[en] The spin/entropy wave propagation was observed in a cylindrical resonant cavity filled with superfluid ³He A₁ phase in 2 T and 22.9 bar. Oscillating superleak transducers were used with Nuclepore membranes (3 μm pores) as active elements. When the drive is increased to a sufficiently high level, saturation in the resonant response is observed. The observed non-linear response will be interpreted in terms of critical velocity. The effects of superfluid fraction anisotropy on the spin/entropy wave propagation are currently under study by changing the relative orientation between the magnetic field and the sound propagation directions. Results of these studies will be reported

[en] Isentropic compression experiments and numerical simulations on metals are performed at Z accelerator facility from Sandia National Laboratory and at Lawrence Livermore National Laboratory in order to study the isentrope, associated Hugoniot and phase changes of these metals [1]. 3D configurations have been calculated here to benchmark the new beta version of the electromagnetism package coupled with the dynamics in Ls-Dyna and compared with the ICE Z shots 1511 and 1555. The electromagnetism module is being developed in the general-purpose explicit and implicit finite element program LS-DYNA(reg_sign) in order to perform coupled mechanical/thermal/electromagnetism simulations. The Maxwell equations are solved using a Finite Element Method (FEM) for the solid conductors coupled with a Boundary Element Method (BEM) for the surrounding air (or vacuum). More details can be read in the reference [2], [3]

[en] Electrical conductivities of fluid oxygen were measured between 30 and 80 GPa at a few 1000 K. These conditions were achieved with a reverberating shock wave technique. The measured conductivities were several orders of magnitude lower than measured previously on the single shock Hugoniot because of lower temperatures achieved under shock reverberation. Extrapolation of these data suggests that the minimum metallic conductivity of a metal will be reached near 100 GPa

[en] Electrical conductivities of fluid oxygen were measured between 30 and 80 GPa at a few 1000 K. These conditions were achieved with a reverberating shock wave technique. The measured conductivities were several orders of magnitude lower than measured previously on the single shock Hugoniot because of lower temperatures achieved under shock reverberation. Extrapolation of these data suggests that the minimum metallic conductivity of a metal will be reached near 100 GPa

[en] We report high pressure dynamic compression experiments of liquid water along a quasi-adiabatic path leading to the formation of ice VII. We observe dynamic features resembling Van der Waals loops and find that liquid water is compacted to a metastable state close to the ice density before the onset of crystallization. By analyzing the characteristic kinetic time scale involved we estimate the nucleation barrier and conclude that liquid water has been compressed to a high pressure state close to its thermodynamic stability limit

[en] The authors observed dynamically driven phase transitions in isentropically compressed bismuth. By changing the stress loading conditions they explored two distinct cases one in which the experimental signature of the phase transformation corresponds to phase-boundary crossings initiated at both sample interfaces, and another in which the experimental trace is due to a single advancing transformation front in the bulk of the material. They introduce a coupled kinetics-hydrodynamics model that for this second case enables them, under suitable simplifying assumptions, to directly extract characteristic transition times from the experimental measurements

[en] The superfluid fraction of ³He A₁ phase is computed from measurements of the velocity of spin/entropy waves induced in a cylindrical chamber, for two different directions of the magnetic field: parallel and perpendicular to the axis of the chamber. The ratio of the superfluid fractions in the parallel and perpendicular orientations is 1.85, and does not depend on the field between 1 and 5 Tesla. We adapt a theoretical texture model to account for the superfluid flow, and the results are consistent with the above ratio and direct estimates of superfluid velocity

[en] We present collective x-ray scattering (CXS) measurements using a Chlorine He-α x-ray source pumped with less than 200 J of laser energy. The experimental scattering spectra show plasmon resonances from shocked samples. These experiments use only 10¹² x-ray photons at the sample of which 10^-5 have been scattered and detected with a highly efficient curved crystal spectrometer. Our results demonstrate that x-ray scattering is a viable technique on smaller laser facilities making CXS measurements accessible to a broad scientific community

[en] An original microwave absorption method for the investigation and analysis of the HTS ceramics, named Direct Microwave Absorption (DMA) was developed. The main advantage of this method represents the possibility of an unambiguous distinction between the intergrain Josephson junctions and grain (bulk) contributions to the microwave absorption signal. (Author)

[en] The propagation of a spin-entropy wave in superfluid ³He-A₁ was observed in a cylindrical chamber with the magnetic field applied perpendicular to the chamber axis. A strong nonlinear response was observed as a function of drive amplitude. When the drive is relatively small, the resonant response is hysteretic and is dependent on the direction of frequency sweep through the resonance. When the drive is increased to a sufficiently large value, the response reverts to nearly linear dependence. copyright 1996 The American Physical Society