Kinematics of the Galactic disk from LAMOST Dwarf sample
  Based on the LAMOST survey and Sloan Digital Sky Survey (SDSS), we use
low-resolution spectra of 130,043 F/G-type dwarf stars to study the kinematics
and metallicity properties of the Galactic disk. Our study shows that the stars
with poorer metallicity and larger vertical distance from Galactic plane tend
to have larger eccentricity and velocity dispersion. After separating the
sample stars into likely thin-disk and thick-disk sub-sample, we find that
there exits a negative gradient of rotation velocity $V_{\phi}$ with
metallicity [Fe/H] for the likely thin-disk sub-sample, and the thick-disk
sub-sample exhibit a larger positive gradient of rotation velocity with
metallicity. By comparing with model prediction, we consider the radial
migration of stars appears to have influenced on the thin-disk formation. In
addition, our results shows that the observed thick-disk stellar orbital
eccentricity distribution peaks at low eccentricity ($e \sim 0.2$) and extends
to a high eccentricity ($e \sim 0.8$). We compare this result with four
thick-disk formation simulated models, and it imply that our result is
consistent with gas-rich merger model.
