1/d corrections to the two-particle properties around the infinite dimensional dynamical mean field limit. Our method is based on a modified version of the scheme of Ref. onlinecite{SchillerIngersent}}. To test our method we study the Hubbard model at half filling within the fluctuation exchange approximation (FLEX), a sel

Alessandro Cuccoli, Andrea Fubini, Valerio Tognetti, Ruggero Vaia

The effects of dissipation on the thermodynamic properties of nonlinear quantum systems are approached by the path-integral method in order to construct approximate classical-like formulas for evaluating thermal averages of thermodynamic quantities. Explicit calculations are presented for one-particle and many-body systems. The effects of the dissipation mec

Sebastian Risau-Gusman, Mirta B. Gordon

The learning properties of finite size polynomial Support Vector Machines are analyzed in the case of realizable classification tasks. The normalization of the high order features acts as a squeezing factor, introducing a strong anisotropy in the patterns distribution in feature space. As a function of the training set size, the corresponding generalization

P. Lajko, L. Turban

The finite-size scaling behaviour for percolation and conduction is studied in two-dimensional triangular-shaped random resistor networks at the percolation threshold. The numerical simulations are performed using an efficient star-triangle algorithm. The percolation exponents, linked to the critical behaviour at corners, are in good agreement with the confo

I. I. Mazin

The Fe_{x}Co_{1-x}S_{2} system is predicted, on the basis of density functional calculations, to be a half metal for a large range of concentrations. Unlike most known half metals, the half metallicity in this system should be very stable with respect to crystallographic disorder and other types of defects. The endmember of the series, CoS_{2}, is not a half

F. Nad, P. Monceau, C. Carcel, J. M. Fabre

Conductivity and permittivity of the quasi-one-dimensionsional organic transfer salt (TMTTF)2PF6 have been measured at low frequencies (10^3-10^7 Hz) between room temperature down to below the temperature of transition into the spin-Peierls state. We interpret the huge real part of the dielectric permittivity (up to 10^6) in the localized state as the realiz

M. Taut

We found that the two-dimensional Schrödinger equation for 3 electrons in an homogeneous magnetic field (perpendicular to the plane) and a parabolic scalar confinement potential (frequency $ω_0$) has exact analytical solutions in the limit, where the expectation value of the center of mass vector $\bf R$ is small compared with the average distance between th

J. C. Martinez, A. Schattke, M. Jourdan, G. Jakob

In this work we report c-axis conductance measurements done on a superlattice based on a stack of 2 layers YBa2Cu3O{7-δ} and 7 layers PrBa2Cu3O{7-δ} (2:7). We find that these quasi-2D structures show no clear superconducting coupling along the c-axis. Instead, we observe tunneling with a gap of Δ_c=5.0\pm 0.5 meV for the direction perpendicular to the superc

V. F. Gantmakher, M. V. Golubkov, V. T. Dolgopolov, G. E. Tsydynzhapov

We have studied the magnetic-field-tuned superconductor-insulator quantum transition (SIT) in amorphous In-O films with different oxygen content and, hence, different electron density. While for states of the film near the zero-field SIT the two-dimensional scaling behaviour is confirmed, for deeper states in the superconducting phase the SIT scenario change

C. J. Olson, N. Gronbech-Jensen

We use three-dimensional molecular dynamics simulations of magnetically interacting pancake vortices to study the dynamic phases of vortex lattices in highly anisotropic materials such as BSCCO. Our model treats the magnetic interactions of the pancakes exactly, with long-range logarithmic interactions both within and between planes. The pancake vortices dec

Bradford B. Behr, Judith G. Cohen, James K. McCarthy

High-resolution optical spectra of eighteen blue horizontal-branch (BHB) stars in the globular cluster M15 indicate that their stellar rotation rates and photospheric compositions vary strongly as a function of effective temperature. Among the cooler stars in the sample, at Teff ~ 8500 K, metal abundances are in rough agreement with the canonical cluster met

Valentin D. Ivanov, Jordanka Borissova, Almudena Alonso-Herrero, Tatiana Russeva

Infrared JKs-band photometry of the Galactic globular clusters M15 and, for the first time, M56 is presented. We estimated the reddening (E(B-V)=0.18+/-0.08 mag) and distance modulus ((m-M)_V=15.43+/-0.30 mag) towards the poorly studied globular cluster M56. We combined our data with observations of other clusters from the literature (12 in total) to extend

M. Kramer, B. Klein, D. R. Lorimer, P. Mueller

We report the status of a search for pulsars in the Galactic Centre, using a completely revised and improved high-sensitivity double-horn system at 4.85-GHz. We also present calculations about the success rate of periodicity searches for such a survey, showing that in contrast to conclusions in recent literature pulsars can be indeed detected at the chosen s

M. Kramer, K. M. Xilouris

We report the most recent progress in understanding the emission properties of millisecond pulsars.

