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991.
We use Janelidze's Categorical Galois Theory to extend Brown and Ellis's higher Hopf formulae for homology of groups to arbitrary semi-abelian monadic categories. Given such a category A and a chosen Birkhoff subcategory B of A, thus we describe the Barr-Beck derived functors of the reflector of A onto B in terms of centralization of higher extensions. In case A is the category Gp of all groups and B is the category Ab of all abelian groups, this yields a new proof for Brown and Ellis's formulae. We also give explicit formulae in the cases of groups vs. k-nilpotent groups, groups vs. k-solvable groups and precrossed modules vs. crossed modules. 相似文献
992.
993.
Ohne Zusammenfassung 相似文献
994.
Two new coordination polymer frameworks Ni(NO2)2 (1) and Ni(4,4′-bipy)(NO2)2 (2) (4,4′-bipy = 4,4′-bipyridine) were synthesized by solvothermal reaction in formamide, and were characterized by elemental analysis, IR spectroscopy, single crystal X-ray diffraction, and magnetic measurement. In compound 1, each Ni2+ ion is linked with four neighboring Ni2+ ions through μ1,3-nitrito bridges forming 2D layered structure. In compound 2, each Ni2+ ion is bridged with six neighboring Ni2+ ions through four μ1,3-nitrito groups and two 4,4′-bipy ligands forming 3D structure. Magnetic measurements show weak ferromagnetism within framework of the two compounds with TN = 19 K (1) and 21 K (2). 相似文献
995.
F. C. McLean und D. D. Van Slyke 《Fresenius' Journal of Analytical Chemistry》1916,55(7):347-348
Ohne Zusammenfassung 相似文献
996.
Niels M. B. Smeets Johan P. A. Heuts Jan Meuldijk Michael F. Cunningham Alex M. Van Herk 《Journal of polymer science. Part A, Polymer chemistry》2009,47(19):5078-5089
The effect the catalytic chain transfer agent, bis[(difluoroboryl) dimethylglyoximato] cobalt(II) (COBF), on the course of the ab initio emulsion polymerization of methyl methacrylate, and the product properties in terms of the molecular weight distribution were investigated. The emulsion polymerization kinetics have been studied with varying surfactant, initiator, and COBF concentrations. The experimentally determined average number of radicals per particle strongly depends on the concentration of COBF and proves to be in good agreement with the results of model calculations. The apparent chain transfer constant, determined up to high conversion, is in excellent agreement with the predicted value based on a mathematical model based on COBF partitioning and the Mayo equation. The results of this work enhance the fundamental understanding of the influence a catalytic chain transfer agent has on the course of the emulsion polymerization and the control of the molecular weight distribution. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5078–5089, 2009 相似文献
997.
Wilhelm Lenz 《Fresenius' Journal of Analytical Chemistry》1880,19(1):297-305
Ohne Zusammenfassung 相似文献
998.
A. J. Birch D. Van Os V. Dykstra und I. Herold 《Fresenius' Journal of Analytical Chemistry》1943,125(1-2):57-58
Ohne Zusammenfassung 相似文献
999.
Models of two important characterisation procedures for oil and oil fractions, ASTM D86 (ASTM = American Society for Testing
of Materials) and EFV (Equilibrium Flash Vaporization), were presented. The purpose was to provide a basis for the construction
of substitute mixtures of real components used in modelling and simulation of chemical engineering processes instead of original
complex mixtures. It was shown how to deal with a possible problem of higher index of differential-algebraic model of the
ASTM D86. A number of examples proved the adequacy of the presented models.
Presented at the 34th International Conference of the Slovak Society of Chemical Engineering, Tatranské Matliare, 21–25 May
2007. 相似文献
1000.
Joseph H Bunton Jesse D Olson Daniel R Lenz Thomas F Kelly 《Microscopy and microanalysis》2007,13(6):418-427
The performance of the pulsed-laser atom probe can be limited by both instrument and specimen factors. The experiments described in this article were designed to identify these factors so as to provide direction for further instrument and specimen development. Good agreement between voltage-pulsed and laser-pulsed data is found when the effective pulse fraction is less than 0.2 for pulsed-laser mode. Under the conditions reported in this article, the thermal tails of the peaks in the mass spectra did not show any significant change when produced with either a 10-ps or a 120-fs pulsed-laser source. Mass resolving power generally improves as the laser spot size and laser wavelength are decreased and as the specimen tip radius, specimen taper angle, and thermal diffusivity of the specimen material are increased. However, it is shown that two of the materials used in this study, aluminum and stainless steel, depend on these factors differently. A one-dimensional heat flow model is explored to explain these differences. The model correctly predicts the behavior of the aluminum samples, but breaks down for the stainless steel samples when the tip radius is large. A more accurate three-dimensional model is needed to overcome these discrepancies. 相似文献