最大似然法在植被信息识别提取中的应用

遥感影像上的植被信息是一个很重要的基础信息源,而植被信息的提取又存在很多方面的影响,如"混合像元"、"异质同像".通常,应用最大似然法不能很好地解决这些方面的影响.笔者提出了"先主要后次要,层次化推进原则",应用最大似然方法进行植被信息识别提取,降低了"异质同像"的误判率,较大程度上避免了"混合像元"的不确定因素,同时将"混合像元"作为进一步区分不同植被类型的参考依据,使可解译的植被信息量增加,取得良好的效果.     

振荡试验确定倾斜承压含水层水文地质参数

为评价振荡试验在获取倾斜承压含水层水文地质参数过程中含水层倾角对计算结果的影响,基于Kipp模型推导了考虑承压含水层倾角的振荡试验解析解模型。倾斜承压含水层量纲一贮水系数和量纲一导水系数不变条件下,测试井-含水层系统的量纲一阻尼系数随着倾角的增加而增加。修正模型计算的量纲一阻尼系数与Kipp模型计算的量纲一阻尼系数偏差10%以上时,必须考虑倾角的影响并且承压含水层倾角对水头响应曲线造成影响临界角度约为34°。修正模型和Kipp模型对现场振荡试验水头响应曲线分析结果的差异表明,忽略含水层倾角会对倾斜承压含水层导水系数和贮水系数的计算结果产生较大误差。     

Estimation of ultimate bond strength for soil nails in clayey soils using maximum likelihood method

This paper presents a maximum likelihood estimation of the ultimate bond strength for soil nails in clays. Both uncensored and censored ultimate bond strength data for soil nails are collected from the literature. Based on the concept of maximum likelihood, a log-likelihood function is constructed for estimating the mean and coefficient of variation (COV) of the ultimate bond strength jointly using the two types of data. The mean and COV are determined as the pair that maximises the log-likelihood function. Two distribution models (normal and lognormal) are used for the estimation. A comparison of the relative competence between the two candidate distribution models that are adopted for describing the collected uncensored and censored data is performed using the Bayesian Information Criterion. Example designs of soil nail walls against internal pullout limit state of nails and overall stability limit state are provided to demonstrate the benefit of taking censored data into account for estimation of the ultimate bond strength of soil nails.     

Computationally efficient restricted maximum likelihood estimation of generalized covariance functions

Computational aspects of the estimation of generalized covariance functions by the method of restricted maximum likelihood (REML) are considered in detail. In general, REML estimation is computationally intensive, but significant computational savings are available in important special cases. The approach taken here restricts attention to data whose spatial configuration is a regular lattice, but makes no restrictions on the number of parameters involved in the generalized covariance nor (with the exception of one result) on the nature of the generalized covariance function's dependence on those parameters. Thus, this approach complements the recent work of L. G. Barendregt (1987), who considered computational aspects of REML estimation in the context of arbitrary spatial data configurations, but restricted attention to generalized covariances which are linear functions of only two parameters.     

松散承压含水层渗透系数变化规律与估算模型研究

我国华北隐伏型煤田的煤系普遍被第四系松散层覆盖,其中的松散承压含水层在煤矿生产中常带来矿井突水、地表沉降、井筒变形破坏等水文地质灾害,造成巨大经济损失和人员伤亡。渗透系数是反映松散承压含水层土体介质渗透能力的重要参数,其数值的合理估算,对该类煤矿水文地质灾害的防治具有重要指导意义。目前,华北隐伏型煤田松散承压含水层渗透系数往往仅通过现场抽水试验确定,基于地质勘探钻孔信息与数据估算松散承压含水层渗透系数的模型研究较少。通过收集淮北煤田祁东煤矿松散承压含水层已有抽水试验的钻孔信息与数据,选取承压含水层厚度、泥层砂层比、最厚砂层占比、有效应力与底砾层厚比作为影响指标,分别与渗透系数进行相关性分析。最终确定底砾层厚比、有效应力、泥层砂层比为关键影响指标,并分析其对渗透系数的影响规律。结果表明,松散承压含水层渗透系数随底砾层厚比的增加而增大,随有效应力和泥层砂层比的增加而减小。在此基础上,采用多元线性回归分析,提出了基于底砾层厚比、有效应力、泥层砂层比的渗透系数估算模型。并将该估算模型应用于淮北煤田祁南、朱仙庄、青东煤矿松散承压含水层的渗透系数估算,结果显示估算结果与试验值一致。     

Statistical Methods for Jointly Estimating the Decay Constant of 40K and the Age of a Dating Standard

