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and was used by the general Li Jinglong in 1400 against Zhu Di, the future Yongle Emperor. The peak of Chinese cannon development prior to the incorporation of European weaponry in the 16th century is exemplified by the muzzle loading wrought iron "great general cannon" (大將軍炮) which weighed up to 360 kilograms and could fire a 4.8 kilogram lead ball. Its heavier variant, the "great divine cannon" (大神銃), could weigh up to 600 kilograms and was capable of firing several iron balls and upward of a hundred iron shots at once. The great general and divine cannons were the last indigenous Chinese cannon designs prior to the incorporation of European models in the 16th century. The lack of larger siege weapons in China unlike the rest of the world where cannons grew larger and more potent has been attributed to the immense thickness of traditional Chinese walls, which Tonio Andrade suggests provided no incentive for creating larger cannons, since even industrial artillery had trouble overcoming them. Asianist Kenneth Chase also argues that larger guns were not particularly useful against China's traditional enemies: horse nomads. === Big guns === The development of large artillery pieces began by Burgundy. Originally a minor power, the duchy grew to become one of the most powerful states in 14th-century Europe, and a great innovator in siege warfare. The Duke of Burgundy, Philip the Bold (1363–1404), based his power on the effective use of big guns and promoted research and development in all aspects of gunpowder weaponry technology. Philip established manufacturers and employed more cannon casters than any European power before him. Whereas most European guns before 1370 weighed about 20 to 40 lbs (9–14 kg), the French siege of Château de Saint-Sauveur-le-Vicomte in 1375 during the Hundred Years War saw the use of guns weighing
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over a ton (900 kg), firing stone balls weighing over 100 lbs (45 kg). Philip used large guns to help the French capture the fortress of Odruik in 1377. These guns fired projectiles far larger than any that had been used before, with seven guns that could shoot projectiles as heavy as 90 kilograms. The cannons smashed the city walls, inaugurating a new era of artillery warfare and Burgundy's territories rapidly expanded. Europe entered an arms race to build ever larger artillery pieces. By the early 15th century both French and English armies were equipped with larger pieces known as bombards, weighing up to 5 tons (4,535 kg) and firing balls weighing up to 300 lbs (136 kg). The artillery trains used by Henry V of England in the 1415 Siege of Harfleur and 1419 Siege of Rouen proved effective in breaching French fortifications, while artillery contributed to the victories of French forces under Joan of Arc in the Loire Campaign (1429). These weapons were transformational for European warfare. A hundred years earlier the Frenchman Pierre Dubois wrote that a "castle can hardly be taken within a year, and even if it does fall, it means more expenses for the king's purse and for his subjects than the conquest is worth," but by the 15th century European walls fell with the utmost regularity. The Ottoman Empire was also developing their own artillery pieces. Mehmed the Conqueror (1432–1481) was determined to procure large cannons for the purpose of conquering Constantinople. Hungarian Urban produced for him a six-meter (20-foot) long cannon, which required hundreds of pounds of gunpowder to fire; during the actual siege of Constantinople the gun proved to be somewhat underwhelming. However, dozens of other large cannons bombarded Constantinople's walls in their weakest sections for 55 days, and despite a
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fierce defense, the city's fortifications were overwhelmed. ==== Changes to fortifications ==== As a response to gunpowder artillery, European fortifications began displaying architectural principles such as lower and thicker walls in the mid-1400s. Cannon towers were built with artillery rooms where cannons could discharge fire from slits in the walls. However this proved problematic as the slow rate of fire, reverberating concussions, and noxious fumes produced greatly hindered defenders. Gun towers also limited the size and number of cannon placements because the rooms could only be built so big. Notable surviving artillery towers include a seven layer defensive structure built in 1480 at Fougères in Brittany, and a four layer tower built in 1479 at Querfurth in Saxony. The star fort, also known as the bastion fort, tracé à l'italienne, or renaissance fortress, was a style of fortification that became popular in Europe during the 16th century. The bastion and star fort was developed in Italy, where the Florentine engineer Giuliano da Sangallo (1445–1516) compiled a comprehensive defensive plan using the geometric bastion and full tracé à l'italienne that became widespread in Europe. The main distinguishing features of the star fort were its angle bastions, each placed to support their neighbor with lethal crossfire, covering all angles, making them extremely difficult to engage with and attack. Angle bastions consisted of two faces and two flanks. Artillery positions positioned at the flanks could fire parallel into the opposite bastion's line of fire, thus providing two lines of cover fire against an armed assault on the wall, and preventing mining parties from finding refuge. Meanwhile, artillery positioned on the bastion platform could fire frontally from the two faces, also providing overlapping fire with the opposite bastion. Overlapping mutually supporting defensive fire was the greatest advantage enjoyed by the star fort. As a
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result, sieges lasted longer and became more difficult affairs. By the 1530s the bastion fort had become the dominant defensive structure in Italy. Outside Europe, the star fort became an "engine of European expansion", and acted as a force multiplier so that small European garrisons could hold out against numerically superior forces. Wherever star forts were erected the natives experienced great difficulty in uprooting European invaders. In China, Sun Yuanhua advocated for the construction of angled bastion forts in his Xifashenji so that their cannons could better support each other. The officials Han Yun and Han Lin noted that cannons on square forts could not support each side as well as bastion forts. Their efforts to construct bastion forts and their results were inconclusive. Ma Weicheng built two bastion forts in his home county, which helped fend off a Qing incursion in 1638. By 1641, there were ten bastion forts in the county. Before bastion forts could be spread any further, the Ming dynasty fell in 1644, and they were largely forgotten as the Qing dynasty was on the offensive most of the time and had no use for them. === Classical cannon === Gun development and design in Europe reached its "classic" form in the 1480s – longer, lighter, more efficient, and more accurate compared to its predecessors only three decades prior. The design persisted, and cannons of the 1480s show little difference and surprising similarity with cannons three centuries later in the 1750s. This 300-year period during which the classic cannon dominated gives it its moniker. The early classical European guns are exemplified by two cannons from 1488 now preserved in a plaza in Neuchâtel, Switzerland. The Neuchâtel guns are 224 centimeters long, with a bore of 6.2 centimeters and the other is slightly longer, 252 centimeters, with
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the same bore size. They are differentiated from older firearms by an assortment of improvements. Their longer length-to-bore ratio imparts more energy into the shot, enabling the projectile to shoot further. Not only longer, they were also lighter as the barrel walls were made thinner to allow for faster dissipation of heat. They also no longer needed the help of a wooden plug to load since they offered a tighter fit between projectile and barrel, further increasing the accuracy of gunpowder warfare – and were deadlier due to developments such as gunpowder corning and iron shot. When these guns reached China in the 1510s, the Chinese were highly impressed by them, primarily for their longer and thinner barrels. The two primary theories for the appearance of the classic gun involve the development of gunpowder corning and a new method for casting guns. The corning hypothesis stipulates that the longer barrels came about as a reaction to the development of corned gunpowder. Not only did "corned" powder keep better, because of its reduced surface area, but gunners also found that it was more powerful and easier to load into guns. Prior to corning, gunpowder would also frequently demix into its constitutive components and was therefore unreliable. The faster gunpowder reaction was suitable for smaller guns, since large ones had a tendency to crack, and the more controlled reaction allowed large guns to have longer, thinner walls. However, the corning hypothesis has been argued against on two grounds: One, the powder makers were probably more worried about spoilage than the effect of corned gunpowder on guns; and two, corning as a practice had existed in China (for explosives) since the 1370s. The second theory is that the key to developing the classic gun may have been a new method of gun casting,
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muzzle side up. Smith observes: "The surviving pieces of ordnance from earlier in the 15th century are big pieces with large bore sizes. They do not look like the long thin gun.… Essentially they are parallel-sided tubes with flat ends. The explanation is, probably, that they were cast muzzle down in the traditional bell-founding method whereas the long thin guns were cast muzzle up.… Perhaps this marks the real 'revolution' in artillery. Once the technique of casting muzzle up with the attendant advantages, and it is not clear what those are at present, had been mastered by cannon founders, the way was open for the development of the 'classic' form of artillery." However, Smith himself states that it is not clear what advantages this technique would have conferred, despite its widespread adoption. ==== Iron and bronze ==== Across the 15th and 16th centuries there were primarily two different types of manufactured cannons. The wrought iron cannon and the cast-bronze cannon. Wrought iron guns were structurally composed of two layers: an inner tube of iron staves held together in a tight fit by an outer case of iron hoops. Bronze cannons on the other hand were cast in one piece similar to bells. The technique used in casting bronze cannons was so similar to the bell that the two were often looked upon as a connected enterprise. Both iron and bronze cannons had their advantages and disadvantages. Forged iron cannons were up to ten times cheaper, but more unstable due to their piece built nature. Even without use, iron cannons were liable to rust away, while bronze cannons did not. Another reason for the dominance of bronze cannons was their aesthetic appeal. Because cannons were so important as displays of power and prestige, rulers liked to commission bronze cannons, which could
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be sculpted into fanciful designs containing artistic motifs or symbols. It was for all these reasons that the cast-bronze cannon became the preferred type by the late 1400s. Some cannons cast in China during the 1370s may have been of steel rather than iron. ==== Composite metal ==== Composite iron/bronze cannons were far less common, but were produced in substantial numbers during the Ming and Qing dynasties. The resulting bronze-iron composite cannons were superior to iron or bronze cannons in many respects. They were lighter, stronger, longer lasting, and able to withstand more intensive explosive pressure. Chinese artisans also experimented with other variants such as cannons featuring wrought iron cores with cast iron exteriors. While inferior to their bronze-iron counterparts, these were considerably cheaper and more durable than standard iron cannons. Both types were met with success and were considered "among the best in the world" during the 17th century. The Chinese composite metal casting technique was effective enough that Portuguese imperial officials sought to employ Chinese gunsmiths for their cannon foundries in Goa, so that they could impart their methods for Portuguese weapons manufacturing. The Gujarats experimented with the same concept in 1545, the English at least by 1580, and Hollanders in 1629. However the effort required to produce these weapons prevented them from mass production. The Europeans essentially treated them as experimental products, resulting in very few surviving pieces today. Of the currently known extant composite metal cannons, there are 2 English, 2 Dutch, 12 Gujarati, and 48 from the Ming-Qing period. === Arquebus and musket === The arquebus was a firearm that appeared in Europe and the Ottoman Empire in the early 15th century. Its name is derived from the German word Hakenbüchse. Although the term arquebus was applied to many different forms of firearms from the
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15th to 17th centuries, it was originally used to describe "a hand-gun with a hook-like projection or lug on its under surface, useful for steadying it against battlements or other objects when firing." These "hook guns" were in their earliest forms defensive weapons mounted on German city walls in the early 1400s, but by the late 1400s had transitioned into handheld firearms, with heavier variants known as "muskets" that were fired from resting Y-shaped supports appearing by the early 1500s. The musket was able to penetrate all forms of armor available at the time, making armor obsolete, and as a consequence the heavy musket as well. Although there is relatively little to no difference in design between arquebus and musket except in size and strength, it was the term musket which remained in use up into the 1800s. It may not be completely inaccurate to suggest that the musket was in its fabrication simply a larger arquebus. At least on one occasion the musket and arquebus have been used interchangeably to refer to the same weapon, and even referred to as an "arquebus musket." A Habsburg commander in the mid-1560s once referred to muskets as "double arquebuses." The definition of arquebus and similar firearms is therefore quite convoluted as the term has been applied to different sorts of firearms as well as acquiring several names like hackbut, harquebus, schiopo, sclopus, tüfenk, tofak, matchlock, and firelock. Some say that the hackbut was a forerunner of the arquebus. The dating of the matchlock firing mechanism's first appearance is disputed. The first references to the use of what may have been arquebuses (tüfek) by the Janissary corps of the Ottoman army date them from 1394 to 1465. However it's unclear whether these were arquebuses or small cannons as late as 1444, but the
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fact that they were listed separate from cannons in mid-15th century inventories suggest they were handheld firearms. In Europe, a shoulder stock, probably inspired by the crossbow stock, was added to the arquebus around 1470 and the appearance of the matchlock mechanism is dated to a little before 1475. The matchlock arquebus was the first firearm equipped with a trigger mechanism. It is also considered to be the first portable shoulder-arms firearm. Matchlock became a common term for the arquebus after it was added to the firearm. Prior to the appearance of the matchlock, handguns were fired from the chest, tucked under one arm, while the other arm maneuvered a hot pricker to the touch hole to ignite the gunpowder. The matchlock changed this by adding a firing mechanism consisting of two parts, the match, and the lock. The lock mechanism held within a clamp a two to three feet long length of smoldering rope soaked in saltpeter, which was the match. Connected to the lock lever was a trigger, which lowered the match into a priming pan when pulled, igniting the priming powder, causing a flash to travel through the touch hole, also igniting the gunpowder within the barrel, and propelling the bullet out the muzzle. While matchlocks provided a crucial advantage by allowing the user to aim the firearm using both hands, it was also awkward to use. To avoid accidentally igniting the gunpowder the match had to be detached while loading the gun. In some instances the match would also go out, so both ends of the match were kept lit. This proved cumbersome to maneuver as both hands were required to hold the match during removal, one end in each hand. The procedure was so complex that a 1607 drill manual published by Jacob de Gheyn
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in the Netherlands listed 28 steps just to fire and load the gun. In 1584 the Ming general Qi Jiguang composed an 11 step song to practice the procedure in rhythm: "One, clean the gun. Two pour the powder. Three tamp the powder down. Four drop the pellet. Five drive the pellet down. Six put in paper (stopper). Seven drive the paper down. Eight open the flashpan cover. Nine pour in the flash powder. Ten close the flashpan, and clamp the fuse. Eleven, listen for the signal, then open the flashpan cover. Aiming at the enemy, raise your gun and fire." Reloading a gun during the 16th century took anywhere from between 20 seconds to a minute under the most ideal conditions. The arquebus is considered to be the first portable "shoulder" arms firearm. Arquebuses were used as early as 1472 by the Spanish and Portuguese at Zamora. Likewise, the Castilians used arquebuses as well in 1476. In 1496 Philip Monch of the Palatinate composed an illustrated Buch der Strynt un(d) Buchsse(n) on guns and "harquebuses." The Mamluks in particular were conservatively against the incorporation of gunpowder weapons. When faced with cannons and arquebuses wielded by the Ottomans they criticized them thus, "God curse the man who invented them, and God curse the man who fires on Muslims with them." Insults were also levied against the Ottomans for having "brought with you this contrivance artfully devised by the Christians of Europe when they were incapable of meeting the Muslim armies on the battlefield." Similarly, musketeers and musket-wielding infantrymen were despised in society by the feudal knights, even until the time of Don Quixote author Miguel de Cervantes (1547–1616). Eventually the Mamluks under Qaitbay were ordered in 1489 to train in the use of al-bunduq al-rasas (arquebuses). However, in 1514 an
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Ottoman army of 12,000 soldiers wielding arquebuses still managed to rout a much larger Mamluk force. The arquebus had become a common infantry weapon by the 16th century due to its relative cheapness – a helmet, breastplate and pike cost about three and a quarter ducats while an arquebus only a little over one ducat. Another advantage of arquebuses over other equipment and weapons was its short training period. While a bow potentially took years to master, an effective arquebusier could be trained in just two weeks. According to a 1571 report by Vincentio d'Alessandri, Persian arms including arquebuses "were superior and better tempered than those of any other nation." In the early 1500s a larger arquebus known as the musket appeared. The heavy musket, while being rather awkward to handle, requiring a fork rest to fire properly, had the advantage of being able to penetrate the best armor within a range of 180 meters, regular armor at 365 meters, and an unarmed man at 548 meters. However, both the musket and arquebus were effectively limited to a range of only 90 to 185 meters regardless of armor since they were incredibly inaccurate. According to some sources, a smoothbore musket was completely incapable of hitting a man sized target past the 73-meter mark. While rifled guns did exist at this time in the form of grooves cut into the interior of a barrel, these were considered specialist weapons and limited in number. In some aspects this made the smoothbore musket an inferior weapon compared to the bow. The average Mamluk archer for example was capable of hitting targets only 68 meters far away but could keep up a pace of six to eight shots per minute. In comparison, sixteenth-century matchlocks fired off one shot every several minutes, and much less
