多肽类生物活性物质的非核糖体合成机理

遗传信息通过信使核糖核酸、转运核糖核酸和核糖体转变成蛋白质的过程是分子生物学的基石。但是 ,许多多肽类生物活性物质是通过非核糖体途径合成的 ,只有非核糖体多肽合成酶系参与。非核糖体多肽合成酶系是一类多功能蛋白质复合体 ,能识别、激活、转运氨基酸底物并按特定顺序合成多肽。非核糖体多肽合成酶系同时具有酶和模板功能 ,因此被称为蛋白质模板。由于底物大部分是稀有氨基酸 ,经由该途径合成的多肽类生物活性物质种类繁多。了解多肽非核糖体合成机理有助于寻找多肽类生物活性物质 ,有利于通过人工操作非核糖体合成酶系生产多肽类药物。近年来的研究已经使人们初步了解了多肽非核糖体合成的机理。本文将介绍非核糖体合成酶系组成、结构和多肽非核糖体合成过程     

Does a representative volume element exist for fatigue life prediction? The case of aggregate composites

In a previous work, discrete modeling and a statistical approach were used to quantify the minimal representative volume element (RVE) size for aggregate composites, such as bituminous materials in the linear elastic regime (Comput. Mater. Sci. 2005; 33 :467–490). In this paper, the discrete model is extended to strain‐softening behavior under cyclic loading. The existence of a RVE for fatigue life prediction is numerically proved and its minimal size is determined. It is found that it is much larger than the minimal RVE size in the elastic regime. Copyright © 2007 John Wiley & Sons, Ltd.     

湘西董家河铅锌矿地质特征及成矿物质来源探讨

湘西董家河铅锌矿区赋存于陡山沱组下部(Zd)微晶白云岩中,顶板为黑色炭质板岩,底板为南沱组冰碛层,矿体产状、矿石矿物组合、矿石组构反映成矿受沉积成岩和后期构造热液活动的双重控制,成矿温度低(130°~170℃),属典型的低温沉积改造型矿床。矿床经历了沉积成岩和后期热液改造阶段,硫、铅、碳氧同位素组成表明成矿物质主要来源于下伏地层和围岩,部分物质来源于深部基底变质岩。     

西藏扎布耶盐湖超大型B、Li矿床成矿物质来源研究

扎布耶盐湖位于西藏高原腹地,是一个现代盐湖矿床。对扎布耶地区地球化学背景的研究表明:变质岩及蚀变岩石中硼锂含量很高以及电气石脉的出现,暗示着扎布耶地区深部曾产生含硼锂高的热流体;沉积岩中除晚石炭世砂岩含硼锂稍高外,其他岩石均低于同类岩石的平均含量;火山岩中除早白垩世基性岩的硼锂含量高于基性岩平均含量外,其他均很低;该区大量发育的第四纪钙华含硼锂非常高,表明早期的热水系统曾提供过大量的成矿物质;河流及泉水中的硼锂含量是世界河水平均含量的数倍至数百倍,表明地表和近地表条件下的水-岩相互作用的产物也是成矿物质来源之一。     

含水率和添加剂对膨润土导热性能影响的研究

膨润土的热学性能是评价膨润土作为高放废物深地质处置库缓冲/回填材料的重要参数。高庙子膨润土矿床初步确定为我国缓冲/回填材料的供应基地,本研究以石英砂作为添加剂,通过实验获得了高庙子膨润土在不同含水率和不同砂含量时所对应的导热系数。结果表明,在相同压实条件下,导热系数随着含水率、石英砂含量的增加而增加。     

缺陷化学在新材料研究中的作用

简述了缺陷的类型及其在新材料制备中的作用,通过实例分析固溶体和非化学计量化合物缺陷对材料物理化学性能的影响,阐明缺陷化学是一种研究新型功能材料的有力手段,根据新材料的发展趋势分析了缺陷化学可能取得的重大突破及新的研究热点。     

Three Secondary Reference Materials for Lithium Isotope Measurements: Li7-N, Li6-N and LiCl-N Solutions

The CRPG (Nancy, France) has prepared secondary reference materials for Li isotope measurements by mixing ⁷Li or ⁶Li spikes and either L-SVEC or IRMM-016 certified reference materials to produce solutions having a known Li concentration and isotopic composition. The Li7-N and Li6-N solution samples (1.5 mol l⁻¹ HNO₃) have nominal δ⁷Li isotopic compositions of 30.1‰ and -9.7‰ respectively relative to L-SVEC and concentrations of 100 mg l⁻¹. Repeated measurement of these samples using the QUAD-ICP-MS at the CRPG yielded δ⁷Li of 30.4 ± 1.1‰ (n = 13) and -8.9 ± 0.9‰ (n = 9) at the 2s level of confidence. An additional LiCl-N solution was measured and yielded a delta value of 9.5 ± 0.6‰ (n = 3). Identical results were obtained at the BRGM (Orléans, France) from determinations performed with a Neptune MC-ICP-MS (30.2 ± 0.3‰, n = 89 for the Li7-N, -8.0 ± 0.3‰, n = 38 for the Li6-N and 10.1 ± 0.2‰, n = 46 for LiCl-N at the 2s level of confidence). The deviation of measured composition relative to the nominal value for the Li6-N solution might be explained by either contamination during preparation or an error during sample weighing. These secondary reference materials, previously passed through ion exchange resin or directly analysed, may be used for checking the accuracy of Li isotopic measurements over a range of almost 40‰ and will be available to the scientific community upon request to J. Carignan or N. Vigier, CRPG.     

Determination of Trace Elements (Ag, B, Ge, Mo, Sn, W, Tl) in Reference Samples of Soils and Bottom Sediments by Atomic Emission Spectrometry: A Traceability and Fitness-for-Purpose Study

Reference samples of soils from the Institute of Applied Physics, Irkutsk (RIAP), the Institute of Geochemistry, Irkutsk (IGI) and the United States Geological Survey, Reston (USGS) were analysed with the aim of determining Ag, B, Ge, Mo, Sn, Tl and W abundances by an atomic emission method with air-stabilised D.C. arc excitation. Two series of reference samples of soils and bottom sediments, GSS-1-8 and GSD-1-12 (IGGE), were used to ensure the traceability link for the analytical results. Traceability was also demonstrated through the comparison of measured results by AES and ICP-MS methods. It is shown that the reference samples GSS-1-8 and GSD-1-12 satisfied the "fitness-for-purpose" criterion (uncertainty U of the certified value should be one-third to one-tenth the magnitude of routine laboratory data uncertainty S (S/U > 3-10)) and can be applied for calibrating AES techniques.     

Isotopic and Elemental Imaging of Geological Materials by Laser Ablation Inductively Coupled Plasma-Mass Spectrometry

Laser ablation ICP-MS represents a promising new development for the acquisition of elemental and isotopic images from a variety of different materials. Compared to existing methods for imaging, it offers relatively rapid throughput, very wide dynamic range, a relatively clean mass spectrum, utility at a variety of scales (from μm to cm) and multi-element/isotopic capability. Although developing rapidly in the biological sciences, the method has not yet seen widespread application to geological materials. This contribution documents some preliminary experiments aimed at understanding the fundamental aspects of elemental and isotopic image acquisition using laser ablation ICP-MS. In particular, we note that ablation cell designs must be optimised to promote rapid system response, in contrast to the signal-smoothing that is often preferred for simple spot analyses. Furthermore, experimental parameters must be carefully evaluated on a system-by-system basis to avoid the blurring effects of re-sampling phenomena. With careful attention to these details, and development of appropriate data processing software, laser ablation ICP-MS imaging has much to offer workers in the Earth and environmental sciences.     

ISO Best Practices in Reference Material Certification and Use in Geoanalysis

The International Organisation for Standardisation (ISO) has published many guides, or technical standards, of great value to analytical geochemists. Two of particular importance are Guide 33 (Uses of Certified Reference Materials) and Guide 35 (Certification of Reference Materials). Both were first developed in the 1980s and undergo regular review and updating by the Reference Materials Committee (REMCO) that operates within ISO. Recent revisions have focused on adding statistical rigour to both guides. Although this offers significant advantages for use by professional metrologists, there are consequent issues of comprehension by the analytical chemists who in fact have the greatest need of them. A major focus of Guide 35 is the development of reference material uncertainties that are in full compliance with the Guide on Measurement Uncertainty (GUM), jointly issued by ISO, IUPAC and others. Guide 35 details handling of uncertainty due to (1) degradation on the shelf and in transport, (2) sample heterogeneity and (3) inter‐method and inter‐laboratory bias, as well as within‐laboratory repeatability. The International Association of Geoanalysts has developed a protocol for reference material certification that applies Guide 35 to the specific needs of the geoanalytical community. The approach being taken by the IAG in developing GUM‐compliant uncertainties for its certified values is presented. Recommendations made in Guide 33 for how a laboratory should compare its own results with certified values in assessing laboratory accuracy are outlined. Additionally, the subject of misusing reference materials is discussed. The apparent misuse occurs because so few CRMs exist that meet critical measurement needs of geoanalytical laboratories and that also meet the rigorous metrological demands of the latest editions of the ISO Guides. All of the focus of the IAG certification programme has been to undertake certifications that would fill gaps in CRM availability and thus serve to limit this misuse.