Health risk assessment of trace metal(loid)s in agricultural soils based on Monte Carlo simulation coupled with positive matrix factorization model in Chongqing, southwest China

This study aimed to investigate the pollution characteristics, source apportionment, and health risks associated with trace metal(loid)s(TMs) in the major agricultural producing areas in Chongqing, China. We analyzed the source apportionment and assessed the health risk of TMs in agricultural soils by using positive matrix factorization(PMF) model and health risk assessment(HRA) model based on Monte Carlo simulation. Meanwhile, we combined PMF and HRA models to explore the health risks of TMs in agricultural soils by different pollution sources to determine the priority control factors. Results showed that the average contents of cadmium(Cd), arsenic (As), lead(Pb), chromium(Cr), copper(Cu), nickel(Ni), and zinc(Zn) in the soil were found to be 0.26, 5.93, 27.14, 61.32, 23.81, 32.45, and 78.65 mg/kg, respectively. Spatial analysis and source apportionment analysis revealed that urban and industrial sources, agricultural sources, and natural sources accounted for 33.0%, 27.7%, and 39.3% of TM accumulation in the soil, respectively. In the HRA model based on Monte Carlo simulation, noncarcinogenic risks were deemed negligible(hazard index <1), the carcinogenic risks were at acceptable level(10^(-6)<total carcinogenic risk ≤ 10^(-4)), with higher risks observed for children compared to adults. The relationship between TMs, their sources, and health risks indicated that urban and industrial sources were primarily associated with As, contributing to 75.1% of carcinogenic risks and 55.7% of non-carcinogenic risks, making them the primary control factors. Meanwhile, agricultural sources were primarily linked to Cd and Pb, contributing to 13.1% of carcinogenic risks and 21.8% of non-carcinogenic risks, designating them as secondary control factors.

Monte Carlo simulation of the exposure factor

In this paper, we simulate the exposure factor by a simple model of a flee-air ionization chamber with the Monte Carlo programme Geant4. Special emphasis is placed on the discussion of the exposure factor related to parameters of the chamber model. The reason for the variation in exposure factor with incident ray energy is also analysed in terms of reaction cross section for different types of reactions. The obtained results indicate that our simulation is accurate in the calculation of the exposure factor and can serve as a reference in designing air ionization chambers.

Stability analysis of underground mine hard rock pillars via combination of finite difference methods,neural networks,and Monte Carlo simulation techniques

Pillar stability is always evaluated using the safety factor(SF),which is defined as the ratio of pillar strength to pillar stress.However,most researchers have estimated pillar stress using the pillar shape ratio(w/h),uniaxial compressive strength(UCS)of the intact rock mass,and pillar depth(H).In this study,the geological strength index(GSI)of hard rock pillars was considered as a new variable for predictive purposes.This index was developed by combining numerical simulation software(i.e.,FLAC3D)and a backpropagation neural network(BPNN).A hard rock pillar stability analysis,based on three methods including deterministic method,sensitivity analysis,and Monte Carlo simulation(MCS),was performed.A new formula was proposed to estimate the SF values based on the predicted stress,considering the GSI variable in the deterministic method.The sensitivity analysis indicated that the variables impacting the SF from high to low are UCS,GSI,w/h,and H.In this study,pillar stability was analyzed mainly using the GSI and MCS techniques.The MCS results revealed that the GSI is also a major factor in pillar stability and has a greater effect on weak pillars than on strong ones.Furthermore,a pillar is more likely to be unstable when both the GSI and the UCS are decreased.This study provides several references and procedures for improving the design of stable pillars considering the GSI as an important factor.

Monte Carlo Simulations of Density Profiles for Hard-Sphere Chain Fluids Confined Between Surfaces

Covering a wide range of bulk densities, density profiles for hard-sphere chain fluids (HSCFs) with chain length of 3,4,8,20,32 and 64 confined between two surfaces were obtained by Monte Carlo simulations using extended continuum configurational-bias (ECCB) method. It is shown that the enrichment of beads near surfaces is happened at high densities due to the bulk packing effect, on the contrary, the depletion is revealed at low densities owing to the configurational entropic contribution. Comparisons with those calculated by density functional theory presented by Cai et al. indicate that the agreement between simulations and predictions is good. Compressibility factors of bulk HSCFs calculated using volume fractions at surfaces were also used to test the reliability of various equations of state of HSCFs by different authors.

Monte Carlo simulation of reflection effects of multi-element materials on gamma rays

To study the effects of the gamma reflection of multi-element materials,gamma ray transport models of single-element materials,such as iron and lead,and multielement materials,such as polyethylene and ordinary concrete,were established in this study.Relationships among the albedo factors of the gamma photons and energies and average energy of the reflected gamma rays by material type,material thickness,incident gamma energy,and incidence angle of gamma rays were obtained by Monte Carlo simulation.The results show that the albedo factors of single-element and multi-element materials increase rapidly with an increase in the material thickness.When the thickness of the material increases to a certain value,the albedo factors do not increase further but rather tend to the saturation value.The saturation values for the albedo factors of the gamma photons,and energies and the reflection thickness are related not only to the type of material but also to the incident gamma energy and incidence angle of the gamma rays.At a given incident gamma energy,which is between 0.2 and 2.5 MeV,the smaller the effective atomic number of the multi-element material is,the higher the saturation values of the albedo factors are.The larger the incidence angle of the gamma ray is,the greater the saturation value of the gamma albedo factor,saturation reflection thickness,and average saturation energy of the reflected gamma photons are.

应用Monte Carlo-JC法评估FRP加固RC梁受弯承载力可靠度

将Monte Carlo随机抽样方法与JC法相结合(称为Monte Carlo-JC法),利用Matlab软件自带的随机数发生器编制了程序,针对ACI 440.2R-02设计指南(称为ACI指南)中的FRP抗弯加固条款进行了较为系统的可靠度评估。可靠度分析结果表明:混凝土强度fc′、CFRP片材配筋率fρ及CFRP片材性能是影响抗力比值均值和标准差的3个主要因素;可靠度指标的平均值随着折减系数的增大而逐步减小,且随着荷载效应比值Ln/Dn的增大而减小。对所有可靠度指标进行统一考虑,得到整体抗弯设计指标0β为4.40,可见该指南的可靠度水平偏高。基于对抗力折减系数的参数研究结果,无论钢筋的应变水平如何,建议取固定值0.90。在所有相关设计指南中,ACI指南最具有代表性,对该指南的可靠度评估具有普遍意义。

金/硅界面X射线剂量增强效应的Monte Carlo模拟

通过建立一个典型的金/硅界面结构模型,对X射线入射界面时的剂量增强效应进行了研究。采用Monte Carlo方法计算了不同能量X射线入射金/硅界面的输运过程。其中,对X射线产生的次级电子在介质中的输运,采用了单次碰撞直接模拟方法;对电子的弹性散射截面和非弹性散射截面,分别采用Mott微分截面和Born近似下的广义振子强度模型计算得到。研究计算了不同能量X射线入射下,金/硅界面的剂量增强系数及特定X射线能量下剂量增强系数随金厚度的变化规律。结果表明:X射线能量为几十至几百keV时,剂量增强效应最明显,最大剂量增强系数对应的X射线能量随距金/硅界面的距离增加而增加;金的厚度影响界面附近剂量增强效果,当X射线能量不变时,剂量增强系数随金的厚度增加而增加,并趋于饱和值。

基于Monte Carlo随机模拟的综合交通网络布局评价与决策方法

针对综合交通网络评价指标权重及属性值具有主观性和随机性的特点,提出了基于模拟运算的布局规划方案排序选优的群体随机决策方法。仿真生成满足集结的多个专家对指标重要性偏好排序统计分布的权重,同时考虑交通需求的不确定性对指标值的影响,结合客观熵权计算方案的综合评价值,由多次模拟得到的排序优势度确定方案的优劣差异。根据设计的仿真流程通过算例说明了方法应用的有效性,评价中考虑了主客观因素及随机性特征,可以为网络布局提供科学决策依据。

链状分子系统相平衡的Monte Carlo模拟

应用修正的Widom试验粒子方法在三维立方格子中计算了链节数分别为r=1,2,4,8的链状分子在不同温度、密度下的剩余化学位,然后运用热力学关系计算了以上系统在不同温度、密度下的化学位、压力和压缩因子,并求得系统的相平衡曲线和临界点。模拟结果与Flory-Huggins理论、Freed的格子场理论及胡英等工作的结果进行了比较。发现Freed理论和胡英等的工作都能较好地描述链状分子系统的相平衡行为。

Ising格子流体相平衡的Monte Carlo模拟

将带空穴偏倚取样的Ｗｉｄｏｍ插入粒子法应用于Ｉｓｉｎｇ格子模型，求得了Ｉｓｉｎｇ格子流体在不同温度、不同密度下的剩余化学位，并通过热力学关系求得了系统的化学位、压力和压缩因子；计算了系统的内能涨落与温度的关系，并据此求得了系统在临界点附近的比热尖峰。最后根据相平衡原理，获得了系统的汽液平衡相图。模拟所得的结果与Ｓｃｅｓｎｅｙ的级数解及Ｆｌｏｒｙ－Ｈｕｇｇｉｎｓ理论进行了比较，表明本文的模拟结果与Ｓｃｅｓｎｅｙ的准确结果十分接近。

基于Monte Carlo模拟的软土基坑隆起分析

基于圆弧滑动模型确定的安全系数,将基坑隆起破坏的不利事件划分为5种情况,利用Monte Carlo模拟确定不利事件发生概率,提出了考虑基坑隆起破坏引起的不利事件发生概率及经济损失的风险评估模型。将所提方法应用于福州地铁2号线某基坑工程中,结果表明,当围护结构插入比小于1.2时,加固对基坑隆起破坏损失期望减小效果显著;当围护结构插入比大于1.2时,加固对基坑隆起破坏损失期望减小效果一般;当插入比小于0.8时,基坑隆起破坏的损失期望等级属于"严重";当插入比介于0.8～1.2时,基坑隆起破坏的损失期望等级属于"需要考虑";当插入比大于1.2时,基坑隆起破坏的损失期望等级属于"可忽略"。

基于优化WOA-BP策略的土体冻胀率因素敏感性定量分析

土体冻胀是寒区工程建设面临的重要挑战之一,对其进行准确预测和敏感性分析,对于保障工程安全与稳定、预防结构变形与破坏至关重要。针对东北某矿区三种土样,在不同冷端温度、含水率和干密度条件下,实施了单向冻结且不补水的冻胀实验。基于实验数据,分析了影响冻胀率的关键因素,构建了以干密度、含水率、冷端温度、比重及结冰温度为输入变量的WOA-BP预测模型,引入Chebyshev混沌映射与自适应权重调整策略,优化得到Chebyshev混沌映射自适应权重的WOA-BP神经网络。经验证,该模型预测误差小,可以较好地预测土体的冻胀率。结合Garson算法、扰动法及蒙特卡洛模拟等三种方法,对土体冻胀率的影响因素进行了敏感性分析,所得结果一致。该矿区土样的冻胀率对干密度、比重、含水率、冷端温度、结冰温度变化的敏感程度依次降低。

基于蒙特卡罗模拟的透射式XRD背景的定量分析

XRD背景主要来源于空气、装置和样品中光子的散射,XRD分析需准确扣除背景,常用的扣背景方法具有一定的局限。蒙特卡罗模拟可实现光子的甄别与统计,因此可将其用于XRD背景来源的定量分析。相干散射的模拟中需考虑物质的Form Factor,这可由Baró等的拟合式、独立原子模型或德拜公式给出;在20 keV能量及透射几何模式下,通过对骨、尼龙、水等物质的XRD模拟,对探测器中光子来源进行了区分和统计。结果表明,德拜公式计算的空气背景大于独立原子模型;空气散射在小角度时背景占比大,随散射角的增加从100%减小至40%以下,而样品中康普顿散射的计数占比则从0增大至60%以上。该方法可对不同样品组成以及复杂装置结构的XRD背景进行定量分析。

全局减方差方法在大空间γ辐射场计算中的应用

为了提高大空间γ辐射场全局计算效率,开展了全局减方差(Global Variance Reduction,GVR)方法在大空间γ辐射场计算中的应用研究。针对计数栅元/网格体积差异造成的过度分裂问题,引入体积修正因子修改全空间权窗参数。体积修正后的基于通量的GVR方法计算的全局品质因子(FOMG)比直接模拟提高约39倍。针对非计数区计算耗时问题,提出了非计数区修正方法,使得FOMG因子进一步提高40%。在引入体积和非计数区修正的基础上,在大空间γ辐射场计算中与基于粒子误差、权重、径迹、数目、能量、碰撞和通量的7种GVR方法进行对比。结果表明:7种GVR方法计算的FOMG因子比直接模拟提高2~3个量级,基于误差的标准差σ降低2~3个量级;而基于权重的GVR方法计算的FOMG因子比直接模拟提高2304倍,在所有GVR方法中减方差效果最好。在基于通量的GVR方法中引入光滑因子SI后,模拟计算的权窗下限随SI增加而减小,FOMG因子随SI的增加先增加后减小。当SI=0.8时,该方法计算的FOMG因子最大,比直接模拟提高3246倍。

基于比例边界有限元法计算应力强度因子的不确定量化分析

应力强度因子是预测荷载作用下结构中裂纹产生和扩展的重要参数。半解析的比例边界有限元法结合了有限元和边界元法的优势,在裂纹尖端或存在奇异应力的区域不需要局部网格细化,可以直接提取应力强度因子。在比例边界有限元法计算应力强度因子的框架下,引入随机参数进行蒙特卡罗模拟(Monte Carlo simulation, MCS),并提出一种新颖的基于MCS的不确定量化分析。与直接的MCS不同,采用奇异值分解构造低阶的子空间,降低系统的自由度,并使用径向基函数对子空间进行近似,通过子空间的线性组合获得新的结构响应,实现基于MCS的快速不确定量化分析。考虑不同荷载状况下,结构形状参数和材料属性参数对应力强度因子的影响,使用改进的MCS计算应力强度因子的统计特征,量化不确定参数对结构的影响。最后通过若干算例验证了该算法的准确性和有效性。

