February 2001 arXiv papers — page 14

F. Frontera, L. Amati, M. Vietri, J. J. M. in 't Zand

We report on the prompt X- and gamma-ray observations of GRB990712 with the BeppoSAX Gamma-Ray Burst Monitor and Wide Field Camera No. 2. Due to Sun constraints, we could not perform a follow-up observation with the BeppoSAX Narrow Field Instruments. The light curve of the prompt emission shows two pulses and a total duration of about 40s in X-rays. In gamma

Stavros Garoufalidis, Jerome Levine

We show that surgery on a connected clover (or clasper) with at least one loop preserves the concordance class of a knot. Surgery on a slightly more special class of clovers preserves invertible concordance. We also show that the converse is false. Similar results hold for clovers with at least two loops vs. S-equivalence.

R. Giraud, W. Wernsdorfer, A. M. Tkachuk, D. Mailly

Staircase hysteresis loops of the magnetization of a LiY_0.998Ho_0.002F_4 single crystal are observed at subkelvin temperatures and low field sweep rates. This behavior results from quantum dynamics at avoided level crossings of the energy spectrum of single Ho^{3+} ions in the presence of hyperfine interactions. Enhanced quantum relaxation in constant trans

Luca Griguolo, Massimo Pietroni

The non-commutative version of the euclidean $g^2ϕ^4$ theory is considered. By using Wilsonian flow equations the ultraviolet renormalizability can be proved to all orders in perturbation theory. On the other hand, the infrared sector cannot be treated perturbatively and requires a resummation of the leading divergencies in the two-point function. This is an

Benjamin Canals, Dmitry Garanin

Thermodynamic quantities and correlation functions (CFs) of the classical antiferromagnet on the checkerboard lattice are studied for the exactly solvable infinite-component spin-vector model, $D \to \infty$. In contrast to conventional two-dimensional magnets with continuous symmetry showing extended short-range order at distances smaller than the correlati

Benjamin Canals

Within a spin wave analysis and a fermionic large-n limit, it is shown that the antiferromagnetic Heisenberg model on the checkerboard lattice may have different ground states, depending on the spin size $S$. Through an additional exchange interaction that corresponds to an inter-tetrahedra coupling, the stability of the Néel state has been explored for all

Chung-Wen Kao, Gouranga C. Nayak, Walter Greiner

We apply the closed-time path integral formalism to study the medium effects of non-equilibrium gluon matter. We derive the medium modified resummed gluon propagator to the one loop level in non-equilibrium in the covariant gauge. The gluon propagator we derive can be used to remove the infrared divergences in the secondary parton collisions to study thermal

F. C. Lombardo, F. D. Mazzitelli, R. J. Rivers

We analyze the onset of classical behaviour after a second-order phase transition by considering a scalar field theory in which the system-field interacts with its environment, represented both by further fields and by its own short-wavelength modes. Within our approximations we see that the long-wavelength modes have become classical by the time that the tr

F. W. Stecker, Sheldon L. Glashow

We use the recent reanalysis of multi-TeV gamma-ray observations of Mrk 501 to constrain the Lorentz invariance breaking parameter involving the maximum electron velocity. Our limit is two orders of magnitude better than that obtained from the maximum observed cosmic-ray electron energy.

M. A. L. Marques, Alberto Castro, Angel Rubio

We present a detailed study of different exchange-correlation (xc) functionals in describing the dynamical properties of finite systems. For that purpose, we calculated the static polarizabilities, ionization potentials and optical absorption spectrum of four small clusters, Na_2, Na_4, SiH_4 and Si_2H_6, using a real-space, real-time technique. The computed

Chao-Hsi Chang, Yu-Qi Chen, Guo-Li Wang, Hong-Shi Zong

The semileptonic decays of meson $B_c$ to a P-wave charmonium state $χ_c(^3P_J)$ or $h_c(^1P_1)$ are computed. The results show that the decays are sizable so they are accessible in Tevatron and in LHC, especially, with the detectors LHCB and BTeV in the foreseeable future, and of them, the one to the $^1P_1$ charmonium state potentially offers us a novel wi

T. S. Grigera, V. Martin-Mayor, G. Parisi, P. Verrocchio

The topological nature of the disorder of glasses and supercooled liquids strongly affects their high-frequency dynamics. In order to understand its main features, we analytically studied a simple topologically disordered model, where the particles oscillate around randomly distributed centers, interacting through a generic pair potential. We present results

A. Lanzara, P. V. Bogdanov, X. J. Zhou, S. A. Kellar

Coupling between electrons and phonons (lattice vibrations) drives the formation of the electron pairs responsible for conventional superconductivity. The lack of direct evidence for electron-phonon coupling in the electron dynamics of the high transition temperature superconductors has driven an intensive search for an alternative mechanism. A coupling of a

Michael J. W. Hall, Marcel Reginatto

An exact uncertainty principle, formulated as the assumption that a classical ensemble is subject to random momentum fluctuations of a strength which is determined by and scales inversely with uncertainty in position, leads from the classical equations of motion to the Schrodinger equation. Thus there is an exact formulation of the uncertainty principle whic

Li-Yi Hsu, Yih-Yuh Chen

The paper has been withdrawn

Yoshihiko Kondo, Osamu Morimatsu

We reinvestigate the QCD sum rule for the pi NN coupling constant, g, starting from the vacuum-to-pion matrix element of the correlation function of the interpolating fields of two nucleons. We study in detail the physical content of the correlation function without referring to the effective theory. We consider the invariant correlation functions by splitti

Kaiki Taro Inoue

We revisit the observational constraints on compact(closed) hyperbolic(CH) models from cosmic microwave background(CMB). We carry out Bayesian analyses for CH models with volume comparable to the cube of the present curvature radius using the COBE-DMR data and show that a slight suppression in the large-angle temperature correlations owing to the non-trivial

Frédéric Bourgeois, Klaus Mohnke

We study the coherent orientations of the moduli spaces of holomorphic curves in Symplectic Field Theory, generalizing a construction due to Floer and Hofer. In particular we examine their behavior at multiple closed Reeb orbits under change of the asymptotic direction. The orientations are determined by a certain choice of orientation at each closed Reeb or

Sabino Matarrese, Roya Mohayaee

A {\it stochastic adhesion} model is introduced, with the purpose of describing the formation and evolution of mildly nonlinear structures, such as sheets and filaments, in the intergalactic medium (IGM), after hydrogen reionization. The model is based on replacing the overall force acting on the baryon fluid -- as it results from the composition of local gr

Pieter Kok

In quantum information and communication, optical schemes provide simple and intuitive experimental implementations. Of particular importance is quantum state preparation. In this thesis, the creation of polarisation entanglement using a particular class of optical circuits is studied. I give a mathematical description of this class of circuits in terms of H

S. Bandyopadhyay

Compared to quantum logic gates, quantum memory has received far less attention. Here, we explore the prognosis for a solid-state, scalable quantum dynamic random access memory (Q-DRAM), where the qubits are encoded by the spin orientations of single quantons in exchange-decoupled quantum dots. We address, in particular, various possibilities for implementin

F. Spineanu, M. Vlad

A systematic method is proposed for the determination of the statistical properties of a field consisting of a coherent structure interacting with turbulent linear waves. The explicit expression of the generating functional of the correlations is obtained, performing the functional integration on a neighbourhood in the function space around the soliton. The

J. R. Mureika

Based on a mathematical simulation which reproduces accurate split and velocity profiles for the 100 and 200 metre sprints, the magnitudes of altitude and mixed wind/altitude-assisted performances as compared to their sea-level equivalents are presented. It is shown that altitude-assisted times for the 200 metre are significantly higher than for the 100 metr

V. A. Kuz'menko

The physical nature of the photon mixing and photon echo processes is discussed on the basis of inequality of the forward and backward optical transitions.

M. Payami

We have used the stabilized spin-polarized jellium model to calculate the equilibrium sizes of metal clusters. Our self-consistent calculations in the local spin-density approximation show that for an $N$-electron cluster, the equilibrium is achieved for a configuration in which the difference in the numbers of up-spin and down-spin electrons is zero or unit

A. M. Chechelnitsky

We present the brief review of some central problems, anomalies, paradoxes of Astrophysics, Cosmology and new approaches to its decisions, proposed by the Wave Universe Concept (WU Concept). All these, anyhow, - Hot Points of modern science of Universe, about which Standard Model have not authentic answers. The represented set of brief (justified) Novels ref

Rowena Ball, Robert L. Dewar

A mathematically and physically sound three-degree-of-freedom dynamical model that emulates low- to high-confinement mode (L--H) transitions is elicited from a singularity theory critique of earlier fragile models. We construct a smooth map of the parameter space that is consistent both with the requirements of singularity theory and with the physics of the

Christopher D. Nantista, Sami G. Tantawi

In this letter, we present a novel four-way divider/combiner in rectangular waveguide. The design is completely two-dimensional in the h-plane, with eight-fold mirror symmetry, and is based on a recent four-port hybrid design [6]. In combining mode, it can function as a phased array with four inputs and four outputs. The planar nature of this design provides

C. D. Nantista, W. R. Fowkes, N. M. Kroll, S. G. Tantawi

Two basic designs have been developed for waveguide hybrids, or 3-dB couplers, capable of handling hundreds of megawatts at X-band. Coupling is provided by one or two connecting waveguides with h-plane junctions and matching elements. In the former case, the connecting waveguide supports two modes. Small apertures and field-enhancing e-bends are avoided to r

Sujay Chattopadhyay, Satyabrata Sahoo, Jayprokas Chakrabarti

The enzyme Glyceraldehyde-3-Phosphate Dehydrogenase (GAPDH) catalyses the decomposition of glucose. The gene that produces the GAPDH is therefore present in a wide class of organisms. We show that for this gene the average value of the fluctuations in nucleotide distribution in the codons, normalized to strand bias, provides a reasonable measure of how the g

R. Aguirre, A. L. De Paoli

We study the propagation of the light mesons sigma, omega, rho, and a0(980) in dense hadronic matter in an extended derivative scalar coupling model. Within the scheme proposed it is possible to unambiguously define effective density-dependent couplings at the Lagrangian level. We first apply the model to study asymmetric nuclear matter with fixed isospin as

L. Ts. Adzhemyan, N. V. Antonov, A. Mazzino, P. Muratore-Ginanneschi

We investigate the scaling properties a model of passive vector turbulence with pressure and in the presence of a large-scale anisotropy. The leading scaling exponents of the structure functions are proven to be anomalous. The anisotropic exponents are organized in hierarchical families growing without bound with the degree of anisotropy. Nonlocality produce

Sami I. Muslih

The Hamilton-Jacobi method of constrained systems is discussed. The equations of motion of a singular system with time dependent constraints are obtained as total differential equations in many variables. The integrability conditions for the relativistic particle in a plane wave lead us to obtain the canonical phase-space coordinates with out using any gauge

Thomas Kwok-keung Au

The dynamical properties, especially the symmetric orbits, of the 2-parameter family of circle maps called off-center reflection is studied.

Thomas Kwok-keung Au, Xiao-song Lin

In this article, we attempt to study the possible link between the dynamics of a circle map and the caustics of its iterations. The attention is on a geometrically defined off-center reflections, which, coincidentally, is also a generalization of standard perturbation of rotation. Some results of the caustics and dynamics of the family of maps are given. The

Michael W Davis, Boris Okun

Associated to any finite flag complex L there is a right-angled Coxeter group W_L and a cubical complex Σ_L on which W_L acts properly and cocompactly. Its two most salient features are that (1) the link of each vertex of Σ_L is L and (2) Σ_L is contractible. It follows that if L is a triangulation of S^{n-1}, then Σ_L is a contractible n-manifold. We descri

Stavros Garoufalidis, Jerome Levine

Using basic topology and linear algebra, we define a plethora of invariants of boundary links whose values are power series with noncommuting variables. These turn out to be useful and elementary reformulations of an invariant originally defined by M. Farber.

