The frustrated spherical model: an alternative to Ginzburg-Landau Hamiltonians with competing interactions

We solve analytically the Langevin dynamics of the classic spherical model considering the ferromagnetic exchange and a long-range antiferromagnetic interaction. Our results in the asymptotic regime, shows an equivalence in the functionality of the spatial and self-correlations between this model and the recently studied Ginzburg-Landau frustrated model within the Hartree approximation. A careful discussion is done about the low temperature behavior in the context of glassy dynamics. The appearance of interesting features regarding the establishment of the ferromagnetic phase is also analyzed in view of the effects of the spherical restriction. We propose a new variant of the spherical model in which the global restriction is substituted by an infinite set of restrictions over finite size regions. This modification leads to a new dynamical equation that suggests the appearance of the low temperature phase transition even in the non-frustrated case were the classic spherical model fails

Event-Driven Monte Carlo: exact dynamics at all time-scales for discrete-variable models

We present an algorithm for the simulation of the exact real-time dynamics of classical many-body systems with discrete energy levels. In the same spirit of kinetic Monte Carlo methods, a stochastic solution of the master equation is found, with no need to define any other phase-space construction. However, unlike existing methods, the present algorithm does not assume any particular statistical distribution to perform moves or to advance the time, and thus is a unique tool for the numerical exploration of fast and ultra-fast dynamical regimes. By decomposing the problem in a set of two-level subsystems, we find a natural variable step size, that is well defined from the normalization condition of the transition probabilities between the levels. We successfully test the algorithm with known exact solutions for non-equilibrium dynamics and equilibrium thermodynamical properties of Ising-spin models in one and two dimensions, and compare to standard implementations of kinetic Monte Carlo methods. The present algorithm is directly applicable to the study of the real time dynamics of a large class of classical markovian chains, and particularly to short-time situations where the exact evolution is relevant

A polyhedral approach for the Equitable Coloring Problem

In this work we study the polytope associated with a 0,1-integer programming formulation for the Equitable Coloring Problem. We find several families of valid inequalities and derive sufficient conditions in order to be facet-defining inequalities. We also present computational evidence that shows the efficacy of these inequalities used in a cutting-plane algorithm

Aproximaciones al arraigo y al desarraigo femenino en el medio rural : mujeres jóvenes en busca de una nueva identidad rural

Los estudios cuantitativos sobre la juventud rural constatan una preferencia de las mujeres jóvenes por el abandono del medio rural. Hemos querido explorar aquí los aspectos cualitativos del desarraigo femenino. Las mujeres rurales que hemos estudiado, de una comarca del Principado de Asturias, viven en una sociedad abierta y global y se ven afectadas por esta apertura, por lo que conforman una percepción de la ruralidad que es nueva. En este escenario, las jóvenes deben tomar decisiones sobre su futuro, deben decidir si permanecer o marchar del territorio donde han nacido. Hemos encontrado mujeres que tienden al arraigo y otras que se orientan hacia el desarraigo, pero todas ellas se han visto afectadas por un conjunto de factores idénticos, característicos de una sociedad rural en transformación. En este artículo constatamos que las jóvenes hacen una análisis diferente de una misma realidad social. De momento, las mujeres que han optado por el arraigo reconocen decidir a contracorriente; de forma poco objetiva, al margen de las opciones más visibles y dominantes de inserción social y laboral. Aún así, son ellas quienes nos están dando las claves para comprender de qué modo el medio rural puede convertirse en la mejor opción, pues estas jóvenes construyen su propia identidad en torno a la ruralidad.Quantitative studies on rural youth establish that in general young girls prefer to leave their rural area behind. What we have intended here is to explore the qualitative aspects of female uprootedness. The rural women that we have researched came from an agricultural district in the Principality of Asturias and live in an open and global society, an opening shaping a new conception of rurality. In this new scene, young girls have to make decisions about their future; they must make up their minds about staying in or leaving their birthplace. We have found women with a tendency towards rootedness, while others go for uprootedness, but all of them have been affected by a number of exactly the same characteristic factors of a rural society going through a changing process. In this work, we establish that young girls analyse the same social reality differently. For the moment, the women who have opted for rootedness admit that they have decided out of step with the times, not very objectively, leaving out more visible and prevailing options for their social and work insertion. Even so, it is these women who are giving us clues to be able to understand the best way in which the rural world can become their best option because these girls are building up their own identity around rurality

El tratamiento institucional de la alimentación : un análisis sobre la intervención contra la obesidad

España tiene una de las tasas de obesidad infantil más altas de Europa. En este trabajo, se estudian las diferentes formas de afrontar institucionalmente el aumento de la obesidad en el entorno europeo en general y en España en particular. En él, se analizan las intervenciones para promover una dieta saludable, tanto las socioeducativas, como las orientadas a los contextos de consumo. La epidemia de la obesidad ha provocado un replanteamiento del papel de la alimentación en las instituciones. En primer lugar, ha pasado a ser un asunto social y ha dejado a un lado su tradicional carácter biológico. En segundo lugar, la alimentación se ha comenzado a tratar con políticas sanitarias, con lo que se ha alejado del tradicional tratamiento agrario. En tercer lugar, el aumento de la obesidad ha propiciado la corresponsabilidad en los problemas alimentarios entre el Estado y las industrias agroalimentarias.Spain has one of the highest childhood obesity rates in Europe. In this paper we study the different ways institutions are dealing with increasing obesity rates in Europe and in Spain in particular. We discuss measures taken to promote a healthy diet in both educational and consumer contexts. The obesity epidemic has led institutions to rethink the role of diet and nutrition. Firstly, diet has become a social issue and left aside much of its biological foundations. Second, diet has begun to form part of health policy agendas, moving away from the traditional agricultural-oriented viewpoint. Thirdly, the rise in obesity has led to corresponsibility between the state and food processing industries regarding food problems

A DSATUR-based algorithm for the Equitable Coloring Problem

This paper describes a new exact algorithm for the Equitable Coloring Problem, a coloring problem where the sizes of two arbitrary color classes differ in at most one unit. Based on the well known DSatur algorithm for the classic Coloring Problem, a pruning criterion arising from equity constraints is proposed and analyzed. The good performance of the algorithm is shown through computational experiments over random and benchmark instances.Fil: Méndez-Díaz, Isabel. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Computación; ArgentinaFil: Nasini, Graciela Leonor. Universidad Nacional de Rosario. Facultad de Ciencias Exactas, Ingeniería y Agrimensura; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Severin, Daniel Esteban. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Rosario. Facultad de Ciencias Exactas, Ingeniería y Agrimensura; Argentin

Non-Arrhenius relaxation of the Heisenberg model with dipolar and anisotropic interactions

The dynamical properties of a 2D Heisenberg model with dipolar interactions and perpendicular anisotropy are studied using Monte Carlo simulations in two different ordered regions of the equilibrium phase diagram. We find a temperature defining a dynamical transition below which the relaxation suddenly slows down and the system aparts from the typical Arrhenius relaxation to a Vogel-Fulcher-Tamann law. This anomalous behavior is observed in the scaling of the magnetic relaxation and may eventually lead to a freezing of the system. Through the analysis of the domain structures we explain this behavior in terms of the domains dynamics. Moreover, we calculate the energy barriers distribution obtained from the data of the magnetic viscosity. Its shape supports our comprehension of both, the Vogel-Fulcher-Tamann dynamical slowing down and the freezing mechanism