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91.
P. Dolle M. Alnot J.J. Ehrhardt A. Cassuto 《Journal of Electron Spectroscopy and Related Phenomena》1979,17(5):299-321
The joint application of various techniques of surface analysis (XPS, UPS, AES and work function measurements) allowed us to pinpoint the initial stages in the oxidation of polycrystalline chromium in the temperature range 180–720 K. At weak exposures ( < 10 L) the oxygen was dissociatively adsorbed without providing any information on the amount of oxygen involved or the sites of adsorption (chemisorption vs. physical interaction due to the roughness of the surface). At stronger exposures the oxide Cr2 O3 is observed to form, and this is covered by a layer of chemisorbed oxygen at ordinary temperatures and below. The maximum thickness of the oxide layer depends on the temperature, as would be expected from the logarithmic oxidation kinetics. The change in shape of the Auger peaks of chromium during oxidation has been interpreted in terms of interatomic transitions made via the 2p levels of oxygen. 相似文献
92.
The process of quantitative densitometry is analyzed with methods developed in information theory. It is shown that the steps involved in densitometry, e.g. gel staining, mechanical, optical and electronic processing, as well as all the steps of data processing, can be viewed as communication channels. The factors affecting both the relevant and irrelevant part of the total information passed through these channels are discussed in the consistent frame provided by information theory. This view leads to a unifying context for analyzing the performance of quantitative densitometers. 相似文献
93.
The problem treated in this paper is the following.Let p 1,...,p k be idempotents in a Banach algebra B, and assume p 1+...+p k =0.Does it follow that p j =0,j=1,..., k? For important classes of Banach algebras the answer turns out to be positive; in general, however, it is negative. A counterexample is given involving five nonzero bounded projections on infinite-dimensional separable Hilbert space. The number five is critical here: in Banach algebras nontrivial zero sums of four idempotents are impossible. In a purely algebraic context (no norm), the situation is different. There the critical number is four. 相似文献
94.
Chemical homogeneity is a relative property of solid-state materials; it depends not only on their ultimate purposes, but also on the parameters of the analytical procedure applied in the investigation. These features are often given inadequate attention in the characterization of solid materials. A statistical model for representative sampling is used here as the starting point to derive relationships which demonstrate quantitatively the increasing rigour of the homogeneity test with increasing spatial resolution and precision of the analytical procedure. It is also shown that chemical homogeneity can be confirmed at a calculated risk, when the tests do not show the material to be significantly inhomogeneous and when maximum permissible deviations in concentration can be given for a practical application. 相似文献
95.
Studies on Catalytically Active Surface Compounds. XI. Influence of the Topology of Silanol Groups on the Formation of Vanadium Oxide Clusters on SiO2 Surfaces Interaction of VOCl3 dissolved in CCl4 with silanol groups of Aerosil gives rise to reaction products, the Cl/V-ratio of which depends on thermal pretreatment of Aerosil and the amount of the vanadium fixed on the surface. Geometrically different arrangements of the silanol groups (centers) show kinetically differing behaviour, thus giving the possibility to establish a mathematic model for the interpretation of experimental data. Quantitative estimation of the population with silanol groups depending on the annealing temperature is achieved and correlated with the existence of two vanadium oxide surface species which differ with respect to their catalytic activity. 相似文献
96.
A method is described for the determination of the total nitrogen content, after conversion to nitrogen gas, of various types of samples before the mass-spectrometric analysis of the 15N abundance. The sample is burned with a mixture of copper oxide, copper and lime in a closed tube under vacuum (modified Dumas method). The gas is released into an evacuated chamber of known volume and the nitrogen pressure is used to determine the nitrogen content of the sample. The gas is then admitted into a mass spectrometer. In order to obtain complete combustion of the material and to generate pure nitrogen gas, various combustion temperatures, combustion times and oxidizing agents were compared. 相似文献
97.
Evelyne Grander Grard Leclerc Jean-Daniel Ehrhardt 《Journal of heterocyclic chemistry》1989,26(6):1781-1785
4-Alkyl-2-methyl-3,4-diphenyl-1,2-thiazetidine 1,1-dioxide 5, 6 and 7 were obtained from 2-methyl-3,4-diphenyl-1,2-thiazetidine 1,1-dioxide 1 by reaction of its anion 4 with alkyl halides. cis- and trans-Configuration of the 4-alkylated products were determined by 1H-nmr and NOE difference spectro-scopy studies. 相似文献
98.
Li DL Li XM Li TG Dang HY Proksch P Wang BG 《Chemical & pharmaceutical bulletin》2008,56(9):1282-1285
Four new (1-4) and seven known (5-11) benzaldehyde derivatives were characterized from the liquid fermentation cultures of Eurotium rubrum, an endophytic fungus that was isolated from the inner tissue of stems of the mangrove plant Hibiscus tiliaceus. The structures of these compounds were determined by extensive analysis of their spectroscopic data. Among these metabolites, compound 1, which was named as eurotirumin, possesses a new carbon skeleton with a cyclopentabenzopyran ring system. 相似文献
99.
[reaction: see text] Two novel bisdolabrane backbone tetraditerpenoids, tagalsins I (1) and J (2), were isolated from the mangrove plant, Ceriops tagal, and their structures were elucidated by means of extensive two-dimensional NMR (COSY, HMQC, HMBC, and NOESY), IR, and MS data analysis. The stereochemistry of 1 was further determined by single-crystal X-ray diffraction. 相似文献
100.
W. E. Garner C. A. Waters H. Lüers C. W. G. Hetterschy Aristides Kanitz F. Liebert A. Uhl W. Kestranek J. M. Kolthoff B. D. Hartong J. Pinkhof E. Biilmann A. Klit F. Haber Z. Klemensiewicz W. S. Hughes A. L. v. Steiger W. E. L. Brown Phyllis M. T. Kerridge Th. Arnd W. Siemers K. H. Goode W. D. Treadwell J. W. Williams Th. A. Whitenack U. Ehrhardt E. Linde 《Analytical and bioanalytical chemistry》1930,80(5-6):203-213