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Turnips were an important crop in the cuisine of Antebellum America. They were grown for their greens as well as the roots, and could yield edible greens within a few weeks of planting, making them a staple of new plantations still in the process of becoming productive. They could be planted as late as the fall and still provide newly arrived settlers with a source of food. The typical southern way of cooking turnip greens was to boil them with a chunk of salt pork. The broth obtained from this process was known as pot likker and was served with crumbled corn pone, often made from coarse meal when little else was available along the antebellum frontier.
Cultivation
The 1881 American Household Cyclopedia advises that turnips can be grown in fields that have been harrowed and ploughed. It recommends planting in late May or June and weeding and thinning with a hoe throughout the summer.
As a root crop, turnips grow best in cool weather; hot temperatures cause the roots to become woody and bad-tasting. They are typically planted in the spring in cold-weather climates (such as the northern US and Canada) where the growing season is only 3–4 months. In temperate climates (ones with a growing season of 5–6 months), turnips may also be planted in late summer for a second fall crop. In warm-weather climates (7 or more month growing season), they are planted in the fall. 55–60 days is the average time from planting to harvest.
Turnips are a biennial plant, taking two years from germination to reproduction. The root spends the first year growing and storing nutrients, and the second year flowers, produces seeds, and dies. The flowers of the turnip are tall and yellow, with the seeds forming in pea-like pods. In areas with less than seven-month growing seasons, temperatures are too cold for the roots to survive the winter. To produce seeds, pulling the turnips and storing them over winter is necessary, taking care not to damage the leaves. During the spring, they may be set back in the ground to complete their lifecycle.
Relevance in human use
In England around 1700, Charles "Turnip" Townshend promoted the use of turnips in a four-year crop-rotation system that enabled year-round livestock feeding. | Turnip | Wikipedia | 483 | 46576 | https://en.wikipedia.org/wiki/Turnip | Biology and health sciences | Brassicales | null |
In Scottish and some other English dialects, the word turnip can also refer to rutabagas (North American English), also known as swedes in England, a variety of Brassica napus, which is a hybrid between the turnip, Brassica rapa, and the cabbage. Turnips are generally smaller with white flesh, while rutabagas are larger with yellow flesh. Scottish English sometimes distinguish turnips as white turnips, and sometimes distinguishes rutabagas as neeps.
In the Austrian region of Wildschönau farmers produce a kind of schnaps called Krautinger from a variation of Brassica rapa ssp. Rapa, since they were granted permission to do so under Empress Maria Theresia in the 18th century. It is notorious for its distinct taste and smell.
Heraldry
The turnip is an old vegetable charge in heraldry. It was used by Leonhard von Keutschach, prince-archbishop of Salzburg. The turnip is still the heart shield in the arms of Keutschach am See.
The arms of the former municipality of Kiikala, Finland, were Gules, a turnip Or. | Turnip | Wikipedia | 243 | 46576 | https://en.wikipedia.org/wiki/Turnip | Biology and health sciences | Brassicales | null |
A hedgehog is a spiny mammal of the subfamily Erinaceinae, in the eulipotyphlan family Erinaceidae. There are 17 species of hedgehog in five genera found throughout parts of Europe, Asia, and Africa, and in New Zealand by introduction. There are no hedgehogs native to Australia and no living species native to the Americas. However, the extinct genus Amphechinus was once present in North America.
Hedgehogs share distant ancestry with shrews (family Soricidae), with gymnures possibly being the intermediate link, and they have changed little over the last 15 million years. Like many of the first mammals, they have adapted to a nocturnal way of life. Their spiny protection resembles that of porcupines, which are rodents, and echidnas, a type of monotreme.
Etymology
The name hedgehog came into use around the year 1450, derived from the Middle English , from , , because it frequents hedgerows, and , , from its piglike snout. Another name that is used is hedgepig.
Description
Hedgehogs are easily recognized by their spines, which are hollow hairs made stiff with keratin. Their spines are not poisonous or barbed and, unlike the quills of a porcupine, do not easily detach from their bodies. However, the immature animal's spines normally fall out as they are replaced with adult spines. This is called "quilling". Spines can also shed when the animal is diseased or under extreme stress. Hedgehogs are usually brown, with pale tips to the spines, though blonde hedgehogs are found on the Channel Island of Alderney.
Hedgehogs roll into a tight spiny ball when threatened, tucking in the furry face, feet, and belly. The hedgehog's back contains two large muscles that direct the quills. Some light-weight desert hedgehog species with fewer spines are more likely to flee or attack, ramming an intruder with the spines, rolling up only as a last resort.
Hedgehogs are primarily nocturnal, with some species also active during the day. Hedgehogs sleep for a large portion of the day under bushes, grasses, rocks, or most commonly in dens dug underground. All wild hedgehogs can hibernate, though the duration depends on temperature, species, and abundance of food.
Hedgehogs are fairly vocal, with a variety of grunts, snuffles and/or squeals. | Hedgehog | Wikipedia | 512 | 46590 | https://en.wikipedia.org/wiki/Hedgehog | Biology and health sciences | Erinaceids | null |
They occasionally perform a ritual called anointing. When the animal encounters a new scent, it will lick and bite the source, then form a scented froth in its mouth and paste it on its spines with its tongue. Some experts believe this might serve to camouflage the hedgehog with the local scent, and might also lead to infection of predators poked by the spines. Anointing is sometimes also called anting after a similar behavior in birds.
Like opossums, mice, and moles, hedgehogs have some natural immunity against some snake venom through the protein erinacin in their muscles, though in such small amounts that a viper bite may still be fatal. In addition, hedgehogs are one of four known mammalian groups with natural protection against another snake venom, α-neurotoxin. Developing independently, pigs, honey badgers, mongooses, and hedgehogs all have mutations in the nicotinic acetylcholine receptor that prevent the binding of the snake venom α-neurotoxin.
The sense of smell has been little studied in the hedgehog, as the olfactory part of the mammal brain is obscured inside the neopallium. Tests have suggested that hedgehogs share the same olfactory electrical activity as cats.
Diet
Although traditionally classified in the abandoned order Insectivora, hedgehogs are omnivorous. They feed on insects, snails, frogs and toads, snakes, bird eggs, carrion, mushrooms, grass roots, berries, and melons. Afghan hedgehogs devour berries in early spring after hibernation.
Hedgehogs have been observed eating cat food left outdoors for pets, but this may not be a proper food for hedgehogs in captivity.[video:1]
Hibernation
When a hedgehog hibernates, its normal body temperature decreases to .
Reproduction and lifespan
Hedgehog gestation lasts 35–58 days, depending on species. The average litter is three to four newborns for larger species and five to six for smaller ones. As with many animals, it is not unusual for an adult male hedgehog to kill newborn males. | Hedgehog | Wikipedia | 432 | 46590 | https://en.wikipedia.org/wiki/Hedgehog | Biology and health sciences | Erinaceids | null |
Hedgehogs have a relatively long lifespan for their size. In captivity, lack of predators and controlled diet contribute to a lifespan of eight to ten years depending on size. In the wild, larger species live four to seven years (some recorded up to 16 years), and smaller species live two to four years (four to seven in captivity). This compares to a mouse at two years and a large rat at three to five years.
Newborn hoglets are blind, with their quills covered by a protective membrane which dries and shrinks over several hours, and falls off after cleaning, allowing the quills to emerge.
Predators
The various species have many predators: while forest hedgehogs are prey primarily to birds (especially owls) and ferrets, smaller species like the long-eared hedgehog are prey to foxes, wolves, and mongooses. Hedgehog bones have been found in the pellets of the Eurasian eagle owl.
In Britain, the main predator is the European badger. European hedgehog populations in the United Kingdom are lower in areas with many badgers, and hedgehog rescue societies will not release hedgehogs into known badger territories. Badgers also compete with hedgehogs for food.
Domestication
The most common pet species of hedgehog are hybrids of the white-bellied hedgehog or four-toed hedgehog (Atelerix albiventris, sometimes known as the African pygmy hedgehog) and the smaller North African hedgehog (A. algirus, pygmy hedgehog). Other species kept as pets are the long-eared hedgehog (Hemiechinus auritus) and the Indian long-eared hedgehog (H. collaris).
, it is illegal to own a hedgehog as a pet in the US states of Hawaii, Georgia, Pennsylvania, and California, as well as in New York City, Washington, D.C. and some Canadian municipalities. Breeding licenses are required. No such restrictions exist in most European countries with the exception of Scandinavia. In Italy, it is illegal to keep wild hedgehogs as pets.
As invasive species
In areas where hedgehogs have been introduced, such as New Zealand and the islands of Scotland, the hedgehog has become a pest, lacking natural predators. In New Zealand it has decimated native species including insects, snails, lizards and ground-nesting birds, particularly shore birds. | Hedgehog | Wikipedia | 494 | 46590 | https://en.wikipedia.org/wiki/Hedgehog | Biology and health sciences | Erinaceids | null |
Eradication can be troublesome. Attempts to eliminate hedgehogs from bird colonies on the Scottish islands of North Uist and Benbecula in the Outer Hebrides were met with international protest. Eradication began in 2003 with 690 hedgehogs killed, though animal welfare groups attempted rescues. By 2007, legal injunctions prohibited the killing, and in 2008, the elimination process was changed to trapping and releasing on the mainland.
In 2022, it was reported that the hedgehog population in rural Britain was declining rapidly, down by 30%-75% since 2000.
Diseases
Hedgehogs suffer many diseases common to mammals, including cancer, fatty liver disease, and cardiovascular disease.
Cancer is very common in hedgehogs. The most common is squamous cell carcinoma, which spreads quickly from bone to the organs, unlike in humans. Surgery to remove the bone tumors is impractical.
Fatty liver and heart disease are believed to be caused by bad diet and obesity. Hedgehogs will eagerly eat foods high in fat and sugar, despite a metabolism adapted for low-fat, protein-rich insects.
Hedgehogs are also highly susceptible to pneumonia, with difficulty breathing and nasal discharge, caused by the bacterium Bordetella bronchiseptica.
Hedgehogs uncommonly transmit a fungal ringworm or dermatophytosis skin infection to human handlers and other hedgehogs, caused by Trichophyton erinacei, a distinct mating group among the Arthroderma benhamiae fungi. | Hedgehog | Wikipedia | 309 | 46590 | https://en.wikipedia.org/wiki/Hedgehog | Biology and health sciences | Erinaceids | null |
Hedgehogs can suffer from balloon syndrome, a rare condition in which gas is trapped under the skin from injury or infection, causing the animal to inflate. The condition is unique to hedgehogs because their skin is baggy enough to curl up. In 2017, the BBC reported a case of a male hedgehog "almost twice its natural size, literally blown up like a beach ball with incredibly taut skin". At Stapeley's Wildlife Hospital, vet Bev Panto, said, "I have seen three or four of these cases and they are very strange every time and quite shocking ... When you first see them they appear to be very big hedgehogs but when you pick them up they feel so light because they are mostly air". The British Hedgehog Preservation Society advises:
There is no single cause for this condition. The air can be removed by incising or aspirating through the skin over the back. Antibiotic cover should be given. This may be associated with lung/chest wall damage or a small external wound acting like a valve or a clostridium type infection.
Human influence
As with most small mammals living around humans, many are run over as they attempt to cross roadways. In Ireland, hedgehogs are one of the most common mammalian road fatalities. Between April 2008 and November 2010 on two stretches of road measuring 227 km and 32.5 km, there were 133 recorded hedgehog fatalities. Of another 135 hedgehog carcasses collected from throughout Ireland, there were significantly more males than females collected, with peaks in male deaths occurring in May and June. Female deaths outnumbered males only in August, with further peaks in female deaths observed in June and July. It is suggested that these peaks are related to the breeding season (adults) and dispersal/exploration following independence.
Domesticated hedgehogs can get their heads stuck in tubes such as toilet paper tubes, and walk around with them. Some owners call this "tubing" and promote the behavior, providing a tube cut lengthwise to allow the hedgehog to remove it. Some hedgehogs intentionally wear tubes for hours. | Hedgehog | Wikipedia | 431 | 46590 | https://en.wikipedia.org/wiki/Hedgehog | Biology and health sciences | Erinaceids | null |
Culinary and medicinal use
Hedgehogs are a food source in many cultures. They were eaten in Ancient Egypt and some recipes of the Late Middle Ages call for hedgehog meat. They are traded throughout Eurasia and Africa for traditional medicine and witchcraft. In the Middle East and especially among Bedouins, hedgehog meat is considered medicine against rheumatism and arthritis. Hedgehogs are also said to cure a variety of disorders from tuberculosis to impotence. In Morocco, inhaling the smoke of the burnt skin or bristles supposedly remedies fever, impotence, and urinary illnesses; the blood is sold as a cure for ringworm, cracked skin and warts, and the flesh is eaten as a remedy for witchcraft. Romani people still eat hedgehogs, boiled or roasted, and also use the blood and the fat as a medicine.
In 1981, British publican Philip Lewis developed a line of Hedgehog Flavoured Crisps, whose taste was apparently based on the flavourings used by Romani to bake hedgehogs. As they did not contain any actual hedgehog product, the Office of Fair Trading ordered him to change the name to Hedgehog Flavour Crisps.
Genera and species
Subfamily Erinaceinae (hedgehogs)
Genus Atelerix
Four-toed hedgehog, Atelerix albiventris
North African hedgehog, Atelerix algirus
Southern African hedgehog, Atelerix frontalis
Somali hedgehog, Atelerix sclateri
Genus Erinaceus
Amur hedgehog, Erinaceus amurensis
Southern white-breasted hedgehog, Erinaceus concolor
European hedgehog, Erinaceus europaeus
Northern white-breasted hedgehog, Erinaceus roumanicus
Genus Hemiechinus
Long-eared hedgehog, Hemiechinus auritus
Indian long-eared hedgehog, Hemiechinus collaris
Genus Mesechinus
Daurian hedgehog, Mesechinus dauuricus
Hugh's hedgehog, Mesechinus hughi
Small-toothed forest hedgehog, Mesechinus miodon
Gaoligong forest hedgehog, Mesechinus wangi
Genus Paraechinus
Desert hedgehog, Paraechinus aethiopicus
Brandt's hedgehog, Paraechinus hypomelas
Indian hedgehog, Paraechinus micropus
Bare-bellied hedgehog, Paraechinus nudiventris
Society and culture | Hedgehog | Wikipedia | 498 | 46590 | https://en.wikipedia.org/wiki/Hedgehog | Biology and health sciences | Erinaceids | null |
In worldwide folklore, hedgehogs are associated with intelligence and wisdom (Asia, Europe), and magic (Africa). | Hedgehog | Wikipedia | 25 | 46590 | https://en.wikipedia.org/wiki/Hedgehog | Biology and health sciences | Erinaceids | null |
Hay is grass, legumes, or other herbaceous plants that have been cut and dried to be stored for use as animal fodder, either for large grazing animals raised as livestock, such as cattle, horses, goats, and sheep, or for smaller domesticated animals such as rabbits and guinea pigs. Pigs can eat hay, but do not digest it as efficiently as herbivores do.
Hay can be used as animal fodder when or where there is not enough pasture or rangeland on which to graze an animal, when grazing is not feasible due to weather (such as during the winter), or when lush pasture by itself would be too rich for the health of the animal. It is also fed when an animal cannot access any pastures—for example, when the animal is being kept in a stable or barn.
Hay production and harvest, commonly known as "making hay", "haymaking", "haying" or "doing hay", involves a multiple step process: cutting, drying or "curing", raking, processing, and storing. Hayfields do not have to be reseeded each year in the way that grain crops are, but regular fertilizing is usually desirable, and overseeding a field every few years helps increase yield.
Composition
Commonly used plants for hay include mixtures of grasses such as ryegrass (Lolium species), timothy, brome, fescue, Bermuda grass, orchard grass, and other species, depending on region. Hay may also include legumes, such as alfalfa (lucerne) and clovers (red, white and subterranean). Legumes in hay are ideally cut pre-bloom. Other pasture forbs are also sometimes a part of the mix, though these plants are not necessarily desired as certain forbs are toxic to some animals.
In the UK some hay is harvested from traditionally managed hay meadows which have a highly diverse flora and which support a rich eco-system. The hay produced by these meadows is species rich and was traditionally used to feed horses. | Hay | Wikipedia | 420 | 46593 | https://en.wikipedia.org/wiki/Hay | Technology | Animal husbandry | null |
Oat, barley, and wheat plant materials are occasionally cut green and made into hay for animal fodder, and more usually used in the form of straw, a harvest byproduct of stems and dead leaves that are baled after the grain has been harvested and threshed. Straw is used mainly for animal bedding. Although straw is also used as fodder, particularly as a source of dietary fiber, it has lower nutritional value than hay.
In agroforestry systems are developed to produce tree hay.
It is the leaf and seed material in the hay that determines its quality, because they contain more of the nutrition value for the animal than the stems do. Farmers try to harvest hay at the point when the seed heads are not quite ripe and the leaf is at its maximum when the grass is mowed in the field. The cut material is allowed to dry so that the bulk of the moisture is removed but the leafy material is still robust enough to be picked up from the ground by machinery and processed into storage in bales, stacks or pits. Methods of haymaking thus aim to minimize the shattering and falling away of the leaves during handling.
Hay production is highly sensitive to weather conditions, particularly during the harvest period. In drought conditions, both seed and leaf production are stunted, resulting in hay with a high ratio of dry, coarse stems that possess very low nutritional value. Conversely, excessively wet weather can cause cut hay to spoil in the field before it can be baled. Consequently, the primary challenge and risk for farmers in hay production is managing the weather, especially during the critical few weeks when the plants are at optimal maturity for harvesting. A lucky break in the weather often moves the haymaking tasks (such as mowing, tedding, and baling) to the top priority on the farm's to-do list. This is reflected in the idiom to make hay while the sun shines. Hay that was too wet at cutting may develop rot and mold after being baled, creating the potential for toxins to form in the feed, which could make the animals sick.
After harvest, hay also has to be stored in a manner to prevent it from getting wet. Mold and spoilage reduce nutritional value and may cause illness in animals. A symbiotic fungus in fescue may cause illness in horses and cattle. | Hay | Wikipedia | 481 | 46593 | https://en.wikipedia.org/wiki/Hay | Technology | Animal husbandry | null |
The successful harvest of maximum yields of high-quality hay is entirely dependent on the coincident occurrence of optimum crop, field, and weather conditions. When this occurs, there may be a period of intense activity on the hay farm while harvest proceeds until weather conditions become unfavourable.
Use
Hay or grass is the foundation of the diet for all grazing animals, and can provide as much as 100% of the fodder required for an animal. Hay is usually fed to an animal during times when winter, drought, or other conditions make pasture unavailable. Animals that can eat hay vary in the types of grasses suitable for consumption, the ways they consume hay, and how they digest it. Therefore, different types of animals require hay that consists of similar plants to what they would eat while grazing, and, likewise, plants that are toxic to an animal in pasture are generally also toxic if they are dried into hay.
Most animals are fed hay in two daily feedings, morning and evening, more for the convenience of humans, as most grazing animals on pasture naturally consume fodder in multiple feedings throughout the day. Some animals, especially those being raised for meat, may be given enough hay that they simply are able to eat all day. Other animals, especially those that are ridden or driven as working animals may be given a more limited amount of hay to prevent them from getting too fat. The proper amount of hay and the type of hay required varies somewhat between different species. Some animals are also fed concentrated feeds such as grain or vitamin supplements in addition to hay. In most cases, hay or pasture forage must make up 50% or more of the diet by weight.
One of the most significant differences in hay digestion is between ruminant animals, such as cattle and sheep, and nonruminant, hindgut fermentors, such as horses. Both types of animals can digest cellulose in grass and hay, but do so by different mechanisms. Because of the four-chambered stomach of cattle, they are often able to break down older forage and have more tolerance of mold and changes in diet. The single-chambered stomach and cecum or "hindgut" of the horse uses bacterial processes to break down cellulose that are more sensitive to changes in feeds and the presence of mold or other toxins, requiring horses to be fed hay of a more consistent type and quality. | Hay | Wikipedia | 488 | 46593 | https://en.wikipedia.org/wiki/Hay | Technology | Animal husbandry | null |
Different animals also use hay in different ways: cattle evolved to eat forages in relatively large quantities at a single feeding, and then, due to the process of rumination, take a considerable amount of time for their stomachs to digest food, often accomplished while the animal is lying down, at rest. Thus quantity of hay is important for cattle, who can effectively digest hay of low quality if fed in sufficient amounts. Sheep will eat between two and four percent of their body weight per day in dry feed, such as hay, and are very efficient at obtaining the most nutrition possible from three to five pounds per day of hay or other forage. They require three to four hours per day to eat enough hay to meet their nutritional requirements.
