68 résultats pour "shaped"
- shaped canvas shaped canvas, terme anglo-saxon signifiant littéralement « toile découpée
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Telescope - astronomy.
Observatory). In some telescopes designed in the 1990s, the mirror’s weight has been dramatically reduced by sandwiching a honeycomb pattern of glass ribs between a thin, butrigid, concave mirror and a flat back plate. Engineers have even developed meniscus mirrors—mirrors that are too thin to support their own weight. An adjustableframework supports the meniscus mirror, and servomechanical actuators, controlled by computer, continually adjust the shape of the mirror as it tracks celestial tar...
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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...
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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...
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Native American Architecture.
B Relationship to the Universe and Nature A more profound difference between European American and Native American perceptions lay in how human beings saw themselves in relationship to the universe andin what they believed their responsibilities were to the natural world and to each other. Most European Americans saw themselves as separate from creation andadversaries of nature, ever struggling to conquer and subdue nature and force it to yield to their will. Native Americans saw themselves as...
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Anthropology.
humans, such as tools, pottery, and buildings) and human fossils (preserved bones). They also examine past environments to understand how natural forces, such as climate and available food, shaped the development of human culture. Some archaeologists study cultures that existed before the development of writing, a time knownas prehistory . The archaeological study of periods of human evolution up to the first development of agriculture, about 10,000 years ago, is also called paleoanthropology....
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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...
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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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Ear.
I
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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Respiratory System.
rapidly, or laughs while swallowing, the swallowing reflex may not work, and food or fluid can enter the larynx. Food, fluid, or other substances in the larynx initiate acough reflex as the body attempts to clear the larynx of the obstruction. If the cough reflex does not work, a person can choke, a life-threatening situation. TheHeimlich maneuver is a technique used to clear a blocked larynx ( see First Aid). A surgical procedure called a tracheotomy is used to bypass the larynx and get air to...
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Cell (biology) - biology.
proteins, or other proteins required by the cell. While relatively simple in construction, prokaryotic cells display extremely complex activity. They have a greater range of biochemical reactions than those found in theirlarger relatives, the eukaryotic cells. The extraordinary biochemical diversity of prokaryotic cells is manifested in the wide-ranging lifestyles of the archaebacteria andthe bacteria, whose habitats include polar ice, deserts, and hydrothermal vents—deep regions of the ocean un...
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Native American Architecture
I
INTRODUCTION
Native American Architecture, traditional architecture of the peoples of who lived in North America before Europeans arrived.
Mound Builders who resided in the area.John Elk III/Bruce Coleman, Inc. Another mound building culture, named Hopewell, also appears to have originated in Ohio but expanded west to Iowa, Kansas, and Oklahoma, south to Louisiana,Mississippi, and Alabama, east to Georgia and the Appalachian Mountains, and north to Wisconsin, Michigan, and lower Ontario in Canada. The Hopewell culture lastedfrom about 200 BC to 400 AD. Hopewell people built large, linear mounds to create enclosures in geometrical...
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Valley.
Except in mountainous terrain, rivers are almost always flanked by floodplains. Floodplains are flat wide deposits of alluvium, river-deposited sediment, on either side of the river channel. During floods, a river overflows its banks and spreads out the sediment near the river to form a floodplain. Floodplains of large rivers, such as thoseof the Mississippi River, can be flat areas tens of kilometers across. River channels migrate back and forth across their floodplains as alluvium is repeate...
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Valley - Geography.
Except in mountainous terrain, rivers are almost always flanked by floodplains. Floodplains are flat wide deposits of alluvium, river-deposited sediment, on either side of the river channel. During floods, a river overflows its banks and spreads out the sediment near the river to form a floodplain. Floodplains of large rivers, such as thoseof the Mississippi River, can be flat areas tens of kilometers across. River channels migrate back and forth across their floodplains as alluvium is repeate...
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Volcano.
before eruption. Very violent explosive eruptions are called Plinian eruptions, after Roman naturalist Pliny the Elder. These eruptions can last for several hours to daysand eject a large amount of pyroclastic material. Some volcanoes can produce much more energetic eruptions that eject materials farther from the vents because oftheir andesitic and dacitic composition. Andesitic and dacitic lava is generally thicker than basaltic lava. Stiff lava generally produces more-explosive eruptions. B No...
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Saturn - astronomy.
measurements of the magnetic field made by the Voyager space probes in the 1980s. Additional Cassini findings reported in March 2007 suggested that particles originating from geysers on the moon Enceladus may provide a partial explanation for thechange. The neutral gas particles become electrically charged and are captured by Saturn’s magnetic field, forming a disk of hot, ionized gas around the planet’sequator. The charged particles interact with the magnetic field and slow down the rotation of...
