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#1426 2022-06-30 14:44:14

ganesh
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Registered: 2005-06-28
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Re: Miscellany

1399) Westminster Abbey

Summary

Westminster Abbey, formally titled the Collegiate Church of Saint Peter at Westminster, is a large, mainly Gothic abbey church in the City of Westminster, London, England, just to the west of the Palace of Westminster. It is one of the United Kingdom's most notable religious buildings and the traditional place of coronation and a burial site for English and, later, British monarchs. Since the coronation of William the Conqueror in 1066, all coronations of English and British monarchs have occurred in Westminster Abbey. Sixteen royal weddings have occurred at the Abbey since 1100.

According to a tradition first reported by Sulcard in about 1080, a church was founded at the site (then known as Thorn Ey (Thorn Island)) in the seventh century at the time of Mellitus, a Bishop of London. Construction of the present church began in 1245 on the orders of King Henry III.

The church was originally part of a Catholic Benedictine abbey, which was dissolved in 1539. It then served as the cathedral of the Diocese of Westminster until 1550, then as a second cathedral of the Diocese of London until 1556. The abbey was restored to the Benedictines by Mary I in 1556, then in 1559 made a royal peculiar—a church responsible directly to the sovereign—by Queen Elizabeth I.

The Abbey is the burial site of more than 3,300 people, usually of prominence in British history: at least 16 monarchs, eight prime ministers, poets laureate, actors, scientists, military leaders, and the Unknown Warrior—the first person interred in the Abbey's Poets' Corner was Geoffrey Chaucer in 1400. As such, Westminster Abbey is sometimes described as "Britain's Valhalla", after the iconic hall of the chosen heroes in Norse mythology.

Details

Westminster Abbey, London church is the site of coronations and other ceremonies of national significance. It stands just west of the Houses of Parliament in the Greater London borough of Westminster. Situated on the grounds of a former Benedictine monastery, it was refounded as the Collegiate Church of St. Peter in Westminster by Queen Elizabeth I in 1560. In 1987 Westminster Abbey, St. Margaret’s Church, and the Houses of Parliament were collectively designated a UNESCO World Heritage site.

Architectural history

Legend relates that Saberht, the first Christian king of the East Saxons, founded a church on a small island in the River Thames, then known as Thorney but later called the west minster (or monastery), and that this church was miraculously consecrated by St. Peter. It is certain that about 785 CE there was a small community of monks on the island and that the monastery was enlarged and remodeled by St. Dunstan of Canterbury about 960. St. Edward the Confessor built a new church on the site, which was consecrated on December 28, 1065. It was of considerable size and cruciform in plan. In 1245 Henry III pulled down the whole of Edward’s church (except the nave) and replaced it with the present abbey church in the pointed Gothic style of the period. The design and plan were strongly influenced by contemporary French cathedral architecture.

The rebuilding of the Norman-style nave was begun by the late 1300s under the architect Henry Yevele and continued intermittently until Tudor times. The Early English Gothic design of Henry III’s time predominates, however, giving the whole church the appearance of having been built at one time. The chapel of Henry VII (begun c. 1503), in Perpendicular Gothic style, replaced an earlier chapel and is famed for its exquisite fan vaulting. Above the original carved stalls hang the banners of the medieval Order of the Bath.

The western towers were the last addition to the building. They are sometimes said to have been designed by Sir Christopher Wren, but they were actually built by Nicholas Hawksmoor and John James and completed about 1745. The choir stalls in the body of the church date from 1847, and the high altar and reredos were remodeled by Sir George Gilbert Scott in 1867. Scott and J.L. Pearson also restored the north transept facade in the 1880s. The abbey was heavily damaged in the bombings that ravaged London in World War II, but it was restored soon after the war.

Coronations, weddings, and burials

Since William the Conqueror, every British sovereign has been crowned in the abbey except Edward V and Edward VIII, neither of whom was crowned. Additionally, Westminster Abbey has a long tradition of royal weddings, beginning with Henry I’s marriage to Matilda of Scotland in 1100. The only other reigning monarch to be wed in the abbey was Richard II, who married Anne of Bohemia in 1382. The abbey was the venue for the wedding of Prince William and Catherine Middleton in 2011.

Many kings and queens are buried near the shrine of Edward the Confessor or in Henry VII’s chapel. The last sovereign to be buried in the abbey was George II (died 1760); since then they have been buried at Windsor Castle. The abbey is crowded with the tombs and memorials of famous British subjects, such as Sir Isaac Newton, David Livingstone, and Ernest Rutherford. Part of the south transept is well known as Poets’ Corner and includes the tombs of Geoffrey Chaucer, Ben Jonson (who was buried upright), John Dryden, Robert Browning, and many others. The north transept has many memorials to British statesmen. The grave of the “Unknown Warrior,” whose remains were brought from Flanders (Belgium) in 1920, is in the centre of the nave near the west door.

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It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

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

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#1427 2022-07-01 14:30:11

ganesh
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Registered: 2005-06-28
Posts: 38,059

Re: Miscellany

1400) Tool

Summary

A tool is an object that can extend an individual's ability to modify features of the surrounding environment. Although many animals use simple tools, only human beings, whose use of stone tools dates back hundreds of millennia, have been observed using tools to make other tools. Early tools, made of such materials as stone, bone, and wood, were used for preparation of food, hunting, manufacture of weapons, and working of materials to produce clothing and useful artifacts. The development of metalworking made additional types of tools possible. Harnessing energy sources such as animal power, wind, or steam, allowed increasingly complex tools to produce an even larger range of items, with the Industrial Revolution marking a marked inflection point in the use of tools. The introduction of automation allowed tools to operate with minimal human supervision, further increasing the productivity of human labor.

Details

A tool is an instrument for making material changes on other objects, as by cutting, shearing, striking, rubbing, grinding, squeezing, measuring, or other processes. A hand tool is a small manual instrument traditionally operated by the muscular strength of the user, and a machine tool is a power-driven mechanism used to cut, shape, or form materials such as wood and metal. Tools are the primary means by which human beings control and manipulate their physical environment.

A brief treatment of tools follows.

The oldest known tools—consisting of primitive hammers, anvils, and cutting tools—were discovered in 2011 and 2012 at the Lomekwi 3 site located in a dry riverbed near Kenya’s Lake Turkana. Found in a layer of rock dating back approximately 3.3 million years, during the middle of the Pliocene Epoch (5.3 million to 2.6 million years ago), the tools predate the emergence of the oldest confirmed specimens of Homo by almost 1 million years. Paleontologists speculate that, barring the discovery of an as-yet-undiscovered species of Homo, the tools were likely constructed by members of Australopithecus or Kenyanthropus, who inhabited the region at that time.

The next oldest tools, found in Ethiopian rocks dating to approximately 2.6 million years ago—the traditional start of the Paleolithic Period, or Old Stone Age—are thought to have been made by H. habilis. That collection was made up of variously sized examples of the pebble tool, or chopper. The chopper typically consisted of a water-worn fist-sized rock, which had been chipped away at one end to create a roughly serrated edge. It was used for cutting through the skin and sinews of animals captured during hunting. The chopper was used by humanity for almost two million years, until the appearance of the hand axe, a superior version of the chopper. In that tool the entire surface of the rock was worked. Because both faces were chipped, the edge of the hand axe was considerably sharper than that of the earlier chopper.


Between 300,000 and 200,000 years ago, Neanderthals evolved. Excellent toolmakers, the Neanderthals used many different types of hand axes, as well as the first borers, knives, and spears. The heavily serrated blades were sawlike, allowing them to be used for carving and cutting horn, bone, and wood.

Cro-Magnons, the first modern humans, appeared between 45,000 and 30,000 years ago and brought into existence new types of tools. Chief among those were the burin, or graver, this being a strong, narrow-bladed flint able to scrape narrow incisions into bone, which made possible the manufacture of needles, hooks, and projectiles. The most-significant later innovation of the period was hafting, or the fitting of a handle to a tool. Knives without handles are merely awkward, but axes or hammers without them are almost impossible to use effectively.

The Neolithic Period (New Stone Age) occurred at different times around the world but is generally thought to have begun sometime between 10,000 and 8,000 BCE, when the first ground and polished tools were made and plant and animal domestication commenced. Grinding stone tools makes them stronger and gives them an even cutting edge; the growth of ground tools enabled Neolithic axe-wielders to clear forests for agriculture, fuel, and shelter. Three thousand years later, however, the stone axes of the Neolithic Period began to give way to the first tools made from metal, usually beaten copper. Centuries later, people learned how to smelt copper and, much afterward, iron, and the use of metal tools spread throughout the world. For the first time, tools with designs approximating current usage were made, largely because the relative ease of ironworking made it possible for individuals to have specialized tools for particular tasks.

Modern hand tools were developed in the period after 1500 BCE. They are now generally considered in the following classes: percussive tools, which deliver blows (the axe, adz, and hammer); cutting, drilling, and abrading tools (the knife, awl, drill, saw, file, chisel, and plane); the screw-based tools (screwdrivers and wrenches); measuring tools (ruler, plumb line, level, square, compass, and chalk line); and accessory tools (the workbench, vise, tongs, and pliers).

With the invention of the steam engine in the 18th century, humankind discovered how to drive tools mechanically. In particular, machine-driven tools became necessary to manufacture the parts for the machines that now made goods formerly produced by hand. Most common machine tools were designed by the middle of the 19th century. Today, scores of different machine tools are used in the workshops of home and industry. Those are frequently classified into seven types: turning machines; shapers and planers; power drills; milling machines; grinding machines; power saws; and presses.

The most fundamental of all seven is the horizontal metal-turning machine called the lathe, which is employed in a vast number of turning, facing, and drilling operations.

Shapers and planers use single-point tools to machine flat surfaces. Shapers move the cutting tool back and forth over the material, peeling away the surface, whereas planers have stationary tools, and the surface is moved to encounter them. Power drills are usually known as drill presses and have a twist drill that cuts holes in metal and other substances. They can also be used for many of the countersinking, boring, tapping, and other purposes for which lathes are frequently used.

Milling machines have rotating cutting surfaces that abrade substances with which they come into contact. In standard milling machines, a sliding table with a workpiece on top is pushed against the whirling cutter. Grinding machines function in a similar manner, except that the cutter is replaced by a spinning abrasive disk called a grinding wheel or by a belt. The most accurate of all machining processes, grinding can create metal surfaces within 0.0001 inch (0.0025 cm) of the desired dimension.

Power saws frequently consist of long thin moving belts or chains lined with teeth, as in band saws or chain saws. Presses are used to ram material against a hard surface; the surface often consists of a die, and the action of the press is to stamp out metal or plastic beaten into the shape of the die.

Some materials and metal alloys are too hard or too brittle to be machined by conventional tools; for those materials, several nonconventional methods have been devised. In electron- or ion-beam machining, a stream of highly energized electrons or ions is directed against the workpiece. In electrical-discharge and electrochemical machining, an electrical charge passing through a liquid medium across a tiny gap dissolves material from the workpiece. In ultrasonic machining a vibrating tool causes a liquid abrasive medium to remove material. Other nonconventional methods are laser, plasma-arc, chemical, photochemical, and water-jet machining.

Automatic machine tools can produce parts repetitively without operator assistance. Computer numerical control creates fully automatic machine-tool systems by feeding the machines instructions that have been reduced to digital or numerical values.

powertools-500x500.jpg


It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

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

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#1428 2022-07-02 14:34:23

ganesh
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Registered: 2005-06-28
Posts: 38,059

Re: Miscellany

1401) Diaphragm (acoustics)

Summary

In the field of acoustics, a diaphragm is a transducer intended to inter-convert mechanical vibrations to sounds, or vice versa. It is commonly constructed of a thin membrane or sheet of various materials, suspended at its edges. The varying air pressure of sound waves imparts mechanical vibrations to the diaphragm which can then be converted to some other type of signal; examples of this type of diaphragm are found in microphones and the human eardrum. Conversely a diaphragm vibrated by a source of energy beats against the air, creating sound waves. Examples of this type of diaphragm are loudspeaker cones and earphone diaphragms and are found in air horns.

Details

In the field of acoustics, a diaphragm is a transducer intended to inter-convert mechanical vibrations to sounds, or vice versa. It is commonly constructed of a thin membrane or sheet of various materials, suspended at its edges. The varying air pressure of sound waves imparts mechanical vibrations to the diaphragm which can then be converted to some other type of signal; examples of this type of diaphragm are found in microphones and the human eardrum. Conversely a diaphragm vibrated by a source of energy beats against the air, creating sound waves. Examples of this type of diaphragm are loudspeaker cones and earphone diaphragms and are found in air horns.

Loudspeaker

In a dynamic loudspeaker, a diaphragm is the thin, semi-rigid membrane attached to the voice coil, which moves in a magnetic gap, vibrating the diaphragm, and producing sound. It can also be called a cone, though not all speaker diaphragms are cone-shaped. Diaphragms are also found in headphones.

Quality midrange and bass drivers are usually made from paper, paper composites and laminates, plastic materials such as polypropylene, or mineral/fiber filled polypropylene. Such materials have very high strength/weight ratios (paper being even higher than metals) and tend to be relatively immune from flexing during large excursions. This allows the driver to react quickly during transitions in music (i.e. fast changing transient impulses) and minimizes acoustical output distortion.

If properly designed in terms of mass, stiffness, and damping, paper woofer/midrange cones can outperform many exotic drivers made from more expensive materials. Other materials used for diaphragms include polypropylene (PP), polyetheretherketone (PEEK) polycarbonate (PC), Mylar (PET), silk, glassfibre, carbon fibre, titanium, aluminium, aluminium-magnesium alloy, nickel, and beryllium. A 12-inch-diameter (300 mm) paper woofer with a peak-to-peak excursion of 0.5 inches at 60 Hz undergoes a maximum acceleration of 92 "g"s.

Paper-based cones account for approximately 85% of the cones sold worldwide. The ability of paper (cellulose) to be easily modified by chemical or mechanical means gives it a practical processing advantage not found in other common cone materials.

The purpose of the cone/surround assembly is to accurately reproduce the voice coil signal waveform. Inaccurate reproduction of the voice coil signal results in acoustical distortion. The ideal for a cone/surround assembly is an extended range of linearity or "pistonic" motion characterized by i) minimal acoustical breakup of the cone material, ii) minimal standing wave patterns in the cone, and iii) linearity of the surrounds force-deflection curve. The cone stiffness/damping plus the surround's linearity/damping play a crucial role in accuracy of the reproduced voice coil signal waveform. This is the crux of high-fidelity stereo.

The surround may be resin-treated cloth, resin-treated non-wovens, polymeric foams, or thermoplastic elastomers over-molded onto the cone body. An ideal surround has a linear force-deflection curve with sufficient damping to fully absorb vibrational transmissions from the cone/surround interface, and the "toughness" to withstand long-term vibration-induced fatigue. Sometimes the conical part and the outer surround are molded in one step and are one piece as commonly used for a Guitar speaker.

Other types of speakers (such as electrostatic loudspeakers) may use a thin membrane instead of a cone.

Microphone

Microphones can be thought of as speakers in reverse. The sound waves strike the thin diaphragm, causing it to vibrate. Microphone diaphragms, unlike speaker diaphragms, tend to be thin and flexible, since they need to absorb as much sound as possible. In a condenser microphone, the diaphragm is placed in front of a plate and is charged. In a dynamic microphone, the diaphragm is glued to a magnetic coil, similar to the one in a dynamic loudspeaker. (In fact, a dynamic speaker can be used as a rudimentary microphone, and vice versa.)

The diaphragm in a microphone works similarly to the human eardrum.

