PHYSICAL MATHEMATICS SEMINAR TITLE: ALL BENT OUT OF SHAPE: PERIODIC BUCKLING OF VISCOUS SHEETS AND JETS AUTHOR: NEIL M. RIBE INSTITUT DE PHYSIQUE DU GLOBE DE PARIS FRANCE ABSTRACT: A sheet of honey poured onto a piece of toast forms a series of periodic folds. I have studied numerically the dynamics of this instability using an asymptotic theory for a thin inertia-free viscous sheet that deforms by combined stretching and bending under the action of gravity and surface tension. As a control parameter proportional to the buoyancy increases, an initial state of forced (kinematically driven) folding bifurcates to a state of free (buoyancy-dominated) folding with two stable branches. The numerically predicted folding frequencies are in good agreement with experimental measurements. I next turn to the more complicated problem of the coiling of a falling viscous filament or jet. Using a large suite of laboratory data, I show that the coiling frequency is governed by a balance between buoyancy and viscous bending resistance, and that multiple states of steady coiling are possible for given values of the control parameters. TUESDAY, DECEMBER 3, 2002 2:30 pm Building 2, Room 338 Refreshments will be served at 3:30 PM in Room 2-349 Massachusetts Institute of Technology Department of Mathematics Cambridge, MA 02139