Methods and apparatus for removing sediment from a liquid are provided. A recess portion is formed inside an area between the source electrode and the drain electrode of the n-GaN layer and at a portion separating from the gate electrode. Both legs are rotatable relative to each other and to the seat between a storage position to be taken in a safety car seat mode of the seat, and an operational position to be taken in a rolling-carrier mode of the seat. These permanent magnet members are sized and spaced such that within the stator arc length the ratio of stator members to permanent magnet members is N to N+1, where N is the number of electrical excitation phases applied to the electromagnets.