May 1997 arXiv papers — page 11

S. Dusini, F. Ferrari, I. Lazzizzera, P. Lee

It is being proved that the neurochip \Totem{} is a viable solution for high quality and real time computational tasks in HEP, including event classification, triggering and signal processing. The architecture of the chip is based on a "derivative free" algorithm called Reactive Tabu Search (RTS), highly performing even for low precision weights. ISA

Serge Droz, Eric Poisson

We ascertain the effectiveness of the second post-Newtonian approximation to the gravitational waves emitted during the adiabatic inspiral of a compact binary system as templates for signal searches with kilometer-scale interferometric detectors. The reference signal is obtained by solving the Teukolsky equation for a small mass moving on a circular orbit ar

N. Bishop, R. Gomez, L. Lehner, J. Winicour

We treat the calculation of gravitational radiation using the mixed timelike-null initial value formulation of general relativity. The determination of an exterior radiative solution is based on boundary values on a timelike worldtube $Γ$ and on characteristic data on an outgoing null cone emanating from an initial cross-section of $Γ$. We present the detail

J P Wilson

Colombeau's theory of generalised functions is used to calculate the contributions, at the rotation axis, to the distributional curvature for a time-dependent radiating cosmic string, and hence the mass per unit length of the string source. This mass per unit length is compared with the mass at null infinity, giving evidence for a global energy conservat

A. Mikovic

We find the general solution of equations of motion for self-gravitating spherical null dust as a perturbative series in powers of the outgoing matter energy-momentum tensor, with the lowest order term being the Vaidya solution for the ingoing matter. This is done by representing the null-dust model as a 2d dilaton gravity theory, and by using a symmetry of

B. V. Ivanov

It is shown that there are three vacuum and one electrovacuum solutions of diagonal plane waves with M=0 and constant Maxwell scalars. Namely, these are the single wave, Stoyanov, Babala and Bell-Szekeres solutions. A comparison is made with the planar solutions of Taub.

Masaru Shibata, Keisuke Taniguchi

Using the ellipsoidal model for the density configuration, we calculate the equilibrium sequence of the corotating binary stars of the polytropic equation of state in the first post-Newtonian approximation of general relativity. After we calibrate this model by comparing with previous numerical results, we perform the stability analysis by calculating the en

Keisuke Taniguchi, Masaru Shibata

We analytically calculate the equilibrium sequence of the corotating binary stars of incompressible fluid in the first post-Newtonian(PN) approximation of general relativity. By calculating the total energy and total angular momentum of the system as a function of the orbital separation, we investigate the innermost stable circular orbit for corotating binar

M. Abolfath, J. J. Palacios, H. A. Fertig, S. M. Girvin

We report on a study of the classical field theory description of charged skyrmions in quantum Hall ferromagnets. The appropriate field theory is a non-linear $σ$ model generalized to include Coulomb and Zeeman interaction terms. We have tested the range of validity of the classical field theory by comparing with microscopic descriptions of the single skyrmi

O. Tchernyshyov

I present a simple analytical model describing the normal state of a superconductor with a pseudogap in the density of states, such as in underdoped cuprates. In nearly two-dimensional systems, where the superconducting transition temperature is reduced from the mean-field BCS value, Cooper pairs may be present as slow fluctuations of the BCS pairing field.

A. V. Postnikov, G. Borstel

In order to arrive at ultimately accurate results available with the LMTO method in the local density approximation, the stability of full-potential LMTO predictions for off-center displacements in KNbO3, as depending on the choice of basis and expansion cutoffs, has been thoroughly investigated. With the calculation setup thus optimized, supercell frozen ph

Martin P. Gelfand, Rajiv R. P. Singh

We study the uniform magnetic susceptibility and spin-gap for recently proposed Heisenberg model Hamiltonians for CaV_4O_9 based on the orbital ordering scenario of Marini and Khomskii and the LDA calculations of Pickett. We argue that the experimentally observed uniform susceptibility data is inconsistent with the weakly coupled dimer picture of Marini and

M. A. Garcia-Bach, R. Valenti, D. J. Klein

Distortions in a family of conjugated polymers are studied within two complementary approaches, i.e. within a many-body Valence Bond (VB) approach using a transfer matrix technique to treat the Heisenberg model of the systems, and also in terms of the tight-binding band-theoretic model with interactions limited to nearest neighbors. The computations indicate