To simultaneously evaluate the decay constant of ⁴⁰K () and the age of a standard (t _std) using isotopic data from geologic materials, we applied a series of statistical methods. The problem of estimating the most probable intercept of many nonlinear curves in and t _std space is formulated by an errors-in-variables nonlinear regression model. Then a maximum likelihood method is applied to the model for a point estimate, which is equivalent to the nonlinear least square method when measurement error distributions are Gaussian. Uncertainties and confidence regions of the estimates can be approximated using three methods: the asymptotic normal approximation, the parametric bootstrap method and Bonferroni confidence regions. Five pairs of published data for samples with ages from 2 ka to 4.5 Ga were used to estimate and the age of Fish Canyon sanidine (t _FCs). The statistical procedure yields most probable estimates of (5.4755 ± 0.0170 × 10^–10 (1)/year) and t _FCs (28.269 ± 0.0661 (1) Ma) which are in between previously published values. These results indicate the power of our approach to provide improved constraints on these parameters, although the preliminary nature of some of the input data require further review before the values can be adopted.     

On the solutions of modeling a slug test performed in a two-zone confined aquifer

The slug test is a popular field method for estimating aquifer parameters. As a finite-thickness skin is present at a wellbore, the result of test-data analysis may represent average hydraulic properties of the skin and formation zones. Moench and Hsieh (Int. Assoc. of Hydrogeology, The IAH 17th International Congress on Hydrology of Rocks of Low Permeability, Int. Assoc. of Hydrogeology. Tucson, Arizona, 7–12 January) provided the Laplace-domain solution for a confined aquifer with a finite-thickness skin that satisfies the governing equations, boundary conditions, and continuity requirements at the interface of the skin and formation zones. Two new formulae presented here relate the modified zero-order Bessel functions of the first and second kinds to their first and second derivatives. Their solution is evaluated using the modified Crump approach for the Laplace inversion. The numerical values obtained by the modified Crump approach are compared with others based on finite-element modeling. The results indicate that the values based on finite-element modeling exhibit poor accuracy, attributed to errors in the mass balance equation and interface condition in their mathematical model.

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Resumen Los ensayos slug o tipo pulso son métodos populares de campo para estimar parámetros de acuíferos. Debido a que en los sondeos existe una membrana de espesor finito, el resultado del análisis de los datos del ensayo pueden representar las propiedades hidráulicas promedio de las zonas de la formación y dicha membrana. Moench AF y Hsieh PA (Asociación Internacional de Hidrogeólogos, 7–12 Enero 1985) Análisis de datos de prueba slug en un pozo con membrana de espesor finito. 17 Congreso Internacional de la Asociación Internacional de Hidrogeólogos sobre Hidrología de Rocas de Baja Permeabilidad. Asociación Internacional de Hidrogeólogos. Tucson, Arizona. 7–12 Enero. han aportado la solución en el ámbito de Laplace para un acuífero confinado con una membrana de espesor finito que satisface los requerimientos de las ecuaciones dominantes, las condiciones restrictivas, y de continuidad en la interfase de las zonas de formación y membrana. Las dos nuevas fórmulas que se presentan aquí relacionan las funciones modificadas Bessel de orden cero de la primera y segunda clase con su primera y segunda derivadas. Se evalúa su solución usando el enfoque modificado de Crump para la inversión Laplace. Los valores numéricos obtenidos mediante el enfoque modificado de Crump se comparan con otros valores numéricos basados en modelos de elementos finitos. Los resultados indican que los valores basados en el modelo de elementos finitos presentan poca precisión, que se atribuye a errores en la ecuación de balance de masa y a las condiciones de interfase en su modelo matemático.

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Résumé Le slug-test représente une méthode populaire de terrain pour estimer les paramètres d’un aquifère. Du fait de la présence d’une couche à l’épaisseur limitée sur un site de forages, le résultat de l’analyse des données du test pourrait représenté le terrain mais aussi cette couche. Moench AF et Hsieh PA (Association Internationale d’Hydrogéologie, 7–12 Jan 1985) Analyses de données de slug test dans un puits présentant une couche d’épaisseur finie. 17ème congrès international de l’AIH sur l’Hydrologie des roches de faible perméabilité, Association Internationale d’Hydrogéologie. Tucson, Arizona, 7–12 Jan. apportent une solution du domaine de Laplace pour un aquifère confiné avec une épaisseur limitée qui satisfait l’équation en question, les conditions aux limites, et les besoins de continuité à l’interface de la couche et de l’encaissant. Deux nouvelles formules présentées dans cet article met en relation les fonctions de Bessel modifiées d’ordre zéro du premier et second type, avec leur dérivées première et deuxième. Leurs solutions sont évaluées en utilisant une approche de Crump modifiée pour l’inversion de Laplace. Les valeurs numériques obtenues avec l’approche de Crump sont comparées avec d’autres approches utilisant les modèles aux éléments finis. Les résultats indiquent que les valeurs basées sur les modèles aux éléments finis montrent une faible précision, du fait d’erreurs dans le bilan hydrologique et les conditions aux limites dans le modèle.

