bluuebunny/crossref_metadata_2025 huggingface dataset:
ON A GROUPOID CONSTRUCTION FOR ACTIONS OF CERTAIN INVERSE SEMIGROUPS
Authors: NICA ALEXANDRU
Published: November 2004

We consider a version of the notion of F-inverse semigroup (studied in the algebraic theory of inverse semigroups). We point out that an action of such an inverse semigroup on a locally compact space has associated a natural groupoid construction, very similar to the one of a transformation group. We discuss examples related to Toeplitz algebras on subsemigroups of discrete groups, to Cuntz-Krieger algebras, and to crossed-products by partial automorphisms in the sense of Exel.
LATTICE QCD CURRENT STATUS AND GOALS AT ONE TERAFLOPS
Authors: DeTAR CARLETON
Published: November 2004

Through numerical simulations over the past decade we have made significant progress toward solving quantum chromodynamics (QCD), the widely accepted theory of the strong interactions. Quantitatively respectable results are beginning to emerge. We are also gaining new qualitative insights into the workings of the theory that will assist in the design and analysis of experiment. I give a few examples of recent progress in lattice QCD and discuss goals and prospects for computations using the coming generation of teraflops-scale supercomputers.
HIGH-PRECISION MONTE CARLO DETERMINATION OF α/ν IN THE 3D CLASSICAL HEISENBERG MODEL
Authors: HOLM CHRISTIAN , JANKE WOLFHARD
Published: November 2004

To study the role of topological defects in the three-dimensional classical Heisenberg model we have simulated this model on simple cubic lattices of size up to 803, using the single-cluster Monte Carlo update. Analysing the specific-heat data of these simulations, we obtain a very accurate estimate for the ratio of the specific-heat exponent with the correlation-length exponent, α/ν, from a usual finite-size scaling analysis at the critical coupling Kc. Moreover, by fitting the energy at Kc, we reduce the error estimates by another factor of two, and get a value of α/ν, which is comparable in accuracy to best field theoretic estimates.
ALGORITHMIC COMPLEXITY OF SOME PHYSICAL PROCESSES
Authors: SAGINTAEV B.S.
Published: November 2004

Measure of algorithmic complexity c(n) which has been suggested by Lempel and Ziv is one of important quantities for characterizing properties of nonlinear dynamical systems. The temporal variation of c(n) is investigated for time series generated by some physical processes. The relationship between algorithmic complexity and other characteristics of nonlinear systems is discussed.
SOME PROPERTIES OF LOCAL AND NONLOCAL SITE EXCHANGE DETERMINISTIC CELLULAR AUTOMATA
Authors: BOCCARA N. , ROGER M.
Published: November 2004

Stationary densities of nonzero sites of one-dimensional range-one deterministic cellular automata are shown to be functions of a parameter m characterizing the degree of mixing of site values. The mixing results from either a local or a nonlocal exchange of the site values. In particular, the asymptotic behavior of the stationary densities of nonzero sites for very small and very large values of the parameter m have been determined.
CRITICAL PROPERTIES OF 3D ISING SYSTEMS WITH NON-HAMILTONIAN DYNAMICS
Authors: HERINGA J.R. , BLÖTE H.W.J. , HOOGLAND A.
Published: November 2004

We investigate two three-dimensional Ising models with non-Hamiltonian Glauber dynamics. The transition probabilities of these models can, just as in the case of equilibrium models, be expressed in terms of Boltzmann factors depending only on the interacting spins and the bond strengths. However, the bond strength associated with each lattice edge assumes different values for the two spins involved. The first model has cubic symmetry and consists of two sublattices at different temperatures. In the second model a preferred direction is present. These two models are investigated by Monte Carlo simulations on the Delft Ising System Processor. Both models undergo a phase transition between an ordered and a disordered state. Their critical properties agree with Ising universality. The second model displays magnetization bistability.
NEGATIVE WEIGHTS IN QUANTUM MONTE CARLO SIMULATIONS AT FINITE-TEMPERATURES USING THE AUXILIARY FIELD METHOD
Authors: GUBERNATIS J.E. , ZHANG X.Y.
Published: November 2004

We study the conditions under which negative weights (the sign problem) can exist in the finite-temperature, auxiliary field, quantum Monte Carlo algorithm of Blankenbecler, Scalapino, and Sugar. We specifically consider whether the sign problem arises from round-off error resulting from operations involving very ill-conditioned matrices or from topological defects in the auxiliary fields mirroring the space-time patterns of the physical fields. While we demonstrate these situations can generate negative weights, the results of our numerical tests suggest that these factors are most likely not the dominant sources of the problem. We also argue that the negative weights should not be considered as just a fermion problem. If it exists for the fermion problem, it will also exist for an analogous boson problem.
AUTOMATIC CALCULATIONS IN HIGH ENERGY PHYSICS BY GRACE AND COMPHEP
Authors: BOOS E.E. , DUBININ M.N. , ILYIN V.A. , PUKHOV A.E. , SHICHANIN S.A. , KANEKO T. , KAWABATA S. , KURIHARA Y. , SHIMIZU Y.
Published: November 2004

Ten three-body processes in e+e− collisions for heavy particle productions such as Higgs, t-quark, W± and Z0 are calculated by two independent computer codes for automatic calculation of Feynman amplitude. The results are in excellent agreement within statistical error of numerical integration (about 0.5%). This demonstrates that these systems are quite powerful for theoretical study for future e+e−, e±γ and γγ colliders. Numerical values of cross sections are summarized in tables and a figure.
DENSITIES OF STATES OF MEGA-DIMENSIONAL HAMILTONIAN MATRICES
Authors: SILVER R.N. , RÖDER H.
Published: November 2004

We propose a statistical method to estimate densities of states (DOS) and thermodynamic functions of very large Hamiltonian matrices. Orthogonal polynomials are defined on the interval between lower and upper energy bounds. The DOS is represented by a kernel polynomial constructed out of polynomial moments of the DOS and modified to damp the Gibbs phenomenon. The moments are stochastically evaluated using matrixvector multiplications on Gaussian random vectors and the polynomial recurrence relations. The resulting kernel estimate is a controlled approximation to the true DOS, because it also provides estimates of statistical and systematic errors. For a given fractional energy resolution and statistical accuracy, the required cpu time and memory scale linearly in the number of states for sparse Hamiltonians. The method is demonstrated for the two-dimensional Heisenberg anti-ferromagnet with the number of states as large as 226. Results are compared to exact diagonalization where available.
WORLD-WIDE WEB IN HIGH-ENERGY PHYSICS EXPERIMENTS ‘A STATUS REPORT’
Authors: DÖNSZELMANN MARC
Published: November 2004

This report presents the status of the use of World-Wide Web (WWW) in High Energy Physics (HEP) experiments. The use of WWW in general, for ‘Online Datataking Systems’ and for ‘Offline Analysis Systems’ is discussed. In each of these cases the current use and a possible outlook for the future is described. Statistics on the actual use of WWW in HEP experiments as well as its current problems and future needs are also presented.
INTERACTIVE BOOKS
Authors: MANZINI G.M. , TICCA A. , ZANETTI G.
Published: November 2004

The possibility to produce scientific reviews with interactive mechanisms allows the user to verify and experiment more directly the contents of such books. There are many reasons that lead to think of the interactive books as a successful means of spread information in the large world of electronic publishing, like the need of the author to capture the attention of the reader and to allow a stronger integration between reader and content of the book.
NEURAL NETWORKS AS OPTIMAL INFORMATION PROCESSORS
Authors: CAMPA ALESSANDRO , GIUDICE PAOLO DEL , NADAL JEAN-PIERRE , PARGA NESTOR
Published: November 2004

We explore the properties of a feed-forward neural network whose couplings are chosen in such a way as to maximize the input-output mutual information, in the case in which the input-output channel is affected by noise.
TEMPORAL CODING AND OSCILLATIONS IN THE VISUAL CORTEX OF MAMMALS
Authors: PARODI OLIVIER
Published: November 2004

Information coding by patterns of spike rates is incompatible with the experimental results on fast recognition of figures or scenes, which may be explained only on the basis of a one-spike-per-neuron computation. It had been suggested that coding may be achieved by means of the spikes arrival times. It is shown here that such a coding will be jammed up everytime a perceptive process extends over several spikes, unless the input integrator neurons are periodically reset.

This resetting may be responsible for the periodic burst firing and the oscillations of the local field potential which have been experimentally found in the cases of motion detection or of sustained attention. A presynchronisation process is required, for the initial coding and for scene fragmentation, and may be achieved by an electrical interneuronal coupling, which is shown to be both realistic and efficient. Information decoding may be implemented by neurons operating in a correlator mode, which is analysed.
ADM FORMALISM APPLIED TO SOME SPACE-TIME MODELS USING EXCALC ALGEBRAIC PROGRAMMING
Authors: VULCANOV DUMITRU N.
Published: November 2004

This article presents the results obtained with new procedures in REDUCE language using EXCALC package (adapted for IBM-PC machines) for algebraic programming in the Hamiltonian formulation of general relativity (ADM formalism). The procedures calculate the dynamic and the constraint equations and, in addition, we have extended the obtained procedures in order to perform a complete ADM reductional procedure: solving the constraint equations, changing of variables, reduction of dynamic variables, etc. The results obtained after processing some examples of space-time models are presented here.
COMPUTER PROGRAMS FOR ANALYTICAL PERTURBATIVE CALCULATIONS IN HIGH ENERGY PHYSICS
Authors: SURGULADZE LEVAN R.
Published: November 2004

A short review of the present status of computer packages for the high order analytical perturbative calculations is presented. The mathematical algorithm and the quantum field theory methods used are briefly discussed. The most recent computer package HEPLoops for analytical computations in high energy physics up to four-loops is also discussed.
COHERENT-ANOMALY APPROACH TO BLUME-EMERY-GRIFFITHS MODEL
Authors: KOLESÍK M.
Published: November 2004

The Blume-Emery-Griffiths model is investigated using the coherent-anomaly method applied to the series of approximations which are based on variational series expansion. Universality of the model is checked directly by calculating the critical exponent γ along second-order-phase-transition lines. It is shown that the coherent-anomaly approach works also in the immediate neighborhood of tricritical points, and that it can differentiate between different universality classes (Potts subspace in the BEG model) without exhibiting a disturbing crossover effect.
ON THE MONTE CARLO SIMULATION APPROACH TO FOKKER-PLANCK EQUATIONS IN QUANTUM OPTICS
Authors: D’ARIANO G.M. , MACCHIAVELLO C. , MORONI S.
Published: November 2004

The suitability of the Monte Carlo simulation approach to Fokker-Planck equations in quantum optics is investigated. The method is especially useful for multimode analysis, and hence for studying realistic models of nonlinear optical systems. Here it is illustrated on the basis of two simple examples of application: i) a one-dimensional Fokker-Planck equation in the number representation, which describes a simple model of optical amplifier, and ii) the Van der Pol two-dimensional equation in the P-function representation.
NOVEL INTERFERENCE EFFECTS IN MULTIPLY CONNECTED NORMAL METAL RINGS
Authors: JAYANNAVAR A.M. , DEO P. SINGHA
Published: November 2004

