7,234 research outputs found
QCD Collisional Energy Loss in an Increasingly Interacting Quark Gluon Plasma
The discovery of the jet quenching in central Au + Au collisions at the
Relativistic Heavy-ion Collider (RHIC) at Brookhaven National Laboratory has
provided clear evidence for the formation of strongly interacting dense matter.
It has been predicted to occur due to the energy loss of high energy partons
that propagate through the quark gluon plasma. In this paper we investigate the
dependence of the parton energy loss due to elastic scatterings in a parton
plasma on the value of the strong coupling and its running with the evolution
of the system. We analyze different prescriptions for the QCD coupling and
calculate the energy and length dependence of the fractional energy loss.
Moreover, the partonic quenching factor for light and heavy quarks is
estimated. We found that the predicted enhancement of the heavy to light
hadrons () ratio is strongly dependent on the running of the QCD
coupling constant.Comment: 16 pages, 8 figures. Version to be published in the International
Journal of Modern Physics
Gravitational waves in the generalized Chaplygin gas model
The consequences of taking the generalized Chaplygin gas as the dark energy
constituent of the Universe on the gravitational waves are studied and the
spectrum obtained from this model, for the flat case, is analyzed. Besides its
importance for the study of the primordial Universe, the gravitational waves
represent an additional perspective (besides the CMB temperature and
polarization anisotropies) to evaluate the consistence of the different dark
energy models and establish better constraints to their parameters. The
analysis presented here takes this fact into consideration to open one more
perspective of verification of the generalized Chapligin gas model
applicability. Nine particular cases are compared: one where no dark energy is
present; two that simulate the -CDM model; two where the gas acts like
the traditional Chaplygin gas; and four where the dark energy is the
generalized Chaplygin gas. The different spectra permit to distinguish the
-CDM and the Chaplygin gas scenarios.Comment: Latex file, 9 pages, 11 figures eps forma
The puzzle of the soft X-ray excess in AGN: absorption or reflection?
The 2-10 keV continuum of AGN is generally well represented by a single power
law. However, at smaller energies the continuum displays an excess with respect
to the extrapolation of this power law, called the ''soft X-ray excess''. Until
now this soft X-ray excess was attributed, either to reflection of the hard
X-ray source by the accretion disk, or to the presence of an additional
comptonizing medium, giving a steep spectrum. An alternative solution proposed
by Gierlinski and Done (2004) is that a single power law well represents both
the soft and the hard X-ray emission and the impression of the soft X-ray
excess is due to absorption of a primary power law by a relativistic wind. We
examine the advantages and drawbacks of reflection versus absorption models,
and we conclude that the observed spectra can be well modeled, either by
absorption (for a strong excess), or by reflection (for a weak excess). However
the physical conditions required by the absorption models do not seem very
realistic: we would prefer an ''hybrid model''.Comment: 4 pages, 3 figures, abstracts SF2A-2005, published by EDP-Sciences
Conference Serie
RAPHAEL SAMÚ: Experiências do muralismo no Espírito Santo
A proposta deste estudo é investigar o processo de criação do artista plástico brasileiro Raphael Samú, tendo como recorte sua obra em mosaico mural, mais especificamente o mural presente na entrada da Universidade Federal do Espírito Santo UFES, em Vitória - Espírito Santo. Para tal, investigaremos através dos pressupostos da Crítica Genética e da Crítica Inferencial quais foram os caminhos tomados pelo artista durante a confecção de tal obra,
apontando assim a intencionalidade do projeto poético. Agregado a este estudo localizaremos grande parte de sua produção no Estado, situando-as no âmbito do Muralismo Capixaba.
Palavras-chave: Processo de Criação. Muralismo. Arte Pública. Mosaico
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