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#851 2020-11-16 00:29:12

ganesh
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Re: Miscellany

829) Rattlesnake

Rattlesnake, any of 33 species of venomous New World vipers characterized by a segmented rattle at the tip of the tail that produces a buzzing sound when vibrated. Rattlesnakes are found from southern Canada to central Argentina but are most abundant and diverse in the deserts of the southwestern United States and northern Mexico. Adults usually vary in length from 0.5 to 2 metres (1.6 to 6.6 feet), but some can grow to 2.5 metres (8.2 feet). A few species are marked with transverse bands, but most rattlesnakes are blotched with dark diamonds, hexagons, or rhombuses on a lighter background, usually gray or light brown; some are various shades of orange, pink, red, or green.

The most common species in North America are the timber rattlesnake (Crotalus horridus) of the eastern United States, the prairie rattlesnake (C. viridis) of the western United States, and the eastern and western diamondbacks (C. adamanteus and C. atrox). These are also the largest rattlers. Twenty-six other species also belong to the genus Crotalus, including the small North American sidewinder (C. cerastes). The other three species belong to a more primitive genus, Sistrurus, which includes the North American massasauga (S. catenatus) and pygmy rattler (S. miliarius). These rattlesnakes have nine large scales on the upper surface of their heads.

Rattlesnakes are not aggressive and will not attack humans if unprovoked; in fact, they are quite shy and timid. However, they are venomous and can be dangerous if molested or handled. With improved methods of treatment and the abandonment of folk cures (many of which presented more danger than benefit to the victim), a rattlesnake bite is no longer the threat to life that it once was, but medical assessment should always be sought after any bite. A rattlesnake bite is very painful, and that of a snake more than 1 metre (3.3 feet) long can be fatal. The snake should be killed and brought in for identification, even for “dry” bites, in which venom is not injected. A person with a “dry” bite should not be treated with antivenin because many people are allergic to the horse serum used in its production. The allergic reaction can result in shock and death. The most dangerous species are the Mexican west coast rattlesnake (C. basiliscus), the Mojave rattlesnake (C. scutulatus), and the South American rattlesnake, or cascabel (C. durissus). Their venom attacks the nervous system more strongly than that of other rattlesnakes. The South American rattlesnake has the largest distribution of any rattlesnake; it ranges from Mexico to Argentina and is the only rattlesnake found throughout Central and South America.

Rattlesnakes are pit vipers (subfamily Crotalinae of the family Viperidae), a group named for the small heat-sensing pit between each eye and nostril that aids in hunting. The pits provide the snake with stereoscopic heat “vision,” enabling them to detect and accurately strike a living target in complete darkness. Most rattlesnakes live in arid habitats and are nocturnal, hiding during the day but emerging in the evening or at twilight to hunt for prey, which consists primarily of small mammals, especially rodents. Young and small rattlesnakes feed largely on lizards.

A rattlesnake fang is similar to a curved hypodermic needle. At the top it meets with the end of the venom duct. Soft tissue surrounds the end of the venom duct and the base of the fang, providing a seal against leakage. Large venom glands at the base of the jaws are responsible for the distinctly triangular shape of the head. Fangs are periodically lost owing to wear and breakage. Each fang has a series of seven developing fangs behind the functional fang, each smaller and less developed than the one preceding it. Fang length depends on the species and size of the snake, but large rattlers can have fangs 10–15 cm (4–6 inches) long. When the snake’s mouth is closed, the fangs are folded back and lie parallel to the roof of the mouth. Linkages of bones in the upper jaw allow the fangs to be deployed into a vertical position for stabbing and biting.

Like other reptiles, rattlesnakes cannot tolerate extreme heat or cold. During the heat of the day, rattlesnakes hide themselves underground in burrows or under rocks. In the fall they congregate in rock slides or crevices for their winter hibernation in dens that may shelter hundreds of individuals of several different species. Upon emerging in the spring, the males mate with females and then disperse from the den site to spend the summer in surrounding countryside. In the fall they all return to the same den.

Rattlesnakes give birth to young that develop from eggs retained inside the mother (ovoviviparous). In the late summer, broods of 1–60 are produced; average broods number 4–10 young. Newborn rattlesnakes have functioning fangs and venom glands. Their venom is more potent but of lesser quantity than that of their mother, a condition that helps ensure that the young can secure food. The newborn babies are also equipped with a single button on the end of the tail. After the first shedding of their skin (within a week of birth), they will have two rattle segments. Once the third rattle segment has been obtained, the young snake can buzz like an adult. The rattle, presumably a warning device, is composed of horny, loosely connected hollow segments, one of which is added every time the snake sheds its skin. The age of a rattlesnake cannot be determined from the number of its rattle segments, as rattlesnakes usually shed three or four times a year. In captivity, 10 species have lived from 20 to 30 years.

Every year in the United States, an estimated 5,000 rattlesnakes are collected and destroyed in about 30 highly commercialized “rattlesnake roundups.” Supposedly conducted to save the lives of people and cattle, these spectacles may only reduce rattlesnakes’ valuable service in the control of rodent pests and in maintaining the natural balance of desert ecosystems.

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#852 2020-11-17 00:54:23

ganesh
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Re: Miscellany

830) Black mamba

Black mamba, (Dendroaspis polylepis), species of mamba snake known for its large size, quickness, and extremely potent venom. It lives in sub-Saharan Africa and is one of the continent’s most dangerous snakes.

The average black mamba is 2–2.5 metres (6.6–8.2 feet) long, with a maximum length of 4.3 metres (14 feet). Despite its name, the snake is not black. Instead, it ranges in colour from gray to dark brown, with a lighter underside. The black actually refers to the colour of the inside of its mouth; green mambas and other snakes have white mouths. The black mamba is found in rocky savannas and lowland forests. Unlike the other mamba species, the black mamba is not primarily arboreal, preferring the ground, where it often sleeps in termite mounds or tree hollows. One of the fastest snakes, it is capable of speeds of more than 12 miles (19 km) per hour. The black mamba typically lays 6 to 20 eggs. Prey consists primarily of small mammals and birds.

Although it has an aggressive reputation, the black mamba is generally shy and nervous, and it will use its incredible speed to escape threats. However, if disturbed or cornered, the snake may rear up and threaten with an open mouth and a slightly expanded or flattened neck (or hood) before striking; once a black mamba attacks, it will bite its victim repeatedly. Its extremely toxic venom—two drops of which will reportedly kill most humans—attacks both the nervous system and the heart. Even though most bites are fatal, it is responsible for only a small number of deaths annually, and unprovoked attacks on humans have not been proved. In the wild, black mambas will typically live at least 11 years, while those in captivity have life spans of more than 20 years.

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It is no good to try to stop knowledge from going forward. Ignorance is never better than knowledge - Enrico Fermi. 

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#853 2020-11-18 00:47:15

ganesh
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Re: Miscellany

831) Reindeer

Reindeer, (Rangifer tarandus), in North America called caribou, species of deer (family Cervidae) found in the Arctic tundra and adjacent boreal forests of Greenland, Scandinavia, Russia, Alaska, and Canada. Reindeer have been domesticated in Europe. There are two varieties, or ecotypes: tundra reindeer and forest (or woodland) reindeer. Tundra reindeer migrate between tundra and forest in huge herds numbering up to half a million in an annual cycle covering as much as 5,000 km (3,000 miles). Forest reindeer are much less numerous.

Large males can stand more than 1.2 metres (3.9 feet) tall at the shoulder and exceed 250 kg (550 pounds) in weight; females are slightly smaller. Reindeer have deeply cloven hoofs so the feet can spread on snow or soft ground; they are also good swimmers. Colour varies from whitish in winter to brown in summer. Heavy guard hairs are hollow, which increases the coat’s insulating properties. Antlers with up to 44 points can grow to 1.4 metres long in males; this is the only deer species in which females also have antlers.

Reindeer mature as yearlings if their nutrition is good, though males cannot compete for females until their fourth autumn, when their antlers and body mass (which are correlated) have grown sufficiently large. The rut occurs in October and lasts only 11 days. Tundra males, aggregated with thousands of females for the fall migration, assess other males’ antler size visually and thus generally avoid serious fights. Forest reindeer, on the other hand, defend discrete harems and fight harder. In both varieties a single calf is born in May or June after a gestation of seven and a half months. The calf grows rapidly on its mother’s milk, which is richer than that of any other ungulate. After one month it can eat fresh plant growth, and by three months it can survive if the mother dies, but normally weaning takes place at five to six months. Half of all calves born may be killed by wolves, bears, and lynx. Longevity is about 15 years in the wild, 20 in captivity.

Eurasian and American forest reindeer live in family groups of 6 to 13, with seasonal ranges of 500 square km (190 square miles) or less. Tundra reindeer spend winter dispersed in forests but aggregate in spring to migrate onto the tundra; in fall they mass again to return to the forest. Summer food is grass, sedges, green leaves of shrubs and new growth of larch, willow, and birch; mushrooms are sought in late summer. In winter, metabolism slows, and reindeer rely on high-carbohydrate lichens called reindeer moss, which they reach by digging craters in the snow. The calf follows its mother and shares this food. The reindeer survive on this low-protein diet by recycling urea (normally a waste product) within the digestive system and making use of its nitrogen.
Females keep their antlers all winter, which enables them to defend feeding craters from each other as well as males, which shed their antlers soon after the rut.

There are about 3.5 million caribou in North America and perhaps 1 million wild reindeer in Eurasia, mostly in Russia. Nearly 3 million domestic reindeer live in northern Europe. They are important to traditional herders such as the Sami (Lapps) of Scandinavia and Russia, who exploit them as pack and draft animals and for meat, milk, and hides; the antlers are carved into tools and totems. The herdsmen use boats to direct herds to offshore islands in summer. In the forests of the Da Hinggan region of northeastern China, the Evenk people use reindeer as pack animals and as mounts, and small numbers of Tsaatan (Dhukha) herders in northern Mongolia utilize the reindeer they keep in a variety of ways.

Of the nine subspecies recognized, two are forest ecotypes, one living in North America and the other in Eurasia. Fossil evidence from Alaska indicates that they evolved during the late Pliocene Epoch (3.6 million to 2.6 million years ago). During the last glaciation  more than 11,700 years ago, they were hunted by the Clovis people of New Mexico and by many early Stone Age tribes in southern Europe.

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It is no good to try to stop knowledge from going forward. Ignorance is never better than knowledge - Enrico Fermi. 

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#854 2020-11-19 00:11:23

ganesh
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Re: Miscellany

832) Wrench

Wrench, also called spanner, tool, usually operated by hand, for tightening bolts and nuts. Basically, a wrench consists of a stout lever with a notch at one or both ends for gripping the bolt or nut in such a way that it can be twisted by a pull on the wrench at right angles to the axes of the lever and the bolt or nut. Some wrenches have ends with straight-sided slots that fit over the part being tightened; these tools are known as open-end wrenches and are made in various sizes to fit specific bolt and nut sizes.

Box-end wrenches have ends that enclose the nut and have 6, 8, 12, or 16 points inside the head. A wrench with 12 points is used on either a hexagonal or a square nut; the 8- and 16-point wrenches are used on square members. Because the sides of the box are thin, these wrenches are suitable for turning nuts that are hard to reach with an open-end wrench.

When a nut or a bolt head is in a recess below the surface of a bolted member, a socket wrench must be used; this is essentially a short pipe with a square or hexagonal hole and either an integral or a removable handle. Modern socket wrenches are made in sets, consisting of a number of short sockets with a square hole in one end that fits a removable handle and 8- or 12-point holes in the other end to fit various bolt and nut sizes. There are several types of handles and extensions, such as a T handle, screwdriver-grip handle, and a ratchet handle.

