An ion beam current density profiler includes a pair of counter-rotating cylindrical masks each featuring a helical slot. More particularly, the present invention relates to certain monoethylenically unsaturated polycarbosiloxane monomers capable of polymerization to form polymeric compositions having desirable physical characteristics useful in the manufacture of ophthalmic devices. During the intake stroke as the piston approaches bottom dead center, the exhaust port is reopened allowing gas from the EGR tank to flow into the cylinder as a portion of the charge prior to compression.