344 résultats pour "back"

• 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...

• Venus (planet) - astronomy.

  level winds circle the planet at 360 km/h (225 mph), making a complete rotation in only four days. These winds are said to super-rotate because they travel muchfaster than the rotation of the planet itself. These high-speed winds cover the planet completely, blowing toward the west at virtually every latitude from equator topole. The motions of descending probes, however, have shown that the bulk of Venus’s tremendously dense atmosphere, closer to the planet’s surface, is almoststagnant. From th...

• Toys. I INTRODUCTION Toys, objects that serve as playthings for children. Although the

  clay. These readily available elements were also used to make more elaborate toys as human society advanced. Archaeologists have found primitive, handmade toys such as wooden or cloth dolls, clay marbles, and terracotta figures that date back thousands of years. In ancientEgypt, Greece, and Rome, people placed dolls or clay figures in the graves or tombs of children for them to play with in the afterlife. The yo-yo may seem like a 20th-century fad, but it actually dates back at least 2,500 years...

• Internet.

  usually pays a fixed monthly fee for a dedicated connection. In exchange, the company providing the connection agrees to relay data between the user’s computer andthe Internet. Dial-up is the least expensive access technology, but it is also the least convenient. To use dial-up access, a subscriber must have a telephone modem, a device thatconnects a computer to the telephone system and is capable of converting data into sounds and sounds back into data. The user’s ISP provides software that con...

• Environment.

  escape into space of the infrared energy radiated back out by Earth. This process is referred to as the greenhouse effect. These gases, primarily carbon dioxide,methane, nitrous oxide, and water vapor, insulate Earth’s surface, helping to maintain warm temperatures. Without these gases, Earth would be a frozen planet with anaverage temperature of about -18°C (about 0°F) instead of a comfortable 15°C (59°F). If the concentration of these gases rises, they trap more heat within theatmosphere, caus...

• 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...

• Wrestling.

  (4) Escapes are scored when a wrestler, controlled by the opponent on the mat, frees himself or herself and moves to a standing position, facing the opponent. Common escapes include the standup and the sitout. V HISTORY Wrestling has been popular throughout recorded history. Origins of the sport can be traced back 15,000 years through depictions in cave drawings in France. EarlyEgyptian and Babylonian reliefs depict wrestlers using most of the holds known to the present-day sport. In ancient G...

• Poetry I INTRODUCTION Phyllis McGinley American poet and author Phyllis McGinley composed light, witty verse, much of which deals with family life.

  repetition of certain lines and the rhyming of certain lines. The Provençal sestina features a set of six words that end lines (end-words), repeated in a dizzyingly complexpattern. The range of effects created by the poetic line varies tremendously depending on its length, its patterns of repetition, and whether the sentence stops at the end of theline (end-stopped) or carries over the end of the line (enjambed). Many of the earliest examples of Old English poetry feature an accentual line with...

• Aboriginal Australians - History.

  Until Europeans began to settle in Australia in 1788, the Aboriginal way of life was supported by hunting, gathering, and fishing. Like other hunting and gatheringpeoples, Aboriginal people had an extremely detailed knowledge of their environment, especially plant ecology and animal behavior. The deep connection betweenAboriginal people and the natural world influenced every part of their culture, including their food gathering, tools, trade, religion, art, music, language, and socialorganizatio...

• From "The Metamorphosis" - anthology.

  As all this was running through his mind at top speed without his being able to decide to leave his bed—the alarm clock had just struck a quarter to seven—therecame a cautious tap at the door behind the head of his bed. 'Gregor,' said a voice—it was his mother's—'it's a quarter to seven. Hadn't you a train to catch?' Thatgentle voice! Gregor had a shock as he heard his own voice answering hers, unmistakably his own voice, it was true, but with a persistent horrible twittering squeakbehind it lik...

• Diving (sport).

  water that creates a larger, more noticeable splash after the diver’s body displaces water under the surface. To minimize this upjet, top-level divers make a quickswimming motion by releasing their hands and collapsing their arms as they submerge. Instead of a large splash, the surface of the water appears to boil as the airbubbles rise from the diver’s entry. For feetfirst entries, which are rare in top-level competitions, divers place their legs and feet together while pointing their toes down...

• Spider (arthropod) - biology.

