means for delivering {HEAD ~ the energy} from the source to {TAIL ~ the inner surface} of the tubular portion 
means for delivering { HEAD ~ the energy } from the source to { TAIL ~ the inner surface } of the tubular portion
OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH