{HEAD ~ A specular layer} is secured to {TAIL ~ the support} on the internal channel surface to provide a relatively highly reflective surface over the region of the support facing the tube 
is secured to
{ HEAD ~ A specular layer } is secured to { TAIL ~ the support } on the internal channel surface to provide a relatively highly reflective surface over the region of the support facing the tube
HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH