bluuebunny/crossref_metadata_2025 huggingface dataset:
*-IDEALS AND FORMAL MORITA EQUIVALENCE OF *-ALGEBRAS
Authors: BURSZTYN HENRIQUE , WALDMANN STEFAN
Published: April 2003

Motivated by deformation quantization, we introduced in an earlier work the notion of formal Morita equivalence in the category of *-algebras over a ring [Formula: see text] which is the quadratic extension by i of an ordered ring [Formula: see text]. The goal of the present paper is twofold. First, we clarify the relationship between formal Morita equivalence, Ara's notion of Morita *-equivalence of rings with involution, and strong Morita equivalence of C*-algebras. Second, in the general setting of *-algebras over [Formula: see text], we define "closed" *-ideals as the ones occurring as kernels of *-representations of these algebras on pre-Hilbert spaces. These ideals form a lattice which we show is invariant under formal Morita equivalence. This result, when applied to Pedersen ideals of C*-algebras, recovers the so-called Rieffel correspondence theorem. The triviality of the minimal element in the lattice of closed ideals, called the "minimal ideal", is also a formal Morita invariant and this fact can be used to describe a large class of examples of *-algebras over [Formula: see text] with equivalent representation theory but which are not formally Morita equivalent. We finally compute the closed *-ideals of some *-algebras arising in differential geometry.
LINEARLY FULL HARMONIC 2-SPHERES IN S4 OF AREA 20π
Authors: BOLTON JOHN , WOODWARD LYNDON M.
Published: April 2003

We give an explicit description of all harmonic 2-spheres of area 20π in the round 4-sphere S4 in terms of their branch points and umbilics. This is obtained by finding canonical forms for the twistor lifts of such maps into [Formula: see text].
ON PROPERTIES OF THE ASYMPTOTIC EXPANSION OF THE HEAT TRACE FOR THE N/D PROBLEM
Authors: DOWKER J. S. , KIRSTEN K. , GILKEY P. B.
Published: April 2003

The spectral problem where the field satisfies Dirichlet conditions on one part of the boundary of the relevant domain and Neumann on the remainder is discussed. It is shown that there does not exist a classical asymptotic expansion for short time in terms of fractional powers of t with locally computable coefficients.
A NOTE ON BERGMAN COMPLETENESS
Authors: CHEN BO-YONG
Published: April 2003

The purpose of this note is to deal with two problems of Kobayashi: 1. Which bounded pseudoconvex domain is Bergman complete? 2. Is a bounded domain Bergman complete if it coincides with its outerhull? We verify Problem 1 for a class of pseudoconvex domains which are not necessary hyperconvex. However, we will show that the answer to Problem 2 is negative in general.
THE ℚ-PICARD GROUP OF THE MODULI SPACE OF CURVES IN POSITIVE CHARACTERISTIC
Authors: MORIWAKI ATSUSHI
Published: April 2003

In this note, we prove that the ℚ-Picard group of the moduli space of n-pointed stable curves of genus g over an algebraically closed field is generated by the tautological classes. We also prove that the cycle map to the second étale cohomology group is bijective.
ON THE SPECTRAL PROPERTIES OF A MARKOV MODEL FOR LEARNING PROCESSES
Authors: ANTONIOU I. , BOSCO F.
Published: April 2003

We study the spectral properties of the evolution operator of densities of the one-dimensional version of a Markov model for instrumental conditioning proposed by Bush and Mosteller in the early '50s. The model is a probabilistic combination of dynamical systems with phase space dependent probability distribution. The spectral properties are derived by restricting the stochastic operator in the space of analytic functions. The nonergodic properties of the model are demonstrated by the spectrum of the stochastic operator.
COMPLEXITY IN A CRITICAL TRAFFIC FLOW
Authors: YUKAWA SATOSHI , KIKUCHI MACOTO
Published: April 2003

The traffic flow near the jamming transition is numerically studied by computer simulations of a coupled-map model. Just above the transition, a variety of velocities with which the traffic jams propagate are observed. The entropy of the traffic flow becomes maximum at the same time. Moreover, the current-concentration relation obtained by local measurements shows clear double-valued behavior near the critical concentration. From these properties, the traffic flow can be said as maximally complex near the critical concentration.
MULTISCALE LATTICE BOLTZMANN SCHEMES: A PRELIMINARY APPLICATION TO AXIAL TURBOMACHINE FLOW SIMULATIONS
Authors: MAZZOCCO F. , ARRIGHETTI C. , BELLA G. , SPAGNOLI L. , SUCCI S.
Published: April 2003

Multiscale Lattice Boltzmann schemes for fluid dynamic applications are described and their efficiency is discussed in terms of accuracy and computational cost. A novel application to axial compressor flows is proposed. Conditions on periodic boundaries have been appropriately developed. Our preliminary results indicate that these schemes hold good potential for the simulation of fluid flows in turbomachines.
QUASIPERIODIC AND CHAOTIC STATES IN THE DING-DONG MODEL FOR N = 3
Authors: GAWRONSKI P. , KULAKOWSKI K.
Published: April 2003

The system considered is a chain of spheres bound harmonically to equidistant points and colliding elastically. This is the so-called "ding-dong" model of Prosen and Robnik, 1992. For 3 spheres we investigate the transition from chaos to quasiperiodicity in a numerical experiment. The character of motion is determined by calculation of the box counting fractal dimension of the t(n + 1) versus t (n) plot, where t (n) is a time between an nth and an (n+1)th collision between spheres. The result is that the transition occurs at many regions of the phase space for all values of the total energy. We conclude that, in the contrast to what was suggested by other authors, the character of motion cannot be deduced from one parameter.
AN EXACT FINITE FIELD RENORMALIZATION GROUP CALCULATION ON A TWO-DIMENSIONAL FRACTAL LATTICE
Authors: NYSTROM J. F.
Published: April 2003

