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971.
来自社交网络的时空大数据具有海量和高动态的特性,有效选择时空数据进行聚焦挖掘分析至关重要。以微博位置签到数据为例,首先,对时空大数据空间聚类挖掘的有效选择问题进行了研究,针对社交网络时空数据不确定性问题,提出了时空大数据针对聚类挖掘的有效选择方法。聚类挖掘有效选择方法提出从空间、时间或属性等维度对时空大数据进行分割。然后,对分割得到的数据集进行空间探索分析(exploratory spatial data analysis,ESDA),得到具有聚类挖掘潜力的数据集。最后,以武汉市微博位置签到数据进行商圈热点探测为例,对提出的社交网络时空大数据聚类挖掘有效选择方法进行验证。结果表明,有效选择方法可以得到挖掘效率和精准性更高的时空数据集。 相似文献
972.
Summary. Results from several recent studies suggest that there are lateral heterogeneities of up to a few per cent in the lowermost 150–200 km of the mantle (Bullen's D " region). Inferred anomaly sizes span the range from less than 50 km to greater than 1000 km.
In this study differences in the velocity structure among regions at the base of the mantle were inferred from an analysis of amplitude ratios of PKPAB and PKPDF for given earthquake-station pairs at distances greater than 155° (Sacks, Snoke & Beach). We distinguish two kinds of regions: A (anomalous) regions in which the mean, median and spread in AB/DF amplitude ratios are significantly higher (> 50 per cent) than for a reference radial earth model and N (normal) regions in which the distribution of the amplitude ratios is as expected.
The AB branch has near-grazing incidence to the core and therefore maximum sensitivity to velocity structure compared to the near-normal incident DF phases. Using an iterative, forward-modelling approach, we have determined general characteristics of the velocity structure for regions at the base of the mantle which can produce amplitude-ratio distributions similar to those for an A region. Agreement between model and data is obtained over the period range from 0.5 s to greater than 10 s using a laterally heterogeneous model for the D " region. the model consists of cells which are 200 km in lateral extent with velocity variations of up to ±1 per cent. This structure is modulated by a region-wide (1000km) perturbation which increases smoothly from zero at the edges of the region to a negative 1 per cent at the centre. Small cells (∼40 km) cannot produce anomalously large amplitude, long-period AB arrivals, and larger cells (∼1000km) cannot match the observed scatter. the ∼200 km scale anomalies could be small-scale convection cells confined to the D " region. 相似文献
In this study differences in the velocity structure among regions at the base of the mantle were inferred from an analysis of amplitude ratios of PKPAB and PKPDF for given earthquake-station pairs at distances greater than 155° (Sacks, Snoke & Beach). We distinguish two kinds of regions: A (anomalous) regions in which the mean, median and spread in AB/DF amplitude ratios are significantly higher (> 50 per cent) than for a reference radial earth model and N (normal) regions in which the distribution of the amplitude ratios is as expected.
The AB branch has near-grazing incidence to the core and therefore maximum sensitivity to velocity structure compared to the near-normal incident DF phases. Using an iterative, forward-modelling approach, we have determined general characteristics of the velocity structure for regions at the base of the mantle which can produce amplitude-ratio distributions similar to those for an A region. Agreement between model and data is obtained over the period range from 0.5 s to greater than 10 s using a laterally heterogeneous model for the D " region. the model consists of cells which are 200 km in lateral extent with velocity variations of up to ±1 per cent. This structure is modulated by a region-wide (1000km) perturbation which increases smoothly from zero at the edges of the region to a negative 1 per cent at the centre. Small cells (∼40 km) cannot produce anomalously large amplitude, long-period AB arrivals, and larger cells (∼1000km) cannot match the observed scatter. the ∼200 km scale anomalies could be small-scale convection cells confined to the D " region. 相似文献
973.
