When exposed to such an elevated temperature and pressure, {HEAD ~ the first and second layers} will melt while {TAIL ~ the core} 12 will remain substantially solid 
melt while
When exposed to such an elevated temperature and pressure , { HEAD ~ the first and second layers } will melt while { TAIL ~ the core } 12 will remain substantially solid
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH