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Worldwide Marine Transportation Network: Efficiency and Container Throughput 总被引:2,自引:0,他引:2 下载免费PDF全文
Through empirical analysis of the global structure of the Worldwide Marine Transportation Network (WMTN), we find that the WMTN, a small-world network, exhibits an exponential-like degree distribution. We hereby investigate the efficiency of the WMTN by employing a simple definition. Compared with many other transportation networks, the WMTN possesses relatively low efficiency. Furthermore, by exploring the relationship between the topological structure and the container throughput, we find that strong correlations exist among the container throughout the degree and the clustering coefficient. Also, considering the navigational process that a ship travels in a real shipping line, we obtain that the weight of a seaport is proportional to the total probability contributed by all the passing shipping lines. 相似文献
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可见近红外非成像光谱分析技术已被广泛用于土壤有机碳(SOC)含量估测,然而该技术的使用受土壤粗糙度的影响,对样本的前处理要求较高,导致模型的实用性受限。针对这一问题,以美国爱荷华州农田土壤为研究对象,使用成像及非成像光谱仪获取土壤样本研磨前后的可见近红外反射光谱,采用去包络线(CR)、吸光度变换(AB)、S-G平滑(SG)、标准正态变换(SNV)、多元散射校正(MSC)5种光谱预处理手段,利用偏最小二乘回归(PLSR)和支持向量回归(SVR)算法构建并对比土壤SOC光谱估算模型,探究利用成像光谱数据估测高粗糙度样本SOC含量的可行性。实验结果表明,使用成像光谱数据能够实现高粗糙度样本的SOC含量估算,而使用非成像光谱数据则无法估算高粗糙度样本的SOC含量;基于成像光谱数据建立的高粗糙度SOC最优PLSR估算模型R2能够达到0.739以及最优SVR估算模型R2为0.712,而基于非成像光谱数据建立的高粗糙度SOC最优PLSR和SVR估算模型R2仅仅分别为0.344和0.311。基于AB,SG,SNV和MSC这4种预处理手段之后的成像光谱数据建立的土壤样本研磨前的PLSR模型性能优于样本研磨之后建立的PLSR模型,而SVR模型性能正好相反。而对于非成像光谱数据来说,土壤样本研磨后建立PLSR和SVR模型精度总是强于样本研磨前建立的模型精度。对于这两种光谱数据和两个估算模型而言,不同的光谱预处理方法提高模型估算精度的能力不同。土壤样本研磨前后,基于成像光谱数据建立的PLSR和SVR模型性能均优于非成像光谱数据所构建的模型。成像光谱技术能够增强高粗糙度土壤样本可见近红外光谱与SOC的相关性,从而提高模型估算精度;能够克服土壤粗糙度的影响;为野外大尺度估测SOC含量提供了新的手段。 相似文献
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It is shown that many real complex networks share distinctive features, such as the small-world effect and the heterogeneous property of connectivity of vertices, which are different from random networks and regular lattices. Although these features capture the important characteristics of complex networks, their applicability depends on the style of networks. To unravel the universal characteristics many complex networks have in common, we study the fractal dimensions of complex networks using the method introduced by Shanker. We find that the average 'density' (p(r ) ) of complex networks follows a better power-law function as a function of distance r with the exponent dl, which is defined as the fractal dimension, in some real complex networks. Furthermore, we study the relation between df and the shortcuts Nadd in small-world networks and the size N in regular lattices. Our present work provides a new perspective to understand the dependence of the fractal dimension df on the complex network structure. 相似文献
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交通是现代社会生活的重要组成部分,随着科技进步与社会发展,交通运输系统也发生着日新月异的变化。100 多年前的中国,广泛存在的“交通”主要通过人的两条腿完成;50 多年前,上下班的自行车大军是城市中一道壮丽的“人工”景观。现在的中国,汽车已成为许多家庭的必备工具。与个人交通工具的快速发展相同,公共交通也发生了翻天覆地的变化。城市中装载着人群穿梭的,不仅有陆地上忙碌的公共汽车,还有地下呼啸奔驰的地铁。绿皮车与轰隆轰隆的车轮声正慢慢成为许多人的记忆,越来越多白色宽敞的动车和高铁伴着嘹亮的鸣叫驶入站台。“飞的”已是许多商务人士的家常便饭,密集的航班和相对低廉的票价使得飞机成为了国际旅行的首选交通工具,为洲际间的交流提供了方便。一艘艘满载着集装箱的货轮交织穿梭于四大洋之间,将整个世界连接成现代化的工厂,为现代化的全球分工协作提供保障。交通如同空气一样,充斥着现代化生活的方方面面。如果将交通中的实体抽象成节点,节点之间的连接抽象成线,它们所织成的大网几乎可以罩住地球上所有有人居住的地方,而这张大网也展现着它迷人的魅力。 相似文献
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