Universiẗat, Diss., 2004--München.

Orientador: Angela Maria Sitta / Banca: Maria Aparecida Soares Ruas / Banca: Claudio Aguinaldo Buzzi / Resumo: Neste trabalho classificamos problemas de bifurcação Z2-equivariantes de corank 2 até co- dimensão 3 via técnicas da Teoria de Singularidades. A abordagem para classificar tais problemas é baseada no processo de redução à forma normal de Birkhoff para estudar a interação de modos Hopf-Pontos de Equilíbrio. O comportamento geométrico das soluções dos desdobramentos das formas normais obtidas é descrito pelos diagramas de bifurcação e estudamos a estabilidade assintótica desses ramos. / Abstract: In this work we classify the Z2-equivariant corank 2 bifurcation problems up to codimension 3 via Singularity Theory techniques. The approach to classify such problems is based on the Birkhoff normal form to study Hopf-Steady- State mode interaction. The geometrical behavior of the solutions of the unfolding of the normal forms is described by the bifurcation diagrams and we study the asymptotic stability of such branches. / Mestre

Made available in DSpace on 2014-06-11T19:27:09Z (GMT). No. of bitstreams: 0 Previous issue date: 2013-06-05Bitstream added on 2014-06-13T19:06:50Z : No. of bitstreams: 1 verri_ja_me_prud.pdf: 7130871 bytes, checksum: 40212cfd999c344f6165b927a8d582c2 (MD5) / Nesta dissertação fazemos um estudo de modelos biológicos do tipo Lotka-Volterra, utilizando como ferramenta principal a teoria qualitativa das equações diferenciais ordinárias. Abordamos, no plano e no espaço, alguns modelos do tipo predador-presa. Analisamos os comportamentos das soluções sob a variação dos parâmetros e tratamos com detalhes a bifurcação de Hopf, que dá origem a uma órbita periódica isolada (ciclo limite). Estudamos também um teorema devido a Li e Muldowney [16] sobre a estabilidade global de um ponto de equilíbrio para um sistema x˙ = f(x), x ∈ Rn. Aplicamos este resultado no estudo de um modelo de HIV tridimensional, provando a estabilidade global de um ponto de equilíbrio, para certos valores dos parâmetros. Para o mesmo modelo, verificamos a ocorrência de uma dupla bifurcação de Hopf, que leva ao surgimento e posterior desaparecimento de um ciclo limite, ao variarmos um dos parâmetros envolvidos no sistema. As bifurcações de Hopf ocorrem simultaneamente à perda de estabilidade global do ponto de equilíbrio / In this work we present a study of biological models of Lotka-Volterra type, using as main tool the qualitative theory of ordinary differential equations. We analyze some two and three dimensional predator-prey models. The behavior of the solutions are studied under the variation of parameters and it is shown that a Hopf bifurcation occurs, leading to the creation of an isolated periodic orbit (limit cycle). We also study a theorem due to Li and Muldowney [16] about the global stability of an equilibrium point of a system x˙ = f(x), x ∈ Rn. We apply this result in the analysis of a three dimensional model of HIV with treatment, showing the global stability of an equilibrium point, for certain parameter values. For the same model, we prove the occurrence of two Hopf bifurcations, leading to the birth and subsequent death of a limit cycle, when we vary one of the parameters of the model. The Hopf bifurcations occurs simultaneously to the lack of global stability of the equilibrium point

