Space-time mapping of soil salinity using probabilistic bayesian maximum entropy     

A. Douaik  M. van Meirvenne  T. Tóth  M. Serre 《Stochastic Environmental Research and Risk Assessment (SERRA)》2004,18(4):219-227

The mapping of saline soils is the first task before any reclamation effort. Reclamation is based on the knowledge of soil salinity in space and how it evolves with time. Soil salinity is traditionally determined by soil sampling and laboratory analysis. Recently, it became possible to complement these hard data with soft secondary data made available using field sensors like electrode probes. In this study, we had two data sets. The first includes measurements of field salinity (EC_a) at 413 locations and 19 time instants. The second, which is a subset of the first (13 to 20 locations), contains, in addition to EC_a, salinity determined in the laboratory (EC_2.5). Based on a procedure of cross-validation, we compared the prediction performance in the space-time domain of 3 methods: kriging using either only hard data (HK) or hard and mid interval soft data (HMIK), and Bayesian maximum entropy (BME) using probabilistic soft data. We found that BME was less biased, more accurate and giving estimates, which were better correlated with the observed values than the two kriging techniques. In addition, BME allowed one to delineate with better detail saline from non-saline areas.  相似文献   

Ar/Ar ages of tephras intercalated in astronomically tuned Neogene sedimentary sequences in the eastern Mediterranean     

K.F. Kuiper  F.J. Hilgen  J.R. Wijbrans 《Earth and Planetary Science Letters》2004,222(2):583-597

We present new ⁴⁰Ar/³⁹Ar data for sanidine and biotite derived from volcanic ash layers that are intercalated in Pliocene and late Miocene astronomically dated sequences in the Mediterranean with the aim to solve existing inconsistencies in the intercalibration between the two independent absolute dating methods. ⁴⁰Ar/³⁹Ar sanidine ages are systematically younger by 0.7-2.3% than the astronomical ages for the same ash layers. The significance of the discrepancy disappears except for the upper Ptolemais ashes, which reveal the largest difference, if an improved full error propagation method is applied to calculate the absolute error in the ⁴⁰Ar/³⁹Ar ages. The total variance is dominated by that of the activity of the decay of ⁴⁰K to ⁴⁰Ar (∼70%) and that the amount of radiogenic ⁴⁰Ar_p in the primary standard GA1550 biotite (∼15%). If the ⁴⁰Ar/³⁹Ar ages are calculated relative to an astronomically dated standard, the influence of these parameters is greatly reduced, resulting in a more reliable age and in a significant reduction of the error in ⁴⁰Ar/³⁹Ar dating.Astronomically calibrated ages for Taylor Creek Rhyolite (TCR) and Fish Canyon Tuff (FCT) sanidine are 28.53±0.02 and 28.21±0.04 Ma (±1 S.E.), respectively, if we start from the more reliable results of the Cretan A1 ash layer. The most likely explanation for the large discrepancy found for the younger Ptolemais ash layers (equivalent to FCT of 28.61 Ma) is an error in the tuning of this part of the sequence.  相似文献   

Seismic performance evaluation of steel arch bridges against major earthquakes. Part 1: dynamic analysis approach     

Tsutomu Usami  Zhihao Lu  Hanbin Ge  Takeshi Kono 《地震工程与结构动力学》2004,33(14):1337-1354

In this study the inelastic behavior of steel arch bridges subjected to strong ground motions from major earthquakes is investigated by dynamic analyses of a typical steel arch bridge using a three‐dimensional (3D) analytical model, since checking seismic performance against severe earthquakes is not usually performed when designing such kinds of bridge. The bridge considered is an upper‐deck steel arch bridge having a reinforced concrete (RC) deck, steel I‐section girders and steel arch ribs. The input ground motions are accelerograms which are modified ground motions based on the records from the 1995 Hyogoken‐Nanbu earthquake. Both the longitudinal and transverse dynamic characteristics of the bridge are studied by investigation of time‐history responses of the main parameters. It is found that seismic responses are small when subjected to the longitudinal excitation, but significantly large under the transverse ground motion due to plasticization formed in some segments such as arch rib ends and side pier bases where axial force levels are very high. Finally, a seismic performance evaluation method based on the response strain index is proposed for such steel bridge structures. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

运用改进系统建模法对南海气象数据的建模研究   总被引：2，自引：0，他引：2  

董言治  周晓东  沈同圣  陈永刚 《热带气象学报》2004,20(4):426-432

在系统建模理论的基础上,运用改进的动态数据建模方法,对南海气象数据中的温度进行建模并验证了模型的适用性.根据模型推导出格林函数、逆函数和自协方差函数等,并讨论了南海气象数据中温度模型的稳定性、可逆性和合理性.对系统的频率特性和谱函数进行分析讨论,并给出建模过程中的一些图像.根据模型的适用性检验发现,对所研究的气象数据而言,ARMA(4, 3)模型是最合适的,具有平稳可逆性.所有的建模和分析过程在MATLAB上实现.实验结果表明这种建模方案简便易行,能够快速准确地确定系统的合理模型.  相似文献   

