ALPHA is large.

In all of our simulations, the effective alpha was at least 0.1 in the outer regions of the accretion disk where the tidal shock waves are excited. However, as predicted by analytic arguments, alpha decays with decreasing radius. In cold disks such as those found in CV systems, this drop is so precipitous that we could not measure an alpha below a radius of only 1/3 that of the outer edge of the disk.

ALPHA is independent of mass ratio.

Varying the mass ratio from 0.2 to 5 did little to change the spiral pattern. Moreover, the strength of the two-armed spiral shocks at their origin near the outer edge of the disk was fairly constant in all of our models, independent of mass ratio, Mach number, or density profile. This has the consequence that, despite all else, one can be confident that the effective alpha in the outer regions of an accretion disk in a binary system is (at least) 0.1.

TIDAL TRUNCATION depends on Mach number.

We found a strong dependence of the tidal radius on the Mach number in the disk, such that colder disks extended out to larger radii. The tidal radius in our coldest model (with q=1) agrees well with the analysis of Paczynski (1977), who found the largest non-intersecting periodic orbit in a pressure-less disk. Our results suggest that pressure effects in a warm disk can significantly decrease the tidal radius (30% smaller for a Mach number of order 10 at the outer edge of the disk).