bluuebunny/crossref_metadata_2025 huggingface dataset:
Quantum Scalar Field in the FRW Universe with a Constant Electromagnetic Background
Authors: Gavrilov S. P. , Gitman D. M. , Odintsov S. D.
Published: October 2003

We discuss a massive scalar field with conformal coupling in the Friedmann–Robertson–Walker (FRW) Universe of a special type with a constant electromagnetic field. Treating an external gravitational–electromagnetic background exactly, at the first time the proper-time representations for out–in, in–in and out–out scalar Green functions are explicitly constructed as proper-time integrals over the corresponding (complex) contours. The vacuum-to-vacuum transition amplitudes and the number of created particles are found and vacuum instability is discussed. The mean values of the current and the energy–momentum tensor are evaluated, and different approximations for them are investigated. The back reaction of the particles created to the electromagnetic field is estimated in different regimes. The connection between the proper-time method and the effective action is outlined. The effective action in scalar QED in the weakly curved FRW Universe (de Sitter space) with a weak constant electromagnetic field is found as a derivative expansion over curvature and electromagnetic field strength. Possible further applications of the results are mentioned.
Path-Integral Quantization of the (2,2) String
Authors: Bischoff Jan , Lechtenfeld Olaf
Published: October 2003

A complete treatment of the (2,2) NSR string in flat (2 + 2)-dimensional space–time is given, from the formal path integral over N = 2 super Riemann surfaces to the computational recipe for amplitudes at any loop or gauge instanton number. We perform in detail the superconformal gauge fixing, discuss the spectral flow, and analyze the supermoduli space with emphasis on the gauge moduli. Background gauge field configurations in all instanton sectors are constructed. We develop chiral bosonization on punctured higher-genus surfaces in the presence of gauge moduli and instantons. The BRST cohomology is recapitulated, with a new space–time interpretation for picture-changing. We point out two ways of combining left- and right-movers, which lead to different three-point functions.
Axial and Gauge Anomalies in the BV Formalism
Authors: Barcelos-Neto J.
Published: October 2003

We discuss the quantization of the Schwinger and the axial Schwinger models in the Batalin–Vilkovisky–Lagrangian framework in order to illustrate how the one-loop order corrections to the action can be chosen in such a way that we may have either the vector current or the axial current conserved. We show for these two models that a BRST invariant local representation can be obtained by introducing extra Wess–Zumino fields. We also discuss the choice of the regulating operator, including the case of the chiral Schwinger model.
Nonlocality in Einstein–Podolsky–Rosen Spin Correlations
Authors: Usha Devi A. R. , Sirsi Swarnamala , Ramachandran G.
Published: October 2003

We study the nonlocal nature of EPR correlations of two spin j particles entangled in a singlet state using the quantum-mechanical joint probabilities.
Thermal Vacuum Polarization Using the Quantum Mechanical Path Integral
Authors: Mckeon D. G. C.
Published: October 2003

It has been shown how the quantum mechanical path integral can be used to do perturbative calculations in both quantum and thermal field theory to any order of the loop expansion. However, it is not readily apparent how gauge invariance is made manifest in this approach; in this paper we demonstrate how the vacuum polarization in electrodynamics at one-loop order is in fact transverse. We employ the one-dimensional Green's function [Formula: see text] in conjunction with an integration-by-parts procedure akin to that used by Strassler and Bern and Kosower. Surface terms in this approach are all zero. We obtain the high temperature expansion for the vacuum polarization in the static limit.
Nonlinear Schrödinger Model with Boundary, Integrability and Scattering Matrix Based on the Degenerate Affine Hecke Algebra
Authors: Komori Yasushi , Hikami Kazuhiro
Published: October 2003

The δ-function interacting many-body systems (nonlinear Schrödinger models) on an infinite interval and with boundary are studied by use of the integrable differential-difference operators, so-called Dunkl operators. These models are related with the classical root systems of type A and BC, and we give a systematic method to construct these integrable operators. This method is based on the infinite-dimensional representation for solutions of the classical Yang–Baxter equation and the classical reflection equation. In addition the scattering matrices of the boundary nonlinear Schrödinger model are investigated.
Measuring Multijet Structure of Hadronic Energy Flow or, What is a jet?
Authors: Tkachov Fyodor V.
Published: October 2003

Ambiguities of jet algorithms are reinterpreted as instability wrt small variations of input. Optimal stability occurs for observables possessing property of calorimetric continuity (C-continuity) predetermined by kinematical structure of calorimetric detectors. The so-called C-correlators form a basic class of such observables and fit naturally into QFT framework, allowing systematic theoretical studies. A few rules generate other C-continuous observables. The resulting C-algebra correctly quantifies any feature of multijet structure such as the "number of jets" and mass spectra of "multijet substates." The new observables are physically equivalent to traditional ones but can be computed from final states bypassing jet algorithms which reemerge as a tool of approximate computation of C-observables from data with all ambiguities under analytical control and an optimal recombination criterion minimizing approximation errors.
Two-Dimensional Extended Poincaré Gravity with Nontrivial Potential
Authors: Mignemi S.
Published: October 2003

