北京地区脑卒中发病率的气象条件研究   总被引：13，自引：1，他引：12  

杨贤为  邹旭恺 《气象》1998,24(9):51-54

根据北京抽样人群的脑卒中发病资料和前期气象资料的对比分析,揭示出不同年龄段人群发病率的年变化特点和多年变化趋势,讨论了前期气象因子与发病率的关系,并在此基础上设计对发病率有预测意义的分辨率为５级的统计模型,经Ｆ检验表明,预测效果较好。  相似文献   

A systematic approach to the input determination for neural network rainfall–runoff models     

Gwo‐Fong Lin  Guo‐Rong Chen 《水文研究》2008,22(14):2524-2530

Input determination has a great influence on the performance of artificial neural network (ANN) rainfall–runoff models. To improve the performance of ANN models, a systematic approach to the input determination for ANN models is proposed. In the proposed approach, the irrelevant inputs are removed. Then an adequate ANN model, which only includes highly relevant inputs, is constructed. Unlike the trial‐and‐error procedure, the proposed approach is more systematic and avoids unnecessary trials. To demonstrate the effectiveness of the proposed approach, an application to actual typhoon events is presented. The results show that the proposed ANN model, which is constructed by the proposed approach, has advantages over those obtained by the trial‐and‐error procedure. The proposed ANN model has a simpler architecture, needs less training time, and performs better. The proposed ANN model is recommended as an alternative to existing rainfall–runoff ANN models. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

迭代逼近科学方法在速度估算中的作用     

陈宝孚  李貅 《地球科学与环境学报》2000,22(2):67-70

以地球物理中的速度为题 ,在详细描述了速度参数重要作用、各类速度基本概念及其应用范围、影响速度估算的各种因素的基础上 ,以模型和处理流程的叠加速度分析为例 ,在两个层面上展现了迭代逼近方法。又以剩余层速度分析为例 ,说明了具有反馈控制思想的迭代逼近算法 ,从而指出该方法在速度估算中的重要作用  相似文献   

Ecophysiological characteristics of invasive Spartina alterniflora and native species in salt marshes of Yangtze River estuary,China     

Li-Fen Jiang  Yi-Qi Luo  Jia-Kuan Chen  Bo Li 《Estuarine, Coastal and Shelf Science》2009

Biological invasions represent one of the significant components of global change. A comparative study of invaders and co-occurring natives is a useful approach to gaining insights into the invasiveness of exotic plants. Spartina alterniflora, a C₄ grass, is a widespread invader in the coastal wetlands in China and other regions of the world. We conducted a comparative study of S. alterniflora and native C₃ species, Phragmites australis and Scirpus mariqueter, in terms of their gas exchange and efficiencies in resource utilization. We tested the hypothesis that S. alterniflora has growth-related ecophysiological advantages over the natives in its non-native range, which result in its rapid growth and enhance its invasiveness. Photosynthesis, leaf area index (LAI), specific leaf area (SLA), and the efficiency of resource use (light, water, and nitrogen) were examined monthly for eight months in 2004. Overall, S. alterniflora had greater LAI, higher maximal net photosynthetic rate (A_max), and longer growing season than those of the native species. On average, the efficiencies of S. alterniflora in light, water, and nitrogen utilization were respectively 10.1%, 26.1%, and 33.1% higher than those of P. australis, and respectively 70.3%, 53.5%, 28.3% higher than those of S. mariqueter. However, SLA of S. alterniflora was significantly lower than those of P. australis and S. mariqueter. Although there was no general pattern in the relationship between invasiveness and plant photosynthetic types, in this study, most of the ecophysiological characteristics that gave S. alterniflora a competitive advantage in the Yangtze River estuary were associated with photosynthetic pathways. Our results offer a greater understanding of the relationship between invasiveness and plant photosynthetic type. Our results also indicate that LAI and the length of the photosynthetic season, which vary with habitats, are also important in invasion success.  相似文献   

加蓬G4-188区块钻井技术实践认识     

石强 《海洋地质译丛》2008,(1):82-87

加蓬G4-188区块是一个新的海外勘探区块,在钻井过程中遇到了井壁垮塌、气侵、井斜控制困难等诸多难题,影响了钻井施工的速度。针对这些难题,实施了解决G4-188区块钻井施工难点的各项技术措施,为G4-188区块后续钻井施工提供了有益的技术支持。  相似文献   

Invasion and morphological variation of the non-indigenous barnacle Chthamalus challengeri (Hoek, 1883) in Yangshan Port and its surrounding areas     

Liu  Yan  Xue  Junzeng  Lin  Junda  Wu  Huixian 《中国海洋大学学报(英文版)》2015,14(3):575-583

