We discuss possible few body processes in the disks of galaxies in relation to resonance rings in galaxies like NGC3081. We complement our HST observations of the inner ring of NGC3081 using an analytical approach and n-body simulations. We find the inner ring forms under a rotating bar perturbation with very strong azimuthal cloud crowding and star formation where the ring crosses the bar major axis. From the dust distribution and radial velocities, the disk turns counterclockwise on the sky, the same as the bar pattern speed. The inner ring at the bar major axis has an orbital rate very close to the pattern speed. From the ring shapes and spacing, the bar strength (maximum tangential/radial force) appears to constant from 7 through 14 kpc. We derive how the perturbation, the fractional long wavelength two-fold intensity and the rotation curve can be used to calculate that the NGC 3081 disk surface density at 7 kpc is 13 >solar masses/square pc rising to 19 at 13 kpc. The latter is insufficient by a factor of seven to generate the rotation curve (halo domination). The surface density may have been reduced at 7 kpc due to inner ring gas cloud scattering. Surface density plus the observed surface brightness gives a disk M/L which increases from 7 kpc through 13 kpc. The ring lifetime of several Gyr in our simulations is consistent with our 400 Myr HST estimates. This long lifetime may mean that repeated passages by gas clouds can be effective in scattering of non-resonant stars at the ring radius at either reducing the surface mass density there or thickening the disk. With a sufficiently low halo, our simulations form gas cloud ``associations" near the ends of the bar as observed. Too low a halo results in a chaotic non-ring gas disk via clump formation, few body interactions, and collisions.
NASA/STScI GO grant 8707 to the University of Alabama and NSF Grant AST 020177 to Bevill State College in Fayette,AL