共查询到20条相似文献,搜索用时 78 毫秒
1.
The linear relaxation of a one-dimensional bonded fluid model is studied in the dynamical mean field approximation at the pair level. The results are compared with simulation data. Relaxation at low temperatures shows a cooperative character that can be understood in terms of a simple diffusion picture. 相似文献
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A generalized formulation of the characteristic boundary conditions for compressible reacting flows is proposed. The new and improved approach resolves a number of lingering issues of spurious solution behaviour encountered in turbulent reacting flow simulations in the past. This is accomplished (a) by accounting for all the relevant terms in the determination of the characteristic wave amplitudes and (b) by accommodating a relaxation treatment for the transverse gradient terms with the relaxation coefficient properly determined by the low Mach number asymptotic expansion. The new boundary conditions are applied to a comprehensive set of test problems including: vortex-convection; turbulent inflow; ignition front propagation; non-reacting and reacting Poiseuille flows; and counterflow cases. It is demonstrated that the improved boundary conditions perform consistently superior to existing approaches, and result in robust and accurate solutions with minimal acoustic wave interactions at the boundary in hostile turbulent combustion simulation conditions. 相似文献
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M.P. Madan 《Journal of Molecular Liquids》1983,25(1):25-37
The dielectric behavior of benzene solutions of four rigid polar molecules, benzophenone, benzotrichloride, ortho- and meta- dichlorobenzenes and their mixtures has been studied in the microwave region over a range of temperatures. The dielectric data has been used to determine the relaxation times and the thermodynamic parameters for the activated state. The relaxation times for single component solutions agree well at temperatures at which literature values are available. The relaxation times for mixtures are consistent with those of other rigid molecules studied previously. The results have been also compared with the computed values obtained from a relation proposed by us. 相似文献
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考虑外延钙钛矿型铁电薄膜内的等效应力、表面晶格变化和表面电荷引起的退极化效应等机电耦合边界条件,利用铁电薄膜系统的动态金茨堡-朗道方程(DGL),系统分析和讨论了外延铁电薄膜相变温度与临界相变厚度的尺寸效应.结果表明,铁电薄膜相变温度与临界相变厚度完全依赖于各种与薄膜厚度相关的力电耦合边界条件.也给出了BaTiO3外延铁电薄膜相变温度在各种边界条件下随厚度的变化,从结果看出,本文的分析与结论更符合实验数据.
关键词:
尺寸效应
外延铁电薄膜
相变温度
力电耦合边界 相似文献
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The Kohlrausch-Williams-Watt (KWW) function, or stretched exponential function, is usually employed to reveal the time dependence
of the polymer backbone relaxation process, the so-called α relaxation, at different temperatures. In order to gain insight into polymer dynamics at temperatures higher than the glass
transition temperature T
g
, the behavior of the Kohlrausch exponent, which is a component of the KWW function, is studied for a series of vinylic polymers,
using an all-atomistic simulation approach. Our data show very good agreement with published experimental results and can
be described by existing phenomenological models. The Kohlrausch exponent exhibits a linear dependence with temperature until
it reaches a constant value of 0.44, at 1.26T
g
, revealing the existence of two regimes. These results suggest that, as the temperature increases, the dynamics progressively
change until it reaches a plateau. The non-exponential character then describes subdiffusive motion characteristic of polymer
melts. 相似文献
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A microscopic derivation using the average Maxwell electric field is given for fluctuation formulas for the dielectric constant of a simulation sample for both periodic and reaction field boundary conditions. The reaction field case is for a spherical cavity reaction field. The derivations put both boundary conditions on an equal footing of microscopic theory and the only nonrigorous part of the derivation is the assumption that the region used to average the electric field is large enough. The fluctuation formula for reaction field boundary conditions is rather different from that used heretofore. The method is applied to a subregion of an isolated spherical system. 相似文献
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利用Bathe模型,理论模拟了氩团簇在飞秒强激光中(100 fs, 1016 W/cm2)的电离和爆炸过程.研究结果显示,在团簇尺寸较小时,离子平均能量与团簇初始半径平方成正比,爆炸机制为典型的库仑爆炸.随着团簇尺寸的增加,能量增加的速度趋缓并在一定团簇尺寸后趋于饱和.模拟结果与实验数据有较好的吻合. 相似文献
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Stabilization of thermal lattice Boltzmann models 总被引:2,自引:0,他引:2
Guy R. McNamara Alejandro L. Garcia Berni J. Alder 《Journal of statistical physics》1995,81(1-2):395-408
A three-dimensional thermal lattice-Boltzmann model with two relaxation times to separately control viscosity and thermal diffusion is developed. Numerical stability of the model is significantly improved using Lax-Wendroff advection to provide and adjustable time step. Good agreement with a conventional fiitedifference Navier-Stokes solver is obtained in modeling compressible Rayleigh-Bénard convestion when boundary conditions are treated similarly. 相似文献
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Hiroyuki Watanabe Akira Owashi Tokuteru Uesugi Yorinobu Takigawa Kenji Higashi 《哲学杂志》2013,93(32):4158-4171
Grain boundary relaxation at elevated temperatures in fine-grained pure magnesium and Mg–Al solid solutions was investigated by measuring damping capacity at low frequencies. A sharp increase in damping capacity caused by grain boundary relaxation was observed at above a certain temperature. The onset temperature depended on aluminum content; the onset temperature increased with aluminum content. It was demonstrated that aluminum was effective in suppressing grain boundary relaxation in magnesium alloys. However, additional measurement of the damping capacity of a dilute Mg–Y alloy revealed that yttrium was more effective in suppressing grain boundary relaxation. 相似文献
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Vibration modes and thermodynamic properties of a body‐centered cubic (bcc) Coulomb crystal with a small admixture of substitutional isotopic impurities are studied analytically applying the perturbation theory of disordered crystal spectra and the Lifshitz‐Krein trace formula. We calculate the density of phonon states of the perfect bcc Coulomb crystal and use it to compute the heat capacity of the crystal with impurities in a wide range of temperatures. It is shown that the ratio of an impurity contribution to the crystal heat capacity over the perfect crystal specific heat tends to a constant in the low‐temperature quantum regime and decays as T–2 in the classic regime of high temperatures. It is also shown that even a small concentration of heavy impurities amplifies significantly the total crystal heat capacity. The results are compared with those obtained using the more conventional linear mixing theory. It is demonstrated that both methods give similar results at all tempera‐tures when the impurity mass is not too different from that of the base ions but a strong discrepancy is observed at low and intermediate temperatures when impurities are noticeably lighter or heavier. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
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The pseudo-spectral time-domain (PSTD) method is an alternative time-marching method to classical leapfrog finite difference schemes in the simulation of wave-like propagating phenomena. It is based on the fundamentals of the Fourier transform to compute the spatial derivatives of hyperbolic differential equations. Therefore, it results in an isotropic operator that can be implemented in an efficient way for room acoustics simulations. However, one of the first issues to be solved consists on modeling wall absorption. Unfortunately, there are no references in the technical literature concerning to that problem. In this paper, assuming real and constant locally reacting impedances, several proposals to overcome this problem are presented, validated and compared to analytical solutions in different scenarios. 相似文献
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在20 mK的极低温下测量了石墨烯纳米带量子点的电子输运性质,观测到清晰的库仑阻塞菱形块和对应量子点激发态的电导峰.对库仑阻塞近邻电导峰间距和峰值进行了统计分析,发现其统计分布分别满足无规矩阵理论描述的Wigner-Dyson分布和Porter-Thomas分布,说明石墨烯纳米带量子点在低温下出现了量子混沌现象.还讨论了这种长方形量子点中量子混沌的可能成因.
关键词:
石墨烯纳米带
量子点
库仑阻塞
量子混沌 相似文献
17.
Ram M. Narayanan Jing Meng 《International Journal of Infrared and Millimeter Waves》1998,19(4):651-671
A set of second-order absorbing boundary conditions is derived for the three-dimensional finite-difference TLM analysis of open region scattering problems. These boundary conditions are implemented into a computer code using a two-level discretization scheme. A simulation experiment using a 4-term Blackman-Harris pulse excitation with very low sidelobes is used to examine the efficiency of the boundary conditions. It is observed that the absorbing boundaries are perfectly transparent to waves impinging upon them at angles between 0 and 45 degrees, and the normal incidence reflection coefficient is less than -35 dB. 相似文献
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David Munton 《Journal of statistical physics》1992,68(5-6):1105-1125
The effects of quenched disorder on the two-dimensional Coulomb gas are studied in the hierarchical approximation. The quenched random variables interact with the charges via a potential that decays as an inverse power () of the distance. Recursion relations for the single block charge activities are derived in which the quenched variables explicitly appear. In a linear approximation, for all1, with some restrictions on the variance of the normally distributed random variables, it is shown that the charge activities converge to the Kosterlitz-Thouless fixed point for all sufficiently low temperatures and sufficiently large blocks. The annealed system is also examined. This model is shown to have a Kosterlitz-Thouless phase only for an intermediate range of temperatures. At low temperatures the activities can diverge, and large charges can exist on all length scales. 相似文献
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本文采用基于嵌入原子势的分子动力学方法模拟了不同粒径的Zr纳米粒子在升温过程中HCP-BCC结构转变的路径。通过对粒子在升温过程中的势能差分曲线的计算,分别确定了小粒径、较大粒径和大粒径粒子的结构转变温度区间,并使用二分法进一步确定了转变温度点。然后借助对结构转变温度点处的形状因子、键对占比和原子堆积结构随弛豫时间的变化的模拟计算,确定了驰豫过程中堆积结构的演变过程。计算结果表明,小粒径粒子存在着多个结构转变温度点,并会在较低的结构转变温度点处出现多结构共存现象,其驰豫过程就是不同结构间相互竞争的过程。随着粒径的增大,在较高温度点处虽然仍会出现多结构共存,但粒子内的大部分原子堆积为BCC结构,并且在大粒径粒子内会出现明显的界面区。 相似文献
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基于Rudin-Osher-Fatemi模型的图像除模糊和除噪音新模型 总被引:1,自引:0,他引:1
介绍一种依赖时间的新模型来解决图像除噪音和除模糊问题.分别使用逆反射、中值两种边界条件的数值试验比较本文新模型和Rudin-Osher-Fatemi模型.试验结果表明中值边界条件的误差比逆反射边界条件误差小. 相似文献