m
• D

F Nous contacter

0

# Research talks  | enregistrements trouvés : 914

O

P Q

Déposez votre fichier ici pour le déplacer vers cet enregistrement.

## Post-edited  ​Construction of lattices defining fake projective planes - Lecture 1 Cartwright, Donald I. (Auteur de la Conférence) | CIRM (Editeur )

Déposez votre fichier ici pour le déplacer vers cet enregistrement.

## Post-edited  ​Construction of lattices defining fake projective planes - Lecture 2 Cartwright, Donald I. (Auteur de la Conférence) | CIRM (Editeur )

Déposez votre fichier ici pour le déplacer vers cet enregistrement.

## Post-edited  Improved bounds for jet differential operators and the Kobayashi conjecture Demailly, Jean-Pierre (Auteur de la Conférence) | CIRM (Editeur )

We will discuss several new ideas that can show the existence of jet differential operators on arbitrary projective varieties, and also on general hypersurfaces of $\mathbb{P}^n$ of sufficiently high degree. These results can be applied to improve degree bounds in several hyperbolicity problems and especially in the proof of the Kobayashi conjecture.

Déposez votre fichier ici pour le déplacer vers cet enregistrement.

## Post-edited  ​On the Lüroth problem for real varieties Benoist, Olivier (Auteur de la Conférence) | CIRM (Editeur )

The Lüroth problem asks whether every unirational variety is rational. Over the complex numbers, it has a positive answer for curves and surfaces, but fails in higher dimensions. In this talk, I will consider the Lüroth problem for real algebraic varieties that are geometrically rational, and explain a counterexample not accounted for by the topology of the real locus or by unramified cohomology. This is joint work with Olivier Wittenberg.

Déposez votre fichier ici pour le déplacer vers cet enregistrement.

## Post-edited  Algebraicity of the metric tangent cones Wang, Xiaowei (Auteur de la Conférence) | CIRM (Editeur )

We proved that any K-semistable log Fano cone admits a special degeneration to a uniquely determined K-polystable log Fano cone. This confirms a conjecture of Donaldson-Sun stating that the metric tangent cone of any close point appearing on a Gromov-Hausdorff limit of Kähler-Einstein Fano manifolds depends only on the algebraic structure of the singularity. This is a joint work with Chi Li and Chenyang Xu.

Déposez votre fichier ici pour le déplacer vers cet enregistrement.

## Post-edited  On the existence of algebraic approximations of compact Kähler manifolds Lin, Hsueh-Yung (Auteur de la Conférence) | CIRM (Editeur )

