July 2000 arXiv papers — page 20

The OPAL collaboration, G. Abbiendi

Searches for final states expected in models with light gravitinos have been performed, including experimental topologies with multi-leptons with missing energy, leptons and photons with missing energy, and jets and photons with missing energy. No excess over the expectations from the Standard Model has been observed. Limits are placed on production cross-se

Masafumi Fukuma, So Matsuura, Tadakatsu Sakai

We give a prescription for calculating the holographic Weyl anomaly in arbitrary dimension within the framework based on the Hamilton-Jacobi equation proposed by de Boer, Verlinde and Verlinde. A few sample calculations are made and shown to reproduce the results that are obtained to this time with a different method. We further discuss continuum limits, and

H. van Hees, Joern Knoll

We study the influence of the finite damping width of pions on the in-medium properties of the rho-meson in an interacting meson gas model at finite temperature. Using vector dominance also implications on the resulting dilepton spectra from the decay of the rho-meson are presented. A set of coupled Dyson equations with self energies up to the sunset diagram

G. Baskaran

A simple microscopic principle of `Valence bond (nearest neighbor singlet) amplitude maximization '(VBAM) is shown to be present in undoped and optimally doped cuprates and unify the very different orderings such as antiferromagnetism in the Mott insulator and the robust superconductivity accompanied by an enhanced charge and stripe correlations in the o

R. L. Willett, J. W. P. Hsu, D. Natelson, K. W. West

Surface morphology of high mobility heterostructures is examined and correlated with d.c. transport. {\it All} samples examined show evidence of lines in the [1$\bar{1}$0] direction with roughness ranging from small amplitude features to severe anisotropic ridges. Transport in these samples is consistent with that in samples having artificially induced 1D ch

M. Revnivtsev, M. Gilfanov, E. Churazov

We analyzed a large number of RXTE/PCA observations of Cyg X-1 in the hard and soft spectral states with total exposure time of ~190 and ~10 ksec respectively and time resolution better than ~250us in order to investigate its variability down to a few milliseconds time scales. The model of modifications of the power density spectra due to the dead time effec

Eleonora Alfinito, Rosario G. Viglione, Giuseppe Vitiello

The decoherence mechanism signals the limits beyond which the system dynamics approaches the classical behavior. We show that in some cases decoherence may also signal the limits beyond which the system dynamics has to be described by quantum field theory, rather than by quantum mechanics.

Olaf Stenull, Hans-Karl Janssen

We study the multifractal moments of the current distribution in randomly diluted resistor networks near the percolation treshold. When an external current is applied between to terminals $x$ and $x^\prime$ of the network, the $l$th multifractal moment scales as $M_I^{(l)} (x, x^\prime) \sim | x - x^\prime |^{ψ_l /ν}$, where $ν$ is the correlation length exp

Roman Juszkiewicz, Enrique Gaztanaga

We present two new dynamical tests of the biasing hypothesis. The first is based on the amplitude and the shape of the galaxy-galaxy correlation function, $ξ_g(r)$, where $r$ is the separation of the galaxy pair. The second test uses the mean relative peculiar velocity for galaxy pairs, $\vs(r)$. This quantity is a measure of the rate of growth of clustering

N. Moussy, H. Courtois, B. Pannetier

We present the design and operation of a very-low temperature Scanning Tunneling Microscope (STM) working at $60 mK$ in a dilution refrigerator. The STM features both atomic resolution and micron-sized scanning range at low temperature. This work is the first experimental realization of a local spectroscopy of mesoscopic structures at very low temperature. W

M. Bauer, O. Golinelli

We study numerically and analytically the spectrum of incidence matrices of random labeled graphs on N vertices : any pair of vertices is connected by an edge with probability p. We give two algorithms to compute the moments of the eigenvalue distribution as explicit polynomials in N and p. For large N and fixed p the spectrum contains a large eigenvalue at

Sandra Chapman, Nicholas Watkins

The characterization of global energy storage and release in the coupled solar wind-magnetosphere system remains one of the fundamental problems of space physics.Recently, it has been realised that a new paradigm in physics, that of Self Organised Criticality (SOC) may encapsulate the mixing and merging of flux on many scales in the magnetotail prompting bur

