Geomagnetic activity associated with magnetic clouds,magnetic cloud-like structures and interplanetary shocks for the period 1995–2003

Using nine years (1995–2003) of solar wind plasma and magnetic field data, solar sunspot number, and geomagnetic activity data, we investigated the geomagnetic activity associated with magnetic clouds (MCs), magnetic cloud-like structures (MCLs), and interplanetary shock waves. Eighty-two MCs and one hundred and twenty-two MCLs were identified by using solar wind and magnetic field data from the WIND mission, and two hundred and sixty-one interplanetary shocks were identified over the period of 1995–2003 in the vicinity of Earth. It is found that MCs are typically more geoeffective than MCLs or interplanetary shocks. The occurrence frequency of MCs is not well correlated with sunspot number. By contrast, both occurrence frequency of MCLs and sudden storm commencements (SSCs) are well correlated with sunspot number.     

Crew autonomy for deep space exploration: Lessons from the Antarctic Search for Meteorites

Future piloted missions to explore asteroids, Mars, and other targets beyond the Moon will experience strict limitations on communication between vehicles in space and control centers on Earth. These limitations will require crews to operate with greater autonomy than any past space mission has demonstrated. The Antarctic Search for Meteorites (ANSMET) project, which regularly sends small teams of researchers to remote parts of the southern continent, resembles a space mission in many ways but does not rely upon a control center. It provides a useful crew autonomy model for planners of future deep space exploration missions. In contrast to current space missions, ANSMET gives the crew the authority to adjust competing work priorities, task assignments, and daily schedules; allows the crew to be the primary monitor of mission progress; demands greater crew accountability for operational errors; requires the crew to make the most of limited communication bandwidth; adopts systems designed for simple operation and failure recovery; and grants the crew a leading role in the selection and stowage of their equipment.     

低量值直流电流表检定及测量不确定度评定

详细地叙述了利用XF1b型交、直流精密电表校验装置采用直流补偿法检定低量值直流电流表示值误差时所存在的问题，并提出一种改进线路。同时，按照JJF1059—1999《测量不确定度评定与表示》规范的要求对上述方法中所阐述的低量值直流电流表示值误差测量结果的不确定度进行了评定。     

风扇进口噪声预测模型的改进

针对Heidmann模型对风扇进口低频噪声(1k Hz)预测结果偏低的情况,通过引入风扇叶尖弦长雷诺数和相关几何参数改进了Heidmann模型中风扇进口宽频噪声的频谱修正函数,确定了其中频谱修正系数为0.085。对比改进模型和Heidmann模型的风扇进口噪声预测结果发现:在亚声速工况下,改进的模型很好地改善了风扇进口低频噪声的预测结果,改进幅值可以达到约45d B;而在超声速工况下,由于风扇进口产生的组合单音噪声成为风扇进口噪声的主要组成部分,除了在小于100Hz的频域内,改进的模型与Heidmann模型的预测结果差别不大。     

基于一致关联数最大化的航迹关联算法

航迹关联(TTTA)是多传感器数据融合系统的核心模块之一,是系统误差估计和航迹融合的前提和基础。传感器存在的固有系统误差使得目标位置状态估计与真值发生偏离,容易诱发TTTA错误。传统的基于全局最小距离准则的TTTA算法,需要获得较高精度的系统误差估计,来对航迹数据进行误差补偿。针对传感器具有系统误差环境下的TTTA问题,在对TTTA进行间接评估的基础上,定义了一致关联数的概念,提出了一致关联数最大化的TTTA准则,并在稳健交替迭代的框架下完成算法设计。与距离函数不同,一致关联数是一个离散量,放松了对系统误差估计精度的要求。最后,仿真实验验证了所提算法的有效性。     

基于左手材料的翼面隐身结构设计及优化

翼面隐身结构能同时满足飞行器机翼气动、结构和隐身的要求,但在空间有限的机翼中应用时,由于结构特点使其隐身效果受到限制。为了解决该问题,在传统隐身结构中加入左手材料(LHM)进行改进。首先选取一种典型的LHM,从隐身设计角度出发,利用其雷达散射截面(RCS)计算不同入射角度下的后向吸收率,对其电磁特性进行研究。然后根据LHM的电磁特性,将其应用于翼面隐身结构,在相同的RCS减缩效果下,应用LHM可有效降低隐身结构体积。最后,为了进一步提高隐身效果,提出一种夹芯型LHM翼面隐身结构,并对该隐身结构中的结构参数利用代理模型进行优化。研究结果表明,相较金属翼面段RCS降低了15dB以上,较相同结构的翼面隐身结构RCS降低了10dB以上。     

脉冲雷达凝视模式下低轨碎片相对运动特征分析

脉冲雷达凝视模式是一种探测低轨小碎片的重要方式,其中低轨碎片与雷达的径向运动关系是碎片统计分析的基础.为推算碎片相对雷达的运动特征,基于坐标系的相互转换,先利用雷达测站信息,得到可见碎片在地惯坐标系下的轨道信息;再逆向将目标不同时刻的位置转换至测站坐标系下,得到目标的径向运动特征.在不同要素（雷达波束指向、雷达仰角、测站纬度、目标距离）下,仿真及对比分析了各个参数对速度模糊度、雷达可见性等的影响,得出在凝视模式下目标相对雷达近似做径向匀加速运动,这为后续试验工作提供有力的依据.     

无人直升机悬停低速段的不确定性仿真验证

在无人直升机控制律的设计过程中,需要对无人直升机进行建模,并对飞行中产生的一些不确定性因素进行仿真验证.目前,很多不确定性因素的描述是在非线性的环境中加入一些简单的扰动,然而能够确切地描述无人直升机动态特性的非线性模型在MATLAB中很难搭建.为此,文章从工程研究的角度,提出了在无人直升机线性模型组的基础上进行不确定性仿真验证的方法,从物理特性的角度描述无人直升机在悬停低速飞行时的对象特性不确定性,选择不确定或扰动因子;在MATLAB中建立了仿真模型,进行了无人直升机悬停低速段不确定性的验证.此方法简单、快速,并且能正确地反应无人直升机悬停低速段的不确定性,具有一定的工程意义.     

Solar activity dependence of total electron content derived from GPS observations over Mbarara

Vertical total electron content (VTEC) observed at Mbarara (geographic co-ordinates: 0.60°S, 30.74°E; geomagnetic coordinates: 10.22°S, 102.36°E), Uganda, for the period 2001–2009 have been used to study the diurnal, seasonal and solar activity variations. The daily values of the 10.7 cm radio flux (F_10.7) and sunspot number (R) were used to represent Solar Extreme Ultraviolet Variability (EUV). VTEC is generally higher during high solar activity period for all the seasons and increases from 0600 h LT and reaches its maximum value within 1400 h–1500 h LT. All analysed linear and quadratic fits demonstrate positive VTEC-F_10.7 and positive VTEC-R correlation, with all fits at 0000 h and 1400 h LT being significant with a confidence level of 95% when both linear and quadratic models are used. All the fits at 0600 h LT are insignificant with a confidence level of 95%. Generally, over Mbarara, quadratic fit shows that VTEC saturates during all seasons for F_10.7 more than 200 units and R more than 150 units. The result of this study can be used to improve the International Reference Ionosphere (IRI) prediction of TEC around the equatorial region of the African sector.     

关于当量空速修正计算的讨论

本文指出了一些手册和教科书中关于当量空速修正计算存在的问题。在讨论了问题的原因后，本文导出了当量空速与校正空速之间的关系；并给出了相应的修正计算图表。