683 résultats pour "used"

• Pottery I INTRODUCTION Pottery, clay that is chemically altered and permanently hardened by firing in a kiln.

  basket, or a clay or plaster form. Liquid clay can be poured into plaster molds. A pot can be coil built: Clay is rolled between the palms of the hands and extended intolong coils, a coil is formed into a ring, and the pot is built up by superimposing rings. Also, a ball of clay can be pinched into the desired shape. The most sophisticatedpottery-making technique is wheel throwing. The potter's wheel, invented in the 4th millennium BC, is a flat disk that revolves horizontally on a pivot. Both...

• Hazardous Wastes.

  A Source Reduction The best way to eliminate hazardous wastes is not to generate them in the first place. For example, improvements have been made in the production of integratedcircuits: The toxic chlorinated hydrocarbons commonly used in the 1970s were replaced in the 1980s by less toxic glycol ethers and in the 1990s by low-toxicity estersand alcohols. B Recycling Recycling is the recovery or reuse of usable materials from waste. About 5 percent of hazardous waste in the United States is re...

• Computer Memory.

  been created, information can be retrieved but not changed. Newer technologies allow ROMs to be semi-permanent—that is, the information can be changed, but ittakes several seconds to make the change. For example, a FLASH memory acts like a ROM because values remain stored in memory, but the values can be changed. C External Memory External memory can generally be classified as either magnetic or optical, or a combination called magneto-optical. A magnetic storage device, such as a computer'shar...

• Animation I INTRODUCTION Finding Nemo A clown fish named Marlin, left, and his friend Dory search for Marlin's son in the computer-animated feature film Finding Nemo (2003).

  Animator at WorkAnimators use computers for every part of the animation process, from creating a storyboard (a scene-by-sceneillustration of the plot) to imitating camera movement. This animator is creating a scene for the motion picture Antz(1998).C. Lepetit/Liaison Agency If an animator is basing the animation project on drawings, one of the most common animation techniques, he or she will first create a series of rough sketches thatoften will be filmed in a pencil test (simple line drawings...

• Algebra I INTRODUCTION Algebra, branch of mathematics in which symbols (usually letters) represent unknown numbers in mathematical equations.

  B Order of Operations and Grouping Algebra relies on an established sequence for performing arithmetic operations. This ensures that everyone who executes a string of operations arrives at the sameanswer. Multiplication is performed first, then division, followed by addition, then subtraction. For example: 1 + 2 · 3 equals 7 because 2 and 3 are multiplied first and then added to 1. Exponents and roots have even higher priority than multiplication: 3 · 2 2 = 3 · 4 = 12 Grouping symbols override...

• Birth Control.

  without a prescription and used alone or with a condom, diaphragm, or cervical cap. Spermicides used alone must be inserted deep into the vagina before each act ofintercourse and a woman should not douche for six to eight hours after intercourse. With typical use, spermicides used alone are effective in preventing pregnancyabout 74 percent of the time. They may cause an allergic reaction such as irritation of the vagina or penis. B Intrauterine Device The intrauterine device (IUD) is a small pl...

• Space Shuttle - astronomy.

  The two SRBs, with their combined thrust of some 26 million newtons (about 5.8 million lb), provide most of the power for the first two minutes of flight. The SRBs takethe space shuttle to an altitude of 45 km (28 mi) and a speed of 4,973 km/h (3,094 mph) before they separate and fall back into the ocean to be retrieved,refurbished, and prepared for another flight. After the boosters fall away, the three main engines continue to provide thrust. These engines are clustered at the rear end of the...

• Cloning - biology.

  found that such embryo cells are totipotent (able to give rise to all the different cell types in the body). Exploiting this characteristic, scientists developed three techniques to clone embryo cells: blastomere separation, blastocyst division, and somatic cell nuclear transfer. A Blastomere Separation In blastomere separation, scientists fertilize an egg cell with a sperm cell in a laboratory dish. The resulting embryo is allowed to divide until it forms a mass of aboutfour cells. Scientist...