Dissertação (mestrado)—Universidade de Brasília, Instituto de Ciências Exatas, Departamento de Matemática, 2008. / Submitted by Jaqueline Oliveira (jaqueoliveiram@gmail.com) on 2008-12-15T15:59:27Z No. of bitstreams: 1 DISSERTACAO_2008_KelemGomesLourenco.pdf: 1422115 bytes, checksum: 20a32fbf536b3c9518ef0a8601e1d847 (MD5) / Approved for entry into archive by Georgia Fernandes(georgia@bce.unb.br) on 2009-02-18T17:36:21Z (GMT) No. of bitstreams: 1 DISSERTACAO_2008_KelemGomesLourenco.pdf: 1422115 bytes, checksum: 20a32fbf536b3c9518ef0a8601e1d847 (MD5) / Made available in DSpace on 2009-02-18T17:36:21Z (GMT). No. of bitstreams: 1 DISSERTACAO_2008_KelemGomesLourenco.pdf: 1422115 bytes, checksum: 20a32fbf536b3c9518ef0a8601e1d847 (MD5) / Neste trabalho analisamos o sistema de equações differenciais com duas presas e um predador do tipo Lotka-Volterra, com e sem colheita. Inicialmente estudamos a estabilidade local e global dos pontos de equilíbrio no primeiro modelo. Posteriormente, no segundo modelo, estudamos o coeficiente de estabilidade das órbitas periódicas, através da forma normal e estimativas numéricas. Através do recurso Maple 11, verificamos o comportamento das soluções e o surgimento das órbitas periódicas. ________________________________________________________________________________________ ABSTRACT / In this work we analyzed the Lotka-Volterra system of diferential equations with two preys and a predator, with and without harvesting. Initially we studied the local and global stability of the points of equilibrium in the first model. Later, in the second model, we studied the coefficient of stability of the periodic orbits, by using normal form and numerical estimatives. By using Maple 11, we verified the behavior of the solutions and the appearance of the periodic orbits.

Made available in DSpace on 2016-06-02T20:28:26Z (GMT). No. of bitstreams: 1 3729.pdf: 608631 bytes, checksum: 9ccfdd58a15118a67f48b346502a277e (MD5) Previous issue date: 2011-03-02 / Financiadora de Estudos e Projetos / In the area of the theory of fixed points and coincidences of Nielsen, this study aims to develop techniques to minimize the set of fixed points in homotopies and the set of coincidences in pairs of homotopies. The techniques are based on Hopf construction for selfmaps of polyhedrons and on the results presented by Helga Schirmer in context of _x-finite homotopies. For pairs of homotopies, we created the concept of coincidences finite and we proved that certain pairs of homotopies can have their set of coincidences minimized in order to become coincidences finite. / No contexto da teoria de pontos fixos e coincidências de Nielsen, este trabalho destina-se ao desenvolvimento de técnicas de minimização do conjunto de pontos fixos em homotopias e do conjunto de coincidências em pares de homotopias. As técnicas baseiam-se na construçãoo de Hopf para auto-aplicações de poliedros e nos resultados apresentados por Helga Schirmer (1979) para homotopias finitamente fixadas. Para pares de homotopias, criamos o conceito de finitamente coincidentes e provamos que certos pares de homotopias podem ter seu conjunto de coincidências minimizado, a fim de se tornarem finitamente coincidentes.

abstract: Using a simple $SI$ infection model, I uncover the overall dynamics of the system and how they depend on the incidence function. I consider both an epidemic and endemic perspective of the model, but in both cases, three classes of incidence functions are identified. In the epidemic form, power incidences, where the infective portion $I^p$ has $p\in(0,1)$, cause unconditional host extinction, homogeneous incidences have host extinction for certain parameter constellations and host survival for others, and upper density-dependent incidences never cause host extinction. The case of non-extinction in upper density-dependent incidences extends to the case where a latent period is included. Using data from experiments with rhanavirus and salamanders, maximum likelihood estimates are applied to the data. With these estimates, I generate the corrected Akaike information criteria, which reward a low likelihood and punish the use of more parameters. This generates the Akaike weight, which is used to fit parameters to the data, and determine which incidence functions fit the data the best. From an endemic perspective, I observe that power incidences cause initial condition dependent host extinction for some parameter constellations and global stability for others, homogeneous incidences have host extinction for certain parameter constellations and host survival for others, and upper density-dependent incidences never cause host extinction. The dynamics when the incidence function is homogeneous are deeply explored. I expand the endemic considerations in the homogeneous case by adding a predator into the model. Using persistence theory, I show the conditions for the persistence of each of the predator, prey, and parasite species. Potential dynamics of the system include parasite mediated persistence of the predator, survival of the ecosystem at high initial predator levels and ecosystem collapse at low initial predator levels, persistence of all three species, and much more. / Dissertation/Thesis / Doctoral Dissertation Mathematics 2017

