13,007 research outputs found
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
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,, with , and
observe that this system seems to have critical exponents and
which are different from the respective exponents of the three-state Potts
model on a regular square lattice. However, the ratio 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 and as a logarithmic divergence for
and Comment: 3 pages, 5 figure
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
Noções de exploração mecanizada para floresta de terra firme: caso Curuá-una.
bitstream/item/58705/1/CPATU-DOC64.pd
Majority-Vote Model on a Random Lattice
The stationary critical properties of the isotropic majority vote model on
random lattices with quenched connectivity disorder are calculated by using
Monte Carlo simulations and finite size analysis. The critical exponents
and are found to be different from those of the Ising and
majority vote on the square lattice model and the critical noise parameter is
found to be .Comment: 4 pages, 6 figure
Optics and pool : play the game
In this communication we will present an experimental work to be carried out by students, from even the early ages of basic school, in a non-formal environment. Using a pool table (a game well known to many students) students will perform a series of experiments learning and demonstrating the laws of light reflection. The idea of associating the use of a pool table to the teaching of geometric optics is based on the need to make the teaching process more appealing on behalf of the students. Being pool a popular and appealing game it would be possible to teach physics concepts in an apparently informal or non-formal context. This assembly is also simplified due to the fact that only day-to-day materials are used, reducing its final cost as we only need to perform a few reversible changes to a pool table
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