Let $X$ be a compact Kähler manifold. The so-called Kodaira problem asks whether $X$ has arbitrarily small deformations to some projective varieties. While Kodaira proved that such deformations always exist for surfaces. Starting from dimension 4, there are examples constructed by Voisin which answer the Kodaira problem in the negative. In this talk, we will focus on threefolds, as well as compact Kähler manifolds of algebraic dimension $a(X) = dim(X) -1$. We will explain our positive solution to the Kodaira problem for these manifolds.
Let $X$ be a compact Kähler manifold. The so-called Kodaira problem asks whether $X$ has arbitrarily small deformations to some projective varieties. While Kodaira proved that such deformations always exist for surfaces. Starting from dimension 4, there are examples constructed by Voisin which answer the Kodaira problem in the negative. In this talk, we will focus on threefolds, as well as compact Kähler manifolds of algebraic dimension $a(X) = ... Déposez votre fichier ici pour le déplacer vers cet enregistrement. ## Post-edited Intermittent weak solutions of the 3D Navier-Stokes equations Vicol, Vlad (Auteur de la Conférence) | CIRM (Editeur ) ​I will discuss recent developments concerning the non-uniqueness of distributional solutions to the Navier-Stokes equation. Déposez votre fichier ici pour le déplacer vers cet enregistrement. ## Post-edited Bayesian econometrics in the Big Data Era Frühwirth-Schnatter, Sylvia (Auteur de la Conférence) | CIRM (Editeur ) Data mining methods based on finite mixture models are quite common in many areas of applied science, such as marketing, to segment data and to identify subgroups with specific features. Recent work shows that these methods are also useful in micro econometrics to analyze the behavior of workers in labor markets. Since these data are typically available as time series with discrete states, clustering kernels based on Markov chains with group-specific transition matrices are applied to capture both persistence in the individual time series as well as cross-sectional unobserved heterogeneity. Markov chains clustering has been applied to data from the Austrian labor market, (a) to understanding the effect of labor market entry conditions on long-run career developments for male workers (Frühwirth-Schnatter et al., 2012), (b) to study mothers’ long-run career patterns after first birth (Frühwirth-Schnatter et al., 2016), and (c) to study the effects of a plant closure on future career developments for male worker (Frühwirth-Schnatter et al., 2018). To capture non- stationary effects for the later study, time-inhomogeneous Markov chains based on time-varying group specific transition matrices are introduced as clustering kernels. For all applications, a mixture-of-experts formulation helps to understand which workers are likely to belong to a particular group. Finally, it will be shown that Markov chain clustering is also useful in a business application in marketing and helps to identify loyal consumers within a customer relationship management (CRM) program. Data mining methods based on finite mixture models are quite common in many areas of applied science, such as marketing, to segment data and to identify subgroups with specific features. Recent work shows that these methods are also useful in micro econometrics to analyze the behavior of workers in labor markets. Since these data are typically available as time series with discrete states, clustering kernels based on Markov chains with ... Déposez votre fichier ici pour le déplacer vers cet enregistrement. ## Post-edited Were the foundations of measurement without theory laid in the 1920s? Pradier, Pierre-Charles (Auteur de la Conférence) | CIRM (Editeur ) In his 1947 essay, Tjalling Koopmans criticized the development of an empirical science that had no theoretical basis, what he referred to as measurement without theory. The controversy over the status of relations based on mere statistical inference has not ceased since then. Instead of looking for the contemporary consequences, however, I will inquire into its early beginnings. As early as the 1900s, Walras, Pareto and Juglar exchanged views on the status of theory and its relation to economic data. These private exchanges acquired the status of scientific controversy in the aftermath of the First World War, with the dissemination of Pareto’s work. It is precisely this moment that I will try to grasp, when engineers began to read and write pure economic treatises, questioning the relation between theory and empirical problems, the nature of their project and the expectations that the subsequent development of economics has tried to fulfill. Cournot Centre session devoted to the transformations that took place in mathematical economics during the interwar period. In his 1947 essay, Tjalling Koopmans criticized the development of an empirical science that had no theoretical basis, what he referred to as measurement without theory. The controversy over the status of relations based on mere statistical inference has not ceased since then. Instead of looking for the contemporary consequences, however, I will inquire into its early beginnings. As early as the 1900s, Walras, Pareto and Juglar exchanged views ... Déposez votre fichier ici pour le déplacer vers cet enregistrement. ## Post-edited ​​​Growth of normalizing sequences in limit theorems Gouëzel, Sébastien (Auteur de la Conférence) | CIRM (Editeur ) ​Assume that a renormalized Birkhoff sum$S_n f/B_n$converges in distribution to a nontrivial limit. What can one say about the sequence$B_n$? Most natural statements in the literature involve sequences$B_n$of the form$B_n = n^\alpha L(n)$, where$L$is slowly varying. We will discuss the possible growth rate of$B_n$both in the probability preserving case and the conservative case. In particular, we will describe examples where$B_n$grows superpolynomially, or where$B_{n+1}/B_n$does not tend to$1$. ​Assume that a renormalized Birkhoff sum$S_n f/B_n$converges in distribution to a nontrivial limit. What can one say about the sequence$B_n$? Most natural statements in the literature involve sequences$B_n$of the form$B_n = n^\alpha L(n)$, where$L$is slowly varying. We will discuss the possible growth rate of$B_n$both in the probability preserving case and the conservative case. In particular, we will describe examples where$B_n$... Déposez votre fichier ici pour le déplacer vers cet enregistrement. ## Post-edited Multiple Bernoulli series and volumes of moduli spaces of flat bundles over surfaces Boysal, Arzu (Auteur de la Conférence) | CIRM (Editeur ) Using Szenes formula for multiple Bernoulli series, we explain how to compute Witten series associated to classical Lie algebras. Particular instances of these series compute volumes of moduli spaces of flat bundles over surfaces, and also certain multiple zeta values. This is joint work with V. Baldoni and M. Vergne. Déposez votre fichier ici pour le déplacer vers cet enregistrement. ## Post-edited Uniform distribution mod 1, results and open problems Katai, Imre (Auteur de la Conférence) | CIRM (Editeur ) Given a fixed integer$q \geq 2$, an irrational number$\xi$is said to be a$q$-normal number if any preassigned sequence of$k$digits occurs in the$q$-ary expansion of$\xi$with the expected frequency, that is$1/q^k$. In this talk, we expose new methods that allow for the construction of large families of normal numbers. This is joint work with Professor Jean-Marie De Koninck. Déposez votre fichier ici pour le déplacer vers cet enregistrement. ## Post-edited Large-time behavior in (hypo)coercive ODE-systems and kinetic models Arnold, Anton (Auteur de la Conférence) | CIRM (Editeur ) In this talk we discuss the convergence to equilibrium in conservative-dissipative ODE-systems, kinetic relaxation models (of BGK-type), and Fokker-Planck equation. This will include symmetric, non-symmetric and hypocoercive evolution equations. A main focus will be on deriving sharp decay rates. We shall start with hypocoercivity in ODE systems, with the ”hypocoercivity index” characterizing its structural complexity. BGK equations are kinetic transport equations with a relaxation operator that drives the phase space distribution towards the spatially local equilibrium, a Gaussian with the same macroscopic parameters. Due to the absence of dissipation w.r.t. the spatial direction, convergence to the global equilibrium is only possible thanks to the transport term that mixes various positions. Hence, such models are hypocoercive. We shall prove exponential convergence towards the equilibrium with explicit rates for several linear, space periodic BGK-models in dimension 1 and 2. Their BGK-operators differ by the number of conserved macroscopic quantities (like mass, momentum, energy), and hence their hypocoercivity index. Our discussion includes also discrete velocity models, and the local exponential stability of a nonlinear BGK-model. The third part of the talk is concerned with the entropy method for (non)symmetric Fokker-Planck equations, which is a powerful tool to analyze the rate of convergence to the equilibrium (in relative entropy and hence in L1). The essence of the method is to first derive a differential inequality between the first and second time derivative of the relative entropy, and then between the entropy dissipation and the entropy. For hypocoercive Fokker-Planck equations, i.e. degenerate parabolic equations (with drift terms that are linear in the spatial variable) we modify the classical entropy method by introducing an auxiliary functional (of entropy dissipation type) to prove exponential decay of the solution towards the steady state in relative entropy. The obtained rate is indeed sharp (both for the logarithmic and quadratic entropy). Finally, we extend the method to the kinetic Fokker-Planck equation (with nonquadratic potential). In this talk we discuss the convergence to equilibrium in conservative-dissipative ODE-systems, kinetic relaxation models (of BGK-type), and Fokker-Planck equation. This will include symmetric, non-symmetric and hypocoercive evolution equations. A main focus will be on deriving sharp decay rates. We shall start with hypocoercivity in ODE systems, with the ”hypocoercivity index” characterizing its structural complexity. BGK equations are kinetic ... Déposez votre fichier ici pour le déplacer vers cet enregistrement. ## Post-edited Mahler's method in several variables Adamczewski, Boris (Auteur de la Conférence) | CIRM (Editeur ) Any algebraic (resp. linear) relation over the field of rational functions with algebraic coefficients between given analytic functions leads by specialization to algebraic (resp. linear) relations over the field of algebraic numbers between the values of these functions. Number theorists have long been interested in proving results going in the other direction. Though the converse result is known to be false in general, Mahler’s method provides one of the few known instances where it essentially holds true. After the works of Nishioka, and more recently of Philippon, Faverjon and the speaker, the theory of Mahler functions in one variable is now rather well understood. In contrast, and despite the contributions of Mahler, Loxton and van der Poorten, Kubota, Masser, and Nishioka among others, the theory of Mahler functions in several variables remains much less developed. In this talk, I will discuss recent progresses concerning the case of regular singular systems, as well as possible applications of this theory. This is a joint work with Colin Faverjon. Any algebraic (resp. linear) relation over the field of rational functions with algebraic coefficients between given analytic functions leads by specialization to algebraic (resp. linear) relations over the field of algebraic numbers between the values of these functions. Number theorists have long been interested in proving results going in the other direction. Though the converse result is known to be false in general, Mahler’s method provides ... Déposez votre fichier ici pour le déplacer vers cet enregistrement. ## Post-edited Approximation and calibration of laws of solutions to stochastic differential equations Bion-Nadal, Jocelyne (Auteur de la Conférence) | CIRM (Editeur ) In many situations where stochastic modeling is used, one desires to choose the coefficients of a stochastic differential equation which represents the reality as simply as possible. For example one desires to approximate a diffusion model with high complexity coefficients by a model within a class of simple diffusion models. To achieve this goal, we introduce a new Wasserstein type distance on the set of laws of solutions to d-dimensional stochastic differential equations. This new distance$\widetilde{W}^{2}$is defined similarly to the classical Wasserstein distance$\widetilde{W}^{2}$but the set of couplings is restricted to the set of laws of solutions of 2$d$-dimensional stochastic differential equations. We prove that this new distance$\widetilde{W}^{2}$metrizes the weak topology. Furthermore this distance$\widetilde{W}^{2}$is characterized in terms of a stochastic control problem. In the case d = 1 we can construct an explicit solution. The multi-dimensional case, is more tricky and classical results do not apply to solve the HJB equation because of the degeneracy of the differential operator. Nevertheless, we prove that this HJB equation admits a regular solution. In many situations where stochastic modeling is used, one desires to choose the coefficients of a stochastic differential equation which represents the reality as simply as possible. For example one desires to approximate a diffusion model with high complexity coefficients by a model within a class of simple diffusion models. To achieve this goal, we introduce a new Wasserstein type distance on the set of laws of solutions to d-dimensional ... Déposez votre fichier ici pour le déplacer vers cet enregistrement. ## Post-edited Graphons and graphexes as limits of sparse graphs - lecture 1 Chayes, Jennifer Tour (Auteur de la Conférence) | CIRM (Editeur ) Graphons and graphexes are limits of graphs which allow us to model and estimate properties of large-scale networks. In this pair of talks, we review the theory of dense graph limits, and give two alterative theories for limits of sparse graphs - one leading to unbounded graphons over probability spaces, and the other leading to bounded graphons (and graphexes) over sigma-finite measure spaces. Talk I, given by Jennifer, will review the general theory, highlight the unbounded graphons, and show how they can be used to consistently estimate properties of large sparse networks. This talk will also give an application of these sparse graphons to collaborative filtering on sparse bipartite networks. Talk II, given by Christian, will recast limits of dense graphs in terms of exchangeability and the Aldous Hoover Theorem, and generalize this to obtain sparse graphons and graphexes as limits of subgraph samples from sparse graph sequences. This will provide a dual view of sparse graph limits as processes and random measures, an approach which allows a generalization of many of the well-known results and techniques for dense graph sequences. Graphons and graphexes are limits of graphs which allow us to model and estimate properties of large-scale networks. In this pair of talks, we review the theory of dense graph limits, and give two alterative theories for limits of sparse graphs - one leading to unbounded graphons over probability spaces, and the other leading to bounded graphons (and graphexes) over sigma-finite measure spaces. Talk I, given by Jennifer, will review the general ... Déposez votre fichier ici pour le déplacer vers cet enregistrement. ## Post-edited Graphons and graphexes as limits of sparse graphs - lecture 2 Borgs, Christian (Auteur de la Conférence) | CIRM (Editeur ) Graphons and graphexes are limits of graphs which allow us to model and estimate properties of large-scale networks. In this pair of talks, we review the theory of dense graph limits, and give two alterative theories for limits of sparse graphs - one