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  • (electronics) In ac, two successive signal alternations of opposite polarity.
  • (chemistry) In the atmosphere or biosphere a sequence of events in repetitive motion in which the final output feeds back into the initial input. Examples of this include biogeochemical cycles, including the nitrogen, carbon, and sulfur cycles in which these species are chemically processed in gas, solid, and solution phase by physical and biological processes which change their form, oxidation state, and physical state. [Living in the Environment; Miller, Tyler; pg 244; 1994; Wadworth; Belmont.] [The Chemistry of the Atmosphere and Oceans; Holland, Heinrich; pg. 1-14; 1978; Wiley Interscience, NY.] Source: Atmospheric Chemistry Glossary