     

侧向有限越流承压含水层中非完整井非稳定流模型及解析解

工程建设中当距离抽水井r=rb处水位基本没有变化或不受抽水影响时,或当此处存在止水帷幕时,含水层系统视为侧向有限延伸,rb为有限半径。为此,构建更加符合工程实际的侧向有限延伸的典型弱透水层-承压水层系统中非完整井非稳定流计算模型,同时考虑井径和井储效应的影响,应用Laplace变换和分离变量法得到了水位降深在拉氏空间下的解析解,并应用拉氏数值逆变换Stehfest法得到真实空间下的水位降深。新建立的解析解可以进一步退化为诸多已有解,并进一步将其与已知解和有限元数值解进行对比,验证了所得解的正确性和可靠性。基于新建解重点分析了侧向边界和井的完整性对承压水层水位降深的影响。结果表明:含水层系统的侧向有限边界仅对抽水后期的水位降深影响明显,含水层系统侧向无限延伸情况下的水位降深要大于情形1(在r=rb处为定水头边界)且明显小于情形2(在r=rb处为不透水边界)下的水位降深,rb越小,两者之间的误差越大;抽水井的完整性对整个抽水期间不同情形下的水位降深均有明显的影响,承压含水层顶板处的水位降深随着抽水井滤管的长度和埋深的增加而减小。     

On estimating the parameters in mixtures of circular normal distributions

The method of maximum likelihood used in analyzing data which are bimodal in the range (0, )is lengthy and not always successful. Two alternative methods are proposed and the results compared with those obtained by using the method of maximum likelihood on orientation data from clasts and shells. It is shown that a procedure based on the Method of Moments gives comparable results and is much more practicable.     

On maximum likelihood estimation of parameters in incorrectly specified models of covariance for spatial data

The analysis of, and from, models of spatial data usually proceeds under the assumption, often implicit, that the correct model has been specified. However, any model identification procedures based on sample data are subject to error, and consequences of such errors then permeate subsequent analysis. Thus, an attempt to quantify some of these consequences is of interest. A standard framework for analysis is extended here, by introduction of information theory, to permit the study of effects of model misspecification on maximum likelihood estimators of parameters of model covariance. Asymptotically valid theoretical results are presented, and the relevance of these results to samples of finite sizes met in practice is assessed in a series of simulation experiments. The effect of model misspecification, and use of estimators of parameters of misspecified covariance models, on the practical problem of prediction at a previously unsampled location is considered briefly, and further areas for possible investigation are outlined.     

Acoustic method for defining the stress state of a rock massif based on solution of the seismic inverse problem

A method for estimating the stress–strain state of a rock massif in the vicinity of underground facilities is substantiated. This method is based on solution of the boundary inverse problem of defining the components of an external stress field from the acoustic sounding data. The acoustic sounding data used are the arrival times of diving head longitudinal waves, recorded in a long mine shaft. Numerical experiments have revealed the optimal arrangement of the recording network and the limited relative error in the input data, which, taken together, provide for solvability of the inverse problem.     

On the maximum width of oil stringers under hydrodynamic flow conditions

An analysis is presented of the maximum thickness of a stationary buoyant oil-mass, trapped under an angled incline, when subjected to hydrodynamic, surface tension and buoyancy forces. For high water-flow speeds down the aquifer, with upward buoyancy forces dominantly combating hydrodynamic pressure, it is shown that the maximum oil thickness occurs at about 60% of the length of the oil stringer measured from the upward end. The length of the oil stringer then is roughly proportional to the square root of the oil-mass contained, as is the maximum thickness. For low water-flow speeds, in which buoyancy and surface tension are dominantly balanced (with only lesser contributions from hydrodynamic pressure), the oil length is effectively constant, whereas the maximum thickness grows proportionately to the 3/4 power of the contained oil mass at low oil masses, and proportionately to the oil mass at high mass values. As the water-flow velocity increases, the shaping of the oil stringer shifts from the small bubble form to the long oil stringer form. Analytic formulae are given to provide approximate methods from which to estimate oil and gas accumulations under more complex conditions.     

On the solution of plane flow of granular media for jump non-homogeneity

This paper deals with the plane plastic equilibrium of a cohesive frictional material in the case of a jump non-homogeneity. Three types of interface separating rigid-plastic bodies with different material parameters are distinguished: (i) a perfect adhesion contact, (ii) a thin layer of a material different from the adjacent bodies, (iii) a combined frictional-adhesive contact. A sliding along the interface may occur if certain conditions are satisfied. For the first two types of joint, the direction and propagation of the velocity jump vector along the interface follow from the classical theory of plane plastic flow. In the third case, the potential sliding rule relating the velocity jump vector to the limit condition of the joint, or to the potential different from the limit condition, may be adopted. The direction of the velocity jump vector results from such a rule. The problem of stability of a slope, being continuously non-homogeneous in one region, and homogeneous in another, is shown in an example. The two regions of the slope are separated by the interface, a thin layer of a different material, (type ii). The associated flow law for both regions of the slope and for the material of the interface is assumed.     

