FIGURE 3.

Trajectories of rotation angle θ (A, C) and torsion angle χ (B, D), calculated as described in the Appendix. Parameter values: u = 8 and r = 50 (10), φ = 2π/50 (7.2°), D_b = 0.256 rad²/s, corresponding to a frictional drag coefficient 2π k_BT/D_b = 0.1 nN nm rad⁻¹ Hz⁻¹ (8), d = 20, k_χ = 0.4 nN nm/rad² (9), T_ex /(nN nm rad⁻¹) = 0 (a), 1.5 (b), −1.53 (c); temperature, 22°C; sampling time, 5 ms; bidirectional stepping model, σ = 0.8 nN nm/rad², α₀ = 200 s⁻¹, λ = 0.5 (A, B); unidirectional stepping model, σ = 23.9 nN nm/rad², α₀ = 500 s⁻¹, λ = 0 (C, D). The relaxation time (ms) for χ (t) in B and the frequency f (Hz) at steady state in A are 13.6 ± 0.7 and 8.7 ± 0.3 (a), 10.2 ± 1.1 and 19.9 ± 0.4 (b), 17.2 ± 0.4 and 0.002 ± 0.2 (c), respectively. The corresponding values for D and C are 41.1 ± 1.6 and 8.6 ± 0.4 (a), 44.4 ± 2.3 and 8.5 ± 0.4 (b), and 42.4 ± 0.6 and 8.8 ± 0.4 (c), respectively.