Short-focus nematic liquid crystal microlens array with a dielectric layer

ABSTRACT

A short-focus microlens array using dielectric layer and inhomogeneous electric field over a homogeneous nematic liquid crystal (LC) layer is proposed. The top substrate has a planar indium tin oxide (ITO) electrode which is coated on the inner surface. The bottom substrate has strip ITO electrodes which are embedded in the dielectric layers. The inhomogeneous electric field generates a required gradient refractive index profile within the LC layer which, in turn, causes the focusing effect. Due to the thinner LC layer (15 μm), the spherical aberration should be negligible. Moreover, the fabrication process of the proposed microlens array can be easily carried out because of the layer-by-layer configuration. The simulation results show that the focal length of the LC microlens can be continuously tuned from infinity to 0.988 mm with the change of applied voltage.     

扫描电化学显微镜直接电沉积法构建葡萄糖氧化酶微米点

利用自制的凹形电极在铂基底电极上直接构建了葡萄糖氧化酶微米点. 首先, 将电聚合和电化学刻蚀法相结合制备了凹形铂微米电极. 然后将此种电极作为参比及辅助电极, 基底铂电极作为工作电极, 利用葡萄糖氧化酶在合适的条件下(浓度、一定量Triton X-100存在、电极电位等)由于电极表面pH的降低可以在铂电极上电沉积这一特性, 将酶固定在铂基底电极上, 微修饰得到了具有活性的葡萄糖氧化酶微米点. 最终用扫描电子显微镜和扫描电化学显微镜对所得微米点进行了表征. 所得微米点直径约20 μm, 且具有催化活性. 该方法简便, 干扰因素较少.     

一类凹与凸算子的推广

运用锥的性质以及单调迭代技巧给出了一类广义凹算子与凸算子正不动点的存在唯一性,并讨论了算子特征值方程的性质.作为应用,利用所获结果研究了一类积分方程正解的存在唯一性.     

凹角区域双曲外问题的精确人工边界条件

研究一类凹角区域双曲型外问题的数值方法.先用Newmark方法对时间进行离散化,在每个时间步求解一个椭圆外问题.然后引入人工边界,并获得精确的人工边界条件.给出半离散化问题的变分问题,证明了变分问题的适定性,并给出了误差估计.最后给出数值例子,以示该方法的可行性与有效性.     

基于标量衍射理论下的球面折射微透镜对高斯光束的准直研究

本文应用瑞利-索末菲标量衍射理论分析了具有球面轮廓的折射微透镜对激光器输出高斯光束的准直特性.数值结果显示,在最佳准直条件下,高斯光束经过球面折射微透镜准直后的传输是一个振荡过程;同时,如果不考虑微透镜的衍射效率,当球面折射微透镜的F数越大,高斯光束经过准直变换后的远场发散角越小.     

H-空间中新的非紧极大极小定理、截口定理及非空交定理

本文在无线性结构Ｈ－空间的框架之下给出一个新的ｖｏｎ Ｎｅｕｍａｎｎ型非紧极大极小定理，并且作为其应用而得到一个新的Ｋｙ Ｆａｎ型截口定理和一个新的非空交定理．结果即使在欧几里得空间中也是全新的     

LES of spatially developing turbulent boundary layer over a concave surface

We revisit the problem of a spatially developing turbulent boundary layer over a concave surface. Unlike previous investigations, we simulate the combined effects of streamline curvature as well as curvature-induced pressure gradients on the turbulence. Our focus is on investigating the response of the turbulent boundary layer to the sudden onset of curvature and the destabilising influence of concave surface in the presence of pressure gradients. This is of interest for evaluating the turbulence closure models. At the beginning of the curve, the momentum thickness Reynolds number is 1520 and the ratio of the boundary layer thickness to the radius of curvature is δ₀/R = 0.055. The radial profiles of the mean velocity and turbulence statistics at different locations along the concave surface are presented. Our recently proposed curvature-corrected Reynolds Averaged Navier-Stokes (RANS) model is assessed in an a posteriori sense and the improvements obtained over the base model are reported. From the large Eddy simulation (LES) results, it was found that the maximum influence of concave curvature is on the wall-normal component of the Reynolds stress. The budgets of wall-normal Reynolds stress also confirmed this observation. At the onset of curvature, the effect of adverse pressure gradient is found to be predominant. This decreases the skin friction levels below that in the flat section.