February 2002 arXiv papers — page 25

U. D. Jentschura, S. V. Aksenov, P. J. Mohr, M. A. Savageau

This work describes numerical methods that are useful in many areas: examples include statistical modelling (bioinformatics, computational biology), theoretical physics, and even pure mathematics. The methods are primarily useful for the acceleration of slowly convergent and the summation of divergent series that are ubiquitous in relevant applications. The

Shin-ichiro Ogawa, Mikko Mottonen, Mikio Nakahara, Tetsuo Ohmi

It has been shown that a vortex in a BEC with spin degrees of freedom can be created by manipulating with external magnetic fields. In the previous work, an optical plug along the vortex axis has been introduced to avoid Majorana flips, which take place when the external magnetic field vanishes along the vortex axis while it is created. In the present work,

A. Cucchieri, J. Engels, S. Holtmann, T. Mendes

We investigate the three-dimensional O(2) model near the critical point by Monte Carlo simulations and calculate the major universal amplitude ratios of the model. The ratio U_0=A+/A- is determined directly from the specific heat data at zero magnetic field. The data do not, however, allow to extract an accurate estimate for alpha. Instead, we establish a st

Vladimir M. Dubovik, Arkadi G. Galperin, Viktor S. Richvitsky, Aleksey A. Lushnikov

Some models of clustering processes are formulated and analytically solved employing generating functions methods. Those models include events which result from combined action of the coagulation and fragmentation processes. Fragmentation processes of two kinds, so-called similar and arbitrary, ones, are brought forward, and the explicit forms of their solut

Christof Gattringer

We discuss a simple formula which connects the field-strength tensor to a spectral sum over certain quadratic forms of the eigenvectors of the lattice Dirac operator. We analyze these terms for the near zero-modes and find that they give rise to contributions which are essentially either self-dual or anti self-dual. Modes with larger eigenvalues in the bulk

Edward E. Boos, Yuri A. Kubyshin, Mikhail N. Smolyakov, Igor P. Volobuev

We derive the second variation Lagrangian of the Randall-Sundrum model with two branes, study its gauge invariance and diagonalize it in the unitary gauge. We also show that the effective four-dimensional theory looks different on different branes and calculate the observable mass spectra and the couplings of the physical degrees of freedom of 5-dimensional

H. V. Klapdor-Kleingrothaus, U. Sarkar

We study the possible structure of the neutrino mass matrix taking into consideration the solar and atmospheric neutrinos and the neutrinoless double beta decay. We emphasize on mass matrices with vanishing elements. There are only a very few possibilities remaining at present. We concentrate on three generation scenarios and find that with three parameters

Olga Piskounova

The spectra of leading and nonleading charmed baryons ($Λ_c$ and $\barΛ_c$) as well as the asymmetries between these spectra measured in $Σ^-A$, $π^-A$ and pA collisions at $p_L= 600 GeV/c$ in the E781 experiment are simultaneously described within the framework of Quark-Gluon String Model (QGSM). It is shown that the charmed baryon spectra can be fitted by

Frank Ferrari

Recently, the author has constructed a series of four dimensional non-critical string theories with eight supercharges, dual to theories of light electric and magnetic charges, for which exact formulas for the central charge of the space-time supersymmetry algebra as a function of the world-sheet couplings were obtained. The basic idea was to generalize the

Sumit R. Das

Assuming the existence of a $dS/CFT$ correspondence we study the holograms of sources moving along geodesics in the bulk by calculating the one point functions they induce in the boundary theory. In analogy with a similar study of uniformly accelerated sources in $AdS$ spacetime, we argue that comoving geodesic observers correspond to a coordinate system on

F. Courbin, G. Meylan, J. P. Kneib, C. Lidman

Optical and near-IR Hubble Space Telescope and Gemini-North adaptive optics images, further improved through deconvolution, are used to explore the gravitationally lensed radio source PKS 1830-211. The line of sight to the quasar at z=2.507 appears to be very busy, with the presence, within 0.5 arcsec from the source of: (i) a possible galactic main-sequence

Peter Mitchell, Sandu Popescu, David Roberts

The notion of genuine three-particle non-locality introduced by Svetlichny \cite{Svetlichny} is discussed. Svetlichny's inequality which can distinguish between genuine three-particle non-locality and two-particle non-locality is analyzed by reinterpreting it as a frustrated network of correlations. Its quantum mechanical maximum violation is derived and

