Variability of foF2 in the African equatorial ionosphere

This paper presents the impact of diurnal, seasonal and solar activity effects on the variability of ionospheric foF2 in the African equatorial latitude. Three African ionospheric stations; Dakar (14.8°N, 17.4°W, dip: 11.4°N), Ouagadougou (12.4°N, 1.5°W, dip: 2.8°N) and Djibouti (11.5°N, 42.8°E, dip: 7.2°N) were considered for the investigation. The overall aim is to provide African inputs that will be of assistance at improving existing forecasting models. The diurnal analysis revealed that the ionospheric critical frequency (foF2) is more susceptible to variability during the night-time than the day-time, with two peaks in the range; 18–38% during post-sunset hours and 35–55% during post-midnight hours. The seasonal and solar activity analyses showed a post-sunset September Equinox maximum and June Solstice maximum of foF2 variability in all the stations for all seasons. At all the stations, foF2 variability was high for low solar activity year. Overall, we concluded that equatorial foF2 variability increases with decreasing solar activity during night-time.     

Using GPS-SCINDA observations to study the correlation between scintillation,total electron content enhancement and depletions over the Kenyan region

This paper presents the first results of total electron content (TEC) depletions and enhancement associated with ionospheric irregularities in the low latitude region over Kenya. At the low latitude ionosphere the diurnal behavior of scintillation is driven by the formation of large scale equatorial depletions which are formed by post-sunset plasma instabilities via the Rayleigh–Taylor instability near the magnetic equator. Data from the GPS scintillation receiver (GPS-SCINDA) located at the University of Nairobi (36.8°E, 1.27°S) for March 2011 was used in this study. The TEC depletions have been detected from satellite passes along the line of sight of the signal and the detected depletions have good correspondence with the occurrence of scintillation patches. TEC enhancement has been observed and is not correlated with increases in S₄ index and consecutive enhancements and depletions in TEC have also been observed which results into scintillation patches related to TEC depletions. The TEC depletions have been interpreted as plasma irregularities and inhomogeneities in the F region caused by plasma instabilities, while TEC enhancement have been interpreted as the manifestation of plasma density enhancements mainly associated with the equatorial ionization anomaly crest over this region. Occurrence of scintillation does happen at and around the ionization anomaly crest over Kenyan region. The presence of high ambient electron densities and large electron density gradients associated with small scale irregularities in the ionization anomaly regions have been linked to the occurrence of scintillation.     

Behavior of the equivalent slab thickness over three European stations

The total electron content (TEC) derived from the global positioning system (GPS) and the F2-layer peak electron density obtained from Digisonde data have been used to study the diurnal, seasonal and solar activity variations of the ionospheric equivalent slab thickness (τ) over three European stations located at Pruhonice (50.0°N, 15.0°E), Ebro (40.8°N, 0.5°E) and El Arenosillo (37.1°N, 353.3°E). The diurnal variation of the τ is characterized by daytime values lower than nighttime ones for all seasons at low solar activity while daytime values larger than nighttime characterizes the diurnal variation for summer at high solar activity. A double peak is noticeable at dusk and at dawn, better expressed for winter at low solar activity. The seasonal variations of τ depend on local time and solar activity, the daytime values of τ increases from winter to summer whereas nighttime values of τ show the opposite. The effect of the solar activity on τ depends on local time and season, there being very sensitive for winter nighttime values of τ. The results of this study are compared with those presented by other authors.     

Comparative analysis of TEC disturbances over tropical cyclone zones in the North–West Pacific Ocean

In this paper, we study ionospheric total electron content (TEC) disturbances associated with tropical cyclones (TCs). The study relies on the statistical analysis of six cyclones of different intensity which occurred in the North–West Pacific Ocean in September–November 2005. We have used TEC data from the international network of two-frequency ground-based GPS receivers and NCEP/NCAR meteorological archive. TEC variations of different period ranges (02–20 and 20–60 min) are shown to be more intense during TC peaks under quiet geomagnetic conditions. The highest TEC variation amplitudes are registered when the wind speed in the cyclone and the TC area are maximum. The intensification of TEC disturbances is more pronounced when several cyclones occur simultaneously. We have revealed that the ionospheric response to TC can be observed only after the cyclone has reached typhoon intensity. The ionospheric response is more pronounced at low satellite elevation angles.     

2D约束Delaunay剖分生成表面模型的表面网格

提出一种生成表面模型的表面非结构化网格的方法.该方法仅假定表面模型的每个面片在取定适当的投影平面时可看成是一个单值函数.对表面模型的每个面片,首先在其相应的投影面上进行二维约束Delaunay剖分,然后对网格顶点进行插值.由于采用联动剖分的策略使得单独生成的各个表面网格在共同边界处匹配.与通常的生成表面网格的网格前沿法相比,本方法无需预先对域的边界进行离散,边界的离散体现在约束Delaunay剖分中恢复限定线段的边界细分过程中,减少了用户干预.通过合理地指定2D约束Delaunay三角化时网格单元尺寸分布函数,可以有效控制表面网格对表面模型的逼近精度和实现自适应的表面网格.实验结果证明了本算法的有效性.     

WAAS电离层延迟网格校正中的用户算法研究

从广域增强系统WAAS中对电离层延迟的网格校正算法出发,分析了用户基于网格校正的电离层校正算法,阐明了核算法的原理并详细推导了计算公式和计算过程.     

排球不同球缝随机气动力建模方法研究

介绍了排球不同球缝随机气动力建模思想，探讨了建模的仿真方法，包括模型及其结构辨识、辨识方法优选及模型检验等，验证结果表明，所建模型与实现吻合，建模方法可行实用，具有直观、简便、灵活、通用、易分析比较、建模精度和效率高等特点，可用于不同球缝机气动力模型的高线或在线辨识。     

地磁活动对电离层f0F2月中值的影响与国际参考电离层误差

利用我国9个中低纬度的电离层观测站在1977-1986年间观测的f0F2月中值,按每月的平均地磁活动指数Ap分为地磁活动高（Ap≥5）和低（Ap＜15）两种情况,研究了地磁活动对f0F2月中值平均低纬电离层驼峰区演变的影响,并考察了国际参考电离层（IRI）的误差．     

航空发动机数据库逻辑结构的研究

成功地建立航空发动机数据库的关键,是根据数据模型分析,研究的结果进行数据库总体逻辑结构设计,经过分析,研究采用关系型数据理论,使航空发动机数据库具有合理的逻辑结构,航空发动机是一种在不断发展中的技术密集型的热动力机械产品,它不但涉及许多学科与技术领域,而且本身结构得杂,型式多样,在建立关系型航空发动机数据库时,研究描述航空发动机的各种数据间的关系模式与函数依赖关系,是建立数据模型的主要环节,数据库     

人体热调节系统数学模型

简要地介绍了人体热调节系统,综述了人体热调节系统数学模型的研究现状,从模型的人体结构表示、循环系统建模、模型的求解和维数等方面,对主要的人体热调节系统数学模型进行了比较,模型包括NASA的41节点人体模型及Kuznetz模型,Wissler模型, Werner模型及北京航空航天大学开发的几个人体热调节模型.对进一步的研究提出了某些观点与建议.