太阳高年期间海南电离层扩展F出现的起始时间研究

电离层扩展F与电离层闪烁现象密切相关,它们出现的起始时间存在着很大程度上的一致性,因此研究电离层扩展F出现的起始时间将对闪烁预报模型的建立具有重要的应用价值.将太阳高年（2002年3月-2003年2月）期间海南地区DPS-4测高仪观测到的扩展F按照频率、区域、混合和强区域扩展等分为四种类型,对其出现的起始时间进行了分析研究.结果表明：频率扩展和混合扩展的起始时间分别集中在0200LT-0800LT和0000LT-0600LT;而区域扩展和强区域扩展出现的起始时间分别集中在2000LT-0200LT和2000LT-2200LT.     

利用热电导理论研究低杂波电流驱动效率

文章在典型的低杂波电流驱动实验中采用低杂波功率扫描的方法研究了低杂波电流驱动效率。利用热电导理论得到的拟合公式拟合实验数据得到了低杂波完全非感应电流驱动效率以及热电导对电流驱动的贡献,低杂波的全波驱动效率为η0=0.349×10^19Am^-2W^-1,由热电导贡献的电流驱动为η1=0.674×10^19Am^-2W^-1。实验发现热电导在等离子体环电压不为零的时候通过和电场的协同作用大大增强了电流驱动。     

一种海面后向散射特性实时仿真的统计模型

提出了一种用于海面后向散射特性实时仿真的三参数模型,导出了分别符合Weibull分布、Log-ormal分布和K-分布等三种统计模型的海杂波生成函数,并讨论了各函数中参数的拟合优化方法.该模型的输出特性既满足实测海面后向散射系数数据的均值和标准偏差,同时又反映出给定的概率密度统计特性,可用于各种仿真系统中的海杂波实时仿真.     

倾听闪电

轰隆隆的雷声或令人振奋，或令人恐惧；淅沥沥的雨声或令人舒心，或令人感怀； 而闪电之声会是怎样的一种声音？ 最近，一群年轻人正在南极倾听 北美发生的闪电之声……     

Range walk and array rotation in space-time adaptive processing: effects and compensations

This paper proposes a unified clutter model incorporating the effects of range walk and array rotation for space-time adaptive processing (STAP) in airborne multi-channel early-warning radar. Based on this clutter model, STAP performance is then analyzed from the perspective of covariance matrix tapering (CMT). For STAP performance degradation due to array rotation, a determinate compensation method is proposed based on the CMT method. Numerical examples are provided to verify the analysis and the proposed compensation method.     

实测数据的降秩空时自适应处理方法

针对全空时自适应处理协方差矩阵估计和计算复杂问题,介绍了在直接处理器结构上基于主分量法和互谱法的两种降秩空时自适应处理方法,这两种方法利用杂波和干扰的低秩属性,应用采样数据来构造降维转换矩阵。对Mountain Top计划进行了详细描述,对从Mountain Top计划测得的数据应用上述两种降秩方法对其进行了分析。仿真实验表明了这两种方法的可行性,减少了计算量,并提高了有效可测收敛性。     

Morphology of polar ionospheric O^＋ ion upflow： FAST observations during quiet time

With energetic ion measurements on FAST satellite, the morphologic features of quiet-time ionospheric O ion upflowing at altitudes of 2000 to 4000 km are drawn out for the first time. The pre-noon cusp/cleft is the predominant region of upflowing occurrence for O with lower energy. Meanwhile the pre-dawn sector near the equatorward edge of the plasma convection dominates the occurrence for the higher energy O ions. No matter whether the energy is lower or higher, the upflows occur often over a wide MLT range of lower latitudes outside the auroral oval. The upflowing within the pre-midnight (21:00― 22:00 MLT) auroral oval carrys larger energy fluxes, with extremely large fluxes for higher energy O appearing near the polar cap boundary. For altitudes of 2000―4200 km under observation, the ion conics occur much more frequently than ion beams. Ion beams are rarely found below 3000 km, while the conics occur uniformly over the observed altitudes.     

Applying partial correlation method to analyzing the correlation between ionospheric NmF2 and height of isobaric level in the lower atmosphere

On the basis of a multiple linear regression model performed for ionospheric NmF2, partial correlation method is first applied to investigating the relation between NmF2 and h (the height of isobaric level) in the lower atmosphere over Wuhan, China during 1957―2004. The results show that partial correlation method can eliminate the influences of solar and geomagnetic activities as well as the seasonal varia- tion factors and reveal the true correlation between NmF2 and h in the lower atmosphere. A weak posi- tive correlation between NmF2 and h is found in the middle stratosphere. In addition, by comparing the partial correlation coefficients between NmF2 and its influence factors, we find that NmF2 is mainly affected by solar activity and the seasonal variation factors, and weakly affected by geomagnetic ac- tivity, but hardly affected by h in the lower atmosphere. The study suggests that partial correlation method is a helpful tool for investigating the correlation between ionospheric parameter and its influ- ence factors.     

电离层多尺度变化对无线电波传播的影响机理研究

1项目简介本项目属于电离层电波传播理论与应用基础研究的前沿课题,在国家自然科学基金重大项目等多个课题的支持下,致力于研究电离层多尺度变化对无线电波传播的影响机理和效应分析方法,开展了电离层媒质电磁特性的长期变化趋势、随机不均匀电离层电波传播理论,以及电离层变化对无线电系统影响的评估方法等研究,取得了重要的科学发现和创新性成果,为认识电离层多尺度变化对无线电波传播的影响机理提供了关键的传播理论基础和新的发现现象;建立了强起伏复杂随机媒质高阶统计矩求解方法,为研究电离层多尺度变化对无线电系统的影响及其对策提供了理论基础.     

FZ-100H型次级整流式直流缝焊机疑难故障的排除

FZ-100H型次级整流式直流缝焊机,因其焊接性能好,广泛使用于汽车、船舶、摩托车等制造行业的零配件的焊接,但此焊机控制部分为数控技术,焊机大部分控制元件和焊接部位靠水冷却,长期工作于潮湿的环境中,故障较多。本文介绍了此焊机较顽固的疑难故障和排除方法。