A useful accessory for a socket-wrench set is a handle equipped with a mechanism that measures the amount of torque, or turning effort, exerted by the wrench on the nut or bolt. One type of torque handle has two arms attached to the head, which carries the socket that fits the bolt or nut to be tightened; one arm carries the torque-indicating scale and remains fixed relative to the head, while the other arm carries the handgrip and is bent, relative to the head and the scale, when a bolt is tightened. A pointer on the bent arm indicates the torque on the scale. The purpose of a torque wrench is to make sure that screws and bolts in bolted assemblies are installed with sufficient tightness to prevent loosening during use, without being overtightened.

Wrenches with one fixed and one adjustable parallel jaw can be used on various sizes of bolts and nuts within a limited range. On one type the jaws are at right angles to the handle; this wrench is known as a monkey wrench. On another type, originally called a Crescent wrench, the jaws are almost parallel to the handle. On both types the movable jaw is adjusted by turning a worm that engages a rack of teeth cut into the jaw.

The adjustable pipe, or Stillson, wrench is used to hold or turn pipes or circular bars. This wrench has serrated jaws, one of which is pivoted on the handle to create a strong gripping action on the work.

Recessed-head screws or set screws commonly have a hexagonally shaped recess and require a special wrench, usually referred to as an Allen wrench; it consists of a hexagonal bar of tool steel shaped into the form of an L, either end of which fits into the recess.
Power or impact wrenches are used for tightening or loosening nuts quickly. They are essentially small handheld electric or pneumatic motors that can rotate socket wrenches at high speed. They are equipped with a torque-limiting device that will stop the rotation of the socket wrench when a preset torque is reached. Pneumatic wrenches are commonly used in automobile service stations, where compressed air is available and the sparking of electric motors is a fire hazard.

AmPro-Adjustable-Wrench-150mm-WREA-T39805-A.jpg


It is no good to try to stop knowledge from going forward. Ignorance is never better than knowledge - Enrico Fermi. 

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

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#855 2020-11-20 00:18:18

ganesh
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Re: Miscellany

833) Oil extraction

Oil extraction, isolation of oil from animal by-products, fleshy fruits such as the olive and palm, and oilseeds such as cottonseed, sesame seed, soybeans, and peanuts. Oil is extracted by three general methods: rendering, used with animal products and oleaginous fruits; mechanical pressing, for oil-bearing seeds and nuts; and extracting with volatile solvents, employed in large-scale operations for a more complete extraction than is possible with pressing.

Rendering originally implied the application of heat; in its most primitive form, it is practiced by heaping fruits such as olives in piles exposed to the sun and collecting the oil that exudes. A similar, somewhat more advanced process is used to extract oil from palm fruits by boiling in water, then skimming the oil from the surface. Whale blubber is cut into small pieces and heated in vats (tryworks) or cooked in steam digesters; the oil is collected by draining or skimming.

Many oil-bearing seeds and nuts are broken up by grinding, flaking, or rolling, then subjected to mechanical pressing to liberate the oil. The modern continuous screw press exerts pressures as high as 30,000 pounds per square inch. In modern press extraction, oilseeds or nuts are cleaned, and the shells or hulls removed; the kernels or meats are ground to a coarse meal that is pressed with or without preliminary heating. Cold-pressed oil, also called cold-drawn, or virgin, oil, is purer and has a better flavour than oil expressed with the aid of heat. After pressing the meals made from oily seeds or nuts, the remaining cake contains about 5 to 15 percent oil. Most of the oil present in these residues, and in meals made from seeds and nuts that naturally contain little oil, can be removed by extraction with volatile solvents, especially petroleum benzin (also known as petroleum ether, commercial hexane, or heptane). The solvent is percolated through the meal, dissolving the oil, which is finally recovered from the solution by evaporating the solvent. The solvent is also recovered and used over again.

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It is no good to try to stop knowledge from going forward. Ignorance is never better than knowledge - Enrico Fermi. 

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#856 2020-11-21 00:19:53

ganesh
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Re: Miscellany

834) Kerosene

Kerosene, also spelled kerosine, also called paraffin or paraffin oil, flammable hydrocarbon liquid commonly used as a fuel. Kerosene is typically pale yellow or colourless and has a not-unpleasant characteristic odour. It is obtained from petroleum and is used for burning in kerosene lamps and domestic heaters or furnaces, as a fuel or fuel component for jet engines, and as a solvent for greases and insecticides.

Discovered by Canadian physician Abraham Gesner in the late 1840s, kerosene was initially manufactured from coal tar and shale oils. However, following the drilling of the first oil well in Pennsylvania by E.L. Drake in 1859, petroleum quickly became the major source of kerosene. Because of its use in lamps, kerosene was the major refinery product for several decades until the advent of the electric lamp reduced its value for lighting. Production further declined as the rise of the automobile established gasoline as an important petroleum product. Nevertheless, in many parts of the world, kerosene is still a common heating and cooking fuel as well as a fuel for lamps. Standard commercial jet fuel is essentially a high-quality straight-run kerosene, and many military jet fuels are blends based on kerosene.

Chemically, kerosene is a mixture of hydrocarbons. The chemical composition depends on its source, but it usually consists of about 10 different hydrocarbons, each containing 10 to 16 carbon atoms per molecule. The main constituents are saturated straight-chain and branched-chain paraffins, as well as ring-shaped cycloparaffins (also known as naphthenes). Kerosene is less volatile than gasoline. Its flash point (the temperature at which it will generate a flammable vapour near its surface) is 38 °C (100 °F) or higher, whereas that of gasoline is as low as −40 °C (−40 °F). This property makes kerosene a relatively safe fuel to store and handle.

With a boiling point between about 150 and 300 °C (300–575 °F), kerosene is considered to be one of the so-called middle distillates of crude oil, along with diesel fuel. It can be produced as “straight-run kerosene,” separated physically from the other crude oil fractions by distillation, or it can be produced as “cracked kerosene,” by chemically decomposing, or cracking, heavier portions of the oil at elevated temperatures.

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It is no good to try to stop knowledge from going forward. Ignorance is never better than knowledge - Enrico Fermi. 

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#857 2020-11-22 00:06:10

ganesh
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Re: Miscellany

835) Cobra

Cobra, any of various species of highly venomous snakes, most of which expand the neck ribs to form a hood. While the hood is characteristic of cobras, not all of them are closely related. Cobras are found from southern Africa through southern Asia to islands of Southeast Asia. Throughout their range, different species are favourites of snake charmers, who frighten them into assuming the upreared defense posture. The snake sways in response to the movement and perhaps also to the music of the charmer, who knows how to avoid the relatively slow strike and who may have removed the snake’s fangs. The short fangs at the front of the mouth have an enclosed groove, which delivers the venom. Cobra venom generally contains neurotoxins active against the nervous system of prey—primarily small vertebrates and other snakes. Bites, particularly from larger species, can be fatal depending on the amount of venom injected. Neurotoxins affect breathing, and although antivenin is effective, it must be administered soon after the bite. Thousands of deaths occur each year in South and Southeast Asia.

The world’s largest venomous snake is the king cobra, or hamadryad (Ophiophagus hannah). Found predominantly in forests from India through Southeast Asia to the Philippines and Indonesia, it preys chiefly on other snakes. Maximum confirmed length is 5.6 metres (18 feet), but most do not exceed 3.6 metres (12 feet). King cobras guard a nest of 20 to 40 eggs, which are laid in a mound of leaves gathered by the female. The guarding parent will strike if a predator or a person approaches too closely. Not all cobras are egg layers.

The Indian cobra (or Indian spectacled cobra, Naja naja) was formerly considered a single species with much the same distribution as the king cobra. Recently, however, biologists have discovered that nearly a dozen species exist in Asia, some being venom spitters and others not. They vary both in size (most ranging between 1.25 and 1.75 metres) and in the toxicity of their venom. Spitters propel venom through the fangs by muscular contraction of the venom ducts and by forcing air out of the single lung.

In Africa there are also spitting and nonspitting cobras, but the African cobras are not related to the Asian cobras, nor are they related to each other. The ringhals, or spitting cobra (Hemachatus haemachatus), of southern Africa and the black-necked cobra (Naja nigricollis), a small form widely distributed in Africa, are spitters. Venom is accurately directed at the victim’s eyes at distances of more than two metres and may cause temporary, or even permanent, blindness unless promptly washed away. The Egyptian cobra (N. haje)—probably the asp of antiquity—is a dark, narrow-hooded species, about two metres long, that ranges over much of Africa and eastward to Arabia. Its usual prey consists of toads and birds. In equatorial Africa there are tree cobras (genus Pseudohaje), which, along with the mambas, are the only arboreal members of the family Elapidae.

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It is no good to try to stop knowledge from going forward. Ignorance is never better than knowledge - Enrico Fermi. 

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#858 2020-11-23 00:17:28

ganesh
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Re: Miscellany

836) Gasoline

Gasoline, also spelled gasolene, also called gas or petrol, mixture of volatile, flammable liquid hydrocarbons derived from petroleum and used as fuel for internal-combustion engines. It is also used as a solvent for oils and fats. Originally a by-product of the petroleum industry (kerosene being the principal product), gasoline became the preferred automobile fuel because of its high energy of combustion and capacity to mix readily with air in a carburetor.

Gasoline was at first produced by distillation, simply separating the volatile, more valuable fractions of crude petroleum. Later processes, designed to raise the yield of gasoline from crude oil, split large molecules into smaller ones by processes known as cracking. Thermal cracking, employing heat and high pressures, was introduced in 1913 but was replaced after 1937 by catalytic cracking, the application of catalysts that facilitate chemical reactions producing more gasoline. Other methods used to improve the quality of gasoline and increase its supply include polymerization, converting gaseous olefins, such as propylene and butylene, into larger molecules in the gasoline range; alkylation, a process combining an olefin and a paraffin such as isobutane; isomerization, the conversion of straight-chain hydrocarbons to branched-chain hydrocarbons; and reforming, using either heat or a catalyst to rearrange the molecular structure.

Gasoline is a complex mixture of hundreds of different hydrocarbons. Most are saturated and contain 4 to 12 carbon atoms per molecule. Gasoline used in automobiles boils mainly between 30° and 200° C (85° and 390° F), the blend being adjusted to altitude and season. Aviation gasoline contains smaller proportions of both the less-volatile and more-volatile components than automobile gasoline.

The antiknock characteristics of a gasoline—its ability to resist knocking, which indicates that the combustion of fuel vapour in the cylinder is taking place too rapidly for efficiency—is expressed in octane number. The addition of tetraethyllead to retard the combustion was initiated in the 1930s but was discontinued in the 1980s because of the toxicity of the lead compounds discharged in the combustion products. Other additives to gasoline often include detergents to reduce the buildup of engine deposits, anti-icing agents to prevent stalling caused by carburetor icing, and antioxidants (oxidation inhibitors) used to reduce “gum” formation.

In the late 20th century the rising price of petroleum (and hence of gasoline) in many countries led to the increasing use of gasohol, which is a mixture of 90 percent unleaded gasoline and 10 percent ethanol (ethyl alcohol). Gasohol burns well in gasoline engines and is a desirable alternative fuel for certain applications because of the renewability of ethanol, which can be produced from grains, potatoes, and certain other plant matter.

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It is no good to try to stop knowledge from going forward. Ignorance is never better than knowledge - Enrico Fermi. 

