  The Maxwell Garnett and Bruggeman formalisms were applied to estimate the
effective permittivity dyadic of active dielectric composite materials. The
active nature of the homogenized composite materials (HCMs) arises from one of
the component materials which takes the form of InAs/GaAs quantum dots.
Provided that the real parts of the permittivities of the component materials
have the same sign, the Maxwell Garnett and Bruggeman formalisms give
physically plausible estimates of the HCM permittivity dyadic that are in close
agreement. However, if the real parts of the permittivities of the component
materials have different signs then there are substantial differences between
the Bruggeman and Maxwell Garnett estimates. Furthermore, these differences
becomes enormous--with the Bruggeman estimate being physically implausible--as
the imaginary parts of the permittivities of the component materials tend to
zero.
