bluuebunny/crossref_metadata_2025 huggingface dataset:
MICROSCOPIC FRACTIONAL PERSISTENT CURRENT OSCILLATIONS IN A METALLIC RING WITH THE ANDERSON IMPURITY
Authors: ZVYAGIN A.A. , BANDOS T.V.
Published: November 2004

Microscopic spin and charge persistent currents in a metallic ring with the Anderson magnetic impurity are studied. It is shown that the impurity changes caused by the external magnetic and electric fluxes, the Aharonov-Bohm and Aharonov-Casher oscillations (magnitudes and periods), contrast with the normal metallic case. Spin-charge separation is the reason for the fractional Φ0/N (N is the number of electrons) period of the Aharonov-Bohm oscillations and F0/(N−2M) (M is the number of paired electrons) period of the Aharonov-Casher oscillations.
ENHANCED PHOTOLUMINESCENCE FROM C60 TRAPPED IN NaY MOLECULAR SIEVE
Authors: GU GANG , DING WEIPING , CHENG GUANGXU , ZANG WENGCENG , ZEN HAO , ZHANG JIANRONG , DU YOUWEI
Published: November 2004

Enhanced photoluminescence from C 60 confined in NaY molecular sieve has been observed. The photophysical properties of C 60 are modified due to the interaction of C 60 with the sketch structure of NaY molecular sieve.
A STUDY OF TWO PARTICLE CLUSTER APPROXIMATION FOR NEMATIC LIQUID CRYSTAL FILMS
Authors: ZHANG ZHIDONG
Published: November 2004

A two-particle cluster variation theory is presented here to treat the inhomogeneous nematic phase. This theory is used to study nematic liquid crystal films. The internal energy per molecule in each layer is calculated and results are in agreement with those of the simulation. It is found that within the two-particle cluster theory, the surface excess free energy in both the nematic phase and the isotropic phase increases with the temperature. This behavior is in contradiction with that of the simulation and the mean field theory.
TRANSPORT CURRENT CHARACTERISTICS OF THE TEXTURED Bi-2223 THICK FILM
Authors: WANG Z. H.
Published: November 2004

The transport current characteristics of the textured Bi-2223 thick film were studied by the measurement of the voltage–current curves for different temperatures and various magnetic fields. The results show that the transitions can be fitted approximately by a power law with n-values at the low electrical field region. The n-value is observed to fall with increased applied magnetic field and temperature, and exhibits the thermally activated flux flow behavior. The activation energies U(T, H, J) derived from the V-I curves were found to follow a (n − 1)k B T × ln (J0/J). The critical temperature T c was found to follow the irreversibility line described by the function of H ∝ (1− T CH /T CO )1.47 for H//ab-plane. The temperature and magnetic field dependences of the transport critical current density follow a power law J c ~ (1−T COH /T COO )m and J c ~ H−α for H//ab-plane. The exponent m increases with increasing magnetic field, and α decreases with decreasing temperature. These indicate that the flux motion may be caused by a weak pinning potential energy.
IMAGE ANALYSIS OF A NEGATIVELY CURVED GRAPHITIC SHEET MODEL FOR AMORPHOUS CARBON
Authors: BURSILL L. A. , BOURGEOIS LAURE N.
Published: November 2004

High-resolution electron micrographs are presented which show essentially curved single sheets of graphitic carbon. Image calculations are then presented for the random surface schwarzite-related model of Townsend et al. (Phys. Rev. Lett.69, 921–924, 1992). Comparison with experimental images does not rule out the contention that such models, containing surfaces of negative curvature, may be useful for predicting some physical properties of specific forms of nanoporous carbon. Some difficulties of the model predictions, when compared with the experimental images, are pointed out. The range of application of this model, as well as competing models, is discussed briefly.
CALCULATIONS OF THE MEAN SQUARE RELATIVE ATOMIC DISPLACEMENTS IN A SIMPLE MODEL OF AN ANHARMONIC CRYSTAL
Authors: PASCUAL M. F. , ZUBOV V. I.
Published: November 2004

We have used the correlative method of unsymmetrized self-consistent field to calculate the mean square relative displacements (MSRD) of atoms in the two-dimensional model of the anharmonic crystal with square lattice. The longitudinal and transversal components of MSRD between the nearest, second, third and next neighbors have been computed. An influence of the anharmonicity on various components as well as peculiarities of the lattice considered are discussed.
MOTIONS OF A POLYMER CHAIN IN SURFACTANT SOLUTIONS
Authors: ANTALEK B. , CHARI K.
Published: November 2004

Recent work on self-diffusion and local segmental motion of poly(ethyleneoxide) (PEO) in self-assembled aggregates of PEO and sodium dodecyl sulfate (SDS) in water is reviewed. The experiments provide us with a better understanding of the shape and transport properties of the aggregates. More importantly they suggest that the polymer-surfactant complex may be a self-similar object with fractal dimension different from that of the surfactant-free polymer coil in a good solvent.
STUDY OF THE ABSORPTION SPECTRUM OF F-CENTER/OH- DEFECT PAIRS IN CsCl, CsI AND CsBr
Authors: WEST J. , TSEN K.T. , LIN S.H.
Published: November 2004

