Influence of load and speed on wear characteristics of grey cast iron in dry sliding — selection for minimum wear

The wear of grey cast iron in dry sliding conditions has been studied with the aims of (1) finding the influence of working conditions on the wear rate, and (2) determining the region of speed and load where low wear is accomplished. Grey cast iron with flake and nodular graphite was submitted to investigation using a pin-on-disc machine. The results indicate that the flake graphite cast iron is more suitable for applications at speeds greater than 4 m s⁻¹ and lower loads, while nodular cast iron has greater wear resistance at lower speeds in the range of loads investigated - from 50 N cm⁻² to 200 N cm⁻²     

Variability in stepping direction explains the veering behavior of blind walkers.

Walking without vision results in veering, an inability to maintain a straight path that has important consequences for blind pedestrians. In this study, the authors addressed whether the source of veering in the absence of visual and auditory feedback is better attributed to errors in perceptual encoding or undetected motor error. Three experiments had the following results: No significant differences in the shapes of veering trajectories were found between blind and blindfolded participants; accuracy in detecting curved walking paths was not correlated with simple measures of veering behavior; and explicit perceptual cues to initial walking direction did not reduce veering. The authors present a model that accounts for the major characteristics of participants' veering behavior by postulating 3 independent sources of undetected motor error: initial orientation, consistent biases in step direction, and, most important, variable error in individual steps. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Crack growth in aluminium alloy sheet material under flight-simulation loading

Crack propagation tests were carried out on 2024-T3 sheet specimens to study the effects of omitting low-amplitude cycles from the gust-dominated TWIST load sequence (MiniTWIST) and the removal of small load ranges from the manoeuvre-dominated FALSTAFF load sequence (short FALSTAFF). In other tests high-amplitude loads of TWIST and MiniTWIST were truncated at different levels. The results are compared with data from similar test programmes, including crack initiation. Attention is paid to unstationary crack growth retardation and a transient retardation during initial crack growth started by an artificial crack.     

微波BJT超宽带低噪声放大器的设计

本文给出了一种频带覆盖达１０－１６００ＭＨｚ的微波ＢＪＴ超宽带低噪声放大器的设计方法，从微波ＢＪＴ的噪声模型出发，通过拟合５０Ω源阻抗下微波ＢＪＴ的噪声系数ＮＦ５０和Ｓ参数来提取其噪声参数，然后根据增益，噪声及驻波比要求优化设计放大器，使放大器在超宽带范围内获得平坦增益和低噪声，本文所给出的微波ＢＪＴ惨数提取及放大器优化设计方法已由实验结果所验证。     

超高层建筑物下嵌岩桩荷载传递性状的长期观测

对美国费城自由广场一号塔楼下的Ｇ一１０号嵌岩桩（８．８ｍＸ２．６～３．０ｍ，设计荷载５３８４９ｋＮ）在成桩后数月及上部结构施工期间和竣工后成功地进行了荷载传递性状的连续观测。本文介绍该桩的地质条件、桩身埋设的量测元件以及历时两年半的观测成果。观测表明，该桩在不同荷载水平下桩顶荷载的６０％～７０％始终由桩侧阻力分担。这一成果与第一作者先前根据嵌岩桩静载试验结果作出的结论相吻合。     

Micromechanical characterisation of fibre/matrix interfaces

Theoretical analyses for the single fibre pull-out and push-out models under monotonic loading are given which are based on a shear-lag analysis in a fracture mechanics approach considering non-constant friction at the debonded interface as a result of fibre Poisson contraction (or expansion). The solutions allow the determination of typical fibre/matrix interfacial properties such as the interfacial fracture toughness, G_ic, the coefficient of friction, μ, and the residual clamping stress, q₀. Under cyclic loading the interfacial properties are expected to degrade as a result of repetitive abrasion, and a power law function is assumed between μ and the number of elapsed cycles, N. However, G_ic is assumed to be unaffected and a fracture mechanics based debond criterion is derived for the relationship between the external applied stress, the debond length and the reduced friction coefficient for both fibre pull-out and fibre push-out. In addition, the relative displacements between the free fibre end and the matrix top are obtained for cyclic fatigue when the fibre is loaded and unloaded. A relationship obtained for the protrusion (or intrusion) length in fibre pull-out (or push-out) experiments allows the severity of the interface frictional degradation to be evaluated and characterised. Similarities and differences in the frictional degradation behaviour between fibre pull-out and push-out are also identified.     

优化非致冷红外探测器设计的理论模型

文章建立了一种改进非致冷红外探测器性能的数学模型，分析了探测器结构和噪声对于噪声等效温差NETD的影响，并给出了NETD与探测器温度TD，背景温度下TB，热导G以及探测单元面积A等因素的关系曲线，指出了探测器性能改进和优化的途径。     

频率伪随机捷变引信信号分析

根据频率捷变技术在无线电引信中的应用特点，分析了无线电引信发射频率伪随机捷变引信的信号特征，研究了其模糊函数和信号所携带的目标信息，指出提高无线电引信系统性能的技术途径，为频率捷变引信各种技术方案提供指导。     

抑制微光波前传感器随机噪声的方法研究

在自适应光学系统微光波前传感器中采用像增强器后，高帧频CCD输出的图像中会产生严重的随机噪声，影响光斑质心计算精度，从而使自适应光学系统波前探测精度降低。本文根据微光波前传感器中CCD输出图像的特点对中值滤波，均值滤波，自相关，延时相关等多种方法进行了仿真和实验比较，并提出了一系列评价方法。研究表明延时相关算法是最佳选择。     

用小波变换抑制SAR图像中的斑点噪声

抑制合成孔径雷达图像中的斑点噪声一直是处理图像并得到准确图像信息的难点，提出了一种基于小波变换抑制合成孔径雷达（SAR）图像中的斑点噪声的方法，对原有的小波变换方法作了改进，能更好地保留图像的边缘信息，并能简化计算量。在仿真实验中使用了合成的模拟图像和真实的合成孔径雷图像，并与以往的小波去噪滤波方法以及一些经典的斑点噪声滤波方法（包括中值滤波，Lee滤波，Frost滤波）进行比较，在综合考虑了滤波算法在均匀区域对斑点噪声的抑制能力以及保留边缘信息能力的情况下，提出的算法有更好的效果。