Dissertations / Theses on the topic 'Planar models'
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Venkateswaran, Ajay. "Analysis of planar EBG structures using transmission line models." Thesis, McGill University, 2009. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=40812.
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The transmission line based analytical solutions have simplified engineering of complex microwave circuits like electromagnetic bandgap structures (EBGs). In this thesis, planar EBG structures are studied by derivation of lumped element and transmission line equivalent circuits followed by utilizing analytical formulations. Based on this approach, a code is developed that predicts the dispersion characteristics of these periodic structures in a matter of few seconds. Planar EBG structures containing meander sections are investigated and a method for development of an equivalent circuit for the meander line portion is presented. The analysis of the studied EBG structures begins from a simple 1D geometry and is extended to more complex 2D geometries. The analytical simulation results are evaluated against full-wave simulations. Inclusion of the meander sections reduces the beginning of the bandgap to below 1GHz resulting in a more attractive structure for low frequency omni-directional filtering.Les solutions analytiques basées sur des lignes de transmission ont simplifié l'ingénierie de circuits micro-ondes complexes, tel que les EBG. La présente thèse étudie les structures coplanaires EBG à partir d'éléments discrets et de modèles de lignes de transmission, auxquels sont ensuite appliquées des formules analytiques. Grâce à cette approche, un logiciel a été développé permettant de prédire les caractéristiques de dispersion de ces structures périodiques en quelques secondes seulement. Les structures coplanaires EBG contenant des sections courbes sont étudiées et un modèle de circuit équivalent à la portion courbe est proposé. L'analyse des structures EBG commence par une simple géométrie 1D, puis est étendue à des géométries 2D plus complexes. Le résultat des simulations analytiques est évalué par rapport au résultat des simulations analogues. Lorsque les sections courbes sont incluses, le début de la bande interdite est porté en deçà de 1GHz, rendant la structure plus intéressante pour le filtrage basse fréquence omni- directionnel.
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Dods, Steven R. A. "A spectral theory for planar dielectric waveguides." Thesis, University of British Columbia, 1990. http://hdl.handle.net/2429/30690.
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The problem of electromagnetic wave propagation across the junction of two similar planar
dielectric waveguides is analysed, within the Kirchhoff approximation, by expanding the field into transverse variations of all possible modes. It is proven that the expansion can represent any solution for any planar dielectric waveguide. The spectral function is introduced into the representation, and this helps resolve some of the theoretical problems in passing from the limit of closed waveguides to open waveguides. Using the spectral function and the Gel'fand-Levitan integral equation some new exact solutions to novel dielectric planar waveguides can be found. Examples of waveguiding by total internal reflection or by Bragg reflection (which are physically very different processes) can be generated by changing a single parameter in the formulation. Usually the representation
for an open dielectric waveguide requires the matrix spectral function. However the Gel'fand-Levitan reconstruction is defined for scalar spectral functions. A technique for constructing the spectral matrix and the scattering solutions from two spectral functions is demonstrated. This technique uses a variational formulation of a scattering experiment. The connection between a dielectric structure and the characteristics of propagation on it is obscure. However the connection between these characteristics and the spectral function
is much clearer. It is sometimes possible to make predictions about the properties of the waveguide by looking at its spectral function only. Since the connection between the spectral function and the dielectric structure is well established by inverse spectral theory, introducing the spectral function has been of help in establishing the desired connection between the dielectric structure and the characteristics of propagation on it.
Such considerations suggest one of the above waveguides is sensitive to small perturbations
and could be used as an electro-optic modulator. Detailed calculations confirm the hypothesis.Applied Science, Faculty of
Electrical and Computer Engineering, Department of
Graduate
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Lazaryan, Shushan, Nika LAzaryan, and Nika Lazaryan. "Discrete Nonlinear Planar Systems and Applications to Biological Population Models." VCU Scholars Compass, 2015. http://scholarscompass.vcu.edu/etd/4025.
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We study planar systems of difference equations and applications to biological models of species populations. Central to the analysis of this study is the idea of folding - the method of transforming systems of difference equations into higher order scalar difference equations. Two classes of second order equations are studied: quadratic fractional and exponential.
We investigate the boundedness and persistence of solutions, the global stability of the positive fixed point and the occurrence of periodic solutions of the quadratic rational equations. These results are applied to a class of linear/rational systems that can be transformed into a quadratic fractional equation via folding. These results apply to systems with negative parameters, instances not commonly considered in previous studies. We also identify ranges of parameter values that provide sufficient conditions on existence of chaotic and multiple stable orbits of different periods for the planar system.
We study a second order exponential difference equation with time varying parameters and obtain sufficient conditions for boundedness of solutions and global convergence to zero. For the autonomous case, we show occurrence of multistable periodic and nonperiodic orbits. For the case where parameters are periodic, we show that the nature of the solutions differs qualitatively depending on whether the period of the parameters is even or odd.
The above results are applied to biological models of populations. We investigate a broad class of planar systems that arise in the study of stage-structured single species populations. In biological contexts, these results include conditions on extinction or survival of the species in some balanced form, and possible occurrence of complex and chaotic behavior. Special rational (Beverton-Holt) and exponential (Ricker) cases are considered to explore the role of inter-stage competition, restocking strategies, as well as seasonal fluctuations in the vital rates.
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Collet, Gwendal. "Enumeration and analysis of models of planar maps via the bijective method." Palaiseau, Ecole polytechnique, 2014. https://tel.archives-ouvertes.fr/tel-01084964/document.
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La combinatoire bijective est un domaine qui consiste à étudier les propriétés énumératives de familles d’objets mathématiques en exhibant des bijections (idéalement explicites) qui préservent ces propriétés entre de telles familles et des objets déjà connus. Cela permet alors d’appliquer tous les outils de la combinatoire analytique à ces nouveaux objets, afin d’en obtenir une énumération explicite, des propriétés asymptotiques, ou encore d’en faire la génération aléatoire. Dans cette thèse, nous nous intéresserons aux cartes planaires qui sont des graphes dessinés dans le plan sans croisement d’arêtes. Dans un premier temps, nous retrouverons une formule simple – établie par Eynard – pour la série génératrice des cartes biparties et cartes quasi-biparties avec des bords de longueurs définies, et nous en donnerons la généralisation naturelle aux p-constellations et quasi-p-constellations. Dans la seconde partie de cette thèse, nous présenterons une bijection originale pour les cartes simples – sans boucles, ni arêtes multiples – à face externe triangulaire et les triangulations eulériennes, nous permettant notamment de faire la génération aléatoire des cartes simples enracinées en contrôlant le nombre de sommets et d’arêtes. Grâce à cette bijection, nous étudierons également les propriétés métriques des cartes simples en démontrant la convergence du profil normalisé des distances vers une mesure aléatoire explicite liée au serpent brownienBijective combinatorics is a field which consists in studying the enumerative properties of some families of mathematical objects, by exhibiting bijections (ideally explicit) which preserve these properties between such families and already known objects. One can then apply any tool of analytic combinatorics to these new objets, in order to get explicit enumeration, asymptotics properties, or to perform random sampling. In this thesis, we will be interested in planar maps – graphs drawn on the plane with no crossing edges. First, we will recover a simple formula –obtained by Eynard – for the generating series of bipartite maps and quasi-bipartite maps with boundaries of prescribed lengths, and we will give anatural generalization to p-constellations and quasi-p-constellations. In the second part of this thesis, we will present an original bijection for outertriangular simple maps – with no loops nor multiple edges – and eulerian triangulations. We then use this bijection to design random samplers for rooted simple maps according to the number of vertices and edges. We will also study the metric properties of simple maps by proving the convergence of the rescaled distance-profile towards an explicit random measure related to the Brownian snake
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Sola, Alan. "Conformal Maps, Bergman Spaces, and Random Growth Models." Doctoral thesis, KTH, Matematik (Avd.), 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-12364.
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This thesis consists of an introduction and five research papers on topics related to conformal mapping, the Loewner equation and its applications, and Bergman-type spaces of holomorphic functions. The first two papers are devoted to the study of integral means of derivatives of conformal mappings. In Paper I, we present improved upper estimates of the universal means spectrum of conformal mappingsof the unit disk. These estimates rely on inequalities obtained by Hedenmalm and Shimorin using Bergman space techniques, and on computer calculations. Paper II is a survey of recent results on the universal means spectrum, with particular emphasis on Bergman spacetechniques.Paper III concerns Bergman-type spaces of holomorphic functions in subsets of $\textbf{C}^d$ and their reproducing kernel functions. By expanding the norm of a function in a Bergman space along the zero variety of a polynomial, we obtain a series expansion of reproducing kernel functions in terms of kernels associated with lower-dimensionalspaces of holomorphic functions. We show how this general approach can be used to explicitly compute kernel functions for certain weighted Bergman and Bargmann-Fock spaces defined in domains in $\textbf{C}^2$.The last two papers contribute to the theory of Loewner chains and theirapplications in the analysis of planar random growth model defined in terms of compositions of conformal maps.In Paper IV, we study Loewner chains generated by unimodular L\'evy processes.We first establish the existence of a capacity scaling limit for the associated growing hulls in terms of whole-plane Loewner chains driven by a time-reversed process. We then analyze the properties of Loewner chains associated with a class of two-parameter compound Poisson processes, and we describe the dependence of the geometric properties of the hulls on the parameters of the driving process. In Paper V, we consider a variation of the Hastings-Levitov growth model, with anisotropic growth. We again establish results concerning scaling limits, when the number of compositions increases and the basic conformal mappings tends to the identity. We show that the resulting limit sets can be associated with solutions to the Loewner equation.We also prove that, in the limit, the evolution of harmonic measure on the boundary is deterministic and is determined by the flow associated with an ordinary differential equation, and we give a description of the fluctuations around this deterministic limit flow.QC 20100414
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Al-Awfi, Saud A. Gh. "Spontaneous emission and atom dynamics in planar and cylindrical structures." Thesis, University of Essex, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.298835.
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Yatsunyk, Liliya. "Synthesis, structure, and magnetic spectroscopies of non-planar hemes as models of the cytochrome B heme centers." Diss., The University of Arizona, 2003. http://hdl.handle.net/10150/280394.
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Models of the heme b centers in the cytochrome bc₁ complex based on octaalkyltetraphenyliron(III) porphyrins (OETPP, OMTPP, and TC₆TPP) with various axial ligands (4-Me₂NPy, 4-CNPy, 1-MeIm, 2-McImH, CN- and t-BuNC) have been synthesized and explored via NMR and EPR spectroscopy and X-ray crystallography. The electron spin distributions and the electronic ground states of the complexes were determined based on the NMR and EPR results. The type of ground state of Fe(III) is defined by the number and nature of the axial ligands and peripheral substituents. Five-coordinate complexes with Cl- are high-spin (HS, S = 5/2) with ∼10% of intermediate spin (IS, S = 3/2) mixed in. Bis-(4-CNPy) porphyrins at relatively high temperatures, as well as five-coordinate perchlorates, have the IS state. Finally, six-coordinate complexes with pyridines, imidazoles, cyanides and isocyanides are all low-spin (LS, S = 1/2), with the (dxy)²(d xz,dyz)³ ground state in the case of strongly and moderately basic axial ligands, and the (dxz,dyz)⁴(dxy)¹ ground state when bound to weak sigma-donors and/or strong pi-acceptors like t-BuNC or 4-CNPy (at low temperatures only). Crystal structures of more than 15 complexes have been obtained in order to establish structure-property relationships in the systems studied. All of them adopt a saddled conformation with different degrees of ruffling and non-planarity and a wide range of dihedral angles between the axial ligands. Non-planar distortion of the macrocycle induced by the steric interaction between the peripheral substituents increases in the order TC₆TPP < OMTPP < OETPP. The rate of ring inversion of the porphyrin cores decreases in the same order, as shown by NMR spectroscopy. While all bis-ligated iron(III) porphyrinate of this study with pyridine or hindered imidazole ligands have close to perpendicular axial ligand orientations, bis-(1-MeIm) complexes have perpendicular as well as close to parallel ligand arrangements both in crystals and in solutions as observed by EPR and Mössbauer spectroscopy and X-ray crystallography. Preliminary Mössbauer studies of four of the complexes of this study have been carried out in the laboratory of Professor A. X. Trautwein, Institute of Physics, University of Lubeck, Germany. The results of the work presented in this dissertation suggest that octaalkyltetraphenylporphyrinatoiron(III) complexes are promising models for the heme b centers in the cytochrome bc₁ complex.
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Espinosa, Diego Alejandro. "Moment-dependent pseudo-rigid-body models for beam deflection and stiffness kinematics and elasticity." [Tampa, Fla] : University of South Florida, 2009. http://purl.fcla.edu/usf/dc/et/SFE0002943.
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Albert, Jacques. "Characterizations and design of planar optical waveguides and directional couplers by two-step K+ -Na+ ion-exchange in glass." Thesis, McGill University, 1987. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=75759.
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Planar optical waveguides fabricated by K$ sp+$-Na$ sp+$ ion-exchange in soda-lime glass substrates are investigated.Experimental characterizations of planar waveguide with respect to a wide range of fabrication conditions have been carried out, including detailed measurements of the refractive index anisotropy resulting from the large induced surface stresses.
Parallel to this, the non-linear diffusion process of ion-exchange was simulated numerically to provide, along with the results of the characterizations, a complete description of the refractive index profile from any set of fabrication conditions.
The magnitude of the maximum surface index change observed was shown theoretically to be almost entirely due to the induced stress at the surface of the substrate, arising from the presence of the larger potassium ions.
Finally, a novel class of single-mode channel waveguides, made by a "two-step" ion-exchange was analyzed. A simple model for these waveguides was developed and used in the design of two directional coupler structures which were fabricated and measured.
The two-step process was conceived because it relaxes waveguides' dimensional control, yielding single-mode guides of larger size, better suited for low-loss connections to optical fibers. It also provides an additional degree of freedom to adjust device properties.
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Besri, Abdelhadi. "Modélisation analytique et outils pour l'optimisation des transformateurs de puissance haute fréquence planars." Phd thesis, Université de Grenoble, 2011. http://tel.archives-ouvertes.fr/tel-00612344.
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Avec un encombrement minimal et rendement de 99% les transformateurs planars haute fréquence sont des solutions technologiques importantes pour les systèmes de conversion et de conditionnement de l'énergie électrique en électronique de puissance. L'objectif de l'étude consiste à rechercher un modèle du composant permettant à la fois de simuler son comportement dans un circuit d'électronique de puissance et d'optimiser ses performances lors de sa conception. Les modèles proposés prennent en compte les propriétés physiques et géométriques du composant. Les validations sont basées sur des confrontations avec les mesures. Une autre motivation forte de ce travail est que les modélisations numériques doivent prendre en compte simultanément les effets des courants induits et les capacités parasites, ce qui conduit, en haute fréquence, à des besoins prohibitifs en termes de capacité mémoire ou de temps de calcul. En se limitant aux transformateurs planar. La modélisation (dite LEEC) présentée ici s'appuie sur une discrétisation à échelle intermédiaire : spire par spire, c'est-à-dire couche par couche. Elle assemble deux approches analytiques déjà introduites par l'équipe : la première traite les aspects électrocinétiques (incluant les courants induits) et magnétiques et l'autre les aspects électrostatiques. Les circuits à constantes localisées basés sur la méthode LEEC montrent un très bon accord avec toutes les mesures jusqu'à 40 MHz. Des outils numériques sont aussi développés pour faciliter l'obtention de ces différents circuits en partant : soit de la description du composant, soit de mesures d'impédances. Pour compléter, la représentation des capacités d'un transformateur quelconque, développée en plusieurs étapes par l'équipe, est résumée et des précautions expérimentales originales appliquées à l'impédancemétrie sont exposées dans le détail. D'autres travaux visant à élargir le champ d'application de la méthode LEEC sont également présentés.
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Câmara, Eder Francisco. "Estudo aerodinâmico do escoamento sobre o modelo de um ônibus." Instituto Tecnológico de Aeronáutica, 1993. http://www.bd.bibl.ita.br/tde_busca/arquivo.php?codArquivo=1766.
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O objetivo deste trabalho e o estudo experimental do escoamento sobre o modelo de um ônibus, de modo a tentar compreender sua configuração e influenciar as características de sua esteira. Um modelo de madeira com arestas vivas foi então construído e acoplado a uma placa plana, também construída de madeira. Esta, alem de servir como suporte, teve a função de simular as condições do solo durante os ensaios. Definimos esta placa plana como mesa automobilística. A partir deste modelo inicial, foram realiza das varias modificações, como arredondamentos destas arestas, para se verificar o comportamento do escoamento. A fixação de dispositivos defletores de escoamento em sua superfície, teve por objetivo estudar a influencia destes na formação da esteira. Tais modificações originaram vários modelos que foram ensaiados individualmente. Estes ensaios constituiram-se da distribuição depressão em torno dos modelos, da medição da forca de arrasto utilizando uma balança eletromecânica construída para esta finalidade, e do estudo da esteira que se forma na parte trasseira, utilizando-se anemometria de fio quente. O calculo do arrasto de base também foi realizado. Como técnica de visualização foram utilizados fios de lã fixados no modelo e na mesa automobilística, bem como de um dispositivo visualizador para a esteira. Com as modificações realizadas, o arredondamento das arestas da superfície frontal proporcionou uma efetiva redução do arrasto total, enquanto que a mais efetiva na diminuição do arrasto de base, foi a instalação de duas entradas de ar, uma em cada superfície lateral. Através de ensaios realizados, propomos uma configuração de escoamento para a esteira do modelo, formada por uma região de recirculação na parte inferior da superfície traseira, seguida do encontro, a uma distancia maior desta superfície, das camadas de cisalhamento livre provenientes das superfícies laterais do modelo.
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Jan, Naeem A. "Anomalous Nature Of Metamaterial Inclusion and Compact Metamaterial-Inspired Antennas Model For Wireless Communication Systems. A Study of Anomalous Comportment of Small Metamaterial Inclusions and their Effects when Placed in the Vicinity of Antennas, and Investigation of Different Aspects of Metamaterial-Inspired Small Antenna Models." Thesis, University of Bradford, 2017. http://hdl.handle.net/10454/16003.
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Metamaterials are humanly engineered artificial electromagnetic materials which produce electromagnetic properties that are unusual, yet can be observed readily in nature. These unconventional properties are not a result of the material composition but rather of the structure formed. The objective of this thesis is to investigate and design smaller and wideband metamaterial-inspired antennas for personal communication applications, especially for WiMAX, lower band and higher band WLAN applications. These antennas have been simulated using HFSS Structure Simulator and CST Microwave Studio software. The first design to be analysed is a low-profile metamaterial-inspired CPW-Fed monopole antenna for WLAN applications. The antenna is based on a simple strip loaded with a rectangular patch incorporating a zigzag E-shape metamaterial-inspired unit cell to enable miniaturization effect. Secondly, a physically compact, CSRR loaded monopole antenna with DGS has been proposed for WiMAX/WLAN operations. The introduction of CSRR induces frequency at lower WLAN 2.45 GHz band while the DGS has provided bandwidth enhancement in WiMAX and upper WLAN frequency bands, keeping the radiation pattern stable. The next class of antenna is a compact cloud-shaped monopole antenna consisting of a staircase-shaped DGS has been proposed for UWB operation ranges from 3.1 GHz to 10.6 GHz. The novel shaped antenna along with carefully designed DGS has resulted in a positive gain throughout the operational bandwidth. Finally, a quad-band, CPW-Fed metamaterial-inspired antenna with CRLH-TL and EBG is designed for multi-band: Satellite, LTE, WiMAX and WLAN.
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Ratsakou, Almpion. "Multi-physical modeling of thermographic inspection methods and fast imaging Fast models dedicated to simulation of eddy current thermography Fast simulation approach dedicated to infrared thermographic inspection of delaminated planar pieces Model based characterisation of delamination by means of thermographic inspection." Thesis, université Paris-Saclay, 2020. http://www.theses.fr/2020UPASS002.
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L’inspection thermographique est une technique populaire de contrôle non destructif qui fournit des images de distributions de température sur de grandes étendues aux surfaces des pièces testées. Détecter les délaminations entre couches métalliques est le sujet ici. La simulation de ces inspections contribue en effet à compléter les études expérimentales, à évaluer les performances en termes de détection, et à être support d'algorithmes basés sur modèles. On se focalise sur un modèle semi-analytique basé sur un développement tronqué en fonctions propres par région. Le problème est résolu dans le domaine de Laplace en temps, et la distribution de température approximée par un développement sur une base produit tensoriel. Les sources considérées sont des lampes flash, mais aussi des sources courants de Foucault (conduisant à un couplage électromagnétisme et chaleur). La description des délaminages sous forme de minces couches d'air se révèle équivalente à l'introduction d'une résistance superficielle au flux de chaleur permettant le traitement via l'approche modale sans discrétisation supplémentaire. Des calculs complémentaires par des codes commercial (méthode des éléments finis) et interne (technique d'intégration finie) confirment l'exactitude. Puis une grande attention est donnée à l'imagerie et la détection. Une procédure en deux étapes est conçue : débruitage des signaux bruts et détection de tout éventuel défaut en utilisant une reconstruction de signal thermographique conduisant à une haute résolution spatiale et temporelle dans le plan transverse, complété par une détection de frontière, puis optimisation itérative, les résultats de la première étape étant utilisées pour la régularisation d'un schéma moindres carrés afin de caractériser épaisseurs et profondeurs. Tout ce qui précède est illustré par de nombreuses simulations numériques dans des conditions proches de l'applicationThermographic inspection is a popular nondestructive testing (NdT) technique that provides images of temperature distribution over large areas at surfaces of tested workpieces. Detecting delaminations between metallic layers is the matter here. Simulation of these inspections indeed helps to complement experimental studies, evaluate performance in terms of detection and support model-based algorithms. A semi-analytical model based on a truncated region eigenfunction expansion for simulation of thermographic inspection is focused onto. The problem is solved in the Laplace domain w.r.t time, and the temperature distribution approximated by expanding it on a tensor product basis. Considered sources are lamps providing thermal excitation but may also be eddy current sources (leading to a coupled electromagnetic and heat problem). The description of the delaminations as thin air gaps between the workpiece layers proves to be equivalent with introduction of a surface resistance to the heat flow, enabling treatment via the applied modal approach without additional discretisation. Complementary computations by industry (Finite Element Method) and in-house (Finite Integration Technique) codes confirm the accuracy of the developments. Then, much attention is put on imaging and detection. A two-step procedure is devised, first denoising of raw signals and detection of any possible defect using a thermographic signal reconstruction leading to high spatial and temporal resolution in the transverse plane, completed by proper edge detection, second an iterative optimization being employed, with results of the first step used for regularization of a least-square scheme to characterize thicknesses and depths. All the above is illustrated by comprehensive numerical simulations in conditions close to practice
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Knoesen, André. "Guided modes in anisotropic dielectric planar waveguides." Diss., Georgia Institute of Technology, 1987. http://hdl.handle.net/1853/14898.
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Leung, Yin-Ling. "Surface studies of planar model HDN catalysts." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp02/NQ34576.pdf.
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Baumgart, Tobias. "Herstellung und physikochemische Charakterisierung von planaren gestützten Lipid-Modellmembran-Systemen Preparation and physicochemical characterisation of planar supported lipid model membrane systems /." [S.l.] : [s.n.], 2001. http://ArchiMeD.uni-mainz.de/pub/2001/0123/diss.pdf.
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Santos, João Cavalcanti. "Análise numérica e experimental da influência da redundância cinemática em um manipulador paralelo planar." Universidade de São Paulo, 2017. http://www.teses.usp.br/teses/disponiveis/18/18149/tde-10112017-094950/.
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Manipuladores paralelos apresentam inércia reduzida, o que lhes permite alcançar altas acelerações e melhor eficiência energética. Porém, frequentemente seu espaço de trabalho possui desempenho pouco uniforme. De fato, a presença de singularidades paralelas é um forte limitante para essa arquitetura robótica. A redundância de atuação já é conhecida como uma alternativa para essa questão. Enquanto que a redundância cinemática ainda não possui consequências claras. Um manipulador com esse tipo de redundância apresenta um número de graus de liberdade do end-effector menor que o número de graus de liberdade do mecanismo como um todo. Considerando essa lacuna, o objetivo desse mestrado é analisar a influência da redundância cinemática no desempenho de manipuladores paralelos através de simulações e testes experimentais. Tal estudo não é trivial, uma vez que com o maior número de atuadores e graus de liberdade, é adicionada também inércia ao sistema. Foram definidas métricas para avaliar o quão favorável é uma dada posição e, com elas, estratégias de resolução de redundância foram analisadas. A estratégia principal proposta se compõe por duas etapas. No primeiro passo, é definida uma movimentação na qual a posição a cada instante é ótima segundo uma dada métrica de desempenho multiobjetivo. Isso resulta em um movimento de referência que em geral possui altas acelerações. Na segunda etapa, aplica-se uma otimização global, procurando manter um compromisso de proximidade com o movimento de referência e com os níveis de aceleração. Além deste, foram aplicados diversos métodos de otimização local (onde a cinemática inversa é resolvida para cada instante isoladamente) e uma estratégia global truncada. Essas opções foram comparadas numericamente e experimentalmente, trazendo uma resposta objetiva da influência da redundância cinemática no manipulador paralelo. A campanha experimental foi realizada em uma protótipo construído no Laboratório de Dinâmica da Escola de Engenharia de São Carlos. Esse protótipo consiste em um manipulador paralelo planar com 6 graus de liberdade, tendo assim, até 3 graus de redundância para a movimentação no plano. Têm-se 6 motores rotativos para atuá-los, sendo 3 deles acoplados a guias lineares com fusos para obtenção de atuação linear. O acionamento ou não destas guias define o grau de redundância do sistema, garantindo a versatilidade do protótipo.As a consequence of their reduced inertia, parallel manipulators present superior energetic efficiency and they are able to reach high accelerations. Nevertheless, their workspace has a poorly uniform performance. Indeed, the presence of parallel singularities is a strong limitant for this kind of robots. On the one hand, actuation redundancy is well-known as a good choice in an effort to solve this issue. On the other hand, kinematic redundancy still have unclear consequences on this matter. A kinematically redundant manipulator presents an end-effector with fewer degrees of freedom than the mechanism as a whole. Considering this gap, the objective of this research is to analyze the influence of kinematic redundancy on the performance of parallel manipulators through simulations and experimental tests. This issue turns out to be complex, once traveling actuators sum additional inertia to the system. Metrics are defined in order to evaluate how favourable is a given position, and redundancy resolution strategies are analyzed using them. The main proposed strategy is composed of two steps. In the first one, a movement is defined so that the position for each instant is optimum for a given multiobjective performance metric. This procedure delivers a refererence movement which generally presents high accelerations. On the second step, a global optimization is applied, seeking for a trade-off between the proximity to the reference and the acceleration levels. In addition, several local methods (which resolve the inverse kinematics for each instant independently) and one truncated global strategy were addressed. These configurations were compared numerically and experimentally, delivering a objective analysis of the influence of kinematic redundancy on the performance of the parallel manipulator. The experimental campaign was executed with a physical prototype built at the São Carlos School of Engineering. This is a planar manipulator with 6 degrees of freedom, consequently presenting up to 3 degrees of redundancy. The mechanism is actuated by 6 rotating motors, of which 3 are coupled to leadscrews, resulting in linear actuators. These leadscrews can be locked, defining different degrees of redundancy and granting the versatility of the prototype.
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Hall, Ian Melvyn. "Quasi-modes and the evolution of coherent planar vortices." Thesis, University of Exeter, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.269719.
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Zhu, Ning. "Planar metallization failure modes in integrated power electtonics modules." Diss., Virginia Tech, 2006. http://hdl.handle.net/10919/27530.
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Miniaturizing circuit size and increasing power density are the latest trends in modern power electronics development. In order to meet the requirements of higher frequency and higher power density in power electronics applications, planar interconnections are utilized to achieve a higher integration level. Power switching devices, passive power components, and EMI (Electromagnetic Interference) filters can all be integrated into planar power modules by using planar metallization, which is a technology involving electrical, mechanical, material, and thermal issues. By processing high dielectric materials, magnetic materials, or silicon chips using compatible manufacturing procedures, and by carefully designing structures and interconnections, we can realize the conventional discrete inductors, capacitors, and switch circuits with planar modules. Compared with conventional discrete components, the integrated planar modules have several advantages including lower profiles, better form factors, and less labor-intensive processing steps. In addition, planar interconnections reduce the wire bond inductive and resistive parasitic parameters, especially for high frequency applications.
However, planar integration technology is a packaging approach with a large contact area between different materials. This may result in unknown failure mechanisms in power applications. Extensive research has already been done to study the performance, processing, and reliability of the planar interconnects in thin film structures. The thickness of the thin films used in integrated circuits (IC) or microelectronics applications ranges from the magnitude of nanometers to that of micrometers. In this work, we are interested in adopting planar interconnections to Integrated Power Electronics Modules (IPEM). In Integrated Power Electronics Modules (IPEMs), copper traces, especially bus traces, need to conduct current ranging from a few amps to tens of amps. One of the major differences between IC and IPEM is that the metal layer in IPEMs (normally >75µm) is much thicker than that of the thin films in IC (normally <1µm). The other major difference, which is also a feature of IPEM, is that the planar metallization is deposited on different brittle substrates. In active IPEM, switching devices are in a bare die form with no encapsulation. The copper deposition is on top of the silicon chips and the insulation polyimide layer. One of the key elements for passive IPEM and the EMI IPEM is the integrated inductor-capacitor (LC) module, which realizes equivalent inductors and capacitors in one single module. The deposition processes for silicon substrates and ceramic substrates are compatible and both the silicon and ceramic materials are brittle. Under high current and high temperature conditions, these copper depositions on brittle materials will cause detrimental failure spots.
Over the last few years, the design, manufacture, optimization, and testing of the IPEMs has been developed and well documented. Up to this time , the research on failure mechanisms of conventional integrated power modules has led to the understanding of failures centered on wire bond or solder layer. However, investigation on the reliability and failure modes of IPEM is lacking, particularly that which uses metallization on brittle substrates for high current operations. In this study, we conduct experiments to measure and calculate the residual stresses induced during the process. We also, theoretically model and simulate the thermo-mechanical stresses caused by the mismatch of thermal expansion coefficients between different materials in the integrated power modules. In order to verify the simulation results, the integrated power modules are manufactured and subjected to the lifetime tests, in which both power cycling and temperature cycling tests are carried out. The failure mode analysis indicates that there are different failure modes for copper films under tensile or compressive stresses. The failure detection process verifies that delamination and silicon cracks happen to copper films due to compressive and tensile stresses respectively.
