• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 413
  • 128
  • 102
  • 54
  • 11
  • 8
  • 7
  • 4
  • 4
  • 4
  • 4
  • 3
  • 3
  • 3
  • 2
  • Tagged with
  • 866
  • 169
  • 167
  • 142
  • 117
  • 108
  • 101
  • 89
  • 87
  • 85
  • 78
  • 76
  • 74
  • 72
  • 71
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
461

Estabilidade assintótica e estrutural de campos vetoriais / Asymptotic and Structural Stability of Vector Fields

Benito Frazão Pires 01 August 2006 (has links)
O objetivo deste trabalho é provar um Closing Lema Parcial para variedades bidimensionais compactas, orientáveis ou não--orientáveis. Para enunciá--lo, considere um campo vetorial \\linebreak $X\\in\\mathfrak^r(M)$, $r\\ge 2$, de classe $C^r$ em uma variedade bidimensional compacta $M$, e seja $\\Sigma$ um segmento transversal a $X$ passando por um ponto recorrente não--trivial $p$ de $X$. Seja $P:\\Sigma\\to\\Sigma$ a correspondente transformação de primeiro retorno. O primeiro resultado deste trabalho consiste em mostrar que se $P$ tem a propriedade de que para todo $n\\ge N$ e $x\\in{m dom}\\,(P^n)$, $\\vert DP^n(x)\\vert<\\lambda$, onde $N\\in\\N$ e $0<\\lambda<1$, então existe um campo vetorial $Y$ arbitrariamente próximo de $X$ na topologia $C^r$ tendo uma trajetória periódica passando por $p$. O segundo resultado consiste em apresentar condições, sobre os expoentes de Lyapunov de $P$, para que $\\vert DP^n\\vert<\\lambda$ para todo $n\\ge N$. Nesta tese, também incluímos um resultado sobre a estabilidade assintótica no infinito de campos planares diferenciáveis, mas não necessariamente de classe $C^1$. / The aim of this work is to provide a Partial $C^r$ Closing Lemma for compact surfaces, orientable or non--orientable. To state it, let $X\\in\\mathfrak^r(M)$, $r\\ge 2$, be a $C^r$ vector field on a compact surface $M$ and let $\\Sigma$ be a transverse segment to $X$ passing through a non--trivial recurrent point $p$ of $X$. Let $P:\\Sigma\\to\\Sigma$ be the corresponding first return map. The first result of this work consists in showing that if $P^n$ has the property that for all $n\\ge N$ and $x\\in{m dom}\\,(P^n)$, $\\vert DP^n(x)\\vert<\\lambda$, where $N\\in\\N$ e $0<\\lambda<1$, then there exists a vector field $Y$ arbitrarily close to $X$ in the $C^r$ topology such that $p$ is a periodic point of $Y$. The second result consists in presenting sufficient conditions, upon the Lyapunov exponents of $P$, so that $\\vert DP^n\\vert<\\lambda$ for all $n\\ge N$. In this thesis, we also include a result concerning the asymptotic stability at infinity of planar differentiable vector fields, not necessarily of class $C^1$.
462

Equações diferenciais funcionais neutras, comportamento assintótico e representação / Neutral functional differential equations, asymptotic behaviour and representation

Patrícia Hilario Tacuri 29 January 2013 (has links)
O objetivo deste trabalho é investigar propriedades qualitativas das equações diferenciais funcionais neutras (EDFNs) e introduzir uma classe geral de equações chamadas EDFNs em medida. Obtemos resultados sobre o comportamento assintótico para uma classe de EDFNs com coeficientes periódicos, onde o período e o retardamento estão racionalmente relacionados. Também, conseguimos mostrar que a dicotomia exponencial do operador solução das equações diferenciais funcionais com retardamento (EDFRs) não autônomas implica na existência de soluções limitadas para EDFRs não homogêneas associadas. Finalmente, através da teoria das equações diferenciais ordinárias generalizas (EDOs generalizadas), obtemos resultados de existência e unicidade, dependência contnua em relação aos dados inicias, das soluções das EDFNs em medida. Os resultados novos apresentados neste trabalho estão contidos nos artigos [31, 43] / The aim of this work is to investigate qualitative properties of neutral functional differential equations (NFDEs) and introduce a general class of equations called measure NFDE . We obtain results on the asymptotic behavior for a class of NFDEs with periodic coefficients, where the period and delay are rationally related. Moreover, we show that the exponential dichotomy of the solution operator of non autonomous retarded functional differential equations (RFDEs) implies the existence of bounded solutions to the associated non homogeneous RFDEs. Finally, using the theory of generalized ordinary differential equations (generalized ODEs), we obtain results of existence and uniqueness, continuous dependence on parameters of the solutions of measure NFDEs. The new results presented in this work are contained in the articles [31,43]
463

Estabilidade assintótica para alguns modelos dissipativos de equações de placas / Asymptotic stability for some dissipative models of plate equations

Marcio Antonio Jorge da Silva 13 March 2012 (has links)
Neste trabalho estudamos questões relativas a existência, unicidade, dependência contínua, continuidade, taxas de decaimento e comportamento assintótico de soluções para uma classe de equações de placas lineares e não lineares. No primeiro capítulo revisamos alguns conteúdos e colecionamos uma série de resultados provenientes da teoria geral de análise funcional, semigrupos lineares e atratores, os quais serão aplicados ao longo desta tese. Nos dois próximos capítulos abordamos uma equação da placa de quarta ordem dissipativa com perturbações não lineares do tipo p- Laplaciano e localmente Lipschitz e com memória. No segundo capítulo provamos a estabilidade exponencial de energia correspondente ao problema homogêneo com memória de segunda ordem. Em seguida, no terceiro capítulo estabelecemos resultados que comprovam a existência de um atrator global com dimensão fractal finita para o sistema dinâmico associado ao problema com história de deslocamento relativo que equivale ao problema original. Finalmente, no quarto capítulo tratamos um modelo viscoelástico de placas de Mindlin-Timoshenko de segunda ordem. Nesta ocasião, consideramos essecialmente dois casos, o primeiro quando o sistema é totalmente dissipativo e, em seguida, quando o sistema é parcialmente dissipativo. No primeiro caso, determinamos que o semigrupo linear associado ao problema é analítico e, como consequência, é exponencialmente estável. No segundo caso, mostramos que o semigrupo perde decaimento exponencial e analiticidade, no entanto, provamos que as soluções possuem decaimento do tipo polinomial / In this work we study some questions concerning with existence, uniqueness, continuous dependence, continuity, rates of decay and asymptotic behavior of solutions for a class of linear and nonlinear plate equations. In the first chapter we review some concepts and collect a series of results provided from general theory of functional analysis, linear semigroups and attractors which will be applied throughout this thesis. In the next two chapters we discuss a damped plate equation of fourth order with nonlinear perturbations of the lower order of p-Laplacian type and locally Lipschitz, and a memory term. In the second chapter we prove the exponential stability of energy corresponding to the homogeneous problem with memory of second order. Then in the third chapter we establish some results that allow us to prove the existence of a global attractor with finite fractal dimension for dynamical system associated to the problem with relative displacement history which is equivalent to the original problem. Finally, in the fourth chapter we deal with a viscoelastic Mindlin-Timoshenko plate model of second order. At this moment we consider essentially two cases. The first one when the system is fully damped, then when the system is partially damped. In the first case we show that the semigroup associated to the Mindlin-Timoskenko system is analytic, which in particular implies exponential decay. In the second case we show that such semigroup loses exponential decay, also loses analyticity. However, we prove in this last case that the solutions have decay of polynomial type
464

Semicontinuidade inferior de atratores para problemas parabólicos em domínios finos / Lower semicontinuity of attactors for parabolic problems in thin domains

Ricardo Parreira da Silva 30 October 2007 (has links)
Neste trabalho estudamos problemas de reação-difusão semilineares do tipo \'u IND..t(x, t) = \'DELTA\'u(x, t)+ f (u(x, t)), x \'PERTENCE A\' \'OMEGA\' \'PARTIAL\' U/\'PARTIAL\'V (x, t) = 0, x \'PERTENCE A\' \'PARTIAL\'\' OMEGA\'. Desenvolvemos uma teoria abstrata para a obtenção da continuidade da dinâmica assintótica de (P) sob perturbações singulares do domínio espacial W e aplicamos a uma série de exemplos dos assim chamados domínios finos / In this work we study semilinear reaction-diffusion problems of the type \'u IND.t(x, t) = \'DELTA\'u(x, t)+ f (u(x, t)), x \' PERTENCE A\' \'OMEGA\' \'PARTIAL\'u/\'ARTIAL\' v (x, t) = 0, x \"PERTENCE A\' \'PARTIAL\' \' OMEGA\' We develop a abstract theory to obtain the continuity of the asymptotic dynamics of (P) under singular perturbations of the spatial domain W and we apply that to many examples in thin domains
465

La réalité augmentée : fusion de vision et navigation / Augmented reality : the fusion of vision and navigation

Zarrouati-Vissière, Nadège 20 December 2013 (has links)
Cette thèse a pour objet l'étude d'algorithmes pour des applications de réalité visuellement augmentée. Plusieurs besoins existent pour de telles applications, qui sont traités en tenant compte de la contrainte d'indistinguabilité de la profondeur et du mouvement linéaire dans le cas de l'utilisation de systèmes monoculaires. Pour insérer en temps réel de manière réaliste des objets virtuels dans des images acquises dans un environnement arbitraire et inconnu, il est non seulement nécessaire d'avoir une perception 3D de cet environnement à chaque instant, mais également d'y localiser précisément la caméra. Pour le premier besoin, on fait l'hypothèse d'une dynamique de la caméra connue, pour le second on suppose que la profondeur est donnée en entrée: ces deux hypothèses sont réalisables en pratique. Les deux problèmes sont posés dans lecontexte d'un modèle de caméra sphérique, ce qui permet d'obtenir des équations de mouvement invariantes par rotation pour l'intensité lumineuse comme pour la profondeur. L'observabilité théorique de ces problèmes est étudiée à l'aide d'outils de géométrie différentielle sur la sphère unité Riemanienne. Une implémentation pratique est présentée: les résultats expérimentauxmontrent qu'il est possible de localiser une caméra dans un environnement inconnu tout en cartographiant précisément cet environnement. / The purpose of this thesis is to study algorithms for visual augmented reality. Different requirements of such an application are addressed, with the constraint that the use of a monocular system makes depth and linear motion indistinguishable. The real-time realistic insertion of virtual objects in images of a real arbitrary environment yields the need for a dense Threedimensional (3D) perception of this environment on one hand, and a precise localization of the camera on the other hand. The first requirement is studied under an assumption of known dynamics, and the second under the assumption of known depth: both assumptions are practically realizable. Both problems are posed in the context of a spherical camera model, which yields SO(3)-invariant dynamical equations for light intensity and depth. The study of theoreticalobservability requires differential geometry tools for the Riemannian unit sphere. Practical implementation on a system is presented and experimental results demonstrate the ability to localize a camera in a unknown environment while precisely mapping this environment.
466

Curves in the Minkowski plane and Lorentzian surfaces

Saloom, Amani Hussain January 2012 (has links)
We investigate in this thesis the generic properties of curves in the Minkowski plane R2 1 and of smooth Lorentzian surfaces. The generic properties of curves in R2 1 are obtained by studying the contacts of curves in R2 1 with lines and pseudo-circles. These contacts are captured by the singularities of the families of height and distancesquared functions on the curves. On the other hand, the generic properties of smooth Lorentzian surfaces are obtained by studying certain Binary Differential Equations defined on the surfaces.
467

