bluuebunny/crossref_metadata_2025 huggingface dataset:
RECENT PROGRESS ON MASS TRANSFER IN SEMICLASSICAL SYSTEMS
Authors: WANG JIANYI
Published: November 2004

We present a brief review of recent progress in the transfer of an electron from a circular Rydberg atom to an impinging ion. This field has attracted considerable interest since the "exotic" semiclassical properties of these atoms afford an opportunity to study mass transfer in a regime where dynamic pathways can be well controlled. We report developments in the past two years in electron transfer between oriented circular Rydberg atoms and protons at collision speeds comparable to the electron orbital speed. Newly discovered results have solved a number of outstanding puzzles in the classical mass transfer theory, such as the Thomas two-step mechanism. Also discussed is the application of circular Rydberg atoms as semiclassical objects in a number of very different areas ranging from atomic physics, beam-foil interactions, to astrophysics.
A FIRST ORDER PHASE TRANSITION IN ISING FERRIMAGNETS
Authors: AL MUKADAM HASAN M. , UZUNOV DIMO I.
Published: November 2004

The mean field theory is used for the analysis of a two-sublattice system of Ising spins, which describes ferro-, antiferro-, and ferrimagnetic orderings. It is proven that the phase transition in these systems is of a first order when the exchange constants of the sublattices are different. The free energy, the order parameter profiles and the latent heat of the phase transition are calculated for almost equivalent sublattices.
MAGNETIC HYSTERESIS AND MAGNETIC RELAXATION STUDIES IN Bi-V-Sr-Ca-Cu-O SUPERCONDUCTING SYSTEM
Authors: NARSINGA RAO G. , MOLINIE P. , GANNE M. , BABU D. SURESH
Published: November 2004

We report magnetic hysteresis and magnetic relaxation studies on Bi 2−x V x Sr 2 Ca 2 Cu 3 O y superconducting system. We have determined the temperature and field dependent critical current density J c and pinning force density F pin from magnetic hysteresis studies and the activation energy U0 from magnetic relaxation measurements of the sample Bi 1.6 V 0.4 Sr 2 Ca 2 Cu 3 O y. Temperature dependent J c and activation energy U0 studies suggested that at low temperatures pinning centres and low activation energy are active and in high temperatures pinning centres with high activation energy are dominating. The field dependent J c and F pin measurements showed that pinning is mainly due to twin boundaries at low temperature (<20 K). In addition, we have also determined the temperature dependent lower critical field. Possible reasons for variation of lower critical field with temperature were discussed.
MAGNETIC RELAXATION, LOWER CRITICAL FIELD AND IRREVERSIBILITY LINE OF W DOPED (Bi, Pb)-2223 SUPERCONDUCTOR
Authors: NARSINGA RAO G. , MOLINIE P. , GANNE M. , BABU D. SURESH
Published: November 2004

We report magnetic relaxation, lower critical field and irreversibility line studies of a single phase W doped (Bi,Pb)-2223 superconductor. The temperature dependence of remanent magnetization exhibited a rapid drop at T ≤ 20 K and was due to the drastic decrease of critical current density (J c ). The activation energy U0 determined from magnetic relaxation measurements showed that there exists two types of pinning centres in the vortex lattice. The temperature dependence of lower critical field (H c1 ) exhibited a kink around 25 K. Possible reasons for exhibited anomaly in H c1 were discussed. The irreversibility line exhibited an exponential decrease with increasing temperature and is due to the existence of break down field of proximity effect, induced superconductivity in layered HTSC. Fermi velocity in superconductivity regions (V FN ) is found to be a factor of ten larger than that in normal regions (V FN ).
STUDY OF SINTERING BEHAVIOR AND ELECTRICAL PROPERTIES OF Cu-Zn-Fe-O SYSTEM
Authors: ABBAS TAHIR , ISLAM M. U. , ASHRAF CH. M.
Published: November 2004

Copper zinc ferrites ( Cu 1−x Zn x Fe 2 O 4) with x = 0.1, 0.2, 0.3 were prepared by solid state reaction technique. The samples were presintered at 900°C for 40 to 45 hrs and finally at 950°C for 4 hrs followed by air quenching. The lattice parameter, X-ray densities (Dm), grain size, bulk densities (D) and porosity (P) were measured for each sample after successive heat treatments and the effect on the above mentioned properties was studied. Electrical resistivity of the samples after final heat treatment was measured in the temperature range of 50 to 230°C. The Arrhenius plots of these samples exhibit linear behavior from which the activation energy of the system has been derived. The room temperature resistivity after quenching from 950°C shows change of species of charge carriers that is from n-type at lower Zn concentration to p-type at higher Zn concentration.
SLATER TRANSITION-STATE CALCULATIONS OF DIPOLE OSCILLATOR STRENGTHS IN NOBLE METAL ISO-ELECTRONIC SERIES
Authors: SEN K. D. , PURI ASHOK
Published: November 2004

Dipole oscillator strengths corresponding to the Rydberg transition (ns → np) within Cu, Ag, and Au isoelectronic series have been calculated using the relativistic local density functional including correlation effects. The Slater transition state concept has been employed. Numerical comparisons between the oscillator strengths of noble and alkali metal isoelectronic series are reported.
ON THE BOUNDARY MAGNETIZATION OF SOME LAYERED MODEL
Authors: PELIZZOLA ALESSANDRO
Published: November 2004

