  A quantitative theory is developed for the vertical mean temperature profile
(MTP) in turbulent Rayleigh-Benard convection (RBC), which explains the recent
experimental and numerical observations of a logarithmic law by Ahlers et
al.(Phys. Rev. Lett., 2012). A multi-layer model is formulated and quantified,
whose predictions agree with DNS and experimental data for the Rayleigh-number
(Ra) over seven decades. In particular, a thermal buffer layer follows a 1/7
scaling like the previously postulated mixing zone (Procaccia et al, Phys. Rev.
A,1991), and yields a Ra-dependent log law constant. A new parameterization of
Nu(Ra) dependence is proposed, based on the present multi-layer quantification
of the bulk MTP.
