February 1999 arXiv papers — page 20

Rama Cont

We present a family of models for the term structure of interest rates which describe the interest rate curve as a stochastic process in a Hilbert space. We start by decomposing the deformations of the term structure into the variations of the short rate, the long rate and the fluctuations of the curve around its average shape. This fluctuation is then descr

Alain Karma, Wouter-Jan Rappel

We investigate dendritic sidebranching during crystal growth in an undercooled melt by simulation of a phase-field model which incorporates thermal noise of microscopic origin. As a non-trivial quantitative test of this model, we first show that the simulated fluctuation spectrum of a one-dimensional interface in thermal equilibrium agrees with the exact sha

C. Groeber, M. G. Zacher, R. Eder

We study the electronic structure of the doped paramagnetic insulator by finite temperature Quantum Monte-Carlo simulations for the 2D Hubbard model. Throughout we use the moderately high temperature T=0.33t, where the spin correlation length has dropped to < 1.5 lattice spacings, and study the evolution of the band structure with hole doping. The effect of

Yuval Oreg, P. W. Brouwer, B. D. Simons, Alexander Altland

We investigate the suppression of the proximity effect in mesoscopic normal metal/superconductor systems induced by Coulomb interaction. We identify and elucidate the mechanism by which disorder leads to an amplification of this effect. In particular, for strong enough disorder, the proximity effect is shown to vanish. An expression for the tunneling density

A. G. Rojo, C. A. Balseiro

We present a mean field treatment of a strongly correlated model of electrons in a three-dimensional anisotropic system. The mass of the bare electrons is larger in one spatial direction (the c-axis direction), than in the other two (the ab-planes). We use a slave fermion decomposition of the electronic degrees of freedom and show that there is a transition

Henry C. Tuckwell

The use of cortical field potentials rather than the details of spike trains as the basis for cognitive information processing is proposed. This results in a space of cognitive elements with natural metrics. Sets of spike trains may also be considered to be points in a multidimensional metric space. The closeness of sets of spike trains in such a space impli

L. A. Falkovsky, E. G. Mishchenko

We propose a kinetic model of transient nonequilibrium phenomena in metals exposed to ultrashort laser pulses when heated electrons affect the lattice through direct electron-phonon interaction. This model describes the destruction of a metal under intense laser pumping. We derive the system of equations for the metal, which consists of hot electrons and a c

Georg Goeppert, Hermann Grabert

The linear conductance of the a small metallic tunnel junction embedded in an electromagnetic environment of arbitrary impedance is determined in the semiclassical limit. Electron tunneling is treated beyond the orthodox theory of Coulomb blockade phenomena by means of a nonperturbative path integral approach. The frequency dependent conductance is obtained

Chinmay Das, A. K. Sood, H. R. Krishnamurthy

We present results from an extensive simulational study of the modulated liquid $\longleftrightarrow$ crystal transition in a 2-d charge-stabilized colloid subject to a 1-d laser field modulation commensurate with the crystalline phase. {\em {Contrary to some earlier simulational and experimental findings we do not find any reentrant liquid phase in our simu

T. V. Shahbazyan, I. E. Perakis

We study the role of collective surface excitations in the electron relaxation in small metal particles. We show that the dynamically screened electron-electron interaction in a nanoparticle contains a size-dependent correction induced by the surface. This leads to new channels of quasiparticle scattering accompanied by the emission of surface collective exc

A. S. Alexandrov, A. M. Bratkovsky

The frequency and temperature dependence of the optical conductivity of ferromagnetic manganites is explained within the framework of the bipolaron theory. As these materials are cooled below the Curie temperature, the colossal magnetoressitance (CMR) is accompanied by a massive transfer of the spectral weight of the optical conductivity to lower frequencies

Kazimierz Dworecki, Tadeusz Kosztolowicz, Slawomir Wasik, Stanislaw Mrowczynski

The near membrane layer is defined as a region where the concentration of the substance transported across the membrane drops $k$ times. The time evolution of such a layer is studied experimentally by means of the laser interferometric method. It is shown that within the experimental errors the thickness of the near membrane layer grows in time as $a \sqrt t

Elman M. Shahverdiev, Shin-ichi Tadaki

It has been shown that the discrete one dimensional gravity model of traffic flow dynamics exhibits temporal chaotic behavior

M. M. Romanova

Models of Blazars based on the propagation of finite discontinuities or fronts in the Poynting flux jet from the innermost regions of an accretion disk around a black hole are discussed. Such fronts may be responsible for short time-scale (from less than hours to days) flares in different wavebands from high frequency radioband to TeV, with delay in low radi

George F. Smoot

This work presents a summary of major cosmological results from the COBE (Cosmic Background Explorer) satellite mission. The results include a precise measurement of the Cosmic Microwave Background (CMB) radiation intensity, discovery and maps of the CMB anisotropy, large scale observations of the CMB polarization, and the detection and measurement of the di

D. M. Katz-Stone, L. Rudnick, C. Butenhoff, A. A. O&#39;Donoghue

We add 20, 6 and 3.6 cm wavelength VLA observations of two WATs, 1231+674 and 1433+553, to existing VLA data at 6 and 20 cm, in order to study the variations of spectral index as a function of position. We apply the spectral tomography process that we introduced in our analysis of 3C67, 3C190 and 3C449. Both spectral tomography and polarization maps indicate