In the present letter we generalize a previous exact result for the boundary magnetization of the two-dimensional layered Ising model, obtaining an expression in which the bulk limits of the interactions do not appear explicitly. The formula we have obtained is applicable even when such limits are not defined, as is for aperiodic systems, which are briefly discussed. The methods used, developed for Ising-like models, are then extended to quantum antiferromagnetic chains at zero temperature.
LASER INDUCED THERMAL LENS EFFECT IN RHODAMINE B — SIGNATURE OF RESONANT TWO PHOTON ABSORPTION
Authors: BINDHU C. V. , HARILAL S. S. , ISSAC RIJU C. , VARIER GEETHA K. , NAMPOORI V. P. N. , VALLABHAN C. P. G.
Published: November 2004

Measurement of thermal lensing signal as a function of laser power made in Rhodamine B solutions in methanol give clear evidence of two photon absorption process within certain concentration ranges when 488 nm Ar + laser beam is used as the pump source. Only one photon process is found to occur when 514 nm and 476 nm beams are used as the pump.
THERMODYNAMICS OF A WEAKLY DEFORMED CRYSTAL LATTICE WITH q-COMPLEX PARAMETER
Authors: DE FALCO L. , MIGNANI R.
Published: November 2004

We use a system of deformed harmonic oscillators with complex deformation parameter to describe, by means of a q-deformed analogous to the Debye model, a solid subjected to external perturbations or with some nonlinear effects inside the lattice. In the case of a weak deformation, the specific heat of the lattice exhibits a departure from the standard behavior only at low temperatures, whereas the usual Dulong–Petit law is recovered in the high-temperature limit.
NON-FERMI LIQUID BEHAVIOR IN THE SINGLE-IMPURITY MIXED VALENCE PROBLEM
Authors: ZHANG GUANG-MING , SU ZHAO-BIN , YU LU
Published: November 2004

An effective Hamiltonian of the Anderson single-impurity model with finite-range Coulomb interactions is derived near a particular limit, which is analogous to the Toulouse limit of the ordinary Kondo problem, and the physical properties around the mixed valence quantum critical point are calculated. At this quantum critical point, the local moment is only partially quenched and X-ray edge singularities are exhibited. Around this point, a new type of non-Fermi liquid behavior is predicted with an extra specific heat C imp ~ T1/4 + AT ln T and spin-susceptibility χ imp ~T−3/4 + B ln T.
AN INVERSE METHOD APPLIED TO THERMAL CONDUCTIVITY MEASURMENT OF LIGHT INSULATING MATERIALS
Authors: CALI' MICHELE , GIARETTO VALTER , RUSCICA GIUSEPPE
Published: November 2004

A simplified procedure for analyzing data obtained from an experimental apparatus in unsteady state conditions, constructed in order to measure thermal conductivity variations of light insulating materials obtained from thermal ageing and humidity cycles, is presented here.

The calculations have been carried out with a lumped thermal model using an inverse method. Several ageing cycles and measurements have been carried out and the method has permitted the reduction of the experimental and calculation costs.
ON THE EIGENOPERATOR OF LOGARITHMIC STATES
Authors: LAKSHMI P. ANANTHA
Published: November 2004

The eigenoperator for the logarithmic states is constructed. It is shown that this can also be written in terms of a displacement operator. The Hamiltonian for which the logarithmic state is an eigenstate is constructed. The Hamiltonian for the Jaynes–Cummings model is constructed using this new eigenoperator and the atomic inversion for the Jaynes–Cummings model is investigated for a variety of initial states of the field.
HOLE–SPIN COUPLING AND SPIN DISTORTION IN HIGH Tc SUPERCONDUCTORS
Authors: TIWARI M. , SINGH R. A.
Published: November 2004

The effect of hole–spin coupling together with spin distortion on the energy and hole correlation function have been studied in detail. Standard Green function theory and Low Temperature Series Expansion method have been utilised to get analytical results.
OPTICAL ABSORPTION OF AMORPHOUS CADMIUM OXIDE IN THE ULTRAVIOLET RANGE
Authors: CAFFARO M.A. GRADO , CAFFARO M. GRADO
Published: November 2004

Theoretical considerations tending to explain optical absorption of amorphous CdO in the ultraviolet region are presented. The calculations performed here are based on Burstein-Moss model and they are related to the influence of oxygen partial pressure on the physical behaviour of CdO films. Our theoretical analysis is compared with experimental results reported by some workers.
DYNAMIC INTERFERENCE PATTERNS FROM FERROFLUIDS
Authors: DU TENGDA , LUO WEILI
Published: November 2004

Time-dependent interference was observed above a critical magnetic field Hc1 in ferrofluids by a novel technique — magnetic thermal lens effect. The onset of the dynamics is associated with the formation of linear structures in the system. When a second critical field, Hc2, was reached, a lattice of quasi-periodic columns was observed by optical microscopy and random rotating patterns were replaced by stable rings, indicating ordering in the system. This technique provides a useful way to detect microstructures that are much smaller than the optical wave length thus unobservable by conventional optical technique. We found that the result crucially depends on boundary conditions.
CRYSTALLIZATION OF POLARONS IN DOPED IONIC MATERIALS
Authors: QUÉMERAIS PASCAL
Published: November 2004

