683 résultats pour "used"

• Microprocessor.

  thin layer of oxide about 75 angstroms deep (an angstrom is one ten-billionth of a meter). Nearly every layer that is deposited on the wafer must be patterned accurately into the shape of the transistors and other electronic elements. Usually this is done in aprocess known as photolithography, which is analogous to transforming the wafer into a piece of photographic film and projecting a picture of the circuit on it. A coatingon the surface of the wafer, called the photoresist or resist, changes...

• Cotton - biology.

  VII COTTONSEED Once a waste-disposal problem for gins, cottonseed is now a valuable by-product. The seed goes to oil mills, where it is delinted of its linters in an operation similar toginning. The bare seed is then cracked and the kernel removed. The meal that remains after the oil has been extracted is high in protein. Linters are used for paddingin furniture and automobiles, for absorbent cotton swabs, and for manufacture of many cellulose products such as rayon, plastics, lacquers, and sm...

• Statistics I INTRODUCTION Statistics, branch of mathematics that deals with the collection, organization, and analysis of numerical data and with such problems as experiment design and decision making.

  Professional pollsters typically conduct their surveys among sample populations of 1,000 people. Statistical measurementsshow that reductions in the margin of error flatten out considerably after the sample size reaches 1,000.© Microsoft Corporation. All Rights Reserved. The raw materials of statistics are sets of numbers obtained from enumerations or measurements. In collecting statistical data, adequate precautions must be taken tosecure complete and accurate information. The first problem of...

• Cobra (snake) - biology.

  Most cobras prey on small rodents or other small mammals. They also eat birds, snakes, lizards, frogs, toads, insects, and even eggs. Water cobras catch fish and kingcobras specialize in eating other snakes. Similar to other venomous snakes, cobras use venom to subdue their prey before swallowing it whole, generally head first. Thevenom may contain substances that also break down the prey for digestion. Despite their potent venom and dramatic threat displays, cobras are hunted and eaten by a num...

• Stem Cell.

  The medical profession used adult stem cells to treat diseases long before anyone isolated one. In 1968 scientists performed the first successful bone marrowtransplant, a procedure in which a patient receives an infusion of healthy bone marrow cells. The purpose of such transplants is to restore the blood-making capabilitiesof the patient’s diseased bone marrow after extremely strong chemotherapy has destroyed that bone marrow. From the beginning investigators suspected that stemcells in the inf...

• Ancient Egypt - history.

  The Nile River runs through the ancient city of Thebes in eastern Egypt. For a time, beginning in 2040 bc, Thebes was the capital ofEgypt.Farrell Grehan/Photo Researchers, Inc. According to inscriptions and documents found by archaeologists, the Egyptians called their country Kemet, meaning “the Black Land,” a reference to the dark, fertile soil that remained after the Nile floodwaters had receded. They also used another term, Deshret, or “the Red Land,” a designation for the desert sands th...

• Skiing.

  Safety is very important to all skiers, and all Alpine resorts have a ski patrol. The ski patrol’s responsibility is to take care of injured skiers, to mark hazardous spots ontrails, to make sure that trails are in good condition before opening them, and, at times, to act as traffic police in congested areas. Skiers are also responsible for takingtheir own safety into consideration, as well as that of others. Anyone who participates in the sport should be aware of the Skier’s Responsibility Code...

• Apollo Program - astronomy.

  Moon’s orbit; rendezvousing and docking with the CSM; and finally, setting a course home to Earth. On return to Earth, the spacecraft was slowed by drag from Earth’satmosphere and by parachutes (just before splashdown), before landing in the ocean. The transit time to and from the Moon was approximately three days each way.Depending on the specific mission, the time in lunar orbit ranged from less than one day for Apollo 8 to over six days for the final three missions, and the time on thelunar s...

• Apollo Program - U.

  Moon’s orbit; rendezvousing and docking with the CSM; and finally, setting a course home to Earth. On return to Earth, the spacecraft was slowed by drag from Earth’satmosphere and by parachutes (just before splashdown), before landing in the ocean. The transit time to and from the Moon was approximately three days each way.Depending on the specific mission, the time in lunar orbit ranged from less than one day for Apollo 8 to over six days for the final three missions, and the time on thelunar s...

• Theater I INTRODUCTION The Art of Theater BBC Worldwide Americas, Inc.

  Theater at EpidaurusAncient Greek dramas were performed in open-air theaters like this one in Epidaurus, Greece, which was designed byPolyclitus the Younger in 350 bc. A festival of ancient Greek drama is still held in the summer in this 14,000-seat theater.Roger Wood/Corbis Fundamental to the theater experience is the act of seeing and being seen; in fact, the word theater comes from the Greek word theatron , meaning 'seeing place.' Throughout the history of world cultures, actors have used...

• Archaeology.

  Prehistoric archaeology is practiced by archaeologists known as prehistorians and deals with ancient cultures that did not have writing of any kind. Prehistory, a term coined by 19th-century French scholars, covers past human life from its origins up to the advent of written records. History—that is, the human past documented insome form of writing—began 5000 years ago in parts of southwestern Asia and as recently as the late 19th century AD in central Africa and parts of the Americas. Becaus...

• Airplane.

  For example, the Anglo-French Concorde, a commercial supersonic aircraft, was generally limited to over-water routes, or to those over sparsely populated regions ofthe world. This limitation impacted the commercial viability of the Concorde, which ended its regular passenger service in October 2003. Designers today believe theycan help lessen the impact of sonic booms created by supersonic airliners but probably cannot eliminate them. One of the most difficult practical barriers to supersonic fl...

• Industrial Revolution I INTRODUCTION Industrial Revolution, widespread replacement of manual labor by machines that began in Britain in the 18th century and is still continuing in some parts of the world.

  The most important advance in iron production occurred in 1784 when Englishman Henry Cort invented new techniques for rolling raw iron, a finishing process thatshapes iron into the desired size and form. These advances in metalworking were an important part of industrialization. They enabled iron, which was relativelyinexpensive and abundant, to be used in many new ways, such as building heavy machinery. Iron was well suited for heavy machinery because of its strength anddurability. Because of t...

• Industrial Revolution .

  The most important advance in iron production occurred in 1784 when Englishman Henry Cort invented new techniques for rolling raw iron, a finishing process thatshapes iron into the desired size and form. These advances in metalworking were an important part of industrialization. They enabled iron, which was relativelyinexpensive and abundant, to be used in many new ways, such as building heavy machinery. Iron was well suited for heavy machinery because of its strength anddurability. Because of t...

• Native Americans of Middle and South America.

  A line that snakes across central Mexico near the Tropic of Cancer forms the northern boundary of Mesoamerica; north of this line rainfall sharply declines and theclimate is much drier. The ancient civilizations of Mesoamerica all arose and developed in the area between this line and the Guatemalan highlands far to the south. Richvolcanic soils are found throughout much of the region. A2 People and Languages Mesoamerica was a great melting pot, home to many peoples and interrelated cultures. In...

• Idaho - geography.

  Idaho-Montana state line in the southern part of the Bitterroot Mountains. Consequently, nearly all the rivers in the state drain toward the Pacific. Most of Idaho lieswithin the drainage basin of the Columbia River system. The Snake River, which is the chief river in southern and central Idaho, follows a crescent-shaped course forabout 790 km (about 490 mi) across southern Idaho. It then swings northward along the Idaho state line and joins the Columbia River in Washington. Major tributariesof...

• Idaho - USA History.

  Idaho-Montana state line in the southern part of the Bitterroot Mountains. Consequently, nearly all the rivers in the state drain toward the Pacific. Most of Idaho lieswithin the drainage basin of the Columbia River system. The Snake River, which is the chief river in southern and central Idaho, follows a crescent-shaped course forabout 790 km (about 490 mi) across southern Idaho. It then swings northward along the Idaho state line and joins the Columbia River in Washington. Major tributariesof...

• Chemical Reaction - chemistry.

  Many groups of elements occur so often as ions that they are given names: nitrate, NO 3-; sulfate, SO 42-; and phosphate, PO 43-. The suffix -ate usually indicates the presence of oxygen. The positive ion, NH 4+, is called ammonium, as in NH 4Cl, ammonium chloride, or (NH 4)3PO4, ammonium phosphate. Rules for naming more complicated compounds exist, but many compounds have been given trivial names—for example, Na 2B4O7·10 H 2O, borax—or proprietary names—F(CF 2)nF, Teflon. These nonsystemat...

• Maya Civilization.

  destruction was directed mostly at temples in the ceremonial precincts; it had little or no impact on the economy or population of a city as a whole. Some city-states didoccasionally conquer others, but this was not a common occurrence until very late in the Classic period when lowland civilization had begun to disintegrate. Until thattime, the most common pattern of Maya warfare seems to have consisted of raids employing rapid attacks and retreats by relatively small numbers of warriors, most o...

• Maya Civilization - History.

  destruction was directed mostly at temples in the ceremonial precincts; it had little or no impact on the economy or population of a city as a whole. Some city-states didoccasionally conquer others, but this was not a common occurrence until very late in the Classic period when lowland civilization had begun to disintegrate. Until thattime, the most common pattern of Maya warfare seems to have consisted of raids employing rapid attacks and retreats by relatively small numbers of warriors, most o...

• Geometry I INTRODUCTION Geometry, branch of mathematics that deals with shapes and sizes.

  Conic sections, a commonly studied topic of geometry, are two-dimensional curves created by slicing a plane through a three-dimensional hollow cone. A Euclid’s Postulates Euclid, who lived about 300 BC, realized that only a small number of postulates underlay the various geometric theorems known at the time. He determined that these theorems could be deduced from just five postulates. 1. A straight line may be drawn through any two given points. 2. A straight line may be drawn infinitely or be...

• Surrealism I INTRODUCTION Surrealism, artistic and literary movement that explored and celebrated the realm of dreams and the unconscious mind through the creation of visual art, poetry, and motion pictures.

  Hieronymus Bosch’s The Garden of Earthly Delights (about 1505-1510).© 2008 Salvador Dali, Gala-Salvador Dali Foundation / Artists Rights Society (ARS), New York./Bridgeman Art Library, London/New York Dreams, according to Freud, were the royal road to studying the unconscious, because it is in dreams that our unconscious, primal desires manifest themselves. Theincongruities in dreams, Freud believed, result from a struggle for dominance of ego and id. In attempting to access the real workings of...

• Latin American Music I INTRODUCTION Tito Puente Playing the Drums Since the 1950s American drummer Tito Puente has popularized Latin American music, especially the mambo, in the United States.

  Panpipe Music of BoliviaWell before the Spanish conquest, native peoples such as the Quechua and Aymara living in the Andes Mountains inBolivia, Peru, and Ecuador, developed a rich musical tradition. Panpipes (set of tuned pipes), made of ceramic, sugarcane,or bone were paired with shell trumpets, cane flutes, and drums, which accompanied dancers during religious and secularceremonies. Large ensembles of 4 to 20 panpipe players are still the norm, and Spanish influences have since beenintegrated...

• Thomas Edison.

  While Edison was working on the electric light, he made a scientific discovery that would become important to future generations. Edison noticed that particles of carbonfrom the filament blackened the insides of his light bulbs. This effect was caused by the emission of electrons from the filament, although Edison made the discoverybefore he and other scientists knew the electron existed. Not until 1897 did British physicist J. J. Thomson prove that the blackening observed by Edison was caused b...

• Thomas Edison - USA History.

  While Edison was working on the electric light, he made a scientific discovery that would become important to future generations. Edison noticed that particles of carbonfrom the filament blackened the insides of his light bulbs. This effect was caused by the emission of electrons from the filament, although Edison made the discoverybefore he and other scientists knew the electron existed. Not until 1897 did British physicist J. J. Thomson prove that the blackening observed by Edison was caused b...

