Newton linearization of the incompressible Navier–Stokes equations

The present study aims to accelerate the convergence to incompressible Navier–Stokes solution. For the sake of computational efficiency, Newton linearization of equations is invoked on non‐staggered grids to shorten the sequence to the final solution of the non‐linear differential system of equations. For the sake of accuracy, the resulting convection–diffusion–reaction finite‐difference equation is solved line‐by‐line using the proposed nodally exact one‐dimensional scheme. The matrix size is reduced and, at the same time, the CPU time is considerably saved due to the decrease of stencil points. The effectiveness of the implemented Newton linearization is demonstrated through computational exercises. Copyright © 2004 John Wiley & Sons, Ltd.     

Transport of carbon dioxide and methane in glassy aromatic polyesters

Solubilities and diffusivities of CO₂ and CH₄ in two aromatic polyesters [Ardel® poly(bisphenol A phthalate) (PAr) and poly(phenolphthalein phthalate) (PPha)] and one polycarbonate [Lexan® (PC)], generated from independent sorption and permeation measurements at 35°C and up to 25 atm, are compared. The permeability ratio for CO₂ over CH₄, at 20 atm and 35°C, ranges from 24 for PC, to 21 for PAr, and 27 for PPha. However, the permeability of PPha and PAr are 40 and 120% higher, respectively, than that of PC. Less than 21% change in the gas diffusivity was observed; therefore, a major portion of the observed higher permeability of PPha and PAr is attributed to an increase in the gas solubility. These data are interpreted qualitatively in terms of changes in the calculated packing density, chain torsional mobility of the polymer, and gas-polymer attraction.     

Insights into the interior-point methods

In this paper, we study the search directions of three important interior-point algorithms, namely, the primal-affine scaling method (with logarithmic barrier function), the dual-affine scaling method (with logarithmic barrier function), and the primal-dual interior point method. From an algebraic point of view, we show that the search directions of these three algorithms are merely Newton directions along three different paths that lead to a solution of the Karush-Kuhn-Tucker conditions of a given linear programming problem. From a geometric point of view, we show that these directions can be obtained by solving certain well-defined subproblems. Both views provide a general platform for studying the existing interior-point methods and deriving new interior-point algorithms. We illustrate the derivation of new interior-point algorithms by replacing the logarithmic barrier function with an entropic barrier function. The results have been generalized and discussed.This work is partially supported by the North Carolina Supercomputing Center 1990 Cray Grant Program sponsored by Cray Research.     

Control of Luminescence by Tuning of Crystal Symmetry and Local Structure in Mn4+‐Activated Narrow Band Fluoride Phosphors

Mn⁴⁺‐doped fluoride phosphors have been widely used in wide‐gamut backlighting devices because of their extremely narrow emission band. Solid solutions of Na₂(Si_xGe_1?x)F₆:Mn⁴⁺ and Na₂(Ge_yTi_1?y)F₆:Mn⁴⁺ were successfully synthesized to elucidate the behavior of the zero‐phonon line (ZPL) in different structures. The ratio between ZPL and the highest emission intensity υ₆ phonon sideband exhibits a strong relationship with luminescent decay rate. First‐principles calculations are conducted to model the variation in the structural and electronic properties of the prepared solid solutions as a function of the composition. To compensate for the limitations of the Rietveld refinement, electron paramagnetic resonance and high‐resolution steady‐state emission spectra are used to confirm the diverse local environment for Mn⁴⁺ in the structure. Finally, the spectral luminous efficacy of radiation (LER) is used to reveal the important role of ZPL in practical applications.     

Five novel norcembranoids from Sinularia leptoclados and S. parva

Three new norcembrane-based diterpenoids, leptocladolides A (1), B (4) and C (5), along with five known metabolites 6-10, have been isolated from the dichloromethane extract of a Taiwanese soft coral Sinularia leptoclados. Furthermore, a chemical investigation on the dichloromethane extract of S. parva has resulted in the isolation of two new related isomers, 1-epi-leptocladolide A (2) and 7E-leptocladolide A (3), in addition to 1 and 7. The structures of new metabolites 1-5 were elucidated on the basis of extensive spectroscopic analyses and their relative stereochemistries were determined by NOESY experiments. The new metabolites 1 and 3 have been shown to exhibit significant cytotoxic activity against KB and Hepa59T/VGH cancer cell lines.     

Electrodeposition of Platinum Nanoparticles on Multi-Walled Carbon Nanotubes for Electrocatalytic Oxidation of Methanol

Platinum (Pt) nanoparticles were deposited at the surface of well-aligned multi-walled carbon nanotubes (MWNTs) by potential cycling between +0.50 and −0.70 V at a scanning rate of 50 mV · s⁻¹ in 5 mM Na₂PtCl₆ solution containing 0.1 M NaCl. The electrocatalytic oxidation of methanol at the nanocomposites of Pt nanoparticles/nanotubes (Pt_nano/MWNTs) has been investigated using 0.2 M H₂SO₄ as supporting electrolyte. The effects of various parameters, such as Pt loading, concentration of methanol, medium temperature as well as the stability of Pt_nano/MWNTs electrode, have been studied. Compared to glassy carbon electrode, carbon nanotube electrode significantly enhances the catalytic efficiency of Pt nanoparticles for methanol oxidation. This improvement in performance is due not only to the high surface area and the fast electron transfer rate of nanotubes but also to the highly dispersed Pt nanoparticles as electrocatalysts at the tips and the sidewalls of nanotubes.     

Metabolites with Cytotoxic Activity from the Formosan Soft Coral Cladiella Australis

The metabolites, (24S)‐3β‐acetoxyergost‐5‐en‐21‐oic acid ( 2 ), 5′‐O‐acetylthymidine ( 3 ), 3′‐O‐acetylthymidine ( 4 ), and p‐vinylbenzyl alcohol ( 5 ), along with a known steroid ( 1 ) were isolated from the EtOAc extract of the Formosan soft coral Caldiella australis. The structures of new metabolites were determined on the basis of spectroscopic (including 1D and 2D NMR) analyses and by comparison of their NMR spectral data with those of related compounds. Except for 3 , all compounds exhibited cytotoxic activity of various degrees of potency against a limited panel of human liver and breast cancer cell lines.     

Interfacial Electrochemical Behavior of RuS2 Single Crystal Electrodes in Sulfuric Acid Medium

The electrochemical behavior of RuS₂ has been studied using cyclic voltammetry and Energy Dispersive X-ray Spectroscopy (EDX) techniques. Cyclic voltammograms reveal one major anodic peak and two major cathodic peaks on the reverse sweep; these peaks are attributed to the electroadsorption/desorption of OH^? groups on the electrode surface. It is proposed that the electroadsorption of the OH^? group on RuS₂ is due to the presence of Ru 4d electrons in the uppermost part of the valence band. Thus, OH^? is oxidized by holes on Ru 4d states in the first step. These groups are transferred to S₂^2?sites in the second step. EDX surface analysis reveals preferential release of S₂^2? from the pyrite lattice. A mechanism for the anodic dissolution of RuS₂ is proposed, according to which elemental sulfur is not a direct product, but rather the end product which forms from thiosulfate.