Large polarons are observed in dielectric materials. Since they have repulsive interactions when the dielectric constants satisfy proper conditions, we propose a model for the crystallization of polarons at low doping concentrations. We calculate the energy at T=0 K and discuss the stability as regards to carriers’ density. With phonons having low frequencies, an instability is related to the polaron dissociation, and we estimate a critical doping density. Applying our model to La 2−x Sr x CuO 4, we find a good agreement with the experimental critical doping concentration xc≈0.06 for the insulator-to-metal transition.
PHOTOINDUCED STRAIN AS A PROBE OF ACOUSTICAL AND ELECTRONIC PROPERTIES OF CONDUCTING POLYMERS
Authors: KANNER G.S. , FROLOV S. , VARDENY Z.V.
Published: November 2004

We discuss applications of photogenerated strain in transient absorption experiments. These include measurements of sound velocity, phonon dispersion relations, and excited electronic state energy levels. In particular, we have

identified a new type of spectroscopy in photoinduced absorption that can be used to detect both allowed and forbidden electronic transitions in thin semiconducting films. This technique was applied to a host of conducting polymers for which we detected energy levels of various excitonic states with odd and even symmetry.
AUXILIARY FERMION LINEARIZED t-J MODEL
Authors: DANANI A. , ZANARDI P.
Published: November 2004

The Auxiliary Fermion linearization scheme is applied to the ferromagnetic t-J model. Spectrum and self-consistency equations are obtained. The numerical analysis shows the existence of solutions describing metallic as well as magnetic phases of different kind. Their interplay is discussed.
LEARNING AND GENERALIZATION THEORIES OF LARGE COMMITTEE-MACHINES
Authors: MONASSON RÉMI , ZECCHINA RICCARDO
Published: November 2004

The study of the distribution of volumes associated to the internal representations of learning examples allows us to derive the critical learning capacity [Formula: see text] of large committee machines, to verify the stability of the solution in the limit of a large number K of hidden units and to find a Bayesian generalization cross-over at a=K.
MULTISCALE ANALYSIS FOR THE BIO-HEAT TRANSFER EQUATION — THE NONISOLATED CASE
Authors: HOCHMUTH REINHARD , DEUFLHARD PETER
Published: November 2004

The bio-heat transfer equation is a macroscopic model for describing the heat transfer in microvascular tissue. In Ref. 8 the authors applied homogenization techniques to derive the bio-heat transfer equation as asymptotic result of boundary value problems which provide a microscopic description for microvascular tissue. Here those results are generalized to a geometrical setting where the regions of blood are allowed to be connected, which covers more biologically relevant geometries. Moreover, asymptotic corrector results are derived under weaker assumptions.
MATHEMATICAL TOPICS ON THE MODELLING COMPLEX MULTICELLULAR SYSTEMS AND TUMOR IMMUNE CELLS COMPETITION
Authors: BELLOMO N. , BELLOUQUID A. , DELITALA M.
Published: November 2004

This paper deals with a critical analysis and some developments related to the mathematical literature on multiscale modelling of multicellular systems involving tumor immune cells competition at the cellular level. The analysis is focused on the development of mathematical methods of the classical kinetic theory to model the above physical system and to recover macroscopic equation from the microscopic description. Various hints are given toward research perspectives, with special attention on the modelling of the interplay of microscopic (at the cellular level) biological and mechanical variables on the overall evolution of the system. Indeed the final aim of this paper consists of organizing the various contributions available in the literature into a mathematical framework suitable to generate a mathematical theory for complex biological systems.
MULTITEMPORAL GENERALIZATION OF THE SCHWARZSCHILD SOLUTION
Authors: IVASHCHUK VLADIMIR D. , MELNIKOV VITALY N.
Published: November 2004

The n-time generalization of the Schwarzschild solution is considered. The equations of geodesics for the metric are integrated. The multitemporal analogues of Newton’s laws for the extended objects described by the solution are suggested. The scalar-vacuum generalization of the solution is also presented.
THE GEOMETRY OF CLASSICAL CHANGE OF SIGNATURE
Authors: CARFORA MAURO , ELLIS GEORGE
Published: November 2004

The proposal of the possibility of change of signature in quantum cosmology has led to the study of this phenomenon in classical general relativity theory, where there has been some controversy about what is and is not possible. Here we present a new analysis of such a change of signature, based on previous studies of the initial value problem in general relativity. We emphasize that there are various continuity suppositions one can make at a classical change of signature, and consider more general assumptions than have been made up to now. We confirm that in general such a change can take place even when the second fundamental form of the surface of change does not vanish.
QUANTIZATION OF A LOCALLY SUPERSYMMETRIC FRIEDMANN MODEL IN THE PRESENCE OF SUPERMATTER
Authors: CHENG A.D.Y. , MONIZ P.R.L.V.
Published: November 2004

The general theory of N=1 supergravity with supermatter is restricted to the special case of a k=+1 Friedmann minisuperspace model with complex scalar fields and fermionic partners. The different supermatter models are given by specifying a Kähler metric for the scalar fields. For the two-dimensional spherically symmetric and flat Kähler geometries new solutions for the quantum states are found. These are shown to have simple form. In particular, although they permit a Hartle-Hawking solution, they do not allow a wormhole state. The role of these solutions with regard to more general issues in supersymmetric quantum cosmology is also briefly discussed.
ELECTROMAGNETIC RADIATION INDUCED BY A GRAVITATIONAL WAVE
Authors: KOLOSNITSYN N.I.
Published: November 2004

