160 résultats pour "chemicals"

• Delaware - USA History.

  D Climate Delaware has generally hot and humid summers and mild winters. D1 Temperature In July, average daytime temperatures are usually in the upper 20°s to lower 30°sC (80°sF) or even higher. But because summer nights tend to be cooler than thedays, July averages are about 24°C (about 75°F). In addition, onshore sea breezes can reduce daytime temperatures along the coast by 3 to 6 Celsius degrees (5 to 10Fahrenheit degrees). January averages range from -1°C (31°F) at Newark, in the north, t...

• Alabama (state) - geography.

  indentations along the coast are measured, the state’s shoreline is 977 km (607 mi) long. It includes the shores of Mobile Bay, an inlet 56 km (35 mi) long at the mouthof the Mobile River. Barrier beaches partly block the entrance to the bay, leaving narrow openings on either side of Dauphin Island. Dauphin and other islands alongAlabama’s coast west of Mobile Bay are separated from the mainland by Mississippi Sound. D Climate Alabama has a humid subtropical climate, with short, relatively mild...

• Alabama (state) - USA History.

  indentations along the coast are measured, the state’s shoreline is 977 km (607 mi) long. It includes the shores of Mobile Bay, an inlet 56 km (35 mi) long at the mouthof the Mobile River. Barrier beaches partly block the entrance to the bay, leaving narrow openings on either side of Dauphin Island. Dauphin and other islands alongAlabama’s coast west of Mobile Bay are separated from the mainland by Mississippi Sound. D Climate Alabama has a humid subtropical climate, with short, relatively mild...

• 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...

• Federal Republic of Germany - country.

  B Rivers and Lakes Rivers have played a major role in Germany’s economic development. The Rhine River flows in a northwesterly direction from Switzerland through much of westernGermany and The Netherlands into the North Sea. It is a major European waterway and a pillar of commerce and trade. Its primary German tributaries include theMain, Mosel, Neckar, and Ruhr rivers. The Oder (Odra) River, along the border between Poland and Germany, runs northward and empties into the Baltic; it provides an...

• 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...

• Persian Gulf War.

  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...

• Persian Gulf War - History.

  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...

• 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...

• Comet - astronomy.

  may exceed the planet Jupiter in size, however. Observations from telescopes on Earth and in space indicate that most of the gases in the coma and tail of a comet are fragmentary molecules, or radicals, of the mostcommon elements in space: hydrogen, carbon, nitrogen, and oxygen. The radicals, for example, of CH, NH, and OH may be broken away from the stable molecules CH 4 (methane), NH 3 (ammonia), and H 2O (water), which may exist as ices or more complex, very cold compounds in the nucleus. Al...

• 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...

• Nanotechnology.

  ever-finer method of reducing material to the nanoscale size. Instead, nanostructures would be assembled atom by atom and molecule by molecule, from the atomiclevel up, just as occurs in nature. However, assembly at this scale has its own challenges. In school, children learn about some of these challenges when they study the random Brownian motion seen in particles suspended in liquids such as water. Theparticles themselves are not moving. Rather, the water molecules that surround the particles...

• Hungary - country.

  Northern Hungary lacks sufficient water, especially between July and October, when precipitation levels are typically low. Canals irrigate the Great Hungarian Plain,which is subject to drought. Because of the country’s mainly flat terrain, only limited water resources can be harnessed for hydroelectric power. F Environmental Issues Rapid industrialization in Hungary following World War II contributed significantly to a number of major environmental problems, including air, water, and soil pollu...

• Columbus (Ohio) - geography.

  A balance among manufacturing, technology, research, and financial activities has helped Columbus’s economy to continue to boom. Much of the city’s expansion resultsfrom its function as a sophisticated service center. By 1990 manufacturing occupied only 12 percent of the area’s labor force. That contrasted with services, includinggovernment, finance, and transportation and utilities, which accounted for almost 60 percent of all employment. The two largest employers in Columbus are state governme...

• Photosynthesis - biology.

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

• 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...

• Natural Satellite - astronomy.

