Tracking the Sleep Onset Process: An Empirical Model of Behavioral and Physiological Dynamics. - Michael J. Prerau; Katie E. Hartnack; Gabriel Obregon-Henao; Aaron L. Sampson; Margaret Merlino; Karen Gannon; Matt T. Bianchi; Jeffrey M. Ellenbogen; Patrick L. Purdon (PLoS Comput. Biol., 2014)