水滴形歧管的结构分析

本文就衣架式模头水滴形歧管的结构设计，根据聚合物加工的流变理论，结合生产实际对水滴形截面的歧管流道分配系统进行分析，使得所设计的挤塑模在尽可能高的流速下，生产出符合尺寸及形状公差的均质片材。     

安全仪表系统设计的多目标优化

安全仪表系统在过程工业中日益受到更多关注,为满足安全仪表系统多目标优化问题对于安全完整性等级的综合要求,提出一种改进的多目标遗传优化方法.首先研究了安全仪表系统多目标优化中存在的问题,然后结合安全仪表系统优化问题的特殊性提出了一种更加适合用于安全仪表系统多目标优化的方法,最后将该方法应用于一个实例.结果表明:改进的方法能够解决安全仪表系统优化对于安全完整性等级要求的优化偏好问题,所得到的解比原有方法的解更具参考价值.     

非线性方程组求解的一种新方法

针对现有的非线性方程组求解方法不能同时收敛到所有解的问题,提出了一种混合小生境遗传算法的求解新方法.采用确定性拥挤小生境创造出种群的小生境进化环境,克服遗传算法的遗传漂移现象,维持种群的多样性,使算法能同时收敛到多个解;以拟牛顿算法作为遗传算法的局部搜索算子进行精确搜索,进一步提高算法收敛速度和精度.选择了几组典型的多解非线性方程组进行了求解验证,结果表明所设计的混合小生境遗传算法能在解的定义域内同时收敛到所有解,收敛速度快、精度高,是求解非线性方程组全局解的一种有效方法.     

一种基于最小生成树的多目标进化算法

怎样保证朝Pareto最优解的方向搜索和如何获得均匀分布且范围广泛的非支配解是多目标进化算法(MOEA)设计时的两个关键问题,它们很大程度上取决于适应度赋值和外部种群维护这两个重要部分.提出了一种基于最小生成树的多目标进化算法(MST_MOEA).在考虑了个体间支配关系的基础上,利用个体与非支配集的距离和不同等级个体的树聚集密度来对适应度赋值;在外部种群的非支配解个数超过规定的种群规模时,用树的度数和树聚集密度对其进行修剪.将其应用于不同维数下9个测试函数,并与NSGA-II,SPEA2进行对比,结果证实了算法良好的收敛性和分布性.     

一种改进的多目标粒子群优化算法

针对多目标粒子群优化算法在迭代过程中收敛速度和多样性方面的不足,提出一种改进的多目标粒子群优化算法(IMOPSO).采用基于栅格和拥挤距离的协同外部档案维护策略,通过更准确地选择收敛性和多样性性能更好的非劣粒子作为全局最优值,加快整个种群的收敛速度;采用分段Logistic混沌映射、外部档案检测机制及修改的粒子速度更新公式,分别在初始化阶段和迭代过程中增强种群的多样性;最后,通过对标准测试函数仿真测试证明了改进后的算法能够快速收敛至Pareto最优前沿并保持较好的多样性.     

Simultaneous extraction of source and drain resistances in top contact organic thin film transistors from a single test structure

A method of extraction of source and drain resistances in linear mode of operation from a single transistor is described. The proposed method can also be used to measure source resistance over the entire operating range from linear to saturation mode of operation. The method uses two floating probes outside the channel, one adjacent to the source and the other to the drain to sense the voltage under these contacts. Using transmission line analysis, the source and drain resistances are directly extracted from these measurements. 2D numerical simulation results confirm the validity of the proposed technique and sensitivity analysis shows that the method is more accurate than the conventional gated four probe technique, especially, when the source resistance is much smaller than the channel resistance. Experimental results obtained with Pentacene top-contact transistors are used to illustrate the proposed technique. Analysis of two devices with very different source resistance is carried out to highlight the ability of the proposed technique to offer insight into the different contributing factors. Current crowding under the source contact and accurate estimation of mobility without the distorting effects of source resistance are also described.     

High-performance and current crowding-free InGaN-GaNbased LEDs integrated by an electrically-reverse-connected Schottky diode and a Mg-delta doped p-GaN

This work demonstrates high-performance and current crowding-free InGaN/GaN light-emitting diodes (LEDs) using an electrically-reverse-connected Schottky diode (SD) and an Mg-delta (δ) doped layer.Poss...     

Improved performance of lateral GaN-based light emitting diodes with novel buried CBL structure in ITO film and reflective electrodes

In this letter, lateral GaN-based Light Emitting Diodes (LEDs) with a SiO₂ current blocking layer (CBL) buried in the indium tin oxide (ITO) film and highly reflective metal materials have been proposed. Compared with the conventional CBL structure which was inserted between ITO film and p-type GaN, simulation results showed that LEDs with a buried CBL in the ITO film effectively facilitated current spreading under the CBL. We demonstrated that buried CBL was beneficial for suppressing current crowding (CC) effect around the edge of CBL and may facilitate higher LED efficiency. Furthermore, experimental results showed that LEDs with the buried structure we proposed showed lower working voltage and higher light output power (LOP) compared with those with conventional CBL structure. These results further confirmed that the buried CBL scheme was effective to reduce current crowding (CC) effect. In addition, highly reflective metal materials of Cr/Al/Pt/Au were employed to reduce light absorption and achieve high light extraction efficiency.     

Temperature and current-density distributions in flip-chip solder joints with Cu traces

Three-dimensional simulation was performed to investigate the temperature and current density distribution in flip-chip solder joints with Cu traces during current stressing. It was found that the Cu traces can reduce the Joule heating effect significantly at high stressing currents. When the solder joints were stressed by 0.6 A, the average temperature increases in solder bumps with the Al traces was 26.7°C, and it was deceased to 18.7°C for the solder joint with the Cu traces. Hot spots exist in the solder near the entrance points of the Al or Cu traces. The temperature increases in the hot spot were 29.3°C and 20.6°C, for solder joints with the Al traces and Cu traces, respectively. As for current density distribution, the maximum current density inside the solder decreased slightly from 1.66×10⁵ A/cm² to 1.46×10⁵ A/cm² when the Al traces were replaced by the Cu traces. The solder joints with the Cu traces exhibited lower Joule heating and current crowding effects than those with the Al traces, which was mainly attributed to the lower electrical conductivity of the Cu traces. Therefore, the solder joints with the Cu traces are expected to have better electromigration resistance.