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A moving mesh finite difference method for non-monotone solutions of non-equilibrium equations in porous media 多孔介质非平衡方程非单调解的移动网格有限差分法
Pub Date : 2016-11-25 DOI: 10.4208/cicp.OA-2016-0220
Hong Zhang, P. Zegeling
An adaptive moving mesh finite difference method is presented to solve two types of equations with dynamic capillary pressure term in porous media. One is the non-equilibrium Richards Equation and the other is the modified Buckley-Leverett equation. The governing equations are discretized with an adaptive moving mesh finite difference method in the space direction and an implicit-explicit method in the time direction. In order to obtain high quality meshes, an adaptive time-dependent monitor function with directional control is applied to redistribute the mesh grid in every time step, and a diffusive mechanism is used to smooth the monitor function. The behaviors of the central difference flux, the standard local Lax-Friedrich flux and the local Lax-Friedrich flux with reconstruction are investigated by solving a 1D modified Buckley-Leverett equation. With the moving mesh technique, good mesh quality and high numerical accuracy are obtained. A collection of one-dimensional and two-dimensional numerical experiments is presented to demonstrate the accuracy and effectiveness of the proposed method.
提出了一种自适应移动网格有限差分法,用于求解两类含动毛细压力项的多孔介质方程。一种是非平衡理查兹方程,另一种是修正的巴克利-莱弗里特方程。在空间方向上采用自适应运动网格有限差分法,在时间方向上采用隐显法对控制方程进行离散。为了获得高质量的网格,采用具有方向控制的自适应时变监控函数在每个时间步重分配网格,并采用扩散机制平滑监控函数。通过求解一维修正Buckley-Leverett方程,研究了中心差通量、标准局部Lax-Friedrich通量和局部Lax-Friedrich通量的重构行为。采用动网格技术,可以获得较好的网格质量和较高的数值精度。通过一维和二维数值实验验证了该方法的准确性和有效性。
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引用次数: 12
ePSproc: Post-processing suite for ePolyScat electron-molecule scattering calculations epspproc:用于ePolyScat电子分子散射计算的后处理套件
Pub Date : 2016-11-01 DOI: 10.22541/au.156754490.06103020
P. Hockett
ePSproc provides codes for post-processing results from ePolyScat (ePS), a suite of codes for the calculation of quantum scattering problems, developed and released by Luchesse & co-workers (Gianturco et al. 1994)(Natalense and Lucchese 1999)(R. R. Lucchese and Gianturco 2016). ePS is a powerful computational engine for solving scattering problems, but its inherent complexity, combined with additional post-processing requirements, ranging from simple visualizations to more complex processing involving further calculations based on ePS outputs, present a significant barrier to use for most researchers. ePSproc aims to lower this barrier by providing a range of functions for reading, processing and plotting outputs from ePS. Since ePS calculations are currently finding multiple applications in AMO physics (see below), ePSproc is expected to have significant reuse potential in the community, both as a basic tool-set for researchers beginning to use ePS, and as a more advanced post-processing suite for those already using ePS. ePSproc is currently written for Matlab/Octave, and distributed via Github: this https URL.
ePSproc提供了ePolyScat (ePS)的后处理结果的代码,ePolyScat (ePS)是Luchesse和同事(Gianturco et al. 1994)(Natalense和Lucchese 1999)开发并发布的一套用于计算量子散射问题的代码。R. Lucchese and Gianturco 2016)。ePS是解决散射问题的强大计算引擎,但其固有的复杂性,加上额外的后处理要求,从简单的可视化到更复杂的处理,包括基于ePS输出的进一步计算,对大多数研究人员来说是一个重大的障碍。epspproc旨在通过提供一系列读取、处理和绘制ePS输出的功能来降低这一障碍。由于ePS计算目前在AMO物理中有多种应用(见下文),ePSproc有望在社区中具有重要的重用潜力,既可以作为开始使用ePS的研究人员的基本工具集,也可以作为已经使用ePS的研究人员的更高级的后处理套件。ePSproc目前是为Matlab/Octave编写的,并通过Github分发:此https URL。
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引用次数: 2
Percolation study for the capillary ascent of a liquid through a granular soil 液体在颗粒状土壤中毛细管上升的渗透研究
Pub Date : 2016-10-31 DOI: 10.1051/epjconf/201714015007
Manuel Cárdenas-Barrantes, J. D. Muñoz, N. Araújo
Capillary rise plays a crucial role in the construction of road embankments in flood zones, where hydrophobic compounds are added to the soil to suppress the rising of water and avoid possible damage of the pavement. Water rises through liquid bridges, menisci and trimers, whose width and connectivity depends on the maximal half-length {lambda} of the capillary bridges among grains. Low {lambda} generate a disconnect structure, with small clusters everywhere. On the contrary, for high {lambda}, create a percolating cluster of trimers and enclosed volumes that form a natural path for capillary rise. Hereby, we study the percolation transition of this geometric structure as a function of {lambda} on a granular media of monodisperse spheres in a random close packing. We determine both the percolating threshold {lambda}_{c} = (0.049 pm 0.004)R (with R the radius of the granular spheres), and the critical exponent of the correlation length {nu} = (0.830 pm 0.051), suggesting that the percolation transition falls into the universality class of ordinary percolation.
