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#451 2019-07-10 00:34:42

ganesh
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Registered: 2005-06-28
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Re: Miscellany

371) Tiger

Tigers: The Largest Cats in the World

Tigers are iconic creatures, and the largest felines in the world.

Tigers are the largest felines in the world and as such, many cultures consider the tiger to be a symbol of strength, courage and dignity. The tiger is one of the twelve Chinese zodiac animals, and those born in the "Year of the Tiger" are thought to be brave, competitive and self-confident.

However, because hunting them is also a sign of bravery in some cultures, tigers are endangered. Tigers are hunted for their meat, pelt and body parts that are used in folk remedies. To make matters worse, these great cats have lost most of their habitat due to logging, road building and development, according to All About Wildlife. Experts estimate there are no more than 3,200 tigers left in the wild.

Do all tigers have stripes?

Most tigers have the characteristic orange fur with black or brown stripes, but these markings vary between subspecies. For example, the very large Siberian tiger has pale orange fur with few stripes, while the smaller Sumatran tigers in the Sunda Islands have dark, thickly striped fur.

No two tigers have the same markings, and their stripes are as individual as fingerprints are for humans. In the wild, a tiger's stripes are important for survival, as they act as camouflage, appearing as moving shadows in long grass and in trees, according to National Geographic.

The white Bengal tigers seen in some zoos are the result of a recessive gene, and are not albinos. In fact, it's unlikely that true albino tigers (with pink eyes) exist. Some historical reports detail tigers with black fur and tan stripes, caused by excessive pigmentation, but these accounts are extremely rare.

On the backs of each ear, tigers have a white spot of fur, called ocelli, according to Tigers.org. It's likely the spots act as fake eyes and they may also help tigers communicate with one another.

A tiger's hind legs are longer than its front legs, allowing it to jump up to 32.5 feet (10 meters), according to Sea World. Tiger claws are up to 4 inches (10 centimeters) long, and are used to grab and hold onto their prey.

The largest tiger subspecies, the Siberian, also called Amur, are 10.75 feet (3.3 m) long and weigh up to 660 pounds (300 kilograms), according to National Geographic. The smallest tiger is the Sumatran, which weighs 165 - 308 pounds (74 - 139 kg), according to the World Wildlife Fund(WWF). Tigers also have very long tails, which can add around 3 feet (one m) to their overall length, according to Sea World.

Adorable Tiger Cubs Aren't So Great at Walking

Where tigers live and what they eat

Wild tigers live in Asia. Larger subspecies, such as the Siberian tiger, tend to live in northern, colder areas, such as eastern Russia and northeastern China. Smaller subspecies live in southern, warmer countries, such as India, Bangladesh, Nepal, Bhutan, Myanmar, Laos, Cambodia, Vietnam, Malaysia and Indonesia.
Depending on the subspecies, tigers live in a variety of environments, including arid forests, flooded mangrove forests, tropical forests and taiga (a cold forest with coniferous trees), according to the San Diego Zoo.

All tigers are carnivores. Most of a tiger's diet consists of large prey, such as pigs, deer, rhinos or elephant calves. To kill their prey, tigers clamp down on the animal's neck with their jaws and suffocate the animal. The tiger's canine teeth have pressure-sensing nerves, so it knows exactly where to deliver a fatal bite to its prey, according to the WWF. Though tigers are fierce hunters, they are no strangers to failure, as they are successful in only 10% of their hunts, according to National Geographic.

The tiger life

Tigers are solitary creatures; they like to spend most of their time alone, roaming their massive territories looking for food. According to the San Diego Zoo, the Siberian tiger has the largest range; its territory spans more than 4,000 square miles (10,000 square km). Tigers mark their territory by spraying a mix of urine and scent gland secretions onto trees and rocks. They also scratch marks into trees with their claws.

Tiger babies are born helpless. At birth, a cub weighs 2.2 pounds (1 kg), and a female may have as many as seven cubs at a time, according to the San Diego Zoo. Around half of all cubs don't live beyond the age of two, according to WWF. The mother must leave the cubs while she hunts, leaving them open to other predators. Most tiger mothers are unable to kill enough prey to feed a large litter, so some cubs may die of starvation.

At just 8 weeks old, tiger cubs are ready to learn how to hunt and go out on hunting expeditions with their mother. At 2 years old, the cubs will set out on their own, and their mother will be ready for another set of cubs. In the wild, tigers typically live 10 to 15 years, according to Smithsonian's National Zoo.

Classification/taxonomy

For many years, scientists classified tigers into nine subspecies: six living subspecies and three extinct ones. But in recent years, some researchers have challenged the traditional classification. A 2015 study published in the journal Science Advances argued that there are only two subspecies of tigers.

However, a study published in the journal Current Biology in 2018 presented genomic evidence supporting six genetically distinct subspecies of tigers:the Bengal tiger (Panthera tigris tigris), the Amur tiger (P.t. altaica), the South China tiger (P.t. amoyensis), the Sumatran tiger (P.t. sumatrae), the Indochinese tiger (P.t. corbetti), and the Malayan tiger (P.t. jacksoni).

The Javan tiger was last recorded in the 1970s, the Caspian tiger was lost in the 1950s, and the Bali tiger became extinct in the 1930s, according to Panthera, a wild-cat conservation organization.

Conservation status

There are more tigers in captivity than there are in the wild. According to the WWF, there are about 5,000 captive tigers in the United States alone, but there are fewer than 3,200 tigers in the wild.

The International Union for the Conservation of Nature's (IUCN's) Red List of Threatened Species categorizes the Amur/Siberian, Indochinese and Bengal tigers as endangered, and the Sumatran, Malayan and South ChinaTigers as critically endangered. Most remaining tigers live on wildlife refuges to protect them from poachers.

Poaching is by far the biggest threat facing tigers today. Illegal demand for tiger bones (used in tonics and medicines), tiger skin (seen as a status symbol) and other body parts, is driving the killing and trafficking, which has had an overwhelming impact on tiger populations and resulted in localized extinctions, according to Save Wild Tigers. The continued demand for tiger parts is pushing the species closer and closer to extinction.

In addition to the threat of poaching, only 7% of the tiger's original range remains due to human agriculture, logging, settlements and roads.

large-Tiger-photo.jpg


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

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

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#452 2019-07-11 15:50:44

Monox D. I-Fly
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From: Indonesia
Registered: 2015-12-02
Posts: 1,759

Re: Miscellany

ganesh wrote:

For many years, scientists classified tigers into nine subspecies: six living subspecies and three extinct ones.

Saber-toothed tiger, Smilodon, and...?


Actually I never watch Star Wars and not interested in it anyway, but I choose a Yoda card as my avatar in honor of our great friend bobbym who has passed away. May his adventurous soul rest in peace at heaven.

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#453 2019-07-11 16:08:36

ganesh
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Registered: 2005-06-28
Posts: 28,716

Re: Miscellany

Monox D. I-Fly wrote:
ganesh wrote:

For many years, scientists classified tigers into nine subspecies: six living subspecies and three extinct ones.

Saber-toothed tiger, Smilodon, and...?

I think they were : The Bali Tiger (Panthera tigris balica), The Caspian Tiger (Panthera tigris virgata), and The Javan Tiger (Panthera tigris sondaica).


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

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

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#454 2019-07-12 19:01:50

Monox D. I-Fly
Member
From: Indonesia
Registered: 2015-12-02
Posts: 1,759

Re: Miscellany

ganesh wrote:
Monox D. I-Fly wrote:
ganesh wrote:

For many years, scientists classified tigers into nine subspecies: six living subspecies and three extinct ones.

Saber-toothed tiger, Smilodon, and...?

I think they were : The Bali Tiger (Panthera tigris balica), The Caspian Tiger (Panthera tigris virgata), and The Javan Tiger (Panthera tigris sondaica).

I... forgot that "extinct" doesn't always mean "prehistoric". Silly me.


Actually I never watch Star Wars and not interested in it anyway, but I choose a Yoda card as my avatar in honor of our great friend bobbym who has passed away. May his adventurous soul rest in peace at heaven.

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#455 2019-07-13 00:16:59

ganesh
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Registered: 2005-06-28
Posts: 28,716

Re: Miscellany

372) Death Valley

Death Valley, structural depression primarily in Inyo county, southeastern California, U.S. It is the lowest, hottest, and driest portion of the North American continent. Death Valley is about 140 miles (225 km) long, trends roughly north-south, and is from 5 to 15 miles (8 to 24 km) wide. The valley is bounded on the west by the Panamint Range and on the east by the Black, Funeral, and Grapevine mountains of the Amargosa Range. It lies near the undefined border between the Great Basin and the Mojave Desert.

Geologically, Death Valley forms part of the southwestern portion of the Great Basin. It is similar to other structural basins of the region but is unique in its depth. Portions of the great salt pan that forms part of the floor of the valley are the lowest land areas of the Americas. About 550 square miles (1,425 square km) of the valley’s floor lie below sea level. A point in Badwater Basin, lying 282 feet (86 metres) below sea level, is the lowest area in North America. Less than 20 miles (30 km) west is the 11,049-foot (3,368-metre) Telescope Peak, the area’s highest point. Death Valley was an obstacle to movements of pioneer settlers (whence its name was derived) and later was a centre of borax exploitation; its extreme environment now attracts tourists and scientists.

Physical Environment

For a short time after its christening in 1849 by a hapless party of emigrants who endured intense suffering while crossing it, Death Valley was little known except to Native Americans (primarily Shoshone) of the area and to prospectors searching the surrounding mountains. The first scientific notice of the valley seems to have been a brief mention published in 1868 by a California state geologist. The area remained seldom visited until the 1870s, when gold and silver were discovered in the surrounding mountains, and 1880s, when boraxdeposits were found in the valley. Borax production, notably at the Harmony Borax Works (1883–88), gave rise to the famous 20-mule team wagons, which hauled the product to Mojave, California. Several ghost towns are located around the valley, and some still contain ruined buildings. They sprang up from the late 19th to the early 20th century following gold, copper, and silver strikes in the area. Deserted when the mines were depleted, each existed for only a few years. For example, Rhyolite, founded in 1904, was a gold-mining boomtown of 10,000 people with its own stock exchange, electric plant, and opera; in 1911 the main mine was closed, and the town was deserted by 1916.

The geologic history of Death Valley is extremely complex and involves different types of fault activity at various periods, in addition to crustal sinking and even some volcanic activity. Essentially, Death Valley is a graben, or rift valley, formed by the sinking of a tremendous expanse of rock lying between parallel uplifted, tilted-block mountain ranges to the east and west. A type of fault activity called block faulting, in which the movement is predominantly vertical, began to form the valley about 30 million years ago. As crustal blocks sank, they formed the great trough of the valley, and other blocks were uplifted to gradually form the adjacent mountain ranges. As the valley sank, it was filled by sediments that were eroded from the surrounding hills; in the central part of the valley the bedrock floor is buried beneath as much as 9,000 feet (2,745 metres) of sediment. The valley floor has continued to tilt and sink.

The floor of Death Valley is noted for its extremes of temperature and aridity. A record world and North American high shaded air temperature of 134 °F (57 °C) was recorded in 1913, and summer temperatures often exceed 120 °F (49 °C). The hottest summer on record in the valley (1996) saw temperatures top 120 °F on 40 days. Ground temperatures as high as 201 °F (94 °C) have been reported. The high temperatures and low humidity contribute to an exceptionally high evaporation rate.
Winter minimum temperatures rarely fall to the freezing point; the record lowest temperature was 15 °F (−9 °C). Most rainfall is blocked by the mountains to the west, so the valley is extremely arid. In a 50-year period in the 20th century, the average annual rainfall at Furnace Creek was only 1.66 inches (42.2 mm), the maximum annual rainfall was 4.5 inches (114.3 mm), and two years passed with no measurable rainfall.

Most of the surface water in Death Valley is in the saline ponds and marshes around the salt pan. The Amargosa River brings some water into the southern end of the valley from desert areas to the east, but most of its flow is underground. Salt Creek, draining the northern arm of the valley, also has only short stretches of perennial surface flow.

At times in the past, much more water reached Death Valley. During the Wisconsin Glacial Stage of the Pleistocene Epoch, perhaps about 50,000 years ago, a body of water (Lake Manly) filled the valley to a depth of as much as 600 feet (180 metres). More recently, some 2,000 to 5,000 years ago, a shallow lake occupied the floor of the valley, its evaporation producing the present salt pan.

Plant And Animal Life

Lack of water makes Death Valley a desert, but it is by no means devoid of life. Plant life above the microscopic level is absent from the salt pan, but salt-tolerant pickleweed, salt grass, and rushes grow around the springs and marshes at its edges. Introduced tamarisks provide shade around some of the springs and in the inhabited areas at Furnace Creek, but, because they crowd out native vegetation, eradication efforts are ongoing. Mesquite flourishes where less-saline water is available. Creosote bush dominates the gravel fan surfaces around most of the valley, giving way to desert holly at the lowest elevations. Cactus is rare in the lowest part of the valley but abundant on the fans farther north. Higher elevations support juniper and piñon pine. Spring rains bring out a great variety of desert wildflowers.

Animal life is varied, although nocturnal habits conceal many of the animals from visitors to the valley. Rabbits and several types of rodents, including antelope ground squirrels, kangaroo rats, and desert wood rats, are present and are the prey of coyotes, kit foxes, and bobcats. The largest native mammal in the area, and perhaps the best-studied member of the fauna, is the desert bighorn. Small herds of these sheep are most commonly found in the mountains surrounding Death Valley, but they occasionally visit the valley floor. Wild burros, descendants of animals lost or abandoned by prospectors and miners, became so numerous as to threaten, through overgrazing, the natural vegetation on which other animals depend. Burro removal began in the 1960s, and live-capture efforts were subsequently attempted in hopes of eliminating the population.

Though it may seem that the only birds present are the raucous and numerous ravens, the first biological survey of the valley, in the 1890s, reported 78 species of birds. More than three times that number are now known to inhabit or visit the area, the roadrunner being a particularly well-known resident. Lizards, snakes (including rattlesnakes such as sidewinders), and scorpions are common. Even native fish are to be found in Death Valley. Several species of pupfish of the genus Cyprinodon live in Salt Creek and other permanent bodies of water; the highly endangered Devils Hole pupfish (C. diabolis) lives in a single desert pool.

Death Valley National Park

Death Valley National Park covers some 5,270 square miles (13,650 square km) of the valley, primarily in California. Much of the park’s northeastern border is the Nevada state line, but a small portion extends into Nevada’s Bullfrog Hills. Inyo National Forest and the Inyo Mountains border it to the west, the Panamint Valley and the Slate Range lie to the southwest, and the U.S. Army’s Fort Irwin and the National Training Center adjoin it to the south. The Amargosa River and the Greenwater Range constitute parts of the southeastern border. Death Valley was originally designated a national monument in 1933 and made a national park in 1994. Today’s national park covers considerably more area than the original national monument. The national monument was expanded several times, including in 1937 and in 1952, when Devils Hole, located in Nevada’s Ash Meadows National Wildlife Refuge, was added. In 1994 the California Desert Protection Act added more than 2,000 square miles (5,100 square km) and redesignated it a national park, the largest in the 48 conterminous U.S. states.

The park contains a number of unique landforms. The five dune areas include the 680-foot- (205-metre-) high Eureka Sand Dunes, California’s tallest. The northern section of the park is dotted with volcanic craters such as Ubehebe Crater, 700 feet (215 metres) deep and 0.5 mile (0.8 km) wide. At Racetrack Playa, rocks as large as 700 pounds (320 kg) leave trails as they mysteriously slide across a flat area; they are probably blown by wind when precipitationcreates a moist, slippery clay surface. Other attractions include Scotty’s Castle, a mansion built in the 1920s by Chicago businessman Albert Johnson and named for his prospector friend Walter Scott, a spinner of tall tales known as “Death Valley Scotty.” Artist’s Drive is an 8-mile (13-km) loop through colourful mountains and canyons. Jagged pinnacles of salt form on the salt pan at Devil’s Golf Course. The main visitor centre is at Furnace Creek in the central part of the park and includes exhibits on history, geology, and nature; a second visitor centre is at Beatty, Nevada, outside the park’s eastern boundary. Nearby attractions include Kings Canyon and Sequoia national parks, Manzanar National Historic Site, and Mojave National Preserve.

featuredeathvalley.jpg

Last edited by ganesh (2019-07-23 23:28:19)


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

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

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#456 2019-07-15 00:53:13

ganesh
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Posts: 28,716

Re: Miscellany

373) Snake gourd

Snake gourd, (Trichosanthes cucumerina), also called serpent gourd, rapid-growing vine of the gourd family (Cucurbitaceae), cultivated for its oddly shaped edible fruits. The snake gourd is native to southeastern Asia and Australia and is also grown in parts of tropical Africa. The whole fruit is eaten as a vegetable when young and can be dried and used as a soap. The leaves and shoots are also edible, and the pulp of mature fruits is sometimes eaten as a tomato substitute.

The snake gourd is an annual plant with forked tendrils and kidney- or heart-shaped leaves that are sometimes palmately lobed. The white unisexual flowers have long lacy fringes on the five petals and open at night. The narrow fruits often reach 1.5 metres (5 feet) in length; they are green with white stripes when young, becoming a red-orange colour when mature.

The important health benefits of snake gourd include its ability to reduce fever, detoxify the body, improve digestion, increase hydration, strengthen the immune system, manages diabetes, improve strength and quality of the hair, and aid in weight loss.

What is Snake Gourd?

Snake gourd is a vine plant that climbs up a tree and then unfurls its flowers and fruits to hang down to the ground. Some of the largest specimens can grow up to five feet in length, which is why this gourd is often used to make the traditional Australian musical instrument, the didgeridoo. This plant is native to Southeast Asia, including Myanmar, India, Indonesia, Sri Lanka, and other neighboring countries, as well as some parts of Australia and Africa. It may not be a type of vegetable that is well-known around the world, but certain cultures have been utilizing this unique food variety for hundreds, and perhaps thousands, of years.

The taste is bitter, but this often disappears when cooking, although once the vegetable is ripe, the bitterness is more difficult to eliminate. The leaves, tendrils, and other leafy parts of the plant are often used as vegetable greens, while the fleshy meat often replaces tomatoes in terms of culinary applications.

It is strange in appearance, name, and taste, but its health benefits cannot be denied. Let’s take a closer look at what specifically makes snake gourd such an important dietary staple in so many cultures around the world.

Snake Gourd Nutrition Facts

Snake gourd contains a rich variety of nutrients, vitamins, and minerals that are essential for human health, including significant levels of dietary fiber, a small number of calories, and high levels of protein.  In terms of vitamins, it possesses vitamin A, B, C, as well as manganese, magnesium, calcium, iron, potassium, and iodine.

Health Benefits of Snake Gourd

Health benefits of snake gourd include the following:

Reduces Fever

In many tropical countries, fever can be a major danger to public health, regardless of its cause. Snake gourd can be turned into a decoction and given to people suffering from fever.  Overnight, fevers tend to break and the natural healing process can begin.

Detoxifies the Body

Snake gourd has been used as a diuretic in traditional medicine for many years, as it stimulates the liver and increases urination, thereby speeding up the elimination of toxins from the body.  It increases the creation of bodily fluids, which can eliminate dryness and dehydration, and help in the normal functioning of the kidneys and bladder. Juice from the leaves can also stimulate vomiting in case something toxic has been consumed.

Treats Digestive Issues

Children with bowel problems have been given snake gourd to ease their discomfort, as it acts as a mild laxative. Furthermore, the high fibercontent of snake gourd can help anyone with bowel disorders and can eliminate constipation, reduce cramping and bloating, and optimize the nutrient absorption process in the body.

Improves Respiratory System

Snake gourd functions as an expectorant, loosening pus and phlegm in the sinuses and respiratory tracts so that they can be eliminated.  This further benefits the immune system, as toxins and other foreign agents often get caught in phlegm and mucus to cause more serious conditions.

Hair Care

For people suffering from alopecia, snake gourd is said to stimulate the growth of new hair and protect weakening follicles from hair loss.  This can be attributed to its rich mineral and vitamin content, particularly its high level of carotenes, which specifically care for the skin and hair. It is also claimed that snake gourd can reduce the frequency and intensity of dandruff.

Boosts Immune System

Some research has shown snake gourd to have antibiotic properties, and when combined with the levels of antioxidant carotenes and vitamin C found in the vegetable, this helpful gourd can significantly boost overall health.  The specifics of what conditions the antibiotic effects are most useful for is still a subject of research.

Manages Diabetes

The low-calorie, high-nutrient composition of snake gourd makes it a favorite anti-diabetic food source, and can also lessen the effects if the condition already exists.  Obesity is one of the major signals of oncoming diabetes, and snake gourd functions as a great dietary option due to its effect of making you feel sated and satisfied without adding many excess calories.

Relieves Stress

In traditional medicine, snake gourd was often utilized to reduce heart palpitations and ease the nervous system to induce lower blood pressure.  This is likely due to the presence of potassium in the vegetable, which acts as a vasodilator and reduces stress on the cardiovascular system.

snake-gourd-serpent-gourd-5.gif


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

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

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#457 2019-07-16 14:40:30

Monox D. I-Fly
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From: Indonesia
Registered: 2015-12-02
Posts: 1,759

Re: Miscellany

ganesh wrote:

This plant is native to Southeast Asia, including Myanmar, India, Indonesia, Sri Lanka, and other neighboring countries, as well as some parts of Australia and Africa.

Yes, this plant is often used for ornaments at city parks in my country (and maybe your country as well, assuming you are from India). It's beautiful and relaxing when you're under it, until one day I looked up to the leaves and noticed a hanging spherical web containing multiple wiggling maggots. It gave me goosebumps and made me immediately left.


Actually I never watch Star Wars and not interested in it anyway, but I choose a Yoda card as my avatar in honor of our great friend bobbym who has passed away. May his adventurous soul rest in peace at heaven.

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#458 2019-07-16 16:11:46

ganesh
Administrator
Registered: 2005-06-28
Posts: 28,716

Re: Miscellany

Monox D. I-Fly wrote:
ganesh wrote:

This plant is native to Southeast Asia, including Myanmar, India, Indonesia, Sri Lanka, and other neighboring countries, as well as some parts of Australia and Africa.

Yes, this plant is often used for ornaments at city parks in my country (and maybe your country as well, assuming you are from India). It's beautiful and relaxing when you're under it, until one day I looked up to the leaves and noticed a hanging spherical web containing multiple wiggling maggots. It gave me goosebumps and made me immediately left.

Oh.....


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

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

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#459 2019-07-17 00:26:42

ganesh
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Registered: 2005-06-28
Posts: 28,716

Re: Miscellany

374) Solar energy

Solar energy, radiation from the Sun capable of producing heat, causing chemical reactions, or generating electricity. The total amount of solar energy incident on Earth is vastly in excess of the world’s current and anticipated energy requirements. If suitably harnessed, this highly diffused source has the potential to satisfy all future energy needs. In the 21st century solar energy is expected to become increasingly attractive as a renewable energy source because of its inexhaustible supply and its nonpolluting character, in stark contrast to the finite fossil fuels coal, petroleum, and natural gas.

The Sun is an extremely powerful energy source, and sunlight is by far the largest source of energy received by Earth, but its intensity at Earth’s surface is actually quite low. This is essentially because of the enormous radial spreading of radiation from the distant Sun. A relatively minor additional loss is due to Earth’s atmosphere and clouds, which absorb or scatter as much as 54 percent of the incoming sunlight. The sunlight that reaches the ground consists of nearly 50 percent visible light, 45 percent infrared radiation, and smaller amounts of ultraviolet and other forms of electromagnetic radiation.

Uses Of Solar Energy

The potential for solar energy is enormous, since about 200,000 times the world’s total daily electric-generating capacity is received by Earth every day in the form of solar energy. Unfortunately, though solar energy itself is free, the high cost of its collection, conversion, and storage still limits its exploitation in many places. Solar radiation can be converted either into thermal energy (heat) or into electrical energy, though the former is easier to accomplish.

Thermal energy

Among the most common devices used to capture solar energy and convert it to thermal energy are flat-plate collectors, which are used for solar heatingapplications. Because the intensity of solar radiation at Earth’s surface is so low, these collectors must be large in area. Even in sunny parts of the world’s temperate regions, for instance, a collector must have a surface area of about 40 square metres (430 square feet) to gather enough energy to serve the energy needs of one person.

The most widely used flat-plate collectors consist of a blackened metal plate, covered with one or two sheets of glass, that is heated by the sunlight falling on it. This heat is then transferred to air or water, called carrier fluids, that flow past the back of the plate. The heat may be used directly, or it may be transferred to another medium for storage. Flat-plate collectors are commonly used for solar water heaters and house heating. The storage of heat for use at night or on cloudy days is commonly accomplished by using insulated tanks to store the water heated during sunny periods. Such a system can supply a home with hot water drawn from the storage tank, or, with the warmed water flowing through tubes in floors and ceilings, it can provide space heating. Flat-plate collectors typically heat carrier fluids to temperatures ranging from 66 to 93 °C (150 to 200 °F). The efficiency of such collectors (i.e., the proportion of the energy received that they convert into usable energy) ranges from 20 to 80 percent, depending on the design of the collector.

Another method of thermal energy conversion is found in solar ponds, which are bodies of salt water designed to collect and store solar energy. The heat extracted from such ponds enables the production of chemicals, food, textiles, and other industrial products and can also be used to warm greenhouses, swimming pools, and livestock buildings. Solar ponds are sometimes used to produce electricity through the use of the organic Rankine cycle engine, a relatively efficient and economical means of solar energy conversion, which is especially useful in remote locations. Solar ponds are fairly expensive to install and maintain and are generally limited to warm rural areas.

On a smaller scale, the Sun’s energy can also be harnessed to cook food in specially designed solar ovens. Solar ovens typically concentrate sunlight from over a wide area to a central point, where a black-surfaced vessel converts the sunlight into heat. The ovens are typically portable and require no other fuel inputs.

Electricity generation

Solar radiation may be converted directly into electricity by solar cells(photovoltaic cells). In such cells, a small electric voltage is generated when light strikes the junction between a metal and a semiconductor (such as silicon) or the junction between two different semiconductors. The power generated by a single photovoltaic cell is typically only about two watts. By connecting large numbers of individual cells together, however, as in solar-panel arrays, hundreds or even thousands of kilowatts of electric power can be generated in a solar electric plant or in a large household array. The energy efficiency of most present-day photovoltaic cells is only about 15 to 20 percent, and, since the intensity of solar radiation is low to begin with, large and costly assemblies of such cells are required to produce even moderate amounts of power.

Small photovoltaic cells that operate on sunlight or artificial light have found major use in low-power applications—as power sources for calculators and watches, for example. Larger units have been used to provide power for water pumps and communications systems in remote areas and for weather and communications satellites. Classic crystalline silicon panels and emerging technologies using thin-film solar cells, including building-integrated photovoltaics, can be installed by homeowners and businesses on their rooftops to replace or augment the conventional electric supply.

Concentrated solar power plants employ concentrating, or focusing, collectors to concentrate sunlight received from a wide area onto a small blackened receiver, thereby considerably increasing the light’s intensity in order to produce high temperatures. The arrays of carefully aligned mirrors or lenses can focus enough sunlight to heat a target to temperatures of 2,000 °C (3,600 °F) or more. This heat can then be used to operate a boiler, which in turn generates steam for a steam turbine electric generator power plant. For producing steam directly, the movable mirrors can be arranged so as to concentrate large amounts of solar radiation upon blackened pipes through which water is circulated and thereby heated.

Other applications

Solar energy is also used on a small scale for purposes other than those described above. In some countries, for instance, solar energy is used to produce salt from seawater by evaporation. Similarly, solar-powered desalination units transform salt water into drinking water by converting the Sun’s energy to heat, directly or indirectly, to drive the desalination process.

Solar technology has also emerged for the clean and renewable production of hydrogen as an alternative energy source. Mimicking the process of photosynthesis, artificial leaves are silicon-based devices that use solar energy to split water into hydrogen and oxygen, leaving virtually no pollutants. Further work is needed to improve the efficiency and cost-effectiveness of these devices for industrial use.

Depositphotos_24609857_original-2-1.jpg


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

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#460 2019-07-19 00:05:47

ganesh
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Re: Miscellany

375) Silver nitrate

Silver nitrate, caustic chemical compound, important as an antiseptic, in the industrial preparation of other silver salts, and as a reagent in analytical chemistry. Its chemical formula is AgNO3. Applied to the skin and mucous membranes, silver nitrate is used either in stick form as lunar caustic (or caustic pencil) or in solutions of 0.01 percent to 10 percent silver nitrate in water. The stick is used for removing warts and granulation tissue and for cauterizing wounds and ulcerations. Very dilute solutions are astringent and mildly antiseptic. A 1 percent or 2 percent solution is effective against gonococcal bacteria and may be applied to the eyes of newborn infants to ensure against blindness from gonorrhea.

