• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 53
  • 8
  • 5
  • 5
  • 5
  • 5
  • 4
  • 4
  • 2
  • 1
  • 1
  • 1
  • 1
  • Tagged with
  • 70
  • 25
  • 17
  • 15
  • 12
  • 12
  • 12
  • 12
  • 11
  • 10
  • 10
  • 9
  • 8
  • 8
  • 8
  • 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.
51

Spectroscopie rovibrationnelle de l'éthylène : Effet Stark : Application à l'éthylène dans les zéolithes / Rovibrational spectroscopy of ethylene : Stark effect : Application to ethylene in zeolites

Sanzharov, Maxim 05 November 2010 (has links)
L’objectif de ce mémoire est de présenter une étude aussi complète que possible de l’effet Stark dans les toupies asymétriques de type X2Y4 possédant le groupe de symétrie D2h et de l’appliquer au problème de la spectroscopie de l’éthylène piégé dans une zéolithe. Pour la première fois, un formalisme tensoriel adapté à l’étude de l’effet Stark pour la chaine de groupes O(3) D2h a été développé. Parallèlement au développement du modèle théorique, des programmes informatiques ont été mis au point sous la forme d’une nouvelle génération de logiciel appelé D2hTDS-ST utilisant une base plus simple, permettant une économie en temps de calcul. Sur la base des outils théoriques et informatiques ainsi qu’à partir des spectres expérimentaux enregistrés au laboratoire, nous avons fait une première estimation de la valeur du champ électrique effectif moyen produit par la silicalite-1. Les valeurs du champ électrique obtenues avec notre méthode sont cohérentes avec les valeurs obtenues par les calculs ab initio PBE1PBE6-31++G(2d,2p). / The objective of this report is to present a study as complete as possible of the Stark effect in the asymmetric top molecules of X2Y4 type possessing the D2h symmetry group and to apply it to the problem of the spectroscopy of the ethylene molecule trapped in a zeolite. For the first time, a tensorial formalism adapted to the study of the Stark effect for the O(3) D2h group chain was developed. In parallel, a computer package was worked out as a new generation of software called D2hTDS-ST using a simpler basis, allowing an economy in the calculation time. On the basis of the theoretical and computing tools as well as from the experimental spectra, recorded in the laboratory, we made a first estimation of the average effective electric field produced by silicalite-1. The values of the electric field obtained with our method are coherent with the values obtained by the ab initio PBE1PBE6-31++G(2d,2p) calculations.
52

Visco-plasticity and damage modeling of single crystal superalloys at high temperatures : a tensorial microstructure-sensitive approach / Visco-plasticité endommageable des superalliages monogranulaires base Ni à haute température : approche couplée à une représentationtensorielle de la microstructure

Mattiello, Adriana 20 February 2018 (has links)
Un modèle phénoménologique 3D de visco-plasticité couplée avec les évolutions microstructurales et l'endommagement est proposé pour les superalliages monogranulaires base Nickel, les matériaux des aubes de turbine à haute pression de moteurs d'hélicoptères. L'anisotropie de la mise en radeaux, la croissance et la dissolution de la phase durcissante sont modélisés. Une variable tensorielle et sa loi d'évolution permettent la description de la variation de la largeur des couloirs de matrice. Ce travail s'appuie sur la décomposition en modes de Kelvin du tenseur d'élasticité. Cette décomposition conduit également à une description multi-critère mésoscopique de la visco-plasticité cubique. Une formulation en (visco-)plasticité cristalline a été également proposée. Une loi d'endommagement avec seuil de type dD/dt=... est formulée pour la modélisation du fluage tertiaire et pour la prévision de la ductilité en traction. Une expression originale du seuil d'endommagement rend compte des effets de vitesse sur l'amorçage de l'endommagement par visco-plasticité. Une étude expérimentale a été conduite sur le CMSX-4, l'alliage au centre de cette étude, parallèlement aux travaux de modélisation. Des essais de dissolution ont été réalisés afin de mesurer la variation de la fraction volumique des précipités avec la température. Les mécanismes de déformation du matériau ont été observés en fluage isotherme à 850°C et 1050°C selon les principales directions cristallines du triangle stéréographique standard et constituent une base d'identification pour le modèle, la réponse mécanique du matériau obtenue. Trois essais de traction ont été réalisés selon la direction <111>, deux à vitesse de chargement constante, le troisième à vitesse variable. Des essais cyclés thermiquement de type 150h-moteur ont été réalisées sur le banc MAATRE. Des analyses EBSD et MET ont été réalisés sur les échantillons orientés selon les directions cristallines <011>, <111> et <112> et testés à 850°C. Ces analyses ont montré que le mâclage est le principal mécanisme de déformation pour des déformations supérieures à $1-2%$ selon ces orientations cristallines en fluage à cette température et à haute contrainte (>400 MPa). Enfin, le modèle a été implanté dans le code à élément Finis ZéBuLon, sans ou avec endommagement, et des calculs de structures ont été réalisés / A 3D phenomenological model coupling viscoplasticity, microstructural evolutions and damage is proposed for Ni-based single crystal superalloys, which are widely used materials for high pressure turbine blade in helicopter engines. The anisotropy of the gamma'-rafting, the gamma'-coarsening and the dissolution of the hardening gamma' phase are modeled. A tensorial variable and its evolution law allow to describe the variation of the gamma channels. The modeling is based on the Kelvin decomposition of the elasticity tensor. This decomposition leads to a phenomenological multi-criterion description of the cubic visco-plasticity. A formulation based on the single crystal (visco-)plasticity framework is also proposed. A damage law of type dD/dt=… is introduced in order to model the tertiary creep stage and the ductility. A novel rate sensitive damage threshold is introduced in order to account for the rate sensitivity of the damage onset by visco-plasticity. An experimental study has been carried out on the CMSX-4 alloy, which is the material of main interest in this study, in parallel to the modeling work. Dissolution tests have been carried out to measure the gamma'-volume fraction variation with temperature. The deformation mechanisms of the CMSX-4 alloy have been observed by performing tensile creep tests at 1050°C and 850°C. These tests have also constituted a database for the model identification. Three tensile tests have been realized along the <111> crystal direction, two at constant strain rate and the third by varying the strain rate. Non-isothermal creep tests reproducing the 150h-type engine test have been performed on the MAATRE bench. EBSD and TEM analysis have been realized on the specimens oriented along the <011>, <011> and <112> crystal directions and crept at 850° C. These analysis have shown that micro-twinning governs the deformation along these crystal directions during creep at this temperature and at high stresses (> 400 MPa) for deformation in excess of 1-2%. Finally, the model (with and without damage) has been encoded in the ZéBuLoN Finite Element solver and structure computations have been performed.
53

Etude de la soudabilité à froid des alliages d’aluminium : influence de la sollicitation mécanique sur la création des jonctions métalliques / Cold weldability of aluminium alloys : influence of the mechanical load on the formation of metallic bonds

