An improved specimen generation method for DEM based on local Delaunay tessellation and distance function

Discretizing a domain of interest into a set of particles for discrete element simulation is the first step to generate a specimen. An improved algorithm, the Seed Expansion Method (SEM), is proposed in this work. A seed is first generated inside a given domain. Then, the domain is filled by the seed expansion based on a local Delaunay tessellation and a distance function. An optional operation, refilling, is suggested to further improve the packing density after the completion of SEM. Polydisperse dense packing can be generated by the proposed method for an arbitrarily shaped domain in both 2D and 3D. A specimen can be obtained that approximately conforms to a specified size distribution and packing density. Multiple subdomains of a domain can be filled by packings with different densities and size distributions. A specimen with higher density can be obtained by comparing it with the existing methods. Mathematically, the features of the method include both simplicity and high efficiency. Copyright © 2011 John Wiley & Sons, Ltd.     

地铁盾构隧道洞门钢环圆心坐标的精确测定

给出了测定与计算钢环圆心坐标和半径的方法,按照最小二乘原理进行求解,并根据实际数据进行了验证和分析,实现了地铁盾构隧道洞门钢环圆心坐标的精确测定。     

地球流体中的完全惯性振荡和惯性波动

在通常描写地球流体运动的Navier-Stokes方程组中考虑了另一个Coriolis参数f′=2Ωcosφ的情况下，首先对中高纬度和低纬度的地球流体中的惯性振荡分别进行了分析和讨论，并把该惯性振荡称为完全惯性振荡，其次对中高纬度的完全惯性波也进行了讨论，结果发现：(1)中高纬度的完全惯性振荡的周期要比不考虑厂的惯性振荡(即通常所说的惯性圆)周期小，完全惯性振荡轨迹为-惯性球，球半径与初始纬向速度成正比；(2)低纬度的完全惯性振荡周期通常远大于中高纬度的完全惯性振荡周期，而且在一定的条件下，周期可以非常大，所以低纬度的完全惯性运动是长周期(或低频)的惯性振荡。(3)中高纬度的完全惯性波的传播速度比不考虑f′的惯性波快，而且是频散波。     

基于加权Voronoi图及Voronoi树图的城市影响范围研究——以山东省为例

基于山东省17地市经济发展数据,构建反映城市综合实力的指标体系,利用因子分析法确定城市综合实力得分,以此为基础,建立加权Voronoi图揭示1995~2012年山东省各城市的空间影响范围及演变规律,运用Voronoi树图方法实现了城市多层级嵌套结构的表达,有效反映了城市之间的空间竞争关系,为城市合理布局规划提供了有效论证。     

21世纪地球物理学的机遇与挑战

21世纪的地球物理学(主要指固体地球物理学)面临着机遇,同时也面临着挑战,其研究的核心领域应为地球深部物质与能量的交换,圈层耦合和其深层动力过程．本文将对以下问题进行探讨：(1)地球物理学的发展和深化与现代科学技术进步的制约．(2)地球物理学必须向高层次的综合研究方向发展．(3)地球物理学面临的机遇与挑战．(4)地球内部圈层结构与大陆动力学研究的思考和内涵．     

Exact solutions of the Lane–Emden-type equation

We classify the Lane–Emden-type equation xy^″+ny^′+x^νf(y)=0 with respect to the standard Lagrangian according to the Noether point symmetries it admits. First integrals of the various cases, which admit Noether point symmetries, and reduction to quadratures for these cases are obtained. Six cases result in new solutions.     

Is the Fisher Distribution Additive?

The Probability Density Function (PDF) of the Fisher distribution is expressed by the expansion in spherical harmonics in order to prove that the product of two Fisher-distributed random rotations has a distribution of different type, which, however, may be well approximated by the Fisher one. The introduced formalism provides the pattern of how to cope with various types of the distribution on the sphere being combined as rotations.     

塔里木河下游生态输水对沙漠化逆转的影响

1 IntroductionThe Tarim River (Figure 1), located in the X injiang U ygur A utonom ous Region in N orthw estChina,is the largestinland river in China.The annualaverage precipitation of the Tarim Rivervaries from 17.4 m m to 42.0 m m w hile the annual aver…     

Batch Dissolution Kinetics: The Shrinking Sphere Model with Salts and Its Potential Application to Biogenic Silica

The full potential of batch dissolution experiments in geochemical and industrial applications has been hampered by the lack of an equation to describe the increase in dissolved solid concentration with time. This study provides new experimental results on the dissolution of salts and new equations, which describe dissolution according to the shrinking sphere model. Sieved salts were found to dissolve according to the shrinking sphere model while the dissolution of the parent material, raw (agglomerated) salt, fitted an exponential dissolution curve. The implications of this to the development of a systematic approach to batch dissolution, irrespective of the solid, is explored. Mathematical equations are derived for the dissolution of solids in under-saturated systems, which are much simpler than ones available, so far. In turn these provide easier comprehension of the workings of the shrinking sphere model. Finally, existing results for biogenic silica dissolution are reviewed in the light of the above-mentioned experimental and modelling advances. An earlier claim that shrinking sphere dissolution had been observed is refuted.     

Least-squares Minimization Approaches to Interpret Total Magnetic Anomalies Due to Spheres

We have developed three different least-squares approaches to determine successively: the depth, magnetic angle, and amplitude coefficient of a buried sphere from a total magnetic anomaly. By defining the anomaly value at the origin and the nearest zero-anomaly distance from the origin on the profile, the problem of depth determination is transformed into the problem of finding a solution of a nonlinear equation of the form f(z)=0. Knowing the depth and applying the least-squares method, the magnetic angle and amplitude coefficient are determined using two simple linear equations. In this way, the depth, magnetic angle, and amplitude coefficient are determined individually from all observed total magnetic data. The method is applied to synthetic examples with and without random errors and tested on a field example from Senegal, West Africa. In all cases, the depth solutions are in good agreement with the actual ones.