Flow of particles suspended in a sheared viscous fluid: Effects of finite inertia and inelastic collisions

We investigate in this article the macroscopic behavior of sheared suspensions of spherical particles. The effects of the fluid inertia, the Brownian diffusion, and the gravity are neglected. We highlight the influence of the solid‐phase inertia on the macroscopic behavior of the suspension, considering moderate to high Stokes numbers. Typically, this study is concerned with solid particles O (100 μm) suspended in a gas with a concentration varying from 5% to 30%. A hard‐sphere collision model (with elastic or inelasic rebounds) coupled with the particle Lagrangian tracking is used to simulate the suspension dynamics in an unbounded periodic domain. We first consider the behavior of the suspension with perfect elastic collisions. The suspension properties reveal a strong dependence on the particle inertia and concentration. Increasing the Stokes number from 1 to 10 induces an enhancement of the particle agitation by three orders of magnitude and an evolution of the probability density function of the fluctuating velocity from a highly peaked (close to the Dirac function) to a Maxwellian shape. This sharp transition in the velocity distribution function is related to the time scale which controls the overall dynamics of the suspension flow. The particle relaxation (resp. collision) time scale dominates the particulate phase behavior in the weakly (resp. highly) agitated suspensions. The numerical results are compared with the prediction of two statistical models based on the kinetic theory for granular flows adapted to moderately inertial regimes. The suspensions have a Newtonian behavior when they are highly agitated similarly to rapid granular flows. However, the stress tensors are highly anisotropic in weakly agitated suspensions as a difference of normal stresses arises. Finally, we discuss the effect of energy dissipation due to inelastic collisions on the statistical quantities. We also tested the influence of a simple modeling of local hydrodynamic interactions during the collision by using a restitution coefficient which depends on the local impact velocities. © 2010 American Institute of Chemical Engineers AIChE J, 2010     

Systems Ln2X3SnX2 (Ln = terres rares et X = S ou Se) composés Ln2SnS5, définition et étude structurale

In the ternary systems LnSnS, intermediate compounds are observed only in the quasi-binary Ln₂S₃SnS₂ sections. They have the general formula Ln₂SnS₅, and exist from La to Dy. They are orthorhombic, with the space group Pbam, and their structure was studied with single crystals of La₂SnS₅ (Jaulmes 1974) and Sm₂SnS₅ (Julien-Pouzol and Jaulmes 1976). These structures are extremely similar; they differ only by the coordination of the rare earth, which is 9 for La (with 2 relatively long bonds), and 8 for Sm. Intermediate compounds were not observed in the other regions of the ternary LnSnS systems. No ternary compound has been found in the LnSnSe systems.     

Carbon-13 and Oxygen-18 Mass Spectrometry as a Potential Tool for the Study of Carbonate Phases in Concretes

The abundance of carbon-13 and oxygen-18 in cement carbonates shows important variations linked to the precipitation process. Three groups of values are observed: (1) the highest values (mean δ₁₃ and δ₁₈= 0 per mil versus PDB and + 30 per mil versus SMOW, PDB and SMOW being the international geochemical isotope standards) are specific of carbonate fillers made from marine sedimentary limestones; (2) the lowest values are linked to direct absorption of atmospheric CO₂ by high-pH cement solutions with important kinetic effects and no isotope equilibration in the high-pH zone (δ₁₃ and δ₁₈ range from -35 per mil to -18 per mil versus PDB and +18 per mil to +8 per mil versus SMOW, respectively); and (3) the intermediate group (δ₁₃ and δ₁₈ range from +20 per mil to +30 per mil versus PDB and -10 per mil to -15 per mil versus SMOW, respectively) is due to precipitation of the mineral-carbon system dissolved in water. Stable isotope measurements, therefore, may provide information on the proportion and chemical origin of various carbonate generations in concrete.     

Preparation et structure de Ga2S3α type wurtzite lacunaire

Preparations of powdered and crystalline αGa₂S₃ are described. Structure of αGa₂S₃ is established from single crystal determination (R = 0.058). These is a superstructure of wurtzite type, with ordered vacancies on gallium positions. A polymorphism of Ga₂S₃ is described.     

