Portuguese Population in France: a snapshot 25 years after their arrival

In year 2000 Portugal is celebrating the 500th anniversary of the arrival to Brazil. The Portuguese overseas adventure is now five centuries old and more than one third of the Portuguese nationals are living outside their homeland; in France they are the largest foreign community. This paper uses the data from the French Employment Survey (Enqujte de l Emploi) 1994 and 1995 to characterise the Portuguese population and to study individual decisions taken by the Portuguese migrants concerning naturalisation, family, residence and education. As a result of the analysis it seems that the decisions of the younger Portuguese are getting closer to the decisions of their French neighbours, increasing the gap with respect to the decisions of their countrymen who stayed in Portugal. In this very sense, we can say that some assimilation by the Portuguese is occurring in France. There is an educational convergence of the Portuguese migrants in France and the French.

Supersymmetric 3D model for gravity with SU(2)SU(2) gauge symmetry, mass generation and effective cosmological constant

A Chern--Simons system in $2+1$ dimensions invariant under local Lorentz rotations, $SU(2)$ gauge transformations, and local $\mathcal{N}=2$ supersymmetry transformations is proposed. The field content is that of $(2+1)$-gravity plus an $SU(2)$ gauge field, a spin-1/2 fermion charged with respect to $SU(2)$ and a trivial free abelian gauge field. A peculiarity of the model is the absence of gravitini, although it includes gravity and supersymmetry. Likewise, no gauginos are present. All the parameters involved in the system are either protected by gauge invariance or emerge as integration constants. An effective mass and effective cosmological constant emerge by spontaneus breaking of local scaling invariance. The vacuum sector is defined by configurations with locally flat Lorentz and $SU(2)$ connections sporting nontrivial global charges. Three-dimensional Lorentz-flat geometries are spacetimes of locally constant negative --or zero--, Riemann curvature, which include Minkowski space, AdS$_3$, BTZ black holes, and point particles. These solutions admit different numbers of globally defined, covariantly constant spinors and are therefore good candidates for stable ground states. The fermionic sector in this system could describe the dynamics of electrons in graphene in the long wavelength limit near the Dirac points, with the spin degree of freedom of the electrons represented by the $SU(2)$ label. If this is the case, the $SU(2)$ gauge field would produce a spin-spin interaction giving rise to strong correlation of electron pairs.Comment: 15 page

Rheology of fractal networks

We model the cytoskeleton as a fractal network by identifying each segment with a simple Kelvin-Voigt element, with a well defined equilibrium length. The final structure retains the elastic characteristics of a solid or a gel, which may support stress, without relaxing. By considering a very simple regular self-similar structure of segments in series and in parallel, in 1, 2 or 3 dimensions, we are able to express the viscoelasticity of the network as an effective generalised Kelvin-Voigt model with a power law spectrum of retardation times, $\cal L\sim\tau^{\alpha}$. We relate the parameter $\alpha$ with the fractal dimension of the gel. In some regimes ($0<\alpha<1$), we recover the weak power law behaviours of the elastic and viscous moduli with the angular frequencies, $G'\sim G''\sim w^\alpha$, that occur in a variety of soft materials, including living cells. In other regimes, we find different power laws for $G'$ and $G''$.Comment: 5 pages, 3 figure

Simple thermodynamics of jet engines

We use the first and second laws of thermodynamics to analyze the behavior of an ideal jet engine. Simple analytical expressions for the thermal efficiency, the overall efficiency, and the reduced thrust are derived. We show that the thermal efficiency depends only on the compression ratio r and on the velocity of the aircraft. The other two performance measures depend also on the ratio of the temperature at the turbine to the inlet temperature in the engine, T-3/T-i. An analysis of these expressions shows that it is not possible to choose an optimal set of values of r and T-3/T-i that maximize both the overall efficiency and thrust. We study how irreversibilities in the compressor and the turbine decrease the overall efficiency of jet engines and show that this effect is more pronounced for smaller T-3/T-i

Generalized inverses of a sum in rings

Documento submetido para revisão pelos pares. A publicar em "Bulletin of the Australian Mathematical Society". ISSN 0004-9727. 82:1 (2010) 156-164.We study properties of the Drazin index of regular elements in a ring with a unity 1. We give expressions for generalized inverses of 1 − ba in terms of generalized inverses of 1 − ab. In our development we prove that the Drazin index of 1 − ba is equal to the Drazin index of 1 − ab.Fundação para a Ciência e a Tecnologia (FCT) através do programa POCTIMinisterio de Educación y Ciencia of Spain - Project MTM2007-6723

Modelos utilizados por las instituciones financieras para medir el riesgo del mercado

120 p.Esta memoria consta de una introducción que explica un elemento básico en los mercados como es la globalización y algunas definiciones conceptuales básicas como la gestión del riesgo, el valor de la gestión del riesgo, el concepto de riesgo, su clasificación y las metodologías para medirlo. Se especifica también el problema que da origen a la investigación y 1os objetivos de la memoria. Posteriormente, el desarrollo de esta memoria consta de cinco capítulos. El primero esboza las distintas metodologías en el contexto de la administración de los riesgos financieros. De esta forma, este capitulo servirá de herramienta para determinar las diferencias entre las distintas metodologías, desde el punto de vista de la administración de los riesgos financieros. Por ello, se hace una descripción del proceso de administración de los riesgos, describiendo la estructura organizacional, el enfoque de la banca comercial para finalmente describe y desarrollar las técnicas y procedimientos de control y gestión del riesgo de mercado. El segundo describe y analiza las distintas metodologías que actualmente utilizan las Instituciones Financieras para medir el riesgo de mercado. Se inicia con el análisis de las Metodologías Tradicionales para terminar con el de las Metodologías de los Modelos Internos. Para cada una de ellas se hace referencia a sus hipótesis, supuestos, modo de calculo, ventajas y desventajas. Se esbozan también algunas conclusiones acerca de la validez teórica de una u otra de estas metodologías que se reafirmaran en la conclusión final de esta investigación