Visualizing light-to-electricity conversion process in InGaN/GaN multi-quantum wells with a p-n junction

Absorption and carrier transport behavior plays an important role in the light-to-electricity conversion process, which is difficult to characterize. Here we develop a method to visualize such a conversion process in the InGaN/GaN multiquantum wells embedded in a p-n junction. Under non-resonant absorption conditions, a photocurrent was generated and the photoluminescence intensity decayed by more than 70% when the p-n junction out-circuit was switched from open to short. However, when the excitation photon energy decreased to the resonant absorption edge, the photocurrent dropped drastically and the photoluminescence under open and short circuit conditions showed similar intensity. These results indicate that the escaping of the photo-generated carriers from the quantum wells is closely related to the excitation photon energy.     

Experimental and numerical investigation of a Hall thruster with a chamfered channel wall

A discharge channel with a chamfered wall not only has application in the design of modern Hall thrusters, but also exists where the channel wall is eroded, and so is a common status for these units. In this paper, the laws and mechanisms that govern the effect of the chamfered wall on the performance of a Hall thruster are investigated. By applying both experimental measurement and particle-in-cell simulation, it is determined that there is a moderate chamfer angle that can further improve the optimal performance obtained with a straight channel. This is because the chamfering of the wall near the channel exit can enhance ion acceleration and effectively reduce ion recombination on the wall, which is favorable to the promotion of the thrust and efficiency. However, the chamfer angle should not be too large; otherwise, both the density of the propellant gas and the distribution of the plasma potential in the channel are influenced, which is undesirable for efficient propellant utilization and beam concentration. Therefore, it is suggested that the chamfer shape of the channel wall is an important factor that must be carefully considered in the design of Hall thrusters.     

一种快速提取连续CT脑肿瘤病灶区的算法

脑肿瘤图像提取就是将肿瘤病灶区域(水肿、坏死、癌变)从正常的脑部组织(灰质、白质、脑脊液)分开,精确的脑肿瘤分割对脑瘤的诊断、研究和治疗有重要的临床意义。针对传统脑部CT肿瘤病灶提取的缺点,即需要耗费大量时间并且分割精度不高的问题,提出一种综合了形态学重建、分水岭分割和改进的区域生长算法。先用形态学重建进行去噪,再用结合多尺度梯度分水岭分割提取整个图像的边界,然后在肿瘤病灶区域内选取种子点进行区域生长,提取肿瘤区域轮廓,滤除其他封闭区域,得到的图像作为改进的区域生长法的初始分割区域,使用改进的区域生长法,滤除过分割区域。实验结果显示该算法分割出的结果有效区域大,分割精度高。结论：该算法提高了分割精度,由于不用匹配结构参数,加快了分割速度,具有一定的临床价值。     

光折变晶体中双光束反向传输引起非稳

实验研究了光折变晶体中双光束反向传输引起非稳的时空特性，从实时信号的功率谱分析和相关维数的计算，确证了系统由准周期运动经周期三到达混沌。     

基于刀口法的视频内窥镜调制传递函数测量

为完善医用硬性内窥镜成像质量的检测方式,设计了基于刀口法的内窥镜调制传递函数测量系统。建立了刀口扫描法的理论模型,通过CMOS对高精度扫描的刀口像的灰度值进行采样获得刀口扩散函数,再将其进行微分和傅里叶变换得到内窥镜的调制传递函数。实验对0°鼻窦镜进行多次测量,经过分析计算得到的调制传递函数曲线较为稳定,结果表明该系统能够实现对内窥镜调制传递函数的自动化测量。     

模糊投资组合选择问题的改进帝企鹅优化算法

模糊投资组合选择问题是在基本投资组合模型中引入模糊集理论,使所建立的模型与实际市场更加吻合,但同时也增加了模型求解难度.因此,本文针对两种不同的模糊投资组合模型,提出一种改进帝企鹅优化算法.算法首先引入可行性准则,处理模糊投资组合模型中的约束.其次,算法中加入变异机制,平衡算法的开发和探索能力,引导种群向最优个体收敛.通过对CEC 2006中的13个标准测试问题及两个模糊投资组合问题实例进行数值实验,并与其他群智能优化算法进行结果比较,发现本文所提出的算法具有较好的优化性能,并且对于求解模糊投资组合选择问题是有效的.     

纳米银的制备及其应用

本文采用紫外光化学法制备了纳米银胶,通过观察发现,在混合溶液搅拌的过程中溶液颜色没有任何变化,在紫外灯照射的过程中混合溶液经历了一系列的颜色变化。通过研究硝酸银的浓度对银胶吸收光谱的影响,发现随着硝酸银浓度的增加,银胶的吸收峰先红移然后蓝移,即随着硝酸银溶液浓度的增大,银粒子尺寸最终将减小。最后通过霉菌实验研究了纳米银的应用,发现纳米银具有较强的杀菌作用。     

Superjunction nanoscale partially narrow mesa IGBT towards superior performance

We present a detailed study of a superjunction(SJ) nanoscale partially narrow mesa(PNM) insulated gate bipolar transistor(IGBT) structure. This structure is created by combining the nanoscale PNM structure and the SJ structure together. It demonstrates an ultra-low saturation voltage(V_(ce(sat))) and low turn-off loss(E_(off)) while maintaining other device parameters. Compared with the conventional 1.2 k V trench IGBT, our simulation result shows that the V_(ce(sat))of this structure decreases to 0.94 V, which is close to the theoretical limit of 1.2 k V IGBT. Meanwhile, the fall time decreases from109.7 ns to 12 ns and the E off is down to only 37% of that of the conventional structure. The superior tradeoff characteristic between V_(ce(sat))and E_(off) is presented owing to the nanometer level mesa width and SJ structure. Moreover, the short circuit degeneration phenomenon in the very narrow mesa structure due to the collector-induced barriers lowering(CIBL) effect is not observed in this structure. Thus, enough short circuit ability can be achieved by using wide, floating P-well technique.Based on these structure advantages, the SJ-PNM-IGBT with nanoscale mesa width indicates a potentially superior overall performance towards the IGBT parameter limit.     

终端设备环境温度检测算法及实验研究

环境温度对于终端电子设备的功耗和温度管理至关重要,而设备内部的温度传感器受内热源影响无法直接检测所在环境的温度。因此,针对含有多个瞬态内热源的终端设备,本文提出基于传热反问题迭代求解的实时环境温度检测算法。通过简化热容热阻网络模型建立系统传热方程,提出双传感器预测偏差修正策略解决由于已知量不足产生的不适定性。此外,基于实际智能手机的实验结果表明算法对实时动态环境温度的检测相对误差在10%以内。