• Parkinson Disease.

  III SYMPTOMS Parkinson disease most notably affects motor control (muscle activity). The disease progresses differently for each individual—symptoms develop swiftly in some peopleand slowly in others. Some Parkinson patients may develop problems that affect their intellect or ability to reason, or they may suffer from depression or anxiety. A Motor Control Problems Doctors look for the presence of four principal symptoms in patients they suspect may have Parkinson disease. Tremor (the involun...

• Intelligence.

  education. Teachers had no way of knowing which of the “slow” students had true learning problems and which simply had behavioral problems or poor prior education.In 1904 the French Ministry of Public Instruction asked Binet and others to develop a method to objectively identify children who would have difficulty with formaleducation. Objectivity was important so that conclusions about a child’s potential for learning would not be influenced by any biases of the examiner. The governmenthoped tha...

• Aztec Empire.

  tribute to the empire in agricultural products, which were used to finance public projects. All able-bodied men owed military service to the empire. Citizens could also bedrafted to work on public lands or build temples, dikes, aqueducts, and roads. Although Aztec society had strict classes, a person’s status could change based on his or her contribution to society. Commoners could improve their rank, especially byperforming well in battle, and become prosperous landowners. Young people of some...

• Aztec Empire - USA History.

  tribute to the empire in agricultural products, which were used to finance public projects. All able-bodied men owed military service to the empire. Citizens could also bedrafted to work on public lands or build temples, dikes, aqueducts, and roads. Although Aztec society had strict classes, a person’s status could change based on his or her contribution to society. Commoners could improve their rank, especially byperforming well in battle, and become prosperous landowners. Young people of some...

• Fossil Fuels.

  water molecules. This crystalline solid is known as gas hydrate. Because technology for the commercial extraction of gas hydrates has not yet been developed, this typeof fossil fuel is not included in most world energy resource estimates. However, in February 2007 the U.S. Department of Energy completed the drilling of a well toretrieve core samples of gas hydrates found in the Prudhoe Bay region of Alaska’s North Slope. By identifying the nature of these gas hydrates, the Energy Departmenthoped...

• Pyramids (Egypt) - geography.

  limestone debris left over from the construction work. When the workers had completed the pyramid and installed the pyramidion, or cap stone, ramps still covered the surface of the pyramid. As the workers dismantled the ramps from the top down, they slowly exposed the pyramid’s stone surface, which stonemasons smoothed and polished. When the ramp was gone, the pyramid wasdisplayed in its full majesty. B Interior The interior of the Great Pyramid is complex, with a series of passages leading t...

• Pyramids (Egypt) - History.

  limestone debris left over from the construction work. When the workers had completed the pyramid and installed the pyramidion, or cap stone, ramps still covered the surface of the pyramid. As the workers dismantled the ramps from the top down, they slowly exposed the pyramid’s stone surface, which stonemasons smoothed and polished. When the ramp was gone, the pyramid wasdisplayed in its full majesty. B Interior The interior of the Great Pyramid is complex, with a series of passages leading t...

• Turbine.

  steam turbine has supplanted the reciprocating engine as a prime mover in large electricity-generating plants and is also used as a means of jet propulsion. Steam turbines are used in the generation of nuclear power and in nuclear ship propulsion. They operate with fuel-fired boilers for power generation. In cogenerationapplications requiring both process heat (heat used in an industrial process) and electricity, steam is raised at high pressure in the boiler and extracted from the turbineat th...

• Classification - biology.

  species based on the fewest number of shared changes that have occurred from generation to generation. IV HISTORY OF CLASSIFICATION SYSTEMS Classification is one of the oldest sciences, but despite its age it is still a vigorous field full of new discoveries and methods. Much like other fields of science, greatthinkers have shaped the course of classification. One of the earliest classification schemes was established by Greek philosopher Aristotle, who lived in the 300s BC. Aristotle believe...

• Neandertals.

  Neandertals made stone tools by striking flakes from rock “cores.” The cores were carefully selected and prepared so that only a single blow was normally required todetach a flake. A number of relatively standardized flakes were sometimes produced from a single core. These sharp flakes served as “blanks” that were further workedand shaped into the desired tools. Suitable stone was sometimes rare, and often tools were sharpened and resharpened to make new tools, yielding a whole variety ofshapes...

• Central Processing Unit.

  Development of the computer chip started in 1958 when Jack Kilby of Texas Instruments demonstrated that it was possible to integrate the various components of aCPU onto a single piece of silicon. These computer chips were called integrated circuits (ICs) because they combined multiple electronic circuits on the same chip.Subsequent design and manufacturing advances allowed transistor densities on integrated circuits to increase tremendously. The first ICs had only tens of transistorsper chip com...

• Deoxyribonucleic Acid - biology.

  bacterium Escherichia coli . In 1998 scientists achieved the milestone of sequencing the complete genome of a multicellular organism—a roundworm identified as Caenorhabditis elegans . The Human Genome Project, an international research collaboration, was established to determine the sequence of all of the 3 billion nucleotide base pairs that make up thehuman genetic material. In 2003 scientists completed the sequencing of the human genome. The project identified nearly all of the estimated 20...

• Programming Language.

  Logic languages use logic as their mathematical base. A logic program consists of sets of facts and if-then rules, which specify how one set of facts may be deducedfrom others, for example: If the statement X is true, then the statement Y is false. In the execution of such a program, an input statement can be logically deduced from other statements in the program. Many artificial intelligence programs are writtenin such languages. IV LANGUAGE STRUCTURE AND COMPONENTS Programming languages use...

• Map - Geography.

  Often only southeast slopes are hachured or shaded, giving somewhat the effect of a bird's-eye view of the area illuminated by light from the northwest. Shadings orcarefully drawn hachures, neither of which give elevations, are more easily interpreted than contour lines and are sometimes used in conjunction with them for greaterclarity. IV MAP PROJECTIONS For the representation of the entire surface of the earth without any kind of distortion, a map must have a spherical surface; a map of this...

• Radio.

  signal, such as a musical note. This form of modulation, AM, is used in many radiotelephony services including standard radiobroadcasts. AM is also employed for carriercurrent telephony, in which the modulated carrier is transmitted by wire, and in the transmission of still pictures by wire or radio. See Broadcasting, Radio and Television. In FM the frequency of the carrier wave is varied within a fixed range at a rate corresponding to the frequency of a sound signal. This form of modulation, p...

• Wireless Communications.

  were large, heavy units. After the invention of the transistor in 1948, radios shrank in size to small handheld radio transceivers. Public two-way radios with severalfrequency options are widely available as well. Usually limited in range to a few miles, these units are great aids for such mobile professionals as construction workers,film crews, event planners, and security personnel. Simpler two-way radios, called walkie-talkies, have been popular children’s toys for years. Most walkie-talkiesb...

• Prints and Printmaking I INTRODUCTION Prints and Printmaking, pictorial images that can be inked onto paper, and the art of creating and reproducing them.

  Bewick’s The SkylarkBritish engraver Thomas Bewick’s The Skylark is part of his History of British Birds (2 vols., 1797 and 1804). Bewick wasthe first artist to demonstrate the full potential of wood engraving and is renowned for his fine natural history illustrations.Each illustration shows some of the bird’s natural habitat.Folio Society, London/Bridgeman Art Library, London/New York Historically, the wood engraving was chiefly used for illustrations in magazines and books. It is similar to th...

• Heat (physics) I INTRODUCTION Heat Loss from a House A thermograph shows the large amount of heat lost through a house's windows during winter.

  Theoretically, the molecules of a substance would exhibit no activity at the temperature termed absolute zero. See Molecule. III TEMPERATURE SCALES Five different temperature scales are in use today: the Celsius scale, known also as the Centigrade scale, the Fahrenheit scale, the Kelvin scale, the Rankine scale, andthe international thermodynamic temperature scale ( see Thermometer). The Celsius scale, with a freezing point of 0° C and a boiling point of 100° C, is widely used throughout the...

• Telephone.

  digits is dialed. The development of inexpensive and reliable amplification provided by the introduction of the transistor in the 1960s made practical the design of adialing system based on the transmission of relatively low power tones instead of the higher-power dial pulses. Today most telephones have push buttons instead of a rotary dial. Touch-Tone is an optional service, and telephone companies still maintain the ability to receive pulsedialing. Push-button telephones usually have a switch...

• Railroads.

  III GAUGES The gauge of track is the distance between the inner edges of the rails at points 1.59 cm (0.626 in) below the top of the heads. In the United States, Canada, theUnited Kingdom, Mexico, Norway, Sweden, and much of continental Europe, the standard gauge is 143.51 cm (56.5 in). Why this measurement became the standard isa matter of speculation. Probably the tradition is inherited from early tramroads built to accommodate wagons with axles 1.5 m (5 ft) long; some of the early edge rail...

• Native American Languages.

  From Nahuatl, spoken in Middle America, come avocado, cacao, cocoa, chile/chili, chocolate, coyote, tamale , tomato , and many others. Contributions from South American languages include jaguar, cashew, tapioca, and toucan from Tupinambá; alpaca, condor, jerky, llama, puma, and quinine from Quechua; and barbecue, canoe, guava, hammock, hurricane, iguana, maize, papaya, and potato from Maipurean (Arawakan). Native American languages, in turn, have borrowed words from European language...

• History of Chemistry - chemistry.

  even better distillation apparatus than the Arabs had made and to condense the more volatile products of distillation. Among the important products obtained in thisway were alcohol and the mineral acids: nitric, aqua regia (a mixture of nitric and hydrochloric), sulfuric, and hydrochloric. Many new reactions could be carried outusing these powerful reagents. Word of the Chinese discovery of nitrates and the manufacture of gunpowder also came to the West through the Arabs. The Chinese atfirst use...

• History of Astronomy - astronomy.

  Egypt, the Sun was directly overhead at noon. On the same date and time in Alexandria, Egypt, the Sun was about 7 degrees south of zenith. With simple geometryand knowledge of the distance between the two cities, he estimated the circumference of the Earth to be 250,000 stadia. (The stadium was a unit of length, derivedfrom the length of the racetrack in an ancient Greek stadium. We have an approximate idea of how big an ancient Greek stadium was, and based on that approximationEratosthenes was...

• World Wide Web.

  browser does not display the URL for the user. Instead, to indicate that an item is selectable, the browser changes the color of the item on the screen and keeps theURL associated with the link hidden. When a user clicks on an item that corresponds to a selectable link, the browser consults the hidden information to find theappropriate URL, which the browser then follows to the selected page. Because a link can point to any page in the Web, the links are known as hyperlinks. See also Hypermedia...

• Technology.

  loose soil in this region, known as the Fertile Crescent, was easily scratched for planting, and an abundance of trees was available for firewood. By 5000 BC, farming communities were established in areas known today as Syria, Turkey, Lebanon, Israel, Jordan, Greece, and the islands of Crete and Cyprus. Agricultural societies in these places constructed stone buildings, used the sickle to harvest grain, developed a primitive plowstick, and advanced their skills inmetalworking. Trade in flint al...

• World War I .

  and troops to Europe from the United States and other overseas sources. In 1914 Britain implemented a sea blockade of Germany to prevent the delivery of importssuch as food and war materials. The same year, Germany began using submarines to disrupt Allied seaborne traffic and prevent supplies from reaching Britain. In 1915Germany instituted a submarine blockade around Britain. From February 1915 to September 1915 and again in 1917, Germany used unrestricted submarine warfare,sinking ships withou...

