The kinetics of hexachloroplatinate(IV) oxidation of uranium(IV) ion in aqueous perchloric acid solutions at a constant ionic strength of 1.0 mol dm
3 has been investigated using the stopped-flow and conventional spectrophotometric techniques. The oxidation reaction was found to proceed through two distinct stages. The initial stage was found to be relatively fast corresponding to the formation of [(H2O)nUIV 3 Cl6PtIV]2+ binuclear intermediate complex (with the rate constant k1 = 1.75  104 dm3 mol
1s
1, k
1 = 6.8 s
1, and the formation constant K = 2.6  103 dm3 mol
1 at [H+] = 1.0mol dm
3 and 25
C for binuclear formation). This stage was followed by a much slower stage corresponding to the transfer of two electrons from UIV to PtIV in the rate-determining step (with the rate constant k = 5.32  10
5 s
1 at [H+] = 1.0 mol dm
3 and 25
C). The reaction stoichiometry was found to depend on the molar ratio of the reactants concentration. The experimental results indicated the decrease of the observed first-order rate constants with increasing the [H+] for the decomposition of the binuclear intermediate complex through the slow-second stage, whereas no change was observed with respect to the rate of formation of the binuclear complex at the initial rapid part. A tentative reaction mechanism consistent with the kinetic results is discussed.

This work is focused on the study of the natural convection boundary-layer flow over a downward-pointing vertical cone in a porous medium saturated with a non-Newtonian nanofluid in the presence of heat generation or absorption. The transformed boundary layer governing equations are solved numerically. The influences of pertinent parameters such as the heat generation or absorption, the solid volume fraction of nanoparticles and the type of nanofluid on the flow and heat transfer rate in terms of Nusselt number are discussed. Comparisons with previously published work on special cases of the problem are performed and found to be in excellent agreement. The generalized governing equations derived in this work can be applied to different cases of non-Newtonian fluids with different values of the power-law viscosity index. The results of this parametric study are shown graphically and the physical aspects of the problem are highlighted and discussed

The free convective heat transfer to the power-law non-Newtonian flow from a vertical plate in a porous medium saturated with nanofluid under laminar conditions is investigated. It is considered that the non-Newtonian nanofluid obeys the mathematical model of power-law. The model used for the nanofluid incorporates the effects of Brownian motion and thermophoresis. The partial differential system governing the problem is transformed into an ordinary system via a usual similarity transformation. The numerical solutions of the resulting ordinary system are obtained. These solutions depend on the power-law index n, Lewis number Le, buoyancy-ratio number Nr, Brownian motion number Nb, and thermophoresis number Nt. For various values of n and Le, the effects of the influence parameters on the fluid behavior as well as the reduced Nusselt number are presented and discussed

The free convective heat transfer to the power-law non-Newtonian flow from a vertical plate in a porous medium saturated with nanofluid under laminar conditions is investigated. It is considered that the non-Newtonian nanofluid obeys the mathematical model of power-law. The model used for the nanofluid incorporates the effects of Brownian motion and thermophoresis. The partial differential system governing the problem is transformed into an ordinary system via a usual similarity transformation. The numerical solutions of the resulting ordinary system are obtained. These solutions depend on the power-law index n, Lewis number Le, buoyancy-ratio number Nr, Brownian motion number Nb, and thermophoresis number Nt. For various values of n and Le, the effects of the influence parameters on the fluid behavior as well as the reduced Nusselt number are presented and discussed

The effect of yield stress on the free convective heat transfer of dilute liquid suspensions of nanofluids flowing on a vertical plate saturated in porous medium under laminar conditions is investigated considering the nanofluid obeys the mathematical model of power-law. The model used for non-Newtonian nanofluid incorporates the effects of Brownian motion and thermophoresis. The governing boundary- layer equations are cast into dimensionless system which is solved numerically using a deferred correction technique and Newton iteration. This solution depends on yield stress parameter Ω, a power-law index n, Lewis number Le, a buoyancy-ratio number Nr, a Brownian motion number Nb, and a thermophoresis number Nt. Analyses of the results found that the reduced Nusselt and Sherwood numbers are decreasing functions of the higher yield stress parameter for each dimensionless numbers, n and Le, except the reduced Sherwood number is an increasing function of higher Nb for different values of yield stress parameter

The effect of yield stress on the free convective heat transfer of dilute liquid suspensions of nanofluids flowing on a vertical plate saturated in porous medium under laminar conditions is investigated considering the nanofluid obeys the mathematical model of power-law. The model used for non-Newtonian nanofluid incorporates the effects of Brownian motion and thermophoresis. The governing boundary- layer equations are cast into dimensionless system which is solved numerically using a deferred correction technique and Newton iteration. This solution depends on yield stress parameter Ω, a power-law index n, Lewis number Le, a buoyancy-ratio number Nr, a Brownian motion number Nb, and a thermophoresis number Nt. Analyses of the results found that the reduced Nusselt and Sherwood numbers are decreasing functions of the higher yield stress parameter for each dimensionless numbers, n and Le, except the reduced Sherwood number is an increasing function of higher Nb for different values of yield stress parameter

Electron spin resonance (ESR) spectra are investigated in order to analyze paramagnetic defects in amorphous SiOx films with 0.8≤x≤1.87 prepared by a co-sputtering of Si-wafer chips and a SiO2 disk target. Effects of the thermal annealing at 900 °C and 1100 °C on the ESR spectra are also investigated. Four types of silicon dangling bond centers with forms of •Si≡Si3−nOn (n=0, 1, 2 or 3) are assumed in order to simulate the ESR spectra. The random bonding model appears to describe the network structure of the films with x~2, that is, near the stochiometric composition of SiO2. It is suggested that the structural fluctuation around silicon dangling bonds is larger in the sputtered SiOx films used in the present work in comparison with those prepared by plasma-enhanced chemical vapor deposition.

The effects of high-temperature thermal annealing on cathodoluminescence (CL) spectra in SiOx (0:9
x
1:87) films prepared by radiofrequency sputtering are investigated. The CL intensities for the as-deposited films are weak but they increase after thermal annealing at 900 and 1100 C. One of features in the CL spectra for the films annealed at 1100 C is a peak at a photon energy of 2:7 eV with an asymmetric tail on the lower energy side. In order to analyze the spectral features, optical transition energies are calculated for Sin clusters with n ¼ 2{5, embedded in a SiOx matrix, by ab initio molecular orbital calculation. In addition, the probabilities of formation are statistically estimated for those Si clusters under the assumption of a chemically ordered random network for the SiOx network. The comparison of the experimental results with the calculated transition energies and the statistics of the Si clusters suggests that a contribution of the Si2 clusters to the CL spectra are dominant, whereas those of the Sin clusters with n > 3 are considerably small. # 2011 The Japan Society of Applied Physics