We have investigated the magnetoconductance of a normal metal loop connected to ideal wires in the presence of magnetic flux. The quantum mechanical potential, V, in the loop is much higher than that in the connecting wires (V=0). The electrons with energies less than the potential height on entering the loop propagate as evanescent modes. In such a situation, the contribution to the conductance arises from two non-classical effects, namely, Aharonov-Bohm effect and quantum tunneling. For this case we show that, on application of a small magnetic field, the conductance initially always decreases, or small field magnetoconductance is always negative. This is in contrast to the behavior in the absence of the barrier, wherein the small field magnetoconductance is either positive or negative depending on the Fermi energy and other geometric details. We also discuss the possibility of a better switch action based on quantum interference effects in such structures.
SOME FEATURES OF ELECTRON TUNNELING IN THE NORMAL AND SUPERCONDUCTING STATES OF METAL OXIDES
Authors: SVISTUNOV V. M. , IGUCHI I. , BELOGOLOVSKII M. A. , KHACHATUROV A. I.
Published: November 2004

A comprehensive review is given for the understanding of high-T c superconducting metal oxides based on the electron tunneling measurements using both superconducting and normal junctions. The deviation of tunnel conductance from parabolic background behavior suggests the manifestation of carrier localization effect, while the linear conductance against bias voltage may reflect the electron–electron correlation effect. The consideration of self-energy effects in the odd part of tunnel conductance and the analysis of gaplike structure indicate that the electron–phonon interaction is of appreciable importance. These results suggest that two electron subsystems may coexist in high-T c materials.
THERMAL EXPANSION OF ALKALI HALIDES: A SEMICLASSICAL MODEL
Authors: MUKHERJEE GOUTAM DEV , BANSAL C. , CHATTERJEE ASHOK
Published: November 2004

A simple-minded semiclassical method is used to obtain the thermal expansion of alkali halides viz. KBr, KCl, Kl, and NaCl. It is observed that our theoretical prediction agrees fairly well with the available experimental data. It is furthermore suggested that the present method can be used for an accurate determination of the Debye temperature of alkali halides.
THE METAL–INSULATOR TRANSITION IN THE HUBBARD MODEL AT ZERO TEMPERATURE II
Authors: ROZENBERG MARCELO J. , MOELLER GOETZ , KOTLIAR GABRIEL
Published: November 2004

We study the metal-to-insulator transition of the Hubbard model at zero temperatures in infinite dimensions. The coexistence of metallic and insulating solutions for a finite range of the interaction is established. It is shown that the metallic solution is lower in energy for any interaction in the coexistence region and that the transition is of second order.
FAR-INFRARED MAGNETO-OPTICAL STUDY ON ZnSe LAYERS
Authors: NAKATA H. , KOMEDA R. , OHYAMA T. , OTSUKA E.
Published: November 2004

We report on a study of the far-infrared (FIR) magneto-absorption of ZnSe layers epitaxially grown on GaAs by metal-organic vapor-phase epitaxy (MOVPE) or molecular-beam epitaxy (MBE). The Zeeman absorption of the residual donors is observed in undoped and p -type ZnSe layers. A main absorption peak is assigned to a 1s to 2p+ transition of an electron bound to a Cl donor. Polaron pinning effect is included to explain the peak position within the framework of Wigner–Brillouin second order perturbation theory.
A TOY MODEL OF INTERLAYER PAIR HOPPING
Authors: MUTHUKUMAR V. N. , BASKARAN G.
Published: November 2004

We extend the correlated electron model of Baskaran (Mod. Phys. Lett.B5, 643 (1991)) to the case of coupled layers. We show that the nature of the non-Fermi liquid ground state leads to the absence of electronlike quasiparticles at the Fermi surface, thereby suppressing coherent transport of electrons between the coupled layers ("confinement"). On the other hand, motion of singlet pairs between the layers is not blocked. We also discuss how pair tunneling can be used to construct a superconducting ground state.
NEAR COLLISIONS IN A COULOMB SYSTEM: QUANTUM TREATMENT
Authors: MENDES R. VILELA
Published: November 2004

We discuss near collisions of equally charged particles in a quantum Coulomb many body system. Using the three-body dominance of near collisions at low energies, we may restrict the study to a system of two positively charged and one negatively charged particle in a box, with periodic boundary conditions. The main low energy collision states are found to be at the top of the negative energy bands. This suggests a hybrid fusion method where deuterons absorbed into a metal lattice would be resonantly excited to collision states by electromagnetic radiation in the ultraviolet range.
A PREDICTIVE SCHEME FOR ENERGIES OF METAL CLUSTERS IN A TIGHT-BINDING LINEARIZED MUFFIN-TIN ORBITAL FORMALISM AND ITS APPLICATION TO SOME SIMPLE METALS
Authors: DATTA ABHIJIT , MOOKERJEE ABHIJIT , BHATTACHARYYA A. K.
Published: November 2004

We have developed a predictive scheme for the energy of metal clusters based on our ideas of Tight-Binding Linearized Muffin-Tin Orbitals formalism (TBLMTO) and the linearized Barth–Hedin density functional. We have applied our methodology to Na and Cu clusters and have shown that the electronic shell structure expected in the physics of such clusters is accurately reproduced.
A COMPARISON BETWEEN WEHRL–LIEB AND VON NEUMANN ENTROPIES FOR TIME-EVOLVING SPIN-1/2 MIXED STATES
Authors: MIZRAHI S. S. , DODONOV V. V. , OTERO D.
Published: November 2004

Years ago, A. Wehrl (Rev. Mod. Phys.50, 221 (1978)) introduced the concept of classicallike entropy of quantum states when a two-label continuous representation is used; for instance, the harmonic oscillator coherent states. Subsequently, E. H. Lieb (Commun. Math. Phys.62, 35 (1978)) extended that concept of entropy to the Bloch coherent spin states. Here, we consider spin-1/2 systems and calculate both the Wehrl–Lieb and von Neumann entropies, and then we compare the results and discuss the Wehrl–Lieb entropy as an alternative formulation to von Neumann's. As illustration, three examples are worked out: (i) the decoherence of a quantum state in a measurement process, (ii) the conservation of coherence, and (iii) the recoherence phenomena that appear in the solutions of a specific master equation that originates from a nonlinear Schrödinger equation.
EFFECTS OF CHARGE PARITY IN TUNNELING THROUGH A SUPERCONDUCTING GRAIN
Authors: MATVEEV K. A. , GLAZMAN L. I. , SHEKHTER R. I.
Published: November 2004

The Coulomb blockade in a small superconducting grain, connected to two macroscopic electrodes by tunnel junctions, is discussed. The ground state energy of the grain with an odd number of electrons is shifted by the value of the superconducting gap due to the presence of one unpaired electron. In the case of superconducting leads, the charge parity effects give rise to a threshold behavior of the critical Josephson current when the superconducting gap is suppressed below the charging energy, e.g. by a magnetic field. The critical current is periodically modulated by the voltage of a gate electrostatically coupled to the grain. We find a characteristic change in this modulation at the threshold. In the case of normal leads, the low-bias conductance of this system is due to electrons passing through the grain in pairs (Andreev reflection). The linear conductance is periodic in the gate voltage. The period and the conductance activation energy are determined by charge 2e, rather than e. At resonance, the current first grows linearly with the applied bias, and then drops when an odd electron is allowed to enter the grain. Due to the high entropy of a state with an unpaired electron, this "poisoning" may also be stimulated by a fairly low temperature.
DONOR BINDING ENERGY IN TWO DIMENSIONS
Authors: ACKLEH E. S. , MAHAN G. D. , WU JI-WEI
Published: November 2004

We calculate numerically the binding energy of an electron bound to a proton in two-dimensional electron gas. Unlike the case in three dimensions, in 2D the binding energy is nonzero for all values of electron density.
NEW WAY OF SYMMETRY REALISATION BY GENERALISED STATISTICS
Authors: SCIPIONI R.
Published: November 2004

By means of the recently introduced g statistics we provide a new way of symmetry realisation in quantum statistical mechanics and, in general, in field theory. Crudely speaking we are able to introduce objects whose statistics depend on the symmetries of ground state.
ONE-DIMENSIONAL MODEL OF OPTICALLY INDUCED THERMOELASTIC WAVES
Authors: MOŽINA J. , DOVČ M.
Published: November 2004

A one-dimensional model of the generation of thermoelastic waves by light beam absorption in solids is described and solved. The exact thermal and mechanical boundary conditions are used. An analytical asymptotic solution of the problem is obtained. The relation between the maximum displacement of the second surface of the sample and the duration of the incident light pulse is determined.
OBSERVATION OF TWO-PHOTON-INDUCED PHOTOEMISSION OPTOGALVANIC EFFECT USING COPPER TARGET ELECTRODE
Authors: AJITHPRASAD K.C. , SASIKUMAR P.R. , HARILAL S.S. , NAMPOORI V.P.N. , VALLABHAN C.P.G.
Published: November 2004

Two-photon-induced photoemission optogalvanic effect using copper as the target electrode has been observed in a nitrogen discharge cell using 532 nm radiation from a frequency-doubled Nd:YAG laser as the pump source.
LAWS OF LARGE NUMBERS FOR PAIRWISE INTERACTING PARTICLE SYSTEMS
Authors: FERLAND RENÉ
Published: November 2004

We consider a system of Markov processes of finitely-many particles which exchange their energies in pairs at random times. A law of large numbers for this system means that the empirical measures of the processes may be approximated (as the number of particles increases) by the solution of a nonlinear evolution equation (the so-called McKean-Vlasov limit). This work presents two results of this type. The first one concerns the empirical processes and gives a probabilistic method for solving the nonlinear equation. The second is stated in the path scheme and extends classical results of chaos propagation by Kac (1956) and McKean (1967).
ASYMPTOTIC ANALYSIS OF THE FOKKER-PLANCK EQUATION RELATED TO BROWNIAN MOTION
Authors: BANASIAK J. , MIKA J.R.
Published: November 2004

In this paper we apply the modified Chapman-Enskog expansion procedure to find the asymptotic solution of the Fokker-Planck equation related to Brownian motion. We prove that the asymptotic solution is defined by the diffusion equation and show that the difference between the exact and asymptotic solutions is of order ε2 where 1/ε is related to the magnitude of the collision operator.
SPECTRAL APPROXIMATION OF A SCHRÖDINGER TYPE EQUATION
Authors: BERNARDI CHRISTINE , PELISSIER MARIE-CLAUDE
Published: November 2004

This paper deals with a linear Schrödinger type equation in a rectangular domain with mixed Dirichlet-Neumann boundary conditions. The well-posedness of the continuous problem is proved, then a discrete problem is defined by combining a Legendre type spectral method in the first direction and a leap-frog scheme in the other one. The numerical analysis of the discretization is performed and error estimates are given. Numerical tests are presented.
METHOD OF UPPER AND LOWER SOLUTIONS FOR NONLINEAR DELAY INTEGRAL EQUATIONS MODELLING EPIDEMICS AND POPULATION GROWTH
Authors: CAÑADA A. , ZERTITI A.
Published: November 2004

In this paper we prove some results about the existence of positive periodic solutions of nonlinear delay integral equations which formulate a model to explain the evolution of some infectious diseases and which have also been used as a growth equation for single species population when the birth rate varies seasonally. We use monotone methods (upper and lower solutions) to obtain our results and we compare them with other results obtained by different authors which have used topological methods to study the mentioned equation.
CHARACTERIZATION OF THE MEMBRANE THEORY OF A CLAMPED SHELL.
Authors: PIILA JYRKI
Published: November 2004

We study the membrane-dominated deformation state of a thin shell, the mid-surface of which is located on a surface of revolution with positive principal radii of curvature. The lateral shape of the shell is assumed to be that of a curvilinear polygon. The shell is loaded by a smooth surface traction acting on its outer surface and rigidly supported throughout its edge. Proceeding from the 3D elastic model, an asymptotic model is constructed to describe the limit behavior of the shell as the thickness tends to zero. The limit model is referred to as membrane theory. A convergence result relating the 3D model and the asymptotic model is proved and the mathematical characteristics of the asymptotic theory are analyzed. Energy methods are used throughout the work.
CRACK PROPAGATION MODELING
Authors: GRAY L.J. , POTYONDY D.O. , LUTZ E.D. , WAWRZYNEK P.A. , MARTHA L.F. , INGRAFFEA A.R.
Published: November 2004

In this paper, we review recent advances in mathematical and computer science techniques for modeling crack propagation in solids. The fracture mechanics aspect of this problem is attacked by boundary integral equation methods, in particular the use of hypersingular integral equations for analyzing crack geometries. Key issues in the development of a software system capable of efficient crack propagation studies are also discussed. As an illustration of these techniques, calculations analyzing crack growth in a fuel door hinge on the Space Shuttle are presented.
PARAXIAL APPROXIMATION OF THE VLASOV-MAXWELL SYSTEM: LAMINAR BEAMS
Authors: NOURI A.
Published: November 2004

The Vlasov-Maxwell stationary system for charged particle laminar beams is studied with a paraxial model of approximation. It leads to a degenerate evolution system, which local existence is proved. Then, using lagrangian coordinates, with sufficient conditions on the initial data and the external electromagnetic field, it is shown that global existence is possible.
STABILITY OF HIGHER ORDER TRIANGULAR HOOD-TAYLOR METHODS FOR THE STATIONARY STOKES EQUATIONS
Authors: BOFFI D.
Published: November 2004

We prove the stability for the approximation of the stationary Stokes equations by means of piecewise continuous velocities of degree k+1 and piecewise continuous pressures of degree k for k≥1. The necessary and sufficient condition required on the triangulation is that it contains at least three triangles. The theorem is compared with previous results.
A SPRAY COMBUSTION PROBLEM
Authors: POULY L. , POUSIN J.
Published: November 2004

In this work, we investigate a mathematical model of a spray combustion problem and we prove an existence and uniqueness result for the time-dependent problem. We consider the vaporization of a polydisperse fuel spray of droplets in an oxidative medium, and we assume that the evaporated fuel is immediately consumed and gives off heat. The mathematical model arising from this combustion problem is a coupled system of three partial differential equations. By using the standard method of successive approximations we prove that the system has a unique solution. Moreover, we prove the existence of a front of vaporization, and we show that the mass rate of evaporated droplets decreases when the size of droplets increases.
A NEW METHOD FOR CALCULATING CLASSICAL PERIODIC TRAJECTORIES IN TWO DIMENSIONS
Authors: DAVIES K.T.R.
Published: November 2004

Previously, the monodromy method has been widely used for calculating classical periodic trajectories for a two-dimensional Hamiltonian system, or a four-dimensional phase space. In this paper, the problem is formulated from a different point of view, involving Gaussian-elimination algorithms. Thus, we present a new method for calculating classical periodic orbits, in which each of the basic matrices is of dimension two. Two variants are obtained, one assuming that the period of the motion is fixed and the other assuming that the total energy is fixed. We emphasize the importance of calculating the periodic orbits in as small a dimensionality as possible, an advantage which has implications for generalizations of the theory and methods to outstanding many-body problems in nuclear and atomic physics. Comparisons are made between various approaches.
SEMICONDUCTOR DEVICES UNDER CIRCUIT BOUNDARY CONDITIONS
Authors: SCHMEISER CHRISTIAN
Published: November 2004

A stationary version of the standard drift-diffusion model for the flow of electrons and holes in semiconductor devices is considered. The boundary conditions are, to a certain extent, capable of describing the influence of the surrounding electrical circuit as opposed to the usual mathematical assumption of prescribed voltages. The existence of solutions and the convergence close to thermal equilibrium of a decoupled iteration method are proved.
CONVERGENCE OF A SEMI-DISCRETE SCHEME FOR THE CURVE SHORTENING FLOW
Authors: DZIUK GERHARD
Published: November 2004

Convergence for a spatial discretization of the curvature flow for curves in possibly higher codimension is proved in L∞((0, T), L2(ℝ/2π)) ∩ L2((0, T) H1(ℝ/2π)). Asymptotic convergence in these norms is achieved for the position vector and its time derivative which is proportional to curvature. The underlying algorithm rests on a formulation of mean curvature flow which uses the Laplace-Beltrami operator and leads to tridiagonal linear systems which can be easily solved.
A NOTE ON UNIFORM SUPERCONVERGENCE FOR THE TIMOSHENKO BEAM USING MIXED FINITE ELEMENTS
Authors: BRANDTS JAN H.
Published: November 2004

In this paper we present some results on the discretization by mixed finite elements of the Timoshenko beam, i.e. the one-dimensional Reissner-Mindlin plate bending problem. The results concern superconvergence. Superconvergence (of the displacement at nodal points and of the gradient at Gaussian points) for plate bending problems was considered before, but these earlier results degenerate for small values of the plate thickness d. Here, we prove superconvergence of the mixed finite element solutions to projections of the real solutions on the approximating spaces in the global H1(I)-norm uniform in d. These facts can be used to obtain asymptotically exact a posteriori error estimators, uniform in d, by means of an easy implementable and cheap post-processing. Numerical experiments illustrate the conclusions.
FREE DISCONTINUITY PROBLEMS WITH UNBOUNDED DATA
Authors: LEACI ANTONIO
Published: November 2004

