Theory Seminar

Monday, 6th February 2012 - 11 h

salle 106, bâtiment commun ILL/ESRF

Natsuhiko YOSHINAGA WPI

Advanced Institute for Materials Research (WPI-AIMR), Tohoku University, Japan

Spontaneous motion or self-propulsion have been attracting attention in last decades for its potential application to biological problems such as cell motility and wound healing. Recently several model experiments showing spontaneous motion have been proposed. The systems in these works consist of relatively simple ingredients for instance oil drops in water nevertheless the motion is as if the drops are alive. The key questions are why the particle moves without external force and why it breaks symmetry and chooses one direction. The first point has been discussed in hydrodynamics of the Marangoni effect in which a liquid droplet is driven by a gradient of surface tension. The mechanism is that the gradient induces convective flow inside and outside of a drop, which leads to swimming motion of the drop itself. The second point was less discussed, but has been discussed in the field of nonlinear dynamics as drift instability. Thus far there are only few attempts to discuss the spontaneous symmetry breaking from hydrodynamics. In this work, we derive the nonlinear equations exhibiting drift instability. This is of importance because all the coefficients are determined with physical quantities.

T. Ziman (ziman@ill.fr)

Please note the unusual time!

General ILL Seminar organized by College 3

Tuesday, 7th February 2012, 9:00

Seminar room ILL1

Guillaume Pignol

LPSC Grenoble

The accelerating expansion of the universe has been recently discovered and confirmed. It is one of the most puzzling observations of modern cosmology: 70% of the energy budget of the universe today has to be attributed to a completely unknown type of "Dark Energy". One theoretical route to address this problem is to assume the existence of a cosmological scalar field, the quintessence, with nontrivial dynamics. If this quintessence field is coupled to ordinary matter particles, it would also mediate a fifth fundamental force displaying very unusual "chameleon like" properties. I will discuss how to probe such a force using bouncing ultracold neutrons, in particular using the GRANIT instrument.

GENERAL ILL SEMINAR College 6

Wednesday, 8 February 2012 11:00 am

ILL, Room 427 (Seminar Room, ILL 04, fourth floor)

J. Kozaily

Institut Laue Langevin (ILL)

CEMHTI site HT, Orléans, France

Because of their special properties as glass-forming systems, molten silicates play an important role in the geology of the Earth’s crust and mantle and are also of industrial interest for nuclear waste treatment. Research in these areas requires fundamental information on the microscopic structure and dynamics of silicate melts, but such measurements are hampered by the very high melting points of these systems. By extending the technique of aerodynamic levitation to inelastic neutron scattering, and also making use of inelastic synchrotron x-ray scattering, we have obtained results on the microscopic dynamics of silicates both above the melting point and in the supercooled regime. In particular, we have determined the temperature evolution of the viscosity and diffusion coefficient of calcium aluminosilicates, and thereby quantified the decrease in fragility of this glass-forming system as a function of increasing silica content. In parallel with our dynamical studies, we have performed x-ray and neutron diffraction experiments on the same compositions at the same temperatures in order to examine the local chemical order pertinent to the observed dynamical properties.

Keywords : Calcium aluminosilicates, Liquids, Levitation, QENS, Diffraction

M. BRUNELLI College 6 Secretary

External visitors may ask for a site access to Brigitte Dubouloz (dubouloz@ill.fr).