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#326 2019-02-07 16:01:59

ganesh
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Registered: 2005-06-28
Posts: 26,841

Re: Miscellany

Hi Monox D. I-Fly,

Porcupines are rodents with a coat of sharp spines, or quills, that protect against predators. The term covers two families of animals, the Old World porcupines of family Hystricidae, and the New World porcupines of family Erethizontidae.

Porcupines.jpg

Echidnas, sometimes known as spiny anteaters, belong to the family Tachyglossidae in the monotreme order of egg-laying mammals. The four extant species, together with the platypus, are the only surviving members of the order Monotremata, and are the only living mammals that lay eggs.

echidna-thinkstock-166243519-335sm5613.jpg

A Hedgehog is any of the spiny mammals of the subfamily Erinaceinae, in the eulipotyphlan family Erinaceidae. There are seventeen species of hedgehog in five genera found through parts of Europe, Asia, and Africa, and in New Zealand by introduction.

hedgehog-300x267.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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#327 2019-02-09 00:24:58

ganesh
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Posts: 26,841

Re: Miscellany

290) Hare

Hare, (genus Lepus), any of about 30 species of mammals related to rabbits and belonging to the same family (Leporidae). In general, hares have longer ears and longer hind feet than rabbits. While the tail is relatively short, it is longer than that of rabbits. The vernacular names hare and rabbit are frequently misapplied to particular species. Jackrabbits of North America, for example, are actually hares, while the hispid hare (Caprolagus hispidus) of Nepal and India is a rabbit, and the mouse hare is another name for the pika. Pikas, rabbits, and hares constitute the mammalian order Lagomorpha.

Hares are the largest lagomorphs. Depending on the species, the body is about 40–70 cm (16–28 inches) long, with feet up to 15 cm (5.9 inches) long and ears up to 20 cm (7.9 inches) that apparently help dissipate excess body heat. Although usually gray-brown throughout the year, hares living in northern latitudes may turn white in winter (in the far north some remain white all year). One such “varying hare” is the smallest member of genus Lepus, the snowshoe hare (L. americanus) of North America. Most Lepus species have very high rates of reproduction, with multiple large litters being produced each year. Young hares (leverets) are typically born fully furred and with their eyes open and are able to hop a few minutes after birth. Throughout their range, hares are important in the diets of various carnivorous birds, mammals, and reptiles. One of the more dramatic ecological patterns known is the boom-and-bust cycle of snowshoe hare populations in the boreal forests of North America. Populations peak every 8–11 years and then sharply decline, with densities decreasing up to 100-fold. Predation is believed to be responsible for this regular pattern. Lynx populations correlate with those of the snowshoe hare but with a one- to two-year time lag. Lynx eat increasing numbers of hares as they become more common, but, owing to the high rate of predation, lynx numbers drop following the resultant crash in the number of hares. Once hare populations begin to recover, lynx numbers build again, and the cycle is repeated. As hares are almost exclusively herbivorous, they can also dramatically damage natural vegetation or crops when their populations are high. Like rabbits, hares provide people with food and fur.

Hares are the most widespread lagomorph genus, occupying most of North America, Europe, Asia, and Africa. A typical species is the European hare (L. europaeus) of central and southern Europe, the Middle East, and Asia westward into Siberia. The mountain hare (L. timidus) of Asia, the Arctic hare (L. arcticus), and the snowshoe hare live in the far north. Several species of jackrabbit (including L. californicus and L. alleni) are found in the extensive deserts of North America. Many species are abundant throughout their range, including the European hare, which has been introduced into many places, including South America, New Zealand, and Australia, where it has become a pest. In contrast, several hares are endangered, such as the Tehuantepec jackrabbit (L. flavigularis) of southern Mexico, the broom hare (L. castroviejoi) of northern Spain, and the Hainan hare (L. hainanus), which lives on Hainan Island off the coast of southern China.

The hare, closely related to the rabbit, is a small mammal found primarily in the Northern hemisphere. Although there are different species of hare found all over the world, the hare is most commonly found in Europe and North America with the Arctic Hare found inhabiting the freezing climates within the Arctic Circle.

The hare is one of the fastest of all the smaller animals, with hares being able to move at speeds of around 45mph. The strong hind legs of the hare, combined with the large feet of the hare give the hare the ability to run so quickly. The hare is also able to jump over large distances with great ease.

The hare differs from the rabbit mainly in size, as hares are much larger than the average bunny rabbit. The baby hares are also born with their eyes open and a full coat of fur, and these hare babies are often able to hop about after just a few minutes in the outside world.

Hares have very long ears with along with their accurate sense of smell, allow the hare to detect any oncoming predators often before the predators have even noticed the hare. The hare then hops very quickly, in a similar way to a kangaroo, in order to make an escape to safety.

There are over 30 different species of hare found close to farmland and open forests worldwide. The hare is a very adaptable animal as there are species of hare also found in desert regions and of course, the bitterly cold Arctic Tundra.

Due to the size and speed of the hare, the hare is generally not a first choice meal for many predators although there are a number of animals that will hunt hares. The predators of the hare include large birds of prey and wild dogs, and also humans who will often hunt hares both to eat and for pest control.

The hare is generally a calm and docile animal, as hares spend most of their time resting and foraging for food. The hare mainly eats plant matter (grass being one of the favourite foods of the hare) but hares also eat seeds, vegetables and fruit in order to fill them up.

Hares have often been used as symbolic signs, the definitions of which differ with cultures, and hare are also one of the most common animals used in folklore and stories in many different cultures around the world.

Unlike rabbits, hares give birth to their young in nest on the ground rather than in burrows below the ground, which allows baby hares to become accustomed to a life of self-protection as the hares are not born in the safety of an underground burrow. Baby hares are often able to look after themselves from a very early age.

Hare Facts

Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Lagomorpha
Family: Leporidae
Genus: Lepus

Scientific Name: Lepus Europaeus

Type: Mammal

Diet: Herbivore

Size: 36-71cm (14-28in)

Weight: 1-5.5kg (3-12lbs)

Top Speed: 72km/h (45mph)

Lifespan: 2-8 years

Lifestyle: Solitary

Conservation Status: Threatened

Colour: Tan, Brown, White, Black

Skin Type: Fur

Favourite Food: Grass

Habitat: Dense vegetation and open fields

Average Litter Size: 6

Main Prey: Grass, Fruit, Seeds

Predators: Owl, Hawk, Coyote

Special Features: Long legs and ears and large body and feet

difference-between-a-rabbit-and-a-hare-300x300.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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#328 2019-02-10 14:21:46

Monox D. I-Fly
Member
From: Indonesia
Registered: 2015-12-02
Posts: 1,336

Re: Miscellany

ganesh wrote:

The hare differs from the rabbit mainly in size, as hares are much larger than the average bunny rabbit. The baby hares are also born with their eyes open and a full coat of fur, and these hare babies are often able to hop about after just a few minutes in the outside world.

By the way, what's the difference between a rabbit and a bunny?


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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#329 2019-02-10 14:54:31

ganesh
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Registered: 2005-06-28
Posts: 26,841

Re: Miscellany

Monox D. I-Fly wrote:
ganesh wrote:

The hare differs from the rabbit mainly in size, as hares are much larger than the average bunny rabbit. The baby hares are also born with their eyes open and a full coat of fur, and these hare babies are often able to hop about after just a few minutes in the outside world.

By the way, what's the difference between a rabbit and a bunny?

Rabbits are small mammals in the family Leporidae of the order Lagomorpha (along with the hare and the pika). Oryctolagus cuniculus includes the European rabbit species and its descendants, the world's 305 breeds of domestic rabbit. Sylvilagus includes 13 wild rabbit species, among them the 7 types of cottontail. The European rabbit, which has been introduced on every continent except Antarctica, is familiar throughout the world as a wild prey animal and as a domesticated form of livestock and pet. With its widespread effect on ecologies and cultures, the rabbit (or bunny) is, in many areas of the world, a part of daily life - as food, clothing, a companion, and as a source of artistic inspiration.

Hares and jackrabbits are leporids belonging to the genus Lepus. Hares are classified in the same family as rabbits. They are similar in size and form to rabbits and have similar herbivorous diets, but generally have longer ears and live solitarily or in pairs. Also unlike rabbits, their young are able to fend for themselves shortly after birth (precocial) rather than emerging blind and helpless (altricial). Most are fast runners. Hare species are native to Africa, Eurasia, North America, and the Japanese archipelago.

Five leporid species with "hare" in their common names are not considered true hares: the hispid hare (Caprolagus hispidus), and four species known as red rock hares (comprising Pronolagus). Conversely, Jackrabbits are hares, rather than rabbits.


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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#330 2019-02-11 00:13:25

ganesh
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Posts: 26,841

Re: Miscellany

291) Scandinavia

Scandinavia, region of N Europe. It consists of the kingdoms of Sweden, Norway, and Denmark; Finland and Iceland are usually considered part of Scandinavia. Physiographically, Denmark belongs to the North European Plain rather than to the geologically distinct Scandinavian peninsula (which is part of the ancient Baltic Shield), occupied by Norway and Sweden. Sometimes the word "Norden" is applied to the five countries because it avoids the physiographic and cultural limitations of the word Scandinavia. The Scandinavian peninsula (c.300,000 sq mi/777,000 sq km) is c.1,150 mi (1,850 km) long and from 230 to 500 mi (370–805 km) wide and is bordered by the Gulf of Bothnia, the Baltic Sea, the Kattegat and Skagerrak straits, the North Sea, the Atlantic Ocean, and the Arctic Ocean. It is mountainous in the west (rising to 8,104 ft/2,470 m at Glittertinden, S Norway) and slopes gently in the east and the south. The region was heavily glaciated during the Ice Age; Jostedalsbreen (W Norway), the largest glacier of mainland Europe, is a remnant of the great ice sheet. The peninsula's western coast is deeply indented by fjords. Short, swift-flowing streams drain to the west, while long parallel rivers and numerous lakes are found in the east; Vänern and Vättern, both in S Sweden, are among Europe's largest lakes. Nearly a quarter of the peninsula lies N of the Arctic Circle, reaching its northernmost point in Cape Nordkyn, Norway. The climate varies from tundra and subarctic in the north, to humid continental in the central portion, and to marine west coast in the south and southwest. The region's best farmland is in S Sweden. The peninsula is rich in timber and minerals (notably iron and copper), and has a great hydroelectricity generating capacity. Its coastal waters are important fishing grounds. Large petroleum and natural-gas deposits have been found off Norway's coast in the North Sea and the Atlantic Ocean. Population is concentrated in the southern part of the peninsula; Stockholm and Göteborg (both in Sweden) and Oslo (Norway) are the largest cities. Except for the Sami (Lapps) and Finns in the north and east, the Scandinavian peoples speak a closely related group of Germanic languages—Norwegian, Danish, Icelandic, Faeroese, and Swedish. The oldest Germanic literature (see Old Norse literature) flourished in Scandinavia, especially in Iceland.

Old Norse Literature

Old Norse literature, the literature of the Northmen, or Norsemen, c.850–c.1350. It survives mainly in Icelandic writings, for little medieval vernacular literature remains from Norway, Sweden, or Denmark.

The Norwegians who settled Iceland late in the 9th cent. brought with them a body of oral mythological poetry that flourished there in a sturdy, seafaring world removed from the warring mainland. The first great period, which lasted until c.1100, was oral, as writing was not introduced until well after the establishment of Christianity (c.1000). From c.1100 to c.1350 both the oral poetry and new compositions were set down. The conscious, clear prose style that developed for both saga and history antedates that of all other modern European literatures except Gaelic. In the later 13th cent., with Iceland's loss of independence to Norway, literary activity declined and had virtually disappeared a century later.

The surviving body of literature can best be discussed as consisting of several types. Eddic writings (see Edda) were condensations of ancient lays, in alliterative verse (see alliteration), on old gods and heroes. Many of the heroic lays involve the legend of Siegfried and Brunhild; the mythological lays, focusing on Norse gods, include "The Lay of Thrym," a narrative about Thor, and "The Seeress' Prophecy," which begins with creation and anticipates the gods' demise.

Also composed in alliterative verse, but more complex and artificial in form, was scaldic poetry, which flourished in Norway about the 10th cent. and reached its height slightly later in Iceland. Comprising poems of praise, triumph, lamentation, and love, it is subjective in approach and highly mannered in technique. Intricate metrical schemes are meticulously observed, and diction is polished to the point of preciousness, especially in the incessant use of the kenning (a metaphoric substituted phrase, e.g., "ship-road" for "sea" ), found also in Anglo-Saxon literature. As the scalds became a group apart, and only the initiated could understand their highly allusive verse, Snorri Sturluson was prompted to write the Prose Edda (c.1222) as a text of scaldic poetry, in a vain attempt to promote and preserve the old techniques.

As scaldic poetry declined, new forms rose to replace it, among them the ballad and the sacred hymn. A new rhymed verse developed, somewhat analogous to that in Middle English literature and used for much the same purpose—translation and paraphrase of foreign romances. The bulk of medieval Norse literature, and the most readable today, survives in the form of sagas, that is, prose narratives, sometimes interspersed with verse, which relate the lives of legendary or historical figures with objectivity and skillful characterization and which reflect the old Icelandic devotion to personal honor and family.

Historical writing of the 11th and 12th cent. is also noteworthy. In this field Snorri Sturlusoncontributed his Heimskringla. Ari Thorgilsson produced Islendingabók (c.1125), an account of the island's history, an abridged version of which has survived. He was probably partly responsible also for the Landnámabók, a topographical and genealogical account of Iceland; other works by Thorgilsson have been lost. Finally, all the Scandinavian countries produced medieval ballads, but these were not written down until much later. There remain numerous unsolved problems concerning oral composition, transmission of origins and influences, and dating.

(Scandinavia is a region in Northern Europe, with strong historical, cultural, and linguistic ties. The term Scandinavia in local usage covers the three kingdoms of Denmark, Norway, and Sweden. The majority national languages of these three, belong to the Scandinavian dialect continuum, and are mutually intelligible North Germanic languages. In English usage, Scandinavia also sometimes refers to the Scandinavian Peninsula, or to the broader region including Finland and Iceland, which is always known locally as the Nordic countries.

While part of the Nordic countries, the remote Norwegian islands of Svalbard and Jan Mayen are not in Scandinavia, nor is Greenland, a constituent country within the Kingdom of Denmark. The Faroe Islands are sometimes included.)

map.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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#331 2019-02-11 14:36:54

Monox D. I-Fly
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From: Indonesia
Registered: 2015-12-02
Posts: 1,336

Re: Miscellany

ganesh wrote:

With its widespread effect on ecologies and cultures, the rabbit (or bunny) is, in many areas of the world, a part of daily life - as food, clothing, a companion, and as a source of artistic inspiration.

