An interacting model for the cosmological dark sector

We discuss a new interacting model for the cosmological dark sector in which the attenuated dilution of cold dark matter scales as $a^{-3}f(a)$, where f(a) is an arbitrary function of the cosmic scale factor $a$. From thermodynamic arguments, we show that f(a) is proportional to entropy source of the particle creation process. In order to investigate the cosmological consequences of this kind of interacting models, we expand f(a) in a power series and viable cosmological solutions are obtained. Finally, we use current observational data to place constraints on the interacting function f(a).Comment: 5 pages, 3 figures, Phys. Rev. D (in press

Decaying Lambda cosmology, varying G and holography

We discuss a class of uniform and isotropic, spatially flat, decaying Lambda cosmologies, in the realm of a model where the gravitation constant G is a function of the cosmological time. Besides the usual de Sitter solution, the models at late times are characterized by a constant ratio between the matter and total energy densities. One of them presents a coasting expansion where the matter density parameter is equal to 1/3, and the age of the universe satisfies Ht = 1. From considerations in line with the holographic conjecture, it is argued that, among the non-decelerating solutions, the coasting expansion is the only acceptable from a thermodynamic viewpoint, and that the time varying cosmological term must be proportional to the square of the Hubble parameter, a result earlier obtained using different arguments.Comment: Minor changes. A short version will appear in the Int. J. Mod. Phys. A (Proceedings of the Sixth Alexander Friedmann International Seminar on Gravitation and Cosmology, Cargese, 2004

Avaliação nutricional de diferentes acessos de sorgo.

O objetivo deste trabalho foi verificar se o sorgo contendo tanino interfere ou nao na digestibilidade da silagem. Dez acessos (variedades, linhagem e hibridos) de sorgo, foram avaliados na Embrapa Gado de leite, quanto a alguns parametros importantes para alimentacao de ruminantes. as amostras foram coletadas na Embrapa Milho e Sorgo. Oitenta mini-silos experimentais, oito de cada material foram analisados em duplicata, apos 60 dias ensilados. Duas amostras foram secas a 55oC durante 72 h, para a determinacao de materia seca total (MST), fibra em detergente neutra (FDN), fibra em detergente acido (FDA), lignina em permanganato de potassio (LIG-P), digestibilidade in vitro (48, 24 e 4 horas), cinza e proteina bruta (PB). oram feitas analises de variancia, e o teste Scott-knott a 5% de probabilidade, para a comparacao de medias. A digestibilidade em 24 e 48 horas, nao mostrou diferencas entre tratamentos, sugerindo que esta nao foi afetada pelo teor de tanino existente na silagem. O hibrido BR701 com tanino apresentou alto teor de proteina bruta de 8,05% e a mais alta digestibilidade em 48 horas com 60,84%. A linhagem CMSXS114 (T), CMSXS165 (ST) e o hibrido BR700 (T) mostraram ser prontamente disponiveis no rumem. Isto sugere que os materiais geneticos com tais caracteristicas sejam mais indicados para vacas com alta producao. Sugere-se que esses materiais sejam analisados quanto ao consumo

Classical and quantum dynamics of confined test particles in brane gravity

A model is constructed for the confinement of test particles moving on a brane. Within the classical framework of this theory, confining a test particle to the brane eliminates the effects of extra dimensions, rendering them undetectable. However, in the quantized version of the theory, the effects of the gauge fields and extrinsic curvature are pronounced and this might provide a hint for detecting them. As a consequence of confinement the mass of the test particle is shown to be quantized. The condition of stability against small perturbations along extra dimensions is also studied and its relation to dark matter is discussed.Comment: 15 pages, no figures, extended, references adde

