24,270 research outputs found
Revisiting the confrontation of the energy conditions with supernovae data
In the standard Friedmann-Lemaitre-Robertson-Walker (FLRW) approach to model
the Universe the violation of the so-called energy conditions is related to
some important properties of the Universe as, for example, the current and the
inflationary accelerating expansion phases. The energy conditions are also
necessary in the formulation and proofs of Hawking-Penrose singularity
theorems. In two recent articles we have derived bounds from energy conditions
and made confrontations of these bounds with supernovae data. Here, we extend
these results in following way: first, by using our most recent statistical
procedure for calculating new q(z) estimates from the \emph{gold} and
\emph{combined} type Ia supernovae samples; second, we use these estimates to
obtain a new picture of the energy conditions fulfillment and violation for the
recent past () in the context of the standard cosmology.Comment: 5 pages. To appear in Int. J. Mod. Phys. D. Talk presented at the 3rd
International Workshop on Astronomy and Relativistic Astrophysics. V2: typos
correcte
Disc formation in turbulent cloud cores: Circumventing the magnetic braking catastrophe
We present collapse simulations of strongly magnetised, 100 M_sun, turbulent
cloud cores. Around the protostars formed during the collapse Keplerian discs
with typical sizes of up to 100 AU build up in contrast to previous simulations
neglecting turbulence. Analysing the condensations in which the discs form, we
show that the magnetic flux loss is not sufficient to explain the build-up of
Keplerian discs. The average magnetic field is strongly inclined to the disc
which might reduce the magnetic braking efficiency. However, the main reason
for the reduced magnetic braking efficiency is the highly disordered magnetic
field in the surroundings of the discs. Furthermore, due to the lack of a
coherently rotating structure in the turbulent environment of the disc no
toroidal magnetic field necessary for angular momentum extraction can build up.
Simultaneously the angular momentum inflow remains high due to local shear
flows created by the turbulent motions. We suggest that the "magnetic braking
catastrophe" is an artefact of the idealised non-turbulent initial conditions
and that turbulence provides a natural mechanism to circumvent this problem.Comment: 4 pages, 2 figures. To appear in the proceedings of 'The Labyrinth of
Star Formation' (18-22 June 2012, Chania, Greece), published by Springe
Tax evasion dynamics and Zaklan model on Opinion-dependent Network
Within the context of agent-based Monte-Carlo simulations, we study the
well-known majority-vote model (MVM) with noise applied to tax evasion on
Stauffer-Hohnisch-Pittnauer (SHP) networks. To control the fluctuations for tax
evasion in the economics model proposed by Zaklan, MVM is applied in the
neighborhood of the critical noise to evolve the Zaklan model. The
Zaklan model had been studied recently using the equilibrium Ising model. Here
we show that the Zaklan model is robust because this can be studied besides
using equilibrium dynamics of Ising model also through the nonequilibrium MVM
and on various topologies giving the same behavior regardless of dynamic or
topology used here.Comment: 14 page, 4 figure
Constraints on Cold Dark Matter Accelerating Cosmologies and Cluster Formation
We discuss the properties of homogeneous and isotropic flat cosmologies in
which the present accelerating stage is powered only by the gravitationally
induced creation of cold dark matter (CCDM) particles (). For
some matter creation rates proposed in the literature, we show that the main
cosmological functions such as the scale factor of the universe, the Hubble
expansion rate, the growth factor and the cluster formation rate are
analytically defined. The best CCDM scenario has only one free parameter and
our joint analysis involving BAO + CMB + SNe Ia data yields
() where
is the observed matter density parameter. In particular, this implies that the
model has no dark energy but the part of the matter that is effectively
clustering is in good agreement with the latest determinations from large scale
structure. The growth of perturbation and the formation of galaxy clusters in
such scenarios are also investigated. Despite the fact that both scenarios may
share the same Hubble expansion, we find that matter creation cosmologies
predict stronger small scale dynamics which implies a faster growth rate of
perturbations with respect to the usual CDM cosmology. Such results
point to the possibility of a crucial observational test confronting CCDM with
CDM scenarios trough a more detailed analysis involving CMB, weak
lensing, as well as the large scale structure.Comment: 12 pages, 3 figures, Accepted for publication by Physical Rev.
Disponibilização de cultivares de soja no Brasil.
Os programas de melhoramento genético são fundamentais no desenvolvimento da agricultura de um país. No Brasil, a Lei de Proteção de Cultivares - LPC (Lei 9.456/97) refletiu na dinâmica das empresas de melhoramento genético. No caso específico da soja, além da LPC outra normativa que causou grande impacto no setor foi a Lei 10.814/2003 que autorizou a inclusão de cultivares transgênicas no Registro Nacional de Cultivares - RNC. O objetivo do referido estudo foi consolidar as informações sobre as cultivares de soja, disponibilizadas no País, no período de dezembro de 1998 a maio de 2011. Foram utilizados dados secundários, disponíveis no site do Ministério da Agricultura Pecuária e Abastecimento na base Cultivar Web do RNC. As informações foram qualificadas com base no ano de inscrição da cultivar, na personalidade jurídica e na natureza do capital das empresas mantenedoras. Com base no referido levantamento verificou-se que, até dezembro de 2003, haviam sido disponibilizadas no País 349 cultivares de soja convencional. Após a autorização da inscrição das cultivares transgênicas no RNC houve redução acentuada no número de cultivares convencionais, de modo que, das 474 inscritas no período de dezembro 2003 a maio de 2011, apenas 153 eram convencionais e 321 transgênicas (306 tolerantes ao herbicida glifosato e 15 resistentes a insetos da ordem Lepidoptera e tolerantes ao herbicida glifosato). Em 1998 o número de empresas mantenedoras de cultivares de soja no País eram 14, das quais cinco eram públicas e nove privadas. Em maio de 2011 as cultivares registradas no RNC totalizavam 823 mantidas por 32 empresas, sendo seis públicas e 26 privadas. Das 502 cultivares convencionais, 274 eram mantidas por empresas públicas, 143 por empresas privadas de capital nacional e 85 por empresas privadas de capital transnacional. Já das 321 cultivares transgênicas, 64 eram mantidas por empresas públicas, 125 por empresas privadas de capital nacional e 132 por empresas privadas de capital transnacional
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