Superconductivity of bulk CaC6

We have obtained bulk samples of the graphite intercalation compound, CaC6, by a novel method of synthesis from highly oriented pyrolytic graphite. The crystal structure has been completely determined showing that it is the only member of the MC6, metal-graphite compounds that has rhombohedral symmetry. We have clearly shown the occurrence of superconductivity in the bulk sample at 11.5 K, using magnetization measurements.     

Three-dimensional recomposition of the absorption field inside a nonbuoyant sooting flame

A remote scanning retrieval method was developed to investigate the soot layer produced by a laminar diffusion flame established over a flat plate burner in microgravity. Experiments were conducted during parabolic flights. This original application of an inverse problem leads to the three-dimensional recomposition by layers of the absorption field inside the flame. This technique provides a well-defined flame length that substitutes for other subjective definitions associated with emissions.     

Rheological properties of paraffin suspensions of surface-modified alumina powder for low-pressure injection moulding

Due to the hygroscopic nature of fine alumina powders, the presence of water may have a detrimental effect on the rheological properties of a suspension in melted paraffin for low-pressure injection moulding (LPIM). For this reason, a modification of the powder surface from hydrophilic to hydrophobic is essential for the production of high-quality moulded ceramics. In our paper, the efficiency of the application and the chemisorption of protective monomolecular layers of a long-chain carboxylic acid or its salts will be presented. The effect of the powder treatment on the shear viscosity and the viscoelastic properties of the suspensions for LPIM as well as on their stability in terms of the detrimental effect of water will be discussed.This paper was presented at the first Annual European Rheology Conference (AERC) held in Guimarães, Portugal, September 11-13, 2003.     

Interaction of femtosecond light filaments with obscurants in aerosols

The interaction of ultrashort laser pulses with opaque droplets in the atmosphere is examined numerically. Intense filaments resulting from the balance between self-focusing and ionization of air molecules are shown to be robust against obscurants sized up to 2/3 of the filament diameter. (3D+1)-dimensional numerical simulations confirm recent experimental data [F. Courvoisier et al., Appl. Phys. Lett. 83, 213 (2003)]. The filament is rapidly rebuilt with minimal loss of energy over a few cm after the interaction region. The replenishment of the pulse mainly proceeds from the nonlinear attractor responsible for the formation of a spatial soliton modeling the filament core.     

Observation of laser driven supercritical radiative shock precursors

We present a supercritical radiative shock experiment performed with the LULI nanosecond laser facility. Using targets filled with xenon gas at low pressure, the propagation of a strong shock with a radiative precursor is evidenced. The main measured shock quantities (electronic density and propagation velocity) are shown to be in good agreement with theory and numerical simulations.     

Surface reconstruction and decahedral structure of bimetallic nanoparticles

We report on energetic surface reconstruction phenomena observed on bimetallic nanoparticle systems of AuPd and AuCu, similar to a resolidification effect observed during the cooling process in lead clusters. These binary alloy nanoparticles show the fivefold edges truncated, resulting in [100] facets on decahedral structures, an effect largely envisioned and reported theoretically, with no experimental evidence so far. We demonstrate experimentally as well as by computational simulations that this new eutectic structure is favored in such nanoalloy systems.