毛细上升在洪水地区的道路堤防建设中起着至关重要的作用,在土壤中添加疏水化合物以抑制水的上升,避免可能对路面造成损害。水通过液桥、半月板和三聚体上升,其宽度和连通性取决于颗粒间毛细管桥的最大半长{lambda}。低{lambda}产生一个断开的结构,到处都是小集群。相反,对于高{lambda},创建一个三聚体的渗透簇和封闭的体积,形成毛细管上升的自然路径。因此,我们研究了这种几何结构在随机紧密堆积的单分散球体颗粒介质上作为{lambda}函数的渗透转变。我们确定了渗流阈值{lambda} _c{ = (0.049 }pm 0.004)R (R为颗粒球半径)和相关长度的临界指数{nu} = (0.830 pm 0.051),表明该渗流过渡属于普通渗流的普遍性。
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引用次数: 0
Enhanced van der Waals epitaxy via electron transfer-enabled interfacial dative bond formation 通过电子转移激活的界面键形成增强范德华外延
Pub Date : 2016-10-24 DOI: 10.1103/PhysRevMaterials.1.063402
W. Xie, T. Lu, Gwo-Ching Wang, I. Bhat, Shengbai Zhang
Enhanced van der Waals (vdW) epitaxy of semiconductors on layered vdW substrate is identified as the formation of dative bonds. For example, despite that NbSe2 is a vdW layered material, first-principles calculations reveal that the bond strength at CdTe-NbSe2 interface is five times as large as that of vdW interaction at CdTe-graphene interface. The unconventional chemistry here is enabled by an effective net electron transfer from Cd dangling-bond states at CdTe surface to metallic non-bonding NbSe2 states, which is a necessary condition to activate the Cd for enhanced binding with Se.
半导体在层状范德华衬底上的增强范德华外延被认为是一种化学键的形成。例如,尽管NbSe2是一种vdW层状材料,但第一线原理计算显示,CdTe-NbSe2界面的键合强度是cdte -石墨烯界面上vdW相互作用的5倍。CdTe表面的Cd悬垂键态有效的净电子转移到金属非键态NbSe2,这是激活Cd增强与Se结合的必要条件。
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引用次数: 1
QuSpin: a Python Package for Dynamics and Exact Diagonalisation of Quantum Many Body Systems part I: spin chains 量子多体系统动力学和精确对角化的Python包。第一部分:自旋链
Pub Date : 2016-10-10 DOI: 10.21468/SciPostPhys.2.1.003
P. Weinberg, Marin Bukov
We present a new open-source Python package for exact diagonalization and quantum dynamics of spin(-photon) chains, called QuSpin, supporting the use of various symmetries in 1-dimension and (imaginary) time evolution for chains up to 32 sites in length. The package is well-suited to study, among others, quantum quenches at finite and infinite times, the Eigenstate Thermalisation hypothesis, many-body localisation and other dynamical phase transitions, periodically-driven (Floquet) systems, adiabatic and counter-diabatic ramps, and spin-photon interactions. Moreover, QuSpin's user-friendly interface can easily be used in combination with other Python packages which makes it amenable to a high-level customisation. We explain how to use QuSpin using four detailed examples: (i) Standard exact diagonalisation of XXZ chain (ii) adiabatic ramping of parameters in the many-body localised XXZ model, (iii) heating in the periodically-driven transverse-field Ising model in a parallel field, and (iv) quantised light-atom interactions: recovering the periodically-driven atom in the semi-classical limit of a static Hamiltonian.
