Immunization and Aging: a Learning Process in the Immune Network

The immune system can be thought as a complex network of different interacting elements. A cellular automaton, defined in shape-space, was recently shown to exhibit self-regulation and complex behavior and is, therefore, a good candidate to model the immune system. Using this model to simulate a real immune system we find good agreement with recent experiments on mice. The model exhibits the experimentally observed refractory behavior of the immune system under multiple antigen presentations as well as loss of its plasticity caused by aging.Comment: 4 latex pages, 3 postscript figures attached. To be published in Physical Review Letters (Tentatively scheduled for 5th Oct. issue

Survival-extinction phase transition in a bit-string population with mutation

A bit-string model for the evolution of a population of haploid organisms, subject to competition, reproduction with mutation and selection is studied, using mean field theory and Monte Carlo simulations. We show that, depending on environmental flexibility and genetic variability, the model exhibits a phase transtion between extinction and survival. The mean-field theory describes the infinite-size limit, while simulations are used to study quasi-stationary properties.Comment: 11 pages, 5 figure

Monte Carlo Simulation of Vesicle Self-Organisation

Vesicles, which are droplets of a fluid encapsulated in a membrane, represent the basic structure of almost all life forms. The amphiphilic membrane that separates different domains acts as a tunable filter, selectively allowing the passage of chemical substances. The formation of these aggregates is subject of increasing interest, both experimental and theoretically, due to the fact that they can be used as drug carrier of even as artificial cells. In this paper, we report the first successful computer simulation of vesicle spontaneous formation obtained by performing extensive Monte Carlo calculations in a microscopic lattice model based on two-tailed amphiphilic chains surrounded by solvent molecules. The dynamical process of aggregation is also shown and some features of this process are discussed

Anomalous phase separation dynamics in the presence of surfactants

We study the phase separation of water and oil in a water-oil-surfactant microemulsion, from a totally disordered phase in both two and three dimensions using extensive Monte Carlo simulations of a spin model of microemulsions. The evolution of the characteristic length scale and the structure factor are measured and compared with recent experiments and theoretical work. At relatively high surfactant concentrations and off-critical quenches, we obtain results in agreement with earlier theoretical approaches. For critical quenches at very low surfactant concentrations, we observe the surprising result that it is easier to get to the scaling regime than in the pure binary cas

A methodology for unveiling global innovation networks : patent citations as clues to cross border knowledge flows.

This paper presents a new methodology to describe global innovations networks. Using 167,315 USPTO patents granted in 2009 and the papers they cited, this methodology shows ??scientific footprints of technology?? that cross national boundaries, and how multinational enterprises interact globally with universities and other firms. The data and the map of these flows provide insights to support a tentative taxonomy of global innovation networks