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901.
902.
On the bases of the topological structures of the three big classes of icosahedral fullerenes: (1) Cn(Ih, n=60h2; h=1, 2,…), (2) Cn(Ih, n=20h2; h=1, 2,…), and (3) Cn(I, n=20(h2+hk+k2), h>k; h, k=1, 2,…), we derived formulas for the decomposition of their nuclear motions into irreducible representations. Hence, we obtained the infrared and Raman active modes for all of the icosahedral (Ih and I) fullerenes theoretically. © 1998 John Wiley & Sons, Inc. Int J Quant Chem 66 : 113–117, 1998 相似文献
903.
904.
汪澍 《理化检验(化学分册)》2005,41(5):362-362,365
在环境分析中,硫化物指的是水溶性无机硫化物和酸溶性金属硫化物,包括溶解性的H2S、HS^-、S^2-和存在于悬浮物中的可溶性硫化物以及酸溶性金属硫化物。用亚甲蓝吸光光度法测定废水中硫化物时,由于废水中的还原性物质、带色物和悬浮物对测定有干扰,故测定前需使用适当的预处理方法将硫化物与干扰物质分离,无色透明、不含悬浮物的水样,可采用沉淀分离法进行预处理, 相似文献
905.
CO2-switchable oligomeric surfactants have good viscosity-reducing properties; however, the complex synthesis of surfactants limits their application. In this study, a CO2-switchable “pseudo”-tetrameric surfactant oleic acid (OA)/cyclic polyamine (cyclen) was prepared by simple mixing and subsequently used to reduce the viscosity of heavy oil. The surface activity of OA/cyclen was explored by a surface tensiometer and a potential for viscosity reduction was revealed. The CO2 switchability of OA/cyclen was investigated by alternately introducing CO2 and N2, and OA/cyclen was confirmed to exhibit a reversible CO2-switching performance. The emulsification and viscosity reduction analyses elucidated that a molar ratio of OA/cyclen of 4:1 formed the “pseudo”-tetrameric surfactants, and the emulsions of water and heavy oil with OA/cyclen have good stability and low viscosity and can be destabilized quickly by introducing CO2. The findings reported in this study reveal that it is feasible to prepare CO2-switchable pseudo-tetrameric surfactants with viscosity-reducing properties by simple mixing, thus providing a pathway for the emulsification and demulsification of heavy oil by using the CO2-switchable “pseudo”-oligomeric surfactants. 相似文献
906.
Huan Dong Shu‐Gui Cao Zheng‐Qiang Li Si‐Ping Han De‐Lin You Jia‐Cong Shen 《Journal of polymer science. Part A, Polymer chemistry》1999,37(9):1265-1275
Polymerization of several lactones were carried out by employing Pseudomonas sp. lipase as the catalyst. The data indicate that water is consumed at the onset of polymerization and released in part during subsequent stages, leading us to propose a complex mechanism for the enzymatic polymerization of lactone. This mechanism involves both ring‐opening and linear condensation polymerization. The former was dominant at the early stage while the latter was dominant in the later stage. In addition, the reaction media showed complex influences on enzymatic polymerization. Some organic solvents increased the degree of polymerization (DP) and decreased the molecular weight distribution. A strategy to increase the molecular weight of the polymer is introduced, which led to the synthesis of a polymer with a number‐average molecular weight (Mn) of 14,500—the highest Mn of poly(ε‐caprolactone) prepared by enzyme‐catalyzed polymerization thus far—and molecular weight distribution of 1.23. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1265–1275, 1999 相似文献
907.
Jeanne Crassous Jos Rivera Nicolette S. Fender Lianhe Shu Luis Echegoyen Carlo Thilgen Andreas Herrmann Franois Diederich 《Angewandte Chemie (International ed. in English)》1999,38(11):1613-1617
The pure enantiomers of D 2 -C 84 as well as a third constitutional isomer of this higher fullerene were produced by a retro-Bingel reaction on the first organic derivatives of C84 (see scheme). These derivatives were synthesized by Bingel cyclopropenation of C84, separated, and unambiguously structurally characterized. 相似文献
908.