We consider two-dimensional gravity models invariant under the local action of the extended Poincaré group, whose Lagrangian contains a nontrivial potential. After eliminating some degrees of freedom, one can write down an effective theory whose symmetries are described in general by a nonlinear algebra.
A Note on the Symmetry Algebra of An Asymmetric XXZ Quantum Spin Chain
Authors: Rego-Monteiro M. A.
Published: October 2003

We show that an interesting open asymmetric XXZ quantum spin chain with surface fields is invariant under a two-parametric generalization of the slq(2) algebra with deformation parameters being a particular root of unit.
Jaynes–Cummings Model with Intensity Independent Interaction and Initial Field in the Binomial State
Authors: Baseia B. , Marques G. C. , Duarte S. B. , De Brito A. L.
Published: October 2003

Recently, we introduced a new version of the Jaynes–Cummings model in which the interaction Hamiltonian is independent of the excitation number, or field intensity. Exact solution for this model was found allowing the study of nonclassical effects exhibited by the atom and the field, the latter initially in a coherent state. Here, we extend this study to the case of a field initially in the binomial state to investigate those nonclassical effects, as population trapping and sub-Poissonian statistics as function of the interpolating parameters of this state. The previous results are obtained from the present treatment, in the limit of a coherent state allowed by the binomial state.
What Effects in Nature the Two-Phase on the O-Cu(001)?
Authors: Sun Chang Q.
Published: October 2003

The modelling analysis herein and corresponding VLEED calculations suggest that the formation of the O -1 and the hybridised- O -1 effects in nature the c(2×2)-O and subsequently the [Formula: see text] phase on the O-Cu(001) surface.
Higher Order Conditional Probabilities and Thermodynamics of Binary Molten Alloys
Authors: Akinlade O.
Published: October 2003

The recently introduced four atom cluster model is used to obtain higher order conditional probabilities that describe the atomic correlations in some molten binary alloys. Although the excess free energy of mixing for all the systems studied are almost symmetrical about the equiatomic composition, most other thermodynamic quantities are not and thus, the study enables us to explain the subtle differences in their physical characteristics required to describe the mechanism of the observed strong heterocoordination in Au–Zn or homocoordination in Cu–Ni within the same framework. More importantly, we obtain all calculated quantities for the whole concentration range thus complimenting experimental evidence.
Thermal Properties of High Temperature Superconductors: Soliton Statistics Approach
Authors: Zhang Ling-Yun , Lin Jia-Tih , Li Bo-Zang , Pu Fu-Cho
Published: October 2003

We develop a soliton statistics approach to discuss the lattice effect of high temperature superconductor in the Davydov model on the basis of the bisoliton idea. We prove that lattice displacement in the Davydov model satisfies ϕ4 field form. Critical temperature of high temperature superconductor is studied from statistics of lattice kink. We have shown that the lattice effect is pronounced for thermal properties of high temperature superconductors. Comparision between theoretical and experimental results are good agreement for LaSrCuO and YBaCuO superconductor materials.
A Nucleation Process Drives the Percolation Transition
Authors: Skal Asya S.
Published: October 2003

The new "special" nodes — the nucleation nodes, which drive the percolation transition for kinetic coefficients are found by using the distribution functions of kinetic coefficients such as conductivity, the Hall and Seebeck coefficients for the resistor network. They belong to the component, opposite to the "special" nodes and create an infinite cluster below the threshold and destroy it above the threshold.

We have divided the "backbone" of an infinite cluster into two parts: (1) the static part which is responsible for analytic background; and (2) the dynamic part or a "scaling region" which equals the volume of the "special" nodes and is responsible for the singular part of kinetic coefficients and probably also for thermodynamic functions.
Squeezing Transformation for Dynamics of An Electron in Uniform Magnetic Field and a Harmonic Potential
Authors: Fan Hong-Yi , Zhang Yan
Published: October 2003

By virtue of the <λ| representation (Hong-yi Fan and Yong Ren, Mod. Phys. Lett.B10, 523 (1996)), which is useful for studying quantum Hall effect, we reveal that a squeezing mechanism directly corresponding to the variation of electron's cyclotron frequency is involved in the dynamics of an electron in a uniform magnetic field and a harmonic potential. Electron's wave functions are also derived by the squeezing transformation in the <λ| representation.
New Method for Latticeal Mean Field Models
Authors: Bundaru Raluca S.
Published: October 2003

We develop a new method to find the free-energy for latticealsystems of classical spins in the mean-field approximation. The simplerecurrence relation which the Hamiltonian satisfies in this case, allows us to obtain the free-energy by solving an ordinary differential equation.
Computer Simulation of Shear-Induced Phase Separation and Rheology in Two-Component Viscoelastic Fluid
Authors: Okuzono Tohru
Published: October 2003

We numerically study the dynamics of polymer solutions in two dimensions at a temperature above the equilibrium coexistence curve under shear flow. Our model is based on the Lagrangian picture of fluid dynamics. We can incorporate viscoelastic effects into the model by introducing a kind of fluid particles which have memories of their own past history. We carry out computer simulations and observe that shear-induced phase separation occur and the system shows a shear thinning rheological property. The most remarkable result is that the dependence of normal stress coefficient on shear rate changes at a shear rate which is comparable to inverse of the stress relaxation time. Our results imply that the shear-induced phase separation can change qualitative features of rheological response.
Surface Morphologies of Pulsed Laser Deposited Ultra-Thin Diamond-like Carbon Films
Authors: Chi Ning , Qingrun Hou , Gao J. , Chan K. Y. , Phillips D. L.
Published: October 2003

The surface morphologies of pulsed laser deposited ultra-thin diamond-like carbon films were studied by optical microscopy and atomic force microscopy. Off-axis deposited films had a larger size of particulates than on-axis deposited films. The root-mean-squared surface roughness was sensitive to deposition temperature. As a protective coating, the film was deposited on porous silicon. The surface morphology of the porous silicon changed considerably after carbon coating.
Huang–Rhys Factor of CdTe Semiconductors Doped with Arsenic and Antimony
Authors: Baskoutas S. , Athanasiou N. S.
Published: October 2003

By using the evolution operator method, we report a careful derivation of the Huang–Rhys factor, based on the Fröhlich continuum model of polarons, for cadmium telluride (CdTe) semiconductors, doped with arsenic (As) and antimony (Sb) acceptors. The calculated values of the Huang–Rhys factor, agree well with the experimental data for the bands at 1.45 eV and 1.54 eV, at large enough (16.5 nm) and zero donor–acceptor pair separation, respectively. They predicted the form of the bands, and provide new insight for the interpretation of the experimental data in terms of sub-Poissonian or super-Poissonian distributions, determining also the number of emitted phonons involved in the recombination process.
Analytical Solutions to Multivalued Maps
Authors: Gonzalez Jorge A. , De Carvalho Lindomar B.
Published: October 2003

We present explicit solutions for a class of chaotic maps. The return-maps generated by a special class of chaotic functions can be multivalued, or even they can represent an erratic set of points. In some cases the produced time series can have an increasing time-dependent maximum Lyapunov exponent. We discuss some applications of the obtained results. In particular, we present a chaotic lattice model for the investigation of the propagation of carriers in the presence of disorder.
Two-Mode Wigner Operator in <η| Representation
Authors: Wu He-Jun , Fan Hong-Yi
Published: October 2003

We derive the <η| representation of two-mode Wigner operator, where the <η| state is the common eigenstate of two particles' relative position and total momentum. By virtue of this representation we can conveniently obtain Wigner functions of some two-mode states and the Weyl correspondence functions of two-mode unitary phase operators.
Entropy and Pressure of Attractive Hard Squares by the Monte Carlo Method
Authors: Sauerwein Ricardo A. , De Oliveira Mário J.
Published: October 2003

The pressure and entropy of hard squares with attractive interactions are calculated from Monte Carlo simulations by an approach that avoids the numerical integration along a path in the thermodynamic space. The approach is useful whenever we are faced to a model that can be written in terms of a transfer matrix. The results coming from this direct approach are compared with those obtained from numerical thermodynamic integration.
The Relaxing Tl2+ Defects in Crystals of β-K2O4 Group
Authors: Efimov Vladimir N. , Mamin George V.
Published: October 2003

EPR of Tl 2+ ions in K 2 SO 4, Rb 2 SO 4, Cs 2 SO 4 crystals have been studied. Noncentrality of Tl 2+ (II) ions was observed. Activation energy values of Tl(II) complexes motion were obtained. Anomalous temperature dependence of EPR line position and appearance of new EPR lines in Rb 2 SO 4, Cs 2 SO 4 crystals were observed.
Structural and Magnetic Characteristics of (Eu1-xGax) Ba2Cu3O7-δ High-Tc Superconductors
Authors: Pop Iuliu , Redac Radu , Borodi Gheorghe , Ioncu Virgil
Published: October 2003

The high-T c ( Eu 1-x Ga x) Ba 2 Cu 3 O 7-δ superconductors with x=0, 0.01, 0.02, 0.03, 0.06 and 0.09 were synthesized by a ceramic technique. The gallium concentration dependence of the lattice parameters was determined. A transition from orthorhombic toward tetragonal structure was relevated for the most gallium concentrated sample. The temperature dependence of the magnetic susceptibility pointed out the diamagnetic transition at 78 and 80 K. In the paramagnetic region the magnetic susceptibility exhibits anomal temperature dependence.
Donor States in Spherical GaAs-Ga1-xAlxAs Quantum Dots
Authors: Niculescu Ecaterina C. , Niculescu Ana
Published: October 2003

The effect of the central cell correction on the binding energies of shallow donors in a spherical GaAs-Ga 1-x Al x As quantum dot is studied. The effective-mass approximation within a variational scheme is adopted and central cell corrections are calculated by using a Coulomb potential modified with an adjustable parameter. For small values of the radius of the dot large corrections are obtained for the shallow donors studied.
A Framework for Multi-Agent Systems with Multi-Modal User Interfaces in Distributed Computing Environments
Authors: Park Sankyu , Choi Key-Sun , Kim K. H. (Kane)
Published: October 2003

In current multi-agent systems, the user is typically interacting with a single agent at a time through relatively inflexible and modestly intelligent interfaces. As a consequence, these systems force the users to submit simplistic requests only and suffer from problems such as the low-level nature of the system services offered to users, the weak reusability of agents, and the weak extensibility of the systems. In this paper, a framework for multi-agent systems called the open agent architecture (OAA) which reduces such problems, is discussed. The OAA is designed to handle complex requests that involve multiple agents. In some cases of complex requests from users, the components of the requests do not directly correspond to the capabilities of various application agents, and therefore, the system is required to translate the user's model of the task into the system's model before apportioning subtasks to the agents. To maximize users' efficiency in generating this type of complex requests, the OAA offers an intelligent multi-modal user interface agent which supports a natural language interface with a mix of spoken language, handwriting, and gesture. The effectiveness of the OAA environment including the intelligent distributed multi-modal interface has been observed in our development of several practical multi-agent systems.
Graph-Based Software Process Management
Authors: Heimann Peter , Krapp Carl-Arndt , Westfechtel Bernhard , Joeris Gregor
Published: October 2003

Software process dynamics challenge the capabilities of process-centered software engineering environments. Dynamic task nets represent evolving software processes by hierarchically organized nets of tasks which are connected by control, data, and feedback flows. Project managers operate on dynamic task nets in order to assess the current status of a project, trace its history, perform impact analysis, handle feedback, adapt the project plan to changed product structures, etc. Developers are supported through task agendas and provision of tools and documents. Chained tasks may be executed in parallel (simultaneous engineering), and cooperation is controlled through releases of document versions.

Dynamic task nets are formally specified by a programmed graph rewriting system. Operations on task nets are specified declaratively by graph rewrite rules at a high level of abstraction. Furthermore, editing, analysis, and execution steps on a dynamic task net, which may be interleaved seamlessly, are described in a uniform formalism.
A Combined Reference Model- and View-Based Approach to System Specification
Authors: Engels Gregor , Heckel Reiko , Taentzer Gabriele , Ehrig Hartmut
Published: October 2003

The idea of a combined reference model- and view-based specification approach has been proposed recently in the software engineering community. In this paper we present a specification technique based on graph transformations which supports such a development approach. The use of graphs and graph transformations supports an intuitive understanding and an integration of static and dynamic aspects on a well-defined semantical base. On this background, formal notions of view and view relation are developed and the behaviour of views is described by a loose semantics. The integration of two views derived from a common reference model is done in two steps. First, dependencies between the views which are not given by the reference model are determined, and the reference model is extended appropriately. This is the task of a model manager. If the two views and the reference model are consistent, the actual view integration can be performed automatically. For the case of more than two views more general scenarios are developed and discussed. All concepts and results are illustrated at the well-known example of a banking system.
A Formal Object Specification Technique Integrating Object and Functional Model
Authors: Wagner Annika
Published: October 2003

In this paper we introduce a formal object specification technique. We call it OST in analogy to the well-known object modelling technique (OMT), because it adapts the OMT methodology. In order to have a better integration of object and functional model we propose to specify the operations of the functional model in terms of instance diagrams in a rule-based way as it is known from graph transformations. Moreover OST allows complex data constraints in the object model concerning existence and uniqueness of objects and attributes in a specific context. These constraints are described graphically over instance diagrams and they can be ensured automatically within the functional model. The correctness of the mechanism for ensuring the constraints is guaranteed by the formal semantics of OST.
Managing Software Projects by Structured Project Planning
Authors: Cimitile A. , Visaggio G.
Published: October 2003

This study is based on the Structured Process Model formalism previously proposed by the same authors, and describes some techniques for scheduling an execution plan which conforms to the chosen process but adapts to all the potential changes in the value of specific variables of the project. The executive plan is generated by means of Incremental Refinements. Each increment is the consequence of one or more decisions taken by the manager.

All the contingencies which can occur during the execution of the project are classified in a finite number of types of events which form the basis for the definition of all the transition laws between the possible states of the process. Naturally, the manager's decisions, and therefore the composition of the increment, take into account the changes in the value of the variables of the process and of the process model itself.

In addition, the study proposes the handling of fuzzy activities, by means of which the problems of recycles and reprocessing are solved. These activities also provide a better management of the execution times of the project.
An Easy Way to Minimal Algebras
Authors: Kiss Emil W.
Published: October 2003

A finite algebra C is called minimal with respect to a pair δ<θ of its congruences if every unary polynomial f of C is either a permutation, or f(θ)⊆δ. It is the basic idea of tame congruence theory developed by Ralph McKenzie and David Hobby [7] to describe finite algebras via minimal algebras that sit inside them. As shown in [7] minimal algebras have a very restricted structure.

