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arXiv 0810.4107cond-mat.stat-mech
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无序系统输运的有效介质理论的推广

Extensions of Effective Medium Theory of Transport in Disordered Systems

V. M. Kenkre, Z. Kalay, P. E. Parris

摘要:

无序系统中输运的有效介质理论,其基础是用时间记忆代替空间无序,在几个实际方向上得到了扩展。限制注意力的1维系统与键无序的特异性,一个转换过程推导出,从给定的分布函数表征系统的障碍,明确的表达式的记忆功能。它示出了如何使用的Lapace域的形式中,他们第一次出现的记忆功能,并在时域的形式,这是通过数值反演算法获得的,以解决时间演化的系统超出了渐近域的大的时间通常治疗。除了反演算法之外,还提供了一种分析但近似的程序来获得存储器。有效介质理论的预测与数值计算的精确结果的良好协议被发现为所有的时间范围内使用的分布,除了附近的渗流极限的预期。合奏平均值的使用进行了研究,以及正常的相关观测。有效mediumtheory上的大小的效果进行了探讨,它表明,即使在渐近极限,有限大小的修正发展到众所周知的调和平均处方找到有效的速率。示出的渗流阈值出现,即使在1-D的有限(但不是无限的)系统中的浓度有关的系统大小的断裂键。空间上的长距离传输率显示自然出现的结果,由时间记忆的空间无序的替代,尽管事实上,原来的速率具有最近的邻居字符。计算了连续时间随机游动中对应于有效介质记忆的停顿时间分布。

英文摘要:

Effective medium theory of transport in disordered systems, whose basis is the replacement of spatial disorder by temporal memory, is extended in several practical directions. Restricting attention to a 1-dimensional system with bond disorder for specificity, a transformation procedure is developed to deduce, from given distribution functions characterizing the system disorder, explicit expressions for the memory functions. It is shown how to use the memory functions in the Lapace domain forms in which they first appear, and in the time domain forms which are obtained via numerical inversion algorithms, to address time evolution of the system beyond the asymptotic domain of large times normally treated. An analytic but approximate procedure is provided to obtain the memories, in addition to the inversion algorithm. Good agreement of effective medium theory predictions with numerically computed exact results is found for all time ranges for the distributions used except near the percolation limit as expected. The use of ensemble averages is studied for normal as well as correlation observables. The effect of size on effective mediumtheory is explored and it is shown that, even in the asymptotic limit, finite size corrections develop to the well known harmonic mean prescription for finding the effective rate. A percolation threshold is shown to arise even in 1-d for finite (but not infinite) systems at a concentration of broken bonds related to the system size. Spatially long range transfer rates are shown to emerge naturally as a consequence of the replacement of spatial disorder by temporal memories, in spite of the fact that the original rates possess nearest neighbor character. Pausing time distributions in continuous time random walks corresponding to the effective medium memories are calculated.

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