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#859 2020-11-24 00:22:31

ganesh
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Re: Miscellany

837) Engineering

Engineering, the application of science to the optimum conversion of the resources of nature to the uses of humankind. The field has been defined by the Engineers Council for Professional Development, in the United States, as the creative application of “scientific principles to design or develop structures, machines, apparatus, or manufacturing processes, or works utilizing them singly or in combination; or to construct or operate the same with full cognizance of their design; or to forecast their behaviour under specific operating conditions; all as respects an intended function, economics of operation and safety to life and property.” The term engineering is sometimes more loosely defined, especially in Great Britain, as the manufacture or assembly of engines, machine tools, and machine parts.

The words engine and ingenious are derived from the same Latin root, ingenerare, which means “to create.” The early English verb engine meant “to contrive.” Thus, the engines of war were devices such as catapults, floating bridges, and assault towers; their designer was the “engine-er,” or military engineer. The counterpart of the military engineer was the civil engineer, who applied essentially the same knowledge and skills to designing buildings, streets, water supplies, sewage systems, and other projects.

Associated with engineering is a great body of special knowledge; preparation for professional practice involves extensive training in the application of that knowledge. Standards of engineering practice are maintained through the efforts of professional societies, usually organized on a national or regional basis, with all members acknowledging a responsibility to the public over and above responsibilities to their employers or to other members of their society.

The function of the scientist is to know, while that of the engineer is to do. Scientists add to the store of verified systematized knowledge of the physical world, and engineers bring this knowledge to bear on practical problems. Engineering is based principally on physics, chemistry, and mathematics and their extensions into materials science, solid and fluid mechanics, thermodynamics, transfer and rate processes, and systems analysis.

Unlike scientists, engineers are not free to select the problems that interest them. They must solve problems as they arise, and their solutions must satisfy conflicting requirements. Usually, efficiency costs money, safety adds to complexity, and improved performance increases weight. The engineering solution is the optimum solution, the end result that, taking many factors into account, is most desirable. It may be the most reliable within a given weight limit, the simplest that will satisfy certain safety requirements, or the most efficient for a given cost. In many engineering problems the social costs are significant.

Engineers employ two types of natural resources—materials and energy. Materials are useful because of their properties: their strength, ease of fabrication, lightness, or durability; their ability to insulate or conduct; their chemical, electrical, or acoustical properties. Important sources of energy include fossil fuels (coal, petroleum, gas), wind, sunlight, falling water, and nuclear fission. Since most resources are limited, engineers must concern themselves with the continual development of new resources as well as the efficient utilization of existing ones.

History Of Engineering

The first engineer known by name and achievement is Imhotep, builder of the Step Pyramid at Ṣaqqārah, Egypt, probably about 2550 BCE. Imhotep’s successors—Egyptian, Persian, Greek, and Roman—carried civil engineering to remarkable heights on the basis of empirical methods aided by arithmetic, geometry, and a smattering of physical science. The Pharos (lighthouse) of Alexandria, Solomon’s Temple in Jerusalem, the Colosseum in Rome, the Persian and Roman road systems, the Pont du Gard aqueduct in France, and many other large structures, some of which endure to this day, testify to their skill, imagination, and daring. Of many treatises written by them, one in particular survives to provide a picture of engineering education and practice in classical times: Vitruvius’s De architectura, published in Rome in the 1st century CE, a 10-volume work covering building materials, construction methods, hydraulics, measurement, and town planning.

In construction, medieval European engineers carried technique, in the form of the Gothic arch and flying buttress, to a height unknown to the Romans. The sketchbook of the 13th-century French engineer Villard de Honnecourt reveals a wide knowledge of mathematics, geometry, natural and physical science, and draftsmanship.

In Asia, engineering had a separate but very similar development, with more and more sophisticated techniques of construction, hydraulics, and metallurgy helping to create advanced civilizations such as the Mongol empire, whose large, beautiful cities impressed Marco Polo in the 13th century.

Civil engineering emerged as a separate discipline in the 18th century, when the first professional societies and schools of engineering were founded. Civil engineers of the 19th century built structures of all kinds, designed water-supply and sanitation systems, laid out railroad and highway networks, and planned cities. England and Scotland were the birthplace of mechanical engineering, as a derivation of the inventions of the Scottish engineer James Watt and the textile machinists of the Industrial Revolution. The development of the British machine-tool industry gave tremendous impetus to the study of mechanical engineering both in Britain and abroad.

The growth of knowledge of electricity—from Alessandro Volta’s original electric cell of 1800 through the experiments of Michael Faraday and others, culminating in 1872 in the Gramme dynamo and electric motor (named after the Belgian Z.T. Gramme)—led to the development of electrical and electronics engineering. The electronics aspect became prominent through the work of such scientists as James Clerk Maxwell of Britain and Heinrich Hertz of Germany in the late 19th century. Major advances came with the development of the vacuum tube by Lee De Forest of the United States in the early 20th century and the invention of the transistor in the mid-20th century. In the late 20th century electrical and electronics engineers outnumbered all others in the world.

Chemical engineering grew out of the 19th-century proliferation of industrial processes involving chemical reactions in metallurgy, food, textiles, and many other areas. By 1880 the use of chemicals in manufacturing had created an industry whose function was the mass production of chemicals. The design and operation of the plants of this industry became a function of the chemical engineer.

Engineering Functions

Problem solving is common to all engineering work. The problem may involve quantitative or qualitative factors; it may be physical or economic; it may require abstract mathematics or common sense. Of great importance is the process of creative synthesis or design, putting ideas together to create a new and optimum solution.
Although engineering problems vary in scope and complexity, the same general approach is applicable. First comes an analysis of the situation and a preliminary decision on a plan of attack. In line with this plan, the problem is reduced to a more categorical question that can be clearly stated. The stated question is then answered by deductive reasoning from known principles or by creative synthesis, as in a new design. The answer or design is always checked for accuracy and adequacy. Finally, the results for the simplified problem are interpreted in terms of the original problem and reported in an appropriate form.

In order of decreasing emphasis on science, the major functions of all engineering branches are the following:

•    Research. Using mathematical and scientific concepts, experimental techniques, and inductive reasoning, the research engineer seeks new principles and processes.
•    Development. Development engineers apply the results of research to useful purposes. Creative application of new knowledge may result in a working model of a new electrical circuit, a chemical process, or an industrial machine.
•    Design. In designing a structure or a product, the engineer selects methods, specifies materials, and determines shapes to satisfy technical requirements and to meet performance specifications.
•    Construction. The construction engineer is responsible for preparing the site, determining procedures that will economically and safely yield the desired quality, directing the placement of materials, and organizing the personnel and equipment.
•    Production. Plant layout and equipment selection are the responsibility of the production engineer, who chooses processes and tools, integrates the flow of materials and components, and provides for testing and inspection.
•    Operation. The operating engineer controls machines, plants, and organizations providing power, transportation, and communication; determines procedures; and supervises personnel to obtain reliable and economic operation of complex equipment.
•    Management and other functions. In some countries and industries, engineers analyze customers’ requirements, recommend units to satisfy needs economically, and resolve related problems.

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#860 2020-11-29 03:54:14

ganesh
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Re: Miscellany

838) Resin

Resin, any natural or synthetic organic compound consisting of a noncrystalline or viscous liquid substance. Natural resins are typically fusible and flammable organic substances that are transparent or translucent and are yellowish to brown in colour. They are formed in plant secretions and are soluble in various organic liquids but not in water. Synthetic resins comprise a large class of synthetic products that have some of the physical properties of natural resins but are different chemically. Synthetic resins are not clearly differentiated from plastics.

Most natural resins are exuded from trees, especially pines and firs. Resin formation occurs as a result of injury to the bark from wind, fire, lightning, or other cause. The fluid secretion ordinarily loses some of its more volatile components by evaporation, leaving a soft residue at first readily soluble but becoming insoluble as it ages. The ancient Chinese, Japanese, Egyptians, and others used resins in preparation of lacquers and varnishes.

Natural resins may be classified as spirit-soluble and oil-soluble. Among the former are balsams, long popular as a healing agent; turpentines used as solvents; and mastics, dragon’s blood, dammar, sandarac, and the lacs, all used as components of varnishes. The oil-soluble resins include rosin, derived along with turpentine from the long-leaf pine and long used for a variety of applications, including soapmaking; copals, used in varnishes; amber, the hardest natural resin, fabricated into jewelry; Oriental lacquer, derived from a tree native to China; and cashew-nutshell oil, derived from cashew nuts.

In modern industry natural resins have been almost entirely replaced by synthetic resins, which are divided into two classes, thermoplastic resins, which remain plastic after heat treatment, and thermosetting resins, which become insoluble and infusible on heating.

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#861 2020-11-30 01:04:49

ganesh
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Re: Miscellany

839) Biofuel

Biofuel, any fuel that is derived from biomass—that is, plant or algae material or animal waste. Since such feedstock material can be replenished readily, biofuel is considered to be a source of renewable energy, unlike fossil fuels such as petroleum, coal, and natural gas. Biofuel is commonly advocated as a cost-effective and environmentally benign alternative to petroleum and other fossil fuels, particularly within the context of rising petroleum prices and increased concern over the contributions made by fossil fuels to global warming. Many critics express concerns about the scope of the expansion of certain biofuels because of the economic and environmental costs associated with the refining process and the potential removal of vast areas of arable land from food production.

Types Of Biofuels

Some long-exploited biofuels, such as wood, can be used directly as a raw material that is burned to produce heat. The heat, in turn, can be used to run generators in a power plant to produce electricity. A number of existing power facilities burn grass, wood, or other kinds of biomass.

Liquid biofuels are of particular interest because of the vast infrastructure already in place to use them, especially for transportation. The liquid biofuel in greatest production is ethanol (ethyl alcohol), which is made by fermenting starch or sugar. Brazil and the United States are among the leading producers of ethanol. In the United States ethanol biofuel is made primarily from corn (maize) grain, and it is typically blended with gasoline to produce “gasohol,” a fuel that is 10 percent ethanol. In Brazil, ethanol biofuel is made primarily from sugarcane, and it is commonly used as a 100-percent-ethanol fuel or in gasoline blends containing 85 percent ethanol. Unlike the “first-generation” ethanol biofuel produced from food crops, “second-generation” cellulosic ethanol is derived from low-value biomass that possesses a high cellulose content, including wood chips, crop residues, and municipal waste. Cellulosic ethanol is commonly made from sugarcane bagasse, a waste product from sugar processing, or from various grasses that can be cultivated on low-quality land. Given that the conversion rate is lower than with first-generation biofuels, cellulosic ethanol is dominantly used as a gasoline additive.

The second most common liquid biofuel is biodiesel, which is made primarily from oily plants (such as the soybean or oil palm) and to a lesser extent from other oily sources (such as waste cooking fat from restaurant deep-frying). Biodiesel, which has found greatest acceptance in Europe, is used in diesel engines and usually blended with petroleum diesel fuel in various percentages. The use of algae and cyanobacteria as a source of “third-generation” biodiesel holds promise but has been difficult to develop economically. Some algal species contain up to 40 percent lipids by weight, which can be converted into biodiesel or synthetic petroleum. Some estimates state that algae and cyanobacteria could yield between 10 and 100 times more fuel per unit area than second-generation biofuels.

Other biofuels include methane gas and biogas—which can be derived from the decomposition of biomass in the absence of oxygen—and methanol, butanol, and dimethyl ether—which are in development.

Economic And Environmental Considerations

In evaluating the economic benefits of biofuels, the energy required to produce them has to be taken into account. For example, the process of growing corn to produce ethanol consumes fossil fuels in farming equipment, in fertilizer manufacturing, in corn transportation, and in ethanol distillation. In this respect, ethanol made from corn represents a relatively small energy gain; the energy gain from sugarcane is greater and that from cellulosic ethanol or algae biodiesel could be even greater.

Biofuels also supply environmental benefits but, depending on how they are manufactured, can also have serious environmental drawbacks. As a renewable energy source, plant-based biofuels in principle make little net contribution to global warming and climate change; the carbon dioxide (a major greenhouse gas) that enters the air during combustion will have been removed from the air earlier as growing plants engage in photosynthesis. Such a material is said to be “carbon neutral.” In practice, however, the industrial production of agricultural biofuels can result in additional emissions of greenhouse gases that may offset the benefits of using a renewable fuel. These emissions include carbon dioxide from the burning of fossil fuels during the production process and nitrous oxide from soil that has been treated with nitrogen fertilizer. In this regard, cellulosic biomass is considered to be more beneficial.

Land use is also a major factor in evaluating the benefits of biofuels. The use of regular feedstock, such as corn and soybeans, as a primary component of first-generation biofuels sparked the “food versus fuel” debate. In diverting arable land and feedstock from the human food chain, biofuel production can affect the economics of food price and availability. In addition, energy crops grown for biofuel can compete for the world’s natural habitats. For example, emphasis on ethanol derived from corn is shifting grasslands and brushlands to corn monocultures, and emphasis on biodiesel is bringing down ancient tropical forests to make way for oil palm plantations. Loss of natural habitat can change the hydrology, increase erosion, and generally reduce biodiversity of wildlife areas. The clearing of land can also result in the sudden release of a large amount of carbon dioxide as the plant matter that it contains is burned or allowed to decay.

Some of the disadvantages of biofuels apply mainly to low-diversity biofuel sources—corn, soybeans, sugarcane, oil palms—which are traditional agricultural crops. One alternative involves the use of highly diverse mixtures of species, with the North American tallgrass prairie as a specific example. Converting degraded agricultural land that is out of production to such high-diversity biofuel sources could increase wildlife area, reduce erosion, cleanse waterborne pollutants, store carbon dioxide from the air as carbon compounds in the soil, and ultimately restore fertility to degraded lands. Such biofuels could be burned directly to generate electricity or converted to liquid fuels as technologies develop.

The proper way to grow biofuels to serve all needs simultaneously will continue to be a matter of much experimentation and debate, but the fast growth in biofuel production will likely continue. In the United States the Energy Independence and Security Act of 2007 mandated the use of 136 billion litres (36 billion gallons) of biofuels annually by 2022, more than a sixfold increase over 2006 production levels. The legislation also requires, with certain stipulations, that 79 billion litres (21 billion gallons) of the total amount be biofuels other than corn-derived ethanol, and it continued certain government subsidies and tax incentives for biofuel production.

One distinctive promise of biofuels is that, in combination with an emerging technology called carbon capture and storage, the process of producing and using biofuels may be capable of perpetually removing carbon dioxide from the atmosphere. Under this vision, biofuel crops would remove carbon dioxide from the air as they grow, and energy facilities would capture the carbon dioxide given off as biofuels are burned to generate power. Captured carbon dioxide could be sequestered (stored) in long-term repositories such as geologic formations beneath the land, in sediments of the deep ocean, or conceivably as solids such as carbonates

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#862 2020-12-01 00:33:51

ganesh
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Re: Miscellany

840) Kite

Kite, any of numerous birds of prey belonging to one of three subfamilies (Milvinae, Elaninae, Perninae) of the family Accipitridae. Typically, a kite is lightly built, with a small head, partly bare face, short beak, and long narrow wings and tail. Kites occur worldwide in warm regions. Some kites live on insects; others are primarily scavengers but also eat rodents and reptiles; and a few are strictly snaileaters. Kites are buoyant in flight, slowly flapping and gliding with wings angled back. Several species are as graceful as terns.

True kites, Milvinae, have rather narrow beaks, the upper mandible being wavy-edged. They are typified by the red kite (Milvus milvus)—of Europe, northern Africa, and the Middle East—and the black, or black-eared, kite (M. migrans)—found over much of the Old World. Both are large (to about 55 cm [22 inches]), reddish birds (the black kite darker), lightly streaked on the head, with long, angled wings and notched tail. The Brahminy kite (Haliastur indus; subfamily Milvinae) ranges from India to northeastern Australia. It is red-brown except for white foreparts. It eats fish and garbage. The buzzard kite (Hamirostra melanosternon; subfamily Milvinae) of Australia is a large black-breasted bird; it lives mainly on rabbits and lizards. It also eats emu eggs, reportedly dropping rocks on them to break the thick shells.

The snail kites, found only in the New World, also belong to the subfamily Milvinae. They have sickle-shaped beaks adapted to feeding on snails, their only food. Best known is the Everglade kite (Rostrhamus sociabilis), now rare in Florida and Cuba but occurring in numbers in eastern Mexico, Central America, and most of eastern South America. It is a blackish or slate-coloured bird, about 50 cm long, with red eyes and white tail-base.

The swallow-tailed kite of the New World (Elanoides forficatus) is a striking black and white bird of the subfamily Perninae. It is about 60 cm long, including its long forked tail. It is most common in tropical eastern South America but also occurs from Central America to the United States.

The swallow-tailed kite of Africa (Chelicti- nia riocourii) is a small gray and white bird of the subfamily Elaninae. It occurs from Nigeria to Somalia. The white-tailed kite (Elanus leucurus; subfamily Elaninae) occurs from Argentina to California, where it is one of the few North American raptors increasing in number. It is gray with a white tail, head, and underparts and conspicuous black shoulder patches. It eats rodents. Similar kites of the genus Elanus occur in tropical Africa, Asia, and Australia.

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#863 2020-12-02 00:21:10

ganesh
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Re: Miscellany

841) Gull

Gull, any of more than 40 species of heavily built web-footed seabirds of the gull and tern family Laridae (order Charadriiformes). Several genera are usually recognized for certain specialized gulls, but many authorities place these in the broad genus Larus. Conspicuous and gregarious, gulls are most abundant as breeders in the Northern Hemisphere, which has about 30 species in temperate to Arctic regions. They are mostly colonial ground nesters, and those that breed inland usually go to coasts in winter.

Adult gulls are mainly gray or white, with variable head markings. In breeding season the head is either pure white, black, gray, or brown; it becomes streaked or smudgy in winter. The bill is strong and slightly hooked and in some species shows a spot of colour. Bill and leg colours help to distinguish species, as do wing patterns.

Adaptable opportunists, gulls feed on insects, mollusks, and crustaceans on beaches; worms and grubs in plowed fields; fish along shores; and garbage from ships. Some of the larger gulls prey on the eggs and the young of other birds, including their own kind.

The herring gull (L. argentatus) is by far the most familiar of the Atlantic gulls. A bird of the Northern Hemisphere, it has a gray mantle, flesh-coloured legs and feet, and black-and-white-spotted wing tips. It was rare at the turn of the century, a casualty of the millinery trade, which used bird feathers as decorations in women’s hats. Legal protection and open garbage dumps helped it stage a spectacular comeback. Today some conservationists worry about these gulls’ depredations on the nests of other shorebirds.

Herring gulls are scavengers as well as expert thieves, boldly stealing food from other birds and sometimes snatching sandwiches out of beachgoers’ hands. They also hunt moles and even rabbits, hovering over their holes waiting for the quarry to appear. Often they eat mollusks, whose hard shells they crack by flying over a hard surface and dropping them in flight.

The black-headed gull (L. ridibundus), a dark-headed bird with crimson legs, breeds in Eurasia and Iceland, winters south in India and the Philippines, and commonly feeds in fields, where its chief food is insects. Bonaparte’s gull (L. philadelphia), of North America, has a black head and bill, a gray mantle, and pinkish to reddish legs. It builds a stick nest in trees and hunts for insects over ponds. In the winter it may plunge into the sea for fish. The California gull (L. californicus) of North America breeds inland and winters on the Pacific coast. This species is credited with having saved the crops of early Mormon settlers in the Salt Lake City region from destruction by the Mormon cricket, a long-horned grasshopper; it is the state bird of Utah. Franklin’s gull (L. pipixcan) breeds in large colonies on inland marshes of North America and winters on the Pacific coast of South America.

The glaucous gull (L. hyperboreus) is mostly white with pinkish legs and a yellow bill with a red spot. It inhabits northern seas, but sometimes it winters as far south as Hawaii and the Mediterranean. The great black-backed gull (L. marinus), with a wingspread of 1.6 metres (63 inches), is the largest gull. It occurs on the coasts of the North Atlantic.

The kelp gull (L. dominicanus) is a very wide-ranging black-backed species of the Southern Hemisphere, including Antarctica. The laughing gull (L. atricilla), a medium-sized bird with a black head, red bill, and red feet, often gives vent to a strident, laughing call. It breeds from Maine to northern South America and winters south in Brazil, often on fresh waters far inland. It is the only gull that breeds both in the Caribbean area and in the North Atlantic Ocean. With a wingspread of about 60 cm (24 inches), the smallest gull is the little gull (L. minutus), a black-headed species of Europe and occasionally North America.

The Pacific gull (L. pacificus) breeds in the region of Tasmania and southern Australia. The ring-billed gull (L. delawarensis) is common on inland lakes in North America and often gathers in large flocks to feed on plowed fields. The sooty gull (L. hemprichi) of the western Indian Ocean has a dark brown hood and a grayish brown mantle. Ross’s gull (Rhodostethia rosea) is an attractive pinkish white bird that breeds in northern Siberia and wanders widely over the Arctic Ocean. Abounding in the Arctic, Sabine’s gull (Xema sabini) has a forked tail and a habit of running and picking up food like a plover. The swallow-tailed gull (Creagrus furcatus) of the Galapagos Islands is a striking bird, the only gull with a deeply forked tail.

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#864 2020-12-03 00:15:23

ganesh
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Re: Miscellany

842) Songbird

Songbird, also called passerine, any member of the suborder Passeri (or Oscines), of the order Passeriformes, including about 4,000 species—nearly half the world’s birds—in 35 to 55 families. Most cage birds belong to this group. Songbirds are alike in having the vocal organ highly developed, though not all use it to melodious effect. Classification in this suborder is much disputed. Alaudidae (larks) and Hirundinidae (swallows) are the most distinctive families.

Songbirds range in size from tiny kinglets and sunbirds to comparatively large crows. They are mainly land birds that live in a wide variety of situations, from open grassland to forest. Although songbirds include some of the best songsters, such as thrushes, some have harsh voices like crows, and some do little or no singing. Songbirds are distinguished from other perching birds by certain anatomical characteristics, especially the more complicated vocal organ, or syrinx.

The syrinx—as the voice-producing structure, or song box, is called—is located at the point where the windpipe divides into two bronchial tubes to go to the lungs. The syrinx is an intricately constructed organ with a firm bony framework and filmlike vibrating internal membranes over which the air, during exhalation, passes rapidly, producing all the many utterances of the bird. A variable number of syringeal muscles and their controlling nerves adjust the tension on the membranes. The song box reaches its greatest complexity in the true songbirds. (But it is not a complicated syrinx alone that determines singing ability, for some true songbirds hardly sing at all). In some birds the windpipe is elongated and elaborately coiled. Sometimes this elongation is enclosed within the breast bone, or sternum. In certain of the birds-of-paradise known as manucodes, the elongated windpipe is coiled on the breast between the skin and the flesh. Presumably this lengthening of the windpipe gives resonance to the voice.

