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41.
基于无人机和MODIS数据的巴丹吉林沙漠植被分布特征与动态变化研究 总被引:4,自引:2,他引:2
荒漠植被在减缓沙漠扩张、阻挡风沙入侵绿洲、维护绿洲稳定性方面具有重要意义。通过无人机搭载多光谱相机获取地面样地高分辨率NDVI数据以计算植被覆盖度,结合MODIS-NDVI数据,分析了MODIS-NDVI与无人机获取NDVI数据之间的一致性,进而建立MODIS-NDVI数据与样方植被覆盖度的空间反演模型,以研究巴丹吉林沙漠植被分布特征、动态变化及其对气温、降水的响应规律。结果表明:(1)基于无人机多光谱数据大样方植被覆盖度和MODIS-NDVI数据构建的植被覆盖度反演模型具有较高的模拟精度。(2)研究区总体植被覆盖度较低,空间上呈由东南向西北递减的趋势。(3)植被覆盖度总体呈现上升趋势,沙漠边缘的增速较沙漠内部更为明显,其中沙漠边缘增长率达1.53%/10a,而沙漠内部为0.84%/10a。沙漠边缘57.12%植被出现改善,而沙漠内部植被改善的面积约为21.26%。(4)植被生长主要受制于生长季降水量并呈现出明显的季节变化,此外植被对降水和气温的响应存在一定的滞后效应。 相似文献
42.
A coupled discrete element model for the simulation of soil and water flow through an orifice 下载免费PDF全文
Soil erosion around defective underground pipes can cause ground collapses and sinkholes in urban areas. Most of these soil erosion events are caused by fluidization of the surrounding soil with subsequent washing into defective sewer pipes. In this study, this soil erosion process is simplified as the gradual washout of sand particles mixed with water through an orifice. The discrete element method is used to simulate the large deformation behavior of the sand particles, and the Darcy fluid model is coupled with this approach to simulate fluid flow through porous sand media. A coupled 3D discrete element model is developed and implemented based on this scheme. To simulate previous experiments using this coupled model considering the current computing capacity, we incorporated a ‘supply layer’ to study the continuous erosion process. The coupled model can predict the erosion flow rates of sand and water and the shape of erosion void. Thus, the model can be used as an effective and efficient tool to investigate the soil erosion process around defective pipes. Copyright © 2017 John Wiley & Sons, Ltd. 相似文献
43.
钨、锡流-熔分配实验结果及其矿床成因意义 总被引:4,自引:1,他引:4
本文用实验确定了钨、锡在成分不同的花岗质熔体相与共存水热流体相的流-熔分配系数(D_(Me)~(V/L))及其与介质溶液(NaF,KF,HF,NaCl等水溶液)摩尔浓度间的函数关系。实验结果表明,钨、锡的分配行为明显不同。在相同条件下,随体系的不同,D_W~(V/L)比D_(Sn)~(V/L)大几倍至二十倍。钠和钾对钨、锡的流-熔分配行为的影响基本相同,而氟和氯对钨、锡的分配行为的影响相差甚远,花岗质熔体的主成分对D_W~(V/L)和D_(Sn)~(V/L)有复杂的影响。利用这些结果探讨与花岗岩有关的钨、锡矿床的成矿机理,得出了一些与前人不同的新认识。 相似文献
44.
引入时间序列分析进行危岩体监测数据的处理,建立了危岩体变形的动态模型,取得了较好的拟会与预报精度。 相似文献
45.
46.
Eugene Yee R. Chan P. R. Kosteniuk G. M. Chandler C. A. Biltoft J. F. Bowers 《Boundary-Layer Meteorology》1995,73(1-2):53-90
The statistics of level crossings and local extremes in concentration fluctuations in plumes dispersing in the atmosphere have been investigated. A set of concentration fluctuation tracer experiments has been utilized to measure the statistical propertics of the upcrossing interval (inter-arrival time between consecutive concentration bursts), excursion duration (persistence or width of concentration bursts), and concentration amplitude (difference between the maximum and minimum concentrations between successive upcrossings) with respect to a range of concentration crossing levels. In particular, the effect of downwind distance and atmospheric stratification on the level-crossing statistics has been studied in detail. It is shown that the effect of increasing atmospheric stability on level-crossing statistics is similar to the effect of increasing distance from the source in the sense that level-crossing statistics of concentration fluctuations in stable stratification resemble those in neutral stratification, but at a greater downwind distance. It is also found that the distribution of the interval between consecutive upcrossings of a concentration level, as well as the duration of an excursion across a concentration level, can be approximated by a lognormal distribution, whereas the distribution of the concentration amplitude is best characterized by a gamma distribution. Some implications of these results for the modeling of level-crossing statistics of concentration fluctuations are discussed. 相似文献
47.
I. Iwasaki T. Ozawa M. Yoshida T. Katsura Chan Kuk Kim M. Aoyagi Y. Yoshiike 《Bulletin of Volcanology》1982,45(2):81-85
Many examples of mixed magmas in banded lavas have been studied. Another type of mixed magmas or inhomogeneity of magma reservoir found in the 1962 lava flows of Miyake-zima Volcano erupted from fissures is reported. 相似文献
48.
The counter-current gas-fluidized cascade (CFC) is a novel pneumatic device for separating mixed granular solids according to specific gravity. The possible utility of the CFC for beneficiation of coal in all size-ranges is presently under investigation, and in this paper some results are reported on pyrite beneficiation of synthetic pyrite-coal mixtures, and also on pyrite and ash beneficiation of as-received coal. The (geometric) mean particle size, by weight, of the coal used with added pyrite was 153 μm, and of the natural coal 233 μm. Preliminary results on the concentration of pyrite and ash in the reject streams indicate that CFC has some potential of being a simple and low-cost device for coal beneficiation. 相似文献
49.
D.J. Henry I.D.R. Mackinnon I. Chan A. Navrotsky 《Geochimica et cosmochimica acta》1983,47(2):277-282
A calorimetric study has shown that glasses along the albite-diopside join in the system albiteanorthite-diopside have positive enthalpies of mixing. Thermodynamic calculations based on these data describe a nearly symmetric, metastable, subliquidus irascibility gap along the join with a critical temperature at 910 K. The existence of the miscibility gap was tested experimentally by annealing an Ab50Di50 glass at 748 K and 823 K. Annealed glasses were examined by optical microscopy and by scanning and transmission electron microscopy. The glasses showed morphological and chemical features consistent with unmixing of two glass phases. The apparent mechanism of phase separation involves initial spinodal decomposition followed by coarsening to produce 0.1 μm–0.3 μm spherical glass phases. 相似文献
50.
Liu Qingsheng Department of Geophysics China University of Geosciences Wuhan The State Key Laboratory of Oil/Gas Reservoir Geology Exploitation of China Institute of Chengdu Technology Chengdu Wu Qifan Li Haixia Department o 《中国地质大学学报(英文版)》2001,12(2)
INTRODUCTIONThepresenceofmagneticanomaliesoveroilandgasfieldshasbeenknownforseveraldecades,butitisonlyinrecentyearsthatthephenomenonhasbeencriticallyinvestigated .Themag neticcharacteristicsofsoilandsedimentarecloselyrelatedtosomegeochemicalprocesses,s… 相似文献