Jesper Lykke Jacobsen

In a recent paper by Wu (Phys. Lett. A 228, 43-47 (1997)) the three-point correlation of the q-state Potts model on a planar graph was related to ratios of dual partition functions under fixed boundary conditions. It was claimed that the method employed could straightforwardly be applied to higher correlations as well; this is however not true. By explicitly

Frederic Mila, Charles Stafford, Sylvain Capponi

Persistent currents in a Moebius ladder are shown to be very sensitive to the effects of intrachain interactions on the hopping of electrons between chains. Their periodicity as a function of flux is doubled for strong enough repulsive interactions because electrons cannot hop coherently between the chains and have to travel along the full edge of the Moebiu

J. Fernandez-Rossier, C. Tejedor

We present a theoretical analysis of a spin-dependent multicomponent condensate in two dimensions. The case of a condensate of resonantly photoexcited excitons having two different spin orientations is studied in detail. The energy and the chemical potentials of this system depend strongly on the spin polarization . When electrons and holes are located in tw

P. W. Brouwer, S. A. van Langen, K. M. Frahm, M. Buttiker

The conductance G of a quantum dot with single-mode ballistic point contacts depends sensitively on external parameters X, such as gate voltage and magnetic field. We calculate the joint distribution of G and dG/dX by relating it to the distribution of the Wigner-Smith time-delay matrix of a chaotic system. The distribution of dG/dX has a singularity at zero

A. Sawada, Z. F. Ezawa, H. Ohno, Y. Horikoshi

We have studied the fractional and integer quantum Hall (QH) effects in a high-mobility double-layer two-dimensional electron system. We have compared the "stability" of the QH state in balanced and unbalanced double quantum wells. The behavior of the n=1 QH state is found to be strikingly different from all others. It is anomalously stable, though a

Georgios Varelogiannis

Momentum decoupling develops when forward scattering dominates the pairing interaction and implies tendency for decorrelation between the physical behavior in the various regions of the Fermi surface. In this regime it is possible to obtain anisotropic s- or d-wave superconductivity even with isotropic pairing scattering. We show that in the momentum decoupl

F. J. Garcia-Vidal, J. M. Pitarke, J. B. Pendry

We present an effective medium theory in order to analyze the reported optical properties of aligned carbon nanotube films (W.A. de Heer et al., Science 268, 845 (1995)). This methodology is based on photonic band structure calculations and allows treatment of complex media consisting of particles that interact strongly. We also develop a simple Maxwell-Garn

Z. F. Ezawa

We analyze the bilayer quantum Hall (QH) system by mapping it to the monolayer QH system with spin degrees of freedom. By this mapping the tunneling interaction term is identified with the Zeeman term. We clarify the mechanism of a spontaneous development of quantum coherence based on the Chern-Simons gauge theory with the lowest-Landau-Level projection take

Henrik J. Pedersen, A. D. Jackson

We present a random matrix model suitable for the quantum mechanical description of a particle confined to move inside a two-dimensional domain. Here, the ensemble average corresponds to an average over domain shapes. Although this approach is formally distinct from that of the familiar Gaussian orthogonal ensemble, there is remarkable agreement in the resul

D. Mouillet, J. D. Larwood, J. C. B. Papaloizou, A. M. Lagrange

We consider the deformation that has recently been observed in the inner part of the circumstellar disk around Beta Pictoris with the HST. Our recent ground based adaptive optics coronographic observations confirm that the inner disk is warped. We investigate the hypothesis that a yet undetected planet is responsible for the observed warp, through simulation

Richard G. Bower, F. J. Castander, Warrick J. Couch, R. S. Ellis

We present a programme of spectroscopic observations of galaxies in a sample of optically-selected clusters taken from the catalogue of Couch et al (1991). Previous ROSAT observations of these clusters have shown them to have lower X-ray luminosities, given their optical richness, than might be expected on the basis of local samples. In the present paper we

Joshua S. Bloom, Nial R. Tanvir, Ralph A. M. J. Wijers

If gamma-ray bursts (GRBs) are cosmological they need not necessarily be spatially coincident with a host galaxy--in many cosmological models the progenitors are ejected to large distances from their parent galaxies. While the optical transient of GRB 970228 may be close to a faint galaxy, there are several other galaxies in the field which could be the host

