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DTSTART:20210328T010000
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DTSTART;TZID=Europe/Paris:20210518T100000
DTEND;TZID=Europe/Paris:20210518T114500
DTSTAMP:20260407T203421
CREATED:20210518T080000Z
LAST-MODIFIED:20211025T103852Z
UID:8555-1621332000-1621338300@www.math.ens.psl.eu
SUMMARY:Des circuits électriques à la rhéologie des suspensions : analyse de problèmes d'homogénéisation raides.
DESCRIPTION:Lien d’accès : https://greenlight.lal.cloud.math.cnrs.fr/b/jul-zjy-etk ************************************************En cas de problème : https://bbb.dma.ens.fr/b/cyr-fpw-ctt********************************************************La théorie classique de l’homogénéisation permet de déterminer les propriétés moyennes d’un milieu diffusif hétérogène en espace\, tant que le coefficient de diffusion reste borné et minoré par une constante positive. Lorsque ce coefficient s’annule (inclusions isolantes dans un mileu conducteur)\, ou devient infini (suspension de particules solides dans un fluide visqueux)\, la dérivation d’un modèle effectif crée de nombreuses difficultés nouvelles\, en particulier lorsque le milieu est aléatoire. Après une présentation générale de cette problématique\, nous décrirons brièvement des travaux récents sur la viscosité effective des suspensions (en commun avec M. Hillairet\, R. Höfer\, A. Mécherbet).
URL:https://www.math.ens.psl.eu/evenement/des-circuits-electriques-a-la-rheologie-des-suspensions-analyse-de-problemes-dhomogeneisation-raides/
LOCATION:En ligne sur BBB
CATEGORIES:Séminaire Analyse non linéaire et EDP
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BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20210521T090000
DTEND;TZID=Europe/Paris:20210521T102000
DTSTAMP:20260407T203421
CREATED:20210521T070000Z
LAST-MODIFIED:20211104T140240Z
UID:8575-1621587600-1621592400@www.math.ens.psl.eu
SUMMARY:Curve-excluding fields
DESCRIPTION:Let T be the theory of fields K of characteristic 0 such that the equation x^4 + y^4 = 1 has only four solutions in K. We show that T has a model companion. More generally\, if K_0 is a field of characteristic 0 and C is a curve (affine or projective) of genus ≥ 2 with C(K_0) = ∅\, then there is a model companion CXF of the theory of fields K extending K_0 with C(K) = ∅.\nWe can use this theory to construct a field K with an interesting combination of properties. On the model-theoretic side\, the theory of K is complete\, decidable\, model-complete\, and algebraically bounded\, and K is a “geometric structure” in the sense of Hrushovski and Pillay. Additionally\, some classification-theoretic properties might hold in K. On the field-theoretic side\, K is non-large—there is a smooth curve C such that C(K) is finite and non-empty. This is unusual; the vast majority of model-theoretically tractable fields are large or finite. On the other hand\, K is “virtually large”—it has a finite extension which is large. In fact\, every proper algebraic extension of K is pseudo algebraically closed (PAC). The absolute Galois group of K is an ω-free profinite group. This negatively answers a question of Junker and Koenigsmann (is every model-complete infinite field large?) and a question of Macintyre (does every model-complete field have a small Galois group?).\nThis is based on joint work with Erik Walsberg and Vincent Ye.
URL:https://www.math.ens.psl.eu/evenement/curve-excluding-fields/
LOCATION:Zoom
CATEGORIES:Séminaire Géométrie et théorie des modèles
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BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20210521T103000
DTEND;TZID=Europe/Paris:20210521T115000
DTSTAMP:20260407T203421
CREATED:20210521T083000Z
LAST-MODIFIED:20211025T103953Z
UID:8576-1621593000-1621597800@www.math.ens.psl.eu
SUMMARY:Pseudo-T-closed fields\,  approximations and NTP2
DESCRIPTION:Joint work with Samaria MontenegroThe striking resemblance between the behaviour of pseudo-algebraically closed\, pseudo real closed and pseudo p-adically fields has lead to numerous attempts at describing their properties in a unified manner. In this talk I will present another of these attempts: the class of pseudo-T-closed fields\, where T is an enriched theory of fields. These fields verify a “local-global” principle with respect to models of T for the existence of points on varieties. Although it very much resembles previous such attempts\, our approach is more model theoretic in flavour\, both in its presentation and in the results we aim for.The first result I would like to present is an approximation result\, generalising a result of Kollar on PAC fields\, respectively Johnson on henselian fields. This result can be rephrased as the fact that existential closeness in certain topological enrichments come for free from existential closeness as a field. The second result is a (model theoretic) classification result for bounded pseudo-T-closed fields\, in the guise of the computation of their burden. One of the striking consequence of these two results is that a bounded perfect PAC field with n independent valuations has burden n and\, in particular\, is NTP2.
URL:https://www.math.ens.psl.eu/evenement/pseudo-t-closed-fields-approximations-and-ntp2/
LOCATION:Zoom
CATEGORIES:Séminaire Géométrie et théorie des modèles
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