河流沉积单元分析与储层宏观非均质性 总被引:11,自引:0,他引:11
沉积单元分析方法是详细解剖陆相盆地沉积过程和研究储集体空间变化的有效途径。本文以胜利油田沾化凹陷的孤东和孤岛油田馆陶组上段为例分析了河流砂体储层非均质性的变化规律。该段河流沉积分别由11种沉积单元组成了3种类型的河流沉积,其中河道的加积沉积单元和河道边缘砂体是主要的储层类型,河床滞留沉积和决口扇砂体以较低的渗透率为特征,储层性能较差。馆陶组上段自下而上,由于可容纳空间和沉积物比值的增大,致使槽状交错层组和层系厚度向上增大,孔隙度、渗透率、保存下来的河道宽度、连续性和连通程度降低,而底形多样性、相的分异性、相的保存程度和非均质性增加。由于可容纳空间/沉积物补给(A/S)比值变小,致使馆陶组上段中部的河流砂体储层最为发育。综合研究表明,馆陶组上段河流沉积的储层宏观、微观非均质性较强,主要受控于沉积单元的分布和可容纳空间的变化等因素。 相似文献
974.
在陆面过程方案中考虑精细的水模型有助于改善对区域水及气候的模拟。建立了一个考虑降水及入诊空间非均匀性的水模型,并将其并入陆面过程方案BATS中。通过区域气候模式耦合模拟试验,得到如下主要结论:陆面水的模拟对降水及入渗空间非均匀性的考虑非常敏感;考虑入渗非均匀性后,提高了径流系数,这与湿润地区水分平衡的观测结果更一致;入渗非均匀参数化方案的引入对区域水及气候模拟的影响比降水非均匀参数化方案的引入要大;不透水面积在区域中的考虑所揭示的特征与我国北方干旱化趋势是一致的。 相似文献
975.
Wells are seldom modeled explicitly in large scale finite difference reservoir simulations. Instead, the well is coupled to the reservoir through the use of a well index, which relates wellbore flow rate and pressure to grid block quantities. The use of an accurate well index is essential for the detailed modeling of nonconventional wells; i.e., wells with an arbitrary trajectory or multiple branches. The determination of a well index for such problems is complicated, particularly when the simulation grid is irregular or unstructured. In this work, a general framework for the calculation of accurate well indices for general nonconventional wells on arbitrary grids is presented and applied. The method entails the use of an accurate semianalytical well model based on Green's functions as a reference single phase flow solution. This result is coupled with a finite difference calculation to provide an accurate well index for each grid block containing a well segment. The method is demonstrated on a number of homogeneous example cases involving deviated, horizontal and multilateral wells oriented skew to the grid. Both Cartesian and globally unstructured multiblock grids are considered. In all these cases, the method is shown to provide results that are considerably more accurate compared to results using standard procedures. The method is also applied to heterogeneous problems involving horizontal wells, where it is shown to be capable of approximating the effects of subgrid heterogeneity in coarse finite difference models. 相似文献
976.
977.
Koen De Ridder 《Boundary-Layer Meteorology》2003,109(1):49-57
A method is described to infer the horizontal scale of roughness variations from land-use maps, for use in flux aggregation schemes designed to account for sub-grid scale terrain heterogeneity in numerical models of the atmosphere. Based on simple statistical-geometrical considerations, it is shown that this horizontal scale is inversely proportional to edge density, which can be readily derived from high-resolution land-use maps. The method is demonstrated for a highly heterogeneous landscape in northern Belgium, the resulting length scale values approximately ranging between 200 and 1500 m. Finally, the extension towards satellite imagery and coarse land-use data is discussed. 相似文献
978.
979.
Foum Tatahouine is one of the rare meteorites that allow studying weathering effects since their fall on Earth. The comparison between clasts collected the very day of the fall (1931) and in 1994 showed some chemical modifications. We report data obtained on samples collected in 2000. The purpose of this study is: (1) to define (REE, Sr isotopes) the terrestrial weathering origin that is to be found in soil carbonates, (2) to show (Sr, Rb, REE) that the weathering effects are small on centimetre-sized samples, and (3) to emphasise (HREE) Foum Tatahouine samples heterogeneity. To cite this article: Y. Bentahila et al., C. R. Geoscience 334 (2002) 267–272. 相似文献
980.