We have used a wavefunction-based model to interpret the absorption spectrum of F-center/OH− defect pairs in CsCl, CsI and CsBr. It is demonstrated that the analysis of the absorption spectrum of these defect systems can provide information such as the position vector of the center of charge of the defect molecule, the orientation of the intrinsic dipole moment, the electronic wavefunctions and energy levels of the defect system and the lattice reconfiguration due to the presence of the defect molecule.
PHONON-LIMITED MOBILITY IN A FREE-STANDING POLAR SEMICONDUCTOR QUANTUM WIRE
Authors: DAT NGUYEN NHU
Published: November 2004

A macroscopic continuum model is used to study the longitudinal optical phonons in a free-standing polar quantum wire with a rectangular cross section. The Fröhlich Hamiltonian describing the electron-phonon interaction is then obtained and used to calculate the electron mobility governed by confined LO phonons by means of the memory function approach, neglecting electron-electron interaction. Numerical calculations are given for a GaAs quantum wire, showing that the mobility is enhanced at least by one order of magnitude in comparison with the bulk-LO-phonon-limited one. It is shown that the contribution of intersubband scattering is important in wires of large width at high temperature.
MORTARING THE TWO-DIMENSIONAL EDGE FINITE ELEMENTS FOR THE DISCRETIZATION OF SOME ELECTROMAGNETIC MODELS
Authors: BEN ABDALLAH ADNENE , BEN BELGACEM FAKER , MADAY YVON , RAPETTI FRANCESCA
Published: November 2004

We describe the mortar element method for the two-dimensional edge finite elements of class H(curl). These finite elements are currently used for the discretization of various models coming from the Maxwell equations and using them in a mortar framework has several interesting applications in the electromagnetic and electrotechnical domains. We develop some technical tools necessary to perform the numerical analysis of this approach. Then, we prove some optimal approximation results and illustrate the theory by some numerical experiences.
IRREVERSIBILITY AND HYSTERESIS FOR A FORWARD–BACKWARD DIFFUSION EQUATION
Authors: EVANS L. C. , PORTILHEIRO M.
Published: November 2004

Our intention in this paper is to publicize and extend somewhat important work of Plotnikov7 on the asymptotic limits of solutions of viscous regularizations of a nonlinear diffusion PDE with a cubic nonlinearity. Since the formal limit PDE is in general ill-posed, we expect that the limit solves instead a corresponding diffusion equation with hysteresis effects. We employ entropy/entropy flux pairs to prove various assertions consistent with this expectation.
HERACLITEAN TIME PROPOSAL REVISITED
Authors: BERTOLAMI ORFEU
Published: November 2004

Difficulties in the interpretation of the wave function of the Universe in canonical quantum gravity suggest that the use of dynamical variables to play the role of time is not quite consistent. A formulation of canonical quantum gravity in which time is an extrinsic variable has been previously studied with the problem of being compatible, at the classical level, with General Relativity with a nonvanishing unspecified cosmological constant. We argue that this last problem can be circumvented by introducing a nondynamical scalar field which allows for a relaxation mechanism for the cosmological term.
THE DE SITTER UNIVERSE MODELS
Authors: ERIKSEN E. , GRØN Ø.
Published: November 2004

The kinematical properties of the de Sitter space-time are reviewed and investigated. The properties of the static sections are clarified. A deduction of the analytic extension, analogous to that of Kruskal and Szekeres for the Schwarzschild space-time, of the static section to the region outside the horizon is given. The representation of the de Sitter space-time as a four-dimensional hyperboloid in Minkowskian five-dimensional spacetime is reviewed. Coordinate transformations between different sections of the de Sitter space-time are found. By means of the transformation formulae the different sections are mapped onto each other in space-time diagrams. These mappings are interpreted kinematically. We have aimed at providing, whenever possible, an intuitive understanding of the kinematical properties of the different sections, and how they are interrelated. Among others we present real coordinate transformations between the static and the three Robertson-Walker sections of the de Sitter space-time on one hand and the vacuum dominated Bianchi type-III model on the other hand. These transformations are used to map the path of a typical Bianchi type-III reference particle into the static and the Robertson-Walker sections.
ANGULAR TWO-POINT CORRELATION FUNCTIONS FOR COSMOLOGICAL GAMMA-RAY BURST MODEL
Authors: KOBAYASHI SHIHO , SASAKI SHIN , SUTO YASUSHI
Published: November 2004

We compute the angular two-point correlation functions of the gamma-ray bursts at cosmological distances. Since the gamma-ray burst emission mechanism is not yet established, we simply assume that the gamma-ray burst sources are associated with high-redshift galaxies in some way. Then on the basis of several simple models for the evolution of galaxy spatial correlations, we calculate the amplitude of angular two-point correlation functions on scales appropriate for the Compton Gamma Ray Observatory data. We find that in most cases the predicted correlations are difficult to detect with the current data rate and the angular resolution, but models in which the bursts preferentially occur at relatively low redshift (z≲0.5) predict correlation amplitudes on θ~5° which will be marginally detectable with the Gamma Ray Observatory data in several years. If future observations detect a signal of angular correlations, it will imply useful information on the correlation of galaxies at high redshifts provided that the gamma-ray bursts are cosmological.
TRAVERSABLE WORMHOLES IN (2+1) AND (3+1) DIMENSIONS WITH A COSMOLOGICAL CONSTANT
Authors: DELGATY M.S.R. , MANN R.B.
Published: November 2004

