风电场雷达杂波动态重构抑制方法

随着风电场的大范围建设，风轮机杂波对雷达的干扰问题日益严重，常规杂波抑制方法难以有效解决风轮机杂波（WTC）干扰问题，因此提出了一种利用动态字典对风轮机杂波进行稀疏重构进而抑制的方法。首先，建立了WTC干扰下的雷达信号模型并分析了风轮机杂波的信号特征。其次，依据WTC的时频特征提出了一种微动参数粗估计方法，利用粗估计结果缩小了字典稀疏重构参数范围，在此基础上利用正交匹配追踪（OMP）算法对字典进行动态生成，并逐级更新字典原子。最后，通过动态字典对风轮机杂波信号进行稀疏重构，从而实现了对WTC的有效抑制。通过仿真实验，分析了风轮机杂波对目标检测的干扰影响，验证了基于动态稀疏重构的风电场杂波抑制方法在不同情况下的有效性。     

Robust three-dimensional path-following control for an under-actuated stratospheric airship

This paper proposes a robust three-dimensional (3-D) path-following controller for an under-actuated stratospheric airship in the presence of uncertainties. The resultant control system exhibits an inner-outer loop control structure. In the outer control loop, the path-following error dynamics is constructed in a moving Serret-Frenet frame and a new guidance law with the sideslip and attack angle compensation is designed, which decreases the path-following steady-state error. In the inner control loop, a disturbance observer based backstepping control law is proposed to achieve the desired dynamic behavior on the path. Furthermore, a new velocity tracking control strategy is developed which aligns the resultant velocity tangent to the path. Finally, numerical simulation results are shown to verify the effectiveness of the proposed controller.     

基于机器视觉的万用表数字识别技术研究

为提高手持式数字万用表校准系统的自动化水平，本文通过研究图像灰度阈值法、传统方法的目标分类和深度学习三种不同类型的字符识别技术，提出了两种基于机器视觉的数字识别方案。测试结果显示，两种方案的字符识别准确率均可达到99.8%，但其在硬件资源占比、编程难易程度上二者还存在显著差异。该机器视觉字符识别功能的成功开发与应用，可为更多无程控通信接口的计量测试设备，及一些不适于人工作业的危险计量工作环境进行类似的数字识别提供借鉴。     

地基光学图像中本体-帆板结构航天器姿态估计方法

提出一种利用地基光学图像估计空间目标姿态的方法。针对本体-帆板结构航天器外形结构特点，定义了一种不易遮挡的两轴结构特征，设计了地基光学图像中该特征的提取方法；根据航天器成像过程建立了特征点二三维几何投影方程，实现了航天器三维姿态的解算。利用单站序列图像，可获得航天器姿态变化角速度信息。在轨航天器的试验结果表明，本方法能有效地从地基光学图像估计出航天器姿态。     

Comparison of RO tropopause height based on different tropopause determination methods

The tropopause is an important boundary in the Earth’s atmosphere, and has been the subject of close attention from atmosphere and climate researchers. To monitor the global tropopause using radio occultation (RO) data, there are two primary methods, one is the widely used temperature lapse rate method, and the other is the bending angle covariance transform method which is unique to RO data. We use FengYun3-C (FY3C) and Meteorological Operational Satellite Program (MetOp) RO data and European Centre for Medium-Range Weather Forecasts (ECMWF) operational analysis data to determine differences in RO tropopause height calculated by these two methods. We compute biases of the RO lapse rate tropopause height (LRTH) and the RO bending angle tropopause height (BATH) relative to the ECMWF LRTH. The dependences of the tropopause height biases on tropopause height (TPH) retrieval method, latitude, season and RO mission are investigated. The results indicate that BATH show a consistent 0.8–1.2 km positive bias over the tropics and high latitude regions compared with LRTH, however, over 25° to 40° latitude in both hemisphere, BATH results are less stable. Furthermore, the mean bias between BATH and LRTH displayed a different symmetrical characteristic from 2017.12 to 2018.2 (DJF) compared to 2018.6–2018.8 (JJA). However, except for some bias over Antarctica, the mean value of both LRTH and BATH show a similar tropopause variation, indicating the consistency of both methods.     

Long-term time-varying characteristics of UPD products generated by a global and regional network and their interoperable application in PPP

The quality and availability of Uncalibrated Phase Delay (UPD) solutions are crucial to the Precise Point Positioning (PPP) service, and the long-term temporal variability and its contributing factors should be better understood. In this paper, we comprehensively investigate the long-term time-varying characteristics of each UPD product respectively generated by a global and regional network and their interoperable application in PPP-AR (ambiguity resolution), the sampling of the WL and NL UPDs are daily and 30 s, respectively. Firstly, in terms of our 30 day Wide-Lane (WL) UPD products of 31 satellites, the Standard Deviation (STD) of each satellite WL UPDs ranges from 0.04 to 0.06 cycles, indicating that the long-term prediction accuracy of satellite WL UPD is sufficient for fixing Wide-Lane ambiguities. Secondly, when a satellite in eclipsing the discontinulity may corrupt the determination of Narrow-Lane (NL) UPD in form of offset, as a result of lacking or poor satellite attitude dynamic modeling. When the influence of discontinuity is removed, the STD of our estimated satellite NL UPDs is less than 0.05 cycles. Thirdly, the STD of our estimated receiver WL UPDs is mainly below 0.2 cycles, which implies that its stability is one order poorer that of the satellite. In addition, if they are used for stations in and around the network covered region, the stability of the UPD products from the CMONOC (Crustal Movement Observation Network of China) is better than that from a global network, benefit from the fact that all the CMONOC stations are equipped with the same receiver type. Finally, the PPP-AR results show that a rate of 82.9% for stations with a WL-ambiguity-fixed rate of over 90% while 69.5% for stations with an NL-ambiguity-fixed rate of over 80% can be achieved when using UPD from the global network, which is worse than that of using UPD from the CMONOC (85.7% for stations with a WL-ambiguity-fixed rate of over 90% while 75% for stations with an NL-ambiguity-fixed rate of over 80%). The results of the experiment on the UPD interoperable application in PPP show that the global network UPD products can provide a fast AR at any single station, and the convergence time is well below 25 min. Particularly, when the location of a station is in and around the regional network, our results show that the PPP results obtained using regional UPDs enable the consistent use of global UPDs. When the location of a station is far away from the regional network, using the regional UPDs can not achieve PPP-AR. Finally, the WL UPDs of the previous day is used for forecasting to estimate the NL UPDs, the stability analysis results of NL UPDs solution and positioning results are demonstrate the validity of forecasted UPD products.     

Solid-State Electrolytes for Lithium-Sulfur Batteries

Secondary lithium-sulfur batteries have attracted extensive attention due to their high energy density,low cost and environment friendly.However,the"shuttle effect"of polysulfides dissolved in liquid electrolytes leads to a decrease of the cell Coulomb efficiency(CE).Therefore,researchers have used solid electrolytes instead of traditional liquid electrolytes and separators to suppress the"shuttle effect"of polysulfides and the growth of lithium dendrites.The progress in electrolytes for solid-state lithium-sulfur batteries including solid-state polymer,inorganic,and composite electrolytes to solve the issues is summarized.     

基于任务的作战飞机效能评估模型

针对作战飞机的任务效能评估问题,提出了基于作战飞机任务的任务效能新概念;采用概率分析方法将飞机作战过程分解并抽象为一组概率值,建立了相应的任务效能评估模型;该模型可以在兼顾传统仿真评估模型结果精度的同时,具有模型简明、计算消耗低、方便快捷等特点;更具有实际作战指挥意义,其快速可信的评估结果有利于作战指挥官进行合理的、科学的任务规划,从而有利于在执行特定任务时更好地运用现有的作战飞机和武器;算例结果表明该模型可以较为有效地对作战飞机携带不同机载武器时在不同作战环境中打击不同作战目标进行效能评估.     

Effect of salt stress on growth and physiology in amaranth and lettuce: Implications for bioregenerative life support system

Growing plants can be used to clean waste water in bioregenerative life support system (BLSS). However, NaCl contained in the human urine always restricts plant growth and further reduces the degree of mass cycle closure of the system (i.e. salt stress). This work determined the effect of NaCl stress on physiological characteristics of plants for the life support system. Amaranth (Amaranthus tricolor L. var. Huahong) and leaf lettuce (Lactuca sativa L. var. Luoma) were cultivated at nutrient solutions with different NaCl contents (0, 1000, 5000 and 10,000 ppm, respectively) for 10 to 18 days after planted in the Controlled Ecological Life Support System Experimental Facility in China. Results showed that the two plants have different responses to the salt stress. The amaranth showed higher salt-tolerance with NaCl stress. If NaCl content in the solution is below 5000 ppm, the salt stress effect is insignificant on above-ground biomass output, leaf photosynthesis rate, Fv/Fm, photosynthesis pigment contents, activities of antioxidant enzymes, and inducing lipid peroxidation. On the other hand, the lettuce is sensitive to NaCl which significantly decreases those indices of growth and physiology. Notably, the lettuce remains high productivity of edible biomass in low NaCl stress, although its salt-tolerant limitation is lower than amaranth. Therefore, we recommended that amaranth could be cultivated under a higher NaCl stress condition (<5000 ppm) for NaCl recycle while lettuce should be under a lower NaCl stress (<1000 ppm) for water cleaning in future BLSS.     

船舶涡旋流堵漏桨叶位置与涡旋流形成效果的关系研究

船舶涡旋流堵漏方法是为克服现有堵漏手段存在的不足而提出的一种新技术思想。在自行设计制作了专门实验装置的基础上,分别利用柔性桨叶和刚性桨叶进行了一系列涡旋流堵漏实验,定量研究了桨叶工作位置对破口进水量的影响规律,进而揭示了桨叶位置与涡旋流形成效果的关系。实验结果发现：当桨叶与破口处于同一高度且距离破口越近时,对降低破口进水量的效果越明显,使用于堵漏的时间可延长300%以上。这一结论可为船舶涡旋流堵漏方法的完善提供必要的理论基础和实验依据。