泡沫镁的制备及应用前景

泡沫镁材料是一种极具潜力的新型材料,相比于实体金属镁和泡沫铝材料有许多特殊性能,然而国内对泡沫镁材料的研究相对较少。为方便学者对泡沫镁材料进行研究,简要介绍了泡沫镁材料的几种性能特点,论述了渗流铸造法、熔模铸造法、粉末冶金法、熔体发泡法、金属-气体共晶定向凝固法等几种重要的泡沫镁材料制备方法的工艺原理和优缺点。列举了国内外制备泡沫镁材料的一些实例,从泡沫镁材料的阻尼性能、吸能性能、仿生性能、散热性能等方面着重分析了泡沫镁材料在航空航天、生物医学、散热器、汽车等领域的应用前景。     

基于特征叠加网络的SAR海上舰船运动状态感知方法

针对合成孔径雷达(SAR)图像中的舰船检测与分类问题,常规的图像处理技术或者机器学习方式难以准确检测出海上舰船的类别以及当前舰船运行状态。因海上舰船目标具有相对于SAR图像尺寸较小、方位难以测算以及容易与其他目标混淆的特点,针对上述问题设计了端到端的海上舰船分类与状态感知模型,加入特征金字塔以达到拥有对于微小目标提取其深度特征,同时又保留其相对位置的目的;使用残差结构以解决特征融合网络层数增加导致的梯度消失问题;最后加入舰船状态感知模块,使其最终可以得到海上舰船目标相对于图像的角度值。使用公开SAR卫星图像进行了多次实验,最终体现出提出的端到端的模型具有较高的识别率以及良好的舰船状态估计能力。     

基于跟踪微分器的姿控喷管故障检测

针对航天飞行器姿控喷管故障的检测问题，提出了一种基于跟踪微分器(TD)的故障检测方法。该方法在考虑测量噪声、安装误差、转动惯量误差、姿控喷管特性、质心偏移等因素的基础上，设计了带低通滤波器的跟踪微分器，用来估计姿控喷管的输出力矩，并根据上述对象的实际偏差设计了无故障时估计力矩随指令力矩变化的力矩包络，即在无故障时估计力矩不会超出包络，通过检测估计力矩是否超出包络来判断是否发生故障。通过数学仿真，表明该方法能有效检测航天飞行器姿控喷管的故障，检测成功率高并且几乎没有误检。     

Correlation-weighted least squares residual algorithm for RAIM

The Least Squares Residual (LSR) algorithm, one of the classical Receiver Autonomous Integrity Monitoring (RAIM) algorithms for Global Navigation Satellite System (GNSS), presents a high Missed Detection Risk (MDR) for a large-slope faulty satellite and a high False Alarm Risk (FAR) for a small-slope faulty satellite. From the theoretical analysis of the high MDR and FAR cause, the optimal slope is determined, and thereby the optimal test statistic for fault detection is conceived, which can minimize the FAR with the MDR not exceeding its allowable value. To construct a test statistic approximate to the optimal one, the Correlation-Weighted LSR (CW-LSR) algorithm is proposed. The CW-LSR test statistic remains the sum of pseudorange residual squares, but the square for the most potentially faulty satellite, judged by correlation analysis between the pseudorange residual and observation error, is weighted with an optimal-slope-based factor. It does not obey the same distribution but has the same non-central parameter with the optimal test statistic. The superior performance of the CW-LSR algorithm is verified via simulation, both reducing the FAR for a small-slope faulty satellite with the MDR not exceeding its allowable value and reducing the MDR for a large-slope faulty satellite at the expense of FAR addition.     

Effect of biases in integrity monitoring for RTK positioning

In road transport, continuous high-accuracy positioning is required in real time. To ensure the proper functioning and safety of vehicular applications, integrity monitoring (IM) is needed to protect from the positioning errors under a certain alert limit (AL) with a pre-defined probability of misleading information (MI). In this study, a detailed threat model is developed for real-time kinematic (RTK) positioning application of short baselines. The model distinguishes between ambiguity-float and -fixed scenarios, and considers the influences of phase and code multipath as well as between-receiver atmospheric residuals. With the float ambiguities temporally constrained, the bias contribution that propagates with time-updated ambiguities was studied analytically for the horizontal protection level (HPL) in IM. Based on real data from both static and kinematic experiments, HPL was computed along the direction of the semi-major axis of the horizontal error ellipse. In ambiguity-float and -fixed cases, the HPL was mostly several meters and decimetres, respectively. It was found that time-propagated biases play a dominant role in the ambiguity-float HPL, and among them, phase and code multipath had in general the largest contributions. For ambiguity-fixed case, the phase multipath was found to play a dominant role in the HPL. This shows the importance of considering the biases in the RTK IM for both the ambiguity-float and -fixed scenarios. Given a horizontal alert limit (HAL) of 5 m, the availabilities of ambiguity-float solutions were low, i.e., below 50% for the static roof tests and below 5% for the kinematic road tests. For the ambiguity-fixed scenario, with HAL at 0.5 m, integrity availability was nearly 100% for the static roof tests and above 85% for the kinematic road tests.     

基于磁记忆技术对含缺陷焊缝的疲劳试验

对含有不同隐形损伤的40Cr焊板进行射线检测、疲劳试验和正交磁记忆信号测量，探索试件在疲劳应力作用下磁记忆信号的变化特征。试验结果表明：单一测量方式下的磁特征值不能表征焊板在疲劳循环载荷下的变化特征，所得结论存在偶然性；研究发现，可用磁场矢量梯度积分特征和磁场矢量合成梯度特征来评价焊板的疲劳损伤过程，并建立了以磁场矢量梯度特征为损伤参量的疲劳损伤模型，从而可以对含有隐形损伤焊接构件的疲劳寿命进行定量评估，为金属磁记忆技术在焊接缺陷定量评价上的进一步研究提供参考依据。     

10 cm ECR中和器性能优化实验研究

针对电子回旋共振(ECR)中和器性能无法满足实际应用需求的问题，开展了10 cm ECR中和器的性能优化实验研究，在分析现有ECR中和器内部结构的基础上，提出新的结构改进方案。通过改进ECR中和器的电子束流引出对比实验，得到了中和器结构对束流引出性能的影响规律。优化后的ECR中和器性能实验表明：相同条件下ECR中和器束流引出大小与气体流量大小不成正相关，但随着微波功率的增加而增加。性能实验得到的中和器最佳工作和性能参数为：微波功率为10 W、氙气流量为0.5 sccm，收集板间距为5 mm时，在50 V引出电压条件下能够引出127 mA的电子束流。     

考虑状态约束的弹性高超声速飞行器自适应饱和容错控制

针对弹性高超声速飞行器跟踪控制问题进行研究，主要考虑状态约束、输入饱和、执行器故障等约束条件。首先，将弹性模态、外界干扰和模型参数不确定性归结为一类带有未知上界的系统干扰。其次，根据被动容错思想，针对速度和高度子系统分别设计抗饱和自适应容错控制器，通过引入双曲正切函数和新型屏障李雅普诺夫函数分别处理了输入饱和与状态约束问题。最后，闭环系统的最终一致有界性采用李雅普诺夫方法证明，并通过仿真验证了所提定理的正确性。     

最优特征选择下多层次分割的城市道路提取

针对道路提取过程中特征维数过高的问题,提出了一种基于ReliefF过滤式和Wrapper封装式的特征选择方法.将粒子群优化算法(PSO)作为Wrapper的搜索算法,优化过的随机森林算法(OPRF)作为Wrapper的分类器构成PSO_OPRF封装式子集评估器,对ReliefF预选后的特征子集进行评估,降低特征维度,选...     

Optimal design of RTCs in digital circuit fault self-repair based on global signal optimization

Since digital circuits have been widely and thoroughly applied in various fields, electronic systems are increasingly more complicated and require greater reliability. Faults may occur in elec-tronic systems in complicated environments. If immediate field repairs are not made on the faults, elec-tronic systems will not run normally, and this will lead to serious losses. The traditional method for improving system reliability based on redundant fault-tolerant technique has been unable to meet the requirements. Therefore, on the basis of (evolvable hardware)-based and (reparation balance technology)-based electronic circuit fault self-repair strategy proposed in our preliminary work, the optimal design of rectification circuits (RTCs) in electronic circuit fault self-repair based on global sig-nal optimization is deeply researched in this paper. First of all, the basic theory of RTC optimal design based on global signal optimization is proposed. Secondly, relevant considerations and suitable ranges are analyzed. Then, the basic flow of RTC optimal design is researched. Eventually, a typical circuit is selected for simulation verification, and detailed simulated analysis is made on five circumstances that occur during RTC evolution. The simulation results prove that compared with the conventional design method based RTC, the global signal optimization design method based RTC is lower in hardware cost, faster in circuit evolution, higher in convergent precision, and higher in circuit evolution success rate. Therefore, the global signal optimization based RTC optimal design method applied in the elec-tronic circuit fault self-repair technology is proven to be feasible, effective, and advantageous.