We prove the existence of a minimizing pair for a free discontinuity problem, i.e. a variational problem in which the unknowns are a closed set K and a function suitably smooth outside K. Examples of such problems come from pattern recognition and mathematical physics, when both “volume” energy and “surface” energy are present.
A GRID REFINEMENT METHOD FOR DETERMINISTIC CONTROL AND DIFFERENTIAL GAMES
Authors: ALZIARY B. , LIONS P.L.
Published: November 2004

We develop here a simple method for the computation of value functions of deterministic optimal control or differential games problems which allows to refine locally a grid and reduce memory space. Given an approximation of optimal trajectories, one can solve the associated Hamilton-Jacobi equation in a tubular neighborhood with state-constraints boundary conditions. We study here the validity of such an approach and we illustrate it on various examples.
NONLOCAL LAGRANGIANS AND HAMILTONIAN FORMALISM
Authors: J. LLOSA , J. VIVES
Published: November 2004

A presymplectic formalism is set up for nonlocal Lagrangian systems. The method is based on an ‘equivalent’ first order Lagrangian that is processed by standard ways of classical mechanics. The Hamiltonian formalism for the latter is then pulled back onto the infinite dimensional phase space of the nonlocal system.
A NONCOMMUTATIVE EXTENSION OF GRAVITY
Authors: MADORE J. , MOURAD J.
Published: November 2004

The commutative algebra of functions on a manifold is extended to a noncommutative algebra by considering its tensor product with the algebra of n×n complex matrices. Noncommutative geometry is used to formulate an extension of the Einstein-Hilbert action. The result is shown to be equivalent to the usual Kaluza-Klein theory with the manifold SUn as an internal space, in a truncated approximation.
CHANGE OF SIGNATURE AND TOPOLOGY IN A FIVE-DIMENSIONAL COSMOLOGICAL MODEL
Authors: MARTIN Jérôme
Published: November 2004

We study the change of signature of the metric in a five-dimensional Kaluza-Klein theory applied to the description of a primordial cosmology.
EFFECTIVE ACTIONS FOR HETEROTIC STRING THEORY
Authors: SUELMANN HAN
Published: November 2004

Heterotic String Theory is an attempt to construct a description of nature that is more satisfying than the Standard Model. A major problem is that it is very difficult to do explicit calculations in string theory. Therefore, it is useful to construct a ’normal’ field theory that approximates HST. The way to construct such a field theory is described briefly. The result is a perturbation expansion in some parameter α′. related to the inverse string tension. There are problems concerning the supersymmetrisation of the [Formula: see text] contribution. These may be caused by the assumption that the action can be written in terms of a local Lagrangian of the physical fields only.
SUPERSPACE DYNAMICS AND PERTURBATIONS AROUND “EMPTINESS”
Authors: SOO CHOPIN , CHANG LAY NAM
Published: November 2004

Superspace parametrized by gauge potentials instead of metric three-geometries is discussed in the context of the Ashtekar variables. Gauge-fixing conditions which lead to the natural geometrical separation of physical from gauge modes are derived with the use of the supermetric in connection-superspace. A perturbation scheme about an unusual background which is inaccessible to conventional variables is presented. The resultant expansion retains much of the simplicity of Ashtekar’s formulation of General Relativity. Quantum mechanically, the super-Hamiltonian constraint assumes the form of the Dirac equation with an “intrinsic time” tied to the signature of the supermetric.
NAKED SINGULARITIES AS CANDIDATES FOR GAMMA-RAY BURSTERS
Authors: CHAKRABARTI SANDIP K. , JOSHI PANKAJ S.
Published: November 2004

Naked singularities appear naturally in dynamically evolving solutions of Einstein equations involving gravitational collapse of radiation, dust, and perfect fluids provided the rate of accretion is less than a critical value. We propose that the gamma-ray bursters (GRBs) are examples of these naked singularity solutions. For illustration, we show that according to solutions involving spherically symmetric collapse of pure radiation field, the energy Eγ and the observed duration Δt0 of a GRB should satisfy, [Formula: see text] being the fraction (10−2 to 10−3) of energy released as gamma rays and the rest possibly as gravitational waves. All the presently observed GRBs satisfy this condition; those satisfying the condition close to equality must necessarily be of cosmological origin with the red-shift factor z not exceeding ~1−10 depending on exact observed flux, red-shift and conversion efficiency of gamma rays. If GRBs are indeed from naked singular regions, they should also be accompanied by a strong burst of gravitational waves which, if detectible, will constitute a basic test for our model.
POSSIBLE SIGNATURES OF THE CONVERSION OF A NEUTRON STAR TO A STRANGE STAR
Authors: BENVENUTO O.G. , KRIVORUCHENKO M.I. , MARTEMYANOV B.V.
Published: November 2004

The problem of the identification of strange stars is discussed. We suggest some characteristic signatures for the search for strange stars: a two-step mechanism for supernova explosions accompanied by the occurrence of strange stars and two neutrino bursts; microstructure analysis in the profile of pulsar emission; and unusual stability in the rotation of millisecond pulsars due to the absence of internal crust in strange stars. The cooling of strange stars is faster than the cooling of ordinary neutron stars, so low surface temperature of pulsars can indicate the existence of massive quark cores in observed pulsars. Low mass strange stars as bursters and/or X-ray sources have peculiar observable features: low luminosity and (for bursters) high recurrence rate, large duration of bursts, low ratio of energy emitted between two bursts and energy emitted during the burst.
ON THE INTERIOR OF THE NEUTRON STAR – I. NONLINEAR BEHAVIOR OF THE MAGNETIC FIELD
Authors: PARUI RAMEN KUMAR
Published: November 2004

