The present invention relates to compounds of formula Iwherein R1 and R2 are as defined in the description and claims, and pharmaceutically acceptable salts thereof. The chassis also has exterior dimensions that correspond to the dimensions of an industry standard drive bay. A deep trench passes through the epitaxial layer. In another embodiment, method of treating bone includes injecting a volume of fill material into a bone and selectively modifying a viscosity of a selected portion of the bone filler to control the direction of flow of the fill material within the bone. A first common control member is provided to cause, by the movement it imparts to the moving unit of one or other head alternately: pinching of the first and second web material between the roller and the counter-pressure member ; cutting of the first web material; and release of the second web material. The conductive plane or ring is coupled to a first contact pad for providing a first power supply potential to the active circuits.