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Documents  Lebeau, Gilles | enregistrements trouvés : 9

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Research talks;Partial Differential Equations;Mathematics in Science and Technology

In this talk, I will focus on a Fokker-Planck equation modeling interacting neurons in a network where each neuron is governed by an Integrate and Fire dynamic type. When the network is excitatory, neurons that discharge, instantaneously increased the membrane potential of the neurons of the network with a speed which is proportional to the amplitude of the global activity of the network. The self-excitable nature of these neurons in the case of excitatory networks leads to phenomena of blow-up, once the proportion of neurons that are close to their action potential is too high. In this talk, we are interested in understanding the regimes where solutions globally exist. By new methods of entropy and upper-solution, we give criteria where the phenomena of blow-up can not appear and specify, in some cases, the asymptotic behavior of the solution.

integrate-and-fire - neural networks - Fokker-Planck equation - blow-up
In this talk, I will focus on a Fokker-Planck equation modeling interacting neurons in a network where each neuron is governed by an Integrate and Fire dynamic type. When the network is excitatory, neurons that discharge, instantaneously increased the membrane potential of the neurons of the network with a speed which is proportional to the amplitude of the global activity of the network. The self-excitable nature of these neurons in the case of ...

92B20 ; 82C32 ; 35Q84

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- ix; 153 p.
ISBN 978-2-85629-858-9

Séminaires et congrès , 0030

Localisation : Collection 1er étage

équation différentielle partielle # dispersion # diffusion # théorie du contrôle

35Q41 ; 35Q40 ; 35B65 ; 35J10 ; 35P20 ; 47A10 ; 35Q55 ; 35B40 ; 34B45 ; 39A10 ; 35R01 ; 35A17 ; 35A18 ; 35B45 ; 35L20 ; 93B28 ; 93B07 ; 47A05 ; 65J10 ; 35Q30 ; 35A02 ; 35B30 ; 76D05 ; 49N35 ; 49J20 ; 35P25

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Research talks;Probability and Statistics

In this talk I will present a stochastic model for the excitability of a neuron in a network. The neuron described by an Hodgkin-Huxley type model receives from the network a random input which is a perturbation of a periodic deterministic signal. For such a model we study ergodicity properties. Then, we prove limit theorems in order to be able to estimate characteristics of the sequence of spiking times. This talk is based on a joint work with R. Hoepfner (Univ. Mainz) and E. Loecherbach (Univ. Cergy-Pontoise).

Hodgkin-Huxley model - ergodicity - limit theorems - estimation
In this talk I will present a stochastic model for the excitability of a neuron in a network. The neuron described by an Hodgkin-Huxley type model receives from the network a random input which is a perturbation of a periodic deterministic signal. For such a model we study ergodicity properties. Then, we prove limit theorems in order to be able to estimate characteristics of the sequence of spiking times. This talk is based on a joint work with ...

60J60 ; 60J25 ; 60H07

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Research talks;Partial Differential Equations

The determination of the shape of an obstacle from its effects on known acoustic waves is an important problem in many technologies such as sonar, geophysical exploration and medical imaging. This inverse obstacle problem (IOP) is difficult to solve, especially from a numerical viewpoint, because of its ill-posed and nonlinear nature. Its investigation requires the understanding of the theory for the associated direct scattering problem, and the mastery of the corresponding numerical solution methods. The main goal of this work is the development of an efficient procedure for retrieving the shape of an elastic obstacle from the knowledge of some scattered far-field patterns, and assuming certain characteristics of the surface of the obstacle. We propose a solution methodology based on a regularized Newton-type method. The solution of the considered IOP by the proposed iterative method incurs, at each iteration, the solution of a linear system whose entries are the Fréchet derivatives of the elasto-acoustic field with respect to the shape parameters. We prove that these derivatives are solutions of the same direct elasto-acoustic scattering problem that differs only in the transmission conditions on the surface of the scatterer. Furthermore, the computational efficiency of the IOP solver depends mainly on the computational efficiency of the solution of the forward problems that arise at each Newton iteration. We propose to solve the direct scattering-type problems using a finite-element method based on discontinuous Galerkin approximations equipped with curved element boundaries. Numerical results will be presented to illustrate the salient features of this computational methodology and highlight its performance characteristics.

acoustics - shape derivative - inverse obstacle problem - Fréchet derivatives - inverse elasto-acoustic scattering problems
The determination of the shape of an obstacle from its effects on known acoustic waves is an important problem in many technologies such as sonar, geophysical exploration and medical imaging. This inverse obstacle problem (IOP) is difficult to solve, especially from a numerical viewpoint, because of its ill-posed and nonlinear nature. Its investigation requires the understanding of the theory for the associated direct scattering problem, and the ...

65N21 ; 76Q05 ; 35R30

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Research talks;Partial Differential Equations;Mathematical Physics

We consider the nonlinear Schrödinger equation in the partially periodic setting $\mathbb{R}^d\times \mathbb{T}$. We present some recent results obtained in collaboration with N. Tzvetkov concerning the Cauchy theory and the long-time behavior of the solutions.

nonlinear Schrödinger equation - Cauchy theory - scattering

35Q55 ; 35B40 ; 35P25

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Research talks;Partial Differential Equations

This talk is devoted to the study of the following inverse boundary value problem: given a Riemannian manifold with boundary determine the magnetic potential in a dynamical Schrödinger equation in a magnetic field from the observations made at the boundary.

inverse problem - Schrödinger equation - magnetic field

35R30 ; 35Q55 ; 35R35 ; 35Q60

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- 319 p.
ISBN 978-2-85629-132-0

Astérisque , 0284

Localisation : Périodique 1er étage;Réserve

équation d'onde quasi-linéaire # intégralité d'énergie # décroissance # explosion # optique géométrique # inégalité de Poincaré # norme à poids # calcul paradifférentiel # estimation bilinéaire # analyse microlocale # calcul pseudodifférentiel de Weyl-Hörmander # faisceau # micro-support # D-module # ind-objet # groupe de Lie # paire symétrique # régularité # Bohr # Sommerfeld # valeur propre # tore # équation de Cauchy-Riemann # inégalité de Sobolev logarithmique # opérateur de Hörmander # hypoellipticité # vitesse de groupe # polynôme hyperbolique # opérateur hyperbolique # variété caractéristique # réflexion de Schwarz # transformation conforme # paire d'arc analytique équation d'onde quasi-linéaire # intégralité d'énergie # décroissance # explosion # optique géométrique # inégalité de Poincaré # norme à poids # calcul paradifférentiel # estimation bilinéaire # analyse microlocale # calcul pseudodifférentiel de Weyl-Hörmander # faisceau # micro-support # D-module # ind-objet # groupe de Lie # paire symétrique # régularité # Bohr # Sommerfeld # valeur propre # tore # équation de Cauchy-Riemann # inégalité de ...

17B15 ; 30C35 ; 30D05 ; 31C10 ; 35Axx ; 35A07 ; 35A27 ; 32C38 ; 35D10 ; 35HXX ; 35L25 ; 35L40 ; 35L55 ; 35L70 ; 35Nxx ; 35P05 ; 37J40 ; 37K05 ; 58J52

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ISBN 978-3-540-66766-7

Lecture notes in mathematics , 1721

Localisation : Collection 1er étage

EDP # EDP d'ordre premier non linéaire # acoustique # algorithmique numérique # diffraction # dispersion # hydrodynamique # intégrale # mécanique des fluides # optique # problème aux frontières # problème aux valeurs limites # son # système # système d'équation intégrale linéaire singulière # équation d'ordre supérieur

35G15 ; 35L05 ; 35L20 ; 45F15 ; 76Q05 ; 78A45

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- xvi; 120 p.
ISBN 978-2-85629-844-2

Astérisque , 0383

Localisation : Périodique 1er étage

décomposition d'un cylindre # D-module # catégorie dérivée # module filtré # objet filtré # filtration # topologie de Grothendieck # cohomologie modérée # catégorie quasi-abélienne # faisceau # espace de Sobolev # ensemble sous-analytique # topologie sous-analytique

16E35 ; 16W70 ; 18A25 ; 18D10 ; 18D35 ; 18F20 ; 32B20 ; 32C05 ; 32C38 ; 32S60 ; 46E35 ; 58A03

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