This paper presents a new tool, the Twin Lemma, which makes it possible to give short proofs of some of these structure theorems. This part can be read as an alternative introduction to the theory. Our method yields new information in the type 1 case, and is especially useful in describing E-minimal algebras (that is, algebras that are minimal with respect to every prime congruence quotient). We complete their theory given in [7] by proving a structure theorem for the type 1 case. Finally we show that if an algebra is minimal with respect to two quotients, then the two types are the same, and if this type is 2, 3, or 4, then the bodies are also equal.
Groups Whose Subgroup Growth is Less than Linear
Authors: Shalev Aner
Published: October 2003

Let G be a residually finite group and let an(G) denote the number of index n subgroups of G. It is shown that an(G)/n →0 if and only if G has a finite index central subgroup whose finite quotients are all cyclic. As an application we show that the degree of a group of polynomial subgroup growth cannot lie strictly between 0 and 1.
On the Asphericity of Length Four Relative Group Presentations
Authors: Baik Y. G. , Bogley W. A. , Pride S. J.
Published: October 2003

Excluding five unresolved cases, asphericity is classified in relative group presentations of the form (H,x: xaxbxcxd).
On the Decidability of Some Equivalence Problems for L Algebraic Series
Authors: Honkala Juha
Published: October 2003

The equivalence problem for Lindenmayerian algebraic series is discussed. While the problem in general is undecidable, decidable special cases of interest are presented.
The Kernel Category and Variants of the Concatenation Product
Authors: Branco Mário J. J.
Published: October 2003

For each variety V of finite monoids, we consider three varieties [Formula: see text] of languages defined in the following way: for each alphabet [Formula: see text] is the Boolean algebra generated by the languages of the form L or L0aL1, where [Formula: see text], a ∈ A and the product L0aL1 is deterministic (resp. codeterministic, bideterministic). We present a description of the corresponding varieties of finite monoids. Such descriptions are done in terms of categories, using the kernel category of a relational morphism. We also give some connections with the positive varieties of languages and with the varieties of finite ordered monoids.
Splitting Epimorphisms of Free Metabelian Groups
Authors: Gupta C. K. , Noskov G. A.
Published: October 2003

Grigorchuk and Kurchanov's conjecture states that, up to natural equivalence, there is precisely one splitting epimorphism F2n→Fn×Fn from a free group F2n onto Fn×Fn. The [Formula: see text]-conjecture, while formally similar to the the Poincaré conjecture, implies the well-known Andrews–Curtis conjecture about the balanced presentations of the trivial group. In this paper we undertake the task of fully analyzing the [Formula: see text]-conjecture modulo the second commutator subgroup F2n″. We derive some consequences for the general [Formula: see text]-conjecture.
Quasiconvexity and Amalgams
Authors: Kapovich Ilya
Published: October 2003

We obtain a criterion for quasiconvexity of a subgroup of an amalgamated free product of two word hyperbolic groups along a virtually cyclic subgroup. The result provides a method of constructing new word hyperbolic group in class (Q), that is such that all their finitely generated subgroups are quasiconvex. It is known that free groups, hyperbolic surface groups and most 3-dimensional Kleinian groups have property (Q). We also give some applications of our results to one-relator groups and exponential groups.
A New Relaxation Method for the Compressible Navier–Stokes Equations
Authors: Bongiovanni Emmanuel , Ern Alexandre , Glinsky-Olivier Nathalie
Published: October 2003

We derive a new relaxation method for the compressible Navier–Stokes equations endowed with general pressure and temperature laws compatible with the existence of an entropy functional and Gibbs relations. Our method is an extension of the energy relaxation method introduced by Coquel and Perthame for the Euler equations. We first introduce a consistent splitting of the diffusion fluxes as well as a global temperature for the relaxation system. We then prove that under the same subcharacteristic conditions as for the relaxed Euler equations and for a specific form of the global temperature and the heat flux splitting, the stability of the relaxation system may be obtained from the non-negativity of a suitable entropy production. A first-order asymptotic analysis around equilibrium states confirms the stability result. Finally, we present a numerical implementation of the method allowing for a straightforward use of Navier–Stokes solvers designed for ideal gases as well as numerical results illustrating the accuracy of the proposed algorithm.
On an Exchange Interaction Model for Quantum Transport: The Schrödinger–Poisson–Slater System
Authors: Bokanowski Olivier , López José L. , Soler Juan
Published: October 2003

We study a mixed-state Schrödinger–Poisson–Slater system (SPSS). This system combines the nonlinear and nonlocal Coulomb interaction with a local potential nonlinearity known as the "Slater exchange term" which models a fermionic effect. The origin of the model is explained and related models are also proposed. Existence, uniqueness and regularity of local-in-time and global solutions are analyzed in ℝ3 with L2 or H1 initial data. Stationary solutions and conservation laws are also analyzed by using a variational approach due to E. Lieb.
Stabilized hp-DGFEM for Incompressible Flow
Authors: Schötzau D. , Schwab C. , Toselli A.
Published: October 2003

