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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
751

Transporte em nanoestruturas: fenômenos quânticos em poços duplos e triplos / Transport in nanostructures: quantum phenomena in double and triple quantum wells

Zahra Sadre Momtaz 22 March 2016 (has links)
Nesta tese apresentamos os estudos de magnetotransporte em poços quânticos largos,\\\\ estreitos e triplos em campos magnéticos baixos. Dependendo dos estudos desejados, me-\\\\dimos a magnetoresistência em regime linear e não linear e sob a aplicação de corrente AC, irradiação de microondas e em gradiente de temperatura ao longo das amostras. Relatamos a observação de efeitos não lineares de corrente alternada em oscilações magneto-inter-sub-bandas de poços quânticos triplos. A oscilação MIS em sistemas de poços quânticos individuais e duplos e também os efeitos não lineares devido à corrente contínua foram estudados antes nestes sistemas. Nossos resultados são explicados de acordo com um modelo generalizado baseado na parte de não equilíbrio da função de distribuição de elétrons. A magnetorresistência não local sob irradiação de microondas é também estudada nesta tese. Os resultados obtidos proporcionam evidências para uma corrente de estado de borda estabilizada por irradiação de microondas, devido às ressonâncias não lineares e foram descritas por um modelo baseado em dinâmica não linear e mapa padrão de Chirikov. Finalmente, observamos uma correlação estreita entre as oscilações de resistência e oscilações de tensão de arraste do fônon induzidas por irradiação de microondas em um sistema bidimensional de eletrons sob campo magnético perpendicular. A influência da resistividade de dissipação modificada por microondas na tensão de arraste do fônon perpendicular ao fluxo de fônons pode explicar nossas observações. Além disso, características nítidas observadas na tensão de arraste do fônon sugerem que os domínios de corrente associados a estes estados podem existir na ausência de condução DC externa. / In this thesis, we present the studies of magneto-transport in narrow , wide and triple quantum wells in low magnetic fields. Depending on the desired studies, we have measured the magneto-resistance both in linear and nonlinear regimes and under the application of AC current, microwave irradiation and temperature gradient along the samples. We have reported the observation of nonlinear effects of AC current on magneto-inter-sub-band oscillations (MIS) of triple quantum wells (TQWs). The MIS oscillations in single and double quantum well system and also nonlinear effects due to DC current have been studied before in these systems. Our results are explained according to a generalized model based on non-equilibrium part of electron distribution function. The nonlocal magneto-resistance under microwave irradiation is also studied within this thesis. The obtained results provide evidence for an edge-state current stabilized by microwave irradiation due to nonlinear resonances and have been described by a model based on the nonlinear dynamics and Chirikov standard map. Finally, we have observed the phonon-drag voltage oscillations correlating with the resistance oscillations under microwave irradiation in a two-dimensional electron gas in perpendicular magnetic field. The influence of dissipative resistivity modified by microwave on phonon-drag voltage perpendicular to the phonon flux can explain our observations. Moreover, sharp features observed in phonon drag voltage suggest the current domains associated with these states can exist in the absence of external DC driving.
752

Geometria do desacoplamento e integração numérica de equações diferenciais não lineares implícitas. / Decoupling geometry and numerical integration of differential equations implicit nonlinear systems.

Iderval Silva de Souza 24 November 2006 (has links)
Existem métodos de integração de equações algébrico diferenciais não lineares (DAEs) considerados clássicos pela literatura. Porém, neste trabalho, através uma abordagem geométrica, apresenta-se um método de integração de DAEs. Tal método é inspirado na teoria de desacoplamento de sistemas não lineares explícitos, quando se considera que as saídas são restrições algébricas. Neste caso, a DAE pode ser identificada como dinâmica zero. O resultado principal desta abordagem é que, dada uma DAE, sob certas condições, é possível a construção de um sistema explícito, de tal maneira, que as soluções desse sistema explícito convergem para as soluções da DAE. / Classical methods for numerical integration of diferential algebraic equations (DAEs) can be formal in the literature. In this work, using a diferential geometric approach, a numerical method of integration of DAEs is established. This method is inspired in the decoupling theory of nonlinear explicit systems, when one considers that the outputs are algebraic constraints. The main result is the construction of an explicit system, whose solutions converge to the solutions of the DAE.
753

