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851.
Eulogio Pardo-Igúzquiza 《Mathematical Geology》1998,30(1):95-108
In this paper, the maximum likelihood method for inferring the parameters of spatial covariances is examined. The advantages of the maximum likelihood estimation are discussed and it is shown that this method, derived assuming a multivariate Gaussian distribution for the data, gives a sound criterion of fitting covariance models irrespective of the multivariate distribution of the data. However, this distribution is impossible to verify in practice when only one realization of the random function is available. Then, the maximum entropy method is the only sound criterion of assigning probabilities in absence of information. Because the multivariate Gaussian distribution has the maximum entropy property for a fixed vector of means and covariance matrix, the multinormal distribution is the most logical choice as a default distribution for the experimental data. Nevertheless, it should be clear that the assumption of a multivariate Gaussian distribution is maintained only for the inference of spatial covariance parameters and not necessarily for other operations such as spatial interpolation, simulation or estimation of spatial distributions. Various results from simulations are presented to support the claim that the simultaneous use of maximum likelihood method and the classical nonparametric method of moments can considerably improve results in the estimation of geostatistical parameters. 相似文献
852.
853.
用时面深概化法估算清江中上游流域可能最大暴雨 总被引：1，自引：0，他引：1
在分析清江流域暴雨洪水特点及含清江流域暴雨一致区内暴雨特性的基础上,推测出形成清江中上游可能最大暴雨的天气形势和梅雨形势类似,暴雨为梅雨雨带中的暴雨,水汽入流方向为西南方向,采用时面深概化法估算了清江中上游流域２４ｈ和３ｄ可能最大暴雨。 相似文献
854.
A seismic coda wave from local earthquakes is an indication of heterogeneity in the crust and upper mantle, and codaQ (Q
c
) is the parameter defining the temporal decay of the coda wave. ButQ
c
estimates obtained with the conventional least-square method are not based on any solid statistical background, assuming the Gaussian distributiona priori. In this study, we propose a statistically reliable estimation method of estimatingQ
c
using the maximum likelihood method, and show its validity and usefulness with the data from the 1986 Joint Seismological Research in the western Nagano Prefecture. We found first that theQ
c
estimation with the maximum likelihood method is statistically valid and its reliability can be checked with the -square test. Next,Q
c
around Ohtaki village, within the studied area, is estimated using the maximum likelihood method. The averageQ
c
value at low frequencies (up to 2 Hz) is one of the lowest in the world, which is in harmony with the geological setting of the site condition directly above an active fault. 相似文献
855.
H. Nagahama 《Mathematical Geology》1992,24(8):947-955
The principle of maximum entropy can be used to determine the shear strain in natural shear zones. When the margin of a shear zone is assumed, the principle leads to the truncated exponential distribution of the shear strain. Ifx is the distance remote from the shear zone center, which possesses the maximum shear strain, the shear strain (x) is given by
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相似文献
856.
Inhomogeneous trends in the onset date of extreme hot days in China over the last five decades
 下载免费PDF全文 基于1960-2018年均一化日最高气温(Tmax)资料,发现中国大部分区域高温初始发生日期(FirstEHD)呈提前趋势,但华北地区一些站点呈推迟趋势,这主要由上述区域Tmax的长期变化趋势决定,但Tmax变率的影响也不可忽视.FirstEHD的变化趋势在1990s出现年代际转折,其中新疆,华北和长江流域在1990s前后FirstEHD变化趋势的符号发生变化,华南地区则表现为1990s前后FirstEHD趋势幅度的不同,但符号保持不变;研究表明FirstEHD趋势的年代际转折转折与大气环流年代际趋势的变化紧密相关. 相似文献
857.
长江流域是我国夏季高温热浪灾害的多发区之一,该地区日最高温度(Tmax)具有显著的低频(10～30 d和30～60 d周期)变化特征,超前-滞后相关分析和气温方程诊断的结果显示,影响长江流域Tmax低频变化的大尺度环流/对流信号包含:自欧亚大陆东移南下的低频波列,自东北亚向西南方向传播的异常环流,以及由西太平洋向东亚传播的低频对流;这些低频对流/环流活动通过改变辐射加热过程及绝热过程,导致长江流域Tmax的低频变化。为了客观且有效地辨识和捕捉这些先兆信号,并考虑长江流域Tmax与大尺度因子间的非线性作用,本文采用机器学习方法中的卷积神经网络(Convolutional Neural Network,CNN)对大量历史数据进行训练,并构建了长江流域Tmax的延伸期预报模型。在独立预报阶段,CNN预报模型对长江流域区域平均Tmax的预报时效达30 d,提前5～30 d预报的Tmax与观测Tmax的时间相关系数介于0.63～0.70(通过99％置信度的显著性检验),量级偏差(均方根误差)小于1个标准差,显示出CNN在延伸期灾害天气预报的应用潜力。 相似文献
858.
Control volume methods are frequently used in porous media flow. This article gives an example on how one method, the Multipoint Flux Approximation method (MPFA), fails to satisfy the maximum principle for strong anisotropies or grid skewnesses, and develops conditions for when the monotonicity property holds for uniform parallelogram grids in homogeneous media. The conditions developed are applicable to any nine-point scheme in 2D or 27-point scheme in 3D, and is useful when the method produces a system matrix which is not an M-matrix. 相似文献
859.
The purpose of this paper is to describe a mathematical and computer model that has been developed by TransCanada for TransCanada
Pipelines (TCPL) and for the Canadian Gas Potential Committee (CGPC) for future Canadian natural gas resource assessment work.
It was developed in the contexts of developing a gas supply model for forecasting future Canadian gas supply for TCPL and
of improving the CGPC's assessment methodologies and software.
The model developed in this paper integrates two discovery process models used by the CGPC and solves the economic truncation
problem for semi-mature to mature plays. It is based on applying techniques developed by G. M. Kaufman and J. D. Fuller and
colleagues in new ways which extends the work of these authors.
This model has a number of important advantages including: fast computational speed, integration of parametric and nonparametric
statistical approaches, integration of the Kaufman and others model and the Arps-Roberts model, overcoming a PETRIMES limitation
of a maximum of 1000 samples, providing a finding rate forecast for economic analysis and providing a fresh look at solving
the economic truncation problem.
The details of the new Modified Arps-Roberts Model (now known as the Truncated Discovery Process Model or TDPM for short)
are discussed in this paper. 相似文献
860.
中国大陆地震活跃期及平静期判断的新方法与应用 总被引：1，自引：1，他引：0
基于小波变换方法,提出了刻画地震活动周期的指标一周期系数,该系数为描述地震活动周期显著程度的一种量度。应用该方法对中国大陆地区1890～2002年22年左右与10年左右周期(活跃期与平静期组成一个周期)内地震活动周期系数的变化过程进行了分析,结果表明,中国大陆地区的地震活跃期及7．5级以上地震的发生时段处于22年周期系数曲线的下降过程中,而平静期则与周期系数曲线的上升过程相对应。10年左右的周期系数将活跃期与平静期进行了大致分离,从而为地震活跃期的开始与结束的判断提供了一种全新的研究思路与方法。研究表明,中国大陆已处于20世纪以来的“第5活跃期”的尾声。 相似文献
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