Unlike ruminants, horses digest their food in small portions throughout the day and can utilize only about 2.5% of their body weight in feed within a 24-hour period. Horses evolved to graze continuously while on the move, covering up to 50 miles (80 km) per day in the wild. Their stomachs digest food quickly, allowing them to extract a higher nutritional value from smaller quantities of feed When horses are fed low-quality hay, they may develop an unhealthy, obese, "hay belly" due to over-consumption of "empty" calories. If their type of feed is changed dramatically, or if they are fed moldy hay or hay containing toxic plants, they can become ill; colic is the leading cause of death in horses. Contaminated hay can also lead to respiratory problems in horses. Hay can be soaked in water, sprinkled with water or subjected to steaming to reduce dust.
Harvest and transport
Methods and the terminology to describe the steps of making hay have varied greatly throughout history, and many regional variations still exist today. Whether done by hand or by modern mechanized equipment, tall grass and legumes at the proper stage of maturity must be cut, then allowed to dry (preferably by the sun), then raked into long, narrow piles known as windrows. Next, the cured hay is gathered up in some form (usually by some type of baling process) and placed for storage into a haystack or into a barn or shed to protect it from moisture and rot. | Hay | Wikipedia | 461 | 46593 | https://en.wikipedia.org/wiki/Hay | Technology | Animal husbandry | null |
During the growing season, which is spring and early summer in temperate climates, grass grows at a fast pace. Hay reaches its peak nutritional value when all leaves are fully developed and seed or flower heads are just shy of full maturity. At this stage of maximum growth in the pasture or field, if timed correctly, the hay is cut. Grass hay cut too early retains high moisture content, making it harder to cure and resulting in a lower yield per acre compared to more mature grass. However, hay cut too late becomes coarser, has a lower resale value, and loses some of its nutrients. Typically, there is a two-week "window" during which grass is at its ideal stage for harvesting hay. The time for cutting alfalfa hay is ideally done when plants reach maximum height and are producing flower buds or just beginning to bloom, cutting during or after full bloom results in lower nutritional value of the hay.
Hay can be raked into rows as it is cut, then turned periodically to dry, particularly if a modern swather is used. Or, especially with older equipment or methods, the hay is cut and allowed to lie spread out in the field until it is dry, then raked into rows for processing into bales afterwards. During the drying period, which can take several days, the process is usually sped up by turning the cut hay over with a hay rake or spreading it out with a tedder. If it rains while the hay is drying, turning the windrow can also allow it to dry faster. Turning the hay too often or too roughly can also cause drying leaf matter to fall off, reducing the nutrients available to animals. Drying can also be sped up by mechanized processes, such as the use of a hay conditioner, or by the use of chemicals sprayed onto the hay to speed evaporation of moisture, though these are more expensive techniques, not in general use except in areas where there is a combination of modern technology, high prices for hay, and too much rain for hay to dry properly.
Once hay is cut, dried and raked into windrows, it is usually gathered into bales or bundles, and then hauled to a central location for storage. In some places, depending on geography, region, climate, and culture, hay is gathered loose and stacked without being baled first.
History
Early methods | Hay | Wikipedia | 470 | 46593 | https://en.wikipedia.org/wiki/Hay | Technology | Animal husbandry | null |
Columella in his De re rustica describes the usual haying process of the early Roman Empire. Much hay was originally cut by scythe by teams of workers, dried in the field and gathered loose on wagons. Later, haying was accomplished with horse-drawn implements such as mowers.
After hay was cut and dried, it was raked or rowed up by raking it into a linear heap by hand or with a horse-drawn implement. Turning hay, when needed, originally was done by hand with a fork or rake. Once the dried hay was rowed up, pitchforks were used to pile it loose, originally onto a horse-drawn cart or wagon, later onto a truck or tractor-drawn trailer, for which a sweep could be used instead of pitch forks.
Loose hay was transported to a designated storage area, typically a slightly elevated location to ensure proper drainage, where it was constructed into a haystack. Building the stack was a skilled task, as it needed to be made waterproof during construction. The haystack would compress under its own weight, allowing the hay to cure through the release of heat generated by the residual moisture and compression forces. The haystack was usually enclosed in a fenced-off area, known as a rick yard, to separate it from the rest of the paddock, and was often thatched or covered with sheets to protect it from moisture. When needed, slices of hay would be cut using a hay knife and fed to animals each day.
On some farms, the loose hay was stored in a barrack, shed, or barn, normally in such a way that it would compress down and cure. Hay could be stored in a specially designed barn with little internal structure to allow more room for the hay loft. Alternatively, an upper storey of a cow-shed or stable was used, with hatches in the floor to allow hay to be thrown down into hay-racks below. Depending on the region, the term "hay rick" could refer to the machine for cutting hay, the haystack or the wagon used to collect the hay. | Hay | Wikipedia | 429 | 46593 | https://en.wikipedia.org/wiki/Hay | Technology | Animal husbandry | null |
With the invention of agricultural machinery such as the tractor and the baler, most hay production became mechanized by the 1930s. Hay baling began with the invention of the first hay press in about 1850. Timothy grass and clover were the most common plants used for hay in the early 20th century in the United States, though both plants are native to Europe. Hay was baled for easier handling and to reduce space required for storage and shipment. The first bales weighed about 300 pounds. The original machines were of a vertical design similar to the one photographed by the Greene Co. Historical Society. They used a horse-driven screw-press mechanism or a dropped weight to compress the hay. The first patent went to HL Emery for a horse-powered, screw-operated hay press in 1853. Other models were reported as early as 1843 built by PK Dederick's Sons of Albany, New York, or Samuel Hewitt of Switzerland County, Indiana. Later, horizontal machines were devised. One was the “Perpetual Press” made by PK Dederick of Albany in 1872. They could be powered by steam engines by about 1882. The continuous hay baler arrived in 1914.
Modern mechanized techniques
Modern mechanized hay production today is usually performed by a number of machines. While small operations use a tractor to pull various implements for mowing and raking, larger operations use specialized machines such as a mower or a swather, which are designed to cut the hay and arrange it into a windrow in one step. Balers are usually pulled by a tractor, with larger balers requiring more powerful tractors.
Mobile balers, machines that gather and bale hay in one process were first developed around 1940. The initial balers produced rectangular bales that were small enough for an individual to lift, typically weighing between 70 and 100 pounds (32 to 45 kg) each. The size and shape of these bales allowed for manual handling, including lifting, stacking on transport vehicles, and constructing a haystack by hand. To reduce labor and enhance safety, loaders and stackers were subsequently developed to mechanize the transportation of small bales from the field to the haystack or hay barn. Later in the 20th century, balers were developed capable of producing large bales that weigh up to . | Hay | Wikipedia | 465 | 46593 | https://en.wikipedia.org/wiki/Hay | Technology | Animal husbandry | null |
Conditioning of hay crop during cutting or soon thereafter is popular. The basic idea is that it decreases drying time, particularly in humid climates or if rain threatens to interfere with haying. Usually, rollers or flails inside a mower conditioner crimp, crack or strip the alfalfa or grass stems to increase evaporation rate. Sometimes, a salt solution is sprayed over the top of the hay (generally alfalfa) that helps to dry the hay.
Fertilization and weed control
Modern hay production often relies on artificial fertilizer and herbicides. Traditionally, manure has been used on hayfields, but modern chemical fertilizers are used today as well. Hay that is to be certified as weed-free for use in wilderness areas must often be sprayed with chemical herbicides to keep unwanted weeds from the field, and sometimes even non-certified hayfields are sprayed to limit the production of noxious weeds. Organic forms of fertilization and weed control are required for hay grown for consumption by animals whose meat will ultimately be certified organic. To that end, compost and field rotation can enhance soil fertility, and regular mowing of fields in the growth phase of the hay will often reduce the prevalence of undesired weeds. In recent times, some producers have experimented with human sewage sludge to grow hay. This is not a certified organic method and no warning labels are mandated by EPA. One concern with hay grown on human sewage sludge is that the hay can take up heavy metals, which are then consumed by animals. Molybdenum poisoning is a particular concern in ruminants such as cows and goats, and there have been animal deaths. Another concern is with a herbicide known as aminopyralid, which can pass through the digestive tract in animals, making their resulting manure toxic to many plants and thus unsuitable as fertilizer for food crops. Aminopyralid and related herbicides can persist in the environment for several years.
Baling | Hay | Wikipedia | 406 | 46593 | https://en.wikipedia.org/wiki/Hay | Technology | Animal husbandry | null |
Small square bales are made in two main variations. The smaller "two-tie" (two twines to hold the bale together) or larger "three-tie" (three twines to hold the bale together). They vary in size within both groups but are generally popular in different markets. The smaller two-tie bales are favored in the hobby animal market and are preferred for their convenient size. The larger, three-tie bales are favored by producers wanting to export bales because of the increase of efficiency in transportation and also by customers for a better price per ton. The two-tie small bales are the original form factor of hay bales. Balers for both types of small bales are still manufactured, as well as stackers, bundlers and bale accumulators for handling them. Some farms still use equipment manufactured over 50 years ago to produce small bales. The small bale remains part of overall ranch lore and tradition with "hay bucking" competitions still held for fun at many rodeos and county fairs. Small square bales are often stacked mechanically or by hand in a crisscrossed fashion sometimes called a "haystack", "rick" or "hayrick". Rain tends to wash nutrition out of hay and can cause spoilage or mold; hay in small square bales is particularly susceptible. Small bales are, therefore, often stored in a haymow or hayshed. Haystacks built outside are usually protected by tarpaulins. If this is not done, the top two layers of the stack are often lost to rot and mold, and if the stack is not arranged in a proper haystack, moisture can seep even deeper into the stack. The rounded shape and tighter compaction of round bales make them less susceptible to spoilage, as the water is less likely to penetrate the bale. Adding net wrap, which is not used on square bales, offers even more weather resistance. People who keep small numbers of animals may prefer small bales that one person can handle without machinery. There is also a risk that hay bales may be moldy or contain decaying carcasses of tiny creatures accidentally killed by baling equipment and swept up into the bale, producing toxins such as botulinum toxin | Hay | Wikipedia | 472 | 46593 | https://en.wikipedia.org/wiki/Hay | Technology | Animal husbandry | null |
Both can be deadly to non-ruminant herbivores such as horses, and when this occurs, the entire contaminated bale generally is thrown out, another reason some people continue to support the market for small bales | Hay | Wikipedia | 45 | 46593 | https://en.wikipedia.org/wiki/Hay | Technology | Animal husbandry | null |
Farmers who need to make large amounts of hay will likely choose balers that produce much larger bales, maximizing the amount of hay protected from the elements. Large bales come in two types: round and square. Large square bales, which can weigh up to , can be stacked and easily transported on trucks. Large round bales, which typically weigh , are more moisture-resistant and pack the hay more densely (especially at the center). Round bales are quickly fed with the use of mechanized equipment. The volume-to-surface area ratio allows many dry-area farmers to leave large bales outside until consumed. Wet-area farmers and those in climates with heavy snowfall can stack round bales under a shed or tarp and use a light but durable plastic wrap that partially encloses outside bales. The wrap repels moisture but leaves the ends of the bale exposed so that the hay itself can "breathe" and does not begin to ferment. When it is possible to store round bales under a shed, they last longer, and less hay is lost to rot and moisture.
For animals that eat silage, a bale wrapper may be used to seal a round bale completely and trigger the fermentation process. It is a technique used as a money-saving process by producers who do not have access to a superior silo, and for producing silage that is transported to other locations. In very damp climates, it is a legitimate alternative to drying hay completely. When processed properly, the natural fermentation process prevents mold and rot. Round bale silage is also sometimes called "haylage", and is seen more commonly in Europe than in either the United States or Australia. Hay stored in this fashion must remain completely sealed in plastic, as any holes or tears will allow the entrance of oxygen and can stop the preservation properties of fermentation and lead to spoilage.
Stacking
Hay requires protection from the weather, and is optimally stored inside buildings, but weather protection is also provided in other ways involving outdoor storage, either in haystacks or in large tight bales (round or rectangular); these methods all depend on the surface of an outdoor mass of hay (stack or bale) taking the hit of the weather and thereby preserving the main body of hay underneath. | Hay | Wikipedia | 472 | 46593 | https://en.wikipedia.org/wiki/Hay | Technology | Animal husbandry | null |
Traditionally, outdoor hay storage was done with haystacks of loose hay, where most of the hay was sufficiently preserved to last through the winter, and the top surface of the stack (being weathered) was consigned to become compost the next summer. The term "loose" means not pressed or baled but does not necessarily mean a light, fluffy lay of randomly oriented stems. Especially in wet climates, such as those of Britain, the degree of shedding of rainwater by the stack's outer surface is an important factor, and the stacking of loose hay was developed into a skilled-labor task that in its more advanced forms even involved thatching the top. In many stacking methods (with or without thatched tops), stems were oriented in sheaves, which were laid in oriented sequence.
With the advent of large bales since the 1960s, today hay is often stored outdoors because the outer surface of the large bale performs the weather-shedding function. The large bales can also be stacked, which allows a given degree of exposed surface area to count for a larger volume of protected interior hay. Plastic tarpaulins are sometimes used to shed the rain, with the goal of reduced hay wastage, but the cost of the tarpaulins must be weighed against the cost of the hay spoilage percentage difference; it may not be worth the cost, or the plastic's environmental footprint.
After World War II, British farmers found that the demand outstripped supply for skilled farm laborers experienced in the thatching of haystacks. This no doubt contributed to the pressure for baling in large bales to increasingly replace stacking, which was happening anyway as haymaking technology (like other farm technology) continued toward extensive mechanization with one-person operation of many tasks. Today tons of hay can be cut, conditioned, dried, raked, and baled by one person, as long as the right equipment is at hand (although that equipment is expensive). These tons of hay can also be moved by one person, again with the right (expensive) equipment, as loaders with long spikes run by hydraulic circuits pick up each large bale and move it to its feeding location.
A fence may be built to enclose a haystack and prevent roaming animals from eating it, or animals may feed directly from a field-constructed stack as part of their winter feeding. | Hay | Wikipedia | 489 | 46593 | https://en.wikipedia.org/wiki/Hay | Technology | Animal husbandry | null |
Haystacks are also sometimes called haycocks; among some users this term refers more specifically to small piles of cut-and-gathered hay awaiting stacking into larger stacks. The words (haystack, haycock) are usually styled as solid compounds, but not always. Haystacks are also sometimes called stooks, shocks, or ricks.
Loose stacks are built to prevent the accumulation of moisture and promote drying or curing. In some places, this is accomplished by constructing stacks with a conical or ridged top. The exterior may look gray on the surface after weathering, but the inner hay retains traces of its fresh-cut aroma and maintains a faded green tint. They can be covered with thatch, or kept within a protective structure. One such structure is a moveable roof supported by four posts, historically called a Dutch roof, hay barrack, or hay cap. Haystacks may also be built on top of a foundation laid on the ground to reduce spoilage, in some places made of wood or brush. In other areas, hay is stacked loose, built around a central pole, a tree, or within an area of three or four poles to add stability to the stack.
One loose hay stacking technique seen in the British Isles is to initially stack freshly cut hay into smaller mounds called foot cocks, hay coles, kyles, hayshocks or haycocks, to facilitate initial curing. These are sometimes built atop platforms or tripods formed of three poles, used to keep hay off the ground and let air into the center for better drying. The shape causes dew and rainwater to roll down the sides, allowing the hay within to cure. People who handle the hay may use hayforks or pitchforks to move or pitch the hay in building haycocks and haystacks. Construction of tall haystacks is sometimes aided with a ramp, ranging from simple poles to a device for building large loose stacks called a beaverslide.
Safety
Mold
Hay is generally one of the safest feeds to provide to domesticated grazing herbivores. Amounts must be monitored so animals do not get too fat or too thin. Supplemental feed may be required for working animals with high energy requirements. | Hay | Wikipedia | 454 | 46593 | https://en.wikipedia.org/wiki/Hay | Technology | Animal husbandry | null |
Animals who eat spoiled hay may develop a variety of illnesses, from coughs related to dust and mold, to various other illnesses, the most serious of which may be botulism, which can occur if a small animal, such as a rodent or snake, is killed by the baling equipment, then rots inside the bale, causing a toxin to form. Some animals are sensitive to particular fungi or molds that may grow on living plants. For example, an endophytic fungus that sometimes grows on fescue can cause abortion in pregnant mares. Some plants themselves may also be toxic to some animals. For example, Pimelea, a native Australian plant, also known as flax weed, is highly toxic to cattle.
Farmer's lung is a hypersensitivity pneumonitis induced by the inhalation of biologic dusts coming from hay dust or mold spores or other agricultural products. Exposure to hay can also trigger allergic rhinitis for people who are hypersensitive to airborne allergens.
Spontaneous combustion
Hay must be fully dried when baled and kept dry in storage. If hay is baled while too moist or becomes wet while in storage, there is a significant risk of spontaneous combustion. Hay stored outside must be stacked in such a way that moisture contact is minimal. Some stacks are arranged in such a manner that the hay itself sheds water when it falls. Other methods of stacking use the first layers or bales of hay as a cover to protect the rest. To completely keep out moisture, outside haystacks can also be covered by tarps, and many round bales are partially wrapped in plastic as part of the baling process. Hay is also stored under a roof when resources permit. It is frequently placed inside sheds, or stacked inside of a barn. On the other hand, care must also be taken that hay is never exposed to any possible source of heat or flame, as dry hay and the dust it produces are highly flammable. | Hay | Wikipedia | 409 | 46593 | https://en.wikipedia.org/wiki/Hay | Technology | Animal husbandry | null |
Hay baled before it is fully dry can produce enough heat to start a fire. Haystacks produce internal heat due to bacterial fermentation. If hay is stacked with wet grass, the heat produced can be sufficient to ignite the hay causing a fire. Farmers have to be careful about moisture levels to avoid spontaneous combustion, which is a leading cause of haystack fires. Heat is produced by the respiration process, which occurs until the moisture content of drying hay drops below 40%. Hay is considered fully dry when it reaches 20% moisture. Combustion problems typically occur within five to seven days of baling. A bale cooler than is in little danger, but bales between need to be removed from a barn or structure and separated so that they can cool off. If the temperature of a bale exceeds more than , it can combust.
To check hay moisture content, the farmer can use a hand, an oven or a moisture tester. The most efficient way is to use a moisture tester which shows the moisture content in a few seconds.
Weight
Due to its weight, hay can cause a number of injuries to humans, particularly those related to lifting and moving bales, as well as risks related to stacking and storing. Hazards include the danger of having a poorly constructed stack collapse, causing either falls to people on the stack or injuries to people on the ground who are struck by falling bales. Large round hay bales present a particular danger to those who handle them, because they can weigh over and cannot be moved without special equipment. Nonetheless, because they are cylindrical in shape, and thus can roll easily, it is not uncommon for them to fall from stacks or roll off the equipment used to handle them. From 1992 to 1998, 74 farm workers in the United States were killed in large round hay bale accidents, usually when bales were being moved from one location to another, such as when feeding animals.
Chemical composition | Hay | Wikipedia | 393 | 46593 | https://en.wikipedia.org/wiki/Hay | Technology | Animal husbandry | null |
Straw is an agricultural byproduct consisting of the dry stalks of cereal plants after the grain and chaff have been removed. It makes up about half of the yield by weight of cereal crops such as barley, oats, rice, rye and wheat. It has a number of different uses, including fuel, livestock bedding and fodder, thatching and basket making.
Straw is usually gathered and stored in a straw bale, which is a bale, or bundle, of straw tightly bound with twine, wire, or string. Straw bales may be square, rectangular, star shaped or round, and can be very large, depending on the type of baler used.
Uses
Current and historic uses of straw include:
Animal feed
Straw may be fed as part of the roughage component of the diet to cattle or horses that are on a near maintenance level of energy requirement. It has a low digestible energy and nutrient content (as opposed to hay, which is much more nutritious). The heat generated when microorganisms in a herbivore's gut digest straw can be useful in maintaining body temperature in cold climates. Due to the risk of impaction and its poor nutrient profile, it should always be restricted to part of the diet. It may be fed as it is, or chopped into short lengths, known as chaff.
Basketry
Bee skeps and linen baskets are made from coiled and bound together continuous lengths of straw. The technique is known as lip work.
Bedding
Straw is commonly used as bedding for ruminants and horses. It may be used as bedding and food for small animals, but this often leads to injuries to mouth, nose and eyes as straw is quite sharp.
The straw-filled mattress, also known as a palliasse, is still used by people in many parts of the world.
Bioplastic
Rice straw, an agricultural waste which is not usually recovered, can be turned into bioplastic with mechanical properties akin to polystyrene in its dry state.
Chemicals
Straw is being investigated as a source of fine chemicals including alkaloids, flavonoids, lignins, phenols, and steroids.