Other uses

In a phonograph reproducer, the diaphragm is a flat disk of typically mica or isinglass that converts the mechanical vibration imparted on the buttress from the recorded groove into sound. In the case of acoustic recording the reproducer converts the sound into the motion of the needle that scribes the groove on the recording media.

Speaker-structure-The-vibration-of-diaphragm-generates-acoustic-signals-Fig-19-depicts.png


It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

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

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#1429 2022-07-03 13:59:46

ganesh
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Registered: 2005-06-28
Posts: 38,059

Re: Miscellany

1402) Vestibular system

Summary

The vestibular system, in vertebrates, is a sensory system that creates the sense of balance and spatial orientation for the purpose of coordinating movement with balance. Together with the cochlea, a part of the auditory system, it constitutes the labyrinth of the inner ear in most mammals.

As movements consist of rotations and translations, the vestibular system comprises two components: the semicircular canals, which indicate rotational movements; and the otoliths, which indicate linear accelerations. The vestibular system sends signals primarily to the neural structures that control eye movement; these provide the anatomical basis of the vestibulo-ocular reflex, which is required for clear vision. Signals are also sent to the muscles that keep an animal upright and in general control posture; these provide the anatomical means required to enable an animal to maintain its desired position in space.

The brain uses information from the vestibular system in the head and from proprioception throughout the body to enable the animal to understand its body's dynamics and kinematics (including its position and acceleration) from moment to moment. How these two perceptive sources are integrated to provide the underlying structure of the sensorium is unknown.

Details

Vestibular system is an apparatus of the inner ear involved in balance. The vestibular system consists of two structures of the bony labyrinth of the inner ear, the vestibule and the semicircular canals, and the structures of the membranous labyrinth contained within them.

Vestibular structures

The two membranous sacs of the vestibule, the utricle and the saccule, are known as the otolith organs. Because they respond to gravitational forces, they are also called gravity receptors. Each sac has on its inner surface a single patch of sensory cells called a macula, which monitors the position of the head relative to the vertical. Each macula consists of neuroepithelium, which is made up of supporting cells and sensory cells, as well as a basement membrane, nerve fibres, nerve endings, and underlying connective tissue. The sensory cells are called hair cells because of the hairlike cilia—stiff nonmotile stereocilia and flexible motile kinocilia—that project from their apical ends. The nerve fibres are from the superior, or vestibular, division of the vestibulocochlear nerve.

Each of the hair cells of the vestibular organs is topped by a hair bundle, which consists of about 100 fine nonmotile stereocilia of graded lengths and a single motile kinocilium. The single kinocilium, which is larger and longer than the stereocilia, rises from a noncuticular area of the cell membrane at one side of the cuticular plate. The longest stereocilia are those closest to the kinocilium. Minute filamentous strands link the tips and shafts of neighbouring stereocilia to one another. When the hair bundles are deflected—e.g., because of a tilt of the head—the hair cells are stimulated to alter the rate of the nerve impulses that they are constantly sending via the vestibular nerve fibres to the brainstem. Covering the entire macula is a delicate acellular structure, the otolithic, or statolithic, membrane. This membrane is sometimes described as gelatinous, although it has a fibrillar pattern. The surface of the membrane is covered by a blanket of rhombohedral crystals, referred to as otoconia or statoconia, which consist of calcium carbonate in the form of calcite. These crystalline particles, which range in length from 1 to 20 m (1 m = 0.000039 inch), are much denser than the membrane and thus add considerable mass to it.

Semicircular canals

The three semicircular canals of the bony labyrinth are designated according to their position: superior, horizontal, and posterior. The superior and posterior canals are in diagonal vertical planes that intersect at right angles. Each canal has an expanded end, the ampulla, which opens into the vestibule. The ampullae of the horizontal and superior canals lie close together, just above the oval window, but the ampulla of the posterior canal opens on the opposite side of the vestibule. The other ends of the superior and posterior canals join to form a common stem, or crus, which also opens into the vestibule. One end of the horizontal canal opens into the vestibule. Thus, the vestibule completes the circle for each of the semicircular canals.

Each membranous ampulla contains a saddle-shaped ridge of tissue called the crista, the sensory end organ that extends across it from side to side. The crista is covered by neuroepithelium, with hair cells and supporting cells. From this ridge rises a gelatinous structure, the cupula, which divides the interior of the ampulla into two approximately equal parts. The hair cells of the cristae have hair bundles projecting from their apices. The kinocilium and the longest stereocilia extend far up into the substance of the cupula, occupying fine parallel channels. Thus, the cupula is attached at its base to the crista but is free to incline toward or away from the utricle. The tufts of cilia move with the cupula and, depending on the direction of their bending, cause an increase or a decrease in the rate of nerve impulse discharges carried by the vestibular nerve fibres to the brainstem.

Vestibular-System-Diagram.png


It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

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

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#1430 2022-07-04 14:13:51

ganesh
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Registered: 2005-06-28
Posts: 38,059

Re: Miscellany

1403) Breadfruit

Summary

Breadfruit (Artocarpus altilis) is a species of flowering tree in the mulberry and jackfruit family (Moraceae) believed to be a domesticated descendant of Artocarpus camansi originating in New Guinea, the Maluku Islands, and the Philippines. It was initially spread to Oceania via the Austronesian expansion. It was further spread to other tropical regions of the world during the Colonial Era. British and French navigators introduced a few Polynesian seedless varieties to Caribbean islands during the late 18th century. Today it is grown in some 90 countries throughout South and Southeast Asia, the Pacific Ocean, the Caribbean, Central America and Africa. Its name is derived from the texture of the moderately ripe fruit when cooked, similar to freshly baked bread and having a potato-like flavor.

The trees have been widely planted in tropical regions, including lowland Central America, northern South America, and the Caribbean. In addition to the fruit serving as a staple food in many cultures, the light, sturdy timber of breadfruit has been used for outriggers, ships, and houses in the tropics.

Breadfruit is closely related to Artocarpus camansi (breadnut or seeded breadfruit) of New Guinea, the Maluku Islands, and the Philippines, Artocarpus blancoi (tipolo or antipolo) of the Philippines, and Artocarpus mariannensis (dugdug) of Micronesia, all of which are sometimes also referred to as "breadfruit". It is also closely related to the jackfruit.

Details

Breadfruit (Artocarpus altilis), is the tree of the mulberry family (Moraceae) and its large fruits that are a staple food of the South Pacific and other tropical areas. Breadfruit contains considerable amounts of starch and is seldom eaten raw. It may be roasted, baked, boiled, fried, or dried and ground into flour. In the South Seas, cloth is made from the fibrous inner bark, the wood is used for canoes and furniture, and glue and caulking material are obtained from the milky juice.

African breadfruit (Treculia africana), native to tropical Africa, is a related species that is less important as a food crop.

Physical description

The breadfruit tree grows 12 to 18 metres (40 to 60 feet) high and has large, oval, glossy green leaves, three- to nine-lobed toward the apex. Male and female flowers are borne in separate groups on the same tree: the staminate (male) flowers appear in dense club-shaped catkins; the numerous female, or pistillate, flowers are grouped and form a large prickly head upon a spongy receptacle. The ripe fruits, or matured ovaries, of these pistillate flowers are roundish, 10 to 20 centimetres (4 to 8 inches) in diameter, and greenish to brownish green and have a white, somewhat fibrous pulp.

History and cultivation

The breadfruit has been cultivated in the Malay Archipelago (where the species is held to be indigenous) since remote antiquity. From this region it spread throughout the tropical South Pacific region in prehistoric times. Its introduction into the New World was connected with the memorable voyage of Capt. William Bligh in HMS Bounty, a voyage recommended by Capt. James Cook, who had seen the breadfruit in the Pacific islands and considered that it would prove highly useful as a foodstuff for slaves in the West Indies. After the failure of Bligh’s first voyage, a second resulted in the successful establishment of the tree in Jamaica, where it failed to live up to expectations because the slaves preferred plantain bananas.

Numerous varieties are cultivated in the Pacific islands, but many of these have not been introduced to tropical America. The tree cannot tolerate frost and has not been successfully grown even in the southernmost parts of Florida. In the West Indies and on the American mainland from Mexico to Brazil, the breadfruit tree is grown in dooryards, and the fruit is sold at market. Seedless forms are propagated by means of root suckers or root cuttings.

Researcher-There-is-enormous-potential-for-breadfruit-in-the-protein-sector.jpg


It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

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

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#1431 2022-07-05 14:40:40

ganesh
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Posts: 38,059

Re: Miscellany

1404) Watermelon

Summary

Watermelon (Citrullus lanatus) is a flowering plant species of the Cucurbitaceae family and the name of its edible fruit. A scrambling and trailing vine-like plant, it is a highly cultivated fruit worldwide, with more than 1,000 varieties.

Watermelon is grown in favorable climates from tropical to temperate regions worldwide for its large edible fruit, which is a berry with a hard rind and no internal divisions, and is botanically called a pepo. The sweet, juicy flesh is usually deep red to pink, with many black seeds, although seedless varieties exist. The fruit can be eaten raw or pickled, and the rind is edible after cooking. It may also be consumed as a juice or as an ingredient in mixed beverages.

Kordofan melons from Sudan are the closest relatives and may be progenitors of modern, cultivated watermelons. Wild watermelon seeds were found in Uan Muhuggiag, a prehistoric site in Libya that dates to approximately 3500 BC. Watermelons were domesticated in Egypt by 2000 BC, although they were not the sweet modern variety. Sweet dessert watermelons spread across the Mediterranean world during Roman times.

Considerable breeding effort has developed disease-resistant varieties. Many cultivars are available that produce mature fruit within 100 days of planting. In 2017, China produced about two-thirds of the world total of watermelons.

Details

Watermelon: Health benefits, risks & nutrition facts

Watermelon (Citrullus lanatus) is a deliciously healthy fruit, soaked with nutrients, low in calories and is free of fat. When eaten in reasonable amounts watermelon is good for you and provides many health benefits. You can eat all parts of the watermelon including the rind and seeds, according to health website Healthline(opens in new tab).

A watermelon is approximately 92% water according to Healthline. Each juicy bite has significant levels of vitamin A(opens in new tab), vitamin B6(opens in new tab) and vitamin C(opens in new tab), lots of lycopene, antioxida(opens in new tab)nts and amino acids(opens in new tab). Watermelon even contains a modest amount of potassium(opens in new tab).

"Foods that are high in antioxidants and amino acids allow your body to function optimally," said Angela Lemond, a Texas-based registered dietitian, nutritionist and spokesperson for the Academy of Nutrition and Dietetics(opens in new tab). "Amino acids are the basic building block for protein, and protein is used in virtually every vital function in the body."

WATERMELON HEALTH BENEFITS

Watermelon contains some of the highest lycopene levels of any type of fresh fruit. Lycopene is a phytonutrient, which is a naturally occurring compound in fruits and vegetables that works with the human body to trigger healthy reactions. It is also the red pigment that gives watermelons, tomatoes, red grapefruits and guavas their color.  According to the U.S. Department of Agriculture, a cup and a half of watermelon contains about 9 to 13 milligrams of lycopene — 40% more lycopene than raw tomatoes.

WATERMELON NUTRITIONAL INFORMATION

Here are the nutrition facts for the watermelon, according to the U.S. Food and Drug Administration(opens in new tab), which regulates food labeling through the National Labeling and Education Act:

– Serving size: 2 cups diced (10 oz / 280 g) Calories: 80 (Calories from Fat 0)

– Amount per serving (and %DV*) *Percent Daily Values (%DV) are based on a 2,000 calorie diet.

– Total Fat: 0g (0%)

– Total Carbohydrate: 21g (7%) Dietary Fiber: 1g (4%) Sugars: 20g

– Cholesterol: 0mg (0%) Sodium: 0mg (0%) Potassium: 270mg (8%) Protein: 1g

– Vitamin A: (30%) Vitamin C: (25%) Calcium: (2%) Iron: (4%)

Lycopene has been linked with heart health, bone health and prostate cancer prevention. It's also a powerful antioxidant thought to have anti-inflammatory properties, according to Victoria Jarzabkowski, a nutritionist with the Fitness Institute of Texas at The University of Texas at Austin.

To really maximize your lycopene intake, you need to let your watermelon fully ripen. The redder your watermelon gets, the higher the concentration of lycopene becomes. Beta-carotene and phenolic antioxidant content also increase as the watermelon ripens. "Beta carotene is an antioxidant found in red-orange fruits and vegetables. It helps with immunity, skin, eye and the prevention of cancer," said Lemond.

A 2011 study in the Journal of Food Composition and Analysis, which investigated five types of watermelon at four stages of ripening, found that unripe watermelon with primarily white flesh has nearly zero beta-carotene present. By the time it is fully red, the fruit is an excellent source of the phytonutrient.

However, that doesn't mean the red parts are the only good ones. "All parts of the watermelon are good. There are a lot of nutrients throughout," said Jarzabkowski. This includes the white flesh nearest the rind, which contains more of the amino acid citrulline than the flesh, according to a 2005 study in the Journal of Chromatography(opens in new tab).

Citrulline is a valuable amino acid that converts to the amino acid arginine. These amino acids promote blood flow, which leads to cardiovascular health, improved circulation, and even treatment for erectile dysfunction, according to research at Texas A&M University.

Recent studies have also found that watermelon seeds are also wonderfully nutritious, especially if they are sprouted and shelled. They are high in protein(opens in new tab), magnesium, vitamin B and good fats, according to an analysis by the International Journal of Nutrition and Food Sciences.

HEART HEALTH AND ANTI-INFLAMMATORY BENEFITS

Watermelon can help lower the risk of heart disease.

The high levels of lycopene in watermelon are very effective at protecting cells from damage and may help lower the risk of heart disease, according to a study at Purdue University(opens in new tab). A study published in the American Journal of Hypertension found that watermelon extracts helped reduce hypertension and lowered blood pressure in obese adults.

Watermelon may also be especially important for older women. A study published in Menopause found that postmenopausal women, a group known to have increased aortic stiffness, who took watermelon extract for six weeks saw decreased blood pressure and arterial stiffness compared to those who did not take watermelon extract. The authors of the study attributed the benefits to citrulline and arginine.

Arginine can help improve blood flow and may help reduce the accumulation of excess fat.

"The lycopene in watermelon makes it an anti-inflammatory fruit," Jarzabkowski said. Lycopene is an inhibitor for various inflammatory processes and also works as an antioxidant to neutralize free radicals. Additionally, the watermelon contains choline, which helps keep chronic inflammation down, according to a 2006 article published in Shock(opens in new tab) medical journal.

Reducing inflammation isn't just good for people suffering from arthritis. "When you're sick, you have cellular damage, which can be caused by a variety of factors including stress, smoking, pollution, disease, and your body becomes inflamed," Jarzabkowski said. "It's called 'systemic inflammation.'" In this way, anti-inflammatory foods can help with overall immunity and general health.

OTHER BENEFITS AND CANCER PREVENTION

"Watermelons help with overall hydration, and that is a great thing," said Lemond. "They say we can get 20-30 percent of our fluid needs through our diet alone, and foods like these certainly help." Additionally, their juice is full of good electrolytes. This can even help prevent heat stroke. 

The watermelon also contains fiber, which encourages a healthy digestive tract and helps keep you regular. 

Vitamin A is also great for your skin, and just a cup of watermelon contains nearly one-quarter of your recommended daily intake. Vitamin A helps keep skin and hair moisturized, and it also encourages healthy growth of new collagen and elastin cells, according to the Cleveland Clinic. Vitamin C is also beneficial in this regard, as it promotes healthy collagen growth.

Like other fruits and vegetables, watermelons may be helpful in reducing the risk of cancer through their antioxidant properties. Lycopene in particular has been linked to reducing prostate cancer cell proliferation, according to the National Cancer Institute.

Watermelon-loving athletes are in luck: drinking watermelon juice before an intense workout helps reduce next-day muscle soreness and heart rate, according to a 2013 study published in the Journal of Agricultural and Food Chemistry. This can be attributed to watermelon's amino acids citrulline and arginine, which help improve circulation.

A 2015 study published in the Journal of Applied Physiology suggests that watermelon's citrulline may also help improve athletic performance. Study participants who took citrulline supplements saw a boosted performance with more power production in high-intensity exercise like cycling and sprinting. 

WHAT HAPPENS IF YOU EAT TOO MUCH WATERMELON?

If eaten in reasonable amounts, watermelons should produce no serious side effects. If you eat an abundance of the fruit daily, however, you may experience problems from having too much lycopene or potassium.

The consumption of more than 30 mg of lycopene daily could potentially cause nausea, diarrhea, indigestion and bloating, according to the American Cancer Society.

People with serious hyperkalemia, or too much potassium in their blood, should probably not consume more than about one cup of watermelon a day, which has less than 140 mg of potassium. According to the National Institutes of Health, hyperkalemia can result in irregular heartbeats and other cardiovascular problems, as well as reduced muscle control.

Loading up on water-dense foods like watermelon can be tempting for those looking to lose weight because they help you feel full, but Lemond cautions against going to extremes. "Eating more fruits and vegetables of any kind naturally helps decrease overall calories (energy) of the diet," she said. "We know that people that eat higher quantities of fruits and vegetables typically have healthier body weights. However, I do not recommend eating only watermelon … You will lose weight, but that weight will be mostly muscle."

Jarzabkowski also warns watermelon lovers to be mindful of their sugar intake. "Though watermelon's sugar is naturally occurring, [watermelon] is still relatively high in sugar."

"My recommendation is always to vary your selections," said Lemond. "Watermelon is a great hydrating food, so keep it in along with other plant foods that offer other benefits. Variety is always key."

SEEDLESS WATERMELON

Seedless watermelons are triploid which means they have three sets of chromosomes. This odd number of chromosomes makes them sterile and unable to produce seeds. The sterile hybrid is created(opens in new tab) by crossing male pollen for a watermelon, containing 22 chromosomes per cell, with a female watermelon flower with 44 chromosomes per cell. When this seeded fruit matures, the small, white seed coats inside contain 33 chromosomes.

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It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

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

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#1432 2022-07-06 14:37:17

ganesh
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Re: Miscellany

1405) Custard apple

Summary

Custard apple, (genus Annona), is a genus of about 160 species of small trees or shrubs of the family Annonaceae, native to the New World tropics. Custard apples are of local importance as traditional medicines, and several species are commercially grown for their edible fruits.

Members of the genus are typically evergreen or semideciduous plants and cannot tolerate frost. The leaves can be leathery or hairy and are generally ovate with smooth margins. The unusual flowers feature six to eight fleshy curved petals in two whorls and numerous stamens and pistils. The fruits are often scaly and succulent and are sometimes segmented.

The fruit of the common custard apple (Annona reticulata), also called sugar apple or bullock’s-heart in the West Indies, is dark brown in colour and marked with depressions giving it a quilted appearance; its pulp is reddish yellow, sweetish, and very soft (hence the common name). Soursop, or guanabana (A. muricata), sweetsop (A. squamosa), and cherimoya (A. cherimola) are widely cultivated worldwide. Alligator apple, or corkwood (A. glabra), a native of South America and West Africa, is valued for its roots, which serve the same purposes as cork; the fruit is not usually eaten fresh but is sometimes used for making jellies.

Details

Custard apple is a common name for a fruit, and the tree which bears it, Annona reticulata.

The fruits vary in shape, heart-shaped, spherical, oblong or irregular. The size ranges from 7 to 12 cm (2.8 to 4.7 in), depending on the cultivar. When ripe, the fruit is brown or yellowish, with red highlights and a varying degree of reticulation, depending again on the variety. The flesh varies from juicy and very aromatic to hard with an astringent taste. The flavor is sweet and pleasant, akin to the taste of 'traditional' custard.

The custard apple is native to the Americas, but has been found on the island of Timor as early as 1000 CE.

Custard apple may also be the name of some similar fruits produced by related trees:

* Annonaceae, the soursop family.
** Asimina triloba, the "pawpaw", a deciduous tree, ranging from southern Ontario to Texas and Florida, that bears the largest edible fruit native to the United States or Canada.
**  Annona cherimola, a tree and fruit also called cherimoya
** Annona squamosa, a tree and fruit also called sugar apple or sweetsop
** Annona senegalensis, a tree and fruit called wild custard-apple
* Casimiroa edulis, in the rue or citrus family, Rutaceae.

custard-apple-500x500.jpg


It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

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

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#1433 2022-07-07 14:33:51

ganesh
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Re: Miscellany

1406) Cylinder

Summary

Cylinder, in geometry, is a surface of revolution that is traced by a straight line (the generatrix) that always moves parallel to itself or some fixed line or direction (the axis). The path, to be definite, is directed along a curve (the directrix), along which the line always glides. In a right circular cylinder, the directrix is a circle. The axis of this cylinder is a line through the centre of the circle, the line being perpendicular to the plane of the circle. In an oblique circular cylinder, the angle that the axis makes with the circle is other than 90°.

The directrix of a cylinder need not be a circle, and if the cylinder is right, planes parallel to the plane of the directrix that intersect the cylinder produce intersections that take the shape of the directrix. For such a plane, if the directrix is an ellipse, the intersection is an ellipse.

The generatrix of a cylinder is assumed to be infinite in length; the cylinder so generated, therefore, extends infinitely in both directions of its axis. A finite cylinder has a finite base, the surface enclosed by the directrix, and a finite length of generatrix, called an element.

Details

A cylinder has traditionally been a three-dimensional solid, one of the most basic of curvilinear geometric shapes. Geometrically, it can be considered as a prism with a circle as its base.

This traditional view is still used in elementary treatments of geometry, but the advanced mathematical viewpoint has shifted to the infinite curvilinear surface and this is how a cylinder is now defined in various modern branches of geometry and topology.

The shift in the basic meaning (solid versus surface) has created some ambiguity with terminology. It is generally hoped that context makes the meaning clear. Both points of view are typically presented and distinguished by referring to solid cylinders and cylindrical surfaces, but in the literature the unadorned term cylinder could refer to either of these or to an even more specialized object, the right circular cylinder.

Types

A cylindrical surface is a surface consisting of all the points on all the lines which are parallel to a given line and which pass through a fixed plane curve in a plane not parallel to the given line. Any line in this family of parallel lines is called an element of the cylindrical surface. From a kinematics point of view, given a plane curve, called the directrix, a cylindrical surface is that surface traced out by a line, called the generatrix, not in the plane of the directrix, moving parallel to itself and always passing through the directrix. Any particular position of the generatrix is an element of the cylindrical surface.

A solid bounded by a cylindrical surface and two parallel planes is called a (solid) cylinder. The line segments determined by an element of the cylindrical surface between the two parallel planes is called an element of the cylinder. All the elements of a cylinder have equal lengths. The region bounded by the cylindrical surface in either of the parallel planes is called a base of the cylinder. The two bases of a cylinder are congruent figures. If the elements of the cylinder are perpendicular to the planes containing the bases, the cylinder is a right cylinder, otherwise it is called an oblique cylinder. If the bases are disks (regions whose boundary is a circle) the cylinder is called a circular cylinder. In some elementary treatments, a cylinder always means a circular cylinder.

The height (or altitude) of a cylinder is the perpendicular distance between its bases.

The cylinder obtained by rotating a line segment about a fixed line that it is parallel to is a cylinder of revolution. A cylinder of revolution is a right circular cylinder. The height of a cylinder of revolution is the length of the generating line segment. The line that the segment is revolved about is called the axis of the cylinder and it passes through the centers of the two bases.

Right circular cylinders

The bare term cylinder often refers to a solid cylinder with circular ends perpendicular to the axis, that is, a right circular cylinder. The cylindrical surface without the ends is called an open cylinder. The formulae for the surface area and the volume of a right circular cylinder have been known from early antiquity.

A right circular cylinder can also be thought of as the solid of revolution generated by rotating a rectangle about one of its sides. These cylinders are used in an integration technique (the "disk method") for obtaining volumes of solids of revolution.

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It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

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#1434 2022-07-08 13:51:36

ganesh
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Re: Miscellany

1407) Melon

Summary

A melon is any of various plants of the family Cucurbitaceae with sweet, edible, and fleshy fruit. The word "melon" can refer to either the plant or specifically to the fruit. Botanically, a melon is a kind of berry, specifically a "pepo". The word melon derives from Latin melopepo, which is the latinization of the Greek meaning "melon", itself a compound of (mēlon), "apple, treefruit (of any kind)" and πέπων (pepōn), amongst others "a kind of gourd or melon". Many different cultivars have been produced, particularly of cantaloupes.

Details

Melon, (Cucumis melo), is atrailing vine in the gourd family (Cucurbitaceae), grown for its often musky-scented edible fruit. The melon plant is native to central Asia, and its many cultivated varieties are widely grown in warm regions around the world. Most commercially important melons are sweet and eaten fresh, though some varieties can be made into preserves or pickled.

Melons are frost-tender annuals with soft hairy trailing stems and clasping tendrils. They bear large round to lobed leaves and yellow unisexual flowers about 2.5 cm (1 inch) across. Botanically, the fruits are a type of berry known as a pepo, and they vary greatly in size, shape, surface texture, and flesh colour and flavour, depending on the variety. They generally weigh 1–4 kg (2–9 pounds). Cantaloupes and netted melons are ripe when they give off a sweet fruity odour, at which time they “slip,” or break, readily at the union of fruit and stalk. Honeydews and casabas are ripe when they turn yellow, at which time they are cut from the vine. They are called the winter melons because they ripen late and mature slowly in storage for many weeks, becoming softer but not noticeably sweeter. Melon plants are susceptible to a number of diseases, including downy mildew, anthracnose, Fusarium wilt, and powdery mildew, though some varieties are more resistant than others.

Seven cultivar groups of melons are recognized:

* Reticulatus group, the netted, or nutmeg, melons, including the small muskmelons, having a net-ribbed rind and sweet orange flesh. The me* lons sold as “cantaloupes” in the United States are often the netted types of this group.
* Cantalupensis group, the true cantaloupes, which are characterized by a rough warty rind and sweet orange flesh. They are common in European markets and are named for Cantalupo, Italy, near Rome, where these melons were early grown from southwestern Asian stock.
* Inodorus group, the winter melons, which are large, smooth-skinned, mildly flavoured, and light green- to white-fleshed. They include the honeydew, casaba, and Persian melons.
* Flexuosus group, the snake or serpent melons, which grow up to 7 cm (3 inches) in diameter and about 1 metre (3 feet) in length. The flesh is slightly acidic and cucumber-like.
* Conomon group, the Asian pickling melons, which have greenish flesh and are neither musky nor sweet.
* Chito group, the mango melons, which are usually the size and shape of a lemon or orange and have whitish cucumber-like flesh.
* Dudaim group, sometimes called the stinking melons, which are characterized by orange-sized, highly fragrant, but inedible ornamental fruit.

Plants resembling true melons include the related watermelon (Citrullus lanatus) and Chinese watermelon, or wax gourd (Benincasa hispida), as well as the unrelated tree melon, or papaya (Carica papaya, family Caricaceae), and melon shrub, or pear melon (Solanum muricatum, family Solanaceae).

Melon-For-Skin-Melon-will-make-your-skin-glow.jpg


It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

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

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#1435 2022-07-09 14:14:32

ganesh
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Re: Miscellany

1408) Lime (fruit)

Summary

A lime (from French lime, from Arabic līma, from Persian līmū, "lemon") is a citrus fruit, which is typically round, green in color, 3–6 centimetres (1.2–2.4 in) in diameter, and contains acidic juice vesicles.

There are several species of citrus trees whose fruits are called limes, including the Key lime (Citrus aurantiifolia), Persian lime, Makrut lime, and desert lime. Limes are a rich source of vitamin C, are sour, and are often used to accent the flavours of foods and beverages. They are grown year-round. Plants with fruit called "limes" have diverse genetic origins; limes do not form a monophyletic group.

Details

Lime is any of several species and hybrids of trees and shrubs of the genus Citrus (family Rutaceae), widely grown in tropical and subtropical areas for their edible acidic fruits. The Persian lime (Citrus ×latifolia) is one of the most common commercial varieties, though the smaller key lime, or Mexican lime (C. ×aurantifolia), is also economically important in many places. The lime fruit is a key ingredient in certain pickles and chutneys, and lime juice is used to flavour drinks, foods, and confections. Limeade and other lime-flavoured drinks have a flavour and bouquet quite distinct from those made from lemons (Citrus ×limon). The juice of lime fruits may be concentrated, dried, frozen, or canned. Lime oil, from the peel of the fruit, is processed mainly in the West Indies. Citrate of lime and citric acid are also prepared from the fruit.

Physical description

The tree seldom grows more than 5 metres (16 feet) high and if not pruned becomes shrublike. Its branches spread and are irregular, with short stiff twigs, small leaves, and many small sharp thorns. The evergreen leaves are pale green, and the small white flowers are usually borne in clusters. The fruit is usually about 3 to 4 cm (1 to 1.5 inches) in diameter, oval to nearly globular in shape, often with a small apical nipple, and the peel is thin and greenish yellow when the fruit is ripe. The pulp is tender, juicy, yellowish green in colour, and decidedly acid. Most limes exceed lemons in both acid and sugar content. There are, however, some varieties so lacking in citric acid that they are known as sweet limes. These are grown to some extent in Egypt and certain tropical countries.

History

Wild limes probably originated in the Indonesian archipelago or the nearby mainland of Asia. Arabian traders may have taken limes, as well as lemons, from India to the eastern Mediterranean countries and Africa about 1000 CE. Limes were introduced to the western Mediterranean countries by returning Crusaders in the 12th and 13th centuries. Christopher Columbus took citrus seeds, probably including limes, to the West Indies on his second voyage in 1493, and the trees soon became widely distributed in the West Indies, Mexico, and Florida. Limes are grown to a limited extent in practically all citrus-growing areas. Limes contain vitamin C (ascorbic acid) and were formerly used in the British navy to prevent scurvy—hence the nickname “limey.”

Types

In addition to the common Persian and key limes, a number of other related plants are commonly known as limes and are used similarly. The fruit and leaves of the Thai lime, or makrut lime (C. hystrix), add distinctive flavour to the cuisines of Southeast Asia and are sometimes used in perfumery. Sweet lime (C. limetta), less tart than the Persian lime, is commonly cultivated in the Mediterranean region. The mandarin lime, also known as the Rangpur lime (C. ×limonia), is thought to be a lemon–mandarin orange hybrid and is commonly used to make marmalade. Finger limes (C. australasica), native to Australia, are a developing crop noted for their discrete juice vesicles, sometimes called “lime caviar.”

benefits-of-lime-607x405.jpg


It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

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

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#1436 2022-07-10 14:25:31

ganesh
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Re: Miscellany

1409. Paleolithic

Summary

The Paleolithic or Palaeolithic or Palæolithic, also called the Old Stone Age (from Greek palaios - old, lithos - stone), is a period in prehistory distinguished by the original development of stone tools that covers 99% of the period of human technological prehistory. It extends from the earliest known use of stone tools by hominins c. 3.3 million years ago, to the end of the Pleistocene c. 11,650 cal BP. (Before Present)

The Paleolithic Age in Europe preceded the Mesolithic Age, although the date of the transition varies geographically by several thousand years. During the Paleolithic Age, hominins grouped together in small societies such as bands and subsisted by gathering plants, fishing, and hunting or scavenging wild animals. The Paleolithic Age is characterized by the use of knapped stone tools, although at the time humans also used wood and bone tools. Other organic commodities were adapted for use as tools, including leather and vegetable fibers; however, due to rapid decomposition, these have not survived to any great degree.

