A theoretical approach to oscillatory zoning affecting wolframite crystals

Oscillatory zoning in (Mn, Fe)WO₄ solid solutions of wolframite consists of a crystalline arrangement of successive Mn-rich and Fe-rich layers. Thermochemical data show that during crystal growth the Mn/Fe ratio in the mineral is greater than in the mineralizing medium. If a diffusion process affects the Mn ion in the solution, a continuous zoning should occur as observed for other solid solutions. The theory developed in this paper emphasises that a continuous zoning cannot appear because the elastic energy needed to adjust two cells with different lattice parameters is greater than the thermodynamic energy required to deposit a cell with the same composition but with a solution of a different Mn/Fe ratio. The reversal of the two energies due to a large depletion in Mn of the solution entails an abrupt change in composition. The relevance of the theory can be checked with the help of a compositional profile found in literature, by calculating with a good approximation the Mn molar value of one layer, if the Mn molar value of the other is known.     

A discrete element method (DEM)-based approach to simulating particle breakage

An approach for particle breakage simulation based on the framework of discrete element method was proposed in the current study. Convex polyhedron blocks were adopted as elementary particles for the complex particle shapes, and the variability of particle breakage strength is modeled using the invertible function method. Additionally, the traditional modified “Brazilian” criterion was adopted as the breakage criterion. Under the assumption that the eventual fractures within a particle can be determined according to the contact points and the centroid of the particle, once a target particle fulfilled the breakage criterion, it was cut into several fragments by a series of virtual cutting faces, which are consistent with the eventual fractures. With this, the production of local stress and the non-conservation of mass and volume can be avoided. A pre-defined fragmentation mode was also unnecessary for this approach. A series of numerical triaxial tests adopting this new presented approach was then conducted according to the configurations reported in the literature and comparisons made with experimental results. It revealed that while the presented approach is capable of reproducing the macroscopic shear responses and particle breakage characteristics of breakable particle assemblies, some fragmentation modes of particles such as surface grinding and corner abrasion cannot be captured using this approach, presenting an area for future investigation.

     

A spectral approach to simulating intrinsic random fields with power and spline generalized covariances

This article presents a variant of the spectral turning bands method that allows fast and accurate simulation of intrinsic random fields with power, spline, or logarithmic generalized covariances. The method is applicable in any workspace dimension and is not restricted in the number and configuration of the locations where the random field is simulated; in particular, it does not require these locations to be regularly spaced. On the basis of the central limit and Berry–Esséen theorems, an upper bound is derived for the Kolmogorov distance between the distributions of generalized increments of the simulated random fields and the normal distribution.     

模拟水压致裂的另一种二维FDEM-flow方法

可考虑岩石本身渗透性的FDEM-flow方法充分利用原FEMDEM中节理单元和三角形单元独特的拓扑连接关系,将节理单元作为流体流动的天然通道,基于立方定律来表征流体在岩石本身及裂隙中的流动,而岩石本身渗透性则通过标定合适节理单元张开度来表征。用一个含解析解自由面稳态渗流算例初步验证了本文渗流算法及标定岩石本身渗透率方法的正确性。最后计算了一个水力压裂算例,验证了该FDEM-flow方法可同时考虑岩石本身的渗透性和裂隙的渗透性,用简单的纯裂隙渗流完成了对复杂问题的处理。研究结果表明:修改后的FDEM-flow方法能够很好地再现压裂过程中流体压力的分布及裂隙的扩展,可简洁地求解水力压裂这一复杂力学的问题,适用范围更广。为模拟页岩气开采、干热岩地热获取中的水力压裂问题提供新的求解工具。     

A new approach to null correlations of proportions

Much work on the statistical analysis of compositional data has concentrated on the difficulty of interpreting correlations between proportions with an assortment of tests for nullcorrelations, for independence except for the constraint, F-independence of bounded variables, neutrality in the mean and in the median. This paper questions the appropriateness of characterizing the dependence structure of proportions in terms of such concepts, suggests an alternative method of modeling, develops necessary distribution theory and tests, and illustrates the methodology in applications.     

