Quark Mass Corrections to the Perturbative Thrust and its Effect on the   determination of $\alpha_s$
  We consider the effects of quark masses to the perturbative thrust in $e^+e^-$ annihilation. In particular we show that perturbative power corrections resulting from non-zero quark masses considerably alters the size of the non-perturbative power corrections and consequently, significantly changes the fitted value of $\alpha_s$. 
Sunanda Banerjee (TIFR, Mumbai) and Rahul Basu (IMSc, Chennai   (Madras))