About 50,000 years ago, a marked increase in the diversity of artifacts occurred. In Africa, bone artifacts and the first art appear in the archaeological record. The first evidence of human fishing is also noted, from artifacts in places such as Blombos cave in South Africa. Archaeologists classify artifacts of the last 50,000 years into many different categories, such as projectile points, engraving tools, knife blades, and drilling and piercing tools.

Humankind gradually evolved from early members of the genus Homo—such as Homo habilis, who used simple stone tools—into anatomically modern humans as well as behaviourally modern humans by the Upper Paleolithic. During the end of the Paleolithic Age, specifically the Middle or Upper Paleolithic Age, humans began to produce the earliest works of art and to engage in religious or spiritual behavior such as burial and ritual. Conditions during the Paleolithic Age went through a set of glacial and interglacial periods in which the climate periodically fluctuated between warm and cool temperatures. Archaeological and genetic data suggest that the source populations of Paleolithic humans survived in sparsely-wooded areas and dispersed through areas of high primary productivity while avoiding dense forest-cover.

By c. 50,000 – c. 40,000 BP, the first humans set foot in Australia. By c. 45,000 BP, humans lived at 61°N latitude in Europe. By c. 30,000 BP, Japan was reached, and by c. 27,000 BP humans were present in Siberia, above the Arctic Circle. At the end of the Upper Paleolithic Age a group of humans crossed Beringia and quickly expanded throughout the Americas.

Details

Paleolithic Period, also spelled Palaeolithic Period, also called Old Stone Age, ancient cultural stage, or level, of human development, characterized by the use of rudimentary chipped stone tools.

The onset of the Paleolithic Period has traditionally coincided with the first evidence of tool construction and use by Homo some 2.58 million years ago, near the beginning of the Pleistocene Epoch (about 2.58 million to 11,700 years ago). In 2015, however, researchers excavating a dry riverbed near Kenya’s Lake Turkana discovered primitive stone tools embedded in rocks dating to 3.3 million years ago—the middle of the Pliocene Epoch (some 5.3 million to 2.58 million years ago). Those tools predate the oldest confirmed specimens of Homo by almost 1 million years, which raises the possibility that toolmaking originated with Australopithecus or its contemporaries and that the timing of the onset of this cultural stage should be reevaluated.

The Paleolithic Period is often divided into three parts: Lower, Middle, and Upper. However, anthropologists resist placing hard time boundaries on each subdivision and the stages within them, because technologies characteristic of different industries emerged at different times in different regions. In addition, there is some level of overlap between stages and subdivisions because it took time for new technologies to spread, which created the circumstance in which some groups of people had access to higher levels of technology earlier than their contemporaries. The Lower Paleolithic is traditionally divided into the Oldowan Stage (about 2.6 million to 1 million years ago), which saw the development of pebble (chopping) tools, and the Acheulean Stage (1.7–1.5 million years ago to about 250,000–200,000 years ago), in which more sophisticated hand axes and cleaving tools emerged. With the discovery of the tools excavated at Lake Turkana, some anthropologists have suggested adding a third stage, the Lomekwian Stage, to account for 700,000 years of early hammering and other rock-chipping tools that predated the Oldowan Stage. The Middle Paleolithic, which was characterized by flake tools and the widespread use of fire, lasted from about 250,000 to 30,000 years ago. The Upper Paleolithic, which saw the emergence of more sophisticated tools, lasted from about 50,000–40,000 years ago until about 10,000 years ago.

Paleolithic toolmaking

At sites dating from the Lower Paleolithic Period, simple pebble tools have been found in association with the remains of what may have been some of the earliest human ancestors. A somewhat more-sophisticated Lower Paleolithic tradition, known as the Chopper chopping-tool industry, is widely distributed in the Eastern Hemisphere, and it is thought to have been the work of the hominin species named Homo erectus. It is believed that H. erectus probably made tools of wood and bone, although no such fossil tools have yet been found, as well as of stone.

About 700,000 years ago a new Lower Paleolithic tool, the hand ax, appeared. The earliest European hand axes are assigned to the Abbevillian industry, which developed in northern France in the valley of the Somme River; a later, more-refined hand-ax tradition is seen in the Acheulean industry, evidence of which has been found in Europe, Africa, the Middle East, and Asia. Some of the earliest known hand axes were found at Olduvai Gorge (Tanzania) in association with remains of H. erectus. Alongside the hand-ax tradition there developed a distinct and very different stone tool industry, based on flakes of stone: special tools were made from worked (carefully shaped) flakes of flint. In Europe the Clactonian industry is one example of a flake tradition. The early flake industries probably contributed to the development of the Middle Paleolithic flake tools of the Mousterian industry, which is associated with the remains of Neanderthals. Other items dating to the Middle Paleolithic are shell beads found in both North and South Africa. In Taforalt, Morocco, the beads were dated to approximately 82,000 years ago, and other, younger examples were encountered in Blombos Cave, Blombosfontein Nature Reserve, on the southern coast of South Africa. Experts determined that the patterns of wear seem to indicate that some of these shells were suspended, some were engraved, and examples from both sites were covered with red ochre.

The Upper Paleolithic Period was characterized by the emergence of regional stone tool industries, such as the Perigordian, Aurignacian, Solutrean, and Magdalenian of Europe as well as other localized industries of the Old World and the oldest known cultures of the New World. Principally associated with the fossil remains of such anatomically modern humans as Cro-Magnons, Upper Paleolithic industries exhibit greater complexity, specialization, and variety of tool types, such as those made of bone, ivory, and antlers, and the emergence of distinctive regional artistic traditions involving paintings and sculpture and musical instruments.

Paleolithic art

Two main forms of Paleolithic art are known to modern scholars: small sculptures; and monumental paintings, incised designs, and reliefs on the walls of caves. Such works were produced throughout the Mediterranean region and other scattered parts of Eurasia and Africa but survived in quantity only in eastern Europe and parts of Spain and France.

Small sculptured pieces evidently dominated the Upper Paleolithic artistic traditions of eastern Europe; typical were small, portable clay figurines and bone and ivory carvings. The works from this area include simple but realistic stone and clay animal figurines, as well as carved stone statuettes of women, referred to by scholars as Venus figures. These small stylized figures are characteristically rotund, emphasizing parts of the female body associated with sexuality and fertility; many are so abstract that only protuberant breasts and exaggerated hips are clearly distinguishable.

Monumental arts flourished in western Europe, the province of the so-called Franco-Cantabrian school, where limestone caves—such as those of Chauvet–Pont d’Arc and Lascaux Grotto—provided a sheltered surface for paintings, incised designs, and relief carvings. These caves have preserved much small carving of fine quality and an abundant and varied sample of prehistoric graphic art, from simple finger tracings in clay to sophisticated polychrome paintings, generally depicting animals, of dynamic naturalism and exquisite design.

The function or purpose of art in Paleolithic life remains a subject of debate. Some scholars see the human and animal representations as evidence of the use of magical rites to ensure success in hunting or to guarantee fertility. Others have suggested that Paleolithic artists’ accurate representations of animals’ coats may be an early attempt to produce a seasonal notation system. Another viewpoint, disregarding utility altogether, sees the art of Paleolithic peoples solely as an outgrowth of a basic human need to creatively record and reproduce aspects of the surrounding world.

Among the bone and ivory carvings dating to the Paleolithic are several examples of partial bone or ivory flutes, including one with five finger holes, found at Hohle Fels Cave, near Ulm, Germany, and dated to about 35,000 years ago. Those flutes give evidence of yet another art form practiced in prehistoric cultures.

Paleolithic_Age_Tools_fbc947b5a0.jpg


It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

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

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#1437 2022-07-11 14:02:39

ganesh
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Re: Miscellany

1410) Mesolithic

Summary

The Mesolithic is the Old World archaeological period between the Upper Paleolithic and the Neolithic. The term Epipaleolithic is often used synonymously, especially for outside northern Europe, and for the corresponding period in the Levant and Caucasus. The Mesolithic has different time spans in different parts of Eurasia. It refers to the final period of hunter-gatherer cultures in Europe and Western Asia, between the end of the Last Glacial Maximum and the Neolithic Revolution. In Europe it spans roughly 15,000 to 5,000 BP; in Southwest Asia (the Epipalaeolithic Near East) roughly 20,000 to 10,000 BP. The term is less used of areas farther east, and not at all beyond Eurasia and North Africa.

The type of culture associated with the Mesolithic varies between areas, but it is associated with a decline in the group hunting of large animals in favour of a broader hunter-gatherer way of life, and the development of more sophisticated and typically smaller lithic tools and weapons than the heavy-chipped equivalents typical of the Paleolithic. Depending on the region, some use of pottery and textiles may be found in sites allocated to the Mesolithic, but generally indications of agriculture are taken as marking transition into the Neolithic. The more permanent settlements tend to be close to the sea or inland waters offering a good supply of food. Mesolithic societies are not seen as very complex, and burials are fairly simple; in contrast, grandiose burial mounds are a mark of the Neolithic.

(BP is Before Present)

Details

Mesolithic, also called Middle Stone Age, is an ancient cultural stage that existed between the Paleolithic (Old Stone Age), with its chipped stone tools, and the Neolithic (New Stone Age), with its polished stone tools. Most often used to describe archaeological assemblages from the Eastern Hemisphere, the Mesolithic is broadly analogous to the Archaic culture of the Western Hemisphere. Mesolithic material culture is characterized by greater innovation and diversity than is found in the Paleolithic. Among the new forms of chipped stone tools were microliths, very small stone tools intended for mounting together on a shaft to produce a serrated edge. Polished stone was another innovation that occurred in some Mesolithic assemblages.

Although culturally and technologically continuous with Paleolithic peoples, Mesolithic cultures developed diverse local adaptations to special environments. The Mesolithic hunter achieved a greater efficiency than did the Paleolithic and was able to exploit a wider range of animal and vegetable food sources. Immigrant Neolithic farmers probably absorbed many indigenous Mesolithic hunters and fishers, and some Neolithic communities seem to have been composed entirely of Mesolithic peoples who adopted Neolithic equipment (these are sometimes called Secondary Neolithic).

Because the Mesolithic is characterized by a suite of material culture, its timing varies depending upon location. In northwestern Europe, for instance, the Mesolithic began about 8000 BCE, after the end of the Pleistocene Epoch (i.e., about 2,600,000 to 11,700 years ago), and lasted until about 2700 BCE. Elsewhere the dates of the Mesolithic are somewhat different. (BCE is Before the Common Era).

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It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

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

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#1438 2022-07-12 14:14:43

ganesh
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Re: Miscellany

1411) Neolithic

Summary

The Neolithic period is the final division of the Stone Age, with a wide-ranging set of developments that appear to have arisen independently in several parts of the world. It is seen about 12,000 years ago when the first developments of farming appeared in the Epipalaeolithic Near East, and later in other parts of the world. The Neolithic lasted (in that part of the world) until the transitional period of the Chalcolithic from about 6,500 years ago (4500 BC), marked by the development of metallurgy, leading up to the Bronze Age and Iron Age. The term "Neolithic" is customarily used only to describe cultures in the Old World.

In other places the Neolithic followed the Mesolithic and then lasted until later. In Ancient Egypt, the Neolithic period lasted until the Protodynastic period, c. 3150 BC. In China it lasted until circa 2000 BC with the rise of the pre-Shang Erlitou culture, while in Northern Europe, the Neolithic lasted until about 1700 BC. Some other parts of the world (including Oceania and some regions of the Americas) remained broadly comparable to the Neolithic stage of development until European contact.

The Neolithic introduced the Neolithic Revolution or "Neolithic package", comprising a progression of behavioral and cultural characteristics and changes, above all the introduction of farming and use of domesticated animals.

The term Neolithic is modern, based on Greek 'new' and 'stone', literally 'New Stone Age'. The term was coined by Sir John Lubbock in 1865 as a refinement of the three-age system.

Details

Neolithic, also called New Stone Age, is the final stage of cultural evolution or technological development among prehistoric humans. It was characterized by stone tools shaped by polishing or grinding, dependence on domesticated plants or animals, settlement in permanent villages, and the appearance of such crafts as pottery and weaving. The Neolithic followed the Paleolithic Period, or age of chipped-stone tools, and preceded the Bronze Age, or early period of metal tools.

A brief treatment of the Neolithic follows.

The Neolithic stage of development was attained during the Holocene Epoch (the last 11,700 years of Earth history). The starting point of the Neolithic is much debated, with different parts of the world having achieved the Neolithic stage at different times, but it is generally thought to have occurred sometime about 10,000 BCE. During that time, humans learned to raise crops and keep domestic livestock and were thus no longer dependent on hunting, fishing, and gathering wild plants. Neolithic cultures made more-useful stone tools by grinding and polishing relatively hard rocks rather than merely chipping softer ones down to the desired shape. The cultivation of cereal grains enabled Neolithic peoples to build permanent dwellings and congregate in villages, and the release from nomadism and a hunting-gathering economy gave them the time to pursue specialized crafts.

Archaeological evidence indicates that the transition from food-collecting cultures to food-producing ones gradually occurred across Asia and Europe from a starting point in the Fertile Crescent. The first evidence of cultivation and animal domestication in southwestern Asia has been dated to roughly 9500 BCE, which suggests that those activities may have begun before that date. A way of life based on farming and settled villages had been firmly achieved by 7000 BCE in the Tigris and Euphrates river valleys (now in Iraq and Iran) and in what are now Syria, Israel, Lebanon, and Jordan. Those earliest farmers raised barley and wheat and kept sheep and goats, later supplemented by cattle and pigs. Their innovations spread from the Middle East northward into Europe by two routes: across Turkey and Greece into central Europe, and across Egypt and North Africa and thence to Spain. Farming communities appeared in Greece as early as 7000 BCE, and farming spread northward throughout the continent over the next four millennia. This long and gradual transition was not completed in Britain and Scandinavia until after 3000 BCE and is known as the Mesolithic.

Neolithic technologies also spread eastward to the Indus River valley of India by 5000 BCE. Farming communities based on millet and rice appeared in the Huang He (Yellow River) valley of China and in Southeast Asia by about 3500 BCE. Neolithic modes of life were achieved independently in the New World. Corn (maize), beans, and squash were gradually domesticated in Mexico and Central America from 6500 BCE on, though sedentary village life did not commence there until much later, at about 2000 BCE.

In the Old World the Neolithic was succeeded by the Bronze Age when human societies learned to combine copper and tin to make bronze, which replaced stone for use as tools and weapons.

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It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

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

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#1439 2022-07-13 15:27:36

ganesh
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Posts: 38,059

Re: Miscellany

1412) Chalcolithic

Summary

The Chalcolithic, a name derived from the Greek: "copper" and "stone" or Copper Age, also known as the Eneolithic or Aeneolithic (from Latin aeneus "of copper"), is an archaeological period that researchers now regard as part of the broader Neolithic. Earlier scholars defined it as a transitional period between the Neolithic and the Bronze Age. In the context of Eastern Europe, archaeologists often prefer the term "Eneolithic" to "Chalcolithic" or other alternatives.

