  We have performed a series of systematic tests to evaluate the effects of
spurious transport in three-dimensional smoothed particle hydrodynamics (SPH)
calculations. Our tests investigate (i) particle diffusion, (ii) shock heating,
(iii) numerical viscosity, and (iv) angular momentum transport. The results are
useful for quantifying the accuracy of the SPH scheme, especially for problems
where shear flows or shocks are present, as well as for problems where true
hydrodynamic mixing is relevant.
  We examine the different forms of artificial viscosity (AV) which have been
proposed by Monaghan, by Hernquist & Katz, and by Balsara. For each form, our
tests suggest a single set of values for the AV parameters $\alpha$ and $\beta$
(coefficients of the linear and quadratic terms) which are appropriate in a
large number of situations. We also discuss how these parameters should be
adjusted depending on the goals of the particular application. We find that
both the Hernquist & Katz and Balsara forms introduce relatively small amounts
of numerical viscosity. Furthermore, both Monaghan's and Balsara's AV do well
at treating shocks and at limiting the amount of spurious mixing. For these
reasons, we endorse the Balsara AV for use in a broad range of applications.
