New semi-analytical approach for ice lens heaving during artificial freezing of fine-grained material

The calculation of frost heaving with ice lens formation is still not standard for construction projects using artificial ground freezing(AGF).In fine-grained material,ice lenses may initiate and lead to significant heaving at the ground surface,which should be considered in advance.However,the complex processes during ice lens formation are still not fully understood and difficult to capture in a simple approach.In the past,the semi-analytical approach of Konrad and Morgenstern used one soil constant,the“segregation potential(SP)”.It has been mainly and most successfully applied to the heave calculation of natural-induced soil freezing in cold regions.Its application to AGF has been so far unsuccessful.To solve this,a new semi-analytical approach is presented in this paper.It includes AGF conditions such as bottom-up freezing,temperature gradients to reach great freezing velocities,and a distinction between two freezing states.One is the freezing-up state until a certain frost body thickness is reached(thermal transient state),and the other is a holding phase where the frost body thickness is kept constant(thermal quasi-steady state).To test its ability,the results are applied to another freezing direction,the top-down freezing.The new approach is validated using two different frost-susceptible soils and,in total,50 frost heave tests.In the thermal transient region,where the SP is applicable,the two semi-analytical approaches are compared,showing improved performance of the current method by about 15%.

FORMULATION OF A SEMI-ANALYTICAL APPROACH BASEDON GURTIN VARIATIONAL PRINCIPLE FOR DYNAMICRESPONSE OF GENERAL THIN PLATES

4 semi-analytical approach for the dynamic response of general thin plates whichemployes finite element discretization in space domain and a series of representation intime demain is developed on the basis of Curtin variational principles.The formulationof time series is also investigated so that the dynamic response of plates with arbitraryshape and boundary constraints can be achieved with adequate accuracy.

MODIFIED SCHEME BASED ON SEMI-ANALYTIC APPROACH FOR COMPUTING NON-PROBABILISTIC RELIABILITY INDEX

A new computation scheme proposed to tackle commensurate problems is devel- oped by modifying the semi-analytic approach for minimizing computational complexity. Using the proposed scheme, the limit state equations, usually referred to as the failure surface, are obtained from transformation of an interval variable to a normalized one. In order to minimize the computational cost, two algorithms for optimizing the calculation steps have been proposed. The monotonicity of the objective function can be determined from narrowing the scope of interval variables in normalized infinite space by incorporating the algorithms into the computational scheme. Two examples are used to illustrate the operation and computational efficiency of the approach. The results of these examples show that the proposed algorithms can greatly reduce the computation complexity without sacrificing the computational accuracy. The advantage of the proposed scheme can be even more efficient for analyzing sophistic structures.

Semi-analytical modeling of tokamak density evolution

Tokamak plasma density evolution is generally modeled by a diffusion-convection equation in cylindrical geometry. By using a semi-analytical approach, we solve such an equation for a given diffusion coefficient and inward convection velocity as an arbitrary function of the radial position. Through variable separation, a Sturm-Liouville-type eigenvalue problem is solved, thereby constructing a complete set of orthogonal eigenfunctions. Based on the decomposition of the solution, the initial function, and the source function in these eigenfunctions, several problems of practical interest about the density evolution are analyzed. They include the density evolution, with boundary density not being zero; the density profile with internal transport barrier; the damping profile during particle source being shut-down. Results are found to be qualitatively consistent with the tokamak experiments.

Semi-analytical finite element method applied for characterizing micropolar fibrous composites

A semi-analytical finite element method(SAFEM),based on the two-scale asymptotic homogenization method(AHM)and the finite element method(FEM),is implemented to obtain the effective properties of two-phase fiber-reinforced composites(FRCs).The fibers are periodically distributed and unidirectionally aligned in a homogeneous matrix.This framework addresses the static linear elastic micropolar problem through partial differential equations,subject to boundary conditions and perfect interface contact conditions.The mathematical formulation of the local problems and the effective coefficients are presented by the AHM.The local problems obtained from the AHM are solved by the FEM,which is denoted as the SAFEM.The numerical results are provided,and the accuracy of the solutions is analyzed,indicating that the formulas and results obtained with the SAFEM may serve as the reference points for validating the outcomes of experimental and numerical computations.

