• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 91
  • 87
  • 37
  • 9
  • 4
  • 4
  • 2
  • 2
  • 2
  • 1
  • 1
  • 1
  • 1
  • 1
  • 1
  • Tagged with
  • 253
  • 75
  • 38
  • 36
  • 28
  • 24
  • 23
  • 22
  • 20
  • 19
  • 19
  • 18
  • 18
  • 16
  • 16
  • 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.
91

O fluxo espectral de caminhos de operadores de Fredholm auto-adjuntos em espaços de Hilbert / Spectral flow of a path of selfadjoint Fredholm operators in Hilbert spaces

Jeovanny de Jesus Muentes Acevedo 26 November 2013 (has links)
O objetivo principal desta dissertação é apresentar o fluxo espectral de um caminho de operadores de Fredholm auto-adjuntos em um espaço de Hilbert e suas propriedades. Pelos resultados clássicos de teoria espectral, sabemos que se H é um espaço de Hilbert e L : H &#8594 H é um operador linear, limitado e auto-adjunto, H pode ser escrito como soma direta ortogonal H+(L)&#8853 H-(L)&#8853 Ker L, onde H+(L) e H-(L) são os subespaços espectrais positivo e negativo de L, respectivamente. No trabalho damos uma definição de fluxo espectral baseada na decomposição acima, aprofundando as conexões deste conceito com a teoria espectral dos operadores de Fredholm em espaços de Hilbert. Entre as propriedades do fluxo espectral, será analisada a invariância homotópica que se apresenta em várias formas. Veremos o conceito de índice de Morse relativo, que estende o clássico índice de Morse, e sua relação com o fluxo espectral. A construção do fluxo espectral dada neste trabalho segue a abordagem de P. M. Fitzpatrick, J. Pejsachowicz e L. Recht em [9]. / The main purpose of this dissertation is to present the spectral flow of a path of selfadjoint Fredholm operators in a Hilbert space and its properties. By classical results in spectral theory, we know that, if H is a Hilbert space and L : H &#8594 H is a bounded self-adjoint linear operator, H may be written as the following orthogonal direct sum H = H+(L)&#8853 H-(L)&#8853 Ker L, where H+(L) and H-(L) are the positive and negative spectral subspaces of L, respectively. In this work we give a definition of spectral flow which is based on the above splitting, examining in depth the connection between this concept and the spectral theory of Fredholm operators in Hilbert spaces. Among the properties of the spectral flow we will analyze the homotopic invariance, which appears on different ways. We will see the concept of relative Morse index, which generalize the classical Morse index, and its relation with the spectral flow. The construction of the spectral flow given in this work follows the approach of P. M. Fitzpatrick, J. Pejsachowicz and L. Recht in [9].
92

RG flows e sistemas dinâmicos / RG Flows and Dynamical Systems

Tiedt, Caio Luiz 21 February 2019 (has links)
No contexto de Renormalização Wilsoniana, os fluxos do grupo de renormalização (RG flows) são um conjunto de equações diferenciais que define como as constantes de acoplamento de uma teoria dependem de uma escala de energia. o conteúdo destes é semelhante a como sistemas termodinâmicos estão relacionados com a temperatura. Neste sentindo, é natural olhar para estruturas nos fluxos que demonstram um comportamento termodinâmico. A teoria matemática para estudar estas equações é chamada de sistemas dinâmicos e aplicações desta têm sido usadas no estudo de RG flows. Como exemplo o teorema-C de Zamolodchikov e os equivalentes teoremas em dimensões maiores mostram que existe uma função monotonicamente decrescente ao longo do fluxo e é uma propriedade que se assemelha à segunda lei da termodinâmica, estão relacionadas com a função de Lyapunov no contexto de sistemas dinâmicos e podem ser usadas para excluir a possibilidade de comportamentos assintóticos exóticos, como fluxos periódicos ou ciclos limites. Estudamos a teoria de bifurcação e a teoria de índice, que foram propostas como sendo úteis no estudo de RG flows: a primeira pode ser usada para explicar constantes cruzando pela marginalidade e a segunda para extrair informação global do espaço em que os fluxos vivem. Nesta dissertação, também olhamos para aplicações em RG flows holográficos e tentamos buscar relações entre as estruturas em teorias holográficas e as suas duais teorias de campos. / In the context of Wilsonian Renormalization, renormalization group (RG) flows are a set of differential equations that defines how the coupling constants of a theory depend on an energy scale. These equations closely resemble thermodynamical equations and how thermodynamical systems are related to temperature. In this sense, it is natural to look for structures in the flows that show a thermodynamics-like behaviour. The mathematical theory to study these equations is called Dynamical Systems, and applications of that have been used to study RG flows. For example, the classical Zamolodchikov\'s C-Theorem and its higher-dimensional counterparts, that show that there is a monotonically decreasing function along the flow and it is a property that resembles the second-law of thermodynamics, is related to the Lyapunov function in the context of Dynamical Systems. It can be used to rule out exotic asymptotic behaviours like periodic flows (also known as limit cycles). We also study bifurcation theory and index theories, which have been proposed to be useful in the study of RG flows, the former can be used to explain couplings crossing through marginality and the latter to extract global information about the space the flows lives in. In this dissertation, we also look for applications in holographic RG flows and we try to see if the structural behaviours in holographic theories are the same as the ones in the dual field theory side.
93

The Leray-Serre spectral sequence in Morse homology on Hilbert manifolds and in Floer homology on cotangent bundles

Schneider, Matti 04 February 2013 (has links) (PDF)
The Leray-Serre spectral sequence is a fundamental tool for studying singular homology of a fibration E->B with typical fiber F. It expresses H (E) in terms of H (B) and H (F). One of the classic examples of a fibration is given by the free loop space fibration, where the typical fiber is given by the based loop space . The first part of this thesis constructs the Leray-Serre spectral sequence in Morse homology on Hilbert manifolds under certain natural conditions, valid for instance for the free loop space fibration if the base is a closed manifold. We extend the approach of Hutchings which is restricted to closed manifolds. The spectral sequence might provide answers to questions involving closed geodesics, in particular to spectral invariants for the geodesic energy functional. Furthermore we discuss another example, the free loop space of a compact G-principal bundle, where G is a connected compact Lie group. Here we encounter an additional difficulty, namely the base manifold of the fiber bundle is infinite-dimensional. Furthermore, as H ( P) = HF (T P) and H ( Q) =HF (T Q), where HF denotes Floer homology for periodic orbits, the spectral sequence for P -> Q might provide a stepping stone towards a similar spectral sequence defined in purely Floer-theoretic terms, possibly even for more general symplectic quotients. Hutchings’ approach to the Leray-Serre spectral sequence in Morse homology couples a fiberwise negative gradient flow with a lifted negative gradient flow on the base. We study the Morse homology of a vector field that is not of gradient type. The central issue in the Hilbert manifold setting to be resolved is compactness of the involved moduli spaces. We overcome this difficulty by utilizing the special structure of the vector field. Compactness up to breaking of the corresponding moduli spaces is proved with the help of Gronwall-type estimates. Furthermore we point out and close gaps in the standard literature, see Section 1.4 for an overview. In the second part of this thesis we introduce a Lagrangian Floer homology on cotangent bundles with varying Lagrangian boundary condition. The corresponding complex allows us to obtain the Leray-Serre spectral sequence in Floer homology on the cotangent bundle of a closed manifold Q for Hamiltonians quadratic in the fiber directions. This corresponds to the free loop space fibration of a closed manifold of the first part. We expect applications to spectral invariants for the Hamiltonian action functional. The main idea is to study pairs of Morse trajectories on Q and Floer strips on T Q which are non-trivially coupled by moving Lagrangian boundary conditions. Again, compactness of the moduli spaces involved forms the central issue. A modification of the compactness proof of Abbondandolo-Schwarz along the lines of the Morse theory argument from the first part of the thesis can be utilized.
94