Meteotsunamis, Proudman resonance and Corioliseffect for water waves / Météotsunamis, résonance de Proudman et effet Coriolis pour les équations de vagues

Melinand, Benjamin 28 June 2016 (has links)
Dans ce travail nous nous intéressons aux comportement de vagues soumises à l’action d’une pression atmosphérique non constante, un fond mobile et la force de Coriolis. Une première partie est dédiée à l’étude de la résonance de Proudman. Nous proposons une approche mathématique rigoureuse pour étudier ce phénomène. Nous commençons par démontrer un résultat d’existence locale dans un cadre irrotationnel sur les équations des vagues (appelées aussi formulation de Zakharov/Craig-Sulem). Puis, nous justifions différents modèles asymptotiques pour généraliser cette résonance dans diverses situations physiques. Nous proposons en particulier une étude détaillée dans des eaux profondes dans un régime linéaire. Nous étudions aussi la propagation de vagues dans des eaux profondes dans un régime faiblement non-linéaire grâce aux équations de Saut-Xu et nous proposons un schéma numérique pour résoudre ces équations. Dans une deuxième partie, nous étudions l’effet de la force de Coriolis sur les vagues. Nous démontrons un résultat d’existence locale sur les équations Castro-Lannes, équations qui généralisent la formulation de Zakharov/Craig-Sulem dans un cadre rotationnel. Nous justifions ensuite différents modèles asymptotiques dans des eaux peu profondes en présence de la force de Coriolis. En particulier, nous proposons une généralisation des équations de Boussinesq (modèle asymptotique dans un régime faiblement linéaire) lorsque la force de Coriolis n’est pas négligeable. Ces équations nous permettent ensuite de justifier mathématiquement les ondes de Poincaré puis l’équation d’Ostrovsky qui généralise l’équation de Korteweg-De-Vries en présence de la force de Coriolis. / In this work, we are interested in the evolution of water waves under the influence of a non constant atmospheric pressure, a moving bottom and a Coriolis forcing. In a first part, we study the Proudman resonance. We propose a mathematical approach to understand this phenomenon. First, we prove a local wellposedness result in a irrotational framework on the water waves equations (also called the Zakharov/Craig-Sulem formulation). Then, we fully justify different asymptotic models. In particular, we carefully study the Proudman resonance in deep water in the linear regime. Finally, we study the propagation of water waves in a weakly nonlinear regime thanks to the Saut-Xu equations and we propose a numerical scheme in order to solve these equations. In a second part, we study the influence of a Coriolis forcing on water waves. We prove a local wellposedness result on the Castro-Lannes equations, which generalize the Zakharov/Craig-Sulem formulation in the rotational framework. Then, we fully justify different asymptotic models when we take into account a Coriolis forcing. In particular, we generalize the Boussinesq equations (asymptotic model in a weakly nonlinear regime) in this setting. Thanks to these equations, we justify the Poincaré waves and then the Ostrovsky equation, which generalize the Korteweg-De- Vries equation when a Coriolis forcing is taking into account.
468

Random Walks on Free Products of Cyclic Groups

Alharbi, Manal 17 April 2018 (has links)
In this thesis, we investigate examples of random walks on free products of cyclic groups. Free products are groups that contain words constructed by concatenation with possible simplifications[20]. Mairesse in [17] proved that the harmonic measure on the boundary of these random walks has a Markovian Multiplicative structure (this is a class of Markov measures which requires fewer parameters than the usual Markov measures for its description ), and also showed how in the case of the harmonic measure these parameters can be found from Traffic Equations. Then Mairesse and Math ́eus in [20] continued investigation of these random walks and the associated Traffic Equations. They introduced the Stationary Traffic Equations for the situation when the measure is shift-invariant in addition to being μ-invariant. In this thesis, we review these developments as well as explicitly describe several concrete examples of random walks on free products, some of which are new.
469

