A device for dispersing gas into molten metal includes an impeller and a shaft having a first end and a second end. As a result, engine start characteristics are improved and an engine operation is maintained even when the signal system is abnormal. The control module also controls the converter assembly such that the second AC signal power signal may flow fromto the second terminal and the second DC power signal may flow fromto the DC bus. The trestle includes a top wall and a third side wall, a fourth side wall, and a support wall that extend from the top wall. The size and dimension of the passive optical structures can be identical with underlying structures, they can merely extend outwardly beyond an exterior shape of the underlying structure, or the passive optical structures can span across a plurality of the underlying structures, including in each instance embodiments with and without the intermediate structures.