Publications (20)50.2 Total impact
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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.01/2009: pages 291302; , ISBN: 9788497454063 
Article: Campos et al. Reply:
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ABSTRACT: A Reply to the Comment by I. A. Campbell and H. Kawamura.Physical Review Letters 07/2007; 99(1). · 7.73 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: It is shown, by means of Monte Carlo simulation and finite size scaling analysis, that the Heisenberg spin glass undergoes a finitetemperature 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 spinglass 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.Physical Review Letters 12/2006; 97(21):217204. · 7.73 Impact Factor 
Article: Ianus: an adaptive FPGA computer
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ABSTRACT: With Ianus, a nextgeneration fieldprogrammable 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.Computing in Science and Engineering 02/2006; · 1.73 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: It was observed previously that the ion temperature profile of lowdetisity electron cyclotron resonanceheated TJII 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 lowdensity (< 10(19)m(3))plasmas. The distribution function is also obtained without considering collisions; thus, nonMaxwellian features are found. The final particle density shows inhomogeneities on a magnetic surface.Fusion Science and Technology 01/2006; 50(3):412418. · 0.52 Impact Factor 
Article: Ianus: an Adpative FPGA Computer
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ABSTRACT: Dedicated machines designed for specific computational algorithms can outperform conventional computers by several orders of magnitude. In this note we describe {\it Ianus}, a new generation FPGA based machine and its basic features: hardware integration and wide reprogrammability. Our goal is to build a machine that can fully exploit the performance potential of new generation FPGA devices. We also plan a software platform which simplifies its programming, in order to extend its intended range of application to a wide class of interesting and computationally demanding problems. The decision to develop a dedicated processor is a complex one, involving careful assessment of its performance lead, during its expected lifetime, over traditional computers, taking into account their performance increase, as predicted by Moore's law. We discuss this point in detail.08/2005;  [Show abstract] [Hide abstract]
ABSTRACT: We have studied the properties of the phase transition in the U(1) compact pure gauge model paying special atention to the influence of the topology of the boundary conditions. From the behavior of the energy cumulants and the observation of an effective \nu > 1/d on toroidal and spherical lattices, we conclude that the transition is first order. Comment: LATTICE98(gauge)Nuclear Physics B  Proceedings Supplements 08/1998; · 0.88 Impact Factor 
Article: On the SU(2)Higgs phase transition
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ABSTRACT: We investigate the properties of the ConfinementHiggs phase transition in the SU(2)Higgs model. The system is shown to exhibit a transient behavior up to L = 24 along which, the order of the phase transition cannot be discerned. In order to get a global vision on the problem, we have introduced a second (nexttonearest neighbors) gaugeHiggs coupling ( κ2). On this extended parameter space we find a line of phase transitions becoming increasely weak as the standard case is approached ( κ2 = 0). From the global behavior on this parameter space we conclude that the transition is also first order in the standard case.Nuclear Physics B  Proceedings Supplements 04/1998; 63(1):676678. · 0.88 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: The properties of the confinementHiggs phase transition in the SU(2)Higgs model with fixed modulus are investigated. We show that the system exhibits a transient behavior up to L = 24 along which the order of the phase transition cannot be discerned. To get stronger conclusions about this point, without going to prohibitively large lattice sizes, we have introduced a second (nexttonearest neighbors) gaugeHiggs coupling (κ2). On this extended parameter space we find a line of phase transitions which become increasingly weaker as κ2 → 0. The results point to a firstorder character for the transition with the standard action (κ2 = 0).Nuclear Physics B 01/1998; · 4.33 Impact Factor 
Article: A study of the phase transition in 4D pure compact U(1) LGT on toroidal and spherical lattices
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ABSTRACT: We have performed a systematic study of the phase transition in the pure compact U(1) lattice gauge theory in the extended coupling parameter space (β, γ) on toroidal and spherical lattices. The observation of a nonzero latent heat in both topologies for all investigated γ ϵ [+0.2, −0.4], together with an exponent when large enough lattices are considered, lead us to conclude that the phase transition is first order. For negative γ, our results point to an increasingly weak firstorder transition as γ is made more negative.Nuclear Physics B 01/1998; · 4.33 Impact Factor 
Article: First order signatures in 4D pure compact U(1) gauge theory with toroidal and spherical topologies
