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

Predicting and distinguishing bankruptcy: an application of a market and hybrid model to US publicly listed firms from 2008 to 2018

Assessing the probability of bankruptcy has been a key topic approached by researchers and academics throughout the last half century. The bankruptcy of considerable firms, such as Enron or WorldCom, coupled with the rigorous regulatory environment triggered by Basel II guidelines, fostered even further the interest in the topic. Moreover, in the outcome of financial crisis, Credit Rating Agencies were criticized for addressing inflated ratings and not properly anticipating defaults. Besides, leading CRA’s do not assess the creditworthiness of all firms, and our intention is to provide to individual investor the best option available to autonomously estimate the probability of bankruptcy We analyse if either a market-based model, KMV, or a hybrid model, CHS, are able to properly anticipate the event of bankruptcy, and in case this is verified, which of them better distinguish between bankrupt and non-bankrupt firms. In order to do so, we resort to a sample of 354 US publicly listed firms, divided into bankrupt and non-bankrupt firms, and applied the ROC technique to assess our results, for a 10-year period. Our results prove that KMV model is slightly superior to the CHS model at maximizing the Area Under the Curve (AUC). Besides, it provided a higher optimal probability’s cut off point that distinguish both type of firms. Our results indicate that the KMV model is the best option available for an individual investor to assess the probability of default, given the results achieved and the easiness of application when compared to the CHS model.A avaliação da probabilidade de falência tem sido um tema-chave abordado por investigadores e académicos ao longo do último meio século. A falência de empresas consideráveis como a Enron ou a WorldCom, aliada ao rigoroso ambiente regulamentar desencadeado pelas diretrizes de Basileia II, fomentou ainda mais o interesse pelo tema. Além disso, na sequência da crise financeira, as agências de notação de crédito (ANC) foram criticadas por endereçarem notações inflacionadas e não anteciparem corretamente os incumprimentos. Ademais, as principais ANC não avaliam todas as empresas, e a nossa intenção é proporcionar ao investidor individual a melhor opção disponível para estimar autonomamente a probabilidade de falência. Neste estudo analisou-se se um modelo baseado em dados de mercado, o KMV, e um modelo híbrido, o CHS, diferenciam o evento de falência e, caso isso seja verificado, qual deles melhor distingue entre empresas falidas e não falidas. Para tal, recorremos a uma amostra de 354 empresas cotadas nos EUA, divididas em empresas falidas e não falidas, aplicando a técnica estatística "ROC", num período de 10 anos. Os nossos resultados sugerem que o modelo KMV é ligeiramente superior ao modelo CHS, maximizando a área sob a curva (AUC). Além disso, o primeiro proporcionou um ponto de corte de probabilidade mais elevado que distingue ambos os tipos de empresas. Os nossos resultados indiciam que o KMV é a melhor opção disponível para um investidor individual avaliar a probabilidade de incumprimento, dado os resultados alcançados e a facilidade de aplicação em comparação com o modelo CHS

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