992 resultados para Constant power
Resumo:
Não há disciplina em qualquer ramo da ciência, seja esta natural, social, humana, descritiva, experimental ou teórica, qualitativa ou quantitativa, que não tenha sido afectada a vários níveis da instrumentalidade, conceptualização, construção de modelos, escolha de metáforas heurísticas ou ontológicas, e sentidO da investigação, em alguns casos muito profunda e decisivamente, pela influência crescente da constelação informacional computacional. A investigação baseada em simulações por computador é uma “terceira espécie de ciência”, que se soma aos tipos teórico e físico-experimental de trabalho científico. A ciber-ciência é um lugar natural para simular ciência, ou meta-ciberciência, mas todo o conhecimento científico cai no domínio da meta-ciberciência ou da filosofia da ciência computacional. A meta-ciência simula a ciência(o estudo computacional da produção do conhecimento científico); a ciber-ciência é por definição simulatória; a ciber-ciência simula a Natureza; a Natureza, segundo alguns físicos, é ela mesma uma simulação. Receber a categoria da informação nas ciências da vida e nas ciências humanas e sociais, da maneira específica como tem vindo a ocorrer, traz um considerável lastro metafísico: os humanos como máquinas, ultrapassáveis por máquinas inteligentes ou “espirituais”. A informação emerge como a alavanca de Arquimedes para as nossas intervenções n o domínio da vida e do espírito, de máquinas informacionais naturais, com evidentes implicações para a ciência política.
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Pedro Feytor Pinto headed the Department of Information Services (SEIT) in the government of Marcello Caetano who replaced Antonio Oliveira Salazar in 1968 as the head of the Portuguese government. Feytor Pinto has just released a book entitled Na Sombra do Poder (In the Shadow of Power)[Lisboa, D. Quixote, 2011, pp. 402]. Not wishing to classify it as history or memoirs, yet hoping that historians may find it useful, the author chooses to narrate events as he experienced them from his vantage point in the shadow of Power, during the years ending with the Carnation Revolt of 25 April 1974, which put an end to half a century of dictatorship, known as Estado Novo.
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RESUMO: Na sociedade da comunicação e da informação, as escolas ainda não conseguiram compreender o seu papel de facilitadoras do conhecimento que o mundo está promovendo entre a realidade da escola e o interesse do educando. Um dos fatores para isso é o crescimento das escolas ao longo dos séculos e a necessidade de superação decorrente do alargamento da educação, que têm gerado um conhecimento complexo que descreve as reflexões e conscientizações sobre o nosso próprio desenvolvimento humano e sobre a nossa participação no mundo em que estamos vivendo. Essas complexidades possibilitam mudanças, principalmente nas questões epistemológicas e paradigmáticas, que proporcionaram outra forma de conceber o conhecimento e os saberes, chamado de “ecologia dos saberes”. Nesse contexto, existe a necessidade de se fazer uma leitura crítica na e da escola e de sua participação junto à comunidade escolar, objetivando minimizar as relações de dominação, de normatizações, de disciplinamento, de concentração de poder, para direcionar a educação num processo emancipatório, democrático, consciente das mudanças, de forma a incluir todos os saberes possíveis para acompanhar e valorizar a realidade escolar, através da participação de alta intensidade na construção e reconstrução do seu projeto político pedagógico. Para tanto, iremos discorrer sobre três escolas, a partir da análise de cada uma dentro da realidade construída por elas, buscando demonstrar que as escolas, dentro dos seus contextos educacionais, possuem diferentes realidades que não podem ser generalizadas, mas que devem ser compreendidas no sentido de que sejam promovidas a autonomia escolar e o fortalecimento da democracia educacional, objetivando a superação das condições atuais da educação para se adequar à sociedade e ao mundo atual. ABSTRACT: In the present society of communication and information, schools have not yet been able to understand their roles as facilitators of the knowledge that the world is promoting between the reality of school and the interest of the learner. One of the reasons for that is the growth of schools along the centuries as well as their constant need for getting over old problems, due to the expansion of education. These questions lead to a complex knowledge which describes reflections on our own human development and on our participation in the world we live in. These complexities lead to changes, especially in epistemological and paradigmatic questions, making it possible for new ways of conceiving knowledge, known as “ecology of knowledge”. In this context, there is a need for making a critical reading about school and its participation in the school community, with the objective to minimize the relations of domination, power concentration and discipline and to direct education towards a process of emancipation and democracy, in which there is conscience of the necessary changes to include all possible knowledge as a way to value the reality of school through a high intensity participation in the construction and reconstruction of its political and pedagogical project. Thus, this study will discuss three schools, basing this discussion on the analysis of each school within the reality built by them, trying to demonstrate that, within their educational contexts, each one possesses different realities that cannot be generalized. These differences must, however, be understood, in order to allow the promotion of school autonomy and the strengthening of educational democracy with the objective to get over education`s present conditions and adjust them to society and to the present world.
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This essay approaches the display of power and rulership both through the art of writing and the art of painting by focusing on George Cavendish's biographical account of Thomas Wolsey.
