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X-WR-CALNAME:Département de mathématiques et applications
X-ORIGINAL-URL:https://www.math.ens.psl.eu
X-WR-CALDESC:évènements pour Département de mathématiques et applications
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TZID:Europe/Paris
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TZOFFSETFROM:+0100
TZOFFSETTO:+0200
TZNAME:CEST
DTSTART:20190331T010000
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TZOFFSETFROM:+0200
TZOFFSETTO:+0100
TZNAME:CET
DTSTART:20191027T010000
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BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20190507T160000
DTEND;TZID=Europe/Paris:20190507T173000
DTSTAMP:20260410T020143
CREATED:20190507T140000Z
LAST-MODIFIED:20211104T140929Z
UID:8508-1557244800-1557250200@www.math.ens.psl.eu
SUMMARY:Groups definable in Presburger arithmetic
DESCRIPTION:I will give a complete description of all groups definable in Presburger arithmetic\, up to finite index subgroups. This builds on previous work on bounded groups in Presburger arithmetic by Mariana Vicaria and Alf Onshuus.
URL:https://www.math.ens.psl.eu/evenement/groups-definable-in-presburger-arithmetic/
LOCATION:Sophie Germain salle 2015
CATEGORIES:Théorie des Modèles et Groupes
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20190510T110000
DTEND;TZID=Europe/Paris:20190510T123000
DTSTAMP:20260410T020143
CREATED:20190510T090000Z
LAST-MODIFIED:20211025T103641Z
UID:8511-1557486000-1557491400@www.math.ens.psl.eu
SUMMARY:Almost strongly minimal ample geometries
DESCRIPTION:The notion of ampleness captures essential properties of projective spaces over fields. It is natural to ask whether any sufficiently ample strongly minimal set arises from an algebraically closed field. In this talk I will explain the question and present recent results on ample strongly minimal structures.
URL:https://www.math.ens.psl.eu/evenement/almost-strongly-minimal-ample-geometries/
CATEGORIES:Séminaire Géométrie et théorie des modèles
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20190510T141500
DTEND;TZID=Europe/Paris:20190510T154500
DTSTAMP:20260410T020143
CREATED:20190510T121500Z
LAST-MODIFIED:20211104T141516Z
UID:8509-1557497700-1557503100@www.math.ens.psl.eu
SUMMARY:Point-wise surjective presentations of stacks\, or why I am not afraid of (infinity) stacks anymore
DESCRIPTION:Any algebraic stack X can be represented by a groupoid object in the category of schemes: that is\, a pair of schemes Ob\, Mor and morphisms source\, target: Mor → Ob\, inversion: Mor → Mor\, composition: Mor ×_{Ob} Mor → Mor and identity: Ob → Mor that satisfy certain axioms. Yet this description of the stack X might be misleading.\nNamely\, given a field F which is not algebraically closed\, we have a natural functor between the groupoid (Ob(F)\,Mor(F)) and the groupoid X(F). While this functor is fully faithful\, it is often not essentially surjective.\nIn joint work with Nir Avni (in progress) we show that any algebraic groupoid has a presentation such that this functor will be essentially surjective for many fields (and under some assumptions on the stack\, for any field). The results are also extended to Henselian rings.\nDespite the title\, the talk will be about usual stacks and not infinity-stacks\, yet in some of the proofs it is more convenient to use the language of higher categories and I’ll try to explain why.\nNo prior knowledge of infinity stacks will be assumed\, but a superficial acquaintance with usual stacks will be helpful.
URL:https://www.math.ens.psl.eu/evenement/point-wise-surjective-presentations-of-stacks-or-why-i-am-not-afraid-of-infinity-stacks-anymore/
LOCATION:ENS Salle W
CATEGORIES:Séminaire Géométrie et théorie des modèles
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20190510T160000
DTEND;TZID=Europe/Paris:20190510T173000
DTSTAMP:20260410T020143
CREATED:20190510T140000Z
LAST-MODIFIED:20211104T132132Z
UID:8507-1557504000-1557509400@www.math.ens.psl.eu
SUMMARY:Non-archimedean and motivic integrals on the Hitchin fibration
DESCRIPTION:Based on mirror symmetry considerations\, Hausel and Thaddeus conjectured an equality between `stringy’ Hodge numbers for moduli spaces of SL_n/PGL_n Higgs bundles. With Michael Groechenig and Paul Ziegler we prove this conjecture using non-archimedean integrals on these moduli spaces\, building on work of Denef-Loeser and Batyrev. Similar ideas also lead to a new proof of the geometric stabilization theorem for anisotropic Hitchin fibers\, a key ingredient in the proof of the fundamental lemma by Ngô.In my talk I will outline the main arguments of the proofs and discuss the adjustments needed\, in order to replace non-archimedean integrals by motivic ones. The latter is joint work with François Loeser.
