双脉冲激光诱导铝等离子体的双波长干涉诊断

双脉冲激光诱导等离子体在激光加工、元素检测、材料去除等领域有广阔的应用前景和发展空间,对其进行诊断具有重要意义。针对延迟双脉冲激光诱导铝等离子体的作用效果和影响机理,采用双波长干涉法对其时间演化规律展开研究。基于马赫-曾德尔干涉仪搭建了双波长干涉诊断系统,得到了双脉冲激光诱导等离子体干涉图。通过对干涉图的处理和分析,得到了等离子体电子密度随双脉冲激光延迟时间的变化规律。结果表明,随着双脉冲激光延迟时间的增加,第二束脉冲激光对等离子体电子密度的增强效果先加强后减弱。其中,双脉冲激光延迟时间为10 ns时,对等离子体电子密度的增强效果最强,在30 ns时刻,其中心区域平均电子密度可达6.49×1019 cm?3,相较于同等能量单脉冲激光诱导等离子体提升了26%。同时研究了延迟时间对第二束脉冲激光作用机制的影响。研究结果为双脉冲激光诱导等离子体的优化方向提供了参考。     

Fast in situ 3D nanoimaging: a new tool for dynamic characterization in materials science

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Synthesis of large-scale atomic-layer SnS<Subscript>2</Subscript> through chemical vapor deposition

Two-dimensional layers of metal dichalcogenides have attracted much attention because of their ultrathin thickness and potential applications in electronics and optoelectronics.Monolayer SnS2,with a band gap of ～2.6 eV,has an octahedral lattice made of two atomic layers of sulfur and one atomic layer of tin.Till date,there have been limited reports on the growth of large-scale and high quality SnS2 atomic layers and the investigation of their properties as a semiconductor.Here,we report the chemical vapor deposition (CVD) growth of atomic-layer SnS2 with a large crystal size and uniformity.In addition,the number of layers can be changed from a monolayer to few layers and to bulk by changing the growth time.Scanning transmission electron microscopy was used to analyze the atomic structure and demonstrate the 2H stacking poly-type of different layers.The resultant SnS2 crystals is used as a photodetector with external quantum efficiency as high as 150％,suggesting promise for optoelectronic applications.     

Synergistic effects of micro-/nano-fillers on conductive and electromagnetic shielding properties of polypropylene nanocomposites

This study presents the synergistic effects of graphene nanosheets (GNSs) and carbon fibers (CFs) additions on the electrical and electromagnetic shielding properties of GNS/CF/polypropylene (PP) composites. These composites were fabricated by the melt blending of different ratios of GNSs and CFs (20:0, 15:5, 10:10, 5:15 and 0:20 wt/wt%) into a PP polymer matrix using a Brabender mixer. Besides, the chemical and crystalline structures and the thermal stability of the resultant GNS/CF/PP composites were characterized by Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD) and thermogravimetric analysis (TGA). FT-IR and XRD showed that with the addition of GNSs content, transmittances at 1373.4?cm^?1 and 1454.4?cm^?1 became smaller and the characteristic peak at 26.82° became stronger. TGA showed that the GNS/CF/PP composite can be used at high temperature below 456°C. Blending 10?wt% CFs and 10?wt% GNSs into the PP polymer resulted in excellent conductivity (0.397 S/cm), which indicated the occurrence of the critical percolation threshold phenomenon, and also reached the maximum electromagnetic shielding effectiveness (EMSE) of 20?dB at 1.28–2.00?GHz. Laminated with five layers of composites, its EMSE achieved 25–38?dB at 0.3–3.0?GHz, corresponding to blocking of 94.38–98.74% electromagnetic waves.     

Optimal classification methods for diagnosing latent skills and misconceptions for option-scored multiple-choice item quizzes

Behaviormetrika - The paper’s extended Diagnostic Classification Modeling setting assumes (a) nominal item (question) coding, thus&nbsp;including multiple-choice (MC) items, and (b)...     

稀土对45钢固体硼氮共渗过程的影响

研究了稀土对４５钢固体硼氮共渗工艺、渗层成分、组织、耐磨性及断口形貌的影响。试验结果表明,稀土的加入使渗速增大,渗层中Ｂ,Ｎ含量特别是Ｎ的含量增加,硼化物针齿变得细密、直长;且ＦｅＢ的相对含量减少,Ｆｅ２Ｂ相增加,渗层耐磨性提高,同时稀土增加了过渡区厚度,减少裂纹源。生产应用证明,稀土硼氮共渗可使烟机配件的使用寿命大幅提高。     

关于Markov过程的强大数定律

本文研究一般马氏过程的强大数定律．     

基于MPC8548的嵌入式设备的光通信接口设计与实现

提出了一种基于PowerPC的光通信接口设计方案,该方案以PowerPC微处理器为核心,通过其集成的三速以太网控制器,实现了1Gb/s的高速以太网协议接口逻辑;文中详细介绍了其硬件结构原理,并在此基础上详细阐述了其在嵌入式Linux操作系统平台上驱动程序的设计思想与具体实现;系统基于嵌入式Linux操作系统平台完成相关驱动软件的开发,实现了数据的高效率采集与高速光纤传输,具有低功耗、高带宽和高集成度等优点;测试结果表明,系统处于全效率运行状态,以太网接口传输速率可以达到1Gb/s左右,满足了系统设计的要求,具有广阔的应用前景.     

基于FPGA的某雷达多功能数字替换板设计

为了提高高技术战争条件下电子装备战场抢修的快捷性、时效性,减少备件携带数量,以某雷达火控计算机中4块数字电路板为背景设计了一种多功能替换版;该替换版以一块FPGA芯片为控制核心,并配以海绵电路区和跳线插座的设计,使得在战场紧急情况下只需更换EPROM存储芯片,并在海绵电路区上焊接相应的集成电路器件以及调整跳线插座来控制信号走向,就可以在短时间内方便快捷地对损坏电路板实施替换;结果证实,该技术可作为一种备用的维修手段,可以在很大程度上提高部队装备战场维修率.