红外半导体激光光镊的实验研究

激光光镊技术是一项在许多科学领域有广阔应用前景的技术。本文详细给出构建一台红外半导体激光光镊的设计思想及实例。由于采用了独特的对大功率多模红外激光选模整形和双透镜陷阱操纵技术等性能价格最优化选择 ,该系统易于构建 ,陷阱操作方便 ,其构建价格仅一般光镊的几十分之一 ,非常适合光镊技术的推广和一般实验室构建     

对米氏粒子轴向光阱力与横向光阱力的测量研究

基于几何光学原理,在强聚焦激光光场中,以射线光学计算模型为基础,对几何尺寸远大于光波长的米氏球状粒子所受的轴向与横向光阱力进行计算.并在给定参数条件下,进行数值仿真,讨论各主要参数与光阱力的关系.     

V型弯曲件回弹规律的有限元分析

以V型件弯曲和回弹过程为分析研究对象，通过对V型件弯曲及回弹过程的有限元数值模拟，分析获得了成形参数对V型件弯曲回弹的影响规律。结果表明：回弹角随弯曲角及材料的硬化系数的增大而增大，随材料的变形程度及硬化指数的增大而减小。     

3-D manipulation of millimeter- and micro-sized objects using an acoustically excited oscillating bubble

This communication describes novel 3-D manipulations of objects using an acoustically excited oscillating bubble deposited on a hydrophobic rod tip. The oscillating bubble captures various millimeter- and micron-sized neighboring objects including glass and polystyrene beads (~100 μm), fish egg, and live water flea (~1 mm). The captured objects are carried in a 3-D space by traversing the bubble tip, and released at desired positions by simply turning off the oscillation. Carrying performance is characterized along with high-speed imaging of oscillating bubbles by varying the frequency and amplitude of the acoustic excitation and the carrying speed. The higher the oscillation amplitude, the higher the carrying efficiency. The maximum carrying speed is measured at over 3 mm/s. This method is effective with a low-level acoustic excitation (bubble oscillation amplitude relative to the diameter ≤5%), possibly providing a cost-effective, soft-contact manipulating tool for handling biological objects.     

Influence of edge velocity on flame front position and displacement speed in turbulent premixed combustion

Using a novel concept, the present study experimentally investigates underlying physics pertaining to statistics of the flame front position and the flame front velocity in turbulent premixed V-shaped flames. The concept is associated with characteristics of the reactants velocity at the vicinity of the flame front, referred to as the edge velocity. The experiments are performed using simultaneous Mie scattering and Particle Image Velocimetry techniques. Three mean streamwise exit velocities of: 4.0, 6.2, and 8.6 m/s along with three fuel–air equivalence ratios of: 0.7, 0.8, and 0.9 are examined. The results show that fluctuations of the flame front position and the flame front velocity are induced by the fluctuations of the component of the edge velocity transverse to the mean flow direction. Analysis of the results show that the mean of the flame front velocity in the normal direction to the flame front is significantly dependent on the vertical distance from the flame-holder. Relatively close to the flame-holder, the mean of the flame front velocity in the direction normal to the flame front is about zero; however, it increases to values several times larger than the laminar flame speed by increasing the vertical distance from the flame-holder.     

Sugar-Pucker Force-Induced Transition in Single-Stranded DNA

The accurate knowledge of the elastic properties of single-stranded DNA (ssDNA) is key to characterize the thermodynamics of molecular reactions that are studied by force spectroscopy methods where DNA is mechanically unfolded. Examples range from DNA hybridization, DNA ligand binding, DNA unwinding by helicases, etc. To date, ssDNA elasticity has been studied with different methods in molecules of varying sequence and contour length. A dispersion of results has been reported and the value of the persistence length has been found to be larger for shorter ssDNA molecules. We carried out pulling experiments with optical tweezers to characterize the elastic response of ssDNA over three orders of magnitude in length (60–14 k bases). By fitting the force-extension curves (FECs) to the Worm-Like Chain model we confirmed the above trend:the persistence length nearly doubles for the shortest molecule (60 b) with respect to the longest one (14 kb). We demonstrate that the observed trend is due to the different force regimes fitted for long and short molecules, which translates into two distinct elastic regimes at low and high forces. We interpret this behavior in terms of a force-induced sugar pucker conformational transition (C3′-endo to C2′-endo) upon pulling ssDNA.     

The influence of lateral forces on the cell stiffness measurement by optical tweezers vertical indentation

We studied the lateral forces arising during the vertical indentation of the cell membrane by an optically trapped microbead, using back focal plane interferometry to determine force components in all directions. We analyzed the cell-microbead interaction and showed that indeed the force had also lateral components. Using the Hertz model, we calculated and compared the elastic moduli resulting from the total and vertical forces, showing that the differences are important and the total force should be considered. To confirm our results we analyzed cells from two breast cancer cell lines: MDA-MB-231 and HBL-100, known to have different cancer aggressiveness and hence stiffness.     

激光微束对球状介质粒子光阱力的计算与仿真分析

基于几何光学原理,以射线光学计算模型为基础,对几何尺寸远大于光波长的米氏球状粒子所受轴向光阱力进行了计算。在给定参量条件下,进行了数值仿真,并根据仿真结果,讨论了光束束腰半径、相对折射率、激光波长及功率等系统主要参量与光阱品质特性的关系。这些参量都是由显微镜和其他一些光学部件的特性所决定的。针对不同介质粒子合理选择上述参量,以得到较大光阱力和光阱刚度。这些仿真结果为各仪器参量的选择提供了理论依据。     

阵列光镊的发展

介绍了光镊的原理及近年来发展起来的各种阵列光镊技术,探讨了阵列光镊技术在不同学科领域的应用.