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11.
THERIVERCHANNELADJUSTMENTASINFLUENCEDBYTHEFLOODPLAINGEOECOSYSTEM:ANEXAMPLEFROMTHEHONGSHANRESERVOIR¥XUJiongxin;SHIChangxing(Pr...  相似文献   
12.
基于本底趋势线的秦俑馆旅游危机后评价研究   总被引:9,自引:0,他引:9  
孙根年  于立新 《地理科学》2008,28(1):107-112
分析了相邻年比较法在旅游危机评价中的不足,提出了基于本底趋势线的旅游危机后影响评价方法。以陕西秦始皇兵马俑1980~2005年统计数据,建立了入境旅游、国内旅游、客流总量和旅游收入4条本底趋势线,对1989年北京6.4风波、1998年亚洲金融危机、2003年SARS瘟疫三个突发事件旅游危机在本景区的响应进行后评价研究,揭示了秦兵马俑景区在三次危机中所造成的客流量损失、旅游收入损失及冲击时间表,为突发事件旅游危机的后评价研究提供了新的理论与方法。  相似文献   
13.
Lacustrine deposits of the Malanzán Formation record sedimentation in a small and narrow mountain paleovalley. Lake Malanzán was one of several water bodies formed in the Paganzo Basin during the Late Carboniferous deglaciation. Five sedimentary facies have been recognized. Facies A (Dropstones-bearing laminated mudstones) records deposition from suspension fall-out and probably underflow currents coupled with ice-rafting processes in a basin lake setting. Facies B (Ripple cross-laminated sandstones and siltstones) was deposited from low density turbidity currents in a lobe fringe environment. Facies C (Massive or graded sandstones) is thought to represent sedimentation from high and low density turbidity currents in sand lobes. Facies D (Folded sandstones and siltstones) was formed from slumping in proximal lobe environments. Facies E (Wave-rippled sandstones) records wave reworking of sands supplied by turbidity currents above wave base level.The Lake Malanzán succession is formed by stacked turbidite sand lobe deposits. These lobes were probably formed in proximal lacustrine settings, most likely relatively high gradient slopes. Paleocurrents indicate a dominant direction from cratonic areas to the WSW. Although the overall sequence shows a regressive trend from basin fine-grained deposits to deltaic and braided fluvial facies, individual lobe packages lack of definite vertical trends in bed thickness and grain size. This fact suggests aggradation from multiple-point sources, rather than progradation from single-point sources. Sedimentologic and paleoecologic evidence indicate high depositional rate and sediment supply. Deposition within the lake was largely dominated by event sedimentation. Low diversity trace fossil assemblages of opportunistic invertebrates indicate recolonization of event beds under stressed conditions.Three stages of lake evolutionary history have been distinguished. The vertical replacement of braided fluvial deposits by basinal facies indicates high subsidence and a lacustrine transgressive episode. This flooding event was probably linked to a notable base level rise during postglacial times. The second evolutionary stage was typified by the formation of sand turbidite lobes from downslope mass-movements. Lake history culminates with the progradation of deltaic and braided fluvial systems  相似文献   
14.
卓潘碱性杂岩体为"三江"地区富碱(高钾)侵入岩的重要组成部分,位于哀牢山-金沙江缝合带的中部,侵位于兰坪盆地南部的白垩系砂岩中,主要由碱性辉长岩、辉石正长岩和霞石正长岩组成。对卓潘碱性杂岩体的岩相学、岩石学、主元素和稀土微量及同位素地球化学特征的系统研究表明,该杂岩体主量元素显示低硅、富钾、高碱(K2O+Na2O为6.92%~13.43%)、低TiO 2(0.31%~1.20%)的特征,属钾质碱性系列岩石;杂岩体的各种岩石均富集Rb、Sr、Ba、Th等大离子亲石元素、亏损Nb、Ta、Ti等高场强元素,并具有轻稀土富集的右倾型稀土元素分布模式、具较高的87Sr/86Sr、206Pb/204Pb、207Pb/204Pb、208Pb/204Pb及较低的143Nd/144Nd等特征,表明源区具有较明显的EMⅡ型富集地幔特征,源区明显受到壳源物质的混染。卓潘岩体形成于印度-欧亚大陆后碰撞的剪切和拉张的构造环境,古扬子板片向西俯冲,诱发了经过陆壳交代混染了的岩石圈地幔的部分熔融。由于兰坪走滑拉分盆地东缘断裂拉伸强度大,岩浆起源的深度大,以及岩浆源区成分(特别是CO2含量)与其它部位不同,因此在卓潘地区形成一套与金沙江-哀牢山-红河断裂带其它新生代富碱斑岩完全不同的过碱性的岩石。  相似文献   
15.
