Fully distributed time-varying formation tracking control for multiple quadrotor vehicles via finite-time convergent extended state observer

This paper investigates a time-varying anti-disturbance formation problem for a group of quadrotor aircrafts with time-varying uncertainties and a directed interaction topology. A novel Finite-Time Convergent Extended State Observer (FTCESO) based fully-distributed formation control scheme is proposed to enhance the disturbance rejection and the formation tracking performances for networked quadrotors. By adopting the hierarchical control strategy, the multi-quadrotor system is separated into two subsystems: the outer-loop cooperative subsystem and the inner-loop attitude subsystem. In the outer-loop subsystem, with the estimation of disturbing forces and uncertain dynamics from FTCESOs, an adaptive consensus theory based cooperative controller is exploited to ensure the multiple quadrotors form and maintain a time-varying pattern relying only on the positions of the neighboring aircrafts. In the inner-loop subsystem, the desired attitude generated by the cooperative control law is stably tracked under a FTCESO-based attitude controller in a finite time. Based on a detailed algorithm to specify the cooperative control protocol, the feasibility condition to achieve the time-varying anti-disturbance formation tracking is derived and the rigorous analysis of the whole closed-loop multi-quadrotor system is given. Some numerical examples are conducted to intuitively demonstrate the effectiveness and the improvements of the proposed control framework.     

拦截高速目标的比例与反比例导引捕获区分析

针对拦截高速目标的作战特点，分析了比例导引(PN)与反比例导引(RPN)的捕获区。首先，通过分析拦截弹与目标的相对运动关系，推导得到了顺轨和逆轨的零控拦截条件，此条件由目标和拦截弹的速度前置角以及二者速度比确定；其次，以拦截弹和目标速度前置角为坐标系，推导得到了PN以及RPN捕获区以及各自导航比设置范围。PN的捕获区由逆轨零控拦截条件以及与其相切且斜率为1/(N-1)的两条直线构成，RPN的捕获区由顺轨零控拦截条件以及与其相切且斜率为1/(-N-1)的两条直线构成；然后，利用函数对称性将PN与RPN捕获区转换到同一坐标区间，得到了相同条件下RPN捕获区要大于PN捕获区的结论；最后，开展了四种情形下的仿真，验证了本文捕获区分析的合理性及有效性。     

Variation of dayside chorus waves associated with solar wind dynamic pressure based on MMS observations

The whistler-mode chorus waves are one of the most important plasma waves in the Earth’s magnetosphere. Generally, the amplitude of whistler-mode chorus waves prefers to strengthen when the energetic fluxes of anisotropic electrons increase outside the plasmapause. This characteristic is commonly associated with the geomagnetic storms or substorms. However, the relationship between the solar wind dynamic pressure (P_sw) and the long-time variation of chorus waves during the quiet period of the geomagnetic activity still needs more detailed investigations. In this paper, based on MMS observations, we present a chorus event just observed in the inner side of magnetopause without obvious geomagnetic storms or substroms. Interestingly, during this time interval, some P_sw fluctuations were recorded. Both the amplitudes and frequencies of chorus waves changed as a response to the variation in P_sw. It proved that the enhancement of P_sw increases the energetic electrons fluxes, which provides free energies for the chorus amplification. Furthermore, the wave growth rates calculated using linear theory increases and the central frequency of the chorus waves shifts to a higher frequency when the P_sw enhancement is greater, which are also consistent well with the observations. The results provide a direct evidence that the P_sw play an important role in the long-time variation of whistler-mode chorus waves inside the magnetopause.     

