Lime plaster is permeable and allows for the diffusion and evaporation of moisture. Laminar flow is a flow regime characterized by high momentum diffusion and low momentum convection. This technique is very useful in biological studies of cell membrane diffusion and protein binding. Ions cross the cell membrane under two influences&colon; diffusion and electric fields. Another method used is liquid thermal diffusion. Such as when using a Gas diffusion electrode. This process is facilitated by molecular diffusion and convection. U-235 and U-238 isotopes by Gaseous diffusion. Measurements of ion diffusion and radii have since shown this not to be possible. Pressure is developed by both diffusion and radial outflow. Plant respiration is limited by the process of diffusion. These recurrence relations are useful for discrete diffusion problems. Radial diffusion is somewhat faster than tangential diffusion. Stability is sometimes achieved by including numerical diffusion. Green's functions are also useful tools in solving wave equations and diffusion equations.