The Λ\LambdaCDM growth rate of structure revisited

We re-examine the growth index of the concordance $\Lambda$ cosmology in the light of the latest 6dF and {\em WiggleZ} data. In particular, we investigate five different models for the growth index $\gamma$, by comparing their cosmological evolution using observational data of the growth rate of structure formation at different redshifts. Performing a joint likelihood analysis of the recent supernovae type Ia data, the Cosmic Microwave Background shift parameter, Baryonic Acoustic Oscillations and the growth rate data, we determine the free parameters of the $\gamma(z)$ parametrizations and we statistically quantify their ability to represent the observations. We find that the addition of the 6dF and {\em WiggleZ} growth data in the likelihood analysis improves significantly the statistical results. As an example, considering a constant growth index we find $\Omega_{m0}=0.273\pm 0.011$ and $\gamma=0.586^{+0.079}_{-0.074}$.Comment: 8 pages, 5 figures, Accepted for publication by International J. of Modern Physics D (IJMPD). arXiv admin note: substantial text overlap with arXiv:1203.672

Anisotropic elastic theory of preloaded granular media

A macroscopic elastic description of stresses in static, preloaded granular media is derived systematically from the microscopic elasticity of individual inter-grain contacts. The assumed preloaded state and friction at contacts ensure that the network of inter-grain contacts is not altered by small perturbations. The texture of this network, set by the preparation of the system, is encoded in second and fourth order fabric tensors. A small perturbation generates both normal and tangential inter-grain forces, the latter causing grains to reorient. This reorientation response and the incremental stress are expressed in terms of the macroscopic strain.Comment: 7 pages, 2 figures. Accepted version. [email protected] [email protected]

Attenuation and damping of electromagnetic fields: Influence of inertia and displacement current

New results for attenuation and damping of electromagnetic fields in rigid conducting media are derived under the conjugate influence of inertia due to charge carriers and displacement current. Inertial effects are described by a relaxation time for the current density in the realm of an extended Ohm's law. The classical notions of poor and good conductors are rediscussed on the basis of an effective electric conductivity, depending on both wave frequency and relaxation time. It is found that the attenuation for good conductors at high frequencies depends solely on the relaxation time. This means that the penetration depth saturates to a minimum value at sufficiently high frequencies. It is also shown that the actions of inertia and displacement current on damping of magnetic fields are opposite to each other. That could explain why the classical decay time of magnetic fields scales approximately as the diffusion time. At very small length scales, the decay time could be given either by the relaxation time or by a fraction of the diffusion time, depending whether inertia or displacement current, respectively, would prevail on magnetic diffusion.Comment: 21 pages, 1 figur

Uso de leitos cultivados no tratamento de efluentes da aquicultura.

In the last fifty years, worldwide aquaculture has increased about 8.8% /year. In Brazil, the tilapia culture, the flagship aquaculture production, represents 39% of the total cultivated fish. The increasing demand for aquatic protein, the demographic increasement and the decline of natural stocks have contributed to the promotion of aquaculture around the world. Nevertheless, concerns about the negative environmental impacts caused by this activity are also increasing. Some of these impacts are: destruction of mangroves, significant inputs of nitrogen, phosphorus and organic matter downstream nurseries, invasion of exotic species in natural aquatic ecosystems. Natural treatment systems such as constructed wetlands are costeffective, do not depend on energy, and the efficiency of removal of the main physico-chemical parameters of water quality are at 70 to 90% on average. By bacteriological metabolism and mechanical filtration, the organic matter is used as food and nutrient for aquatic plants. This study aims to assess the efficiency of constructed wetlands for treatment of effluents from tilapia culture, using a closed cycle of water. At Embrapa Environment (Jaguariúna, SP), a system composed by 54 plastic boxes was constructed to test three kinds of substrates: pebbles, expanded clay and a mixture of both. The plant Vetiver was used as another part of the treatment system. We expect to verify a great reduction in important parameters such as total nitrogen, total phosphorus, biochemical oxygen demand, total suspended solids and others. This system could be very useful at smallholder aquaculture worried with best management practices