• Hawaii (state) - geography.

  limestone along the coast. The volcanoes of the Hawaiian Islands are all so-called shield volcanoes, or lava domes. Unlike the volcanoes of Alaska and South America, those of Hawaii were notcreated by very explosive eruptions. Formed mostly by lava flows, they are great rounded mountain masses, rather than steep-sided cones. Mauna Kea, dormant forcenturies, is the highest mountain in the state. It rises to 4,205 m (13,796 ft) above sea level, and its summit is dotted with cinder cones formed by...

• Hawaii (state) - USA History.

  limestone along the coast. The volcanoes of the Hawaiian Islands are all so-called shield volcanoes, or lava domes. Unlike the volcanoes of Alaska and South America, those of Hawaii were notcreated by very explosive eruptions. Formed mostly by lava flows, they are great rounded mountain masses, rather than steep-sided cones. Mauna Kea, dormant forcenturies, is the highest mountain in the state. It rises to 4,205 m (13,796 ft) above sea level, and its summit is dotted with cinder cones formed by...

• Leukemia.

  leukemia, and normal or mildly decreased in chronic lymphocytic leukemia. Nearly all chronic leukemia patients have increased white cell counts. In chronic myelocyticleukemia, some of these leukemic white cells are capable of functioning as normal cells do by fighting infectious microbes. Hence, infection is no more common than in ahealthy individual. In chronic lymphocytic leukemia the blood contains large numbers of malignant lymphocytes that do not function normally. Normal lymphocytescoexist...

• Uganda - country.

  Uganda’s population is predominantly rural and is concentrated in the south, particularly in the crescent at the edge of Lake Victoria and in the southwest. Almost allUgandans are black Africans. Foreign residents make up less than 4 percent of the population and come mostly from neighboring states. In 2008 Uganda’s population was estimated at 31,367,972. The estimated growth rate of the population in 2008 was 3.6 percent. The birth rate was 48 per 1,000people and the death rate 12 per 1,000. Th...

• Electronic Games.

  arcade game of all time. With Pizza Time Theaters legitimizing the idea of arcades and hits such as Ms. Pac-Man , Asteroids , Donkey Kong , Tempest , Frogger , and Defender bringing new excitement to gaming, the coin-operated video game business boomed. In 1981 Americans spent 75,000 person-years and $5 billion playing video games at anestimated 4,300 arcades in the United States. Many popular arcade games also were translated for use on the Atari 2600 and its chief rivals in the homemarket—M...

• Ballet I INTRODUCTION Tchaikovsky's The Nutcracker The Nutcracker is a classic ballet with music by Peter Ilyich Tchaikovsky.

  Joffrey Ballet SchoolTraining for classical ballet dancers must begin when the students are very young. Here, teacher Dorothy Lister workswith her pre-ballet class of six-year-olds at the Joffrey Ballet School. These students are learning the five basic positions ofclassical ballet.Susan Kunklin/Photo Researchers, Inc. Different systems of ballet training have evolved, named after countries (Russia, France) or teachers (Italian dancer Enrico Cecchetti, Danish choreographer AugustBournonville). T...

• Aksum.

  doctrine that Christ was both divine and human. The Council of Chalcedon condemned Monophysitism in 451, and since that time the Coptic Church has beenindependent of other Christian churches. After the Council of Chalcedon, priests who continued to teach Monophysitism were persecuted in the eastern Roman Empire, and many migrated to Aksum. The influxof priests, along with the support of the royal family, strengthened missionary efforts in Aksum. Many churches and monasteries were founded after 4...

• Rap I INTRODUCTION Jay-Z Rapper Jay-Z rose to popularity with such albums as Vol.

  Run-DMCTypically in rap music, vocalists recite rhyming lyrics in time to a beat that may be sampled from prerecorded music byother groups. Black youths developed rap music on the streets of inner cities in the United States during the 1970s, butthe style has expanded to include a wider variety of performers and audiences. The rap group Run-DMC, shown here, wasa powerful early influence in the genre. The group helped bring rap music into the mainstream when it released “WalkThis Way” (1986), a s...