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一次西南低涡东移引发长江中下游暴雨的诊断研究   总被引：1，自引：0，他引：1  

刘晓波  储海 《气象》2015,41(7):825-832

利用常规观测资料和NECP再分析资料,对2013年6月6—7日西南低涡东移加强发展造成长江中下游大暴雨过程进行了诊断分析,重点探讨了西南低涡东移和发展维持的物理机制以及最强降水的变化特征。结果表明,沿着700 hPa高空切变线东移的西南低涡是造成此次长江中下游地区暴雨的直接影响系统,西南低涡沿着700 hPa切变线东移发展,深厚阶段正涡度柱伸展到400 hPa高度,自下而上呈近垂直结构。西南低涡附近低层辐合与高层辐散的大尺度环境条件、西南低涡与西南低空急流耦合发展动力结构、低空暖平流和高空槽前正涡度平流输送等条件是导致西南低涡东移到长江中下游后加强发展的主要因子。与西南低涡相伴随的强降雨区主要位于低涡南部3个纬距以内,该处的西南季风和副高西南侧东南气流两支水汽输送的汇合为暴雨发生提供了充沛的水汽和对流不稳定能量,而对流层中低层携带的冷空气侵入低层低涡的后部,不仅加强了低涡的斜压性,也促进了上冷下暖不稳定层结的产生和发展,为强降水的发生提供了不稳定对流触发条件。  相似文献   

Go with the flow: geospatial analytics to quantify hydrologic landscape connectivity for passively dispersed microorganisms     

Alexander Hohl  Ross K. Meentemeyer 《International journal of geographical information science》2014,28(8):1626-1641

Understanding the diverse ways that landscape connectivity influences the distribution of microbial species is central to managing the spread and persistence of numerous biological invasions. Here, we use geospatial analytics to examine the degree to which the hydrologic connectivity of landscapes influences the transport of passively dispersed microbes, using the invasive plant pathogen Phytophthora ramorum as a case study. Pathogen occurrence was analyzed at 280 stream baiting stations across a range of watersheds – exposed to variable inoculum pressure – in California over a 7-year period (2004–2010). Using logistic regression, we modeled the probability of pathogen occurrence at a baiting station based on nine environmental variables. We developed a novel geospatial approach to quantify the hydrologic connectivity of host vegetation and inoculum pressure derived from least cost distance analyses in each watershed. We also examined the influence of local environmental conditions within the immediate neighborhood of a baiting station. Over the course of the sampling period, the pathogen was detected at 67 baiting stations associated with coastal watersheds with mild climate conditions, steep slopes, and higher levels of inoculum pressure. At the watershed scale, hydrologic landscape connectivity was a key predictor of pathogen occurrence in streams after accounting for variation in climate and exposure to inoculum. This study illustrates a geospatial approach to modeling the degree to which hydrologic systems play a role in shaping landscape structures conducive for the transport of passively dispersed microbes in heterogeneous watersheds.  相似文献   

Late Holocene Isotopic and Molecular Signals in Saline Sediments of Lake Cantara South,Australia     

WANG Ruiliang  ZHANG Shuichang 《《地质学报》英文版》2014,88(Z1):160-160

正Isotopic,biomarker,and trace elements of a 65 cm long sedimentary core from Lake Cantara south in Adelaide,Australia were measured in an effort to trace environmental change clues in the southern Hemisphere.The geochemical  相似文献   

Approximate analytical and numerical solutions for radial non‐Darcian flow to a well in a leaky aquifer with wellbore storage and skin effect     

Zhang Wen  Quanrong Wang 《国际地质力学数值与分析法杂志》2013,37(11):1453-1469

This study investigated non‐Darcian flow to a well in a leaky aquifer considering wellbore storage and a finite‐thickness skin. The non‐Darcian flow is described by the Izbash equation. We have used a linearization procedure associated with the Laplace transform to solve such a non‐Darcian flow model. Besides, the Stehfest method has been used to invert the Laplace domain solutions for the drawdowns. We further analyzed the drawdowns inside the well for different cases. The results indicated that a smaller B_D results in a smaller drawdown at late times and the leakage has little effect on the drawdown inside the well at early times, where B_D is a dimensionless parameter reflecting the leakage. We have also found that the flow for the negative skin case approaches the steady‐state earlier than that for the positive skin. In addition, the drawdown inside the well with a positive skin is larger than that without skin effect at late times, and a larger thickness of the skin results in a greater drawdown inside the well at late times for the positive skin case. A reverse result has been found for the negative skin case. Finally, we have developed a finite‐difference solution for such a non‐Darcian flow model and compared the numerical solution with the approximate analytical solution. It has been shown that the linearization procedure works very well for such a non‐Darcian flow model at late times, and it underestimates the drawdowns at early times. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献