Recurrence relations for Clifford algebra-valued orthogonal polynomials

The theory of orthogonal polynomials of one real or complex variable is well established as well as its generalization for the multidimensional case. Hypercomplex function theory (or Clifford analysis) provides an alternative approach to deal with higher dimensions. In this context, we study systems of orthogonal polynomials of a hypercomplex variable with values in a Clifford algebra and prove some of their properties.

Application of wavelets to the study of political history

\The idea that social processes develop in a cyclical manner is somewhat like a `Lorelei'. Researchers are lured to it because of its theoretical promise, only to become entangled in (if not wrecked by) messy problems of empirical inference. The reasoning leading to hypotheses of some kind of cycle is often elegant enough, yet the data from repeated observations rarely display the supposed cyclical pattern. (...) In addition, various `schools' seem to exist which frequently arrive at di erent conclusions on the basis of the same data." (van der Eijk and Weber 1987:271). Much of the empirical controversies around these issues arise because of three distinct problems: the coexistence of cycles of di erent periodicities, the possibility of transient cycles and the existence of cycles without xed periodicity. In some cases, there are no reasons to expect any of these phenomena to be relevant. Seasonality caused by Christmas is one such example (Wen 2002). In such cases, researchers mostly rely on spectral analysis and Auto-Regressive Moving-Average (ARMA) models to estimate the periodicity of cycles.1 However, and this is particularly true in social sciences, sometimes there are good theoretical reasons to expect irregular cycles. In such cases, \the identi cation of periodic movement in something like the vote is a daunting task all by itself. When a pendulum swings with an irregular beat (frequency), and the extent of the swing (amplitude) is not constant, mathematical functions like sine-waves are of no use."(Lebo and Norpoth 2007:73) In the past, this di culty has led to two di erent approaches. On the one hand, some researchers dismissed these methods altogether, relying on informal alternatives that do not meet rigorous standards of statistical inference. Goldstein (1985 and 1988), studying the severity of Great power wars is one such example. On the other hand, there are authors who transfer the assumptions of spectral analysis (and ARMA models) into fundamental assumptions about the nature of social phenomena. This type of argument was produced by Beck (1991) who, in a reply to Goldstein (1988), claimed that only \ xed period models are meaningful models of cyclic phenomena".We argue that wavelet analysis|a mathematical framework developed in the mid-1980s (Grossman and Morlet 1984; Goupillaud et al. 1984) | is a very viable alternative to study cycles in political time-series. It has the advantage of staying close to the frequency domain approach of spectral analysis while addressing its main limitations. Its principal contribution comes from estimating the spectral characteristics of a time-series as a function of time, thus revealing how its di erent periodic components may change over time. The rest of article proceeds as follows. In the section \Time-frequency Analysis", we study in some detail the continuous wavelet transform and compare its time-frequency properties with the more standard tool for that purpose, the windowed Fourier transform. In the section \The British Political Pendulum", we apply wavelet analysis to essentially the same data analyzed by Lebo and Norpoth (2007) and Merrill, Grofman and Brunell (2011) and try to provide a more nuanced answer to the same question discussed by these authors: do British electoral politics exhibit cycles? Finally, in the last section, we present a concise list of future directions.

A new empirical system for rock slope stability analysis in exploitation stage

An empirical system was developed to obtain a quality index for rock slopes in road infrastructures, named Slope Quality Index (SQI), and it was applied to a set of real slopes.The SQI is supported in nine factors affecting slope stability that contemplate the evaluation of different parameters. Consequently, each factor is classified by the degree of importance and influence by assigned weights. These weights were established through a statistical analysis of replies to a survey that was distributed to several experienced professionals in the field. The proposed SQI varies between1 and 5, corresponding to slopes in very good and very bad condition state, respectively. Besides the advantage linked to a quantitative and qualitative evaluation of slopes, theSQI also allows identifying the most critical factors on the slope stability, which is a fundamental issue for an efficient management of the slope network in the road infrastructure, namely in the planning of conservation and maintenance operations.

Perplexidades e incertezas da regulação dos media na Europa

A regulação dos media tem ganho relevo nas agendas nacionais e internacionais mas nem sempre a utilização corrente do conceito é consistente, correndo o risco de significar tudo e nada em simultâneo. Independentemente do intenso e profícuo debate concetual que o tema suscita na comunidade académica, julgamos pertinente o estudo das estruturas de regulação mediática que operam no terreno da União Europeia. Este trabalho reflete sobre as entidades de regulação mediática que atuam na defesa do interesse público, ainda que existam as mais diversas modalidades de enunciação e de defesa desse interesse pelos vários estados, e decorre de um esforço de investigação coletivo, enquadrado no projeto “Regulação dos Media em Portugal: O Caso da ERC”, que agregou elementos sobre os organismos reguladores dos media na Europa.