Xinhua Peng, Xiwen Zhu, Ximing Fang, Mang Feng

A quantum circuit is introducted to describe the preparation of a labeled pseudo-pure state by mutiplet-component excitation scheme which has been experimentally implemented on a 4-qubit nuclear magnetic resonance quantum processor. Meanwhile, we theoretically analyze and numerically inverstigate the low-power selective single-pulse implementation of a contr

S. Fritsch, N. Kaiser, W. Weise

We extend a recent three-loop calculation of nuclear matter in the systematic framework of chiral perturbation theory to finite temperatures T. The contributions from one- and two-pion exchange diagrams which cause nuclear binding and saturation at T=0 are included for T>0 in the density and temperature dependent free energy per particle, $\bar F(rho,T)$. Th

P. Bruno

The zero-point quantum fluctuations of the electromagnetic field in vacuum are known to give rise to a long-range attractive force between metal plates (Casimir effect). For ferromagnetic layers separated by vacuum, it is shown that the interplay of the Casimir effect and of the magneto-optical Kerr effect gives rise to a long-range magnetic interaction. The

K. Koike, M. Nakagawa, C. Koike, M. Okada

Interstellar matter is known to be strongly irradiated by radiation and several types of cosmic ray particles. Simulated interstellar matter, such as forsterite $\rm Mg_{2}SiO_{4}$, enstatite $\rm MgSiO_{3}$ and magnesite $\rm MgCO_{3}$ has been irradiated with the $\rm ^{60}Co$ gamma-rays in liquid nitrogen, and also irradiated with fast neutrons at 10 K an

Hisakazu Minakata, Hiroaki Sugiyama

Assuming positive observation of neutrinoless double bata decay together with the CHOOZ reactor bound, we derive constraints imposed on neutrino mixing parameters, the solar mixing angle θ_{12} and the observable mass parameter < m >_β in single beta decay experiments. We show that 0.05 eV < < m >_β < 2 eV at the best fit parameters of the LMA MSW solar neut

Dao-Neng Gao

We study the CP-violating asymmetry {\cal A}_{\rm CP}, which arises, in η\toπ^+π^- e^+e^-, from the angular correlation of the e^+ e^- and π^+π^- planes due to the interference between the magnetic and electric decay amplitudes. With the phenomenologically determined magnetic amplitude and branching ratio as input, the asymmetry, induced by the electric brem

Rutwig Campoamor-Stursberg

The invariants of all complex solvable rigid Lie algebras up to dimension eight are computed. Moreover we show, for rank one solvable algebras, some criteria to deduce to non-existence of non-trivial invariants or the existence of fundamental sets of invariants formed by rational functions of the Casimir invariants of the associated nilradical.

Kensuke Kobayashi, Hisashi Aikawa, Shingo Katsumoto, Yasuhiro Iye

The Fano effect, which arises from an interference between a localized state and the continuum, reveals a fundamental aspect of quantum mechanics. We have realized a tunable Fano system in a quantum dot (QD) in an Aharonov-Bohm interferometer, which is the first convincing demonstration of this effect in mesoscopic systems. With the aid of the continuum, the

A. Oosawa, T. Ono, H. Tanaka

The magnetization measurements have been performed on the doped spin gap system TlCu_{1-x}Mg_xCl_3 with x <= 0.025. The parent compound TlCuCl_3 is a three-dimensional coupled spin dimer system with the excitation gap Delta/k_B = 7.7 K. The impurity-induced antiferromagnetic ordering was clearly observed. The easy axis lies in the (0,1,0) plane. It was found

Masahito Hayashi

We discuss two quantum analogues of Fisher information, symmetric logarithmic derivative (SLD) Fisher information and Kubo-Mori-Bogoljubov (KMB) Fisher information from a large deviation viewpoint of quantum estimation and prove that the former gives the true bound and the latter gives the bound of consistent superefficient estimators. In another comparison,

Masahito Hayashi

We derive the optimal exponent of the error probability of the quantum fixed-length pure state source coding in both cases of blind coding and visible coding. The optimal exponent is universally attained by Jozsa et al. (PRL, 81, 1714 (1998))&#39;s universal code. In the direct part, a group representation theoretical type method is essential. In the convers

Masahito Hayashi, Keiji Matsumoto

We construct an optimal quantum universal variable-length code that achieves the admissible minimum rate, i.e., our code is used for any probability distribution of quantum states. Its probability of exceeding the admissible minimum rate exponentially goes to 0. Our code is optimal in the sense of its exponent. In addition, its average error asymptotically t

