1868 résultats pour "this"
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Planetary Science - astronomy.
III ORIGINS AND COMPOSITIONS OF PLANETS Astronomers believe that planetary systems are formed of elemental materials that were created in the interiors of giant stars. Some of this material comes from giantstars that shed material into space as they age. Most of the matter to form planets, however, comes from stars that explode as supernovas and spread debris enrichedwith the heavier chemical elements into space. According to the currently accepted views, the most likely first stage in the evo...
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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...
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Physics
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INTRODUCTION
Physics, major science, dealing with the fundamental constituents of the universe, the forces they exert on one another, and the results produced by these forces.
Starting about 1665, at the age of 23, Newton enunciated the principles of mechanics, formulated the law of universal gravitation, separated white light into colors,proposed a theory for the propagation of light, and invented differential and integral calculus. Newton's contributions covered an enormous range of naturalphenomena: He was thus able to show that not only Kepler's laws of planetary motion but also Galileo's discoveries of falling bodies follow a combination of his ownsecond law of m...
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Adolf Hitler
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INTRODUCTION
Adolf Hitler (1889-1945), German political and military leader and one of the 20th century's most powerful dictators.
A Economic Collapse At the end of World War I, the Allies (those countries who had fought against Germany) had demanded that Germany pay reparations—that is, payments for wardamages. The government refused to pay all that was demanded by the Allies. When Germany failed to pay enough, France and Belgium occupied the coal mines in theRuhr industrial area in west central Germany in January 1923. In protest, the German government halted all reparation payments and called for passive resistance by a...
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Adolf Hitler.
A Economic Collapse At the end of World War I, the Allies (those countries who had fought against Germany) had demanded that Germany pay reparations—that is, payments for wardamages. The government refused to pay all that was demanded by the Allies. When Germany failed to pay enough, France and Belgium occupied the coal mines in theRuhr industrial area in west central Germany in January 1923. In protest, the German government halted all reparation payments and called for passive resistance by a...
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Adolf Hitler .
A Economic Collapse At the end of World War I, the Allies (those countries who had fought against Germany) had demanded that Germany pay reparations—that is, payments for wardamages. The government refused to pay all that was demanded by the Allies. When Germany failed to pay enough, France and Belgium occupied the coal mines in theRuhr industrial area in west central Germany in January 1923. In protest, the German government halted all reparation payments and called for passive resistance by a...
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Poliomyelitis.
Physical therapy helps patients with paralytic polio stretch and move affected muscles. This movement minimizes the atrophy, or shrinkage, of affected muscles andlimbs and builds strength. Exercises can also retrain working muscles to compensate for other muscles that have permanently lost the ability to move. Rehabilitativetherapy trains patients to use braces, crutches, and other devices that provide support and aid mobility. V PREVENTION OF POLIO Immunization with polio vaccine is the best w...
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Excerpt from Hard Times - anthology.
Mr Bounderby, the two gentlemen at this present moment walking through Coketown, and both eminently practical, who could, on occasion, furnish more tabularstatements derived from their own personal experience, and illustrated by cases they had known and seen, from which it clearly appeared—in short it was the onlyclear thing in the case—that these same people were a bad lot altogether, gentlemen; that do what you would for them they were never thankful for it, gentlemen; thatthey were restless,...
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Jupiter (planet) - astronomy.
Beneath the supercritical fluid zone, the pressure reaches 3 million Earth atmospheres. At this depth, the atoms collide so frequently and violently that the hydrogenatoms are ionized—that is, the negatively charged electrons are stripped away from the positively charged protons of the hydrogen nuclei. This ionization results in asea of electrically charged particles that resembles a liquid metal and gives rise to Jupiter’s magnetic field. This liquid metallic hydrogen zone is 30,000 to 40,000 k...
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Toys.
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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...
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Wolfgang Amadeus Mozart.
including the sacred style of church music and the so-called galant (courtly) idiom. The elegant though often superficial galant style dominated much instrumental music of the 1760s and 1770s. Mozart’s mastery often demonstrates itself in an ability to expand and deepen the stylistic possibilities of the time. The manner in which heextended the character and form of the concerto, for instance, owes much to his experience in writing operatic arias. A Musical Expressiveness In the masterful Je...
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United States (Overview) - country.
parts. IV UNITED STATES PEOPLE When Europeans first reached North America in the 1520s, they encountered other people—Native Americans—and they also encountered a new geography. Someimagined they were entering “a howling wilderness”—an environment filled with exotic flora and fauna but sparsely populated. In reality, they found their way to alandmass that was widely settled. But soon after the Europeans’ arrival, the population of the Americas plummeted, largely because Native Americans lacked...