Conversion of a gravitational wave into an electromagnetic one in a laser coherent emission field is studied. As a result two electromagnetic waves are created. For calculation the Maxwell equations in three-dimensional vector form are used. Optimal detection of the gravitational wave is discussed. In a particular case it is the laser interferometric antenna. This approach is identical to those based on integration of the isotropic geodesic equation, the eikonal equation, giving the three-pulsing response of the electromagnetic signal obtained by Estabrook and Wahlquist. It also results in the matrix method developed by Vinet for calculation of laser interferometric antennae.
MASSIVE BINARY BLACK HOLE IN ACTIVE GALACTIC NUCLEI AS COSMIC RAYS GENERATOR
Authors: DOKUCHAEV V.I.
Published: November 2004

A model of bow shocks generated by a supersonic orbital motion of a gravitationally bound massive binary black hole in the dense environment of active galactic nuclei (AGN) is proposed. The binary orbit is evolutionary contracting due to gravitational radiation and frictional drag in the ambient gas. The model provides the suitable conditions for the acceleration of cosmic rays up to the ultra-high energies.
ON THE DERIVATION OF THE STRING EFFECTIVE ACTION FROM AN ACCELERATION FIELD
Authors: CAPOZZIELLO S. , RITIS R. DE , FEOLI A.
Published: November 2004

We show that the string cosmology with dilaton can be derived, as a special case, from Caianiello’s model of General Relativity with maximal acceleration interpreting the dilaton as an acceleration field. In fact Caianiello’s theory allows us to recover the stringdilaton effective action starting from a gravitational action which is minimally coupled to a scalar field by means of a particular conformal transformation of the Friedman-Robertson-Walker (FRW) metric. We show that this scheme works near the Planck scale where the pure string-dilaton dynamics works.
APPROXIMATE SOLUTIONS OF STATIONARY GAUGE STRINGS ON THE (r, z)-PLANE
Authors: SLAGTER R.J.
Published: November 2004

We derive a class of approximate solutions of the coupled Einstein-scalar-gauge field equations on an axially symmetric spacetime. An analytic solution of the resulting elliptic PDE’s can be obtained to any desired order by constructing the Riemann functions. As an example model, a solution is presented, which resembles the Nielsen-Olesen vortex close to the z=0 hyperplane. However, the solution shows some significant deviation from the classical vortex off the z=0 plane. The singular behavior, which one usually encounters in line-mass models, manifests itself through the second-order solutions in the approximation scheme. Further, in this “toy”-model, with sufficient angular momentum of the spinning string, gφφ becomes negative for some values of r.
POST-INFLATIONARY COSMOLOGICAL MODEL BASED ON THE SEVEN-DIMENSIONAL SUPERGRAVITY
Authors: FABRIS JÚLIO CÉSAR , KERNER RICHARD , TOSSA JOËL
Published: November 2004

We study classical solutions of the bosonic sector of seven-dimensional supergravity theory. This study is three-fold: first, we look for power law solutions in a space which is the Cartesian product of a four-dimensional Robertson-Walker metric and a compact internal space; next, for the same geometric configuration, we sketch the phase diagram of all possible stable solutions; finally, we consider the evolution of scalar fluctuations on the background of the exact solutions found here. We observe that in spite of the presence of a potential term and a nontrivial coupling of three scalar fields, no inflationary scenario can emerge from such theory, and that all stable solutions display a big-bang type singularity. We conclude that the supersymmetric theories are well suited to describe the post-inflationary behavior of the Universe emerging from the inflationary phase before it enters the pure radiation stage.
THE INTERVENING GALAXIES HYPOTHESIS OF THE ABSORPTION SPECTRA OF QUASI-STELLAR OBJECTS: SOME STATISTICAL STUDIES
Authors: DUARI DEBIPROSAD , NARLIKAR JAYANT V.
Published: November 2004

This paper examines, in the light of the available data, the hypothesis that the heavy element absorption line systems in the spectra of QSOs originate through en-route absorption by intervening galaxies, halos etc. Several statistical tests are applied in two different ways to compare the predictions of the intervening galaxies hypothesis (IGH) with actual observations. The database is taken from a recent 1991 compilation of absorption line systems by Junkkarinen, Hewitt and Burbidge. Although, prima facie, a considerable gap is found between the predictions of the intervening galaxies hypothesis and the actual observations despite inclusion of any effects of clustering and some likely selection effects, the gap narrows after invoking evolution in the number density of absorbers and allowing for the incompleteness and inhomogeneity of samples examined. On the latter count the gap might be bridgeable by stretching the parameters of the theory. It is concluded that although the intervening galaxies hypothesis is a possible natural explanation to account for the absorption line systems and may in fact do so in several cases, it seems too simplistic to be able to account for all the available data. It is further stressed that the statistical techniques described here will be useful for future studies of complete and homogenous samples with a view to deciding the extent of applicability of the IGH.
COBE CONSTRAINTS ON KALUZA-KLEIN COSMOLOGIES
Authors: FARAONI V. , COOPERSTOCK F.I. , OVERDUIN J.M.
Published: November 2004

A class of Kaluza-Klein cosmologies recently proposed is compared with observations of the cosmic microwave background. Some models are ruled out, while others turn out to be viable, with the number of extra dimensions being constrained by the COBE and Tenerife experiments.
EXTRA DIMENSIONS AND POSSIBLE SPACE-TIME SIGNATURE CHANGES
Authors: BRONNIKOV K.A.
Published: November 2004

Exact static, spherically symmetric solutions to the Einstein-Maxwell-scalar equations, with a dilatonic-type scalar-vector coupling, in D-dimensional gravity with a chain of n Ricci-flat internal spaces are considered, with the Maxwell field potential having two nonzero components: the temporal, Coulomb-like one and the one pointing to one of the extra dimensions. The properties and special cases of the solutions are discussed, in particular, those when there are horizons in the space-time. Two types of horizons are distinguished: the conventional black-hole (BH) ones and those at which the physical section of the space-time changes its signature (the latter are called T-horizons). Two theorems are proved, one fixing the BH- and T-horizon existence conditions, the other claiming that the system under study cannot have a regular center. The stability of a selected family of solutions under spherically symmetric perturbations is studied. It is shown that only black-hole solutions are stable, while all others, in particular, those with T-horizons are unstable.
STANDARD COSMOLOGY: CAUSAL HOMOGENIZATION CONDITION AND ENERGY DISSIPATION
Authors: CHALLANE-TLEMSANI SOFIANE , DENMAT GÉRARD LE
Published: November 2004

The effect of a transient dissipative phase, during the early evolution of the cosmic fluid, is investigated in the framework of the Extended Irreversible Thermodynamics. The role played by the bulk viscosity is considered in the case of a spatially flat Friedmann-Robertson-Walker model, and we discuss a solution which allows the condition of causal homogenization of a hypersurface t=constant to be satisfied.
PHYSICAL ASPECTS OF SOLITONS IN (4+1) GRAVITY
Authors: BILLYARD ANDREW , WESSON PAUL S. , KALLIGAS DIMITRI
Published: November 2004

The augmentation of general relativity’s spacetime by one or more dimensions is described by Kaluza-Klein theory and is within testable limits. Should an extra dimension be observable and significant, it would be beneficial to know how physical properties would differ from “conventional” relativity. In examining the class of five-dimensional solutions analogous to the four-dimensional Schwarzschild solution, we examine where the origin to the system is located and note that it can differ from the four-dimensional case. Furthermore, we study circular orbits and find that the 5D case is much richer; photons can have stable circular orbits in some instances, and stable orbits can exist right to the new origin in others. Finally, we derive both gravitational and inertial masses and find that they do not generally agree, although they can in a limiting case. For all three examinations, it is possible to obtain the four-dimensional results in one limiting case, that of the Schwarzschild solution plus a flat fifth dimension, and that the differences between 4D and 5D occur when the fifth dimension obtains any sort of significance.
NONMINIMAL COUPLING AND QUANTUM COSMOLOGY
Authors: NOVELLO M. , PEREIRA V.M.C. , PINTO-NETO N.
Published: November 2004

We consider a minisuperspace cosmological model generated by coupling nonminimally a vector field with the gravitational field. The classical solutions are divided into three sets: singular solutions, eternal universes with an expansion phase and flat spacetime. We apply quantum cosmological arguments to investigate which of them is the most probable classical solution. The semiclassical cosmological wave functions satisfy the correspondence principle, and examples are shown in which the three sets of classical solutions can be predicted from different classes of WKB wave functions. As a particular example we have considered the no-boundary wave function, which predicts flat spacetime. No solutions can be obtained from the tunneling boundary condition.
ACCRETION OF HOT DARK MATTER ONTO SLOWLY MOVING COSMIC STRINGS
Authors: AGUIRRE ANTHONY N. , BRANDENBERGER ROBERT H.
Published: November 2004

Cosmic strings with small-scale structure have a coarse-grained mass per unit length μ which is larger than the string tension. This leads to an effective Newtonian gravitational line source and to a characteristic translational velocity which is smaller than for strings without small-scale structure. Here, the accretion of hot dark matter onto such strings is studied by means of the Zel’dovich approximation. We find that clustering is greatly enhanced by the Newtonian line source. In the limit of vanishing translational velocity, the first nonlinear filaments form at a redshift of greater than 100 for standard values of μ.
CHARGED COSMIC STRING NUCLEATION IN DE SITTER SPACE
Authors: AXENIDES MINOS , LARSEN ARNE L.
Published: November 2004

We investigate aspects of the nucleation of charged circular cosmic strings in de Sitter space. By including the self-gravity for a single circular string loop we obtain the classical potential energy barrier and compute the quantum mechanical tunneling probability to horizon sizes in the semiclassical approximation. We also discuss the classical evolution of a pair of oppositely charged circular strings after their nucleation.
CANONICAL QUANTIZATION OF THE BELINSKIĬ-ZAKHAROV ONE-SOLITON SOLUTIONS
Authors: MANOJLOVIC NENAD , MARUGÁN GUILLERMO A. MENA
Published: November 2004

We apply the algebraic quantization programme proposed by Ashtekar to the analysis of the Belinskiĭ-Zakharov classical spacetimes, obtained from the Kasner metrics by means of a generalized soliton transformation. When the solitonic parameters associated with this transformation are frozen, the resulting Belinskiĭ-Zakharov metrics provide the set of classical solutions to a gravitational minisuperspace model whose Einstein equations reduce to the dynamical equations generated by a homogeneous Hamiltonian constraint and to a couple of second-class constraints. The reduced phase space of such a model has the symplectic structure of the cotangent bundle over R+×R+. In this reduced phase space, we find a complete set of real observables which form a Lie algebra under Poisson brackets. The quantization of the gravitational model is then carried out by constructing an irreducible unitary representation of that algebra of observables. Finally, we show that the quantum theory obtained in this way is unitarily equivalent to that which describes the quantum dynamics of the Kasner model.
NONMINIMAL COUPLING, QUARTIC POTENTIAL AND PERFECT FLUID COSMOLOGIES
Authors: CAPOZZIELLO S. , DE RITIS R. , RUBANO C. , SCUDELLARO P.
Published: November 2004

