This paper expands on a method proposed in  for stabilizing oscillatory system with positive, delayed feedback. The closed-loop system obtained is shown (using the Nyquist criterion) to be stable for a range of delays.
1993 American Control Conference
Clocks, Delay systems, Feedback loop
Abdallah, Chaouki T.; Peter Dorato; J. Benites-Read; and R. Byrne. "Delayed positive feedback can stabilize oscillatory systems." 1993 American Control Conference (1993): 3106-3107. http://digitalrepository.unm.edu/ece_fsp/80