Construction material
In many parts of the world, straw is used to bind clay and concrete. A mixture of clay and straw, known as cob, can be used as a building material. There are many recipes for making cob. | Straw | Wikipedia | 495 | 46594 | https://en.wikipedia.org/wiki/Straw | Technology | Animal husbandry | null |
When baled, straw has moderate insulation characteristics (about R-1.5/inch according to Oak Ridge National Lab and Forest Product Lab testing). It can be used, alone or in a post-and-beam construction, to build straw bale houses. When bales are used to build or insulate buildings, the straw bales are commonly finished with earthen plaster. The plastered walls provide some thermal mass, compressive and ductile structural strength, and acceptable fire resistance as well as thermal resistance (insulation), somewhat in excess of North American building code. Straw is an abundant agricultural waste product, and requires little energy to bale and transport for construction. For these reasons, straw bale construction is gaining popularity as part of passive solar and other renewable energy projects.
Wheat straw can be used as a fibrous filler combined with polymers to produce composite lumber.
Enviroboard can be made from straw.
Strawblocks are strawbales that have been recompressed to the density of woodblocks, for compact cargo container shipment, or for straw-bale construction of load-bearing walls that support roof-loads, such as a "living" or green roofs.
Crafts
Craft usages of straw include:
Corn dollies
Straw marquetry
Straw mobile (straw art)
Straw painting
Straw plaiting
Scarecrows
Japanese Traditional Cat's House
Japanese wara art
Construction site sediment control
Straw bales are sometimes used for sediment control at construction sites. However, bales are often ineffective in protecting water quality and are maintenance-intensive. For these reasons the U.S. Environmental Protection Agency (EPA) and various state agencies recommend use of alternative sediment control practices where possible, such as silt fences, fiber rolls and geotextiles.
They can also be used as burned area emergency response, as ground cover or as in-stream check dams.
Fuel source
The use of straw as a carbon-neutral energy source is increasing rapidly, especially for biobutanol. Straw or hay briquettes are a biofuel substitute to coal.
Straw, processed first as briquettes, has been fed into a biogas plant in Aarhus University, Denmark, in a test to see if higher gas yields could be attained. | Straw | Wikipedia | 457 | 46594 | https://en.wikipedia.org/wiki/Straw | Technology | Animal husbandry | null |
The use of straw in large-scale biomass power plants is becoming mainstream in the EU, with several facilities already online. The straw is either used directly in the form of bales, or densified into pellets which allows for the feedstock to be transported over longer distances. Finally, torrefaction of straw with pelletisation is gaining attention, because it increases the energy density of the resource, making it possible to transport it still further. This processing step also makes storage much easier, because torrefied straw pellets are hydrophobic. Torrefied straw in the form of pellets can be directly co-fired with coal or natural gas at very high rates and make use of the processing infrastructures at existing coal and gas plants. Because the torrefied straw pellets have superior structural, chemical and combustion properties to coal, they can replace all coal and turn a coal plant into an entirely biomass-fed power station. First generation pellets are limited to a co-firing rate of 15% in modern IGCC plants.
Gardening
Straw bale gardening is also popular among gardeners who do not have enough space for soil gardening. When properly conditioned, straw bales can be used as a perfect soil substitute.
Hats
There are several styles of straw hats that are made of woven straw.
Many thousands of women and children in England (primarily in the Luton district of Bedfordshire), and large numbers in the United States (mostly Massachusetts), were employed in plaiting straw for making hats. By the late 19th century, vast quantities of plaits were being imported to England from Canton in China, and in the United States most of the straw plait was imported.
A fiber analogous to straw is obtained from the plant Carludovica palmata, and is used to make Panama hats.
Traditional Japanese rain protection consisted of a straw hat and a mino cape.
Horticulture
Straw is used in cucumber houses and for mushroom growing.
In Japan, certain trees are wrapped with straw to protect them from the effects of a hard winter as well as to use them as a trap for parasite insects. (see Komomaki)
It is also used in ponds to reduce algae by changing the nutrient ratios in the water.
The soil under strawberries is covered with straw to protect the ripe berries from dirt, and straw is also used to cover the plants during winter to prevent the cold from killing them.
Straw also makes an excellent mulch.
Packaging | Straw | Wikipedia | 501 | 46594 | https://en.wikipedia.org/wiki/Straw | Technology | Animal husbandry | null |
Straw is resistant to being crushed and therefore makes a good packing material. A company in France makes a straw mat sealed in thin plastic sheets.
Straw envelopes for wine bottles have become rarer, but are still to be found at some wine merchants.
Wheat straw is also used in compostable food packaging such as compostable plates. Packaging made from wheat straw can be certified compostable and will biodegrade in a commercial composting environment.
Paper
Straw can be pulped to make paper.
Rope
Rope made from straw was used by thatchers, in the packaging industry and even in iron foundries.
Saekki is a traditional Korean rope made of woven straw.
Shoes
The Chinese wore cailu or caixie, shoes and sandals made of straw, well into modernity.
Koreans wear jipsin, sandals made of straw.
Several types of traditional Japanese shoes, such as waraji and zōri, are made of straw.
In some parts of Germany like Black Forest and Hunsrück people wear straw shoes at home or at carnival.
Targets
Heavy-gauge straw rope is coiled and sewn tightly together to make archery targets. This is no longer done entirely by hand, but is partially mechanised. Sometimes a paper or plastic target is set up in front of straw bales, which serve to support the target and provide a safe backdrop.
Thatching
Thatching uses straw, reed or similar materials to make a waterproof, lightweight roof with good insulation properties. Straw for this purpose (often wheat straw) is grown specially and harvested using a reaper-binder.
Health and safety
Dried straw presents a fire hazard that can ignite easily if exposed to sparks or an open flame. It can also trigger allergic rhinitis in people who are hypersensitive to airborne allergens such as straw dust. | Straw | Wikipedia | 369 | 46594 | https://en.wikipedia.org/wiki/Straw | Technology | Animal husbandry | null |
A loom is a device used to weave cloth and tapestry. The basic purpose of any loom is to hold the warp threads under tension to facilitate the interweaving of the weft threads. The precise shape of the loom and its mechanics may vary, but the basic function is the same.
Etymology and usage
The word "loom" derives from the Old English geloma, formed from ge- (perfective prefix) and loma, a root of unknown origin; the whole word geloma meant a utensil, tool, or machine of any kind. In 1404 "lome" was used to mean a machine to enable weaving thread into cloth.
By 1838 "loom" had gained the additional meaning of a machine for interlacing thread.
Components and actions
Basic structure
Weaving is done on two sets of threads or yarns, which cross one another. The warp threads are the ones stretched on the loom (from the Proto-Indo-European *werp, "to bend"). Each thread of the weft (i.e. "that which is woven") is inserted so that it passes over and under the warp threads.
The ends of the warp threads are usually fastened to beams. One end is fastened to one beam, the other end to a second beam, so that the warp threads all lie parallel and are all the same length. The beams are held apart to keep the warp threads taut.
The textile is woven starting at one end of the warp threads, and progressing towards the other end. The beam on the finished-fabric end is called the cloth beam. The other beam is called the warp beam.
Beams may be used as rollers to allow the weaver to weave a piece of cloth longer than the loom. As the cloth is woven, the warp threads are gradually unrolled from the warp beam, and the woven portion of the cloth is rolled up onto the cloth beam (which is also called the takeup roll). The portion of the fabric that has already been formed but not yet rolled up on the takeup roll is called the fell.
Not all looms have two beams. For instance, warp-weighted looms have only one beam; the warp yarns hang from this beam. The bottom ends of the warp yarns are tied to dangling loom weights.
Motions
A loom has to perform three principal motions: shedding, picking, and battening. | Loom | Wikipedia | 496 | 46595 | https://en.wikipedia.org/wiki/Loom | Technology | Industrial machinery | null |
Shedding. Shedding is pulling part of the warp threads aside to form a shed (the space between the raised and unraised warp yarns). The shed is the space through which the filling yarn, carried by the shuttle, can be inserted, forming the weft.
Sheds may be simple: for instance, lifting all the odd threads and all the even threads alternately produces a tabby weave (the two sheds are called the shed and countershed). More intricate shedding sequences can produce more complex weaves, such as twill.
Picking. A single crossing of the weft thread from one side of the loom to the other, through the shed, is known as a pick. Picking is passing the weft through the shed. A new shed is then formed before a new pick is inserted.
Conventional shuttle looms can operate at speeds of about 150 to 160 picks per minute.
Battening. After the pick, the new pass of weft thread has to be tamped up against the fell, to avoid making a fabric with large, irregular gaps between the weft threads. This compression of the weft threads is called battening.
There are also usually two secondary motions, because the newly constructed fabric must be wound onto cloth beam. This process is called taking up. At the same time, the warp yarns must be let off or released from the warp beam, unwinding from it. To become fully automatic, a loom needs a tertiary motion, the filling stop motion. This will brake the loom if the weft thread breaks. An automatic loom requires 0.125 hp to 0.5 hp to operate (100W to 400W).
Components
A loom, then, usually needs two beams, and some way to hold them apart. It generally has additional components to make shedding, picking, and battening faster and easier. There are also often components to help take up the fell.
The nature of the loom frame and the shedding, picking, and battening devices vary. Looms come in a wide variety of types, many of them specialized for specific types of weaving. They are also specialized for the lifestyle of the weaver. For instance, nomadic weavers tend to use lighter, more portable looms, while weavers living in cramped city dwellings are more likely to use a tall upright loom, or a loom that folds into a narrow space when not in use.
Shedding methods | Loom | Wikipedia | 502 | 46595 | https://en.wikipedia.org/wiki/Loom | Technology | Industrial machinery | null |
It is possible to weave by manually threading the weft over and under the warp threads, but this is slow. Some tapestry techniques use manual shedding. Pin looms and peg looms also generally have no shedding devices. Pile carpets generally do not use shedding for the pile, because each pile thread is individually knotted onto the warps, but there may be shedding for the weft holding the carpet together.
Usually weaving uses shedding devices. These devices pull some of the warp threads to each side, so that a shed is formed between them, and the weft is passed through the shed. There are a variety of methods for forming the shed. At least two sheds must be formed, the shed and the countershed. Two sheds is enough for tabby weave; more complex weaves, such as twill weaves, satin weaves, diaper weaves, and figured (picture-forming) weaves, require more sheds.
Heddle-bar and shed-rod
Heddle-rods and shedding-sticks are not the fastest way to weave, but they are very simple to make, needing only sticks and yarn. They are often used on vertical and backstrap looms. They allow the creation of elaborate supplementary-weft brocades. They are also used on modern tapestry looms; the frequent changing of weft colour in tapestry makes weaving tapestry slow, so using faster, more complex shedding systems isn't worthwhile. The same is true of looms for handmade knotted-pile carpet; hand-knotting each pile thread to the warp takes far more time than weaving a couple of weft threads to hold the pile in place.
At its simplest, a heddle-bar is simply a stick placed across the warp and tied to individual warp threads. It is not tied to all of the warp threads; for a plain tabby weave, it is tied to every other thread. The little loops of string used to tie the wraps to the heddle bar are called heddles or leashes. When the heddle-bar is pulled perpendicular to the warp, it pulls the warp threads it is tied to out of position, creating a shed. | Loom | Wikipedia | 448 | 46595 | https://en.wikipedia.org/wiki/Loom | Technology | Industrial machinery | null |
A warp-weighted loom (see diagram) typically uses a heddle-bar, or several. It has two upright posts (C); they support a horizontal beam (D), which is cylindrical so that the finished cloth can be rolled around it, allowing the loom to be used to weave a piece of cloth taller than the loom, and preserving an ergonomic working height. The warp threads (F, and A and B) hang from the beam and rest against the shed rod (E). The heddle-bar (G) is tied to some of the warp threads (A, but not B), using loops of string called leashes (H). So when the heddle rod is pulled out and placed in the forked sticks protruding from the posts (not lettered, no technical term given in citation), the shed (1) is replaced by the counter-shed (2). By passing the weft through the shed and the counter-shed, alternately, cloth is woven.
Several heddle-bars can be used side-by-side; three or more can be used to weave twill weaves, for instance.
There are also other ways to create counter-sheds. A shed-rod is simpler and easier to set up than a heddle-bar, and can make a counter-shed. A shed-rod (shedding stick, shed roll) is simply a stick woven through the warp threads. When pulled perpendicular to the threads (or rotated to stand on edge, for wide, flat shedding rods), it creates a counter shed. The combination of a heddle-bar and a shedding-stick can create the shed and countershed needed for a plain tabby weave, as in the video.
There are also slitted heddle-rods, which are sawn partway through, with evenly-placed slits. Each warp thread goes in a slit. The odd-numbered slits are at 90 degrees to the even slits. The rod is rotated back and forth to create the shed and countershed, so it is often large-diameter.
Tablet weaving
Tablet weaving uses cards punched with holes. The warp threads pass through the holes, and the cards are twisted and shifted to created varied sheds. This shedding technique is used for narrow work. It is also used to finish edges, weaving decorative selvage bands instead of hemming.
Rotating-hook heddles | Loom | Wikipedia | 497 | 46595 | https://en.wikipedia.org/wiki/Loom | Technology | Industrial machinery | null |
There are heddles made of flip-flopping rotating hooks, which raise and lower the warp, creating sheds. The hooks, when vertical, have the weft threads looped around them horizontally. If the hooks are flopped over on side or another, the loop of weft twists, raising one or the other side of the loop, which creates the shed and countershed.
Rigid heddles
Rigid heddles are generally used on single-shaft looms. Odd warp threads go through the slots, and even ones through the circular holes, or vice-versa. The shed is formed by lifting the heddle, and the countershed by depressing it. The warp threads in the slots stay where they are, and the ones in the circular holes are pulled back and forth. A single rigid heddle can hold all the warp threads, though sometimes multiple rigid heddles are used.
Treadles may be used to drive the rigid heddle up and down.
Non-rigid heddles
Rigid heddles or (above) are called "rigid" to distinguish them from string and wire heddles. Rigid heddles are one-piece, by non-rigid ones are multi-piece. Each warp thread has its own heald (also, confusingly, called a heddle). The heald has an eyelet at each end (for the staves, also called shafts) and one in the middle, called the mail, (for the warp thread). A row of these healds is slid onto two staves, the upper and lower staves; the staves together, or the staves together with the healds, may be called a heald frame, which is, confusingly, also called a shaft and a harness. Replacable, interchangable healds can be smaller, allowing finer weaves.
Unlike a rigid heddle, a flexible heddle cannot push the warp thread. This means that two heald frames are needed even for a plain tabby weave. Twill weaves require three or more heald frames (depending on the type of twill), and more complex figured weaves require still more frames.
The different heald frames must be controlled by some mechanism, and the mechanism must be able to pull them in both directions. They are mostly controlled by treadles; creating the shed with the feet leaves the hands free to ply the shuttle. However in some tabletop looms, heald frames are also controlled by levers. | Loom | Wikipedia | 511 | 46595 | https://en.wikipedia.org/wiki/Loom | Technology | Industrial machinery | null |
Treadle-controlled looms
In treadle looms, the weaver controls the shedding with their feet, by treading on treadles. Different treadles and combinations of treadles produce different sheds. The weaver must remember the sequence of treadling needed to produce the pattern.
The precise mechanism by which the treadles control the heddles varies. Rigid-heddle treadle looms do exist, but the heddles are usually flexible. Sometimes, the treadles are tied directly to the staves (with a Y-shaped bridle so they stay level). Alternately, they may be tied to a stick called a lamm, which in turn is tied to the stave, to make the motion more controlled and regular. The lamm may pivot or slide.
Counterbalance looms are the most common type of treadle loom globally, as they are simple and give a smooth, quiet, quick motion. The heald frames are joined together in pairs, by a cord running over heddle pulleys or a heddle roller. When one heald frame rises, the other falls. It takes a pair of treadles to control a pair of frames. Counterbalance looms are usually used with two or four frames, though some have as many as ten.
In theory each pair of heald frames has to have an equal number to warps pulled by each frame, so the patterns that can be made on them are limited. In practice, fairly unbalanced tie-ups just make the shed a bit smaller, and as the shed on a counterbalance loom is adjustable in size and quite large to start with (compared to other types of loom), so it is entirely possible to weave good cloth on a counterbalance loom with unbalanced heald frames, unless the loom is extremely shallow (that is, the length of warp being pulled on is short, less than 1 meter or 3 feet), which exacerbates the slightly uneven tension. Limited patterns are not, of course, a disadvantage when weaving plainer patterns, such as tabbies and twills. | Loom | Wikipedia | 432 | 46595 | https://en.wikipedia.org/wiki/Loom | Technology | Industrial machinery | null |
Jack looms (also called single-tieup-looms and rising-shed looms), have their treadles connected to jacks, levers that push or pull the heald frames up; the harnesses are weighted to fall back into place by gravity. Several frames can be connected to a single treadle. Frames can also be raised by more than one treadle. This allows treadles to control arbitrary combinations of frames, which vastly increases the number of different sheds that can be created from the same number of frames. Any number of treadles can also be engaged at once, meaning that the number of different sheds that can be selected is two to the power of the number of treadles. Eight is a large but reasonable number of treadles, giving a maximum of 28=256 sheds (some of which will probably not have enough threads on one side to be useful). Having more possible sheds allows more complex patterns, such as diaper weaves.
Jack looms are easy to make and to tie up (if not quite as easy as counterbalance looms). The gravity return makes jack looms heavy to operate. The shed of a jack loom is smaller for a given length of warp being pulled aside by the heddles (loom depth). The warp threads being pulled up by the jacks are also tauter than the other warp threads (unlike a counter balance loom, where the threads are pulled an equal amount in opposite directions). Uneven tension makes weaving evenly harder. It also lowers the maximum tension at which one can practically weave. If the threads are rough, closely-spaced, very long or numerous, it can be hard to open the sheds on the jack loom. Jack looms without castles (the superstructure above the weft) have to lift the heald frames from below, and are noiser due to the impact of wood on wood; elastomer pads can reduce the noise. | Loom | Wikipedia | 395 | 46595 | https://en.wikipedia.org/wiki/Loom | Technology | Industrial machinery | null |
In countermarch looms, the treadles are tied to lamms, which may pivot at one end or slide up and down. Half of the lamms in turn connect to jacks, which also pivot, and push or pull the staves up or down. Some countermarches have two horizontal jacks per shaft, others a single vertical jack. Each treadle is tied to all of the heald frames, moving some of them up and the rest of them down. This allows the complex combinatorial treadles of a jack loom, with the large shed and balanced, even tension of a counterbalance loom, with its quiet, light operation. Unfortunately, countermarch looms are more complex, harder to build, slower to tie up, and more prone to malfunction.
Figure harness and the drawloom
A drawloom is for weaving figured cloth. In a drawloom, a "figure harness" is used to control each warp thread separately, allowing very complex patterns. A drawloom requires two operators, the weaver, and an assistant called a "drawboy" to manage the figure harness.
The earliest confirmed drawloom fabrics come from the State of Chu and date c. 400 BC. Some scholars speculate an independent invention in ancient Syria, since drawloom fabrics found in Dura-Europas are thought to date before 256 AD. The draw loom was invented in China during the Han dynasty (State of Liu?); foot-powered multi-harness looms and jacquard looms were used for silk weaving and embroidery, both of which were cottage industries with imperial workshops. The drawloom enhanced and sped up the production of silk and played a significant role in Chinese silk weaving. The loom was introduced to Persia, India, and Europe.
Dobby head
A dobby head is a device that replaces the drawboy, the weaver's helper who used to control the warp threads by pulling on draw threads. "Dobby" is a corruption of "draw boy". Mechanical dobbies pull on the draw threads using pegs in bars to lift a set of levers. The placement of the pegs determines which levers are lifted. The sequence of bars (they are strung together) effectively remembers the sequence for the weaver. Computer-controlled dobbies use solenoids instead of pegs.
Jacquard head | Loom | Wikipedia | 491 | 46595 | https://en.wikipedia.org/wiki/Loom | Technology | Industrial machinery | null |
The Jacquard loom is a mechanical loom, invented by Joseph Marie Jacquard in 1801, which simplifies the process of manufacturing figured textiles with complex patterns such as brocade, damask, and matelasse. The loom is controlled by punched cards with punched holes, each row of which corresponds to one row of the design. Multiple rows of holes are punched on each card and the many cards that compose the design of the textile are strung together in order. It is based on earlier inventions by the Frenchmen Basile Bouchon (1725), Jean Baptiste Falcon (1728), and Jacques Vaucanson (1740). To call it a loom is a misnomer. A Jacquard head could be attached to a power loom or a handloom, the head controlling which warp thread was raised during shedding. Multiple shuttles could be used to control the colour of the weft during picking. The Jacquard loom is the predecessor to the computer punched card readers of the 19th and 20th centuries.
