Riffles, ruffles, and the turning algebra
  The rising algebra is a subalgebra of the group algebra of the symmetric group S_n, gotten by lumping together permutations having the same number of rising sequences. This well-known algebra arises naturally when studying riffle shuffles. Here we introduce a number of other subalgebras that arise naturally when studying `ruffles', which are like riffles except that after cutting the deck you turn over the bunch of cards that were on the bottom.   This orphaned draft offers no context or motivation, and uses idiosyncratic notation and terminology that `seemed like a good idea at the time'. We're making it available because it has been cited in this form. 
Peter G. Doyle and Dan Rockmore