Entropic lattice Boltzmann method for turbulent flow simulations: Boundary conditions

We introduce a new concept of boundary conditions for realization of the lattice Boltzmann simulations of turbulent flows. The key innovation is the use of a universal distribution function for particles, analogous to the Tamm–Mott-Smith solution for the shock wave in the classical Boltzmann kinetic equation. Turbulent channel flow simulations demonstrate that the new boundary enables accurate results even with severely under-resolved grids. Generalization to complex boundary is illustrated with an example of turbulent flow past a circular cylinder.     

Adsorption of a spherical nanoparticle in polymer brushes: Brownian dynamics investigation

We use Brownian dynamics simulations to study the adsorption behavior of a nanosized particle in polymer brushes. The adsorption process, the dynamic behavior of the nanoparticle in the brush, the penetration depth, the diffusion coefficient of the nanoparticle in different depths of the brush, and the forces exerted on the nanoparticle by the surrounding brush are all investigated for different grafting densities.     

FJ中子屏蔽层设计及虚拟装配

基于单元块的概念设计,对FJ中子屏蔽层进行了空间布局,并提出命名方法。基于真空室扇区与扇区接口确定的虚拟设计空间,将三维模型特征数字化。通过反求设计方法,对FJ中子屏蔽层进行了结构设计。为缩短设计周期,提高设计效率,采用了骨架建模和Instance建模方法。同时,对FJ中子屏蔽层进行了虚拟装配。     

Influence of packing on the vibrations of homogeneous bundles of C60 peapods

The non-resonant Raman spectra of homogeneous bundles of C₆₀ peapods (C₆₀ inserted in single-walled carbon nanotubes) are calculated in the framework of spectral moment method, together with a bond-polarizability model. The evolutions of the low wavenumber range of the Raman spectrum of homogeneous bundles of C₆₀ peapods as a function of the nanotube diameter and the size of bundles are discussed. The effect of the C₆₀ filling factor is investigated in detail. The results are compared to experimental Raman data measured on various samples of C₆₀ peapods.     

Experimental and numerical study of a conical turbulent partially premixed flame

The structure and dynamics of a turbulent partially premixed methane/air flame in a conical burner were investigated using laser diagnostics and large-eddy simulations (LES). The flame structure inside the cone was characterized in detail using LES based on a two-scalar flamelet model, with the mixture fraction for the mixing field and level-set G-function for the partially premixed flame front propagation. In addition, planar laser induced florescence (PLIF) of CH and chemiluminescence imaging with high speed video were performed through a glass cone. CH and CH₂O PLIF were also used to examine the flame structures above the cone. It is shown that in the entire flame the CH layer remains very thin, whereas the CH₂O layer is rather thick. The flame is stabilized inside the cone a short distance above the nozzle. The stabilization of the flame can be simulated by the triple-flame model but not the flamelet-quenching model. The results show that flame stabilization in the cone is a result of premixed flame front propagation and flow reversal near the wall of the cone which is deemed to be dependent on the cone angle. Flamelet based LES is shown to capture the measured CH structures whereas the predicted CH₂O structure is somewhat thinner than the experiments.     

蛋白质空间结构的实验技术和理论方法

文章主要介绍几种蛋白质空间结构的实验测定方法，在现代生物学研究中，最常用的方法包括X射线晶体学、二维核磁共振（2D-NMR）和低温冷冻电镜，近几年发展起来的单分子技术在生物大分子动态结构的研究中应用越来越多，这些方法都有它们特定的时间和空间分辨率，所测定的结构及其动力学受环境热运动涨落的影响也非常不同，文章对这些问题作了较详细的分析，在蛋白质结构的理论方法方面，介绍了一个新的折叠理论及其与现有折叠模型的关系．讨论了模拟计算在研究蛋白质构象变化和动力学方面的应用，同时强调了分子动力学和蒙特卡罗方法．指出粗粒化模型是研究的热点之一，对生物学中经常遇到的多长度多时问尺度问题提供了一个可行的解决方案。     

Molecular dynamics simulations of structural disordering and forming defects in a milling process for selenium

In our previous paper, structural changes of selenium powders ground by a planetary ball mill at various rotational speeds were investigated for the nanostructural modification of particles using mechanical grinding process. The experimental results indicated that the amorphisation of Se by grinding accompanies lattice strain, and the lattice strain arises from impact energy which is more than an energy related to intermolecular interaction. In this paper, molecular dynamics simulations of selenium have been carried out under compressing conditions of various pressure strengths for obtaining information of the lattice strain at atomic level. Then, dynamical behaviour of atomic configuration has been discussed in this process. The structural disordering and formation of the structural defects were estimated by deviations of bond length and angle and the number of created defects before and after compressing from simulated results. The disordering took place during compressing at various pressure strengths, and the disordered atoms return to their initial positions at lower pressure. Stable disordered state and defects after the compression can however remain by compression at more than a certain pressure strength mainly associated with binding energy of selenium.     

Simulation of the track growth and determining the track parameters

We have found the equation of the etch pit wall in solid state nuclear track detectors, as follows:

where: x is the distance along a track from the point where the particle entered the detector; V(x) is the ratio of the track etch rate to the bulk etch rate; C is the integration constant that can be determined from particle penetration depth, and y is the normal distance from the particle trajectory to the etch pit wall. The equation is derived assuming the increasing track etch rate V_t along the particle trajectory.

The above equation can be used for the simulation of the track growth and calculating the major and the minor axis of the etch pit opening. The corresponding computer program was set up. The input parameters of this program are: alpha particle energy, incidence angle and removed layer: the output are track parameters. The results obtained by this method are compared with another approach given by Somogyi and Szalay (1973) and reasonably good agreement is found.     

Predicting the Mechanical Properties of Binary Blends of Immiscible Polymers

We couple a morphological study of an immiscible binary AB mixture with a micromechanical simulation to determine how the spatial distribution of the A and B domains and the interfacial region (interphase) affects the mechanical behavior of the blend. The morphological studies are conducted through a three-dimensional Cahn-Hilliard (CH) simulation. Through the CH calculations, we obtain the size and structure of the domains for different blend compositions. The output of the CH model serves as the input to the Lattice Spring Model (LSM), which consists of a three-dimensional network of springs. In particular, the location of the different phases is mapped onto the LSM lattice and the appropriate force constants are assigned to the LSM sites. A stress is applied to the LSM lattice and we calculate the elastic response of the material. We find that the local stress and strain fields are highly dependent on the morphology of the system. By integrating the morphological and mechanical models, we can isolate how modifications in the composition of the mixture affect the macroscopic behavior. Thus, we can establish how choices made in the components affect the ultimate performance of the material.