11,181 research outputs found
Rural-urban migration in d-dimensional lattices
The rural-urban migration phenomenon is analyzed by using an agent-based
computational model. Agents are placed on lattices which dimensions varying
from d=2 up to d=7. The localization of the agents in the lattice define their
social neighborhood (rural or urban) not being related to their spatial
distribution. The effect of the dimension of lattice is studied by analyzing
the variation of the main parameters that characterizes the migratory process.
The dynamics displays strong effects even for around one million of sites, in
higher dimensions (d=6, 7).Comment: 9 pages, 7 figures, to be published in International Journal of
Modern Physics C 1
Classical and quantum wormholes in a flat -decaying cosmology
We study the classical and quantum wormholes for a flat {\it Euclidean}
Friedmann-Robertson-Walker metric with a perfect fluid including an ordinary
matter source plus a source playing the role of dark energy (decaying
cosmological term). It is shown that classical wormholes exist for this model
and the quantum version of such wormholes are consistent with the Hawking-Page
conjecture for quantum wormholes as solutions of the Wheeler-DeWitt equation.Comment: 8 pages, 4 figures, accepted for publication in IJT
The CDM growth rate of structure revisited
We re-examine the growth index of the concordance cosmology in the
light of the latest 6dF and {\em WiggleZ} data. In particular, we investigate
five different models for the growth index , by comparing their
cosmological evolution using observational data of the growth rate of structure
formation at different redshifts. Performing a joint likelihood analysis of the
recent supernovae type Ia data, the Cosmic Microwave Background shift
parameter, Baryonic Acoustic Oscillations and the growth rate data, we
determine the free parameters of the parametrizations and we
statistically quantify their ability to represent the observations. We find
that the addition of the 6dF and {\em WiggleZ} growth data in the likelihood
analysis improves significantly the statistical results. As an example,
considering a constant growth index we find and
.Comment: 8 pages, 5 figures, Accepted for publication by International J. of
Modern Physics D (IJMPD). arXiv admin note: substantial text overlap with
arXiv:1203.672
Coasting cosmologies with time dependent cosmological constant
The effect of a time dependent cosmological constant is considered in a
family of scalar tensor theories. Friedmann-Robertson-Walker cosmological
models for vacumm and perfect fluid matter are found. They have a linear
expansion factor, the so called coasting cosmology, the gravitational
"constant" decreace inversely with time; this model satisfy the Dirac
hipotesis. The cosmological "constant" decreace inversely with the square of
time, therefore we can have a very small value for it at present time.Comment: 7 pages, latex file (ijmpal macro), accepted for publication in Int.
Mod. Phys.
Dinâmica da liberação de nutrientes de compostos orgânicos e exigências nutricionais do abacaxizeiro BRS Imperial.
As adubações para diferentes culturas trabalhadas na Embrapa Mandioca e Fruticultura são recomendadas em função das fontes de corretivos de solo e dos fertilizantes convencionais. Com exceção da cultura da banana, inexistem recomendações consolidadas com critérios científicos para fertilização orgânica ou orgânica enriquecida com fontes não convencionais. Nesse sentido, a compreensão do comportamento dos materiais genéticos frente a esse sistema de produção torna-se importante
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