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