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排序方式: 共有263条查询结果,搜索用时 15 毫秒
191.
Lindeman's criterion for melting of covalent crystals is formulated using Debye's model. The contribution of the acoustical, especially transverse-like acoustical phonon modes to the total mean-square displacement is predominant at higher temperatures and essential to the melting scheme. Using the volume-dependence of the transverse-like Grüneisen constant at higher temperatures, the volume effect on the melting temperature of Si and Ge is studied by Lindeman's melting law. The obtained melting curve decreases as function of the compressed volume, and is qualitatively in agreement with the observed tendency for Si and Ge. 相似文献
192.
The phase transition of AlP, AlAs and AlSb under pressure is studied from the electronic theory of solids by using our presented binding force, which includes mainly covalent interactions in the pseudo-potential formalism and partially ionic interactions. The partially ionic forces bring the essential contributions to the high-pressure phase of AlP, AlAs and AlSb, and stabilize the NaCl-type structure for the high-pressure phase of these compounds, although not reported experimentally. Then, numerical results for the transition pressure, the volume discontinuity, the transition heat and the lattice parameter in NaCl-type lattice of AlP, AlAs and AlSb are predicted theoretically. 相似文献
193.
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195.
Sz. Vass B. Vorsatz E. Szabó E. Kelen B. Keszei S. Cseh S. Saly 《Journal of Radioanalytical and Nuclear Chemistry》1971,8(2):325-334
A non-destructive simultaneous method has been developed for the rapid determination of Al, Si and K in WO3 powders and W metal powders. The samples were activated by 14 MeV neutrons and the radioactive isotopes identified by their
γ-ray spectra with a 3″×3″ NaI(Tl) detector. Quantitative analysis was carried out by measuring the full energy peak areas.
The determined concentrations of Al, Si and K were above 100, 100 and 500 ppm, the sensitivities being about 20, 10 and 100
ppm, respectively. 相似文献
196.
197.
Yoshio Umezawa Koreshige Ito Hiroshi Hata Masao Sugawara Etelka Graf Harsányi Klára Tóth Ernö Pungor Mitsuyuki Soma Atsushi Tanaka 《Mikrochimica acta》1990,100(3-4):231-239
Dissolution of membraneous composite ions of copper sulfide precipitate-based ion-selective electrodes (ISEs) has been measured in various ligand solutions by ICP atomic emission spectrometry and atomic absorption spectrometry from the solution side and by X-ray photoelectron spectrometry on the electrode surface. Asymmetric dissolution, amount of copper dissolved is higher than that of sulfur, was generally observed. The copper dissolution is correlated with the potential response as well as conditional stability constants. The results are discussed in terms of the charge separation caused by the asymmetric dissolution and electrostatic interaction of charged ligands with the space charge on the electrode surface in view of microscopic characterization of ISEs in metal buffer solutions in general. The results were also used to clarify the reason for some discrepancies of complex stability constants obtained by precipitate-based ISEs and other methods.Dedicated to Professor W. Simon on the occasion of his 60th birthday 相似文献
198.
T Nishizawa H Inagawa H Oshima T Okutomi D Tsukioka M Iguchi G Soma D Mizuno 《Chemical & pharmaceutical bulletin》1992,40(2):479-483
Based on our new concept of ontogenic inflammation, we have sought a substance which can prime macrophage in terms of the endogenous production of tumor necrosis factor (TNF). A lipopolysaccharide (LPSw) was found in wheat flour, purified and characterized. The molecular size of LPSw was about 5 kDa on sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and it contained 3-deoxy-D-manno-octulosonic acid: 1, hexosamine: 4 and one phosphorus in a single molecule. LPSw can prime macrophage to release TNF when given intradermally, percutaneously or even orally in mice as well as in humans, in exactly the same way as intravenous administration of interferon gamma. 相似文献
199.
The quenching of the fluorescence of HPTS (1-hydroxypyrene-3,6,8-trisulfonate) by Cu(2+), Ni(2+), Co(2+), I(-), and CP(+) (cetylpyridinium cation) has been studied in the w/o microemulsion medium formed with water, AOT [sodium salt of bis (2-ethylhexyl) sulfosuccinic acid], and heptane as components at two [H(2)O]/[AOT] ratios (omega), 6 and 20. The quenching process has been found to be dynamic in nature. The lifetimes of HPTS in the microemulsion medium in the absence and in the presence of quencher have been determined. The analysis of the results has been performed in terms of the Stern-Volmer equation and the quenching sphere of action model. The Poisson distribution equation has been also used in the analysis of the probability of quencher distribution in the microemulsion compartment. The quenching of HPTS has been found to be much lower in microemulsion than in bulk water. 相似文献
200.
Pradeep Mathur Saurav Chatterjee Soma Chakraborty Michael J. McGlinchey 《Journal of organometallic chemistry》2004,689(1):122-133
Room temperature reaction of a benzene solution of [Cp2Mo2Fe2(CO)7(μ3-E)(μ3-E′)] (EE′=Se2 (1), STe (2), SeTe (3)) with PriNC or ButNC resulted in the formation of iron bonded isocyanide clusters [Cp2Mo2Fe2(RNC)(CO)6 (μ3-E)(μ3-E′)], [E=E′=Se, R=Pri (5) or But (9); E=S, E′=Te, R=Pri (6a, 6b) or R=But (10a, 10b); E=Se, E′=Te, R=Pri (7a, 7b) or R=But (11a, 11b)] and molybdenum bonded isocyanide clusters [Cp2(RNC)Mo2Fe2(CO)6(μ3-E)(μ3-E′)], [E=E′=Se, R=Pri(13) or But (17); E=S, E′=Te, R=Pri (14) or R=But, (18); E=Se, E′=Te, R=Pri (15) or R=But (19)]. Two isomers (a and b) were detected by 1H NMR spectroscopy for the mixed-chalcogen clusters 6, 7, 10 and 11, where the isocyanide group is bonded to an iron atom. Thermolytic reaction conditions were necessary for the reaction of [(η5-C5H5)2Mo2Fe2(CO)7(μ3-Te)2] (4) with Pri NC or But NC to give [Cp2Mo2Fe2(RNC)(CO)6(μ3-Te)2] (R=Pri (8) or R=But, (12)) and [Cp2(RNC)Mo2Fe2(CO)6(μ3-Te)2] (R=Pri (8)). Compounds 5-19 have been characterised by IR and 1H and 13C NMR spectroscopy. The Se- and Te-bridged compounds have been further characterised by 77Se and 125Te NMR spectroscopy. The structures of compounds 12 and 14 were determined by single crystal X-ray diffraction methods. Redox properties of the mixed-metal clusters, 2, 6, 8, 12 and 14 have been studied by cyclic voltammetry in the potential range ±2.5 V at 298 K, using a platinum working electrode. 相似文献