enriched uranium See enrichment (def.
enrichment 1. The planting of young trees in a forest, e.g. after timber extraction.
2. The addition of nutrients, for example, from agricultural runoff or sewage effluent, to surface water. It greatly increases the growth of algae and aquatic plants. See eutrophication.
3. The processing of uranium to increase the proportion of the fissionable form U-235 in relation to U-238, or to add plutonium P-239 to natural uranium, for use in nuclear reactors or nuclear weapons. Enriched uranium contains up to 3% U-235, as compared with 0.7% in natural uranium. See radioactive isotope.
entropy Symbol: S. In a given system, the availability of energy to do work. In any system that undergoes a reversible change, the change of entropy is defined as the heat absorbed divided by the thermo-dynamic temperature:
dS = dQ/T The concept of entropy has been widened to take in the general idea of disorder - the higher the entropy, the more disordered the system. For example, a chemical reaction involving polymerization may exhibit a decrease in entropy because there is a change to a more ordered system.
environment The complete range of external conditions under which an organism lives, including physical, chemical, and biological factors, such as temperature, light, the availability of food and water, and the effects of other organisms.
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