Picking (weft insertion)
The weft may be passed across the shed as a ball of yarn, but usually this is too bulky and unergonomic. Shuttles are designed to be slim, so they pass through the shed; to carry a lot of yarn, so the weaver does not need to refill them too often; and to be an ergonomic size and shape for the particular weaver, loom, and yarn. They may also be designed for low friction.
Stick shuttles
Unnotched stick shuttles
At their simplest, these are just sticks wrapped with yarn. They may be specially shaped, as with the bobbins and bones used in tapestry-making (bobbins are used on vertical warps, and bones on horizontal ones).
Notched stick shuttles, rag shuttles, and ski shuttles
Boat shuttles
Boat shuttles may be closed (central hollow with a solid bottom) or open (central hole goes right through). The yarn may be side-feed or end-feed. They are commonly made for 10-cm (4-inch) and 15-cm (6-inch) bobbin lengths.
Flying shuttle | Loom | Wikipedia | 456 | 46595 | https://en.wikipedia.org/wiki/Loom | Technology | Industrial machinery | null |
Hand weavers who threw a shuttle could only weave a cloth as wide as their armspan. If cloth needed to be wider, two people would do the task (often this would be an adult with a child). John Kay (1704–1779) patented the flying shuttle in 1733. The weaver held a picking stick that was attached by cords to a device at both ends of the shed. With a flick of the wrist, one cord was pulled and the shuttle was propelled through the shed to the other end with considerable force, speed and efficiency. A flick in the opposite direction and the shuttle was propelled back. A single weaver had control of this motion but the flying shuttle could weave much wider fabric than an arm's length at much greater speeds than had been achieved with the hand thrown shuttle.
The flying shuttle was one of the key developments in weaving that helped fuel the Industrial Revolution. The whole picking motion no longer relied on manual skill and it was just a matter of time before it could be powered by something other than a human.
Weft insertion in power looms
Different types of power looms are most often defined by the way that the weft, or pick, is inserted into the warp. Many advances in weft insertion have been made in order to make manufactured cloth more cost effective. Weft insertion rate is a limiting factor in production speed. , industrial looms can weave at 2,000 weft insertions per minute. | Loom | Wikipedia | 290 | 46595 | https://en.wikipedia.org/wiki/Loom | Technology | Industrial machinery | null |
There are five main types of weft insertion and they are as follows:
Shuttle: The first-ever powered looms were shuttle-type looms. Spools of weft are unravelled as the shuttle travels across the shed. This is very similar to projectile methods of weaving, except that the weft spool is stored on the shuttle. These looms are considered obsolete in modern industrial fabric manufacturing because they can only reach a maximum of 300 picks per minute.
Air jet: An air-jet loom uses short quick bursts of compressed air to propel the weft through the shed in order to complete the weave. Air jets are the fastest traditional method of weaving in modern manufacturing and they are able to achieve up to 1,500 picks per minute. However, the amounts of compressed air required to run these looms, as well as the complexity in the way the air jets are positioned, make them more costly than other looms.
Water jet: Water-jet looms use the same principle as air-jet looms, but they take advantage of pressurized water to propel the weft. The advantage of this type of weaving is that water power is cheaper where water is directly available on site. Picks per minute can reach as high as 1,000.
Rapier loom: This type of weaving is very versatile, in that rapier looms can weave using a large variety of threads. There are several types of rapiers, but they all use a hook system attached to a rod or metal band to pass the pick across the shed. These machines regularly reach 700 picks per minute in normal production.
Projectile: Projectile looms utilize an object that is propelled across the shed, usually by spring power, and is guided across the width of the cloth by a series of reeds. The projectile is then removed from the weft fibre and it is returned to the opposite side of the machine so it can be reused. Multiple projectiles are in use in order to increase the pick speed. Maximum speeds on these machines can be as high as 1,050 ppm. | Loom | Wikipedia | 422 | 46595 | https://en.wikipedia.org/wiki/Loom | Technology | Industrial machinery | null |
Circular: Modern circular looms use up to ten shuttles, driven in a circular motion from below by electromagnets, for the weft yarns, and cams to control the warp threads. The warps rise and fall with each shuttle passage, unlike the common practice of lifting all of them at once. Circular looms are used to create seamless tubes of fabric for products such as hosiery, sacks, clothing, fabric hoses (such as fire hoses) and the like. | Loom | Wikipedia | 103 | 46595 | https://en.wikipedia.org/wiki/Loom | Technology | Industrial machinery | null |
Battening
The newest weft thread must be beaten against the fell. Battening can be done with a long stick placed in the shed parallel to the weft (a sword batten), a shorter stick threaded between the warp threads perpendicular to warp and weft (a pin batten), a comb, or a reed (a comb with both ends closed, so that it has to be sleyed, that is have the warp threads threaded through it, when the loom is warped). For rigid-heddle looms, the heddle may be used as a reed.
Secondary motions
Dandy mechanism
Patented in 1802, dandy looms automatically rolled up the finished cloth, keeping the fell always the same length. They significantly speeded up hand weaving (still a major part of the textile industry in the 1800s). Similar mechanisms were used in power looms.
Temples
The temples act to keep the cloth from shrinking sideways as it is woven. Some warp-weighted looms had temples made of loom weights, suspended by strings so that they pulled the cloth breadthwise. Other looms may have temples tied to the frame, or temples that are hooks with an adjustable shaft between them. Power looms may use temple cylinders. Pins can leave a series of holes in the selvages (these may be from stenter pins used in post-processing).
Frames
Loom frames can be roughly divided, by the orientation of the warp threads, into horizontal looms and vertical looms. There are many finer divisions. Most handloom frame designs can be constructed fairly simply.
Backstrap loom
The back-strap loom (also known as belt loom) is a simple loom with ancient roots, still used in many cultures around the world (such as Andean textiles, and in Central, East and South Asia). It consists of two sticks or bars between which the warps are stretched. One bar is attached to a fixed object and the other to the weaver, usually by means of a strap around the weaver's back. The weaver leans back and uses their body weight to tension the loom.
Both simple and complex textiles can be woven on backstrap looms. They produce narrowcloth: width is limited to the weaver's armspan. They can readily produce warp-faced textiles, often decorated with intricate pick-up patterns woven in complementary and supplementary warp techniques, and brocading. Balanced weaves are also possible on the backstrap loom. | Loom | Wikipedia | 511 | 46595 | https://en.wikipedia.org/wiki/Loom | Technology | Industrial machinery | null |
Warp-weighted loom
The warp-weighted loom is a vertical loom that may have originated in the Neolithic period. Its defining characteristic is hanging weights (loom weights) which keep bundles of the warp threads taut. Frequently, extra warp thread is wound around the weights. When a weaver has woven far enough down, the completed section (fell) can be rolled around the top beam, and additional lengths of warp threads can be unwound from the weights to continue. This frees the weaver from vertical size constraint. Horizontally, breadth is limited by armspan; making broadwoven cloth requires two weavers, standing side by side at the loom.
Simple weaves, and complex weaves that need more than two different sheds, can both be woven on a warp-weighted loom. They can also be used to produce tapestries.
Pegged or floor loom
In pegged looms, the beams can be simply held apart by hooking them behind pegs driven into the ground, with wedges or lashings used to adjust the tension. Pegged looms may, however, also have horizontal sidepieces holding the beams apart.
Such looms are easy to set up and dismantle, and are easy to transport, so they are popular with nomadic weavers. They are generally only used for comparatively small woven articles. Urbanites are unlikely to use horizontal floor looms as they take up a lot of floor space, and full-time professional weavers are unlikely to use them as they are unergonomic. Their cheapness and portability is less valuable to urban professional weavers.
Treadle loom
In a treadle loom, the shedding is controlled by the feet, which tread on the treadles.
The earliest evidence of a horizontal loom is found on a pottery dish in ancient Egypt, dated to 4400 BC. It was a frame loom, equipped with treadles to lift the warp threads, leaving the weaver's hands free to pass and beat the weft thread.
A pit loom has a pit for the treadles, reducing the stress transmitted through the much shorter frame. | Loom | Wikipedia | 434 | 46595 | https://en.wikipedia.org/wiki/Loom | Technology | Industrial machinery | null |
In a wooden vertical-shaft loom, the heddles are fixed in place in the shaft. The warp threads pass alternately through a heddle, and through a space between the heddles (the shed), so that raising the shaft raises half the threads (those passing through the heddles), and lowering the shaft lowers the same threads — the threads passing through the spaces between the heddles remain in place.
A treadle loom for figured weaving may have a large number of harnesses or a control head. It can, for instance, have a Jacquard machine attached to it .
Tapestry looms
Tapestry can have extremely complex wefts, as different strands of wefts of different colours are used to form the pattern. Speed is lower, and shedding and picking devices may be simpler. Looms used for weaving traditional tapestry are called not as "vertical-warp" and "horizontal-warp", but as "high-warp" or "low-warp" (the French terms haute-lisse and are also used in English).
Ribbon, Band, and Inkle weaving
Inkle looms are narrow looms used for narrow work. They are used to make narrow warp-faced strips such as ribbons, bands, or tape. They are often quite small; some are used on a tabletop. others are backstraps looms with a rigid heddle, and very portable.
Darning looms
There exist very small hand-held looms known as darning looms. They are made to fit under the fabric being mended, and are often held in place by an elastic band on one side of the cloth and a groove around the loom's darning-egg portion on the other. They may have heddles made of flip-flopping rotating hooks . Other devices sold as darning looms are just a darning egg and a separate comb-like piece with teeth to hook the warp over; these are used for repairing knitted garments and are like a linear knitting spool. Darning looms were sold during World War Two clothing rationing in the United Kingdom and Canada, and some are homemade.
Circular handlooms
Circular looms are used to create seamless tubes of fabric for products such as hosiery, sacks, clothing, fabric hoses (such as fire hoses) and the like. Tablet weaving can be used to knit tubes, including tubes that split and join. | Loom | Wikipedia | 502 | 46595 | https://en.wikipedia.org/wiki/Loom | Technology | Industrial machinery | null |
Small jigs also used for circular knitting are also sometimes called circular looms, but they are used for knitting, not weaving.
Handlooms to power looms
A power loom is a loom powered by a source of energy other than the weaver's muscles. When power looms were developed, other looms came to be referred to as handlooms. Most cloth is now woven on power looms, but some is still woven on handlooms.
The development of power looms was gradual. The capabilities of power looms gradually expanded, but handlooms remained the most cost-effective way to make some types of textiles for most of the 1800s. Many improvements in loom mechanisms were first applied to hand looms (like the dandy loom), and only later integrated into power looms.
Edmund Cartwright built and patented a power loom in 1785, and it was this that was adopted by the nascent cotton industry in England. The silk loom made by Jacques Vaucanson in 1745 operated on the same principles but was not developed further. The invention of the flying shuttle by John Kay allowed a hand weaver to weave broadwoven cloth without an assistant, and was also critical to the development of a commercially successful power loom. Cartwright's loom was impractical but the ideas behind it were developed by numerous inventors in the Manchester area of England. By 1818, there were 32 factories containing 5,732 looms in the region. | Loom | Wikipedia | 301 | 46595 | https://en.wikipedia.org/wiki/Loom | Technology | Industrial machinery | null |
The Horrocks loom was viable, but it was the Roberts Loom in 1830 that marked the turning point. Incremental changes to the three motions continued to be made. The problems of sizing, stop-motions, consistent take-up, and a temple to maintain the width remained. In 1841, Kenworthy and Bullough produced the Lancashire Loom which was self-acting or semi-automatic. This enabled a youngster to run six looms at the same time. Thus, for simple calicos, the power loom became more economical to run than the handloom – with complex patterning that used a dobby or Jacquard head, jobs were still put out to handloom weavers until the 1870s. Incremental changes were made such as the Dickinson Loom, culminating in the fully automatic Northrop Loom, developed by the Keighley-born inventor Northrop, who was working for the Draper Corporation in Hopedale. This loom recharged the shuttle when the pirn was empty. The Draper E and X models became the leading products from 1909. They were challenged by synthetic fibres such as rayon.
By 1942, faster, more efficient, and shuttleless Sulzer and rapier looms had been introduced.
Symbolism and cultural significance
The loom is a symbol of cosmic creation and the structure upon which individual destiny is woven. This symbolism is encapsulated in the classical myth of Arachne who was changed into a spider by the goddess Athena, who was jealous of her skill at the godlike craft of weaving. In Maya civilization the goddess Ixchel taught the first woman how to weave at the beginning of time.
Gallery | Loom | Wikipedia | 344 | 46595 | https://en.wikipedia.org/wiki/Loom | Technology | Industrial machinery | null |
Drainage is the natural or artificial removal of a surface's water and sub-surface water from an area with excess water. The internal drainage of most agricultural soils can prevent severe waterlogging (anaerobic conditions that harm root growth), but many soils need artificial drainage to improve production or to manage water supplies.
History
Early history
The Indus Valley Civilization had sewerage and drainage systems. All houses in the major cities of Harappa and Mohenjo-daro had access to water and drainage facilities. Waste water was directed to covered gravity sewers, which lined the major streets.
18th and 19th century
The invention of hollow-pipe drainage is credited to Sir Hugh Dalrymple, who died in 1753.
Current practices
Simple infrastructure such as open drains, pipes, and berms are still common. In modern times, more complex structures involving substantial earthworks and new technologies have been common as well.
Geotextiles
New storm water drainage systems incorporate geotextile filters that retain and prevent fine grains of soil from passing into and clogging the drain. Geotextiles are synthetic textile fabrics specially manufactured for civil and environmental engineering applications. Geotextiles are designed to retain fine soil particles while allowing water to pass through. In a typical drainage system, they would be laid along a trench which would then be filled with coarse granular material: gravel, sea shells, stone or rock. The geotextile is then folded over the top of the stone and the trench is then covered by soil. Groundwater seeps through the geotextile and flows through the stone to an outfell. In high groundwater conditions a perforated plastic (PVC or PE) pipe is laid along the base of the drain to increase the volume of water transported in the drain.
Alternatively, a prefabricated plastic drainage system made of HDPE, often incorporating geotextile, coco fiber or rag filters can be considered. The use of these materials has become increasingly more common due to their ease of use, since they eliminate the need for transporting and laying stone drainage aggregate, which is invariably more expensive than a synthetic drain and concrete liners.
Over the past 30 years, geotextile, PVC filters, and HDPE filters have become the most commonly used soil filter media. They are cheap to produce and easy to lay, with factory controlled properties that ensure long term filtration performance even in fine silty soil conditions. | Drainage | Wikipedia | 489 | 46596 | https://en.wikipedia.org/wiki/Drainage | Technology | Hydraulic infrastructure | null |
21st century alternatives
Seattle's Public Utilities created a pilot program called Street Edge Alternatives Project. The project focuses on designing a system "to provide drainage that more closely mimics the natural landscape prior to development than traditional piped systems".
The streets are characterized by ditches along the side of the roadway, with plantings designed throughout the area.
An emphasis on non-curbed sidewalks allows water to flow more freely into the areas of permeable surface on the side of the streets. Because of the plantings, the run off water from the urban area does not all directly go into the ground, but can also be absorbed into the surrounding environment.
Monitoring conducted by Seattle Public Utilities reports a 99 percent reduction of storm water leaving the drainage project.
Drainage has undergone a large-scale environmental review in the recent past in the United Kingdom. Sustainable urban drainage systems (SUDS) are designed to encourage contractors to install drainage system that more closely mimic the natural flow of water in nature. Since 2010 local and neighbourhood planning in the UK is required by law to factor SUDS into any development projects that they are responsible for.
Slot drainage is a channel drainage system designed to eliminate the need for further pipework systems to be installed in parallel to the drainage, reducing the environmental impact of production as well as improving water collection. Stainless steel, concrete channel, PVC and HDPE are all materials available for slot drainage which have become industry standards on construction projects.
In the construction industry
The civil engineer is responsible for drainage in construction projects. During the construction process, they set out all the necessary levels for roads, street gutters, drainage, culverts and sewers involved in construction operations.
Civil engineers and construction managers work alongside architects and supervisors, planners, quantity surveyors, and the general workforce, as well as subcontractors. Typically, most jurisdictions have some body of drainage law to govern to what degree a landowner can alter the drainage from their parcel. | Drainage | Wikipedia | 392 | 46596 | https://en.wikipedia.org/wiki/Drainage | Technology | Hydraulic infrastructure | null |
Drainage options for the construction industry include:
Point drainage, which intercepts water at gullies (points). Gullies connect to drainage pipes beneath the ground surface, so deep excavation is required to facilitate this system. Support for deep trenches is required in the shape of planking, strutting or shoring.
Channel drainage, which intercepts water along the entire run of the channel. Channel drainage is typically manufactured from concrete, steel, polymer or composites. The interception rate of channel drainage is greater than point drainage and the excavation required is usually much less deep.
The surface opening of channel drainage usually comes in the form of gratings (polymer, plastic, steel or iron) or a single slot (slot drain) that run along the ground surface (typically manufactured from steel or iron).
In retaining walls
Earth retaining structures such as retaining walls also need to have groundwater drainage considered during their construction. Typical retaining walls are constructed of impermeable material, which can block the path of groundwater. When groundwater flow is obstructed, hydrostatic water pressure buildups against the wall and may cause significant damage. If the water pressure is not drained appropriately, retaining walls can bow, move, and fracture, causing seams to separate. The water pressure can also erode soil particles, leading to voids behind the wall and sinkholes in the above soil. Traditional retaining wall drainage systems can include French drains, drain pipes or weep holes. To prevent soil erosion, geotextile filter fabrics are installed with the drainage system.
In planters
Drainage in planters refers to the implementation of effective drainage systems specifically designed for plant containers or pots. Proper drainage is crucial in planters to prevent waterlogging and promote healthy plant growth. Planter Drainage involves the incorporation of drainage holes, drainage layers, or specialized drainage systems to ensure excess water can escape from the planter. This helps to prevent root rot, water accumulation, and other issues that can negatively impact plant health. By providing adequate drainage in planters, it supports optimal plant growth and contributes to the overall success of gardening or landscaping projects. | Drainage | Wikipedia | 425 | 46596 | https://en.wikipedia.org/wiki/Drainage | Technology | Hydraulic infrastructure | null |
Drainage options for the planter include:
Surface drains are typically used to manage runoff from paved surfaces, such as sidewalks and parking lots. Catch basins, which collect water and debris, are connected to underground pipes that carry the water away from the site.
Subsurface drains, on the other hand, are designed to manage water that seeps into the soil beneath the planting surface. French drains, which are gravel-filled trenches with perforated pipes at the bottom, are the most common type of subsurface drain. Trench drains, which are similar but shallower and wider, are also used in some situations.
Reasons for artificial drainage
Wetland soils may need drainage to be used for agriculture. In the northern United States and Europe, glaciation created numerous small lakes, which gradually filled with humus to make marshes. Some of these were drained using open ditches and trenches to make mucklands, which are primarily used for high-value crops such as vegetables.
The world's largest project of this type has been in process for centuries in the Netherlands. The area between Amsterdam, Haarlem and Leiden was, in prehistoric times, swampland and small lakes. Turf cutting (peat mining), subsidence and shoreline erosion gradually caused the formation of one large lake, the Haarlemmermeer, or lake of Haarlem. The invention of wind-powered pumping engines in the 15th century permitted some of the marginal land drainage. Still, the final drainage of the lake had to await the design of large steam-powered pumps and agreements between regional authorities. The lake was eliminated between 1849 and 1852, creating thousands of km2 of new land.
Coastal plains and river deltas may have seasonally or permanently high water tables and must have drainage improvements if they are to be used for agriculture. An example is the flatwoods citrus-growing region of Florida, United States. After periods of high rainfall, drainage pumps are employed to prevent damage to the citrus groves from overly wet soils. Rice production requires complete water control, as fields must be flooded or drained at different stages of the crop cycle. The Netherlands has also led the way in this type of drainage by draining lowlands along the shore and pushing back the sea until the original nation has been greatly enlarged. | Drainage | Wikipedia | 457 | 46596 | https://en.wikipedia.org/wiki/Drainage | Technology | Hydraulic infrastructure | null |
In moist climates, soils may be adequate for cropping with the exception that they become waterlogged for brief periods each year, from snow melt or from heavy rains. Soils that are predominantly clay will pass water very slowly downward. Meanwhile, plant roots suffocate because the excessive water around the roots eliminates air movement through the soil.
Other soils may have an impervious layer of mineralized soil, called a hardpan, or relatively impervious rock layers may underlie shallow soils. Drainage is especially important in tree fruit production. Soils that are otherwise excellent may be waterlogged for a week of the year, which is sufficient to kill fruit trees and cost the productivity of the land until replacements can be established. In each of these cases, appropriate drainage carries off temporary flushes of water to prevent damage to annual or perennial crops.