M. D. Nunez-Regueiro, C. Lacroix

Non-conventional mechanisms have been recently invoked in order to explain the ferromagnetic ground state of A2Mn2O7 pyrochlores (A=Y, In, Lu and Tl) and the puzzling decrease of their Curie temperatures with applied pressure. Here we show, using a perturbation expansion in the Mn-O hopping term, that both features can be understood within the superexhange m

Heinz Horner

Low temperature and low frequency properties of a spin-boson model are investigated within a super operator and Liouville space formulation. The leading contributions are identified with the help of projection operators projecting onto the equilibrium state. The quantities of interest are expressed in terms of weighted bath propagators and static linear and

Takahiro Miura, Eiichi Takasugi, Masaki Yoshimura

We investigate the quantum effects for the democratic-type neutrino mass matrix given at the right-handed neutrino mass scale $m_R$ in order to see (i) whether $θ_{23}=-π/4$ predicted by the model is stable to explain the atmospheric neutrino anomaly, (ii) how $θ_{12}$ and $θ_{13}$ behave, and (iii) whether the predicted Dirac CP phase $δ$ keeps maximal size

R. Foot

Recently the SuperKamiokande collaboration have claimed that their data exclude the $ν_μ--> ν_s$ solution to the atmospheric neutrino anomaly at more than 99% C.L. We critically examine this claim.

T. Pradhan

It is shown that the excited states of hydrogen atom in a uniform electric field (Stark States) posess magnetic charge whose magnitude is given by a Dirac-Saha type relation: $$ {eg\over \hbar c} = \sqrt 3 n $$ An experiment is proposed to fabricate such states and to detect their magnetic charge.

Farhan Saif

We study the phase space of periodically modulated gravitational cavity by means of quantum recurrence phenomena. We report that the quantum recurrences serve as a tool to connect phase space of the driven system with spectrum in quantum domain. With the help of quantum recurrences we investigate the quasi-energy spectrum of the system for a certain fixed mo

Luigi Accardi, Massimo Regoli

Starting from the late 60's many experiments have been performed to verify the violation Bell's inequality by Einstein-Podolsky-Rosen (EPR) type correlations. The idea of these experiments being that: (i) Bell's inequality is a consequence of locality, hence its experimental violation is an indication of non locality; (ii) this violation is a typ

Armin Uhlmann

Simultaneous decompositions of a pair of states into pure ones are examined. There are privileged decompositions which are distinguished from all the other ones.

Mark Dewing

A two level sampling method is applied to variational Monte Carlo (VMC) that samples the one and two body parts of the wave function separately. The method is demonstrated on a single Li_2 molecule in free space and 32 H_2 molecules in a periodic box. This simple modification increases the efficiency of a VMC simulation by up to 72%.

C. Nantista, C. Adolphsen, R. L. Brown, R. Fuller

The transverse current profile in the Next Linear Collider Test Accelerator (NLCTA) electron beam can be monitored at several locations along the beam line by means of profile monitors. These consist of insertable phosphor screens, light collection and transport systems, CID cameras, a frame-grabber, and PC and VAX based image analysis software. In addition

Judith A. McGovern, Michael C. Birse, K. B. Vijaya Kumar

We present a calculation of the fourth-order (NLO) contribution to spin-dependent Compton scattering in heavy-baryon chiral perturbation theory, and we give results for the four spin polarisabilities. These results have been presented before, in hep-ph/0002133. Here we address the issue of whether one-particle reducible graphs in the heavy baryon theory cont

W. Cassing

The production and decay of vector mesons ($ρ, ω$) in $pA$ reactions at COSY energies is studied with particular emphasis on their in-medium spectral functions. It is explored within transport calculations, if hadronic in-medium decays like $π^+π^-$ or $π^0 γ$ might provide complementary information to their dilepton ($e^+e^-$) decays. Whereas the $π^+ π^-$

E877 Collaboration

New data on Lambda production in Au+Au collisions at 11.5 A GeV/c are presented. The measurements cover the rapidity range from y=2.0 to 3.5 and transverse momenta from pt=0.15 GeV/c to 1.5 GeV/c. The rapidity distributions, transverse momentum spectra, and azimuthal distributions are presented for different centralities of the collision. A strong positive d

