A switching control circuit for multi-channels and multi-phases power converter according to the present invention comprises a master control circuit and a slave control circuit. The filter element includes a substrate, which may include a nonwoven fiber web, a plurality of particles, or both of these. The transition duct extends between a fuel nozzle and a turbine section, and has an inlet, an outlet, and a passage extending between the inlet and the outlet and defining a longitudinal axis, a radial axis, and a tangential axis.