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201.
基于西安地裂缝成因、基本特征和未来活动趋势分析,通过几何缩比为1:5的地裂缝活动模型试验和地裂缝活动对盾构隧道影响的数值模拟计算,研究了西安地铁2号线隧道正交穿越地裂缝带的设防参数。通过分析地裂缝年平均活动速率和历史最大活动量,确定了与地铁2号线相交的各条地裂缝的最大垂直位移量的预测值和设计建议值。模型试验和数值模拟结果表明,正交条件下地铁隧道在地裂缝活动地段的设防宽度为60 m,即上盘为35 m,下盘为25 m;沿隧道纵向地裂缝两侧地层变形规律呈现台阶状突变变形,隧道纵向设计可将上盘视为整体下降来考虑;地铁隧道穿越地裂缝带必须分段设缝以适应地裂缝的变形,其分段长度在地裂缝主影响区按10 m进行设防,在一般影响区可按10~15 m进行分段设防。研究结果可为地铁隧道穿越地裂缝带的结构设计提供参考。 相似文献
202.
Flocculation has an important impact on particle trapping in estuarine turbidity maximum (ETM) through associated increases in particle settling velocity. To quantify the importance of the flocculation processes, a size-resolved flocculation model is implemented into an ocean circulation model to simulate fine-grained particle trapping in an ETM. The model resolves the particle size from robust small flocs, about 30 μm, to very large flocs, over 1000 μm. An idealized two-dimensional model study is performed to simulate along-channel variations of suspended sediment concentrations driven by gravitational circulation and tidal currents. The results indicate that the flocculation processes play a key role in generating strong tidal asymmetrical variations in suspended sediment concentration and particle trapping. Comparison with observations suggests that the flocculation model produces realistic characteristics of an ETM. 相似文献
203.
遥感图像分类一直是遥感研究领域的核心问题。然而,传统遥感分类方法在地物复杂地区不能取得满意效果。不但分类精度不够理想,分类灵活性也存在不足。本文尝试引入证据推理"软"分类方法,选择小兴安岭山区一景TM遥感图像,基于用户知识和经验,通过人机交互处理,以累计信任度(CBV)最大为划分像元归类的原则得到证据推理方法的分类图像。结果表明,整体分类精度从最大似然法的78.74%提高到82.28%,kappa系数从0.67提高到0.71。但该方法对于裸地分类精度不高,通过人为设定各类别CBV阈值的方法,获得了人为干预的证据推理方法分类图,其整体分类精度达到了87.80%,kappa系数也达到了0.81,所有类别的生产者和用户精度相比于最大似然法都有提高。研究表明,证据推理方法在遥感分类精度和分类灵活性方面都具有优越性。 相似文献
204.
205.
2013年7月10日发生的四川省都江堰市中兴镇三溪村五里坡滑坡-碎屑流,属于典型的降雨型高位斜向层状岩质滑坡-碎屑流灾害。在前人研究成果梳理和进一步野外调查的基础上,分析总结了五里坡滑坡-碎屑流的成因及演化模式,并对五里坡高位滑坡在降雨作用下的后缘裂隙扩展判据和滑坡启动判据进行了定量计算。研究表明,五里坡滑坡的演化模式为后缘拉张裂隙形成→降雨作用下裂缝开始扩展→动、静水压力联合作用下斜坡沿泥质软弱层滑动→后缘拉裂槽形成→“7?10”强降雨诱发滑坡复活→滑体前缘临空崩落、加速→崩滑体沿沟谷铲刮、运移→堆积停止。从力学角度推导了前期降雨作用下滑体后缘裂缝自动扩展的最小深度、滑坡失稳的临界水头高度和临界降雨强度的计算公式,得出充满水的后缘裂缝在静水压力作用下开始自行扩展的临界深度为11.3 m;后缘裂隙贯通至滑带后,当五里坡斜坡体在后缘裂缝水头高度达到9.8 m时滑坡处于启动的临界状态。 相似文献
206.