NiCrAl/Diatomite可磨耗封严涂层制备及性能

分别利用大气等离子喷涂技术制备了Ni/Al粘结底层、火焰喷涂技术制备了NiCrAl/Diatomite可磨耗封严涂层，研究了喷涂距离、送粉速率、火焰气体总流量、喷涂角度和氧燃比等喷涂参数对生长速率和涂层硬度的影响。结果表明，在较低的氧燃比条件下（O₂∶C₂H₂<1.6），随着喷涂距离的增大，涂层生长速率逐渐下降，硬度先保持不变后逐渐上升；当O₂∶C₂H₂>1.6时，涂层的生长速率会随着喷涂距离的增大先增大后减小，硬度随之逐渐下降。随着喷枪对基体相对移动速度的增大，涂层生长速率略微下降，硬度略有上升。气体总流量的增大使得涂层的生长速率明显上升，硬度明显下降。随着送粉量的增大，涂层生长速率明显提高，硬度随之先上升后下降。     

Effect of moderate geomagnetic storms on equatorial plasma bubbles over eastern Africa in the year 2012: Evolution and electrodynamics

Equatorial plasma bubbles (EPBs) are common features of the equatorial and low-latitude ionosphere and are known to cause radio wave scintillation which leads to the degradation of communication and navigation systems. Although these structures have been studied for decades, a full understanding of their evolution and dynamics remains important for space weather mitigation purposes. In this study, we present cases of EPBs occurrences around April and July 2012 geomagnetic storm periods over the African equatorial sector. The EPBs were observed from the Communications/Navigation Outage Forecasting System (C/NOFS) and generally correlated well to the ionospheric irregularities observed from the Global Positioning System total electron content (GPS-TEC) measurements (rate of TEC change, ROT). This study revealed that the evolution of the EPBs during moderate storms is controlled by the strength of the daytime equatorial electrojet (EEJ) currents regardless of the strength of the equatorial ionization anomaly (EIA), the latter is observed during the July storm case in particular. These effects were more evident during the main and part of the early recovery phases of the geomagnetic storm days considered. However, the evening hours TEC gradients between regions of the magnetic equator and ionization crests also played roles in the existence of ionospheric irregularities.     

一种基于虚拟页地址映射的NAND Flash管理算法

本文提出了一种基于虚拟页地址映射的NAND Flash管理算法.该算法通过定义坏块表、对应表等结构，以及设计的坏块替换策略和虚拟页地址到实际物理页地址的转换算法，实现上层软件采用虚拟地址对NAND Flash的无坏块连续页地址访问.该算法是一种高效的地址映射算法，能高效地对数据进行索引，占用SRAM空间较少，使系统达到高性能，并使得闪存使用的更加稳定持久.     

亚超剪切混合层燃油雾化特性试验研究

为了摸清亚超大梯度剪切混合层内直射式喷嘴的燃油雾化特性，设计了用于向亚超剪切混合流中进行燃油喷射的直射式喷嘴，建立了亚超剪切混合层中燃油雾化试验系统。利用粒子图像测速系统（PIV），对亚超大梯度混合层中油雾场进行测量。通过改变喷嘴流量、喷射角度和喷嘴数量研究不同参数对雾化特性的影响，并应用图像处理技术对亚超大梯度剪切混合层内的油雾场进行分析，总结归纳其雾化规律。试验结果显示：随着流量增大，穿透深度会随之增大，破碎后的颗粒分布峰值所对应的液滴直径会逐渐变小，雾化效果提升；相同流量条件下，喷嘴的角度改变对雾化效果有影响，顺喷和逆喷的雾化效果均好于垂直喷射；逆喷的喷射高度最高，随着流量的增长，燃料将会碰壁；顺喷条件下，随着角度的增加，穿透长度会有所增加；综合燃油轨迹边界，逆喷的效果相对较好。相同流量条件下，喷孔个数的改变对雾化效果和穿透深度的影响不大。     

多种工质下螺旋波等离子体源波场结构数值模拟

针对螺旋波等离子体放电机理，开展了多种工质条件下的螺旋波放电等离子体内波场结构数值模拟研究。计算发现:氦气等离子体的Er分量在径向边界处的峰值更为突出，有利于等离子体在径向的输运，波电场径向分量决定了电流密度径向分量在内部的表现。在0.266 Pa和1.064 Pa两种气体压强条件下，通过波场结构验证了气压对于波阻尼影响的结论。波场结构是螺旋波在等离子体内传播以及能量沉积的微观体现，研究螺旋波波场结构是揭示其高电离效率的重要途径。初步探索了功率耦合机制，为实验系统优化及实验方案设定奠定理论基础。     

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.