• Conservation.

  cancers, Hodgkin’s disease and leukemia. Unfortunately, human activities have greatly reduced biodiversity around the world. The 20th century encompasses one of the greatest waves of extinction, orelimination of species, to occur on the planet. The greatest threat to biodiversity is loss of habitat as humans develop land for agriculture, grazing livestock, industry,and habitation. The most drastic damage has occurred in the tropical rain forests, which cover less than seven percent of the Earth’...

• Dinosaur - biology.

  The behavior of dinosaurs was governed by their metabolism and by their central nervous system. The dinosaurs’ metabolism—the internal activities that supply thebody’s energy needs—affected their activity level. It is unclear whether dinosaurs were purely endothermic (warm-blooded), like modern mammals, or ectothermic (cold-blooded), like modern reptiles. Endotherms regulate their body temperature internally by means of their metabolism, rather than by using the temperature oftheir surroundin...

• Calligraphy I INTRODUCTION Japanese Calligraphy This hanging scroll is an example of Japanese calligraphy.

  Section of the Egyptian Book of the DeadThe Egyptian Book of the Dead was a text containing prayers, spells, and hymns, the knowledge of which was to be usedby the dead to guide and protect the soul on the hazardous journey through the afterlife. This section of one such book,dating from the early 19th Dynasty, shows the final judgment of the deceased (in this case Hu-Nefer, the royal scribe)before Osiris, the god of the dead. Hieroglyphs as well as illustrations portray the ritual of weighing t...

• Forensic Science.

  barbiturates, cocaine, amphetamines, and heroin. When a body is discovered in a lake, stream, river, or ocean and the lungs are found to be filled with water, the medical examiner must determine if the drowningoccurred where the body was found or elsewhere. A standard microscope that can magnify objects to 1500 times their actual size is used to look for the presence orabsence of diatoms, single-celled algae that are found in all natural bodies of water. The absence of diatoms raises the possi...

• Photosynthesis - biology.

  P680 in Photosystem II is now electron deficient because it has donated electrons to P700 in Photosystem I. P680 electrons are replenished by the water that has beenabsorbed by the plant roots and transported to the chloroplasts in the leaves. The movement of electrons in Photosystems I and II and the action of an enzyme split thewater into oxygen, hydrogen ions, and electrons. The electrons from water flow to Photosystem II, replacing the electrons lost by P680. Some of the hydrogen ions maybe...

• Comics I INTRODUCTION Comics, series of drawings arranged to tell a story.

  is still used to refer to sensationalistic techniques that publishers use to draw more readers to their newspapers. Outcault finally won the right to continue his strip andgradually adopted the panel style and balloon narration that mark “The Yellow Kid” as the first true comic strip. Other early comics included “Little Bears” by JamesSwinnerton, which first appeared in the San Francisco Examiner in 1892, and “The Katzenjammer Kids” by Rudolph Dirks, which first appeared in The American Humo...

• Saudi Arabia - country.

  C Natural Resources Some of the world’s largest oil and natural gas fields lie beneath Saudi Arabia and its offshore waters, representing the country’s most economically important naturalresource. In 2007 Saudi Arabia’s oil reserves were estimated at 264 billion barrels. Before the discovery and exploitation of these reserves in the mid-20th century,Saudi Arabia was one of the poorest countries in the world. Its relatively small population subsisted in a harsh environment with little agricultur...

• Helium - chemistry.

  the bends. This synthetic atmosphere is also used in medicine to relieve sufferers of respiratory difficulties because helium moves more easily than nitrogen throughconstricted respiratory passages. In surgery, beams of ionized helium from synchrocyclotron sources are proving useful in treating eye tumors, by stabilizing or evenshrinking the tumors. Such beams are also used to shrink blood-vessel malformations in the brains of patients. Helium is used in inert-gas arc welding for light metals, s...

