多分量雷达辐射源信号的检测与分离

针对多分量雷达辐射源信号难以有效检测与分离的问题,提出了时频变换结合时变滤波的方法。通过图像分割中的区域生长法在时频平面对各分量进行检测,对其中的线性调频分量采用分数阶傅里叶变换进行优先分离,再对时频或频域没有耦合的分量进行滤波,最后通过支持向量机划分分类线,用于时频耦合分量的分离。仿真实验结果表明,该方法可以对多分量信号进行有效的检测与分离。     

Atmosphere sounding by GPS radio occultation: First results from TanDEM-X and comparison with TerraSAR-X

On 21 June 2010 the TerraSAR-X satellite was joined by the TanDEM-X satellite. A Global Positioning System (GPS) radio occultation (RO) experiment using the twin satellites has been carried out to estimate the precision of GPS atmospheric soundings. For the Day Of Year (DOY) 330–336, 2011, we analyze phase and amplitude data recorded by GPS receivers separated by a few hundred meters in a low earth orbit and derive collocated atmospheric refractivity profiles. In the altitude range 10–20 km the standard deviation between TerraSAR-X and TanDEM-X refractivity does not exceed 0.15%. The standard deviation is rapidly increasing for lower and higher altitudes; close to the surface and at an altitude of 30 km the standard deviation reaches 0.8% and 0.5%, respectively. Systematic deviations between TerraSAR-X and TanDEM-X refractivity in the considered altitude range (0–30 km) are negligible. The results confirm the anticipated high precision of the GPS RO technique. However, the difference in the retrieved refractivity in the lower troposphere for different Open Loop (OL) signal tracking parameters, altered onboard TanDEM-X for DOY 49–55, 2012, calls for an in depth analysis. At the moment we can not exclude that a potential bias in the OL Doppler model introduces a bias in our retrieved refractivity at altitudes <8$<8$ km.     

Stochastic processes for line shapes and intensities

Stochastic processes provide flexible and fast calculations for modeling dynamical interactions between an atom and charged particles. We use a stochastic renewal process for the plasma microfield being the cause of Stark broadening. The accuracy and improvement possibilities of Lyman profiles calculations with a renewal process are analyzed by comparing to ab initio simulations for ion broadening only. Stochastic processes may also be applied to out of equilibrium plasmas. We present our first results for the effect of Langmuir waves on a line broadened by electrons only, and for the changes of atomic populations submitted to strong temperature fluctuations.     

尺寸公差的工艺能力指数评价方法

根据对尺寸公差分析方法和工艺能力评价方法在统计学方面的理论成果,结合飞机装配中的尺寸协调准确度控制目标与控制要求,实现对航空制造的尺寸公差分配。研究了飞机数字化装配协调过程中采用基于工艺能力指数的方法评估装配尺寸的协调准确度。     

航母运动对舰载飞机着舰安全性的影响

总结了舰载飞机的着舰安全性分类等级,研究了航母的航行运动以及随海浪的摇晃和振荡运动对舰载机着舰安全性的影响规律,并给出了与舰载机进舰速度适配的最优航母航行速度.研究结果表明:由于航母的航行方向与舰载机的进舰方向存在一定的夹角,驾驶员在进舰过程中必须协调操纵副翼和方向舵才能保证舰载机安全准确地着舰;航母航行速度越大,驾驶员操纵量越大,着舰偏差也越大.海况越恶劣,着舰信号指挥官对航母运动的预报和补偿效果越差,着舰失败概率越大.因此,为保证舰载机的着舰安全,必须选择合适的航母航行速度,同时应尽量选择在平稳的海况下进舰着舰.      

基于“世界大学城”空间平台的空间课程建设的研究与实践

针对教师空间课程建设中广泛存在的问题,对空间课程建设进行了研究。介绍了基于“世界大学城”空间平台的空间课程建设过程中的基本理论和基本原则,详细说明了空间课程建设的内容和建设过程,并给出了《ASP.NET技术》空间课程建设实例。     

一种非周期调制直扩信号扩频码估计方法

对卫星测控中一类扩频码周期与信息码周期之比为非整数的直扩信号进行了研究,得出这类信号可建模成非周期调制直扩信号,提出并讨论了一种基于差分主元分析（D PCA）的非周期调制直扩信号扩频码估计方法,该方法通过计算与差分序列协方差矩阵的最大特征值对应的特征向量完成信息码个数、子序列、信息码同步点等参数的估计,解决了传统矩阵分解方法在估计码序列时码序列相位模糊问题,理论分析和仿真结果表明该方法可以在低信噪比下进行有效估计。     

基于空域稀疏性的宽带DOA估计

利用宽带阵列接收信号的空域稀疏性,将宽带信号的波达方向(DOA)估计转化为一个稀疏信号重构的问题,提出了一种新的宽带信号DOA估计算法。该算法将宽带信号分解为多个子带信号,联合利用多个子带信号的空域稀疏性进行重构。它是对用于稀疏重构的标准的稀疏贝叶斯学习算法的推广,可适用于多冗余字典的信号模型。另外,通过对多快拍的阵列接收信号进行奇异值分解(SVD),提取信号子空间作为算法的输入数据,可以在有效减少运算复杂度的同时,提高对噪声的稳健性。与传统的宽带阵列DOA估计方法相比,该算法能够用于低信噪比、快拍有限和信源相关性较高的场合,同时算法的性能对信源个数的估计值不太敏感。仿真实验表明,该算法相对现有的基于子空间类的方法,具有更好的DOA估计性能。     

基于浴盆曲线故障率函数的FFOP预计方法

与传统可靠性指标中假设产品的随机失效不可避免不同,无故障工作期(FFOP)内产品不会发生任何故障(即零故障)。首先阐述了FFOP的概念内涵、与平均故障间隔时间(MTBF)的区别和联系,提出了一种FFOP的预计方法。该方法假设产品的故障率函数具有浴盆曲线特征、故障发生过程为泊松过程、产品具有固定的免维修工作期。然后以一种改进的Weibull分布函数描述具有浴盆曲线函数特征产品的故障率。基于泊松过程理论,给出了FFOP的预计算法、流程和仿真验证手段。最后以某型无人机舵机为案例对研究方法的可用性进行了验证。结果表明:FFOP与免维修工作期(MFOP)、置信度水平密切相关,及时维修的产品能够保证较长的FFOP。在工程应用时,FFOP的确定应综合考虑运行维护费用进行权衡。     

A Fault Sample Simulation Approach for Virtual Testability Demonstration Test

Virtual testability demonstration test has many advantages,such as low cost,high efficiency,low risk and few restrictions.It brings new requirements to the fault sample generation.A fault sample simulation approach for virtual testability demonstration test based on stochastic process theory is proposed.First,the similarities and differences of fault sample generation between physical testability demonstration test and virtual testability demonstration test are discussed.Second,it is pointed out that the fault occurrence process subject to perfect repair is renewal process.Third,the interarrival time distribution function of the next fault event is given.Steps and flowcharts of fault sample generation are introduced.The number of faults and their occurrence time are obtained by statistical simulation.Finally,experiments are carried out on a stable tracking platform.Because a variety of types of life distributions and maintenance modes are considered and some assumptions are removed,the sample size and structure of fault sample simulation results are more similar to the actual results and more reasonable.The proposed method can effectively guide the fault injection in virtual testability demonstration test.