  The spider’s abdomen is soft and saclike. On the underside of the tip of the abdomen are three pairs of spinnerets. Each spinneret is studded with many fine, hairliketubes called spigots, which produce a variety of silk threads. The spigots lead to several large silk glands inside the abdomen. Silk is formed as a liquid inside theseabdominal glands. As the silk is drawn out through the spigots, protein molecules within the silk line up parallel to one another, causing the silk to harden and form...

• Christopher Columbus I INTRODUCTION Christopher Columbus (1451-1506), Italian-born Spanish navigator who sailed west across the Atlantic Ocean in search of a route to Asia but achieved fame by making landfall in the Americas instead.

  explorers, adventurers, entrepreneurs, merchants, and any others who saw their fortunes tied to the trade winds and ocean currents. Columbus’s brother Bartholomewworked in Lisbon as a mapmaker, and for a time the brothers worked together as draftsmen and book collectors. Later that year, Columbus set sail on a convoy loadedwith goods to be sold in northern Atlantic ports. In 1478 or 1479 Columbus met and married Felipa Perestrello e Moniz, the daughter of a respected, though relatively poor, nob...

• Christopher Columbus.

  explorers, adventurers, entrepreneurs, merchants, and any others who saw their fortunes tied to the trade winds and ocean currents. Columbus’s brother Bartholomewworked in Lisbon as a mapmaker, and for a time the brothers worked together as draftsmen and book collectors. Later that year, Columbus set sail on a convoy loadedwith goods to be sold in northern Atlantic ports. In 1478 or 1479 Columbus met and married Felipa Perestrello e Moniz, the daughter of a respected, though relatively poor, nob...

• Christopher Columbus.

  explorers, adventurers, entrepreneurs, merchants, and any others who saw their fortunes tied to the trade winds and ocean currents. Columbus’s brother Bartholomewworked in Lisbon as a mapmaker, and for a time the brothers worked together as draftsmen and book collectors. Later that year, Columbus set sail on a convoy loadedwith goods to be sold in northern Atlantic ports. In 1478 or 1479 Columbus met and married Felipa Perestrello e Moniz, the daughter of a respected, though relatively poor, nob...

• Christopher Columbus - explorer.

  explorers, adventurers, entrepreneurs, merchants, and any others who saw their fortunes tied to the trade winds and ocean currents. Columbus’s brother Bartholomewworked in Lisbon as a mapmaker, and for a time the brothers worked together as draftsmen and book collectors. Later that year, Columbus set sail on a convoy loadedwith goods to be sold in northern Atlantic ports. In 1478 or 1479 Columbus met and married Felipa Perestrello e Moniz, the daughter of a respected, though relatively poor, nob...

• five or fifty minutes.

  THE ONLY ANIMAL   I read thefirst chapter of A Brief History ofTime when Dadwasstillalive, andIgot incredibly heavybootsabout how relatively insignificant lifeis,and how, compared tothe universe andcompared totime, itdidn't evenmatter ifIexisted at all. When Dadwastucking meinthat night andwewere talking aboutthebook, Iasked ifhe could thinkofasolution to that problem. "Whichproblem?" "Theproblem ofhow relatively insignificant weare." Hesaid, "Well, whatwould happen ifaplane dropped youinthe mid...

• It wasn't until the day before we were going to go that the renter asked the obvious question.

  I told her, "Ipromise I'mgoing tobe better soon." She said, "There's nothingwrongwithyou." "I'll behappy andnormal." She putherfingers around theback ofmy neck. I told her, "Itried incredibly hard.Idon't know howIcould havetriedharder." She said, "Dad would havebeen veryproud ofyou." "Do youthink so?" "I know so." I cried some more. Iwanted totell her allofthe liesthat I'dtold her. And then Iwanted hertotell me that itwas OK, because sometimes youhave todo something badtodo something good.Andthe...

• Greenhouse Effect.

  addition, humans cut down huge tracts of trees for lumber or to clear land for farming or building. This process, known as deforestation, can both release the carbonstored in trees and significantly reduce the number of trees available to absorb carbon dioxide. As a result of these human activities, carbon dioxide in the atmosphere is accumulating faster than Earth’s natural processes can absorb the gas. By analyzing airbubbles trapped in glacier ice that is many centuries old, scientists have d...

• Antelope - biology.

  antelopes still display complex patterns of behavior, although much of it is instinctive rather than learned. In open habitats, antelopes run a high risk of predation (being preyed upon). To survive they use several kinds of defensive strategy, including living in herds. Herd living ensures that many pairs of eyes and ears are on the alert for danger. Herd living also gives individuals a better chance of avoiding attack, because predators canchoose from many potential targets. When danger thre...