Kim Hyeon-Deuk, Hisao Hayakawa

The velocity distribution function of the steady-state Boltzmann equation for hard-core molecules in the presence of a temperature gradient has been obtained explicitly to second order in density and the temperature gradient. Some thermodynamical quantities are calculated from the velocity distribution function for hard-core molecules and compared with those

Laurent Bartholdi, Rostislav I. Grigorchuk, Volodymyr V. Nekrashevych

This paper is a survey, with few proofs, of ideas and notions related to self-similarity of groups, semi-groups and their actions. It attempts to relate these concepts to more familiar ones, such as fractals, self-similar sets, and renormalizable dynamical systems. In particular, it presents a plausible definition of what a "fractal group" should be, and giv

T. Gasenzer

We study the limitations for entanglement due to collisional decoherence in a Bose-Einstein condensate. Specifically we consider relative number squeezing between photons and atoms coupled out from a homogeneous condensate. We study the decay of excited quasiparticle modes due to collisions, in condensates of atoms with one or two internal degrees of freedom

Xinhua Peng, Xiwen Zhu, Ximing Fang, Mang Feng

The remarkable capability of quantum Fourier transformation (QFT) to extract the periodicity of a given periodic function has been exhibited by using nuclear magnetic resonance (NMR) techniques. Two separate sets of experiments were performed. In a full QFT, the periodicity were validated with state tomography and fidelity measurements. For a simplified QFT,

Dirk Schlingemann

In a previous paper a straight forward construction method for quantum error correcting codes, based on graphs, has been presented. These graph codes are directly related to cluster states which have been introduced by Briegel and Raussendorf. We show that the preparation of a cluster state as well as the coding operation for a graph code, can be implemented

Peter Domokos, Peter Horak, Helmut Ritsch

We present a time dependent quantum calculation of the scattering of a few-photon pulse on a single atom. The photon wave packet is assumed to propagate in a transversely strongly confined geometry, which ensures strong atom-light coupling and allows a quasi 1D treatment. The amplitude and phase of the transmitted, reflected and transversely scattered part o

Xinhua Peng, Xiwen Zhu, Ximing Fang, Mang Feng

We have experimentally implemented remote state preparation (RSP) of a qubit from a hydrogen to a carbon nucleus in molecules of carbon-13 labeled chloroform $^{13}$CHCl$_{3}$ over interatomic distances using liquid-state nuclear magnetic resonance (NMR) technique. Full RSP of a special ensemble of qubits, i.e., a qubit chosen from equatorial and polar great

Robert Alicki, Stanisław Kryszewski

The density operator of the arbitrary physical system must be positive definite. Employing the general master equation technique which preserves this property we derive equations of motion for the density operator of an active atom which interacts collisionally with the reservoir of perturber atoms. The obtained general relations applied to the two-level ato

V. Yu. Ponomarev

Some general features of the phonon damping model are presented. It is concluded that the fits performed within this model have no physical content.

Kazuhiro Yabana, Manabu Ueda, Takashi Nakatsukasa

Application of the absorbing boundary condition is discussed to analyse breakup reactions of weakly bound nuclei. The key ingredient is an introduction of the absorbing potential outside the physical area which simulates the outgoing boundary condition approximately. The scattering problem is then recasted into the Schroedinger like equation with a source te

Takashi Nakatsukasa, Kazuhiro Yabana, George F Bertsch

Density functional theory (DFT) is applied to atomic spectra under perturbations of superfluid liquid helium. The atomic DFT of helium is used to obtain the distribution of helium atoms around the impurity atom, and the electronic DFT is applied to the excitations of the atom, averaging over the ensemble of helium configurations. The shift and broadening of

A. Kuriyama, C. Providencia, J. da Providencia, Y. Tsue

Two types of boson-pair coherent states, which were proposed independently by the present authors, are investigated. Main conclusion is as follows : Although the two states are superposed contrastively in terms of the boson-pairs, the expectation values of the boson-pair operators for these states are the same as one another with high accuracy.

