bluuebunny/crossref_metadata_2025 huggingface dataset:
USING EVOLUTIONARY ALGORITHM TO CALCULATE THE GROUND-STATE ENERGY OF DOUBLE-ELECTRON ATOMS IN A UNIFORM MAGNETIC FIELD (B ≤ 109G)
Authors: LIU LIANJUN , ZHAO LI , MAO YOUDONG , YU DONG , XU JINGWEN , LI YUANXIANG
Published: May 2003

It is very difficult to calculate the accurate ground-state energies of the double-electron atom like helium in a uniform magnetic field. By using the modified configuration interaction (MCI) method and the evolutionary algorithm (EA), we obtained highly accurate results. We discuss the role of magnetic field in the ground state of the double-electron system and the possibility of variational ground-state energy calculation by using evolutionary algorithm directly. Results show that compared with other algorithms, such as the simplex method, EA is more efficient in calculating atomic energies, and can be used in other fields of physics.
NUMERICAL SOLUTIONS OF THE STOCHASTIC EQUATIONS OF CRYSTAL GROWTH
Authors: MAZZONE A. M. , PALERMO V.
Published: May 2003

This work analyzes explicit and implicit methods for the solution of differential stochastic equations for crystal growth. The usefulness of these methods is analyzed by practical computations.
REEXAMINATION OF SEVEN-DIMENSIONAL SITE PERCOLATION THRESHOLD
Authors: STAUFFER DIETRICH , ZIFF ROBERT M.
Published: May 2003

Monte Carlo simulations alone could not clarify the corrections to scaling for the size-dependent pc(L) above the upper critical dimension. Including the previous series estimate for the bulk threshold pc (∞) gives preference for the complicated corrections predicted by renormalization group and against the simple 1/L extrapolation. Additional Monte-Carlo simulations using the Leath method corroborate the series result for pc.
BUILDING PARTIALLY ENTANGLED STATES WITH GROVER'S AMPLITUDE AMPLIFICATION PROCESS
Authors: AZUMA HIROO
Published: May 2003

In the present study, we discuss how to build some partially entangled states of n two-state quantum systems (qubits). The optimal partially entangled state with a high degree of symmetry is considered to be useful for overcoming a shot noise limit of Ramsey spectroscopy under some decoherence. This state is invariant under permutation of any two qubits, and inversion between the ground state |0> and an excited state |1> for each qubit. We show that by using selective phase shifts in certain basis vectors and Grover's inversion about average operations, we can construct this high symmetric entangled state by (polynomial in n) ×2n/2 successive unitary transformations that are applied on two or three qubits.
NUMERICAL SOLUTION OF THE SPINLESS SALPETER EQUATION BY A SEMIANALYTICAL MATRIX METHOD (A MATHEMATICA 4.0 ROUTINE)
Authors: LUCHA WOLFGANG , SCHÖBERL FRANZ F.
Published: May 2003

In quantum theory, the "spinless Salpeter equation", the relativistic generalization of the nonrelativistic Schrödinger equation, is used to describe both the bound states of scalar particles and the spin-averaged spectra of bound states of fermions. A numerical procedure solves the spinless Salpeter equation by approximating this eigenvalue equation by a matrix eigenvalue problem with explicitly known matrices.
STATIC PROPERTIES AND WAVEGUIDE MODES OF A WIDE LATERAL WINDOW JOSEPHSON JUNCTION
Authors: CAPUTO JEAN-GUY , EFREMIDIS NIKOS , FLYTZANIS NIKOS , LAZARIDES NIKOS , GAIDIDEI YURI , MOULITSA IRENE , VAVALIS EMMANUEL
Published: May 2003

We developed an efficient hybrid mode expansion method to study the maximum tunneling current as a function of the external magnetic field for a 2D large area lateral window junction. We consider the inhomogeneity in the critical current density, which is taken a piecewise constant. The natural modes of the expansion in y, are the linearized eigen-modes around a static solution which satisfies the 1D sine-Gordon equation with the critical current variation in y, and the boundary conditions determined by the overlap component of the bias current, which can be inline or overlap like. The magnetic field along with the inline component of the bias current enters as a boundary condition on the modal amplitudes. We obtain fast convergent results and for a ratio of idle to window widths of w0/w = 4 (in units of λJ), only two modes are needed. A simple scaling is obtained for the maximum tunneling current as we vary the idle region width. We also present the linear electromagnetic waveguide modes taking into account the variation normal to the waveguide of the critical current and the capacitance.
MARKET VOLATILITY AND THE DISTRIBUTION OF MEAN CLUSTER SIZES FOR PERCOLATION
Authors: STAUFFER DIETRICH
Published: May 2003

The tail of the distribution for the "mean cluster size" (susceptibility) at the site percolation threshold is found by Monte Carlo simulations to be exponential. Similar distributions might be expected for the market volatility, if stock price fluctuations are described by Cont–Bouchaud percolation.
BIOLOGICAL AGING — CRITERIA FOR MODELING AND A NEW MECHANISTIC MODEL
Authors: PLETCHER SCOTT D. , NEUHAUSER CLAUDIA
Published: May 2003

To stimulate interaction and collaboration across scientific fields, we introduce a minimum set of biological criteria that theoretical models of aging should satisfy. We review results of several recent experiments that examined changes in age-specific mortality rates caused by genetic and environmental manipulation. The empirical data from these experiments is then used to test mathematical models of aging from several different disciplines, including molecular biology, reliability theory, physics, and evolutionary biology/population genetics. We find that none of the current models are consistent with all of the published experimental findings. To provide an example of how our criteria might be applied in practice, we develop a new conceptual model of aging that is consistent with our observations.
THE SIMULATION OF THE TWO-DIMENSIONAL ISING MODEL IN THE PRESENCE OF AN EXTERNAL MAGNETIC FIELD ON THE CREUTZ CELLULAR AUTOMATON
Authors: KUTLU B. , KASAP M. , TURAN S.
Published: May 2003

The two-dimensional Ising model in a small external magnetic field, is simulated on the Creutz cellular automaton. The values of the static critical exponents for 0.0025 ≤ h ≤ 0.025 are estimated within the framework of the finite size scaling theory. The value of the field critical exponent is in a good agreement with its theoretical value of δ = 15. The results for 0.0025 ≤ h ≤ 0.025 are compatible with Ising critical behavior for T < Tc.
GROUND STATES IN THREE-DIMENSIONAL ±J EDWARDS–ANDERSON SPIN GLASSES WITH FREE BOUNDARIES
Authors: LIERS FRAUKE , JÜNGER MICHAEL
Published: May 2003

By an exact calculation of the ground states for the ±J Edwards–Anderson spin glass, one can extrapolate the ground state energy to infinite system sizes. We calculate the exact ground states for the three-dimensional spin glass with free boundaries for system sizes up to 10 and fit different finite-size functions. We cannot decide, only from the quality of the fit, which fitting function to choose. Relying on the literature values for the extrapolated energy, we find the finite-size corrections to vary as 1/L.
EFFICIENCY OF MODIFIED GENETIC ALGORITHMS ON TWO-DIMENSIONAL SYSTEM
Authors: FAN LEWEN , FANG HAIPING , LIN ZHIFANG
Published: May 2003

The genetic algorithms (GA) have been successfully applied to optimization problems in a variety of areas. In this paper, some modifications to GA are designed to study their performance and efficiency on a typical 2D system, 2D Ising spin glass. In particular, two kinds of modified GAs are compared for their searching ability (performance) and efficiency (convergence), by presenting a direct and visual criterion. Finally, some constructive comments and prospects on GA are presented.
ON THE DYNAMICS OF LOCAL HAWK-DOVE GAME
Authors: AHMED E. , ELGAZZAR A. S.
Published: May 2003

Cellular automata are used to study two-dimensional local hawk-dove games. Both Nash and Pareto optimal concepts are used. The systems have fixed point, cyclic and chaotic-like regimes. The results differ significantly from that of the normal one.
A UNIVERSAL NEURAL NETWORK REPRESENTATION FOR HADRON–HADRON INTERACTIONS AT HIGH ENERGY
Authors: EL-METWALLY KHALED. A. , HAWEEL TAREK I. , EL-BAKRY MAHMOUD Y.
Published: May 2003

An efficient neural network (NN) has been designed to simulate the hadron–hadron interaction at high energy. Two cases have been considered simultaneously, the proton–proton (p–p) and the pion–proton (π-p) interactions. The neural network has been trained to produce the charged multiplicity distribution for both cases based on samples from the overlapping functions. The trained NN shows a good performance in matching the trained distributions. The NN is then used to predict the distributions that are not present in the training set and matched them effectively. The robustness of the designed NN in the presence of uncertainties, in the overlapping functions has been demonstrated.
NONEXTENSIVE MICROSCOPIC BEHAVIOR OF LONG-RANGE INTERACTING PARTICLES IN PERIODIC MEDIA
Authors: CURILEF SERGIO
Published: May 2003

This work presents a possible way to study the long-range interacting particles in finite-infinite (mesoscopic-macroscopic) systems with periodic boundary conditions. A symmetric lattice and their contributions over all space are used in the problem. In the present model, we assume that at long distances, the two-body attractive potential decays as a 1/rα law. We verified that the potential in any particle converges (diverges) when the interactions are short(long)-ranged. On the other hand, forces in any particle converge rapidly in all cases. However, we adopt a nonextensive scaling and we guarantee that the potential converges anywhere.
NUMERICAL MODELING OF WATER CIRCULATION AND POLLUTANT TRANSPORT IN A SHALLOW BASIN
Authors: CHARAFI MY. M. , SADOK A. , KAMAL A. , MENAI A.
Published: May 2003

A two-dimensional numerical model was developed1–3 to simulate the sediment and pollutant transport in a shallow basin. The developed model consist of two modules: Hydrodynamic module and sediment/pollutant transport module. A numerical hydrodynamic module based on the Saint-Venant equations, is resolved by a MacCormack numerical scheme and is used to simulate the circulation pattern in the basin. The obtained flow circulation is used as an input to the sediment/pollutant transport module to simulate the transport and dispersion of a pollutant emitted into the basin. To calibrate the numerical model, the distorted scale model of the Windermere Basin4 was used. In this physical model, the flow visualization and pollutant transport experiments provide a good calibration. The simulated results were found to be in good agreement with the experimental measurements and the results in Ref. 4. With the aid of the validated model, the influence of the construction of dikes on the residence time distributions in the basin was examined.
COMPUTATIONAL ASPECTS OF THE LOCAL ITERATIVE MONTE CARLO TECHNIQUE
Authors: JAKUMEIT JÜRGEN
Published: May 2003

Lately, the Local Iterative Monte Carlo technique was introduced for an efficient simulation of effects connected to sparsely populated regions in semiconductor devices like hot electron effects in silicon MOSFETs. This paper focuses on computational aspects of this new Monte Carlo technique, namely the reduction of the computation time by parallel computation and the reuse of drift information. The Local Iterative Monte Carlo technique combines short Monte Carlo particle flight simulations with an iteration process to a complete device simulation. The separation between short Monte Carlo simulations and the iteration process makes a simple parallelization strategy possible. The necessary data transfer is small and can be performed via the Network File System. An almost linear speed up could be achieved. Besides by parallelization, the computational expenses can be significantly reduced, when the results of the short Monte Carlo simulations are memorized in a drift table and used several times. A comparison between a bulk, a one-dimensional and the two-dimensional Local Iterative Monte Carlo simulation reveals that by using the drift information more than once, becomes increasingly efficient with increasing dimension of the simulation.
DYNAMICS OF EDEN CLUSTERS: CONFIRMATION OF APPERT–DERRIDA UNIVERSALITY
Authors: WEICHSEL INGO
Published: May 2003

Universality of ratios of cumulants depends on the minor changes in the definition of time.
SOCIAL PERCOLATION ON INHOMOGENEOUS SPANNING NETWORK
Authors: GUPTA ABHIJIT KAR , STAUFFER DIETRICH
Published: May 2003

The Social Percolation model recently proposed by Solomon et al. is studied on the Ising correlated inhomogeneous network. The dynamics in this is studied so as to understand the role of correlations in the social structure. Thus, the possible role of the structural social connectivity is examined.
STUDY OF AUTOCORRELATION TIMES IN 2D POTTS MODEL UNDER QUENCHED BOND RANDOMNESS
Authors: YAŞAR FATIH , GÜNDÜÇ YIĞIT , ÇELIK TARÍK
Published: May 2003

The q = 8 state Potts model with varying amount of quenched bond randomness is simulated in two dimensions by using a cluster algorithm. It is shown that, by monitoring the autocorrelation times, one can trace down the threshold value of the introduced quenched bond randomness for the rounding of the first-order phase transition.
INCREMENTS OF UNCORRELATED TIME SERIES CAN BE PREDICTED WITH A UNIVERSAL 75% PROBABILITY OF SUCCESS
Authors: SORNETTE D. , ANDERSEN J. V.
Published: May 2003

We present a simple and general result that the sign of the variations or increments of uncorrelated times series are predictable with a remarkably high success probability of 75% for symmetric sign distributions. The origin of this paradoxical result is explained in details. We also present some tests on synthetic, financial and global temperature time series.
OPTIMIZATION OF ENERGY SUPPLY SYSTEMS: SIMULATED ANNEALING VERSUS GENETIC ALGORITHM
Authors: GONZALEZ-MONROY LUIS I. , CORDOBA A.
Published: May 2003

We have applied two methods (simulated annealing and genetic algorithms) to search the solution of a problem of optimization with constraints in order to determine the best way to fulfill different energy demands using a set of facilities of energy transformation and storage. We have introduced a computational efficiency factor that measures the efficiency of the optimization algorithm and, as a result, we can conclude that for short computation times, genetic algorithms are more efficient than simulated annealing when demand profiles are not very long, whereas the latter is more efficient than the former for long computation time or for big demand profiles.
WINDING ANGLE DISTRIBUTION OF SELF-AVOIDING WALKS IN TWO DIMENSIONS
Authors: CHANG IKSOO
Published: May 2003

Winding angle problem of two-dimensional self-avoiding walks (SAWs) on a square lattice is studied intensively by the scanning Monte Carlo simulation at high, theta (Θ), and low-temperatures. The winding angle distribution PN(θ) and the even moments of winding angle [Formula: see text] are calculated for lengths of SAWs up to N = 300 and compared with the analytical prediction. At the infinite temperature (good solvent regime of linear polymers), PN(θ) is well described by either a Gaussian function or a stretched exponential function which is close to Gaussian, so, it is not incompatible with an analytical prediction that it is a Gaussian function exp [-θ2/ ln N] in terms of a variable [Formula: see text] and that [Formula: see text]. However, the results for SAWs at Θ and low-temperatures (Θ and bad solvent regime of linear polymers) significantly deviate from this analytical prediction. PN(θ) is then described much better by a stretched exponential function exp [-|θ|α/ln N] and [Formula: see text] with α = 1.54 and 1.51 which is far from being a Gaussian. We provide a consistent numerical evidence that the winding angle distribution for SAWs at the finite temperatures may not be a Gaussian function but a nontrivial distribution, possibly a stretched exponential function.
WINDING ANGLE DISTRIBUTION OF LATTICE TRAILS IN TWO DIMENSIONS
Authors: CHANG IKSOO
Published: May 2003

The winding angle problem of two-dimensional lattice trails on a square lattice is studied intensively by the scanning Monte Carlo simulation at infinite, tricritical, and low-temperatures. The winding angle distribution PN(θ) and the even moments of winding angle [Formula: see text] are calculated for the lengths of trails up to N = 300. At infinite temperature, trails share the same universal winding angle distribution with self-avoiding walks (SAWs), which is a stretched exponential function close to a Gaussian function exp [-θ2/ln N] and [Formula: see text]. However, trails at tricritical and low-temperatures do not share the same winding angle distribution with SAWs. For trails, PN(θ) is described well by a stretched exponential function exp [-|θ|α/ln N] and [Formula: see text] with α ~ 1.69 which is far from being a Gaussian and also different from those of SAWs at Θ and low-temperatures with α ~ 1.54. We provide a consistent numerical evidence that the winding angle distribution for trails at finite temperatures may not be a Gaussian function, but, a nontrivial distribution, possibly a stretched exponential function. Our result also demonstrates that the universality argument between trails and SAWs at infinite and tricritical temperatures indeed persists to the distribution function of winding angle and its associated scaling behavior.
HOUSEKEEPING GENES AND DEATH GENES IN THE PENNA AGING MODEL
Authors: NIEWCZAS E. , KURDZIEL A. , CEBRAT S.
Published: May 2003