• Helicopter.

  naturally flaps down so as to increase lift. Flapping allows the differences in lift caused by uneven rotor tip speed to cancel out, producing a stable ride. Many helicoptersuse mechanical hinges with lubricated bearings, but some use flexible straps made of a composite material in order to reduce the required maintenance. Helicopters require different amounts of lift and thrust at different times during flight, because the aerodynamic forces acting on them change during hovering andacceleration...

• Chemical Analysis - chemistry.

  inorganic reactions than by organic functional group chemistry. VII SPECTROSCOPIC TECHNIQUES Spectroscopy, or the study of the interactions of electromagnetic radiation with matter, is the largest and most nearly accurate class of instrumental methods used inchemical analysis and indeed in all of chemistry ( see Spectroscopy; Spectrum). The electromagnetic radiation (emr) spectrum is divided into the following wavelength regions: X ray, ultraviolet, visible, infrared, microwave, and radiowave....

• Persian Gulf War.

  to “use all necessary means” to force Iraq from Kuwait if Iraq remained in the country after January 15, 1991. The Iraqis rejected the ultimatum. Soon after the vote,the United States agreed to a direct meeting between Secretary of State James Baker and Iraq’s foreign minister. The two sides met on January 9. Neither offered tocompromise. The United States underscored the ultimatum, and the Iraqis refused to comply with it, even threatening to attack Israel. For the United States, themeeting was...

• Persian Gulf War - History.

  to “use all necessary means” to force Iraq from Kuwait if Iraq remained in the country after January 15, 1991. The Iraqis rejected the ultimatum. Soon after the vote,the United States agreed to a direct meeting between Secretary of State James Baker and Iraq’s foreign minister. The two sides met on January 9. Neither offered tocompromise. The United States underscored the ultimatum, and the Iraqis refused to comply with it, even threatening to attack Israel. For the United States, themeeting was...

• Persian Gulf War - U.

  to “use all necessary means” to force Iraq from Kuwait if Iraq remained in the country after January 15, 1991. The Iraqis rejected the ultimatum. Soon after the vote,the United States agreed to a direct meeting between Secretary of State James Baker and Iraq’s foreign minister. The two sides met on January 9. Neither offered tocompromise. The United States underscored the ultimatum, and the Iraqis refused to comply with it, even threatening to attack Israel. For the United States, themeeting was...

• Uzbekistan - country.

  E Environmental Issues The evaporation of the Aral Sea is one of the worst ecological disasters in the world. The Aral has shrunk so much that it now holds only about one-fifth the volume ofwater it held in 1960. The shrinkage is due to irrigation withdrawals from the Amu Darya and Syr Darya, a practice that began on a massive scale in the early 1960s aspart of the Soviet Union’s ill-conceived drive to increase cotton yields in Central Asia. Growing cotton in the naturally arid and saline soil...

• Stonehenge - History.

  In 2006 excavations at Durrington Walls, about 3 km (less than 2 mi) from Stonehenge, uncovered a large settlement dating to 2600 or 2500 BC. The settlement consisted of wooden structures laid out in the same pattern as Stonehenge and, according to the archaeologists who conducted the excavations, probably housed theworkers who built Stonehenge. However, the remains of large amounts of pottery and animal bones found at the site suggest that it was a place of feasting, which maymean that it hous...

• Stonehenge.

  A Recent Excavations In 2006 excavations at Durrington Walls, about 3 km (less than 2 mi) from Stonehenge, uncovered a large settlement dating to 2600 or 2500 BC. The settlement consisted of wooden structures laid out in the same pattern as Stonehenge and, according to the archaeologists who conducted the excavations, probably housed theworkers who built Stonehenge. However, the remains of large amounts of pottery and animal bones found at the site suggest that it was a place of feasting, whic...