一种Ka频段超低交叉极化宽频带波纹喇叭天线

波纹喇叭天线是一种结构紧凑、具有良好辐射性能的馈源天线,特别是轴向槽波纹喇叭天线可以在宽频段内实现极低的交叉极化,对扩展工作频段、实现极化复用有重要的价值。文章对轴向槽波纹喇叭天线的设计方法进行了研究,利用模式匹配法和全波算法软件设计了一种Ka频段超低交叉极化宽频带轴向槽波纹喇叭天线。实测数据表明,该喇叭天线工作频段可覆盖整个Ka频段（26.5~40 GHz）,在频段内回波损耗小于-20 dB、交叉极化小于-45 dB,同时天线具备良好的方向图对称性和相位中心稳定性,在卫星通信领域具有广阔的应用前景。     

一种用于TOF激光雷达的多通道时数转换芯片设计

时间数字转换器(Time-to-Digital Converter,TDC)是一种将连续时间信号转换为数字信号输出的器件,是飞行时间(TOF)激光雷达中的关键部件.在利用计数器粗采样和多相位内插细采样的传统结构上,设计了一种基于相位内插的双级粗细结合型时间数字转换电路,并增加了双回波接收通路来接收多脉冲回波信号,在此基础上设计了一款17通道多路TDC系统芯片.芯片采用CMOS 0.11 μm工艺设计,版图面积为0.6 mm×3 mm.后仿真结果显示,在1.2 V电源下其功耗小于100 mW,单输入精度平均值为51.7 ps,动态范围为3.4 μm,且线性度良好.该TDC芯片适用于飞行时间脉冲激光雷达的信号计时.     

基于灰度-梯度共生矩阵的车轮踏面缺陷聚类分析北大核心CSCD

车轮作为列车走行部的关键部件之一,其踏面产生缺陷后会直接影响到列车的运行安全。为了能够在检测时准确识别车轮踏面缺陷不同类型,提出一种基于灰度-梯度共生矩阵的纹理特征提取方法,对踏面图像的灰度和梯度特征分析之后,根据灰度-梯度共生矩阵提取踏面图像纹理特征矢量,再结合K-均值(K-means)聚类优化算法对踏面缺陷特征量进行聚类,从而将踏面缺陷类型进行分类,并将分类结果用可视化数据显示。实验结果表明,采用上述所提方法,对车轮踏面缺陷不同类型的分类识别精度达96%以上。     

On the Growth of Thin-Film AlGaN/GaN Epitaxial Heterostructures on Hybrid Substrates Containing Layers of Silicon Carbide and Porous Silicon

Semiconductors - Abstract—In our work, we carry out a structural-spectroscopic study of AlGaN/GaN epitaxial layers grown by molecular-beam epitaxy with nitrogen-plasma activation on a hybrid...     

基于6H-SiC衬底外延石墨烯的被动锁模掺镱光纤激光器

报道了6H-SiC衬底外延生长的石墨烯作为可饱和吸收体,环形腔结构的全正色散被动锁模掺镱光纤激光器。在注入抽运功率为250mW时,得到稳定的重复频率为1.05MHz的自锁模脉冲,平均输出功率为6mW;当注入抽运功率增加到480mW时,最大平均输出功率为20mW,相应的最高单脉冲能量为19nJ,激光脉冲宽度约为520ps。     

大功率半导体激光器腔面氮钝化的研究

针对980 nm大功率半导体激光器腔面离子铣氮钝化处理工艺进行了研究,发现腔面离子铣氮钝化可以提高激光器的输出特性及COD功率,器件输出功率提高了32.14%;老化实验后,经过氮钝化的半导体激光器没有明显退化,而未经氮钝化处理的激光器退化严重;使用俄歇谱测试仪(AES)对钝化处理后的半导体激光器试验片进行测试,发现有部分的氮离子遗留在腔面处;氮元素含量由原有的0%上升到20%,与此同时,氧元素的含量由原来的61%降至30%。结果表明,该技术能够改善半导体激光器的腔面特性,器件的可靠性和使用寿命可望得到提高。     

Synthesis and gas transport properties of polypentafluorostyrene

Polypentafluorostyrene (PPFS) (M _w = 1.7 × 10⁵ Da, M _w /M _n = 1.6, and Т _g = 110°С) has been synthesized by radical polymerization of pentafluorostyrene. The chemical structure of the polymer has been confirmed by ¹H and ¹⁹F NMR data. The permeability and diffusion coefficients of gases (He, H₂, O₂, N₂, CO₂, and CH₄) have been measured on a barometric setup. The permeability, diffusion, and solubility coefficients of gases have been shown to increase with the increases in the fluorine content in the repeat unit of the polymer in the polystyrene–poly(p-fluorostyrene)–PPFS series. Such behavior of transport parameters in the polymer series is associated with the growth in the fractional free volume and decrease in the cohesive energy density. The investigated polymers on the basis of styrene and its derivatives including PPFS are located in the middle of clouds of Robeson diagrams for N₂/CH₄, CO₂/CH₄, and O₂/N₂ and are not of interest for their separation.     

Deformation properties of modified polyacrylonitrile fibres

Conclusions Deformation properties of polyacrylonitrile fibres modified with alkali metal salts have been studied.The introduction of alkali metals by treatment of freshly spun gel-fibre with solutions of the appropriate salts aids in loosening fibre structure.Both the form of cation and also of the anion in the salt introduced affect the deformability of the modified fibres.Translated from Khimicheskie Volokna, No. 4, pp. 40–41, July–August, 1989.     

Chemical cross-linking of carboxymethylated viscose yarns

Conclusions The parameters of chemical cross-linking of yarns based on carboxymethylcellulose (CMC) and their physicomechanical properties depend on the concentration of the cross-linking agent — formaldehyde — the catalyst concentration, and also on the reaction temperature and time.A bound formaledhyde content of 0.5% by wt., in the form of methylene bridges in the make-up of CMC yarns, leads to a 31% increase in their strength in the wet state.Chemical cross-linking of CMC fibres with formaldehyde helps increase their resistance to biodegradation and correspondingly leads to a larger strength retention in living organisms.Translated from Khimicheskie Volokna, No. 5, pp. 18–20, September–October, 1989.