边坡落石运动轨迹计算新方法

考虑落石形状对落石运动轨迹的影响,将落石近似成椭圆形。根据落石运动的5种常见形式,即自由落体运动、斜抛运动、碰撞、滑动和滚动,分别得到了各种运动形式的运动速度计算公式。在碰撞阶段考虑了地面的弹塑性变形,得到了与碰撞前速度、落石形状和地面材料有关的恢复系数计算公式,并根据接触力学的有关理论得到了碰撞冲击力的计算公式,给出了落石连续滚动的判别条件。将理论公式应用于重庆万州首立山落石运动轨迹预测,验证了理论公式的可行性和有效性。     

高速公路边坡稳定性评价新方法

为能在初期勘察阶段及少量室内和现场试验的基础上快速、准确地对高速公路边坡进行稳定性评价,提出了一种新的边坡稳定性评价方法。基于福建省高速公路边坡资料,以现场稳定情况为因变量,影响边坡稳定性的14个因子为自变量,利用Logistic逐步回归遴选显著影响因子,建立了边坡稳定性评价的Logistic回归模型。该模型符合拟合优度检验,模型稳定性良好,且预测结果准确。另外,模型影响因子的调查和获取比较容易,模型可处理定性因素,边坡稳定评价过程亦方便、快捷,因而边坡稳定性评价的Logistic回归分析可在高速公路边坡工程中推广应用。     

一个新的矿物面扫描分析方法开发和地质学应用

LA-ICP-MS面扫描分析近些年来发展的新兴技术,相对于其他面扫描仪器,其具有样品制样流程简单、仪器购置和分析成本低、分析时间短、检测限低、多元素表面分析(5μm)、近乎无损等分析优势,在地球科学和生物学领域有着大量的应用。本文系统介绍了作者应用Photon Machines激光剥蚀系统与安捷伦ICP-MS新开发矿物元素面扫描分析方法。该方法基于近些年来开发的双室样品仓技术和Matlab软件,通过自主开发的LaIcpMsSoftware(LIMS)进行数据处理来完成的。本次研究开发的激光面扫描分析技术可以在短时间内(2小时)分析3mm×3mm区域,并同时给出多组元素(包括稀土元素等)在二维平面的分布特征。论文详细描述了LIMS工作原理和特点,相对于国外同类型软件,LIMS具有操作简单,并具有多种数据显示模式和剖面切割展示,元素比值面分布分析等优势,便于后期数据分析与解译。同时,还展示了对斜长石、白钨矿和石榴子石进行面扫描分析的初步结果。研究表明,通过LA-ICP-MS面扫描,可以获得比点分析更为准确的元素分布特征,并能够更为直观的展示不同元素在矿物分布特征和相关关系,更好的开展矿物地球化学研究。     

A new approach to analysis of landslide slope stability

This paper is based on data from engineering-geological research on the landslide slopes of the Moscow River valley from the site of a proposed bridge crossing reconstruction. A method for delineating the slippage surface is suggested, which allows a more reliable evaluation of landslide stability and pressure for planning and decision-making purposes during the reconstruction of the bridge crossing, and an appropriate mitigation strategy.     

A new approach to the estimation of analytical precision

Methods used for the estimation of analytical precision commonly suffer from two deficiencies which give rise to misleading results. These are: (1) the methods take no account of changes in absolute or relative error over the concentration range, and (2) they tend for other reasons to produce optimistically-biassed results. The difficulties can be avoided by the correct use of duplicate determinations. One method presented allows precision parameters to be estimated. The other gives rise to a simple control chart for use in geochemical analysis.     

模拟摩擦接触问题的新型无网格数值方法

针对摩擦接触问题,给出一种新型的无网格数值方法。该方法基于单位分解思想,在标准无网格Galerkin法的位移模式中嵌入不连续函数和裂尖奇异函数,分别反映接触面的不连续性和接触面端点的奇异性;结合接触摩擦定律,继而构造出求解摩擦接触问题的无网格线性互补模型。在该方法中,接触面方程使用接触点对离散,全局离散系统方程则转化为标准的线性互补问题,可以很方便地使用Lemke算法求解。算例分析证明,本文方法的正确性和有效性。     

桩基支护方式选择的新方法

针对深基坑施工中桩基支护方式的选择,以机器学习的新方法--支持向量机为工具,建立了桩基支护方式选择的支持向量机模型,并将该模型应用于具体的工程进行验证中。研究结果表明,该种方法是适应性较好的,具有很好的应用前景。     

堆石料碾压试验的颗粒流模拟新方法

针对堆石料现场碾压试验,研究基于颗粒流的仿真模拟新方法。首先,以随机多边形颗粒簇形式,建立堆石料的颗粒流模型,充分体现了堆石料的级配、细观组构和破碎效应,从而可以较为真实地模拟堆石料在碾压过程中的宏、细观力学响应;然后,提出振动碾压荷载及碾压过程的模拟新方法,实现振动碾压荷载及碾压过程的仿真模拟;最后,结合水布垭主堆石料的现场碾压试验,利用该方法进行模拟验证,从而论证该方法的可靠性。该方法可为仿真模拟堆石料碾压试验以及研究碾压效应对堆石料宏观力学特性的影响奠定基础,具有重要工程指导意义。     

A new approach to monitoring seismic activity: California case study

Preliminary work on the creation of a method for monitoring of seismic activity, on the basis of discrete mathematical analysis for further seismic hazard assessment of a territory, is presented. The method developed is tested for the territory of California and adjacent areas of the United States. The results obtained are analyzed for the period of 1980–2015. The nonrandomness of the results is shown by means of an error chart.     

