Dispersal of massive star products and consequences for galactic   chemical evolution
  The processes that disperse the products of massive stars from their birth sites play a fundamental role in determining the observed abundances. I discuss parameterizations for element dispersal and their roles in chemical evolution, with an emphasis on understanding present-day dispersion and homogeneity in metallicity. Turbulence dominates mixing processes, with characteristic timescales of order 10^8 yr, implying significant dilution of metals into the ISM. This permits a rough estimate of the metallicity distribution function of enrichment events. Many systems, including the Milky Way and nearby galaxies, show metallicity dispersions that as yet appear consistent with pure inhomogeneous evolution. There are also systems like I Zw~18 that show strong homogenization, perhaps tied to small galaxy size, high star formation rate, and/or superwinds. 
M.S. Oey (Lowell Observatory)