Development and performance evaluation of tropospheric scintillation model on Ku-band satellite link over Akure,Nigeria

Existing amplitude scintillation prediction models often perform less satisfactorily when deployed outside the regions where they were formulated. This necessitates the need to evaluate the performance of scintillation models developed in one region using data data from other regions while documenting their relative errors. Due to its variation with elevation angle, frequency, other link parameters and meteorological factors, we employed three years (January 2016 to December 2018) of concurrently measured satellite radio beacons and tropospheric weather parameters to develop a location-based amplitude scintillation prediction model over the Earth-space path of Akure (7.17^oN, 5.18^oE), South-western Nigeria. The satellite beacon measurement used Tektronix Y400 NetTek Analyzer at 1 s integration time while meteorological parameters, namely; temperature, pressure and relative humidity were measured using Davis Vantage Vue weather station at 1 min integration time. Comparative study of the model’s performance with nine (9) existing scintillation prediction models indicates that the best and worst performing models, in terms of root mean square error (RMSE), are the Statistical Temperature and Refractivity (STN) and direct physical and statistical prediction (DPSP) models with values 11.48 and 51.03 respectively. Also, worst month analysis indicates that April, with respective enhancement and fade values of 0.88 and 0.90 dB for 0.01% exceedance, is the overall worst calendar month for amplitude scintillation.     

基于梯度提升决策树的量子科学实验卫星光学实验预测

量子科学实验卫星在轨运行期间完成4种光学实验，地面监测人员通过遥测参数阈值判断卫星是否进行光学实验、实验类型及实验结果.这种方法需要预先设定大量阈值，并且这些阈值需要根据在轨卫星重新设定，可扩展性较差.针对以上问题，提出一种基于机器学习的光学实验判别方法，将量子科学实验卫星的光学实验监测任务抽象为机器学习中的多元分类问题，构建分类模型，利用量子科学实验卫星的真实历史遥测数据对模型进行训练，并通过真实实验计划对训练得到的模型进行验证.实验结果表明，本文提出的方法在没有专家先验知识的前提下，判别准确率达到99%，可用于量子科学实验卫星光学实验的实时监测任务.提出的基于机器学习的判别方法具有较强的可扩展性，可应用于卫星在轨运行的其他监测任务.      

基于随机维纳过程的航空发动机性能衰退研究

针对发动机下发间隔预测的问题，研究了发动机性能衰退规律。基于发动机排气温度裕度（EGTM）数据，建立了随机维纳模型，并使用严酷度因子修正模型，表征不同的工作条件对发动机的影响。利用期望最大化（EM）算法结合贝叶斯定理，对模型参数求解，最终得到了基于性能衰退的发动机平均下发间隔。研究结果表明，在严酷度因子为1.2696的使用条件下，某型号航空发动机性能衰退平均下发间隔为8219循环；基于该模型预测的发动机平均下发间隔与厂商建议的下发时间之间的误差仅为1.7%。     

基于变马赫数的五孔探针三维插值方法

探讨了五孔探针气动数据的插值方法,为提高插值精度,开发了基于传统线性插值法的三维线性插值法。该方法把同一探针在不同马赫数下的校准图形成三维数据库,将实验数据通过三维图进行插值。并使用改进前后的两种插值方法分别对校准风洞测得的数据进行整理,对比结果证明:在实验工况连续变化的情况下,三维线性插值法在插值精度上要优于传统线性插值法。特别是在来流马赫数变化较大时,该方法可以改善单一校准文件处理造成的数据精度问题,可用于自动化流场采集系统,为流场高速高精度采集奠定基础。     

电工电子线路虚拟实验室的建设与应用

虚拟技术的发展使电子线路的分析设计过程得以在计算机上轻松、准确、快捷地完成。这样,一方面克服了实验室在元器件和规格上的限制,避免了损坏仪器等不利因素,另一方面使得实验不受时间及空间的限制,从而促进电子线路实验教学的现代化。     

最小二乘直线函数的特性分析

证明了最小二乘直线函数是一种严格的凸函数。F(a,b)=∑(y-ax_i-b)~2是一个椭圆抛物面。a=[n∑x_iy_i-∑x_i∑y_i]/[n∑x_i^2-(∑x_i)~2]和b=[∑x_i^2∑y_i-∑x_i∑x_i∑y_i]/[n∑x_i^2-(∑x_i)~2]仅表示极值点。a=∑x_iy_i/∑x_i和 b=[∑x_i^2∑y_i-∑x_i∑x_iy_i]/[n∑x_i^2]在某些情况下可以是极值点,但不是在每种情况下都是极值点。     

A Novel Onboard-gateway-based Mechanism to Improve TCP Performance in Aeronautical Satellite Networks

The IP-based networks on aircraft serve to support Internet services via satellites. However, in aeronautical satellite hybrid net- works,the TCP protocol performance often deteriorates due to improper decreases and slow recovery of the congestion window. This paper proposes a window size determination and notification mechanism, onboard-gateway-based mechanism (OGBM), which is based on the onboard gateway in the networks on aircraft. A cross-layer approach is adopted by the onboard gateway to obtain the satellite link bandwidth information. And then, by the gateway, through changing the receiver’s advertised window field in ACK packets, TCP sources are notified of the window size of each TCP source calculated on the ground of bandwidth delay product and flow numbers. The mechanism is able to avoid improper changes of TCP window and serve multiple users. Simulation results show that the mechanism with the fairness index close to 1 improves TCP performance in aeronautical satellite networks.     

VO2薄膜制备工艺及电阻开关特性研究

用溶胶－凝胶法在非晶玻璃上制备VO2薄膜，经过熔融、涂膜、烘干和热处理等工艺最后得到电阻相变2－3个量级的VO2薄膜。对烘干温度、熔融温度、膜厚和热处理温度对薄膜电阻开关特性的影响进行了研究。通过XRD（X－ray diffraction)和XPS（X－ray photoelectron spectroscopy）对薄膜的结构和价态进行分析，表明用溶胶－凝胶法制图VO2膜工艺简单，重复性好。     

数据采集系统的总体评价

从性能指标出发，综述了数据采集系统总结评价技术的发展状况。并提出了对数据采集系统性能指标的两类分类方法 。     

铝合金冷挤压工艺的优化

本文介绍了6A02、6063铝合金冷挤压试验过程。通过专门装置测试铝合金冷挤压中不同凹模表面粗糙度、挤压速度、润滑剂、坯料状态的下的挤压力,利用正交试验L9(34)得出最优工艺参数。结果表明冷挤压过程中模具表面并非越光越有利于成形,坯料也要针对不同的挤压材料应选用不同的热处理方法。本实验为铝合金冷挤压提供了可行的实验方法和生产依据。