A system for modifying dislocation distributions in semiconductor materials is provided. Hypothetical locations among the set are propagated to respective hypothetical next locations, using respective location-specific propagation models associated with the hypothetical locations. In the methods of the present invention, no etch step is required to form the air gaps. The plate-shaped coupling units may also have spiral shapes. The bottom frame also has four corners with roller tracks at each corner. With this start-up circuit, all the control and supporting circuitries are connected at the converter output low voltage side and protected from high input DC voltage.