This study confirms that the high stresses between the metallization and the silicon are the failure drivers in integrated power electronics modules.. We also discuss the driving forces behind several different failure modes. Further understanding of thesefailure mechanisms enables the failure modes to be engineered for safer electrical operation of IPEM modules and helps to enhance the reliability of system-level operation. It is also the basis to improve the design and to optimize the process parameters so that IPEM modules can have a high resistance to recognized failures.Ph. D.
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Araújo, Manoel Silvino Batalha de. "Extensão de GENSMAC para escoamentos de fluidos governados pelos modelos integrais Maxwell e K-BKZ." Universidade de São Paulo, 2006. http://www.teses.usp.br/teses/disponiveis/55/55134/tde-08022007-151417/.
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Este trabalho tem como objetivo desenvolver um método numérico para simular escoamentos incompressíveis, isotérmicos, confinados ou com superfícies livres, de fuidos viscoelásticos governados pelos modelos integrais de Maxwell e K-BKZ (Kaye-Bernstein, Kearsley e Zapas). A técnica numérica apresentada é uma extensão do método GENSMAC (Tomé McKee - J. Comp. Phys., (110), pp 171--186, 1994 ) para a solução das equações de conservação, juntamente com as equações constitutivas integrais de Maxwell e K-BKZ. As equações governantes são resolvidas pelo método de diferenças finitas em uma malha deslocada. O tensor de Finger, B_t\'(t) é calculado com base nas idéias do método de campos de deformação (Peters et al. - J. Non-Newtonian Fluid Mech. (89), de maneira que não há a necessidade de seguir a trajetória da partícula de fuido para descrever a história de deformação da partícula. Uma abordagem diferente para a discretização do instante passado é utilizada e o tensor de Finger e o tensor das tensões são calculados utilizando um método de segunda ordem. A validação do método numérico descrito nesse trabalho foi feita utilizando o escoamento em um canal bidimensional e a solução numérica obtida para a velocidade e para as componentes de tensão com o modelo de Maxwell foram comparadas com as respectivas soluções analíticas no estado estacionário, mostrando excelente concordância. Os resultados numéricos para a simulação do escoamento em uma contração planar 4 : 1 mostraram bons resultados, tanto qualitativos quanto quantitativos, quando comparados com os resultados experimentais de Quinzani et al. ( J. Non-Newtonian Fluid Mech. (52), pp 1?36, 1994 ). Além disso, utilizando os modelos Maxwel e K-BKZ, o escoamento em uma contração planar 4 : 1 foi simulado para vários números de Weissenberg e os resultados obtidos estão de acordo com os encontrados na literatura. Resultados numéricos de escoamentos com superfícies livres modelados pelas equações integrais de Maxwell e K-BKZ são apresentados. Em particular, a simulação numérica do jato oscilante para diferentes números de Weissenberg e diferentes números de Reynolds é apresentada.The aim of this work is to develop a numerical technique for simulating incompressible, isothermal, free surface (also con¯ned) viscoelastic flows of fuids governed by the integral models of Maxwell and K-BKZ (Kaye-Bernstein, Kearsley and Zapas). The numerical technique described herein is an extension of the GENSMAC method (Tome and McKee, J. Comput. Phys., 110, pp. 171-186, 1994) to the solution of the momentuum and mass conservation equations together with the integral constitutive Maxwell and K-BKZ equations. The governing equations are solved by the finite difference method on a staggered grid using a Marker-and-Cell approach. The fluid is represented by marker particles on the fluid surface only. This provides the visualization and location of the fluid free surface so that the free surface stress conditions can be applied. The Finger tensor Bt0(t) is computed using the ideias of the deformation fields method (Peters et al. J. Non-Newtonian Fluid Mech., 89, pp. 209-228, 2001) so that it is not necessary to track a fluid particle in order to calculate its deformation history. However, in this work modifcations to the deformation fields method are introduced: the past time is discretized using a different formula, the Finger tensor Bt0(x; t) is obtained by a second order method and the stress tensor ? (x; t) is computed by a second order quadrature formula. The numerical method presented in this work is validated by simulating the flow of a Maxwell fluid in a two-dimensional channel and the numerical solutions of the velocity and the stress components are compared with the respective analytic solutions providing a good agreement. Further, the flow through a 4:1 planar contraction of a specific fuid studied experimentally by Quinzani et al. (J. Non-Newtonian Fluid Mech., 52, pp. 1-36, 1994) was simulated and the numerical results were compared qualitatively and quantitatively with the experimental results and very good agreement was obtained. The Maxwell and the K-BKZ models were applied to simulate the 4:1 planar contraction problem using various Weissenberg numbers and the numerical results were in agreement with those published in the literature. Finally, numerical results of free surface flows using the Maxwell and K-BKZ integral constitutive equations are presented. In particular, the numerical simulation of jet buckling using several Weissenberg numbers and various Reynolds numbers are presented
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Ball, Eddie H. "Virtual Planar Motion Mechanism Testing of 8:1 Spheroids." Thesis, Virginia Tech, 2015. http://hdl.handle.net/10919/53515.
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PMM testing is a method used to identify the added mass and damping coefficients used in the equations of motion of a vehicle by attempting to decouple the forces on a body due to velocity and acceleration as a result of creating "hydrodynamically pure" velocities and accelerations. This makes it possible to use quasi-steady state models with terms independent of both velocity and acceleration. This paper explores the ability of simple damping models (solely a function of velocity) with added mass terms (solely a function of acceleration) to simulate the heave force of an 8:1 ellipsoid undergoing PMM testing. In order to help explain the complexity of the flow during PMM tests, a flow analysis of the 8:1 spheroid is provided, which discusses the flow topology of spheroids at steady angle of attack, validity of quasi-steady models, and some other basic flow features seen in PMM testing.
In this paper, a simple proportionality relationship between a linear and quadratic damping model is revealed. It is also shown that variations in the heave force response during PMM tests are most heavily influenced by viscous effects, especially cross flow separation. Finally, it is shown where these models break down, owing to the increasing nonlinearity of the flow induced by the harsher motions of large amplitude and/or large frequency tests.Master of Science
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MOREIRA, Roemir Pereira Machado. "Aspectos de teorias planares com violação da simetria de Lorentz." Universidade Federal do Maranhão, 2011. http://tedebc.ufma.br:8080/jspui/handle/tede/1859.
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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
The gauge sector of the Standard Model Extended (MPE) has been investigated in many respects in recent years, discussing the effects of Lorentz symmetry violation in physical systems and the limitations on the magnitude of the parameters of violation. This work revisited some planar theories derived from the dimensional reduction of the gauge sector of the MPE, and perform an original contribution: the dimensional reduction of the CPT-even and nonbirefringent gauge sector of the MPE, composed of nine components. The resulting planar theory includes a gauge sector and scalar sector (which has an nonsual kinetic term), coupled together by a 3-vector Cα Lorentz violation. Both sectors, gauge and scale, are affected by the six components of a symmetric tensor violates Lorentz, kµρ. The energy-momentum tensor is explicitly calculated, revealing that the energy of the gauge and scalar sectors is stable for small values of the parameters of violation. The equations of motion for the electric and magnetic elds, as well as the potentials, are written and analyzed in the steady state. Then employ the method of Green to get the stationary solutions of classical electrodynamics to rst order in the parameters of violation. It is observed that the coe cients of Lorentz violation does not alter the asymptotic behavior of the elds, but does not induce an angular dependence observed in the planar theory of Maxwell. The dispersion relation is exactly computed and is compatible with a theory does not birefringent, and demonstrating that the theory is stable, but in general, not causal. Finally, we calculate the Feynman propagator for the gauge elds and scalar theory of planar, accurately, using a set of 11 projectors that form a closed algebra. We use the expression of the Feynman propagator to analyze the consistency of the theory regarding its stability, causality and unitarity.
O setor de gauge do Modelo Padrão Estendido (MPE) tem sido investigado em muitos aspectos nos últimos anos, discutindo os efeitos da violação da simetria de Lorentz em sistemas físicos e as limitações da magnitude dos parâmetros de violação. Neste trabalho, rediscutimos algumas teorias planares obtidas a partir da redução dimensional do setor de gauge do MPE, e realizamos uma contribuição original: a redução dimensional do setor de gauge CPT-par e não-birrefringente do MPE, composto por nove componentes. A resultante teoria planar abarca um setor de gauge e um setor escalar (dotado de um termo cinético não usual), acoplados entre si por um 3-vetor Cα de violação de Lorentz (LV). Ambos os setores, de gauge e escalar, são afetados pelas seis componentes de um tensor simétrico violador de Lorentz, kµρ. O tensor de energia-momento É explicitamente calculado, revelando que a energia dos setores de gauge e escalar são estáveis para pequenos valores dos parâmetros de violação. As equações de movimento para os campos elétrico e magnético, assim como para os potenciais, são escritas e analisadas no regime estacionário. Empregamos então o método de Green para obter as soluções clássicas estacionárias desta eletrodinâmica em primeira ordem nos parâmetros de violação. É observado que os coefi cientes de violação de Lorentz não alteram o comportamento assintótico dos campos, mas induzem uma dependência angular não observada na teoria planar de Maxwell. A relação de dispersão é exatamente computada, sendo compatível com uma teoria não birrefringente, e demonstrando que a teoria é estável, mas, em geral, não causal. Por fim, calculamos o propagador de Feynman para os campos de gauge e escalar desta teoria planar, de forma exata, usando um conjunto de 11 projetores que formam uma álgebra fechada. Usamos a expressão do propagador de Feynman para analisar a consistência da teoria no que concerne a sua estabilidade, causalidade e unitariedade.
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Grande, Helder Luciani Casa. "Modelos de dímeros em redes planas. Matriz de transferência e soluções por meio da representação de férmions." Universidade de São Paulo, 2009. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-12052009-100334/.
