The Flavor Asymmetry of the Nucleon Sea
  We re-examine the effects of anti-symmetry on the anti-quarks in the nucleon sea arising from gluon exchange and pion exchange between confined quarks. While the effect is primarily to suppress anti-down relative to anti-up quarks, this is numerically insignificant for the pion terms. 
F. M. Steffens and A. W. Thomas (Univ. of Adelaide)