Victor Bovdi

We give an explicit list of all p-groups G with a cyclic subgroup of index p^2, such that the group algebra KG over the field K of characteristic p has a filtered multiplicative K-basis. We also proved that such a K-basis does not exist for the group algebra KG, in the case when G$ is either a powerful p-group or a two generated p-group (p\not=2) with a cent

John Atwell Moody

Let V be an irreducible affine algebraic variety over a field k of characteristic zero, and let (f_0,...,f_m) be a sequence of elements of the coordinate ring. There is probably no elementary condition on the f_i and their derivatives which determines whether the blowup of V along (f_0,...,f_m) is nonsingular. The result is that there indeed is such an eleme

N. Dokuchaev

It is given an effective upper estimate of expectation of |T_1-T_2|, where T_1 and T_2 are the first exit times from a region for two vector diffusion processes.

Hugh R. Morton

The Murphy operators in the Hecke algebra H_n of type A are explicit commuting elements whose sum generates the centre. They can be represented by simple tangles in the Homfly skein theory version of H_n. In this paper I present a single tangle which represents their sum, and which is obviously central. As a consequence it is possible to identify a natural b

Alexander Polishchuk

We describe a family of $q$-series generating the space of weight 1 modular forms coming from indefinite binary quadratic forms and study linear relations between these series.

Vladlen Timorin

We investigate some combinatorial properties of convex polytopes simple in edges. For polytopes whose nonsimple vertices are located sufficiently far one from another, we prove an analog of the Hard Lefschetz theorem. It implies Stanley's conjecture for such polytopes.

Thomas Kwok-keung Au, Luen-fai Tam, Tom Yau-heng Wan

Non-polynomial growth harmonic maps from the complex plane to the hyperbolic space are studied. Some non-surjectivity results are obtained. Moreover, images of such harmonic maps are investigated with reference to their Hopf differentials.

Thomas Kwok-keung Au, Tom Yau-heng Wan

We study the conditions on the physical parameters in the Helfrich bending energy of lipid bilayer vesicles. Among embedded surfaces with a biconcave axisymmetric shape, the variation equation is analyzed in detail. This leads to simple conditions which guarantee the solution the information about the geometry.

G. N. J. Ananos, N. F. Svaiter

We discuss the $ϕ^4$ and $ϕ^6$ theory defined in a flat $D$-dimensional space-time. We assume that the system is in equilibrium with a thermal bath at temperature $β^{-1}$. To obtain non-perturbative result, the $ 1/N $ expansion is used. The method of the composite operator (CJT) for summing a large set of Feynman graphs, is developed for the finite tempera

Joseph A. Minahan

We study the fluctuation modes for lump solutions of the tachyon effective potential in p-adic open string theory. We find a discrete spectrum with equally spaced mass squared levels. We also find that the interactions derived from this field theory are consistent with p-adic string amplitudes for excited string states.

M. Mangin-Brinet, J. Carbonell, V. A. Karmanov

We show that in the system of two fermions interacting by scalar exchange, the solutions for J$^π$=$0^+$ bound states are stable without any cutoff regularization for coupling constant below some critical value.

C. P. Martin

Chiral gauge anomalies on noncommutative Minkowski Space-time are computed and have their origin elucidated. The consistent form and the covariant form of the anomaly are obtained. Both Fujikawa's method and Feynman diagram techniques are used to carry out the calculations

Mariusz P. Dabrowski

We discuss various superstring effective actions and, in particular, their common sector which leads to the so-called pre-big-bang cosmology (cosmology in a weak coupling limit of heterotic superstring). Then, we review the main ideas of the Horava-Witten theory which is a strong coupling limit of heterotic superstring theory. Using the conformal relationshi

M. Cadoni, P. Carta

We review recent progress in understanding the anti-de Sitter/conformal field theory correspondence in the context of two-dimensional dilaton gravity theory.

J. Kluson

In this paper we would like to discuss the emergence of D-branes from infinite many D-instantons in bosonic and type IIA string theory in the framework of boundary string field theory.

