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171.
Choudhary MI Shah SA Musharraf SG Shaheen F Atta-Ur-Rahman 《Natural product research》2003,17(3):215-220
Transformation of dehydroepiandrosterone (DHEA) (1) was carried out by a plant pathogen Rhizopus stolonifer, which resulted in the production of seven metabolites. These metabolites were identified as 3beta,17beta-dihydroxyanandrost-5-ene (2), 3beta,17beta-dihydroxyandrost-4ene (3), 17beta-hydroxyandrost-4-ene-3-one (4), 3beta,11-dihydroxyandrost-4-ene-17-one (5), 3beta,7alpha-dihydroandrost-5-ene-17-one (6), 3A,7alpha,17beta-trihydroxyandrost-5-ene (7) and 11beta-hydroxyandrost-4,6-diene-3,17-dione (8). The structures of the transformed products were determined by the spectroscopic techniques. 相似文献
172.
173.
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175.
N. K. Mishra R. Sati R. N. P. Choudhary 《Journal of Physics and Chemistry of Solids》1999,60(12):114-1972
Polycrystalline samples of modified lead germanate Pb4.9A0.1Ge2.7Si0.3O11 (A=Ca,Sr,Ba) have been prepared by solid-state reaction technique. X-ray studies have been carried out to check the formation of single-phase composition and to obtain preliminary structural data. Measurements of dielectric permittivity () and loss (tan δ) have been studied both as a function of frequency (102–104 Hz) and temperature (room temperature to 180°C). Phase transition was observed in all three cases but with different Tc value. From the plots of conductivity vs. temperature using dielectric data, collected at 10 kHz activation energy was calculated to investigate the conduction mechanism in them. 相似文献
176.
Saumya R. Mohapatra Awalendra K. Thakur R. N. P. Choudhary 《Journal of Polymer Science.Polymer Physics》2009,47(1):60-71
A novel combination of dispersed phase polymer nanocomposite electrolyte based on PEO8‐LiClO4+ x wt % nano‐CeO2 has been investigated. A model for ion transport mechanism has been proposed to account for substantial enhancement of its electrical conductivity by ~ 2 orders of magnitude at low volume fraction of the filler reinforcement in the polymer nanocomposite films. The strength of the proposed model is based on unambiguous evidences from FTIR, TEM, and conductivity analysis. The FTIR results provide clear role of nanofiller concentration on ion–ion interaction quantified in terms of the fraction of free anion and ion‐pairs present in the nanocomposite films and its excellent correlation with conductivity versus filler concentration. The presence of asymmetry in the ν4(ClO4?) band observed at 625 cm?1 is attributed to its resolved degeneracy suggesting the presence of both uncoordinated and cation‐coordinated ClO4? anion in the matrix due to ion–ion and ion–filler interactions assisted by Lewis acid–base interaction. The enhancement in conductivity at low concentration is possibly due to direct interaction of nano‐CeO2 with both polymer host and anions resulting in the release of ionic charges. Drastic conductivity reduction at higher concentration is related to charge immobilization because of ion/ion‐pair entrapment by local clusters of filler as evidenced in TEM. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 60–71, 2009 相似文献
177.
178.
Zinc oxide (ZnO) nanowhiskers have been prepared using a multilayer ZnO(50 nm)/Zn(20 nm)/ZnO(2μm) structure on a polished stainless steel (SS) substrate by high rate magnetron sputtering. The formation of uniformly distributed
ZnO nanowhiskers with about 20 nm dia. and 2 to 5 μm length was observed after a postdeposition annealing of the prepared
structure at 300–400° C. An array of highlyc-axis oriented ZnO columns (70–300 nm in dia. and up to 10 μm long) were grown on Si substrates by pulsed laser deposition
(PLD) at a high pressure (1 Torr), and Raman studies showed the activation of surface phonon modes. The nanosized powder (15–20
nm) and nanoparticle ZnO films on glass substrate were also prepared by a chemical route. Nanowhiskers showed enhanced UV
light detection characteristics, and the chemically prepared ZnO nanoparticle films exhibited good sensing properties for
alcohol 相似文献
179.
R.N.P. Choudhary K. Perez P. Bhattacharya R.S. Katiyar 《Applied Physics A: Materials Science & Processing》2007,86(1):131-138
The polycrystalline (Bi1-xPbx)(Fe1-xZr0.6xTi0.4x)O3 (x=0.15, 0.25, 0.40, 0.50) (BPFZT) nanoceramic composites were synthesized using mechanical activation and solid-state reaction techniques. The formation of single-phase compounds with 100% solubility of BiFeO3 and Pb(Zr0.6Ti0.4)O3 was confirmed by an X-ray diffraction (XRD) technique. Detailed structural analysis of the fabricated BPFZT composites suggests the formation of tetragonal structure (i.e., distorted perovskite) for all composition. The dielectric constant and loss-tangent of the BPFZT composites decrease on increasing frequency and temperature. It has also been observed that the leakage current and loss-tangent are reduced by increasing the contents of PZT in the BPFZT composites, and hence they may be considered useful for some applications. The values of activation energies and the nature of variation of conductivity with temperature and frequencies suggest that the space charge and oxygen ion vacancies play a significant role in the conduction process. PACS 61.10.Nz; 77.22.Ch; 77.84.Lf; 81.20.Ev 相似文献
180.
In this paper we present a unified treatment that combines the analyticity properties of the scattering amplitudes, the threshold
and asymptotic behaviors, the invariance group of Moebius transformations, the automorphic functions defined over this invariance
group, the fundamental region in (Poincaré) geometry, and the generators of the invariance group as they relate to the fundamental
region. Using these concepts and techniques, we provide a theoretical basis for Veneziano type amplitudes with the ghost elimination
condition built in, related the Regge trajectory functions to the generators of the invariance group, constrained the values
of the Regge trajectories to take only inverse integer values at the threshold, used the threshold behavior in the forward
direction to deduce the Pomeranchuk trajectory as well as other relations. The enabling tool for this unified treatment came
from the multi-sheet conformal mapping techniques that map the physical sheet to a fundamental region which in turn defines
a Riemann surface on which a global uniformization variable for the scattering amplitude is calculated via an automorphic
function, which in turn can be constructed as a quotient of two automorphic forms of the same dimension.
Received: 22 October 2002 / Revised version: 19 February 2003 Published online: 23 May 2003
RID="a"
ID="a" e-mail: arc@lucent.com 相似文献