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Historical texts
Written accounts of leprosy date back thousands of years. Various skin diseases translated as leprosy appear in the ancient Indian text, the Atharava Veda, by 600 BC. Another Indian text, the Manusmriti (200 BC), prohibit contact with those infected with the disease and make marriage to a person infe... | Leprosy | Wikipedia | 353 | 44700 | https://en.wikipedia.org/wiki/Leprosy | Biology and health sciences | Infectious disease | null |
All three Synoptic Gospels of the New Testament describe instances of Jesus healing people with leprosy (Matthew 8:1–4, Mark 1:40–45, and Luke 5:12–16). The Bible's description of leprosy is congruous (if lacking detail) with the symptoms of modern leprosy, but the relationship between this disease, tzaraath, and Hanse... | Leprosy | Wikipedia | 297 | 44700 | https://en.wikipedia.org/wiki/Leprosy | Biology and health sciences | Infectious disease | null |
Early medieval understanding of leprosy was influenced by early Christian writers such as Gregory of Nazianzus and John Chrysostom, whose writings were later embraced by Byzantine and Latin writers. Gregory, for example, composed sermons urging Christians to assist victims of the disease, and he condemned pagans or Chr... | Leprosy | Wikipedia | 259 | 44700 | https://en.wikipedia.org/wiki/Leprosy | Biology and health sciences | Infectious disease | null |
As the disease became more prevalent in western Europe in the 5th century, efforts began to set up permanent institutions to house and feed lepers. These efforts were, inclusively, the work of bishops in France at the end of the sixth century, such as in Chalon-sur-Saône. The increase in hospitals or leprosaria (sing. ... | Leprosy | Wikipedia | 363 | 44700 | https://en.wikipedia.org/wiki/Leprosy | Biology and health sciences | Infectious disease | null |
Norway was the location of a progressive stance on leprosy tracking and treatment and played an influential role in European understanding of the disease. In 1832, Dr. JJ Hjort conducted the first leprosy survey, thus establishing a basis for epidemiological surveys. Subsequent surveys resulted in the establishment of ... | Leprosy | Wikipedia | 507 | 44700 | https://en.wikipedia.org/wiki/Leprosy | Biology and health sciences | Infectious disease | null |
The National Leprosarium at Carville, Louisiana, known in 1955 as the Louisiana Leper Home, was the only leprosy hospital in the mainland United States. Leprosy patients from all over the United States were sent to Carville to be kept in isolation away from the public, as not much about leprosy transmission was known a... | Leprosy | Wikipedia | 505 | 44700 | https://en.wikipedia.org/wiki/Leprosy | Biology and health sciences | Infectious disease | null |
A goal of the WHO is to "eliminate leprosy," and in 2016 the organization launched "Global Leprosy Strategy 2016–2020: Accelerating towards a leprosy-free world". Elimination of leprosy is defined as "reducing the proportion of (people with) leprosy in the community to very low levels, specifically to below one case pe... | Leprosy | Wikipedia | 306 | 44700 | https://en.wikipedia.org/wiki/Leprosy | Biology and health sciences | Infectious disease | null |
Josephine Cafrine of Seychelles (1877–1907) had leprosy from age 12 and kept a journal that documented her struggles and suffering. It was published as an autobiography in 1923.
Saint Damien De Veuster (1840–1889), a Catholic priest from Belgium, contracted leprosy and ministered to lepers who had been placed under a ... | Leprosy | Wikipedia | 255 | 44700 | https://en.wikipedia.org/wiki/Leprosy | Biology and health sciences | Infectious disease | null |
— the short story collection Life's Handicap by Rudyard Kipling has a story "The Mark of the Beast" in which a traveller on horseback literally stumbles into a leper colony in India.
— Jack London published "Koolau the Leper" in his Tales of Hawai'i about Molokai and people consigned to it circa 1893.
