Conjugaisons finies et milieux continus en relativité générale

We present here the main elements of a mechanics of relativistic continua relying upon a concept of 《finite conjugacy》 between two relativistic motions described by two unit vector-fields u and u' defined on two different relativistic manifolds $\text{M}$-and $\text{M}$'.This purely relativistic, global, and intrinsic theory leads, together with a new approach of the deformation tensors in relativity, to a differential system of equations for the conjugacies which is neither under-determined nor over-determined. A rough study of the propagation of the conjugacy-waves shows then that it is advisable to consider the notion of a finite conjugacy as a satisfying relativistic extension of the classical and tridimensional notion of a finite deformation in mechanics, and to identify the spatial conjugacy-waves obtained with the ordinary acoustic waves.Drastic particularizations of the space-times $\text{M}$ and $\text{M}$', of the motions u and u', of the admissible types of conjugacies and of the elastic behaviour of the continua under study allow to recover, as very important but particular cases, the tridimensional non-relativistic theory of elasticity for finite deformations and non-linear behaviour, as well as the main theories of relativistic elasticity already proposed by Mmes Choquet-Bruhat and Lamoureux-Brousse, Rayner, Carter and Carter-Quintana, Grot-Eringen…. The obtained system of equations generalizes also to the finite case some aspects of the infinitesimal theory of Weber and Papapetrou.     

Evolution avec la température de la réflectivité, de l'indice complexe et de la sélectivité spectrale du nitrure de zirconium

The reflectance of zirconium nitride has been measured at 20, 500 and 700°C, within the range 0.22 to 5.50 μ m. The optical constants have been determined using Kramers-Kronig analysis. The spectral selectivity of this compound noticeably depends on temperature; the absorptance increases from 0.28 at 20°C to 0.36 at 700°C while the emittance increases from 0.06 to 0.14.     

Mesure de la diffusivité longitudinale de matériaux anisotropes

Measurement of in-plane diffusivity of anisotropic solid samples. Survey of the techniques developed at LEMTA. Three techniques for the measurement of in-plane diffusivity of anisotropic solid samples have been developed at the Laboratory and are presented here :

• •the two directional heat pulse (flash) method with local contact measurement of two temperatures;
• •the fin method with local contact or contactless measurement of two temperatures;
• •the two directional heat pulse method with measurement of the temperature field by an infrared camera and data processing through integral transformations.