Pure silver nitrate is an intermediate in the preparation of other silver salts, including the colloidal silver compounds used in medicine and the silver halides incorporated into photographic emulsions.

In analytical chemistry, aqueous solutions of silver nitrate are used in the volumetric determination of halides, and thiocyanates, as well as for the detection of reducing agents and of the cations of various acids that form insoluble silver salts.

Silver nitrate is made in large quantities by dissolving silver in nitric acid. It crystallizes in transparent plates that melt at 212 °C (414 °F). The solubility at 20 °C (68 °F) is 222 grams per 100 grams of water. It is moderately soluble in methyl and ethyl alcohols and to a lesser extent in various other organic solvents. When heated to about 320° C (608° F), silver nitrate loses oxygen and forms silver nitrite. At a red heat, silver is formed.

Ingestion of silver nitrate causes violent abdominal pains, vomiting, and diarrhea, with the development of gastroenteritis. Treatment includes oral administration of common salt solutions, milk (or white of egg and water), and soap in water to protect the mucous membranes of the esophagus and stomach and precipitate the poisonous free silver ions as silver chloride.

silver-nitrate-powder-250x250.jpg


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

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#461 2019-07-21 00:21:03

ganesh
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Re: Miscellany

376) Induction coil

Induction coil, an electrical device for producing an intermittent source of high voltage. An induction coilconsists of a central cylindrical core of soft iron on which are wound two insulated coils: an inner or primary coil, having relatively few turns of copper wire, and a surrounding secondary coil, having a large number of turns of thinner copper wire. An interrupter is used for making and breaking the current in the primary coil automatically. This current magnetizes the iron core and produces a large magnetic field throughout the induction coil.

The principle of operation of the induction coil was given in 1831 by Michael Faraday. Faraday’s law of induction showed that if the magnetic field through a coil is changed an electromotive force is induced whose value depends on the time rate of change of magnetic field through the coil. This induced electromotive force is always, by Lenz’s law, in such a direction as to oppose the change in the magnetic field.

When a current in the primary coil is started, induced electromotive forces are created in both the primary and secondary coils. The opposing electromotive force in the primary coil causes the current to rise gradually to its maximum value. Thus when the current starts, the time rate of change of the magnetic field and the induced voltage in the secondary coil are relatively small. On the other hand, when the primary current is interrupted, the magnetic field is reduced rapidly and a relatively large voltage is produced in the secondary coil. This voltage, which may reach several tens of thousands of volts, lasts only for a very short time during which the magnetic field is changing. Thus an induction coil produces a large voltage lasting for a short time and a small reverse voltage lasting a much longer time. The frequency of these changes is determined by the frequency of the interrupter.

After Faraday’s discovery, many improvements were made on the induction coil. In 1853 the French physicist Armand-Hippolyte-Louis Fizeau placed a capacitor across the interrupter, thus breaking the primary current much more rapidly. Methods for winding the secondary coil were greatly improved by Heinrich Daniel Ruhmkorff (1851) in Paris, by Alfred Apps in London, and by Friedrich Klingelfuss in Basel, who was able to obtain sparks in air about 150 cm (59 inches) long. There are various kinds of interrupters. For the small induction coils a mechanical one is attached to the coil, while the larger coils use a separate device such as a mercury jet interrupter or the electrolytic interrupter invented by Arthur Wehnelt in 1899.

Induction coils were used to provide the high voltage for electrical discharges in gases at low pressureand as such were instrumental in the discovery of cathode rays and X-rays in the early 20th century. Another form of induction coil is the Tesla coil, which generates high voltages at high frequencies. The larger induction coils used with X-ray tubes were displaced by the transformer-rectifier as a source of voltage. In the 21st century smaller induction coils remained in widespread use as a crucial component in the ignition systems of gasoline engines.

maynooth8a.JPG


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

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

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#462 2019-07-23 00:03:44

ganesh
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Re: Miscellany

377) Cumin

Cumin, also spelled Cummin, (Cuminum cyminum), small, slender annual herb of the family Apiaceae (Umbelliferae) with finely dissected leaves and white or rose-coloured flowers. Native to the Mediterranean region, cumin is also cultivated in India, China, and Mexico for its fruits, called seeds, which are used to flavour a variety of foods.

Cumin, or comino, seeds are actually dried fruits. They are thin, yellowish brown, elongated ovals about 0.25 inch (6 mm) long with five prominent longitudinal dorsal ridges interspersed with less-distinctive secondary ridges forming a tiny, gridlike pattern. An essential ingredient in many mixed spices, chutneys, and chili and curry powders, cumin seeds are especially popular in Asian, North African, and Latin American cuisines. Their distinctive aroma is heavy and strong; their taste warm and reminiscent of caraway. At one time cumin seeds were widely used as home medicinals; their medicinal use today is chiefly veterinary. The seeds contain between 2.5 and 4.5 percent essential oil, the principal component of which is cumaldehyde. The oil is used in perfumery, for flavouring a variety of liquors, and for medicinal purposes.

Black cumin, or fennel flower (Nigella sativa), a similar Eurasian herb of the family Ranunculaceae, also is used as a seasoning.

graines_de_cumin_nePaJor.jpg


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

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

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#463 2019-07-25 01:25:49

ganesh
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Re: Miscellany

378) Potassium Nitrate

Potassium nitrate (KNO3) is a soluble source of two major essential plant nutrients. It’s commonly used as a fertilizer for high-value crops that benefit from nitrate (NO3-) nutrition and a source of potassium (K+) free of chloride (Cl-).

Production

Manufacturers typically make potassium nitrate fertilizer (sometimes referred to as nitrate of potash or NOP by reacting potassium chloride (KCl) with a nitrate source. Depending on the objectives and available resources, the nitrate may come from sodium nitrate, nitric acid or ammonium nitrate. The resulting KNO3 is identical regardless of the manufacturing process. Potassium nitrate is commonly sold as a water-soluble, crystalline material primarily intended for dissolving and applying with water or in a prilled form for soil application. Traditionally, this compound is known as saltpeter.

Agricultural use

Growers value fertilizing with KNO3 especially in conditions where a highly soluble, chloride-free nutrient source is needed. In such soils, all of the N is immediately available for plant uptake as nitrate, requiring no additional microbial action and soil transformation. Growers of high-value vegetable and orchard crops sometime prefer to use a nitrate-based source of nutrition in an effort to boost yield and quality. Potassium nitrate contains a relatively high proportion of K, with an N to K ratio of approximately one to three. Many crops have high K demands and can remove as much or more K than N at harvest.

Applications of KNO3 to the soil are made before the growing season or as a supplement during the growing season. A diluted solution is sometimes sprayed on plant foliage to stimulate physiological processes or to overcome nutrient deficiencies. Foliar application of K during fruit development  advantages some crops, since this growth stage often coincides with high K demands during the time of declining root activity and nutrient uptake. It’s also commonly used for greenhouse plant production and hydroponic culture.

Management practices

Both N and K are required by plants to support harvest quality, protein formation, disease resistance and water-use efficiency. Therefore, to support healthy growth, farmers often apply KNO3to soil or through the irrigation system during the growing season.

Potassium nitrate accounts for only a small portion of the global K fertilizer market. It’s primarily used where its unique composition and properties can provide specific benefits to growers. Further, it’s easy to handle and apply, and is compatible with many other fertilizers, including specialty fertilizers for many high-value specialty crops, as well as those used on grain and fiber crops.

The relatively high solubility of KNO3 under warm conditions allows for a more concentrated solution than for other common K fertilizers. However, farmers must carefully manage the water to keep the nitrate from moving below the root zone.

Non-agricultural uses

Potassium nitrate has long been used for fireworks and gunpowder. It’s now more commonly added to food to maintain the quality of meat and cheese. Specialty toothpastes often contain KNO3 to alleviate tooth sensitivity. A mixture of KNO3 and sodium nitrate (NaNO3) is used for storing heat in solar energy installations.

potassium-nitrate-250x250.jpg


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

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#464 2019-07-27 01:13:16

ganesh
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Re: Miscellany

379) King Fahd’s Fountain

(in Saudi Arabia : aka Jeddah’s Fountain--the tallest water fountain in the world!)

King Fahd’s Fountain, also known as Jeddah’s Fountain, is the tallest water fountain in the world. It dominates the skyline of the city of Jeddah, the commercial capital of Saudi Arabia and the wealthiest city in the Middle East and western Asia, located on the coast of the Red Sea. The fountain was built in the 1980's and is listed in Guinness World Records as the highest water fountain in the world, with a reach of over one thousand feet. The salt-water fountain was donated to the City of Jeddah by the late King Fahd bin Abdul Aziz.

Visible throughout the entire city of Jeddah, the water fountain consists of a single massive plume of water shooting vertically into the air at a speed of 233 miles per hour. On a calm day the water reaches a height of one thousand and twenty-four feet, higher than Paris’ Eiffel Tower (excluding the antenna). At any given moment, the water hanging in the air weighs in excess of eighteen tons (thirty-six thousand pounds)!

The first construction of the fountain was developed between 1980 and 1983, after the style of Lake Geneva’s freshwater fountain, which reaches four hundred and sixty feet into the air at speeds of approximately one hundred and twenty-four miles per hour. This scale was found to be insufficiently impressive for planners.

The fountain as it stands today began operating in 1985, and has been running without any significant difficulties for over twenty years. A comprehensive maintenance system includes daily, weekly, bi-weekly, monthly, half-yearly and annual inspections and maintenance operations.

Because Jeddah’s Fountain operates using sea water running at unusually high speeds; corrosion and abrasion were key challenges to the builders, SETE Technical Services Latsis Group. The intakes for the pumps are in a special pit that is continually pumped dry and treated annually with anti-fouling paint that prevents growth of marine life. The water is passed through a series of screens before it reaches the pumps, filtering out soil, sand, and organic matter. The pipes and pump systems are isometrically designed and made of special stainless steel. Water exits the pumps via a 350 meter high-pressure output line constructed with steadily decreasing diameters towards the nozzles. The nozzles are constructed of a specially designed alloy which can withstand a constant pressure of forty-two bar (over 609 pounds per square inch). The five hundred high-intensity spotlights that illuminate the fountain also had to be specially designed to withstand the constant barrage of thousands of tons of water an hour falling from several hundred feet. The spots are mounted on special islands. A cathodic system was installed in 1987 to protect the pipelines from the corrosive effects of the falling seawater, consisting of fifty-seven anodes and twenty-nine reference electrodes at seventeen points along the system.

It took over two years of constant development to arrive at the current successful design, which has resulted in not only a record-setting water fountain, but has brought about the first real development of specialized knowledge on high pressure seawater.

king-fahd-fountain.jpg


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

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

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#465 2019-07-29 00:15:58

ganesh
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Re: Miscellany

380) Penguin

Penguin, (order Sphenisciformes), any of 18 species of flightless marine birds that live only in the Southern Hemisphere. The majority of the 18 species live not in Antarctica but rather between latitudes 45° and 60° S, where they breed on islands. A few penguins inhabit temperate regions, and one, the Galapagos penguin (Spheniscus mendiculus), lives at the Equator.

General Features

The stocky, short-legged appearance of penguins has endeared them to people worldwide. They range from about 35 cm (14 inches) in height and approximately 1 kg (about 2 pounds) in weight in the blue, or fairy, penguin(Eudyptula minor) to 115 cm (45 inches) and 25 to 40 kg (55 to 90 pounds) in the emperor penguin (Aptenodytes forsteri). Most are black on the back and white below, often with lines of black across the upper breast or spots of white on the head. Colour is rare, being limited to red or yellow irises of the eye in some species; red beaks or feet in a few; yellow brow tufts in the three species of Eudyptes; and orange and yellow on the head, neck, and breast in the emperor and king (A. patagonica) penguins.

The total populations of some species, such as the emperor, are estimated in the hundreds of thousands, but most species of smaller penguins certainly run into the millions. Immense island breeding colonies, some teeming with hundreds of thousands of nesting pairs, represent a large potential food resource, but the economic importance of penguins is negligible. Nineteenth-century whalers and seal hunters visited some colonies for meat and eggs, and a penguin oil industry once took large numbers of the birds. By the early 20th century, however, this exploitation was no longer profitable, and most colonies were left alone or actively protected. Some species are now increasing in numbers, apparently as a result of the mid-20th century’s decimation of Antarctic whales, which compete with penguins for the krill (minute crustaceans) on which both feed. Penguin populations, however, are highly vulnerable to changes in climate and ocean temperature, including recent global warming. Penguins also are very sensitive to depletion of local fish populations by humans.

Natural History

Reproduction

Many features of the penguin life cycle vary with body size and geographic distribution; the chronology of breeding may also vary within a species in relation to latitude. The majority of species breed only once each year. Certain species, such as the African penguin (Spheniscus demersus), probably other members of this genus, and the blue penguin, breed twice a year. The king penguin breeds twice in three years. One egg is laid by the emperor and king penguins; all others lay two or occasionally three. Most penguins begin breeding in the austral (southern) spring or summer. King penguins are on a 14- to 18-month cycle, and the timing of an individual pair depends on the success or failure of the previous breeding attempt. Some populations of the gentoo penguin (Pygoscelis papua) also breed in winter. The breeding of the emperor penguin begins in autumn, apparently timed so that the long developmental period will produce the young in midsummer, when their chances of survival are greatest.

The gentoo, which has a circumpolar distribution, is notable for its lack of synchrony among populations, but otherwise its breeding schedule is essentially comparable to that of most other species. In the Crozet Islandsoff southern Africa, for example, egg laying takes place in July. The two eggs are incubated for 35 or 36 days, and the rearing of the chick takes two months. The last immature birds go to sea in January.

Many types of visual and vocal displays are employed between the arrival of the birds at the colony and their departure. Courtship calls are used during pairing and to a lesser degree during the succeeding phases of breeding. There are marked vocal differences between sexes in the emperor penguin and the king penguin and less-marked dimorphisms in some other species. Upon arrival at the colony each bird returns to the nest that it left the previous year and generally rejoins its mate of the previous year, unless the death of the latter forces it to choose another partner. This applies even to the emperor penguin, which is capable of finding its mate despite the absence of a nest and the large size of the colony.

The displays that occur with the reassembly of the colony and the finding of mates, as well as those preceding copulation, are quite similar among the majority of species, but the accompanying vocalizations are more diverse. Various species have been described as trumpeting, croaking, cackling, and cooing; members of the genus Spheniscus are called jackass penguins for the braying sounds they make. The behaviour of experienced older birds is more elaborate and more effective than that of younger individuals. For example, Adélie penguins (Pygoscelis adeliae) may return to the reproductive colony from their third year onward but do not breed successfully until their fifth or sixth year.

