NUMERICAL ANALYSIS OF THE EFFECTS OF LOCAL HYDRODYNAMICS ON MASS TRANSFER IN HETEROGENEOUS POROUS MEDIA

Many engineering problems require the estimation of mass transfer coefficients in porous materials. In heterogeneous materials or in cases where mass transfer sites are not spatially uniform, empirical equations for mass transfer coefficients vary widely, and the origin of these differences is not well understood. In this article, we use a stochastic algorithm to model mass transfer from single particles in a two-dimensional heterogeneous packed bed. The computed mass transfer coefficients are used to generate a distribution of local Peclet numbers in the bed. Detailed hydrodynamics are then used to interpret variations in the local Peclet number. The results show clear relationships between pore structure, streamline patterns, and mass transfer rates.     

A hybrid finite element method for near bodies of revolution (EM scattering)

A genetic formulation for a hybrid finite element solution for three-dimensional electromagnetic scattering is given using the equivalent current approach. The major computational tasks involved in monostatic scattering calculations are analyzed and compared as a function of the method of implementing the near-field radiation condition, i.e. method of moments, model expansion, and body of revolution (BOR). A method utilizing a BOR formulation that addresses these computational issues is given. This BOR implementation utilizes Hermite cubic basis functions and a variable number of modes per basis function in order to achieve the greatest efficiency. The combined field integral equation formulation is used to eliminate nonphysical resonance of the mesh boundary. Examples are given showing the efficiency and accuracy of this BOR code by itself, and as part of this hybrid finite-element method.<>     

Properties of WN x /GaAs Schottky contacts prepared by ion implantation of nitrogen

The formation of WN _x /GaAs Schottky contacts using selective ion implantation of nitrogen into the sputtered tungsten film has been demonstrated. The contacts were characterized by Auger electron spectroscopy and current-voltage measurements. The composition of WN _x films and the thermal stability of WN _x /GaAs contacts were investigated. Good thermal stability of WN _x /GaAs contacts compared with a W/GaAs contact was observed after capless rapid thermal annealing at 450, 800 and 950°C for 10 s.     

Chemical inhibitors when timing is critical: a pharmacological concept for the maturation of T cell contacts

Cellular signal transduction proceeds through a complex network of molecular interactions and enzymatic activities. The timing of these molecular events is critical for the propagation of a signal and the generation of a specific cellular response. To define the timing of signalling events, we introduce the combination of high-resolution confocal microscopy with the application of small-molecule inhibitors at various stages of signal transduction in T cells. Inhibitors of Src-family tyrosine kinases and actin dynamics were employed to dissect the role of the lymphocyte-specific tyrosine kinase Lck in the formation and maintenance of T cell receptor/CD3-dependent contacts. Anti-CD3epsilon-coated coverslips served as a highly defined stimulus. The kinetics of the recruitment of the yellow fluorescent protein-tagged signalling protein ZAP-70 were detected by high-resolution confocal microscopy. The analysis revealed that at 5 min after receptor engagement, Lck activity was required for maintenance of contacts. In contrast, after 20 min of receptor engagement, the contacts were Lck-independent. The relevance of the timing of inhibitor application provides a pharmacological concept for the maturation of T cell-substrate contacts.     

Investigations on the adhesion and interfacial properties of polyurethane foam/thermoplastic materials

The adhesion and interfacial properties of polyurethane (PU) foams with thermoplastic (TP) materials were investigated using different techniques. The adhesion performance of PU foam with TP materials was evaluated using the peel test method, and the adhesion durability was checked after different climate treatments. X‐ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and contact angle measurements were used to study the surface and interface morphology of PU foam and TP material system. Three types of PU foam samples which differ in their composition and also five commercially available TP blends systems, based on poly(carbonate), poly(styrene‐co‐maleic anhydride), poly(acrylonitrile‐butadiene‐styrene), and silicone acrylate rubber have been used. The slow reacting foam shows the best adhesion properties with all the TP materials. The climate treatments strongly effected the PU foam adhesion durability with poly(carbonate) containing TP materials (70–80% loss in adhesion), but nearly no effect with poly(styrene‐co‐maleic anhydride). The samples with lowered adhesion could be separated by peeling without visible foam residues on the TP surface. AFM, XPS, and surface tension studies have shown that the surface properties of the TP material are still governed by the PU foam. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 479–488, 2007     

Untersuchung des Passivierungsmechanismus von Eisen in Phosphatelektrolyten an erosiv beanspruchten Oberflächen

Investigation into the passivation mechanism of iron in phosphate electrolytes on surfaces exposed to erosive attack On iron electrodes in neutral phosphate electrolytes by continuous solid particle impingement a reaction layer is formed within the transition potential region under anodic polarization. XPS and AES investigations show that the reaction layer formed under impingement will be replaced by an oxide layer during the transition into the passive state under simultaneous decrease of the layer thickness. The active/passive transition in phosphate electrolytes may be attached to the equilibrium potential of the reaction . According to this thermodynamic interpretation of both the active/passive transition and the passive/active transition, respectively on iron in presence of phosphate ions may be described as the Fe(II)/Fe(III)-redox reaction with two solid phases, the iron(II)-phosphate phase and the iron(III)-oxide phase. The increase of the interfacial dynamic processes at the solid/liquid interface causes in consequence of the solid particle impingement that thermodynamic laws govern the course of reactions.     

Combining the triangle method with thermal inertia to estimate regional evapotranspiration — Applied to MSG-SEVIRI data in the Senegal River basin

Spatially distributed estimates of evaporative fraction and actual evapotranspiration are pursued using a simple remote sensing technique based on a remotely sensed vegetation index (NDVI) and diurnal changes in land surface temperature. The technique, known as the triangle method, is improved by utilizing the high temporal resolution of the geostationary MSG-SEVIRI sensor. With 15 min acquisition intervals, the MSG-SEVIRI data allow for a precise estimation of the morning rise in land surface temperature which is a strong proxy for total daytime sensible heat fluxes. Combining the diurnal change in surface temperature, dT_s with an interpretation of the triangular shaped dT_s − NDVI space allows for a direct estimation of evaporative fraction. The mean daytime energy available for evapotranspiration (R_n − G) is estimated using several remote sensors and limited ancillary data. Finally regional estimates of actual evapotranspiration are made by combining evaporative fraction and available energy estimates. The estimated evaporative fraction (EF) and actual evapotranspiration (ET) for the Senegal River basin have been validated against field observations for the rainy season 2005. The validation results showed low biases and RMSE and R² of 0.13 [−] and 0.63 for EF and RMSE of 41.45 W m^− 2 and R² of 0.66 for ET.