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when taking into consideration misfires and malfunctions which occurred up to half the time. This is not to say that firearms of the 16th century were inferior to the bow and arrow, for it could better penetrate armor and required less training, but the disadvantages of the musket were very real, and it would not be until the 1590s that archers were for the most part phased out of European warfare. This was possibly a consequence of the increased effectiveness of musket warfare due to the rise of volley fire in Europe as first applied by the Dutch. At this time gunners in European armies reached as high as 40 percent of infantry forces. As the virtues of the musket became apparent it was quickly adopted throughout Eurasia so that by 1560 even in China generals were giving praise to the new weapon. Qi Jiguang, a noted partisan of the musket, gave a eulogy on the effectiveness of the gun in 1560: It is unlike any other of the many types of fire weapons. In strength it can pierce armor. In accuracy it can strike the center of targets, even to the point of hitting the eye of a coin [i.e., shooting right through a coin], and not just for exceptional shooters.… The arquebus [鳥銃] is such a powerful weapon and is so accurate that even bow and arrow cannot match it, and … nothing is so strong as to be able to defend against it. Other East Asian powers such as Đại Việt also adopted the matchlock musket in quick order. Đại Việt in particular was considered by the Ming to have produced the most advanced matchlocks in the world during the 17th century, surpassing even Ottoman, Japanese, and European firearms. European observers of the Trịnh–Nguyễn War also corroborated
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with the Ming in the proficiency of matchlock making by the Vietnamese. The Vietnamese matchlock was said to have been able to pierce several layers of iron armour, kill two to five men in one shot, yet also fire quietly for a weapon of its caliber. == Gunpowder Empires == The Gunpowder Empires generally refer to the Islamic Ottoman, Safavid and Mughal empires. The phrase was first coined by Marshall Hodgson in the title of Book 5 ("The Second Flowering: The Empires of Gunpowder Times") of his highly influential three-volume work, The Venture of Islam (1974). Hogdson applied the term "gunpowder empire" to three Islamic political entities he identified as separate from the unstable, geographically limited confederations of Turkic clans that prevailed in post-Mongol times. He called them "military patronage states of the Later Middle Period," which possessed three defining characteristics: first, a legitimization of independent dynastic law; second, the conception of the whole state as a single military force; third, the attempt to explain all economic and high cultural resources as appanages of the chief military families. Connecting these empires were their traditions which grew "out of Mongol notions of greatness," but "[s]uch notions could fully mature and create stable bureaucratic empires only after gunpowder weapons and their specialized technology attained a primary place in military life." William H. McNeill further expanded on the concept of gunpowder empires by arguing that such states "were able to monopolize the new artillery, central authorities were able to unite larger territories into new, or newly consolidated, empires." In 2011 Douglas E. Streusand criticized the Hodgson-McNeill Gunpowder-Empire hypothesis, calling it into disfavor as a neither "adequate [n]or accurate" explanation, although the term remains in use. The main problem he saw with the Hodgson-McNeill theory is that the acquisition of firearms does not seem
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to have preceded the initial acquisition of territory constituting the imperial critical mass of any of the three early modern Islamic empires, except in the case of the Mughals. Moreover, it seems that the commitment to military autocratic rule pre-dated the acquisition of gunpowder weapons in all three cases. Whether or not gunpowder was inherently linked to the existence of any of these three empires, it cannot be questioned that each of the three acquired artillery and firearms early in their history and made such weapons an integral part of their military tactics. === Ottoman Empire === It's not certain when the Ottomans started using firearms, however it's argued that they had been using cannons since the Battles of Kosovo (1389) and Nukap (1396) and most certainly by the 1420s. Some argue that field guns only entered service shortly after the Battle of Varna (1444) and more certainly used in the Second Battle of Kosovo (1448). Firearms, (especially grenades) were used in the 1683 siege of Vienna The arquebus reached them around 1425. === India and the Mughal Empire === In India, guns made of bronze were recovered from Calicut (1504) and Diu (1533). By the 17th century, Indians were manufacturing a diverse variety of firearms; large guns in particular, became visible in Tanjore, Dacca, Bijapur and Murshidabad. Gujarāt supplied Europe saltpeter for use in gunpowder warfare during the 17th century. Bengal and Mālwa participated in saltpeter production. The Dutch, French, Portuguese, and English used Chāpra as a center of saltpeter refining. Fathullah Shirazi (c. 1582), who worked for Akbar the Great as a mechanical engineer, developed an early multi gun shot. Shirazi's rapid-firing gun had multiple gun barrels that fired hand cannons loaded with gunpowder. Mysorean rockets were an Indian military weapon, the first iron-cased rockets successfully deployed for
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military use. The Mysorean army, under Hyder Ali and his son Tipu Sultan, used the rockets effectively against the British East India Company during the 1780s and 1790s. The Indian war rockets were formidable weapons before such rockets were used in Europe. They had bam-boo rods, a rocket-body lashed to the rod, and iron points. They were directed at the target and fired by lighting the fuse, but the trajectory was rather erratic. The use of mines and counter-mines with explosive charges of gunpowder is mentioned for the times of Akbar and Jahāngir. == Civil engineering == === Canals === Gunpowder was used for hydraulic engineering in China by 1541. Gunpowder blasting followed by dredging of the detritus was a technique which Chen Mu employed to improve the Grand Canal at the waterway where it crossed the Yellow River. In Europe, gunpowder was used in the construction of the Canal du Midi in Southern France. It was completed in 1681 and linked the Mediterranean sea with the Atlantic with 240 km of canal and 100 locks. Another noteworthy consumer of black powder was the Erie Canal in New York, which was 585 km long and took eight years to complete, starting in 1817. === Mining === Before gunpowder was applied to civil engineering, there were two ways to break up large rocks, by hard labor or by heating with large fires followed by rapid quenching. The earliest record for the use of gunpowder in mines comes from Hungary in 1627. It was introduced to Britain in 1638 by German miners, after which records are numerous. Until the invention of the safety fuse by William Bickford in 1831, the practice was extremely dangerous. Another reason for danger were the dense fumes given off and the risk of igniting flammable gas when
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used in coal mines. === Tunnel construction === Gunpowder was also extensively used in railway construction. At first railways followed the contours of the land, or crossed low ground by means of bridges and viaducts, but later railways made extensive use of cuttings and tunnels. One 2400-ft stretch of the 5.4 mi Box Tunnel on the Great Western Railway line between London and Bristol consumed a ton of gunpowder per week for over two years. The 12.9 km long Mont Cenis Tunnel was completed in 13 years starting in 1857 but, even with black powder, progress was only 25 cm a day until the invention of pneumatic drills sped up the work. == United States == === Revolutionary War === During the American Revolutionary War, a number of caves were mined for saltpeter to make gunpowder when supplies from Europe were embargoed. Abigail Adams reputedly also made gunpowder at her family farm in Massachusetts. The New York Committee of Safety produced some essays on making gunpowder that were printed in 1776. === Civil War === During the American Civil War, British India was the main source for saltpeter for the manufacture of gunpowder for the Union armies. This supply was threatened by the British government during the Trent Affair, when Union naval forces stopped a British ship, the RMS Trent, and removed two Confederate diplomats. The British government responded in part by halting all exports of saltpeter to the United States, threatening their gunpowder manufacturing resources. Shortly thereafter, the situation was resolved and the Confederate diplomats were released. The Union Navy blockaded the southern Confederate States, which reduced the amount of gunpowder that could be imported from overseas. The Confederate Nitre and Mining Bureau was formed to produce gunpowder for the army and the navy from domestic resources. Nitre is
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the English spelling of "Niter". While carbon and sulfur were readily available throughout the south, potassium nitrate was often produced from the Calcium nitrate found in cave dirt, tobacco barn floors and barn stalls other places. A number of caves were mined, and the men and boys who worked in the caves were called "peter monkey", somewhat in imitation of the naval term "powder monkey" that was used for the boys who brought up charges of gunpowder on gunboats. On 13 November 1862, the Confederate government advertised in the Charleston Daily Courier for 20 or 30 "able bodied Negro men" to work in the new nitre beds at Ashley Ferry, S.C. The nitre beds were large rectangles of rotted manure and straw, moistened weekly with urine, "dung water", and liquid from privies, cesspools and drains, and turned over regularly. The process was designed to yield saltpeter, an ingredient of gunpowder, which the Confederate army needed during the Civil War. The South was so desperate for saltpeter for gunpowder that one Alabama official reportedly placed a newspaper ad asking that the contents of chamber pots be saved for collection. In the winter of 1863, scores of enslaved people were set to work extracting it from a huge cave in Barstow County, Ga., where they labored by torchlight in grim conditions, hauling out and processing the so-called "peter dirt",. In South Carolina, in April 1864, the Confederate government hired 31 enslaved people to work at the Ashley Ferry Nitre Works. == Decline == The latter half of the 19th century saw the invention of nitroglycerin, nitrocellulose and smokeless powders which soon replaced traditional gunpowder in most civil and military applications. == See also == == Notes == == References == Adle, Chahryar (2003), History of Civilizations of Central Asia: Development in Contrast:
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from the Sixteenth to the Mid-Nineteenth Century Ágoston, Gábor (2005), Guns for the Sultan: Military Power and the Weapons Industry in the Ottoman Empire, Cambridge University Press, ISBN 978-0-521-60391-1 Agrawal, Jai Prakash (2010), High Energy Materials: Propellants, Explosives and Pyrotechnics, Wiley-VCH Andrade, Tonio (2016), The Gunpowder Age: China, Military Innovation, and the Rise of the West in World History, Princeton University Press, ISBN 978-0-691-13597-7. Arnold, Thomas (2001), History of Warfare: The Renaissance at War koichIro, Thomas (2001), The Renaissance at War, Cassell & Co, ISBN 978-0-304-35270-8 Benton, Captain James G. (1862). A Course of Instruction in Ordnance and Gunnery (2nd ed.). West Point, New York: Thomas Publications. ISBN 978-1-57747-079-3. {{cite book}}: ISBN / Date incompatibility (help) Breverton, Terry (2012), Breverton's Encyclopedia of Inventions Brown, G. I. (1998), The Big Bang: A History of Explosives, Sutton Publishing, ISBN 978-0-7509-1878-7. Buchanan, Brenda J. (2006), "Gunpowder, Explosives and the State: A Technological History", Technology and Culture, 49 (3), Aldershot: Ashgate: 785–86, doi:10.1353/tech.0.0051, ISBN 978-0-7546-5259-5, S2CID 111173101 Chase, Kenneth (2003), Firearms: A Global History to 1700, Cambridge University Press, ISBN 978-0-521-82274-9. Cocroft, Wayne (2000), Dangerous Energy: The archaeology of gunpowder and military explosives manufacture, Swindon: English Heritage, ISBN 978-1-85074-718-5 Cook, Haruko Taya (2000), Japan at War: An Oral History, Phoenix Press Cowley, Robert (1993), Experience of War, Laurel. Cressy, David (2013), Saltpeter: The Mother of Gunpowder, Oxford University Press Crosby, Alfred W. (2002), Throwing Fire: Projectile Technology Through History, Cambridge University Press, ISBN 978-0-521-79158-8. Curtis, W. S. (2014), Long Range Shooting: A Historical Perspective, WeldenOwen. Earl, Brian (1978), Cornish Explosives, Cornwall: The Trevithick Society, ISBN 978-0-904040-13-5. Easton, S. C. (1952), Roger Bacon and His Search for a Universal Science: A Reconsideration of the Life and Work of Roger Bacon in the Light of His Own Stated Purposes, Basil Blackwell Ebrey, Patricia B. (1999), The
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{
"page_id": 12063194,
"source": null,
"title": "History of gunpowder"
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|
Cambridge Illustrated History of China, Cambridge University Press, ISBN 978-0-521-43519-2 Grant, R.G. (2011), Battle at Sea: 3,000 Years of Naval Warfare, DK Publishing. Hadden, R. Lee. 2005. "Confederate Boys and Peter Monkeys." Armchair General. January 2005. Adapted from a talk given to the Geological Society of America on 25 March 2004. Haines, Spencer (2017). "The 'Military Revolution' Arrives on the Central Eurasian Steppe: The Unique Case of the Zunghar (1676–1745)". Mongolica: An International Journal of Mongolian Studies. 51. International Association of Mongolists: 170–185. Harding, Richard (1999), Seapower and Naval Warfare, 1650–1830, UCL Press Limited Smee, Harry (2020), Gunpowder and Glory Haw, Stephen G. (2013), Cathayan Arrows and Meteors: The Origins of Chinese Rocketry al-Hassan, Ahmad Y. (2001), "Potassium Nitrate in Arabic and Latin Sources", History of Science and Technology in Islam, archived from the original on 2019-05-20, retrieved 2007-07-23. Hobson, John M. (2004), The Eastern Origins of Western Civilisation, Cambridge University Press. Johnson, Norman Gardner. "explosive". Encyclopædia Britannica. Chicago. Kelly, Jack (2004), Gunpowder: Alchemy, Bombards, & Pyrotechnics: The History of the Explosive that Changed the World, Basic Books, ISBN 978-0-465-03718-6. Khan, Iqtidar Alam (1996), "Coming of Gunpowder to the Islamic World and North India: Spotlight on the Role of the Mongols", Journal of Asian History, 30: 41–45. Khan, Iqtidar Alam (2004), Gunpowder and Firearms: Warfare in Medieval India, Oxford University Press Khan, Iqtidar Alam (2008), Historical Dictionary of Medieval India, The Scarecrow Press, Inc., ISBN 978-0-8108-5503-8 Kinard, Jeff (2007), Artillery An Illustrated History of its Impact Konstam, Angus (2002), Renaissance War Galley 1470-1590, Osprey Publisher Ltd.. Liang, Jieming (2006), Chinese Siege Warfare: Mechanical Artillery & Siege Weapons of Antiquity, Singapore, Republic of Singapore: Leong Kit Meng, ISBN 978-981-05-5380-7 Lidin, Olaf G. (2002), Tanegashima – The Arrival of Europe in Japan, Nordic Inst of Asian Studies, ISBN 978-8791114120 Lorge, Peter (2005),
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{
"page_id": 12063194,
"source": null,
"title": "History of gunpowder"
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|
Warfare in China to 1600, Routledge Lorge, Peter A. (2008), The Asian Military Revolution: from Gunpowder to the Bomb, Cambridge University Press, ISBN 978-0-521-60954-8 Lu, Gwei-Djen (1988), "The Oldest Representation of a Bombard", Technology and Culture, 29 (3): 594–605, doi:10.2307/3105275, JSTOR 3105275, S2CID 112733319 Lu, Yongxiang (2015), A History of Chinese Science and Technology 2 May, Timothy (2012), The Mongol Conquests in World History, Reaktion Books McLahlan, Sean (2010), Medieval Handgonnes McNeill, William Hardy (1992), The Rise of the West: A History of the Human Community, University of Chicago Press. Morillo, Stephen (2008), War in World History: Society, Technology, and War from Ancient Times to the Present, Volume 1, To 1500, McGraw-Hill, ISBN 978-0-07-052584-9 Needham, Joseph (1971), Science and Civilization in China, Volume 4 Part 3, Cambridge University Press Needham, Joseph (1976), Science and Civilization in China, Volume 5 Part 3, Cambridge University Press Needham, Joseph (1980), Science & Civilisation in China, Volume 5 Part 4, Cambridge University Press, ISBN 978-0-521-08573-1 Needham, Joseph (1986), Science & Civilisation in China, Volume 5 Part 7: The Gunpowder Epic, Cambridge University Press, ISBN 978-0-521-30358-3 Nicolle, David (1990), The Mongol Warlords: Genghis Khan, Kublai Khan, Hulegu, Tamerlane Nicolle, David (1983), Armies of the Ottoman Turks 1300-1774 Nolan, Cathal J. (2006), The Age of Wars of Religion, 1000–1650: an Encyclopedia of Global Warfare and Civilization, Vol 1, A-K, vol. 1, Westport & London: Greenwood Press, ISBN 978-0-313-33733-8 Norris, John (2003), Early Gunpowder Artillery: 1300–1600, Marlborough: The Crowood Press. Padmanabhan, Thanu (2019), The Dawn of Science: Glimpses from History for the Curious Mind, Bibcode:2019dsgh.book.....P Partington, J. R. (1960), A History of Greek Fire and Gunpowder, Cambridge, UK: W. Heffer & Sons. Partington, J. R. (1999), A History of Greek Fire and Gunpowder, Baltimore: Johns Hopkins University Press, ISBN 978-0-8018-5954-0 Patrick, John Merton (1961), Artillery and warfare
|
{
"page_id": 12063194,
"source": null,
"title": "History of gunpowder"
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|
during the thirteenth and fourteenth centuries, Utah State University Press. Pauly, Roger (2004), Firearms: The Life Story of a Technology, Greenwood Publishing Group. Perrin, Noel (1979), Giving up the Gun, Japan's reversion to the Sword, 1543–1879, Boston: David R. Godine, ISBN 978-0-87923-773-8 Petzal, David E. (2014), The Total Gun Manual (Canadian edition), WeldonOwen. Phillips, Henry Prataps (2016), The History and Chronology of Gunpowder and Gunpowder Weapons (c.1000 to 1850), Notion Press Pregadio, Fabrizio (2011), The Seal of the Unity of the Three Purton, Peter (2009), A History of the Early Medieval Siege c. 450–1200, The Boydell Press Purton, Peter (2010), A History of the Late Medieval Siege, 1200–1500, Boydell Press, ISBN 978-1-84383-449-6 Robins, Benjamin (1742), New Principles of Gunnery Romane, Julian (2020), The First & Second Italian Wars 1494-1504 Rose, Susan (2002), Medieval Naval Warfare 1000–1500, Routledge Roy, Kaushik (2015), Warfare in Pre-British India, Routledge Sasaki, Randall J. (2015). The Origins of the Lost Fleet of the Mongol Empire. Schmidtchen, Volker (1977a), "Riesengeschütze des 15. Jahrhunderts. Technische Höchstleistungen ihrer Zeit", Technikgeschichte 44 (2): 153–173 (153–157) Schmidtchen, Volker (1977b), "Riesengeschütze des 15. Jahrhunderts. Technische Höchstleistungen ihrer Zeit", Technikgeschichte 44 (3): 213–237 (226–228) Tran, Nhung Tuyet (2006), Viêt Nam Borderless Histories, University of Wisconsin Press. Turnbull, Stephen (2003), Fighting Ships Far East (2: Japan and Korea AD 612–1639, Osprey Publishing, ISBN 978-1-84176-478-8 Urbanski, Tadeusz (1967), Chemistry and Technology of Explosives, vol. III, New York: Pergamon Press. Villalon, L. J. Andrew (2008), The Hundred Years War (part II): Different Vistas, Brill Academic Pub, ISBN 978-90-04-16821-3 Wagner, John A. (2006), The Encyclopedia of the Hundred Years War, Westport & London: Greenwood Press, ISBN 978-0-313-32736-0 Watson, Peter (2006), Ideas: A History of Thought and Invention, from Fire to Freud, Harper Perennial (2006), ISBN 978-0-06-093564-1 Wilkinson, Philip (9 September 1997), Castles, Dorling Kindersley, ISBN 978-0-7894-2047-3 Wilkinson-Latham,
|
{
"page_id": 12063194,
"source": null,
"title": "History of gunpowder"
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|
Robert (1975), Napoleon's Artillery, France: Osprey Publishing, ISBN 978-0-85045-247-1 Willbanks, James H. (2004), Machine guns: an illustrated history of their impact, ABC-CLIO, Inc. Williams, Anthony G. (2000), Rapid Fire, Shrewsbury: Airlife Publishing Ltd., ISBN 978-1-84037-435-3 Kouichiro, Hamada (2012), 日本人はこうして戦争をしてきた Tatsusaburo, Hayashiya (2005), 日本の歴史12 - 天下一統 == External links == "A Guide to Geometry, Surveying, the Launching of Missiles, and the Planting of Mines" from 1791, in Arabic, discusses the storing of gunpowder and related subjects in the 18th-century Muslim world.
