Evaluation of subgrain formation in Al2O3–SiC nanocomposites

Both theoretical analysis and transmission electron microscopy (TEM) complementary studies have been conducted to evaluate the possible role of subgrain formation as a strengthening mechanism in a nanocomposite consisting of Al2O3 and 5 vol % 0.15 m SiC particles. The theoretical calculation predicted that the residual stresses due to thermal expansion mismatch between Al2O3 and SiC are insufficient to induce the extensive plastic deformation required for subgrain formation upon annealing. This prediction was consistent with TEM observations that the bulk of the material was completely free from subgrains, and that only a low density of dislocations was present in isolated areas. The results suggest, therefore, that microstructure refinement through subgrain formation cannot account for the superior mechanical behaviour of the nanocomposite reported in previous studies.TEM examination of the ground surfaces revealed significant plastic deformation in both single phase Al2O3 and the nanocomposite. Upon annealing at 1300°C for 2 h, dislocation-free subgrains were formed in Al2O3, whereas a high density of tangled dislocations were present in the nanocomposite. These observed differences are consistent with the fact that during annealing, residual stress relaxation is more difficult in the nanocomposite than in Al2O3.     

基于DFT基的矿井视频监控图像分块压缩感知方法

针对矿井视频监控图像受噪声干扰影响大,采用常规的图像采样和压缩方法存在图像模糊和传输时间过长等问题,提出了一种矿井视频监控图像分块压缩感知方法。该方法通过建立矿井视频监控图像分块压缩感知模型,在井下图像采集节点利用稀疏随机矩阵进行压缩采样,然后在地面监控中心利用正交匹配追踪( OMP )算法重构图像。研究结果表明,采用本文算法的重构图像误差小、重构时间短,所需信号采样点数少;与扰频Hadamard矩阵相比,采用稀疏随机矩阵和高斯随机矩阵作为观测矩阵对图像信号重构的峰值信噪比( PSNR)提高4 dB~5 dB;本文算法与基于小波基的算法相比,信号重构的PSNR提高1 dB~4 dB,重构时间缩短至少80％以上。     

缓变曲线改善120°弯道水沙运动的三维数值模拟

人工河道的弯道段大多曲率单一,水流动力轴线的曲率与弯道曲率难以匹配,导致了流固分离和弯道二次流的产生。针对弯道曲率突变问题,引入两种插有缓变曲线的弯道形式,研究缓变曲线对120°弯道水沙特性的影响和流态的改善。运用MIKE 3水动力模型和泥沙输移模型对单曲线弯道、缓圆缓弯道和对称凸弯道进行数值模拟,对比分析不同弯道型式在冲刷和定床两种工况下的近底流速、水面横比降和超高、弯道环流和河床冲淤变形。研究结果表明：插有缓变曲线的两种弯道可以遏制弯道中水体湍动的发展,改善120°弯道水流的流态,能够有效减小弯道凹岸冲刷、凸岸淤积的现象,缓解河床的冲淤变形。     

面心立方金属冷拔织构的计算机模拟

为了预测面心立方金属线材在冷拔过程中形变织构的演变规律,采用Taylor模型对面心立方金属冷拔织构进行模拟.采用线性规划求解剪切速率,通过计算每五个滑移系组合对应的晶粒转动的平均值作为最终的晶粒转动来解决滑移系选择模糊性问题.模拟结果表明,面心立方金属线材在拉拔过程中产生〈111〉和〈001〉纤维织构组分,〈111〉为稳定的织构组分.在变形量较小的情况下,〈001〉、〈111〉纤维织构组分比较漫散.随着变形量的增加,〈001〉、〈111〉纤维织构组分的漫散程度变小.模拟与拉拔铜线材形变织构实测结果的对比表明,采用Taylor模型能够很好模拟冷拔面心立方金属材料形变织构的演变规律.     

Fabrication of integrated resistors in printed circuit boards

In order to utilize integrated passive technology in printed circuit boards (PCBs),manufacturing processing for integrated resistors by lamination method was investigated.Integrated resistors fabricated from Ohmega technologies in the experiment were 1 408 pieces per panel with four different patterns A,B,C and D and four resistance values of 25,50,75 and 100 Ω.Six panel per batch and four batches were performed totally.The testing was done for 960 pieces of integrated resistors randomly selected with the s...     

草酸反萃沉淀法从负载钇的P507中提取富钇

研究了草酸反萃并直接沉淀负载富钇的P507有机相中富钇的工艺参数,考察了草酸反萃富钇过程中草酸用量、反萃温度、反萃相比O/A、反萃时间、反萃级数对稀土反萃率的影响。结果表明,草酸反萃最佳的工艺参数为:草酸用量为理论值的130%、反萃温度25℃、O/A=1/1、反萃时间20min、反萃级数11级,在此条件下,富钇稀土反萃率为99.45%,所得富钇产品质量为TREO98.0%、Cl~-0.05%、残碳0.042%。     

A generalization of the potential function method to multiclass pattern classification†

A generalization of the potential function method is made for multi-class pattern classification. Based on the construction of a set of separation functions an algorithm is proposed for teaching automata to classify various classes of input patterns. Using a basic assumption that the potential functions are bounded and the separation functions can be represented by a linear combination of a set of certain real scalar functions, the convergence of the algorithm is proved.     

A computational method for optimal control problems with a free final time using the modified quasilinearization and the gradient method†

This paper presents a computational method for the solution of a class of optimal control problems with a free final time. The method is based on the combination of the modified quasilinearization and the gradient method. A numerical example is included for illustration.     

THE CURRENT DISTRIBUTION IN THROUGH-HOLE ELECTRODEPOSITION.I:MASS TRANSFER

A realistic representation of through-hole geometry consists of a cylindrical tube with an abrupt decrease in the radius in the middle section of the tube. Fluid flow, mass transfer, and geometric effects were included in modeling through-hole electrodeposition process. The current distribution under mass-transfer limited conditions was computed for both the inside and outside surfaces of a through-hole.     

The effect of in-stent restenosis on hemodialysis access patency

Endovascular stents have recently been shown to extend access patency in thrombosed and stenotic arteriovenous grafts (AVG). Concern remains over the frequency and severity of in-stent restenosis, though this has not been rigorously defined to date. The study was a retrospective analysis of hemodialysis patients referred for access dysfunction during a 2-year period. Using a prospectively collected, vascular access database, we identified 76 patients seen for follow-up angiography due to access dysfunction after stent placement. We compared the effect of in-stent restenosis vs. de novo lesions in patients with previously placed endovascular stents. Measured outcomes were primary assisted patency and frequency of in-stent and de novo lesions. Thirty-five (46.1%) patients had de novo lesions, while 41 (53.9%) had in-stent restenosis. In-stent restenosis was found to be the only factor associated with severity of luminal stenosis (β=0.35, 95% confidence interval 2.21–15.48, P=0.01). In-stent restenosis was associated with increased primary patency among AVGs (hazards ratio 3.10; 95% confidence interval 1.35–7.10; P=0.008). Primary patency of in-stent restenosis vs. de novo lesions for AVGs were respectively: 78% vs. 94% at 1 month, 56% vs. 42% at 3 months, 33% vs. 6% at 6 months. For arteriovenous fistulae, the difference in primary patency of in-stent vs. de novo lesions was not statistically significant. In-stent restenosis is associated with higher percent luminal diameter lesions, while de novo lesions rather than in-stent restenosis are associated with higher risk of AVG access failure and reduced primary patency.