采用激光声磁技术检测钢轨踏面缺陷

钢轨踏面与车轮之间的滚动接触疲劳形成的大量表面缺陷严重危害着铁路行车安全,传统的无损检测(NDT)方法已不能适应铁路快速发展的需要。根据激光声磁技术的基本原理和钢轨踏面缺陷检测的特点,研究了钢轨踏面缺陷检测的激光声磁检测技术。通过对比激光声磁技术与压电超声检测钢轨踏面横向裂纹缺陷的实验,表明本文方法能准确的检测和定位踏面横向裂纹。通过小波阈值去噪技术对激光声磁信号进行处理,在保留了原始信号的各种特征的同时大大提高了信噪比(SNR),更有利于缺陷的识别和特征的提取。分析了提离效应对激光声磁信号的影响,获得了提离距离与接收信号幅值变化曲线图。实验结果表明,本文方法无需耦合剂、对钢轨表面状况要求低,可实现钢轨踏面缺陷的非接触、快速和准确的检测。     

基于光纤传导的钢轨踏面缺陷激光声磁检测

针对较容易产生缺陷的钢轨 踏面检测要求,建立了基于光纤传导技术的钢轨踏面裂纹缺陷激光声磁检测(EMAT)系统。 系统通过光纤传导 脉冲激光照射到钢轨踏面激发出超声表面波,表面波在传播过程中遇到钢轨踏面缺陷时发 生模式转换成 横波,再使用电磁超声技术接收超声转换成横波信号。通过本文系统对钢轨试样不同位置 进行扫查,能精 确检测出钢轨踏面裂纹缺陷。实验结果表明,本文系统具有非接触、结构灵活和灵敏度高 等优点,可实现钢轨踏面裂纹缺陷的有效检测。     

钢轨螺孔伤损激光声磁检测系统研究

为检测钢轨螺孔伤损,根据激光声磁技术的基本原理和钢轨螺孔伤损检测的特点,建立了钢轨激光声磁检测系统。通过检测钢轨无伤损螺孔和有上裂伤损螺孔的对比实验,表明本系统能准确检测螺孔上裂伤损。通过小波阈值去噪技术对激光声磁信号进行处理,在保留原始信号各种特征的同时大大提高了信噪比(SNR)。实验结果表明,本文方法无需耦合剂,对钢轨表面状况要求低,可实现钢轨螺孔伤损非接触、快速和准确的检测。     

钢轨轨脚裂纹红外热波无损检测实验(英文)

目前,超声检测在钢轨裂纹检测中得到了广泛的应用,但在钢轨裂纹检测过程中,超声波检测方法存在一定的盲区,未能检测到轨脚两侧的裂纹。针对超声波检测方法的不足,搭建了一种红外热波钢轨踏面裂纹无损检测平台。钢轨裂纹红外热波无损检测平台是红外无损检测领域的一个新的研究方向,实验平台的建立主要包括3部分:热激励源的选择、实验平台的搭建、红外图像的提取。该技术用于通过热激励源加热轨底表面。根据热波理论,钢轨表面到轨底内侧的传热过程受钢轨的物理特性和内部结构的影响,如果钢轨内部存在缺陷,则缺陷类型会影响钢轨表面的温度分布。根据钢轨表面温度信息的分布,确定钢轨内部缺陷的位置,达到检测钢轨裂纹的目的。实验结果表明,裂纹对应的轨底表面温度高于无裂纹对应的轨底表面温度,证明红外热波无损检测对钢轨裂纹检测是可行的。     

基于激光超声方法的钢轨缺陷检测

针对钢轨探伤可靠性试验及缺陷信号采集处理要求,建立了一套基于激光超声技术的无损检测系统。该系统主要包括高能量脉冲激光器、电磁超声换能器、嵌入式信号采集处理系统以及带有人工缺陷裂缝的P60钢轨试件。在分析利用瑞利波探伤机理的基础上,重点研究了激励线圈阻抗匹配方法,介绍了嵌入式信号采集处理系统工作原理及其信号处理过程。最后利用搭建的激光超声检测系统,实现钢轨表面深度不少于0.5 mm缺陷的定位,并给出了接收信号幅度与提离距离以及缺陷尺寸的关系。     

基于空间变换技术的脉冲激光声信号检测

针对目前脉冲激光声信号检测方法极易受到环境噪声的影响,导致检测精确度不理想的问题。提出基于空间变换技术的脉冲激光声信号检测方法。首先,采用小波阈值法去除脉冲激光声信号中的噪声;其次,利用球傅里叶空间变换技术对声信号中的声源展开定位,获取声信号的准确位置;最后,分别提取声信号中的比值特征、比重特征、频率特征三种参数,在此基础上通过SVM算法对其展开分类识别,以此实现脉冲激光声信号的有效检测。实验结果表明,所提方法的声信号检测精度超过96%。     

激光焊接缺陷多向磁场激励下磁光成像检测

为了研究交叉焊缝缺陷的磁光图像特征,对中碳钢板进行十字对接激光焊,获得同时具有横向和纵向焊后裂纹的试验样本,同时采用恒定磁场和交变磁场对试验样本进行多角度励磁, 用磁光成像传感器采集不同角度磁场激励下焊接缺陷处的磁光图像,并对磁光图像的缺陷特征进行分析。结果表明,多向磁场激励下的磁光成像技术能明显检测出多角度的焊接缺陷,且能有效避免曲线裂纹在焊接缺陷检测中的漏检现象; 同时,交变磁场激励下, 同一裂纹成像的分辨率提高了40pixel~50pixel,能更精确地定位缺陷位置。此研究为提高焊接缺陷的检出率提供了依据。     

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。     

基于目标检测网络的轮对踏面缺陷检测方法

针对传统图像处理算法难以快速、准确识别轮对踏面缺陷的问题,提出一种采用双深度神经网络对轮对踏面缺陷进行检测的算法。该双网络分为踏面提取网络与缺陷识别网络。根据踏面为大目标的特点,分析与测试SSD网络,并用该网络提取轮对图像中的踏面区域。为提高踏面缺陷识别效率,在提取出踏面图像后,针对踏面缺陷属于中、小目标的特点,对YOLOv3网络结构进行优化得到M-YOLOv3。实验测试表明:提取踏面区域时,SSD算法的精度均值(AP)最高,达99.8%;识别踏面缺陷时,M-YOLOv3的AP达89.9%,相较于原始YOLOv3,单张图像计算耗时减少7.1%,同时AP仅有0.6%的损耗。结果表明,所提算法具有较高的检测准确率。     

落轮轮对三维外形重构与参数检测

轮对缺陷将严重影响列车安全运行,如何快速高精确度进行缺陷检测是技术难题。采用二维电荷耦合器件采集系统和线激光相结合获取轮对外形尺寸的方法,对检测原理进行理论推导并建立了相应模型,实现了轮对踏面360°检测与轮对外形三维重构。用所建立算法处理测量数据,获得轮缘厚度、轮缘宽度、垂直磨耗和踏面磨耗等重要参数。通过误差分析,研究影响检测精确度的多种因素。实验结果表明,该方法能快速、高精确度地测量出轮对外形尺寸,并能准确发现缺陷。     

Interfacial reaction and shear strength of SnAgCu-xNi/Ni solder joints during aging at 150 °C

The interfacial microstructure and shear strength of Sn3.8Ag0.7Cu-xNi (SAC-xNi, x = 0.5, 1, and 2) composite solders on Ni/Au finished Cu pads were investigated in detail after aging at 150 °C for up to 1000 h. The interfacial characteristics of composite solder joints were affected significantly by the weight percentages of added Ni micro-particles and aging time. After aging for 200 h, the solder joints of SAC, SAC-0.5Ni and -1Ni presented duplex intermetallic compound (IMC) layers regardless of the initial interfacial structure on as-reflowed joints, whose upper and lower IMC layers were comprised of (CuNi)₆Sn₅ and (NiCu)₃Sn₄, respectively. Only a single (NiCu)₃Sn₄ IMC layer was ever observed at the SAC-2Ni/Ni interface on whole aging process. Based on the compositional analysis, the amount of Ni within the IMC regions increased as the proportion of Ni addition increased. The IMC (NiCu)₃Sn₄ layer thickness on the interface of SAC and SAC-0.5Ni grew more slowly when compared to that of SAC-1Ni and -2Ni, while for the (CuNi)₆Sn₅ layer the reverse is true. Except the IMCs sizes are increased with increased aging time, the interfacial IMCs tended to transfer their morphologies to polyhedra. In all composite joints testing, the shear strengths were approximately equal to non-composite joints. The fracturing observed during shear testing of composite joints occurred in the bulk solder, indicating that the SAC-xNi/Ni solder joints had a desirable joint reliability.     