A two-dimensional fractal lattice, herein referred to as the tetrahedral gasket, is used as a model for an exact two-dimensional real-space renormalization group calculation. It is shown that this Ising spin-system has exact solutions which includes a nontrivial phase transition even in the presence of a finite field. The calculation also introduces a new analysis tool, the free energy surface plot, which gives further insight into the phase diagram of the spin-system. The discussion includes comments concerning the apparent preference of the system to maintain some finite entropy, even in the presence of an extremely large spin–spin coupling.
ORIGINATIONS AND EXTINCTIONS: ANALYSES OF FOSSIL DATA AND SIMULATIONS
Authors: RAY TANE , MOSELEY LEO , JAN NAEEM
Published: April 2003

We analyse the fossil data of Benton1 with and without interpolation schemes. By Fourier transform analysis, we find a frequency dependence of the amplitude of 1/f for the various interpolation schemes used in the past. We illustrate that shuffling the interpolated data changes the spectra only slightly. On the other hand, an identical analysis performed on the raw (uninterpolated) fossil data gives a flat frequency spectrum. We conclude that the 1/f behavior is an artifact of the interpolation schemes. We next introduce a simulation of extinctions driven only by interactions between two trophic levels. Fourier transform analysis of the simulation data shows a frequency dependence of 1/f. When the data are grouped into a form resembling the fossil record the frequency dependence vanishes, giving a flat spectrum. Our simulation produces a frequency spectrum that agrees with the observed fossil record.
STABILITY IN THE SOCIAL PERCOLATION MODELS FOR TWO TO FOUR DIMENSIONS
Authors: HUANG ZHI-FENG
Published: April 2003

The social percolation model proposed by Solomon et al. as well as its modification are studied in two to four dimensions for the phenomena of self-organized criticality. Stability in the models is obtained and the systems are shown to automatically drift towards the percolation threshold.
SEARCHING FOR SCALING IN THE PENNA BIT-STRING MODEL OF BIOLOGICAL AGING
Authors: MALARZ K.
Published: April 2003

In this paper the Penna bit-string model of biological aging with different lengths of bit-strings genome is considered. We show from computer simulation that changes in genome length may be crucial for determining population characterization and seem to be irreversible by scaling the other model control parameters.
A MOLECULAR DYNAMICS RUN WITH 5 180 116 000 PARTICLES
Authors: ROTH J. , GÄHLER F. , TREBIN H.-R.
Published: April 2003

We report on the development of IMD, a scalable program for classical molecular dynamics simulations on massively parallel supercomputers. New features like online-visualization and metacomputing are described.
QUANTUM COMPUTING AND SYMBOLICC++ SIMULATIONS
Authors: STEEB WILLI-HANS , HARDY YORICK
Published: April 2003

We show how SymbolicC++ can be used to simulate quantum circuits.
EFFECTS OF ON- AND OFF-RAMPS IN CELLULAR AUTOMATA MODELS FOR TRAFFIC FLOW
Authors: DIEDRICH G. , SANTEN L. , SCHADSCHNEIDER A. , ZITTARTZ J.
Published: April 2003

We present results on the modeling of on- and off-ramps in cellular automata for traffic flow, especially the Nagel–Schreckenberg model. We study two different types of on-ramps that cause qualitatively the same effects. In a certain density regime ρ low < ρ < ρ high one observes plateau formation in the fundamental diagram. The plateau value depends on the input-rate of cars at the on-ramp. The on-ramp acts as a local perturbation that separates the system into two regimes: A regime of free flow and another one where only jammed states exist. This phase separation is the reason for the plateau formation and implies a behavior analogous to that of stationary defects. This analogy allows to perform very fast simulations of complex traffic networks with a large number of on- and off-ramps because one can parametrise on-ramps in an exceedingly easy way.
POLYMERIZATION-INDUCED PHASE SEPARATION: INTERMEDIATE DYNAMICS
Authors: LEE J. C.
Published: April 2003

When phase separation is induced by polymerizating monomers in a mixture of monomers and nonreacting molecules, the dynamics is different depending on the time scale of polymerization τpl and the time scale of phase separation τps. Previous studies have explored the dynamic regimes where τpl ≪ τps and that where τpl ≫ τps. In the former, a spanning gel emerges before the phase separation and the phase separation is driven largely by activation. In the latter, phase separation occurs first between polymers and nonbonding molecules and then the polymers turn into a gel, and therefore the driving mechanism is the same as in the usual liquid–liquid demixing processes. Using Molecular Dynamics simulations, we explore in this paper the intermediate dynamic regime where the two time scales are comparable. When the polymerization is done by means of the thermal condensation reaction, we observe the expected crossover, one limit behavior at early times and then the other at late times. When the polymerization is done by means of the radical addition reaction, the results suggest that the driving mechanism changes more than once.
EVALUATION OF THE QUANTITATIVE PREDICTION OF A TREND REVERSAL ON THE JAPANESE STOCK MARKET IN 1999
Authors: JOHANSEN ANDERS , SORNETTE DIDIER
Published: April 2003

In January 1999, the authors published a quantitative prediction that the Nikkei index should recover from its 14-year low in January 1999 and reach ≈20 500 a year later. The purpose of the present paper is to evaluate the performance of this specific prediction as well as the underlying model: the forecast, performed at a time when the Nikkei was at its lowest (as we can now judge in hindsight), has correctly captured the change of trend as well as the quantitative evolution of the Nikkei index since its inception. As the change of trend from sluggish to recovery was estimated quite unlikely by many observers at that time, a Bayesian analysis shows that a skeptical (resp. neutral) Bayesian sees prior belief in our model amplified into a posterior belief 19 times larger (resp. reach the 95% level).
COMPUTATION OF COHOMOLOGY OF LIE SUPERALGEBRAS OF VECTOR FIELDS
Authors: KORNYAK V. V.
Published: April 2003

The cohomology of Lie (super)algebras has many important applications in mathematics and physics. It carries most fundamental ("topological") information about algebra under consideration. At present, because of the need for very tedious algebraic computation, the explicitly computed cohomology for different classes of Lie (super)algebras is known only in a few cases. That is why application of computer algebra methods is important for this problem. We describe here an algorithm and its C implementation for computing the cohomology of Lie algebras and superalgebras. The program can proceed finite-dimensional algebras and infinite-dimensional graded algebras with finite-dimensional homogeneous components. Among the last algebras, Lie algebras and superalgebras of formal vector fields are most important. We present some results of computation of cohomology for Lie superalgebras of Buttin vector fields and related algebras. These algebras being super-analogs of Poisson and Hamiltonian algebras have found many applications to modern supersymmetric models of theoretical and mathematical physics.
A FAMILY OF HYBRID EIGHTH ORDER METHODS WITH MINIMAL PHASE-LAG FOR THE NUMERICAL SOLUTION OF THE SCHRÖDINGER EQUATION AND RELATED PROBLEMS
Authors: AVDELAS G. , KONGUETSOF A. , SIMOS T. E.
Published: April 2003

In this paper a family of hybrid methods with minimal phase-lag are developed for the numerical solution of periodic initial-value problems. The methods are of eighth algebraic order and have large intervals of periodicity. The efficiency of the new methods is presented by their application to the wave equation and to coupled differential equations of the Schrödinger type.
SELECTION EXPERIMENTS IN THE PENNA MODEL FOR BIOLOGICAL AGING
Authors: MEDEIROS G. , IDIART M. A. , DE ALMEIDA R. M. C.
Published: April 2003

We consider the Penna model for biological aging to investigate correlations between early fertility and late life survival rates in populations at equilibrium. We consider inherited initial reproduction ages together with a reproduction cost translated in a probability that mother and offspring die at birth, depending on the mother age. For convenient sets of parameters, the equilibrated populations present genetic variability in what regards both genetically programmed death age and initial reproduction age. In the asexual Penna model, a negative correlation between early life fertility and late life survival rates naturally emerges in the stationary solutions. In the sexual Penna model, selection experiments are performed where individuals are sorted by initial reproduction age from the equilibrated populations and the separated populations are evolved independently. After a transient, a negative correlation between early fertility and late age survival rates also emerges in the sense that populations that start reproducing earlier present smaller average genetically programmed death age. These effects appear due to the age structure of populations in the steady state solution of the evolution equations. We claim that the same demographic effects may be playing an important role in selection experiments in the laboratory.
SIMULATING THE MITOCHONDRIAL DNA BOTTLENECK
Authors: RADOMSKI JAN P. , DE OLIVEIRA S. MOSS
Published: April 2003

A probabilistic model is proposed with dynamics which naturally leads to a bottleneck in the number of mitochondria transmitted from one host-cell generation to the other. We take into account deleterious mutations during the replication of mitochondria within a cell of a germ-line and introduce selection inside the cell reproduction mechanism. The bottleneck size strongly depends on the selection mechanism and on the maximum number of mitochondria per cell. We obtain that the smaller the maximum allowed number of mitochondria per cell during replication, the tighter the bottleneck. Such a result is in agreement with the fact that species producing small litters provide developing oocytes with a smaller number of mitochondria. This amplifies the differences among oocytes leading to competition and removal of inferior cells.
STUDY OF PHASE CONVERSION IN THREE-DIMENSIONAL q = 3 POTTS MODEL
Authors: ARKIN H. , ÇELIK T.
Published: April 2003

In order to see the phase conversion taking place in a weak first-order phase transition, we have simulated the q = 3 state Potts model in three dimensions and studied the time evolutions of oriented clusters forming after a rapid temperature quench. Our results indicate that the phase conversion mechanism following a deep temperature quench is spinodal decomposition while a rather shallow quench to temperatures near the phase transition point proceeds through usual nucleation.
COLLISION-BASED COMPUTING IN BIOPOLYMERS AND THEIR AUTOMATA MODELS
Authors: ADAMATZKY ANDREW
Published: April 2003

In collision-based computing, quanta of information are represented by autonomous mobile signals. The signals travel in a uniform architectureless medium. They collide to each other. Assuming the presence or abscence of a signal represent truth or falsity values of logical variable, we can consider logical functions are calculated at the sites of signals' collision. Physically, the signals are localized compact disturbances of medium's characteristics. In this paper, we extensively exploit results published in Refs. 1–7. We consider three types of localizations: breathers in one-dimensional arrays of DNA molecules, excitons and groups of antialigned dipoles in two-dimensional arrays of Scheibe aggregates and microtubules respectively. Several forms of logical gates are extracted from published results on numerical simulation of breathers and excitons. In cellular automata models, we study interactions of the localizations with each other. We show what kinds of logical gates can be realized in such interactions. Parallels between physical and discrete automata models are provided.
DIFFUSION UNDER CROSSED LOCAL AND GLOBAL BIASES IN DISORDERED SYSTEMS
Authors: SANTRA SITANGSHU BIKAS , SEITZ WILLIAM A.
Published: April 2003

