A New Look at Simple Inhomogeneous Chemical Evolution
  A rudimentary, one-zone, closed-box model for inhomogeneous chemical evolution is offered as an alternative reference than the Simple model in the limit of no mixing. The metallicity distribution functions (MDFs) of Galactic halo and bulge stars can be matched by varying a single evolutionary parameter, nQ. Q is the filling factor of contaminating regions and n is the number of star-forming generations. Therefore, Q and n have equivalent roles, and combinations of n and Q yield systems with different metallicities at any given age. The model also revises interpretation of observed MDFs. Unevolved systems probe the parent distribution of metal production f(z), for example, the high-metallicity tail of the halo distribution agrees with a power-law f(z). 
M. S. Oey (STScI)