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31.
32.
对雷诺数Re = 100 间距比s/D = 2.5 和5.0 的并列双圆柱流致振动进行了数值模拟研究, 其中圆柱质量比m = 2.0, 折合流速Ur 在2.0~10.0 之间, 两圆柱仅能做横流向振动. 研究发现, 当间距比s/D = 2.5 时, 在折合流速4.4 < Ur< 4.8区间内, 两圆柱流致振动响应出现不对称振动现象, 在折合流速4.4 < Ur< 4.8 区间内, 两圆柱流致振动响应出现对称性迟滞现象; 而当间距比s/D = 2.5时, 圆柱流致振动响应与单圆柱涡激振动响应相似, 没有出现不对称振动和对称性迟滞现象. 在不对称振动区间内, 两圆柱的升、阻力参数也出现了不相等的情况. 此外, 当两圆柱不对称振动时, 圆柱间隙流稳定地偏斜向其中的一个圆柱; 相应地, 尾涡也出现了宽窄不等的模式. 窄尾流圆柱的振幅和升、阻力均较宽尾流圆柱的大. 通过对比不对称振动现象发生前后的尾涡模式, 对新现象的产生机制进行了阐述. 相似文献
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在温和条件下制备了L-脯氨酸稳定并修饰的负载型金属铱催化剂,用于苯乙酮及其衍生物不对称催化加氢反应. 考察了L-脯氨酸的量、溶剂、碱以及碱的量和氢气压力对苯乙酮不对称催化加氢反应的影响. 结果显示,该催化剂催化苯乙酮不对称加氢反应获得了92.1%的转化率和32.9%的对映选择性(e.e.),催化2′-(三氟甲基)苯乙醇的对映选择性为39.3,这一结果高于目前报道的天然手性修饰剂修饰的负载型金属催化剂. 该催化循环使用5次, 对映选择性只有小幅度下降. 相似文献
35.
螯合辅助溶剂挥发共组装法制备的炭-氧化铝复合材料为载体,分别使用水、乙醇或二者混合物为氯铂酸的分散介质,浸渍制备炭-氧化铝复合材料负载Pt催化剂.通过XRD,N2物理吸附以及TEM表征可知,乙醇作为浸渍溶剂时,最有利于Pt的分散,而混合溶剂浸渍制备的催化剂Pt颗粒最大.2-氧-4-苯基丁酸乙酯不对称加氢反应结果表明,氯铂酸水溶液浸渍得到的催化剂Pt纳米粒子的粒径有利于获得高的光学选择性,催化剂经辛可尼丁修饰后,以乙酸为反应溶剂,可获得最高84.8%的光学选择性.此外,该催化剂重复利用性能优异,可以重复利用22次,活性没有下降. 相似文献
36.
将苯乙胺衍生的手性膦-亚磷酰胺酯配体应用在Rh-催化α-烯醇酯膦酸酯的不对称氢化反应中,考察了配体结构及反应条件对反应结果的影响,并在优化的条件下研究了各种底物的适用范围,产物的对映选择性最高>99%ee. 相似文献
37.
使用低耗散的Roe格式,数值模拟了Reynolds数(Re)对大攻角细长旋成体绕流滚转角效应的影响.模型头部加了几何小扰动块以引发流场的不对称.在较大的Re数(Re=10 5)下,本文的计算结果与实验是相符的,此时细长体的滚转会导致双稳态、双周期现象,即侧向力随滚转角呈现类似方波形式的双周期变化,方波中侧向力基本保持不变的状态对应于流场的正则态,且两个正则态的侧向力方向相反,方波中侧向力基本保持不变的状态对应于流场的正则态,且两个正则态的侧向力方向相反;而在较小的Re数(Re=4 000)下,如果扰动足够大,细长体的滚转将导致不同的双稳态现象,此时两个正则态的侧向力方向相同,而在较小扰动下双稳态现象不再出现;Re数更小时(Re=1 000),即使在较大的扰动下,双稳态现象也不再出现,侧向力随滚动角仍是连续变化的.本文的计算结果表明,Re数越小,流场对头部扰动的感受性越弱. 相似文献
38.
