  Wake patterns due to a uniformly traveling source are a result of the
resonant emission of the medium's collective excitations. When there exists a
frequency range where such excitations possess a negative group velocity, their
interference leads to a wake pattern resembling the Kelvin ship wake: while
there are "transverse" and "divergent" wavefronts trailing the source, they are
oriented oppositely to Kelvin's. This is illustrated by an explicit calculation
of "roton" wake patterns in superfluid $^{4}He$ where a Kelvin-like wake
emerges when the speed of the source marginally exceeds the Landau critical
roton velocity.

Mesoscale and Nanoscale Physics;Fluid Dynamics