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31.
Reflection and transmission of seismic waves at an interface betwen two saturated soils 总被引:2,自引:0,他引:2
ReflectionandtransmisionofseismicwavesataninterfacebetwentwosaturatedsoilsJUNYANG(杨峻)SHIMINGWU(吴世明)ZhejiangUniversity,Hangz... 相似文献
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Crustacean zooplankton distribution patterns and their biomass as related to trophic indicators of 29 shallow subtropical lakes 总被引:3,自引:0,他引:3
A comparative limnological study was carried out to present a snapshot of crustacean zooplankton communities and their relations to environmental factors to test whether there is a consistent relationship between crustacean biomass and trophic indicators among lake groups with similar trophic conditions. The study lakes showed a wide range of trophic status, with total phosphorus (TP) ranging from 0.008 to 1.448 mg L−1, and chlorophyll a from 0.7 to 146.1 μg L−1, respectively. About 38 species of Crustacea were found, of which Cladocera were represented by 25 taxa (20 genera), and Copepoda by 13 taxa (11 genera). The most common and dominant species were Bosmina coregoni, Moina micrura, Diaphanosoma brachyurum, Cyclops vicinus, Thermocyclops taihokuensis, Mesocyclops notius and Sinocalanus dorrii. Daphnia was rare in abundance. Canonical correspondence analysis showed that except for four species (D. hyalina, S. dorrii, C. vicinus and M. micrura), almost all the dominant species had the same preference for environmental factors. Temperature, predatory cyclopoids and planktivorous fishes seem to be the key factors determining species distribution. TP was a relatively better trophic indicator than chlorophyll a to predict crustacean biomass. Within the three groups of lakes, however, there was no consistent relationship between crustacean biomass and trophic indicators. The possible reason might be that top-down and bottom-up control on crustaceans vary with lake trophic state. The lack of significant negative correlation between crustacean biomass and chlorophyll a suggests that there was little control of phytoplankton biomass by macrozooplankton in these shallow subtropical lakes. 相似文献
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地震前兆综合危险度是以系统论为基础的一种综合地震预报的新方法。利用山东省每年年底的地震会商报告给出的地震前兆异常,而不是取震后的震例总结或论文给出的异常,通过“专家系统”的思想,对每一异常事件进行综合评估,计算出无量纲的、归一化的地震前兆综合危险度,分析了1995年9月20日山东苍山52Ms级地震前综合危险度的变化特征。震前综合危险度出现了一次明显的高值异常变化,震后危险度很快下降恢复到正常水平。 相似文献
36.
Optimization of concurrent mining and reclamation plans for single coal seam: a case study in northern Anhui, China 总被引:5,自引:0,他引:5
The extraction of underground ore body inevitably causes a large amount of land subsidence. Current reclamation technologies in China mainly focus on stable subsided land, which means most of the affected lands are submerged into water because of the high groundwater table in some areas, leading to the loss of soils and inefficient reclamation. Therefore, a new technology for reclaiming unstable subsiding land is being studied for restoring farmland as much as possible, based on a case study in northern Anhui, China. In consideration of the mining plan, subsidence processes in various stages were analyzed and some related factors such as vertical subsidence, post-mining slope, water area, and land use condition were also simulated. Due to mining activities, useful farmland has gradually decreased to merely 14.4 % of the pre-mining area. In this study, the following stages were modeled from pre-mining to post-mining: (1) percentage of farmland was 100 % in stage (a) (pre-mining), (2) 72.5 % in stage (b), (3) 67.3 % in stage (c), and (4) 14.4 % in stage (d) (post-mining). The results show that 86.6 % of cultivated land was submerged into water and lost its capacity for cultivation after coal mining. Reclamation plans for stages (b), (c), and (d) were made by a traditional reclamation method called “Digging Deep to Fill Shallow”. Based on scenario simulation of reclamation, the farmland reclamation percentages were improved to 78.3, 73.3, and 40.70 %, respectively. Taking the percentage of reclaimed farmland as the preferred standard, concurrent mining and reclamation for stage (b) and (c) could increase farmland reclamation percentages to 37.6 and 32.6 %, respectively, compared with the farmland reclamation percentage of post-mining [reclaiming the land in stage (d)]. The results reveal that optimum reclamation time should be at stage (b). Therefore, under current technical conditions, concurrent mining and reclamation could enhance the quantity of cultivated land and provide better land protection and food security in the mined areas with high groundwater table. 相似文献
37.
Ge Tongming Liu Jian Fan Limin Zhong Shuixian Wu Nengyou Hsu Vindell A. Baksi 《《地质学报》英文版》1995,8(2):221-233
Abstract This paper discusses the Cretaceous-Tertiary magnetic polarity sequence of the the Hengyang Basin on the basis of magnetostratigraphic study. The age of each stratigraphic unit has been determined with the magnetic polarity time scale combined with <sup>39</sup>Ar/<sup>40</sup>Ar dating, thus providing evidence for determining the geological ages of different formations. The authors assign the age of the Dongjing Formation of the Hengyang Basin to Early Cretaceous, the Shenhuangshan Formation to Early-Late Cretaceous, the Daijiaping Formation to Late Cretaceous, and the Dongtang and Xialiushi formations to Palaeocene. 相似文献
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The pyroxenite xenoliths in the volcanic rocks of Hoh Xil consist of clinopyroxenes and orthopyroxenes. The mineral composition of these pyroxenes is similar to that of mantle xenoliths including peridotite and pyroxenite from China and abroad, and different from that of granulites. The pyroxenes formed at 1101–1400°C (averaging 1250°C) and under 30–60 kb (averaging 46 kb). We deduced that the magma was derived from the mantle at a depth of more than 150 km, which fits in with the geophysical conclusion that the low-velocity layer existed in the mantle under 150 km.
相似文献40.
Zuo Qihua Yang Zhengji .
Senior Engieer River Harbour Department Nanjing Hydraulic Research Institute Nanjing 《中国海洋工程》1996,(3)
- The variation of the amplitude of waves with varying incident angles when waves propagate through a typical approach channel is discussed by a numerical calculation method, the result of which shows that the influence of the channel on wave propagation is obvious. When the wave propagation direction is in coincidence with the channel axis, the wave amplitude ratio will decrease with the increase of propagation distance. When the incident angle is 15 - 30 , there appears an area of larger wave amplitude ratio on the side slope facing the waves, but at the another side, the wave amplitude ratio is generally small, indicating that the channel has a shielding effect. When waves propagate across the channel perpendicularly, the wave amplitude ratio can be calculated with the shallow water coefficient. 相似文献