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.
Clearing-out of dipoles for minimisers of 2-dimensional discrete energies with topological singularities.
Abstract: A key question in the analysis of discrete models for material defects, such as vortices in spin systems and superconductors or isolated dislocations in metals, is whether information on boundary energy for a domain can be sufficient for controlling the number of defects in the interior. We present a general combinatorial dipole-removal argument for a large class of discrete models including XY systems and screw dislocation models, allowing to prove sharp conditions under which controlled flux and boundary energy guarantee tohave...
Machine learning-driven COVID-19 early triage and large-scale testing strategies based on the 2021 Costa Rican Actualidades survey.
Resumen: Due to resource limitations, the COVID-19 pandemic presented substantial challenges for large-scale testing. Traditional approaches often fail to balance detection rates with limited reagents and laboratory capacity. In this work we introduced a machine learning–driven triage framework to stratify individuals by contagion risk and deploy adaptive testing protocols accordingly. We adapted the strategies according to the characteristics of RT-PCR tests, which offer high sensitivity, but they require specialized laboratories, and...
Caracterización de relaciones regionalmente proximales mediante el semigrupo envolvente.
RESUMEN: El estudio de los sistemas de orden d ha despertado gran interés por sus aplicaciones en sistemas dinámicos, teoría de números y combinatoria. Un aspecto interesante es el estudio de las propiedades algebraicas de sus semigrupos envolventes. En esta charla se abordará la conexión entre el semigrupo envolvente y la relación regionalmente proximal, la cual define a los sistemas de orden d. En particular, se presentará una caracterización algebraica de estas relaciones. Luego mencionaré aplicaciones de estos resultados a la estructura...
Column Generation and the Feature Selection Problem.
Abstract: Column generation is a well-known decomposition method to solve linear and mixed integer problems with a large number of variables. A similar column generation decomposition method can be constructed for conic optimization problems. In this talk we present work that explores whether this can be a competitive solution method for the continuous relaxation of the feature selection problem.
Poisson representation of Brownian bridge.
Resumen: We consider Brownian motion $(B(t))$, for $t\in[0,1]$, and Brownian bridge $BB(t)$, the Brownian motion conditioned to return to $0$ at time~$1$. The following identity is well known,(1)\,\hfill law of $(BB(t))_{t\in[0,1]}= $ law of $(B(t)- tB(1))_{t\in[0,1]}$. \hfill\ A centered and rescaled Poisson point process $B^\varepsilon(t)$ converges to Brownian motion, where $\varepsilon$ is the scaling parameter going to $0$. For each $\varepsilon>0$, we construct a coupling $(B^\varepsilon(t),BB^\varepsilon (t))$ satisfying an...
The Haagerup property.
Abstract: The Haagerup property is an analytic property of groups that generalises amenability. It originated from the study of C*-algebras, and it has found applications in several areas of mathematics, including harmonic analysis, geometric group theory, topology, and ergodic theory. This talk will consist in an introduction to this property and its connections to group actions on Banach spaces.
Computer-assisted proof of robust transitivity.
RESUMEN: A smooth dynamical system is transitive if it has a dense orbit, loosely meaning that it has some chaos in a topological sense. If this property holds for all diffeomorphisms in a C¹-neighborhood, we say that systems in this neighborhood are robustly transitive. By Bonatti, Diaz and Pujals (2003), robustly transitive diffeomorphisms are volume hyperbolic, and thus they have positive topological entropy, being chaotic in a strict sense and in a robust way. Robust properties are key in classifying smooth dynamical systems, and they are...
Prophet Inequalities with Moment Knowledge.
Abstract: In this talk, we study a variant of the prophet inequality with limited information, where the decision maker only has access to the first k moments of each random variable, rather than their full distributions. Our main result is that, for any k, even one dependent on n, the best possible competitive ratio is Θ(1/ log(n)), which we show can already be achieved with knowledge of the first moment only. Our result implies that the moments are not very informative in this setting, so extra information is needed if one aims for better...
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...
