I followed the “Dark rings” link on today's APOD (2013-4-14) and found an interesting image:
A closeup of the Fraternity arc in Voyager 2 image FDS 11412.46 looks like a twisted rope. The caption continues: “The rope "strands" are really individual clumps that have smeared out during the 111 second exposure. The clumps are only 0.5 to 0.8 degrees apart and are very difficult to understand.”
I believe that the strands are real records of the (smeared) movement of bright clumps. There is no Newtonian reason why the clumps cannot be generally orbiting in the ring around Neptune, and each clump can be simultaneously swirling (i.e., barrelling or spiralling) around other close clumps on the opposite side of the envelope of the ring. That is, the clumps are cycling in and out radially AND are are synchronously cycling in and out of the orbital plane as well. To use other words, each clump is oscillating radially AND oscillating transversely in the ring but at the same frequency to provide a corkscrewing trajectory.
The idea of a tangential oscillation appears in http://articles.adsabs.harvard.edu/cgi- ... lassic=YES
But, I believe, that because the clumps are oscillating transversely, and not tangentially in the ring, they do not interfere with each other and cause friction. Mush in the middle of the ring does not oscillate, it just orbits the planet.
I have detected similar twisted rope in some of Saturn's rings as well.
To explain how the barrelling started, one would only need to invoke the gravitational influence of a moon that is not exactly in the equatorial plane.
Ian G. Kennedy. (firstname.lastname@example.org