Variability of the ionosphere over Irkutsk at low solar activity

Statistical and spectral analyses are performed to investigate variations of two ionosphere F2 layer key parameters, the critical frequency (foF2) and the peak height (hmF2), that were measured over Irkutsk (52.5°N, 104.0°E) from December 2006 to January 2008 under solar minimum. The analyses showed that both parameters contain quasi-harmonic oscillations with periods of T_n = 24/n hours (n = 1–7), among which the diurnal (n = 1) and semidiurnal (n = 2) ones are the strongest. Seasonal variations are explored of mean and median values, spectrum, amplitude, and phase of the diurnal and semidiurnal components of foF2 and hmF2.     

Disturbances in the ionospheric F-region peak heights in the American longitudinal sector during geomagnetic storms of September 2005

In this paper, we use the modified GSM TIP model to explore how the thermosphere–ionosphere system in the American longitudinal sector responded to the series of geomagnetic storms on September 9–14, 2005. Comparison of modeling results with experimental data at Millstone Hill, USA (42.6°N, 71.5°W), Ramey, Puerto Rico (18.3°N, 66.8°W) and Jicamarca, Peru (11.9°S, 76.9°W) has shown a good agreement of ionospheric disturbances in the F-region maximum height. We examine in detail the formation mechanisms of these disturbances at different latitudes and describe some of the important physical processes affecting the behavior of the F-region. In addition, we consider the propagation of thermospheric wind surge and the formation of additional layers in the low-latitude ionosphere during geomagnetic storms.     

高动态下的星体目标质心提取方法

高动态情况下,星点像斑在星敏感器探测器上会呈现出拖尾现象,星点质心无法被准确提取。针对上述难点,本文提出了一种高动态条件下基于差异哈希算法的星点质心提取方法。该方法分为三步：第一,建立动态星斑的数学模型;第二,利用差异哈希算法和汉明距离实现星跟踪窗口内星体目标粗定位;第三,在粗定位区域使用阈值分割与连通域法提取星点质心。实验结果表明,该方法能够适应各种长度的曝光时间,并实现星敏感器在3（°）/s条件下的稳定跟踪。在曝光时间50ms,角速度3（°）/s的条件下,星对角距误差为13”,平均提取率为96%,相比于传统方法,分别提高了29.6%和22.9%。     

B样条技术在RPM切片数据处理中的应用

首先介绍了RPM切片数据的处理问题,其次阐述了B样条的基本原理,最后研究了用三次B样条的反求技术对切片数据进行插值修补处理,并用弦高差方法对插值点进行取舍,生成最终的轮廓数据。     

学生成绩的Logistic回归模型研究

研究了Logistic回归模型,进行分组数据,计算对数发生比,为了修正异方差性,在做常规最小二乘估计之前,转换数据,建立某校学生结业考试成绩与第一学期考试成绩及学生性别关系的Logistic回归模型,结果表明, 结业考试成绩不但与第一学期考试成绩有关而且与学生性别的关系也不容忽视,为研究三者之间的关系,选择适当的方法提高学生成绩提供理论根据.     

小迎角轴对称体跨声速绕流的一种Euler解法

应用小迎角展开的方法将小迎角下旋成体绕流Ｅｕｌｅｒ方程进行摄动展开，对零介和一阶方程分别采用隐式ＮＮＤ格式进行了计算，与实验进行比较得到了较为满意的结果。该方法采用二维的计算得到了三维的结果，大大提高了计算的效率。     

Towards a new reference model of hmF2 for IRI

A numerical model of the peak height of the F2 layer, hmF2_top, is derived from the topside sounding database of 90,000 electron density profiles for a representative set of conditions provided by ISIS1, ISIS2, IK19 and Cosmos-1809 satellites for the period of 1969–1987. The model of regular hmF2 variations is produced in terms of local time, season, geomagnetic latitude, geodetic longitude and solar radio flux. No geomagnetic activity trends were discernible in the topside sounding data. The nighttime peak of hmF2_top evident for mid-latitudes disappears near the geomagnetic equator where a maximum of hmF2_top occurs at sunset hours when it can exceed 500 km at solar maximum. The hmF2 given by the IRI exceeds hmF2_top at the low solar activities. The hmF2_top, obtained by extrapolation of the first derivative of the topside profile to zero shows saturation similar to foF2 the greater the solar activity. The proposed model differs from hmF2 given by IRI based on M(3000)F2 to hmF2 conversion by empirical relationships in terms of foF2, foE and R12 with these quantities mapped globally by the ITU-R (former CCIR) from ground-based ionosonde data. The differences can be attributed to the different techniques of the peak height derivation, different epochs and different global distribution of the source data as well as the different mathematical functions involved in the maps and the model presentation.     

COMPUTATION OF COMPRESSIBLE FLOW PAST SLENDER WING－BODY USING FULL－POTENTIAL EQUATION

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烧蚀外形计算的一种自动调节人工粘性项的差分格式

在再入端头烧蚀外形计算中,通过对物形参数的自动滤波处理,构造出了一种附加人工粘性项三层显式差分格式。这种格式在外形变化波动区达一阶精度,在外形变化平稳区达二阶精度。数值试验表明,这种格式在保障外形计算精度和增大时间步长、节省计算机时都是有效的。