Values of ( a − b ) plotted against sliding velocity V
for the five samples tested in this study. Vertical bars indicate error bars. Squares are (a − b) values after stepping down in Vsliding, while circles are those values after stepping up in Vsliding. The inset illustrates the mixed friction-flow law of Takahashi et al. (2011, 2013), where the steady-state friction coefficient (μss) after a stepwise change in Vsliding from V* to eV* is reached after a flow response following the direct and evolutionary effects (a and b). d, displacement; μ, friction coefficient; μss*, steady-state friction coefficient at V*; ∆μss, difference between μss and μss *.