|
{
"page_id": 12063194,
"source": null,
"title": "History of gunpowder"
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The molecular formula C24H46O4 (molar mass: 398.62 g/mol, exact mass: 398.3396 u) may refer to: Nebraskanic acid Dilauroyl peroxide
|
{
"page_id": 60363228,
"source": null,
"title": "C24H46O4"
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A land lab is an area of land that has been set aside for use in biological studies. Thus, it is literally an outdoor laboratory based on an area of land. Studies may be elementary or advanced. For instance, students may simply be given the task of identifying all the tree species in a land lab, or an advanced student may be doing an intensive survey of the microbial life forms found in a soil sample. Hands on, tangible, project-base learning is a key aspect of land labs within an educational context. Land labs can exist anywhere with outdoor access: educational campuses, residential neighborhoods, peri-urban settings, urban settings, or even a small courtyard. The driving principle behind land lab education is getting outside and interacting with the world directly. Land labs are often marked out in plots or transects for studies. A plot may be any size, usually marked out in square meters. This allows for more intensive, delimited studies of changes and inventories of biota. Transects are straight lines at which, at intervals, measurements are taken for a profile of the ecological community. Land labs serve an important role in giving students access to a natural environment to observe native plants and wildlife, apply STEM concepts with hands on projects, and build a better understanding of how critical biodiversity is for ecological health. == Common educational projects conducted at a land lab often include == Surveying pollinator species in pollinator gardens or in the native flora Restoring old agricultural land back to original landscapes such as: wetlands, prairie, or forest Composting biomass to rebuild healthy soil Maintaining beehives or other pollinator habitats for moths, ground bees, and other pollinators Recording weather conditions to better understand the microclimate Conducting nature studies to identify and observe local flora and fauna Planting
|
{
"page_id": 70111,
"source": null,
"title": "Land lab"
}
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native trees, grasses, and flowers to increase biodiversity Encouraging native riparian plant growth along ponds and streams Installing bird houses, bat houses and owl houses Holding art classes where students can paint flora, fauna and landscapes Collecting and removing trash and other man-made pollutants Designing low-impact trails and paths for visitors to explore the land lab == Studying humans needs and sustainability in land labs == Learning to produce food, fiber and energy in sustainable ways is a tremendous opportunity for students of all ages within land labs. Students can explore biomass energy, biogas fuels, solar energy, permaculture, composting, organic gardening, and many other facets of sustainability through land labs. By designing systems that mimic natural processes (biomimicry), we are able to produce food, fiber, and energy in more sustainable ways for local communities. Numerous environmental and economic benefits exist to growing food locally and producing energy locally. These biomimicry inspired systems are circular in nature. Nothing is wasted, as the outputs of one circular system become the inputs of another. == Circular systems in land labs == Circular system experiments, promoting a circular economy, are a natural fit for educational land labs. Circular systems function by ensuring that nothing is wasted. Every output of a system becomes an input for another system. For example: Food scraps feed chickens, chicken manure fertilizes the garden, the garden grows more vegetables, food scraps are then available from the vegetables to feed chickens. Circular systems that are well-suited for land labs include: Biogas methane digesters for generating clean cooking fuel and liquid fertilizer for gardens Composting rollers for composting leaves, grass clippings, & food scraps Raising black soldier fly larvae on food waste to become feed for chickens or fish Solar panels for providing on-site power Free range chickens for providing eggs and
|
{
"page_id": 70111,
"source": null,
"title": "Land lab"
}
|
manure Greenhouses for growing mushrooms and seedlings Raised beds for market garden vegetables Beehives for garden pollination, honey, and wax Rotationally grazed pastures for goats, cattle, pigs, sheep, etc Biochar production to improve soil quality and sequester carbon Aquaponics systems for growing fish and greens symbiotically Rainwater collection systems for retaining water for gardens == Multi-disciplinary environment within land labs == Land labs help to form an ecosystem well suited for long-term project-based learning. Students, teachers, and community members can participate in multi-disciplinary activities ranging from land restoration, animal husbandry, gardening, weather analysis to outdoor art studies. The multi-disciplinary context within a land lab is perfect for cross-curricular education. The following disciplines and subjects can all tie into land lab activities in an integrated fashion: Ecology - nature studies, increasing biodiversity, studying water cycle Biology - gardening, agriscience projects, botany Sustainable Agriculture - composting, permaculture, local food movement Engineering - building aquaponics, rainwater collection, animal shelters Chemistry - methane digesters, plant fertilization, solar power Life Sciences - carbon cycle, water cycle, composting biomass Animal Husbandry - free range chickens, goats, apiary Climate Studies - weather observation, weather logging History & Culture Studies - local food culture, history of agriculture, natural resources Culinary Arts - cooking garden produce using clean energy like biomass, biogas, or solar power Multi media arts - designing pollinator landscapes, bird houses, bat houses, murals Painting - nature studies, murals Pottery - watering pots, plant pots Wood working - pollinator houses, chicken coop == Goals and outcomes of land lab education experiences == Land labs exist as perpetual educational projects that can span years to decades or more. Common goals within a land lab are often: Restoring degraded land back into a balanced, biodiverse state Establishing an environment for native flora and fauna to thrive Building deep,
|
{
"page_id": 70111,
"source": null,
"title": "Land lab"
}
|
rich soil with an active microbiome Growing local produce, herbs, and flowers Raising livestock with sustainable, ethical methods Producing healthy food for local communities Producing local energy to power the land lab operations Inspiring young people to care about biodiversity, agriculture, and nature Building real-life, practical STEM skills for students and adults Building strong communities around unique outdoor projects in nature Educating people about the benefits and simple joys found in gardening == Footprints and Sizes of Land Labs == Land labs can be designed in all shapes and sizes. The key attributes of a land lab are typically the following: Building an outdoor learning area designated for cross-curricular studies in a STEM environment Establishing a focus on increasing biodiversity and restoring local environmental features Educating people about meeting humans needs sustainably through agriculture, energy production, shelter, and sanitation A small land lab could be as little as a courtyard, balcony garden, or a designated patch of land outside of a classroom window. Conversely, larger land lab could encompass hundreds of acres. The ideal size for a flexible land lab space allowing for many different ecological activities and circular systems is between 1/4 of an acre to 5 acres. == Sustainable societal solutions originating from land labs == Land labs are real-life environments by design. The project-based environment encourages students, teachers, and community members to experiment with ecological solutions that can be implemented on a small scale. Ideally, the solutions and systems implemented in a land lab are transferred beyond the land lab and into the surrounding community. Composting, rainwater catchment, food-waste upcycling with methane digesters and BSF, local food production, harnessing of solar power, and other land lab systems can all be implemented throughout a community at various scales: residential, schools, community gardens, and local businesses. The purpose of
|
{
"page_id": 70111,
"source": null,
"title": "Land lab"
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|
a land lab is to allow students to develop, implement, and learn about practical, sustainable solutions for addressing the five basic physiological needs all humans have: The need for clean water The need for healthy food The need for shelter The need for energy The need for sanitation Our industrial systems of providing food, water, energy, shelter, and sanitation have inherent weaknesses to their centralized models. Long supply chains, fossil-fuel dependance, environmental damage, and the fragmented production of goods are common traits to industrial models. Land labs tie these 5 basic human needs together in integrated systems. Permaculture is a concept of integrating these human needs into local, ecological, human-scale systems. Land labs can be thought of as an education area for promoting creative solutions for meeting these needs, while ensuring the land and local ecology are being restored in the process. Land labs provide students with real-world experiences to help change their behavior as consumers, and get them more involved with meeting their 5 physiological needs. Land labs are focused on production rather than just consumption. Western consumer culture makes the provision of our 5 basic physiological needs very abstract and far removed from the daily life of most people. When these 5 basic needs are abstracted away from consumers, it is easier for the underlying systems providing these needs to operate without supervision to ensure they are ethical and sustainable. == Mental health benefits for students being outside == In today's digital world, many students spend inordinate amounts of time on a screen both at home and at school. Inherent limits exist to project based learning that takes place entirely behind a screen or within a classroom. Land labs help break students out of a digital environment by providing much needed time outdoors. Studies have shown that as
|
{
"page_id": 70111,
"source": null,
"title": "Land lab"
}
|
our digital landscape of social media has exploded in popularity, depression and mental struggles have increased dramatically in students. Studies also show that student's mental health benefits immensely from being outdoors and participating in hands on projects with meaningful outcomes. == Waste streams used in land labs == Multiple types of local "waste" streams, that can often be obtained freely, can be used to supply a land lab with the raw materials to build soil, generate power, grow food, and restore biodiversity. Woodchips - Used for garden paths, mulch, composting & biochar. Often available from local tree companies or municipalities for free. Grass clippings - Used for compost and mulch. Available from neighbors and onsite. Leaves - Used for compost and mulch. Available from neighbors and onsite. Food waste - Used for composting, methane production, liquid fertilizer, and feeding BSF. Coffee grounds - Used for composting and BSF production. Pallets (Non-treated) - Used for making raised beds, biochar, composting bins, and other structures. IBC totes (Food grade) - Used for storing rainwater and liquid fertilizer. 5 Gallon Buckets - Used for collecting food waste, and other waste streams. Shredded paper - Used for composting. Shredded cardboard - Used for composting. Newspapers - Used for composting and mulching. Logs - Used for pollinator habitats. Freely availably from many tree companies. Reclaimed lumber (non treated) - Used for raised beds, biochar, and small building projects. Billboard tarps - Used for rainwater catchment, roofing, and shade cloths. Freely available from billboard companies. Part of the process of building a land lab is developing relationships with local businesses, neighbors, restaurants, and community members to begin upcycling these wastes into the materials and systems needed within a land lab. Many people have a desire to help students who are working hard on a meaningful community
|
{
"page_id": 70111,
"source": null,
"title": "Land lab"
}
|
project. Much of the materials listed above can be had for little to no cost as relationships are formed. == References ==
|
{
"page_id": 70111,
"source": null,
"title": "Land lab"
}
|
Methyl salicylate (oil of wintergreen or wintergreen oil) is an organic compound with the formula C8H8O3. It is the methyl ester of salicylic acid. It is a colorless, viscous liquid with a sweet, fruity odor reminiscent of root beer (in which it is used as a flavoring), but often associatively called "minty", as it is an ingredient in mint candies. It is produced by many species of plants, particularly wintergreens. It is also produced synthetically, used as a fragrance and as a flavoring agent. == Biosynthesis and occurrence == Methyl salicylate was first isolated (from the plant Gaultheria procumbens) in 1843 by the French chemist Auguste André Thomas Cahours (1813–1891), who identified it as an ester of salicylic acid and methanol. The biosynthesis of methyl salicylate arises via the hydroxylation of benzoic acid by a cytochrome P450 followed by reaction with a methyltransferase enzyme. == Methyl salicylate as a plant metabolite == Many plants produce methyl salicylate in small quantities. Methyl salicylate levels are often upregulated in response to biotic stress, especially infection by pathogens, where it plays a role in the induction of resistance. Methyl salicylate is believed to function by being metabolized to the plant hormone salicylic acid. Since methyl salicylate is volatile, these signals can spread through the air to distal parts of the same plant or even to neighboring plants, whereupon they can function as a mechanism of plant-to-plant communication, "warning" neighbors of danger. Methyl salicylate is also released in some plants when they are damaged by herbivorous insects, where they may function as a cue aiding in the recruitment of predators, notably hoverflies, lacewings, and lady beetles. Some plants produce methyl salicylate in larger quantities, where it likely involved in direct defense against predators or pathogens. Examples of this latter class include: some species of
|
{
"page_id": 856544,
"source": null,
"title": "Methyl salicylate"
}
|
the genus Gaultheria in the family Ericaceae, including Gaultheria procumbens, the wintergreen or eastern teaberry; some species of the genus Betula in the family Betulaceae, particularly those in the subgenus Betulenta such as B. lenta, the black birch; all species of the genus Spiraea in the family Rosaceae, also called the meadowsweets; species of the genus Polygala in the family Polygalaceae. Methyl salicylate can also be a component of floral scents, especially in plants dependent on nocturnal pollinators like moths, scarab beetles, and (nocturnal) bees. == Commercial production == Methyl salicylate can be produced by esterifying salicylic acid with methanol. Commercial methyl salicylate is now synthesized, but in the past, it was commonly distilled from the twigs of Betula lenta (sweet birch) and Gaultheria procumbens (eastern teaberry or wintergreen). == Uses == Methyl salicylate is used in high concentrations as a rubefacient and analgesic in deep heating liniments (such as Bengay) to treat joint and muscular pain. Randomised double blind trials report that evidence of its effectiveness is weak, but stronger for acute pain than chronic pain, and that effectiveness may be due entirely to counterirritation. However, in the body it metabolizes into salicylates, including salicylic acid, a known NSAID. Methyl salicylate is used in low concentrations (0.04% and under) as a flavoring agent in root beer, chewing gum, mints and medicine such as Pepto-Bismol. When mixed with sugar and dried, it is a potentially entertaining source of triboluminescence, for example by crushing Wint-O-Green Life Savers in a dark room. When crushed, sugar crystals emit light; methyl salicylate amplifies the spark because it fluoresces, absorbing ultraviolet light and re-emitting it in the visible spectrum. It is used as an antiseptic in Listerine mouthwash produced by the Johnson & Johnson company. It provides fragrance to various products and as an odor-masking
|
{
"page_id": 856544,
"source": null,
"title": "Methyl salicylate"
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|
agent for some organophosphate pesticides. Methyl salicylate is also used as a bait for attracting male orchid bees for study, which apparently gather the chemical to synthesize pheromones, and to clear plant or animal tissue samples of color, and as such is useful for microscopy and immunohistochemistry when excess pigments obscure structures or block light in the tissue being examined. This clearing generally only takes a few minutes, but the tissue must first be dehydrated in alcohol. It has also been discovered that methyl salicylate works as a kairomone that attracts some insects, such as the spotted lanternfly. Unlike some other kairomone's, Methyl Salicylate attracts all stages of the spotted lanternflies life. Other niche uses include: as a simulant or surrogate for the research of chemical warfare agent sulfur mustard, due to its similar chemical and physical properties; restoring (at least temporarily) the elastomeric properties of old rubber rollers, especially in printers; as a transfer agent in printmaking (to release toner from photocopied images and apply them to other surfaces); as a historical substitute for cedar oil as an immersion oil in microscopy, given its refractive index (1.538) being close to that of crown glass (1.515) and being less prone to drying than cedar oil; as a penetrating oil to loosen rusted parts. == Safety and toxicity == Methyl salicylate is potentially deadly, especially for young children who may accidentally ingest preparations containing methyl salicylate, such as an essential oil solution. A single teaspoon (5 mL) of methyl salicylate contains approximately 6 g of salicylate, which is equivalent to almost twenty 300 mg aspirin tablets (5 mL × 1.174 g/mL = 5.87 g). Toxic ingestions of salicylates typically occur with doses of approximately 150 mg/kg body weight. This can be achieved with 1 mL of oil of wintergreen, which equates
|
{
"page_id": 856544,
"source": null,
"title": "Methyl salicylate"
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|
to 140 mg/kg of salicylates for a 10 kg child (22 lbs). The lowest published lethal dose is 101 mg/kg body weight in adult humans, (or 7.07 grams for a 70 kg adult). It has proven fatal to small children in doses as small as 4 mL. A seventeen-year-old cross-country runner at Notre Dame Academy on Staten Island died in April 2007 after her body absorbed methyl salicylate through excessive use of topical muscle-pain relief products (using multiple patches against the manufacturer's instructions). Most instances of human toxicity due to methyl salicylate are a result of overapplication of topical analgesics, especially involving children. Salicylate, the major metabolite of methyl salicylate, may accumulate in blood, plasma or serum which may help professionals to confirm a diagnosis of poisoning in hospitalized patients or to assist in an autopsy. == Compendial status == British Pharmacopoeia Japanese Pharmacopoeia == See also == Trolamine salicylate == References == == External links == MedlinePlus – Methyl salicylate overdose MedlinePlus – Sports cream overdose CNN – Medical examiner: Sports cream caused teen's death Wayback machine link to this article NLM Hazardous Substances Databank – Methyl salicylate
|
{
"page_id": 856544,
"source": null,
"title": "Methyl salicylate"
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|
The molecular formula C18H25N5O4 (molar mass: 375.42 g/mol, exact mass: 375.1907 u) may refer to: Metazosin Neldazosin
|
{
"page_id": 41554401,
"source": null,
"title": "C18H25N5O4"
}
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The squid giant axon is the very large (up to 1.5 mm in diameter; typically around 0.5 mm) axon that controls part of the water jet propulsion system in squid. It was first described by L. W. Williams in 1909, but this discovery was forgotten until English zoologist and neurophysiologist J. Z. Young demonstrated the axon's function in the 1930s while working in the Stazione Zoologica in Naples, the Marine Biological Association in Plymouth and the Marine Biological Laboratory in Woods Hole. Squids use this system primarily for making brief but very fast movements through the water. On the underside of the squid's body, between the head and the mantle, is a siphon through which water can be rapidly expelled by the fast contractions of the body wall muscles of the animal. This contraction is initiated by action potentials in the giant axon. Action potentials travel faster in an axon with a large diameter than a smaller one, and squid have evolved the giant axon to improve the speed of their escape response. The increased radius of the squid axon decreases the internal resistance of the axon, as resistance is inversely proportional to the cross sectional area of the object. This increases the space constant ( λ = ( r × ρ m ) / ( 2 × ρ i ) \lambda ={\sqrt {(r\times \rho _{m})/(2\times \rho _{i})}} ), leading to faster local depolarization and a faster action potential conduction ( E = E o e − x / λ E=E_{o}e^{-x/\lambda } ). In their Nobel Prize-winning work uncovering ionic mechanism of action potentials, Alan Hodgkin and Andrew Huxley performed experiments on the squid giant axon, using the longfin inshore squid as the model organism. The prize was shared with John Eccles. The large diameter of the axon provided a
|
{
"page_id": 3215842,
"source": null,
"title": "Squid giant axon"
}
|
great experimental advantage for Hodgkin and Huxley as it allowed them to insert voltage clamp electrodes inside the lumen of the axon. While the squid axon is very large in diameter it is unmyelinated which decreases the conduction velocity substantially. The conduction velocity of a typical 0.5 mm squid axon is about 25 m/s. During a typical action potential in the cuttlefish Sepia giant axon, an influx of 3.7 pmol/cm2 (picomoles per centimeter2) of sodium is offset by a subsequent efflux of 4.3 pmol/cm2 of potassium. == See also == Lateral giant neuron Squid giant synapse Hodgkin–Huxley model == References ==
|
{
"page_id": 3215842,
"source": null,
"title": "Squid giant axon"
}