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World Energy Supply.
In the 1990s, oil production by non-OPEC countries remained strong and production by OPEC countries rebounded. The result at the end of the 20th century was aworld oil surplus and prices (when adjusted for inflation) that were lower than in 1972. Experts are uncertain about future oil supplies and prices. Low prices have spurred greater oil consumption, and experts question how long world petroleum reservescan keep pace with increased demand. Many of the world’s leading petroleum geologists beli...
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Churchill: "The Sinews of Peace"
On March 5, 1946, in a
safeguards to make it effective, these powers would naturally be confided to that world organisation. Now I come to the second danger of these two marauders which threatens the cottage, the home, and the ordinary people—namely, tyranny. We cannot be blind tothe fact that the liberties enjoyed by individual citizens throughout the British Empire are not valid in a considerable number of countries, some of which are verypowerful. In these States control is enforced upon the common people by variou...
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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...
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Relativity - astronomy.
beta, for example, might be as large as 0.5, and the mass of the electron doubled. The mass of a rapidly moving electron could be easily determined by measuring thecurvature produced in its path by a magnetic field; the heavier the electron, the greater its inertia and the less the curvature produced by a given strength of field ( see Magnetism). Experimentation dramatically confirmed Einstein's prediction; the electron increased in mass by exactly the amount he predicted. Thus, the kinetic ener...
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Ottoman Empire .
fleets at Suez, Egypt; though the Portuguese were not expelled, Selim did manage to prevent the establishment of a total Portuguese monopoly over the spice trade. Selim I died in 1520 after having spent most of his short reign on matters pertaining to the east. His son and successor Süleyman I (reigned 1520-1566) again turnedthe attention of the Ottomans to the west. In August 1521 Süleyman, later known as Süleyman the Magnificent, opened the road to Hungary by capturing Belgrade, aHungarian str...
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Ottoman Empire - History.
fleets at Suez, Egypt; though the Portuguese were not expelled, Selim did manage to prevent the establishment of a total Portuguese monopoly over the spice trade. Selim I died in 1520 after having spent most of his short reign on matters pertaining to the east. His son and successor Süleyman I (reigned 1520-1566) again turnedthe attention of the Ottomans to the west. In August 1521 Süleyman, later known as Süleyman the Magnificent, opened the road to Hungary by capturing Belgrade, aHungarian str...
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Gravitation
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INTRODUCTION
Gravitation, the force of attraction between all objects that tends to pull them toward one another.
precise observations possible, and Galileo was one of the first to use a telescope to study astronomy. In 1609 Galileo observed that moons orbited the planet Jupiter, afact that could not reasonably fit into an earth-centered model of the heavens. The new heliocentric theory changed scientists' views about the earth's place in the universe and opened the way for new ideas about the forces behind planetarymotion. However, it was not until the late 17th century that Isaac Newton developed a theory...
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Gravitation - astronomy.
precise observations possible, and Galileo was one of the first to use a telescope to study astronomy. In 1609 Galileo observed that moons orbited the planet Jupiter, afact that could not reasonably fit into an earth-centered model of the heavens. The new heliocentric theory changed scientists' views about the earth's place in the universe and opened the way for new ideas about the forces behind planetarymotion. However, it was not until the late 17th century that Isaac Newton developed a theory...
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Earth (planet).
Milky Way to complete one revolution around the Galaxy’s center. Earth’s axis of rotation is inclined (tilted) 23.5° relative to its plane of revolution around the Sun. This inclination of the axis creates the seasons and causes the height of the Sun in the sky at noon to increase and decrease as the seasons change. The Northern Hemisphere receives the most energy from the Sun when it is tiltedtoward the Sun. This orientation corresponds to summer in the Northern Hemisphere and winter in the S...
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Earth (planet) - astronomy.
Milky Way to complete one revolution around the Galaxy’s center. Earth’s axis of rotation is inclined (tilted) 23.5° relative to its plane of revolution around the Sun. This inclination of the axis creates the seasons and causes the height of the Sun in the sky at noon to increase and decrease as the seasons change. The Northern Hemisphere receives the most energy from the Sun when it is tiltedtoward the Sun. This orientation corresponds to summer in the Northern Hemisphere and winter in the S...
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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...
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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...
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THE CONTRACT (droit anglais)
REQUIREMENT FOR TERMS OF A CONTRACT Although contracts can be interpreted as almost any monetary exchange for goods or services, the terms of an agreement are often required so that compensation can be obtained if one party fails in its responsibilities. Without such specifications, it becomes almost impossible to seek reparations; for example, "we agree to sell/purchase a car for a fair price" is too vague for any decision to be reached at a later date. That being said, many contracts of a ve...
