Accretion and Diffusion Timescales in Sheets and Filaments
  A comparison of accretion and (turbulent) magnetic diffusion timescales for sheets and filaments demonstrates that dense star-forming clouds generally will -- under realistic conditions -- become supercritical due to mass accretion on timescales at least an order of magnitude shorter than ambipolar and/or turbulent diffusion timescales. Thus, ambipolar or turbulent diffusion -- while present -- is unlikely to control the formation of cores and stars. 
Fabian Heitsch (1) and Lee Hartmann (2) ((1) UNC Chapel Hill, (2) U of   Michigan)
astro-ph.GA