Noticias en español
Seminars appear in decreasing order in relation to date. To find an activity of your interest just go down on the list. Normally seminars are given in English. If not, they will be marked as Spanish Only.
Dynamics of Concentrated Vorticities In 2d and 3d Euler Flows.
Abstract: A classical problem that traces back to Helmholtz and Kirchhoff is the understanding of the dynamics of solutions to the Euler equations of an inviscid incompressible fluid when the vorticity of the solution is initially concentrated near isolated points in 2d or vortex lines in 3d. We discuss some recent results on these solutions’ existence and asymptotic behavior. We describe, with precise asymptotics, interacting vortices, and traveling helices, and extension of these results for the 2d generalized SQG. In particular we...
Braiding groups of homeomorphisms of the Cantor set.
Abstract: In this talk we will discuss some recent work on groups which connect self-similar and Higman-Thompson groups to big mapping class groups via “braiding”. We will explain some results on the topological finiteness properties of the resulting groups, which are topological generalizations of the algebraic properties of being finitely generated and finitely presented. The talk will involve recent joint works with Xiaolei Wu (Fudan) and Matthew Zaremsky (Albany).
Existence of quasi-stationary distributions for downward skip-free Markov chains.
Abstract: I talk about existence of a quasi-stationary distribution for downward skip-free continuous-time Markov chains on non-negative integers stopped at zero. The scale function for these processes is introduced and the boundary is classified by a certain integrability condition on the scale function, which gives an extension of Feller’s classification of the boundary for birth-and-death processes.The existence and the set of quasi-stationary distributions are characterized by the scale function and the new classification of the...
Decomposition of Probability Marginals for Security Games in Abstract Networks and Ideal Clutters.
Abstract: Consider a set system on a finite ground set E, where each set P in the system is equipped with a required hitting probability r(P) and each element e of E has a probability marginal p(e). We study the question whether the marginals can be decomposed into a distribution over all subsets of E such that the resulting random set intersects each set P from the system with probability at least r(P). A simple necessary condition is that for every set P in the system, the sum of the marginals of elements in P is at least r(P). Extending a...
Estimación Adaptativa en Modelos de Regresión Funcional Asociado a Proceso de Wiener.
Resumen: En esta charla, estudiaremos métodos de suavizamiento para estimar funciones no-paramétricas. Veremos cómo elegir los parámetros de suavizamiento con el objetivo de tener estimadores óptimos. Más específicamente, introduciremos el método de Goldenshluger-Lepski (2011) que permite obtener estimadores que se adaptan a la regularidad de la función. Mostraremos cómo extender este método en el caso de la regresión funcional donde la variable regresora es un proceso de Wiener. Definiremos una familia de estimadores para la función de...
Mean equicontinuity – beyond minimality.
Abstract:: In this talk we present recent developments and new results in the study of mean equicontinuity and weak mean equicontinuity in the context of countable discrete amenable groups, such as a characterization in terms of spectral theory. It is known that the notions of mean eq. and weak mean eq. do not depend on the process of averaging (the Følner sequence), whenever the action is minimal, or the acting group is Abelian. However, we present an example of a (non-minimal, but transitive) action where mean equicontinuity and weak mean...
Uniform a priori estimates for positive solutions of the Lane-Emden equation and system in the plane.
Abstract A few years ago we proved that positive solutions of the superlinear Lane-Emden equation in a two-dimensional smooth bounded domain are bounded independently of the exponent in the equation. Apart from being interesting in itself, this information plays a pivotal role in the asymptotic study of solutions for large exponents, as well as contributes to the old and hard conjecture of uniqueness of positive solutions in a convex domain. We recently took up a similar study for the Lane-Emden system and discovered that, contrary to initial...
Combinatorial Contracts.
Abstract: An emerging frontier in Algorithmic Game Theory is Algorithmic Contract Theory, which studies the classic hidden-action principal-agent problem of contract theory through the computational lens. In this talk, I will present three basic ways in which the problem can be combinatorial and survey both hardness and poly-time (approximation) results. The analysis will uncover some surprising connections (but also fundamental differences) to combinatorial auctions.
Turbulent steady states in the nonlinear Schrodinger equation.
Abstract: The nonlinear Schrodinger (NLS) equation, also known as the Gross-Pitaevskii equation, is one of the most common equations in physics. Its applications go from the propagation of light in nonlinear media to the description of gravity waves and Bose-Einstein condensates. In general, the NLS equation describes the evolution of nonlinear waves. Such waves interact and transfer energy and other invariants along scales in a cascade process. This phenomenon is known as wave turbulence and is described by the (weak) wave turbulence theory...
Evaluación del coeficiente de atenuación difusa de la radiación fotosintéticamente activa en el lago Villarrica.
Resumen: “El coeficiente de atenuación difusa de la radiación fotosintéticamente activa es una propiedad óptica inherente importante del campo de luz subacuático. Este parámetro, como medida de la transparencia del medio, es un buen indicador de la calidad del agua. En este estudio, se utilizaron imágenes Landsat 8 OLI y Sentinel-2A/B MSI basadas en algoritmos para estimar el coeficiente de atenuación difusa de la radiación fotosintéticamente activa en un lago en el centro-sur de Chile. Los datos estimados de los algoritmos del módulo ACOLITE...