Drier areas are often farmed by irrigation, and one would not consider drainage necessary. However, irrigation water always contains minerals and salts, which can be concentrated to toxic levels by evapotranspiration. Irrigated land may need periodic flushes with excessive irrigation water and drainage to control soil salinity. | Drainage | Wikipedia | 236 | 46596 | https://en.wikipedia.org/wiki/Drainage | Technology | Hydraulic infrastructure | null |
An embedded system is a specialized computer system—a combination of a computer processor, computer memory, and input/output peripheral devices—that has a dedicated function within a larger mechanical or electronic system. It is embedded as part of a complete device often including electrical or electronic hardware and mechanical parts.
Because an embedded system typically controls physical operations of the machine that it is embedded within, it often has real-time computing constraints. Embedded systems control many devices in common use. , it was estimated that ninety-eight percent of all microprocessors manufactured were used in embedded systems.
Modern embedded systems are often based on microcontrollers (i.e. microprocessors with integrated memory and peripheral interfaces), but ordinary microprocessors (using external chips for memory and peripheral interface circuits) are also common, especially in more complex systems. In either case, the processor(s) used may be types ranging from general purpose to those specialized in a certain class of computations, or even custom designed for the application at hand. A common standard class of dedicated processors is the digital signal processor (DSP).
Since the embedded system is dedicated to specific tasks, design engineers can optimize it to reduce the size and cost of the product and increase its reliability and performance. Some embedded systems are mass-produced, benefiting from economies of scale.
Embedded systems range in size from portable personal devices such as digital watches and MP3 players to bigger machines like home appliances, industrial assembly lines, robots, transport vehicles, traffic light controllers, and medical imaging systems. Often they constitute subsystems of other machines like avionics in aircraft and astrionics in spacecraft. Large installations like factories, pipelines, and electrical grids rely on multiple embedded systems networked together. Generalized through software customization, embedded systems such as programmable logic controllers frequently comprise their functional units.
Embedded systems range from those low in complexity, with a single microcontroller chip, to very high with multiple units, peripherals and networks, which may reside in equipment racks or across large geographical areas connected via long-distance communications lines.
History
Background | Embedded system | Wikipedia | 432 | 46630 | https://en.wikipedia.org/wiki/Embedded%20system | Technology | Computer hardware | null |
The origins of the microprocessor and the microcontroller can be traced back to the MOS integrated circuit, which is an integrated circuit chip fabricated from MOSFETs (metal–oxide–semiconductor field-effect transistors) and was developed in the early 1960s. By 1964, MOS chips had reached higher transistor density and lower manufacturing costs than bipolar chips. MOS chips further increased in complexity at a rate predicted by Moore's law, leading to large-scale integration (LSI) with hundreds of transistors on a single MOS chip by the late 1960s. The application of MOS LSI chips to computing was the basis for the first microprocessors, as engineers began recognizing that a complete computer processor system could be contained on several MOS LSI chips.
The first multi-chip microprocessors, the Four-Phase Systems AL1 in 1969 and the Garrett AiResearch MP944 in 1970, were developed with multiple MOS LSI chips. The first single-chip microprocessor was the Intel 4004, released in 1971. It was developed by Federico Faggin, using his silicon-gate MOS technology, along with Intel engineers Marcian Hoff and Stan Mazor, and Busicom engineer Masatoshi Shima.
Development
One of the first recognizably modern embedded systems was the Apollo Guidance Computer, developed ca. 1965 by Charles Stark Draper at the MIT Instrumentation Laboratory. At the project's inception, the Apollo guidance computer was considered the riskiest item in the Apollo project as it employed the then newly developed monolithic integrated circuits to reduce the computer's size and weight.
An early mass-produced embedded system was the Autonetics D-17 guidance computer for the Minuteman missile, released in 1961. When the Minuteman II went into production in 1966, the D-17 was replaced with a new computer that represented the first high-volume use of integrated circuits. | Embedded system | Wikipedia | 404 | 46630 | https://en.wikipedia.org/wiki/Embedded%20system | Technology | Computer hardware | null |
Since these early applications in the 1960s, embedded systems have come down in price and there has been a dramatic rise in processing power and functionality. An early microprocessor, the Intel 4004 (released in 1971), was designed for calculators and other small systems but still required external memory and support chips. By the early 1980s, memory, input and output system components had been integrated into the same chip as the processor forming a microcontroller. Microcontrollers find applications where a general-purpose computer would be too costly. As the cost of microprocessors and microcontrollers fell, the prevalence of embedded systems increased.
A comparatively low-cost microcontroller may be programmed to fulfill the same role as a large number of separate components. With microcontrollers, it became feasible to replace, even in consumer products, expensive knob-based analog components such as potentiometers and variable capacitors with up/down buttons or knobs read out by a microprocessor. Although in this context an embedded system is usually more complex than a traditional solution, most of the complexity is contained within the microcontroller itself. Very few additional components may be needed and most of the design effort is in the software. Software prototype and test can be quicker compared with the design and construction of a new circuit not using an embedded processor.
Applications
Embedded systems are commonly found in consumer, industrial, automotive, home appliances, medical, telecommunication, commercial, aerospace and military applications.
Telecommunications systems employ numerous embedded systems from telephone switches for the network to cell phones at the end user. Computer networking uses dedicated routers and network bridges to route data.
Consumer electronics include MP3 players, television sets, mobile phones, video game consoles, digital cameras, GPS receivers, and printers. Household appliances, such as microwave ovens, washing machines and dishwashers, include embedded systems to provide flexibility, efficiency and features. Advanced heating, ventilation, and air conditioning (HVAC) systems use networked thermostats to more accurately and efficiently control temperature that can change by time of day and season. Home automation uses wired and wireless networking that can be used to control lights, climate, security, audio/visual, surveillance, etc., all of which use embedded devices for sensing and controlling. | Embedded system | Wikipedia | 471 | 46630 | https://en.wikipedia.org/wiki/Embedded%20system | Technology | Computer hardware | null |
Transportation systems from flight to automobiles increasingly use embedded systems. New airplanes contain advanced avionics such as inertial guidance systems and GPS receivers that also have considerable safety requirements. Spacecraft rely on astrionics systems for trajectory correction. Various electric motors — brushless DC motors, induction motors and DC motors — use electronic motor controllers. Automobiles, electric vehicles, and hybrid vehicles increasingly use embedded systems to maximize efficiency and reduce pollution. Other automotive safety systems using embedded systems include anti-lock braking system (ABS), electronic stability control (ESC/ESP), traction control (TCS) and automatic four-wheel drive.
Medical equipment uses embedded systems for monitoring, and various medical imaging (positron emission tomography (PET), single-photon emission computed tomography (SPECT), computed tomography (CT), and magnetic resonance imaging (MRI) for non-invasive internal inspections. Embedded systems within medical equipment are often powered by industrial computers.
Embedded systems are used for safety-critical systems in aerospace and defense industries. Unless connected to wired or wireless networks via on-chip 3G cellular or other methods for IoT monitoring and control purposes, these systems can be isolated from hacking and thus be more secure. For fire safety, the systems can be designed to have a greater ability to handle higher temperatures and continue to operate. In dealing with security, the embedded systems can be self-sufficient and be able to deal with cut electrical and communication systems.
Miniature wireless devices called motes are networked wireless sensors. Wireless sensor networking makes use of miniaturization made possible by advanced integrated circuit (IC) design to couple full wireless subsystems to sophisticated sensors, enabling people and companies to measure a myriad of things in the physical world and act on this information through monitoring and control systems. These motes are completely self-contained and will typically run off a battery source for years before the batteries need to be changed or charged.
Characteristics
Embedded systems are designed to perform a specific task, in contrast with general-purpose computers designed for multiple tasks. Some have real-time performance constraints that must be met, for reasons such as safety and usability; others may have low or no performance requirements, allowing the system hardware to be simplified to reduce costs. | Embedded system | Wikipedia | 455 | 46630 | https://en.wikipedia.org/wiki/Embedded%20system | Technology | Computer hardware | null |
Embedded systems are not always standalone devices. Many embedded systems are a small part within a larger device that serves a more general purpose. For example, the Gibson Robot Guitar features an embedded system for tuning the strings, but the overall purpose of the Robot Guitar is to play music. Similarly, an embedded system in an automobile provides a specific function as a subsystem of the car itself.
The program instructions written for embedded systems are referred to as firmware, and are stored in read-only memory or flash memory chips. They run with limited computer hardware resources: little memory, small or non-existent keyboard or screen.
User interfaces
Embedded systems range from no user interface at all, in systems dedicated to one task, to complex graphical user interfaces that resemble modern computer desktop operating systems. Simple embedded devices use buttons, light-emitting diodes (LED), graphic or character liquid-crystal displays (LCD) with a simple menu system. More sophisticated devices that use a graphical screen with touch sensing or screen-edge soft keys provide flexibility while minimizing space used: the meaning of the buttons can change with the screen, and selection involves the natural behavior of pointing at what is desired.
Some systems provide user interface remotely with the help of a serial (e.g. RS-232) or network (e.g. Ethernet) connection. This approach extends the capabilities of the embedded system, avoids the cost of a display, simplifies the board support package (BSP) and allows designers to build a rich user interface on the PC. A good example of this is the combination of an embedded HTTP server running on an embedded device (such as an IP camera or a network router). The user interface is displayed in a web browser on a PC connected to the device.
Processors in embedded systems
Examples of properties of typical embedded computers when compared with general-purpose counterparts, are low power consumption, small size, rugged operating ranges, and low per-unit cost. This comes at the expense of limited processing resources.
Numerous microcontrollers have been developed for embedded systems use. General-purpose microprocessors are also used in embedded systems, but generally, require more support circuitry than microcontrollers. | Embedded system | Wikipedia | 452 | 46630 | https://en.wikipedia.org/wiki/Embedded%20system | Technology | Computer hardware | null |
Ready-made computer boards
PC/104 and PC/104+ are examples of standards for ready-made computer boards intended for small, low-volume embedded and ruggedized systems. These are mostly x86-based and often physically small compared to a standard PC, although still quite large compared to most simple (8/16-bit) embedded systems. They may use DOS, FreeBSD, Linux, NetBSD, OpenHarmony or an embedded real-time operating system (RTOS) such as MicroC/OS-II, QNX or VxWorks.
In certain applications, where small size or power efficiency are not primary concerns, the components used may be compatible with those used in general-purpose x86 personal computers. Boards such as the VIA EPIA range help to bridge the gap by being PC-compatible but highly integrated, physically smaller or have other attributes making them attractive to embedded engineers. The advantage of this approach is that low-cost commodity components may be used along with the same software development tools used for general software development. Systems built in this way are still regarded as embedded since they are integrated into larger devices and fulfill a single role. Examples of devices that may adopt this approach are automated teller machines (ATM) and arcade machines, which contain code specific to the application.
However, most ready-made embedded systems boards are not PC-centered and do not use the ISA or PCI busses. When a system-on-a-chip processor is involved, there may be little benefit to having a standardized bus connecting discrete components, and the environment for both hardware and software tools may be very different.
One common design style uses a small system module, perhaps the size of a business card, holding high density BGA chips such as an ARM-based system-on-a-chip processor and peripherals, external flash memory for storage, and DRAM for runtime memory. The module vendor will usually provide boot software and make sure there is a selection of operating systems, usually including Linux and some real-time choices. These modules can be manufactured in high volume, by organizations familiar with their specialized testing issues, and combined with much lower volume custom mainboards with application-specific external peripherals. Prominent examples of this approach include Arduino and Raspberry Pi. | Embedded system | Wikipedia | 465 | 46630 | https://en.wikipedia.org/wiki/Embedded%20system | Technology | Computer hardware | null |
ASIC and FPGA SoC solutions
A system on a chip (SoC) contains a complete system - consisting of multiple processors, multipliers, caches, even different types of memory and commonly various peripherals like interfaces for wired or wireless communication on a single chip. Often graphics processing units (GPU) and DSPs are included such chips. SoCs can be implemented as an application-specific integrated circuit (ASIC) or using a field-programmable gate array (FPGA) which typically can be reconfigured.
ASIC implementations are common for very-high-volume embedded systems like mobile phones and smartphones. ASIC or FPGA implementations may be used for not-so-high-volume embedded systems with special needs in kind of signal processing performance, interfaces and reliability, like in avionics.
Peripherals
Embedded systems talk with the outside world via peripherals, such as:
Serial communication interfaces (SCI): RS-232, RS-422, RS-485, etc.
Synchronous Serial Interface: I2C, SPI, SSC and ESSI (Enhanced Synchronous Serial Interface)
Universal Serial Bus (USB)
Media cards (SD cards, CompactFlash, etc.)
Network interface controller: Ethernet, WiFi, etc.
Fieldbuses: CAN bus, LIN-Bus, PROFIBUS, etc.
Timers: Phase-locked loops, programmable interval timers
General Purpose Input/Output (GPIO)
Analog-to-digital and digital-to-analog converters
Debugging: JTAG, In-system programming, background debug mode interface port, BITP, and DB9 ports. | Embedded system | Wikipedia | 347 | 46630 | https://en.wikipedia.org/wiki/Embedded%20system | Technology | Computer hardware | null |
Tools
As with other software, embedded system designers use compilers, assemblers, and debuggers to develop embedded system software. However, they may also use more specific tools:
In circuit debuggers or emulators (see next section).
Utilities to add a checksum or CRC to a program, so the embedded system can check if the program is valid.
For systems using digital signal processing, developers may use a computational notebook to simulate the mathematics.
System-level modeling and simulation tools help designers to construct simulation models of a system with hardware components such as processors, memories, DMA, interfaces, buses and software behavior flow as a state diagram or flow diagram using configurable library blocks. Simulation is conducted to select the right components by performing power vs. performance trade-offs, reliability analysis and bottleneck analysis. Typical reports that help a designer to make architecture decisions include application latency, device throughput, device utilization, power consumption of the full system as well as device-level power consumption.
A model-based development tool creates and simulates graphical data flow and UML state chart diagrams of components like digital filters, motor controllers, communication protocol decoding and multi-rate tasks.
Custom compilers and linkers may be used to optimize specialized hardware.
An embedded system may have its own special language or design tool, or add enhancements to an existing language such as Forth or Basic.
Another alternative is to add a RTOS or embedded operating system
Modeling and code generating tools often based on state machines
Software tools can come from several sources:
Software companies that specialize in the embedded market
Ported from the GNU software development tools
Sometimes, development tools for a personal computer can be used if the embedded processor is a close relative to a common PC processor
As the complexity of embedded systems grows, higher-level tools and operating systems are migrating into machinery where it makes sense. For example, cellphones, personal digital assistants and other consumer computers often need significant software that is purchased or provided by a person other than the manufacturer of the electronics. In these systems, an open programming environment such as Linux, NetBSD, FreeBSD, OSGi or Embedded Java is required so that the third-party software provider can sell to a large market. | Embedded system | Wikipedia | 458 | 46630 | https://en.wikipedia.org/wiki/Embedded%20system | Technology | Computer hardware | null |
Debugging
Embedded debugging may be performed at different levels, depending on the facilities available. Considerations include: does it slow down the main application, how close is the debugged system or application to the actual system or application, how expressive are the triggers that can be set for debugging (e.g., inspecting the memory when a particular program counter value is reached), and what can be inspected in the debugging process (such as, only memory, or memory and registers, etc.).
From simplest to most sophisticated debugging techniques and systems are roughly grouped into the following areas:
Interactive resident debugging, using the simple shell provided by the embedded operating system (e.g. Forth and Basic)
Software-only debuggers have the benefit that they do not need any hardware modification but have to carefully control what they record in order to conserve time and storage space.
External debugging using logging or serial port output to trace operation using either a monitor in flash or using a debug server like the Remedy Debugger that even works for heterogeneous multicore systems.
An in-circuit debugger (ICD), a hardware device that connects to the microprocessor via a JTAG or Nexus interface. This allows the operation of the microprocessor to be controlled externally, but is typically restricted to specific debugging capabilities in the processor.
An in-circuit emulator (ICE) replaces the microprocessor with a simulated equivalent, providing full control over all aspects of the microprocessor.
A complete emulator provides a simulation of all aspects of the hardware, allowing all of it to be controlled and modified, and allowing debugging on a normal PC. The downsides are expense and slow operation, in some cases up to 100 times slower than the final system.
For SoC designs, the typical approach is to verify and debug the design on an FPGA prototype board. Tools such as Certus are used to insert probes in the FPGA implementation that make signals available for observation. This is used to debug hardware, firmware and software interactions across multiple FPGAs in an implementation with capabilities similar to a logic analyzer. | Embedded system | Wikipedia | 459 | 46630 | https://en.wikipedia.org/wiki/Embedded%20system | Technology | Computer hardware | null |
Unless restricted to external debugging, the programmer can typically load and run software through the tools, view the code running in the processor, and start or stop its operation. The view of the code may be as high-level programming language, assembly code or mixture of both.
Tracing
Real-time operating systems often support tracing of operating system events. A graphical view is presented by a host PC tool, based on a recording of the system behavior. The trace recording can be performed in software, by the RTOS, or by special tracing hardware. RTOS tracing allows developers to understand timing and performance issues of the software system and gives a good understanding of the high-level system behaviors. Trace recording in embedded systems can be achieved using hardware or software solutions. Software-based trace recording does not require specialized debugging hardware and can be used to record traces in deployed devices, but it can have an impact on CPU and RAM usage. One example of a software-based tracing method used in RTOS environments is the use of empty macros which are invoked by the operating system at strategic places in the code, and can be implemented to serve as hooks.
Reliability
Embedded systems often reside in machines that are expected to run continuously for years without error, and in some cases recover by themselves if an error occurs. Therefore, the software is usually developed and tested more carefully than that for personal computers, and unreliable mechanical moving parts such as disk drives, switches or buttons are avoided.
Specific reliability issues may include:
The system cannot safely be shut down for repair, or it is too inaccessible to repair. Examples include space systems, undersea cables, navigational beacons, bore-hole systems, and automobiles.
The system must be kept running for safety reasons. Reduced functionality in the event of failure may be intolerable. Often backups are selected by an operator. Examples include aircraft navigation, reactor control systems, safety-critical chemical factory controls, train signals.
The system will lose large amounts of money when shut down: Telephone switches, factory controls, bridge and elevator controls, funds transfer and market making, automated sales and service. | Embedded system | Wikipedia | 426 | 46630 | https://en.wikipedia.org/wiki/Embedded%20system | Technology | Computer hardware | null |
A variety of techniques are used, sometimes in combination, to recover from errors—both software bugs such as memory leaks, and also soft errors in the hardware:
watchdog timer that resets and restarts the system unless the software periodically notifies the watchdog subsystems
Designing with a trusted computing base (TCB) architecture ensures a highly secure and reliable system environment
A hypervisor designed for embedded systems is able to provide secure encapsulation for any subsystem component so that a compromised software component cannot interfere with other subsystems, or privileged-level system software. This encapsulation keeps faults from propagating from one subsystem to another, thereby improving reliability. This may also allow a subsystem to be automatically shut down and restarted on fault detection.
Immunity-aware programming can help engineers produce more reliable embedded systems code. Guidelines and coding rules such as MISRA C/C++ aim to assist developers produce reliable, portable firmware in a number of different ways: typically by advising or mandating against coding practices which may lead to run-time errors (memory leaks, invalid pointer uses), use of run-time checks and exception handling (range/sanity checks, divide-by-zero and buffer index validity checks, default cases in logic checks), loop bounding, production of human-readable, well commented and well structured code, and avoiding language ambiguities which may lead to compiler-induced inconsistencies or side-effects (expression evaluation ordering, recursion, certain types of macro). These rules can often be used in conjunction with code static checkers or bounded model checking for functional verification purposes, and also assist in determination of code timing properties.
High vs. low volume
For high-volume systems such as mobile phones, minimizing cost is usually the primary design consideration. Engineers typically select hardware that is just good enough to implement the necessary functions.
For low-volume or prototype embedded systems, general-purpose computers may be adapted by limiting the programs or by replacing the operating system with an RTOS.
Embedded software architectures
In 1978 National Electrical Manufacturers Association released ICS 3-1978, a standard for programmable microcontrollers, including almost any computer-based controllers, such as single-board computers, numerical, and event-based controllers.
There are several different types of software architecture in common use. | Embedded system | Wikipedia | 486 | 46630 | https://en.wikipedia.org/wiki/Embedded%20system | Technology | Computer hardware | null |
Simple control loop
In this design, the software simply has a loop which monitors the input devices. The loop calls subroutines, each of which manages a part of the hardware or software. Hence it is called a simple control loop or programmed input-output.
Interrupt-controlled system
Some embedded systems are predominantly controlled by interrupts. This means that tasks performed by the system are triggered by different kinds of events; an interrupt could be generated, for example, by a timer at a predefined interval, or by a serial port controller receiving data.
