arXivDaily arXiv每日学术速递 周一至周五更新
arXiv 1109.6567cond-mat.stat-mech
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从各向同性到定向渗流的交叉

Crossover from Isotropic to Directed Percolation

Zongzheng Zhou, Ji Yang, Robert M. Ziff, Youjin Deng

摘要:

我们广义的定向渗流(DP)模型放松DP的严格方向性,使传播可以发生在任何方向,但各向异性的概率。我们将概率表示为$p_{\downarrow}= p \cdot p_d$和$p_{\uparrow}=p \cdot (1-p_d)$,其中$p $表示平均占用概率,而$p_d$控制各向异性。Leath-Alexandrowicz方法用于从活动种子站点生长集群。我们称这种具有两个主要生长方向的模型为{ \em偏置定向渗流}(BDP)。标准各向同性渗流(IP)和DP是BDP模型的两种极限情况,分别对应于$p_d=1/2$和$p_d=0,1$。在这项工作中,除了IP和DP,我们还考虑了$1/2<p_d<1$区域。在正方形和简单立方晶格上进行了广泛的蒙特卡罗模拟,并通过有限尺寸标度对数值数据进行了分析。我们找到了$p_d=0.6$和0.8的BDP模型的逾渗阈值,并确定了各种临界指数。发现这些指数与标准DP的指数一致。我们还确定了重整化指数与非对称扰动,由于$p_d -1/2 \neq 0$ IP附近,并确认这种非对称标度场是相关的IP。

英文摘要:

We generalize the directed percolation (DP) model by relaxing the strict directionality of DP such that propagation can occur in either direction but with anisotropic probabilities. We denote the probabilities as $p_{\downarrow}= p \cdot p_d$ and $p_{\uparrow}=p \cdot (1-p_d)$, with $p $ representing the average occupation probability and $p_d$ controlling the anisotropy. The Leath-Alexandrowicz method is used to grow a cluster from an active seed site. We call this model with two main growth directions {\em biased directed percolation} (BDP). Standard isotropic percolation (IP) and DP are the two limiting cases of the BDP model, corresponding to $p_d=1/2$ and $p_d=0,1$ respectively. In this work, besides IP and DP, we also consider the $1/2<p_d<1$ region. Extensive Monte Carlo simulations are carried out on the square and the simple-cubic lattices, and the numerical data are analyzed by finite-size scaling. We locate the percolation thresholds of the BDP model for $p_d=0.6$ and 0.8, and determine various critical exponents. These exponents are found to be consistent with those for standard DP. We also determine the renormalization exponent associated with the asymmetric perturbation due to $p_d -1/2 \neq 0$ near IP, and confirm that such an asymmetric scaling field is relevant at IP.

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