A multi-stage, two-flow, axial flow expander close-coupled to a driven machine, such as a generator. The communication system includes a variable-bit-rate transmitter that generates digital data at a first or a second bit rate and a variable-bit-rate receiver that receives the digital data. The retaining portion has a pair of leg portions which abut against two side surfaces forming the corner portion of the battery. In response to the query, a searching unit in the server scans data records in a second storage unit, thus recognizing that the terminal in question has been relocated. Subsequently, the pulsed beam emits from the outlet ports of the source housing.