In the Chalcolithic period, copper predominated in metalworking technology. Hence it was the period before it was discovered that by adding tin to copper one could create bronze, a metal alloy harder and stronger than either component.

The archaeological site of Belovode, on Rudnik mountain in Serbia, has the world's oldest securely dated evidence of copper smelting at high temperature, from c. 5000 BC (7000 BP (Before Present)). The transition from Copper Age to Bronze Age in Europe occurred between the late 5th and the late 3rd millennia BC. In the Ancient Near East the Copper Age covered about the same period, beginning in the late 5th millennium BC and lasting for about a millennium before it gave rise to the Early Bronze Age.

Details

The Chalcolithic period refers to that part of Old World prehistory wedged between the first farming societies called Neolithic, and the urban and literate societies of the Bronze Age. In Greek, Chalcolithic means "copper age" (more or less), and indeed, the Chalcolithic period is generally--but not always--associated with wide-spread copper metallurgy.

Copper metallurgy was likely developed in northern Mesopotamia; the earliest known sites are in Syria such as Tell Halaf, about 6500 years BC. The technology was known considerably longer ago than that--isolated copper axes and adzes are known from Catalhoyuk in Anatolia and Jarmo in Mesopotamia by 7500 cal BC. But the intensive production of copper tools is one of the hallmarks of the Chalcolithic period.

Chronology

Pinning a specific date on the Chalcolithic is difficult. Like other broad categories such as Neolithic or Mesolithic, rather than referring to a particular group of people residing in one place and time, "Chalcolithic" is applied to a broad mosaic of cultural entities located in different environments, which have a handful of common characteristics. The earliest recognized of the two most prevalent characteristics--painted pottery and copper processing--are found in the Halafian culture of northeastern Syria about 5500 BC. 

* Early (5500-3500 calendar years BC [cal BC]): began in the Near East (Anatolia, the Levant, and Mesopotamia)
* Developed (4500-3500 BC): arrived in the Near East and Central and Eastern Europe in SE Europe, followed by Carpathian basin, East-central Europe and SW Germany and Eastern Switzerland
* Late (3500-3000 cal BC): arrived in Central and Western Mediterranean (North and central Italy, southern France, Eastern France and Western Switzerland)
* Terminal (3200-2000 cal BD): arrived in the Iberian peninsula

The spread of Chalcolithic culture appears to have been part migration and part adoption of new technologies and material culture by local indigenous people.

Chalcolithic Lifestyles

A main identifying characteristic of the Chalcolithic period is polychrome painted pottery. Ceramic forms found on Chalcolithic sites include "fenestrated pottery", pots with openings cut into the walls, which may have been used for burning incense, as well as large storage jars and serving jars with spouts. Stone tools include adzes, chisels, picks and chipped stone tools with central perforations.

Farmers typically raised domestic animals such as sheep-goats, cattle, and pigs, a diet supplemented by hunting and fishing. Milk and milk by-products were important, as were fruit trees (such as fig and olive). Crops grown by Chalcolithic farmers included barley, wheat, and pulses. Most of the goods were locally produced and used, but the Chalcolithic societies dabbled in some long-distance trade in figurines of laden animals, copper and silver ores, basalt bowls, timber, and resins.

Houses and Burial Styles

Houses built by Chalcolithic farmers were constructed of stone or mudbrick. One characteristic pattern is a chain building, a row of rectangular houses connected to one another by shared party walls on the short ends. Most of the chains are no more than six houses long, leading researchers to suspect that they represent extended farming families living close together. Another pattern, seen in larger settlements, is a set of rooms around a central courtyard, which may have facilitated the same sort of social arrangement. Not all houses were in chains, not all were even rectangular: some trapezoid and circular houses have been identified.

Burials varied widely from group to group, from single interments to jar burials to small box-shaped above-ground ossuaries and even rock-cut tombs. In some cases, secondary burial practices included the disinterment and placement of older burials into family or clan vaults. In some sites, bone stacking--the careful arrangement of skeletal materials--has been noted. Some burials were outside of the communities, others were within the houses themselves.

Teleilat Ghassul

The archaeological site of Teleilat Ghassul (Tulaylât al-Ghassûl) is a Chalcolithic site located in the Jordan Valley about 80 kilometers (50 miles) northeast of the Dead Sea. Excavated first in the 1920s by Alexis Mallon, the site contains a handful of mud-brick houses built beginning about 5000 BC, that grew over the next 1,500 years to include a multiroom complex and sanctuaries. Recent excavations have been led by Stephen Bourke of the Unversity of Sydney. Teleilat Ghassul is the type site for the local version of the Chalcolithic period, called Ghassulian, which is found throughout the Levant.

Several polychrome murals were painted on the interior walls of buildings at Teleilat Ghassul. One is an intricate geometric arrangement which appears to be an architectural complex viewed from above. Some scholars have suggested it is a drawing of the sanctuary area on the southwestern edge of the site. The schematic appears to include a courtyard, a stepped pathway leading to a gatehouse, and a brick-walled thatch-roofed building surrounded by a stone or mud-brick platform.

Polychrome Paintings

The architectural plan is not the only polychrome painting at Teleilat Ghassul: there is a "Processional" scene of robed and masked individuals led by a larger figure with a raised arm. The robes are complex textiles in red, white and black with tassels. One individual wears a conical headpiece that may have horns, and some scholars have interpreted this to mean there was a priestly class of specialists at Teleilat Ghassul.

The "Nobles" mural shows a row of seated and standing figures facing a smaller figure positioned in front of a red and yellow star. The murals were repainted up to 20 times on successive layers of lime plaster, containing geometric, figurative and naturalistic designs with a variety of mineral-based colors, including red, black, white and yellow. The paintings may have originally also had blue (azurite) and green (malachite) as well, but those pigments react poorly with lime plaster and if used are no longer preserved.

Some Chalcolithic Sites: Be'er Sheva, Israel; Chirand (India); Los Millares, Spain; Tel Tsaf (Israel), Krasni Yar (Kazakhstan), Teleilat Ghassul (Jordan), Areni-1 (Armenia).

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It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

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

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#1440 2022-07-14 13:45:05

ganesh
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Posts: 38,059

Re: Miscellany

1413) Bronze Age

Summary

The Bronze Age is a historic period, approximately 3300 BC to 1200 BC, that was characterized by the use of bronze, in some areas writing, and other early features of urban civilization. The Bronze Age is the second principal period of the three-age system, as proposed in 1836 by Christian Jürgensen Thomsen, for classifying and studying ancient societies and history.

An ancient civilization is deemed to be part of the Bronze Age because it either produced bronze by smelting its own copper and alloying it with tin, math, or other metals, or traded other items for bronze from production areas elsewhere. Bronze was harder and more durable than other metals available at the time, allowing Bronze Age civilizations to gain a technological advantage.

While terrestrial iron is naturally abundant, the higher temperature required for smelting, 1,250 °C (2,280 °F), in addition to the greater difficulty of working with the metal, placed it out of reach of common use until the end of the second millennium BC. Tin's low melting point of 231.9 °C (449.4 °F) and copper's relatively moderate melting point of 1,085 °C (1,985 °F) placed them within the capabilities of the Neolithic pottery kilns, which date back to 6,000 BC and were able to produce temperatures greater than 900 °C (1,650 °F).[1] Copper and tin ores are rare, since there were no tin bronzes in Western Asia before trading in bronze began in the 3rd millennium BC. Worldwide, the Bronze Age generally followed the Neolithic period, with the Chalcolithic serving as a transition.

Bronze Age cultures differed in their development of writing. According to archaeological evidence, cultures in Mesopotamia (cuneiform script) and Egypt (hieroglyphs) developed the earliest practical writing systems.

Details

Bronze Age is the third phase in the development of material culture among the ancient peoples of Europe, Asia, and the Middle East, following the Paleolithic and Neolithic periods (Old Stone Age and New Stone Age, respectively). The term also denotes the first period in which metal was used. The date at which the age began varied with regions; in Greece and China, for instance, the Bronze Age began before 3000 BCE, whereas in Britain it did not start until about 1900 BCE.

The beginning of the period is sometimes called the Chalcolithic (Copper-Stone) Age, referring to the initial use of pure copper (along with its predecessor toolmaking material, stone). Scarce at first, copper was initially used only for small or precious objects. Its use was known in eastern Anatolia by 6500 BCE, and it soon became widespread. By the middle of the 4th millennium, a rapidly developing copper metallurgy, with cast tools and weapons, was a factor leading to urbanization in Mesopotamia. By 3000 the use of copper was well known in the Middle East, had extended westward into the Mediterranean area, and was beginning to infiltrate the Neolithic cultures of Europe.

This early copper phase is commonly thought of as part of the Bronze Age, though true bronze, an alloy of copper and tin, was used only rarely at first. During the 2nd millennium the use of true bronze greatly increased; the tin deposits at Cornwall, England, were much used and were responsible for a considerable part of the large production of bronze objects at that time. The age was also marked by increased specialization and the invention of the wheel and the ox-drawn plow. From about 1000 BCE the ability to heat and forge another metal, iron, brought the Bronze Age to an end, and the Iron Age began.

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It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

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

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#1441 2022-07-15 14:31:30

ganesh
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Re: Miscellany

1414) Iron Age

Summary

Iron Age is the final technological and cultural stage in the Stone–Bronze–Iron Age sequence. The date of the full Iron Age, in which this metal for the most part replaced bronze in implements and weapons, varied geographically, beginning in the Middle East and southeastern Europe about 1200 BCE but in China not until about 600 BCE. Although in the Middle East iron had limited use as a scarce and precious metal as early as 3000 BCE, there is no indication that people at that time recognized its superior qualities over those of bronze. Between 1200 and 1000, however, the export of knowledge of iron metallurgy and of iron objects was rapid and widespread. With the large-scale production of iron implements came new patterns of more permanent settlement. On the other hand, utilization of iron for weapons put arms in the hands of the masses for the first time and set off a series of large-scale movements of peoples that did not end for 2,000 years and that changed the face of Europe and Asia.

Details

The Iron Age is the final epoch of the three-age division of the prehistory and protohistory of humanity. It was preceded by the Stone Age (Paleolithic, Mesolithic, Neolithic), and the Bronze Age (Chalcolithic). The concept has been mostly applied to Europe and the Ancient Near East, but also, by analogy, to other parts of the Old World.

The duration of the Iron Age varies depending on the region under consideration. It is defined by archaeological convention. The "Iron Age" begins locally when the production of iron or steel has advanced to the point where iron tools and weapons replace their bronze equivalents in common use. In the Ancient Near East, this transition took place in the wake of the so-called Bronze Age collapse, in the 12th century BC. The technology soon spread throughout the Mediterranean Basin region and to South Asia. Its further spread to Central Asia, Eastern Europe, and Central Europe is somewhat delayed, and Northern Europe was not reached until around the start of the 5th century BC.

The Iron Age is taken to end, also by convention, with the beginning of the historiographical record. This usually does not represent a clear break in the archaeological record; for the Ancient Near East, the establishment of the Achaemenid Empire c. 550 BC is traditionally and still usually taken as a cut-off date, later dates being considered historical by virtue of the record by Herodotus, despite considerable written records from far earlier (well back into the Bronze Age) now being known. In Central and Western Europe, the Roman conquests of the 1st century BC serve as marking for the end of the Iron Age. The Germanic Iron Age of Scandinavia is taken to end c. AD 800, with the beginning of the Viking Age.

In the Indian sub-continent, the Iron Age is taken to begin with the ironworking Painted Gray Ware culture. Recent estimates suggest that it ranges from the 15th century BC, through to the reign of Ashoka in the 3rd century BC. The use of the term "Iron Age" in the archaeology of South, East, and Southeast Asia is more recent and less common than for western Eurasia. In China, written history started before iron-working arrived, so the term is infrequently used. The Sahel (Sudan region) and Sub-Saharan Africa are outside of the three-age system, there being no Bronze Age, but the term "Iron Age" is sometimes used in reference to early cultures practicing ironworking, such as the Nok culture of Nigeria.

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It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

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

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#1442 2022-07-16 14:40:45

ganesh
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Re: Miscellany

1415) Pomegranate

Summary

The pomegranate (Punica granatum) is a fruit-bearing deciduous shrub in the family Lythraceae, subfamily Punicoideae, that grows between 5 and 10 m (16 and 33 ft) tall.

The pomegranate was originally described throughout the Mediterranean region. It was introduced into Spanish America in the late 16th century and into California by Spanish settlers in 1769.

The fruit is typically in season in the Northern Hemisphere from October to February, and in the Southern Hemisphere from March to May. As intact sarcotestas or juice, pomegranates are used in baking, cooking, juice blends, meal garnishes, smoothies, and alcoholic beverages, such as math and wine.

Pomegranates are widely cultivated throughout the Middle East and Caucasus region, north and tropical Africa, Iran, Armenia, the Indian subcontinent, Central Asia, the drier parts of Southeast Asia, and the Mediterranean Basin.

Details

Overview

Pomegranate is a tree. Various parts of the tree and fruit are used to make medicine.

People use pomegranate for high blood pressure, athletic performance, heart disease, diabetes, and many other conditions, but there is no good scientific evidence to support most of these uses.

Pomegranate has been used for thousands of years. It is in Greek, Hebrew, Buddhist, Islamic, and Christian mythology and writings. It is described in records dating from around 1500 BCE as a treatment for tapeworm and other parasites.

Many cultures use pomegranate as a folk medicine. Pomegranate is native to Iran. It is primarily cultivated in Mediterranean counties, parts of the United States, Afghanistan, Russia, India, China, and Japan. You'll see pomegranate in some royal and medical coats of arms.

How does it work ?

Pomegranate contains a variety of chemicals that might have antioxidant effects. Some preliminary research suggests that chemicals in pomegranate juice might slow the progression of atherosclerosis (hardening of the arteries) and possibly fight cancer cells. But it is not known if pomegranate has these effects when people drink the juice.

Uses & Effectiveness ?

Possibly Effective for

High blood pressure. Some research shows that drinking pomegranate juice daily can lower systolic blood pressure (the top number) by about 5 mmHg. Lower doses might work the same as higher doses. Pomegranate juice doesn't seem to reduce diastolic pressure (the lower number).

Possibly Ineffective for

* A lung disease that makes it harder to breathe (chronic obstructive pulmonary disease or COPD). Drinking pomegranate juice does not seem to improve symptoms or breathing in people with this condition.
* High levels of cholesterol or other fats (lipids) in the blood (hyperlipidemia). Taking pomegranate doesn't seem to lower cholesterol in people with or without high cholesterol.

