植被变化对辽西夏季气候影响的数值试验   总被引：6，自引：0，他引：6  

刘宁微  周小珊 《南京气象学院学报》2004,27(5):632-640

利用2001年6、7、8月份的资料及中尺度模式MM5V3．5对当年夏季辽西生态脆弱区进行了气候模拟性能试验，模拟出植被退化和恢复后辽西地区的温度变化。试验结果表明：在辽西部分地区植被退化后，当地夏季平均温度明显升高；在部分地区植被恢复后，当地夏季平均温度降低；在下垫面状况改变的周边地区，平均温度有一定程度的变化。同时，植被状况的改变对高空气压场和温度场也产生一定影响。  相似文献   

铝钛柱撑改性膨润土处理两种模拟废水的实验研究   总被引：10，自引：1，他引：10  

邵红 王恩德马勇  袁俊斌 《岩石矿物学杂志》2004,23(2):181-185

以钠基膨润土为原料制备了铝钛无机柱撑、铝钛有机柱撑改性膨润土，确定了改性膨润土的最佳铝钛比和铝土比，并将其应用于模拟废水、化学实验室废水的处理。与原土进行比较，探讨了用量、pH值、搅拌时间等对COD去除率、色度去除率、浊度去除率的影响，通过正交实验对实验条件进行了优化。结果表明：有机柱撑改性膨润土、无机柱撑改性膨润土对废水的处理效果均明显好于原土，对废水色度、浊度的去除率均大于93％；对废水COD的去除效果，有机柱撑改性膨润土比无机柱撑改性膨润土有较大提高，去除率最高达66．31％，结果令人满意。  相似文献   

化学腐蚀下砂岩三轴细观损伤机理及损伤变量分析   总被引：10，自引：4，他引：10  

陈四利  冯夏庭  周辉 《岩土力学》2004,25(9):1363-1367

利用CT识别技术对化学腐蚀下的砂岩进行了三轴加载全过程的即时扫描试验，得到了在不同级荷载作用下砂岩的压密、微裂纹萌生、扩展和破裂的CT图像和CT数，分析了砂岩损伤演化的细观机理。同时，建立了一个基于化学腐蚀影响和CT数的损伤变量模型。  相似文献   

内蒙古二连浩特市—东乌珠穆沁旗半干旱荒漠草原区区域化探方法试验   总被引：5，自引：0，他引：5       下载免费PDF全文

孔凡吉  张青  曹金虎 《地质找矿论丛》2004,19(4):261-269

内蒙古二连浩特市-东乌珠穆沁旗地区属半干旱荒漠草原区.1∶20万区域化探扫面应针对该类景观区微景观特点,选择土壤或水系沉积物测量方法开展工作.经试验确定采样粒级为-5～ 20目;采样密度2个点/km2;采样介质为残坡积物或冲、洪积物.经4个1∶20万图幅的区域化探扫面工作,取得了明显的异常圈定和地质找矿效果,方法技术有效.  相似文献   

Kinetic-simulating experiment combined with GC-IRMS analysis: application to identification and assessment of coal-derived methane from Zhongba Gas Field (Sichuan Basin, China)   总被引：2，自引：0，他引：2  

Yongqiang Xiong  Ansong Geng  Jingzhong Liu 《Chemical Geology》2004,213(4):325-338

The main purpose of this study is to model the δ¹³C values of methane derived from coal by combining kinetic-simulating experiment with the gas chromatography-isotope ratio mass spectrum (GC-IRMS) analysis. The stable carbon isotopic variation of methane in pyrolysates with heating temperature indicates that the assumptions for both a constant kinetic isotope effect (α) and a uniform initial isotopic composition (δ¹³C_o) are impractical for explaining the carbon isotopic fractionation during coalification. For purposes of simplification, two approaches are used in this paper to deal with the heterogeneity of terrestrial organic matter. One is that, assuming a uniform initial isotopic composition (i.e., δ¹³C_{i, o}=δ¹³C_o) for all methane-generating precursors in coal, the isotopic variation of methane is fitted by adjusting ΔE_{a, i} (E_{a¹³C, i}−E_{a¹²C, i}) for each hypothetical reaction. The other is that, assuming a constant kinetic isotope effect during the whole gas formation, that is all ΔE_{a, i} values are identical, the modeling of methane isotopic composition is achieved by changing the ¹³CH₄ generation potential of each reaction (f_{i, ¹³C}), namely, by adjusting the initial δ¹³C value (δ¹³C_{i, o}) for each methane-generating precursor. Results of the kinetic calculation shows that the two simulating methods can yield a similar result at a geological heating rate of 2 °C/My, which further demonstrates that those natural gases with methane δ¹³C value being approximately −36‰ are possibly sourced from the upper Triassic coal measure strata in the Northwestern Sichuan Basin.  相似文献   

Local Modeling模式及其在月径流预测中的应用   总被引：5，自引：2，他引：5  

蓝永超  丁永建  王书功  康尔泗  宋克超 《中国沙漠》2004,24(3):313-316

Local Modeling方法是一种动力系统预测方法，将其应用于河西内陆区黑河干流出山口莺落峡水文站月平均流量的中长期预测预报，取得了较为理想的成果。预测试验的结果表明，该预测模型有较高计算精度，尤其适用于非主汛期各月的月平均流量的预测；对于主汛期6～9月的月平均流量的预测，在考虑前期来水与预见期内降水的影响后，亦可获到较为理想的预测结果。可以认为，该方法的预报精度达到了水文情报预报规范的要求，Local Modeling方法的应用，将为西北干旱地区河川径流的中长期预报提供了一个新的途径。  相似文献   

Biomineralization of Uranium: A Simulated Experiment and Its Significance   总被引：5，自引：0，他引：5  

L. L. BARTON  H. WIATROWSKI 《《地质学报》英文版》2005,79(1):134-138

A simulated experimental reduction of U^v1 and the synthesis of uraninite by a sulfate-reducing bacteria,Desulfovibrio desulfuricans DSM 642, are first reported. The simulated physicochemical experimental conditions were:35℃, pH=7.0-7.4, corresponding to the environments of formation of the sandstone-hosted interlayer oxidation-zone type uranium deposits in Xinjiang, NW China. Uraninite was formed on the surface of the host bacteria after a one-week‘s incubation. Therefore, sulfate-reducing bacteria, which existed extensively in Jurassic sandstone-producing environments,might have participated in the biomineralization of this uranium deposit. There is an important difference in the orderdisorder of the crystalline structure between the uraninite produced by Desulfovibrio desulfuricans and naturally occurring uraninite. Long time and slow precipitation and growth of uraninite in the geological environment might have resulted in larger uraninite crystals, with uraninite nanocrystals arranged in order, whereas the experimentally produced uraninite is composed of unordered uraninite nanocrystals which, in contrast, result from the short time span of formation and rapid precipitation and growth of uraninite. The discovery has important implications for understanding genetic significance in mineralogy, and also indicates that in-situ bioremediation of U-contaminated environments and use of biotechnology in the treatment of radioactive liquid waste is being contemplated.  相似文献   

Transport rate of calcareous sand in unidirectional flow     

DAVID A. SMITH  KWOK FAI CHEUNG 《Sedimentology》2005,52(5):1009-1020

This paper examines the transport of calcareous sand in unidirectional flow and its prediction through existing sediment transport models. A flume experiment of four sand samples collected on Oahu, Hawaii, provides 29 sets of sediment transport data in the bed-form and suspended transport stages. The measured transport data are compared with direct predictions from four energy-based transport models developed for siliceous particles. Corrections for the grain-size, fall velocity, and critical velocity of calcareous sand based on recent research are applied to the models and the results are compared with the direct calculations and measured data. The comparison illustrates the important role particle shape plays in the transport of calcareous sand. All four sediment transport models give consistent predictions and good agreement with the majority of the measured data. Two of the models respond positively to the corrections in both the bed-form and suspended transport stages indicating that such an approach may provide an interim solution for the transport of calcareous sand.  相似文献   