Alexander Heger, Laurent Jeannin, Norbert Langer, Isabelle Baraffe

We investigate the pulsational properties of RSG models --- which we evolve from ZAMS masses in the range 10 to $20 \Msun$ --- by means of linear and non-linear calculations. We find period and growth rate of the dominant fundamental mode to increase with increasing luminosity-to-mass ratio $L/M$. Our models obtain relatively large $L/M$ values due to the in

E. Zucca, G. Zamorani, G. Vettolani, A. Cappi

(Abridged) The ESO Slice Project (ESP) is a galaxy redshift survey we have completed as an ESO Key-Project over ~23 square degrees, in a region near the South Galactic Pole. The survey is nearly complete to the limiting magnitude b_J=19.4 and consists of 3342 galaxies with reliable redshift determination. The ESP survey is intermediate between shallow, wide

James Dunlop

The most passive galaxies at high redshift are unlikely to be identified by either narrow-band emission-line searches, or by Lyman limit searches (both techniques which have been highlighted at this meeting) simply because such selection methods rely on the presence of a strong ultraviolet component. Selection on the basis of extreme radio power has also pro

David Hughes, J. S. Dunlop, Steve Rawlings

We present new results of a study of the sub-millimetre continuum emission from a sample of 9 radio galaxies and 4 radio-quiet quasars at redshifts $z = 0.75 - 4.26$. The observations were made at 800$μm$, using the single-element bolometer UKT14 on the James Clerk Maxwell Telescope (JCMT), reaching a typical r.m.s. sensitivity of $σ_{rms} \sim 4$ mJy and re

N. Aghanim, A. De Luca, F. R. Bouchet, G. Gispert

In order to assess the potential of future microwave anisotropy space experiments for detecting clusters by their Sunyaev-Zeldovich (SZ) thermal effect, we have simulated maps of the large scale distribution of their Compton parameter $y$ and of the temperature anisotropy $ΔT/T$ induced by their proper motion. Our model is based on a predicted distribution o

Aparna Venkatesan, Angela V. Olinto, James W. Truran

We consider the contribution of neutron stars and black holes to the dynamical mass of galactic halos. In particular, we show that if these compact objects were produced by an early generation of stars with initial metallicity less than about $10^{-4} Z_\odot$, they can contribute at most 30--40% of the Galactic halo mass without creating supersolar levels o

Guo-Hong Wu, Ken Kiers, John N. Ng

We provide a general analysis of time reversal invariance violation in the exclusive semileptonic B decays B to D l nu and B to D* l nu. Measurements of the lepton and D* polarizations can be used to search for and identify non-standard model sources of T violation. Upper limits are placed on the T-odd polarization observables in both the supersymmetric R-pa

Alexander A. Chernitskii

Born-Infeld nonlinear electrodynamics are considered. Main attention is given to existence of singular point at static field configuration that M.Born and L.Infeld are considered as a model of electron. It is shown that such singularities are forbidden within the framework of the Born-Infeld model. It is proposed a modernized action that make possible an exi

B. Keimer, H. F. Fong, S. H. Lee, D. L. Milius

We report inelastic neutron scattering experiments on the doping dependence of the energy and spectral weight of the sharp magnetic resonance peak in YBa_2 Cu_3 O_{6+x}. These measurements also shed light on the relationship between the magnetic excitations in the normal and superconducting states.

Fabio Bernardini, Vincenzo Fiorentini, David Vanderbilt

The spontaneous polarization, dynamical Born charges, and piezoelectric constants of the III-V nitrides AlN, GaN, and InN are studied ab initio using the Berry phase approach to polarization in solids. The piezoelectric constants are found to be up 10 times larger than in conventional III-V's and II-VI's, and comparable to those of ZnO. Further prope

Matthias Neubert, Berthold Stech

We present a detailed study of non-leptonic two-body decays of B mesons based on a generalized factorization hypothesis. We discuss the structure of non-factorizable corrections and present arguments in favour of a simple phenomenological description of their effects. To evaluate the relevant transition form factors in the factorized decay amplitudes, we use

Frank Ferrari

This is a general introduction to electric-magnetic duality in non-abelian gauge theories. In chapter I, I review the general ideas which led in the late 70s to the idea of electric/magnetic duality in quantum field theory. In chapters II and III, I focus mainly on N=2 supersymmetric theories. I present the lagrangians and explain in more or less detail the

J. E. Garcia-Ramos, J. M. Arias, J. Dukelsky, E. Moya de Guerra

A Hartree-Bose mean-field approximation for the IBM-3 is presented. A Hartree- Bose transformation from spherical to deformed bosons with charge-dependent parameters is proposed which allows bosonic pair correlations and includes higher angular momentum bosons. The formalism contains previously proposed IBM-2 and IBM-3 intrinsic states as particular limits.