On the length of bank-firm relationships: an empirical application to a major French bank

NIPE - WP 01/ 2016

Specification and testing of multiplicative time-varying GARCH models with applications

In this article, we develop a specification technique for building multiplicative time-varying GARCH models of Amado and Teräsvirta (2008, 2013). The variance is decomposed into an unconditional and a conditional component such that the unconditional variance component is allowed to evolve smoothly over time. This nonstationary component is defined as a linear combination of logistic transition functions with time as the transition variable. The appropriate number of transition functions is determined by a sequence of specification tests. For that purpose, a coherent modelling strategy based on statistical inference is presented. It is heavily dependent on Lagrange multiplier type misspecification tests. The tests are easily implemented as they are entirely based on auxiliary regressions. Finite-sample properties of the strategy and tests are examined by simulation. The modelling strategy is illustrated in practice with two real examples: an empirical application to daily exchange rate returns and another one to daily coffee futures returns.

Pseudofermion dynamical theory for the spin dynamical correlation functions of the half-filled 1D Hubbard model

A modified version of the metallic-phase pseudofermion dynamical theory (PDT) of the 1D Hubbard model is introduced for the spin dynamical correlation functions of the half-filled 1D Hubbard model Mott– Hubbard phase. The Mott–Hubbard insulator phase PDT is applied to the study of the model longitudinal and transverse spin dynamical structure factors at finite magnetic field h, focusing in particular on the sin- gularities at excitation energies in the vicinity of the lower thresholds. The relation of our theoretical results to both condensed-matter and ultra-cold atom systems is discussed.

As disfunções da memória organizacional e suas implicações no uso dos sistemas de informação: um caso de estudo

Dissertação de mestrado integrado em Engenharia e Gestão de Sistemas de Informação

A estimulação cognitiva através da aprendizagem mediada: uma proposta de promoção das habilidades cognitivas em crianças de meio social desfavorecido

Partindo de dois referenciais teóricos da inteligência, psicométrico e cognitivo, esta tese centra-se no conceito de modificabilidade cognitiva e nos programas de estimulação (treino) cognitiva. Em particular é feita uma descrição detalhada do Programa de Enriquecimento Instrumental-PEI (Feuerstein et al., 1980), nomeadamente alguns conceitos centrais à sua fundamentação e implementação, por exemplo a experiência de aprendizagem mediada, o mapa cognitivo e a modificação cognitiva estrutural, pois que foi o programa considerado no nosso estudo empírico. Em termos empíricos procedemos à aplicação do PEI (tarefa de organização de pontos) junto de um grupo de crianças de 10 a 13 anos, do 4º ano do ensino fundamental, provenientes de um meio sociocultural desfavorecido. Este grupo representava a globalidade de uma turma da escola escolhida (25 crianças), havendo uma outra turma similar da mesma escola que serviu de grupo de comparação (26 crianças). O plano experimental inclui uma avaliação de pré-teste e pósteste com provas cognitivas e de leitura. Igualmente foi considerado o rendimento escolar das crianças, acrescentando-se no grupo experimental uma avaliação mais qualitativa assente nas funções cognitivas, atitudes e comportamentos das crianças ao longo da realização das atividades propostas no programa de estimulação cognitiva. Os resultados obtidos apontam para um efeito benéfico do programa quando comparamos as crianças do grupo experimental e de controlo no pós-teste em termos das habilidades cognitivas e numa das provas de leitura. Igualmente se observam melhorias nas suas funções cognitivas, atitudes e comportamentos de implicação na realização das tarefas ao longo do programa, registando-se uma melhoria do pré-teste para o pós-teste no rendimento académico, contudo esta melhoria ocorre igualmente no grupo de controlo. Estes resultados são discutidos à luz da investigação sobre os programas de treino cognitivo, e em particular do PEI, retirando-se ilações para a prática educativa e para a continuidade da investigação nesta área.

Certificação ISO 9001 e Gestão de Recursos Humanos: precedentes e consequentes: estudo de caso das Unidades de Serviços Certificadas da Universidade do Minho

Dissertação de mestrado em Gestão de Recursos Humanos