Stead, Christina (Ellen) (b. July 17, 1902, Rockdale, Sydney, Austl.—d. March 31, 1983, Sydney) Australian novelist. She traveled widely and at various times lived in London, Paris, and the U.S., where in the early 1940s she worked as a screenwriter for MGM. She returned to Australia in 1974. Her first published work was a collection of short stories, The Salzburg Tales (1934). She is best remembered for her novel The Man Who Loved Children (1940), the story of a disintegrating family.
steady-state theory Concept of an expanding universe whose average density remains constant, matter being continuously created throughout it to form new stars and galaxies at the same rate that old ones recede from sight. A steady-state universe has no beginning or end, and its average density and arrangement of galaxies are the same as seen from every point. Galaxies of all ages are intermingled. The theory was first put forward by William Macmillan (1861-1948) in the 1920s and modified by Fred Hoyle to deal with problems that had arisen in connection with the big-bang model. Much evidence obtained since the 1950s contradicts the steady- state theory and supports the big-bang model.
stealth Any military technology intended to make vehicles or missiles nearly invisible to enemy radar or other electronic detection. Research in antidetection technology began soon after radar was invented. In World War II the Germans coated their U-boat snorkels with radar-absorbent material. By the end of the 20th century the U.S. had developed models of stealth technology, including the F-117 Nighthawk fighter-bomber and the B-2 Spirit strategic bomber. The aircraft featured surface materials and coatings that absorbed radar transmissions, faceted or rounded sur¬ faces that reduced radar reflections, and shielded engine exhausts that reduced infrared radiation. Stealth technology has also been incorporated into the design of naval submarines and surface vessels.
steam Invisible gas consisting of vaporized water. When mixed with minute droplets of water, it has a white, cloudy appearance. In nature, steam is produced by the heating of underground water by volcanic pro¬ cesses and is emitted from hot springs, geysers, fumaroles, and some vol¬ canoes. Steam also can be generated on a large scale by technological systems, such as those using fossil-fuel-burning boilers and nuclear reac¬ tors. Modern industrial society relies on steam power; water is heated to steam in power plants, and the pressurized steam drives turbines that pro¬ duce electric current: thermal energy is converted to mechanical energy, which is converted into electricity.
steam engine Machine that uses steam power to perform mechanical work through the agency of heat (hence a prime mover). In a steam engine, hot steam, usually supplied by a boiler, expands under pressure, and part of the heat energy is converted into work. The rest of the heat may be allowed to escape, or, for maximum engine efficiency, the steam may be condensed in a separate apparatus, a condenser, at comparatively low temperature and pressure. For high efficiency, the steam must decrease substantially in temperature as it expands within the engine. The most efficient performance (i.e., the greatest output of work in relation to the heat supplied) is obtained by using a low condenser temperature and a high boiler pressure. See also Thomas Newcomen, James Watt.
steamboat or steamship Watercraft propelled by steam; more nar¬ rowly, a shallow-draft paddle-wheel steamboat widely used on rivers in the 19th century, particularly the Mississippi River and its tributaries. Though U.S. experiments with steam-powered boats began in 1787, the first regular steamboat service, operating on the Mississippi, was not established until 1812. Until c. 1870 the steamboat dominated the economy, agriculture, and commerce of the middle of the U.S. Because the paddle wheel created turbulence that eroded the banks of narrow channels, river steamboats worked best on broad rivers. The first ocean voyage of a steamboat occurred along the eastern coast of the U.S. in
1809, and Europeans soon developed steamboats capable of crossing Europe’s stormy, narrow seas. The first transatlantic steamboat journey was made by the Savannah in 1819, and the first commercial shipping line, the Cunard Line (see Samuel Cunard), was established in 1840. The screw propeller replaced the paddle wheel in oceanic steamers in the later 19th century. See also ocean liner.
Steamers Robert E. Lee and the Natchez in the race from New Orleans to St. Louis, lithograph by Currier and Ives
BBC HULTON PICTURE LIBRARY
Stebbins, G(eorge) Ledyard (b. Jan. 6, 1906, Lawrence, N.Y., U.S.—d. Jan. 19, 2000, Davis, Calif.) U.S. botanist. He received his Ph.D. from Harvard University and later taught in the University of California system. In Variation and Evolution in Plants (1950) he became the first biologist to apply the modern synthetic theory of evolution—a theory that distinguishes the basic processes of gene mutation and recombination, natural selection, changes in structure and number of chromosomes, and reproductive isolation—to higher organisms. Working with polyploid plants (new species that originated by a spontaneous doubling of the chromosomes of an existing species), he employed a technique for dou¬ bling a plant’s chromosomal number artificially to produce successful artificial polyploids from wild-grass species, becoming the first person to artificially hybridize a plant species that could thrive under natural con¬ ditions.
Stedinger Crusade (1229-34) Crusade against the Stedinger, a body of peasants labeled as heretics by the archbishop of Bremen, who secured papal support for a crusade. In fact, the charge of heresy was unsubstan¬ tiated, and the “crusade” was an attack led by the archbishop’s brother and other nobles of the region. In 1234 Pope Gregory IX was persuaded to summon a crusade with full privileges.
steel Alloy of iron and about 2% or less carbon. Pure iron is soft, but carbon greatly hardens it. Several iron-carbon constituents with different compositions and/or crystal structures exist: austenite, ferrite, pearlite, cementite, and martensite can coexist in complex mixtures and combina¬ tions, depending on temperature and carbon content. Each microstructure differs in hardness, strength, toughness, corrosion resistance, and electri¬ cal resistivity, so adjusting the carbon content changes the properties. Heat treating, mechanical working at cold or hot temperatures, or addition of alloying elements may also give superior properties. The three major classes are carbon steels, low-alloy steels, and high-alloy steels. Low-alloy steels (with up to 8% alloying elements) are exceptionally strong and are used for machine parts, aircraft landing gear, shafts, hand tools, and gears, and in buildings and bridges. High-alloy steels, with more than 8% alloy¬ ing elements (e.g., stainless steels) offer unusual properties. Making steel involves melting, purifying (refining), and alloying, carried out at about 2,900°F (1,600°C). Steel is obtained by refining iron (from a blast fur¬ nace) or scrap steel by the basic oxygen process, the open-hearth process, or in an electric furnace, then by removing excess carbon and impurities and adding alloying elements. Molten steel can be poured into molds and solidified into ingots; these are reheated and rolled into semifinished shapes which are worked into finished products. Some steps in ingot pouring can be saved by continuous casting. Forming semifinished steel into finished shapes may be done by two major methods: hot-working consists primarily of hammering and pressing (together called forging), extrusion, and rolling the steel under high heat; cold-working, which includes rolling, extrusion, and drawing (see wire drawing), is generally
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1816 I steel drum ► Stein
used to make bars, wire, tubes, sheets, and strips. Molten steel can also be cast directly into products. Certain products, particularly of sheet steel, are protected from corrosion by electroplating, galvanizing, or tinplating.