Uncertainty propagation in dynamics of composite plates: A semi-analytical non-sampling-based approach

In this study,the influences of spatially varying stochastic properties on free vibration analysis of composite plates were investigated via development of a new approach named the deterministic-stochastic Galerkin-based semi-analytical method.The material properties including tensile modulus,shear modulus,and density of the plate were assumed to be spatially varying and uncertain.Gaussian fields with first-order Markov kernels were utilized to define the aforementioned material properties.The stochastic fields were decomposed via application of the K arhunen-Loeve theorem.A first-order shear deformation theory was assumed,following which the displacement field was defined using admissible trigonometric modes to derive the potential and kinetic energies.The stochastic equations of motion of the plate were obtained using the variational principle.The deterministic-stochastic Galerkin-based method was utilized to find the probability space of natural frequencies,and the corresponding mode shapes of the plate were determined using a polynomial chaos approach.The proposed method significantly reduced the size of the mathematical models of the structure,which is very useful for enhancing the computational efficiency of stochastic simulations.The methodology was verifed using a stochastic finite element method and the available results in literature.The sensitivity of natural frequencies and corresponding mode shapes due to the uncertainty of material properties was investigated,and the results indicated that the higher-order modes are more sensitive to uncertainty propagation in spatially varying properties.

Discussion on the paper “Analyzing short time series data from periodically fluctuating rodent populations by threshold models: A nearestblock bootstrap approach”

This is a very attractive article. It combines fascinating new methodology with a most interesting dataset, and a highly motivating presentation. However, despite the many

Discussion on the paper “Analyzing short time series data from periodically fluctuating rodent populations by threshold models: A nearestblock bootstrap approach”

The authors are to be congratulated for an innovative paper in terms of both modelling methodology and subject matter significance. The analysis of short time series is known to be

混凝土结构课程的教学方法初探

本文首先对混凝土结构课程的特点进行了分析 ,然后分别从如何把握课程的基本思路、用何种教学方法阐述实验结果、与其它课程的联系、如何加强理论分析教学的逻辑性、如何讲解构造内容、重视实践和规范应用以及如何确定考题形式等几个方面 ,对课程的教学方法进行了初步的探讨。

室内空气和灰尘中全(多)氟烷基化合物的研究进展

全(多)氟烷基化合物(per(poly)fluoroalkyl substances,PFASs)在环境各个介质及人体样品中广泛被检出,近年,在室内空气和灰尘中也普遍发现PFASs.研究表明,室内空气中PFASs的含量普遍高于室外空气,室内空气和灰尘中的PFASs可能是室外空气的污染来源及人体暴露源,因此室内环境中PFASs成为环境领域的又一个研究热点.但目前为止,我国还没有开展室内空气中PFASs的相关研究,室内灰尘中PFASs的研究也相对较少.本文就室内空气和灰尘中PFASs的采样与分析方法、污染现状、来源分析及人体暴露等4个方面进行了综合阐述,以期为我国室内环境中PFASs的研究提供参考.

国外相对渗透率计算方法对比与分析

随着油田开发的进一步深入,油藏属性参数变化规律及其变化机理的研究越来越重要.油水相对渗透率曲线是油水两相渗流特征的综合反映,是油藏数值模拟工作最基础的资料之一,如何准确认识、合理选取并处理油水相对渗透率曲线越来越得到重视.准确计算相对渗透率,确定相对渗透率曲线能够有效确定油气水在储油层中的分布、利用相渗透率资料分析油井产水规律.国外在研究方法和手段上取得较大进展,相对渗透率计算方法主要分为分析法、半分析法和历史拟合法3类,分别具有优缺点,对中国一些经过长期注水开发的成熟油田后期开发具有指导和借鉴意义.

