深空合作目标高概率捕获复合扫描策略研究

针对深空目标长距离星间激光通信时间滞后大、光轴抖动明显、不确定区域大的问题,设计了一种基于两级执行机构的抗抖动高概率捕获复合扫描策略。将目标位置不确定区域划分为等大正方形子区域,在子区域内采用光栅扫描,通过快摆镜实现;在子区域间按照光栅螺旋扫描顺序覆盖,通过伺服转台实现子区域间的跳转。然后在考虑光轴抖动的情况下基于遗传算法对子区域大小、扫描光斑重叠大小进行了优化,得到了参数优化后的扫描方案,并通过仿真进行了验证。1000次蒙特卡洛打靶结果表明,在目标位置不确定区域3.6mrad、激光束散角0.1mrad、光轴抖动标准差5μrad的情况下,优化后的扫描方案对目标的捕获概率为99.2%,对不确定区域的扫描时间为41.34s,扫描到目标的平均扫描时间为9.62s。     

一种新的星载自动识别系统检测概率计算方法

针对现有星载AIS检测概率计算方法没有考虑不同解调算法对检测结果影响的问题,提出了一种基于泊松分布船舶检测模型的星载AIS检测概率计算方法。该方法首先计算混叠信号功率差和频差的联合概率分布,以及算法的解调概率,进而将两者相结合得到表征算法能力的关键参数,代入AIS检测概率模型进行计算,可使得原有模型具有适应不同解调算法的能力。仿真表明该方法可有效应用于实际工程的评估,对星载AIS的系统设计有重要的参考价值。     

基于概率神经网络的相似度排序方法

为了研究相似度排序问题,对概率神经网络的结构进行了分析,对其输出进行了改进,使之输出后验概率,进而进行相似度排序。结合电火工品发火性能的预测问题,对方法进行了验证,结果表明：基于概率神经网络的相似度排序方法与实际结果相符,方法是可行的。     

基于自适应Kriging代理模型的交叉熵重要抽样法

对于复杂失效域和小失效概率耦合的可靠性分析问题,本文提出了一种交叉熵重要抽样（CE-IS）方法结合自适应Kriging （AK）代理模型的求解方法（CE-IS-AK）。所提方法基于交叉熵原理,用混合高斯模型逐步逼近最优重要抽样密度函数,并采用AK模型协助逼近过程中混合高斯模型的参数的更新,从而提高了CE-IS方法的计算效率。另外,本文还改进了CE-IS方法的收敛准则,避免了方法的冗余迭代,扩大了方法的适用范围。由于在CE-IS方法中引入了AK模型,因此,本文方法所构建的重要抽样函数在保证精度的基础上提高了效率。相较于AK-MCS方法,本文方法中引入了重要抽样的思想,因此在Kriging训练点数目基本相同的情况下,大幅缩减小失效概率计算时样本池规模,并且由于利用了混合高斯模型,因而对多失效域具有较好的适用性。算例分析也证明了本文所提方法的优越性。     

Latitudinal variation of the topside electron temperature at different levels of solar activity

A database of electron temperature (T_e) measurements comprising of most of the available satellite measurements in the topside ionosphere is used for studying the solar activity variations of the electron temperature T_e at different latitudes, altitudes, local times and seasons. The T_e data are grouped into three levels of solar activity (low, medium, high) at four altitude ranges, for day and night, and for equinox and solstices. We find that in general T_e changes with solar activity are small and comparable in magnitude with seasonal changes but much smaller than the changes with altitude, latitude, and from day to night. In all cases, except at low altitude during daytime, T_e increases with increasing solar activity. But this increase is not linear as assumed in most empirical T_e models but requires at least a parabolic approximation. At 550 km during daytime negative as well as positive correlation is found with solar activity. Our global data base allows to quantify the latitude range and seasonal conditions for which these correlations occur. A negative correlation with solar activity is found in the invdip latitude range from 20 to 55 degrees during equinox and from 20 degrees onward during winter. In the low latitude (20 to −20 degrees invdip) F-region there is almost no change with solar activity during solstice and a positive correlation during equinox. A positive correlation is also observed during summer from 30 degrees onward.     

火星磁层顶形成和变化的理论研究

考虑太阳风动压与行星电离层中的带电粒子热压及磁压之和平衡,建立了有大气（电离层）的行星磁层顶形成的理论模型,结合卫星对火星的观测数据,对子午面内向日侧火星磁层顶位形进行了数值计算和分析,研究了火星磁层顶位形及其与太阳风动压之间的变化关系．结果认为,火星磁层顶位形与地球磁层顶相似．太阳风动压越大,火星磁层顶越靠近火星;太阳风动压越弱,火星磁层顶越远离火星．根据火星内秉磁矩从古到今逐渐减小的观点,探索了大尺度磁场（内禀磁矩）对火星磁层顶的贡献作用,结果认为大尺度磁场越强,火星磁层顶越远离行星．这对于进一步研究火星磁层的长期演化以及其他行星磁层的位形变化都具有重要的意义．     

An attempt to study long-term variation of sporadic E layers using neural networks

Strong positive correlation between sporadic E layers and the solar activity and the long-term declining trend of Es were found in this paper. Then the feed-forward back propagation neural networks (NNs) were used to simulate the long-term variation of Es at four stations and predict foEs yearly average values. The inputs used for NNs are the yearly mean values of foEs in the daytime of the past ten years and the yearly averaged data of solar 10.7 cm radio flux (F107) of the present year, and the output is the present yearly mean value of daytime foEs. The outputs of trained NNs have high correlation with the desired values and the foEs yearly mean values predicted by NNs have good agreement with the observed data. The results indicate that NNs can make full use of the observed data to simulate the long variation rule of Es. Also, the results confirm the effect of solar activity on Es.     

Statistical characterisation of spread F over South Africa

The occurrence of mid-latitude spread F (SF) over South Africa has not been extensively studied since the installation of the DPS-4 digisondes in 1996 and 2000 at Grahamstown (33.32 °S, 26.50 °E) and Madimbo (22.38 °S, 30.88 °E) respectively. This study is intended to quantify the probability of occurrence of F region disturbances associated with SF over South Africa. A study was conducted using data for 8 years (2001–2008) over Madimbo (with a time resolution of 30 min) and Grahamstown (with a variable time resolution of 15 and 30 min). In this study, SF has been classified into frequency SF (FSF), range SF (RSF) and mixed SF (MSF). The SF events were identified by manually identifying ionograms showing SF and tabulating them according to type for further statistical analysis. The results show that the diurnal pattern of SF peaks strongly between 01:00 and 02:00 local time, LT (LT = UT + 2 h), where UT is the universal time. This pattern is true for all seasons and types of SF at Madimbo and Grahamstown in 2001 and 2005, except for RSF which had peaks during autumn and spring in 2001 at Madimbo. The probability of both MSF and FSF tends to increase with decreasing solar activity, with a peak in 2005 (a moderate solar activity period). The seasonal peaks of MSF and FSF are more frequent during winter months at both Madimbo and Grahamstown. In this study, SF was evident in ∼0.03% and ∼0.06% of the available ionograms at Madimbo and Grahamstown respectively during the 8 years.     

结构可靠性分析的模糊概率积分法

针对传统应力-强度干涉法计算结构可靠度时求解材料疲劳强度分布困难的情况,提出了一种利用模糊概率理论直接求解结构可靠度的算法——模糊概率积分法。对该方法进行了理论推导;同时考虑到方法应用过程中可能出现方程重积分困难的情况,又给出了以该方法为基础的数值抽样技术,用以计算结构可靠度的近似值。最后给出一个在航空发动机上的应用算例,计算结果表明该方法快速、有效,适合于工程应用。     

疲劳寿命估算的线性累积破坏率准则研究

介绍了一种新的疲劳寿命估算方法——线性累积破坏率准则,其物理意义明确,简单明了。在对恒幅载荷疲劳寿命统计分析的基础上,求出对应的疲劳寿命概率密度函数,从而利用线性累积破坏率准则可估算出变幅载荷下结构的疲劳寿命。线性累积破坏率准则没有限定试验条件和疲劳寿命分布形式,因此对一般环境下和腐蚀环境下的疲劳均具适用性。利用两组疲劳试验数据对该方法进行了验证,结果表明在中值寿命附近预测寿命与实测寿命非常接近,精度较高、有较好的工程应用价值。