电容提取的新摄动方程及小波边界元解法

提出一种解决含高电容率介质结构电容提取问题的新摄动方程,使计算时间减少一半.建立新摄动方程的快速小波Galerkin边界元解法.算例证明新摄动方程精度高且受介质电容率影响小;用小波Galerkin边界元求解的效率高,时间和内存消耗达到最优O(N)(N为未知量数目).     

N体问题的几种数值算法比较

对N体问题的数值积分中的Runge-Kutta-Fehlberg法(简称RKF法)、辛算法和厄米算法在N体问题中应用时引起的能量误差、半长径和偏心率的变化进行比较.结果发现:RKF法精度最高,但长时间内有误差积累;辛算法无人工耗散,能较好保持能量误差的稳定性;厄米算法虽然误差较大,但构造简单,耗机时较少.     

基于幂次相互作用的二维磁性团簇耦合能研究

在扩散限制凝聚模型基础上,采用Monte Carlo方法模拟了磁耦合作用随粒子间距离幂次变化的磁性粒子动力学凝聚过程.重点研究了在不同幂指数α值下团簇在生长过程中,即随着粒子数N的增加,团簇平均耦合能E_c(N)的演化过程.模拟结果表明:对于α≥5时,E_c(N)随着粒子数N的增加变化较小;当α=2时,E关键词： 扩散限制凝聚模型 幂次相互作用 耦合能     

PPV中极化子动力学方程的龙格-库塔求解

构造求解-阶微分方程组初值问题的八阶龙格-库塔递推公式,结合描述有机分子运动的-维紧束缚模型,研究PPV原子链中极化子的形成及运动.对碳原子数N=160的PPV原子链,由可控步长八阶龙格-库塔公式求解2N(2N+1)=102720个方程组成的方程组,用Fortran语言编程计算,得到稳定的极化子结构和运动图像;在场强E=1×105V·cm^-1的电场作用下,极化子沿分子链的运动速率约为0.2635Å·fs^-1.计算结果表明,八阶龙格-库塔方程可以有效地用于有机分子链中载流子运动的模拟.     

LiF插层对有机发光二极管磁场效应的调控

制备了有LiF插层的有机发光二极管,以八羟基喹啉铝（Alq₃）作为电子传输层,N, N′-二苯基-N, N′-二(1-萘基)-1,1′-联苯-4,4′-二胺（NPB）作为空穴传输层.通过改变Alq₃与NPB间LiF插层的厚度,研究了不同温度下器件的光电特性及电致发光的磁场效应.测量结果表明:LiF插层可以影响器件内部载流子的输运和激发态的形成.较厚的插层阻碍了空穴的传输,使器件的电流效率变低.但实验中发现, 关键词： LiF插层结构 磁场效应 三重态激子     

平面行星夹具的物理气相沉积均匀性计算

建立了平面行星夹具薄膜淀积无量纲模型,通过对蒸发源位置L/H、行星主轴与副轴距离P/H、夹角倾角A以及蒸发源蒸汽发射特性N等因素的分析,得到了典型径向理论均匀的优化几何配置.并从优化几何配置的膜料效率、角向均匀性和膜厚分布对蒸发源蒸汽发射特性变化的敏感性方面评价优化结果,得到了最优化设计区域.结果表明,优化配置的L/H+P/H小,则角分布差异小;L/H+P/H和A小,则膜料效率高L<P,A=-15°时,优化配置对N变化最不敏感L>P时,由N变化引起的典型径向分布变化小于0.5%.     

N=28丰中子核的形变和形状共存研究

利用同位旋依赖的尼尔逊势,在宏观-微观理论框架下,计算了幻数N=28同中子链上原子核的性质,研究了N=28同中子链上原子核的形变和形状共存现象. 研究结果表明,N=28这个幻数在Na,Mg, Al同位素链上有着强的形状共存现象. 此外,计算表明⁴²Si的基态为扁椭球,同时在Si同位素链上的形状共存现象相对较弱. 关键词： 同位旋 幻数 形变 形状共存     

