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991.
992.
This paper presents the overall sinkhole distributions and conducts hypothesis tests of sinkhole distributions and sinkhole formation using data stored in the Karst Feature Database (KFD) of Minnesota. Nearest neighbor analysis (NNA) was extended to include different orders of NNA, different scales of concentrated zones of sinkholes, and directions to the nearest sinkholes. The statistical results, along with the sinkhole density distribution, indicate that sinkholes tend to form in highly concentrated zones instead of scattered individuals. The pattern changes from clustered to random to regular as the scale of the analysis decreases from 10–100 km2 to 5–30 km2 to 2–10 km2. Hypotheses that may explain this phenomenon are: (1) areas in the highly concentrated zones of sinkholes have similar geologic and topographical settings that favor sinkhole formation; (2) existing sinkholes change the hydraulic gradient in the surrounding area and increase the solution and erosional processes that eventually form more new sinkholes. 相似文献
993.
Mei Mingxiang Ma Yongsheng Deng Jun Meng Qingfen Li Donghai 《中国地质大学学报(英文版)》2005,16(3):231-249
INTRODUCTION Alotofprogresshasbeenmadeinthestudyof Carboniferoussedimentologyandstratigraphyinthe Dianqianguibasinanditsadjacentareas,whichin cludethecomprehensivesummariesonchronostratigraphyandbiostratigraphybyJinetal.(2000)and Kuangetal.(1999);theoverallandsystematicsum mariesonCarboniferouslithostratigraphybyDong(1997),Yin(1997)andZhao(1996);thecompre hensivestudyonCarboniferoussedimentaryfacies andpaleogeographybyChenetal.(1994)andFeng etal.(1998)etc..AsshowninFig.1,theDian qiang… 相似文献
994.
采用尼龙网袋法和砂滤管法研究了稻草不同还田方式下的腐解及养分释放规律。结果表明:稻草还田后,前期腐解快,后期较慢。翻埋还田的稻草腐解速率明显快于覆盖还田稻草,整个试验期间(210d)翻埋还田的稻草腐解率达到76.55%,而覆盖还田的稻草仅为53.50%。稻草覆盖与翻埋两种还田方式下养分释放速率均以钾(K)最快,磷(P)次之,氮(N)最慢。还田10d内,两种方式下K分别释放了50.32%和90.13%。稻草与土壤充分混合条件下,稻草和土壤矿化释放的氮以NO3-N为主(〉80%),NH4-N和可溶性有机氮较少;在稻草还田后的前40d存在土壤微生物与作物竞争土壤矿质氮的现象,40d之后此现象消失,稻草开始氮的净矿化;在稻草埋入土壤时同时配施适量的氮肥,则不会出现微生物的夺氮现象。整个试验期间,该土壤氮净矿化量达90.4mg/kg土。 相似文献
995.
线法监测作为一种监测基桩应变的新技术,正逐渐在全球范围内推广。笔者介绍了其原理,并结合工程实例阐明了线法监测的特点、可靠性和先进性。 相似文献
996.
997.
Dong WANG Shaoming PAN Jichun WU Qingping ZHU Chang LIU 《中国地球化学学报》2006,25(B08):168-169
In the history, the Yellow River nurtured Chinese civilization. It is respected as the "ancestor of the four large rivers in China" and praised as "the mother river of China". At the same time, the Yellow River is regarded as "the misery of China" and considered as the most complex river hard to control in the world. Today, the Yellow River is also one large river greatly influenced by human activities in the world. The safety of the Yellow River, particularly flood control, is always the most important issue for governing and developing the country. Great achievements have been made after many years of efforts for controlling the Yellow River. However, since the nineties of 20 century, some new problems occurred, such as sharp reduction of flux to sea, dry rivercourse, worsen environment, etc. Rapidly shrinking riverbed and two-level perched stream are disadvantageous to flood safety especially. The new concepts and new practices are urgently needed to control the river. Therefore, the Yellow River Conservancy Committee of Ministry of Water Resources had continuously carded out flow and sediment diversion each year from 2002 to 2005. To timely probe into the new issues produced after flow and sediment diversion, and in order to deepen the understanding of rules for the Yellow River's water and sediment and provide reference and experience to the researchers for other large rivers, five hydrologic and hydraulic characteristics of the Yellow River, such as lack of water, much of sediment, different resources of water and sediment, inconsistency between water and sediment and frequency of sink switching and route changing, are described. Flow and sediment diversion of the Yellow River is also reviewed. Under flow and sediment diversion, 相似文献
998.
智能大厦接地电阻检测中应注意的问题 总被引:9,自引:0,他引:9
根据目前常用接地电阻检测仪器的测量原理,对在日常检测中所出现导致接地电阻检测数据失真的情况进行了分析和探讨,同时针对不同的成因,提出了不同的解决方法。 相似文献
999.
Aquatic macrophytes can severely retard flow rates in the river channels that they occupy. Consequently, there is a need to improve our ability to model vegetation resistance, to aid flood prediction and allow for better-informed channel management. An empirical model is developed to calculate flow resistance (Manning’s resistance coefficient) of channels containing the submergent macrophyte Ranunculus (water-crowfoot). Blockage factors (the proportion of a cross-section blocked by vegetation) were determined for up to nine cross-sections at each of 35 river sites. These were used to create blockage-factor percentiles, which were regressed against vegetation resistance. An exponential best-fit relation involving the 69th blockage-factor percentile gave the best results. A parameter relating the length of the vegetated/solid boundary in contact with the open channel to the length of the conventionally-defined wetted perimeter improved the model fit by acting as a pseudo-measure of the turbulent-energy losses generated within the unvegetated stream by the macrophytes. The model was tested on three additional sites containing different macrophyte species and much higher vegetation blockages, and was found to work well. 相似文献
1000.
Norio Hori Norio Inoue Dangol Purushotam Tetsuya Nishida Jun Kobayashi 《地震工程与结构动力学》2006,35(13):1699-1719
To improve the seismic performance of masonry structures, confined masonry that improves the seismic resistance of masonry structures by the confining effect of surrounding bond beams and tie columns is constructed. This study investigated the earthquake resisting behaviour of confined masonry structures that are being studied and constructed in China. The structural system consists of unreinforced block masonry walls with surrounding reinforced concrete bond beams and tie columns. The characteristics of the structure include: (1) damage to blocks is reduced and brittle failure is avoided by the comparatively lower strength of the joint mortar than that of the blocks, (2) the masonry walls and surrounding reinforced concrete bond beams and tie columns are securely jointed by the shear keys of the tie columns. In this study, wall specimens made of concrete blocks were tested under a cyclic lateral load and simulated by a rigid body spring model that models non‐linear behaviour by rigid bodies and boundary springs. The results of studies outline the resisting mechanism, indicating that a rigid body spring model is considered appropriate for analysing this type of structure. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献