918 resultados para stochastic PDE
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I analyze two inequalities on entropy and information, one due to von Neumann and a recent one to Schiffer, and show that the relevant quantities in these inequalities are related by special doubly stochastic matrices (DSM). I then use generalization of the first inequality to prove algebraically a generalization of Schiffer's inequality to arbitrary DSM. I also give a second interpretation to the latter inequality, determine its domain of applicability, and illustrate it by using Zeeman splitting. This example shows that symmetric (degenerate) systems have less entropy than the corresponding split systems, if compared at the same average energy. This seemingly counter-intuitive result is explained thermodynamically. © 1991.
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Power-law distributions, i.e. Levy flights have been observed in various economical, biological, and physical systems in high-frequency regime. These distributions can be successfully explained via gradually truncated Levy flight (GTLF). In general, these systems converge to a Gaussian distribution in the low-frequency regime. In the present work, we develop a model for the physical basis for the cut-off length in GTLF and its variation with respect to the time interval between successive observations. We observe that GTLF automatically approach a Gaussian distribution in the low-frequency regime. We applied the present method to analyze time series in some physical and financial systems. The agreement between the experimental results and theoretical curves is excellent. The present method can be applied to analyze time series in a variety of fields, which in turn provide a basis for the development of further microscopic models for the system. © 2000 Elsevier Science B.V. All rights reserved.
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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)
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This paper is concerned with the stability of discrete-time linear systems subject to random jumps in the parameters, described by an underlying finite-state Markov chain. In the model studied, a stopping time τ Δ is associated with the occurrence of a crucial failure after which the system is brought to a halt for maintenance. The usual stochastic stability concepts and associated results are not indicated, since they are tailored to pure infinite horizon problems. Using the concept named stochastic τ-stability, equivalent conditions to ensure the stochastic stability of the system until the occurrence of τ Δ is obtained. In addition, an intermediary and mixed case for which τ represents the minimum between the occurrence of a fix number N of failures and the occurrence of a crucial failure τ Δ is also considered. Necessary and sufficient conditions to ensure the stochastic τ-stability are provided in this setting that are auxiliary to the main result.
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The GPS observables are subject to several errors. Among them, the systematic ones have great impact, because they degrade the accuracy of the accomplished positioning. These errors are those related, mainly, to GPS satellites orbits, multipath and atmospheric effects. Lately, a method has been suggested to mitigate these errors: the semiparametric model and the penalised least squares technique (PLS). In this method, the errors are modeled as functions varying smoothly in time. It is like to change the stochastic model, in which the errors functions are incorporated, the results obtained are similar to those in which the functional model is changed. As a result, the ambiguities and the station coordinates are estimated with better reliability and accuracy than the conventional least square method (CLS). In general, the solution requires a shorter data interval, minimizing costs. The method performance was analyzed in two experiments, using data from single frequency receivers. The first one was accomplished with a short baseline, where the main error was the multipath. In the second experiment, a baseline of 102 km was used. In this case, the predominant errors were due to the ionosphere and troposphere refraction. In the first experiment, using 5 minutes of data collection, the largest coordinates discrepancies in relation to the ground truth reached 1.6 cm and 3.3 cm in h coordinate for PLS and the CLS, respectively, in the second one, also using 5 minutes of data, the discrepancies were 27 cm in h for the PLS and 175 cm in h for the CLS. In these tests, it was also possible to verify a considerable improvement in the ambiguities resolution using the PLS in relation to the CLS, with a reduced data collection time interval. © Springer-Verlag Berlin Heidelberg 2007.
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This paper deals with exponential stability of discrete-time singular systems with Markov jump parameters. We propose a set of coupled generalized Lyapunov equations (CGLE) that provides sufficient conditions to check this property for this class of systems. A method for solving the obtained CGLE is also presented, based on iterations of standard singular Lyapunov equations. We present also a numerical example to illustrate the effectiveness of the approach we are proposing.
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Deterministic Optimal Reactive Power Dispatch problem has been extensively studied, such that the demand power and the availability of shunt reactive power compensators are known and fixed. Give this background, a two-stage stochastic optimization model is first formulated under the presumption that the load demand can be modeled as specified random parameters. A second stochastic chance-constrained model is presented considering uncertainty on the demand and the equivalent availability of shunt reactive power compensators. Simulations on six-bus and 30-bus test systems are used to illustrate the validity and essential features of the proposed models. This simulations shows that the proposed models can prevent to the power system operator about of the deficit of reactive power in the power system and suggest that shunt reactive sourses must be dispatched against the unavailability of any reactive source. © 2012 IEEE.
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The transcription process is crucial to life and the enzyme RNA polymerase (RNAP) is the major component of the transcription machinery. The development of single-molecule techniques, such as magnetic and optical tweezers, atomic-force microscopy and single-molecule fluorescence, increased our understanding of the transcription process and complements traditional biochemical studies. Based on these studies, theoretical models have been proposed to explain and predict the kinetics of the RNAP during the polymerization, highlighting the results achieved by models based on the thermodynamic stability of the transcription elongation complex. However, experiments showed that if more than one RNAP initiates from the same promoter, the transcription behavior slightly changes and new phenomenona are observed. We proposed and implemented a theoretical model that considers collisions between RNAPs and predicts their cooperative behavior during multi-round transcription generalizing the Bai et al. stochastic sequence-dependent model. In our approach, collisions between elongating enzymes modify their transcription rate values. We performed the simulations in Mathematica® and compared the results of the single and the multiple-molecule transcription with experimental results and other theoretical models. Our multi-round approach can recover several expected behaviors, showing that the transcription process for the studied sequences can be accelerated up to 48% when collisions are allowed: the dwell times on pause sites are reduced as well as the distance that the RNAPs backtracked from backtracking sites. © 2013 Costa et al.
