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61.
A. M. Vinogradov 《Acta Appl Math》1986,5(2):169-180
First we propose a model of visual perception essentially based on the Keldysh-Chernavsky-Sossinsky three-channel theorem, from which three-dimensionality of space follows. Second, we associate with a system of subgroups H
1, ..., Hs of a given group G a geometric object, called a group crystal, in order to visualize G. How this notion works is illustrated via the Burnside problem. 相似文献
62.
Michael SchwarzPeter Winterhalter 《Tetrahedron letters》2003,44(41):7583-7587
Anthocyanins, isolated from natural sources by countercurrent chromatography, were reacted with cinnamic acids bearing at least one electron-donating substituent at the para-position. The resulting pyranoanthocyanins obtained by this simple one-step reaction were much less susceptible to pH shifts and retained their original colour over a wide pH-range. Through reaction with p-dimethylamino cinnamic acid, synthetic malvidin- and cyanidin-based anthocyanins with a unique violet hue were prepared. 相似文献
63.
John A. Bishop 《Analytica chimica acta》1973,63(2):305-311
Four different methods for the calculation of the formation constants of fluorescing complexes are discussed. The methods were used to determine constants for the complexes of aluminum(III), gallium(III) and indium(III) with 8-quinolinol-5-sulfonate anion. 相似文献
64.
The cyclopeptide, squamtin A (1, formula: C39H60O11N8S), was found to crystallized in two pseudopolymorphisms, i.e. 1·(H2O)3.5 and 1·(H2O)3.9. The composition of the amino acids and their linkage sequences are the same. The main differences between the two kinds of crystals lie in the positions and occupancies of the water molecules, the positions of the sulfur atoms and the conformation of the side chains. The absolute configuration of 1 is established by X-ray analysis in combination with the Marfey's analysis of its hydrolysates. 相似文献
65.
An electrochemical method has been developed for determining the relative amounts of V(II) and V(III) in polyolefin catalysts prepared using aluminum alkyls and vanadium trichloride. The catalyst, usually obtained as a slurry in n-heptane, is titrated potentiometrically with ceric sulfate using a platinum indicator electrode. Under proper experimental conditions, 2 breaks are obtained, corresponding to the reactions V(II) →V(III) + e and V(III) →V(IV) + e. Interferences from other components of the catalyst are negligible. The method is useful for the analysis of both laboratory catalysts and grab samples taken from pilot plant reactors. 相似文献
66.
Frank D. King 《Tetrahedron》2007,63(9):2053-2056
A high yielding cyclisation of the readily available N-(4,4-diethoxybutyl)-2-(3,4-dimethoxyphenyl)acetamide to 8,9-bis(methyloxy)-2,3,6,10b-tetrahydropyrrolo[2,1-a]isoquinolin-5(1H)-one is described. The latter can be reduced with either AlH3 or BH3 to (±)-crispine A in an overall yield of 55%. 相似文献
67.
S.D. Christian J. Grundnes P. Klaeboe C.J. Nielsen T. Woldbaek 《Journal of Molecular Structure》1976,34(1):33-45
The infrared spectra of 1,1,2-trichloroethane were recorded from 4000 to 50 cm?1 in the vapour and liquid states. Additional spectra above 200 cm?1 of the low temperature crystal and of two crystalline solids, prepared by compressing the sample in a diamond anvil cell, were obtained. Also, infrared spectra of the liquid and of the compound dissolved in CS2 were recorded at increased pressures. Raman spectral data of the liquid (including polarization measurements) and of the low temperature crystal were obtained.The fundamental frequencies for each of the two conformers, C1 and Cs, were assigned and the results checked by normal coordinate analysis. The same diagonal and off-diagonal force constants were employed for the two conformers and the force fields were derived by means of a least squares refinement, including data for chloroethane, 1,1-dichloroethane and various deuterated species. A standard deviation of 3 % was obtained in the final fit.From the changes in relative intensities for infrared bands belonging to the C1 and Cs conformers with increasing pressure, the volume differences (ΔV¯between the conformers were determined in CS2 solution and in the pure liquid. 相似文献
68.
针对使用预测函数控制(Predictive Function Control, PFC)的 DC / DC 变换器在负载切换时产生的扰动对变
换器响应速度有较大影响的问题,提出通过设计观测器观测扰动来优化预测函数控制算法的控制效果;相对于其
他提高系统抗扰动的方法,通过设计观测器来提高变换器抗扰动的方法的优点是实现简单、优化后控制效果好等;
设计 Luenberger 观测器对负载切换时产生的扰动进行观测,将观测值反馈给预测函数控制算法进行最优化分析,
并结合仿真结果对目标函数进行调整,优化后的目标函数能更好地响应扰动并尽快达到稳态;最后将优化后的控
制算法与 PI 双闭环控制方法进行比较,结果显示优化后的控制算法在受到扰动后比双 PI 控制方法动态性能更
好,实现了应对负载切换时提高系统动态性能的目标,增强了 DC / DC 变换器的抗干扰能力;优化后的算法只考虑
了负载切换时的扰动对于系统其他方面的扰动没有考虑进去,可以通过设计整个系统的观测器来进一步提高 DC /
DC 变换器抗扰动的能力。 相似文献
69.
David Cruz-Uribe 《Integral Equations and Operator Theory》1994,20(2):231-237
In this note I give necessary and sufficient conditions on outer functionsf andg for the operator
to be bounded and invertible on H2. I also discuss the relationship of this question to two open questions in operator theory and weighted norm inequalities. 相似文献
70.
Ruey-Jen Jang-Lewis Harold Dean Victory Jr. 《Integral Equations and Operator Theory》1994,18(1):88-108
LetE be a Banach lattice having order continuous norm. Suppose, moreover,T is a nonnegative reducible operator having a compact iterate and which mapsE into itself. The purpose of this work is to extend the previous results of the authors, concerning nonnegative solvability of (kernel) operator equations on generalL
p-spaces. In particular, we provide necessary and sufficient conditions for the operator equation x=T
x+y to possess a nonnegative solutionxE wherey is a given nonnegative and nontrivial element ofE and is any given positive parameter. 相似文献