A Hybrid Link‐Node Approach for Finding Shortest Paths in Road Networks with Turn Restrictions          下载免费PDF全文

Qingquan Li  Bi Yu Chen  Yafei Wang  William H. K. Lam 《Transactions in GIS》2015,19(6):915-929

Turn restrictions, such as ‘no left turn’ or ‘no U‐turn’, are commonly encountered in real road networks. These turn restrictions must be explicitly considered in the shortest path problem and ignoring them may lead to infeasible paths. In the present study, a hybrid link‐node Dijkstra's (HLND) algorithm is proposed to exactly solve the shortest path problem in road networks with turn restrictions. A new hybrid link–node labelling approach is devised by using a link–based labelling strategy at restricted nodes with turn restrictions, and a node‐based labelling strategy at unrestricted nodes without turn restrictions. Computational results for several real road networks show that the proposed HLND algorithm obtains the same optimal results as the link‐based Dijkstra's algorithm, while having a similar computational performance to the classical node‐based Dijkstra's algorithm.  相似文献   

考虑桩-土相互作用的某海底隧道岸边段结构抗震性能分析研究          下载免费PDF全文

尹训强  蒋园豪  赵杰  王桂萱 《地震工程学报》2021,43(3):679-686

随着我国沿海及沿江城市交通发展的需要,水下沉管隧道工程建设的迫切性不断提高,其抗震性能也是备受关注的重要内容。以某海底隧道建设工程隧道北岸岸边段为工程研究背景,基于ANSYS软件建立沉管隧道-土体-桩基-沉箱三维有限元模型,管节接头采用COMBIN39单元模拟止水带和剪力杆,通过非线性F-D曲线模拟其物理力学性能,采用无厚度接触单元对桩-土间的接触效应进行描述,在外边界处设置黏弹性人工边界来反映远场地基辐射效应。计算结果表明:在罕遇地震作用下,沉箱接口处具有较大的应力,主要是接口处材料发生变化,容易出现应力集中现象;管节接头处止水带上部位移比下部位移大,更容易发生破坏。可为海底隧道岸边段及类似结构的抗震安全评价及优化设计提供参考。  相似文献   

MicrotopsⅡ型太阳光度计的使用、计算及定标   总被引：1，自引：0，他引：1  

毕雪岩  吴兑  谭浩波  李菲  邓雪娇 《气象科技》2007,35(4):583-588

通过研究文献和在使用仪器过程中积累的一些经验,介绍MicrotopsⅡ型5通道手持式太阳光度计的特征、仪器使用前的参数设置、使用中应该注意的问题以及大气气溶胶光学厚度(AOD)的计算原理和仪器定标方法,以便为仪器的使用者提供借鉴。对广州热带海洋气象研究所2004年9月19日在国家南岭森林公园的一次对比试验观测数据进行分析,结果显示,两台仪器大气气溶胶光学厚度值非常接近,500 nm通道的AOD值相差小于0.01,说明两台仪器的厂家定标常数仍然适用。  相似文献   

刀郎文化旅游区开发构想——以喀什经济特区为背景     

毕剑 《地域研究与开发》2012,31(4):110-112,117

随着我国文化旅游的快速发展及喀什经济特区设立,地处喀什和阿克苏等地区的刀郎文化逐渐成为关注的重要内容。刀郎文化在其形成过程中不断融合蒙古族等其他民族的文化因子,逐步发展成为维吾尔民族独特的地域文化,在我国目前大力发展文化旅游的背景下,建立刀郎文化旅游区具有重要的现实意义。在对刀郎文化旅游区建立的必要性进行分析的基础上,从机遇、知名度和基础3个角度探讨了刀郎文化旅游区建立的可行性。在喀什经济特区背景下建立刀郎文化旅游区,需要打破行政区划限制,运用前台-帷幕-后台理论,设立三级支撑系统,彰显刀郎文化特色,突出民族和谐,并使刀郎文化旅游区与喀什经济特区进行整合式发展。  相似文献   

Magnetic interactions during sympathetic solar eruptions     

Yun-Chun Jiang Yi Bi Jia-Yan Yang Rui-Sheng Zheng Jing-Xiu Wang 《中国天文和天体物理学报》2009,9(5)

We present the first evidence for occurrences of magnetic interactions between a jet, a filament and coronal loops during a complex event, in which two flares sequen-tially occurred at different positions of the same active region and were closely associated with two successive coronal mass ejections (CMEs), respectively. The coronal loops were located outside but nearby the filament channel before the flares. The jet, originating from the first flare during its rise phase, not only hit the filament body but also met one of the ends of the loops. The filament then underwent an inclined eruption followed by the second flare and met the same loop end once more. Both the jet and the filament erup- tion were accompanied by the development of loop disturbances and the appearances of brightenings around the meeting site. In particular, the erupting filament showed clear manifestations of interactions with the loops. After a short holdup, only its portion passed through this site, while the other portion remained at the same place. Following the fila-ment eruption and the loop disappearance, four dimmings were formed and located near their four ends. This is a situation that we define as "quadrupolar dimmings." It appears that the two flares consisted of a sympathetic pair physically linked by the interaction between the jet and the filament, and their sympathy indicated that of the two CMEs.Moreover, it is very likely that the two sympathetic CMEs were simultaneously associ-ated with the disappearing loops and the quadrupole dimmings.  相似文献   