So, rabbit and bunny are synonymous?


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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#332 2019-02-11 15:18:45

ganesh
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Registered: 2005-06-28
Posts: 26,841

Re: Miscellany

Monox D. I-Fly wrote:
ganesh wrote:

With its widespread effect on ecologies and cultures, the rabbit (or bunny) is, in many areas of the world, a part of daily life - as food, clothing, a companion, and as a source of artistic inspiration.

So, rabbit and bunny are synonymous?

More or less.

bunny:

1. Informal. a rabbit, especially a small or young one. (dictionary.com)

2. A child's term for a rabbit. (en.oxforddictionaries.com)

3. a rabbit; also bunny rabbit child's word. (dictionary.cambridge.org)

4. informal : RABBIT; especially : a young rabbit.  (merriam-webster.com)

5. bunny -  bunny or bunny rabbit :- a rabbit. This word is used by children or when talking to children. (macmillandictionary.com)


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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#333 2019-02-11 15:26:46

Monox D. I-Fly
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From: Indonesia
Registered: 2015-12-02
Posts: 1,336

Re: Miscellany

So it's not exactly synonymous, then. It's either A child term for a rabbit or a term for a child rabbit.


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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#334 2019-02-11 15:44:02

ganesh
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Registered: 2005-06-28
Posts: 26,841

Re: Miscellany

Monox D. I-Fly wrote:

So it's not exactly synonymous, then. It's either A child term for a rabbit or a term for a child rabbit.

Not synonymous, but almost the same, depending on the context.


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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#335 2019-02-13 01:17:16

ganesh
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Re: Miscellany

292) Guava

Alternative Title: Psidium

Guava, (Psidium guajava), small tropical tree or shrub of the family Myrtaceae, cultivated for its edible fruits. Guava trees are native to tropical America and are grown in tropical and subtropical areas worldwide. Guava fruits are processed into jams, jellies, and preserves and are common pastry fillings. Fresh guavas are rich in vitamins A, B, and C; they are commonly eaten raw and may be sliced and served with sugar and cream as a dessert.

Physical Description And Cultivation

The common guava has quadrangular branchlets, oval to oblong leavesabout 7.6 cm (3 inches) in length, and four-petaled white flowers about 2.5 cm (1 inch) broad. The fruits are round to pear-shaped and measure up to 7.6 cm in diameter; their pulp contains many small hard seeds (more abundant in wild forms than in cultivated varieties). The fruit has a yellow skin and white, yellow, or pink flesh. The musky, at times pungent, odour of the sweet pulp is not always appreciated.
Propagation is usually by seeds, but improved varieties must be perpetuated by plant parts. The plant’s hard dry wood and thin bark prevent cutting and conventional methods of grafting. Veneer grafting, using as rootstocks young plants in vigorous growth, gives excellent results.

The plant is not frost-resistant but is successfully grown throughout southern Florida; in several tropical regions it grows so abundantly in a half-wild state as to have become a pest.

Related Species

The cattley, or strawberry, guava (Psidium cattleianum) is considerably more frost-resistant than the common guava. It occurs in two forms: one has fruits with a bright yellow skin, and the other has fruits with a purplish red skin. The plant is a large shrub with thick glossy green oval leaves and white flowers. The fruits are round, up to 5 cm (2 inches) in diameter, and contain many hard seeds. The soft pulp has a strawberry-like flavour. This species is frequently planted in gardens throughout southern California and other subtropical regions but is not commercially important.

Other guavas include the cás, or wild guava, of Costa Rica (P. friedrichsthalianum) and the guisaro, or Brazilian guava (P. guineense), both of which have acidic fruits.

The so-called pineapple guava, or feijoa (Acca sellowiana), is an unrelated species.

Guava  is a common tropical fruit cultivated in many tropical and subtropical regions. Psidium guajava (common guava, lemon guava) is a small tree in the myrtle family (Myrtaceae), native to Mexico, Central America, and northern South America. Although related species may also be called guavas, they belong to other species or genera, such as the "pineapple guava" Acca sellowiana. In 2011, India was the largest producer of guavas.

Types

The most frequently eaten species, and the one often simply referred to as "the guava", is the apple guava (Psidium guajava). Guavas are typical Myrtoideae, with tough dark leaves that are opposite, simple, elliptic to ovate and 5–15 centimetres (2.0–5.9 in) long. The flowers are white, with five petals and numerous stamens. The fruits are many-seeded berries.

The genera Accara and Acca (formerly Feijoa, pineapple guava) were formerly included in Psidium.

Etymology and regional names

The term "guava" appears to have been derived from Arawak guayabo "guava tree", via the Spanish guayaba. It has been adapted in many European and Asian languages, having a similar form.

Another term for guavas is peru, derived from pear. It is common in countries bordering the western Indian Ocean and probably derives from Spanish or Portuguese. In parts of the Indian subcontinent and Middle-East, guava is called amrood, possibly a variant of armoot meaning "pear" in the Arabic and Turkish languages. It is known as the payara in Bangladesh. It is known as bayabas in the Philippines.

Origin and distribution

Guavas originated from an area thought to extend from Mexico or Central America and were distributed throughout tropical America and the Caribbean region. They were adopted as a crop in subtropical and tropical Asia, the southern United States (from Tennessee and North Carolina south, as well as the west and Hawaii), tropical Africa, South Asia, Southeast Asia, and Oceania. Guavas are now cultivated in many tropical and subtropical countries. Several species are grown commercially; apple guava and its cultivars are those most commonly traded internationally. Guavas also grow in southwestern Europe, specifically the Costa del Sol on Málaga, (Spain) and Greece where guavas have been commercially grown since the middle of the 20th century and they proliferate as cultivars.

Mature trees of most species are fairly cold-hardy and can survive temperatures slightly colder than 25 °F (−4 °C) for short periods of time, but younger plants will likely freeze to the ground.

Guavas were introduced to Florida in the 19th century and are now grown in Florida as far north as Sarasota, Chipley, Waldo and Fort Pierce. However, they are a primary host of the Caribbean fruit fly and must be protected against infestation in areas of Florida where this pest is present.

Guavas are of interest to home growers in subtropical areas as one of the few tropical fruits that can grow to fruiting size in pots indoors. When grown from seed, guavas bear fruit as soon as two years and as long as 40 years.

Ecology

Psidium species are used as food plants by the caterpillars of some Lepidoptera, mainly moths like the Ello Sphinx (Erinnyis ello), Eupseudosoma aberrans, E. involutum, and Hypercompe icasia. Mites, like Pronematus pruni and Tydeus munsteri, are known to be crop pests of the apple guava (P. guajava) and perhaps other species. The bacterium Erwinia psidii causes rot diseases of the apple guava.

Although the fruit is cultivated and favored by humans, many animals and birds consume it, readily dispersing the seeds in their droppings and, in Hawaii, strawberry guava (P. littorale) has become an aggressive invasive species threatening extinction to more than 100 other plant species. By contrast, several guava species have become rare due to habitat destruction and at least one (Jamaican guava, P. dumetorum), is already extinct.

Guava wood is used for meat smoking in Hawaii and is used at barbecue competitions across the United States. In Cuba and Mexico, the leaves are used in barbecues.

