On time variation of G in multidimensional models with two curvatures
  Expressions for G-dot are considered in a multidimensional model with an Einstein internal space and a multicomponent perfect fluid. In the case of two non-zero curvatures without matter, a mechanism for prediction of small G-dot is suggested. The result is compared with exact   (1+3+6)-dimensional solutions. A two-component example with two matter sources (dust + 5-brane) and two Ricci-flat factor spaces is also considered. 
H. Dehnen, V. D. Ivashchuk, S. A. Kononogov and V. N. Melnikov