Siret, Olivier 12 October 2010 (has links)
En soudage en phase solide, si la température peut avoir un rôle favorable, une sollicitation mécanique est également nécessaire pour s’affranchir de la couche d’oxyde recouvrant naturellement l’aluminium. Dans ce travail, on a ainsi cherché à comprendre l’importance de la sollicitation mécanique vis-à-vis de la création des jonctions métalliques. Dans ce but, 2 essais de soudabilité à froid ont été mis en place. L’essai de compression plane (CP) a pour but d’augmenter la surface à l’interface de soudage, de sorte à morceler la couche d’oxyde. Grâce à la microscopie, à une analyse par EF et à un modèle tensoriel de caractérisation de l’évolution des surfaces, les essais ont montré que, plus que l’importante déformation globale, le soudage se produit dans les zones de cisaillement maximum.Par conséquent, le second essai repose sur le cisaillement de l’interface de soudage : un tube sectionné est soumis à un effort de compression et de torsion alternée. Comme pour l’essai de CP, l’influence de divers paramètres a été étudiée. Parmi ceux-ci, l’état de surface (rugosités et propreté), l’angle de torsion (faible amplitude) et le nombre de cycles ont un rôle prépondérant. Les assemblages soudés ont ensuite été caractérisés mécaniquement et observés en microscopie (MEB-FEG, EBSD). Par rapport à l’essai de CP, on a pu constater une meilleure quantité et qualité des jonctions en compression-torsion alternée. De plus, un modèle thermodynamique a permis de conclure que les énergies mises en jeu sont trop faibles pour permettre un échauffement significatif : le soudage, sur environ 50% de l’interface en l’état actuel des choses, n’est réalisé que par des effets mécaniques locaux. / In solid-state welding, if the temperature generally has an important role (diffusion, recrystallization, etc.), a mechanical load is also necessary to override the oxide layer which naturally covers aluminium alloys. This work aims to understand the influence of the mechanical load on the formation of metallic bonds. To this end two cold weldability tests have been introduced. Firstly the plane strain channel-die compression of two cuboids sample aims to increase the surface at the welding interface in order to break up the oxide layer. Thanks to microscopy, a FEA model and a tensorial model of surfaces evolution, those results showed that, more than the important global deformation, welds were created in areas with maximum shear. Subsequently the second test aims to shear the welding interface: a tube is cut through its section and undergoes both a compression and a cyclic torsion load. As for our first weldability test, the influence of some parameters has been studied. Among them, the surface condition (roughness and cleanliness), the torsion angle (low amplitude) and the number of cycles are the most influential. Then the welded joints have been mechanically tested and microscopically observed (FEG-SEM and EBSD). In comparison with our first test, a higher quality and quantity of the joining has been showed. Moreover, a thermodynamic model concludes that the energies involved in this experimental process are too low to imply any local heating: the joining, on 50% of the welding interface as things stand, is only achieved thanks local mechanical effects.
54

TSS e TSB: novos descritores de forma baseados em tensor scale / TSS & TSB: new shape descriptors based on tensor scale

Freitas, Anderson Meirelles 24 October 2017 (has links)
Neste trabalho são apresentados dois novos descritores de forma para tarefas de recuperação de imagens por conteúdo (CBIR) e análise de formas, que são construídos sobre uma extensão do conceito de tensor scale baseada na Transformada de Distância Euclidiana (EDT). Primeiro, o algoritmo de tensor scale é utilizado para extrair informações da forma sobre suas estruturas locais (espessura, orientação e anisotropia) representadas pela maior elipse contida em uma região homogênea centrada em cada pixel da imagem. Nos novos descritores, o limite do intervalo das orientações das elipses do modelo de tensor scale é estendido de 180º para 360º, de forma a melhor discriminar a descrição das estruturas locais. Então, com base em diferentes abordagens de amostragem, visando resumir informações mais relevantes, os novos descritores são construídos. No primeiro descritor proposto, Tensor Scale Sector (TSS), a distribuição das orientações relativas das estruturas locais em setores circulares é utilizada para compor um vetor de características de tamanho fixo, para uma caracterização de formas baseada em região. No segundo descritor, o Tensor Scale Band (TSB), foram considerados histogramas das orientações relativas extraídos de bandas concêntricas, formando também um vetor de características de tamanho fixo, com uma função de distância de tempo linear. Resultados experimentais com diferentes bases de formas (MPEG-7 e MNIST) são apresentados para ilustrar e validar os métodos. TSS demonstra resultados comparáveis aos métodos estado da arte, que geralmente dependem de algoritmos custosos de otimização de correspondências. Já o TSB, com sua função de distância em tempo linear, se demonstra como uma solução adequada para grandes coleções de formas. / In this work, two new shape descriptors are proposed for tasks in Content-Based Image Retrieval (CBIR) and Shape Analysis tasks, which are built upon an extended tensor scale based on the Euclidean Distance Transform (EDT). First, the tensor scale algorithm is applied to extract shape attributes from its local structures (thickness, orientation, and anisotropy) as represented by the largest ellipse within a homogeneous region centered at each image pixel. In the new descriptors, the upper limit of the interval of local orientation of tensor scale ellipses is extended from 180º to 360º, to better discriminate the description of local structures. Then, the new descriptors are built based on different sampling approaches, aiming to summarize the most relevant features. In the first proposed descriptor, Tensor Scale Sector descriptor (TSS), the local distributions of relative orientations within circular sectors are used to compose a fixed-length feature vector, for a region-based shape characterization. For the second method, the Tensor Scale Band (TSB) descriptor, histograms of relative orientations are considered for each circular concentric band, to also compose a fixed-length feature vector, with linear time distance function for matching. Experimental results for different shape datasets (MPEG-7 and MNIST) are presented to illustrate and validate the methods. TSS can achieve high retrieval values comparable to state-of-the-art methods, which usually rely on time-consuming correspondence optimization algorithms, but uses a simpler and faster distance function, while the even faster linear complexity of TSB leads to a suitable solution for very large shape collections.
55

Análise de tensões induzidas em linhas de distribuição de baixa tensão frente a uma descarga atmosférica

CHAMIÉ FILHO, Ricardo Hachem Thomé 15 September 2009 (has links)
Submitted by Irvana Coutinho (irvana@ufpa.br) on 2011-03-29T13:52:50Z No. of bitstreams: 1 CHAMIÉ FLHO, Ricardo Hachem Thomé PPGEngenharia Elétrica.pdf: 6458600 bytes, checksum: 7f4cd65026c6bc0401a6b6a74bcaca75 (MD5) / Made available in DSpace on 2011-03-29T13:52:50Z (GMT). No. of bitstreams: 1 CHAMIÉ FLHO, Ricardo Hachem Thomé PPGEngenharia Elétrica.pdf: 6458600 bytes, checksum: 7f4cd65026c6bc0401a6b6a74bcaca75 (MD5) Previous issue date: 2009 / FAPESPA - Fundação Amazônia de Amparo a Estudos e Pesquisas / Neste trabalho são apresentadas simulações computacionais inéditas para o cálculo de tensões induzidas em linhas de baixa tensão provenientes de descargas atmosféricas em estações rádio-base de telefonia celular (ERBs). Foram construídas estruturas representativas que denotam um grau de complexidade bastante avançado e semelhante ao encontrado em campo, visando assim a obtenção o de resultados bem próximos aos da realidade. Para tal, desenvolveu-se um software, no qual as equações de Maxwell são resolvidas numericamente utilizando o Método das Diferenças Finitas no Domínio do Tempo (FDTD), associado à truncagem de domínio de análise pela técnica da UPML e representação de condutores elétricos pela formulação de fio fino para meios condutivos, gerando soluções de onda completa para o problema. / Numerical full-wave solutions of induced voltages on low-voltage energy lines due to atmospheric discharges on cell phone radio base stations (RBS), installed at the proximities of such lines, are presented for the first time in this work. Structures, such as towers and buildings, which present high structural complexity, have been modeled in order to obtain realistic results. In particular, this paper shows the importance of considering the effects related to real electrical conductivity and permittivity of the soil (in technical literature, PECs have been used to represent the soil in similar problems). For this purpose, a software has been developed in which Maxwell’s equations are numerically solved by using a parallel implementation of the Finite-Difference Time-Domain Method (FDTD), producing full wave solutions for the problem. The thin wire formulation has been implemented for representing thin cylindrical electric conductors and transmission lines.
56

Mesoscopic modelling of the geometry of dislocations and point-defect dynamics in single crystals

Van Goethem, Nicolas 19 January 2007 (has links)
Le travail a consisté, dans une première partie, à modéliser la dynamique des défauts ponctuels dans les mono-cristaux de silicium. Il s'est agi en premier lieu d'analyser en profondeur le modèle physique, pour introduire et comprendre le rôle de la thermodiffusion dans le modèle de transport-diffusion et recombinaison des interstitiels et des lacunes. Par une analyse asymptotique, nous sommes parvenus à prédire la composition du cristal en termes des densités de lacunes ou d'interstitiels. Nous avons également proposé un nouvel ensemble de paramètres matériels tenant compte de résultats d'expériences récentes sur la diffusivité des lacunes. Enfin, nous avons simulé numériquement le calcul des défauts ponctuels dans le procédé Czochralski de croissance de cristaux de silicium et l'avons validé par comparaison avec des résultats expérimentaux. Le travail principal dans cette thèse a consisté en l'élaboration d'une théorie mathématique permettant de décrire de manière rigoureuse la géométrie des dislocations dans les mono-cristaux. Par nature, ces défauts sont concentrés sur des lignes qui sont libres de former des réseaux complexes interagissant à leur tour avec les défauts ponctuels. Il s'est agi de proposer une théorie à l'échelle mésoscopique qui tienne compte à la fois de la multiformité des champs de déplacement et rotation tout en admettant que les effets non-élastiques soient concentrés dans la ligne. Les principaux champs intervenant dans cette théorie sont des densités de dislocations et de disclinations représentés par des tenseurs d'ordre 2 tenant compte à la fois de l'orientation de la ligne et des vecteurs de Frank et Burgers, qui sont des invariants caractérisant respectivement les défauts de rotation et de déplacement dans le cristal. Ces champs sont reliés à l'incompatibilité de la déformation élastique par l'intermédiaire de termes concentrés sur les lignes, qu'il a fallu décrire et formaliser dans un cadre mathématique rigoureux et cohérent. La description de la physique des dislocations a été rendue possible par l'application à la théorie des dislocations de certains nouveaux outils mathématiques tels, par exemple, la théorie des distributions, la théorie géométrique de la mesure, et la géométrie non-riemannienne. Enfin, l'homogénéisation de l'échelle mésoscopique vers l'échelle macroscopique des densités de dislocations, représentées par des tenseurs d'ordre 2, a permis de poser le problème à l'échelle du cristal, où les champs sont réguliers, obéissent à des lois de conservation, de constitution et d'évolution. Le travail de thèse s'est arrêté précisément au moment de modéliser l'échelle macroscopique, notamment les lois de constitution des densités de dislocations. / This thesis comprises two main parts and provides contributions to the fields of point- and line defects in single crystals. The point-defect transport, diffusion and recombination mechanisms are modeled in silicon crystals, whereas a theoretical approach is developped for the description of the geometry of dislocations. Therefore, plasticity, which is caused by the motion of dislocations, is not the topic of the present work. Dislocations are typical line-defects. Once generated during the growth of a silicon or other crystal, they can instantaneously multiply and generate dislocation networks, that render the material unusable for device manufacturing. We develop a theory to represent dislocated single crystals at the mesoscopic scale by considering concentrated effects along the dislocation line, as governed by the distribution theory combined with multiple-valued kinematic fields. Fundamental 2D identities relating the incompatibility tensor to the Frank and Burgers vectors are proved under global assumptions on the elastic strain, relying on the geometric measure theory, thereby giving rise to rigorous homogenisation from mesoscopic to macroscopic scale. The class of point-defects comprises the monoatomic defects which form the fundamental building blocks for grown-in defects in silicon crystals. A general model is build to conduct fully time-dependent and global simulations in order to predict the distribution of point-defects in a growing silicon crystal. Furthermore, the defect governing model is adapted in order to better agree with available measurements of self-interstitial and vacancy diffusion coefficients while respecting the V/G criterion, which characterises the interstitial-vacancy transition in the crystal. It is shown that introducing a thermal drift effect can facilitate the construction of a relevant model satisfying both conditions.
57

Remo??o de ru?dos s?smicos utilizando transformada de wavelet 1D e 2D com software em desenvolvimento

Ecco, Daniel 05 April 2011 (has links)
Made available in DSpace on 2014-12-17T14:08:44Z (GMT). No. of bitstreams: 1 DanielE_DISSERT.pdf: 1217613 bytes, checksum: edb565b9e30a0c09780fcf4efd4a52dc (MD5) Previous issue date: 2011-04-05 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / In the Hydrocarbon exploration activities, the great enigma is the location of the deposits. Great efforts are undertaken in an attempt to better identify them, locate them and at the same time, enhance cost-effectiveness relationship of extraction of oil. Seismic methods are the most widely used because they are indirect, i.e., probing the subsurface layers without invading them. Seismogram is the representation of the Earth s interior and its structures through a conveniently disposed arrangement of the data obtained by seismic reflection. A major problem in this representation is the intensity and variety of present noise in the seismogram, as the surface bearing noise that contaminates the relevant signals, and may mask the desired information, brought by waves scattered in deeper regions of the geological layers. It was developed a tool to suppress these noises based on wavelet transform 1D and 2D. The Java language program makes the separation of seismic images considering the directions (horizontal, vertical, mixed or local) and bands of wavelengths that form these images, using the Daubechies Wavelets, Auto-resolution and Tensor Product of wavelet bases. Besides, it was developed the option in a single image, using the tensor product of two-dimensional wavelets or one-wavelet tensor product by identities. In the latter case, we have the wavelet decomposition in a two dimensional signal in a single direction. This decomposition has allowed to lengthen a certain direction the two-dimensional Wavelets, correcting the effects of scales by applying Auto-resolutions. In other words, it has been improved the treatment of a seismic image using 1D wavelet and 2D wavelet at different stages of Auto-resolution. It was also implemented improvements in the display of images associated with breakdowns in each Auto-resolution, facilitating the choices of images with the signals of interest for image reconstruction without noise. The program was tested with real data and the results were good / Na atividade explorat?ria de hidrocarbonetos a grande inc?gnita ? a localiza??o das jazidas. Grandes esfor?os s?o empreendidos na tentativa de melhor identific?-las, localiz?-las e, ao mesmo tempo, otimizar a rela??o custo-benef?cio da extra??o de Petr?leo. Os m?todos s?smicos s?o os mais utilizados pelo fato de serem indiretos, isto ?, sondam as camadas de subsuperf?cie sem invadi-las. O sismograma ? a representa??o do interior da Terra e de suas estruturas atrav?s de um arranjo convenientemente disposto dos dados obtidos por meio da s?smica de reflex?o. Um grande problema nessa representa??o ? a intensidade e variedade de ru?dos presentes no sismograma, como o ru?do de rolamento superficial que contamina os sinais relevantes e pode mascarar as informa??es desejadas, trazidas por ondas espalhadas em regi?es mais profundas das camadas geol?gicas. Desenvolvemos uma ferramenta para suprimir estes ru?dos que usa transformadas Wavelets 1D e 2D. O programa, em linguagem Java, faz a separa??o das imagens S?smicas considerando as dire??es (horizontal, vertical e mistas ou locais) e faixas de comprimentos de ondas que formam essas imagens, usando Wavelets de Daubechies, Autoresolu??o que duplica o comprimento das ondas e Produto Tensorial das bases de Wavelets. Desenvolvemos a op??o, em uma mesma imagem, de usar o produto tensorial de Wavelets de dimens?o 2 ou produto tensorial de Wavelets de dimens?o 1 pelas identidades. Neste ?ltimo caso, temos a Decomposi??o em Wavelets de um sinal bidimensional em uma ?nica dire??o. Esta decomposi??o permite alongar numa determinada dire??o as Wavelets bidimensionais, corrigindo efeitos de escalas ao aplicarmos Autoresolu??es. Em outras palavras, aperfei?oamos o tratamento de uma imagem s?smica, usandoWavelet 1D eWavelet 2D em etapas diferentes de Autoresolu??es. Tamb?m implementamos melhorias na visualiza??o das imagens associadas ?s decomposi??es em cada Autoresolu??o, facilitando as escolhas das imagens com os sinais de interesse para reconstru??o da imagem sem os ru?dos. O programa foi testado com dados reais e os resultados obtidos foram de boa qualidade
58

Modelos cosmológicos numa teoria geométrica escalar - tensorial da gravitação: aspectos clássicos e quânticos

Alves Júnior, Francisco Artur Pinheiro 27 September 2016 (has links)
Submitted by Vasti Diniz (vastijpa@hotmail.com) on 2017-09-18T11:29:37Z No. of bitstreams: 1 arquivototal.pdf: 1956067 bytes, checksum: 845c3d0cd5113c8498d955af9cdcd907 (MD5) / Made available in DSpace on 2017-09-18T11:29:37Z (GMT). No. of bitstreams: 1 arquivototal.pdf: 1956067 bytes, checksum: 845c3d0cd5113c8498d955af9cdcd907 (MD5) Previous issue date: 2016-09-27 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / In this thesis, we deal with a particular geometric scalar tensor theory, which is a version of the Brans-Dicke gravitation, formulated in aWeyl integrable space-time. This formulation is done using the Palatini's variation procedure. The main point of our work is to perform two particular applications of the geometrical Brans-Dicke theory. The rst one is the study of geometric fase transition phenomena, that's related to a continuous change in the space-time structure of the universe from a Riemann's geometry to a Weyl's geometry, or in the inverse sense, from Weyl's geometry to Riemann's geometry. This phenomena seems to take place when the universe starts to expand in a accelerated rate. The second one is the investigation of classical and quantum behaviour of a anisotropic n-dimensional universe . To nd solutions that display the dynamical compacti cation of non observed extra dimensions is the main motivation to study such universe. / Nesta tese, reapresentamos uma teoria escalar tensorial geométrica, que é uma versão da gravitação de Brans-Dicke formulada em um espaço-tempo de Weyl integrável. Com esta teoria fazemos duas aplicações especí cas. Uma delas para o estudo de um fenômeno, que chamamos de transição de fase geométrica, uma mudança contínua na estrutura geom étrica do espaço-tempo. Este fenômeno parece ocorrer quando o universo se expande aceleradamente. A segunda aplicação reside no estudo clássico e quântico do comportamento de um modelo de universo n-dimensional anisotrópico. A motivação para esta investigação é a busca de soluções que exibem o compactação dinâmica das dimensões extras, que não são observadas.
59

Linearização de aplicações multilineares contínuas entre espaços de Banach e multi-ideais de composição / Linearization of continuous multilinear mappings between Banach spaces and composition multi-ideals

Silva, Alessandra Ribeiro da 23 February 2010 (has links)
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The rst aim of this dissertation is to construct the tensor product of nitely many linear spaces from elementary tensors and to show that this is the space through which multilinear mappings can be linearized. Next continuous multilinear mappings between Banach spaces are studied. The projective norm is introduced in the tensor product in order to perform the linearization of continuous multilinear mappings. The last chapter is devoted to the study of operator ideals and their generalization to the multilinear setting. The interplay between the theory of multi-ideals and the projective tensor product is established by the theory of composition multi-ideals. / O primeiro objetivo desta dissertação é construir o produto tensorial de um número finito de espaços vetoriais a partir dos tensores elementares e mostrar que e atraves desse espaco que aplicações multilineares podem ser linearizadas. Em seguida são estudadas as aplicações multilineares contnuas entre espacos de Banach. A norma projetiva e introduzida no produto tensorial para realizar a linearização das aplicações multilineares contnuas. No ultimo captulo os ideais de operadores lineares são estudados e generalizados para o contexto de ideais de aplicações multilineares. A conexão da teoria de multi-ideais com o produto tensorial projetivo e feita atraves dos multi-ideais de composição. / Mestre em Matemática
60

AnÃlise do contexto e dos resultados da aprendizagem da avaliaÃÃo educacional em um curso de graduaÃÃo em Engenharia / Analysis of the context and results of educational evaluation of learning in an undergraduate degree in Engineering

