There is provided a vector control device for an alternating-current electric motor having a damping controller which automatically calculates an optimum damping operation amount and does not require any gain setting itself, whereby an adjustment work of a control system can be simplified. The re-circulating water flow retains air bubbles within the reaction chamber for a longer period of time, increasing the capacity of the air bubbles to attract waste material and remove the waste material from the aquarium. Where two or more appliances are used, audio commands can cause the delivery of messages to stop in one appliance and resume in another appliance. After delivery of the period-specific targeted curriculum over the period, re-assessments of the current skill of the group members are made, and a period-specific curriculum for the subsequent period is generated and delivered.