Today, {HEAD ~ the trend} is to increase {TAIL ~ the temperature} of operation of gas turbine engines 
is to increase
Today , { HEAD ~ the trend } is to increase { TAIL ~ the temperature } of operation of gas turbine engines
OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH