脉冲爆震火箭发动机高频实验研究

为了研究脉冲爆震发动机的高频工作特性,以航空煤油和压缩氧气为推进剂,采用爆震增强装置,增大推进剂供给压力以及增大电磁阀控制气压力等措施,在脉冲爆震火箭发动机模型上进行了实验,成功获得45Hz时的爆震压力波形。实验结果表明,频率增高,爆震波峰值压力下降,有利于加速缓燃向爆震的转变(Defla-gration to Detonation Transition,DDT)。当爆震充分发展时,爆震波波速基本不变,峰值压力上升时间趋于定值。工作频率为45 Hz时,爆震波峰值的压力为3.2 MPa,爆震波的波速为1 715.5m/s。     

Linkage of the ionospheric peak electron density and height deduced from the topside sounding data

Topside sounding electron density profiles are analyzed to explore interrelations of the F2 layer critical frequency and the peak height for a representative set of conditions provided by ISIS1, ISIS2, IK19 and Cosmos-1809 satellites for the period of 1969–1987. The foF2 and hmF2 are delivered with exponential extrapolation of electron density profile to zero of its 1st derivative. It is shown that the linear regression exists between foF2 and hmF2 under different conditions. The linkage between the two parameters amended to the empirical model of the peak height [Gulyaeva, T.L., Bradley, P.A., Stanislawska, I., Juchnikowski, G. Towards a new reference model of hmF2 for IRI. Adv. Space Res. 42, 666–672, doi:10.1016/j.asr.2008.02.021, 2008] results in an empirical model of the both foF2 and hmF2 expressed by superposition of functions in terms of local-time, season, geodetic longitude, modified dip latitude and solar activity. For the solar activity we use a proxy Fsp index averaged from the mean solar radio flux F10.7s for the past 81 days (3 solar rotations) and F10.7 value for 1 day prior the day of observation. Impact of geomagnetic activity is not discernible with the topside sounding data due to mixed positive and negative storm-time effects. Appreciable differences have been revealed between IRI-CCIR predictions and outcome of the new model which might be attributed to the different techniques of the peak electron density and 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.     

应用BP神经网络针对高通量质子事件的通量数值预报

质子事件的爆发与太阳软X射线辐射有着很强的相关性,利用GOES卫星的1～8 (A)波段和0.5～4 (A)波段的软X射线数据,选取一些特征参量验证该相关性并应用到质子事件短期预报中.在当前质子事件传输物理机制不完全明确的情况下,在现有的预报质子事件有无的模型基础上,利用BP神经网络,根据软X射线通量水平等预测事件质子峰值通量水平,再对训练后的网络进行检验,检验预测所得结果与实际探测值误差小于一个量级,具备一定实用意义.      

SAR图像目标峰值特征提取与方位角估计方法研究

目标峰值特征是SAR图像目标识别的重要特征之一。峰值特征提取是SAR图像目标识别的一个重要步骤，为了由SAR图像快速、精确地提取目标峰值特征．本文首先研究了SAR图像目标峰值特征提取方法，提出了一种“子像素”级精度的SAR图像目标峰值特征提取方法．并通过仿真实验分析了峰值位置、峰值幅度的估计精度。由于目标SAR图像或SAR图像特征矢量对目标方位角变化的敏感性，因此，为了提高SAR图像目标识别系统的分类效率，本文还研究了SAR图像目标方位角估计方法，提出了一种利用峰值特征基于线性回归的sAR目标方位角估计方法，和现有方法相比，该方法除了计算速度快，估计精度较高之外，还能在估计方位角的同时，给出该估计的置信区间，从而更好的满足SAR ATR的实际需要。文中通过对大量实测MSTAR SAR图像目标方位角的估计实验，验证了本文目标峰值特征提取及方位角估计方法的有效性。     

Calibration of IRI–ITU-R peak density and height over the oceans with topside sounding data

