838 research outputs found
Closed Spaces in Cosmology
This paper deals with two aspects of relativistic cosmologies with closed
(compact and boundless) spatial sections. These spacetimes are based on the
theory of General Relativity, and admit a foliation into space sections S(t),
which are spacelike hypersurfaces satisfying the postulate of the closure of
space: each S(t) is a 3-dimensional, closed Riemannian manifold. The discussed
topics are: (1) A comparison, previously obtained, between Thurston's
geometries and Bianchi-Kantowski-Sachs metrics for such 3-manifolds is here
clarified and developed. (2) Some implications of global inhomogeneity for
locally homogeneous 3-spaces of constant curvature are analyzed from an
observational viewpoint.Comment: 20 pages, 6 figures, revised version of published paper. In version
2: several misprints corrected, 'redshifting' in figures improved. Version 3:
a few style corrections; couple of paragraphs in subsection 2.4 rewritten.
Version 4: figures 5 and 6 corrrecte
QCD traveling waves phenomenology revisited
In this paper we review and update the Amaral-Gay Ducati-Betemps-Soyez
saturation model, by testing it against the recent H1-ZEUS combined data on
deep inelastic scattering, including heavy quarks in the dipole amplitude. We
obtain that this model, which is based on traveling wave solutions of the
Balitsky-Kovchegov equation and built in the momentum space framework, yields
very accurate descriptions of the reduced cross section,
, as well as DIS structure functions such as
and , all measured at HERA. Additionally, it
provides good descriptions of heavy quark structure functions, and
at small- and GeV. We also use the
improved model to make predictions for structure functions to be measured in
the near future at LHeC.Comment: 13 pages, 7 figure
Some integrals ocurring in a topology change problem
In a paper presented a few years ago, De Lorenci et al. showed, in the
context of canonical quantum cosmology, a model which allowed space topology
changes (Phys. Rev. D 56, 3329 (1997)). The purpose of this present work is to
go a step further in that model, by performing some calculations only estimated
there for several compact manifolds of constant negative curvature, such as the
Weeks and Thurston spaces and the icosahedral hyperbolic space (Best space).Comment: RevTeX article, 4 pages, 1 figur
Soft diffraction within the QCD color dipole picture
In this work we consider the QCD parton saturation models to describe soft
interactions at the high energy limit. The total and elastic cross sections as
well as the elastic slope parameter are obtained for proton-proton and
pion-proton collisions and compared to recent experimental results. The
analyses are done within the color dipole formalism taking into account
saturation models which have been tested against DIS data. The main point is
that the match between soft and hard interaction occurs in the saturation
region which can be described by high density QCD approaches. Discussion is
performed on the main theoretical uncertainties associated with calculations.Comment: 12 pages, 6 figures. Final version to be published in Physical Review
Avaliação de agroecossistemas em propriedades de produção orgânica no município de Jaguariúna, SP, através de indicadores de sustentabilidade.
A extensão universitária pode dar grande contribuição ao processo de transição da agricultura convencional para modelos de agricultura de base ecológica, que buscam o desenvolvimento sustentável e incorporam princípios e técnicas da Agroecologia. Neste contexto, duas ferramentas vêm sendo associadas com grande eficiência: as metodologias participativas e o uso de indicadores de sustentabilidade. Este trabalho avaliou a sustentabilidade de duas propriedades orgânicas no município de Jaguariúna, através de indicadores construídos e avaliados participativamente. A metodologia empregada permitiu avaliar o estado de cada unidade produtiva, além de classificar a fase de transição agroecológica destas, estabelecendo os gargalos para a sustentabilidade e gerando discussões sobre alternativas que podem embasar seu gerenciamento
Fixação biológica de nitrogênio na cultura do arroz irrigado por inundação: Parte I: bactérias endofíticas diazotróficas isoladas das cultivares BRS 7 "Taim" e BRS Pelota.
bitstream/item/44624/1/documento-303.pd
ANALYSIS OF A COMBINED BRAYTON/RANKINE CYCLE WITH TWO REGENERATORS IN PARALLEL
This work presents a configuration of two regenerators in parallel for a power generation Brayton/Rankine cycle where the output power is 10 MW. The working fluids considered for the Brayton and Rankine cycles are air and water, respectively. The addition of a regenerator with the previous existing cycle of this kind resulted in the addition of a second-stage turbine in the Rankine cycle of reheat. The objective of this modification is to increase the thermal efficiency of the combined cycle. In order to examine the efficiency of the new configuration, it is performed a thermodynamic modelling and numerical simulations for both cases: a regular Brayton/Rankine cycle and the one with the proposed changes. At the end of the simulations, the two cycles are compared, and it is seen that the new configuration reaches a 0.9% higher efficiency. In addition, the vapor quality at the exit of the higher turbine is higher, reducing the required mass flow rate in 14%
Inferring introduction routes of invasive species using approximate Bayesian computation on microsatellite data
Determining the routes of introduction provides not only information about the history of an invasion process, but also information about the origin and construction of the genetic composition of the invading population. It remains difficult, however, to infer introduction routes from molecular data because of a lack of appropriate methods. We evaluate here the use of an approximate Bayesian computation (ABC) method for estimating the probabilities of introduction routes of invasive populations based on microsatellite data. We considered the crucial case of a single source population from which two invasive populations originated either serially from a single introduction event or from two independent introduction events. Using simulated datasets, we found that the method gave correct inferences and was robust to many erroneous beliefs. The method was also more efficient than traditional methods based on raw values of statistics such as assignment likelihood or pairwise F(ST). We illustrate some of the features of our ABC method, using real microsatellite datasets obtained for invasive populations of the western corn rootworm, Diabrotica virgifera virgifera. Most computations were performed with the DIYABC program (http://www1.montpellier.inra.fr/CBGP/diyabc/)
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