• Obesity.

  of a day, contributing to the development of obesity. V TREATMENTS FOR OBESITY Obesity can become a chronic lifelong condition caused by overeating, physical inactivity, and even genetic makeup. No matter what the cause, however, obesity can beprevented or managed with a combination of diet, exercise, behavior modification, and in severe cases, weight-loss medications and surgery. A Diets The most common and conservative treatment for obesity utilizes a nutritionally balanced, low calorie diet...

• Hurricane.

  V HOW HURRICANES ARE DETECTED AND MONITORED Since 1943 U.S. military and civilian aircraft have been flying into hurricanes to measure wind velocities and directions, the location and size of the eye, air pressures,and temperatures in different parts of the storm. A coordinated system of tracking hurricanes was developed in the mid-1950s, and steady improvements have beenmade over the years. In addition to reports from aircraft, geosynchronous weather satellites (since 1966) and ocean buoys tha...

• Warfare.

  organizations as the League of Nations in 1920 and the United Nations in 1945, and détente (suggested for scaling down the cold war). See Arms Control. Modern antiwar sentiment and organized peace movements are derived in large part from the beliefs of religious sects such as the Society of Friends and the MennoniteChurch. The first peace societies in history were established in the U.S. in 1815, and since then pacifists have actively opposed wars and conscription, and promoted thecause of con...

• Electricity I INTRODUCTION Electricity, one of the basic forms of energy.

  electrons in the neutral object are attracted to the positive object. Some of these electrons flow to the side of the neutral object that is nearest to the positive object.This side of the neutral object accumulates electrons and becomes negatively charged. Because electrons leave the far side of the neutral object while its protonsremain stationary, that side becomes positively charged. Since the negatively charged side of the neutral object is closest to the positive object, the attraction bet...

• Madrid - geography.

  Madrid’s Plaza MayorBuilt in the early 17th century, the Plaza Mayor was used for a variety of activities, including bullfights, executions during theInquisition, and festivals. Today it is one of Madrid’s main tourist attractions.Cesar Lucas/The Image Bank The traditional heart of Madrid is an area 3.9 sq km (1.5 sq mi). In 1656 King Philip IV had a city wall built around the area. Over the next 200 years the city grew throughconstruction of taller buildings and the use of open land within the...

• Affirmative Action.

  hiring, purchasing, and other government business. In 1998 Washington State voters passed Initiative 200, a measure that banned affirmative action in state and localgovernment hiring, contracting, and education. Around the same time, federal courts began considering lawsuits from white students denied admission to state universities with affirmative action programs. In somecases, the courts have invalidated such programs on the grounds that they promote reverse racial discrimination. For example...

• Calculus (mathematics) I INTRODUCTION Limits This graph, which charts the function f(x)=1x, shows that the value of the function approaches zero as x becomes larger and larger.

  DerivativesThe derivative of a function at a given point is equal to the slope of the line that is tangent to the function at that givenpoint. In this example, the derivative of f(x) at x0 is defined as the slope of AB in the limit of h going to zero. As hbecomes increasingly smaller, B moves along the curve towards A, and AB increasingly approximates T, the tangent to thecurve at x0.© Microsoft Corporation. All Rights Reserved. Let the dependent variable y be a function of the independent vari...

• Leaf - biology.

  The mesophyll, sandwiched between the upper and lower epidermis, consists of many thin-walled cells that are usually arranged in two layers. The palisade layer is next to the upper epidermis. It consists of cylindrical cells that are packed closely together. Next to the palisade layer and making up most of the thickness of the leaf bladeis the spongy layer. The spongy layer consists of roundish cells that are packed loosely together and have numerous air spaces between them. In most plants t...

• Sudan - country.

  B Principal Cities and Political Divisions The principal city is Khartoum, the capital; other major cities include Omdurman and Khartoum North, major industrial centers, and Port Sudan, a seaport on the RedSea. Sudan is divided into 26 states. C Religion and Language About 70 percent of the people of Sudan are Muslims, some 15 percent are Christians, and most of the remainder follow traditional religions. The people of northernSudan are predominantly Sunni Muslims (Sunni Islam). Most of the pe...

