Thesis (M.S.)--University of Delaware, 2006. / Principal faculty advisor: Robert P. Gilbert, Dept. of Mathematical Sciences. Includes bibliographical references.

Thesis (Ph. D.)--Ohio State University, 2006. / Title from first page of PDF file. Includes bibliographical references (p. 129-135).

Dans cette thèse, nous étudions la diffraction électromagnétique par des réseau et surfaces rugueuse aléatoire. Le méthode C est une méthode exacte développée pour ce but. Il est basé sur équations de Maxwell sous forme covariante écrite dans un système de coordonnées non orthogonal. Le méthode C conduisent à résoudre le problème de valeur propre. Le champ diffusé est expansé comme une combinaison linéaire des solutions propres satisfaisant à la condition d’onde sortant.Nous nous concentrons sur l’aspect numérique de la méthode C, en essayant de développer une application efficace de cette méthode exacte. Pour les réseaux, nous proposons une nouvelle version de la méthode C qui conduit `a un système différentiel avec les conditions initiales. Nous montrons que cette nouvelle version de la méthode C peut être utilisée pour étudier les réseaux de multicouches avec un médium homogène.Nous vous proposons un algorithme QR parallèle conçu spécifiquement pour la méthode C pour résoudre le problème de valeurs propres. Cet algorithme QR parallèle est une variante de l’algorithme QR sur la base de trois tech- niques: “décalage rapide”, poursuite de renflement parallèle et de dégonflage parallèle agressif précoce (AED). / We study the electromagnetic diffraction by gratings and random rough surfaces. The C-method is an exact method developed for this aim. It is based on Maxwell’s equations under covariant form written in a nonorthogonal coordinate system. The C-method leads to an eigenvalue problem, the solution of which gives the diffracted field.We focus on the numerical aspect of the C-method, trying to develop an efficient application of this exact method. For gratings, we have developed a new version of C-method which leads to a differential system with initial conditions. This new version of C-method can be used to study multilayer gratings with homogeneous medium.We implemented high performance algorithms to the original versions of C-method. Especially, we have developed a specifically designed parallel QR algorithm for the C- method and spectral projection method to solve the eigenvalue problem more efficiently. Experiments have shown that the computation time can be reduced significantly.

This thesis describes a combined model and laboratory investigation of the generation and mutual interactions of fluid waves whose characteristic scales differ by an order of magnitude or more. The principal aims are to study how waves on one scale can generate waves on another, much shorter scale, and to examine the subsequent nonlinear feedback of the short waves on the long waves. The underlying motive is to better understand such interactions in rotating, stratified, planetary fluids such as atmospheres and oceans. The first part of the thesis describes a laboratory investigation using a rotating, two-layer annulus, forced by imposing a shear across the interface between the layers. A method is developed for making measurements of the two-dimensional interface height field which are very highly-resolved both in space and time. The system's linear normal modes fall into two distinct classes: 'slow' waves which are relatively long in wavelength and intrinsic period, and 'fast' waves which are much shorter and more quickly-evolving. Experiments are performed to categorize the flow at a wide range of points in the system's parameter space. At very small background rotation rates, the interface is completely devoid of waves of both types. At higher rates, fast modes only are generated, and are shown to be consistent with the Kelvin-Helmholtz instability mechanism based on a critical Richardson number. At rotation rates which are higher still, baroclinic instability gives rise to the onset of slow modes, with subsequent localized generation of fast modes superimposed in the troughs of the slow waves. In order to examine the generation mechanism of these coexisting fast modes, and to assess the extent of their impact upon the evolution of the slow modes, a quasi-geostrophic numerical model of the laboratory annulus is developed in the second part of the thesis. Fast modes are filtered out of the model by construction, as the phase space trajectory is confined to the slow manifold, but the slow wave dynamics is accurately captured. Model velocity fields are used to diagnose a number of fast wave radiation indicators. In contrast to the case of isolated fast waves, the Richardson number is a poor indicator of the generation of the coexisting fast waves that are observed in the laboratory, and so it is inferred that these are not Kelvin-Helmholtz waves. The best indicator is one associated with the spontaneous emission of inertia-gravity waves, a generalization of geostrophic adjustment radiation. A comparison is carried out between the equilibrated wavenumbers, phase speeds and amplitudes of slow waves in the laboratory (which coexist with fast modes), and slow waves in the model (which exist alone). There are significant differences between these wave properties, but it is shown that these discrepancies can be attributed to uncertainties in fluid properties, and to model approximations apart from the neglect of fast modes. The impact of the fast modes on the slow modes is therefore sufficiently small to evade illumination by this method of inquiry. As a stronger test of the interaction, a stochastic parameterization of the inertia-gravity waves is included in the model. Consistent with the laboratory/model intercomparison, the parameterized fast waves generally have only a small impact upon the slow waves. However, sufficiently close to a transition curve between two different slow modes in the system's parameter space, it is shown that the fast modes can exert a dominant influence. In particular, the fast modes can force spontaneous transitions from one slow mode to another, due to the phenomenon of stochastic resonance. This finding should be of interest to the meteorological and climate modelling communities, because of its potential to affect model reliability.

