Status  Confirmed 
Seminar Series  SEMLPTMC 
Subjects  condmat.meshall 
Date  Thursday 19 December 2019 
Time  15:00 
Institute  LPTMC 
Seminar Room  Jussieu tower 1312 5th floor room 523 
Speaker's Last Name  Levernier 
Speaker's First Name  Nicolas 
Speaker's Email Address  nicolas [dot] levernier [at] gmail [dot] com 
Speaker's Institution  IUSTI Marseille 
Title  Firstpassage time of nonmarkovian random walks 
Abstract  In this talk, I will recall some results I got during my PhD and show new results obtained since then. In a second part, I will present part of the results I got during my postdoc in Geneva. The question of firstpassage time, typically the time needed for two particles to encounter, is of importance to quantify the rate of reaction of any diffusionlimited process. If the problem is essentially solved for markovian (that is memoryless) random walks such as brownian motion, only sparse results do exist for nonmarkovian random walks. I will present a formalism we have developed to quantify the mean first passage time to a target for a confined nonmarkovian random walker, whose position statistics is gaussian and with stationary increments. Then, I will present some features of confined ageing processes (that is : if the stationary increments hypotheses is relaxed), and decipher the links with the associated unconfined processes. In particular, the importance of the socalled persistance exponent will be emphasised. I will finally show how our gaussian formalism can be extended to ageing unconfined processes in order to get the value of the persistance exponent. In a second part, I will present a physical description of the actin cytoskeleton, which is a layer of fibers in interaction with molecular motors. This layer is polymerizing along the plasma membrane. Usual model typically see it as a thin layer, that is neglecting the dynamics in the direction orthogonal to the membrane. I will show that a more precise description that account for this direction leads to a new instability mechanism that cannot be observed within the thinlayer approach. Finally, I will briefly mention experimental works in agreement with this predicted instability. 
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