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Stock Exchange.
A Example of a Trade In an example of a trade, an investor wanting to buy 200 shares—also known as two round lots, of 100 shares each—of IBM stock will telephone or e-mail the order to abrokerage firm. This communication is normally made to an individual called a stockbroker. The investor might desire to buy the shares at the market, or current, price.On the other hand, the investor may choose to pay no more than a set amount per share. The brokerage firm then contacts one of its floor brokers...
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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...
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Medical Ethics.
medical profession. In recent years, however, the field of medical ethics has struggled to keep pace with the many complex issues raised by new technologies for creating and sustaininglife. Artificial-respiration devices, kidney dialysis, and other machines can keep patients alive who previously would have succumbed to their illnesses or injuries.Advances in organ transplantation have brought new hope to those afflicted with diseased organs. New techniques have enabled prospective parents to con...
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Interstellar Matter - astronomy.
silhouette of a cloud of dust. At other times, it blocks only a percentage of the light from behind it, a process known by astronomers as extinction . The long, narrow dark lanes in the Milky Way as seen from Earth are examples of extinction. The amount of extinction is different for different wavelengths of light. A2 Reddening Starlight that does not get completely absorbed by interstellar dust can still be changed by the dust’s effects. As light passes through less dense patches of interstel...
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Memory (psychology).
memory span —how many items people can correctly recall in order. Researchers would show people increasingly long sequences of digits or letters and then ask them to recall as many of the items as they could. In 1956 American psychologist George Miller reviewed many experiments on memory span and concluded that peoplecould hold an average of seven items in short-term memory. He referred to this limit as “the magical number seven, plus or minus two” because the results of thestudies were so consi...
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Abortion.
Intact dilation and extraction, also referred to as a partial birth abortion, consists of partially removing the fetus from the uterus through the vaginal canal, feet first,and using suction to remove the brain and spinal fluid from the skull. The skull is then collapsed to allow complete removal of the fetus from the uterus. III SOCIAL AND ETHICAL ISSUES Abortion has become one of the most widely debated ethical issues of our time. On one side are pro-choice supporters—individuals who favor a...
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Electricity
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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...
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Kidney.
secretion. An additional function of the kidney is the processing of vitamin D; the kidney converts this vitamin to an active form that stimulates bone development. Several hormones are produced in the kidney. One of these, erythropoietin, influences the production of red blood cells in the bone marrow. When the kidney detectsthat the number of red blood cells in the body is declining, it secretes erythropoietin. This hormone travels in the bloodstream to the bone marrow, stimulating theproducti...
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First Americans.
bones and artifacts helped 19th-century archaeologists establish the age of ancient human encampments in Europe. Yet, search as they might, American archaeologists found no comparable evidence of a Pleistocene-era human presence. But several sites revealed stone artifacts thatsome scholars believed looked similar to the ancient stone tools found in Europe. On the basis of this similarity, these experts claimed the American artifacts must be asold. By the 1890s, however, other scholars had challe...
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First Americans - Canadian History.
bones and artifacts helped 19th-century archaeologists establish the age of ancient human encampments in Europe. Yet, search as they might, American archaeologists found no comparable evidence of a Pleistocene-era human presence. But several sites revealed stone artifacts thatsome scholars believed looked similar to the ancient stone tools found in Europe. On the basis of this similarity, these experts claimed the American artifacts must be asold. By the 1890s, however, other scholars had challe...
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Diabetes Mellitus.
Once diabetes is diagnosed, treatment consists of controlling the amount of glucose in the blood and preventing complications. Depending on the type of diabetes, thiscan be accomplished through regular physical exercise, a carefully controlled diet, and medication. Individuals with Type 1 diabetes must receive insulin, often two to four times a day, to provide the body with the hormone it does not produce. Insulin cannot be takenorally, because it is destroyed in the digestive system. Consequent...
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Invertebrate - biology.
animals with a five-pointed design. They live in the sea and move with the help of tiny fluid-filled feet—another feature found nowhere else in the animal world. Zoologists recognize several different groups of worms. The phylum known as flatworms contains the simplest animals possessing heads. Nerves and sense organs areconcentrated in the head. Most flatworms are paper-thin and live in a variety of wet or damp habitats, including the digestive systems of other animals. Roundwormsrepresent anot...
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Invertebrate - biology.
animals with a five-pointed design. They live in the sea and move with the help of tiny fluid-filled feet—another feature found nowhere else in the animal world. Zoologists recognize several different groups of worms. The phylum known as flatworms contains the simplest animals possessing heads. Nerves and sense organs areconcentrated in the head. Most flatworms are paper-thin and live in a variety of wet or damp habitats, including the digestive systems of other animals. Roundwormsrepresent anot...