• 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...

• Greek Mythology I INTRODUCTION Temple of Apollo at Didyma The Greeks built the Temple of Apollo at Didyma, Turkey (about 300 bc).

  A1 The Creation of the Gods According to Greek myths about creation, the god Chaos (Greek for “Gaping Void”) was the foundation of all things. From Chaos came Gaea (“Earth”); the bottomlessdepth of the underworld, known as Tartarus; and Eros (“Love”). Eros, the god of love, was needed to draw divinities together so they might produce offspring. Chaosproduced Night, while Gaea first bore Uranus, the god of the heavens, and after him produced the mountains, sea, and gods known as Titans. The Tita...

• Korean War.

  During the summer of 1949, South Korea had expanded its army to about 90,000 troops, a strength the North matched in early 1950. The North had about 150 SovietT-34 tanks and a small but effective air force of 70 fighters and 62 light bombers—weapons either left behind when Soviet troops evacuated Korea or bought from theUSSR and China in 1949 and 1950. By June 1950 American data showed the two armies at about equal strength, with roughly equal numbers amassed along the 38thparallel. However, thi...

• Korean War - History.

  During the summer of 1949, South Korea had expanded its army to about 90,000 troops, a strength the North matched in early 1950. The North had about 150 SovietT-34 tanks and a small but effective air force of 70 fighters and 62 light bombers—weapons either left behind when Soviet troops evacuated Korea or bought from theUSSR and China in 1949 and 1950. By June 1950 American data showed the two armies at about equal strength, with roughly equal numbers amassed along the 38thparallel. However, thi...

• Korean War - U.

  During the summer of 1949, South Korea had expanded its army to about 90,000 troops, a strength the North matched in early 1950. The North had about 150 SovietT-34 tanks and a small but effective air force of 70 fighters and 62 light bombers—weapons either left behind when Soviet troops evacuated Korea or bought from theUSSR and China in 1949 and 1950. By June 1950 American data showed the two armies at about equal strength, with roughly equal numbers amassed along the 38thparallel. However, thi...

• John F.

  by the United States, was unable to withstand the advance of Communist forces under Mao Zedong (Mao Tse-tung). By the end of 1949 government troops had beenoverwhelmingly defeated, and Chiang led his forces into exile on Taiwan. The triumphant Mao formed the People’s Republic of China. Truman’s critics, includingKennedy, charged that the administration had failed to support Chiang Kai-shek against the Communists. Kennedy easily won reelection to Congress in 1948 and 1950. In 1952 he decided to r...

• John F.

  by the United States, was unable to withstand the advance of Communist forces under Mao Zedong (Mao Tse-tung). By the end of 1949 government troops had beenoverwhelmingly defeated, and Chiang led his forces into exile on Taiwan. The triumphant Mao formed the People’s Republic of China. Truman’s critics, includingKennedy, charged that the administration had failed to support Chiang Kai-shek against the Communists. Kennedy easily won reelection to Congress in 1948 and 1950. In 1952 he decided to r...

• Beetle - biology.

  cut, or crush prey. Beetles that consume nectar from flowers use tubelike mouthparts to suck up nectar like a primitive straw. C Thorax The thorax, the body region behind the head, consists of three segments that provide attachments for the legs and wings. Each segment of the thorax carries a pair oflegs. The middle segment also bears the stiff wing sheaths called elytra, and the hind segment holds the membranous hind wings. D Legs Beetles have six jointed legs, each leg with five parts. The f...

• Whale - biology.

  III BEHAVIOR OF WHALES Studies of whales in captivity have taught scientists much about the complex social behavior of whales. Since the late 1980s, advances in the use of satellite trackingsystems have also broadened opportunities for scientists to observe how whales behave in the wild. A Swimming and Diving Whales swim by making powerful up-and-down movements of the tail flukes, which provide thrust. The power comes from body muscles that flex the lower spine upand down in a wavelike motion...

• Light - astronomy.

  Each different frequency or wavelength of visible light causes our eye to see a slightly different color. The longest wavelength we can see is deep red at about 700 nm.The shortest wavelength humans can detect is deep blue or violet at about 400 nm. Most light sources do not radiate monochromatic light. What we call white light,such as light from the Sun, is a mixture of all the colors in the visible spectrum, with some represented more strongly than others. Human eyes respond best to greenlight...

• 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...

• Geographic Exploration.

  The commercial reason for exploration has been a consistent driving force. In 1492 the great navigator Christopher Columbus sailed west across the Atlantic Oceanseeking a new, shorter, and cheaper route to reach the riches of East Asia, and Portuguese explorer Vasco da Gama circumnavigated Africa for much the same reason.Yet similar investigations of the profitable eastern trade had already been made by Arab sailors. Arab trading ships were sailing from the Arabian Sea to southeasternAsia probab...

• Geographic Exploration - explorer.

  The commercial reason for exploration has been a consistent driving force. In 1492 the great navigator Christopher Columbus sailed west across the Atlantic Oceanseeking a new, shorter, and cheaper route to reach the riches of East Asia, and Portuguese explorer Vasco da Gama circumnavigated Africa for much the same reason.Yet similar investigations of the profitable eastern trade had already been made by Arab sailors. Arab trading ships were sailing from the Arabian Sea to southeasternAsia probab...

• Lyndon B.

  A1 First Years in Office Johnson quickly made a two-fold reputation. He was a firm supporter of Roosevelt’s program, both domestic and foreign, and he was also a tireless worker on behalf ofthe voters he represented. Often the two activities coincided, as was the case when he helped to bring public power into Texas through the Rural ElectrificationAdministration and the Lower Colorado River Authority. He also secured funds for the building of dams, roads, and other public improvements in his di...

• mean? Over." "Well, they always seem to run out. Everyone's

  I could hearherkissing herfingers andthen blowing. 4. Buckminster 3. Mom I blew herakiss back. 2. Grandma "Over andout," oneofus said. 1. Dad We need much bigger pockets, Ithought asIlay inbed, counting offthe seven minutes thatittakes anormal personto fall asleep. Weneed enormous pockets,pocketsbigenough forour families, andourfriends, andeven thepeople who aren't onour lists, people we'venevermetbutstill want toprotect. Weneed pockets forboroughs andforcities, a pocket thatcould holdtheunivers...

• exactly what to do.

  him upthe next Saturday at7:00, andwewould startthen. Itold him, "I'mnoteven through withtheA's." Hesaid, "OK," and thesound ofhis own voice made himcrythe most. Message three.9:31A.M. Hello? Hello?Hello? When Momtucked meinthat night, shecould tellthat something wasonmy mind, andasked ifIwanted totalk. Idid, but not toher, soIsaid, "Nooffense, butno." "Are yousure?" " Tresfatigué, " Isaid, waving myhand. "Doyouwant meto read something toyou?" "It'sOK." "Wecould gothrough the New YorkTimes for m...

• Penguin - biology.

  B Parents and Offspring Once female penguins lay their eggs, both the parents incubate the eggs. The incubation period varies according to species, ranging from 33 days for the little penguinto about 63 days for the emperor penguin. In most medium-sized penguins incubation takes 35 to 38 days. The incubation routine is highly variable among penguinspecies, although in general both sexes participate in incubation and feeding of young. Male and female Adélie penguins take turns incubating their e...

• Excerpt from Persuasion - anthology.

  “Yes, dear ma'am,” said Mrs. Croft, “or an uncertain engagement, an engagement which may be long. To begin without knowing that at such a time there will be themeans of marrying, I hold to be very unsafe and unwise, and what I think all parents should prevent as far as they can.” Anne found an unexpected interest here. She felt its application to herself, felt it in a nervous thrill all over her; and at the same moment that her eyes instinctivelyglanced towards the distant table, Captain Wen...

• Glacier.

  covered. In spring the snow cover begins to melt in the lower reaches, exposing the ice surface. As temperatures increase, the melting moves up the glacier. Thesnowline is the highest position the melting reaches during the year. Firn is old granular snow. The firn limit may not exactly coincide with the annual snowline since insome years rapid melting leaves behind firn patches below the snowline. Some glaciers exhibit features called ice streams and icefalls. Ice streams are valley glaciers th...

• Brain.

  The hypothalamus lies beneath the thalamus on the midline at the base of the brain. It regulates or is involved directly in the control of many of the body's vital drivesand activities, such as eating, drinking, temperature regulation, sleep, emotional behavior, and sexual activity. It also controls the function of internal body organs bymeans of the autonomic nervous system, interacts closely with the pituitary gland, and helps coordinate activities of the brain stem. D Brain Stem The brain st...

