Finite-temperature properties of frustrated classical spins coupled to the lattice

We present extensive Monte Carlo simulations for a classical antiferromagnetic Heisenberg model with both nearest ($J_1$) and next-nearest ($J_2$) exchange couplings on the square lattice coupled to the lattice degrees of freedom. The Ising-like phase transition, that appears for $J_2/J_1>1/2$ in the pure spin model, is strengthened by the spin-lattice coupling, and is accompanied by a lattice deformation from a tetragonal symmetry to an orthorhombic one. Evidences that the universality class of the transition does not change with the inclusion of the spin-lattice coupling are reported. Implications for ${\rm Li_2VOSiO_4}$, the prototype for a layered $J_1{-}J_2$ model in the collinear regime, are also discussed.Comment: 6 pages and 8 figure

Ising transition driven by frustration in a 2D classical model with SU(2) symmetry

We study the thermal properties of the classical antiferromagnetic Heisenberg model with both nearest ($J_1$) and next-nearest ($J_2$) exchange couplings on the square lattice by extensive Monte Carlo simulations. We show that, for $J_2/J_1 > 1/2$, thermal fluctuations give rise to an effective $Z_2$ symmetry leading to a {\it finite-temperature} phase transition. We provide strong numerical evidence that this transition is in the 2D Ising universality class, and that $T_c\to 0$ with an infinite slope when $J_2/J_1\to 1/2$.Comment: 4 pages with 4 figure

Desobediencia debida : justificación doctrinal del alzamiento cristero : México (1926-1929)

El alzamiento de católicos mexicanos contra las leyes anticatólicas sancionadas durante la presidencia de Plutarco Elías Calle, entre 1926 y 1929, sigue siendo, hasta hoy, muy poco conocido. Son escasos los trabajos que han desempolvado los antiguos archivos de una historia que aún desata polémicas. En este artículo se prueba, a través del repaso de la doctrina católica, que el “caso cristero" fue la aplicación práctica del antiguo derecho de alzamiento contra un gobierno opresor.The Mexican Catholic insurrection against anti-Catholic laws passed during the presidency of Plutarco Elias Calle, between 1926 and 1929, remains, to date, very little known. There are few who, through hard work, have dusted off the old files of a story that still sparks controversy. This article is tested through the review of Catholic doctrine, that the “Cristero case" was the practical application of the ancient right of rebellion against an oppressive government.Fil: Olivera Ravasi, Javier P.

BAYESIAN CONTROL OF THE NUMBER OF SERVERS IN A GI/M/C QUEUING SYSTEM

In this paper we consider the problem of designing a GI/M/c queueing system. Given arrival and service data, our objective is to choose the optimal number of servers so as to minimize an expected cost function which depends on quantities, such as the number of customers in the queue. A semiparametric approach based on Erlang mixture distributions is used to model the general interarrival time distribution. Given the sample data, Bayesian Markov chain Monte Carlo methods are used to estimate the system parameters and the predictive distributions of the usual performance measures. We can then use these estimates to minimize the steady-state expected total cost rate as a function of the control parameter c. We provide a numerical example based on real data obtained from a bank in Madrid.

Strong solution of the stochastic Burgers equation

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)This work introduces a pathwise notion of solution for the stochastic Burgers equation, in particular, our approach encompasses the Cole-Hopf solution. The developments are based on regularization arguments from the theory of distributions.This work introduces a pathwise notion of solution for the stochastic Burgers equation, in particular, our approach encompasses the Cole-Hopf solution. The developments are based on regularization arguments from the theory of distributions933646652FAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOFundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)FAEPEX [1324/12]FAPESP [2012/18739-0]2012/18739-