双相位共轭镜的工作条件参数分析

本文讨论了纯扩散机制的光折变晶体用作单作用区的双相位共轭镜（ＤＰＣＭ）时的阈值耦合强度和允许的输入光强比范围，并与双作用区的情况进行比较后，给出了在输入光强比远离１的条件下，双相位共轭镜的正常工作的条件参数。     

Stress concentration and fatigue of profiled reinforcing steels

Stress concentrations arise from profiles of ribbed reinforcing steel bars and in this study the results of calculated stress concentration factors (SCF), by using finite element method, are related to the fatigue test results. It is apparent that the degree of confinement of a ribbed bar embedded in concrete not only affects the magnitude of the ultimate bond stress but also the bond stress-slip relation. Thus the rib geometry or profile pattern is designed for optimum bond characteristics and not for fatigue considerations. However the rib geometry influences the fatigue performance through the SCFs arising from the root radius, width and flank angles of the profiles. It is shown that these latter factors have a significant influence on the fatigue behaviour of reinforcing steel bars.     

基于LabVIEW的超声信号小波阈值去噪方法

图形化编程软件LabVIEW具有强大的信号采集功能,但对于需要进行大量数据运算处理的复杂应用就显得力不从心。数学工具软件MATLAB强大的计算功能及较高的编程效率可以弥补LabVIEW开发的不足。文中结合两者软件的优点,采用混合编程的方法进行实际工程的去噪处理,同时针对超声缺陷回波信号信噪比低、易于被噪声淹没的特点,选取小波阈值去噪的方法,通过调用LabVIEW里的MATLAB Script节点对信号进行仿真实验,仿真结果表明采用stein的无偏风险阈值去噪的方法消噪效果最为明显,得到较高的信噪比。     

一种改进的基于多项式滤波的稳态检测方法

化工过程的数据中常常含有较多的随机误差和粗差干扰,导致传统的稳态检测方法无法得到准确的结果,从而降低系统故障诊断的可靠性。针对实际的工业过程数据,提出一种融合自适应平滑技术的稳态检测方法,该方法首先以基于导数分析的自适应平滑算法进行降噪处理,消除随机误差的影响,然后引入阈值拟合技术进一步抑制粗差干扰,以多项式滤波方法对数据进行稳态检测,根据测量信号的趋势特征确定过程是否处于稳态。仿真实验研究表明:融合自适应平滑技术的稳态检测方法能够克服传统稳态检测方法中随机误差和粗差干扰对检测结果的影响,进而显著提高稳态检测处理的准确性,检测结果明显优于传统的基于多项式滤波的检测方法。     

Majority gates vs. general weighted threshold gates

In this paper we study small depth circuits that contain threshold gates (with or without weights) and parity gates. All circuits we consider are of polynomial size. We prove several results which complete the work on characterizing possible inclusions between many classes defined by small depth circuits. These results are the following:

基于阈值分割的松材线虫病树计数与定位

松材病虫病是最紧迫的威胁之一,最近对中国针叶林造成了严重破坏,为了阻止松材病虫病的快速传播,必须在早期准确检测和计数受感染的树木。提出了一种基于密度图的方法,用于从高分辨率航拍图像中估计具有松材病虫病的树木数量,方法引入了阈值分割、形态处理和超像素技术,以最大限度地减少由于建筑物和岩石等相似背景物体引起的误差。实验表明,所提出的方法优于密度学习 算法,平均绝对误差、均方根误差和绝对误差方差分别从21.3、22.2和127.2减少到8.0、11.7和59.6,计数准确率从54.7%提高到81.3%。     

Surface contact degradation of multilayer ceramics under cyclic subcritical loads and high number of cycles

Alumina/alumina–zirconia ceramic laminated composites produced by tape casting present a compressive residual stress at the alumina surface due to the thermal expansion mismatch between layers developed during processing. Because of this residual stress, the mechanical properties at the surface, such as wear or surface fracture, have proven to be better than the properties of a monolithic stress-free alumina. In a previous work, it was shown that this laminate composite has better resistance to the development of a ring crack when loaded with a spherical indenter, under both cyclic and static loads below the critical load for cone cracking. In this work, cyclic Hertzian indentations with subcritical loads are performed on the same laminate ceramic and a monolithic alumina, but with a higher number of cycles than the necessary to provoke the first damage (ring crack). Results show that for low and intermediate number of cycles, the laminated composite presents better resistance to damage than the monolithic alumina. However, for high number of cycles, spalling at the surface of the laminate material appears, whereas the monolithic alumina develops secondary cone cracking. This difference is attributed to the fact that laminate ceramics present an enhanced apparent fracture toughness of the material, which implies a higher quasi-plasticity due to shear driven microcracking. For a high number of cycles, these microcracks grow until coalescence at the surface, provoking exfoliation of the material at the contact area, enhanced by the fact that the indented and the indenter material have different elastic properties.     

Experimental Investigation of Epoxy Bonded Polymethylmethacrylate Joints

This paper presents an experimental investigation into various aspects of epoxy-bonded polymethylmethacrylate (PMMA) and PMMA-to-aluminium joints. The effects of adhesive thickness, overlap area, surface roughness, and environmental exposure on the joint strength were studied. Results indicated that the joint strength was not directly proportional to the overlap area, while sanding had a positive effect on the joint strength. A negative effect was observed when adhesive thickness was increased. The fatigue behaviour of adhesively-bonded joints under dynamic loading was found to be independent of frequency, for the range of values tested; however, it was dependent on the test temperature with greater reduction in fatigue life observed in PMMA-to-aluminium joints at higher temperature. Empirical equations from which the fatigue life of joints can be predicted were obtained by regression analysis. Intermittent fatigue testing of the joints was also performed. The epoxy adhesive tested proved to be a satisfactory choice for outdoor exposure. The rate of degradation of the adhesive was slow with the adherend itself degrading at a faster rate than the adhesive or the bondline.     

在线化工设备疲劳分析专家系统的研究

运用应力分析、疲劳分析的理论，综合专家学者的知识和经验，针对现代化大型联合企业技术管理的现状，提出了建立在线化工设备及管道安全评定中疲劳分析的专家系统方法，并编制了初级的软件。用简化试验来模拟一条高温高压蒸汽管线的疲劳裂纹扩展，并用之考评本软件。     

弯道岸坡上粗细泥沙统一起动流速公式

该文基于概率论与泥沙起动基本理论,考虑了起动概率、相对暴露度与细颗粒泥沙间黏结力和附加下压力对泥沙起动的影响,采用滑动起动模型,从理论上推导出了适用于弯道岸坡上粗、细泥沙颗粒起动的统一流速公式,完善了已有研究成果对泥沙起动概率考虑的不足。公式综合了弯道岸坡、顺直岸坡、正负坡及平坡等条件下粗细泥沙颗粒起动流速计算,可简化为各简单条件下泥沙起动流速公式。通过各简单条件下泥沙起动流速实测资料验证,该文公式与实测数据符合良好。