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  • Ackerman, Edward A. (American geographer)
    ...belief that the methods for defining regions were out of line with the scientific approaches characterizing other disciplines. Some felt that geographers had not contributed well to the war effort: Edward A. Ackerman, a professor of geography at the University of Chicago from 1948 to 1955 (and later head of the Carnegie Foundation), claimed that those working in the U.S. government’s......
  • “Ackermann aus Böhmen, Der” (work by Johannes von Tepl)
    Bohemian author of the remarkable dialogue Der Ackermann aus Böhmen (c. 1400; Death and the Ploughman), the first important prose work in the German language....
  • Ackermann, Konrad Ernst (German actor and manager)
    actor-manager who was a leading figure in the development of German theatre....
  • Ackermann, Louise-Victorine (French poet)
    French poet who is best-known for works characterized by a deep sense of pessimism....
  • Ackermann system (mechanics)
    Steering of trucks, with their relatively heavy loads, was a problem until power steering came into use in the early 1950s. Steering is always by the Ackermann system, which provides a kingpin for each front wheel. Maximum cramp angle of the front wheels is about 35 degrees. The minimum turning radius is dependent on the wheelbase. A few vehicles have been built with two steering axles in the......
  • Ackermann, Wilhelm (German logician)
    ...of the semantic and syntactic notions necessary to characterize consistency precisely. The first clear proof of the consistency of the first-order predicate logic is found in the work of Hilbert and Wilhelm Ackermann from 1928. Here the problem was not only the precise awareness of consistency as a property of formal theories but also of a rigorous statement of first-order predicate logic as a....
  • Ackland-Snow, Brian (British production designer and art director)
    ...Screenplay: Woody Allen for Hannah and Her SistersAdapted Screenplay: Ruth Prawer Jhabvala for A Room with a ViewCinematography: Chris Menges for The MissionArt Direction: Brian Ackland-Snow and Gianni Quaranta for A Room with a ViewOriginal Score: Herbie Hancock for “Round Midnight”Original Song: “Take My Breath Away” from Top.....
  • Ackroyd, Peter (British author, biographer, critic and scholar)
    British novelist, critic, biographer, and scholar whose technically innovative novels present an unconventional view of history....
  • Aclla Cuna (Inca religion)
    in Inca religion, women who lived in temple convents under a vow of chastity. Their duties included the preparation of ritual food, the maintenance of a sacred fire, and the weaving of garments for the emperor and for ritual use. They were under the supervision of matrons called Mama Cuna. At the time of the Spanish conquest in the early 16th century, the Virgins numbered several thousand and were...
  • ACLU (American organization)
    organization founded by Roger Baldwin and others in New York City in 1920 to champion constitutional liberties in the United States. The ACLU works to protect Americans’ constitutional rights and freedoms as set forth in the U.S. Constitution and its amendments. The ACLU works in three basic areas: freedom of expression, conscience, and association; due process of law; an...
  • ACM (American science society)
    organization founded by Roger Baldwin and others in New York City in 1920 to champion constitutional liberties in the United States. The ACLU works to protect Americans’ constitutional rights and freedoms as set forth in the U.S. Constitution and its amendments. The ACLU works in three basic areas: freedom of expression, conscience, and association; due process of law; an...
  • Acmaeidae (gastropod family)
    ...rocky areas.Superfamily Patellacea (Docoglossa)Conical-shelled limpets, without slits or holes, found in rocky shallow waters (Acmaeidae and Patellidae).Superfamily TrochaceaSmall to large spiral shells in shallow to deep ocean waters, often brightly coloured,....
  • Acme Colored Giants (American sports team)
    ...being raised. Black players were in the minor leagues for the next few years, but their numbers declined steadily. The last black players in the recognized minor leagues during 19th century were the Acme Colored Giants, who represented Celoron, New York, in the Iron and Oil Leagues in 1898....