Diffusion on 2D site percolation clusters at p = 0.7, 0.8, and 0.9 above pc on the square lattice in the presence of two crossed bias fields, a local bias B and a global bias E, has been investigated. The global bias E is applied in a fixed global direction whereas the local bias B imposes a rotational constraint on the motion of the diffusing particle. The rms displacement Rt ~ tk in the presence of both biases is studied. Depending on the strength of E and B, the behavior of the random walker changes from diffusion to drift to no-drift or trapping. There is always diffusion for finite B with no global bias. A crossover from drift to no-drift at a critical global bias Ec is observed in the presence of local bias B for all disordered lattices. At the crossover, value of the rms exponent changes from k = 1 to k < 1, the drift velocity vt changes from constant in time t to decreasing power law nature, and the "relaxation" time τ has a maximum rate of change with respect to the global bias E. The value of critical bias Ec depends on the disorder p as well as on the strength of local bias B. Phase diagrams for diffusion, drift, and no-drift are obtained as a function of bias fields E and B for these systems.
ENERGY EIGENVALUE LEVEL MOTION AND A SYMBOLICC++ IMPLEMENTATION
Authors: STEEB WILLI-HANS , HARDY YORICK
Published: April 2003

We consider the Hamilton operator [Formula: see text]. We assume that [Formula: see text] has a discrete spectrum. We show that the energy eigenvalues and eigenvectors obey an autonomous system of ordinary differential equations. An implementation of this system of differential equations is given using SymbolicC++.
ON THE USELESSNESS OF MEN — COMPARISON OF SEXUAL AND ASEXUAL REPRODUCTION
Authors: STAUFFER D. , SÁ MARTINS J. S. , DE OLIVEIRA S. MOSS
Published: April 2003

A comparison of sexual with asexual reproduction in the Penna aging model for a single species shows the separation into males and females at a disadvantage due to the halved number of births. Also meiotic and apomictic parthenogenesis and hermaphroditism seem better than sex, even when the individuals follow the suggestion of Jan et al. to engage in sex only when their lifes are endangered by a large number of harmful mutations. In our comparison, we looked only for intrinsic effects, not for external influences like parasites or environmental catastrophes.
GENETIC MANIPULATION AND THE POPULATION'S FATE
Authors: LICHOTA KRZYSZTOF , PȨKALSKI ANDRZEJ , RADOMSKI JAN P.
Published: April 2003

We present a dynamic model of a population under selection pressure and in a changing habitat. Two kinds of changes are considered: In the first climate changes in one direction only, like in coming of the glacial era; in the second, the changes are randomly fluctuating. We compare four evolutionary strategies: First: evolution without any external influence; second: evolution where ill-fitted individuals are eliminated; third: where the phenotypes of the progeny are improved to make them better fit to the existing conditions, and finally evolution where the last two procedures are applied together. We show that the systematic phenotype improvement is the most successful strategy in the long run and the elimination of the ill-fitted almost always leads to a disaster.
COMPARING THE CORRELATION LENGTH OF GRAIN MARKETS IN CHINA AND FRANCE
Authors: ROEHNER BERTRAND M. , SHIUE CAROL H.
Published: April 2003

In economics, comparative analysis plays the same role as experimental research in physics. In this paper, we closely examine several methodological problems related to comparative analysis by investigating the specific example of grain markets in China and France respectively. This enables us to answer a question in economic history which has so far remained pending, namely whether or not market integration progressed in the 18th century. In economics as in physics, before any new result being accepted, it has to be checked and re-checked by different researchers. This is what we call the replication and comparison procedures. We show how these procedures should (and can) be implemented.
BOUNDARY CONDITION DEPENDENCE OF CLUSTER SIZE RATIOS IN RANDOM PERCOLATION
Authors: da SILVA C. R. , LYRA M. L. , VISWANATHAN G. M.
Published: April 2003

We study the ratio of the number of sites in the largest and second largest clusters in random percolation. Using the scaling hypothesis that the ratio / of the mean cluster sizes M1 and M2 scales as f ((p - pc) L1/ν), we employ finite-size scaling analysis to find that / is nonuniversal with respect to the boundary conditions imposed. The mean  of the ratios behaves similarly although with a distinct critical value reflecting the relevance of mass fluctuations at the percolation threshold. These zero exponent ratios also allow for reliable estimates of the critical parameters at percolation from relatively small lattices.
MONTE CARLO STUDY OF THE VACANCY MECHANISM IN DILUTE FCC BINARY ALLOYS
Authors: HASNAOUI A.
Published: April 2003

The vacancy mechanism is simulated by means of Monte Carlo (MC) method. In this model, the impurity diffusion occurs by migration of substitutional atoms B via the exchange with vacancies whose frequencies near a solute atom differ from a free vacancy. Whenever a defect leaves the lattice, periodic boundary conditions are made to bring it into the lattice. The solute concentration profiles are given using a technique developed by Murch which has been shown to be equivalent to a finite source. The fit of these profiles allows the comparison between our results and analytical solutions. The parameters extracted from a Gaussian function fit which agrees well with numerical profiles are in very good quantitative agreement with theoretical predictions.
QUASI-THREE-DIMENSIONAL MATHEMATICAL MODELING OF MORPHOLOGICAL PROCESSES BASED ON EQUILIBRIUM SEDIMENT TRANSPORT
Authors: CHARAFI MY. M. , SADOK A. , KAMAL A. , MENAI A.
Published: April 2003

