Comptes Rendus de l'Académie des Sciences - Series IIB - Mechanics-Physics-Chemistry-Astronomy最新文献

Strongly anharmonic pressure oscillations generated by fluid injection stops have been observed at the well head of an underground cavern. They are due to a small gas pocket, trapped in the well head, whose existence was unknown.

A new family of lanthanide oxalate, [Ln(H₂O)₃]₂(C₂O₄)₃ with Ln = Eu−Dy, has been characterized through the X-ray structural study of the gadolinium derivative. In contrast to the lanthanide oxalates already known, this structure is free of zeolitic water but it remains layered and the basic building blocks are preserved. The loss of zeolitic water leads to some deformations of the network units.

European space research carried out by ESA, the European Space Agency, has enabled Europe to reclaim the leading positions it had conceded to the USA. But an eventual return to the situation that prevailed in the sixties, when European space research was totally dependent on US planning and technologies is to be feared. Actually, Europe is only spending a quarter of the amount NASA devotes to its space activities. A new approach is required if there is to be any hope of preserving the achievements of almost 40 years of efforts, which isstarting to bear fruit. Halt the budget erosion, improve the , methods of management and the execution of missions, start researches in ‘high tech’, avoid the dispersal of technical and scientific activities, coordinate national efforts with those of ESA: these necessary measures, taken as soon as possible, would allow Europe to keep its rank of a scientific, technological and cultural force.

A multiscale closure model for compressible turbulent mixing flows is developed in order to take into account their spectral nature and unsteadiness. A new method is introduced to calibrate the phenomenological coefficients, using the spectral properties of the multiscale closure model. It is based on the Canuto-Goldman analytical model. The Meshkov shock tube experiment is simulated.

In this mini review we describe various aspects of semiclassical coherent-state propagation, ranging from recent experiments in atomic physics to mathematical aspects of ‘quantum chaology’.

A stereoselective synthesis of β-thymidine using 2-deoxy-D-erythro-pentofuranosyl-trichloroacetimidate as the activating group is reported. This five-step route includes only one chromatographic purification with an overall yield of 30% in β-thymidine and stereoselectivity of approximately 80%.

A micromechanical relaxation is observed in a heterogeneous Polymer Modified Bitumen (PMB). This relaxation, theoritically studied by Fröhlich and Sack, arises when a microscopic elastic deformation develops in dispersed phase particles. Thus, two reinforcement domains are highlighted when the material is sheared under a low-strain dynamic mechanical deformation: at low frequency, the polymer-rich dispersed particles are harder than the matrix and behave as hard spheres (undeformable inclusions). At high frequencies, they are soft (deformable), causing a subsequent decrease in the modulus of the PMB. The hard/soft relaxation results in a minimum of phase angle versus frequency.

New Mo_xCo_yFe_{3 − x − y}O₄ ferrites have been prepared from hydroxide precursors leading to fine spherical particles. The so-obtained products have quite high substitution rates (x ≈ 0.5 and 0 ⩽ y ⩽ 1), higher than those ever reported for Mo-Co ferrites. The substitution of Fe²⁺ ions by Co²⁺ ions, which have a stronger magnetocrystalline anisotropy, and the directional order phenomenon both involve an enhancement in coercivity. Nevertheless, because of differences in composition, in cationic distribution and in particle morphology, the Mo-Co ferrites synthesized according to our process show a coercive force lower than that observed by other workers. The cobalt element stabilizes the spinel structure of the ferrites by decreasing their reactivity towards oxygen. Besides, for high cobalt content, a proportion of these ions has the valency state + III.

The photocatalytic degradation of acetic acid in an aqueous suspension of TiO₂ has been studied. The influence of [TiO₂], [CH₃COOH] and irradiation time on the rate of disappearance of acetic acid has been demonstrated. We have brought to the fore that the disappearance of acetic acid follows the Langmuir-Hinshelwood model. Finally we have observed the effect of granulometry and the crystalline structure of the catalyst that shows that the degradation is made at the TiO₂ surface.