运载火箭并联级间分离动力学仿真与分析

基于间接预测法对并联两级运载火箭的级间分离过程进行了动力学仿真,获得了并联两体分离特性和规律。结果表明,气动力将有利于提高两级间的相对速度和距离,气动力矩对一级的姿态影响小,但会使二级产生较大的俯仰角与攻角。为了改善二级的姿态,基于分离的特性规律提出了分离优化措施,仿真结果表明优化后二级的姿态更加稳定、优化措施有效。最后分析了单一偏差因素、多偏差因素组合对分离运动的影响规律,并通过蒙特卡洛仿真得到了并联级间分离轨迹和姿态的包络范围,以此来评估分离的安全性。

Influence of random heterogeneity of shear wave velocity on sliding mass response and seismic deformations of earth slopes

Soil shear wave velocity has been recognized as a governing parameter in the assessment of the seismic response of slopes.The spatial variability of soil shear wave velocity can influence the seismic response of sliding mass and seismic displacements.However,most analyses of sliding mass response have been carried out by deterministic models.This paper stochastically investigates the effect of random heterogeneity of shear wave velocity of soil on the dynamic response of sliding mass using the correlation matrix decomposition method and Monte Carlo simulation(MCS).The software FLAC 7.0 along with a Matlab code has been utilized for this purpose.The influence of statistical parameters on the seismic response of sliding mass and seismic displacements in earth slopes with different inclinations and stiffnesses subject to various earthquake shakings was investigated.The results indicated that,in general,the random heterogeneity of soil shear modulus can have a notable impact on the sliding mass response and that neglecting this phenomenon could lead to underestimation of sliding deformations.

Analysing Delay Impact from Potential Risk Factors on Project Delivery of Oil and Gas Pipeline:A Case Study in IRAQ

The aim of this paper is to present the design and specifications of an integrated Delay Analysis Framework(DAF),which could be used to quantify the delay caused by the Risk Factors(RFs)in Oil and Gas Pipelines(OGPs)projects in a simple and systematic way.The main inputs of the DAF are(i)the potential list of RFs in the projects and their impact levels on the projects and the estimated maximum and minimum duration of each task.Monte Carlo Simulation integrated within@Risk simulator was the key process algorithm that used to quantify the impact of delay caused by the associated RFs.The key output of the DAF is the amount of potential delay caused by RFs in the OGP project.The functionalities of the developed DAF were evaluated using a case study of newly developed OGP project,in the south of Iraq.It is found that the case study project might have delayed by 45 days if neglected the consideration of the RFs associated with the project at the construction stage.The paper concludes that identifying the associated RFs and analysing the potential delay in advance will help in reducing the construction delay and improving the effectiveness of the project delivery by taking suitable risk mitigation measures.

典型煤矿区土壤中多环芳烃类化合物的污染特征

以3个煤矿区土壤中多环芳烃类化合物(PACs)为研究对象,结合正定矩阵因子分析(PMF)和蒙特卡洛(Monte-Carlo)模拟,分析典型煤矿区土壤中PACs污染的来源和致癌风险.结果显示,石嘴山煤矿、棋盘井煤矿和石炭井煤矿周边土壤中ΣPACs分别为21862,6226,2278μg/kg.受煤矿区影响显著的地区土壤中PACs组成类型丰富且以低环为主.同时,烷基多环芳烃(aPAHs)含量明显高于母体多环芳烃(16PAHs).PMF溯源结果显示煤矿区土壤中PACs污染以煤和煤矸石颗粒为主要污染源,其次是交通源.Monte-Carlo模拟显示,3个煤矿区均对当地居民存在潜在致癌风险,尽管研究区受涉煤污染源影响显著,但煤炭燃烧才是致癌风险的主要贡献者.此外,Monte-Carlo模拟相较于终生致癌风险模型(ILCR)准确性更高,而传统采取ILCR进行风险评估低估了实际成人的致癌风险.

碳达峰视角下的机场航空器CO_(2)减排潜力研究

科学测算机场航空器CO_(2)的减排潜力对民航实现“双碳”目标具有重要意义。基于中国31个省域(除港澳台)机场航空器CO_(2)排放量,采用面板回归方法分析了4类影响因素的减排效应;从理论最优与最佳实践视角测算了CO_(2)减排潜力;最后利用情景分析与蒙特卡洛模拟方法研究了CO_(2)达峰水平与路径。结果表明:影响因素均有积极减排效应;理论最优视角下,机场航空器CO_(2)减排潜力为1 325.79万吨,其中开放程度减排潜力最高;而最佳实践视角下,CO_(2)排放将增加;基准发展与政策减排情景下,可分别在2045年、2034年达峰;减缓机场航线网络扩张等可加速实现碳达峰。