\bibitem{Davidovitch01} B.~Davidovitch, M.H.~Jensen, A.~Levermann, J.~Mathiesen, I.~Procaccia,
                        {\it Thermodynamic Formalism of the Harmonic Measure of Diffusion Limited Aggregates: Phase Transition},
                        Phys.~Rev.~Lett {\bf 87}, 164101, 2001.