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

Different configurations of unstable interfaces between miscible fluids are described. Behavior qualitatively similar to that generally observed between immiscible fluids is reported. Owing to the slowness of molecular diffusion, the density gradient between the two species may induce an equivalent surface tension which could explain these similitudes.

A predictive model of a pneumatic actuator is introduced and validated without any restrictive assumption about the thermal evolution of gas volumes. Taking the thermal balance into account requires the identification of the equivalent exchange coefficient. Estimated values are found not to be sensitive to the jack extension.

The rate constants of the 3rd order reactions have been measured for the reaction between 3-bromopropyltriphenylphosphonium bromide and sodium hydroxide in water-methanol and water-dioxane media of various compositions. The reaction rate increases continuously with decreasing water content of the solvent. The dominant effect is the extent of solvation of the hydroxyl ions in methanol and dioxane media. The reaction in water-dioxane media is always faster than in methanol-water media and the difference is dependent on solvent composition, where the solvent structure and solvating power vary. The rate of decomposition of 3-bromopropyltriphenylphosphonium is larger than that of tetraphenylphosphonium ion in similar conditions, which is attributed to an inductive effect increasing the positive charge on phosphorus upon introduction of the 3-bromopropyl group. The desolvation of reactants and the solvation of transition states of the two reactions in the two solvents considered were discussed.

A model taking into account unilateral contact condition, friction and adhesion is presented. In the framework of continuum thermodynamics, the contact zone is considered as a material surface and the local constitutive laws are derived by choosing conveniently two specific surface potentials. The adhesion is characterized by a variable β, introduced by Frémond (1987), which represents the intensity of adhesion. A quasistatic variational formulation and an incremental one are proposed. A numerical method is given to solve the problem. The model is used to simulate an indentation experiment which is conducted to characterize the behaviour of fiber/matrix interfaces in a ceramic composite.

An oriented single grain of a γ/γ′ superalloy is deformed by dynamic compression (12%, 20 °C) along [001]. Thin deformation twins are observed for the first time in such a single grain using high resolution electron microscopy. They appear to develop more easily in γ corridors between γ′ precipitates.

A rubber film is loaded with hard ferromagnetic particles (with a strongly preferred magnetisation axis). The film is prepared with alternate, regions (ribbon-like) of + and — magnetisation, and is fixed on a solid substrate. When a tangential magneticfield H is applied, the free surface should deform into ridges and valleys — thus becoming more wettable.

The inverse problem is solved by least-squares matching of theoretical fields (for trial objects), employing an approximate field ansatz, to the scattered acoustic wavefield measured on a cylinder fully enclosing the object.

The present work takes stock of either classical or relaxor ferroelectric ceramics related to BaTiO₃. The homovalent substitutions in the 12 C.N. site lead to a sharp transition at T_C and to a classical ferroelectric phase. On the contrary, the substitutions in the 6 C.N. site lead to a diffuse transition, and a relaxor ferroelectric phase; these substitutions may be either homovalent (e.g. Ba(Ti_{1 − x}Zr_x)O₃) or heterovalent (e.g. Ba_{1 − x}K_x(Ti_{1 − x}Nb_x)O₃).

The solid mass of the saturated viscous, heat-conducting sediment-water layer below temperate glaciers grows by abrading the underlying rockbed. We propose to model this layer as a saturated mixture continuum of fluid and solid. We formulate its balance laws in volume and jump local forms following, e.g. Germain and Muller (1986). The water balance accounts for its drainage into the rockbed and the melting of ice within the overlaid ice sheet. Dissipation due to the power expended by stresses, the Darcy interaction force and sliding friction governs this thermomechanical system. Our analysis establishes that, contrary to what is stated in the literature, the listed dissipative mechanisms are all relevant.

This paper concerns the influence of high frequency vibrations on interfaces (free surface of a fluid, interface of two immiscible fluids, surface of a solid body immersed in a liquid). Such interfaces are described by different equations and boundary conditions, but in all the cases they are oriented perpendicularly to the vibration axis.