M. V. Pomazanov

We study the systems of ordinary differential equations which are implicit with respect to the higher derivatives, appearing in the linear form, and their solutions near the singular points. The invertibility of the higher derivatives reduces to the singular surface where the theorem of uniqueness and existence is violated.A set of the singular solution is o

Dror Bar-Natan, Ruth Lawrence

We write a formula for the LMO invariant of a rational homology sphere presented as a rational surgery on a link in S^3. Our main tool is a careful use of the Aarhus integral and the (now proven) "Wheels" and "Wheeling" conjectures of B-N, Garoufalidis, Rozansky and Thurston. As steps, side benefits and asides we give explicit formulas for th

B. L. Cerchiai, G. Fiore, J. Madore

We sketch our recent application of a non-commutative version of the Cartan `moving-frame' formalism to the quantum Euclidean space $R^N_q$, the space which is covariant under the action of the quantum group $SO_q(N)$. For each of the two covariant differential calculi over $R^N_q$ based on the $R$-matrix formalism, we summarize our construction of a fra

Wendelin Werner

In this review paper, we first discuss some open problems related to two-dimensional self-avoiding paths and critical percolation. We then review some closely related results (joint work with Greg Lawler and Oded Schramm) on critical exponents for two-dimensional simple random walks, Brownian motions and other conformally invariant random objects.

S. V. Astashkin

It is shown that a specific ordering of the Rademacher chaos leads to a basic sequence in a wide class of symmetric spaces on the segment [0,1]. Necessary and sufficient conditions on a such space are found for Rademacher chaos to possess the unconditionality property.

G. Arutyunov, A. Pankiewicz, S. Theisen

We determine the AdS exchange diagrams needed for the computation of 4--point functions of chiral primary operators in the SCFT_2 dual to the D=6 N=4b supergravity on the AdS_3\times S^3 background and compute the corresponding cubic couplings. We also address the issue of consistent truncation.

A. A. Khelashvili

Homogeneous Bethe-Salpeter equation for simplest Wick-Cutkosky model is studied in the case when the mass of the two-body system is more then the sum of constituent particles masses. It is shown that there is always a small attraction between the like-sigh charged particles as a pure relativistic effect. If the coupling constant exceeds some critical values

Sergio Ferrara, Emery Sokatchev

We carry out a general analysis of the representations of the superconformal algebras OSp(8/4,R) and OSp(8*/2N) in terms of harmonic superspace. We present a construction of their highest-weight UIR's by multiplication of the different types of massless conformal superfields ("supersingletons"). Particular attention is paid to the so-called "

V. A. Kudryavtsev

It is considered here the possibility of unitary spinor representations of the Virasoro and super-Virasoro algebras for conformal spin to be equal 1/k; k are integers.

Charles M. Sommerfield, Hisakazu Minakata

The exact wave functions that describe scattering of a charged particle by a confined magnetic field (Aharonov-Bohm effect) and by a Coulomb field are analyzed. It is well known that the usual procedure of finding asymptotic forms of these functions which admit a separation into a superposition of an incident plane wave and a circular or spherical scattered

S. G. Rubin

The dynamics of false vacuum decay at the end of inflation is studied. It is shown that the creation of a new phase is mainly stimulated by temperature fluctuations. Moving walls of O(3)-symmetric bubbles weakly interact with their surroundings at the inflation stage. Large field fluctuations might arise as a result of wall collisions.

F. M. Steffens

We present a simple and intuitive picture for the deconfinement of quarks and gluons at finite temperature: as the temperature increases, QCD behaves like QED at T=0. We show this by calculating the QCD coupling constant as a function of the temperature and of the external momenta used to probe quarks and gluons.

Howard Baer, J. K. Mizukoshi, Xerxes Tata

We examine the reach of the CERN LHC pp collider for supersymmetric models where the dominant contribution to soft SUSY breaking parameters arises from the superconformal anomaly. In the simplest viable anomaly mediated SUSY breaking (AMSB) model, tachyonic slepton squared masses are made positive by adding a universal contribution m_0^2 to all scalars. We u

H. Arthur Weldon

The thermal Green function $D^{μν}(x)$ for free, massless gauge bosons is computed exactly in a variety of gauges (Feynman, covariant, Coulomb, and Landshoff-Rebhan). At large temporal separations it falls exponentially. At large spatial separations it falls like $T/r$. In contrast, the zero-temperature propagator falls quadratically in both regimes, being p

Helmut Satz

QCD predicts that strongly interacting matter will undergo a transition from a state of hadronic constituents to a plasma of unbound quarks and gluons. We first survey the conceptual features of this transition and its description in finite temperature lattice QCD, before we address its experimental investigation through high energy nucleus-nucleus collision

D. de Florian, R. Sassot

We perform a combined next to leading order analysis to both inclusive and semi-inclusive polarized deep inelastic scattering data, assessing the impact of new data in the extraction of the sea quark and gluon spin dependent densities. In particular, we find that semi-inclusive data show a clear preference for a positive 'Delta ubar' distribution, al

Vacca Gian Paolo

A general relation between families of (n+1) gluon and n gluon eigenstates of the BKP evolution kernels in the multicolour limit of QCD is derived. It allows to construct an (n+1) gluon eigenstate if an n gluon eigenstate is known; this solution is Bose symmetric and thus physical for even n. A recently found family of odderon solutions corresponds to the pa

D. H. Huang, W. B. Lin, X. M. Zhang

We re-examine approximations in the analytical calculation of the primordial spectrum of cosmological perturbation produced during inflation. Taking two inflation models (chaotic inflation and natural inflation) as examples, we numerically verify the accuracy of these approximations.

Cheng-Wei Chiang, Frederick J. Gilman

The decays K_{L,S} -> π^o π^o ν\barν and K_{L,S} -> π^+ π^- ν\barν involve the weak transition from a strange to a non-strange quark. Although they have considerably smaller branching ratios than those for the corresponding rare processes involving single pions, some may be more distinguishable experimentally from background processes and thus could provide

A. Belyaev

The prospects of single top quark physics at colliders of the TeV energy scale are discussed. Single top quark study allows a direct measurement of the $Wtb$ vertex and a precise probing physics beyond the Standard Model in various scenarios.

B. A. Berg, E. Bittner, M. -P. Lombardo, H. Markum

We investigate the eigenvalue spectrum of the staggered Dirac matrix in SU(3) gauge theory and in full QCD as well as in quenched U(1) theory on various lattice sizes. As a measure of the fluctuation properties of the eigenvalues, we consider the nearest-neighbor spacing distribution, $P(s)$. We further study two-color QCD at nonzero chemical potential, $μ$,

B. Delcourt

The charge of the leading particle in DIS interactions is studied with the QCD models LEPTO, ARIADNE, RAPGAP and HERWIG. It is predicted to be preferentially positive, as is expected from the modified quark parton model and is studied over a wide range of x and Q^2.

K. W. Edwards, CLEO Collaboration

In a sample of $9.66\times 10^6 B\bar{B}$ pairs collected with the CLEO detector we make the first observation of B decays to an $η_c$ and a kaon. We measure branching fractions $BR(B^+\toη_c K^+) = (0.69 + 0.26 - 0.21 +- 0.08 +- 0.20)\times 10^{-3}$ and $BR(B^0\toη_c K^0) = (1.09 + 0.55 - 0.42 +- 0.12 +- 0.31)\times 10^{-3}$, where the first error is statis

Samir D. Mathur

The recent progress in string theory strongly suggests that formation and evaporation of black holes is a unitary process. This fact makes it imperative that we find a flaw in the semiclassical reasoning that implies a loss of information. We propose a new criterion that limits the domain of classical gravity: the hypersurfaces of a foliation cannot be stret

Janos Kannar

The existence of symmetries in asymptotically flat space-times are studied from the point of view of initial value problems. General necessary and sufficient (implicit) conditions are given for the existence of Killing vector fields in the asymptotic characteristic and in the hyperboloidal initial value problem (both of them are formulated on the conformally

Clarissa-Marie Claudel

It is standard assertion in relativity that, subject to an energy condition and the cosmic censorship hypothesis, closed trapped surfaces are not visible from future null infinity. A proof given by Hawking & Ellis in ''The Large Scale Structure of Space-Time'' is flawed since it is formulated in terms of an inadequate definition of a weakly a

