superconductivity Almost total lack of electrical resistance in certain materials when they are cooled to a temperature near absolute zero. Super¬ conducting materials allow low power dissipation, high-speed operation, and high sensitivity. They also have the ability to prevent external mag¬ netic fields from penetrating their interiors and are perfect diamagnets (see diamagnetism). Since it was first discovered in mercury by Heike Kamerlingh Onnes in 1911, similar behaviour has been found in some 25 other chemi¬ cal elements and in thousands of alloys and compounds. Superconductors have applications in medical imaging, magnetic energy-storage systems, motors, generators, transformers, computer components, and sensitive magnetic-field measuring devices.
superego In Freudian psychoanalytic theory, one of the three aspects of the human personality, along with the id and the ego. The last of the three elements to develop, the superego is the ethical component of the personality, providing the moral standards by which the ego operates. The superego is formed during the first five years of life in response to paren¬ tal punishment and approval; children internalize their parents’ moral standards as well as those of the surrounding society, and the developing superego serves to control aggressive or other socially unacceptable impulses. Violation of the superego’s standards gives rise to feelings of guilt or anxiety.
superfluidity Unusual property of liquid helium cooled below -455.75 °F (-270.97 °C). At such low temperatures, helium exhibits an enormous rise in heat conductivity and rapid flow through capillaries or over the rim of its container. To explain such behaviour, the substance is described in terms of a “two-fluid” mixture model consisting of normal helium and superfluid helium. In normal helium the atoms are in excited states (see excitation), whereas in superfluid helium they are in their ground state. As the temperature is lowered below -455.75 °F, more of the helium becomes superfluid. It is assumed that the superfluid component can move through the container without friction, thereby explaining the unusual behaviour.
Superfund U.S. government fund intended to pay for the cleanup of hazardous-waste dump sites and spills. The 1980 act creating it called for financing by a combination of general revenues and taxes on polluting industries. The Environmental Protection Agency was directed to create a list of the most dangerous sites; it would then compel the polluter to pay for the cleanup or would pay for the cleanup itself through the Superfund and sue for reimbursement. By the 1990s the Superfund had received bil¬ lions of dollars, and work had begun on many sites. In response to wide¬
spread charges of waste, mismanagement, and inefficiency, the Superfund streamlined its procedures, and by the beginning of the 21st century clean¬ ups at more than 750 sites had been completed. In the early 21st century, various proposals were introduced to alter the financing of the Superfund. See also Love Canal.
supergiant star Star of very great natural luminosity and relatively enormous size, typically several magnitudes brighter and several times larger than a giant star. Like other classes of stars, they are distinguished in practice by examination of certain lines in their spectra (see spectros¬ copy). A supergiant may have a diameter several hundred times that of the Sun and a luminosity nearly a million times as great. Supergiants live probably only a few million years, an extremely short life for a star.
Superior, Lake Lake, U.S. and Canada. The largest of the five Great Lakes, Superior is the world’s largest freshwater lake. It is 383 mi (616 km) long and 160 mi (258 km) at its widest, with an area of 31,800 sq mi (82,362 sq km) and depths reaching 1,330 ft (405 m). Lake Superior is known for its picturesque coastline and its numerous shipwrecks; its islands include Isle Royale. The head of the Great Lakes-SAINT Lawrence Seaway system, it is connected to Lake Huron at its southeastern end via the Sault Ste. Marie locks. Ships transport grain, flour, and iron ore dur¬ ing the eight-month navigation season. The French Jesuit missionary Claude-Jean Allouez charted the lake in 1667. The region came under British control (1763-83) and remained in British hands until 1817, when the American Fur Co. took over south of the Canadian border.
supermarket Large retail store operated on a self-service basis, sell¬ ing groceries, produce, meat, bakery and dairy products, and sometimes nonfood goods. Supermarkets were first established in the U.S. during the 1930s as no-frills retail stores offering low prices. In the 1940s and ’50s they became the major food marketing channel in the U.S.; the 1950s also saw them spread through much of Europe. Their growth is part of a trend in developed countries toward reducing cost and simplifying marketing. In the 1960s supermarkets began appearing in developing countries in the Middle East, Asia, and Latin America, where they appealed to individu¬ als who had the necessary buying power and food storage facilities.
supernova Any of a class of violently exploding stars whose luminos¬ ity after eruption suddenly increases many millions of times above its normal level. Like novas, supernovas undergo a tremendous, rapid bright¬ ening lasting a few weeks, followed by a slow dimming, and show blue- shifted emission lines on spectroscopy, which implies that hot gases are blown outward. Unlike a nova, a supernova explosion is a catastrophic event for a star, leading to its collapse into a neutron star or back hole. Amounts of its matter equal to the mass of several Suns may be blasted into space with such energy that the exploding star outshines its entire home galaxy. Only seven supernovas are known to have been recorded before the 17th century, the most famous in ad 1054; its remnants are visible today as the Crab Nebua. The closest and most studied supernova in modem times is SN 1987A, which appeared in 1987 in the Large Magelanic Cloud. Supernova explosions release not only tremendous amounts of radio energy and X-rays but also cosmic rays; in addition, they create and fling into interstellar space many of the heavier elements found in the universe, including those forming Earth’s solar system.
supervenience \,su-p9r-'ven-y3ns\ In philosophy, the asymmetrical reation of ontological dependence that holds between two generically different sets of properties (e.g., mental and physical properties) if and only if every change in an object’s properties belonging to the first set— the supervening properties—entails and is due to a change in properties belonging to the second set (the base properties). Supervenience has often been appealed to by philosophers who want to uphold physicalism while rejecting the identity theory: Though it may be impossible to identify men¬ tal properties with physical properties in a one-to-one fashion, mental properties may still supervene on, and thus be grounded in, physical prop¬ erties. Thus, no two things that are physically alike can be mentally (or psychologically) different, and a being’s mental properties will be deter¬ mined by its physical ones.
supply and demand Relationship between the quantity of a com¬ modity that producers have available for sale and the quantity that con¬ sumers are willing and able to buy. Demand depends on the price of the commodity, the prices of related commodities, and consumers’ incomes and tastes. Supply depends not only on the price obtainable for the com¬ modity but also on the prices of similar products, the techniques of pro¬ duction, and the availability and costs of inputs. The function of the market
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supply-side economics ► surfing I 1847
is to equalize demand and supply through the price mechanism. If buy¬ ers want to purchase more of a commodity than is available on the mar¬ ket, they will tend to bid the price up. If more of a commodity is available than buyers care to purchase, suppliers will bid prices down. Thus, there is a tendency toward an equilibrium price at which the quantity demanded equals the quantity supplied. The measure of the responsiveness of sup¬ ply and demand to changes in price is their elasticity.