The generation of very strong magnetic fields on the surface of a neutron star has long been an outstanding problem. A spinning neutron star is considered as one of the anticipated gravitational wave sources. Here I have shown the nonlinear behavior of this magnetic field in the interior of both uncharged and charged neutron stars at equilibrium radii and obtained results favouring a gravitational wave source.
WEAK FIELD LIMIT OF GENERAL RELATIVITY IN TERMS OF NEW VARIABLES: A HAMILTONIAN FRAMEWORK
Authors: ASHTEKAR ABHAY , LEE JOOHAN
Published: November 2004

A self-contained treatment of the linearization procedure for constrained Hamiltonian systems is first presented in a general setting. The procedure is then applied to general relativity using triads and self-dual connections as the basic canonical variables. These results have paved the way to the quantization of weak gravitational waves in the connection and loop representations and to a study of the relation between these quanta and nonperturbative canonical gravity. In the classical theory, they suggest a new approach to the treatment of gravitational perturbations and may be useful also to the theory underlying weak gravity waves.
NARROW QUASAR ABSORPTION LINES AND THE HISTORY OF THE UNIVERSE
Authors: LIEBSCHER DIERCK-EKKEHARD
Published: November 2004

In order to get an estimation of the parameters of the cosmological model the statistics of narrow absorption lines in quasar spectra is evaluated. To this end a phenomenological model of the evolution of the corresponding absorbers in density, size, number and dimension is presented and compared with the observed evolution in the spectral density of the lines and their column density seen in the equivalent width. In spite of the wide range of possible models, the Einstein-deSitter model is shown to be unlikely because of the implied fast evolution in mass.
EXPERIMENTS ON WIMPS, SIMPS, AND HOT DARK MATTER
Authors: CALDWELL DAVID O.
Published: November 2004

The particle which constitutes more than 90% of the mass of the universe is not one of those in the Standard Model of particle physics. The search for this dark matter particle has now eliminated or severely restricted many candidates. While accelerator-produced results and indirect searches have helped, the most extensive exclusions have come from attempts at direct detection using semiconductor ionization detectors. The region excluded by direct detection extends over 12 orders of magnitude in particle mass and 20 orders of magnitude in cross section for Dirac particles. The need is now to get to cross sections less than one-tenth the weak cross section for Dirac masses >20 GeV and to use detectors having nuclei with spin for Majorana masses ≳10 GeV. Light neutrinos, while not detectable directly, can be eliminated as dominant dark matter if the 17-keV neutrino exists.
TRIPLET AND HIGHER MULTIPLET CORRELATIONS IN INTERMEDIATE-ENERGY HEAVY-ION COLLISIONS
Authors: JIANG JINGHUA , KEANE DECLAN , LIU YIMING
Published: November 2004

We review the topic of high-order correlations in heavy-ion collisions, concentrating on two classes of correlation that are of interest at intermediate bombarding energy: Bose-Einstein correlations among the produced pions, and collective flow correlations among the nuclear fragments.
ELASTIC SCATTERING OF 58Ni ON 46Ti AT ENERGIES NEAR THE COULOMB BARRIER: SEARCH FOR RESONANT STATES
Authors: ABBONDANNO U. , DEMANINS F. , VANNINI G. , BOCCACCIO P. , VANNUCCI L. , RICCI R.A. , BRUNO M. , D’AGOSTINO M. , MILAZZO P.M. , CINDRO N.
Published: November 2004

In a search for possible resonant behavior in medium and heavy composite systems, the 46Ti(58Ni, 58Ni)46Ti elastic scattering was studied in the 58 Ni incident energy range from 216.2 to 240 MeV. A kinematic coincidence technique employing position sensitive silicon detectors was used to obtain the mass identification of the binary events. Evidence was found for two structures of non-statistical nature in the elastic excitation function at, respectively, incident 58 Ni energies of 223.9 and 227.4 MeV (Ecm=99.0 and 100.6 MeV). A statistical analysis of the corresponding angular distributions disclosed periodical behavior analogous to that caused by single partial waves of J=(36 ± 1) and (47 ± 1), respectively.
NEW TRENDS IN KINETIC FRAGMENTATION THEORY
Authors: BOTET ROBERT , PLOSZAJCZAK MAREK
Published: November 2004

Recent theoretical developments in the kinetic fragmentation theory are presented with a particular emphasis on the newly proposed Fragmentation-Inactivation Binary (FIB) cascading model. We also discuss the origin of scale-invariant, intermittent fluctuations in the cluster fragmentation models such as the percolation model and the binary cascading models.
NEUTRINO NEUTRAL CURRENT EXCITATION OF 12C*(1+; T=1; 15.1 MeV)
Authors: PARTHASARATHY R.
Published: November 2004

We report here the total cross-sections for [Formula: see text][Formula: see text], for incident neutrino energies from 16 MeV to 54 MeV, so as to provide theoretical values for comparison with the recent Karlsruhe-Rutherford Medium Energy Neutrino Experiment (KARMEN). The effects of the isospin mixing from the 1+; T=0; 12.7 MeV level of 12C are taken into account. The effect of the only strong interaction induced weak magnetism form factor is studied, as well as that of the isovector axial coupling. The nuclear models used are the combination of general 1p-shell wave functions of Cohen-Kurath for the 15.1 MeV level, and Gillet-VinhMau particle-hole wave functions with 2ħω excitations for 12.7 MeV level. The neutrino (antineutrino) flux averaged sum [Formula: see text] is found to be 9.86×10−42 cm2without isospin mixing and 9.83×10−42 cm2with isospin mixing (δ=0.05) to be compared with the KARMEN result for the sum as [10.8±1.1(stat)±1.2(syst)]×10−42 cm2.
NUCLEAR INSTABILITY AND SOLITON THEORY
Authors: KARTAVENKO V.G. , GRIDNEV K.A. , GREINER W.
Published: November 2004

