An intake port is connected to a combustion chamber of an internal combustion engine via an intake valve, and a volatile liquid fuel is injected from a fuel injector provided in the intake port. The cam follower mechanism utilizes guide rails located to reduce side thrust on the valve stem. The prescription entry system transmits and receives information from the communications network and provides an input system for the prescriber to electronically enter individual prescriptions for each patient. The circuit arrangement further comprises a first transistor component of a first conduction type. One method comprises selecting a high purity metal foil, growing a layer of graphene on a first face of the metal foil, patterning the second face of the graphene-modified foil with a polymer, wherein the second face of the graphene-modified foil has an exposed region and etching the second face of the graphene-modified foil in the exposed region until exposing the first layer of graphene. For some embodiments, a plurality of the charge pump circuits can be selectively connected in parallel in response to corresponding select signals to generate various drive currents.