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Resolvemos o modelo de d´meros em duas redes planas diferentes, a rede 4-8 e a rede hexagonal (favo de mel). Na rede 4-8 ocorre uma transição do tipo Ising (bidimensional); na rede hexagonal há uma transição conhecida como 3/2. Após a definição do modelo mostramos que o cálculo da função de partição pode ser formulado em termos do traço de uma matriz de transferência escrita numa representação de matrizes de Pauli. Usando a transformação de Jordan-Wigner, os operadores de Pauli são transformados em operadores de criação e aniquilação de férmions, e a matriz de transferência pode ser diagonalizada pela redução a um problema de férmions livres. Comparamos as soluções do modelo de dímeros na rede 4-8 e do modelo de Ising bidimensional; em particular, comparamos o comportamento do calor específico e analisamos o espectro da matriz de transferência. Verificamos que as nossas soluções concordam com resultados obtidos pelas técnicas combinatórias. Utilizamos a formulação da matriz de transferência para construir uma versão de tempo contínuo dos modelos de dímeros nas redes quadrada, 4-8 e hexagonal. Ao contrário do modelo de Ising, no caso dos dímeros essa aproximação de tempo contínuo altera a natureza do comportamento crítico.We solve the dimer model on two different planar lattices, the 4-8 lattice and the honeycomb lattice. In the dimer model on the 4-8 lattice there is a phase transition of the (two-dimensional) Ising type; on the honeycomb lattice there is a phase transition known as 3/2. After defining the model we show that the calculation of the partition function can be formulated as the trace of a transfer matrix that is written in terms of Pauli matrices. Using the Jordan-Wigner transformation, the Pauli matrices give rise to fermion creation and annihilation operators, and the problem is reduced to the diagonalization of a system of free fermions. We compare the solutions of the dimer model on the 4-8 lattice and of the two-dimensional Ising model; in particular, we compare the behavior of the specific heat and we analyze the spectrum of the transfer matrix. These solutions agree with well-known results from combinatorial techniques. We then use the transfer matrix approach to obtain a continuum time formulation for the dimer models on the square, 4-8 an d honeycomb lattices. In contrast to the Ising case, for the dimer models this approximation changes the nature of critical behavior.
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Emir-Farinas, Hulya. "Aggregation of demand points for the planar covering location model." [Gainesville, Fla.]: University of Florida, 2002. http://purl.fcla.edu/fcla/etd/UFE0000530.
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Dumbuya, Karifala. "Synthesis and characterisation of planar model catalysts for Olefin metathesis." [S.l.] : [s.n.], 2005. http://www.diss.fu-berlin.de/2005/324/index.html.
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Bowen, Adam Mark Alexander. "Video Based Rendering and Coding using a Planar Patch Model." Thesis, University of Warwick, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.504799.
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Free viewpoint video is a rapidly evolving field with many challenging problems. The work in this thesis focuses on a number of these problems, from capture through to reconstruction, and aims to resolve them in a common 'patch based' framework. The patch based representation models scenes as a collection of disjoint, planar surface elements. This approach offers the advantages of continuous representations, such as geometric meshes, for reconstruction, and those of discontinuous representations, such as dense-depth maps, for tracking. Much like point based representations of geometry, patch based representations contain a large number of elements. In order to track and process such representations it is desirable to be able to model these data hierarchically. To this end, a novel bottom-up process is introduced for -modelling arbitrary objects as a hierarchical mixture of Gaussian densities. The approach is contrasted with some existing general purpose methods, and found to be superior for hierarchical object modelling. A reconstruction algorithm is introduced for computing high quality synthesised views from patch based representations. The proposed algorithm employs a local visual hull to overcome problems in representing object edges using patches. The results are examined over a variety of sequences, captured under a variety of scenarios. Quantitative analysis suggests the algorithm significantly outperforms simple approaches and is comparable with recently published approaches. In addition, a simple extension to MPEG-2 for the compression of multiview sequences is introduced and contrasted with state-of-the-art approaches. Although not competitive with approaches based upon H.264, the proposed method has the advantage of simplicity in implementation and execution. This is important when dealing with the substantial volumes of data present in multiview video sequences. Keywords: Image Based Rendering, Free Viewpoint Video, Hierarchical Clustering, Multiresolution Gaussian Mixture, Patch Based Representations.
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Joshi, Atul Ravindra. "Design and control of a three degree-of-freedom planar parallel robot." Ohio : Ohio University, 2003. http://www.ohiolink.edu/etd/view.cgi?ohiou1175180058.
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Jakel, Roland. "Analysis of Hyperelastic Materials with Mechanica - Theory and Application Examples." Universitätsbibliothek Chemnitz, 2010. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-201000705.
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Part 1: Theoretic background information - Review of Hooke’s law for linear elastic materials - The strain energy density of linear elastic materials - Hyperelastic material - Material laws for hyperelastic materials - About selecting the material model and performing tests - Implementation of hyperelastic material laws in Mechanica - Defining hyperelastic material parameters in Mechanica - Test set-ups and specimen shapes of the supported material tests - The uniaxial compression test - Stress and strain definitions in the Mechanica LDA analysis Part 2: Application examples - A test specimen subjected to uniaxial loading - A volumetric compression test - A planar test - Influence of the material law Appendix - PTC Simulation Services Introduction - Dictionary Technical English-GermanTeil 1: Theoretische Hintergrundinformation - Das Hookesche Gesetz für linear-elastische Werkstoffe - Die Dehnungsenergiedichte für linear-elastische Materialien - Hyperelastisches Material - Materialgesetze für Hyperelastizität - Auswählen des Materialgesetzes und Testdurchführung - Implementierung der hyperelastischen Materialgesetze in Mechanica - Definieren der hyperelastischen Materialparameter in Mechanica - Testaufbauten und Prüfkörper der unterstützten Materialtests - Der einachsige Druckversuch - Spannungs- und Dehnungsdefinition in der Mechanica-Analyse mit großen Verformungen Teil 2: Anwendungsbeispiele - Ein einachsig beanspruchter Prüfkörper - Ein volumetrischer Drucktest - Ein planarer Test - Einfluss des Materialgesetzes Anhang: - Kurzvorstellung der PTC Simulationsdienstleistungen - Wörterbuch technisches Englisch-Deutsch
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Peterson, Keith A. "An experimental approach for studying creep behavior of model planar interfaces." Thesis, Monterey, California. Naval Postgraduate School, 2000. http://hdl.handle.net/10945/7693.
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Approved for public release; distribution is unlimitedAn apparatus for measuring the steady state creep behavior of interfaces in aluminum-silicon-aluminum multilayered specimens has been assembled. In the experiment scheme, a double-shear specimen geometry was used to load the interfaces in a state of nominally constant shear. The deformation kinetics for interfacial sliding during constant shear stress creep experiments were measured for various applied interfacial shear Stress levels and temperatures. Interfacial shear strain rates were measured using displacement and capacitance gauges. The planar interfaces between the aluminum and silicon layers were prepared by diffusion bonding. Preliminary results indicate that that interfacial sliding occurs via time-dependent relaxation mechanisms and that there is a threshold stress for interfacial sliding, in agreement with previous work on lead-Quartz and lead- nickel interfaces
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Lemme, Brian D. "Non-planar silicon oxidation : an extension of the Deal-Grove model." Manhattan, Kan. : Kansas State University, 2009. http://hdl.handle.net/2097/1394.
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Brown, Matthew Lee. "Dynamics of Rigid Fibers in a Planar Converging Channel." Diss., Georgia Institute of Technology, 2005. http://hdl.handle.net/1853/6894.
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The influence of turbulence on the orientation state of a dilute suspension of stiff fibers at high Reynolds number in a planar contraction is investigated. High speed imaging and
LDV techniques are used to quantify fiber orientation distribution
and turbulent characteristics. A nearly homogenous, isotropic grid
generated turbulent flow is introduced at the contraction inlet.
Flow Reynolds number and inlet turbulent characteristics are
varied in order to determine their effects on orientation
distribution. The orientation anisotropy is shown to be accurately
modelled by a Fokker-Planck type equation. Results show that
rotational diffusion is highly influenced by inlet turbulent
characteristics and decays exponentially with convergence ratio.
Furthermore, the effect of turbulent energy production in the
contraction is shown to be negligible. Also, the results show
that the flow Reynolds number has negligible effect on the
development of orientation anisotropy, and the influence of
turbulence on fiber rotation is negligible for $mathrm{Pe_r}>$
10. It was concluded that inertia induced fiber motion played a
negligible role in the experiments.
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Sousa, Welington Fernandes de. "A geometria analítica como um modelo para a geometria euclidiana." reponame:Repositório Institucional da UnB, 2017. http://repositorio.unb.br/handle/10482/31974.
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Dissertação (mestrado)—Universidade de Brasília, Instituto de Ciências Exatas, Departamento de Matemática, Programa de Mestrado Profissional em Matemática em Rede Nacional, 2017.Submitted by Raquel Almeida (raquel.df13@gmail.com) on 2017-11-07T16:23:55Z No. of bitstreams: 1 2017_VitorSoaresRabeloAdriano.pdf: 10962275 bytes, checksum: c8cb507a31646087a77dfce259e055db (MD5)
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Este trabalho mostra, com ênfase na geometria plana, o modelo dedutivo formulado por Euclides de Alexandria pelo qual ele constrói e organiza todo o conhecimento geométrico conhecido até então. Este modelo euclidiano, chamado axiomático, com o passar dos anos revelou falhas em demonstrações de algumas proposições que são citadas e comentadas neste trabalho. As tentativas para corrigir as falhas e formalizar o modelo axiomático de Euclides, levou a um novo modelo axiomático mais formal, que corrige as falhas cometidas por Euclides e traz uma linguagem mais coerente com a proposta da matemática moderna. Tal modelo foi publicado por David Hilbert em seu trabalho Grundlagen der Geometrie, e também está presente neste trabalho. Após mostrar como a geometria euclidiana plana foi formulada em função de seus axiomas, o trabalho chega ao seu ponto principal: mostrar que a geometria euclidiana plana pode ser demonstrada na geometria sobre corpos (geometria analítica). E para isso, este trabalho disponibiliza a demonstração de todos os axiomas de Hilbert, para a geometria euclidiana plana, em um plano cartesiano sobre um corpo. Veremos que não haverá necessidade de trabalharmos sobre o corpo dos números reais para que esta geometria euclidiana plana seja demonstrada pela geometria analítica. Além disso o trabalho traz um pouco das características e propriedades de corpos e suas extensões à medida que as demonstrações se aprofundam. Chegaremos à conclusão de que todos os axiomas da geometria euclidiana plana podem ser demonstrados na geometria analítica, sobre um corpo ordenado com extensão às raízes quadradas de elementos positivos.
