第22太阳周地磁活动峰值和时间的预计

本文讨论了从第13—22太阳周太阳和地磁周的特征.运用自激励门限自回归时间序列模型和最大熵谱原理自回归数学方法来模拟和预报地磁aa指数年均值峰值和时间.峰值时间是1993年秋天或1994年春天.地磁aa指数年均值峰值是26—29.第22地磁周是一个中等活动的周.     

Dynamical Simulations of Plasmapause Deformations

Dynamical simulations have been developed at IASB-BIRA to model the deformations of the plasmasphere during geomagnetic substorms and other variations in the level of geomagnetic activity. The simulations are based on the mechanism of plasma instability and use the empirical Kp-dependent electric field E5D. The results of the simulations are compared with IMAGE observations that provide the first global comprehensive images of the Earth’s plasmasphere. The predicted plasmapause positions correspond generally rather satisfactorily with the EUV observations. The plasmasphere is rather extended in all MLT sectors during quiet periods. During or just after geomagnetic substorms, the plasmaspause is sharper and becomes closer to the Earth in the night sector. Periods of enhanced geomagnetic activity are associated to the formation of plumes that rotate with the plasmasphere. The simulations reproduce the formation and the motion of these plumes, as well as the development of other structures like shoulders observed at the plasmapause by EUV on IMAGE.     

再入弹头非平衡尾迹的回波特性分析

本文利用文[1]方法计算了纯空气非平衡再入弹头尾迹流场,分析了尾迹等离子体场对雷达波的频响效应,并进一步估算了几种高程条件下的雷达散射截面,说明影响截面大小和分布的几个重要因素。分析和计算表明,以物体底部直径和环境参数表征的雷诺数达到转捩值以后,在完全湍流尾迹中可能出现散射截面的突增现象。     

地磁导航技术研究进展

地磁场是地球的固有资源,利用地磁场匹配进行导航是一种新型导航技术.与传统的惯性导航和卫星导航比较,地磁导航具有无积累误差、抗干扰、隐蔽性好、导航信息丰富等优势.文章介绍了地磁导航的3个基本要素,即磁场测量技术、地磁模型以及定位与导航技术.分析了弱磁场磁力仪在地磁导航中的应用及其优缺点,讨论了地磁场模型和地磁匹配算法,展望了地磁导航技术的应用前景.     

基于UKF的高动态飞行器无源组合导航系统研究

针对飞行器在进行高动态飞行中卫星导航系统易受干扰、GPS可能被屏蔽,从而导致导航系统失稳甚至发散的问题,采用无迹卡尔曼滤波(UKF)算法对基于捷联惯导系统(SINS)、地磁导航系统(GNS)和嵌入式大气数据系统(FADS)的组合无源导航系统性能进行了改进.建立了地磁数据模型和无源组合导航模型,并针对新的组合导航系统观测方程非线性程度较高问题,提出了利用非线性UKF对导航数据进行融合的方法.利用高动态飞行轨迹对所提出的组合导航系统进行了仿真及误差分析,结果表明该系统对SINS误差估计具有适中的精度.     

一种基于地理信息系统的用频台站电磁态势仿真分析方法

针对复杂电磁环境下,对电磁场强分布进行有效定量分析这一普遍存在而又难以解决的问题,提出了一种基于地理信息系统的用频台站电磁态势仿真分析方法。从三维空间地理信息系统建模、用频设备行为级仿真、电波在三维空间传播计算以及场强影响分析等几个方面,分析并实验验证该仿真方法的有效性。采用该方法可有效分析用频台站电磁态势分布和指导用频台站科学合理选址。     

硅橡胶基绝热材料高温热行为研究

采用高温管式炉在惰性气氛下研究了硅橡胶基绝热材料在1 073～1 873 K的热行为,利用X射线衍射和红外光谱等手段探索了高温固相残余物的产生历程和碳化硅的生成机制,采用热重-差热联用表征了高温固相残余物的热氧化性能。研究结果表明,随着处理温度升高,硅橡胶基绝热材料的固相残余物逐渐向高温陶瓷转化,其热稳定性和耐氧化性相应提高;硅橡胶基体在1 073 K已分解完毕,其固相残余物为碳、硅氧碳化物和SiO2等;随温度上升,有机碳向更加耐氧化的无机碳转变;硅氧碳化物随温度升高向碳化硅转化;气相SiO2高温下由无定型转化为方石英晶体,并与碳发生碳热反应生成碳化硅。     

Correction of B2bot for NeQuick during low solar activity at Hainan station

This work is a continuation of the previous article and it focuses on low solar activity and modeling effort. NeQuick model uses Epstein layer formalism to model each part of the profile. We study the diurnal and seasonal variations of B2_bot, ΔB2 (B2_best − B2_NeQuick2) and R (B2_best/B2_{NeQuick 2}) at Hainan station during low solar activity. The results show it is possible to improve the B2_bot parameter of the NeQuick model at that region during low solar activity. Then, we use a function ?(t) with LT in different seasons to correct the B2_bot formula of NeQuick 2. The correction shows that (1) By the correction formula, the B2_bot of NeQuick is improved. The maximum standard deviation is improved for 9 km. (2) The correction formula is more effective in summer than in equinox and winter and performs better during early morning hours than during the rest of the day.     

Near 13.5-day periodicity in Muon Detector data during late 2001 and early 2002

In this study we perform a continuous Morlet wavelet transform method in time series of secondary cosmic rays and 1 AU interplanetary medium parameters for the interval from October 2001 to October 2002. The near 13.5-day periodicity was obtained during late 2001, and it was remarkable for muon data. Even though some works have pointed out that the main activations of the 13.5 day recurrence in near-Earth solar wind are related, e.g., with the heliosheet crossings or to the occurrence at 1 AU of two high speed streams approximately 180° apart in solar longitude per solar rotation, we aim to show that the period of about half the solar rotation during the end months of 2001 present in muon time series was apparently due to the occurrence of non-recurrent interplanetary disturbances. The interconnections among successive Forbush decreases, recovery phases and gradual muon depressions (associated with corotating interaction regions) seem to play an important role in such 13.5-day periodicity.     

基于优化信任评估的Ad Hoc安全路由协议

针对Ad Hoc网络中自私节点造成的攻击问题,提出了一种基于信任评估的Ad Hoc安全路由协议TEAR。该协议在节点行为信任评估方案的基础上,通过使用链路信任值和路径信任值表示节点和路径的可信度,同时,在链路信任值计算时,引入了基于公共邻居节点的间接信任评估方法和可变时间窗机制,保证了信任值计算的准确性和实效性;协议中每个节点维护一张信任表,并重新定义了路由请求和路由回复消息格式,实现了安全路径的快速选择。使用NS2进行模拟验证,又与AODV以及基于固定时间窗信任评估的安全路由协议TA-AODV进行性能对比。结果表明,改进的信任评估方案具有更好的性能,采用该方案的安全路由协议能较快地发现自私节点,并准确选择安全路径,提高了Ad Hoc网络性能。