共查询到20条相似文献,搜索用时 68 毫秒
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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 总被引:3,自引:0,他引:3
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。 相似文献
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提出了一基于Sierpinski分形结构的Si/Ge纳米复合材料结构,以调控纳米复合材料的热导率.采用非平衡分子动力学方法模拟研究了分形结构Si/Ge纳米复合材料的导热性能,给出了硅原子百分比、轴向长度以及截面尺寸对分形结构纳米复合材料热导率的影响规律,并与传统矩形结构进行了对比.研究结果表明,分形结构纳米复合材料增强了Si/Ge界面散射作用,使得热导率低于传统矩形结构,这为提高材料的热电效率提供了有效途径.Si原子百分比、截面尺寸、轴向长度皆对分形结构纳米复合材料热导率存在着重要影响.纳米复合材料热导率随着Si原子百分比的增加呈先减小后增加的趋势,随轴向长度的增加则呈单调增大趋势. 相似文献
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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. 相似文献
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卫星上某些介质结构会遭遇较大范围的温度变化, 其电导率会随之出现数量级的变化, 这将显著影响内带电结果. 受限于电导率-温度模型和内带电三维仿真工具, 该温度效应远没有得到深入研究. 为此, 在真空变温(253-353 K)和强电场(MV/m量级)条件下测试了某种星用改性聚酰亚胺介质的电导率, 借鉴Arrhenius电导率-温度模型并考虑强电场下电导率的增强效应, 发现电导活化能取值为0.40 eV时, 可得到良好的拟合结果. 在此基础上, 同时考虑辐射诱导电导率, 采用地球同步轨道恶劣电子辐射能谱, 对该类介质盘环结构进行内带电三维仿真, 发现其内带电程度随温度降低而显著增加, 带电最严重的区域位于靠近辐射源的接地面边线. 温度低于250 K时, 2 mm屏蔽铝板下该区域的场强可达到107 V/m量级, 发生介质击穿放电的可能性较大. 所讨论的电导率-温度模型与内带电三维建模方法对进一步评估卫星介质结构内带电程度和做好防护设计具有重要参考意义. 相似文献
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Alexander I. Melker Alexander N. Efleev 《Journal of Macromolecular Science: Physics》2013,52(5-6):769-785
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. 相似文献
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M. B. Smirnov A. O. Koshkin S. V. Karpov B. V. Novikov A. N. Smirnov I. V. Shtrohm G. E. Cirlin A. D. Bouravleuv Yu. B. Samsonenko 《Physics of the Solid State》2013,55(6):1220-1230
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. 相似文献
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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. 相似文献
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In the present study, we compare the structure of NiZr2 and CuZr2 disordered (liquid and amorphous) alloys. While Cu and Ni have similar atomic radii, the formation heats of these alloys differ by more than a factor of two. Moreover, the most stable crystal phase in the CuZr2 alloy has the C11b lattice while the most stable phase in the NiZr2 alloy has the C16 lattice. Comparing these two alloys allows us to directly explore how the chemistry and atomic size affect the disordered phase structure. We find that all differences in the structures of the disordered alloys are readily explained by the smaller Ni–Zr separation driven by the higher heat of mixing and the structure of the disordered alloys does not necessarily resemble the local packing structure of their crystalline counterparts. Comparison of the disordered alloys and their most stable crystal phase structures explains the better glass formability of the CuZr2 alloy. 相似文献
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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. 相似文献