Definition of coupled Neumann boundary condition

Hallo every one,

I am now dealing with heat transfer in porous media, for which I need some special boundary conditions, which I am not sure if it is possible in FEniCS.
In my case I have a bc looks like:
(at Y=0 T_s = T_f as well)
So my question is, how should I implement this kind of neumann boundary condition in FEniCS?

thanks in advance!

T. Xie