Gerald Penn

Constraint Handling Rules (CHR) have provided a realistic solution to an over-arching problem in many fields that deal with constraint logic programming: how to combine recursive functions or relations with constraints while avoiding non-termination problems. This paper focuses on some other benefits that CHR, specifically their implementation in SICStus Pro

Francis Wolinski, Frantz Vichot, Mathieu Stricker

For years, Caisse des Depots et Consignations has produced information filtering applications. To be operational, these applications require high filtering performances which are achieved by using rule-based filters. With this technique, an administrator has to tune a set of rules for each topic. However, filters become obsolescent over time. The decrease of

Gerard Escudero, Lluis Marquez, German Rigau

This paper describes an experimental comparison between two standard supervised learning methods, namely Naive Bayes and Exemplar-based classification, on the Word Sense Disambiguation (WSD) problem. The aim of the work is twofold. Firstly, it attempts to contribute to clarify some confusing information about the comparison between both methods appearing in

Gerard Escudero, Lluis Marquez, German Rigau

In this paper Schapire and Singer's AdaBoost.MH boosting algorithm is applied to the Word Sense Disambiguation (WSD) problem. Initial experiments on a set of 15 selected polysemous words show that the boosting approach surpasses Naive Bayes and Exemplar-based approaches, which represent state-of-the-art accuracy on supervised WSD. In order to make boosti

D. N. Aristov, S. V. Maleyev

Dzyaloshinskii-Moriya (DM) interaction in the paramagnetic state leads to the incommensurate spin fluctuations with incommensurate vector proportional to the relative strength of the DM interaction. We show that the DM interaction leads to helical spin fluctuations which may be observed by the polarized neutron scattering.

Belen Valenzuela, Maria A. H. Vozmediano

The deformation of the Fermi surface induced by Coulomb interactions is investigated in the t-t'-Hubbard model. The interplay of the local U and extended V interactions is analyzed. It is found that exchange interactions V enhance small anisotropies producing deformations of the Fermi surface which break the point group symmetry of the square lattice at

Aiman Al-Omari, A. H. Nayyar

A linear spin wave analysis of dimerization of alternating Heisenberg system with spins $s_{1}$ and $s_{2}$ on linear chain as well as square lattice is presented. Among the several possible dimerized configurations considered in two dimensions the plaquette configuration is found to be energetically the most favored one. Inclusion of a variable nearest neig

Marek Cieplak, Joel Koplik, Jayanth R. Banavar

Novel technological applications often involve fluid flows in the Knudsen regime in which the mean free path is comparable to the system size. We use molecular dynamics simulations to study the transition between the dilute gas and the dense fluid regimes as the fluid density is increased.

Romualdo Pastor-Satorras, Alessandro Vespignani

We perform large-scale simulations of directed sandpile models with both deterministic and stochastic toppling rules. Our results show the existence of two distinct universality classes. We also provide numerical simulations of directed models in the presence of bulk dissipation. The numerical results indicate that the way in which dissipation is implemented

Audun Bakk, Alex Hansen, Kim Sneppen

We explain the physical basis of a model for small globular proteins with water interactions. The water is supposed to access the protein interior in an "all-or-none" manner during the unfolding of the protein chain. As a consequence of this mechanism (somewhat speculative), the model exhibits fundamental aspects of protein thermodynamics, as cold, a

Francesco Ancilotto, Fabio Faccin, Flavio Toigo

We have studied the wetting properties of He4 adsorbed on the surface of heavy alkali metals by using a non-local free-energy density-functional which describes accurately the surface properties of liquid He4 in the temperature range 0<T<3 K.Our results for He4 on the Cs surface give both the temperature dependence of the contact angle and the wetting temper

A. Brunello, F. Dalfovo, L. Pitaevskii, S. Stringari

We propose an experiment, based on two consecutive Bragg pulses, to measure the momentum distribution of quasiparticle excitations in a trapped Bose gas at low temperature. With the first pulse one generates a bunch of excitations carrying momentum $q$, whose Doppler line is measured by the second pulse. We show that this experiment can provide direct access

A. Malevanets, J. M. Yeomans

We present numerical and analytical results describing the effect of hydrodynamic interactions on the dynamics of a short polymer chain in solution. A molecular dynamics algorithm for the polymer is coupled to a direct simulation Monte Carlo algorithm for the solvent. We give an explicit expression for the velocity autocorrelation function of the centre of m

