Record 353

Title: ISDEP: Integrator of stochastic differential equations for plasmas

Author(s): Velasco, JL; Bustos, A; Castejon, F; Fernandez, LA; Martin-Mayor, V; Tarancon, A

Source: COMPUTER PHYSICS COMMUNICATIONS Volume:  183 Issue:  9 Pages: 1877-1883  DOI:  10.1016/j.cpc.2012.04.005  Published: SEP 2012

Abstract: In this paper we present a general description of the ISDEP code (Integrator of Stochastic Differential Equations for Plasmas) and a brief overview of its physical results and applications so far. ISDEP is a Monte Carlo code that calculates the distribution function of a minority population of ions in a magnetized plasma. It solves the ion equations of motion taking into account the complex 3D structure of fusion devices, the confining electromagnetic field and collisions with other plasma species. The Monte Carlo method used is based on the equivalence between the Fokker-Planck and Langevin equations. This allows ISDEP to run in distributed computing platforms without communication between nodes with almost linear scaling. This paper intends to be a general description and a reference paper in ISDEP. (C) 2012 Elsevier B.V. All rights reserved.

Accession Number: WOS:000306824200005

ISSN: 0010-4655

Record 352

Title: A transfer integral technique for solving a class of linear integral equations: Convergence and applications to DNA

Author(s): Alvarez-Estrada, RF ; Calvo, GF; Serrano, H

Source:  JOURNAL OF COMPUTATIONAL AND APPLIED MATHEMATICS Volume: 236  Issue:  15 Special Issue:  SI Pages:  3561-3571 DOI:10.1016/j.cam.2011.04.022  Published:  SEP 2012

Abstract: An eigenvalue problem, the convergence difficulties that arise and a mathematical solution are considered. The eigenvalue problem is motivated by simplified models for the dissociation equilibrium between double-stranded and single-stranded DNA chains induced by temperature (thermal denaturation), and by the application of the so-called transfer integral technique. Namely, we extend the Peyrard-Bishop model for DNA melting from the original one-dimensional model to a three-dimensional one, which gives rise to an eigenvalue problem defined by a linear integral equation whose kernel is not in L-2. For the one-dimensional model, the corresponding kernel is not in L-2 either, which is related to certain convergence difficulties noticed by previous researchers. Inspired by methods from quantum scattering theory, we transform the three-dimensional eigenvalue problem, obtaining a new L-2 kernel which has improved convergence properties. (c) 2011 Elsevier B.V. All rights reserved.

Accession Number: WOS:000305360000004

Conference Title: 15th International Congress on Computational and Applied Mathematics (ICCAM)

Conference Date: JUL 05-09, 2010

Conference Location: Leuven, BELGIUM

Conference Sponsors: Ghent Univ, Fac Sci

Conference Host: Univ Leuven

ISSN: 0377-0427

Record 351

Title: Neutron scattering experiments and simulations near the magnetic percolation threshold of FexZn1-xF2

Author(s): Alvarez, G; Aso, N; Belanger, DP; Durand, AM; Martin-Mayor, V; Motoya, K; Muro, Y

Source: PHYSICAL REVIEW B Volume: 86 Issue: 2  Article Number: 024416  DOI: 10.1103/PhysRevB.86.024416 Published: JUL 12 2012 

Abstract: The low temperature excitations in the anisotropic antiferromagnetic Fe1-xZnxF2 for x = 0.25 and 0.31, at and just above the magnetic percolation threshold concentration x(p) = 0.25, were measured using inelastic neutron scattering. The excitations were simulated for x = 0.31 using a localized, classical excitation model, which accounts well for the energies and relative intensities of the excitations observed in the scattering experiments.

Accession Number: WOS:000306309600004

ISSN: 1098-0121

Record 350

Title: Nonlinear relativistic single-electron Thomson scattering power spectrum for incoming laser of arbitrary intensity

Author(s): Alvarez-Estrada, RF; Pastor, I; Guasp, J; Castejon, F

Source:  PHYSICS OF PLASMAS Volume:  19 Issue:  6 Article Number: 062302  DOI:  10.1063/1.4725190 Published:  JUN 2012

Abstract: The classical nonlinear incoherent Thomson scattering power spectrum from a single relativistic electron with incoming laser radiation of any intensity, investigated numerically by the present authors in a previous publication, displayed both an approximate quadratic behavior in frequency and a redshift of the power spectrum for high intensity incoming radiation. The present work is devoted to justify, in a more general setup, those numerical findings. Those justifications are reinforced by extending suitably analytical approaches, as developed by other authors. Moreover, our analytical treatment exhibits differences between the Doppler-like frequencies for linear and circular polarization of the incoming radiation. Those differences depend nonlinearly on the laser intensity and on the electron initial velocity and do not appear to have been displayed by previous authors. Those Doppler-like frequencies and their differences are validated by new Monte Carlo computations beyond our previuos ones and reported here. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4725190]

Accession Number: WOS:000305835100016

ISSN: 1070-664X

Record 349

Title: Dynamic relaxation of a liquid cavity under amorphous boundary conditions

Author(s): Cavagna, A; Grigera, TS; Verrocchio, P

Source:  JOURNAL OF CHEMICAL PHYSICS Volume: 136  Issue: 20  Article Number:  204502 DOI:  10.1063/1.4720477 Published:  MAY 28 2012

Abstract: The growth of cooperatively rearranging regions was invoked long ago by Adam and Gibbs to explain the slowing down of glass-forming liquids. The lack of knowledge about the nature of the growing order, though, complicates the definition of an appropriate correlation function. One option is the point-to-set (PTS) correlation function, which measures the spatial span of the influence of amorphous boundary conditions on a confined system. By using a swap Monte Carlo algorithm we measure the equilibration time of a liquid droplet bounded by amorphous boundary conditions in a model glass-former at low temperature, and we show that the cavity relaxation time increases with the size of the droplet, saturating to the bulk value when the droplet outgrows the point-to-set correlation length. This fact supports the idea that the point-to-set correlation length is the natural size of the cooperatively rearranging regions. On the other hand, the cavity relaxation time computed by a standard, nonswap dynamics, has the opposite behavior, showing a very steep increase when the cavity size is decreased. We try to reconcile this difference by discussing the possible hybridization between mode-coupling theory and activated processes, and by introducing a new kind of amorphous boundary conditions, inspired by the concept of frozen external state as an alternative to the commonly used frozen external configuration. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4720477]

Accession Number: WOS:000304818400034

ISSN: 0021-9606

Record 348

Title: Thermodynamic glass transition in a spin glass without time-reversal symmetry

Author(s): Banos, RA; Cruz, A; Fernandez, LA; Gil-Narvion, JM; Gordillo-Guerrero, A; Guidetti, M; Iniguez, D; Maiorano, A; Marinari, E; Martin-Mayor, V; Monforte-Garcia, J; Sudupe, AM; Navarro, D; Parisi, G; Perez-Gaviro, S; Ruiz-Lorenzo, JJ; Schifano, SF; Seoane, B; Tarancon, A; Tellez, P; Tripiccione, R; Yllanes, D

Source: PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Volume: 109 Issue: 17 Pages: 6452-6456 DOI: 10.1073/PNAS.1203295109 Published: APR 24 2012

Abstract: Spin glasses are a longstanding model for the sluggish dynamics that appear at the glass transition. However, spin glasses differ from structural glasses in a crucial feature: they enjoy a time reversal symmetry. This symmetry can be broken by applying an external magnetic field, but embarrassingly little is known about the critical behavior of a spin glass in a field. In this context, the space dimension is crucial. Simulations are easier to interpret in a large number of dimensions, but one must work below the upper critical dimension (i.e., in d < 6) in order for results to have relevance for experiments. Here we show conclusive evidence for the presence of a phase transition in a four-dimensional spin glass in a field. Two ingredients were crucial for this achievement: massive numerical simulations were carried out on the Janus special-purpose computer, and a new and powerful finite-size scaling method.

ISSN: 0027-8424

Record 346

Title: Equilibrium Fluid-Solid Coexistence of Hard Spheres

Author(s): Fernandez, LA; Martin-Mayor, V; Seoane, B; Verrocchio, P

Source: PHYSICAL REVIEW LETTERS Volume: 108 Issue: 16 Article Number: 165701 DOI: 10.1103/PhysRevLett.108.165701 Published: APR 16 2012

Abstract: We present a tethered Monte Carlo simulation of the crystallization of hard spheres. Our method boosts the traditional umbrella sampling to the point of making practical the study of constrained Gibbs' free energies depending on several crystalline order parameters. We obtain high-accuracy estimates of the fluid-crystal coexistence pressure for up to 2916 particles enough to accommodate fluid-solid interfaces). We are able to extrapolate to infinite volume the coexistence pressure [P-co = 11.5727(10)k(B)T/sigma(3)] and the interfacial free energy [gamma({100}) = 0.636(11)k(B)T/sigma(2)].

ISSN:

Record 345

Title: Classical and Quantum Models in Non-Equilibrium Statistical Mechanics: Moment Methods and Long-Time Approximations

Author(s): Alvarez-Estrada, RF

Source: ENTROPY  Volume: 14  Issue: 2  Pages: 291-322  DOI: 10.3390/e14020291  Published: FEB 2012  

Abstract: We consider non-equilibrium open statistical systems, subject to potentials and to external "heat baths" (hb) at thermal equilibrium at temperature T (either with ab initio dissipation or without it). Boltzmann's classical equilibrium distributions generate, as Gaussian weight functions in momenta, orthogonal polynomials in momenta (the position-independent Hermite polynomials H-n's). The moments of non-equilibrium classical distributions, implied by the H-n's, fulfill a hierarchy: for long times, the lowest moment dominates the evolution towards thermal equilibrium, either with dissipation or without it (but under certain approximation). We revisit that hierarchy, whose solution depends on operator continued fractions. We review our generalization of that moment method to classical closed many-particle interacting systems with neither a hb nor ab initio dissipation: with initial states describing thermal equilibrium at T at large distances but non-equilibrium at finite distances, the moment method yields, approximately, irreversible thermalization of the whole system at T, for long times. Generalizations to non-equilibrium quantum interacting systems meet additional difficulties. Three of them are: (i) equilibrium distributions (represented through Wigner functions) are neither Gaussian in momenta nor known in closed form; (ii) they may depend on dissipation; and (iii) the orthogonal polynomials in momenta generated by them depend also on positions. We generalize the moment method, dealing with (i), (ii) and (iii), to some non-equilibrium one-particle quantum interacting systems. Open problems are discussed briefly.

ISSN: 1099-4300

Record 344

Title: Sample-to-sample fluctuations of the overlap distributions in the three-dimensional Edwards-Anderson spin glass

Author(s): Banos, RA; Cruz, A; Fernandez, LA; Gil-Narvion, JM; Gordillo-Guerrero, A; Guidetti, M; Iniguez, D; Maiorano, A; Mantovani, F; Marinari, E; Martin-Mayor, V; Monforte-Garcia, J; Sudupe, AM; Navarro, D; Parisi, G; Perez-Gaviro, S; Ricci-Tersenghi, F; Ruiz-Lorenzo, JJ; Schifano, SF; Seoane, B; Tarancon, A; Tripiccione, R; Yllanes, D

Source: PHYSICAL REVIEW B Volume: 84 Issue: 17Article Number: 174209 DOI: 10.1103/PhysRevB.84.174209 Published: NOV 28 2011

Abstract: We study the sample-to-sample fluctuations of the overlap probability densities from large-scale equilibrium simulations of the three-dimensional Edwards-Anderson spin glass below the critical temperature. Ultrametricity, stochastic stability, and overlap equivalence impose constraints on the moments of the overlap probability densities that can be tested against numerical data. We found small deviations from the Ghirlanda-Guerra predictions, which get smaller as system size increases. We also focus on the shape of the overlap distribution, comparing the numerical data to a mean-field-like prediction in which finite-size effects are taken into account by substituting delta functions with broad peaks.

ISSN:

Record 343

Title: Constrained macromolecular chains at thermal equilibrium: A quantum-mechanical approach

Author(s): Alvarez-Estrada, RF; Calvo, GF

Source: EUROPEAN PHYSICAL JOURNAL-SPECIAL TOPICS Volume:  200 Issue: 1  Pages: 225-258  DOI: 10.1140/epjst/e2011-01526-8 Published: NOV 2011 

Abstract: Many approaches to three-dimensional constrained macromolecular chains at thermal equilibrium, at about room temperatures, are based upon constrained Classical Hamiltonian Dynamics (cCHDa). Quantum-mechanical approaches (QMa) have also been treated by different researchers for decades. QMa address a fundamental issue (constraints versus the uncertainty principle) and are versatile: they also yield classical descriptions (which may not coincide with those from cCHDa, although they may agree for certain relevant quantities). Open issues include whether QMa have enough practical consequences which differ from and/or improve those from cCHDa. We shall treat cCHDa briefly and deal with QMa, by outlining old approaches and focusing on recent ones. In QMa, we start with Hamiltonians for N(a parts per thousand << 1) non-relativistic quantum particles, interacting among themselves through potentials which include strong vibrational ones (constraining bond lengths and bond angles) and other weaker interactions. We get (by means of variational calculations) effective three-dimensional constrained quantum partition functions at equilibrium (Z (Q) ) and Hamiltonians (H (Q) ) for single-stranded (ss) macromolecules (freely-jointed, freely-rotating, open or closed) and for double-stranded (ds) open macromolecules. Due to crucial cancellations, we can neatly separate the constrained degrees of freedom (by getting the large constant vibrational zero-point energies associated to them) from the slow unconstrained angular variables (accounted for by Z (Q) and H (Q) ). In the classical limit, we obtain classical partition functions Z (c) from Z (Q) . The Z (c) 's are respectively different from the classical partition functions found starting from cCHDa for similar chains. Thus, they differ in determinants of the sort referred to in a companion tutorial article [1]: QMa determinants are simpler than cCHDa ones. For ss macromolecules, we compare several quantities (bond-bond correlations, squared end-to-end distances, etc) from QMa with the standard Gaussian model in Polymer Science: the comparisons display good consistencies (which are also met with cCHDa). For double-stranded DNA (dsDNA) macromolecules, the Z (c) 's from QMa have structures which enable one to study thermal denaturation.

ISSN:

Record 342

Title: Finite-size scaling analysis of the distributions of pseudo-critical temperatures in spin glasses

Author(s): Billoire, A; Fernandez, LA; Maiorano, A; Marinari, E; Martin-Mayor, V; Yllanes, D

Source: JOURNAL OF STATISTICAL MECHANICS-THEORY AND EXPERIMENT  Article Number: P10019  DOI: 10.1088/1742-5468/2011/10/P10019  Published: OCT 2011  

Abstract: Using the results of large scale numerical simulations we study the probability distribution of the pseudo-critical temperature for the three-dimensional Edwards-Anderson Ising spin glass and for the fully connected Sherrington-Kirkpatrick model. We find that the behaviour of our data is nicely described by straightforward finite-size scaling relations.

ISSN: 1742-5468

Record 341

Title: Critical behavior of the dilute antiferromagnet in a magnetic field

Author(s): Fernandez, LA; Martin-Mayor, V; Yllanes, D

Source: PHYSICAL REVIEW B  Volume: 84  Issue: 10  Article Number: 100408  DOI: 10.1103/PhysRevB.84.100408  Published: SEP 26 2011  

Abstract: We study the critical behavior of the diluted antiferromagnet in a field with the tethered Monte Carlo formalism. We compute the critical exponents (including the elusive hyperscaling violations exponent theta). Our results provide a comprehensive description of the phase transition and clarify the inconsistencies between previous experimental and theoretical work. To do so, our method addresses the usual problems of numerical work (large tunneling barriers and self-averaging violations).

ISSN: 1098-0121

Record 340

Title: Universal amplitude ratios in the Ising model in three dimensions

Author(s): Gordillo-Guerrero, A; Kenna, R; Ruiz-Lorenzo, JJ

Source: JOURNAL OF STATISTICAL MECHANICS-THEORY AND EXPERIMENT  Article Number: P09019  DOI: 10.1088/1742-5468/2011/09/P09019  Published: SEP 2011  

Abstract: We use a high-precision Monte Carlo simulation to determine the universal specific-heat amplitude ratio A(+)/A(-) in the three-dimensional Ising model via the impact angle phi of complex temperature zeros. We also measure the correlation-length critical exponent nu from finite-size scaling and the specific-heat exponent a through hyperscaling. Extrapolations to the thermodynamic limit yield phi = 59.2(1.0)degrees, A(+)/A(-) = 0.56(3), nu = 0.630 48(32) and alpha = 0.1086(10). These results are compatible with some previous estimates from a variety of sources and rule out recently conjectured exact values.

ISSN: 1742-5468

Record 339

Title: Quantum Brownian motion and generalizations of Hermite polynomials

Author(s): Alvarez-Estrada, RF

Source: JOURNAL OF COMPUTATIONAL AND APPLIED MATHEMATICS  Volume: 236  Issue: 1  Pages: 7-18  DOI: 10.1016/j.cam.2010.01.051  Published: AUG 1 2011  

Abstract: We introduce new families of orthogonal polynomials H(D,n), motivated by the non-equilibrium evolution of a quantum Brownian particle (qBp). The H(D,n)'S generalize non-trivially the standard Hermite polynomials, employed for classical Brownian motion. We treat several models (labelled by D) for a non-equilibrium qBp, by means of the Wigner function W, in the presence of a "heat bath" at thermal equilibrium, with and without ab initio friction. For long times (for a suitable class of initial conditions), the non-equilibrium Wigner function W should approach, in some sense, the (time-independent) equilibrium Wigner function W(eq,D), which describes the thermal equilibrium of the qBp with the "heat bath" and plays a central role. W(eq,D) is chosen to be the weight function which orthogonalizes the H(D,n)'S. New results on W(eq,D) and on the H(D,n)'S are reported. We justify the key role of the H(D,n)'S as follows. Using the H(D,n)'S, moments W(eq,D,n) and W(n) are introduced for W(eq,D) and W, respectively. At equilibrium, all moments W(eq,D,n) except the lowest one (W(eq,D,0)) vanish identically. Off-equilibrium, one expects that, for long times (for suitable initial conditions): (i) all non-equilibrium moments W(n) (except the lowest moment W(0)), will approach zero, while (ii) the lowest non-equilibrium moment W(0) will tend to W(eq,D,0)(not equal 0). To complete the justification, we outline how the approximate long-time non-equilibrium theories determined by W(0) for the different models (D) yield Smoluchowski equations and irreversible evolutions of the qBp towards thermal equilibrium. (C) 2010 Elsevier B.V. All rights reserved.

ISSN: 0377-0427

Record 338

Title: Ensemble equivalence in spin systems with short-range interactions

Author(s): Takahashi, K; Nishimori, H; Martin-Mayor, V

Source: JOURNAL OF STATISTICAL MECHANICS-THEORY AND EXPERIMENT  Article Number: P08024  DOI: 10.1088/1742-5468/2011/08/P08024  Published: AUG 2011  

Abstract: We study the problem of ensemble equivalence in spin systems with short-range interactions under the existence of a first-order phase transition. The spherical model with nonlinear nearest-neighbour interactions is solved exactly for both canonical and microcanonical ensembles. The result reveals apparent ensemble inequivalence at the first-order transition point in the sense that the microcanonical entropy is non-concave as a function of the energy and consequently the specific heat is negative. In order to resolve the paradox, we show that an unconventional saddle point should be chosen in the microcanonical calculation that represents a phase separation. The XY model with nonlinear interactions is also studied by microcanonical Monte Carlo simulations in two dimensions to see how this model behaves in comparison with the spherical model.

ISSN: 1742-5468

Record 337

Title: Kinetic simulations of fast ions in stellarators

Author(s): Bustos, A; Castejon, F; Osakabe, M; Fernandez, LA; Martin-Mayor, V; Guasp, J; Fontdecaba, JM

Source: NUCLEAR FUSION  Volume: 51 Issue:  8 Article Number:083040 DOI: 10.1088/0029-5515/51/8/083040 Published: AUG 2011

Abstract: The steady-state distribution function of neutral beam injection (NBI) fast ions is calculated numerically for the LHD and TJ-II stellarators using the code ISDEP (Integrator of Stochastic Differential Equations for Plasmas). ISDEP is an orbit code that solves the guiding centre motion of fast ions using Cartesian coordinates in position space, allowing arbitrary magnetic configurations and the re-entering of particles in the plasma. It takes into account collisions of fast ions with thermal ions and electrons using the Boozer and Kuo-Petravic collision operator. The steady-state distribution function is computed with a time integral following Green's function formalism for a time-independent source. The rotation profiles of the fast ions are also estimated, thus computing their contribution to the total plasma current. In addition, energy slowing down time and escape distribution are studied in detail for both devices.

ISSN:

Record 336

Title: Tethered Monte Carlo: Managing Rugged Free-Energy Landscapes with a Helmholtz-Potential Formalism

Author(s): Martin-Mayor, V (Martin-Mayor, V.); Seoane, B (Seoane, B.); Yllanes, D (Yllanes, D.)

Source: JOURNAL OF STATISTICAL PHYSICS Volume: 144 Issue: 3 Pages: 554-596 DOI: 10.1007/s10955-011-0261-4 Published: AUG 2011

Abstract: Tethering methods allow us to perform Monte Carlo simulations in ensembles with conserved quantities. Specifically, one couples a reservoir to the physical magnitude of interest, and studies the statistical ensemble where the total magnitude (system+reservoir) is conserved. The reservoir is actually integrated out, which leaves us with a fluctuation-dissipation formalism that allows us to recover the appropriate Helmholtz effective potential with great accuracy. These methods are demonstrating a remarkable flexibility. In fact, we illustrate two very different applications: hard spheres crystallization and the phase transition of the diluted antiferromagnet in a field (the physical realization of the random field Ising model). The tethered approach holds the promise to transform cartoon drawings of corrugated free-energy landscapes into real computations. Besides, it reduces the algorithmic dynamic slowing-down, probably because the conservation law holds non-locally.

ISSN:

Record 335

Title: Three-dimensional Heisenberg spin glass under a weak random anisotropy

Author(s): Martin-Mayor, V; Perez-Gaviro, S

Source: PHYSICAL REVIEW B Volume: 84 Issue: 2 Article Number: 024419 DOI: 10.1103/PhysRevB.84.024419 Published: JUL 14 2011

Abstract: We perform a finite-size scaling study of the three-dimensional Heisenberg spin glass in the presence of weak random anisotropic interactions, up to lattice sizes L = 32. Anisotropies have a major impact on the phase transition. The chiral-glass susceptibility does not diverge due to a large anomalous dimension. It follows that the anisotropic spin glass belongs to a Universality Class different from the isotropic model, which questions the applicability of the chirality scenario.

ISSN:

Record 334

Title: A Phase Solubility Study on the Chiral Discrimination of Ibuprofen by beta-Cyclodextrin Complexe

Author(s): Crupi, V; Guella, G; Majolino, D; Mancini, I; Rossi, B; Stancanelli, R; Venuti, V; Verrocchio, P; Viliani, G

Source: FOOD BIOPHYSICS Volume: 6 Issue: 2 Special Issue: SI Pages: 267-273 DOI: 10.1007/s11483-011-9211-6 Published: JUN 2011

Abstract: The effects of chiral discrimination in inclusion complexes formed by native beta-cyclodextrin and its substituted form (namely methyl-beta-cyclodextrin) with racemate or pure enantiomers of the non-steroidal anti-inflammatory drug ibuprofen have been investigated in water. Stability constants and complexation efficiency have been determined for these host-guest systems with a 1: 1 molar ratio from phase solubility profiles, showing that in aqueous solution, methylated cyclodextrin is a better complex agent than native cyclodextrin, with more enhanced effects for the (R)-enantiomer. These results have been validated using NMR technique. In particular, (1)H NMR spectra in D(2)O show a splitting of the signals for the methyl group and the aromatic protons close to the asymmetric centre of the racemate ibuprofen included in cyclodextrin cavity.

ISSN:

Record 333

Title: Monte Carlo approach to Thomson scattering in relativistic fusion plasmas with allowance for ultraintense laser radiation

Author(s): Pastor, I; Guasp, J; Alvarez-Estrada, RF; Castejon, F

Source: NUCLEAR FUSION Volume: 51 Issue: 4 Article Number: 043011 DOI: 10.1088/0029-5515/51/4/043011 Published: APR 2011

Abstract: Thomson scattering (TS) of electromagnetic radiation by relativistic electrons is of great interest as an electron distribution diagnostics in high temperature plasma devices. A Monte Carlo approach to TS simulation has been implemented. It is based on first principles, i.e. on the integration of electron trajectories and on the computation and averaging of radiated Lienard-Wiechert fields. The treatment is relativistic. Nonlinear effects, arising from ultraintense lasers (both linear and circular polarizations having been considered) and/or from highly energetic electrons, are included from the outset. TS spectra from isotropic monoenergetic electron distribution functions and from the relativistic Maxwellian distribution have been extensively studied, both for low-intensity and for ultraintense incoming laser. A particularly simple quadratic dependence of S(2)(omega) on omega has been found in the case of monoenergetic distributions. Numerical results are checked against known analytical results for low-intensity lasers, and found to be in agreement with them. For high-intensity lasers, new effects on scattered spectra arise, like an overall red-shift or the appearance of higher harmonics. The numerical methods developed in this work are general enough to deal with anisotropic and/or non-Maxwellian distribution functions.

ISSN:

Record 332

Title: On the high-density expansion for Euclidean random matrices

Author(s): Grigera, TS; Martin-Mayor, V; Parisi, G; Urbani, P; Verrocchio, P

Source: JOURNAL OF STATISTICAL MECHANICS-THEORY AND EXPERIMENT Article Number: P02015 DOI: 10.1088/1742-5468/2011/02/P02015 Published: FEB 2011

Abstract: Diagrammatic techniques to compute perturbatively the spectral properties of Euclidean random matrices (ERM) in the high-density regime are introduced and discussed in detail. Such techniques are developed in two alternative and very different formulations of the mathematical problem and are shown to give identical results up to second order in the perturbative expansion. One method, based on writing the so-called resolvent function as a Taylor series, allows us to group the diagrams into a small number of topological classes, providing a simple way to determine the infrared (small momenta) behaviour of the theory up to third order, which is of interest for the comparison with experiments. The other method, which reformulates the problem as a field theory, can instead be used to study the infrared behaviour at any perturbative order.

ISSN:

Record 331

Author(s): Alvarez-Estrada, RF

Editor(s): Garrido, PL; Marro, J; DeLosSantos, F

Title: Classical systems: moments, continued fractions, long-time approximations and irreversibility

Source: NON-EQUILIBRIUM STATISTICAL PHYSICS TODAY, 1332: 261-262 2011

Book series title: AIP Conference Proceedings

Conference Title: 11th Granada Seminar on Computational and Statistical Physics

Conference Date: SEP 13-17, 2010

Conference Location: La Herradura, SPAIN

ISSN: 0094-243X

ISBN: 978-0-7354-0887-6

DOI: 10.1063/1.3569525

Record 330

Author(s): Fontana, A; Verrocchio, P

Title: Twelfth International Workshop on Complex Systems: Andalo (Trento) Italy. 15-18 March 2010 INTRODUCTION

Source: PHILOSOPHICAL MAGAZINE, 91 (13-15): 1765-1766 Sp. Iss. SI 2011

ISSN: 1478-6435

DOI: 10.1080/14786435.2010.574419

Record 329

Author(s): Crupi, V; Guella, G; Majolino, D; Mancini, I; Paciaroni, A; Rossi, B; Venuti, V; Verrocchio, P; Viliani, G

Title: Effect of the chiral discrimination on the vibrational properties of (R)-, (S)- and (R, S)-ibuprofen/methyl-beta-cyclodextrin inclusion complexes

Source: PHILOSOPHICAL MAGAZINE, 91 (13-15): 1776-1785 Sp. Iss. SI 2011

Abstract: The effects of chiral discrimination of ibuprofen (IBP) on the complexation process with methyl-beta-cyclodextrin (Me-beta-CD) were investigated in the solid phase by FTIR-ATR spectroscopy and numerical simulation. The inclusion mechanism was deduced from the temperature-dependent analysis of the vibrational spectra, in the C=O stretching region, of complexes formed by Me-beta-CD with the two enantiomeric and the racemic forms of IBP. The mechanism turned out to be enthalpy-driven, with IBP enantiomers giving rise to more stable inclusion complexes with respect to the racemate.

ISSN: 1478-6435

DOI: 10.1080/14786435.2010.512575

Record 328

Author(s): Leuzzi, L; Parisi, G; Ricci-Tersenghi, F; Ruiz-Lorenzo, JJ

Title: Bond diluted Levy spin-glass model and a new finite-size scaling method to determine a phase transition

Source: PHILOSOPHICAL MAGAZINE, 91 (13-15): 1917-1925 Sp. Iss. SI 2011

Abstract: A spin-glass transition occurs both within and outside of the limits of validity of mean-field theory for a diluted one-dimensional chain of Ising spins where exchange bonds occur with a probability decaying as the inverse power of the distance. Varying the power in this long-range model corresponds, in a one-to-one relationship, to changing the dimension in spin-glass short-range models. Using different finite-size scaling methods, evidence for a spin-glass transition is also found for systems whose equivalent dimension is below the upper critical dimension at zero magnetic field. The application of a new method is discussed, which can be exported to systems in a magnetic field.

ISSN: 1478-6435

DOI: 10.1080/14786435.2010.534741

Record 327

Author(s): Pastor, I ; Guasp, J; Alvarez-Estrada, RF; Castejon, F

Title: Monte Carlo approach to Thomson scattering in relativistic fusion plasmas with allowance for ultraintense laser radiation

Source: NUCLEAR FUSION, 51 (4): Art. No. 043011 APR 2011

Abstract: Thomson scattering (TS) of electromagnetic radiation by relativistic electrons is of great interest as an electron distribution diagnostics in high temperature plasma devices. A Monte Carlo approach to TS simulation has been implemented. It is based on first principles, i.e. on the integration of electron trajectories and on the computation and averaging of radiated Lienard-Wiechert fields. The treatment is relativistic. Nonlinear effects, arising from ultraintense lasers (both linear and circular polarizations having been considered) and/or from highly energetic electrons, are included from the outset. TS spectra from isotropic monoenergetic electron distribution functions and from the relativistic Maxwellian distribution have been extensively studied, both for low-intensity and for ultraintense incoming laser. A particularly simple quadratic dependence of S-2(omega) on omega has been found in the case of monoenergetic distributions. Numerical results are checked against known analytical results for low-intensity lasers, and found to be in agreement with them. For high-intensity lasers, new effects on scattered spectra arise, like an overall red-shift or the appearance of higher harmonics. The numerical methods developed in this work are general enough to deal with anisotropic and/or non-Maxwellian distribution functions.

ISSN: 0029-5515

Article Number: 043011

DOI: 10.1088/0029-5515/51/4/043011

Record 326

Author(s): Grigera, TS; Martin-Mayor, V; Parisi, G; Urbani, P; Verrocchio, P

Title: On the high-density expansion for Euclidean random matrices

Source: JOURNAL OF STATISTICAL MECHANICS-THEORY AND EXPERIMENT: Art. No. P02015 FEB 2011

Abstract: Diagrammatic techniques to compute perturbatively the spectral properties of Euclidean random matrices (ERM) in the high-density regime are introduced and discussed in detail. Such techniques are developed in two alternative and very different formulations of the mathematical problem and are shown to give identical results up to second order in the perturbative expansion. One method, based on writing the so-called resolvent function as a Taylor series, allows us to group the diagrams into a small number of topological classes, providing a simple way to determine the infrared (small momenta) behaviour of the theory up to third order, which is of interest for the comparison with experiments. The other method, which reformulates the problem as a field theory, can instead be used to study the infrared behaviour at any perturbative order.

ISSN: 1742-5468

Article Number: P02015

DOI: 10.1088/1742-5468/2011/02/P02015

Record 325

Author(s): Cavagna, A; Grigera, TS; Verrocchio, P

Title: Numerical simulations of liquids with amorphous boundary conditions

Source: JOURNAL OF STATISTICAL MECHANICS-THEORY AND EXPERIMENT: Art. No. P10001 OCT 2010

Abstract: It has recently become clear that simulations under amorphous boundary conditions (ABCs) can provide valuable information on the dynamics and thermodynamics of disordered systems with no obvious order parameter. In particular, they allow the detection of a correlation length that is not measurable with standard correlation functions. Here we explain what exactly is meant by ABCs, discuss their relation with point-to-set correlations and briefly describe some recent results obtained with this technique.

ISSN: 1742-5468

Article Number: P10001

DOI: 10.1088/1742-5468/2010/10/P10001

Record 324

Author(s): Bustos, A; Castejon, F; Fernandez, LA; Garcia, J; Martin-Mayor, V; Reynolds, JM; Seki, R; Velasco, JL

Title: Impact of 3D features on ion collisional transport in ITER

Source: NUCLEAR FUSION, 50 (12): Art. No. 125007 DEC 2010

Abstract: The influence of magnetic ripple on ion collisional transport in ITER (Shimada et al 2007 Progress in the ITER Physics Basis: chapter 1. Overview and summary Nucl. Fusion 47 S1) is calculated using the Monte Carlo orbit code ISDEP (Castejon et al 2007 Plasma Phys. Control. Fusion 49 753). The ripple is introduced as a perturbation to the 2D equilibrium configuration of the device, given by the HELENA code (Huysmans 1991 CP90 Conf. on Computational Physics (Amsterdam, The Netherlands, 1990) (Singapore: World Scientific) p 371), obtaining a 3D configuration. Since the intensity of the ripple can change depending on the design of the test blanket modules that will be introduced in ITER, a scan of the ripple intensity has been performed to study the changes in confinement properties. The main result is that an increase in the perturbation leads to a degradation of the confinement due to an increase in the radial fluxes. The selective ion losses cause modifications in the ion distribution function. In this work most of the computing time has been provided by a new Citizen Supercomputer called Ibercivis.

ISSN: 0029-5515

Article Number: 125007

DOI: 10.1088/0029-5515/50/12/125007

Record 323

Author(s): Castejon, F; Gomez-Iglesias, A; Bustos, A; Campos, I; Cappa, CE; Cardenas-Montes, M; Fernandez, LA; Flores, LA; Guasp, J; Huedo, E; Lopez-Bruna, D; Llorente, IM; Martin-Mayor, V; Mayo, R; Montero, RS; Montes, E; Reynolds, JM; Rodriguez, M; Rubio-Montero, AJ; Tarancon, A; Tereshchenko, M; Vazquez-Poletti, JL; Velasco, JL

Editor(s): Garcia, VH; Barreira, G; Espert, IB; Gomes, J

Title: Grid Computing for Fusion Research

Source: IBERGRID: 3RD IBERIAN GRID INFRASTRUCTURE CONFERENCE PROCEEDINGS: 291-302 2009

Conference Title: 3rd Iberian Grid Infrastructure Conference (IBERGRID)

Conference Date: MAY 20-22, 2009

Conference Location: Valencia, SPAIN

Abstract: This work deals with the problems solved in fusion research by means of grid computing. The computing necessities for fusion are discussed and the applications that have been ported to grid as well as their main physical results are described. The range of plasma physics research covered by this set of tools is analysed and the future of grid computing for fusion research is discussed. The possibility of establishing complex workflows between grid and high performance computers (HPC) applications has been also explored.

ISBN: 978-84-9745-406-3

Record 322

Author(s): Banos, RA ; Cruz, A; Fernandez, LA; Gil-Narvion, JM; Gordillo-Guerrero, A; Guidetti, M; Maiorano, A; Mantovani, F; Marinari, E; Martin-Mayor, V; Monforte-Garcia, J; Sudupe, AM; Navarro, D; Parisi, G; Perez-Gaviro, S; Ruiz-Lorenzo, JJ; Schifano, SF; Seoane, B; Tarancon, A; Tripiccione, R; Yllanes, D

Title: Static versus Dynamic Heterogeneities in the D=3 Edwards-Anderson-Ising Spin Glass

Source: PHYSICAL REVIEW LETTERS, 105 (17): Art. No. 177202 OCT 20 2010

Abstract: We numerically study the aging properties of the dynamical heterogeneities in the Ising spin glass. We find that a phase transition takes place during the aging process. Statics-dynamics correspondence implies that systems of finite size in equilibrium have static heterogeneities that obey finite-size scaling, thus signaling an analogous phase transition in the thermodynamical limit. We compute the critical exponents and the transition point in the equilibrium setting, and use them to show that aging in dynamic heterogeneities can be described by a finite-time scaling ansatz, with potential implications for experimental work.

ISSN: 0031-9007

Article Number: 177202

DOI: 10.1103/PhysRevLett.105.177202

Record 321

Author(s): Mattarelli, M; Gasperi, G; Montagna, M; Verrocchio, P

Title: Transparency and long-ranged fluctuations: The case of glass ceramics

Source: PHYSICAL REVIEW B, 82 (9): Art. No. 094204 SEP 29 2010

Abstract: Glass ceramics with nanosized crystallites shows an unexpected high transparency, which is not accounted for by the Rayleigh theory of light scattering. Simple analytic arguments ascribe this large transparency to large spatial correlations in the number distribution of the nanocrystallites. Introducing a two-dimensional lattice model that mimics the nucleation and the coarsening phenomena leading to their formation, we show that the extent of such correlations is determined by the spatially limited diffusion of the particles that form the crystallites.

ISSN: 1098-0121

Article Number: 094204

DOI: 10.1103/PhysRevB.82.094204

Record 320

Author(s): Banos, RA; Cruz, A; Fernandez, LA; Gil-Narvion, JM; Gordillo-Guerrero, A; Guidetti, M; Maiorano, A; Mantovani, F; Marinari, E; Martin-Mayor, V; Monforte-Garcia, J; Sudupe, AM; Navarro, D; Parisi, G; Perez-Gaviro, S; Ruiz-Lorenzo, JJ; Schifano, SF; Seoane, B; Tarancon, A; Tripiccione, R; Yllanes, D

Title: Nature of the spin-glass phase at experimental length scales

Source: JOURNAL OF STATISTICAL MECHANICS-THEORY AND EXPERIMENT: Art. No. P06026 JUN 2010

Abstract: We present a massive equilibrium simulation of the three-dimensional Ising spin glass at low temperatures. The Janus special-purpose computer has allowed us to equilibrate, using parallel tempering, L = 32 lattices down to T approximate to 0.64T(c). We demonstrate the relevance of equilibrium finite size simulations to understanding experimental non-equilibrium spin glasses in the thermodynamical limit by establishing a time-length dictionary. We conclude that non-equilibrium experiments performed on a timescale of 1 h can be matched with equilibrium results on L approximate to 110 lattices. A detailed investigation of the probability distribution functions of the spin and link overlap, as well as of their correlation functions, shows that Replica Symmetry Breaking is the appropriate theoretical framework for the physically relevant length scales. Besides, we improve over existing methodologies in ensuring equilibration in parallel tempering simulations.

ISSN: 1742-5468

Article Number: P06026

DOI: 10.1088/1742-5468/2010/06/P06026

Record 319

Author(s): Fernandez, LA; Martin-Mayor, V; Seoane, B; Verrocchio, P

Title: Separation and fractionation of order and disorder in highly polydisperse systems

Source: PHYSICAL REVIEW E, 82 (2): Art. No. 021501 Part 1 AUG 5 2010

Abstract: We study a polydisperse soft-spheres model for colloids by means of microcanonical Monte Carlo simulations. We consider a polydispersity as high as 24%. Although solidification occurs, neither a crystal nor an amorphous state are thermodynamically stable. A finite size scaling analysis reveals that in the thermodynamic limit: (a) the fluid-solid transition is rather a crystal-amorphous phase-separation, (b) such phase-separation is preceded by the dynamic glass transition, and (c) small and big particles arrange themselves in the two phases according to a complex pattern not predicted by any fractionation scenario.

ISSN: 1539-3755

Article Number: 021501

DOI: 10.1103/PhysRevE.82.021501

Record 318

Author(s): Cammarota, C ; Cavagna, A ; Giardina, I; Gradenigo, G; Grigera, TS; Parisi, G; Verrocchio, P

Title: Phase-Separation Perspective on Dynamic Heterogeneities in Glass-Forming Liquids

Source: PHYSICAL REVIEW LETTERS, 105 (5): Art. No. 055703 JUL 29 2010

Abstract: We study dynamic heterogeneities in a model glass former whose overlap with a reference configuration is constrained to a fixed value. We find that the system phase separates into regions of small and large overlap, indicating that a nonzero surface tension plays an important role in the formation of dynamical heterogeneities. We calculate an appropriate thermodynamic potential and find evidence of a Maxwell construction consistent with a spinodal decomposition of two phases. Our results suggest that even in standard, unconstrained systems dynamic heterogeneities are the expression of an ephemeral phase-separating regime ruled by a finite surface tension.

ISSN: 0031-9007

Article Number: 055703

DOI: 10.1103/PhysRevLett.105.055703

Record 317

Author(s): Crupi, V; Majolino, D; Venuti, V; Guella, G; Mancini, I; Rossi, B; Verrocchio, P; Viliani, G; Stancanelli, R

Title: Temperature Effect on the Vibrational Dynamics of Cyclodextrin Inclusion Complexes: Investigation by FTIR-ATR Spectroscopy and Numerical Simulation

Source: JOURNAL OF PHYSICAL CHEMISTRY A, 114 (25): 6811-6817 JUL 1 2010

Abstract: The vibrational dynamics of solid inclusion complexes of the nonsteroidal anti-inflammatory drug Ibuprofen (IBP) with beta-cyclodextrin (beta-CD) and methyl-beta-cyclodextrin (Me-beta-CD) has been investigated by using attenuated total reflection-Fourier transform infrared FTIR-ATR spectroscopy, in order to monitor the changes induced, as a consequence of complexation, on the vibrational spectrum of IBP, in the wavenumber range 600-4000 cm(-1). Quantum chemical calculations were performed on monomeric and dimeric structures of IBP, derived from symmetric hydrogen bonding of the two carboxylic groups, in order to unambiguously assign some characteristic IR bands in the IBP spectrum. The evolution in temperature from 250 to 340 K of the C=O stretching vibration, described by a best-fit procedure, allowed us to extract the thermodynamic parameter Delta H associated to the binding of IBP with beta CDs in the solid phase. By comparing these results, Me-beta-CD has been shown to be the most effective carrier for IBP.

ISSN: 1089-5639

DOI: 10.1021/jp101888g

Record 316

Author(s): Alvarez-Estrada, RF

Title: Expressing complementarity and the x-p commutation relation through further quantum inequalities

Source: EUROPEAN JOURNAL OF PHYSICS, 31 (2): 407-418 MAR 2010

Abstract: Complementarity and the commutation relation of position (x) and momentum (p) imply much more than the fundamental x-p uncertainty inequality. Here, we display some further consequences of the former that could have certain pedagogical interest and, so, contribute to the teaching of quantum mechanics. Inspired by an elementary derivation of the x-p uncertainty inequality, based upon a positive quadratic polynomial, we explore one possible extension, via quartic polynomials and simple algebra and integrations. Our analysis, aimed at providing some further pedagogic expression of genuine quantum behaviours, yields other quantum inequalities for expectation values, expressed through suitable discriminants associated with quartic algebraic equations, which differ from (and are not a strict consequence of) the x-p uncertainty inequality. Those quantum inequalities are confirmed, and genuine non-classical behaviours are exhibited, for simple cases: a harmonic oscillator, a hydrogenic atom and free Gaussian wave packets. The physical interest of the expectation values involved in the quantum inequalities and of the latter is discussed, in the framework of quantum optics and squeezing phenomena.

ISSN: 0143-0807

DOI: 10.1088/0143-0807/31/2/019

Record 315

Author(s): Crupi, V; Guella, G; Majolino, D; Mancini, I; Rossi, B; Stancanelli, R; Venuti, V; Verrocchio, P; Viliani, G

Title: T-dependence of the vibrational dynamics of IBP/diME-beta-CD in solid state: A FT-IR spectral and quantum chemical study

Source: JOURNAL OF MOLECULAR STRUCTURE, 972 (1-3): 75-80 Sp. Iss. SI MAY 19 2010

Conference Title: 18th International Conference on Horizons in Hydrogen Bond Research

Conference Date: SEP 14-18, 2009

Conference Location: Paris, FRANCE

Conference Host: Lab Leon-Brillouin CEA-CNRS

Abstract: Solid inclusion complex of the non-steroidal anti-inflammatory drug Ibuprofen (IBP, (2-[4-(2-methylpropyl)phenyl]-propanoic acid) with (2,6-dimethyl)-beta-cyclodextrin (diME-beta-CD) has been investigated by Fourier transform infrared spectroscopy in attenuated total reflectance geometry (FTIR-ATR spectroscopy) and numerical simulation.
The complexation-induced changes in the FTIR-ATR spectrum of IBP have been interpreted by comparison with the theoretical vibrational wavenumbers and IR intensities of dimeric structures of IBP, derived from symmetric hydrogen bonding of the two carboxylic groups, computed by using Density Functional Theory (DFT) calculations.
From temperature-dependent studies, the enthalpy change Delta H associated with the binding of IBP with diME-beta-CD for 1:1 stoichiometry, in solid phase, has been estimated. (c) 2010 Elsevier B.V. All rights reserved.

ISSN: 0022-2860

DOI: 10.1016/j.molstruc.2010.01.055

Record 314

Author(s): Alvarez Banos, R.; Cruz, A; Fernandez, LA; Gordillo-Guerrero, A; Gil-Narvion, JM; Guidetti, M; Maiorano, A; Mantovani, F; Marinari, E; Martin-Mayor, V; Monforte-Garcia, J; Sudupe, AM; Navarro, D; Parisi, G; Perez-Gaviro, S; Ruiz-Lorenzo, JJ; Seoane, B; Schifano, SF; Tarancon, A; Tripiccione, R; Yllanes, D

Title: Critical behavior of three-dimensional disordered Potts models with many states

Source: JOURNAL OF STATISTICAL MECHANICS-THEORY AND EXPERIMENT: Art. No. P05002 MAY 2010

Abstract: We study the 3D disordered Potts model with p = 5 and 6. Our numerical simulations (that severely slow down for increasing p) detect a very clear spin glass phase transition. We evaluate the critical exponents and the critical value of the temperature, and we use known results at lower p values to discuss how they evolve for increasing p. We do not find any sign of the presence of a transition to a ferromagnetic regime.

ISSN: 1742-5468

Article Number: P05002

DOI: 10.1088/1742-5468/2010/05/P05002

Record 313

Author(s): Fernandez, LA; Martin-Mayor, V; Parisi, G; Seoane, B

Title: Spin glasses on the hypercube

Source: PHYSICAL REVIEW B, 81 (13): Art. No. 134403 APR 1 2010

Abstract: We present a mean field model for spin glasses with a natural notion of distance built in, namely, the Edwards-Anderson model on the diluted D-dimensional unit hypercube in the limit of large D. We show that finite D effects are strongly dependent on the connectivity, being much smaller for a fixed coordination number. We solve the nontrivial problem of generating these lattices. Afterward, we numerically study the nonequilibrium dynamics of the mean field spin glass. Our three main findings are the following: (i) the dynamics is ruled by an infinite number of time sectors, (ii) the aging dynamics consists of the growth of coherent domains with a nonvanishing surface-volume ratio, and (iii) the propagator in Fourier space follows the p(4) law. We study as well the finite D effects in the nonequilibrium dynamics, finding that a naive finite size scaling ansatz works surprisingly well.

ISSN: 1098-0121

Article Number: 134403

DOI: 10.1103/PhysRevB.81.134403

Record 312

Author(s): Cammarota, C; Cavagna, A; Gradenigo, G; Grigera, TS; Verrocchio, P

Title: Evidence for a spinodal limit of amorphous excitations in glassy systems

Source: JOURNAL OF STATISTICAL MECHANICS-THEORY AND EXPERIMENT: Art. No. L12002 DEC 2009

Abstract: What is the origin of the sharp slowdown displayed by glassy systems? Physical common sense suggests there must be a concomitant growing correlation length, but finding this length has been nontrivial. In random first-order theory, it is given by the size of amorphous excitations, which depends on a balance between their mutual interfacial energy and their configurational entropy. But how these excitations disappear when crossing over to the normal high temperature phase is unclear, chiefly due to lack of data about the surface tension. We measure the energy cost for creating amorphous excitations in a model glass-former, and discover that the surface tension vanishes at a well-defined spinodal energy, above which amorphous excitations cannot be sustained. This spinodal therefore marks the true onset of glassiness.

ISSN: 1742-5468

Article Number: L12002

DOI: 10.1088/1742-5468/2009/12/L12002

Record 311

Author(s): Belletti, F; Cotallo, M; Cruz, A; Fernandez, LA; Gordillo, A; Maiorano, A; Mantovani, F; Marinari, E; Martin-Mayor, V; Munoz-Sudupe, A; Navarro, D; Perez-Gaviro, S; Rossi, M; Ruiz-Lorenzo, JJ; Schifano, SF; Sciretti, D; Tarancon, A; Tripiccione, R; Velasco, JL

Editor(s): Bischof, C; Bucker, C; Gibbon, P; Joubert, G; Lippert, T; Mohr, B; Peters, F

Title: IANUS: Scientific Computing on an FPGA-Based Architecture

Source: PARALLEL COMPUTING: ARCHITECTURES, ALGORITHMS AND APPLICATIONS, 15: 553-560 2008

Book series title: Advances in Parallel Computing

Conference Title: International Parallel Computing Conference 2007

Conference Date: SEP 04-07, 2007

Conference Location: Aachen, FRANCE

Conference Host: RWTH Aachen Univ

Abstract: This paper describes the architecture and FPGA-based implementation of a massively parallel processing system (IANUS). carefully tailored to the computing requirements of a class of simulation problems relevant in statistical physics. we first discuss the system architecture in general and then focus on the configuration of the system for Monte Carlo simulation of spin-glass systems. This is the first large-scale application of the machine, on which IANUS achieves impressive performance. Our architecture uses large-scale on chip parallelism (similar or equal to 1000 computing cores on each processor) so it is a relevant example in the quickly expanding field of many-core architectures.

ISSN: 0927-5452

ISBN: 978-1-58603-796-3

Record 310

Author(s): Leuzzi, L; Parisi, G; Ricci-Tersenghi, F; Ruiz-Lorenzo, JJ

Title: Ising Spin-Glass Transition in a Magnetic Field Outside the Limit of Validity of Mean-Field Theory

Source: PHYSICAL REVIEW LETTERS, 103 (26): Art. No. 267201 DEC 31 2009

Abstract: The spin-glass transition in a magnetic field is studied both in and out of the limit of validity of mean-field theory on a diluted one dimensional chain of Ising spins where exchange bonds occur with a probability decaying as the inverse power of the distance. Varying the power in this long-range model corresponds, in a one-to-one relationship, to changing the dimension in spin-glass short-range models. Evidence for a spin-glass transition in a magnetic field is found also for systems whose equivalent dimension is below the upper critical dimension in a zero magnetic field.

ISSN: 0031-9007

Article Number: 267201

DOI: 10.1103/PhysRevLett.103.267201

Record 309

Author(s): Alvarez-Estrada, RF

Title: Brownian motion, quantum corrections and a generalization of the Hermite polynomials

Source: JOURNAL OF COMPUTATIONAL AND APPLIED MATHEMATICS, 233 (6): 1453-1461 Sp. Iss. SI JAN 15 2010

Conference Title: International Conference on Special Functions, Information Theory and Mathematical Physics

Conference Date: SEP 17-19, 2007

Conference Location: Granada, SPAIN

Abstract: The nonequilibrium evolution of a Brownian particle, in the presence of a "heat bath" at thermal equilibrium (without imposing any friction mechanism from the outset), is considered. Using a suitable family of orthogonal polynomials, moments of the nonequilibrium probability distribution for the Brownian particle are introduced, which fulfill a recurrence relation. We review the case of classical Brownian motion, in which the orthogonal polynomials are the Hermite ones and the recurrence relation is a three-term one. After having performed a long-time approximation in the recurrence relation, the approximate nonequilibrium theory yields irreversible evolution of the Brownian particle towards thermal equilibrium with the "heat bath". For quantum Brownian motion, which is the main subject of the present work, we restrict ourselves to include the first quantum correction: this leads us to introduce a new family of orthogonal polynomials which generalize the Hermite ones. Some general properties of the new family are established. The recurrence relation for the new moments of the nonequilibrium distribution, including the first quantum correction, turns out to be also a three-term one, which justifies the new family of polynomials. A long-time approximation on the new three-term recurrence relation describes irreversible evolution towards equilibrium for the new moment of lowest order. The standard Smoluchowski equations for the lowest order moments are recovered consistently, both classically and quantum-mechanically. (C) 2009 Elsevier B.V. All rights reserved.

ISSN: 0377-0427

DOI: 10.1016/j.cam.2009.02.061

Record 308

Author(s): Fernandez, LA; Gordillo-Guerrero, A; Martin-Mayor, V; Ruiz-Lorenzo, JJ

Title: Microcanonical finite-size scaling in second-order phase transitions with diverging specific heat

Source: PHYSICAL REVIEW E, 80 (5): Art. No. 051105 Part 1 NOV 2009

Abstract: A microcanonical finite-size ansatz in terms of quantities measurable in a finite lattice allows extending phenomenological renormalization (the so-called quotients method) to the microcanonical ensemble. The ansatz is tested numerically in two models where the canonical specific heat diverges at criticality, thus implying Fisher renormalization of the critical exponents: the three-dimensional ferromagnetic Ising model and the two-dimensional four-state Potts model (where large logarithmic corrections are known to occur in the canonical ensemble). A recently proposed microcanonical cluster method allows simulating systems as large as L=1024 (Potts) or L=128 (Ising). The quotients method provides accurate determinations of the anomalous dimension, eta, and of the (Fisher-renormalized) thermal nu exponent. While in the Ising model the numerical agreement with our theoretical expectations is very good, in the Potts case, we need to carefully incorporate logarithmic corrections to the microcanonical ansatz in order to rationalize our data.

ISSN: 1539-3755

Article Number: 051105

DOI: 10.1103/PhysRevE.80.051105

Record 307

Author(s): Yuste, SB; Ruiz-Lorenzo, JJ; Lindenberg, K

Title: Coagulation reactions in low dimensions: Revisiting subdiffusive A plus A reactions in one dimension

Source: PHYSICAL REVIEW E, 80 (5): Art. No. 051114 Part 1 NOV 2009

Abstract: We present a theory for the coagulation reaction A+A -> A for particles moving subdiffusively in one dimension. Our theory is tested against numerical simulations of the concentration of A particles as a function of time ("anomalous kinetics") and of the interparticle distribution function as a function of interparticle distance and time. We find that the theory captures the correct behavior asymptotically and also at early times, and that it does so whether the particles are nearly diffusive or very subdiffusive. We find that, as in the normal diffusion problem, an interparticle gap responsible for the anomalous kinetics develops and grows with time. This corrects an earlier claim to the contrary on our part.

ISSN: 1539-3755

Article Number: 051114

DOI: 10.1103/PhysRevE.80.051114

Record 306

Author(s): Cammarota, C; Cavagna, A; Gradenigo, G; Grigera, TS; Verrocchio, P

Title: Numerical determination of the exponents controlling the relationship between time, length, and temperature in glass-forming liquids

Source: JOURNAL OF CHEMICAL PHYSICS, 131 (19): Art. No. 194901 NOV 21 2009

Abstract: There is a certain consensus that the very fast growth of the relaxation time tau occurring in glass-forming liquids on lowering the temperature must be due to the thermally activated rearrangement of correlated regions of growing size. Even though measuring the size of these regions has defied scientists for a while, there is indeed recent evidence of a growing correlation length xi in glass formers. If we use Arrhenius law and make the mild assumption that the free-energy barrier to rearrangement scales as some power Sigma of the size of the correlated regions, we obtain a relationship between time and length, T log tau similar to xi(Sigma). According to both the Adam-Gibbs and the random first order theory the correlation length grows as xi similar to(T-T-k)(-1/(d-theta)), even though the two theories disagree on the value of theta. Therefore, the super-Arrhenius growth of the relaxation time with the temperature is regulated by the two exponents Sigma and theta through the relationship T log tau similar to(T-T-k)(-Sigma/(d-theta)). Despite a few theoretical speculations, up to now there has been no experimental determination of these two exponents. Here we measure them numerically in a model glass former, finding Sigma=1 and theta=2. Surprisingly, even though the values we found disagree with most previous theoretical suggestions, they give back the well-known VFT law for the relaxation time, T log tau similar to(T-T-k)(-1).

ISSN: 0021-9606

Article Number: 194901

DOI: 10.1063/1.3257739

Record 305

Author(s): Gordillo-Guerrero, A; Kenna, R; Ruiz-Lorenzo, JJ

Title: Site-diluted Ising model in four dimensions

Source: PHYSICAL REVIEW E, 80 (3): Art. No. 031135 Part 1 SEP 2009

Abstract: In the literature, there are five distinct fragmented sets of analytic predictions for the scaling behavior at the phase transition in the random-site Ising model in four dimensions. Here, the scaling relations for logarithmic corrections are used to complete the scaling pictures for each set. A numerical approach is then used to confirm the leading scaling picture coming from these predictions and to discriminate between them at the level of logarithmic corrections.

ISSN: 1539-3755

Article Number: 031135

DOI: 10.1103/PhysRevE.80.031135

Record 304

Author(s): Martin-Mayor, V; Yllanes, D

Title: Cluster Monte Carlo algorithm with a conserved order parameter

Source: PHYSICAL REVIEW E, 80 (1): Art. No. 015701 Part 2 JUL 2009

Abstract: We propose a cluster simulation algorithm for statistical ensembles with fixed order parameter. We use the tethered ensemble, which features Helmholtz's effective potential rather than Gibbs's free energy and in which canonical averages are recovered with arbitrary accuracy. For the D=2,3 Ising model our method's critical slowing down is comparable to that of canonical cluster algorithms. Yet, we can do more than merely reproduce canonical values. As an example, we obtain a competitive value for the 3D Ising anomalous dimension from the maxima of the effective potential.

ISSN: 1539-3755

Article Number: 015701

DOI: 10.1103/PhysRevE.80.015701

Record 303

Author(s): Fernandez, LA; Martin-Mayor, V; Perez-Gaviro, S; Tarancon, A; Young, AP

Title: Phase transition in the three dimensional Heisenberg spin glass: Finite-size scaling analysis

Source: PHYSICAL REVIEW B, 80 (2): Art. No. 024422 JUL 2009

Abstract: We have investigated the phase transition in the Heisenberg spin glass using massive numerical simulations to study very large sizes, 48(3). A finite-size scaling analysis indicates that the data are compatible with the most economical scenario: a common transition temperature for spins and chiralities.

ISSN: 1098-0121

Article Number: 024422

DOI: 10.1103/PhysRevB.80.024422

Record 302

Author(s): Alvarez-Estrada, RF

Title: Nonequilibrium quantum anharmonic oscillator and scalar field: high temperature approximations

Source: ANNALEN DER PHYSIK, 18 (6): 391-409 JUN 2009

Abstract: We treat a relativistic quantum boson gas, described by a scalar quantum field, with quartic self-interaction (phi(4)) in three spatial dimensions: we review the known equilibrium case and present new proposals off-equilibrium. For high temperature and large spatial scales, the behaviour of the gas at equilibrium simplifies nonperturbatively (equilibrium dimensional reduction or EDR): its thermodynamics is described by classical statistical mechanics with some quantum field effects. By assumption, the initial state of the gas off-equilibrium includes interactions and inhomogeneities and is not far from thermal equilibrium. We employ real-time generating functionals and obtain the free nonequilibrium correlators at non-zero temperature. The nonequilibrium quantum gas appears to simplify nonperturbatively in the regime of high temperature and large temporal and spatial scales (nonequilibrium dimensional reduction or NEDR), its dynamics being described by classical statistical mechanics with some quantum field effects. We outline the renormalization of the phi(4) theory, the nonequilibrium statistical mechanics of a quantum anharmonic oscillator and the high temperature simplifications, all of which provide very useful hints for NEDR in the field case. Our main proposals are NEDR and the associated new (renormalized) real-time nonequilibrium generating functionals for the phi(4) theory. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

ISSN: 0003-3804

DOI: 10.1002/andp.200810355

Record 301

Author(s): Belletti, F; Cruz, A; Fernandez, LA; Gordillo-Guerrero, A; Guidetti, M; Maiorano, A; Mantovani, F; Marinari, E; Martin-Mayor, V; Monforte, J; Sudupe, AM; Navarro, D; Parisi, G; Perez-Gaviro, S; Ruiz-Lorenzo, JJ; Schifano, SF; Sciretti, D; Tarancon, A; Tripiccione, R; Yllanes, D

Title: An In-Depth View of the Microscopic Dynamics of Ising Spin Glasses at Fixed Temperature

Source: JOURNAL OF STATISTICAL PHYSICS, 135 (5-6): 1121-1158 Sp. Iss. SI JUN 2009

Abstract: Using the special-purpose computer Janus, we follow the nonequilibrium dynamics of the Ising spin glass in three dimensions for eleven orders of magnitude. The use of integral estimators for the coherence and correlation lengths allows us to study dynamic heterogeneities and the presence of a replicon mode and to obtain safe bounds on the Edwards-Anderson order parameter below the critical temperature. We obtain good agreement with experimental determinations of the temperature-dependent decay exponents for the thermoremanent magnetization. This magnitude is observed to scale with the much harder to measure coherence length, a potentially useful result for experimentalists. The exponents for energy relaxation display a linear dependence on temperature and reasonable extrapolations to the critical point. We conclude examining the time growth of the coherence length, with a comparison of critical and activated dynamics.

ISSN: 0022-4715

DOI: 10.1007/s10955-009-9727-z

Record 300

Author(s): Alvarez-Estrada, RF

Title: Nonequilibrium quantum meson gas: Dimensional reduction

Source: EUROPEAN PHYSICAL JOURNAL A, 41 (1): 53-70 JUL 2009

Abstract: A nonequilibrium quantum gas of interacting relativistic effective mesons, ressembling qualitatively those produced in a heavy-ion collision, is described by a scalar phi(4) quantum field in (1+3)-dimensional Minkowski space. For high temperature and large temporal and spatial scales, we justify that classical statistical mechanics including quantum renormalization effects describe approximately the gas: nonequilibrium dimensional reduction (NEDR). As a source of hints, we treat the gas at equilibrium in real-time formalism and obtain simplifications for high temperature and large spatial scales, thereby extending a useful equilibrium dimensional reduction known for the imaginary-time formalism. By assumption, the nonequilibrium initial state of the gas, not far from thermal equilibrium, includes interactions and inhomogeneities. We use nonequilibrium real-time generating functionals and correlators at nonzero temperature. In the NEDR regime, our arguments yield: 1) renormalized correlators simplify, 2) the perturbative series for those simplified correlators can be resummed into a new nonequilibrium generating functional, Z'(r,dr), which is super-renormalizable and includes renormalization effects (large position-dependent thermal self-energies and effective couplings). Z'(r,dr) could enable to study nonperturbatively changes in the phase structures of the field, by proceeding from the nonequilibrium quantum regime to the NEDR one.

ISSN: 1434-6001

DOI: 10.1140/epja/i2009-10785-6

Record 299

Author(s): Fernandez, LA; Martin-Mayor, V; Yllanes, D

Title: Erratum to: Tethered Monte Carlo: Computing the effective potential without critical slowing down (vol 807, pg 424, 2009)

Source: NUCLEAR PHYSICS B, 818 (3): 212-212 SEP 11 2009

ISSN: 0550-3213

DOI: 10.1016/j.nuclphysb.2009.04.022

Record 298

Author(s): Fernandez, LA; Martin-Mayor, V

Title: Mean-value identities as an opportunity for Monte Carlo error reduction

Source: PHYSICAL REVIEW E, 79 (5): Art. No. 051109 Part 1 MAY 2009

Abstract: In the Monte Carlo simulation of both lattice field theories and of models of statistical mechanics, identities verified by exact mean values, such as Schwinger-Dyson equations, Guerra relations, Callen identities, etc., provide well-known and sensitive tests of thermalization bias as well as checks of pseudo-random-number generators. We point out that they can be further exploited as control variates to reduce statistical errors. The strategy is general, very simple, and almost costless in CPU time. The method is demonstrated in the two-dimensional Ising model at criticality, where the CPU gain factor lies between 2 and 4.

ISSN: 1539-3755

Article Number: 051109

DOI: 10.1103/PhysRevE.79.051109

Record 297

Author(s): Sokolov, IM; Yuste, SB; Ruiz-Lorenzo, JJ; Lindenberg, K

Title: Mean field model of coagulation and annihilation reactions in a medium of quenched traps: Subdiffusion

Source: PHYSICAL REVIEW E, 79 (5): Art. No. 051113 Part 1 MAY 2009

Abstract: We present a mean field model for coagulation (A+A -> A) and annihilation (A+A -> 0) reactions on lattices of traps with a distribution of depths reflected in a distribution of mean escape times. The escape time from each trap is exponentially distributed about the mean for that trap, and the distribution of mean escape times is a power law. Even in the absence of reactions, the distribution of particles over sites changes with time as particles are caught in ever deeper traps, that is, the distribution exhibits aging. Our main goal is to explore whether the reactions lead to further (time dependent) changes in this distribution.

ISSN: 1539-3755

Article Number: 051113

DOI: 10.1103/PhysRevE.79.051113

Record 296

Author(s): Cruz, A; Fernandez, LA; Gordillo-Guerrero, A; Guidetti, M; Maiorano, A; Mantovani, F; Marinari, E; Martin-Mayor, V; Sudupe, AM; Navarro, D; Parisi, G; Perez-Gaviro, S; Ruiz-Lorenzo, JJ; Schifano, SF; Sciretti, D; Tarancon, A; Tripiccione, R; Velasco, JL; Yllanes, D; Young, AP

Title: Spin glass phase in the four-state three-dimensional Potts model

Source: PHYSICAL REVIEW B, 79 (18): Art. No. 184408 MAY 2009

Abstract: We perform numerical simulations, including parallel tempering, a four-state Potts glass model with binary random quenched couplings using the JANUS application-oriented computer. We find and characterize a glassy transition, estimating the critical temperature and the value of the critical exponents. Nevertheless, the extrapolation to infinite volume is hampered by strong scaling corrections. We show that there is no ferromagnetic transition in a large temperature range around the glassy critical temperature. We also compare our results with those obtained recently on the "random permutation" Potts glass.

ISSN: 1098-0121

Article Number: 184408

DOI: 10.1103/PhysRevB.79.184408

Record 295

Author(s): Tsallis, C; Plastino, AR; Alvarez-Estrada, RF

Title: Escort mean values and the characterization of power-law-decaying probability densities

Source: JOURNAL OF MATHEMATICAL PHYSICS, 50 (4): Art. No. 043303 APR 2009

Abstract: Escort mean values (or q-moments) constitute useful theoretical tools for describing basic features of some probability densities such as those which asymptotically decay like power laws. They naturally appear in the study of many complex dynamical systems, particularly those obeying nonextensive statistical mechanics, a current generalization of the Boltzmann-Gibbs theory. They recover standard mean values (or moments) for q=1. Here we discuss the characterization of a (non-negative) probability density by a suitable set of all its escort mean values together with the set of all associated normalizing quantities, provided that all of them converge. This opens the door to a natural extension of the well-known characterization, for the q=1 instance, of a distribution in terms of the standard moments, provided that all of them have finite values. This question would be specially relevant in connection with probability densities having divergent values for all nonvanishing standard moments higher than a given one (e.g., probability densities asymptotically decaying as power laws), for which the standard approach is not applicable. The Cauchy-Lorentz distribution, whose second and higher even order moments diverge, constitutes a simple illustration of the interest of this investigation. In this context, we also address some mathematical subtleties with the aim of clarifying some aspects of an interesting nonlinear generalization of the Fourier transform, namely, the so-called q-Fourier transform.

ISSN: 0022-2488

Article Number: 043303

DOI: 10.1063/1.3104063

Record 294

Author(s): Rossi, B Verrocchio, P; Viliani, G; Mancini, I; Guella, G; Rigo, E; Scarduelli, G; Mariotto, G

Title: Vibrational properties of ibuprofen-cyclodextrin inclusion complexes investigated by Raman scattering and numerical simulation

Source: JOURNAL OF RAMAN SPECTROSCOPY, 40 (4): 453-458 APR 2009

Abstract: The modifications to the vibrational spectra produced by inclusion into cyclodextrins on the vibrational spectra of of the non-steroidal anti-inflammatory drug ibuprofen, by inclusion into cyclodextrins have been investigated by means of Raman scattering and numerical simulation. These changes are discussed and explained by comparison with the theoretical vibrational wavenumbers frequencies and Raman intensities obtained by quantum and classical numerical simulations, disentangling the effects directly related to the complexation process, from those to be ascribed to non-covalent dimerization of ibuprofen due to hydrogen bonding. Copyright (C) 2008 John Wiley & Sons, Ltd.

ISSN: 0377-0486

DOI: 10.1002/jrs.2150

Record 293

Author(s): Belletti, F; Cruz, A; Fernandez, LA; Gordillo-Guerrero, A; Guidetti, M; Maiorano, A; Mantovani, F; Marinari, E; Martin-Mayor, V; Sudupe, AM; Navarro, D; Parisi, G; Perez-Gaviro, S; Ruiz-Lorenzo, JJ; Schifano, SF; Sciretti, D; Tarancon, A; Tripiccione, R; Yllanes, D

Editor(s): Garrido, PL; Hurtado, PI; Marro, J

Title: Nonequilibrium spin glass dynamics with Janus

Source: MODELING AND SIMULATION OF NEW MATERIALS, 1091: 228-230 2009

Book series title: AIP CONFERENCE PROCEEDINGS

Conference Title: 10th Granada Seminar

Conference Date: SEP 15-19, 2008

Conference Location: Granada, SPAIN

Conference Host: Univ Granada, Fac Ciencias

Abstract: The out of equilibrium evolution for an Edwards-Anderson spin glass is followed for a tenth of a second, a long enough time to let us make safe predictions about the behaviour at experimental scales. This work has been made possible by Janus, an FPGA based special purpose computer. We have thoroughly studied the spin glass correlation functions and the growth of the coherence length for L = 80 lattices in 3D. Our main conclusion is that these spin glasses follow noncoarsening dynamics, at least up to the experimentally relevant time scales.

ISSN: 0094-243X

ISBN: 978-0-7354-0624-7

Record 292

Author(s): Alvarez-Estrada, RF

Title: Nonequilibrium quasi-classical effective meson gas

Source: NUCLEAR PHYSICS A, 820: 299C-302C APR 1 2009

Abstract: We treat a gas of interacting relativistic effective mesons (similar to those produced in a heavy-ion collision), regarded as a nonequilibrium statistical system. The large number of degrees of freedom gives rise to statistical features. We suppose large occupation numbers, temperature somewhat below typical critical temperatures and the quasi-classical regime. At the initial time to, the gas is off-equilibrium. We analyze the time evolution of the quasi-classical effective meson gas for t > t(0) by using a, new moment method. Long-time approximations, which could yield the approach to global thermal equilibrium, are presented.

ISSN: 0375-9474

DOI: 10.1016/j.nuclphysa.2009.01.074

Record 291

Author(s): Martin-Mayor, V

Editor(s): Janke, W; Pelster, A

Title: MICROCANONICAL METHOD FOR THE STUDY OF FIRST-ORDER TRANSITIONS

Source: PATH INTEGRALS: NEW TRENDS AND PERSPECTIVES, PROCEEDINGS: 335-341 2008

Conference Title: 9th International Conference on Path Integrals

Conference Date: SEP 23-28, 2007

Conference Location: Dresden, GERMANY

Conference Host: Max Planck Inst Phys Comlex Syst

Abstract: A simple microcanonical strategy for the simulation of first-order phase transitions is presented. The method does not require iterative parameters optimization, nor long waits for tunneling between the ordered and the disordered phases. It is illustrated in the Q-states Potts model in two dimensions for which several exact results are known, and where a cluster method nicely works.

ISBN: 978-981-283-726-4

Record 290

Author(s): Belletti, F; Cotallo, M; Cruz, A; Fernandez, LA; Gordillo-Guerrero, A; Guidetti, M; Maiorano, A; Mantovani, F; Marinari, E; Martin-Mayor, V; Sudupe, AM; Navarro, D; Parisi, G; Perez-Gaviro, S; Rossi, M; Ruiz-Lorenzo, JJ; Saenz-Lorenzo, JF; Schifano, SF; Sciretti, D; Tarancon, A; Tripiccione, R; Velasco, JL; Yllanes, D; Zanier, G

Group Author(s): JANUS Collaboration

Title: Monte Carlo simulations for statistical physics: Janus

Source: NUOVO CIMENTO DELLA SOCIETA ITALIANA DI FISICA B-GENERAL PHYSICS RELATIVITY ASTRONOMY AND MATHEMATICAL PHYSICS AND METHODS, 123 (6-7): 972-974 JUN-JUL 2008

Conference Title: Italian Meeting on High Energy Physics

Conference Date: MAR 26-28, 2008

Conference Location: Bologna, ITALY

Abstract: Janus is an FPGA-based computer optimized for the simulation of spin glasses or similar condensed matter systems. Computing requirements in this area, are still riot met by available commercial systems, so all application-driven machine, boosting performance by approximately a factor 100x is in this case the only viable option to simulate large systems for a time window comparable with experiments.

ISSN: 1594-9982

DOI: 10.1393/ncb/i2008-10621-8

Record 289

Author(s): Martin-Garcia, JM; Yllanes, D; Portugal, R

Editors: Oscoz, A; Mediavilla, E; SerraRicart, M

Title: INVAR: COMPUTER ALGEBRA FOR THE INVARIANTS OF THE RIEMANN TENSOR

Source: SPANISH RELATIVITY MEETING, ERE2007: RELATIVISTIC ASTROPHYSICS AND COSMOLOGY, 30: 223-226 2008

Book series title: EAS PUBLICATIONS SERIES

Conference Title: 30th Spanish Relativity Conference

Conference Date: SEP 10-14, 2007

Conference Location: Tenerife, SPAIN

Conference Host: Inst Astrofis Canarias

Abstract: We report on the systematic listing of polynomial relations among the algebraic invariants of a Riemann tensor. We construct all such relations for the 3 x 10(29) invariants with tip to seven Riemann tensors, and provide the computer algebra system Invar (both for Mathematica and Maple) which uses them to maximally simplify any invariant within seconds. We also report work in progress to extend Invar and its database to handle all differential Riemann invariants up to 12 derivatives of the metric.

ISSN: 1633-4760

ISBN: 978-2-7598-0062-9

Record 288

Author(s): Belletti, F; Guidetti, M; Maiorano, A; Mantovani, F; Schifano, SF; Tripiccione, R; Cotallo, M; Perez-Gaviro, S; Sciretti, D; Velasco, JL; Cruz, A; Navarro, D; Tarancon, A; Fernandez, LA; Martin-Mayor, V; Munoz-Sudupe, A; Yllanes, D; Gordillo-Guerrero, A; Ruiz-Lorenzo, JJ; Marinari, E; Parisi, G; Rossi, M; Zanier, G

Title: Janus: An FPGA-Based System for High-Performance Scientific Computing

Source: COMPUTING IN SCIENCE & ENGINEERING, 11 (1): 48-58 JAN-FEB 2009

Abstract: Janus is a modular, massively parallel, and reconfigurable FPGA-based computing system that's tailored to a class of hard scientific applications. Monte Carlo statistical mechanics simulations provide a good example of how to use this configurable architecture.

ISSN: 1521-9615

Record 287

Author(s): Fontana, A; Verrocchio, P; Viliani, G

Title: Eleventh International Workshop on Complex Systems, Andalo (Trento), Italy 17-20 March 2008 PREFACE

Source: PHILOSOPHICAL MAGAZINE, 88 (33-35): 3875-3875 2008

ISSN: 1478-6435

DOI: 10.1080/14786430802608182

Record 286

Author(s): Mattarelli, M; Montagna, M; Verrocchio, P

Title: Optical scattering in glass ceramics

Source: PHILOSOPHICAL MAGAZINE, 88 (33-35): 4125-4130 2008

Conference Title: 11th International Workshop on Complex Systems

Conference Date: MAR 17-20, 2008

Conference Location: Andalo, ITALY

Abstract: The transparency of glass ceramics with nanocrystals is generally higher than that expected from the theory of Rayleigh scattering. We attribute this ultra-transparency to the spatial correlation of the nanoparticles. The structure factor is calculated for a simple model system, the random sequential addition (RSA) of equal spheres, at different volume filling factor. The spatial correlation given by the constraint that particles cannot superimpose produces a diffraction peak with a low S(q) in its low-q tail, which is relevant for light scattering. The physical mechanism producing high transparency in glass ceramics is demonstrated to be the low density fluctuation in the number of scatterers. The addition of a size distribution of the spherical particles produces important changes in the q-dependence of the scattering intensity in the region of the diffraction peak, but it has minor effects on the low-q tail.

ISSN: 1478-6435

DOI: 10.1080/14786430802555722

Record 285

Author(s): Fernandez, LA; Martin-Mayor, V; Yllanes, D

Title: Tethered Monte Carlo: Computing the effective potential without critical slowing down

Source: NUCLEAR PHYSICS B, 807 (3): 424-454 FEB 1 2009

Abstract: We present Tethered Monte Carlo, a simple, general purpose method of computing the effective potential of the order parameter (Helmholtz free energy). This formalism is based on a new statistical ensemble, closely related to the micromagnetic one, but with an extended configuration space (through Creutz-like demons). Canonical averages for arbitrary values of the external magnetic field are computed without additional simulations. The method is put to work in the two-dimensional Ising model, where the existence of exact results enables us to perform high precision checks. A rather peculiar feature of our implementation, which employs a local Metropolis algorithm. is the total absence. within errors, of critical slowing down for magnetic observables. Indeed, high accuracy results are presented for lattices as large as L = 1024. (C) 2008 Elsevier B.V. All fights reserved.

ISSN: 0550-3213

DOI: 10.1016/j.nuclphysb.2008.07.009

Record 284

Author(s): Fernandez, LA; Gordillo-Guerrero, A; Martin-Mayor, V; Ruiz-Lorenzo, JJ

Editors: Bruscolini, P; ClementeGallardo, J; Echenique, P; SaebzLorenzo, JF; Castejon, F

Title: First Order Phase Transition in a 3D disordered system

Source: LARGE SCALE SIMULATIONS OF COMPLEX SYSTEMS, CONDENSED MATTER AND FUSION PLASMA, 1071: 46-57 2008

Book series title: AIP CONFERENCE PROCEEDINGS

Conference Title: 111th BIFI International Congress 2008

Conference Date: FEB 06-08, 2008

Conference Location: Zaragoza, SPAIN

Abstract: We present a detailed numerical study on the effects of adding quenched impurities to a three dimensional system which in the pure case undergoes a strong first order phase transition (specifically, the ferromagnetic/paramagnetic transition of the site-diluted four states Potts model). We can state that the transition remains first-order in the presence of quenched disorder (a small amount of it) but it turns out to be second order as more impurities are added. A tricritical point, which is studied by means of Finite-Size Scaling, separates the first-order and second-order parts of the critical line. The results were made possible by a new definition of the disorder average that avoids the diverging-variance probability distributions that arise using the standard methodology. We also made use of a recently proposed microcanonical Monte Carlo method in which entropy, instead of free energy, is the basic quantity.

ISSN: 0094-243X

ISBN: 978-0-7354-0602-5

Record 283

Author(s): Velasco, JL; Castejon, F; Fernandez, LA; Martin-Mayor, V; Tarancon, A

Editors: Bruscolini, P; ClementeGallardo, J; Echenique, P; SaebzLorenzo, JF; Castejon, F

Title: Ion kinetic transport in TJ-II

Source: LARGE SCALE SIMULATIONS OF COMPLEX SYSTEMS, CONDENSED MATTER AND FUSION PLASMA, 1071: 109-123 2008

Book series title: AIP CONFERENCE PROCEEDINGS

Conference Title: 111th BIFI International Congress 2008

Conference Date: FEB 06-08, 2008

Conference Location: Zaragoza, SPAIN

Abstract: The ion Drift Kinetic Equation (DKE) which describes the ion collisional transport is solved for the TJ-II device plasmas. This non-linear equation is computed by performing a mean field iterative calculation. In each step of the calculation, a Fokker-Planck equation is solved by means of the Langevin approach: one million particles are followed in a realistic TJ-II magnetic configuration, taking into account collisions and electric field. This allows to avoid the assumptions made in the usual neoclassical approach, namely considering radially narrow particle trajectories, diffusive transport, energy conservation and infinite parallel transport. As a consequence, global features of transport, not present in the customary neoclassical models, appear: non-diffusive transport and asymmetries on the magnetic surfaces.

ISSN: 0094-243X

ISBN: 978-0-7354-0602-5

Record 282

Author(s): Martin-Garcia, JM; Yllanes, D; Portugal, R

Title: The Invar tensor package: Differential invariants of Riemann

Source: COMPUTER PHYSICS COMMUNICATIONS, 179 (8): 586-590 OCT 15 2008

Abstract: The long standing problem of the relations among the scalar invariants of the Riemann tensor is computationally solved for all 6 × 10²³ objects with up to 12 derivatives of the metric. This covers cases ranging from products of up to 6 undifferentiated Riemann tensors to cases with up to 10 covariant derivatives of a single Riemann. We extend our computer algebra system Invar to produce within seconds a canonical form for any of those objects in terms of a basis. The process is as follows: (I) an invariant is converted in real time into a canonical form with respect to the permutation symmetries of the Riemann tensor; (2) Invar reads a database of more than 6 × 10⁵ relations and applies those coming from the cyclic symmetry of the Riemann tensor; (3) then applies the relations coming from the Bianchi identity, (4) the relations coming from commutations of covariant derivatives, (5) the dimensionally-dependent identities for dimension 4. and finally (6) simplifies invariants that can be expressed as product of dual invariants. Invar runs on top of the tensor computer algebra systems xTensor (for Mathematica) and Canon (for Maple).

ISSN: 0010-4655

DOI: 10.1016/j.cpc.2008.04.018

Record 281

Author(s): Belletti, F, Cotallo, M; Cruz, A; Fernandez, LA; Gordillo-Guerrero, A; Guidetti, M; Maiorano, A; Mantovani, F; Marinari, E; Martin-Mayor, V; Sudupe, AM; Navarro, D; Parisi, G; Perez-Gaviro, S; Ruiz-Lorenzo, JJ; Schifano, SF; Sciretti, D; Tarancon, A; Tripiccione, R; Velasco, JL; Yllanes, D

Title: Nonequilibrium Spin-Glass Dynamics from Picoseconds to a Tenth of a Second

Source: PHYSICAL REVIEW LETTERS, 101 (15): Art. No. 157201 OCT 10 2008

Abstract: We study numerically the nonequilibrium dynamics of the Ising spin glass, for a time spanning 11 orders of magnitude, thus approaching the experimentally relevant scale (i.e., seconds). We introduce novel analysis techniques to compute the coherence length in a model-independent way. We present strong evidence for a replicon correlator and for overlap equivalence. The emerging picture is compatible with noncoarsening behavior.

ISSN: 0031-9007

DOI: 10.1103/PhysRevLett.101.157201

Record 280

Author(s): Kenna, R (Kenna, R.); Ruiz-Lorenzo, JJ (Ruiz-Lorenzo, J. J.)

Title: Scaling analysis of the site-diluted Ising model in two dimensions

Source: PHYSICAL REVIEW E, 78 (3): Art. No. 031134 Part 1 SEP 2008

Abstract: A combination of recent numerical and theoretical advances are applied to analyze the scaling behavior of the site-diluted Ising model in two dimensions, paying special attention to the implications for multiplicative logarithmic corrections. The analysis focuses primarily on the odd sector of the model (i.e., that associated with magnetic exponents), and in particular on its Lee-Yang zeros, which are determined to high accuracy. Scaling relations are used to connect to the even (thermal) sector, and a first analysis of the density of zeros yields information on the specific heat and its corrections. The analysis is fully supportive of the strong scaling hypothesis and of the scaling relations for logarithmic corrections.

ISSN: 1539-3755

DOI: 10.1103/PhysRevE.78.031134

Record 279

Author(s): Biroli, G (Biroli, G.); Bouchaud, JP (Bouchaud, J. -P.); Cavagna, A (Cavagna, A.); Grigera, TS (Grigera, T. S.); Verrocchio, P (Verrocchio, P.)

Title: Thermodynamic signature of growing amorphous order in glass-forming liquids

Source: NATURE PHYSICS, 4 (10): 771-775 OCT 2008

Abstract: Supercooled liquids exhibit a pronounced slowdown of their dynamics on cooling(1) without showing any obvious structural or thermodynamic changes(2). Several theories relate this slowdown to increasing spatial correlations(3-6). However, no sign of this is seen in standard static correlation functions, despite indirect evidence from considering specific heat(7) and linear dielectric susceptibility(8). Whereas the dynamic correlation function progressively becomes more non-exponential as the temperature is reduced, so far no similar signature has been found in static correlations that can distinguish qualitatively between a high-temperature and a deeply supercooled glass-forming liquid in equilibrium. Here, we show evidence of a qualitative thermodynamic signature that differentiates between the two. We show by numerical simulations with fixed boundary conditions that the influence of the boundary propagates into the bulk over increasing length scales on cooling. With the increase of this static correlation length, the influence of the boundary decays non-exponentially. Such long-range susceptibility to boundary conditions is expected within the random first-order theory(4,9,10) (RFOT) of the glass transition. However, a quantitative account of our numerical results requires a generalization of RFOT, taking into account surface tension fluctuations between states.

ISSN: 1745-2473

DOI: 10.1038/nphys1050

Record 278

Author(s): Leuzzi, L (Leuzzi, L.); Parisi, G (Parisi, G.); Ricci-Tersenghi, F (Ricci-Tersenghi, F.); Ruiz-Lorenzo, JJ (Ruiz-Lorenzo, J. J.)

Title: Dilute one-dimensional spin glasses with power law decaying interactions

Source: PHYSICAL REVIEW LETTERS, 101 (10): Art. No. 107203 SEP 5 2008

Abstract: We introduce a diluted version of the one-dimensional spin-glass model with interactions decaying in probability as an inverse power of the distance. In this model, varying the power corresponds to changing the dimension in short-range models. The spin-glass phase is studied in and out of the range of validity of the mean-field approximation in order to discriminate between different theories. Since each variable interacts only with a finite number of others the cost for simulating, the model is drastically reduced with respect to the fully connected version, and larger sizes can be studied. We find both static and dynamic indications in favor of the so-called replica symmetry breaking theory.

ISSN: 0031-9007

DOI: 10.1103/PhysRevLett.101.107203

Record 277

Author(s): Velasco, JL (Velasco, J. L.); Castejon, F (Castejon, F.); Fernandez, LA (Fernandez, L. A.); Martin-Mayor, V (Martin-Mayor, V.); Tarancon, A (Tarancon, A.); Estrada, T (Estrada, T.)

Title: Ion heating in transitions to CERC in the stellarator TJ-II

Source: NUCLEAR FUSION, 48 (6): Art. No. 065008 JUN 2008

Abstract: In TJ-II stellarator plasmas, in the electron cyclotron heating regime, an increase in the ion temperature is observed, synchronized with that of the electron temperature, during the transition to the core electron-root confinement (CERC) regime. This rise in ion temperature should be attributed to the joint action of the electron-ion energy transfer ( which changes slightly during the CERC formation) and an enhancement of the ion confinement. This improvement must be related to the increase in the positive electric field in the core region. In this paper, we confirm this hypothesis by estimating the ion collisional transport in TJ-II under the physical conditions established before and after the transition to CERC. We calculate a large number of ion orbits in the guiding-centre approximation considering the collisions with a background plasma composed of electrons and ions. The ion temperature profile and the thermal flux are calculated in a self-consistent way, so that the change in the ion heat transport can be assessed.

ISSN: 0029-5515

DOI: 10.1088/0029-5515/48/6/065008

Record 276

Author(s): Fernandez, LA (Fernandez, L. A.); Maiorano, A (Maiorano, A.); Marinari, E (Marinari, E.); Martin-Mayor, V (Martin-Mayor, V.); Navarro, D (Navarro, D.); Sciretti, D (Sciretti, D.); Tarancon, A (Tarancon, A.); Velasco, JL (Velasco, J. L.)

Title: Critical properties of the four-state commutative random permutation glassy Potts model in three and four dimensions

Source: PHYSICAL REVIEW B, 77 (10): Art. No. 104432 MAR 2008

Abstract: We investigate the critical properties of the four-state commutative random permutation glassy Potts model in three and four dimensions by means of Monte Carlo simulations and a finite-size scaling analysis. By using a field programmable gate array, we have been able to thermalize a large number of samples of systems with large volume. This has allowed us to observe a spin-glass ordered phase in d=4 and to study the critical properties of the transition. In d=3, our results are consistent with the presence of a Kosterlitz-Thouless transition, but also with different scenarios: transient effects due to a value of the lower critical dimension slightly below 3 could be very important.

ISSN: 1098-0121

DOI: 10.1103/PhysRevB.77.104432

Record 275

Author(s): Fernandez, LA (Fernandez, L. A.); Gordillo-Guerrero, A (Gordillo-Guerrero, A.); Martin-Mayor, V (Martin-Mayor, V.); Ruiz-Lorenzo, JJ (Ruiz-Lorenzo, J. J.)

Title: First-order transition in a three-dimensional disordered system

Source: PHYSICAL REVIEW LETTERS, 100 (5): Art. No. 057201 FEB 8 2008

Abstract: We present the first detailed numerical study in three dimensions of a first-order phase transition that remains first order in the presence of quenched disorder (specifically, the ferromagnetic-paramagnetic transition of the site-diluted four states Potts model). A tricritical point, which lies surprisingly near the pure-system limit and is studied by means of finite-size scaling, separates the first-order and second-order parts of the critical line. This investigation has been made possible by a new definition of the disorder average that avoids the diverging-variance probability distributions that plague the standard approach. Entropy, rather than free energy, is the basic object in this approach that exploits a recently introduced microcanonical Monte Carlo method.

ISSN: 0031-9007

DOI: 10.1103/PhysRevLett.100.057201

Record 274

Author(s): Belletti, F (Belletti, F.); Cotallo, M (Cotallo, M.); Cruz, A (Cruz, A.); Fernandez, LA (Fernandez, L. A.); Gordillo, A (Gordillo, A.); Maiorano, A (Maiorano, A.); Mantovani, F (Mantovani, F.); Marinari, E (Marinari, E.); Martin-Mayor, V (Martin-Mayor, V.); Munoz-Sudupe, A (Munoz-Sudupe, A.); Navarro, D (Navarro, D.); Perez-Gaviro, S (Perez-Gaviro, S.); Ruiz-Lorenzo, JJ (Ruiz-Lorenzo, J. J.); Schifano, SF (Schifano, S. F.); Sciretti, D (Sciretti, D.); Tarancon, A (Tarancon, A.); Tripiccione, R (Tripiccione, R.); Velasco, JL (Velasco, J. L.)

Title: Simulating spin systems on IANUS, an FPGA-based computer

Source: COMPUTER PHYSICS COMMUNICATIONS, 178 (3): 208-216 FEB 1 2008

Abstract: We describe the hardwired implementation of algorithms for Monte Carlo simulations of a large class of spin models. We have implemented these algorithms as VHDL codes and we have mapped them onto a dedicated processor based on a large FPGA device. The measured performance on one such processor is comparable to 0 (100) carefully programmed high-end PCs: it turns out to be even better for some selected spin models. We describe here codes that we are currently executing on the IANUS massively parallel FPGA-based system. (C) 2007 Elsevier B.V. All rights reserved.

ISSN: 0010-4655

DOI: 10.1016/j.cpc.2007.09.006

Record 273

Author(s): Calvo, GF (Calvo, Gabriel F.); Alvarez-Estrada, RF (Alvarez-Estrada, Ramon F.)

Title: The time duration for DNA thermal denaturation

Source: JOURNAL OF PHYSICS-CONDENSED MATTER, 20 (3): Art. No. 035101 JAN 23 2008

Abstract: Motivated by the thermal denaturation of DNA, we consider two interacting three-dimensional macromolecular chains, bound to each other, in a medium at thermal equilibrium from about room temperature up to about the melting one (T-m), at which they become unbound. We outline models for the non-equilibrium evolution of the double-stranded system, based upon the Smoluchowski equation, and allow for heterogeneities, excluded-volume effects and hydrodynamic interactions. A moment method leads us to approximate the Smoluchowski equation by a one-dimensional differential equation for the lowest order moment, containing a global effective potential between the two strands. We concentrate on the time duration (tau) required for thermal denaturation to occur, for long times and temperature T similar or equal to T-m. Here tau is approximated by the so-called mean first passage time (MFPT) for the relative separation of the centres of mass of the two chains. An approximate formula for the MFPT is obtained and employed for estimates. The consistency of the MFPT with experimental results is discussed for both Rouse and Zimm regimes.

ISSN: 0953-8984

DOI: 10.1088/0953-8984/20/03/035101

Record 272

Author(s): Maiorano, A (Maiorano, A.); Martin-Mayor, V (Martin-Mayor, V.); Ruiz-Lorenzo, JJ (Ruiz-Lorenzo, J. J.); Tarancon, A (Tarancon, A.)

Title: Weak first-order transition in the three-dimensional site-diluted Ising antiferromagnet in a magnetic field

Source: PHYSICAL REVIEW B, 76 (6): Art. No. 064435 AUG 2007

Abstract: We perform intensive numerical simulations of the three-dimensional site-diluted Ising antiferromagnet in a magnetic field at high values of the external applied field. Even if data for small lattice sizes are compatible with second-order criticality, the critical behavior of the system shows a crossover from second-order to first-order behavior for large system sizes, where signals of latent heat appear. We propose "apparent" critical exponents for the dependence of some observables on the lattice size for a generic (disordered) first-order phase transition.

ISSN: 1098-0121

DOI: 10.1103/PhysRevB.76.064435

Record 271

Author(s): Mattarelli, M (Mattarelli, M.); Montagna, M (Montagna, M.); Verrocchio, P (Verrocchio, P.)

Title: Ultratransparent glass ceramics: The structure factor and the quenching of the Rayleigh scattering

Source: APPLIED PHYSICS LETTERS, 91 (6): Art. No. 061911 AUG 6 2007

Abstract: Glass ceramics with nanocrystals present a transparency higher than that expected from the theory of Rayleigh scattering. This ultratransparency is attributed to the spatial correlation of the nanoparticles. The structure factor is calculated for a simple model system, the random sequential addition of equal spheres, at different volume filling factor. The spatial correlation given by the constraint that particles cannot superimpose produces a diffraction peak with a low S(q) in its low-q tail, which is relevant for light scattering. The physical mechanism producing high transparency in glass ceramics is demonstrated to be the low density fluctuation in the number of scatterers.

ISSN: 0003-6951

DOI: 10.1063/1.2768642

Record 270

Author(s): Gordillo-Guerrero, A (Gordillo-Guerrero, A.); Ruiz-Lorenzo, JJ (Ruiz-Lorenzo, J. J.)

Title: Self-averaging in the three-dimensional site diluted Heisenberg model at the critical point

Source: JOURNAL OF STATISTICAL MECHANICS-THEORY AND EXPERIMENT: Art. No. P06014 JUN 2007

Abstract: We study the self-averaging properties of the three-dimensional site diluted Heisenberg model. The Harris criterion states that disorder is irrelevant since the specific heat critical exponent of the pure model is negative. According to some analytical approaches, this implies that the susceptibility should be self-averaging at the critical temperature (R chi = 0). We have checked this theoretical prediction for a large range of dilution (including strong dilution) at criticality and we have found that the introduction of scaling corrections is crucial for obtaining 'self-averageness' in this model. Finally we have computed critical exponents and cumulants which compare very well with those of the pure model, supporting the universality predicted by the Harris criterion.

ISSN: 1742-5468

DOI: 10.1088/1742-5468/2007/06/P06014

Record 269

Author(s): Campos, I (Campos, I.); Cotallo-Aban, M (Cotallo-Aban, M.); Martin-Mayor, V (Martin-Mayor, V.)

Title: Comment on "Spin-glass transition of the three-dimensional Heisenberg spin glass" - Reply

Source: PHYSICAL REVIEW LETTERS, 99 (1): Art. No. 019702 JUL 6 2007

ISSN: 0031-9007

DOI: 10.1103/PhysRevLett.99.019702

Record 268

Author(s): Castejon, F (Castejon, F.); Fernandez, LA (Fernandez, L. A.); Guasp, J (Guasp, J.); Martin-Mayor, V (Martin-Mayor, V.); Tarancon, A (Tarancon, A.); Velasco, JL (Velasco, J. L.)

Title: Ion kinetic transport in the presence of collisions and electric field in TJ-II ECRH plasmas

Source: PLASMA PHYSICS AND CONTROLLED FUSION, 49 (6): 753-776 JUN 2007

Abstract: The ion collisional transport is estimated for the TJ-II device without the assumption of radially narrow particle trajectories, which is usually made in neoclassical transport studies. One million particles are followed in a realistic TJ-II magnetic configuration, taking into account collisions and the electric field. Global features of transport, not present in the customary neoclassical models, appear. The main results reached by considering the actual particle geometries are the monotonic increasing of heat and particle fluxes with minor radius, the non-diffusive character of transport, the appearance of asymmetries on the magnetic surfaces and the non-Maxwellian character of the distribution function.

ISSN: 0741-3335

DOI: 10.1088/0741-3335/49/6/005

Record 267

Author(s): Cavagna, A (Cavagna, Andrea); Grigera, TS (Grigera, Tomas S.); Verrocchio, P (Verrocchio, Paolo)

Title: Mosaic multistate scenario versus one-state description of supercooled liquids

Source: PHYSICAL REVIEW LETTERS, 98 (18): Art. No. 187801 MAY 4 2007

Abstract: According to the mosaic scenario, relaxation in supercooled liquids is ruled by two competing mechanisms: surface tension, opposing the creation of local excitations, and entropy, providing the drive to the configurational rearrangement of a given region. We test this scenario through numerical simulations well below the Mode Coupling temperature. For an equilibrated configuration, we freeze all the particles outside a sphere and study the thermodynamics of this sphere. The frozen environment acts as a pinning field. Measuring the overlap between the unpinned and pinned equilibrium configurations of the sphere, we can see whether it has switched to a different state. We do not find any clear evidence of the mosaic scenario. Rather, our results seem compatible with the existence of a single (liquid) state. However, we find evidence of a growing static correlation length, apparently unrelated to the mosaic one.

ISSN: 0031-9007

DOI: 10.1103/PhysRevLett.98.187801

Record 266

Author(s): Alvarez-Estrada, RF (Alvarez-Estrada, R. F.)

Title: Initial states and time evolution in nonequilibrium quantum field theory

Source: NUCLEAR PHYSICS A, 785 (1-2): 218C-221C MAR 15 2007

Conference Title: 7th International Conference on Strong and Electroweak Matter

Conference Date: MAY 10-13, 2006

Conference Location: Long Isl, NY

Conference Host: Brookhaven Natl Lab

ISSN: 0375-9474

DOI: 10.1016/j.nuclphysa.2006.11.062

Record 265

Author(s): Martin-Mayor, V (Martin-Mayor, V.)

Title: Microcanonical approach to the simulation of first-order phase transitions

Source: PHYSICAL REVIEW LETTERS, 98 (13): Art. No. 137207 MAR 30 2007

Abstract: A simple microcanonical strategy for the simulation of first-order phase transitions is proposed. At variance with flat-histogram methods, there is no iterative parameters optimization nor long waits for tunneling between the ordered and the disordered phases. We test the method in the standard benchmark: the Q-states Potts model (Q=10 in two dimensions and Q=4 in D=3). We develop a cluster algorithm for this model, obtaining accurate results for systems with more than 10(6) spins.

ISSN: 0031-9007

DOI: 10.1103/PhysRevLett.98.137207

Record 264

Author(s): Alvarez-Estrada, RF (Alvarez-Estrada, R. F.)

Title: Nonequilibrium quasi-classical effective meson gas: Thermalization

Source: EUROPEAN PHYSICAL JOURNAL A, 31 (4): 761-765 MAR 2007

Conference Title: 4th International Conference on Quarks and Nuclear Physics

Conference Date: JUN 05-10, 2006

Conference Location: Madrid, SPAIN

Abstract: We consider a gas of interacting relativistic effective mesons (qualitatively, like those produced in a heavy-ion collision), regarded as an out-of-equilibrium statistical system. We suppose large occupation numbers, temperature somewhat below typical critical temperatures and the quasi-classical regime. At some initial time t(0), let the gas be in a nonequilibrium state, with spatial inhomogeneities. The time evolution of the gas for t > t (0) is studied by a moment method, and appropriate long-time approximations, which could yield the approach to global thermal equilibrium, are discussed.

ISSN: 1434-6001

DOI: 10.1140/epja/i2006-10289-y

Record 263

Author(s): Fernandez, LA (Fernandez, L. A.); Martin-Mayor, V (Martin-Mayor, V.); Verrocchio, P (Verrocchio, P.)

Title: Phase diagram of a polydisperse soft-spheres model for liquids and colloids

Source: PHYSICAL REVIEW LETTERS, 98 (8): Art. No. 085702 FEB 23 2007

Abstract: The phase diagram of soft spheres with size dispersion is studied by means of an optimized Monte Carlo algorithm which allows us to equilibrate below the kinetic glass transition for all size distributions. The system ubiquitously undergoes a first-order freezing transition. While for a small size dispersion the frozen phase has a crystalline structure, large density inhomogeneities appear in the highly disperse systems. Studying the interplay between the equilibrium phase diagram and the kinetic glass transition, we argue that the experimentally found terminal polydispersity of colloids is a purely kinetic phenomenon.

ISSN: 0031-9007

DOI: 10.1103/PhysRevLett.98.085702

Record 262

Author(s): Fontana, A (Fontana, A.); Verrocchio, P (Verrocchio, P.); Viliani, G (Viliani, G.)

Title: Tenth International Workshop on Disordered Systems Molveno-Andalo (Trento), Italy, 18-21 March 2006 - Preface

Source: PHILOSOPHICAL MAGAZINE, 87 (3-5): 355-355 Sp. Iss. SI JAN-FEB 2007

ISSN: 1478-6435

DOI: 10.1080/14786430601063035

Record 261

Author(s): Rossi, B (Rossi, B.); Verrocchio, P (Verrocchio, P.); Viliani, G (Viliani, G.); Scarduelli, G (Scarduelli, G.); Mancini, I (Mancini, I.); Guella, G (Guella, G.); Rossi, F (Rossi, F.)

Title: Vibrational dynamics of inclusion complexes by Raman scattering: an experimental and numerical study

Source: PHILOSOPHICAL MAGAZINE, 87 (3-5): 559-567 Sp. Iss. SI JAN-FEB 2007

Conference Title: 10th International Workshop on Disordered Systems Moveno-Andalo

Conference Date: MAR 18-21, 2006

Conference Location: Trento, ITALY

Abstract: Raman spectroscopy has been applied to the study of interactions involved in the formation of inclusion complexes between cyclodextrins and indomethacin. Raman spectra of free molecules and of their inclusion complexes have been recorded in the energy ranges 10-50 and 100-3500 cm(-1), and significant energy shifts, intensity variations and broadening have been observed due to complexation. The experimental data have been interpreted by comparison with the results of numerical simulation.

ISSN: 1478-6435

DOI: 10.1090/14786430600887657

Record 260

Author(s): Fernandez, LA (Fernandez, L. A.); Martin-Mayor, V (Martin-Mayor, V.); Verrocchio, P (Verrocchio, P.)

Title: Optimized Monte Carlo method for glasses

Source: PHILOSOPHICAL MAGAZINE, 87 (3-5): 581-586 Sp. Iss. SI JAN-FEB 2007

Conference Title: 10th International Workshop on Disordered Systems Moveno-Andalo

Conference Date: MAR 18-21, 2006

Conference Location: Trento, ITALY

Abstract: A new Monte Carlo algorithm is introduced for the simulations of super-cooled liquids and glass formers, and tested in two model glasses. The algorithm thermalizes well below the mode coupling temperatures and outperforms other optimized Monte Carlo methods.

ISSN: 1478-6435

DOI: 10.1080/14786430600919302

Record 259

Author(s): Lancaster, DJ (Lancaster, D. J.); Ruiz-Lorenzo, JJ (Ruiz-Lorenzo, J. J.)

Title: Numerical simulations of the random phase sine-Gordon model and renormalization group predictions

Source: JOURNAL OF STATISTICAL MECHANICS-THEORY AND EXPERIMENT: Art. No. P01003 JAN 2007

Abstract: Numerical simulations of the random phase sine-Gordon model suffer from strong finite size effects preventing the non-Gaussian log(2) r component of the spatial correlator from following the universal infinite volume prediction. We show that a finite size prediction based on perturbative renormalization group (RG) arguments agrees well with new high precision simulations for small coupling and close to the critical temperature.

ISSN: 1742-5468

DOI: 10.1088/1742-5468/2007/01/P01003

Record 258

Author(s): Ruiz-Lorenzo, JJ (Ruiz-Lorenzo, J. J.); Yuste, SB (Yuste, Santos B.); Lindenberg, K (Lindenberg, Katja)

Title: Simulations for trapping reactions with subdiffusive traps and subdiffusive particles

Source: JOURNAL OF PHYSICS-CONDENSED MATTER, 19 (6): Art. No. 065120 FEB 14 2007

Abstract: While there are many well known and extensively tested results involving diffusion-limited binary reactions, reactions involving subdiffusive reactant species are far less well understood. Subdiffusive motion is characterized by a mean square displacement < x(2)> similar to t(gamma) with 0 < gamma < 1. Recently, we calculated the asymptotic survival probability P(t) of a (sub) diffusive particle (gamma') surrounded by (sub)diffusive traps (gamma) in one dimension. These are among the few known results for reactions involving species characterized by different anomalous exponents. Our results were obtained by bounding, above and below, the exact survival probability by two other probabilities that are asymptotically identical (except when gamma' = 1 and 0 < gamma < 2/3). Using this approach, we were not able to estimate the time of validity of the asymptotic result, nor the way in which the survival probability approaches this regime. Toward this goal, here we present a detailed comparison of the asymptotic results with numerical simulations. In some parameter ranges the asymptotic theory describes the simulation results very well even for relatively short times. However, in other regimes more time is required for the simulation results to approach asymptotic behaviour, and we arrive at situations where we are not able to reach asymptotes within our computational means. This is regrettably the case for gamma' = 1 and 0 < gamma < 2/3, where we are therefore not able to prove or disprove even conjectures about the asymptotic survival probability of the particle.

ISSN: 0953-8984

DOI: 10.1088/0953-8984/19/6/065120

Record 257

Author(s): Verrocchio, P (Verrocchio, P.)

Title: Universal properties of high-frequency spectra in glass formers

Source: JOURNAL OF NON-CRYSTALLINE SOLIDS, 352 (42-49): 4536-4540 Sp. Iss. SI NOV 15 2006

Conference Title: 5th International Discussion Meeting on Relaxations in Complex Systems

Conference Date: JUL 07-13, 2005

Conference Location: Lille, FRANCE

Conference Host: Univ Sci & Technologies

Abstract: The vibrational spectra of glass formers follow different laws with respect to crystals. A rationale for their anomalous behavior is provided by the euclidean random matrix theory. Experiments on glass formers at different densities might be a suitable route to test the prediction of the theory. (c) 2006 Elsevier B.V. All rights reserved.

ISSN: 0022-3093

DOI: 10.1016/jnoncrysol.2006.02.139

Record 256

Author(s): Alvarez-Estrada, RF

Editors: Eskola, KJ; Kainulainen, K; Kajantie, K; Rummukainen, K

Title: Out-of-equilibrium massless Schwinger Model

Source: STRONG AND ELECTROWEAK MATTER 2004, PROCEEDINGS: 321-325 2005

Conference Title: 6th International Conference on Strong and Electroweak Matter (SEWM 2004)

Conference Date: JUN 16-19, 2004

Conference Location: Helsinki, FINLAND

Abstract: An isolated statistical many-particle system, with microscopic dynamics described by massless Quantum Electrodynamics (QED) in one spatial dimension (massless Schwinger Model) is studied in out-of-equilibrium cases. This constitutes a model of Non-Equilibrium Relativistic Quantum Field Theory. The initial condition is chosen to correspond to local equilibrium but, on the other hand, to a global out of equilibrium situation, with a spatially-inhomogeneous distribution of temperatures on suitably large length scales. The out-of-equilibrium generating functionals are discussed and some partial results are outlined.

ISBN: 981-256-135-8

Record 255

Author(s): Fernandez, L (Fernandez, L. A.); Martin-Mayor, V (Martin-Mayor, V.); Verrocchio, P (Verrocchio, P.)

Editors: Tokuyama, M; Maruyama, S

Title: Finite size effects in the specific heat of glass-formers

Source: Flow Dynamics, 832: 128-133 2006

Book series title: AIP CONFERENCE PROCEEDINGS

Conference Title: 2nd International Conference on Flow Dynamics

Conference Date: NOV 16-18, 2005

Conference Location: Sendai, JAPAN

Abstract: We report clear finite size effects in the specific heat and in the relaxation times of a model glass former at temperatures considerably smaller than the Mode Coupling transition. A crucial ingredient to reach this result is a new Monte Carlo algorithm which allows us to reduce the relaxation time by two order of magnitudes. These effects signal the existence of a large correlation length in static quantities.

ISSN: 0094-243X

ISBN: 0-7354-0324-4

Record 254

Author(s): Campos, I (Campos, I.); Cotallo-Aban, M (Cotallo-Aban, M.); Martin-Mayor, V (Martin-Mayor, V.); Perez-Gaviro, S (Perez-Gaviro, S.); Tarancon, A (Tarancon, A.)

Title: Spin-glass transition of the three-dimensional Heisenberg spin glass

Source: PHYSICAL REVIEW LETTERS, 97 (21): Art. No. 217204 NOV 24 2006

Abstract: It is shown, by means of Monte Carlo simulation and finite size scaling analysis, that the Heisenberg spin glass undergoes a finite-temperature phase transition in three dimensions. There is a single critical temperature, at which both a spin glass and a chiral glass ordering develop. The Monte Carlo algorithm, adapted from lattice gauge theory simulations, makes it possible to thermalize lattices of size L=32, larger than in any previous spin-glass simulation in three dimensions. High accuracy is reached thanks to the use of the Marenostrum supercomputer. The large range of system sizes studied allows us to consider scaling corrections.

ISSN: 0031-9007

DOI: 10.1103/PhysRevLett.97.217204

Record 253

Author(s): Yuste, SB (Yuste, S. B.); Ruiz-Lorenzo, JJ (Ruiz-Lorenzo, J. J.); Lindenberg, K (Lindenberg, Katja)

Title: Target problem with evanescent subdiffusive traps

Source: PHYSICAL REVIEW E, 74 (4): Art. No. 046119 Part 2 OCT 2006

Abstract: We calculate the survival probability of a stationary target in one dimension surrounded by diffusive or subdiffusive traps of time-dependent density. The survival probability of a target in the presence of traps of constant density is known to go to zero as a stretched exponential whose specific power is determined by the exponent that characterizes the motion of the traps. A density of traps that grows in time always leads to an asymptotically vanishing survival probability. Trap evanescence leads to a survival probability of the target that may go to zero or to a finite value indicating a probability of eternal survival, depending on the way in which the traps disappear with time.

ISSN: 1539-3755

DOI: 10.1103/PhysRevE.74.046119

Record 252

Author(s): Castejon, F (Castejon, F.); Reynolds, JM (Reynolds, J. M.); Fontdecaba, JM (Fontdecaba, J. M.); Balbin, R (Balbin, R.); Guasp, J (Guasp, J.); Lopez-Bruna, D (Lopez-Bruna, D.); Campos, I (Campos, I.); Fernandez, LA (Fernandez, L. A.); Fernandez-Fraile, D (Fernandez-Fraile, D.); Martin-Mayor, V (Martin-Mayor, V.); Tarancon, A (Tarancon, A.)

Title: Ion orbits and ion confinement studies on ECRH plasmas in TJ-II stellarator

Source: FUSION SCIENCE AND TECHNOLOGY, 50 (3): 412-418 OCT 2006

Conference Title: 15th International Stellarator Workshop

Conference Date: OCT 03-07, 2005

Conference Location: Madrid, SPAIN

Conference Host: Lab Nacl Fus, CIEMAT

Abstract: It was observed previously that the ion temperature profile of low-detisity electron cyclotron resonance-heated TJ-II plasmas is almost flat and that energetic ions are present well outside the last closed magnetic surface. The heat diffusivity obtained for such ion temperature profiles is very high, and therefore, transport cannot be described by Fick's law. In this work, ion trajectories with different pitches and starting points have been calculated for the relevant magnetic configuration. It is found that a feasible explanation for such a flat mean energy profile is that ion orbits are wide enough to communicate distant parts of the plasma radius, thus giving an effective flat ion temperature profile, for these low-density (< 10(19)-m(-3))plasmas. The distribution function is also obtained without considering collisions; thus, non-Maxwellian features are found. The final particle density shows inhomogeneities on a magnetic surface.

ISSN: 1536-1055

Record 251

Author(s): Rossi, B (Rossi, Barbara); Verrocchio, P (Verrocchio, Paolo); Viliani, G (Viliani, Gabriele); Scarduelli, G (Scarduelli, Giorgina); Guella, G (Guella, Graziano); Mancini, I (Mancini, Ines)

Title: Vibrational properties of inclusion complexes: The case of indomethacin-cyclodextrin

Source: JOURNAL OF CHEMICAL PHYSICS, 125 (4): Art. No. 044511 JUL 28 2006

Abstract: Vibrational properties of inclusion complexes with cyclodextrins are studied by means of Raman spectroscopy and numerical simulation. In particular, Raman spectra of the nonsteroidal, anti-inflammatory drug indomethacin undergo notable changes in the energy range between 1600 and 1700 cm(-1) when inclusion complexes with cyclodextrins are formed. By using both ab initio quantum chemical calculations and molecular dynamics, we studied how to relate such changes to the geometry of the inclusion process, disentangling single-molecule effects, from changes in the solid state structure or dimerization processes. (c) 2006 American Institute of Physics.

ISSN: 0021-9606

DOI: 10.1063/1.2217952

Record 250

Author(s): Alvarez-Estrada, RE

Title: Lionville and Fokker-Planck dynamics for classical plasmas and radiation

Source: ANNALEN DER PHYSIK, 15 (6): 379-415 JUN 2006

Abstract: electric charges (plasma) and by the classical dynamical electromagnetic (EM) field. The charges interact with one another directly through instantaneous Coulomb potentials and with the dynamical degrees of freedom of the transverse EM field. The system may also be subject to external influences of: i) either static, but spatially inhomogeneous, electric and magnetic fields (case 1)), or ii) weak distributions of electric charges and currents (case 2)). The particles and the dynamical EM field are described, for any time t > 0, by the classical phase-space probability distribution functional (CPSPDF) f and, at the initial time (t = 0), by the initial CPSPDF fin. The CPSPDF f and f(in), multiplied by suitable Hermite polynomials (for particles and field) and integrated over all canonical momenta, yield new moments. The Liouville equation and fin imply a new nonequilibrium linear infinite hierarchy for the moments. In case 1), fin describes local equilibrium but global nonequilibrium, and we propose a long-time approximation in the hierarchy, which introduces irreversibility and relaxation towards global thermal equilibrium. In case 2), the statistical system, having been at global thermal equilibrium, without external influences, for t <= 0, is subject to weak external charge-current distributions: then, new hierarchies for moments and their long-time behaviours are discussed in outline. As examples, approximate mean-field (Vlasov) approximations are treated for both cases 1) and 2). (c) 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

ISSN: 0003-3804

DOI: 10.1002/andp.200510180

Record 249

Author(s): Gaviro, SP; Ruiz-Lorenzo, JJ; Tarancon, A

Title: Study of the phase transition in the 3D Ising spin glass from out-of-equilibrium numerical simulations

Source: JOURNAL OF PHYSICS A-MATHEMATICAL AND GENERAL, 39 (27): 8567-8577 JUL 7 2006

Abstract: Using the decay of the out- of- equilibrium spin - spin correlation function we compute the equilibrium Edward - Anderson order parameter in the threedimensional binary Ising spin glass in the spin glass phase. We have checked that the Edward - Anderson order parameter computed from out- of-equilibrium numerical simulations follows with good precision the critical law as determined in experiments and in numerical studies at equilibrium ( which allow us to estimate the beta critical exponent). Finally, we present a large time study of the off- equilibrium fluctuation - dissipation relations and find strong discrepancies ( in the low-temperature region) between the numerical data and the droplet theory predictions and agreement with the predictions of the replica symmetry breaking theory.

ISSN: 0305-4470

DOI: 10.1088/0305-4470/39/27/001

Record 248

Author(s): Fernandez, LA; Martin-Mayor, V; Verrocchio, P

Title: Critical behavior of the specific heat in glass formers

Source: PHYSICAL REVIEW E, 73 (2): Art. No. 020501 Part 1 FEB 2006

Abstract: We show numeric evidence that, at low enough temperatures, the potential energy density of a glass-forming liquid fluctuates over length scales much larger than the interaction range. We focus on the behavior of translationally invariant quantities. The growing correlation length is unveiled by studying the finite-size effects. In the thermodynamic limit, the specific heat and the relaxation time diverge as a power law. Both features point towards the existence of a critical point in the metastable supercooled liquid phase.

ISSN: 1539-3755

DOI: 10.1103/PhysRevE.73.020501

Record 247

Author(s): Ruiz-Lorenzo, JJ; Moro, E; Cuerno, R

Title: Single tensionless transition in the Laplacian roughening model

Source: PHYSICAL REVIEW E, 73 (1): Art. No. 015103 Part 2 JAN 2006

Abstract: We report large scale Monte Carlo simulations of the equilibrium discrete Laplacian roughening (dLr) model, originally introduced as the simplest one accommodating the hexatic phase in two-dimensional melting. The dLr model is also relevant to surface roughening in molecular beam epitaxy (MBE). Our data suggest a single phase transition, possibly of the Kosterlitz-Thouless type, between a flat low-temperature phase and a rough, tensionless, high-temperature phase. Thus, earlier conclusions on the order of the phase transition and on the existence of a hexatic phase are seen as due to finite size effects, the phase diagram of the dLr model being similar to that of a continuum analog previously formulated in the context of surface growth by MBE.

ISSN: 1539-3755

DOI: 10.1103/PhysRevE.73.015103

Record 246

Author(s): Calvo, GF; Alvarez-Estrada, RF

Title: Three-dimensional models for homogeneous DNA near denaturation

Source: JOURNAL OF PHYSICS-CONDENSED MATTER, 17 (50): 7755-7781 DEC 21 2005

Abstract: Motivated by the melting transition of DNA, we study genuinely three-dimensional models for two interacting open, flexible and homogeneous macromolecular chains, bound or unbound to each other, at thermal equilibrium from about room temperature up to about the denaturation temperature (T-un). In each chain, angular constraints on bond angles (due to covalent bonding) determine monomers: each monomer contains n(e) nucleotides and has an effective length d(e). These monomers could remain practically unaltered for temperatures in a range above and below Tu, down to 300 K. Estimates for n(e) and d(e) are provided and justified. Upon proceeding from Quantum Mechanics to the classical limit and using suitable large-distance approximations (partly, due to those monomer configurations), we get a generalization of Edwards' model, which includes effective potentials between monomers. The classical partition function for the two-chain system is reduced to an integral of a generalized and discretized two-chain Green's function. We analyse conditions for the denaturing transition. The fact that each single chain is an extended one-dimensional system modifies their mutual global interaction, in comparison with typical potentials between nucleotides: this is simply illustrated by computing a global effective potential between the two chains. Applications for Morse potentials are presented. Our models seem to be physically compatible with some previous one-dimensional ones and could allow us to efficiently extend the latter to three spatial dimensions.

ISSN: 0953-8984

DOI: 10.1088/0953-8984/17/50/001

Record 245

Author(s): Belletti, F; Campos, I; Maiorano, A; Gaviro, SP; Sciretti, D; Tarancon, A; Velasco, JL; Flor, AC; Navarro, D; Tellez, P; Fernandez, LA; Martin-Mayor, V; Sudupe, AM; Jimenez, S; Marinari, E; Mantovani, F; Poli, G; Schifano, SF; Tripiccione, L; Ruiz-Lorenzo, JJ

Title: Ianus: An adaptive FPGA computer

Source: COMPUTING IN SCIENCE & ENGINEERING, 8 (1): 41-49 JAN-FEB 2006

Abstract: With Ianus, a next-generation field-programmable gate array (FPGA)-based machine, the authors hope to build a system that can fully exploit the performance potential of FPGA devices. A software platform that simplifies Ianus programming will extend its intended application range to a wide class of interesting and computationally demanding problems.

ISSN: 1521-9615

Record 244

Author(s): Fernandez, LA; Martin-Mayor, V; Sciretti, D; Tarancon, A; Velasco, JL

Title: Numerical study of the enlarged O(5) symmetry of the 3D antiferromagnetic RP2 spin model

Source: PHYSICS LETTERS B, 628 (3-4): 281-290 NOV 10 2005

Abstract: We investigate by means of Monte Carlo simulation and finite-size scaling analysis the critical properties of the three-dimensional 0(5) non-linear sigma model and of the antiferromagnetic RP2 model, both of them regularized on a lattice. High accuracy estimates are obtained for the critical exponents, universal dimensionless quantities and critical couplings. It is concluded that both models belong to the same universality class, provided that rather non-standard identifications are made for the momentum-space propagator of the RP2 model. We have also investigated the phase diagram of the RP2 model extended by a second-neighbor interaction. A rich phase diagram is found, where most of the phase transitions are of the first order. (c) 2005 Elsevier B.V. All rights reserved.

ISSN: 0370-2693

DOI: 10.1016/j.physletb.2005.09.049

Record 243

Author(s): Jimenez, S; Martin-Mayor, V; Perez-Gaviro, S

Title: Rejuvenation and memory in model spin glasses in three and four dimensions

Source: PHYSICAL REVIEW B, 72 (5): Art. No. 054417 AUG 2005

Abstract: We numerically study aging for the Edwards-Anderson model in three and four dimensions using different temperature-change protocols. In D=3, time scales a thousand times larger than in previous work are reached with the Spin Update Engine (SUE) machine. Deviations from cumulative aging are observed in the nonmonotonic time behavior of the coherence length. Memory and rejuvenation effects are found in a temperature-cycle protocol, revealed by vanishing effective waiting times. Similar effects are reported for the D=3 site-diluted ferromagnetic Ising model (without chaos). However, rejuvenation is reduced if off-equilibrium corrections to the fluctuation-dissipation theorem are considered. Memory and rejuvenation are quantitatively describable in terms of the growth regime of the spin-glass coherence length.

ISSN: 1098-0121

DOI: 10.1103/PhysRevB.72.054417

Record 242

Author(s): Jimenez, S; Martin-Mayor, V; Perez-Gaviro, S

Title: Rejuvenation and memory in model spin glasses

Source: PROGRESS OF THEORETICAL PHYSICS SUPPLEMENT, (157): 25-28 2005

Conference Title: International Conference on Statistical Physics of Disordered Systems and Its Applications

Conference Date: JUL 12-15, 2004

Conference Location: Hayama, JAPAN

Abstract: We study memory and rejuvenation effects in Ising spin-glasses in 3 and 4 dimensions. In D = 3, 1000 times larger than in previous work are reached using the SUE machine. Memory and rejuvenation are found in a 2 temperatures cycle. Similar effects are reported for the site-diluted Ising model (without chaos). However, rejuvenation is reduced if off-equilibrium corrections to the fluctuation-dissipation theorem are considered. Memory and rejuvenation are describable in terms of the growth-regime of a coherence-length.

ISSN: 0375-9687

Record 241

Author(s): Ciliberti, S; Grigera, TS; Martin-Mayor, V; Parisi, G; Verrocchio, P

Title: Anderson localization in Euclidean random matrices

Source: PHYSICAL REVIEW B, 71 (15): Art. No. 153104 APR 2005

Abstract: We study the spectra and localization properties of Euclidean random matrices defined on a random graph. We introduce a powerful method to find the density of states and the localization threshold in topologically disordered (off-lattice) systems. We solve numerically an equation (exact on the random graph) for the probability distribution function of the diagonal elements of the resolvent matrix, with a population dynamics algorithm (PDA). We show that the localization threshold can be estimated by studying the stability of a population of real resolvents under the PDA. An application is given in the context of the instantaneous normal modes of a liquid.

ISSN: 1098-0121

DOI: 10.1103/PhysRevB.71.153104

Record 240

Author(s): Ruiz-Lorenzo, JJ; Cuerno, R; Moro, E; Sanchez, A

Title: Phase transition in tensionless surfaces

Source: BIOPHYSICAL CHEMISTRY, 115 (2-3): 187-193 APR 1 2005

Conference Title: International Symposium on Biology after the Genome - A Physical View

Conference Date: FEB 11-13, 2004

Conference Location: Zaragoza, SPAIN

Conference Host: Univ Zaragoza

Abstract: We study the critical behavior of the Laplacian roughening model, which describes the growth of tensionless surfaces. This type of growth phenomena is very important, for instance, in biological membranes and in molecular beam epitaxy. We summarize previous analytical and numerical results and point out their contradictions and differences, thus making clear the context of our work. Our contribution, achieved through large-scale numerical simulations, is the confirmation that the model exhibits a single continuous phase transition: the transition takes place between a continuum massless (i.e., with infinite correlation length) bilaplacian behavior and a massive propagator (finite correlation length). (c) 2004 Elsevier B.V. All rights reserved.

ISSN: 0301-4622

DOI: 10.1016/j.bpc.2004.12.025

Record 239

Author(s): Alonso, JL; Cruz, A; Fernandez, LA; Jimenez, S; Martin-Mayor, V; Ruiz-Lorenzo, JJ; Tarancon, A

Title: Phase diagram of the bosonic double-exchange model

Source: PHYSICAL REVIEW B, 71 (1): Art. No. 014420 JAN 2005

Abstract: The phase diagram of the simplest approximation to double-exchange systems, the bosonic double-exchange model with antiferromagnetic (AFM) superexchange coupling, is fully worked out by means of Monte Carlo simulations, large-N expansions, and variational mean-field calculations. We find a rich phase diagram, with no first-order phase transitions. The most surprising finding is the existence of a segmentlike ordered phase at low temperature for intermediate AFM coupling which cannot be detected in neutron-scattering experiments. This is signaled by a maximum (a cusp) in the specific heat. Below the phase transition, only short-range ordering would be found in neutron scattering. Researchers looking for a quantum critical point in manganites should be wary of this possibility. Finite-size scaling estimates of critical exponents are presented, although large scaling corrections are present in the reachable lattice sizes.

ISSN: 1098-0121

DOI: 10.1103/PhysRevB.71.014420

Record 238

Author(s): Calvo, GF; Alvarez-Estrada, RF

Title: Confined propagation of thermal neutrons using nanotubes

Source: NANOTECHNOLOGY, 15 (12): 1870-1876 DEC 2004

Abstract: We study the possible confined propagation of thermal neutrons along carbon nanotubes (CNTs) behaving as waveguides with total transverse cross section Omega(tot) at nanometre scales. Our approach extends previous proposals regarding similar phenomena along waveguides with Omega(tot) in the micron scale and it receives additional motivation by recent studies on the possible focusing of x-rays at the nanoscale. We consider single wall and multiwall CNTs (SWCNTs and MWCNTs). A proper description of the confined propagation appears to require quantum mechanics. All (or most) thermal neutrons would propagate along the MWCNT (the most favourable possibility) in the fundamental mode. We estimate various possible loss mechanisms in the intensity of thermal neutron beams propagating confined along the CNT: nuclear absorption and diffuse scattering, bending losses and tunnelling effects across the walls of the CNT. According to our purely theoretical model, and due to the smallness of Omega(tot), the transmitted neutron flux through a sole MWCNT would be rather small (roughly, about one or a few per hour across the whole Omega(tot), for an incoming flux outside the MWCNT of 10(14) neutrons cm(-2) s(-1)). We also discuss the potential interest of the confined propagation of thermal neutrons at the nanoscale and the possibility of the latter phenomenon in other types of nanotubes (NTs) different from CNTs.

ISSN: 0957-4484

DOI: 10.1088/0957-4484/15/12/032

Record 237

Author(s): Ciliberti, S; Grigera, TS; Martin-Mayor, V; Parisi, G; Verrocchio, P

Editors: Tokuyama, M; Oppenheim, I

Title: The Boson peak and the phonons in glasses

Source: SLOW DYNAMICS IN COMPLEX SYSTEMS, 708: 565-570 2004

Book series title: AIP CONFERENCE PROCEEDINGS

Conference Title: 3rd International Symposium on Slow Dynamics in Complex Systems

Conference Date: NOV 03-08, 2003

Conference Location: Sendai, JAPAN

Abstract: Despite the presence of topological disorder, phonons seem to exist also in glasses at very high frequencies (THz) and they remarkably persist into the supercooled liquid. A universal feature of such a systems is the Boson peak, an excess of states over the standard Debye contribution at the vibrational density of states. Exploiting the euclidean random matrix theory of vibrations in amorphous systems. we show that this peak is the signature of a phase transition in the space of the stationary points of the energy, from a minima-dominated phase (with phonons) at low energy to a saddle-point dominated phase (without phonons). The theoretical predictions are checked by means of numeric simulations.

ISSN: 0094-243X

ISBN: 0-7354-0183-7

Record 236

Author(s): Alvarez-Estrada, RF; Calvo, ML

Title: Neutron fibres and possible applications to NCT

Source: APPLIED RADIATION AND ISOTOPES, 61 (5): 841-844 NOV 2004

Conference Title: 11th World Congress on Neutron Capture Therapy

Conference Date: OCT 11-15, 2004

Conference Location: Boston, MA

Abstract: We summarize previous researches regarding neutron guides of small transverse cross-section (neutron fibres), smaller than those of the standard hollow guides and collimators employed currently. Those studies may not be widely known in the neutron capture therapy (NCT) community, but they may be interesting for it. Such neutron fibres could allow to deliver and concentrate neutron beams selectively in regions of size smaller than 1 mm. We present new estimates and point out and discuss some new possible specific applications of those neutron fibres, which would not replace standard NCT but could supplement it. Thus, we entertain the possibility that neutron fibres could be useful for additional therapies (in typical NCT durations) of: (i) rather small tumours, (ii) thin borders of tumours. The use of these neutron fibres could reduce the undesirable delivery of radiation to healthy tissue around regions with malignant tissue. (C) 2004 Elsevier Ltd. All rights reserved.

ISSN: 0969-8043

DOI: 10.1016/j.apradiso.2004.05.039

Record 235

Author(s): Grigera, TS; Martin-Mayor, V; Parisi, G; Verrocchio, P

Title: Asymptotic aging in structural glasses

Source: PHYSICAL REVIEW B, 70 (1): Art. No. 014202 JUL 2004

Abstract: Using a nonlocal Monte Carlo algorithm, we study the aging of a fragile glass, being able to follow it up to equilibrium, down to 0.89T(MC) (T-MC is the mode-coupling temperature), and up to long waiting times at lower temperatures. We show that the fluctuation-dissipation ratio is independent of the dynamics chosen and is compatible with a phase transition and that the scaling behavior of the aging part of the correlation supports the full-aging scenario.

ISSN: 1098-0121

DOI: 10.1103/PhysRevB.70.014202

Record 234

Author(s): Alvarez-Estrada, RF; Calvo, GF

Title: Flexible macromolecular chains with constraints: a quantum mechanical approach

Source: JOURNAL OF PHYSICS-CONDENSED MATTER, 16 (22): S2037-S2046 Sp. Iss. SI JUN 9 2004

Conference Title: 2nd International Conference on Applied Statistical Physics - Molecular Engineering

Conference Date: AUG 24-29, 2003

Conference Location: Puerto Vallarta, MEXICO

Abstract: Models for three-dimensional macromolecular chains with various angular constrains at thermal equilibrium at room temperature, based on quantum mechanics and a variational procedure, are presented. We get: (i) compact and systematic expressions for the effective quantum kinetic energy Hamiltonian operators (for the unconstrained slowly varying angular degrees of freedom characterizing the macromolecule, responsible for its flexibility), consistently with general requirements, and (ii) effective quantum partition functions. Both (i) and (ii) could, at a later stage, provide further-insight or be helpful for specific computations. Open freely rotating chains are studied in detail: the method also yields classical partition functions for them, which imply the existence of persistence lengths consistently. Other macromolecular chains also treated, more succinctly, are: (1) closed-ring freely rotating, (2) open freely rotating with further constraints (helical-like, star-like...) (3) open freely rotating double-stranded.

ISSN: 0953-8984

DOI: 10.1088/0953-8984/16/22/001

Record 233

Author(s): Alvarez, G; Alvarez-Estrada, RF

Title: Third-order equation for harmonic generation: complex canonical transformation and JWKB solution

Source: JOURNAL OF PHYSICS A-MATHEMATICAL AND GENERAL, 37 (7): 2611-2624 FEB 20 2004

Abstract: The quantum description of third harmonic generation can be formulated as an eigenvalue problem for a third-order linear differential equation. We perform a semiclassical study of this third-order equation, generalizing the familiar JWKB theory for the second-order Schrodinger equation, and deriving explicit (albeit approximate) formulas for the eigenvalues within this semiclassical context. A central role in this analysis is played by a nonlinear complex canonical transformation which permits a complete description of the classical motion (generated by a complex polynomial Hamiltonian function) in the complexified position and momentum planes.

ISSN: 0305-4470

DOI: 10.1088/0305-4470/37/7/007

Record 232

Author(s): Alvarez-Estrada, RF

Editors: Schmidt, MG

Title: Initial states and time evolution for out-of-equilibrium matter

Source: STRONG AND ELECTROWEAK MATTER 2002, PROCEEDINGS: 384-388 2003

Conference Title: 5th International Conference on Strong and Electroweak Matter (SEWM 2002)

Conference Date: OCT 02-05, 2002

Conference Location: HEIDELBERG, GERMANY

Conference Host: UNIV HEIDELBERG, INST THEORET PHYS

Abstract: Quantum gauge and (fermionic) matter fields, with microscopic dynamics described by Relativistic Quantum Field Theory (RQFT), are studied in out-of-equilibrium situations. Possible initial non-equilibrium states are represented by suitable initial density operators rho(Q,in). Suitable functional integrals for rho(Q,in), which generalize those in Equilibrium Thermal Field Theory, are considered. The subsequent time evolution of the system is formulated in some model.

ISBN: 981-238-333-6

Record 231

Author(s): Jimenez, S; Martin-Mayor, V; Parisi, G; Tarancon, A

Title: Ageing in spin-glasses in three, four and infinite dimensions

Source: JOURNAL OF PHYSICS A-MATHEMATICAL AND GENERAL, 36 (43): 10755-10771 OCT 31 2003

Abstract: The spin update engine (SUE) machine is used to extend, by a factor of 1000, the timescale of previous studies of the ageing, out-of-equilibrium dynamics of the Edwards-Anderson model with binary couplings, on large lattices (L = 60). The correlation function, C(t + t(w), t(w)), t(w) being the time elapsed under a quench from high-temperature, follows nicely a slightly-modified power law for t > t, Very small (logarithmic), yet clearly detectable deviations from the full-ageing t/t(w) scaling can be observed. Furthermore, the t < t(w) data show clear indications of the presence of more than one time sector in the ageing dynamics. Similar results are found in four dimensions, but a rather different behaviour is obtained in the infinite-dimensional z = 6 Viana-Bray model. Most surprisingly, our results in infinite dimensions seem incompatible with dynamical ultrametricity. A detailed study of the link correlation function is presented, suggesting that its ageing properties are the same as for the spin correlation function.

ISSN: 0305-4470

Record 230

Author(s): Ciliberti, S; Grigera, TS; Martin-Mayor, V; Parisi, G; Verrocchio, P

Title: Brillouin and boson peaks in glasses from vector Euclidean random matrix theory

Source: JOURNAL OF CHEMICAL PHYSICS, 119 (16): 8577-8591 OCT 22 2003

Abstract: A simple model of harmonic vibrations in topologically disordered systems, such as glasses and supercooled liquids, is studied analytically by extending Euclidean random matrix theory to include vector vibrations. Rather generally, it is found that (i) the dynamic structure factor shows soundlike Brillouin peaks whose longitudinal/transverse character can only be distinguished for small transferred momentum, p; (ii) the model presents a mechanical instability transition at small densities, for which scaling laws are analytically predicted and confirmed numerically; (iii) the Brillouin peaks persist deep into the unstable phase, the phase transition being noticeable mostly in their linewidth; (iv) the Brillouin linewidth scales like p(2) in the stable phase, and like p in the unstable one. The analytical results are checked numerically for a simple potential. The main features of glassy vibrations previously deduced from scalar are not substantially altered by these new results. (C) 2003 American Institute of Physics.

ISSN: 0021-9606

DOI: 10.1063/1.1610439

Record 229

Author(s): Calabrese, P; Martin-Mayor, V; Pelissetto, A; Vicari, E

Title: Three-dimensional randomly dilute Ising model: Monte Carlo results

Source: PHYSICAL REVIEW E, 68 (3): Art. No. 036136 Part 2 SEP 2003

Abstract: We perform a high-statistics simulation of the three-dimensional randomly dilute Ising model on cubic lattices L-3 with Lless than or equal to256. We choose a particular value of the density, x=0.8, for which the leading scaling corrections are suppressed. We determine the critical exponents, obtaining nu=0.683(3), eta=0.035(2), beta=0.3535(17), and alpha=-0.049(9), in agreement with previous numerical simulations. We also estimate numerically the fixed-point values of the four-point zero-momentum couplings that are used in field-theoretical fixed-dimension studies. Although these results somewhat differ from those obtained using perturbative field theory, the field-theoretical estimates of the critical exponents do not change significantly if the Monte Carlo result for the fixed point is used. Finally, we determine the six-point zero-momentum couplings, relevant for the small-magnetization expansion of the equation of state, and the invariant amplitude ratio R-xi(+) that expresses the universality of the free-energy density per correlation volume. We find R-xi(+)=0.2885(15).

ISSN: 1063-651X

DOI: 10.1103/PhysRevE.68.036136

Record 228

Author(s): Calabrese, P; Martin-Mayor, V; Pelissetto, A; Vicari, E

Title: Dynamic structure factor of the three-dimensional Ising model with purely relaxational dynamics

Source: PHYSICAL REVIEW E, 68 (1): Art. No. 016110 Part 2 JUL 2003

Abstract: We compute the dynamic structure factor for the three-dimensional Ising model with a purely relaxational dynamics (model A). We perform a perturbative calculation in the epsilon expansion, at two loops in the high-temperature phase and at one loop in the temperature magnetic-field plane, and a Monte Carlo simulation in the high-temperature phase. We find that the dynamic structure factor is very well approximated by its mean-field Gaussian form up to moderately large values of frequency omega and momentum k. In the region we can investigate, kxiless than or similar to5, omegatauless than or similar to10, where xi is the correlation length and tau is the zero-momentum autocorrelation time, deviations are at most of a few percent.

ISSN: 1063-651X

DOI: 10.1103/PhysRevE.68.016110

Record 227

Author(s): Alonso, JL; Fernandez, LA; Guinea, F; Lesmes, F; Martin-Mayor, V

Title: Phase diagram and influence of defects in the double perovskites

Source: PHYSICAL REVIEW B, 67 (21): Art. No. 214423 JUN 1 2003

Abstract: The phase diagram of the double perovskites of the type Sr2-xLaxFeMoO6 is analyzed, with and without disorder due to antisites. In addition to an homogeneous half metallic ferrimagnetic phase in the absence of doping and disorder, we find antiferromagnetic phases at large dopings, and other ferrimagnetic phases with lower saturation magnetization, in the presence of disorder.

ISSN: 1098-0121

DOI: 10.1103/PhysRevB.67.214423

Record 226

Author(s): Cruz, A; Fernandez, LA; Jimenez, S; Ruiz-Lorenzo, JJ; Tarancon, A

Title: Off-equilibrium fluctuation-dissipation relations in the 3d Ising spin glass in a magnetic field

Source: PHYSICAL REVIEW B, 67 (21): Art. No. 214425 JUN 1 2003

Abstract: We study the fluctuation-dissipation relations for a three dimensional Ising spin glass in a magnetic field both in the high temperature phase as well as in the low temperature one. In the region of times simulated we have found that our results support a picture of the low temperature phase with broken replica symmetry, but a droplet behavior cannot be completely excluded.

