An Exploration of the Interplay between the Measurement Uncertainty and the Number of Samples in Contaminated Land Investigations

In the assessment of potentially contaminated land, the number of samples and the uncertainty of the measurements (including that from sampling) are both important factors in the planning and implementation of an investigation. Both parameters also effect the interpretation of the measurements produced, and the process of making decisions based upon those measurements. However, despite their importance, previously there has been no method for assessing if an investigation is fit‐for‐purpose with respect to both of these parameters. The Whole Site Optimised Contaminated Land Investigation (WSOCLI) method has been developed to address this issue, and to allow the optimisation of an investigation with respect to both the number of samples and the measurement uncertainty, using an economic loss function. This function was developed to calculate an ‘expectation of (financial) loss’, incorporating costs of the investigation itself, subsequent land remediation, and potential consequential costs. To allow the evaluation of the WSOCLI method a computer program ‘OCLISIM’ has been developed to produce sample data from simulated contaminated land investigations. One advantage of such an approach is that as the ‘true’ contaminant concentrations are created by the program, these values are known, which is not the case in a real contaminated land investigation. This enables direct comparisons between functions of the ‘true’ concentrations and functions of the simulated measurements. A second advantage of simulation for this purpose is that the WSOCLI method can be tested on many different patterns and intensities of contamination. The WSOCLI method performed particularly well at high sampling densities producing expectations of financial loss that approximated to the true costs, which were also calculated by the program. WSOCLI was shown to produce notable trends in the relationship between the overall cost (i.e., expectation of loss) and both the number of samples and the measurement uncertainty, which are: (a) low measurement uncertainty was optimal when the decision threshold was between the mean background and the mean hot spot concentrations. (b) When the hot spot mean concentration is equal to or near the decision threshold, then mid‐range measurement uncertainties were optimal. (c) When the decision threshold exceeds the mean of the hot spot, mid‐range measurement uncertainties were optimal. The trends indicate that the uncertainty may continue to rise if the difference between hot spot mean and the decision threshold increases further. (d) In any of the above scenarios, the optimal measurement uncertainty was lower if there is a large geochemical variance (i.e., heterogeneity) within the hot spot. (e) The optimal number of samples for each scenario was indicated by the WSOCLI method, and was between 50 and 100 for the scenarios considered generally; although there was significant noise in the predictions, which needs to be addressed in future work to allow such conclusions to be clearer.     

A depth average SPH model including μ(I) rheology and crushing for rock avalanches

Classical depth-integrated smoothed particle hydrodynamics (SPH) models for avalanches are extended in the present work to include a μ(I)− rheological model enriched with a fragmentation law. With this improvement, the basal friction becomes grain distribution dependent. Rock avalanches, where grain distribution tends to change with time while propagating, are the appropriate type of landslide to apply the new numerical proposal. The μ(I)− rheological models considered in the present work are those of Hatano and Gray, combined with two different fragmentation laws, a hyperbolic and a fractal-based law. As an application, Frank avalanche, which took place in Canada in 1903, is analyzed under the scope of the present approach, focusing in the influence of the rheological and fragmentation laws in the evolution of the avalanche.     

川北砂岩-泥岩系混合作用地球化学特征

根据沉积岩混合作用判别原理,应用元素铬－钍判别法,判明川北砂岩－泥岩系为二元混合成因。再根据二元混合元素丰度关系定律,由混合变换式求出丰度关系常数,认为川北砂岩－泥岩系既具有互稀释混合作用,又具有稀释混合作用,进而可以对沉积岩端员物质组成进行估算。     

一种生成大周期伪随机数的新算法——改进的混合同余法

为了克服当前所生成的伪随机数周期小、每个随机数仅能出现1次而不能重复的缺点,本文提出了一种生成伪随机数的新方法,称为改进的混合同余法。     

几个天然矿物中某些阳离子近邻结构的EXAFS研究

本文利用EXAFS方法对镁铝榴石、几种锰矿和不同铁含量的闪锌矿中有关阳离子的近邻结构进行了研究,得到了有关阳离子在相应矿物中的近邻结构参数.对闪锌矿的研究,得到了杂质Fe绝大部分以六配位的形式存在的结果,这与传统的观点不同;提出了闪锌矿不仅可作为地质温度计,还可能作为地质温度、压力变化记录仪的设想。     

三维交叉裂隙渗流传质特性数值模拟

对交叉裂隙渗流传质特性的定量描述是研究整个裂隙网络渗透传质特性的基础。为真实模拟水流及溶质在三维交叉裂隙中的运移过程,首先通过三维轮廓仪获取天然岩石裂隙表面的形貌数据,再应用三维重构技术生成相应的三维交叉裂隙模型,随后求解Navier-Stokes方程,假定溶质运移满足Fick定律,模拟水流和溶质在三维交叉裂隙中的运移过程。通过对比粗糙裂隙模型与平行平板模型的模拟结果发现：粗糙度对流体的分布及流动状态存在显著的影响;不同进、出口工况下的流体流动及溶质运移状态亦表明：裂隙交叉的几何形貌会显著地影响溶质混合行为。这些结果表明,目前被广泛采用的平行平板模型在评估岩体内特别是交叉口的物质运移特性时将导致较大的偏差,在将来的研究中有必要针对裂隙交叉口的几何特征建立修正的模型以提高评估的准确性。     

马斯京根法洪水演进反演计算方法的探讨

从计算理论上系统分析和认识了马斯京根法洪水演进反演计算算法产生的坏条件,通过引入样条函数辅助进行修匀处理和对于x数值小的情况采用反演正算的算法,使得马斯京根法洪水演进反演计算可以进行多段连续演算并具有好的效果,在工程水文设计计算中具有实用价值。     

锥束CT的CT值标定方法

CT值是医学CT重建图像的一个必备要素,在某些场合下已成为医生诊断疾病的辅助工具,比如骨密度测量、图像分割与识别等。本文介绍一种锥束CT的CT值转换方法。借助Sedentex CT模体,分别获得5种材料的标称CT值和锥束CT衰减系数重建值,并经线性拟合,建立起标称CT值和衰减系数重建值之间的转换方程。最后,分析对比度噪声比和图像灰度值均匀性偏差在CT值转换后的变化情况。     

雅安雨量站站网布设优化试验

雨量监测的准确性对天气预报、气候变化、服务决策、防灾减灾等有着重要的影响和意义,而雨量站网布设直接影响雨量监测的准确性。选取四川省雅安市作为研究对象,在现有站网布设的基础上,采用相关性分析,提出基于抽站的站网布设优化方法,并对抽站后的站网布设合理性进行评价。结果表明：(1)雅安雨量站有265站,各站点的控制面积为2.64～510.78 km²,邻近站间距离为0.3～12.28 km,邻近站间降水相关系数为0.62～0.993;(2)逐次抽站后,雨量站控制面积和邻近站间距离逐渐增大,邻近站点间降水相关系数逐渐减小;(3)抽站后站网面雨量与原站网面雨量较一致,误差较小,泰森多边形法面雨量变化幅度小于算术平均法;(4)从降水过程来看,各次抽站后,降水落区和各量级降水范围基本一致,站网对降水极值的捕捉能力较好,误差较小,但随着站点数的减少,对于降水形态刻画的精细程度有所下降。     

Advection in plankton models with variable elemental ratios

As ocean biogeochemical models evolve to permit the elemental composition of plankton populations and dissolved organic matter to vary, each element is normally assigned a separate state variable, which is advected and mixed independently of the others. In a population of cells with varying elemental quotas, the proper currency of the advection operator is subpopulations of similar cells. The spatial gradient in total C, N, or P summed over the spectrum of such subpopulations is identical to that calculated for the population means, so treating the various elements as independent should generally be a valid approximation. However, errors can arise in high-order advection schemes with nonlinear corrector terms, which are not additive across the subpopulations. Some numerical examples indicate that these errors are relatively small [O(10⁻³–10⁻⁴)] but can be as high as O(10⁻²) in certain cases. As grid resolution varies, the error scales approximately to the Courant number.