Orbital stability close to asteroid 624 Hektor using the polyhedral model

We investigate the orbital stability close to the unique L4-point Jupiter binary Trojan asteroid 624 Hektor. The gravitational potential of 624 Hektor is calculated using the polyhedron model with observational data of 2038 faces and 1021 vertexes. Previous studies have presented three different density values for 624 Hektor. The equilibrium points in the gravitational potential of 624 Hektor with different density values have been studied in detail. There are five equilibrium points in the gravitational potential of 624 Hektor no matter the density value. The positions, Jacobian, eigenvalues, topological cases, stability, as well as the Hessian matrix of the equilibrium points are investigated. For the three different density values the number, topological cases, and the stability of the equilibrium points with different density values are the same. However, the positions of the equilibrium points vary with the density value of the asteroid 624 Hektor. The outer equilibrium points move away from the asteroid’s mass center when the density increases, and the inner equilibrium point moves close to the asteroid’s mass center when the density increases. There exist unstable periodic orbits near the surface of 624 Hektor. We calculated an orbit near the primary’s equatorial plane of this binary Trojan asteroid; the results indicate that the orbit remains stable after 28.8375?d.     

Evaluation of a regional real-time precise positioning system based on GPS/BeiDou observations in Australia

The performance of real-time (RT) precise positioning can be improved by utilizing observations from multiple Global Navigation Satellite Systems (GNSS) instead of one particular system. Since the end of 2012, BeiDou, independently established by China, began to provide operational services for users in the Asia-Pacific regions. In this study, a regional RT precise positioning system is developed to evaluate the performance of GPS/BeiDou observations in Australia in providing high precision positioning services for users. Fixing three hourly updated satellite orbits, RT correction messages are generated and broadcasted by processing RT observation/navigation data streams from the national network of GNSS Continuously Operating Reference Stations in Australia (AUSCORS) at the server side. At the user side, RT PPP is realized by processing RT data streams and the RT correction messages received. RT clock offsets, for which the accuracy reached 0.07 and 0.28?ns for GPS and BeiDou, respectively, can be determined. Based on these corrections, an accuracy of 12.2, 30.0 and 45.6?cm in the North, East and Up directions was achieved for the BeiDou-only solution after 30 min while the GPS-only solution reached 5.1, 15.3 and 15.5?cm for the same components at the same time. A further improvement of 43.7, 36.9 and 45.0 percent in the three directions, respectively, was achieved for the combined GPS/BeiDou solution. After the initialization process, the North, East and Up positioning accuracies were 5.2, 8.1 and 17.8?cm, respectively, for the BeiDou-only solution, while 1.5, 3.0, and 4.7?cm for the GPS-only solution. However, we only noticed a 20.9% improvement in the East direction was obtained for the GPS/BeiDou solution, while no improvements in the other directions were detected. It is expected that such improvements may become bigger with the increasing accuracy of the BeiDou-only solution.     

基于结构加权低秩近似的泊松图像去模糊

针对由高斯模糊和泊松噪声引起的图像降质问题，提出了一种基于结构加权低秩近似的图像去模糊方法。首先，通过依次组合缩放、旋转、剪切和翻折等四种基本操作引入结构变换，以增加搜索空间内候选图像块的相似性。然后，构造新的目标函数，利用相似图像块的低秩性，在正则项中使用加权核范数（WNN）对结构变换后的图像块进行惩罚，以在去模糊的同时抑制泊松噪声。最后，基于半正定二次分裂（HQS）方法设计交替优化方案，用于求解目标函数，从泊松图像中去除模糊。实验结果表明:在多种泊松噪声强度下，所提方法取得的峰值信噪比（PSNR）和结构相似性（SSIM）都高于当前同类去模糊方法。      

飞轮微振动的组合隔振装置设计及实验研究

针对光学遥感卫星飞轮微振动引起的成像质量下降问题，设计了一种组合隔振装置，并采用仿真分析与实验测试相结合的方法对隔振方案设计的合理性进行验证。首先，将测量的飞轮扰振数据引入光学卫星的有限元模型中，计算出飞轮扰振对光学相机的像素偏移影响；其次，设计了组合隔振方案并基于有限元方法对其隔振效果进行验证；最后，搭建了光学成像微振动实验测试平台，对不同转速下飞轮微振动造成的像素偏移影响进行精确测量。实验结果表明，组合隔振装置对300 Hz以上高频段飞轮扰振有较大衰减作用，最大像素偏移降到0.01个像素以下，隔振效率达到80%以上；通过对比可知，实验测试与仿真计算得到的像素偏移结果在低频段一次谐波响应及模态响应表现出较好一致性，但在高频段二者存在一定偏差。     

