Figure 2.

The dispersion branches for the comb-like structure. Solid lines are from (3.2), and the light-line Ω=κ is the dotted line. (a–d) Are for a=1, 3, 5 and 7, respectively. Asymptotics from HFH (2.16), with T given in table 1 for a=7 (d), are depicted as dashed curves.