In one embodiment, a system includes a generator frame that includes a spring ring configured to mount removably between an outer annular support and a stator. The invention may be embodied as a computer-based method, a computerized system that performs the method, or a machine readable storage medium containing instructions that when executed cause performance of the method using the computerized system. The circuit enables the coupler to assume the decoupled position when the master and tool units are coupled and the circuit is closed. The washer includes an oblong aperture, and the nut includes a projecting sleeve. In a preferred embodiment, the nucleoside is L-FMAU, or a pharmaceutically acceptable salt or prodrug thereof.