A quasi-three-dimensional mathematical model has been developed to study the morphological processes based on equilibrium sediment transport method. The flow velocities are computed by a two-dimensional horizontal depth-averaged flow model (H2D) in combination with logarithmic velocity profiles. The transport of sediment particles by a flow water has been considered in the form of bed load and suspended load. The bed load transport rate is defined as the transport of particles by rolling and saltating along the bed surface and is given by the Van Rijn relationship (1987). The equilibrium suspended load transport is described in terms of an equilibrium sediment concentration profile (ce) and a logarithmic velocity (u). Based on the equilibrium transport, the bed change rate is given by integration of the sediment mass-balance equation. The model results have been compared with a Van Rijn results (equilibrium approach) and good agreement has been found.
DISTRIBUTION OF TRAFFIC PENALTIES IN RIO DE JANEIRO
Authors: NÓBREGA RAFAELLA A. , RODEGHERI CRICIA C. , POVOAS RENATO C.
Published: April 2003

Brazilian drivers caught in traffic violations accumulate points in their official personal files. Here, we analyze the distribution probability of these data for the state of Rio de Janeiro where 4199 drivers accumulated 20 or more penalty points during one year.
SHORT-TIME RELAXATION OF SU(2) LATTICE GAUGE THEORY IN (3 + 1) DIMENSIONS
Authors: JASTER A.
Published: April 2003

We investigate the dynamic relaxation for SU(2) gauge theory at finite temperatures in (3 + 1) dimensions. Using the Hybrid Monte Carlo algorithm, we examine the time dependence of the system in the short-time regime. Starting from the ordered state, the critical exponents β, ν and z are calculated from the power law behavior of the Polyakov loop and the cumulant at or near the critical point. The results for the static exponents are in agreement with those obtained from simulations in equilibrium and those of the three-dimensional Ising model. The value for the dynamic critical exponent was determined with z = 2.0(1).
LEARNING, EXPLORATION AND CHAOTIC POLICIES
Authors: POTAPOV ALEXEI B. , ALI M. K.
Published: April 2003

We consider different versions of exploration in reinforcement learning. For the test problem, we use navigation in a shortcut maze. It is shown that chaotic ∊-greedy policy may be as efficient as a random one. The best results were obtained with a model chaotic neuron. Therefore, exploration strategy can be implemented in a deterministic learning system such as a neural network.
CORRELATIONS BETWEEN RECONSTRUCTED EUR EXCHANGE RATES VERSUS CHF, DKK, GBP, JPY AND USD
Authors: AUSLOOS M. , IVANOVA K.
Published: April 2003

On 1 January 1999, the European Union introduced a common currency Euro (EUR), to become the legal currency in all eleven countries which form the EUR. In order to test the EUR behavior and understand various features, the EUR exchange rate is artificially extrapolated back to 1993 by a linear superposition of the exchange rates of the 11 currencies composing EUR with respect to several currencies not belonging to the EUR, i.e., Swiss Franc (CHF), Danish Kroner (DKK), British Pound (GBP), Japanese Yen (JPY) and U.S. Dollar (USD) of interest for reasons given in the text. The distribution of fluctuations of the exchange rates is shown to be Gaussian for the central part of the distribution, and having fat tails for the large size fluctuations. Within the Detrended Fluctuation Analysis (DFA) statistical method, we have obtained the power law behavior describing the root-mean-square deviation of the exchange rate fluctuations as a function of time. For the period between January 1995 and January 1999, we have compared the time-dependent exponent of these exchange rate fluctuations for EUR and that of the 11 currencies which form the EUR. The German Mark (DEM) and the French Franc (FRF) have been the currencies primarily leading the fluctuations of the exchange rates, while Italian Lira (ITL) and Portuguese Escudo (PTE) are the less relevant currencies from this point of view. Technical considerations for the EUR implementation are given as conclusions. The cases of exchange rates with DKK appear quite different from the other four major currencies.
DAMAGE SPREADING, COARSENING DYNAMICS AND DISTRIBUTION OF POLITICAL VOTES IN SZNAJD MODEL ON SQUARE LATTICE
Authors: BERNARDES A. T. , COSTA U. M. S. , ARAUJO A. D. , STAUFFER D.
Published: April 2003

In the Sznajd model of sociophysics on the square lattice, neighbors having the same opinion convince their neighbors of this opinion. We study scaling of the cluster growth. The spreading-of-damage technique is applied for the spread of opinions. We study the time evolution of the damage and compare it with the magnetization evolution. We also compare this model with the Ising model at low temperatures. It was recently shown that the distribution of votes in Brazilian elections follows a power law behavior with exponent ≃ -1.0. A model for elections based on the Sznajd model is proposed. The exponent obtained for the distribution of votes during the transient agrees with that obtained for elections.
ON THE EXISTENCE OF A VARIATIONAL PRINCIPLE FOR DETERMINISTIC CELLULAR AUTOMATON MODELS OF HIGHWAY TRAFFIC FLOW
Authors: BOCCARA NINO
Published: April 2003