ISSN: 1098-0121

DOI: 10.1103/PhysRevB.67.214425

Record 225

Author(s): Carmona, JM; Cruz, A; Fernandez, LA; Jimenez, S; Martin-Mayor, V; Munoz-Sudupe, A; Pech, J; Ruiz-Lorenzo, JJ; Tarancon, A; Tellez, P

Title: Dynamical generation of a gauge symmetry in the double-exchange model

Source: PHYSICS LETTERS B, 560 (1-2): 140-148 MAY 8 2003

Abstract: It is shown that a bosonic formulation of the double-exchange model, one of the classical models for magnetism, generates dynamically a gauge-invariant phase in a finite region of the phase diagram. We use analytical methods, Monte Carlo simulations and finite-size scaling analysis. We study the transition line between that region and the paramagnetic phase. The numerical results show that this transition line belongs to the universality class of the antiferromagnetic RP2 model. The fact that one can define a universality class for the antiferromagnetic RP2 model, different from the one of the O (N) models, is puzzling and somehow contradicts naive expectations about universality. (C) 2003 Published by Elsevier Science B.V.

ISSN: 0370-2693

DOI: 10.1016/S0370-2693(03)00382-4

Record 224

Author(s): Grigera, TS; Martin-Mayor, V; Parisi, G; Verrocchio, P

Title: Phonon interpretation of the 'boson peak' in supercooled liquids

Source: NATURE, 422 (6929): 289-292 MAR 20 2003

Abstract: Glasses(1,2) are amorphous solids, in the sense that they display elastic behaviour. In crystalline solids, elasticity is associated with phonons, which are quantized vibrational excitations. Phonon-like excitations also exist in glasses at very high (terahertz; 10(12) Hz) frequencies; surprisingly, these persist in the supercooled liquids'. A universal feature of such amorphous systems is the boson peak: the vibrational density of states has an excess compared to the Debye squared-frequency law. Here we investigate the origin of this feature by studying the spectra of inherent structures' (local minima of the potential energy) in a realistic glass model. We claim that the peak is the signature of a phase transition in the space of the stationary points of the energy, from a minima-dominated phase (with phonons) at low energy to a saddle-point-dominated phase(5-7) (without phonons). The boson peak moves to lower frequencies on approaching the phonon-saddle transition, and its height diverges at the critical point. Our numerical results agree with the predictions of euclidean random matrix theory(8) on the existence of a sharp phase transition(9) between an amorphous elastic phase and a phonon-free one.

ISSN: 0028-0836

DOI: 10.1038/nature01475

Record 223

Author(s): Correale, L; Marinari, E; Martin-Mayor, V

Title: Eigenvalue analysis of the density matrix of four-dimensional spin glasses supports replica symmetry breaking

Source: PHYSICAL REVIEW B, 66 (17): Art. No. 174406 NOV 1 2002

Abstract: We present a general and powerful numerical method useful to study the density matrix of spin models. We apply the method to finite-dimensional spin glasses, and analyze in detail the four-dimensional Edwards-Anderson model with Gaussian quenched random couplings. Our results clearly support the existence of replica symmetry breaking in the thermodynamical limit.

ISSN: 1098-0121

DOI: 10.1103/PhysRevB.66.174406

Record 222

Author(s): Alonso, JL; Fernandez, LA; Guinea, F; Laliena, V; Martin-Mayor, V

Title: Interplay between double-exchange, superexchange, and Lifshitz localization in doped manganites

Source: PHYSICAL REVIEW B, 66 (10): Art. No. 104430 SEP 1 2002

Abstract: Considering the disorder caused in manganites by the substitution Mn-->Fe or Ga, we accomplish a systematic study of doped manganites begun in previous papers. To this end, a disordered model is formulated and solved using the variational mean-field technique. The subtle interplay between double exchange, superexchange, and disorder causes similar effects on the dependence of T-C on the percentage of Mn substitution in the cases considered. Yet, in La2/3Ca1/3Mn1-yGayO3 our results suggest a quantum critical point (QCP) for yapproximate to0.1-0.2, associated to the localization of the electronic states of the conduction band. In the case of LaxCaxMn1-yFeyO3 (with x=1/3,3/8) no such QCP is expected.

ISSN: 1098-0121

DOI: 10.1103/PhysRevB.66.104430

Record 221

Author(s): Burgy, J; Mayr, M; Martin-Mayor, V; Moreo, A; Dagotto, E

Title: Colossal effects in transition metal oxides caused by intrinsic inhomogeneities

Source: INTERNATIONAL JOURNAL OF MODERN PHYSICS B, 16 (20-22): 3293-3293 AUG 30 2002

Conference Title: 4th Conference on Physical Phenomena at High Magnetic Filds

Conference Date: OCT 19-25, 2001

Conference Location: SANTA FE, NEW MEXICO

ISSN: 0217-9792

Record 220

Author(s): Marinari, E; Parisi, G; Ruiz-Lorenzo, JJ

Title: Low T dynamical properties of spin glasses smoothly extrapolate to T=0

Source: JOURNAL OF PHYSICS A-MATHEMATICAL AND GENERAL, 35 (32): 6805-6814 AUG 16 2002

Abstract: We compare ground state properties of 3D Ising spin glasses with Gaussian couplings using results from off-equilibrium numerical simulations at non-zero (but low) temperatures. We find that the non-zero temperature properties of the system smoothly connect to the T = 0 behaviour, confirming the point of view that results established at T = 0 typically also give relevant information about the T not equal 0 physics of the system.

ISSN: 0305-4470

Record 219

Author(s): Martin-Mayor, V; Pelissetto, A; Vicari, E

Title: Critical structure factor in Ising systems

Source: PHYSICAL REVIEW E, 66 (2): Art. No. 026112 Part 2 AUG 2002

Abstract: We perform a large-scale Monte Carlo simulation of the three-dimensional Ising model on simple cubic lattices of size L-3 with L=128 and 256. We determine the corresponding structure factor (Fourier transform of the two-point function) and compare it with several approximations and with experimental results. We also compute the turbidity as a function of the momentum of the incoming radiation, focusing in particular on the deviations from the Ornstein-Zernike expression of Puglielli and Ford.

ISSN: 1063-651X

DOI: 10.1103/PhysRevE.66.026112

Record 218

Author(s): Alvarez-Estrada, RF; Calvo, GF

Title: Models for polymers and biopolymers based on quantum mechanics

Source: MOLECULAR PHYSICS, 100 (18): 2957-2970 SEP 2002

Conference Title: 1st International Conference on Applied Statistical Physics Molecular Engineering (ASTATPHYS-MEX-2001)

Conference Date: JUL 23-27, 2001

Conference Location: CANCUM, MEXICO

Abstract: A study has been made of several types of 3-dimensional macromolecular chains: open and closed-ring linear chains, star polymers and double-stranded chains. Chains in thermal equilibrium at room temperature are assumed, and typical harmonic-oscillator-like vibrational potentials with frequencies omega(i) for the interactions of nearest-neighbour atoms along the same chain. For the double-stranded chain, the interactions between atoms in different strands behave like the Morse potential. In physically interesting cases omega(i) is large, so that all rapidly varying vibrational degrees of freedom have to be treated quantum mechanically, and these are represented approximately by ground state wavefunctions; they decouple consistently, yielding constant bond lengths. This generates effective quantum Hamiltonians and partition functions for the macromolecules, depending only on the remaining and relevant slowly varying degrees of freedom (angles determining internal rotations). At room temperature, the classical limit of the slowly varying quantum description yields simpler effective classical Hamiltonians and partition functions. Previous results for the open linear chain are discussed together with former work for the closed-ring linear chain, and new models are presented for star polymers and double-stranded macromolecules. The model appears to describe consistently a double-stranded chain at temperatures below thermal denaturation.

ISSN: 0026-8976

DOI: 10.1080/00268970210121623

Record 217

Author(s): Alvarez-Estrada, RF

Title: New hierarchy for the Lionville equation, irreversibility and Fokker-Planck-like structures

Source: ANNALEN DER PHYSIK, 11 (5): 357-385 MAY 2002

Abstract: The issue of irreversibility is revisited for a closed system formed by N classical non-relativistic particles inside a volume Omega, interacting through two-body potentials, for large N and Omega. The classical phase-space distribution function f, multiplied by suitable Hermite polynomials and integrated over all momenta, yields new moments. The Liouville equation and the initial distribution f(in) imply a new non-equilibrium linear infinite hierarchy for the moments. That hierarchy differs from the BBGKY one for distribution functions and displays some suggestive Fokker-Planck-like structures. A physically motivated ansatz for f(in) (which introduces statistical assumptions), used by previous authors, is chosen. All moments of order n greater than or equal to n(0) are expressed in terms of those of order n(0) - 1 and of f(in). The properties of the Fokker-Planck-like structures (hermiticity, non-negative eigenvalues) allow for implementing a natural long-time approximation in the hierarchy, so as to introduce relaxation to equilibrium and irreversibility, consistently with the hydrodynamical balance equations. Further (more restrictive) assumptions and approximations lead to new irreversible models, generalizing non-trivially the Fokker-Planck equation. They are described through a truncated hierarchy of linear equations for moments of order n less than or equal to n(0) - 1 (n(0) being finite). The connections with Brownian particle dynamics and Fluid Dynamics are analyzed, for consistency.

ISSN: 0003-3804

Record 216

Author(s): Grigera, TS; Martin-Mayor, V; Parisi, G; Verrocchio, P

Title: Vibrational spectra in glasses

Source: PHILOSOPHICAL MAGAZINE B-PHYSICS OF CONDENSED MATTER STATISTICAL MECHANICS ELECTRONIC OPTICAL AND MAGNETIC PROPERTIES, 82 (6): 637-649 APR 2002

Conference Title: 8th International Workshop on Disordered Systems

Conference Date: MAR 12-15, 2001

Conference Location: ANDALO, ITALY

Abstract: The findings of X-ray and neutron scattering experiments on amorphous systems are interpreted within the framework of the theory of Euclidean random matrices. This allows us to take into account the topological nature of the disorder. a key ingredient which strongly affects the vibrational spectra of those systems. We present a resummation scheme for a perturbative expansion in the inverse particle density. allowing an accurate analytical computation of the dynamic structure factor within the range of densities encountered in real systems.

ISSN: 0141-8637

DOI: 10.1080/13642810110084588

Record 215

Author(s): Grigera, TS; Martin-Mayor, V; Parisi, G; Verrocchio, P

Title: Vibrations in glasses and Euclidean random matrix theory

Source: JOURNAL OF PHYSICS-CONDENSED MATTER, 14 (9): 2167-2179 MAR 11 2002

Conference Title: International Conference on Scaling Concepts and Complex Systems

Conference Date: JUL 09-14, 2001

Conference Location: MERIDA, MEXICO

Abstract: We study numerically and analytically a simple off-lattice model of scalar harmonic vibrations by means of Euclidean random matrix theory. Since the spectrum of this model shares the most puzzling spectral features with the high-frequency domain of glasses (non-Rayleigh broadening of the Brillouin peak, boson peal: and secondary peak), Euclidean random matrix theory provides a single and fairly simple theoretical framework for their explanation.

ISSN: 0953-8984

Record 214

Author(s): Verges, JA; Martin-Mayor, V; Brey, L

Title: Lattice-spin mechanism in colossal magnetoresistive manganites

Source: PHYSICAL REVIEW LETTERS, 88 (13): Art. No. 136401 APR 1 2002

Abstract: We present a single-orbital double-exchange model, coupled with cooperative phonons (the so called breathing modes of the oxygen octahedra in manganites). The model is studied with Monte Carlo simulations. For a finite range of doping and coupling constants, a first-order metal-insulator phase transition is found, which coincides with the paramagnetic-ferromagnetic phase transition. The insulating state is due to the self-trapping of every carrier within an oxygen octahedron distortion.

ISSN: 0031-9007

DOI: 10.1103/PhysRevLett.88.136401

Record 213

Author(s): Coluzzi, B; Verrocchio, P

Title: The liquid-glass transition of silica

Source: JOURNAL OF CHEMICAL PHYSICS, 116 (9): 3789-3794 MAR 1 2002

Abstract: We studied the liquid-glass transition of SiO2 by means of replica theory, utilizing an effective pair potential which was proved to reproduce a few experimental features of silica. We found a finite critical temperature T-0, where the system undergoes a phase transition related to replica symmetry breaking, in a region where experiments do not show any transition. The possible sources of this discrepancy are discussed. (C) 2002 American Institute of Physics.

ISSN: 0021-9606

DOI: 10.1063/1.1447905

Record 212

Author(s): Burgy, J; Mayr, M; Martin-Mayor, V; Moreo, A; Dagotto, E

Title: Colossal effects in transition metal oxides caused by intrinsic inhomogeneities

Source: PHYSICAL REVIEW LETTERS, 87 (27): Art. No. 277202 DEC 31 2001

Abstract: The influence of quenched disorder on the competition between ordered states separated by a first-order transition is investigated. A phase diagram with features resembling quantum-critical behavior is observed, even using classical, models. The low-temperature paramagnetic regime consists of coexisting, ordered clusters, with randomly oriented order parameters. Extended to manganites, this state is argued to have a colossal magnetoresistance effect. A scale T* for cluster formation is discussed. This is the analog of the Griffiths temperature, but for the case of two competing orders, producing a strong susceptibility to external fields. Cuprates may have similar features, compatible with the large proximity effect of the very underdoped regime.

ISSN: 0031-9007

DOI: 10.1103/PhysRevLett.87.277202

Record 211

Author(s): Alvarez, G; Alvarez-Estrada, RF

Title: Third harmonic generation as a third-order quasi-exactly solvable system

Source: JOURNAL OF PHYSICS A-MATHEMATICAL AND GENERAL, 34 (47): 10045-10056 NOV 30 2001

Abstract: The two degrees of freedom in the usual third harmonic generation effective Hamiltonian can be separated, both classically and quantum mechanically, into a harmonic oscillator and a nonlinear oscillator. In turn, the quantum Hamiltonian of the nonlinear oscillator can be written as a cubic polynomial in the generators of a quasi-exactly solvable Lie algebra, and the physically relevant eigenstates are precisely those that can be determined exactly (although, in general, not explicitly). Since the standard Jeffreys-Wentzel-Kramers-Brillouin methods are not easily applicable to general third-order differential equations, we use a Bohr-Sommerfeld quantization of the classical orbits to obtain approximate explicit formulas for the corresponding quantum eigenvalues.

ISSN: 0305-4470

Record 210

Author(s): Alonso, JL; Fernandez, LA; Guinea, F; Laliena, V; Martin-Mayor, V

Title: First-order transitions in double exchange materials

Source: JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 226: 849-850 Part 1 Sp. Iss. SI MAY 2001

Conference Title: International Conference on Magnetism

Conference Date: AUG 06-11, 2000

Conference Location: RECIFE, BRAZIL

Abstract: it is shown that the double-exchange Hamiltonian, with weak antiferromagnetic interactions, has a rich variety of first-order transitions between phases with different electronic densities and/or magnetizations. For band fillings in the range 0.3 less than or equal to x less than or equal to 0.5, and at finite temperatures. a discontinuous transition between phases with similar electronic densities but different magnetizations takes place. (C) 2001 Elsevier Science B.V. All rights reserved.

ISSN: 0304-8853

Record 209

Author(s): Grigera, TS; Martin-Mayor, V; Parisi, G; Verrocchi, R

Title: Vibrational spectrum of topologically disordered systems

Source: PHYSICAL REVIEW LETTERS, 87 (8): Art. No. 085502 AUG 20 2001

Abstract: The topological nature of the disorder of glasses and supercooled liquids strongly affects their high-frequency dynamics. In order to understand its main features, we analytically studied a simple topologically disordered model, where the particles oscillate around randomly distributed centers, interacting through a generic pair potential. We present results of a resummation of the perturbative expansion in the inverse particle density for the dynamic structure factor and density of states. This gives accurate results for the range of densities found in real systems.

ISSN: 0031-9007

DOI: 10.1103/PhysRevLett.87.085502

Record 208

Author(s): Alonso, JL; Capitan, JA; Fernandez, LA; Guinea, R; Martin-Mayor, V

Title: Monte Carlo determination of the phase diagram of the double-exchange model

Source: PHYSICAL REVIEW B, 64 (5): Art. No. 054408 AUG 1 2001

Abstract: We study the phase diagram of the double exchange model, with antiferromagnetic interactions, in a cubic lattice both at zero and finite temperature. There is a rich variety of magnetic phases, combined with regions where phase separation takes place. We identify phases, intrinsic to the cubic lattice, which are stable for realistic values of the interactions and dopings. Some of these phases break chiral symmetry, leading to unusual features.

ISSN: 0163-1829

Record 207

Author(s): Martin-Mayor, V; Mezard, M; Parisi, G; Verrocchio, P

Title: The dynamical structure factor in topologically disordered systems

Source: JOURNAL OF CHEMICAL PHYSICS, 114 (18): 8068-8081 MAY 8 2001

Abstract: A computation of the dynamical structure factor of topologically disordered systems, where the disorder can be described in terms of Euclidean random matrices, is presented. Among others, structural glasses and supercooled liquids belong to that class of systems. The computation describes their relevant spectral features in the region of the high frequency sound. The analytical results are tested with numerical simulations and are found to be in very good agreement with them. Our results may explain the findings of inelastic x-ray scattering experiments in various glassy systems. (C) 2001 American Institute of Physics.

ISSN: 0021-9606

Record 206

Author(s): Alonso, JL; Fernandez, LA; Guinea, F; Laliena, V; Martin-Mayor, V

Title: Hybrid Monte Carlo algorithm for the double exchange model

Source: NUCLEAR PHYSICS B, 596 (3): 587-610 MAR 5 2001

Abstract: The Hybrid Monte Carlo algorithm is adapted to the simulation of a system of classical degrees of freedom coupled to non self-interacting lattices fermions. The diagonalization of the Hamiltonian matrix is avoided by introducing a path-integral formulation of the problem, in d + I Euclidean space-time. A perfect action formulation allows to work on the continuum Euclidean time, without need for a Trotter-Suzuki extrapolation. To demonstrate the feasibility of the method we study the Double Exchange Model in three dimensions. The complexity of the algorithm grows only as the system volume, allowing to simulate in lattices as large as 16(3) on a personal computer. We conclude that the second order paramagnetic-ferromagnetic phase transition of Double Exchange Materials close to half-filling belongs to the Universality Class of the three-dimensional classical Heisenberg model. (C) 2001 Elsevier Science B.V. All rights reserved.

ISSN: 0550-3213

Record 205

Author(s): Alonso, JL; Fernandez, LA; Guinea, F; Laliena, V; Martin-Mayor, V

Title: Discontinuous transitions in double-exchange materials

Source: PHYSICAL REVIEW B, 63 (6): Art. No. 064416 FEB 1 2001

Abstract: It is shown that the double-exchange Hamiltonian, with weal; antiferromagnetic interactions, has a rich variety of first-order transitions between phases with different electronic densities and/or magnetizations. The paramagnetic-ferromagnetic transition moves towards lower temperatures, and becomes discontinuous as the relative strength of the: double-exchange mechanism and antiferromagnetic coupling is changed. This trend is consistent with the observed differences between compounds with the same nominal doping, such as La2/3Sr1/3MnO3 and La2/3Ca1/3MnO3. Our results suggest that,in the low doping regime, a simple magnetic mechanism suffices to explain the main features of the phase diagram.

ISSN: 0163-1829

Record 204

Author(s): Alonso, JL; Fernandez, LA; Guinea, F; Laliena, V; Martin-Mayor, V

Title: Variational mean-field approach to the double-exchange model

Source: PHYSICAL REVIEW B, 63 (5): Art. No. 054411 FEB 1 2001

Abstract: It has been recently shown that the double exchange Hamiltonian, with weak antiferromagnetic interactions, has a richer variety of first- and second-order transitions than previously anticipated, and that such transitions are consistent with the magnetic properties of manganites. Here we present a thorough discussion of the variational mean-field approach that leads to these results. We also show that the effect of the Berry phase turns out to be crucial to produce first-order paramagnetic-ferromagnetic transitions near half filling with transition temperatures compatible with the experimental situation. The computation relies on two crucial f'acts: the use of a mean-field ansatz: that retains the complexity of a system of electrons with off-diagonal disorder, not fully taken into account by the mean-held techniques, and the small but significant antiferromagnetic superexchange interaction between the localized spins.

ISSN: 0163-1829

Record 203

Author(s): Ballesteros, HG; Cruz, A; Fernandez, LA; Martin-Mayor, V; Pech, J; Ruiz-Lorenzo, JJ; Tarancon, A; Tellez, P; Ullod, CL; Ungil, C

Title: Critical behavior of the three-dimensional Ising spin glass

Source: PHYSICAL REVIEW B, 62 (21): 14237-14245 DEC 1 2000

Abstract: We have simulated, using parallel tempering, the three-dimensional Ising spin glass model with binary couplings in a helicoidal geometry. The largest lattice (L=20) has been studied using a dedicated computer (the SUE machine). We have obtained, measuring die correlation length in the critical region, strong evidence for a second-order finite-temperature phase transition, ruling out other possible scenarios like a Kosterlitz-Thouless phase transition. Precise values for the nu and eta critical exponents are also presented.

ISSN: 0163-1829

Record 202

Author(s): Calvo, GF; Alvarez-Estrada, RF

Title: Quantum statistical mechanics of closed-ring molecular chains

Source: MACROMOLECULAR THEORY AND SIMULATIONS, 9 (8): 585-599 NOV 14 2000

Abstract: A model for a closed-ring unhindered three-dimensional macromolecular chain. based on Quantum Mechanics, is presented. Upon starting from an extract non-relativistic Hamiltonian operator, we integrate out all electronic degrees of freedom, in the Born-Oppenheimer framework, giving rise to an effective vibro-rotational Hamiltonian for the chain. Then, assuming a harmonic oscillator-like vibrational potential between nearest-neighbour atoms, the integration of the atomic radial degrees of freedom is carried in the limit of high frequencies. Thus, all bond lengths become fixed, including the one which makes the chain to become a closed ring. This formulation leads to a specific Hamiltonian for the remaining angular variables of the closed-ring chain, and constitutes an alternative in comparison with standard Gaussian models, which do not, Use is made of a variational inequality by Peierls to find an approximate quantum partition function for the angular variables of the system. We then proceed to obtain approximately another representation for the angular partition function in the classical partition function are discussed.

ISSN: 1022-1344

Record 201

Author(s): Marinari, E; Martin-Mayor, V; Pagnani, A

Title: Spin-glass ordering in diluted magnetic semiconductors: A Monte Carlo study

Source: PHYSICAL REVIEW B, 62 (8): 4999-5002 AUG 15 2000

Abstract: We study the temperature-dilution phase diagram of a site-diluted Heisenberg antiferromagnet on a face-certered-cubic lattice, with and without the Dzyaloshinskii-Moriya anisotropic term, fixed to realistic microscopic parameters for IIB1-xMnxTe(IIB= Cd,Hg,Zn). We show that the dipolar Dzyaloshinskii-Moriya anisotropy induces a finite-temperature phase transition to a spin-glass phase, at dilutions larger than 80%. The resulting probability distribution of the order parameter P(q) is similar to the one found in the cubic lattice Edwards-Anderson-Ising model. The critical exponents undergo large finite-size corrections, but tend to values similar to the ones of the Edwards-Anderson-Ising model.

ISSN: 0163-1829

Record 200

Author(s): Martin-Mayor, V; Parisi, G; Verrocchio, P

Title: Dynamical structure factor in disordered systems

Source: PHYSICAL REVIEW E, 62 (2): 2373-2379 Part B AUG 2000

Abstract: We study the spectral width as a function of the external momentum for the dynamical structure factor of a disordered harmonic solid, considered as a toy model for supercooled liquids and glasses. In the contexts of both the single-link coherent potential approximation and a single-defect approximation, two different regimes are clearly identified: if the density of states at zero energy is zero, the usual p(4) law is recovered for small momentum. On the contrary, if the disorder induces a nonvanishing density of states at zero energy, a linear behavior is obtained. The dynamical structure factor is numerically calculated in lattices as large as 96(3) and satisfactorily agrees with the analytical computations.

ISSN: 1063-651X

Record 199

Author(s): Alonso, JL; Fernandez, LA; Martin-Mayor, V

Title: A measure of conductivity for lattice fermions at finite density

Source: PHYSICS LETTERS B, 480 (3-4): 392-398 MAY 11 2000

Abstract: We study the linear response to an external electric field of a system of fermions in a lattice at zero temperature. This allows to measure numerically the Euclidean conductivity which turns out to he compatible with an analytical calculation for fr ce fermions. The numerical method is generalizable to systems with dynamical interactions where no analytical approach is possible. (C) 2000 Elsevier science B.V. All rights reserved.

ISSN: 0370-2693

Record 198

Author(s): Marinari, E; Parisi, G; Ricci-Tersenghi, F; Ruiz-Lorenzo, JJ; Zuliani, F

Title: Replica symmetry breaking in short-range spin glasses: Theoretical foundations and numerical evidences

Source: JOURNAL OF STATISTICAL PHYSICS, 98 (5-6): 973-1047 MAR 2000

Abstract: We discuss replica symmetry breaking (RSB) in spin glasses. We update worth in this area, From both the analytical and numerical points of view. We give particular attention to the difficulties stressed by Newman and Stein concerning the problem of constructing pure states in spin lass systems. We mainly discuss what happens in finite-dimensional, realistic spin glasses. Together with a detailed review of some of the most important features, facts, data, and phenomena, we present some new theoretical ideas and numerical results. We discuss among others the basic idea of the RSB theory, correlation functions, interfaces, overlaps, pure states. random Field. and the dynamical approach. We present new numerical results For the behaviors of coupled replicas and about the numerical verification of sum rules, and we review some of the available numerical results that we consider of larger importanes for example, the determination of the phase transition point. the correlation functions, the window overlaps, and the dynamical behavior of the system.

ISSN: 0022-4715

Record 197

Author(s): Marinari, E; Parisi, G; Ricci-Tersenghi, F; Ruiz-Lorenzo, JJ

Title: Off-equilibrium dynamics at very low temperatures in three-dimensional spin glasses

Source: JOURNAL OF PHYSICS A-MATHEMATICAL AND GENERAL, 33 (12): 2373-2382 MAR 31 2000

Abstract: We present a high-statistic systematic study of the overlap correlation function well below the critical temperature in the three-dimensional Gaussian spin glass. The off-equilibrium correlation function has been studied confirming the power law behaviour for the dynamical correlation length. In particular, we have computed the dynamical critical exponent z in a wide range of temperatures, 0.35 less than or equal to T less than or equal to 0.9, obtaining a dependence z(T) = 6.2/T in very good agreement with recent experiments. Moreover, we report a study of the violation of the fluctuation-dissipation theorem for very low temperatures T = 0.5 and 0.35. All our numerical results avoid a droplet model interpretation even when T is as low as T = 0.35.

ISSN: 0305-4470

Record 196

Author(s): Alvarez, G; Martin-Mayor, V; Ruiz-Lorenzo, JJ

Title: Summability of the perturbative expansion for a zero-dimensional disordered spin model

Source: JOURNAL OF PHYSICS A-MATHEMATICAL AND GENERAL, 33 (5): 841-850 FEB 11 2000

Abstract: We show analytically that the perturbative expansion For the free energy of the zero-dimensional (quenched) disordered Ising model is Borel summable in a certain range of parameters, provided that the summation is carried out in two steps: first, in the strength of the original coupling of the Ising model and subsequently in the variance of the quenched disorder. This result is illustrated by some high-precision calculations of the free energy obtained by a straightforward numerical implementation of our sequential summation method.

ISSN: 0305-4470

Record 195

Author(s): Ballesteros, HG; Fernandez, LA; Martin-Mayor, V; Sudupe, AM; Parisi, G; Ruiz-Lorenzo, JJ

Title: Critical behavior in the site-diluted three-dimensional three-state Potts model

Source: PHYSICAL REVIEW B, 61 (5): 3215-3218 FEB 1 2000

Abstract: We have studied numerically the effect of quenched site dilution on a weak first-order phase transition in three dimensions. We have simulated the site diluted three-states Potts model studying in detail the second-order region of its phase diagram. We have found that the v exponent is compatible with the one of the three-dimensional diluted Ising model, whereas the eta exponent is definitely different.

ISSN: 1098-0121

Record 194

Author(s): Alvarez-Estrada, RF

Title: Models of macromolecular chains based on Classical and Quantum Mechanics: comparison with Gaussian models

Source: MACROMOLECULAR THEORY AND SIMULATIONS, 9 (2): 83-114 FEB 2000

Abstract: Feature Article: Different approaches to the study of open linear Freely-jointed (unhindered) threedimensional macromolecular chains at thermal equilibrium, based Classical Hamiltonian Dynamics with constraints (namely, a formulation equivalent to Kramers one) or Quantum Mechanics (with stiff harmonic springs), are reviewed and discussed in detail. Results from those approaches are compared to those arising from the standard Gaussian model. Fraenkel's approach, based upon Classical Mechanics (with stiff harmonic springs) and its comparison with the Gaussian model are also treated. It is that the quantum formulation is required in order that the treatment of the high-frequency vibrations be consistent. The role of the uncertainty principle is discussed, on support the quantum-mechanical approach. At a later stage, internal rotations can be treated through Classical Statistical mechanics, under certain conditions. The quantum-Mechanics-based model appears to be consistent with the Gaussian model, while the one based upon constrained Hamiltonian Dynamics yields certain discrepancies with the latter Classical and quantum-mechanical approaches to open linear freely-rotating (hindered) threedimensional macromolecular chains are also treated: the consistency of the quantum-mechanics-based model is displayed by deriving approximately the existence of a persistence length. It is argued that the possible advantages of the quantum-mechanical formulation should be expected not at large scales but at shorter ones. The specific topics to be treated are described in the summary of contents given below.

ISSN: 1022-1344

Record 193

Author(s): Ruiz-Lorenzo, JJ; Ullod, CL

Title: Study of a microcanonical algorithm on the +/- J spin glass model in d=3

Source: COMPUTER PHYSICS COMMUNICATIONS, 125 (1-3): 210-220 MAR 2000

Abstract: We consider a microcanonical local algorithm to be applied on the +/-J spin glass model. We have compared the results coming from a microcanonical Monte Carlo simulation with those from a canonical one: Thermalization times, spin glass susceptibilities and Binder parameters. For a fixed lattice size we found different results between the two thermodynamic ensembles, which tend to vanish at bigger volumes. Moreover, microcanonical thermalization times are longer than the canonical ones. Finally we have checked that one of the Guerra relations is satisfied with good precision for the two largest lattices. (C) 2000 Elsevier Science B.V. All rights reserved.

ISSN: 0010-4655

Record 192

Author(s): Alonso, JL; Boucaud, P; Martin-Mayor, V; van der Sijs, AJ

Title: Phase diagram and quasiparticles of a lattice SU(2) scalar-fermion model in 2+1 dimensions

Source: PHYSICAL REVIEW D, 61 (3): Art. No. 034501 FEB 1 2000

Abstract: The phase diagram at zero temperature of a lattice SU(2) scalar-fermion model in 2+1 dimensions is studied numerically and with mean-field methods. Special attention is devoted to the strong coupling regime. We have developed a new method to adapt the hybrid Monte Carlo algorithm to the O(3) non-linear sigma model constraint. The charged excitations in the various phases are studied at the mean field level. Bound states of two charged fermions are found in a strongly coupled paramagnetic phase. On the other hand, in the strongly coupled antiferromagnetic phase fermionic excitations around momenta (+/- pi/2,+/-pi/2,+/-pi/2) emerge.

ISSN: 0556-2821

Record 191

Author(s): Coluzzi, B; Parisi, G; Verrocchio, P

Title: Lennard-Jones binary mixture: A thermodynamical approach to glass transition

Source: JOURNAL OF CHEMICAL PHYSICS, 112 (6): 2933-2944 FEB 8 2000

Abstract: We study the liquid-glass transition of the Lennard-Jones binary mixture introduced by Kob and Andersen from a thermodynamic point of view. By means of the replica approach, translating the problem in the study of a molecular liquid, we study the phase transition due to the entropy crisis and we find that the Kauzmann's temperature T-K is similar to 0.32. At the end we compare analytical predictions with numerical results. (C) 2000 American Institute of Physics. [S0021-9606(00)50106-8].

ISSN: 0021-9606

Record 190

Author(s): Coluzzi, B; Parisi, G; Verrocchio, P

Title: Thermodynamical liquid-glass transition in a Lennard-Jones binary mixture

Source: PHYSICAL REVIEW LETTERS, 84 (2): 306-309 JAN 10 2000

Abstract: We use results derived in the framework of the replica approach to study the liquid-glass thermodynamic transition. The main results are derived without using replicas and applied to the study of the Lennard-Jones binary mixture introduced by Kob and Andersen. We find that there is a phase transition due to the entropy crisis. We compute both analytically and numerically the value of the phase transition point T-K and the specific heat in the low temperature phase.

ISSN: 0031-9007

Record 189

Author(s): Parisi, G; Ricci-Tersenghi, F; Ruiz-Lorenzo, JJ

Title: Universality in the off-equilibrium critical dynamics of the three-dimensional diluted Ising model

Source: PHYSICAL REVIEW E, 60 (5): 5198-5201 Part A NOV 1999

Abstract: We study the off-equilibrium critical dynamics of the three-dimensional diluted Ising model. We compute the dynamical critical exponent z and we show that it is independent of the dilution only when we take into account the scaling corrections to the dynamics. Finally, we will compare our results with the experimental data [S1063-651X(99)02511-8].

ISSN: 1063-651X

Record 188

Author(s): Coluzzi, B; Mezard, M; Parisi, G; Verrocchio, P

Title: Thermodynamics of binary mixture glasses

Source: JOURNAL OF CHEMICAL PHYSICS, 111 (19): 9039-9052 NOV 15 1999

Abstract: We compute the thermodynamic properties of the glass phase in a binary mixture of soft spheres. Our approach is a generalization to mixtures of the replica strategy, recently proposed by Mezard and Parisi, providing a first principle statistical mechanics computation of the thermodynamics of glasses. The method starts from the interatomic potentials, and translates the problem into the study of a molecular liquid. We compare our analytical predictions to numerical simulations, focusing onto the values of the thermodynamic transition temperature and the configurational entropy. (C) 1999 American Institute of Physics. [S0021- 9606(99)51443-8].

ISSN: 0021-9606

Record 187

Author(s): Parisi, G; Ricci-Tersenghi, F; Ruiz-Lorenzo, JJ

Title: Generalized off-equilibrium fluctuation-dissipation relations in random Ising systems

Source: EUROPEAN PHYSICAL JOURNAL B, 11 (2): 317-325 SEP 1999

Abstract: We show that the numerical method based on the off-equilibrium fluctuation-dissipation relation does work and is very useful and powerful in the study of disordered systems which show a very slow dynamics. We have verified that it gives the right information in the known cases (diluted ferromagnets and random field Ising model far from the critical point) and we used it to obtain more convincing results on the frozen phase of four-dimensional spin glasses. Moreover we used it to study the Griffiths phase of the diluted and the random field Ising models.

ISSN: 1434-6028

Record 186

Author(s): Marinari, E; Parisi, G; Ruiz-Lorenzo, JJ; Zuliani, F

Title: Comment on "Evidence for the droplet picture of spin glasses"

Source: PHYSICAL REVIEW LETTERS, 82 (25): 5176-5176 JUN 21 1999

ISSN: 0031-9007

Record 185

Author(s): Fernandez, LA; Martin-Mayor, V

Title: On the universality class of monopole percolation in scalar QED

Source: PHYSICS LETTERS B, 452 (3-4): 310-317 APR 22 1999

Abstract: We study the critical properties of the monopole-percolation transition in U(1) lattice gauge theory coupled to scalars at infinite (beta = 0) gauge coupling. We find strong scaling corrections in the critical exponents that must be considered by means of an infinite-volume extrapolation. after the extrapolation, our results are as precise as the obtained for the four dimensional site-percolation and, contrary to previously stated, fully compatible with them. (C) 1999 Published by Elsevier Science B.V. All rights reserved.

ISSN: 0370-2693

Record 184

Author(s): Alvarez-Estrada, RF; Sanchez-Gomez, JL

Title: On the absence of the Zeno effect in relativistic quantum field theory

Source: PHYSICS LETTERS A, 253 (5-6): 252-258 MAR 29 1999

Abstract: Pie study the time evolution of decaying particles in renormalizable models of relativistic quantum field theory (RQFT). Significant differences between the latter and nonrelativistic quantum mechanics are found - in particular, the Zeno effect seems to be absent in such RQFT models. Conventional renormalization yields finite time behaviour in some cases but fails to produce finite survival probabilities in others. (C) 1999 Elsevier Science B.V.

ISSN: 0375-9601

Record 183

Author(s): Ballesteros, HG; Fernandez, LA; Martin-Mayor, V; Sudupe, AM; Parisi, G; Ruiz-Lorenzo, JJ

Title: Scaling corrections: site percolation and Ising model in three dimensions

Source: JOURNAL OF PHYSICS A-MATHEMATICAL AND GENERAL, 32 (1): 1-13 JAN 8 1999

Abstract: Using finite-size scaling techniques we obtain accurate results for critical quantities of the Ising model and the site percolation, in three dimensions. We pay special attention to parametrizing the corrections-to-scaling, which is necessary to bring the systematic errors below the statistical ones.

ISSN: 0305-4470

Record 182

Author(s): Ballesteros, HG; Fernandez, LA; Martin-Mayor, V; Sudupe, AM

Title: Finite Size Scaling and "perfect" actions: the three dimensional Ising model

Source: PHYSICS LETTERS B, 441 (1-4): 330-338 NOV 26 1998

Abstract: Using Finite-Size Scaling techniques, we numerically show that the first irrelevant operator of the lattice lambda phi(4) theory in three dimensions is (within errors) completely decoupled at lambda = 1.0. This interesting result also holds in the Thermodynamical Limit, where the renormalized coupling constant shows an extraordinary reduction of the scaling-corrections when compared with the Ising model. It is argued that Finite-Size Scaling analysis can be a competitive method for finding improved actions. (C) 1998 Elsevier Science B.V. All rights reserved.

ISSN: 0370-2693

Record 181

Author(s): Marinari, E; Parisi, G; Ruiz-Lorenzo, JJ

Title: Phase structure of the three-dimensional Edwards-Anderson spin glass

Source: PHYSICAL REVIEW B, 58 (22): 14852-14863 DEC 1 1998

Abstract: We characterize numerically the properties of the phase transition of the three-dimensional Ising spin glass with Gaussian couplings and of the low-temperature phase. We compute critical exponents on large lattices. We study in detail the overlap probability distribution and the equilibrium overlap-overlap correlation functions. We find a clear agreement with off-equilibrium results from previous work. These results strongly support the existence of a continuous spontaneous replica symmetry breaking in three-dimensional spin glasses. [S0163-1829(98)03141-5].

ISSN: 0163-1829

Record 180

Author(s): Carmona, JM; Marconi, UMB; Ruiz-Lorenzo, JJ; Tarancon, A

Title: Critical properties of the Ising model on Sierpinski fractals: A finite-size scaling-analysis approach

Source: PHYSICAL REVIEW B, 58 (21): 14387-14396 DEC 1 1998

Abstract: The present paper focuses on the order-disorder transition of an Ising model on a self-similar lattice. We present a detailed numerical study, based on the Monte Carlo method in conjunction with the finite-size scaling method, of the critical properties of the Ising model on some two-dimensional deterministic fractal lattices with different Hausdorff dimensions. Those with finite ramification order do not display ordered phases at any finite temperature, whereas the lattices with infinite connectivity show genuine critical behavior. In particular, we considered two Sierpinski carpets constructed using different generators and characterized by Hausdorff dimensions d(H)=ln 8/ln 3=1.8927... and d(H)=ln 12/ln 4 =1.7924..., respectively. The data show in a clear way the existence of an order-disorder transition at finite temperature in both Sierpinski carpets. By performing several Monte Carlo simulations at different temperatures and on lattices of increasing size in conjunction with a finite-size scaling analysis, we were able to determine numerically the critical exponents in each case and to provide an estimate of their errors. Finally, we considered the hyperscaling relation and found indications that it holds, if one assumes that the relevant dimension in this case is the Hausdorff dimension of the lattice. [S0163-1829(98)02545-4].

ISSN: 0163-1829

Record 179

Author(s): Ballesteros, HG; Martin-Mayor, V

Title: Test for random number generators: Schwinger-Dyson equations for the Ising model

Source: PHYSICAL REVIEW E, 58 (5): 6787-6791 Part B NOV 1998

Abstract: We use a set of Schwinger-Dyson equations for the Ising model to check several random number generators. For the model in two and three dimensions, it is shown that the equations are sensitive tests of bias originating with the random numbers. The method is almost costless in computer time when added to any simulation. [S1063-651X(98)05411-7].

ISSN: 1063-651X

Record 178

Author(s): Ruiz-Lorenzo, JJ

Title: Logarithmic corrections for spin glasses, percolation and Lee-Yang singularities in six dimensions

Source: JOURNAL OF PHYSICS A-MATHEMATICAL AND GENERAL, 31 (44): 8773-8787 NOV 6 1998

Abstract: We study analytically the logarithmic corrections to the critical exponents of the critical behaviour of correlation length, susceptibility and specific heat for the temperature and the finite-size scaling behaviour, for a generic phi(3) theory at its upper critical dimension (six). We have also computed the leading correction to scaling as a function of the lattice size. We distinguish the obtained formulae to the following special cases: percolation, Lee-Yang singularities and m-component spin glasses. We have compared our results for the Ising spin glass case with numerical simulations finding a very good agreement. Finally, and using the results obtained for the Lee-Yang singularities in six dimensions, we have computed the logarithmic corrections to the singular part of the free energy for lattice animals in eight dimensions.

ISSN: 0305-4470

Record 177

Author(s): Alvarez-Estrada, RF

Title: A quantum mechanical Hamiltonian for unhindered macromolecular chains: consistency with Gaussian models

Source: MACROMOLECULAR THEORY AND SIMULATIONS, 7 (5): 457-468 SEP 1998

Abstract: A model for an open unhindered three-dimensional macromolecular chain, based upon quantum mechanics and proposed in previous works, is studied in order to investigate its physical properties and consistency. The chain is formed by N particles interacting through harmonic-like vibrational potentials in the high-frequency limit (in which all successive bond lengths become fixed). This formulation leads to a specific Hamiltonian for the chain: it constitutes an improvement in comparison with standard Gaussian models, which do not. The classical partition function Z(c) resulting from the quantum formulation is represented through an integral, which exhibits explicitly rotational invariance in the integrand and provides the basis for further approximations for large N. Approximate formulae are obtained for correlations between pairs of bond vectors, the distribution function for the end-to-end vector, distribution functions for individual bond vectors, "rubber eleasticity" (when stretching forces act) and the structure factor for small wave vector. In all cases, the results which have arisen from the quantum mechanical formulation coincide with those obtained for the standard Gaussian chain. This agreement appears to confirm the physical consistency of the quantum Hamiltonian characterizing the model.

ISSN: 1022-1344

Record 176

Author(s): Alvarez-Estrada, RF

Title: Hindered macromolecular chains: A quantum mechanical model

Source: MACROMOLECULAR THEORY AND SIMULATIONS, 7 (5): 469-482 SEP 1998

Abstract: A model for an open hindered three-dimensional macromolecular chain, based upon quantum mechanics, is proposed, which improves previous work. The chain is formed by N particles (so that all bond lengths between successive particles take on given values) and harmonic-like vibrational potentials in the high-frequency limit constrain all successive bond angles. This formulation leads, via a variational procedure and a suitable choice of variables, to a specific quantum Hamiltonian for the chain. Issues related to overall rotational invariance are clarified. Some properties of the resulting classical partition function are analyzed. Several checks of consistency are given.

ISSN: 1022-1344

Record 175

Author(s): Ballesteros, HG; Fernandez, LA; Martin-Mayor, V; Sudupe, AM; Parisi, G; Ruiz-Lorenzo, JJ

Title: Critical exponents of the three-dimensional diluted Ising model

Source: PHYSICAL REVIEW B, 58 (5): 2740-2747 AUG 1 1998

Abstract: We study the phase diagram of the site-diluted Ising model in a wide dilution range, through Monte Carlo simulations and finite-size scaling techniques. Our results for the critical exponents and universal cumulants turn out to be dilution independent, but only after a proper infinite volume extrapolation, taking into account the leading corrections-to-scaling terms. [S0163-1829(98)00429-9].

ISSN: 0163-1829

Record 174

Author(s): Marinari, E; Parisi, G; Ricci-Tersenghi, F; Ruiz-Lorenzo, JJ

Title: Small window overlaps are effective probes of replica symmetry breaking in three-dimensional spin glasses

Source: JOURNAL OF PHYSICS A-MATHEMATICAL AND GENERAL, 31 (26): L481-L487 JUL 3 1998

Abstract: We numerically compute small window overlaps in the three-dimensional Edwards-Anderson spin glass. We show that they behave in the way implied by the replica symmetry breaking ansatz, that they do not qualitatively differ from the full volume overlap and do not tend to a trivial function when increasing the lattice volume. In contrast we show that they are affected by small finite-volume effects, and are interesting tools for the study of the features of the spin-glass phase.

ISSN: 0305-4470

Record 173

Author(s): Parisi, G; Ricci-Tersenghi, F; Ruiz-Lorenzo, JJ

Title: Dynamics of the four-dimensional spin glass in a magnetic field

Source: PHYSICAL REVIEW B, 57 (21): 13617-13623 JUN 1 1998

Abstract: We study the four-dimensional Gaussian spin glass in presence of a magnetic field. Using off-equilibrium numerical simulations we have found that the probability distribution of the overlaps is built in the same way as that of the mean-field approximation with replica symmetry breaking. Finally, we have studied the violation of the fluctuation-dissipation theorem in presence of a magnetic field.

ISSN: 0163-1829

Record 172

Author(s): Parisi, G; Ruiz-Lorenzo, JJ; Stariolo, DA

Title: Crossovers in the two-dimensional Ising spin glass with ferromagnetic next-nearest-neighbour interactions

Source: JOURNAL OF PHYSICS A-MATHEMATICAL AND GENERAL, 31 (20): 4657-4668 MAY 22 1998

Abstract: By means of extensive computer simulations we analyse in detail the two-dimensional +/-J Ising spin glass with ferromagnetic next-nearest-neighbour interactions. We found a crossover from ferromagnetic to 'spin glass'-like order both from numerical simulations and analytical arguments. We also present proof of a second crossover from die 'spin glass' behaviour to a paramagnetic phase for the largest volume studied.

ISSN: 0305-4470

Record 171

Author(s): Alonso, JL; Boucaud, P; Martin-Mayor, V; van der Sijs, AJ

Title: A model for the doped copper oxide compounds

Source: EUROPHYSICS LETTERS, 42 (5): 541-546 JUN 1 1998

Abstract: We present a relativistic spin-fermion model for the cuprates, in which both the charge and spin degrees of freedom are treated dynamically. The spin-charge coupling parameter is associated with the doping fraction. The model is able to account for the various phases of the cuprates and their properties, not only at low and intermediate doping but also for (highly) over-doped compounds. In particular, we acquire a qualitative understanding of high-T-c superconductivity through Bose-Einstein condensation of bound charge pairs. The mechanism that binds these pairs does not require a Fermi sea.

ISSN: 0295-5075

Record 170

Author(s): Ballesteros, HG; Carmona, JM; Fernandez, LA; Tarancon, A

Title: Antiferromagnetic O(N) models in four dimensions

Source: PHYSICS LETTERS B, 419 (1-4): 303-310 FEB 12 1998

Abstract: We study the antiferromagnetic O(N) model in the F-4 lattice. Monte Carlo simulations are applied for investigating the behavior of the transition for N = 2,3. The numerical results show a first order nature but with a large correlation length. The N --> infinity limit is also considered with analytical methods. (C) 1998 Elsevier Science B.V.

ISSN: 0370-2693

Record 169

Author(s): Ballesteros, HG; Fernandez, LA; Martin-Mayor, V; Sudupe, AM; Parisi, G; Ruiz-Lorenzo, JJ

Title: Finite-size scaling study of the d=4 site-diluted Ising model

Source: NUCLEAR PHYSICS B-PROCEEDINGS SUPPLEMENTS, 63: 625-627 APR 1998

Conference Title: XVth International Symposium on Lattice Field Theory (Lattice 97)

Conference Date: JUL 22-26, 1997

Conference Location: EDINBURGH, SCOTLAND

Abstract: We study the four dimensional site-diluted Ising model using finite-size scaling techniques. We explore the whole parameter space (density-coupling) in order to determine the Universality Class of the transition line. Our data are compatible with Mean Field behavior plus logarithmic corrections.

ISSN: 0920-5632

Record 168

Author(s): Alonso, JL; Boucaud, P; Martin-Mayor, V; van der Sijs, AJ

Title: A lattice field theoretical model for high-T-c superconductivity

Source: NUCLEAR PHYSICS B-PROCEEDINGS SUPPLEMENTS, 63: 658-660 APR 1998

Conference Title: XVth International Symposium on Lattice Field Theory (Lattice 97)

Conference Date: JUL 22-26, 1997

Conference Location: EDINBURGH, SCOTLAND

Abstract: We present a 2+1-dimensional lattice model for the copper oxide superconductors and their parent compounds, in which both the charge and spin degrees of freedom are treated dynamically. The spin-charge coupling parameter is associated to the doping fraction in the cuprates. The model is able to account for the various phases of the cuprates and their properties, not only at low and intermediate doping but also for (highly) over-doped compounds. We acquire a qualitative understanding of high-T-c superconductivity as a Bose-Einstein condensation of bound charge pairs.

ISSN: 0920-5632

Record 167

Author(s): Marinari, E; Parisi, G; Ricci-Tersenghi, F; Ruiz-Lorenzo, JJ

Title: Violation of the fluctuation-dissipation theorem in finite-dimensional spin glasses

Source: JOURNAL OF PHYSICS A-MATHEMATICAL AND GENERAL, 31 (11): 2611-2620 MAR 20 1998

Abstract: We study the violation of the fluctuation-dissipation theorem in the three-and four-dimensional Gaussian Ising spin glasses using on and off equilibrium simulations. We have characterized numerically the function X(C) that determine the violation and we have studied its scaling properties. Moreover we have computed the function x(C) which characterize the breaking of the replica symmetry directly from equilibrium simulations. The two functions are numerically equal and in this way we have established that the conjectured connection between the violation of fluctuation-dissipation theorem in the off-equilibrium dynamics and the replica symmetry breaking at equilibrium holds for finite-dimensional spin glasses. These results point to a spin-glass phase with spontaneously broken replica symmetry in finite-dimensional spin glasses.

ISSN: 0305-4470

Record 166

Author(s): Alvarez-Estrada, RF; Nicola, AG

Title: Schwinger and Thirring models at finite chemical potential and temperature

Source: PHYSICAL REVIEW D, 57 (6): 3618-3633 MAR 15 1998

Abstract: The imaginary time generating functional Z for the massless Schwinger model at nonzero chemical potential mu and temperature T is studied in a torus with spatial length L. The lack of Hermiticity of the Dirac operator gives rise to a nontrivial mu- and T-dependent phase J in the effective action. When the Dirac operator has no zero modes (trivial sector), we evaluate J, which is a topological contribution, and we find exactly Z, the thermodynamical partition function, the boson propagator and the thermally averaged Polyakov loop. The mu-dependent contribution of the free partition function cancels exactly the nonperturbative one from J, for L-->infinity, yielding a zero charge density for the system, which bosonizes at nonzero mu. The boson mass is e/root pi, independent of T and mu, which is also the inverse correlation length between two opposite charges. Both the boson propagator and the Polyakov loop acquire a new T- and mu-dependent term at L-->infinity. The imaginary time generating functional for the massless Thirring model at nonzero T and mu is obtained exactly in terms of the above solution of the Schwinger model in the trivial sector. For this model, the mu dependences of the thermodynamical partition function, the total fermion number density and the fermion two-point correlation function are obtained. The phase J displayed here leads to our new results and allows us to complement nontrivially previous studies on those models.

ISSN: 0556-2821

Record 165

Author(s): Ballesteros, HG; Fernandez, LA; Martin-Mayor, V; Sudupe, AM; Parisi, G; Ruiz-Lorenzo, JJ

Title: The four-dimensional site-diluted Ising model: A finite-size scaling study

Source: NUCLEAR PHYSICS B, 512 (3): 681-701 FEB 23 1998

Abstract: Using finite-size scaling techniques, we study the critical properties of the site-diluted Ising model in four dimensions. We carry out a high-statistics Monte Carlo simulation for several values of the dilution. The results support the perturbative scenario: there is only the Ising fixed point with large logarithmic scaling corrections, We obtain, using the Perturbative Renormalization Group, functional forms for the scaling of several observables that are in agreement with the numerical data. (C) 1998 Elsevier Science B.V.

ISSN: 0550-3213

Record 164

Author(s): Porzi, G; Sandri, S; Verrocchio, P

Title: Stereoselective synthesis of sterically constrained dipeptides. Part 2

Source: TETRAHEDRON-ASYMMETRY, 9 (1): 119-132 JAN 16 1998

Abstract: The alkylation of the diastereomeric mixture of lactims 2 and 3 occurs in total regioselectivity and good to high facial stereoselectivity (d.s. ranging from 82 to 97%). Cleavage of the lactim 4e gives enantiomerically pure dipeptide 12, sterically constrained at the alpha-carbon. The absolute configuration of the new stereocentres has been assigned on the basis of H-1-NMR data and NOE measurements. (C) 1998 Elsevier Science Ltd. All rights reserved.

ISSN: 0957-4166

Record 163

Author(s): Cruz, A; Iniguez, D; Fernandez, LA; Munoz-Sudupe, A; Tarancon, A

Title: Study of the Coulomb-Higgs transition in the abelian Higgs model

Source: PHYSICS LETTERS B, 416 (1-2): 163-168 JAN 1 1998

Abstract: The order of the Coulomb-Higgs transition in the U(1)-Higgs model with unfrozen modulus of the scalar field is studied. Large lattices (up to 24(4) in one case) and high statistics are used. We fix beta=1.15 and explore specially a region of lambda-values where metastability is observed. We study the thermodynamical limit of several observables, in particular, the latent heat, the specific heat, the decrement of the free energy between the maxima and the central minimum of the two-peaked histogram, the Binder cumulant and the displacement of the critical coupling with the lattice size. The results point towards a second order transition for lambda greater than or similar to 0.005, while for smaller values of lambda the strong metastability growing with the lattice size seems to derive from a first order character. (C) 1998 Elsevier Science B.V.

ISSN: 0370-2693

Record 162

Author(s): Ballesteros, HG; Fernandez, LA; Martin-Mayor, V; Sudupe, AM; Parisi, G; Ruiz-Lorenzo, JJ

Title: Ising exponents in the two-dimensional site-diluted Ising model

Source: JOURNAL OF PHYSICS A-MATHEMATICAL AND GENERAL, 30 (24): 8379-8383 DEC 21 1997

Abstract: We study the site-diluted Ising model in two dimensions with Monte Carlo simulations. Using finite-size scaling techniques we compute the critical exponents observing deviations from the pure Ising ones. The differences can be explained as the effects of logarithmic corrections, without requiring us to change the universality class.

ISSN: 0305-4470

Record 161

Author(s): AlvarezEstrada, RF

Title: Open three-dimensional unhindered molecular chains: Partition function

Source: MACROMOLECULAR THEORY AND SIMULATIONS, 6 (6): 1237-1261 NOV 1997

Abstract: An open molecular chain, formed by N classical particles moving in three dimensions and having N - 1 bands of constant lengths between successive neighbours, is considered. Hamiltonian methods with manifest rotational invariance allow to characterize all constraints. The classical partition function, Z(0), for a large open chain in thermal equilibrium is analyzed in general. Simpler integral representations for Z(0) are obtained, with the following advantages: i) explicit rotational invariance in the integrands, ii) only tridiagonal matrices appear and, moreover, approximations for their determinants can be obtained. For a two-dimensional open chain, an approximate factorized formula for Z(0) is presented, and its essentials are generalized to the three-dimensional case. In both cases, the features of the partition functions bear certain similarities to that for a classical ideal gas. The approximate partition functions lead to approximate analytical computations of the correlations between pairs of different bond vectors, of the squared end-to-end distance, of the probability distribution for the end-to-end vector and of the structure factor, which display some novel features. Some comparisons with the corresponding results for the Gaussian chain are made.

