An Explicit-Implicit Predictor-Corrector Domain Decomposition Method for Time Dependent Multi-Dimensional Convection Diffusion Equations

The numerical solution of large scale multi-dimensional convection diffusion equations often requires efficient parallel algorithms. In this work, we consider the extension of a recently proposed non-overlapping domain decomposition method for two dimensional time dependent convection diffusion equations with variable coefficients. By combining predictor-corrector technique, modified upwind differences with explicitimplicit coupling, the method under consideration provides intrinsic parallelism while maintaining good stability and accuracy. Moreover, for multi-dimensional problems, the method can be readily implemented on a multi-processor system and does not have the limitation on the choice of subdomains required by some other similar predictorcorrector or stabilized schemes. These properties of the method are demonstrated in this work through both rigorous mathematical analysis and numerical experiments.     

Density functional study of the conformations and intramolecular proton transfer in thiohydroxamic acids

The conformational preferences of thiohydroxamic acids (N-hydroxythioamides) are investigated by the density functional B3LYP/6-311++G(3df,3pd)//B3LYP/6-31G(d) method in this work. Unlike hydroxamic acids, the thione and thiol forms are found to be equally stable in the gas phase, and the reaction pathways for the interconversion between the thione and thiol forms have been deduced to involve rotation about the C[double bond, length as m-dash]N bond of the thiol tautomer in the rate-determining step. The effect of aqueous solvation on the reactions has also been investigated. It is found that inclusion of a few explicit water molecules in an implicit solvent calculation is necessary in order to accurately account for hydrogen bonding effects. Thiohydroxamic acids, like their hydroxamic acid analogues, are found to be N-acids, both in the gas phase and in aqueous solution.     

Effect of Ammonium Salts on the Volumetric and Viscometric Behavior of D(+)-Glucose,D(−)-Fructose and Sucrose in Aqueous Solutions at 25°C

Apparent molar volumes, V _φ, and viscosity, η, of D(+)-glucose, D(−)-fructose and sucrose in water and in 0.02, 0.05, 0.5, 1.0 and 2.0 mol·kg⁻¹ aqueous solutions of ammonium bromide, tetraethylammonium bromide and tetra-n-butylammonium bromide have been determined at 25 °C from density and efflux time measurements by using a vibrating-tube digital densimeter and a capillary viscometer, respectively. Partial molar volumes, , at infinite dilution that were extrapolated from the V _φ data were used to obtain the corresponding transfer volumes, , for saccharides from water to different aqueous solutions of co-solutes. The Jones-Dole equation viscosity B-coefficients were obtained from the viscosity data. Positive values of were obtained for the saccharides in the presence of ammonium bromide, whereas both positive and negative values were obtained in the presence of tetraethylammonium and tetra-n-butylammonium bromides. The negative values at very low concentrations have small magnitudes. Volumetric interaction coefficients have been calculated by using the McMillan-Mayer theory and Gibbs energies of activation of viscous flow have been calculated by using Feakin’s transition-state theory equation. The parameters obtained from the volumetric and viscometric studies were used to understand various mixing effects due to the interactions between saccharides and ammonium salts in aqueous solutions.     

Studies on complexation of rna with polycationic compounds and use of complexed rna as a substrate for ribonuclease

The effect of a wide array of positively charged compounds, comprising antibiotics, basic proteins, metal coordinates and drugs, on the activity of pancreatic ribonuclease has been studied. All the tested compounds inhibit the enzyme activity in a range of 30-70%, when used in optimal concentrations at pH 4.8. The fall in the enzyme activity in homogeneous mileu could be due to the inhibition of the enzyme by these polycations or to an altered state of the substrate on reacting with polycations. For this purpose, optimal conditions for complexation of RNA with these polycations were determined, and the rates of hydrolysis of the insolubilized RNA by RNase have been monitored in a heterogeneous system. The highest rate of hydrolysis is obtained in the case of protamine-RN A (11 %) and the lowest in the case of propamidine-RNA (3%). Rates of hydrolysis of insolubilized RNA show an exponential fall when the reaction is prolonged up to 2 h. Moreover, the level of inhibition obtained in all the cases was nearly the same, despite considerable variance in size and conformation of the compounds used. It is proposed that these compounds, on complexing with RNA, make the hydrolyzable bonds unavailable by forming a protective layer upon the RNA surface. Biological implications of these investigations are also discussed.     

Does the radical Me3O√ exist in the gas phase? A joint experimental and theoretical study

A combination of experiment and theory indicate that when Me₃O⁺ undergoes vertical Franck–Condon one-electron reduction, it does not produce a stable Me₃O√ species, but decomposes to give MeOMe and Me√. Theoretical calculations at the CCSD(T)/aug-cc-pVDZ//B3LYP/6-311G(d) level of theory indicate that the symmetrical radical Me₃O√ is not a stable species. However, there is a stable doublet neutral corresponding to a van der Waals complex MeOMeMe, a species which requires only 4.5 kJ mol⁻¹ of excess energy to cause decomposition to MeOMe and Me√.