  Magnetic excitations in the quasi-one-dimensional quantum antiferromagnets
PbNi2V2O8 and SrNi2V2O8 are measured all the way up to the zone boundary energy
using inelastic neutron scattering from powder samples. An estimate for
next-nearest-neighbor in-chain interactions is obtained. The role played by
these interactions in spin-vacancy induced magnetic ordering in PbNi2V2O8 is
discussed.
