Combining ECCI and FIB milling techniques to prepare site-specific TEM samples for crystal defect analysis of deformed minerals at high pressure

Dislocation microstructures in experimentally deformed single-crystal pyrope-rich garnet, (Mg,Fe)₃(Al,Cr)₃Si₃O₁₂, and polycrystalline forsterite, Mg₂SiO₄, were investigated by using electron channeling contrast imaging (ECCI) and transmission electron microscopy (TEM) combined with a focused ion beam (FIB)-microsampling. In the orientation-optimized ECCI method, we successfully observed individual dislocations across subgrain boundaries in a low-atomic-number mineral, pyrope-rich garnet (averaged Z-numbers, AZs ～ 10). Dislocations in a deformed forsterite (iron-free olivine) were also visible in the ECCI. In the ECCI on the single-crystal garnet, deformation bands consisting of dislocations, unusual contrasts in stripes and inhomogeneous distributions of sub-micrometer-sized pores were found. Further site-specific TEM observation on the deformation band revealed a high density of partial dislocations and stacking fault ribbons. The site-specific characterizations from ECCI to TEM, with assistance of FIB, can provide a new approach to investigate dislocation microstructures of deformed materials at high pressure and high temperature.     

Secondary Ion Mass Spectrometry Methodology for Isotopic Ratio Measurement of Micro‐Grains in Thin Sections: True Grain Size Estimation and Deconvolution of Inter‐Grain Size Gradients and Intra‐Grain Radial Gradients

In a thin section, grains that were approximately spherical in situ appear circular in cross section, and the distribution of apparent diameters frequently assumed to be their size distribution. Scanning ion imaging by secondary ion mass spectrometry (SIMS) is capable of providing precise (< 1‰) stable isotope ratio measurements of such grains, but, importantly, also registers their rate of evolution in apparent size as they are ablated by the primary beam. By assessing rates of radius change with depth, the described methodology enables the ‘true’ size of grains to be estimated, as well as the distance of the sectioned surface from the original grain centre. Transects in three dimensions are made possible, and this capability enables better identification (and thus separation) of both inter‐grain chemical signatures as a function of grain size, and intra‐grain radial trends. In this example, we highlight the specific application to pyrite (FeS₂) minerals, which are frequently analysed by SIMS to determine their inter‐grain and intra‐grain geochemical variations, particularly in their sulfur stable isotopic ratios (δ³⁴S). Benefits of the new methodology over the Faraday cup ‘spot mode’ are described. Data correction algorithms and precision considerations are discussed.     

Determination of cave geometry by using a geoelectrical resistivity inverse model

Determination of the geometry and the dimensions of a cave is an important factor considered for planning geotechnical, archeological, speleological studies, and quarrying activities. In recent years, researchers have raised an increasing number of questions related to the shape and size of cavities using 2D geoelectrical resistivity imaging techniques. The inverse model is valuable in detecting the location and extent of subterranean cavities. In this study, a 2D geoelectrical resistivity imaging technique is employed to determine the geometry of a known subterranean cavity. The results provided valuable information and demonstrated the effectiveness of the technique for exploring the size of cavities.     

成像测井系统软件主控模块的设计与分析

成像测井系统中的主控模块主要包括刻度、测井、回放、重测井等子模块．系统的测井主控采用双进程、多线程的设计方案,一个进程是采集管理器,它主要负责和前端机进行通讯．另一个进程就是主控软件,其中多个线程共享同一个内存空间．线程之间的通讯方便．系统采用实时抢占式调度控制方式．可及时处理在测井过程中的紧急事例和数据采集．根据windows NT中的DLL技术和面向对象中的动态联编技术,采用动态添加新仪器的设计思想,设计了测井仪器类及动态添加机制,可以将各种测井仪器的动态链接库动态安装到测井系统中．达到动态添加新仪器的目的,     

Subduction,fluids, and accessory minerals: a celebration of the career of Sorena S. Sorensen

ABSTRACT

This is a preface to the topical issue entitled ‘Subduction, Fluids, and Accessory Minerals: A Celebration of the Career of Sorena S. Sorensen’     

