An examination of directional discontinuities and magnetic polarity changes around interplanetary sector boundaries usingE > 2 keV electrons     

S. W. Kahler  R. P. Lin 《Solar physics》1995,161(1):183-195

Past studies of interplanetary magnetic sector boundaries have been based on the assumption that one can determine the field polarities by comparing the field directions with those of the nominal Parker spiral angles. Previous investigators have found evidence for decreases of B, the magnitude of the magnetic fieldB, and increases of , the angle betweenB and the ecliptic plane, at sector boundaries. Others have argued that the characteristic thickness of sector boundaries exceeds that of tangential discontinuities, making sector boundaries a separate class of structures.We use a simple technique for inferring the polarities of interplanetary magnetic fields based on the assumption thatE > 2 keV electrons are always flowing along the magnetic field away from the Sun. Electron data from the UC Berkeley experiment on the ISEE-3 spacecraft are used to examine periods around several apparent sector boundaries in 1978 and 1979. We compare properties of (a) boundaries with field polarity changes and (b) large-angle ( > 60°) directional discontinuities with no field polarity changes. We find no significant differences between the sector boundaries and the directional discontinuities in terms of associated decreases in B or of values of . These results suggest no significant difference between sector boundaries and directional discontinuities other than the change in field polarities. Within limited statistics we find that about half the polarity changes would not have been identified using a requirement that > 90° and that half of the > 120° discontinuities would have been misidentified as polarity changes.  相似文献   

Models for the motions of flare loops and ribbons   总被引：1，自引：0，他引：1  

J. Lin  T. G. Forbes  E. R. Priest  T. N. Bungey 《Solar physics》1995,159(2):275-299

We have found a conformal mapping which is valid for any magnetic boundary condition at the photosphere and which can be used to determine the evolution of an open, two-dimensional magnetic field configuration as it relaxes to a closed one. Solutions obtained with this mapping are in quasi-static equilibrium, and they contain a vertical current sheet and have line-tied boundary conditions. As a specific example, we determine the solution for a boundary condition corresponding to a submerged, two-dimensional dipole below the photosphere. We assume that the outer edges of the hottest X-ray loops correspond to field lines mapping from the outer edges of the H ribbon to the lower tip of the current sheet where field lines reconnect at aY-type neutral line which rises with time. The cooler H loops are assumed to lie along the field lines mapping to the inner edges of the flare ribbons. With this correspondence between the plasma structures and the magnetic field we determine the shrinkage that field lines are observed to undergo as they are disconnected from the neutral line. During the early phase of the flare, we predict that shrinkage inferred from the height of the H and X-ray loops is close to 100% of the loop height. However, the shrinkage should rapidly decrease with time to values on the order of 20% by the late phase. We also predict that the shrinkage in very large loops obeys a universal scaling law which is independent of the boundary condition, provided that the field becomes self-similar (i.e., all field lines have the same shape) at large distances. Specifically, for any self-similar field containing aY-type neutral line, the observed shrinkage at large distances should decrease as (X/X _R)^–2/3, where X is the ribbon width andX _Ris the ribbon separation. Finally, we discuss the relation between the electric field at the neutral line and the motions of the flare loops and ribbons.  相似文献   

基于ArcObjects的GIS系统的二次开发--以济源市水土保持决策支持系统为例   总被引：2，自引：0，他引：2  

陈南祥  董贵明  邱林  苏万益  常直福 《地域研究与开发》2006,25(3):125-128,F0003

COM技术是新一代组件式GIS发展的主流，文章阐述了COM，COMGIS的基本原理，介绍了AreOhjects的组成结构、开发的关键技术、开发方式，以及AreGIS Engine的功能，对使用两种组件式GIS进行二次开发进行了比较。最后给出了使用ArcObjects开发的一个实例——济源市水土保持决策支持系统，描述了系统的设计原则。系统的结构设计和系统的功能，并简要说明了系统的主要功能所使用的关键接口。  相似文献   

