A compound having the structural formula . The forend element defines a plurality of rail mounting apertures extending from the interior surface to the exterior surface. The fan, the radiator, the accumulator tank, and the pump are mounted on the shroud to be carried thereby, and the pump is located on an exterior side of the of the fan shroud and outside of the radiator and the accumulator tank. The stents may include an annulus section, a sinus section with the membranes attached over sinus apertures, and an outflow section.