metabolism \m3-'ta-b3- l li-z3m\ Sum of all the chemical reactions that take place in every cell of a living organism, providing energy for the processes of life and synthesizing new cellular material. The term inter¬ mediary metabolism refers to the vast web of interconnected chemical reactions by which all the cell’s constituents, many rarely found outside it, are created and destroyed. Anabolic reactions use energy to build com¬ plex molecules from simpler organic compounds (e.g., proteins from amino acids, carbohydrates from sugars, fats from fatty acids and glycerol); cata- bolic reactions break complex molecules down into simpler ones, releas¬ ing chemical energy. For most organisms, the energy comes ultimately from the Sun, whether they obtain it by photosynthesis and store it in organic compounds or by consuming those organisms that do so. In some bacteria in special environments such as deep-sea vents, the energy comes from chemical reactions instead. Energy is transferred within the cell and the organism by ATP; anabolic reactions consume it, and catabolic reac¬ tions generate it. Every cellular chemical reaction is mediated by a spe¬ cific enzyme. The process that breaks down a substance is usually not the reverse of the process that makes it, using a different enzyme. See also digestion; fermentation; glycolysis; tricarboxylic acid cycle.
Metabolist Vms-'ta-bo-listV school Japanese architectural movement of the 1960s. Tange Kenzo launched the movement with his Boston Har¬ bor Project design (1959), which included two gigantic A-frames hung with “shelving” for homes and other buildings. Led by Tange, Isozaki Arata, Kikutake Kiyonori (b. 1928), and Kurokawa Kisho (b. 1934), the Metabolists focused on structures that combined high-tech imagery, Bru- talism, and megastructures (multifunctional complexes that verge on self¬ containment). The Metabolist manifestos put out at the World Design Conference in 1960 paved the way for such later projects as Paolo Sol- eri’s Arcosanti. Their advocacy of such devices as artificial land platforms above cities, which grew out of a desire for economy of land use, revo¬ lutionized architectural thinking.
Metacom Vme-ts-.kamX or Metacomet or King Philip (b. 1638, Massachusetts—d. Aug. 12, 1676, Rhode Island) Wampanoag Indian sachem (head of a confederation of Algonquian tribes). His father, Mas- sasoit, had negotiated peace with the Pilgrims in 1621. Embittered by the subsequent humiliations to which he and his people were continually sub¬ jected by whites, Metacom in June 1675 led a confederation of Wampanoag, Narragansett, Abenaki, Nipmuck, and Mohawk warriors into battle. Known as King Philip’s War, the ensuing conflict was the most brutal Indian war in New England history. After considerable loss of life and property on both sides, the confederation began to disintegrate, and food became scarce. Metacom returned to his ancestral home, where he was betrayed and killed in 1676 by an Indian informant allied with the colonists. He was beheaded and quartered, and his head was displayed on a pole for 25 years at Plymouth.
metal Any of a class of substances with, to some degree, the following properties: good heat and electricity conduction, malleability, ductility, high light reflectivity, and capacity to form positive ions in solution and hydroxides rather than acids when their oxides meet water. About three- quarters of the elements are metals; these are usually fairly hard and strong crystalline (see crystal) solids with high chemical reactivity that readily form alloys with each other. Metallic properties increase from lighter to heavier elements in each vertical group of the periodic table and from right to left in each row. The most abundant metals are aluminum, iron, cal¬ cium, sodium, potassium, and magnesium. The vast majority are found as ores rather than free. The cohesiveness of metals in a crystalline struc¬ ture is attributed to metallic bonding: The atoms are packed close together, with their very mobile outermost electrons all shared throughout the struc¬ ture. Metals fall into the following classifications (not mutually exclusive and most not rigidly defined): alkali metals, alkaline earth metals, transition elements, noble (precious) metals, platinum metals, lanthanide (rare earth) metals, actinide metals, light metals, and heavy metals. Many have essen¬ tial roles in nutrition or other biochemical functions, often in trace amounts, and many are toxic as both elements and compounds (see mer¬ cury POISONING, LEAD POISONING).
metal fatigue Weakened condition of metal parts of machines, vehicles, or structures caused by repeated stresses or loadings, ultimately resulting in fracture under a stress much weaker than that necessary to cause frac¬ ture in a single application. Fatigue-resistant metals have been developed and their performance improved by surface treatments, and fatigue stresses have been significantly reduced in aircraft and other applications by designing to avoid stress concentrations.
Olivier Messiaen.
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1244 I metal point ► metasomatic replacement
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metal point or silverpoint Method of drawing with a small sharp¬ ened metal rod—of lead, copper, gold, or most commonly silver—on specially prepared paper or parch¬ ment. Silverpoint produces a fine gray line that oxidizes to a light brown; the technique is best suited for small-scale work. It first appeared in medieval Italy and achieved great popularity in the 15th century. Albrecht Durer and Leonardo da Vinci were its greatest exponents.
It went out of fashion in the 17 th cen¬ tury with the rise of the graphite pen¬ cil but was revived in the 18th century by the miniaturists and in the 20th century by Joseph Stella.
metallography \,me-t 3 l-'a-gr3- fe\ Study of the structure of metals and alloys, particularly using micro¬ scopic and X-ray diffraction tech¬ niques. Visual and optical microscopic observation of metal surfaces and fractures can reveal valuable information about the crys¬ talline, chemical, and mechanical makeup of the material. In electron microscopes a beam of electrons instead of a beam of light is directed onto the specimen. The development of transmission electron microscopes has made it possible to examine internal details of very thin metal foils. X-ray diffraction techniques are used to study phenomena related to the grouping of the atoms themselves. See also materials science, Henry C. Sorby.
metallurgy \'me-t a l- l 9r-je\ Art and science of extracting metals from their ores and modifying the metals for use. Metallurgy usually refers to commercial rather than laboratory methods. It also concerns the chemi¬ cal, physical, and atomic properties and structures of metals and the prin¬ ciples by which metals are combined to form alloys. Metals are extracted from crude ore in two phases, mineral processing (also known as ore dress¬ ing) and process metallurgy. In mineral processing, the ore is broken down to isolate the desired metallic elements from the crude ore. In process metallurgy, the resulting minerals are reduced to metal, alloyed, and made available for use. See also blast furnace; powder metallurgy; smelting.
m eta logic Vme-to-.la-jikX Study of the syntax and the semantics of for¬ mal languages and formal systems. It is related to, but does not include, the formal treatment of natural languages (e.g., English, Russian, etc.). Metalogic has led to a great deal of work of a mathematical nature in axiomatic set theory, model theory, and recursion theory (in which func¬ tions that are computable in a finite number of steps are studied).