\bibitem{Yablonskiy02}  D.A.~Yablonskiy, A.L.~Sukstanskii, J.C.~Leawoods, D.S.~Gierada, G.L.~Bretthorst, S.S.~Lefrak, J.D.~Cooper, M.S.~Conradi,
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                        PNAS {\bf 99} (5), 3111-3116, 2002.