1,500 research outputs found
Particle based gPC methods for mean-field models of swarming with uncertainty
In this work we focus on the construction of numerical schemes for the
approximation of stochastic mean--field equations which preserve the
nonnegativity of the solution. The method here developed makes use of a
mean-field Monte Carlo method in the physical variables combined with a
generalized Polynomial Chaos (gPC) expansion in the random space. In contrast
to a direct application of stochastic-Galerkin methods, which are highly
accurate but lead to the loss of positivity, the proposed schemes are capable
to achieve high accuracy in the random space without loosing nonnegativity of
the solution. Several applications of the schemes to mean-field models of
collective behavior are reported.Comment: Communications in Computational Physics, to appea
The role of quenching time in the evolution of the mass-size relation of passive galaxies from the WISP survey
We analyze how passive galaxies at z 1.5 populate the mass-size plane
as a function of their stellar age, to understand if the observed size growth
with time can be explained with the appearance of larger quenched galaxies at
lower redshift. We use a sample of 32 passive galaxies extracted from the Wide
Field Camera 3 Infrared Spectroscopic Parallel (WISP) survey with spectroscopic
redshift 1.3 z 2.05, specific star-formation rates lower
than 0.01 Gyr, and stellar masses above 4.5 10
M. All galaxies have spectrally determined stellar ages from fitting of
their rest-frame optical spectra and photometry with stellar population models.
When dividing our sample into young (age 2.1 Gyr) and old (age 2.1
Gyr) galaxies we do not find a significant trend in the distributions of the
difference between the observed radius and the one predicted by the mass-size
relation. This result indicates that the relation between the galaxy age and
its distance from the mass-size relation, if it exists, is rather shallow, with
a slope alpha -0.6. At face value, this finding suggests that
multiple dry and/or wet minor mergers, rather than the appearance of newly
quenched galaxies, are mainly responsible for the observed time evolution of
the mass-size relation in passive galaxies.Comment: Accepted for publication in ApJ Letters; 6 pages, 3 figures, 1 tabl
Soil quality and fertility in sustainable agriculture, with a contribution to the biological classification of agricultural soils
Soils and crops are particularly vulnerable to climate change and environmental stresses. In many agrosystems, soil biodiversity and ecosystem services provided by soils are under threat from a range of natural and human drivers. Agricultural soils are often subject to agronomic practices that disrupt soil trophic networks and make soils less productive in the long term. In this scenario, sustainable soil use aimed at improving plant/root status, growth and development plays a crucial role for enhancing the biological capacity of agricultural soils. This commentary paper is divided into the following four main sections: (i) the contentious nature of soil organic matter; (ii) soil biological quality/fertility; (iii) soil classification; and, (iv) which agricultural practices can be defined as sustainable? The published literature was analyzed within a holistic framework, with agrosystems considered as living systems where soil, vegetation, fauna and microorganisms co-evolve and are reciprocally influenced. Ultimately, this article will suggest a better stewardship of agricultural soils as a natural capital
A nonequilibrium renormalization group approach to turbulent reheating
We use nonequilibrium renormalization group (RG) techniques to analyze the
thermalization process in quantum field theory, and by extension reheating
after inflation. Even if at a high scale the theory is described by a
non-dissipative theory, the RG running induces nontrivial
noise and dissipation. For long wavelength, slowly varying field
configurations, the noise and dissipation are white and ohmic, respectively.
The theory will then tend to thermalize to an effective temperature given by
the fluctuation-dissipation theorem.Comment: 8 pages, 2 figures; to appear in J. Phys. A; more detailed account of
the calculation of the noise and dissipation kernel
Mumificaçao fetal em suínos associada à toxoplasmose.
bitstream/item/58346/1/CUsersPiazzonDocuments271.pd
Determinação da concentração de canamicina na seleção de plantas transgênicas do clone 3336 de Eucalyptus urograndis.
Estudos da patogenicidade do circovirus suíno tipo 2 (PCV2) em suínos e do papel do macho suíno na disseminação viral dentro do plantel.
Projeto/Plano de Ação: 03.03.230.01
On the He II Emission In Eta Carinae and the Origin of Its Spectroscopic Events
We describe and analyze Hubble Space Telescope (HST) observations of
transient emission near 4680 {\AA} in Eta Car, reported earlier by Steiner &
Damineli (2004). If, as seems probable, this is He II 4687, then it is
a unique clue to Eta Car's 5.5-year cycle. According to our analysis, several
aspects of this feature support a mass-ejection model of the observed
spectroscopic events, and not an eclipse model. The He II emission appeared in
early 2003, grew to a brief maximum during the 2003.5 spectroscopic event, and
then abruptly disappeared. It did not appear in any other HST spectra before or
after the event. The peak brightness was larger than previously reported, and
is difficult to explain even if one allows for an uncertainty factor of order
3. The stellar wind must provide a temporary larger-than-normal energy supply,
and we describe a special form of radiative amplification that may also be
needed. These characteristics are consistent with a class of mass-ejection or
wind-disturbance scenarios, which have implications for the physical structure
and stability of Eta Car.Comment: 47 pages (including all appendices, tabs, & figs), 9 figures, 3
tables; submitted to Astrophysical Journal (2005 March 29), accepted for
publication in Ap
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