University of Marne-la-Vallée

About: University of Marne-la-Vallée is a based out in . It is known for research contribution in the topics: Estimator & Context (language use). The organization has 831 authors who have published 1855 publications receiving 55316 citations.

The settling of fine cohesive powders

Abstract: We investigate the settling of an initially fluidized bed of a fine cohesive powder. Experimental results on the sedimentation rate cannot be fitted by theoretical and empirical equations existing in the literature and derived for non-cohesive spheres. We extend these equations to account for the adhesion-induced aggregation of fine particles. The number of particles per aggregate N and the ratio of aggregate radius R to particle radius, a, have been chosen as fitting parameters. Results from two independent approaches are in very good agreement with the experimental data for approximately the same values of N and R. Pictures taken from the fluidized bed show that the average aggregate radius matches the predicted one.

On a stabilized colocated Finite Volume scheme for the Stokes problem

Abstract: We present and analyse in this paper a novel colocated Finite Volume scheme for the solution of the Stokes problem. It has been developed following two main ideas. On one hand, the discretization of the pressure gradient term is built as the discrete transposed of the velocity divergence term, the latter being evaluated using a natural finite volume approximation; this leads to a non-standard interpolation formula for the expression of the pressure on the edges of the control volumes. On the other hand, the scheme is stabilized using a finite volume analogue to the Brezzi-Pitkaranta technique. We prove that, under usual regularity assumptions for the solution (each component of the velocity in H2 (∞) and pressure in H1 (∞)), the scheme is first order convergent in the usual finite volume discrete H1 norm and the L2 norm for respectively the velocity and the pressure, provided, in particular, that the approximation of the mass balance flux is of second order. With the above-mentioned interpolation formulae, this latter condition is satisfied only for particular meshes: acute angles triangulations or rectangular structured discretizations in two dimensions, and rectangular parallelepipedic structured discretizations in three dimensions. Numerical experiments confirm this analysis and show, in addition, a second order convergence for the velocity in a discrete L2 norm.

New insights into the colour origin of archaeological Egyptian blue and green by XAFS at the Cu K-edge

Abstract: New results on the local chemical environment of Cu2+ in archaeological Egyptian blue and green and also modern Egyptian green were obtained by x-ray absorption fine structure (XAFS) analysis. The information is essential for the understanding of the colouring mechanisms in both pigments. In a previous study, a clear physico-chemical characterisation of Egyptian blue and green was achieved using a complementary analytical approach with ancient and modern synthesized pigments. Electron microscopy (SEM–EDX and TEM), x-ray diffraction and micro-Raman and UV–visible spectroscopy were used to gain information about the conditions of the ancient Egyptian fabrication processes and permitted the clear distinction of both pigments. However, the exact colouring mechanisms could not be elucidated by these methods. Different Cu-bearing amorphous and crystalline phases were found in both pigments. These phases should be at the origin of the blue and turquoise colours. Using XAFS data at the Cu K-edge, new insights into the origin of the colouring mechanisms of both pigments could be obtained from the precision of the Cu speciation. In Egyptian blue, Cu2+ is mainly allocated in a square-planar site in a crystalline cuprorivaite phase, whereas in Egyptian green, Cu2+ is basically situated in a distorted octahedral site in an amorphous phase. Copyright © 2006 John Wiley & Sons, Ltd.

A note on the Burrows-Wheeler transformation

Abstract: We relate the Burrows-Wheeler transformation with a result in combinatorics on words known as the Gessel-Reutenauer transformation.