  • Acmeists (Russian poets)
    member of a small group of early-20th-century Russian poets reacting against the vagueness and affectations of Symbolism. It was formed by the poets Sergey Gorodetsky and Nikolay S. Gumilyov. They reasserted the poet as craftsman and used language freshly and with intensity. Centred in St. Petersburg, the Acmeists were associated with the review Apollon (1909–17). ...
  • acmite (mineral)
    ...occurs in crystalline schists. Aegirine forms a continuous chemical series with aegirine-augite, in which calcium replaces sodium, and magnesium and aluminum replace iron. In this series, the name acmite is given to crystals with the composition NaFeSi2O6 as well as to the reddish brown or greenish black pointed crystals approximating that composition. Aegirine generally.....
  • acne (dermatology)
    any inflammatory disease of the sebaceous, or oil, glands of the skin. There are some 50 different types of acne. In common usage, the term acne is frequently used alone to designate acne vulgaris, or common acne, probably the most prevalent of all chronic skin disorders....
  • acne vulgaris (dermatology)
    Acne vulgaris (common acne) is a prevalent skin condition that has its onset during adolescence. At puberty, androgenic stimulation of the skin’s sebaceous (oil) glands (which empty into the canals of the hair follicles) causes increased production of the fatty substance sebum. In susceptible individuals, there is oversecretion of sebum. Sebum and cellular debris then form a plug in the......
  • Acochlidacea (gastropod order)
    ...shell; operculum present; gill and radula absent; long proboscis with stylet; ectoparasitic; in warm oceanic areas; generally minute.Order AcochlidaceaThree families with visceral mass longer than foot; 4 species in fresh water; a few with sexes in separate animals; size......
  • Acoela (flatworm order)
    ...endocommensal (i.e., living, respectively, outside or inside another organism without harming it), or parasitic; about 3,000 species.Order AcoelaExclusively marine; mouth present; pharynx simple or lacking; no intestine; without protonephridia, oviducts, yolk glands, or definitely delimited......
  • acoelomate (biology)
    Flatworms (phyla Platyhelminthes, Nemertea, and Mesozoa) lack a coelom, although nemerteans have a fluid-filled cavity at their anterior, or head, end, which is used to eject the proboscis rapidly. The lack of a fluid-filled cavity adjacent to the muscles reduces the extent to which the muscles can contract and the force they exert (see below Support and movement). Because most also lack a......
  • Acoemetae (Byzantine monks)
    monks at a series of 5th- to 6th-century Byzantine monasteries who were noted for their choral recitation of the divine office in constant and never interrupted relays. Their first monastery, at Constantinople, was founded in about 400 by St. Alexander Akimetes, who, after long study of the Bible, put into practice his conviction that God should be perpetually praised; he arranged for relays of mo...
  • Acoemeti (Byzantine monks)
    monks at a series of 5th- to 6th-century Byzantine monasteries who were noted for their choral recitation of the divine office in constant and never interrupted relays. Their first monastery, at Constantinople, was founded in about 400 by St. Alexander Akimetes, who, after long study of the Bible, put into practice his conviction that God should be perpetually praised; he arranged for relays of mo...
  • Acolhua (people)
    city built in the present-day Valley of Mexico by the Acolhuas, a pre-Columbian people of the Nahuatl-speaking group of tribes, which gained mastery of the valley after the collapse of the Toltec hegemony in the mid-12th century ad. The rulers of Texcoco were the first among Nahuatl tribal leaders to establish their rule over Anáhuac (the Valley of Mexico). By the turn of the...
  • Acoli (people)
    ethnolinguistic group of northern Uganda and southernmost Sudan. Numbering more than one million at the turn of the 21st century, they speak a Western Nilotic language of the Eastern Sudanic branch of the Nilo-Saharan family and are culturally and historically related to their traditional enemies, the neighbouring ...
  • acolyte (religion)
    (from Greek akolouthos, “server,” “companion,” or “follower”), in the Roman Catholic church, a person is installed in a ministry in order to assist the deacon and priest in liturgical celebrations, especially the eucharistic liturgy. The first probable reference to the office dates from the time of Pope Victor I (189–199), ...