URL:https://www.math.ens.psl.eu/evenement/non-archimedean-and-motivic-integrals-on-the-hitchin-fibration/
LOCATION:ENS Salle W
CATEGORIES:Séminaire Géométrie et théorie des modèles
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20190514T093000
DTEND;TZID=Europe/Paris:20190514T120000
DTSTAMP:20260410T020143
CREATED:20190514T073000Z
LAST-MODIFIED:20211025T103550Z
UID:8493-1557826200-1557835200@www.math.ens.psl.eu
SUMMARY:Nonuniqueness for the Navier–Stokes equations and model equations / Singularities in Fluid Mechanics
DESCRIPTION:JG: In this talk\, I will discuss fundamental properties of the solutions to the incompressible Navier–Stokes equations in three dimensions. After reviewing the classical local well-posedness results\, I will explain how numerical simulations suggest local ill-posedness at the borderline of the known results. I will discuss a plausible scenario of non-uniqueness from smooth initial data through finite-time blow-up. Finally\, I will describe how this scenario is actually happening in a model equation sharing the same fundamental properties as the Navier–Stokes equations.KM: Singularities of the Navier-Stokes equations occur when some derivative of the velocity field is infinite at any point of a field of flow (or\, in an evolving flow\, becomes infinite at any point within a finite time). Such singularities can be mathematical but unphysical (as e.g. in two-dimensional flow near a sharp corner) in which case they can be ‘resolved’ by improving the physical model considered; or they can be physical but non-mathematical (as e.g. in the case of cusp singularities at a fluid/fluid interface) in which case resolution of the singularity may involve incorporation of additional physical effects; these examples will be briefly reviewed. The `finite-time singularity problem’ for the Navier-Stokes equations will then be discussed and a new analytical approach will be presented; here it will be shown that there is indeed a singularity of the ‘physical but non-mathematical’ type\, in that\, at suf- ficiently high Reynolds number\, vorticity can be amplified by an arbitrarily large factor within a finite time. In this case\, the singularity is resolved by three-dimensional vortex re- connection in a manner that admits analytical description.
URL:https://www.math.ens.psl.eu/evenement/nonuniqueness-for-the-navier-stokes-equations-and-model-equations-singularities-in-fluid-mechanics/
LOCATION:ENS Salle W
CATEGORIES:Séminaire Analyse non linéaire et EDP
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20190514T140000
DTEND;TZID=Europe/Paris:20190514T170000
DTSTAMP:20260410T020143
CREATED:20190514T120000Z
LAST-MODIFIED:20211104T135214Z
UID:8510-1557842400-1557853200@www.math.ens.psl.eu
SUMMARY:Après-midi de théorie de groupes
DESCRIPTION:14.00-14.45 Stefan Witzel (Ecole Polytehchnique)15.00-15.45 Katie Vokes (IHES)15.45-16.15 coffee break16.15-16.45 Adrien Le Boudec (ENS Lyon)Stefan Witzel\, Arithmetic approximate groups and their finiteness propertiesI will talk about approximate groups\, a geometric generalization of groups. Approximate groups were discovered independently in various contexts and I will describe how they arise very naturally in the context of arithmetic groups. I will then explain how to extend topological finiteness properties of groups to approximate groups. This allows to make a connection betweenarithmetic groups in positive characteristic and arithmetic approximate groups in characteristic zero. The talk is based on joint work with Tobias Hartnick.Katie Vokes\, Hierarchical hyperbolicity of graphs associated to surfacesIn a paper of 2000\, Masur and Minsky studied the geometry of mapping class groups of surfaces using projections to certain Gromov hyperbolic graphs (the curve graphs) associated to subsurfaces. This inspired the definition by Behrstock\, Hagen and Sisto of hierarchically hyperbolic spaces\, which are equipped with similar projection maps\, satisfying conditions which guarantee a structure analogous to that of the mapping class group. I will give some background on these concepts and present a result demonstrating that a large family of graphs associated to surfaces are hierarchically hyperbolic spaces.Adrien Le Boudec\, Simple groups having a wreath product as a geometric modelThe goal of the talk will be to describe groups that are finitelygenerated\, simple\, and that act properly and cocompactly on thenatural Cayley graph of the wreath product A wr F\, where A is afinite group and F a non-abelian free group.
URL:https://www.math.ens.psl.eu/evenement/apres-midi-de-theorie-de-groupes-3/
LOCATION:Salle W (DMA)
CATEGORIES:Séminaire de théorie des groupes à l’ENS
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20190528T093000
DTEND;TZID=Europe/Paris:20190528T123000
DTSTAMP:20260410T020143
CREATED:20190528T073000Z
LAST-MODIFIED:20211104T112027Z
UID:8494-1559035800-1559046600@www.math.ens.psl.eu
SUMMARY:Quelques méthodes pour le temps long : inégalités fonctionnelles\, couplage. Application à Fokker-Planck cinétique.
DESCRIPTION:
URL:https://www.math.ens.psl.eu/evenement/quelques-methodes-pour-le-temps-long-inegalites-fonctionnelles-couplage-application-a-fokker-planck-cinetique/
LOCATION:ENS Salle W
CATEGORIES:Séminaire Analyse non linéaire et EDP
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