Ionospheric Effects of Geomagnetic Storms in Different Longitude Sectors

This paper analyzes the state of the ionosphere during two geomagnetic storms of a different intensity evolving in different sectors of local time in different seasons. There were used the data from a network of ionospheric stations located in the opposite longitudinal sectors of 80°-150° E and 250°-310° E.This analysis has permitted us to conclude that the detected differences in the variations of the disturbances are likely to be determined by the local time difference of the geomagnetic storm development, its intensity and by the different illumination conditions of the ionosphere.      

Interplanetary shocks and sudden impulses during solar maximum (2000) and solar minimum (1995–1996)

In this work a study is performed on the correlation between fast forward interplanetary shock parameters at 1 Astronomical Unit and sudden impulse (SI) amplitudes in the H-component of the geomagnetic field, for periods of solar activity maximum (year 2000) and minimum (year 1995–1996). Solar wind temperature, density and speed, and total magnetic field, were taken to calculate the static pressures (thermal and magnetic) both in the upstream and downstream sides of the shocks. The variations of the solar wind parameters and pressures were then correlated with SI amplitudes. The solar wind speed variations presented good correlations with sudden impulses, with correlation coefficients larger than 0.70 both in solar maximum and solar minimum, whereas the solar wind density presented very low correlation. The parameter better correlated with SI was the square root dynamic pressure variation, showing a larger correlation during solar maximum (r = 0.82) than during solar minimum (r = 0.77). The correlations of SI with square root thermal and magnetic pressure were smaller than with the dynamic pressure, but they also present a good correlation, with r > 0.70 during both solar maximum and minimum. Multiple linear correlation analysis of SI in terms of the three pressure terms have shown that 78% and 85% of the variance in SI during solar maximum and minimum, respectively, are explained by the three pressure variations. Average sudden impulse amplitude was 25 nT during solar maximum and 21 nT during solar minimum, while average square root dynamic pressure variation is 1.20 and 0.86 nPa^1/2 during solar maximum and minimum, respectively. Thus on average, fast forward interplanetary shocks are 33% stronger during solar maximum than during solar minimum, and the magnetospheric SI response has amplitude 20% higher during solar maximum than during solar minimum. A comparison with theoretical predictions (Tsyganenko’s model corrected by Earth’s induced currents) of the coefficient of sudden impulse change with solar wind dynamic pressure variation showed excellent agreement, with values around 17 nT/nPa^1/2.     

遗传算法在电子战干扰规划中的应用

电子对抗干扰资源任务规划问题对于充分发挥干扰机作战效能,取得最佳干扰效益有重要作用.结合现代电子战特点,利用搜索论推导出了干扰机压制概率的计算公式,建立了干扰任务分配模型,并阐述了传统匈牙利方法在这一问题处理上的局限性.结合智能优化算法,提出了基于遗传算法的干扰资源优化分配模型.解决了优化分配模型所需的符号编码方式,并给出了相关的选择、交叉、变异等遗传算子的具体设计.利用该模型,解决了2个实例.结果表明,该模型在干扰资源任务配置问题上具有很强的实用性,遗传算法可以有效地辅助指挥员解决干扰资源部署决策这一复杂而困难的问题.     

动态桨叶RCS特性的实验研究

在微波暗室中测量了金属平板桨叶动态模型的高频雷达散射截面RCS(Radar Cross Section),并通过快速傅立叶变换FFT(Fast Fourier Transform)得到相应的频谱图;详细分析了时域和频域RCS随桨叶片数、雷达波入射方向、入射频率、极化状态和桨叶转速等因素的变化.实验结果表明主要特征是时域RCS呈周期性起伏,频谱图因前行桨叶与后行桨叶散射有差别而不对称,且频谱宽度反映了多普勒效应.取得的结果与已有文献的计算分析一致,对直升机的探测和识别具有重要的参考价值.      

Non-Thermal Processes in Cosmological Simulations

Non-thermal components are key ingredients for understanding clusters of galaxies. In the hierarchical model of structure formation, shocks and large-scale turbulence are unavoidable in the cluster formation processes. Understanding the amplification and evolution of the magnetic field in galaxy clusters is necessary for modelling both the heat transport and the dissipative processes in the hot intra-cluster plasma. The acceleration, transport and interactions of non-thermal energetic particles are essential for modelling the observed emissions. Therefore, the inclusion of the non-thermal components will be mandatory for simulating accurately the global dynamical processes in clusters. In this review, we summarise the results obtained with the simulations of the formation of galaxy clusters which address the issues of shocks, magnetic field, cosmic ray particles and turbulence.     

