Theoretical Study on the Capillary Force between an Atomic Force Microscope Tip and a Nanoparticle

Considering that capillary force is one of the most important forces between nanoparticles and atomic force microscope （AFM） tips in ambient atmosphere, we develop an analytic approach on the capillary force between an AFM tip and a nanoparticle. The results show that the capillary forces are considerably affected by the geometry of the AFM tip, the humidity of the environment, the vertical distance between the AFM tip and the nanoparticle, as well as the contact angles of the meniscus with an AFM tip and a nanoparticle. It is found that the sharper the AFM tip, the smaller the capillary force. The analyses and results are expected to be helpful for the quantitative imaging and manipulating of nanoparticles by AFMs.     

Simulation of Operating a Cyclic Actuator Based on a Circular Force Element Made of Shape Memory Material

Technical Physics - We consider a linear cyclic unilateral actuator based on a force element made of a material with the shape memory (SM) effect and a return spring. We have developed a model of...     

Design and Fabrication of Integrated-Optic Disk Pickup on LiNbO3 Substrate

An integrated-optic disk pickup device has been realized on a LiNbO3 substrate. The device is constructed by integrating an aplanatic double-convex aspherical waveguide lens (ADCAWL), a twin-grating focusing beam splitter (TGFBS) and two waveguide deflecting prisms (WDP) on a Ti∶LiNbO3 planar waveguide. The design considerations and fabrication of prototype device are summarized.     

Design and Fabrication of Integrated-Optic Disk Pickup on LiNbO_3 Substrate

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The Casimir Force between Parallel Plates in Randall--Sundrum I Model

The Casimir effect for parallel plates within the frame of the five-dimensional Randall-Sundrum model with two branes is re-examined. We argue that the nature of Casimir force is repulsive if the distance between the plates is not extremely tiny, which is not consistent with the experimental phenomena, meaning that the Randall-Sundrum I model can not be acceptable. We also point out that the estimation of the separation between the two branes, by means of Casimir effect for two-parallel-plate system, is not feasible, in contrast to another recent study.     

Analysis of Optical Disk Readout Signal Deterioration Caused by Dust on the Substrate

A noise power spectrum estimation method is presented for optical disk readout signal influenced by dust on the substrate. The noise due to dust has been modeled using geometrical optics and assuming the Poisson distribution for the dust particles. The noise power spectrum consists of two components: one comes from the effect of individual dust particles passing across the light beam, and the other comes from the effect of overlapping area of a particle and the inverted image of another particle. The feasibility of a thin-substrate optical disk was studied using this model. Dust will not have a serious effect on the readout signal when a 0.6 mm-thick substrate is used in place of the conventional 1.2 mm-thick substrate.     

微尺度串列双圆柱绕流的分子动力学并行模拟

本文采用基于空间分解算法的分子动力学并行模拟方法,研究了微尺度、低雷诺数（Re=40）下串列等大的双圆柱绕流现象。结果表明：随着间距比L＊／D＊的增加,流动存在3种特征状态：当L＊／D＊〈1．1时,同单一物体的绕钝体流动相似;当1．1〈L＊／0＊〈3．5时,涡脱落现象只在下游圆柱出现,在两圆柱之间有交替附着于下游圆柱的...     

原子力显微镜的研究型教学实验设计探讨

介绍了原子力显微镜的基本工作原理及其应用,阐述了在大学物理实验课程中开设原子力显微镜有关实验的必要性和重要意义,结合在教学和科研方面的经验,指出了在大学物理实验课中开设原子力显微镜有关实验的设计。最后,以分析半导体薄膜的形貌特性为例,探讨了原子力显微镜在大学物理实验课中的具体应用。     

改进用斜槽做的两个力学实验

研究平抛物体的运动实验，新教材与老教材相比，虽然有两点改进，用坐标纸代替白纸，用铅笔试碰找出小球经过的位置，但是，在桌边做这个实验，坐标原点很难记录准确，在重复实验过程中，很难使木板跟斜槽的相对位置保持不变，用铅笔找小球经过的位置，实验误差较大，实验效果也不尽如     

Influence of the Rotation Frequency of a Disk Substrate Holder on the Crystal Structure Characteristics of MOCVD-Grown GaAs Layers

The influence of the rotation frequency of a disk substrate holder on the growth mechanism and crystal structure characteristics of MOCVD-grown GaAs layers has been studied. In the frequency range of 0–400 rpm, variations have been observed in the growth mechanism and rate, as well as of crystal perfection.     

Capillary Interactions between a Probe Tip and a Nanoparticle

To understand capillary interactions between probe tips and nanoparticles under ambient conditions, a theoretical model of capillary forces between them is developed based on the geometric relations. It is found that the contribution of surface tension force to the total capillary force attains to similar order of magnitude as the capillary pressure force in many cases. It is also shown that the tip shape and the radial distance of the meniscus have great influence on the capillary force. The capillary force decreases with the increasing separation distances, and the variance of the contact angles may change the magnitudes of capillary forces several times at large radial distances. The applicability of the symmetric meniscus approximation is discussed.     

微机在制作圆光栅和编码盘中的应用

才文叙述了在圆光栅、编码盘光刻工艺的基础上,用TP-801单板机控制刻机,实现了任意刻线数、任意编码、不等分分度等各种各样类型的光栅盘、编码盘的动态光刻。     

圆形射流湍流场的大涡模拟研究

使用发展的大涡模拟并行程序,数值模拟了圆形射流湍流场,与实验值进行详细比较,对大涡模拟程序进行检验,并分析网格尺度对计算结果的影响。结果表明,大涡模拟计算的平均速度场和雷诺应力场与实验值符合得非常好,验证了该大涡模拟计算程序的可靠性和精确度。同时发现一阶统计矩受网格尺度影响不大,二阶及高阶矩与网格尺度有较大的关系,因此使用大涡模拟方法计算湍流及湍流燃烧问题应对网格依赖性进行必要分析,至少保证二阶统计矩具有较好的精度。     

Computerized Simulation and Chromatic Adaptation Experiments Based on a Model of Aged Human Lens

Color appearance seen by old people does not significantly differ from that seen by young subjects even though their ocular lens has become more yellow with age. We calculated the age-related change of lights reflected from Munsell color chips onto the retina, and derived results that show that the chromaticity values of all the color chips shifted to the yellow region of the xy-chromaticity diagram. However, a replot on the CIELAB diagram and the estimation by means of the von Kries adaptation model suggests that old people may compensate their color vision using a general chromatic adaptation process. To test this hypothesis, we conducted two experiments: a chromatic adaptation experiment and a color matching experiment to simulate D65-lights as seen by older people but using young subjects. The results indicate that chromatic adaptation does not provide a complete explanation for color compensation by older people, suggesting that an age-related change of the yellow-blue opponent color mechanism may contribute to this compensation.     

弹性基底表面薄膜起皱的计算机模拟

本文设计了一种起皱模型用以研究起皱现象的动态过程.模拟表明整个起皱过程包括三个阶段.在孵化和起皱阶段,水平方向上软基底的应力在回缩过程中传递给硬膜.而在构象松弛平衡阶段,硬膜上的应力又缓慢地传回给软基底,整个起皱过程体系的总能量持续下降.研究发现起皱后软基底上的应力集中在上表层,尤其是在波谷处.而硬膜上的应力分布则取决于方向,在垂直方向,平衡位置的应力要大于波峰和波谷处,与此相反,在水平方向应力则更集中于波峰和波谷.我们的模型既能重现起皱现象,又能重现起皮现象,为材料应力释放导致的结构失稳机理研究提供了一个非常有利的工具.     

Capillary aging of the contacts between glass spheres and a quartz resonator surface

The strength of the contacts between small glass spheres and the surface of a quartz crystal resonator has been probed based on the increase of resonance frequency induced upon sphere contact. The acoustic interaction between the sphere and the plate is modeled as a low-frequency coupled resonance; the dependence of the resonant parameters on overtone order lends support to this model. After exposing the sample to humid air and drying it again, the contact strength increases at least tenfold due to capillary forces--we observe a hysteretic form of the sand-castle effect. Repeated wet-dry cycles reveal logarithmic capillary aging with time. The experiments suggest that the drying of the liquid bridges leads to a contraction of small voids in the contact zone, subsequently increasing cohesion.     

Stability of an Isothermal Disk with Three-Dimensional Magnetic Fields and Radial Viscous Force

The stability of an isothermal thin disk with three-dimensional magnetic fields and radial viscous force is examined in this paper. We find that the radial viscous force has no influence on the stability of viscous modes. But there is more influence on the stability of magneto-acoustic modes, which is related to the perturbation wavelength and different parts of disk. Finally, we use our model to explain the long-term variability of Quasar 3C345.     

Lattice Boltzmann Simulation of the Cross Flow Over a Cantilevered and Longitudinally Vibrating Circular Cylinder

The multiple-relaxation-time lattice Boltzmann method （MRT-LBM） is implemented to numerically simulate the cross flow over a longitudinal vibrating circular cylinder. This research is carried out on a three-dimensional （3D） finite cantilevered cylinder to investigate the effect of forced vibration on the wake characteristics and the 3D effect of a cantilevered cylinder. To meet the accuracy of this method, the present calculation is carried out at a low Reynolds number Re =100, as well as to make the vibration obvious, we make the vibration strong enough. The calculation results indicate that the vibration has significant influence on the wake characteristics. When the vibrating is big enough, our early works show that the 2D vortex shedding would be locked up by vibration. Contrarily, this phenomenon would not appear in the present 3D case because of the end effect of the cantilevered cylinder.     

Self-Assembling Process of Colloidal Particles into Two-Dimensional Arrays Induced by Capillary Immersion Force: A Simulation Study With Discrete Element Method

This paper presents a simulation study for self-assembling process of colloidal particles into two-dimensional arrays due to capillary immersion force. Discrete element method is used to simulate the dynamics of colloidal particles trapped in a thin liquid film. The previous model is improved in the following two points: a modification of the screening effect of capillary immersion force and introduction of periodic boundary condition. Snapshots provided by the simulations agree well with experimental images taken by atomic force microscopy. The self-assembling process is quantified with pair correlation function and coordination number. At lower coverage, colloidal particles rapidly form small clusters that consist of several particles in the early stage. Subsequently, chain-like structures with some branches are mainly generated. On the other hand, at higher coverage, large domains of hexagonal close-packed (HCP) structures are gradually generated. The rate of the growth of HCP domains is much slower than that of the generation of the small clusters and the chain-like structures.