Current constraints on the epoch of cosmic acceleration
  The cosmographic expansion history of the universe is investigated by using
the 557 type Ia supernovae from the Union2 Compilation set along with the
current estimates involving the product of the CMB acoustic scale $\ell_{A}$
and the BAO peak at two different redshifts. Using a well-behaved
parameterization for the deceleration parameter, $q(z) = q_0 + q_1z/(1 + z)$,
we estimate the accelerating redshift $z_{acc}=-q_0/(q_0 + q_1)$ (at which the
universe switches from deceleration to acceleration) and investigate the
influence of a non-vanishing spatial curvature on these estimates. We also use
the asymptotic value of $q(z)$ at high-$z$ to place more restrictive bounds on
the model parameters $q_0$ and $q_1$, which results in a more precise
determination of the epoch of cosmic acceleration.