类氦离子高双激发态电子关联效应的研究

采用超球坐标方法研究了类氦O⁶⁺高双激发态的电子关联效应、能级结构、辐射跃迁率和Auger跃迁率,并采用新的量子数集K,T,A标识这些双激发态的Rydberg系列.研究表明,在超球方法的框架下,能级结构、辐射跃迁率和Auger跃迁率均显示出规律性的变化. 关键词： 电子关联效应 高双激发态 Auger跃迁率     

非球体填充的组合球模型及松弛算法

现有的松弛算法由于仅用于球填充而只考虑颗粒的平动,故提出考虑非球体转动的改进松弛算法并采用组合球模型,使其能够模拟任意形状非球体的随机填充以及多种非球体的混合填充.用多个球体的外包络面近似一个非球体外形的组合球模型,将非球体之间的接触转化为球体之间的接触,从而简化并统一非球体接触判断算法.通过引入非球体的转矩和转角松弛机制,使改进松弛算法克服了"自锁"现象,并能生成非球体的随机密填充.算例表明,填充结果与现有的数值模拟及实验结果相符.     

通过纠缠交换实现N粒子任意态的概率传态

量子隐形传态的杰出安全特性使其在未来的通讯领域充满潜力.量子力学的不确定性原理和不可克隆定理禁止对量子态进行直接复制,因此,量子隐形传态将量子态划分为经典和量子两部分,信息分别经由经典和量子通道从发送者Alice传递给远方的接收者Bob,根据这两种信息,Bob实行相应操作就可以以一定的几率重建初始传送态.利用一般意义的隐形传态方案,提出一种简便的新方法实现了一个N粒子任意态的概率传态.方法采用N个非最大纠缠的三粒子GHZ态作为量子通道,避免了引入额外的辅助粒子.为了实现传态,Alice将所有粒子分成N份,对第i份的粒子对(i,x_i)实行Bell测量并将结果通过经典通道通知Bob,Bob对粒子(y_i,z_i)进行相应的操作就可以完成第i个粒子信息的传送.当完成N次相似的重复操作后,Bob就可以准确地重建初始传送态.文中以Bell态测量为基本手段,重复的操作同时也降低了实验难度,作为一个特例,文中给出了一个两粒子任意态的传态方案.     

Numerical Simulation of Random Close Packing with Tetrahedra

The densest packing of tetrahedra is still an unsolved problem. Numerical simulations of random close packing of tetrahedra are carried out with a sphere assembly model and improved relaxation algorithm. The packing density and average contact number obtained for random close packing of regular tetrahedra is 0.6817 and 7.21 respectively, while the values of spheres are 0.6435 and 5.95. The simulation demonstrates that tetrahedra can be randomly packed denser than spheres. Random close packings of tetrahedra with a range of height are simulated as well. We find that the regular tetrahedron might be the optimal shape which gives the highest packing density of tetrahedra.     

Polytetrahedral nature of the dense disordered packings of hard spheres

We study the structure of numerically simulated hard sphere packings at different densities by investigating local tetrahedral configurations of the spheres. Clusters of tetrahedra adjacent by faces present relatively dense aggregates of spheres atypical for crystals. The number of spheres participating in such polytetrahedral configurations increases with densification of the packing, and at the Bernal's limiting density (the packing fraction around 0.64) all spheres of the packing become involved in such tetrahedra. Thus the polytetrahedral packing cannot provide further increase in the density, and alternative structural change (formation of crystalline nuclei) begins henceforth.     

Numerical Simulation of Random Close Packings in Particle Deformation from Spheres to Cubes

Variation of packing density in particle deforming from spheres to cubes is studied. A new model is presented to describe particle deformation between different particle shapes. Deformation is simulated by relative motion of component spheres in the sphere assembly model of a particle. Random close packings of particles in deformation form spheres to cubes are simulated with an improved relaxation algorithm. Packings in both 2D and 3D cases are simulated. With the simulations, we find that the packing density increases while the particle sphericity decreases in the deformation. Spheres and cubes give the minimum (0.6404) and maximum (0.7755) of packing density in the deformation respectively. In each deforming step, packings starting from a random configuration and from the final packing of last deforming step are both simulated. The packing density in the latter case is larger than the former in two dimensions, but is smaller in three dimensions. The deformation model can be applied to other particle shapes as well.     