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Alcoholism.
Although a consensus is growing among health professionals that alcohol dependence is a disease, society’s attitudes toward individuals with drinking problems remainambivalent and confused. Until the mid-20th century, the typical picture of the alcoholic was of someone without steady employment, unable to sustain familyrelationships and most likely in desperate financial straits. But this stereotype was largely dispelled when highly respected people publicly admitted their alcoholdependence and...
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Cosmology - astronomy.
In 1917 American scientist Harlow Shapley measured the distance to several groups of stars known as globular clusters. He measured these distances by using amethod developed in 1912 by American astronomer Henrietta Leavitt. Leavitt’s method relates distance to variations in brightness of Cepheid variables, a class of starsthat vary periodically in brightness. Shapley’s distance measurements showed that the clusters were centered around a point far from the Sun. The arrangement of theclusters was...
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Qur'an.
man who profoundly influenced the history of the world. See Spread of Islam. Muhammad’s home, the Arab city of Mecca, was a major religious center and site of the revered sanctuary and shrine, the Kaaba. According to legend, the ancientreligious patriarch of the Hebrew Bible, Abraham, and his son, Ishmael, built the shrine using foundations laid by the first human being and father of humankind, Adam.During Muhammad’s years there, from about AD 570 to 622, Mecca was also an environment of spir...
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Michelangelo
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INTRODUCTION
Michelangelo (1475-1564), Italian painter, sculptor, architect, and poet whose artistic accomplishments exerted a tremendous influence on his contemporaries and on
subsequent European art.
(17 ft) tall, was carved from a block of stone that another sculptor had left unfinished. Michelangelo drew on the classical tradition in depicting David as a nude,standing with his weight on one leg, the other leg at rest ( see contrapposto). This pose suggests impending movement, and the entire sculpture shows tense waiting, as David sizes up his enemy and considers his course of action. While David reveals Michelangelo's expert knowledge of anatomy (he had been dissecting corpses for about...
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Michelangelo.
(17 ft) tall, was carved from a block of stone that another sculptor had left unfinished. Michelangelo drew on the classical tradition in depicting David as a nude,standing with his weight on one leg, the other leg at rest ( see contrapposto). This pose suggests impending movement, and the entire sculpture shows tense waiting, as David sizes up his enemy and considers his course of action. While David reveals Michelangelo's expert knowledge of anatomy (he had been dissecting corpses for about...
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Industrial Revolution
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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...
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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...
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Cubism
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INTRODUCTION
Cubism, movement in modern art, especially in painting, invented by Spanish artist Pablo Picasso and French artist Georges Braque in 1907 and 1908.
Mont Sainte-Victoire by CézanneFrench artist Paul Cézanne painted Mont Sainte-Victoire, a mountain near his home in Provence in southern France, onmany occasions. Over time, the images he produced became flatter, less realistic, and more abstract. In this late version,painted from 1902 to 1904, patches of color barely indicate the mountain, sky, and foreground, while creating a rhythmicpattern across the painting’s surface. The mountain and sky, both intensely blue, appear almost to merge.Philad...
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Skin.
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INTRODUCTION
Skin, outer body covering of an animal. The term skin
III SKIN APPENDAGES In humans, the skin appendages, or structures embedded in the skin, include hair, nails, and several types of glands. Glands are groups of cells that produce andsecrete substances needed by other parts of the body. In other vertebrates, the skin appendages include scales (in fish and reptiles) and feathers (in birds). Together,the skin and the skin appendages are known as the integumentary system of the body. A Hair Hair is a distinguishing characteristic of mammals, a gro...
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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...
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Race - biology.
distributed as a cline, generally varying along a north-south line. Skin color is lightest in northern Europeans, especially in those who live around the Baltic Sea, andbecomes gradually darker as one moves toward southern Europe, the Mediterranean, the Middle East, and into northern Africa and northern subtropical Africa. Skin isdarkest in people who live in the tropical regions of Africa. The lack of clear-cut discontinuities makes any racial boundary based on skin color totally arbitrary. Sim...
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From Bush v.
legal requirements. This case has shown that punch card balloting machines can produce an unfortunate number of ballots which are not punched in a clean, complete way by the voter.After the current counting, it is likely legislative bodies nationwide will examine ways to improve the mechanisms and machinery for voting. B The individual citizen has no federal constitutional right to vote for electors for the President of the United States unless and until the state legislature chooses astatewide...