Vocalization in birds includes a wide variety of calls besides the song proper and provides a means of social communication. Bird song is best considered the vocalization that is used in courtship and breeding, chiefly by the male, to advertise that he is ready to mate, to attract the female and perhaps stimulate her,  to keep the pair together, and to inform rival males that he has established a territory from which they will be excluded. The male’s calls are also part of a threat display that takes the place of actual combat in repelling intruding rivals. However, similar song is sometimes given spontaneously when there is no obvious use for it. Occasionally females sing, and especially in tropical species pairs may duet, again perhaps as a method of reinforcing the bond between the pair. Often the song is delivered from a series of regularly used perches. Some species, especially those that live in grasslands, have flight songs.

Bird song need not be pleasing to the human ear. The hooting of the owl, the monotonously repeated phrases of the North American whippoorwill, the crazed, repeated whistle of a Malayan cuckoo that has given it the name of the brain-fever bird, and the African tinkerbird’s repeated notes, which, from their resemblance to hammering on metal, have given the bird its name—all must be called songs.

Which birds are the best songsters is a question that is subjective. The nightingale of Europe (Erithacus, or Luscinia, megarhynchos), a small thrush, perhaps heads the list of famous songsters of European literature. Also a favourite of the poets was the European skylark (Alaudia arvensis). In North America the mockingbird (Mimus polyglottos) is a wonderful performer with a rich, melodious, long-continued song. In Australia the lyrebirds, which are not true songbirds, have songs that are superlative in variety and intensity and have a dramatic quality. Though the best songsters may be true songbirds, some birds of other groups have pleasing or musical utterances, like the quavering trill of the screech owl and the cheery whistle of the bobwhite quail.

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#865 2020-12-05 02:52:35

ganesh
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Re: Miscellany

843) Raven

Raven, any of approximately 10 species of heavy-billed dark birds, larger than crows. Closely related, both ravens and crows are species of the genus Corvus. The raven has a heavier bill and shaggier plumage than the crow, especially around the throat. The raven’s lustrous feathers also have a blue or purplish iridescence.

The common raven (C. corax) is the largest of the perching birds: it reaches a length of up to 66 cm (26 inches) and has a wingspan of more than 1.3 metres (4 feet). (Some magpies and the lyrebird exceed the raven in length, but their bodies are smaller.) In the white-necked raven (C. cryptoleucus) of western North America, the bases of the neck feathers are white. Other species of ravens—some with white or brown markings—occur in Africa, southern Asia, Australia, and North America.

Formerly abundant throughout the Northern Hemisphere, the raven is now restricted to the wilder, undisturbed parts of its range. It is among the hardiest of birds, inhabiting the northern tundra and boreal forests as well as barren mountains and desert. It is keen-sighted and notably wary. Long before it was immortalized in Edgar Allan Poe’s poem “The Raven,” the common raven was a near-universal symbol of dark prophecy—of death, pestilence, and disease—though its cleverness and fearless habits also won it a degree of admiration, as evidenced in its noble heraldic roles in the mythology of some peoples.

Like other members of the family Corvidae, the raven is a noisy, aggressive omnivore whose diet includes rodents, insects, grain, and birds’ eggs. In winter, especially, it is a scavenger and feeds on carrion, dead fish, and garbage. The raven is an intelligent bird with a large and varied vocabulary, including guttural croaks, gurglings, and a sharp metallic “tok.” Studies have shown that the common raven is capable of saving items of value that can be used later as tools or as goods for barter, behaviour that strongly suggests that this bird has the ability to plan for a future when these items might be needed.

The common raven usually is solitary but may feed in small flocks. The raven’s spectacular courtship flight involves soaring and all kinds of aerial acrobatics. The birds’ crudely made nest of coarse sticks, usually lined with hair or shredded bark, is a bulky structure up to 1.5 metres (5 feet) in diameter that may be built on a cliff or the top of a large tree. The young remain in the nest for about a month. If captured as a nestling, a raven may make an interesting pet capable of learning to mimic a few words. One captive bird on record lived 69 years.

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#866 2020-12-06 00:24:53

ganesh
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Re: Miscellany

844) Swift

Swift, any of about 75 species of agile, fast-flying birds of the family Apodidae (sometimes Micropodidae), in the order Apodiformes, which also includes the hummingbirds. The family is divided into the subfamilies Apodinae, or soft-tailed swifts, and Chaeturinae, or spine-tailed swifts. Almost worldwide in distribution, swifts are absent only from polar regions, southern Chile and Argentina, New Zealand, and most of Australia.

Closely resembling swallows, swifts range in length from about 9 to 23 cm (3.5 to 9 inches). They have exceptionally long wings and chunky, powerful bodies. Their compact plumage is a dull or glossy gray, brown, or black, sometimes with pale or white markings on the throat, neck, belly, or rump. The head is broad, with a short, wide, slightly curved bill. The tail, although often short, may be long and deeply forked. The feet are tiny and weak; with the aid of sharp claws they are used only to cling to vertical surfaces. A swift that lands on flat ground may be unable to regain the air. In soft-tailed forms, the hind toe is rotated forward as an aid in gripping vertical surfaces; in spine-tailed swifts, support is gained from the short needle-tipped tail feathers, and the feet are less modified.

In feeding, swifts course tirelessly back and forth, capturing insects with their large mouths open. They also drink, bathe, and sometimes mate on the wing. They fly with relatively stiff, slow wingbeats (four to eight per second), but the scimitar-like design of the wing makes it the most efficient among birds for high-speed flight. The fastest of small birds, swifts are believed to reach 110 km (70 miles) per hour regularly; reports of speeds three times that figure are not confirmed. The only avian predators known to take swifts with regularity are some of the larger falcons.

The nest of a swift is made of twigs, buds, moss, or feathers and is glued with its sticky saliva to the wall of a cave or the inside of a chimney, rock crack, or hollow tree. A few species attach the nest to a palm frond, an extreme example being the tropical Asian palm swift (Cypsiurus parvus), which glues its eggs to a tiny, flat feather nest on the surface of a palm leaf, which may be hanging vertically or even upside down. Swifts lay from one to six white eggs (usually two or three). Both eggs and young may be allowed to cool toward the environmental temperature in times of food scarcity, slowing development and conserving resources. The young stay in the nest or cling near it for 6 to 10 weeks, the length of time depending largely on the food supply. Upon fledging, they resemble the adults and immediately fly adeptly.

Among the best-known swifts is the chimney swift (Chaetura pelagica), a spine-tailed, uniformly dark gray bird that breeds in eastern North America and winters in South America, nesting in such recesses as chimneys and hollow trees; about 17 other Chaetura species are known worldwide. The common swift (Apus apus), called simply “swift” in Great Britain, is a soft-tailed, black bird that breeds across Eurasia and winters in southern Africa, nesting in buildings and hollow trees; nine other Apus swifts are found throughout temperate regions of the Old World, and some Apus species inhabit South America. The white-collared swift (Streptoprocne zonaris), soft-tailed and brownish black with a narrow white collar, is found from Mexico to Argentina and on larger Caribbean islands, nesting in caves and behind waterfalls. The white-rumped swift (Apus caffer), soft-tailed and black with white markings, is resident throughout Africa south of the Sahara. The white-throated swift (Aeronautes saxatalis), soft-tailed and black with white markings, breeds in western North America and winters in southern Central America, nesting on vertical rock cliffs.

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#867 2020-12-07 01:33:54

ganesh
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Re: Miscellany

845) Falcon

Falcon, any of nearly 60 species of hawks of the family Falconidae (order Falconiformes), diurnal birds of prey characterized by long, pointed wings and swift, powerful flight. The name is applied in a restricted sense, as true falcons, to the genus Falco, which numbers more than 35 species. Falcons occur virtually worldwide. They range in size from about 15 cm (6 inches) long in the falconets (Microhierax) to about 60 cm (24 inches) in the gyrfalcon, an Arctic species. In true falcons the female is the larger and bolder of the males and females  and is preferred for the sport of falconry. Falcons have plumes called “flags” on their legs and a notch in the beak that is well developed in the genus Falco to form a “tooth.

Falcons commonly nest in holes in trees or on natural ledges on cliffs. The eggs are usually four or five in number and buffy white in colour, speckled and blotched with reddish brown. The incubation period is about 28 or 35 days, and the young are cared for in the nest for as long as 35 days.

The flight of falcons is fast and direct with the wings rapidly digging through the air. Some falcons habitually hover while scanning the ground for prey. Some species capture birds of their own size or smaller in midair. Others live mainly on hares, mice, lizards, and insects.

The bat falcon (F. albigularis) of Mexico and Central and South America is a little bird with a dark back, white throat, barred black-and-white breast, and reddish belly. It preys upon birds. The forest falcon (Micrastur semitorquatus) of tropical America hunts birds and reptiles in the jungles. The laughing falcon (Herpetotheres cachinnans) of the wooded lowlands of Central and South America is a noisy brown bird that eats snakes. The prairie falcon (F. mexicanus), a desert falcon, inhabits canyon and scrub country in western North America.

The falconets (Microhierax species) and pygmy falcons (Polihierax) are tiny birds of the Old World tropics. They eat insects and birds.

The cuckoo falcons, several species of Aviceda, are kites of the subfamily Perninae (family Accipitridae). They range over Asia and the South Pacific, hunting at twilight, mainly for insects. Some hunt lizards.

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#868 2020-12-08 00:04:57

ganesh
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Re: Miscellany

846) Bison

Bison, (genus Bison), also called buffalo or wisent, either of two species of oxlike grazing mammals that constitute the genus Bison of the family Bovidae. The American bison (B. bison), commonly known as the buffalo or the plains buffalo, is native to North America, and the European bison (B. bonasus), or wisent, is native to Europe. Both species were drastically reduced in numbers by hunting and now occupy small protected areas that are tiny fractions of their former ranges.

The American bison differs from domestic cattle or oxen in several respects. It is larger and has a broad heavy head that is carried low and cannot be raised to shoulder level. The bison also has a pronounced hump at the shoulders, heavy forequarters, and 14 ribs instead of the 13 found in cattle. The coarse, shaggy fur is dark brown in colour. It grows especially long on the head, neck, and shoulders and usually forms a beard on the chin. On rare occasions a white bison is born; these unusual specimens were especially honoured—and even worshipped—by American Indians. Both bison males and females bear short, upcurved horns, those of the cow being smaller. Bison are large, powerful animals. A mature bull stands about 2 metres (6.5 feet) at the shoulder and weighs more than 900 kg (1,980 pounds). The female is about 1.5 metres (5 feet) tall and weighs about 320 kg (700 pounds).

Bison live in small groups, or bands, whose basic unit is one or more females and several generations of their offspring. Adult males live on the band’s periphery or form their own small groups. Large temporary herds of bison may arise from the congregation of dozens or even hundreds of individual bands. During the mating season, which reaches its height in August, bulls engage in head-butting contests to determine their social dominance. The cow usually gives birth to a single calf in May after about nine months’ gestation. All members of the band protect the young. Bison prefer grass and herbs, but they will also eat twigs and leaves. Bison herds undertake short seasonal migrations, moving a few hundred miles southward in winter and then moving back north when warmer weather returns. Their usual gait is a plodding walk, but they also trot, canter in a stiff-legged manner, or run with a rolling motion. In spite of their bulk, they are agile and fast, having been clocked at speeds of 65 km (40 miles) per hour. Bison are unpredictable animals. Sometimes they can be approached closely without evincing alarm, but at other times they stampede at the least provocation.