Statistical Analysis of Simulated Random Packings of Spheres

This paper describes two algorithms for the generation of random packings of spheres with arbitrary diameter distribution. The first algorithm is the force‐biased algorithm of Mościński and Bargieł. It produces isotropic packings of very high density. The second algorithm is the Jodrey‐Tory sedimentation algorithm, which simulates successive packing of a container with spheres following gravitation. It yields packings of a lower density and of weak anisotropy. The results obtained with these algorithms for the cases of log‐normal and two‐point sphere diameter distributions are analysed statistically, i. e. standard characteristics of spatial statistics such as porosity (or volume fraction), pair correlation function of the system of sphere centres and spherical contact distribution function of the set‐theoretical union of all spheres are determined. Furthermore, the mean coordination numbers are analysed. These results are compared for both algorithms and with data from the literature based on other numerical simulations or from experiments with real spheres.     

Experiments on random packings of ellipsoids

Recent simulations indicate that ellipsoids can pack randomly more densely than spheres and, remarkably, for axes ratios near 1.25:1:0.8 can approach the densest crystal packing (fcc) of spheres, with a packing fraction of 74%. We demonstrate that such dense packings are realizable. We introduce a novel way of determining packing density for a finite sample that minimizes surface effects. We have fabricated ellipsoids and show that, in a sphere, the radial packing fraction phi(r) can be obtained from V(h), the volume of added fluid to fill the sphere to height h. We also obtain phi(r) from a magnetic resonance imaging scan. The measurements of the overall density phi(avr), phi(r) and the core density phi(0) = 0.74 +/- 0.005 agree with simulations.     

受振颗粒“毛细”系统中的对流与有序化

将球形颗粒倒入内径较窄的管状容器时,管壁的曲率会对颗粒的堆积结构产生影响,存在壁效应. 实验表明通过连续的竖直方向的振动,壁效应可以被强化,颗粒可以经由对流由无序排列转变为稳定的同轴筒形“壳层”结构. 每一壳层内,颗粒是二维的六角密堆积, 在这一转变过程中,颗粒堆积率的径向分布由初始的衰减振荡转变为等幅振荡. 分析了堆积率的不均匀性及空气在对流中的作用,以及形成“壳层”结构的动力学过程,对“壳层”结构的稳定性亦进行了讨论. 关键词： 颗粒物质 对流 有序化 毛细     

Morphology and Magnetic Properties of Hollow Co3O4 Spheres

Physics of the Solid State - Nanostructured hollow Co3O4 spheres are synthesized by ultrasonic spray pyrolysis. Nanocrystals forming the sphere structure have different sizes and packing density,...     

On hydraulic permeability of random packs of monodisperse spheres: Direct flow simulations versus correlations

Hydraulic permeability is studied in porous media consisting of randomly distributed monodisperse spheres by means of computational fluid dynamics (CFD) simulations. The packing of spheres is generated by inserting a certain number of nonoverlapping spherical particles inside a cubic box at both low and high packing fractions using proper algorithms. Fluid flow simulations are performed within the interparticulate porous space by solving Navier-Stokes equations in a low-Reynolds laminar flow regime. The hydraulic permeability is calculated from the Darcy equation once the mean values of velocity and pressure gradient are calculated across the particle packing. The simulation results for the pressure drop across the packing are verified by the Ergun equation for the lower range of porosities (<0.75), and the Stokes equation for higher porosities (∼1). Using the results of simulations, the effects of porosity and particle diameters on the hydraulic permeability are investigated. Simulations precisely specified the range of applicability of empirical or semi-empirical correlations for hydraulic permeability, namely the Carman-Kozeny, Rumpf-Gupte, and Howells-Hinch formulas. The number of spheres in the model is gradually decreased from 2000 to 20 to discover the finite-size effect of pores on the hydraulic permeability of spherical packing, which has not been clearly addressed in the literature. In addition, the scale dependence of hydraulic permeability is studied via simulations of the packing of spheres shrunk to lower scales. The results of this work not only reveal the validity range of the aforementioned correlations, but also show the finite-size effect of pores and the scale-independence of direct CFD simulations for hydraulic permeability.