A. Kuriyama, C. Providencia, J. da Providencia, Y. Tsue

The treatment for the multiboson coherent state is extended for the completeness of the formulation. The basic idea for the extension is presented in terms of expanding the boson space. The MYT boson mapping plays a central role. The resultant multiboson coherent state includes the state obtained in our previous treatment and the form suggests various multib

R. D. Benguria, M. C. Depassier

We study travelling fronts of equations of the form $u_{tt} + ϕ(u) u_x = u_{xx} + f(u)$. A criterion for the transition from linear to nonlinear marginal stability is established for positive functions $ϕ(u)$ and for any reaction term $f(u)$ for which the usual parabolic reaction diffusion equation $u_t = u_{xx} + f(u)$ admits a front. As an application, we

Sergey V. Naydenov, Vladimir V. Yanovsky

The billiard problem of statistical physics is considered in a new geometric approach with a symmetric phase space. The structure and topological features of typical billiard phase portrait are defined. The connection between geometric, dynamic and statistic properties of smooth billiard is established. Other directions of the theory on development are point

Maciej Blaszak

Separability theory of one-Casimir Poisson pencils, written down in arbitrary coordinates, is presented. Separation of variables for stationary Harry-Dym and the KdV dressing chain illustrates the theory.

M. Saralegi-Aranguren, R. Wolak

In the paper we introduce the notions of a singular fibration and a singular Seifert fibration. These notions are natural generalizations of the notion of a locally trivial fibration to the category of stratified pseudomanifolds. For singular foliations defined by such fibrations we prove a de Rham type theorem for the basic intersection cohomology introduce

Vladimir Voevodsky

In this paper we give a direct geometric proof of the fact that tensoring with the Tate motive in the triangulated category of effective motives DM is a full embedding. The main part of the proof is given in the context of schemes of finite type over a noetherian base scheme.

Mu-Tao Wang

Let Σbe a minimal submanifold of \R^{n+m} that can be represented as the graph of a smooth map f:\R^n-->\R^m. We apply a formula we derived in the study of mean curvature flow to obtain conditions under which Σmust be an affine subspace. Our result covers all known ones in the general case. The conditions are stated in terms of the singular values of $df$.

Helga Baum

This paper is a survey on special geometric structures that admit conformal Killing spinors based on lectures, given at the ``Workshop on Special Geometric Structures in String Theory&#39;&#39;, Bonn, September 2001 and at ESI, Wien, November 2001. We discuss the case of Lorentzian signature and explain which geometries occur up to dimension 6.

T. Mansour

In this paper, we find an explicit formulas, or recurrences, in terms of generating functions for the cardinalities of the sets $S_n(T;τ)$ of all permutations in $S_n$ that contain $τ\in S_k$ exactly once and avoid a subset $T\subseteq S_3$, $|T|\geq2$. The main body of the paper is divided into three sections corresponding to the cases $|T|=2,3$ and $|T|\ge

Jiun-Cheng Chen

The main propose of this paper is to show that Bridgeland&#39;s moduli space of perverse point sheaves for certain flopping contractions gives the flops, and the Fourier-Mukai transform given by the birational correspondence of the flop is an equivalence between bounded derived categories.

Frederic Chapoton, Sergey Fomin, Andrei Zelevinsky

In hep-th/0111053, a complete simplicial fan was associated to an arbitrary finite root system. It was conjectured that this fan is the normal fan of a simple convex polytope (a generalized associahedron of the corresponding type). Here we prove this conjecture by explicitly exhibiting a family of such polytopal realizations.

George Androulakis

The methods of &#34;minimal vectors&#34; were introduced by Ansari and Enflo and strengthened by Pearcy, in order to prove the existence of hyperinvariant subspaces for certain operators on Hilbert space. In this note we present the method of minimal vectors for operators on super-reflexive Banach spaces and we give a new sufficient condition for the existen

J. Maurice Rojas, M. Vidyasagar

In this note, we derive an improved upper bound for the VC-dimension of neural networks with polynomial activation functions. This improved bound is based on a result of Rojas on the number of connected components of a semi-algebraic set.

Luuk Hoevenaars

It is known that electric-magnetic duality transformations are symmetries of the generalized Witten-Dijkgraaf-Verlinde-Verlinde (WDVV) equations. In Seiberg-Witten theory the solutions to these equations come in certain sets according to the gauge group. We show that the duality transformations transform solutions within a set to another solution within the

Nandinii Barbosa-Cendejas, Alfredo Herrera-Aguilar

We present a pair of symmetric formulations of the matter sector of the stationary effective action of heterotic string theory that arises after the toroidal compactification of d dimensions. The first formulation is written in terms of a pair of matrix potentials Z_1 and Z_2 which exhibits a clear symmetry between them and can be used to generate new famili

Kamran Diba, David A. Lowe

We study black hole evaporation of near-extremal black holes in spherically reduced models with asymptotically Minkowskian spacetime, with the effects of the back-reaction on the geometry included semi-classically. The stress-energy tensor is calculated for null in-falling observers. It is shown that the evaporation proceeds smoothly and there are no instabi

F. Astorga

We discuss an environmentally friendly renormalization group approach to analyze phase transitions. We intend to apply this method to the Electroweak Phase Transition. This work is in progress. We present some previously obtained results concerning a scalar theory, where the main features of this algorithm are introduced.

U. Baur, R. Clare, A. Denner, J. L. Diaz Cruz

We discuss the experimental and theoretical uncertainties on precision electroweak observables and their relationship to the indirect constraints on the Higgs-boson mass, $\MH$, in the Standard Model (SM). The critical experimental measurements ($\MW$, $\sweff$, $\mt$, ...) are evaluated in terms of their present uncertainties and their prospects for improve

A. V. Lipatov, V. A. Saleev, N. P. Zotov

Processes of heavy quark production at TEVATRON energies are considered using the semihard (k_T factorization) QCD approach with emphasis of the BFKL dynamics of gluon distributions. We investigate the dependence of the p_T distribution of heavy quark production (presented in the form of integrated cross-sections) on different forms of the unintegrated gluon

Wolfgang Lohmann

A summary of results obtained from e^+e^- annihilations at LEP is given. The precision measurements around the Z resonance, the results from charged gauge boson production and searches for new particles are reviewed. Particular emphasis is devoted to the Higgs boson. The prospects of an e^+e^- linear collider in the energy range of about 1 TeV are discussed.

LVD Collaboration

The present study is based on the sample of about 3 mln single muons observed by LVD at underground Gran Sasso Laboratory during 36500 live hours from June 1992 to February 1998. We have measured the muon intensity at slant depths from 3 km w.e. to 20 km w.e. Most events are high energy downward muons produced by meson decay in the atmosphere. The analysis o

The BABAR Collaboration, B. Aubert

The B0 lifetime has been measured with a sample of 23 million BBbar pairs collected by the BaBar detector at the PEP-II e+e- storage ring during 1999 and 2000. Events from the semileptonic decay B0 --> D*- l+ nu have been selected with a partial reconstruction method in which only the charged lepton and the slow pion from the D*- --> D0bar pi- decay are reco

J-C. Brient, H. Videau

The physics programme for a coming electron linear collider is dominated by events with final states containing many jets. We develop in this paper the opinion that the best approach is to optimise the independent measurement of the tracks in the tracker, the photons in the electromagnetic calorimeter and the neutral hadrons in the camorimetry, together with

Z. Juan Medellin, Jurgen Engelfried, Antonio Morelos

We report very preliminary results of a Dalitz-plot analysis of Lambda_c+ in the decay to p K- pi+ with the helicity formalism. We used the data from the fixed target experiment SELEX (E781) in Fermilab. We report about branching-ratios of the resonant states involved, and a possible initial state polarization.

Ibrahim Torres, Jurgen Engelfried, Antonio Morelos

We will present here the simulations of RICH detectors which will be used in the CKM experiment. We will verify their performance, critical to the experiment.

A. A. Bel&#39;kov, N. N. Karpenko, A. V. Lanyov, A. A. Spiridonov

The paper was withdrawn by the authors since it has not been reviewed and approved by an official body within the collaboration.

Marc Mars, M. M. Martin-Prats, Jose M. M. Senovilla

We prove that all spherically symmetric static spacetimes which are both regular at r=0 and satisfying the single energy condition rho + p_r + p_t >= 0 cannot contain any black hole region (equivalently, they must satisfy 2m/r <= 1 everywhere). This result holds even when the spacetime is allowed to contain a finite number of matching hypersurfaces. This the

G. Oliveira-Neto

We study an analytical solution to the Einstein&#39;s equations in 2+1-dimensions, representing the self-similar collapse of a circularly symmetric, minimally coupled, massless, scalar field. Depending on the value of certain parameters, this solution represents the formation of naked singularities. Since our solution is asymptotically flat, these naked sing