Fruit

Guava fruits, usually 4 to 12 centimetres (1.6 to 4.7 in) long, are round or oval depending on the species. They have a pronounced and typical fragrance, similar to lemon rind but less sharp. The outer skin may be rough, often with a bitter taste, or soft and sweet. Varying between species, the skin can be any thickness, is usually green before maturity, but may be yellow, maroon, or green when ripe. The pulp inside may be sweet or sour and off-white ("white" guavas) to deep pink ("red" guavas). The seeds in the central pulp vary in number and hardness, depending on species.

Production

Official world production data for guava are not available. In 2011, one source reported that India was the world production leader with 17.6 million tonnes, an amount not exceeded by the cumulative total of the next seven largest guava producers (table). According to the National Horticulture Board of India, guava ranks fourth among the commercially important fruits of India.

Culinary uses

In Mexico and other Latin American countries, the guava-based beverage agua fresca is popular. The entire fruit is a key ingredient in punch, and the juice is often used in culinary sauces (hot or cold), ales, candies, dried snacks, fruit bars, and desserts, or dipped in chamoy. Pulquede guava is a popular alcoholic beverage in these regions.
In many countries, guava is eaten raw, typically cut into quarters or eaten like an apple, whereas in other countries it is eaten with a pinch of salt and pepper, cayenne powder or a mix of spices (masala). It is known as the winter national fruit of Pakistan. In the Philippines, ripe guava is used in cooking sinigang. Guava is a popular snack in Taiwan, sold on many street corners and night markets during hot weather, accompanied by packets of dried plum powder mixed with sugar and salt for dipping.
In east Asia, guava is commonly eaten with sweet and sour dried plum powder mixtures. Guava juice is popular in many countries. The fruit is also often included in fruit salads.

Because of its high level of pectin, guavas are extensively used to make candies, preserves, jellies, jams, and marmalades (such as Brazilian goiabada and Colombian and Venezuelan bocadillo), and as a marmalade jam served on toast.

Red guavas can be used as the base of salted products such as sauces, substituting for tomatoes, especially to minimize acidity. A drink may be made from an infusion of guava fruits and leaves, which in Brazil is called chá-de-goiabeira, i.e., "tea" of guava tree leaves, considered medicinal.

Constituents

Nutrients

Guavas are rich in dietary fiber and vitamin C, with moderate levels of folic acid. Having a generally broad, low-calorie profile of essential nutrients, a single common guava (P. guajava) fruit contains about four times the amount of vitamin C as an orange.

However, nutrient content varies across guava cultivars. Although the strawberry guava (P. littorale var. cattleianum) has only 25% of the amount found in more common varieties, its total vitamin C content in one serving (90 mg) still provides 100% of the Dietary Reference Intake.

Phytochemicals

Guava leaves contain both carotenoids and polyphenols like (+)-gallocatechin and leucocyanidin. As some of these phytochemicals produce the fruit skin and flesh color, guavas that are red-orange tend to have more polyphenol and carotenoid content than yellow-green ones.

Guava seed oil

Possibly used for culinary or cosmetics products, guava seed oil is a source of beta carotene, vitamin A, vitamin C, copper, zinc and selenium.

The composition of fatty acids in guava seed oil is presented in the following table, showing that the oil is particularly rich in linoleic acid.

Lauric acid <1.5%
Myristic acid <1.0%
Palmitic acid : 8-10%
Stearic acid : 5-7%
Oleic acid : 8-12%
Linoleic acid : 65-75%
Saturated fats, total : 14%
Unsaturated fats, total : 86%

Folk medicine

Since the 1950s, guavas – particularly the leaves – have been studied for their constituents, potential biological properties and history in folk medicine.

guava-nutrition-facts.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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#336 2019-02-15 00:16:50

ganesh
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Registered: 2005-06-28
Posts: 26,841

Re: Miscellany

293) Beans

Beans, widely cultivated legumes that have nourished the people of Latin America for millennia. Throughout the region, few meals lack beans. In Mexico, people typically eat mashed beans with corn tortillas, whereas in Brazil, since colonial times, a ladle of soupy beans poured over rice is the core component of many daily diets. In this way, the majority of Latin Americans survive on the near complete protein provided by a mixture of beans and rice or maize.

While hundreds of species exist, many of them indigenous to the American tropics, the multiple varieties of the common bean (phaseolus vulgaris), including dried black, pinto, and red beans, are the most widespread in Latin America. Another species, commonly known as lima or butter beans (phaseolus lunatus), is also widely grown in the region. Both were among the earliest domesticated plants of the Western Hemisphere, with evidence of their cultivation dating from 7000–5000 bce.

Archaeologists differ over the locations in which bean agriculture first developed in America, but it is now believed that it occurred independently in Mexico's Tamaulipas desert and Peru's highland Callejon de Hayulas valley. The culture gradually spread throughout North and South America well before 1492. After Columbus, Europeans eventually recognized the utility of dried beans on long ocean voyages, and their journeys helped introduce American beans throughout the world.

The production of beans has generally been taken for granted in Latin America. Their low cost and high nutritional value assured that they were always being cultivated by someone. Indians grew them with maize, weaving the vines between stalks of corn. On sugarcane plantations, captive Africans commonly received small plots of land in order to grow beans to feed themselves. Peasants invariably mixed beans with other subsistence crops. Coffee growers frequently left extra space between the rows of trees in order to intercrop beans and other vegetables.

Competing export crops and livestock land uses have caused problems for bean farming in Latin America. The expansion of soybean agriculture in the last decades of the twentieth century reduced the land devoted to growing common beans, and in Brazil the once ubiquitous black bean nearly disappeared from the market. At the same time, the population explosion caused increased demand, and bean prices skyrocketed. To keep underpaid workers fed, some governments subsidized bean farmers, while many others artificially manipulated prices. All the same, as late as 1980, small family farmers produced more than three-quarters of the beans grown in Latin America, revealing the continued decentralization of bean cultivation.

Bean supply shortages and price hikes worsened as Latin American governments tried to liberalize their economies. Strapped by heavy foreign debt burdens, officials simultaneously encouraged foreign exchange-earning export crops while cutting back on subsidies for staple crops like beans. In the inflation-plagued 1980s and 1990s, fluctuations in the availability of beans and other basic foodstuffs contributed to social and political unrest in Peru, Argentina, and Venezuela. In Brazil, the looting of supermarkets in cities such as Rio de Janeiro became commonplace in 1992.

In the twenty-first century, soybean production has continued to expand, due to the large demand from China. However, this expansion has sparked debate because Brazil in 2005 lifted its ban on genetically modified (GM) crops. GM soybeans are productive but both environmental and consumer groups have raised concerns about their unknown effects. The increase in soybean production has also been a major driver of Amazon deforestation.

Phaseolus vulgaris, also known as the common bean, green bean and French bean, among other names, is a herbaceous annual plant grown worldwide for its edible dry seeds or unripe fruit (both commonly called beans). The main categories of common beans, on the basis of use, are dry beans (seeds harvested at complete maturity), snap beans (tender pods with reduced fibre harvested before the seed development phase) and shell (shelled) beans (seeds harvested at physiological maturity). Its leaf is also occasionally used as a vegetableand the straw as fodder. Its botanical classification, along with other Phaseolus species, is as a member of the legume family Fabaceae, most of whose members acquire the nitrogen they require through an association with rhizobia, a species of nitrogen-fixing bacteria.

The common bean is a highly variable species that has a long history of cultivation. All wild members of the species have a climbing habit, but many cultivars are classified either as bush beans or dwarf beans, or as pole beans or climbing beans, depending on their style of growth. These include the kidney bean, the navy bean, the pinto bean, and the wax bean. The other major types of commercially grown bean are the runner bean (Phaseolus coccineus) and the broad bean (Vicia faba). Beans are grown on every continent except Antarctica. Worldwide, 27 million tonnes of dried beans and 24 million tonnes of green beans were grown in 2016. In 2016, Myanmar was the largest producer of dried beans, while China produced 79% of the world total of green beans.

The wild P. vulgaris is native to the Americas. It was originally believed that it had been domesticated separately in Mesoamerica and in the southern Andes region, giving the domesticated bean two gene pools. However, recent genetic analyses show that it was actually domesticated in Mesoamerica first, and traveled south, probably along with squash and maize (corn). The three Mesoamerican crops constitute the "Three Sisters" central to indigenous North American agriculture.

Description

The common bean is a highly variable species with a long history. Bush varieties form erect bushes 20–60 cm (8–20 in) tall, while pole or running varieties form vines 2–3 m (7–10 ft) long. All varieties bear alternate, green or purple leaves, which are divided into three oval, smooth-edged leaflets, each 6–15 cm (2–6 in) long and 3–11 cm (1–4 in) wide. The white, pink, or purple flowers are about 1 cm long, and they give way to pods 8–20 cm (3–8 in) long and 1–1.5 cm wide. These may be green, yellow, black, or purple in color, each containing 4–6 beans. The beans are smooth, plump, kidney-shaped, up to 1.5 cm long, range widely in color, and are often mottled in two or more colors.

As the name implies, snap beans break easily when the pod is bent, giving off a distinct audible snap sound. The pods of snap beans (green, yellow and purple in colour) are harvested when they are rapidly growing, fleshy, tender (not tough and stringy), bright in colour, and the seeds are small and underdeveloped (8 to 10 days after flowering). Raw or undercooked beans contain a toxic protein called phytohaemagglutinin.

Dry beans

Similar to other beans, the common bean is high in starch, protein, and dietary fiber, and is an excellent source of iron, potassium, selenium, molybdenum, thiamine, vitamin B6, and folate.

Dry beans will keep indefinitely if stored in a cool, dry place, but as time passes, their nutritive value and flavor degrade and cooking times lengthen. Dried beans are almost always cooked by boiling, often after being soaked in water for several hours. While the soaking is not strictly necessary, it shortens cooking time and results in more evenly textured beans. In addition, soaking beans removes 5 to 10% of the gas-producing sugars that can cause flatulence for some people. The methods include simple overnight soaking and the power soak method in which beans are boiled for three minutes and then set aside for 2–4 hours. Before cooking, the soaking water is drained off and discarded. Dry common beans take longer to cook than most pulses: cooking times vary from one to four hours, but are substantially reduced with pressure cooking.

In Mexico, Central America, and South America, the traditional spice used with beans is epazote, which is also said to aid digestion. In East Asia, a type of seaweed, kombu, is added to beans as they cook for the same purpose. Salt, sugar, and acidic foods such as tomatoes may harden uncooked beans, resulting in seasoned beans at the expense of slightly longer cooking times.

Dry beans may also be bought cooked and canned as refried beans, or whole with water, salt, and sometimes sugar.

Green beans and wax beans

The three commonly known types of green beans are: string or snap beans, which may be round or have a flat pod; stringless or French beans, which lack a tough, fibrous "string" running along the length of the pod; and runner beans, which belong to a separate species, Phaseolus coccineus. Green beans may have a purple rather than green pod, which changes to green when cooked. Wax beans are P. vulgaris beans that have a yellow] or white pod. Wax bean cultivars are commonly grown; the plants are often of the bush or dwarf form.

Compared to dry beans, green and wax beans provide less starch and protein and more vitamin A and vitamin C. Green beans and wax beans are often steamed, boiled, stir-fried, or baked in casseroles.

Shelling beans

Shell, shelled, or shelling beans are beans removed from their pods before being cooked or dried. Common beans can be used as shell beans, but the term also refers to other species of beans whose pods are not typically eaten, such as lima beans, soybeans, peas, and fava beans. Fresh shell beans are nutritionally similar to dry beans, but are prepared more like a vegetable, often being steamed, fried, or made into soups.

Popping beans

The nuña is an Andean subspecies, P. v. subsp. nunas (formerly P. vulgaris Nuñas group), with round, multicolored seeds that resemble pigeon eggs. When cooked on high heat, the bean explodes, exposing the inner part, in the manner of popcorn and other puffed grains.

Cultivars and varieties

Some scientists have proposed Mesoamerica as a possible origin for the common bean. Scientists disagree over whether the common bean was a product of one or multiple domestication events. Over time two diverse gene pools emerged: the Andean gene pool from Southern Peru to Northwest Argentina and the Mesoamerican gene pool between Mexico and Colombia.

Toxicity

The toxic compound phytohaemagglutinin, a lectin, is present in many common bean varieties, but is especially concentrated in red kidney beans. White kidney beans contain about a third as much toxin as the red variety; broad beans (Vicia faba) contain 5 to 10% as much as red kidney beans.

Phytohaemagglutinin can be deactivated by cooking beans for ten minutes at boiling point (100 °C, 212 °F). Insufficient cooking, such as in a slow cooker at 80 °C/ 176 °F, however, is not sufficient to deactivate all toxin To safely cook the beans, the U.S Food and Drug Administration recommends boiling for 30 minutes to ensure they reach a sufficient temperature for long enough to completely destroy the toxin. For dry beans, the FDA also recommends an initial soak of at least 5 hours in water which should then be discarded. Outbreaks of poisoning have been associated with cooking kidney beans in slow cookers.

The primary symptoms of phytohaemagglutinin poisoning are nausea, vomiting, and diarrhea. Onset is from one to three hours after consumption of improperly prepared beans, and symptoms typically resolve within a few hours. Consumption of as few as four or five raw, soaked kidney beans can cause symptoms. Canned red kidney beans, though, are safe to use immediately.

Beans are high in purines, which are metabolized to uric acid. Uric acid is not a toxin as such, but may promote the development or exacerbation of gout. However, more recent research has questioned this association, finding that moderate intake of purine-rich foods is not associated with increased risk of gout.

Other uses

Bean leaves have been used to trap bedbugs in houses. Microscopic hairs (trichomes) on the bean leaves entrap the insects.

From ancient times, beans were used as device in various methods of divination. Fortune-telling using beans is called favomancy.

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#337 2019-02-17 00:36:17

ganesh
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Re: Miscellany

294) Citrus limetta

Citrus limetta , alternatively considered to be a cultivar of Citrus limon, C. limon 'Limetta', is a species of citrus, commonly known as mousambi, musambi, sweet lime, sweet lemon, and sweet limetta, it is a member of the sweet lemons. It is a cross between the citron(Citrus medica) and a bitter orange (Citrus × aurantium).

It is native to southern regions of Iran  and also cultivated in the Mediterranean Basin.

•    In Iran it is called Limu Shirin ( meaning “Sweet lemon” in Persian).
•    In North India, it is commonly called mousambi, mosambi, or musambi  (in Hindi/Urdu and Marathi).
•    In East India, and Malayalam, Bathayi in Telugu, and sathukudi or sathukodi in Tamil.
•    In Nepali, it is called Mausam.
•    In Sindh it is known as mosami.
•    In France it is sometimes called bergamot; it should not be confused with Citrus bergamia, the Bergamot orange.

