Virtual target guidance-based distributed model predictive control for formation control of multiple UAVs

The paper proposes a Virtual Target Guidance (VTG)-based distributed Model Predictive Control (MPC) scheme for formation control of multiple Unmanned Aerial Vehicles (UAVs). First, a framework of distributed MPC scheme is designed in which each UAV only shares the information with its neighbors, and the obtained local Finite-Horizon Optimal Control Problem (FHOCP) can be solved by swarm intelligent optimization algorithm. Then, a VTG approach is developed and integrated into the distributed MPC scheme to achieve trajectory tracking and obstacle avoidance. Further, an event-triggered mechanism is proposed to reduce the computational burden for UAV formation control, which takes into consideration the predictive state errors as well as the convergence of cost function. Numerical simulations show that the proposed VTG-based distributed MPC scheme is more computationally efficient to achieve formation control of multiple UAVs in comparison with the traditional distributed MPC method.     

Simulator of pyroshock environment and effect rules of its adjustable parameters

During the launching of spacecraft, the on-board devices will undergo a series of pyroshock environments. In order to verify the reliability of these devices under these pyroshock environments, all of them are needed to take the shock test before launching. This paper has carried out an in-depth research on the simulation method of the pyroshock based on the true explosive excitation. In this study, a simulator containing multiple adjustment parameters is presented and the safety is considered by the design of the protective cover. And the working process of this setup is simulated with the explicit dynamic codes LS-DYNA. What’s more, the effects of the adjustment parameters on the three factors of shock Response Spectrum (SRS) of the resonant board are explored carefully. The rules achieved in this paper are verified by a typical example. The results indicate that the improved simulator can avoid the danger of explosive and make full use of the advantage of actual explosive excitation. And the test condition can be quickly realized at the simulator according to the effect rules of the three adjustable parameters.     

An optimal selection of probability distribution functions for unsupervised land cover classification of PALSAR-2 data

Different types of classification techniques are available in the literature for the classification of Synthetic Aperture Radar (SAR) data into various land cover classes. Various SAR images are available for land cover classification such as ALOS PALSAR (PALSAR-1, PALSAR-2), RADARSAT and ENVISAT. In this paper, we have attempted to explore probability distribution function (pdf) based land cover classification using PALSAR-2 data. Over 20 different statistical distribution functions are analyzed for different classes based on statistical parameters. Probability distribution functions are selected based on Chi-squared goodness of fit test for each individual class. A decision tree based classifier is developed for classification based on the selected pdf functions and its statistical parameters. The proposed classification approach has an accuracy of 83.93%.     

LaBr3(Ce)元件破损在线监测关键核素确定及效率校准

常用的元件破损在线监测方法受外在因素影响较大，以γ能谱中关键裂变产物核素比活度进行在线定量分析是一种可靠的元件破损监测方法。针对新型LaBr₃(Ce)元件破损监测仪，设计了元件破损模拟实验，对逸出的裂变产物采用HPGe和LaBr₃(Ce)探测器进行了对比测量。通过不同冷却时间γ能谱的核素分析，确定了¹³⁵Xe，⁸⁸Kr，¹³⁸Xe，⁸⁸Rb，¹³⁸Cs等可作为LaBr₃(Ce)元件破损γ能谱监测的关键核素。同时，制备了覆盖能量范围(250～2 400)keV，含⁶⁰Co，¹³⁷Cs，¹³³Ba；²⁴¹Am，¹⁵²Eu；¹⁰⁹Cd，⁸⁸Y，⁵⁷Co及²⁴Na的4组放射性标准溶液，在建立的效率校准系统上，校准了LaBr₃(Ce)在线监测仪的效率。在反应堆一次异常情况分析中，已校准的LaBr₃(Ce)元件破损监测仪对关键核素的现场分析结果与HPGe的取样分析结果一致，表明效率校准结果准确，校准方法可靠。     

新一代运载火箭氢氧模块动力系统试验风险分析

针对新一代运载火箭氢氧模块动力系统试车试验台进行了风险分析.分析方法采用基于元件的系统级FMECA和基于工艺流程的过程FMECA相结合的方法,引入“发生可能性”和“严酷度”两个指标,建立FMECA工作表,实现了风险因素量化分析与控制,并引入“风险指数”对风险事项排序.通过分析共识别Ⅰ、Ⅱ类单点故障模式45项,提出了试验台在设计、生产、使用和操作中应采取的控制措施,使系统可靠性得到了增长.该方法有效拓展了大型地面试验风险管理的思路.     

