1. a Department of Physics , Bryn Mawr College , Bryn Mawr , Pennsylvania , 19010 , U.S.A.
2. b Western Electric , 555 Union Boulevard, Allentown , Pennsylvania , 18103 , U.S.A.
3. d Department of Material Science and Engineering , University of Pennsylvania , Philadelphia , Pennsylvania , 19104 , U.S.A.
4. c University Information Processing, University of Southern California , Los Angeles , California , 90007 , U.S.A.