Hossein Motavali, Mahdi Golshani

We consider the existence of a Noether symmetry in the scalar-tensor theory of gravity in flat Friedman Robertson Walker (FRW) cosmology. The forms of coupling function $ω(ϕ)$ and generic potential $V(ϕ)$ are obtained by requiring the existence of a Noether symmetry for such theory. We derive exact cosmological solutions of the field equations from a point-l

Michael McNeil Forbes, Ariel R. Zhitnitsky

We present a mechanism for generating primordial magnetic fields with large correlation lengths on the order of 100 kpc today. The mechanism is based on recently conjectured QCD domain walls or similar CP violating domain walls with QCD scale structure. Such domain walls align the electric and magnetic dipole moments of the nucleons shortly after the QCD pha

Vladimir Gribanov, Sergey Kovalenko, Ivan Schmidt

We study possible contributions of heavy sterile neutrinos $ν_h$ to the decays $τ^-\to e^{\pm}(μ^{\pm})π^{\mp}π^-$. From the experimental upper bounds on their rates we derive new constraints on the $ν_h-ν_τ$ mixing in the mass region $140.5{MeV}\leq m_{ν_h}\leq 1637$ MeV. We discuss cosmological and astrophysical status of $ν_h$ in this mass region and comp

R. C. Hwa

The gluon distribution of a nucleon propagating through a nucleus can change depending on how far the penetration depth is. It is a nonperturbative process that we describe by an evolution equation. The kernel of the integral equation is to be determined by a phenomenological study of J/psi suppression in pA collision. The data of E866 on alpha(x_F) shows si

A. Cooper-Sarkar

Recent HERA data on structure functions and reduced cross-sections are presented and their significance for our understanding of the low-x region is discussed.

Joannis Papavassiliou

The consistent description of resonant transition amplitudes within the framework of perturbative field theories necessitates the definition and resummation of off-shell Green's functions, which must respect several crucial physical requirements. In particular, the generalization of the usual Breit-Wigner formalism in a non-Abelian context constitutes a

Thomas A. Trainor

Implications of hadronization as a rapid traversal of the QCD phase boundary are explored for correlation structures in jets, N-N collisions and heavy-ion collisions. Hadronization viewed as a partition of the prehadonic system restricts the scale interval over which power-law jet correlation structures survive. Rapid traversal of the QCD phase boundary may

Thomas Kress

The large statistics of millions of hadronic Z0 decays, accumulated by the four LEP experiments between 1989 and 1995, allowed for detailed investigations of the fragmentation process. Inclusive Lambda_b baryons and Lambda hyperons at intermediate and high momentum have been found to show longitudinal polarization. This may be related to the primary quark an

Jose A. Gonzalez, Daniel Sudarsky

There is a theorem known as a Virial theorem that restricts the possible existence of non-trivial static solitary waves with scalar fields in a flat space-time with 3 or more spatial dimensions. This raises the following question: Does the analogous curved space-time version hold?. We investigate the possibility of solitons in a 4-D curved space-time with a

K. Buchner

In order to get geodesically complete Reissner - Nordstroem space - times, it is necessary to identify pairs of singular points. This can be done in such a way that "wormholes" are created which generate electric field lines without any charge. Finally, it is shown that it is possible to glue these space - times not in the singularities r=0, but at s

Bijan Saha, G. N. Shikin

Self-consistent solutions to nonlinear spinor field equations in General Relativity are studied for the case of Bianchi type-I space-time. It has been shown that introduction of $Λ$-term in the Lagrangian generates oscillations of the Bianchi type-I model.

L. Herrera, A. Di Prisco, J. Ospino, E. Fuenmayor

The condition for the vanishing of the Weyl tensor is integrated in the spherically symmetric case. Then, the resulting expression is used to find new, conformally flat, interior solutions to Einstein equations for locally anisotropic fluids. The slow evolution of these models is contrasted with the evolution of models with similar energy density or radial p

Joshua Wood, William Moreau

The field equations of Mannheim's theory of conformal gravity with dynamic mass generation are solved numerically in the interior and exterior regions of a model spherically symmetric sun with matched boundary conditions at the surface. The model consists of a generic fermion field inside the sun, and a scalar Higgs field in both the interior and exterio

Leonard S. Abrams

The historical postulates for the point mass are shown to be satisfied by an infinity of space-times, differing as to the limiting acceleration of a radially approaching test particle. Taking this limit to be infinite gives Schwarzschild's result, which for a point mass at x = y = z = 0 has C(0+) = a^2, where a = 2m and C(r) denotes the coefficient of th

