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991.
An integrated linear/non-linear flow model for the conduit-fissure-pore media in the karst triple void aquifer system 总被引:2,自引:0,他引:2
Most karstic aquifer media may be characterized as the triple-void media with highly-varied hydraulic properties, including matrix pore, fissure and conduit, in which liner flow may co-exist with non-linear flow. In this paper, an attempt is made to couple linear flow with non-linear flow in a single unified flow governing equations by introducing the concept of equivalent hydraulic conductivity (EHC) and deriving a general Darcys law for various flow. The expression of EHC in the karst conduit and fissure are also derived. The procedures of numerical implementation are demonstrated via an ideal model and a case study of karst aquifer system in the Beishan Ore Formation area, Guangxi Autonomous Region, China. 相似文献
992.
IGCP448:岩溶生态系统全球对比研究进展 总被引:12,自引:3,他引:9
综述了IGCP 448项目"全球岩溶地质及有关生态系统对比"(2000-2004)执行四年来所取得的学术成果.其中比较重要的新认识有:(1)岩溶地区的植被,常常是涵养水分,增加含水层的贮水能力,改善水文生态环境的重要因素,但在澳大利亚南部岩溶区广泛分布的桉树,则以其强烈的蒸发作用,而被用于降低地下水位,防治土壤盐碱化;(2)在北方(Boreal) 或温带湿润气候生态区,地下岩溶系统则被用于排除沼泽地区过多积水,偏碱性的碳酸盐岩也有利于中和酸性环境,凡是岩溶发育的地方,都成了主要农业基地;(3)通过洞穴探险发现一类完全不同于靠光合作用产生有机质的生物群--化学自养微生物(甲烷菌);(4)中国西南典型岩溶区的研究表明,表层土壤微生物可以加速碳酸盐岩的溶解作用,并揭示了植物根系与土壤微生物是产生碳酸酐酶(CA)的两个重要供给源. 相似文献
993.
Prediction of permafrost distribution on the Qinghai-Tibet Plateau in the next 50 and 100 years 总被引:14,自引:0,他引:14
NAN Zhuotong LI Shuxun & CHENG Guodong State Key Laboratory of Frozen Soil Engineering Cold Arid Regions Environmental Engineering Research Institute Chinese Academy of Sciences Lanzhou China Correspondence should be addressed to Nan Zhuotong 《中国科学D辑(英文版)》2005,48(6):797-804
The Qinghai-Tibet Plateau(QTP)has the highestand largest permafrost coverage in the low-middlelatitudes all over the world.With the progress ofChina’s Western Development,human activities areincreasing significantly on the QTP.For instance,theQinghai-Tibet Railway project started in June2001iscurrently under construction,but permafrost problemwill be one of the critical factors for the engineeringconstruction.Frost heave and permafrost settlementmay destroy engineering construction[1,2]… 相似文献
994.
Khalid Qahman Abdelkader Larabi Driss Ouazar Ahmed Naji Alexander H. -D. Cheng 《Stochastic Environmental Research and Risk Assessment (SERRA)》2005,19(2):99-110
Four examples are investigated for the optimal and sustainable extraction of groundwater from a coastal aquifer under the threat of seawater intrusion. The objectives and constraints of these management scenarios include maximizing the total volume of water pumped, maximizing the profit of selling water, minimizing the operational and water treatment costs, minimizing the salt concentration of the pumped water, and controlling the drawdown limits. The physical model is based on the density-dependent advective-dispersive solute transport model. Genetic algorithm is used as the optimization tool. The models are tested on a hypothetical confined aquifer with four pumping wells located at various depths. These solutions establish the feasibility of simulating various management scenarios under complex three-dimensional flow and transport processes in coastal aquifers for the optimal and sustainable use of groundwater. 相似文献
995.
Chung-Chieh Cheng 《Solar physics》1977,55(2):413-419
The analysis of the high temperature plasma in Fe xxiii–xxiv in the 15 June 1973 flare is presented. The observations were obtained with the NRLXUV spectroheliograph on Skylab. The results are: (1) There was preheating of the active region in which the flare occurred. In particular, a large loop in the vicinity of the flaring region showed enhanced brightness for many hours before the flare. The loop disappeared when the flare occurred, and returned in the postflare phase, as if the energy flux which had been heating the large loop was blocked during the flare and restored after the flare was gone. The large magnetic fields did not change significantly. (2) The flare occurred in low-lying loop or loops. The spatial distribution of flare emission shows that there was a temperature gradient along the loop. (3) The high temperature plasma emitting Fe xxiii and xxiv had an initial upward motion with a velocity of about 80 km s–1. (4) There was large turbulent mass motion in the high temperature plasma with a random velocity of 100 to 160 km s–1. (5) The peak temperature of the hot plasma, determined from the Fe xxiii and xxiv intensity ratio, was 14 × 106 K. It decreased slightly and then, for a period of 4 min, remained at 12.6 × 106 K before dropping sharply to below 10 × 106 K. The density of the central core of the hot plasma, determined from absolute intensity of Fe xxiv 255 Å line, was of the order of 1011 cm–3.The persistence of the high level of turbulence and of the high temperature plateau in the decaying phase of the flare indicates the presence of secondary energy release. From the energy balance equation the required energy source is calculated to be about 3 to 7 ergs cm–3 s–1.Ball Brothers Research Corporation. 相似文献
996.
中天山坡地冰缘地貌的若干问题 总被引:1,自引:0,他引:1
由 1985—1989年野外调查结果和定位重复观测资料可知,本区坡地冰缘地貌的分布特征为:1.各类坡地冰缘形态彼此具有成因联系;2.不同序次的冰缘地貌类型具有各自的时空分异;3.不同的坡地冰缘地貌类型在一定条件下可有所转化。再则,本区风化以寒冻剥裂和寒冻楔入为主,呈现在时空和状态上为不可逆过程的耗散结构。 相似文献
997.
最近,一个困扰人们达十几年之久的γ射线源Geminga被证认为X、γ射线脉冲星,其光学对应体也被确定为一颗光谱偏蓝的25等星。对Geminga脉冲星的确证说明存在着一类没有射电辐射的脉冲单星。 相似文献
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