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

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.

Optimized Monte Carlo method for glasses

A new Monte Carlo algorithm is introduced for the simulation of supercooled liquids and glass formers, and tested in two model glasses. The algorithm thermalizes well below the Mode Coupling temperature and outperforms other optimized Monte Carlo methods.

Critical behavior of the specific heat in glass formers

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.

Ianus: an adaptive FPGA computer

Dedicated machines designed for specific computational algorithms can outperform conventional computers by several orders of magnitude. In this note we describe 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.

Finite size effects in the specific heat of glass-formers

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.

Numerical study of the enlarged O(5) symmetry of the 3D antiferromagnetic RP^(2) spin model

We investigate by means of Monte Carlo simulation and finite-size scaling analysis the critical properties of the three dimensional O (5) non-linear σ model and of the antiferromagnetic RP^(2) 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 RP^(2) model. We have also investigated the phase diagram of the RP^(2) model extended by a second-neighbor interaction. A rich phase diagram is found, where most of the phase transitions are of the first order.

Phase diagram of the bosonic double-exchange model

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.

Phase diagram and influence of defects in the double perovskites

The phase diagram of the double perovskites of the type Sr_(2-x)La_(x)FeMoO_(6) 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.

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

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.

Aplicación de videojuegos educativos teatrales en dispositivos móviles y fijos

En un mundo dominado por las nuevas tecnologías, donde en cada casa podemos encontrar más dispositivos tecnológicos que personas, seguimos teniendo un sistema educativo basado en libros de texto, cuaderno y bolígrafo. Esto, combinado con una generación de estudiantes considerados como nativos digitales (Prensky, 2010), está haciendo que los resultados académicos sean cada vez peores, aumentando el fracaso escolar (Fernández Pérez, 1986). Sin embargo, dada la aparición de los llamados videojuegos educativos, o "serious games", y la digitalización de las aulas, se ha demostrado que aprender jugando no sólo es más divertido, sino que además es más efectivo (Wong et al., 2007). Pero, cuando un centro educativo decide invertir dinero en traer nuevas tecnologías a las aulas, surge la siguiente pregunta: ¿en qué tipo de dispositivo debo invertir? Hasta la aparición de las tablets, esta pregunta tenía una clara respuesta, ordenadores. Pero con la llegada de éstas, la respuesta no está tan clara. ¿Qué dispositivo funciona mejor en las aulas? Otro ámbito que pierde adeptos entre los más jóvenes con la llegada de tanta tecnología a los hogares, es el mundo del teatro. Cada vez son menos los jóvenes interesados en acudir al teatro, convirtiendo a éste en un espectáculo de minorías. Una vez más los videojuegos educativos pueden ser una solución, como se demuestra en la tesis doctoral de Borja Manero (Manero, Torrente, Serrano, Martínez-Ortiz, & Fernández-Manjón, 2015). Esto llamó la atención del Compañía Nacional de Teatro Clásico (CNTC), queriendo realizar más videojuegos educativos que ayuden a incrementar el interés de los más jóvenes por el teatro. Por lo tanto, tenemos dos retos por delante: el principal es encontrar el mejor dispositivo para aplicar estos videojuegos educativos. Esto nos lleva a un segundo objetivo. Desarrollar el videojuego que servirá como herramienta para el desarrollo del experimento. Desarrollamos un videojuego educativo, basado en la obra de teatro “La Cortesía de España”, representada por la CNTC. Se realizaron varios procesos de adaptación para transformar una obra de teatro clásico en un videojuego divertido y útil para la investigación. Utilizando este videojuego como herramienta educativa, realizamos un experimento en el colegio de la Comunidad de Madrid Benito Pérez Galdós(Móstoles), proporcionándonos más de 150 alumnos, de entre 9 y 11 años, para participar en el mismo. Este experimento tiene como fin demostrar qué dispositivo funciona mejor con esta generación: los dispositivos móviles (tablets) o dispositivos fijos (ordenadores). Aunque previamente los investigadores sospechaban que el resultado del experimento sería claramente a favor de las tablets, por su cercanía con los jóvenes a los que estaba dirigido, los resultados arrojan otra conclusión completamente distinta. Efectivamente los más jóvenes utilizan más las tablets que los ordenadores para jugar, pero, analizados los resultados, son los ordenadores los que mejor funcionan como herramienta de aprendizaje.

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

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 RP^(2) model. The fact that one can define a universality class for the antiferromagnetic RP^(2) model, different from the one of the O(N) models, is puzzling and somehow contradicts naive expectations about universality.

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

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 La_(2/3)Ca_(1/3)Mn_(1-y)Ga_(y)O_(3) our results suggest a quantum critical point (QCP) for y ≈ 0.1–0.2, associated to the localization of the electronic states of the conduction band. In the case of La_(x)Ca_(x)Mn_(1-y)Fe_(y)O_(3) (with x = 1/3,3/8) no such QCP is expected.

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

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.

Universal critical behavior of the two-dimensional Ising spin glass

We use finite size scaling to study Ising spin glasses in two spatial dimensions. The issue of universality is addressed by comparing discrete and continuous probability distributions for the quenched random couplings. The sophisticated temperature dependency of the scaling fields is identified as the major obstacle that has impeded a complete analysis. Once temperature is relinquished in favor of the correlation length as the basic variable, we obtain a reliable estimation of the anomalous dimension and of the thermal critical exponent. Universality among binary and Gaussian couplings is confirmed to a high numerical accuracy.

La restauración del libro Cirugía Universal de Juan Fragoso, impreso en Alcalá de Henares en 1607

En el presente artículo se ofrecen los procedimientos y resultados de la restauración del libro Cirugía Universal (1607) de Juan Fragoso, llevada a cabo por las autoras durante las prácticas curriculares del Título Superior de Conservación y Restauración de Bienes Culturales en la especialidad de Documento Gráfico y durante las prácticas realizadas en el marco de la “Campaña de Verano” 2016 respectivamente, gracias al acuerdo de colaboración entre la Biblioteca Histórica y la Escuela Superior de Conservación y Restauración de Bienes Culturales.