We consider stabilized mixed hp-discontinuous Galerkin methods for the discretization of the Stokes problem in three-dimensional polyhedral domains. The methods are stabilized with a term penalizing the pressure jumps. For this approach it is shown that ℚk-ℚk and ℚk-ℚk-1 elements satisfy a generalized inf–sup condition on geometric edge and boundary layer meshes that are refined anisotropically and non quasi-uniformly towards faces, edges, and corners. The discrete inf–sup constant is proven to be independent of the aspect ratios of the anisotropic elements and to decrease as k-1/2 with the approximation order. We also show that the generalized inf–sup condition leads to a global stability result in a suitable energy norm.
Effective Chemical Processes in Porous Media
Authors: Conca C. , Díaz J. I. , Timofte C.
Published: October 2003

In the book by Hornung, Chap. 6, the author proposes a homogenization strategy for the effective behavior of some chemical processes involving adsorption and reactions arising in porous media. Rigorous proofs of the convergence results are given in the case of linear adsorption rates and linear chemical reactions. The author leaves as an open question the case of a nonlinear adsorption rate. Our goal in this paper is to study two well-known examples of such nonlinear models, namely the so-called Freundlich and Langmuir kinetics.
Stability of a Thermodynamically Coherent Multiphase Model
Authors: Després B. , Lagoutière F. , Ramos D.
Published: October 2003

We analyze a hyperbolic system of conservation laws in dimension one, which is a drastic simplification of a multi-phase or multi-velocity fluid model. The physical domain of hyperbolicity is bounded, which is a characteristic of multi-phase models. Our main result is the stability of the domain of hyperbolicity. Due to the degeneracy of the model on the boundary of the hyperbolicity domain, rarefaction waves are not unique. We also propose a numerical scheme for approximate resolution of the model and prove the stability of this scheme.
Mathematical and Numerical Analysis of a Tsunami Problem
Authors: di Martino B. , Flori F. , Giacomoni C. , Orenga P.
Published: October 2003

In this paper, we present a tsunami model based on the displacement of the lithosphere and the mathematical and numerical analysis of this model. More precisely, we give an existence and uniqueness result for a problem which models the flow and formation of waves at the time of a submarine earthquake in the vicinity of the coast. We propose a model which describes the behavior of the fluid using a bi-dimensional shallow-water model by means of a depth-mean velocity formulation. The ocean is coupled to the Earth's crust whose movement is assumed to be controlled on a large scale by plate equations. Finally, we give some numerical results showing the formation of a tsunami.
Subgrid Modeling for Convection-Diffusion-Reaction in Two Space Dimensions Using a Haar Multiresolution Analysis
Authors: Hoffman Johan
Published: October 2003

In this paper we study a subgrid model based on extrapolation of a modeling residual, in the case of a linear convection-diffusion-reaction problem Lu=f in two dimensions. The solution u to the exact problem satisfies an equation Lhu=[f]h+Fh(u), where Lh is the operator used in the computation on the finest computational scale h, [f]h is the approximation of f on the scale h, and Fh(u) is a modeling residual, which needs to be modeled. The subgrid modeling problem is to compute approximations of Fh(u) without using finer scales than h. In this study we model Fh(u) by extrapolation from coarser scales than h, where Fh(u) is directly computed with the finest scale h as reference. We show in experiments that a solution with subgrid model on a scale h in most cases corresponds to a solution without subgrid model on a mesh of size less than h/4.
Knowledge-Based Software Prototyping and Reuse
Authors: Rubin Stuart H.
Published: October 2003

Models are executable prototypes. Modeling is closely tied to simulation, which refers to the exercise of a model over a variable parametric space. Model simulations not only provide the engineer with feedback pertaining to the validity of a proposed design, but additionally allow competing designs to be compared on one or more parameters (i.e., sensitivity analysis). Models are defined from a base of several hundred primitive constructs. These constructs can define additional constructs hierarchically.

An expertn–system was constructed, which retrieves software for reuse. This expert system is itself reusable and consists of many sub-systems – any one of which can invoke any other. A key feature is that any expertn–system need never be modified, for purposes of reuse, once saved in a repository. Rather, it communicates all information back to the caller and lets the caller decide how and when to use it. Thus, blocks in an expertn–system have very low coupling (i.e., no off-model connections). In addition, expertn–systems are, as their name suggests, organized in a hierarchy. This means that very complex decision-making systems can be called into play with minimal effort. Growing the repository is equivalent to learning.
An Application of Wavelet-Based Vector Quantization in Target Recognition
Authors: Chan Lipchen Alex , Nasrabadi Nasser M.
Published: October 2003

An automatic target recognition (ATR) classifier is constructed that uses a set of dedicated vector quantizers (VQs). The background pixels in each input image are properly clipped out by a set of aspect windows. The extracted target area for each aspect window is then enlarged to a fixed size, after which a wavelet decomposition splits the enlarged extraction into several subbands. A dedicated VQ codebook is generated for each subband of a particular target class at a specific range of aspects. Thus, each codebook consists of a set of feature templates that are iteratively adapted to represent a particular subband of a given target class at a specific range of aspects. These templates are then further trained by a modified learning vector quantization (LVQ) algorithm that enhances their discriminatory characteristics.
A Model-Based Gaze Tracking System
Authors: Stiefelhagen Rainer , Yang Jie , Waibel Alex
Published: October 2003

