height of the layer $h_{\scriptscriptstyle A}$ when the number of chains per area is $\sigma
(h_{\scriptscriptstyle A})$ is given by $$\begin{aligned}
v(\beta) - v(\beta-h_{\scriptscriptstyle A}/R)&=&
\sigma(h_{\scriptscriptstyle A}) n_{\scriptscriptstyle A} 
\Omega_{\scriptscriptstyle A} a(\beta) / R \label{eq:htcov0} \\
v(\beta+h_{\scriptscriptstyle B}/R)-v(\beta)&=&
\sigma(h_{\scriptscriptstyle B}) n_{\scriptscriptstyle B} 
\Omega_{\scriptscriptstyle B} a(\beta) / R
\label{eq:htcov}\end{aligned}$$ where $h_{\scriptscriptstyle A}$ is the height of the growing A-layer, which is measured relative to the junction at $z_d$; and similarly for $B$.

An important quantity is the monomer chemical potential $\mu(\phi)$ (the hydrostatic pressure, in an incompressible system), which is a decreasing function of distance from the dividing surface and is microscopically responsible for the stretching of the chains as their monomers seek regions of lower chemical potential. Under the assumption that there are free ends at all distances from the dividing surface, the chemical potential is quadratic in the distance from the dividing surface:[@mwc88a] $$\mu(z_{\scriptscriptstyle A}) = 
{3\pi^2\over 8 \Omega_{\scriptscriptstyle A}
 R_{\scriptscriptstyle A}^2}\left[
h_{\scriptscriptstyle A}^2
- \left(z_{\scriptscriptstyle A} - z_d\right)^2\right].
\label{eq:mu}$$ A similar equation holds for the $B$-species. For the inwardly curved parts of the structure, this is exact; for the outwardly curved parts, this assumption leads to an unphysical negative density of free ends [@semenov85], but has been shown 