It is a different fruit from the Palestinian sweet lime[6] and from familiar sour limes such as the Key lime and the Persian lime. However, genomic analysis revealed it to be highly similar to the Rhobs el Arsa, and the two likely shared a common origin.

Description

C. limetta is a small tree up to 8 m (26 ft) in height, with irregular branches and relatively smooth, brownish-grey bark. It has numerous thorns, 1.5–7.5 cm (0.59–2.95 in) long. The petioles are narrowly but distinctly winged, and are 8–29 mm (0.31–1.14 in) long. Leaves are compound, with acuminate leaflets 5–17 cm (2.0–6.7 in) long and 2.8–8 cm (1.1–3.1 in) wide. Flowers are white, 2–3 cm (0.79–1.18 in) wide. Fruits are oval and green, ripening to yellow, with greenish pulp. The pith is white and about 5 mm (0.20 in) thick. Despite the name sweet lime, the fruit is more similar to a greenish orange in appearance.

C. limetta grows in tropical and subtropical climates. It begins bearing fruit at 5 to 7 years old, with peak production at 10 to 20 years. It is propagated by seed.

Flavor

As the name sweet lime suggests, the flavor is sweet and mild, but retains the essence of lime. The lime's taste changes rapidly in contact with air, and will turn bitter in few minutes, but if juiced and drunk rapidly the taste is sweet. The flavor is a bit flatter than most citrus due to its lack of acidity. It can be compared to limeade and pomelo.

Uses

Sweet lime is almost exclusively served as juice, and is the most common available citrus juice in India, and Bangladesh. The juice is commonly sold at mobile road stalls, where it is freshly pressed, sometimes served with a salty chat masala or kala namak, unless the vendor is told not to add it.

Like most citrus, the fruit is rich in vitamin C, providing 50 mg per 100 g serving. In Iran it is used to treat influenza and common cold.

The tree is used for ornamental purposes as well as for graft stock.

Sweet Lime

Nutritional value per 100 g (3.5 oz)
Energy : 180 kJ (43 kcal)
Carbohydrates : 9.3 g
Sugars : 1.7g
Dietary fiber : 0.5 g
Fat : 0.3 g
Protein : 0.7-0.8 g

Vitamins Quantity %DV Vitamin C : 60%
50 mg

Minerals Quantity%DV
Calcium 4%
40 mg
Iron
5%
0.7 mg
Phosphorus
4%
30 mg
Potassium
10%
490 mg

Other constituents    Quantity

Water    88 g

•    Units
•    mg = milligrams
•    IU = International units

Percentages are roughly approximated using US recommendations for adults.

Checking for ripeness

Like most citrus, sweet limes will not ripen off the tree, and must be picked when fully ripe. This is indicated by its tennis ball size and lustrous greenish yellow sheen. Gently scratch the surface of a sweet lime: If its oils give way in the fingernails, it is ripe. The juiciest fruits feel heavy for their size.

Underripe fruit feels light for its size, and is hard with tart flesh. Overripe fruit is dull and shrunken, with dry, spongy skin. Avoid fruit with brownish-yellow discoloration.

Storage

Sweet limes keep fresh for up to two weeks at room temperature, and four to eight weeks refrigerated. Frozen juice will keep for up to six months. It is possible to freeze slices of the fruit, though the limonin content may cause the pulp to taste bitter over time. This can be avoided by submerging the slices in sweet syrup within an airtight glass jar.

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#338 2019-02-19 00:28:09

ganesh
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Re: Miscellany

295) Potentiometers and Rheostats

What is potentiometer?

Potentiometer definition

A potentiometer is a three terminal resistor in which the resistance is manually varied to control the flow of electric current.

Construction of potentiometer

The potentiometer consists of three terminals among which two are fixed and one is variable. The two fixed terminals of the potentiometer are connected to both ends of the resistive element called track and third terminal is connected to the sliding wiper. The wiper that moves along the resistive element varies the resistance of the potentiometer. The resistance of the potentiometer is changed when the wiper is moved over the resistive path.

The resistive element of the potentiometer is either flat or angled. If the resistive element is flat, the wiper moves linearly. On the other hand, if the resistive element is angled, the wiper moves in a rotary manner.

The materials used to construct the resistive element of the potentiometer include carbon particles in plastic, graphite, resistive wires, and cermets (combination of ceramics and metals). Potentiometers are also sometimes referred as pots.

Potentiometer controls the flow of electric current

Increasing or decreasing the resistance of the potentiometer controls the flow of electric current. If we increase the resistance of the potentiometer, large amount of electric current is blocked and only a small amount of electric current is allowed. On the other hand, if we reduce the resistance of the potentiometer, a large amount of electric current is allowed and only a small amount of electric current is blocked.

Potentiometer resistance is varied by adjusting the wiper

If the wiper is adjusted in such a way that the resistive path is reduced, the resistance decreases, because the electric current has to travel only a small distance through the resistive path. On the other hand, if the wiper is adjusted in such a way that the resistive path is increased, the resistance increases, because the electric current has to travel a large distance through the resistive path.

Applications of potentiometers

•    Potentiometers are used to control volume in audio equipments, frequency attenuation, changing loudness, and changing other characteristics of audio signals.
•    Potentiometers are used in televisions and computers to control the picture contrast and brightness.

Rheostat

Rheostat definition

Rheostat is a variable resistor, which is used to control the flow of electric current by manually increasing or decreasing the resistance. The English scientist Sir Charles Wheatstone coined the word rheostat, it is derived from the Greek word “rheos” and “-statis” which means a stream controlling device or a current controlling device.

What is rheostat?

The electric current flowing through an electrical circuit is determined by two factors: the amount of voltage applied and the total resistance of the electrical circuit. If we reduce the circuit resistance, the flow of electric current through the circuit will be increased. On the other hand, if we increase the circuit resistance, the flow of electric current through the circuit will be decreased.

By placing the rheostat in the electrical circuit, we can control (increase or decrease) the flow of electric current in the circuit. Rheostat reduces the electric current flow to certain level. However, it does not completely blocks the electric current flow. To completely block the electric current flow, we need infinite resistance. Practically it is not possible to completely block the electric current.

Construction of rheostat

The construction of rheostat is almost similar to the potentiometer. Like the potentiometer, the rheostat also consists of three terminals: terminal A, terminal B and terminal C. However, we use only two terminals: either A and B or B and C. Terminal A and terminal C are the two fixed terminals connected to both ends of the resistive element called track and terminal B is the variable terminal connected to the sliding wiper or slider.

The wiper that moves along the resistive element varies the resistance of the rheostat. The resistance of the rheostat is changed when the slider or wiper is moved over the resistive path. The resistive element of the rheostat is made of a coil of wire or a thin carbon film. 

Rheostats are mostly wire wound. Hence, rheostats are also sometimes referred as variable wire wound resistors. Generally, rheostats are made by winding the Nichrome wire around an insulating ceramic core. The ceramic core of the rheostat acts as the insulating material to the heat. Hence, the ceramic core does not allow heat through it.

Resistance of rheostat is depends on the length of the resistive track

The resistance of the rheostat is depends on the length of the resistive track through which electric current is flowing.

If we use the terminals A and B in the rheostat, the minimum resistance is achieved when we move the slider or wiper close to the terminal A, because the length of the resistive path decreases. As a result, only a small amount of electric current is blocked and large amount of electric current is allowed.

