instant Emax effect model. Effect E is calculated using an equation

     Emax * c

E = ----------

     c50 + c

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 half maximum effect

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