BNBST无铅压电陶瓷的制备工艺研究

设计了（Bi0.55Na0.5）1-X（BaaSrb）xTiO3（BNBST[100x-100a／100b]）无铅压电陶瓷新体系。该体系压电陶瓷具有工艺特性及压电响应好，压电常数高的特点，且有实际应用前景的新型压电陶瓷材料体系。采用传统的陶瓷工艺制备了（Bi0.55Na0.5）1-X（BaaSrb）xTiO3无铅压电陶瓷，研究了制备工艺参数对其物化结构性能的影响。生料的热重-差热（TGA-DTA）分析表明，粉料合成过程中，先是SrTiO3、BaTiO3的形成，然后是（Bi0．5Na0．5）Tio，的形成，同时三者形成固溶体；密度测试表明，陶瓷的体积密度随烧结温度的升高而增大，可较易获得理论密度94％的陶瓷；X-射线能谱分析（EDAX）研究表明，陶瓷的Bi、Na的挥发随着烧结温度的升高而加剧。研究结果表明，要制备性能优良的无铅压电陶瓷，需要精确控制制备工艺。     

有机发光二极管中ADN掺杂ErQ的1.54μm电致发光

自行设计了基于8-羟基喹啉铒(ErQ)为发射层(EMLs)和二硝酰胺铵(ADN)为蓝光主体材料的近红外有机发光二级管.器件的基本结构为(p-Si/NPB/EML/Bphen/Bphen:Cs2CO3/Sm/Au),设计并比较了三套不同发射层结构(ErQ/ADN为双层结构器件,(ErQ/ADN)×3为多层结构器件,ErQ:ADN为掺杂结构器件)的器件.三组器件在一定的偏压下,均可发出1.54μm的光,对应三价铒离子4I13/2→4I15/2的跃迁.其中,ADN:ErQ(1∶1)掺杂结构的近红外电致发光强度是ADN/ErQ双层结构中的三倍.此外,不同掺杂浓度的ADN:ErQ复合膜做了以下表征:吸收谱、光致发光谱和荧光寿命谱.实验结果证实了在近红外电致发光过程中存在从ADN主体分子到ErQ发射分子的高效率的能量转移.     

Emerging interconnects: a state-of-the-art review and emerging solutions

Aluminium was a primary material for interconnection in integrated circuits (ICs) since their inception. Later, copper was introduced as interconnect material which has better metallic conductivity and resistance to electromigration. As the aggressive technology scaling continues, the copper resistivity increased because of size effects, which causes increase in delay, power dissipation and electromigration. The need to reduce the resistor-capacitor??????? delay, dynamic power utilisation and the crosstalk commotion is as of now the fundamental main impetus behind the presentation of new materials. The purpose of this paper is to do a survey of interconnect material used in IC from introduction of ICs to till date. This paper studies and reviews new materials available for interconnect application which are optical interconnects, carbon nanotube (CNT), graphene nanoribbons (GNRs) and silicon nanowires which are alternatives to copper. While doing a survey of interconnect material, it is found that multiwalled CNTs, multilayer GNR and mixed CNT bundles are promising candidates and are ultimate choice that can strongly address the problems faced by copper but on integration basis copper would last for coming years.     

聚对苯撑苯并双(口恶)唑发光及其器件制备

采用光谱技术,研究了聚对苯撑苯并双(口恶)唑(PBO)溶液的光敏发光特性,并用相对法估算出溶液发光效率在50%范围.结合光谱技术、半导体电学和电化学等研究手段,具体研究了以PBO为发光层的单层电致发光器件,研究结果显示,电致发光与薄膜的光致发光有具有相同的发光中心,峰值位于510 nm左右.同时发现,由于存制备过程中不同处理条件使得不同厚度薄膜残留的掺杂物质浓度不同,从而引起薄膜的导电性的不同.使得器件的阈值场强随PBO厚度的减小而逐渐增加.     

钠离子对poly(dT).poly(dA).poly(dT)三螺旋DNA分子呼吸模式的影响

利用分子结构的螺旋对称性,建立了一个包括钠离子的三链DNA分子poly(dT)*poly(dA)*poly(dT)的晶格动力学模型,计算了poly(dT)*poly(dA)*poly(dT)的氢键呼吸模式.结果发现钠离子的加入明显地淬灭了位于较低频率的几个最为强烈的Hoogensteen氢键呼吸模式,而对Watson-Crick氢键呼吸模式影响不明显,这说明钠离子能提高poly(dT)*poly(dA)*poly(dT)三螺旋结构的稳定性.该计算结果很好地解释了poly(dT)*poly(dA)*poly(dT)的热融化实验.     

人小肠粘膜免疫酶的定位研究—光镜和电镜免疫组织化学染色法

本文对免疫酶组织化学的样品制备程序和染色方法做了详细的阐述。用直接法、间接法和ABC法,对人小肠免疫酶的定位,进行了光镜和电镜的观察,染色阳性反应显著,获得了满意的效果。并对染色技巧做了分析和探讨。     

Arsenic deposition as a precursor layer on silicon (211) and (311) surfaces

We investigate the properties of arsenic (As) covered Si(211) and Si(311) surfaces by analyzing data from x-ray photoelectron spectroscopy (XPS) and low-energy electron diffraction (LEED) images. We then create a model using total surface energy calculations. It was found that both Si(211) and Si(311) had 0.68±0.08 surface As coverage. Si(211) had 0.28±0.04 Te coverage and Si(311) had 0.24±0.04 Te coverage. The Si(211) surface replaces the terrace and trench Si atoms with As for a lower surface energy, while the Si edge atoms form dimers. The Si(311) surface replaces all terrace atoms and adsorbs an As dimer every other edge site. These configurations imply an improvement in the mean migration path from the bare silicon surface by allowing the impinging atoms for the next epitaxial layer, tellurium (Te), to bind at every other pair of edge atoms, and not the step terrace sites. This would ensure a nonpolar, B-face growth.     

Joint estimation of TOA and DOA in IR-UWB system using a successive propagator method

Impulse radio ultra-wideband (IR-UWB) ranging and positioning require accurate estimation of time-of-arrival (TOA) and direction-of-arrival (DOA). With receiver of two antennas, both of the TOA and DOA parameters can be estimated via two-dimensional (2D) propagator method (PM), in which the 2D spectral peak searching, however, renders much higher computational complexity. This paper proposes a successive PM algorithm for joint TOA and DOA estimation in IR-UWB system to avoid 2D spectral peak searching. The proposed algorithm firstly gets the initial TOA estimates in the two antennas from the propagation matrix, then utilises successively one-dimensional (1D) local searches to achieve the estimation of TOAs in the two antennas, and finally obtains the DOA estimates via the difference in the TOAs between the two antennas. The proposed algorithm, which only requires 1D local searches, can avoid the high computational cost in 2D-PM algorithm. Furthermore, the proposed algorithm can obtain automatically paired parameters and has better joint TOA and DOA estimation performance than conventional PM algorithm, estimation of signal parameters via rotational invariance techniques algorithm and matrix pencil algorithm. Meanwhile, it has very close parameter estimation to that of 2D-PM algorithm. We have also derived the mean square error of TOA and DOA estimation of the proposed algorithm and the Cramer-Rao bound of TOA and DOA estimation in this paper. The simulation results verify the usefulness of the proposed algorithm.     

系统级封装新型埋入式电源滤波结构的研究

在高密度小尺寸的系统级封装(SiP)中,对供电系统的完整性要求越来越高,多芯片共用一个电源网路所产生的电压抖动除了会影响到芯片的正常工作,还会通过供电网路干扰到临近电路和其他敏感电路,导致芯片误动作,以及信号完整性和其他电磁干扰问题.这种电压抖动所占频带相当宽,几百MHz到几个GHz的中频电源噪声普通方法很难去除.结合埋入式电容和电源分割方法的特点,提出一种新型高性能埋入式电源低通滤波结构直接替代电源/地平面.研究表明,在0.65～4GHz的频带内隔离深度可达-40～75 dB,电源阻抗均在0.25ohm以下,实现了宽频高隔离度的高性能滤波作用.分别用电磁场和广义传输线两种仿真器模拟,高频等效电路模型分析这种低通滤波器的工作原理以及结构对隔离性能的影响,并进行了实验验证.