X. Yeast sequencing reports. Sequence analysis of a 40·2 kb DNA fragment located near the left telomere of yeast chromosome X

We have sequenced on both strands a 40,257 bp fragment located near the left telomere of chromosome X of Saccharomyces cerevisiae. The sequenced segment contains 21 open reading frames (ORFs) at least 100 amino acids long. Five of the ORFs correspond to known amino acid sequences: two hypothetical proteins in the subtelomeric Y′ repeat region of 65·4 and 12·8 KDa, the cytochrome B pre-mRNA processing CBP1 protein, the mitochondrial nuclease NUC1 and the CRT1 protein. Of the 16 remaining ORFs, eight show highest homologies with the S. cerevisiae hexose transporters family (two ORFs), the yeast α-glucosidase (two ORFs), the yeast PEP1 precursor, the Escherichia coli galactoside O-acetyltransferase, the S. cerevisiae 137·7 KDa protein located in the Y′ region and a protein of unknown function of Schizosaccharomyces pombe. Finally, eight of the ORFs exhibit no significant similarity with any amino acid sequences described in data banks. DNA sequence comparison has revealed the presence of different repeated elements characteristic of yeast chromosome ends. Disruption studies have been performed on two ORFs encoding putative proteins of unknown function. The sequence has been entered in the EMBL Data Library under Accession Number Z34098.     

Physicochemical equilibria of cement-based materials in aggressive environments—experiment and modeling

Assessment of the integrity of concrete structures during their service life begins by considering the durability of the material in its environment. Experiments have clearly improved the understanding of the degradation mechanisms of concrete, mortars, and cement pastes under various aggressive environments. As far as radioactive waste containers are concerned, leaching by water has to be considered. Leaching experiments of cement pastes by aggressive solutions are shown to result in degradations with different kinetics. Three cement pastes with variable water-to-cement (w/c) ratio (0.25, 0.4, and 0.5) in two solutions (pure water and mineralized water) were investigated by TG/DTA, SEM-EDS, and by application of the NIST (National Institute of Standards and Technology) microstructure models. Leaching kinetics, evolution of the solid skeleton, and pore solution were experimentally studied and successfully modeled, using a reactive-transport approach. The discrepancies between modeling and experimental results highlight the understanding of complex degradation mechanisms. New results on the interactions on the aggressive solution and the cementitious material, through the pore solution, are presented.     

Sur une nouvelle famille de combinaisons soufrees,de type “melilite”

Two kinds of compounds belong to this family: the compounds L_10/3Ga₆S₁₄ (L = La and Ce) and the compounds MLGa₃S₇ and MLAl₃S₇ (M = Ca, Sr or Eu″; L = La and in some cases Ce, Pr, Nd). All these compounds have the same tetragonal structure of the melilite type: Al or Ga cations have a tetrahedral environment of sulphur, M and L cations occupy the same 8 coordinated crystal sites. The absence of a continuous solid solution between La_10/3Ga₆S₁₄ and CaLaGa₃S₇ could be explained by the presence of a superstructure in the last compound.     

Genetic variations in serum lipid levels of inbred mice and response to hypercholesterolemic diet

The serum lipid contents of a number of inbred and congenic strains of mice were measured. There were interstrain variations in each of the lipid fractions in mice fed a normal diet. Male and female C3H mice had the highest total cholesterol level; AKR mice showed the lowest values. Serum phospholipids were correlated well with cholesterolemia. The greatest variations between strains were in the triglyceride levels. There also was significant variation in the high density lipoprotein cholesterol serum levels (from 73–88% of the total cholesterol). The response to a hypercholesterolemic diet (1% cholesterol) was tested in seven inbred strains. All strains showed changes in serum cholesterol and in the proportions of the lipoproteins fractions. There was a large increase in the low density lipoprotein+very low density lipoprotein fractions. Feeding the diet revealed marked interstrain differences in the responses of the serum cholesterol and electrophoretic lipoprotein profiles. The C57BL/6 and B10.D2 strains were hyperresponders to the hypercholesterolemic diet with 71% and 63% of their serum cholesterol in the low density lipoprotein plus very low density lipoprotein fractions, respectively.