11,990 research outputs found
Viscous Cosmology
We discuss the possibility to implement a viscous cosmological model,
attributing to the dark matter component a behaviour described by bulk
viscosity. Since bulk viscosity implies negative pressure, this rises the
possibility to unify the dark sector. At the same time, the presence of
dissipative effects may alleviate the so called small scale problems in the
CDM model. While the unified viscous description for the dark sector
does not lead to consistent results, the non-linear behaviour indeed improves
the situation with respect to the standard cosmological model.Comment: Latex file, 7 pages, 6 figures. To appear in the proceedings of the
XIIth International Conference on Gravitation, Astrophysics and Cosmology,
June 28-July 5, 2015, PFUR, Moscow, Russi
Identificação de fungos em mudas de mangueiras apresentando morte súbita.
Suplemento. Edição dos Resumos do 44 Congresso Brasileiro de Fitopatologia, Bento Gonçalves, ago. 2011
Early appraisal of the fixation probability in directed networks
In evolutionary dynamics, the probability that a mutation spreads through the
whole population, having arisen in a single individual, is known as the
fixation probability. In general, it is not possible to find the fixation
probability analytically given the mutant's fitness and the topological
constraints that govern the spread of the mutation, so one resorts to
simulations instead. Depending on the topology in use, a great number of
evolutionary steps may be needed in each of the simulation events, particularly
in those that end with the population containing mutants only. We introduce two
techniques to accelerate the determination of the fixation probability. The
first one skips all evolutionary steps in which the number of mutants does not
change and thereby reduces the number of steps per simulation event
considerably. This technique is computationally advantageous for some of the
so-called layered networks. The second technique, which is not restricted to
layered networks, consists of aborting any simulation event in which the number
of mutants has grown beyond a certain threshold value, and counting that event
as having led to a total spread of the mutation. For large populations, and
regardless of the network's topology, we demonstrate, both analytically and by
means of simulations, that using a threshold of about 100 mutants leads to an
estimate of the fixation probability that deviates in no significant way from
that obtained from the full-fledged simulations. We have observed speedups of
two orders of magnitude for layered networks with 10000 nodes
Desenvolvimento de bezerros Guzeras e cruzados Canchim X Guzerá na região de Governador Valadares, MG.
Estudaram-se os pesos ao nascimento, a desmama, aos 12, aos 18 meses de idade , de bezerros filhos de vacas Guzeras e touros da raça Canchim.Resumo
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