The network of Barabasi and Albert, a preferential growth model where a new node is linked to the old ones with a probability proportional to their connectivity, is applied to Brazilian election results. The application of the Sznajd rule, that only agreeing pairs of people can convince their neighbours, gives a vote distribution in good agreement with reality.Comment: 7 pages including two figures, for Eur. Phys. J.

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In the Sznajd model of sociophysics on the square lattice, neighbors having the same opinion convince their neighbors of this opinion. We study scaling of the cluster growth. The spreading-of-damage technique is applied for the spread of opinions. We study the time evolution of the damage and compare it with the magnetization evolution. We also compare this model with the Ising model at low temperatures. It was recently shown that the distribution of votes in Brazilian elections follows a power law behavior with exponent ≃ -1.0. A model for elections based on the Sznajd model is proposed. The exponent obtained for the distribution of votes during the transient agrees with that obtained for elections.

We have investigated the aggregation into micelles of nonionic amphiphiles in water through Monte Carlo simulations of a very simple model system. Amphiphiles and water are modeled, respectively, as three-site and one-site molecules on a square lattice. The model presents characteristic properties of experimental micellization, namely, monomer vs amphiphile concentration with a plateau above a ‘‘critical’’ concentration (cmc) and a distribution of micelle sizes (polydispersity). Results of the numerical experiment were compared with predictions from statistical thermodynamic theory. Sample size and relaxation properties of the simulation have also been analyzed.

An improved version of an earlier Larson-type model of solution of amphiphiles is used to simulate the spontaneous formation of vesicles. Starting with a solution of amphiphiles either uniformly distributed or aggregated in an ordered way, self-organization into vesicles was observed by carrying out extensive Monte Carlo simulations. The aggregation of single-tailed amphiphiles and the role of the bending rigidity in the chains are also discussed.

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When a new individual is formed (independently of the reproduction process) it inherits harmful mutations. Moreover, new mutations are acquired even in the genetic code formation, most of them deleterious ones. This might lead to a time decay in the mean fitness of the whole population that, for long enough time, would produce the extinction of the species. This process is called Mutational Meltdown and such question used to be considered in the biological literature as a problem that only occurs in small populations. In contrast with earlier biological assumptions, here we present results obtained in different models showing that the mutational meltdown can occur in large populations, even in sexual reproductive ones. We used a bit-string model introduced to study the time evolution of age-structured populations and a genetically inspired model that allows to observe the time evolution of the population mean fitness

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