— James Mich... | Leprosy | Wikipedia | 501 | 44700 | https://en.wikipedia.org/wiki/Leprosy | Biology and health sciences | Infectious disease | null |
Infection of animals
Between 15 and 20% of nine-banded armadillos (Dasypus novemcinctus) in the south-central United States carry M. leprae.Liang, Jiayu (10/16/2023). "Leprosy in Florida: medical experts monitoring unusual, new cases of Hansen's disease". University of Florida Emerging Pathogens Institute. https://epi... | Leprosy | Wikipedia | 333 | 44700 | https://en.wikipedia.org/wiki/Leprosy | Biology and health sciences | Infectious disease | null |
Armadillos have been used in immunological research to fight leprosy. Some notable reagents include recombinant interleukin-2 and recombinant interferon-gamma reagents. Additionally, they have been key and have been useful models of leprosy for studies regarding neuropathy. In clinical procedures such as electrophysiol... | Leprosy | Wikipedia | 441 | 44700 | https://en.wikipedia.org/wiki/Leprosy | Biology and health sciences | Infectious disease | null |
It has been shown that leprosy can reprogram cells in mouse and armadillo models, similar to how induced pluripotent stem cells are generated by the transcription factors Myc, Oct3/4, Sox2, and Klf4. A notable study conducted by Charles Shepard used mice to find how leprosy, an infection that has a preference for coole... | Leprosy | Wikipedia | 297 | 44700 | https://en.wikipedia.org/wiki/Leprosy | Biology and health sciences | Infectious disease | null |
Printing is a process for mass reproducing text and images using a master form or template. The earliest non-paper products involving printing include cylinder seals and objects such as the Cyrus Cylinder and the Cylinders of Nabonidus. The earliest known form of printing evolved from ink rubbings made on paper or clot... | Printing | Wikipedia | 475 | 44723 | https://en.wikipedia.org/wiki/Printing | Technology | Media and communication | null |
Printing spread early to Korea and Japan, which also used Chinese logograms, but the technique was also used in Turpan and Vietnam using a number of other scripts. This technique then spread to Persia and Russia. This technique was transmitted to Europe by around 1400 and was used on paper for old master prints and pla... | Printing | Wikipedia | 427 | 44723 | https://en.wikipedia.org/wiki/Printing | Technology | Media and communication | null |
Around 1040, the first known movable type system was created in China by Bi Sheng out of porcelain. Bi Sheng used clay type, which broke easily, but Wang Zhen by 1298 had carved a more durable type from wood. He also developed a complex system of revolving tables and number-association with written Chinese characters t... | Printing | Wikipedia | 478 | 44723 | https://en.wikipedia.org/wiki/Printing | Technology | Media and communication | null |
Compared to woodblock printing, movable type page setting and printing using a press was faster and more durable. Also, the metal type pieces were sturdier and the lettering more uniform, leading to typography and fonts. The high quality and relatively low price of the Gutenberg Bible (1455) established the superiority... | Printing | Wikipedia | 402 | 44723 | https://en.wikipedia.org/wiki/Printing | Technology | Media and communication | null |
Conventional printing has four types of process:
Planographics, in which the printing and non-printing areas are on the same plane surface and the difference between them is maintained chemically or by physical properties, the examples are: offset lithography, collotype, and screenless printing.
Relief, in which the ... | Printing | Wikipedia | 394 | 44723 | https://en.wikipedia.org/wiki/Printing | Technology | Media and communication | null |
Offset printing is a widely used modern printing process. This technology is best described as when a positive (right-reading) image on a printing plate is inked and transferred (or "offset") from the plate to a rubber blanket. The blanket image becomes a mirror image of the plate image. An offset transfer moves the im... | Printing | Wikipedia | 477 | 44723 | https://en.wikipedia.org/wiki/Printing | Technology | Media and communication | null |
Other printing techniques
The other significant printing techniques include:
Dye-sublimation printer
Inkjet, used typically to print a small number of books or packaging, and also to print a variety of materials: from high quality papers simulating offset printing, to floor tiles. Inkjet is also used to apply mailing... | Printing | Wikipedia | 301 | 44723 | https://en.wikipedia.org/wiki/Printing | Technology | Media and communication | null |
In the Muslim world, printing, especially in Arabic scripts, was strongly opposed throughout the early modern period, partially due to the high artistic renown of the art of traditional calligraphy. However, printing in Hebrew or Armenian script was often permitted. Thus, the first movable type printing in the Ottoman ... | Printing | Wikipedia | 427 | 44723 | https://en.wikipedia.org/wiki/Printing | Technology | Media and communication | null |
Social impact
Print gave a broader range of readers access to knowledge and enabled later generations to build directly on the intellectual achievements of earlier ones without the changes arising within verbal traditions. Print, according to Acton in his 1895 lecture On the Study of History, gave "assurance that the w... | Printing | Wikipedia | 481 | 44723 | https://en.wikipedia.org/wiki/Printing | Technology | Media and communication | null |
The language of scholarship
Before the invention of the printing press, most written material was in Latin. However, after the invention of printing the number of books printed expanded as well as the vernacular. Latin was not replaced completely, but remained an international language until the eighteenth century.
U... | Printing | Wikipedia | 477 | 44723 | https://en.wikipedia.org/wiki/Printing | Technology | Media and communication | null |
Vendors typically stress the total cost to operate the equipment, involving complex calculations that include all cost factors involved in the operation as well as the capital equipment costs, amortization, etc. For the most part, toner systems are more economical than inkjet in the long run, even though inkjets are le... | Printing | Wikipedia | 504 | 44723 | https://en.wikipedia.org/wiki/Printing | Technology | Media and communication | null |
Calcium carbonate is a chemical compound with the chemical formula . It is a common substance found in rocks as the minerals calcite and aragonite, most notably in chalk and limestone, eggshells, gastropod shells, shellfish skeletons and pearls. Materials containing much calcium carbonate or resembling it are described... | Calcium carbonate | Wikipedia | 430 | 44731 | https://en.wikipedia.org/wiki/Calcium%20carbonate | Physical sciences | Salts | null |
In a laboratory, calcium carbonate can easily be crystallized from calcium chloride (), by placing an aqueous solution of in a desiccator alongside ammonium carbonate . In the desiccator, ammonium carbonate is exposed to air and decomposes into ammonia, carbon dioxide, and water. The carbon dioxide then diffuses into ... | Calcium carbonate | Wikipedia | 471 | 44731 | https://en.wikipedia.org/wiki/Calcium%20carbonate | Physical sciences | Salts | null |
At high saturation, vaterite is typically the first phase precipitated, which is followed by a transformation of the vaterite to calcite. This behavior seems to follow Ostwald's rule, in which the least stable polymorph crystallizes first, followed by the crystallization of different polymorphs via a sequence of increa... | Calcium carbonate | Wikipedia | 433 | 44731 | https://en.wikipedia.org/wiki/Calcium%20carbonate | Physical sciences | Salts | null |
Annelids in the family Lumbricidae, earthworms, possess a regionalization of the digestive track called calciferous glands, Kalkdrüsen, or glandes de Morren, that processes calcium and into calcium carbonate, which is later excreted into the dirt. The function of these glands is unknown but is believed to serve as a ... | Calcium carbonate | Wikipedia | 509 | 44731 | https://en.wikipedia.org/wiki/Calcium%20carbonate | Physical sciences | Salts | null |
Role in taphonomy
Calcium carbonate can preserve fossils through permineralization. Most of the vertebrate fossils of the Two Medicine Formation—a geologic formation known for its duck-billed dinosaur eggs—are preserved by permineralization. This type of preservation conserves high levels of detail, even down to the m... | Calcium carbonate | Wikipedia | 425 | 44731 | https://en.wikipedia.org/wiki/Calcium%20carbonate | Physical sciences | Salts | null |
Calcium carbonate in the form of chalk has traditionally been a major component of blackboard chalk. However, modern manufactured chalk is mostly gypsum, hydrated calcium sulfate . Calcium carbonate is a main source for growing biorock. Precipitated calcium carbonate (PCC), pre-dispersed in slurry form, is a common fil... | Calcium carbonate | Wikipedia | 259 | 44731 | https://en.wikipedia.org/wiki/Calcium%20carbonate | Physical sciences | Salts | null |
Calcium carbonate is widely used as an extender in paints, in particular matte emulsion paint where typically 30% by weight of the paint is either chalk or marble. It is also a popular filler in plastics. Some typical examples include around 15–20% loading of chalk in unplasticized polyvinyl chloride (uPVC) drainpipes,... | Calcium carbonate | Wikipedia | 350 | 44731 | https://en.wikipedia.org/wiki/Calcium%20carbonate | Physical sciences | Salts | null |
In ceramic glaze applications, calcium carbonate is known as whiting, and is a common ingredient for many glazes in its white powdered form. When a glaze containing this material is fired in a kiln, the whiting acts as a flux material in the glaze. Ground calcium carbonate is an abrasive (both as scouring powder and as... | Calcium carbonate | Wikipedia | 367 | 44731 | https://en.wikipedia.org/wiki/Calcium%20carbonate | Physical sciences | Salts | null |
Excess calcium from supplements, fortified food, and high-calcium diets can cause milk-alkali syndrome, which has serious toxicity and can be fatal. In 1915, Bertram Sippy introduced the "Sippy regimen" of hourly ingestion of milk and cream, and the gradual addition of eggs and cooked cereal, for 10 days, combined with... | Calcium carbonate | Wikipedia | 502 | 44731 | https://en.wikipedia.org/wiki/Calcium%20carbonate | Physical sciences | Salts | null |
Household cleaning
Calcium carbonate is a key ingredient in many household cleaning powders like Comet and is used as a scrubbing agent.
Pollution mitigation
In 1989, a researcher, Ken Simmons, introduced into the Whetstone Brook in Massachusetts. His hope was that the calcium carbonate would counter the acid in the ... | Calcium carbonate | Wikipedia | 454 | 44731 | https://en.wikipedia.org/wiki/Calcium%20carbonate | Physical sciences | Salts | null |
The table shows that this partial pressure is not achieved until the temperature is nearly 800 °C. For the outgassing of from calcium carbonate to happen at an economically useful rate, the equilibrium pressure must significantly exceed the ambient pressure of . And for it to happen rapidly, the equilibrium pressure m... | Calcium carbonate | Wikipedia | 510 | 44731 | https://en.wikipedia.org/wiki/Calcium%20carbonate | Physical sciences | Salts | null |
{|
| width=250|
| Ka1 = at 25 °C
|}
Some of the breaks up into water and dissolved carbon dioxide according to
{|
|width=250|
| Kh = at 25 °C
|}
And dissolved carbon dioxide is in equilibrium with atmospheric carbon dioxide according to
{|
| width=250| =
| where = 29.76 atm/(mol/L) at 25 °C (Henry volatilit... | Calcium carbonate | Wikipedia | 335 | 44731 | https://en.wikipedia.org/wiki/Calcium%20carbonate | Physical sciences | Salts | null |
The adjacent table shows the result for and (in the form of pH) as a function of ambient partial pressure of (Ksp = has been taken for the calculation).
At atmospheric levels of ambient the table indicates that the solution will be slightly alkaline with a maximum solubility of 47 mg/L.
As ambient partial pres... | Calcium carbonate | Wikipedia | 484 | 44731 | https://en.wikipedia.org/wiki/Calcium%20carbonate | Physical sciences | Salts | null |
allow the prediction of concentrations of each dissolved inorganic carbon species in solution, from the added concentration of (which constitutes more than 90% of Bjerrum plot species from pH 7 to pH 8 at 25 °C in fresh water). Addition of will increase concentration at any pH. Rearranging the equations given above,... | Calcium carbonate | Wikipedia | 279 | 44731 | https://en.wikipedia.org/wiki/Calcium%20carbonate | Physical sciences | Salts | null |
Solubility in a strong or weak acid solution
Solutions of strong (HCl), moderately strong (sulfamic) or weak (acetic, citric, sorbic, lactic, phosphoric) acids are commercially available. They are commonly used as descaling agents to remove limescale deposits. The maximum amount of that can be "dissolved" by one liter... | Calcium carbonate | Wikipedia | 504 | 44731 | https://en.wikipedia.org/wiki/Calcium%20carbonate | Physical sciences | Salts | null |
{| class="wikitable"
![A] (mol/L)
| [] ≈ 0.5 []
| 10−1
| 10−2
| 10−3
| 10−4
| 10−5
| 10−6
| 10−7
| 10−10
|-
!Initial pH
| 2.38||2.88||3.39||3.91||4.47||5.15||6.02||6.79||7.00
|-
!Final pH
| 6.75||7.25||7.75||8.14||8.25||8.26||8.26||8.26||8.27
|-
!|Dissolved (g/L of acid)
| 49.5||4.99||0.513||0.0848||0.0504||0.0474||0.... | Calcium carbonate | Wikipedia | 391 | 44731 | https://en.wikipedia.org/wiki/Calcium%20carbonate | Physical sciences | Salts | null |
{| class="wikitable"
! [A] (mol/L)
| 1
| 10−1
| 10−2
| 10−3
| 10−4
| 10−5
| 10−6
| 10−7
| 10−10
|-
! Initial pH
| 1.08||1.62||2.25||3.05||4.01||5.00||5.97||6.74||7.00
|-
! Final pH
| 6.71||7.17||7.63||8.06||8.24||8.26||8.26||8.26||8.27
|-
! Dissolved (g/L of acid)
| 62.0||7.39||0.874||0.123||0.0536||0.0477||0.0471||0.... | Calcium carbonate | Wikipedia | 273 | 44731 | https://en.wikipedia.org/wiki/Calcium%20carbonate | Physical sciences | Salts | null |
Chalk is a soft, white, porous, sedimentary carbonate rock. It is a form of limestone composed of the mineral calcite and originally formed deep under the sea by the compression of microscopic plankton that had settled to the sea floor. Chalk is common throughout Western Europe, where deposits underlie parts of France,... | Chalk | Wikipedia | 474 | 44734 | https://en.wikipedia.org/wiki/Chalk | Physical sciences | Sedimentary rocks | Earth science |
Formation
In Western Europe, chalk was formed in the Late Cretaceous Epoch and the early Palaeocene Epoch (between 100 and 61 million years ago). It was deposited on extensive continental shelves at depths between , during a time of nonseasonal (likely arid) climate that reduced the amount of erosion from nearby expose... | Chalk | Wikipedia | 511 | 44734 | https://en.wikipedia.org/wiki/Chalk | Physical sciences | Sedimentary rocks | Earth science |
Chalk of Oligocene to Neogene age has been found in drill cores of rock under the Pacific Ocean at Stewart Arch in the Solomon Islands.
There are layers of chalk, containing Globorotalia, in the Nicosia Formation of Cyprus, which formed during the Pliocene.
Mining
Chalk is mined from chalk deposits both above ground... | Chalk | Wikipedia | 509 | 44734 | https://en.wikipedia.org/wiki/Chalk | Physical sciences | Sedimentary rocks | Earth science |
Previous uses
In southeast England, deneholes are a notable example of ancient chalk pits. Such bell pits may also mark the sites of ancient flint mines, where the prime object was to remove flint nodules for stone tool manufacture. The surface remains at Cissbury are one such example, but perhaps the most famous is t... | Chalk | Wikipedia | 290 | 44734 | https://en.wikipedia.org/wiki/Chalk | Physical sciences | Sedimentary rocks | Earth science |
Goldbach's conjecture is one of the oldest and best-known unsolved problems in number theory and all of mathematics. It states that every even natural number greater than 2 is the sum of two prime numbers.
The conjecture has been shown to hold for all integers less than but remains unproven despite considerable effor... | Goldbach's conjecture | Wikipedia | 311 | 44758 | https://en.wikipedia.org/wiki/Goldbach%27s%20conjecture | Mathematics | Sums and products | null |
Partial results
The strong Goldbach conjecture is much more difficult than the weak Goldbach conjecture, which says that every odd integer greater than 5 is the sum of three primes. Using Vinogradov's method, Nikolai Chudakov, Johannes van der Corput, and Theodor Estermann showed (1937–1938) that almost all even numbe... | Goldbach's conjecture | Wikipedia | 465 | 44758 | https://en.wikipedia.org/wiki/Goldbach%27s%20conjecture | Mathematics | Sums and products | null |
In 1951, Yuri Linnik proved the existence of a constant such that every sufficiently large even number is the sum of two primes and at most powers of 2. János Pintz and Imre Ruzsa found in 2020 that works. Assuming the generalized Riemann hypothesis, also works, as shown by Roger Heath-Brown and Jan-Christoph Schla... | Goldbach's conjecture | Wikipedia | 505 | 44758 | https://en.wikipedia.org/wiki/Goldbach%27s%20conjecture | Mathematics | Sums and products | null |
A modern version of the marginal conjecture is:
And a modern version of Goldbach's older conjecture of which Euler reminded him is:
These modern versions might not be entirely equivalent to the corresponding original statements. For example, if there were an even integer larger than 4, for a prime, that could not b... | Goldbach's conjecture | Wikipedia | 480 | 44758 | https://en.wikipedia.org/wiki/Goldbach%27s%20conjecture | Mathematics | Sums and products | null |
Since , this quantity goes to infinity as increases, and one would expect that every large even integer has not just one representation as the sum of two primes, but in fact very many such representations.
This heuristic argument is actually somewhat inaccurate because it assumes that the events of and being prime ... | Goldbach's conjecture | Wikipedia | 450 | 44758 | https://en.wikipedia.org/wiki/Goldbach%27s%20conjecture | Mathematics | Sums and products | null |
Related problems
Although Goldbach's conjecture implies that every positive integer greater than one can be written as a sum of at most three primes, it is not always possible to find such a sum using a greedy algorithm that uses the largest possible prime at each step. The Pillai sequence tracks the numbers requiring... | Goldbach's conjecture | Wikipedia | 383 | 44758 | https://en.wikipedia.org/wiki/Goldbach%27s%20conjecture | Mathematics | Sums and products | null |
Goldbach's conjecture is used when studying computation complexity. The connection is made through the Busy Beaver function, where BB(n) is the maximum number of steps taken by any n state Turing machine that halts. There is a 27-state Turing machine that halts if and only if Goldbach's conjecture is false. Hence if... | Goldbach's conjecture | Wikipedia | 154 | 44758 | https://en.wikipedia.org/wiki/Goldbach%27s%20conjecture | Mathematics | Sums and products | null |
Luminosity is an absolute measure of radiated electromagnetic energy per unit time, and is synonymous with the radiant power emitted by a light-emitting object. In astronomy, luminosity is the total amount of electromagnetic energy emitted per unit of time by a star, galaxy, or other astronomical objects.
In SI units,... | Luminosity | Wikipedia | 411 | 44790 | https://en.wikipedia.org/wiki/Luminosity | Physical sciences | Observational astronomy | null |
While bolometers do exist, they cannot be used to measure even the apparent brightness of a star because they are insufficiently sensitive across the electromagnetic spectrum and because most wavelengths do not reach the surface of the Earth. In practice bolometric magnitudes are measured by taking measurements at cer... | Luminosity | Wikipedia | 462 | 44790 | https://en.wikipedia.org/wiki/Luminosity | Physical sciences | Observational astronomy | null |
An alternative way to measure stellar luminosity is to measure the star's apparent brightness and distance. A third component needed to derive the luminosity is the degree of interstellar extinction that is present, a condition that usually arises because of gas and dust present in the interstellar medium (ISM), the E... | Luminosity | Wikipedia | 442 | 44790 | https://en.wikipedia.org/wiki/Luminosity | Physical sciences | Observational astronomy | null |
Blue and white supergiants are high luminosity stars somewhat cooler than the most luminous main sequence stars. A star like Deneb, for example, has a luminosity around 200,000 L⊙, a spectral type of A2, and an effective temperature around 8,500 K, meaning it has a radius around . For comparison, the red supergiant Be... | Luminosity | Wikipedia | 447 | 44790 | https://en.wikipedia.org/wiki/Luminosity | Physical sciences | Observational astronomy | null |
For example, consider a 1 Jy signal from a radio source at a redshift of 1, at a frequency of 1.4 GHz.
Ned Wright's cosmology calculator calculates a luminosity distance for a redshift of 1 to be 6701 Mpc = 2×1026 m giving a radio luminosity of .
To calculate the total radio power, this luminosity must be integrated o... | Luminosity | Wikipedia | 384 | 44790 | https://en.wikipedia.org/wiki/Luminosity | Physical sciences | Observational astronomy | null |
Luminosity is an intrinsic measurable property of a star independent of distance. The concept of magnitude, on the other hand, incorporates distance. The apparent magnitude is a measure of the diminishing flux of light as a result of distance according to the inverse-square law. The Pogson logarithmic scale is used to ... | Luminosity | Wikipedia | 488 | 44790 | https://en.wikipedia.org/wiki/Luminosity | Physical sciences | Observational astronomy | null |
Welding is a fabrication process that joins materials, usually metals or thermoplastics, primarily by using high temperature to melt the parts together and allow them to cool, causing fusion. Common alternative methods include solvent welding (of thermoplastics) using chemicals to melt materials being bonded without he... | Welding | Wikipedia | 508 | 44883 | https://en.wikipedia.org/wiki/Welding | Technology | Metallurgy | null |
Etymology
The term weld is derived from the Middle English verb well (; plural/present tense: ) or welling (), meaning 'to heat' (to the maximum temperature possible); 'to bring to a boil'. The modern word was probably derived from the past-tense participle welled (), with the addition of d for this purpose being commo... | Welding | Wikipedia | 467 | 44883 | https://en.wikipedia.org/wiki/Welding | Technology | Metallurgy | null |
In 1800, Sir Humphry Davy discovered the short-pulse electrical arc and presented his results in 1801. In 1802, Russian scientist Vasily Petrov created the continuous electric arc, and subsequently published "News of Galvanic-Voltaic Experiments" in 1803, in which he described experiments carried out in 1802. Of great ... | Welding | Wikipedia | 457 | 44883 | https://en.wikipedia.org/wiki/Welding | Technology | Metallurgy | null |
World War I caused a major surge in the use of welding, with the various military powers attempting to determine which of the several new welding processes would be best. The British primarily used arc welding, even constructing a ship, the "Fullagar" with an entirely welded hull. Arc welding was first applied to aircr... | Welding | Wikipedia | 502 | 44883 | https://en.wikipedia.org/wiki/Welding | Technology | Metallurgy | null |
Other recent developments in welding include the 1958 breakthrough of electron beam welding, making deep and narrow welding possible through the concentrated heat source. Following the invention of the laser in 1960, laser beam welding debuted several decades later, and has proved to be especially useful in high-speed,... | Welding | Wikipedia | 457 | 44883 | https://en.wikipedia.org/wiki/Welding | Technology | Metallurgy | null |
These processes use a welding power supply to create and maintain an electric arc between an electrode and the base material to melt metals at the welding point. They can use either direct current (DC) or alternating current (AC), and consumable or non-consumable electrodes. The welding region is sometimes protected by... | Welding | Wikipedia | 466 | 44883 | https://en.wikipedia.org/wiki/Welding | Technology | Metallurgy | null |
Gas tungsten arc welding (GTAW), or tungsten inert gas (TIG) welding, is a manual welding process that uses a non-consumable tungsten electrode, an inert or semi-inert gas mixture, and a separate filler material. Especially useful for welding thin materials, this method is characterized by a stable arc and high-quality... | Welding | Wikipedia | 459 | 44883 | https://en.wikipedia.org/wiki/Welding | Technology | Metallurgy | null |
Arc welding power supplies
To supply the electrical power necessary for arc welding processes, a variety of different power supplies can be used. The most common welding power supplies are constant current power supplies and constant voltage power supplies. In arc welding, the length of the arc is directly related to t... | Welding | Wikipedia | 271 | 44883 | https://en.wikipedia.org/wiki/Welding | Technology | Metallurgy | null |
The type of current used plays an important role in arc welding. Consumable electrode processes such as shielded metal arc welding and gas metal arc welding generally use direct current, but the electrode can be charged either positively or negatively. In welding, the positively charged anode will have a greater heat c... | Welding | Wikipedia | 477 | 44883 | https://en.wikipedia.org/wiki/Welding | Technology | Metallurgy | null |
Seam welding also relies on two electrodes to apply pressure and current to join metal sheets. However, instead of pointed electrodes, wheel-shaped electrodes roll along and often feed the workpiece, making it possible to make long continuous welds. In the past, this process was used in the manufacture of beverage cans... | Welding | Wikipedia | 502 | 44883 | https://en.wikipedia.org/wiki/Welding | Technology | Metallurgy | null |
Other solid-state welding processes include friction welding (including friction stir welding and friction stir spot welding), magnetic pulse welding, co-extrusion welding, cold welding, diffusion bonding, exothermic welding, high frequency welding, hot pressure welding, induction welding, and roll bonding.
Geometry
... | Welding | Wikipedia | 478 | 44883 | https://en.wikipedia.org/wiki/Welding | Technology | Metallurgy | null |
Many distinct factors influence the strength of welds and the material around them, including the welding method, the amount and concentration of energy input, the weldability of the base material, filler material, and flux material, the design of the joint, and the interactions between all these factors.
For example,... | Welding | Wikipedia | 345 | 44883 | https://en.wikipedia.org/wiki/Welding | Technology | Metallurgy | null |
Heat-affected zone
The heat-affected zone (HAZ) is a ring surrounding the weld in which the temperature of the welding process, combined with the stresses of uneven heating and cooling, alters the heat-treatment properties of the alloy. The effects of welding on the material surrounding the weld can be detrimental—depe... | Welding | Wikipedia | 505 | 44883 | https://en.wikipedia.org/wiki/Welding | Technology | Metallurgy | null |
Most solids used are engineering materials consisting of crystalline solids in which the atoms or ions are arranged in a repetitive geometric pattern which is known as a lattice structure. The only exception is material that is made from glass which is a combination of a supercooled liquid and polymers which are aggreg... | Welding | Wikipedia | 498 | 44883 | https://en.wikipedia.org/wiki/Welding | Technology | Metallurgy | null |
A reduction in fracture toughness may also be attributed to the embrittlement effect of impurities, or for body-centred cubic metals, from a reduction in temperature. Metals and in particular steels have a transitional temperature range where above this range the metal has acceptable notch-ductility while below this ra... | Welding | Wikipedia | 282 | 44883 | https://en.wikipedia.org/wiki/Welding | Technology | Metallurgy | null |
While many welding applications are done in controlled environments such as factories and repair shops, some welding processes are commonly used in a wide variety of conditions, such as open air, underwater, and vacuums (such as space). In open-air applications, such as construction and outdoors repair, shielded metal ... | Welding | Wikipedia | 313 | 44883 | https://en.wikipedia.org/wiki/Welding | Technology | Metallurgy | null |
Since many common welding procedures involve an open electric arc or flame, the risk of burns and fire is significant; this is why it is classified as a hot work process. To prevent injury, welders wear personal protective equipment in the form of heavy leather gloves and protective long-sleeve jackets to avoid exposur... | Welding | Wikipedia | 491 | 44883 | https://en.wikipedia.org/wiki/Welding | Technology | Metallurgy | null |
Costs and trends
As an industrial process, the cost of welding plays a crucial role in manufacturing decisions. Many different variables affect the total cost, including equipment cost, labor cost, material cost, and energy cost. Depending on the process, equipment cost can vary, from inexpensive for methods like shiel... | Welding | Wikipedia | 508 | 44883 | https://en.wikipedia.org/wiki/Welding | Technology | Metallurgy | null |
The trend of accelerating the speed at which welds are performed in the steel erection industry comes at a risk to the integrity of the connection. Without proper fusion to the base materials provided by sufficient arc time on the weld, a project inspector cannot ensure the effective diameter of the puddle weld therefo... | Welding | Wikipedia | 344 | 44883 | https://en.wikipedia.org/wiki/Welding | Technology | Metallurgy | null |
Glass welding is a common practice during glassblowing. It is used very often in the construction of lighting, neon signs, flashtubes, scientific equipment, and the manufacture of dishes and other glassware. It is also used during glass casting for joining the halves of glass molds, making items such as bottles and jar... | Welding | Wikipedia | 408 | 44883 | https://en.wikipedia.org/wiki/Welding | Technology | Metallurgy | null |
There are many types of glass, and it is most common to weld using the same types. Different glasses often have different rates of thermal expansion, which can cause them to crack upon cooling when they contract differently. For instance, quartz has very low thermal expansion, while soda-lime glass has very high therma... | Welding | Wikipedia | 416 | 44883 | https://en.wikipedia.org/wiki/Welding | Technology | Metallurgy | null |
Thermoplastics, by contrast, form long molecular chains, which are often coiled or intertwined, forming an amorphous structure without any long-range, crystalline order. Some thermoplastics may be fully amorphous, while others have a partially crystalline/partially amorphous structure. Both amorphous and semicrystallin... | Welding | Wikipedia | 430 | 44883 | https://en.wikipedia.org/wiki/Welding | Technology | Metallurgy | null |
Many thermoplastics can also be welded using chemical solvents. When placed in contact with the plastic, the solvent will begin to soften it, bringing the surface into a thick, liquid solution. When two melted surfaces are pressed together, the molecules in the solution mix, joining them as one. Because the solvent can... | Welding | Wikipedia | 193 | 44883 | https://en.wikipedia.org/wiki/Welding | Technology | Metallurgy | null |
Asthma is a common long-term inflammatory disease of the airways of the lungs. Asthma occurs when allergens, pollen, dust, or other particles, are inhaled into the lungs, causing the bronchioles to constrict and produce mucus, which then restricts oxygen flow to the alveoli. It is characterized by variable and recurrin... | Asthma | Wikipedia | 489 | 44905 | https://en.wikipedia.org/wiki/Asthma | Biology and health sciences | Illness and injury | null |
Asthma is characterized by recurrent episodes of wheezing, shortness of breath, chest tightness, and coughing. Sputum may be produced from the lung by coughing but is often hard to bring up. During recovery from an asthma attack (exacerbation), the sputum may appear pus-like due to high levels of white blood cells call... | Asthma | Wikipedia | 434 | 44905 | https://en.wikipedia.org/wiki/Asthma | Biology and health sciences | Illness and injury | null |
Many environmental factors have been associated with asthma's development and exacerbation, including allergens, air pollution, and other environmental chemicals. There are some substances that are known to cause asthma in exposed people and they are called asthmagens. Some common asthmagens include ammonia, latex, pes... | Asthma | Wikipedia | 496 | 44905 | https://en.wikipedia.org/wiki/Asthma | Biology and health sciences | Illness and injury | null |
Hygiene hypothesis
The hygiene hypothesis attempts to explain the increased rates of asthma worldwide as a direct and unintended result of reduced exposure, during childhood, to non-pathogenic bacteria and viruses. It has been proposed that the reduced exposure to bacteria and viruses is due, in part, to increased clea... | Asthma | Wikipedia | 453 | 44905 | https://en.wikipedia.org/wiki/Asthma | Biology and health sciences | Illness and injury | null |
Medical conditions
A triad of atopic eczema, allergic rhinitis and asthma is called atopy. The strongest risk factor for developing asthma is a history of atopic disease; with asthma occurring at a much greater rate in those who have either eczema or hay fever. Asthma has been associated with eosinophilic granulomatosi... | Asthma | Wikipedia | 508 | 44905 | https://en.wikipedia.org/wiki/Asthma | Biology and health sciences | Illness and injury | null |
Asthma is the result of chronic inflammation of the conducting zone of the airways (most especially the bronchi and bronchioles), which subsequently results in increased contractability of the surrounding smooth muscles. This among other factors leads to bouts of narrowing of the airway and the classic symptoms of whee... | Asthma | Wikipedia | 405 | 44905 | https://en.wikipedia.org/wiki/Asthma | Biology and health sciences | Illness and injury | null |
Spirometry
Spirometry is recommended to aid in diagnosis and management. It is the single best test for asthma. If the FEV1 measured by this technique improves more than 12% and increases by at least 200 millilitres following administration of a bronchodilator such as salbutamol, this is supportive of the diagnosis. It... | Asthma | Wikipedia | 360 | 44905 | https://en.wikipedia.org/wiki/Asthma | Biology and health sciences | Illness and injury | null |
