Figure 3.

Comparison of tensile force f (plotted in units of $k_{B}T/l_p$) against the filament extension factor $x=R/L$, for the Marko-Siggia, Ha-Thirumalai, MacKintoish-Käs-Janmey and Blundell-Terentjev models. In all cases the filament stiffness is such that $L=l_p$ (although the M-S model does not depend on this ratio). Dashed lines of the M-K-J and B-T models show the outward force in the compression regime with $x<x_0$ (the effect of zero force at $x=0$, in the full closed loop configuration of an elastica of the B-T model is because the force in Equation (12) is defined along the tangent of the first/last monomer); the H-T model does not predict a zero-force average filament extension, and therefore has no compression regime.