Dynamics of perfect fluid Unified Dark Energy models

In this paper we show that a \emph{one-to-one} correspondence exists between any dark energy model and an equivalent (from a cosmological point of view, in the absence of perturbations) quartessence model in which dark matter and dark energy are described by a single perfect fluid. We further show that if the density fluctuations are small, the evolution of the sound speed squared, $c_s^2$, is fully coupled to the evolution of the scale factor and that the transition from the dark matter to the dark energy dominated epoch is faster (slower) than in a standard $\Lambda$CDM model if $c_s^2 > 0$ ($c_s^2 < 0$). In particular, we show that the mapping of the simplest quintessence scenario with constant $w_Q \equiv p_Q/ \rho_Q$ into a unified dark energy model requires $c_s^2 -1$) contrasting to the Chaplygin gas scenario where one has $c_s^2 > 0$. However, we show that non-linear effects severely complicate the analysis, in particular rendering linear results invalid even on large cosmological scales. Although a detailed analysis of non-linear effects requires solving the full Einstein field equations, some general properties can be understood in simple terms. In particular, we find that in the context of Chaplygin gas models the transition from the dark matter to the dark energy dominated era may be anticipated with respect to linear expectations leading to a background evolution similar to that of standard $\Lambda$CDM models. On the other hand, in models with $c_s^2 > 0$ the expected transition from the decelerating to the accelerating phase may never happen.Comment: 5 page

Modeling and simulation of a mechanism with CATIA

Los objetivos del Proyecto Fin de Carrera son los siguientes: - Proponer soluciones originales y eficaces a un problema planteado - Diseñar el mecanismo desde cero. - Ensamblar las diferentes piezas de las que se compone el mecanismo y dotarlas de restricciones para poder simular el movimiento de las diferentes piezas - Simular el mecanismo en la medida de lo posible. - Analizar la estructura de soporte mediante elementos finitos en caso estático ______________________________________________________________________________________________________________________The objectives of this final project are the next ones: - Propose originals and effectives solutions to solve a proposed problem. - Design the main parts of the mechanism from scratch. - Assemble the various parts which make up the mechanism and provide them with constraints to simulate the relative movement between different parts. - Simulating the mechanism as far as possible. - Analyze the structure which supports the mechanism with Finite Element Method in static case.Ingeniería Industria

The Impact of the Economic Crisis on the Corporate Insolvency's Evolution in Romania

AbstractThis article aims to analyze the impact of the financial crisis on the corporate insolvency's evolution and the changes in the Romanian insolvency regime. The Romanian government was determined, as other European Union member states’ governments did, to improve its insolvency law in order to save the viable businesses and to stimulate the creation of new ones. We want to highlight Romania's position within the European Union in terms of time, cost of insolvency, recovery rate and dynamics of business insolvencies’ number and to propose specific measures to improve its situation

Alternative Feedbase Systems for Southern Australia Dairy Farms: 1. Predicted Pasture/Crop Consumption and Farm Financial Performance

Traditional perennial ryegrass-based pastures have significant limitations for efficient feeding of dairy cattle in dryland dairy regions of southern Australia. These include strong seasonality of growth, with 50 - 60% of total annual dry matter arriving in spring and little or no growth during summer. There is clear potential for improving total forage production and the seasonality of forage supply in these regions through the use of alternative pastures (Nie et al. 2004) and fodder crops. This series of papers applies a modelling approach to investigate the potential improvements in farm productivity and profitability resulting from their use