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Gottlieb Conrad Christian Storr (June 16, 1749, Stuttgart – February 27, 1821, Tübingen) was a German physician, chemist, and naturalist. In 1768 he obtained his doctorate from the University of Tübingen, where he also served as a professor of chemistry, botany, and natural history from 1774 to 1801. He is the taxonomic authority of several genera, including Mellivora, whose only species is the honey badger (Mellivora capensis). == Published works == In 1781 he performed extensive scientific investigations in the Swiss Alps, publishing "Alpenreise vom Jahre 1781" (1784–86, 2 vols.) as a result. Other noted written efforts by Storr include: "Dissertatio inauguralis medica, de curis viperinis", 1768 (with Ferdinand Christoph Oetinger). Entwurf einer Folge von Unterhaltungen zur Einleitung in die Naturgeschichte, 1777. Ueber seine Bearbeitungsart der Naturgeschichte, 1780. "Investigandae crystallifodinarum oeconomiae quaedam pericula", 1785. "Idea methodi fossilium", 1807. == References ==
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"page_id": 1053155,
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"title": "Gottlieb Conrad Christian Storr"
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Dynamic Markov compression (DMC) is a lossless data compression algorithm developed by Gordon Cormack and Nigel Horspool. It uses predictive arithmetic coding similar to prediction by partial matching (PPM), except that the input is predicted one bit at a time (rather than one byte at a time). DMC has a good compression ratio and moderate speed, similar to PPM, but requires somewhat more memory and is not widely implemented. Some recent implementations include the experimental compression programs hook by Nania Francesco Antonio, ocamyd by Frank Schwellinger, and as a submodel in paq8l by Matt Mahoney. These are based on the 1993 implementation in C by Gordon Cormack. == Algorithm == DMC predicts and codes one bit at a time. It differs from PPM in that it codes bits rather than bytes, and from context mixing algorithms such as PAQ in that there is only one context per prediction. The predicted bit is then coded using arithmetic coding. === Arithmetic coding === A bitwise arithmetic coder such as DMC has two components, a predictor and an arithmetic coder. The predictor accepts an n-bit input string x = x1x2...xn and assigns it a probability p(x), expressed as a product of a series of predictions, p(x1)p(x2|x1)p(x3|x1x2) ... p(xn| x1x2...xn–1). The arithmetic coder maintains two high precision binary numbers, plow and phigh, representing the possible range for the total probability that the model would assign to all strings lexicographically less than x, given the bits of x seen so far. The compressed code for x is px, the shortest bit string representing a number between plow and phigh. It is always possible to find a number in this range no more than one bit longer than the Shannon limit, log2 1 / p(x). One such number can be obtained from phigh by dropping all
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{
"page_id": 11014633,
"source": null,
"title": "Dynamic Markov compression"
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|
of the trailing bits after the first bit that differs from plow. Compression proceeds as follows. The initial range is set to plow = 0, phigh = 1. For each bit, the predictor estimates p0 = p(xi = 0|x1x2...xi–1) and p1 = 1 − p0, the probability of a 0 or 1, respectively. The arithmetic coder then divides the current range, (plow, phigh) into two parts in proportion to p0 and p1. Then the subrange corresponding to the next bit xi becomes the new range. For decompression, the predictor makes an identical series of predictions, given the bits decompressed so far. The arithmetic coder makes an identical series of range splits, then selects the range containing px and outputs the bit xi corresponding to that subrange. In practice, it is not necessary to keep plow and phigh in memory to high precision. As the range narrows the leading bits of both numbers will be the same, and can be output immediately. === DMC model === The DMC predictor is a table which maps (bitwise) contexts to a pair of counts, n0 and n1, representing the number of zeros and ones previously observed in this context. Thus, it predicts that the next bit will be a 0 with probability p0 = n0 / n = n0 / (n0 + n1) and 1 with probability p1 = 1 − p0 = n1 / n. In addition, each table entry has a pair of pointers to the contexts obtained by appending either a 0 or a 1 to the right of the current context (and possibly dropping bits on the left). Thus, it is never necessary to look up the current context in the table; it is sufficient to maintain a pointer to the current context and follow the links. In the original
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"page_id": 11014633,
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"title": "Dynamic Markov compression"
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DMC implementation, the initial table is the set of all contexts of length 8 to 15 bits that begin on a byte boundary. The initial state is any of the 8 bit contexts. The counts are floating point numbers initialized to a small nonzero constant such as 0.2. The counts are not initialized to zero in order to allow values to be coded even if they have not been seen before in the current context. Modeling is the same for compression and decompression. For each bit, p0 and p1 are computed, bit xi is coded or decoded, the model is updated by adding 1 to the count corresponding to xi, and the next context is found by traversing the link corresponding to xi. === Adding new contexts === DMC as described above is equivalent to an order-1 context model. However, it is normal to add longer contexts to improve compression. If the current context is A, and the next context B would drop bits on the left, then DMC may add (clone) a new context C from B. C represents the same context as A after appending one bit on the right as with B, but without dropping any bits on the left. The link from A will thus be moved from B to point to C. B and C will both make the same prediction, and both will point to the same pair of next states. The total count, n = n0 + n1 for C will be equal to the count nx for A (for input bit x), and that count will be subtracted from B. For example, suppose that state A represents the context 11111. On input bit 0, it transitions to state B representing context 110, obtained by dropping 3 bits on the left. In context
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"page_id": 11014633,
"source": null,
"title": "Dynamic Markov compression"
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A, there have been 4 zero bits and some number of one bits. In context B, there have been 3 zeros and 7 ones (n = 10), which predicts p1 = 0.7. C is cloned from B. It represents context 111110. Both B and C predict p1 = 0.7, and both go to the same next states, E and F. The count for C is n = 4, equal to n0 for A. This leaves n = 6 for B. States are cloned just prior to transitioning to them. In the original DMC, the condition for cloning a state is when the transition from A to B is at least 2, and the count for B is at least 2 more than that. (When the second threshold is greater than 0, it guarantees that other states will still transition to B after cloning). Some implementations such as hook allow these thresholds to be set as parameters. In paq8l, these thresholds increase as memory is used up to slow the growth rate of new states. In most implementations, when memory is exhausted the model is discarded and reinitialized back to the original bytewise order 1 model. == References == == External links == Data Compression Using Dynamic Markov Modelling Google Developers YouTube channel: Compressor Head Episode 3 (Markov Chain Compression) ( Page will play audio when loaded)
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{
"page_id": 11014633,
"source": null,
"title": "Dynamic Markov compression"
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Polyhaline is a salinity category term applied to brackish estuaries and other water bodies with a salinity between 18 and 30 parts per thousand. It is the most dense saltwater type that is classified as "brackish." == References == == See also == Salinity
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"page_id": 8851953,
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"title": "Polyhaline"
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A geopolymer is an inorganic, often ceramic-like material, that forms a stable, covalently bonded, non-crystalline to semi-crystalline network through the reaction of aluminosilicate materials with an alkaline or acidic solution. Many geopolymers may also be classified as alkali-activated cements or acid-activated binders. They are mainly produced by a chemical reaction between a chemically reactive aluminosilicate powder e.g. metakaolin or other clay-derived powders, natural pozzolan, or suitable glasses, and an aqueous solution (alkaline or acidic) that causes this powder to react and re-form into a solid monolith. The most common pathway to produce geopolymers is by the reaction of metakaolin with sodium silicate, which is an alkaline solution, but other processes are also possible. The term geopolymer was coined by Joseph Davidovits in 1978 due to the rock-forming minerals of geological origin used in the synthesis process. These materials and associated terminology were popularized over the following decades via his work with the Institut Géopolymère (Geopolymer Institute). Geopolymers are synthesized in one of two conditions: in alkaline medium (Na+, K+, Li+, Cs+, Ca2+…) in acidic medium (phosphoric acid: H3PO4) The alkaline route is the most important in terms of research and development and commercial applications. Details on the acidic route have also been published. Commercially produced geopolymers may be used for fire- and heat-resistant coatings and adhesives, medicinal applications, high-temperature ceramics, new binders for fire-resistant fiber composites, toxic and radioactive waste encapsulation, and as cementing components in making or repairing concretes. Due to the increasing demand for low-emission building materials, geopolymer technology is being developed as a lower-CO₂ alternative to traditional Portland cement, with the potential for widespread use in concrete production. The properties and uses of geopolymers are being explored in many scientific and industrial disciplines such as modern inorganic chemistry, physical chemistry, colloid chemistry, mineralogy, geology, and in other
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"page_id": 11932146,
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"title": "Geopolymer"
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types of engineering process technologies. In addition to their use in construction, geopolymers are utilized in resins, coatings, and adhesives for aerospace, automotive, and protective applications. == Composition == In the 1950s, Viktor Glukhovsky developed concrete materials originally known as "soil silicate concretes" and "soil cements", but since the introduction of the geopolymer concept by Joseph Davidovits, the terminology and definitions of the word geopolymer have become more diverse and often conflicting. The word geopolymer is sometimes used to refer to naturally occurring organic macromolecules; that sense of the word differs from the now-more-common use of this terminology to discuss inorganic materials which can have either cement-like or ceramic-like character. A geopolymer is essentially a mineral chemical compound or mixture of compounds consisting of repeating units, for example silico-oxide (-Si-O-Si-O-), silico-aluminate (-Si-O-Al-O-), ferro-silico-aluminate (-Fe-O-Si-O-Al-O-) or alumino-phosphate (-Al-O-P-O-), created through a process of geopolymerization. This method of describing mineral synthesis (geosynthesis) was first presented by Davidovits at an IUPAC symposium in 1976. Even within the context of inorganic materials, there exist various definitions of the word geopolymer, which can include a relatively wide variety of low-temperature synthesized solid materials. The most typical geopolymer is generally described as resulting from the reaction between metakaolin (calcined kaolinitic clay) and a solution of sodium or potassium silicate (waterglass). Geopolymerization tends to result in a highly connected, disordered network of negatively charged tetrahedral oxide units balanced by the sodium or potassium ions. In the simplest form, an example chemical formula for a geopolymer can be written as Na2O·Al2O3·nSiO2·wH2O, where n is usually between 2 and 4, and w is around 11-15. Geopolymers can be formulated with a wide variety of substituents in both the framework (silicon, aluminium) and non-framework (sodium) sites; most commonly potassium or calcium takes on the non-framework sites, but iron or phosphorus
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"page_id": 11932146,
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can in principle replace some of the aluminum or silicon. Geopolymerization usually occurs at ambient or slightly elevated temperature; the solid aluminosilicate raw materials (e.g. metakaolin) dissolve into the alkaline solution, then cross-link and polymerize into a growing gel phase, which then continues to set, harden, and gain strength. == Geopolymer synthesis == === Covalent bonding === The fundamental unit within a geopolymer structure is a tetrahedral complex consisting of silicon or aluminum coordinated through covalent bonds to four oxygens. The geopolymer framework results from the cross-linking between these tetrahedra, which leads to a 3-dimensional aluminosilicate network, where the negative charge associated with tetrahedral aluminium is balanced by a small cationic species, most commonly an alkali metal cation (Na+, K+ etc). These alkali metal cations are often ion-exchangeable, as they are associated with, but only loosely bonded to the main covalent network, similarly to the non-framework cations present in zeolites. === Oligomer formation === Geopolymerization is the process of combining many small molecules known as oligomers into a covalently bonded network. This reaction process takes place via formation of oligomers (dimer, trimer, tetramer, pentamer) which are believed to contribute to the formation of the actual structure of the three-dimensional macromolecular framework, either through direct incorporation or through rearrangement via monomeric species. These oligomers are named by some geopolymer chemists as sialates following the scheme developed by Davidovits, although this terminology is not universally accepted within the research community due in part to confusion with the earlier (1952) use of the same word to refer to the salts of the important biomolecule sialic acid. The image shows five examples of small oligomeric potassium aluminosilicate species (labelled in the diagram according to the poly(sialate) / poly(sialate-siloxo) nomenclature), which are key intermediates in potassium-based alumino-silicate geopolymerization. The aqueous chemistry of aluminosilicate oligomers is
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complex, and plays an important role in the discussion of zeolite synthesis, a process which has many details in common with geopolymerization. Example of geopolymerization of a metakaolin precursor, in an alkaline medium The reaction process broadly involves four main stages: Alkaline hydrolysis of the layered structure of the calcined kaolinite Formation of monomeric and oligomeric species In the presence of waterglass (soluble potassium or sodium silicate), cyclic Al-Si structures can form (e.g. #5 in the figure), whereby the hydroxide is liberated by condensation reactions and can react again Geopolymerization (polycondensation) into polymeric 3D-networks. The reaction processes involving other aluminosilicate precursors (e.g. low-calcium fly ash, crushed or synthetic glasses, natural pozzolans) are broadly similar to the steps described above. === Geopolymer 3D-frameworks and water === Geopolymerization forms aluminosilicate frameworks that are similar to those of some rock-forming minerals, but lacking in long-range crystalline order, and generally containing water in both chemically bound sites (hydroxyl groups) and in molecular form as pore water. This water can be removed at temperatures above 100 – 200°C. Cation hydration and the locations, and mobility of water molecules in pores are important for lower-temperature applications, such as in usage of geopolymers as cements. The figure shows a geopolymer containing both bound (Si-OH groups) and free water (left in the figure). Some water is associated with the framework similarly to zeolitic water, and some is in larger pores and can be readily released and removed. After dehydroxylation (and dehydration), generally above 250°C, geopolymers can then crystallise above 800-1000°C (depending on the nature of the alkali cation present). == Commercial applications == There exists a wide variety of potential and existing applications. Some of the geopolymer applications are still in development, whereas others are already industrialized and commercialized. They are listed in three major categories: === Geopolymer
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cements and concretes === Building materials (for example, clay bricks) Low-CO2 cements and concretes Radioactive and toxic waste containment === Geopolymer resins and binders === Fire-resistant materials, thermal insulation, foams Low-energy ceramic tiles, refractory items, thermal shock refractories High-tech resin systems, paints, binders and grouts Bio-technologies (materials for medicinal applications) Foundry industry (resins), tooling for the manufacture of organic fiber composites Composites for infrastructure repair and strengthening Fire-resistant and heat-resistant high-tech carbon-fiber composites for aircraft interiors and automobiles === Arts and archaeology === Decorative stone artifacts, arts and decoration Cultural heritage, archaeology and history of sciences == Geopolymer cements == From a terminological point of view, geopolymer cement is a binding system that hardens at room temperature, like regular Portland cement. Geopolymer cement is being developed and utilised as an alternative to conventional Portland cement for use in transportation, infrastructure, construction and offshore applications. Production of geopolymer cement requires an aluminosilicate precursor material such as metakaolin or fly ash, a user-friendly alkaline reagent (for example, sodium or potassium soluble silicates with a molar ratio (MR) SiO2:M2O ≥ 1.65, M being sodium or potassium) and water (See the definition for "user-friendly" reagent below). Room temperature hardening is more readily achieved with the addition of a source of calcium cations, often blast furnace slag. Geopolymer cements can be formulated to cure more rapidly than Portland-based cements; some mixes gain most of their ultimate strength within 24 hours. However, they must also set slowly enough that they can be mixed at a batch plant, either for pre-casting or delivery in a concrete mixer. Geopolymer cement also has the ability to form a strong chemical bond with silicate rock-based aggregates. There is often confusion between the meanings of the terms 'geopolymer cement' and 'geopolymer concrete'. A cement is a binder, whereas concrete is the
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composite material resulting from the mixing and hardening of cement with water (or an alkaline solution in the case of geopolymer cement), and stone aggregates. Materials of both types (geopolymer cements and geopolymer concretes) are commercially available in various markets internationally. === Alkali-activated materials vs. geopolymer cements === There exists some confusion in the terminology applied to geopolymers, alkali-activated cements and concretes, and related materials, which have been described by a variety of names including also "soil silicate concretes" and "soil cements". Terminology related to alkali-activated materials or alkali-activated geopolymers is also in wide (but debated) use. These cements, sometimes abbreviated AAM, encompass the specific fields of alkali-activated slags, alkali-activated coal fly ashes, and various blended cementing systems. === User-friendly alkaline-reagents === Geopolymerization uses chemical ingredients that may be dangerous and therefore requires some safety procedures. Material Safety rules classify the alkaline products in two categories: corrosive products (named here: hostile) and irritant products (named here: friendly). The table lists some alkaline chemicals and their corresponding safety labels. Alkaline reagents belonging to the second (less elevated pH) class may also be termed as User-friendly, although the irritant nature of the alkaline component and the potential inhalation risk of powders still require the selection and use of appropriate personal protective equipment, as in any situation where chemicals or powders are handled. The development of some alkali-activated-cements, as shown in numerous published recipes (especially those based on fly ashes) use alkali silicates with molar ratios SiO2:M2O below 1.20, or are based on concentrated NaOH. These conditions are not considered so user-friendly as when more moderate pH values are used, and require careful consideration of chemical safety handling laws, regulations, and state directives. Conversely, geopolymer cement recipes employed in the field generally involve alkaline soluble silicates with starting molar ratios ranging from 1.45
|
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to 1.95, particularly 1.60 to 1.85, i.e. user-friendly conditions. It may happen that for research, some laboratory recipes have molar ratios in the 1.20 to 1.45 range. === Examples of materials that are sometimes called geopolymer cements === Commercial geopolymer cements were developed in the 1980s, of the type (K,Na,Ca)-aluminosilicate (or "slag-based geopolymer cement") and resulted from the research carried out by Joseph Davidovits and J.L. Sawyer at Lone Star Industries, USA, marketed as Pyrament® cement. The US patent 4,509,985 was granted on April 9, 1985 with the title 'Early high-strength mineral polymer'. In the 1990s, using knowledge of the synthesis of zeolites from fly ashes, Wastiels et al., Silverstrim et al. and van Jaarsveld and van Deventer developed geopolymeric fly ash-based cements. Materials based on siliceous (EN 197), also called class F (ASTM C618), fly ashes are known: alkali-activated fly ash geopolymer: In many (but not all) cases requires heat curing at 60-80°C; not manufactured separately as a cement, but rather produced directly as a fly-ash based concrete. NaOH + fly ash: partially-reacted fly ash particles embedded in an alumino-silicate gel with Si:Al= 1 to 2, zeolitic type (chabazite-Na and sodalite) structures. slag/fly ash-based geopolymer cement: Room-temperature cement hardening. Alkali metal silicate solution + blast furnace slag + fly ash: fly ash particles embedded in a geopolymeric matrix with Si:Al ~ 2. Can be produced with "user-friendly" (not extremely high pH) activating solutions. The properties of iron-containing "ferri-sialate"-based geopolymer cements are similar to those of rock-based geopolymer cements but involve geological elements, or metallurgical slags, with high iron oxide content. The hypothesised binder chemistry is (Ca,K)-(Fe-O)-(Si-O-Al-O). Rock-based geopolymer cements can be formed by the reaction of natural pozzolanic materials under alkaline conditions, and geopolymers derived from calcined clays (e.g. metakaolin) can also be produced in the form of cements.
