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75
Some thermodynamic aspects of black holes and singularities”, eprint grqc/9601006
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Spin Glasses
 in Physics of Novel Materials (World Scientific
, 1999
"... An introduction and overview is given of the theory of spin glasses and its application. 1 ..."
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An introduction and overview is given of the theory of spin glasses and its application. 1
Parallelization of the twodimensional Ising Model on a Cluster of IBM RISC System/6000 Workstations
"... Using the PVM programming environment for parallel applications, we have parallelized a simulation of the twodimensional Ising Model on a cluster of IBM RISC System/6000 1 workstations connected by a Token Ring (16Mb/sec) and by Serial Optical Channels (220 Mb/sec) via a NSC 2 DX Router. The p ..."
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Using the PVM programming environment for parallel applications, we have parallelized a simulation of the twodimensional Ising Model on a cluster of IBM RISC System/6000 1 workstations connected by a Token Ring (16Mb/sec) and by Serial Optical Channels (220 Mb/sec) via a NSC 2 DX Router. The parallelization is done by dividing the lattice into sublattices, each sublattice being associated with one workstation. On each sublattice, a Metropolis algorithm using Multispin Coding techniques is used to generate new configurations. We provide numerical results concerning the number of spin updates per second, speedups, and efficiencies for various numbers of processors and lattice sizes. Keywords. Statistical Physics; Ising Model; Workstation Cluster; Geometric Parallelization. 1 Introduction The goal of Theoretical Statistical Physics is a mathematical description of thermodynamic properties (e.g. of magnetism or phase transitions) of macroscopic bodies, commercing with a description ...
An Analysis of Various Elastic Net Algorithms
, 1995
"... The Elastic Net Algorithm (ENA) for solving the Traveling Salesman Problem is analyzed applying statistical mechanics. Using some general properties of the free energy function of stochastic Hopfield Neural Networks, we argue why Simic's derivation of the ENA from a Hopfield network is incor ..."
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The Elastic Net Algorithm (ENA) for solving the Traveling Salesman Problem is analyzed applying statistical mechanics. Using some general properties of the free energy function of stochastic Hopfield Neural Networks, we argue why Simic's derivation of the ENA from a Hopfield network is incorrect. However, like the HopfieldLagrange method, the ENA may be considered a specific dynamic penalty method , where, in this case, the weights of the various penalty terms decrease during execution of the algorithm. This view on the ENA corresponds to the view resulting from the theory on `deformable templates', where the term stochastic penalty method seems to be most appropriate. Next, the ENA is analyzed both on the level of the energy function as well as on the level of the motion equations. It will be proven and shown experimentally, why a nonfeasible solution is sometimes found. It can be caused either by a too rapid lowering of the temperature parameter (which is avoidable), or...
A statistical superfield and its observable consequences
 Int. J. Mod. Phys. A
, 1997
"... A new kind of fundamental superfield is proposed, with an Isinglike Euclidean action. Near the Planck energy it undergoes its first stage of symmetrybreaking, and the ordered phase is assumed to support specific kinds of topological defects. This picture leads to a lowenergy Lagrangian which is s ..."
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A new kind of fundamental superfield is proposed, with an Isinglike Euclidean action. Near the Planck energy it undergoes its first stage of symmetrybreaking, and the ordered phase is assumed to support specific kinds of topological defects. This picture leads to a lowenergy Lagrangian which is similar to that of standard physics, but there are interesting and observable differences. For example, the cosmological constant vanishes, fermions have an extra coupling to gravity, the gravitational interaction of Wbosons is modified, and Higgs bosons have an unconventional equation of motion.
Spindynamics simulations of the threedimensional XY model: structure factor and transport properties, Phys
 Rev. B
, 1999
"... We present extensive MonteCarlo spin dynamics simulations of the classical XY model in three dimensions on a simple cubic lattice with periodic boundary conditions. A recently developed efficient integration algorithm for the equations of motion is used, which allows a substantial improvement of st ..."
