Modelling exchange bias in core/shell nanoparticles

We present an atomistic model of a single nanoparticle with core/shell structure that takes into account its lattice strucutre and spherical geometry, and in which the values of microscopic parameters such as anisotropy and exchange constants can be tuned in the core, shell and interfacial regions. By means of Monte Carlo simulations of the hysteresis loops based on this model, we have determined the range of microscopic parameters for which loop shifts after field cooling can be observed. The study of the magnetic order of the interfacial spins for different particles sizes and values of the interfacial exchange coupling have allowed us to correlate the appearance of loop asymmetries and vertical displacements to the existence of a fraction of uncompensated spins at the shell interface that remain pinned during field cycling, offering new insight on the microscopic origin of the experimental phenomenology.Comment: 7 pages, 3 figures. Contribution presented at HMM 2007 held at Napoli 4-6 June 2007. To be published in J. Phys. Condens. Matte

Measuring satisfaction in societies with opinion leaders and mediators

An opinion leader-follower model (OLF) is a two-action collective decision-making model for societies, in which three kinds of actors are considered:Preprin

Cooperation through social influence

We consider a simple and altruistic multiagent system in which the agents are eager to perform a collective task but where their real engagement depends on the willingness to perform the task of other influential agents. We model this scenario by an influence game, a cooperative simple game in which a team (or coalition) of players succeeds if it is able to convince enough agents to participate in the task (to vote in favor of a decision). We take the linear threshold model as the influence model. We show first the expressiveness of influence games showing that they capture the class of simple games. Then we characterize the computational complexity of various problems on influence games, including measures (length and width), values (Shapley-Shubik and Banzhaf) and properties (of teams and players). Finally, we analyze those problems for some particular extremal cases, with respect to the propagation of influence, showing tighter complexity characterizations.Peer ReviewedPostprint (author’s final draft

Consum d'oxigen estimat i despesa energètica en competicions d'esgrima

Es realitza una estimació del consum d'oxigen i una anàlisi de les demandes energètiques de l'esgrima en competició. En assalts de competició, el consum d'oxigen estimat en dones ( x = 39,6 mL·kg-'·min-1) és inferior al dels homes (X = 53,9 mL·kg-'·min-1). La intensitat individual mitjana es troba entre el 56 % i el 74 % del Vo2max, amb màxims entre el 75 % i el 99 % del Vo2max, el que confirma la rellevància dels requeriments aeròbics en l'esgrima. Les demandes energètiques en la competició internacional són superiors a les registrades en una competició autonòmica i al de diferents situacions d'entrenament. La potència energètica mitjana es-timada al llarg de competicions de nivell internacional i autonòmic és, respectivament, de 15,4 kcal-min-1 (64,5 I<J·min-1) i 12,3 kcal·min-1 (51,6 kj·min-1). Entre tiradors del mateix gènere no s'aprecien diferències significatives en funció de l'arma. De l'anàlisi en competició destaca la variabilitat de la resposta funcional dels esgrimidors atesa la influència de factors com l'adaptació cardiocirculatòria individual, importància de la competició, eliminatòria registrada, nivell del rival, dinàmica competitiva, arma i gènere