Van der Waals Effects on semiconductor clusters

Van der Waals (vdW) interactions play an important role on semiconductors in nanoscale. Here, we utilized first‐principles calculations based on density functional theory to demonstrate the growth mode transition from prolate to multiunit configurations for Ge_n (n = 10–50) clusters. In agreement with the injected ion drift tube techniques that “clusters with n < 70 can be thought of as loosely bound assemblies of small strongly bound fragments (such as Ge₇ and Ge₁₀),” we found these stable fragments are connected by Ge₆, Ge₉, or Ge₁₀ unit (from bulk diamond), via strong covalent bonds. Our calculated cations usually fragment to Ge₇ and Ge₁₀ clusters, in accordance with the experiment results that the spectra Ge₇ and Ge₁₀ correspond to the mass abundance spectra. By controlling a germanium cluster with vdW interactions parameters in the program or not, we found that the vdW effects strengthen the covalent bond from different units more strikingly than that in a single unit. With more bonds between units than the threadlike structures, the multiunit structures have larger vdW energies, explaining why the isolated nanowires are harder to produce. © 2015 Wiley Periodicals, Inc.     

天然生物质腰果壳液的分离研究进展

天然生物质腰果壳液中的主要组分腰果酚可替代石油酚,广泛应用于油田、涂料等领域;腰果酸和强心酚具有较高的反应活性,通过化学改性,可广泛应用于医药和材料领域,且各组分均具有很好的生物降解性。然而,各组分的精确分离成为腰果壳液广泛应用的关键。本文通过对国内外腰果壳液的分离方法的系统总结,综述了腰果酚、腰果酸、强心酚的精细分离方法以及其优缺点,并对各组分的应用前景进行了简单的介绍和展望,为这类来源广泛的生物质的应用提供理论支持。     

A time-domain circuit simulator for coupled-cavity traveling-wavetubes

The Curnow equivalent circuit was used to predict the dispersion of cold coupled-cavity traveling-wave tubes, as wen as the voltage and current characteristics for lossless and lossy multicavity circuits. The equivalent circuit is extended to have three ports. The added beam port allows the future modeling of the interaction between beam and cavity. Losses are introduced into the circuit as resistors in series with the corresponding inductors. The time-domain solution to the multicavity circuit is developed. It can be applied to the full-spectrum signal. It is also useful for the transient analysis for both single frequency and full-spectrum signals, including the turn-on transients. Numerical methods to solve the time-domain equations are discussed; a second-order leap-frog method and a fourth-order Runge-Kutta method are implemented and analyzed. Simulation results from both codes are compared, and match well with the theory     

基于LXI总线的某弹用自动测试系统设计

随着测试总线技术的不断发展,当前基于VXI总线技术某弹用自动测试系统在满足现代战争高强度、高效率保障需求方面存在缺点,无法适应未来高科技战争的需求;通过对比VXI总线与LXI总线,提出了基于LXI总线技术的某弹用远程分布式自动测试系统设计,分析了该型炸弹的测试需求,进行了系统方案和软件架构的设计,描述了系统软件的工作流程,提高了系统的标准化、智能化、模块化和通用化水平,加强了系统机动性和保障效率。     

杆系结构静强度和疲劳失效机理及可靠性分析

根据疲劳载荷造成的疲劳累积损伤对结构极限承载力的影响情况,讨论了结构系统承载能力的可靠度计算方法,分析了结构系统中每一个单元在静载和疲劳载荷作用下的两种失效模式,并考虑了二者之间的相关性对该单元可靠性的影响,具体分析了结构系统在这两种载荷作用下的失效机理,给出了在这两种载荷作用下结构系统的可靠性分析方法. 算例表明,在不同的使用年限内,静载和疲劳载荷对结构系统可靠性的影响是不同的;在结构系统主要失效路径中既有单元静强度失效又有单元疲劳失效,这是符合结构系统使用真实情况的.     

关于既约非负矩阵优势比的界

本文改进了Ａ．Ｍ．Ｏｓｔｒｏｗｓｋｉ和佟文廷的结果,得到了关于既约非负矩阵优势比的新界．     

Impact toughness of a gradient hardened layer of Cr5Mo1V steel treated by laser shock peening

Laser shock peening (LSP) is a widely used surface treatment technique that can effectively improve the fatigue life and impact toughness of metal parts. Cr5Mo1V steel exhibits a gradient hardened layer after a LSP process. A new method is proposed to estimate the impact toughness that considers the changing mechanical properties in the gradient hardened layer. Assuming a linearly gradient distribution of impact toughness, the parameters controlling the impact toughness of the gradient hardened layer were given. The influences of laser power densities and the number of laser shots on the impact toughness were investigated. The impact toughness of the laser peened layer improves compared with an untreated specimen, and the impact toughness increases with the laser power densities and decreases with the number of laser shots. Through the fracture morphology analysis by a scanning electron microscope, we established that the Cr5Mo1V steel was fractured by the cleavage fracture mechanism combined with a few dimples. The increase in the impact toughness of the material after LSP is observed because of the decreased dimension and increased fraction of the cleavage fracture in the gradient hardened layer.     

基于高速面阵像机扫描成像的弹丸攻角测量方法

攻角是指飞行中弹丸的轴线与其质心运动方向的夹角,是描述弹丸飞行姿态的重要参数,以往都是采用狭缝相机来进行测量。提出了一种基于高速面阵像机测量弹丸攻角的方法。该方法是从面阵序列图像每帧中提取出固定列像元,然后按时序拼接形成一幅图像,等同于线阵扫描的图像;对于扫描速度同影像运动速度不同步时,建立了攻角计算修正模型。采用2台像机从非正交方向进行拍摄,基于面面交会原理,得到三维攻角。实测结果表明:该方法能完成弹速达到1 000 m/s的目标测试,攻角测量精度优于0.1。     

Ugi反应的研究新进展

Ugi反应是组合合成中所用的一个重要反应.本文从以下三方面综述了近年来Ugi反应的研究及应用进展:(1)醛(酮)、胺、酸、异腈等各组分的变化,尤其是异腈结构的变化及双官能团化合物的应用;(2)多于四组分的Ugi反应;(3)某些天然产物及类药物物质合成中Ugi反应的应用.