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=== CO2 emissions during manufacturing === Geopolymer cements can be designed to have lower attributed CO2 emissions compared to other widely-used materials such as ordinary Portland cement. Geopolymers use industrial byproducts/waste containing aluminosilicate phases in manufacturing, which minimizes CO₂ emissions and therefore have a lower global warming potential (GWP). However, emissions still arise from various stages of production of geopolymer concretes. The extraction and processing of raw materials, such as fly ash, slag, or metakaolin, require energy and contribute to CO₂ emissions, though they are often industrial by-products with a lower environmental impact than clinker production in Portland concrete. A significant source of emissions in geopolymer concrete manufacturing is the production of alkali activators like sodium hydroxide (NaOH) and sodium silicate, which require high-temperature processing and contribute to the overall global warming potential. Additionally, energy consumption during mixing, transportation, and curing, especially when elevated temperatures are used, can further contribute to emissions. While studies suggest that geopolymer concrete can reduce global warming potential by up to 64% compared to Portland concrete through material selection and optimized activator use, the overall impact depends on the specific composition and processing methods employed. While geopolymer concrete generally has a lower global warming potential (GWP) than ordinary Portland concrete, its environmental impact varies based on the choice of raw materials and activators. In particular, the production of alkali activators like sodium hydroxide plays a crucial role in determining the overall sustainability of geopolymer concrete. A life cycle assessment (LCA) study by Salas et al. (2018) shows that sodium hydroxide production is a major factor in the environmental impact of geopolymer concrete, as it is also essential for sodium silicate production. The energy mix used in its production significantly influences emissions, with a 2018 mix (85% hydroelectricity) reducing impacts by 30–70% compared to a 2012
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mix (62% hydroelectricity). The source of sodium hydroxide also affects geopolymer concrete’s sustainability, with solar salt-based production and hydropower reducing its GWP by 64% compared to conventional concrete (CC). However, geopolymer concrete has higher ozone depletion potential due to CFC emissions from the chlor-alkali process, a drawback not present in CC production. Other environmental impacts vary, with geopolymer concrete slightly outperforming CC in fossil fuel depletion and eutrophication but performing slightly worse in acidification and photochemical oxidant formation. === The need for standards === In June 2012, the institution ASTM International organized a symposium on Geopolymer Binder Systems. The introduction to the symposium states: When performance specifications for Portland cement were written, non-portland binders were uncommon...New binders such as geopolymers are being increasingly researched, marketed as specialty products, and explored for use in structural concrete. This symposium is intended to provide an opportunity for ASTM to consider whether the existing cement standards provide, on the one hand, an effective framework for further exploration of geopolymer binders and, on the other hand, reliable protection for users of these materials. The existing Portland cement standards are not adapted to geopolymer cements; they must be elaborated by an ad hoc committee. Yet, to do so requires the presence of standard geopolymer cements. Presently, every expert is presenting their own recipe based on local raw materials (wastes, by-products or extracted). There is a need for selecting the right geopolymer cement category. The 2012 State of the Geopolymer R&D, suggested to select two categories, namely: type 2 slag/fly ash-based geopolymer cement: fly ashes are available in the major emerging countries; ferro-sialate-based geopolymer cement: this geological iron-rich raw material is present in all countries throughout the globe. along with the appropriate user-friendly geopolymeric reagent. === Health effects === Similarly to the Environmental Impacts, the production of
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geopolymer concrete has some notable human health implications, primarily due to the use of alkaline activators such as sodium hydroxide (NaOH) and sodium silicate (Na₂SiO₃). These chemicals are highly caustic and can cause severe skin burns, respiratory issues, and eye damage if not handled properly. Additionally, the manufacturing of NaOH and Na₂SiO₃ contributes to greenhouse gas emissions and releases pollutants linked to human toxicity and ozone depletion. Fly ash and silica fume, commonly used in geopolymer concrete, also pose risks when not properly managed, as fine particulate matter from these materials can contribute to dust pollution and respiratory diseases. However, geopolymer concrete can still provide environmental and health benefits by diverting industrial byproducts from landfills and reducing the hazardous emissions associated with traditional cement production. In addition, the selection of certain precursors and alkaline activators can minimize the health risks associated with geopolymer concrete production. == Geopolymers as ceramics == Geopolymers can be used as a low-cost and/or chemically flexible route to ceramic production, both to produce monolithic specimens, and as the continuous (binder) phase in composites with particulate or fibrous dispersed phases. === Room-temperature processed materials === Geopolymers produced at room temperature are typically hard, brittle, castable, and mechanically strong. This combination of characteristics offers the opportunity for their usage in a variety of applications in which other ceramics (e.g. porcelain) are conventionally used. Some of the first patented applications of geopolymer-type materials - actually predating the coining of the term geopolymer by multiple decades - relate to use in automobile spark plugs. === Thermal processing of geopolymers to produce ceramics === It is also possible to use geopolymers as a versatile pathway to produce crystalline ceramics or glass-ceramics, by forming a geopolymer through room-temperature setting, and then heating (calcining) it at the necessary temperature to convert it from
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the crystallographically disordered geopolymer form to achieve the desired crystalline phases (e.g. leucite, pollucite and others). == Geopolymer applications in arts and archaeology == Because geopolymer artifacts can look like natural stone, several artists started to cast in silicone rubber molds replicas of their sculptures. For example, in the 1980s, the French artist Georges Grimal worked on several geopolymer castable stone formulations. === Egyptian pyramid stones === In the mid-1980s, Joseph Davidovits presented his first analytical results carried out on samples sourced from Egyptian pyramids. He claimed that the ancient Egyptians used a geopolymeric reaction to make re-agglomerated limestone blocks. Later on, several materials scientists and physicists took over these archaeological studies and have published results on pyramid stones, claiming synthetic origins. However, the theories of synthetic origin of pyramid stones have also been stridently disputed by other geologists, materials scientists, and archaeologists. === Roman cements === It has also been claimed that the Roman lime-pozzolan cements used in the building of some important structures, especially works related to water storage (cisterns, aqueducts), have chemical parallels to geopolymeric materials. == See also == Zeolite == References == == External links == Geopolymer science. Science Direct. Elsevier. 2024
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Cerium is a chemical element; it has symbol Ce and atomic number 58. It is a soft, ductile, and silvery-white metal that tarnishes when exposed to air. Cerium is the second element in the lanthanide series, and while it often shows the oxidation state of +3 characteristic of the series, it also has a stable +4 state that does not oxidize water. It is considered one of the rare-earth elements. Cerium has no known biological role in humans but is not particularly toxic, except with intense or continued exposure. Despite always occurring in combination with the other rare-earth elements in minerals such as those of the monazite and bastnäsite groups, cerium is easy to extract from its ores, as it can be distinguished among the lanthanides by its unique ability to be oxidized to the +4 state in aqueous solution. It is the most common of the lanthanides, followed by neodymium, lanthanum, and praseodymium. Its estimated abundance in the Earth's crust is 68 ppm. Cerium was the first of the lanthanides to be discovered, in Bastnäs, Sweden. It was discovered by Jöns Jakob Berzelius and Wilhelm Hisinger in 1803, and independently by Martin Heinrich Klaproth in Germany in the same year. In 1839 Carl Gustaf Mosander separated cerium(III) oxide from other rare earths, and in 1875 William Francis Hillebrand became the first to isolate the metal. Today, cerium and its compounds have a variety of uses: for example, cerium(IV) oxide is used to polish glass and is an important part of catalytic converters. Cerium metal is used in ferrocerium lighters for its pyrophoric properties. Cerium-doped YAG phosphor is used in conjunction with blue light-emitting diodes to produce white light in most commercial white LED light sources. == Characteristics == === Physical === Cerium is the second element of the lanthanide
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"page_id": 24580596,
"source": null,
"title": "Cerium"
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series. In the periodic table, it appears between the lanthanides lanthanum to its left and praseodymium to its right, and above the actinide thorium. It is a ductile metal with a hardness similar to that of silver. Its 58 electrons are arranged in the configuration [Xe]4f15d16s2, of which the four outer electrons are valence electrons. The 4f, 5d, and 6s energy levels are very close to each other, and the transfer of one electron to the 5d shell is due to strong interelectronic repulsion in the compact 4f shell. This effect is overwhelmed when the atom is positively ionised; thus Ce2+ on its own has instead the regular configuration [Xe]4f2, although in some solid solutions it may be [Xe]4f15d1. Most lanthanides can use only three electrons as valence electrons, as afterwards the remaining 4f electrons are too strongly bound: cerium is an exception because of the stability of the empty f-shell in Ce4+ and the fact that it comes very early in the lanthanide series, where the nuclear charge is still low enough until neodymium to allow the removal of the fourth valence electron by chemical means. Cerium has a variable electronic structure. The energy of the 4f electron is nearly the same as that of the outer 5d and 6s electrons that are delocalized in the metallic state, and only a small amount of energy is required to change the relative occupancy of these electronic levels. This gives rise to dual valence states. For example, a volume change of about 10% occurs when cerium is subjected to high pressures or low temperatures. In its high pressure phase (α-Cerium), the 4f electrons are also delocalized and itinerate, as opposed to localized 4f electrons in low pressure phase (γ-Cerium). It appears that the valence changes from about 3 to 4 when
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"page_id": 24580596,
"source": null,
"title": "Cerium"
}
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it is cooled or compressed. === Chemical properties of the element === Like the other lanthanides, cerium metal is a good reducing agent, having standard reduction potential of E⦵ = −2.34 V for the Ce3+/Ce couple. It tarnishes in air, forming a passivating oxide layer like iron rust. A centimeter-sized sample of cerium metal corrodes completely in about a year. More dramatically, metallic cerium can be highly pyrophoric: Ce + O2 → CeO2 Being highly electropositive, cerium reacts with water. The reaction is slow with cold water but speeds up with increasing temperature, producing cerium(III) hydroxide and hydrogen gas: 2 Ce + 6 H2O → 2 Ce(OH)3 + 3 H2 === Allotropes === Four allotropic forms of cerium are known to exist at standard pressure and are given the common labels of α to δ: The high-temperature form, δ-cerium, has a bcc (body-centered cubic) crystal structure and exists above 726 °C. The stable form below 726 °C to approximately room temperature is γ-cerium, with an fcc (face-centered cubic) crystal structure. The DHCP (double hexagonal close-packed) form β-cerium is the equilibrium structure approximately from room temperature to −150 °C. The fcc form α-cerium is stable below about −150 °C; it has a density of 8.16 g/cm3. Other solid phases occurring only at high pressures are shown on the phase diagram. Both γ and β forms are quite stable at room temperature, although the equilibrium transformation temperature is estimated at 75 °C. At lower temperatures the behavior of cerium is complicated by the slow rates of transformation. Transformation temperatures are subject to substantial hysteresis and values quoted here are approximate. Upon cooling below −15 °C, γ-cerium starts to change to β-cerium, but the transformation involves a volume increase and, as more β forms, the internal stresses build up and suppress further transformation.
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Cooling below approximately −160 °C will start formation of α-cerium but this is only from remaining γ-cerium. β-cerium does not significantly transform to α-cerium except in the presence of stress or deformation. At atmospheric pressure, liquid cerium is more dense than its solid form at the melting point. === Isotopes === Naturally occurring cerium is made up of four isotopes: 136Ce (0.19%), 138Ce (0.25%), 140Ce (88.4%), and 142Ce (11.1%). All four are observationally stable, though the light isotopes 136Ce and 138Ce are theoretically expected to undergo double electron capture to isotopes of barium, and the heaviest isotope 142Ce is expected to undergo double beta decay to 142Nd or alpha decay to 138Ba. Thus, 140Ce is the only theoretically stable isotope. None of these decay modes have yet been observed, though the double beta decay of 136Ce, 138Ce, and 142Ce have been experimentally searched for. The current experimental limits for their half-lives are: 136Ce: >3.8×1016 y 138Ce: >5.7×1016 y 142Ce: >5.0×1016 y All other cerium isotopes are synthetic and radioactive. The most stable of them are 144Ce with a half-life of 284.9 days, 139Ce with a half-life of 137.6 days, and 141Ce with a half-life of 32.5 days. All other radioactive cerium isotopes have half-lives under four days, and most of them have half-lives under ten minutes. The isotopes between 140Ce and 144Ce inclusive occur as fission products of uranium. The primary decay mode of the isotopes lighter than 140Ce is inverse beta decay or electron capture to isotopes of lanthanum, while that of the heavier isotopes is beta decay to isotopes of praseodymium. Some isotopes of neodymium can alpha decay or are predicted to decay to isotopes of cerium. The rarity of the proton-rich 136Ce and 138Ce is explained by the fact that they cannot be made in the most
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common processes of stellar nucleosynthesis for elements beyond iron, the s-process (slow neutron capture) and the r-process (rapid neutron capture). This is so because they are bypassed by the reaction flow of the s-process, and the r-process nuclides are blocked from decaying to them by more neutron-rich stable nuclides. Such nuclei are called p-nuclei, and their origin is not yet well understood: some speculated mechanisms for their formation include proton capture as well as photodisintegration. 140Ce is the most common isotope of cerium, as it can be produced in both the s- and r-processes, while 142Ce can only be produced in the r-process. Another reason for the abundance of 140Ce is that it is a magic nucleus, having a closed neutron shell (it has 82 neutrons), and hence it has a very low cross section towards further neutron capture. Although its proton number of 58 is not magic, it is granted additional stability, as its eight additional protons past the magic number 50 enter and complete the 1g7/2 proton orbital. The abundances of the cerium isotopes may differ very slightly in natural sources, because 138Ce and 140Ce are the daughters of the long-lived primordial radionuclides 138La and 144Nd, respectively. == Compounds == Cerium exists in two main oxidation states, Ce(III) and Ce(IV). This pair of adjacent oxidation states dominates several aspects of the chemistry of this element. Cerium(IV) aqueous solutions may be prepared by reacting cerium(III) solutions with the strong oxidizing agents peroxodisulfate or bismuthate. The value of E⦵(Ce4+/Ce3+) varies widely depending on conditions due to the relative ease of complexation and hydrolysis with various anions, although +1.72 V is representative. Cerium is the only lanthanide which has important aqueous and coordination chemistry in the +4 oxidation state. === Halides === Cerium forms all four trihalides CeX3 (X = F,
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Cl, Br, I) usually by reaction of the oxides with the hydrogen halides. The anhydrous halides are pale-colored, paramagnetic, hygroscopic solids. Upon hydration, the trihalides convert to complexes containing aquo complexes [Ce(H2O)8-9]3+. Unlike most lanthanides, Ce forms a tetrafluoride, a white solid. It also forms a bronze-colored diiodide, which has metallic properties. Aside from the binary halide phases, a number of anionic halide complexes are known. The fluoride gives the Ce(IV) derivatives CeF4−8 and CeF2−6. The chloride gives the orange CeCl2−6. === Oxides and chalcogenides === Cerium(IV) oxide ("ceria") has the fluorite structure, similarly to the dioxides of praseodymium and terbium. Ceria is a nonstoichiometric compound, meaning that the real formula is CeO2−x, where x is about 0.2. Thus, the material is not perfectly described as Ce(IV). Ceria reduces to cerium(III) oxide with hydrogen gas. Many nonstoichiometric chalcogenides are also known, along with the trivalent Ce2Z3 (Z = S, Se, Te). The monochalcogenides CeZ conduct electricity and would better be formulated as Ce3+Z2−e−. While CeZ2 are known, they are polychalcogenides with cerium(III): cerium(IV) derivatives of S, Se, and Te are unknown. === Cerium(IV) complexes === The compound ceric ammonium nitrate (CAN) (NH4)2[Ce(NO3)6] is the most common cerium compound encountered in the laboratory. The six nitrate ligands bind as bidentate ligands. The complex [Ce(NO3)6]2− is 12-coordinate, a high coordination number which emphasizes the large size of the Ce4+ ion. CAN is a popular oxidant in organic synthesis, both as a stoichiometric reagent and as a catalyst. It is inexpensive, stable in air, easily handled, and of low toxicity. It operates by one-electron redox. Cerium nitrates also form 4:3 and 1:1 complexes with 18-crown-6 (the ratio referring to that between the nitrate and the crown ether). Classically, CAN is a primary standard for quantitative analysis. Cerium(IV) salts, especially cerium(IV) sulfate, are often
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used as standard reagents for volumetric analysis in cerimetric titrations. Due to ligand-to-metal charge transfer, aqueous cerium(IV) ions are orange-yellow. Aqueous cerium(IV) is metastable in water and is a strong oxidizing agent that oxidizes hydrochloric acid to give chlorine gas. In the Belousov–Zhabotinsky reaction, cerium oscillates between the +4 and +3 oxidation states to catalyze the reaction. === Organocerium compounds === Organocerium chemistry is similar to that of the other lanthanides, often involving complexes of cyclopentadienyl and cyclooctatetraenyl ligands. Cerocene (Ce(C8H8)2) adopts the uranocene molecular structure. The 4f electron in cerocene is poised ambiguously between being localized and delocalized and this compound is considered intermediate-valent. Alkyl, alkynyl, and alkenyl organocerium derivatives are prepared from the transmetallation of the respective organolithium or Grignard reagents, and are more nucleophilic but less basic than their precursors. == History == Cerium was discovered in Bastnäs in Sweden by Jöns Jakob Berzelius and Wilhelm Hisinger, and independently in Germany by Martin Heinrich Klaproth, both in 1803. Cerium was named by Berzelius after the asteroid Ceres, formally 1 Ceres, discovered two years earlier. Ceres was initially considered to be a planet at the time. The asteroid is itself named after the Roman goddess Ceres, goddess of agriculture, grain crops, fertility and motherly relationships. Cerium was originally isolated in the form of its oxide, which was named ceria, a term that is still used. The metal itself was too electropositive to be isolated by then-current smelting technology, a characteristic of rare-earth metals in general. After the development of electrochemistry by Humphry Davy five years later, the earths soon yielded the metals they contained. Ceria, as isolated in 1803, contained all of the lanthanides present in the cerite ore from Bastnäs, Sweden, and thus only contained about 45% of what is now known to be pure ceria. It
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was not until Carl Gustaf Mosander succeeded in removing lanthana and "didymia" in the late 1830s that ceria was obtained pure. Wilhelm Hisinger was a wealthy mine-owner and amateur scientist, and sponsor of Berzelius. He owned and controlled the mine at Bastnäs, and had been trying for years to find out the composition of the abundant heavy gangue rock (the "Tungsten of Bastnäs", which despite its name contained no tungsten), now known as cerite, that he had in his mine. Mosander and his family lived for many years in the same house as Berzelius, and Mosander was undoubtedly persuaded by Berzelius to investigate ceria further. The element played a role in the Manhattan Project, where cerium compounds were investigated in the Berkeley site as materials for crucibles for uranium and plutonium casting. For this reason, new methods for the preparation and casting of cerium were developed within the scope of the Ames daughter project (now the Ames Laboratory). Production of extremely pure cerium in Ames commenced in mid-1944 and continued until August 1945. == Occurrence and production == Cerium is the most abundant of all the lanthanides and the 25th most abundant element, making up 68 ppm of the Earth's crust. This value is the same of copper, and cerium is even more abundant than common metals such as lead (13 ppm) and tin (2.1 ppm). Thus, despite its position as one of the so-called rare-earth metals, cerium is actually not rare at all. Cerium content in the soil varies between 2 and 150 ppm, with an average of 50 ppm; seawater contains 1.5 parts per trillion of cerium. Cerium occurs in various minerals, but the most important commercial sources are the minerals of the monazite and bastnäsite groups, where it makes up about half of the lanthanide content. Monazite-(Ce)
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is the most common representative of the monazites, with "-Ce" being the Levinson suffix informing on the dominance of the particular REE element representative. Also the cerium-dominant bastnäsite-(Ce) is the most important of the bastnäsites. Cerium is the easiest lanthanide to extract from its minerals because it is the only one that can reach a stable +4 oxidation state in aqueous solution. Because of the decreased solubility of cerium in the +4 oxidation state, cerium is sometimes depleted from rocks relative to the other rare-earth elements and is incorporated into zircon, since Ce4+ and Zr4+ have the same charge and similar ionic radii. In extreme cases, cerium(IV) can form its own minerals separated from the other rare-earth elements, such as cerianite-(Ce) and (Ce,Th)O2. Bastnäsite, LnIIICO3F, is usually lacking in thorium and the heavy lanthanides beyond samarium and europium, and hence the extraction of cerium from it is quite direct. First, the bastnäsite is purified, using dilute hydrochloric acid to remove calcium carbonate impurities. The ore is then roasted in the air to oxidize it to the lanthanide oxides: while most of the lanthanides will be oxidized to the sesquioxides Ln2O3, cerium will be oxidized to the dioxide CeO2. This is insoluble in water and can be leached out with 0.5 M hydrochloric acid, leaving the other lanthanides behind. The procedure for monazite, (Ln,Th)PO4, which usually contains all the rare earths, as well as thorium, is more involved. Monazite, because of its magnetic properties, can be separated by repeated electromagnetic separation. After separation, it is treated with hot concentrated sulfuric acid to produce water-soluble sulfates of rare earths. The acidic filtrates are partially neutralized with sodium hydroxide to pH 3–4. Thorium precipitates out of solution as hydroxide and is removed. After that, the solution is treated with ammonium oxalate to convert
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rare earths to their insoluble oxalates. The oxalates are converted to oxides by annealing. The oxides are dissolved in nitric acid, but cerium oxide is insoluble in HNO3 and hence precipitates out. Care must be taken when handling some of the residues as they contain 228Ra, the daughter of 232Th, which is a strong gamma emitter. == Applications == Cerium has two main applications, both of which use CeO2. The industrial application of ceria is for polishing, especially chemical-mechanical planarization (CMP). In its other main application, CeO2 is used to decolorize glass. It functions by converting green-tinted ferrous impurities to nearly colorless ferric oxides. Ceria has also been used as a substitute for its radioactive congener thoria, for example in the manufacture of electrodes used in gas tungsten arc welding, where ceria as an alloying element improves arc stability and ease of starting while decreasing burn-off. === Gas mantles and pyrophoric alloys === The first use of cerium was in gas mantles, invented by Austrian chemist Carl Auer von Welsbach. In 1885, he had previously experimented with mixtures of magnesium, lanthanum, and yttrium oxides, but these gave green-tinted light and were unsuccessful. Six years later, he discovered that pure thorium oxide produced a much better, though blue, light, and that mixing it with cerium dioxide resulted in a bright white light. Cerium dioxide also acts as a catalyst for the combustion of thorium oxide. This resulted in commercial success for von Welsbach and his invention, and created great demand for thorium. Its production resulted in a large amount of lanthanides being simultaneously extracted as by-products. Applications were soon found for them, especially in the pyrophoric alloy known as "mischmetal" composed of 50% cerium, 25% lanthanum, and the remainder being the other lanthanides, that is used widely for lighter flints. Usually
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iron is added to form the alloy ferrocerium, also invented by von Welsbach. Due to the chemical similarities of the lanthanides, chemical separation is not usually required for their applications, such as the addition of mischmetal to steel as an inclusion modifier to improve mechanical properties, or as catalysts for the cracking of petroleum. This property of cerium saved the life of writer Primo Levi at the Auschwitz concentration camp, when he found a supply of ferrocerium alloy and bartered it for food. === Pigments and phosphors === The photostability of pigments can be enhanced by the addition of cerium, as it provides pigments with lightfastness and prevents clear polymers from darkening in sunlight. An example of a cerium compound used on its own as an inorganic pigment is the vivid red cerium(III) sulfide (cerium sulfide red), which stays chemically inert up to very high temperatures. The pigment is a safer alternative to lightfast but toxic cadmium selenide-based pigments. The addition of cerium oxide to older cathode-ray tube television glass plates was beneficial, as it suppresses the darkening effect from the creation of F-center defects due to the continuous electron bombardment during operation. Cerium is also an essential component as a dopant for phosphors used in CRT TV screens, fluorescent lamps, and later white light-emitting diodes. The most commonly used example is cerium(III)-doped yttrium aluminium garnet (Ce:YAG) which emits green to yellow-green light (550–530 nm) and also behaves as a scintillator. === Other uses === Cerium salts, such as the sulfides Ce2S3 and Ce3S4, were considered during the Manhattan Project as advanced refractory materials for the construction of crucibles which could withstand the high temperatures and strongly reducing conditions when casting plutonium metal. Despite desirable properties, these sulfides were never widely adopted due to practical issues with their synthesis. Cerium
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is used as alloying element in aluminium to create castable eutectic aluminium alloys with 6–16 wt.% Ce, to which other elements such as Mg, Ni, Fe and Mn can be added. These Al-Ce alloys have excellent high temperature strength and are suitable for automotive applications (e.g. in cylinder heads). Other alloys of cerium include Pu-Ce and Pu-Ce-Co plutonium alloys, which have been used as nuclear fuel. Other automotive applications for the lower sesquioxide are as a catalytic converter for the oxidation of CO and NOx emissions in the exhaust gases from motor vehicles. == Biological role and precautions == The early lanthanides have been found to be essential to some methanotrophic bacteria living in volcanic mudpots, such as Methylacidiphilum fumariolicum: lanthanum, cerium, praseodymium, and neodymium are about equally effective. Cerium is otherwise not known to have biological role in any other organisms, but is not very toxic either; it does not accumulate in the food chain to any appreciable extent. Because it often occurs together with calcium in phosphate minerals, and bones are primarily calcium phosphate, cerium can accumulate in bones in small amounts that are not considered dangerous. Cerium nitrate is an effective topical antimicrobial treatment for third-degree burns, although large doses can lead to cerium poisoning and methemoglobinemia. Like all rare-earth metals, cerium is of low to moderate toxicity. A strong reducing agent, it ignites spontaneously in air at 65 to 80 °C. Fumes from cerium fires are toxic. Cerium reacts with water to produce hydrogen gas, and thus cerium fires can only be effectively extinguished using class D dry powder extinguishing media. Workers exposed to cerium have experienced itching, sensitivity to heat, and skin lesions. Cerium is not toxic when eaten, but animals injected with large doses of cerium have died due to cardiovascular collapse. Cerium is
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more dangerous to aquatic organisms because it damages cell membranes; it is not very soluble in water and can cause environmental contamination. Cerium oxide, the most prevalent cerium compound in industrial applications, is not regulated in the United States by the Occupational Safety and Health Administration (OSHA) as a hazardous substance. In Russia, its occupational exposure limit is 5 mg/m3. Elemental cerium has no established occupational or permissible exposure limits by the OSHA or American Conference of Governmental Industrial Hygienists, though it is classified as a flammable solid and regulated as such under the Globally Harmonized System of Classification and Labelling of Chemicals. Toxicological reports on cerium compounds have noted their cytotoxicity and contributions to pulmonary interstitial fibrosis in workers. == References == == Bibliography == Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 978-0-08-037941-8.
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The Afrotropical realm is one of the Earth's eight biogeographic realms. It includes Sub-Saharan Africa, the southern Arabian Peninsula, the island of Madagascar, and the islands of the western Indian Ocean. It was formerly known as the Ethiopian Zone or Ethiopian Region. == Major ecological regions == Most of the Afrotropical realm, except for Africa's southern tip, has a tropical climate. A broad belt of deserts, including the Atlantic and Sahara deserts of northern Africa and the Arabian Desert of the Arabian Peninsula, separates the Afrotropic from the Palearctic realm, which includes northern Africa and temperate Eurasia. === Sahel and Sudan === South of the Sahara, two belts of tropical grassland and savanna run east and west across the continent, from the Atlantic Ocean to the Ethiopian Highlands. Immediately south of the Sahara lies the Sahel belt, a transitional zone of semi-arid short grassland and vachellia savanna. Rainfall increases further south in the Sudanian Savanna, also known simply as the Sudan region, a belt of taller grasslands and savannas. The Sudanian Savanna is home to two great flooded grasslands: the Sudd wetland in South Sudan, and the Niger Inland Delta in Mali. The forest-savanna mosaic is a transitional zone between the grasslands and the belt of tropical moist broadleaf forests near the equator. === Southern Arabian woodlands === South Arabia, which includes Yemen and parts of western Oman and southwestern Saudi Arabia, has few permanent forests. Some of the notable ones are Jabal Bura, Jabal Raymah, and Jabal Badaj in the Yemeni highland escarpment and the seasonal forests in eastern Yemen and the Dhofar region of Oman. Other woodlands that scatter the land are small, predominantly Juniperus or Vachellia forests. === Forest zone === The forest zone, a belt of lowland tropical moist broadleaf forests, runs across most of equatorial
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Africa's Intertropical Convergence Zone. The Upper Guinean forests of West Africa extend along the coast from Guinea to Togo. The Dahomey Gap, a zone of forest-savanna mosaic that reaches to the coast, separates the Upper Guinean forests from the Lower Guinean forests, which extend along the Gulf of Guinea from eastern Benin through Cameroon and Gabon to the western Democratic Republic of the Congo. The largest tropical forest zone in Africa is the Congolian forests of the Congo Basin in Central Africa. A belt of tropical moist broadleaf forest also runs along the Indian Ocean coast, from southern Somalia to South Africa. === Somali–Masai region === In northeastern Africa, semi-arid Acacia-Commiphora woodlands, savannas, and bushlands are the dominant plant communities. This region is called the Somali-Masai center of endemism or Somali-Masai region. It extends from central Tanzania northwards through the Horn of Africa and covers portions of Tanzania, Kenya, Ethiopia, Somalia, Djibouti, and Eritrea. Thorny, dry-season deciduous species of Vachellia and Senegalia (formerly Acacia) and Commiphora are the dominant trees, growing in open-canopied woodlands, open savannas, dense bushlands, and thickets. This region includes the Serengeti ecosystem, which is renowned for its wildlife. === Eastern Africa's highlands === The Afromontane region extends from the Ethiopian Highlands to the Drakensberg Mountains of South Africa, including the East African Rift. This region is home to distinctive flora, including Podocarpus and Afrocarpus, as well as giant Lobelias and Senecios. Ethiopian Highlands Albertine rift montane forests East African montane forests and Eastern Arc forests === Zambezian region === The Zambezian region includes woodlands, savannas, grasslands, and thickets. Characteristic plant communities include Miombo woodlands, drier mopane and Baikiaea woodlands, and higher-elevation Bushveld. It extends from east to west in a broad belt across the continent, south of the rainforests of the Guineo-Congolian region, and north of
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the deserts of southeastern Africa, the countries are Malawi, Angola, Botswana, Mozambique, Zambia, and Zimbabwe, and the subtropical. === Deserts of Southern Africa === Southern Africa contains several deserts. The Namib Desert is one of the oldest deserts in the world and extends for over 2,000 kilometers along the Atlantic coasts of Angola, Namibia, and South Africa. It is characterized by towering dunes and a diversity of endemic wildlife. Further inland concerning the Namib Desert, the Kalahari Desert is a semi-arid savanna spanning Botswana, Namibia, and South Africa. The Kalahari is known for its diversity of mineral resources, particularly diamonds, as well as a variety of flora. South of the Namib and Kalahari deserts is the Karoo. A semi-desert natural region, the Karoo desert spans across parts of the Western and Eastern Cape in South Africa and contains vast open spaces and unique vegetation, such as certain species of Asteraceae flowering plants. Within the boundaries of the larger Karoo, the Tankwa Karoo is a more arid sub-region known for harsher conditions and starker landscapes. Further to the west, the Richtersveld, a mountainous desert in the northwestern corner of South Africa, presents a rugged landscape. It is celebrated as a UNESCO World Heritage Site for its unique biodiversity and cultural significance to the local Nama people. === Cape floristic region === The Cape floristic region at Africa's southern tip is a Mediterranean climate region that is home to a significant number of endemic taxa, as well as to plant families like the proteas (Proteaceae) that are also found in the Australasian realm. === Madagascar and the Indian Ocean islands === Madagascar and neighboring islands form a distinctive sub-region of the realm, with numerous endemic taxa, such as lemurs. Madagascar and the Granitic Seychelles are old pieces of the ancient supercontinent of
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Gondwana, and broke away from Africa millions of years ago. Other Indian Ocean islands, like the Comoros and Mascarene Islands, are volcanic islands that formed more recently. Madagascar contains various plant habitats, from rainforests to mountains and deserts, as its biodiversity and ratio of endemism are extremely high. == Endemic plants and animals == === Plants === The Afrotropical realm is home to several endemic plant families. Madagascar and the Indian Ocean Islands are home to ten endemic families of flowering plants; eight are endemic to Madagascar (Asteropeiaceae, Didymelaceae, Didiereaceae, Kaliphoraceae, Melanophyllaceae, Physenaceae, Sarcolaenaceae, and Sphaerosepalaceae), one to Seychelles (Medusagynaceae), and one to the Mascarene Islands (Psiloxylaceae). Twelve plant families are endemic or nearly endemic to South Africa (including Curtisiaceae, Heteropyxidaceae, Penaeaceae, Psiloxylaceae, and Rhynchocalycaceae) of which five are endemic to the Cape floristic province (including Grubbiaceae). Other endemic Afrotropic families include Barbeyaceae, Dirachmaceae, Montiniaceae, Myrothamnaceae, and Oliniaceae. === Animals === The East African Great Lakes (Victoria, Malawi, and Tanganyika) are the center of biodiversity of many freshwater fishes, especially cichlids (they harbor more than two-thirds of the estimated 2,000 species in the family). The West African coastal rivers region covers only a fraction of West Africa, but harbors 322 of West Africa's fish species, with 247 restricted to this area and 129 restricted even to smaller ranges. The central rivers fauna comprise 194 fish species, with 119 endemics and only 33 restricted to small areas. The Afrotropic has various endemic bird families, including ostriches (Struthionidae), the secretary bird (Sagittariidae), guineafowl (Numididae), and mousebirds (Coliidae). Several families of passerines are limited to the Afrotropics, including rock-jumpers (Chaetopidae) and rockfowl (Picathartidae). Africa has three endemic orders of mammals, the Tubulidentata (aardvarks), Afrosoricida (tenrecs and golden moles), and Macroscelidea (elephant shrews). The East-African plains are well known for their diversity of large
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{
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mammals. Four species of great apes (Hominidae) are endemic to Central Africa: both species of gorilla (western gorilla, Gorilla gorilla, and eastern gorilla, Gorilla beringei) and both species of chimpanzee (common chimpanzee, Pan troglodytes, and bonobo, Pan paniscus). Humans and their ancestors originated in Africa. == Afrotropical terrestrial ecoregions == == Habitats == The tropical environment is rich in terms of biodiversity. Tropical African forest is 18 percent of the world's total and covers over 3.6 million square kilometers of land in West, East, and Central Africa. This total area can be subdivided to 2.69 million square kilometers (74%) in Central Africa, 680,000 square kilometers (19%) in West Africa, and 250,000 square kilometers (7%) in East Africa. In West Africa, a chain of rain forests up to 350 km long extends from the eastern border of Sierra Leone to Ghana. In Ghana, the forest zone gradually dispels near the Volta river, following a 300 km stretch of Dahomey savanna gap. The rain forest of West Africa continues from east of Benin through southern Nigeria and officially ends at the border of Cameroon along the Sanaga river. Semi-deciduous rainforests in West Africa begin at the fringed coastline of Guinea Bissau (via Guinea) and run through the coasts of Sierra Leone, Liberia, Ivory Coast, Ghana, continuing through Togo, Benin, Nigeria and Cameroon, and ending at the Congo Basin. Rainforests such as these are the richest, oldest, most prolific, and most complex systems on Earth, are dying, and in turn, are upsetting the delicate ecological balance. This may disturb global hydrological cycles, release vast amounts of greenhouse gases into the atmosphere, and lessen the planet's ability to store excess carbon. The rainforest vegetation of the Guinea-Congolian transition area, extending from Senegal to western Uganda is constituted of two main types: The semi-deciduous rainforest
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is characterized by a large number of trees whose leaves are left during the dry season. It appears in areas where the dry period (rainfall below about 100 mm) reaches three months. Then, the evergreen or the semi-evergreen rainforest climatically adapted to somewhat more humid conditions than the semi-deciduous type and is usually there in areas where the dry period is shorter than two months. This forest is usually richer in legumes and a variety of species and its maximum development is around the Bight of Biafra, from Eastern Nigeria to Gabon, and with some large patches leaning to the west from Ghana to Liberia and to the east of Zaïre-Congo basin. Among rainforest areas in other continents, most of the African rainforest is comparatively dry and receives between 1600 and 2000 mm of rainfall per year. Areas receiving more rain than this mainly are in coastal areas. The circulation of rainfall throughout the year remains less than in other rainforest regions in the world. The average monthly rainfall in nearly the whole region remains under 100 mm throughout the year. The variety of the African rainforest flora is also less than the other rainforests. This lack of flora has been credited to several reasons such as the gradual infertility since the Miocene, severe dry periods during Quaternary, or the refuge theory of the cool and dry climate of tropical Africa during the last severe ice age of about 18,000 years ago. == Fauna == The Tropical African rainforest has rich fauna, commonly smaller mammal species rarely seen by humans. New species are being discovered. For instance, in late 1988 an unknown shrub species was discovered on the shores of the Median River in Western Cameroon. Since then many species have become extinct. However, undisturbed rainforests are some of the
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richest habitats for animal species. Today, undisturbed rainforests are remnant but rare. Timber extraction not only changes the edifice of the forest, but it also affects the tree species spectrum by removing economically important species and terminating other species in the process. The species that compose African rainforests are of different evolutionary ages because of the contraction and expansion of the rainforest in response to global climatic fluctuations. The pygmy hippopotamus, the giant forest hog, the water chevrotain, insectivores, rodents, bats, tree frogs, and bird species inhabit the forest. These species, along with a diversity of fruits and insects, make a special habitat that allows for a diversity of life. The top canopy is home to monkey species like the red colobus, Black-and-white Colobus, and many other Old-World monkey species. Many of these rare and unique species are endangered or critically endangered and need protection from poachers and provided ample habitat to thrive. == Flora == In Tropical Africa, about 8,500 plant species have been documented, including 403 orchid species. Species unfamiliar with the changes in forest structure for industrial use might not survive. If timber use continues and an increasing amount of farming occurs, it could lead to the mass killing of animal species. The home of nearly half of the world's animals and plant species are tropical rainforests. The rainforests provide economic resources for over-populated developing countries. Despite the stated need to save the West African forests, there are varied opinions on how best to accomplish this goal. In April 1992, countries with some of the largest surviving tropical rainforests banned a rainforest protection plan proposed by the British government. It aimed at finding endangered species of tropical trees to control their trade. Experts estimate that the rainforest of West Africa, at the present rate of deforestation, may
|
{
"page_id": 201208,
"source": null,
"title": "Afrotropical realm"
}
|
disappear by the year 2020. Africa's rainforest, like many others emergent in the world, has a special significance to the indigenous peoples of Africa who have occupied them for millennia. == Region protection == Many African countries are in economic and political change, overwhelmed by conflict, making various movements of forest exploitation to maintain forest management and production more and more complicated. Forest legislation of ATO member countries aims to promote the balanced utilization of the forest domain and of wildlife and fishery to increase the input of the forest sector to the economic, social, cultural, and scientific development of the country. === Deforestation === The rate of deforestation in Africa is less known than the rate of other tropical regions. A lack of dependable data and survey information in some countries has made change in areas of unbroken forest difficult to ascertain. The cultivation of various cash crops has led to forest depletion. West African countries depend on products like gum, copal, rubber, cola nuts, and palm oil as a source of steady income. Land use change spoils entire habitats with the forests. The conversion of forests into timber is another cause of deforestation. Over decades, the primary forest product was commercial timber. Urbanized countries account for a great percentage of the world's wood consumption, which increased greatly between 1950 and 1980. Simultaneously, preservation measures were reinforced to protect European and American forests. Economic growth and growing environmental protection in industrialized European countries caused increased demand for tropical hardwood from West Africa. In the first half of the 1980s, an annual forest loss of 7,200 km2 (2,800 sq mi) was noted down along the Gulf of Guinea, a figure equivalent to 4-5 percent of the total remaining rainforest area. By 1985, 72% of West Africa's rainforests had been transformed
|
{
"page_id": 201208,
"source": null,
"title": "Afrotropical realm"
}
|
into fallow lands and an additional 9% had been opened up by timber exploitation. Tropical timber was used in Europe following World War II, as trade with East European countries stopped and timber noticeably became sparse in western and southern Europe. Despite efforts to promote lesser-known timber species use, the market continued to focus on part of the usable timber obtainable. West Africa was prone to selective harvesting practices; while conservationists blamed the timber industry and the farmers for felling trees, others believe rainforest destruction is connected to the problem of fuel wood. The contribution of fuel wood consumption to tree stock decline in Africa is believed to be significant. It is generally believed that firewood provides 75% of the energy used in sub-Sahara Africa. With the high demand, the consumption of wood for fuel exceeds the renewal of forest cover. Other observed changes in these forests are forest disintegration (changing the spatial continuity and creating a mosaic of forest blocks and other land cover types), and selective logging of woody species for profitable purposes that affect the forest subfloor and the biodiversity. The rainforests that remain in West Africa now greatly differ in condition from their state 30 years ago. In Guinea, Liberia, and the Ivory Coast, there is almost no primary forest cover left unscathed; in Ghana, the situation is much worse, and nearly all of the rainforest is being removed. Guinea-Bissau loses 200 to 350 km2 (77 to 135 sq mi) of forest yearly, Senegal 500 km2 (190 sq mi) of wooded savanna, and Nigeria 6,000,050,000 of both. Liberia loses 800 km2 (310 sq mi) of forests each year. Extrapolating from present rates of loss, botanist Peter Raven pictures that the majority of the world's moderate and smaller rainforests (such as in Africa) could be destroyed in
|
{
"page_id": 201208,
"source": null,
"title": "Afrotropical realm"
}
|
forty years. Tropical Africa comprises 18% of the world's total land area covering 20 million km2 (7.7 million sq mi) of land in West and Central Africa. The region has been facing deforestation in various degrees of intensity throughout the recent decades. The actual rate of deforestation varies from one country to another and accurate data does not exist yet. Recent estimates show that the annual pace of deforestation in the region can vary from 150 km2 (58 sq mi) in Gabon to 2,900 km2 (1,100 sq mi) in Côte d'Ivoire. The remaining tropical forests still cover major areas in Central Africa but are abridged by patches in West Africa. The African Timber Organization member countries eventually recognized the cooperation between rural people and their forest environment. Customary law gives residents the right to use trees for firewood, fell trees for construction, and collect of forest products and rights for hunting or fishing and grazing or clearing of forests for maintenance agriculture. Other areas are called "protected forests", which means that uncontrolled clearings and unauthorized logging are forbidden. After World War II, commercial exploitation increased until no West African forestry department was able to make the law. By comparison with rainforests in other places of the world in 1973, Africa showed the greatest infringement though in total volume means, African timber production accounted for just one-third compared to that of Asia. The difference was due to the variety of trees in Africa forests and the demand for specific wood types in Europe. Forestry regulations in East Africa were first applied by colonial governments. The Tropical Forestry Action Plan was conceived in 1987 by the World Resources Institute in cooperation with the Food and Agriculture Organization, the United Nations Development Program, and the World Bank with hopes of halting tropical forest
|
{
"page_id": 201208,
"source": null,
"title": "Afrotropical realm"
}
|
destruction. In its bid to stress forest conservation and development, the World Bank provided $111,103 million to developing countries, especially in Africa, to help in developing long-range forest conservation and management programs meant for ending deforestation. == Historical temperature and climate == In early 2007, scientists created an entirely new proxy to determine the annual mean air temperature on land—based on molecules from the cell membrane of soil-inhabiting bacteria. Scientists from the NIOZ, Royal Netherlands Institute for Sea Research conducted a temperature record dating back to 25,000 years ago. In concordance with their German colleagues at the University of Bremen, this detailed record shows the history of land temperatures based on the molecular fossils of soil bacteria. When applying this to the outflow core of the Congo River, the core contained eroded land material and microfossils from marine algae. That concluded that the land environment of tropical Africa cooled more than the bordering Atlantic Ocean during the last ice age. Since the Congo River drains a large part of tropical central Africa, the land-derived material gives an integrated signal for a very large area. These findings further enlighten natural disparities in climate and the possible costs of a warming earth on precipitation in central Africa. Scientists discovered a way to measure sea temperature—based on organic molecules from algae growing off the surface layer of the Ocean. These organisms acclimatize the molecular composition of their cell membranes to ambient temperature to sustain regular physiological properties. If such molecules sink to the sea floor and are buried in sediments where oxygen does not go through, they can be preserved for thousands of years. The ratios between the different molecules from the algal cell membrane can approximate the past temperature of the sea surface. The new “proxy” used in this sediment core obtained
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{
"page_id": 201208,
"source": null,
"title": "Afrotropical realm"
}
|
both a continental and a sea surface temperature record. In comparison, both records show that ocean surface and land temperatures behaved differently during the past 25,000 years. During the last ice age, African temperatures were 21 °C, about 4 °C lower than today, while the tropical Atlantic Ocean was only about 2.5 °C cooler. Lead author Johan Weijers and his colleagues concluded that the land-sea temperature difference has by far the largest influence on continental rainfall. The relation of air pressure to temperature strongly determines this factor. During the last ice age, the land climate in tropical Africa was drier than it is now, whereas it favors the growth of a lush rainforest. == See also == African Rainforest Conservancy (ARC) Global 200 Plant Resources of Tropical Africa == References == == Bibliography == Burgess, N., J.D. Hales, E. Underwood, and E. Dinerstein (2004). Terrestrial Ecoregions of Africa and Madagascar: A Conservation Assessment. Island Press, Washington, D.C. Thieme, M.L., R. Abell, M.L.J. Stiassny, P. Skelton, B. Lehner, G.G. Teugels, E. Dinerstein, A.K. Toham, N. Burgess & D. Olson. 2005. Freshwater ecoregions of Africa and Madagascar: A conservation assessment. Washington D.C.: World Wildlife Fund. == Further reading == Production Land use study == External links == Terrestrial ecoregions of the world African Invertebrates — A journal of Afrotropical biodiversity research Manual of Afrotropical Diptera CGIAR Research Program on integrated systems in the humid tropics
|
{
"page_id": 201208,
"source": null,
"title": "Afrotropical realm"
}
|
Head III is an oil painting by Francis Bacon, one of series of works made in 1949 for his first one-man exhibition at the Hanover Gallery, in London. As with the other six paintings in the series, it focuses on the disembodied head of male figure, who looks out with a penetrating gaze, but is fixed against an isolating, flat, nondescript background, while also enfolded by hazy horizontal foreground curtain-like folds which seems to function like a surrounding cage. Head III was first exhibited in November 1949 at the Hanover in a showing commissioned by one of the artist's early champions, Erica Brausen. The six head paintings were painted during a short period of time, when Bacon was under pressure to provide works for the Hanover exhibition. Of the series, Head I, Head II, and Head VI are today seen as artistically successful, with Head VI as ground breaking, and a direct precursor to Bacon's seminal 1950s many representations of Popes. Head III is important in the development in that it is the first of the series in which Bacon masters the effect of the horizontal folds, and the ambiguous facial expression of the subject nears that of his Diego Velázquez's Portrait of Innocent X; his primary source for these paintings. The painting is in a private collection, having been sold at auction at Sotheby's in 2013 for £10,442,500. == Description == The painting measures 81 by 66 centimetres (32 in × 26 in). Perhaps a portrait of Bacon's lover Eric Hall, the grisaille work depicts a bald man's head with pock-marked discolored off-white face, partially concealed by diaphanous curtains. The face has an enigmatic expression, with his cold eyes - emphasised by bright marks of zinc white - looking out through broken pince-nez spectacles. This is the first occasion
|
{
"page_id": 53416441,
"source": null,
"title": "Head III"
}
|
when the motif of broken glasses appears in Bacon's work, inspired by the image of an injured nurse in the 1925 film Battleship Potemkin. The open-mouthed scream of the nurse in the film would also become a theme of Bacon's work, including Head VI, and Fragment of a Crucifixion. == Commission and provenance == The 1949 Hanover gallery exhibition included the six Head paintings, and four other important early works by Bacon: Three Studies for Figures at the Base of a Crucifixion, Figure in a landscape, Study from the Human Body (also known as Study for Figure) and Study for Portrait (also known as Man in a Blue Box). They are usually interpreted as intermediate steps from the preliminary images in Head I and Head II towards the final image of Head VI, the first of Bacon's paintings to reference Velázquez and his Portrait of Innocent X of 1650. Head III was the first of the six paintings to be sold at the Hanover Gallery exhibition. It was acquired by US art collector Wright Saltus Ludington (brother of Charles Townsend Ludington) in October 1949, shortly before the exhibition opened in November 1949. It was later sold to Sir Edward and Lady Hulton, and passed through the hands of several private collectors. It was included in Bacon retrospective at the Tate Gallery in 1985, and sold again at Sotheby's in London in 2013. == Reception == Head III was described by Wyndham Lewis in The Listener on 12 May 1949, page 811: "Bacon's picture, as usual, is in lamp-black monochrome, the zinc white of the monster’s eyes glittering in the cold crumbling grey of the face. Bacon is a Grand Guignol artist: the mouths in his heads are unpleasant places, evil passions make a glittering white mess of the lips." and
|
{
"page_id": 53416441,
"source": null,
"title": "Head III"
}
|
then in The Listener on 17 November 1949, page 860. He later wrote that "part of the head is rotting away into space". == References == === Notes === === Sources ===
