994 resultados para path integral quantization


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A new composition path, Xi-Xj=constant, is suggested for the semi-empirical calculation of the thermodynamic properties of ternary ‘substitutional’ solutions from binary data, when the binary systems show deviations from the regular solution model. A comparison is made between the results obtained for integral and partial properties using this composition path and those calculated employing other composition paths suggested in literature. It appears that the best estimate of the ternary properties is obtained when binary data at compositions closest to the ternary composition are used.

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This paper considers the problem of determining the time-optimal path of a fixed-wing Miniature Air Vehicle (MAV), in the presence of wind. The MAV, which is subject to a bounded turn rate, is required to eventually converge to a straight line starting from a known initial position and orientation. Earlier work in the literature uses Pontryagin's Minimum Principle (PMP) to solve this problem only for the no-wind case. In contrast, the present work uses a geometric approach to solve the problem completely in the presence of wind. In addition, it also shows how PMP can be used to partially solve the problem. Using a 6-DOF model of a MAV the generated optimal path is tracked by an autopilot consisting of proportional-integral-derivative (PID) controllers. The simulation results show the path generation and tracking for cases with steady and time-varying wind. Some issues on real-time path planning are also addressed.

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This paper presents a strategy to determine the shortest path of a fixed-wing Miniature Air Vehicle (MAV), constrained by a bounded turning rate, to eventually fly along a given straight line, starting from an arbitrary but known initial position and orientation. Unlike the work available in the literature that solves the problem using the Pontryagin's Minimum Principle (PMP) the trajectory generation algorithm presented here considers a geometrical approach which is intuitive and easy to understand. This also computes the explicit solution for the length of the optimal path as a function of the initial configuration. Further, using a 6-DOF model of a MAV the generated optimal path is tracked by an autopilot consisting of proportional-integral-derivative (PID) controllers. The simulation results show the path generation and tracking for different cases.

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The mode I plane strain crack tip field with strain gradient effects is presented in this paper based on a simplified strain gradient theory within the framework proposed by Acharya and Bassani. The theory retains the essential structure of the incremental version of the conventional J_2 deformation theory No higher-order stress is introduced and no extra boundary value conditions beyond the conventional ones are required. The strain gradient effects are considered in the constitutive relation only through the instantaneous tangent modulus. The strain gradient measures are included into the tangent modulus as internal parameters. Therefore the boundary value problem is the same as that in the conventional theory Two typical crack Problems are studied: (a) the crack tip field under the small scale yielding condition induced by a linear elastic mode-I K-field and (b) the complete field for a compact tension specimen. The calculated results clearly show that the stress level near the crack tip with strain gradient effects is considerable higher than that in the classical theory The singularity of the strain field near the crack tip is nearly equal to the square-root singularity and the singularity of the stress field is slightly greater than it. Consequently, the J-integral is no longer path independent and increases monotonically as the radius of the calculated circular contour decreases.

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Ireland experienced two critical junctures when its economic survival was threatened: 1958/9 and 1986/7. Common to both crises was the supplanting of long established practices, that had become an integral part of the political culture of the state, by new ideas that ensured eventual economic recovery. In their adoption and implementation these ideas also fundamentally changed the institutions of state – how politics was done, how it was organised and regulated. The end result was the transformation of the Irish state. The main hypothesis of this thesis is that at those critical junctures the political and administrative elites who enabled economic recovery were not just making pragmatic decisions, their actions were influenced by ideas. Systematic content analysis of the published works of the main ideational actors, together with primary interviews with those actors still alive, reveals how their ideas were formed, what influenced them, and how they set about implementing their ideas. As the hypothesis assumes institutional change over time historical institutionalism serves as the theoretical framework. Central to this theory is the idea that choices made when a policy is being initiated or an institution formed will have a continuing influence long into the future. Institutions of state become ‘path dependent’ and impervious to change – the forces of inertia take over. That path dependency is broken at critical junctures. At those moments ideas play a major role as they offer a set of ready-made solutions. Historical institutionalism serves as a robust framework for proving that in the transformation of Ireland the role of ideas in punctuating institutional path dependency at critical junctures was central.

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Relatório da Prática de Ensino Supervisionada, Mestrado em Ensino das Artes Visuais, Universidade de Lisboa, 2014

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We return to the description of the damped harmonic oscillator with an assessment of previous works, in particular the Bateman-Caldirola-Kanai model and a new model proposed by one of the authors. We argue the latter has better high energy behavior and is connected to existing open-systems approaches. (C) 2011 Elsevier B.V. All rights reserved.

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In this work we show how to define the action of a scalar field such that the Robin boundary condition is implemented dynamically, i.e. as a consequence of the stationary action principle. We discuss the quantization of that system via functional integration. Using this formalism, we derive an expression for the Casimir energy of a massless scalar field under Robin boundary conditions on a pair of parallel plates, characterized by constants c(1) and c(2). Some special cases are discussed; in particular, we show that for some values of cl and c(2) the Casimir energy as a function of the distance between the plates presents a minimum. We also discuss the renormalization at one-loop order of the two-point Green function in the philambda(4) theory subject to the Robin boundary condition on a plate.

