The determination of alpha_s from lattice QCD with 2+1 flavors of   dynamical quarks
  We describe the first lattice determination of the strong coupling constant with 3 flavors of dynamical quarks. The method follows previous analyses in using a perturbative expansion for the plaquette and Upsilon spectroscopy to set the scale. Using dynamical configurations from the MILC collaboration with 2+1 flavors of dynamical quarks we are able to avoid previous problems of having to extrapolate to 3 light flavors from 0 and 2. Our results agree with our previous work: alpha_s_MSbar(M_Z) = 0.121(3). 
C.Davies, A.Gray, M.Alford, E.Follana, J.Hein, P.Lepage, Q.Mason,   M.Nobes, J.Shigemit su, H.Trottier, M.Wingate