我们提出了一个新的开源Python包,用于精确对角化和自旋(光子)链的量子动力学,称为QuSpin,支持在一维和(虚)时间演化中使用各种对称性,长度可达32个位点。该封装非常适合研究有限和无限时间的量子猝灭,本征态热化假设,多体局部化和其他动态相变,周期性驱动(Floquet)系统,绝热和反绝热斜坡,以及自旋光子相互作用。此外,QuSpin的用户友好界面可以很容易地与其他Python包结合使用,这使得它可以进行高级定制。我们通过四个详细的例子解释了如何使用QuSpin:(i) XXZ链的标准精确对角化(ii)多体局部XXZ模型中参数的绝热倾斜,(iii)在平行场中周期性驱动的横场Ising模型中的加热,以及(iv)量子化光原子相互作用:在静态哈密顿量的半经典极限中恢复周期性驱动的原子。
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引用次数: 221
Effects of Orthogonal Rotating Electric Fields on Electrospinning Process 正交旋转电场对静电纺丝工艺的影响
Pub Date : 2016-10-03 DOI: 10.1063/1.4997086
M. Lauricella, F. Cipolletta, G. Pontrelli, D. Pisignano, S. Succi
Electrospinning is a nanotechnology process whereby an external electric field is used to accelerate and stretch a charged polymer jet, so as to produce fibers with nanoscale diameters. In quest of a further reduction in the cross section of electrified jets hence of a better control on the morphology of the resulting electrospun fibers, we explore the effects of an external rotating electric field orthogonal to the jet direction. Through extensive particle simulations, it is shown that by a proper tuning of the electric field amplitude and frequency, a reduction of up to a $30 %$ in the aforementioned radius can be obtained, thereby opening new perspectives in the design of future ultra-thin electrospun fibres. Applications can be envisaged in the fields of nanophotonic components as well as for designing new and improved filtration materials.
静电纺丝是一种纳米技术,利用外电场来加速和拉伸带电聚合物射流,从而生产出纳米级直径的纤维。为了进一步减小带电射流的横截面,从而更好地控制所得到的静电纺纤维的形态,我们探索了与射流方向正交的外部旋转电场的影响。通过大量的粒子模拟,表明通过适当调整电场振幅和频率,可以使上述半径减少高达30%,从而为未来超薄电纺丝纤维的设计开辟了新的前景。应用可以设想在纳米光子元件领域以及设计新的和改进的过滤材料。
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引用次数: 23
RMPCDMD: Simulations of colloids with coarse-grained hydrodynamics, chemical reactions and external fields RMPCDMD:具有粗粒度流体力学、化学反应和外场的胶体模拟
Pub Date : 2016-08-17 DOI: 10.5334/jors.142
P. Buyl, Mu-Jie Huang, Laurens Deprez
The RMPCDMD software package performs hybrid Molecular Dynamics simulations, coupling Multiparticle Collision Dynamics to model the solvent and Molecular Dynamics to model suspended colloids, including hydrodynamics, thermal fluctuations, and chemically active solvent particles and catalytic colloids. The main usage of RMPCDMD is the simulation of chemically powered nanomotors, but other setups are considered: colloids in the presence of a thermal gradients or forced flows. RMPCDMD is developed in Fortran 2008 with OpenMP for multithreaded operation and uses the HDF5-based H5MD file format for storing data. RMPCDMD comes with documentation and a tutorial for the simulation of chemically powered nanomotors.
RMPCDMD软件包执行混合分子动力学模拟,耦合多粒子碰撞动力学来模拟溶剂和分子动力学来模拟悬浮胶体,包括流体动力学、热波动、化学活性溶剂颗粒和催化胶体。RMPCDMD的主要用途是模拟化学驱动的纳米马达,但也考虑了其他设置:存在热梯度或强制流动的胶体。RMPCDMD是在Fortran 2008中开发的,使用OpenMP进行多线程操作,使用基于hdf5的H5MD文件格式存储数据。RMPCDMD附带了用于模拟化学动力纳米马达的文档和教程。
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引用次数: 6
High order volume-preserving algorithms for relativistic charged particles in general electromagnetic fields 一般电磁场中相对论性带电粒子的高阶体积保持算法
Pub Date : 2016-06-24 DOI: 10.1063/1.4962677
Yang He, Yajuan Sun, Ruili Zhang, Yulei Wang, Jian Liu, H. Qin
We construct high order symmetric volume-preserving methods for the relativistic dynamics of a charged particle by the splitting technique with processing. Via expanding the phase space to include time $t$, we give a more general construction of volume-preserving methods that can be applied to systems with time-dependent electromagnetic fields. The newly derived methods provide numerical solutions with good accuracy and conservative properties over long time of simulation. Furthermore, because of the use of processing technique the high order methods are explicit, and cost less than the methods derived from standard compositions, thus are more efficient. The results are verified by the numerical experiments. Linear stability analysis of the methods show that the high order processed method allows larger time step size during integration.
