Considere o problema de valor inicial e de fronteira \'u IND.t\'= \'delta\'u + f(u) em \'ômega\' x (0, T), u(x, 0) = \'fi\'(x) se x \'PERTENCE A\' \'ômega\', u(x, t) = 0 se x \'PERTENCE A\' \'delta\' \'ômega\', 0 < t < T, onde ­\'ômega\' é um domínio limitado em \'R POT.n\'com bordo \'C POT.2\', f é continuamente diferenciável com f(s) > 0, e \'fi\' é não-negativa e suave sobre \'ômega\'\'BARRA\' com \'fi\'=0 sobre \'delta\'\'ômega\'. Suponha que a única solução u(x,t) possui blow-up em tempo finito T < \'INFINITO\'. A questão que se coloca é: onde ocorre o blow-up? Neste trabalho provamos que: se \'ômega\'=\'B IND.R\'\'ESTÁ CONTIDO EM\'\'R POT. n\', então o blow-up ocorre apenas em r=0, Além disso, se f(u)=\'u POT.p\'p > 1, então u(r,t)\'< OU = \'C/\'r POT.2\'(\'gama\'-1) para qualquer 1 < \'gama\'< p, e assim \'limsup IND. t\'SETA\'T\'-||u(u.\'t)||q < \'INFINITO\'se q < n(p-1)/2. No caso não simétrico onde \'ômega\' é um domínio complexo, provamos que conjunto de blow-up é um subconjunto compacto de \'ômega\'. Se f(u)=\'u POT.p\', p > 1, então u(x,t)\'< OU = \'C/\'(T-t) POT. 1/p-1\' e, se n=1,2 ou se n\'< OU=\'3 p\'< OU=\'(n+2)/(n-2), então \'tau\'POT. \'beta\'u(x+\'Ksi\', T-\'tau\'\'SETA\'\'C IND. 0\' quando \'tau\'\'SETA\'\'0 POT. 1/2\'e \'C IND. 0\'= \'beta\'POT.\'beta\'\'onde \'beta\'= \'(p-1) POT. -1\'. As provas das estimativas essenciais para demonstração desses resultados são feitas utilizando o Princípio do Máximo / Consider the initial-boundary value problem \'u IND.t\'= \'delta\'u + f(u) in \'ômega\' x (0, T), u(x, 0) = \'fi\'(x) if x \'BELONGS\' \'ômega\', u(x, t) = 0 if x \'BELONGS \' \'\\PARTIAL\' \'ômega\', 0 < t < T, where ­\'ômega\' is a bounded domain in \'R POT.n\'with \'C POT.2\', f is continuously differentiable with f(s) > 0, and \'fi\' is nonnegative and smooth on \'ômega\'\'BARRA\' with \'fi\'=0 on \'\\PARTIIAL\'\'ômega\'. Assume that the unique solution u(x,t) blows up in finite time T < \'INFINITO\'. The question addressed is: where does the blow-up occur? In this work we prove: if \'ômega\'=\'B IND.R\'\'IS CONTAINED EM\'\'R POT. n\', then blow-up occurs only at r=0, Moreover, if f(u)=\'u POT.p\'p > 1, then u(r,t)\'< OU = \'C/\'r POT.2\'(\'gama\'-1) for any 1 < \'gama\'< p, and hence \'limsup IND. t\'SETA\'T\'-||u(u.\'t)||q < \'INFINITO\'se q < n(p-1)/2. In the nonsymmetric case where \'ômega\' is a convex domain, we prove that the blow-up set lies in a compact subset of \'ômega\'. If f(u)=\'u POT.p\', p > 1, then u(x,t)\'< OU = \'C/\'(T-t) POT. 1/p-1\' and, if n=1,2 or if n\'< OU=\'3 and p\'< OU=\'(n+2)/(n-2), then \'tau\'POT. \'beta\'u(x+\'Ksi\', T-\'tau\'\'SETA\'\'C IND. 0\' where \'tau\'\'SETA\'\'0 POT. 1/2\'e \'C IND. 0\'= \'beta\'POT.\'beta\'\'where \'beta\'= \'(p-1) POT. -1\'. Elementary applications of the Maximum Principle are used to prove the essential estimate for the proofs of these results.

