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BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20200114T113000
DTEND;TZID=Europe/Paris:20200114T123000
DTSTAMP:20260416T055311
CREATED:20191004T072822Z
LAST-MODIFIED:20200127T110238Z
UID:6603-1579001400-1579005000@lmv.math.cnrs.fr
SUMMARY:AG : Raphaël Beuzard-Plessis (Université d'Aix-Marseille) : Une nouvelle preuve du lemme fondamental de Jacquet-Rallis
DESCRIPTION:Le lemme fondamental de Jacquet-Rallis est une égalité entre des intégrales orbitales (relatives) locales qui peut se reformuler comme une égalité combinatoire de comptage de réseaux. Ce lemme est issu d’une approche à la conjecture de Gan-Gross-Prasad pour les groupes unitaires\, qui relie les valeurs centrales de certaines fonctions L à des périodes automorphes\, via une comparaison de formules des traces relatives. C’est d’ailleurs un ingrédient essentiel dans la preuve récente par Wei Zhang de nombreux cas de cette conjecture. Le lemme fondamental en question a été démontré peu après sa formulation par Zhiwei Yun en caractéristique positive par des méthodes géométriques inspirées du travail de Ngô puis transféré en caractéristique nulle par Julia Gordon via des techniques de théorie des modèles. Dans cet exposé\, je présenterai une preuve alternative de ce lemme fondamental qui est purement locale et basée sur des outils élémentaires d’analyse harmonique (transformation de Fourier). Combiné avec le travail récent de Jingwei Xiao\, ceci fournit une preuve totalement élémentaire du lemme fondamental endoscopique pour les groupes unitaires (théorème de Laumon-Ngô).
URL:https://lmv.math.cnrs.fr/evenenement/expose-de-raphael-beuzard-plessis/
LOCATION:Bâtiment Fermat\, salle 2205\, 45 avenue des Etats-Unis\, Versailles\, 78000\, France
CATEGORIES:Séminaire AG
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20200114T113000
DTEND;TZID=Europe/Paris:20200114T123000
DTSTAMP:20260416T055311
CREATED:20191008T134330Z
LAST-MODIFIED:20200127T110247Z
UID:6638-1579001400-1579005000@lmv.math.cnrs.fr
SUMMARY:PS : Lionel Truquet (ENSAI\, Univ. Rennes 1) : Modelling non stationarity from perturbation techniques for Markov chains
DESCRIPTION:Relaxing the stationarity assumption in time series analysis is a challenging problem. We will present an approach based on Markov chain techniques through a notion called local stationarity and which consists in replacing the usual asymptotic by an « infill » one. \nThe main idea is to consider time-inhomogenous Markov chains for which two successive Markov kernels are closer when the sample size increases. Such new infill  asymptotics will be shown to be fundamental to give a meaning to local statistical inference when the Markov kernels depend on a functional parameter. In particular\, we use contraction properties of Markov kernels to control the local approximation of the time-inhomogenous Markov chain by a stationary one. As a consequence\, many parametric geometrically ergodic Markov chain models have a locally stationary version. \nTo recover the standard nonparametric rates of convergence for estimating functional parameters\, we combine mixing properties of the Markov chains (for controlling variance terms) and differentiability properties of some families of invariant probability measures depending on a parameter (for controlling bias terms). As a consequence\, we obtain a first theory for defining time-inhomogenous Markov chains models compatible with nonparametric statistical inference.
