Material response and failure mechanism of unidirectional metal matrix composites under impulsive shear loading

The material response and failure mechanism of unidirectional metal matrix composite under impulsive shear loading are investigated in this paper. Both experimental and analytical studies were performed. The shear strength of unidirectional C-f/A356.0 composite and A356.0 aluminum alloy at high strain rate were measured with a modified split Hopkinson torsional bar technique. The results indicated that the carbon fibers did not improve the shear strength of aluminum matrix if the fiber orientation aligned with the shear loading axis. The microscopic inspection of the fractured surface showed a multi-scale zigzag feature which implied a complicated shear failure mechanism in the composite. In addition to testing, the micromechanical stress field in the composite was analyzed by the generalized Eshelby equivalent method (GEEM). The influence of cracking in matrix on the micromechanical stress field was investigated as well. The results showed that the stress distribution in the composite is quite nonhomogeneous and very high shear stress concentrations are found in some regions in the matrix. The high shear stress concentration in the matrix induces tensile cracking at 45 degrees to the shear direction. This in turn aggravates the stress concentration at the fiber/matrix interface and finally leads to a catastrophic failure in the composite. From the correlation between the analysis and experimental results, the shear failure mechanism of unidirectional C-f/A356.0 composite can be elucidated qualitatively.

A linkage map of common carp (Cyprinus carpio) based on AFLP and microsatellite markers

P>Common carp (Cyprinus carpio) is an important fish for aquaculture, but genomics of this species is still in its infancy. In this study, a linkage map of common carp based on Amplified Fragment Length Polymorphism (AFLP) and microsatellite (SSR) markers has been generated using gynogenetic haploids. Of 926 markers genotyped, 151 (149 AFLPs, two SSRs) were distorted and eliminated from the linkage analyses. A total of 699 AFLP and 20 microsatellite (SSR) markers were assigned to the map, which comprised 64 linkage groups and covered 5506.9 cM Kosambi, with an average interval distance of 7.66 cM Kosambi. The normality tests on interval map distances showed a non-normal marker distribution. Visual inspection of the map distance distribution histogram showed a cluster of interval map distances on the left side of the chart, which suggested the occurrence of AFLP marker clusters. On the other hand, the lack of an obvious cluster on the right side showed that there were a few big gaps which need more markers to bridge. The correlation analysis showed a highly significant relatedness between the length of linkage group and the number of markers, indicating that the AFLP markers in this map were randomly distributed among different linkage groups. This study is helpful for research into the common carp genome and for further studies of genetics and marker-assisted breeding in this species.

Isolation, characterization and electron microscopic single particle analysis of the NADH : ubiquinone oxidoreductase (complex I) from the hyperthermophilic eubacterium Aquifex aeolicus

The proton-translocating NADH:ubiquinone oxidoreductase (complex I) has been purified from Aquifex aeolicus, a hyperthermophilic eubacterium of known genome sequence. The purified detergent solubilized enzyme is highly active above 50 degreesC. The specific activity for electron transfer from NADH to decylubiquinone is 29 U/mg at 80 degreesC. The A. aeolicus complex I is completely sensitive to rotenone and 2-n-decyl-quinazoline-4-yl-amine. SDS polyacrylamide gel electrophoresis shows that it may contain up to 14 subunits. N-terminal amino acid sequencing of the bands indicates the presence of a stable subcomplex, which is composed of subunits E, F, and G. The isolated complex is highly stable and active in a temperature range from 50 to 90 degreesC, with a half-life of about 10 h at 80 degreesC. The activity shows a linear Arrhenius plot at 50-85 degreesC with an activation energy at 31.92 J/mol K. Single particle electron microscopy shows that the A. aeolicus complex I has the typical L-shape. However, visual inspection of averaged images reveals many more details in the external arm of the complex than has been observed for complex I from other sources. In addition, the angle (90degrees) between the cytoplasmic peripheral arm and the membrane intrinsic arm of the complex appears to be invariant.

LURR's Twenty Years and Its Perspective

Seismogenic process is a nonlinear and irreversible one, so that the response to loading of a seismogenic zone is different from the unloading one. This difference reflects quantitatively the process of an earthquake preparation. A physics-based new parameter-Load/Unload Response Ratio (LURR) was proposed to measure quantitatively the proximity to a strong earthquake and then used to be an earthquake predictor. In the present paper, a brief history of LURR is recalled; inspection of real earthquake cases, numerical simulations and laboratory studies of LURR, prediction efforts in terms of LURR, probability problem of LURR and its prospect are also expatiated.

加氢反应器壁原子氢分布的在线、实时、无损检测新技术

为了在线、实时、无损检测高温高压条件下运行的加氢反应器的多层器壁中原子氢的渗透速率和在任何指定剖面上的体浓度分布，发展了一种新型的检测技术．介绍了检测仪的结构设计及其特征。

激光拼焊焊缝质量在线检测技术研究

激光拼焊作为一种新的高质量焊接技术，已经广泛应用于汽车，航空、造船等领域，对提高我国装备制造水平有重要意义。激光拼焊过程中由于焊接装置与焊接工艺的一些时变因素，导致焊接质量存在一定波动，因此，必须对焊缝进行在线实时质量检测，这不仅可以保证焊接质量，而且有助于实现焊接的自动化。目前，国外成熟的激光拼焊系统中，焊缝质量实时检测技术已经成为实现激光拼焊自动化的关键部分。但该项技术国内目前仍处于研究阶段。因此，研制应用于激光拼焊的焊缝质量实时检测系统，实现焊接过程的自动化在学术理论性及工程应用性上具有重要研究意义。本文以激光拼焊为背景，针对激光焊接焊缝质量检测中存在的科学问题和实际应用需求，参考了国外先进的焊缝质量检测系统，应用机器视觉原理对焊缝质量检测方法进行了研究。 本文首先介绍了基于结构光视觉检测原理建立的焊缝质量检测系统。其次重点研究了焊缝质量检测系统的图像处理算法。图像处理算法是整个检测系统的核心内容，其处理的速度与精度直接影响到系统的实时性与准确性。本文依据ISO13919-1 B级焊缝质量标准设计了基于结构光的焊缝图像处理算法。算法主要分三步：首先准确提取结构光光纹中心线，其次提取光纹中心线特征点，最后，根据光纹的几何形状以及所提取的特征点，计算焊缝缺陷参数。第二部分系统介绍了结构光视觉传感器的标定原理及方法，针对激光拼焊焊缝质量检测应用需求，研究了焊缝质量检测视觉传感器直接标定方法。并设计了标定方法的具体实现，通过在局部区域建立光平面到像平面之间的线性函数关系，像平面中的任意一个像点对应的物理坐标，可以通过线性插值算出。实验结果表明，标定精度可以满足激光拼焊质量检测系统的精度要求，且便于工程实现。第三部分针对激光拼焊质量检测需求，进行了焊缝质量检测系统的软、硬件设计及实现。重点研究了软件实现中的一些关键问题，如Windows实现检测系统的方法，进程、线程的优先级，三维重建等。最后在该检测系统实验平台上进行了图像处理算法的精度与速度的验证，实验结果表明图像算法结果满足系统要求。最后，本文对所做的研究工作进行了总结，并对今后的工作进行了展望。

图像采集与处理系统的USB通信接口设计

本文介绍了一种利用DSP处理DM642、CPLD及USB芯片等器件构造的带有USB接口的图像采集和处理系统。设计了USB通信接口的硬件电路,在DSP/BIOS架构上编写了USB的固件程序和主机端的设备驱动程序。该系统可用于香烟包装流水线上的条包检测等对生产速度要求较高的工业流程领域。

空间注意系统中的动物特异性模块

Human being’s visual attentional system is the direct results of millions of years of evolutionary selection. As an adaptation to the environment, the most prominent function of attentional system is to facilitate the effective selection and subsequent processing of the most critical information and events from the environment with the aim of enhancing a given individual’s chance of passing his/her gene to the next generation. In the living environment of ancestral human beings, animals were undoubtedly one of those stimulus categories of great evolutionary significance. Since the process of animal-related information had life-or-death consequences for ancestral human beings, some researchers proposed a so-called animate monitoring hypothesis which states that there exists a category-specific module in the attentional system of human beings which specializes in the detection and frequent re-inspection of animal stimuli. Drawing on the available findings and theories regarding the inhibition-of-return effect, the present study utilized several variants of the spatial cueing paradigm to test the two main predictions of animate monitoring hypothesis：（1） animal stimuli in the environment are capable of summon attention in a reflexive way; （2） the inhibitory effect of attentional process on animal stimuli is less pronounced when compared to stimuli of other categories. The results of the present study provide supportive evidence to the existence of a category-specific module for animals in the attentional system. The present study contributes to the further understanding of the important role played by attentional mechanism in solving the critical adaptive problem faced by ancestral human beings during the course of evolution.