  Ambipolar diffusion is important in redistributing magnetic flux and in
damping Alfven waves in molecular clouds. The importance of ambipolar diffusion
on a length scale $\ell$ is governed by the ambipolar diffusion Reynolds
number, $\rad=\ell/\lad$, where $\lad$ is the characteristic length scale for
ambipolar diffusion. The logarithmic mean of the AD Reynolds number in a sample
of 15 molecular clumps with measured magnetic fields (Crutcher 1999) is 17,
comparable to the theoretically expected value. We identify several regimes of
ambipolar diffusion in a turbulent medium, depending on the ratio of the flow
time to collision times between ions and neutrals; the clumps observed by
Crutcher (1999) are all in the standard regime of ambipolar diffusion, in which
the neutrals and ions are coupled over a flow time. We have carried out
two-fluid simulations of ambipolar diffusion in isothermal, turbulent boxes for
a range of values of $\rad$. The mean Mach numbers were fixed at $\calm=3$ and
$\ma=0.67$; self-gravity was not included. We study the properties of
overdensities--i.e., clumps--in the simulation and show that the slope of the
higher-mass portion of the clump mass spectrum increases as $\rad$ decreases,
which is qualitatively consistent with Padoan et al. (2007)'s finding that the
mass spectrum in hydrodynamic turbulence is significantly steeper than in ideal
MHD turbulence. For a value of $\rad$ similar to the observed value, we find a
slope that is consistent with that of the high-mass end of the Initial Mass
Function for stars. However, the value we find for the spectral index in our
ideal MHD simulation differs from theirs, presumably because our simulations
have different initial conditions. This suggests that the mass spectrum of the
clumps in the Padoan et al. (2007) turbulent fragmentation model for the IMF
depends on the environment, which would conflict with evidence ...
