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具有固定末端取向的蠕虫状链模型的端到端距离矢量分布。

End-to-end distance vector distribution with fixed end orientations for the wormlike chain model.

作者信息

Spakowitz Andrew J, Wang Zhen-Gang

机构信息

Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, USA.

出版信息

Phys Rev E Stat Nonlin Soft Matter Phys. 2005 Oct;72(4 Pt 1):041802. doi: 10.1103/PhysRevE.72.041802. Epub 2005 Oct 7.

Abstract

We find exact expressions for the end-to-end distance vector distribution function with fixed end orientations for the wormlike chain model. This function in Fourier-Laplace space adopts the form of infinite continued fractions, which emerges upon exploiting the hierarchical structure of the moment-based expansion. Our results are used to calculate the root-mean-square end displacement in a given direction for a chain with both end orientations fixed. We find that the crossover from rigid to flexible chains is marked by the root-mean-square end displacement slowly losing its angular dependence as the coupling between chain conformation and end orientation wanes. However, the coupling remains strong even for relatively flexible chains, suggesting that the end orientation strongly influences chain conformation for chains that are several persistence lengths long. We then show the behavior of the distribution function by a density plot of the probability as a function of the end-to-end distance vector for a wormlike chain in two dimensions with one end pointed in a fixed direction and the other end free (in its orientation). As we progress from high to low rigidity, the distribution function shifts from being peaked at a location near the full contour length of the chain in the forward direction, corresponding to a straight configuration, to being peaked near zero end separation, as in the Gaussian limit. The function exhibits double peaks in the crossover between these limiting behaviors.

摘要

我们找到了蠕虫状链模型在固定末端取向情况下端到端距离矢量分布函数的精确表达式。该函数在傅里叶 - 拉普拉斯空间中采用无限连分数的形式,这是在利用基于矩的展开式的层次结构时出现的。我们的结果用于计算两端取向均固定的链在给定方向上的均方根末端位移。我们发现,从刚性链到柔性链的转变以均方根末端位移随着链构象与末端取向之间的耦合减弱而逐渐失去其角度依赖性为标志。然而,即使对于相对柔性的链,这种耦合仍然很强,这表明对于长度为几个持久长度的链,末端取向对链构象有强烈影响。然后,我们通过二维蠕虫状链的概率密度图展示了分布函数的行为,该链一端指向固定方向,另一端自由(在其取向上),概率是端到端距离矢量的函数。随着我们从高刚性向低刚性推进,分布函数从在向前方向上接近链的全轮廓长度处达到峰值(对应于直线构型)转变为在接近零末端间距处达到峰值,如同在高斯极限情况下。该函数在这些极限行为之间的转变过程中呈现出双峰。

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