This work shows, with emphasis on plane geometry, the deductive model formulated by Euclid of Alexandria by which he constructed and organized all known geometric knowledge until then. This Euclidean model, called axiomatic, over the years revealed aws in demonstrations of some propositions that are cited and commented on in this work. The attempts to correct the failures and formalizing the axiomatic model of Euclid led to a new more formal axiomatic model that corrects Euclid's failures which is more and uses a language more consistent to proposal of modern mathematics. Such a model was published by David Hilbert in his work Grundlagen der Geometrie, and is also present in this work. After showing how Euclidean geometry is formulated in terms of its axioms, the work reaches its main point: to show that Euclidean plane geometry can be demonstrated in geometry over elds (analytic geometry). And for this, we provide the demonstration of all axioms of Hilbert, for Euclidean plane geometry, in a Cartesian plane over a eld. We will see that there will be no need to work on the eld of real numbers for this Euclidean plane geometry to be demonstrated by analytic geometry. In addition the work brings some of the characteristics and properties of elds and their extensions as the demonstrations deepen. We will arrive at the conclusion that all the axioms of Euclidean plane geometry can be demonstrated in analytical geometry, on an ordered eld with extension to the square roots of positive elements.
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關福延 and Folk-year Kwan. "An intelligent approach to automatic medical model reconstruction fromserial planar CT images." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2002. http://hub.hku.hk/bib/B31243216.
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Luttrell, Timothy. "Photocatalysis and Grazing-Ion Beam Surface Modifications of Planar TiO2 Model Systems." Scholar Commons, 2014. https://scholarcommons.usf.edu/etd/5064.
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This dissertation is related to the understanding of catalytic reactions of metal oxides. For several decades, the surfaces and bulk of materials have been probed to determine additional properties that relate to photocatalytic applications. This investigation furthers these efforts by the (a) modification of a metal oxide surface to isolate known influences of chemical properties and (b) proposing and utilizing a novel methodology for attribution of photocatalytic activity to a discernable influence. For the first effort, by effectively utilizing a known technique for a new application on a metal oxide, such isolations can be made despite unfavorable states. For the second effort, a reduction in the influence of surface states for metal oxides is effectively performed, providing the isolation of influences originating from the bulk. The challenge with such a proposal is verifying such bulk states have been adequately isolated as external influences would obviously distort any conclusions. Thus, techniques to both create such bulk states and eliminate unwanted combinations thereof are additionally required and must be provided for. Lastly, a determination of the photocatalytic activity is made to these states and results are provided.
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Iqbal, Kamran. "Stability and control in a planar neuro-musculo-skeletal model with latencies /." The Ohio State University, 1992. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487780393265452.
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Lang, Cheng-Lien. "Existence and stability of a planar wave solution to a combustion model /." The Ohio State University, 1992. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487780393266681.
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Elmegri, Fauzi O. M. "Model and design of small compact dielectric resonator and printed antennas for wireless communications applications : model and simulation of dialectric resonator (DR) and printed antennas for wireless applications : investigations of dual band and wideband responses including antenna radiation performance and antenna design optimization using parametric studies." Thesis, University of Bradford, 2015. http://hdl.handle.net/10454/14742.
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Dielectric resonator antenna (DRA) technologies are applicable to a wide variety of mobile wireless communication systems. The principal energy loss mechanism for this type of antenna is the dielectric loss, and then using modern ceramic materials, this may be very low. These antennas are typically of small size, with a high radiation efficiency, often above 95%; they deliver wide bandwidths, and possess a high power handling capability. The principal objectives of this thesis are to investigate and design DRA for low profile personal and nomadic communications applications for a wide variety of spectrum requirements: including DCS, PCS, UMTS, WLAN, UWB applications. X-band and part of Ku band applications are also considered. General and specific techniques for bandwidth expansion, diversity performance and balanced operation have been investigated through detailed simulation models, and physical prototyping. The first major design to be realized is a new broadband DRA operating from 1.15GHz to 6GHz, which has the potential to cover most of the existing mobile service bands. This antenna design employs a printed crescent shaped monopole, and a defected cylindrical DRA. The broad impedance bandwidth of this antenna is achieved by loading the crescent shaped radiator of the monopole with a ceramic material with a permittivity of 81. The antenna volume is 57.0 37.5 5.8 mm3, which in conjunction with the general performance parameters makes this antenna a potential candidate for mobile handset applications. The next class of antenna to be discussed is a novel offset slot-fed broadband DRA assembly. The optimised structure consists of two asymmetrically located cylindrical DRA, with a rectangular slot feed mechanism. Initially, designed for the frequency range from 9GHz to 12GHz, it was found that further spectral improvements were possible, leading to coverage from 8.5GHz to 17GHz. Finally, a new low cost dual-segmented S-slot coupled dielectric resonator antenna design is proposed for wideband applications in the X-band region, covering 7.66GHz to 11.2GHz bandwidth. The effective antenna volume is 30.0 x 25.0 x 0.8 mm3. The DR segments may be located on the same side, or on opposite sides, of the substrate. The end of these configurations results in an improved diversity performance.
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Elmegri, Fauzi. "Model and design of small compact dielectric resonator and printed antennas for wireless communications applications. Model and simulation of dialectric resonator (DR) and printed antennas for wireless applications; investigations of dual band and wideband responses including antenna radiation performance and antenna design optimization using parametric studies." Thesis, University of Bradford, 2015. http://hdl.handle.net/10454/14742.
Full textAbstract:
Dielectric resonator antenna (DRA) technologies are applicable to a wide variety of
mobile wireless communication systems. The principal energy loss mechanism for this
type of antenna is the dielectric loss, and then using modern ceramic materials, this
may be very low. These antennas are typically of small size, with a high radiation
efficiency, often above 95%; they deliver wide bandwidths, and possess a high power
handling capability.
The principal objectives of this thesis are to investigate and design DRA for low profile
personal and nomadic communications applications for a wide variety of spectrum
requirements: including DCS, PCS, UMTS, WLAN, UWB applications. X-band and part
of Ku band applications are also considered. General and specific techniques for
bandwidth expansion, diversity performance and balanced operation have been
investigated through detailed simulation models, and physical prototyping.
The first major design to be realized is a new broadband DRA operating from 1.15GHz
to 6GHz, which has the potential to cover most of the existing mobile service bands.
This antenna design employs a printed crescent shaped monopole, and a defected
cylindrical DRA. The broad impedance bandwidth of this antenna is achieved by
loading the crescent shaped radiator of the monopole with a ceramic material with a
permittivity of 81. The antenna volume is 57.0 37.5 5.8 mm3, which in conjunction
with the general performance parameters makes this antenna a potential candidate for
mobile handset applications.
The next class of antenna to be discussed is a novel offset slot-fed broadband DRA
assembly. The optimised structure consists of two asymmetrically located cylindrical
DRA, with a rectangular slot feed mechanism. Initially, designed for the frequency
range from 9GHz to 12GHz, it was found that further spectral improvements were
possible, leading to coverage from 8.5GHz to 17GHz.
Finally, a new low cost dual-segmented S-slot coupled dielectric resonator antenna
design is proposed for wideband applications in the X-band region, covering 7.66GHz
to 11.2GHz bandwidth. The effective antenna volume is 30.0 x 25.0 x 0.8 mm3. The DR
segments may be located on the same side, or on opposite sides, of the substrate. The
end of these configurations results in an improved diversity performance.General Secretariat of Education and Scientific Research Libya
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Rabelo, Nilson Rafael. "Spectral fields in planar multilayered structures excited by embedded sources." Instituto Tecnológico de Aeronáutica, 2015. http://www.bd.bibl.ita.br/tde_busca/arquivo.php?codArquivo=3391.
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This thesis picks up from the full-wave spectral-domain formalism developed at ITA's Antenna and Propagation Laboratory (LAP) for the analysis of electromagnetic radiation, scattering and propagation in structures composed of multiple layers made up of complex media. Besides the analysis and design of planar, cylindrical and spherical microstrip antennas, the methodology has also been successfully extended to remote sensing applications. Either way, a representative model needs to account for the geometric and electromagnetic characteristics of the particular structure, and for the electromagnetic excitation mechanism. Nonetheless, the focus so far had been on applications whose sources were distributed along the layer interfaces. So the goal in Chapters 2 and 3 is to extend the model coverage to vertical electric and magnetic sources embedded in planar structures made up of isotropic dielectric layers. Their spectral Green's functions are calculated using the auxiliary vector potential approach. In addition, horizontal electrical and magnetic sources are analyzed using LAP's technique, thus providing a consistent formalism to handle any combination. The limit case of infinitesimal current elements is derived, as well as that of a dipole holding a sinusoidal current distribution. Careful analysis of the boundary conditions affecting the tangential field components produces two uncoupled systems, one on the spectral electric field amplitudes, and another on the magnetic field, cutting down the mathematical workload and processing time. Hybrid microstrip antennas provide interesting means to overcome conventional antenna drawbacks, such as the significant H-plane cross-polarization level. Probe-fed hybrid microstrip antennas are analyzed in Chapter 4 via the resonant cavity and surface electric current models. The primary goal of systematically determining adequate design criteria is achieved and proved by predesigning an antenna for operation in 2.45 GHz. The design criteria are also validated by excellent experimental results for an antenna prototype that was manufactured and tested. As a side benefit, the use of analytical models permits the analysis of effects such as a radiation pattern asymmetry in the E plane, and a systematic study of its cross-polarization. Stratified layered structures containing scattering elements are used for modeling distributed natural targets. Their electromagnetic properties can be synthesized by the scattering matrix, which describes the dependence on signal polarization. From the scattering matrix, mathematical models for natural targets and other polarimetric target descriptors can be derived. Chiral effects and the stratified layer representation for certain natural targets are accounted for in the analysis presented in Chapter 5.From the target modeling, the scattering matrix elements are determined for planar, thin electric and magnetic dipoles embedded in a three-layer planar structure consisting of a chiral layer between free space and an isotropic ground. In addition, the full-wave equivalent circuit technique was efficiently utilized in the determination of the Green's functions of stratified structures.
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Castro, Davi Rogério da Silva. "Optimization models for allocation of air strike assets with persistence /." Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2002. http://library.nps.navy.mil/uhtbin/hyperion-image/02Dec%5FCastro.pdf.
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Thesis (M.S. in Operations Research)--Naval Postgraduate School, December 2002.Thesis advisor(s): Richard E. Rosenthal, R. Kevin Wood. Includes bibliographical references (p. 53-56). Also available online.
