Díaz Díaz, Jesús IldefonsoKawohl, B.2023-06-202023-06-201993-07-150022-247X10.1006/jmaa.1993.1257https://hdl.handle.net/20.500.14352/57488"We consider some degenerate parabolic problems on a convex (or starshaped) ring. We prove that if the initial data have convex (or starshaped) level sets, then the solution u(t,⋅) has the same property for any positive t. Similar results are shown for the corresponding stationary problems. Our results imply in particular the convexity (or starshapedness) of certain free boundaries. Other nonlinear parabolic problems are also discussed.''engjournal articlehttp://www.sciencedirect.com/science/article/pii/S0022247X83712576http://www.sciencedirect.com/science/journal/0022247Xrestricted access517.954porous-medium equationgeometrical propertiesobstacle problemfree-boundarydiffusionstabilizationcontinuityregularityconcavitysupportEcuaciones diferenciales1202.07 Ecuaciones en Diferencias