Influence of a coarse interlayer on seawater intrusion and contaminant migration in coastal aquifers          下载免费PDF全文

Yi Liu  Xiaomin Mao  Jian Chen  D. A. Barry 《水文研究》2014,28(20):5162-5175

Vertical 2D slice laboratory experiments were carried out in homogenous and layered sand tanks to elucidate the effects of a highly permeable (coarse‐grained sand) interlayer on seawater intrusion and transport of contaminants to a coastal sea. Tidal fluctuations produced oscillations in the seawater–freshwater transition zone, fluctuations of the contaminant infiltration rate and a zigzag contaminant plume outline. The seawater wedge became discontinuous at the (vertical) edges of the interlayer because of increased lateral movement of the seawater–freshwater interface within the interlayer. The contaminant plume formed a tail within the interlayer depending on the tidal stage, and similar to the wedge, its movement was accentuated. A simple analytical model that neglected vertical flow reliably predicted steady‐state seawater intrusion into the coastal aquifer. Numerical modeling was used to gain insight into the groundwater hydrodynamics and contaminant migration. The numerical results confirmed the experimental findings, i.e. that a highly permeable interlayer can provide a rapid transit path for contaminants to reach the seaward boundary and that the interlayer amplifies the effects of tidal fluctuations, resulting in wider transition zones for the seawater wedge and contaminant plume. Numerical simulations further showed that, with increasing interlayer hydraulic conductivity, the maximum seawater intrusion distance inside the interlayer increases approximately linearly. For the fixed‐head contaminant injection condition used, the model showed that contaminant infiltration increases approximately logarithmically with increasing interlayer hydraulic conductivity (other factors held fixed). Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Autogenic avulsion,channelization and backfilling dynamics of debris‐flow fans          下载免费PDF全文

Tjalling de Haas  Wilco van den Berg  Lisanne Braat  Maarten G. Kleinhans 《Sedimentology》2016,63(6):1596-1619

Alluvial fans develop their semi‐conical shape by quasi‐cyclic avulsions of their geomorphologically active sector from a fixed fan apex. On debris‐flow fans, these quasi‐cyclic avulsions are poorly understood, partly because physical scale experiments on the formation of fans have been limited largely to turbidite and fluvial fans and deltas. In this study, debris‐flow fans were experimentally created under constant extrinsic forcing, and autogenic sequences of backfilling, avulsion and channelization were observed. Backfilling, avulsion and channelization were gradual processes that required multiple successive debris‐flow events. Debris flows avulsed along preferential flow paths given by the balance between steepest descent and flow inertia. In the channelization phase, debris flows became progressively longer and narrower because momentum increasingly focused on the flow front as flow narrowed, resulting in longer run‐out and deeper channels. Backfilling commenced when debris flows reached their maximum possible length and channel depth, as defined by channel slope and debris‐flow volume and composition, after which they progressively shortened and widened until the entire channel was filled and avulsion was initiated. The terminus of deposition moved upstream because the frontal lobe deposits of previous debris flows created a low‐gradient zone forcing deposition. Consequently, the next debris flow was shorter which led to more in‐channel sedimentation, causing more overbank flow in the next debris flow and resulting in reduced momentum to the flow front and shorter runout. This topographic feedback is similar to the interaction between flow and mouth bars forcing backfilling and transitions from channelized to sheet flow in turbidite and fluvial fans and deltas. Debris‐flow avulsion cycles are governed by the same large‐scale topographic compensation that drives avulsion cycles on fluvial and turbidite fans, although the detailed processes are unique to debris‐flow fans. This novel result provides a basis for modelling of debris‐flow fans with applications in hazards and stratigraphy.  相似文献