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61.
62.
Hall mobilities in high purity epitaxial layers of n-type Ga1?xAxAs alloys with room-temperature electron concentrations in the range (5–10) × 1015 cm?3 have been measured at 300 K for alloy compositions in the range 0? x ? 0.78. Models for the variation of various material parameters with composition are developed. The acoustic deformation potentials for the Π and X conduction band minima, the intervalley coupling constants for electron scattering among the X-X and L-X minima and the longitudinal optical phonon temperature for these scatterings and the polar optical scattering in the X minima have been determined from a theoretical fit to the experimental data. The electron mobilities in the Π, L and X minima are found to decrease with the composition in the range 0≦ x ? 0.45, show a minimum at x ? 0.50 and then increase again with composition. These mobility variations are reflected in the minimum in the Hall mobility at x ? 0.5 due to intense non-equivalent electron scattering involving the L and x minima. The minimum in the electron mobilities in the Π and X minima have been identified to occur mainly due to the space charge and intervalley scattering among the L and X minima, respectively. The number of equivalent x minima in Ga1?x Alx As alloys are estimated to be three and are, thus, situated at the zone edge. 相似文献
63.
O. P. Suri R. K. Khajuria D. B. Saxena N. S. Rawat C. K. Atal 《Journal of heterocyclic chemistry》1983,20(3):813-814
This communication describes synthesis and spectral data of new 2-mercaptobenzimidazole derivatives. 相似文献
64.
Glycogen phosphorylase (GP(a)) is a specific target for the design of inhibitors and may prevent glycogenolysis under high glucose conditions in type II diabetes. The carboxamides first reported by Hoover D. J. et al. (J. Med. Chem. 1998, 41, 2934-2938) are one of the major classes of GP(a) inhibitors other than glucose derivatives. The recent, X-ray crystallographic analyses (Oikonomakos et al. Biochim. Biophys. Acta 2003, 1647, 325-332) have revealed a distinct mechanism of action for these inhibitors, which bind at a new allosteric site away from the inhibitory and catalytic sites. To elucidate the essential structural and physicochemical requirements responsible for binding to the GP(a) enzyme and to develop predictive models, CoMFA and docking studies have been carried out on a series of indole-2-carboxamide derivates. The CoMFA model developed using pharmacophoric alignments and hydrogen-bonding fields demonstrated high predictive ability against the training (r2 = 0.98, q2 = 0.68) and the test set (r2pred = 0.85). Further the superimposition of PLS coefficient contour maps from CoMFA with the GP(a) active site (PDB: 1lwo) has shown a high level of compatibility. 相似文献
65.
We propose a framework to model elastic properties of polycrystals by coupling crystal orientational degrees of freedom with elastic strains. Our model encodes crystal symmetries and takes into account explicitly the strain compatibility induced long-range interaction between grains. The coupling of crystal orientation and elastic interactions allows for the rotation of individual grains by an external load. We apply the model to simulate uniaxial tensile loading of a 2D polycrystal within linear elasticity and a system with elastic anharmonicities that describe structural phase transformations. We investigate the constitutive response of the polycrystal and compare it to that of single crystals with crystallographic orientations that form the polycrystal. 相似文献
66.
A. W. Carbonari J. Mestnik-Filho R. N. Saxena H. Saitovitch 《Hyperfine Interactions》2001,133(1-4):77-81
Magnetic hyperfine fields (mhf) at 111Cd and 140Ce nuclei, dilutely substituting the In and Ce sites, respectively, have been measured in the intermetallic compound CeIn3 using perturbed angular correlation technique. A pure electric quadrupole interaction with an axially symmetric electric field gradient was observed at 111In(EC)111Cd probe nuclei at room temperature while a combined magnetic dipole and electric quadrupole interaction is observed below 10K. Below the ordering temperature, only a magnetic interaction is observed at 140La(–)140Ce probe. The values of mhf measured experimentally as a function of temperature are discussed in terms of critical behavior. 相似文献
67.
Dulić D Pimenov A van der Marel D Broun DM Kamal S Hardy WN Tsvetkov AA Sutjaha IM Liang R Menovsky AA Loidl A Saxena SS 《Physical review letters》2001,86(18):4144-4147
We present microwave and infrared measurements on SmLa0.8Sr0.2CuO4-delta, which are direct evidence for the existence of a transverse optical plasma mode, observed as a peak in the c-axis optical conductivity. This mode appears as a consequence of the existence of two different intrinsic Josephson couplings between the CuO2 layers, one with a Sm2O2 block layer, and the other one with a (La,Sr)2O2-delta block layer. From the frequencies and the intensities of the collective modes we determine the value of the compressibility of the two dimensional electron fluid in the copper oxygen planes. 相似文献
68.
M. E. Mercurio A. W. Carbonari M. R. Cordeiro R. N. Saxena 《Hyperfine Interactions》2007,180(1-3):1-5
We report on the first NMR study of 73Ge nuclear spin decoherence in germanium single crystals with different abundance of the 73Ge isotope. Hahn echo decays are well fit by a superposition of two exponentials. The deviation from the single exponential is more pronounced in the more spin-diluted sample, causing long-lived echoes. We show that the decay of these echoes becomes slower with the reduction of 73Ge abundance and is therefore caused by dipole–dipole interaction, reflecting the fundamental decoherence process in the spin system. The fast decay at the beginning of the relaxation process is shown to be mainly caused by the quadrupole interaction. Our experimental findings are supported by the calculations of Hahn echo decays in the germanium crystals under study. Quite good agreement between the theory and experiment is demonstrated. 相似文献
69.
A. L. Lapolli A. W. Carbonari J. Mestnik-Filho D. M. T. Leite R. N. Saxena 《Hyperfine Interactions》2007,176(1-3):75-79
Perturbed gamma-gamma angular correlation (PAC) technique was used to measure the hyperfine interactions in the intermetallic compound GdPdIn using 111In→ 111Cd and 140La→ 140Ce probe nuclei at the In and Gd sites, respectively. The PAC results for 111Cd show two well-defined electric quadrupole frequencies above T C assigned to probes occupying Gd and In sites, with ~50% of site occupation each. The fraction corresponding to In sites increases with temperature reaching 95% around 500 K. Below T C the measurements for 111Cd probe showed combined electric quadrupole plus magnetic dipole interaction with sharp increase in the magnetic field below around 80 K. A pure magnetic interaction with lower hyperfine field values was observed at the Gd sites occupied by 140Ce below 100 K. 相似文献
70.
Mazaahir Kidwai Preeti Misra Bhavesh Dave Kumar R. Bhushan Rajendra K. Saxena Meena Singh 《Monatshefte für Chemie / Chemical Monthly》2000,17(3):1207-1212
A novel synthesis of 6-fluoro-7-(5-aryl-1,3,4-thiadiazol/oxadiazol-2-yl-sulfanyl)-4-quinolone-3-carboxylic acids from 7-chloro-6-fluoro-4-quinolone-3-carboxylic acid and 5-substituted 1,3,4-thiadiazoles/oxadiazoles on basic alumina under microwave activation is described. All compounds were screened for their in vitro antibacterial activity against B. lichenformis, 2689, K. aerogens 2281, S. typhimurium 2501, E. herbicola 2491, and P. vulgaris 2027 and found to possess activities comparable to that of the standard drug norfloxacin. 相似文献