光线跟踪的最佳期望时间搜索算法

 在计算机图形显示学中,采用光线跟踪(ray tracing)算法能够生成质量很高的、非常逼真的图象,但机时花费太高。据统计,在光线跟踪算法中花费在搜索与光线相交的物体及计算出交点所用的时间大约占75％。本文提出一种用于光线跟踪的与始点无关的搜索算法。此算法不管光线在物空间的始点位置如何,都能生成精确的图象,因此具有通用性;此算法将物空间适当地划分为小立方体,通过只检测光线路径上的立方体,以实现最佳期望时间搜索,所以具有最佳期望时间的复杂性。     

CME-geometry and cosmic-ray anisotropy observed by a prototype muon detector network

We analyze the cosmic-ray anisotropy observed by a prototype network of muon detectors during geomagnetic storms associated with coronal mass ejections (CMEs). The network currently consists of multidirectional surface muon detectors at Nagoya (Japan) and Hobart (Australia), together with a prototype detector at São Martinho (Brazil) which has been in operation since March, 2001. In this report, we analyze the anisotropy recorded in both the muon detector and neutron monitor (the Spaceship Earth) networks and find significant enhancements of cosmic-ray anisotropy during geomagnetic storms. Following the analysis by Bieber and Evenson [Bieber, J.W., Evenson, P. CME geometry in relation to cosmic ray anisotropy. Geophys. Res. Lett. 25 (1998) 2955–2958] for the neutron monitor data at 10 GeV, we also derive cosmic-ray density gradients from muon data at higher-energy (50 GeV), possibly reflecting the larger-scale geometry of CMEs causing geomagnetic storms. We particularly find in some events the anisotropy enhancement clearly starting prior to the storm onset in both the muon and neutron data. This is the first result of the CME-geometry derived from simultaneous observations of the anisotropy with networks of multidirectional muon detectors and neutron monitors.     

Optical search for gamma-ray bursts

The preliminary results from optical search for light pulses associated with gamma ray bursts by means of the Czechoslovak Fireball Network plate collection at the Ondřejov observatory are given. Optical monitoring represents more than 7700 hours, but no real optical counterpart was found. Problems associated with the optical search for gamma ray bursts are discussed.     

太阳宇宙线在电离层D层中的电离

本文根据带电粒子对D层大气电离的理论,导出了太阳宇宙线在D层的电子产生率Q(h)的表达式,并计算了不同级别的太阳宇宙线事件、不同能谱参数下,Q(h)在极区随高度的分布。结果表明,不同级别、不同能谱的太阳宇宙线事件在极区产生的电离有显著的差别。同一级别,能谱指数γ越大,在较高的高度上电子产生率越大;能谱指数越小,在较低的高度上电子产生率越大。电子产生率的分布曲线出现明显的双峰,一个峰位于60公里左右,另一个峰位于85公里左右。前一个峰主要由太阳宇宙线中质子产生的,后一个峰主要是z≥2的重粒子成分产生的。本文所得结果明显好于Velinov等人的结果。      

机载曳光弹的紫外产生机理

立足于现有装备的基础上,大力发展经济,可靠,方便的紫外干扰技术,对我军而言不啻是一种我服的有效手段,在原子物理学理论指导下,本文详细地介绍了产生紫外线光谱重要的一环,原子材料紫外光谱的产生方法,文章的末尾还给出了实验的结果。     

X射线天文卫星观测需求分析与控制总体设计

对X射线天文卫星观测需求进行了分析,提炼了观测任务对观测模式、源的高精度定位与对准、轨道、热控、测控数传等多项需求与约束;针对X射线观测的多需求、多约束难点,设计了集巡天观测、定点观测与小天区扫描观测于一体的观测模式,解决了一颗卫星同时实现全天扫描、银道面深度扫描、重要惯性区域扫描、重要及机遇目标深度观测以及伽马暴全天监测的多种观测需求的难题,该技术已在我国硬X射线调制望远镜卫星上得到应用.     

Remnants of compact binary mergers

We investigate the long-term evolution and observability of remnants originating from the merger of compact binary systems and discuss the differences to supernova remnants. Compact binary mergers expel much smaller amounts of mass at much higher velocities, as compared to supernovae, which will affect the dynamical evolution of their remnants. The ejecta of mergers consist of very neutron rich nuclei. Some of these neutron rich nuclei will produce observational signatures in form of gamma ray lines during their decay. The composition of the ejecta might even give interesting constraints about the internal structure of the neutron star. We further discuss the possibility that merger remnants appear as recently discovered ‘dark accelerators’ which are extended TeV sources which lack emission in other bands.     

Constraints on injection parameters of cosmic rays in the Galactic center from resolved HESS observations

In this study, we investigate how restrictive the γ-ray emission from the Galactic center region, as seen by HESS and other Cherenkov air shower arrays, is against various models for cosmic ray injection. We derive diffusion coefficients which fit the observed spatial scales of diffuse γ-ray emission from the extended emission associated with the molecular clouds SgrA, B and C. Using these diffusion coefficients, we then obtain a limit for time scale of assumed recent proton acceleration near the SMBH, as the spatial size of SgrA^∗ in VHE γ-rays has to be consistent with the observed unresolved HESS point source size at this position. The signal from this hadronic component may be mixed with the expected VHE inverse Compton emission from the nearby unresolved pulsar wind nebula.     

以捷径法提高射线追踪效率

为改善计算效率,提出了一种捷径法对射线追踪法进行改进. 射线追踪的计算时间主要耗费在求交判断上. 通过实际计算并记录一条射线管的轨迹,作为其后若干条射线管求交计算的优先参考,避免了再次进行漫无目的的遍历式求交,从而大量减少进行实际计算的射线管数量,节省射线求交运算时间. 经编程计算验证,该优化算法能够在保证相当精度的前提下,大幅度提高射线追踪法的计算效率,具备一定的实用价值.      

一种固体发动机光线投射体绘制加速方法

固体发动机ICT断层图像构成的体数据场规模大、空体素比例小,现有的光线投射加速方法效果不明显,并且在其三维可视化故障诊断中,不是体数据场中的所有信息都对内部故障检测有意义,三维重建出所有体数据大大增加了计算量.为此,提出一种在同体发动机体数据分割基础上的光线投射加速方法.该方法利用分割结果,建立分割信息体数据场,结合现...