Deep Analyses of Nulling in Arecibo Pulsars Reveal Further Periodic   Behavior
  Sensitive Arecibo observations provide an unprecedented ability to detect nulls for an accurate pulse-modulation quelling (PMQ) analysis. We demonstrate that a number of conal pulsars show "periodic nulling" similar to the phenomenon found earlier in pulsar B1133+16. 
Jeffrey Herfindal and Joanna Rankin