Juan A. Valiente Kroon

A study of the linearised gravitational field (spin 2 zero-rest-mass field) on a Minkowski background close to spatial infinity is done. To this purpose, a certain representation of spatial infinity in which it is depicted as a cylinder is used. A first analysis shows that the solutions generically develop a particular type of logarithmic divergence at the s

Faiz Arni, KayLiang Ong, Shalom Tsur, Haixun Wang

This paper describes the LDL++ system and the research advances that have enabled its design and development. We begin by discussing the new nonmonotonic and nondeterministic constructs that extend the functionality of the LDL++ language, while preserving its model-theoretic and fixpoint semantics. Then, we describe the execution model and the open architect

Jaeup U. Kim, Ben O&#39;Shaughnessy

Designable media can control properties of nanocomposite materials by spatially organizing nanoparticles. Here we theoretically study particle organization by ultrathin polymer films of grafted chains (``brushes&#39;&#39;). Polymer-soluble nanoparticles smaller than a brush-determined threshold disperse in the film to a depth scaling inversely with particle

D. M. Jezek, P. Capuzzi

We investigate the role of the interparticle-interaction strength in the distribution of two species of atoms inside a condensate. We focus upon the study of systems for which the minima of the trapping potentials for the species are displaced from each other by a distance that is small compared to the size of the total condensate. We show that in a small ra

Ines Samengo

We study the capacity with which a system of independent neuron-like units represents a given set of stimuli. We assume that each neuron provides a fixed amount of information, and that the information provided by different neurons has a random overlap. We derive analytically the dependence of the mutual information between the set of stimuli and the neural

Peter Grassberger

We present high statistics Monte Carlo results for the Drossel-Schwabl forest fire model in 2 dimensions. They extend to much larger lattices (up to $65536\times 65536$) than previous simulations and reach much closer to the critical point (up to $θ\equiv p/f = 256000$). They are incompatible with all previous conjectures for the (extrapolated) critical beha

S. -R. Eric Yang, A. H. MacDonald

We have investigated the interplay between the metal-insulator transition and ferromagnetism in $({\rm III}_{1-x},{\rm Mn}_x){\rm V}$ ferromagnetic semiconductors. Our study is based on a model in which $S=5/2$ Mn local moments are exchange-coupled to band electrons that interact via Coulomb interactions which each other, with ionized Mn acceptors, and with

S. L. A. de Queiroz

We investigate the finite-temperature corrections to scaling in the three-state square-lattice Potts antiferromagnet, close to the critical point at T=0. Numerical diagonalization of the transfer matrix on semi-infinite strips of width $L$ sites, $4 \leq L \leq 14$, yields finite-size estimates of the corresponding scaled gaps, which are extrapolated to $L\t

F. Adjémian, P. Evesque

This paper is concerned with the trends of stress fluctuations in dry granular materials as functions of the sample size D and of the grain diameter d. Results are obtained in the plateau regime of large axial deformation, during axi-symmetric uni-axial compression. Two cases have to be distinguished depending on whether the material generates or does not ge

S. Lubeck

We analyse numerically the critical behavior of an absorbing phase transition in a conserved lattice gas in an external field. The external field is realized as a spontaneous creation of active particles which drives the system away from criticality. Nevertheless, the order parameter obeys certain scaling laws for sufficiently small external fields. These sc

P. J. Jensen, G. M. Pastor

The magnetic ordering due to the long range dipole coupling in an ensemble of magnetic islands is investigated. If the islands are large enough and closely separated, the average dipole energy per island can explain the magnitude of the observed ordering temperature of such an ensemble. The energetical degeneracy with respect to a continuous in-plane rotatio

Tat-Sang Choy, Jian Chen, Selman Hershfield

The maximum current-perpendicular-to-plane giant magnetoresistance is searched for in magnetic multilayers made of Co, Ni, and Cu with disorder levels similar to those found in room temperature experiments. The calculation is made possible by a highly optimized linear response code, which uses the impurity averaged Green&#39;s function technique and a 9-band

D. Gerace, E. Pavarini, L. C. Andreani

We calculate the conductance through a quantum dot weakly coupled to metallic leads, modeled by the spin-1/2 Anderson model with finite Coulomb repulsion $U$. We adopt the non-crossing approximation method in its finite-$U$ extension (UNCA). Our results can be compared to those obtained with the exact numerical renormalization group method, and good agreemen