Macroscopic traversable wormhole solutions to Einstein’s field equations in (2+1) and (3+1) dimensions with a cosmological constant are investigated. Ensuring traversability severely constrains the material used to generate the wormhole’s spacetime curvature. Although the presence of a cosmological constant modifies to some extent the type of matter permitted [for example it is possible to have a positive energy density for the material threading the throat of the wormhole in (2+1) dimensions], the material must still be “exotic,” that is matter with a larger radial tension than total mass-energy density multiplied by c2. Two specific solutions are applied to the general cases and a partial stability analysis of a (2+1) dimensional solution is explored.
SHANNON-WEHRL ENTROPY FOR COSMOLOGICAL AND BLACK HOLE SQUEEZING
Authors: ROSU HARET C. , REYES MARCO
Published: November 2004

We apply the Shannon-Wehrl entropy to the squeezed graviton states by making use of the numerical estimates for the gravitational squeezing parameter as provided by Grishchuk and Sidorov [Phys. Rev.D42, 3413 (1990)]. Compared to the same quantity for laboratory squeezing, we obtain a much higher value for this entropy as an indication of the huge gravitational squeezing during cosmological evolution. We also plot the Shannon-Wehrl entropy for the “thermal” radiation of a Schwarzschild horizon.
NUMERICAL INVESTIGATION OF INTEGRABLE WEYL GEOMETRY IN MULTIDIMENSIONAL COSMOLOGY
Authors: KONSTANTINOV M. YU. , MELNIKOV V.N. , NOVELLO M.
Published: November 2004

The evolution of 4-dimensional and (4+D)-dimensional (D=1, 2) cosmological models based on the integrable Weyl geometry are considered numerically both for empty space-time and for scalar field with nonminimal coupling with gravity. In both cases nonsingular solutions exist only for the open exterior space and flat (with torus topology) interior space. It is shown that in the nonsingular case the scenario of dynamical dimension reduction is realized. Some characteristic features of the considered models and their possible generalizations are discussed.
ENERGY AND HEAT FLUX
Authors: GARIEL J. , SANTOS N.O. , DENMAT G. LE
Published: November 2004

The total energy in a sphere containing an isotropic shear-free conducting heat fluid is studied in the frame of a spherically symmetric metric. Firstly, we examine the role played by the heat flux. Secondly, we point out the contribution to the energy by the Weyl tensor. We obtain different formulas for the total energy, and those formulas are shown to be equivalent. We derive the general solution for a conformally flat spacetime, and give an example for a nonconformally flat spacetime.
BARYOGENESIS FROM BLACK HOLE EVAPORATION
Authors: MAJUMDAR A.S. , GUPTA P. DAS , SAXENA R.P.
Published: November 2004

The possibility of baryogenesis through the evaporation of black holes formed during extended inflation is explored. These black holes are produced due to the collapse of trapped regions of false vacuum during the inflationary phase transition. Immediately after formation, the accretion of mass from the surrounding hot radiation bath in the universe is shown to be an important effect. This causes the lifetime of the black holes to be considerably elongated before they evaporate out through the process of Hawking radiation. It is shown that a sufficient number of black holes last up to well past the electroweak era and hence contribute to the surviving baryon asymmetry in the universe.
HAMILTONIAN FORMALISM FOR BLACK HOLES AND QUANTIZATION
Authors: CAVAGLIÀ MARCO , DE ALFARO VITTORIO , FILIPPOV ALEXANDRE T.
Published: November 2004

Starting from the Lagrangian formulation of the Einstein equations for the vacuum static spherically symmetric metric, we develop a canonical formalism in the radial variable r that is timelike inside the Schwarzschild horizon. The Schwarzschild mass turns out to be represented by a canonical function that commutes with the r-Hamiltonian. We investigate the Wheeler-DeWitt quantization and give the general representation for the solution as superposition of eigenfunctions of the mass operator.
NON-EQUILIBRIUM APPROACH TO DENSE HADRONIC MATTER
Authors: VOSKRESENSKY D.N. , BLASCHKE D. , RÖPKE G. , SCHULZ H.
Published: November 2004

A general approach to the kinetics of a hadronic many-particle system is formulated employing a nonequilibrium diagram technique. The investigation of medium effects is based on the analysis of the coupled set of nonequilibrium Dyson equations for the π, N, and Δ components. Some model approaches to their solution are considered. The results are applied to the study of expanding hadronic fireballs containing pions, nucleons, and deltas as produced in the course of heavy-ion collisions at energies provided by the GSI-SIS up to the CERN-SpS.
POLARIZED AND UNPOLARIZED INCLUSIVE ELECTRON SCATTERING IN NUCLEI AND THE INCLUSIVE NEUTRINO CROSS-SECTION
Authors: MINTZ S.L. , POURKAVIANI M.
Published: November 2004

The unpolarized and parity violating polarized inclusive inelastic electron scattering cross-sections are calculated for incident electrons from threshold to 100 MeV, for the 12C nucleus. The relationship between these cross-sections and the inclusive neutrino cross-section on this same nucleus is discussed. The possibility of using the parity violating polarized electron scattering interaction to obtain the average nuclear excitation is also discussed.
SOME FEATURES OF INELASTIC INTERACTIONS OF 28Si AND 12C IONS IN NUCLEAR EMULSION AT 4.5A GeV/c
Authors: TARIQ M. , ZAFAR M. , TUFAIL A. , AHMAD S.
Published: November 2004

