Figure 5.

Comparison of motor remodelling dynamics at different speeds and IMF levels. (a) A zoomed-in look at the early, most dynamic region from the plots in figure 4; lines shown are fits of equation (2.3) to the data in that figure. As previously, dashed lines represent results in the lowered PMF condition and solid lines in plain MB. The same colour scheme for magnet speed is used throughout this paper. We extrapolate the zero-torque speed in the plain MB condition to vary between 201 and 301 Hz, and between 101 and 201 Hz in the butanol condition; dynamics at these speeds are similar, while those at appreciably higher loads (i.e. 101 Hz in MB, solid blue line) and appreciably lower loads (i.e. 301 Hz in butanol + MB, dashed green line) diverge. (b) Binding rates k_on remain relatively constant in both IMF conditions across all four speed levels while (c) unbinding rates k_off vary as speed is increased and are on average higher in the lowered IMF condition as compared to in plain MB. Rates k_on and k_off were calculated from exponential fits to the data of figure 4, except for the points outlined in red (see text for details). These independent effects suggest that the effect of both speed and IMF on stator dynamics in the BFM quite likely works via the relationship of these factors to the load on the motor. Our results also show behaviour consistent with that of a catch bond, as did those of a prior investigation in the higher load regime [18]. (Online version in colour.)