Incubation of eggs is performed by both sexes in all species except the emperor penguin, in which it is done exclusively by the male, and it is begun immediately after egg laying. With the advent of incubation, the bustle and myriad cries that characterized mating give way to quiet and inactivity. Faulty incubation behaviour by inexperienced birds frequently results in the abandonment or breakage of eggs. The mortality rate (eggs and chicks) is very important at the egg stage, varying from year to year depending on climatic conditions, the percentage of young birds in the reproductive population, and the pressure of predation. In general, mortality (eggs and chicks) is from 40 to 80 percent of the eggs laid. In coastal colonies predators include, in order of importance: skuas, sheathbills, and the giant petrel. On the Australian, African, and South American continents, the nocturnal habits of certain penguins and the fact that they nest in burrows substantially limit predation, which is mostly by gulls and man.

Following egg laying, the female usually departs for the sea to feed, returning to relieve her mate after about 10 to 20 days. Thereafter, father and mother alternate in periods of a week or two. The female emperor penguin, however, must often walk 80 to 160 km (50 to 100 miles) from the colony to the sea and does not return until the end of the incubation period. During the 64-day incubation period, which extends through the height of the Antarctic winter, the male emperor penguin incubates the egg, holding it on his feet and living on stored fat reserves. During violent winter storms, members of the colony gather for mutual protection from wind and cold in tightly packed crowds called huddles.

Emergence from the shell takes 24 to 48 hours, during which the brooding parent is particularly irritable. The chick shows feeding behaviour immediately on hatching, receiving a regurgitated “soup” of crustaceans or fish by inserting its bill into the open mouth of the parent. During its early days the young bird is sheltered under the body of one of its parents, who take turns foraging and brooding. Growing larger, the young bird remains at a parent’s side, although the fledgling is able to maintain its body heat and move about alone. The chick then joins 100 or more of its contemporaries in a nursery group, or crèche, sometimes guarded by a few adults, while both its parents forage at sea. Upon returning with food, the parent calls its chick from the crèche and is able to distinguish it from other chicks (which frequently respond) by voice and appearance. During the breeding season the number of “unemployed” adults in the colony increases with the addition of those who have lost eggs or chicks. In emperor penguin colonies, these unemployed birds often interfere with parents that have young and cause increased mortality. During the crèche stage the fuzzy down that has covered the chick since hatching is replaced by a coat of short stiff feathers, which are similar to those of the adult but usually somewhat different in colour. Once this molt is complete, the juvenile leaves the colony to seek its own food at sea.

The period of growth of the young bird from hatching to complete independence varies from two months, in the smallest species of the genus Eudyptula, to 51/2 months in the emperor and 12 to 14 months in the king penguin.

Adult penguins molt all of their feathers once a year following the breeding period. While in molt the bird is unable to enter the water and instead withdraws to a communal molting site usually situated in a sheltered area away from the colony. The duration of the molt varies from about two weeks in small species to more than a month in the larger ones.

The principal enemies of penguins at sea are the leopard seal and the killer whale (orca). Seals also take penguins near Australia, New Zealand, and other subantarctic regions.

Locomotion and orientation

Penguins are adapted for rapid locomotion in water, in which the wings, or flippers, are used for propulsion; the birds “fly” underwater. When moving at high speed, they frequently leave the water in leaps that may carry them a metre or more through the air; it is during this time that they breathe.

On land, penguins are much more awkward, even amusing, as they rock from side to side as they walk. Despite their short legs, however, penguins can run with surprising speed. Some, such as the northern rockhopper(Eudyptes moseleyi), the southern rockhopper (E. chrysocome), and Adélie penguins, move among rocks with agility, using the flippers for balance. On snow or ice, many penguins “toboggan,” sliding on the belly as they propel themselves with the feet and flippers. The flippers, along with the beak, are the prime weapons in defense and attack.

Scientists have long wondered how penguins are able to find their way back to their colonies from far out at sea, where currents may have carried them great distances. Also perplexing is how they are able to direct themselves correctly on land in the absence of clear-cut landmarks. Studies of penguins transported to the interior of Antarctica have found that they are able to find their way back to the ocean by using the sun as a directional aid. It is probable that the same means of orientation is used at sea. Upon approaching the coast they are able to recognize features of the shoreline and ocean bottom.

Food habits

The type of food utilized varies with the species, the geographic region, and the time of year. Most of the smaller southern penguins feed primarily upon krill, which attain high densities in the rich, well-oxygenated Antarctic waters. Cephalopods (squid and cuttlefish) and small fishes may form substantial fractions of the food, and in a few, such as the African penguin, fish is the basic element of the diet. The total weight of food consumed by a large penguin colony is prodigious, often exceeding several tons per day.

Form And Function

The penguins are highly specialized for their flightless aquatic existence. The feet are located much farther back than those of other birds, with the result that the bird carries itself mostly upright; its walk can thus be described as plantigrade (i.e., on the soles). The sole comprises the whole foot instead of just the toes, as in other birds. The most notable characteristic of the group is the transformation of the forelimb into a paddle. This is accompanied by a body morphology particularly adapted to movement in a liquid medium. The thoracic (rib) cage is well developed, and the sternum bears a pronounced keel for the attachment of the pectoral muscles, which move the flippers. The flipper has the same skeletal base as the wing of flying birds but with its elements shortened and flattened, producing a relatively rigid limb covered with very short feathers—an ideal organ for rapid propulsion. The body plumage likewise consists of very short feathers, which minimize friction and turbulence. The density of the plumage and the layer of air that it retains provide almost complete insulation of the body.

Insulation of the bird’s body is particularly important for Antarctic speciesthat live in water that is always below 0 °C (32 °F). The cooling power of seawater at −1.9 °C (28.6 °F) is equal to that of a temperature of −20 °C (−4 °F) with a wind of 110 km (70 miles) per hour. The skin is insulated by a layer of air trapped under the plumage, and the only bare skin in direct contact with the water is that of the feet. In the case of the emperor penguin on land, the feet are in almost constant contact with ice. The skin temperature is in the neighbourhood of 0 °C, and snow does not melt upon contact. This is possible because of remarkable anatomical arrangements in the lower limb, whereby closely adjacent arteries and veins form a system of heat exchange between opposing flows of blood. This arrangement permits cooled blood from the feet to absorb heat from outflowing blood, providing maximum economy of heat consistent with the functioning of the foot.

Like other seabirds, penguins have salt glands that enable them to ingest salt from seawater. Excess chloride is excreted in the form of a solution the concentration of which is greater than that of seawater. These glands are located above the eyes and are already functional in the young chick, which begins to consume food of marine origin from its first day of life.

Recent research has shown that the species most isolated geographically, such as the emperor penguin, can be subject to diseases. Some, such as the Adélie penguin, carry in their bodies trace amounts of pollutants, albeitin lower quantities than are found in many birds that live closer to humans.

Evolution And Classification

Fossil record

Evidence from paleontology indicates that the penguins and the order Procellariiformes (albatrosses, shearwaters, and petrels) had a common origin. Both groups are represented by well-defined fossils dating to about 50 million years ago. The flightless sphenisciform line produced a number of distinctive side branches, all recognizably penguins, some giant in size. All of the fossil remains of penguins have been collected within the zone of the present-day distribution of the Sphenisciformes. Some apparently lived in warmer regions than do most of today’s penguins.

Phylogenetic analysis of living and fossil penguins shows that the group evolved a large body size early in its history. For example, two of the largest fossil penguins known—Icadyptes, which stood some 1.5 metres (about 5 feet) tall, and Anthropornis, which stood about 1.8 metres (6 feet) tall—date to the Eocene Epoch (56 million to 33.9 million years ago). Living penguins make up a separate lineage characterized by smaller, highly aquatic species that began about 8 million years ago. The comparatively small size of living penguins is thus a geologically recent phenomenon that postdates the original radiation of giant penguins.

penguin.jpg


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

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#466 2019-07-31 00:27:26

ganesh
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Re: Miscellany

381) Brain

Brain, the mass of nerve tissue in the anterior end of an organism. The brain integrates sensory information and directs motor responses; in higher vertebrates it is also the centre of learning.

In lower vertebrates the brain is tubular and resembles an early developmental stage of the brain in higher vertebrates. It consists of three distinct regions: the hindbrain, the midbrain, and the forebrain. Although the brain of higher vertebrates undergoes considerable modification during embryonic development, these three regions are still discernible.

The hindbrain is composed of the medulla oblongata and the pons. The medulla transmits signals between the spinal cord and the higher parts of the brain; it also controls such autonomic functions as heartbeat and respiration. The pons is partly made up of tracts connecting the spinal cord with higher brain levels, and it also contains cell groups that transfer information from the cerebrum to the cerebellum.

The midbrain, the upper portion of which evolved from the optic lobes, is the main centre of sensory integration in fish and amphibians. It also is involved with integration in reptiles and birds. In mammals the midbrain is greatly reduced, serving primarily as a connecting link between the hindbrain and the forebrain.
Connected to the medulla, pons, and midbrain by large bundles of fibres is the cerebellum. Relatively large in humans, this “little brain” controls balance and coordination by producing smooth, coordinated movements of muscle groups.

The forebrain includes the cerebral hemispheres and, under these, the brainstem, which contains the thalamus and hypothalamus. The thalamus is the main relay centre between the medulla and the cerebrum; the hypothalamus is an important control centre for gender drive, pleasure, pain, hunger, thirst, blood pressure, body temperature, and other visceral functions. The hypothalamus produces hormones that control the secretions of the anterior pituitary gland, and it also produces oxytocin and antidiuretic hormone, which are stored in and released by the posterior pituitary gland.

The cerebrum, originally functioning as part of the olfactory lobes, is involved with the more complex functions of the human brain. In humans and other advanced vertebrates, the cerebrum has grown over the rest of the brain, forming a convoluted (wrinkled) layer of gray matter. The degree of convolution is partly dependent on the size of the body. Small mammals (e.g., lesser anteater, marmoset) generally have smooth brains, and large mammals (e.g., whale, elephant, dolphin) generally have highly convoluted ones.

The cerebral hemispheres are separated by a deep groove, the longitudinal cerebral fissure. At the base of this fissure lies a thick bundle of nerve fibres, called the corpus callosum, which provides a communication link between the hemispheres. The left hemisphere controls the right half of the body, and vice versa, because of a crossing of the nerve fibres in the medulla or, less commonly, in the spinal cord. Although the right and left hemispheres are mirror images of one another in many ways, there are important functional distinctions. In most people, for example, the areas that control speech are located in the left hemisphere, while areas that control spatial perceptions are located in the right hemisphere.

Two major furrows—the central sulcus and the lateral sulcus—divide each cerebral hemisphere into four sections: the frontal, parietal, temporal, and occipital lobes. The central sulcus, also known as the fissure of Rolando, also separates the cortical motor area (which is anterior to the fissure) from the cortical sensory area (which is posterior to the fissure). Starting from the top of the hemisphere, the upper regions of the motor and sensory areas control the lower parts of the body, and the lower regions of the motor and sensory areas control the upper parts of the body. Other functional areas of the cerebral hemispheres have been identified, including the visual cortex in the occipital lobe and the auditory cortex in the temporal lobe. A large amount of the primate cortex, however, is devoted to no specific motor or sensory function; this so-called association cortex is apparently involved in higher mental activities.

Human Brain: Facts, Functions & Anatomy

The human brain is the command center for the human nervous system. It receives signals from the body's sensory organs and outputs information to the muscles. The human brain has the same basic structure as other mammal brains but is larger in relation to body size than any other brains.

Facts about the human brain

•    The human brain is the largest brain of all vertebrates relative to body size.
•    It weighs about 3.3 lbs. (1.5 kilograms).
•    The average male has a brain volume of 1,274 cubic centimeters.
•    The average female brain has a volume of 1,131 cm3.
•    The brain makes up about 2 percent of a human's body weight.
•    The cerebrum makes up 85 percent of the brain's weight.
•    It contains about 86 billion nerve cells (neurons) — the "gray matter."
•    It contains billions of nerve fibers (axons and dendrites) — the "white matter."
•    These neurons are connected by trillions of connections, or synapses.

Anatomy of the human brain

The largest part of the human brain is the cerebrum, which is divided into two hemispheres, according to the Mayfield Clinic. Underneath lies the brainstem, and behind that sits the cerebellum. The outermost layer of the cerebrum is the cerebral cortex, which consists of four lobes: the frontal, parietal, temporal and occipital.
Like all vertebrate brains, the human brain develops from three sections known as the forebrain, midbrain and hindbrain. Each of these contains fluid-filled cavities called ventricles. The forebrain develops into the cerebrum and underlying structures; the midbrain becomes part of the brainstem; and the hindbrain gives rise to regions of the brainstem and the cerebellum.

The cerebral cortex is greatly enlarged in human brains and is considered the seat of complex thought. Visual processing takes place in the occipital lobe, near the back of the skull. The temporal lobe processes sound and language, and includes the hippocampus and amygdala, which play roles in memory and emotion, respectively. The parietal lobe integrates input from different senses and is important for spatial orientation and navigation.

The brainstem connects to the spinal cord and consists of the medulla oblongata, pons and midbrain. The primary functions of the brainstem include relaying information between the brain and the body; supplying some of the cranial nerves to the face and head; and performing critical functions in controlling the heart, breathing and consciousness.

Between the cerebrum and brainstem lie the thalamus and hypothalamus. The thalamus relays sensory and motor signals to the cortex and is involved in regulating consciousness, sleep and alertness. The hypothalamus connects the nervous system to the endocrine system — where hormones are produced — via the pituitary gland.
The cerebellum lies beneath the cerebrum and has important functions in motor control. It plays a role in coordination and balance and may also have some cognitive functions.

Humans vs. other animals

Overall brain size doesn't correlate with level of intelligence. For instance, the brain of a sperm whale is more than five times heavier than the human brain but humans are considered to be of higher intelligence than sperm whales.  The more accurate measure of how intelligent an animal may be is the ratio between the size of the brain and the body size, according to the University of California San Diego's Temporal Dynamics of Learning Center.

Among humans, however, brain size doesn't indicate how smart someone is. Some geniuses in their field have smaller- than-average brains, while others larger than average, according to Christof Koch, a neuroscientist and president of the Allen Institute for Brain Science in Seattle. For example, compare the brains of two highly acclaimed writers. The Russian novelist Ivan Turgenev's brain was found to be 2,021 grams, while writer Anatole France's brain weighed only 1,017 grams.
Humans have a very high brain-weight-to-body-weight ratio, but so do other animals. The reason why the human's intelligence, in part, is neurons and folds. Humans have more neurons per unit volume than other animals, and the only way to do that with the brain's layered structure is to make folds in the outer layer, or cortex, said Eric Holland, a neurosurgeon and cancer biologist at the Fred Hutchinson Cancer Research Center and the University of Washington.

"The more complicated a brain gets, the more gyri and sulci, or wiggly hills and valleys, it has," Holland told Live Science. Other intelligent animals, such as monkeys and dolphins, also have these folds in their cortex, whereas mice have smooth brains, he said.

Humans also have the largest frontal lobes of any animal, Holland said. The frontal lobes are associated with higher-level functions such as self-control, planning, logic and abstract thought — basically, "the things that make us particularly human," he said.

Left brain vs. right brain

The human brain is divided into two hemispheres, the left and right, connected by a bundle of nerve fibers called the corpus callosum. The hemispheres are strongly, though not entirely, symmetrical. The left brain controls all the muscles on the right-hand side of the body and the right brain controls the left side. One hemisphere may be slightly dominant, as with left- or right-handedness.

The popular notions about "left brain" and "right brain" qualities are generalizations that are not well supported by evidence. Still, there are some important differences between these areas. The left brain contains regions involved in speech and language (called the Broca's area and Wernicke's area, respectively) and is also associated with mathematical calculation and fact retrieval, Holland said. The right brain plays a role in visual and auditory processing, spatial skills and artistic ability — more instinctive or creative things, Holland said — though these functions involve both hemispheres. "Everyone uses both halves all the time," he said.

BRAIN Initiative

In April 2013, President Barack Obama announced a scientific grand challenge known as the BRAIN Initiative, short for Brain Research through Advancing Innovative Neurotechnologies. The $100-million-plus effort aimed to develop new technologies that will produce a dynamic picture of the human brain, from the level of individual cells to complex circuits.

Like other major science efforts such as the Human Genome Project, although it's expensive, it's usually worth the investment, Holland said. Scientists hope the increased understanding will lead to new ways to treat, cure and prevent brain disorders.

The project contains members from several government agencies, including the National Institutes of Health (NIH), the National Science Foundation (NSF) and the Defense Advanced Research Projects Agency (DARPA), as well as private research organizations, including the Allen Institute for Brain Science and the Howard Hughes Medical Institute in Chevy Chase, Maryland.

In March 2013, the project's backers outlined their goals in the journal Science. In September 2014, the NIH announced $46 million in BRAIN Initiative grants. Members of industry pledged another $30 million to support the effort, and major foundations and universities also agreed to apply more than $240 million of their own research toward BRAIN Initiative goals.

When the project was announced, President Obama convened a commission to evaluate the ethical issues involved in research on the brain. In May 2014, the commission released the first half of its report, calling for ethics to be integrated early and explicitly in neuroscience research. In March 2015, the commission released the second half of the report, which focused on issues of cognitive enhancement, informed consent and using neuroscience in the legal system.

The Brain Initiative has achieved several of its goals. As of 2018, the National Institutes of Health (NIH) has "invested more than $559 million in the research of more than 500 scientists," and Congress appropriated "close to $400 million in NIH funding for fiscal year 2018," according to the initiative's website. The research funding facilitated the development of new brain-imaging and brain-mapping tools, and helped create the BRAIN Initiative Cell Census Network — an effort to catalog the brain's "parts' list." Together, these efforts contribute to major advancements in understanding the brain.

brain_f2.jpg


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

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

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#467 2019-08-02 01:09:05

ganesh
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Registered: 2005-06-28
Posts: 28,716

Re: Miscellany

382) Locomotive

Locomotive, any of various self-propelled vehicles used for hauling railroad cars on tracks.

Although motive power for a train-set can be incorporated into a car that also has passenger, baggage, or freight accommodations, it most often is provided by a separate unit, the locomotive, which includes the machinery to generate (or, in the case of an electric locomotive, to convert) power and transmit it to the driving wheels. Today there are two main sources of power for a locomotive: oil (in the form of diesel fuel) and electricity. Steam, the earliest form of propulsion, was in almost universal use until about the time of World War II; since then it has been superseded by the more efficient diesel and electric traction.

The steam locomotive was a self-sufficient unit, carrying its own water supply for generating the steam and coal, oil, or wood for heating the boiler. The diesel locomotive also carries its own fuel supply, but the diesel-engine output cannot be coupled directly to the wheels; instead, a mechanical, electric, or hydraulic transmission must be used. The electric locomotive is not self-sufficient; it picks up current from an overhead wire or a third rail beside the running rails. Third-rail supply is employed only by urban rapid-transit railroads operating on low-voltage direct current.

In the 1950s and ’60s the gas turbine was adopted by one American railroad and some European ones as an alternative to the diesel engine. Although its advantages have been nullified by advances in diesel traction technology and increases in oil price, it is still proposed as an alternative means for installing high-speed rail service for regions where no infrastructure for electric power is in place.

Steam Locomotives

The basic features that made George and Robert Stephenson’s ‘Rocket’ of 1829 successful—its multitube boiler and its system of exhausting the steam and creating a draft in its firebox—continued to be used in the steam locomotive to the end of its career. The number of coupled drive wheels soon increased.

The ‘Rocket’ had only a single pair of driving wheels, but four coupled wheels soon became common, and eventually some locomotives were built with as many as 14 coupled drivers.

Steam-locomotive driving wheels were of various sizes, usually larger for the faster passenger engines. The average was about a 1,829–2,032-mm (72–80-inch) diameter for passenger engines and 1,372–1,676 mm (54–66 inches) for freight or mixed-traffic types.

Supplies of fuel (usually coal but sometimes oil) and water could be carried on the locomotive frame itself (in which case it was called a tank engine) or in a separate vehicle, the tender, coupled to the locomotive. The tender of a typical European main-line locomotive had a capacity of 9,000 kg (10 tons) of coal and 30,000 litres (8,000 gallons) of water. In North America, higher capacities were common.

To meet the special needs of heavy freight traffic in some countries, notably the United States, greater tractive effort was obtained by using two separate engine units under a common boiler. The front engine was articulated, or hinge-connected to the frame of the rear engine, so that the very large locomotive could negotiate curves. The articulated locomotive was originally a Swiss invention, with the first built in 1888. The largest ever built was the Union Pacific’s ‘Big Boy’, used in mountain freight service in the western United States. ‘Big Boy’ weighed more than 600 short tons, including the tender. It could exert 61,400 kg (135,400 pounds) of tractive force and developed more than 6,000 horsepower at 112 km (70 miles) per hour.

One of the best-known articulated designs was the Beyer-Garratt, which had two frames, each having its own driving wheels and cylinders, surmounted by water tanks. Separating the two chassis was another frame carrying the boiler, cab, and fuel supply. This type of locomotive was valuable on lightly laid track; it could also negotiate sharp curves. It was widely used in Africa.

Various refinements gradually improved the reciprocating steam locomotive. Some included higher boiler pressures (up to 2,000–2,060 kilopascals [290–300 pounds per square inch] for some of the last locomotives, compared with about 1,300 kilopascals [200 pounds per square inch] for earlier designs), superheating, feed-water preheating, roller bearings, and the use of poppet (perpendicular) valves rather than sliding piston valves.

Still, the thermal efficiency of even the ultimate steam locomotives seldom exceeded about 6 percent. Incomplete combustion and heat losses from the firebox, boiler, cylinders, and elsewhere dissipated most of the energy of the fuel burned. For this reason the steam locomotive became obsolete, but only slowly, because it had compensating advantages, notably its simplicity and ability to withstand abuse.
Electric Traction

Efforts to propel railroad vehicles using batteries date from 1835, but the first successful application of electric traction was in 1879, when an electric locomotive ran at an exhibition in Berlin. The first commercial applications of electric traction were for suburban or metropolitan railroads. One of the earliest came in 1895, when the Baltimore and Ohio electrified a stretch of track in Baltimore to avoid smoke and noise problems in a tunnel. One of the first countries to use electric traction for main-line operations was Italy, where a system was inaugurated as early as 1902.

By World War I a number of electrified lines were operating both in Europeand in the United States. Major electrification programs were undertaken after that war in such countries as Sweden, Switzerland, Norway, Germany, and Austria. By the end of the 1920s nearly every European country had at least a small percentage of electrified track. Electric traction also was introduced in Australia (1919), New Zealand (1923), India (1925), Indonesia (1925), and South Africa (1926). A number of metropolitan terminals and suburban services were electrified between 1900 and 1938 in the United States, and there were a few main-line electrifications. The advent of the diesel locomotive inhibited further trunk route electrification in the United States after 1938, but following World War II such electrification was rapidly extended elsewhere. Today a significant percentage of the standard-gauge track in national railroads around the world is electrified—for example, in Japan (100 percent), Switzerland (92 percent), Belgium (91 percent), the Netherlands (76 percent), Spain (76 percent), Italy (68 percent), Sweden (65 percent), Austria (65 percent), Norway (62 percent), South Korea (55 percent), France (52 percent), Germany (48 percent), China (42 percent), and the United Kingdom (32 percent). By contrast, in the United States, which has some 225,000 km (140,000 miles) of standard-gauge track, electrified routes hardly exist outside the Northeast Corridor, where Amtrak runs the 720-km (450-mile) Acela Express between Boston and Washington, D.C.

The century’s second half also was marked by the creation in cities worldwide of many new electrified urban rapid-transit rail systems, as well as extension of existing systems.

Advantages and disadvantages

Electric traction is generally considered the most economical and efficient means of operating a railroad, provided that cheap electricity is available and that the traffic density justifies the heavy capital cost. Being simply power-converting, rather than power-generating, devices, electric locomotives have several advantages. They can draw on the resources of the central power plant to develop power greatly in excess of their nominal ratings to start a heavy train or to surmount a steep grade at high speed. A typical modern electric locomotive rated at 6,000 horsepower has been observed to develop as much as 10,000 horsepower for a short period under these conditions. Moreover, electric locomotives are quieter in operation than other types and produce no smoke or fumes. Electric locomotives require little time in the shop for maintenance, their maintenance costs are low, and they have a longer life than diesels.

The greatest drawbacks to electrified operation are the high capital investment and maintenance cost of the fixed plant—the traction current wires and structures and power substations—and the costly changes that are usually required in signaling systems to immunize their circuitry against interference from the high traction-current voltages and to adapt their performance to the superior acceleration and sustained speeds obtainable from electric traction.

Types of traction systems

Electric-traction systems can be broadly divided into those using alternating current and those using direct current. With direct current, the most popular line voltages for overhead wire supply systems have been 1,500 and 3,000. Third-rail systems are predominantly in the 600–750-volt range. The disadvantages of direct current are that expensive substations are required at frequent intervals and the overhead wire or third rail must be relatively large and heavy. The low-voltage, series-wound, direct-current motor is well suited to railroad traction, being simple to construct and easy to control. Until the late 20th century it was universally employed in electric and diesel-electric traction units.

The potential advantages of using alternating instead of direct current prompted early experiments and applications of this system. With alternating current, especially with relatively high overhead-wire voltages (10,000 volts or above), fewer substations are required, and the lighter overhead current supply wire that can be used correspondingly reduces the weight of structures needed to support it, to the further benefit of capital costs of electrification. In the early decades of high-voltage alternating current electrification, available alternating-current motors were not suitable for operation with alternating current of the standard commercial or industrial frequencies (50 hertz [cycles per second] in Europe; 60 hertz in the United States and parts of Japan). It was necessary to use a lower frequency (16 2/3 hertz is common in Europe; 25 hertz in the United States); this in turn required either special railroad power plants to generate alternating current at the required frequency or frequency-conversion equipment to change the available commercial frequency into the railroad frequency.

Nevertheless, alternating-current supply systems at 16 2/3 hertz became the standard on several European railroads, such as Austria, Germany, and Switzerland, where electrification began before World War II. Several main-line electrifications in the eastern United States were built using 25-hertz alternating current, which survives in the Northeast Corridor operated by Amtrak.

Interest in using commercial-frequency alternating current in the overhead wire continued, however; and in 1933 experiments were carried out in both Hungary and Germany. The German State Railways electrified its Höllenthal branch at 20,000 volts, 50 hertz.
In 1945 Louis Armand, former president of the French railroads, went ahead with further development of this system and converted a line between Aix-Les-Bains and La Roche-sur-Foron for the first practical experiments. This was so successful that the 25,000-volt, 50- or 60-hertz system has become virtually the standard for new main-line electrification systems.

With commercial-frequency, alternating-current systems, there are two practical ways of taking power to the locomotive driving wheels: (1) by a rotary converter or static rectifier on the locomotive to convert the alternating-current supply into direct current at low voltage to drive standard direct-current traction motors and (2) by a converter system to produce variable-frequency current to drive alternating-current motors. The first method, using nonmechanical rectifiers, was standard practice until the end of the 1970s.

The power-to-weight ratios obtainable with electric traction units had been greatly increased by the end of World War II. Reduction in the bulk of on-board electric apparatus and motors, coupled in the latter with a simultaneous rise in attainable power output, enabled Swiss production for the Bern-Lötschberg-Simplon Railway in 1944 of a 4,000-horsepower locomotive weighing only 80,000 kg (176,370 pounds). Its four axles were all motored. There was no longer need of nonmotorized axles to keep weight on each wheel-set within limits acceptable by the track.

By 1960 the electric industry was producing transformer and rectifier packages slim enough to fit under the frames of a motored urban rapid-transit car, thereby making almost its entire body available for passenger seating. This helped to accelerate and expand the industrialized world’s electrification of metropolitan railway networks for operation by self-powered train-sets (i.e., with some or all vehicles motored). A virtue of the self-powered train-set principle is its easy adaptation to peaks of traffic demand. When two or more sets are coupled, the additional sets have the extra needed traction power. With both electric and diesel traction it is simple to interconnect electrically the power and braking controls of all the train-sets so that the train they form can be driven from a single cab. Because of this facility such train-sets are widely known as multiple-units. Modern multiple-units are increasingly fitted with automatic couplers that combine a draft function with connection of all power, braking, and other control circuits between two train-sets; this is achieved by automatic engagement, when couplers interlock, of a nest of electric contacts built into each coupler head.

From about 1960 major advances in electric traction accrued from the application of electronics. Particularly significant was the perfection of the semiconductor thyristor, or “chopper,” control of current supply to motors. The thyristor—a rapid-action, high-power switch with which the “on” and “off” periods of each cycle can be fractionally varied—achieved smoothly graduated application of voltage to traction motors. Besides eliminating wear-prone parts and greatly improving an electric traction unit’s adhesion, thyristor control also reduced current consumption.

