Demonstramos o seguinte teorema: Seja M uma variedade Riemanniana compacta, conexa e sem bordo. Dados um endomorismo f : M ightarrow M, uma função contínua \\phi: M ightarrow R e \\epsilon > 0, então existe um endomorísmo \\tilde f : M ightarrow M tal que d(f; \\tide f) = \\max_{x \\in M} d(f(x); \\tilde f(x)) < \\epsilon, e existe uma medida \\phi-maximizante para \\tilde f que está suportada em uma orbita periodica. Este teorema e uma generalização dos resultados obtidos por S. Addas-Zanatta e F. Tal. / We prove the following theorem: Let M be a bondaryless, compact and connected Riemannian Manifold. Given an endomorphism f on M, a continuous function \\phi : M ightarrow R and \\epsilon > 0, then there exist an endomorphism \\tilde f on M with d(f; \\tilde f) < \\epsilon such that, some \\phi-maximizing measure for \\tilde f is supported on a periodic orbit. This theorem is a generalization of the results obtained by S. Addas-Zanatta and F. Tal.

O propósito deste trabalho é estudar a existência de solução periódica para problemas de oscilação não linear de barras submetidas a forças periódicas. Estudaremos concretamente dois problemas, que serão interpretados como equações diferenciais abstratas de segunda ordem cuja classe foi considerada em Ceron e Lopes [1]. Para garantir a existência de solução periódica dos problemas considerados, mostraremos que a aplicação de Poincaré S é limitada dissipativa e alfa-contração. Isso garante a existência de um atrator invariante compacto e a existência de um ponto fixo de S, o que é equivalente a existência da solução periódica. / Our aim in this work is to study the existence of periodic solution to oscillation in nonlinear problems of beams submitted to periodic forcing. We will study concretely two problems, which can be interpreted as an abstract second order diferential equation studied by Ceron and Lopes [1]. Our intention is to prove the existence of periodic solution to these problems. To this end, we will show that the Poincaré map S is uniform ultimately bounded and alpha-contraction. Thus we have the existence of invariant compact attractor, therefore S have a fixed point, which is equivalent the existence of a periodic solution.

Demonstramos o seguinte teorema: Seja M uma variedade Riemanniana compacta, conexa e sem bordo. Dados um endomorismo f : M ightarrow M, uma função contínua \\phi: M ightarrow R e \\epsilon > 0, então existe um endomorísmo \\tilde f : M ightarrow M tal que d(f; \\tide f) = \\max_{x \\in M} d(f(x); \\tilde f(x)) < \\epsilon, e existe uma medida \\phi-maximizante para \\tilde f que está suportada em uma orbita periodica. Este teorema e uma generalização dos resultados obtidos por S. Addas-Zanatta e F. Tal. / We prove the following theorem: Let M be a bondaryless, compact and connected Riemannian Manifold. Given an endomorphism f on M, a continuous function \\phi : M ightarrow R and \\epsilon > 0, then there exist an endomorphism \\tilde f on M with d(f; \\tilde f) < \\epsilon such that, some \\phi-maximizing measure for \\tilde f is supported on a periodic orbit. This theorem is a generalization of the results obtained by S. Addas-Zanatta and F. Tal.

We propose a dynamical systems approach to the study of weak turbulence(spatiotemporal chaos) based on the periodic orbit theory, emphasizing the role of recurrent patterns and coherent structures. After a brief review of the periodic orbit theory and its application to low-dimensional dynamics, we discuss its possible extension to study dynamics of spatially extended systems. The discussion is three-fold. First, we introduce a novel variational scheme for finding periodic orbits in high-dimensional systems. Second, we prove rigorously the existence of periodic structures (modulated amplitude waves) near the first instability of the complex Ginzburg-Landau equation, and check their role in pattern formation. Third, we present the extensive numerical exploration of the Kuramoto-Sivashinsky system in the chaotic regime: structure of the equilibrium solutions, our search for the shortest periodic orbits, description of the chaotic invariant set in terms of intrinsic coordinates and return maps on the Poincare section.

O propósito deste trabalho é estudar a existência de solução periódica para problemas de oscilação não linear de barras submetidas a forças periódicas. Estudaremos concretamente dois problemas, que serão interpretados como equações diferenciais abstratas de segunda ordem cuja classe foi considerada em Ceron e Lopes [1]. Para garantir a existência de solução periódica dos problemas considerados, mostraremos que a aplicação de Poincaré S é limitada dissipativa e alfa-contração. Isso garante a existência de um atrator invariante compacto e a existência de um ponto fixo de S, o que é equivalente a existência da solução periódica. / Our aim in this work is to study the existence of periodic solution to oscillation in nonlinear problems of beams submitted to periodic forcing. We will study concretely two problems, which can be interpreted as an abstract second order diferential equation studied by Ceron and Lopes [1]. Our intention is to prove the existence of periodic solution to these problems. To this end, we will show that the Poincaré map S is uniform ultimately bounded and alpha-contraction. Thus we have the existence of invariant compact attractor, therefore S have a fixed point, which is equivalent the existence of a periodic solution.

