Statistical seismo-ionospheric precursors of M7.0+ earthquakes in Circum-Pacific seismic belt by GPS TEC measurements

The Circum-Pacific seismic belt is the region heavily affected by earthquakes in the world. The relationship between earthquake (e.g., the geographic location, occurrence time, magnitude, and focal depth) and ionospheric anomalies in the belt was investigated using 100 M7.0+ earthquakes during 2006–2015. The ground-based GPS measurements and global ionosphere map (GIM) data were used for the analyses of the ionospheric variations preceding the earthquakes. The results indicated that the occurrence rate of total electron content (TEC) anomalies was proportional to the magnitude and inversely proportional to the focal depth to a certain degree, and the occurrence frequency of anomalies had a rising trend with the days getting close to the main shock. The occurrence rate of TEC anomalies in the Southern hemisphere was larger than that in the Northern hemisphere. Besides, the spatial characteristics of TEC anomalies showed that the anomalies in low-middle latitudes did not coincide with the epicenter, sometimes the anomalies were also observed in the corresponding conjugated region. However, the TEC anomalies in the high latitude usually appeared around the epicenter and within the seismogenic zone while no TEC anomalies appeared in the conjugated area. These results may have potential applications to the earthquake prediction in the Circum-Pacific seismic belt.     

Optimal trajectory planning of free-floating space manipulator using differential evolution algorithm

The existence of the path dependent dynamic singularities limits the volume of available workspace of free-floating space robot and induces enormous joint velocities when such singularities are met. In order to overcome this demerit, this paper presents an optimal joint trajectory planning method using forward kinematics equations of free-floating space robot, while joint motion laws are delineated with application of the concept of reaction null-space. Bézier curve, in conjunction with the null-space column vectors, are applied to describe the joint trajectories. Considering the forward kinematics equations of the free-floating space robot, the trajectory planning issue is consequently transferred to an optimization issue while the control points to construct the Bézier curve are the design variables. A constrained differential evolution (DE) scheme with premature handling strategy is implemented to find the optimal solution of the design variables while specific objectives and imposed constraints are satisfied. Differ from traditional methods, we synthesize null-space and specialized curve to provide a novel viewpoint for trajectory planning of free-floating space robot. Simulation results are presented for trajectory planning of 7 degree-of-freedom (DOF) kinematically redundant manipulator mounted on a free-floating spacecraft and demonstrate the feasibility and effectiveness of the proposed method.     

星载跟踪控制系统设计及其抗扰动分析

针对星载目标跟踪要求高精度及快速响应能力,但同时存在力矩扰动等影响,分析提出了跟踪控制系统性能指标,根据预设指标,对系统进行了初步设计及串联滞后校正,并在增加加速度计的情况下,对系统进行了抗扰动分析.利用Matlab进行系统幅频特性仿真结果表明,设计的系统能较好满足预设指标,具有良好的稳定跟踪性能.     

Connectivity preservation and collision avoidance control for spacecraft formation flying in the presence of multiple obstacles

This paper addresses connectivity preservation and collision avoidance problem of spacecraft formation flying with multiple obstacles and parametric uncertainties under a proximity graph. In the proximity graph, each spacecraft can only get the states of the neighbor spacecraft within its sensing region. Connectivity preservation of a graph means that the connectivity of the graph should be preserved at all times during spacecraft formation flying. We consider two cases: (i) the obstacles are static, and (ii) the obstacles are dynamic. In the first case, a distributed continuous control algorithm based on artificial potential function and equivalent certainty principle is proposed to account for the unknown parameters and the static obstacles. In the second case, a sliding surface combined with a distributed adaptive control algorithm is proposed to tackle the influence of the dynamic obstacles and the unknown parameters at the same time. With the distributed control algorithms, the desired formation configuration can be achieved while the connectivity of the graph is preserved and the collisions between the spacecraft and the obstacles are avoided. Numerical simulations are presented to illustrate the theoretical results.     