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Nowadays, the Portuguese insurance industry operates in a market with a much more aggressive structure than a few decades ago. Markets and the economy have become globalised since the last decade of the 20th century. Market forces have gradually shifted – power is now mainly on the demand side. In order to meet the new requirements, the insurance industry must develop a strong strategic ability to respond to constant changes of the new international economic order.One of the basic aspects of this strategic development will focus on the ability to predict the future. We introduce the subject by briefly describing the sector, its organisational structure in the Portuguese market, and challenges arising from the development of the European Union. We then analyse the economic and financial structure of the sector. From this point of view, we aim at the possibility of designing models that could explain the demand for insurance, claims and technical reserves evolution. Such models, (even if based on the past), would resolve, at least partly, one of the greatest difficulties experienced by insurance companies when estimating the budget. Thus, we examine the existence of variables that explain the previous points, which are capable of forming a basis for designing models that are simple but efficient, and can be used for strategic planning.
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The increased integration of wind power into the electric grid, as nowadays occurs in Portugal, poses new challenges due to its intermittency and volatility. Wind power prediction plays a key role in tackling these challenges. The contribution of this paper is to propose a new hybrid approach, combining particle swarm optimization and adaptive-network-based fuzzy inference system, for short-term wind power prediction in Portugal. Significant improvements regarding forecasting accuracy are attainable using the proposed approach, in comparison with the results obtained with five other approaches.
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As wind power generation undergoes rapid growth, lightning and overvoltage incidents involving wind power plants have come to be regarded as a serious problem. Firstly, lightning location systems are discussed, as well as important parameters regarding lightning protection. Also, this paper presents a case study, based on a wind turbine with an interconnecting transformer, for the study of adequate lightning and overvoltage protection measures. The electromagnetic transients circuit under study is described, and computational results are presented.
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This paper presents the Direct Power Control of Three-Phase Matrix Converters (DPC-MC) operating as Unified Power Flow Controllers (UPFC). Since matrix converters allow direct AC/AC power conversion without intermediate energy storage link, the resulting UPFC has reduced volume and cost, together with higher reliability. Theoretical principles of DPC-MC method are established based on an UPFC model, together with a new direct power control approach based on sliding mode control techniques. As a result, active and reactive power can be directly controlled by selection of an appropriate switching state of matrix converter. This new direct power control approach associated to matrix converters technology guarantees decoupled active and reactive power control, zero error tracking, fast response times and timely control actions. Simulation results show good performance of the proposed system.
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In this paper, a mixed-integer nonlinear approach is proposed to support decision-making for a hydro power producer, considering a head-dependent hydro chain. The aim is to maximize the profit of the hydro power producer from selling energy into the electric market. As a new contribution to earlier studies, a risk aversion criterion is taken into account, as well as head-dependency. The volatility of the expected profit is limited through the conditional value-at-risk (CVaR). The proposed approach has been applied successfully to solve a case study based on one of the main Portuguese cascaded hydro systems.
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Sliding mode controllers for power converters usually employ hysteresis comparators to directly generate the power semiconductors switching states. This paper presents a new sliding mode modulator based on the direct implementation of the sliding mode stability condition, which for multilevel power converters shows advantages, as branch equalized switching frequencies and less distortion on the ac currents when operating near the rated converter power. The new sliding mode multilevel modulator is used to control a three-phase multilevel converter, operated as a reactive power compensator (STATCOM), implementing the stability condition in a digital signal processing system. The performance of this new sliding mode modulator is compared with a multilevel modulator based on hysteresis comparators. Simulation and experimental results are presented in order to highlight the system operation and control robustness.
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We start by studying the existence of positive solutions for the differential equation u '' = a(x)u - g(u), with u ''(0) = u(+infinity) = 0, where a is a positive function, and g is a power or a bounded function. In other words, we are concerned with even positive homoclinics of the differential equation. The main motivation is to check that some well-known results concerning the existence of homoclinics for the autonomous case (where a is constant) are also true for the non-autonomous equation. This also motivates us to study the analogous fourth-order boundary value problem {u((4)) - cu '' + a(x)u = vertical bar u vertical bar(p-1)u u'(0) = u'''(0) = 0, u(+infinity) = u'(+infinity) = 0 for which we also find nontrivial (and, in some instances, positive) solutions.
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In this paper, two wind turbines equipped with a permanent magnet synchronous generator (PMSG) and respectively with a two-level or a multilevel converter are simulated in order to access the malfunction transient performance. Three different drive train mass models, respectively, one, two and three mass models, are considered in order to model the bending flexibility of the blades. Moreover, a fractional-order control strategy is studied comparatively to a classical integer-order control strategy. Computer simulations are carried out, and conclusions about the total harmonic distortion (THD) of the electric current injected into the electric grid are in favor of the fractional-order control strategy.
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This paper presents new integrated model for variable-speed wind energy conversion systems, considering a more accurate dynamic of the wind turbine, rotor, generator, power converter and filter. Pulse width modulation by space vector modulation associated with sliding mode is used for controlling the power converters. Also, power factor control is introduced at the output of the power converters. Comprehensive performance simulation studies are carried out with matrix, two-level and multilevel power converter topologies in order to adequately assert the system performance. Conclusions are duly drawn.