Exponential Distributions in a Mechanical Model for Earthquakes

We study statistical distributions in a mechanical model for an earthquake fault introduced by Burridge and Knopoff [R. Burridge and L. Knopoff, {\sl Bull. Seismol. Soc. Am.} {\bf 57}, 341 (1967)]. Our investigations on the size (moment), time duration and number of blocks involved in an event show that exponential distributions are found in a given range of the paramenter space. This occurs when the two kinds of springs present in the model have the same, or approximately the same, value for the elastic constants. Exponential distributions have also been seen recently in an experimental system to model earthquake-like dynamics [M. A. Rubio and J. Galeano, {\sl Phys. Rev. E} {\bf 50}, 1000 (1994)].Comment: 11 pages, uuencoded (submitted to Phys. Rev. E

Chaos and Synchronized Chaos in an Earthquake Model

We show that chaos is present in the symmetric two-block Burridge-Knopoff model for earthquakes. This is in contrast with previous numerical studies, but in agreement with experimental results. In this system, we have found a rich dynamical behavior with an unusual route to chaos. In the three-block system, we see the appearance of synchronized chaos, showing that this concept can have potential applications in the field of seismology.Comment: To appear in Physical Review Letters (13 pages, 6 figures

Transient expression of a translation initiation factor is conservatively associated with embryonic gene activation in murine and bovine embryos.

In the present study the abundance of mRNAs for eukaryotic translation initiation factors eIF-1A (formerly known as eIF-4C), -2alpha, -4A, -4E, and -5 was examined in in vivo-derived mouse embryos throughout preimplantation development using a semiquantitative reverse transcription-polymerase chain reaction assay. Although the mRNA profile for each gene is unique, only mRNA for eIF-1A transiently increases during embryonic gene activation (EGA) at the 2-cell stage, and this was confirmed by an independent hybridization-based assay. In in vitro-developed bovine embryos, mRNA for eIF-1A was transiently detected at the 8-cell stage, when the major activation of the genome occurs in this species. As in the mouse, detection in 8-cell bovine embryos was sensitive to the transcriptional inhibitor alpha-amanitin. It was also observed at the same time relative to cleavage in embryos cultured in defined medium under a reduced oxygen environment, and in medium supplemented with serum and somatic cells in 5% CO2 in air. Neither the chronology of early cleavage divisions nor the yield of bovine blastocysts differed in these culture media. Our results suggest that transient expression of eIF-1A in the mouse and cow is a conserved pattern of gene expression associated with EGA in mammals

An ABC Method for Estimating the Rate and Distribution of Effects of Beneficial Mutations

Determining the distribution of adaptive mutations available to natural selection is a difficult task. These are rare events and most of them are lost by chance. Some theoretical works propose that the distribution of newly arising beneficial mutations should be close to exponential. Empirical data are scarce and do not always support an exponential distribution. Analysis of the dynamics of adaptation in asexual populations of microorganisms has revealed that these can be summarized by two effective parameters, the effective mutation rate, Ue, and the effective selection coefficient of a beneficial mutation, Se. Here, we show that these effective parameters will not always reflect the rate and mean effect of beneficial mutations, especially when the distribution of arising mutations has high variance, and the mutation rate is high. We propose a method to estimate the distribution of arising beneficial mutations, which is motivated by a common experimental setup. The method, which we call One Biallelic Marker Approximate Bayesian Computation, makes use of experimental data consisting of periodic measures of neutral marker frequencies and mean population fitness. Using simulations, we find that this method allows the discrimination of the shape of the distribution of arising mutations and that it provides reasonable estimates of their rates and mean effects in ranges of the parameter space that may be of biological relevance.Fundação Calouste Gulbenkian, FCT, LAO/ITQB, Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), Fundação de Amparo à Ciência e Tecnologia do Estado de Pernambuco (FACEPE), program PRONEX/MCT-CNPq-FACEPE

Estrutura de renda dos produtores da Reserva Extrativista do Rio Cajari, Amapá.

Neste estudo caracterizou-se a estrutura de renda e a posse de bens das famílias residentes em três comunidades representativas do macro ambiente de terra firme da Reserva Extrativista do Rio Cajari no Estado do Amapá. A área de estudo abrangeu as comunidades de Açaizal, Marinho e Martins. Por meio de painéis temáticos e de questionários aplicados junto a 41 famílias selecionadas por amostragem, coletou-se dados que constituíram um cross section, ano agrícola 1999/2000. Constatou-se que, em média, a renda bruta familiar corresponde, em termos mensais, a 3,5 vezes o salário mínimo vigente no ano da pesquisa. Na composição dessa renda bruta, as atividades agrícolas participam com 38,9%, as ligadas ao extrativismo com 35,0%, a criação de pequenos animais com 2,9% e outras formas de renda com 23,1%. Em relação aos produtos do extrativismo, a comercialização e o consumo de 70 hectolitros de castanha-do-pará coletados por ano, por família, representam 25,7% da renda bruta e 31,6% da renda monetária. Quanto aos produtos agrícolas, a farinha de mandioca representa 14,6% da renda bruta e 11,6% da renda monetária, seguida pelas frutas que contribuem para a formação dessas rendas com 9,5% e 10,6%, respectivamente. Outras rendas como as provenientes de programas sociais governamentais, aposentadorias, salários de funcionários públicos, atividades mercantis e venda de mão-de-obra, representam 23,1% da renda bruta e 28,7% da renda monetária e, em média, por família, equivalem a um valor mensal igual a 0,8 vezes o salário mínimo vigente no ano da pesquisa. Fogão a gás, rádio, televisor com antena parabólica e geladeira/freezer são os bens que apresentam os maiores percentuais de posse por parte dos produtoresbitstream/CPAF-AP/7752/1/Boletim200255.PD