The authors thank Mackenzie Kinney, Kevin Raymond, Natalie Koay, Sofia Magkiriadou, Dr. Caitlin Howell,
and Prof. Mathias Kolle for helpful discussions. This work was supported by the US Air Force Office of Scientific
Research Multidisciplinary University Research Initiative under Award FA9550-09-1-0669-DOD35CAP (optical
properties), and by the US Federal Railroad Administration under contract number DTFR5314C00015 (volatility
analysis). IBB acknowledges support from a Banting Postdoctoral Fellowship funded by the Natural Sciences and
Engineering Research Council of Canada.