Multi-Agent Systems with Reciprocal Interaction Laws

Chen, Xudong 06 June 2014 (has links)
In this thesis, we investigate a special class of multi-agent systems, which we call reciprocal multi-agent (RMA) systems. The evolution of agents in a RMA system is governed by interactions between pairs of agents. Each interaction is reciprocal, and the magnitude of attraction/repulsion depends only on distances between agents. We investigate the class of RMA systems from four perspectives, these are two basic properties of the dynamical system, one formula for computing the Morse indices/co-indices of critical formations, and one formation control model as a variation of the class of RMA systems. An important aspect about RMA systems is that there is an equivariant potential function associated with each RMA system so that the equations of motion of agents are actually a gradient flow. The two basic properties about this class of gradient systems we will investigate are about the convergence of the gradient flow, and about the question whether the associated potential function is generically an equivariant Morse function. We develop systematic approaches for studying these two problems, and establish important results. A RMA system often has multiple critical formations and in general, these are hard to locate. So in this thesis, we consider a special class of RMA systems whereby there is a geometric characterization for each critical formation. A formula associated with the characterization is developed for computing the Morse index/co-index of each critical formation. This formula has a potential impact on the design and control of RMA systems. In this thesis, we also consider a formation control model whereby the control of formation is achieved by varying interactions between selected pairs of agents. This model can be interpreted in different ways in terms of patterns of information flow, and we establish results about the controllability of this control system for both centralized and decentralized problems. / Engineering and Applied Sciences
95

Existência e multiplicidade de solução para uma classe de equações elípticas via teoria de Morse. / Existence and multiplicity of solution for a class of elliptic equations via Morse theory.

PEREIRA, Denilson da Silva. 25 July 2018 (has links)
Submitted by Johnny Rodrigues (johnnyrodrigues@ufcg.edu.br) on 2018-07-25T17:05:28Z No. of bitstreams: 1 DENILSON DA SILVA PEREIRA - DISSERTAÇÃO PPGMAT 2010..pdf: 630527 bytes, checksum: 8a6ec5b5fb5e2a462945183d2180a573 (MD5) / Made available in DSpace on 2018-07-25T17:05:28Z (GMT). No. of bitstreams: 1 DENILSON DA SILVA PEREIRA - DISSERTAÇÃO PPGMAT 2010..pdf: 630527 bytes, checksum: 8a6ec5b5fb5e2a462945183d2180a573 (MD5) Previous issue date: 2010-12 / Neste trabalho estudamos a existência e multiplicidade de soluções para uma certa classe de problemas elípticos. Utilizaremos métodos variacionais juntamente com a teoria de Morse em dimensão infinita. / In this work, we study the existence and multiplicity of solution for a large class of Elliptic problems. The main tools used are variational methods together with the infinite dimensional Morse Theory.
96

Robustez da dinâmica sob perturbações: da semicontinuidade superior à estabilidade estrutural / Robustness of the dynamics under perturbations: from the upper semicontinuity to the structural stability

Arthur Geromel Fischer 04 September 2015 (has links)
O objetivo principal deste trabalho é o estudo da estabilidade estrutural dos atratores de semigrupos. Começamos este trabalho apresentando o conceito e propriedades básicas de semigrupos que possuem atratores globais. Estudamos, então, semigrupos gradientes e dinamicamente gradientes, mostrando que eles são equivalentes e que uma pequena perturbação autônoma de um semigrupo gradiente continua sendo gradiente. Estudamos as variedades estável e instável de um ponto de equilíbrio hiperbólico e o comportamento de soluções periódicas sob perturbação. Concluímos este trabalho com o estudo dos semigrupos Morse-Smale. / The main goal of this work is the study of structural stability of global attractors. We start this work by presenting the concept and basic properties of semigroups and global attractors. We then studied gradient and dinamically gradient semigroups, showing that these concepts are equivalent and that a small autonomous pertubation of a gradient semigroup remains a gradient semigroup. We studied the stable and unstable manifolds in the neighbourhood of a hyperbolic equilibrium point and the behavior of periodic solutions under perturbation. Finally, we studied the Morse-Smale semigroups.
97

Matrizes de conexão via o complexo de Morse-Witten / Connection matrices via the Morse-Witten