URL:https://lmv.math.cnrs.fr/evenenement/ps-lionel-truquet-ensai-univ-rennes-1-titre-a-venir/
LOCATION:Bâtiment Fermat\, salle 2107
CATEGORIES:Séminaire PS
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20200121T113000
DTEND;TZID=Europe/Paris:20200121T123000
DTSTAMP:20260416T055311
CREATED:20191008T134712Z
LAST-MODIFIED:20200124T141522Z
UID:6640-1579606200-1579609800@lmv.math.cnrs.fr
SUMMARY:PS : Elena Di Bernardino (CNAM) : Lipschitz-Killing curvatures of excursion sets for two-dimensional random fields
DESCRIPTION:Lipschitz-Killing (LK) curvatures are geometrical tools which permit to analyze d dimensional objects. Considering a black and white image in dimension d= 2\, there are three LK curvatures: the surface area\, the half perimeter and the Euler characteristic. Each of them brings distinct information on the geometry of the black (resp. white) zone. The surface area is related to its occupation density\, the perimeter to its regularity and the Euler characteristic to its connectivity. Considering real-life data as a realization of a random field and analyzing them with the help of Lipschitz-Killing curvatures is an effective approach that has already been successfully applied in various disciplines in the past decades. For instance\, in cosmology\, the question of Gaussianity and anisotropy of the Cosmic Microwave Background radiation has been tackled in a huge amount of publications. A similar methodology is also applied for analyzing the distribution of galaxies. Another domain where the LK curvatures are used as methodological tools is in medical imaging as\, for example\, brain imaging or mammograms. In this context\, the main purpose could be to find the locations of high brain activity or to study the breast density. In our papers\, we study the three Lipschitz-Killing curvatures for the excursion sets of a 2-dimensionalstandard (centered and unit variance) stationary isotropic random field X. These geometrical characteristics can be estimated without bias if the field satisfies a kinematic formula\, such as a smooth Gaussian field or some shot noise fields. If the field is Gaussian\, we show how to remove the constraining assumption that the field is standard. To cope with the unknown location and scale parameters of X\, we introduce novel fundamental quantities called effective level and effective spectral moment and we propose unbiased and asymptotically normal estimators of these parameters. Finally\, we use these tools to build a test to determine if two images of excursion sets can be compared. This test is applied on both synthesized and real mammograms. Meanwhile\, we establish the consistency of the empirical variance estimators of the third LK curvature under a weak condition on the correlation function of X. \nTravail en collaboration avec  H. Biermé\, C. Duval et A. Estrade
URL:https://lmv.math.cnrs.fr/evenenement/ps-elena-di-bernardino-cnam-on-the-excursion-area-of-perturbed-gaussian-fields/
LOCATION:Bâtiment Fermat\, salle 2107
CATEGORIES:Séminaire PS
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20200121T113000
DTEND;TZID=Europe/Paris:20200121T123000
DTSTAMP:20260416T055311
CREATED:20191219T065406Z
LAST-MODIFIED:20200124T141531Z
UID:7206-1579606200-1579609800@lmv.math.cnrs.fr
SUMMARY:AG : Jenia Tevelev (UMass Amherst) : Moduli of points and lines
DESCRIPTION:Projective duality identifies arrangements of n lines in the projective plane and arrangements of n points in the dual projective plane. We ask: how does projective duality behave under degenerations? Kapranov introduced the compactified moduli space of line arrangements\, later studied by Lafforgue\, Keel-Tevelev\, and others. On the other hand\, compactified moduli space of point arrangements was introduced by Gerrizen and Piwek. In joint work with Luca Schaffler\, we investigate how these two moduli spaces are related.
URL:https://lmv.math.cnrs.fr/evenenement/expose-de-jenia-tevelev-umass-amherst/
LOCATION:Bâtiment Fermat\, salle 2205\, 45 avenue des Etats-Unis\, Versailles\, 78000\, France
CATEGORIES:Séminaire AG
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20200123T140000
DTEND;TZID=Europe/Paris:20200123T150000
DTSTAMP:20260416T055311
CREATED:20190925T084037Z
LAST-MODIFIED:20200124T141616Z
UID:6527-1579788000-1579791600@lmv.math.cnrs.fr
SUMMARY:EDP : François Bolley (Sorbonne Université) : Dynamique d'un gaz de Coulomb en dimension deux
DESCRIPTION:Motivés par un modèle de matrices aléatoires\, on s’intéresse à l’évolution de N particules du plan soumises à de la diffusion et une interaction coulombienne\, et notamment aux limites en N et temps grands. On comparera notamment à l’analogue undimensionnel\, plus classique\, appelé mouvement brownien de Dyson.
URL:https://lmv.math.cnrs.fr/evenenement/edp-francois-bolley-sorbonne-univ-tba/
LOCATION:Bâtiment Sophie Germain\, salle G210
CATEGORIES:Séminaire EDP
END:VEVENT
BEGIN:VEVENT
DTSTART;VALUE=DATE:20200124
DTEND;VALUE=DATE:20200125
DTSTAMP:20260416T055311
CREATED:20191105T135749Z
LAST-MODIFIED:20200124T142101Z
UID:6812-1579824000-1579910399@lmv.math.cnrs.fr
SUMMARY:Journée autour des thèmes de recherche d'Abdelkader Mokkadem
DESCRIPTION:Programme
URL:https://lmv.math.cnrs.fr/evenenement/journee-autour-des-themes-de-recherche-dabdelkader-mokkadem/
CATEGORIES:Evénement scientifique
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20200128T113000
DTEND;TZID=Europe/Paris:20200128T123000
DTSTAMP:20260416T055311
CREATED:20191108T155208Z
LAST-MODIFIED:20200131T084946Z
UID:6848-1580211000-1580214600@lmv.math.cnrs.fr
SUMMARY:PS : Zacharie Naulet (Univ. Paris Saclay) : Optimal disclosure risk assessment
DESCRIPTION:Protection against disclosure is a legal and ethical obligation for agencies releasing microdata files for public use. Any decision about releasing data  is supported by the estimation of measures of disclosure risk. The most common measure is arguably the number $\tau_{1}$ of sample unique records that are population uniques. We first study nonparametric estimation of $\tau_{1}$. We introduce a class of linear estimators of $\tau_{1}$ that are simple\, computationally efficient and scalable to massive datasets\, and we give uniform theoretical guarantees for them. We then establish a lower bound for the minimax NMSE for the estimation of $\tau_{1}$.
URL:https://lmv.math.cnrs.fr/evenenement/ps-zacharie-naulet-univ-paris-saclay-titre-a-venir/
LOCATION:Bâtiment Fermat\, salle 2107
CATEGORIES:Séminaire PS
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20200128T113000
DTEND;TZID=Europe/Paris:20200128T123000
DTSTAMP:20260416T055311
CREATED:20191219T065556Z
LAST-MODIFIED:20200131T084939Z
UID:7208-1580211000-1580214600@lmv.math.cnrs.fr
SUMMARY:AG : Bernhard Keller (IMJ-PRG) : Algèbres amassées et invariants de Donaldson-Thomas
DESCRIPTION:Cet exposé est consacré aux invariants de Donaldson-Thomas géométriques et amassés. Après avoir dressé le panorama des liens entre les deux\, nous décrirons la construction\, entièrement combinatoire\, du DT-invariant amassé (dans le cas où il existe une suite verte maximale). Pour donner une impression du DT-invariant géométrique\, nous construirons ensuite son ancêtre topologique : l’invariant de Casson.
URL:https://lmv.math.cnrs.fr/evenenement/expose-de-bernhard-keller-imj-prg/
LOCATION:Bâtiment Fermat\, salle 2205\, 45 avenue des Etats-Unis\, Versailles\, 78000\, France
CATEGORIES:Séminaire AG
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20200130T140000
DTEND;TZID=Europe/Paris:20200130T150000
DTSTAMP:20260416T055311
CREATED:20191021T083711Z
LAST-MODIFIED:20200131T085020Z
UID:6656-1580392800-1580396400@lmv.math.cnrs.fr
SUMMARY:EDP : Tahar Boulmezaoud (LMV) : Transformation de Fourier et espaces de Sobolev à poids
DESCRIPTION:On expose quelques résultats et quelques surprises concernant l’image par transformation de Fourier des espaces de Sobolev avec poids. On montrera en particulier que la transformation de Fourier est une isométrie dans certains espaces (généralisant au passage le Théorème de Plancherel).
URL:https://lmv.math.cnrs.fr/evenenement/edp-tahar-boulmezaoud-lmv-tba/
LOCATION:Bâtiment Sophie Germain\, salle G210
CATEGORIES:Séminaire EDP
END:VEVENT
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