基于新直觉模糊相似度的大规模群决策方法

研究了群体规模较大情况下基于直觉模糊评价信息的决策方法。提出一种新的直觉模糊相似度公式,研究了一种新的直觉模糊聚类方法,设计了一种基于新的聚类方法的核心决策者权重确定方法。实例分析说明了该方法的合理性和可行性。     

Different influences of u-InGaN upper waveguide on the performance of GaN-based blue and green laser diodes

Performances of blue and green laser diodes(LDs) with different u-InGaN upper waveguides(UWGs) are investigated theoretically by using LASTIP. It is found that the slope efficiency(SE) of blue LD decreases due to great optical loss when the indium content of u-InGaN UWG is more than 0.02, although its leakage current decreases obviously. Meanwhile the SE of the green LD increases when the indium content of u-InGaN UWG is varied from 0 to 0.05, which is attributed to the reduction of leakage current and the small increase of optical loss. Therefore, a new blue LD structure with In_(0.05) Ga_(0.95)N lower waveguide(LWG) is designed to reduce the optical loss, and its slope efficiency is improved significantly.     

Role of Ga vacancies in enhancing the leakage current of GaN Schottky barrier ultraviolet photodetectors

The leakage current of GaN Schottky barrier ultraviolet photodetectors is investigated. It is found that the photodetectors adopting undoped GaN instead of lightly Si-doped GaN as an active layer show a much lower leakage current even when they have a higher dislocation density. It is also found that the density of Ga vacancies in undoped GaN is much lower than in Si-doped GaN. The Ga vacancies may enhance tunneling and reduce effective Schottky barrier height, leading to an increase of leakage current. It suggests that when undoped GaN is used as the active layer, it is necessary to reduce the leakage current of GaN Schottky barrier ultraviolet photodetector.     

GaN-based violet laser diodes grown on free-standing GaN substrate

A violet laser diode (LD) structure is grown on a free-standing c-plane GaN substrate and 4~μ m× 800~μ m ridge waveguide LDs are fabricated. The electrical and the optical characteristics of LDs under different facet-coating and chip-mounting conditions are investigated under pulse mode operation. The active region temperatures of p-side up and p-side down mounted LDs are calculated with different injection currents. The calculated thermal resistances of p-side up and p-side down mounted LDs are 4.6~K/W and 3~K/W, respectively. The threshold current of the p-side down mounted LD is much lower than that of the p-side up mounted LD. The blue shift of the emission wavelength with increasing injection current is observed only for the LD with p-side down mounting configuration, due to the more efficient heat dissipation.     

宽带大功率声呐AM信号发射机的设计与实现

发射机是宽带大功率声呐的重要组成部分,其性能关系着声呐系统工作的有效性。本文研究一种程控的宽带大功率声呐AM信号发射机,信号源基于Delta-sigma DA原理设计,以现场可编程门阵列(Field-programmable gate array,FPGA)为核心器件,采用"FPGA+滤波器"的简化电路结构,单个IO引脚即可实现一个通道AM信号的产生,功率放大电路采用并联推挽的乙类线性放大电路结构,驱动相控基阵使其声源级水池测试可达238 d B,且具备连续相控发射15个脉宽5 ms脉冲信号的能力,达到了50%的相对带宽。水池测试验证了设计方案,工作稳定可靠。     

基于证据推理的不完全信息决策方法研究及应用

提出了一种基于证据推理和优化模型的不完全信息决策方法。针对专家认知偏好的多样性以及决策问题的复杂性特点,提出了一类评价指标不尽相同的不完全信息决策问题;运用证据理论中的基本信度分配来描述专家意见,给出了此类问题的信度函数、似真度函数、合成法则和不同专家贡献度的定义,计算了各个指标的基本信度分配值;从最大程度保持专家原始判断偏好的角度,建立了指标权重确定的优化模型;文后以商用飞机成本管控风险的重要性评价为例,说明了方法的应用步骤和有效性。     

纳米尺度点接触的实验研究

由交叉微米线构成了T形结构,并测量了Pt-Pt和Pt-Au节点的接触热阻和接触电阻。分析表明,增大接触点长度与宽度的比值,线接触模型和椭圆接触模型计算得到的接触热阻的差别逐渐减小,当比值超过20时,椭圆接触模型不再适用。测量得到的接触热阻随温度变化不明显,而接触电阻随温度升高而增大。由于存在表面绝缘层,接触热阻将远大于Wiedemann-Franz定律的预测值。考虑Kundsen数的影响以后,由接触电阻计算得到的金属接触点尺寸近似与温度无关。     

基于贝叶斯算法的CPU散热片结构自动优化

本文基于数值模拟、结构设计、优化设计以及贝叶斯优化算法提出一种针对散热片结构的自动优化框架，并对CPU正弦式散热片的振幅、周期和高度进行结构优化。结果表明，优化后的正弦式散热片与平板式散热片和初始正弦式散热片相比，表面平均努塞尔数提高了195%，表面最高温度降低了6.51?C。分析了优化前后正弦散热片场协同角的变化，进一步证实了流场和温度场协同性能对散热的本质影响。