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We present extensive MonteCarlo spin dynamics simulations of the classical XY model in three dimensions on a simple cubic lattice with periodic boundary conditions. A recently developed efficient integration algorithm for the equations of motion is used, which allows a substantial improvement of statistics and large integration times. We find spin wave peaks in a wide range around the critical point and spin diffusion for all temperatures. At the critical point we find evidence for a violation of dynamic scaling in the sense that independent components of the dynamic structure factor S(q,ω) require different dynamic exponents in order to obtain scaling. Below the critical point we investigate the dispersion relation of the spin waves and the linewidths of S(q,ω) and find agreement with mode coupling theory. Apart from strong spin wave peaks we observe additional peaks in S(q,ω) which can be attributed to twospin wave interactions. The overall lineshapes are also discussed and compared to mode coupling predictions. Finally, we present first results for the transport coefficient D(q,ω) of the outofplane magnetization component at the critical point, which is related to the thermal conductivity of 4 He near the superfluidnormal transition.
Boulevard of Broken Symmetries
"... Effective theories of quantum liquids (superconductors and superfluids of various types) are derived starting from microscopic models at the absolute zero of temperature. Special care is taken to assure Galilei invariance. The effective theories are employed to investigate the quantum numbers carrie ..."
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Effective theories of quantum liquids (superconductors and superfluids of various types) are derived starting from microscopic models at the absolute zero of temperature. Special care is taken to assure Galilei invariance. The effective theories are employed to investigate the quantum numbers carried by the topological defects present in the phases with spontaneously broken symmetries. Due to topological terms induced by quantum fluctuations, these numbers are sometimes found to be fractional. The zerotemperature effective theories are further used to study the quantum critical behavior of the liquidtoinsulator transition which these systems undergo as the applied magnetic field, the amount of impurities, or the charge carrier density varies. The classical, finitetemperature phase transitions to the normal state are discussed from the point of view of dual theories, where the defects of the original formulation become the elementary
Anomalous thermal escape in Josephson systems perturbed by microwaves
, 2004
"... We investigate, by experiments and numerical simulations, thermal activation processes of Josephson tunnel junctions in the presence of microwave radiation. When the applied signal resonates with the Josephson plasma frequency oscillations, the switching current may become multivalued temperature r ..."
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We investigate, by experiments and numerical simulations, thermal activation processes of Josephson tunnel junctions in the presence of microwave radiation. When the applied signal resonates with the Josephson plasma frequency oscillations, the switching current may become multivalued temperature ranges both below and above the the classical to quantum crossover temperature. Switching current distributions are obtained both experimentally and numerically at temperatures both near and far above the quantum crossover temperature. Plots of the switching currents traced as a function of the applied signal frequency show very good agreement with a simple anharmonic theory for Josephson resonance frequency as a function of bias current. Throughout, experimental results and direct numerical simulations of the corresponding thermally driven classical Josephson junction model show very good agreement. 1
Equation of state for spin systems with Goldstone bosons: The 3d O(4
, 2005
"... We propose an improved parametric form for the equation of state of threedimensional O(N) spin systems. The proposed form is a series expansion with two sets of terms, which contribute (mainly) separately to the description of the high and lowtemperature regions of the phase diagram. Our goal is a ..."
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We propose an improved parametric form for the equation of state of threedimensional O(N) spin systems. The proposed form is a series expansion with two sets of terms, which contribute (mainly) separately to the description of the high and lowtemperature regions of the phase diagram. Our goal is a better description of the lowtemperature phase at zero magnetic field (i.e. the coexistence line), characterized by singularities induced by Goldstone modes. We test our proposed form by comparison with existing Monte Carlo data for the N = 4 case, which is of interest in studies of the QCD phase transition and for which the Goldstonemode effects are quite pronounced. We find that the description of the numerical equation of state is indeed improved with respect to other fitting forms. In all cases considered we determine the coefficients nonperturbatively, from fits to the data. As a consequence, we are able to obtain a very precise characterization of the pseudocritical line for the model. 1
Correlations in twodimensional vortex liquids
 Physical Review B
, 1994
"... We report on a high temperature perturbation expansion study of the superfluiddensity spatial correlation function of a GinzburgLandaumodel superconducting film in a magnetic field. We have derived a closed form which expresses the contribution to the correlation function from each graph of the p ..."
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We report on a high temperature perturbation expansion study of the superfluiddensity spatial correlation function of a GinzburgLandaumodel superconducting film in a magnetic field. We have derived a closed form which expresses the contribution to the correlation function from each graph of the perturbation theory in terms of the number of Euler paths around appropriate subgraphs. We have enumerated all graphs appearing out to 10th order in the expansion and have evaluated their contributions to the correlation function. Low temperature correlation functions, obtained using Padé approximants, are in good agreement with Monte Carlo simulation results and show that the vortexliquid becomes strongly correlated at temperatures well above the vortex solidification temperature.