K. E. Nagaev, M. Buttiker

We present a semiclassical theory of shot noise in diffusive superconductor - normal metal contacts. At subgap voltages, we reproduce the doubling of shot noise with respect to conventional normal-metal contacts, which is interpreted in terms of an energy balance of electrons. Above the gap, the voltage dependence of the noise crosses over to the standard on

Bora Orcal, Erkan Tuzel, Volkan Sevim, Naeem Jan

An asexual set of primitive bacteria is simulated with a bit-string Penna model with a Fermi function for survival. A recent hypothesis by Jan, Stauffer and Moseley on the evolution of sex from asexual cells as a strategy for trying to escape the effects of deleterious mutations is checked. This strategy is found to provide a successful scenario for the evol

Manas Sardar, Satadeep Bhattacharjee

Recently it is seen\cite{Nature},that both $\rm{T}_c$ and the buckling of the $CuO_2$ planes goes through a maximum at the same doping level. We show that only for optimal doping concentration the Fermi surface touches the M($0,π$) point in the BZ, where the matrix element for interlayer pair tunneling amplitude is largest, so that the gain in delocalization

Satadeep Bhatttacharjee, Manas Sardar

We point out in this short communique, that be it a s-wave or d-wave superconductor, in a non equalibrium situation(i.e. in presence of excess unpolarised/polarised quasi-particles maintained by an injection current) the superconducting gap suppresion by the presence of same amount excess quasi-particles, can at best differ by a factor of 2, for a convention

J. E. Hirsch

Photoemission experiments in high $T_c$ cuprates indicate that quasiparticles are heavily &#39;dressed&#39; in the normal state, particularly in the low doping regime. Furthermore these experiments show that a gradual undressing occurs both in the normal state as the system is doped and the carrier concentration increases, as well as at fixed carrier concent

Kay Joerg Wiese

In this article, we introduce a generalization of the diffusive motion of point-particles in a turbulent convective flow with given correlations to a polymer or membrane. In analogy to the passive scalar problem we call this the passive polymer or membrane problem. We shall focus on the expansion about the marginal limit of velocity-velocity correlations whi

P. Meszaros, M. J. Rees

Sub-photospheric internal shocks and transverse differences of the bulk Lorentz factor in relativistic fireball models of GRB lead to neutron diffusion relative to protons, resulting in inelastic nuclear collisions. This produces significant fluxes of ~3 GeV muon neutrinos (antineutrinos) and ~2 GeV electron neutrinos (antineutrinos), scaling with the Lorent

Wayne R. Lundberg

Results from string theory conclude that a spatial dimension R is equivalent to *&#39;/R. If R is considered as a four-space dimension, several interesting results emerge. In this paradigm, *&#39;/R exists in a time-reversed, &#34;anti- parallel&#34; universe. Cosmological distances in our real-time universe are equivalent to the compact dimensions at the in

Gaspar Galaz

Recently acquired near-IR imaging (J and Ks) of low surface brightness galaxies is presented. The data includes 52 galaxies with log[MHI/Msolar] < 9.0 and 58 galaxies with log[MHI/Msolar] > 9.5. These galaxies have been selected from the catalogue of Impey et al. (1996), and all of them are observable from both hemispheres. The principal goal of this researc

T. Joseph W. Lazio, Alan L. Fey, R. A. Gaume

We review observational constraints on the structures responsible for extreme scattering events, focussing on a series of observations of the quasar PKS 1741-038. VLA observations were conducted to search for changes in the rotation measure and H I absorption during the ESE, while VLBI observations sought ESE-induced changes in the source&#39;s image. No RM

C. Trigilio, P. Leto, F. Leone, G. Umana

Radio observations of the magnetic chemically peculiar star CU Vir, carried out with the VLA in three different days, show that the radio emission at 20 cm is characterized by a strong enhancement at particular rotational phases. This radio emission is found to be right hand polarized with a degree of polarization close to 100 %. As common for this class of

Guy Pelletier, Evy Kersale

Gamma-Ray Bursts are good candidates of the ``bottom up&#39;&#39; scenario for the generation of the UHE Cosmic Rays. In the most discussed model of GRBs, namely the ``fireball&#39;&#39; model, a highly relativistic shock forms and seems capable of accelerating the cosmic rays up to the EeV range. However, only the first Fermi cycle produces a large energy g