abstract: One explanation for membrane accommodation in response to a slowly rising current, and the phenomenon underlying the dynamics of elliptic bursting in nerves, is the mathematical problem of dynamic Hopf bifurcation. This problem has been studied extensively for linear (deterministic and stochastic) current ramps, nonlinear ramps, and elliptic bursting. These studies primarily investigated dynamic Hopf bifurcation in space-clamped excitable cells. In this study we introduce a new phenomenon associated with dynamic Hopf bifurcation. We show that for excitable spiny cables injected at one end with a slow current ramp, the generation of oscillations may occur an order one distance away from the current injection site. The phenomenon is significant since in the model the geometric and electrical parameters, as well as the ion channels, are uniformly distributed. In addition to demonstrating the phenomenon computationally, we analyze the problem using a singular perturbation method that provides a way to predict when and where the onset will occur in response to the input stimulus. We do not see this phenomenon for excitable cables in which the ion channels are embedded in the cable membrane itself, suggesting that it is essential for the channels to be isolated in the spines. / Dissertation/Thesis / Ph.D. Applied Mathematics 2012

CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel Superior / Nesta dissertaÃÃo fazemos um estudo de geometria das superfÃcies isometricamente imersas numa forma espacial tridimensional impondo algumas condiÃÃes sobre as curvaturas mÃdia e gaussiana. Se a curvatura à nÃo positiva prova-se que a superfÃcie à uma esfera, um produto de cÃrculos ou um cilindro. TambÃm à provado que se uma superfÃcie localmente H-deformÃvel à um toro, entÃo sua curvatura mÃdia à constante. / In this dissertation we study the geometry of surfaces isometrically immersed in a 3-dimensional space form imposing some conditions on its mean and gaussian curvature. If the gaussian curvature is non-positive we prove that the surface is a sphere, a product of circles or a cylinder. It is also proved that if a surface locally H-deformable is a torus; then it mean curvature is constant.

Made available in DSpace on 2014-06-12T18:32:55Z (GMT). No. of bitstreams: 2 arquivo8675_1.pdf: 657729 bytes, checksum: 804c61b142d2c137eb094b7809772630 (MD5) license.txt: 1748 bytes, checksum: 8a4605be74aa9ea9d79846c1fba20a33 (MD5) Previous issue date: 2006 / Conselho Nacional de Desenvolvimento Científico e Tecnológico / Esta dissertação tem como principal objetivo apresentar, de maneira auto-sufuciente, a demonstração de M. Atiyah e R. Bott do Teorema de Periodicidade de Bott em K-Teoria. Para isto, somos levados a fazermos uma introdução à teoria de fibrados vetoriais e à K-teoria, discutindo os vários conceitos e resultados necessários. Ao final, como aplicação do que foi desenvolvido, apresentamos a singela demonstração de M. Atiyah do teorema de F. Adam sobre o invariante de Hopf, e como consequência deste resolvemos os problemas clássicos da paralelizabilidade das esferas e das álgebras de divisão

In this thesis we use the theory of algebraic operads to define a complete invariant of real and rational homotopy classes of maps of topological spaces and manifolds. More precisely let f,g : M -&gt; N be two smooth maps between manifolds M and N. To construct the invariant, we define a homotopy Lie structure on the space of linear maps between the homology of M and the homotopy groups of N, and a map mc from the set of based maps from M to N, to the set of Maurer-Cartan elements in the convolution algebra between the homology and homotopy. Then we show that the maps f and g are real (rational) homotopic if and only if mc(f) is gauge equivalent to mc(g), in this homotopy Lie convolution algebra. In the last part we show that in the real case, the map mc can be computed by integrating certain differential forms over certain subspaces of M. We also give a method to determine in certain cases, if the Maurer-Cartan elements mc(f) and mc(g) are gauge equivalent or not. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 1: Manuscript. Paper 2: Manuscript. Paper 3: Manuscript.</p>