Conditional Simulation of Random Fields with Bivariate Gamma Isofactorial Distributions

This work focuses on a random function model with gamma marginal and bivariate isofactorial distributions, which has been applied in mining geostatistics for estimating recoverable reserves by disjunctive kriging. The objective is to widen its use to conditional simulation and further its application to the modeling of continuous attributes in geosciences. First, the main properties of the bivariate gamma isofactorial distributions are analyzed, with emphasis in the destructuring of the extreme values, the presence of a proportional effect (higher variability in high-valued areas), and the asymmetry in the spatial correlation of the indicator variables with respect to the median threshold. Then, we provide examples of stationary random functions with such bivariate distributions, for which the shape parameter of the marginal distribution is half an integer. These are defined as the sum of squared independent Gaussian random fields. An iterative algorithm based on the Gibbs sampler is proposed to perform the simulation conditional to a set of existing data. Such ‘multivariate chi-square’ model generalizes the well-known multigaussian model and is more flexible, since it allows defining a shape parameter which controls the asymmetry of the marginal and bivariate distributions.     

Characterization of Geochemical Distributions Using Multifractal Models

The use of multifractals in the applied sciences has proven useful in the characterization and modeling of complex phenomena. Multifractal theory has also been recently applied to the study and characterization of geochemical distributions, and its relation to spatial statistics clearly stated. The present paper proposes a two-dimensional multifractal model based on a trinomial multiplicative cascade as a proxy to some geochemical distribution. The equations for the generalized dimensions, mass exponent, coarse Lipschitz–Hölder exponent, and multifractal spectrum are derived. This model was tested with an example data set used for geochemical exploration of gold deposits in Northwest Portugal. The element used was arsenic because a large number of sample assays were below detection limit for gold. Arsenic, however, has a positive correlation with gold, and the two generations of arsenopyrite identified in the gold quartz veins are consistent with different mineralizing events, which gave rise to different gold grades. Performing the multifractal analysis has shown problems arising in the subdivision of the area with boxes of constant side length and in the uncertainty the edge effects produce in the experimental estimation of the mass exponent. However, it was possible to closely fit a multifractal spectrum to the data with enrichment factors in the range 2.4–2.6 and constant K₁ = 1.3. Such parameters may give some information on the magnitude of the concentration efficiency and heterogeneity of the distribution of arsenic in the mineralized structures. In a simple test with estimated points using ordinary lognormal kriging, the fitted multifractal model showed the magnitude of smoothing in estimated data. Therefore, it is concluded that multifractal models may be useful in the stochastic simulation of geochemical distributions.     

Robust and reliable metamodels for mechanized tunnel simulations

The main objective of this paper is to construct a robust and reliable metamodel for the mechanized tunnel simulation in computationally expensive applications. To accomplish this, four metamodeling approaches have been implemented and their performance has been systematically evaluated through a comparative study utilizing pure mathematical test functions. These metamodels are quadratic polynomial regression, moving least squares, proper orthogonal decomposition with radial basis functions, and an extended version of the latest approach. This extended version has been proposed by the authors and named proper orthogonal decomposition with extended radial basis functions. After that, a system identification study for mechanized tunneling has been conducted through the back analysis of synthetic measurements. In this study, the best performing metamodel, that is the one suggested by the authors, has been employed to surrogate a complex and computationally expensive 3D finite element simulation of the mechanized tunnel. The obtained results demonstrate that the proposed metamodel can reliably replace the finite element simulation model and drastically reduce the expensive computation time of the back analysis subroutine.     

工程计算力学中的正交基无网格方法

发现并研究了无网格伽辽金法(EFGM)节点不良分布以及采用一般高次多项式基构造形函数时产生数值解振荡的问题.提出工程计算力学的正交基无网格伽辽金法(MLMBOB),并以罚函数法引入强加边界条件,离散化得到偏微分方程的数值解.该方法保留了无网格伽辽金法所拥有的优秀品质,去除了其中的一些缺陷,使得用高次正交基作逼近时有高计算精度,它适合于工程计算中诸多计算问题.并用算例及其误差分析证实了该方法的优越性.     