The problems of dynamical instability and clustering (stable fragments formation) in a breakup of excited nuclear systems are considered from the points of view of the soliton concept. It is shown that the volume (spinodal) instability can be associated with nonlinear terms, and the surface (Rayleigh-Taylor type) instability, with the dispersion terms in the evolution equations. Both instabilities may compensate each other and lead to stable solutions (solitons).
Titin isoform-dependent effect of calcium on passive myocardial tension
Authors: Fujita Hideaki , Labeit Dietmar , Gerull Brenda , Labeit Siegfried , Granzier Henk L.
Published: November 2004

We studied the effects of Ca2+ on titin (connectin)-based passive tension in skinned myocardium expressing either predominantly N2B titin (rat right ventricle, RRV) or predominantly N2BA titin (bovine left atrium, BLA). Actomyosin-based tension was abolished to undetectably low levels by selectively removing the thin filaments with a Ca2+-insensitive gelsolin fragment (FX-45). Myocardium was stretched in the presence and absence of Ca2+, and passive tension was measured. Ca2+ significantly increased passive tension during and after stretch in the BLA. The increase was insensitive to the actomyosin inhibitor 2,3-butanedione 2-monoxime, supporting the conclusion that the effect is titin based. Passive tension did not respond to calcium in the RRV, indicating that passive tension developed by N2B titin is calcium insensitive. Western blot analysis and immunofluorescence studies indicated that N2BA titin expresses E-rich PEVK motifs, whereas they are absent from N2B titin, supporting earlier single molecule studies that reported that E-rich motifs are required for calcium sensitivity. We conclude that calcium affects passive myocardial tension in a titin isoform-dependent manner.
Programming blood pressure in adult SHR by shifting perinatal balance of NO and reactive oxygen species toward NO: the inverted Barker phenomenon
Authors: Racasan Simona , Braam Branko , Koomans Hein A. , Joles Jaap A.
Published: November 2004

The “programming hypothesis” proposes that an adverse perinatal milieu leads to adaptation that translates into cardiovascular disease in adulthood. The balance between nitric oxide (NO) and reactive oxygen species (ROS) is disturbed in cardiovascular diseases, including hypertension. Conceivably, this balance is also disturbed in pregnancy, altering the fetal environment; however, effects of perinatal manipulation of NO and ROS on adult blood pressure (BP) are unknown. In spontaneously hypertensive rats (SHR), NO availability is decreased and ROS are increased compared with normotensive Wistar-Kyoto rats, and, despite the genetic predisposition, the perinatal environment can modulate adult BP. Our hypothesis is that a disturbed NO-ROS balance in the SHR dam persistently affects BP in her offspring. Dietary supplements, which support NO formation and scavenge ROS, administered during pregnancy and lactation resulted in persistently lower BP for up to 48 wk in SHR offspring. The NO donor molsidomine and the superoxide dismutase mimic tempol-induced comparable effects. Specific inhibition of inducible nitric oxide synthase (NOS) reduces BP in adult SHR, suggesting that inducible NOS is predominantly a source of ROS in SHR. Indeed, inducible NOS inhibition in SHR dams persistently reduced BP in adult offspring. Persistent reductions in BP were accompanied by prevention of proteinuria in aged SHR. We propose that in SHR the known increase in ANG II type 1 receptor density during development leads to superoxide production, which enhances inducible NOS activity. The relative shortage of substrate and cofactors leads to uncoupling of inducible NOS, resulting in superoxide production, activating transcription factors that subsequently again increase inducible NOS expression. This vicious circle probably is perpetuated into adult life.
L-type calcium channels in the renal microcirculatory response to endothelin
Authors: Pollock David M. , Jenkins John M. , Cook Anthony K. , Imig John D. , Inscho Edward W.
Published: November 2004

The signaling pathways of endothelin (ET)-1-mediated vasoconstriction in the renal circulation have not been elucidated but appear to be distinct between ETAand ETBreceptors. The purpose of this study was to determine the role of L-type Ca2+channels in the vasoconstrictor response to ET-1 and the ETBreceptor agonist sarafotoxin 6c (S6c) in the rat kidney. Renal blood flow (RBF) was measured with an ultrasonic flow probe in anesthetized rats, and a microcatheter was inserted into the renal artery for drug infusion. All rats were given vehicle (0.9% NaCl) or three successive bolus injections (1, 10, and 100 pmol) of ET-1 or S6c at 30-min intervals ( n = 6 in each group). ET-1 and S6c produced dose-dependent decreases in RBF. The Ca2+channel blocker nifedipine (1.5 μg) significantly attenuated the RBF response only at the highest doses of ET-1 and S6c. In the isolated blood-perfused juxtamedullary nephron preparation, Ca2+channel blockade with diltiazem had a very small inhibitory effect on ET-1-induced decreases in afferent arteriolar diameter only at the lowest concentrations of ET-1. In vascular smooth muscle cells isolated from preglomerular vessels, ET-1 produced a typical biphasic Ca2+response, whereas S6c had no effect on cytosolic Ca2+. Furthermore, Ca2+channel blockade (diltiazem or Ni2+) had no effect on the peak or sustained increase in cytosolic Ca2+produced by ET-1. These results support the hypothesis that L-type Ca2+channels play only a minor role in the constrictor responses to ET-1 in the renal microcirculation.