• Radar.

  gathers the weak returning radar signals and converts them into an electric current. Because a radar antenna may both transmit and receive signals, the duplexerdetermines whether the antenna is connected to the receiver or the transmitter. The receiver determines whether the signal should be reported and often does furtheranalysis before sending the results to the display. The display conveys the results to the human operator through a visual display or an audible signal. B1 The Antenna The rec...

• Track and Field.

  VI RUNNING EVENTS Running events are competitions that test athletes’ quickness, speed, and endurance. Athletes win running races by completing the distance or course in the leastamount of time. A Sprints The shortest running events, called sprints or dashes, are the premier events at a track-and-field meet. The outdoor sprints consist of the 100-meter, 200-meter, and400-meter events. Sprints contested at indoor meets include the 50-meter, 60-meter, 200-meter, and 400-meter events. Past champ...

• Quantum Theory I INTRODUCTION Quantum Theory, in physics, description of the particles that make up matter and how they interact with each other and with energy.

  electron in the same way a particle with momentum would: It bumps the electron and changes the electron’s path. The light is also affected by the collision as though itwere a particle, in that its energy and momentum changes. Momentum is a quantity that can be defined for all particles. For light particles, or photons, momentum depends on the frequency, or color, of the photon, which in turndepends on the photon’s energy. The energy of a photon is equal to a constant number, called Planck’s cons...

• Bicycle.

  narrow as possible to minimize weight and interference with pedaling. F Specialty Bicycles Many other types of bicycles are designed for special purposes. Although not as common as standard single-rider racing, touring, mountain, or recreational bicycles,they nonetheless have significant niches. Recumbent bicycles are bicycles on which the rider sits upright as if in a chair, with legs and feet stretched out in front. Because they support the rider’s lower back,recumbents allow the rider far mo...

• French Revolution.

  B2 Assembly of Notables and Estates-General To pressure the parlements into accepting the plan, Calonne decided to gain prior approval of it from an Assembly of Notables—a group of hand-picked dignitaries hethought would sympathize with his views. But Calonne had badly miscalculated. Meeting in January 1787, the assembly refused to believe that a financial crisis reallyexisted. They had been influenced by Necker’s argument that state finances were sound and suspected that the monarchy was only...

• French Revolution .

  B2 Assembly of Notables and Estates-General To pressure the parlements into accepting the plan, Calonne decided to gain prior approval of it from an Assembly of Notables—a group of hand-picked dignitaries hethought would sympathize with his views. But Calonne had badly miscalculated. Meeting in January 1787, the assembly refused to believe that a financial crisis reallyexisted. They had been influenced by Necker’s argument that state finances were sound and suspected that the monarchy was only...

• Mars (planet) - astronomy.

  The Martian core is probably much like Earth’s, consisting mostly of iron, with a small amount of nickel. If other light elements, particularly sulfur, exist there as well, thecore may be larger than presently thought. From studying Earth’s magnetic field and core, scientists theorize that the motions of the liquid rock in Earth’s core generateits magnetic field. Mars does not have a significant magnetic field, so scientists believe that Mars’s core is probably solid. However, spacecraft data in...

• American Revolution.

  C1 The South Southern agriculture was founded on the cultivation of tobacco, wheat, and corn in Virginia, Maryland, and North Carolina, and of rice and indigo (a blue dye) in SouthCarolina and Georgia. There was a large demand for these crops in Europe. These crops were cultivated with the help of black slaves imported from Africa. The whiteplanter class in the South was the most powerful, both politically and economically. C2 The North Wheat was the main cash crop of the mid-Atlantic colonies...

• American Revolution - U.

  C1 The South Southern agriculture was founded on the cultivation of tobacco, wheat, and corn in Virginia, Maryland, and North Carolina, and of rice and indigo (a blue dye) in SouthCarolina and Georgia. There was a large demand for these crops in Europe. These crops were cultivated with the help of black slaves imported from Africa. The whiteplanter class in the South was the most powerful, both politically and economically. C2 The North Wheat was the main cash crop of the mid-Atlantic colonies...

• Heros and legend

  ‘Relax, Anna,’ he said to her—your dadhad this deep baritone, see, and this British accent.” My grandfathertucks his chin into his neck at this point, to capture the full effect.“ ‘Relax, Anna,’ he said. ‘I only wanted to teach the chap a lessonabout the proper care of other people’s property!’ ”Gramps would start to laugh again until he started to cough,and Toot would mutter under her breath thats he supposed it was a good thing that my father had realized that dropping the pipe had ju...