On the Nano/Micro-Mechanics of Metallic Glass

Metallic glass (MG) is amorphous and has some outstanding properties such as ultrahigh strength, superior elasticity, and excellent thermo-plasticity. However, as MG is relatively new to the metal family, the relationship between its physical properties and amorphous structure is still unclear. This article aims to provide an insightful discussion through a comprehensive review about the investigations in the past few decades on the scientific mechanisms of this class of material. The discussion of the paper will include the following key aspects: (1) the formation mechanism of an amorphous structure through glass transition, (2) the structural characterization and models, (3) the micromechanics of plastic event and shear band, and (4) the correlation between the amorphous structure and its mechanical properties.     

Adaptive nematic liquid crystal lens array with resistive layer

ABSTRACT

We propose an adaptive nematic liquid crystal (LC) lens array using a dielectric layer with low dielectric constant as resistive layer. With the resistive layer and periodic-arranged iridium tin oxide (ITO) electrodes, the vertical electric field across the LC layer varies linearly over the lens aperture is obtained in the voltage-on state. As a result, a centrosymmetric gradient refractive index profile within the LC layer is generated, which causes the focusing behaviour. As a result of the optimisation, a thin cell gap which greatly reduces the switching time of the LC lens array can be achieved in our design. The main advantages of the proposed LC lens array are in the comparatively low operating voltage, the flat substrate surface, the simple electrodes, and the uniform LC cell gap. The simulation results show that the focal length of the LC lens array can be tuned continuously from infinity to 3.99 mm by changing the applied voltage.     

CRISPR-Cas System for RNA Detection and Imaging

The system of clustered regularly interspaced short palindromic repeats(CRISPR)and CRISPR-associated endonucleases(Cas)have been widely used in gene editing,disease treatment,molecular diagnosis and chromosome imaging.On account of the programmable target recognition of CRISPR-Cas system and the specific targeting function toward RNA of type Ⅵ class Ⅱ Cas proteins,CRISPR-Cas system has been deployed as RNA recognition and detection tools,exhibiting promising application potentials in the field of RNA detection and imaging.In this review,we summarize the latest research progresses as well as development prospects of CRISPR-Cas system in RNA diagnosis and live cell RNA imaging.     

一种弹体入水冲击波阴影成像可视化系统及其试验研究

扩大成像视野对于开展充水容器中弹体入水冲击波传播及弥散方面的可视化研究具有重要的实际意义。阴影成像技术适用于大视野实验,且对流场冲击波和扰动的可视化研究具有简单性和通用性,其中直接阴影成像最为简单,但可靠点光源的缺乏是阻碍其发展应用的瓶颈。因此基于国产短弧氙灯管,自制了短弧氙灯点光源,根据阴影成像原理,设计出一种弹体入水冲击波阴影成像可视化系统,详细介绍了其组成和运行原理。利用该系统对高速弹体入水进行了试验研究,获得了弹体入水冲击波的阴影成像和冲击波信号的压力时程曲线,通过阴影成像和冲击波信号相结合分析了弹体入水冲击波的传播特性,并进行了理论验证。结果表明:该弹体入水冲击波阴影成像可视化系统具有可靠性和设计的合理性。弹体高速入水后,初始冲击波的强度最大,随着冲击波的传播,冲击波强度逐渐降低,水中冲击波的传播速度不断降低,球形冲击波的半径逐渐增大。     

Exact Solutions to Short Pulse Equation

In this paper, dependent and independent variable transformations are introduced to solve the short pulse equation. It is shown that different kinds of solutions can be obtained to the short pulse equation.     

Short Tm3+-doped fiber lasers with watt-level output near 2 μm

High-power operation of diode-pumped fiber lasers at wavelength near 2μm are demonstrated with short length of heavily Tm3 -doped silica glass fibers. With 7-cm long fiber, a laser at near 2 μm is obtained with the threshold of 135 mW, maximum output power of 1.09 W, and slope efficiency of 9.6% with respect to the launched power from a laser diode at 790 nm. The output stability of this fiber laser is within 5%.The dependence of the performance of fiber lasers on the operation temperature and cavity configuration parameters is also investigated.     

Harmonic operation of high gain harmonic generation free electron laser

In high gain harmonic generation (HGHG) free electron laser (FEL), with the right choice of parameters of the modulator undulator, the dispersive section and the seed laser, one may make the spatial bunching of the electron beam density distribution correspond to one of the harmonic frequencies of the radiator radiation, instead of the fundamental frequency of the radiator radiation in conventional HGHG, thus the radiator undulator is in harmonic operation (HO) mode. In this paper, we investigate HO of HGHG FEL.Theoretical analyses with universal method are derived and numerical simulations in ultraviolet and deep ultraviolet spectral regions are given. It shows that the power of the 3rd harmonic radiation in the HO of HGHG may be as high as 18.5% of the fundamental power level. Thus HO of HGHG FEL may obtain short wavelength by using lower beam energy.     

On Short Time Asymptotic Behavior of Some Symmetric Diffusions on General State Spaces

For conservative symmetric diffusions on a general state space (X,m), the short time asymptotic behavior of tlog _X 1 _A T _t 1 _B dm is investigated, where T _t is the associated semigroup and A and B are measurable subsets of X. It is proved that the superior limit is dominated by the inferior limit up to some absolute constant. When ₂ of the associated Dirichlet form is lower bounded, it is shown that the limit exists for any A and B, and is described by the intrinsic metric between them. Applications to infinite-dimensional spaces and fractals are given.     

利用射线追踪法研究超短外腔半导体激光器的输出特性

基于射线追踪法，推导了外腔半导体激光器的连续输出谱的隐函表达式.在此基础上，结合载流子速率方程，对超短外腔半导体激光器的输出谱及P-I特性进行了研究.结果表明：当外腔长度发生波长量级的变化时，超短外腔激光器的P-I特性将发生显著变化；随着外腔长度的变化，超短外腔激光器的激射波长在10nm范围内呈周期性跳变，当外腔长度介于40μm—70μm范围内，激射波长跳变范围最大.理论模拟结果与实验报道结果符合.