中国农业劳动生产率的稳态趋同:产出增长率与劳动力转移的影响

文章运用横截面分析法对我国1990-2002年间的农业劳动生产率进行了趋同测试,结果表明,农业劳动生产率不仅发生了显著的条件β趋同,还存在显著的σ趋同,且处于向其稳态转型的最后阶段。通过研究,我们发现,我国农业劳动生产率在此期间的趋同是由农业产出增长率变化与农业劳动力转移所引起的农业就业增长率变化共同作用的结果,而且放任经济的自由发展,这种区域农业劳动生产率差距不会自动消失。因此,我们必须通过投资导向、制度创新、农村工业企业和第三产业的发展等来缩小区域农业劳动生产率差距,以协调区域经济发展。

高面膜堆石坝发展的需求与关键技术——高面膜堆石坝关键技术(一)

面膜堆石坝是指上游坝面用土工膜防渗的堆石坝。综述了面膜堆石坝半个世纪以来的发展状况,分析了该坝型的特点及该坝型技术在我国的使用现状与需求:面膜防渗结构具有渗透性低微、差异变形适应性强、施工简捷、工期短、造价低等特点;由于国外专利保护等原因,面膜堆石坝技术未能如面板堆石坝和碾压混凝土坝那样广泛交流与推广,自国外第一座面膜堆石坝建成以来,国内尚未建成一座高面膜堆石坝,而我国水电清洁能源的需求、许多深覆盖层坝址与黏土防渗体取土受到环境生态制约的状况,需要高面膜堆石坝发挥其作用,相应的设计分析技术需要较系统深入的研究梳理和集成。概述了该坝型关键技术研究的初步成果,包括高面膜堆石坝的周边夹具效应与设计方法、面膜双向拉伸分析方法、数值精细模拟方法、非散粒体面膜垫层技术、膜顶胀损缺性状量化分析方法。

社区自然资源管理方法的推广进展分析

通过对社区自然资源管理方法推广的进展进行了调查 ,了解到推广的进展情况及一些值得注意的问题。对问题进行了分析 。

我院1996～2006年医学进修教育基本情况的分析与探讨

医学进修教育是继续医学教育的一种形式,其基本职能是使各类卫生人员不断充实和提高医疗服务、教学、科研和管理能力,跟上当今日新月异科学技术的发展。通过医学进修学习,培养了重点学科带头人、又提高了本单位的医疗水平、增进了学术交流、拓宽了医疗服务面,在有利于病人的同时,也增加了医院的经济效益。本文对我院10年间6963名医学进修生的基本情况进行了分析和探讨。

炮兵武器装备体系关键性能参数分析方法研究

为满足炮兵武器装备体系作战需求论证的需要,介绍了关键性能参数(Key Performance Parameter,KPP)的概念和性质,在此基础上提出了一种KPP的分析方法和流程,实现了需求论证过程中任务、能力、KPP的转换。最后结合实例给出了KPP分析过程和描述模型,说明了所提方法的有效性。

体裁分析法与大学英语阅读教学

20世纪 90年代兴起的体裁分析法 ,以全方位多层次的语篇分析 ,为大学英语阅读教学提供了新的发展契机。它一改传统教学法只见树木不见森林的语篇分析弊端 ,对培养学生语篇意识 ,驾驶语篇能力 ,从而发展学生语言交际能力有极强的推动作用。

铁矿石中铁含量无汞法测定实验的改进

采用H3PO4-H2SO4-HNO3分解试样,改变Na2WO4的浓度和加液顺序,明确了TiCl3还原试样时的温度.此法与经典的无汞法相比,无显著性差异,且随机误差小、成功率高,可在实验教学中推广采用.

应用统计学方法建立矿山表层土壤重金属污染基线模型

环境地球化学基线是将某一地区或数据集合作为参照时某一元素在特定物质中(土壤、沉积物、岩石)的自然丰度,并可以表述为区分地球化学背景和异常的单一的极限,是区分自然的和人为的环境影响的重要参照,是进行环境污染状况分析的基础。因此采用科学合理的方法确定土壤环境地球化学基线具有重要意义。采用统计学方法建立了矿山表层土壤中重金属元素As、Cd、Co、Cr、Cu、Hg、Mn、Ni、Pb、Zn的环境地球化学基线,为下一步评价矿山表层土壤的重金属污染打下了良好的基础。

pH在线分析仪在化工生产应用中的技术改进

以型号为PH8EFP-05-TN的pH仪KCl填充型电极为研究对象,分析了影响pH在线分析仪测量不稳定的因素。针对各因素提出了pH在线分析仪在化工生产应用中的技术改进措施。改进后的复合型电极代替原来的填充型电极,很好地解决了介质温度的剧变对pH电极的影响。