Dynamical properties of a cosmological model with diffusion

The description of the dynamics of particles undergoing diffusion in general relativity has been an object of interest in the last years. Most recently a new cosmological model with diffusion has been studied in which the evolution of the particle system is described by a Fokker-Planck equation. This equation is then coupled to a modified system of Einstein equations, in order to satisfy the energy conservation condition. Continuing with this work, we study in the present paper a spatially homogeneous and isotropic spacetime model with diffusion velocity. We write the system of ordinary differential equations of this particular model and obtain the solutions for which the scale factor in the RobertsonWalker metric is linear in time. We analyse the asymptotic behavior of the subclass of spatially flat solutions. The system representing the homogeneous and isotropic model with diffusion is rewritten using dynamical variables. For the subclass of spatially flat solutions we were able to determine all equilibrium points and analyse their local stability properties.http://www.springer.com/gp/book/9783319166360#otherVersion=9783319166377Fundação para a Ciência e a Tecnologia (FCT

A new plant modelling approach for formal verification purposes

This paper presents a new approach in plant modeling for the formal verification of real time systems. A system composed by two tanks is used, where all its components are modeled by simple modules and all the interdependences of the system?s modular models are presented. As innovating parameters in the plant modeling, having as purpose its use on formal verification tasks, the plant is modeled using Dymola software and Modelica programming language. The results obtained in simulation are used to define the plant models that are used for the formal verification tasks, using the model-checker UPPAAL. The paper presents, in a more detailed way, the part of this work that is related to formal verification, being pointing out the used plant modeling approach.SCAPS Project supported by FCT, the Portuguese Foundation for Science and Technology, and FEDER, the European regional development fund, under contract POCI/EME/61425/2004 that deals with safety control of automated production syste

Modelling and analysis of time dependent processes in a chemically reactive mixture

In this paper, we study the propagation of sound waves and the dynamics of local wave disturbances induced by spontaneous internal fluctuations in a reactive mixture. We consider a non-diffusive, non-heat conducting and non-viscous mixture described by an Eulerian set of evolution equations. The model is derived from the kinetic theory in a hydrodynamic regime of a fast chemical reaction. The reactive source terms are explicitly computed from the kinetic theory and are built in themodel in a proper way. For both time-dependent problems, we first derive the appropriate dispersion relation, which retains the main effects of the chemical process, and then investigate the influence of the chemical reaction on the properties of interest in the problems studied here. We complete our study by developing a rather detailed analysis using the Hydrogen–Chlorine system as reference. Several numerical computations are included illustrating the behavior of the phase velocity and attenuation coefficient in a low-frequency regime and describing the spectrum of the eigenmodes in the small wavenumber limit.The paper is partially supported by the Research Centre of Mathematics of the University of Minho, with the Portuguese Funds from the Foundation for Science and Technology (FCT) through the Project UID/MAT/00013/2013. We wish to thank the anonymous Referees for their valuable comments and suggestions that helped us to improve the paper.info:eu-repo/semantics/publishedVersio

Automating psycholinguistic statistics computation: procura palavras

This article describes psycholinguistic lexical databases available in various languages, including English, Spanish and Portuguese. These lexical databases are important for re- searchers in Psycholinguistics and other related areas, providing a pool of experimental materials and allowing for an efficient process of selection of these experimental materials. The process of gathering statistics is slow, resulting in a small pool of materials in the short-term. The need to find an alternative method to gather limited or yet unavailable statistics for a specific language led us to consider gathering statistics from other languages and to compute their triangulation. Our aim was to automatize the computation of statistics such as Fa- miliarity, Imageability, Age of Acquisition and Written Word Frequency for that specific language. We will describe the process of preparing this data and tri- angulating and comparing statistics for some languages in an at- tempt of finding a relationship between them. The results were analysed considering correlations between each statistic in each pair of languages and by computing the mean of absolute dif- ferences between each language’s values.Fundação para a Ciência e a Tecnologia (FCT) - "European Portuguese words” (PTDC/PSI-PCO/104679/2008)National Strategic Reference Framework (NSRF)Operational Agenda for Competitiveness Factors (COMPETE)European Regional Development Fund (ERDF)