The effect of a magnetic field on the onset of Bénard convection in variable viscosity couple-stress fluids using classical Lorenz model

Applications of Mathematics - The Rayleigh-Bénard convection for a couple-stress fluid with a thermorheological effect in the presence of an applied magnetic field is studied using both linear...     

Creation of a broad-range and highly stereoselective D-amino acid dehydrogenase for the one-step synthesis of D-amino acids

Using both rational and random mutagenesis, we have created the first known broad substrate range, nicotinamide cofactor dependent, and highly stereoselective d-amino acid dehydrogenase. This new enzyme is capable of producing d-amino acids via the reductive amination of the corresponding 2-keto acid with ammonia. This biocatalyst was the result of three rounds of mutagenesis and screening performed on the enzyme meso-diaminopimelate d-dehydrogenase. The first round targeted the active site of the wild-type enzyme and produced mutants that were no longer strictly dependent on the native substrate. The second and third rounds produced mutants that had an increased substrate range including straight- and branched-aliphatic amino acids and aromatic amino acids. The very high selectivity toward the d-enantiomer (95 to >99% ee) was shown to be preserved even after the addition of the five mutations found in the three rounds of mutagenesis and screening. This new enzyme could complement and improve upon current methods for d-amino acid synthesis.     

Raman scattering studies on n-heptane under high pressure

High-pressure Raman scattering studies at ambient temperature are performed on n-heptane. We observe a liquid-solid transition around 1.5 GPa from the changes in the Raman spectra. This has been reported in earlier works. With increasing pressure, we observe large changes in the Raman modes and the spectra show a distinct change around 7.5 GPa. This marks the solid-solid transition at 7.5 GPa observed in n-heptane for the first time. As predicted in theoretical work, we observe dampening of methyl rotation in n-heptane below 7.5 GPa. With increase in pressure above 7.5 GPa we observe a definitive conversion of gauche to trans conformation in the solid phase. Upon release of pressure we do not observe any hysteresis, which suggests that the solid-solid transition takes place with no volume change or is a second-order transition. In this paper we propose this transition to be an orientational order-disorder transition driven by the dampening of the rotation of the methyl group.     

Modulational instability of optically induced nematicon propagation

We report the modulational instability （MI） analysis for the modulation equations governing the propagation of coherent polarized light through a nematic liquid crystal （NLC） slab, in the limit of low light intensity and local material response. The linear stability analysis of the nonlinear plane wave solutions is performed by considering both the wave vectors （k,l） of the basic states and wave vectors （K,L） of the perturbations as free parameters. We compute the MI gain, and the MI gain peak is reduced and the stable bandwidth is widened with the increase of the strength of the applied electric field. Further, we invoke the extended homogeneous balance method and Exp-function method aided with symbolic computation and obtain a series of periodic solitonic humps of nematicon profiles admitting the propagation of laser light in the NLC medium.     

Studies on azotetrazolate based high nitrogen content high energy materials potential additives for rocket propellants

This paper reports the synthesis, characterisation and thermolysis studies of a series of azotetrazolate salts, viz., ammonium/guanidinium/triaminoguanidinium [azotetrazolate]. TG-DTA and DSC results of these compounds exhibited their thermal stability up to 180°C. DSC indicated the highest heat release (2804 J g^–1) for guanidinium azotetrazolate salt during exothermic decomposition. FTIR of the decomposition products of azotetrazolate salts showed bands at 3264 and 2358 cm^–1 which may be attributed to gaseous species such as NH₃ and HCN or NH₂CN. The sensitivity data suggests low vulnerability of ammonium and guanidinium salts. In cyclic voltammetric studies all the salts showed similar response in reduction reactions. Triamino guanidinium azotetrazolate (TAGAZ) was incorporated into solid propellant formulations in order to establish the compatibility of this class of compounds. DSC results revealed that it does not have adverse effect on thermal stability of double base matrix. The burning rate data obtained indicated that TAGAZ acts as an efficient energetic additive in composite modified double base (CMDB) propellant formulations in high-pressure region.The authors are grateful to Dr. Haridwar Singh, Outstanding Scientist and Director, HEMRL for constant encouragement to carry out this work. Authors also thankful to Dr. R. S. Satpute, Dr. A. N. Nazare and Dr. C. N. Divekar for their assistance in propellant processing.     

1,3-Dipolar reactions involving corannulene: how does its rim and spoke addition vary?

[reaction: see text] Corannulene undergoes 1,3-dipolar reactions with the dipoles, diazomethane, nitrile oxide, and nitrone through its rim and spoke pi bonds; the rim addition yields "one possible" adduct whereas two "regioselective" adducts are formed by spoke addition. Mechanisms of these reactions have been investigated at the B3LYP/6-31G(d) level. Computations show that both rim and spoke additions prefer concerted pathways that lie 2-5 kcal/mol lower in energy than stepwise paths. Stepwise additions can take place in two ways and the activation energies of these two modes differ by 1-2 kcal/mol. A close inspection of the energy profiles reveals that rim addition is more favorable kinetically and thermodynamically than spoke addition in view of lower activation energy and higher exothermicity observed for rim addition. The rim bond of corannulene is more flexible for distortion and also has a stronger double bond (i.e. pi-character) than the spoke bond and this facilitates rim addition over spoke addition. Deformation energy analysis also confirms the above through higher deformation in corannulene from the spoke addition when compared to rim addition. In the spoke addition, regio1 reaction is kinetically more favored than regio2 reaction. Attempts to react corannulene in an endohedral fashion have led to the exohedral adduct. Computed activation energies suggest that corannulene acts as a deactivated dipolarophile compared to ethylene. Even more striking is the observation that rim and spoke double bonds in corannulene are part of the local aromatic system but it shows remarkable reactivity compared to benzene despite the loss of aromaticity during the reaction. This is well indicated by computed NICS values. Inclusion of acetonitrile as solvent through the PCM model increases the reaction rate and exothermicity.     

Unveiling the Anticancer and Antibiofilm Potential of Catechin Overlaid Reduced Graphene Oxide/Zinc Oxide Nanocomposites

Journal of Cluster Science - In the present study, catechin was successfully grafted in reduced graphene oxide Zinc oxide (rGO/ZnO) nanocomposite by solvent free hydrothermal method. Absorption...