Sur les proprietes magnetiques du fluorure KxVF3β (0,45 ⩽ x ⩽ 0,55)

The magnetic properties of β-K_xVF₃ (0,45 ≤ x ≤ 0,55), have been investigated.At high temperature (T > 150 K), the molar susceptibility follows a Curie-Weiss law. The experimental values of the Curie constant and of the effective moment are in good agreement with the calculated values. The paramagnetic Curie temperatures are negative and involve preponderant antiferromagnetic interactions. At low temperature a strong ferromagnetic component appears (T < 58 K); its origin is discussed and several hypotheses are proposed.     

Structure of colloidal particles in water oil mixtures stabilized by polymeric emulsifiers: 1. Phase diagrams and electron microscope studies

The phase diagrams of toluene/water mixtures, stabilized by amphiphilic graft copolymers in the presence of an alcohol, show two domains in which these systems are optically clear. The composition of the continuous phase of the polymeric microemulsions was determined by dialysis experiments. The results indicate a preferential solvation of the copolymer sequences by the ternary solvent mixture. The micellar particles were observed by electron microscopy on carbon replicas of freeze-fractured samples. Depending on the copolymer composition and the location of the system in the phase diagram, the micrographs reveal either individual particles ($\text{50}\text{A}\text{?}\text{<}\text{radius}\text{< 250}\text{A}\text{?}$), well-dispersed in the continuous medium, or inter-particle clusters.     

Improved anticontaminator for cryo-electron microscopy with a Philips EM 400

Electron microscopy of frozen-hydrated specimens is frequently impaired by atmospheric humidity, introduced together with the cold specimen and subsequently condensing on it. This effect can be prevented in the Philips 400 electron microscope operating with the cold stage PW6591 by an improved anticontaminator described in this note. The retractable anticontaminator is formed by two adjustable liquid-nitrogen cooled blades placed just above and below the specimen. It does not interfere with any other feature of the microscope.     

Proprietes magnetiques de nouvelles phases obtenues par hypertrempe a haute temperature

Splat cooling technics are applied to the BaOFe₂O₃ systems. The gun technic is used on the liquid melt with induction-warming or plasma torch. Nearly enterly amorphous phases are performed, the magnetic and structural properties of these phases are studied. An explanation of recristallisation mechanism is proposed.     

A generalized Semenov model for thermal ignition in nonuniform temperature systems

Critical properties of the Semenov model which describes thermal ignition in a uniform temperature system have been reanalyzed in terms of independent parameters, nondimensional activation energy, and surface heat loss. The analysis is then extended to the distributed temperature problem by the introduction of a correlation factor which effectively establishes a link between the Semenov model and the Frank-Kamenetskii parameter. This approach is capable of giving satisfactory results for properties such as ignition criteria, ignition times, and temperature profiles for a system with nonuniform temperature distributions. Specific results are presented mostly for the slab, but extensions to the cylinder and the sphere are also discussed.     

A new approach for the visualization of molecular arrangement in biological micro-crystals

Biological molecules often form micro-crystals that are in a size range that is unsuited for study either by X-ray crystallography or by electron microscopy. The method described here allows the use of most of these crystals. It consists of cutting sections through the crystal deposited on a grid after a preliminary observation in the electron microscope to determine its precise location. It allows visualization of the crystal molecular packing in any plane normal to the grid plane at the resolution usually obtained by negative staining. If the crystal is thin enough, two orthogonal views of the same crystal can be obtained. The orientation and the position of the sections along the crystal axis are precisely determined using latex particles as reference points. Crystals as small as 1 μm in length can be studied.     

Modifications structurales de l'oxynitrure de silicium sous contraintes thermiques

Structural modifications of silicon oxynitride have been studied at high temperature up to 1200°C by time of flight neutron diffraction method. The thermal expansion along the three cristallographic axes are 1.4 ± 0.7 10^?6 deg^?1 along a, 4.4 ± 0.3 10^?6 deg^?1 along b, and 4.1 ± 0.4 10^?6 deg^?1 along c. The variation of the atomic positions are given, and also the evolution of bond angles and bond lengths between 20 and 1200°C. It is shown that the main contribution to the deformation is the evolution of the SiOSi angle which permits the rearrangement of SiN₃O tetrahedra by rotation around oxygen atoms.     

A readout system for the delphi TPC prototype

Our purpose is to test a TPC prototype and, simultaneously, to evaluate a digitising electronics based on an 8 bit video-speed flash A/D converter.     

Review of Vers une logique des significations.

Reviews the book, Vers une logique des significations by Jean Piaget and Rolando Garcia (1987). This volume is a collection of Piaget's works. Each chapter describes one of his logico-mathematical studies on the play activities of children. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sur les zones absorbantes et les zones chaotiques d’un endomorphisme bidimensionnel

A complex dynamical behaviour called chaos is observed in second-order recurrences with a non-unique inverse (endomorphisms). The chaotic solutions of such second-order point-mappings are located in bounded domains of the phase plane, called chaotic areas. All the attractive limit sets of an endomorphism, such that fixed point, cycle, invariant closed curve or chaotic solution are located in phase plane domains designated by absorptive areas. Two methods for the construction of absorptive areas and chaotic areas are done. Different bifurcations giving rise to a modification of the nature of these areas are described. Various examples whose one is related to a sampled-data control system are done.