Binary evolution in the light of barium and related stars

Dermine, Tijl 23 September 2011 (has links)
Si l'évolution des étoiles simples est relativement bien comprise, l'étude des étoiles binaires, qui représentent la majorité des étoiles, nécessite encore des progrès majeurs, particulièrement en ce qui concerne leurs différents modes d'interactions. Dans ces systèmes, la composition de surface d'une étoile peut être altérée non seulement par l'accrétion d'éléments synthétisés au sein de l'étoile compagnon, mais également par des processus de mélanges internes induits par les forces de marées et d'un transport du moment angulaire. Plusieurs classes d'étoiles post-transfert de masse (les étoiles à baryum, CH et S) possèdent effectivement des compositions de surface caractérisées par la présence d'éléments lourds, tel que le baryum. Ces systèmes sont présumés se former au sein de systèmes binaires incluant une étoile de la branche asymptotique des géantes (appelé étoile AGB). Ces dernières sont des étoiles remarquables qui représentent l'unique site d'une nucléosynthèse particulière. En effet, elles constituent les contributeurs essentiels de la production de fluor ou de baryum. Les étoiles AGB sont également caractérisées par une importante perte de masse par vent qui éjecte progressivement leur enveloppe enrichie en ces éléments. Au sein d'un système binaire, une partie de ce vent est accréditée par l'étoile compagnon et pollue ainsi sa surface, laissant une signature spectrale distincte qui subsistera longtemps après que l'étoile AGB ait disparu. Ce scénario est suggéré comme étant responsable de la formation d'une grande variété d'étoiles chimiquement particulières, tels que les étoiles à baryum.<p>Cependant, plusieurs propriétés clés de ces systèmes, en particulier leurs distributions de périodes orbitales et d'excentricités, demeurent inexpliquées depuis des décennies. L'incapacité de nos modèles à reproduire ces propriétés orbitales met en évidence notre compréhension limitée des mécanismes d'interaction qui gouvernent l'évolution des systèmes binaires. Plus particulièrement, des mécanismes qui génèrent des orbites excentriques au sein des étoiles à baryum et des systèmes analogues sont requis. Nous examinons ainsi la possibilité qu'à sa naissance l'étoile naine blanche subisse un kick ou que la présence d'un disque entourant le système binaire soit à l'origine des fortes excentricités observées chez les étoiles à baryum. Ces deux mécanismes permettent pour la première fois depuis l'étude de ces systèmes d'apporter une solution à ces problèmes. Il est montré comment comprendre les signatures induites par un compagnon étoile AGB et les corréler avec les propriétés orbitales du système binaire est essentiel pour tester et améliorer notre connaissance de l'évolution des étoiles binaires; l'objectif de ce travail.<p> / Doctorat en Sciences / info:eu-repo/semantics/nonPublished
470

Testy nezávislosti pro mnohorozměrná data / Tests of independence for multivariate data

Kudlík, Michal January 2016 (has links)
Title: Tests of independence for multivariate data Author: Bc. Michal Kudlík Department: Department of Probability and Mathematical Statistics Supervisor: Ing. Marek Omelka, PhD., Department of Probability and Mathema- tical Statistics Abstract: This thesis is an overview of tests of independence for multidimensi- onal data. The report includes tests on independence of categorical and conti- nuous random variables, tests assuming normal distribution of data, asymptotic nonparametric tests and permutation tests with application of the Monte Carlo method. This thesis shows the suitability of tests with properly chosen real data and checks significance level and compares the strength of the selected tests by simulation study while using appropriate statistical software. Based on the simu- lation study the thesis discusses an appropriateness of the use of different tests for different situations. Keywords: independence, permutation and asymptotic tests of independence, Monte Carlo method, simulation study 1

Page generated in 0.0461 seconds