Submitted by Renata Lopes (renatasil82@gmail.com) on 2017-05-26T17:51:05Z No. of bitstreams: 1 sandramachadodesouzalima.pdf: 680308 bytes, checksum: 1b724b63bb7a52093f6e1411a716269f (MD5) / Approved for entry into archive by Adriana Oliveira (adriana.oliveira@ufjf.edu.br) on 2017-05-29T18:54:12Z (GMT) No. of bitstreams: 1 sandramachadodesouzalima.pdf: 680308 bytes, checksum: 1b724b63bb7a52093f6e1411a716269f (MD5) / Made available in DSpace on 2017-05-29T18:54:12Z (GMT). No. of bitstreams: 1 sandramachadodesouzalima.pdf: 680308 bytes, checksum: 1b724b63bb7a52093f6e1411a716269f (MD5) Previous issue date: 2014-07-03 / FAPEMIG - Fundação de Amparo à Pesquisa do Estado de Minas Gerais / A variedade de Nehari para a equação −∆u(x) = λa(x)u(x)q + b(x)u(x)p, com x ∈ Ω, junto com a condição de fronteira de Dirichlet é investigada no caso em que a(x) = 1, λ ∈R, q = 1 e 0 < p < 1, e também no caso em que λ > 0 e 0 < q < 1 < p < 2∗−1. Explorando a relação entre a variedade de Nehari e a aplicação fibração ( isto é, aplicações da forma t → J(tu) onde J é o funcional de Euler associado ao problema em questão), iremos discutir a existência e multiplicidade de soluções não negativas. / The Nehari Manifold for the equation −∆u(x) = λa(x)u(x)q + b(x)u(x)p, for x ∈ Ω together with Dirichlet boundary conditions is investigated in which case a(x) = 1, λ ∈R, q = 1 and 0 < p < 1, and also in the case that λ > 0 and 0 < q < 1 < p < 2∗−1. Exploring the relationship between the Nehari manifold and fibering maps (i.e., maps of the form t → J(tu) where J is the Euler functional associated to the above equation), we will discuss the existence and multiplicity of non negative solutions.

Submitted by HERACLIO LEDGAR LÓPEZ LÁZARO null (herack_11@hotmail.com) on 2016-03-21T12:48:28Z No. of bitstreams: 1 Heracliodissertação.pdf: 1074830 bytes, checksum: eacc291c2e8f474bef30477ea2c47a2f (MD5) / Approved for entry into archive by Juliano Benedito Ferreira (julianoferreira@reitoria.unesp.br) on 2016-03-22T14:20:35Z (GMT) No. of bitstreams: 1 lazaro_hll_me_sjrp.pdf: 1074830 bytes, checksum: eacc291c2e8f474bef30477ea2c47a2f (MD5) / Made available in DSpace on 2016-03-22T14:20:35Z (GMT). No. of bitstreams: 1 lazaro_hll_me_sjrp.pdf: 1074830 bytes, checksum: eacc291c2e8f474bef30477ea2c47a2f (MD5) Previous issue date: 2016-03-07 / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / The problem that we are going to study in this work, is motivated by the dynamics of differential equations nonautonomous. We will establish the existence and uniqueness of solution for a class of parabolic semilineares equations with Dirichlet boundary condition, in a family of domains that varies with time. In addition, certain hypotheses about the non-linearity, we will show the existence of a family of attractors pullback. / O problema que vamos estudar neste trabalho é motivado pela dinâmica de equações diferenciais não autônomas. Vamos estabelecer a existência e unicidade de solução para uma classe de equaçõoes parabólicas semilineares com condição de fronteira de Dirichlet, em uma família de domínios que varia com o tempo. Além disso, sob certas hipóteses sobre a não linearidade, mostraremos a existência de uma família de atratores pullback.

Elastic waves describe particles vibrating in materials holding the property of elasticity. Particularly, several kinds of resistance in elasticity lead to the models of elastic waves with different damping mechanisms. In the thesis, the influence from friction, structural damping, Kelvin-Voigt damping on the linear and semilinear elastic waves in two or three dimensions are studied. Concerning the Cauchy problem for linear elastic waves, some qualitative properties of solutions including well-posedness, smoothing effect, propagation of singularities, energy estimates and diffusion phenomena, are derived by using WKB analysis associated with diagonalization procedures or the spectral theory. By constructing suitable time-weighted Sobolev spaces and using Banach's fixed point theorem, global (in time) existence of small data solutions to the weakly coupled systems for semilinear elastic waves with different damping terms have been proved. The main tools to treat the nonlinear terms in Sobolev spaces are some fractional tools in Harmonic Analysis. Finally, well-posedness and Lp-Lq estimates for elastic waves without any damping terms in three dimensions are analyzed by employing Riesz transform theory and stationary phase methods.

