  We investigate the effect of different mass of a Bose- and a Fermi-particle
on the collective oscillations of the degenerate boson-fermion mixtures. In
particular we consider the monopole and the quadrupole modes of the
oscillations and study their characters and the frequencies by using
variational-sum-rule approach. We find that for both the modes there exists a
critical value of the ratio of boson-fermion mass below and above which the
character and the frequency of the respective modes are significantly
different.
