Large-eddy simulation of turbulent flow and heat transfer in plane and rib-roughened channels

Large-eddy simulation results are presented and discussed for turbulent flow and heat transfer in a plane channel with and without transverse square ribs on one of the walls. They were obtained with the finite-difference code Harwell-FLOW3D, Release 2, by using the PISOC pressure-velocity coupling algorithm, central differencing in space, and Crank-Nicolson time stepping. A simple Smagorinsky model, with van Driest damping near the walls, was implemented to model subgrid scale effects. Periodic boundary conditions were imposed in the streamwise and spanwise directions. The Reynolds number based on hydraulic diameter (twice the channel height) ranged from 10 000 to 40 000. Results are compared with experimental data, k-? predictions, and previous large-eddy simulations.     

Surface modification of ZnO using triethoxysilane-based molecules

Zinc oxide (ZnO) is an important material for hybrid inorganic-organic devices in which the characteristics of the interface can dominate both the structural and electronic properties of the system. These characteristics can be modified through chemical functionalization of the ZnO surface. One of the possible strategies involves covalent bonding of the modifier using silane chemistry. Whereas a significant body of work has been published regarding silane attachments to glass and SiO2, there is less information about the efficacy of this method for controlling the surface of metal oxides. Here we report our investigation of molecular layers attached to polycrystalline ZnO through silane bonding, controlled by an amine catalyst. The catalyst enables us to use triethoxysilane precursors and thereby avoid undesirable multilayer formation. The polycrystalline surface is a practical material, grown by sol-gel processing, that is under active exploration for device applications. Our study included terminations with alkyl and phenyl groups. We used water contact angles, infrared spectroscopy, and X-ray photoemission spectroscopy to evaluate the modified surfaces. Alkyltriethoxysilane functionalization of ZnO produced molecular layers with submonolayer coverage and evidence of disorder. Nevertheless, a very stable hydrophobic surface with contact angles approaching 106 degrees resulted. Phenyltriethoxysilane was found to deposit in a similar manner. The resulting surface, however, exhibited significantly different wetting as a result of the nature of the end group. Molecular layers of this type, with a variety of surface terminations that use the same molecular attachment scheme, should enable interface engineering that optimizes the chemical selectivity of ZnO biosensors or the charge-transfer properties of ZnO-polymer interfaces found in oxide-organic electronics.     

Mass spectrometric studies of the path of carbon in photosynthesis: positional isotopic analysis of (13)C-labelled C(4) to C(7) sugar phosphates

The (EIMS) electron ionization mass spectrometric fragmentation patterns of the methoxime- and ethoxime-trimethylsilyl (TMS) derivatives of C(4) to C(7) sugars involved as phosphates in the Calvin pathway of photosynthesis in plants were analysed by gas chromatography/EIMS using specifically labelled (13)C analogs. In general, most but not all of the major ions in the mass spectra arise from single carbon-carbon bond cleavages of the straight-chain derivatives. The results confirm that GC/MS of the alkoxime-TMS derivatives is a viable method for measuring (13)C incorporations at individual carbon atoms in each of the sugar phosphates during photosynthetic experiments with (13)CO(2).     

A model of lubricant gelling in synovial joints

A new unified theory is proposed to describe the rate of initial build-up of a lubricant mucopolysaccharide gel on the articular surfaces of the principal weight-bearing joints during normal walking. The fluid transport in the deformable porous cartilaginous matrix is computed from a simple analysis of the coupled equations of motion and incorporates the measured dependence of cartilage permeability on pressure and compressive strain. The resulting flow into the intra-articular gap space (5000 ~ 10,000 Å) provides the required boundary condition for the subsequent analysis of the transport of mucopolysaccharide (mucin) long-chain molecules which may form a lubricant gel layer at local concentrations exceeding a critical value. It is shown that the initial rate of formation of lubricant gel depends upon the cartilage permeability and bulk modulus, the loading function, the viscosity and ambient concentration of the long-chain mucin molecules in synovial fluid, and most particularly upon the magnitude of the transverse flux due to ultrafiltration of fluid through the loaded cartilage by exudation and imbibition. The model may provide a framework for much needed further careful experimentation, and serve as a basis for the preliminary design of articular prostheses to function on physiological principles.

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Résumé On propose une nouvelle théorie globale pour décrire le taux initial de formation d'un gel mucopolysaccharide lubrifiant les surfaces articulaires du genou et de la hanche pendant la marche normale. Le transport de fluide dans la matrice poreuse et déformable que constitue le cartilage se calcule à partir d'une analyse simple des équations couplées régissant les mouvements, et tenant compte des variations mesurées de la perméabilité du cartilage en fonction des pressions et des déformations. Le champs des écoulements qui en résulte au sein de l'espace intra-articulaire (5000 à 10.000 Å) fournit la condition limite requise pour passer à la seconde phase de l'analyse. Celle-ci a pour but de déterminer le transport des molécules polysaccharides à longue chaine susceptibles de former une couche de gel lubrifiant à des concentrations dépassant un seuil critique. On démontre que le taux initial de formation de gel est fonction de la perméabilité et du module de dilatation volumique du cartilage, de l'application de la charge, de la viscosité et de la concentration ambiante des molécules de mucine du liquide synovial, et plus particulièrement des flux transversaux dus à l'ultrafiltration à travers le cartilage sous charge par les mécanismes d'exsudation et imbibition. Ce modèle pourrait servir de plan directeur pour l'élaboration de futures expérimentations qui s'avèreraient nécessaires. Il servirait également comme base de départ à la conception préliminaire de prothèses articulaires fonctionnant sur les principes naturels de la physiologie.