The Penna model of aging predicts the accumulation of defective genes expressed after the organism reaches the minimum reproduction age in the genetic pool of the population. The accumulation of defects in the genomes implicates the specific age structure of the modeled populations. Nevertheless, the fraction of defective alleles at loci switched on before the reproduction period does not depend on exact age when precisely they are switched on, it may be just after conception or after birth. We have modeled the mortality of a population in the period before the minimum reproduction age, even before birth, assuming that sets of genes of different size are switched on in different periods of the life span.
EXPONENTIALLY FITTED RUNGE–KUTTA FOURTH ALGEBRAIC ORDER METHODS FOR THE NUMERICAL SOLUTION OF THE SCHRÖDINGER EQUATION AND RELATED PROBLEMS
Authors: WILLIAMS P. S. , SIMOS T. E.
Published: May 2003

Fourth order exponential and trigonometric fitted Runge–Kutta methods are developed in this paper. They are applied to problems involving the Schrödinger equation and to other related problems. Numerical results show the superiority of these methods over conventional fourth order Runge–Kutta methods. Based on the methods developed in this paper, a variable-step algorithm is proposed. Numerical experiments show the efficiency of the new algorithm.
WHAT ARE STORIES MADE OF? — QUANTITATIVE CATEGORICAL DECONSTRUCTION OF CREATION
Authors: STOLOV Y. , IDEL M. , SOLOMON S.
Published: May 2003

We extend the Microscopic Representation approach to the quantitative study of religious and folk stories: A story encrypting symbolically the creation is deconstructed into its simplest conceptual elements and their relationships. We single out a particular kind of relationship which we call "diagonal (or transitive) link": given two relations between the couples of elements AB and respectively BC, the "diagonal link" is the (composite) relation AC. We find that the diagonal links are strongly and systematically correlated with the events in the story that are considered crucial by the experts. We further compare the number of diagonal links in the symbolic creation story with a folk tale, which ostensibly narrates the same overt succession of events (but without pretensions of encrypting additional meanings). We find that the density of diagonal links per word in the folk story is lower by a factor of two. We speculate that, as in other fields, the simple transitive operations acting on elementary objects are at the core of the emergence and recognition of macroscopic meaning and novelty in complex systems.
DYNAMICS AND SIMULATION OF MICELLAR SELF-REPRODUCTION
Authors: MAYER BERND , RASMUSSEN STEEN
Published: May 2003

Molecular self-assembly plays a crucial role as a structural and an organizational principle in supramolecular architecture. The key feature of this process is the generation of higher order molecular structures, and is solely determined by the dynamics of the individual molecular objects, characterized by an overall minimum free energy situation. Equally important as the constructional aspect of the formation process, these macromolecular assemblies carry novel functionalities which can be solely observed at the level of the supramolecular aggregates and not at any of the organizational levels below. This paper discusses the formation and successive self-reproduction of membraneous compartments in a polar environment in 2D using a lattice gas based simulation technique, the Lattice Molecular Automaton. This method describes realistic physico-chemical interactions as well as chemical reactivity between molecular units via discrete force fields propagated on the lattice. We investigate the formation dynamics of micelles, i.e., organized amphiphilic polymers in polar environment, as well as the kinetics of a concomittant micelle self-reproduction based on the formation of catalytic interfaces closely following in vitro experimental results: Micelle self-reproduction is a complex phenomenon based on concerted dynamics of the individual polymers within the many particle aggregate. All observables, i.e., micelle formation and autocatalytic micelle self-reproduction, are solely based on the properties of the individual chemical objects (amphiphilic polymers in polar environment), and are therefore emergent phenomena generated by the implicitly defined system dynamics. We introduce the formal concept of the emergence of novel functions in dynamical hierarchies and finally discuss these issues within the context of self-reproducing dynamical hierarchies.
THE INFLUENCE OF TRUCKS ON TRAFFIC FLOW — AN INVESTIGATION ON THE NAGEL–SCHRECKENBERG-MODEL
Authors: EBERSBACH ANJA , SCHNEIDER JOHANNES , MORGENSTERN INGO , HAMMWÖHNER RAINER
Published: May 2003

A few years ago Nagel and Schreckenberg introduced a model for traffic flow,1 which, though quite simple, is able to reproduce the basic properties of traffic. Meanwhile many variations of the model have been developed, part of them concentrate on introducing an inhomogenous fleet of cars with different maximum velocities.

Here we also want to study the effect of introducing a certain fraction of vehicles with a lower maximum velocity ("trucks") to the Nagel–Schreckenberg-model. We give a detailed description of this effect and focus on the time development of the influence of trucks on traffic flow.
NONGAUSSIAN DISTRIBUTION OF PERCOLATION THRESHOLDS IN FINITE SIZE LATTICES
Authors: WESTER F.
Published: May 2003

The distribution of site percolation thresholds for finite size lattices is a nonGaussian distribution. In this paper, we try to find out the real form of it.
DISTRIBUTION OF POINT CHARGES ON A THIN CONDUCTING DISK
Authors: OYMAK H. , ERKOÇ Ş.
Published: May 2003

We investigate the minimum energy configuration of N equal point charges interacting via the Coulomb potential 1/r, and placed on an infinitely thin conducting disk. By minimizing total interaction energy, we obtain numerically the minimum energy configurations from which the rules for the distribution of charges on the disk are obtained.
DIFFUSION AND AGGREGATION IN AN AGENT BASED MODEL OF STOCK MARKET FLUCTUATIONS
Authors: CASTIGLIONE FILIPPO
Published: May 2003

We describe a new model to simulate the dynamic interactions between market price and the decisions of two different kind of traders. They possess spatial mobility allowing to group together to form coalitions. Each coalition follows a strategy chosen from a proportional voting "dominated" by a leader's decision. The interplay of both kind of agents gives rise to complex price dynamics that is consistent with the main stylized facts of financial time series. The present model incorporates many features of other known models and is meant to be the first step toward the construction of an agent-based model that uses more realistic markets rules, strategies, and information structures.
A SYNTHESIS OF INVARIANT STRUCTURES WITH MEMORY IN TWO-DIMENSIONAL SPACE
Authors: YUDASHKIN ALEXANDER
Published: May 2003

A problem of self-organized structure storage and retrieving is considered. The novel model of nonlinear dynamical system for multi-unit structures memorizing is proposed and its properties are investigated in this paper. The multi-unit system consists of N points in the two-dimensional Euclidean space, and its dynamics is defined by a potential function, that is translation and rotation invariant relatively points coordinates. The nonlinear potential function allows to compose attractors corresponding to the proper configurations of points, while these configurations are memorized by the system. Any initial form flows to one of the attractors independently from possible rotations and spatial shifts. The system can memorize and successfully restore up to N-2 required configurations. The characteristics of structure retrieving in the presence of beginning form distortion are considered, and the stability of method is shown even in the case of high level noise. The proposed approach could be helpful to design physical, technical and informational objects with the desired self-assembling properties.
NO-SLIP BOUNDARY CONDITION IN DISSIPATIVE PARTICLE DYNAMICS
Authors: WILLEMSEN S. M. , HOEFSLOOT H. C. J. , IEDEMA P. D.
Published: May 2003

Dissipative Particle Dynamics (DPD) has, with only a few exceptions, been used to study hydrodynamic behavior of complex fluids without confinement. Previous studies used a periodic boundary condition, and only bulk behavior can be studied effectively. However, if solid walls play an important role in the problem to be studied, a no-slip boundary condition in DPD is required. Until now the methods used to impose a solid wall consisted of a frozen layer of particles. If the wall density is equal to the density of the simulated domain, slip phenomena are observed. To suppress this slip, the density of the wall has to be increased. We introduce a new method, which intrinsically imposes the no-slip boundary condition without the need to artificially increase the density in the wall. The method is tested in both a steady-state and an instationary calculation. If repulsion is applied in frozen particle methods, density distortions are observed. We propose a method to avoid these distortions. Finally, this method is tested against conventional computational fluid dynamics (CFD) calculations for the flow in a lid-driven cavity. Excellent agreement between the two methods is found.
ON A COMBINED SHORT-RANGE AND LONG-RANGE INTERACTING EARTHQUAKE MODEL
Authors: ELGAZZAR A. S. , AHMED E.
Published: May 2003

A self-organized critical earthquake model is proposed taking into account the effect of both short-range and long-range interactions. The model obeys both Gutenberg–Richter and Omori laws in addition to being more realistic than other models.
SYSTEM FOR AUTOMATIC DETECTION OF CLUSTERED MICROCALCIFICATIONS IN DIGITAL MAMMOGRAMS
Authors: BAZZANI A. , BOLLINI D. , BRANCACCIO R. , CAMPANINI R. , LANCONELLI N. , ROMANI D. , BEVILACQUA A.
Published: May 2003

In this paper, we investigate the performance of a Computer Aided Diagnosis (CAD) system for the detection of clustered microcalcifications in mammograms. Our detection algorithm consists of the combination of two different methods. The first, based on difference-image techniques and gaussianity statistical tests, finds out the most obvious signals. The second, is able to discover more subtle microcalcifications by exploiting a multiresolution analysis by means of the wavelet transform. We can separately tune the two methods, so that each one of them is able to detect signals with similar features. By combining signals coming out from the two parts through a logical OR operation, we can discover microcalcifications with different characteristics. Our algorithm yields a sensitivity of 91.4% with 0.4 false positive cluster per image on the 40 images of the Nijmegen database.
TESTING A HYPOTHESIS FOR THE EVOLUTION OF SEX
Authors: ÖRÇAL BORA , TÜZEL ERKAN , SEVİM VOLKAN , JAN NAEEM , ERZAN AYŞE
Published: May 2003

An asexual set of primitive bacteria is simulated with a bit-string Penna model with a Fermi function for survival. A recent hypothesis by Jan, Stauffer, and Moseley on the evolution of sex from asexual cells as a strategy for trying to escape the effects of deleterious mutations is checked. This strategy is found to provide a successful scenario for the evolution of a stable macroscopic sexual population.
MOLECULAR-DYNAMICS SIMULATION OF STEPPED Si(100) SURFACE
Authors: KATIRCIOĞLU ŞENAY , SALMAN SAED A. , ERKOÇ ŞAKIR
Published: May 2003

We have investigated the relaxation of single and double layer stepped Si(100) surfaces depending on working cell size and heat treatment by MD simulation based on LJ–AT empirical potential energy function. It is found that smooth relaxation can be satisfied for both types of stepped Si(100) surfaces by continuous MD runs. The dependence of relaxation on the size of working cell is found only for single layer stepped Si(100) surface. The total potential energy calculation by MD shows that double layer Si(100) surface is more stable than the single layer stepped Si(100) surface.
MOLECULAR-DYNAMICS SIMULATIONS OF NICKEL CLUSTERS
Authors: ERKOÇ ŞAKIR , GÜNEŞ BILAL , GÜNEŞ PERVIN
Published: May 2003