This architecture is used if event handlers need low latency, and the event handlers are short and simple. These systems run a simple task in a main loop also, but this task is not very sensitive to unexpected delays. Sometimes the interrupt handler will add longer tasks to a queue structure. Later, after the interrupt handler has finished, these tasks are executed by the main loop. This method brings the system close to a multitasking kernel with discrete processes.
Cooperative multitasking
Cooperative multitasking is very similar to the simple control loop scheme, except that the loop is hidden in an API. The programmer defines a series of tasks, and each task gets its own environment to run in. When a task is idle, it calls an idle routine which passes control to another task.
The advantages and disadvantages are similar to that of the control loop, except that adding new software is easier, by simply writing a new task, or adding to the queue.
Preemptive multitasking or multi-threading
In this type of system, a low-level piece of code switches between tasks or threads based on a timer invoking an interrupt. This is the level at which the system is generally considered to have an operating system kernel. Depending on how much functionality is required, it introduces more or less of the complexities of managing multiple tasks running conceptually in parallel.
As any code can potentially damage the data of another task (except in systems using a memory management unit) programs must be carefully designed and tested, and access to shared data must be controlled by some synchronization strategy such as message queues, semaphores or a non-blocking synchronization scheme. | Embedded system | Wikipedia | 453 | 46630 | https://en.wikipedia.org/wiki/Embedded%20system | Technology | Computer hardware | null |
Because of these complexities, it is common for organizations to use an off-the-shelf RTOS, allowing the application programmers to concentrate on device functionality rather than operating system services. The choice to include an RTOS brings in its own issues, however, as the selection must be made prior to starting the application development process. This timing forces developers to choose the embedded operating system for their device based on current requirements and so restricts future options to a large extent.
The level of complexity in embedded systems is continuously growing as devices are required to manage peripherals and tasks such as serial, USB, TCP/IP, Bluetooth, Wireless LAN, trunk radio, multiple channels, data and voice, enhanced graphics, multiple states, multiple threads, numerous wait states and so on. These trends are leading to the uptake of embedded middleware in addition to an RTOS.
Microkernels and exokernels
A microkernel allocates memory and switches the CPU to different threads of execution. User-mode processes implement major functions such as file systems, network interfaces, etc.
Exokernels communicate efficiently by normal subroutine calls. The hardware and all the software in the system are available to and extensible by application programmers.
Monolithic kernels
A monolithic kernel is a relatively large kernel with sophisticated capabilities adapted to suit an embedded environment. This gives programmers an environment similar to a desktop operating system like Linux or Microsoft Windows, and is therefore very productive for development. On the downside, it requires considerably more hardware resources, is often more expensive, and, because of the complexity of these kernels, can be less predictable and reliable.
Common examples of embedded monolithic kernels are embedded Linux, VXWorks and Windows CE.
Despite the increased cost in hardware, this type of embedded system is increasing in popularity, especially on the more powerful embedded devices such as wireless routers and GPS navigation systems.
Additional software components
In addition to the core operating system, many embedded systems have additional upper-layer software components. These components include networking protocol stacks like CAN, TCP/IP, FTP, HTTP, and HTTPS, and storage capabilities like FAT and flash memory management systems. If the embedded device has audio and video capabilities, then the appropriate drivers and codecs will be present in the system. In the case of the monolithic kernels, many of these software layers may be included in the kernel. In the RTOS category, the availability of additional software components depends upon the commercial offering. | Embedded system | Wikipedia | 508 | 46630 | https://en.wikipedia.org/wiki/Embedded%20system | Technology | Computer hardware | null |
Domain-specific architectures
In the automotive sector, AUTOSAR is a standard architecture for embedded software. | Embedded system | Wikipedia | 20 | 46630 | https://en.wikipedia.org/wiki/Embedded%20system | Technology | Computer hardware | null |
A radio telescope is a specialized antenna and radio receiver used to detect radio waves from astronomical radio sources in the sky. Radio telescopes are the main observing instrument used in radio astronomy, which studies the radio frequency portion of the electromagnetic spectrum, just as optical telescopes are used to make observations in the visible portion of the spectrum in traditional optical astronomy. Unlike optical telescopes, radio telescopes can be used in the daytime as well as at night.
Since astronomical radio sources such as planets, stars, nebulas and galaxies are very far away, the radio waves coming from them are extremely weak, so radio telescopes require very large antennas to collect enough radio energy to study them, and extremely sensitive receiving equipment. Radio telescopes are typically large parabolic ("dish") antennas similar to those employed in tracking and communicating with satellites and space probes. They may be used individually or linked together electronically in an array. Radio observatories are preferentially located far from major centers of population to avoid electromagnetic interference (EMI) from radio, television, radar, motor vehicles, and other man-made electronic devices.
Radio waves from space were first detected by engineer Karl Guthe Jansky in 1932 at Bell Telephone Laboratories in Holmdel, New Jersey using an antenna built to study radio receiver noise. The first purpose-built radio telescope was a 9-meter parabolic dish constructed by radio amateur Grote Reber in his back yard in Wheaton, Illinois in 1937. The sky survey he performed is often considered the beginning of the field of radio astronomy.
Early radio telescopes | Radio telescope | Wikipedia | 309 | 46656 | https://en.wikipedia.org/wiki/Radio%20telescope | Technology | Optical instruments | null |
The first radio antenna used to identify an astronomical radio source was built by Karl Guthe Jansky, an engineer with Bell Telephone Laboratories, in 1932. Jansky was assigned the task of identifying sources of static that might interfere with radiotelephone service. Jansky's antenna was an array of dipoles and reflectors designed to receive short wave radio signals at a frequency of 20.5 MHz (wavelength about 14.6 meters). It was mounted on a turntable that allowed it to rotate in any direction, earning it the name "Jansky's merry-go-round." It had a diameter of approximately and stood tall. By rotating the antenna, the direction of the received interfering radio source (static) could be pinpointed. A small shed to the side of the antenna housed an analog pen-and-paper recording system. After recording signals from all directions for several months, Jansky eventually categorized them into three types of static: nearby thunderstorms, distant thunderstorms, and a faint steady hiss above shot noise, of unknown origin. Jansky finally determined that the "faint hiss" repeated on a cycle of 23 hours and 56 minutes. This period is the length of an astronomical sidereal day, the time it takes any "fixed" object located on the celestial sphere to come back to the same location in the sky. Thus Jansky suspected that the hiss originated outside of the Solar System, and by comparing his observations with optical astronomical maps, Jansky concluded that the radiation was coming from the Milky Way Galaxy and was strongest in the direction of the center of the galaxy, in the constellation of Sagittarius.
An amateur radio operator, Grote Reber, was one of the pioneers of what became known as radio astronomy. He built the first parabolic "dish" radio telescope, in diameter, in his back yard in Wheaton, Illinois in 1937. He repeated Jansky's pioneering work, identifying the Milky Way as the first off-world radio source, and he went on to conduct the first sky survey at very high radio frequencies, discovering other radio sources. The rapid development of radar during World War II created technology which was applied to radio astronomy after the war, and radio astronomy became a branch of astronomy, with universities and research institutes constructing large radio telescopes. | Radio telescope | Wikipedia | 467 | 46656 | https://en.wikipedia.org/wiki/Radio%20telescope | Technology | Optical instruments | null |
Types
The range of frequencies in the electromagnetic spectrum that makes up the radio spectrum is very large. As a consequence, the types of antennas that are used as radio telescopes vary widely in design, size, and configuration. At wavelengths of 30 meters to 3 meters (10–100 MHz), they are generally either directional antenna arrays similar to "TV antennas" or large stationary reflectors with movable focal points. Since the wavelengths being observed with these types of antennas are so long, the "reflector" surfaces can be constructed from coarse wire mesh such as chicken wire.
At shorter wavelengths parabolic "dish" antennas predominate. The angular resolution of a dish antenna is determined by the ratio of the diameter of the dish to the wavelength of the radio waves being observed. This dictates the dish size a radio telescope needs for a useful resolution. Radio telescopes that operate at wavelengths of 3 meters to 30 cm (100 MHz to 1 GHz) are usually well over 100 meters in diameter. Telescopes working at wavelengths shorter than 30 cm (above 1 GHz) range in size from 3 to 90 meters in diameter.
Frequencies
The increasing use of radio frequencies for communication makes astronomical observations more and more difficult (see Open spectrum).
Negotiations to defend the frequency allocation for parts of the spectrum most useful for observing the universe are coordinated in the Scientific Committee on Frequency Allocations for Radio Astronomy and Space Science.
Some of the more notable frequency bands used by radio telescopes include:
Every frequency in the United States National Radio Quiet Zone
Channel 37: 608 to 614 MHz
The "Hydrogen line", also known as the "21 centimeter line": 1,420.40575177 MHz, used by many radio telescopes including The Big Ear in its discovery of the Wow! signal
1,406 MHz and 430 MHz
The Waterhole: 1,420 to 1,666 MHz
The Arecibo Observatory had several receivers that together covered the whole 1–10 GHz range.
The Wilkinson Microwave Anisotropy Probe mapped the cosmic microwave background radiation in 5 different frequency bands, centered on 23 GHz, 33 GHz, 41 GHz, 61 GHz, and 94 GHz.
Big dishes | Radio telescope | Wikipedia | 434 | 46656 | https://en.wikipedia.org/wiki/Radio%20telescope | Technology | Optical instruments | null |
The world's largest filled-aperture (i.e. full dish) radio telescope is the Five-hundred-meter Aperture Spherical Telescope (FAST) completed in 2016 by China. The dish with an area as large as 30 football fields is built into a natural karst depression in the landscape in Guizhou province and cannot move; the feed antenna is in a cabin suspended above the dish on cables. The active dish is composed of 4,450 moveable panels controlled by a computer. By changing the shape of the dish and moving the feed cabin on its cables, the telescope can be steered to point to any region of the sky up to 40° from the zenith. Although the dish is 500 meters in diameter, only a 300-meter circular area on the dish is illuminated by the feed antenna at any given time, so the actual effective aperture is 300 meters. Construction began in 2007 and was completed July 2016 and the telescope became operational September 25, 2016.
The world's second largest filled-aperture telescope was the Arecibo radio telescope located in Arecibo, Puerto Rico, though it suffered catastrophic collapse on 1 December 2020. Arecibo was one of the world's few radio telescope also capable of active (i.e., transmitting) radar imaging of near-Earth objects (see: radar astronomy); most other telescopes employ passive detection, i.e., receiving only. Arecibo was another stationary dish telescope like FAST. Arecibo's dish was built into a natural depression in the landscape, the antenna was steerable within an angle of about 20° of the zenith by moving the suspended feed antenna, giving use of a 270-meter diameter portion of the dish for any individual observation.
The largest individual radio telescope of any kind is the RATAN-600 located near Nizhny Arkhyz, Russia, which consists of a 576-meter circle of rectangular radio reflectors, each of which can be pointed towards a central conical receiver. | Radio telescope | Wikipedia | 401 | 46656 | https://en.wikipedia.org/wiki/Radio%20telescope | Technology | Optical instruments | null |
The above stationary dishes are not fully "steerable"; they can only be aimed at points in an area of the sky near the zenith, and cannot receive from sources near the horizon. The largest fully steerable dish radio telescope is the 100 meter Green Bank Telescope in West Virginia, United States, constructed in 2000. The largest fully steerable radio telescope in Europe is the Effelsberg 100-m Radio Telescope near Bonn, Germany, operated by the Max Planck Institute for Radio Astronomy, which also was the world's largest fully steerable telescope for 30 years until the Green Bank antenna was constructed. The third-largest fully steerable radio telescope is the 76-meter Lovell Telescope at Jodrell Bank Observatory in Cheshire, England, completed in 1957. The fourth-largest fully steerable radio telescopes are six 70-meter dishes: three Russian RT-70, and three in the NASA Deep Space Network. The planned Qitai Radio Telescope, at a diameter of , is expected to become the world's largest fully steerable single-dish radio telescope when completed in 2028.
A more typical radio telescope has a single antenna of about 25 meters diameter. Dozens of radio telescopes of about this size are operated in radio observatories all over the world.
Gallery of big dishes
Radio Telescopes in space
Since 1965, humans have launched three space-based radio telescopes. The first one, KRT-10, was attached to Salyut 6 orbital space station in 1979. In 1997, Japan sent the second, HALCA. The last one was sent by Russia in 2011 called Spektr-R.
Radio interferometry | Radio telescope | Wikipedia | 331 | 46656 | https://en.wikipedia.org/wiki/Radio%20telescope | Technology | Optical instruments | null |
One of the most notable developments came in 1946 with the introduction of the technique called astronomical interferometry, which means combining the signals from multiple antennas so that they simulate a larger antenna, in order to achieve greater resolution. Astronomical radio interferometers usually consist either of arrays of parabolic dishes (e.g., the One-Mile Telescope), arrays of one-dimensional antennas (e.g., the Molonglo Observatory Synthesis Telescope) or two-dimensional arrays of omnidirectional dipoles (e.g., Tony Hewish's Pulsar Array). All of the telescopes in the array are widely separated and are usually connected using coaxial cable, waveguide, optical fiber, or other type of transmission line. Recent advances in the stability of electronic oscillators also now permit interferometry to be carried out by independent recording of the signals at the various antennas, and then later correlating the recordings at some central processing facility. This process is known as Very Long Baseline Interferometry (VLBI). Interferometry does increase the total signal collected, but its primary purpose is to vastly increase the resolution through a process called aperture synthesis. This technique works by superposing (interfering) the signal waves from the different telescopes on the principle that waves that coincide with the same phase will add to each other while two waves that have opposite phases will cancel each other out. This creates a combined telescope that is equivalent in resolution (though not in sensitivity) to a single antenna whose diameter is equal to the spacing of the antennas furthest apart in the array. | Radio telescope | Wikipedia | 335 | 46656 | https://en.wikipedia.org/wiki/Radio%20telescope | Technology | Optical instruments | null |
A high-quality image requires a large number of different separations between telescopes. Projected separation between any two telescopes, as seen from the radio source, is called a baseline. For example, the Very Large Array (VLA) near Socorro, New Mexico has 27 telescopes with 351 independent baselines at once, which achieves a resolution of 0.2 arc seconds at 3 cm wavelengths. Martin Ryle's group in Cambridge obtained a Nobel Prize for interferometry and aperture synthesis. The Lloyd's mirror interferometer was also developed independently in 1946 by Joseph Pawsey's group at the University of Sydney. In the early 1950s, the Cambridge Interferometer mapped the radio sky to produce the famous 2C and 3C surveys of radio sources. An example of a large physically connected radio telescope array is the Giant Metrewave Radio Telescope, located in Pune, India. The largest array, the Low-Frequency Array (LOFAR), finished in 2012, is located in western Europe and consists of about 81,000 small antennas in 48 stations distributed over an area several hundreds of kilometers in diameter and operates between 1.25 and 30 m wavelengths. VLBI systems using post-observation processing have been constructed with antennas thousands of miles apart. Radio interferometers have also been used to obtain detailed images of the anisotropies and the polarization of the Cosmic Microwave Background, like the CBI interferometer in 2004.
The world's largest physically connected telescope, the Square Kilometre Array (SKA), is planned to start operations in 2025.
Astronomical observations
Many astronomical objects are not only observable in visible light but also emit radiation at radio wavelengths. Besides observing energetic objects such as pulsars and quasars, radio telescopes are able to "image" most astronomical objects such as galaxies, nebulae, and even radio emissions from planets. | Radio telescope | Wikipedia | 381 | 46656 | https://en.wikipedia.org/wiki/Radio%20telescope | Technology | Optical instruments | null |
Xylem is one of the two types of transport tissue in vascular plants, the other being phloem; both of these are part of the vascular bundle. The basic function of the xylem is to transport water upward from the roots to parts of the plants such as stems and leaves, but it also transports nutrients. The word xylem is derived from the Ancient Greek word, (xylon), meaning "wood"; the best-known xylem tissue is wood, though it is found throughout a plant. The term was introduced by Carl Nägeli in 1858.
Structure
The most distinctive xylem cells are the long tracheary elements that transport water. Tracheids and vessel elements are distinguished by their shape; vessel elements are shorter, and are connected together into long tubes that are called vessels.
Xylem also contains two other type of cells: parenchyma and fibers.
Xylem can be found:
in vascular bundles, present in non-woody plants and non-woody parts of woody plants
in secondary xylem, laid down by a meristem called the vascular cambium in woody plants
as part of a stelar arrangement not divided into bundles, as in many ferns.
In transitional stages of plants with secondary growth, the first two categories are not mutually exclusive, although usually a vascular bundle will contain primary xylem only.
The branching pattern exhibited by xylem follows Murray's law.
Primary and secondary xylem
Primary xylem is formed during primary growth from procambium. It includes protoxylem and metaxylem. Metaxylem develops after the protoxylem but before secondary xylem. Metaxylem has wider vessels and tracheids than protoxylem. | Xylem | Wikipedia | 358 | 46675 | https://en.wikipedia.org/wiki/Xylem | Biology and health sciences | Plant tissues | Biology |
Secondary xylem is formed during secondary growth from vascular cambium. Although secondary xylem is also found in members of the gymnosperm groups Gnetophyta and Ginkgophyta and to a lesser extent in members of the Cycadophyta, the two main groups in which secondary xylem can be found are:
conifers (Coniferae): there are approximately 600 known species of conifers. All species have secondary xylem, which is relatively uniform in structure throughout this group. Many conifers become tall trees: the secondary xylem of such trees is used and marketed as softwood.
angiosperms (Angiospermae): there are approximately 250,000 known species of angiosperms. Within this group secondary xylem is rare in the monocots. Many non-monocot angiosperms become trees, and the secondary xylem of these is used and marketed as hardwood. | Xylem | Wikipedia | 203 | 46675 | https://en.wikipedia.org/wiki/Xylem | Biology and health sciences | Plant tissues | Biology |
Main function – upwards water transport
The xylem, vessels and tracheids of the roots, stems and leaves are interconnected to form a continuous system of water-conducting channels reaching all parts of the plants. The system transports water and soluble mineral nutrients from the roots throughout the plant. It is also used to replace water lost during transpiration and photosynthesis. Xylem sap consists mainly of water and inorganic ions, although it can also contain a number of organic chemicals as well. The transport is passive, not powered by energy spent by the tracheary elements themselves, which are dead by maturity and no longer have living contents. Transporting sap upwards becomes more difficult as the height of a plant increases and upwards transport of water by xylem is considered to limit the maximum height of trees. Three phenomena cause xylem sap to flow:
Pressure flow hypothesis: Sugars produced in the leaves and other green tissues are kept in the phloem system, creating a solute pressure differential versus the xylem system carrying a far lower load of solutes—water and minerals. The phloem pressure can rise to several MPa, far higher than atmospheric pressure. Selective inter-connection between these systems allows this high solute concentration in the phloem to draw xylem fluid upwards by negative pressure.
Transpirational pull: Similarly, the evaporation of water from the surfaces of mesophyll cells to the atmosphere also creates a negative pressure at the top of a plant. This causes millions of minute menisci to form in the mesophyll cell wall. The resulting surface tension causes a negative pressure or tension in the xylem that pulls the water from the roots and soil.
Root pressure: If the water potential of the root cells is more negative than that of the soil, usually due to high concentrations of solute, water can move by osmosis into the root from the soil. This causes a positive pressure that forces sap up the xylem towards the leaves. In some circumstances, the sap will be forced from the leaf through a hydathode in a phenomenon known as guttation. Root pressure is highest in the morning before the opening of stomata and allow transpiration to begin. Different plant species can have different root pressures even in a similar environment; examples include up to 145 kPa in Vitis riparia but around zero in Celastrus orbiculatus. | Xylem | Wikipedia | 494 | 46675 | https://en.wikipedia.org/wiki/Xylem | Biology and health sciences | Plant tissues | Biology |
The primary force that creates the capillary action movement of water upwards in plants is the adhesion between the water and the surface of the xylem conduits. Capillary action provides the force that establishes an equilibrium configuration, balancing gravity. When transpiration removes water at the top, the flow is needed to return to the equilibrium.
Transpirational pull results from the evaporation of water from the surfaces of cells in the leaves. This evaporation causes the surface of the water to recess into the pores of the cell wall. By capillary action, the water forms concave menisci inside the pores. The high surface tension of water pulls the concavity outwards, generating enough force to lift water as high as a hundred meters from ground level to a tree's highest branches.
Transpirational pull requires that the vessels transporting the water be very small in diameter; otherwise, cavitation would break the water column. And as water evaporates from leaves, more is drawn up through the plant to replace it. When the water pressure within the xylem reaches extreme levels due to low water input from the roots (if, for example, the soil is dry), then the gases come out of solution and form a bubble – an embolism forms, which will spread quickly to other adjacent cells, unless bordered pits are present (these have a plug-like structure called a torus, that seals off the opening between adjacent cells and stops the embolism from spreading). Even after an embolism has occurred, plants are able to refill the xylem and restore the functionality.