Made available in DSpace on 2016-06-02T20:02:53Z (GMT). No. of bitstreams: 1 5679.pdf: 4162918 bytes, checksum: ac6b2b355a8fab7b17251dc590282ffb (MD5) Previous issue date: 2013-09-11 / The use of digital learning objects (DLO) in the classroom has become more relevant and frequent. Therefore, reflecting on pupils and teacher s attitude, in real-class situations about the insertion of new educational technologies has proved pertinent and up to date. This paperwork presents a didactic sequence about Physics of Waves using mainly PhET Interactive Simulations. The methodological approach is based on the Meaningful Learning Theory by Ausubel and coworkers and the Face-to-Face Collaborative Method developed by Moreira. The sequence was applied in two Physics classes of two different Brazilian High Schools which use a Teaching Structured System. All the activities are designed in the form of a preliminary, Interaction with the DLO, and outcome and planned for double 45-minute classes. The continuous use of Maps of Concepts in order to follow the evolution of concepts understanding of the student has allowed to conclude that there have been effective learning gains in the process of hierarchical organization and relationship between the concepts involved in the Physics of Waves. The work described here has shown that it is possible successfully insert DLO in the regular classrooms of a traditional private school. However, the most important result from this work has been the change in the attitudes of students and teacher and their behavior in the classroom. After this practice, the teacher has planned the classes more carefully, introducing new teaching initiatives, and the students have experienced a more active and protagonist role in the process of knowledge building. / O uso dos Objetos Virtuais de Aprendizagem (OA) em sala de aula tem se tornado mais relevante e frequente. Portanto, refletir sobre a atitude de alunos e professores, em situações reais de sala de aula e considerando a inserção de novas tecnologias educacionais, torna-se pertinente e atual. Esse trabalho apresenta uma sequência didática sobre Física Ondulatória, construída a partir das simulações disponibilizadas pela Universidade do Colorado (PhET Physics Interactive Simulations). A abordagem metodológica se baseia na Aprendizagem Significativa de Ausubel e no Método Colaborativo Presencial de Moreira. A sequência foi aplicada em aulas de física de duas distintas turmas do Ensino Médio que utilizam como material didático as apostilas do Sistema Anglo de Ensino. Todas as atividades foram construídas apoiadas em três momentos distintos: preliminar, interação e desfecho planejadas para aulas duplas de 45 minutos cada. Foi fundamental, para avaliação da compreensão dos alunos, o uso contínuo de mapas de conceitos. Ademais, pudemos concluir o que de fato eles haviam aprendido quanto à hierarquização e relação entre os conceitos da Física Ondulatória. O trabalho descrito aqui permite evidenciar a possibilidade de inserção de OA em salas de aula regulares de um ensino médio privado. E o resultado mais importante desse trabalho é, enfim, a mudança nas atitudes, tanto de professor, quanto de alunos, em relação ao comportamento em sala de aula. Depois dessa prática, o professor passou a planejar mais cuidadosamente a aula, tornando o processo autoral e os alunos experimentaram uma posição mais ativa e protagonista no processo de construção do conhecimento.