Molar tooth structures of the Neoarchean Monteville Formation, Transvaal Supergroup, South Africa. I: Constraints on microcrystalline CaCO3 precipitation

Molar tooth (MT) structures are enigmatic, contorted millimetre‐ to decimetre‐long veins and spheroids of microcrystalline calcite that formed during very early diagenesis in Precambrian sediments. MT structures in the ca 2·6 Ga Monteville Formation are 600–800 Myr older than previously reported occurrences and establish that conditions necessary for MT genesis were met locally throughout much of the Precambrian. In the Monteville Formation, MT structures were formed shallow subtidally, extending to depths near storm wave base, in shale host sediments intercalated with storm‐generated carbonate sand lenses. They are filled with microcrystalline calcite and rare pyrite. Microcrystalline calcite identical to that in MT structures fills other pore space, including porosity between grains in carbonate sand lenses, moldic porosity in sand grains, sheet cracks in columnar stromatolites, and shallow cracks on sandy bedding planes. Relationships in the Monteville Formation demonstrate that microcrystalline CaCO₃ precipitated in fluid‐filled cracks and pores; microcrystalline calcite characteristics, as well as the paucity of carbonate mud in host rocks, are inconsistent with injection of lime mud as the origin of MT structures. Locally, MT cracks were filled by detrital sediment before or during precipitation. Precipitation occurred in stages, and MT CaCO₃ evolved from granular cores to a rigid mass of cores with overgrowths – allowing both plastic and brittle deformation of MT structures, as well as reworking of eroded MT structures as rigid clasts and lime mud. Crystal size distributions and morphology suggest that cores precipitated through nucleation, Ostwald ripening and size‐dependent crystal growth, whereas overgrowths formed during size‐independent crystal growth.     

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通过工程实例，介绍了单管法高压旋喷桩施工工艺、技术参数、施工中存在的问题以及注意事项。阐述了一些常见故障及预防措施。     

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基于对国内地质工程机械的研发现状的考虑，根据虚拟样机技术的特点，讨论了在地质工程机械领域实施虚拟样机技术的必要件，并提出了建立地质工程机械虚拟样机的策略。联合PRO／E、ANSYS及ADAMS建立了气动潜孔锤的虚拟样机模型，对气动潜孔锤虚拟样机进行了仿真，阐明了虚拟样机技术在地质工程机械领域的应用前景。     

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介绍了一种新型齿形的复合片钻头，在硬致密泥岩中钻进，与常规复合片钻头相比，具有很高的钻进效率和高的钻头寿命，解决了泥岩钻进效率低的难题。     

Organizational Dynamics of the U.S. Logistics Industry: An Economic Geography Perspective*

Although the logistics industry provides critical services to all sectors of the economy, few studies exist in economic geography that examine and explain the organizational dynamics of this industry. This article highlights the significance of the logistics industry in contemporary industrialization and argues that an enriched understanding of the interaction between technology and space can be achieved by examining the evolution of an industry that plays a central role in the contemporary economy. We focus on dimensions that are identified as particularly important: organizational, geographic, and risk and security.     

遥感技术在煤炭地质中的应用现状及前景

介绍了遥感技术在煤炭资源调查和评价、煤矿区地质灾害调查和评估、生态环境及污染调查评价和监测以及煤矿三维可视化仿真规划系统建设方面的应用研究现状及所取得的主要成果，并结合遥感技术的发展方向，展望了其在煤炭地质中的应用前景。     

GPS高程拟合的方式及可靠性分析

在范围不大的区域中，高程异常具有一定的几何相关性，GPS高程拟合就是利用这一原理，求解正常高。在解析法求解过程中，首先用最小二乘法确定拟合数学模型的系数，在此基础上计算出待测点的高程异常值。通过实例验证：GPS高程拟合的精度主要取决于GPS大地高的精度、重合点正常高的精度、重合点的分布及拟模型的选择。一般在重合点数量充足且分布均匀的情况下，GPS高程拟合的精度可达到四等水准网的精度要求。     

基于GIS的供电台区经营综合评价

探讨了运用GIS技术对供电台区经营综合评价的实现方法,选取了业务属性和空间属性两个方面评价因子,介绍了从系统软硬件、评价实现过程及显示结果等方面评价过程的具体技术实现。     

VLBI资料处理软件系统OCCAM V6.0简介

OCCAM V6．0是在PC机上开发的一套VLBI大地测量数据处理软件。该软件用标准FORTRAN77(90)语言编写，可在Windows95以上版本和LINUX环境下的PC机上运行，其主要特点是操作简便、兼容性好、处理容量大、速度快和结果输出多样化等。随着该软件的不断改进和发展，利用OCCAM进行VLBI数据分析的学者逐渐增多，OCCAM软件的使用也日益广泛。本文简要介绍了OCCAM软件的安装、各个模块的主要功能和在运行中的注意事项，供今后OCCAM用户在使用过程中参考。     

圆形标志中心子像素定位方法的研究与实现

采用回光反射材料制作圆形回光反射标志，经摄影后得到标志的“准二值影像”；对标志的椭圆影像进行亚像素边缘提取，经最小二乘椭圆拟合后得到标志中心的子像素级位置。试验表明，可以达到0．02像素的定位精度。