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971.
Soft corals of the genus Sinularia are widely distributed in the South China Sea. Two new lipid analogues (Z)-N-(3,4-dihydroxyphenethyl)-3-methyldo-dec-2-enamide (1) and (E)-1-(2,5-dihydroxy-4-methylphenyl)-6-acetoxy-2,3,7-trihydroxy-3,7,11,15-tetramethylhexadeca-11,14-dien (2), together with three known compounds (3–5) were isolated from the soft coral Sinularia flexibilis. Their structures were elucidated on the basis of extensive spectroscopic analysis, including one and two-dimensional NMR, MS, IR, UV, as well as by comparison with published data. 相似文献
972.
Yangpeng Duan Gaoming Mo Haijun Chen Yanqin Liang Zhenduo Cui Xianjin Yang Shengli Zhu Zhaoyang Li Liu He Qing Huang Zhengren Huang 《应用有机金属化学》2019,33(2)
The synthesis of polyaluminocarbosilane (PACS) using liquid polysilacarbosilane (PSCS) and aluminum acetylacetonate [Al (acac)3] by a high‐pressure method is reported for the first time. The effects of reaction time, temperature and feed ratio on the structure of PACS are investigated in detail by gel permeation chromatography, Fourier transform‐infrared, 1H‐NMR, 29Si‐NMR and 27Al‐NMR methods. It was found that the molecular weight and its polydispersity, as well as the branching degree of the molecular structure of PACS, increase with reaction time and temperature. Increasing the weight percentage of Al (acac)3 has a similar effect as temperature. Combined with the gas chromatography–mass spectroscopy results, the reaction mechanism is proposed, which contains three main reactions: (i) cleavage and rearrangement reaction of PSCS; (ii) silicon‐free radicals react with Al (acac)3, leading to cleavage of O=C and/or O‐C bonds and formation of AlOx ligands; and (iii) conversion reaction of Al ligands from AlO6 into AlO5 and AlO4. It is also found that PACS prepared by high‐pressure method has a lower branched molecular structure in comparison to its analog prepared under ambient pressure conditions, and it is achieved to increase the molecular weight and ceramic yield of PACS, which is beneficial for the processing and overall quality of the final product. 相似文献
973.
具有表面凹坑的半无限体三维应力集中系数有限元研究 总被引:1,自引:0,他引:1
利用ANSYS有限元软件对半无限体表面球形和半椭球形凹坑的三维应力集中系数进行了计算,该方法简单易行,省时省力;并将所得数据与试验结果作了对比,两者吻合较为一致,说明利用该软件分析三维应力集中问题有效可行。研究结果表明:应力集中系数随泊松比μ、曲率r及凹坑与结构相对尺寸的增加而变大;对于椭球凹坑,在深度一定时,增加凹坑与表面相交面积,可以减小应力集中系数,削去部分的形状,以与凹坑相切,且在载荷方向上有长轴的椭圆或圆弧组合为宜。 相似文献
974.
Yongrui Duan Peng Tian Weiping Zhang 《Journal of Applied Mathematics and Computing》2004,14(1-2):173-183
Data envelopment analysis (DEA) is a mathematical programming approach to assess relative efficiency of a group of decision-making units. In view of the defects of existing models in evaluating efficiency of the system with P independent subsystems, Yang et al. [10] introduced YMK model with the assumption that decision-making unit (DMU) is independent of each other. But in some production systems, decision-making units usually have some relationships in this way or that. In this paper, DEA model is given by assuming that DMUs can cooperate with others in its subgroups. Some property and the efficiency relationship of the whole system and its subsystems are given. 相似文献
975.
In light of the φ-mapping topological current theory, two important vortex structures in two-component spinor BEC—the velocity field vortices and the Mermin-Ho vortices are discussed. It is revealed that these two different kinds of vortices are created respectively from the zero points of two different order parameter configurations in the condensates, and both their topological charges, locations and motions can be determined by the φ-mapping theory. 相似文献
976.
纳米晶体ZnS:Mn2+中Mn2+粒子4T1→6A1的发光寿命比晶体减缩了5个量级,这颇令人费解,因为通常解除自旋禁戒的磁作用远无如此强的效应.假定基质态的自旋不为零,且考虑了Mn2+的d电子和基质之间的交换库仑作用.若基质存在比Mn2+的4T1激发态能量略高的某种激发态,则这种交换库仑作用将导致这两种激发态之间的混合,从而可解除发光能级弛豫中的自旋禁戒.这种混合随基质颗粒尺寸的减小而加强.我们并对此机制进行粗略的数值估计,给出了和实验相容的结果. 相似文献
977.
T.B. Wei R.F. Duan J.X. Wang J.M. Li Z.Q. Huo P. Ma Zh. Liu Y.P. Zeng 《Applied Surface Science》2007,253(18):7423-7428
Large-scale GaN free-standing substrate was obtained by hydride vapor phase epitaxy directly on sapphire with porous network interlayer. The bottom surface N-face and top surface Ga-face showed great difference in anti-etching and optical properties. The variation of optical and structure characteristics were also microscopically identified using spatially resolved cathodoluminescence and micro-Raman spectroscopy in cross-section of the GaN substrate. Three different regions were separated according to luminescent intensity along the film growth orientation. Some tapered inversion domains with high free carrier concentration of 5 × 1019 cm−3 protruded up to the surface forming the hexagonal pits. The dark region of upper layer showed good crystalline quality with narrow donor bound exciton peak and low free carrier concentration. Unlike the exponential dependence of the strain distribution, the free-standing GaN substrate revealed a gradual increase of the strain mainly within the near N-polar side region with a thickness of about 50 μm, then almost kept constant to the top surface. 相似文献
978.
Huo-yuanDuan Da-LiZhang 《应用数学学报(英文版)》2003,19(1):25-30
A finite element method is proposed for the sing ularly perturbed reaction-diffusion problem.An optimal error bound is derived,independent of the perturbation parameter. 相似文献
979.
980.
利用场强与电势的关系计算非平行平板电容器的电容 总被引:1,自引:0,他引:1
对于非平行平板电容器,利用电场与电势的基本关系,求解微分方程,得到电容器的电容值. 相似文献