Structural stability and energetics of nickel clusters, NiN (N =3-459), have been investigated by molecular-dynamics simulations. A size-dependent empirical model potential energy function has been used in the simulations. Stable structures of the microclusters with sizes N = 3-55 and clusters generated from fcc crystal structure with sizes N = 79-459 have been determined by molecular-dynamics simulations. It has been found that the five-fold symmetry appears on the surface of the spherical clusters. The average coordination number shows a size-dependent characteristic, on the other hand the average nearest-neighbor distance does not show a size-dependence.
COMPUTER SIMULATION OF THE UV OH BAND SPECTRUM
Authors: de IZARRA C.
Published: May 2003

This paper is devoted to the computer simulation of OH band at 306.357 nm (transition A2Σ, ν = 0 → X2Π, ν′ = 0) for both a given rotational temperature and an optical apparatus function profile, when existing data at a reference temperature are known. This kind of numerical simulation may be of great interest for spectroscopic temperature determinations in flames and hot gases containing the OH radical, by direct comparison of experimental data with a simulated spectrum.
MOLECULAR-DYNAMICS SIMULATION OF RADIATION DAMAGE ON COPPER CLUSTERS
Authors: ERKOÇ ŞAKIR
Published: May 2003

The effect of radiation damage on copper clusters has been investigated by performing molecular-dynamics simulation using empirical potential energy function for interaction between copper atoms. The external radiation is modeled by giving extra kinetic energy in the range of 5–50 eV to initially chosen atom in the cluster. It has been found that the atom having extra kinetic energy dissociates independently from the amount of given energy in the studied range.
SMART AND WRONG VERSUS CORRECT MONTE CARLO SIMULATIONS OF KAWASAKI–ISING MODEL
Authors: SHIDA CLAUDIO S. , HENRIQUES VERA B.
Published: May 2003

We present simple arguments and numerical evidence in order to show that "efficient" Kawasaki exchange does not lead to Boltzmann equilibrium distributions.
A TWO-LEVEL, DISCRETE PARTICLE APPROACH FOR LARGE-SCALE SIMULATION OF COLLOIDAL AGGREGATES
Authors: DZWINEL WITOLD , YUEN DAVID A.
Published: May 2003

Most numerical techniques employed for aggregation simulation are based on equilibrium growth assumption and Smoluchowski theory. We present a new two-level discrete particle model, which can be employed in simulating large colloidal clusters in highly nonequilibrium physical conditions. We consider the system of colloidal particles (CP) interacting via conservative CP–CP repulsive-attractive two-body forces, which is initially mixed in a dissipative solvent. In order to obtain a high-resolution picture of colloidal dynamics, we employ around 20 million particles consisting of two kinds of particles. For bridging the spatio-temporal scales between nanoscale colloidal and the solvent particles (SP), the solvent is modeled by dissipative particle dynamics (DPD) fluid. We focus on the systems size for which the CP–SP interactions can also be described by the DPD forces. Unlike previous numerical techniques, the two-level particle model can display much more realistic physics, thus allowing for the simulation of aggregation for various types of colloids and solvent liquids in a broad range of conditions. We show that not only large and static clusters but also the initial stages of aggregation evolution can be better scrutinized. The large-scale simulation results obtained in two-dimensions show that the mean cluster size grows with time t according to the power law tκ. Because of the time-dependence of growth mechanism, the value of κ necessarily must change. We have first κ = 1 with a value of 1 achieved asymptotically with time. We can also discern intermediate-scale structures. We emphasize that the method developed here can be easily extended to algorithms dealing with multi-level hierarchy and multiphase fluid dynamics.
REINVESTIGATION OF SELF-ORGANIZING SOCIAL HIERARCHIES
Authors: SOUSA A. O. , STAUFFER DIETRICH
Published: May 2003

The Monte Carlo simulation of Bonabeau, Theraulaz and Deneubourg is reinvestigated. The phase transition between an egalitarian and an hierarchical society found was due to an instability when the past fights are not forgotten fast enough. Their model is also changed to include pair-specific memories, which again favor egalitarian societies.
DECOMPOSITION OFC60MOLECULES ON Si(100)(2 × 1) SURFACE
Authors: ERKOÇ ŞAKIR , KATIRCIOĞLU ŞENAY
Published: May 2003

We have investigated the decomposition of C60molecules with low and high coverages on Si(100)(2×1) surface at elevated temperatures. We also investigated the decomposition of an isolated C60molecule. We employed molecular-dynamics simulation using a model potential. It has been found that C60decomposes on Si(100) surface after 1000 K in the case of low coverage (0.11), however in high coverage case (0.67), C60molecules decompose after 900 K. On the other hand, isolated C60molecule decomposes after 7500 K, interestingly it shows a phase change from 3D to 2D at higher temperatures.
EFFECT OF LOCAL CORRELATIONS ON s-WAVE SYMMETRY SUPERCONDUCTIVITY
Authors: SCHMIDT A. A. , RODRÍGUEZ-NÚÑEZ J. J.
Published: May 2003

We derive superconducting mean-field equations for an attractive interaction V in the s-wave channel when local Coulomb interactions are taken into account for any value of U. Results show that Coulomb repulsion diminishes the critical temperature Tc to the order parameter Δ(T) for values of U ≥ |V|. Furthermore, the results are also quite sensible to band filling. In the presence of local correlations, 2Δ(0)/Tc differs from the BCS ratio since Coulomb interactions affect much more superconducting critical temperature Tc than superconducting order parameter Δ(T). Some consequences of our findings for experimental measurements in narrow band systems are discussed.
GENERAL ANALYTIC DENSITY DISTRIBUTION FUNCTION FOR ATOMS
Authors: ERKOÇ ŞAKIR
Published: May 2003