O. Saremi

We study a minisuperspace quantum cosmology for a 2+1 dimensional de Sitter universe and find the wave function both exactly and in WKB approximation. Then we extend the model to a canonically quantized field theory for quantum gravity, i.e., a midisuperspace, and obtain the wave functional of the resulting field theory in the saddle point approximation. It

Nikolai V. Mitskievich, Alberto A. Garcia

The exact charged rotating solution of 2+1 Einstein-Maxwell equations with $Λ$ term is obtained and its properties outlined. It generalizes the Cataldo-Cruz-del Campo-Garc{\'ı}a relativistic charged massive black hole on the 2+1 anti-de Sitter cosmological background. We show that rotating solutions correspond to inhomogeneous field equations, thus prese

M. Casas, N. J. Davidson, M. de Llano, T. A. Mamedov

A two-dimensional (2D) assembly of noninteracting, temperature-dependent, composite-boson Cooper pairs (CPs) in chemical and thermal equilibrium with unpaired fermions is examined in a binary boson-fermion statistical model as the superconducting singularity temperature is approached from above. The model is derived from {\it first principles} for the BCS mo

Nara Guisoni, Vera Bohomoletz Henriques

Square water takes into account the directionality of hydrogen bonds. The model is reviewed and its properties as a solvent for apolar particles are studied through Monte Carlo simulations. Specific heat measurements are used to identify phase separation. Data for comparison with the lattice gas on the square lattice are presented and the relation to non-ass

T. Yu. Astakhova, O. D. Gurin, M. Menon, G. A. Vinogradov

We present the results on the soliton excitations in carbon nanotubes (CNT) using Brenner's many-body potential. Our numerical simulations demonstrate high soliton stability in (10,10) CNT. The interactions of solitons and solitary excitations with CNT defects are found to be inelastic if the excitations and defects length scales are comparable, resultin

B. Braunecker, P. -A. Bares

We investigate the transport properties of a model of an interacting electronic resonant level system. The hybridization of the localized resonant level is treated in perturbation and the contributions to all orders are computed. This includes an exact treatment of the electron scattering from the localized level. The renormalization of the direct tunneling

H. H. M. Vasconcelos, U. M. S. Costa, M. P. Almeida

The influence of turbulent effects on a fluid flow through a (pseudo) porous media is studied by numerically solving the set of Reynolds-averaged Navier-Stokes equations with the $κ$-$ε$ model for turbulence. The spatial domains are two-dimensional rectangular grids with different {\it porosities} obtained by the random placing of rigid obstacles. The object

Benjamin Canals, Dmitry Garanin

Correlation functions (CFs) of the classical Heisenberg antiferromagnet on the pyrochlore lattice are studied by solving exactly the infinite-component spin-vector model. % As in many Fully Frustrated Lattices, the constraint due to the minimization of the energy and the particular structure based on corner sharing tetrahedra both contribute to the creation

Y. Avishai, Y. Tokura

Electron transport in a finite one dimensional quantum spin chain (with ferromagnetic exchange) is studied within an $s-d$ exchange Hamiltonian. Spin transfer coefficients strongly depend on the sign of the $s-d$ exchange constant. For a ferromagnetic coupling, they exhibit a novel resonant pattern, reflecting the salient features of the combined electron-sp

D. A. Ivanov, L. B. Ioffe, V. B. Geshkenbein, G. Blatter

As the size of a Josephson junction is reduced, charging effects become important and the superconducting phase across the link turns into a periodic quantum variable. Isolated Josephson junction arrays are described in terms of such periodic quantum variables and thus exhibit pronounced quantum interference effects arising from paths with different winding

M. Ya. Amusia, V. R. Shaginyan

A model of a Fermi liquid with the fermion condensate (FC) is applied to the consideration of quasiparticle excitations in high temperature superconductors, in their superconducting and normal states. Within our model the appearance of the fermion condensate presents a quantum phase transition, that separates the regions of normal and strongly correlated ele