Perfect-fluid matter, satisfying the equation of state p=(γ−1)ρ, is considered in cosmologies where the geometry is nonminimally coupled with a scalar field ɸ and the potential of ɸ is λɸ4+Λ. Exact solutions are found when γ is a constant describing the ordinary forms of matter (γ=1, dust, γ=4/3, radiation, γ=2, stiff matter and γ=0, scalar field matter) and a discussion is done in order to recover Einstein gravity and the Newton constant observed today. The various solutions can be classified according to the different values of γ, λ and Λ.
INCLUSIVE (3He, t) REACTION IN DELTA EXCITATION REGION
Authors: KELKAR NEELIMA G. , JAIN B.K.
Published: November 2004

Using the one step reaction mechanism, calculations are presented for the overall features of the inclusive (3 He , t) reaction on various target nuclei in the delta excitation region. The interaction for the elementary pp→nΔ++ process is given by one-pion-exchange, and is written in the covariant relativistic form. The values of the parameters in the interaction are chosen such that the interaction successfully describes the spin averaged experimental elementary cross-sections. The distortion in the entrance and exit channels is described in the eikonal approximation, and the nuclear response is described in the “distorted wave Fermi gas model”. The cross-sections for the triton energy spectrum, angular distribution, and the total events at 0° on several nuclei, are calculated and compared with the corresponding experimental data. The main features of the measured cross-sections are reproduced.
THREE-BODY FORCES FROM n-BODY INVERSION
Authors: GAVIN E.J.O. , FIEDELDEY H. , SOFIANOS S.A.
Published: November 2004

Within the context of the lowest order approximation to the calculation of the n-body bound state in the Hyperspherical Harmonic Expansion Method, the hypercentral potential may be determined from n-body spectral data. Previously, we showed how the two-body force can be determined exactly from the hypercentral potential in the absence of three-body forces. In this paper, we investigate to what extent the three-body force can be determined if the two-body force is assumed to be known. For this purpose, a three-quark system is considered.
THE PROBABILITY OF POPULATING THE SECOND POTENTIAL WELL STATES IN FISSION DYNAMICS
Authors: D’ARRIGO A. , GIARDINA G. , LAMBERTO A. , EREMENKO D.O. , FOTINA O.V. , PLATONOV S. Yu , YUMINOV O.A. , MALAGUTI F.
Published: November 2004

We study the probability of populating the second well states in the de-excitation of the compound nucleus during the competition between fission and emission of light particles. We consider the cases of underdamped and overdamped fission processes caused by a different influence of nuclear dissipation. The probability dependencies on the second well depth and the excitation energy are also analyzed.
PRE-EQUILIBRIUM FRACTION IN ALPHA INDUCED REACTIONS FROM THRESHOLD TO 40 MeV
Authors: VARSHNEY K.S. , GUPTA J.P.
Published: November 2004

α-particle induced excitation functions for the reactions 55Mn (α, n), 63Cu (α, n), 65Cu (α, n), 107Ag (α, n), 121Sb (α, n), 123Sb (α, n), 165Ho (α, n), 197Au (α, n), in a number of target nuclei from A=55 to 197(Z=25 to 83) have been calculated using the Statistical Model with and without inclusion of pre-equilibrium particle emission in the energy from threshold to 40 MeV. It is found that without consideration of pre-equilibrium decay, the data are not reproducible. As expected, inclusion of pre-equilibrium emission in compound nucleus calculation agree well with the experimental excitation functions. The pre-equilibrium fraction (FR) is found to be dependent on excitation energy, target mass number, neutron number, atomic number and, asymmetry parameter (N−Z).
LEPTON PAIR PRODUCTION BY LOW ENERGY BREMSSTRAHLUNG IN RELATIVISTIC HEAVY-ION COLLISIONS IN SECOND ORDER PERTURBATION THEORY
Authors: WEINBRENNER JÖRG , SCHEID WERNER , VALLURI SREE RAM
Published: November 2004

Dileptons can be produced through the mechanism of virtual bremsstrahlung during the deceleration of nuclei in relativistic heavy-ion collisions. The dilepton spectrum is studied in the framework of second order perturbation theory. Coherence effects are found to enhance the contributions to pair emission through constructive interference, since the main deceleration of nuclear matter in these collisions takes place in a small space-time region. Differential and total probabilities for lepton pairs are calculated for central 238U + 238U collisions at energies of 15 GeV/N and 60 GeV/N. Whereas the antisymmetrization of the lepton states plays a non-negligible role for the differential probabilities, it is not significant for the total probability.
PROJECTED SHELL MODEL AND HIGH-SPIN SPECTROSCOPY
Authors: HARA KENJI , SUN YANG
Published: November 2004

Most of the nuclei in the nuclear chart are deformed except for those in the vicinity of the magic numbers. It is difficult to treat such nuclei within the framework of the standard (spherical) shell model. On the other hand, the necessity for a proper quantum mechanical treatment of high-spin states has been steadily growing ever since modern experimental techniques made it possible to measure the fine details of the high-spin states of heavy nuclei.