ISSN: 1022-1344

Record 160

Author(s): Iniguez, D; Marinari, E; Parisi, G; RuizLorenzo, JJ

Title: 3D spin glass and 2D ferromagnetic XY model: a comparison

Source: JOURNAL OF PHYSICS A-MATHEMATICAL AND GENERAL, 30 (21): 7337-7347 NOV 7 1997

Abstract: We compare the probability distributions and Binder cumulants of the overlap in the 3D Ising spin glass with those of the magnetization in the ferromagnetic 2D XY model. We analyse similarities and differences. Evidence for the existence of a phase transition in the spin glass model is obtained thanks to the crossing of the Binder cumulant. We show, that the behaviour of the XY model is fully compatible with the Kosterlitz-Thouless scenario. Finite size effects have to be dealt with carefully in order to differentiate between two very different physical pictures that can look very similar.

ISSN: 0305-4470

Record 159

Author(s): Parisi, G; Ranieri, P; RicciTersenghi, F; RuizLorenzo, JJ

Title: Mean field dynamical exponents in finite-dimensional Ising spin glass

Source: JOURNAL OF PHYSICS A-MATHEMATICAL AND GENERAL, 30 (20): 7115-7131 OCT 21 1997

Abstract: We have studied numerically the remanent magnetization in the six-and eight-dimensional Ising spin glass and we have compared it with the behaviour observed in the SK model, that we have also computed analytically. We also report the value of the dynamical critical exponent z in six dimensions measured in three different ways: from the behaviour of the energy and the susceptibility as a function of the Monte Carlo time and by studying the overlap-overlap correlation function as a function of space and time. These three results are in very good agreement with the mean field prediction z = 4. Finally we have checked numerically the analytical prediction, obtained by assuming spontaneously broken replica symmetry, for the most singular part of the propagator in the spin-glass phase. This last result supports the existence of spontaneously broken replica symmetry in finite-dimensional spin glasses.

ISSN: 0305-4470

Record 158

Author(s): Coluzzi, B; Marinari, E; RuizLorenzo, JJ

Title: New evidence for super-roughening in crystalline surfaces with a disordered substrate

Source: JOURNAL OF PHYSICS A-MATHEMATICAL AND GENERAL, 30 (11): 3771-3778 JUN 7 1997

Abstract: We study the behaviour of the Binder cumulant related to long-distance correlation functions of the discrete Gaussian model of disordered substrate crystalline surfaces. We exhibit numerical evidence that the non-Gaussian behaviour in the low-T region persists on large-length scales, in agreement with the broken phase being super-rough.

ISSN: 0305-4470

Record 157

Author(s): Ballesteros, HG; Fernandez, LA; MartinMayor, V; Sudupe, AM; Parisi, G; RuizLorenzo, JJ

Title: Measures of critical exponents in the four-dimensional site percolation

Source: PHYSICS LETTERS B, 400 (3-4): 346-351 MAY 15 1997

Abstract: Using finite-size scaling methods we measure the thermal and magnetic exponents of the site percolation in four dimensions, obtaining a value for the anomalous dimension very different from the results found in the literature. We also obtain the leading corrections-to-scaling exponent and, with great accuracy, the critical density. (C) 1997 Published by Elsevier Science B.V.

ISSN: 0370-2693

Record 156

Author(s): Ballesteros, HG; Carmona, JM; Fernandez, LA; MartinMayor, V; Sudupe, AM; Tarancon, A

Title: Is the antiferromagnetic RP2 model in four dimensions trivial?

Source: PHYSICAL REVIEW D, 55 (8): 5067-5074 APR 15 1997

Abstract: We study the antiferromagnetic RP2 model in four dimensions. We find a second order transition with two order parameters, one ferromagnetic and the other antiferromagnetic. The antiferromagnetic sector has mean-field critical exponents and a renormalized coupling which goes to zero in the continuum limit. The exponents of the ferromagnetic channel are not the mean-field ones, but the difference can be interpreted as logarithmic corrections. We perform a detailed analysis of these corrections and conclude the triviality of the continuum limit of this model.

ISSN: 0556-2821

Record 155

Author(s): Parisi, G; RuizLorenzo, JJ

Title: Scaling above the upper critical dimension in Ising models (vol 54, pg R3698, 1996)

Source: PHYSICAL REVIEW B, 55 (9): 6082-6082 MAR 1 1997

ISSN: 0163-1829

Record 154

Author(s): Campos, I; Fernandez, LA; Tarancon, A

Title: Antiferromagnetic four-dimensional O(4) model

Source: PHYSICAL REVIEW D, 55 (5): 2965-2973 MAR 1 1997

Abstract: We study the phase diagram of the four-dimensional O(4) model with first-(beta(1)) and second-(beta(2)) neighbor couplings, especially in the beta(2) < 0 region, where we find a line of transitions which seems to be second order. We also compute the critical exponents on this line at the point beta(1) = 0 (F-4 lattice) by finite-size scaling techniques up to a lattice size of 24, these exponents being different from the mean-field ones.

ISSN: 0556-2821

Record 153

Author(s): Bergamini, R; Sedici, P; Verrocchio, P

Title: Inflation for Bianchi type IX models

Source: PHYSICAL REVIEW D, 55 (4): 1896-1900 FEB 15 1997

Abstract: The influence of inflation on the initial (i.e., at Planck's epoch) large anisotropy of the Universe is studied. To this end we consider a more general metric than the isotropic one: the locally rotationally symmetric Bianchi type IX metric. We find, then, a large set of initial conditions of intrinsic curvature and shear allowing an inflationary epoch that make the anisotropy negligible. These are not trivial because of the nonlinearity of Einstein's equations.

ISSN: 0556-2821

Record 152

Author(s): Alonso, JL; Ballesteros, HG; Campos, I; Carmona, JM; Gallardo, JC; Fernandez, LA; Iniguez, D; MartinMayor, V; Sudupe, AM; Tarancon, A; Ullod, CL

Title: Antiferromagnetism in four dimensions: Search for non-triviality

Source: NUCLEAR PHYSICS B: 680-682 Suppl. 53 FEB 1997

Conference Title: XIV International Conference on Lattice Gauge Theory

Conference Date: JUN 04-08, 1996

Conference Location: ST LOUIS, MO

Conference Host: WASHINGTON UNIV

Abstract: We present antiferromagnetism as a mechanism capable of modifying substantially the phase diagram and the critical behaviour of statistical mechanical models. This is particularly relevant in four dimensions, due to the connection between second order transition points and the continuum limit as a quantum field theory.
We study three models with an antiferromagnetic interaction: the Ising and the O(4) Models with a second neighbour negative coupling, and the RP(2) Model. Different conclusions are obtained depending on the model.

ISSN: 0550-3213

Record 151

Author(s): Ballesteros, HG; Fernandez, LA; MartinMayor, V; Sudupe, AM

Title: Critical exponents and unusual properties of the broken phase in the 3d-RP(2) antiferromagnetic model.

Source: NUCLEAR PHYSICS B: 686-689 Suppl. 53 FEB 1997

Conference Title: XIV International Conference on Lattice Gauge Theory

Conference Date: JUN 04-08, 1996

Conference Location: ST LOUIS, MO

Conference Host: WASHINGTON UNIV

Abstract: We present the results of a Monte Carlo simulation of the antiferromagnetic RP(2) model in three dimensions. With finite-size scaling techniques are accurately measure the critical exponents and compare them with those of O(N) models. We are able to parameterize the corrections-to-scaling. The symmetry properties of the broken phase are also studied.

ISSN: 0550-3213

Record 150

Author(s): RuizLorenzo, JJ

Title: Griffiths singularities in the two-dimensional diluted Ising model

Source: JOURNAL OF PHYSICS A-MATHEMATICAL AND GENERAL, 30 (2): 485-493 JAN 21 1997

Abstract: We study numerically the probability distribution of the Yang-Lee zeroes inside the Griffiths phase for the two-dimensional site diluted Ising model and we check that the shape of this distribution is that predicted in previous analytical works. By studying the finite-size scaling of the averaged smallest zero at the phase transition we extract, for two values of the dilution, the anomalous dimension, eta, which agrees very weil with the previous estimated values.

ISSN: 0305-4470

Record 149

Author(s): Ballesteros, HG; Fernandez, LA; MartinMayor, V; Sudupe, AM

Title: Critical properties of the antiferromagnetic RP(2) model in three dimensions

Source: NUCLEAR PHYSICS B, 483 (3): 707-736 JAN 13 1997

Abstract: We study the behavior of the antiferromagnetic RP(2) model in d = 3. The vacuum structure is analyzed in the critical and low temperature regions, paying special attention to the spontaneous symmetry breaking pattern. Near the critical point we observe a full breakdown of the O(3) symmetry of the action. Several methods for computing critical exponents are compared. We conclude that the most solid determination is obtained using a measure of the correlation length. Corrections-to-scaling are parameterized, yielding a very accurate determination of the critical coupling and a 5% error measure of the related exponent This is used to estimate the systematic errors due to finite-size effects.

ISSN: 0550-3213

Record 148

Author(s): Parisi, G; RicciTersenghi, F; RuizLorenzo, JJ

Title: Equilibrium and off-equilibrium simulations of the 4d Gaussian spin glass

Source: JOURNAL OF PHYSICS A-MATHEMATICAL AND GENERAL, 29 (24): 7943-7957 DEC 21 1996

Abstract: We study the on- and off-equilibrium properties of the four dimensional Gaussian spin glass. In the static case we determine the critical temperature and the critical exponents with more precision than in previous simulations. In the off-equilibrium case we settle the general form of the autocorrelation function, and show, for the first time, that is possible to obtain, dynamically, a value for the order parameter.

ISSN: 0305-4470

Record 147

Author(s): Ballesteros, HG; Fernandez, LA; MartinMayor, V; Sudupe, AM

Title: Finite size effects on measures of critical exponents in d=3 O(N) models

Source: PHYSICS LETTERS B, 387 (1): 125-131 OCT 10 1996

Abstract: We study the critical properties of three-dimensional O(N) models, for N = 2, 3, 4. Parameterizing the leading corrections-to-scaling for the eta exponent, we obtain a reliable infinite volume extrapolation, incompatible with previous Monte Carlo values, but in agreement with epsilon-expansions. We also measure the critical exponent related with the tensorial magnetization as well as the nu exponents and critical couplings.

ISSN: 0370-2693

Record 146

Author(s): Parisi, G; RuizLorenzo, JJ

Title: Scaling above the upper critical dimension in Ising models

Source: PHYSICAL REVIEW B, 54 (6): R3698-R3701 AUG 1 1996

Abstract: We rederive the finite-size scaling formula for the apparent critical temperature by using mean-field theory for the Ising model above the upper critical dimension. We have also performed numerical simulations in five dimensions and our numerical data are in good agreement with the mean-field theoretical predictions, in particular, with the finite-size exponent of the connected susceptibility and with the value of the Binder cumulant.

ISSN: 0163-1829

Record 145

Author(s): Iniguez, D; Parisi, G; RuizLorenzo, JJ

Title: Simulation of three-dimensional Ising spin glass model using three replicas: Study of Binder cumulants

Source: JOURNAL OF PHYSICS A-MATHEMATICAL AND GENERAL, 29 (15): 4337-4345 AUG 7 1996

Abstract: We have carried out numerical simulations of the three-dimensional Ising spin glass model with first neighbour Gaussian couplings using three replicas for each sample of couplings. We have paid special attention to the measure of two types of Binder cumulant that can be constructed from the three possible overlaps between the replicas. We obtain new information about the possible phase transition and perform an initial analysis of the ultrametricity issue.

ISSN: 0305-4470

Record 144

Author(s): AlvarezEstrada, RF; Nicola, AG

Title: Effective chiral lagrangian from QCD at nonzero chemical potential (vol 355, pg 288, 1995)

Source: PHYSICS LETTERS B, 380 (3-4): 491-492 JUL 11 1996

ISSN: 0370-2693

Record 143

Author(s): Ballesteros, HG; Fernandez, LA; MartinMayor, V; Sudupe, AM

Title: New universality class in three dimensions? The antiferromagnetic RP(2) model

Source: PHYSICS LETTERS B, 378 (1-4): 207-212 JUN 20 1996

Abstract: We present the results of a Monte Carlo simulation of the RP(2) model in three dimensions with negative coupling. We observe a second order phase transition between the disordered phase and an antiferromagnetic, unfrustrated, ordered one. We measure, with a finite size scaling analysis, the thermal exponent, obtaining v = 0.784(8). We have found two magnetic-type relevant operators whose related eta exponents are 0.038(2) and 1.338(8) respectively.

ISSN: 0370-2693

Record 142

Author(s): Alonso, JL; Carmona, JM; Gallardo, JC; Fernandez, LA; Iniguez, D; Tarancon, A; Ullod, CL

Title: Phase diagram of d=4 Ising model with two couplings

Source: PHYSICS LETTERS B, 376 (1-3): 148-153 MAY 23 1996

Abstract: We study the phase diagram of the four dimensional Ising model with first and second neighbour couplings, especially in the antiferromagnetic region, by using Mean Field and Monte Carlo methods. From the latter, all the transition lines seem to be first order except that between ferromagnetic and disordered phases in a region including the first-neighbour Ising transition point.

ISSN: 0370-2693

Record 141

Author(s): Cruz, A; Fernandez, LA; Iniguez, D; Tarancon, A

Title: A multisite microcanonical updating method

Source: PHYSICS LETTERS B, 374 (1-3): 152-158 MAY 2 1996

Abstract: We have made a study of several update algorithms using the XY model. We find that sequential local overrelaxation is not ergodic at the scale of typical Monte Carlo simulation time. We have introduced a new multisite microcanonical update method, which yields results compatible with those of random overrelaxation and the microcanonical demon algorithm, which are very much slower, all being incompatible with the sequential overrelaxation results.

ISSN: 0370-2693

Record 140

Author(s): AlvarezEstrada, RF; SanchezGomez, JL

Title: The survival amplitude for unstable particles at short times in relativistic quantum field theory

Source: REVISTA MEXICANA DE FISICA, 42 (2): 216-235 APR 1996

Abstract: We study in general the survival probability for unstable systems in relativistic quantum field theory (RQFT) and, then, in particular, the short-time behavior. Two specific models are investigated here: one superrenormalizable and the other simply renormalizable. In both models, we find that the said survival probability behaves like P(t) = 1 - ct at very small t (c being a model-dependent constant). This -linear in t- behavior is essentially different from the quadratic one obtained in non-relativistic quantum mechanics also at very short times. The physical reason of this discrepancy is analyzed. Some related results in non-relativistic quantum field theory are also shown. Finally, some possibly relevant consequences of such a kind of short-time behavior of the survival probability for unstable relativistic particles are discussed.

ISSN: 0035-001X

Record 139

Author(s): Alonso, JL; Tarancon, A; Ballesteros, HG; Fernandez, LA; MartinMayor, V; Sudupe, AM

Title: Monte Carlo study of O(3) antiferromagnetic models in three dimensions

Source: PHYSICAL REVIEW B, 53 (5): 2537-2545 FEB 1 1996

Abstract: We study three antiferromagnetic formulations of the O(3) spin model in three dimensions by means of Monte Carlo simulations: (1) a two parameter sigma model with nearest- and next-nearest neighbors couplings in a cubic lattice; (2) a face-centered-cubic lattice with nearest-neighbor interaction; (3) a cubic lattice with a set of fully frustrating couplings. We discuss in all cases the vacua properties and analyze the phase transitions. Using finite-size scaling analysis we conclude that all phase transitions found are of first order.

ISSN: 0163-1829

Record 138

Author(s): Marinari, E; Parisi, G; RuizLorenzo, J; Ritort, F

Title: Numerical evidence for spontaneously broken replica symmetry in 3D spin glasses

Source: PHYSICAL REVIEW LETTERS, 76 (5): 843-846 JAN 29 1996

Abstract: Using numerical simulations of the 3D Ising spin glass we find evidence that spontaneous replica symmetry breaking theory and not the droplet model describes with good accuracy the equilibrium behavior of the system.

ISSN: 0031-9007

Record 137

Author(s): Campos, I; Tarancon, A; Clerot, F; Fernandez, LA

Title: Thermal and repulsive traffic flow

Source: PHYSICAL REVIEW E, 52 (6): 5946-5954 Part A DEC 1995

Abstract: We study a particle how model that may be used to gain insight into various real traffic problems. The model is implemented using a discrete lattice, in which particles move towards their destination, fluctuating about the minimal distance path. A repulsive interaction between particles is introduced seas to avoid the appearance of a traffic jam. We have studied the parameter space finding regions of fluid traffic, and saturated ones, both regions being separated by abrupt changes. The improvement of the system performance is also explored by introducing a nonconstant potential acting on the particles. Finally, we deal with the behavior of the system when temporary failures in transmission occur.

ISSN: 1063-651X

Record 136

Author(s): LANCASTER, DJ; RUIZLORENZO, JJ

Title: NUMERICAL SIMULATIONS OF THE RANDOM-PHASE SINE-GORDON MODEL

Source: JOURNAL OF PHYSICS A-MATHEMATICAL AND GENERAL, 28 (22): L577-L583 NOV 21 1995

Abstract: We have performed comprehensive numerical simulations of the random phase sine-Gordon model, studying both statics and dynamics for various values of the coupling. The glass transition can be seen both in static and dynamic signals at a temperature that depends on the coupling. Our results, for reduced temperature dependence, agree qualitatively (statics) and quantitatively (dynamics) with renormalization-group predictions.

ISSN: 0305-4470

Record 135

Author(s): ALVAREZESTRADA, RF

Title: APPROXIMATE QUANTUM-MECHANICAL HAMILTONIANS FOR SLOW INTERNAL ROTATIONS OF MACROMOLECULES (VOL 3, PG 479, 1994)

Source: MACROMOLECULAR THEORY AND SIMULATIONS, 4 (6): 1127-1127 NOV 1995

ISSN: 1022-1344

Record 134

Author(s): ALVAREZESTRADA, RF

Title: MOLECULAR CHAINS WITH FIXED BOND LENGTHS AND ANGLES - A STUDY BASED ON QUANTUM-STATISTICAL MECHANICS (VOL 4, PG 367, 1995)

Source: MACROMOLECULAR THEORY AND SIMULATIONS, 4 (6): 1127-1127 NOV 1995

ISSN: 1022-1344

Record 133

Author(s): ALVAREZ, G; ALVAREZESTRADA, RF

Title: SEMICLASSICAL ANALYSIS OF A QUASI-EXACTLY SOLVABLE SYSTEM - 2ND-HARMONIC GENERATION

Source: JOURNAL OF PHYSICS A-MATHEMATICAL AND GENERAL, 28 (20): 5767-5781 OCT 21 1995

Abstract: The usual second harmonic generation effective Hamiltonian is shown to be equivalent to a one-dimensional Schrodinger operator with a sextic polynomial potential. This operator belongs to the class of quasi-exactly solvable models, for which a finite number of eigenvalues and eigenvectors can be determined exactly. A Jeffreys-Wentzel-Kramers-Brillouin analysis provides accurate asymptotic expansions for these eigenvalues in the limit of large unperturbed energies.

ISSN: 0305-4470

Record 132

Author(s): FERNANDEZ, LA; MARINARI, E; RUIZLORENZO, JJ

Title: TEMPERING DYNAMICS AND RELAXATION-TIMES IN THE 3D ISING-MODEL

Source: JOURNAL DE PHYSIQUE I, 5 (10): 1247-1254 OCT 1995

Abstract: We discuss the tempering Monte Carlo method, and its critical slowing down behavior in the 3D Ising model. We show that at T-c the tempering does not change the critical slowing down exponent z. We also discuss the exponential slowing down for the flip-flop from plus to minus state in the cold phase, and we show that tempering reduces it to a power law slowing down. We discuss the relation of the flip-hop rate to the surface tension for local dynamical schemes.

ISSN: 1155-4304

Record 131

Author(s): ALVAREZESTRADA, RF; NICOLA, AG

Title: EFFECTIVE CHIRAL LAGRANGIAN FROM QCD AT NONZERO CHEMICAL-POTENTIAL

Source: PHYSICS LETTERS B, 355 (1-2): 288-294 JUL 27 1995

Abstract: We start from the euclidean QCD action for gluons and massless quarks with N-c colours at finite baryon chemical potential ps and zero temperature. For mu(B) of the order of external momenta o(p) we derive an euclidean effective real chiral lagrangian at finite pe, up to and including o(p(4)), in terms of Goldstone Bosons (GB), in the large N-c limit, including gluon contributions. Our effective action generalizes non-trivially the one obtained for mu(B) = 0 by previous authors, and it includes new mu(B)-dependent terms. In particular, a topological term mu(B)N(B) is found, N-B being the baryon number in terms of GB fields with the correct normalization factor. Physical implications of the remaining mu(B)-dependent terms are discussed briefly.

ISSN: 0370-2693

Record 130

Author(s): PARISI, G; RUIZLORENZO, JJ

Title: ON THE 4-DIMENSIONAL DILUTED ISING-MODEL

Source: JOURNAL OF PHYSICS A-MATHEMATICAL AND GENERAL, 28 (14): L395-L401 JUL 21 1995

Abstract: In this letter we show strong numerical evidence that the four dimensional diluted Ising model for a large dilution is not described by the mean-field exponents. These results suggest the existence of a new fixed point with non-Gaussian exponents.

ISSN: 0305-4470

Record 129

Author(s): MARINARI, E; MONASSON, R; RUIZLORENZO, JJ

Title: HOW (SUPER) ROUGH IS THE GLASSY PHASE OF A CRYSTALLINE SURFACE WITH A DISORDERED SUBSTRATE

Source: JOURNAL OF PHYSICS A-MATHEMATICAL AND GENERAL, 28 (14): 3975-3984 JUL 21 1995

Abstract: We discuss the behaviour of a crystalline surface with a disordered substrate. We focus on the possible existence of a super-rough glassy phase, with height-height correlation functions which vary as the square logarithm of the distance. With numerical simulations we establish the presence of such a behaviour, that does not seem to be connected to finite-size effects. We comment on the variational approach, and suggest that a more general extension of the method could be needed to fully explain the behaviour of the model.

ISSN: 0305-4470

Record 128

Author(s): ALVAREZESTRADA, RF; NICOLA, AG; SANCHEZSOTO, LL; LUIS, A

Title: A QUASI-CLASSICAL ANALYSIS OF 2ND-HARMONIC GENERATION

Source: JOURNAL OF PHYSICS A-MATHEMATICAL AND GENERAL, 28 (12): 3439-3451 JUN 21 1995

Abstract: We investigate a quantum two-oscillator model for second-harmonic generation. The total Hamiltonian is the sum of two commuting Hamiltonians with eigenvalues E(0) and E(int). The exact determination of these eigenvalues is studied using tridiagonal matrices. We present two general equations in the quasiclassical regime yielding the largest E(int) for a given E(0) and a representation for both eigenvalues in terms of an additional quantum number. Some numerical analysis shows that both equations are fairly consistent for suitably large quantum numbers with the exact quantum results. An approximate analytical expression for the wavefunction is also given.

ISSN: 0305-4470

Record 127

Author(s): ANTONELLI, S; BARTOLONI, A; BATTISTA, C; BELLACCI, M; CABASINO, S; CABIBBO, N; FERNANDEZ, LA; PANIZZI, E; PAOLUCCI, PS; MUNOZSUDUPE, A; RUIZLORENZO, JJ; SARNO, R; TARANCON, A; TODESCO, GM; TORELLI, M; VICINI, P

Title: APE RESULTS OF HADRON MASSES IN FULL QCD SIMULATIONS

Source: NUCLEAR PHYSICS B: 300-302 Suppl. 42 APR 1995

Conference Title: XIIth International Symposium on Lattice Field Theory (LATTICE 94)

Conference Date: SEP 27-OCT 01, 1994

Conference Location: BIELEFELD, GERMANY

Abstract: We present numerical results obtained in full QCD with 2 flavors of Wilson fermions. We discuss the relation between the phase of Polyakov loops and the sea quarks boundary conditions. We report preliminary results about the HMC autocorrelation of the hadronic masses, on a 16(3) x 32 lattice volume, at beta = 5.55 with kappa(sea) = 0.1570.

ISSN: 0550-3213

Record 126

Author(s): CRUZ, A; INIGUEZ, D; TARANCON, A; FERNANDEZ, LA; SUDUPE, AM

Title: THE COULOMB-HIGGS TRANSITION OF THE 3-PARAMETER U(1)-HIGGS MODEL

Source: NUCLEAR PHYSICS B: 606-608 Suppl. 42 APR 1995

Conference Title: XIIth International Symposium on Lattice Field Theory (LATTICE 94)

Conference Date: SEP 27-OCT 01, 1994

Conference Location: BIELEFELD, GERMANY

Abstract: We find a first order Coulomb-Higgs phase transition at moderately large values of the coupling lambda, and no evidence for a change of order at any finite value of it.

ISSN: 0550-3213

Record 125

Author(s): FERNANDEZ, LA; SUDUPE, AM; RUIZLORENZO, JJ; TARANCON, A

Title: A PROPOSAL OF A MONTE-CARLO RENORMALIZATION-GROUP TRANSFORMATION

Source: NUCLEAR PHYSICS B: 802-804 Suppl. 42 APR 1995

Conference Title: XIIth International Symposium on Lattice Field Theory (LATTICE 94)

Conference Date: SEP 27-OCT 01, 1994

Conference Location: BIELEFELD, GERMANY

Abstract: We propose a family of renormalization group transformations characterized by free parameters that may be tuned in order to reduce the truncation effects. As a check we test them in the three dimensional XY model. The Schwinger-Dyson equations are used to study the renormalization group flow.

ISSN: 0550-3213

Record 124

Author(s): ALVAREZESTRADA, RF

Title: MOLECULAR CHAINS WITH FIXED BOND LENGTHS AND ANGLES - A STUDY BASED ON QUANTUM-STATISTICAL MECHANICS

Source: MACROMOLECULAR THEORY AND SIMULATIONS, 4 (2): 367-395 MAR 1995

Abstract: This work studies large three-dimensional open molecular chains at thermal equilibrium in which bond lengths and angles are fixed (hard variables), based upon quantum statistics. A model for a chain formed by N particles interacting through harmonic-like vibrational potentials is treated in the high-frequency limit in which all bond lengths and angles become constrained, while other N angles (soft variables) remain unconstrained. The associated quantum partition function is bounded rigorously, using a variational inequality (related to the Born-Oppenheimer approximation), by another quantum partition function, Z. The total vibrational zero-point energy is shown to be independent of the soft variables thereby solving for this model a generic difficulty in the elimination of hard variables. Z depends only on soft variables and, under certain conditions, it can be approximated by a classical partition function Z(c). The latter satisfies the equipartition principle and it differs from other classical partition functions for related molecular chains. The extension of the model when only part of the bond angles become fixed in the high-frequency limit is outlined. As another generalization, a systematic study of macromolecules, as composed of electrons and heavy particles with Coulomb interactions, is also presented. Its exact quantum partition function is bounded, supposing that the effective molecular potential also tends to constrain all bond lengths and angles, and under suitable assumptions, by another quantum partition function. The latter depends only on the remaining soft variables and it generalizes the one obtained for the first model.

ISSN: 1022-1344

Record 123

Author(s): ANTONELLI, S; BELLACCI, M; FERNANDEZ, LA; MUNOZSUDUPE, A; RUIZLORENZO, JJ; SARNO, R; TARANCON, A; BARTOLONI, A; BATTISTA, A; CABIBBO, N; CABASINO, S; PANIZZI, E; PAOLUCCI, PS; TODESCO, GM; TORELLI, M; TRIPICCIONE, R; VICINI, P

Title: POLYAKOV LOOPS AND FINITE-SIZE EFFECTS OF HADRON MASSES IN FULL LATTICE QCD