A heterojunction bipolar transistor in a silicon-on-insulator structure is disclosed. A transparent optical material is suitably shaped to cover at least a portion of an eyeglass lens. At least a segment of the channel follows an arcuate path. To provide a thin, fully aerated biofilm of bacteria on the carrier material so that no oxygen has to be dissolved under pressure in the liquid, the filter bed is kept at the most partially submerged in the liquid percolating therethrough. On the other hand, when the macroblock to be processed is subjected to field-based encoding, a field-based context model is applied for the syntax elements described below. Each of the side parts has a spring arm to which a bracket is attached that grips the shaped collar of the plug-in part from behind in such a way that the collar, after pushing in the plug-in part from the entry side, is in contact with a termination rib.