Non‐ergodicity and PEER's framework formula     

Armen Der Kiureghian 《地震工程与结构动力学》2005,34(13):1643-1652

A framework formula for performance‐based earthquake engineering, advocated and used by researchers at the Pacific Earthquake Engineering Research (PEER) Center, is closely examined. The formula was originally intended for computing the mean annual rate of a performance measure exceeding a specified threshold. However, it has also been used for computing the probability that a performance measure will exceed a specified threshold during a given period of time. It is shown that the use of the formula to compute such probabilities could lead to errors when non‐ergodic variables (aleatory or epistemic) are present. Assuming a Poisson model for the occurrence of earthquakes in time, an exact expression is derived for the probability distribution of the maximum of a performance measure over a given period of time, properly accounting for non‐ergodic uncertainties. This result is used to assess the approximation involved in the PEER formula for computing probabilities. It is found that the PEER approximation of the probability has a negligible error for probabilities less than about 0.01. For larger probabilities, the error depends on the magnitude of non‐ergodic uncertainties and the duration of time considered and can be as much as 20% for probabilities around 0.05 and 30% for probabilities around 0.10. The error is always on the conservative side. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

The Uncertainty of Mesoscale Numerical Prediction of Heavy Rain in South China and the Ensemble Simulations?          下载免费PDF全文

CHEN Jing  XUE Jishan  YAN Hong 《Acta Meteorologica Sinica》2005,19(1):1-18

In the context of non-hydrostatic MM5 version we have explored the impact of convective parameterization schemes on uncertainty in mesoscale numerical prediction of South China heavy rain and mesoscale heavy rainfall short-range ensemble simulation by using two kinds of physics perturbation methods through a heavy rain case occurring on June 8, 1998 in Guangdong and Fujian Provinces. The results show the physical process of impacts of convective schemes on heavy rainfall is that different latent heat of convective condensation produced by different convective schemes can make local temperature perturbation, leading to the difference of local vertical speed by the intrinsic dynamic and thermodynamic processes of atmosphere,and therefore, making difference of the timing, locations and strength of mesh scale and subgrid scale precipitation later. New precipitations become the new source of latent heat and temperature perturbation,which finally make the dynamic and thermodynamic structures different in the simulations. Two kinds of methods are used to construct different model version stochastically. The first one is using different convective parameterization and planetary boundary layer schemes, the second is adjusting different parameters of convective trigger functions in Grell scheme. The results indicate that the first ensemble simulations can provide more uncertainty information of location and strength of heavy rainfall than the second. The single determinate predictions of heavy rain are unstable; physics ensemble predictions can reflect the uncertainty of heavy rain, provide more useful guidance and have higher application value.Physics ensembles suggest that model errors should be taken into consideration in the heavy rainfall ensembles. Although the method of using different parameters in Grell scheme could not produce good results, how to construct the perturbation model or adjust the parameter in one scheme according to the physical meaning of the parameter still needs further investigation. The limitation of the current study is that it is based on a single case and more cases will be addressed in the future researches.  相似文献   

GGR Critical Review of Analytical Developments in 2006–2007     

Janet M. Hergt  L. Paul Bédard  Stefanie M. Brueckner  Klaus Peter Jochum  Kathryn L. Linge  Paul J. Sylvester  Michael Wiedenbeck  Jon D. Woodhead 《Geostandards and Geoanalytical Research》2008,32(4):397-398

In 2005 the Geostandards and Geoanalytical Research editorial team, in the true spirit of scientific endeavour, embarked on an experiment of our own. We decided to trial a new kind of review, somewhat different from those more typically observed in journals, and one that would provide readers with a summary of analytical developments across a broad range of topics appropriate to the Earth sciences. The first contribution of this kind appeared in 2005, and reported on developments in 2003 (Hergt et al. 2005). The second, this time a biennial review, was published in 2006 and reported on highlights of the 2004 and 2005 literature (Hergt et al. 2006). Based on reprint requests, positive remarks at conferences and strong citations we consider the experiment a resounding success and proudly present here the third in this series. This comprises six individual review sections that cover the main analytical technologies and topical application fields in geoanalysis and geochemistry, including geological and environmental reference materials, ICP‐thermal and secondary ionisation‐mass spectrometry, as well as neutron activation analysis, X‐ray fluorescence and atomic absorption spectrometry.  相似文献   

Site-specific prediction of West Nile virus mosquito abundance in Greater Toronto Area using generalized linear mixed models     

Eun-Hye Yoo 《International journal of geographical information science》2014,28(2):296-313

Mosquito surveillance programs provide a primary means of understanding mosquito vector population dynamics for the risk assessment of human exposure to West Nile virus (WNv). The lack of spatial coverage and missing observations in mosquito surveillance data often challenge our efforts to predict this vector-borne disease and implement control measures. We developed a WNv mosquito abundance prediction model in which local meteorological and environmental data were synthesized with entomological data in a generalized linear mixed modeling framework. The discrete nature of mosquito surveillance data is accommodated by a Poisson distributional assumption, and the site-specific random effects of the generalized linear mixed model (GLMM) capture any fluctuation unexplained by a general trend. The proposed Poisson GLMMs efficiently account for the nested structure of mosquito surveillance data and incorporate the temporal correlation between observations obtained at each trap by a first-order autoregressive model. In the case study, Bayesian inference of the proposed models is illustrated using a subset of mosquito surveillance data in the Greater Toronto Area. The relevance of the proposed GLMM tailored to WNv mosquito surveillance data is highlighted by the comparison of model performance in the presence of inevitable but quantifiable uncertainties.  相似文献   

Spatial-temporal difference between nitrate in groundwater and nitrogen in soil based on geostatistical analysis          下载免费PDF全文

Xiu-bo Sun  Chang-lai Guo  Jing Zhang  Jia-quan Sun  Jian Cui  Mao-hua Liu 《地下水科学与工程》2023,11(1):37-46

The study of temporal and spatial variations of nitrate in groundwater under different soil nitrogen environments is helpful to the security of groundwater resources in agricultural areas. In this paper, based on 320 groups of soil and groundwater samples collected at the same time, geostatistical analysis and multiple regression analysis were comprehensively used to conduct the evaluation of nitrogen contents in both groundwater and soil. From May to August, as the nitrification of groundwater is dominant, the average concentration of nitrate nitrogen is 34.80 mg/L; The variation of soil ammonia nitrogen and nitrate nitrogen is moderate from May to July, and the variation coefficient decreased sharply and then increased in August. There is a high correlation between the nitrate nitrogen in groundwater and soil in July, and there is a high correlation between the nitrate nitrogen in groundwater and ammonium nitrogen in soil in August and nitrate nitrogen in soil in July. From May to August, the area of low groundwater nitrate nitrogen in 0–5 mg/L and 5–10 mg/L decreased from 10.97% to 0, and the proportion of high-value area (greater than 70 mg/L) increased from 21.19% to 27.29%. Nitrate nitrogen is the main factor affecting the quality of groundwater. The correlation analysis of nitrate nitrogen in groundwater, nitrate nitrogen in soil and ammonium nitrogen shows that they have a certain period of delay. The areas with high concentration of nitrate in groundwater are mainly concentrated in the western part of the study area, which has a high consistency with the high value areas of soil nitrate distribution from July to August, and a high difference with the spatial position of soil ammonia nitrogen distribution in August.  相似文献   

辽宁地区近期地壳垂直运动的演化特征     

杨国华  胡惠民  孙惠娟 《东北地震研究》1995,(3)

根据最近十年来三期复测精密水准资料，分析了辽宁地区近期地壳垂直运动的演化状况，结果表明辽宁地区在１９８４年－１９８９年期间表现为整体范围的隆升，且没有明显的原有继承性运动特征，这反映了应力应变在加强；１９８９年－１９９３年则显示出该区已处于应力应变的调整与恢复状态之中，其运动性质也体现为以继承性运动为主。辽宁地区的这一运动过程与华北北部地区的运动过程是相一致的。目前该区域内的差异运动量值偏大。  相似文献   

巢湖水环境因子的时空变化及对水华发生的影响   总被引：6，自引：4，他引：2  

王书航  姜霞  金相灿 《湖泊科学》2011,23(6):873-880

为研究巢湖水环境因子与藻类生物量的相互作用,筛选出对藻类生物量相对重要的环境因子,以2008年巢湖水质监测数据为基础,采用多元统计方法对巢湖监测点数值数据进行了聚类分析、判别分析及污染特征识别,研究了水环境因子与藻类生物量的关系.结果表明:巢湖水环境自西向东分为重度污染区、中度污染区和轻度污染区,叶绿素、溶解性总氮可作...  相似文献   

不同形态氮对微囊藻叶绿素a合成及产毒的影响   总被引：1，自引：0，他引：1  

张亚丽  李涵  许秋瑾  储昭升  席北斗 《湖泊科学》2011,23(6):881-887

利用室内培养实验比较研究了铵氮和硝氮对河北洋河水库微囊藻(Microcystissp.)生长、叶绿素a合成及产毒的影响.结果显示,铵氮培养条件下,在对数生长期,生物量及叶绿素a含量随铵氮浓度的升高而逐渐增多,但高铵氮浓度( 10.0 mg/L)培养条件则下降.藻细胞MCRR含量随铵氮浓度的升高呈波动变化,高铵氮浓度(1...  相似文献   

Partitioning evapotranspiration fluxes into soil evaporation and plant transpiration using water stable isotopes under controlled conditions   总被引：1，自引：0，他引：1  

Youri Rothfuss  Philippe Biron  Isabelle Braud  Laurent Canale  Jean‐Louis Durand  Jean‐Paul Gaudet  Patricia Richard  Michel Vauclin  Thierry Bariac 《水文研究》2010,24(22):3177-3194

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河南省大风日数时空分布及其对沙尘天气的影响     

姬兴杰  朱业玉  顾万龙  张贵龙  苗冬 《辽宁气象》2012,(1):31-37

利用1971—2009年河南省110个气象站观测资料,采用气候统计学分析方法,对河南省大风日数时间演变、空间分布及与扬沙和沙尘暴日数的关系进行分析。结果表明：近39a来,河南省年平均大风日数以2.2d/10a的速率显著减少;四季大风日数亦均呈显著减少,表现出春季（0.8d/10a）大于冬季（0.6d/10a）大于秋季（0.4d/10a）大于夏季（0.3d/10a）的特征。无论在年尺度还是季尺度,河南省大风日数表现出随年代增加而减少的趋势。河南省大风天气主要出现在春季和冬季,集中于春季（3—5月）,占全年的40.8%,秋季最少;4月最多（15.5%）9,月最少（1.9%）。河南省大风日数的空间分布与地形有很大关系,大风日数较多的区域主要分布在太行山东南部以及海拔自低至高的河南省中北部地区,而在地势较为平坦的东部地区和山系较多海拔较高的西部地区相对较少。1971—2009年,河南省年平均扬沙日数和沙尘暴日数随时间增加均显著减少,其减少速率分别为0.4d/10a和0.3d/10a。相关分析表明,年平均扬沙日数和沙尘暴日数与年平均大风日数平均呈极显著正相关,其相关系数分别为0.88和0.75;大风日数随时间的变化对沙尘天气随时间的变化具有显著作用,大风日数的减少是沙尘天气减少的主要原因。  相似文献