Ralph Werner, Claudius Gros

We present a theory for the spin-Peierls transition in CuGeO_3. We map the elementary excitations of the dimerized chain (solitons) on an effective Ising model. Inter-chain coupling (or phonons) then introduce a linear binding potential between a pair of soliton and anti-soliton, leading to a finite transition temperature. We evaluate, as a function of tempe

R. Kirschner, L. Szymanowski

Contributions from gluon interactions, which are non-leading in high-energy semi-hard processes, are studied and represented in terms of reggeon exchanges. Unlike the leading gluonic reggeon, related to the BFKL pomeron, the non-leading reggeons are sensitive to the spin and transverse momentum distributions of scattering partons. There are several gluonic r

Stephane Lafortune, Basil Grammaticos, Alfred Ramani

We present a systematic construction of integrable third order systems based on the coupling of an integrable second order equation and a Riccati equation. This approach is the extension of the Gambier method that led to the equation that bears his name. Our study is carried through for both continuous and discrete systems. In both cases the investigation is

D. J. Wineland, C. Monroe, D. M. Meekhof, B. E. King

A single laser-cooled and trapped 9Be+ ion is used to investigate methods of coherent quantum-state synthesis and quantum logic. We create and characterize nonclassical states of motion including "Schroedinger-cat" states. A fundamental quantum logic gate is realized which uses two states of the quantized ion motion and two ion internal states as qub

G. M. D'Ariano, M. F. Sacchi

We present an optical scheme that realizes the standard von Neumann measurement model, providing an indirect measurement of a quadrature of the field with controllable Gaussian state-reduction. The scheme is made of simple optical elements, as laser sources, beam splitters, and phase sensitive amplifiers, along with a feedback mechanism that uses a Pockels c

G. M. D'Ariano, M. F. Sacchi

We derive simple formulas connecting the generalized Wigner functions for $s$-ordering with the density matrix, and vice-versa. These formulas proved very useful for quantum mechanical applications, as, for example, for connecting master equations with Fokker-Planck equations, or for evaluating the quantum state from Monte Carlo simulations of Fokker-Planck

Joseph Samuel

We study the behaviour of the geometric phase under isometries of the ray space. This leads to a better understanding of a theorem first proved by Wigner: isometries of the ray space can always be realised as projections of unitary or anti-unitary transformations on the Hilbert space. We suggest that the construction involved in Wigner's proof is best vi

Lu-Ming Duan, Guang-Can Guo

A fundamental question in quantum mechanics is, whether it is possible to replicate an arbitrary unknown quantum state. Then famous quantum no-cloning theorem [Nature 299, 802 (1982)] says no to the question. But it leaves open the following question: If the state is not arbitrary, but secretly chosen from a certain set $\$={ | Ψ_1> ,| Ψ_2> ,... ,| Ψ_n> } $,

H. Falomir

Ellipticity of boundary value problems is characterized in terms of the Calderon projector. The presence of topological obstructions for the chiral Dirac operator under local boundary conditions in even dimension is discussed. Functional determinants for Dirac operators on manifolds with boundary are considered. The functional determinant for a Dirac operato

Ion I. Cotăescu, Gheorghe Draganescu

The operator algebras of a new family of relativistic geometric models of the relativistic oscillator are studied. It is shown that, generally, the operator of number of quanta and the pair of the shift operators of each model are the generators of a non-unitary representation of the $so(1,2)$ algebra, except a special case when this algebra becomes the stan

Ion I. Cotăescu

We analyze the supersymmetry and the shape invariance of the potentials of the (1+1) relativistic oscillators we have recently proposed.