珠江三角洲霾天气的近地层输送条件研究   总被引：68，自引：4，他引：64       下载免费PDF全文

吴兑  廖国莲  邓雪娇  毕雪岩  谭浩波  李菲  蒋承霖  夏冬  范绍佳 《应用气象学报》2008,19(1):1-9

近年来, 珠江三角洲地区气溶胶污染日趋严重, 霾天气造成能见度恶化和空气质量下降。近地层输送条件即地面流场与大气污染物稀释扩散密切相关。利用2004—2005年广东省466个地面自动气象站资料、广州观象台常规气象资料、珠江三角洲大气成分站网器测能见度资料、珠江三角洲城市环境监测站网的PM₁₀浓度资料等, 使用矢量和分析方法, 分析珠江三角洲近地层风及其对严重霾天气过程和清洁对照过程的影响。结果表明: 2004年霾天气高发季节, 东亚纬向环流比2005年同期显著, 纬向环流不显著的年份, 气流南北交换显著, 冷空气跨越南岭、到达珠江三角洲的机会比较大, 伴随冷空气的大风等天气有利于污染物扩散; 纬向环流显著的年份, 冷空气跨越南岭、到达珠江三角洲的机会比较小, 污染物易于堆积。珠江三角洲霾天气具有区域性特征, 旱季出现最多, 雨季出现最少。严重霾天气过程出现在每年12月至次年4月, 清洁对照过程出现在台风直接影响或冷空气活动频繁的季节。与2004年相比, 2005年的静风频率较低, 且旱季风速较大, 不利于霾天气的形成。矢量和分析表明:区域霾天气过程与区域内静小风过程, 即出现气流停滞区有密切联系, 清洁对照过程与强平流输送有关。  相似文献   

东半球夏季低空越赤道气流的年际变化   总被引：3，自引：0，他引：3  

唐碧  郭品文  杨丽萍 《南京气象学院学报》2009,32(2):298-305

利用1948—2006年NECP/NCAR的风场、高度场、海平面气压场以及地表温度再分析资料,采用相关分析、合成分析及回归分析等方法,探讨了东半球夏季低空越赤道气流的年际变化特征以及越赤道气流强度与环流系统和前期海陆热力差异的关系。结果表明,越赤道气流强度的年际变化和同期南北半球低纬环流系统,特别是亚澳大陆气压差关系密切。此外,索马里急流和孟加拉湾越赤道气流受海陆热力差异的影响,而东亚越赤道气流则主要受海温影响。  相似文献   

减少发展中国家毁林及森林退化排放(REDD)的各方观点及对策建议   总被引：3，自引：0，他引：3       下载免费PDF全文

毕欣欣  李玉娥  高清竹  万运帆  秦晓波 《气候变化研究进展》2010,6(1):65-69

减少发展中国家毁林及森林退化的温室气体排放已成为《联合国气候变化框架公约》谈判的重要议题。从该公约的第十一次缔约方大会(COP11)以来,各缔约国就此议题提出了各自的观点,除在方法学等问题上存在争议外,在激励机制和毁林纳入清洁发展机制(CDM)与否上也存在分歧,巴西、中美洲及非洲的发展中国家希望通过基金的方式获得额外的资金和技术支持,而美国、澳大利亚和欧盟等发达国家却更倾向于CDM市场机制。结合中国森林管理方面的现状,分析了中国在此议题上可能受到的影响并提出了谈判的对策建议。  相似文献   

Speciation of aluminum in the stream waters from the Susquehanna River watershed, Chesapeake Bay     

Shuping Bi 《Environmental Geology》2001,40(3):300-304

 The aim of this paper was to analyze the processing and transport of aluminum speciation through the terrestrial and aquatic ecosystems of the Chesapeake Bay landscape. Stream waters were sampled in 14 different streams from the Susquehanna River watershed to the upper reach of Chesapeake Bay. The basic water quality data were documented and Al speciation was evaluated by modified MINEQL computer model. It was found that the increase in acidity in some of the stream waters near New York were closely linked with a marked decline in basic cation concentrations. In these areas, the sum of the toxic forms of Al³⁺ plus AlOH²⁺ and Al(OH)₂ ⁺ concentrations exceeds the critical level of 5 μmol l^–1. A potential threat from aluminum may occur. Received: 3 January 2000 · Accepted: 21 March 2000  相似文献   

中央气象台短期降雨预报水平初步分析   总被引：10，自引：1，他引：10       下载免费PDF全文

林明智  毕宝贵 《应用气象学报》1995,6(4):392-399

该文利用1988～1993年资料，对中央气象台降雨预报水平状况进行了初步分析。结果表明:最近6年，中央气象台的有雨预报、小雨预报、中雨预报和等级综合预报的准确率和技巧水平均有不同程度的提高；暴雨和大暴雨两个等级的落点预报的准确率均超过气候概率，具有正技巧（技巧评分＞0），但技巧水平提高不明显。  相似文献