David A. Neufeld

Observations at far-infrared and submillimeter wavelengths promise to revolutionize the study of high redshift galaxies and AGN by providing a unique probe of the conditions within heavily extinguished regions of star formation and nuclear activity. Observational capabilities in this spectral region will expand greatly in the next decade as new observatories

D. L. Tucker, H. Lin, S. Shectman

The Las Campanas Redshift Survey (LCRS) is among the first galaxy redshift surveys to sample a reasonably fair volume of the local Universe. On the largest scales (>> 100/h Mpc), the galaxy distribution appears smooth; on relatively small scales (<10/h Mpc), the LCRS tends to confirm the clustering characteristics observed in previous, shallower surveys. Her

M. Cappi, L. Bassani, A. Comastri, M. Guainazzi

A new BeppoSAX broad-band (0.6-150 keV) spectrum of the Seyfert 2 galaxy Mkn 3 is presented. The spectrum provides a direct measurement of a large, neutral column of gas with Nh~10**24 cm**-2 in the source direction. The source, as bright as 3C 273 above 10 keV, has a steep (Gamma~1.8) spectrum without any evidence of a high-energy cutoff up to at least 150

Michel Fioc, Brigitte Rocca-Volmerange

Galaxy counts from bright ultraviolet (UV) and deep optical spectroscopic surveys have revealed an unexpectedly large number of very blue galaxies. The colors and luminosities of these objects indicate that they are dwarf galaxies undergoing bursts of star formation. We use a galaxy evolution model (PEGASE, Fioc & Rocca-Volmerange 1997) to describe this popu

L. Feretti, D. Dallacasa, F. Govoni, G. Giovannini

We present new, multiwavelength Very Large Array observations of the 3 radio galaxies in the cluster Abell 119: 0053-015, 0053-016 and 3C 29. The first two radio galaxies, which lie close to the cluster center, show a narrow-angle-tailed structure, with many twists in the tails. The third radio source is located at the cluster periphery, and shows an undisto

Christian R. Kaiser, Paul Alexander

We present results of a numerical integration of the hydrodynamical equations governing the self-similar, two-dimensional gas flow behind the bow shock of an FRII radio source embedded in an IGM with a power law density profile. The model predicts pressure gradients within the cocoons consistent with modest backflow. For very steep external density profiles

Arnon Dar

Recent studies suggest that when cold nuclear matter is compressed to high nuclear densities, diquarks with spin zero and antisymmetric color wave function Bose condensate into a superfluid/superconducting state that is several times as dense. Various astrophysical phenomena may be explained by gravitational collapse of neutron stars (NSs) to (di)quark stars

F. Combes

In this review, I discuss some highlights of recent research on molecular gas in galaxies; large-scale CO maps of nearby galaxies are being made, which extend our knowledge on global properties, radial gradients, and spiral structure of the molecular ISM. Very high resolution are provided by the interferometers, that reveal high velocity gradients in galaxy

Gilles Chabrier

We briefly outline the physics underlying the mechanical and thermal properties of brown dwarfs, which characterizes their interiors and their atmospheres. We mention the most recent improvements realyzed in the theory of brown dwarfs and the connection with experimental and observational tests of this theory.

Daniele Fargion, Roberto Conversano

Dark matter influence globally galactic Keplerian motions and individually, by microlensing, star&#39;s acromatic luminosities. Moreover gravity slows down time as probed by gravitational redshift. Therefore pulsar&#39;s (PSR&#39;s) periods may record, by slowing and speeding up, any Dark MACHO crossing along the line-of-sight. This phase delay, a Shapiro Ph

L. Piro, E. Costa, M. Feroci, F. Frontera

We report the possible detection (99.3% of statistical significance) of redshifted Fe iron line emission in the X-ray afterglow of Gamma-ray burst GRB970508 observed by BeppoSAX. Its energy is consistent with the redshift of the putative host galaxy determined from optical spectroscopy. The line disappeared about 1 day after the burst. We have also analyzed

L. Bergstrom, J. Edsjo, P. Ullio

The flux of cosmic ray antiprotons from neutralino annihilations in the galactic halo is computed for a large sample of models in the MSSM (the Minimal Supersymmetric extension of the Standard Model). We also revisit the problem of estimating the background of low-energy cosmic ray induced secondary antiprotons, taking into account their subsequent interacti

T. Oosterloo, R. Morganti, E. M. Sadler

We summarize the HI properties of early-type galaxies, in particular the differences in HI morphologies observed in early-type galaxies of different luminosities. We find that in low-luminosity early-type galaxies the HI is almost always in a disk-like structure, with central surface densities high enough for star formation to occur. In a few luminous early-

J. M. Oliveira, B. H. Foing

We present results on spectroscopic observations of the fast-rotating active giant FK Comae, obtained mainly with the ESA-MUSICOS spectrograph at the Isaac Newton Telescope (INT) in 1996 and 1997 and also with the Aurelie spectrograph at the Observatoire de Haute Provence (OHP) in 1997. The profiles analysed are those of the Balmer, Halpha and Hbeta, and He

M. D. Roberts, P. McGee, S. A. Dazeley, P. G. Edwards

Despite extensive surveys of extragalactic TeV gamma-ray candidates only 3 sources have so far been detected. All three are northern hemisphere objects and all three are low-redshift X-ray selected BL Lacs (XBLs). In this paper we present the results of observations of the three nearest southern hemisphere XBLs (PKS0548-322, PKS2005-489 and PKS2155-304) with