火星空间大尺度电流体系分布特征

在MHD模型基础上, 对火星空间环境的电流分布进行了模拟. 结果表明, 火星空间存在着弓激波电流、磁堆积区电流、电离层电流和磁尾电流. 弓激波电流在激波曲面上均由北向南自成体系, 电流密度在弓激波顶区域较大. 在向阳面磁堆积区边界电流与电离层电流彼此耦合形成完整的回路, 在背阳面磁堆积区边界电流与磁尾中心电流片耦合形成完整的回路.      

Dynamics of the plasma sheet in the magnetotail: Interrelation of turbulent flows and thin current sheet structures

Dynamics of the magnetotail involves elementary processes of magnetic field merging (reconnection layer formation) occurring on medium spatial scales. Every such process features two different stages, a fast one and a subsequent slower one. The corresponding short time scale _T1$T_1$ is associated with disturbances propagating in the tail lobes. The longer time scale _T2$T_2$ is associated with plasma motions in the plasma sheet. A disturbance appearing in the magnetotail on the time scale _T1$T_1$ results in a loss of equilibrium in the plasma sheet. By means of theoretical argument and numerical simulation, it is shown that the relaxation process which follows on the time scale _T2$T_2$, produces extremely thin embedded current sheets, along with generation of fast plasma flows. The process provides an effective mechanism for transformation of magnetic energy accumulated in the magnetotail, into energy of plasma flows. The fast flows may drive turbulent motions on shorter spatial scales. In their turn, those motions can locally produce very thin current sheets; after that, nonlinear tearing process leads to generation of neutral lines, and reconnection. The latter produces new fast disturbances on the time scale _T1$T_1$ closing the feedback loop.     

民用飞机燃油泵的点火源防护

本文介绍民用飞机点火源防护的历史来源,提出接地故障保护的概念,分析接地故障中断继电器的基本工作原理及其在民用飞机上的应用。     

Numerical Modeling of the Ring Current and Plasmasphere

Over the last 25 years, considerable scientific effort has been expended in the development of quantitative models of the dynamics of Earth's inner magnetosphere, particularly on studies of the injection of the storm-time ring current and of dynamic variations in the shape and size of the plasmasphere. Nearly all modeling studies of ring-current injection agree that time-varying magnetospheric convection can produce approximately the ion fluxes that are observed in the storm-time ring current, but the truth of that assumption has never been demonstrated conclusively. It is not clear that the actual variations of convection electric fields are strong enough to explain the observed flux increases in ~100 keV ions at the peak of the storm-time ring current. Observational comparisons are generally far from tight, primarily due to the paucity of ring-current measurements and to basic limitations of single-point observations. Also, most of the theoretical models combine state-of-the-art treatment of some aspects of the problem with highly simplified treatment of other aspects. Even the most sophisticated treatments of the sub-problems include substantial uncertainties, including the following: (i) There is still considerable theoretical and observational uncertainty about the dynamics of the large-scale electric fields in the inner magnetosphere; (ii) No one has ever calculated a force-balanced, time-dependent magnetic-field model consistent with injection of the storm-time ring current; (iii) The most obvious check on the overall realism of a ring-current injection model would be to compare its predicted Dst index against observations; however, theoretical calculations of that index usually employ the Dessler-Parker-Sckopke relation, which was derived from the assumption of a dipole magnetic field and cannot be applied reliably to conditions where the plasma pressure significantly distorts the field; (iv) Although loss rates by charge exchange and Coulomb scattering can be calculated with reasonable accuracy, it remains unclear whether wave-induced ion precipitation plays an important role in the decay of the ring current. However, considerable progress could be made in the next few years. Spacecraft that can provide images of large regions of the inner magnetosphere should eliminate much of the present ambiguity associated with single-point measurements. On the theoretical side, it will soon be possible to construct models that, for the first time, will solve a complete set of large-scale equations for the entire inner magnetosphere. The biggest uncertainty in the calculation of the size and shape of the plasmasphere lies in the dynamics and structure of the electric field. It is still not clear how important a role interchange instability plays in determining the shape of the plasmapause or in creating density fine structure.     

使用电流传感器的ACI／DCV转换电路

介绍一种使用电流传感器的交流电流－直流电压（ＡＣＩ／ＤＣＶ）转换电路，具有与被测电路隔离、体积小、测量范围广、线性度好等特点。     

多重保护的传感器用线性稳压电源设计

设计了一种适用于为传感器供电的线性稳压电源,可以兼容24 VDC和220 VAC供电,解决了传感器交、直流供电兼容性问题,同时具备输入过压保护、输出过压保护、输出限流保护等多重保护功能,很大程度上提高了传感器的通用性和安全性。从理论设计和仿真分析两方面阐述了电源各部分的工作原理,以及针对特定参数的优化、调整方法,最终通过试验验证了设计的合理性。     

基于银焊膏电流烧结的航天功率分立器件气密封装

由于传统气密封装方法在封装的过程中会给电子器件带来不利的影响，本文基于银焊膏电流烧结快速互连技术，提出了一种新型的气密封装方法，可用于航天功率分立器件的密封。本文研究了通电过程中接头温度、微观形貌以及剪切强度的变化。在银焊膏电流烧结的过程中，随着有机物的去除，烧结银层升温速率急剧下降，并且最初被有机物分离的银颗粒逐渐相互接触。随着通电时间延长，烧结银接头越来越致密，伴随着接头强度的不断提高。最终获得的烧结银密封接头可以满足封装器件对气密性的要求。     

Investigation of anode shaping process during co-rotating electrochemical machining of convex structure on inner surface

A novel co-rotating electrochemical machining method is proposed for fabricating convex structures on the inner surface of a revolving part. The electrodes motion and material removal method of co-rotating electrochemical machining are different from traditional electrochemical machining. An equivalent kinematic model is established to analyze the novel electrodes motion,since the anode and cathode rotate in the same direction while the cathode simultaneously feeds along the line of centres. Acc...     

一种提高GNSS测速精度的自适应Kalman滤波算法

在卫星导航系统动态定位中,采用基于瞬时多普勒观测量的最小二乘法确定速度,当载体高机动时,多普勒误差迅速增大,从而导致测速精度大幅度降低。针对该问题,提出一种同时实现动态模型自适应修正和观测模型自适应更新的Kalman滤波算法。算法采用滑动窗方式来建立实时更新的动态模型参数,使当前统计模型自适应地跟踪载体的动态特性。此外,算法提出观测模型的自适应更新方法,通过设置载体状态判决门限,高、中机动时仅进行受动态应力影响小的伪距更新,低机动下添加精度较高的伪距率更新。通过Sprient GSS8000模拟器产生的动态场景验证表明,相对于最小二乘法和常规Kalman滤波算法,提出的自适应Kalman滤波算法能够全面提高载体在多种运动状态下的测速精度。