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101.
Byron C. Shumate Claire L. Schelske Thomas L. Crisman William F. Kenney 《Journal of Paleolimnology》2002,27(1):71-77
A paleolimnological evaluation of cladoceran microfossils was initiated to study limnological changes in Lake Apopka, a large (125 km2), shallow (mean depth = 1.6 m), warm, polymictic lake in central Florida. The lake switched from macrophyte to algal dominance in the late 1940s, creating a Sediment Discontinuity Layer (SDL) that can be visually used to separate sediments derived from macrophytes and phytoplankton. Cladoceran microfossils were enumerated as a means of corroborating extant eutrophication data from the sediment record. Inferences about the timing and trajectory of eutrophication were made using the cladoceran-based paleo-reconstruction. The cladoceran community of Lake Apopka began to change abruptly in both total abundance and relative percent abundance just before the lake shifted from macrophyte to algal dominance. Alona affinis, a mud-vegetation associated cladoceran, disappeared before the SDL was formed. Planktonic and benthic species also began to increase below the SDL, indicating an increase in production of both planktonic and benthic species. Chydorus cf. sphaericus, an indicator of nutrient loading, increased relative to all other cladocerans beginning in the layer below the SDL and continuing upcore. Changes in the transitional sediment layer formed before the lake switched to phytoplankton dominance, including an increase in total phosphorus concentration, suggest a more gradual eutrophication process than previously reported. Data from this study supported conclusions from other paleolimnological studies that suggested anthropogenic phosphorus loading was the key factor in the hypereutrophication of Lake Apopka. 相似文献
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105.
静力触探中土层界面效应试验研究 总被引:2,自引:2,他引:2
根据成层土模型试验结果,对静力触探中土层面效应进行试验研究和机理分析,取得了成层土界面效应的规律性,为利用静力触探划分土层提供了理论和实践依据。 相似文献
106.
地热回灌的发展现状 总被引:15,自引:0,他引:15
刘久荣 《水文地质工程地质》2003,30(3):100-104
地热回灌是一种避免地热废水直接排放引起的热污染和化学污染的措施,并对维持热储压力,保证地热田的开采技术条件具有重要的作用。目前回灌已经成为世界范围内数十个重要的地热田生产运行中的一项日常工作,在美国、新西兰、冰岛、意大利、法国、日本、罗马尼亚、丹麦、菲律宾和萨尔瓦多等十多个国家得到了广泛的应用。在国内,北京、天津的地热回灌也已经有了良好的开端。回灌是地热田管理中最为复杂的一项技术,为了避免因回灌而引起热储冷却,需要进行回灌试验和示踪试验,并在回灌过程进行全面的监测工作。 相似文献
107.
格尔木地磁台观测环境测试与分析 总被引:2,自引:0,他引:2
通过实验测试和计算,分析了高压输出电线等干扰源对格尔木地磁台观测环境的影响,进一步对格尔木地磁台观测环境现状,及今后观测环境保护工作的要点进行了综合分析讨论。 相似文献
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Zhao-Dong Xu Ya-Peng Shen Hong-Tie Zhao 《Soil Dynamics and Earthquake Engineering》2003,23(8):683-689
The paper introduces a synthetic optimization analysis method of structures with viscoelastic (VE) dampers, namely the simplex method. The optimal parameters and location of VE dampers can be determined by this method. Numerical example and a shaking table test about reinforced concrete structures with VE dampers show that the seismic responses of structures will be reduced more effectively when the parameters and location of VE dampers are designed in accordance with the results calculated by the simplex method. 相似文献
110.
A critical state interpretation for the cyclic liquefaction resistance of silty sands 总被引:1,自引:0,他引:1
George D. Bouckovalas Konstantinos I. Andrianopoulos Achilleas G. Papadimitriou 《Soil Dynamics and Earthquake Engineering》2003,23(2):115-125
Contrary to many laboratory investigations, common empirical correlations from in situ tests consider that the increase in the percentage of fines leads to an increase of the cyclic liquefaction resistance of sands. This paper draws upon the integrated Critical State Soil Mechanics framework in order to study this seemingly not univocal effect. Firstly the effect of fines on the Critical State Line (CSL) is studied through a statistical analysis of a large data set of published monotonic triaxial tests. The results show that increasing the content of non-plastic fines practically leads to a clockwise rotation of the CSL in (e–ln p) space. The implication of this effect on cyclic liquefaction resistance is subsequently evaluated with the aid of a properly calibrated critical state elasto-plastic constitutive model, as well as a large number of published experimental results and in situ empirical correlations. Both sets of data show clearly that a fines content, less than about 30% by weight, may prove beneficial at relatively small effective stresses (p0<50–70 kPa), such as the in situ stresses prevailing in most liquefaction case studies, and detrimental at larger confining stresses, i.e. the stresses usually considered in laboratory tests. To the extent of these findings, a correction factor is proposed for the practical evaluation of liquefaction resistance in terms of the fines content and the mean effective confining stress. 相似文献