Séminaire du CMAP

Octobre 2018

Mardi 23 Octobre

11h00 Petr Grinevich (Moscow, en visite au CMAP) - Fermi-Pasta-Ulam recurrence for anomalous waves in nonlinear optics and Nonlinear Schrodinger equation

Résumé de P. Grinevich: One of the basic model for anomalous (rogue) waves generation in nonlinear medias including nonlinear optics and ocean waves is the focusing Nonlinear Schrodinger equation (NLS) with special initial data. In the spatial-periodic setting generic NSL solutions are provided using the finite-gap approach, but the corresponding formulas are very complicated. Recently, for the Cauchy data corresponding to anomalous waves, we found very simple explicit approximate solution in terms of elementary functions. These formulas were used in our joint work with experimental group from university Roma-1, in which the recurrence of anomalous waves in photorefractive crystals was studied. The talk is based on joint papers [1], [2] with P.M. Santini.

[1] P. G. Grinevich and P. M. Santini, "The finite gap method and the analytic description of the exact rogue wave recurrence in the periodic NLS Cauchy problem. 1", To appear in "Nonlinearity", arXiv:1707.05659

[2] P. G. Grinevich and P. M. Santini, The exact rogue wave recurrence in the NLS periodic setting via matched asymptotic expansions, for 1 and 2 unstable modes, Physics Letters A, 382 (2018), 973-979.

Novembre 2018

Mardi 6 Novembre

10h15 Sophie Ramananarivo (LadHyX, Ecole polytechnique) - Handling flows to self-propel
11h15 Nathalie Ayi (LJLL) - Un schéma "Asymptotic Preserving" pour la limite de diffusion d'une équation cinétique stochastique linéaire

Résumé de S. Ramananarivo: Bird flight and fish swimming are fascinating examples of moving bodies interacting with a fluid. By flapping its wings or fins, the animal imparts momentum to the surrounding flow and creates a jet which in turn propels it forward. Those body/fluid couplings are complex owing to the unsteady nature of the flows involved and a better understanding offers promising routes for man-made propellers.
The first part of this talk will look into how flapping flight is affected by the shape of the wings. Here we use an evolutionary algorithm to improve the forward speed of 3D-printed wings that heave up-and-down and propel within water. This iterative process leads to marked improvement in relatively few generations, with faster swimmers sharing distinct shape features.
In a second part, I will discuss how the locomotion of an individual is affected by the flows produced by neighbors. Using physical experiments that mimic the movements of fins or wings, we discovered that flapping bodies not only swim or fly faster when grouped together but that the flows also organize the group into ordered patterns with specific spacings. These findings suggest an intriguing analogy between animal groups and states of matter, in that a school might be viewed as a ‘swimming crystal’ of fish organized by flows.

Résumé de N. Ayi: On présente un schéma AP basé sur la décomposition micro-macro pour une équation cinétique stochastique linéaire. On est alors capable d'établir la stabilité uniformément en le libre parcours moyen pour ce schéma. Quelques simulations numériques validant notre schéma seront présentées. (Travail en commun avec Erwan Faou)

Mardi 20 Novembre

10h15 Clément Rey (CMAP)
11h15 Kilian Raschel (Univ. de Tours)

Décembre 2018

Mardi 4 Décembre

10h15 Alex Ferrer (CMAP)
11h15 George Papanicolaou (Stanford Univ.) - Mathematical problems in space surveillance

Mardi 18 décembre

Janvier 2019

Mardi 8 Janvier

10h15 Karim Lounici (CMAP)
11h15 Stanley Durrleman (Inria et ICM) - Geometrical approaches in statistical learning for the construction of digital models of the Human brain

Mardi 22 Janvier

Février 2019

Mardi 5 Février

Mardi 19 Février

10h15 Jean-Marc Bardet (Univ. Paris 1)
11h15 Sébastien Darses (Univ. Aix-Marseille)

Mars 2019

Mardi 12 Mars

Mardi 26 Mars

10h15
11h15 Bastien Mallein (LAGA)

Avril 2019

Mardi 9 Avril

10h15
11h15 Nathael Gozlan (MAP5)

Mai 2019

Mardi 7 Mai

Mardi 21 Mai

Juin 2019

Mardi 11 Juin

Mardi 25 Juin

Les organisateurs: Antonin Chambolle, Lucas Chesnel et Amandine Véber