Diffusion Coefficients of Noble Gases in Natural Minerals: An Apparent Experimental Time Dependence Caused by Domain Size Spectra     

C. Fulda  H. J. Lippolt 《Mathematical Geology》2000,32(1):31-47

Noble gas diffusion coefficients in natural minerals are of use for evaluating geochronometric dates and other geochemical data. Usually, they are determined by degassing at elevated temperatures grain powders of natural samples containing radiogenic or cosmogenic noble gases. For conventional evaluations of diffusion parameters from degassing experiments, the grains should be uniform with respect to structure, composition, shape, and size. The shape and size prerequisites can hardly be fulfilled, because even two very narrowly meshed sieves produce spectra of domain sizes, partly because of the inhomogeneity of the minerals. Accurate determination of the actual spectrum is difficult and hardly practicable. Calculations of the fractional gas loss of a sample with a spectrum of domain sizes, presented in this study, show that almost any domain size spectrum leads to apparent diffusion coefficients that depend on the extent of degassing. The exception of this rule is given. The deviation from the physical diffusion coefficient can be several orders of magnitude as shown by examples. This effect, resulting from shape and width of the domain size spectra, possibly is responsible both for the large spread of Arrhenius parameters for the same mineral in the literature and for the deviation from linearity of some published Arrhenius lines. For limited domain size spectra and short degassing times, the formula for fractional gas loss is very similar to the formula of the fractional gas loss of a single domain size. An effective domain radius, which ensures that at least the measured diffusion coefficient for very short degassing times equals the physical diffusion coefficient, is given. In addition, the dimensionless treatment of the problem is presented that leads to a method to determine Arrhenius parameters without knowing the domain size spectrum. Accurate diffusion measurements of samples with a spectrum of domain sizes may also be possible if the domain size spectrum is taken into consideration. To this end the domain size spectra should be approximated by Taylor-expandable functions or by series of discrete domain sizes. For both cases, the formulae are given.  相似文献   

MS-215型大直径绳索取心器及其在煤层气井中的应用     

唐胜利  刘凤琴 《煤田地质与勘探》2002,30(5):61-63

根据煤层气井快速、安全的取心要求,结合现场条件,研制了MS-215大直径绳索取心器。文中介绍了取心器的设计思路、结构特点及现场应用效果。结果表明,该取心器设计合理,机构动作可靠,岩煤心直径大、采取率高、提出速度快,尤其适合煤层气井煤心的采取。   相似文献   

近300a来古里雅与长江下游温度变化所受太阳活动、火山活动的影响分析   总被引：4，自引：1，他引：3  

杨保  施雅风  周清波 《冰川冻土》2002,24(1):40-45

分析了近300a来古里雅冰芯δ¹⁸O值和长江下游温度变化与太阳活动、火山活动的关系.结果表明,无论在年际尺度,还是在10a尺度上,西昆仑山的古里雅冰芯和中国东部的长江下游地区的温度与以太阳辐照和太阳黑子周期长度为代用指标的太阳活动有良好的相关关系.火山活动对古里雅、合肥冬温和杭州春温有明显的降温作用.1810’s—1830’s时段不仅合肥冬温和杭州春温发生了剧烈的变化,而且处于高亚洲中西部的古里雅冰芯δ¹⁸O值也急剧下降,同时在北半球温度重建曲线上这一时段也是一个冷谷,表明该时段的气候变化可能具有全球性,而强烈的火山活动和微弱的太阳活动可能对温度的快速降低起触发作用。  相似文献   

三维地层模型中地层划分的探讨   总被引：51，自引：15，他引：36  

贺怀建  白世伟  赵新华  陈健 《岩土力学》2002,23(5):637-639

地层作为三维地层模型的一个重要概念,在三维地层模型的建立中起着关键作用。如何以岩性来刻划这些层面就显得非常重要了。根据地质钻孔资料中岩层分界点的排列,确定地层的排序。根据多层DEM建模的概念,按岩性对多层DEM进行了交叉划分处理。形成空间中严格按照岩性为要素进行划分的三维地层模型的骨架结构。  相似文献   

