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101.
Min Deng Xuexi Yang Jianya Gong Yang Liu Huimin Liu 《International journal of geographical information science》2019,33(3):466-488
Existing spatial clustering methods primarily focus on points distributed in planar space. However, occurrence locations and background processes of most human mobility events within cities are constrained by the road network space. Here we describe a density-based clustering approach for objectively detecting clusters in network-constrained point events. First, the network-constrained Delaunay triangulation is constructed to facilitate the measurement of network distances between points. Then, a combination of network kernel density estimation and potential entropy is executed to determine the optimal neighbourhood size. Furthermore, all network-constrained events are tested under a null hypothesis to statistically identify core points with significantly high densities. Finally, spatial clusters can be formed by expanding from the identified core points. Experimental comparisons performed on the origin and destination points of taxis in Beijing demonstrate that the proposed method can ascertain network-constrained clusters precisely and significantly. The resulting time-dependent patterns of clusters will be informative for taxi route selections in the future. 相似文献
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ABSTRACTThe size and spatial distribution of loess slides are important for estimating the yield of eroded materials and determining the landslide risk. While previous studies have investigated landslide size distributions, the spatial distribution pattern of landslides at different spatial scales is poorly understood. The results indicate that the loess slide distribution exhibits a power-law scaling across a range of the size distribution. The mean landslide size and size distribution in the different geomorphic types are different. The double Pareto and inverse gamma functions can coincide well with the empirical probability distribution of the loess slide areas and can quantitatively reveal the rollover location, maximum probability, and scaling exponents. The frequency of loess slides increases with mean monthly precipitation. Moreover, point distance analysis showed that > 80% of landslides are located < 3 km from other loess slides. We found that the loess slides at the two study sites (Zhidan and Luochuan County) in northern Shaanxi Province, China show a significant clustered distribution. Furthermore, analysis results of the correlated fractal dimension show that the landslides exhibit a dispersed distribution at smaller spatial scales and a clustered distribution at larger spatial scales. 相似文献
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Factors controlling typhoons and storm rain on the Korean Peninsula during the Little Ice Age 总被引:1,自引:0,他引:1
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Natural Resources Research - Coal and gas outbursts often result in a large number of casualties and economic losses. Its complex processes involve the multi-field coupling of gas flow, coal... 相似文献
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107.
Nannochloropsis oculata CS179, a unicellular marine microalga, is rich in long-chain polyunsaturated fatty acids (LCPUFAs). Elongase and desaturase
play a key role in the biosynthesis of PUFAs. A new elongase gene, which encodes 322 amino acids, was identified via RT-PCR and 5′ and 3′ RACE. The sequence of the elongase gene was blast-searched in the NCBI GenBank and showed a similarity
to those of the cryptosporidium. But the NJ-tree revealed that the N. oculata CS179 elongase clustered with those of the microalgae Phaeodactylum tricornutum, Ostreococcus tauri and Thalassiosira pseudonana. 相似文献
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全国第二次土地调查数据库利用以后,城市建设用地审批、大型的线状用地、土地复垦、矿山治理等工程的前期可研及预审工作等基本都以二调数据为基础数据。将正确的用地红线用ArcGis软件处理成面文件(.Shp),然后把处理后的.shp文件复制到二调数据库里的KCDJ层里。再使用农村土地调查专用软件导出各级用地面积汇总表。通过文中介绍的方法,可以实现快速、准确的制作指定范围的各种地类面积表。 相似文献
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A postbuckling analysis is presented for a shear deformable anisotropic laminated cylindrical shell with stiffener of finite length subjected to axial compression. The material of each layer of the shell is assumed to be linearly elastic, anisotropic and fiber-reinforced. The governing equations are based on a higher order shear deformation shell theory with von Kármán-Donnell-type of kinematic nonlinearity and including the extension/twist, extension/flexural and flexural/twist couplings. The ‘smeared stiffener’ approach is adopted for the beam stiffeners. This arrangement allows the beam stiffeners to be assembled directly into the global stiffness matrix. The nonlinear prebuckling deformations and initial geometric imperfections of the shell are both taken into account. A singular perturbation technique is employed to determine the buckling loads and postbuckling equilibrium paths. The numerical illustrations concern the postbuckling response of perfect and imperfect, grid, axial, ring stiffened, and unstiffened shells. The results confirm that there exists a compressive stress along with an associate shear stress and twisting when the anisotropic shell is subjected to axial compression. The postbuckling equilibrium path is unstable for the moderately thick cylindrical shell under axial compression and the stiffened shell structure is imperfection-sensitive. 相似文献