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.
Domination criterion for some positive operators and quasi-stationary distributions.
Resumen: After a short introduction to the concept of quasi-stationary distributions, I will present the typical and well known “finite state space” convergence results. In a second time, I will present domination criteria for the quasi-compactness of positive operators and show some applications of these spectral theoretical results for the study of quasi-stationary distributions. The talk will conclude with an illustration on the interplay between these results and recent ones on weighted branching processes, obtained in...
Well-posedness for 2D non-homogeneous incompressible fluids with general density-dependent odd viscosity
Abstract: Viscosity in fluids is often related to the dissipation of energy. However, in physical systems where the microscopic dynamics do not obey time-reversal symmetry, a non-dissipative viscosity can emerge, often referred to as “odd viscosity”. In this talk, we will consider the initial value problem for a system of equations describing the motion of two-dimensional non homogeneous incompressible fluids exhibiting odd viscosity effects. We will prove the local existence and uniqueness of strong solutions in sufficiently...
The Ramsey Number of Hypergraph Cycles.
Abstract: In 1999, Łuczak proved that the three-coloured Ramsey number of the cycle of length $n$ is less than $(4+o(1))n$, presenting a technique that, conceptually, through the use of Szemerédi’s regularity lemma, reduces the problem to that of finding the Ramsey number of a connected matching. Ever since then, Łuczak’s method has been applied successfully in many results. There are many natural ways to generalize cycles for $k$-uniform hypergraphs. In this talk, we first present a brief survey of the Ramsey numbers of Berge,...
Central limit theorems for strcutured branching processes
Abstract: Branching processes are mathematical models for populations that evolve by random reproduction: each individual lives for some time and then gives birth to new individuals, whose lives and offspring evolve independently. When such systems are enriched with spatial or structural information—allowing individuals to move, interact, or carry traits—they form infinite-dimensional stochastic processes that capture a wide range of phenomena, from cell division to particle systems. In this talk, I will discuss recent results on the central...
Optimal Control of Sweeping Processes: Addressing the Challenge of Mixed Constraint.
Abstract: In the quest to model elastoplastic mechanical systems, J.J. Moreau introduced the concept of a ‘sweeping process’ in the 1970s. These systems are characterized by their dynamics, described by a discontinuous differential inclusion that can be expressed in terms of a cone, posing a unique challenge. This presentation delves into the complexities of establishing necessary optimality conditions for optimal control problems involving such dynamics, particularly when subject to mixed constraints on state and control...
Nonexistence of positive supersolutions for semilinear fractional elliptic equations in exterior domains.
Abstract: In this talk, our goal is to investigate the nonexistence of positive solutions to nonlinear fractional elliptic inequalities in exterior domains of Rn, n ≥ 1. Our results extend the classical Liouville-type theorems of Gidas–Spruck [3] for semilinear elliptic equations, as well as the framework of Armstrong–Sirakov [1] for supersolutions of elliptic equations, to the nonlocal setting. They are also closely related to the fundamental solution approach of Felmer–Quaas [2] for nonlinear integral operators, although our arguments...
Fingerprinting Techniques for Lower Bounds in Differential Privacy and a New Fingerprinting Lemm.
Abstract: Analyzing sensitive data presents a fundamental dilemma: how can we extract population-level insights while protecting individual privacy? Differential Privacy (DP) provides a rigorous mathematical framework to address this challenge, offering formal guarantees against sensitive data exposure. Beyond its widespread adoption in practice, DP has revealed surprising connections to various fields like online learning, machine learning generalization, and robust statistics. In this talk, I’ll provide a brief introduction to the...
Secretary Problems and Combinatorial Optimal Stopping.
Abstract: Secretary problems constitute a classical setting of online decision-making, where discrete elements arrive in uniformly random order, reveal their weight, and must be accepted or rejected irrevocably, with the aim of maximizing a given function over the selected set. In the most general form of the problem, we are given a combinatorial feasibility constraint (e.g. a matroid) and the selected set has to be feasible with respect to that constraint. In such problems, the objective is to design algorithms which guarantee a...
The Fractional Anisotropic Calderón Problem
RESUMEN: We will discuss some recent progress on the anisotropic Calderón problem for the fractional Laplacian.
Weakly aperiodic Wang subshifts with minimal alphabet size on free groups.
RESUMEN Motivated by the work of E.Jeandel and M.Rao [1], where the authors establish the minimal amount of ℤ²-Wang tiles needed to produce a nonempty aperiodic ℤ²-Wang subshift to be 11, as well as the article of Piantadosi [2] which develops some aspects of symbolic dynamics on free groups related to aperiodicity, we study Wang subshifts on (k). We obtain that the minimal amount of Wang tiles needed to generate a nonempty weakly aperiodic Wang subshift on (k) is 3, and characterize every such example.