Submitted by Rosivalda Pereira (mrs.pereira@ufma.br) on 2017-05-25T18:35:51Z No. of bitstreams: 1 JoaoBatistaCoelho.pdf: 361466 bytes, checksum: 8dfadcca6698d693f11831f28755fa34 (MD5) / Made available in DSpace on 2017-05-25T18:35:51Z (GMT). No. of bitstreams: 1 JoaoBatistaCoelho.pdf: 361466 bytes, checksum: 8dfadcca6698d693f11831f28755fa34 (MD5) Previous issue date: 2017-04-25 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / In this paper, we discussed the article ”The Semilinear Heat Equation with a Localized Nonlinear Source and Non-Continuous Initial Data”due to Lucas Ferreira and Elder Villamizar-Roa. In this paper they consider the Cauchy problem for the Semilinear Heat Equation with a nonlinear term presenting a nonlinear source centered on a closed region of a spatial domain. Under these conditions, they prove that this problem admits local solution and that this solution depends continuously on the initial data and is positive. / Neste trabalho, dissertamos sobre o artigo “A Semilinear Heat Equation with a Localized Nonlinear Source and Non-continuos Initial Data” devido a Lucas Ferreira e Elder Villamizar-Roa. Neste artigo eles consideram o problema de Cauchy para a Equação do Calor semilinear com um termo não linear apresentando uma fonte não linear centrada em uma região fechada de um domínio espacial. Nestas condições, eles provam que este problema admite solução local e que esta solução depende continuamente dos dados iniciais e é positiva.

Under adequate conditions on $g$, we show the density in $L^2((0,\pi),(0,2\pi))$ of the set of functions $p$ for which \begin{equation*} u_{tt}(x,t)-u_{xx}(x,t)= g(u(x,t)) + p(x,t) \end{equation*} has a weak solution subject to \begin{equation*} \begin{aligned} u(x,t)&=u(x,t+2\pi)\\ u(0,t)&=u(\pi,t)=0. \end{aligned} \end{equation*} To achieve this, we prove a Saddle Point Principle by means of a refined variant of the deformation lemma of Rabinowitz. Generally, inf-sup techniques allow the characterization of critical values by taking the minimum of the maximae on some particular class of sets. In this version of the Saddle Point Principle, we introduce sufficient conditions for the existence of a saddle-structure which is not restricted to finite-dimensional subspaces.

We studied some semilinear elliptic equations on the entire space R^N. Our approach was variational, and the major obstacle was the breakdown in compactness due to the unboundedness of the domain. First, we considered an asymptotically linear Scltrodinger equation under the presence of a steep potential well. Using Lusternik-Schnirelmann theory, we obtained multiple solutions depending on the interplay between the linear, and nonlinear parts. We also exploited the nodal structure of the solutions. For periodic potentials, we constructed infinitely many homoclinic-type multibump solutions. This recovers the analogues result for the superlinear case. Finally, we introduced weights on the linear and nonlinear parts, and studied how their interact ion affects the local and global compactness of the problem. Our approach is based on the Caffarelli-Kohn-Nirenberg inequalities.

Variational structure plays an important role in critical point theory and methods. However many differential problems are non-variational i.e. they are not the Euler- Lagrange equations of any variational functionals, which makes traditional critical point approach not applicable. In this thesis, two types of non-variational problems, a nonlinear eigen solution problem and a non-variational semi-linear elliptic system, are studied. By considering nonlinear eigen problems on their variational energy profiles and using the implicit function theorem, an implicit minimax method is developed for numerically finding eigen solutions of focusing nonlinear Schrodinger equations subject to zero Dirichlet/Neumann boundary condition in the order of their eigenvalues. Its mathematical justification and some related properties, such as solution intensity preserving, bifurcation identification, etc., are established, which show some significant advantages of the new method over the usual ones in the literature. A new orthogonal subspace minimization method is also developed for finding multiple (eigen) solutions to defocusing nonlinear Schrodinger equations with certain symmetries. Numerical results are presented to illustrate these methods. A new joint local min orthogonal method is developed for finding multiple solutions of a non-variational semi-linear elliptic system. Mathematical justification and convergence of the method are discussed. A modified non-variational Gross-Pitaevskii system is used in numerical experiment to test the method.

A class of parametric optimal control problems for semilinear parabolic equations is considered. Using recent regularity results for solutions of such equations, sufficient conditions are derived under which the solutions to optimal control problems are locally Lipschitz continuous functions of the parameter in the L1-norm. It is shown that these conditions are also necessary, provided that the dependence of data on the parameter is sufficiently strong.

An optimal control problem governed by the heat equation with nonlinear boundary conditions is considered. The objective functional consists of a quadratic terminal part and a quadratic regularization term. It is known, that an SQP method converges quadratically to the optimal solution of the problem. To handle the quadratic optimal control subproblems with high precision, very large scale mathematical programming problems have to be treated. The constrained problem is reduced to an unconstrained one by a method due to Bertsekas. A multigrid approach developed by Hackbusch is applied to solve the unconstrained problems. Some numerical examples illustrate the behaviour of the method.