Excitations of amorphous solid helium

We present neutron scattering measurements of the dynamic structure factor, $S(Q,\omega)$, of amorphous solid helium confined in 47 $\AA$ pore diameter MCM-41 at pressure 48.6 bar. At low temperature, $T$ = 0.05 K, we observe $S(Q,\omega)$ of the confined quantum amorphous solid plus the bulk polycrystalline solid between the MCM-41 powder grains. No liquid-like phonon-roton modes, other sharply defined modes at low energy ($\omega<$ 1.0 meV) or modes unique to a quantum amorphous solid that might suggest superflow are observed. Rather the $S(Q,\omega)$ of confined amorphous and bulk polycrystalline solid appear to be very similar. At higher temperature ($T>$ 1 K), the amorphous solid in the MCM-41 pores melts to a liquid which has a broad $S(Q,\omega)$ peaked near $\omega \simeq$ 0 characteristic of normal liquid $^4$He under pressure. Expressions for the $S(Q,\omega)$ of amorphous and polycrystalline solid helium are presented and compared. In previous measurements of liquid $^4$He confined in MCM-41 at lower pressure the intensity in the liquid roton mode decreases with increasing pressure until the roton vanishes at the solidification pressure (38 bars), consistent with no roton in the solid observed here

Modeling the wind circulation around mills with a Lagrangian stochastic approach

This work aims at introducing model methodology and numerical studies related to a Lagrangian stochastic approach applied to the computation of the wind circulation around mills. We adapt the Lagrangian stochastic downscaling method that we have introduced in [3] and [4] to the atmospheric boundary layer and we introduce here a Lagrangian version of the actuator disc methods to take account of the mills. We present our numerical method and numerical experiments in the case of non rotating and rotating actuator disc models. We also present some features of our numerical method, in particular the computation of the probability distribution of the wind in the wake zone, as a byproduct of the fluid particle model and the associated PDF method

L'helium trois solide aux tres basses temperatures : etude neutronique

SIGLECNRS T 57540 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

L'hélium trois solide aux très basses températures. Etude neutronique

No abstractPas de résum

L'hélium trois solide aux très basses températures. Etude neutronique

No abstractPas de résum

Phonons, rotons, and localized Bose-Einstein condensation in liquid He 4 confined in nanoporous FSM-16

International audienc

Phonon-roton modes in liquid 4 He coincide with Bose-Einstein condensation

International audienc

Localized Bose-Einstein condensation in disordered liquid He 4 films

International audienc

Amorphous solid helium in porous media

International audienc