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排序方式: 共有263条查询结果,搜索用时 15 毫秒
41.
42.
Yifan Wang Mingjun Zhong Jie Li Hao Tang Richard Berndt Yajie Zhang Shimin Hou Yongfeng Wang 《中国化学快报》2022,33(2):1074-1076
Geometries of molecule-molecule interfaces strongly influence the current passing from one molecule to another. The contact conductance of molecule-molecule junctions which consist of fullerene and tin phthalocyanine molecules is investigated with a low-temperature scanning tunneling microscope. Two types of molecules are deposited onto Cu(111). Fullerene molecules are transferred to tips through controlled contact of STM tips on molecules. The molecule-molecule junctions are formed by approachi... 相似文献
43.
结合特殊的镀金聚酯薄膜表面的粗糙度和半球反射率,依据基尔霍夫近似及粗糙面脉冲散射互相关函数,数值计算了脉冲激光(1.06 μm)在不同入射角照射下该材料薄膜双频互相关散射截面随相干带宽频差和散射角的变化情况。并给出δ脉冲和高斯脉冲波入射下,其散射功率随时间和散射角的波形分布。计算结果表明:该薄膜材料激光双频互相关散射截面在镜反射方向有最大的散射峰值,在非镜反射方向上,其散射值随相干带宽频差的增大迅速减小,当窄脉冲垂直入射时,粗糙面散射功率展宽现象明显。 相似文献
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45.
以 4 ,4′ (α ,ω 烷亚甲基二酰氧 )二苯甲醛和二氨基二苯并 14 冠 4为单体 ,采用溶液缩聚方法 ,首次合成了一类新的含冠醚环的席夫碱型液晶高分子 .一种单体采用脂族二酰氯和对羟基苯甲醛反应制备 ,另一种新的单体采用二硝基二苯并 14 冠 4 ,在钯 碳催化剂存在下 ,水合肼还原制备 .通过1H NMR、13 C NMR和分子力学计算方法研究了二氨基二苯并 14 冠 4的两种异构体的空间立体结构 ,发现能从1H NMR谱图上区分它们的立体结构 .它们的立体结构近似属于Cs 和C2 群 .聚合物的分子量不高 ,Mn 在 130 0 0~ 2 4 0 0 0之间 .单体的结构通过元素分析、IR、1H NMR和MS等方法确证 .聚合物的性质采用GPC、DSC、TG和POM等方法进行了研究 .发现所有的聚合物加热到各自的熔融温度 (Tm)以上都能形成液晶态 ,在液晶态可以观察到向列相的丝状织构和纹影织构 .聚合物的玻璃化转变温度 (Tg)、熔融温度和各向同性温度 (Ti)随聚合物分子中柔性间隔基的变化而变化 ,它们有较高的清亮点温度和宽的液晶态温度范围 .WAXD的研究进一步证实了聚合物的液晶性 相似文献
46.
Jianyuan Tang Lei Wang Gang Liu Yan Liu Yazhuo Hou Wenxiang Zhang Mingjun Jia Werner R. Thiel 《Journal of molecular catalysis. A, Chemical》2009,313(1-2):31-37
A hybrid mesoporous SBA-15 material (2a) containing an oxodiperoxo tungsten complex of the type [WO(O2)2L] (L = pyrazolylpyridine) was synthesized by a post-grafting route. The organic–inorganic hybrid catalyst was characterized by means of XRD, N2 adsorption–desorption and FT-IR. The catalytic property of 2a in the epoxidation of cyclooctene with H2O2 as the oxidant was investigated in comparison with other three kinds of hybrid tungsten containing SBA-15 materials bearing ethylenediamine, imidazole or 4,4′-bipyridine ligands. It was found that all oxodiperoxo tungsten catalysts were active at the reaction temperature of 55 °C with CH3CN as solvent. However, only the catalyst with the pyrazolylpyridine ligand showed good recoverability and relatively high stability against leaching of active tungsten species. Moreover, this catalyst showed very high efficiency for H2O2 utilization, and its catalytic activity could be further improved by using solvent mixtures of CH3CN and CH3COOH. 相似文献
47.
对流扩散方程QUICK格式的数值摄动高精度重构格式 总被引:2,自引:1,他引:1
利用高智提出的数值摄动算法, 把对流扩散方程的常用QUICK格式(黏性和对流项分别用二阶中心和QUICK格式离散)进行了高精度重构, 包括利用离散单元内所有结点的全域重构和分别利用离散单元内上下游结点的上下游重构, 得到两类新的更高阶精度的数值摄动重构格式, 称为高的QUICK格式(G-QUICK格式). G-QUICK格式与QUICK格式相比简单性相当, 但精度更高; 全域重构G-QUICK格式和QUICK格式均为条件稳定, 上下游重构得到一些绝对稳定的G-QUICK格式. 解析分析和数值算例均证实了G-QUICK格式的优良性能, 上下游重构的G-QUICK格式为在对流扩散方程的QUICK格式中避免使用人工黏性提供了新途径. 相似文献
48.
A Numerical Study of Jet Propulsion of an Oblate Jellyfish Using a Momentum Exchange-Based Immersed Boundary-Lattice Boltzmann Method 下载免费PDF全文
Hai-Zhuan Yuan Shi Shu Xiao-Dong Niu Mingjun Li & Yang Hu 《advances in applied mathematics and mechanics.》2014,6(3):307-326
In present paper, the locomotion of an oblate jellyfish is numerically
investigated by using a momentum exchange-based immersed boundary-Lattice
Boltzmann method based on a dynamic model describing the oblate jellyfish.
The present investigation is agreed fairly well with the previous experimental
works. The Reynolds number and the mass density of the jellyfish are found to
have significant effects on the locomotion of the oblate jellyfish. Increasing
Reynolds number, the motion frequency of the jellyfish becomes slow due to the
reduced work done for the pulsations, and decreases and increases before and
after the mass density ratio of the jellyfish to the carried fluid is 0.1. The
total work increases rapidly at small mass density ratios and slowly increases
to a constant value at large mass density ratio. Moreover, as mass density ratio
increases, the maximum forward velocity significantly reduces in the contraction
stage, while the minimum forward velocity increases in the relaxation stage. 相似文献
49.
The far-field noise radiated from mixing layers is determined by the near-field flow dynamics which is sensitive to the initial perturbation of instability introduced physically or numerically. This study focuses on the effects of the phase delay in two initial perturbations, one at the fundamental wave number and the other at its subharmonic both calculated from linear instability analysis, on the sound generation in mixing layers. When different phase delays φ1 changing from zero to 2π is applied on the fundamental mode, we observe different vortex merging processes (e.g. vortex pairing or tearing). The strong nonlinear interaction in the merging process generates most of the noise from mixing layers. There shows a pattern in a period of 2π for the response of far-field sound to the change of φ1. Similar effects on the dynamics and acoustics can be achieved by adding different phase delays φ2 to the subharmonic mode instead, however, the response repeats in a period of only π for φ2. The effects of the combination of different phase delays to other parameters, including the amplitude and wave number for each perturbations, are also investigated. All the results indicate a critical role of nonlinearity in the sound generation mechanism of mixing layers. 相似文献
50.
Based on the Zufiria theoretical model, a new model regarding the asymptotic bubble velocity for the Rayleigh-Taylor (RT) instability is presented by use of the complex velocity potential proposed by Sohn. The proposed model is an extension of the ordinary Zufiria model and can deal with non-ideal fluids. With the control variable method, the effect of the viscosity and surface tension on the bubble growth rate of the RT instability is studied. The result is consistent with Cao’s result if we only consider the viscous effect and with Xia’s result if we only consider the surface tension effect. The asymptotic bubble velocity predicted by the Zufiria model is smaller than that predicted by the Layzer model, and the result from the Zufiria model is much closer to White’s experimental data. 相似文献