Identification of domain walls in coarsening systems at finite temperature

Recently B. Derrida [Phys. Rev. E 55, 3705 (1997)] introduced a numerical technique that allows one to measure the fraction of persistent spins in a coarsening nonequilibrium system at finite temperature. In the present work we extend this method in a way that domain walls can be clearly identified. To this end we consider three replicas instead of two. As an application we measure the surface area of coarsening domains in the two-dimensional Ising model at finite temperature. We also discuss the question of to what extent the results depend on the algorithmic implementation.