733 research outputs found
Inhomogeneous models of interacting dark matter and dark energy
We derive and analyze a class of spherically symmetric cosmological models
whose source is an interactive mixture of inhomogeneous cold dark matter (DM)
and a generic homogeneous dark energy (DE) fluid. If the DE fluid corresponds
to a quintessense scalar field, the interaction term can be associated with a
well motivated non--minimal coupling to the DM component. By constructing a
suitable volume average of the DM component we obtain a Friedman evolution
equation relating this average density with an average Hubble scalar, with the
DE component playing the role of a repulsive and time-dependent term.
Once we select an ``equation of state'' linking the energy density () and
pressure () of the DE fluid, as well as a free function governing the radial
dependence, the models become fully determinate and can be applied to known
specific DE sources, such as quintessense scalar fields or tachyonic fluids.
Considering the simple equation of state with , we show that the free parameters and boundary conditions can be selected
for an adequate description of a local DM overdensity evolving in a suitable
cosmic background that accurately fits current observational data. While a DE
dominated scenario emerges in the asymptotic future, with total and
tending respectively to 1 and -1/2 for all cosmic observers, the effects of
inhomogeneity and anisotropy yield different local behavior and evolution rates
for these parameters in the local overdense region. We suggest that the models
presented can be directly applied to explore the effects of various DE
formalisms on local DM cosmological inhomogeneities.Comment: 15 pages, revtex4, 10 eps figure
Creation of the department of physical education of the São Paulo state (1925-1932)
O artigo aborda a criação do Departamento de Educação Física do Estado de São Paulo (DEF-SP), procurando analisar os debates que fomentaram sua implantação, identificar as posições assumidas pelos sujeitos que contribuíram para isso e examinar as iniciativas implementadas durante seu primeiro ano de funcionamento. A criação do DEF-SP esteve relacionada aos debates próprios dos campos esportivo e intelectual paulistas, em intersecção com disputas e tensões sobre a identidade nacional. Foi promovida por figuras do universo esportivo, como cronistas e atletas, e por médicos. A justificativa para sua criação apresentou teor eugenista, sendo a manifestação esportiva interpretada como uma forma de desenvolver o vigor físico e moral da população49171264286This paper focuses on the creation of the Departamento de Educação Física do Estado de São Paulo [Department of Physical Education of São Paulo State] (DEF-SP). Its objectives are: a) to analyze the debates that led to the creation of the DEF-SP; b) to identify the positions assumed by the subjects who contributed to its creation; c) to verify the initiatives that were implemented in its first year of activity. The creation of the DEF-SP was linked to the debates of the sports field of São Paulo in intersection with disputes and tensions about the national identity. It was promoted by sports figures, such as sports journalist, athletes and also by doctors. The justification for its creation presented a eugenic content, and the sport was interpreted as means to develop physical and moral vigor of the populatio
Potential alternative feed sources for ruminant feeding from the biodiesel production chain by-products
This study aimed to evaluate the chemical composition, fractionation of nitrogen compounds and carbohydrates, digestibility parameters, gas production kinetics and ruminal fermentation of fruit seed cakes. The experiment was conducted in a completely randomized design with three fruit seed cakes (treatments) and four replications. The cakes were made of seeds of custard apple (Annona squamosa), soursop (Annona muricata) and passion fruit (Passiflora edulis), which were collected in a biodiesel plant. The passion fruit seed cake presented the highest content of dry matter, neutral detergent fibre crude protein (NDFcp), acid detergent fibre (ADF), lignin and total carbohydrates (P<0.05). The custard apple seed cake presented high proportions of crude protein, condensed tannins and digestible energy (P<0.05). The soursop seed cake presented higher values for ether extract and total digestible nutrients (P<0.05). For potential degradability, the authors detected a difference between the custard apple, soursop and passion fruit seed cakes. The total volume of gases was higher for custard apple and soursop seed cakes. Custard apple seed cake presented higher proportions of in vitro degradation parameters (P<0.05). Thus this cake could provide greater nutrient levels when supplied in ruminant diets, followed by soursop seed cake and passion fruit seed cake.
