Implication of local moment at Ti and Fe sites for the electrical and magneto-transport properties of degenerate semiconducting Ti?-xFexO?-d epitaxial films

We have investigated the effect of local magnetic moment on the electrical and magneto-transport properties of thin films of the degenerate semiconductor Ti(1-x)Fe(x)O(2-d) (x = 0,0.04). The electrical measurements of these films reveal high temperature metallic behavior and resistivity minima. The behavior below the resistivity minimum temperature is ascribed to Kondo like scattering. The coupling between the local moment and the charge carriers is reflected in the magnetoresistance measurements in these films. This work indicates competition between the magnetic ordering mechanism by J(RKKY) and the moment screening mechanism by J(Kondo). Accordingly the role of carrier density in achieving the magnetic ordering in such materials either by defect engineering or by transition metal doping is discussed.     

Electronic structure calculations of substitutional and interstitial hydrogen in Nb

We report the results of a theoretical study on the effects of substitutional and interstitial hydrogen atoms in niobium. We confirm that any contaminated hydrogen will occupy the interstitial site over the substitutional site in niobium. For interstitial hydrogens, the lattice deformation increases with the percentage content of hydrogen, though it is negligible at low concentrations. Substitutional hydrogens are found to prefer off-center sites in the host lattice.     

Brownian dynamics of rigid body by fluctuating hydrodynamic equations

In this work, Brownian dynamics of rigid body in an incompressible fluid with fluctuating hydrodynamic equations is presented. To demonstrate the Brownian motion of rigid body, fluctuating hydrodynamic equations have been coupled with equations of motion of rigid body. Thermal fluctuation is included in the fluid equations via random stress terms unlike the random terms in the conventional Brownian dynamics type approach. Calculation of random stress terms in the fluid is easier in comparison to the random terms in the particle motion. Direct numerical simulation for the Brownian motion of rigid body with a meshfree framework is analysed. (© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Thermal expansion coefficient of ternary liquid mixture using hard sphere models and Flory’s statistical theory

The coefficients of thermal expansion (α) of ternary liquid mixtures of heterocyclic compounds viz., pyridine/quinoline with phenol in benzene have been evaluated at 308.15, 318.15 and 328.15 K, respectively. A comparative study of thermal expansivity using different models for hard sphere equation of state and Flory’s statistical theory has been made. The computed values of thermal expansivity are compared with the experimental results. The excess values of thermal expansivity have also been computed and utilized to discuss the existence and strength of intermolecular interactions in the ternary liquid system under investigation.     

Steady-state and transient Raman gain in magnetoactive narrow band-gap semiconductors

Using the hydrodynamic model of semiconductor-plasmas and following the coupled-mode approach, a detailed analytical investigation is undertaken to study both steady-state and the transient Raman gain in transversely magnetized narrow band-gap semiconductors arising from electron density perturbations and molecular vibrations of the medium. Using the fact that the origin of stimulated Raman scattering (SRS) lies in the third-order susceptibility of the medium, we obtain an expression for the gain coefficient of the backward Stokes mode in steady-state and transient regimes and study the dependence of the magnetic field and pump pulse duration on its growth rate. The threshold pump intensity and optimum pulse duration for the onset of transient SRS are estimated. An externally applied magnetic field substantially enhances the transient SRS gain coefficient in narrow band-gap semiconductors, which can be of great use in the compression of scattered pulses.     

Convergent approach toward the synthesis of the stereoisomers of C-6 homologues of 1-deoxynojirimycin and their analogues: evaluation as specific glycosidase inhibitors

A new and stereoselective strategy is developed to synthesize an appropriate template 9 to obtain C-6 homologues of 1-deoxyazasugars such as 1-deoxy-D-galactohomonojirimycin (5), 1-deoxy-4-hydroxymethyl-D-glucohomonojirimycin (6), and their enantiomers. The template 9 is also used to obtain neutral nonbasic pseudo-glyconolactam (8), C-4 amino, and methyl analogues of 1-deoxy-homonojirimycin as new analogues of 1-deoxyhomoazasugars. Compound 5 is found to be a potent and specific inhibitor to alpha-galactosidase (Ki = 1.7 microM). Similarly compounds 6 (Ki= 28 microM), ent-5 (Ki= 129 microM), and ent-6 (Ki= 12 microM) exhibited specific inhibition of beta-glucosidase.     