A new simple approach to evaluate pedogenic clay transformation in a Vertic Calcisol

The aim of this study is to characterize the pedogenic clay minerals by using simple approach: mixing mineralogical and geochemical findings.The fine clay fractions (< 0.1 μm) of a Vertic Cambisol profile were studied by means of X-ray diffraction (XRD), infrared spectroscopy (FTIR) and cation exchange capacity (CEC).Qualitative and quantitative mineralogical compositions of the clay mixture were determined.Moreover, chemical equilibria and thermodynamic stabilities of minerals (calcite, gypsum, kaolinite, smectites and illites) were studied using results of ionic activities obtained from total concentration of various aqueous species in water extracts from soil-saturated pastes.XRD analysis shows a good homogeneity in the mineralogical composition of the soil material, with depth of soil profiles. The identified clay minerals are mainly illite–smectite mixed layers (I/S) and kaolinite. The chemical analysis of saturated paste extracts with clay minerals shows a slight undersaturation of the illitic phase while smectites and also calcite and gypsum reach the thermodynamic equilibrium along the soil profile.     

A new approach to time-load-deformation-stress hypersurface of rocks to stability analysis of underground openings

The most important developments in rock engineering are about time-dependent deformation behavior of rocks under different loads. Many studies have been done for the purpose of identifying mathematically time-load-deformation (TLD) characteristics of the rocks. These studies have made an important contribution to the research on the stability of constructions built in rock masses, and rock material is the main part of the rock mass in which the engineering constructions. When considered from this point of view, the time-dependent deformation behavior of the rocks under different loads is important to determine unstable conditions of the rock constructions in the long term. Researches in rock masses use surfaces based on TLD data. On the other hand, the strength of the rock is also part of these analyzes. The new model developed in this study has four variables such as time, load, deformation, and strength. Therefore, TLD surfaces developed for time-load-deformation has been associated with another variable and three-component (TLD) surfaces eventually transformed into four-component (time-load-deformation-strength; TLDS) hypersurfaces. Hypersurfaces, which illustrate new TLDS behaviors of the rocks, developed in underground openings in different rock constructions in different areas. It is thought that the TLDS hypersurfaces will especially be contributed to the numerical modeling studies of rock construction analysis.     

A new approach to the determination of methane content of coal seams

Summary An approach to the determination of methane content of coal seams is proposed. The method utilizes the transformed Airey's empirical equation on desorption of methane from coals. The methane content values estimated by this method correspond well with actual values from laboratory experiments. In the case of Indian coals, the applicability of the relationship for the calculation of the gas lost from coal lumps during long periods of time loss appears to be limited due to poor agreement with the experimental values.     

A new approach to modeling the surface magnetic fields of chemically peculiar stars

A reconstruction of the line-of-sight component and modulus of the surface-magnetic-field vector is proposed, using a model with artificial point sources of the magnetic field with “virtual” magnetic charges in the body of a star. This approach for the direct calculation of the field from the superposition of the potentials of individual magnetic charges enables the reconstruction of most possible configurations of the surface magnetic field of a star. Proper choice of the axis orientations for the three coordinate systems used makes it possible to obtain a simple representation for the vector components of the surface magnetic field. In a dipole approximation, the expression for the line-of-sight component of the magnetic field averaged over the visible disk of the star reduces to the form obtained in other studies.     

A new numerical approach to the hyperstatic reaction method for segmental tunnel linings

This paper proposes a numerical approach to the hyperstatic reaction method (HRM) for the analysis of segmental tunnel linings. The influence of segmental joints has been considered directly using a fixity ratio that is determined on the basis of the rotational stiffness. The parameters necessary for the calculation are presented. A specific implementation has been developed using a FEM framework. This code is able to consider the three‐dimensional (3D) effect of segment joints in successive rings on the tunnel lining behaviour. The present HRM allows one to take an arbitrary distribution of segment joints along the tunnel boundary into consideration. In addition, the rotational stiffness of segment joints has been simulated using nonlinear behaviour, as it is closer to the true behaviour of a joint than linear or bilinear behaviour. The numerical results of three hypotheses on ring interaction, which allow the 3D effect of a segmental tunnel lining to be taken into account, have been compared with data obtained from the shield‐driven tunnel of the Bologna–Florence high‐speed railway line project. The numerical results presented in the paper show that the proposed HRM can be used to effectively estimate the behaviour of a segmental tunnel lining. Copyright © 2014 John Wiley & Sons, Ltd.