  Superfluid and dissipative regimes in the dynamics of a two-component
quasi-one-dimensional Bose-Einstein condensate (BEC) with unequal atom numbers
in the components have been explored. The system supports localized waves of
the symbiotic type owing to the same-species repulsion and cross-species
attraction. The minority BEC component moves through the majority component and
creates excitations. To quantify the emerging excitations we introduce a
time-dependent function called disturbance. Through numerical simulations of
the coupled Gross-Pitaevskii equations with periodic boundary conditions, we
have revealed a critical velocity of the localized wave, above which a
transition from superfluid to dissipative regime occurs, evidenced by a sharp
increase in the disturbance function. The factors responsible for the
discrepancy between the actual critical velocity and the speed of sound,
expected from theoretical arguments, have been discussed.
