O. Pla

Competition, efficiency and collective behavior in the “El Farol” bar model

Abstract:The El Farol bar model, proposed to study the dynamics of competition of agents in a variety of contexts (W.B. Arthur, Amer. Econ. Assoc. Pap. Proc. 84, 406 (1994)) is studied. We characterize in detail the three regions of the phase diagram (efficient, better than random and inefficient) of the simplest version of the model (D. Challet, Y.-C. Zhang, Physica A 246, 407 (1997)). The efficient region is shown to have a rich structure, which is investigated in some detail. Changes in the payoff function enhance further the tendency of the model towards a wasteful distribution of resources.

Energy radiation of moving cracks

The energy radiated by moving cracks in a discrete background is analyzed. The energy flow through a given surface is expressed in terms of a generalized Poynting vector. The velocity of the crack is determined by the radiation by the crack tip. The radiation becomes more isotropic as the crack velocity approaches the instability threshold.

A model for predation pressure in colonial birds

Different explanations have been proposed for the existence of colonial breeding behavior in birds, but field studies offer no conclusive results. We analyze the interplay between learning habits and predation pressure by means of numerical simulations. Our analysis suggests that extremely simple learning processes and equally simplistic models of predation pressure lead to the formation of stable colonies.

Modelling fracture driven by a thermal gradient

Motivated by recent experiments by Yuse and Sano (1993 Nature 362 329), we propose a discrete model of linear springs for studying fracture in thin and elastically isotropic brittle films. The method enables us to draw a map of the stresses in the material. Cracks generated by the model, imposing a moving thermal gradient in the material, can branch or wiggle depending on the driving parameters. The results may be used to compare with other recent theoretical work, or to design future experiments.