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Martin-Mayor V.,Complutense University of Madrid | Martin-Mayor V.,Institute Biocomputacion | Perez-Gaviro S.,Institute Biocomputacion | Perez-Gaviro S.,University of Rome La Sapienza
Physical Review B - Condensed Matter and Materials Physics | Year: 2011

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. © 2011 American Physical Society.

Fernandez L.A.,Complutense University of Madrid | Fernandez L.A.,Institute Biocomputacion | Martin-Mayor V.,Complutense University of Madrid | Martin-Mayor V.,Institute Biocomputacion | And 2 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2011

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 θ). 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). © 2011 American Physical Society.

Calvo I.,CIEMAT | Cuchi J.C.,University of Lleida | Esteve J.G.,University of Zaragoza | Esteve J.G.,Institute Biocomputacion | And 2 more authors.
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2012

In the classical theorems of extreme value theory the limits of suitably rescaled maxima of sequences of independent, identically distributed random variables are studied. The vast majority of the literature on the subject deals with affine normalization. We argue that more general normalizations are natural from a mathematical and physical point of view and work them out. The problem is approached using the language of renormalization-group transformations in the space of probability densities. The limit distributions are fixed points of the transformation and the study of its differential around them allows a local analysis of the domains of attraction and the computation of finite-size corrections. © 2012 American Physical Society.

Cavagna A.,CNR Institute of Neuroscience | Cavagna A.,University of Rome La Sapienza | Grigera T.S.,National University of La Plata | Grigera T.S.,CONICET | And 3 more authors.
Journal of Statistical Mechanics: Theory and Experiment | Year: 2010

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. © 2010 IOP Publishing Ltd and SISSA.

Lopez-Bruna D.,CIEMAT | Lopez-Bruna D.,Institute Biocomputacion | Romero J.A.,CIEMAT | Lopez-Fraguas A.,CIEMAT | And 10 more authors.
Contributions to Plasma Physics | Year: 2010

Low order rational values of the rotational transform -magnetic resonances, for brevity-can be present inside ECR-heated plasmas of the TJ-II Heliac, in low magnetic shear conditions, without causing damage to confinement. Moreover, in agreement with previous experience in the TJ-II, the resonances seem to benefit confinement and are associated to changes in the radial electric field, at least in the density gradient region. These results encourage considering magnetic resonances as possible external actuators on confinement in stellarator/heliotron devices. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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