In an exemplary embodiment of the present invention, D is a value selected over the range of about 0.5 to about 1, preferably a value of 0.7, (Rret/Rdraw) is a value selected over the range of about 0.1 to about 1, preferably a value of 0.5, and (Vsvnr/Vsvn) is a value selected over the range of about 0.03 to about 0.05.