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Ancient Rome .
attributed to Numa, including the selection of virgins to be priestesses of the goddess Vesta. He also established a calendar to differentiate between normal workingdays and those festival days sacred to the gods on which no state business was allowed. His peaceful reign lasted from 715 to 673 BC. Under Tullus Hostilius (672–641 BC) the Romans waged an aggressive foreign policy and began to expand their lands by the conquest of nearby cities like Alba Longa. When the warlike King Hostilius co...
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Ancient Rome - USA History.
attributed to Numa, including the selection of virgins to be priestesses of the goddess Vesta. He also established a calendar to differentiate between normal workingdays and those festival days sacred to the gods on which no state business was allowed. His peaceful reign lasted from 715 to 673 BC. Under Tullus Hostilius (672–641 BC) the Romans waged an aggressive foreign policy and began to expand their lands by the conquest of nearby cities like Alba Longa. When the warlike King Hostilius co...
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LES SHAPED CANVAS DE STELLA
Le minimalisme, ou la mort de la peinture Si la critique reste longtemps réser vée, dès ses prem ières expositions, Stella attire l'attention de quelques artistes. La peinture , avec lui, semble menée à ses limites. Les ressources de la surface picturale explorées à fond, il faut passe r à la création de volume s. Or, si Stella envisage l'œ uvre peinte dans ses trois dimensions, il reste un peintre et s'inte rdit de de ven ir un créateur...
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Stone Age.
limestone, quartzite, and indurated shale. Ground stone tools could be made on a wider range of raw material types, including coarser grained rock such as granite. Flaking produces several different types of stone artifacts, which archaeologists look for at prehistoric sites. The parent pieces of rock from which chips have beendetached are called cores, and the chips that have been removed from cores are called flakes. A flake that has had yet smaller flakes removed from one or more edgesin orde...
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Africa.
The highest elevations in Africa are found in the various ranges of East Africa. After Kilimanjaro, the next highest peaks are Mount Kenya (5,199 m/17,057 ft), north ofKilimanjaro in central Kenya; Margherita Peak (5,109 m/ 16,762 ft) in the Ruwenzori Range on the border between Uganda and the Democratic Republic of the Congo(DRC); Ras Dashen (4,620 m/ 15,157 ft) in the Ethiopian Highlands of northern Ethiopia; Mount Meru (4,565 m/ 14,977 ft), close to Kilimanjaro in Tanzania; and MountElgon (4,...
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Africa - Geography.
The highest elevations in Africa are found in the various ranges of East Africa. After Kilimanjaro, the next highest peaks are Mount Kenya (5,199 m/17,057 ft), north ofKilimanjaro in central Kenya; Margherita Peak (5,109 m/ 16,762 ft) in the Ruwenzori Range on the border between Uganda and the Democratic Republic of the Congo(DRC); Ras Dashen (4,620 m/ 15,157 ft) in the Ethiopian Highlands of northern Ethiopia; Mount Meru (4,565 m/ 14,977 ft), close to Kilimanjaro in Tanzania; and MountElgon (4,...
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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...
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Tree - biology.
The major parts of a tree are its roots, trunk, leaves, flowers, and seeds. These components play vital roles in a tree’s growth, development, and reproduction. A Roots Trees are held in place by anchoring organs called roots. In addition to anchoring the tree, roots also absorb water and minerals through tiny structures called roothairs. From the roots the water and mineral nutrients are carried upward through the wood cells to the leaves. Although the internal structure of most kinds of roots...
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Canadian Architecture
I
INTRODUCTION
L'Anse aux Meadows
In around ad 1000 Norse Vikings sailed from Greenland to North America and set up a village on the tip of what is now
the island of Newfoundland's Great Northern Peninsula.
IglooSome Inuit peoples in the Arctic regions of Canada live in domed houses of snow, or igloos, which provide good insulationand protection from wind. The word igloo comes from the Inuit iglu, meaning “house.”George Holton/Photo Researchers, Inc. Canada’s original inhabitants are known as the First Nations. At the time of European arrival, about 40 nations were scattered across Canada. Many of them lived alongthe coasts, where they could fish. These nations can be classified into five major gro...
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Moon - astronomy.
B Volcanic Features Maria, domes, rilles, and a few craters display indisputable characteristics of volcanic origin. Maria are plains of dark-colored rock that cover approximately 40 percent ofthe Moon's visible hemisphere. The maria formed when molten rock erupted onto the surface and solidified between 3.16 billion and 3.96 billion years ago. This rockresembles terrestrial basalt, a volcanic rock type widely distributed on Earth, but the rock that formed the maria has a higher iron content an...
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Africa - history.
Africa’s other major mountainous regions occur at the northern and southern fringes of the continent. The Atlas Mountains, a system of high ranges, extend for 2,200 km(1,400 mi) across Morocco, Algeria, and Tunisia, roughly parallel to the northern coast. These ranges enclose a number of broad inland basins and plateaus. In the west, theHigh (or Grand) Atlas contains Toubkal (4,165 m/ 13,665 ft), the highest peak of the system. Toward the east, the Atlas consists of two parallel ranges: the Tell...
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Africa.
The highest elevations in Africa are found in the various ranges of East Africa. After Kilimanjaro, the next highest peaks are Mount Kenya (5,199 m/17,057 ft), north ofKilimanjaro in central Kenya; Margherita Peak (5,109 m/ 16,762 ft) in the Ruwenzori Range on the border between Uganda and the Democratic Republic of the Congo(DRC); Ras Dashen (4,620 m/ 15,157 ft) in the Ethiopian Highlands of northern Ethiopia; Mount Meru (4,565 m/ 14,977 ft), close to Kilimanjaro in Tanzania; and MountElgon (4,...
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Coral Reef.
sensitive to particles of mud or sediment settling on them, which means that corals rarely grow close to rivers or other sources of sediment. In the sea, light is filteredout by depth, so reef-building corals can only grow in relatively shallow water. Even in the clearest oceans few reef-building corals grow below a depth of 80 to 100 m(260 to 328 ft). Although corals need nutrients, they cannot thrive in areas where there are large amounts of nutrients. Typically, microscopic organisms in the p...
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Turtle.
Turtles use their jaws to cut and handle food. Instead of teeth, a turtle’s upper and lower jaws are covered by horny ridges, similar to a bird’s beak. Meat-eating turtlescommonly have knife-sharp ridges for slicing through their prey. Plant-eating turtles often have ridges with serrated edges that help them cut through tough plants.Turtles use their tongues in swallowing food, but unlike many other reptiles, such as chameleons, they cannot stick out their tongues to capture food. C Limb Structu...
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Turtle - biology.
Turtles use their jaws to cut and handle food. Instead of teeth, a turtle’s upper and lower jaws are covered by horny ridges, similar to a bird’s beak. Meat-eating turtlescommonly have knife-sharp ridges for slicing through their prey. Plant-eating turtles often have ridges with serrated edges that help them cut through tough plants.Turtles use their tongues in swallowing food, but unlike many other reptiles, such as chameleons, they cannot stick out their tongues to capture food. C Limb Structu...
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Automobile.
Electric motors have been used to power automobiles since the late 1800s. Electric power supplied by batteries runs the motor, which rotates a driveshaft, the shaftthat transmits engine power to the axles. Commercial electric car models for specialized purposes were available in the 1980s. General Motors Corporation introduced amass-production all-electric car in the mid-1990s. Automobiles that combine two or more types of engines are called hybrids. A typical hybrid is an electric motor with ba...
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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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Carbon - chemistry.
Graphite is black and slippery and conducts electricity. In graphite, the atoms form planar, or flat, layers. Each layer is made up of rings containing six carbon atoms.The rings are linked to each other in a structure that resembles the hexagonal mesh of chicken wire. Each atom has three sigma bonds (with 120° between any two ofthe bonds) and belongs to three neighboring rings. The fourth electron of each atom becomes part of an extensive pi bond system. Graphite conducts electricity,because th...
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Library of Congress.
manuscripts, books, and films. The Digital Library’s eventual goal is to make available 80 million items from the Library of Congress’s collection that are not easilyavailable elsewhere. V ORGANIZATION AND FUNDING The librarian of Congress serves as the director of the institution. Tradition, politics, and strong personalities have shaped the function of this office. Although the Libraryof Congress was established in 1800, the office of librarian was not created until passage of a law in 1802....
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Mountain Climbing.
teeth on one side, and a straight, flat, metal blade called an adze on the other. Ice axes have many uses. One of the most common is to help the climber stay balanced on steep slopes. The climber swings the axe with a short, quick movement to lodge the pick in snow or ice, creating a secure anchor. If a climber should slip and beginsliding down a snowfield, a self-arrest can be performed by turning face down on the snow and burying the pick in the snow surface. The climber’s weight over the...
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Fishing.
directly to the spool and turns the spool one rotation at a time. C Fishing Lines Fishing lines serve as the link between the angler’s reel and the lure or bait. The most popular line used for sportfishing is monofilament nylon line, which is strong anddurable and has a certain amount of stretch, which helps when an angler sets the hook. The line comes in a variety of strengths, from 2-pound test to more than 100-pound test. (Pound test is the amount of pressure that can be put on a line before...
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Bear - biology.
programs sponsored by zoos or other breeding centers have attempted to breed giant pandas in captivity, although most of these programs have proved unsuccessful.Among the difficulties faced by captive breeders has been the problem of encouraging a female giant panda to mate with a selected male during the two to three daysof the year when she is most fertile, a period known as estrus. B Spectacled Bear Creamy-white rings surrounding the eyes give the spectacled bear its name. Its shaggy coat of...