Daniel Egret, Robert J. Hanisch, Fionn Murtagh

A growing number of astronomical resources and data or information services are made available through the Internet. However valuable information is frequently hidden in a deluge of non-pertinent or non up-to-date documents. At a first level, compilations of astronomical resources provide help for selecting relevant sites. Combining yellow-page services and

O. Petruk

Approximations of the Sedov self-similar solution for a strong point explosion in a medium with the power-law density distribution ρ^o\propto r^{-m} are reviewed and their accuracy are analyzed. Taylor approximation is extended to cases m\neq 0. Two approximations of the solution are presented in the Lagrangian coordinates for spherical, cylindrical and plan

L. E. Kuchinski, W. L. Freedman, Barry F. Madore, M. Trewhella

We have undertaken an imaging survey of 34 nearby galaxies in far-ultraviolet (FUV, ~1500A) and optical (UBVRI) passbands to characterize galaxy morphology as a function of wavelength. This sample, which includes a range of classical Hubble types from elliptical to irregular with emphasis on spirals at low inclination angle, provides a valuable database for

Marc Wenger, Francois Ochsenbein, Daniel Egret, Pascal Dubois

Simbad is the reference database for identification and bibliography of astronomical objects. It contains identifications, `basic data&#39;, bibliography, and selected observational measurements for several million astronomical objects. Simbad is developed and maintained by CDS, Strasbourg. Building the database contents is achieved with the help of several

Francois Bonnarel, Pierre Fernique, Olivier Bienayme, Daniel Egret

The Aladin interactive sky atlas, developed at CDS, is a service providing simultaneous access to digitized images of the sky, astronomical catalogues, and databases. The driving motivation is to facilitate direct, visual comparison of observational data at any wavelength with images of the optical sky, and with reference catalogues. The set of available sky

Tal Alexander, Dieter Lutz, Eckhard Sturm, Reinhard Genzel

The ISO-SWS 2.5-45 um infrared spectroscopic observations of the nucleus of the Seyfert 2 galaxy NGC 1068 (see companion paper) are combined with a compilation of UV to IR narrow emission line data to determine the spectral energy distribution (SED) of the obscured extreme-UV continuum that photoionizes the narrow line emitting gas in the active galactic nuc

A. Burkert, D. N. C. Lin

The radiative cooling of optically thin gaseous regions and the formation of a two-phase medium and of cold gas clouds with a clumpy substructure is investigated. In optically thin clouds, the growth rate of small isobaric density perturbations is independent of their length scale. However, the growth of a perturbation is limited by its transition from isoba

A. Accomazzi, G. Eichhorn, M. J. Kurtz, C. S. Grant

The powerful discovery capabilities available in the ADS bibliographic services are possible thanks to the design of a flexible search and retrieval system based on a relational database model. Bibliographic records are stored as a corpus of structured documents containing fielded data and metadata, while discipline-specific knowledge is segregated in a set

M. J. Kurtz, G. Eichhorn, A. Accomazzi, C. Grant

The NASA Astrophysics Data System Abstract Service has become a key component of astronomical research. It provides bibliographic information daily, or near daily, to a majority of astronomical researchers worldwide. We describe the history of the development of the system and its current status. We show several examples of how to use the ADS, and we show ho

C. Grant, A. Accomazzi, G. Eichhorn, M. J. Kurtz

Since its inception in 1993, the ADS Abstract Service has become an indispensable research tool for astronomers and astrophysicists worldwide. In those seven years, much effort has been directed toward improving both the quantity and the quality of references in the database. From the original database of approximately 160,000 astronomy abstracts, our datase

G. Eichhorn, M. J. Kurtz, A. Accomazzi, C. S. Grant

The ADS Abstract and Article Services provide access to the astronomical literature through the World Wide Web (WWW). The forms based user interface provides access to sophisticated searching capabilities that allow our users to find references in the fields of Astronomy, Physics/Geophysics, and astronomical Instrumentation and Engineering. The returned info

D. L. Clements

We have conducted observations of the environment around the z=2.15 radio loud quasar 1550-269 in search of distant galaxies associated either with it or the z=2.09 CIV absorber along its line of sight. Such objects will be distinguished by their red colours, R-K > 4.5. We find five such objects in a 1.5 arcmin^2 field around the quasar, with typical K&#39;

Paul R. Shapiro, Alejandro C. Raga

The first sources of ionizing radiation to condense out of the dark and neutral IGM sent ionization fronts sweeping outward through their surroundings, overtaking other condensed objects and photoevaporating them. This feedback effect of universal reionization on cosmic structure formation is demonstrated here for the case of a cosmological minihalo of dark

A. Karastergiou, M. Kramer, N. Wex, A. von Hoensbroech

A change of the component separation in the profiles of the binary pulsar PSR B1913+16 has been observed for the first time (Kramer 1998) as expected by geodetic precession. In this work we extend the previous work by accounting for recent data from the Effelsberg 100-m telescope and Arecibo Observatory and testing model predictions. We demonstrate how the n

Ewine F. van Dishoeck, Floris F. S. van der Tak

Recent observational studies of intermediate- and high-mass star-forming regions at submillimeter and infrared wavelengths are reviewed, and chemical diagnostics of the different physical components associated with young stellar objects are summarized. Procedures for determining the temperature, density and abundance profiles in the envelopes are outlined. A

Maria J. Rioja, Richard W. Porcas

We present results from 3.6 cm observations of the quasar pair 1038+528 A and B, made in 1995 using the VLBA together with the Effelsberg 100m telescope. We describe the use of a phase-referencing technique to measure the astrometric separation between the quasars. We also introduce a new data analysis method -&#34;hybrid double mapping&#34;- which preserves

D. Dultzin-Hacyan, P. Marziani, J. W. Sulentic

We review constraints on models of the broad line region that are imposed by observations of the emission lines in Active Galactic Nuclei. Comparison of high and low ionization lines in sources with FWHM Hbeta < 4000 km/s points toward low ionization line emission produced in a flattened geometry (the accretion disk?) with an associated high ionization wind.

Francoise Genova, Daniel Egret, Olivier Bienayme, Francois Bonnarel

The Centre de Donnees astronomiques de Strasbourg (CDS) provides homogeneous access to heterogeneous information of various origins: information about astronomical objects in Simbad; catalogs and observation logs in VizieR and in the catalogue service; reference images and overlays in Aladin; nomenclature in the Dictionary of Nomenclature; Yellow Page servic