  We compute the temperature-dependent barrier for alpha-relaxations in several
liquids, without adjustable parameters, using experimentally determined
elastic, structural, and calorimetric data. We employ the random first order
transition(RFOT) theory, in which relaxation occurs via activated
reconfigurations between distinct, aperiodic minima of the free energy. Two
different approximations for the mismatch penalty between the distinct
aperiodic states are compared, one due to Xia and Wolynes, which scales
universally with temperature as for hard spheres, and one due to Rabochiy and
Lubchenko, which employs measured elastic and structural data for individual
substances. The agreement between the predictions and experiment is
satisfactory, given the uncertainty in the measured experimental inputs. The
explicitly computed barriers are used to calculate the glass transition
temperature for each substance---a kinetic quantity---from the static input
data alone. The temperature dependence of both the elastic and structural
constants enters the temperature dependence of the barrier over an extended
range to a degree that varies from substance to substance. The lowering of the
configurational entropy, however, seems to be the dominant contributor to the
barrier increase near the laboratory glass transition, consistent with previous
experimental tests of the RFOT theory using the XW approximation. In addition,
we compute the temperature dependence of the dynamical correlation length, also
without using adjustable parameters. These agree well with experimental
estimates obtained using the Berthier et al. procedure. Finally, we find the
temperature dependence of the complexity of a rearranging region is consistent
with the picture based on the RFOT theory but is in conflict with the
assumptions of the Adam-Gibbs and "shoving" scenarios for the viscous slowing
down in supercooled liquids.
