NSC Seminar Two talks: Geometry and statistics in turbulence, Nonlinear dynamics in invertebrate phototransduction

2006-03-24 15:00 - 2006-03-24 16:30
Alain Pumir (Institut Non Lineaire de Nice)
Geometry and statistics in turbulenceVelocity fluctuations in hydrodynamic turbulent flows have a non trivial structure, characterized by the correlations of the velocity gradient tensor. I will discuss a phenomenological model, incorporating the main known features of hydrodynamic turbulence, aimed at predicting the structure of the velocity gradient tensor, M, coarse-grained at scale r. This model is formulated as a set of stochastic differential equations.I will discuss the origin of this model, and describe the solutions obtained by using a semiclassical approach.--Nonlinear dynamics in invertebrate phototransductionPhototransduction is the process whereby a photon leads to the generation of an electrical current in a retina’s cell. In invertebrate (flies), one photon leads to a well-characterized electric pulse. I will discuss the mechanism leading to the generation of this current. Due to Calcium mediated feedbacks, the process is highly nonlinear. Fluctuations also play a key role, due to the small number of key molecular species participating in the signal transduction.