连续爆轰发动机的研究进展

连续爆轰发动机是一种基于爆轰波将推进剂的化学能转化成热能的新概念发动机,近年来受到世界各主要国家的高度关注。现已成功获得多种燃料长时间稳定的连续爆轰,较深入地认识了连续爆轰流场结构,初步测得推力和比冲,验证了连续爆轰发动机的性能优势并在火箭模态、冲压模态以及涡轮模态下都实现了稳定连续爆轰。对连续爆轰发动机的工作原理,以及近年来世界各主要国家在连续爆轰发动机的基础研究和应用研究方面取得的代表性成果进行了综述,并给出尚待解决的问题,为其进一步工程化应用提供参考。     

The asymmetrical features in electron density during extreme solar minimum

The variations of plasma density in topside ionosphere during 23rd/24th solar cycle minimum attract more attentions in recently years. In this analysis, we use the data of electron density (Ne) from DEMETER (Detection of Electromagnetic Emissions Transmitted from Earthquake Regions) satellite at the altitude of 660–710 km to investigate the solstitial and equinoctial asymmetry under geomagnetic coordinate system at LT (local time) 1030 and 2230 during 2005–2010, especially in solar minimum years of 2008–2009. The results reveal that ΔNe (December–June) is always positive over Southern Hemisphere and negative over northern part whatever at LT 1030 or 2230, only at 0–10°N the winter anomaly occurs with ΔNe (December–June) > 0, and its amplitude becomes smaller with the declining of solar flux from 2005 to 2009. The ΔNe between September and March is completely negative during 2005–2008, but in 2009, it turns to be positive at latitudes of 20°S–40°N at LT 1030 and 10°S–20°N at LT 2230. Furthermore, the solstitial and equinoctial asymmetry index (AI) are calculated and studied respectively, which all depends on local time, latitude and longitude. The notable differences occur at higher latitudes in solar minimum year of 2009 with those in 2005–2008. The equinoctial AI at LT 2230 is quite consistent with the variational trend of solar flux with the lowest absolute AI occurring in 2009, the extreme solar minimum, but the solstitial AI exhibits abnormal enhancement during 2008 and 2009 with bigger AI than those in 2005–2007. Compared with the neutral compositions at 500 km altitude, it illustrates that [O/N₂] and [O] play some roles in daytime and nighttime asymmetry of Ne at topside ionosphere.     

雷达站站址误差对多机协同航迹欺骗干扰的影响分析

多机协同航迹欺骗干扰是专门针对雷达网的一种新的电子干扰手段。文章在介绍了多机协同航迹欺骗干扰基本原理的基础上,重点对雷达网内雷达站址误差对航迹欺骗干扰的影响进行了分析,推导了有关理论模型,并以融合中心采用K近似域(K-NN)航迹关联准则为背景,仿真分析了雷达站址误差对航迹欺骗干扰的影响,得出了雷达站址误差对航迹欺骗干扰性能有重要影响、但此影响随电子战飞机与雷达站间的距离增大而降低的结论。     

一种直升机总体概念设计方法

使用分析以及统计的方法,针对单旋翼带尾桨构型直升机提出了一种直升机总体概念设计的方法.首先根据直升机的主要设计要求,确定直升机总质量、发动机需用功率、旋翼半径、桨叶实度、废阻面积以及桨尖速度等总体参数.然后通过对直升机气动布局参数的统计与归纳,初步确定直升机的气动布局参数,利用这些参数对直升机总质量重新估算,经反复迭代后得到一组可以进行飞行性能以及操稳性计算的概念设计参数.     

论高职网络专业簇形课程体系的构建

课程体系的构建问题是高职专业教学的核心问题,是高职教育课程改革的基础,是高职教育领域中的一切改革成果的缩影和归宿,本文就校企合作模式下高职网络专业的课程体系构建提出了一些新的想法和思路。     

飞行模拟器操纵负荷系统的无源性设计

 操纵负荷系统是飞行员与飞行模拟器之间的接口装置。提出了这种人在回路的实时控制系统的一种新的设计思想,这种设计将无源性与阻抗的概念结合,并将系统阻抗的频率特性作为定量设计的手段。基于频率分析,控制器设计中应增加一个阻尼项,使传递到操作员手上的阻抗与飞行环境的阻抗相匹配。并指出,系统中的力伺服系统的阻尼比应在0.5~0.8范围内以满足这个虚拟环境的无源性要求。操纵负荷系统的无源性可保证整个仿真系统的稳定性。所提出的设计思想还可推广应用于其他各种虚拟环境的设计。