Multi-technique investigation reveals new mineral, chemical, and textural heterogeneity in the Tagish Lake C2 chondrite

The Tagish Lake meteorite, an ungrouped C2 chondrite that is related to CI and CM chondrites, is a heterogeneous accretionary breccia with several distinct lithologies that, in bulk, are thought to represent the first known sample of a primitive carbonaceous D-type asteroid. Textural and chemical zoning of clasts and matrix have been little studied and promise additional insight into early solar system processes in both the solar nebula and on the Tagish Lake parent asteroid. We have examined an intact 2.9 g fragment and two polished thin sections from the spring 2000 (non-pristine) Tagish Lake collection to ascertain the major mineralogy and textures of notable features such as chondrules, amoeboid olivine aggregates (AOAs), inclusions, clasts, matrix, and fusion crust. We designed three stages of analysis for this friable meteorite: an initial, non-destructive in situ reconnaissance by μXRD to document meteorite mineralogy and textures and to identify features of interest, followed by spatially correlated μXRD, SEM-EDX and colour SEM-CL analysis of polished thin sections to fully understand mineralogy and the record of texture development, and finally higher resolution SEM-BSE mapping to document smaller scale relationships.Our analyses reveal several previously unreported or poorly characterized features: (1) distinctive colour cathodoluminescence (CL) zoning in relict CAI spinel, in chondrule and AOA forsterite, and in calcite nodules occurring throughout the Tagish Lake matrix. Forsterite frequently shows CL colour and intensity zonation that does not correspond with major or minor element differences resolvable with EPMA, indicating a trace element and/or structural CL-activation mechanism for the zonation that is likely of secondary origin; (2) an irregular inclusion dominated by magnesioaluminate spinel, dolomite, and phyllosilicates with traces of a Ca, Ti oxide phase (likely perovskite) interpreted to be a relict CAI; (3) variable preservation of mesostasis glass in porphyritic olivine chondrules. We anticipate that our multi-technique methodology, particularly non-destructive μXRD, can be successfully applied to other rare and friable materials such as the pristine Tagish Lake fragments.     

基于ArcEngine的CAD图中GIS栅格影像数据的自动处理

CAD与GIS的交叉应用越来越多,国内有很多人对CAD与GIS的数据集成和功能集成做过研究,但主要集中在矢量数据的交叉使用方面,对于栅格数据的交叉使用研究较少。以管道完整性工程图为例,针对传统生成管道完整性工程图需要手工处理栅格影像、速度慢的问题,通过程序快速实现在生成管道施工图时自动切割GIS影像并插入CAD图中,提出了在CAD图中快速使用GIS栅格影像数据的方法。     

CAD环境下地形图变化检测技术

本文在分析城市大比例尺地形图变化检测技术的基础上,基于地理要素的抽象特征,从多个角度研究地理要素变化特征、地理要素表达规则、CAD实体结构,并进行地理要素变化逻辑分析。基于变化检测的"相同"原则,研究并实现了基于CAD平台自动获取变化信息文件的检测方法,为增量更新GIS数据库提供更新依据。     

基于GIS的天津市滨海新区地下管线管理系统设计与实现

以天津市滨海新区为例,给出了城市地下管线管理系统的设计框架,分析了管线系统与一般GIS的差别,实现了管线信息的动态更新与维护、空间及属性分析与统计、各种数据输出等功能.     

CAD真三维实体模型在地下洞室边墙稳定性评价中的应用

CAD技术日益成熟,已成为工程应用技术的业界标准。CAD技术在地质工程领域的应用多基于二次开发,通过程序计算剖面线及剖面上的各种界线,再以线、面作为基本图元成图,这样计算相对复杂,特别是作三维分析不但数据量大、计算复杂,而且三维图形展示的效果通常不佳,本文结合大型水电工程应用实践,针对以往地下厂房边墙稳定性分析中长大结构面所控制块体组合的搜索、三维图形的分析、展示中的一些不足,探讨以实体来描述地质体的一种应用方法,通过数学建模,建立研究目标的CAD真三维实体模型,不但能得到良好的三维图形展示效果,而且能直接由图获取三维数据,为地下洞室边墙的稳定性分析提供了一种有力的辅助手段。     

设计企业怎样走进协同设计

本文分析了一般勘察设计企业在实际工作中面临的问题,介绍了中国电子工程设计院在协同设计方面的探索,并给出了设计企业采用协同设计需要着重处理的几个关键点。最后还介绍了最新的希达协同设计管理平台的功能和特点。     

土石方计算软件在CAD下的设计与开发

根据实际工作需要,开发并完善了一套土石方计算软件,提出了设计思想和利用数字地面模型进行土石方计算的方法,并用实例验证。     

AutoCAD与VCT数据格式转换实现

通过分析AutoCAD与VCT 2种数据格式的数据组织特点,研究了两者几何图形的对应关系,以点状要素为例,找到了一条实现AutoCAD到VCT数据格式转换的技术路线．经实践证明该路线是可行的,可以满足我国标准数据格式要求。     

Modelling and analysing 3D buildings with a primal/dual data structure

While CityGML permits us to represent 3D city models, its use for applications where spatial analysis and/or real-time modifications are required is limited since at this moment the possibility to store topological relationships between the elements is rather limited and often not exploited. We present in this paper a new topological data structure, the dual half-edge (DHE), which permits us to represent the topology of 3D buildings (including their interiors) and of the surrounding terrain. It is based on the idea of simultaneously storing a graph in 3D space and its dual graph, and to link the two. We propose Euler-type operators for incrementally constructing 3D models (for adding individual edges, faces and volumes to the model while updating the dual structure simultaneously), and we also propose navigation operators to move from a given point to all the connected planes or polyhedra for example. The DHE also permits us to store attributes to any element. We have implemented the DHE and have tested it with different CityGML models. Our technique allows us to handle important query types, for example finding the nearest exterior exit to a given room, as in disaster management planning. As the structure is locally modifiable the model may be adapted whenever a particular pathway is no longer available. The proposed DHE structure adds significant analytic value to the increasingly popular CityGML model.     

航道水下数字高程模型的构建方法

以东莞市某航道水下数字地形构建为例,应用GPS—RTK技术并配合测深仪,荻取水下地形测量原始数据。通过VC＋ObjectARXCAD二次开发,在构建格网DEM精度和运行效率方面,利用几种内插方法实现了数字航道水下地形模型的构建,得出在水下地形起伏不大的情况下．TIN线性内插在构建航道格网DEM中是一种高效率、高精度的方法。