A method for downloading episodes from the internet to a portable media playback device that allows users freely define the daily playtime, the storage capacity to use, and then select and schedule episodes to be downloaded as a function of the available storage capacity and playtime. This is achieved in that the units to be cooled, such as, for example, gasification burners, burner muffles, or the like, are equipped with an independent cooling circuit, whereby this cooling circuit is directly connected with the main cooling circuit. The reference circuit further includes a sigma-delta modulator coupled to the at least one controlled current source. If the movement speed of the mobile object is judged to be less than a predetermined value, the control section may generate a relay control signal indicating that a relay function of the relay apparatus is to be activated. The semiconductor layer includes at least a quantum well layer which is made of a second compound semiconductor material and has a plurality of projections of at least two different sizes.