  Spectral anti-crossings between the fundamental guided mode and core wall
resonances alter the dispersion in hollow-core anti-resonant-reflection
photonic crystal fibers. Here we study the effect of this dispersion change on
the nonlinear propagation and dynamics of ultrashort pulses. We find that it
causes emission of narrow spectral peaks through a combination of four-wave
mixing and dispersive wave emission. We further investigate the influence of
the anti-crossings on nonlinear pulse propagation and show that their impact
can be minimized by adjusting the core-wall thickness in such a way that the
anti-crossings lie spectrally distant from the pump wavelength.
