The method 1 wherein {HEAD ~ the step} of applying alternating forward and reverse bias potentials is effected by {TAIL ~ a bipolar signal} having a reverse bias potential of significantly larger magnitude than said forward bias potential 
is effected by
The method 1 wherein { HEAD ~ the step } of applying alternating forward and reverse bias potentials is effected by { TAIL ~ a bipolar signal } having a reverse bias potential of significantly larger magnitude than said forward bias potential
OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH