A study on preconditioning iterative methods and relativity of pressure in the numerical calculation of fluid flow

This article presents the effect of preconditioning iterative methods on boundary conditions of the pressure‐correction in the numerical computation of fluid flow with known velocity components on all boundaries using the SIMPLE algorithm. In such computation, a set of solutions of the pressure‐correction is indefinite, because only the Neumann condition is imposed on all boundaries. However, solutions become unique if the value of pressure‐correction is fixed at least on one boundary point, and the Dirichlet condition is additionally imposed. Though both conditions must give exactly the same velocity and temperature fields, this problem arises from the relativity of the pressure. The mathematical illustration for this problem is provided using the numerical computation of the natural convection in an enclosure. It is concluded that the preconditioner adopted and the condition that only the Neumann condition on all boundaries is given are effective to reduce the number of iterations in solving the linear system of equations of the pressure‐correction at the computation of the natural convection. © 2004 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2004     

Properties of a-Si : H : F deposited in SiF4/SiH4/Ar Gas mixtures by a glow-discharge technique

Films of silicon-hydrogen-fluorine alloys (a-Si : H : F) were prepared by capacitive coupling rf glow discharge in an SiF₄/SiH₄/Ar gas mixture. Up to 4% fluorine can be incorporated in films prepared with a gas mixture of SiF₄/(SiF₄ + SiH₄) = 0.72. The hydrogen concentration decreases as fluorine concentration increases but there is still more hydrogen than fluorine in films with the highest density of fluorine, which is in sharp contrast to the best films produced by the Madan and co-workers. Both dark conductivity and photoconductivity decrease as fluorine increases, though improvement of doping efficiency was observed in films with moderate concentrations of fluorine. The influence of hydrogen is more important than the influence of fluorine in the present silicon-hydrogen-fluorine alloys.     

Theory of space-charge polarization for determining ionic constants of electrolytic solutions

A theoretical expression of the complex dielectric constant attributed to space-charge polarization has been derived under an electric field calculated using Poisson's equation considering the effects of bound charges on ions. The frequency dependence of the complex dielectric constant of chlorobenzene solutions doped with tetrabutylammonium tetraphenylborate (TBATPB) has been analyzed using the theoretical expression, and the impact of the bound charges on the complex dielectric constant has been clarified quantitatively in comparison with a theory that does not consider the effect of the bound charges. The Stokes radius of TBA+(=TPB-) determined by the present theory shows a good agreement with that determined by conductometry in the past; hence, the present theory should be applicable to the direct determination of the mobility of ion species in an electrolytic solution without the need to measure ionic limiting equivalent conductance and transport number.     

Crystalline alignment of metal ions templated by β-chitin ester

The highly crystalline β-chitin from diatom Thalassiosira weissflogii was esterified via intercalation with succinic anhydride followed by simple heating, maintaining the original crystalline order. Due to the introduced free carboxyl groups, the chitin ester crystal showed ion exchange ability for metal cations in aq. solution. Heavy metal cations such as Pb²⁺ bound to the β-chitin succinate gave characteristic X-ray diffraction patterns, indicating regular alignment of metal ions. Such materials represent a new type of organometallic architecture, possibly leading to novel functionalities.     

4-Carbomethoxybenzaldehyde as a highly sensitive pre-column fluorescence derivatization reagent for 9,10-phenanthrenequinone

9,10-Phenanthrenequinone (PQ) is harmful environmental pollutant that is detected in airborne particulates. The measurement of PQ in the air should be necessary to evaluate the potential adverse effects of PQ on human health. We have recently developed a determination method for PQ based on the fluorescence derivatization of PQ using benzaldehyde and ammonium acetate as a reagent. In this study, in order to obtain more sensitive and selective fluorescence derivatization reaction, we measured the fluorescence of the reaction mixture of PQ with 21 kinds of aromatic aldehydes in the presence of ammonium acetate. Among the tested aldehydes, 4-carbomethoxybenzaldehyde was found to be the best reagent in regard to fluorescence intensity and emission wavelength maximum. Based on the fluorescence derivatization with 4-carbomethoxybenzaldehyde, a highly sensitive chromatographic method was developed for the determination of PQ with the detection limit (S/N=3) of 1.2 fmol/injection.     

Critical concentration for colloidal crystallization determined with microliter centrifuged suspensions

We report an elegant method using centrifugal sedimentation for determining the critical particle concentration for colloidal crystallization. A small amount of a dilute suspension of monodispersed particles stored in a flat capillary cell was centrifuged to temporarily generate a nonequilibrium gradient of the particle concentration including a crystalline-noncrystalline phase boundary in the cell. In the recovering process after the centrifugation, the particle concentration of the crystalline phase at the boundary was found to always have the equilibrium value, although the global concentration distribution evolved with time. The critical concentration was determined based on spatially resolved spectrometry. The present method requires only one batch of a suspension of the order of microliters and is applicable up to high concentration regions near the closest packing without the effect of the particle aggregation.     

Layered [3.3]Orthocyclophane Tricarbonylchromium Complexes

The preparation of the layered [3.3]orthocyclophane tricarbonylchromium mono- and bis complexes, 4 and 5 , are described. X-ray crystallographic analysis reveals the fact that the distances and the dihedral angle between the planes of the two benzo rings in mono complex 4 decrease as compared to those in 1 . This is due to the decrease in π electron density in one benzo unit.     

Preparation and applications of novel amphiphilic fluoroalkyl end‐capped oligomers‐clay nanocomposites

Nonionic‐type amphiphilic fluoroalkyl end‐capped acryloylmorpholine and N,N‐dimethylacrylamide homooligomers were found to be new convenient intercalating agents for the achievement of an enlarged basal spacing of the clay layers to afford fluorinated oligomers‐clay nanocomposites. These novel fluoroalkyl end‐capped oligomers‐clay nanocomposites were found to exhibit good dispersibility and stability in aqueous and organic media, and were applied to the surface modification of traditional organic polymeric materials such as poly(methyl methacrylate). Copyright © 2006 John Wiley & Sons, Ltd.