Optical/infrared observations unveiling the formation,nature and evolution of High-Mass X-ray Binaries

In this review I first describe the nature of the three kinds of High-Mass X-ray Binaries (HMXBs), accreting through: (i) Be circumstellar disc, (ii) supergiant stellar wind, and (iii) Roche lobe filling supergiants.     

IGMP V3协议研究与实现

针对IPV4下Windows 2000系统不支持指定源组播模型的问题,通过对3个版本IGMP（互联网组管理协议）的分析研究,采用原始套接字截获IGMP V3查询包,模拟生成组成员关系上报电文的方法,达到了欺骗交换机/路由器、维持其组成员关系的目的,解决了Windows 2000终端设备无法实现指定源组播通信的难题。仿真测试以及实际应用表明,这种方法完全可以应用于不支持IGMP V3协议的其他系统。     

A new approach on necking constitutive relationships of ductile materials at elevated temperatures

A new method is presented to determine the full-range, uniaxial constitutive relationship of materials by tensile tests on funnel specimens with small curvature radius and finite element anal-ysis (FEA). An iteration method using FEA APDL (ANSYS parametric design language) program-ming has been developed to approach the necking constitutive relationship of materials. Test results from SAE 304 stainless steel at room temperature show that simulated load vs displacement curve, diameter at funnel root vs displacement curve, and funnel deformation contours are close to mod-eled results. Due to this new method, full-range constitutive relationships and true stress and effec-tive true strain at failure are found for 316L stainless steel, TA17 titanium alloy and A508-III stainless steel at room temperature, and 316L stainless steel at various elevated temperatures.     

A new inversion method of plasma density distribution of plasmasphere in the geomagnetic equatorial plane from IMAGE data

The plasma density distribution of plasmasphere in the geomagnetic equatorial plane can help us study the magnetosphere like plasmasphere, ionosphere and their kinetics. In this paper, we introduce a new inversion method, GE-ART, to calculate the plasma density distribution in the geomagnetic equatorial plane from the Extreme Ultraviolet (EUV) data of IMAGE satellite under the assumption that the plasma density is constant along each geomagnetic field line. The new GE-ART algorithm was derived from the traditional Algebraic Reconstruction Techniques (ART) in Computed Tomography (CT) which was different from the several existing methods. In this new method, each value of the EUV image data was back-projected evenly to the geomagnetic field lines intersected by this EUV sight. A 3-D inversion matrix was produced by the contributions of all the voxels contained in the plasmasphere covered by the EUV sensor. That is, we considered that each value of the EUV image data was relative to the plasma densities of all the voxels passed through by the corresponding EUV radiation, which is the biggest difference to all the existing inversion methods. Finally, the GE-ART algorithm was evaluated by the real EUV data from the IMAGE satellite.     

CCSDS空间网络互联协议发展及启示

空间互联网将是由各种区域网构成的复杂异构网络,为了使其能够逐步实现自动化运行,网络效益得到最大程度的发挥,须做好网络互联的顶层规划与设计,并开发具体的标准技术.根据近年CCSDS (Consultative Committee for Space Data Systems,空间数据系统咨询委员会)发布的建议书,以及相关工作组的项目规划情况,介绍了SSI(Solar System Internetwork,太阳系互联网)体系结构、IPoC(IP over CCSDS space links,在CCSDS空间链路之上承载IP),以及DTN(Delay Tolerant Networking,容延迟网络)等标准项目.从CCSDS空间网络互联技术的发展历程不难得出结论:我国未来空间网络互联应注重区域网之间互联的顶层设计;区域网内部各子网之间的互联技术应选择以航天任务需求牵引为主;DTN将在区域网之间互联以及区域网从简单到复杂发展中都发挥重要作用.