Keywords: alternative food, by-products, ruminant feeding, seed cake, semi-ari
Macroscopic anisotropy in superconductors with anisotropic gaps
It is shown within the weak-coupling model that the macroscopic
superconducting anisotropy for materials with the gap varying on the Fermi
surface cannot be characterized by a single number, unlike the case of clean
materials with isotropic gaps. For clean uniaxial materials, the anisotropy
parameter defined as the ratio of London penetration depths,
, is evaluated for all 's. Within the two-gap model
of MgB, is an increasing function of .Comment: 4 pages, 2 figure
Bulk Viscous LRS Biachi-I Universe with variable and decaying
The present study deals with spatially homogeneous and totally anisotropic
locally rotationally symmetric (LRS) Bianchi type I cosmological model with
variable and in presence of imperfect fluid. To get the
deterministic model of Universe, we assume that the expansion in the
model is proportional to shear . This condition leads to , where ,\; are metric potential. The cosmological constant
is found to be decreasing function of time and it approaches a small
positive value at late time which is supported by recent Supernovae Ia (SN Ia)
observations. Also it is evident that the distance modulus curve of derived
model matches with observations perfectly.Comment: 11 pages, 4 figures and 1 table, Accepted for publication in
Astrophysics and Space Scienc
Determination of superconducting anisotropy from magnetization data on random powders as applied to LuNiBC, YNiBC and MgB
The recently discovered intermetallic superconductor MgB2 appears to have a
highly anisotopic upper critical field with Hc2(max)/Hc2(min} = \gamma > 5. In
order to determine the temperature dependence of both Hc2(max) and Hc2(min) we
propose a method of extracting the superconducting anisotropy from the
magnetization M(H,T) of randomly oriented powder samples. The method is based
on two features in dM/dT the onset of diamagnetism at Tc(max), that is commonly
associated with Hc2, and a kink in dM/dT at a lower temperature Tc(min).
Results for LuNi2B2C and YNi2B2C powders are in agreement with anisotropic Hc2
obtained from magneto-transport measurements on single crystals. Using this
method on four different types of MgB2 powder samples we are able to determine
Hc2(max)(T) and Hc2(min)(T) with \gamma \approx 6
Constraining the dark energy with galaxy clusters X-ray data
The equation of state characterizing the dark energy component is constrained
by combining Chandra observations of the X-ray luminosity of galaxy clusters
with independent measurements of the baryonic matter density and the latest
measurements of the Hubble parameter as given by the HST key project. By
assuming a spatially flat scenario driven by a "quintessence" component with an
equation of state we place the following limits on the
cosmological parameters and : (i) and (1) if the
equation of state of the dark energy is restricted to the interval (\emph{usual} quintessence) and (ii) and
() if violates the null energy condition and assume values (\emph{extended} quintessence or ``phantom'' energy). These results are in
good agreement with independent studies based on supernovae observations,
large-scale structure and the anisotropies of the cosmic background radiation.Comment: 6 pages, 4 figures, LaTe
Extended tachyon field, Chaplygin gas and solvable k-essence cosmologies
We investigate a flat Friedmann-Robertson-Walker spacetime filled with
k-essence and find the set of functions F which generate three different
families of extended tachyon fields and Chaplygin gases. They lead to
accelerated and superaccelerated expanding scenarios.
For any function F, we find the first integral of the k-field equation when
the k-field is driven by an inverse square potential or by a constant one. In
the former, we obtain the general solution of the coupled Einstein-k-field
equations for a linear function F. This model shares the same kinematics of the
background geometry with the ordinary scalar field one driven by an exponential
potential. However, they are dynamically different. For a constant potential,
we introduce a k-field model that exhibits a transition from a power-law phase
to a de Sitter stage, inducing a modified Chaplygin gas.Comment: 24 pages, revised version accepted for publication in Phys. Rev.
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