Leaky-box model of galactic chemical evolution

The leaky-box model adds a galactic outflow to the closed box. If the outflow has the ambient gas metallicity and constant mass-loading factor $\lambda$, its effective yield is reduced to $y/(1+\lambda )$ when returned fractions are absorbed into the definitions.

The effective yield is the yield that a simple closed-box relation would need to reproduce an observed gas fraction and metallicity. Outflow and pristine inflow generally lower it below the nucleosynthetic yield.