  • Acoma (people)
    ...boundaries of what are now the U.S. states of Arizona, New Mexico, Colorado, and Utah intersect. The descendents of the Ancestral Pueblo comprise the modern Pueblo tribes, including the Hopi, Zuni, Acoma, and Laguna. As farmers, Ancestral Pueblo peoples and their nomadic neighbours were often mutually hostile; this is the source of the term Anasazi, a Navajo word meaning “ancestors of th...
  • Acoma (pueblo, New Mexico, United States)
    Indian pueblo, Valencia county, west-central New Mexico, U.S. The pueblo lies 55 miles (89 km) west-southwest of Albuquerque and is known as the “Sky City.” Its inhabitants live in terraced dwellings made of stone and adobe atop a precipitous sandstone butte 357 feet (109 metres) high. They have always engaged in farming (on the plains below) and...
  • Acominatus, Michael (Byzantine historian)
    Byzantine humanist scholar and archbishop of Athens whose extensive Classical literary works provide the principal documentary witness to the political turbulence of 13th-century Greece after its occupation by the Western Crusaders....
  • Acominatus, Nicetas (Byzantine historian)
    Byzantine statesman, historian, and theologian. His chronicle of Byzantium’s humiliations during the Third and Fourth Crusades (1189 and 1204) and his anthology of 12th-century theological writings constitute authoritative historical sources for this period and established him among the most brilliant medieval Greek historiographers....
  • Acomys (mammal genus)
    any of more than a dozen species of small to medium-sized rodents characterized by the harsh, inflexible spiny hairs of their upperparts. African spiny mice have large eyes and ears and scaly, nearly bald tails that are shorter than or about as long as the body. The tail is brittle and breaks off readily either as a whole or in part. The golden spiny mouse (Acomys russatu...
  • Acomys cahirinus (mammal)
    ...Depending upon the species, fur covering the upperparts may be gray, grayish yellow, brownish red, or reddish. Black (melanistic) individuals occur in populations of the golden spiny mouse and the Cairo spiny mouse (A. cahirinus)....
  • Acomys cilicicus (mammal)
    ...The Cairo spiny mouse has the most extensive distribution, extending from northern Africa to the Indus River; it lives near or with humans in some parts of its range. The most restricted is A. cilicicus, which is known only from a single locality in southern Turkey....
  • Acomys russatus (mammal)
    ...spiny mice have large eyes and ears and scaly, nearly bald tails that are shorter than or about as long as the body. The tail is brittle and breaks off readily either as a whole or in part. The golden spiny mouse (Acomys russatus), found from Egypt to Saudi Arabia, is one of the largest, with a body up to 25 cm (9.8 inches) long and a shorter tail of up to 7 cm. The Cape......
  • Acomys subspinosus (mammal)
    ...The golden spiny mouse (Acomys russatus), found from Egypt to Saudi Arabia, is one of the largest, with a body up to 25 cm (9.8 inches) long and a shorter tail of up to 7 cm. The Cape spiny mouse (A. subspinosus) of South Africa is one of the smallest, with a body up to 10 cm long and a tail of less than 2 cm. Depending upon the species, fur covering the......
  • Aconcagua, Cerro (mountain, Argentina)
    mountain in Argentina. It is commonly regarded as the highest summit in the Western Hemisphere, rising 22,834 feet (6,959 metres) above sea level. Aconcagua lies in the Southern Andes, its peak being in Mendoza province in northwestern Argentina, but its western flanks build up from the coastal lowlands of Chile, just north of Santiago. It is of volcanic origin, but it is not itself an active volc...
  • Aconcagua, Mount (mountain, Argentina)
    mountain in Argentina. It is commonly regarded as the highest summit in the Western Hemisphere, rising 22,834 feet (6,959 metres) above sea level. Aconcagua lies in the Southern Andes, its peak being in Mendoza province in northwestern Argentina, but its western flanks build up from the coastal lowlands of Chile, just north of Santiago. It is of volcanic origin, but it is not itself an active volc...