Estudo da degradação do p-nitrofenol por ferro de valência zero: avaliação de processos redutivos e oxidativos / Study of p-nitrophenol degradation by zero-valent iron: evaluation of reductive and oxidative processes

Luciana Serra Soeira 26 October 2007 (has links)
Neste trabalho estudou-se o uso do ferro de valência zero em meio redutivo e oxidativo, a fim de desenvolver um processo que promova tanto a degradação quanto a mineralização de substâncias orgânicas com centros deficientes de elétrons, como, por exemplo, espécies que contêm o grupo nitro ligado ao anel aromático. O processo de degradação empregando-se ferro metálico, em ambos os meios estudados, apresentou grande eficiência no tratamento do p-nitrofenol, utilizado como poluente modelo. Para soluções contendo concentração inicial de p-nitrofenol igual a 100 mg L-1, tanto para o meio redutivo quanto para o oxidativo, em condições ótimas, as taxas de degradação obtidas foram superiores a 98% ao final de 15 minutos de tratamento. Para o meio com atmosfera oxidante, foi possível observar a geração de H2O2 in situ (cerca de 0,030 mmol L-1, em 45 minutos), proporcionando uma reação do tipo Fenton. Dessa forma, foi possível obter uma redução do teor de carbono orgânico dissolvido de cerca de 20%, em 60 minutos de reação. A fim de elevar a taxa de mineralização do p-nitrofenol, realizou-se a integração dos processos redutivo e oxidativo. O emprego deste sistema de tratamento proporcionou um aumento de 100% na redução do teor de carbono orgânico dissolvido, para o mesmo tempo de tratamento. Assim, pode-se inferir que a associação dos processos estudados levou à formação de substâncias mais susceptíveis ao ataque de agentes oxidantes. Por fim, avaliou-se o emprego de ferro de valência zero sintetizado via redução de íons Fe2+ por boridreto de sódio. Utilizando-se o sistema de tratamento integrado, este material proporcionou uma taxa de mineralização de cerca de 50%, demonstrando-se como uma boa alternativa para a obtenção do ferro de valência zero. Dessa forma, pode-se concluir que o sistema integrado apresenta-se como uma alternativa viável e eficiente, com grande potencial de aplicabilidade para o tratamento de substâncias recalcitrantes aos processos de tratamento convencionais, uma vez que apresentou bons resultados na degradação/mineralização da substância modelo. / In this work, we studied the use of zero-valent iron under reductive and oxidative medium, in order to develop a process that promotes the degradation and the mineralization of organic substances with deficient electron centers, such as nitroaromatic compounds. In both mediums, the degradation process promoted by the metallic iron showed good efficiency to degrade p-itrophenol, used as pollutant model. For solutions of p-nitrophenol with initial concentration of 100 mg L-1, degradation percentages were above 98% after 15 minutes of the treatment in reductive and oxidative mediums (optimal conditions). Under oxidant atmosphere, the in situ generation of H2O2 (about 0,030 mmol L-1, in 45 minutes) leaded to a Fenton-like reaction. So, it provided a reduction of total organic carbon levels up to 20% in 60 minutes. In order to raise the mineralization of p-nitrophenol, the reductive and oxidative processes were integrated. The used of this treatment system provided an increase of 100% in the reduction of the dissolved organic carbon, for the same treatment time. Thus, we can in infer that the association of the two processes led to the formation of more susceptible substances to the attack of oxidant agents. Finally, it was evaluated the use zero-valent iron synthesized through reduction of Fe2+ ions by NaBH4. The obtained material provided about 50% of p-nitrophenol mineralization, showing to be a good source of zero-valent iron. So, it can be concluded that the use of the integrated system is a viable and efficient alternative, with a great potential of applicability for the treatment of recalcitrants substances to the conventional treatment processes, because it presented good results in the degradation/mineralization of studied pollutant model.
754

Medidas de secções de choque de fusão dos sistemas 16o + 46,50ti / Measures sections of shock melting systems 16th ti + 46.50

