树状分形结构形成过程的实验研究

对大量金属小球在强电场作用下运动形态的演化全过程用联机摄像装置进行了实时拍摄,通过用Sandbox方法计算其稳定状态的分维数,系统地研究了分维数随电压的变化关系.结果表明：在一定电压范围内金属小球聚集体通过自组织过程形成稳定的树状分形结构,其分维数随外加电压的增加而减小.该结果对研究耗散结构的形成机理和外界动力对耗散结构的形貌影响具有参考价值.关键词：分形生长自组织过程树状结构分维数     

薄膜中缩聚型分形的计算机模拟

在计算机生成的二维多晶上,利用不均匀晶粒的熟化机理,对薄膜中的缩聚型分形进行了计算机模拟．分析了影响缩聚过程的各主要因素,引入了三个参数：晶界速率因子ｂ,弛豫范围Ｌ和周界曲率因素Ｕ．在一定的参数范围内,均可得到与实验图像相类似的多分叉的分形图样     

分形聚集逾渗性质的计算机模拟

提出3种模型——小尺寸随机逐次成核生长模型和二维及三维代代聚集生长模型,在不同的近邻条件下和不同尺寸的网格中,通过蒙特卡罗模拟,系统地研究了一维、二维和三维分形聚集的逾渗性质.计算结果显示,分形聚集的逾渗阈值仅取决于空间维数和近邻条件,与模型的网格大小无关,是分形系统固有的临界属性;生长概率等于逾渗阈值时,聚集体可以无限生长并保持分形维数恒定,此时的分形维数只是空间维数的线性函数.     

a—Ge／Au双层膜分形过程的计算机模拟

从实验观察结果出发,提出与传统扩散控制聚集(DLA)模型不同的分形生长模型,用Monte-Carlo方法模拟了具有不同界面结构的a-Ge/Au双层膜在晶化过程的分形行为,得到了和实验结果相符合的分形结构。结果表明:在a-Ge/Au双层膜的退火过程中,由非晶晶化潜热形成的局域温度场在分形过程中起主要作用;密集分枝结构的出现是由粒子扩散的局域性引起的;模拟结果还表明DLA形态的分形结构也可以在粒子扩散距离相对短的条件下获得。     

酶表面上的分形反应

本文报道了酶反应中的分形几何效应，用模拟方法研究了催化中的表面标度关系，假设“聚集态酶”有ＤＬＡ形态。每个酶分子作为逾集团中的一个分形体，则酶表面的活性点几率分布的ＤＡＳ（ａ，Ｍ）∝ｅｘｐ（－Ａ／ｌｎＭ）（ａ－ａ０（Ｍ），分雏为Ｄｘ＝Ｉｎ（ｂ－θ）（ｂ－θ＋１）／２＋２θ）／Ｉｎｂ。这里Ｍ是定域质量，ａ０（Ｍ）＝ＢＩｎＭ，Ａ，Ｂ是常数，ｂ是回转半径，θ是酶集团表面“空位”数，模拟知“中毒”时间Ｔｐ     

多孔介质分形结构热方程的多重双尺度概率模型与数值模拟

多孔介质分形结构既含有大量微米量级甚至纳米量级的微孔隙,也含有大量厘米甚至米量级的宏观孔洞。如果又假设复相材料和孔隙的就位性及形状大小服从某一概率分布。此时无论是理论分析或是数值计算均非常困难。本文对此问题,初步建立多重双尺度概率模型,井给出数值实验结果。     

铁超微粒聚集体的分形结构

由铁超微粒组成的聚集集团的形态结构具有明显的分形体特征和规律性.随着集团聚集密度的增加,呈现出扩展态、补偿态和塌缩态,而且自相似性逐步减弱.关键词：     

二级树状管路的优化分析

本文讨论了Y型二级管路分别在占地面积、体积以及占地面积、表面积约束下的最优管径比、最优管长比、最优分岔角度。优化方法采用拉格朗日乘子法和虚功原理方法。通过分析发现;最优树状管路的结构参数随约束条件和流动状态的变化而变化.这意味着对层流流动和湍流流动的情况,树状结构最优参数会表现出差异。本文的忧化结果为不同情况下的树状结构设计提供了基本参考。     

Computer simulation of the structure of noble metal glasses

A model of an amorphous alloy structure of 600 atoms was designed using a RCPSS method. The model cluster was relaxed by using a Morse potential according to the original methodology. Paired and angular correlation functions, distribution histograms of nearest neighbors, and the coherent component of x-ray beam scattering were calculated for the relaxed cluster. The short-range fine structure was analyzed. It is shown that the cluster has a clearly expressed icosahedral character. These results are a logical consequence of the relaxation of a centrally symmetric potential.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 74–79, February, 1992.     