Multiplicity distributions of various types of tracks produced in inelastic interactions of 28 Si and 12 C at 4.5A GeV/c with nuclear emulsion nuclei have been investigated. The correlations of the type  where Ni, Nj=Ng, Nb, Nh or Ns with i≠j have been studied and compared with the results from p-Em interactions at the same momentum per nucleon. Some saturation effects in the values of  with Ng are observed. Furthermore, some of these correlations show almost similar dependence in nucleus-nucleus and proton-nucleus interactions at same per particle momenta. The values of  have been obtained by subtracting the contribution of Z=1 fragments to the observed showers. The dependence of  so obtained on the number of interacting projectile nucleons shows that the nucleus-nucleus collisions at these energies can be interpreted in terms of multiple N-N collisions.
A MICROSCOPIC VIEW OF THE SYMMETRY PROPERTIES OF REFLECTION-ASYMMETRIC NUCLEI
Authors: KVASIL J. , SHELINE R.K. , ALEXA P.
Published: November 2004

The symmetry properties of reflection-asymmetric nuclei are discussed in the framework of the Hartree-Fock-Bogoliubov method. A comparison of reflection-symmetric and reflection-asymmetric approaches is made.
REVIEW OF RAPIDITY DENSITY DISTRIBUTIONS IN HEAVY-ION INDUCED INTERACTIONS AT RELATIVISTIC ENERGIES
Authors: AGGARWAL MADAN M. , GARPMAN STEN I.A.
Published: November 2004

Violent interactions among colliding nuclei ultimately provide the suitable conditions for creating new and hitherto unexplored phenomena like color rope and quark-gluon plasma formation. The systemmatics achieved so far in pseudorapidity and density distributions of charged particles emitted from relativistic nucleus-nucleus collisions is reviewed and comparisons to model predictions are made. Data from both emulsion and counter experiments are utilized and the dependence of the angular spectra on projectile energy, centrality measured by means of forward charge or enegy flow, and on the projectile/target masses are reported. For a few central events, energy densities of the hot overlap zone are estimated to be beyond onset of deconfinement phase transition.
ORDER AND CHAOS IN ROTO-VIBRATIONAL STATES OF ATOMIC NUCLEI
Authors: MANFREDI V.R. , SALASNICH L.
Published: November 2004

Using a classical analytical criterion (that of curvature) and numerical results (Poincare sections and spectral statistics), a transition order-chaos-order in the roto-vibrational model of atomic nuclei has been shown. Numerical calculations were performed for some deformed nuclei.
STUDIES OF CONTINUUM COUPLING EFFECTS IN 6Li (α, α′) AND 6Li (p, p′) EXCITATION
Authors: KANUNGO RITUPARNA , LAHIRI M. , SAMANTA C. , REBEL H.
Published: November 2004

The nonresonant continuum part of 6Li⇒α+d breakup at low relative fragment energies, induced by 50 MeV α-particle and 65 MeV proton scattering, is discretized in two separate energy bins. Realistic coupled-channel analyses are carried out, coupling the 1+ ground state with both the resonant 31+ state as well as the two nonresonant discretized continuum states, including selfcoupling. A simultaneous fit to the data puts stringent constraints on the coupling strengths. It delineates that their arbitrary variation is unacceptable and that the complex coupling schemes in CDCC calculations need sufficient experimental control. The coupling effects by multistep processes (virtual excitations) through intermediate continuum states prove to be marginal in the considered 6Li(α, α′)6Li* and 6Li(p, p′)6Li* cases.
PROTON SUPERFLUIDITY IN NEUTRON STAR MATTER WITH AN EFFECTIVE INTERACTION
Authors: LAZZARI G. , DE BLASIO F.V.
Published: November 2004

The isotropic proton superfluidity in Neutron Star Matter is evaluated in the conventional BCS approach using Gogny effective force as the nucleon-nucleon interaction. We have found that, neglecting the polarizability effects and including different proton concentrations in neutron star matter, the 1S0 proton energy gap is considerably smaller than the corresponding neutron isotropic gap. It is shown that at higher densities proton superfluidity could prevail in a considerable range of density in the interior of a neutron star.
TESTING THE ROBUSTNESS OF THE STEADY-STATE CHARACTERISTICS OF A METABOLIC PATHWAY: PARAMETER SENSITIVITIES AS A BASIC FEATURE FOR MODEL VALIDATION
Authors: CASCANTE MARTA , CURTO RAUL , SORRIBAS ALBERT
Published: November 2004

Mathematical models are useful for analyzing metabolic problems. To build up these models, we need: (1) A scheme of the target system, (2) Measurements of concentrations and fluxes in steady-state, (3) The rate law of each reaction and (4) The set of differential equations that reflects the model behaviour. Usually, the rate-laws are identified from in vitro data, which could result in unrealistic models when compared with the behavior of the intact system. Hence, mathematical models must be carefully validated before one can trust their behavior.

We can use different features of a biological system as a reference for validating a model. The steady-state robustness to parameter changes can be used as an index for such an evaluation. In this sense, a realistic model should reflect a fundamental property of a living system: small perturbations are compatible with system performance.

