Connecting examples of these things with a Killing vector field can foliate a static spacetime. Strain from non-commensurate lattices can cause Stranski-Krastonov growth at these things, which can be used to manufacture quantum dots with MBE. Non-conservative growth of these things can be modelled by the Edwards-Wilkinson equation, adding non-linear terms to which gives the KPZ equation. MOCVD and (*) sputtering can be used in growth upon these things. Dirichlet problems in electrostatics have the potential energy specified along these things. (10[1])An energy (10[1])named for these things appears in the Young equation which gives the wetting angle. The partial derivative of energy with respect to area is these things' namesake tension. (10[1])For 10 points, name these things which mark the boundary between two volumes. ■END■