Sidney Loeb (1917–2008) made reverse osmosis (RO) practical by developing, together with Srinivasa Sourirajan, semi-permeable anisotropic membranes. The invention of the practical reverse osmosis membrane revolutionized the concept of water desalination. Loeb invented the power generating process pressure retarded osmosis (PRO)--making accessible a rich previously unknown source of green energy, and a method of producing power by a reverse electrodialysis (RED) heat engine, among other inventions in related fields. The production of energy by PRO and RED, among others, is sometimes called "osmotic power."