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51.
Liang Wei Zuo‐Fei Wang Lu Yao Guofu Qiu Haiyan Tao Hua Li Chun‐Jiang Wang 《Advanced Synthesis \u0026amp; Catalysis》2016,358(24):3955-3959
An unprecedented copper(II)‐catalyzed enantioselective 1,3‐dipolar [3+4] cycloaddition of azomethine imines with in situ formed azoalkenes has been realized. This strategy provides a facile access to biologically important 1,2,4,5‐tetrazepine derivatives in high yield with exclusive regioselectivity and high stereoselectivity. Moreover, enantioenriched azomethine imines could be obtained via an efficient kinetic resolution using the same approach.
52.
Based on the results of one-dimensional free swelling tests, the coupled effects of NaCl-Na2SO4 solutions and temperature on the swelling deformation property of compacted GMZ bentonite-sand mixtures were analyzed. The concentrations of the NaCl-Na2SO4 solutions were 0, 0.008, 0.04, 0.08 and 0.16 mol/L, the temperatures were 20 °C, 40 °C, 60 °C, 80 °C and 90 °C and the sand contents were 0, 30 and 50%. X-ray diffraction (XRD) and mercury intrusion porosimetry (MIP) tests were also performed to find the influences of the temperature, solution concentration and sand content on the mineral composition and microstructure. The results showed that the maximum swelling strain of the specimens increased with an elevated temperature, while it decreased with increases in the solution concentration and sand content. The swelling process was accelerated by the rising temperature. The XRD tests indicated that the combined effect of a high temperature and a high solution concentration may have caused more Na+ from the saline solutions to enter the interlayer, partly displacing the divalent cations. The MIP tests demonstrated that adding sand to the bentonite could reduce the amount of inter-granular pores and increase the intra-aggregate pores. These findings are advantageous to the transfer of heat and pour fluid in the specimens; and thus, the swelling deformation capacity of the bentonite-sand mixtures was higher than that of pure bentonite under the same conditions. 相似文献
53.
Hai‐Long Hu Dong‐Xu Yao Yong‐Feng Xia Kai‐Hui Zuo Yu‐Ping Zeng 《International Journal of Applied Ceramic Technology》2014,11(5):845-850
Porous Si3N4/SiC ceramics with high porosity were prepared via nitridation of Si powder, using SiC as the second phase and Y2O3 as sintering additive. With increasing SiC addition, porous Si3N4/SiC ceramics showed high porosity, low flexural strength, and decreased grain size. However, the sample with 20wt% SiC addition showed highest flexural strength and lowest porosity. Porous Si3N4/SiC ceramics with a porosity of 36–45% and a flexural strength of 107‐46MPa were obtained. The linear shrinkage of all porous Si3N4/SiC ceramics is below 0.42%. This study reveals that the nitridation route is a promising way to prepare porous Si3N4/SiC ceramics with favorable flexural strength, high porosity, and low linear shrinkage. 相似文献
54.
屈曲约束支撑作为耗能减震构件,其与钢框架连接形成屈曲约束支撑钢框架结构体系。然而目前对于屈曲约束支撑与节点板不同连接形式的抗震性能和破坏模式尚缺乏研究。为了获悉不同连接形式对屈曲约束支撑钢框架结构抗震性能和破坏机理的影响,进行5榀屈曲约束支撑与钢框架节点板连接试件的水平低周往复荷载试验,观察试验现象和破坏特征,考察屈曲约束支撑与节点板两端采用销轴连接、螺栓连接、焊接连接和混合连接对钢结构抗震性能的影响,研究屈曲约束支撑与钢框架节点板连接试件的滞回曲线、骨架曲线、延性系数、刚度退化、耗能能力等抗震性能指标,探讨屈曲约束支撑与钢框架节点板转动变形和关键部位的应变规律,分析结构的破坏模式和各构件屈服顺序。结果表明:屈曲约束支撑的芯板先于梁、柱和节点板屈服,试件滞回曲线饱满,表现出良好的抗震性能和延性。文章研究成果以期为屈曲约束支撑钢框架结构设计和应用提供科学依据。 相似文献
55.
Offshore wind turbines are vulnerable to external vibration sources such as wind and wave excitations due to the increasing size and flexibility. It is necessary to mitigate the excessive vibrations of offshore wind turbines to ensure the safety and serviceability during their operations. Some research works have been carried out to control the excessive vibrations of the tower and the in-plane vibrations of blades. Very limited study focuses on the out-of-plane vibration mitigation of blades. In the present study, a detailed finite element (FE) model of the latest NREL 5MW wind turbine is developed by using the FE code ABAQUS. The tower and blades are explicitly modelled, and the rotating of the blades is considered. Multiple tuned mass dampers (MTMDs) are proposed to be installed in the tower and each blade to simultaneously mitigate the out-of-plane vibrations of the tower and blades when the wind turbine is subjected to the combined wind and wave loadings. The effectiveness and robustness of the proposed method are systematically investigated. Numerical results show that MTMDs can effectively mitigate the out-of-plane vibrations of the tower and blades when the wind turbine is in either the operational or parked condition. 相似文献
56.
摩梭文化习俗影响下的摩梭民居 总被引:1,自引:0,他引:1
民居是特定地域社会文化的映射,位于我国云南省宁蒗县与四川省盐源县交界处存在着一个至今还保持着母系氏族大家庭的"国度"--"摩梭女儿国".摩梭村寨中的摩梭民居介入和融合了摩梭文化习俗,形成了独特的建筑文化圈.该文对摩梭村落选址聚落、摩梭民居类型、居室功能、基本构造和建筑装饰及其民俗承传作了初步研究. 相似文献
57.
58.
世界是一个立体的太极球,以美国为代表的西方文明是一种阳性文明,加州则是阳性文明的阴点;以中国为代表的东方文明是一种阴性文明,广东则是阴性文明的阳点,两大文明相互激活,相互补充,定能够造就一种全新的文明。 相似文献
59.
熨平板是摊铺机上的重要部件,焊接变形和金加工精度难以保证一直是熨平板生产工艺中的难题.熨平板的焊接量大,焊缝位置复杂,而且片件(零件)材质和厚度都不均匀,在焊接过程中使用了搭焊平台、焊接变位机和焊夹具等工装,可以有效地控制焊接变形量.由于焊接冷却后焊缝收缩会使焊接后尺寸减小,采用反变形法能使焊接冷却后的尺寸控制在公差范围内.熨平板金加工理想的加工方式是在卧式加工中心上用专用工装夹具定位夹紧工件后,按照合理的顺序加工.为了保证VB1250熨平板金工精度和避免产生加工振动和装夹变形,设计出两套合理的工装夹具,使VB1250型熨平板的金加工合格率一直在95%以上. 相似文献
60.