The power of positive feedback

Ple a s e no t e: Ch a n g e s m a d e a s a r e s ul t of p u blishing p roc e s s e s s uc h a s copy-e di ting, for m a t ting a n d p a g e n u m b e r s m ay no t b e r eflec t e d in t his ve r sion. For t h e d efini tive ve r sion of t his p u blica tion, ple a s e r efe r to t h e p u blish e d sou rc e . You a r e a dvis e d to cons ul t t h e p u blish e r’s ve r sion if you wis h to ci t e t his p a p er.