大型空间站航天员出舱条件及相对运动轨迹

应用航天器近距离相对运动动力学方程,在计及空间站尺寸的条件下,研究了大型空间站航天员出舱条件及相对运动轨迹。研究表明, 当航天员在空间站的上、下表面或前表面下方、后表面上方时, 如果没有约束, 将发生自由漂移,其相对运动的轨道平面内模态为中心漂移的椭圆; 如果航天员在相应的位置上有动力 （主动） 出舱, 其相对运动的轨道平面内模态可以为直线、定常椭圆和中心漂移的椭圆, 这与把空间站简化为质点时的结果有本质差别, 因此不能再将空间站视为质点。通过改变航天员的离舱点和离舱速度, 可以改变出舱相对运动轨迹,以满足一定的舱外活动要求     

Study on segmented distribution for reliability evaluation

In practice, the failure rate of most equipment exhibits different tendencies at different stages and even its failure rate curve behaves a multimodal trace during its life cycle. As a result, traditionally evaluating the reliability of equipment with a single model may lead to severer errors. However, if lifetime is divided into several different intervals according to the characteristics of its failure rate, piecewise fitting can more accurately approximate the failure rate of equipment. There-fore, in this paper, failure rate is regarded as a piecewise function, and two kinds of segmented dis-tribution are put forward to evaluate reliability. In order to estimate parameters in the segmented reliability function, Bayesian estimation and maximum likelihood estimation (MLE) of the seg-mented distribution are discussed in this paper. Since traditional information criterion is not suit-able for the segmented distribution, an improved information criterion is proposed to test and evaluate the segmented reliability model in this paper. After a great deal of testing and verification, the segmented reliability model and its estimation methods presented in this paper are proven more efficient and accurate than the traditional non-segmented single model, especially when the change of the failure rate is time-phased or multimodal. The significant performance of the segmented reli-ability model in evaluating reliability of proximity sensors of leading-edge flap in civil aircraft indi-cates that the segmented distribution and its estimation method in this paper could be useful and accurate.     

台风激发的声重力波的可探测性研究

通过对北京大学高频多普勒台站(39.4°N,116.2°E)多年的观测资料及相关台风资料的统计分析,着重研究了高频多普勒探测手段对由台风引起的扰动电离层响应的可探测性问题.通过对台风登陆前后的高频多普勒观测记录的细致分析及与宁静条件下记录的对比研究,表明高频多普勒观测手段可以很好地探测由台风激发的声重力波,尤其是对台风登陆前后所激发的扰动具有较高的可探测性.在所分析的24次台风事件中有明显扰动记录的高达22次(22/24).结合观测事实与Huang等的统计结果(2/12)进行了比较,并进行了可能的原因分析.通过数值模拟的方法对观测到的主要扰动的非线性传播过程进行了模拟再现,结果基本上与观测结果及线性传播理论一致.确认了一般情况下高可探测性这一事实,但同时也表明可探测性和台风激发源与探测位置及中尺度TIDs在电离层中的传播模式有密切关系.      

纳米CeO2/Zn复合粉末的高能球磨法制备与表征

采用高能球磨法制备了用于热浸镀锌的纳米C eO2/Zn复合粉末,并利用X射线衍射(X-ray d iffraction,XRD)、X射线光电子能谱(X-ray photoe lectron spectroscopy,XPS)、透射电镜(T ransm iss ion e lectron m i-croscopy,TEM)、扫描电镜(Scann ing e lectron m icroscopy,SEM)以及能谱分析(X-ray energy d ispers ive spec-trum,EDS)等方法,对复合粉末的显微结构、表面成分、晶粒大小、微观形貌以及元素分布进行了研究。结果表明,随着球磨时间的延长,纳米C eO2硬团聚体逐渐解聚,Zn晶粒不断细化,形成层片状复合粉末;球磨120 m in后纳米C eO2粒子分散良好,呈理想的单个均匀弥散分布状态包覆在Zn颗粒上形成近似球形的复合粒子,其粒径分布均匀。     

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.     

Analysis of BDS-3 distributed autonomous navigation based on BeiDou system simulation platform

Satellite autonomous navigation is an important function of the BeiDou-3 navigation System (BDS-3). Satellite autonomous navigation means that the navigation satellite uses long-term forecast ephemeris and Inter-Satellite Link (ISL) measurements to determinate its own spatial position and time reference without the support of the ground Operation and Control System (OCS) for a long time to ensure that the navigation system can normally maintain the time and space reference. This paper aims to analyze the feasibility of distributed autonomous navigation algorithms. For the first time, a ground parallel autonomous navigation test system (GPANTS) is built. The performance of distributed autonomous navigation is then analyzed using the two-way ISL ranging of BDS-3 satellites. First, the BDS simulation platform and the GPANTS are introduced. Then, the basic principles of distributed satellite autonomous orbit determination and time synchronization based on ISL measurements are summarized. Preliminary evaluation of the performance of the BDS-3 constellation autonomous navigation service under ideal conditions through simulation data. Then the performance of autonomous navigation for 22 BeiDou-3 satellites using ISL measurements is evaluated. The results show that when satellites operate autonomously for 50 days without the support of any ground station, the User Range Error (URE) of autonomous orbit determination is better than 3 m, and the time synchronization accuracy is better than 4 ns.     

Assembly Line Balancing Based on Double Chromosome Genetic Algorithm

Aiming at assembly line balancing problem, a double chromosome genetic algorithm （DCGA） is proposed to avoid trapping in local optimum, which is a disadvantage of standard genetic algorithm （SGA）. In this algorithm, there are two chromosomes of each individual, and the better one, regarded as dominant chromosome, determines the fitness. Dominant chromosome keeps excellent gene segments to speed up the convergence, and re cessive chromosome maintains population diversity to get better global search ability to avoid local optimal solu- tion. When the amounts of chromosomes are equal, the population size of DCGA is half that of SGA, which significantly reduces evolutionary time. Finally, the effectiveness is verified by experiments.     

地方高等师范院校学生心理健康状况调查及对策研究

通过对四所地方高等师范院校学生进行心理健康状况调查,结果表明:每个年级都有较高比例的学生存在心理问题。本文针对调查结果,分析了影响师范生心理问题形成的因素,并提出了相应的对策和建议。     

Evaluation and analysis on positioning performance of BDS/QZSS satellite navigation systems in Asian-Pacific region

By using the observation data and products of precise obit and clock offset from Multi-GNSS Experiment (MGEX) of the International GNSS Service (IGS) and GNSS Research Centre, Curtin University in this paper, the positioning performance of BDS/QZSS satellite navigation system has been analyzed and evaluated in aspects of the quantity of visible satellites, DOP value, multipath effect, signal-to-noise ratio, static PPP and kinematic PPP. The analysis results show that compared to BDS single system when the cutoff angle are 30°and 40°, the DOP value of BDS/QZSS combined system has decreased above 20%, and the quantity of visible satellites increased about 16–30% respectively, because of the improved spatial geometric configuration. The magnitude of satellite multipath effect of BDS system shows the trend of MEO?>?IGSO?>?GEO, which is consistent with that of QZSS satellite system, as the constellation structure of the two systems is similar. The variation tendencies of signal-to-noise ratio with respect to elevation angle of the two systems are almost the same at all frequencies, showing that at the same elevation angle the signal-to-noise ratio of MEO satellites is higher than that of IGSO satellites, as the higher obit is the lower transmitting power is obtained. For having a specially designed obit, the variation of signal-to-noise ratio of BDS system is more stable. However, the magnitude of signal-to-noise ratio of QZSS system appears the trend of frequency 3?>?frequency 2?>?frequency 1. The static PPP performance of the BDS/QZSS combination system has been improved more significantly than the BDS single system in E, N and U directions. When the cutoff angle are at 7°, 15° and 30°, the PPP accuracy is increased about 25–34% in U direction, 10–13% and 23–34% in E and N directions respectively. When the elevation angle is large (40°), compared to BDS single system at lower elevation angles (7° and 15°) the PPP accuracy of the BDS/QZSS combination system is improved above 30% in U direction. In kinematic PPP performance, compared to BDS single system, the accuracy, availability and reliability of the BDS/QZSS combination system has been improved too, especially at large elevation angles (30° and 40°), the kinematic PPP accuracy in E and U directions has been improved about 10–50%, and above 50% in U direction. It can be concluded that the combination with QZSS system can improve the positioning accuracy, reliability and stability of BDS system. In the future, with the improvement of the satellite construction of Japan’s QZSS system and the global networking of China’s BDS satellites, the QZSS satellites will contribute greatly to improve the positioning accuracy, reliability, availability and stability of GNSS systems in areas such as cities, mountains, densely-packed buildings and severely covered areas in Asian-Pacific region.     

微米级自动扫描磨粒形态分析仪运动系统的设计及制造

介绍了自动扫描磨粒形态分析仪运动系统的设计、关键技术的解决途径及制造过程中的关键工艺问题的研究成果．