Maxwell model for viscoelasticity using the upper-convected time

derivative of the stress tensor.  See
http://en.wikipedia.org/wiki/Upper-convected_Maxwell_model

The model includes an additional viscosity (nu) from the transport
model from which it is instantiated, which makes it equivalent to the
Oldroyd-B model for the case of an incompressible transport model.
See https://en.wikipedia.org/wiki/Oldroyd-B_model