The present article reviews an approach based on the angular momentum projection technique which was initiated in the late seventies for the purpose of carrying out shell model configuration mixing calculations efficiently. A large number of examples is presented with an emphasis on the physical interpretation of the numerical results.

Computing time for the whole spectrum up to spin ≈ 40 of an axially symmetric rare-earth nucleus takes only a few minutes on a Mainframe, showing the efficiency of the method. Most of the present calculations were carried out on a Workstation, but computation on a modern PC also presents no problem, so that one can enjoy a genuine quantum mechanical analysis of high-spin data using a facility available everywhere. Detailed technical information which may be useful for programming purposes is given in an Appendix.
MODELING THE CELL DIVISION CYCLE: A QUALITATIVE APPROACH
Authors: TANG BETTY
Published: November 2004

The underlying biochemical mechanisms that drive the cell division cycle involve the interactions and feedback controls between the cytoplasmic proteins cdc2 and cyclin, and the activities of the cdc2-cyclin complex MPF. Alternation between interphase and mitosis is associated with oscillatory MPF and cyclin levels. This paper describes an ordinary differential equations (ODE) model and a functional differential equations (FDE) model of the cell cycle based on experimental work with the newly fertilized frog egg. One major difference of these models from previous ones is the use of nonspecific reaction terms in describing the interactions between cdc2, cyclin and MPF. This qualitative approach makes possible the evaluation of the roles of the various reactions and feedback mechanisms in the control of the cell cycle.
TEMPORAL VARIABILITY GENERATED BY COUPLING OF MITOTIC TIMERS
Authors: VOLKOV EVGENII I. , STOLYAROV MAKSIM N.
Published: November 2004

Cell proliferation is considered as a periodic process which is governed by a two-variable relaxation timer. The collective behavior of a system composed of three identical relaxation oscillators is numerically studied under the condition that diffusion of the slow mode (inhibitor) dominates. The phase diagrams for cyclic and linear configurations show unexpectable diversity of stable periodic regimes, some of them are only observable under intermediate but reasonable values of coupling and stiffness. For cyclic configuration we demonstrate: (1) the existence of three periodic regimes with different periods and phase relations and unsymmetrical stable steady state (USSS); (2) the coexistence of in-phase oscillations and USSS; (3) the coexistence of periodic attractors and (4) the emergence of special kind of rotating wave which is manifested as two-loop limit cycle. The natural asymmetry of linear configuration leads to the appearance of many periodic attractors. The most of them are characterized by the large period oscillations of the middle element which has the step-like dependence of period versus coupling. The qualitative reasons for such a diversity and its possible role in the generation of cell cycle variability are discussed.
A KINETIC MODEL OF PHOSPHOLIPID TRANSLOCATION IN THE ERYTHROCYTE MEMBRANE
Authors: BRUMEN MILAN , HEINRICH REINHART , HERRMANN ANDREAS , MÜLLER PETER
Published: November 2004

A mathematical model is presented to simulate transverse lipid movement in the human erythrocyte membrane from one membrane monolayer to the other. The model is based on a system of differential equations describing the time-dependence of phospholipid redistribution and the steady-state distribution. Different translocation mechanisms are considered in a combined way. These are the ATP-dependent carrier mediated translocation, the carrier mediated facilitated diffusion and carrier independent transbilayer diffusion. Using realistic values of model parameters the model allows calculation of the transbilayer motion and distribution of phospholipids of the human erythrocyte membrane for several biologically relevant conditions and different experimental conditions.
VALUE OF CONTROL THEORY IN THE STUDY OF CELLULAR METABOLISM — BIOMEDICAL IMPLICATIONS
Authors: MALGAT MONIQUE , LETELLIER THIERRY , JOUAVILLE SOPHIE L. , MAZAT JEAN-PIERRE
Published: November 2004

We use some examples to show that Metabolic Control Theory (MTC) not only allows the determination of the controlling steps of a metabolic network with the so-called control coefficients, but also leads to better understanding of the functioning of metabolic networks. The examples are taken partly from our own work on mitochondrial myopathies, partly from the literature:

— the threshold effect observed in mitochondria diseases;

— the problem of the diagnosis of complex I, II or III defects by measuring the NADH-cytochrome-c-reductase or the succinate-cytochrome-c-reductase activities with illustration by some cases. The possibility of a sum of control coefficients greater than one is also considered.
ASSESSING OPTIMAL DESIGNS IN METABOLIC PATHWAYS
Authors: PUIGJANER J. , CASCANTE M. , SORRIBAS A.
Published: November 2004

The evolution of metabolic pathways is characterized by the search of the optimum reaction network, both as for chemical transformations and for the associated pattern of regulation. Understanding this process requires the evaluation of alternative designs for a given function. After this evaluation, we would be in a good situation for drawing general conclusions on the evolution of the considered system. This goal can be undertaken by means of different complementary approaches. The method of Control Comparisons, first developed within Biochemical Systems Analysis, has produced some valuable insights on this kind of problems. In this contribution, we present this method within the context of Metabolic Control Analysis.
USING SOME RECENT TECHNIQUES FROM CHAOS THEORY TO ANALYZE TIME-SERIES IN ECOLOGY
Authors: BOUDJEMA G. , MESTIVIER D. , CAZELLES B. , CHAU N.P.
Published: November 2004

Extraction of the underlying dynamics of large biological systems is a crucial step to understanding their mechanisms and predicting their future behaviors. Some of the techniques developed in physics to analyze chaotical phenomena should be applied with caution when the data are short and noisy.

