An internal combustion engine has a crankcase, a crankshaft, a cylinder block, at least one piston, a cylinder head assembly, and a cooling system for cooling at least a portion of the engine. The instant disclosure uses thinner solar panels, where the supporting frames can be less rigid, in lowering the solar greenhouse cost. Embodiments of waveguides having slots, electrical contacts, and input waveguide couplers are discussed. The sealing ring includes at least two sealing ring segments and a radially-extending, second face. The increased penetration enhancement can also lead to a reduction in the total concentration of skin irritants in the formulation.