We present an example of such analysis in the case of the ethanolic fermentation pathway of Saccharomyces cerevisiae. The parameter sensitivities of the model are computed in two experimental conditions and a diagnostic is made on the validity of the corresponding model. Translation of the mechanistic model into an S-system model facilitates the analysis of parameter sensitivity. After the analysis, a high parameter sensitivity suggest the need for a careful estimation of the involved parameters.
THE POSSIBLE CONSEQUENCES OF LARGE-SCALE ENZYME ALTERATIONS ON THE METABOLIC EFFICIENCY OF RED BLOOD CELLS AS STUDIED ON THE BASIS OF A MATHEMATICAL MODEL
Authors: SCHUSTER RONNY , HOLZHÜTTER HERMANN-GEORG
Published: November 2004

Based on a comprehensive mathematical model of the energy and redox metabolism of human erythrocytes we calculated stationary metabolic states of the cell varying the activity of the participating enzymes by several orders of magnitude. To compare the computational results with clinical and experimental data reported for various enzymopathies of the red cell, the three essential metabolic variables ATP, GSH and osmolarity were included in a “homeostasis function” which allows us to estimate the range of enzyme activities in which the metabolic alterations should be either tolerable, associated with non-chronic or chronic hemolytic diseases, or letal.
ENTROPY-DRIVEN PROTEIN SELF-AGGREGATION AS THE BASIS FOR SELF/NOT-SELF DISCRIMINATION IN THE CROWDED CYTOSOL
Authors: FORSDYKE D.R.
Published: November 2004

Cytotoxic T cells recognize cell surface complexes of MHC class I proteins with peptides derived from proteins synthesized within the recognized cell. A mechanism permitting some intracellular discrimination between self proteins and not-self proteins (encoded by a foreign species) would allow the preferential loading of MHC proteins with peptides derived from not-self proteins. This would decrease competition with peptides derived from self proteins and decrease gaps in the T cell repertoire. A possible mechanism has been derived from studies of the specificity of self-aggregation of erythrocytes and of virus coat protein. It is postulated that genes whose products occupy a common cytosol have co-evolved such that product concentrations are fine-tuned to a maximum consistent with avoiding self-aggregation. Cytosolic proteins collectively generate a pressure tending to drive protein molecules into self-aggregates. Each individual protein species both contributes to, and is influenced by, this pressure. The aggregation involves a liberation of bound water and an increase in entropy. The concentrations of proteins encoded by viral genes (not-self) readily exceed the solubility limits imposed by the crowded host cytosol. This leads to their preferential degradation to peptides which associate with MHC proteins. The intracellular and extracellular self/not-self discrimination systems complement each other to ensure that there is no immunological reaction against normal self tissue components.
FOOD WEBS WITH PREDATOR INTERFERENCE
Authors: MICHALSKI JERZY , ARDITI ROGER
Published: November 2004

Interfering predators have a feeding rate (functional response) which is a decreasing function of their abundance. We propose equations that describe the dynamics of an arbitrary food web with predator interference and study their consequences. In particular we show that, due to interference, some of the trophic links do not effectively exist. Their presence (or absence) depends on the interplay of competition efficiencies and food preferences as well as on species abundances. As a consequence, the effective structure of a food web may vary with time and from one place to another (as competition efficiencies and food preferences vary with seasons and from one place to another) as well as due to an external perturbation (as abundances change). The simplification of the food web structure due to predator interference allows qualitative predictions concerning the response of a food web to an external perturbation.
FEEDBACK LOOPS, STABILITY AND MULTISTATIONARITY IN DYNAMICAL SYSTEMS
Authors: PLAHTE ERIK , MESTL THOMAS , OMHOLT STIG W.
Published: November 2004

By fairly simple considerations of stability and multistationarity in nonlinear systems of first order differential equations it is shown that under quite mild restrictions a negative feedback loop is a necessary condition for stability, and that a positive feedback loop is a necessary condition for multistationarity.
MATHEMATICAL MODELING OF IMMUNE-INFLAMMATORY REACTION IN ACUTE PNEUMONIA
Authors: RUDNEV S. G. , ROMANYUKHA A. A.
Published: November 2004

Using ordinary differential equations, we propose a mathematical model describing an “averaged” dynamics of variables involved in which some parameters are shown to be important characteristics of lung resistance. The model consists of modified D.A. Lauffenburger’s mathematical model for inflammatory reaction in lungs, and the model of humoral immune response (G. I. Marchuk). Coefficients are identified against clinical and experimental data. We attempt to elucidate some disease characteristics in terms of sensitivity analysis of model solutions with respect to parameters variations.
T-CELL VACCINATION VIA REVERSE ENGINEERING: TRANSIENT DISEASE
Authors: SEGEL LEE A. , JÄGER EVA
Published: November 2004

The “reverse engineering” approach to modelling is applied to T-cell vaccination. The novelty here is the representation of the diseased state as a transient.
STATIONARY STATES IN FOOD WEB MODELS WITH THRESHOLD RELATIONSHIPS
Authors: PLAHTE ERIK , MESTL THOMAS , OMHOLT STIG W.
Published: November 2004

A new method for analysing stationary states in complex differential equation systems when the interaction terms contain sigmoid functions is presented. Originally aimed at simplifying the analysis of certain gene regulatory networks, the method is applicable to models comprising a wide range of sigmoid functions. The basic idea is to analyse the limiting case when the sigmoids approach the step function, and consider sigmoids with finite steepness as a perturbation. After a brief presentation the method is applied to a model for a herbivore feeding on two competing autotrophs. Analytical expresssions for the stationary points in the step function limit are given, and their dependence on the parameter values is analysed and interpreted.
AGGREGATION METHODS IN DISCRETE MODELS
Authors: BRAVO DE LA PARRA RAFAEL , AUGER PIERRE , SÁNCHEZ EVA
Published: November 2004

