A canonical transformation and the tunneling probability for the birth of an asymptotically DeSitter universe with dust

In the present work, we study the quantum cosmology description of closed Friedmann-Robertson-Walker models in the presence of a positive cosmological constant and a generic perfect fluid. We work in the Schutz's variational formalism. If one uses the scale factor and its canonically conjugated momentum as the phase space variables that describe the geometrical sector of these models, one obtains Wheeler-DeWitt equations with operator ordering ambiguities. In order to avoid those ambiguities and simplify the quantum treatment of the models, we introduce new phase space variables. We explicitly demonstrate that the transformation leading from the old set of variables to the new one is canonical. In order to show that the above canonical transformations simplify the quantum treatment of those models, we consider a particular model where the perfect fluid is dust. We solve the Wheeler-DeWitt equation numerically using the Crank-Nicholson scheme and determine the time evolution of the initial wave function. Finally, we compare the results for the present model with the ones for another model where the only difference is the presence of a radiative perfect fluid, instead of dust.Comment: Revtex4, 18 pages, 2 EPS figure

Reply to "Comment on 'Quantization of FRW spacetimes in the presence of a cosmological constant and radiation'"

The Comment by Amore {\it et al.} [gr-qc/0611029] contains a valid criticism of the numerical precision of the results reported in a recent paper of ours [Phys. Rev. D {\bf 73}, 044022 (2006)], as well as fresh ideas on how to characterize a quantum cosmological singularity. However, we argue that, contrary to what is suggested in the Comment, the quantum cosmological models we studied show hardly any sign of singular behavior.Comment: 4 pages, accepted by Physical Review

Acúmulo de matéria seca dos capins Panicum maximum cv. Tanzânia, cv. Tobiatã e Pennisetum purpureum.

Disponível em: . Acesso em: 10 dez. 2003

Produção de forragem e desempenho de bovinos em pastagens de Paspalum regnellii submetidas ao manejo intensivo.

O presente trabalho objetivou avaliar o ganho de peso e a produção de forragem do acesso BRA-019186 de "Paspalum regnellii" quando comparado com a de "Paspalum atratum" cv. Pojuca e a de "Brachiaria decumbens" sob pastejo. As gramíneas foram plantadas em três repetições de área. Os animais foram manejados em pastejo rotacionado. Os piquetes receberam adubação de 200 kg N/ha/ano da fórmula NPK 20-05-20. Bezerros Nelore e cruzados desmamados foram utilizados no ano I e garrotes "threecross" foram utilizados no ano 11. Os períodos de avaliação foram 112 e 147 dias no ano I e 147 e 42 dias no ano 11, nos períodos das águas e seca, respectivamente. "Paspalum regnellii" apresentou produção de matéria seca de forragem maior que aquela das outras gramíneas no períododas chuvas e semelhante no período da seca. O ganho diário de peso (GDP) foi semelhante entre anos e gramíneas, com média de 0,75 kg no período das águas. No período da seca do ano I, os animais do "Paspalum regnellii" apresentaram GDP (0,50 kg), semelhante aos da Brachiaria (0,39 kg) e maior que os do Pojuca (0,09 kg), contudo, no ano II apresentaram GDP (0,16 kg) semelhante aos do Pojuca (0,04 kg) e menor que os da Brachiaria (0,40 kg). A média estimada de taxa de lotação das pastagens. não diferiu para as gramíneas estudadas nos dois anos, sendo igual a 4,8 UA/ha no período das águas, enquanto que no período da seca foi igual a 1,8 UA/ha no ano I e 3,0 UA/ha no ano 11

The cyclonic dryer: a numerical and experimental analysis of the influence of geometry on average particle residence time

Particle residence time is an extremely important variable in a cyclonic dryer project. With the goal of obtaining a device that conduces to a long particle residence time, the influence of cyclone dimensions on particle residence time and on the type of flow is discussed here. The research was based on a device with a very high ratio of cyclone diameter to other dimensions. Simulations were developed with computational fluid dynamics techniques by the use of the commercial code CFX 4.4® of AEA Technology. Particles were treated individually. The fit of a turbulence model was also discussed. Theoretical and experimental results showed that the dimensions of the conical part of the cyclone had a very important influence on flow and consequently on particle residence time. The influences of volumetric concentration and particle diameter on particle residence time were also observed.103112Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

Avaliação de acessos de camu-camuzeiro em terra firme.

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