Contrôle par rotation ou par aspiration de l'écoulement autour d'un cylindre calculé par Simulation des Grandes Échelles

Control of the flow around a circular cylinder is studied using Large Eddy Simulation. The influence of control by rotation and suction on the flow characteristics is considered for several Reynolds numbers. Comparisons with experiments were conducted at $\mathit{Re}={10}^5$ for the flow with and without control. A drag reduction up to 30% is obtained for an usual suction intensity. To cite this article: G. Fournier et al., C. R. Mecanique 333 (2005).     

A crack perpendicular to and terminating at a bimaterial interface

Using dislocation simulation approach, the basic equation for a finite crack perpendicular to and terminating at a bimaterial interface is formulated. A novel expansion method is proposed for solving the problem. The complete solution to the problem, including the explicit formulae for theT stresses ahead of the crack tip and the stress intensity factors are presented. The stress field characteristics are analysed in detail. It is found that normal stresses {ie27-1} and {ie27-2} ahead of the crack tip, are characterised byQ fields if the crack is within a stiff material and the parameters |p _T | and |q _T | are very small, whereQ is a generalised stress intensity factor for a crack normal to and terminating at the interface. If the crack is within a weak material, the normal stresses {ie27-3} and {ie27-4} are dominated by theQ field plusT stress. This work was supported by the Swedish Research Council for Engineering Sciences.     

Motion of a viscoplastic liquid in a porous inhomogeneous medium

Equations of motion are derived for a viscoplastic liquid in a nonuniform medium of type 2 (piecewise uniform) or type 3 (with a variable filtration coefficient) [1] on the assumption that the motion is of steady-state type. Solutions are presented for a parallel flow and a flow with axial symmetry.     

Use of a sliding plate rheometer to measure the first normal stress difference at high shear rates

The use of a sliding plate rheometer (SPR) to determine the first normal stress difference of molten polymers and elastomers at high shear rates is demonstrated. The simple shear flow in this instrument is not subject to the flow instabilities that limit the use of rotational rheometers to shear rates often below 1 s⁻¹. However, issues of secondary flow and wall slip must be addressed to obtain reliable data using an SPR. A highly entangled, monodisperse polybutadiene and a commercial polystyrene were the polymers studied. The inclusion of the polystyrene made it possible to compare data with those obtained by Lodge using a stressmeter, which is an instrument based on the measurement of the hole pressure. The data from the two instruments are in good agreement and are also close to the predictions of an empirical equation of Laun based on the storage and loss moduli.     

Polymer Composites with Plasma-Treated Fillers

A Large-volume Microwave Plasma (LMP) generator has been used to irradiate mica and ground-wood fibers in inert and active gas environments. Irradiated fillers were subsequently incorporated in a polypropylene matrix at solids levels of 10 and 20%. Calorimetrically measured heats of immersion showed that substantial changes in surface properties of fillers were effected by irradiation in ethylene, ammonia, and similar active gases. These surface changes are reflected In ultimate tensile and elongation properties of composites which show marked improvement over controls based on unirradiated fillers. Although no appreciable response in melt viscosity has been observed, surface treatment of fillers does seem to increase significantly melt elasticity of filled composites. The implications of improved performance motivate a more detailed study of the use potential of LMP in the fomulation of polymer composites.     

Addition Polymerization of Aliphatic Dlthlols with Diene Monomers

The photoinitiated free radical polymerization of triethylene-glycoldithiol and hydrochinonebisallylether or ethyleneglycoldivi-nylether leads to poly (the ethers) having anti-Markovnikov structure M _n: 14,000, 12,000 (VPO), respectively. The chain propagation is limited by a cyclic product (nearly 4%). Telechelics may be obtained by the use of nonequivalent molar ratio of the thioVenemonomers. They are useful in preparation of block copol-ymers and networks, respectively. By means of ESR-spectroscopic investigations, it is shown that in dithiole/diene mixtures, which are free of daylight and oxygen, radicals are formed spontaneously. Using the spin-trapping technique, the existence of sulfur and carbon radicals could be proved unambiguously.     

Nanoalloy Based on Clays: Intercalated‐Exfoliated Layered Silicate in High Performance Elastomer

A novel method is described for the preparation of nanocomposites comprising a high performance rubber for tire application and layered silicates clay. In this work nanocomposites of solution‐styrene butadiene rubber (S‐SBR) with montmorillonite layered silicate were prepared with carboxylated nitrile rubber (XNBR), a polar rubber, as a compatibilizer. A sufficient amount of organomodified layered silicate was loaded in carboxylated nitrile rubber (XNBR) and this compound was blended as a master batch in the S‐SBR. Mixed intercalated/exfoliated morphologies in the nanocomposite are evinced by X‐ray diffraction measurements and transmission electron microscopy. Dynamic mechanical analysis also supports the compatibility of the composites. A good dispersion of the layered silicate in the S‐SBR matrix was reflected from the physical properties of the nanocomposites, especially in terms of tensile strength and high elongation properties.     

Synthesis,Photophysics and Nonlinear Optical Properties of Stilbenoid Pyrimidine‐Based Dyes Bearing Methylenepyran Donor Groups

The nonlinear properties and the photophysical behavior of two π‐conjugated chromophores that incorporate an electron‐deficient pyrimidine core (A) and γ‐methylenepyrans as terminal donor (D) groups have been thoroughly investigated. Both dipolar and quadrupolar branching strategies are explored and rationalized on the basis of the Frenkel exciton model. Even though a cooperative effect is clearly observed if the dimensionality is increased, the nonlinear optical (NLO) response of this series is moderate if one considers the nature of the D/A couple and the size of the chromophores (as measured by the number of π electrons). This effect was attributed to a disruption in the electronic conjugation within the dyes’ scaffold for which the geometry deviates from planarity owing to a noticeable twisting of the pyranylidene end‐groups. This latter structural parameter also has a strong influence on the excited‐state dynamics, which leads to a very efficient fluorescence quenching.     

Killing Bacterial Spores with Blue Light: When Innate Resistance Meets the Power of Light

This article is a highlight of the study by Maclean et al. in this issue of Photochemistry and Photobiology describing the sporicidal effects 405 nm visible light alone on endospores of the Clostridium and Bacillus genera. 1.73 kJ cm^?2 was capable of reducing endospore colony‐forming units by up to 4‐log₁₀. These findings have never been previously demonstrated and may be incorporated into decontamination methods that span medical, military and food preparatory applications.