Inhomogeneous Dark Radiation Dynamics on a de Sitter Brane

Assuming spherical symmetry we analyse the dynamics of an inhomogeneous dark radiation vaccum on a Randall and Sundrum 3-brane world. Under certain natural conditions we show that the effective Einstein equations on the brane form a closed system. On a de Sitter brane and for negative dark energy density we determine exact dynamical and inhomogeneous solutions which depend on the brane cosmological constant, on the dark radiation tidal charge and on its initial configuration. We also identify the conditions leading to the formation of a singularity or of regular bounces inside the dark radiation vaccum.Comment: 6 pages, LaTeX, 1 EPS figure. Talk given at the Workshop The Cosmology of Extra Dimensions and Varying Fundamental Constants of the Conference JENAM 2002, The Unsolved Universe: Challenges for the Future, 2-7 September 2002, Porto, Portuga

Dark Radiation and Localization of Gravity on the Brane

We discuss the dynamics of a spherically symmetric dark radiation vaccum in the Randall-Sundrum brane world scenario. Under certain natural assumptions we show that the Einstein equations on the brane form a closed system. For a de Sitter brane we determine exact dynamical and inhomogeneous solutions which depend on the brane cosmological constant, on the dark radiation tidal charge and on its initial configuration. We define the conditions leading to singular or globally regular solutions. We also analyse the localization of gravity near the brane and show that a phase transition to a regime where gravity propagates away from the brane may occur at short distances during the collapse of positive dark energy density.Comment: 7 pages, latex with 2 eps figures. Talk given by Rui Neves, Fourth International Workshop on New Worlds in Astroparticle Physics, Algarve University, Faro, 5-7 September, 2002. To be published in the corresponding proceedings, World Scientifi

TiFEE : an input event-handling framework with touchless device support

Tese de mestrado integrado. Engenharia Informática e Computação. Universidade do Porto. Faculdade de Engenharia. 201

Positive or negative? : the impact of anti-takeover legislation on R&D investment

Anti-takeover laws are laws designed to protect target companies from hostile activity by making the bidder’s attempt of acquisition more expensive and/or time consuming, as there are three different types anti-takeover laws. The aim of this dissertation is analyzing the impact of different kind of antitakeover laws (fair price laws, control share acquisition laws, and business combination laws) on firm R&D expenditures. In order to do so, this study uses data about U.S. public firms between 1970 and 2011. The empirical findings indicate that fair Price laws increase R&D activities because of the possibility of increasing the expected takeover premium for managers, whereas control share acquisition laws and business combination laws decrease it by reducing the external pressure, which is the biggest incentive for firm managers to remain competitive in the market. Alongside, Business Combination laws seem not to have a significant impact on firm’s R&D expenditures

Scordator: A digital map of all scordature

Scordatura is often used in stringed instruments to overcome constraints posed by their tuning. Finding the right scordatura for a particular situation may be a time-consuming task, especially for non-guitarist composers. In this contribution, we present a web application designed to show a tuning chart for any chordophone equipped with a maximum of eight strings, each tunable to a pitch in the range of a full keyboard. The application also provides visualization of the available positions for live MIDI notes within a given scordatura

Avaliação de desempenho de lojas de retalho utilizando um modelo de data envelopment analysis multi-nível

Este artigo descreve um método de avaliação de desempenho de lojas de retalho baseado na técnica de Data Envelopment Analysis(DEA). O método desenvolvido tem em conta que as lojas são organizações complexas que agregam várias secções, com alguma autonomia de gestão. Assim, desenvolveu-se um modelo de DEA multi-nível, que considera dois níveis de análise: a loja e as secções que a constituem. A análise do desempenho de cada secção comercial resulta da comparação com secções similares localizadas noutras lojas da cadeia e permite averiguar se existe disparidade no seu desempenho. A avaliação ao nível da loja permite definir objectivos de melhoria de desempenho, tendo em conta que as secções partilham os recursos limitados. Para isso, define-se um modelo de ``Network DEA''~que permite determinar os níveis óptimos das vendas da loja e que poderá sugerir a realocação de área entre as secções. O método desenvolvido é aplicado a um caso real de uma cadeia Portuguesa de lojas de base alimentar

Shear strength of reinforced concrete bridge deck slabs

Reinforced concrete bridge deck slabs without shear reinforcement can be subjected to concentrated or distributed loads of important magnitude. Under these loads their structural response is not always ductile. In particular under concentrated loads their deformation capacity can be limited by shear or punching shear failures, which prevent them from reaching the ultimate load predicted by pure flexural analysis. This problem has been studied in this research by means of an important experimental program and theoretical modeling. The limited ductility of bridge decks was investigated by means of full scale tests on bridge deck cantilevers under groups of concentrated loads. Six large scale laboratory tests were performed on two bridge deck cantilevers with a span of 2.8 m and a length of 10.0 m. All slabs failed in a brittle manner, in shear or punching shear. The theoretical flexural failure load estimated using the yield-line method was never attained. Despite the brittle failures, the results of tests on cantilevers have shown that some amount of yielding can occur before the shear failure and therefore reduce the shear strength. This effect was quantified on eleven full scale tests on slab strips without shear reinforcement with a length of 8.4 m. The results clearly show that the increase of plastic strains in the flexural reinforcement leads to a reduction of the shear strength. The measured rotation capacity of the plastic hinge was thus limited by a shear failure. A particular problem of bridge deck slabs is the introduction of concentrated loads applied by wheels with pneumatic pressure. Punching shear with these loads is usually treated in a manner similar to punching by a column. A punching shear test was performed with a concentrated load simulating a vehicle wheel with pneumatic pressure to investigate the differences. It appears that punching shear with a wheel with pneumatic pressure is less critical because curvatures tend to be distributed over the surface of the applied load rather than concentrated near the edges of the column. In order to investigate the experimental results on slab strips without shear reinforcement, a mechanical model is proposed to predict the shear strength and rotation capacity of plastic hinges. The shear strength is formulated as a function of the opening of the shear crack and of the strength of the concrete compression zone. The results of the mechanical model are in good agreement with the measured values, both for the shear strength and for the shear carried across the shear crack. Based on the mechanical model, a simplified equation is proposed. The model can also be used to predict the shear capacity of yield-lines. A non linear finite element model was implemented during this work and used to correctly predict the measured rotations and load-displacements curves of the tested cantilevers and other full scale tests performed by other researchers. The measured failure loads are accurately estimated by using the results of the non-linear model and the one-way shear and punching shear criteria proposed by Prof. A. Muttoni (Muttoni 2003)