It is shown that a variety of deterministic cellular automaton models of highway traffic flow obey a variational principle which states that, for a given car density, the average car flow is a nondecreasing function of time. This result is established for systems whose configurations exhibits local jams of a given structure. If local jams have a different structure, it is shown that either the variational principle may still apply to systems evolving according to some particular rules, or it could apply under a weaker form to systems whose asymptotic average car flow is a well-defined function of car density. To establish these results, it has been necessary to characterize among all number-conserving cellular automaton rules which ones may reasonably be considered as acceptable traffic rules. Various notions such as free-moving phase, perfect and defective tiles, and local jam play an important role in the discussion. Many illustrative examples are given.
LEVY-STABLE DISTRIBUTIONS REVISITED: TAIL INDEX > 2 DOES NOT EXCLUDE THE LEVY-STABLE REGIME
Authors: WERON RAFAŁ
Published: April 2003

Power-law tail behavior and the summation scheme of Levy-stable distributions is the basis for their frequent use as models when fat tails above a Gaussian distribution are observed. However, recent studies suggest that financial asset returns exhibit tail exponents well above the Levy-stable regime (0 < α ≤ 2). In this paper, we illustrate that widely used tail index estimates (log–log linear regression and Hill) can give exponents well above the asymptotic limit for α close to 2, resulting in overestimation of the tail exponent in finite samples. The reported value of the tail exponent α around 3 may very well indicate a Levy-stable distribution with α ≈ 1.8.
FERMI SYSTEMS, HUBBARD MODEL AND A SYMBOLICC++ IMPLEMENTATION
Authors: HARDY YORICK , STEEB WILLI-HANS
Published: April 2003

We show how the anticommutation relations for Fermi operators can be implemented with computer algebra using SymbolicC++. We describe applications to the Hubbard model. An important identity for Fermi operators is proved. Then, we test for higher order constants of motion for the Hubbard model. Finally, the matrix representation for the four point Hubbard model is calculated.
SYMBOLIC COMPUTATION FOR THE NONLINEAR SCHRÖDINGER EQUATIONS RELEVANT TO THE RAYLEIGH–TAYLOR INSTABILITY IN THE SPACE AND LABORATORY PLASMA SYSTEMS
Authors: GAO YI-TIAN , TIAN BO
Published: April 2003

The Rayleigh–Taylor (RT) instability occurs in many dynamic plasma systems, from the impoding laser targets to planets and collapsing massive stars. In two different wave-number regions, the RT instability could be respectively described by the unstable and stable nonlinear Schrödinger equations, the former also models the nonlinear modulation of the high-frequency mode in the electron beam plasma. In this paper, for those types of nonlinear Schrödinger equations, we perform computerized symbolic computation and find some similarity solutions. Dark and bright solitons are also seen.
PERCOLATION-LIKE PHASE TRANSITION IN A NONEQUILIBRIUM STEADY STATE
Authors: BOSE INDRANI , CHAUDHURI INDRANATH
Published: April 2003

We study the Gierer–Meinhardt model of reaction-diffusion on a site-disordered square lattice. Let p be the site occupation probability of the square lattice. For p greater than a critical value pc, the steady state consists of stripe-like patterns with long-range connectivity. For p < pc, the connectivity is lost. The value of pc is found to be much greater than that of the site percolation threshold for the square lattice. In the vicinity of pc, the cluster-related quantities exhibit power-law scaling behavior. The method of finite-size scaling is used to determine the values of the fractal dimension df, the ratio, γ/ν, of the average cluster size exponent γ and the correlation length exponent ν. The values appear to indicate that the disordered GM model belongs to the universality class of ordinary percolation.
CRITICAL DYNAMICS OF TWO-REPLICA CLUSTER ALGORITHMS
Authors: LI X.-N. , MACHTA J.
Published: April 2003

The dynamic critical behavior of the two-replica cluster algorithm is studied. Several versions of the algorithm are applied to the two-dimensional, square lattice Ising model with a staggered field. The dynamic exponent for the full algorithm is found to be less than 0.4. It is found that odd translations of one replica with respect to the other together with global flips are essential for obtaining a small value of the dynamic exponent.
MOLECULAR MODELING OF TWO HEXAPEPTIDE REPEAT MOTIFS OF HMW GLUTENIN SUBUNITS
Authors: ARKIN HANDAN , YAŞAR FATİH , ÇELİK TARIK , ÇELİK SÜEDA , KÖKSEL HAMİT
Published: April 2003

The three-dimensional structures of two hexapeptide repeat motifs (PGQGQQ and SGQGQQ, in one letter code) in the repetitive central domain of HMW glutenin subunits are investigated by using the multicanonical simulation procedure. Ramachandran plots were prepared and analyzed to predict the relative occurrence probabilities of β-turn and γ-turn structures and helical state. Structural predictions of PGQGQQ repeat motif indicated the presence of high level of β-turns and considerable level of γ-turns. Simulations of the repeat motifs in the repetitive central domain of HMW glutenin subunits indicated that these structures take important part in the three-dimensional structures of repeat motifs.
GRADIENT DRIVEN FLOW: LATTICE GAS, DIFFUSION EQUATION AND MEASUREMENT SCALES
Authors: PANDEY R. B. , WOOD WARREN T. , GETTRUST J. F.
Published: April 2003

Tracer diffusion and fluid transport are studied in a model for a geomarine system in which fluid constituents move from regions of high to low concentration. An interacting lattice gas is used to model the system. Collective diffusion of fluid particles in lattice gas is consistent with the solution of the continuum diffusion equation for the concentration profile. Comparison of these results validates the applicability and provides a calibration for arbitrary (time and length) units of the lattice gas. Unlike diffusive motion in an unsteady-state regime, both fluid and tracer exhibit a drift-like transport in a steady-state regime. The transverse components of fluid and tracer displacements differ significantly. While the average tracer motion becomes nondiffusive in the long time regime, the collective motion exhibits an onset of oscillation.
ENERGETICS AND STABILITY OF DISCRETE CHARGE DISTRIBUTION ON THE SURFACE OF A SPHERE
Authors: OYMAK HÜSEYIN , ERKOÇ ŞAKIR
Published: April 2003

