The pulse train fed to {TAIL ~ the base} of transistor Q1 has a period P and {HEAD ~ a duty cycle} less than 50 percent 
The pulse train fed to { TAIL ~ the base } of transistor Q1 has a period P and { HEAD ~ a duty cycle } less than 50 percent
OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH