On the equivalence of Lambda(t) and gravitationally induced particle production cosmologies

The correspondence between cosmological models powered by a decaying vacuum energy density and gravitationally induced particle production is investigated. Although being physically different in the physics behind them we show that both classes of cosmologies under certain conditions can exhibit the same dynamic and thermodynamic behavior. Our method is applied to obtain three specific models that may be described either as Lambda(t)CDM or gravitationally induced particle creation cosmologies. In the point of view of particle production models, the later class of cosmologies can be interpreted as a kind of one-component unification of the dark sector. By using current type Ia supernovae data, recent estimates of the cosmic microwave background shift parameter and baryon acoustic oscillations measurements we also perform a statistical analysis to test the observational viability within the two equivalent classes of models and we obtain the best-fit of the free parameters. By adopting the Akaike information criterion we also determine the rank of the models considered here. Finally, the particle production cosmologies (and the associated decaying Lambda(t)-models) are modeled in the framework of field theory by a phenomenological scalar field model.Comment: 9 pages, 3 figures, new comments and 8 references added. Accepted for publication in Physics Letters

Deteccao de doencas na cultura do pimentao no submedio do Vale Sao Francisco-1998 a 2000.

A deteccao de doencas em 172 amostras de pimentao, provenientes de areas do Submedio do Vale do Sao Francisco, foi realizada no Laboratorio de Fitopatologia da Embrapa Semi-Arido, Petrolina, PE, no periodo de 1998 a 2000. Em 162 (94,2% ) amostras foram detectados fungos, bacterias e virus e em 7 (4,07%) amostras foram verificados danos causados por insetos, deficiencia nutricional e danos causados por herbicidas. Em 3 (1,7%) amostras, as causas dos sintomas nao foram identificadas. Infeccoes causadas por bacterias e por fungos foram detectadas em 32 (18,6%) e 27 ( 15,7% ) amostras, respectivamente. Cinco genero de fungos -Leveil,ula 9 ( 15,2% ), Cercospora 7 (11,8%), Colletotrichum 6 (10,2%), Rhizoctonia 4 (6,8%) e Sclerotium 1 ( l'7% ) -e tres de bacteria -Xanthomonas 26 ( 44, 1% ), Erwinia 3 ( 5, 1% ) e Ralstonia 3 (5,1%) -foram identificados nas amostras analisadas. A especie de tospovirus Groundnut ringspot virus foi detectada em 103 amostras.Suplemento. Edição do 41 Congresso Brasileiro de Olericultura; 1 Encontro sobre Plantas Medicinais, Aromáticas e Condimentares, Brasília, DF, jul. 2001

Critical Behavior of a Three-State Potts Model on a Voronoi Lattice

We use the single-histogram technique to study the critical behavior of the three-state Potts model on a (random) Voronoi-Delaunay lattice with size ranging from 250 to 8000 sites. We consider the effect of an exponential decay of the interactions with the distance,$J(r)=J_0\exp(-ar)$, with $a>0$, and observe that this system seems to have critical exponents $\gamma$ and $\nu$ which are different from the respective exponents of the three-state Potts model on a regular square lattice. However, the ratio $\gamma/\nu$ remains essentially the same. We find numerical evidences (although not conclusive, due to the small range of system size) that the specific heat on this random system behaves as a power-law for $a=0$ and as a logarithmic divergence for $a=0.5$ and $a=1.0$Comment: 3 pages, 5 figure

Reação de 55 genótipos de abóboras e morangas à infecção natural com Papaya ringspot virus - type watermelon (PRSV-W) e Zucchini yellow mosaic virus (XYNV) em campo.

Resumo 1712

An interacting model for the cosmological dark sector

We discuss a new interacting model for the cosmological dark sector in which the attenuated dilution of cold dark matter scales as $a^{-3}f(a)$, where f(a) is an arbitrary function of the cosmic scale factor $a$. From thermodynamic arguments, we show that f(a) is proportional to entropy source of the particle creation process. In order to investigate the cosmological consequences of this kind of interacting models, we expand f(a) in a power series and viable cosmological solutions are obtained. Finally, we use current observational data to place constraints on the interacting function f(a).Comment: 5 pages, 3 figures, Phys. Rev. D (in press

Custo de implantação dos sistemas intensivos de criação de suínos confinado e ao ar livre.

bitstream/item/85041/1/DCOT-207.pd

Similaridade genética de acesso de mangueira de diferentes origens geográficas avaliadas por marcadores AFLP.

O objetivo do presente trabalho foi determinar as relações genéticas, com base no marcador AFLP, dos acessos do banco de germoplasma de mangueira da Embrapa Semi-Árido, de forma a orientar trabalhos de melhoramento genético e de manejo de recursos genéticos da espécie

New Cosmic Accelerating Scenario without Dark Energy

We propose an alternative, nonsingular, cosmic scenario based on gravitationally induced particle production. The model is an attempt to evade the coincidence and cosmological constant problems of the standard model ($\Lambda$CDM) and also to connect the early and late time accelerating stages of the Universe. Our space-time emerges from a pure initial de Sitter stage thereby providing a natural solution to the horizon problem. Subsequently, due to an instability provoked by the production of massless particles, the Universe evolves smoothly to the standard radiation dominated era thereby ending the production of radiation as required by the conformal invariance. Next, the radiation becomes sub-dominant with the Universe entering in the cold dark matter dominated era. Finally, the negative pressure associated with the creation of cold dark matter (CCDM model) particles accelerates the expansion and drives the Universe to a final de Sitter stage. The late time cosmic expansion history of the CCDM model is exactly like in the standard $\Lambda$CDM model, however, there is no dark energy. This complete scenario is fully determined by two extreme energy densities, or equivalently, the associated de Sitter Hubble scales connected by $\rho_I/\rho_f=(H_I/H_f)^{2} \sim 10^{122}$, a result that has no correlation with the cosmological constant problem. We also study the linear growth of matter perturbations at the final accelerating stage. It is found that the CCDM growth index can be written as a function of the $\Lambda$ growth index, $\gamma_{\Lambda} \simeq 6/11$. In this framework, we also compare the observed growth rate of clustering with that predicted by the current CCDM model. Performing a $\chi^{2}$ statistical test we show that the CCDM model provides growth rates that match sufficiently well with the observed growth rate of structure.Comment: 12 pages, 3 figures, accepted for publication by Phys. Rev. D. (final version, some references have corrected). arXiv admin note: substantial text overlap with arXiv:1106.193