Computer simulation of structure and mechanical properties of polymer liquid crystals

In this contribution, we report on a study of the self-organization and mechanical properties of polymer liquid crystals (PLCs). Both processes are computer simulated by the method of molecular dynamics. We investigated two real longitudinal PLCs (thermotropic polyesters) with macromolecules that consist of rigid and flexible parts arranged in a regular way. One rigid and one flexible part form a monomer containing 45 or 47 atoms. The total number of atoms in the macromolecules studied was 4700 (100 monomers) and 5400 (75 monomers). The self-organization was similar to that obtained earlier for a beads-on-a-string model, so compression calculations were done using this simpler model containing 1200 beads (100 monomers). Macroscopic characteristics such as the stress-strain relation, temperature change during deformation, as well as microscopic changes in structure, were investigated.     

Computer simulation of the structure and raman spectra of GaAs polytypes

The structure, energy of formation, and Raman spectra of several polytypes (3C, 2H, 4H, and 8H) of gallium arsenide GaAs have been investigated using quantum mechanical calculations based on the local density functional theory. It has been found that the energy of the formation of hexagonal polytypes increases with an increase in the length of the periodicity and approaches the value corresponding to the ground state, i.e., to the structure of the 3C polytype. It has been shown that the calculated frequencies of normal vibrations of different polytypes are consistent, with good accuracy (±6 cm^?1), with the scheme of folding of the phonon branches. In the calculated Raman spectra of the polytypes, there are new lines (forbidden in the spectrum of the 3C polytype) which can serve as characteristic lines of other polytypes. Similar lines can be found in the Raman spectra of GaAs nanowhiskers. This result has opened up new prospects for the application of Raman spectroscopy to the characterization of the structure of these nano-objects.     

Computer simulation of crystal structure formation upon transition from amorphous state

The structure of a solid has been studied by the molecular dynamics technique upon transition from the amorphous state to the crystalline state. The influence of initial conditions in the simulation of an amorphous sample and the temperature of its heating on the resulting structure is examined. It is found that structures of two types can be formed in the sample: single crystals consisting of face-centered cubic (fcc) and hexagonal close-packed (hcp) cells with a small number of pentahedral cells in the boundary region of the sample and block crystals with an ordered pentahedral structure composed of fcc, hcp, pentahedral, and icosahedral cells. Linear chains of vacancies are revealed at the boundaries of blocks.     

Dynamic fractal structure of emulsions due to motion and interaction of the particles: Numerical simulation

The method of numerical simulation is used to study the geometrical structure of micro-emulsions in the plane. It is found that the interaction between the particles leads to the formation of a dynamic homogeneous fractal structure of the micro-emulsion. In the absence of any interaction between the particles the structure of the emulsion is homogeneous. The interaction energy of the particles at which the fractal inhomogeneity arises is close in magnitude to the interaction energy of the particles in real (e.g., aqueous) micro-emulsions. It is also found that the size of the inhomogeneities (correlation radius) depends on the particle density in the system and is largest for the density of the percolation transition. The numerical simulation data qualitatively coincide with the results of measurements in real micro-emulsions. Zh. éksp. Teor. Fiz. 111, 1314–1319 (April 1997)     

Computer simulation model of the structure of ion implanted impurities in semiconductors

A system of ion implanted impurities in a semiconductor is described by a Monte Carlo simulation of a non-equilibrium system of random distributed hard spheres. The radial distribution function of this system is found. The comparison is made with the fluid hard sphere case. The assumption that the absence either of annealing or diffusion of the impurities after the implantation process is also made.     

Dynamic conductivity of composites of fractal structure

We have studied the dynamic conductivity of a composite consisting of well- and weak-conducting components with random fractal structure. In order to calculate effective properties of composite medium, we used hierarchic structure model and innovative iterative averaging method based on renormalization group transformations idea. Our results show, that the behavior of a composite over a magnetic field become even more complicated.Unusual peaks and oscillations appear in frequency dependencies of effective conductivity, permittivity and other properties. We discuss the influence of fractal parameters of the composite structure on such unusual behavior of effective properties.     

Quantum waveguide theory of a fractal structure

The electronic transport properties of fractal quantum waveguide networks in the presence of a magnetic field are studied. A Generalized Eigen-function Method (GEM) is used to calculate the transmission and reflection coefficients of the studied systems unto the fourth generation Sierpinski fractal network with node number N=123$N=123$. The relationship among the transmission coefficient T, magnetic flux Φ and wave vector k is investigated in detail. The numerical results are shown by the three-dimensional plots and contour maps. Some resonant-transmission features and the symmetry of the transmission coefficient T to flux Φ are observed and discussed, and compared with the results of the tight-binding model.