I. Shlimak, V. I. Safarov, I. D. Vagner

The idea of quantum computation is the most promising recent developments in the high-tech domain, while experimental realization of a quantum computer poses a formidable challenge. Among the proposed models especially attractive are semiconductor based nuclear spin quantum computer's (S-NSQC), where nuclear spins are used as quantum bistable elements, &

Peter Johansson, S. Peter Apell, D. R. Penn

We propose a theory for a type of apertureless scanning near field microscopy that is intended to allow the measurement of magnetism on a nanometer length scale. A scanning probe, for example a scanning tunneling microscope (STM) tip, is used to scan a magnetic substrate while a laser is focused on it. The electric field between the tip and substrate is enha

F. Restagno, J. Crassous, E. Charlaix, M. Monchanin

We present a new capacitive sensor for displacement measurement in a Surface Forces Apparatus (SFA) which allows dynamical measurements in the range of 0-100 Hz. This sensor measures the relative displacement between two macroscopic opaque surfaces over periods of time ranging from milliseconds to in principle an indefinite period, at a very low price and do

Wen-Fa Lu, Chul Koo Kim

Within the sine-Gordon formalism of a two-dimensional neutral classical Coulomb gas, a convergent expansion with non-perturbative nature is performed to calculate the thermodynamic potential and construct the phase diagram. It is shown that truncation at the first order yields the Gaussian approximation. The second- and third-order corrections are analyzed f

Masahito Mochizuki, Masatoshi Imada

The properties and mechanism of the magnetic phase transition of the perovskite-type Ti oxides, which is driven by the Ti-O-Ti bond angle distortion, are studied theoretically by using the effective spin and pseudospin Hamiltonian with strong Coulomb repulsion. It is shown that the A-type antiferromagnetic (AFM(A)) to ferromagnetic (FM) phase transition occu

A. A. Louis

This contribution briefly reviews some recent work demonstrating the partial breakdown of the colloidal fluid <--> atomic fluid analogy. The success of liquid state theory for atomic fluids stems in part from the van der Waals picture, where steric interactions dominate the structure, and attractive interactions can be added as a perturbation. For complex fl

A. A. Louis, R. Roth

We propose that the behavior of asymmetric binary fluid mixtures with a large class of attractive or repulsive interparticle interactions can be understood by mapping onto effective non-additive hard-sphere models. The latter are best analyzed in terms of their underlying depletion potentials which can be exactly scaled onto known additive ones. By tuning th

G. Dubus, J. -M. Hameury, J. -P. Lasota

We study the prospect of explaining the outbursts of Soft X-ray Transients (SXTs) by the thermal-viscous instability in a thin disc. This instability is linked to hydrogen ionization and is significantly changed when irradiation of the disc by X-rays from the inner regions is included. We present the first numerically reliable, physically consistent calculat

J. M. Paredes, J. Marti, M. Ribo, M. Massi

Microquasars are stellar x-ray binaries that behave as a scaled down version of extragalactic quasars. The star LS 5039 is a new microquasar system with apparent persistent ejection of relativistic plasma at a 3 kiloparsec distance from the sun. It may also be associated with a gamma-ray source discovered by the Energetic Gamma Ray Experiment Telescope (EGRE

Dae-Sik Moon, Stephen S. Eikenberry

We report the discovery of coupling between periodic and aperiodic variability and ~12-mHz X-ray quasi-periodic oscillations (QPOs) from the X-ray binary pulsar Her X-1 using data from the Rossi X-Ray Timing Explorer. We found two different couplings, one during the pre-eclipse dips and the other during the normal state of the source, using a method which di

S. S. Doeleman, Z. -Q. Shen, A. E. E. Rogers, G. C. Bower

At radio wavelengths, images of the compact radio source Sagittarius A* (Sgr A*) in the Galactic Center are scatter broadened with a lambda^2 dependence due to an intervening ionized medium. We present VLBI observations of Sgr A* at 86 GHz using a six station array including the VLBA antennas at Pie Town, Fort Davis and Los Alamos, the 12m antenna at Kitt Pe