Synthesis of 1,2,4-trioxepanes and 1,2,4-trioxocanes via photooxygenation of homoallylic alcohols

Homoallylic alcohols 4a-d, easily accessible in two steps from cyclopropyl methyl ketone, underwent a highly regioselective reaction with singlet oxygen to yield gamma-hydroxyhydroperoxides 5a-d in 57-72% yield. Acid-catalyzed reaction of 5a-d with acetone, cyclopentanone, and cyclohexanone furnished 1,2,4-trioxepanes 8a-d, 9a-d, and 10a-d in good yields. Homoallylic alcohol 12 also underwent a highly regioselective photooxygenation to yield gamma-hydroxyhydroperoxide 13 in 67% yield, which on reaction with acetone, cyclopentanone, and cyclohexanone, furnished 1,2,4-trioxocanes 16-18 in 41-55% yield.     

Monotone method for singular BVP in the presence of upper and lower solutions

In this paper we examine existence of monotone approximations of solutions of singular boundary value problem -(p(x)y^′(x))^′=q(x)f(x,y,py^′) for 0<x?b and lim_x→0⁺p(x)y^′(x)=0,α₁y(b)+β₁p(b)y^′(b)=γ₁. Under quite general conditions on f(x,y,py^′) we show that solution of the singular two point boundary value problem is unique. Here is allowed to have integrable singularity at x=0 and we do not assume .     

Determination of track registration efficiency and radiation chemical yield for loss of ester bonds due to gamma rays in Cellulose Acetate Butyrate (CAB) nuclear track detector

The fission track registration efficiency of an indigenously prepared Cellulose Acetate Butyrate (CAB) solid state nuclear track detector (SSNTD) has been determined and is found to be (0.89 ± 0.04). Radiation chemical yield, G-value for loss of ester bonds in this detector exposed to gamma rays from a Co-60 source has also been determined by FT-IR spectrometry. The amount of ester bonds lost due to the exposure was estimated from the change in absorbance of C=O and C–O–C bonds with the gamma dose. The G-value for breaking of ester bonds in CAB detector is found to be about 37/100 eV.     

Effect of the chain-length compatibility of surfactants and mechanical properties of mixed micelles on surfaces

Force/distance curves for silicon nitride tip/flat silica or alumina coated by a layer of mixed micelles of cationic/anionic surfactant are measured by using AFM. Mixtures of SDS/C(n)TAB (with molecular ratios of 3:1 and 20:1) and C(n)TAB/SDS (with molecular ratio of 85:15) were used for alumina and silica substrates, respectively. The number of carbon atoms per C(n)TAB molecule, n, was in the range of 8 to 16. On the basis of the force/distance curves, the elastic modulus, E, and yield strength, Y, of surface micelles are calculated. It is shown that in surfactant mixtures containing SDS the maximal repulsive force (the barrier F(bar)) at which the tip punctured the micelles, as well as the magnitudes of E and Y, attained the maximal values for C(12)TAB ( i.e., when the hydrocarbon chain lengths of two oppositely charged surfactants are the same). Obviously, it can be related to the highest density structure of these micelles. Note that the literature data for the surface micelles from pure C(n)TAB solutions demonstrate a monotonic dependence of F(bar), E, and Y on n in the range of n = 8-16, whereas the oppositely charged mixed surfactant systems yield much higher values of F(bar), E, and Y than does an equivalent chain length from the homologue series plots. The results obtained for mechanical characteristics of mixed micelles at the surface are compared with the results for the relaxation time, tau(2), that characterizes the lifetime (and therefore structure) of the bulk micelles. Both the dependence of F(bar), E, and Y on n for the surface mixed micelles and tau(2) on n for the bulk mixed micelles demonstrate a maximum at n = 12 for the C(n)TAB + SDS system. This correlation between properties of the surface and bulk micelles suggests that the mechanical properties of the surface micelles are largely determined by the interactions between surfactant molecules with surfactant-substrate interactions playing a secondary role.