Tuning The Geometrical Parameters Of Biomimetic Fibrillar Structures To Enhance Adhesion

Fibrillar structures are common features on the feet of many animals, such as geckos, spiders and flies. Theoretical analyses often use periodical array to simulate the assembly, and each fibril is assumed to be of equal load sharing (ELS). On the other hand, studies on a single fibril show that the adhesive interface is flaw insensitive when the size of the fibril is not larger than a critical one. In this paper, the Dugdale Barenblatt model has been used to study the conditions of ELS and how to enhance adhesion by tuning the geometrical parameters in fibrillar structures. Different configurations in an array of fibres are considered, such as line array, square and hexagonal patterns. It is found that in order to satisfy flaw-insensitivity and ELS conditions, the number of fibrils and the pull-off force of the fibrillar interface depend significantly on the fibre separation, the interface interacting energy, the effective range of cohesive interaction and the radius of fibrils. Proper tuning of the geometrical parameters will enhance the pull-off force of the fibrillar structures. This study may suggest possible methods to design strong adhesion devices for engineering applications.

关于三维Navier－Stokes方程的粘性项计算

借助于张量分析和张量计算，在贴体曲线坐标系下本文讨论了不同求解变量导致了粘性项个数上的重大差异和不同大小的计算量，并提出了便于粘性计算的最佳形式。文中借助于有限体积离散技术，通过引进两个对称辅助矩阵［Ａ］和［Ｂ］，使粘性项的计算量大大减少，这对完成三维粘性流的数值计算具有重要的指导意义。借助于上述方法，本文完成了某型真实进气道两种工况的三维粘性Ｎａｖｉｅｒ－Ｓｔｏｋｅｓ方程计算（即Ｍ∞＝３．０，α＝０°和设计工况Ｍ∞＝２．６５，α＝０°），获得了满意的全场结果；对于Ｍ∞＝２．６５的设计工况，同实验数据作了比较，符合良好。由于本文的方法明显的减少了粘性项的计算量且节省了大量内存，以致于使三维流场的Ｎ－Ｓ求解能在普通微机上进行。

Molecular dynamics simulations of DFZ

Dislocation emission from the crack tip in copper under mode II loading is simulated with molecular dynamics method. After 26 partial dislocations are emitted and then relaxed to reach the equilibrium under the constant displacement, the double pile-ups (including an inverse pile-up and a pile-up) are formed. i.e., the first dislocation is piled up before the obstruction, and the last dislocation is piled up ahead of the crack tip. These results conform to the TEM observations.

对Rensch计算谐振腔中场分布差分法的校正

用校正的Rensch差分法计算了Gerry的GDL器件中的场分布,结果与Rensch的计算很好地相符,并已将它用于较广的耦合度范围。因而,为什么不稳定腔输出功率只有稳定腔的一半的问题能更确切地解释为所用耦合度远大于最佳值。

微槽道气体流动的统计模拟

利用基于分子模型的统计模拟方法-信息保存方法（IP）统计模拟了实验条件下微槽道气体流动，仔细讨论了用IP方法模拟长槽道稀薄气流时遇到的问题，并给出了解决的方法，即采取守恒形式的控制方法避免质量流量计算误差积累，并利用超松弛方法使收敛过程加速。将IP计算结果与压力分布和质量流量实验数据进行了比较。

Controllable group velocity of the probe light in a Lambda-type system with two fold levels

The group velocities of the probe laser field are studied in a A-type system where one lower state has two fold levels coupled by a control field. It is found that the interaction of double dark states leads to controllable group velocity of the probe field in this system. It can be easily realized, due to the interacting double dark resonances, that one of the group velocities at transparency positions is much slower than the other by tuning the control field to be off resonance. In particular, when the control field is on resonance. we can obtain two equal slow group velocities with a broader EIT width, which provides potential applications in quantum storage and retrieval of light. (c) 2005 Elsevier B.V. All rights reserved.

Effect of plasma temperature on electrostatic shock generation and ion acceleration by laser

The effect of plasma temperature on electrostatic shock generated by a circularly polarized laser pulse in overdense plasma is studied by particle-in-cell simulation. Ion reflection and transmission in the collisionless electrostatic shock (CES) are investigated analytically. As the initial ion temperature is varied, a distinct transition from the laser-driven piston scenario with all ions being reflected to the CES scenario with partial ion reflection is found. The results show that at low but finite temperatures the ions are much more accelerated than if they were cold.

中国古代玻璃的起源--中国最早的古代玻璃研究

研究了西汉（公元前200年）以前不同地区的最早的中国古代玻璃．古玻璃样品出土于新疆维吾尔自治区、湖北省、湖南省、四川省、云南省、广东省和贵州省等地．用质子激发X光荧光技术、能量分散X光荧光技术和电感耦合等离子发射光谱等方法测定了玻璃的化学成分．这些古玻璃样品的化学成分属于以下玻璃系统：Na2O（K2O）-CaO—SiO2（K2O：Na2O〈1），K2O（Na2O）-CaO—SiO2（K2O：Na2O〉1），K2O—SiO2和BaO—PbO—SiO2．从考古和历史学观点讨论了这些最早的中国古代玻璃的起源，指