Francisco Herbert Lima Vasconcelos 20 March 2015 (has links)
Banco do Nordeste do Brasil / A avaliaÃÃo educacional dispÃe de mÃtodos para a obtenÃÃo de dados que podem ser Ãteis para avaliar grupos de indivÃduos (alunos, professores, administradores, tÃcnicos e outros), projetos, produtos e materiais, instituiÃÃes e sistemas educacionais, nos seus diversos nÃveis e competÃncias. No campo da educaÃÃo em engenharia, os processos avaliativos podem ajudar os gestores a tomarem decisÃes e a realizarem mudanÃas em cursos de graduaÃÃo. Esta tese investiga de forma inÃdita uma nova abordagem para a anÃlise e interpretaÃÃo de dados no campo da educaÃÃo em engenharia com Ãnfase no processo de avaliaÃÃo, levando em consideraÃÃo dois aspectos de modo integrado: a) a percepÃÃo/opiniÃo dos estudantes sobre o contexto/ambiente educacional (Learning Context - LC) e b) os resultados/rendimentos obtidos pelos mesmos discentes (Learning Outcomes - LO). Para a realizaÃÃo desta pesquisa, foram coletados dados de estudantes do curso de graduaÃÃo em Engenharia de TeleinformÃtica (ETI) do Centro de Tecnologia (CT) da Universidade Federal do Cearà (UFC). Os dados de LC foram coletados a partir da aplicaÃÃo do instrumento SEEQ (Studentâs Evaluation of Educational Quality) da metodologia SETE (Student Evaluate Teaching Effetivecness). Os dados de LO foram coletados a partir das informaÃÃes dos resultados de desempenho da aprendizagem dos mesmos discentes. Na realizaÃÃo do processamento da informaÃÃo dos dados matriciais e tensoriais obtidos, foram utilizadas duas ferramentas matemÃticas: a decomposiÃÃo bilinear, por meio da AnÃlise de Componentes Principais (Principal Component Analysis - PCA) e a decomposiÃÃo multilinear tensorial por meio da AnÃlise de Fatores Paralelos (Parallel Factor Analysis - PARAFAC). Os resultados obtidos permitem identificar caracterÃsticas comuns e semelhanÃas em componentes curriculares, tanto em termos da percepÃÃo quanto do desempenho dos estudantes. Os modelos PCA e PARAFAC tambÃm demonstraram um potencial significativo para extrair informaÃÃes de dados relacionados com variÃveis latentes em contextos educativos. / Educational evaluation provides methods to obtain data that can be useful for evaluating groups of individuals (students, teachers, administrators, technicians and others), projects, products and materials, educational institutions and systems at different levels and skills. In engineering education, evaluation processes can help managers to make decisions and changes in undergraduate courses. This thesis investigates in unprecedented way a new approach to the analysis and interpretation of data in the field of engineering education with emphasis in the evaluation process, taking into account two aspects in an integrated manner: a) perception / opinion of students about the context / educational environment (Learning Context - LC) and b) the results / income earned by the same students (Learning outcomes - LO). For this research, we collected data related to undergraduate students in Teleinformatics Engineering (TEI), at Technology Center (CT) of the Federal University of Cearà (UFC). LC data were collected from the application of SEEQ (Studentâs Evaluation of Educational Quality) instrument of SETE (Student Teaching Evaluate Effetivecness) methodology. The LO data was collected from the information of the performance of the studentsâ learning outcomes. Carrying out the information processing of the obtained tensor and matrix data, we have used two mathematical tools: the bilinear decomposition, called Principal Component Analysis - PCA decomposition and the multilinear tensor decomposition by Parallel Factor Analysis - PARAFAC. The results allow us to identify common features and similarities in curriculum components, both in terms of perception as the performance of students. The PCA and PARAFAC models also showed significant potential to extract data information related to latent variables in educational settings.

Page generated in 0.0802 seconds