一种高精度的X射线脉冲星导航TOA估计方法

针对X射线脉冲星导航（XPNAV）系统的基本观测量--脉冲到达时间（TOA）的估计问题,提出一种高精度的TOA估计方法。该方法基于特征子空间分解类算法的高精度的参数估计特性,首先通过细致分析标准轮廓与折叠轮廓之间的互相关结果,构造新的观测方程;然后对该方程进行特征值分解得到两个相互正交的特征矢量;最后利用两个特征矢量之间的正交性完成TOA估计。数值仿真结果有效校验了算法的性能。     

太阳X射线暴在地球大气中传输的Monte Carlo模拟

应用MonteCarlo方法对太阳X射线暴(1-8?及0.5-4?)与地球大气相互作用过程进行跟踪模拟,得到了X射线暴在电离层D层产生的电子产生率,并计算了由此产生的宇宙噪声吸收值。结果与作者在南极观测得到的X射线暴期间宇宙噪声吸收值符合较好.      

基于GCF-SB视觉注意模型的红外目标检测算法

针对复杂背景、低对比度条件下的红外目标检测,提出了一种基于灰度对比度特征 相似性贝叶斯(GCF SB)模型的红外显著性目标检测算法.建立了一种灰度对比度特征(GCF)模型,该模型利用两个通道分别提取红外图像的灰度特征和对比度特征,然后通过特征融合获得初级显著图;建立了一种基于相似性的贝叶斯(SB)模型,该模型根据初级特征图分别计算目标和背景的先验概率和似然函数,然后利用贝叶斯公式获得最终显著图,进而实现红外图像的显著性目标检测.实验结果表明,所提出算法能够有效抑制复杂背景、低对比度红外图像的噪声,增强对比度,具有较高的检测精度和鲁棒性.     

基于改进YOLOv3网络的遥感目标快速检测方法

针对将来卫星在轨实时目标检测需求,且在其内存和算力都受限的条件下,提出一种改进的YOLOv3,利用轻量化网络代替YOLOv3的特征提取网络,实现遥感目标的高效检测。在目标检测精度相近的情况下,改进模型参数相比原先降低了1.5倍,计算量降低了3.3倍。同时提出了一种基于交并比的迭代聚类算法,分别在YOLOv3和改进YOLOv3上实现了7.0%和2.3%的平均精度均值(mAP)提升。实验表明:改进模型的检测速度最快能达到101 frame/s,当其mAP比YOLOv3高6%时,检测速度仍是YOLOv3的1.6倍。本文提出的改进YOLOv3是一种高效遥感目标检测方法,为未来星上应用打下基础。     

The X-Ray Spectrometer on the MESSENGER Spacecraft

NASA’s MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) mission will further the understanding of the formation of the planets by examining the least studied of the terrestrial planets, Mercury. During the one-year orbital phase (beginning in 2011) and three earlier flybys (2008 and 2009), the X-Ray Spectrometer (XRS) onboard the MESSENGER spacecraft will measure the surface elemental composition. XRS will measure the characteristic X-ray emissions induced on the surface of Mercury by the incident solar flux. The Kα lines for the elements Mg, Al, Si, S, Ca, Ti, and Fe will be detected. The 12° field-of-view of the instrument will allow a spatial resolution that ranges from 42 km at periapsis to 3200 km at apoapsis due to the spacecraft’s highly elliptical orbit. XRS will provide elemental composition measurements covering the majority of Mercury’s surface, as well as potential high-spatial-resolution measurements of features of interest. This paper summarizes XRS’s science objectives, technical design, calibration, and mission observation strategy.     

The local bubble

Recently, observations with the rosat PSPC instrument and the spectrometers onboard the euve satellite have given new detailed information on the structure and physical conditions of the Local Bubble. From the early rocket experiments, and in particular from the WISCONSIN Survey, the existence of a diffuse hot gas in the vicinity of the solar system, extending out to about 100 pc, has been inferred in order to explain the emission below 0.3 keV. The higher angular resolution and sensitivity of rosat made it possible to use diffuse neutral clouds as targets for shadowing the soft X-ray background. Thus, in some directions, more than half of the flux in the 0.25 keV band appears to come from outside the Local Bubble. Further, measurements of the diffuse EUV in the LISM, show surprisingly few emission lines. These findings are in conflict with the standard LHB model, which assumes a local hot (T 10⁶ K) plasma in CIE. Model calculations, based on the non-equilibrium cooling of an expanding plasma, show a promising way of reconciling all available observations. Thus the present temperature within the LB may be as low as 4 × 10⁴ K and its number density as large as 2 × 10^–2 cm ^–3, giving a total pressure that is roughly in agreement with the Local Cloud.Abbreviations CIE collisional ionization equilibrium - ISM Interstellar Medium - LHB Local Hot Bubble - LB Local Bubble - LISM Local ISM - SB superbubble - SXR soft X-ray - SXRB SXR Background - VLISM Very Local ISM Heisenberg Fellow     

Incone1 718合金的定量相分析

给出了Inconel718合金奥氏体点阵参数与δ、γ"、γ'相含量的关系式,并借助X射线衍射技术及奥氏体点阵参数与δ、γ"、γ'相含量的关系确定了Inconel718合金中析出相的含量。     

孔挤压强化残余应力场的三维有限元模拟和实验研究

运用有限元软件ANSYS建立了孔挤压强化残余应力场的三维有限元模型,模拟计算了不同厚度7050-T7451铝合金构件孔挤压强化的三维残余应力场分布.模拟结果表明,孔边残余应力沿厚度方向呈梯度分布,人口残余压应力最小,是易于产生裂纹的部位;入口残余压应力随构件厚度增加而增大,达到最大值后,随厚度增加而减小并逐渐趋于稳定值...     

基于组合跟踪的景象匹配分析评估方法

景象匹配飞行试验中,图像序列中存在的剧烈尺度变化及多种外界因素影响导致的几何变形等成像质量变化,增加了景象匹配全流程自动评估的难度.为了解决这个问题,提出1种基于组合跟踪的景象匹配图像全流程评估方法.首先,基于序列图关键帧选取原则,提出序列图关键帧匹配方法;然后将该方法与多种目标跟踪算法进行对比分析;再根据对比分析的结...