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Consider a one-dimensional environment with N randomly distributed sites. An agent explores this random medium moving deterministically with a spatial memory μ. A crossover from local to global exploration occurs in one dimension at a well-defined memory value μ1=log2N. In its stochastic version, the dynamics is ruled by the memory and by temperature T, which affects the hopping displacement. This dynamics also shows a crossover in one dimension, obtained computationally, between exploration schemes, characterized yet by the trajectory size (Np) (aging effect). In this paper we provide an analytical approach considering the modified stochastic version where the parameter T plays the role of a maximum hopping distance. This modification allows us to obtain a general analytical expression for the crossover, as a function of the parameters μ, T, and Np. Differently from what has been proposed by previous studies, we find that the crossover occurs in any dimension d. These results have been validated by numerical experiments and may be of great value for fixing optimal parameters in search algorithms. © 2013 American Physical Society.
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Pós-graduação em Educação - IBRC
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Pós-graduação em Educação Escolar - FCLAR
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Este estudo sobre A democratização da gestão escolar no Município de Santa Bárbara do Pará a partir do PDE buscou identificar quais as contribuições do Plano de Desenvolvimento da Escola para a gestão escolar, a partir de análises das ações implementadas na Escola Municipal do Livramento. Ele contempla uma discussão sobre a reforma do Estado e a nova proposta de gestão pública, que tornou-se mais flexível, capaz de se adaptar ao desenvolvimento tecnológico e às novas exigências da economia globalizada, que fizeram a reforma do Estado ser orientada pelos valores da eficiência, da qualidade na prestação de serviços e pela cultura gerencial nas organizações. Este trabalho mostra, também, a articulação existente entre sistema escolar e capitalismo, que exigiu, devido a crise no setor agrário-exportador (nos anos vinte) e a emergência do setor urbano-industrial, melhor escolarização, principalmente para as populações dos centros urbanos, associando, dessa forma, a educação ao desenvolvimento e à economia como solução para a crise. Observa-se, a partir da pesquisa, que as políticas públicas educacionais emanadas dos organismos internacionais têm suscitado novas formas de regulação e de gestão no país, nesse contexto surge a perspectiva de gestão da proposta do Fundescola/ PDE, na qual é reforçado o papel da liderança do diretor. O estudo identifica que o atendimento educacional no Pará e na Região Norte está centrado no ensino fundamental, revelando uma desproporção com relação à educação infantil e ensino médio. A discussão, aqui apresentada, a respeito da modernização da gestão enfatiza a importância da autonomia e da participação na escola pública como meio de alcançar a qualidade desejável na educação. Revela, ainda, o caráter impositivo da proposta do PDE ao ignorar a comunidade escolar e externa na sua formulação, sendo distinta e até contraditória com a proposta estabelecida pela legislação educacional brasileira, apesar do discurso dos idealizadores apontarem-na como uma proposta participativa e democrática.
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Este estudo é sobre O Plano de Desenvolvimento da Educação (PDE/MEC), lançado no segundo mandato do Governo Lula (2006-2010). A sua efetivação se deu por meio do Plano de Ações Articuladas (PAR) no município de São Miguel do Guamá (Pará). Nosso objetivo é compreender e analisar como o PDE se implanta e vem se efetivando através da Secretaria Municipal de Educação de São Miguel do Guamá enfatizando o regime de colaboração na promoção de Políticas Públicas Educacionais no município no período de 2008 a 2011. A metodologia utilizada nessa pesquisa é qualitativa para isso utilizamos a revisão bibliográfica para a sustentação da temática no trabalho empírico e de analise documental, de entrevista semiestruturada e observação não participante. O PAR se constitui enquanto ferramenta de planejamento e ações que tem como propósito melhorar a qualidade da educação, permitindo uma relação direta entre Governo Federal e Governo Municipal. Em São Miguel do Guamá, o PAR segundo os entrevistados representou um avanço considerável na qualidade da educação, pela oferta de cursos e pela disponibilização de recursos técnicos e financeiros para as escolas, ao mesmo tempo que levou a SEMED ao planejamento e aplicação do Projeto Político Pedagógico das escolas, porém, esses avanços se desenvolveram por meio de imposição do Governo Federal ao Governo Municipal, devido o seu baixo IDEB e culminou em perda de autonomia municipal e adoção de medidas involuntárias por parte da comunidade escolar.
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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
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Resumo O presente artigo objetiva promover uma análise da implantação do PDE-Escola em duas unidades educacionais do município de Limeira-SP, que apresentaram o IDEB/2007 abaixo da média nacional e que foram direcionadas a implantar o Programa a partir de 2009. O PDE-Escola trata-se de um programa do Governo Federal que se proclama capaz de viabilizar a autonomia, a obtenção de melhores resultados educacionais e a modernização da estrutura, organização e gestão escolar a partir da adoção de modelos administrativos gerenciais. A finalidade deste estudo foi constatar se os objetivos delineados por tal Programa, no que tange à garantia da autonomia escolar, ganham concretude na prática. A metodologia utilizada nesta pesquisa qualitativa foi o estudo de casos, concretizado por meio de coleta de dados (entrevistas e questionários semiestruturados, análise documental e revisão bibliográfica). Os resultados obtidos acenaram para a imposição de uma metodologia padronizada e burocrática, pautada em mecanismos de monitoramento, cobrança e controle que dificultaram a conquista gradativa da autonomia das escolas pesquisadas. Palavras-chave: PDE-Escola. Autonomia Escolar. Gestão.