Insufficient Evidence for

* Hardening of the arteries (atherosclerosis). Early research shows that drinking pomegranate juice might help to keep the arteries in the neck (carotid arteries) clear of the build-up of fatty deposits.
* Athletic performance. Early research shows that taking pomegranate extract might make cycling feel easier. It might also increase how long cycling can be done. But doesn't improve cycling time in competitive athletes.
* Heart disease. Some early research shows that drinking pomegranate juice might improve blood flow to the heart. But drinking pomegranate juice doesn't seem to prevent narrowing of blood vessels in the heart (stenosis). There is also not enough information to know if drinking pomegranate juice helps prevent heart disease-related events such as heart attack.
* Tooth plaque. Early research shows that rinsing with pomegranate extract mouthwash for one minute once or twice daily reduces dental plaque.
* Diabetes. Early research shows that drinking fresh pomegranate juice 1.5 mL/kg improves blood sugar in some people with diabetes.
* Serious kidney disease (end-stage renal disease or ESRD). The effects of pomegranate in people with ESRD are unclear. Results from research are inconsistent. Some early research shows that drinking pomegranate juice during or after dialysis helps to reduce blood pressure and to improve "good" (HDL) cholesterol and triglyceride levels. But other early research shows that drinking pomegranate juice before dialysis sessions or taking pomegranate extract for only 4 weeks doesn't improve blood pressure or cholesterol in people on dialysis.
* Erectile dysfunction (ED). Early research shows that drinking pomegranate juice daily for 4 weeks does not improve erectile dysfunction in men.
* Muscle soreness caused by exercise. Early research in trained men shows that drinking pomegranate juice twice daily for 15 days reduces muscle soreness after exercising in the elbow but not the knee. But other research in untrained men shows that drinking pomegranate juice twice daily for 9 days doesn't reduce muscle soreness in the elbow.
* Symptoms of menopause. Early research shows that taking pomegranate seed oil for 12 weeks does not reduce hot flashes but might improve sleep in some women with symptoms of menopause.
* A grouping of symptoms that increase the risk of diabetes, heart disease, and stroke (metabolic syndrome). Early research shows that drinking pomegranate juice daily for one month improves blood vessel function in adolescents with metabolic syndrome.
* Muscle strength. Early research shows that taking pomegranate extract can improve muscle strength recovery after exercise.
* Obesity. Most research shows that taking pomegranate products doesn't help with weight loss. But many studies of these studies included people who were not overweight or obese. And some research does show benefit of certain pomegranate products. More research is needed to know if some products are better than others in people who are overweight or obese.
* Thrush. Applying a gel containing pomegranate extract to the gums improves symptoms in people with thrush.
* A serious gum infection (periodontitis). There is some evidence that painting the gums with pomegranate fruit peel extract in combination with gotu kola extract might improve gum disease.
* Prostate cancer. Early research shows that drinking pomegranate juice or taking pomegranate extract for up to 2 years might slow the progression of prostate cancer. Other early research shows that taking a combination of pomegranate powder and other ingredients for 6 months can slows the rising of prostate-specific antigen (PSA) levels in men with prostate cancer. PSA levels are linked with prostate cancer growth, with faster increases indicating more growth.
* Rheumatoid arthritis (RA). Early research shows that taking pomegranate extract twice daily for 12 weeks can improve symptoms of rheumatoid arthritis.
* Sunburn. Early research shows that taking pomegranate extract by mouth does not prevent sunburn.
* A sexually transmitted infection caused by Trichomonas vaginalis (trichomoniasis). Early research shows that taking pomegranate extract might clear up trichomoniasis infections in women.
* Diarrhea.
* Hemorrhoids.
* Intestinal worm infestations.
* A hormonal disorder that causes enlarged ovaries with cysts (polycystic ovary syndrome or PCOS).
* Sore throat.
* Other conditions.

More evidence is needed to rate pomegranate for these uses.

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It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

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

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#1443 2022-07-17 13:52:50

ganesh
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Re: Miscellany

1416) Zoo

Summary

A zoo (short for zoological garden; also called an animal park or menagerie) is a facility in which animals are housed within enclosures, cared for, displayed to the public, and in some cases bred for conservation purposes.

The term zoological garden refers to zoology, the study of animals. The term is derived from the Greek 'animal', and the 'study of'. The abbreviation zoo was first used of the London Zoological Gardens, which was opened for scientific study in 1828 and to the public in 1847. In the United States alone, zoos are visited by over 181 million people annually.

Details

Zoo, also called zoological garden or zoological park, is a place where wild animals and, in some instances, domesticated animals are exhibited in captivity. In such an establishment, animals can generally be given more intensive care than is possible in nature reserves or sanctuaries. Most long-established zoos exhibit general collections of animals, but some formed more recently specialize in particular groups—e.g., primates, big cats, tropical birds, or waterfowl. Marine invertebrates, fishes, and marine mammals are often kept in separate establishments known as aquariums. The word zoo was first used in the late 19th century as a popular abbreviation for the zoological gardens in London.

For information on particular zoos, see articles at their specific names—e.g., Basel Zoological Garden, Lincoln Park Zoo, Prague Zoological Gardens, and so on.

It is not known when the earliest zoos were established, but it is possible that they were associated with the first attempts at animal domestication. Pigeons were kept in captivity as early as 4500 BCE in what is now Iraq, and 2,000 years later elephants were semidomesticated in India. Antelopes, including the addax, ibex, oryx, and gazelle, are depicted wearing collars on Egyptian tomb pictures at Ṣaqqārah, dating from 2500 BCE. In China the empress Tanki, who probably lived about 1150 BCE, built a great marble “house of deer,” and Wen Wang, who apparently reigned just before 1000 BCE, established a zoo of 1,500 acres in extent, which he named the Ling-Yu, or Garden of Intelligence.

The biblical king Solomon, who also reigned about 1000 BCE, was a farmer-zoologist, and he was followed, for at least the next 600 years, by other royal zookeepers, including Semiramis and Ashurbanipal of Assyria and King Nebuchadrezzar of Babylonia.

Collections of captive animals were in existence in Greece by the 7th century BCE, and by the 4th century BCE it is probable that such collections existed in most, if not all, of the Greek city-states. Aristotle (384–322 BCE) was obviously well acquainted with zoos; his most famous pupil, Alexander the Great, sent back to Greece many animals that were caught on his military expeditions.

The earlier Egyptian and Asian zoos were kept mainly as public spectacles and only secondarily for study, but the Greeks of Aristotle’s time were more concerned with study and experiment. The Romans had two types of animal collections: those destined for the arena and those kept as private zoos and aviaries.

With the end of the Roman Empire, zoos went into a decline, but animal collections were maintained by the emperor Charlemagne in the 8th century CE and by Henry I in the 12th century. In Europe Philip VI had a menagerie in the Louvre, Paris, in 1333, and many members of the house of Bourbon kept collections of animals at Versailles.

In the New World, Hernán Cortés discovered a magnificent zoo in Mexico in 1519. The collection, which included birds of prey, mammals, and reptiles, was so large that it needed a staff of 300 keepers.

Modern zookeeping may be said to have started in 1752 with the founding of the Imperial Menagerie at the Schönbrunn Palace in Vienna. This menagerie, which still flourishes, was opened to the general public in 1779. In 1775 a zoo was founded in a Royal Park in Madrid, and 18 years later the zoological collection of the Jardin des Plantes, Paris, was begun. The Zoological Society of London established its collection in Regent’s Park in 1828, two years after the society itself was founded.

By the mid-19th century, zoos were being opened all over the world; among those existing today, more than 40, most of which are in Europe, are more than 100 years old. Since the end of World War II there has been a rapid and worldwide proliferation of zoos, many of which have as their aim not the study of animals but public entertainment and commercial gain. The total number of animal collections open to the public in the world today is not accurately known but exceeds 1,000.

Function and purpose

The primary object of zoos that are in the charge of scientific societies is the study of animals. Thus, the purpose of the Zoological Society of London, as stated in its Royal Charter, is “the advancement of Zoology and Animal Physiology and the introduction of new and curious subjects of the Animal Kingdom.” This society has been the model for many other zoological societies throughout the world. In the 19th century the emphasis of the investigations carried out in scientific zoos was mainly on taxonomy, comparative anatomy, and pathology. Today the opportunities for scientific inquiry are much wider, and a few societies have established special research institutions. In the United States the Penrose Research Laboratory, of the Philadelphia Zoo, is particularly concerned with comparative pathology. The New York Zoological Society maintains an Institute for Research in Animal Behavior and, in Trinidad, the William Beebe Tropical Research Station. In Great Britain the Zoological Society of London maintains, in addition to a modern hospital and pathology laboratories, two general research institutes—the Nuffield Institute of Comparative Medicine and the Wellcome Institute of Comparative Physiology.

Many zoos publish scientific journals and periodicals, which range in their contents from the popular to the highly technical. Again, the Zoological Society of London led the way. Its “Proceedings,” now known as the Journal of Zoology, has appeared uninterruptedly since 1830.

In recent years a few zoos have intensified their efforts, frequently in cooperation with educational authorities, to provide an educational program for school children and students. Some zoos have full-time or voluntary guides on their staff, whose job it is to provide more information for visitors than can be given on labels attached to cages. Others meet this need by providing “talking labels,” prerecorded tapes operated by the visitors themselves.

Since World War II a number of zoos have been developed as breeding centres for animal species in danger of becoming extinct in the wild. Many threatened species have been saved by breeding in captivity. For example, in 1947 it was estimated that there were only 50 nenes, or Hawaiian geese, left on Hawaii and none anywhere else in the world. In 1950 two nenes were housed at the Wildfowl Trust at Slimbridge, England, and in 1951 a gander was hatched. The birds continued to breed successfully, and gradually the captive stock in Europe was spread over a dozen different menageries to minimize the risk of losses from disease or predators. Another species that has been saved by breeding in zoos is the European bison, or wisent, the last wild specimen of which died in 1925. Other species that zoos have helped to survive include Père David’s deer and many rare game birds. The increasing number of zoo births gives hope that zoos, rather than capturing wild animals for exhibition, will perhaps be able to restock the wild with zoo-born animals.

Design and architecture

Zoo design and architecture must meet two often conflicting needs: those of the animals (and the menagerie staff caring for them) and those of the visiting public. Zoos vary so widely in site, size, layout, age, and climatic conditions that there can hardly be a standard form of architecture.

Urban zoos (perhaps 80 percent of all zoos) are necessarily limited in size and have to make the best possible use of the available space. The animals are usually kept in houses, sometimes with associated outdoor enclosures. Cages, or some form of barrier, are usually necessary to prevent the animals from escaping and to discourage the public from getting too close to the animals. In addition to the simplest equipment in cages, such as scratching posts for the lions and tigers and branches and suspended chains or ropes for the monkeys, modern materials are increasingly used for the construction of backgrounds, artificial rocks, and trees to simulate a more natural habitat.

Elephants and rhinoceroses, which are among the largest mammals, are often accommodated within the same building, which is sometimes designed also to house hippopotamuses and tapirs. These animals are usually also provided with outdoor paddocks, always incorporating a pool for the hippopotamuses and often for the other species. Giraffes, whose height may exceed 4.5 metres (15 feet), obviously need buildings that provide proper headroom and also outdoor enclosures where they can exercise. Horses, zebras, okapis, camels, pigs, cattle, and antelopes require both houses and paddocks. Only the small mammals can be conveniently housed under one roof without outdoor paddocks.

Nocturnal animals are exhibited successfully in a number of zoos in buildings in which the normal cycle of daylight is reversed by means of artificial light. During daylight hours, when the animals would normally be asleep but when zoos are open to the public, the building is illuminated by dim white light or red light and the animals become active. At nightfall the houses are fully illuminated and the animals go to sleep.

Aviaries in urban zoos can take a number of forms. They may be a collection of small cages, each containing one or a pair of birds, within a building. They may be considerably larger cages, containing a number of species either representing closely related forms or providing a habitat display of, for example, seashore or woodland birds. There are various ways to keep birds within the aviary and still display them to the public. Wire mesh is the most common means, but a less visible barrier consists of vertically placed piano wire at one-half inch to one inch intervals. Glass is sometimes used, but unless it is very carefully positioned it may give unwanted reflections. Birds can also be confined in aviaries that are “enclosed” simply and effectively by brightly lighting certain portions of the enclosure and darkening the public area. The “walk-through” aviary is one in which the birds are given free run of a large space into which visitors are admitted through “air-lock” type doors. Such aviaries can simulate a natural environment with vegetation and streams.

Water birds and birds of prey are usually housed in outdoor aviaries with an attached shelter. Modern aviaries for these species are very large so that the birds can exercise sufficiently.

One of the most magnificent aviaries in the world is in the San Diego Zoo, in California, where it has proved possible to roof over natural canyons, of which one, used as a walk-through aviary, is about 25 metres (82 feet) high, 46 metres (150 feet) long, and 21 metres (69 feet) wide. The walk-through Snowdon Aviary, at the London Zoo, is of a similar size but built over an artificial cliff. Opened in 1965, it is of unique design. Galvanized steel tension cables and aluminum tube shear legs support mesh on tetrahedral frames held in midair. The walk-through path cantilevers 12 metres (about 39 feet) out from the cliff top.

Reptiles may be kept in individual cages in an enclosed reptile house. In subtropical and tropical zoos they are often kept outdoors in semi-natural enclosures or pits.

When animals are confined in houses, conditions such as ventilation, light, temperature, and humidity are adjusted to the particular needs of the species involved. Central heating plants and humidifiers may have to be installed in each building, with separate control systems for different cages. Many animals like to bask in a “hot spot” and feed in surroundings at a lower temperature. Infrared lamps are sometimes used to this end, and, in species such as desert-living reptiles, ultraviolet light also is used. Direct sunlight is adequate if the windows allow passage of ultraviolet rays.

A number of open-range zoos have been established since the early 1930s in rural surroundings. The prototype is Whipsnade Park, established by the Zoological Society of London in 1932. Fewer species of animals are exhibited in such zoos than in urban zoos, but they are kept in more natural conditions in large paddocks. Animals are confined by a variety of methods including water-filled moats, dry moats, and wire-mesh fences.

While many open-space zoos exhibit their animals in paddocks containing only a single species—e.g., a pride of lions or a herd of wildebeest or llamas—some try to create habitat displays consisting of mixed groups of animals. One of the best of these is at Borasparken, Sweden, where the African exhibit contains elephants, white rhinoceroses, Grant’s zebras, reticulated giraffes, white-tailed gnus, crowned cranes, ground hornbills, ostriches, and guinea fowl.

In some modern zoo parks, sometimes called safari parks or lion farms, the animals are confined in very large paddocks through which visitors drive in their cars. While this practice is based on that observed in African nature reserves, it can prove dangerous when the density of traffic is high and when visitors fail to keep the windows of their cars closed or leave their cars. Provided that open-space zoos are run by experienced and properly trained staff, with veterinarians who have specialized in the care of exotic animals in attendance, those zoos could become very important as breeding centres for rare or endangered species.

Procurement and care of animals

It has been estimated that in a good modern zoo, for every 20 animals on display, only about 5 were bred in captivity, the remainder having been collected in the wild and usually purchased through dealers. Equally, for every animal that ends up in a dealer’s hands, several others were probably killed in attempts at capture or died before they were sold to a zoo or other purchaser. In the interest of animal conservation, the breeding of captive animals is encouraged.

On arrival, zoo animals are quarantined and acclimatized to their new surroundings. Information on proper nutrition is exchanged between zoos directly or published in the International Zoo Yearbook. Temperature and other environmental requirements are also studied. Certain penguins, for example, have to be kept in refrigerated rooms if they are to thrive and breed. Adequate sleeping quarters, such as dens for foxes and wolves or burrows for rodents, also are provided.

Funding

Zoos are funded in various ways. In the United States most zoos are supported partially or wholly out of public funds by the town, city, or state in which they are located. The National Zoological Park, in Washington, D.C., was founded by Congress in 1889–90. Its site was purchased by the U.S. government, and running expenses are provided from public funds. The Zoological Park in the Bronx, New York City, and the Philadelphia Zoological Garden are managed by zoological societies. Both are supported partly by the subscriptions of members, partly by entrance fees, and partly by annual civic subsidies. In Britain most of the older zoos are maintained by zoological societies or trusts, all of which have an educational purpose. The running costs of the zoos are met by admission charges, membership subscriptions, and gifts and bequests.

Most European zoos, especially those in Germany, are run as civic institutions, but, in addition, entrance fees are charged. Some famous zoos, including those in Cologne and Frankfurt, are supported by the municipality but are run by zoological societies. The Paris zoo is one of the many institutions directly supported by the French Ministry of Education, in the same way as the Moscow zoo is a state organization.

In a number of countries, zoo associations or federations have been set up. The largest of these is the American Association of Zoological Parks and Aquariums, founded in 1924. Other zoo federations include those of Great Britain and Ireland, Spain and Spanish America, Japan, Poland, and Germany. Related organizations include the International Union of Directors of Zoological Gardens and the Wild Animal Propagation Trust. Federations generally have among their objects the gathering and dissemination of facts and information relating to the management of zoological parks, the maintenance and raising of standards in zoos, the facilitation of the exchange and importation of zoological specimens, and the conservation of wildlife.

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It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

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

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#1444 2022-07-18 14:42:15

ganesh
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Re: Miscellany

1417) Thermal Conduction

Summary

Thermal conduction is transfer of energy (heat) arising from temperature differences between adjacent parts of a body.

Thermal conductivity is attributed to the exchange of energy between adjacent molecules and electrons in the conducting medium. The rate of heat flow in a rod of material is proportional to the cross-sectional area of the rod and to the temperature difference between the ends and inversely proportional to the length; that is the rate H equals the ratio of the cross section A of the rod to its length l, multiplied by the temperature difference (T2 − T1) and by the thermal conductivity of the material, designated by the constant k. This empirical relation is expressed as:
H = −k(A/l)(T2 − T1). The minus sign arises because heat flows always from higher to lower temperature.

A substance of large thermal conductivity k is a good heat conductor, whereas one with small thermal conductivity is a poor heat conductor or good thermal insulator. Typical values are 0.093 kilocalories/second-metre-°C for copper (a good thermal conductor) and 0.00003 kilocalories/second-metre°C for wood (poor thermal conductor).

Details

The process by which heat is transferred from the hotter end to the colder end of object is known as conduction.

Heat spontaneously flows from a hotter to a colder body. For example, heat is conducted from the hotplate of an electric stove to the bottom of a saucepan in contact with it. In the absence of an opposing external driving energy source, within a body or between bodies, temperature differences decay over time, and thermal equilibrium is approached, temperature becoming more uniform.

In conduction, the heat flow is within and through the body itself. In contrast, in heat transfer by thermal radiation, the transfer is often between bodies, which may be separated spatially. Heat can also be transferred by a combination of conduction and radiation. In solids, conduction is mediated by the combination of vibrations and collisions of molecules, propagation and collisions of phonons, and diffusion and collisions of free electrons. In gases and liquids, conduction is due to the collisions and diffusion of molecules during their random motion. Photons in this context do not collide with one another, and so heat transport by electromagnetic radiation is conceptually distinct from heat conduction by microscopic diffusion and collisions of material particles and phonons. But the distinction is often not easily observed unless the material is semi-transparent.

In the engineering sciences, heat transfer includes the processes of thermal radiation, convection, and sometimes mass transfer. Usually, more than one of these processes occurs in a given situation.

The conventional symbol for thermal conductivity is k.

Walking on bathroom tile in winter is annoying since it feels so much colder than the carpet. This is interesting, since the carpet and tile are usually both at the same temperature (i.e. the temperature of the interior of the house). The different sensations we feel is explained by the fact that different materials transfer heat at different rates. Tile and stone conduct heat more rapidly than carpet and fabrics, so tile and stone feel colder in winter since they transfer heat out of your foot faster than the carpet does.

In general, good conductors of electricity (metals like copper, aluminum, gold, and silver) are also good heat conductors, whereas insulators of electricity (wood, plastic, and rubber) are poor heat conductors. The (average) kinetic energy of a molecule in the hot body is higher than in the colder body. If two molecules collide, an energy transfer from the hot to the cold molecule occurs. The cumulative effect from all collisions results in a net flux of heat from the hot body to the colder body. We call this transfer of heat between two objects in contact thermal conduction.

The letter Q represents the amount of heat transferred in a time t, k is the thermal conductivity constant for the material, A is the cross sectional area of the material transferring heat,  ΔT,  T is the difference in temperature between one side of the material and the other, and d is the thickness of the material. These factors can be seen visually in the diagram below.

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It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

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

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#1445 2022-07-19 14:12:50

ganesh
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Re: Miscellany

1418) Convection

Summary

Convection is single or multiphase fluid flow that occurs spontaneously due to the combined effects of material property heterogeneity and body forces on a fluid, most commonly density and gravity (see buoyancy). When the cause of the convection is unspecified, convection due to the effects of thermal expansion and buoyancy can be assumed. Convection may also take place in soft solids or mixtures where particles can flow.

Convective flow may be transient (such as when a multiphase mixture of oil and water separates) or steady state (see Convection cell). The convection may be due to gravitational, electromagnetic or fictitious body forces. Heat transfer by natural convection plays a role in the structure of Earth's atmosphere, its oceans, and its mantle. Discrete convective cells in the atmosphere can be identified by clouds, with stronger convection resulting in thunderstorms. Natural convection also plays a role in stellar physics. Convection is often categorised or described by the main effect causing the convective flow, e.g. Thermal convection.

Convection cannot take place in most solids because neither bulk current flows nor significant diffusion of matter can take place.

Details

Convection is a process by which heat is transferred by movement of a heated fluid such as air or water.

Natural convection results from the tendency of most fluids to expand when heated—i.e., to become less dense and to rise as a result of the increased buoyancy. Circulation caused by this effect accounts for the uniform heating of water in a kettle or air in a heated room: the heated molecules expand the space they move in through increased speed against one another, rise, and then cool and come closer together again, with increase in density and a resultant sinking.

Forced convection involves the transport of fluid by methods other than that resulting from variation of density with temperature. Movement of air by a fan or of water by a pump are examples of forced convection.

Atmospheric convection currents can be set up by local heating effects such as solar radiation (heating and rising) or contact with cold surface masses (cooling and sinking). Such convection currents primarily move vertically and account for many atmospheric phenomena, such as clouds and thunderstorms.

Convection is a way for heat to move, also referred to as a heat transfer mechanism. This transfer of heat happens when a fluid such as air or water is in motion. Convection is driven by temperature differences across that fluid. When a fluid is heated, the region in closest contact with the heat source becomes less dense due to increased kinetic energy in the particles. The portion of fluid that is less dense then rises, while the denser portion of fluid sinks. The process repeats itself because the less dense fluids cool down as they move away from their heat source, making them sink, while the denser fluids heat up as they near the heat source, making them rise. This creates convection currents.

Convection plays a large role in wind patterns and in passive ventilation. The movement of wind across the globe is dependent on various spots where warm air rises and cool air sinks, creating large wind currents that affect weather. For example, air over land will typically get heated up by the sun during the day, while air over the sea will remain cool. The hot air over land will rise in the atmosphere. As it rises, it also cools down and becomes denser, causing it to sink once more.

Forced convection

While natural convection can be used inside houses, forced convection is more common. This is where air currents are forced through a room by a fan. Forced convection can achieve the same effects as natural convection, the process is simply aided through devices like fans. If your house has heating vents on the bottom of your walls, this is an example of forced convection.

Convection is one of the fundamental ways that heat is transferred. The others are thermal conduction, radiant energy and evapotranspiration.

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It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

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

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#1446 2022-07-20 14:09:02

ganesh
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Re: Miscellany

1419) Radiation

Summary

In physics, radiation is the emission or transmission of energy in the form of waves or particles through space or through a material medium. This includes:

* electromagnetic radiation, such as radio waves, microwaves, infrared, visible light, ultraviolet, x-rays, and gamma radiation (γ)
* particle radiation, such as alpha radiation (α), beta radiation (β), proton radiation and neutron radiation (particles of non-zero rest energy)
* acoustic radiation, such as ultrasound, sound, and seismic waves (dependent on a physical transmission medium)
* gravitational radiation, that takes the form of gravitational waves, or ripples in the curvature of spacetime

Radiation is often categorized as either ionizing or non-ionizing depending on the energy of the radiated particles. Ionizing radiation carries more than 10 eV, which is enough to ionize atoms and molecules and break chemical bonds. This is an important distinction due to the large difference in harmfulness to living organisms. A common source of ionizing radiation is radioactive materials that emit α, β, or γ radiation, consisting of helium nuclei, electrons or positrons, and photons, respectively. Other sources include X-rays from medical radiography examinations and muons, mesons, positrons, neutrons and other particles that constitute the secondary cosmic rays that are produced after primary cosmic rays interact with Earth's atmosphere.

Gamma rays, X-rays and the higher energy range of ultraviolet light constitute the ionizing part of the electromagnetic spectrum. The word "ionize" refers to the breaking of one or more electrons away from an atom, an action that requires the relatively high energies that these electromagnetic waves supply. Further down the spectrum, the non-ionizing lower energies of the lower ultraviolet spectrum cannot ionize atoms, but can disrupt the inter-atomic bonds which form molecules, thereby breaking down molecules rather than atoms; a good example of this is sunburn caused by long-wavelength solar ultraviolet. The waves of longer wavelength than UV in visible light, infrared and microwave frequencies cannot break bonds but can cause vibrations in the bonds which are sensed as heat. Radio wavelengths and below generally are not regarded as harmful to biological systems. These are not sharp delineations of the energies; there is some overlap in the effects of specific frequencies.

The word "radiation" arises from the phenomenon of waves radiating (i.e., traveling outward in all directions) from a source. This aspect leads to a system of measurements and physical units that are applicable to all types of radiation. Because such radiation expands as it passes through space, and as its energy is conserved (in vacuum), the intensity of all types of radiation from a point source follows an inverse-square law in relation to the distance from its source. Like any ideal law, the inverse-square law approximates a measured radiation intensity to the extent that the source approximates a geometric point.

Details

Radiation is flow of atomic and subatomic particles and of waves, such as those that characterize heat rays, light rays, and X rays. All matter is constantly bombarded with radiation of both types from cosmic and terrestrial sources. This article delineates the properties and behaviour of radiation and the matter with which it interacts and describes how energy is transferred from radiation to its surroundings. Considerable attention is devoted to the consequences of such an energy transfer to living matter, including the normal effects on many life processes (e.g., photosynthesis in plants and vision in animals) and the abnormal or injurious effects that result from the exposure of organisms to unusual types of radiation or to increased amounts of the radiations commonly encountered in nature. The applications of various forms of radiation in medicine and technological fields are touched upon as well.

General background

Types of radiation

Radiation may be thought of as energy in motion either at speeds equal to the speed of light in free space—approximately 3 × {10}^{10} centimetres (186,000 miles) per second—or at speeds less than that of light but appreciably greater than thermal velocities (e.g., the velocities of molecules forming a sample of air). The first type constitutes the spectrum of electromagnetic radiation that includes radio waves, microwaves, infrared rays, visible light, ultraviolet rays, X rays, and gamma rays, as well as the neutrino. These are all characterized by zero mass when (theoretically) at rest. The second type includes such particles as electrons, protons, and neutrons. In a state of rest, these particles have mass and are the constituents of atoms and atomic nuclei. When such forms of particulate matter travel at high velocities, they are regarded as radiation. In short, the two broad classes of radiation are unambiguously differentiated by their speed of propagation and corresponding presence or absence of rest mass. In the discussion that follows, those of the first category are referred to as “electromagnetic rays” (plus the neutrino) and those of the second as “matter rays.”

At one time, electromagnetic rays were thought to be inherently wavelike in character—namely, that they spread out in space and are able to exhibit interference when they come together from two or more sources. (Such behaviour is typified by water waves in the way they propagate and periodically reinforce and cancel one another.) Matter rays, on the other hand, were considered to be inherently particle-like in character—i.e., localized in space and incapable of interference. During the early 1900s, however, major experiments and attendant theories revealed that all forms of radiation, under appropriate conditions, can exhibit both particle-like and wavelike behaviour. This is referred to as the wave–particle duality and provides in large part the foundation for the modern quantum theory of matter and radiation. The wave behaviour of radiation is apparent in its propagation through space, while the particle behaviour is revealed by the nature of interactions with matter. Because of this, care must be exercised to use the terms waves and particles only when appropriate.

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It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

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

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#1447 2022-07-21 14:19:00

ganesh
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Re: Miscellany

1420) Echidna

Summary

Echidnas, sometimes known as spiny anteaters, are quill-covered monotremes (egg-laying mammals) belonging to the family Tachyglossidae. The four extant species of echidnas and the platypus are the only living mammals that lay eggs and the only surviving members of the order Monotremata. The diet of some species consists of ants and termites, but they are not closely related to the true anteaters of the Americas, which (along with sloths and armadillos) are xenarthrans. Echidnas live in Australia and New Guinea.

Echidnas evolved between 20 and 50 million years ago, descending from a platypus-like monotreme. This ancestor was aquatic, but echidnas adapted to life on land.

Details

Epiny anteater is any of four species of peculiar egg-laying mammals from Australia, Tasmania, and New Guinea that eat and breathe through a bald tubular beak protruding from a dome-shaped body covered in spines. Echidnas have beady eyes and mere slits for ears, and at the end of their beaks are two small nostrils and a tiny mouth. Electroreceptors in the skin of the beak may sense electrical signals produced by the muscles of invertebrate prey. Echidnas can be active day or night, probing along the ground slowly and deliberately as they search for prey, but they will shelter themselves from extreme midday heat in burrows or caves. Like their relative the platypus, echidnas have an unusually low but variable body temperature of 29–32 °C (84–90 °F) and cannot tolerate more extreme heat. In spite of echidnas’ outward resemblance to hedgehogs, the two animals are not related and belong to separate mammalian orders. Echidna species can be distinguished by their spines, by the number of claws on their feet, and by the shape and length of the beak.

Short-beaked echidna

The short-beaked echidna (Tachyglossus aculeatus) has a straight forward-pointing beak and a heavy coat of spines. It is fairly common in suitable habitats throughout Australia; it is also found in New Guinea, although little is known to science about its range and habits there. The short-beaked echidna is probably Australia’s most widely distributed native mammal, but it is common only where hollow logs, underbrush, and caves allow it to find shelter and ample food in the form of ants, termites, and other invertebrates. It catches prey whole with its long, sticky tongue, but it may break larger, soft-bodied victims into smaller pieces with its beak. It can open its tiny mouth only wide enough to allow its wormlike tongue to protrude.

The animal’s head-and-body length, including the rudimentary tail, is usually 30–45 cm (12–18 inches). Its body is covered with a combination of fur and spines (modified hairs). Echidnas from colder regions such as Tasmania have long fur that partially obscures the spines, whereas echidnas of arid zones can appear to be covered in spines to the exclusion of fur. Beneath the coat of spines is a well-developed subcutaneous muscle layer, which in part accounts for the animal’s surprising strength. This muscle layer allows the echidna to alter the contours of its stout body and thereby wedge itself into cracks and between tree roots. Echidnas are also able to dig themselves quickly into the ground when disturbed. In doing so, they appear to sink straight down into the soil, and, once dug in, they are well camouflaged by their spines. This combination of spines, strength, and strategy makes the short-beaked echidna difficult prey, and in fact it does enjoy a fairly predator-free existence—although dingos and nonnative foxes, as well as automobiles, are occasional hazards. High temperature is another hazard faced by short-beaked echidnas. They have few sweat glands and cannot pant to shed excess heat; thus, echidnas may die of heat stress if cool shelter is not found. If the temperature drops too low, torpor or hibernation results.