J. Helgesson, J. Randrup

In-medium properties derived for nuclear matter in a microscopic pi + nucleon-hole + delta-hole model are incorporated into transport simulations of nuclear collisions by means of a local-density approximation and by utilizing a local medium frame. Certain features of the transport results differ from those based on the corresponding vacuum properties. Compa

Ron Workman

We question the reliability of current estimates for the Delta(+) mass. We explain why the standard value, determined from pion photoproduction, should not be used in conjunction with present estimates for the Delta(++) and Delta(0) masses, determined from pion-nucleon scattering. The resultant mass splittings are internally inconsistent. We also briefly com

Koichi Saito

The quark-meson coupling model, based on a mean-field description of non-overlapping nucleon bags bound by the self-consistent exchange of $σ$, $ω$ and $ρ$ mesons, is reviewed. In particular, I present the changes in the hadron masses of the (non-strange) vector mesons and the nucleon in a nucleus. I also give a new, simple scaling relation among the changes

G. Michaud, R. C. Myers

A low-energy background field solution describing D-membrane configurations is constructed which is distinguished by the appearance of a Hermitian metric on the internal space. This metric is composed of a number of independent harmonic functions on the transverse space. Thus this construction generalizes the usual harmonic superposition rule. The BPS bound

Juan M. Maldacena

D-branes have been used to describe many properties of extremal and near extremal black holes. These lecture notes provide a short review of these developments.

D. G. Barci, C. M. Naón

We use path-integral methods to analyze the vacuum properties of a recently proposed extension of the Thirring model in which the interaction between fermionic currents is non-local. We calculate the exact ground state wave functional of the model for any bilocal potential, and also study its long-distance behavior. We show that the ground state wave functio

P. C. Argyres

Lectures presented at the 33rd Karpacz Winter School ``Duality: Strings and Fields'' briefly introducing dualities in four-dimensional quantum field theory, and summarizing results found in supersymmetric field theories. The first lecture describes physical aspects of electric-magnetic (EM), strong-weak coupling (S), and infrared (IR) dualities. The

Constantin Bachas, Michael R. Douglas, Michael B. Green

In certain circumstances when two branes pass through each other a third brane is produced stretching between them. We explain this phenomenon by the use of chains of dualities and the inflow of charge that is required for the absence of chiral gauge anomalies when pairs of D-branes intersect.

D. V. Antonov

Perturbation theory in the nonperturbative QCD vacuum and the non-Abelian Stokes theorem, representing a Wilson loop in the SU(2) gluodynamics as an integral over all the orientations in colour space, are applied to derivation of the correction to the background-induced string effective action. This correction is due to accounting in the lowest order of pert

Uwe Trittmann

The annihilation channel is implemented into the front form calculations of the positronium spectrum presented in a previous publication. The effective Hamiltonian is calculated analytically. Its eigensolutions are obtained numerically. A complete separation of the dynamical and instantaneous part of the annihilation interaction is observed. We find the rema

A. P. C. Malbouisson, M. B. Silva-Neto, N. F. Svaiter

We perform the dimensional reduction of the linear $σ$ model at one-loop level. The effective potential of the reduced theory obtained from the integration over the nonzero Matsubara frequencies is exhibited. Thermal mass and coupling constant renormalization constants are given, as well as the thermal renormalization group equation which controls the depend

Takayuki Hirayama, Nobuhiro Maekawa, Shigeki Sugimoto

We study deformations of dualities in finite N=2 supersymmetric QCD. Adding mass terms for some quarks and the adjoint matter to the finite N=2 theory, which is known to have dual descriptions, the correspondence of gauge invariant operators between the original and dual theory is deformed. As a result, we naturally obtain N.Seiberg's N=1 duality. Furthe

Alan R. White

Conformally invariant reggeon interactions derived from $t$-channel unitarity are discussed and progress towards understanding the ``physical Pomeron'', via massless quark reggeon interactions, is briefly outlined.

H. Navelet, S. Wallon

We compute the onium-onium scattering amplitude at fixed impact parameter in the framework of the perturbative QCD dipole model. Relying on conformal properties of the dipole cascade and of the elementary dipole-dipole scattering amplitude, we obtain an exact result for this onium-onium scattering amplitude, which is proven to be identical to the BFKL result

P. Nason, C. Oleari

We recently completed a calculation of the process $e^+e^- \to Q\bar{Q}+X$, where Q is a heavy quark, at order $O(α_s^2)$. As a first application of this calculation we compute the momentum correlations of $b\bar{b}$ pairs at next-to-leading-order. This quantity is interesting since it may affect the determination of $R_b$ as measured in $Z^0$ decays. We fin

M. Kuroda, I. Kuss, D. Schildknecht

Using the SU(2) gauge coupling, $g_{W^\pm} (M^2_{W^\pm})$, at the high-energy scale of $M_{W^\pm}$, defined by the (theoretical value of the) leptonic W-width, rather than using the low-energy value, defined via the Fermi coupling, $G_μ$, in the Born approximation, and supplementing with Coulomb corrections and initial state radiation, errors with respect to

G. Grunberg

In the dispersive approach of Dokshitzer, Marchesini and Webber, standard power-behaved contributions of infrared origin are described with the notion of an infrared regular QCD coupling. I argue that their framework suggests the existence of non-standard contributions, arising from short distances (hence unrelated to renormalons and the operator product exp

S. Saito, M. Uehara

The seagull terms for the electric polarizability of the nucleon are shown to vanish, if one introduces fluctuations around the Skyrmion, and the origin of the eletric polarizability cannot be attributed to the seagull terms in the Skyrme model.

M. Talevi

We discuss the status and the problems related to the application of the off-shell non-perturbative renormalization method in a fixed gauge to operators relevant to weak decays. In particular, we critically reappraise the method recently proposed for the $ΔI=1/2$ rule. We also present a general analysis of the renormalization for the $ΔI=3/2$ operators, and

Simon Hands, John B. Kogut

We present results from a Monte Carlo simulation of the Nambu - Jona-Lasinio model, with continuous SU(2)xSU(2) chiral symmetry, in four Euclidean dimensions. Different model equations of state, corresponding to different theoretical scenarios, are tested against the order parameter data. The results are sensitive to necessary assumptions about the shape and

Naresh Dadhich

We consider a spacetime corresponding to uniform relativistic potential analogus to Newtonian potential as an example of ``minimally curved spacetime''. We also consider a radially symmetric analogue of the Rindler spacetime of uniform proper acceleration relative to infinity.

F. Ghaboussi

It is shown that the observed potential drops on QHE samples can be considered as a realization of uncertainty relation for the quantized two dimensional electromagnetic potential.

F. F. Balakirev, I. E. Trofimov, S. Guha, Marta Z. Cieplak

Measurements of resistivity, Hall effect, and magnetoresistance have been made on seven c-axis oriented thin-film specimens of La(2-x)Sr(x)CuO(4) with values of x from 0.048 to 0.275, and one specimen that also contains Nd. The orbital magnetoresistance is found not to be proportional to the square of the tangent of the Hall angle except for values of x near

M. C. Bergere

We prove Serban's conjecture which simplifies greatly the expression of the advanced single-particle Green function in the Calogero-Sutherland model. The importance of proving this conjecture is that it reorganizes the form factor in terms of two dimensional Coulomb gaz correlators and confirms the possible existence of a bosonization procedure for this

Siegfried Clar, Barbara Drossel, Klaus Schenk, Franz Schwabl

We investigate the percolation properties of a two-state (occupied - empty) cellular automaton, where at each time step a cluster of occupied sites is removed and the same number of randomly chosen empty sites are occupied again. We find a finite region of critical behavior, formation of synchronized stripes, additional phase transitions, as well as violatio

Axel Gross, Matthias Scheffler

The dissociative adsorption of hydrogen on Pd(100) has been studied by ab initio quantum dynamics and ab initio molecular dynamics calculations. Treating all hydrogen degrees of freedom as dynamical coordinates implies a high dimensionality and requires statistical averages over thousands of trajectories. An efficient and accurate treatment of such extensive

D. A. Johnston, P. Plechac

In a recent paper hep-lat/9704020 we investigated Potts models on ``thin'' random graphs -- generic Feynman diagrams, using the idea that such models may be expressed as the N --> 1 limit of a matrix model. The models displayed first order transitions for all q greater than 2, giving identical behaviour to the corresponding Bethe lattice. We use here

H. Kallabis, L. Brendel, J. Krug, D. E. Wolf

We present a theory for the damping of layer-by-layer growth oscillations in molecular beam epitaxy. The surface becomes rough on distances larger than a layer coherence length which is substantially larger than the diffusion length. The damping time can be calculated by a comparison of the competing roughening and smoothening mechanisms. The dependence on t

Jakub Zavrel, Walter Daelemans

This paper analyses the relation between the use of similarity in Memory-Based Learning and the notion of backed-off smoothing in statistical language modeling. We show that the two approaches are closely related, and we argue that feature weighting methods in the Memory-Based paradigm can offer the advantage of automatically specifying a suitable domain-spe

Marc Dymetman

Recently researchers working in the LFG framework have proposed algorithms for taking advantage of the implicit context-free components of a unification grammar [Maxwell 96]. This paper clarifies the mathematical foundations of these techniques, provides a uniform framework in which they can be formally studied and eliminates the need for special purpose run

C. Appert, M. H. Ernst

The thermodynamic formalism of Ruelle, Sinai, and Bowen, in which chaotic properties of dynamical systems are expressed in terms of a free energy-type function - called the topological pressure - is applied to a Lorentz Lattice Gas, as typical for diffusive systems with static disorder. In the limit of large system sizes, the mechanism and effects of localiz

Angelica de Oliveira-Costa, A. Kogut, Mark J. Devlin, C. Barth Netterfield

We cross-correlate the Saskatoon Q-Band data with different spatial template maps to quantify possible foreground contamination. We detect a correlation with the Diffuse Infrared Background Experiment (DIRBE) 100 microm map, which we interpret as being due to Galactic free-free emission. Subtracting this foreground power reduces the Saskatoon normalization o

S. Ali, R. K. Schaefer, M. Limon, L. Piccirillo

We have used the 2- year Differential Microwave Radiometer data from the COsmic Background Explorer (COBE) satellite to systematically search for millimetric (31 - 90 GHz) emission from the Gamma Ray Bursts (GRBs) in the Burst And Transient Source Experiment (BATSE) GRB 3B catalog. The large beamsize of the COBE instrument (7 degs FWHM) allows for an efficie

J. J. Dalcanton, D. N. Spergel, J. E. Gunn, M. Schmidt

We present results of a large area CCD survey for low surface brightness galaxies (LSBs) that reaches central surface brightnesses of mu_0=25 mag/sqr-" in V. We have analyzed 17.5 degrees of transit scan data, and identified a statistical subset of 7 pure disk LSB's with mu_0 fainter than 23V-mag/sqr-" and with angular exponential scale lengths l

T. J. Turner, I. M. George, K. Nandra, R. F. Mushotzky

We discuss the importance of X-ray scattering and Compton reflection in type-2 Seyfert galaxies, based upon the analysis of ASCA observations of 25 such sources. Consideration of the iron Kalpha, [O III] line and X-ray variability suggest that NGC 1068, NGC 4945, NGC 2992, Mrk 3, Mrk 463E and Mrk 273 are dominated by reprocessed X-rays. We examine the proper

Greg J. Schwarz, S. Starrfield, Steven N. Shore, Peter H. Hauschildt

We determine the elemental abundances for the ejecta of the slow nova PW Vul 1984. Our technique uses a minimization of the emission line fits of a photoionization model to available ultraviolet, optical and infrared spectra. We find the following abundances (by number) with respect to solar: He/H = 1.0 $\pm$ 0.4, C/H = 7.0 $^{+7}_{-4}$, N/H = 85 $^{+59}_{-4

Ivan Hubeny, Veronika Hubeny

We present self-consistent models of the vertical structure and emergent spectrum of AGN accretion disks. The central object is assumed to be a supermassive Kerr black hole. We demonstrate that NLTE effects and the effects of a self-consistent vertical structure of a disk play a very important role in determining the emergent radiation, and therefore should

A. M. Beloborodov, M. A. Abramowicz, I. D. Novikov

In the innermost region of the advective accretion disk orbiting a black hole of high spin, the inertia of heat stored in the accreting gas is comparable to that of the gas rest mass itself. Accounting for this effect, we derive additional terms in the disk structure equations, and show that the heat inertia plays a significant role in the global energy cons

