Methods for forming an ultrathin GO membrane are provided. The ink stick has an electronically-readable memory device attached thereto, with the memory device having stored therein electronic data associated with the ink stick. The proposed regenerator further comprises a non-deterministic adaptation unit comprising means for compensating time variant non-deterministic transmission impairments, in particular polarisation mode dispersion. The system also includes a third filter to filter uplink TDM transmissions, associated with the user device, during the first and second periods of time, to generate a third interference estimate. Current signals I1\u2032 and I3\u2032 are added to produce a first output current of the input stage. In one embodiment, a VAD system can be implanted with open surgery.