小卫星的自适应姿态控制

分析了小卫星的姿态动力学及运动学方程；利用姿态动力学方程为一动力学参数矢量的线性函数这一事实，考虑存在参数不确定性，提出了一种自适应控制方法；证明了这种方法可以保证控制系统全局渐近稳定。仿真结果验证了该方法的有效性。     

Great solar bursts of October 19, 22 and 23, 1989

Itapetinga measurements at 48 GHz with the multibeam technique are used to determine the relative position of solar burst centroid of emission with high spatial accuracy and time resolution. For the Great Bursts of October 19,22, 1989, with a large production of relativistic particles, and October 23, it is suggested that, at 48 GHz, the bursts might have originated in more then one source in space and time. Additionally the October 19 and 22 Ground Level Events exhibited very unusual intensity-time profiles including double component structures for the onset phase. The Bern observatory spectral radio emission data show a strong spectral flattening typical for large source inhomogeneties. The interpretation for this is that large solar flares are a superposition of a few strong bursts (separated both in space and time) in the same flaring region.     

捷联式天线平台的稳定性研究

将Rudin提出的红外成像捷联稳定模型用于天线平台的稳定,并应用不变性原理,采取匹配滤波方法,提高了稳定平台的解耦精度.具体仿真结果表明:在0.5 Hz~1.0 Hz频段解耦精度提高了35 dB.同时,在考虑传感器测量噪声的情况下,对天线平台的稳定误差进行了仿真分析,结果显示,传感器测量噪声对稳定误差有较大的影响,但通过滤波稳定误差可减小50%左右.      

Models of P/Borrelly: Activity and dust mantle formation

Comet 19P/Borrelly was observed by Deep Space One spacecraft on September 22, 2001 (Soderblom et al., 2002).The DS1 images show a very dark and elongate nucleus with a complex topography; the IR spectra show a strong red-ward slope consistent with a very hot and dry surface (345K to 300K). During DS1 encounter the comet coma was dominated by a prominent jet but most of the comet was inactive, confirming the Earth-based observations that <10% of the surface is actively sublimating. We have developed a thermal evolution model of comet PBorrelly, using a numerical code that is able to solve the heat conduction and gas diffusion equations at the same time across an idealized spherical nucleus ( De Sanctis et al., 1999, 2000; Capria et al., 2000; Coradini et al., 1997a,b). The comet nucleus is composed by water, volatiles ices and dust in different proportions. The refractory component is made by grains that are embedded in the icy matrix. The code is able to account for the dust release, contributing to the dust flux, and the formation of dust mantles on the comet surface. The model was applied to a cometary nucleus with the estimated physical and dynamical characteristics of P/Borrelly in order to infer the status and activity level of a body on such an orbit during the DS1 observation. The comet gas flux, differentiation and thermal behavior were simulated and reproduced. The model results are in good agreement with the DS1 flyby results and the ground based observations, in terms of activity, dust coverage and temperatures of the surface.     

Measurements of bidirectional reflectance of ordinary chondrite for muses-C in-situ detection

MUSES-C, a Japanese sample return mission, is targeting a small near Earth asteroid, 1998SF36, which is considered an S-type asteroid and is similar in spectroscopy to LL class ordinary chondrite meteorite ([Binzel et al., 2001]). Although this mission will bring us detailed photometric data, that is, disk-resolved bidirectional reflectance data of the asteroid, there were few bidirectional reflectance data of ordinary chondrite meteorites. For the purpose of comparison with the data obtained by the in-situ observation, we have performed measurements of bidirectional reflectance of ordinary chondrite samples.

Here we summarize the result of our laboratory measurements of the bidirectional reflectance and compare them with the scattering property of 1998SF36. Although the geometric albedo of 1998SF36 is higher than the typical value of S-type asteroids, however, the laboratory data of ordinary chondrite are similar to or brighter than the model disk-resolved reflectance of 1998SF36 derived from disk-integrated ground-based data. We found in our laboratory data that there is a positive correlation between the surface roughness and the strength of the opposition effect. A stronger opposition effect in the reflectance of 1998SF36 than the laboratory data may therefore indicate that the surface of the asteroid has rougher structure than our laboratory samples.