L. L. Kiss, B. A. Skiff

We present an analysis of eleven years of Stromgren by photometry of the red semiregular variable star AI Aurigae. An early period determination of 63.9 days is confirmed by the long-term light curve behaviour. The light curve shows semi-regular changes with a mean period of 65 days reaching an amplitude of 0.6 mag in some cycles. The b-y colour changes perf

M. Dessauges-Zavadsky, S. D&#39;Odorico, R. G. McMahon, P. Molaro

We present the first high-resolution (6.2 to 7.7 km/s FWHM) spectra of the APM BR J0307-4945 quasar at z_em = 4.73 obtained with UVES on the 8.2m VLT Kueyen telescope. We focus our analysis on a damped Ly-alpha (DLA) system at z_abs = 4.466 with a neutral hydrogen column density N(HI) = (4.68 +/- 0.97) 10^{20} cm^{-2}. It is the most distant DLA system known

V. Kalogera, K. Belczynski

In this paper we present a brief overview of population synthesis methods with a discussion of their main advantages and disadvantages. In the second part, we present some recent results from synthesis models of close binary compact objects with emphasis on the predicted rates, their uncertainties, and the model input parameters the rates are most sensitive

Grazyna Stasinska, Daniel Schaerer, Claus Leitherer

We constructed diagnostic diagrams using emission line ratios and equivalent widths observed in several samples of HII galaxies. The diagrams are compared to predictions from new photoionization models for evolving starbursts. We find that HII galaxies from objective-prism surveys are not reproduced by models of instantaneous starbursts surrounded by constan

P. T. Zycki, A. Rozanska

A number of recent results from X-ray observations of Active Galactic Nuclei involving the Fe K alpha line (reduction of line variability compared to the X-ray continuum variability, the X-ray ``Baldwin effect&#39;&#39;) were attributed to a presence of a hot, ionized skin of an accretion disc, suppressing emission of the line. The ionized skin appears as a

K. Kohri, Shoichi Yamada

The vacuum polarization tensor in strong external magnetic fields has been evaluated numerically for various strengths of magnetic fields and momenta of photons under the threshold of the $e^{\pm}$ pair creation. The fitting formula has been obtained which reproduces the calculated results within 10 % of error. The proper time method is employed further to o

C. A. L. Bailer-Jones, R. Gupta, H. P. Singh

Artificial neural networks are algorithms which have been developed to tackle a range of computational problems. These range from modelling brain function to making predictions of time-dependent phenomena to solving hard (NP-complete) problems. In this introduction we describe a single, yet very important, type of network known as a feedforward network. This

C. A. L. Bailer-Jones

Current and future large astronomical surveys will yield multiparameter databases on millions or even billions of objects. The scientific exploitation of these will require powerful, robust, and automated classification tools tailored to the specific survey. Partly motivated by this, the past five to ten years has seen a significant increase in the amount of

Yutaka Fujita

In order to find the conditions which determine whether X-Ray hot gas in galaxy groups (intragroup gas; IGG) is heated externally or internally, we investigate the evolution of blast waves in galaxy groups growing on a hierarchical clustering scenario. We find that the blast waves driven by quasars are confined in groups and heat the IGG internally at z<~ 1.

James R. Graham, Richard R. Treffers

We describe the design, fabrication, and operation of an infrared camera which is in use at the 30-inch telescope of the Leuschner Observatory. The camera is based on a Rockwell PICNIC 256 x 256 pixel HgCdTe array, which is sensitive from 0.9-2.5 micron. The primary purpose of this telescope is for undergraduate instruction. The cost of the camera has been m

Alberto J. Castro-Tirado

GRBs have remained a puzzle for many high-energy astrophysicists since their discovery in 1967. With the advent of the X-ray satellites BeppoSAX and RossiXTE, it has been possible to carry out deep multi-wavelength observations of the counterparts associated with the long GRBs class just within a few hours of occurence, thanks to the observation of the fadin

H. -J. He, N. Polonsky, S. Su

The standard model accommodates, but does not explain, three families of leptons and quarks, while various extensions suggest extra matter families. The oblique corrections from extra chiral families with relatively light (weak-scale) masses, $M_{f} \sim <H> $, are analyzed and used to constrain the number of extra families and their spectrum. The analysis i