Phonon structure and dynamics of boron nitride single wall nanotube

We report a detailed study of the phonon properties of hexagonal boron nitride (BN) monolayers as well as nanotubes by using De Launay type of angular force model. The force constants used for calculation of phonon dispersion relations of the nanotube are derived from those for the monolayers of hexagonal by employing force constant method. These force constants have been modified to include the effect of curvature of the tubule. The results are then used to derive the phonon dispersion relations for (10,10) BN nanotubes using ‘zone-folding’ method. Calculated phonon modes are in good agreement with the experimental values obtained so far, for (10,10) armchair BN nanotubes.     

Generalized mean-square amplitudes of vibration in some XY4 type ions (II)

The generalized mean-square amplitudes of vibration and mean amplitudes of vibration have been computed for CrO^3-₄, Mn¹⁸O^-₄, MoSe^2-₄ and WSe^2-₄ ions at three temperatures, T = 0°K, T = 298°K, T = 500°K, employing Cyvin's method. The results have been discussed in the light of atomic weight and electronegativity of the atom in the ionic system.     

Liquid chromatographic separation of derivatives of diospyrin, a bioactive bisnaphthoquinonoid plant-product, and analogous naphthyl compounds

Isocratic reversed-phase liquid chromatography (LC) method was developed using acetonitrile and water for the determination of diospyrin, a pharmacologically important bisnaphthoquinonoid plant-product. The method was validated for precision, accuracy and reproducibility, and was found to be linear over the concentration range of 1-1000 microg/ml; the limits of detection and quantitation were 8 and 20 ng, respectively. The technique was used to determine the amount of diospyrin in plant extracts from four climatic regions in India. It was also applied for differentiation and separation of 27 naphthyl compounds. While a composition of 50:50 was preferable for dimeric compounds, the composition 40:60 was a better choice for the monomers. Also, the isomeric alpha- and beta-naphthols and their dimers could be distinguished by conversion into the respective methyl ethers.     

Heavy-metal remediation by a fungus as a means of production of lead and cadmium carbonate crystals

We show here that reaction of the fungus, Fusarium oxysporum, with the aqueous heavy-metal ions Pb2+ and Cd2+ results in the one-step formation of the corresponding metal carbonates. The metal carbonates are formed by reaction of the heavy-metal ions with CO2 produced by the fungus during metabolism and thus provide a completely biological method for production of crystals of metal carbonates. The PbCO3 and CdCO3 crystals thus produced have interesting morphologies that are shown to arise because of interaction of the growing crystals with specific proteins secreted by the fungus during reaction. An additional advantage of this approach is that the reaction leads to detoxification of the aqueous solution and could have immense potential for bioremediation of heavy metals. Under conditions of this study, the metal ions are not toxic to the fungus, which readily grows after exposure to the metal ions.     

Application of accelerated molecular dynamics schemes to the production of amorphous silicon

The evolving nature of a Stillinger-Weber modeled silicon glass is studied using two accelerated molecular dynamics scheme, specifically, hyperdynamics and self-guided algorithms due to Voter and due to Wu and Wang, respectively. We obtain an acceleration of the dynamics, a "boost," on the order of 20 without incurring any significant computational overhead. The validity of the results using accelerated methods is provided by comparison to a conventional molecular dynamics (MD) algorithm simulated under constant temperature conditions for more than 100 ns. We found that performing a sensitivity analysis of the effect of the parameters lambda and t1 before applying the self-guided MD scheme was important. Values of lambda greater than 0.1 and t1 equal to 1 ps were found to give improved structural evolution as compared to a conventional MD scheme. The hyperdynamics approximation scheme was found to be effective in obtaining boosts in the range of 4-12 for a small system without changing the dynamics of the evolution. However, for a large system size such an approach introduces significant perturbations to the pertinent equations of motion.     

Determination of micro amounts of quadrivalent vanadium with chrome azurol S

Summary The use of chrome azurol S for the colorimetric determination of quadrivalent vanadium is described. The reagent forms a violet coloured chelate ( _max = = 580 nm) with the metal at p_H 4.0±0.2. Beer's law is followed with 0.203 to 3.40 ppm of metal. The sensitivity is 0.02g/cm² (Sandell) and 0.2g/cm² (practical). Many ions interfere.

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Zusammenfassung Die kolorimetrische Bestimmung von Vanadin(IV) mit Chromazurol S wurde beschrieben. Das Reagens bildet mit Vanadin(IV) einen violetten ChelatkompleX ( _max = 580 nm) bei p_H 4,0±0,2. Zwischen 0,203 und 3,40 ppm Metall ist das Beersche Gesetz erfüllt. Die Empfindlichkeit beträgt 0,02g/cm² (Sandell) bzw. 0,2g/cm² (praktisch). Viele Fremdionen stören.

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Résumé On décrit l'emploi du chrome-azurol S pour le dosage colorimétrique du vanadium-IV. Le réactif forme un chélate coloré en violet ( _max = 580 nm) avec le métal à p_H 4,0 ± 0,2. La loi de Beer est vérifiée de 0,203 à 3,40 p. p. m. de métal. La sensibilité est de 0,02g/cm³ (Sandell) et 0,2g/cm³ (en pratique). De nombreux ions interfèrent.

     

Uranium (V) fluorides

Rhenium and uranium hexafluorides oxidise iodine in iodine pentafluoride at ambient temperature to give the I₂⁺ cation. With UF₆ additional reaction occurs to give β-uranium pentafluoride as one product (J.A. Berry, A. Prescott, D.W.A. Sharp, and J.M. Winfield, $\text{J. Fluorine Chem}$., 1977, $\text{10}$, 247). Further work on the latter reaction together with an electronic spectroscopic study of the oxidation of I₂ by phosphorus pentafluoride in IF₅, suggests that the fate of the I₂⁺ cation depends on the nature and quantity of the oxidising agent. Oxidation of I₂ by PF₅ can be conveniently followed by monitoring its visible spectrum. The reaction occurs over several hours and eventually an apparent equilibrium between I₂ and I₂⁺ results. Formation of I₂⁺UF₆^?is rapid and, with the mole ratio UF₆:I₂ > 10:1, UF₅ is precipitated rapidly from solution, I₂⁺ being oxidised further, apparently to IF₅. With a smaller UF₆:I₂ mole ratio UF₅ is contaminated by I₂, the latter is presumed to result from the disproportion-ation of an I^I or I^III fluoride.β-UF₅ is very soluble in acetonitrile and reacts with thallium(I) fluoride in this solvent to give Tl^IUF₆. It reacts with trimethyl(methoxo)silane to give (CH₃)₃SiF, U(OCH₃)₅, and an insoluble solid, believed to be a mixture of U^V methoxide, fluorides. Both reactions are conveniently followed by near i.r. spectroscopy.