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ABSTRACT: We study the pure compact U(1) gauge theory with the extended Wilson action (\beta, \gamma couplings) by finite size scaling techniques, in lattices ranging from L=6 to L=24 in the region of \gamma <= 0 with toroidal and spherical topologies. The phase transition presents a double peak structure which survives in the thermodynamical limit in the torus. In the sphere the evidence support the idea of a weaker, but still first order, phase transition. For negative values of gamma the transition becomes weaker and larger lattices are needed to find its asymptotic behaviour. Along the transient region the behaviour is the typical one of a weak first order transition for both topologies, with a region where 1/d < nu < 0.5, which becomes nu compatible with 1/d when larger lattices are used. Comment: Some references added; changes in the text mainly wording. To appear in Phys. Lett. BPhysics Letters B 11/1997; · 4.57 Impact Factor  [Show abstract] [Hide abstract]
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. Comment: 4 pages LateX. Contribution to Lat96Nuclear Physics B  Proceedings Supplements 07/1997; 53:680682. · 0.88 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We study numerically the critical properties of the U(1)Higgs lattice model, with fixed Higgs modulus, in the region of small gauge coupling where the Higgs and confining phases merge. We find evidence for a firstorder transition line that ends in a secondorder point. By means of a rotation in parameter space we introduce thermodynamic magnitudes and critical exponents in close resemblance with simple models that show analogous critical behaviour. The measured data allow us to fit the critical exponents finding values in agreement with the meanfield prediction. The location of the critical point and the slope of the firstorder line are accurately measured.Nuclear Physics B 07/1997; · 4.33 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We study the phase diagram of the fourdimensional O(4) model with first (β1) and second (β2) neighbor couplings, especially in the β2<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 β1=0 (F4 lattice) by finitesize scaling techniques up to a lattice size of 24, these exponents being different from the meanfield ones.Physical review D: Particles and fields 02/1997; 55(5). 
Article: Thermal and repulsive traffic flow
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ABSTRACT: We study a message passing model, applicable also to traffic problems. The model is implemented in a discrete lattice, where particles move towards their destination, with fluctuations around the minimal distance path. A repulsive interaction between particles is introduced in order to avoid the appearance of traffic jam. We have studied the parameter space finding regions of fluid traffic, and saturated ones, being separated by abrupt changes. The improvement of the system performance is also explored, by the introduction of a nonconstant potential acting on the particles. Finally, we deal with the behavior of the system when temporary failures in the transmission occurs. Comment: 22 pages, uuencoded gzipped postscript file. 11 figures includedPhysical Review E 05/1995; 52:5946. · 2.31 Impact Factor 
Article: Critical behavior of random walks.
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ABSTRACT: We have studied numerically the trapping problem in a twodimensional lattice where particles are continuously generated. We have introduced interaction between particles and directionality of their movement. This model presents a critical behavior with a rich phase structure similar to spin systems. We interpret a change in the asymptotic density of particles as a phase transition. For high directionality the change is abrupt, possibly of first order. For small directionality the phase transition is of higher order. We have computed the phase diagram, the volume dependence of the critical point, and the relaxation time of the system in the large volume limit.Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics 08/1994; 50(1):9196.  [Show abstract] [Hide abstract]
ABSTRACT: We study SU(2) lattice gauge theory in small volumes and with twist m = (1, 1, 1). We investigate the presence of the periodic instantons of and determine their free energy and their contribution to the splitting of energy flux sectors E(e = (1, 1, 1)) − E(e = (0, 0, 0)).Physics Letters B 05/1993; · 4.57 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We stimulate the U(1)Higgs lattice model with fixed Higgs modulus, in the region where the transition between the Higgs and Confining phases diappears. We find a first order transition line that ends in a second order point. Thermodynamic magnitudes and their associated critical exponents are introduced. The measured data allow us to fit the critical exponents finding values in agreement with the mean field prediction. The location of the critical point and the slope of the first order line are accurately given.Nuclear Physics B  Proceedings Supplements 01/1993; 30:701704. · 0.88 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We simulate the compact U(1)Higgs model in a fourdimensional lattice. We present a numerical study for the behaviour around the region where the transition between the confining and Higgs phases disappears. The transition line is found to be first order and to end in a secondorder point. We measure the critical exponents of the endpoint obtaining the mean field ones within errors.Physics Letters B 01/1992; 296:154158. · 4.57 Impact Factor 
Publication Stats
141  Citations  
50.20  Total Impact Points  
Top Journals
Institutions

2009

Instituto de Física de Cantabria
Santander, Cantabria, Spain


2005–2007

Institute for Biocomputation and Physics of Complex Systems
Caesaraugusta, Aragon, Spain


1992–1998

University of Zaragoza
 Departamento de Física Teórica
Zaragoza, Aragon, Spain