天目湖热力学状况的监测与分析   总被引：16，自引：0，他引：16       下载免费PDF全文

张运林  陈伟民  杨顶田  黄文钰  江晶 《水科学进展》2004,15(1):61-67

根据2001年6月～2002年5月在天目湖进行的每月一次的全湖水温观测以及2002年5月25～26日在1号点的定点24h连续水温观测资料,分析研究了天目湖水温时空分布、垂直分布、温跃层的形成与变化以及湖泊热力学对溶解氧、营养盐的影响,揭示了各自的基本变化规律。结果表明:天目湖水温的日变化、年变化及垂直分布明显,而其水平差异不大;温跃层随着季节的变化而呈现增强-稳定-减弱-消失的周期变化;水温的变化以及温跃层的存在引起了水中溶解氧以及营养盐的变化。  相似文献   

地下水水位时间序列中的混沌特征   总被引：20，自引：0，他引：20  

宋宇  陈家军  孙雄 《水文地质工程地质》2004,31(1):14-18

利用相空间重构技术、G -P算法以及Wolf提出的从单变量中提取Lyapunov指数的方法 ,分别计算了太原盆地 4组地下水水位时间序列的关联维数和Lyapunov指数。结果揭示在自然状态下 ,太原盆地某些孔隙潜水和孔隙承压水水位变化存在明显的混沌特征。这不仅为以后建立水位预测模型提供了理论依据 ,并且也为运用分形理论研究地质参数的时空变异性以及含水层结构的自相似性提供了进一步的支持。  相似文献   

四川雅安地质灾害时空预警试验区初步研究   总被引：11，自引：2，他引：11  

刘传正  李云贵  温铭生  肖智林  钟沛林  周策  李媛  朱晓冬 《水文地质工程地质》2004,31(4):20-30

借鉴美国旧金山湾和香港地区的经验,提出了地质灾害监测预警试验区建设和研究思路。经过近两年的工作,初步建成了四川雅安地质灾害监测预警试验区。取得的阶段性成果主要有:(1)根据现场考察和试验区地质灾害数据库,统计研究了降雨型滑坡的几何特征;(2)建成了由20台遥测雨量计构成的降雨观测网,取得了2002年4月～2003年8月的降雨观测数据;(3)结合历史降雨资料分析,初步研究了雅安试验区的年、日、小时和十分钟最大降雨特征;(4)研制了斜坡岩土体含水量野外监测仪,取得了桑树坡试验点2003年4月～8月的实时监测数据;(5)自上而下分4层研究了斜坡岩土层含水量变化,发现了岩土层含水量变化对降雨过程的滞后性;(6)基于区域地质灾害评价预警的递进分析理论与方法(AMFP),利用地质灾害因子分析结果,分别计算了雅安试验区地质灾害"发育度"和"潜势度";(7)利用2003年8月23～25日的过程降雨观测资料,对雅安试验区在该降雨过程中发生的地质灾害事件进行了时空预警反演模拟研究,计算出的地质灾害"危险度"分布比较符合实际,"危险度"可以作为预警指数使用。  相似文献   

Nuclear Waste Disposal Simulations: Couplex Test Cases     

H. Hoteit  Ph. Ackerer  R. Mosé 《Computational Geosciences》2004,8(2):99-124

We give some results obtained for the Couplex test cases proposed by the ANDRA. In this paper our aim is twofold. Firstly, to compute the release of nuclides out of the repository by concentrating on the 3D near field (Couplex 2). The simulation of the transport phenomena takes into account the dissolution of the glass containers and congruent emissions of the radio-nuclides including filiation chains and some simplified chemistry. Secondly, it is to use the near field computations in order to simulate the nuclide migrations in a 2D far field (Couplex 3). Coupling in between the two simulations takes into consideration the periodicity of the disposal modules and the geometry of the repository described in Couplex 1. The mixed finite element and discontinuous Galerkin methods are used to solve the convection–diffusion equations. In order to handle the nonlinear precipitation/dissolution term, we developed a new iterative technique that combines Picard and Newton–Raphson methods.  相似文献   

At the heart of the cultural approach in geography: Thinking space     

Paul Claval 《GeoJournal》2004,60(4):321-328

The way that space is thought of is at the heart of the cultural approach in geography. The passing down of all the components of a culture depends upon the way data is aquired and processed, the results memorized or broadcast. Communication shapes the experience and the knowledge of space and time. It gives to everyone the idea that the real world is doubled by a beyond which plays a central role in social life, since it is upon such a beyond that normative thinking relies and that a significance is given to individual and social life. The spheres of lived-in and known space and time, as well as that of the beyond, vary according to available technologies. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

塔里木盆地南缘历史时期气候环境变化的过程与特征   总被引：2，自引：9，他引：2  

钟巍  塔西甫拉提·特依甫  王立国  李偲 《中国沙漠》2004,24(3):261-267

根据塔里木盆地南缘具较高分辨率的湖沼相沉积物碳酸盐δ^13C和粒度等记录，恢复出2162-850BC期间为一相对稳定的温暖干旱时期，之后迅速转冷湿，湿润程度呈持续、阶段式增加，50 BC至500 AD期间呈现的显著冷湿特征于550 AD之后突变转暖干而结束。550 AD和1000 AD前后的具突变性质的气候事件在南疆地区近2．0ka的气候变化中具有重要意义，反映气候状况有过重大调整。850—1300AD期间(相当于中世纪温暖期)冷暖、干湿多变，但温暖特征并不明显。特别是1100—1200AD期间气候快速、频繁变化之后，奠定了本地区现代稳定干旱环境特征。区域对比表明，尼雅剖面记录的气候变化具有广泛的区域一致性。  相似文献