Comment on "Origin of the excess wing and slow beta relaxation of glass formers: a unified picture of local orientational fluctuations".
In a recent paper [Phys. Rev. E 69, 021502 (2004)]], Tanaka commented on an old coupling model interpretation of the Johari-Goldstein (JG) secondary relaxation [J. Chem. Phys. 115, 1405 (2001)]]; namely, that it implies not all molecules contribute to the JG relaxation. In this Comment, I point out to the readers that this old interpretation has been revised in recent publications [J. Phys.: Condens. Matter 15, S1107 (2003)]; J. Phys. Chem. B 107, 6865 (2003)]; J. Chem. Phys. 120, 857 (2004)]; Macromolecules 37, 8123 (2004)]]. In the new interpretation, essentially all molecules contribute to the JG relaxation. Another comment of Tanaka that applies to both the old and the new interpretation is discussed and shown to be of no practical significance.