Persistence in the two dimensional ferromagnetic Ising model
  We present very accurate numerical estimates of the time and size dependence of the zero-temperature local persistence in the $2d$ ferromagnetic Ising model. We show that the effective exponent decays algebraically to an asymptotic value $\theta$ that depends upon the initial condition. More precisely, we find that $\theta$ takes one universal value $0.199(2)$ for initial conditions with short-range spatial correlations as in a paramagnetic state, and the value $0.033(1)$ for initial conditions with the long-range spatial correlations of the critical Ising state. We checked universality by working with a square and a triangular lattice, and by imposing free and periodic boundary conditions. We found that the effective exponent suffers from stronger finite size effects in the former case. 
Thibault Blanchard, Leticia F. Cugliandolo, Marco Picco
cond-mat.stat-mech