Transit time evaluation using a chloride concentration input step shift after forest cutting in a Japanese headwater catchment

Mean transit times were estimated for a small headwater catchment in Japan (the Fukuroyamasawa Experimental Watershed) using the step shift in input chloride (Cl^?) concentrations that occurred immediately after an episode of forest clear‐cutting. Measured Cl^? concentrations in stream water began to decrease immediately after clear‐cutting, and this trend continued for 6 years. Before clear‐cutting, the input Cl^? concentrations were controlled by wet and dry deposition processes, and most of the dry Cl^? deposition was collected by the forest canopy and reached the ground as throughfall and stemflow. After clear‐cutting, dry deposition was no longer collected by the canopy in this way, thus causing a sharp decrease in input Cl^? concentrations. By comparing measured Cl^? concentrations in stream water with estimates based on the input and evaporative Cl^? concentrations, it was shown that the decrease in stream water Cl^? concentrations was caused mainly by this step shift in the Cl^? input. It was proposed that the change in Cl^? concentrations after forest cutting could be used to represent the replacement of ‘old’ water that existed before cutting by ‘new’ water that was supplied after cutting. The breakthrough curve for the new water fraction gave an approximately exponential distribution of transit times in flow‐corrected time. The mean flow‐corrected transit time was estimated as 1068 days (runoff: 3497 mm). It was therefore concluded that the step change in input Cl^? concentrations immediately following forest clear‐cutting could be successfully used to estimate transit times for the entire catchment. Copyright © 2009 John Wiley & Sons, Ltd.     

RELATION BETWEEN THE MRT BUILDING AND UNDERGROUND SPACE EXPLOITATION——A Case in Guangzhou City

Thehumandevelopmentalhistoryrevealsthatmanhasneverneglected exploitingtheundergroundspace, fromtheprimitive'caveliving' tothe'undergroundvillage' inMatermataofTunis,fromthesubsided'cavedwelling' inthenorthwestofChinatothepre-sent'undergroundcity'.Theundergroundspacehasbeenexploitedwidelyanddeeply. Thewidespreadutilization oftheurbanunder-groundspacetookplaceafter thebeginningofindus-trialrevolutionsandurbanization.Dueto seriesofproblemsonurbandevelopmentresultedfromtheoverconcentrationofpo…     

基于网络大数据的城市轨道交通时空溢价效应研究

城市轨道交通是大城市缓解交通拥堵的重要公共交通方式,其对周边住宅的时空溢价效应一直是城市研究热点,但传统研究存在样本量少、数据时间跨度短、忽视预期效应等问题。该文利用网络爬虫获取住宅交易大数据,以天津市地铁6号线为例,采用直接比较法、特征价格模型测度城市轨道交通对沿线住宅价格的时空溢价效应,结果表明:1)空间尺度上,轨道交通对沿线住宅价格具有显著溢价效应,但溢价程度并非随着距轨道交通站点距离的增加而下降,而是呈现先上升后下降的“倒U形”趋势。其中,500~1000 m的影响区溢价幅度最大,溢价率高达17.2%。2)时间尺度上,轨道交通对住宅价格的影响具有超前效应,在施工期溢价就已显现,且在首个开通运营年达到峰值,说明住宅价格对开通运营这一“标志性”事件反应强烈。3)受心理预期效应的影响,轨道交通全线开通运营的溢价效应明显低于首个开通运营年的溢价效应。研究结论可为公共交通导向模式下城市综合开发和轨道交通的“溢价回收”策略提供决策支持。     

城市轨道交通站点周边商业环境特征与评价——以天津市为例

城市轨道交通站点周边商业环境包括微观商业环境和宏观商业环境两个层次。通过构建城市轨道交通站点周边商业环境的定量评价体系,并采用理想点法对天津地铁1号线的6个典型站点进行实证研究。城市轨道交通站点周边商业环境存在明显的空间分异、等级分异和职能分异,即位于城市中心区的轨道交通站点其周边商业环境优于位于城市外围地区的轨道交通站点,继而从空间选址、等级设置和功能提升3个方面提出城市外围地区轨道交通站点周边商业环境的提升建议。     

轨道交通振动对邻近建筑物的影响及其评价

发展城市轨道交通是解决城市交通问题的有效措施,所产生的振动和噪声形成环境问题,成为发展的“瓶颈”.文中以北京城轨道交通13号线霍营-回龙观段的观测振动信号作为输入,选择6层、10层和16层钢筋混凝土结构以及5层砌体结构,建立土结相互作用三维有限元模型,计算结构各层振动响应以及傅氏谱,从这两方面分析结构响应随距离的变化关...     

