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971.
Kenichi HOSHINO Yuki YAMAMOTO Xiangping GU Su Young LEE Makoto WATANABE 《Resource Geology》2000,50(3):185-190
Abstract: Possible ore deposition by fluid mixing was preliminarily examined using MIX 99, a FORTRAN program developed for simulating water-rock interactions. We consider mixing of two fluids, the low fO2 and high temperature source fluid and the high fO2 and low temperature seawater. Oxygen fugacity of a mixed fluid formed by titration of seawater into the source fluid gradually decreases with decreasing temperature (model A). Sequential precipitation of ore-forming minerals was examined in this model. On the other hand, simultaneous precipitation of the minerals could be followed by simulation of instantaneous overall mixing of the two fluids (model B). Results of simulation of the both models revealed that a temporal sequence of mineralization observed in the Karuizawa mine, NE Japan, can be formed by model A, while model B is suitable for the mineralization of an active chimney found in the Rainbow hydrothermal area of the Mid-Atlantic Ridge. 相似文献
972.
973.
安徽舒城旅游客源市场定量分析 总被引:2,自引:0,他引:2
运用定性与定量相结合的方法进行旅游客源市场分析。考查诸多可能影响旅游客源市场的因素后 ,精选出 11个因子 ,采用专家打分模型 ,对安徽省舒城县旅游客源地 (舒城及其邻近的 90个市、县 )的诸多因素进行考察 ,得出这 90个市、县作为舒城旅游客源地的无量纲分值 ,据此作出客源市场的等级划分。 相似文献
974.
975.
976.
新疆吐鲁番盆地艾丁湖的环境变化 总被引:13,自引:3,他引:10
艾丁湖是我国最低的湖泊,海拔-154.4m,位于亚洲中部极端干旱区,蒸发量是降水量110~500倍,自然环境严酷.有史以来,在以人为实践主体、人口、资源、环境和发展整个系统相互协调的过程中,艾丁湖的环境发生了很大的变化,湖水面不断缩小,以致一度干涸.近10a来,受气候变暖湿事件的影响,暴雨洪水给艾丁湖以新的面貌,湖水面变化与河流水量增大同步. 相似文献
977.
西藏冈底斯带花岗岩的时空分布特征及地壳生长演化信息 总被引:159,自引:1,他引:158
花岗岩是大陆特有的重要组成部分,同时与矿产资源有密切的关系。西藏花岗岩约占西藏自治区面积的12%,其中,80%分布在冈底斯岩浆岩带。在空间上,冈底斯花岗岩带大致可以分为3个亚带:北带、中带和南带;在时间上,以印度一亚洲大陆碰撞事件为标尺,可将青藏高原构造一岩浆事件划分为碰撞前(〉65Ma)、碰撞期(65~45Ma)、后碰撞(〈45Ma)3大阶段。在这3个阶段中,冈底斯带都产生了具有各自特点的花岗岩构造一岩浆类型。冈底斯花岗岩类的形成演化与新特提斯班公湖一怒江洋及雅鲁藏布洋的形成演化,有密切的关系。因此,其岩石的Nd,Sr同位素资料,对地壳生长与演化有重要的指示意义。冈底斯南带的大部分地区的花岗岩,均具有εNd(t)(+)值(+1.64~+5.21),模式年龄tDM也很年青(〈500Ma),具有初生(juvenile)地壳的特征。在花岗岩成因中地幔物质有重要的贡献。而冈底斯中带、北带及南带西段的花岗岩类以εNd(t)(-)值为特征(-5.3~-17.3),模式年龄tDM有两组值1.2Ga及2.0~2.5Ga,暗示这些地区的地壳具有古元古代一中元古代基底在花岗岩成因中,地壳组分具有主要贡献。 相似文献
978.
979.
Impact of dissipation and dispersion terms on simulations of open‐channel confluence flow using two‐dimensional depth‐averaged model
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The flow patterns in confluence channel and the simulation of confluence flow are more complex than that in straight channel. Additional terms in the momentum equations, i.e. dissipation terms, denoting the impact of turbulence, and dispersion terms, denoting the vertical non‐uniformity of velocity, show great impacts on the accuracy of numerical simulations. The dissipation terms, i.e. the product of eddy viscosity coefficient and velocity gradient, are much larger than those of the flow in straight channel. In this study, the zero equation model and the depth‐averaged k‐ε model are used to analyse the impact of eddy viscosity. Meanwhile, the dispersion terms in the momentum equation, depending on the vertical non‐uniformity of velocity, are usually neglected in routine simulation. With the use of detailed experimental data for verification, this study presents the distribution of parameters of vertical non‐uniformity and the intimated connection between non‐uniformity parameters and accuracy of numerical simulations of confluence flow with depth‐averaged models. The results present that simulation accuracy of confluence flow is very sensitive to the turbulence modes, which cannot be handled by normal, simple turbulence model. On the contrary, the impact of dispersion terms is both flow‐condition‐dependent and place‐dependent, and such impact is negligible when secondary circulation is weak. The results indicate the key elements in modelling confluence flow and are helpful for selecting suitable numerical model and solving engineering problems encountered in confluence channel. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
980.
Real‐time river bed scour monitoring and synchronous maximum depth data collected during Typhoon Soulik in 2013
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A critical concern regarding river bed stabilization and river engineering is the short‐term general scour that occurs in a field setting far from a river‐crossing structure or embankment during a typhoon‐induced flood. This study investigated the improvement of existing techniques that have been used to measure river bed scour. One of these techniques is the numbered‐brick column or scour chains method, in which only the maximum general scour depth of river bed is observed. A wireless tracer for monitoring real‐time scour was set‐up with a numbered‐brick column and was employed to collect synchronous data. The proposed method was successfully used to observe both real‐time scour and the maximum depth at flood peak. This observation was conducted at a steep gravel‐bed reach of the Shuideliaw Embankment on the intermittent Choshui River in Central Taiwan during Typhoon Soulik, which occurred in 2013. Future studies must be conducted to complete the development of an automatic real‐time scour and flood monitoring system for use in severe weather and flow conditions; this would facilitate the identification of river bed scour during conditions of unstable flow and the improvement of flood prevention engineering, bridge closure detection and emergency evacuation procedures. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献