I. Zinchenko, C. Henkel, R. Q. Mao

We surveyed 81 dense molecular cores associated with regions of massive star formation and Sgr A in the 5_{05}-4_{04} and 10_{010}-9_{09} lines of HNCO. Line emission was detected towards 57 objects. Selected subsamples were also observed in other HNCO lines covering a frequency range from 22 to 461 GHz. HNCO lines from the K_{-1} = 2,3 ladders were detected

K. Werner, J. Deetjen

We present the first non-LTE model atmospheres for neutron stars (NS). We study their structure and NLTE effects on the emergent thermal radiation of old isolated NS.

Carlos Feinstein, Gustavo Baume, Ruben Vazquez, Virpi Niemela

We have carried out multicolor linear polarimetry (UBVRI) of the brightest stars in the area of the open cluster Trumpler 27. Our data show a high level of polarization in the stellar light with a considerable dispersion, from $P = 4%$ to $P = 9.5%$. The polarization vectors of the cluster members appear to be aligned. Foreground polarization was estimated f

Friedrich Meyer, Bifang Liu, Emmi Meyer-Hofmeister

We present a model for a corona above a geometrically thin standard disk around a black hole. This corona is fed by matter from the thin disk which evaporates from the cool layers underneath. An equilibrium establishes between the cool accretion stream and the hot flow. In the inner region evaporation becomes so efficient that at low accretion rates all matt

Anna Wolter, Gabriele Ghisellini, Gianpiero Tagliaferri, Fabrizio Tavecchio

The bright X-ray selected BL Lac object 1ES1101--232 shows a flat X-ray spectrum, making it detectable with high statistics over the wide BeppoSAX energy range. We have observed it in two different epochs with BeppoSAX, and found a variation of the flux of about 30% that can be explained by a change in the spectral index above the synchrotron peak. We presen

Volker Beckmann, Anna Wolter

We present results for the Hamburg BL Lac sample, based on data provided by the RASS-BSC. By fitting a single power law to the X-ray data we find, in a number of objects, an additional absorbing component to the galactic value of NH, which might be attributed to intrinsic absorption. A more probable cause seems however to be a curvature in the X-ray spectra

H. Korhonen, S. V. Berdyugina, T. Hackman, K. G. Strassmeier

We present new surface (Doppler) images of the late-type single giant FK Com for June-July 1996, July-August 1996, April 1997 and June 1997. These images are compared with the previously published images from 1994 and 1995. The consecutive maps are cross-correlated to see the possible migration of the spots and the effects of differential rotation. The cross

Chris Pearson

Using new cosmological models for galaxy evolution, predictions for the next generation of deep mid-IR surveys are presented for both the ASTRO-F space telescope (due for launch 2003) and the proposed HII/L2 mission (2010). Although ASTRO-F will be able to detect between 20,000-40,000 sources in the mid-IR, deep surveys will be severely constrained by confus

Junichiro Makino

In this paper we describe the current status of the GRAPE-6 project to develop a special-purpose computer with a peak speed exceeding 100 Tflops for the simulation of astrophysical N-body problems. One of the main targets of the GRAPE-6 project is the simulation of dense stellar systems. In this paper, therefore, we overview the basic algorithms we use for t

Isao Takahashi, Yasushi Fukazawa, Keiichi Kodaira, Kazuo Makishima

X-ray observations of three Shakhbazyan&#39;s Compact Groups of Galaxies, SCGG 202, SCGG 205, and SCGG 223, are presented for the first time. Extended X-ray emission was detected from SCGG 202 and SCGG 223 with 0.5-2 keV luminosity of 1E42 erg/s and 3E42 erg/s (for H_0 = 75 km/s/Mpc), respectively, while no significant emission was detected from SCGG 205 wit

Hiranya V. Peiris

Fitting Galactic structure models to star counts only provides useful information about the Galaxy in some directions. In this paper, we investigate the use of $χ^2$ goodness-of-fit tests to discriminate between degenerate Galactic structure models, and the implications of this technique for the Galactic spheroid and thick disk components. The axis ratio of

Lieven M. K. Vandersypen, Matthias Steffen, Gregory Breyta, Costantino S. Yannoni

