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????????????????????????????в??????????????????У??????????????о??????????????????????仯??????????????????????????????в??????????????仯??????????£??????????????????????????????????????????????????ζ????????????????????????????????????????????ж???????????????????- ?????????????????????????????????????????????????????????? 相似文献
374.
Permafrost temperatures from the surface down to about 9 m from 3 bore holes distributed around Kangiqsualujjuaq village on the coast of Hudson Strait were recorded and analyzed for the period 1989-1998. The results indicate that the permafrost is getting warm along the southern shore of Hudson Strait from 1993 to 1998 though it became cooling for the past 40 a or more. The observed trend in the order of 0. 098℃/a at the 9 m depth is consistent with the long-term regional warming observed in air temperatures. It also coincides with that all the global circulation models predict an enhanced warming in polar regions associated with the increase in concentration of greenhouse gases in the atmosphere. 相似文献
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介绍了菏泽科普馆布展的主题、定位和展览教育、展品配置的原则,综述了菏泽科普馆分类布展情况及达到的效果,总结了科普馆日常开馆和管理情况,为气象部门建设和管理综合类科普馆提供借鉴。 相似文献
377.
Guang-an Zhu Lin-ming Dou Chang-bin Wang Jing Li Wu Cai Zi-wei Ding 《Arabian Journal of Geosciences》2017,10(24):549
A systematic approach to numerically simulating an island longwall panel operation is proposed: it aims to investigate the evolution of overlying strata, static stress and displacement response and dynamic load arising from roof fracturing and fault slip. The results show that due to a small gob width (70 m) on both sides, the evolution height of overlying strata is limited, i.e. the heights of the cave-in zone and fracture zone are 30.98 and 66.91 m, respectively. The numerical model matches the theoretical analysis and field observations. Dynamic analysis reveals that the envelope of mine tremors confirms the good correlation with the evolution of the fracture zone. As the mining panel is far from the fault, fault slip does not occur; at this time, the dynamic load mainly comes from roof fracturing. When mining activities approach the fault, the calculation of the dynamic response of fault slip is performed over the area where the increase of relative shear displacement during dynamic analysis exceeds 0.05 m and where the shear stress along the fault decreases. It is shown that during the initial stage of the mining process, and in a square mining panel, fault slip is more likely to occur, leading to strong tremors and rock bursts, which become more notable in the later stages of the mining of the island panel. 相似文献
378.
波浪引起的海床不稳定性是海洋工程中需要考虑的重要问题。在对现有波致海床滑动稳定性计算方法进行分析的基础上,提出了一种波致海床滑动稳定性计算的全应力状态法,将其与现有计算方法进行了对比分析,并进一步研究了波致砂土海床和软土海床的滑动失稳特征。结果分析表明,全应力状态法在波致海床滑动稳定性分析中具有较好的适用性。对于砂土海床,其滑动稳定性受饱和度的影响较大,且当海床计算厚度约为0.2倍波长时对应的滑动深度最大。波浪作用下坡度不超过2°的均质软土海床,其最危险滑动面的位置仅与波长有关,其滑动深度约为0.21倍波长,滑动面半弦长约为0.33倍波长;海床表面的波压力数值只影响其安全系数的大小,而不影响其滑动深度。 相似文献
379.
Yaomin Zheng Zhenguo Niu Peng Gong Mengna Li Lile Hu Lei Wang Yuxiang Yang Haijun Gu Jinrong Mu Gejia Dou Hui Xue Lin Wang Hua Li Gejie Dou Zhicairang Dang 《中国地理科学(英文版)》2017,27(5):784-799
Accurate wetland delineation is the basis of wetland definition and mapping, and is of great importance for wetland management and research. The Zoigê Plateau on the Qinghai-Tibet Plateau was used as a research site for research on alpine wetland delineation. Several studies have analyzed the spatiotemporal pattern and dynamics of these alpine wetlands, but none have addressed the issues of wetland boundaries. The objective of this work was to discriminate the upper boundaries of alpine wetlands by coupling ecological methods and satellite observations. The combination of Landsat 8 images and supervised classification was an effective method for rapid identification of alpine wetlands in the Zoigê Plateau. Wet meadow was relatively stable compared with hydric soils and wetland hydrology and could be used as a primary indicator for discriminating the upper boundaries of alpine wetlands. A slope of less than 4.5° could be used as the threshold value for wetland delineation. The normalized difference vegetation index(NDVI) in 434 field sites showed that a threshold value of 0.3 could distinguish grasslands from emergent marsh and wet meadow in September. The median normalized difference water index(NDWI) of emergent marsh remained more stable than that of wet meadow and grasslands during the period from September until July of the following year. The index of mean density in wet meadow zones was higher than the emergent and upland zones. Over twice the number of species occurred in the wet meadow zone compared with the emergent zone, and close to the value of upland zone. Alpine wetlands in the three reserves in 2014 covered 1175.19 km2 with a classification accuracy of 75.6%. The combination of ecological methods and remote sensing technology will play an important role in wetland delineation at medium and small scales. The correct differentiation between wet meadow and grasslands is the key to improving the accuracy of future wetland delineation. 相似文献
380.
基于大气辐射传输理论分别建立Ku波段和C波段的降雨模型,模拟热带气旋降雨区洋面的雷达回波并反演了洋面10 m风场,用于研究降雨对测风的影响以及风云三号双频风场雷达 (WFR) 的测风能力。分析表明:回波的衰减或增强取决于降雨衰减项和后向散射项的相对大小;热带气旋的降雨使反演风速偏小,风向精度降低,Ku波段相对于C波段更易受影响,在高风速 (超过30 m·s-1) 条件下,可达5~20 m·s-1的负风速偏差。反演结果表明:双频反演的新方法能够结合Ku波段与C波段的优势,双频最大似然估计 (MLE) 方法在分辨率上优于C波段单频反演,相对Ku单频反演能降低降雨对测风的衰减作用,结合双频MLE方法和C波段单频反演优势的分区反演方法可以显著减小降雨偏差,提高风速反演精度,在有风云三号湿度计同步观测的条件下,是提高热带气旋降雨区测风精度的有效手段。 相似文献