Long-beaked echidnas

The three living species of long-beaked echidnas (genus Zaglossus) are found only on the island of New Guinea, and they are usually described as being about 60 cm (24 inches) in length, although one individual was recorded at 100 cm (39 inches). Like the short-beaked echidna, these species are highly variable in their fur and spine cover. Generally, its spines are much shorter and less numerous than those of the short-beaked echidna, and the fur ranges from medium to dark brown. The beak is similarly used to probe leaf litter of the forest floor for food. The tongue, however, is shorter than that of the short-beaked echidna and is covered with backward-pointing barbs used to hook earthworms.

Long-beaked echidnas live at a wide range of elevations, generally in forested areas and only where human populations are low. The International Union for Conservation of Nature (IUCN) Red List of Threatened Species considers all three species to be critically endangered because of hunting (echidnas are edible) and loss of habitat.

Sir David’s long-beaked echidna (Z. attenboroughi), first described scientifically in 1999, is about the size of a short-beaked echidna. It is distinguished from other long-beaked echidnas by its smaller size and by a shorter, straighter beak, although in other respects it resembles the western long-beaked echidna (Z. bruijnii). The species inhabits a tiny pocket of highland forest near Jayapura, Papua, Indonesia. At present, there is too little known about Sir David’s long-beaked echidna to describe its habits in any detail.

The western long-beaked echidna, which inhabits the Indonesian province of West Papua, has a downward-pointing beak. Compared with short-beaked echidnas, it has smaller, fewer spines dispersed through its brown fur. Western long-beaked echidnas are nearly identical to eastern long-beaked echidnas (Z. bartoni); however, they are often larger and heavier. Large western long-beaked echidnas often approach 77.5 cm (about 31 inches) in length and weigh up to 16.5 kg (about 36 pounds). In contrast, the adult weight of the eastern long-beaked echidna ranges from 4.2 to 9.1 kg (about 9 to 20 pounds). The number of claws on each forefoot and hindfoot is also used to separate one species from the other. Although claw number has been shown to vary among individuals of the same species, western long-beaked echidnas tend to have three claws on each of their feet, whereas eastern long-beaked echidnas tend to have five.

Reproduction and life cycle

Echidnas appear to congregate only during the breeding season, when a female may be followed by a train of suitors. After a gestation period of about 23 days, the female usually lays a single leathery egg into a temporary pouch formed by abdominal muscles and subcutaneous mammary tissue. The egg is incubated for another 10 days before the tiny offspring hatches with the aid of an egg tooth and fleshy bulb (caruncle)—structural holdovers from the creature’s reptilian ancestry. The young echidna is protected in a special nursery burrow, where it drags milk from special mammary hairs (teats and nipples are absent). When the young echidna is fully covered by spines and fur and is capable of feeding, it leaves the burrow for a solitary life. Echidnas are very long-lived; one echidna was reliably recorded at 45 years of age in the wild, and one captive individual was well over 50 years old at the time of its death.

Classification, evolution, and paleontology

Echidnas constitute the family Tachyglossidae, and their only living relative is the platypus. Together these animals constitute the mammalian order Monotremata. Echidnas probably evolved from some unknown monotreme ancestor during the Paleogene Period (65.5 to 23 million years ago). Echidnas’ lack of teeth has hampered study of their evolutionary history, because teeth fossilize well and often help to determine relationships between mammals. The oldest known fossil echidna was recovered from an eastern Australian cave deposit from about 17 million years ago (during the early Miocene Epoch). Although the material is fragmentary, it suggests that basic echidna characteristics, such as the birdlike, toothless skull and robust skeleton specialized for digging, had evolved by this time. Echidnas appear to have once been widespread and diverse, and one especially large form measured more than 1 metre (3.3 feet) in length. Most fossil echidnas (genus Megalibgwilia) of recent epochs represent a type intermediate between today’s short- and long-beaked families.

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It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

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

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#1448 2022-07-22 14:02:43

ganesh
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Posts: 38,059

Re: Miscellany

1421) Decathlon

Summary

Decathlon is a composite contest that consists of the 100-meter, 400-meter, and 1500-meter runs, the 110-meter high hurdles, the javelin and discus throws, shot put, pole vault, high jump, and long jump

The decathlon is a combined event in athletics consisting of ten track and field events. The word "decathlon" was formed, in analogy to the word "pentathlon", from Greek (déka, meaning "ten") and (áthlos, áthlon, meaning "contest" or “prize”). Events are held over two consecutive days and the winners are determined by the combined performance in all. Performance is judged on a points system in each event, not by the position achieved. The decathlon is contested mainly by male athletes, while female athletes typically compete in the heptathlon.

Traditionally, the title of "World's Greatest Athlete" has been given to the person who wins the decathlon. This began when Gustav V of Sweden told Jim Thorpe, "Sir, you are the world's greatest athlete" after Thorpe won the decathlon at the Stockholm Olympics in 1912.

The event is similar to the pentathlon held at the ancient Greek Olympics, and also similar to a competition called an "all-around", which was contested at the United States amateur championships in 1884. Another all-around was held at the 1904 Summer Olympics. The modern decathlon first appeared at the 1912 Games.

The current official decathlon world record holder is Frenchman Kevin Mayer, who scored a total of 9,126 points at the 2018 Décastar in France.

Historical background

The decathlon developed from the ancient pentathlon competitions held at the ancient Greek Olympics. Pentathlons involved five disciplines – long jump, discus throw, javelin throw, sprint and a wrestling match. Introduced in Olympia during 708 BC, this competition was extremely popular for many centuries.

A ten-event competition known as the "all-around" or "all-round" championship, similar to the modern decathlon, was first contested at the United States amateur championships in 1884 and reached a consistent form by 1890. While an all-around event was held at the 1904 Summer Olympics, whether it was an official Olympic event has been disputed.

The modern decathlon first appeared on the Olympic athletics program at the 1912 Games in Stockholm.

Details

Decathlon is an athletic competition lasting two consecutive days in which contestants take part in 10 track-and-field events. It was introduced as a three-day event at the Olympic Games in 1912. Decathlon events are: (first day) 100-metre dash, running long (broad) jump, shot put, high jump, and 400-metre run; (second day) 110-metre hurdles, discus throw, pole vault, javelin throw, and 1,500-metre run. Competitors are scored for their performance in each event according to a table established by the International Association of Athletics Federations (IAAF).

The table has been changed periodically to keep pace with improvements in world records. The first one was used from 1912 to 1936, while the decathlon was still a three-day event; a second from 1936 to 1950 (with minor revisions in 1952); and a third from 1952 to 1964. All emphasized excellent performances in the individual events. A fourth table in use from 1964 to 1985 and a fifth introduced in 1985 favoured the athlete who could score evenly in all 10 events.

The American athlete Jim Thorpe was the first Olympic decathlon champion. Akilles Järvinen of Finland, James Bausch of the United States, and Hans Sievert of Germany were leading competitors under the first table, with Sievert setting the final record of 8,790.46 points in 1934.

Glenn Morris of the United States, with a world record of 7,900 points in 1936, and Bob Mathias of the United States, with two Olympic titles and a record of 8,042 points in 1950, excelled under the second table. Mathias also set the first record of 7,887 under the third table in 1952, but this was later broken several times, by Rafer Johnson of the United States, Vasily Kuznetsov of the Soviet Union, and Yang Chuan-kwang of Taiwan, who set the final record of 9,121 points in 1963.

Outstanding performers under the fourth table included Bruce Jenner of the United States and Daley Thompson of Great Britain. Dan O’Brien of the United States and Tomàs Dvoràk of the Czech Republic were among the athletes who excelled under the fifth table.

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It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

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

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#1449 2022-07-23 14:24:51

ganesh
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Registered: 2005-06-28
Posts: 38,059

Re: Miscellany

1422) Discus Throw

Summary

The discus throw, also known as disc throw, is a track and field event in which an athlete throws a heavy disc—called a discus—in an attempt to mark a farther distance than their competitors. It is an ancient sport, as demonstrated by the fifth-century-BC Myron statue Discobolus. Although not part of the modern pentathlon, it was one of the events of the ancient Greek pentathlon, which can be dated back to at least 708 BC, and it is part of the modern decathlon.

Details

Discus throw is a sport in athletics (track and field) in which a disk-shaped object, known as a discus, is thrown for distance. In modern competition the discus must be thrown from a circle 2.5 metres (8.2 feet) in diameter and fall within a 40° sector marked on the ground from the centre of the circle.

The sport was known in the days of the Greek poet Homer, who mentions it in both the Iliad and the Odyssey, and it was one of five events included in the pentathlon in the ancient Olympic Games. Throwing the discus was introduced as an event in modern athletics when the Olympic Games were revived at Athens in 1896.

Early modern athletes threw the discus from an inclined pedestal, using an exaggerated style derived from ancient representations of the sport. Throwing from a 2.13-metre (7-foot) circle on the ground superseded this, and the circle was enlarged to its present size in 1912.

The modern throwing style is a graceful whirling movement, with the athlete making about one and a half quick turns while accelerating across the circle. Thus, the discus is slung out and not really thrown at all; the difficulty lies in controlling the discus, which is held under and against the hand and wrist chiefly by centrifugal force.

The modern discus used in men’s competition is circular, about 219 mm (8.6 inches) in diameter and 44 mm (1.75 inches) thick at its centre. It is made of wood or similar material, with a smooth metal rim and small, circular brass plates set flush into its sides. Its weight must be not less than 2 kg (4.4 pounds).

A discus event was included when women’s track and field was added to the Olympic program in 1928. A slightly smaller discus weighing 1 kg (2 pounds 3.2 ounces) and 180 mm (7.1 inches) is used in women’s events.

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It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

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

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#1450 2022-07-24 14:11:33

ganesh
Administrator
Registered: 2005-06-28
Posts: 38,059

Re: Miscellany

1423) Javelin throw

The javelin throw is a track and field event where the javelin, a spear about 2.5 m (8 ft 2 in) in length, is thrown. The javelin thrower gains momentum by running within a predetermined area. Javelin throwing is an event of both the men's decathlon and the women's heptathlon.

Rules and competitions

The size, shape, minimum weight, and center of gravity of the javelin are all defined by IAAF rules. In international competition, men throw a javelin between 2.6 and 2.7 m (8 ft 6 in and 8 ft 10 in) in length and 800 g (28 oz) in weight, and women throw a javelin between 2.2 and 2.3 m (7 ft 3 in and 7 ft 7 in) in length and 600 g (21 oz) in weight. The javelin has a grip, about 150 mm (5.9 in) wide, made of cord and located at the javelin's center of gravity (0.9 to 1.06 m (2 ft 11 in to 3 ft 6 in)) from the javelin tip for the men's javelin and 0.8 to 0.92 m (2 ft 7 in to 3 ft 0 in) from the javelin tip for the women's javelin.

Unlike the other throwing events (shot put, discus, and hammer), the technique used to throw the javelin is dictated by IAAF rules and "non-orthodox" techniques are not permitted. The javelin must be held at its grip and thrown overhand, over the athlete's shoulder or upper arm. Further, the athlete is prohibited from turning completely around or starting with their back facing the direction of the throw. This prevents athletes from attempting to spin and hurl the javelin sidearm in the style of a discus throw. This rule was put in place when a group of athletes began experimenting with a spin technique referred to as "free style". On 24 October 1956, Pentti Saarikoski threw 99.52 m (326 ft 6 in) using the technique holding the end of the javelin. Officials were so afraid of the out of control nature of the technique that the practice was banned through these rule specifications.

Instead of being confined to a circle, javelin throwers have a runway 4 m (13 ft) wide and at least 30 m (98 ft) in length, ending in an 8 m (26 ft) radius throwing arc from which their throw is measured; athletes typically use this distance to gain momentum in a "run-up" to their throw. Like the other throwing events, the competitor may not leave the throwing area (the runway) until after the implement lands. The need to come to a stop behind the throwing arc limits both how close the athlete can come to the line before the release as well as the maximum speed achieved at the time of release.

The javelin is thrown towards a 28.96º circular sector that is centered on the center point of the throwing arc. The angle of the throwing sector (28.96º) provides sector boundaries that are easy to construct and lay out on a field. A throw is only legal if the tip of the javelin lands within this sector and first strikes the ground with its tip before any other part. The distance of the throw is measured from the throwing arc to the point where the tip of the javelin landed, rounded down to the nearest centimeter.

Competition rules are similar to other throwing events: a round consists of one attempt by each competitor in turn, and competitions typically consist of three to six rounds. The competitor with the longest single legal throw (over all rounds) is the winner; in case of a tie, the competitors' second-longest throws are also considered. Competitions involving large numbers of athletes sometimes use a cut whereby all competitors compete in the first three rounds but only those who are currently among the top eight or have achieved some minimum distances are permitted to attempt to improve on their distance in additional rounds (typically three).

Javelin redesigns

On 1 April 1986, the men's javelin (800 grams (1.76 lb)) was redesigned by the governing body (the IAAF Technical Committee). They decided to change the rules for javelin design because of the increasingly frequent flat landings and the resulting discussions and protests when these attempts were declared valid or invalid by competition judges. The world record had also crept up to a potentially dangerous level, 104.80 m (343.8 ft) by Uwe Hohn. With throws exceeding 100 meters, it was becoming difficult to safely stage the competition within the confines of a stadium infield. The javelin was redesigned so that the centre of gravity was moved 4 cm (1.6 in) forward. In addition, the surface area in front of centre of gravity was reduced, while the surface area behind the centre of gravity was increased. This had an effect similar to that produced by the feathers on an arrow. The javelin turns into the relative wind. This relative wind appears to originate from the ground as the javelin descends, thus the javelin turns to face the ground. As the javelin turns into the wind less lift is generated, reducing the flight distance by around 10% but also causing the javelin to stick in the ground more consistently. In 1999, the women's javelin (600 grams (1.32 lb)) was similarly redesigned.

Modifications that manufacturers made to recover some of the lost distance, by increasing tail drag (using holes, rough paint or dimples), were forbidden at the end of 1991 and marks made using implements with such modifications removed from the record books. Seppo Räty had achieved a world record of 96.96 m (318.1 ft) in 1991 with such a design, but this record was nullified.

Technique and training

Unlike other throwing events, javelin allows the competitor to build speed over a considerable distance. In addition, the core and upper body strength is necessary to deliver the implement, javelin throwers benefit from the agility and athleticism typically associated with running and jumping events. Thus, the athletes share more physical characteristics with sprinters than with others, although they still need the skill of heavier throwing athletes.

Traditional free-weight training is often used by javelin throwers. Metal-rod exercises and resistance band exercises can be used to train a similar action to the javelin throw to increase power and intensity. Without proper strength and flexibility, throwers can become extremely injury prone, especially in the shoulder and elbow. Core stability can help in the transference of physical power and force from the ground through the body to the javelin. Stretching and sprint training are used to enhance the speed of the athlete at the point of release, and subsequently, the speed of the javelin. At release, a javelin can reach speeds approaching 113 km/h (70 mph).

The javelin throw consists of three separate phases: the run-up, the transition, and the delivery. During each phase, the position of the javelin changes while the thrower changes his or her muscle recruitment. In the run-up phase as Luann Voza states, "your arm is bent and kept close to your head, keeping the javelin in alignment with little to no arm movement". This allows the thrower's bicep to contract, flexing the elbow. In order for the javelin to stay up high, the thrower's deltoid flexes. In the transition phase, the thrower's "back muscles contract" as "the javelin is brought back in alignment with the shoulder with the thrower's palm up". This, according to Voza, "stretches your pectoral, or chest, muscles. From there, a stretch reflex, an involuntary contraction of your chest, helps bring your throwing arm forward with increased force". During the final phase, the rotation of the shoulders initiates the release, which then "transfers movement through the triceps muscles, wrists and fingers to extend the throwing arm forward to release the javelin".

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It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

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

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