Jason W. Ferguson, Kirk T. Korista, Jack A. Baldwin, Gary J. Ferland

The narrow emission line spectra of active galactic nuclei are not accurately described by simple photoionization models of single clouds. Recent Hubble Space Telescope images of Seyfert 2 galaxies show that these objects are rich with ionization cones, knots, filaments, and strands of ionized gas. Here we extend to the narrow line region the ``locally optim

Jason W. Ferguson, Kirk T. Korista, Gary J. Ferland

The launch of the Infrared Space Observatory and new atomic data have opened a window to the study of high ionization gas in active galactic nuclei (AGN). We present the results of a large number of photoionization simulations of the ``coronal line'' region in AGN, employing new atomic data from the Opacity and Iron Projects. Our grid of line emissio

R. P. van der Marel, N. Cretton, P. T. de Zeeuw, H. W. Rix

Axisymmetric dynamical models are constructed for the E3 galaxy M32 to interpret high spatial resolution stellar kinematical HST data. Models are studied with two-integral phase-space distribution functions, and with fully general three- integral distribution functions. The latter are built using a new extension of Schwarzschild's orbit superposition app

Helio J. Rocha-Pinto, Walter J. Maciel

We examine the possibility of the inclusion of objects having lifetimes lower than the disk age in the database of recent determinations of the G dwarf metallicity distribution for the solar neighbourhood. As a preliminary step, stars with lifetimes potentially lower than the disk age are identified by means of a relation between (b-y), or mass, and [Fe/H],

T. Di Matteo, E. G. Blackman, A. C. Fabian

We show that coronal magnetic dissipation in thin active sheets that sandwich standard thin accretion disks in active galactic nuclei may account for canonical electron temperatures of a few $\times 10^9$K if protons acquire most of the dissipated energy. Coulomb collisions transfer energy from the ions to the electrons, which subsequently cool rapidly by in

Neil F. Comins, Richard V. E. Lovelace, Thomas Zeltwanger, Peter Shorey

Motivated by observations of disk galaxies with counter-rotating stars, we have run two-dimensional, collisionless N-body simulations of disk galaxies with significant counter-rotating components. For all our simulations the initial value of Toomre's stability parameter was Q = 1.1. The percentage of counter-rotating particles ranges from 25% to 50%. A s

Isabelle Baraffe, France Allard

Over the past decade considerable effort, both observational and theoretical, has been directed towards a more accurate determination of the stellar lower main sequence and of the sub-stellar domain covered by Brown Dwarfs and Planets. A review of the recent improvement in the theory of cool model atmospheres is presented.

Takashi Murayama, Yoshiaki Taniguchi

The nuclear gas kinematics probed by water vapor maser emission has shown that two nearby active galaxies, NGC 1068 and NGC 4258, have a supermassive object in their nuclei and their masses are nearly comparable; a few 10^7 solar masses. Nevertheless, the activity of the central engine of NGC 1068 is more powerful by two orders of magnitude than that of NGC

Yoshiaki Taniguchi, Takashi Murayama, Kimiaki Kawara, Nobuo Arimoto

We report the discovery of a high-z quasar with unambiguous [OIII]5007 emission; PKS 1937-101 at redshift 3.8. This quasar, however, shows little evidence for rest-frame ultraviolet and optical FeII emission. It is thus shown that PKS 1937-101 does not belong to a class of super iron-rich high-z quasars reported by Elston, Thompson, & Hill (1994). The epoch

Nantel Bergeron, Frank Sottile

We use geometry to prove a number of new identities among the Littlewood-Richardson coefficients for Schubert polynomials (Schubert classes in a flag manifold). For many of these identities, there is a companion result about the Bruhat order which should imply the identity, were it known how to express these coefficients in terms of the Bruhat order. This an

M. Rickert, Kai Nagel

We describe a simple framework for micro simulation of city traffic. A medium sized excerpt of Dallas was used to examine different levels of simulation fidelity of a cellular automaton method for the traffic flow simulation and a simple intersection model. We point out problems arising with the granular structure of the underlying rules of motion.

Marco Godina, Andrzej Borowiec, Marco Ferraris, Mauro Francaviglia

%auto-ignore This paper has been withdrawn by the authors.

Valter Moretti

A method which uses a generalized tensorial $ζ$-function to compute the renormalized stress tensor of a quantum field propagating in a (static) curved background is presented. The starting point of the method is the direct computation of the functional derivatives of the Euclidean one-loop effective action with respect to the background metric. This method,