T. Domanski, J. Ranninger

We study a pseudogap region of the mixed boson fermion system using a recent formulation of the renormalization group technique through the set of infinitesimal unitary transformations. Renormalization of fermion energies gives rise to a depletion of the low energy states (pseudogap) for temperatures $T^{*}>T>T_{c}$ which foreshadows appearance of the pairwi

Kateryna Medvedyeva, Beom Jun Kim, Petter Minnhagen

The frequency $ω$ and temperature T dependent complex conductivity $σ$ of two weakly coupled 2D XY models subject to the RSJ dynamics is studied through computer simulations. A double dissipation-peak structure in $Re[ωσ]$ is found as a function of T for a fixed frequency. The characteristics of this double-peak structure, as well as its frequency dependence

Nicola Scafetta, Paolo Grigolini

The methods currently used to determine the scaling exponent of a complex dynamic process described by a time series are based on the numerical evaluation of variance. This means that all of them can be safely applied only to the case where ordinary statistical properties hold true even if strange kinetics are involved. We illustrate a method of statistical

Akira Furukawa, Akira Onuki

We present hydrodynamic equations of compressible fluids in gravity as a generalization of those in the Boussinesq approximation used for nearly incompressible fluids. They account for adiabatic processes taking place throughout the cell (the piston effect) and those taking place within plumes (the adiabatic temperature gradient effect). Performing two-dimen

G. Vignale, M. E. Flatte&#39;

A domain wall separating two oppositely magnetized regions in a ferromagnetic semiconductor exhibits, under appropriate conditions, strongly nonlinear I-V characteristics similar to those of a p-n diode. We study these characteristics as functions of wall width and temperature. As the width increases or the temperature decreases, direct tunneling between the

V. V. Laguta, M. D. Glinchuk, I. P. Bykov, R. Blinc

The 93Nb and 45Sc NMR spectra in PbSc_1/2Nb_1/2O_3 (PSN) and PbMg_1/3Nb_2/3O_3 (PMN) disordered relaxor ferroelectrics at the temperature T > T_0 (T_0 is the temperature of the dielectric susceptibility maximum) have been studied. Spectra analysis was performed on the base both of the analytical description of NMR lines shapes, allowing for homogeneous and i

C. W. Gardiner J. R. Anglin, T. I. A. Fudge

We show how to adapt the ideas of local energy and momentum conservation in order to derive modifications to the Gross-Pitaevskii equation which can be used phenomenologically to describe irreversible effects in a Bose-Einstein condensate. Our approach involves the derivation of a simplified quantum kinetic theory, in which all processes are treated locally.

Sharon M. Morsink

The r-modes of neutron stars can be driven unstable by gravitational radiation. While linear perturbation theory predicts the existence of this instability, linear theory can&#39;t provide any information about the nonlinear development of the instability. The subject of this paper is the weakly nonlinear regime of fluid dynamics. In the weakly nonlinear reg

Eva Villaver, Guillermo Garcia-Segura, Arturo Manchado

We have investigated the dynamical interaction of low- and-intermediate mass stars (from 1 to 5 Msun) with their interstellar medium (ISM). In this first paper, we examine the structures generated by the stellar winds during the Asymptotic Giant Branch (AGB) phase, using a numerical code and the wind history predicted by stellar evolution. The influence of t

Takamitsu Miyaji, Richard E. Griffiths

We show the results of the fluctuation analysis applied to the off-source areas from the two 1 Million second Chandra Deep Fields, including our new results on the Chandra Deep Field-South (CDF-S) in the 0.5-2 keV band in addition to those on the Chandra Deep Field-North (CDF-N), which have already been reported. The distribution of the X-ray counts in cells

C. -H. Rosie Chen, You-Hua Chu, Robert Gruendl, Shih-Ping Lai

NGC 5471B has been suggested to contain a hypernova remnant because of its extraordinarily bright X-ray emission. To assess its true nature, we have obtained high-resolution images in continuum bands and nebular lines with the Hubble Space Telescope, and high-dispersion long-slit spectra with the Kitt Peak National Observatory 4-m echelle spectrograph. The i

Eric D. Feigelson, Gordon P. Garmire, Steven H. Pravdo

To address the role of energetic processes in the solar nebula, we provide a detailed characterization of magnetic flaring in stellar analogs of the pre-main sequence Sun based on 23 hours observations of 43 analogs of the young Sun in the Orion Nebula Cluster obtained with the Chandra X-ray Observatory. We find the X-ray luminosities are strongly elevated o

D. M. Alexander, F. E. Bauer, W. N. Brandt, A. E. Hornschemeier

We provide constraints on optically faint (I>=24) X-ray sources, z>6 AGN, Very Red Objects (VROs; I-K>=4), and optically faint radio sources using the 1 Ms Chandra Deep Field North survey. We argue that the majority of the optically faint X-ray sources are obscured AGN at z=1-3. These sources comprise up to 50% of the X-ray detected AGN. Approximately 30% of

N. W. Evans, V. Belokurov

At any instant, there are roughly 1000 ongoing microlensing events to sources brighter than 20th magnitude in the Milky Way Galaxy. Large-scale maps of the microlensing optical depth and the mean timescale are constructed for a number of models of the Galactic bar and disk, incorporating the effects of streaming and spiral structure. Freudenreich&#39;s model

Guillermo García-Segura

Hydrodynamical (HD) simulations played an important role in understanding the dynamics and shaping of Planetary Nebulae (PNe) in the past century. However, HD solutions are just a first order approach. The new millennium arrives with the generalized understanding that the effects of magnetic fields (i.e., MHD) are necessary to study the dynamics of PNe. Thus

Feng Ma

While the accretion power in astrophysics has been studied in many astronomical environments, the ``spin--down power&#39;&#39; is often neglected. In this essay I demonstrate that the spin--down power alone may drive a rotating system from sub-critical condition to critical condition with a small but finite probability. In the case of an isolated spinning-do

A. A. Berezhnoi, S. G. Gusev, O. B. Khavroshkin, B. A. Poperechenko

The direct impact of the American spacecraft Lunar Prospector into the Moon on July 31, 1999 was accompanied by seismic effects comparable to a big moonquake. Such an impact can be accompanied by radio seismic radiation of the lunar surface layers. For registration of the lunar radio seismic radiation after the Lunar Prospector impact radio observations of t

Anita L. Cochran, William D. Cochran

On 3 and 4 October, 1995, we obtained high spectral resolving power (R=λ/Δλ= 60,000) observations of comet 122P/de Vico using the 2DCoude cross-dispersed echelle spectrograph on the 2.7-m telescope of McDonald Observatory. The spectra cover the wavelength range from 3830A--10192A. The spectra from 3830--5776A are continuous; from 5777--10192A there are incre

J. C. N. de Araujo, O. D. Miranda, O. D. Aguiar

We study the generation of a stochastic gravitational wave (GW) background produced from a population of core-collapse supernovae, which form black holes in scenarios of structure formation. We obtain, for example, that the formation of a population (Population III) of black holes, in cold dark matter scenarios, could generate a stochastic GW background with

Sebastian Lopez, Dieter Reimers, Sandro D&#39;Odorico, Jason X. Prochaska

We have obtained a high resolution, high S/N UVES spectrum of the bright QSO HE2243-6031 to analyze the damped Ly-alpha system (DLA) observed at z=2.33. The metallicity of this system is 1/12 solar at a neutral hydrogen column density of log N(HI)=20.7. From the observed ratios [Zn/Cr]=-0.01+/-0.05 and [S/Si]=-0.06+/-0.03$ we conclude that dust is very likel

Marco Chiaberge, F. Duccio Macchetto, William B. Sparks, Alessandro Capetti

We have studied the nuclei of 28 radio galaxies from the 3CR sample in the UV band. Unresolved nuclei (central compact cores, CCC) are observed in 10 of the 13 FR I, and in 5 of the 15 FR II. All sources that do not have a CCC in the optical, do not have a CCC in the UV. Two FR I (3C 270 and 3C 296) have a CCC in the optical but do not show the UV counterpar

Joel H. Kastner, Jingqiang Li, Ralf Siebenmorgen, David A. Weintraub

We present polarimetric imaging of the protoplanetary nebula RAFGL 2688 obtained at 4.5 microns with the Infrared Space Observatory (ISO). We have deconvolved the images to remove the signature of the point spread function of the ISO telescope, to the extent possible. The deconvolved 4.5 micron image and polarimetric map reveal a bright point source with fai

Davide Lazzati, Enrico Ramirez-Ruiz, Gabriele Ghisellini

We report the discovery of a transient and fading hard X-ray emission in the BATSE lightcurves of a sample of short gamma-ray bursts. We have summed each of the four channel BATSE light curves of 76 short bursts to uncover the average overall temporal and spectral evolution of a possible transient signal following the prompt flux. We found an excess emission