An examination of the mitochondrial DNA of a 120,000-year-old fossil long-horned bison (B. latifons) from Colorado and a 130,000-year-old fossil of what was likely a steppe bison (Bison cf. priscus) from the Yukon suggested that the first bison in North America migrated from Asia across the Bering Land Bridge sometime between 95,000 and 135,000 years ago before spreading rapidly throughout the continent. Some authorities distinguish two subspecies of American bison, the plains bison (B. bison bison) and the wood bison (B. bison athabascae), though the differences between them are minor. The plains bison formerly inhabited most of the United States east of the Rocky Mountains and the Great Plains provinces of Canada. It greatly outnumbered the wood bison, which lived in northwestern Canada and Alaska. An estimated 50 million plains bison, probably the largest aggregation of large animals known to recorded history, roamed over North America when Europeans arrived. The bison formed the mainstay of the economy of the Plains Indians, providing them with meat for food, hides and fur for clothing and shelter, and sinew and horn for tools, yet the Indians’ hunting activities had little impact on the bison population.

With the westward movement of white civilization in the 18th and 19th centuries, the bison were wantonly slaughtered in ever-growing numbers: they were hunted for subsistence, for the commercial sale of their meat and hides, or simply for sport. By the early 19th century the bison had been exterminated east of the Mississippi River. The extension of railroads across the Great Plains in the 1860s led to the decimation of the immense herds that foraged on the vast grasslands there. One hunter alone, William F. Cody (“Buffalo Bill”), killed 4,280 animals in 1867–68 while supplying buffalo meat for railroad construction crews. The white man’s slaughter of the bison also had a conscious political objective—to deprive the Indians of their means of subsistence, thereby making it easier to drive them on to reservations or make them adopt settled agricultural pursuits. Much of the hostility between the Indians and the whites was caused by the whites’ unremitting destruction of the bison herds. By 1870 the bison population on the Great Plains had been divided into two parts, lying north and south, respectively, of the Union Pacific railway line. The southern herd was completely destroyed by 1875 and the northern one by 1885. By 1889 there were fewer than 1,000 bison left alive in all of North America.

About 1900, as the bison neared extinction, concerted action by American and Canadian cattlemen and conservationists resulted in the protection of the remaining animals in government preserves, zoos, and ranches on both sides of the border. The present commercial herds now total as many as 400,000 individuals. Some 20,000 plains bison are protected in preserves in the United States and Canada, and more than 10,000 wood bison reside on preserves in Canada. This number is sufficient to ensure the survival of the species, though a major concern of conservationists is the maintenance of genetic diversity among protected bison herds. The wood bison is considered to be a threatened subspecies in Canada.

The European bison, or wisent, differs from the American bison in several respects. It lives in woodlands and is slightly larger and longer-legged than the American bison but is less heavily built. The European bison’s range originally extended eastward across Europe to the Volga River and the Caucasus Mountains. It became extinct in the wild after World War I, but herds built from zoo-bred animals were subsequently reestablished, most notably in the Belovezhskaya (Polish: Białowieża) Forest in Belarus and Poland. Other countries that are home to the European bison include Lithuania, Russia, and Ukraine.

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#869 2020-12-09 00:32:10

ganesh
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Re: Miscellany

847) Boa

Boa, common name for a variety of nonvenomous constricting snakes. There are more than 40 species of true boas (family Boidae). In addition, boa may also refer to two other groups of snakes: the Mascarene, or split-jawed, boas (family Bolyeriidae) and dwarf boas (ground and wood boas of the family Tropidophiidae); these two families are not closely related to each other or to the true boas.

The true boas are divided into two subfamilies, Boinae and Erycinae. Boinae includes the boa constrictor (Boa constrictor), tree boas (genus Corallus), and anacondas (genus Eunectes) of the American tropics; two other genera are found on Madagascar and islands of the southwestern Pacific. Members of Boinae range from 1 metre (3.3 feet) long in some species to commonly more than 4 metres in the giant, or green, anaconda. The boa constrictor occupies a variety of habitats from coastal northern Mexico and the Lesser Antilles to Argentina; though seldom more than 3.3 metres (11 feet) long, some have grown to more than 5 metres. One subspecies, the red-tailed boa (Boa constrictor constrictor), is particularly popular in the pet trade. Several tree boas possess sizable teeth used for catching birds. An example is the 1.8-metre (6-foot) emerald tree boa (Corallus caninus) of tropical South America; the adult is green above, with a white dorsal stripe and crossbars, and yellow below. The rainbow boa (Epicrates cenchria) of Costa Rica to Argentina is not strongly patterned but is markedly iridescent. Except for the anacondas, most boines are terrestrial to strongly arboreal. The young often move from the trees to the ground as they get older and larger. Most species have labial (lip) pits with heat-sensing organs that complement their sense of smell and excellent vision. Mammals and birds are common prey, which is usually captured by a bite-grasp followed by constriction.

Subfamily Erycinae includes 10 Asian, Indian, and African species of sand boa (genus Eryx) and the West African earth python (Charina reinhardtii), in addition to two North American species. Erycines are live-bearers (as opposed to egg layers) that have stout cylindrical bodies, blunt heads, and short tails. Most measure less than 70 cm (28 inches). These terrestrial snakes are often subterranean, and most live in arid and semiarid habitats, where they prey on lizards and small mammals. The brown, 45-cm (18-inch) rubber boa (Charina bottae) of western North America is the most northerly boa and is a burrower that looks and feels rubbery. The 90-cm (35-inch) rosy boa (Charina trivirgata), ranging from southern California and Arizona into Mexico, usually is brown- or pink-striped.

Except for two egg-laying Asian species (genus Xenophidion), the 24 dwarf boas of family Tropidophiidae bear live young and live in the West Indies, Central America, and northern South America. They are predominantly terrestrial, occasionally foraging in low trees and bushes to hunt small vertebrates, especially amphibians and lizards.

The single surviving species of family Bolyeriidae (Casarea dussumieri) lives on Mauritius and Round Island. It is unique among snakes in that the lower jaw is hinged in the middle, which enables the snake to grasp hard-bodied skinks with a firm ratchetlike grip. It is a 0.8–1.4-metre-long egg layer. Bolyeria multocarinata was similar and went extinct owing to human introduction of rats and other predators.

One extinct relative of modern boas (Titanoboa cerrejonensis) lived between the end of the Cretaceous Period (some 65.5 million years ago) and the middle of the Eocene Epoch (about 40 million years ago). At the time it was the largest terrestrial vertebrate in the world. Known from a single fossilized vertebra, T. cerrejonensis probably weighed 1,135 kilograms (about 2,500 pounds) and reached a length of 13 metres (about 43 feet).

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#870 2020-12-10 01:22:29

ganesh
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Re: Miscellany

848) Alpaca

Alpaca, (Lama pacos), South American member of the camel family, Camelidae (order Artiodactyla), that is closely related to the llama, guanaco, and vicuña, which are known collectively as lamoids. The alpaca and the llama were both apparently domesticated several thousand years ago by the Indians of the Andes Mountains of South America. The other two lamoid species, the guanaco and vicuña, exist basically in the wild state.

Like other lamoids, alpacas are slender-bodied animals with a long neck and legs, a short tail, a small head, and large, pointed ears. Alpacas are readily distinguished from llamas by their smaller size; they stand approximately 90 cm (35 inches) high at the shoulder and weigh 55 to 65 kg (121 to 143 pounds). The alpaca also differs from the llama in having a rounded, rather than squarish, body and in its habit of pressing its tail close to the body rather than holding it erect, as does the llama. The alpaca’s shaggy coat varies in colour from the usual black or brown through lighter shades of gray and tan to pale yellow and, occasionally, white. The present distribution of alpacas is limited to central and southern Peru and western Bolivia. Alpacas are the most limited in range and the most specialized of the four lamoids, being adapted to marshy ground at altitudes from 4,000 to 4,800 metres (13,000 to 15,700 feet). In adaptation to the reduced oxygen content of the air, their red blood corpuscles are exceptionally numerous.

Alpacas are the most important of the lamoids for fleece production. During the period of Incan civilization, the wearing of robes made of alpaca and vicuña fleeces was reserved for the nobility and royalty. Two breeds of alpaca, the huacaya and the suri, were developed in pre-Columbian times. The fleece of the suri is fine and silky and grows long enough to touch the ground if the animal is not sheared. The fleece of the huacaya is shorter and coarser by comparison. The alpaca’s fleece is remarkably lightweight, strong, lustrous, high in insulation value, and resistant to rain and snow. It is used in parkas, sleeping bags, and fine coat linings. Alpaca fibre is sometimes combined with other fibres to make dress and lightweight suit fabrics and is also woven as a pile fabric used both for coating and as a lining for outerwear. Peru is the leading producer of the fleece, with most of it being marketed in the city of Arequipa. The Peruvian government has established a breeding program to improve the quality of alpaca fleece and increase its production.

Alpacas are normally sheared every two years, the suris yielding fine fleeces of about 3 kg (6.5 pounds) per animal and the huacayas giving coarser fleeces weighing about 2.5 kg. Hair growth in two years is about 30 cm (12 inches) in the huacaya and 60 cm in the suri. Individual fibres within the fleece range from about 20 to 40 cm in length at the time of shearing. Alpacas have a natural life span of 15–20 years.

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#871 2020-12-11 00:36:48

ganesh
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Re: Miscellany

849) Glacier

A glacier is a huge mass of ice that moves slowly over land

A glacier is a huge mass of ice that moves slowly over land. The term “glacier” comes from the French word glace (glah-SAY), which means ice. Glaciers are often called “rivers of ice.”

Glaciers fall into two groups: alpine glaciers and ice sheets.

Alpine glaciers form on mountainsides and move downward through valleys. Sometimes, alpine glaciers create or deepen valleys by pushing dirt, soil, and other materials out of their way. Alpine glaciers are found in high mountains of every continent except Australia (although there are many in New Zealand). The Gorner Glacier in Switzerland and the Furtwangler Glacier in Tanzania are both typical alpine glaciers. Alpine glaciers are also called valley glaciers or mountain glaciers.

Ice sheets, unlike alpine glaciers, are not limited to mountainous areas. They form broad domes and spread out from their centers in all directions. As ice sheets spread, they cover everything around them with a thick blanket of ice, including valleys, plains, and even entire mountains. The largest ice sheets, called continental glaciers, spread over vast areas. Today, continental glaciers cover most of Antarctica and the island of Greenland.

Massive ice sheets covered much of North America and Europe during the Pleistocene time period. This was the last glacial period, also known as the Ice Age. Ice sheets reached their greatest size about 18,000 years ago. As the ancient glaciers spread, they carved and changed the Earth’s surface, creating many of the landscapes that exist today. During the Pleistocene Ice Age, nearly one-third of the Earth’s land was covered by glaciers. Today, about one-tenth of the Earth’s land is covered by glacial ice.

How Glaciers Form

Glaciers begin forming in places where more snow piles up each year than melts. Soon after falling, the snow begins to compress, or become denser and tightly packed. It slowly changes from light, fluffy crystals to hard, round ice pellets. New snow falls and buries this granular snow. The hard snow becomes even more compressed. It becomes a dense, grainy ice called firn. The process of snow compacting into glacial firn is called firnification.

As years go by, layers of firn build on top of each other. When the ice grows thick enough—about 50 meters (160 feet)—the firn grains fuse into a huge mass of solid ice. The glacier begins to move under its own weight. The glacier is so heavy and exerts so much pressure that the firn and snow melt without any increase in temperature. The meltwater makes the bottom of the heavy glacier slicker and more able to spread across the landscape.

Pulled by gravity, an alpine glacier moves slowly down a valley. Some glaciers, called hanging glaciers, don't flow the entire length of a mountain. Avalanches and icefalls transfer glacial ice from hanging glaciers to a larger glacier beneath them, or directly to the valley below.

An ice sheet spreads out from its center. The great mass of ice in a glacier behaves plastically, or like a liquid. It flows, oozes, and slides over uneven surfaces until it covers everything in its path.

Different parts of a glacier move at different speeds. The flowing ice in the middle of the glacier moves faster than the base, which grinds slowly along its rocky bed.

The different speeds at which the glacier moves causes tension to build within the brittle, upper part of the ice. The top of the glacier fractures, forming cracks called crevasses. Crevasses are in the top 50 meters (160 feet) of the glacier. Crevasses can be very dangerous for mountaineers. They can open quickly and be very deep.

Moulins are another formation that carve into glaciers. A moulin is a deep, nearly-vertical pipeline in the glacier formed by meltwater on top of the glacier falling through a crack in the ice. Moulins are often much deeper than crevasses, going all the way to the bottom of the glacier.

Most glaciers move very slowly—only a few centimeters a day. Some, though, can move 50 meters (160 feet) a day. These fast-moving rivers of ice are called galloping glaciers.

Where a glacier meets the coast, it becomes a tidewater glacier. Its leading edge lifts and floats in the water, forming cliffs of ice that may be 60 meters (200 feet) high. Chunks of ice at the edge of the tidewater glacier break away into the water—a process called calving. Calving is a violent process. It results in large waves and loud crashes. Floating chunks of glacial ice, broken off during calving, are called icebergs.

Glacial Features

Although glaciers move slowly, they are extremely powerful. Like huge bulldozers, they plow ahead year after year, crushing, grinding, and toppling almost everything in their paths. Forests, hills, and mountainsides are no match for glaciers.

Sometimes, glaciers form on volcanoes. When these volcanoes erupt, they are especially dangerous. They send floods of water, ice, and rocks over the land and into the atmosphere.

Alpine glaciers begin to flow downhill from bowl-shaped mountain hollows called cirques. As the glaciers overflow the cirque, they move downward. They dig deep into the terrain, forming rugged, dramatic landscapes.

As they move, glaciers erode or wear away the land beneath and around them. Glaciers carry great amounts of soil, rock, and clay. Some of the boulders they carry are as big as houses.

Rocks carried hundreds and even thousands of kilometers by glaciers are called glacial erratics. Glacial erratics differ significantly from the landscape in which they were deposited. The Big Rock, for instance, is a 15,000-ton quartzite boulder near Okotoks, Alberta, Canada. The Big Rock was deposited from what is now northern Alberta, about 1,640 kilometers (500 miles) away, during the last ice age.

Embedded, or stuck, in a glacier’s base, these large rocks grind against the ground like the prongs of a rake. They dig long grooves, called striations, in the surface of the Earth. Geologists can tell in what direction an ancient glacier moved by studying striations left in rock.

Glaciers eventually deposit their loads of rock, dirt, and gravel. These materials are called moraine. Piles of moraine dumped at a glacier’s end, or snout, are called terminal moraines.

Lateral moraine forms along the side of a glacier. Medial moraine appears as dark lines near the center of the glacier. Supraglacial moraine appears on the surface of the glacier—dirt, dust, leaves, and anything else that falls onto a glacier and sticks. Ogives are frozen “waves,” or ridges, on the surface of a glacier.
When glaciers began their final retreat 10,000 years ago, they left behind many landscape features, such as lakes, valleys, and mountains.

Many hollowed-out areas carved by glaciers became lakes. Bowl-shaped cirques, where most alpine glaciers form, became mountain lakes. These alpine lakes are called tarns.

Glaciers can also create lakes by leaving depressions in the earth. The Finger Lakes in the western part of the U.S. state of New York were excavated during the last Ice Age. The lakes were once stream valleys. Along the streams, the glacier scooped out troughs that now contain deep lakes.

Glacial retreat created other features of the landscape. Materials deposited by a glacier as it retreats are called ground moraines. The jumble of rock, gravel, and dirt making up ground moraines is called till. Much of the fertile soil in the Great Plains of North America was formed from layers of till left by ancient ice sheets.

Glacial valleys exist on almost every continent. These valleys are scooped out as a glacier scrapes through them. There are no glaciers in Australia, but Mount Kosciuszko still has glacial valleys from the last Ice Age.

Distinctive mountain formations called aretes and horns are the result of glacial activity. An arête is a sharp ridge of rock that forms when two glaciers collide. Each glacier erodes a glacial valley on either side of the arête. Glacier National Park in the U.S. state of Montana is filled with deep glacial valleys and sharp arêtes.

An arête where three or more glaciers meet to form a peak is called a horn. These tall, singular landforms are also called pyramidal peaks. The Matterhorn in Switzerland and Italy (and its copy in Disneyland, California) is a glacial horn.

Roche moutonnee is a smooth, rounded rock formation created as a glacier crushes and rearranges rocks in its path. Roche moutonnee is visible in many hilly areas as outcroppings of flat rock.

In contrast to alpine glaciers, ice sheets do not create landscape features as they spread. They tend to smooth out the land beneath them.

People and Glaciers

Glaciers provide people with many useful resources. Glacial till provides fertile soil for growing crops. Deposits of sand and gravel are used to make concrete and asphalt.
The most important resource provided by glaciers is freshwater. Many rivers are fed by the melting ice of glaciers. The Gangotri Glacier, one of the largest glaciers in the Himalayan Mountains, is the source of the River : Ganges River. The Ganges is the most important source of freshwater and electricity in India and Bangladesh. (Electricity is created by dams and hydroelectric power plants along the Ganges.)

Some companies link glacial water to clean, fresh taste. Because water has been trapped in the glacier for so long, many people believe it has not been exposed to pollutants that liquid water is exposed to.

Glaciers dug basins for most of the world’s lakes and carved much of the Earth’s most spectacular mountain scenery. The dramatic, diverse landscape of Yosemite Valley, California, was sculpted entirely by glaciers during the last Ice Age.

Threats to Glaciers

The processes that remove snow, ice, and moraine from a glacier or ice sheet are called ablation. Ablation includes melting, evaporation, erosion, and calving.

Glaciers melt when ice melts more quickly than firn can accumulate. Earth’s average temperature has been increasing dramatically for more than a century. Glaciers are important indicators of global warming and climate change in several ways.

Melting ice sheets contribute to rising sea levels. As ice sheets in Antarctica and Greenland melt, they raise the level of the ocean. Tons of fresh water are added to the ocean every day. In March 2009, a 160-square-mile piece of the Wilkins Ice Shelf broke off of the Antarctic Peninsula. Large icebergs created by such an event create hazards for shipping.

Large additions of fresh water also change the ocean ecosystem. Organisms, such as many types of corals, depend on salt water for survival. Some corals may not be able to adjust to a more freshwater habitat.

The loss of glacial ice also reduces the amount of fresh water available for plants and animals that need fresh water to survive. Glaciers near the Equator, such as those on the tropical island of Papua or in South America, are especially at risk.

The residents below Chacaltaya Glacier in Bolivia, for instance, depended on the glacier for almost all of their fresh water and electricity. Chacaltaya Glacier provided these resources to La Paz, Bolivia’s largest city. Chacaltaya Glacier was also the world’s highest ski resort. In 2009, Chacaltaya Glacier melted entirely.

A few glaciers may actually be benefiting from global warming. Although winter temperatures are rising, so is the amount of snowfall in areas like Pakistan’s Upper Indus River Basin. Glaciers are growing quickly there.

Less precipitation also affects some glaciers. In 1912, the glaciers on Tanzania’s Mount Kilimanjaro covered 12 square kilometers (4.6 square miles). In 2009, Kilimanjaro’s alpine glaciers had shrunk to two square kilometers (0.8 square miles). This reduction is the result of few heavy snowfalls.

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#872 2020-12-12 00:26:42

ganesh
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Re: Miscellany

850) Turpentine

Turpentine, the resinous exudate or extract obtained from coniferous trees, particularly those of the genus Pinus. Turpentines are semifluid substances consisting of resins dissolved in a volatile oil; this mixture is separable by various distillation techniques into a volatile portion called oil (or spirit) of turpentine and a nonvolatile portion called rosin. Although the term turpentine originally referred to the whole oleoresinous exudate, it now commonly refers to its volatile turpentine fraction only, which has various uses in industry and the visual arts.

Oil of turpentine is a colourless, oily, odorous, flammable, water-immiscible liquid with a hot, disagreeable taste. It is a good solvent for sulphur, phosphorus, resins, waxes, oils, and natural rubber. It hardens upon exposure to air. Chemically, oil of turpentine is a mixture of cyclic monoterpene hydrocarbons, the predominant constituent being pinene.

Formerly, the largest use for turpentine oil was as a paint and varnish solvent. Oil painters generally prefer it as a paint thinner and brush cleaner to petroleum solvents (mineral spirits), even though the latter are less expensive. But the largest use of turpentine oil is now in the chemical industry, as a raw material in the synthesis of resins, insecticides, oil additives, and synthetic pine oil and camphor. Turpentine oil is also used as a rubber solvent in the manufacture of plastics.

Turpentine oil is generally produced in countries that have vast tracts of pine trees. The principal European turpentines are derived from the cluster pine (P. pinaster) and the Scotch pine (P. sylvestris), while the main sources of turpentine in the United States are the longleaf pine (P. palustris) and the slash pine (P. caribaea).

Turpentine oil is classified according to the way it is produced. Sulfate turpentine, used widely in the chemicals industry, is obtained as a by-product of the kraft, or sulfate, process of cooking wood pulp in the course of the manufacture of kraft paper. Wood turpentine is obtained by the steam distillation of dead, shredded bits of pine wood, while gum turpentine results from the distillation of the exudate of the living pine tree obtained by tapping. Crude turpentine obtained from the living pine by tapping typically contains 65 percent gum rosin and 18 percent gum turpentine.

Various other oleoresins (solutions of resins dispersed in essential oils) are known as turpentines. Venice turpentine, for example, is a pale green, viscous liquid that is collected from the larch (Larix decidua, or L. europea). It is used for lithographic work and in sealing wax and varnishes.

Crude turpentine is one of a group of pine-tree derivatives that are known as naval stores.

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It is no good to try to stop knowledge from going forward. Ignorance is never better than knowledge - Enrico Fermi. 

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#873 2020-12-13 00:37:47

ganesh
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Re: Miscellany

851) Polymer

Polymer, any of a class of natural or synthetic substances composed of very large molecules, called macromolecules, that are multiples of simpler chemical units called monomers. Polymers make up many of the materials in living organisms, including, for example, proteins, cellulose, and nucleic acids. Moreover, they constitute the basis of such minerals as diamond, quartz, and feldspar and such man-made materials as concrete, glass, paper, plastics, and rubbers.

The word polymer designates an unspecified number of monomer units. When the number of monomers is very large, the compound is sometimes called a high polymer. Polymers are not restricted to monomers of the same chemical composition or molecular weight and structure. Some natural polymers are composed of one kind of monomer. Most natural and synthetic polymers, however, are made up of two or more different types of monomers; such polymers are known as copolymers.

Organic polymers play a crucial role in living things, providing basic structural materials and participating in vital life processes. For example, the solid parts of all plants are made up of polymers. These include cellulose, lignin, and various resins. Cellulose is a polysaccharide, a polymer that is composed of sugar molecules. Lignin consists of a complicated three-dimensional network of polymers. Wood resins are polymers of a simple hydrocarbon, isoprene. Another familiar isoprene polymer is rubber.