A general analytic function is proposed to represent the radial distribution of charge density for atoms. The proposed function fits perfectly to the radial charge density generated numerically by local spin density functional method for atoms from He to Kr.
DYNAMICALLY SPANNING THE LENGTH SCALES FROM THE QUANTUM TO THE CONTINUUM
Authors: ABRAHAM FARID F.
Published: May 2003

A challenging paradigm in computational sciences is the coupling of the continuum, the atomistic, and the quantum descriptions of matter for a unified dynamic treatment of a single physical problem. We described the recent achievement of such a goal. We have spanned the length scales in a concerted simulation comprising the finite-element method, classical molecular dynamics, quantum tight-binding dynamics and seamless bridges between these different physical descriptions. We illustrate and validate the methodology for rapid crack propagation in silicon.
THE TEMPERATURE IN DISSIPATIVE PARTICLE DYNAMICS
Authors: DEN OTTER W. K. , CLARKE J. H. R.
Published: May 2003

The two most popular algorithms for dissipative particle dynamics (DPD) are critically discussed. In earlier papers, the Groot–Warren algorithm with λ = 1/2 was recommended over the original Hoogerbrugge–Koelman scheme on the basis of a marked difference in their equilibrium temperatures. We show, however, that both schemes produce identical trajectories. Expressions for the temperatures of an ideal gas and a liquid as functions of the simulation parameters are presented. Our findings indicate that the current DPD algorithms do not possess a unique temperature because of the way in which the dissipative and random forces are included. The commonly used large time steps are beyond the stability limits of the conservative force field integrator.
SCALING IN A CONTINUOUS TIME MODEL FOR BIOLOGICAL AGING
Authors: DE ALMEIDA R. M. C. , THOMAS G. L.
Published: May 2003

In this paper, we consider a generalization to the asexual version of Penna model for biological aging, where we take a continuous time limit. The genotype associated to each individual is an interval of real numbers over which Dirac δ-functions are defined, representing genetically programmed diseases to be switched on at defined ages of the individual life. We discuss two different continuous limits for the evolution equation and two different mutation protocols, to be implemented during reproduction. Exact stationary solutions are obtained and scaling properties are discussed.
A NEW MODIFIED RUNGE–KUTTA–NYSTRÖM METHOD WITH PHASE-LAG OF ORDER INFINITY FOR THE NUMERICAL SOLUTION OF THE SCHRÖDINGER EQUATION AND RELATED PROBLEMS
Authors: SIMOS T. E. , AGUIAR JESUS VIGO
Published: May 2003

In this paper, a new approach for developing efficient Runge–Kutta–Nyström methods is introduced. This new approach is based on the requirement of annihilation of the phase-lag (i.e., the phase-lag is of order infinity) and on a modification of Runge–Kutta–Nyström methods. Based on this approach, a new modified Runge–Kutta–Nyström fourth algebraic order method is developed for the numerical solution of Schrödinger equation and related problems. The new method has phase-lag of order infinity and extended interval of periodicity. Numerical illustrations on the radial Schrödinger equation and related problems with oscillating solutions indicate that the new method is more efficient than older ones.
ENERGETICS OF ARSENIC TERMINATED GaAs(001) SURFACES
Authors: ERKOÇ ŞAKIR , KÖKTEN HATICE
Published: May 2003

We have investigated systematically the energetics of arsenic terminated GaAs(001) surfaces. Available surface models proposed in the literature have been considered, and relaxation and surface energies of each model have been calculated using an empirical many-body potential energy function comprising two and three-body atomic interactions.
GENERALIZATION TO SQUARE LATTICE OF SZNAJD SOCIOPHYSICS MODEL
Authors: STAUFFER D. , SOUSA A. O. , DE OLIVEIRA S. MOSS
Published: May 2003

The one-dimensional Sznajd model "united we stand, divided well fall" is generalized to the square lattice with similar fixed points. Only in two of the variants are the distribution of equilibration times roughly log-normal. Probabilistic generalizations destroyed the "dictatorial" fixed points.
FROM CARBON NANOTUBES TO CARBON NANORODS
Authors: ERKOÇ ŞAKIR
Published: May 2003

The structural properties of single and multi-wall carbon nanotubes and the formation of carbon nanorods from multi-wall carbon nanotubes have been investigated by performing molecular-dynamics computer simulations. Calculations have been realized by using an empirical many-body potential energy function for carbon. It has been found that carbon nanorod formation takes place with smallest possible multi-wall nanotubes under heat treatment. On the other hand, it has been also found that single-wall carbon nanotubes are stronger than the multi-wall nanotubes against heat treatment.
SELF-ORGANIZED CRITICALITY IN AN ASEXUAL MODEL?
Authors: CHISHOLM COLIN , JAN NAEEM , GIBBS PETER , ERZAN AYŞE
Published: May 2003

Recent work has shown that the distribution of steady state mutations for an asexual "bacteria" model has features similar to that seen in Self-Organized Critical (SOC) sandpile model of Bak et al. We investigate this coincidence further and search for "self-organized critical" state for bacteria but instead find that the SOC sandpile critical behavior is very sensitive; critical behavior is destroyed with small perturbations effectively when the absorption of sand is introduced. It is only in the limit when the length of the genome of the bacteria tends to infinity that SOC properties are recovered for the asexual model.
POWER LAW DISTRIBUTION IN EDUCATION: UNIVERSITY ENTRANCE EXAMINATION
Authors: GUPTA HARI M. , CAMPANHA JOSÉ R. , PRADO FERNANDO D.
Published: May 2003

