In {TAIL ~ the directly heated oxide cathode}, {HEAD ~ the core metal wire} comprises a tungsten core wire or a rhenium tungsten core wire 
In
In { TAIL ~ the directly heated oxide cathode } , { HEAD ~ the core metal wire } comprises a tungsten core wire or a rhenium tungsten core wire
REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH