972 résultats pour "called"
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Comparative Anatomy.
In comparing two species, anatomists have to be careful to differentiate between homologous structures, which are ones that have evolved from a shared ancestor, andanalogous structures, which have developed from different origins. Homologous structures are built on the same underlying plan. A human arm, a bat’s wing, and awhale’s flipper look quite different from the outside, but the bones inside reveal that these limbs all have the same basic structure. Analogous structures, by contrast,often l...
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Abraham Lincoln
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INTRODUCTION
Abraham Lincoln (1809-1865), 16th president of the United States (1861-1865) and one of the great leaders in American history.
fence in 4 hectares (10 acres) to grow corn. Then he hired out to neighbors, helping them to split rails. That year, Lincoln attended a political rally and was persuaded tospeak on behalf of a local candidate. It was his first political speech. A witness recalled that Lincoln “was frightened but got warmed up and made the best speech of theday.” In 1831 Lincoln made a second trip to New Orleans. He was hired, along with his stepbrother and a cousin, by Denton Offutt, a Kentucky trader and specul...
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Abraham Lincoln.
fence in 4 hectares (10 acres) to grow corn. Then he hired out to neighbors, helping them to split rails. That year, Lincoln attended a political rally and was persuaded tospeak on behalf of a local candidate. It was his first political speech. A witness recalled that Lincoln “was frightened but got warmed up and made the best speech of theday.” In 1831 Lincoln made a second trip to New Orleans. He was hired, along with his stepbrother and a cousin, by Denton Offutt, a Kentucky trader and specul...
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Abraham Lincoln
fence in 4 hectares (10 acres) to grow corn. Then he hired out to neighbors, helping them to split rails. That year, Lincoln attended a political rally and was persuaded tospeak on behalf of a local candidate. It was his first political speech. A witness recalled that Lincoln “was frightened but got warmed up and made the best speech of theday.” In 1831 Lincoln made a second trip to New Orleans. He was hired, along with his stepbrother and a cousin, by Denton Offutt, a Kentucky trader and specul...
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Abraham Lincoln - USA History.
fence in 4 hectares (10 acres) to grow corn. Then he hired out to neighbors, helping them to split rails. That year, Lincoln attended a political rally and was persuaded tospeak on behalf of a local candidate. It was his first political speech. A witness recalled that Lincoln “was frightened but got warmed up and made the best speech of theday.” In 1831 Lincoln made a second trip to New Orleans. He was hired, along with his stepbrother and a cousin, by Denton Offutt, a Kentucky trader and specul...
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Football.
C Special Teams Each team has players who enter the game during special plays such as kickoffs, field goals, punts, and returns. The kicker kicks off at the beginning of a game or half,and after his team has scored. The kicker also scores points for the offensive team by kicking the ball through the goalpost’s vertical posts, also known as the uprights;these scores are called field goals. When the offensive team must surrender the ball to the opponents, a punter comes in to kick the ball downfi...
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Ship.
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INTRODUCTION
Ship, vessel that is buoyant in the water and used
B1 Biremes Experience soon proved that longer ships posed a new set of problems: They were weaker structurally, more difficult to maneuver, and presented a larger target to anyenemy ship with a ram. In the 8th century BC Mediterranean shipbuilders eliminated these problems with the bireme , a war galley built to accommodate two levels, or banks , of oarsmen. Oarsmen on the lower level rowed oars from ports cut into the side of the vessel, while those above rowed from the deck. This arrangemen...
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Heart.
situation. A Cardiac Cycle Although the right and left halves of the heart are separate, they both contract in unison, producing a single heartbeat. The sequence of events from the beginning ofone heartbeat to the beginning of the next is called the cardiac cycle. The cardiac cycle has two phases: diastole, when the heart’s chambers are relaxed, and systole,when the chambers contract to move blood. During the systolic phase, the atria contract first, followed by contraction of the ventricles. T...
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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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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...
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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...
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Igneous Rock.
As a magma cools, the first crystals to form will be of minerals that become solid at relatively high temperatures (usually olivine and a type of feldspar known asanorthite). The composition of these early-formed mineral crystals will be different from the initial composition of the magma. Consequently, as these growing crystalstake certain elements out of the magma in certain proportions, the composition of the remaining liquid changes. This process is known as magmatic differentiation.Sometime...
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Meteorology.
to find the corresponding relative humidity and dew-point temperature. III SPECIAL METEOROLOGICAL INSTRUMENTS Meteorologists have developed several sophisticated instruments that measure multiple physical characteristics of the air simultaneously and at more than one location.The most important of these special instruments are radiosondes, Doppler radar, and weather satellites. A Radiosonde A radiosonde measures air temperature, air pressure, and humidity from the earth’s surface up to an alt...
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Indian Music
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INTRODUCTION
Classical Dance of South India
The southern Indian kathakali is a dance drama that dates from the 17th century.
Sangita Ratnakara, was written in the 13th century. However, subsequent writers tended to focus on the emotional connotations of individual ragas, associating them with moods, performance times, colors, and deities, and grouping them in terms of families. The modern theoretical system began in the 16th century, when ragasbegan to be classified according to scale—72 in the Karnāṭak system and 10 principal ones in the Hindustani. The 72 mela, as the Karn āṭak scales are called, are derived thro...
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Ear.
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INTRODUCTION
Ear, organ of hearing and balance. Only vertebrates, or animals
line or rotates in any direction. Each canal also contains sensory areas with sensory hair cells that project into a cone-shaped cap of gelatin. Two of the semicircularcanals are in a vertical position and are used to detect vertical movement, such as jumping or falling. The third canal is horizontal and detects horizontal movement,such as turning or spinning. The action of the canals depends on the inertia of the fluid inside. When the motion of the body changes, the fluid lags behind, causing...
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Hardware (computer).
Magnetic tape drives use magnetic tape similar to the tape used in VCR cassettes. Tape drives have a very slow read/write time, but have a very high capacity; in fact,their capacity is second only to hard disk drives. Tape drives are mainly used to back up data. Compact disc drives store information on pits burned into the surface of a disc of reflective material ( see CD-ROM). CD-ROMs can store up to 737 megabytes (MB) of data. A Compact Disc-Recordable (CD-R) or Compact Disc-ReWritable (CD-RW)...
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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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Atom
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INTRODUCTION
Water Molecule
A water molecule consists of an oxygen atom and two hydrogen atoms, which are attached at an angle of 105°.
spontaneously break apart and change, or decay, into other atoms. Unlike electrons, which are fundamental particles, protons and neutrons are made up of other, smaller particles called quarks. Physicists know of six different quarks.Neutrons and protons are made up of up quarks and down quarks —two of the six different kinds of quarks. The fanciful names of quarks have nothing to do with their properties; the names are simply labels to distinguish one quark from another. Quarks are unique amo...
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Cancer (medicine).
unable to repair the DNA damage, p53 instructs the cell to undergo programmed cell death, or apoptosis , putting a stop to runaway cell division before it starts. Programmed cell death is a normal part of cell life and is tightly controlled by many genes, primarily p53. In a cancerous cell, one or more mutations prevent these genes from doing their jobs. When mutated, p53 allows a cell to continue to divide, even with damaged DNA.This can lead to additional mutations in proto-oncogenes or tumor...
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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...
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Gemstones.
In the late 1960s a method was developed for “growing” diamonds by heating a diamond particle to a high temperature and subjecting it to methane gas. The gasdecomposes into carbon atoms, which adhere to the diamond crystal. The crystal structure of the enlarged diamond is identical to that of a natural diamond. Diamondsof about 1 carat (200 mg or 0.007 oz) have been produced by this method, but their cost is still considerably higher than that of naturally occurring diamonds. Sapphires are made...
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Observatory - astronomy.
Ultraviolet radiation, X rays, and gamma rays have shorter wavelengths than visible light has. These types of radiation tell astronomers about the hottest and mostviolent phenomena in the universe. Earth’s atmosphere blocks most of this radiation, so astronomers must send their observatories above the atmosphere aboardballoons, rockets, or satellites. Ultraviolet telescopes are much like visible light telescopes, but X-ray telescopes must have special nested cylindrical mirrors to prevent Xrays...