Raphael Liguori Neto 29 September 1986 (has links)
Foram medidas funções de excitação para a fusão completa dos sistemas 16O+46,50Ti em energias abaixo e em torno da barreira Coulombiana. A seção de choque de fusão foi obtida utilizando-se os métodos da espectroscopia em linha e fora da linha através da soma das seções de choque dos canais de decaimento do núcleo composto formado, observados experimen- talmente. As vantagens e limitações do método são discutidas em detalhes. As funções de excitação da fusão dos sistemas citados foram analisados utilizando-se modelos semiclássicos de penetração de barreira. Através desta análise determinamos o raio e a altura da barreira de fusão para estes sistemas. Os valores obtidos concordam com valores da literatura na mesma região de massa. A seção de choque de fusão calculada pelo modelo de penetração de barreira unidimensional utilizando potenciais que descrevem a interação entre íons pesados, é subestimada em energias abaixo da barreira Coulombiana. A introdução da vibração de ponto zero da superfície dos núcleos interagentes, apesar de produzir um aumento da seção de choque em energias sub- Coulombianas, não consegue reproduzir os dados de maneira satisfatória, pois prevê uma diferença isotópica nas funções de excitação que não e observada experimentalmente. As previsões do modelo estatístico para o decaimento do núcleo composto (programa CASCA- DE) apresentam uma concordância satisfatória para os canais de decaimento mais intensos. / Excitation functions for complete fusion of the systems 16O + 46,50Ti, with energies near and below the Coulomb barrier, were measured. With the use of the in-beam and out of beam spectroscopy, the formation of the compound nucleus was experimentally detected. The fusi- on cross section was then attained by the sum of all observed compound nucleus decay chan- nels. The limitation and advantages of measurements methods are discussed. Theoretical analysis of the experimental results using the semi-classical barrier penetration model allowed us to obtain the fusion barrier height and radius for the studied systems. These values are in good agreement with others reported for this mass range. Using the unidimensionaL barrier penetration model with different nuclear potentials, descri- bing the heavy ion interactions gave theoretical fusion cross section values systematically smaller than our measured values in the energy region below the Coulomb barrier. The introduction of the nuclear surface zero point vibrations enhances the theoreticaL fusion cross sections in the sub-Coulomb region, but simultaneously introduces an isotopic difference in the fusion excitation functions that is not observed experimentally. The statistical model predictions for the compound nucleus decay (calculated by the CASCADE program) show reasonable agreement for the more intense decay channels.
755

Sobre existência de estados de equilíbrio e limite em temperatura zero para shifts de Markov topologicamente mixing / On equilibrium states existence and zero temperature limit for topologically mixing Markov shifts.

Victor Andres Vargas Cubides 16 October 2015 (has links)
O objetivo desta tese é demonstrar que para um subshift de Markov topologicamente transitivo com alfabeto enumerável e um potencial &#402 com pressão de Gurevic finita e variação limitada (&#402) < &#8734, existe um único estado de equilíbrio &#181t&#402 para cada t > 1, e a família (&#181t&#402)t>1 tem um ponto de acumulação quando t > &#8734. Além disso se também supomos que o &#402 é um potencial de Markov, demonstramos que a família de estados de equilíbrio (&#181t&#402)t>1 converge quando t > &#8734. Finalmente demonstramos a continuidade em &#8734 da entropia com respeito ao parâmetro t. Estes resultados não dependem da hipótese de existência de medidas de Gibbs. / The aim of this thesis is to prove that for a topologically transitive Markov subshift with countable alphabet and a summable potential &#402 with finite topological pressure Gurevic and bounded variation (&#402) < &#8734, there exists an equilibrium state &#181t&#402 tf for each t > 1 and the family of equilibrium states (&#181t&#402)t>1 associated to each potential tf has an accumulation point at t > &#8734. Moreover if we also assume that &#402 is a Markov potential we prove that the equilibrium states family (&#181t&#402)t>1 converges when t > &#8734. Finally we prove the continuity at &#8734 of the entropy with respect to the parameter t. These results do not depend on assuming the existence of Gibbs measures.
756

Do Fome Zero ao Bolsa Família: da emancipação ao assistencialismo?

Martins, Barby de Bittencourt 22 September 2011 (has links)
Made available in DSpace on 2014-08-20T13:46:54Z (GMT). No. of bitstreams: 1 Barby_Bittencourt_Martins_Dissertacao.pdf: 182456 bytes, checksum: a540f57cf1de83f4cab5ffe11050edbf (MD5) Previous issue date: 2011-09-22 / As the moment Luis Inácio da Silva has rise to power in Brasil, the country witnessed to a change in social policies. President Lula's government soon began to implement the Zero Hunger Programme (Programa Fome Zero), a series of initiatives aimed at eliminating hunger in Brasil. This programme contained huge proportions and represented the social flag against the poverty. By the way, with time the programme lost attention and the Family Grant Programme (Programa Bolsa Família) became the centre of attention for the government. Besides, critics started to indicate that Family Grant is not such emancipative programme as Zero Hunger seems to be. Therefore the need to comprehend those programmes and discover their forms arises as a question point. That will be transitioned from a emancipative programme to a welfare one? / Com a ascensão de Luis Inácio Lula da Silva à presidência do Brasil, o país presenciou uma mudança no que se refere às políticas sociais. Seu governo inicia apostando em um programa de dimensões elevadas onde continha políticas localizadas, assim como políticas estruturantes para combater a fome no Brasil. De modo geral, o programa Fome Zero assim denominado trazia a idéia de promover mudanças em vários aspectos na sociedade a fim de interromper o ciclo da pobreza e, dessa forma, eliminar a fome no Brasil. O programa representava a bandeira social do governo na luta contra a pobreza. Contudo, com o tempo, o programa foi sendo deixado de lado pelos governantes e, em seu lugar, o programa Bolsa Família um programa de transferência de renda condicionada começa a ser o centro das atenções governamentais. Críticos apontam nisso uma falha do governo, pois se deixa de investir em um programa de perfil emancipatório para investir-se em um programa de perfil assistencialista. Dessa maneira, surge a necessidade de discutir sobre essa questão para apreender o perfil dessas políticas. Será que se transitou de uma política emancipatória ao assistencialismo?
757

ZERO et le devenir immatériel de l’art à l’épreuve de la technique, 1958-1964 / ZERO and the dematerialization of art through the prism of technology, 1958-1964

Joly, Noémi 28 April 2017 (has links)
ZERO apparaît le 24 avril 1958 à l’occasion de la septième « exposition d’un soir » qui a lieu à Düsseldorf, dans l’atelier d’Otto Piene et de Heinz Mack. La thématique de cette exposition, « Le tableau rouge », rejoint celle du premier numéro de cette nouvelle revue d’artistes, ZERO. S’ensuivent deux autres numéros, respectivement sortis en octobre 1958 (« Vibration ») et en juillet 1961 (« Dynamo »). Autour de la revue pilotée par Mack et Piene se nouent alors différents projets collaboratifs et expositions collectives, à partir desquels ZERO devient une sorte d’échangeur entre plusieurs tendances nées au tournant des années 1950-1960. Cette recherche monographique a pour ambition première de renouveler les perspectives sur une revue et une mouvance artistique peu étudiées en France, et ce à partir de la question de l’immatériel réfractée au prisme de la technique. L’optimisme technologique présumé de ZERO est réexaminé à l’aune du « discours autorisé », de la poïétique des œuvres, de l’expérience esthétique et de leur réception critique. Dès lors, les œuvres et les discours dévoilent une image bien moins nette du passé, tissée de contradictions, qui traduit d’une part la difficile négociation d’un tournant sociétal marqué par la mécanisation et l’automation, l’information, l’accélération et la menace nucléaire et, d’autre part, l’ambition pour l’art dynamique (vitaliste) et « idéaliste » de ZERO de jouer un rôle actif dans la définition de l’époque, en s’adressant aux imaginaires et en occupant les territoires de l’expérience sensible. / ZERO was created on the 24th of April 1958, on the occasion of the seventh « Night Exhibition », which took place in Otto Piene’s and Heinz Mack’s studio in Düsseldorf. The theme of this exhibition, « The Red Painting » was the same as the inaugural edition of ZERO, a new artist magazine. Following this initiative, two other issues were published, one dedicated to “Vibration” (October 1958), the other to “Dynamo” (July 1961). Various collaborative projects and collective exhibitions revolved around the magazine edited by Mack and Piene, from which ZERO became a platform between several tendencies which had come into being by the early 1960s. This study aims at renewing and enriching knowledge of both a magazine and a movement that have not been the subject of any extensive examination so far. For this purpose, this research focuses on the immaterial art of ZERO as refracted through the prism of technology. ZERO’s alleged technological optimism is explored by the light of the “authorized discourses”, the poietic of the works of art, their aesthetic experience and their critical reception. Therefore, the works of art and the discourses reveal a far less clear picture of the past, which is not free of discrepancies. On the one hand, this reflects the complex issue of dealing with societal shifts characterized by mechanization and automation, information, acceleration, nuclear threat; and, on the other hand, this demonstrates the ambition for ZERO’s both dynamic (vitalist) and “idealistic” art to play an active role in defining the spirit of the era by addressing imaginaries and by occupying territories of sensitive experience.
758

