Two-dimensional measurements of laser-induced breakdown in air by high-speed two-frame shadowgraphy

We present two-dimensional measurements of the laser-induced plasma development and shock wave evolution in air. The breakdown is induced by a Q-switched Nd:YAG laser (λ=1064 nm) with a pulse duration of 4 ns. To study these fast laser-induced phenomena, we have developed a high-speed, two frame shadowgraph method. It enables 2D visualization of a laser-induced event in two time instances, which are delayed by an arbitrary time interval in the range from 300 ps to 30 ns. The established method is based on 30 ps, green (λ=532 nm), and linearly polarized laser pulse, which is split into two orthogonally polarized illumination pulses for direct and delayed illumination of the breakdown area. Exploiting polarization of the probe pulses, we capture two temporally and spatially separated frames with two CCD cameras. Special attention is given to the subsequent data processing, especially to the minimization of the systematic error due to alignment of both images, and to the determination of 2D velocity distribution from the captured image pairs.     

激光驱动强流电子束产生和控制

在惯性约束聚变（ICF）电子束快点火物理方案中,需要超强拍瓦激光脉冲驱动MeV能量的强流电子束,并沉积数十kJ能量到压缩氘氚芯区。强流电子束的束流品质是影响点火成功的关键因素之一,为深入了解强流电子束产生物理过程,研制成了三维高性能、适应上万CPU核规模的并行粒子模拟程序,并开展了大规模数值模拟研究,探索了强流电子束的产生机制和输运规律。回顾了近几年来快点火研究团队围绕强流电子束产生和控制开展的研究,介绍了导致束流品质差的两大物理原因：预等离子体效应和束流不稳定性磁场的随机散射。针对这两个物理原因,提出了四种提高强流电子束品质的方法：（1）双层金锥靶减弱预等离子体的负面效应;（2）输运丝产生环向磁场准直强流电子束;（3）外加磁场导引强流电子束提高耦合效率;（4）抑制束流不稳定性以降低随机磁场对电子束流的散射。     

PERTURBED SOLUTION OF SEA-AIR OSCILLATOR FOR THE EL NINO/LA NINO-SOUTHERN OSCILLATION MECHANISM

A class of coupled system to oscillate of the E1 Nino/La Nino-Southern Oscillation （ENSO） mechanism is studied. Using the perturbed theory, the asymptotic expansions and asymptotic behavior of the solution for an ENSO model are obtained.     

Terfenol-D超磁致伸缩换能器的有限元模拟

本文研究了利用ＡＮＳＹＳ软件分析磁致伸缩换能器,使这一有限元分析软件能够用于Ｔｅｒｆｅｎｏｌ－Ｄ换能器的分析设计。设计了１４ｋＨｚ Ｔｅｒｆｅｎｏｌ－Ｄ纵向换能器,计算结果与实验结果符合很好。     

Preparation and Characterization of Poly(ethylene oxide)/Graphene Nanocomposites from an Aqueous Medium

The nanocomposite films of a functionalized graphene sheet (FGS) and poly(ethylene oxide) (PEO) were cast from the physical blend of an aqueous FGS dispersion assisted by sodium dodecyl sulfate and an aqueous PEO solution. The thermal properties observed by differential scanning calorimetry suggested that FGS had a nucleating effect on the PEO crystallization. However, we found FGS actually hindered the growth of PEO crystals. The dynamic mechanical properties indicated that FGS effectively reinforced the matrix PEO. The FGS also efficiently improved the electric conductivity of PEO. With the addition of 2 parts of FGS per 100 parts of PEO, the conductivity was increased by more than 10³-fold from that of pristine PEO.     

Transport mechanism of reverse surface leakage current in AlGaN/GaN high-electron mobility transistor with SiN passivation

The transport mechanism of reverse surface leakage current in the AlGaN/GaN high-electron mobility transistor(HEMT) becomes one of the most important reliability issues with the downscaling of feature size.In this paper,the research results show that the reverse surface leakage current in AlGaN/GaN HEMT with SiN passivation increases with the enhancement of temperature in the range from 298 K to 423 K.Three possible transport mechanisms are proposed and examined to explain the generation of reverse surface leakage current.By comparing the experimental data with the numerical transport models,it is found that neither Fowler-Nordheim tunneling nor Frenkel-Poole emission can describe the transport of reverse surface leakage current.However,good agreement is found between the experimental data and the two-dimensional variable range hopping(2D-VRH) model.Therefore,it is concluded that the reverse surface leakage current is dominated by the electron hopping through the surface states at the barrier layer.Moreover,the activation energy of surface leakage current is extracted,which is around 0.083 eV.Finally,the SiN passivated HEMT with a high Al composition and a thin AlGaN barrier layer is also studied.It is observed that 2D-VRH still dominates the reverse surface leakage current and the activation energy is around 0.10 eV,which demonstrates that the alteration of the AlGaN barrier layer does not affect the transport mechanism of reverse surface leakage current in this paper.     

Optodynamic analysis of direct laser writing of graduation lines

The direct laser writing of graduation lines in Cr thin films on glass substrates has been investigated. The Nd-YAG laser and the astigmatic optical system have been used to write rectangular holes in the Cr film. The optimal writing parameters: the laser pulse energy, the Cr layer thickness and the substrate-objective distance were determined using the optoacoustic probe beam deflection method to detect the evaporation of the material. The evaporation is concluded to be the essential process in the laser writing of graduation lines. The rims formed by the surface tension gradient at the hole edges indicate that the laser writing of graduation lines is a typical two-phase removal process.     

“禁戒光”近场光学显微镜原理与系统

扫描近场光学显微术是８０年代后期发展起来的一种分辨率超过衍射极限的新型光学显微镜技术。本文介绍了国外最近出现的“禁戒光”近场光学显微镜系统的工作原理及结构。透射式ＳＮＯＭ中部分光沿着光轴向前传播；部分光沿着大于全内反射临界角的方向传播。前者称为允许光；后者称为禁戒光。应用“禁戒光”近场光学显微镜可同时获得三幅图像，即允许光像、禁戒光像和反映样品表面形貌的剪切力图像。禁戒光图像能够提供很好的对比度和分辨率。     

The role of strap muscles in phonation—In vivo caninelaryngeal model

In spite of the presumed importance of the strap muscles on laryngealvalving and speech production, there is little research concerning the physiological role and the functional differences among the strap muscles. Generally, the strap muscles have been shown to cause a decrease in the fundamental frequency (F₀) of phonation during contraction. In this study, an in vivo canine laryngeal model was used to show the effects of strap muscles on the laryngeal function by measuring the F₀, subglottic pressure, vocal intensity, vocal fold length, cricothyroid distance, and vertical laryngeal movement. Results demonstrated that the contraction of sternohyoid and sternothyroid muscles corresponded to a rise in subglottic pressure, shortened cricothyroid distance, lengthened vocal fold, and raised F₀ and vocal intensity. The thyrohyoid muscle corresponded to lowered subglottic pressure, widened cricothyroid distance, shortened vocal fold, and lowered F₀ and vocal intensity. We postulate that the mechanism of altering F₀ and other variables after stimulation of the strap muscles is due to the effects of laryngotracheal pulling, upward or downward, and laryngotracheal forward bending, by the external forces during strap muscle contraction.