In this paper we present a non-intrusive model-based gaze tracking system. The system estimates the 3-D pose of a user's head by tracking as few as six facial feature points. The system locates a human face using a statistical color model and then finds and tracks the facial features, such as eyes, nostrils and lip corners. A full perspective model is employed to map these feature points onto the 3D pose. Several techniques have been developed to track the features points and recover from failure. We currently achieve a frame rate of 15+ frames per second using an HP 9000 workstation with a framegrabber and a Canon VC-C1 camera. The application of the system has been demonstrated by a gaze-driven panorama image viewer. The potential applications of the system include multimodal interfaces, virtual reality and video-teleconferencing.
Solving the Processor Configuration Problems with a Mutation-Based Genetic Algorithm
Authors: Lau T. L. , Tsang E. P. K.
Published: October 2003

The Processor Configuration Problem (PCP) is a real life Constraint Optimization Problem. The task is to link up a finite set of processors into a network, whilst minimizing the maximum distance between these processors. Since each processor has a limited number of communication channels, a carefully planned layout will help reduce the overhead for message switching.

In this paper, we present a Genetic Algorithm (GA) approach to the PCP. Our technique uses a mutation-based GA, a function that produces schemata by analyzing previous solutions, and an efficient data representation. Our approach has been shown to out-perform other published techniques in this problem.
An Evolutionary Approach for Time Dependent Optimization
Authors: Collard Philippe , Escazut Cathy , Gaspar Alessio
Published: October 2003

Many real-world problems involve measures of objectives that may be dynamically optimized. The application of evolutionary algorithms, such as genetic algorithms, in time dependent optimization is currently receiving growing interest as potential applications are numerous ranging from mobile robotics to real time process command. Moreover, constant evaluation functions skew results relative to natural evolution so that it has become a promising gap to combine effectiveness and diversity in a genetic algorithm. This paper features both theoretical and empirical analysis of the behavior of genetic algorithms in such an environment. We present a comparison between the effectivenss of traditional genetic algorithm and the dual genetic algorithm which has revealed to be a particularly adaptive tool for optimizing a lot of diversified classes of functions. This comparison has been performed on a model of dynamical environments which characteristics are analyzed in order to establish the basis of a testbed for further experiments. We also discuss fundamental properties that explain the effectiveness of the dual paradigm to manage dynamical environments.
Usage Patterns of Codons Versus Complementary Codons Among Cellular Organisms and Organelles
Authors: Ma Fei , Zhuang Yonglong , Li Yanda , Xu Xiaofeng , Chen Xueping
Published: October 2003

Genetic code is one of the most important biological languages in communications between DNA and protein, so peoples have been paying a great attention to the usage bias of synonymous codons. Based on Grosjean and Ikemura's "optimum combination of codon-anticodon complex" and "translation efficiency" hypotheses, in this paper, we put forward that a biased codon usage is identical to its corresponding complementary codon usage preference. To testify the hypothesis and reveal usage patterns between codons and corresponding complementary codons among different cellular organisms and organelles, the usage data of both codons and corresponding complementary ones from 28 cellular organisms and 20 organelles were analyzed. The results showed that: (1) there is a significantly positive correlation between codons and their complementary ones in most cellular organisms, chloroplasts and mitochondria; (2) all 32 single pairs codon versus complementary codon shared the likely usage correlation patterns, with the significantly positive, unrelated and significantly negative pair number of 18, 12 and 2 within 28 cellular organisms as well as 11, 17 and 4 within 20 organelles respectively, and some usage patterns of 32 single pairs codon versus complementary codon of cellular organisms are highly consistency with two kinds of organelles, which strongly implied that their codon usage has undergone the similar evolutionary selection in their wobbling and modification; (3) the codon-frequency tree agreed fairly well with the traditional one. These results demonstrated the validity of our hypothesis, and indicated the usefulness of correlation between codon and complementary codon in elucidating molecular evolutionary mechanisms.
On a Food Web Consisting of a Specialist and a Generalist Predator
Authors: Gakkhar S. , Naji R. K.
Published: October 2003

A biologically feasible continuous time model of a three level food web consisting of a specialist and a generalist predator is investigated. The boundedness of the unique solution of the model establishes the dissipative nature of the food web. Necessary and sufficient criteria for the coexistence of the three interacting populations are established. Complex behavior of the system is evident from the bifurcation diagrams. Abundance of periodic and chaotic behavior of the species with the variation of the key parameters are also observed. The strange attractors for the time evolution of the coexisting species are drawn.
Second Order Schemes for Age-Structured Population Equations
Authors: Abia L. M. , López-Marcos J. C.
Published: October 2003

We formulate second order finite difference schemes based on Padé rational approximations for the numerical integration of nonlinear age-dependent population models. The schemes are completely analysed and some numerical experiments are also reported in order to show numerically their accuracy.
Ecological Species Coevolution
Authors: Apaloo Joseph
Published: October 2003

The concepts of evolutionary stable strategies (ESS) and neighborhood invader strategies (NIS) are used to examine the dynamics of coevolving species. When an ESS as well as its near neighbors are ecologically stable and phenotypic space is unconstrained, the strong NIS concept shows that each member of the ESS coalition can always be repelled by some coalition strategies that are sufficiently close to the ESS. Thus an ESS for coevolving species may not be attained by selection unless phenotypic constraints are imposed.
Genetic Information Transfer in Populations Under Selection
Authors: Bartoloni N.
Published: October 2003

It is important to understand the dynamics of biological information in a genetic population for it determines the dynamics of energy and, thus, of matter. In another work we have initiated the characterization of a genetic population transmitting information from one generation to the next. In this work the genetic information flow under selection is analyzed in a genetic population under random mating. A one-locus diallelic model has been utilized in the derivations. Based upon the Schmalhausen's model of information circulation and the Shannon's theory of information we have focused on the analysis of information flow in the stage of transformation under the input of selective forces. The measures of information are important parameters to take account of when the process of populational evolution is analyzed. Several expressions relating information measures with selection coefficients corresponding to each genotype have been obtained. They are conditional entropies and mutual information (information transfer). Finally, a numerical survey employing a great deal of fitness values has been performed.
Determination of the Volume of the Blood of Rabbits and Pigs Using Electron Spin Resonance
Authors: Goroncy Alexander K. , Farach Horacio A. , Poole Charles P. , Gonzalez M. Francisco , De Paoli Tomas , Hager Alfredo
Published: October 2003

Blood volume of rabbits and pigs was determined by an electron spin resonance (ESR) measurement of erythrocytes spin labelled by attaching the radical ion 4-maleimido-2,3,6,6,-tetramethylpiperidine-1-oxyl (MAL-4) to reduced glutathione. All correction factors were considered in detail, including the stability of MAL-4 in erythrocytes inside and outside the blood stream (by taking multiple blood samples and measuring the strength of the signal). It was found that exercise and certain anesthetics (Midazolam, pentobarbitone (rompum), Ketamine) did not affect the in vivo stability. Some measurements were taken to determine how fast the fluid lost after haemorrhage is replaced in the blood stream as well as when the excess fluid after transfusion is removed from the blood stream. The time decay data were fitted to stretched exponential functions. This method of blood volume determination is believed to be superior to the usual radioactive labeling method.
Mass Balance Equation Versus Logistic Equation in Food Chains
Authors: Kooi B. W. , Boer M. P. , Kooijman S. A. L. M.
Published: October 2003

The dynamic behavior of tri-trophic food chains consisting of resources, prey, predator and top-predator is dealt with. We compare a formulation whereby the prey growth is logistic, with a mass balance formulation. In the case of the mass balance formulation both the linear and the hyperbolic functional response are discussed. The consequences of the different formulations on the dynamics of a microbial food chain in chemostat situation are described. Bifurcation diagrams for the nonlinear dynamic systems are given. When the prey grows logistically there is no coexistence of the three species for biologically realistic parameter values for a microbial food chain. The same holds for the mass balance equations with a linear functional response for the prey. For a hyperbolic functional response, however, there is a stable equilibrium for the whole food chain in a rather large region of the parameter space. Furthermore, this model shows more complex dynamic behaviors; besides point attractors, limit cycles and chaotic attractors.
Fast Oscillating Migrations in Predation Models
Authors: Poggiale J. C. , Auger P. M.
Published: October 2003

We consider a predator-prey model in a multi-patch environment. We assume the existence of two time scales: the migration process takes place on the behavioural level and is thus much faster than the population dynamics. Each population is subdivided into subpopulations which correspond to the spatial distribution. The model is thus a large system of ordinary differential equations. We assume that the migration rates are fastly oscillating: it is the case for some aquatic populations for example. Indeed, these populations undergo regular vertical movements in the water column every day. In order to study our model, we use a reduction method which allows us to simplify the initial model. It is then possible to bring to light that some properties emerge from the coupling between the fast migration process and the slow population dynamics. We give an explicit example of the emerging property.
Bounds on Endemic Disease Levels, Risks and Basic Reproductive Numbers in Heterogenous Models for HIV/AIDS Amongst Injecting Drug Users
Authors: Greenhalgh David
Published: October 2003

In this paper we examine the effect of heterogenous mixing on the spread of HIV and AIDS amongst a population of injecting drug users. We consider heterogeneity in addicts' shooting gallery visiting rates, their syringe cleaning probabilities and their choice of shooting gallery. We discuss two models. In the first the size of the populations of the different groups of drug users are assumed to be constant whereas the second models recruitment of new drug users into the population and their attrition due to HIV and AIDS. We show that homogenous visiting and cleaning and completely random choice of needles minimises both the basic reproductive number Ro and the equilibrium probability that any given type of addict is exposed to HIV on any single visit. If in addition all addicts have the same preferences for different shooting galleries then homogenous mixing minimises the fraction of needles infected and the equilibrium probability that an addict arriving at a shooting gallery is infected. Simulations with realistic parameter values confirm these results and the importance of heterogeneity in the model. Our simulations indicate that it is possible for homogenous mixing to maximise the overall fraction of addicts infected.