Cohesion-tension theory
The cohesion-tension theory is a theory of intermolecular attraction that explains the process of water flow upwards (against the force of gravity) through the xylem of plants. It was proposed in 1894 by John Joly and Henry Horatio Dixon. Despite numerous objections, this is the most widely accepted theory for the transport of water through a plant's vascular system based on the classical research of Dixon-Joly (1894), Eugen Askenasy (1845–1903) (1895), and Dixon (1914,1924). | Xylem | Wikipedia | 450 | 46675 | https://en.wikipedia.org/wiki/Xylem | Biology and health sciences | Plant tissues | Biology |
Water is a polar molecule. When two water molecules approach one another, the slightly negatively charged oxygen atom of one forms a hydrogen bond with a slightly positively charged hydrogen atom in the other. This attractive force, along with other intermolecular forces, is one of the principal factors responsible for the occurrence of surface tension in liquid water. It also allows plants to draw water from the root through the xylem to the leaf.
Water is constantly lost through transpiration from the leaf. When one water molecule is lost another is pulled along by the processes of cohesion and tension. Transpiration pull, utilizing capillary action and the inherent surface tension of water, is the primary mechanism of water movement in plants. However, it is not the only mechanism involved. Any use of water in leaves forces water to move into them.
Transpiration in leaves creates tension (differential pressure) in the cell walls of mesophyll cells. Because of this tension, water is being pulled up from the roots into the leaves, helped by cohesion (the pull between individual water molecules, due to hydrogen bonds) and adhesion (the stickiness between water molecules and the hydrophilic cell walls of plants). This mechanism of water flow works because of water potential (water flows from high to low potential), and the rules of simple diffusion.
Over the past century, there has been a great deal of research regarding the mechanism of xylem sap transport; today, most plant scientists continue to agree that the cohesion-tension theory best explains this process, but multiforce theories that hypothesize several alternative mechanisms have been suggested, including longitudinal cellular and xylem osmotic pressure gradients, axial potential gradients in the vessels, and gel- and gas-bubble-supported interfacial gradients.
Measurement of pressure
Until recently, the differential pressure (suction) of transpirational pull could only be measured indirectly, by applying external pressure with a pressure bomb to counteract it. When the technology to perform direct measurements with a pressure probe was developed, there was initially some doubt about whether the classic theory was correct, because some workers were unable to demonstrate negative pressures. More recent measurements do tend to validate the classic theory, for the most part. Xylem transport is driven by a combination of transpirational pull from above and root pressure from below, which makes the interpretation of measurements more complicated. | Xylem | Wikipedia | 488 | 46675 | https://en.wikipedia.org/wiki/Xylem | Biology and health sciences | Plant tissues | Biology |
Evolution
Xylem appeared early in the history of terrestrial plant life. Fossil plants with anatomically preserved xylem are known from the Silurian (more than 400 million years ago), and trace fossils resembling individual xylem cells may be found in earlier Ordovician rocks. The earliest true and recognizable xylem consists of tracheids with a helical-annular reinforcing layer added to the cell wall. This is the only type of xylem found in the earliest vascular plants, and this type of cell continues to be found in the protoxylem (first-formed xylem) of all living groups of vascular plants. Several groups of plants later developed pitted tracheid cells independently through convergent evolution. In living plants, pitted tracheids do not appear in development until the maturation of the metaxylem (following the protoxylem).
In most plants, pitted tracheids function as the primary transport cells. The other type of vascular element, found in angiosperms, is the vessel element. Vessel elements are joined end to end to form vessels in which water flows unimpeded, as in a pipe. The presence of xylem vessels (also called trachea) is considered to be one of the key innovations that led to the success of the angiosperms. However, the occurrence of vessel elements is not restricted to angiosperms, and they are absent in some archaic or "basal" lineages of the angiosperms: (e.g., Amborellaceae, Tetracentraceae, Trochodendraceae, and Winteraceae), and their secondary xylem is described by Arthur Cronquist as "primitively vesselless". Cronquist considered the vessels of Gnetum to be convergent with those of angiosperms. Whether the absence of vessels in basal angiosperms is a primitive condition is contested, the alternative hypothesis states that vessel elements originated in a precursor to the angiosperms and were subsequently lost. | Xylem | Wikipedia | 423 | 46675 | https://en.wikipedia.org/wiki/Xylem | Biology and health sciences | Plant tissues | Biology |
To photosynthesize, plants must absorb from the atmosphere. However, this comes at a price: while stomata are open to allow to enter, water can evaporate. Water is lost much faster than is absorbed, so plants need to replace it, and have developed systems to transport water from the moist soil to the site of photosynthesis. Early plants sucked water between the walls of their cells, then evolved the ability to control water loss (and acquisition) through the use of stomata. Specialized water transport tissues soon evolved in the form of hydroids, tracheids, then secondary xylem, followed by an endodermis and ultimately vessels.
The high levels of Silurian-Devonian times, when plants were first colonizing land, meant that the need for water was relatively low. As was withdrawn from the atmosphere by plants, more water was lost in its capture, and more elegant transport mechanisms evolved. As water transport mechanisms, and waterproof cuticles, evolved, plants could survive without being continually covered by a film of water. This transition from poikilohydry to homoiohydry opened up new potential for colonization. Plants then needed a robust internal structure that held long narrow channels for transporting water from the soil to all the different parts of the above-soil plant, especially to the parts where photosynthesis occurred. | Xylem | Wikipedia | 277 | 46675 | https://en.wikipedia.org/wiki/Xylem | Biology and health sciences | Plant tissues | Biology |
During the Silurian, was readily available, so little water needed expending to acquire it. By the end of the Carboniferous, when levels had lowered to something approaching today's, around 17 times more water was lost per unit of uptake. However, even in these "easy" early days, water was at a premium, and had to be transported to parts of the plant from the wet soil to avoid desiccation. This early water transport took advantage of the cohesion-tension mechanism inherent in water. Water has a tendency to diffuse to areas that are drier, and this process is accelerated when water can be wicked along a fabric with small spaces. In small passages, such as that between the plant cell walls (or in tracheids), a column of water behaves like rubber – when molecules evaporate from one end, they pull the molecules behind them along the channels. Therefore, transpiration alone provided the driving force for water transport in early plants. However, without dedicated transport vessels, the cohesion-tension mechanism cannot transport water more than about 2 cm, severely limiting the size of the earliest plants. This process demands a steady supply of water from one end, to maintain the chains; to avoid exhausting it, plants developed a waterproof cuticle. Early cuticle may not have had pores but did not cover the entire plant surface, so that gas exchange could continue. However, dehydration at times was inevitable; early plants cope with this by having a lot of water stored between their cell walls, and when it comes to it sticking out the tough times by putting life "on hold" until more water is supplied.
To be free from the constraints of small size and constant moisture that the parenchymatic transport system inflicted, plants needed a more efficient water transport system. During the early Silurian, they developed specialized cells, which were lignified (or bore similar chemical compounds) to avoid implosion; this process coincided with cell death, allowing their innards to be emptied and water to be passed through them. These wider, dead, empty cells were a million times more conductive than the inter-cell method, giving the potential for transport over longer distances, and higher diffusion rates. | Xylem | Wikipedia | 458 | 46675 | https://en.wikipedia.org/wiki/Xylem | Biology and health sciences | Plant tissues | Biology |
The earliest macrofossils to bear water-transport tubes are Silurian plants placed in the genus Cooksonia. The early Devonian pretracheophytes Aglaophyton and Horneophyton have structures very similar to the hydroids of modern mosses.
Plants continued to innovate new ways of reducing the resistance to flow within their cells, thereby increasing the efficiency of their water transport. Bands on the walls of tubes, in fact apparent from the early Silurian onwards, are an early improvisation to aid the easy flow of water. Banded tubes, as well as tubes with pitted ornamentation on their walls, were lignified and, when they form single celled conduits, are considered to be tracheids. These, the "next generation" of transport cell design, have a more rigid structure than hydroids, allowing them to cope with higher levels of water pressure. Tracheids may have a single evolutionary origin, possibly within the hornworts, uniting all tracheophytes (but they may have evolved more than once).
Water transport requires regulation, and dynamic control is provided by stomata.
By adjusting the amount of gas exchange, they can restrict the amount of water lost through transpiration. This is an important role where water supply is not constant, and indeed stomata appear to have evolved before tracheids, being present in the non-vascular hornworts.
An endodermis probably evolved during the Silu-Devonian, but the first fossil evidence for such a structure is Carboniferous. This structure in the roots covers the water transport tissue and regulates ion exchange (and prevents unwanted pathogens etc. from entering the water transport system). The endodermis can also provide an upwards pressure, forcing water out of the roots when transpiration is not enough of a driver.
Once plants had evolved this level of controlled water transport, they were truly homoiohydric, able to extract water from their environment through root-like organs rather than relying on a film of surface moisture, enabling them to grow to much greater size. As a result of their independence from their surroundings, they lost their ability to survive desiccation – a costly trait to retain. | Xylem | Wikipedia | 454 | 46675 | https://en.wikipedia.org/wiki/Xylem | Biology and health sciences | Plant tissues | Biology |
During the Devonian, maximum xylem diameter increased with time, with the minimum diameter remaining pretty constant. By the middle Devonian, the tracheid diameter of some plant lineages (Zosterophyllophytes) had plateaued. Wider tracheids allow water to be transported faster, but the overall transport rate depends also on the overall cross-sectional area of the xylem bundle itself. The increase in vascular bundle thickness further seems to correlate with the width of plant axes, and plant height; it is also closely related to the appearance of leaves and increased stomatal density, both of which would increase the demand for water.
While wider tracheids with robust walls make it possible to achieve higher water transport tensions, this increases the likelihood of cavitation. Cavitation occurs when a bubble of air forms within a vessel, breaking the bonds between chains of water molecules and preventing them from pulling more water up with their cohesive tension. A tracheid, once cavitated, cannot have its embolism removed and return to service (except in a few advanced angiosperms which have developed a mechanism of doing so). Therefore, it is well worth plants' while to avoid cavitation occurring. For this reason, pits in tracheid walls have very small diameters, to prevent air entering and allowing bubbles to nucleate. Freeze-thaw cycles are a major cause of cavitation. Damage to a tracheid's wall almost inevitably leads to air leaking in and cavitation, hence the importance of many tracheids working in parallel. | Xylem | Wikipedia | 329 | 46675 | https://en.wikipedia.org/wiki/Xylem | Biology and health sciences | Plant tissues | Biology |
Once cavitation has occurred, plants have a range of mechanisms to contain the damage. Small pits link adjacent conduits to allow fluid to flow between them, but not air – although these pits, which prevent the spread of embolism, are also a major cause of them. These pitted surfaces further reduce the flow of water through the xylem by as much as 30%. The diversification of xylem strand shapes with tracheid network topologies increasingly resistant to the spread of embolism likely facilitated increases in plant size and the colonization of drier habitats during the Devonian radiation. Conifers, by the Jurassic, developed bordered pits had valve-like structures to isolate cavitated elements. These torus-margo structures have an impermeable disc (torus) suspended by a permeable membrane (margo) between two adjacent pores. When a tracheid on one side depressurizes, the disc is sucked into the pore on that side, and blocks further flow. Other plants simply tolerate cavitation. For instance, oaks grow a ring of wide vessels at the start of each spring, none of which survive the winter frosts. Maples use root pressure each spring to force sap upwards from the roots, squeezing out any air bubbles.
Growing to height also employed another trait of tracheids – the support offered by their lignified walls. Defunct tracheids were retained to form a strong, woody stem, produced in most instances by a secondary xylem. However, in early plants, tracheids were too mechanically vulnerable, and retained a central position, with a layer of tough sclerenchyma on the outer rim of the stems. Even when tracheids do take a structural role, they are supported by sclerenchymatic tissue.
Tracheids end with walls, which impose a great deal of resistance on flow; vessel members have perforated end walls, and are arranged in series to operate as if they were one continuous vessel. The function of end walls, which were the default state in the Devonian, was probably to avoid embolisms. An embolism is where an air bubble is created in a tracheid. This may happen as a result of freezing, or by gases dissolving out of solution. Once an embolism is formed, it usually cannot be removed (but see later); the affected cell cannot pull water up, and is rendered useless. | Xylem | Wikipedia | 506 | 46675 | https://en.wikipedia.org/wiki/Xylem | Biology and health sciences | Plant tissues | Biology |
End walls excluded, the tracheids of prevascular plants were able to operate under the same hydraulic conductivity as those of the first vascular plant, Cooksonia.
The size of tracheids is limited as they comprise a single cell; this limits their length, which in turn limits their maximum useful diameter to 80 μm. Conductivity grows with the fourth power of diameter, so increased diameter has huge rewards; vessel elements, consisting of a number of cells, joined at their ends, overcame this limit and allowed larger tubes to form, reaching diameters of up to 500 μm, and lengths of up to 10 m.
Vessels first evolved during the dry, low periods of the late Permian, in the horsetails, ferns and Selaginellales independently, and later appeared in the mid Cretaceous in angiosperms and gnetophytes.
Vessels allow the same cross-sectional area of wood to transport around a hundred times more water than tracheids! This allowed plants to fill more of their stems with structural fibers, and also opened a new niche to vines, which could transport water without being as thick as the tree they grew on. Despite these advantages, tracheid-based wood is a lot lighter, thus cheaper to make, as vessels need to be much more reinforced to avoid cavitation.
Development
Xylem development can be described by four terms: centrarch, exarch, endarch and mesarch. As it develops in young plants, its nature changes from protoxylem to metaxylem (i.e. from first xylem to after xylem). The patterns in which protoxylem and metaxylem are arranged are essential in studying plant morphology. | Xylem | Wikipedia | 351 | 46675 | https://en.wikipedia.org/wiki/Xylem | Biology and health sciences | Plant tissues | Biology |
Protoxylem and metaxylem
As a young vascular plant grows, one or more strands of primary xylem form in its stems and roots. The first xylem to develop is called 'protoxylem'. In appearance, protoxylem is usually distinguished by narrower vessels formed of smaller cells. Some of these cells have walls that contain thickenings in the form of rings or helices. Functionally, protoxylem can extend: the cells can grow in size and develop while a stem or root is elongating. Later, 'metaxylem' develops in the strands of xylem. Metaxylem vessels and cells are usually larger; the cells have thickenings typically either in the form of ladderlike transverse bars (scalariform) or continuous sheets except for holes or pits (pitted). Functionally, metaxylem completes its development after elongation ceases when the cells no longer need to grow in size.
Patterns of protoxylem and metaxylem
There are four primary patterns to the arrangement of protoxylem and metaxylem in stems and roots.
Centrarch refers to the case in which the primary xylem forms a single cylinder in the center of the stem and develops from the center outwards. The protoxylem is thus found in the central core, and the metaxylem is in a cylinder around it. This pattern was common in early land plants, such as "rhyniophytes", but is not present in any living plants.
The other three terms are used where there is more than one strand of primary xylem. | Xylem | Wikipedia | 327 | 46675 | https://en.wikipedia.org/wiki/Xylem | Biology and health sciences | Plant tissues | Biology |
Exarch is used when there is more than one strand of primary xylem in a stem or root, and the xylem develops from the outside inwards towards the center, i.e., centripetally. The metaxylem is thus closest to the center of the stem or root, and the protoxylem is closest to the periphery. The roots of vascular plants are generally considered to have exarch development.
Endarch is used when there is more than one strand of primary xylem in a stem or root, and the xylem develops from the inside outwards towards the periphery, i.e., centrifugally. The protoxylem is thus closest to the center of the stem or root, and the metaxylem is closest to the periphery. The stems of seed plants typically have endarch development.
Mesarch is used when there is more than one strand of primary xylem in a stem or root, and the xylem develops from the middle of a strand in both directions. The metaxylem is thus on both the peripheral and central sides of the strand, with the protoxylem between the metaxylem (possibly surrounded by it). The leaves and stems of many ferns have mesarch development.
History | Xylem | Wikipedia | 263 | 46675 | https://en.wikipedia.org/wiki/Xylem | Biology and health sciences | Plant tissues | Biology |
In his book De plantis libri XVI (On Plants, in 16 books) (1583), the Italian physician and botanist Andrea Cesalpino proposed that plants draw water from soil not by magnetism (ut magnes ferrum trahit, as magnetic iron attracts) nor by suction (vacuum), but by absorption, as occurs in the case of linen, sponges, or powders. The Italian biologist Marcello Malpighi was the first person to describe and illustrate xylem vessels, which he did in his book Anatome plantarum ... (1675). Although Malpighi believed that xylem contained only air, the British physician and botanist Nehemiah Grew, who was Malpighi's contemporary, believed that sap ascended both through the bark and through the xylem. However, according to Grew, capillary action in the xylem would raise the sap by only a few inches; to raise the sap to the top of a tree, Grew proposed that the parenchymal cells become turgid and thereby not only squeeze the sap in the tracheids but force some sap from the parenchyma into the tracheids. In 1727, English clergyman and botanist Stephen Hales showed that transpiration by a plant's leaves causes water to move through its xylem. By 1891, the Polish-German botanist Eduard Strasburger had shown that the transport of water in plants did not require the xylem cells to be alive. | Xylem | Wikipedia | 314 | 46675 | https://en.wikipedia.org/wiki/Xylem | Biology and health sciences | Plant tissues | Biology |
In mathematics, Euler's identity (also known as Euler's equation) is the equality
where
is Euler's number, the base of natural logarithms,
is the imaginary unit, which by definition satisfies , and
is pi, the ratio of the circumference of a circle to its diameter.
Euler's identity is named after the Swiss mathematician Leonhard Euler. It is a special case of Euler's formula when evaluated for . Euler's identity is considered to be an exemplar of mathematical beauty as it shows a profound connection between the most fundamental numbers in mathematics. In addition, it is directly used in a proof that is transcendental, which implies the impossibility of squaring the circle.
Mathematical beauty
Euler's identity is often cited as an example of deep mathematical beauty. Three of the basic arithmetic operations occur exactly once each: addition, multiplication, and exponentiation. The identity also links five fundamental mathematical constants:
The number 0, the additive identity
The number 1, the multiplicative identity
The number ( = 3.14159...), the fundamental circle constant
The number ( = 2.71828...), also known as Euler's number, which occurs widely in mathematical analysis
The number , the imaginary unit such that
The equation is often given in the form of an expression set equal to zero, which is common practice in several areas of mathematics.
Stanford University mathematics professor Keith Devlin has said, "like a Shakespearean sonnet that captures the very essence of love, or a painting that brings out the beauty of the human form that is far more than just skin deep, Euler's equation reaches down into the very depths of existence". And Paul Nahin, a professor emeritus at the University of New Hampshire, who has written a book dedicated to Euler's formula and its applications in Fourier analysis, describes Euler's identity as being "of exquisite beauty".
Mathematics writer Constance Reid has opined that Euler's identity is "the most famous formula in all mathematics". And Benjamin Peirce, a 19th-century American philosopher, mathematician, and professor at Harvard University, after proving Euler's identity during a lecture, stated that the identity "is absolutely paradoxical; we cannot understand it, and we don't know what it means, but we have proved it, and therefore we know it must be the truth". | Euler's identity | Wikipedia | 508 | 46740 | https://en.wikipedia.org/wiki/Euler%27s%20identity | Mathematics | Calculus and analysis | null |
A poll of readers conducted by The Mathematical Intelligencer in 1990 named Euler's identity as the "most beautiful theorem in mathematics". In another poll of readers that was conducted by Physics World in 2004, Euler's identity tied with Maxwell's equations (of electromagnetism) as the "greatest equation ever".
At least three books in popular mathematics have been published about Euler's identity:
Dr. Euler's Fabulous Formula: Cures Many Mathematical Ills, by Paul Nahin (2011)
A Most Elegant Equation: Euler's formula and the beauty of mathematics, by David Stipp (2017)
Euler's Pioneering Equation: The most beautiful theorem in mathematics, by Robin Wilson (2018).
Explanations
Imaginary exponents
Euler's identity asserts that is equal to −1. The expression is a special case of the expression , where is any complex number. In general, is defined for complex by extending one of the definitions of the exponential function from real exponents to complex exponents. For example, one common definition is:
Euler's identity therefore states that the limit, as approaches infinity, of is equal to −1. This limit is illustrated in the animation to the right.
Euler's identity is a special case of Euler's formula, which states that for any real number ,
where the inputs of the trigonometric functions sine and cosine are given in radians.
In particular, when ,
Since
and
it follows that
which yields Euler's identity:
Geometric interpretation
Any complex number can be represented by the point on the complex plane. This point can also be represented in polar coordinates as , where is the absolute value of (distance from the origin), and is the argument of (angle counterclockwise from the positive x-axis). By the definitions of sine and cosine, this point has cartesian coordinates of , implying that . According to Euler's formula, this is equivalent to saying .