We have investigated the minimum-energy distribution of N, 3 ≤ N ≤ 97, equal point charges confined to the surface of a sphere. Charges interact with each other via the Coulomb potential of the form 1/r. Minimum-energy distributions have been determined by minimizing the tangential forces on each charge. Further numerical evidence shows that in the minimum-energy state of N charges on the sphere, it is not possible to place a charge at the geometrical center. Besides, it has been found that the most and reliable information about the relative stability properties of the distributions can be obtained with the help of second difference energy consideration.
ON THE MAP NAVIGATION USING THE LAPLACE EQUATION
Authors: ANDRECUT M. , ALI M. K.
Published: April 2003

In the framework of vectorial field analysis, the problem of map navigation can be reduced to the construction of the appropriate goal gradients. The solution of the Laplace equation with boundary conditions can be used to build such goal gradients. Inspired by this classical method, we present a more efficient cellular automaton algorithm for robotic map navigation.
PREDICTION OF ELECTROSTATIC POTENTIAL VARIATIONS WITH THE TETRAGONAL DISTORTION OF THE PbFCl-TYPE LATTICE
Authors: SABRY ABDELHADI , AYADI MOHAMED
Published: April 2003

The Coulomb potential is estimated for the tetragonal distortion of the PbFCl-type lattice using Ewald's formula over a large lattice ratio c/a range. The expressions describing the lattice self-potentials for distinct ion sites as functions of c/a are derived by taking into account the regular symmetric crystallization. The obtained results will be useful for elucidate the ionic behavior with high-pressure of this type of layered crystals.
CATASTROPHIC SENESCENCE OF THE PACIFIC SALMON WITHOUT MUTATION-ACCUMULATION
Authors: MEYER-ORTMANNS HILDEGARD
Published: April 2003

We derive catastrophic senescence of the Pacific salmon from an aging model which was recently proposed by Stauffer. The model is based on the postulates of a minimum reproduction age and a maximal genetic lifespan. It allows for self-organization of a typical age of first reproduction and a typical age of death. Our Monte Carlo simulations of the population dynamics show that the model leads to catastrophic senescence for semelparous reproduction as it occurs in the case of salmon, to a more gradually increase of senescence for iteroparous reproduction.
POWER LAWS ARE DISGUISED BOLTZMANN LAWS
Authors: RICHMOND PETER , SOLOMON SORIN
Published: April 2003

Using a previously introduced model on generalized Lotka–Volterra dynamics together with some recent results for the solution of generalized Langevin equations, we derive analytically the equilibrium mean field solution for the probability distribution of wealth and show that it has two characteristic regimes. For large values of wealth, it takes the form of a Pareto style power law. For small values of wealth, w ≤ wm, the distribution function tends sharply to zero. The origin of this law lies in the random multiplicative process built into the model. Whilst such results have been known since the time of Gibrat, the present framework allows for a stable power law in an arbitrary and irregular global dynamics, so long as the market is "fair", i.e., there is no net advantage to any particular group or individual.

We further show that the dynamics of relative wealth is independent of the specific nature of the agent interactions and exhibits a universal character even though the total wealth may follow an arbitrary and complicated dynamics.

In developing the theory, we draw parallels with conventional thermodynamics and derive for the system some new relations for the "thermodynamics" associated with the Generalized Lotka–Volterra type of stochastic dynamics. The power law that arises in the distribution function is identified with new additional logarithmic terms in the familiar Boltzmann distribution function for the system. These are a direct consequence of the multiplicative stochastic dynamics and are absent for the usual additive stochastic processes.
A DYNAMICAL MODEL OF B–T CELL REGULATION
Authors: KÜRTEN KARL E. , CASTIGLIONE FILIPPO
Published: April 2003

We present a minimal regulatory model for the dynamics of the humoral immune response of two lymphocytes populations (B and T helper) interacting with a specific antigen pool (bacterium). Stability analysis reveals that the system accounts for the occurrence of multiple steady states in the absence as well as in the presence of the antigen population. The model exhibits (i) a state of immune memory, (ii) one state with high antigen and low helper concentration (disease), and (iii) one state with low antigen and high helper concentration (tolerance). The latter state allows oscillatory behavior. Injection of high antigen doses as well as minimal changes of structural parameters provoke the system to jump from the state of disease to the state of tolerance. This is reminiscent of therapies where the patient is treated with allergen, immuno-suppressants or drugs.
A SYSTEM OF THE COUPLED KORTEWEG-DE VRIES EQUATIONS AND COMPUTERIZED SYMBOLIC COMPUTATION
Authors: TIAN BO , GAO YI-TIAN
Published: April 2003

In physical and engineering sciences, the studies of the Korteweg-de Vries (KdV)-typed equations are of crucial significance. Performing computerized symbolic computation, we hereby obtain an auto-Bäcklund transformation for a system of the coupled KdV equations. Sample exact analytic solutions are also presented, which are the rational solutions and solitary waves.
MONTE CARLO SIMULATION OF NUCLEATION AND GROWTH IN THE 3D NEAREST-NEIGHBOR ISING MODEL
Authors: SCHMELZER JÜRN , LANDAU D. P.
Published: April 2003