In the similar way, the maximum resistance is achieved when we move the slider close to terminal C, because the length of the resistive path increases. As a result, a large amount of electric current is blocked and only a small amount of electric current is allowed.

If we use the terminals B and C, the minimum resistance is achieved when we move the slider or wiper close to the terminal C, because the length of the resistive path decreases. As a result, only a small amount of electric current is blocked and large amount of electric current is allowed.

In the similar way, the maximum resistance is achieved when we move the slider close to terminal A, because the length of the resistive path increases. As a result, a large amount of electric current is blocked and only a small amount of electric current is allowed.

Remember we are not reducing the resistance of the wire or resistive path; instead, we are just reducing the length of the resistive path to decrease the resistance. When we turn the outside knob with our hands, the wiper or slider moves along the resistive path.

Types of rheostats

Rheostats are of two types:

•    Rotary rheostats
•    Linear rheostats

Rotary rheostats

Rotary rheostat is also sometimes referred as circular rheostat because its resistive element looks like a circle. The resistive element of the rotary rheostat is circular or angled. In these types of resistors, the wiper or slider moves in a rotary manner. Rotary rheostats are used in most of the applications than the linear rheostats because their size is smaller than the linear rheostats.

Linear rheostats

Linear rheostat is also sometimes referred as cylindrical rheostat because its resistive element looks like a cylinder. In these types of resistors, the wiper or slider moves in a linear manner. Linear rheostats are used in laboratories of doing research and teaching.

Difference between potentiometer and rheostat

The construction of both the potentiometer and rheostat is same. The main difference is the way we used it for operation. In potentiometers, we use all the three terminals for performing the operation whereas in rheostats, we use only two terminals for performing the operation.

Applications of rheostat

•    Rheostat is generally used in the applications where high voltage or current is required.
•    Rheostats are used in dim lights to change the intensity of light. If we increase the resistance of the rheostat, the flow of electric current through the light bulb decreases. As a result, the light brightness decreases. In the similar way, if we decrease the resistance of the rheostat, the flow of electric current through the light bulb increases. As a result, the light brightness increases.
•    Rheostats are used to increase or decrease the volume of a radio and to increase or decrease the speed of an electric motor.

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

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#339 Today 00:48:20

ganesh
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Posts: 26,841

Re: Miscellany

296) Thermistors and Photoresistors

Thermistor

A resistor is a type of passive component that restricts the flow of electric current to certain level. Resistors are mainly classified into two types: fixed resistors and variable resistors.

Fixed resistor is a type of resistor that only restricts the flow of electric current but does not control (increase and decrease) the flow of electric current. On the other hand, variable resistor is a type of resistor that controls (increases and decreases) the flow of electric current by manually decreasing and increasing its resistance.

In the fixed or variable resistors, if we manually set the resistance as constant, the resistance changes slightly as temperature increases or decreases. However, by using a special type of resistor we can rapidly change the resistance of the resistor with change in temperature.  This special type of resistor is called thermistor.

The demand for the precise components or devices (thermistors) is increased in the recent years. Thermistors measure the temperature accurately and work efficiently for years.

Thermistor definition

Thermistor is a type of resistor whose resistance changes rapidly with the small change in temperature. In other words, it is a type of resistor in which the flow of electric current changes rapidly with small change in temperature. The word thermistor is derived from the combination of words “thermal” and “resistor”.
.

Types of thermistors

Thermistors are classified into two types based on how they behave with the change in temperature:
•    Negative Temperature Co-efficient (NTC) thermistors
•    Positive Temperature Co-efficient (PTC) thermistors

•    Negative Temperature Co-efficient (NTC) thermistors

The resistance of the NTC (Negative Temperature Co-efficient) thermistors decreases with increasing temperature. In other words, the electric current flow through the NTC (Negative Temperature Co-efficient) thermistors increases with the increase in temperature.

Most of the NTC thermistors are made from a pressed disc, rod or cast chip of semiconductor material such as sintered metal oxides.

In NTC thermistors, charge carriers are generated by doping process. Because of this doping process, a large number of charge carriers are generated.

If the temperature is slightly increased, a large number of charge carriers (free electrons) collides with the valence electrons of other atoms and provides them sufficient energy. The valence electrons which gains sufficient energy will breaks the bonding with the parent atom and moves freely from one place to another place. The electrons that move freely from one place to another place are called free electrons. These electrons carry the electric current while moving from one place to another place. The valence electron, which becomes a free electron will again collide with the other valence electrons and makes them free.

Likewise, a small increase in temperature produces millions of free electrons. More free electrons or charge carriers means more electric current. Thus, a small increase in temperature will rapidly decrease the resistance of NTC thermistor and allows a large amount of electric current.

•    Positive Temperature Co-efficient (PTC) thermistors

The resistance of Positive Temperature Co-efficient (PTC) thermistors increases with increase in temperature. Most of the Positive Temperature Co-efficient (PTC) thermistors are made from doped polycrystalline ceramic. Thermistors with Positive Temperature Co-efficient (PTC) are also called posistors.

History of thermistors

The first NTC (Negative Temperature Co-efficient) thermistor was discovered by Michael Faraday in1833. Michael Faraday observed that the resistance of silver sulfide decreased rapidly when the temperature is increased.

Advantages and disadvantages of thermistors

Advantages of thermistors
•    The resistance of thermistors changes rapidly with small change in temperature.
•    Low cost
•    Small size
•    It is easy to carry thermistors from one place to another place.

Disadvantages of thermistors

•    Thermistors are not suitable over a wide operating range
•    The resistance versus temperature characteristics is non-linear.

Applications of thermistors

•    Thermistors are used in medical equipments
•    Thermistors are used in hot ends of 3d printers.
•    Thermistors are used in home appliances such as ovens, hair dryers, toasters, refrigerators, etc.
•    Modern coffee makers use thermistors to accurately measure and control water temperature.
•    Thermistors are used in computers.
•    Thermistors are used as temperature sensors.
•    Thermistors are used as inrush current limiter.

Photoresistor

Photoresistor definition

The name photoresistor is the combination of words: photon (light particles) and resistor. A photoresistor is a type of resistor whose resistance decreases when the intensity of light increases. In other words, the flow of electric current through the photoresistor increases when the intensity of light increases.

Photoresistors are also sometimes referred as LDR (Light Dependent Resistor), semiconductor photoresistor, photoconductor, or photocell. Photoresistor changes its resistance only when it is exposed to light.

How photoresistor works?

When the light falls on the photoresistor, some of the valence electrons absorbs energy from the light and breaks the bonding with the atoms. The valence electrons, which break the bonding with the atoms, are called free electrons.

When the light energy applied to the photoresistor is highly increased, a large number of valence electrons gain enough energy from the photons and breaks the bonding with the parent atoms. The large number of valence electrons, which breaks the bonding with the parent atoms will jumps into the conduction band.

The electrons present in the conduction band are not belongs to any atom. Hence, they move freely from one place to another place. The electrons that move freely from one place to another place are called free electrons.

When the valence electron left the atom, a vacancy is created at a particular location in an atom from which the electron left. This vacancy is called as hole. Therefore, the free electrons and holes are generated as pairs.

The free electrons that are moving freely from one place to another place carry the electric current. In the similar way, the holes moving in the valence band carry electric current. Likewise, both free electrons and holes will carry electric current. The amount of electric current flowing through the photoresistor is depends on the number of charge carriers (free electrons and holes) generated.

When the light energy applied to the photoresistor increases, the number of charge carriers generated in the photoresistor also increases. As a result, the electric current flowing through the photoresistor increases.

Increase in electric current means decrease in resistance. Thus, the resistance of the photoresistor decreases when the intensity of applied light increases.

Photoresistors are made of high resistance semiconductor such as silicon or germanium. They are also made of other materials such as cadmium sulfide or cadmium selenide.

In the absence of light, the photoresistors acts as high resistance materials whereas in the presence of light, the photoresistors acts as low resistance materials.
Types of photoresistors based on material used to construct them

Photoresistors are classified into two types based on the material used to construct them:
•    Intrinsic photoresistor
•    Extrinsic photoresistor

•    Intrinsic photoresistor

Intrinsic photoresistors are made from the pure semiconductor materials such as silicon or germanium. The outermost shell of any atom is capable to hold up to eight valence electrons. However, in silicon or germanium, each atom consists of only four valence electrons. These four valence electrons of each atom form four covalent bonds with the neighboring four atoms to completely fill the outermost shell. As a result, no electron is left free.

When we apply light energy to the intrinsic photo resistor, only a small number of valence electrons gain enough energy and becomes free from the parent atom. Hence, a small number of charge carriers are generated. As a result, only a small electric current flows through the intrinsic photo resistor.

We already have known that increase in electric current means decrease in resistance. In intrinsic photoresistors, the resistance decreases slightly with the increase in light energy. Hence, intrinsic photoresistors are less sensitive to the light. Therefore, they are not reliable for the practical applications.

•    Extrinsic photoresistor

Extrinsic photoresistors are made from the extrinsic semiconductor materials. Let us consider an example of extrinsic photoresistor, which is made from the combination of silicon and impurity (phosphorus) atoms.

Each silicon atom consists of four valence electrons and each phosphorus atom consists of five valence electrons. The four valence electrons of the phosphorus atom form four covalent bonds with the neighboring four silicon atoms. However, the fifth valence electron of the phosphorus atom cannot able to form the covalent bond with the silicon atom because the silicon atom has only four valence electrons. Hence, the fifth valence electron of each phosphorus atom becomes free from the atom. Thus, each phosphorus atom generates a free electron.

The free electron, which is generated will collides with the valence electrons of other atoms and makes them free. Likewise, a single free electron generates multiple free electrons. Therefore, adding a small number of impurity (phosphorus) atoms generates millions of free electrons.

In extrinsic photoresistors, we already have large number of charge carriers. Hence, providing a small amount of light energy generates even more number of charge carriers. Thus, the electric current increases rapidly.

Increase in electric current means decrease in resistance. Therefore, the resistance of the extrinsic photoresistor decreases rapidly with the small increase in applied light energy. Extrinsic photoresistors are reliable for the practical applications.

Applications of photoresistors

•    Photoresistors are used in streetlights to control when the light should turn on and when the light should turn off. When the surrounding light falls on the photo resistor, it causes the streetlight to turnoff. When there is no light, the photoresistor causes the street light to turn on. This reduces the wastage of electricity.
•    They are also used in various devices such as alarm devices, solar street lamps, night-lights, and clock radios.

Advantages and disadvantages of photoresistor

Advantages of photoresistor
•    Small in size
•    Low cost
•    It is easy to carry from one place to another place.

Disadvantages of photoresistor
•    The accuracy of photoresistor is very low.

photoresistor.png


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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#340 Today 17:21:35

ganesh
Administrator
Registered: 2005-06-28
Posts: 26,841

Re: Miscellany

297) Humistor

The name humistor is obtained from the combination of words: humidity and resistor. Humistor is very sensitive to the humidity. Therefore, it is used as a sensor for measuring the humidity in the surrounding air.

Humistor definition

A humistor is a type of variable resistor whose resistance changes with the change in humidity of the surrounding air. Humistors are also sometimes referred as humidity sensitive resistor or resistive humidity sensor. Humidity is the amount of gaseous water or water vapor present in the air.

Construction and working of humistor

Humistor is generally made of an organic polymer such as polyamide resin, polyethylene, or a metal oxide.

The resistance of the humistor is depends on the concentration of absorbed water molecules. When the humidity increases, the water molecules absorbed by the humistor increases and the humistor becomes more electrically conductive. As a result, the resistance of the humistor decreases. On the other hand, when the humidity decreases, the water molecules absorbed by the humistor decreases and humistor becomes less electrically conductive. As a result, the resistance of the humistor increases. Likewise, the humistor detects and measures the change in humidity.


Advantages and disadvantages of humistor

Advantages of humistor

•    Low cost
•    High accuracy
•    Small size
•    Long-term stability
•    Highly sensitive to humidity

Disadvantages of humistor

•    The resistance of the humistor varies non-linearly with the change in humidity.

Applications of humistor

•    Industrial process control
•    Atmospheric environmental monitoring
•    Agriculture

Introduction DHT11 : DHT11 humidity and temperature sensor

The DHT11 is a basic, low cost digital temperature and humidity sensor.

DHT11 is a single wire digital humidity and temperature sensor, which provides humidity and temperature values serially with one-wire protocol.
DHT11 sensor provides relative humidity value in percentage (20 to 90% RH) and temperature values in degree Celsius (0 to 50 °C).

DHT11 sensor uses resistive humidity measurement component, and NTC temperature measurement component.

Communication with Microcontroller

DHT11 uses only one wire for communication. The voltage levels with certain time value defines the logic one or logic zero on this pin.

The communication process is divided in three steps, first is to send request to DHT11 sensor then sensor will send response pulse and then it starts sending data of total 40 bits to the microcontroller.

Communication process/ Response

DHT11 Response

After getting start pulse from, DHT11 sensor sends the response pulse which indicates that DHT11 received start pulse.

After sending the response pulse, DHT11 sensor sends the data, which contains humidity and temperature value along with checksum.
The data frame is of total 40 bits long, it contains 5 segments (byte) and each segment is 8-bit long.
In these 5 segments, first two segments contain humidity value in decimal integer form. This value gives us Relative Percentage Humidity. 1st 8-bits are integer part and next 8 bits are fractional part.
Next two segments contain temperature value in decimal integer form. This value gives us temperature in Celsius form.
Last segment is the checksum which holds checksum of first four segments.
Here checksum byte is direct addition of humidity and temperature value. And we can verify it, whether it is same as checksum value or not. If it is not equal, then there is some error in the received data.
Once data received, DHT11 pin goes in low power consumption mode till next start pulse.

End of Frame

After sending 40-bit data, DHT11 sensor sends 54us low level and then goes high. After this DHT11 goes in sleep mode.

DHT11 vs DHT22

Two versions of the DHT sensor, they look a bit similar and have the same pinout, but have different characteristics and specifications:

DHT11

Ultra-low cost
3 to 5V power and I/O
2.5mA max current use during conversion (while requesting data)
Good for 20-80% humidity readings with 5% accuracy
Good for 0-50°C temperature readings ±2°C accuracy
No more than 1 Hz sampling rate (once every second)
Body size 15.5mm x 12mm x 5.5mm
4 pins with 0.1" spacing

DHT22

Low cost
3 to 5V power and I/O
2.5mA max current use during conversion (while requesting data)
Good for 0-100% humidity readings with 2-5% accuracy
Good for -40 to 125°C temperature readings ±0.5°C accuracy
No more than 0.5 Hz sampling rate (once every 2 seconds)
Body size 15.1mm x 25mm x 7.7mm
4 pins with 0.1" spacing

DHT11_new.png


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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