A diode is described with a III-N material structure, an electrically conductive channel in the III-N material structure, two terminals, wherein a first terminal is an anode adjacent to the III-N material structure and a second terminal is a cathode in ohmic contact with the electrically conductive channel, and a dielectric layer over at least a portion of the anode. A first portion of the rod is inserted into the damaged hole. The graph is coarsened recursively by performing iterated weighted aggregation to form larger blocks and obtain hierarchical decomposition of the image while forming a pyramid structure over the image. An electrical spark discharge is thus generated between the injection valve and the valve seat upon opening of the valve.