Séminaires 2016-2017

  jeudi 13 juillet à 16h, salle 114

Marceau Henot (LPS Orsay) : A quantitative comparison of the solid polymer melt or solid-elastomer friction : a proof of the Navier interfacial equation

If the Navier-Stokes equation is often considered as one of the most difficult mathematical equations for a physicist or a mathematician, the question of the boundary conditions to describe the flow of a liquid in a pipe is often considered as trivial. It is usually assumed that the tangential velocity of a fluid close to a surface at rest is equal to zero. Nevertheles, already in his treatise on the movement of fluids, Navier introduced a more general equation, assuming a linear boundary condition : the shear stress at the solid-liquid interface is proportional to the component of the fluid velocity tangent to the surface. If for simple liquids, the slip effect is very small, it can become important in the case of polymer melts. We present measurements done on such melts using a velocimetry technique based on fluorescent photobleaching.

  mercredi 2 mai à 16h30, salle 114

Hadrien Vroylandt (LPT) : Stochastic thermodynamics and fluctuating efficiency

Engine efficiency is one of the key points of the thermodynamics. Since the work of Carnot in the XIXth century, much work has been done, in particular the development of the thermodynamics for small scales. I will review this recent work on the stochastic thermodynamics and present my work on efficiency fluctuation.

  mercredi 22 mars à 16h30, salle 114

Steven Arbeltier (LPGP) : Modeling of Radio Frequency Plasma Mangetron in N_2 with lithium oxide target

This study is focused on deposition of one of thin film battery component the electrolyte It is deposited by magnetron sputtering of a target in pure nitrogen plasma. A magnetron contains a low pressure plasma and a strong magnetic field to increase the ionization degree. The ions are attracted toward a target to sputter it and project particles onto a substrate in front of the target, in order to make a thin film deposition.

In spite of the successful implementation of this technology, the understanding of the elementary processes governing the complex kinetics in such type of plasma is still sparse. Moreover, the magnetic field has a tremendous influence on the position of incident ions on the target and is different on each reactor. An interesting approach to learn more the phenomena occurring is modeling.The present results are obtained from two models : a 0D model resolving by a self-consistent method the Boltzmann inhomogeneous equation for magnetized electrons in magnetron plasma and balance equations describing the reactional kinetics of gaseous species, and a 2D model using Particle-In-Cell-Monte-Carlo approach.

  mercredi 1 mars à 16h30, salle 114

Antoine Léhebel (LPT Orsay) : Modifying Gravity

General Relativity has been a successful theory for more than one century now. I will briefly review its accomplishments. However, most of the talk will be devoted to the reasons — both observational and theoretical — that encourage us to modify our current theory of gravity. I will discuss some alternative theories of gravity and their implications. Among these, I will focus on the addition of one scalar degree of freedom to standard GR. We will see some implications for cosmology and black holes.