Concentration versus streamflow trends of major ions and tritium in headwater streams as indicators of changing water stores

Documenting the processes that control the variations in stream geochemistry at different streamflows is important for being able to use chemical tracers to understand catchment functioning. The concentrations of most solutes, including reactive cations (e.g., Na, Ca, K, and Mg) and anions that are primarily derived from precipitation (Cl and Br), in five headwater streams from southeast Australia vary little with streamflow and are close to being chemostatic. By contrast, NO₃ and SO₄ concentrations are higher at high streamflows. There is also a systematic increase of ³H activities from as low as 1.1 to as high as 2.6 TU with increasing streamflow. The changes in geochemistry cannot be explained solely by increased mineral dissolution at high streamflows or enhanced baseflow driven by hydraulic loading. They are best explained by an increased baseflow input augmented by water mobilized from shallower stores as the catchments wet up. The mean transit times of the water sustaining streamflow varies from 35 to 70 years at low streamflows to <7 years at high streamflows. The use of a range of geochemical tracers, including radioactive isotopes, allows the different possible causes of chemostatic behaviour to be assessed and improves our understanding of catchment functioning.     

城市轨道交通高架桥梁抗震设计中的关键问题

伴随我国城市轨道交通建设的快速发展,轨道交通抗震安全已成为我国大中型城市和地区生命安全、交通秩序、正常的经济和社会活动的重要保障。本文针对城市轨道交通高架桥梁结构和线路运行特点,结合国内外地震中铁路和轨道交通桥梁破坏特征,参照桥梁抗震设计思想和国内外桥梁抗震设计规范内容,综合论述了轨道交通抗震设计中抗震设防分类、设防标准与性能目标的确定,结构安全和行车安全指标的选取,桩-土相互作用、轨道系统和车辆作用的模拟等关键问题,并结合设计工作特点,对研究工作与设计工作的结合提出了建议。     

基于符号集合近似的城市轨道交通站点分类研究

轨道站点是城市轨道交通基本线网系统中的关键节点,科学的轨道站点分类,对了解城市功能分区及评价轨道交通基础设施建设情况具有重要意义。轨道交通站点时间序列客观记录了所观测的站点在各个时刻点的重要信息,研究其时间序列聚类,是认识和理解轨道交通站点时间序列形成本质的重要手段,也是挖掘轨道交通站点时间序列中隐含的有较高价值规律知识的重要方法。本文以北京IC卡轨道站点刷卡数据为研究对象,提出了描述轨道站点的4个数据集,即工作日进站数据集(WB)、工作日出站数据集(WA)、休息日进站数据集(RB)和休息日出站数据集(RA);并首次引入时间序列分析方法（符号集合近似(SAX)方法）对4个数据集进行聚类分析,实现了高维数据的有效降维和轨道站点之间的相似性度量。采用层次聚类方法并根据聚类有效性DB指数确定将195个站点分为8类更为合理。通过分析每类站点的日客流特征和空间位置分布情况,为轨道交通站点规划设计和管理服务提供一定的客观参考依据。     

城市商务人士的行为活动特征

移动信息技术的使用和快速交通技术的出现对商务人士行为活动产生了较大影响。在这一新的技术背景下,商务活动的特征研究值得关注。以医疗器械行业某跨国公司的南京销售团队为例,采用GPS技术、活动日志、深度访谈等方法,获取该团队11位成员在连续7个工作日内的时空数据。经描述分析和模型分析发现:① 在商务活动过程中,快速交通技术和移动信息技术的使用具有共变关系,使承载商务活动的空间成为流空间的外在表现形式。② 交通技术间接影响商务活动,但影响程度比信息技术使用大,导致商务活动的空间破碎化。③ 信息技术使用对商务活动的影响是多方面的,包括直接影响和间接影响,具体表现在商务活动的时间破碎化。     

新加坡常规公交系统发展经验及对我国的启示

优先发展公共交通是解决我国城市交通问题、实现城市交通可持续发展的必由之路。在我国社会经济发展的新阶段,公交优先对落实能源战略、促进环境保护、集约节约用地、建设低碳城市具有重要意义。通过解析新加坡常规公交系统的成功经验,探求其对我国城市常规公交系统新一轮发展策略的有益启示,以期为我国城市交通的进一步跨越式发展提供参考依据。