Probing the dynamical behavior of dark energy
  We investigate dynamical behavior of the equation of state of dark energy
$w_{de}$ by employing the linear-spline method in the region of low redshifts
from observational data (SnIa, BAO, CMB and 12 $H(z)$ data). The redshift is
binned and $w_{de}$ is approximated by a linear expansion of redshift in each
bin. We leave the divided points of redshift bins as free parameters of the
model, the best-fitted values of divided points will represent the turning
positions of $w_{de}$ where $w_{de}$ changes its evolving direction
significantly (if there exist such turnings in our considered region). These
turning points are natural divided points of redshift bins, and $w_{de}$
between two nearby divided points can be well approximated by a linear
expansion of redshift. We find two turning points of $w_{de}$ in $z\in(0,1.8)$
and one turning point in $z\in (0,0.9)$, and $w_{de}(z)$ could be oscillating
around $w=-1$. Moreover, we find that there is a $2\sigma$ deviation of
$w_{de}$ from -1 around $z=0.9$ in both correlated and uncorrelated estimates.