Lima, Dahisy Valadão de Souza, 1986- 08 May 2010 (has links)
Orientador: Ketty Abaroa de Rezende / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Matemática, Estatística e Computação Científica / Made available in DSpace on 2018-08-16T15:34:50Z (GMT). No. of bitstreams: 1 Lima_DahisyValadaodeSouza_M.pdf: 1595993 bytes, checksum: 49a95ad790c477c7d049695a123d9acd (MD5) Previous issue date: 2010 / Resumo: Dada uma variedade suave e fechada M, o complexo de Morse-Witten associado a uma função de Morse f : M ? R e a uma métrica Riemanniana g em M consiste de grupos de cadeia gerados pelos pontos críticos de f e um operador bordo que conta linhas de fluxos isoladas do fluxo gradiente negativo. A homologia do complexo de Morse-Witten é isomorfa à homologia singular de M. Dado um conjunto invariante isolado S, uma matriz de conexão para uma decomposição de Morse de S é uma matriz de homomorfismos entre os índices homológicos de Conley dos conjuntos de Morse. A matriz de conexão é capaz de prover informações dinâmicas sobre um fluxo. De fato, esta matriz pode detectar a existência de órbitas conectantes entre os conjuntos de Morse de S. O complexo de Morse-Witten está relacionado à teoria de matrizes de conexão. Mais precisamente, o operador bordo do complexo de Morse-Witten é um caso especial de matriz de conexão / Abstract: Given a smooth closed manifold M, the Morse-Witten complex associated to a Morse function f : M ? R and a Riemannian metric g on M consists of chain groups generated by the critical points of f and a boundary operator counting isolated flow lines of the negative gradient flow. The homology of the Morse-Witten complex is isomorphic to the singular homology of M. Give a isolated invariant set S, a connection matrix for a Morse decomposition of S is a matrix of homomorphism between the Conley homology indices of Morse sets. The connection matrix is capable of providing dynamical information of a flow. In fact, this matrix can detect the existence of connecting orbits among Morse sets of S: The Morse-Witten complex is related to connection matrices theory. More precisely, the boundary operator of the Morse-Witten complex is a special case of connection matrix / Mestrado / Matematica / Mestre em Matemática
98

Multiplicidade de soluções para sistemas gradientes semilineares ressonantes / Multiplicity of solutions for semilinear resonance gradient systems

Silva, Edcarlos Domingos da 05 November 2009 (has links)
Orientadores: Djairo Guedes de Figueiredo, Francisco Odair Vieira de Paiva / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Matematica, Estatistica e Computação Cientifica / Made available in DSpace on 2018-08-13T06:21:00Z (GMT). No. of bitstreams: 1 Silva_EdcarlosDomingosda_D.pdf: 993704 bytes, checksum: d68d4e58a916f7d2428f76207a8cb4da (MD5) Previous issue date: 2009 / Resumo: Nesta tese lidamos com três classes de sistemas gradientes ressonantes. A primeira classe é um sistema com ressonância do tipo Landesman-Lazer. A segunda classe é um sistema fortemente ressonante enquanto a terceira classe é um sistema com ressonância no infinito e na origem. Analisamos as questões de existência e multiplicidade de soluções em cada uma das classes mencionadas. Para obtermos os nossos principais resultados aplicamos alguns métodos variacionais, tais como, teoremas Min-Max e minimização. Além disso, usamos a Teoria de Morse para distinguirmos soluções dados por métodos variacionais distintos. / Abstract: In this thesis we deal with three classes of gradient elliptic systems with resonance. The first class is a resonant system of Landesman-Lazer type. The second class is a system of strong resonance type while the third class is a system with resonance at infinity and at origin. We are concerned about the questions of existence and multiplicity of solutions in each of the classes mentioned. To obtain our main results we apply variational methods, such as, Min-max theorems and minimization. Moreover, we use Morse Theory to distinguish the solutions given by different variational methods. / Doutorado / Doutor em Matemática
99

A dinamica por tras da sequencia espectral / The dynamic behind the spectral sequence

Silveira, Mariana Rodrigues da 30 April 2008 (has links)
Orientador: Ketty Abaroa de Rezende / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Matematica, Estatistica e Computação Cientifica / Made available in DSpace on 2018-08-10T21:02:39Z (GMT). No. of bitstreams: 1 Silveira_MarianaRodriguesda_D.pdf: 1531895 bytes, checksum: 3c73a8eb791483b1f0216d6f2627969b (MD5) Previous issue date: 2008 / Resumo: Neste trabalho, apresentamos um algoritmo para um complexo de cadeias C e sua diferencial dada por uma matriz de conexão _ que determina uma seqüência espectral associada (Er, dr). Mais especificamente, um sistema gerador de Er em termos da base original de C é obtido bem como a identificação de todas as diferenciais dr p : Er p ! Er p-r. Explorando a implicação dinâmica da diferencial não nula, mostramos a existência de um caminho unindo a singularidade que gera E0 p e a singularidade que gera E0 p-r no caso em que a conexão direta pelo fluxo não existe. Este caminho é composto pela justaposição de órbitas do fluxo e do fluxo reverso e prova ser importante em algumas aplicações / Abstract: In this work, we present an algorithm for a chain complex C and its di_erential given by a connection matrix _ which determines an associated spectral sequence (Er, dr). More specifically, a system spanning Er in terms of the original basis of C is obtained as well as the identi_cation of all di_erentials dr p : Er p ! Er p-r. In exploring the dynamical implication of a nonzero di_erential, we prove the existence of a path joining the singularities generating E0 p and E0 p-r in the case that a direct connection by a _ow line does not exist. This path is made up of juxtaposed orbits of the _ow and of the reverse _ow and which proves to be importantin some applications / Doutorado / Geometria e Topologia/Sistemas Dinamicos / Doutor em Matemática
100

