Synthesis and liquid crystalline properties of novel compounds containing a 3‐fluoro‐4‐cyanophenoxy group

A series of novel compounds containing a 3‐fluoro‐4‐cyanophenoxy group were synthesized and fully characterized by IR and ¹H NMR, and their mesomorphic properties were studied. Seven compounds exhibited enantiotropic nematic phases and three compounds exhibited monotropic nematic phases, as confirmed by differential scanning calorimetry and polarizing optical microscopy. Selected properties of the liquid crystalline compounds synthesized were calculated by ab initio methods at a HF/6‐31G level. The bond lengths, bond angles and dihedral angles of the fragments with the same structure change little between the compounds. All the compounds with a terminal alkoxy chain approached a planar structure.     

两种物理气相沉积氮化钛涂层的结构及摩擦性能研究

分别利用磁过滤阴极弧等离子体沉积装置和直流磁控溅射装置在不锈钢基底上制备了 Ti N涂层 ,采用 X射线光电子能谱仪、X射线衍射仪和扫描电子显微镜对涂层的结构及形貌进行了表征 ;利用纳米压痕仪测定了涂层的硬度 ;在 DF- PM型动摩擦系数精密测定仪上考察了涂层的摩擦学性能 .结果表明 :与采用直流磁控溅射法在 40 0℃基底上制备的 Ti N涂层相比 ,采用磁过滤沉积装置在室温下制备的 Ti N涂层更加致密 ,表面平滑 ,最大硬度达 3 5 GPa,摩擦系数明显较小 ( 0 .1～ 0 .4) ,耐磨性较好     

高阶紧致格式求解二维粘性不可压缩复杂流场

提出了一种求解二维不可压缩复杂流场的高精度算法．控制方程为原始变量、压力Ｐｏｉｓｓｏｎ方程提法．在任意曲线坐标下，采用四阶紧致格式求解Ｎａｖｉｅｒ－Ｓｔｏｋｅｓ方程组，时间推进采用交替方向隐式（ＡＤＩ）格式，在非交错网格上用松弛法求解压力Ｐｏｉｓｓｏｎ方程．对于复杂的流场，采用了区域分解方法，并在每一时间步对各子域实施松弛迭代使之能精确地反映非定常流场．利用该算法计算了二维受驱空腔流动，弯管流动和垂直平板的突然起动问题．计算结果与实验结果和其他研究者的计算结果相比较吻合良好．对于平板起动流动，成功地模拟了流场中旋涡的生成以及Ｋａｒｍａｎ涡街的形成     

液体晃动等效力学模型的参数识别

本文研究确定贮箱内液体晃动等效力学模型的参数的试验方法。通过对充液贮箱试验系统的简化分析得到系统的传递函数表达式,应用频响函数拟合方法得到了模型参数,在曲线拟合过程中利用权函数解决液体晃动的非线性影响因素。应用本文所述方法研究了某型号卫星推进剂贮箱的液体晃动问题。     

基于行波型超声马达的超声波振动减摩试验研究

提出了行波型超声马达振动减摩的几何模型,采用电磁电机驱动、电磁电机结合一路驻波振动驱动及行波型超声马达驱动3种驱动方式模拟行波型超声马达摩擦驱动特点,借助超声马达摩擦特性模拟试验装置,引入摩擦系数降低率的概念,研究了电机转速、预压力、超声波激励电压和摩擦材料等对定、转子摩擦副摩擦系数的影响.结果表明:在较高相对滑动速度、小预压力及大振幅条件下,超声波振动减摩现象显著.     

垂直下降管中两相流的流型以及液相粘度对流型的影响

对空气－油在垂直下降管中的流型进行了实验研究，采用的管径为２９ｍｍ，油和空气的折算流速分别达到４ｍ／ｓ和２０ｍ／ｓ，并借助于压降脉动分析和目测观察相结合的方法来进行流型的识别。研究表明，油气两相流的流型不同于低粘液体的两相流流动，通过实验研究并结合前人的研究成果，给出了液相粘度对流型转变的影响趋势。     

具有非广延分布电子的碰撞等离子体磁鞘的结构

很多关于等离子体鞘层的研究工作都是基于电子满足经典的麦克斯韦速度分布函数,而等离子体中的粒子具有长程电磁相互作用,使用Tsallis提出的非广延分布来描述电子更为恰当.本文建立一个具有非广延分布电子的碰撞等离子体磁鞘模型,理论推导出受非广延参数q影响的玻姆判据,离子马赫数的下限数值会随着参数q的增大而减小.经过数值模拟,发现与具有麦克斯韦分布(q=1)电子的碰撞等离子体磁鞘对比,具有超广延分布(q<1)和亚广延分布(q>1)电子的碰撞等离子体磁鞘的结构各有不同,包括空间电势分布、离子电子密度分布、空间电荷密度分布.模拟结果显示非广延分布的参数q对碰撞等离子体磁鞘的结构具有不可忽略的影响.希望这些结论对相关的天体物理、等离子体边界问题的研究有参考价值.     

Analysis of Glasses Coated with Zn–Cr–Sn–O Thin Films by Picosecond Laser-Induced Breakdown Spectroscopy and Transmission Spectroscopy

Journal of Applied Spectroscopy - Glasses coated with different thin fi lm layers exhibit different optical properties. Thus, ZnO thin films with Sn and Cr admixture (ZCTO) were deposited on the...     

Rubbing angle effect on in‐plane switching liquid crystal displays

The rubbing angle effect on transmissive in‐plane switching liquid crystal displays is analysed by the Jones matrix method. Simulation results show that the optimum rubbing angle is around 30°–40°; the cell gap/birefringence product (dΔn) is about 0.33 µm. Increasing the rubbing angle can shorten the rise time and enlarge the grey scale voltage intervals. The optical characteristics are similar in two cells with different rubbing angles. These effects are particularly attractive for liquid crystal TV applications.     

Numerical approach for quantification of epistemic uncertainty

In the field of uncertainty quantification, uncertainty in the governing equations may assume two forms: aleatory uncertainty and epistemic uncertainty. Aleatory uncertainty can be characterised by known probability distributions whilst epistemic uncertainty arises from a lack of knowledge of probabilistic information. While extensive research efforts have been devoted to the numerical treatment of aleatory uncertainty, little attention has been given to the quantification of epistemic uncertainty. In this paper, we propose a numerical framework for quantification of epistemic uncertainty. The proposed methodology does not require any probabilistic information on uncertain input parameters. The method only necessitates an estimate of the range of the uncertain variables that encapsulates the true range of the input variables with overwhelming probability. To quantify the epistemic uncertainty, we solve an encapsulation problem, which is a solution to the original governing equations defined on the estimated range of the input variables. We discuss solution strategies for solving the encapsulation problem and the sufficient conditions under which the numerical solution can serve as a good estimator for capturing the effects of the epistemic uncertainty. In the case where probability distributions of the epistemic variables become known a posteriori, we can use the information to post-process the solution and evaluate solution statistics. Convergence results are also established for such cases, along with strategies for dealing with mixed aleatory and epistemic uncertainty. Several numerical examples are presented to demonstrate the procedure and properties of the proposed methodology.