We studied the statistical distribution of candidate's performance which is measured through their marks in university entrance examination (Vestibular) of UNESP (Universidade Estadual Paulista) for years 1998, 1999, and 2000. All students are divided in three groups: Physical, Biological and Humanities. We paid special attention to the examination of Portuguese language which is common for all and examinations for the particular area. We observed long ubiquitous power law tails in Physical and Biological sciences. This indicate the presence of strong positive feedback in sciences. We are able to explain completely these statistical distributions through Gradually Truncated Power law distributions which we developed recently to explain statistical behavior of financial market. The statistical distribution in case of Portuguese language and humanities is close to normal distribution. We discuss the possible reason for this peculiar behavior.
SELF-ORGANIZED PERCOLATION AND CRITICAL SALES FLUCTUATIONS
Authors: WEISBUCH GÉRARD , SOLOMON SORIN
Published: May 2003

There is a discrepancy between the standard view of equilibrium through price adjustment in economics and the observation of large fluctuations in stock markets. We study here a simple model where agents decisions not only depend upon their individual preferences but also upon information obtained from their neighbors in a social network. The model shows that information diffusion coupled to the adjustment process drives the system to criticality with large fluctuations rather than converging smoothly to equilibrium.
LOW LUMINOSITY SUSY SEARCHES AT LARGE tanβ IN CMS
Authors: DŽELALIJA M. , ANTUNOVIĆ Ž. , ABDULLIN S. , CHARLES F.
Published: May 2003

We evaluate the maximal reach of the CMS detector for the discovery of squarks and gluinos at large tan β=35 in [Formula: see text] final states during the initial low luminosity phase of LHC. For an integrated luminosity of 1 fb-1 a signal should be observed if squarks and gluinos have masses not exceeding ≈1.3 TeV.
SEEKING TeV SCALE QUANTUM GRAVITY AT AN eγ COLLIDER
Authors: GHOSH DILIP KUMAR , POULOSE P. , SRIDHAR K.
Published: May 2003

Theories with large extra compact dimensions predict exciting phenomenological consequences at the TeV scale. Such theories can, consequently, be tested/verified in experiments at future colliders like the Next Linear Collider (NLC). In this letter, we study the production of the spin-2 Kaluza–Klein excitations in NLC operating in the eγ mode. Results for unpolarized and polarized cases are presented and it is shown that it is possible to use this process to test these theories to values of the effective string scale between 1–7 TeV.
GENERALIZED 2-D BF MODEL QUANTIZED IN THE AXIAL GAUGE
Authors: LEITGEB R. , RANT J. , SCHWEDA M. , ZERROUKI H.
Published: May 2003

We discuss the uv finiteness of the two-dimensional BF model coupled to topological matter quantized in the axial gauge. This noncovariant gauge fixing avoids the ir problem in the two-dimensional space–time. The BF model together with the matter coupling is obtained by dimensional reduction of the ordinary three-dimensional BF model. This procedure furnishes the usual linear vector supersymmetry and an additional scalar supersymmetry. The whole symmetry content of the model allows one to apply the standard algebraic renormalization procedure which we use to prove that this model is uv finite and anomaly free to all orders of perturbation theory.
RADON TRANSFORMATION OF THE WIGNER OPERATOR FOR TWO-MODE CORRELATED SYSTEM IN GENERALIZED ENTANGLED STATE REPRESENTATION
Authors: FAN HONG-YI , YU GUI-CHUAN
Published: May 2003

We introduce a generalized entangled state |η,λ1,λ2>, which spans a complete and orthonormal representation. Using the technique of integration within an ordered product of operators we prove that the projection operator |η,λ1,λ2><η,λ1,λ2| is just the Radon transformation of the entangled Wigner operator. The inverse Radon transformation is also derived and the tomography theory for two-mode correlated system is established.
MOMENTUM EXPANSION OF MASSIVE TWO-LOOP FEYNMAN GRAPHS AROUND A FINITE VALUE
Authors: GHINCULOV ADRIAN , YAO YORK-PENG
Published: May 2003

We give an algorithm for obtaining expansions of massive two-loop Feynman graphs in powers of the external momentum around a finite, nonzero value of the momentum. Such momentum derivatives are encountered while evaluating physical radiative corrections, such as in wave function renormalization constants. This is based on our general two-loop formalism to reduce massive two-loop graphs with renormalizable interactions into a standard set of special functions. After the algebraic reduction, the final results are obtained by numerical integration. We apply the expansion algorithm to treat the top-dependent corrections of [Formula: see text] to the b-quark self-energy and extract its momentum expansion on-shell.
Q-BALL FORMATION IN THE MSSM WITH EXPLICIT CP VIOLATION
Authors: BOZ M. , DEMIR D. A. , PAK N. K.
Published: May 2003

Q-balls generically exist in the supersymmetric extensions of the standard model. Taking into account the additional sources of CP violation, which are naturally accommodated by the supersymmetric models, it is shown that the Q-ball matter depends additionally on individual CP phases, whereas mass per unit charge in the Q-ball depends only on the relative phases. There are regions of the parameter space where there is no stable Q-ball solution in the CP-conserving limit whereas finite CP phases induce a stable Q-ball.
TIME REVERSAL IN STOCHASTIC PROCESSES AND THE DIRAC EQUATION II: COUPLING TO AN EXTERNAL ELECTROMAGNETIC FIELD
Authors: MCKEON D. G. C. , ORD G. N.
Published: May 2003

We extend a stochastic model underlying the Dirac equation in (1+1) dimensions to include the electromagnetic field. The mechanism which produces quantum behavior is the allowed Brownian motion in both time and space. The necessary complexification of the spinor field is achieved by allowing the movement of a particle from one sublattice in (1+1) dimensions to another orthogonal sublattice in a manner dictated by the external "electromagnetic" field. The Dirac equation is obtained without recourse to a formal analytic continuation in either the time variable or the probabilities involved.