经自适应网格改造后的SHASTA程序和磁重联数值实验

SHASTA(Shaarp and smooth Transport Algorithm)是求解二维磁流体动力学问题的单一网格程序.在将其用于磁重联问题的数值模拟时,它被修改成为采用自适应网格方法的程序.修改后的程序可以针对扩散区进行细化计算.在SHASTA程序的自适应计算实现过程中,采用了插入式的自适应修改策略,原二维磁流体力学偏微分方程的求解算法被作为独立单元使用.另外,修改中使用分层的数据结构,将每个细化层次的物理量用二维可变数组描述,并标记磁场和压强分布的陡变区为细化区域,再通过插值的方法得到细化层网格点上的物理量分布和边界条件,最后细化区域的细化计算结果被赋予给其上一层网格,并对其内容进行更新.采用细化计算进行的磁重联的模拟实验表明,相比单一网格计算,细节分辨率得到提高,相应的计算时间的增加则与模拟中的参数选择有关;而自适应程序部分带来的计算精度和稳定性的影响则依赖于边界设置,单步长的推进策略和插值算法.     

幂律电子谱轫致辐射积分的快速计算

SSW(Solar SoftWare)的能量电子产生X光子的轫致辐射积分计算发展到版本2时,其性能相比初始的版本1提高很多.在版本2的基础上,对这个积分进一步改进.通过对比几种轫致辐射积分方案,结果显示,最终的方案性能上比版本2可以快约2～5倍.在积分的精确性上比版本1及版本2均改进了很多,在缺省的积分控制精度下也不再产生光子谱的尖刺现象.而且,积分耗时不再敏感于积分上限取值.由于积分性能的提高,使得利用精确的轫致辐射截面计算轫致积分成为可能.结果显示,用精确轫致辐射截面比先前的近似截面积分的结果光子流量略小(≤4%),积分时间大约比先前使用近似截面多30%.     

耀斑加速电子能谱的不变点及其意义

在厚靶非热韧致辐射模型下,考察产生耀斑硬Ｘ 射线暴的非热电子幂律能谱随时间的变化。结果发现,对有些耀斑,不同时刻的非热电子能谱总是具有一个粗略的共同交点。该交点可能反映了有些电子加速机制的固有性质———饱和及低端阈能。     

利用TALYS计算太阳耀斑伽玛射线

太阳耀斑伽玛射线能谱是加速粒子与太阳大气介质原子碰撞的结果,它是研究太阳耀斑中加速粒子和高能电子最为直接的手段.通过分析伽玛射线能谱,可以获得耀斑过程中加速粒子的成分、能谱、角分布及太阳大气元素丰度等重要信息.TALYS程序是一套模拟核反应的软件,对核反应过程中的所有信息均能完整地描述.利用TALYS计算得到了完整的太阳耀斑伽玛射线的核反应截面数据,开发了一套新的耀斑伽玛射线谱计算程序.详细介绍了耀斑伽玛射线计算的理论模型,并简单探讨了耀斑伽玛射线的特性,为未来的耀斑伽玛射线能谱分析奠定了理论基础.     

1989年8月17日太阳边缘耀斑和速度场研究

本文云南天文台二维光谱仪观测的１９８９年８月１７日耀斑的Ｈβ波 段光谱资料，采用多云模型的方法，得到此耀斑的观测视向速度分布，并在一定的简化和假设下，采用ＭＨＤ理论计算了几种情况下光耀斑环内物质运动的视向速度分布，与观测的视向速度分布加以比较，研究和探讨耀斑环中的物质运动情况。     

1984年2月18日耀斑后环系的H_α轮廓不对称场和总辐射

本文通过对1984年2月18日耀斑后环系的太阳分光照相光谱资料进行Hα谱线轮廓不对称因子和Hα总辐射量的计算,定量地给出了该环珥系的轮廓不对称场和Hα辐射分布,计算结果表明:1.环珥系大部份轮廓不对称因子|P|<0.5,说明整个环珥系的Hα谱线轮廓基本上是对称的或近似对称的。2.整个环珥系Hα谱线轮廓主要表观为紫不对称。3.具有红移视向速度的地方谱线轮廓都是紫不对称。4.采用不对称因子P进行谱线轮廓不对称计算,比传统的二等分法更优。5.该环珥系的总辐射能量级为10~(31)尔格。     

非线性相对运动下空间碎片碰撞概率计算的研究

空间目标碰撞概率的计算是航天器进行空间碎片预警和规避机动的基础.为了简化计算,目前国内外在计算碰撞概率问题过程中大多基于线性相对运动的条件,将三维碰撞概率计算积分问题简化为位置误差概率密度函数在圆域内的二维积分问题.但是当空间目标相对运动速度较小时,这种线性运动条件不再成立,就需要在真实的非线性相对运动状态下重新考虑碰...     

正常恒星的演化模型计算

本文提供了正常恒星演化模型的一种计算方法.它对常用的计算方法作了改进.计算程序用Algol-60语言编成,并在国产TQ-16型扩体的计算机上对质量为2.82M_⊙的恒星进行了演化模型计算.计算结果给出的各种演化特性证明这种方法和计算程序都是正确可用的.     

针对ASO-S/HXI光栅摆放角分布的测试与分析

先进天基太阳天文台(ASO-S)卫星的3大载荷之一硬X射线成像仪(Hard X-ray Imager, HXI)是一套基于傅立叶变换调制成像技术的望远镜.它利用91组不同摆放角和节距的光栅子准直器排列摆布,获得45个基于空间调制的傅立叶变换对,重建太阳耀斑源30–200 keV的硬X射线像,最高分辨率可达3.1′′.在光栅节距已经确定的前提下,它的摆放角分布仍会影响成像质量.通过对HXI仪器傅立叶分量μν分布与点扩散函数(PSF)的空间演化关系分析研究,寻求HXI光栅摆放角的最优分布.其结果将作为改进HXI仪器设计和开发相应科学分析软件的依据.     

1989年8月17日太阳边缘耀斑和速度场研究

本文利用云南天文台二维光谱仪观测的１９８９年８月１７日耀斑的Ｈβ波段光谱资料，采用多云模型的方法，得到此耀斑的观测视向速度分布，并在一定的简化和假设下，采用ＭＨＤ理论计算了几种情况下耀斑环内物质运动的视向速度分布，与观测的视向速度分布加以比较，研究和探讨耀斑环中的物质运动情况。通过分析比较，得出此耀斑环内物质运动可能属于下述两种模式：物质从环顶沿两环腿螺旋下落和物质从环足沿一环腿螺旋上升到环顶后沿另一腿螺旋下落     

Lepidocrocite to maghemite to hematite: A pathway to magnetic and hematitic Martian soil

Abstract— We examined decomposition products of lepidocrocite, which were produced by heating the phase in air at temperatures up to 525 °C for 3 and 300 h, by x-ray diffraction (XRD), transmission electron microscopy (TEM), magnetic methods, and reflectance spectroscopy (visible and near-infrared (IR)). Single-crystal lepidocrocite particles dehydroxylated to polycrystalline particles of disordered maghemite that subsequently transformed to polycrystalline particles of hematite. Essentially pure maghemite was obtained at 265 and 223 °C for the 3 and 300 h heating experiments, respectively. Its saturation magnetization (J_s) and mass specific susceptibility are ～50 Am²/kg and ～400 × 10^?6 m³/kg, respectively. Because hematite is spectrally dominant, spectrally hematitic samples (i.e., a minimum near 860 nm and a maximum near 750 nm) also could be strongly magnetic (J_s up to ～30 Am²/kg) from the masked maghemite component. Analyses by TEM showed that individual particles are polycrystalline with respect to both maghemite and hematite. The spectrally hematitic and magnetic Mh + Hm particles can satisfy the spectral and magnetic constraints for Martian surface materials over a wide range of values of Mh/(Mh + Hm) either as pure oxide powders or (within limits) as components of multiphase particles. These experiments are consistent with lepidocrocite as the precursor of Mh + Hm assemblages on Mars, but other phases (e.g., magnetite) that decompose to Mh and Hm are also possible precursors. Simulations done with a copy of the Mars Pathfinder magnet array showed that spectrally hematitic Mh + Hm powders having J_s equal to 20.6 Am²/kg adhered to all five magnets.     

How to compare the surface of Io to laboratory samples

Since one does not know the photometric functions of various parts of Io, one cannot convert the observed geometric albedo of the satellite to a parameter more directly measurable in the laboratory. One must therefore convert laboratory reflectances to geometric albedos before quantitative comparisons between Io's surface and a laboratory sample are made. This procedure involves determining the wavelength dependence of the sample's photometric function. For substances such as sulfur, whose reflectance varies strongly with wavelength, it is incorrect to assume that the photometric function, and hence the ratio (laboratory reflectance/geometric albedo) is independent of wavelength. To illustrate this point, measurements of the color dependence of this ratio for sulfur are presented for the specific case in which the measured laboratory reflectance is the sample's normal reflectance. In general, unless the laboratory reflectance is precisely the geometric albedo, a wavelength-dependent correction factor must be determined before the laboratory sample can be compared quantitatively with Io's surface.     

Report to cross sections related to plasma-planetary atmosphere interaction processes

As a recent trend, the continuous increase of new technologies for space observations of new missions to Mars, Venus, and Titan, has stimulated vigorous experimental and theoretical studies on the collision process induced by interactions between plasma and planetary atmosphere. In order to facilitate the comprehension of these processes, this brief paper chose a collection of cross section data not always easily accessible. With the purpose of making a useful collection of such data we have collected both experimental and theoretical estimate for most of the expected collisions processes.     

An Introduction to Observations Relevant to Astrophysical Jets and Nebulae

This article reviews the basic physics and jargon associated with astronomical observations of nebulae, with an emphasis on processes relevant to shock waves in astrophysical jets.