Hierarchical community detection and functional area identification with OSM roads and complex graph theory     

Ye Hong 《International journal of geographical information science》2019,33(8):1569-1587

An in-depth analysis of the urban road network structure plays an essential role in understanding the distribution of urban functional area. To concentrate topologically densely connected road segments, communities of urban roads provide a new perspective to study the structure of the network. In this study, based on OpenStreetMap (OSM) roads and points-of-interest (POI) data, we employ the Infomap community detection algorithm to identify the hierarchical community in city roads and explore the shaping role roads play in urban space and their relation with the distribution of urban functional areas. The results demonstrate that the distribution of communities at different levels in Guangzhou, China reflects the urban spatial relation between the suburbs and urban centers and within urban centers. Moreover, the study explored the functional area characteristics at the community scale and identified the distribution of various functional areas. Owing to the structure information contained in the identification process, the detected community can be used as a basic unit in other urban studies. In general, with the community-based network, this study proposes a novel method of combining city roads with urban space and functional zones, providing necessary data support and academic guidance for government and urban planners.  相似文献   

Effects of wave directionality on extreme response for a long end-anchored floating bridge     

《Applied Ocean Research》2019

Reliable design codes are of great importance when constructing new civil engineering concepts such as floating bridges. Previously only a scarce number of floating bridges have been built in rough wave conditions and only limited knowledge of the extreme environmental conditions and the associated extreme response exists. To form a better design basis an increased understanding of the sensitivity in the structural response towards changes in short-crested sea parameters is needed. Furthermore, acquiring the necessary accuracy in simulated extreme response is often a computationally expensive endeavour and the number of simulations needed is often based on experience. The present study investigates the wave-induced short-term extreme response of a simplified end-anchored floating bridge concept for several wave environments with a return period of 100 years. The study includes convergence of the coefficient of variation for the extreme response for different realization lengths as well as number of realizations. The sensitivity in the structural response towards different main wave directions and spreading exponents is investigated and includes both transverse and vertical displacement response spectra and extreme Von Mises stress in the bridge girder cross-section. The extreme response is based on an accuracy of 2% in the coefficient of variation equivalent to 40 3-h realizations and a low sensitivity in the response is found for natural occurring spreading exponents and for main wave directions within 15° from beam sea.  相似文献   

Evaluation of a simple,inexpensive, in situ sampler for measuring time‐weighted average concentrations of suspended sediment in rivers and streams     

Nicholas J.C. Doriean  Peter R. Teasdale  David T. Welsh  Andrew P. Brooks  William W. Bennett 《水文研究》2019,33(5):678-686

The accurate measurement of suspended sediment (<200 μm) in aquatic environments is essential to understand and effectively manage changes to sediment, nutrient, and contaminant concentrations on both temporal and spatial scales. Commonly used sampling techniques for suspended sediment either lack the ability to accurately measure sediment concentration (e.g., passive sediment samplers) or are too expensive to deploy in sufficient number to provide landscape‐scale information (e.g., automated discrete samplers). Here, we evaluate a time‐integrated suspended sediment sampling technique, the pumped active suspended sediment (PASS) sampler, which collects a sample that can be used for the accurate measurement of time‐weighted average (TWA) suspended sediment concentration and sediment particle size distribution. The sampler was evaluated against an established passive time‐integrated suspended sediment sampling technique (i.e., Phillips sampler) and the standard discrete sampling method (i.e., manual discrete sampling). The PASS sampler collected a sample representative of TWA suspended sediment concentration and particle size distribution of a control sediment under laboratory conditions. Field application of the PASS sampler showed that it collected a representative TWA suspended sediment concentration and particle size distribution during high flow events in an urban stream. The particle size distribution of sediment collected by the PASS and Phillips samplers were comparable and the TWA suspended sediment concentration of the samples collected using the PASS and discrete sampling techniques agreed well, differing by only 4% and 6% for two different high flow events. We should note that the current configuration of the PASS sampler does not provide a flow‐weighted measurement and, therefore, is not suitable for the determination of sediment loads. The PASS sampler is a simple, inexpensive, and robust in situ sampling technique for the accurate measurement of TWA suspended sediment concentration and particle size distribution.  相似文献   

