Shape effect of diamagnetic susceptibility of a hydrogenic donor in a nano structured semiconductor systems

The diamagnetic susceptibility of a hydrogenic donor in GaAs/ Al_xGa_1-xAs semiconductor nanostructured systems like Quantum Well Wire and Quantum Dot has been computed for various cross-sectional geometries of these systems for various width of the confining potential in the effective mass approximation using variational method. The non parabolicity of the conduction band has also been included. This calculation may throw some light on the effect of geometries on the semiconductor–metal transition in these systems.     

Minimal hypersurfaces inS 4 with vanishing Gauss-Kronecker curvature

This work was supported by a grant from the Regents of the University of Michigan     

Microstructural characterization of materials by neural network technique

Ultrasonic signals received by pulse echo technique from plane parallel Zircaloy 2 samples of fixed thickness and of three different microstructures, were subjected to signal analysis, as conventional parameters like velocity and attenuation could not reliably discriminate them. The signals, obtained from these samples, were first sampled and digitized. Modified Karhunen Loeve Transform was used to reduce their dimensionality. A multilayered feed forward Artificial Neural Network was trained using a few signals in their reduced domain from the three different microstructures. The rest of the signals from the three samples with different microstructures were classified satisfactorily using this network.     

Density functional study on the structural conformations and intramolecular charge transfer from the vibrational spectra of the anticancer drug combretastatin‐A2

Combretastatin‐A2 (CA2), a potential anticancer drug in advanced preclinical development, is extracted from the medicinal plant C ombretum caffrum. The NIR‐FT Raman and FT‐IR spectral studies of the molecule were carried out and a b initio calculations performed at the B3LYP/6‐31G(d) level to derive the equilibrium geometry as well as the vibrational wavenumbers and intensities of the spectral bands. The vibrational analysis showed that the molecule has a similar geometry as that of c is‐stilbene, and has undergone steric repulsion resulting in twisting of the phenyl ring with respect to the ethylenic plane. Vibrational analysis was used to investigate the lowering of the stretching modes, and enhancement of infrared band intensities of the C–H stretching modes of Me2 may be attributed to the electronic effects caused by back‐donation and induction from the oxygen atom. Analysis of phenyl ring modes shows that the CA2 stretching mode 8 and the aromatic C–H in‐plane bending mode are equally active as strong bands in both IR and Raman spectra, which can be interpreted as the evidence of intramolecular charge transfer (ICT) between the OH and OCH₃groups via conjugated ring path and is responsible for bioactivity of the molecule. Copyright © 2008 John Wiley & Sons, Ltd.     

Azure A chloride: computational and spectroscopic study

Fourier transform Raman and IR as well as UV–visible spectra of the phenothiazine dye Azure A chloride, 3‐amino‐7‐(dimethylamino) phenothiazin‐5‐ium chloride were recorded and analyzed. The spectral interpretation was done following full structure optimization and vibrational wavenumber calculations based on the density functional theory (DFT) using the standard B3LYP/6‐31G(d) basis set. The N H stretching wavenumber is found to be lowered owing to intermolecular N H···S hydrogen bonding. The downshift of C H stretching wavenumber is discussed. The first hyperpolarizability of the dye is calculated. Time‐dependent density functional theory (TD‐DFT) calculations of electronic spectra were performed on the optimized structure and compared with the experimental UV–visible spectrum. The atomic net charges of the molecule reveal the  M effect of the nitrogen atoms in the molecule. Stability of the molecule arising from hyperconjugative interactions leading to its nonlinearity and bioactivity, charge delocalization and mesomeric effects have been analyzed using natural bond orbital (NBO) analysis. Copyright © 2008 John Wiley & Sons, Ltd.     

Positron annihilation studies in ZnO nanoparticles

We report results on positron annihilation spectroscopic (PAS) studies using lifetime and coincidence Doppler broadening techniques in zinc oxide (ZnO) nanoparticles (4 to 40 nm) synthesized by solid state pyrolytic reaction followed by annealing in the temperature range of 200 ^°C to 800 ^°C. Positron lifetime in the nanoparticles are observed to be higher than bulk lifetime in all the cases. Theoretical calculation of lifetime indicates the presence of either Zn or (Zn, O) vacancy clusters which migrate and anneal out at high temperature. Comparison of ratio spectra from coincidence Doppler broadening measurement and calculated electron momentum distribution indicates the presence of either Zn or (Zn, O) vacancies. In addition, photoluminescence (PL) measurements have been carried out to examine the role of defects on the intensity of emission in the visible region.     

Sonication induced sheet formation at the air-water interface

A hydrophobic pentadecapeptide, AGAAAA-GAVVGGLGG (1), part of the prion sequence PrP (106-127), on fresh aqueous dissolution takes a mixture of random and sheet conformations which forms a stable monolayer with a high beta-sheet content when compressed at the air-water interface. This also develops into a kinetically stabilized beta-sheet structure on sonication.     

Vibrational spectroscopic studies on the natural product,columbianadin

NIR-FT Raman and FT-IR spectra of columbianadin, extracted from seeds and roots of Heracleum candolleaum, were recorded and analyzed. The vibrational frequencies of the compound have been computed using semi-empirical AM1 method and compared with experimental values. The C=O stretching frequencies of the carbonyl groups have been lowered due to conjugation. The CH stretching and bending vibrations of CH3 groups of the ester part indicate the presence of hyperconjugation effect. Characteristic ring vibrations have also been identified.     

Influence of manufacturing parameters on development of contraceptive steroid loaded injectable microspheres

The main objective of this work was to develop a system consisting of polymeric microspheres loaded with steroid drugs. The drugs were encapsulated using biodegradable poly(lactide-co-glycolide) (PLG) and poly(epsilon-caprolactone) (PCL) by double emulsion solvent evaporation method. The lipophilic drugs, levonorgestrel and ethinylestradiol were made soluble by adding ethanol/water mixture. The effects of parameters like polymer concentration and stabilizer concentration were studied on the size, size distribution, surface properties and loading efficiencies of microspheres. The formulated microspheres were smooth, spherical and uniform in shape and size. Fourier transformed infrared spectroscopy and differential scanning calorimetry studies seemed to confirm the absence of chemical interaction between the drugs and the polymers, while the drugs were dispersed in the polymer. The increase in polymer concentrations increased the size as well as the loading efficiency of microspheres. Data obtained in this study demonstrated that the PLG/PCL microspheres may be a suitable polymeric carrier for long acting injectable drug delivery.     

Beddomeilactone: a new triterpene from Dysoxylum beddomei

An investigation of the leaves of Dysoxylum beddomei has yielded a novel triterpene, named beddomeilactone, together with six known triterpenoids: 3-oxotirucalla-7,24-dien-23-ol, dipterocarpol, niloticin, melianone, melianodiol and 24-epi-melianodiol. The structure and stereochemistry of the new compound were determined on the basis of mass, 1D and 2D NMR spectroscopies including NOE difference and spin-spin decoupling studies.