  • Aconcagua, Río (river, Chile)
    river in central Chile. It rises in the northwestern foothills of Mount Aconcagua of the Andes Mountains and flows westward from the Argentine border area to enter the Pacific Ocean north of the city of Viña del Mar after a course of 120 miles (190 km). Much of the Chilean trackage of the Transandine Railway to Mendoza, Arg., follows the river valley, as does the highway ...
  • Aconcagua River (river, Chile)
    river in central Chile. It rises in the northwestern foothills of Mount Aconcagua of the Andes Mountains and flows westward from the Argentine border area to enter the Pacific Ocean north of the city of Viña del Mar after a course of 120 miles (190 km). Much of the Chilean trackage of the Transandine Railway to Mendoza, Arg., follows the river valley, as does the highway ...
  • Aconcio, Giacomo (Italian religious reformer)
    advocate of religious toleration during the Reformation whose revolt took a more extreme form than that of Lutheranism....
  • aconitase (enzyme)
    ...to cis-aconitate in such a way that isocitrate is formed. It is probable that all three reactants—citrate, cis-aconitate, and isocitrate—remain closely associated with aconitase, the enzyme that catalyzes the isomerization process, and that most of the cis-aconitate is not released from the enzyme surface but is immediately converted to isocitrate....
  • aconitate (chemical compound)
    ...(i.e., a rearrangement of certain atoms comprising the molecule) to form isocitrate [39]. The reaction involves first the removal of the elements of water from citrate to form cis-aconitate, and then the re-addition of water to cis-aconitate in such a way that isocitrate is formed. It is probable that all three reactants—citrate, cis-aconitate, and......
  • aconite (plant common name)
    any member of two genera of perennial herbs of the buttercup family (Ranunculaceae): Aconitum, consisting of summer-flowering poisonous plants (see monkshood), and Eranthis, consisting of spring-flowering ornamentals (see winter aconite)....
  • aconitine (drug)
    A few species are cultivated in gardens, including A. henryi, A. carmichaelii, and A. uncinatum. All species contain the powerful poison aconitine. The common monkshood, or friar’s cap (A. napellus), native to mountain slopes in Europe and east to the Himalayas, has been the most important source of this drug, which in ancient times was administered to criminals ...
  • Aconitum (plant)
    any of 100 or more species of showy, poisonous, perennial herbs of the buttercup family (Ranunculaceae). They occur in the North Temperate Zone, usually in partial shade and in rich soil. The roots are thick or tuberous and the leaves have fingerlike lobes. The hood-shaped flowers, borne mostly in spikelike clusters, are usually purple or blue, sometimes yellow or white. There are five sepals and ...
  • Aconitum napellus (plant)
    A few species are cultivated in gardens, including A. henryi, A. carmichaelii, and A. uncinatum. All species contain the powerful poison aconitine. The common monkshood, or friar’s cap (A. napellus), native to mountain slopes in Europe and east to the Himalayas, has been the most important source of this drug, which in ancient times was administered to criminals ...
  • Aconquija, Sierra del (mountain range, Argentina)
    provincia (province), northwestern Argentina. The western fringe of the province is occupied by the Sierra del Aconquija, which consists of northeast-southwest-trending outlying ridges of the Andes with elevations of 8,000–18,000 feet (2,400–5,500 m). The eastern part of the province, by contrast, is flat, alluvial, and agriculturally fertile.....
  • Acontius (Greek legendary figure)
    in Greek legend, a beautiful youth of the island of Ceos. During the festival of Artemis at Delos, Acontius saw and loved Cydippe, a girl of a rich and noble family. He wrote on an apple the words “I swear to wed Acontius” and threw it at her feet. She picked it up and mechanically read the words aloud, thus binding herself by an oath. Thereafter, although she was betrothed three tim...
  • Acontius, Jacobus (Italian religious reformer)
    advocate of religious toleration during the Reformation whose revolt took a more extreme form than that of Lutheranism....
  • Aconzio, Giacomo (Italian religious reformer)
    advocate of religious toleration during the Reformation whose revolt took a more extreme form than that of Lutheranism....
  • Acorales (plant order)
    the sweet flag order of flowering plants and the most basal lineage among the monocotyledons (monocots), which are characterized by having a single seed leaf. This order contains the single family Acoraceae and one genus (Acorus), which comprises two to four species of plants that resemble the irises....
  • Açores, Arquipélago dos (archipelago, Portugal)
    archipelago composed of nine major islands, in the North Atlantic Ocean; they lie roughly 1,000 miles (1,600 km) west of Portugal and are an autonomous part of that country. The islands are divided into three widely separated groups: the eastern group, consisting of São Miguel, Santa Maria, and the Formigas islets; ...
  • acorn (fruit)
    Acorns provide food for small game animals and are used to fatten swine and poultry. Red- and white-oak lumber is used in construction, flooring, furniture, millwork, cooperage, and the production of crossties, structural timbers, and mine props....
  • acorn and nut weevil (insect subfamily)
    any of approximately 45 species of weevils in the family Curculionidae (order Coleoptera) that have extremely long and slender snouts, which in females can be almost twice the length of the body. The mandibles are located at the tip of the snout. Eggs are deposited in holes chewed in a nut. These weevils are common in both Europe and North America. Different species prefer certain nuts: Curculi...
  • acorn barnacle (crustacean)
    ...six pairs of cirri and more or less complete shells. Pedunculate (stalked) forms include the common goose barnacle (genus Lepas), found worldwide on driftwood. Acorn barnacles, also called rock barnacles, are sessile (not stalked); their symmetrical shells tend to be barrellike or broadly conical. This group includes Balanus, responsible for much of the fouling of ships......
  • acorn shell (crustacean)
    ...six pairs of cirri and more or less complete shells. Pedunculate (stalked) forms include the common goose barnacle (genus Lepas), found worldwide on driftwood. Acorn barnacles, also called rock barnacles, are sessile (not stalked); their symmetrical shells tend to be barrellike or broadly conical. This group includes Balanus, responsible for much of the fouling of ships......
  • acorn weevil (insect)
    any of approximately 45 species of weevils in the family Curculionidae (order Coleoptera) that have extremely long and slender snouts, which in females can be almost twice the length of the body. The mandibles are located at the tip of the snout. Eggs are deposited in holes chewed in a nut. These weevils are common in both Europe and North America. Different species prefer certain nuts:......
  • acorn woodpecker (bird)
    The acorn woodpecker (M. formicivorus) is about 20 cm (8 inches) long and is found from the deciduous woodlands of western North America south to Colombia. It depends on acorns for winter food, storing a supply in holes it drills in the bark of trees. The red-headed woodpecker (M. erythrocephalus) is roughly the same size (19–23 cm.....
  • acorn worm (hemichordate)
    any of the soft-bodied invertebrates of the class Enteropneusta, phylum Hemichordata. The front end of these animals is shaped like an acorn, hence their common name. The “acorn” consists of a muscular proboscis and a collar that may be used to burrow into soft sand or mud. The animals vary in length from about 5 cm (about 2 inches) in certain Saccoglossus species to more than...
  • acornworm (hemichordate)
    any of the soft-bodied invertebrates of the class Enteropneusta, phylum Hemichordata. The front end of these animals is shaped like an acorn, hence their common name. The “acorn” consists of a muscular proboscis and a collar that may be used to burrow into soft sand or mud. The animals vary in length from about 5 cm (about 2 inches) in certain Saccoglossus species to more than...
  • Acorus (plant genus)
    ...plants and the most basal lineage among the monocotyledons (monocots), which are characterized by having a single seed leaf. This order contains the single family Acoraceae and one genus (Acorus), which comprises two to four species of plants that resemble the irises....
  • Acorus calamus (plant)
    Acorus calamus (sweet flag) occurs in the wetlands of North America and from India to Indonesia. Other species are distributed in temperate areas in Asia and Europe, where they are often found at pond margins or along fast-moving streams....
  • acosmism (philosophy)
    in philosophy, the view that God is the sole and ultimate reality and that finite objects and events have no independent existence. Acosmism has been equated with pantheism, the belief that everything is God. G.W.F. Hegel coined the word to defend Benedict de Spinoza, who was accused of atheism for rejecting the traditional view of a created world existing outside God. Hegel ar...
  • Acosta, Joaquín (Colombian scientist)
    Colombian scientist, historian, and statesman who sought to preserve knowledge of his country’s early history....
  • Acosta, José de (Spanish theologian)
    Jesuit theologian and missionary to the New World, chiefly known for his Historia natural y moral de las Indias, the earliest survey of the New World and its relation to the Old. His works, missionary and literary, mark the end of the period of the religious and scientific incorporation of the newly discovered lands into Western culture....
  • Acosta, Uriel (Jewish philosopher)
    freethinking rationalist who became an example among Jews of one martyred by the intolerance of his own religious community. He is sometimes cited as a forerunner of the renowned philosopher Benedict de Spinoza....
  • acouchi (rodent)
    either of two species of South American rodents that resemble the small tropical-forest-dwelling hoofed animals of Africa and Asia (see royal antelope; chevrotain). Weighing 1 to 1.5 kg (2.2 to 3.3 pounds), acouchys are 30 to 39 cm (12 to 15 inches) long, with a very short (4 to 8 cm), pencil-thin tail with white hairs on ...
  • acouchy (rodent)
    either of two species of South American rodents that resemble the small tropical-forest-dwelling hoofed animals of Africa and Asia (see royal antelope; chevrotain). Weighing 1 to 1.5 kg (2.2 to 3.3 pounds), acouchys are 30 to 39 cm (12 to 15 inches) long, with a very short (4 to 8 cm), pencil-thin tail with white hairs on ...
  • acousmatics (Pythagorean sect)
    ...“something heard,” viz., the esoteric teachings) and mathēmatikoi (Greek: mathēmatikos, “scientific”), may have occurred at that time. The acousmatics devoted themselves to the observance of rituals and rules and to the interpretation of the sayings of the master; the “mathematics” were concerned with the scientific aspects.....
  • acoustic absorption (physics)
    In addition to the geometric decrease in intensity caused by the inverse square law, a small part of a sound wave is lost to the air or other medium through various physical processes. One important process is the direct conduction of the vibration into the medium as heat, caused by the conversion of the coherent molecular motion of the sound wave into incoherent molecular motion in the air or......
  • acoustic bridge (sound instrument)
    ...an actual measurement of the acoustic impedance of the ear, representing the state of the ossicular chain and the mobility of the tympanic membrane. This information can be obtained by means of the acoustic bridge—a device that enables the examiner to listen simultaneously to a sound reflected from the tympanic membrane of the subject and a sound of equal intensity reflected in an......
  • acoustic communication system (device)
    ...the target (such as a ship, submarine, or torpedo). Waveforms thus detected may be analyzed for identifying characteristics as well as direction and distance. The third category of sonar devices is acoustic communication systems, which require a projector and receiver at both ends of the acoustic path....
  • acoustic emission (acoustics)
    Structural flaws in materials can also be studied by subjecting the materials to stress and looking for acoustic emissions as the materials are stressed. Acoustic emission, the general name for this type of nondestructive study, has developed as a distinct field of acoustics....
  • acoustic filtration (acoustics)
    Filtration of sound plays an important part in the design of air-handling systems. In order to attenuate the level of sound from blower motors and other sources of vibration, regions of larger or smaller cross-sectional area are inserted into air ducts, as illustrated in Figure 3. The impedance mismatch introduced into a duct by a change in the area of the duct or by the addition of a side......
  • acoustic gas meter
    Acoustic gas meters measure the rate of gas flow by comparing the frequency shifts of two initially identical signals (one sent upstream, the other downstream) after they are reflected....
  • acoustic guitar (musical instrument)
    plucked stringed musical instrument that probably originated in Spain early in the 16th century, deriving from the guitarra latina, a late-medieval instrument with a waisted body and four strings. The early guitar was narrower and deeper than the modern guitar, with a less pronounced waist. It was closely related to the vihuela,...
