Bond length distortions associated with torsion potentials; ab-initio studies on methanedio

The 4-31G basis set is used to study the bond length variations as functions of dihedral angels in methanediol. This study is compared with O---C---O bond angle optimization studies by Gorenstein and Kar and the possible reason for bond length shorteing in the trans---trans configuration is analysed.

Length-independent voltage fluctuations in small conductors

The mean-squared voltage fluctuation of a disordered conductor of lengthL smaller than the phase coherence lengthL ϕ, is independent of the distance between the probes. We obtain this result using the voltage additivity and the known results for the conductance fluctuation. Our results complement the recent theoretical and experimental findings.

Outward spherical solidification of a superheated melt with time dependent boundary flux

Short-time analytical solutions of solid and liquid temperatures and freezing front have been obtained for the outward radially symmetric spherical solidification of a superheated melt. Although results are presented here only for time dependent boundary flux, the method of solution can be used for other kinds of boundary conditions also. Later, the analytical solution has been compared with the numerical solution obtained with the help of a finite difference numerical scheme in which the grid points change with the freezing front position. An efficient method of execution of the numerical scheme has been discussed in details. Graphs have been drawn for the total solidification times and temperature distributions in the solid.

Spatially dependent correlation functions in the Anderson model

We report results from a first principles calculation of spatially dependent correlation functions around a magnetic impurity in metals described by the nondegenerate Anderson model. Our computations are based on a combination of perturbative scaling theory and numerical renormalization group methods. Results for the conduction election charge density around the impurity and correlation functions involving the conduction electron and impurity charge and spin densities will be presented. The behavior in various regimes including the mixed valent regime will be explored.

A Comparative Study of Liapunov Stability Analyses of Flexible Damped Satellites

A literal Liapunov stability analysis of a spacecraft with flexible appendages often requires a division of the associated dynamic potential into as many dependent parts as the number of appendages. First part of this paper exposes the stringency in the stability criteria introduced by such a division and shows it to be removable by a “reunion policy.” The policy enjoins the analyst to piece together the sets of criteria for each part. Employing reunion the paper then compares four methods of the Liapunov stability analysis of hybrid dynamical systems illustrated by an inertially coupled, damped, gravity stabilized, elastic spacecraft with four gravity booms having tip masses and a damper rod, all skewed to the orbital plane. The four methods are the method of test density function, assumed modes, and two and one-integral coordinates. Superiority of one-integral coordinate approach is established here. The design plots demonstrate how elastic effects delimit the satellite boom length.

Time Dependent Operator-split and Unsplit Schemes for One Dimensional Premixed Flames

This paper is concerned with a study of an operator split scheme and unsplit scheme for the computation of adiabatic freely propagating one-dimensional premixed flames. The study uses unsteady method for both split and unsplit schemes employing implicit chemistry and explicit diffusion, a combination which is stable and convergent. Solution scheme is not sensitive to the initial starting estimate and provides steady state even with straight line profiles (far from steady state) in small number of time steps. Two systems H2-Air and H2-NO (involving complex nitrogen chemistry) are considered in presentinvestigation. Careful comparison shows that the operator split approach is slightly superior than the unsplit when chemistry becomes complex. Comparison of computational times with those of existing steady and unsteady methods seems to suggest that the method employing implicit-explicit algorithm is very efficient and robust.

Two-dimensional NMR spectroscopy of connected transitions by linear combination of flip angle dependent cosy: An alternative scheme for E.COSY

An alternative pulse scheme which simplifies and improves the recently proposed P.E.COSY experiment is suggested for the retention of connected or unconnected transitions in a coupled spin system. An important feature of the proposed pulse scheme is the improved phase characteristics of the diagonal peaks. A comparison of various experiments designed for this purpose, namely COSY-45, E.COSY, P.E.COSY and the present scheme (A.E.COSY), is also presented. The suppression of unconnected transitions and the measurement of scalar coupling constants and their relative signs are illustrated from A.E.COSY spectra of 2,3-dibromopropionic acid and 2-(2-thienyl)pyridine.

Microscopic expression for frequency and wave vector dependent dielectric constant of a dipolar liquid

A microscopic expression for the frequency and wave vector dependent dielectric constant of a dense dipolar liquid is derived starting from the linear response theory. The new expression properly takes into account the effects of the translational modes in the polarization relaxation. The longitudinal and the transverse components of the dielectric constant show vastly different behavior at the intermediate values of the wave vector k. We find that the microscopic structure of the dense liquid plays an important role at intermediate wave vectors. The continuum model description of the dielectric constant, although appropriate at very small values of wave vector, breaks down completely at the intermediate values of k. Numerical results for the longitudinal and the transverse dielectric constants are obtained by using the direct correlation function from the mean‐spherical approximation for dipolar hard spheres. We show that our results are consistent with all the limiting expressions known for the dielectric function of matter.

Support-Dependent Activity of Noble Metal Substituted Oxide Catalysts for the Water Gas Shift Reaction

The water gas shift reaction was carried out over noble metal ion substituted nanocrystalline oxide catalysts with different supports. Spectroscopic studies of the catalysts before and after the reaction showed different surface phenomena occurring over the catalysts. Reaction mechanisms were proposed based upon the surface processes and intermediates formed. The dual site mechanism utilizing the oxide ion vacancies for water dissociation and metal ions for CO adsorption was proposed to describe the kinetics of the reaction over the reducible oxides like CeO2. A mechanism based on the interaction of adsorbed CO and the hydroxyl group was proposed for the reaction over ZrO2. A hybrid mechanism based on oxide ion vacancies and surface hydroxyl groups was proposed for the reaction over TiO2. The deactivation of the catalysts was also found to be support dependent. Kinetic models for both activation and deactivation were proposed. (C) 2010 American Institute of Chemical Engineers AIChE J, 56: 2662-2676, 2010

A XANES study of the K-absorption edge of copper in some of its compounds and use of the same in the determination of bond length

XANES in the K-edge of copper in the systems CuO, Cu(OH)2, La2CuO4, Cu3AsO4 and CuOHF have been investigated and transitions have been assigned to the observed structures. The measurements have been used for calculating the first coordination bond distance in the above systems. It is observed that the values so determined agree fairly well with crystallographic values.

Chloroquine Inhibits Heme-Dependent Protein Synthesis in Plasmodium falciparum

A cell-free protein-synthesizing system has been reconstituted using the S-30 fraction or ribosomes and the S-100 fraction from Plasmodium falciparum. Addition of heme in vitro stimulates cell-free protein synthesis strikingly. Chloroquine inhibits the heme-dependent protein synthesis in the parasite lysate. The drug has also been found to inhibit parasite protein synthesis in situ at therapeutic concentrations soon after addition to parasite cultures. Ribosomes as well as the S-100 fraction isolated from such chloroquine-treated cultures are defective in protein synthesis. Addition of hemin plus glucose 6-phosphate or high concentrations of GTP, cAMP, and an active preparation of eIF-2 to the parasite cell-free system restores protein synthesis to a significant extent in chloroquine-treated cultures. Under conditions of inhibition of protein synthesis in situ by chloroquine in the culture, the parasite eukaryotic initiation factor 2-alpha- (eIF-2-alpha) is phosphorylated in the parasite lysate to a greater extent than that observed in the control culture. Addition of hemin in vitro suppresses this phosphorylation. eIF-2-alpha kinase activity is present in the parasite lysate and is not a contaminant derived from the human erythrocytes used to culture the parasite. The heme-chloroquine interactive effects can also be demonstrated with purified eIF-2-alpha kinase from rabbit reticulocyte lysate. It is proposed that chloroquine inhibits heme-dependent protein synthesis in the parasite and this is an early event mediating the growth-inhibitory effects of the drug.

Early pregnancy termination in rats immunized with denatured chicken riboflavin carrier protein

Immunoneutralization of the maternal riboflavin carrier protein in the pregnant rat with antibodies to chicken egg vitamin carrier has earlier been shown to terminate their pregnancies. In order to understand the nature of the epitopic conformations capable of eliciting antibodies bioneutralizing the endogenous riboflavin carrier protein in the pregnant rat, we compared pregnancy progression in the fertile rodents following active immunization with either the native, SDS-denatured, reduced-carboxymethylated or SDS-treated reduced carboxymethylated avian egg white riboflavin carrier protein. The data revealed that despite the total antibody titers being higher in the animals immunized with the native protein, the antibodies elicited against the denatured avian vitamin carrier exhibited relatively better potencies to bioneutralize the endogenous maternal protein as evidenced by higher rates of early fetal resorption.

Temperature dependent optical constants of amorphous Ge2Sb2Te5 thin films

This study focuses on the temperature dependent optical band gap changes in the amorphous Ge2Sb2Te5 (GST) films. The behavior of the amorphous GST thin films at low temperatures has been studied. The band gap increment of around 0.2 eV is observed at low temperature (4.2 K) compared to room temperature (300 K). The band gap changes associated with the temperature are completely reversible. The other optical parameters like Urbach energy and Tauc parameter (B-1/2) are studied for different temperatures and discussed. The observed changes in optical band gap (E-g) are fitting to Fan's one phonon approximation. Phonon energy ((h) over bar omega) corresponding to a frequency of 3.59 THz is derived from Fan's approximation, which is close to the reported value of 3.66 THz. (C) 2010 Elsevier B.V. All rights reserved.