The aim of this work is to extend approximate aggregation methods for multi-time scale systems of ordinary differential equations to time discrete models. We give general methods in order to reduce a large scale time discrete model into an aggregated model for a few number of slow macro-variables. We study the case of linear systems. We demonstrate that the elements defining the asymptotic behaviours of the initial and aggregate models are similar to first order. We apply this method to the case of an agestructured population with sub-populations in each age classes associated to different spacial patches or different individual activities. A fast time scale is assumed for patch or activity dynamics with respect to aging and reproduction processes. Our method allows us to aggregate the system into a classical Leslie model in which the fecundity and aging parameters of the aggregated model are expressed in terms of the equilibrium proportions of individuals in the different activities or patches.
QUALITATIVE PROPERTIES OF CHEMOSTAT EQUATIONS WITH TIME DELAYS
Authors: BERETTA E. , TAKEUCHI Y.
Published: November 2004

The mathematical properties of chemostat equations with delayed growth and delayed nutrient recycling are summarized.
BIPOLAR CONTROL IN AGONISTIC ANTAGONISTIC NETWORKS AND PARTICULARLY IN IMBALANCED STRANGE ATTRACTORS
Authors: BERNARD-WEIL E.
Published: November 2004

In some previous papers, we have already demonstrated how the problem of strange attractors (SA) was not confined only to the nature of their dynamics and how the aim of control did not depend only on the fact, that such a dynamics was considered as favourable or wrong for the functioning of the system modelled by these SA. The topology in the phase space of a SA is of the same importance because ergodic theory allows us to take into account the mean values of the various trajectories in this SA. As far as biomathematical models are concerned, these mean values may correspond either to physiological values or to pathological ones. In this regard rather than trying to eliminate (or re-establish) a chaotic dynamics (CD), control should sometimes try to displace the SA in order to let the mean values return to some physiological value. This paper reports a theoretical study of such a type of SA-control by using a so-called "model for the regulation of agonistic antagonistic (AA) couples" or "AA networks", including equations governing the values of certain control variables and has initially been connected to periodic dynamics; we recall these principles of control in case of an elementary AA-model (imbalanced limit-cycles). In case of AA-networks showing a CD, it is also possible to re-establish the balance between the variables with or without eliminating the CD of the attractor; in the second case, the control variables disclose a CD by themselves.
NONLINEAR MATHEMATICAL MODELS OF HORMONAL SYSTEMS
Authors: NAUROSCHAT J. , AN DER HEIDEN U.
Published: November 2004

The paper considers various approaches to mathematical modelling of endocrine systems. The functional and operational complexity of hormonal activities turns out to be the result of the cooperation of three factors: global feedback structures on the level of glands, subtle feedback and regulatory mechanisms on the level of single cells and molecules (including messengers, receptors and functional proteins like G-proteins) and finally, coupling to other organs (predominantly to the brain, e.g. via hypothalamus).

To date, it is practically impossible to construct a mathematical model comprising together all these aspects. The paper aims at providing some major building bricks to such an endeavor. In the first part we summarize some of our recent models on the gobal structure of hormonal systems, in the form of nonlinear differential equations containing delay terms; oscillatory input from the brain is taken into account. Solutions of the equations display nearly all kinds of dynamical behaviour as stable limit cycles, phase locking, quasi-periodic and chaotic motions.

Special emphasis is put on developing a mathematical model for the fine-tuned sequence of hormone-induced transmembrane signalling, where agonist couples to some cellular effector via transfer-proteins — this principle is widely spread among the hormone-targeted cells and crucially involved in regulating cells' behaviour towards external stimuli, e.g. their ability to desensitize as a reaction to sustained hormonal input.
ADAPTIVE DYNAMIC MODELLING OF HIV/AIDS EPIDEMIC USING EXTENDED KALMAN FILTER
Authors: CAZELLES B. , CHAU N. P.
Published: November 2004

A simple compartment model was used to describe the observed HIV/AIDS epidemic in the homo/bisexual male community in Paris (France). In the first step, the model was fitted to the available data, using least squares procedures. The fitting of the model to subsets of the data could perfectly account for the observations, but did not afford a coherent estimation of the model parameters, and was unable to predict the actual development of the disease. These difficulties might result from the fact that many factors have modified the course of the HIV/AIDS epidemic in the recent years. So, a recursive estimation technique known as the Kalman filter has been used. The Kalman filter accounts for stochastic fluctuations both in the model and in the data, and enables to assess the possible progressive adaptation of the model parameters suggested by the new observations. Our study disclosed a noticeable change of some parameters of important epidemiological significance (average transmission rate and mean incubation rate) around the year 1988, most probably due to intervention measures like prevention and/or gradual introduction of early treatment for infected but asymptomatic individuals.
DETERMINISTIC AND STOCHASTIC PAIR FORMATION MODELS FOR THE SPREAD OF SEXUALLY TRANSMITTED DISEASES
Authors: KRETZSCHMAR MIRJAM
Published: November 2004

A modelling approach is discussed in which a deterministic pair formation model is used in combination with a related stochastic simulation model. We study the spread of a sexually transmitted disease in a population with steady and casual partnerships. Two situations are considered: one is a population with pure serial monogamy, the other a population where individuals may have one or more casual partnerships next to their steady partnership. For the same parameter values the spread of the epidemic in a population with concurrent partnerships is faster than in a population with pure serial monogamy.
MODELLING AGE-DEPENDENT TRANSMISSION RATES FOR CHILDHOOD INFECTIONS
Authors: MASSAD EDUARDO , DE AZEVEDO NETO RAYMUNDO SOARES , YANG HYUN MO , BURATTINI MARCELO NASCIMENTO , COUTINHO FRANCISCO ANTONIO BEZERRA
Published: November 2004

Two different theoretical functions are proposed for the age-dependent transmission coefficients which takes into account the distribuitions of the contact probabilities between susceptible individuals of age a with infected individuals of age a′. A numerical simulation is presented with measles and rubella data from two distinct communities. The impact of control measures is also simulated using the assumed functions for the age-dependent transmission coefficients.
A 2-DIMENSIONAL MODEL FOR MACROPARASITIC INFECTIONS IN A HOST WITH LOGISTIC GROWTH
Authors: PUGLIESE ANDREA , ROSÀ ROBERTO
Published: November 2004

We analysed a model for the interaction of a macroparasite and a host population growing logistically. The model is obtained by approximating the parasite distribution with a negative binomial with a fixed clumping parameter.

By letting the contact rate k vary, we found a complex pattern of bifurcations, including subcritical bifurcations of the disease-free equilibrium, Hopf and homoclinic bifurcations. The specific pattern depends on the interaction of the various parameters; in particular, alternative stable equilibria may occur only when the carrying capacity KN is sufficiently large, while periodic solutions may occur for all values of KN, if k is large enough.
INTERLEUKIN MATHEMATICAL MODEL OF AN IMMUNE SYSTEM
Authors: FORYS URSULA
Published: November 2004

Some generalizations of Marchuk's model of an infectious disease with respect to the role of interleukins are presented in this paper. Basic properties of the models are studied. Results of numerical simulations with different coefficients corresponding to the different forms of the disease are shown.
THE MODELLING OF DIFFUSIVE TUMOURS
Authors: CRUYWAGEN GERHARD C. , WOODWARD DIANA E. , TRACQUI PHILIPPE , BARTOO GRACE T. , MURRAY J. D. , ALVORD ELLSWORTH C.
Published: November 2004

The mathematical modelling of diffusive tumours is investigated. We argue that diffusive tumours can be modelled by adding diffusion to simple multipopulation solid tumour models, such as the Lotka-Volterra competition and Jansson-Revesz models. As a specific example a clinical case study of a diffusive brain tumour is considered.
MODELLING THE SPATIAL PATTERNING OF THE TEETH PRIMORDIA IN THE LOWER JAW OF Alligator mississippiensis
Authors: KULESA P. M. , CRUYWAGEN G. C. , LUBKIN S. R. , MAINI P. K. , SNEYD J. , MURRAY J. D.
Published: November 2004

We propose a model mechanism for the initiation and spatial positioning of teeth primordia in the alligator, Alligator mississippiensis. Detailed embryological studies12–14 have shown that jaw growth plays a crucial role in the developmental patterning of the tooth initiation process. The development of the spatial pattern occurs on a timescale comparable to jaw growth. Based on biological data we develop a dynamic patterning mechanism, which crucially includes domain growth. The mechanism can reproduce the spatial pattern development of the first seven teeth primordia in the lower jaw of A. mississippiensis. The results for the precise spatio-temporal sequence compare well with experiment.
CELLULAR AUTOMATA FOR MODELLING SHELL PIGMENTATION OF MOLLUSCS
Authors: MARKUS MARIO , KUSCH INGO
Published: November 2004

A minimum cellular automaton, carrying precise biophysical significance in each rule, is presented to model pigmentation patterns on molluscan shells. We find the following types of modes: self-organisation into stationary (Turing) structures, travelling waves, chaos, and so-called class IV behaviour. The latter consists of a disordered spatio-temporal distribution of periodic and chaotic patches; it differs from chaos in that it has no well-defined error propagation rate. The calculations of the modes agree well with observations in natural shells. In particular, our results suggest evidence in nature for class IV behaviour, a mode that had so far been reported only as the result of simulations. Moreover, we show that patchiness results in a class IV mode from the same algorithm that renders chaos and periodicity; thus, there is no need to invoke two competing pattern generators, as in previous approaches.
A MECHANICAL MODEL FOR FIBROBLAST-DRIVEN WOUND HEALING
Authors: TRACQUI P. , WOODWARD D. E. , CRUYWAGEN G. C. , COOK J. , MURRAY J. D.
Published: November 2004

We present a mathematical model for the contraction and relaxation phases of healing dermal wounds based upon the extracellular control of the traction forces exerted by the migrating fibroblastic cells. We assume that these cell-extracellular medium interactions are controlled by the viscoelastic properties of both the provisional matrix formed initially in the lesion and the newly synthesised collagenous matrix concomitantly secreted. In addition, the plastic response of the collagenous matrix to the cell traction has been considered. The mechanical model proposed here accounts for the different experimental phases of the wound boundaries' movement with time. Furthermore, it provides a quantification of the residual strain and stress resulting from the plastic response and remodelling of the extracellular matrix which could help to characterise the scar tissue formation in wound healing.
HOW TO MAKE GOOD USE OF MULTILAYER NEURAL NETWORKS
Authors: PAUGAM-MOISY HÉLÈNE
Published: November 2004

This article is a survey of recent advances on multilayer neural networks. The first section is a short summary on multilayer neural networks, their history, their architecture and their learning rule, the well-known back-propagation. In the following section, several theorems are cited, which present one-hidden-layer neural networks as universal approximators. The next section points out that two hidden layers are often required for exactly realizing d-dimensional dichotomies. Defining the frontier between one-hidden-layer and two-hidden-layer networks is still an open problem.