  • acoustic impedance (physics)
    absorption of sound in a medium, equal to the ratio of the sound pressure at a boundary surface to the sound flux (flow velocity of the particles or volume velocity, times area) through the surface. In analogy to electrical circuit theory, pressure corresponds to voltage, volume velocity to current, and acoustic impedance is expressed as a complex number, the real part being referred to as the re...
  • acoustic intensity (physics)
    amount of energy flowing per unit time through a unit area that is perpendicular to the direction in which the sound waves are travelling. Sound intensity may be measured in units of energy or work—e.g., microjoules (10-6 joule) per second per square centimetre—or in units of power, as microwatts (10-6 watt) per square centimetre. Unlike loudness, sound ...
  • acoustic interferometer (instrument)
    device for measuring the velocity and absorption of sound waves in a gas or liquid. A vibrating crystal creates the waves that are radiated continuously into the fluid medium, striking a movable reflector placed accurately parallel to the crystal source. The waves are then reflected back to the source. The strength of the standing wave pattern set up between the source and the reflector as the di...
  • acoustic maculae (ear anatomy)
    ...as the otolith organs (Figure 4). Because they respond to gravitational forces, they are also called gravity receptors. Each sac has on its inner surface a single patch of sensory cells called a macula, which is about 2 millimetres (0.08 inch) in diameter and which monitors the position of the head relative to the vertical (see The physiology of balance: vestibular function: Detection of......
  • acoustic meatus, external (anatomy)
    passageway that leads from the outside of the head to the tympanic membrane, or eardrum membrane, of each ear. The structure of the external auditory canal is the same in all mammals. In appearance it is a slightly curved tube that extends inward from the floor of the auricle, or protruding portion of the outer ear, and ends blindly at the eardrum membrane, which separates it fr...
  • acoustic microscope (instrument)
    In the early 1940s Soviet physicist Sergei Y. Sokolov proposed the use of ultrasound in a microscope and showed that sound waves with a frequency of 3,000 megahertz (MHz) would have a resolution equal to that of the optical microscope. However, at that time the required technology did not exist. Since then the technology has been developed, and the high frequencies required for Sokolov’s......
  • acoustic mine (submarine mine)
    ...circuit in the other chamber to explode the mine. The pressure mine reacts only to a pressure change produced by a ship larger than a minesweeper (q.v.), thus making it difficult to clear. Acoustic mines once depended on hydrophones to pick up the sound made by a ship’s propellers when the ship came within range. They had limited lifetimes owing to deterioration of their component...
  • acoustic nerve (anatomy)
    nerve in the human ear, serving the organs of equilibrium and of hearing. It consists of two anatomically and functionally distinct parts: the cochlear nerve, distributed to the hearing organ, and the vestibular nerve, distributed to the organ of equilibrium....
  • acoustic neuroma (pathology)
    benign tumour on the vestibulocochlear nerve (also called acoustic nerve) near its point of entry into the inner ear. The tumour, though benign, may spread into the brain cavity if not detected in its first stages. Early symptoms include mild unilateral hearing impairment, tinnitus (ringing in the ear), and sometimes dizziness. If the tumour has extended into the brain cavity, headache and paraly...
  • acoustic ohm (unit of measurement)
    The unit of specific acoustic impedance is the pascal second per metre, often called the rayl, after Lord Rayleigh. The unit of acoustic impedance is the pascal second per cubic metre, called an acoustic ohm, by analogy to electrical impedance....
  • acoustic scansion (prosody)
    ...eighth notes for unstressed syllables, quarter or half notes for stressed syllables, and musical rests for pauses) record accentual differences. Machines such as the oscillograph are used by modern acoustic linguists to catch even slightly varying degrees of stress. ...
  • acoustic sensillum (animal anatomy)
    ...thousands of axons. Another example is the ear of a noctuid moth. Each ear is essentially a tympanic membrane forming the outer wall of an air-filled cavity in the thorax. A five-tissue strand, the acoustic sensillum, runs from the centre of the tympanic membrane across the tympanic cavity to a nearby skeletal support. This sensillum has two acoustic sensory receptors, called A cells. From the....
  • acoustic suspension system (sound)
    ...horn, or other enclosure in order to separate the waves from the front and the rear of the loudspeaker and thereby prevent them from canceling each other. The most common type of enclosure is the acoustic suspension system, in which the loudspeaker is mounted in an airtight box. To prevent resonances in the box of the type described by equation (36) in the article sound, the inside is......
  • acoustic transducer (instrument)
    any type of device that either converts an electrical signal into sound waves (as in a loudspeaker) or converts a sound wave into an electrical signal (as in the microphone). Many of the transducers used in everyday life operate in both directions, such as the speakerphone on certain intercoms....
  • acoustic trauma (physiology)
    physiological changes in the body caused by sound waves. Sound waves cause variations in pressure, the intensity of which depends upon the range of oscillation, the force exerting the sound, and the distribution of waves....
  • acoustical engineering
    Much recent study has centred on the problem of acoustics in the ancient theatre. The difficulty in achieving audibility to an audience of thousands, disposed around three-fifths to two-thirds of a full circular orchestra in the open air, seems to have been insoluble so long as the performer remained in the orchestra. A more direct path between speaker and audience was therefore essential if......
  • acoustical horn (acoustics)
    A horn enclosure uses a flared tube to obtain the best acoustic coupling between the loudspeaker cone and the outside, thereby radiating the best possible coherent wave from the speaker cone. Such a system is extremely efficient and is therefore used in public-address systems, open-air theatres, or other places in which great acoustic power is desired. Because a good quality bass horn enclosure......
  • acoustical shadow (physics)
    Acoustic shadows, regions in which some frequency regions of sound are attenuated, can be caused by diffraction effects as the sound wave passes around large pillars and corners or underneath a low balcony. Large reflectors called clouds, suspended over the performers, can be of such a size as to reflect certain frequency regions while allowing others to pass, thus affecting the mixture of the......
  • acoustico-lateralis system (anatomy)
    ...(the labyrinth) arise. The common embryologic origin and structural similarities of mature neuromasts and labyrinthine cell groups have led to the designation of all of these organs as the acoustico-lateralis system. The nerves to all the sense organs of the system arise from a common neural centre (called the acoustic tubercle in the wall of the brain’s medulla oblongata). Among such......
  • acoustics (physics)
    the science concerned with the production, control, transmission, reception, and effects of sound. The term is derived from the Greek akoustos, meaning “hearing.”...
  • acoustics, architectural
    Architectural acoustics...
  • ACP (chemical compound)
    Malonyl coenzyme A and a molecule of acetyl coenzyme A react (in bacteria) with the sulfhydryl group of a relatively small molecule known as acyl-carrier protein (ACP–SH); in higher organisms ACP–SH is part of a multienzyme complex called fatty acid synthetase. ACP–SH is involved in all of the reactions leading to the synthesis of a fatty acid such as palmitic acid from acetyl...
  • ACP-SH (chemical compound)
    Malonyl coenzyme A and a molecule of acetyl coenzyme A react (in bacteria) with the sulfhydryl group of a relatively small molecule known as acyl-carrier protein (ACP–SH); in higher organisms ACP–SH is part of a multienzyme complex called fatty acid synthetase. ACP–SH is involved in all of the reactions leading to the synthesis of a fatty acid such as palmitic acid from acetyl...
  • Acquackanonk (New Jersey, United States)
    city, Passaic county, northeastern New Jersey, U.S., on the Passaic River, 9 miles (14 km) north of Newark. It was established by the Dutch in 1678 as a fur-trading post. In 1685 Hartman Michielson purchased the site, then called Acquackanonk, from the Delaware Indians. It was renamed for the Passaic River in 1854. During ...
  • Acquainted with Grief (work by Gadda)
    Gadda’s La cognizione del dolore (1963, revised 1970; Acquainted with Grief) is autobiographical, though its setting is transferred from modern Italy to an invented South American country....
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