多极子声波测井资料在辽河油田硬地层中的应用   总被引：4，自引：4，他引：0  

刘景武 《现代地质》2004,18(3):378-382

通过声波全波列测井中斯通利波的反射和差异能量分析,在辽河油田中进行了裂缝识别并评价了其有效性。利用由4个波列旋转得到的交叉能量成分可以描述碳酸盐岩中的有效裂缝。通过分析计算各向异性的最小和最大能量,并通过不同井的实际产量已证实这些计算结果的一致性,从而对有效裂缝进行了描述。用多极子声波测井可以提高地震资料解释的精度,确定岩性与岩石特征,并探测气层与裂缝。编制出适合辽河油田使用的岩石力学性质参数图并应用在生产中。  相似文献   

某特深基坑支护的非线性三维有限元分析   总被引：37，自引：4，他引：33  

宋二祥  娄鹏  陆新征  沈伟 《岩土力学》2004,25(4):538-543

讨论了润扬长江大桥北锚碇基础施工开挖中50 m特深基坑的三维非线性有限元分析,介绍了工程的有关情况,讨论了其计算模型和参数取值,给出主要计算结果并对有关影响因素进行了分析,在此基础上对该基坑支护的设计作出评价,最后结合施工结果讨论了计算分析的可靠性。  相似文献   

3维城市模型的可视化研究   总被引：74，自引：0，他引：74  

杨必胜  李清泉  梅宝燕 《测绘学报》2000,29(2):149-154

本文在对已有的３维（３Ｄ）城市模型进行分析的基础上,着重探讨了建筑物模型的构造方法,提出了一种分层组合模型方法构造建筑 及在此模型基础上的动态显示、空间分析和交互操作等功能,并开发了一个应用系统（３ＤＴＯＯＬ）对３Ｄ城市模型中的地形和建筑物进行整体维动态显示和操作。最后利用约４ｋｍ＾２试验区对本文提出的模型和开发系统进行了全面的实验研究。  相似文献   

The instability of the vortex sheet along the shear line   总被引：13，自引：1，他引：12  

Gao Shouting 《大气科学进展》2000,17(4):525-537

The traditional Kelvin-Helmholtz notion of studying the shear instability is not suitable for the case associated with shear line with the strong wind shear in the vortex sheet. Since then, the shear instability be-comes the instability of the vortex sheet. If the velocity is induced by the vortex sheet, the inequalities (1 – Rv + Rid)> 0 and U (y,t)> U{A(t)} become the criterion of the vortex sheet instability. This criterion indicates that 1) the disposition of environment field restrains the disturbance developing along the shear line. 2) There exist multi-scale interactions in the unstable process of the shear line. The calculation of the necessary condition for the instability is also presented in this paper.  相似文献   

Complex site effects and building codes: Making the leap   总被引：1，自引：0，他引：1  

Francisco J. Chávez-García  Ezio Faccioli 《Journal of Seismology》2000,4(1):23-40

The engineering community is aware of the importance of site effects, but it lags behind seismological studies when it comes to incorporating site effect considerations in design spectra for seismic norms. This lag is reflected in the conspicuous fact that current building codes make allowance for 1D site effects but ignore complex site effects. The purpose of this paper is to explore a way for including complex site effects in a building code environment. We take as example Eurocode 8, which is a modern code that exemplifies the current approach to site effect consideration. We examine the restrictions that we have imposed to make the problem of a feasible size and discuss the approach we have taken. We propose a strategy to incorporate a class of complex site effects in a design elastic spectrum.  相似文献   

给水管线震害预测方法及实例分析   总被引：1，自引：0，他引：1  

王明钰 《四川地震》2000,(4):23-28

根据地下管线抗震计算理论,对给水管线震害做出预测,为城市给水管网规划,对已建管网的改建加固,制定防灾措施提供依据。  相似文献