Euler's identity says that . Since is for = 1 and , this can be interpreted as a fact about the number −1 on the complex plane: its distance from the origin is 1, and its angle from the positive x-axis is radians. | Euler's identity | Wikipedia | 469 | 46740 | https://en.wikipedia.org/wiki/Euler%27s%20identity | Mathematics | Calculus and analysis | null |
Additionally, when any complex number is multiplied by , it has the effect of rotating counterclockwise by an angle of on the complex plane. Since multiplication by −1 reflects a point across the origin, Euler's identity can be interpreted as saying that rotating any point radians around the origin has the same effect as reflecting the point across the origin. Similarly, setting equal to yields the related equation which can be interpreted as saying that rotating any point by one turn around the origin returns it to its original position.
Generalizations
Euler's identity is also a special case of the more general identity that the th roots of unity, for , add up to 0:
Euler's identity is the case where .
A similar identity also applies to quaternion exponential: let be the basis quaternions; then,
More generally, let be a quaternion with a zero real part and a norm equal to 1; that is, with Then one has
The same formula applies to octonions, with a zero real part and a norm equal to 1. These formulas are a direct generalization of Euler's identity, since and are the only complex numbers with a zero real part and a norm (absolute value) equal to 1.
History
While Euler's identity is a direct result of Euler's formula, published in his monumental work of mathematical analysis in 1748, Introductio in analysin infinitorum, it is questionable whether the particular concept of linking five fundamental constants in a compact form can be attributed to Euler himself, as he may never have expressed it.
Robin Wilson states the following. | Euler's identity | Wikipedia | 337 | 46740 | https://en.wikipedia.org/wiki/Euler%27s%20identity | Mathematics | Calculus and analysis | null |
The Virginia opossum (Didelphis virginiana), also known as the North American opossum, is a member of the opossum family found from southern Canada to northern Costa Rica (making it the northernmost marsupial in the world). Commonly referred to simply as the possum, it is a solitary nocturnal animal about the size of a domestic cat, and a successful opportunist.
Opossums are familiar to many North Americans as they frequently inhabit settled areas near food sources like trash cans, pet food, compost piles, gardens or housemice. Their slow, nocturnal nature and their attraction to roadside carrion make opossums more likely to become roadkill.
Name
The Virginia opossum is the original animal named "opossum", a word which comes from Algonquian wapathemwa, meaning "white animal". Colloquially, the Virginia opossum is frequently just called a "possum". The term is applied more generally to any of the other marsupials of the families Didelphidae and Caenolestidae. The generic name (Didelphis) is derived from Ancient Greek: , "two", and , "womb".
The possums of Australia, whose name derives from their similarity to the American species, are also marsupials, but of the order Diprotodontia.
The Virginia opossum is known in Mexico as tlacuache, tacuachi, and tlacuachi, from the Nahuatl word tlacuatzin.
Range
The Virginia opossum's ancestors evolved in South America, but spread into North America as part of the Great American Interchange, which occurred mainly after the formation of the Isthmus of Panama about 3 million years ago. Didelphis was apparently one of the later migrants, entering North America about 0.8 million years ago. It is now found throughout Central America and North America from Costa Rica to southern Ontario and is expanding its range northward, northwesterly and northeasterly at a significant pace. | Virginia opossum | Wikipedia | 424 | 46750 | https://en.wikipedia.org/wiki/Virginia%20opossum | Biology and health sciences | Marsupials | Animals |
Its pre-European settlement range was generally as far north as Maryland; southern Ohio, Indiana and Illinois; Missouri and Kansas. The clearing of dense forests in these areas and further north by settlers allowed the opossum to move northward. Elimination of the opossum's main predators in these areas also contributed to their expansion. Since 1900, it has expanded its range to include most of New England (including Maine); New York, extreme southwestern Quebec; most of southern and eastern Ontario; most of Michigan and Wisconsin; most of Minnesota, southeastern South Dakota and most of Nebraska.
Areas such as Rhode Island and Waterloo Region and Simcoe County in southern Ontario rarely had sightings of opossums in the 1960s, but now have them regularly; some speculate that this is likely due to global warming causing winters to be warmer. Some people speculate the expansion into Ontario mostly occurred by opossums accidentally being transferred across the St. Lawrence, Niagara, Detroit and St. Clair rivers by motor vehicles or trains they may have climbed upon. As the opossum is not adapted to colder winters or heavy snow, its population may be significantly reduced if a colder winter with heavier snow occurs in a particular northern region.
The Virginia opossum was not originally native to the West Coast of the United States. It was intentionally introduced into the West during the Great Depression, probably as a source of food, and now occupies much of the Pacific coast. Its range has been expanding steadily northward into British Columbia.
Description
Virginia opossums can vary considerably in size, with larger specimens found to the north of the opossum's range and smaller specimens in the tropics. They measure long from their snout to the base of the tail, with the tail adding another . Males are slightly larger, with an average body length of with an average tail length of , while females are long with a tail. Weight for males ranges from and for females from .
Their coats are a dull grayish brown, other than on their faces, which are white. Opossums have long, hairless, prehensile tails, which can be used to grab branches and carry small objects. They also have hairless ears and a long, flat nose. Opossums have 50 teeth, more than any other North American land mammal, and opposable, clawless thumbs on their rear limbs. Opossums have 13 nipples, arranged in a circle of 12 with one in the middle. | Virginia opossum | Wikipedia | 498 | 46750 | https://en.wikipedia.org/wiki/Virginia%20opossum | Biology and health sciences | Marsupials | Animals |
The dental formula of an opossum is . No other mammal in North America has more than 6 upper incisors, but the Virginia opossum has 10.
Perhaps surprisingly for such a widespread and successful species, the Virginia opossum has one of the lowest encephalization quotients of any marsupial.
Its brain is one-fifth the size of a raccoon's.
Tracks
Virginia opossum tracks generally show five finger-like toes in both the fore and hind prints. The hind tracks are unusual and distinctive due to the opossum's opposable thumb, which generally prints at an angle of 90° or greater to the other fingers (sometimes near 180°). Individual adult tracks generally measure 1.9 in long by 2.0 in wide (4.8 × 5.1 cm) for the fore prints and 2.5 in long by 2.3 in wide (6.4 × 5.7 cm) for the hind prints. Opossums have claws on all fingers fore and hind except on the two thumbs (in the photograph, claw marks show as small holes just beyond the tip of each finger); these generally show in the tracks. In a soft medium, such as the mud in this photograph, the foot pads clearly show (these are the deep, darker areas where the fingers and toes meet the rest of the hand or foot, which have been filled with plant debris by wind due to the advanced age of the tracks).
The tracks in the photograph were made while the opossum was walking with its typical pacing gait. The four aligned toes on the hind print show the approximate direction of travel.
In a pacing gait, the limbs on one side of the body are moved simultaneously, just prior to moving both limbs on the other side of the body. This is illustrated in the pacing diagram, which explains why the left-fore and right-hind tracks are generally found together (and vice versa). If the opossum was not walking (perhaps running), the prints would fall in a different pattern. Other animals that generally employ a pacing gait are raccoons, bears, skunks, badgers, woodchucks, porcupines, and beavers. | Virginia opossum | Wikipedia | 460 | 46750 | https://en.wikipedia.org/wiki/Virginia%20opossum | Biology and health sciences | Marsupials | Animals |
When pacing, the opossum's 'stride' generally measures from 7 to 10 in, or 18 to 25 cm (in the pacing diagram the stride is 8.5 in, where one grid square is equal to 1 in2). To determine the stride of a pacing gait, measure from the tip (just beyond the fingers or toes in the direction of travel, disregarding claw marks) of one set of fore/hind tracks to the tip of the next set. By taking careful stride and track-size measurements, one can usually determine what species of animal created a set of tracks, even when individual track details are vague or obscured.
Behavior
"Playing possum"
If threatened, an opossum will either flee or take a stand. To appear threatening, an opossum will first bare its 50 teeth, snap its jaw, hiss, drool, and stand its fur on end to look bigger. If this does not work, the Virginia opossum is noted for feigning death in response to extreme fear. This is the genesis of the term "playing possum", which means pretending to be dead or injured with intent to deceive.
In this inactive state it lies limp and motionless on its side, mouth and eyes open, tongue hanging out, and feet clenched. Fear can also cause the opossum to release a green fluid from its anus with a putrid odor that repels predators. Heart rate drops by half, and breathing rate is so slow and shallow it is hardly detectable. Death feigning normally stops when the threat withdraws, and it can last for several hours. Besides discouraging animals that eat live prey, playing possum also convinces some large animals that the opossum is no threat to their young. "Playing possum" in response to threats from oncoming traffic often results in death.
Diet
Opossums are omnivorous (sometimes said to be insectivorous) and eat a wide range of plant-based food, as well as animal-based food like small invertebrates, carrion, eggs, fish, amphibians, reptiles, birds, small mammals, and other small animals. | Virginia opossum | Wikipedia | 445 | 46750 | https://en.wikipedia.org/wiki/Virginia%20opossum | Biology and health sciences | Marsupials | Animals |
Insects such as grasshoppers, crickets, and beetles make up the bulk of the animal foods eaten by opossums. It has been stated that opossums eat up to 95% of the ticks they encounter and may eat up to 5,000 ticks per season, helping to prevent the spread of tick-born illnesses, including Lyme disease and Rocky Mountain spotted fever. This interpretation has been challenged. A widely publicized 2009 study by the Cary Institute indicated that Virginia opossums in a laboratory setting could eat thousands of ticks per week grooming. However, subsequent studies of the stomach contents of wild Virginia opossums have not found any ticks in their diet.
Small animals include young rabbits, meadow voles, mice, rats, birds, snakes, lizards, frogs, fish, crayfish, gastropods, and earthworms. The Virginia opossum has been found to be very resistant to snake venom. Attracted to carrion on the side of the highway, opossums are at an increased risk of being hit by motor vehicles.
Plant foods are mainly eaten in late summer, autumn, and early winter. These include raspberries, blackberries, apples, acorns, beechnuts, seeds, grains, bulbs, and vegetables. Persimmons are one of the opossum's favorite foods during the autumn. Opossums in urban areas scavenge from bird feeders, vegetable gardens, compost piles, garbage cans, and food dishes intended for dogs and cats.
Opossums in captivity are known to engage in cannibalism, though this is probably uncommon in the wild. Because of this, placing an injured opossum in a confined space with its healthy counterparts is inadvisable.
Seasonality
The Virginia opossum is most active during the spring and summer. It does not hibernate but reduces its activity during the winter. It may not leave its den for several days if the temperature drops below . Both males and females are at greater risk of injury during breeding season. Males extend their range in search of mates which puts them at greater risk of injury from motor vehicles and predators as they venture into unfamiliar territory. Females carrying young are slower moving and have to forage earlier in the evening and later into the night, also increasing their risk of injury from motor vehicles and predation. | Virginia opossum | Wikipedia | 481 | 46750 | https://en.wikipedia.org/wiki/Virginia%20opossum | Biology and health sciences | Marsupials | Animals |
Reproduction
The breeding season for the Virginia opossum can begin as early as December and continue through October with most young born between February and June. A female opossum may have one to three litters per year. During the mating season, the male attracts the female by making clicking sounds with his mouth. The female's estrus cycle is 28 days and lasts 36 hours. Gestation lasts 11–13 days and the average litter size is 8–9 infants, although over 20 infants may be born. Opossums have a very high mortality rate of their young; only one in ten offspring survive to reproductive adulthood.
Newborns are the size of a honeybee. Once delivered through the median vagina or central birth canal, newborn opossums climb up into the female opossum's pouch and latch onto one of her 13 teats. The young remain latched for two months and in the pouch for months. The young then climb onto the mother's back, where she carries them for the remainder of their time together. It is during this time that the young learn survival skills. They leave their mother after about four or five months.
Like all female marsupials, the female's reproductive system is bifid, with two lateral vaginae, uteri, and ovaries. The male's penis is also bifid, with two heads, and as is common in New World marsupials, the sperm pair up in the testes and only separate as they come close to the egg. Males have three pairs of Cowper's glands.
Lifespan
Compared to other mammals, including most other marsupials except dasyuromorphians, opossums have unusually short lifespans for their size and metabolic rate. The Virginia opossum has a maximal lifespan in the wild of only about two years. Even in captivity, opossums live only about four years. The rapid senescence of opossums is thought to reflect the fact that they have few defenses against predators; given that they would have little prospect of living very long regardless, they are not under selective pressure to develop biochemical mechanisms to enable a long lifespan. In support of this hypothesis, one population on Sapelo Island, off the coast of Georgia, which has been isolated for thousands of years without natural predators, was found by Dr. Steven Austad to have evolved lifespans up to 50% longer than those of mainland populations. | Virginia opossum | Wikipedia | 496 | 46750 | https://en.wikipedia.org/wiki/Virginia%20opossum | Biology and health sciences | Marsupials | Animals |
Historical references
An early description of the opossum comes from explorer John Smith, who wrote in Map of Virginia, with a Description of the Countrey, the Commodities, People, Government and Religion in 1608 that "An Opassom hath an head like a Swine, and a taile like a Rat, and is of the bignes of a Cat. Under her belly she hath a bagge, wherein she lodgeth, carrieth, and sucketh her young."
The opossum was more formally described in 1698 in a published letter entitled "Carigueya, Seu Marsupiale Americanum Masculum. Or, The Anatomy of a Male Opossum: In a Letter to Dr Edward Tyson", from Mr William Cowper, Chirurgeon, and Fellow of the Royal Society, London, by Edward Tyson, M.D. Fellow of the College of Physicians and of the Royal Society. The letter suggests even earlier descriptions.
Relationship with humans
Opossums are not considered dangerous to humans. Though their open-mouth hiss when frightened is often mistaken as rabid behavior, opossums are naturally resistant to rabies due to their low body temperature. Opossums can however host parasites and carry diseases such as tuberculosis, leptospirosis, and tularemia, among others.
Like raccoons, opossums can be found in urban environments, where they eat pet food, rotten fruit, and human garbage. They also are considered a common predator of poultry farming in North America. Research suggests that proximity to humans causes an increase in body size for opossums living in or near urban environments. Though sometimes mistakenly considered to be rats, opossums are not closely related to rodents or any other placental mammals.
The opossum was once a favorite game animal in the United States, particularly in the southern regions which have a large body of recipes and folklore relating to it. Their past wide consumption in regions where present is evidenced by recipes available online and in books such as older editions of The Joy of Cooking. A traditional method of preparation is baking, sometimes in a pie or pastry, though at present "possum pie" most often refers to a sweet confection containing no meat of any kind.
Around the turn of the 20th century, the opossum was the subject of numerous songs, including "Carve dat Possum", a minstrel song written in 1875 by Sam Lucas. | Virginia opossum | Wikipedia | 502 | 46750 | https://en.wikipedia.org/wiki/Virginia%20opossum | Biology and health sciences | Marsupials | Animals |
Although it is widely distributed in the United States, the Virginia opossum's appearance in folklore and popularity as a food item has tied it closely to the American Southeast. In animation, it is often used to depict uncivilized characters or "hillbillies". Not surprisingly, then, the Virginia opossum is featured in several episodes of the hit TV show The Beverly Hillbillies, such as the "Possum Day" episode in 1965. The title character in Walt Kelly's long-running comic strip Pogo was an opossum. In an attempt to create another icon like the teddy bear, President William Howard Taft was tied to the character Billy Possum. The character did not do well, as public perception of the opossum led to its downfall. In December 2010, a cross-eyed Virginia opossum in Germany's Leipzig Zoo named Heidi became an international celebrity. She appeared on a TV talk show to predict the 2011 Oscar winners, similar to the World Cup predictions made previously by Paul the Octopus, also in Germany.
The Perelman Building in Philadelphia, Pennsylvania, an annex of the Philadelphia Museum of Art, was formerly the Fidelity Mutual Life Insurance Company Building. Built in the late 1920s its facade is decorated with polychrome sculptures of animals symbolizing various attributes of insurance, including a possum to represent "protection". | Virginia opossum | Wikipedia | 279 | 46750 | https://en.wikipedia.org/wiki/Virginia%20opossum | Biology and health sciences | Marsupials | Animals |
Artiodactyls are placental mammals belonging to the order Artiodactyla ( , ). Typically, they are ungulates which bear weight equally on two (an even number) of their five toes (the third and fourth, often in the form of a hoof). The other three toes are either present, absent, vestigial, or pointing posteriorly. By contrast, most perissodactyls bear weight on an odd number of the five toes. Another difference between the two orders is that many artiodactyls (except for Suina) digest plant cellulose in one or more stomach chambers rather than in their intestine (as perissodactyls do). Molecular biology, along with new fossil discoveries, has found that cetaceans (whales, dolphins, and porpoises) fall within this taxonomic branch, being most closely related to hippopotamuses. Some modern taxonomists thus apply the name Cetartiodactyla () to this group, while others opt to include cetaceans within the existing name of Artiodactyla. Some researchers use "even-toed ungulates" to exclude cetaceans and only include terrestrial artiodactyls, making the term paraphyletic in nature.
The roughly 270 land-based even-toed ungulate species include pigs, peccaries, hippopotamuses, antelopes, deer, giraffes, camels, llamas, alpacas, sheep, goats and cattle. Many are herbivores, but suids are omnivorous, and cetaceans are entirely carnivorous. Artiodactyls are also known by many extinct groups such as anoplotheres, cainotheriids, merycoidodonts, entelodonts, anthracotheres, basilosaurids, and palaeomerycids. Many artiodactyls are of great dietary, economic, and cultural importance to humans.
Evolutionary history | Artiodactyl | Wikipedia | 431 | 46764 | https://en.wikipedia.org/wiki/Artiodactyl | Biology and health sciences | Artiodactyla | null |
The oldest fossils of even-toed ungulates date back to the early Eocene (about 53 million years ago). Since these findings almost simultaneously appeared in Europe, Asia, and North America, it is very difficult to accurately determine the origin of artiodactyls. The fossils are classified as belonging to the family Diacodexeidae; their best-known and best-preserved member is Diacodexis. These were small animals, some as small as a hare, with a slim build, lanky legs, and a long tail. Their hind legs were much longer than their front legs. The early to middle Eocene saw the emergence of the ancestors of most of today's mammals.
Two formerly widespread, but now extinct, families of even-toed ungulates were Entelodontidae and Anthracotheriidae. Entelodonts existed from the middle Eocene to the early Miocene in Eurasia and North America. They had a stocky body with short legs and a massive head, which was characterized by two humps on the lower jaw bone. Anthracotheres had a large, porcine (pig-like) build, with short legs and an elongated muzzle. This group appeared in the middle Eocene up until the Pliocene, and spread throughout Eurasia, Africa, and North America. Anthracotheres are thought to be the ancestors of hippos, and, likewise, probably led a similar aquatic lifestyle. Hippopotamuses appeared in the late Miocene and occupied Africa and Asia—they never got to the Americas.
The camels (Tylopoda) were, during large parts of the Cenozoic, limited to North America; early forms like Cainotheriidae occupied Europe. Among the North American camels were groups like the stocky, short-legged Merycoidodontidae. They first appeared in the late Eocene and developed a great diversity of species in North America. Only in the late Miocene or early Pliocene did they migrate from North America into Eurasia. The North American varieties became extinct around 10,000 years ago.
Suina (including pigs) have been around since the Eocene. In the late Eocene or the Oligocene, two families stayed in Eurasia and Africa; the peccaries, which became extinct in the Old World, exist today only in the Americas. | Artiodactyl | Wikipedia | 490 | 46764 | https://en.wikipedia.org/wiki/Artiodactyl | Biology and health sciences | Artiodactyla | null |
South America was settled by even-toed ungulates only in the Pliocene, after the land bridge at the Isthmus of Panama formed some three million years ago. With only the peccaries, lamoids (or llamas), and various species of capreoline deer, South America has comparatively fewer artiodactyl families than other continents, except Australia, which has no native species.
Taxonomy and phylogeny
The classification of artiodactyls was hotly debated because ocean-dwelling cetaceans evolved from land-dwelling even-toed ungulates. Some semiaquatic even-toed ungulates (hippopotamuses) are more closely related to ocean-dwelling cetaceans than to other even-toed ungulates.
Phylogenetic classification only recognizes monophyletic taxa; that is, groups that descend from a common ancestor and include all of its descendants. To address this problem, the traditional order Artiodactyla and infraorder Cetacea are sometimes subsumed into the more inclusive Cetartiodactyla taxon. An alternative approach is to include both land-dwelling even-toed ungulates and ocean-dwelling cetaceans in a revised Artiodactyla taxon.
Classification | Artiodactyl | Wikipedia | 270 | 46764 | https://en.wikipedia.org/wiki/Artiodactyl | Biology and health sciences | Artiodactyla | null |
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