Faraday cup (or cylinder) collector, 553 fast atom bombardment ionization, 553 fast neutrons, 553 fast-atom bombardment (FAB) mass spectroscopy, 553 fatigue of a photochromic system, 553 fatty acids, 554 feed rate in catalysis , 554 feed-back inhibition (end product inhibition) in biotechnology , 554 feedback in analysis , 554 feedback in kinetics , 554 femto, 555 fenestranes, 555