We thank the following funding sources for supporting our
research.
National Science Foundation (CNS# 1058753, 2010-2012)
National Science Foundation (CNS# 0910842, 2009-2012)
National Science Foundation CAREER (IIS #0845683, 2009-2014)
National Science Foundation (IIS # 0433637, 2004-2009)
Swiss National Science Foundation
Nokia Corporation
Any opinions, findings or conclusions are those of the authors and do
not necessarily reflect the views of the funding agencies.