Each set of {TAIL ~ resources} is allocated only for {HEAD ~ the period} of time needed to perform the required function 
Each set of { TAIL ~ resources } is allocated only for { HEAD ~ the period } of time needed to perform the required function
OTH OTH OTH TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH