REVIEWS of MODERN PHYSICS A quarterly journal seeking to enhance communication among physicists by publishing comprehensive scholarly American Physical Society reviews of physics topics, as well as colloquia and tutorial articles in rapidly developing fields of physics. Officers President ROGER FALCONE Speaker of Council TIMOTHY GAY Editor: RANDALL KAMIEN, University of Pennsylvania Chief Executive Officer KATE P. KIRBY Colloquia Editor in Chief MICHAEL THOENNESSEN Editor: A. H. CASTRO NETO, National University of Singapore Publisher MATTHEW SALTER Chief Information Officer MARK D. DOYLE Chief Financial Officer MARGARET BANDERA Associate ASTROPHYSICS Deputy Executive Officer and Editors: FRIEDRICH-KARL THIELEMANN, Universitat¨ Basel Chief Operating Officer JAMES TAYLOR Chief Government Affairs ATOMIC, MOLECULAR, AND OPTICAL PHYSICS (Experimental) Officer FRANCIS SLAKEY KLAUS MØLMER, University of Aarhus One Physics Ellipse BIOLOGICAL PHYSICS College Park, MD 20740-3844 MARGARET S. CHEUNG, University of Houston; Center for Theoretical Biological Physics, Rice University CLIMATE SCIENCE APS Editorial Office WILLIAM D. COLLINS, University of California, Berkeley; Directors Lawrence Berkeley National Laboratory Editorial DANIEL T. KULP CONDENSED MATTER PHYSICS (Experimental) Journal Operations CHRISTINE M. GIACCONE ARTHUR F. HEBARD, University of Florida 1 Research Road CONDENSED MATTER PHYSICS (Theoretical) Ridge, NY 11961-2701 Phone: (631) 591-4000 DIETRICH BELITZ, University of Oregon Email:
[email protected] ASTROPHYSICS Web: http://journals.aps.org/ VICKY KALOGERA, Northwestern University Submissions:
[email protected] or MATHEMATICAL PHYSICS http://authors.aps.org/Submissions/ IGOR KLEBANOV, Princeton University NUCLEAR PHYSICS Member Subscriptions: WITOLD NAZAREWICZ, National Superconducting Cyclotron Laboratory, Michigan State University; Oak Ridge National Laboratory APS Membership Department One Physics Ellipse PARTICLE PHYSICS (Experimental) College Park, MD 20740-3844 PAUL D.