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991.
Colter J. Kelly Christopher R.M. McFarlane David A. Schneider Simon E. Jackson 《Geostandards and Geoanalytical Research》2014,38(4):389-407
Laser ablation‐inductively coupled plasma‐mass spectrometry (LA‐ICP‐MS) was examined as a tool for measuring isotopic variation as a function of ablation depth in unpolished zircon from an Archaean metasediment specimen. This technique was able to identify micrometre‐thin (> 3 μm) isotopically distinct mineral domains characterised by ca. 100 Myr younger 207Pb/206Pb ages associated with 2s age uncertainties as low ~ 0.2%, as well as elevated U content relative to grain interiors (up to an order of magnitude). Our calculated drilling rate suggests that each laser pulse excavated depths of ~ 0.06 μm. Ages resolved through the LA‐ICP‐MS methods overlap the 2s uncertainties of 207Pb/206Pb ages measured using SIMS depth profiling on the same zircon population. The rims were further evinced by the detection of relative enrichment (> 3 orders of magnitude) in REE in the outermost micrometres of the same zircon, measured using a different and independent LA‐ICP‐MS depth profiling technique. We propose a LA‐ICP‐MS U–Pb technique capable of quickly identifying and quantifying rims, which are indication of late, yet geologically significant, fluid events that are otherwise undefined. 相似文献
992.
993.
根据“西部煤炭资源高精度三维地震勘探技术”项目中对国内外各种深度域偏移成像方法和特点的调研成果.对各类深度域成像的算法和特点进行了总结,指出不同深度域成像算法选取原则主要依据构造复杂程度和横向速度变化情况。结合克希霍夫叠前三维深度域偏移模块说明深度域偏移原理和工作流程,并以实例说明叠前深度域成像能够解决因第四系地层厚度剧烈变化造成的下覆煤层赋存形态被扭曲、深度误差大、断层平面位置不准确等问题。该实例中,叠前深度域成像划分的煤层深度比时间域偏移剖面解释结果向下移动40多m,钻探结果证实其解释的煤层深度和断层位置比较准确。 相似文献
994.
超固结地层发生地面沉降需要一个大于超固结应力的起始附加应力来驱动。依据有效应力原则,临界水位与超固结应力之间存在线性相关关系,则超固结地层垂向形变机理亦可通过临界水位描述为:当人为开采地下水引起的起始水位降深大于临界水位时,地面沉降将明显发生。西安南郊地质技校钻孔埋深100-300m内土样试验资料分析及计算结果表明:该地层普遍呈现超固结特性;第一、二承压含水组的临界水位值分别为63.44m及73.76m;将“临界水位”作为控制地面沉降与最大限度开采地下水资源的主控指标来考虑,是地面沉降的有效防治措施。 相似文献
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A recently proposed general definition of wave breaking is further discussed, in order to deal with some points on which misunderstanding appears to have arisen. As with surface and internal gravity waves, the classification of Rossby waves into breaking and not breaking is a generic classification based on dynamical considerations, and not a statement about any unique signature or automatically recognizable shape. Nor is it a statement about passive tracers uncorrelated with potential vorticity on isentropic surfaces. A strong motivation for the definition is that proofs of the nonacceleration theorem of wave, mean-flow interaction theory rely, explicitly or implicitly, on a hypothesis that the waves do not break in the sense envisaged.The general definition refers to the qualitative behaviour of a certain set of material contours, namely those, and only those, which would undulate reversibly, with small slopes, under the influence of the waves' restoring mechanism, in those circumstances for which linearized, nondissipative wave theory is a self-consistent approximation to nonlinear reality. The waves' restoring mechanism depends upon the basic-state vertical potential density gradient in the case of gravity waves, and upon the basic-state isentropic gradient of potential vorticity in the case of Rossby waves. In the usual linearized theory of planetary scale Rossby waves on a zonal shear flow, the relevant material contours lie along latitude circles when undisturbed. 相似文献
1000.
K. V. K. Iyengar 《Journal of Astrophysics and Astronomy》1985,6(4):227-231
As dust emission in the far infrared (FIR) is a characteristic property of planetary nebulae we searched the Infrared Astronomical
Satellite (IRAS) point-source catalogue for confirmatory evidence on the two new possible planetary nebulae S 68 and 248 -
5 identified by Fesen, Gull & Heckathorn (1983) and the high-excitation planetary nebula 76 + 36 detected by Sanduleak (1983).
We identify the nebulae 248 - 5 and 76 + 36 with IRAS sources 07404 - 3240 and 17125 + 4919, respectively and have determined
their dust temperature, total FIR emission and optical depth. We also set a lower limit ranging in value from 1.2 × 10-6 to 3.7 × 10-5 forM
dust
/M
bd
of the nebula 248 - 5 depending on whether its grain material is silicate or graphite. S 68 could not be identified with
an IRAS source. 相似文献