• Shang Dynasty - History.

  The dynastic ancestors belonged to an elaborate religious pantheon that also included various nature powers and the Shang high god, Di. The higher powers were lessconcerned with the well-being of Shang society than the ancestors were. Di, whose wishes were often hard to determine, could even cause the Shang harm. The naturepowers could occasionally influence the wind, rain, and harvests, but only Di could actually order the weather. For an agricultural society such as the Shang, this wasperhaps...

• Tunisia - country.

  mixture of Berber and Arab stock, and they regard themselves as Arabs. Nearly everyone speaks Arabic. The population of Tunisia is concentrated in the coastal plain. It is fairly dense in the hilly north, but the arid plateau, basin, and south are thinly settled. About two-thirds of the country’s people live in urban areas. A Principal Cities The capital and largest city of Tunisia is the seaport of Tunis. Other important cities include Sfax, a port and center of trade on the eastern coast; Sūs...

• Marketing.

  Where advertising reaches a mass audience, personal or direct selling focuses on one customer at a time. That kind of individual attention makes direct sellingexpensive, but it also makes it effective. As the costs of personal selling have risen, the utilization of salespeople has changed. Simple transactions are completed byclerks. Salespeople are now used primarily where the products are complex and require detailed explanation, customized application, or careful negotiation over priceand paym...

• Holy Roman Empire I INTRODUCTION Holy Roman Empire, political entity of lands in western and central Europe, founded by Charlemagne in AD 800 and dissolved by Emperor Francis II in 1806.

  acquired the imperial title and an area running from the North Sea through Lotharingia (Lorraine) and Burgundy to northern Italy; Louis II received East Francia (theGerman duchies of Saxony, Swabia, and Bavaria). In 870 Lothair’s middle kingdom was divided by the Treaty of Mersen, which gave Lotharingia to East Francia and therest to West Francia. This division created the foundation for today’s states of Germany and France, respectively; however, in the 9th century these were highly fractured d...

• Holy Roman Empire .

  acquired the imperial title and an area running from the North Sea through Lotharingia (Lorraine) and Burgundy to northern Italy; Louis II received East Francia (theGerman duchies of Saxony, Swabia, and Bavaria). In 870 Lothair’s middle kingdom was divided by the Treaty of Mersen, which gave Lotharingia to East Francia and therest to West Francia. This division created the foundation for today’s states of Germany and France, respectively; however, in the 9th century these were highly fractured d...

• Network (computer science).

  computer. Since there is only one token in the network, only one computer can transmit information at a time. Token Ring networks are now quite rare. Most LANs nowuse Ethernet technology. International Business Machines Corporation (IBM), the company that invented Token Ring in the early 1980s, no longer promotes thetechnology. In the mid-1990s a new protocol called Asynchronous Transfer Mode (ATM) was introduced. This protocol encodes data in fixed-sized packets called cells rather thanvariable...

• Crafts.

  VI POTTERY Ceramic objects can be molded completely by hand or thrown (shaped) on a potter's wheel, a device with a rotating horizontal disk. When the clay hardens, it is fired ina high-temperature oven, or kiln, to strengthen it. To make the object waterproof, glazes may then be applied and the piece fired again. Although hand construction iseasy to master, throwing on the potter's wheel requires practice. Several simple tools are used by potters, including sponges, trimming tools, wooden sha...

• Electric Lighting.

  successful arc lamp in 1878. Tungsten filaments were substituted for carbon filaments in incandescent lamps in 1907, and gas-filled incandescent lamps were developedin 1913. The fluorescent lamp was introduced in 1938. See also Lamp. For most of the 20th century the incandescent light bulb was widely used for lighting in homes. More energy-efficient and longer-lasting fluorescent lamps were adoptedfor industrial and office use. In 1979 a compact fluorescent bulb that screwed into ordinary lig...