Supernova constraints on decaying vacuum cosmology

There is mounting observational evidence that the expansion of our Universe is undergoing a late-time acceleration. Among many proposals to describe this phenomenon, the cosmological constant seems to be the simplest and the most natural explanation. However, despite its observational successes, such a possibility exacerbates the well known cosmological constant problem, requiring a natural explanation for its small, but nonzero, value. In this paper we consider a cosmological scenario driven by a varying cosmological term, in which the vacuum energy density decays linearly with the Hubble parameter. We show that this model is indistinguishable from the standard one in that the early radiation phase is followed by a long dust-dominated era, and only recently the varying cosmological term becomes dominant, accelerating the cosmic expansion. In order to test the viability of this scenario we have used the most recent type Ia supernova data, i.e., the High-Z SN Search (HZS) Team and the Supernova Legacy Survey (SNLS) Collaboration data. In particular, for the SNLS sample we have found the present matter density and Hubble parameters in the intervals [0.27, 0.37] and [0.68, 0.72], respectively (at 95% c.l.), which is in good agreement with the currently accepted estimates for these parameters.Comment: Version accepted for publication in Physical Review

Development and experimental assessment of a numerical modelling code to aid the design of profile extrusion cooling tools

On the extrusion of thermoplastic profiles, upon the forming stage that takes place in the extrusion die, the profile must be cooled in a metallic calibrator. This stage must be done at a high rate, to assure increased productivity, but avoiding the development of high temperature gradients, in order to minimize the level of induced thermal residual stresses. In this work, we present a new coupled numerical solver, developed in the framework of the OpenFOAM® computational library, that computes the temperature distribution in both domains simultaneously (metallic calibrator and plastic profile), whose implementation aimed the minimization of the computational time. The new solver was experimentally assessed with an industrial case study.SFRH/BPD/100353/2014info:eu-repo/semantics/publishedVersio

Ruminal degradability of starch from corn silage containing different glycerin concentrations.

The use of glycerin as energy source for ruminants is a viable option (ÍTAVO et al., 2011), once its energetic value is similar to corn starch (Duque et al., 2011). Gomes et al. (2011) verified that glycerin, purified or not, added to roughages improves the in vitro digestibility of organic matter and the total digestible nutrients. Many others researches were carried out to study the effects of glycerin in ruminant feeding and animal production (Duque et al., 2011; Gomes et al., 2011)

Effect of the inclusion of glycerin on organic acids production in corn silage.

The silage is based on spontaneous lactic fermentation, where under anaerobic conditions the soluble carbohydrates are fermented with lactic acid production and rapid decrease in pH. Corn is considered the best forage to be ensiled due to its high dry matter productivity, low buffer capacity and adequate levels of soluble carbohydrates for fermentation (McDonald et. al. 1991). The use of crude glycerin as ingredient in ruminant concentrates has been studied in the last years (Gonçalves et. al. 2006; França et. al. 2012). The objective of this work was to evaluate the changes on concentrations of organic acids in corn silage occurring during the use of crude glycerin

Slip flows of Newtonian and viscoelastic fluids in a 4:1 contraction

This work presents a numerical study of the 4:1 planar contraction flow of a viscoelastic fluid described by the simplified Phan-Thien–Tanner model under the influence of slip boundary conditions at the channel walls. The linear Navier slip law was considered with the dimensionless slip coefficient varying in the range ½0; 4500. The simulations were carried out for a small constant Reynolds number of 0.04 and Deborah numbers (De) varying between 0 and 5. Convergence could not be achieved for higher values of the Deborah number, especially for large values of the slip coefficient, due to the large stress gradients near the singularity of the reentrant corner. Increasing the slip coefficient leads to the formation of two vortices, a corner and a lip vortex. The lip vortex grows with increasing slip until it absorbs the corner vortex, creating a single large vortex that continues to increase in size and intensity. In the range De = 3–5 no lip vortex was formed. The flow is characterized in detail for De ¼ 1 as function of the slip coefficient, while for the remaining De only the main features are shown for specific values of the slip coefficient.The authors gratefully acknowledge funding by COMPETE, FEDER and Fundacao para a Ciencia e a Tecnologia (FCT) through projects PEst-C/CTM/LA0025/2013 (Strategic Project - LA 25 - 2013-2014, PTDC/EME-MFE/113988/2009 and PTDC/EME-MFE/114322/2009. AMA would also like to thank FCT for the financial support through the scholarship SFRH/BPD/75436/2010