随着玻色-爱因斯坦凝聚（BEC）的实现及其非线性效应研究的快速发展,原子光学的一门新兴分支学科——“非线性原子光学”已初步形成,并取得了一系列重大的实验进展.文章重点介绍了非线性原子光学的研究内容、实验结果及其最新进展,主要包括原子孤子、原子物质波中的四波混频、光速减慢与负群速现象、超流及涡流（vortex）、Josephson效应和物质波的相位相干放大等. 相似文献
39.
Guan ZHOU;Libo LI;Di FU;Yafei ZHANG;Yutao FENG;Changhai LIU 《光子学报》2022,51(6):286-295
The wind information of the middle and upper atmosphere is very important to study the coupling of the upper and lower atmosphere and energy, to ensure the smooth development of spacecraft space activities, and to carry out medium and long-term meteorological predictions. The doppler asymmetric spatial heterodyne wind measurement technology is a technique based on the Fourier transform of the interferogram to realize the detection of the doppler frequency shift of the wind. Doppler asymmetric spatial heterodyne is a new passive wind detection technology. For the interferometer, the processing and assembly errors of optical components and structural components, and the aberration of the optical system will distort the interference image. Introducing inversion error in the process of wind speed measurement. The current research on DASH interferogram distortion has not analyzed the influence of interferogram distortion on the accuracy of Doppler phase inversion and lacks the quantitative theoretical basis for the design, processing, and adjustment of Doppler asymmetric spatial heterodyne. In this paper, we analyzed the sources of different distortion in Doppler asymmetric spatial heterodyne. Then by adding different types and sizes of interferogram distortions to the interferograms of the red and green oxygen emission line, the simulation compares the difference between the distorted interferogram’s and the ideal interferogram’s Doppler phase. By adding optical distortion, local bending, slanted fringes and frequency changed these four different forms of interferogram distortion, we got the influence of distortion on the accuracy of Doppler phase inversion. The results show that the Doppler phase error will increase with the increase of the target wind field and interferogram distortion. The Doppler phase error of optical distortion is also will increase with the increase of the target wind field but will fluctuate increase with the increase of interferogram distortion. Among these four different forms of interferogram distortion, the local bending of fringes has the greatest influence on Doppler phase inversion. The phase error increases by 0.113‰ for each additional pixel of the local bending. But the maximum phase error is only 0.03‰ under the condition of 2% distortion. To further explore the influence of local bending sizes and location, we simulate various interferograms with local bending of different sizes and locations. The result shows that the Doppler phase error fluctuation decreases and gradually converges when the size increases. And the phase error fluctuates with the change of position. The fluctuation amount in the first half is small, and the fluctuation in the second half increases gradually. The phase error generated by the same bending at the sampling center is larger than that at the sampling edge. Therefore, attention should be paid to the small distortion in the sampling center area, and if necessary, interferogram correction should be performed to reduce the phase error. The simulation of errors caused by local bending on systems with different fringe frequencies shows that the same amount of bending will have a greater impact on systems with high fringe frequencies. In addition, interferogram with a low signal-to-noise ratio usually uses multiple rows of pixels of the interferogram to reduce uncertainty of phase. Local modulation is reduced when multiple rows of pixels of the distorted interferogram are merged. In order to find out the actual impact of the distorted interferogram in multiple rows of pixels of interferogram, we simulate different interferograms with local bending of different local bending max offset, in different signal-to-noise ratio and modulation. The result shows that even local modulation is reduced when multiple rows of pixels of the distorted interferogram are merged, but the phase uncertainty of the interferogram will not increase. Therefore, even if the interferogram has defects, multiple rows of pixels can be merged to increase the signal-to-noise ratio and reduce the phase uncertainty. This article may provide a quantitative theoretical reference for the design, processing, and adjustment of the Doppler asymmetric spatial heterodyne. 相似文献
40.
Adelio Matamala‐Vsquez Josep Planelles 《International journal of quantum chemistry》2000,77(4):704-709
A pure algebraic treatment of the eigenvalue equation corresponding to the asymmetric top is presented. The algebraic method employs the Holstein–Primakoff bosonic realization of the angular momentum algebra. Explicit determination of the linear boson transformation coefficients of the eigenstates is carried out by means of the coherent states formalism. No reference to special functions is needed and a completely algebraic approach is achieved. © 2000 John Wiley & Sons, Inc. Int J Quant Chem 77: 704–709, 2000 相似文献