双酚S的环境污染现状及对脂质代谢紊乱的影响

双酚S (Bisphenol S，BPS) 是双酚A (Bisphenol A，BPA) 的替代品，被广泛用于制造各种聚合物。由于其广泛的使用，造成的环境污染已经严重威胁生态环境和人体健康。近年来，BPS所引起的脂质代谢紊乱逐渐引起大家的关注。 本文对BPS导致环境污染的现状及人群暴露风险进行总结，并从其对脂质合成、转运和降解基因的表达，代谢组学以及对过氧化物酶体增殖物激活受体γ (PPARγ)的作用等方面来探讨BPS所致脂质代谢异常的潜在机制。     

一种软件脆弱性自动分析定位的方法

摘要： 为了更好地满足航空航天领域中使用的多种嵌入式软件的高可靠性要求，设计一种软件脆弱性自动分析定位的方法.该方法基于程序切片技术，改进现有的前向计算动态切片算法，利用动态程序切片收集程序运行时的动态信息，构造程序切片谱，设定相关统计量统计程序语句的脆弱性可疑度，生成脆弱性定位报告.在发现软件中存在的脆弱性后，该方法对导致此脆弱性的程序代码根源实现了自动分析定位.基于此方法设计开发了软件脆弱性自动定位工具并进行了实例验证分析，实验证明了该方法的有效性.     

航空电子产品电磁环境效应模块化设计方法

对高强度辐射场（HIRF）环境特点与干扰类型进行分析，采用理论计算、计算机仿真技术（CST）的仿真分析及实测等方法分别对某型飞机航空电子系统综合显示单元的外部强电磁辐射场孔缝耦合、场线耦合及芯片前端电路影响关键芯片的相关规律进行了研究，给出了相关设计建议。结果表明，可通过分析孔缝、场线耦合获得进入关键芯片前端电路的电磁干扰能量，再结合关键芯片前端电路网络对干扰的插入损耗分析，获得关键芯片在外部强场激励下的感应电压。     

微通道中液滴和粒子的运动特性研究

微流控技术的快速发展反映了新型检测器件对微型化和集成化的要求，以及当前科学研究和工程应用逐步向多学科交叉领域过渡的趋势。其中，液滴和粒子是微流控技术中两种重要的操控对象。液滴和粒子的微尺度流动通常处于层流范围，然而尺度效应和界面效应将非线性因素引入流动，且受到通道结构、流动条件等多个控制参数的耦合影响，使得微尺度系统表现出多种复杂的流动现象。因此，从流体动力学的机理研究出发揭示微尺度流动的物理机制至关重要。本文综述了课题组近年来关于微通道中液滴和粒子运动的研究，分析了液滴/粒子特征参数的变化规律，界定了不同流动模式的分布状况及临界条件，明确了主导流动的关键参数并建立了相应的受力模型，以期探寻不同行为的操控方法。本文工作可为微尺度下复杂流动理论体系的完善及相关工程应用提供参考。     

Review and propositions for the sliding/impact wear behavior in a contact interface

A thermal-solid-liquid complex operational environment induces structural interface developing a typical coupling sliding/impact wear behavior. It results in contact damage until systems fail, which may cause significant economic losses and catastrophic consequences. The key point of solving this problem is to reveal the coupling damage mechanism of the sliding/impact behavior in typical systems and life characterization under a complicate evolving environment. This has been a hot topic in the area of mechanical reliability. The main work in this paper can be concluded as follows. Firstly, the main industries in which the “sliding/impact behavior” takes place have been introduced. Then, existing studies on the wear mechanism and degree analysis are presented, which includes surface morphology analysis, wear debris analysis, and wear degree measurement. Meanwhile, existing problems in theoretical modeling and experiments in current research are summarized, so as to point out a bright direction for future research on wear prediction. They include interface contact modeling, mathematic coupling mechanism modeling, wear equation establishment, and wear life characterization, which can provide some new ideas for improving the existing studies on the sliding/impact wear behavior.     

Unsteady wakes-secondary flow interactions in a high-lift low-pressure turbine cascade

Detailed experimental measurements were conducted to study the interactions between incoming wakes and endwall secondary flow in a high-lift Low-Pressure Turbine (LPT) cascade. All of the measurements were conducted in both the presence and absence of incoming wakes, and numerical analysis was performed to elucidate the flow mechanism. With increasing Reynolds number, the influence of the incoming wakes on suppressing the secondary flow gradually increased owing to the greater influence of incoming wakes on reducing the negative incidence angle at higher Reynolds numbers, leading to a lower blade loading near the leading edge and suppression of the Pressure Side (PS) leg of the horseshoe vortex. However, the effect of unsteady wakes on suppressing the profile losses gradually became weaker owing to the reduced size of the Suction Side (SS) separation bubble and increased mixing loss in the free-flow region at high Reynolds numbers. Incoming wakes clearly improved the aerodynamic performance of the low-pressure turbine cascade at low Reynolds numbers of 25,000 and 50,000. In contrast, at the high Reynolds number of 100,000, the profile loss at the midspan and mass-averaged total losses downstream of the cascade were higher in the presence of wakes than in the absence of wakes, and the unsteady wakes exerted a negative influence on the aerodynamic performance of the LPT cascade.