Accuracy of IRI electron density profile depends on the F2 layer peak density and height converted by empirical formulae from the critical frequency and M3000F2 factor provided by the ITU-R (former CCIR). The CCIR/ITU-R maps generated from ground-based ionosonde measurements suffer from model assumptions, in particular, over the oceans where relatively few measurements are available due to a scarcity of ground-based ionosondes. In the present study a grid-point calibration of IRI/ITU-R maps for the foF2 and hmF2 over the oceans is proposed using modeling results based on the topside true-height profiles provided by ISIS1, ISIS2, IK-19 and Cosmos-1809 satellites for the period of 1969–1987. Topside soundings results are compared with IRI and the Russian standard model of ionosphere, SMI, and grouped to provide an empirical calibration coefficient to the peak density and height generated from ITU-R maps. The grid-point calibration coefficients maps are produced in terms of the solar activity, geodetic latitude and longitude, universal time and season allowing update of IRI–ITU-R predictions of the F2 layer peak parameters.     

Cross-hemisphere comparison of mid-latitude ionospheric variability during 1996–2009: Juliusruh vs. Hobart

Analysis of a long-time series of hourly median characteristics of the ionospheric plasma at two mid-latitude locations in the Northern and Southern hemisphere, Juliusruh (54.6N; 13.4E) and Hobart (42.9S; 147.3E), reveals patterns of their synchronous and independent variability. We studied timelines of GPS vTEC, ionogram-derived F2-layer peak electron density NmF2, ionospheric equivalent slab thickness τ, and their ratios at two locations during the complete 23rd solar cycle and its following period of the extremely low solar activity in 2008–2009. This study has also involved the comparative analysis of the observed data versus the model predictions by IRI-2012. During the high solar activity in 2000–2002, seasonal variations show a complicated cross-hemisphere behavior influenced by the winter and semi-annual anomalies, with the largest noon-time values of TEC and NmF2 observed around equinoxes. Strength of the winter anomaly in NmF2 was significantly greater at Juliusruh in comparison with Hobart. The winter anomaly in GPS vTEC values was much weaker than in NmF2 for the Northern hemisphere mid-latitudes and was entirely absent at the Southern hemisphere. Cross-hemisphere analysis of the equivalent slab thickness shows its clear seasonal dependence for all levels of solar activity: the day-time maximum τ_max is observed during local summer, whereas the day-time minimum τ_min is observed during local winter. The night-time values of τ were higher compared to the day-time values during the winter and equinox seasons. Comparative model-data study shows rather good IRI performance of the day-time NmF2 for mid-latitudes of both hemispheres and rather noticeable overestimations for the mid-night NmF2 values during high solar activity. Analysis of IRI vTEC demonstrates the model limitations, related with the absence of the plasmaspheric part, and actual demand in a reliable and standard ionosphere–plasmasphere model for analysis of GPS vTEC.     

腰绑式行人导航系统基于缓存区的启发式航向补偿算法研究

腰绑式行人导航系统通过航位推算方法实现行人定位导航，对于实行灾难救援和单兵作战等任务十分便利。行人行进步长和航向的准确估计是实现航位推算的前提。根据腰绑式惯性传感器信号的特征，采用基于三轴合成加速度的峰值检测进行单步划分；利用步频和加速度方差信息构建线性步长模型。针对人员执行任务过程中由于运动方向不确定性导致传统启发式航向漂移消除算法过度修正甚至失效的问题，提出了一种基于缓存区的启发式航向补偿算法。根据运动方式选定N个复步作为一个缓存区，计算缓存区内相邻复步航向差值的方差，依据方差动态调整航向补偿算法的修正强度，避免过度修正。利用所提算法进行了矩形实验和操场实验，终点定位误差小于1%，表明了所提方法的有效性。     

Modeling spatial density in low earth orbits using wavelets and random search

The events that occurred after 2007 such as Chinese anti-satellite test, explosion of Briz-M upper stage, break up of cosmos-2421 and collision of cosmos-2251 with Iridium-33 satellites have completely changed the spatial density patterns in low earth orbits. This has increased the risk of collision between active satellites and debris created by them. Aftermath, the risk assessment of possible collisions called as conjunction analysis of working satellites from day to day has become more crucial. Spatial density models are useful in understanding the long-term likelihood of a collision in a particular region of space and helpful in pre-launch orbit planning. In this paper we present an algorithmic procedure for automatically estimating exact model parameters corresponding to the peak location and number of peaks using wavelets that will speed up the parameter estimation process for the models with peaks.     

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.     

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.