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.
Sampling tree-weighted balanced graph partitions in polynomial time.
Abstract: When judging the fairness of a political redistricting map, it is useful to be able to generate a large ensemble of “random” alternative maps. Formally, this is a graph partitioning problem. The objective is to output random partitions of the vertex set into k equal-sized pieces inducing connected subgraphs. Numerous algorithms have been developed to sample either exactly or approximately from the so-called “spanning tree distribution,” where each partition is weighted by the product of the numbers of...
El Grupo de Automorfismos de un Subshift.
RESUMEN: El grupo de automorfismos de un subshift es una invariante algebraica que ha sido muy estudiada desde los años 60s. Daré una introducción al tema pasando por los teoremas clásicos y terminaré presentando un resultado reciente que relaciona estos grupos con aspectos de la geometría del grupo subyacente al subshift. Trabajo en conjunto con Nicanor Carrasco Vargas y Paola Rivera Burgos.
Shortest Odd path on undirected graphs with conservative weights.
Abstract: We consider the Shortest Odd Path (SOP) problem, where given an undirected graph $G$, a weight function on its edges, and two vertices $s$ and $t$ in $G$, the aim is to find an $(s,t)$-path with odd length and, among all such paths, of minimum weight. For the case when the weight function is conservative, i.e., when every cycle has non-negative total weight, the complexity of the SOP problem had been open for 20 years, and was recently shown to be NP-hard. I’ll present a polynomial-time algorithm for the special case when the...
The role of Korteweg-de Vries symmetries in the partition function of extremal Black Holes.
Abstract: Abstract: In this talk, we will explore the role of generalized symmetries—symmetry groups that classify families of partial differential equations—in identifying fundamental symmetries in physics. We will also examine how this framework is crucial for defining conservation laws, building on Noether’s theorems and the contribution of Sophus Lie to the understanding of continuous symmetries. We focus on gravity, particularly within the Hamiltonian formalism, and highlight the importance of surface integrals to define conserved...
A (dis)continuous percolation phase transition on the hierarchical lattice.
Abstract: For long-range percolation on $\mathbb{Z}$ with translation-invariant edge kernel $J$, it is a classical theorem of Aizenman and Newman (1986) that the phase transition is discontinuous when $J(x-y)$ is of order $|x-y|^{-2}$ and that there is no phase transition at all when $J(x-y)=o(|x-y|^{-2})$. We prove analogous theorems for the hierarchical lattice, where the relevant threshold is at $|x-y|^{-2d} \log \log |x-y|$ rather than $|x-y|^{-2}$: There is a continuous phase transition for kernels of larger order, a discontinuous...
Parabolic trapped subvarieties in globally hyperbolic spacetimes.
Abstract: Abstract: Since 1965 when Penrose defined the concept of a trapped surface (compact and without boundary) in a 4-dimensional space-time, these surfaces have been an important object of study for geometricians and theoretical physicists, standing out for their mathematical properties as well as for their applications in general relativity. Trapped surfaces can be defined in terms of the causal character of their mean curvature vector, which allows us to generalize them to subvarieties, not necessarily compact and of any...
El uso de imágenes satelitales en Argentina y sus aplicaciones en espacios urbanos
En el seminario se hará un recorrido por el uso de imágenes satelitales para el análisis de procesos urbanos en Argentina, particularmente en ciudades intermedias bonaerenses. Se presentarán estudios de casos aplicados y metodológicos sobre: la extracción de firmas espectrales para el estudio de densidades urbanas, comparación de productos Landsat y Sentinel 2, efectos de la pandemia en concentraciones de NO2, análisis de procesos de urbanización y consecuencias en el ambiente, y la utilización de productos mixtos para el análisis de patrones...
Two-Edge Connectivity via Pac-Man Gluing.
Abstract: We study the 2-edge-connected spanning subgraph (2-ECSS) problem: Given a graph G, compute a connected subgraph H of G with the minimum number of edges such that H is spanning, i.e., V(H) = V(G), and H is 2-edge-connected, i.e., H remains connected upon the deletion of any single edge, if such an H exists. The 2-ECSS problem is known to be NP-hard. In this work, we provide a polynomial-time (5/4 + epsilon)-approximation for the problem for an arbitrarily small epsilon>0, improving the previous best approximation ratio of 13/10 +...
Long time asymptotics for critical birth and death diffusion processes.
Resumen: We study the long time behavior for the distribution of a critical birth and death diffusion process, motivated by population dynamics in changing environment (cf. a recent paper by Calvez, Henry, Méléard, Tran). The birth rates are bounded but death rates are unbounded. Our analysis is based on the spectral properties of the associated Feynman Kac semigroup. We require a standard spectral gap property for this semigroup with a dominant eigenfunction vanishing at infinity. Some examples of diffusions, diffusions with jump,...
Evaluación Del Uso De Estrategias Metacognitivas en Procesos de Modelización Matemática.
Resumen: El currículum escolar chileno incluye la modelización matemática como una habilidad clave a desarrollar a lo largo de todo el proceso formativo en matemática. Sin embargo, los procesos de modelización son altamente complejos, poco estructurados y se caracterizan por ser desafiantes. En este sentido, se reconoce la importancia de las estrategias metacognitivas para lograr un desarrollo exitoso y orientado a objetivos. En esta presentación, se abordará la adaptación de un cuestionario que permitió evaluar las estrategias...