Monitoring Contact State of Laboratory Fault with Coda Transmission Waves     

XIE Fan  REN Yaqiong  HOU Jinxin 《中国地震研究》2019,33(3):431-436

We monitored the amplitude changes of coda transmission waves around 500kHz across the frictional interface of a simulated 1.5-meter-long fault during normal stress holding test. We find that the amplitude of coda transmission waves increases with the logarithm of stationary contact time. Localized increase amounted to a level ranging from 4% to 16% along the fault is observed during the 1-hour experiment. We discuss that the frictional strength at mesoscopic scale, which is related to the amplitude of coda transmission waves, is responsible for the phenomenon. Combining the reported method with other complementary approaches will enhance the understanding of fault mechanism either at laboratory or on-site applications.  相似文献   

海城、盖州地区地震震源机制及一致性参数特征研究     

段梦乔  赵翠萍 《地震》2019,39(4):39-53

本文选取辽宁海城、 盖州地区(40°~41°N, 122°~123°E)作为研究区, 利用广义极性振幅技术(GPAT)方法, 反演得到研究区2012—2017年6月共184个地震震源机制解, 并利用Misfit角度分析震源机制一致性参数特征。 研究结果表明: ① 研究区地震震源机制解以走滑型和正断型为主。 海城地区地震震源机制解以NW—SE向节面的左旋走滑型和NWW向节面的正断型为主。 发震构造以NW向海城河断裂为主, NE向节面为主的地震可能受到NE向金州断裂带的控制。 ② 青石岭地区的发震构造为与九寨—盖县北段共轭的NW向未知断裂, 西海域的地震活动可能是NE向的雁式断裂和NW向共轭的未知断裂共同作用的结果。 ③ 震源机制一致性结果显示, 一致性增强后发生了震级相对较大的地震。 研究区的震源机制一致性较强, 表明该区域的应力较为集中。 但由于2016年以来活动趋于平静, 尚难以根据震源机制解一致性程度做出当前应力状态的判断。  相似文献   

滇东北地区地震弱活动前兆异常特征研究     

李利波  付虹  李琼  何德强 《地震》2019,39(3):115-126

以鲁甸M_S6.5地震震中附近的鲁甸大坪子泉水氡、 水质观测资料为基础, 通过对其地震前后的异常特征进行差异性对比, 分析认为震前地震活动丛集, 水氡、 水质异常持续时间较长, 幅度较大, 表现为破年变异常现象; 震后为小震群弱活动, 水氡、 水质异常幅度相对较小, 持续时间较短, 多次出现同步转折, 表现为介质弱化区的前兆异常特征。 从水样测试结果, GNSS位移观测资料、 GPS时间序列曲线及地震活动性等方面分析了鲁甸水氡、 水质的异常机理, 认为鲁甸的水质离子组分群体异常, 与区域的变形活动有关, 局部应力的不断积累, 加剧了地下深部物质活动及构造活动; 近期的同步转折现象属于介质弱化区应力调整状态下的前兆异常。  相似文献   

基于ShakeMap_CNST的2017年精河6.6级地震灾害快速评估     

刘军  谭明  宋立军  郝婧  毕雪梅  王新刚  常想德 《中国地震》2019,35(2):381-388

基于考虑区域地震动衰减关系、场地效应及震中破裂等多因素的烈度快速评估模型，结合震害预测方法，研发了一套震害预测系统，并以2017年8月9日精河M_S6.6地震的震害预测为例，将对其的预测结果与当前主流系统进行对比。结果表明，采用ShakeMap_CNST系统能对地震的影响范围和烈度进行更为准确的估计，在人员伤亡、受灾人口估计、紧急安置人数及经济损失评估等方面，相对于其他系统，本系统的结果与现场调查的结果更为接近。  相似文献   

京西北地区地震重定位及构造特征     

刘燕翔  卫俊  李金  王妍  李峰  王曰风  蔡玲玲 《地震地磁观测与研究》2019,41(1):19-24

采用双差定位法对京西北地区（39.5°—41.5° N，113°—117° E）2013年1月1日至2017年12月31日6 223次有效地震进行精确定位，得到该区震源分布的精细图像和震源深度剖面图。结果显示，重新定位后地震的水平分布更集中，沿断裂带分布特征更加明显，震中在断裂带呈更明显的条带状、簇状分布，地震与线状的深浅断裂构造的关系密切；大部分地震发生在中上地壳，震源分布为典型震源密集区的空间形态，呈纵深约15 km、直径20—40 km的近圆形“厚饼状”。  相似文献   