In this paper, we compared the Eckmann-Ruelle Linearization (ERL) local prediction method, and Neural Network (NN), fitting of a global nonlinear function, in the context of population dynamics. Data were generated by a discrete model and subjected to measurement noise. Prediction errors were analyzed according to noise level and length of the observations, using the above two methods

Where the noise level is high, ERL is more effective for prediction than NN. On the basis of these results, we proposed for short series of available observations, that additional data be generated by the Eckmann—Ruelle linearization method and these data be used as input for Neural Nets in order to obtain a global function for the observed dynamics. This gave more reliable results than when we apply the NN method directly .

Two examples are given, in ecology and epidemiology.
A MATHEMATICAL MODEL FOR TROPHIC INTERACTIONS IN AN ACARINE PREDATOR-PREY SYSTEM
Authors: BUFFONI G. , DI COLA G. , BAUMGÄRTNER J. , MAURER V.
Published: November 2004

An acarine predator-prey model is introduced and some results concerning the stability of this system are derived. The existence and uniqueness of positive steady state solutions are shown, and stability criteria are estabilished in function of ecological and behavioral parameters. Some special cases include Ivlev and Lotka-Volterra predation. Theoretical and numerical results allow us to assess the feasibility of a biological control of the prey.
DIPLOID MODELS ON SEQUENCE SPACE
Authors: BAAKE ELLEN
Published: November 2004

The “decoupled” version of the selection mutation as adapted to (binary) sequence space is investigated. For diploid analogues of the single-peaked landscape, dominance effects on error thresholds are found both in the deterministic and the stochastic case. For more complicated landscapes, nonlinear oscillations may emerge during the transition to equidistribution.
EVOLUTIONARY OPTIMIZATION OF ENZYME KINETIC PARAMETERS
Authors: KLIPP EDDA
Published: November 2004

The distribution of the kinetic parameters of a reversible enzymic reaction with an ordered mechanism is theoretically studied under the assumption that during evolution the increase in reaction rate was an important target of natural selection. The optimal individual rate constants in the steady state for fixed reactant concentrations are determined from optimization principles. The reaction rate is a homogeneous function of first degree of the elementary rate constants and the determination of states of maximal activity is only possible if constraints for the rate constants are taken into account. Besides a fixed thermodynamical equilibrium constant, this concerns upper limits for the values of the individual rate constants. In extension of previous work on the optimization of enzyme kinetic parameters the influence of constraints concerning upper limits of the rate constants is analyzed. Two different models are introduced: the separate limit model and the overall limit model. The concept of “evolutionary effort” is applied to derive an expression for the cost function leading to an overall upper limit for the values of the rate constants. The resulting optimization problem is solved for ordered mechanisms involving different numbers of elementary steps depending on the reactant concentrations and on the thermodynamical equilibrium constant.
MODELLING THE ROLE OF IMMUNITY IN MACROPARASITE INFECTIONS
Authors: HYUN MO YANG , COUTINHO FRANCISCO ANTONIO BEZERRA , MASSAD EDUARDO
Published: November 2004

A stochastic model is proposed to analyse the role of immunity processes in modulating the infection by macroparasites, with applications in schistosomiasis.
A MATHEMATICAL MODEL OF DRUG ADMINISTRATION BY PHAGOCYTOSIS OF LOADED ERYTHROCYTES
Authors: SOLIMANO FORTUNATA
Published: November 2004

A mathematical model for the drug delivery to macrophages of the tissues by using a preassigned cohort of red blood cells loaded with a drug is presented. This model is a system of three nonlinear differential equations, with a discrete time delay and an input depending on the time. The input should be controlled in order to obtain the longest duration of the therapeutic effect.
POSITIVE LOOPS AND DIFFERENTIATION
Authors: THIEFFRY D. , SNOUSSI E.H. , RICHELLE J. , THOMAS R.
Published: November 2004

This paper focuses on the relation between the presence of positive feedback loops and the occurrence of multiple states of gene expression. After a short recall on single feedback loops and their properties, we discuss more extensively the properties of positive loops. This discussion includes a theorem (demonstrated elsewhere) which states that the presence of positive loop(s) is a necessary condition for multistationarity. We also discuss some general principles for pattern formation, in terms of involvement of different types of positive feedback loops. Finally, we briefly mention recent experimental results involving positive loops in crucial differentiative processes.
DISCRETE AND CONTINUOUS TIME POPULATION MODELS, A COMPARISON CONCERNING PROLIFERATION BY FISSION
Authors: KOOI B.W. , BOER M.P.
Published: November 2004

We present two approaches, discrete time and continuous time models, for individuals which propagate through binary fission. The volumes of the two daughters are a fixed part of that of the mother, not necessarily the half, and their growth rates may differ. The discrete time approach gives more insight into the results obtained with the continuous time model. We define classes in the continuous time model such that the total number of individuals in these classes at specific moments in time is equal to the unknown number in a discrete time model. Then the discrete time model is homologous to the continuous one in the sense of having the same solutions at specific moments. Population matrix theory applies when the ratio of the inter-division times of the two daughters is rational. There is inter-class convergence but no intra-class convergence. The latter feature implies that there is no convergence of the size distribution in the continuous time model either. When the ratio is irrational the continuous time model holds and there is convergence but the rate of convergence can become infinitesimally small. This phenomenon is linked with quasi-periodicity on a 2-dimensional torus.