$D$ is the diffusion constant of the protein conformation along the reaction coordinate,
$l_b$ is the characteristic length of the bound state $l_b \equiv 1/\rho_b$,
$\rho_b$ is the density of states in the bound state, and
-$l_{ts}$ is the characteristic length of the transition state
-\begin{equation}
- l_{ts} = TODO
-\end{equation}
+$l_{ts}$ is the characteristic length of the transition state.
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\nomenclature{$U_b(F)$}{The barrier energy as a function of force
(\cref{eq:kramers-saddle}).}