2000年以来青藏高原湖泊面积变化与气候要素的响应关系   总被引：1，自引：0，他引：1  

闾利  张廷斌  易桂花  苗加庆  李景吉  别小娟  黄祥麟 《湖泊科学》2019,31(2):573-589

青藏高原星罗密布的湖泊对气候变化十分敏感，在自然界水循环和水平衡中发挥着重要作用.以MODIS MOD09A1和SRTM DEM为数据源，提取了2000-2016年青藏高原丰水期面积大于50 km²的湖泊边界，从内外流分区、湖泊主要补给来源和湖水矿化度三个方面对2000年以来湖泊面积变化进行分析，并结合青藏高原近36年气象数据，根据气象要素变化趋势分区，初步探讨青藏高原湖泊面积变化与气候要素的关系.结果表明：青藏高原面积大于50 km²的138个湖泊整体扩张趋势显著，总面积增加2340.67 km²，增长率为235.52 km²/a.其中，扩张型湖泊占67.39%，萎缩型湖泊占12.32%，稳定型湖泊占20.29%.内流湖扩张趋势显著，外流湖扩张趋势较明显；以冰雪融水为主要补给来源的湖泊整体扩张趋势明显，以地表径流和河流补给为主要补给源的湖泊也呈扩张趋势；盐湖和咸水湖以扩张为主，淡水湖的扩张、萎缩和稳定三种类型较均衡.在青藏高原气候暖湿化方向发展背景下，湖泊面积变化与气候要素具有显著的区域相关性.气温和降水变化趋势分区结果表明，气温增加、降水增加强趋势的高原Ⅰ区湖泊扩张程度（78.18%）依次大于气温降低、降水量呈增加趋势的Ⅴ区（66.67%），气温、降水量呈增加趋势的Ⅱ区（60.78%），气温呈降低、降水量呈增加强趋势的Ⅳ区（58.83%）和气温呈增加、降水量呈减少趋势的Ⅲ区（50.00%）.湖泊面积变化对气候变化响应研究表明，升温引起的冰雪融水补给对Ⅰ区、Ⅱ区和Ⅲ区湖泊面积扩张的影响显著，加之降水量的增加，湖泊扩张速率明显；Ⅳ区和Ⅴ区湖泊面积扩张主要受降水量增加影响显著.整体而言，气温主要影响以冰雪融水为主要补给来源的湖泊，降水量主要影响以降水和地表径流为主要补给来源的湖泊.  相似文献   

太湖不同生态型湖区枝角类组成和丰度长期变化的差异性     

程龙娟  姚书春  薛滨  李玲玲  刘金亮 《湖泊科学》2019,31(6):1670-1684

枝角类作为淡水湖泊生态系统中的初级消费者之一,对生存环境的改变极为敏感.本文分析了太湖西、中和东部等湖区的钻孔沉积物、表层沉积物以及春夏秋季活体枝角类的组成与丰度.结果表明:活体枝角类组成以象鼻溞(Bosmina spp.)为优势种,秋季枝角类属种数量最多.太湖不同生态型湖区表层沉积物枝角类组成均以象鼻溞为优势种,其中西部与中心湖区的枝角类组成与丰度较为相似,种类单一,枝角类绝对丰度高;东部湖区枝角类属种较为丰富,绝对丰度低,优势种由浮游种象鼻溞以及沿岸种圆形盘肠溞(Chydorus sphaericus sl)和西方笔纹溞(Graptoleberis testudinaria)等种属构成.百年以来,太湖枝角类组成与丰度随着营养水平增加而改变,富营养指示种(Bosmina longirostris)丰度的增加与贫营养指示种(Bosmina longispina)丰度的下降,响应了湖区生态环境的演变过程.1970s末期,太湖西部与中心湖区在进入富营养化阶段,枝角类组成单一,象鼻溞占有绝对优势,与东部湖区相比,沿岸种、底栖种稀少.东部湖区在1960s以后,枝角类属种数量增加,但丰度下降,响应了1960s以来该区域营养水平提高、沉水植被生物量增加以及沼泽化加剧的环境过程.  相似文献