Electronic properties of semiconducting Cd2GeO4

Cd₂GeO₄ has been prepared from CdO and GeO₂ by solid state reaction at 850°C as a low resistivity (? ? 1 Ω · cm) n-type semiconductor. Its conductivity is increased by doping with trivalent metal ions and decreased by heating oxygen. The electrons originate from shallow donors and their mobility is determined by a combination of large polaron formation and impurity scattering. From photoelectrolysis data the band gap is determined to be indirect, at 3.15 eV; the first direct transition occurs at 4.1 eV. The relations between conditions of preparation, defect structure, and carrier concentration have been examined, but the available data do not allow an unambiguous identification of the nature of the donor center.     

Lie-optic matrix algorithm for computer simulation of paraxial self-focusing in a plasma

Propagation algorithm for computer simulation of stationary paraxial self-focusing laser beam in a medium with saturating nonlinearity is given in Lie-optic form. Accordingly, a very natural piece-wise continuous Lie transformation that reduces to a restricted Lorentz group of the beam results. It gives rise to a matrix method for self-focusing beam propagation that is constructed and implemented. Although the results use plasma nonlinearities of saturable type, and a gaussian initial beam, these results are applicable for other media like linear optical fibers and to more general situations.     

Experimental study of turbulence in isothermal and stably stratified homogeneous shear flows: Mean flow measurements

The evolution of freestream turbulence under the combined action of linear shear and stable linear temperature profile is investigated. The experiment is carried out in a small, open circuit, low-speed test cell that uses air as working fluid. The temperature gradient formed at the entrance to the test section by means of an array of 24 horizontal, differentially heated elements is varied to get a maximum Brunt-Vaisala frequency N_o[=({g/T_m}{∂T/∂y})^1/2] of 3.1⁻¹. Linear velocity profiles are produced using screens of variable mesh size. The Reynolds number Re_M based on centre-line velocity and mesh size is varied from 80 to 175. Isothermal studies are carried out in four different experiments with varying velocity gradients. The effect of inlet turbulence level on growth of turbulence is studied in these flows by keeping the shear parameter Sh (=(x/u)(∂u/∂y)) constant. The range of shear parameters considered is 2.5–7.0. Shear and stratification combined produce a maximum gradient Richardson number Ri_g (= N_o²/(∂u/∂y)²) of 0.0145. Results have been presented in terms of evolution of variance of velocity fluctuations, Reynolds shear stress and temperature fluctuations. Measurements show the following: In isothermal flows the growth rate of turbulence quantities depends on both shear parameter and inlet turbulence level. There are distinct stages in the evolution of the flow and that can be identified by the power-law exponent of growth of turbulence. Shear is seen to promote the growth of turbulence and accelerate it towards a fully developed equilibrium state. Stratification initially suppresses the growth of turbulence and, hence, enhances the degree of underdevelopment. Under these conditions shear becomes active and subsequently enhances the growth rate of turbulence quantities.     

14N nuclear quadrupole resonance study of substituted anilines and prediction of in vitro activity of sulfanilamides

¹⁴N nuclear quadrupole resonance (NQR) spectra of 22 monosubstituted anilines are reported and analyzed in the framework of the Townes and Dailey theory. Satisfactory correlations of the NQR data with both the Hammett σ parameters and the in vitro biological activities of the corresponding sulfanilamides have been found. The results obtained suggest that the nitrogen lone-pair orbital is more sensitive than the nitrogen–carbon sigma orbital is to substituent effects.     

Molecular modeling on pyruvate phosphate dikinase of Entamoeba histolytica and in silico virtual screening for novel inhibitors

Pyruvate phosphate dikinase (PPDK) is the key enzyme essential for the glycolytic pathway in most common and perilous parasite Entamoeba histolytica. Inhibiting the function of this enzyme could control the wide spread of intestinal infections caused by Entamoeba histolytica in humans. With this objective, we modeled the three dimensional structure of the PPDK protein. We used templates with 51% identity and 67% similarity to employ homology-modeling approach. Stereo chemical quality of protein structure was validated by protein structure validation program PROCHECK and VERIFY3D. Experimental proof available in literature along with the in silico studies indicated Lys21, Arg91, Asp323, Glu325 and Gln337 to be the probable active sites in the target protein. Virtual screening was carried out using the genetic docking algorithm GOLD and a consensus scoring function X-Score to substantiate the prediction. The small molecule libraries (ChemDivision database, Diversity dataset, Kinase inhibitor database) were used for screening process. Along with the high scoring results, the interaction studies provided promising ligands for future experimental screening to inhibit the function of PPDK in Entamoeba histolytica. Further, the phylogeny study was carried out to assess the possibility of using the proposed ligands as inhibitors in related pathogens.     

Polyaniline nanofibers by surfactant‐assisted dilute polymerization for supercapacitor applications

Polyaniline nanofibers doped with citric acid was prepared by a novel surfactant‐assisted dilute polymerization technique. It was possible to synthesize polyaniline nanofibers without using any organic solvent by easier pathway. Polyaniline salt was characterized by conductivity, FTIR, and X‐ray diffraction studies. The specific capacitance behavior of the polyaniline nanofibers was characterized using cyclic voltammetry which exhibits highest specific capacitance of 298 F g^?1. The morphology of the obtained nanofibers was characterized by SEM studies. So, these kinds of specific properties of polyaniline nanofibers could be beneficial to the development of energy storage devices. Copyright © 2008 John Wiley & Sons, Ltd.     

ChemInform Abstract: Magnetic and X‐Ray Absorption Studies on the RE5X2Sb6 (RE: Eu,Yb; X: Al,Ga, In) Compounds.

The title compounds (obtained by a high frequency induction heating method) are characterized by magnetic measurements, XANES, and XRD.     

Apical functionalization of chiral heterohelicenes

We describe a synthetic protocol to selectively functionalize chiral bridged triarylamines at the apical position using regioselective copper-catalyzed amination reaction. This protocol allows the coupling of diphenylamines with a sterically hindered but electronically activated aryl-Br bond in the presence of a sterically unhindered but electronically unactivated aryl-Br bond. The unactivated aryl-Br bond was utilized further to synthesize a chiral heterohelicene homodimer using Stille coupling.