52 research outputs found
Effects of gluon number fluctuations on photon - photon collisions at high energies
We investigate the effects of gluon number fluctuations on the total
, cross sections and the photon structure
function . Considering a model which relates the
dipole-dipole and dipole-hadron scattering amplitudes, we estimate these
observables by using event-by-event and physical amplitudes. We demonstrate
that both analyses are able to describe the LEP data, but predict different
behaviours for the observables at high energies, with the gluon fluctuations
effects decreasing the cross sections. We conclude that the study of interactions can be useful to constrain the QCD dynamics.Comment: 9 pages, 6 figures. Improved version with two new figures. Version to
be published in Physical Review
cross section from the dipole model in momentum space
We reproduce the DIS measurements of the proton structure function at high
energy from the dipole model in momentum space. To model the dipole-proton
forward scattering amplitude, we use the knowledge of asymptotic solutions of
the Balitsky-Kovchegov equation, describing high-energy QCD in the presence of
saturation effects. We compare our results with the previous analysis in
coordinate space and discuss possible extensions of our approach.Comment: 9 pages, 3 figure
Modelagem do crescimento de culturas: aplicações à cultura do milho.
CaracterÃsticas gerais dos modelos de culturas; Principais modelos de culturas; Possibilidades de aplicação dos modelos de cultura; Aplicação no manejo da cultura; Aplicação na análise da resposta de culturas à irrigação e no planejamento do uso de recursos hÃdricos; Aplicação no manejo de nitrogênio; Aplicação na avalização de risco climático e no prognóstico de safras; Aplicação na análise da sustentabilidade de sistemas de sucessão de culturas; Aplicação em estudos de variabilidade espacial e em manejo sÃtio-especÃfico; Aplicação no planejamento de uso da terra e dos recursos naturais; Aplicação na genética e melhoramento e na análise da interação genótipo x ambiente; Aplicação na simulação do efeito de pragas, doenças e plantas daninhas; Aplicação nos estudos de mudanças climáticas; Aplicação como ferramenta de educação e transferência de tecnologia; Limitações dos modelos de crescimento de culturas; Potencialidades de aplicação de modelos de simulação de culturas no Brasil.bitstream/CNPMS-2010/22537/1/Doc-91.pd
DIS and the effects of fluctuations: a momentum space analysis
Among the dipole models of deep inelastic scattering at small values of the
Bjorken variable , one has been recently proposed which relates the virtual
photon-proton cross section to the dipole-proton forward scattering amplitude
in momentum space. The latter is parametrized by an expression which
interpolates between its behavior at saturation and the travelling wave,
ultraviolet, amplitudes predicted by perturbative QCD from the
Balitsky-Kovchegov equation. Inspired by recent developments in coordinate
space, we use this model to parametrize the proton structure function and
confront it to HERA data on deep inelastic scattering. Both event-by-event
and the physical amplitudes are considered, the latter used to investigate the
effect of gluon number fluctuations, beyond the mean-field approximation. We
conclude that fluctuations are not present in DIS at HERA energies.Comment: 9 pages, 2 figure
QCD at small x and nucleus-nucleus collisions
At large collision energy sqrt(s) and relatively low momentum transfer Q, one
expects a new regime of Quantum Chromo-Dynamics (QCD) known as "saturation".
This kinematical range is characterized by a very large occupation number for
gluons inside hadrons and nuclei; this is the region where higher twist
contributions are as large as the leading twist contributions incorporated in
collinear factorization. In this talk, I discuss the onset of and dynamics in
the saturation regime, some of its experimental signatures, and its
implications for the early stages of Heavy Ion Collisions.Comment: Plenary talk given at QM2006, Shanghai, November 2006. 8 pages, 8
figure
Circumstances and factors associated with accidental deaths among children, adolescents and young adults in Cuiaba, Brazil
Detecting Network Communities: An Application to Phylogenetic Analysis
This paper proposes a new method to identify communities in generally weighted
complex networks and apply it to phylogenetic analysis. In this case, weights
correspond to the similarity indexes among protein sequences, which can be used
for network construction so that the network structure can be analyzed to
recover phylogenetically useful information from its properties. The analyses
discussed here are mainly based on the modular character of protein similarity
networks, explored through the Newman-Girvan algorithm, with the help of the
neighborhood matrix . The most relevant
networks are found when the network topology changes abruptly revealing distinct
modules related to the sets of organisms to which the proteins belong. Sound
biological information can be retrieved by the computational routines used in
the network approach, without using biological assumptions other than those
incorporated by BLAST. Usually, all the main bacterial phyla and, in some cases,
also some bacterial classes corresponded totally (100%) or to a great
extent (>70%) to the modules. We checked for internal consistency in
the obtained results, and we scored close to 84% of matches for community
pertinence when comparisons between the results were performed. To illustrate
how to use the network-based method, we employed data for enzymes involved in
the chitin metabolic pathway that are present in more than 100 organisms from an
original data set containing 1,695 organisms, downloaded from GenBank on May 19,
2007. A preliminary comparison between the outcomes of the network-based method
and the results of methods based on Bayesian, distance, likelihood, and
parsimony criteria suggests that the former is as reliable as these commonly
used methods. We conclude that the network-based method can be used as a
powerful tool for retrieving modularity information from weighted networks,
which is useful for phylogenetic analysis
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