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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...
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Genetics - biology.
construct identical buildings. Just as each contractor would require a full copy of the blueprint to construct a complete building, each new cell needs a complete copy ofan organism’s genetic information to function properly. Organisms use two types of cell division to ensure that DNA is passed down from cell to cell during reproduction. Simple one-celled organisms and other organisms thatreproduce asexually—that is, without the joining of cells from two different organisms—reproduce by a proces...
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Circulatory System.
C Additional Functions In addition to oxygen, the circulatory system also transports nutrients derived from digested food to the body. These nutrients enter the bloodstream by passingthrough the walls of the intestine. The nutrients are absorbed through a network of capillaries and veins that drain the intestines, called the hepatic portal circulation.The hepatic portal circulation carries the nutrients to the liver for further metabolic processing. The liver stores a variety of substances, suc...
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Fish - biology.
pectoral fins provide fine movements, add forward thrust, or, together with the pelvic fins, serve as brakes. Typically, fins consist of a thin membrane stretched over afanlike series of thin rods called spines or rays. Most fish breathe underwater with the help of special respiratory organs called gills. Gills are made of a series of thin sheets or filaments through which blood circulates.As water moves into a fish’s mouth and passes over the gills, dissolved oxygen passes across the thin gill...
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Butterflies and Moths - biology.
The smallest butterflies are certain blues that have wingspans of a mere 0.7 cm (0.25 in). The largest are the female giant birdwings of Papua New Guinea, whichmeasure up to 30 cm (12 in) across. Moths range in size from tiny Microlepidoptera, several groups of small moths with wings no more than 0.16 cm (0.06 in) across, togiant silk moths, such as the atlas moth, which may exceed 30 cm (12 in) in wingspan. IV REPRODUCTION AND LIFE CYCLE Butterflies locate potential mates by sight, identifyin...
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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...
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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...
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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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Shark - biology.
Sharks have two-chambered hearts that are relatively small compared to the rest of their bodies. Blood flows from the heart to the gills, where it collects oxygen fromwater and then distributes it to the other organs and tissues. The small heart produces weak blood pressure, and many sharks must swim continuously to create themuscular contractions needed to circulate blood throughout their bodies. Most sharks are cold-blooded—that is, they do not generate heat by digesting food. Instead, the bod...
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Paris (city, France) - geography.
and its vibrant public square, frequented by street performers, soon became among the most popular landmarks in the city. West of the Pompidou Center is Les Halles, the site of the central market of Paris from the 12th century until 1969. The market was subsequently replaced by the Forum LesHalles, a multilevel underground complex featuring a shopping mall, museums, the Paris film library ( vidéothèque ), and a sports center. The street level of Les Halles features a garden, the Jardin des Halle...
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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...
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Russian Revolutions of 1917 (Histoire) .
as Marxists. They believed that the working class—with its struggles to organize trade unions and to bring about political reforms of benefit to the majority ofpeople—would become the primary force for revolutionary change. The Russian Marxists formed the Russian Social Democratic Labor Party (RSDLP) in 1898. By 1903,however, the RSDLP had split into two factions. The faction called the Bolsheviks (from the Russian word for “majority”), led by Vladimir Ilich Lenin, favored a more centralized a...
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Horse - biology.
Horses reach sexual maturity at about one and a half years. The estrous cycle in the mare—a mature female horse—typically lasts 21 days. During the first five days ofthe cycle, the mare is usually receptive to mating. The estrous cycle stops during winter and resumes in the spring, which is the start of the breeding season. Astallion—a mature male horse—approaching a mare in estrus engages in various courtship rituals. These include uttering nickering sounds and sniffing and licking themare’s ge...
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Animal Courtship and Mating - biology.
activity. These animals frequently copulate in water, and the penis helps transfer sperm before it is carried away by the currents Ostriches and rheas also contain apenis within the cloaca. Virtually all snakes and lizards display yet another variation of internal fertilization. Located in the tail are two penises, called hemepenes, which are covered by spinesand knobs that help lock it into place during mating. The male uses one hemepene at a time for copulation. Male salamanders secrete large...
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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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Globalization.
higher living standard for their people. The World Bank made loans to developing countries for dams and other electrical-generating plants, harbor facilities, and otherlarge projects. These projects were intended to lower costs for private businesses and to attract investors. Beginning in 1968 the World Bank focused on low-cost loansfor health, education, and other basic needs of the world’s poor. B International Monetary Fund The IMF makes loans so that countries can maintain the value of thei...
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United States Senate.
providing for military forces, and declaring war. Article I, Section 8, also gives Congress implied powers—to “make all laws which shall be necessary and proper” forcarrying out the enumerated powers, and to investigate and oversee the executive branch. The Senate also has the power to conduct impeachment trials against thepresident, federal judges, and other officials. The Senate can only impeach someone after the House brings charges, however. A two-thirds majority vote of thesenators in the c...
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Chromosome.
chromosome breaks off and attaches to another chromosome. A translocation involving chromosomes 9 and 22 is linked to a type of leukemia called chronic myelogenicleukemia. On the sex chromosomes, problems arise in men when an abnormal gene is present on the X chromosome. With no healthy gene found on the Y chromosometo override the abnormal gene, disease may result. For example, men who inherit a mutated gene that causes hemophilia from their mother on the X chromosome willdevelop this bleeding...
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Aging - biology.
Different theories have been proposed to explain how SF works. One theory is based on the assumption that aging, and diseases that occur more frequently withadvancing age, are caused by structural damage to cells. This damage accumulates in tiny amounts each time the cell divides, eventually preventing the cell fromcarrying out normal functions. One cause of this damage may be free radicals, which are chemical compounds found in the environment and also generated by normal chemical reactions in...
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Machine
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INTRODUCTION
Machine, simple device that affects the force, or effort, needed to do a certain amount of work.
to decrease the amount of force needed to do work or to change the direction of the force. The wheel and axle and some levers can also be used to increase the speedof performance of a task, but doing so always increases the amount of force needed. A Inclined Plane NutsNuts are pieces of metal with a hole in the middle. They are screwed on the end of a bolt as a fastening. Nuts come invarying shapes, depending on their intended use.© Microsoft Corporation. All Rights Reserved. Ramps and staircas...
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Crusades.
modern Lebanon; the Principality of Antioch, in modern Syria; and the County of Edessa, in modern northern Syria and southern Turkey. IV CRUSADES OF THE 12TH CENTURY The Crusades of the 12th century, through the end of the Third Crusade in 1192, illustrate the tensions and problems that plagued the enterprise as a whole. For thelords of Outremer a compromise with the residents and Muslim powers made sense; they could not live in constant warfare. And yet as European transplants theydepended on...
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Crusades .
modern Lebanon; the Principality of Antioch, in modern Syria; and the County of Edessa, in modern northern Syria and southern Turkey. IV CRUSADES OF THE 12TH CENTURY The Crusades of the 12th century, through the end of the Third Crusade in 1192, illustrate the tensions and problems that plagued the enterprise as a whole. For thelords of Outremer a compromise with the residents and Muslim powers made sense; they could not live in constant warfare. And yet as European transplants theydepended on...
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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...
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Teeth.
treatments to reduce the risk of tooth decay; clear plastic coatings painted on the teeth, called dental sealants, and applications of the mineral fluoride, which fortifiestooth enamel, are two such treatments. Fluoride is also added to public water supplies in a process called fluoridation, which benefits more than 150 million Americans. Gum disease, or periodontal disease, is a progressive condition that worsens with age. Gum disease occurs when bacteria eat away at gum tissue, causing it to p...
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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...
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Development (biology) - biology.
Understanding the molecular machinery within cells gives biologists a direct basis for understanding growth, because growth is the synthesis of new protoplasm, andbiologists know the basic mechanism of this synthesis. One key gap, however, exists in this knowledge. Biologists want to know not only how substances aresynthesized but also how growth is controlled so that the proportions of an animal or plant remain consistent from generation to generation. The direction and amountof growth, which a...