Three-phase alternating-current motor traction became practicable in the 1980s. With electronics it was possible to compress to manageable weight and size the complex equipment needed to transmute the overhead wire or third-rail current to a supply of variable voltage and frequency suitable for feeding to three-phase alternating-current motors. For railroad traction the alternating-current motor is preferable to a direct-current machine on several counts. It is an induction motor with a squirrel-cage rotor (that is, solid conductors in the slots are shorted together by end rings), and it has no commutators or brushes and no mechanically contacting parts except bearings, so that it is much simpler to maintain and more reliable. It is more compact than a direct motor, so more power is obtainable for a specified motor size and weight; the 6,000-kg (14,000-pound) alternating-current motor in each truck of a modern French National Railways electric locomotive delivers a continuous 3,750 horsepower.

The torque of an alternating-current motor increases with speed, whereas that of a direct-current motor is initially high and falls with rising speed; consequently, the alternating-current motor offers superior adhesion for acceleration of heavy trainloads. Finally, the alternating-current motor is more easily switched into a generating mode to act as a dynamic(rheostatic) or regenerative vehicle brake. (In dynamic braking the current generated to oppose the train’s momentum is dissipated through on-board resistances. In regenerative braking, adopted on mountain or intensively operated urban lines where the surplus current can be readily taken up by other trains, it is fed back into the overhead wire or third rail.) The drawbacks of three-phase alternating-current traction are the intricacy of the on-board electrical equipment needed to convert the current supply before it reaches the motors and its higher capital cost by comparison with direct-current motor systems.

A separate traction motor normally serves each axle via a suitably geared drive. For simplicity of final drive it was for many years standard practice to mount the traction motors on a locomotive’s axles. As train speeds rose, it became increasingly important to limit the impact on the track of unsprung masses. Now motors are either suspended within a locomotive’s trucks or, in the case of some high-speed units, suspended from the locomotive’s body and linked to the axles’ final drive gearboxes by flexible drive shafts.

The direct-current motor’s torque:speed characteristics make a locomotive designed for fast passenger trains, whether electric or diesel-electric, generally unsuitable for freight train work. The heavier loads of the latter require different gearing of the final drives—which will reduce maximum speed—and possibly an increase in the number of motored axles, for increased adhesion. But considerable mixed-traffic haulage capability is obtainable with three-phase alternating-current motors because of their superior adhesion characteristics.

Direct-current motor technology was employed in Japan’s first Shinkansen and France’s first Paris-Lyon TGV trains, but by the early 1990s three-phase alternating-current traction had been adopted for both Japanese and European very-high-speed train-sets—and by extension the systems around the world that have been derived from them. In Europe, international train operation without a locomotive change at frontiers is complicated by the railways’ historic adoption of different electrification systems, either 1,500 or 3,000 volts direct current or 25,000 volts 50 hertz or 15,000 volts 16 2/3 hertz alternating current. For instance, TGV-type trains could not operatie at full efficiency between London, Paris, and Brussels on the Eurostar line via the Channel Tunnel as long as they had to accommodate French 25,000-volt alternating-current overhead wire, Belgian 3,000-volt direct-current overhead wire, and British 750-volt third-rail supply. The French had perfected traction units capable of operating on more than one voltage system soon after they decided to adopt 25,000-volt alternating-current electrification in areas not wired at their previous 1,500-volt direct current. Nevertheless, where very-high-speed traction was concerned, it was impossible to contain within acceptable locomotive weight limits the equipment needed for equivalent high-power output under each system. Only after all the new high-speed lines were electrified on high-voltage alternating current was a true high-speed service available on the Eurostar line.

Since about 1980 the performance and economy of both electric and diesel traction units have been considerably advanced by the interposition between driving controls and vital components of microprocessors, which ensure that the components respond with maximum efficiency and that they are not inadvertently overtaxed. Another product of the application of electronics to controls is that in the modern electric locomotive the engine operator can set the train speed he wishes to reach or maintain, and the traction equipment will automatically apply or vary the appropriate power to the motors, taking account of train weight and track gradient. The microprocessors also serve a diagnostic function, continuously monitoring the state of the systems they control for signs of incipient or actual fault. The microprocessors are linked to a main on-board computer that instantly reports the nature and location of an actual or potential malfunction to a visual display in the driving cab, generally with advice for the cab crew on how it might be rectified or its effects temporarily mitigated. The cab display also indicates the effectiveness of the countermeasures taken. The computer automatically stores such data, either for downloading to maintenance staff at the journey’s end or, on a railroad equipped with train-to-ground-installation radio, for immediate transmission to a maintenance establishment so that preparations for repair of a fault are in place as soon as the traction unit ends its run. In newer very-high-speed, fixed-formation train-sets, a through-train fibre-optics transmission system concentrates data from the microprocessor controls—both those of passenger car systems, such as air-conditioning and power-operated entrance doors, and those of the rear locomotive or, in the Japanese Shinkansen train-sets, the traction equipment dispersed among a proportion of its cars.

Diesel Traction

By the end of the 1960s, diesel had almost completely superseded steam as the standard railroad motive power on nonelectrified lines around the world. The change came first and most quickly in North America, where, during the 25 years 1935–60 (and especially in the period 1951–60), railroads in the United States completely replaced their steam locomotives.

What caused the diesel to supersede the steam locomotive so rapidly was the pressure of competition from other modes of transport and the continuing rise in wage costs, which forced the railroads to improve their services and adopt every possible measure to increase operating efficiency. Compared with steam, the diesel traction unit had a number of major advantages:
1. It could operate for long periods with no lost time for maintenance; thus, in North America the diesel could operate through on a run of 3,200 km (2,000 miles) or more and then, after servicing, start the return trip. Steam locomotives required extensive servicing after only a few hours’ operation.
2. It used less fuel energy than a steam locomotive, for its thermal efficiency was about four times as great.
3. It could accelerate a train more rapidly and operate at higher sustained speeds with less damage to the track.

In addition, the diesel was superior to the steam locomotive because of its smoother acceleration, greater cleanliness, standardized repair parts, and operating flexibility (a number of diesel units could be combined and run by one operator under multiple-unit control).

The diesel-electric locomotive is, essentially, an electric locomotive that carries its own power plant. Its use, therefore, brings to a railroad some of the advantages of electrification, but without the capital cost of the power distribution and feed-wire system. As compared with an electric locomotive, however, the diesel-electric has an important drawback: since its output is essentially limited to that of its diesel engine, it can develop less horsepower per locomotive unit. Because high horsepower is required for high-speed operation, the diesel is, therefore, less desirable than the electric for high-speed passenger services and very fast freight operations.

Diesel development

Experiments with diesel-engine locomotives and railcars began almost as soon as the diesel engine was patented by the German engineer Rudolf Diesel in 1892. Attempts at building practical locomotives and railcars (for branch-line passenger runs) continued through the 1920s. The first successful diesel switch engine went into service in 1925; “road” locomotives were delivered to the Canadian National and New York Central railroads in 1928. The first really striking results with diesel traction were obtained in Germany in 1933. There, the Fliegende Hamburger, a two-car, streamlined, diesel-electric train, with two 400-horsepower engines, began running between Berlin and Hamburg on a schedule that averaged 124 km (77 miles) per hour. By 1939 most of Germany’s principal cities were interconnected by trains of this kind, scheduled to run at average speeds up to 134.1 km (83.3 miles) per hour between stops.

The next step was to build a separate diesel-electric locomotive unit that could haul any train. In 1935 one such unit was delivered to the Baltimore and Ohio and two to the Santa Fe Railway Company. These were passenger units; the first road freight locomotive, a four-unit, 5,400-horsepower Electro-Motive Division, General Motors Corporation demonstrator, was not built until 1939.

By the end of World War II, the diesel locomotive had become a proven, standardized type of motive power, and it rapidly began to supersede the steam locomotive in North America. In the United States a fleet of 27,000 diesel locomotives proved fully capable of performing more transportationwork than the 40,000 steam locomotives they replaced.

After World War II, the use of diesel traction greatly increased throughout the world, though the pace of conversion was generally slower than in the United States.
Elements of the diesel locomotive

Although the diesel engine has been vastly improved in power and performance, the basic principles remain the same: drawing air into the cylinder, compressing it so that its temperature is raised, and then injecting a small quantity of oil into the cylinder. The oil ignites without a spark because of the high temperature. The diesel engine may operate on the two-stroke or four-stroke cycle. Rated operating speeds vary from 350 to 2,000 revolutions per minute, and rated output may be from 10 to 4,000 horsepower. Railroads in the United States use engines in the 1,000-revolutions-per-minute range; in Europe and elsewhere, some manufacturers have favoured more compact engines of 1,500–2,000 revolutions per minute.

Most yard-switching and short-haul locomotives are equipped with diesel engines ranging from 600 to 1,800 horsepower; road units commonly have engines ranging from 2,000 to 4,000 horsepower. Most builders use V-type engines, although in-line types are used on smaller locomotives and for underfloor fitment on railcars and multiple-unit train-sets.

The most commonly employed method of power transmission is electric, to convert the mechanical energy produced by the diesel engine to current for electric traction motors. Through most of the 20th century the universal method was to couple the diesel engine to a direct-current generator, from which, through appropriate controls, the current was fed to the motors. Beginning in the 1970s, the availability of compact semiconductor rectifiers enabled replacement of the direct-current generator by an alternator, which is able to produce more power and is less costly to maintain than an equivalent direct-current machine. For supply of series-wound direct-current traction motors, static rectifiers converted the three-phase alternating-current output of the alternator to direct current. Then in the 1980s European manufacturers began to adopt the three-phase alternating-current motor for diesel-electric traction units seeking advantages similar to those obtainable from this technology in electric traction. This requires the direct-current output from the rectifier to be transmuted by a thyristor-controlled inverter into a three-phase variable voltage and frequency supply for the alternating-current motors.

On some railroads with lightly laid track, generally those with narrow rail gauge, locomotives may still need nonmotored as well as motored axles for acceptable weight and bulk distribution. But the great majority of diesel-electric locomotives now have all axles powered.

Other types of transmissions also are used in diesel locomotives. The hydraulic transmission, which first became quite popular in Germany, is often favoured for diesel railcars and multiple-unit train-sets. It employs a centrifugal pump or impeller driving a turbine in a chamber filled with oil or a similar fluid. The pump, driven by the diesel engine, converts the engine power to kinetic energy in the oil impinging on the turbine blades. The faster the blades move, the less the relative impinging speed of the oil and the faster the locomotive moves.

Mechanical transmission is the simplest type; it is mainly used in very low-power switching locomotives and in low-power diesel railcars. Basically it is a clutch and gearbox similar to those used in automobiles. A hydraulic coupling, in some cases, is used in place of a friction clutch.
Types of diesel motive power

There are three broad classes of railroad equipment that use diesel engines as prime movers:
1. The light passenger railcar or rail bus (up to 200 horsepower), which usually is four-wheeled and has mechanical transmission. It may be designed to haul a light trailer car. Use of such vehicles is very limited.
2. The four-axle passenger railcar (up to 750 horsepower), which can be operated independently, haul a nonpowered trailer, or be formed into a semipermanent train-set such as a multiple-unit with all or a proportion of the cars powered. In the powered cars the diesel engine and all associated traction equipment, including fuel tanks, are capable of fitting under the floor to free space above the frames for passenger seating. Transmission is either electric or hydraulic. Modern railcars and railcar train-sets are mostly equipped for multiple-unit train operation, with driving control from a single cab.
3. Locomotives (10 to 4,000 horsepower), which may have mechanical transmission if very low-powered or hydraulic transmission for outputs of up to about 2,000 horsepower but in most cases have electric transmission, the choice depending on power output and purpose.

A substantial increase of diesel engine power-to-weight ratios and the application of electronics to component control and diagnostic systems brought significant advances in the efficiency of diesel locomotives in the last quarter of the 20th century. In 1990 a diesel engine with a continuous rating of 3,500 horsepower was available at almost half the weight of a similar model in 1970. At the same time, the fuel efficiency of diesel engines was significantly improved.

Electronics have made a particularly important contribution to the load-hauling capability of diesel-electric locomotives in road freight work, by improving adhesion at starting or in grade-climbing. A locomotive accelerating from rest can develop from 33 to 50 percent more tractive force if its powered wheels are allowed to “creep” into a very slight, steady, and finely controlled slip. In a typical “creep control” system, Doppler radar mounted under the locomotive precisely measures true ground speed, against which microprocessors calculate the ideal creep speed limit in the prevailing track conditions and automatically regulate current supply to the traction motors. The process is continuous, so that current levels are immediately adjusted to match a change in track parameters. In the 1960s, North Americans considered that a diesel-electric locomotive of 3,000–3,600 horsepower or more must have six motored axles for effective adhesion: two railroads had acquired a small number of eight-motored-axle locomotives, each powered by two diesel engines, with outputs of 5,000–6,600 horsepower. Since the mid-1980s four-axle locomotives of up to 4,000 horsepower have become feasible and are widely employed in fast freight service (though for heavy freight duty six-axle locomotives were still preferred). But today a 4,000-horsepower rating is obtainable from a 16-cylinder diesel engine, whereas in the 1960s a 3,600-horsepower output demanded a 20-cylinder engine. This, coupled with the reduction in the number of locomotives required to haul a given tonnage due to improved adhesion, has been a key factor in decreasing locomotive maintenance costs.

Outside North America, widespread electrification all but ended production of diesel locomotives purpose-built for passenger train haulage in the 1960s. The last development for high-speed diesel service was on British Railways, which, for its nonelectrified trunk routes, mass-produced a semipermanent train-set, the InterCity 125, that had a 2,250-horsepower locomotive at each end of seven or eight intermediate cars. In 1987 one of these sets established a world speed record for diesel traction of 238 km (148 miles) per hour. Some InterCity 125 sets are expected to remain in service under various other designations until well into the 21st century. In North America, Amtrak in the United States and VIA in Canada, as well as some urban mass-transit authorities, still operate diesel locomotives exclusively on passenger trains. Elsewhere road haul diesel locomotives are designed either for exclusive freight haulage or for mixed passenger and freight work.

Traction operating methods

Multiple-unit connection and operation of locomotives, to adjust power to load and track gradient requirements, is standard practice in North America and is common elsewhere. Where considerable gradients occur or freight trains are unusually long and heavy, concentration of locomotives at a train’s head can strain couplings and undesirably delay transmission of full braking power to the train’s rearmost cars. In such conditions several railroads, principally in North America, employ crewless “slave” locomotives that are inserted partway down the train. Radio signals transmitted from the train’s leading locomotive cause the slave locomotive’s controls to respond automatically and correspondingly to all operations of the controls. A world record for freight train weight and length was set in August 1989 on South Africa’s electrified, 830-km (516-mile), 1,065-mm (3-foot 6-inch) gauge Sishen-Saldanha ore line. In the course of research into the feasibility of increasing the line’s regular trainloads, a 660-car train grossing 71,600 tons and 7.2 km (4.47 miles) long was run from end to end of the route. Power was furnished by five 5,025-horsepower electric locomotives at the front, four more inserted after the 470th freight car, and at the rear, to avoid overtaxing the traction current supply system, seven 2,900-horsepower diesel locomotives.

After World War II easy directional reversibility of passenger train-sets became increasingly important for intensively operated short- and medium-haul services, to reduce terminal turnround times and minimize the number of train-sets needed to provide the service. The most popular medium has been the self-powered railcar or multiple-unit train-set, with a driving cab at each end, so that reversal requires only that the crew change cabs. An alternative, known as push-pull, has a normal locomotive at one end and, at the other, a nonpowered passenger or baggage car, known as the driving or control trailer, with a driving cab at its extremity. In one direction the locomotive pulls the train; in the other, unmanned, it propels the train, driven via through-train wiring from the control trailer’s cab. A potential operating advantage of push-pull as opposed to use of self-powered train-sets on a railroad running both passenger and freight trains is that at night, when passenger operation has ceased, the locomotives can be detached for freight haulage.

Turbine Propulsion

In the 1950s gas-turbine instead of diesel propulsion was tried for a few locomotives in the United States and Britain, but the results did not justify continuing development. There was a longer but very limited career in rail use for the compact and lightweight gas turbines developed for helicopters that became available in the 1960s. Their power-to-weight ratio, superior to that of contemporary diesel engines, made them preferable for lightweight, high-speed train-sets. They were applied to Canadian-built train-sets placed in service in 1968 between Montreal and Toronto and in 1969 between New York City and Boston, but these were short-lived because of equipment troubles, operating noise, and the cost of fuel. The technology has not been entirely abandoned, however. At the end of the 20th and beginning of the 21st centuries, the Bombardier company of Canada presented its gas-turbine JetTrain locomotive as an alternative to electric traction for new North American high-speed systems.

Several attempts have been made to adapt the steam turbine to railroad traction. One of the first such experiments was a Swedish locomotive built in 1921. Other prototypes followed in Europe and the United States. They all functioned, but they made their appearance too late to compete against the diesel and electrification.

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

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

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#468 2019-08-04 00:33:08

ganesh
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Posts: 28,716

Re: Miscellany

383) Sunflower

Sunflower, (genus Helianthus), genus of nearly 70 species of herbaceous plants of the aster family (Asteraceae). Sunflowers are native primarily to North and South America, and some species are cultivated as ornamentals for their spectacular size and flower heads and for their edible seeds. The Jerusalem artichoke (Helianthus tuberosus) is cultivated for its edible underground tubers.

The common sunflower (H. annuus) is an annual herb with a rough hairy stem 1–4.5 metres (3–15 feet) high and broad, coarsely toothed, rough leaves 7.5–30 cm (3–12 inches) long arranged in spirals. The attractive heads of flowers are 7.5–15 cm wide in wild specimens and often 30 cm or more in cultivated types. The disk flowers are brown, yellow, or purple, while the petal like ray flowers are yellow. The fruit is a single-seeded achene. Oilseed varieties typically have small black achenes, while those grown for direct seed consumption, known as confection varieties, have larger black-and-white achenes that readily separate from the seed within.

The common sunflower is valuable from an economic as well as from an ornamental point of view. The leaves are used as fodder, the flowers yield a yellow dye, and the seeds contain oil and are used for food. The sweet yellow oil obtained by compression of the seeds is considered equal to olive or almond oil for table use. Sunflower oil cake is used for stock and poultry feeding. The oil is also used in soap and paints and as a lubricant. The seeds may be eaten dried, roasted, or ground into nut butter and are common in birdseed mixes.

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

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

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#469 2019-08-06 01:45:22

ganesh
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Re: Miscellany

384) Polyethylene terephthalate

Polyethylene terephthalate (PET or PETE), a strong, stiff synthetic fibre and resin, and a member of the polyester family of polymers. PET is spun into fibres for permanent-press fabrics, blow-molded into disposable beverage bottles, and extruded into photographic film and magnetic recording tape.

PET is produced by the polymerization of ethylene glycol and terephthalic acid. Ethylene glycol is a colourless liquid obtained from ethylene, and terephthalic acid is a crystalline solidobtained from xylene. When heated together under the influence of chemical catalysts, ethylene glycol and terephthalic acid produce PET in the form of a molten, viscous mass that can be spun directly to fibres or solidified for later processing as a plastic. In chemical terms, ethylene glycol is a diol, an alcohol with a molecular structure that contains two hydroxyl (OH) groups, and terephthalic acid is a dicarboxylic aromatic acid, an acid with a molecular structure that contains a large, six-sided carbon (or aromatic) ring and two carboxyl (CO2H) groups. Under the influence of heat and catalysts, the hydroxyl and carboxyl groups react to form ester(CO-O) groups, which serve as the chemical links joining multiple PET units together into long-chain polymers. Water is also produced as a by-product.

The presence of a large aromatic ring in the PET repeating units gives the polymer notable stiffness and strength, especially when the polymer chains are aligned with one another in an orderly arrangement by drawing (stretching). In this semicrystalline form, PET is made into a high-strength textile fibre marketed under such trademarked names as Dacron, by the American DuPont Company, and Terylene, by the British Imperial Chemical Industries PLC. The stiffness of PET fibres makes them highly resistant to deformation, so they impart excellent resistance to wrinkling in fabrics. They are often used in durable-press blends with other fibres such as rayon, wool, and cotton, reinforcing the inherent properties of those fibres while contributing to the ability of the fabric to recover from wrinkling.

PET is also made into fibre filling for insulated clothing and for furniture and pillows. When made in very fine filaments, it is used in artificial silk, and in large-diameter filaments it is used in carpets. Among the industrial applications of PET are automobile tire yarns, conveyor belts and drive belts, reinforcement for fire and garden hoses, seat belts (an application in which it has largely replaced nylon), nonwoven fabrics for stabilizing drainage ditches, culverts, and railroad beds, and nonwovens for use as diaper topsheets and disposable medical garments. PET is the most important of the man-made fibres in weight produced and in value.

At a slightly higher molecular weight, PET is made into a high-strength plastic that can be shaped by all the common methods employed with other thermoplastics. Magnetic recording tape and photographic film are produced by extrusion of PET film (often sold under the trademarks Mylar and Melinex). Molten PET can be blow-molded into transparent containers of high strength and rigidity that are also virtually impermeable to gas and liquid. In this form, PET has become widely used in carbonated-beverage bottles and in jars for food processed at low temperatures. The low softening temperature of PET—approximately 70 °C (160 °F) prevents it from being used as a container for hot-filled foods.

PET is the most widely recycled plastic. PET bottles and containers are commonly melted down and spun into fibres for fibrefill or carpets. When collected in a suitably pure state, PET can be recycled into its original uses, and methods have been devised for breaking the polymer down into its chemical precursors for resynthesizing into PET. The recycling code number for PET is #1.

PET was first prepared in England by J. Rex Whinfield and James T. math of the Calico Printers Association during a study of phthalic acid begun in 1940. Because of wartime restrictions, patent specifications for the new material were not immediately published. Production by Imperial Chemical of its Terylene-brand PET fibre did not begin until 1954. Meanwhile, by 1945 DuPont had independently developed a practical preparation process from terephthalic acid, and in 1953 the company began to produce Dacron fibre. PET soon became the most widely produced synthetic fibre in the world. In the 1970s, improved stretch-molding procedures were devised that allowed PET to be made into durable crystal-clear beverage bottles—an application that soon became second in importance only to fibre production.

What-is-Polyethylene-terephthalate-PETE-or-PET-and-What-is-it-Used-For-300x171.jpg


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

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

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#470 2019-08-06 19:15:49

ganesh
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Posts: 28,716

Re: Miscellany

385) Voltmeter

Voltmeter, instrument that measures voltages of either direct or alternating electric currenton a scale usually graduated in volts, millivolts (0.001 volt), or kilovolts (1,000 volts). The typical commercial or laboratory standard voltmeter in use today is likely to employ an electromechanical mechanism in which current flowing through turns of wire is translated into a reading of voltage. Other types of voltmeters include the electrostatic voltmeter, which uses electrostatic forces and, thus, is the only voltmeter to measure voltage directly rather than by the effect of current. The potentiometer operates by comparing the voltage to be measured with known voltage; it is used to measure very low voltages.

The electronic voltmeter, which has largely replaced the vacuum-tube voltmeter, uses amplification or rectification (or both) to measure either alternating- or direct-current voltages. The current needed to actuate the meter movement is not taken from the circuit being measured; hence, this type of instrument does not introduce errors of circuit loading.

The instruments just described provide readings in analogue form, by moving a pointer that indicates voltage on a scale. Digital voltmeters give readings as numerical displays. They also provide outputs that can be transmitted over distance, can activate printers or typewriters, and can feed into computers. Digital voltmeters generally have a higher order of accuracy than analogue instruments.
An instrument that also measures ohms and amperes (in milliamperes) is known as a volt-ohm-milliammeter, or sometimes as a multimeter.

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

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

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#471 2019-08-08 01:35:24

ganesh
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Re: Miscellany

386) Mona Lisa

Mona Lisa, also called Portrait of Lisa Gherardini, wife of Francesco del Giocondo, Italian La Gioconda, or French La Joconde, oil painting on a poplar wood panel by Leonardo da Vinci, probably the world’s most famous painting. It was painted sometime between 1503 and 1519, when Leonardo was living in Florence, and it now hangs in the Louvre Museum, in Paris, where it remained an object of pilgrimage in the 21st century. The sitter’s mysterious smile and her unproven identity have made the painting a source of ongoing investigation and fascination.

Subject

The painting presents a woman in half-body portrait, which has as a backdrop a distant landscape. Yet this simple description of a seemingly standard composition gives little sense of Leonardo’s achievement. The three-quarter view, in which the sitter’s position mostly turns toward the viewer, broke from the standard profile pose used in Italian art and quickly became the convention for all portraits, one used well into the 21st century. The subject’s softly sculptural face shows Leonardo’s skillful handling of sfumato (use of fine shading) and reveals his understanding of the musculature and the skull beneath the skin. The delicately painted veil, the finely wrought tresses, and the careful rendering of folded fabric demonstrate Leonardo’s studied observations and inexhaustible patience. Moreover, the sensuous curves of the sitter’s hair and clothing are echoed in the shapes of the valleys and rivers behind her. The sense of overall harmony achieved in the painting—especially apparent in the sitter’s faint smile—reflects Leonardo’s idea of the cosmic link connecting humanity and nature, making this painting an enduring record of Leonardo’s vision. In its exquisite synthesis of sitter and landscape, the Mona Lisa set the standard for all future portraits.

There has been much speculation and debate regarding the identity of the portrait’s sitter. Scholars and historians have posited numerous interpretations, including that she is Lisa del Giocondo (née Gherardini), the wife of the Florentine merchant Francesco di Bartolomeo del Giocondo, hence the alternative title to the work, La Gioconda. That identity was first suggested in 1550 by artist biographer Giorgio Vasari. Another theory was that the model may have been Leonardo’s mother, Caterina. That interpretation was put forth by, among others, Sigmund Freud, who seemed to think that the Mona Lisa’s mysterious smile emerged from a—perhaps unconscious—memory of Caterina’s smile. A third suggestion was that the painting was, in fact, Leonardo’s self-portrait, given the resemblance between the sitter’s and the artist’s facial features. Some scholars suggested that disguising himself as a woman was the artist’s riddle. The sitter’s identity has not been definitively proven. Numerous attempts in the 21st century to settle the debate by seeking Lisa del Giocondo’s remains to test her DNA and recreate an image of her face were inconclusive.

History

Leonardo da Vinci began painting the Mona Lisa about 1503, and it was in his studio when he died in 1519. He likely worked on it intermittently over several years, adding multiple layers of thin oil glazes at different times. Small cracks in the paint, called craquelure, appear throughout the whole piece, but they are finer on the hands, where the thinner glazes correspond to Leonardo’s late period.

French King Francis I, in whose court Leonardo spent the last years of his life, acquired the work after the artist’s death, and it became part of the royal collection. For centuries the portrait was secluded in French palaces, until insurgents claimed the royal collection as the property of the people during the French Revolution (1787–99). Following a period hanging in Napoleon’s bedroom, the Mona Lisa was installed in the Louvre Museum at the turn of the 19th century.

In 1911 the painting was stolen, causing an immediate media sensation. People flocked to the Louvre to view the empty space where the painting had once hung, the museum’s director of paintings resigned, and the poet Guillaume Apollinaire and artist Pablo Picasso were even arrested as suspects. Two years later an art dealer in Florence alerted local authorities that a man had tried to sell him the painting. Police found the portrait stashed in the false bottom of a trunk belonging to Vincenzo Peruggia, an Italian immigrant who had briefly worked at the Louvre fitting glass on a selection of paintings, including the Mona Lisa. He and two other workers had taken the portrait from the wall, hid with it in a closet overnight, and ran off with it in the morning. Peruggia was arrested, tried, and imprisoned, while the Mona Lisa took a tour of Italy before making its triumphant return to France.

During World War II the Mona Lisa, singled out as the most-endangered artwork in the Louvre, was evacuated to various locations in France’s countryside, returning to the museum in 1945 after peace had been declared. It later traveled to the United States in 1963, drawing about 40,000 people per day during its six-week stay at the Metropolitan Museum of Artin New York City and at the National Gallery of Art in Washington, D.C. It also toured to Tokyo and Moscow in 1974.

Condition

Scholars have noted that the Mona Lisa is in fairly good condition for its age. The poplar panel shows some evidence of warping from resistance to its original frame and to braces added by early restorers. To prevent the widening of a small crack, visible near the centre of the upper edge of the painting, dovetails were added to the back of the painting. Restorers later pasted heavy canvas over the crack and replaced the top dovetail.

The glass protecting the Mona Lisa was replaced with a bulletproof case after several attacks in 1956, one of which damaged an area near the subject’s left elbow. The Mona Lisa thus escaped harm from acts of vandalism in 1974 during the work’s visit to Tokyo and in 2009 when a museumgoer threw a ceramic mug at it.

The Mona Lisa And Its Influence

The influence of the Mona Lisa on the Renaissance and later times has been enormous, revolutionizing contemporary portrait painting. Not only did the three-quarter pose become the standard, but also Leonardo’s preliminary drawings encouraged other artists to make more and freer studies for their paintings and stimulated connoisseurs to collect those drawings. Through the drawings, his Milanese works were made known to the Florentines. Also, his reputation and stature as an artist and thinker spread to his fellow artists and assured for them a freedom of action and thought similar to his own. One such painter was the young Raphael, who sketched Leonardo’s work in progress and adopted the Mona Lisa format for his portraits; it served as a clear model for his Portrait of Maddalena Doni (c. 1506).

Leonardo even influenced the fashion in which artists dressed their subjects. In his Treatise on Painting, published long after his death, he wrote that art should avoid the fashion:

As far as possible avoid the costumes of your own day.…Costumes of our period should not be depicted unless it be on tombstones, so that we may be spared being laughed at by our successors for the mad fashions of men and leave behind only things that may be admired for their dignity and beauty.

The Mona Lisa demonstrates this aspect of his treatise perfectly in that La Giaconda is dressed in a coloured shift, loosely pleated at the neck, instead of the tight clothes that were then popular.

Other Mona Lisas

At least a dozen excellent replicas of the Mona Lisa exist, many of them by Leonardo’s students. One such copy at the Prado Museum in Madrid was thought to have been painted years after the original. However, during restoration of the painting in the early 2010s, which included using infrared reflectology to examine the work beneath the surface, conservators discovered that the painting had changes that mirrored those of the original. The findings suggested that the artist—likely one of the master’s assistants—painted the copy as Leonardo worked on the Mona Lisa in his studio. Thus, the Prado version became the only known copy completed during Leonardo’s lifetime. Conservators cleaned the entire painting and removed its black background, revealing a detailed landscape resembling Leonardo’s version and vibrant colours, possibly evoking those of the original before the varnish applied by early restorers darkened over time.

Other copies of the Mona Lisa include the so-called Isleworth Mona Lisa, which some commentators asserted was Leonardo’s first version of the famed portrait. The claim was a controversial one, with several leading Leonardo scholars flatly denying it. Numerous seminude interpretations, often referred to as Monna Vanna, also exist and were likely completed by Leonardo’s students with occasional input from their master. The proliferation of Mona Lisas reflects, at least in part, the subject’s almost immediate embodiment of the ideal woman—beautiful, enigmatic, receptive, and still just out of reach.

Over the centuries, this quintessential woman has taken on a new life in popular culture. In the 20th century alone, her iconic status was mocked in schoolboy fashion—the addition of a mustache and goatee to a postcard reproduction—in Marcel Duchamp’s readymade L.H.O.O.Q. (1919). His irreverent defacing of this best known of iconic paintings expressed the Dadaists’ rejection of the art of the past, which in their eyes was part of the infamy of a civilization that had produced the horrors of the First World Warjust ended. Andy Warhol too took aim at the painting’s status, in such serigraphs as Thirty Are Better than One (1963).

Mona Lisa Off The Wall


References in the visual arts have been complemented by musical examinations. La Giaconda’s personality and quirks were examined in a 1915 opera by Max von Schillings. Leonardo’s portrait is also the inspiration for the classic song “Mona Lisa” by American lyricist Ray Evans and songwriter Jay Harold Livingston:

Mona Lisa, Mona Lisa
Men have named you
You’re so like the lady with the mystic smile
Is it only ’cause you’re lonely
They have blamed you
For that Mona Lisa strangeness in your smile


Do you smile to tempt a lover, Mona Lisa
Or is this your way to hide a broken heart
Many dreams have been brought to your doorstep
They just lie there, and they die there
Are you warm, are you real, Mona Lisa
Or just a cold and lonely, lovely work of art

It was famously recorded in 1950 by the jazz pianist and vocalist Nat King Cole and later by his daughter Natalie, as well as many others.
There have been films, notably Mona Lisa (1986), and several novels, including William Gibson’s cyberpunk Mona Lisa Overdrive (1988) and Canadian novelist Rachel Wyatt’s Mona Lisa Smiled a Little (1999), linked to the painting. The Argentine writer Martín Caparrós’s novel Valfierno (2004) brings to life the man who masterminded the 1911 theft of the Mona Lisa from the Louvre.

Both fine art and kitsch continue to refer to Leonardo’s portrait. Bath towels, tapestries, umbrellas, and many other household items bear her image, and that image is reproduced using everything from train tickets to rice plants. Five centuries after its creation, the Mona Lisa remains a touchstone for people around the world.

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

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

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#472 2019-08-10 00:42:57

ganesh
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Re: Miscellany

387) Angkor Wat

Angkor Wat: History of Ancient Temple

Built between roughly A.D. 1113 and 1150, and encompassing an area of about 500 acres (200 hectares), Angkor Wat is one of the largest religious monuments ever constructed. Its name means "temple city."

Originally built as a Hindu temple dedicated to the god Vishnu, it was converted into a Buddhist temple in the 14th century, and statues of Buddha were added to its already rich artwork. Sometime later it was turned into a military fortification. Today it is a UNESCO World Heritage Site that scientists are struggling to preserve.

Its 213-foot-tall (65 meters) central tower is surrounded by four smaller towers and a series of enclosure walls, a layout that recreates the image of Mount Meru, a legendary place in Hindu mythology that is said to lie beyond the Himalayas and be the home of the gods.

Within the largest city in the world

The city where the temple was built, Angkor, is located in modern-day Cambodia and was once the capital of the Khmer Empire. This city contains hundreds of temples. The population may have been over 1 million people. It was easily the largest city in the world until the Industrial Revolution.

Angkor had an urban core that could easily have held 500,000 people and a vast hinterland that had many more inhabitants airborne laser scanning (lidar) research has shown. Researchers have also identified a "lost" citycalled Mahendraparvata, which is located about 25 miles (40 kilometers) north of Angkor Wat. 

A moat, towers, spiral structure and hidden paintings

Angkor Wat itself is surrounded by a 650-foot-wide (200 m) moat that encompasses a perimeter of more than 3 miles (5 km). This moat is 13 feet deep (4 m) and would have helped stabilize the temple's foundation, preventing groundwater from rising too high or falling too low.

Angkor Wat's main entrance was to the west (a direction associated with Vishnu) across a stone causeway, with guardian lions marking the way. Recently, archaeologists found the remains of eight towers made of sandstone and laterite by the western gateway. These towers may be the remains of shrines that were in use before Angkor Wat was fully constructed. To the east of the temple was a second, more modest, entrance.

The heart of the temple was the central tower, entered by way of a steep staircase, a statue of Vishnu at top. This tower "was at once the symbolic center of the nation and the actual center where secular and sacred power joined forces," writes researcher Eleanor Mannikka in the book "Angkor: Celestial Temples of the Khmer Empire" (Abbeville Press, 2002). "From that unparalleled space, Vishnu and the king ruled over the Khmer people."

Hidden paintings have been discovered in the central tower. One chamber in the tower has a scene showing a traditional Khmer ensemble of musical instruments known as the pinpeat, which is made up of different gongs, xylophones, wind instruments and other percussion instruments. In the same chamber, there's also an intricate scene featuring people riding horses between two structures, which might be temples. These two paintings are among 200 that have been discovered in Angkor Wat since 2010. 

A mile long sand structure containing a variety of spiral designs was recently discovered beside Angkor Wat by archaeologists using lidar. It would have existed for a brief period during the mid-to-late 12th century. Archaeologists are not certain what it was used for, and it's possible that the structure was never completed.

The remains of homes and ponds used by workers who lived near Angkor Wat, and serviced the temple, were also found recently during lidar research.

Vishnu and the king

The builder of Angkor Wat was a king named Suryavarman II. A usurper, he came to power in his teenage years by killing his great uncle, Dharanindravarman I, while he was riding an elephant. An inscription says that Suryavarman killed the man "as Garuda [a mythical bird] on a mountain ledge would kill a serpent."

Suryavarman's bloodlust would continue into his rule; he launched attacks into Vietnam in an effort to gain control over the territory. He also made peaceful diplomatic advances, re-opening relations with China.

He venerated the god Vishnu, a deity often depicted as a protector, and installed a statue of the god in Angkor Wat's central tower. This devotion can also be seen in one of the most remarkable reliefs at Angkor Wat, located in the southeast of the temple. The relief shows a chapter in the Hindu story of creation known as the "churning of the sea of milk."

As archaeologist Michael Coe writes, the relief "describes how the devas(gods) and the asuras (demons) churned the ocean under the aegis of Vishnu, to produce the divine elixir of immortality," ("Angkor and the Khmer Civilization," Thames & Hudson, 2003). Scholars consider this relief to be one of the finest art pieces at Angkor Wat.
Suryavarman's devotion to Vishnu is also shown in the posthumous name he was given, "Paramavishnuloka" which, according to researcher Hélène Legendre-De Koninck, means "he who is in the supreme abode of Vishnu." ("Angkor Wat: A Royal Temple," VDG, 2001).

Construction techniques

Building Angkor Wat was an enormous undertaking that involved quarrying, careful artistic work and lots of digging. To create the moat around the temple, 1.5 million cubic meters (53 million cubic feet) of sand and silt were moved, a task that would have required thousands of people working at one time.

The buildings at Angkor Wat posed their own challenges. To support them a tough material called laterite was used, which in turn was encased with softer sandstone that was used for carving the reliefs. These sandstone blocks were quarried at the Kulen Hills, about 18 miles (30 km) to the north. A series of canals were used to transport the blocks to Angkor Wat, research shows.

Beneath the central tower was a shaft that leads to a chamber where, in 1934, archaeologists found "two pieces of crystal and two gold leaves far beneath where the Vishnu statue must have been," Coe writes, adding that deposits like these "spiritually 'energized' a temple, much as a battery will provide power to a portable electronic device."

Purpose

Although Angkor Wat is dedicated to Vishnu, the full purpose of the temple is still debated. One question is whether the ashes of Suryavarman II were interred in the monument, perhaps in the same chamber where the deposits were found. If that were the case it would give the temple a funerary meaning.

Eleanor Mannikka has noted that Angkor Wat is located at 13.41 degrees north in latitude and that the north-south axis of the central tower's chamber is 13.43 cubits long. This, Mannikka believes, is not an accident. "In the central sanctuary, Vishnu is not only placed at the latitude of Angkor Wat, he is also placed along the axis of the earth," she writes, pointing out that the Khmer knew the Earth was round.

In addition, in her writing, Mannikka notes a dozen lunar alignments with Angkor Wat's towers, suggesting that it served an important astronomical role. "During the long and clear Cambodian nights, when the stars filled every inch of the black sky, the astronomer-priests stood on the long western causeway ... and recorded the movements of the moon against the towers in the top two galleries of the temple."

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

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

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#473 2019-08-12 00:23:21

ganesh
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Registered: 2005-06-28
Posts: 28,716

Re: Miscellany

388) Butterfly

Butterfly, (superfamily Papilionoidea), any of numerous species of insects belonging to multiple families. Butterflies, along with the moths and the skippers, make up the insect order Lepidoptera. Butterflies are nearly worldwide in their distribution.

The wings, bodies, and legs, like those of moths, are covered with dustlike scales that come off when the animal is handled. Unlike moths, butterflies are active during the day and are usually brightly coloured or strikingly patterned. Perhaps the most distinctive physical features of the butterfly are its club-tipped antennae and its habit of holding the wings vertically over the back when at rest. The lepidopteran life cycle has four stages: egg, larva (caterpillar), pupa(chrysalis), and adult (imago). The larvae and adults of most butterflies feed on plants, often only specific parts of specific types of plants.

The butterfly families include: Pieridae, the whites and sulfurs, known for their mass migrations; Papilionidae, the swallowtails and parnassians; Lycaenidae, including the blues, coppers, hairstreaks, and gossamer-winged butterflies; Riodinidae, the metalmarks, found chiefly in the American tropics; Nymphalidae, the brush-footed butterflies; Hesperiidae, the skippers; and Hedylidae, the American moth-butterflies (sometimes considered a sister group to Papilionoidea). The brush-footed butterflies represent the largest and most diverse family and include such popular butterflies as the admirals, fritillaries, monarchs, zebras, and painted ladies.

Monarch-Butterfly.jpg


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#474 2019-08-12 15:35:09

Monox D. I-Fly
Member
From: Indonesia
Registered: 2015-12-02
Posts: 1,759

Re: Miscellany

ganesh wrote:

Butterfly, (superfamily Papilionoidea), any of numerous species of insects belonging to multiple families. Butterflies, along with the moths and the skippers, make up the insect order Lepidoptera. Butterflies are nearly worldwide in their distribution.

What are skippers?


Actually I never watch Star Wars and not interested in it anyway, but I choose a Yoda card as my avatar in honor of our great friend bobbym who has passed away. May his adventurous soul rest in peace at heaven.

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#475 2019-08-12 23:19:17

ganesh
Administrator
Registered: 2005-06-28
Posts: 28,716

Re: Miscellany

Monox D. I-Fly wrote:
ganesh wrote:

Butterfly, (superfamily Papilionoidea), any of numerous species of insects belonging to multiple families. Butterflies, along with the moths and the skippers, make up the insect order Lepidoptera. Butterflies are nearly worldwide in their distribution.

What are skippers?

Skipper, (family Hesperiidae), any of the approximately 3,500 species of insects (order Lepidoptera) that occur worldwide and are named for their fast, darting flight. Skippers are considered an intermediate form between butterflies and moths. The head and small, stout body of the adult tend to resemble those of a moth. However, when at rest, most skippers hold the first pair of wings vertically, as butterflies do. In addition, skippers usually lack the wing-coupling structures (frenula) typical of most moths. Their antennae are clubbed like those of the butterfly, but in most, the club ends in a slender hooked tip.

Skippers are generally small, but their powerful wing muscles enable them to attain speeds up to 30 km (20 miles) per hour. Larvae feed on plants such as legumes and grasses and usually live inside folded or rolled leaves often woven together. Pupation occurs in thin cocoons of silk or silk and leaves.

Many authorities do not classify certain skippers in the family Hesperiidae but separate them into the regent skipper family (Euschemonidae), which contains one Australian species, and the New World giant skipper family (Megathymidae), whose adults have a wingspan of about 9 cm (3.5 inches). The larvae, which bore in agaves and yuccas, are considered a delicacy in Mexico, where they are fried in deep fat, canned, and sold as gusanos de maguey.


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

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