The dynamics of the decagonal AlNiCo phase has been
investigated on a single-grain quasicrystalline sample using inelastic
neutron
scattering. The decagonal structure can be viewed as a periodic stacking of
quasiperiodic planes. The anisotropy between the modes propagating in the
periodic and quasiperiodic directions is found to be much weaker than
theoretically predicted. A strong resonance splitting is observed at an energy
transfer of 15 meV for transverse modes polarized in the quasiperiodic
plane