我们用带处理的分裂技术构造了带电粒子相对论动力学的高阶对称体积保持方法。通过扩展相空间以包含时间$t$,我们给出了可应用于具有时相关电磁场的系统的更一般的体积保持方法的构造。新导出的数值解在长时间的模拟中具有良好的精度和保守性。此外,由于使用了处理技术,高阶方法是显式的,并且成本低于标准组合物的方法,因此效率更高。数值实验验证了计算结果。对方法的线性稳定性分析表明,高阶处理方法在积分时允许较大的时间步长。
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引用次数: 23
Hamiltonian particle-in-cell methods for Vlasov-Maxwell equations Vlasov-Maxwell方程的哈密顿粒子胞内方法
Pub Date : 2016-06-18 DOI: 10.1063/1.4962573
Yang He, Yajuan Sun, H. Qin, Jian Liu
In this paper, we develop Hamiltonian particle-in-cell methods for Vlasov-Maxwell equations by applying conforming finite element methods in space and splitting methods in time. For the spatial discretisation, the criteria for choosing finite element spaces are presented such that the semi-discrete system possesses a discrete non-canonical Poisson structure. We apply a Hamiltonian splitting method to the semi-discrete system in time, then the resulting algorithm is Poisson preserving and explicit. The conservative properties of the algorithm guarantee the efficient and accurate numerical simulation of the Vlasov-Maxwell equations over long-time.
本文采用空间上的一致性有限元方法和时间上的分裂方法,建立了求解Vlasov-Maxwell方程的哈密顿粒子单元法。对于空间离散化,给出了选择有限元空间的准则,使得半离散系统具有离散的非正则泊松结构。我们对半离散系统在时间上应用哈密顿分裂方法,得到的算法是泊松保持的和显式的。该算法的保守性保证了对Vlasov-Maxwell方程组的长时间高效、准确的数值模拟。
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引用次数: 47
Electric potential and field calculation of charged BEM triangles and rectangles by Gaussian cubature 用高斯法计算带电边界元三角形和矩形的电势和电场
Pub Date : 2016-06-12 DOI: 10.2528/PIERB17011107
F. Gluck, D. Hilk
It is a widely held view that analytical integration is more accurate than the numerical one. In some special cases, however, numerical integration can be more advantageous than analytical integration. In our paper we show this benefit for the case of electric potential and field computation of charged triangles and rectangles applied in the boundary element method (BEM). Analytical potential and field formulas are rather complicated (even in the simplest case of constant charge densities), they have usually large computation times, and at field points far from the elements they suffer from large rounding errors. On the other hand, Gaussian cubature, which is an efficient numerical integration method, yields simple and fast potential and field formulas that are very accurate far from the elements. The simplicity of the method is demonstrated by the physical picture: the triangles and rectangles with their continuous charge distributions are replaced by discrete point charges, whose simple potential and field formulas explain the higher accuracy and speed of this method. We implemented the Gaussian cubature method for the purpose of BEM computations both with CPU and GPU, and we compare its performance with two different analytical integration methods. The ten different Gaussian cubature formulas presented in our paper can be used for arbitrary high-precision and fast integrations over triangles and rectangles.
人们普遍认为解析积分比数值积分更精确。然而,在某些特殊情况下,数值积分可能比解析积分更有利。在本文中,我们展示了在边界元法(BEM)中对带电三角形和矩形的电势和电场计算的这种好处。解析势和场公式是相当复杂的(即使在最简单的恒定电荷密度的情况下),它们通常有很大的计算时间,并且在远离元素的场点上,它们遭受很大的舍入误差。另一方面,高斯法是一种有效的数值积分方法,它可以得到简单、快速的势和场的计算公式,这些公式在远离单元的地方是非常精确的。物理图表明了该方法的简便性:将连续电荷分布的三角形和矩形替换为离散的点电荷,其简单的势和场公式解释了该方法较高的精度和速度。我们在CPU和GPU上分别实现了高斯立方化方法,并比较了两种不同的解析积分方法的性能。本文提出的十种不同的高斯计算公式可用于任意高精度、快速的三角形和矩形积分。
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引用次数: 5
期刊
arXiv: Computational Physics
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