1. Aschoff J, Giedke H, Pöppel E, Wever R. (1972) The influence of sleep-interruption and of sleep-deprivation on circadian rhythms in human performance. In: Aspects of Human efficiency. Diurnal Rhythm and Loss of Sleep. Colquhoun WP, ed. London: English University Press, pp. 133–150.
2. Aserinsky E, Kleitman N. (1953) Regularly occurring periods of eye motility, and concomitant phenomena, during sleep. Science 118(3062): 273–274.
3. Balzer I, Neuhaus-Steinmetz U, Quentin E, van Wüllen M, Hardeland R. (1989) Concomitance of circadian and circa-4-hour ultradian rhythms in Euglena gracilis. J Interdiscipl Cycle Res 20: 15–24.
4. Binkley S. (1990) The Clockwork Sparrow. Englewood Cliffs, NJ: Prentice-Hall, 262 pp.
5. Bitman J, Lefcourt A, Wood DL, Stroud B. (1984) Circadian and ultradian temperature rhythms of lactating dairy cows. J Dairy Sci 67(5): 1014–1023.