indirect first order stimulation effect model. Effect E is calculated using an differential equation

                      Emax * c  

E' = kIn - kOut*(1 + ----------)*E

                      c + c50

where c is the free concentration (either tissue or blood/plasma, depending on the switch) at the BloodTissueConcentrationPort connector.

Emax - maximal effect

c50 - concentration producing 50% of maximum stimulation

Boolean cBSwitch - false: use tissue free conc, true: use blood free conc