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Cadorin, Jair Libero. "Estudo de diagramas de fases de alguns variantes do modelo ANNNI e de um modelo planar clássico helicoidal." Universidade de São Paulo, 1993. http://www.teses.usp.br/teses/disponiveis/43/43133/tde-26022014-145535/.
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Nesse trabalho estudamos dois tipos de modelos para a descrição dos sistemas magnéticos modulados. O primeiro é o modelo ANNNI (\"Axial Next-Nearest-Neighbor Ising\"). Dentro dos limites da aproximação de campo médio estudamos vários efeitos que surgem quando as interações intraplanares são menores que as interações interplanares. Investigamos em particular a ocorrência de fases desordenadas, assim denominadas por apresentar planos com magnetização nula. Estudamos ainda o comportamento dos pontos de acumulação de pontos de ramificação que determinam o limite entre as transições do tipo comensurável-comensurável e comensurável-incomensurável. Também investigamos dois variantes do modelo ANNNI, um com spin qualquer e outro com spin 1 e anisotropia de campo cristalino. O segundo tipo de modelo estudado, apropriado para sistemas apresentando modulações helicoidais das magnetizações, é um modelo planar clássico com interações competitivas entre primeiros e segundos vizinhos numa direção axial. Restringimos o nosso estudo ao zero absoluto de temperatura. Fizemos expansões das magnetizações em série de Fourier para campos baixos e altos. Também fizemos análise de estabilidade das fases comensuráveis, dentro de uma aproximação contínua, utilizando a teoria dos sólitons. Finalmente, estudamos numericamente o diagrama de fases do modelo aplicando o método dos potenciais efetivos.In this work we have studied two types of models for the description of modulated magnetic systems. The first is the ANNNI (Axial NextNearest-Neighbor Ising) model. Within the mean-field approximation we have studied various effects which comes about when the intralayer interactions are weaker than the interlayer interactions. We have investigated in particular the possibility of partially disordered phases, characterized by the presence of layers with zero magnetization. We also have studied the behavior of the accumulation points of the branching points, which separates the commensurate-commensurate transitions from the commensurate-incommensurate transitions. We have also investigated two variants of the ANNNI model, one with an arbitrary spin and the other with spin 1 and a term of crystal-field anisotropy. The second type of the model we have studied, appropriate for systems presenting helicoidal modulation of the magnetization, is a classical planar model with nearest and next-nearest interactions along an axial direction. \\\'Ve have restricted our study to the absolute zero of the temperature. The magnetization is expanded in Fourier series for high and low fields. We also analyse the stability of the commensurate phases, within a continuum approximation, using the soliton theory. Finally, we construct numerically the phase diagram of the model using the method of effective potentials.
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Treviso, Felipe. "Estudo de um atuador planar de indução para a inspeção de superfícies metálicas." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2016. http://hdl.handle.net/10183/141822.
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Um atuador planar de indução é um dispositivo baseado no mesmo princípio de funcionamento de um motor linear de indução, onde a interação de um campo magnético viajante produzido pelo primário do dispositivo com uma superfície de boa condutividade elétrica induz correntes parasitas que levam à produção de uma força de propulsão. O movimento planar sobre essa superfície é produzido através da movimentação linear em dois eixos ortogonais. Uma aplicação deste movimento é na propulsão de uma plataforma equipada com câmeras e sensores para a realização da inspeção em uma superfície metálica, que se beneficiaria da força normal que o motor planar de indução produz quando acionado sobre uma superfície ferromagnética para anexar a plataforma à superfície. Um modelo analítico que fornece equações para o campo elétrico e magnético é apresentado, e simulações numéricas baseadas no método dos elementos finitos são realizadas para avaliar o comportamento do dispositivo utilizando três tipos diferentes de superfícies como secundário: um secundário com duas camadas formadas por uma chapa de alumínio com outra de aço por baixo; apenas a chapa de alumínio; e apenas a chapa de aço. As distribuições de campo magnético calculadas por estes dois modelos teóricos mostram boa concordância entre si, e são utilizadas para calcular as forças de propulsão e normal produzidas pelo atuador. Medidas experimentais são realizadas em um protótipo de atuador planar de indução, e seus resultados são comparados com os resultados obtidos nos modelos teóricos, mostrando uma boa concordância e potencial para a aplicação do atuador planar de indução na inspeção de superfícies horizontais.An induction planar actuator is a device that, based on the operating principle of a linear induction motor, in which the interaction between a travelling magnetic field produced by the primary of the device and a conducting surface generates eddy currents in the surface and leads to the generation of a thrust force. The device produces planar motion over this surface through movement on two orthogonal axis. An application of this movement is in a platform for the inspection of metallic surfaces, which is driven by the planar induction motor and equipped with cameras and sensors to inspect the surface. This application benefits from the normal force produced by the induction planar actuator operating over a ferromagnetic surface to attach the driving platform to it. An analytical model with equations for the electric and magnetic fields is presented, and numerical simulations based on the finite element method are carried out to assess the behaviour of the device using three different surfaces as secondary: a double-layered secondary formed by an aluminum plate over a steel plate; a aluminum only plate; and a single steel plate. The distributions for the magnetic field computed through these theoretical models show good agreement, and are employed to evaluate the thrust and normal forces produced by the planar induction actuator. Experimental measurements are made on a prototype of the device, and the results are compared to the results of the theoretical models, showing good agreement and potential in the application of the induction planar motor for the inspection of horizontal metallic surfaces.
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Khajehnasiri, Amirreza. "A Generalized 2-D Multiport Model for Planar Circuits with Slots in Ground Plane." Thesis, University of Waterloo, 2005. http://hdl.handle.net/10012/777.
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With increasing complexity of microwave integrated circuits and tendency towards building integrated modules, real estate in printed circuit boards becomes more at premium. On the other hand, building MIC's on a single semiconductor substrate such as GaAs has other drawbacks as substrate requirements for different components are sometimes contradictory. This has motivated researchers to consider multi-layer and stacked designs. Multi-layer planar circuits offer advantages that cannot be equaled by traditional single layer designs. In this respect, a new class of planar structures, based upon a multi-layered stack of dual-mode stripline or microstrip patches is becoming increasingly popular. In the new stacked design coupling between planar circuits separated by a ground plane is accomplished through coupling apertures in the common ground plane. This thesis is about developing a new approximate multiport network model for fast analysis of multi-layered planar structures with ground plane slots. To extend applicability of multiport network model (MNM) to the class of planar structures containing ground plane slots, a generalized network formulation for aperture problems is combined with traditional MNM to account for the presence of the slot. To this end, the slot is replaced by an unknown equivalent surface magnetic current. Slot ports are defined in terms of electric and magnetic fields over the slot in accordance with the generalized network formulation for aperture problems. While traditional MNM for planar circuits is based on generalized impedance matrices, we adopt a hybrid matrix approach for multi-layer structures. The hybrid matrix consists of four sub-matrices that relate terminal voltages and currents of edge and slot ports. The same generalized impedance matrix in the absence of the slot can be used to relate terminal voltages and currents of edge ports when the slot ports are short-circuited. Open circuit voltage at edge ports due to terminal voltages at slot ports and terminal currents at slot ports due to input currents at edge ports are represented by two transfer matrices. Both these transfer matrices can be calculated from 2D analysis which only considers TMz modes.
Interaction among slot ports, represented by a generalized admittance matrix, however, requires considering both TMz and TEz modes. This generalized admittance matrix is obtained from tangential component of the magnetic field over the slot due to the equivalent surface magnetic current and relates terminal voltages and currents of slot ports. Full modal expansion consisting of both TMz and TEz modes is used to compute the generalized admittance matrix of a slot in a regularly shaped planar cavity. For irregularly shaped patches, modal expansion is not available. Instead, a new contour integral equation for magnetic field, derived for the first time in this thesis, is combined with complex images method for calculation of generalized admittance matrix of a slot radiating in a planar cavity of arbitrary shape.
Once the hybrid matrix representation of a planar circuit on a ground plane containing a slot is derived, it can be connected to the hybrid matrix of any other planar circuit on the other side of the ground plane. This can be done by enforcing network equivalent of continuity of tangential fields across the slot. This leads to a generalized impedance matrix for the multi-layer structure relating terminal voltages and currents of edge ports of both planar circuits.
To show the accuracy of the proposed method of analysis, several proof-of-concept structures have been analyzed by both this method and ANSOFT HFSS full-wave simulator as a reference. In most cases excellent agreement is achieved in predicting the return loss and radiation patterns of these multi-layer structures which proves the validity of the proposed approach for fast analysis and design of multi-layer planar structures.
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Johnson, David Craig. "A coning motion apparatus for hydrodynamic model testing in a non-planar cross-flow." Thesis, Massachusetts Institute of Technology, 1989. http://hdl.handle.net/10945/25780.
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As part of continuing research into the flow about slender bodies of revolution, a coning motion apparatus for hydrodynamic model testing was built and demonstrated. This is the first known use of a rotary balance apparatus for external flow hydrodynamic applications. The vorticity shed by the hull and appendages creates a wake field that interacts with the velocity distribution over the vehicle's surface. This in turn effects the surface pressure distribution and thus, when integrated over the body's surface, the total force on the hull/appendage combination. It is this interaction that prevents a closed-form analytic solution to the problem. Keywords: Fluid mechanics. (JES)
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Bonifácio, Paulo Roberto de Oliveira. "Vibração aleatória de placas, vigas e estruturas acopladas." Florianópolis, SC, 2003. http://repositorio.ufsc.br/xmlui/handle/123456789/85401.
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Tese (doutorado) - Universidade Federal de Santa Catarina, Centro Tecnológico. Programa de Pós-Graduação em Engenharia Mecânica.Made available in DSpace on 2012-10-20T18:19:43Z (GMT). No. of bitstreams: 0
Sistemas mecânicos, tais como estruturas aeroespaciais, navais, automobilísticas e plataformas de prospecção e produção de petróleo, estão sujeitos a carregamentos dinâmicos aleatórios, os quais transferem vibrações através de seus acoplamentos. Estes sistemas são normalmente formados por estruturas periódicas, compostas de placas e vigas metálicas, e possuem boa eficiência de irradiação sonora. Tendo em vista a complexidade e as grandes dimensões destes sistemas, as análises numéricas através de métodos determinísticos são possíveis somente na faixa de freqüência restrita aos primeiros modos globais de vibração, o que
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Koell, Perrine. "Développement d'un modèle biomécanique du rachis basé sur les relations 3D internes - externes : radiographie bi-planaire et franges de Moiré." Phd thesis, Université Claude Bernard - Lyon I, 2010. http://tel.archives-ouvertes.fr/tel-00577629.
