Coupled quintessence and vacuum decay

We discuss observational consequences of a class of cosmological models characterized by the dilution of pressureless matter attenuated with respect to the usual $a^{-3}$ scaling due to the decay of vacuum energy. We carry out a joint statistical analysis of observational data from the new \emph{gold} sample of 182 SNe Ia, recent estimates of the CMB shift parameter, and BAO measurements from the SDSS to show that such models favor the decay of vacuum only into the dark matter sector, and that the separately conserved baryons cannot be neglected. In order to explore ways to more fundamentally motivated models, we also derive a coupled scalar field version for this general class of vacuum decay scenarios.Comment: 6 pages, 3 figures, LaTe

The Seyfert Population in the Local Universe

The magnitude-limited catalog of the Southern Sky Redshift Survey (SSRS2), is used to characterize the properties of galaxies hosting Active Galactic Nuclei. Using emission-line ratios, we identify a total of 162 (3%) Seyfert galaxies out of the parent sample with 5399 galaxies. The sample contains 121 Seyfert 2 galaxies and 41 Seyfert 1. The SSRS2 Seyfert galaxies are predominantly in spirals of types Sb and earlier, or in galaxies with perturbed appearance as the result of strong interactions or mergers. Seyfert galaxies in this sample are twice as common in barred hosts than the non-Seyferts. By assigning galaxies to groups using a percolation algorithm we find that the Seyfert galaxies in the SSRS2 are more likely to be found in binary systems, when compared to galaxies in the SSRS2 parent sample. However, there is no statistically significant difference between the Seyfert and SSRS2 parent sample when systems with more than 2 galaxies are considered. The analysis of the present sample suggests that there is a stronger correlation between the presence of the AGN phenomenon with internal properties of galaxies (morphology, presence of bar, luminosity) than with environmental effects (local galaxy density, group velocity dispersion, nearest neighbor distance).Comment: 35 pages, 13 figures, Accepted to be publised in Astronomical Journa

Dynamic model of gene regulation for the lac operon

Gene regulatory network is a collection of DNA which interact with each other and with other matter in the cell. The lac operon is an example of a relatively simple genetic network and is one of the best-studied structures in the Escherichia coli bacteria. In this work we consider a deterministic model of the lac operon with a noise term, representing the stochastic nature of the regulation. The model is written in terms of a system of simultaneous first order differential equations with delays. We investigate an analytical and numerical solution and analyse the range of values for the parameters corresponding to a stable solution

On the Nature of the Cosmological Constant Problem

General relativity postulates the Minkowski space-time to be the standard flat geometry against which we compare all curved space-times and the gravitational ground state where particles, quantum fields and their vacuum states are primarily conceived. On the other hand, experimental evidences show that there exists a non-zero cosmological constant, which implies in a deSitter space-time, not compatible with the assumed Minkowski structure. Such inconsistency is shown to be a consequence of the lack of a application independent curvature standard in Riemann's geometry, leading eventually to the cosmological constant problem in general relativity. We show how the curvature standard in Riemann's geometry can be fixed by Nash's theorem on locally embedded Riemannian geometries, which imply in the existence of extra dimensions. The resulting gravitational theory is more general than general relativity, similar to brane-world gravity, but where the propagation of the gravitational field along the extra dimensions is a mathematical necessity, rather than being a a postulate. After a brief introduction to Nash's theorem, we show that the vacuum energy density must remain confined to four-dimensional space-times, but the cosmological constant resulting from the contracted Bianchi identity is a gravitational contribution which propagates in the extra dimensions. Therefore, the comparison between the vacuum energy and the cosmological constant in general relativity ceases to be. Instead, the geometrical fix provided by Nash's theorem suggests that the vacuum energy density contributes to the perturbations of the gravitational field.Comment: LaTex, 5 pages no figutres. Correction on author lis

Crescimento do coqueiro jovem no nordeste de São Paulo.

bitstream/item/81095/1/CPATC-COM.-TEC.-21-98.pd

Germinação da semente e desenvolvimento da plântula de coqueiro anão verde no Nordeste de São Paulo.

Avalia o comportamento germinativo da semente e o desenvolvimento da plântula de coqueiro Anão, em condições definidas.bitstream/item/79800/1/CPATC-COM.-TEC.-12-97.pd

Influência da temperatura no desenvolvimento de Rhopalosiphum maidis (Fitch, 1856) (Hemiptera: Aphididae) em condições de laboratório.

O pulgão Rhopalosiphum maidis (Fitch) tem sido encontrado em todos os estádios de desenvolvimento do milho e na maioria dos municípios do Estado de Minas Gerais, e sua importância tem aumentado principalmente nas áreas onde se cultiva o milho "safrinha". Por isso, objetivou-se estudar a influência da temperatura sobre alguns aspectos biológicos das fases de ninfa e adulta desse afídeo em diferentes temperaturas em condições de laboratório. Os ensaios foram conduzidos em câmaras climatizadas reguladas a 15, 18, 21, 24, 27 e 30 ± 1oC, UR de 70 ± 10% e fotofase de 12 horas, no Laboratório de Biologia de Insetos do Departamento de Entomologia da Universidade Federal de Lavras - UFLA, MG, em delineamento inteiramente casualizado com cinco repetições com oito espécimens cada uma. Verificou-se uma correlação positiva entre todas as fases de desenvolvimento e a fecundidade de R. maidis com a temperatura, com exceção de 24 a 27oC, em que ocorreu uma redução na fecundidade, observando-se uma relação ciclo biológico/fecundidade maior na temperatura 24oC. Observou-se que a duração da fase de ninfa foi de 13,3; 10,7; 6,7; 4,5; 4,7 e 4,5 dias a 15, 18, 21, 24, 27 e 30oC, respectivamente, constatando-se um decréscimo linear em todos os ínstares, em razão do aumento da temperatura na faixa de 15 a 24oC. Acima dessa temperatura, houve uma tendência de estabilização da velocidade de desenvolvimento. O período reprodutivo foi de 28 dias a 15 e 18oC, estabilizando-se entre 21 e 27oC, com uma duração próxima a 12 dias, ao passo que a 30oC houve uma redução para cinco dias. O ciclo biológico a 15oC foi de 52 dias, decrescendo em cerca de seis dias com a elevação para 18oC. A maior redução foi observada entre 18 e 21oC, registrando-se um decréscimo de 18 dias