Seja K um conjunto de Cantor. Neste trabalho apresentamos dois teoremas relacionados a densidade do conjunto das dinâmicas simbólicas. No caso de endomorfismos provamos que, dado uma dinâmica T : K K, existe uma T : K K próxima a T, tal que toda órbita é finalmente periódica. Já no caso de homeomorfismos, mostramos que, dado uma dinâmica T : K K, existe uma T : K K próxima a T, tal que o w-limite de toda órbita de T é uma órbita periódica. Em particular, mostramos que, em ambos os casos, todas as medidas ergódicas estão suportadas em órbitas periódicas. / Let K be a Cantor set. In this work we present two theorems related to the density of symbolic dynamics. We prove that given an endomorphism T : K K then there exists an endomorphism ~ T : K K close to T such that every orbit is finally periodic. We also prove that given a homeomorphism T : K K then there exists a homeomorphism ~ T : K K close to T such that the w-limit of every orbit is a periodic orbit. In particular, we have shown, in both cases, that all ergodic measures have support on periodic orbits.

Seja K um conjunto de Cantor. Neste trabalho apresentamos dois teoremas relacionados a densidade do conjunto das dinâmicas simbólicas. No caso de endomorfismos provamos que, dado uma dinâmica T : K K, existe uma T : K K próxima a T, tal que toda órbita é finalmente periódica. Já no caso de homeomorfismos, mostramos que, dado uma dinâmica T : K K, existe uma T : K K próxima a T, tal que o w-limite de toda órbita de T é uma órbita periódica. Em particular, mostramos que, em ambos os casos, todas as medidas ergódicas estão suportadas em órbitas periódicas. / Let K be a Cantor set. In this work we present two theorems related to the density of symbolic dynamics. We prove that given an endomorphism T : K K then there exists an endomorphism ~ T : K K close to T such that every orbit is finally periodic. We also prove that given a homeomorphism T : K K then there exists a homeomorphism ~ T : K K close to T such that the w-limit of every orbit is a periodic orbit. In particular, we have shown, in both cases, that all ergodic measures have support on periodic orbits.

The term spatiotemporal chaos refers to physical phenomena that exhibit irregular oscillations in both space and time. Examples of such phenomena range from cardiac dynamics to fluid turbulence, where the motion is described by nonlinear partial differential equations. It is well known from the studies of low dimensional chaotic systems that the state space, the space of solutions to the governing dynamical equations, is shaped by the invariant sets such as equilibria, periodic orbits, and invariant tori. State space of partial differential equations is infinite dimensional, nevertheless, recent computational advancements allow us to find their invariant solutions (exact coherent structures) numerically. In this thesis, we try to elucidate the chaotic dynamics of nonlinear partial differential equations by studying their exact coherent structures and invariant manifolds. Specifically, we investigate the Kuramoto-Sivashinsky equation, which describes the velocity of a flame front, and the Navier-Stokes equation for an incompressible fluid in a circular pipe. We argue with examples that this approach can lead to a theory of turbulence with predictive power.

Gene networks can be modeled by piecewise-linear (PL) switching systems of differential equations, called Glass networks after their originator. Networks of interacting genes that regulate each other may have complicated interactions. From a `systems biology' point of view, it would be useful to know what types of dynamical behavior are possible for certain classes of network interaction structure. A useful way to describe the activity of this network symbolically is to represent it as a directed graph on a hypercube of dimension $n$ where $n$ is the number of elements in the network. Our work here is considering this problem backwards, i.e. we consider different types of cycles on the $n$-cube and show that there exist parameters, consistent with the directed graph on the hypercube, such that a periodic orbit exists. For any simple cycle on the $n$-cube with a non-branching vertex, we prove by construction that it is possible to have a stable periodic orbit passing through the corresponding orthants for some sets of focal points $F$ in Glass networks. When the simple cycle on the $n$-cube doesn't have a non-branching vertex, a structural principle is given to determine whether it is possible to have a periodic orbit for some focal points. Using a similar construction idea, we prove that for self-intersecting cycles where the vertices revisited on the cycle are not adjacent, there exist Glass networks which have a periodic orbit passing through the corresponding orthants of the cycle. For figure-8 patterns with more than one common vertex, we obtain results on the form of the return map (Poincar{\'e} map) with respect to how the images of the returning cones of the 2 component cycle intersect the returning cone themselves. Some of these allow complex behaviors.

In this dissertation, regularization of simultaneous binary collision, existence of a Schubart-like periodic orbit, existence of a planar symmetric periodic orbit with multiple simultaneous binary collisions, and their linear stabilities are studied. The detailed background of those problems is introduced in chapter 1. The singularities of simultaneous binary collision in the collinear four-body problem is regularized in chapter 2. We use canonical transformations to collectively analytically continue the singularities of the simultaneous binary collision solutions in both the decoupled case and the coupled case. All the solutions are found and more importantly, we find a crucial first integral which describes the relationship between the decoupled solutions and the coupled solutions. In chapter 3, we show the existence of a Schubart-like orbit, a periodic orbit with singularities in the symmetric collinear four-body problem. In each period of the orbit, there is a binary collision (BC) between the inner two bodies and a simultaneous binary collision (SBC) of the two clusters on both sides of the origin. The system is regularized and the existence is proven by using a "turning point" technique and a continuity argument on differential equations of the regularized Hamiltonian. Analytical methods are used in chapter 4 to prove the existence of a periodic, symmetric solution with singularities in the planar 4-body problem. A numerical calculation and simulation are used to generate the orbit. The analytical method can be extended to any even number of bodies. Multiple simultaneous binary collisions are a key feature of the orbits generated. In chapter 5, we apply the analytic-numerical method of Roberts to determine the linear stability of time-reversible periodic simultaneous binary collision orbits in the symmetric collinear four body problem with masses 1, m, m , 1, and also in a symmetric planar four-body problem with equal masses. For the collinear problem, this verifies the earlier numerical results of Sweatman for linear stability.