On parallel solution of linear elasticity problems: Part I: theory

The discretized linear elasticity problem is solved by the preconditioned conjugate gradient (pcg) method. Mainly we consider the linear isotropic case but we also comment on the more general linear orthotropic problem. The preconditioner is based on the separate displacement component (sdc) part of the equations of elasticity. The preconditioning system consists of two or three subsystems (in two or three dimensions) also called inner systems, each of which is solved by the incomplete factorization pcg-method, i.e., we perform inner iterations. A finite element discretization and node numbering giving a high degree of partial parallelism with equal processor load for the solution of these systems by the MIC(0) pcg method is presented. In general, the incomplete factorization requires an M-matrix. This property is studied for the elasticity problem. The rate of convergence of the pcg-method is analysed for different preconditionings based on the sdc-part of the elasticity equations. In the following two parts of this trilogy we will focus more on parallelism and implementation aspects. © 1998 John Wiley & Sons, Ltd.     

碳纤维阴极发射均匀性的实验研究

 分别用自制浸渍碘化铯（CsI）针式环状碳纤维阴极和环状不锈钢阴极所产生的电子束轰击尼龙目击靶,研究碳纤维阴极发射均匀性。在碳纤维阴极电子束轰击的目击靶上得到了均匀的烧蚀痕迹,而不锈钢阴极电子束轰击的目击靶上烧蚀痕迹不均匀,表明碳纤维阴极发射电子束的均匀性优于不锈钢阴极。分析认为两阴极不同的发射机制及其所特有的材料性质和结构导致其发射电子束均匀性的差异。用光学显微镜和电子显微镜对不锈钢阴极尖端和碳纤维阴极尖端和侧面进行扫描,发现不锈钢阴极仅尖端处被烧蚀,而碳纤维阴极尖端和侧面都有烧蚀痕迹,验证了碳纤维阴极由场发射和表面闪络共同作用的发射机制的假设分析。     

Electrodeposition of alginate with PEDOT/PSS coated MWCNTs to make an interpenetrating conducting hydrogel for neural interface

Neural interface is a critical component for the communication between the central nervous system and outside devices. But neural tissues withstand constant mechanical activity with outside devices which aggravates inflammation response. The investigation about soft interfacial modification materials for neural implants is a promising way to reduce the mechanical mismatch of neural tissues and implants. In this study, soft alginic acid gel and poly(3, 4-ethylenedioxythiophene)/poly(styrene sulfate)(PEDOT/PSS) coated multi-walled carbon nanotubes(MWCNT) was co-deposited on a microwire neural electrode, then PEDOT/PSS was electrochemically grown through the coating material to form a kind of soft interpenetrating networks (IPNs) for the improvement of neural interface. Compared to unmodified electrodes, the modified electrodes possess higher charge storage capacity (CSC) and lower electrochemical impedance, which would benefit the performance of stimulating and recording respectively. The IPNs are very soft after reswelling in brain tissue, and the cell experiment indicate its fantastic biocompatibility. Furthermore, acute neural recording experiments revealed that the IPNs reduced the noise floor. All these characteristics are greatly desired for the neural interface. Overall, we developed a soft interpenetrating conducting hydrogel coating material on the neural interface with excellent electrical and biological performance.     

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基于以前的偏滤器研究,提出了中国核聚变工程实验堆(CFETR)偏滤器靶板的概念设计.在最差工况下进行的热工水力分析和力学分析表明,应力和温度都在允许范围内,验证了该设计模型的可靠性.该概念模型和对其所做的分析可以为以后的工程设计提供参考.     

高光谱成像技术的柚类品种鉴别研究

柚类种质和品种资源繁多,现有的柚类品种鉴别方法检测时间长,费用高。旨在利用高光谱成像技术探索主要柚类品种快速识别的可行性。试验选用4个具有代表性的柚类品种,利用高光谱成像技术,采集240个叶片样本(60个/品种)上表面和下表面的高光谱图像。高光谱图像标定后,提取样本感兴趣区域平均光谱信息作为样本的光谱进行分析。利用Kennard-Stone法将样本划分为校正集(192个)和验证集(48个)。采用多元散射校正(MSC)和标准正态变量变换(SNV)对原始光谱曲线进行预处理后,分别采用主成分分析 (PCA)和连续投影算法 (SPA )提取最佳主成分和有效波长,并将其作为最小二乘支持向量机(LS-SVM)的输入变量,建立基于叶片上表面和下表面光谱信息的PCA-LS-SVM和SPA-LS-SVM 模型。结果显示,基于叶片上表面光谱信息建立的PCA-LS-SVM和SPA-LS-SVM 模型对建模集样本的识别正确率分别为99.46%和98.44%,对预测集样本的识别正确率均为95.83%。基于叶片下表面光谱信息建立的PCA-LS-SVM和SPA-LS-SVM模型对建模集样本和预测集样本的识别正确率皆为100%。表明,利用高光谱成像技术结合PCA-LS-SVM和SPA-LS-SVM可实现柚类品种的快速鉴别,叶片下表面光谱信息鉴别效果优于叶片上表面。该研究为柚类的品种快速鉴别提供了一种新方法。     

双邻位甲基取代的聚芳醚酮合成与表征

两种单体 2 ,2′ ,6 ,6′ 四甲基 4 ,4′ 二苯氧基二苯酮 (o M2 DPOBP)和 2 ,2′ ,6 ,6′ 四甲基 4 ,4′ 二苯氧基三苯二酮 (o M2 DPOTPDK) ,分别与对苯二甲酰氯 (TPC)和间苯二甲酰氯 (IPC)低温亲电溶液缩聚 ,合成了 4种含双邻位甲基侧基聚醚酮醚酮酮 (DM PEKEKK和DM PEKEKMK)及含双邻位甲基侧基聚醚酮酮醚酮酮 (DM PEKKEKK和DM PEKKEKMK)聚合物 .用FT IR、1 H NMR、DSC、TGA、WAXD等方法对聚合物进行了表征 ,研究了聚合物的溶解性能 .结果表明 ,该 4种聚合物具有较高的玻璃化转变温度 ,良好的热稳定性和优良的溶解性能 .     

聚氨酯泡沫低温下平均线膨胀系数的测定

使用相对比较法对聚氨酯泡沫从液氮温度到室温的平均线膨胀系数进行了测试。采用的试验装置具有微机自动测温系统、抽真空系统以及电加热系统 ,保证了测试的准确性。结果表明 :聚氨酯泡沫具有非常低的平均线膨胀系数 ,在平行与垂直发泡方向的膨胀性能差异不大。最后对试验进行了误差分析 ,得到最大相对误差为 8%。     

低温液体管路输送中几个问题的分析

对低温液体传输过程中气体置换、预冷过程、竖直管道中间歇泉现象、盲支管填充时和阀门开启时的不稳定现象作了较详细分析,指出了其可能造成的危害,并提出了相应的解决方法。