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1.
Exact closed-form solutions are exhibited for the Hopf equation for stationary incompressible 3D Navier-Stokes flow, for the cases of homogeneous forced flow (including a solution with depleted nonlinearity) and inhomogeneous flow with arbitrary boundary conditions. This provides an exact method for computing two- and higher-point moments, given the mean flow. 相似文献
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Vilsmeier-formylation of the copper(II) complex of chlorin-e6 trimethyl ester (2), under mild conditions, gives selective substitution in the 3-vinyl group. In contrast chlorination of 2 is shown to lead to selective substitution at position 20 of the macrocycle. A similar result is found for [3-ethyl]-isochlorin-e4 dimethyl ester (17) although further reaction leads to more highly chlorinated products which have been isolated and identified. 13C NMR data for some of these compounds and several related chlorin derivatives are reported. In particular, after correction of the literature, many of the quaternary carbon signals of the macrocycle are assigned and substituent effects assessed. Consideration of the shifts of the α-pyrrolic carbons confirms that chlorin and its derivatives exist in a tautomeric form with the two inner H atoms on diagonally opposite pyrrole rings A and C. Such a form allows a satisfactory explanation of the substituent chemical shifts of the formyl group at positions 15 and 20 to be made. 相似文献
4.
Franz-Josef Marner Yasmin Karimi-Nejad Lothar Jaenicke Victor Wray 《Helvetica chimica acta》1990,73(2):433-438
The novel iridal 10 has been isolated from rhizome extracts of Iris foetidissima. Its structure was established by spectroscopic methods and oxidative degradation. Final proof of the spirobicyclic nature of the compound – a new feature in the triterpenoid field – was afforded by the correlations observed in the 2D-HMBC- (1H-detected multiple-bond heteronuclear multiple-quantum coherence) spectrum. The possible biogenesis of this unusual compound is discussed. 相似文献
5.
MENG Jian REN Yu-Fang LI Xiao-GuangLaboratory of Rare Earth Chemistry Physics Changchun Institute of Applied Chemistry Chinese Academy of Sciences Changchun Jilin ChinaPopov V.V. Repin S.M. Smirnov LA. loffe Physicotechnical Institute Russian Academy of Sciences Saint Petersburg Russia 《中国化学》1994,12(5):419-424
YBa2Cu3-xVxO7-y(x=0, 0.1, 0.2, 0.3, 0.4, 0.5 and 0.6) superconductors have been prepared. X-ray diffraction shows that the system remains orthorhombic for all compositions studied, but for x > 0.4 V2O5 was detected as an impurity phase. Substitution of V5+ for Cu2+ occurs in the Cu(2) sites on the Cu(2)-O planes. The introduction of the high valence element, vanadium, produces the extra free-electrons. These electrons recombine with the positive carrier of the system. It makes depression of the mobility and the Hall number of YBa2Cu3-xVxO7-v and also results in a depression of TC. 相似文献
6.
Rudolf F. X. Bauer Ikhlas A. Khan Hermann Lotter Hildebert Wagner Victor Wray 《Helvetica chimica acta》1985,68(8):2355-2358
The structure elucidation of four new constituents from the roots of Echinacea purpurea is described. They are shown to be cinnamoyl esters of sesquiterpene alcohols with a germacrane or a guaiane skeleton. First pharmacological results indicate immunological activities. 相似文献
7.
MARIAN ELBANOWSKI MARIA PAETZ JANUSZ SIAWINSKI LESZEK CIELA 《Photochemistry and photobiology》1988,47(3):463-466
Abstract— Chemiluminescence of the Eu(II)/Eu(III)-adenine nucleotide-H2 O2 system and fluorescence of the Eu(III)-adenosine triphosphate system have been investigated. The spectral distribution of the chemiluminescence emission has shown an occurrence of three main bands (Λ=470–480,590–620 and ca. 700 nm). The energy transfer process from the adenosine triphosphate molecules to the Eu(III) ions has been observed in the fluorescence spectrum. The examined chemiluminescence and fluorescence spectra show that these both kinds of emission originate from the 5 D *** τ7 F*** ( n =1–4) transitions in the Eu(III) ions. 相似文献
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针对纤维材料变温环境力学性能测试的需要,在华中科技大学研制的纤维材料试验机的基础上引入了温控装置,从而实现纤维材料在高低温环境下的力学性能测试。采用该装置对不同直径微米铜丝在不同温度、不同拉伸速率条件下的力学性能开展实验研究,测试结果表明弹性模量和抗拉强度随温度的降低而线性增加,屈服强度的变化不太明显。另外,低温环境下微米铜丝的力学性能表现出与其直径相关的尺度效应,而这一现象在常温下一直没有观测到。最后,还研究了拉伸速率对微米铜丝的力学性能影响,结果表明,在现有装置的许用范围之内,拉伸速率对其力学性能的影响不大。 相似文献
10.
The synthesis of 1H-indazoles is achieved from o-aminobenzoximes by the selective activation of the oxime in the presence of the amino group. The reaction occurs with a variety of substituted o-aminobenzoximes using a slight excess of methanesulfonyl chloride and triethylamine at 0-23 degrees C and is amenable to scale-up. The synthesis of 1H-indazoles under these conditions is extremely mild compared with previous synthetic approaches and affords the desired compounds in good to excellent yields. 相似文献