Avaliação in vitro do colar de implantes cone Morse de diferentes diâmetros sob cargas cêntrica e excêntrica: estudo por meio da Interferometria Eletrônica por Padrões de Speckle / In vitro evaluation of the collar of Morse taper dental implants with different diameters under centric and eccentric loads: an electronic speckle pattern interferometry study

Sergio Rodrigues Sizo 15 September 2011 (has links)
Cargas oclusais excessivas podem promover tensões exageradas às estruturas de implantes/pilares/próteses, resultando em deformação, desadaptação ou mesmo fratura dos componentes e do próprio implante. Além disso, tais sobrecargas podem gerar necrose por compressão e perda óssea peri-implantar e, ainda, a ocorrência de microdeslocamentos na interface de conexão implante-pilar (I-P) ocasionando a formação de fendas propícias à colonização bacteriana, o que pode levar ao desenvolvimento de peri-implantite, contribuindo para o insucesso do conjunto. O presente estudo objetivou avaliar, por meio de uma técnica já amplamente utilizada na Engenharia e na Física a Interferometria Eletrônica por Padrões de Speckle (ESPI) as deformações a nível do colar de implantes com conexão cônica interna (cone Morse) de diferentes diâmetros (Kopp 4,3/5,5 mm e Neodent 3,5/5,0 mm), sob dois tipos (cêntrica e excêntrica) e intensidades (50 N e 100 N) de cargas, similares as quais os implantes ficam expostos durante a função mastigatória. Testou-se a hipótese de que a deformação do colar do implante seria inversamente proporcional ao diâmetro do implante. Além disso, discutiu-se vantagens e limitações da técnica ESPI frente a outros métodos comumente utilizados na avaliação de tensões. As maiores deformações foram sempre associadas às cargas excêntricas, com exceção do G1-Kopp. A maior deformação ocorreu no G1-Neodent sob carga excêntrica de 100 N e a menor, no G2-Neodent sob carga cêntrica de 50 N. A técnica ESPI mostrou-se altamente sensível e reprodutível para avaliar deformações a nivel do colar de implantes sendo possível confirmar a hipótese inicial, visto que a maior deformação esteve sempre associada aos implantes de menor diâmetro, em ambos os sistemas de implante pesquisados. / Occlusal overloading may promote excessive stresses to the implants/abutments/prosthesis, resulting in deformation, misfit or fracture of the components, until the implants. Futhermore, strains of the implant-abutment connection can cause the formation of microgaps propitious to bacterial colonization, which leads to the development of peri-implant sites, leading to the failure of the rehabilitation. This study aimed to evaluate, by a technique widely used in the engineering and physics Electronic Speckle Pattern Interferometry (ESPI) the strains related to the implant collar with internal tappered connection (Morse taper) with different diameters (Kopp 4.3/5.5 mm and Neodent 3,5/5,0 mm), under two types (centric and eccentric) and intensities (50 N and 100 N) of loads, similar which implants are exposed during masticatory function. We tested the hypothesis that the strains of the implants collar would be inversely proportional to the diameter of the implant. In addition, the survey discussed the advantages and limitations of the ESPI technique over other methods commonly used to assess strains. The largest strain was always associated with eccentric loads, except for G1-Kopp. The largest strain occurred in the G1-Neodent under the eccentric loads of 100 N and the lowest in the G2-Neodent under the centric loads of 50 N. The ESPI technique was a highly sensitive and reproducible to evaluate the strains at the level of the collar of implants being possible to confirm the initial hypothesis, since most strains was always associated with narrower-diameter implants in both implant systems studied.

Page generated in 0.0705 seconds