70,978 research outputs found
Low redshift constraints on energy-momentum-powered gravity models
There has been recent interest in the cosmological consequences of
energy-momentum-powered gravity models, in which the matter side of Einstein's
equations is modified by the addition of a term proportional to some power,
, of the energy-momentum tensor, in addition to the canonical linear term.
In this work we treat these models as phenomenological extensions of the
standard CDM, containing both matter and a cosmological constant. We
also quantitatively constrain the additional model parameters using low
redshift background cosmology data that are specifically from Type Ia
supernovas and Hubble parameter measurements. We start by studying specific
cases of these models with fixed values of which lead to an analytic
expression for the Friedmann equation; we discuss both their current
constraints and how the models may be further constrained by future
observations of Type Ia supernovas for WFIRST complemented by measurements of
the redshift drift by the ELT. We then consider and constrain a more extended
parameter space, allowing to be a free parameter and considering scenarios
with and without a cosmological constant. These models do not solve the
cosmological constant problem per se. Nonetheless these models can
phenomenologically lead to a recent accelerating universe without a
cosmological constant at the cost of having a preferred matter density of
around instead of the usual . Finally we
also briefly constrain scenarios without a cosmological constant, where the
single component has a constant equation of state which needs not be that of
matter; we provide an illustrative comparison of this model with a more
standard dynamical dark energy model with a constant equation of state.Comment: 13+2 pages, 12+1 figures; A&A (in press
Diversidade genética de acessos de cupuaçuzeiro (Theobroma grandiflorum) utilizando marcadores microssatélites.
Índice de sustentabilidade do uso da água de cisternas no semi-árido brasileiro.
A disponibilidade hídrica no Semi-Árido brasileiro é baixa, embora, nos anos secos possam ocorrer, no mínimo, 300,Omm, que são suficientes para abastecer uma cisterna com capacidade de 16.000 litros e atender as necessidades básicas de uma família com cinco pessoas. Nesta região, a quantidade e a qualidade da água são indicadores que devem ser considerados na gestão sustentável da água, principalmente para consumo das famílias. Assim, este estudo avaliou os resultados obtidos pelo P1 MC/Ministério do Desenvolvimento Social - MDS, objetivando propor um índice de sustentabilidade do uso da água de cisterna. Foram utilizados procedimentos de análise fatorial em componentes principais e de agrupamento, integrando-se diferentes bases dados. A partir das variáveis analisadas foram definidos quatro indicadores de sustentabilidade da água das cisternas: a) uso da água de outras fontes; b) condições ecológicas dos domicílios; c) capacitação comunitária e d) qualidade da água. Os indicadores poderão auxiliar no monitoramento e gestão da água, no que concerne ao fornecimento da água necessária e sua qualidade, visando à melhoria da qualidade de vida dos usuários das cisternas. Os indicadores propostos poderão auxiliar na decisão dos gestores do P1 MC no sentido de revisar e reformular suas ações estratégias
Tunnel and thermal c-axis transport in BSCCO in the normal and pseudogap state
We consider the problem of c-axis transport in double-layered cuprates, in
particular with reference to BiSrCaCuO
compounds. We exploit the effect of the two barriers on the thermal and tunnel
transport. The resulting model is able to describe accurately the normal state
c-axis resistivity in BiSrCaCuO, from the
underdoped side up to the strongly overdoped. We extend the model, without
introducing additional parameters, in order to allow for the decrease of the
barrier when an external voltage bias is applied. The extended model is found
to describe properly the c-axis resistivity for small voltage bias above the
pseudogap temperature , the c-axis resistivity for large voltage bias
even below , and the differential curves taken in mesa structures.Comment: 12 pages, 6 figures. Submitted to Superconductor Science and
Technolog
Nonlinear c-axis transport in Bi_2Sr_2CaCu_2O_(8+d) from two-barrier tunneling
Motivated by the peculiar features observed through intrinsic tunneling
spectroscopy of BiSrCaCuO mesas in the normal state,
we have extended the normal state two-barrier model for the c-axis transport
[M. Giura et al., Phys. Rev. B {\bf 68}, 134505 (2003)] to the analysis of
curves. We have found that the purely normal-state model reproduces all
the following experimental features: (a) the parabolic -dependence of
in the high- region (above the conventional pseudogap temperature),
(b) the emergence and the nearly voltage-independent position of the "humps"
from this parabolic behavior lowering the temperature, and (c) the crossing of
the absolute curves at a characteristic voltage . Our
findings indicate that conventional tunneling can be at the origin of most of
the uncommon features of the c axis transport in
BiSrCaCuO. We have compared our calculations to
experimental data taken in severely underdoped and slightly underdoped
BiSrCaCuO small mesas. We have found good agreement
between the data and the calculations, without any shift of the calculated
dI/dV on the vertical scale. In particular, in the normal state (above
) simple tunneling reproduces the experimental dI/dV quantitatively.
Below quantitative discrepancies are limited to a simple rescaling of
the voltage in the theoretical curves by a factor 2. The need for such
modifications remains an open question, that might be connected to a change of
the charge of a fraction of the carriers across the pseudogap opening.Comment: 7 pages, 5 figure
Caracterização molecular dos parentais de uma nova cultivar de cupuaçuzeiro, utilizando marcadores microssatélites.
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