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

The dissolution of a random binary glass with strongly different solubilities is studied by Monte-Carlo simulations in two dimensions. The soluble species represents Na₂O or B₂O₃. The other species, SiO₂, has a local environment-dependent solubility. For a finite volume of liquid a rapid dissolution is found until an apparent equilibrium is reached. Nevertheless, a steady state porosification continues at a lower but constant speed with restructuration of the porous surface. The simulation reproduces the restarting of dissolution at apparent equilibrium, recently observed experimentally. Dynamical percolation permits us to explain the strong dependence of the dissolution rate on the concentration.

The aim of this paper is to present modifications brought to a standard Lagrangian model for turbulent dispersion so that the forces acting on a heavy particle in a turbulent boundary layer can be taken into account. A satisfying validation of this modified model for Lagrangian trajectography is then obtained and compared with the experimental results of Tanière et al. performed in the boundary layer of a wind tunnel.

The stability of Hagen-Poiseuille flow in a viscoelastic tube is determined using a linear stability analysis. It is found that such a flow is unstable, while the Hagen-Poiseuille flow is stable, as is well known. In this paper, we study the instability arising from an axisymmetric disturbance. The neutrality curves in several planes formed by the physical parameters of the problem are plotted. In particular, the effect of the Reynolds number, which was neglected in previous work, is examined. Particular attention is payed to the effect of the viscosity of the viscoelastic tube.

As an adapted, adaptable and optimized structure, the bone architecture modified itself by bone formation or resorption. The aim of this note is to generalize and to study the stability of an analytical and unidimensional model of this bone remodeling phenomena. The evolutive equations are solved by the finite difference method and heterogenous spatial organisations like that of the trabecular bone have been obtained.

A diffuse approximation method for solving Navier-Stokes equations in primitive variables is proposed. The results of a numerical example show the accuracy and efficiency of this approach.

The Space Research Institute of the Ministry of Science, Academy of Sciences of Kazakstan, monitors the territory of Kazakstan using the NOAA satellite data. This year, significant anomalies in the distribution of snow cover and underlying surface temperature have been detected in the region of the former Semipalatinsk nuclear test site (SNTS).

In the first article, we presented a review on the Cepheid PL relation as a tool formeasuring distances, and showed the sensitivity of the method to metallicity.Accounting for it brings the recent differing estimates of H₀ into agreement.

We experimentally confirm an expression derived by Boutreux and de Gennes for the shape of a granular pile filling a two-dimensional silo. The analytical formula is retrieved from a model of kinks using the vertical translational invariance of the heap surface. We also look at the dependence of the shape on the energy of the particles poured into the cell.

The upwind schemes are well suited to inviscid transonic flow but not to viscous flow. It is the opposite for central schemes. This paper presents a new approach which combines the central scheme and the upwind scheme. Liou's flux splitting is selected to define this new mixed AUSM⁺ Liou scheme. The results, obtained on supersonic viscous configuration, are compared to other schemes' results and to semi-empirical results. These calculations show the benefit of the present approach.

This note deals with optimal control with piezoelectric devices for a radiating structure excited by an unknown acoustic field. A state-space model is first identified from the Frequency Response Functions measured between the actuators and the sensors, a Linear Quadratic Gaussian controller is then synthesized to minimize a relevant acoustic index. Real-time optimal control was implemented and applied to a radiating plate enclosing a reverberant cavity.