A wireless communications system includes a core packet network coupled to multiple base transceiver stations, each station providing wireless services to mobile units. A hollow cylindrical metal member having an outer surface with projections to be cast-wrapped by a metal cast article is manufactured in such a manner that a hollow cylindrical metal raw material 13 is inserted in a die 17 having a inner peripheral surface with longitudinal grooves of a depth H and a width W, and the hollow cylindrical metal raw material 13 is subjected to hot-extrusion. Alternatively, the evaporative condenser is disposed between the compressor and the air cooling condenser, in which the evaporative condenser is placed in the air discharge side of the air cooling condenser to evaporate moisture via air forcibly introduced by a condenser fan and coolant so that coolant can be condensed via latent heat of vaporization. The first and second photo-sensitive cells are positioned at one diagonal corners and the other diagonal corners, respectively, at opposite sides of each vertical transfer path such that the first and second photo-sensitive cells have photo-sensitive areas whose centers of gravity form a rectangle when connected by a virtual line. An output terminal outputs the potential generated by the sensor. Desirably the ammonium salts are selected from the group consisting of ammonium oxalate and ammonium tartrate.