An asymmetrical periodic vortical structures and appearance of the self induced pressure gradient in the modified Taylor flow

An incompressible liquid flow in the gap between two coaxial cylinders, such that the inner rotating (wavy) cylinder has a periodically varying radius along the axial direction while the outer stationary cylinder has a constant radius, is studied experimentally and theoretically. Basic attention is focused on the symmetry-breaking phenomenon of the vortex flow arising from the rotation of the inner wavy cylinder. It is found that the symmetry-breaking phenomenon of the vortical flow structures in this geometry is accompanied by the occurrence of a self-induced axial pressure gradient. A theoretical formulation of the problem of periodic vortical flow prevailing in such a geometry having large axial length is presented. The comparison between the computed and the experimental results is presented and the underlying phenomena are discussed.     

Synthesis of new (pyrazol-1-yl)(7-nitro-1h-indol-2-yl)ketone derivatives

The condensation of 7-nitroindole-2-carbohydrazide derivatives with acetylacetone lead to (pyrazol-1-yl)(7-nitroindol-2-yl)ketones.     

Computational studies of 1:2 complex between retinol propionate and β cyclodextrin

[M05-2X/6-31G*:PM3MM] and [B3LYP/6-31G*:PM3] ONIOM2 methods have been used to investigate the vitamin A propionate/β cyclodextrin complex with 1:2 stoichiometry. Both methods give almost the same lowest energy minimum. The minimum energy structure of the complex is found in good agreement with experimental data. In this configuration, the major structure of propionate of vitamin A (PVA) is embedded inside the two cavities of βCD while the propionate group is kept outside. However, the three methyl groups of PVA are positioned in the free space between both βCD molecules. The driving forces for complexation are dominated by Van der Waals interactions between PVA and the βCD molecules assisted with multiple hydrogen bond interactions between the two cyclodextrin molecules. These interactions were investigated using the natural bond orbital approach.     

Distinct adsorption kinetics of Qβ and GA bacteriophages on drinking water biofilms

The data of adsorption kinetics of F-specific RNA bacteriophages Qβ and GA on drinking water biofilms under hydrostatic conditions was modeled. The rate limitation of virus adsorption was shown to be the free diffusion in water for GA where as another rate limiting step was demonstrated for Qβ. Modeling results also showed that the number of adsorbed viruses can be fitted with a limitless equation in static conditions. However sorption–desorption assays carried out in dynamic conditions showed that Qβ and GA phages have a similar affinity for the biofilm and reinforced that no significant virus desorption occurred during the first 10 h of adsorption from a bulk containing virus in static conditions. The small surface properties variations between the two phages do not induce significant differences of their adsorbed quantities in hydrodynamic conditions but they significantly affect the rate at which adsorption occurs in hydrostatic conditions.     

Non-linear viscoelasticity and temporal behavior of typical yield stress fluids: Carbopol, Xanthan and Ketchup

The viscoelastic properties of yield stress fluids are difficult to measure outside the linear viscoelastic regime, in particular above their yield stress. These properties are investigated for several common yield stress fluids using inertio-elastic oscillations. From this coupling between the instrument’s inertia and the viscoelasticity of the materials, the complete simple shear rheology can be determined, including viscoelasticity under flow. Findings show that the tested materials have an almost constant elasticity below and above the yield stress, even for applied stresses several times larger than the yield stress. Moreover, the temporal behavior of the materials is unambiguously determined. Concentrated Xanthan is shown to be thixotropic, while Ketchup mainly shows retarded viscoelasticity. Carbopol does not show long-term temporal dependance but apparently exhibits fracturation.     

Visualisation de l'écoulement de Taylor–Dean ouvert

Results of flow visualisation in a Taylor–Dean open device are given. Observations made at the inlet, the core and the outlet of the flow show that different flow patterns can develop simultaneously. The formation and the growth of the structures observed versus control parameters are described. To cite this article: A. Ait Aider et al., C. R. Mecanique 333 (2005).     

Cycloadditions [3+2] et [4+2] de l'α-nitrosostyrène sur le 2-hydroxyméthylène indanone et ses dérivés

The preferred [3+2] cycloaddition before hetero-Diels-Alder reaction of 2-hydroxymethylene indanones derivatives with α-nitrosostyrene is described. New fused spiro-pyrroles-1′-oxide and spiro-1′,2′-oxazines structures are reported. The stereospecificity and regiospecificity of the cycloadditions are discussed.