http://www.pnas.org/content/112/31/9493.full
An interesting article, part of the special series of PNAS 100th
Anniversary articles to commemorate exceptional research published in
PNAS over the last century. See the companion article, "Analytical
Note on Certain Rhythmic Relations in Organic Systems" on page
<http://www.pnas.org/lookup/doi/10.1073/pnas.6.7.410>410 in issue 7
of volume 6.