We report the realization of a nuclear magnetic resonance (NMR) quantum computer which combines the quantum Fourier transform (QFT) with exponentiated permutations, demonstrating a quantum algorithm for order-finding. This algorithm has the same structure as Shor&#39;s algorithm and its speed-up over classical algorithms scales exponentially. The implementat

Shyamoli Chaudhuri

We show that the recent world-sheet analysis of the quantum fluctuations of a short flux tube in type II string theory leads to a simple and precise description of a pair of stuck D0branes in an orientifold compactification of the type I&#39; string theory. The existence of a stable type I&#39; flux tube of sub-string-scale length is a consequence of the con

Tsunehide Kuroki, Soo-Jong Rey

We explore some aspects of causal time-delay in open string scattering studied recently by Seiberg, Susskind and Toumbas. By examining high-energy scattering amplitudes at higher order in perturbation theory, we argue that causal time-delay at G-th order is 1/(G+1) times smaller than the time-delay at tree level. We propose a space-time interpretation of the

Eric Bergshoeff, Renata Kallosh, Antoine Van Proeyen

We develop the concept of supersymmetry in singular spaces, apply it in an example for 3-branes in D=5 and comment on 8-branes in D=10. The new construction has an interpretation that the brane is a sink for the flux and requires adding to the standard supergravity a (D-1)-form field and a supersymmetry singlet field. This allows a consistent definition of s

O. W. Greenberg

I discuss theories of violations of statistics, including intermediate statistics, parastatistics, parons, and quons. I emphasize quons, which allow small violations of statistics. I analyze the quon algebra and its representations, implications of the algebra including the observables allowed by the superselection rule separating inequivalent representation

D. S. Berman, P. Sundell

The dual supergravity description of the flow between (2,0) five-brane theory and the noncommutative five-brane (OM) theory is examined at critical five-brane field strength. The self-duality of the field strength is shown to arise as a consequence of the supergravity solution. Open membrane solutions are examined in the background of the five-brane giving r

Ioannis Giannakis, Hai-cang Ren

We solve the Einstein equations in the Randall-Sundrum framework with a static, spherically symmetric matter distribution on the {\it physical brane} and obtain an approximate expression for the gravitational field outside the source to second order in the gravitational coupling. This expression when confined on the {\it physical brane} coincides with the st

Zahid Zakir

The paper was a preliminary and rejected by the author attempt to describe compact relativistic objects.

Daniel Kabat, Gilad Lifschytz, David A. Lowe

We develop an approximation scheme for the quantum mechanics of N D0-branes at finite temperature in the &#39;t Hooft large-N limit. The entropy of the quantum mechanics calculated using this approximation agrees well with the Bekenstein-Hawking entropy of a ten-dimensional non-extremal black hole with 0-brane charge. This result is in accord with the dualit

A. A. Bichl, J. M. Grimstrup, H. Grosse, L. Popp

We introduce the notion of superoperators on noncommutative R^4 and re-investigate in the framework of superfields the noncommutative Wess-Zumino model as a quantum field theory. In a highly efficient manner we are able to confirm the result that this model is renormalizable to all orders.

Violeta Gotcheva, S. Teitel

We use Monte Carlo simulations of the 2D one component Coulomb gas on a triangular lattice, to study the depinning transition of a 2D vortex lattice in a commensurate periodic potential. A detailed finite size scaling analysis indicates this transition to be first order. No significant changes in behavior were found as vortex density was varied over a wide r

Tatiana A. Ivanova, Olaf Lechtenfeld

It is known for ten years that self-dual Yang-Mills theory is the effective field theory of the open N=2 string in 2+2 dimensional spacetime. We uncover an infinite set of abelian rigid string symmetries, corresponding to the symmetries and integrable hierarchy of the self-dual Yang-Mills equations. The twistor description of the latter naturally connects wi

J. P. Halpern, E. V. Gotthelf, K. M. Leighly, D. J. Helfand

The identity of the persistent EGRET sources in the Galactic plane is largely a mystery. For one of these, 3EG J2227+6122, our complete census of X-ray and radio sources in its error circle reveals a remarkable superposition of an incomplete radio shell with a flat radio spectrum, and a compact, power-law X-ray source with photon index Gamma = 1.5 and with n