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对比研究了中国西部地区发生的6次中强地震前b值与C(n)值异常变化特征.6次地震前,b值和C(n)值都有异常显示.b值异常一般出现较早,最早出现在震前1年左右;C(n)值异常大多在震前半年至2~3个月出现.b值曲线异常形态一般不太典型,而C(n)值异常形态较典型,表现为峰值异常.地震前2种异常同时出现.还对计算上述参数的空间范围的选取及窗长和步长的选取进行了讨论. 相似文献
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目的:在ABCD2评分基础上,评估结合弥散加权成像(DWI)及CTA对短暂性脑缺血(TIA)后短期内发生脑梗死风险的预测价值。方法:连续选取本院2015年1月至2017年6月170例TIA患者(平均年龄62.4岁±5.4岁),全部患者均行DWI及CTA检查,且随访3个月。分别于7天、3个月记录患者ABCD2评分、DWI阳性结果及CTA诊断大动脉粥样硬化(LAA),以评估所有患者短期内发生脑梗死风险的预测价值。结果:170例患者中,68例(40%)患者DWI阳性,43例(25%)诊断LAA。DWI阳性患者中单侧肢体无力(OR=2.3;95% CI,1.1~4.8),TIA症状持续时间≥ 60 min(OR=3.7;95% CI,1.4~9.9),ABCD2> 5(OR=5.4;95% CI,1.5~18.8),LAA(OR=2.7;95% CI,1.3至5.5)。随访期间,7天内发生脑梗死1例,7天至3个月内发生脑梗死6例,ABCD2评分> 5(OR=24.4;95% CI,2.5~238.7),DWI阳性结果(OR=9.8;95% CI,1.1~83.1),LAA(OR=20.4;95% CI,2.4~175.1)。除1例患者外,3个月内发生脑梗死的DWI均为阳性。ABCD2评分、DWI阳性结果及LAA与7天、3个月脑梗死风险的增加是相关联的。结论:在ABCD2评分基础上引入DWI和CTA检查作为辅助,能提高对TIA后发生脑梗死风险的预测能力。 相似文献
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1资料的选取及记录连续性分析以中国地震局地球物理研究所CDSN技术管理中心出版的《中国数字台网台站通讯》为依据,选取1987年1月至1996年12月的资料(1992年前不含拉萨、西安,1992~1995年不含西安)。其中缺记只包括记录停止和邮寄,不含... 相似文献
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日本发生中强地震的灰色预测 总被引:1,自引:0,他引:1
应用“灰色控制系统”理论,选取1980年1月至1988年12月日本的地震序列资料,将(6.0,7.0]级地震作为样本,建立了预报地震发震时刻的动态模型。选取了最佳模型对日本未来发生中强地震的时间进行了预测。从函数变换的观点,对GM(1,1)模型进行了广义解释,指出序列建模必须从满足光滑度的时刻计起。大量计算表明,用“足够小量”样本建模比大量样本建模拟合与外推精度要高,并从信息论角度进行了剖析。 相似文献
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根据关东-东海地区1980年1月至1993年4月期间的地震资料,描绘出了菲律宾海板块和欧亚板块之间目前地震平静的边界。关东-东海地区的大多数地震,不是发生在上覆板块(欧亚板块)之内,就是发生在俯冲板块(菲律宾海板块)之中,其震源深度不到30km。 相似文献
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《地球物理学报》1998,(2)
1997年天灾预测总结会议于12月!7日至19日在北京召开.会议共收到论文22篇.来自水利、地震、气象和有关院校的30名学者、专家到会交流.会议自始至终充满着热烈争鸣的气氛.会议的中心议题是总结1997年天灾预测专业委员会以各种形式提出的预测意见的效果和经验教训.与会代表认为1997年的天灾预测效果是可喜的.(l)预测1997年至2000年期间,中国大陆特别是105”以西地区,面临发生7.5级以上强震的危险.实际情况是:1997年11月8日旧时02分(北京时间),在中国大陆东经105”E以西地区的昆仑山区(35.2”N,87.3”E),发生了一次7… 相似文献
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Considering complexity in groundwater modeling can aid in selecting an optimal model, and can avoid over parameterization, model uncertainty, and misleading conclusions. This study was designed to determine the uncertainty arising from model complexity, and to identify how complexity affects model uncertainty. The Ajabshir aquifer, located in East Azerbaijan, Iran, was used for comprehensive hydrogeological studies and modeling. Six unique conceptual models with four different degrees of complexity measured by the number of calibrated model parameters (6, 10, 10, 13, 13 and 15 parameters) were compared and characterized with alternative geological interpretations, recharge estimates and boundary conditions. The models were developed with Model Muse and calibrated using UCODE with the same set of observed data of hydraulic head. Different methods were used to calculate model probability and model weight to explore model complexity, including Bayesian model averaging, model selection criteria, and multicriteria decision-making (MCDM). With the model selection criteria of AIC, AICc and BIC, the simplest model received the highest model probability. The model selection criterion, KIC, and the MCDM method, in addition to considering the quality of model fit between observed and simulated data and the number of calibrated parameters, also consider uncertainty in parameter estimates with a Fisher information matrix. KIC and MCDM selected a model with moderate complexity (10 parameters) and the best parameter estimation (model 3) as the best models, over another model with the same degree of complexity (model 2). The results of these comparisons show that in choosing between models, priority should be given to quality of the data and parameter estimation rather than degree of complexity. 相似文献
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The effect of forcing and landscape distribution on performance and consistency of model structures
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It is often challenging to determine the appropriate level of spatial model forcing and model distribution in conceptual rainfall‐runoff modelling. This paper compares the value of incorporating both spatially distributed forcing data and spatially distributed model conceptualisations based on landscape heterogeneity, applied to the Ourthe catchment in Belgium. Distributed forcing data were used to create a spatial distribution of model states. Eight different configurations were tested: a lumped and distributed model structure, each with four levels of model state distribution. The results show that in the study catchment the distributed model structure can in general better reproduce the dynamics of the hydrograph, and furthermore, that the differences in performance and consistency between calibration and validation are smallest for the distributed model structure with distributed model states. For the Ourthe catchment, it can be concluded that the positive effect of incorporating a distributed model structure is larger than that of incorporating distributed model states. Distribution of model structure increases both model performance and consistency. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
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建立符合油气储层近地表复杂介质强衰减性质的数学-物理模型是油气勘探和开发的重要课题.本文针对D'Alembert黏弹性介质模型存在的量纲不统一和不能充分刻画孔隙介质结构的不足,通过引入孔隙度和渗透率等参数修改耗散项,改进了原D'Alembert模型,获得了能精细刻画具有强吸收衰减特征的近地表复杂介质模型,即改进的近地表黏弹性模型.基于这种改进的模型,推导了波频散和衰减的表达式,并研究了孔隙度、流体黏度等物理参数对波频散和衰减的影响,获得了相应的规律性认识.为了验证新模型预测近地表介质中波衰减的有效性,本文将新模型应用于胜利油田YX工区的近地表实测数据,同时与弹性Biot模型和BISQ模型以及黏弹性BISQ模型进行了比较.结果表明,与其它三个模型比较,改进的近地表黏弹性模型能够很好地刻画近地表介质的强衰减性,而且新模型所涉及到的物理参数明显少于其它几种模型,有利于新模型在油气储层近地表复杂介质地震勘探的实际应用. 相似文献
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合理选择本构模型是土动力学问题数值模拟中的一项重要工作。利用PLAXIS 2D软件的土工实验模拟功能分别对4种常用的岩土本构模型——线弹性模型、摩尔库伦模型、土体硬化模型和小应变土体硬化模型在往复荷载下的理论滞回曲线进行了对比分析,并在此基础上研究了选择不同本构模型对自由场地震反应分析结果的影响以及不同本构模型中各参数的变化对场地动力计算结果的敏感性分析。研究结果为土动力学问题数值模拟中如何选择本构模型和合理判断数值分析结果提供了参考依据。 相似文献
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Land surface temperature is a key parameter in monitoring the status of crop water stress by remote sensing, and studying the water and energy balance in cropland ecosystem. The component temperatures of crop and soil are especially significant in remote … 相似文献
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Ming-Chang Wu Gwo-Fong Lin Hsuan-Yu Lin 《Stochastic Environmental Research and Risk Assessment (SERRA)》2013,27(7):1661-1671
The model performance is usually influenced by the quality of the data used in model construction. If the model performance is less affected by data quality, the resulting estimates will be more reliable. In this paper, the variation in model performance due to different data quality is explored in a field-scale application. Hence, two models, the proposed support vector machine (SVM) based model and the Stephen and Stewart (SS) model, are employed for daily estimation of evaporation at an experiment station. Five scenarios corresponding to different data qualities are designed to evaluate the effect of data quality on model performance. Additionally, the most effective meteorological variables influencing evaporation are obtained by a systematic input determination process. These most effective meteorological variables are used as inputs to the SVM-based model. The results show that the model performance decreases as the data quality decreases (i.e. the percentage of missing data increases). However, the estimation accuracy of SVM-based models is still better than that of the SS model. Moreover, the variation of model performance of the SVM-based model is smaller than that of the SS model. That is, the negative impact of different data quality is effectively decreased by using the SVM-based model instead of the SS model. 相似文献
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In this paper, a three-dimensional semi-idealized model for tidal motion in a tidal estuary of arbitrary shape and bathymetry is presented. This model aims at bridging the gap between idealized and complex models. The vertical profiles of the velocities are obtained analytically in terms of the first-order and the second-order partial derivatives of surface elevation, which itself follows from an elliptic partial differential equation. The surface elevation is computed numerically using the finite element method and its partial derivatives are obtained using various methods. The newly developed semi-idealized model allows for a systematic investigation of the influence of geometry and bathymetry on the tidal motion which was not possible in previously developed idealized models. The new model also retains the flexibility and computational efficiency of previous idealized models, essential for sensitivity analysis. As a first step, the accuracy of the semi-idealized model is investigated. To this end, an extensive comparison is made between the model results of the semi-idealized model and two other idealized models: a width-averaged model and a three-dimensional idealized model. Finally, the semi-idealized model is used to understand the influence of local geometrical effects on the tidal motion in the Ems estuary. The model shows that local convergence and meandering effects can have a significant influence on the tidal motion. Finally, the model is applied to the Ems estuary. The model results agree well with observations and results from a complex numerical model. 相似文献
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合理的随机模型是确定高精度卫星轨道的前提条件,目前广泛应用于地面观测数据的随机模型主要有高度角模型和载噪比模型,本文通过对GRACE卫星实测数据的分析表明上述随机模型均不能很好地描述GRACE卫星星载GPS观测值的噪声特点,为此,文中提出了扩展的高度角模型和扩展的载噪比随机模型.利用自主研发的精密定轨软件,分别采用高度角模型、扩展的高度角模型、载噪比模型、扩展的载噪比模型对GRACE卫星进行了轨道确定.数值结果表明:(1)高度角模型的运动学轨道径向精度为3.4 cm,扩展的高度角模型的为3.3 cm;(2)载噪比模型的运动学轨道径向精度为4.9 cm,扩展的载噪比模型的则为3.4 cm,精度提高了1.5 cm.经比较分析,文中提出的扩展的高度角模型和载噪比模型能更好地描述GRACE卫星观测值噪声特点,并能取得更高的卫星定轨精度. 相似文献