Interstellar Scintillation observations for PSR B0355+54
  In this paper, we report our investigation of pulsar scintillation phenomena
by monitoring PSR B0355$+$54 at 2.25 GHz for three successive months using
\emph{Kunming 40-m radio telescope}. We have measured the dynamic spectrum, the
two-dimensional correlation function, and the secondary spectrum. In those
observations with high signal-to-noise ratio ($S/N\ge100$), we have detected
the scintillation arcs, which are rarely observable using such a small
telescope. The sub-microsecond scale width of the scintillation arc indicates
that the transverse scale of structures on scattering screen is as compact as
AU size. Our monitoring has also shown that both the scintillation bandwidth,
timescale, and arc curvature of PSR B0355$+$54 were varying temporally. The
plausible explanation would need to invoke multiple-scattering-screen or
multiple-scattering-structure scenario that different screens or ray paths
dominate the scintillation process at different epochs.