基于光谱吸收特征分析的彩绘文物颜料识别研究

高光谱成像技术作为一种无损高效的检测方法,对于彩绘文物颜料的鉴别具有重要意义。由于全波段参与光谱相似度计算会造成数据的冗余,没有充分利用光谱的细微特征。为此,本文首先对文物颜料光谱吸收特征进行参量化分析,并通过改进的光谱吸收特征拟合算法与标准光谱进行匹配识别,从而得到识别结果。实验以获取的一幅波长为400~1000nm的古代壁画高光谱影像为例,通过光谱吸收特征分析识别出壁画的颜料主要成分有朱砂、赭粉、石绿和石青,4种颜料的光谱吸收特征拟合度分别是:0.95、0.77、0.92、0.81。实验结果表明:对光谱吸收特征分析可以帮助识别彩绘文物的颜料信息,该方法可为以后文物修复提供参考。     

2004年11月磁暴期间环电流的演化过程——TC-2卫星中性原子成像仪观测结果

本文通过对TC-2卫星上搭载的中性原子成像仪(NUADU)在2004年11月发生的一次大磁暴期间观测到的一系列中性原子(ENA)图像的分析,试图给出环电流在磁暴期间的演化模式.研究表明,南向的行星际磁场(IMF)分量在离子从磁尾向内磁层注入和随后的环电流增长过程中起着关键的作用.IMF转为北向后,离子注入随即很快停止.在离子注入增强期间,离子的漂移路径是开放的,以致大量环电流离子从黄昏侧注入后快速地损失在黄昏至正午的磁层顶.所以,环电流往往在离子漂移路径从开放变为封闭后才达到最大强度,而不是在这之前,尽管那时的离子注入强度更大.在该磁暴主相期间,离子注入发生在17∶00~22∶00 LT范围内,形成极其不对称的环电流分布形态.而在恢复相期间,由于受大的IMF B_y分量的影响,离子注入区的地方时分布范围东向扩张.对称环电流在磁尾对流减小、离子漂移路径变为封闭形态之后形成.在磁暴恢复相后期,从ENA图像看环电流基本衰减到平静时期的水平,而Dst指数仍然显示较强的磁扰动,这说明越尾电流对Dst指数有很重要的影响.     

汶川MS8.0大震前的电磁现象

本文应用最大熵谱估计方法(MEM)等处理了2008年四川汶川M_S8.0地震震中周围电磁台的观测数据,研究了地电、地磁场变化,得到:(1) 在汶川大震前,位于青藏高原东北缘的电磁台记录了显著的自然电场变化、地电场功率谱值增大以及地磁场日变化波形畸变等电磁现象,特别是地电场周期约小于3 h的低频成分的谱值增大了3个数量级以上.(2) 在距离主震震中约500 km范围内,记录了地电、地磁场低频谱值增大为主的电磁现象,特别是距离主震震中最近的成都台地电场谱值增大了4个数量级.(3) 震前电磁现象的时空分布与青藏高原的大震活动(包括2008年新疆于田M_S7.3地震)有大空间尺度的构造关联性.本文讨论了电磁现象的机理,认为在震前地下介质内部的微裂隙发展、定向排列过程中,微破裂"机-电转换"作用和地下水运移等多因素引起了地电、地磁场变化.在本次大震前电磁现象的时空强图像很复杂,可能原因是台站所在处的地下局部介质作用和震源孕育激发的电磁辐射引起了复杂的电磁现象.     

Two- and three-dimensional double-sandbar system behaviour under intense wave forcing and a meso–macro tidal range

Five weeks of hourly, 10-min time-exposure video images were used to analyze the meso–macro-tidal double-barred Truc Vert Beach, SW France, under intense wave forcing. The four storms experienced, one of which with an offshore significant wave height over 8 m, induced dramatic changes in the double sandbar system. The subtidal outer bar migrated offshore rapidly (up to 30–50 m/day) and its pre-existing crescentic pattern was wiped out. The seaward-protruding parts of the outer bar barely migrated offshore during the most intense storm, whereas a landward-protruding part was shed off. Over the entire study period, the outer-bar dynamics was dominated by alongshore-averaged changes rather than alongshore non-uniform changes, while the opposite was observed for the inner bar. In addition, the outer-bar dynamics was predominantly controlled by the time-varying offshore wave conditions, whereas the inner-bar dynamics was influenced largely by the tide-range variations. Our observations put forward the key role of morphological settings (the presence of a subtidal bar and its shape) and tidal range in governing inner-bar behaviour within a double sandbar dynamics, and provide strong support for previous suggestions that sandbars cannot be studied in isolation.