An oblique factor analysis solution for the analysis of mixtures

The problems involved in the factor analysis of data consisting of measurements of material quantity or proportion are discussed, and the inability of existing factor analysis solutions to properly model such data is pointed out. A new factor analysis solution using the linear programming technique is presented which properly analyzes mixture data. A numerical example is presented in which a body of suspended sediment grain-size distribution data is analyzed using the new factor analysis solution. FORTRAN-IV subroutines for computing this solution are included in an Appendix.     

试论主要类型矿床的形成深度与最大延深垂幅

在大量典型矿床实地调查和国内外综合对比研究的基础上,基于深部找矿的现实需要和存在问题,本文首先回顾评述了主要矿床类型的原始成矿深度,按受控于中下地壳尺度大规模岩浆堆积体的超深成岩浆矿床与受控于流体渗透率制约的中上地壳深成、中成和浅成岩浆热液矿床序列展开。在此基础上尝试探讨主要类型矿床的最大延深垂幅,探讨分析了以Bushveld层状岩体和Voisey’s Bay小岩体为代表的铜镍矿床、驱龙为代表的斑岩铜矿床、Muruntau为代表的造山型金矿、胶东金矿省的已控制延深垂幅、剥蚀程度以及深部可能的延深空间。内生矿床系统具有很宽的成矿深度范围,大型层状岩体的成矿深度可逾20 km,最大矿化垂直延深幅度可达6~8 km。岩浆热液矿床的最大成矿深度以地壳尺度流体渗透的下限为底界,其中造山型金矿床成矿深度最大(约12~15 km),伟晶岩和花岗岩型矿床次之,斑岩型矿床居中(约2~6 km),浅成低温金银矿床深度最浅(1 km至近地表);相应的最大延深垂幅则依次可达4~7 km、2~3 km和1 km。评述了高渗透性的聚矿构造空间、成矿作用顶峰、合适的矿床保存条件等控制因素及部分标志。并对如何确定合理统一的成岩成矿深度(压力)的估算方法以及确定最大成矿深度与矿化体系最大延深幅度的理论依据、判断标志、综合辨识方法体系等未来研究方向进行了展望。     

应用最大熵原理分析水利工程经济效益的风险

采用层次分析方法,将水利工程经济效益系统分为防洪、发电、灌溉效益子系统,辩识出风险因子,建立了基于最大熵原理(准则)的经济效益风险分析模型,并给出求解方法。对总系统经济效益风险分析采用了两种方法:一是直接对辩识出的风险因子进行概率分析,得出总效益指标的最大熵密度函数;二是按照"风险树"的思路,分析子系统效益的风险特性,再进行风险组合,从而考察总效益的风险性。用实例验证了该模型的可行性和实用性。     

A statistical cyclone intensity prediction (SCIP) model for the Bay of Bengal

A statistical model for predicting the intensity of tropical cyclones in the Bay of Bengal has been proposed. The model is developed applying multiple linear regression technique. The model parameters are determined from the database of 62 cyclones that developed over the Bay of Bengal during the period 1981–2000. The parameters selected as predictors are: initial storm intensity, intensity changes during past 12 hours, storm motion speed, initial storm latitude position, vertical wind shear averaged along the storm track, vorticity at 850 hPa, Divergence at 200 hPa and sea surface temperature (SST). When the model is tested with the dependent samples of 62 cyclones, the forecast skill of the model for forecasts up to 72 hours is found to be reasonably good. The average absolute errors (AAE) are less than 10 knots for forecasts up to 36 hours and maximum forecast error of order 14 knots occurs at 60 hours and 72 hours. When the model is tested with the independent samples of 15 cyclones (during 2000 to 2007), the AAE is found to be less than 13 knots (ranging from 5.1 to 12.5 knots) for forecast up to 72 hours. The model is found to be superior to the empirical model proposed by Roy Bhowmik et al (2007) for the Bay of Bengal.     

On the application of the maximum entropy meshfree method for elastoplastic geotechnical analysis

In this study, the Maximum Entropy Meshfree (MEM) method is employed for analysing geotechnical problems involving material nonlinearity, assuming small strains. The efficiency of the MEM method is evaluated through several solution schemes for the global governing equations as well as the local constitutive equations. The conventional implicit approach involving the Newton-Raphson method and an explicit adaptive dynamic relaxation technique are employed for solving the governing equations, while local constitutive equations are solved numerically as well as analytically. Two- and three-dimensional numerical experiments are performed to study the efficiency of different configurations of the solution scheme, which leads to some important conclusions about application of the MEM method in geotechnical problems.