Several bounds on the size of a multilayer network which learns from examples are presented and we enhance the fact that, even if all can be done with only one hidden layer, more often, things can be done better with two or more hidden layers. Finally, this assertion 'is supported by the behaviour of multilayer neural networks in two applications: prediction of pollution and odor recognition modelling.
IMPACT OF TOPOLOGICAL VARIABILITY ON DENDRITIC GEOMETRY
Authors: VAN PELT JAAP , SCHIERWAGEN ANDREAS
Published: November 2004

The development of neuronal branching patterns mainly proceeds by branching events at terminal segments. The randomness in the occurrences of these events is the major cause of the variability that is observed in the final topological structures of neuronal trees. A general observation in neuronal trees is the existence of a branch power relation between the diameters of the segments at branch points. Because of this correlation, total area and volume will become dependent on branching pattern topology. A quantitative assessment of this finding is given. How topological variation propagates into variation in total area and volume, using topological growth models for producing random tree topologies and a simple metrical parametrization is discussed.
Adrenergic modulation ofEscherichia coliO157:H7 adherence to the colonic mucosa
Authors: Green Benedict T. , Lyte Mark , Chen Chunsheng , Xie Yonghong , Casey Melissa A. , Kulkarni-Narla Anjali , Vulchanova Lucy , Brown David R.
Published: November 2004

Enteric neurotransmitters can modulate the biodefensive functions of the intestinal mucosa, but their role in mucosal interactions with enteropathogens is not well defined. Here we tested the hypothesis that norepinephrine (NE) modulates interactions between enterohemorrhagic Escherichia coli O157:H7 (EHEC) and the colonic epithelium. Mucosal sheets from porcine distal colon were mounted in Ussing chambers. Drugs and an inoculum of either Shiga toxin-negative or -positive EHEC were added to the contraluminal and luminal bathing medium, respectively. After 90 min, adherent bacteria were quantified by an adherence assay and by immunohistochemical methods; short-circuit current ( Isc) was measured continuously to assess changes in active ion transport. NE-treated tissues exhibited concentration-dependent increases in Iscand EHEC adherence. NE did not alter adherence of a rodent-adapted, noninfectious E. coli strain or two porcine-adapted non-O157 E. coli strains. The actions of NE on EHEC adherence but not Iscwere prevented by the α-adrenergic antagonist yohimbine and the PKA activator Sp-8-bromoadenosine-3′,5′-cyclic monophosphorothioate. Like NE, the PKA inhibitor Rp-8-bromoadenosine-3′,5′-cyclic monophosphorothioate or indirectly acting sympathomimetic agents increased EHEC adherence. Nerve fibers immunoreactive for the NE-synthesizing enzymes tyrosine hydroxylase and dopamine β-hydroxylase appeared to innervate the colonic epithelium. EHEC-like immunoreactivity on the colonic surface had the appearance of bacterial microcolonies and increased after NE treatment by a phentolamine-sensitive mechanism. Through interactions with α2-adrenergic receptors, NE appears to increase EHEC adherence to the colonic mucosa. Changes in sympathetic neural outflow may alter intestinal susceptibility to infection.
Polynomial spline collocation methods for second‐order Volterra integrodifferential equations
Authors: Rawashdeh Edris , Mcdowell David , Rakesh Leela
Published: November 2004

We have presented a method for the construction of an
approximation to the initial‐value second‐order Volterra
integrodifferential equation (VIDE). The polynomial spline
collocation methods described here give a superconvergence to the
solution of the equation.
Pure imaginary solutions of the second Painlevé equation
Authors: Abdullayev Alisher S.
Published: November 2004

We prove the existence and obtain local asymptotic formulas
for pure imaginary solutions of the general second Painlevé equation.
On stability and bifurcation of solutions of an SEIR epidemic model with vertical transmission
Authors: El-Sheikh M. M. A. , El-Marouf S. A. A.
Published: November 2004

A four‐dimensional SEIR epidemic model is considered. The stability
of the equilibria is established. Hopf bifurcation and center
manifold theories are applied for a reduced three‐dimensional epidemic
model. The boundedness, dissipativity, persistence, global
stability, and Hopf‐Andronov‐Poincaré bifurcation for the
four‐dimensional epidemic model are studied.
In utero Meconium SuctioningMay Prevent Meconium As piration
Authors: Petrikovsky Boris
Published: November 2004

Objective: To assess usefulness of in utero meconium suctioning using endoscopic approach. Materials and Methods: In utero meconium suctioning under direct endoscopic visualization was successfully performed in 11 fetuses in whom thick meconium was detected upon rupture of the membranes. A gas-sterilized flexible fiberoptic scope with an operational channel was introduced via cervix, and meconium was aspirated from the fetal mouth. Definitive suction was performed in all neonates immediately after birth. Results: Endoscopic meconium suctioning was successfully performed in 11 out of 16 fetuses with retrieval of 3–12 ml of meconium. Only 1 neonate in this series of cases had meconium below the vocal cords and none developed meconium aspiration syndrome postnatally. Conclusion: Because fatal meconium aspiration syndrome is largely an intrauterine event, the concept of in utero prophylactic meconium suctioning may serve as an effective modality for its prevention.