废泥浆固液分离的正交试验研究

运用正交设计原理,通过具有代表性的试验,研究分析了各因素对泥浆固发离效果的影响,结果表明,影响混凝析主次因素为：混凝剂浓度、加量、搅拌时间。并指出混凝剂选择的方法和应注意的问题,以供工程参考。     

饶阳凹陷古近系层序发育的控制因素分析

在分析饶阳凹陷古近系层序类型和发育模式的基础上，根据层序的结构特点，对每种层序发育的控制因素进行了分析。认为在沉积物供应速率变化不大的情况下，盆地基底的的沉降速率和沉降高峰期的时间决定着裂谷期层序的结构、各体系域开始发育和结束的时期。沉积物供应速率和可容空间变化的速率的比值决定着准层序组的类型，局部高速率的沉积物供应回在湖侵期发育进积式准层序组。气候的变化也是层序发育的控制因素，在干旱期，湖平面变化和层序的结构主要受气候控制。     

混合显色体系同时测定铁和钛

在Fe、Ti共存时,邻菲啰啉作Fe的显色剂,邻苯二酚紫、盐酸羟胺和溴化十六烷基三甲基铵与Ti形成四元络合物。在此混合显色体系中,分别在490nm和720nm波长测定Fe和Ti互不干扰。方法用于水系沉积物和岩石中Fe和Ti的同时测定,取得了满意的结果。     

A New Type of Neural Network For Reservoir Identification Using Geophysical Well Logs

We have developed a neural network algorithm of radial basis network (RBN) type for geoscience applications. This new probabilistic neural network (PNN), referred to as “gravity-capturing neural network,” employs multidimensional even distance and introduces the resultant force competition mechanism for the output layer. When used for geological pattern recognition with well-logging data, it avoids misjudgment due to a magnitude jump of a single parameter and can extract complex and hidden formulas from laboratory and field measurements more efficiently. A field case study of reservoir identification with geophysical well logs is presented to demonstrate the advantages of this neural network over the conventional PNN in such classification applications.     

正交混凝试验在矿井水处理设计中的应用

针对高悬浮物矿井水,设计了5水平6因素的L25(56)正交混凝试验,并通过极差分析确定了混凝的最优化条件,即选择PAC作为混凝剂,pH值调节为9,混凝剂与助凝剂浓度比为20∶1,助凝剂PAM投加滞后30 s,水力条件依次为n=350 r.min-1快速搅拌30 s,n=120 r.min-1中速搅拌4 min,n=60 r.min-1慢速搅拌6 min。通过单因素分析了6种因素对混凝的影响程度,即:PAM投量>混凝剂种类>pH值>混凝剂投量>水力条件>投加时间。依试验结果,对垂向轴式混合反应池进行了参数设计。     

Estimation of regionalized compositions: A comparison of three methods

A regionalized composition is a random vector function whose components are positive and sum to a constant at every point of the sampling region. Consequently, the components of a regionalized composition are necessarily spatially correlated. This spatial dependence—induced by the constant sum constraint—is a spurious spatial correlation and may lead to misinterpretations of statistical analyses. Furthermore, the cross-covariance matrices of the regionalized composition are singular, as is the coefficient matrix of the cokriging system of equations. Three methods of performing estimation or prediction of a regionalized composition at unsampled points are discussed: (1) the direct approach of estimating each variable separately; (2) the basis method, which is applicable only when a random function is available that can he regarded as the size of the regionalized composition under study; (3) the logratio approach, using the additive-log-ratio transformation proposed by J. Aitchison, which allows statistical analysis of compositional data. We present a brief theoretical review of these three methods and compare them using compositional data from the Lyons West Oil Field in Kansas (USA). It is shown that, although there are no important numerical differences, the direct approach leads to invalid results, whereas the basis method and the additive-log-ratio approach are comparable.     

A Comparison of Random Field Models Beyond Bivariate Distributions

In order to determine to what extent a spatial random field can be characterized by its low-order distributions, we consider four models (specifically, random spatial tessellations) with exactly the same univariate and bivariate distributions and we compare the statistics associated with various multiple-point configurations and the responses to specific transfer functions. The three- and four-point statistics are found to be the same or experimentally hardly distinguishable because of ergodic fluctuations, whereas change of support and flow simulation produce very different outcomes. This example indicates that low-order distributions may not discriminate between contending random field models, that simulation algorithms based on such distributions may not reproduce the spatial properties of a given model or training image, and that the inference of high-order distribution may require very large training images.     

深立井多层位自动监测研究与应用

分析了影响深立井井壁应力、应变分布规律和井筒稳定性的主要因素,根据正交实验的“均匀分散性和整齐可比性”原理,运用矢量分析理论,在t阶有限域上(t为素数或素数主幂),构造出ut(u为向量的维数)个独立的空间向量,作为实验的序号,构造出适应深立井安全监测的正交实验表。配合智能化测试系统,克服了井筒穿越多种地层,受力状态复杂、含水量大、温度变化大、活动空间窄小等诸多困难,在多个煤矿深立井中实现了全深度、多层位、长时间智能化监控,达到了用最少的测点获得最多的有效信息的目的。     

电子探针多道波谱仪同时测试同一个元素的方法：以石英中Al 和Ti 含量的测试为例

电子探针显微分析是常用的原位分析矿物中各种主量元素含量的技术方法,但是对于微量元素的分析,提高测试精确度和准确度长期以来面临着各种挑战。常用的提高精确度方法有改变加速电压、加大电流和增加计数时间,但是这些方法容易使样品遭到破坏,发生元素迁移从而造成测试结果的不准确,增加计数时间还会降低测试效率。文章提出了一种利用电子探针多道波谱仪同时测试同一个元素的方法来提高待测元素特征X射线的强度值。该方法利用电子探针不同波谱仪同时测试同一个待测元素,通过测试标准样品中待测元素的总净计数和待测样品中待测元素的总净计数,结合标准样品中待测元素的浓度计算待测样品中待测元素的含量。该方法在同等测试条件下可以有效的提高待测元素特征X射线的强度值,从而提高了测试的精确度,降低了测试的检测限。文章以石英中Al和Ti含量的测试为例,验证了多道波谱仪同时测试同一个元素的方法在微量元素测试中的应用。测试Al元素时使用一个TAP晶体和一个TAPL晶体,测试Ti元素时使用三个PETL晶体,结合多点背景测试法准确测试了石英中Al和Ti的含量,在20 kV电压、500 nA束流和20 μm束斑直径的条件下可将Al的检测限降低至2.6×10-6 (3σ),将Ti的检测限降低至2.1×10-6 (3σ),测试获得石英参考标样中Al和Ti的含量分别为163.8×10-6±5.8×10-6 (3σ)和56.5×10-6±2.0×10-6 (3σ),皆在参考值区间(Al：154×10-6±15×10-6;Ti：57×10-6±4×10-6)内,并且具有较好的长期稳定性。     

沈北煤田煤炭地下气化初步探讨

主要阐述了沈北煤田煤炭地下气化原理、条件、煤炭气化开采依据,煤炭气化开采的发展远景及对国民经济发展的重要意义。     

论“重力归一化总梯度法”中的问题

重力归一化总梯度G^H(z)的没有明确的物理意义,归一化总梯度方法本身无完整的数学理论作为基础,二维和三维情况都只能探索其实验性的规律.弄清楚G^H(z)有无物理、数学的理论依据很有益处,这使人们在使用G^H(z)方法时不得不采取谨慎的探索态度     

煤田火区碳排放量计算模型和关键参数研究

完善碳排放清单,是进行减排工作的基础,为了查明煤田火区对大气碳排放的贡献量,以煤氧复合作用学说为理论基础,从不同的研究思路出发,提出了烧失煤量法和排放通量法两种火区碳排放量计算模型。在明确模型中关键参数“释放因子”“排放系数α”“排放通量”“排放系数β”的具体含义的基础上,重点对各参数所对应的获取途径进行了研究论述：(1)释放因子通过在室内进行煤自燃模拟实验得出;(2)排放系数α通过煤岩吸附实验结合火区实地勘测得出;(3)排放通量通过对火区现场煤自燃气体排放及环境因素的实时监测得出;(4)排放系数β通过对遥感图像裂隙信息的提取得到。上述两种计算模型在我国乌达实验区进行了实际应用,并对其可实现性进行了检验。     

A Comparative Study of Soil Liquefaction Assessment Using Machine Learning Models

Geotechnical and Geological Engineering - Liquefaction of saturated granular soils is marked by the total loss of shear strength of soil under dynamic cyclic or transient loading conditions due to...     

A Methodology for Assessing Landslide Hazard Using Deterministic Stability Models

Deterministic stability models are used to assess the potential for mass movement within Hamilton City, New Zealand using sensitivity analysis for critical environmental variables. Discrete geomorphic zones are recognised on the basis of material properties and slope characteristics; generic slope profiles are derived for each of these zones by averaging slope profiles determined from a Digital Elevation Model. Stability analysis models are used to derive critical failure surfaces for these profiles using measured or estimated material properties, and sensitivity analysis allows the conditions of water table level and seismic acceleration under which the slopes become unstable to be determined. This method is applied to Hamilton City to assess the citywide hazard associated with mass movement. For the slopes studied, conditions of elevated water table alone may initiate failure, but this is seen as unlikely as the materials are well drained. Combinations of water tables above 10% of the slope elevation together with seismic accelerations of approximately 0.2 g (150 year return period) represent likely failure conditions for many slopes. This information provides emergency management planners with estimates of the likely extent of failure in different regions of the city, and hence facilitates identification of lifelines and infrastructure at risk. The method cannot provide site-specific information, but in combination with knowledge of cultural features gives indications of critical locations where detailed engineering assessments are required.     

Models on Snowball Earth and Cambrian explosion: A synopsis

During the late Proterozoic from 1000 to 542 Ma, the Earth is thought to have been frozen at least during two times: in the Sturtian (715–680 Ma) and in the Marinoan (680–635 Ma) global glaciations. Following the Marinoan Snowball Earth, large multi-cellular animals of the Ediacara fauna flourished as a prelude to the Phanerozoic world. Here we summarize the most popular models on the cause and cessation of Snowball Earth. Episodic decrease of greenhouse gas occurs through the effect of erosion and weathering promoted by either mountain building or by an increase in the coastlines during the break-up of supercontinents. Effects on the globe caused by true polar wander, eruption of voluminous flood basalts, or dramatic reduction in planetary obliquity can also lead to ice ages and mass extinction. A radically revised concept based on Earth's magnetic intensity has also been proposed, which explains the true polar wander through a quasi-polar dynamo model. The ‘switch-on’ and ‘switch-off’ of the Earth's strong dynamo can lead to the onset and disappearance of the Snowball Earth. The galactic model infers that gamma ray burst associated with starburst creates huge amounts of clouds which would cut off sun rays and freeze the Earth.The Snowball Earth event is considered to have exerted a significant control on the subsequent revolutionary changes in the evolution of life forms. Although according to the biological clock, extensive re-organisation of genome is thought to have been completed by around 900 Ma, the evolution of modern life in Cambrian occurred only after the geochemical bridge was in place with elevated oxygen and nutrient levels in lakes that developed within continental rifts where the hydrothermal system in the granitic basement created the chemical environment enriched in Ca²⁺, Fe²⁺, V, Mo, HCO₃, phosphate and other elements required for building the skeleton and bone of the first modern animals. With cosmic radiation exerting a significant control on the mutation, the Neoproterozoic Earth history illustrates the possible link from Galaxy to the genome level.