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排序方式: 共有387条查询结果,搜索用时 93 毫秒
381.
Wei Cao Yu Sheng Jichun Wu Jing Li Yaling Chou Jinping Li 《Environmental Earth Sciences》2017,76(20):711
Based on two-dimensional heat-conduction equations with a phase-change component, this study investigates the impact of underground mining on the permafrost environment in an opencast coal mining pit. The dynamics of the maximum thawed and freezing depths at different depths around a borehole wall are determined. The spatial distributions of these dynamics are also determined at different locations of the wall profile. The results show that (1) the maximum freezing depth tends to increase over 100 years; (2) the maximum thawed depth increases along a borehole wall over 100 years. In particular, the maximum thawed depth increases faster near the junctions of permafrost and seasonally frozen soil; (3) due to the small cross section of mining laneways, coal mining does not cause rapid increases in permafrost temperature around borehole walls. Once disturbance to permafrost around a borehole wall decreases, the once-insignificant effect of temperature will become more obvious. Underground mining does have some impacts on permafrost surrounding borehole walls, but it does not cause large areas of deformation due to thermal disturbance. 相似文献
382.
巷道围岩稳定性的判据及岩石分类 总被引:4,自引:0,他引:4
本文通过套筒致裂法测试巷道围岩应力及力学性质,并以此进行围岩稳定性分析和分类;提出了巷道围岩稳定性判据以及巷道围岩分类的原则;介绍了本稳定性分析方法在若干煤矿巷道围岩及立井井壁应力测试地点的应用。 相似文献
383.
384.
近几十年来,在入湖营养盐增加,水质持续下降,藻类生物量逐年升高及水位大幅波动下,洱海沉水植物群落演替速度加剧.2016年7月调查显示:洱海沉水植被退化严重,物种数量显著低于近期(2011年)历史水平,分布面积较有记录的历史最高水平(1980s)下降超过70%,优势物种由1960s的海菜花(Ottelia acuminata)、蓖齿眼子菜(Stuckenia pectinata)和大茨藻(Najas marina)等转变为微齿眼子菜(Potamogeton maackianus)、金鱼藻(Ceratophyllum demersum)以及苦草(Vallisneria natans).沉水植物群落在浅水区(0~2.5 m)主要遭受了浮叶植物细果野菱(Trapa maximowiezii)过度生长带来的生境胁迫,在中等水深区(2.5~4 m)面临微齿眼子菜和金鱼藻的过度生长导致的群落结构的单一化影响,而在深水区(>4 m)面临着面积萎缩的风险,这些严重抑制了沉水植物清水稳态效应的发挥.通过对比洱海典型湖湾洱滨村水域沉水植物群落结构在恢复与优化前后的变化,发现洱滨村水域各水深区间沉水植物群落各项多样性指标与恢复物种的丰度均显著提升.因此,我们总结提出了针对洱海典型富营养湖湾沉水植被恢复和管理的建议和对策,以期为后续进一步开展洱海生态系统恢复相关工作提供依据. 相似文献
385.
ZHANG Ying-bin XIANG Chen-lin CHEN Yan-long CHENG Qian-gong XIAO Li YU Peng-cheng CHANG Zhi-wang 《山地科学学报》2019,(6)
The permanent displacement of seismic slopes can be regarded as an effective criterion for stability estimation. This paper studied the characteristics of permanent displacements induced by velocity pulse-like ground motions and developed an empirical model to readily evaluate the stability of seismic slopes in a near-fault region. We identified 264 velocity pulse-like ground motions from the Next Generation Attenuation(NGA) database using the latest improved energy-based approach. All selected ground motions were rotated to the orientation of the strongest observed pulse for considering the directivity of the pulse effect, so that the most dangerous condition for slopes was considered. The results show the velocity pulse-like ground motions have a much more significant effect on permanent displacement of slopes than non-pulse-like ground motions. A regression model based on a function of peak ground velocity(PGV), peak ground acceleration(PGA) and critical acceleration(ac), was generated. A significant difference was found by comparing the presented model with classical models from literatures. This model can be used to evaluate the seismic slope stability considering the effects of nearfault pulse-like characteristics. 相似文献
386.
The impact of climate change on agriculture has received wide attention by the scientific community. This paper studies how to assess the grain yield impact of climate change, according to the climate change over a long time period in the future as predicted by a climate system model. The application of the concept of a traditional "yield impact of meteorological factor (YIMF)" or "yield impact of weather factor" to the grain yield assessment of a decadal or even a longer timescale would be suffocated at the outset because the YIMF is for studying the phenomenon on an interannual timescale, and it is difficult to distinguish between the trend caused by climate change and the one resulting from changes in non-climatic factors. Therefore, the concept of the yield impact of climatic change (YICC), which is defined as the difference in the per unit area yields (PUAY) of a grain crop under a changing and an envisaged invariant climate conditions, is presented in this paper to assess the impact of global climate change on grain yields. The climatic factor has been introduced into the renowned economic Cobb-Douglas model, yielding a quantitative assessment method of YICC using real data. The method has been tested using the historical data of Northeast China, and the results show that it has an encouraging application outlook. 相似文献
387.
Taiwanese fishing boats have been hijacked many times this year. Trouble at sea can usually be attributed to communication problems, inappropriate management and an unfair salary system. The majority of boats hijacked are high sea (long-line) fishing boats. Although fishery authorities ask the fishing boats to set up vessel monitoring systems (VMSs), this precaution has not been sufficient. There is a further need for improved management by the fishing boat owner and for an improved employment policy for seamen. The issue of maritime security is not new, but it remains a major concern and continues to be a threat to Taiwan and other countries. To date, there have been many cases of hijacking in the South China Sea. This paper analyzes the reasons for the hijackings and provides potential strategies to prevent future incidents. 相似文献