Isolated Single-Stage Interleave Resonant PFC Rectifier with Active and Novel Passive Output Ripple Cancellation Circuit

Eleyele, Abidemi Oluremilekun January 2020 (has links)
With the increasing demand for fast, cheaper, and efficient power converters come the need for a single-stage power factor correction (PFC) converter. Various single-stage PFC converter proposed in the literature has the drawback of high DC bus voltage at the input side and together with the shift to wide bandgap switches like GaN drives the converter cost higher. However, an interleaved topology with high-frequency isolation was proposed in this research work due to the drastic reduction in the DC bus voltage and extremely low input current ripple thereby making the need for an EMI filter circuit optional.   Meanwhile, this research work focuses on adapting the proposed topology for a high voltage low current application (EV charger - 400V, 7KW) and low voltage high current application (telecom power supply - 58V,  58A) owing to cost benefits. However, all single-stage PFC are faced with the drawback of second-order (100Hz) output harmonic ripple. Therefore, the design and simulation presented a huge peak to peak ripple of about 50V/3A and 26V/26A for the EV charger and telecom power supply case, respectively. This created the need for the design of a ripple cancellation circuit as the research required a peak to peak ripple of 8V and 200mV for the EV - charger and telecom power supply, respectively.   A novel output passive ripple cancellation technique was developed for the EV charger case due to the ease it offers in terms of control, circuit complexity and extremely low THDi when compared with the active cancellation approach. The ripple circuit reduced the 50V ripple to 431mV with the use of a total of 2.2mF capacitance at the output stage.   Despite designing the passive technique, an active ripple cancellation circuit was designed using a buck converter circuit for the telecom power supply. The active approach was chosen because the passive has a slow response and incurs more loss at a high current level. Adding the active ripple cancellation circuit led to a quasi-single stage LLC PFC converter topology. A novel duty-ratio feedforward control was added to synchronize the PFC control of the input side with the buck topology ripple cancellation circuit. The addition of the ripple circuit with the feedforward control offered a peak to peak ripple of 6.7mV and a reduced resonant inductor current by half.   After analysis, an extremely low THDi of 0.47%, PF of 99.99% and a peak efficiency of 97.1% was obtained for the EV charger case. The telecom power supply offered a THDi of 2.3%, PF of 99.96% with a peak efficiency of 95%.
759

Analýza automatizovaného generování signatur s využitím Honeypotu / Analysis of Automated Generation of Signatures Using Honeypots

Bláha, Lukáš January 2012 (has links)
In this paper, system of automatic processing of attacks using honeypots is discussed. The first goal of the thesis is to become familiar with the issue of signatures to detect malware on the network, especially the analysis and description of existing methods for automatic generation of signatures using honeypots. The main goal is to use the acquired knowledge to the design and implementation of tool which will perform the detection of new malicious software on the network or end user's workstation.
760

Jak rozvíjet myšlení žáků ve výtvarné výchově / Possibilities of the art education to develop thinking dispositions of pupils

Štěpánová, Ivana January 2019 (has links)
Student studied and presents the principles of Harvard University Project Zero programs The Artful Thinking and The Visible Thinking. The goal of both programs is to help teachers to create a connection between works of art and curriculum and to use the art to develop thinking dispositions of pupils. Student introduces in details principles, reports and impact of the project on the american education system. She then considers it in the context of czech primary school art education and connects it with the czech curriculum domain. The integral part of the thesis is a visual project realized in primary school. The author analyzes different ways of children's thinking and percieving and construction of meaning in the context of visual literacy. On basis of the findings the art project was proposed. KEY WORDS Artful Thinking, Visible Thinking, project Zero, visual literacy, art education, thinking dispositions development, work of art, case study

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