Spontaneous emergence of spatial patterns ina a predator-prey model

We present studies for an individual based model of three interacting populations whose individuals are mobile in a 2D-lattice. We focus on the pattern formation in the spatial distributions of the populations. Also relevant is the relationship between pattern formation and features of the populations' time series. Our model displays travelling waves solutions, clustering and uniform distributions, all related to the parameters values. We also observed that the regeneration rate, the parameter associated to the primary level of trophic chain, the plants, regulated the presence of predators, as well as the type of spatial configuration.Comment: 17 pages and 15 figure

Observational constraints on late-time Lambda(t) cosmology

The cosmological constant, i.e., the energy density stored in the true vacuum state of all existing fields in the Universe, is the simplest and the most natural possibility to describe the current cosmic acceleration. However, despite its observational successes, such a possibility exacerbates the well known cosmological constant problem, requiring a natural explanation for its small, but nonzero, value. In this paper we study cosmological consequences of a scenario driven by a varying cosmological term, in which the vacuum energy density decays linearly with the Hubble parameter. We test the viability of this scenario and study a possible way to distinguish it from the current standard cosmological model by using recent observations of type Ia supernova (Supernova Legacy Survey Collaboration), measurements of the baryonic acoustic oscillation from the Sloan Digital Sky Survey and the position of the first peak of the cosmic microwave background angular spectrum from the three-year Wilkinson Microwave Anisotropy Probe.Comment: Some important revisions. To appear in Physical Review

Evolution of density perturbations in decaying vacuum cosmology: The case of non-zero perturbations in the cosmological term

We extend the results of a previous paper where a model of interacting dark energy, with a cosmological term decaying linearly with the Hubble parameter, is tested against the observed mass power spectrum. In spite of the agreement with observations of type Ia supernovas, baryonic acoustic oscillations and the cosmic microwave background, we had shown previously that no good concordance is achieved if we include the mass power spectrum. However, our analysis was based on the ad hoc assumption that the interacting cosmological term is strictly homogeneous. Now we perform a more complete analysis, by perturbing such a term. Although our conclusions are still based on a particular, scale invariant choice of the primordial spectrum of dark energy perturbations, we show that a cosmological term decaying linearly with the Hubble parameter is indeed disfavored as compared to the standard model.Comment: Version accepted for publication in Physical Review

Segmentação de sistemas de produção de leite como instrumento de apoio a decisão e gestão da atividade leiteira.

Qualquer sistema de produção pode ser considerado como um caixa preta, em que os insumos e produtos são conhecidos e mensuráveis, embora o processo de transformação dos insumos em produtos seja desconhecidos. Neles, a correta colocação de recursos, muitas vezes, fica prejudicada pela impossibilidade de se conhecer a exata dimensão ou quantidade de recursos utilizados em cada uma das fases do processo produtivo. Uma das formas de melhorar o entendimento de processos produtivos complexos é segmentar o sistema em partes menores, ou seja em abrir alguns dos compartimentos ue compõem a caixa preta, em que cada um representa uma parte do processo de transformacao. O que se propoe neste estudo e segmentar o sistema global de producao de leite em quatro setores quais sejam: a) producao de leite; b) producao de novilhas para reposição do plantel de vacas; c)producao de alimentos volumosos; e d)maquinas e implementos. Acredita-se que a analise segmentada da atividade leiteira traga grandes vantagens em vista da organização e administracao da producao

Agrobacterium-mediated genetic transformation of a tropical elite maize line.

ABSTRACT: The efficiency of maize transformation mediated by Agrobacterium tumefaciens is influenced by various factors. The aim of this study was to test the effect of different concentrations of N6 salts (50% ? half strength, and 100% - full strength) in the infection and cocultivation media on genetic transformation efficiency of the L3 tropical elite maize line. Immature embryos were transformed via A. tumefaciens harboring the binary vector pTF102 containing the genes uidA and BAR under control of the CaMV35S promoter. The efficiency of the transgenic events produced was 3% for full strength and 1.1% for half strength N6 salts. Although under a lower concentration of salts, GUS expression was stronger; under this concentration, regeneration was less efficient. Thus, the results showed that the presence of 100% N6 salts in the infection and cocultivation media favored genetic transformation of the L3 maize inbred line mediated by A. tumefaciens