![Characterization of sleep stages by correlations in the magnitude and sign of heartbeat increments]()
Characterization of sleep stages by correlations in the magnitude and sign of heartbeat incrementsKantelhardt, Jan W.; Ashkenazy, Yosef; Ivanov, Plamen Ch.; Bunde, Armin; Havlin, Shlomo; Penzel, Thomas; Peter, Jörg-Hermann; Stanley, H. Eugene · Physical Review E · 2002