Experiment and analysis of the effect of fine tracking system on the unstable platform in laser communication

Atmospheric turbulence and platform vibration in the space optical communication can cause the offset and jitter of beam, which further result in the fluctuations of received optical power. To resist this effect, a communication system with fine tracking systems in the receiver and transmitter is designed. The system is used in the experiment of laser communication between high-rise buildings over a distance of 3.5 km. After adding a vibration source to the transmitter, the centroids of spots captured by the camera of the transmitter and the optical power of receiver are recorded for the purpose of analysis. When the vibration source works at the designated frequency, a peak appears at the corresponding frequency in the spectrum of the spot centroids and the optical power of receiver. Then the peak disappears once the fine tracking system begins to work. Compared with the condition without the fine tracking system, the minimum value of the optical power of receiver is increased by 5 dB, and the standard deviation is decreased by 30%.     

空间遥感器CCD模块热设计与仿真分析

某星载差分吸收光谱仪是一种高精度的空间光学遥感器,利用成像光谱仪成像到电荷耦合器件(charge coupled device,CCD)面阵探测器,获取高光谱、高空间分辨率的光谱信息。由于采用了多块CCD作为关键的探测器,CCD模块的温度水平、波动范围和速率、每轨温度波动及温度梯度对仪器的正常工作与测量精度有较大影响,温控指标要求较高。由于光机结构紧凑复杂,且需兼顾光路系统的温度要求,导致CCD模块的散热成为整个系统中的难点。综合分析了该太阳同步轨道载荷的外热流变化情况,针对CCD模块的结构布局特点及热耗分布情况,为满足探测器对温度环境的要求,提出了被动热控为主,主动热控为辅的设计方案;利用I-DEAS/TMG热分析软件对光谱仪CCD模块的在轨温度水平进行了仿真计算,得到典型工况下各CCD散热环节的温度分布及温度波动情况;计算结果显示:紫外光通道CCD发热面温度在22℃以下,可见光通道CCD发热面温度在15℃以下,每轨温度波动在2℃以内。光学箱侧板温度较均匀,设计的导热路径合理有效,能够将CCD模块热耗及时排散,同时将CCD发热面温度控制在较好的范围内。结果满足指标要求,热设计合理可行。     

功率MOSFET零温度系数点的研究

为研究功率MOSFET零温度系数点（Zero Temperature Coefficient,ZTC）,不同栅极电压对温度系数的影响,本文基于阈值电压和迁移率的温度关系并结合功率MOSFET输出特性模型,得到了随栅极电压变化而出现的三种不同温度系数。利用实际测试验证了温度系数的变化规律,结果表明：在小栅极电压条件下,线性区和饱和区均为正温度系数;随栅极电压增大,线性区先进入负温度系数,饱和区仍然为正温度系数,并因此产生了零温度系数点;随栅极电压进一步增大,线性区和饱和区都进入负温度系数。同时根据测试数据,分析了ZTC在不同栅极电压条件下随温度的变化原因,并基于测试数据讨论了迁移率随栅极电压和温度的变化关系。     

A Method for Quantification of the Effects of Size and Geometry on the Microstructure of Miniature Interconnects

Because the heterogeneity of microstructure has significant effects on the material properties of ultrafine interconnects, it should be quantified, to facilitate high-fidelity prediction of reliability. To address this challenge, a method based on autocorrelation and singular value decomposition is proposed for quantitative characterization of microstructure. The method was validated by developing a quantitative relationship between reported microstructure and tensile strength for SnAgCuRE solders reported in the literature. The method was used to study the effects of size and geometry in ultrafine Sn37Pb interconnects on microstructure and von Mises stress, which were obtained simultaneously by coupling a phase-field model with an elastic mechanical model. By use of this method the degree of heterogeneity of the microstructure in relation to preferred growth directions of the phases was quantified by use of a scalar microstructure index. It was found that microstructure heterogeneity increases with decreasing standoff height, and is higher for hourglass-shaped solder joints. The average von Mises stress was found to be positively related to the microstructure index. The strong correlation between microstructure index and average von Mises stress was confirmed by nonlinear regression analysis using an artificial neural network. This indicates that the mechanical behavior of ultrafine interconnects can be predicted more accurately on the basis of the microstructure index.     

A novel low-complexity power allocation algorithm based on the NOMA system in a low-speed environment

For future wireless communication systems, Power Domain Non-Orthogonal Multiple Access (PD-NOMA) using an advanced receiver has been considered as a promising radio access technology candidate. Power allocation plays an important role in the PD-NOMA system because it considerably affects the total throughput and Geometric Mean User Throughput (GMUT) performance. However, most existing studies have not completely accounted for the computational complexity of the power allocation process when the User Terminals (UTs) move in a slow fading channel environment. To resolve such problems, a power allocation method is proposed to considerably reduce the search space of a Full Search Power (FSP) allocation algorithm. The initial power reallocation coefficients will be set to start with former optimal values by the proposed Lemma before searching for optimal power reallocation coefficients based on total throughput performance. Step size and correction granularity will be adjusted within a much narrower power search range while invalid power combinations may be reasonably discarded during the search process. The simulation results show that the proposed power reallocation scheme can greatly reduce computational complexity while the total throughput and GMUT performance loss are not greater than 1.5% compared with the FSP algorithm.     

聚乙二醇阴极修饰层改善聚合物太阳能电池光电性能的研究

通过将聚乙二醇(PEG)掺入活性层制备聚合物太阳 能电池,利用PEG的迁移特性获得阴极修饰层,研 究PEG阴极修饰层对聚合物太阳能电池光电性能的影响。X射线光电子能谱(XPS)分 析表明,掺入活性层中的 PEG迁移到活性层与Al电极之间,形成了阴极缓冲层。吸收光谱、电流密度-电压 特性曲线和外量子 效率谱的分析表明,PEG阴极缓冲层的形成改善了活性层与阴极的界面接触特性, 降低了活性层与电 极之间的能级势垒,有利于载流子传输,因此显著地改善了聚合物太阳能电池的光电性能, 使得器件的开 路电压Voc、短路电流密度Jsc和填充因子(FF)都有明显提高。当P3HT:PCBM 活性层中掺入体积比为0.5%的PEG时,聚合物太阳能电池的能量转换 效率(P CE)最高,达到了3.07%,比未掺杂PEG的参考器件提 高了38.5%。     

Evanescent-Coupled Ge p-i-n Photodetectors on Si-Waveguide With SEG-Ge and Comparative Study of Lateral and Vertical p-i-n Configurations

Si-waveguide-integrated lateral Ge p-i-n photodetectors using novel Si/SiGe buffer and two-step Ge-process are demonstrated for the first time. Comparative analysis between lateral Ge p-i-n and vertical p-Si/i-Ge/n-Ge p-i-n is made. Light is evanescently coupled from Si waveguide to the overlaying Ge- detector, achieving high responsivity of 1.16 A/W at 1550 nm with f_{3 dB} bandwidth of 3.4 GHz for lateral Ge p-i-n detector at 5 V reverse bias. In contrast, vertical p-Si/i-Ge/n-Ge p-i-n has lower responsivity of 0.29 A/W but higher bandwidth of 5.5 GHz at -5 V bias. The higher responsivity of lateral p-i-n detectors is attributed to smaller optical mode overlap with highly doped Ge region as in vertical p-i-n configuration.     

用冠层温度计算作物缺水指标的一种简化模式

本文对Ｊａｃｓｋｏｎ等人提出利用作物冠层温度计算作物缺水指标的模式进行了简化，并根据甘肃民勤县棉花和宁夏吴忠春小麦的田间试验资料进行了验证，结果表明该简化模式可用于诊断作物缺水状况。     

泥石流浆体屈服应力的计算方法

大量试验资料表明，泥石流浆体具有屈服应力，很多研究成果表明，浆体屈服应力由两部分组成，即网格结构的联结力和沙粒间的摩擦力，本文以颗粒电化学理论为基础，从理论上导出这两部分的表达式，得到浆体屈服应力公式，并用试验资料进行了验证。     

三峡地区的水土流失与水土保持

三峡地区沟壑纵横、地形破碎，交通不便、生态环境恶化，经济和社会发展一直比较缓慢，三峡工程的兴建，给三峡地区的经济和社会发展带来了良好的机遇，了对这一地区的农业生产和生态保护提出出更高的要求。１９８８年，国务院批准将长江上游列为国家水土保持重点防治区，这是增强三峡地区的农业基础设施改善生态环境，实现该地区经济可持续发展的基础工程。