Monte Carlo simulations of nucleation and growth processes in an Ising-binary alloy model are presented. The evolution of the cluster size distribution function and its characteristic properties (mean radius and concentration of the clusters) has been investigated from the initial quench into the metastable region of the phase diagram until the establishment of the final equilibrium. All classical stages of nucleation and growth could be observed, the stages of steady-state nucleation, independent growth and Ostwald ripening. A quantitative analysis of the simulational results in terms of the theory of regular solutions shows the validity of classical nucleation theory in the region of the phase diagram considered and provides evidence for a size and structure dependent interfacial tension between the two newly formed phases.
DYNAMIC BEHAVIOR OF A GRANULAR CAYLEY TREE
Authors: SCHULZE CHRISTIAN
Published: April 2003

The bifurcated, ordered Cayley tree with disorder and frustration as a model for relaxing granular media is examined numerically. Surprisingly, only exponential time dependencies are found despite frustration. Extensions to bidirectional models are discussed extensively and qualitatively new behavior is detected.
GROUND-STATES OF TWO DIRECTED POLYMERS
Authors: PETÄJÄ V. T. , ALAVA M. J. , RIEGER H.
Published: April 2003

Joint ground states of two directed polymers in a random medium are investigated. Using exact min-cost flow optimization, the true two-line ground-state is compared with the single line ground state plus its first excited state with "worst-possible" initial conditions, where the two lines start next to each other. It is found that these two-line configurations are (for almost all disorder configurations) distinct implying that the true two-line ground-state is nonseparable, which means that the two-line ground state cannot be obtained by adding a second line to the first line in the one-line ground state without deforming the first line. The effective interaction energy between the two lines scales with the system size with the scaling exponents 0.39 ± 0.03 and 0.21 ± 0.02 in 2D and 3D, respectively.
A COOPERATIVE STOCHASTIC MODEL OF GENE EXPRESSION
Authors: ROY SIDDHARTHA , BOSE INDRANI , MANNA SUBHRANGSHU SEKHAR
Published: April 2003

Recent experiments at the level of a single cell have shown that gene expression occurs in abrupt stochastic bursts. Further, in an ensemble of cells, the levels of proteins produced have a bimodal distribution. In a large fraction of cells, the gene expression is either off or has a high value. We propose a stochastic model of gene expression, the essential features of which are stochasticity and cooperative binding of RNA polymerase. The model can reproduce the bimodal behavior seen in experiments.
AN ELASTIC-COLLISION SCHEME FOR LATTICE BOLTZMANN METHODS
Authors: ZHOU J. G.
Published: April 2003

An elastic-collision scheme is developed to achieve slip and semi-slip boundary conditions for lattice Boltzmann methods. Like the bounce-back scheme, the proposed scheme is efficient, robust and generally suitable for flows in arbitrary complex geometries. It involves an equivalent level of computation effort to the bounce-back scheme. The new scheme is verified by predicting wind-driven circulating flows in a dish-shaped basin and a flow in a strongly bent channel, showing good agreement with analytical solutions and experimental data. The capability of the scheme for simulating flows through multiple bodies has also been demonstrated.
EXPECTATION BUBBLES IN A SPIN MODEL OF MARKETS: INTERMITTENCY FROM FRUSTRATION ACROSS SCALES
Authors: BORNHOLDT STEFAN
Published: April 2003

A simple spin model is studied, motivated by the dynamics of traders in a market, where expectation bubbles and crashes occur. The dynamics is governed by interactions, which are frustrated across different scales: while ferromagnetic couplings connect each spin to its local neighborhood, an additional coupling relates each spin to the global magnetization. This new coupling is allowed to be anti-ferromagnetic. The resulting frustration causes a metastable dynamics with intermittency and phases of chaotic dynamics. The model reproduces main observations of real economic markets as power-law distributed returns and clustered volatility.
BACTERIAL EVOLUTION AND THE BAK–SNEPPEN MODEL
Authors: BOSE INDRANI , CHAUDHURI INDRANATH
Published: April 2003

Recently, Lenski et al.1–3 have carried out several experiments on bacterial evolution. Their findings support the theory of punctuated equilibrium in biological evolution. They have further quantified the relative contributions of adaptation, chance and history to bacterial evolution. In this paper, we show that a modified M-trait Bak–Sneppen model can explain many of the experimental results in a qualitative manner.
EXPLICIT NUMEROV TYPE METHODS FOR SECOND ORDER IVPs WITH OSCILLATING SOLUTIONS
Authors: PAPAGEORGIOU G. , TSITOURAS CH. , TH. FAMELIS I.
Published: April 2003

New explicit hybrid Numerov type methods are presented in this paper. These efficient methods are constructed using a new approach, where we do not need the use of the intermediate high accuracy interpolatory nodes, since only the Taylor expansion of the internal points is needed. The methods share sixth algebraic order at a cost of five stages per step while their phase-lag order is 14 and partly satisfy the dissipation order conditions. It has be seen that the property of phase-lag is more important than the nonempty interval in constructing numerical methods for the solution of Schrödinger equation and related problems.1–3 Numerical results over some well known problems in physics and mechanics indicate the superiority of the new methods.
THE CONSTRUCTION OF GENERALIZED DIRAC OPERATORS ON THE LATTICE
Authors: HASENFRATZ P. , HAUSWIRTH S. , HOLLAND K. , JÖRG T. , NIEDERMAYER F. , WENGER U.
Published: April 2003

We discuss the steps to construct Dirac operators, which have arbitrary fermion offsets, gauge paths, a general structure in Dirac space and satisfy the basic symmetries (gauge symmetry, hermiticity condition, charge conjugation, hypercubic rotations and reflections) on the lattice. We give an extensive set of examples and offer help to add further structures.