Justification of Sexual Reproduction by Modified Penna Model of Ageing

We generalize the standard Penna bit-string model of biological ageing by assuming that each deleterious mutation diminishes the survival probability in every time interval by a small percentage. This effect is added to the usual lethal but age-dependent effect of the same mutation. We then find strong advantages or disadvantages of sexual reproduction (with males and females) compared to asexual cloning, depending on parameters.Comment: 4 pages, 2 figures, submitted to Physica

Critical behavior at edge singularities in one dimensional spin models

In ferromagnetic spin models above the critical temperature ($T > T_{cr}$) the partition function zeros accumulate at complex values of the magnetic field ($H_E$) with a universal behavior for the density of zeros \rho (H) \sim | H - H_E |^{\sg}. The critical exponent \sg is believed to be universal at each space dimension and it is related to the magnetic scaling exponent $y_h$ via \sg = (d-y_h)/y_h. In two dimensions we have y_h=12/5 (\sg = -1/6) while y_h=2 (\sg=-1/2) in $d=1$. For the one dimensional Blume-Capel and Blume-Emery-Griffiths models we show here, for different temperatures, that a new value y_h=3 (\sg =-2/3) can emerge if we have a triple degeneracy of the transfer matrix eigenvalues.Comment: to appear in Phys. Rev. E, 16 pages, 3 figure

Two loops calculation in chiral perturbation theory and the unitarization program of current algebra

In this paper we compare two loop Chiral Perturbation Theory (ChPT) calculation of pion-pion scattering with the unitarity second order correction to the current algebra soft-pion theorem. It is shown that both methods lead to the same analytic structure for the scattering amplitude.Comment: 13 pages, Revtex 3.0, no figures, submitted to Phys. Lett.

The influence of differential rotation on the detectability of gravitational waves from the r-mode instability

Recently, it was shown that differential rotation is an unavoidable feature of nonlinear r-modes. We investigate the influence of this differential rotation on the detectability of gravitational waves emitted by a newly born, hot, rapidly-rotating neutron star, as it spins down due to the r-mode instability. We conclude that gravitational radiation may be detected by the advanced laser interferometer detector LIGO if the amount of differential rotation at the time the r-mode instability becomes active is not very high.Comment: 8 pages, 6 figures, revtex

Como as descobertas do LBA podem ser úteis para a agricultura na Amazônia?

Resumo 17.1

Dinâmica recente no espaço rural do município de Nossa Senhora da Glória/SE.

O objetivo desse artigo é analisar a dinâmica recente no espaço rural de um município do semi-árido sergipano, reconhecido pelo dinamismo da sua economia que gira em torno da produção e processamento do leite por agricultores familiares, a despeito da inexistência de políticas específicas e continuadas para esse fim. A área de pesquisa é o município de Nossa Senhora da Glória localizado no Alto Sertão sergipano. A metodologia privilegiou o contato com atores-chave através de entrevistas, observações de campo, caminhadas transversais para observação da paisagem, participação em reuniões e levantamento de dados secundários. Os principais resultados demonstram que o município de Glória contem na sua totalidade três unidades de desenvolvimento com dinâmicas particulares a depender das estratégias dos agricultores, acesso e qualidade dos recursos naturais e vinculação com os mercados (trabalho, produto e financeiro