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De nos jours, la radiographie est l'examen de référence pour le suivi des pathologies de la colonne vertébrale. La radiographie bi-planaire permet de plus, par reconstruction 3D, d'évaluer la configuration spatiale de la colonne vertébrale. Cependant, les expositions radiographiques répétées entrainent une augmentation du risque de cancer. Une solution pour réduire les doses de radiation peut être de remplacer certains examens radiographiques par une mesure de la surface du dos. Cette mesure non-invasive permet, entre autre, d'obtenir un grand nombre de paramètres cliniques utiles pour le diagnostic et le suivi des pathologies. Cette mesure permet également d'estimer la configuration du rachis si l'on met en place une modélisation biomécanique adaptée. Le travail réalisé dans cette thèse consiste à développer et mettre en oeuvre une telle modélisation basée sur les informations personnalisées à la fois internes et externes. Le dispositif Biomod 3S (développé par la société AXS Ingénierie, Bordeaux) offre la possibilité d'une acquisition simultanée de radiographies et de surfaces du dos par franges de Moiré. Cette acquisition sur une quinzaine de sujets scoliotiques (des Hôpitaux Universitaires de Bordeaux) a notamment permis d'évaluer les relations entre plusieurs paramètres 3D internes (e.g., la rotation axiale des vertèbres) et de nombreux paramètres 3D externes (e.g., les gibbosités et flèches). Cette acquisition simultanée permet également de prédire la nouvelle configuration de la colonne vertébrale dans une seconde posture où seule la mesure de surface du dos est effectuée. Pour cela, la modélisation en multi-corps rigides articulés qui a été développée (sous Scilab) utilise (a) la géométrie personnalisée de la colonne vertébrale reconstruite dans la première posture et (b) des contraintes issues de la mesure de la surface du dos dans les deux postures (e.g., position de C7). Le modèle a pu être validé sur une dizaine de sujets sains dont la colonne vertébrale et la surface du dos ont été reconstruits en 3D dans différentes positions (debout, penché en avant) à l'aide d'un IRM positionnel. Le modèle a pu également être exploité sur quelques sujets pathologiques. Ce travail, qui a exploré et exploité de nombreuses informations 3D internes et externes, ouvre des perspectives pour le diagnostic et le suivi non-invasif des pathologies de la colonne vertébrale
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Ayliffe, Benjamin A. "Giant planet formation and migration." Thesis, University of Exeter, 2009. http://hdl.handle.net/10036/85873.
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This thesis describes efforts to improve the realism of numerical models of giant planet formation and migration in an attempt to better understand these processes. A new approach has been taken to the modelling of accretion, designed to mimic reality by allowing gas to accumulate upon a protoplanetary surface. Implementing this treatment in three-dimensional self-gravity radiation hydrodynamics calculations provides an excellent model for planet growth, allowing an exploration of the factors that affect accretion. Moreover, these calculations have also been extended to investigate the migration of protoplanets through their parent discs as they grow. When focusing on the growth of non-migrating protoplanets, the models are performed using small sections of disc, enabling excellent resolution right down to the core; gas structures and flow can be resolved on scales from ~ 10^4 to 10^11 metres. Using radiative transfer, these models reveal the importance of opacity in determining the accretion rates. For the low mass protoplanets, equivalent in mass to a giant planet core (~ 10 M⊕), the accretion rates were found to increase by up to an order of magnitude for a factor of 100 reduction in the grain opacity of the parent circumstellar disc. However, even these low opacities lead to growth rates that are an order of magnitude slower than those obtained in locally-isothermal conditions. For high mass protoplanets (>~ 100M⊕), the accretion rates show very little dependence upon opacity. Nevertheless, the rates obtained using radiative transfer are still lower than those obtained in locally-isothermal models by a factor of ~2, due to the release of accretion energy as heat. Only high mass protoplanets are found to be capable of developing circumplanetary discs, and this ability is dependent upon the opacity, as are the scaleheights of such discs. However, their radial extents were found to be independent of the opacity and the protoplanet mass, all reaching ≈ RH/3, inline with analytic predictions. Migration is investigated using global models, ensuring a self-consistently evolved disc. Using locally-isothermal calculations, it was found that the capture radius of an accreting sink particle, used to model a protoplanet without a surface, must be small (<< RH) to yield migration timescales consistent with linear theory of Type I migration. In the low mass regime of Type I migration, accreting sinks with such small radii yield timescales consistent with those models in which a protoplanetary surface is used. However, for high mass protoplanets, undergoing Type II migration, the surface treatment leads to faster rates of migration, indicating the importance of a realistic accretion model. Using radiative transfer, with high opacities, leads to a factor of ~ 3 increase in the migration timescale of the lowest mass protoplanets, improving their chances of survival. As suitable gas giant progenitors, their survival is key to understanding the growth of giant planets. An unexpected result of the radiative transfer was a reduction in the migration timescale of high mass planets. This appears to be a result of the less thoroughly evacuated gaps created by planets in non-locally-isothermal discs, which affects the corotation torque.
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Poncelet, Olivier. "Ondes planes hétérogènes à fréquence complexe : modes propres de plaques immergées." Bordeaux 1, 1996. http://www.theses.fr/1996BOR10707.
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La propagation des ondes planes heterogenes a frequence complexe est etudiee dans le cadre de l'acoustique lineaire. Leur structure spatio-temporelle modelisee par un vecteur lenteur et une frequence complexes ainsi que leur celerite de l'energie sont examinees comparativement au cas des ondes planes heterogenes harmoniques. Dans les milieux isotropes, la partie reelle du bivecteur lenteur represente alors la direction de propagation de l'energie ; cette direction ne coincidant plus forcement avec la direction de propagation de la phase donnee par la partie reelle du bivecteur d'onde. Le formalisme de l'onde plane heterogene a frequence complexe est applique a l'etude des ondes de lamb. L'analyse des equations caracteristiques de la plaque immergee en termes de frequence complexe, revele des courbes de dispersion, pour les modes propres dits transitoires, relativement differentes de celles de la plaque dans le vide (presence d'une frequence de coupure pour les modes a0 et s0). De plus, contrairement a la vision classique des modes de plaque se propageant en perdant de l'energie par rayonnement dans le fluide, il est montre que les ondes de lamb transitoires ne subissent pas quant a elles, d'attenuation au cours de leur propagation. Enfin, une analyse temporelle de la diffusion d'un faisceau acoustique plan, borne dans le temps, confirme que les phenomenes transitoires sont relatifs a la generation d'ondes de lamb a frequence complexe. Un comportement singulier est observe en ce qui concerne le mode a0, pour lequel le regime transitoire fait apparaitre des exponentielles croissantes en fonction du temps (contrairement a l'ensemble de tous les autres modes). Dans le cas de la diffusion par une plaque d'une onde plane homogene dont le signal est harmonique rectangulaire, ceci se manifeste par l'existence d'un precurseur dans le signal reflechi, qui precede en temps le signal d'excitation. Quelques resultats experimentaux sont proposes
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PARLETTE, EDWARD BRUCE. "GENERALIZED FUNCTION SOLUTIONS TO THE FOKKER-PLANCK EQUATION." Diss., The University of Arizona, 1985. http://hdl.handle.net/10150/187933.
Full textAbstract:
In problems involving highly forward-peaked scattering, the Boltzmann transport equation can be simplified using the Fokker-Planck model. The purpose of this project was to develop an analytical solution to the resulting Fokker-Planck equation. This analytical solution can then be used to benchmark numerical transport codes. A numerical solution to the Fokker-Planck equation was also developed. The analytical solution found is a generalized function. It satisfies the purpose of the project with two limitations. The first limitation is that the solution can only be evaluated for certain sources. The second limitation is that the solution can only be evaluated for small times. The moments of the Fokker-Planck equation can be evaluated for any time. The numerical solution developed works for all sources and all times. The analytical solution, then, provides an accurate and precise benchmark under certain conditions. The numerical solution provides a less accurate benchmark under all conditions.
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Lacorte, Caniato Serrano Ariana Maria da Conceição. "Synthesis and design of tunable microwave bandpass filters using planar patch resonators." Thesis, Grenoble, 2011. http://www.theses.fr/2011GRENT029/document.
Full textAbstract:
L'objectif de la thèse était la conception et la synthèse de filtres RF passe-bande reconfigurables, basés sur des résonateurs de type “Patch”. Une méthode de conception dédiée à la synthèse des filtres reconfigurables a été développée et appliquée à deux filtres reconfigurables basés sur des « patchs » triangulaire et circulaire. La technique de synthèse repose sur l'analyse de la matrice de couplage, facilitée par une analyse électromagnétique des modes propres des résonateurs « Patch ». Les filtres reconfigurables ont été conçus et optimisés à l'aide de simulations électromagnétiques 3D en incluant le modèle électrique des composants localisés utilisés, diodes varactors et capacités fixes. Les deux filtres reconfigurables ont été réalisés en technologie circuit imprimé. Les dimensions minimum du « layout » ont été choisies afin d'être compatibles avec une technologie bas coût, la dimension la plus faible n'étant pas inférieure à 0,5 mmThe objective of this thesis is the design and synthesis of tunable bandpass filters at microwave frequencies using planar patch resonators. A methodology for the design and synthesis of tunable patch filters is developed and applied to two filters with triangular and circular topologies. The methodology provides techniques to extract the coupling scheme that models the filter behavior and the necessary equations for calculating the corresponding coupling matrix. Then, the theoretical filter response resulting from the analysis of the coupling matrix coefficients is compared to the results of complete simulations. The complete simulations combine the results of the 3D electromagnetic (EM) simulation of the filter layout with the results of the electrical simulation of the tuning devices, represented by their lumped elements equivalent model. This allows the correct model of the tuning effect and the definition of the tuning possibilities and limits. In order to validate the methodology, the tunable patch filters are fabricated using Microwave Integrated Circuit (MIC) technology on flexible substrates. The minimum dimensions are greater than 0.5 mm, ensuring a low cost fabrication process