Briefly, a stage amplifier comprises a differential amplifier having stages and a switch to connect a first differential output of a stage with a second differential output of the stage at a beginning of a conversion cycle. The cooling apparatus of the present invention separates the gas introduced into the cooling liquid, mixes the separated gas with the air supplied to or exhausted from the fuel cell, and then exhausts the gas. The surface roughness is formed in a surface of a mold and is infused by a subsequently cast layer of material. In this way, a wireless device seeking to discover the neighboring access devices may scan for the beacons for a shorter period of time.