Asthma is clinically classified according to the frequency of symptoms, forced expiratory volume in one second (FEV1), and peak expiratory flow rate. Asthma may also be classified as atopic (extrinsic) or non-atopic (intrinsic), based on whether symptoms are precipitated by allergens (atopic) or not (non-atopic). While... | Asthma | Wikipedia | 483 | 44905 | https://en.wikipedia.org/wiki/Asthma | Biology and health sciences | Illness and injury | null |
Signs occurring during an asthma attack include the use of accessory muscles of respiration (sternocleidomastoid and scalene muscles of the neck), there may be a paradoxical pulse (a pulse that is weaker during inhalation and stronger during exhalation), and over-inflation of the chest. A blue colour of the skin and na... | Asthma | Wikipedia | 396 | 44905 | https://en.wikipedia.org/wiki/Asthma | Biology and health sciences | Illness and injury | null |
Asthma as a result of (or worsened by) workplace exposures is a commonly reported occupational disease. Many cases, however, are not reported or recognized as such. It is estimated that 5–25% of asthma cases in adults are work-related. A few hundred different agents have been implicated, with the most common being isoc... | Asthma | Wikipedia | 298 | 44905 | https://en.wikipedia.org/wiki/Asthma | Biology and health sciences | Illness and injury | null |
Non-atopic asthma
Non-atopic asthma, also known as intrinsic or non-allergic, makes up between 10 and 33% of cases. There is negative skin test to common inhalant allergens. Often it starts later in life, and women are more commonly affected than men. Usual treatments may not work as well. The concept that "non-atopic... | Asthma | Wikipedia | 471 | 44905 | https://en.wikipedia.org/wiki/Asthma | Biology and health sciences | Illness and injury | null |
Asthma phenotyping and endotyping has emerged as a novel approach to asthma classification inspired by precision medicine which separates the clinical presentations of asthma, or asthma phenotypes, from their underlying causes, or asthma endotypes. The best-supported endotypic distinction is the type 2-high/type 2-low ... | Asthma | Wikipedia | 431 | 44905 | https://en.wikipedia.org/wiki/Asthma | Biology and health sciences | Illness and injury | null |
Prevention
The evidence for the effectiveness of measures to prevent the development of asthma is weak. The World Health Organization recommends decreasing risk factors such as tobacco smoke, air pollution, chemical irritants including perfume, and the number of lower respiratory infections. Other efforts that show pro... | Asthma | Wikipedia | 251 | 44905 | https://en.wikipedia.org/wiki/Asthma | Biology and health sciences | Illness and injury | null |
Management
While there is no cure for asthma, symptoms can typically be improved. The most effective treatment for asthma is identifying triggers, such as cigarette smoke, pets or other allergens, and eliminating exposure to them. If trigger avoidance is insufficient, the use of medication is recommended. Pharmaceutica... | Asthma | Wikipedia | 488 | 44905 | https://en.wikipedia.org/wiki/Asthma | Biology and health sciences | Illness and injury | null |
Improving people's knowledge about asthma and using a written action plan has been identified as an important component of managing asthma. Providing educational sessions that include information specific to a person's culture is likely effective. More research is necessary to determine if increasing preparedness and k... | Asthma | Wikipedia | 460 | 44905 | https://en.wikipedia.org/wiki/Asthma | Biology and health sciences | Illness and injury | null |
Medications
Medications used to treat asthma are divided into two general classes: quick-relief medications used to treat acute symptoms; and long-term control medications used to prevent further exacerbation. Antibiotics are generally not needed for sudden worsening of symptoms or for treating asthma at any time.
Med... | Asthma | Wikipedia | 64 | 44905 | https://en.wikipedia.org/wiki/Asthma | Biology and health sciences | Illness and injury | null |
Short-acting beta2-adrenoceptor agonists (SABAs), such as salbutamol (albuterol USAN) are the first-line treatment for asthma symptoms. They are recommended before exercise in those with exercise-induced symptoms.
Anticholinergic medications, such as ipratropium, provide additional benefit when used in combination wit... | Asthma | Wikipedia | 494 | 44905 | https://en.wikipedia.org/wiki/Asthma | Biology and health sciences | Illness and injury | null |
Corticosteroids are generally considered the most effective treatment available for long-term control. Inhaled forms are usually used except in the case of severe persistent disease, in which oral corticosteroids may be needed. Dosage depends on the severity of symptoms. High dosage and long-term use might lead to the ... | Asthma | Wikipedia | 297 | 44905 | https://en.wikipedia.org/wiki/Asthma | Biology and health sciences | Illness and injury | null |
Leukotriene receptor antagonists (anti-leukotriene agents such as montelukast and zafirlukast) may be used in addition to inhaled corticosteroids, typically also in conjunction with a LABA. For adults or adolescents who have persistent asthma that is not controlled very well, the addition of anti-leukotriene agents al... | Asthma | Wikipedia | 490 | 44905 | https://en.wikipedia.org/wiki/Asthma | Biology and health sciences | Illness and injury | null |
Macrolide antibiotics, particularly the azalide macrolide azithromycin, are a recently added Global Initiative for Asthma (GINA)-recommended treatment option for both eosinophilic and non-eosinophilic severe, refractory asthma based on azithromycin's efficacy in reducing moderate and severe exacerbations combined. Azit... | Asthma | Wikipedia | 286 | 44905 | https://en.wikipedia.org/wiki/Asthma | Biology and health sciences | Illness and injury | null |
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