Beyond the Butler-Volmer equation. Curved Tafel slopes from steady-state current-voltage curves

We report the discovery and analysis of curved Tafel slopes from the electrochemical reduction of hexamminecobalt(III) under steady-state conditions. In order to confirm the existence of the curvature, random assemblies of carbon microelectrodes (RAM? electrodes) were employed to obtain experimental data over more than three orders of magnitude, without significant double layer charging currents and without ohmic distortion. Since the rate-determining step in the reduction reaction is electron transfer, and no ligand substitution reactions occur on the timescale of experiments, the curvature of the Tafel plot is attributed to the dependence of the symmetry factor on electrode potential.     

Integrated Adsorption–Photodegradation of Organic Pollutants by Carbon Xerogel/Titania Composites

Recent studies on the removal of pollutants via adsorption include the use of carbon-based adsorbents, due to their high porosity and large surface area; however, such materials lack photoactive properties. This study evaluates the synergistic effect of integrated mesoporous carbon xerogel (derived from resorcinol formaldehyde) and titanium dioxide (TiO₂) for combined adsorption and photodegradation application. The complex formed between carbon xerogel and TiO₂ phase was investigated through FTIR, proving the presence of a Ti-O–C chemical linkage. The physicochemical properties of the synthesised adsorbent–photocatalyst were probed using FESEM, BET analysis and UV–Vis analysis. The kinetics, equilibrium adsorption, effect of pH, and effect of adsorbent dosage were investigated. The expansion of the absorbance range to the visible range was verified, and the corresponding band gap evaluated. These properties enabled a visible light response when the system was exposed to visible light post adsorption. Hence, an assistive adsorption–photodegradation phenomenon was successfully executed. The adsorption performance exhibited 85% dye degradation which improved to 99% following photodegradation. Further experiments showed the reduction of microorganisms under visible light, where no microbial colonies were observed after treatment, indicating the potential application of these composite materials.     

Zur Darstellung von Schwefelwasserstoffgas

Ohne Zusammenfassung     

Convergence acceleration of segregated algorithms using dynamic tuning additive correction multigrid strategy

A convergence acceleration method based on an additive correction multigrid–SIMPLEC (ACM‐S) algorithm with dynamic tuning of the relaxation factors is presented. In the ACM‐S method, the coarse grid velocity correction components obtained from the mass conservation (velocity potential) correction equation are included into the fine grid momentum equations before the coarse grid momentum correction equations are formed using the additive correction methodology. Therefore, the coupling between the momentum and mass conservation equations is obtained on the coarse grid, while maintaining the segregated structure of the single grid algorithm. This allows the use of the same solver (smoother) on the coarse grid. For turbulent flows with heat transfer, additional scalar equations are solved outside of the momentum–mass conservation equations loop. The convergence of the additional scalar equations is accelerated using a dynamic tuning of the relaxation factors. Both a relative error (RE) scheme and a local Reynolds/Peclet (ER/P) relaxation scheme methods are used. These methodologies are tested for laminar isothermal flows and turbulent flows with heat transfer over geometrically complex two‐ and three‐dimensional configurations. Savings up to 57% in CPU time are obtained for complex geometric domains representative of practical engineering problems. Copyright © 1999 John Wiley & Sons, Ltd.     

LIGHT SCATTERING SPECTROPHOTOMETRY FROM ISOLATED CONTROL AND TRIAZOLE-TREATED CHLOROPLASTS

Light scattering relaxation spectrophotometry has proven to be a useful technique to monitor rapid cytophysical changes in chloroplast suspensions brought about by flash illumination. This paper compares the Mg-ATP dependent light scattering behaviour of cholorplasts isolated from control and triazole-treated wheat seedlings. Our results suggest that triazole-treatment enhances Mg-ATP dependent activity. This same enhancement in control chloroplasts can be brought about by introducing potassium ion in the presence of valinomycin. Therefore, the potassium ion might account for part of the stress resistance conferred by triazole treatment.     

Cyclisation reactions of bis-protected guanidines

The cyclisation of N-allyl- and N-homoallylguanidines using DMDO or I₂/K₂CO₂ leading to novel heterocycles is reported.     

Application of the Dorodnitsyn finite element method to swirling boundary layer flow

The Dorodnitsyn finite element method for turbulent boundary layer flow with surface mass transfer is extended to include axisymmetric swirling internal boundary layer flow. Turbulence effects are represented by the two-layer eddy viscosity model of Cebeci and Smith¹ with extensions to allow for the effect of swirl. The method is applied to duct entry flow and a 10 degree included-angle conical diffuser, and produces results in close agreement with experimental measurements with only 11 grid points across the boundary layer. The introduction of swirl (w_e/u_e = 0.4) is found to have little effect on the axial skin friction in either a slightly favourable or adverse pressure gradient, but does cause an increase in the displacement area for an adverse pressure gradient. Surface mass transfer (blowing or suction) causes a substantial reduction (blowing) in axial skin friction and an increase in the displacement area. Both suction and the adverse pressure gradient have little influence on the circumferential velocity and shear stress components. Consequently in an adverse pressure gradient the flow direction adjacent to the wall is expected to approach the circumferential direction at some downstream location.