Transport in a network of Josephson junctions in the insulating state 

We consider motion of Cooper pairs in a system of Josephson junctions in
the limit of a small coupling between the superconducting grains. In
this limit the macroscopic superconductivity is destroyed due to Coulomb
blockade. We show that in a sufficiently clean system the temperature
dependence of the conductivity is described by an activation law with
the gap equal to the energy of adding one Cooper pair to the grain. At
stronger disorder or lower temperature one comes to the Anderson
localization of the Cooper pairs and to a faster decay of the
conductivity with temperature.