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471.
Accuracy of Laser Ablation U-Pb Zircon Dating: Results from a Test Using Five Different Reference Zircons 总被引:2,自引:0,他引:2
Urs Klötzli Eva Klötzli Zekeriya Günes Jan Kosler 《Geostandards and Geoanalytical Research》2009,33(1):5-15
Using a state‐of‐the‐art 193 nm‐LA‐MC‐ICP‐MS system and with careful control of analytical procedures, the long term external reproducibility and accuracy of the ages Phanerozoic zircons measured over a period of months using calibrator bracketing for the 206Pb/238U and 207Pb/206Pb ages were ca. 1% (2 RSD) if a single reference zircon was used for the matrix‐matched calibration. When different reference zircons were used for the calibration, suspicious systematic shifts in the obtained ages were observed and thus a reduction in the overall accuracy of the dating method became obvious. Such shifts were within a few percent range of the U‐Pb and Pb/Pb ages and seemed to vary independently of zircon age and composition. A “test of accuracy” experiment was conducted reducing instrumental effects as far as possible by analysing five different reference zircons mounted on a single mount eight times during the same session. An identical protocol was used for all analyses, with unchanged instrument parameters and with ion beam intensities kept as identical as possible. For data reduction, every zircon served consecutively as the reference zircon for calibration, with the others in the batch treated as unknowns. The known reference age and the four calculated ages obtained using the four other RMs for calibration were then compared. Even using such a strict analytical protocol, shifts in 206Pb/238U, 207Pb/235U and 207Pb/206Pb ratios were still present. They varied non‐systematically and ranged from ?4.35% to 3.08% for the investigated age range (1065 Ma to 226 Ma). Assuming the absence of instrumental effects (i.e., memory, dead‐time correction, non‐linearity of ion counters and interdetector calibration, crystallographic orientation, ablation cell geometry and setup, gas flows), the observed shifts were attributed to matrix and/or ablation related effects. It is proposed that non‐spectral matrix effects in the Ar plasma torch resulted in non‐uniform signal enhancement (or depression?) leading to shifts both in elemental and Pb isotopic ratios. Additionally, the ablated particle size distribution could be an important factor controlling plasma conditions and thus mass bias and fractionation. Until such effects are well understood and controlled, it would seem that any LA‐ICP‐MS zircon U‐Pb and 207Pb/206Pb age determination cannot be meaningfully interpreted at below a ca. 3% to 4% (2 RSD) confidence level. 相似文献
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473.
Landfill is the most commonly used method for disposal of waste materials since it is one of the least expensive methods. In order to dispose of any hazardous material to a landfill, a liner is used, which protects the underlying land and groundwater since it acts as a barrier to fluid movement. Of the various methods available for providing improved and more effective properties of landfills, methods involving the use of bentonite, cement, lime, gypsum, etc., have been explored in the laboratory. The aim is to overcome the problem and deficiencies of the existing liners. It is observed from the experimental results that the metal concentrations of the input waste solution can be reduced to 80–98% using a soil‐cement admixture, 60–95% using a soil‐gypsum mixture, 45–95% using a soil‐bentonite mixture, 50–90% for soil, 35–80% using a soil‐lime mixture, as liner materials. The permeation rate of different metals through the different soil‐admixture media depends on various factors. A simple mathematical treatment of the phenomenon related to the permeation of liquid through the admixture of the clay and other components has been developed. The experimental results show satisfactory agreement with the predictions. 相似文献
474.
475.
砂岩类脆性无序介质连续破坏过程的细观模拟 总被引:1,自引:0,他引:1
为了分析砂岩类无序介质在各种荷载作用下的连续破坏过程,本文提出了梁-颗粒细观模型。在此模型中,介质被离散为一系列的颗粒单元,这些颗粒单元均由弹脆性的梁单元联结。颗粒的力学行为由离散单元法和有限单元法确定。当某个梁单元所受应力超过其强度时,就随即将它从计算网络中剔除,以模拟介质的破坏行为。为了验证数值模型的可靠性,分别从破坏模式和荷载-位移曲线两方面与物理模型实验进行了对比,结果表明两者基本一致。此外,探讨了无序性对介质裂纹分布形式的影响,并用分维表述了裂纹分布与荷载强度之间的内在联系。 相似文献
476.
Predicting the long-term safety and performance of a repository for intermediate- to high-level radioactive wastes requires the evaluation of various scenarios which may influence the integrity of the repository system. One such scenario, radionuclide transport, is described, and some of the geochemical processes which serve to enhance or retard transport are illustrated with examples selected from natural analogue or natural system studies. These studies, as distinct from laboratory simulations, help considerably in understanding how near- and far-field radionuclide transport mechanisms work over geological timescales (thousands to hundreds of thousands of years), more in line with the anticipated lifespan of a repository.
Processes addressed include: stability of the spent fuel UO2 matrix; bentonite backfill as a barrier to radionuclide diffusion; retention of radionuclides by absorption on fracture minerals; transport and diffusion of radionuclides controlled by interconnected bedrock porosity; geochemical influence and behaviour of repository construction materials on radionuclide transport. 相似文献
477.
东胜煤系砂岩型高岭土的富集机理 总被引:6,自引:0,他引:6
通过对东胜含煤地层成煤期沉积环境、古介质等的分析,并用有机吸附实验对高岭石与有机质的吸附关系进行了实验,探讨了东胜砂岩型高岭土的富集机理。结果表明,高岭石在河流环境中的富集成矿与水介质中大量有机质的存在有关,植物分解产生的腐殖质具有很强的吸附性,在pH值>5.5和适量的多价阳离子存在的条件下,介质水中的腐殖质可通过多价阳离子与高岭石和石英相互牢固吸附,形成高岭石-有机质-石英复合体,从而使高岭石能够与石英一起搬运、沉积;某些具有一定疏水性的有机质与矿物的吸附,改变了矿物颗粒表面的亲水性,促进了高岭石的沉积富集。 相似文献
479.
480.
Sarah E. Mouring 《Ocean Engineering》1999,26(8):793
The U.S. shipbuilding industry recently has started incorporating composite materials in the construction of both military and commercial ships due to the advantages of composite construction. These advantages include the reduction in total life costs, corrosion resistance, high strength- and stiffness-to-weight ratios, and improved stealth for military applications. One disadvantage is the higher costs of composites compared to steel and other conventional materials. Therefore, new higher quality materials with lower costs and new fabrication methods need to be developed before composite materials will be fully accepted for the construction of large ships. A new composite preform framing technology shows promise in the reduction of fabrication costs for large ship construction. There already has been significant cost savings using this framing technology in the construction of small recreational boats and large yachts. This framing technology involves casting a dry glass fiber-reinforced plastic (GRP) fabric into shape in a closed mold with a foam core. One unresolved issue using this framing technology is the orientation of the fiber for the frames. This paper summarizes experimental results of the testing of composite panels stiffened with preform frames under in-plane uniaxial compressive loads. Biaxial (0,90), quadaxial (0,90,+45,−45), and triaxial (+45,−45,0) laminates were used in the frames. 相似文献