General Scalar Fields as Quintessence

We study the cosmological evolution of scalar fields with arbitrary potentials in the presence of a barotropic fluid (matter or radiation) without making any assumption on which term dominates. We determine what kind of potentials V(phi) permits a quintessence interpretation of the scalar field phi and to obtain interesting cosmological results. We show that all model dependence is given in terms of lambda= - V'/V only and we study all possible asymptotic limits: lambda approaching zero, a finite constant or infinity. We determine the equation of state dynamically for each case. For the first class of potentials, the scalar field quickly dominates the universe behaviour, with an inflationary equation of state allowing for a quintessence interpretation. The second case gives the extensively studied exponential potential. While in the last case, when lambda approaches infinity, if it does not oscillate then the energy density redshifts faster than the barotropic fluid but if lambda oscillates then the energy density redshift depends on the specific potential.Comment: 14 pages, LaTeX, 4 postscript figure

Dinâmica de Fusarium spp. e da atividade microbiana no solo após a disponibilização de palhada para cultivo de feijoeiro comum em sistema plantio direto.

O objetivo deste trabalho foi avaliar o efeito de diferentes culturas de cobertura antecedentes ao plantio do feijoeiro comum na dinâmica de Fusarium spp. e na atividade microbiana no solo

Multicomponent Activity Cycles using Hilbert-Huang Analysis

The temporal analysis of stellar activity evolution is usually dominated by a complex trade-off between model complexity and interpretability, often by neglecting the non-stationary nature of the process. Recent studies appear to indicate that the presence of multiple coexisting cycles in a single star is more common than previously thought. The correct identification of physically meaningful cyclic components in spectroscopic time series is therefore a crucial task, which cannot overlook local behaviors. Here we propose a decomposition technique which adaptively recovers amplitude- and frequency-varying components. We present our results for the solar activity as measured both by the sunspot number and the $K$-line emission index, and we consistently recover the Schwabe and Gleissberg cycles as well as the Gnevyshev-Ohl pattern probably related to the Hale cycle. We also recover the known 8-year cycle for 61 Cygni A, in addition to evidence of a three-cycles long pattern reminiscent of the Gnevyshev-Ohl rule. This is particularly interesting as we cannot discard the possibility of a relationship between the measured field polarity reversals and this Hale-like periodicity.Comment: 8 pages, 3 figure

Centrifugal separation and equilibration dynamics in an electron-antiproton plasma

Charges in cold, multiple-species, non-neutral plasmas separate radially by mass, forming centrifugally-separated states. Here, we report the first detailed measurements of such states in an electron-antiproton plasma, and the first observations of the separation dynamics in any centrifugally-separated system. While the observed equilibrium states are expected and in agreement with theory, the equilibration time is approximately constant over a wide range of parameters, a surprising and as yet unexplained result. Electron-antiproton plasmas play a crucial role in antihydrogen trapping experiments

Tunneling in Λ\Lambda Decaying Cosmologies and the Cosmological Constant Problem

The tunneling rate, with exact prefactor, is calculated to first order in $\hbar$ for an empty closed Friedmann-Robertson-Walker (FRW) universe with decaying cosmological term $\Lambda \sim R^{-m}$ ($R$ is the scale factor and $m$ is a parameter $0\leq m \leq 2$). This model is equivalent to a cosmology with the equation of state $p_{\chi}=(m/3 -1)\rho_{\chi}$. The calculations are performed by applying the dilute-instanton approximation on the corresponding Duru-Kleinert path integral. It is shown that the highest tunneling rate occurs for $m=2$ corresponding to the cosmic string matter universe. The obtained most probable cosmological term, like one obtained by Strominger, accounts for a possible solution to the cosmological constant problem.Comment: 21 pages, REVTEX, The section 3 is considerably completed including some physical mechanisms supporting the time variation of the cosmological constant, added references for the section 3. Accepted to be published in Phys. Rev.