leading to unbounded graphons over probability spaces, and the other leading to bounded graphons (and graphexes) over sigma-finite measure spaces. Talk I, given by Jennifer, will review the general theory, highlight the unbounded graphons, and show how they can be used to consistently estimate properties of large sparse networks. This talk will also give an application of these sparse graphons to collaborative filtering on sparse bipartite networks. Talk II, given by Christian, will recast limits of dense graphs in terms of exchangeability and the Aldous Hoover Theorem, and generalize this to obtain sparse graphons and graphexes as limits of subgraph samples from sparse graph sequences. This will provide a dual view of sparse graph limits as processes and random measures, an approach which allows a generalization of many of the well-known results and techniques for dense graph sequences. Graphons and graphexes are limits of graphs which allow us to model and estimate properties of large-scale networks. In this pair of talks, we review the theory of dense graph limits, and give two alterative theories for limits of sparse graphs - one leading to unbounded graphons over probability spaces, and the other leading to bounded graphons (and graphexes) over sigma-finite measure spaces. Talk I, given by Jennifer, will review the general ... Déposez votre fichier ici pour le déplacer vers cet enregistrement. ## Post-edited Mathematical modelling of angiogenesis Maini, Philip (Auteur de la Conférence) | CIRM (Editeur ) Tumour vascular is highly disordered and has been the subject of intense interest both clinically (anti-angiogenesis therapies) and theoretically (many models have been proposed). In this talk, I will review aspects of modelling tumour angiogenesis and how different modelling assumptions impact conclusions on oxygen delivery and, therefore, predictions on the possible effects of radiation treatments. Déposez votre fichier ici pour le déplacer vers cet enregistrement. ## Post-edited Local acyclicity in$p$-adic geometry Scholze, Peter (Auteur de la Conférence) | CIRM (Editeur ) Motivated by applications to the geometric Satake equivalence and in particular the construction of the fusion product, we define a notion of universally locally acyclic for rigid spaces and diamonds, and prove that it has the expected properties. Déposez votre fichier ici pour le déplacer vers cet enregistrement. ## Post-edited The evolution of cooperation in an iterated survival game Wakeley, John (Auteur de la Conférence) | CIRM (Editeur ) A new type of a simple iterated game with natural biological motivation is introduced. Two individuals are chosen at random from a population. They must survive a certain number of steps. They start together, but if one of them dies the other one tries to survive on its own. The only payoff is to survive the game. We only allow two strategies: cooperators help the other individual, while defectors do not. There is no strategic complexity. There are no conditional strategies. Depending on the number of steps we recover various forms of stringent and relaxed cooperative dilemmas. We derive conditions for the evolution of cooperation. Specifically, we describe an iterated game between two players, in which the payoff is to survive a number of steps. Expected payoffs are probabilities of survival. A key feature of the game is that individuals have to survive on their own if their partner dies. We consider individuals with simple, unconditional strategies. When both players are present, each step is a symmetric two-player game. As the number of iterations tends to infinity, all probabilities of survival decrease to zero. We obtain general, analytical results for n-step payoffs and use these to describe how the game changes as n increases. In order to predict changes in the frequency of a cooperative strategy over time, we embed the survival game in three different models of a large, well-mixed population. Two of these models are deterministic and one is stochastic. Offspring receive their parent’s type without modification and fitnesses are determined by the game. Increasing the number of iterations changes the prospects for cooperation. All models become neutral in the limit$(n \rightarrow \infty)\$. Further, if pairs of cooperative individuals survive together with high probability, specifically higher than for any other pair and for either type when it is alone, then cooperation becomes favored if the number of iterations is large enough. This holds regardless of the structure of pairwise interactions in a single step. Even if the single-step interaction is a Prisoner’s Dilemma, the cooperative type becomes favored. Enhanced survival is crucial in these iterated evolutionary games: if players in pairs start the game with a fitness deficit relative to lone individuals, the prospects for cooperation can become even worse than in the case of a single-step game.
A new type of a simple iterated game with natural biological motivation is introduced. Two individuals are chosen at random from a population. They must survive a certain number of steps. They start together, but if one of them dies the other one tries to survive on its own. The only payoff is to survive the game. We only allow two strategies: cooperators help the other individual, while defectors do not. There is no strategic complexity. There ...

Z