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# La semaine de l’IMB

• Du 20 juin 2022 au 24 juin 2022
• Manifestations Scientifiques
Palais de Congrès Arcachon
Organisateurs : JF. Aujol, JD. Boissonat, A. Cohen, T. Lyche, ML. Mazure , Q. Mérigot, G. Peyré
Curves and Surfaces 2022 - La conférence aura lieu du lundi 20 juin au vendredi 24 juin 2022 au Palais des Congrès d’Arcachon

• Le 23 juin 2022
• Manifestations Scientifiques
Palais de Congrès Arcachon
Comité d'organisation : Mathieu Colin (Bordeaux INP) - David Lannes (CNRS)
Colloque en l'honneur de Pierre Fabrie - 23 juin - ENSEIRB-MATMECA - Amphi F

• Le 23 juin 2022 à 14:00
• Séminaire d'Analyse
Salle de Conférences
Ahmed Sebbar (IMB)
Fonctions de Nevanlinna-Pick et transformation de Darboux
La transformation de Darboux permet d'obtenir de nouveaux potentiels pour l’équation de Schrodinger à partir d'anciens. Elle est utilisée en Géométrie Différentielle (Darboux) et en Mécanique Quantique. Le lemme de Bargmann-Schifferpermet d'obtenir de nouvelles R-fonctions (fonctions holomorphes dans le demi-plan supérieur, de partie imaginaire positive) à partir d'anciennes. C'est un opération utilisée en Analyse (théorèmes de Loewner) et aussi en Mécanique Quantique (Wigner, von Neumann...)Nous établissons une correspondance entre ces deux constructions. Les deux ingrédients fondamentauxsont les fonctions de Green (et l'effet de la transformation de Darboux sur celles-ci) et la représentation de Herglotz pour les R-fonctions et l'effet du lemme de Bargman-Schiffer sur celles-ci).
• Le 23 juin 2022 à 15:30
• Le Colloquium
Salle de Conférences
Mireille Bousquet-Melou (Labri)
Dénombrement de marches confinées dans des cônes
The study of lattice walks confined to cones is a lively topic in enumerative combinatorics, and has witnessed rich developments in the past 20 years. Typically, one is given a finite set of steps $S$ in $Z^d$, and a cone $C$ in $R^d$. Exactly $|S|^n$ walks of length $n$ start from the origin and take their steps in $S$. But how many remain in the cone $C$?One of the motivations for studying such questions is that such walks encode many objects in discrete mathematics, statistical physics, probability theory, among other fields.In the past 20 years, several approaches have been combined to understand how the choice of the steps and of the cone influence the nature of the counting sequence $a(n)$, or of the the associated series $A(t)=\sum a(n) t^n$. Is $A(t)$ rational, algebraic, or solution of a differential equation? This is now completely understood when $C$ is the first quadrant of the plane and $S$ only consists of 'small' steps. This 'simple' case involves tools coming from an attractive variety of fields: algebra on formal power series, complex analysis, computer algebra, differential Galois theory. Much remains to be done, for other cones and sets of steps.
• Le 23 juin 2022 à 17:00
• Séminaire de Physique Mathématique - EDP
Visioconférence
Chris Henderson (Univ. Arizona at Tucson)
FKPP with nonlocal advection: pushed and pulled fronts
A central focus in the study of traveling wave solutions to reaction-diffusion equations is the determination of their speed, which often represents the rate of invasion of a population. In settings with rigid structure, simple formulas for the speed have been determined; however, many physical and biological systems fall outside this setting. In this talk, I will consider a model for the spread of a species in which individuals interact, creating a nonlocal drift (advection). A special case of this is the Keller-Segel-FKPP model for a reproducing population influenced by chemotaxis. We show that there is a threshold on the chemotaxis parameters (strength, length-scale) under which the nonlocal advection does *not* influence the speed and above which the nonlocal advection `pushes' the front at a faster speed.Lien zoom: https://u-bordeaux-fr.zoom.us/j/86758445364?pwd=WGppMTVVNVFiYnV4Q2dsY0tCcStpdz09
• Le 24 juin 2022 à 10:45
• Séminaire de Géométrie
Salle 2
Juan Souto (Rennes)
Counting certain kinds of geodesics
It is a classical result of Huber that the number of closed geodesics in a closed hyperbolic surface with length at most $L$ is asymptotic to $e^L/L$. I will discuss the asymptotic growth of the number of closed geodesics satisfying further topological conditions such as, for example, arising as the boundary of an immersed one-holed torus. This is ongoing work with Viveka Erlandsson.
• Le 24 juin 2022 à 11:00
• Séminaire Calcul Scientifique et Modélisation
Salle 1