# Séminaire du LPTMS: Ken Sekimoto

## Coarse-Graining of Momentum Flow

### Ken Sekimoto (MSC, Université Denis Diderot & Gulliver, ESPCI)

Like the energy and mass, the momentum is also a conserved quantity. Usually, however, we pay less attention to the role played by the last one as compared with the former ones. In the present talk, I will discuss the three examples in which the concept of momentum flow helps and simplifies our understanding of phenomena.

First we discuss the “adiabatic-piston” for which the physical origin of the non-equilibrium force has long been unclear. The consideration of the momentum flux of both the gases and piston allows to reach the central results in a few lines of elementary calculation, elucidating how the non-equilibrium force emerges.

Secondly we present a method of coarse-graining the overdamped dynamics of dense cellular packing of matters.” We show that the coarse graining of the momentum and angular momentum fluxes leads naturally to the Irving-Kirkwood type formula for the stress tensor irressective of the underlying dynamics.

Lastly we discuss the Newton’s cradle with modified repulsive laws. This classical 1D system can show the similarity to the quantum Mössbauer absorption and emission. By considering the momentum flow through the cluster, we reach the coarse-grained dynamics for the center of mass coupled with an “evanescent” wave.

**Date/Time : ** 23/05/2017 - *11:00 - 12:00*

**Location : ** LPTMS, salle 201, 2ème étage, Bât 100, Campus d'Orsay

#### Upcoming seminars

- Physics-Biology interface seminar: Knut Drescher - 27 Jun 2018 - 11:00