Ground experiments of Chang’e-5 lunar regolith penetrating radar

The Lunar Regolith Penetrating Radar (LRPR) is an Ultra-Wideband (UWB) array-based Ground penetrating radar (GPR) onboard the lander of Chang’e-5 (CE-5) mission. The primary scientific objectives of the LRPR are to probe the thickness and structure of lunar regolith of the landing site, and support the drilling and sampling process. In order to evaluate the performance of the LRPR, a series of ground experiments are performed using the LRPR prototype mounted on a CE-5 lander model. The performance of the LRPR is evaluated by comparing the experimental data with the simulated data. Data processing and imaging method are verified, and the interferences from the lander and other aspects are analyzed. The results of the ground experiments and simulation demonstrate that the LRPR is able to meet the design requirement of 2-m detection depth. They also indicate that the upper and lower interfaces of the stratified structure in the lunar regolith can be well distinguished by the LRPR when the dielectric constant difference is greater than 0.3, and the imaging effect of the location under the dense antennas is better than that of other positions. However, the identification capability of the LRPR to the independent blocky objects is relatively poor mainly due to the clutters caused by the lander, the sparsity of the antenna elements compared to the size of the basalt block, the limited aperture of the antenna array, and the tail of the transmitted waveform.     

利用视加速度补偿和推力逐级释放的垂直着陆制导方法

针对运载火箭子级垂直返回着陆段的制导问题，本文在应用凸优化的滚动时域在线规划基础上研究了制导鲁棒性的改善策略。为应对着陆后期控制能力不足的情况，在滚动规划过程中引入了推力上界逐级释放的策略。同时，考虑缓解干扰和误差累积的影响，在制导周期内引入视加速度信息对在线规划的推力指令进行补偿，以进一步改善滚动规划的递归可行性。最后，通过数值算例仿真及对比分析验证所提出的补偿策略的有效性。     

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.     

Numerical Analysis of Dry Friction-Induced Vibration of Moving Slider-Elastic Annular Beam System

A disc-pad friction system is modelled as that two moving pads act symmetrically on an annular beam with flexible boundary condition.Simulation procedure is proposed to deal with the moving interactions and calculation is carried out by using the finite difference method,which shows that only the first-order mode vibration of the beam can be induced.Then the partial differential equation of motion of the disk is reduced to a first-order mode vibration system with time-varying stiffness.As the disk speed is decreased below the critical speeds,the relative equilibrium of the pad on the disk loses its stability and stick-slip type limit cycle vibrations are resulted in all directions′movements.Acceleration of the disk motion on the frictional instability is also investigated.The period of stick-slip vibration with large amplitude will be shortened with higher moving deceleration.     

Effect of matching between the magnetic field and channel length on the performance of low sputtering Hall thrusters

Discharge characteristics of a non-wall-loss Hall thruster were studied under different channel lengths using a design based on pushing a magnetic field through a double permanent magnet ring. The effect of different magnetic field intensities and channel lengths on ionization, efficiency, and plume divergence angle were studied. The experimental results show that propellant utilization is improved for optimal matching between the magnetic field and channel length. While matching the magnetic field and channel length, the ionization position of the neutral gas changes. The ion flow is effectively controlled, allowing the thrust force, specific impulse, and efficiency to be improved. Our study shows that the channel length is an important design parameter to consider for improving the performance of non-wall-loss Hall thrusters.     

寒冷地区农村建筑围护结构热工性能优化及经济性研究

农村建筑热工性能较差,采暖季能耗居高不下。本文通过Dest软件建立模型,对寒冷地区农村建筑不同围护结构下能耗情况进行模拟,并建立P1-P2经济分析模型,以全生命周期费用最小或者净现值最大确定合理的外墙保温层厚度及窗户类型。     

一种适用于封闭场景下的遥测信号接收方法

常规的遥测信号接收多是在开阔场景进行,被测对象除了在起飞或降落时短暂低仰角,大部分时间其信号是视距传输,其遥测信道近似于高斯白噪声信道。随着遥测应用场景的逐步扩展,封闭场景下的遥测需求逐步被提出,应用模式和信道条件发生了巨大变化。针对某封闭场景,分析常规遥测接收方法存在的一些问题,提出一种双天线加盲均衡的分集合成和接力接收方案,有效解决了封闭场景下的遥测信号中断问题。方案成功应用于某测试系统,实测结果表明,方案能够极大提升遥测系统的健壮性。     

A two-step weighted least-squares method for joint estimation of source and sensor locations: A general framework

It is well known that the Two-step Weighted Least-Squares(TWLS) is a widely used method for source localization and sensor position refinement. For this reason, we propose a unified framework of the TWLS method for joint estimation of multiple disjoint sources and sensor locations in this paper. Unlike some existing works, the presented method is based on more general measurement model, and therefore it can be applied to many different localization scenarios.Besides, it does not have the initialization and local convergence problem. The closed-form expression for the covariance matrix of the proposed TWLS estimator is also derived by exploiting the first-order perturbation analysis. Moreover, the estimation accuracy of the TWLS method is shown analytically to achieve the Cramér-Rao Bound(CRB) before the threshold effect takes place. The theoretical analysis is also performed in a common mathematical framework, rather than aiming at some specific signal metrics. Finally, two numerical experiments are performed to support the theoretical development in this paper.     

Aircraft Engine Gas Path Fault Diagnosis Based on Hybrid PSO-TWSVM

Twin support vector machine(TWSVM)is a new development of support vector machine(SVM)algorithm.It has the smaller computation scale and the stronger ability to cope with unbalanced problems.In this paper,TWSVM is introduced into aircraft engine gas path fault diagnosis.The generalization capacity of Gauss kernel function usually used in TWSVM is relatively weak.So a mixed kernel function is used to improve performance to ensure that the TWSVM algorithm can better balance a strong generalization ability and a good learning ability.Experimental results prove that the cross validation training accuracy of TWSVM using the mixed kernel function averagely increases 2%.Grid search is usually applied in parameter optimization of TWSVM,but it heavily depends on experience.Therefore,the hybrid particle swarm algorithm is introduced.It can intelligently and rapidly find the global optimum.Experiments prove that its training accuracy is better than that of the classical particle swarm algorithm by 5%.     

环雄安新区康养人才培养模式探讨

康养产业在国内尚属于新型的一个产业,而中国的康养产业发展迅速,显示出了勃勃的生机和巨大的发展潜力,但同时也出现了很多问题,其中人才培养是重要的一个环节。当前高等院校在康养行业专业人才培养方面,已经进行了许多探索和尝试,但就整体而言,我国康养行业高校人才培养还存在诸多问题。本文通过分析国内康养人才培养的现状,同时结合雄安新区的实际情况,提出环雄安新区康养人才培养的策略。