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Rain Forest.
dropped into the heart of the forest by helicopters. Suspended from the crane’s long, movable arm is a large gondola that functions as a mobile treetop laboratory.Moving from tree to tree, forest researchers collect specimens, conduct experiments, and observe life in the canopy frontier. The highest stratum of the rain forest is made up of the emergent trees, those individuals that stick up above the forest canopy. Emergents, which do not form acontinuous layer, are usually the giants of the for...
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Submarine.
B Propulsion Modern submarines use either diesel-electric or nuclear power to drive the sub's propeller and to provide internal electric power. Diesel-electric power emerged as themost efficient propulsion system for submarines in the early 20th century, following unsuccessful attempts to use steam or gasoline power. While on the surface, thesubmarine uses a diesel engine to drive the propeller and generate electricity. When submerged, a battery-driven electrical motor takes over for propulsion...
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Metalwork
I
INTRODUCTION
Metalwork, in the fine arts, objects of artistic, decorative, and utilitarian value made of one or more kinds of metal--from precious to base--fashioned by either casting,
hammering, or joining or a combination of these techniques.
Early Bronze DiskThis disk with the head of Acheloos, an Etruscan river god, was made of bronze, an alloy of copper and tin, sometime inthe early 5th century bc. It comes from the necropolis of Monte Quaglieri in Tarquinia. Alloys are made by smelting twodifferent metals together.Scala/Art Resource, NY Knowledge of smelting ultimately led to knowledge of mixing different ores together in the smelting process to produce simple alloys. This followed an intermediateperiod, about 3000 BC, when comp...
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Native American Art.
folding, braiding or weaving, could also be sewn onto the hide. The production of decorated clothing and bags increased after contact with Europeans as a greater variety of textiles and other materials became available throughtrade. Imported glass beads inspired native women, who quickly adapted quillwork techniques for the creation of beaded apparel. European curvilinear and floraldesigns of the 19th century proved as meaningful for the native women who worked with them as they were for the non...
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Rocket.
the vacuum of space, however, demonstrated that this belief was not true. In fact, rockets produce more thrust in the vacuum of space than on Earth. Air pressure andfriction with the air reduce a rocket’s thrust by about 10 percent on Earth as compared to the rocket’s performance in space. B Thrust and Efficiency Thrust is a measurement of the force of a rocket, or the amount of “push” exerted backward to move a rocket forward. Thrusts vary greatly from rocket to rocket.Engineers measure thrust...
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Rocket - astronomy.
the vacuum of space, however, demonstrated that this belief was not true. In fact, rockets produce more thrust in the vacuum of space than on Earth. Air pressure andfriction with the air reduce a rocket’s thrust by about 10 percent on Earth as compared to the rocket’s performance in space. B Thrust and Efficiency Thrust is a measurement of the force of a rocket, or the amount of “push” exerted backward to move a rocket forward. Thrusts vary greatly from rocket to rocket.Engineers measure thrust...
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Child Development.
developmental scientists have studied how cultural values guide the skills and attitudes that children acquire as they mature, and how brain maturation influences thedevelopment of thinking and feeling. For a more detailed discussion of child development theories, see the Theories of Child Development section of this article. III BASIC QUESTIONS A Nature and Nurture Scholars have long debated the relative importance of nature (hereditary influences) and nurture (environmental influences) i...
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Northwest Territories - Geography.
million years ago by the severe bending (folding) and faulting (breaking) of sedimentary rock that was once part of the Interior Plains. During the Wisconsin Ice Age,alpine glaciers covered the Cordillera, and the movement of the glaciers created razor-sharp peaks and ridges in these mountains. The moving glaciers also createdbroad U-shaped valleys. To the east of the Interior Plains, the ancient rocks of the Canadian Shield are exposed at the Earth’s surface, resulting in a rough, rolling terra...
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Northwest Territories - Canadian History.
million years ago by the severe bending (folding) and faulting (breaking) of sedimentary rock that was once part of the Interior Plains. During the Wisconsin Ice Age,alpine glaciers covered the Cordillera, and the movement of the glaciers created razor-sharp peaks and ridges in these mountains. The moving glaciers also createdbroad U-shaped valleys. To the east of the Interior Plains, the ancient rocks of the Canadian Shield are exposed at the Earth’s surface, resulting in a rough, rolling terra...
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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...
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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...
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Nevada - geography.
The Truckee, Carson, and Walker rivers flow out of the Sierra Nevada, thread their way around several of the desert ranges, and also end in closed basins. The Walkerflows into Walker Lake, the Carson into Lahontan Reservoir. The major part of the Truckee’s flow is now diverted to Lahontan Reservoir, although as required by lawsome of it empties into Pyramid Lake. Because these three streams flow constantly, the lakes into which they empty never dry up. Winnemucca Lake formerly receivedoverflow w...