Coupling Poisson and Transport

Hi,

I am using Comsol 4.3a and want to couple Poisson and transport for determining the flow of charge (or electrical current) within an wire due to application of voltage across it. Now, the output variable for Poisson is "u", while the input variable for "Transport using diluted species" is "V".

How can I couple these two modules (i.e., Poisson and Transport using diluted species) by feeding output of Poisson "u" into the input of transport as "V", because "u" is used in the transport equation for defining a different quantity "velocity field". Can I redefine the variables for either Poisson or Transport module?

- Ahmad