Abstract: A fiber-reinforced lighweight alloy piston for an internal-combustion engine, comprising a piston body having a compression ring groove whose bounding surface is reinforced with alumina fibers. At least those alumina fibers positioned in the region of the annular opening of the groove has a crystalline structure of .theta./.alpha.-Al.sub.2 O.sub.3 type and a specific gravity limited to a value between 3.7 and 3.9.

Abstract: A screw blower comprising a pair of rotary driving shafts disposed in parallel relation and a pair of rotors rotatable with the driving shafts. The rotors are provided with meshing teeth each having a helix angle. A casing surrounds the rotors and forms therewith an intake chamber and an exhaust chamber. Grooves, which are formed between the meshing teeth, come into communication with an opening of the exhaust chamber as the rotors undergo rotation. The opening of the exhaust chamber extends over the full length of the rotors. Each of the rotors has a predetermined number of teeth and a sufficiently large helix angle such that gases trapped within the grooves are immediately discharged to the exhaust chamber without being compressed as the rotors rotate. The opposedly disposed meshing teeth are meshed in a male and female relationship.