摘要：We describe a few mathematical tools which allow to investigate whether air-water interfaces exist(under prescribed conditions)and are mechanically stable and temporally *** terms of physics,air-water interfaces are governed by the Young-Laplace *** they are surfaces of constant mean curvature which represent solutions of a nonlinear elliptic partial differential *** explicit solutions of this equation can be obtained only in very special cases,it is -under moderately special circumstances-possible to establish the existence of a solution without actually solving the differential *** also derive criteria for mechanical stability and temporal persistence of an air *** we calculate the lifetime of a non-persistent air ***,we apply these tools to two examples which exhibit the symmetries of 2D *** examples can be viewed as abstractions of the biological model represented by the aquatic fern Salvinia.