Les deplacements chimiques carbone 13 des groupements methyles traites en termes d'interactions H/H,H/Me,Me/Me

The different conformations of the methyl groups for a series of saturated cyclic and linear hydrocarbons were analysed. From these results we were able to identify the different interactions H/H, H/Me, Me/Me and calculate the chemical shifts of the methyl group for a series of hydroxylated stereoisomers.     

The influence of superficial conduction on the magnetoresistivity of antimony

The difference between adiabatic- and isothermal-magnetoresistivity has been used to study the dependence of the superficial current in antimony monocrystals upon the condition of the surfaces of the sample.     

Ultra-high-contrast few-cycle pulses for multipetawatt-class laser technology

We report the generation of few-cycle multiterawatt light pulses with a temporal contrast of 10(10), when measured as close as 2 ps to the pulse's peak. Tens of picoseconds before the main pulse, the contrast value is expected to spread much beyond the measurement limit. Separate measurements of contrast improvement factors at different stages of the laser system indicate that real contrast values may reach 10(19) and 10(14), when measured 50 and 25 ps before the pulse's peak, respectively. The combination of the shortest pulse duration and the highest contrast renders our system a promising front-end architecture for future multipetawatt laser facilities.     

Determination of liquid water content and dielectric constant in porous media by the capacitive methodDétermination,par la méthode capacitive,de la teneur en eau liquide et de la constante diélectrique dans un milieu poreux

A capacitive sensor-based apparatus has been settled to determine the liquid water amount and dielectric constant in consolidated porous media. This technique relies on the dielectric properties of water, air, and mineral substrate. The experimental procedure is described for successively oven-dried samples at 323 K. It allows us to determine the sample dielectric constant as a function of the sample water amount. For limestones from Caen region, an affine relationship is found at 293 K. This is then compared with other empirical soils data and with existing homogeneisation techniques applied to undeformable heterogeneous dielectrics. To cite this article: T. Fen-Chong et al., C. R. Mecanique 332 (2004).