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21.
Joseph B. Schlenoff W. Jack Rink Lawrence Seger 《Physica C: Superconductivity and its Applications》1991,180(5-6):387-393
Single crystals and polycrystalline pellets of the high-temperature cuprate superconductor Bi2Sr2Ca1Cu2O8 were doped at room temperature by electrochemical reduction at > 95% Coulombic efficiency using lithium dopant ions in propylene carbonate electrolyte. Cyclic voltammetry and potential step measurements on single crystals suggest an unusual reduction mechanism, with a diffusion coefficient for Li+ in the c-axis direction of bulk superconductor of ca. 3 × 10−11 cm2s−1. Sintered pellets of polycrystalline powder could be doped more rapidly, with an apparent diffusion coefficient of 7 × 10−8 cm2s−1. X-ray susceptibility analysis show extensive disordering occurs on heavy Li doping, with a first-order transition from a crystalline/superconducting to an amorphous/non-superconducting phase. Single, crystals of Bi2Sr2Ca1Cu2O8 exhibited a color change on reduction from metallic gray to golden bronze. The reduced material was highly air-sensitive, forming a hydroxide surface film on exposure to ambient atmosphere. 相似文献
22.
The proportional hazards regression model, when subjects enter the study in a staggered fashion, is studied. A strong martingale approach is used to model the two-time parameter counting processes. It is shown that well-known univariate results such as weak convergence and martingale inequalities can be extended to this two-dimensional model. Strong martingale theory is also used to prove weight convergence of a general weighted goodness-of-fit process and its weighted bootstrap counterpart. 相似文献
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Heptakis(2,6-di-O-methyl)-β-cyclodextrin interacts with 5,15-diphenylporphine to produce a 2:1 complex in dimethyl sulfoxide. This complex possesses a hydrophobic groove that circumscribes the metal binding site of the porphyrin moiety. 相似文献
27.
A method was developed for collection and analysis of bioaerosols by matrix-assisted laser desorption/ionization (MALDI) time-of-flight mass spectrometry using a modified Andersen N6 bioaerosol collector. The overall goal of the study was to develop methods for obtaining mass spectra with minimal reagents and treatment steps for potential use in remote collection and analysis systems. Test bioaerosol particles were generated from a nebulized E. coli bacterial suspension and collected on MALDI targets placed in an Andersen N6 single-stage aerosol impactor. The bioaerosols were mixed with matrix either by deposition on a bare target with the matrix solution added later, or by deposition on a target pre-coated with matrix. The matrix compounds alpha-cyano-4-hydroxycinnamic acid (CHCA) and sinapic acid (SA) were tested and the SA matrix was found to give the best results in number of peaks, resolution, and signal-to-noise ratio. Deposition of bioaerosol particles onto the matrix pre-coated target did not produce signal in the m/z region above 1000, but the signal could be recovered with the addition of a 1:1 (v/v) acetonitrile/water solvent. Addition of solvent by pipette to the pre-coated targets after particle deposition recovered signal comparable to the dried-droplet sample preparations, whereas solvent sprayed into the impactor recovered fewer peaks. Deposition on pre-coated targets with post-collection solvent addition was superior to deposition on bare target followed by post-collection addition of matrix solution. 相似文献
28.
Shimin Xu Lawrence S. Bartell 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1994,31(1):117-123
Molecular dynamics simulations of the behavior of molecules in crystalline clusters of TeF6 were carried out on systems of 100, 150, 250, and 350 molecules. Several diagnostic functions were applied to investigate whether rotational melting occurred before translational melting. These functions included the coefficient of rotational diffusionD θ(T), the “orientational Lindemann index” δθ(T), the “orientational angular distribution function”Q(θ,T), and the “orientational pair-correlation function”g θ(r, T). All indicators implied that rotational melting occurred before translational melting, that it began with the outermost molecules, and that its onset for smaller clusters was at lower temperatures than for larger clusters. Results also showed that the rotational transition coincided with the transition from a lower symmetry phase (monoclinic) to cubic, a phenomenon that had been noted by others to occur with some regularity for systems of globular molecules. 相似文献
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Novel proline-thiazole based cyclopeptides were produced by cyclooligomerisation of an L-proline thiazole amino acid HCl in the presence of pentafluorophenyl diphenylphosphinate (FDPP) or diphenyl phosphorazidate (DPPA). 相似文献
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Abstract—Applying criteria used for higher plants, phytochrome mediation of uredospore germination in the stem-rust fungus, Puccinia graminis f. sp. tritici (Eriks & Henn) Guyot is established. A 1 min red irradiation at 660 nm promotes uredospore germination and this potentiation of promotion is photoreversible by a 1 min far-red irradiation at 730 nm. 相似文献