microchip See integrated circuit microcircuit See integrated circuit
microclimate Climatic condition in a relatively small area, within a few feet above and below the Earth’s surface and within canopies of veg¬ etation. Microclimates are affected by such factors as temperature, humid¬ ity, wind and turbulence, dew, frost, heat balance, evaporation, the nature of the soil and vegetation, the local topography, latitude, elevation, and season. Weather and climate are sometimes influenced by microclimatic conditions, especially by variations in surface characteristics.
microcline Common feldspar mineral, one form of potassium alumino¬ silicate (KAlSi 3 0 8 ) that occurs in many rock types. Green specimens are called amazonstone and may be used as gems. It is an end-member com¬ position in the alkali feldspar series. See also orthoclase.
micrococcus V.mr-kro-'ka-kssN Any of the spherical bacteria that make up the genus Micrococcus. Widespread in nature, these gram-positive (see gram stain) cocci (see coccus) are usually not considered to cause disease. They are normal inhabitants of the human body and may even be essen¬ tial in keeping the balance among the various microorganisms found on the skin. Some species are found in the dust of the air, in soil, in marine waters, and on the skin of vertebrates. Certain species are found in milk and can result in spoilage.
microcomputer Small digital computers whose CPU is contained on a single integrated semiconductor chip. As large-scale and then very large- scale integration (VLSI) have progressively increased the number of tran¬ sistors that can be placed on one chip, the processing capacity of microcomputers has grown immensely. The personal computer is the most common example of a microcomputer, but high-performance microcom¬ puter systems are widely used in business, in engineering, and in “smart” machines in manufacturing. See also integrated circuit, microprocessor.
microeconomics Study of the economic behaviour of individual con¬ sumers, firms, and industries and the distribution of total production and income among them. It considers individuals both as suppliers of land, labour, and capital and as the ultimate consumers of the final product, and it examines firms both as suppliers of products and as consumers of labour and capital. Microeconomics seeks to analyze the market or other mecha¬ nisms that establish relative prices among goods and services and allo¬ cate society’s resources among their many possible uses. See also MACROECONOMICS.
microelectromechanical system (MEMS) Miniature devices formed by combining mechanical parts and electronic circuits, typically on a semiconductor chip, with dimensions from tens to a few hundred micrometres (millionths of a metre). Common applications for MEMS include sensors, actuators, and process-control units.
micromanipulation See microsurgery
micrometer (caliper) Vml-'kra-mo-toiA Instrument for making precise linear measurements of dimensions such as diameters, thicknesses, and lengths of solid bodies. It consists of a C-shaped frame with a movable jaw operated by a screw. The accuracy of the measurements depends on the accuracy of the screw-nut combination.
Micronesia Island group, western Pacific Ocean. A subdivision of Oce¬ ania, it comprises Kiribati, Guam, Nauru, the Northern Marianas, the Fed¬ erated States of Micronesia, the Marshall Islands, and Palau. Located mostly north of the Equator, Micronesia includes the westernmost of the Pacific Islands.
Micronesia, Federated States of Island country, western Pacific Ocean. It comprises the four states Yap, Chuuk (Truk), Pohnpei (Ponape), and Kosrae, all in the Caroline Islands. Area: 271 sq mi (701 sq km).
Population (2005 est.): 113,400. Capitaclass="underline" Palikir, on Pohnpei, the largest island. The people are Micronesian. Languages: Malayo-Polynesian lan¬ guages, English. Religion: Christianity (mostly Roman Catholic; also Protestant). Currency: U.S. dollar. The islands and atolls extend about 1,750 mi (2,800 km) east-west and about 600 mi (965 km) north-south. U.S. government grants constitute the main source of revenue; subsistence farming and fishing are the principal economic activities. Micronesia is a republic in free association with the U.S.; it has one legislative house, and its head of state and government is the president. The islands were prob¬ ably settled by people from eastern Melanesia some 3,500 years ago. They were colonized by Spain in 1886 and came under Japanese rule after World War I. They were captured by U.S. forces during World War II, and in 1947 they became part of the UN Trust Territory of the Pacific Islands, administered by the U.S. The islands became an internally self-governing federation in 1979. In 1982 it signed a compact of free association with the U.S., which is responsible for Micronesia’s defense.
microphone Device for converting sound waves into electric power that has wave characteristics essentially similar to those of the sound. By proper design, a microphone may be given directional characteristics so that it will pick up sound primarily from a single direction, from two directions, or more or less uniformly from all directions. In addition to their use in telephone transmitters, microphones are most widely applied in hearing aids, sound-recording systems (principally magnetic and digi¬ tal tape recorders), and public-address systems.
In a moving-coil microphone, sound waves cause the diaphragm to vibrate, and this oscillating motion causes a wire voice coil to move back and forth through a magnetic field, generating a current that varies in proportion to the original sound wave. This varying current is transmitted through a wire lead to a transformer, which converts it to a current that can be carried by wire cable to a recorder or loudspeaker.
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microprocessor Miniature electronic device that contains the arith¬ metic, logic, and control circuitry needed to function as a digital comput¬ er’s CPU. Microprocessors are integrated circuits that can interpret and execute program instructions as well as handle arithmetic operations. Their development in the late 1970s enabled computer engineers to
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microprogramming ► Middlebury College I 1253
develop microcomputers. Microprocessors led to “intelligent” terminals, such as bank ATMs and point-of-sale devices, and to automatic control of much industrial instrumentation and hospital equipment, programmable microwave ovens, and electronic games. Many automobiles use microprocessor-controlled ignition and fuel systems.
microprogramming Process of writing microcode for a microproces¬ sor. Microcode is low-level code that defines how a microprocessor should function when it executes machine-language instructions. Typically, one machine-language instruction translates into several microcode instructions. On some computers, the microcode is stored in ROM and cannot be modified; on some larger computers, it is stored in EPROM and therefore can be replaced with newer versions.
microscope Instrument that produces enlarged images of small objects, allowing them to be viewed at a scale convenient for examination and analysis. Formed by various means, the image is received by direct imag¬ ing, electronic processing, or a combination of these methods. The most familiar type of microscope is the optical, or light, microscope, in which lenses are used to form the image. Other types of microscopes use the wave nature of various physical processes, the most important being the electron microscope (see electron microscopy), which uses a beam of elec¬ trons in its image formation. Crude microscopes date to the mid-15th century, but not until 1674 were the powerful microscopes of A. van Leeu¬ wenhoek able to detect phenomena as small as protozoa.
Microsoft Corp. U.S. computer firm, the leading developer of personal-computer software systems and applications. Microsoft, head¬ quartered in Redmond, Wash., also publishes books and multimedia titles and manufactures hardware. It was founded in 1975 by Bill Gates and Paul G. Allen (b. 1954), who adapted BASIC for use on personal computers. They licensed versions of it to various companies, developed other pro¬ gramming languages, and in 1981 released MS-DOS for the IBM PC. The subsequent adoption of MS-DOS by most other personal-computer manu¬ facturers generated vast revenues for Microsoft, which became a publicly owned corporation in 1986. It issued the first version of Microsoft Word, its popular word-processing program, in 1983, and Microsoft Windows, a graphical user interface for MS-DOS-based computers, in 1985. In 2001 Microsoft released Xbox, a video game console that quickly captured second place in the $10 billion video gaming market. In 2002 Microsoft launched Xbox Live, a broadband gaming network for their consoles.