On determination of the large-${1\over x}$ gluon distribution at HERA
  We discuss corrections to the Leading-Log$Q^{2}$ relationships between the gluon density $g(x,Q^{2})$ and $F_{L}(x,Q^{2}),\,\partial F_{T}(x,Q^{2}) /\partial \log Q^{2}$ in the HERA range of large ${1\over x}$. We find that the above quantities probe the gluon density $g(x,Q_{T,L}^{2})$ at $Q_{T,L}^{2}=C_{T,L}Q^{2}$, with the $Q^{2}$-rescaling factors $C_{T}\approx 2.2$ and $C_{L}\approx 0.42$. The possibility of treating charm as an active flavour is critically re-examined. 
N.N. Nikolaev and B.G. Zakharov