Knowledge of the spatial and temporal variations in Alpine glaciations is essential for reconstructing the regional and global timing of ice ages. This study investigates glacial deposits at the mouth of the Muksu catchment in the northern Pamir using 10Be surface-exposure age dating. We sampled boulders from the furthest downstream recessional moraine (20 samples) and five lateral moraines (41 samples) near the former terminus of the Fedchenko Glacier, the longest (∼72 km) present-day Alpine glacier of the Pamir. After the identification of outliers, the boulder population of the recessional moraine yielded a mean exposure age of 17.5 ± 1.9 ka. The maximum exposure age of the lateral moraines, collected ∼5 km up-valley of the recessional moraine, is 18.2 ± 1.7 ka. The boulder ages reflect glacial deposition during the Last Glacial Maximum (Marine Isotope Stage 2) in the region; they are in accordance with published glacial deposition ages in the western Tian Shan. 相似文献
207.
对比分析了太平洋(Site 806)、大西洋(Site 664)和加勒比海地区(Site 999)末次冰期最盛期和全新世钻孔顶部不同尺寸大小的浮游有孔虫Globigerinoides sacculifer(500~600μm和300~355μm)和Globi-gerinoides ruber(300~355μm和250~300μm)的硼同位素组分变化,发现个体相对较小的有孔虫样品由于受到样品量以及样品前处理过程的影响,其硼同位素在末次冰期最盛期出现异常,浮游有孔虫硼同位素分析,尤其是冰期-间冰期时间尺度上的硼同位素分析,适合用个体相对较大的有孔虫。末次冰期最盛期太平洋和加勒比海地区溶解作用可能加强,其G.sacculifer的硼同位素偏低,但G.ruber的硼同位素不受溶解作用的影响,能够反映末次冰期海水pH值的变化。三个钻孔末次冰期最盛期G.ruber的硼同位素比全新世的硼同位素平均高(1.3±1.2)‰(2s.e.),与理论预测值1.6‰一致。 相似文献
208.
半参数p-范极大似然回归 总被引:2,自引:0,他引:2
应用核权函数,在观测为误差单峰、对称的情况下,得到了一元p-范分布的半参数模型的计算公式.详细推导了p已知时一元p-范分布极大似然方程的解算公式,将半参数回归模型应用到极大似然平差的参数估计理论中,得到了一个比较好的算法.最后,构造了两个模拟平差问题,说明了此方法的优越性. 相似文献
209.
L. Sedda P.M. Atkinson M.R. Filigheddu G. Cotzia S. Dettori 《International journal of geographical information science》2013,27(7):1083-1096
Cork oak is one of the most valuable natural forest genera in the Mediterranean basin. Modelling cork oak growth has been a challenge for foresters in recent years because of strong site and genetic influences, below-ground competition, management regimes and age effects. Because cork productivity is related to forest height, which is, in turn, related directly with site characteristics, an increase in the accuracy of height prediction implies improved productivity estimation. A Bayesian maximum entropy (BME) geostatistical model was applied to characterize the space–time pattern of height of young cork oak in a forest stand from central Sardinia in the years 2000, 2002, 2003, 2006 and 2008. Cork oak height maps were produced for each of the 5 years. The main goals were to analyse and interpret through time (i) the changes in spatial correlation and (ii) the changes in spatial distribution of cork oak height. The plantation was characterized by an increasing spatial dependence through time, whereas the temporal range was 2 years. Cork oak height was significantly correlated with wind speed (reduced by a neighbouring forest) in all the years implying a single trend. The correlations were larger for 2006 and 2008 than for previous years. Three other environmental variables (shade, elevation and slope) were less significant and their influence restricted to 2 years only. This research has several implications for the management of cork oak in the young phase. 相似文献
210.
Approximation of Gaussian spatial autoregressive models for massive regular square tessellation data
Daniel A. Griffith 《International journal of geographical information science》2013,27(12):2143-2173
Most of the literature to date proposes approximations to the determinant of a positive definite n × n spatial covariance matrix (the Jacobian term) for Gaussian spatial autoregressive models that fail to support the analysis of massive georeferenced data sets. This paper briefly surveys this literature, recalls and refines much simpler Jacobian approximations, presents selected eigenvalue estimation techniques, summarizes validation results (for estimated eigenvalues, Jacobian approximations, and estimation of a spatial autocorrelation parameter), and illustrates the estimation of the spatial autocorrelation parameter in a spatial autoregressive model specification for cases as large as n = 37,214,101. The principal contribution of this paper is to the implementation of spatial autoregressive model specifications for any size of georeferenced data set. Its specific additions to the literature include (1) new, more efficient estimation algorithms; (2) an approximation of the Jacobian term for remotely sensed data forming incomplete rectangular regions; (3) issues of inference; and (4) timing results. 相似文献