Optimal Constants in the Theory of Sobolev Spaces and PDEs

Recent research activities on sharp constants and optimal inequalities have shown their impact on a deeper understanding of geometric, analytical and other phenomena in the context of partial differential equations and mathematical physics. These intrinsic questions have applications not only to a-priori estimates or spectral theory but also to numerics, economics, optimization, etc

International Conference on Nonlinear Differential Equations and Applications

Dear Participants, Colleagues and Friends It is a great honour and a privilege to give you all a warmest welcome to the first Portugal-Italy Conference on Nonlinear Differential Equations and Applications (PICNDEA). This conference takes place at the Colégio Espírito Santo, University of Évora, located in the beautiful city of Évora, Portugal. The host institution, as well the associated scientific research centres, are committed to the event, hoping that it will be a benchmark for scientific collaboration between the two countries in the area of mathematics. The main scientific topics of the conference are Ordinary and Partial Differential Equations, with particular regard to non-linear problems originating in applications, and its treatment with the methods of Numerical Analysis. The fundamental main purpose is to bring together Italian and Portuguese researchers in the above fields, to create new, and amplify previous collaboration, and to follow and discuss new topics in the area

On the parabolic-elliptic Patlak-Keller-Segel system in dimension 2 and higher

This review is dedicated to recent results on the 2d parabolic-elliptic Patlak-Keller-Segel model, and on its variant in higher dimensions where the diffusion is of critical porous medium type. Both of these models have a critical mass $M_c$ such that the solutions exist globally in time if the mass is less than $M_c$ and above which there are solutions which blowup in finite time. The main tools, in particular the free energy, and the idea of the methods are set out. A number of open questions are also stated.Comment: 26 page

Resultados de existência para equações elípticas com termos singulares

Doutoramento em Matemática e AplicaçõesEsta dissertação estuda em detalhe três problemas elípticos: (I) uma classe de equações que envolve o operador Laplaciano, um termo singular e nãolinearidade com o exponente crítico de Sobolev, (II) uma classe de equações com singularidade dupla, o expoente crítico de Hardy-Sobolev e um termo côncavo e (III) uma classe de equações em forma divergente, que envolve um termo singular, um operador do tipo Leray-Lions, e uma função definida nos espaços de Lorentz. As não-linearidades consideradas nos problemas (I) e (II), apresentam dificuldades adicionais, tais como uma singularidade forte no ponto zero (de modo que um "blow-up" pode ocorrer) e a falta de compacidade, devido à presença do exponente crítico de Sobolev (problema (I)) e Hardy-Sobolev (problema (II)). Pela singularidade existente no problema (III), a definição padrão de solução fraca pode não fazer sentido, por isso, é introduzida uma noção especial de solução fraca em subconjuntos abertos do domínio. Métodos variacionais e técnicas da Teoria de Pontos Críticos são usados para provar a existência de soluções nos dois primeiros problemas. No problema (I), são usadas uma combinação adequada de técnicas de Nehari, o princípio variacional de Ekeland, métodos de minimax, um argumento de translação e estimativas integrais do nível de energia. Neste caso, demonstramos a existência de (pelo menos) quatro soluções não triviais onde pelo menos uma delas muda de sinal. No problema (II), usando o método de concentração de compacidade e o teorema de passagem de montanha, demostramos a existência de pelo menos duas soluções positivas e pelo menos um par de soluções com mudança de sinal. A abordagem do problema (III) combina um resultado de surjectividade para operadores monótonos, coercivos e radialmente contínuos com propriedades especiais do operador de tipo Leray- Lions. Demonstramos assim a existência de pelo menos, uma solução no espaço de Lorentz e obtemos uma estimativa para esta solução.This dissertation study mainly three elliptical problems: (I) a class of equations, which involves the Laplacian operator, a singular term and a nonlinearity with the critical Sobolev exponent, (II) a class of equations with double singularity, the critical Hardy-Sobolev exponent and a concave term and (III) a class of equations in divergent form, which involves a singular term, a Leray-Lions operator, and a function defined on Lorentz spaces. The nonlinearities considered in problems (I) and (II), bring additional difficulties which, as the strong singularity at zero (so blow-up may occur) and the lack of compactness due to the presence of a Sobolev critical exponent (problem (I)) and a Hardy-Sobolev critical exponent (problem (II)). In problem (III), the singularity implies that the standard definition of weak solution may not make sense. Therefore is necessary to introduce a special notion of weak solution on open subsets of the domain. Variational methods and Critical Point Theory techniques are used to prove the existence of solutions in the two first problems. In problem (I), our method combines Nehari's techniques, Ekeland's variational principle, minimax methods, a translation argument and integral estimates of the energy level. In this case, we prove the existence of (at least) four nontrivial solutions where at least one of them is sign-changing. In problem (II), we prove the existence of at least two positive solutions and a pair of sign-changing solutions, using the concentration-compactness method and the mountain pass theorem. The approach in problem (III) combines a surjectivity result for monotone, coercive and radially continuous operators with special properties of Leray-Lions operators. We prove the existence of at least one solution in a Lorentz space and obtain an estimative for the solution