  We study by simulation a mixture of active (run-and-tumble) and passive
(Brownian) particles with repulsive exclusion interactions in one dimension,
subject to a ratchet (smoothed sawtooth) potential. Such a potential is known
to rectify active particles at one-body level, creating a net current in the
`easy direction'. This is the direction in which one encounters the lower
maximum force en route to the top of a potential barrier. The exclusion
constraint results in single-file motion, so the mean velocities of active and
passive particles are identical; we study the effects of activity level,
Brownian diffusivity, particle size, initial sequence of active and passive
particles, and active/passive concentration ratio on this mean velocity (i.e.,
the current per particle). We show that in some parameter regimes the sign of
the current is reversed. This happens when the passive particles are at high
temperature and so would cross barriers relatively easily, and without
rectification, except that they collide with `cold' active ones, which would
otherwise be localized near the potential minima. In this case, the reversed
current arises because hot passive particles push cold active ones
preferentially in the direction with the lower spatial separation between the
bottom and top of the barrier. A qualitatively similar mechanism operates in a
mixture containing passive particles of two very different temperatures,
although there is no quantitative mapping between that case and the systems
studied here.