Jing Jin Yi-Qing Lv Wei-Zhong He Da Li Ying Ye Zai-Fa Shu Jing-Na Shao Jia-Hao Zhou Ding-Mi Chen Qing-Sheng Li Jian-Hui Ye 《Molecules (Basel, Switzerland)》2021,26(23)
Both UV and blue light have been reported to regulate the biosynthesis of flavonoids in tea plants; however, the respective contributions of the corresponding regions of sunlight are unclear. Additionally, different tea cultivars may respond differently to altered light conditions. We investigated the responses of different cultivars (‘Longjing 43’, ‘Zhongming 192’, ‘Wanghai 1’, ‘Jingning 1’ and ‘Zhonghuang 2’) to the shade treatments (black and colored nets) regarding the biosynthesis of flavonoids. For all cultivars, flavonol glycosides showed higher sensitivity to light conditions compared with catechins. The levels of total flavonol glycosides in the young shoots of different tea cultivars decreased with the shade percentages of polyethylene nets increasing from 70% to 95%. Myricetin glycosides and quercetin glycosides were more sensitive to light conditions than kaempferol glycosides. The principal component analysis (PCA) result indicated that shade treatment greatly impacted the profiles of flavonoids in different tea samples based on the cultivar characteristics. UV is the crucial region of sunlight enhancing flavonol glycoside biosynthesis in tea shoots, which is also slight impacted by light quality according to the results of the weighted correlation network analysis (WGCNA). This study clarified the contributions of different wavelength regions of sunlight in a field experiment, providing a potential direction for slightly bitter and astringent tea cultivar breeding and instructive guidance for practical field production of premium teas based on light regimes. 相似文献
909.
Burst event detection in wall turbulence by WVITA method 总被引:2,自引:0,他引:2
Wavelet Variable Interval Time Average (WVITA) is introduced as a method incorporating burst event detection in wall turbulence.
Wavelet transform is performed to unfold the longitudinal fluctuating velocity time series measured in the near wall region
of a turbulent boundary layer using hot-film anemometer. This unfolding is both in time and in space simultaneously. The splitted
kinetic of the longitudinal fluctuating velocity time series among different scales is obtained by integrating the square
of wavelet coefficient modulus over temporal space. The time scale that related to burst events in wall turbulence passing
through the fixed probe is ascertained by maximum criterion of the kinetic energy evolution across scales. Wavelet transformed
localized variance of the fluctuating velocity time series at the maximum kinetic scale is put forward instead of localized
short time average variance in Variable Interval Time Average (VITA) scheme. The burst event detection result shows that WVITA
scheme can avoid erroneous judgement and solve the grouping problem more effectively which is caused by VITA scheme itself
and can not be avoided by adjusting the threshold level or changing the short time average interval.
The project supported by the National Natural Science Foundation of China (19732005) and the National Climbing Project of
China 相似文献
910.
有机阴离子柱撑水滑石催化酯交换合成碳酸二苯酯 总被引:10,自引:0,他引:10
A series of organic anion-pillared hydrotalcites were synthesized by the ion exchange method and characterized by X-ray diffraction and Fourier transform infrared spectroscopy. The hydrotalcite precursor and pillared hydrotalcites with different anions was tested as catalysts in transesterification of dimethyl carbonate (DMC) with phenol. The results show that the catalytic selectivity of this transesterification reaction over these organic anion-pillared hydrotalcites is significantly improved. The catalytic selectivities of C4H4O4-, C6H8O4-, C10H16O4-, 1,4-C8H4O4-, and C7H5O2-pillared hydrotalcites for transesterified products (diphenyl carbonate and methyl phenyl carbonate) are all greater than 90%, at least 10% higher than that of the hydrotalcite precursor. Under the conditions of n(phenol)/n(DMC)=4, catalyst amount=1.5%, and t=10 h, the C6H8O4-pillared hydrotalcite presents the best catalytic performance, and the DMC conversion and the selectivity for transesterified products reach 43.8% and 93.2%, respectively. 相似文献