  Titan, Saturn’s largest moon, also has few impact craters. Although icy volcanism from water and ammonia may occur along with some tectonic activity, Titan’s youngsurface is most likely the result of weather processes. Titan’s dense, cold atmosphere precipitates particles of complex organic molecules that accumulate as dunes andmountains. Methane rain erodes the surface and creates lakes at the moon’s poles. Triton’s young surface also may result from processes in its atmosphere, as well aserupt...

• Astrobiology - astronomy.

  water to help reactions along. American chemists Stanley Miller and Harold Urey tested part of Oparin and Haldane’s hypothesis in the early 1950s by simulating conditions of the early Earth. In whathas become known as the Miller-Urey experiment, the two scientists connected two flasks with a loop of glass tubing that allowed the gases to pass between the flasks.They filled the upper flask with methane, ammonia, and hydrogen—components thought to have been in the early atmosphere. They filled the...

• Pollination - biology.

  rapidly as in cross-pollination, because one plant with a beneficial gene can transmit it only to its own offspring and not to other plants. Self-pollination evolved laterthan cross-pollination, and may have developed as a survival mechanism in harsh environments where pollinators were scarce. IV POLLEN TRANSFER Unlike animals, plants are literally rooted to the spot, and so cannot move to combine sex cells from different plants; for this reason, species have evolved effectivestrategies for ac...

• Laser.

  their atoms into laser light. Consequently, they are the most powerful continuous wave (CW) lasers—that is, lasers that emit light continuously rather than in pulses. C Liquid Lasers The most common liquid laser media are inorganic dyes contained in glass vessels. They are pumped by intense flash lamps in a pulse mode or by a separate gas laserin the continuous wave mode. Some dye lasers are tunable, meaning that the color of the laser light they emit can be adjusted with the help of a prism lo...

• Hormone.

  women is called a follicle-stimulating hormone. When a follicle-stimulating hormone binds to an ovary cell, it stimulates the enzymes needed for the synthesis ofestradiol, a female sex hormone. Another gonadotropin called luteinizing hormone regulates the production of eggs in women and the production of the male sexhormone testosterone. Produced in the male gonads, or testes, testosterone regulates changes to the male body during puberty, influences sexual behavior, and playsa role in growth. T...

• 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...

• 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...

• Bird. I INTRODUCTION Bird, animal with feathers and wings. Birds are the only

  B Physical Adaptations for Flight The internal body parts of all birds, including flightless ones, reflect the evolution of birds as flying creatures. Birds have lightweight skeletons in which many of themajor bones are hollow. A unique feature of birds is the furculum, or wishbone, which is comparable to the collarbones of humans, although in birds the left and rightportions are fused together. The furculum absorbs the shock of wing motion and acts as a spring to help birds breathe while they...

• Bird - biology.

  B Physical Adaptations for Flight The internal body parts of all birds, including flightless ones, reflect the evolution of birds as flying creatures. Birds have lightweight skeletons in which many of themajor bones are hollow. A unique feature of birds is the furculum, or wishbone, which is comparable to the collarbones of humans, although in birds the left and rightportions are fused together. The furculum absorbs the shock of wing motion and acts as a spring to help birds breathe while they...

• 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...

• Uzbekistan - country.

  E Environmental Issues The evaporation of the Aral Sea is one of the worst ecological disasters in the world. The Aral has shrunk so much that it now holds only about one-fifth the volume ofwater it held in 1960. The shrinkage is due to irrigation withdrawals from the Amu Darya and Syr Darya, a practice that began on a massive scale in the early 1960s aspart of the Soviet Union’s ill-conceived drive to increase cotton yields in Central Asia. Growing cotton in the naturally arid and saline soil...

• Nuclear Energy I INTRODUCTION Gundremmingen Nuclear Power Plant, Germany The first of three boiling-water nuclear reactors at Germany's Gundremmingen plant began operating in 1966 but was permanently shut down after being decommissioned in 1983.

  such as ¯U is induced by the absorption of a neutron as in producing cesium-140, rubidium-93, three neutrons, and 200 MeV, or 3.2 × 10 -11 J (7.7 × 10 -12 cal). A nuclear fission reaction releases 10 million times as much energy as is released in a typical chemical reaction. See Nuclear Chemistry. III NUCLEAR ENERGY FROM FISSION The two key characteristics of nuclear fission important for the practical release of nuclear energy are both evident in equation (2). First, the energy per fiss...

• Anatomy.

  The body defends itself against foreign proteins and infectious microorganisms by means of a complex dual system that depends on recognizing a portion of the surfacepattern of the invader. The two parts of the system are termed cellular immunity, in which lymphocytes are the effective agent, and humoral immunity, based on theaction of antibody molecules. When particular lymphocytes recognize a foreign molecular pattern (termed an antigen), they release antibodies in great numbers; other lymphocy...

• West Virginia - geography.

  Forests, mostly of hardwood varieties, cover 79 percent of West Virginia. The principal commercial species are the oak, yellow poplar, maple, birch, beech, black walnut,hickory, and gum. Softwoods include pines and hemlock firs. Flowering trees include the wild crab apple, dogwood, hawthorn, and redbud. Among the many floweringbushes and plants are the rhododendron, which is the state flower, the laurel, blueberry, hepatica, wild geranium, and black-eyed Susan. Insects and disease, mostly introd...

• West Virginia - USA History.

  Forests, mostly of hardwood varieties, cover 79 percent of West Virginia. The principal commercial species are the oak, yellow poplar, maple, birch, beech, black walnut,hickory, and gum. Softwoods include pines and hemlock firs. Flowering trees include the wild crab apple, dogwood, hawthorn, and redbud. Among the many floweringbushes and plants are the rhododendron, which is the state flower, the laurel, blueberry, hepatica, wild geranium, and black-eyed Susan. Insects and disease, mostly introd...

• New Jersey - geography.

  C Soils Broadly defined, all of New Jersey’s soils are podzolic soils; that is, they are acidic and contain fairly high amounts of iron oxides. The soils in northern New Jersey areirregular in quality and contain rock fragments and small stones deposited by the continental glaciers of the last Ice Age. The soils of the inner coastal plain, unaffectedby glaciation, are the richest in the state, while those of the outer coastal plain are generally infertile. The newer soil classification system d...

• New Jersey - USA History.

  C Soils Broadly defined, all of New Jersey’s soils are podzolic soils; that is, they are acidic and contain fairly high amounts of iron oxides. The soils in northern New Jersey areirregular in quality and contain rock fragments and small stones deposited by the continental glaciers of the last Ice Age. The soils of the inner coastal plain, unaffectedby glaciation, are the richest in the state, while those of the outer coastal plain are generally infertile. The newer soil classification system d...

• Iraq - country.

  The Euphrates begins in Turkey, crosses Syria, and enters Iraq at Abū Kam āl. The flow of the Euphrates into Iraq has been greatly reduced by dams built by Turkeyand Syria. The gradient of the Euphrates above the town of H īt, in west central Iraq, is steep. In the 2,640 km (1,640 mi) from its source in Turkey to H īt, the river fallsfrom 3,000 m (10,000 ft) to a low water elevation of 50 m (170 ft) above sea level, an average drop of 1 m per km (6 ft per mi). In Iraq below H īt the fall is very...

• Physics I 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...

• Isotope - chemistry.

  depends on the fact that when water undergoes electrolysis, the lighter hydrogen isotope tends to come off first, leaving behind a residue of water that is enriched inthe heavier isotope. D Gaseous Diffusion This and the electromagnetic method of separating isotopes of uranium afforded the first large-scale separation ever achieved. The problem of separating uranium-235from uranium-238 arose in 1940 after the demonstration of the susceptibility of the 235 isotope to fission by neutrons. Uranium...

• Digestive System.

  The stomach, located in the upper abdomen just below the diaphragm, is a saclike structure with strong, muscular walls. The stomach can expand significantly to storeall the food from a meal for both mechanical and chemical processing. The stomach contracts about three times per minute, churning the food and mixing it with gastricjuice. This fluid, secreted by thousands of gastric glands in the lining of the stomach, consists of water, hydrochloric acid, an enzyme called pepsin, and mucin (the...

• 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...

• Kentucky - geography.

  The climate of Kentucky is characterized by warm or hot summers and cool winters. Throughout the year, temperatures do not vary greatly from place to place,although they are generally slightly lower in the Appalachian Plateaus region than elsewhere in the state. Average July temperatures are usually from 24° to 27°C (76°to 80°F) in the central and western areas and from 23° to 24°C (74° to 76°F) in the east. January averages range from below 1°C (34°F) in the northern Bluegrassregion to more tha...

• Kentucky - USA History.

  The climate of Kentucky is characterized by warm or hot summers and cool winters. Throughout the year, temperatures do not vary greatly from place to place,although they are generally slightly lower in the Appalachian Plateaus region than elsewhere in the state. Average July temperatures are usually from 24° to 27°C (76°to 80°F) in the central and western areas and from 23° to 24°C (74° to 76°F) in the east. January averages range from below 1°C (34°F) in the northern Bluegrassregion to more tha...

• Italy - country.

  C Natural Resources Italy is poor in natural resources. Much of the land is unsuitable for agriculture because of mountainous terrain or unfavorable climate. Italy, moreover, lacks substantialdeposits of basic natural resources such as coal, iron, and petroleum. Natural gas is the country’s most important mineral resource. Other deposits include feldspar andpumice. Many of Italy’s mineral deposits on the islands of Sicily and Sardinia had been heavily depleted by the early 1990s. Italy is rich...

• Antibiotics.

  In some species of bacteria the cell wall consists primarily of a thick layer of peptidoglycan. Other species have a much thinner layer of peptidoglycan and an outer aswell as an inner membrane. When bacteria are subjected to Gram's stain, these differences in structure affect the differential staining of the bacteria with a dye calledgentian violet. The differences in staining coloration (gram-positive bacteria appear purple and gram-negative bacteria appear colorless or reddish, depending on t...

• 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...

• Insect - biology.

  they almost always have six legs. In some insects, such as beetles, the legs are practically identical, but in other insects each pair is a slightly different shape. Still otherinsects have specialized leg structures. Examples are praying mantises, which have grasping and stabbing forelegs armed with lethal spines, and grasshoppers andfleas, which have large, muscular hind legs that catapult them into the air. Mole crickets’ front legs are modified for digging, and backswimmers have hind legs de...

• 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...

• Evolution - biology.

  genetic diversity to extinction. Sexual reproduction ensures that the genes in a population are rearranged in each generation, a process termed recombination. Although the combinations of genes inindividuals change with each new generation, the gene frequency, or ratio of different alleles in the entire population, remains relatively constant if no evolutionaryforces act on the population. One such force is the introduction of new genes into the genetic material of the population, or gene pool...

• Japan - country.

  island’s fertile soils support agriculture and provide the vast majority of Japan’s pasturelands. In addition, Hokkaidō contains coal deposits, and the cold currents off itsshores supply cold-water fish. Winters are long and harsh, so most of Hokkaid ō is lightly settled, housing about 5 percent of Japan’s population on approximately 20 percent of its land area. However,its snowy winters and unspoiled natural beauty attract many skiers and tourists. Hokkaid ō is thought of as Japan’s northern fr...

• 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...

• Manhattan Project - U.

  other possible uses of nuclear energy, such as using uranium to operate large power plants or, perhaps, as power sources for ships or submarines. Then Nazi Germanyinvaded Poland on September 1, 1939, and Europe plunged into war. The scientists realized that any plans to build large-scale nuclear power plants would have to waituntil the war was over. Two weeks after the invasion of Poland, Hitler made a radio speech in which he threatened Britain with “a weapon against which there is no defense.”...

• irak

           After   the end  of the 1    st      Gulf  War      a mandate  was sent,  it was called  the “United   Nations Security Council Resolution”. This mandate stipulated that all Iraq weapons:   missiles, chemical, biological and nuclear weapons were destroyed. In 1998 the US signed  a political act where  they asked  for a change  in government   in   Iraq.   With   the   Act   the   CIA   spent   8   million   dollars   per   year   to   try   to   remove   Saddam Hussein from power. When ...