Inter-American Development Bank (IDB) international organi¬ zation founded in 1959 by 20 governments in North and South America to finance economic and social development in the Western Hemisphere. The largest charter subscribers were Argentina, Brazil, Mexico, Venezu¬ ela, and the U.S. Subscribers now include nearly 30 countries in North and South America and more than 15 countries in Europe, as well as Japan and Israel. The IDB group also includes the Inter-American Investment Corp. and the Multilateral Investment Fund. It is headquartered in Wash¬ ington, D.C.
interchangeable parts Identical components that can substitute one for another, particularly important in manufacturing. Mass production, which transformed the organization of work, came about by the develop¬ ment of the machine-tool industry by a series of 19th-century innovators.
With precision equipment, large numbers of identical parts could be pro¬ duced at low cost and with a small workforce. See also American System of manufacture; armoury practice; automobile industry; factory; Henry Ford; Henry Leland.
intercolumniation In architecture, the space between columns that support an arch or entablature. Classical, Renaissance, and Baroque archi¬ tecture used a system codified by Vitruvius in which the measurement is expressed in terms of the columns’ diameters (e.g., two columns might be described as being three diameters apart). The system conveniently expressed the measurement of a unit of space whose size varied from building to building according to the Classical order used.
intercontinental ballistic missile See ICBM
interest Price paid for the use of credit or money. It is usually figured as a percentage of the money borrowed and is computed annually. Interest is charged by the lender as payment for the loss of his or her money for a period of time. The interest rate reflects the risk of lending and is higher for loans that are considered higher-risk, a relationship known as the risk/ return tradeoff. Like the prices of goods and services, interest rates are responsive to supply and demand. Theories explaining the need for interest include the time-preference theory, according to which interest is the inducement to engage in time-consuming but more productive activities, and the liquidity-preference theory of John Maynard Keynes, according to which interest is the inducement to sacrifice a desired degree of liquidity for a nonliquid contractual obligation. Interest rates may also be used as a tool for implementing monetary policy (see discount rate). High interest rates may dampen the economy by making it difficult for consumers, businesses, and home buyers to secure loans, while lower rates tend to stimulate the economy and encourage both investment and consumption.
interference In physics, the net effect of combining two or more wave trains moving on intersecting or coincident paths. Constructive interfer¬ ence occurs if two components have the same frequency and phase; the wave amplitudes are reinforced. Destructive interference occurs when the two waves are out of phase by one-half period (see periodic motion); if the waves are of equal amplitude, they cancel each other. Two waves mov¬ ing in the same direction but having slightly different frequencies inter¬ fere constructively at regular intervals, resulting in a pulsating frequency called a beat. Two waves traveling in opposite directions but having equal frequencies interfere constructively in some places and destructively in others, resulting in a standing wave.
interferon V.in-tor-'fir-.anN Any of several related proteins produced by all vertebrates and possibly some invertebrates. They play an important role in resistance to infection. The body’s most rapidly produced and important defense against viruses, they can also combat bacteria and para¬ sites (see parasitism), inhibit cell division, and promote or impede cell dif¬ ferentiation. Interferon’s effect is indirect—it reacts with susceptible cells, which then resist virus multiplication—in contrast to antibodies, which act by combining directly with a specific virus. Various types of interferons are distinguished by their characteristics as proteins and by which cells produce them. Some are now produced by genetic engineering. Initial hopes that interferon would be a wonder drug for a wide variety of diseases were deflated by its serious side effects, but a few rare conditions respond to it.
interior design Design of interior spaces, closely related to architec¬ ture and sometimes including interior decoration. The designer’s goal is to produce a coordinated and harmonious whole in which the architec¬ ture, site, function, and visual aspects of the interior are unified, pleasing to mind and body, and appropriate to the activities to be pursued there. Design criteria include harmony of colour, texture, lighting, scale, and proportion. Furnishings must be in proportion to the space they occupy and to the needs and lifestyles of the residents. The design of such non- residential spaces as offices, hospitals, stores, and schools places clear organization of functions ahead of purely aesthetic concerns.
interleukin N.in-tor-'lii-konX Any of a class of naturally occurring pro¬ teins important in regulation of lymphocyte function. Several known types are recognized as crucial constituents of the body’s immune system (see immunity). Antigens and microbes stimulate production of interleukins, which induce production of various types of lymphocytes in a complex series of reactions that ensure a plentiful supply of T cells that fight spe¬ cific infectious agents.
intermediate goods See producer goods
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948 I intermediate-range nuclear weapons ► International Court of Justice
intermediate-range nuclear weapons Class of nuclear weapons with a range of 620-3,400 mi (1,000-5,500 km). Some multiple warheads developed by the Soviet Union could strike several targets anywhere in Western Europe in less than 10 minutes. The U.S. could send a single nuclear warhead from central Europe to Moscow in less than 10 minutes. Both were regarded as offensive, first-strike weapons. U.S.-Soviet arms- control negotiations (1980-87) led to the intermediate nuclear forces (INF) treaty, signed by Mikhail Gorbachev and Ronald Reagan, to com¬ pletely remove and dismantle these and shorter-range weapons.
internal-combustion engine Any engine in which a fuel-air mix¬ ture is burned in the engine proper so that the hot gaseous products of combustion act directly on the surfaces of its moving parts, such as those of pistons (see piston and cylinder) or turbine rotor blades. Internal- combustion engines include gasoline engines, diesel engines, gas turbine engines, pure jet engines, and rocket engines and motors, and are one class of heat engines. They are commonly divided into continuous-combustion engines and intermittent-combustion engines. In the first type (e.g., jet engines) fuel and air flow steadily into the engine, where a stable flame is maintained for continuous combustion. In the second (e.g., gasoline- reciprocating-piston engines), discrete quantities of fuel and air are peri¬ odically ignited. See also automobile industry, machine, steam engine.