Other important natural polymers include the proteins, which are polymers of amino acids, and the nucleic acids, which are polymers of nucleotides—complex molecules composed of nitrogen-containing bases, sugars, and phosphoric acid. The nucleic acids carry genetic information in the cell. Starches, important sources of food energy derived from plants, are natural polymers composed of glucose.

Many inorganic polymers also are found in nature, including diamond and graphite. Both are composed of carbon. In diamond, carbon atoms are linked in a three-dimensional network that gives the material its hardness. In graphite, used as a lubricant and in pencil “leads,” the carbon atoms link in planes that can slide across one another.

Synthetic polymers are produced in different types of reactions. Many simple hydrocarbons, such as ethylene and propylene, can be transformed into polymers by adding one monomer after another to the growing chain. Polyethylene, composed of repeating ethylene monomers, is an addition polymer. It may have as many as 10,000 monomers joined in long coiled chains. Polyethylene is crystalline, translucent, and thermoplastic—i.e., it softens when heated. It is used for coatings, packaging, molded parts, and the manufacture of bottles and containers. Polypropylene is also crystalline and thermoplastic but is harder than polyethylene. Its molecules may consist of from 50,000 to 200,000 monomers. This compound is used in the textile industry and to make molded objects.

Other addition polymers include polybutadiene, polyisoprene, and polychloroprene, which are all important in the manufacture of synthetic rubbers. Some polymers, such as polystyrene, are glassy and transparent at room temperature, as well as being thermoplastic. Polystyrene can be coloured any shade and is used in the manufacture of toys and other plastic objects.

If one hydrogen atom in ethylene is replaced by a chlorine atom, vinyl chloride is produced. This polymerizes to polyvinyl chloride (PVC), a colourless, hard, tough, thermoplastic material that can be manufactured in a number of forms, including foams, films, and fibres. Vinyl acetate, produced by the reaction of ethylene and acetic acid, polymerizes to amorphous, soft resins used as coatings and adhesives. It copolymerizes with vinyl chloride to produce a large family of thermoplastic materials.

Many important polymers have oxygen or nitrogen atoms, along with those of carbon, in the backbone chain. Among such macromolecular materials with oxygen atoms are polyacetals. The simplest polyacetal is polyformaldehyde. It has a high melting point and is crystalline and resistant to abrasion and the action of solvents. Acetal resins are more like metal than are any other plastics and are used in the manufacture of machine parts such as gears and bearings.

A linear polymer characterized by a repetition of ester groups along the backbone chain is called a polyester. Open-chain polyesters are colourless, crystalline, thermoplastic materials. Those with high molecular weights (10,000 to 15,000 molecules) are employed in the manufacture of films, molded objects, and fibres such as Dacron.

The polyamides include the naturally occurring proteins casein, found in milk, and zein, found in corn (maize), from which plastics, fibres, adhesives, and coatings are made. Among the synthetic polyamides are the urea-formaldehyde resins, which are thermosetting. They are used to produce molded objects and as adhesives and coatings for textiles and paper. Also important are the polyamide resins known as nylons. They are strong, resistant to heat and abrasion, noncombustible, and nontoxic, and they can be coloured. Their best-known use is as textile fibres, but they have many other applications.

Another important family of synthetic organic polymers is formed of linear repetitions of the urethane group. Polyurethanes are employed in making elastomeric fibres known as spandex and in the production of coating bases and soft and rigid foams.

A different class of polymers are the mixed organic-inorganic compounds. The most important representatives of this polymer family are the silicones. Their backbone consists of alternating silicon and oxygen atoms with organic groups attached to each of the silicon atoms. Silicones with low molecular weight are oils and greases. Higher-molecular-weight species are versatile elastic materials that remain soft and rubbery at very low temperatures. They are also relatively stable at high temperatures.

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#874 2020-12-14 00:26:34

ganesh
Administrator
Registered: 2005-06-28
Posts: 32,464

Re: Miscellany

852) Solution

Solution, in chemistry, a homogenous mixture of two or more substances in relative amounts that can be varied continuously up to what is called the limit of solubility. The term solution is commonly applied to the liquid state of matter, but solutions of gases and solids are possible. Air, for example, is a solution consisting chiefly of oxygen and nitrogen with trace amounts of several other gases, and brass is a solution composed of copper and zinc.

A brief treatment of solutions follows.

Life processes depend in large part on solutions. Oxygen from the lungs goes into solution in the blood plasma, unites chemically with the hemoglobin in the red blood cells, and is released to the body tissues. The products of digestion also are carried in solution to the different parts of the body. The ability of liquids to dissolve other fluids or solids has many practical applications. Chemists take advantage of differences in solubility to separate and purify materials and to carry out chemical analysis. Most chemical reactions occur in solution and are influenced by the solubilities of the reagents. Materials for chemical manufacturing equipment are selected to resist the solvent action of their contents.

The liquid in a solution is customarily designated the solvent, and the substance added is called the solute. If both components are liquids, the distinction loses significance; the one present in smaller concentration is likely to be called the solute. The concentration of any component in a solution may be expressed in units of weight or volume or in moles. These may be mixed—e.g., moles per litre and moles per kilogram.

Crystals of some salts contain lattices of ions—i.e., atoms or groups of atoms with alternating positive and negative charges. When such a crystal is to be dissolved, the attraction of the oppositely charged ions, which are largely responsible for cohesion in the crystal, must be overcome by electric charges in the solvent. These may be provided by the ions of a fused salt or by electric dipoles in the molecules of the solvent. Such solvents include water, methyl alcohol, liquid ammonia, and hydrogen fluoride. The ions of the solute, surrounded by dipolar molecules of the solvent, are detached from each other and are free to migrate to charged electrodes. Such a solution can conduct electricity, and the solute is called an electrolyte.

The potential energy of attraction between simple, nonpolar molecules (nonelectrolytes) is of very short range; it decreases approximately as the seventh power of the distance between them. For electrolytes the energy of attraction and repulsion of charged ions drops only as the first power of the distance. Accordingly, their solutions have very different properties from those of nonelectrolytes.

It is generally presumed that all gases are completely miscible (mutually soluble in all proportions), but this is true only at normal pressures. At high pressures, pairs of chemically dissimilar gases may very well exhibit only limited miscibility. Many different metals are miscible in the liquid state, occasionally forming recognizable compounds. Some are sufficiently alike to form solid solutions.

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#875 2020-12-15 01:01:47

ganesh
Administrator
Registered: 2005-06-28
Posts: 32,464

Re: Miscellany

853) Combustion

Combustion, a chemical reaction between substances, usually including oxygen and usually accompanied by the generation of heat and light in the form of flame. The rate or speed at which the reactants combine is high, in part because of the nature of the chemical reaction itself and in part because more energy is generated than can escape into the surrounding medium, with the result that the temperature of the reactants is raised to accelerate the reaction even more.

A familiar example of a combustion reaction is a lighted match. When a match is struck, friction heats the head to a temperature at which the chemicals react and generate more heat than can escape into the air, and they burn with a flame. If a wind blows away the heat or the chemicals are moist and friction does not raise the temperature sufficiently, the match goes out. Properly ignited, the heat from the flame raises the temperature of a nearby layer of the matchstick and of oxygen in the air adjacent to it, and the wood and oxygen react in a combustion reaction. When equilibrium between the total heat energies of the reactants and the total heat energies of the products (including the actual heat and light emitted) is reached, combustion stops. Flames have a definable composition and a complex structure; they are said to be multiform and are capable of existing at quite low temperatures, as well as at extremely high temperatures. The emission of light in the flame results from the presence of excited particles and, usually, of charged atoms and molecules and of electrons.

Combustion encompasses a great variety of phenomena with wide application in industry, the sciences, professions, and the home, and the application is based on knowledge of physics, chemistry, and mechanics; their interrelationship becomes particularly evident in treating flame propagation.

In general terms, combustion is one of the most important of chemical reactions and may be considered a culminating step in the oxidation of certain kinds of substances. Though oxidation was once considered to be simply the combination of oxygen with any compound or element, the meaning of the word has been expanded to include any reaction in which atoms lose electrons, thereby becoming oxidized. As has been pointed out, in any oxidation process the oxidizer takes electrons from the oxidizable substance, thereby itself becoming reduced (gaining electrons). Any substance at all can be an oxidizing agent. But these definitions, clear enough when applied to atomic structure to explain chemical reactions, are not as clearly applicable to combustion, which remains, generally speaking, a type of chemical reaction involving oxygen as the oxidizing agent but complicated by the fact that the process includes other kinds of reactions as well and by the fact that it proceeds at an unusually fast pace. Furthermore, most flames have a section in their structure in which, instead of oxidations, reduction reactions occur. Nevertheless, the main event in combustion is often the combining of combustible material with oxygen.


Combustion is a chemical reaction that occurs between a fuel and an oxidizing agent that produces energy, usually in the form of heat and light. Combustion is considered an exergonic or exothermic chemical reaction. It is also known as burning. Combustion is considered to be one of the first chemical reactions intentionally controlled by humans.

The reason combustion releases heat is because the double bond between oxygen atoms in O2 is weaker than the single bonds or other double bonds. So, although energy is absorbed in the reaction, it is released when the stronger bonds are formed to make carbon dioxide (CO2) and water (H2O). While the fuel plays a role in the energy of the reaction, it's minor in comparison because the chemical bonds in the fuel are comparable to the energy of the bonds in the products.

Mechanics

Combustion occurs when fuel and an oxidant react to form oxidized products. Typically, energy must be supplied to initiate the reaction. Once combustion starts, the released heat can make combustion self-sustaining.

For example, consider a wood fire. Wood in the presence of oxygen in the air does not undergo spontaneous combustion. Energy must be supplied, as from a lit match or exposure to heat. When the activation energy for the reaction is available, the cellulose (a carbohydrate) in wood reacts with oxygen in the air to produce heat, light, smoke, ash, carbon dioxide, water, and other gases. The heat from the fire allows the reaction to proceed until the fire becomes too cool or the fuel or oxygen is exhausted.

Example Reactions

A simple example of a combustion reaction is the reaction between hydrogen gas and oxygen gas to produce water vapor:

2H2(g) + O2(g) → 2H2O(g)

A more familiar type of combustion reaction is the combustion of methane (a hydrocarbon) to produce carbon dioxide and water:

CH4 + 2O2 → CO2 + 2H2O

which leads to one general form of a combustion reaction:

hydrocarbon + oxygen → carbon dioxide and water.

Oxidants

The oxidation reaction may be thought of in terms of electron transfer rather than the element oxygen. Chemists recognize several fuels capable of acting as oxidants for combustion. These include pure oxygen and also chlorine, fluorine, nitrous oxide, nitric acid, and chlorine trifluoride. For example, hydrogen gas burns, releasing heat and light, when reacted with chlorine to produce hydrogen chloride.

Catalysis

Combustion isn't usually a catalyzed reaction, but platinum or vanadium can act as catalysts.

Complete Versus Incomplete Combustion

Combustion is said to be "complete" when the reaction produces a minimal number of products. For example, if methane reacts with oxygen and produces only carbon dioxide and water, the process is complete combustion.

Incomplete combustion occurs when there is insufficient oxygen for the fuel to convert completely to carbon dioxide and water. Incomplete oxidation of a fuel may also occur. It also results when pyrolysis occurs before combustion, as is the case with most fuels. In pyrolysis, organic matter undergoes thermal decomposition at high temperatures without reacting with oxygen. Incomplete combustion may yield many additional products, including char, carbon monoxide, and acetaldehyde.

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