根据1998年6~9月采集于南海海域沉积岩芯中的浮游有孔虫氧、碳同位素和SiO2、CaCO3地球化学地层序列,标定了南海的年代框架,并应用UK 37指标重建了南海南、北部末次盛冰期以来表层海水的古温度。结果显示:南海南部冰后期和末次盛冰期时UK 37海水表层估温分别为24.5~27.4℃和23.8~25.3℃,平均水温分别为26.3℃和24.3℃。南海北部冰后期和末次盛冰期时UK 37海水表层估温分别为23.3~26.9℃和22.2~23.8℃,平均水温分别为26.6℃和22.8℃。南海北部温差比南部大,也比同一纬度的其它观察点大得多,充分表明南海对气候变化响应的敏感程度远大于开放性大洋,同时也进一步证实了边缘海对于冰期旋回的环境信号具有放大效应。  相似文献   
16.
Dynamics of ships and fenders during berthing in a time domain   总被引:2,自引:0,他引:2  
When designing fixed or semi-fixed structures used for berthing ships, it is generally assumed that the entire kinetic energy of the ship is absorbed by the fender or the system of fenders. The fenders have the functions of ensuring a safe berthing both for the ships and the piers by absorbing shock loads and preventing direct contact between the berthed ship and the pier. In this study, the problem is analyzed in the stages of berthing, collision and leaving. Each of the stages is analyzed and solved in the time domain. The system is assumed to consist of three components: pier, fender and the ship. Environmental effects that simultaneously affect berthing are wave, current and wind effects. Cummins equation was assumed to be a good representation of the problem and was solved in time domain taking various factors into account. Nonlinear effects related to the instantaneous values of forces, moments and ship motions, which are time dependent, were studied by the Cummins equation and its later developments by Ogilvie. Fender forces were added to the calculation scheme by the authors. A case study for a passenger ferry operating in Izmir bay is presented.  相似文献   
17.
于1996年5月,在青岛市红岛镇后阳育苗场,采用饲养实验的方法对患肠道疾病的中国对虾仔虾的康复进行观察研究。结果表明,中国对虾仔虾的某些肠道疾病的康复与蜕 存在极为密切的关系。肠道杆菌病对虾状幼体和糠虾幼体危害极大,患病个体死亡率为100%,而患病率的仔虾幼体较高的存活率(32%),存活者多数为病症出现时已处蜕皮前期的个体,而在蜕皮间期开始患病的个体极少能发育至蜕皮变态。肠道堵塞是仔虾期纪体的幼体  相似文献   
18.
Pollen analysis of 3.25 m of late glacial and Holocene sediments gives a mid‐altitude (600 m) record of vegetation development after the last or Margaret Glaciation. Alpine herbfield, coniferous heath and Nothofagus gunnli scrub developed on the moraines until 11,400 BP. Wet montane forest and heath then developed with Phyllocladus aspleniifolius, Nothofagus cunninghamii and Eucalyptus until c. 10,000 BP. After 10,000 BP a mosaic of N. cunninghamii rainforest, Myrtaceae and Proteaceae scrub and Sprengelia incarnata heath occurred. The development of the vegetation from alpine communities to temperate rainforest, which is near its limit at 600 m, occurred under the influence of improving climatic conditions with rapid upslope migration or local expansion of taxa during the late glacial. Temperatures were warm enough for the development of rainforest at 600 m by 10,000 BP, if not earlier. The development of a mosaic of rainforest, scrub and heath vegetation rather than extensive rainforest after 10,000 BP reflects the influence of poor soils, bad drainage and fires. Comparison with similar pollen diagrams from western Tasmania suggests that the development of pollen/vegetation associations was time transgressive with altitude during the late glacial when climatic influences and migration rates were important, and that the mosaic of vegetation communities became more complex during the Holocene because of adjustment to or control by local ecological factors.  相似文献   
19.
震后趋势决策支持系统PTDSS   总被引:2,自引:0,他引:2       下载免费PDF全文
庄昆元  黄冰树  王炜  章纯 《地震工程学报》2001,23(4):404-409,411
介绍了作者研制的“震后趋势决策支持系统PTDSS”的构成及预报效果,该系统使用模糊联想记忆FAM(Fuzzy Associative Menory)模型将神经网络与模糊系统结合起来,使之具有第2代专家系统的学习功能,系统知识库中除存有专家多年来总结的有关地震现场预报的知识外,还通过系统学习得到了一批十分有意义的,目前专家尚未总结的知识,震例检验的结果该系统有较好的预报效果。  相似文献   
20.
本文基于长期序列统计数据分析,指出战后日本城市化具有如下特征:(1)战后日本城市化可以分为四个阶段;(2)人口30万以上的大城市在城市规模体系中居于主导地位;(3)城市化在地域上高度集中,东京、大阪和名古屋三大都市圈集中了半数以上的人口;(4)都市圈之间基本不存在工作机会差别所导致的人口流动。  相似文献   
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