  We present local and non-local electron transport measurements on individual
multi-wall nanotubes for bias voltage between 0 and about 4 V. Local
current-voltage characteristics are quite linear. In contrast, non-local
measurements are highly non-linear; the differential non-local conductance can
even become negative in the high-bias regime. We discuss the relationship
between these results and transport parameters such as the elastic length, the
number of current carrying shells, and the number of conducting modes.