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Pós-graduação em Educação Matemática - IGCE

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Pós-graduação em Psicologia - FCLAS

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Pós-graduação em Serviço Social - FCHS

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In this thesis work I analyze higher spin field theories from a first quantized perspective, finding in particular new equations describing complex higher spin fields on Kaehler manifolds. They are studied by means of worldline path integrals and canonical quantization, in the framework of supersymmetric spinning particle theories, in order to investigate their quantum properties both in flat and curved backgrounds. For instance, by quantizing a spinning particle with one complex extended supersymmetry, I describe quantum massless (p,0)-forms and find a worldline representation for their effective action on a Kaehler background, as well as exact duality relations. Interesting results are found also in the definition of the functional integral for the so called O(N) spinning particles, that will allow to study real higher spins on curved spaces. In the second part, I study Weyl invariant field theories by using a particular mathematical framework known as tractor calculus, that enable to maintain at each step manifest Weyl covariance.

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In today’s world heritage worldwide are at the risk not only because of natural process of decay and destruction but also by social change like urbanization, globalization and homogenization of cultures. With these emerging problems, the heritage conservation discourse also has reached to a new dimension including broader range of concepts like tangible heritage, intangible heritage, community participation, indigenous knowledge and many more. Even with the changing scenario in the international context about the heritage conservation, Nepal’s heritage conservation still focus on monuments, sites and buildings. In add to that the conservation practices are still top-down approach and community involvements are limited only in plans. While numerous intangible heritages like masking dances chariot processions, festivals and rituals, which form an integral part of the daily social life of people are still being continued and managed by the community and its people, without with out serious attention form the government. In Kathmandu Valley these heritages has been maintained with the traditional social association of people known as “Guthi” which has been continuing since 5th Century. Most of the tangible and intangible heritages have survived for centuries because of this unique association of people. Among the numerous festivals of the Kathmandu Valley, the festival Yenya Punhi was chosen as a case for this study, which is also a major festival of Kathmandu. This festival is the perfect example for the study as its celebrated in the city that is the most urbanized city of Nepal with the challenges of the every modern city like social changes and urbanization. Despite modern challenges Guthi still plays a major role in the heritage conservation in Kathmandu Valley. Now there are some interventions of the various formal institutions. So this study will be focusing on the management, continuity and problems of the festival along with Nepal’s position in terms of intangible heritage conservation. The problem of Kathmandu and Yenya Punhi festival is the problem of every country in the similar situation so with this case study it can be a good example for finding solutions of the similar problem not only the other festivals within Nepal but also elsewhere in the world; Resumo: Conexão de Património: Festival Yenya Punhi um caminho de fortalecimento de identidade: A experiência de Catmandu Nos dias de hoje, os patrimónios mundiais encontram-se em risco, não só devido ao processo natural de degradação e destruição, mas também pelas mudanças sociais, tais como a urbanização, globalização e homogeneização de culturas. Com o emergir destes problemas, o discurso de conservação de Património atingiu também uma nova dimensão, incluíndo uma área mais abrangente de conceitos, como por exemplo, património material, património imaterial, participação da comunidade, conhecimento indígena, entre outros. Mesmo com este cenário de mudança no contexto mundial de conservação do património, a preservação do património do Nepal continua a focar-se em monumentos, sítios e edíficios. A acrescentar a isso, as práticas de conservação ainda têm uma abordagem descendente e os envolvimentos da comunidade são limitados por planificações. Enquanto que os numerosos patrimónios imateriais como danças com máscaras, procissões, festivais e rituais, os quais formam uma parte integral da vida diária social das pessoas que as continuam e as gerem em comunidade, sem uma atenção séria por parte do governo. No Vale de Catmandu, este património tem sido mantido pela associação tradicional de pessoas conhecidas como ''Guthi'' desde o século V. A maior parte destes patrimónios materiais e imateriais tem sobrevivido durante séculos graças a esta associação única de pessoas. Entre os numerosos festivais do Vale de Catmandu, o festival Yenya Puhni foi escolhido para este estudo, pois é também um grande festival em Catmandu. Este festival é o exemplo perfeito para este estudo, pois é celebrado na cidade mais urbanizada do Nepal, com os desafios das cidades modernas tais como mudanças sociais e urbanização. Apesar dos desafios da modernização, os ''Guthi'' ainda desempenham um papel importante na preservação do património do Vale de Catmandu. Agora, existem algumas intervenções de várias instituições formais Então, este estudo irá focar-se na gestão, continuidade e problemas do festival, juntamente com a posição do Nepal em termos de conservação de património imaterial. O problema de Catmandu e do festival Yenya Punhi é o problema de todos os países em situação semelhante então, este estudo pode ser um bom exemplo para encontrar soluções de problemas parecidos, não só em outros festivais no Nepal mas também para qualquer parte do mundo.