长白山锦北雨养泥炭剖面元素富集规律分析   总被引：3，自引：2，他引：3  

贾琳  王国平  刘景双 《湿地科学》2006,4(3):187-192

为了揭示长白山锦北泥炭沼泽区泥炭沉积环境和重金属元素的历史变化及其对环境的指示意义,利用荷兰W ardenaar泥炭采样器采取泥炭样品并对样品进行高分辨率切割。用原子吸收分光光度计和等离子体发射光谱仪测定不同深度剖面Ca,Mg,Na,K,A l,Ti,Cu,Zn,Fe,Mn,Pb,Cr,N i和Co的浓度。研究分析了Ca,Mg,Na,K,A l,Ti,Mn,Zn,Cu,Pb,Cr,N i和Co在泥炭剖面的分布趋势并对其进行了相关分析和富集分析,得出Mn,Zn,Cu,Pb,Cr,N i和Co呈显著相关且在泥炭表层明显累积,揭示出泥炭表层重金属元素的大气沉降来源,表明近年来人类重金属消耗量及排放量的增加是大气沉降重金属元素的主要释放源,而且环境中重金属污染有加重的趋势。  相似文献   

南极菌Pseudoalteromonas sp．S-15-13产胞外多糖的研究及其分子鉴定   总被引：2，自引：1，他引：2       下载免费PDF全文

李江  陈靠山  林学政  李光友 《极地研究》2006,17(2):130-135

本文对影响南极细菌S-15-13生长和胞外多糖产量的主要环境因子进行了研究,同时采用16S rDNA序列分析及系统发育分析方法对其进行了分子鉴定。结果表明：菌株S-15-13最佳产糖条件为：培养时间,56h；培养温度,8℃；碳源,1．0%葡萄糖；NaCl浓度,3．0%；pH,6．0-7．0。16S rDNA序列分析和系统发育分析表明,菌株S-15-13属于假交替单胞菌属(Pseudoaltero- monas)。  相似文献   

Spontaneous Structural Reform in Australian Local Government: the case of the Gilgandra Co-operative Model in New South Wales     

Brian Dollery  Warrick Moppett  Lin Crase 《The Australian geographer》2006,37(3):395-409

Dire financial constraints and the threats of forced structural reform have had the unforeseen effect of forcing municipal councils across Australia to reconsider their operational activities and organisational arrangements. With considerable ingenuity, numerous municipalities have proposed and sometimes adopted new structural formations that embody various forms of co-operative service provision. This remarkable development has unfortunately been largely ignored in the scholarly literature on Australian local government. In a modest effort aimed at remedying this neglect, the present paper seeks to outline the small, rural New South Wales Gilgandra Shire Council's (2004) ‘Co-operative/Local Government Service Company’ model, place it in the broader context of alternative models of local governance suitable for Australian conditions, and evaluate its characteristics.  相似文献   

Fission track evidence for the Mesozoic Cenozoic tectonic uplift of Mt. Bogda, Xinjiang, Northwest China     

沈传波  梅廉夫彭蕾 张士万刘麟  汤济广 《中国地球化学学报》2006,25(2):143-151

1 IntroductionThe Mesozoic-Cenozoic tectonic evolution and ki-netics mechanism of the intracontinental orogen are thekey subjects of continental dynamics (Ma Zongjin andGao Xianglin, 2004) and the key to understanding theregional geological tectonics (Qia…  相似文献   

东南沿海地震活动特征量     

周峥嵘  林树  鲍挺 《福建地震》2006,(Z2)

1970年以来,东南沿海地区经历了上世纪末以来明显的第Ⅴ活跃幕(或轮回)平静和活跃时段,本文通过分析研究这两个时段地震活动在时空强上的差异性,定量提取其活动演化过程参量,为该区未来地震活动期判定提供相对定量的参考依据。  相似文献   

电子地图中多尺度地图数据显示的研究   总被引：10，自引：2，他引：10  

吕华新  李霖  翟亮 《测绘信息与工程》2005,30(6):22-24

将计算机三维模型简化中的LOD思想引入到电子地图的组织和显示中,提出了同一比例尺数字地图不同详细程度的分层显示方法和不同比例尺数字地图嵌套显示方法,实现了电子地图的多级缩放。  相似文献   

镉的地球化学研究现状及展望   总被引：13，自引：0，他引：13  

叶霖潘自平  李朝阳刘铁庚 夏斌 《岩石矿物学杂志》2005,24(4):339-348

镉是重金属有毒元素,其环境污染一直是众多学者研究的焦点。近年来研究发现,镉等分散元素并不“分散”,它在特定的条件下会富集,甚至形成独立矿床或矿体,因此有必要对镉等分散元素的地球化学行为进行重新认识和再研究。本文介绍了有关镉的分布和赋存状态的一些研究进展,总结了我国镉矿资源的分布及特点和地球化学研究现状,提出应加强镉的超常富集机制、铅锌矿床表生地球化学过程中镉的释放及其对环境的影响方面的研究。  相似文献