|
{
"page_id": 53416441,
"source": null,
"title": "Head III"
}
|
Elaphidion irroratum is a species of beetle in the family Cerambycidae. It was described by Carl Linnaeus in his 1767 12th edition of Systema Naturae. == Description == Head very dark brown, almost black; front dappled with cream colour. Antennae dark brown, and about the length of the insect; having spines at each joint, except that next the head. Thorax spineless, brownish black, with white patches on its sides; and, when viewed through a microscope, punctured. Scutellum very small, and nearly triangular. Elytra brownish black, margined at the sides and suture, with whitish patches thereon, punctured; having two spines at the extremity of each. Abdomen and breast black, and covered with short grey hairs like pile. Legs reddish brown, with a small spine at the tip of each of the femora (except the fore ones), and another at the tips of the tibiae. Length of body 3⁄4 inch (19 mm). == References ==
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{
"page_id": 42799608,
"source": null,
"title": "Elaphidion irroratum"
}
|
The Indomalayan realm is one of the eight biogeographic realms. It extends across most of South and Southeast Asia and into the southern parts of East Asia. Also called the Oriental realm by biogeographers, Indomalaya spreads all over the Indian subcontinent and Southeast Asia to lowland southern China, and through Indonesia as far as Sumatra, Java, Bali, and Borneo, east of which lies the Wallace line, the realm boundary named after Alfred Russel Wallace which separates Indomalaya from Australasia. Indomalaya also includes the Philippines, lowland Taiwan, and Japan's Ryukyu Islands. Most of Indomalaya was originally covered by forest, and includes tropical and subtropical moist broadleaf forests, with tropical and subtropical dry broadleaf forests predominant in much of India and parts of Southeast Asia. The tropical forests of Indomalaya are highly variable and diverse, with economically important trees, especially in the families Dipterocarpaceae and Fabaceae. == Major ecological regions == The World Wildlife Fund (WWF) divides Indomalayan realm into three bio-regions, which it defines as "geographic clusters of eco-regions that may span several habitat types, but have strong biogeographic affinities, particularly at taxonomic levels higher than the species level (genus, family)". === Indian subcontinent === The Indian subcontinent bioregion covers most of India, Bangladesh, Nepal, Bhutan, and Sri Lanka and eastern parts of Pakistan. The Hindu Kush, Karakoram, Himalaya, and Patkai ranges bound the bioregion on the northwest, north, and northeast; these ranges were formed by the collision of the northward-drifting Indian subcontinent with Asia beginning 45 million years ago. The Hindu Kush, Karakoram, and Himalaya are a major biogeographic boundary between the subtropical and tropical flora and fauna of the Indian subcontinent and the temperate-climate Palearctic realm. === Indochina === The Indochina bioregion includes most of mainland Southeast Asia, including Myanmar, Thailand, Laos, Vietnam, and Cambodia, as well as the
|
{
"page_id": 201211,
"source": null,
"title": "Indomalayan realm"
}
|
subtropical forests of southern China. === Sunda Shelf and the Philippines === Malesia is a botanical province which straddles the boundary between Indomalaya and Australasia. It includes the Malay Peninsula and the western Indonesian islands (known as Sundaland), the Philippines, the eastern Indonesian islands, and New Guinea. While the Malesia has much in common botanically, the portions east and west of the Wallace Line differ greatly in land animal species; Sundaland shares its fauna with mainland Asia, while terrestrial fauna on the islands east of the Wallace line are derived at least in part from species of Australian origin, such as marsupial mammals and ratite birds. == History == The flora of Indomalaya blends elements from the ancient supercontinents of Laurasia and Gondwana. Gondwanian elements were first introduced by India, which detached from Gondwana approximately 90 MYA, carrying its Gondwana-derived flora and fauna northward, which included cichlid fish and the plant families Crypteroniaceae and possibly Dipterocarpaceae. India collided with Asia 30-45 MYA, and exchanged species. Later, as Australia-New Guinea drifted north, the collision of the Australian and Asian plates pushed up the islands of Wallacea, which were separated from one another by narrow straits, allowing a botanic exchange between Indomalaya and Australasia. Asian rainforest flora, including the dipterocarps, island-hopped across Wallacea to New Guinea, and several Gondwanian plant families, including podocarps and araucarias, moved westward from Australia-New Guinea into western Malesia and Southeast Asia. == Flora == The subfamily Dipterocarpoideae comprises characteristic tree species in Indomalaya's moist and seasonally dry forests, with the greatest species diversity in the moist forests of Borneo. Teak (Tectona) is characteristic of the seasonally dry forests of the Indomalaya, from India through Indochina, Malaysia, and the Philippines. Tropical pitcher plants (Nepenthes) are also characteristic of Indomalaya, and the greatest diversity of species is in Sumatra,
|
{
"page_id": 201211,
"source": null,
"title": "Indomalayan realm"
}
|
Borneo, and the Philippines. The tropical forests of Indomalaya and Australasia share many lineages of plants, which have managed over millions of years to disperse across the straits and islands between Sundaland and New Guinea. The two floras evolved in long isolation, and the fossil record suggests that Asian species dispersed to Australasia starting 33 million years ago as Australasia moved northwards, and dispersal increased 12 million years ago as the two continents approached their present positions. The exchange was asymmetric, with more Indomalayan species spreading to Australasia than Australasian species to Indomalaya. == Fauna == Two orders of mammals, the colugos (Dermoptera) and treeshrews (Scandentia), are endemic to the realm, as are families Craseonycteridae (Kitti's hog-nosed bat), Diatomyidae, Platacanthomyidae, Tarsiidae (tarsiers) and Hylobatidae (gibbons). Large mammals characteristic of Indomalaya include the leopard, tigers, water buffalos, Asian elephant, Indian rhinoceros, Javan rhinoceros, Malayan tapir, orangutans, and gibbons. Indomalaya has three endemic bird families, the Irenidae (fairy bluebirds), Megalaimidae and Rhabdornithidae (Philippine creepers). Also characteristic are pheasants, pittas, Old World babblers, and flowerpeckers. Indomalaya has 1000 species of amphibians in 81 genera, about 17 of global species. 800 Indomalayan species, or 80%, are endemic. Indomalaya has three endemic families of amphibians, Nasikabatrachidae, Ichthyophiidae, and Uraeotyphlidae. 329, or 33%, of Indomalayan amphibians are considered threatened or extinct, with habitat loss as the principal cause. More information is available under Indomalayan realm fauna. == Indomalayan ecoregions == == See also == Ecoregions of India Ecoregions of the Philippines Mainland Southeast Asia (the Indochinese Peninsula) Malesia Sundaland == Bibliography == Wikramanayake, E., E. Dinerstein, C. J. Loucks, D. M. Olson, J. Morrison, J. L. Lamoreux, M. McKnight, and P. Hedao. 2002. Terrestrial ecoregions of the Indo-Pacific: a conservation assessment. Island Press, Washington, DC, USA, [3]. == References ==
|
{
"page_id": 201211,
"source": null,
"title": "Indomalayan realm"
}
|
Head V is a 1949 painting by Irish-born British artist Francis Bacon, one of the series of works made in 1949 for his first one-man exhibition at the Hanover Gallery, in London. It measures 82 by 66 centimetres (32 in × 26 in) and is held in a private collection. The painting is part of a series of six works from the late 1940s depicting heads. Like Head II, the work depicts a distorted head in a space in a space shrouded with vertical bands interpreted as curtains, with several safety pins in the curtains. Bacon's six Head paintings were first exhibited at the Hanover Gallery in 1949, alongside four other important early works by Bacon: Three Studies for Figures at the Base of a Crucifixion, Figure in a landscape, Study from the Human Body (also known as Study for Figure) and Study for Portrait (also known as Man in a Blue Box). It has been described as one of the most elusive images produced by Bacon and also as the most abstract or indistinct picture of the series. It has not been exhibited since 1958, and was owned by a private collector in Switzerland in 1964. == References == == Sources == Dawson, Barbara; Sylvester, David. Francis Bacon in Dublin. London: Thames & Hudson, 2000. ISBN 978-0-500-28254-0 Farr, Dennis; Peppiatt, Michael; Yard, Sally. Francis Bacon: A Retrospective. NY: Harry N Abrams, 1999. ISBN 978-0-8109-2925-8 Peppiatt, Michael. Anatomy of an Enigma. London: Westview Press, 1996. ISBN 978-0-8133-3520-9 Russell, John. Francis Bacon (World of Art). NY: Norton, 1971. ISBN 978-0-500-20169-5 == External links == Head V (1949), francis-bacon.com Head V, 1949, Artimage Wyndham Lewis and Francis Bacon, Jan Cox
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{
"page_id": 53416446,
"source": null,
"title": "Head V"
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|
Human genetic resistance to malaria refers to inherited changes in the DNA of humans which increase resistance to malaria and result in increased survival of individuals with those genetic changes. The existence of these genotypes is likely due to evolutionary pressure exerted by parasites of the genus Plasmodium which cause malaria. Since malaria infects red blood cells, these genetic changes are most common alterations to molecules essential for red blood cell function (and therefore parasite survival), such as hemoglobin or other cellular proteins or enzymes of red blood cells. These alterations generally protect red blood cells from invasion by Plasmodium parasites or replication of parasites within the red blood cell. These inherited changes to hemoglobin or other characteristic proteins, which are critical and rather invariant features of mammalian biochemistry, usually cause some kind of inherited disease. Therefore, they are commonly referred to by the names of the blood disorders associated with them, including sickle-cell disease, thalassemia, glucose-6-phosphate dehydrogenase deficiency, and others. These blood disorders cause increased morbidity and mortality in areas of the world where malaria is less prevalent. == Development of genetic resistance to malaria == Microscopic parasites, like viruses, protozoans that cause malaria, and others, cannot replicate on their own and rely on a host to continue their life cycles. They replicate by invading the hosts' cells and usurping the cellular machinery to replicate themselves. Eventually, unchecked replication causes the cells to burst, killing the cells and releasing the infectious organisms into the bloodstream where they can infect other cells. As cells die and toxic products of invasive organism replication accumulate, disease symptoms appear. Because this process involves specific proteins produced by the infectious organism as well as the host cell, even a very small change in a critical protein may render infection difficult or impossible. Such changes
|
{
"page_id": 24973826,
"source": null,
"title": "Human genetic resistance to malaria"
}
|
might arise by a process of mutation in the gene that codes for the protein. If the change is in the gamete, that is, the sperm or egg that join to form a zygote that grows into a human being, the protective mutation will be inherited. Since lethal diseases kill many persons who lack protective mutations, in time, many persons in regions where lethal diseases are endemic come to inherit protective mutations. When the P. falciparum parasite infects a host cell, it alters the characteristics of the red blood cell membrane, making it "stickier" to other cells. Clusters of parasitized red blood cells can exceed the size of the capillary circulation, adhere to the endothelium, and block circulation. When these blockages form in the blood vessels surrounding the brain, they cause cerebral hypoxia, resulting in neurological symptoms known as cerebral malaria. This condition is characterized by confusion, disorientation, and often terminal coma. It accounts for 80% of malaria deaths. Therefore, mutations that protect against malaria infection and lethality pose a significant advantage. Malaria has placed the strongest known selective pressure on the human genome since the origin of agriculture within the past 10,000 years. Plasmodium falciparum was probably not able to gain a foothold among African populations until larger sedentary communities emerged in association with the evolution of domestic agriculture in Africa (the agricultural revolution). Several inherited variants in red blood cells have become common in parts of the world where malaria is frequent as a result of selection exerted by this parasite. This selection was historically important as the first documented example of disease as an agent of natural selection in humans. It was also the first example of genetically controlled innate immunity that operates early in the course of infections, preceding adaptive immunity which exerts effects after several
|
{
"page_id": 24973826,
"source": null,
"title": "Human genetic resistance to malaria"
}
|
days. In malaria, as in other diseases, innate immunity leads into, and stimulates, adaptive immunity. Mutations may have detrimental as well as beneficial effects, and any single mutation may have both. Infectiousness of malaria depends on specific proteins present in the cell walls and elsewhere in red blood cells. Protective mutations alter these proteins in ways that make them inaccessible to malaria organisms. However, these changes also alter the functioning and form of red blood cells that may have visible effects, either overtly, or by microscopic examination of red blood cells. These changes may impair the function of red blood cells in various ways that have a detrimental effect on the health or longevity of the individual. However, if the net effect of protection against malaria outweighs the other detrimental effects, the protective mutation will tend to be retained and propagated from generation to generation. These alterations which protect against malarial infections but impair red blood cells are generally considered blood disorders since they tend to have overt and detrimental effects. Their protective function has only in recent times, been discovered and acknowledged. Some of these disorders are known by fanciful and cryptic names like sickle-cell anemia, thalassaemia, glucose-6-phosphate dehydrogenase deficiency, ovalocytosis, elliptocytosis and loss of the Gerbich antigen and the Duffy antigen. These names refer to various proteins, enzymes, and the shape or function of red blood cells. == Innate resistance == The potent effect of genetically controlled innate resistance is reflected in the probability of survival of young children in areas where malaria is endemic. It is necessary to study innate immunity in the susceptible age group (younger than four years) because, in older children and adults, the effects of innate immunity are overshadowed by those of adaptive immunity. It is also necessary to study populations in which
|
{
"page_id": 24973826,
"source": null,
"title": "Human genetic resistance to malaria"
}
|
random use of antimalarial drugs does not occur. Some early contributions on innate resistance to infections of vertebrates, including humans, are summarized in Table 1. It is remarkable that two of the pioneering studies were on malaria. The classical studies on the Toll receptor in Drosophila fruit fly were rapidly extended to Toll-like receptors in mammals and then to other pattern recognition receptors, which play important roles in innate immunity. However, the early contributions on malaria remain as classical examples of innate resistance, which have stood the test of time. === Mechanisms of protection === The mechanisms by which erythrocytes containing abnormal hemoglobins, or are G6PD deficient, are partially protected against P. falciparum infections are not fully understood, although there has been no shortage of suggestions. During the peripheral blood stage of replication malaria parasites have a high rate of oxygen consumption and ingest large amounts of hemoglobin. It is likely that HbS in endocytic vesicles is deoxygenated, polymerizes and is poorly digested. In red cells containing abnormal hemoglobins, or which are G6PD deficient, oxygen radicals are produced, and malaria parasites induce additional oxidative stress. This can result in changes in red cell membranes, including translocation of phosphatidylserine to their surface, followed by macrophage recognition and ingestion. The authors suggest that this mechanism is likely to occur earlier in abnormal than in normal red cells, thereby restricting multiplication in the former. In addition, binding of parasitized sickle cells to endothelial cells is significantly decreased because of an altered display of P. falciparum erythrocyte membrane protein-1 (PfMP-1). This protein is the parasite's main cytoadherence ligand and virulence factor on the cell surface. During the late stages of parasite replication red cells are adherent to venous endothelium, and inhibiting this attachment could suppress replication. Sickle hemoglobin induces the expression of heme oxygenase-1
|
{
"page_id": 24973826,
"source": null,
"title": "Human genetic resistance to malaria"
}
|
in hematopoietic cells. Carbon monoxide, a byproduct of heme catabolism by heme oxygenase-1(HO-1), prevents an accumulation of circulating free heme after Plasmodium infection, suppressing the pathogenesis of experimental cerebral malaria. Other mechanisms, such as enhanced tolerance to disease mediated by HO-1 and reduced parasitic growth due to translocation of host micro-RNA into the parasite, have been described. == Types of innate resistance == The first line of defense against malaria is mainly exerted by abnormal hemoglobins and glucose-6-phosphate dehydrogenase deficiency. The three major types of inherited genetic resistance – sickle cell disease, thalassemias, and G6PD deficiency – were present in the Mediterranean world by the time of the Roman Empire. === Hemoglobin abnormalities === ==== Distribution of abnormal hemoglobins ==== Malaria does not occur in the cooler, drier climates of the highlands in the tropical and subtropical regions of the world. Tens of thousands of individuals have been studied, and high frequencies of abnormal hemoglobins have not been found in any population that was malaria-free. The frequencies of abnormal hemoglobins in different populations vary greatly, but some are undoubtedly polymorphic, having frequencies higher than expected by recurrent mutation. There is no longer doubt that malarial selection played a major role in the distribution of all these polymorphisms. All of these are in malarious areas, Sickle cell – The gene for HbS associated with sickle-cell is today distributed widely throughout sub-Saharan Africa, the Middle East, and parts of the Indian subcontinent, where carrier frequencies range from 5–40% or more of the population. Frequencies of sickle-cell heterozygotes were 20–40% in malarious areas of Kenya, Uganda, and Tanzania. Later studies by many investigators filled in the picture. High frequencies of the HbS gene are confined to a broad belt across Central Africa, but excluding most of Ethiopia and the East African highlands; this
|
{
"page_id": 24973826,
"source": null,
"title": "Human genetic resistance to malaria"
}
|
corresponds closely to areas of malaria transmission. Sickle-cell heterozygote frequencies up to 20% also occur in pockets of India and Greece that were formerly highly malarious. The thalassemias have a high incidence in a broad band extending from the Mediterranean basin and parts of Africa, throughout the Middle East, the Indian subcontinent, Southeast Asia, Melanesia, and into the Pacific Islands. α-thalassemia, which attains frequencies of 30% in parts of West Africa; β-thalassemia, with frequencies up to 10% in parts of Italy; HbE, which attains frequencies up to 55% in Thailand and other Southeast Asian countries; HbE is found in the eastern half of the Indian subcontinent and throughout Southeast Asia, where, in some areas, carrier rates may exceed 60% of the population. HbC, which attains frequencies approaching 20% in northern Ghana and Burkina-Faso. HbC is restricted to parts of West and North Africa. concurrent polymorphisms – double heterozygotes for HbS and β-thalassemia, and for HbS and HbC, suffer from variant forms of sickle-cell disease, milder than SS but likely to reduce fitness before modern treatment was available. As predicted, these variant alleles tend to be mutually exclusive in populations. There is a negative correlation between frequencies of HbS and β-thalassemia in different parts of Greece and of HbS and HbC in West Africa. Where there is no adverse interaction of mutations, as in the case of abnormal hemoglobins and G6PD deficiency, a positive correlation of these variant alleles in populations would be expected and is found. ==== Sickle-cell ==== Sickle-cell disease was the genetic disorder to be linked to a mutation of a specific protein. Pauling introduced his fundamentally important concept of sickle cell anemia as a genetically transmitted molecular disease. The molecular basis of sickle cell anemia was finally elucidated in 1959 when Ingram perfected the techniques of tryptic
|
{
"page_id": 24973826,
"source": null,
"title": "Human genetic resistance to malaria"
}
|
peptide fingerprinting. In the mid-1950s, one of the newest and most reliable ways of separating peptides and amino acids was by means of the enzyme trypsin, which split polypeptide chains by specifically degrading the chemical bonds formed by the carboxyl groups of two amino acids, lysine and arginine. Small differences in hemoglobin A and S will result in small changes in one or more of these peptides . To try to detect these small differences, Ingram combined paper electrophoresis and the paper chromotography methods. By this combination he created a two-dimensional method that enabled him to comparatively "fingerprint" the hemoglobin S and A fragments he obtained from the tryspin digest. The fingerprints revealed approximately 30 peptide spots, there was one peptide spot clearly visible in the digest of haemoglobin S which was not obvious in the haemoglobin A fingerprint. The HbS gene defect is a mutation of a single nucleotide (A to T) of the β-globin gene replacing the amino acid glutamic acid with the less polar amino acid valine at the sixth position of the β chain. HbS has a lower negative charge at physiological pH than does normal adult hemoglobin. The consequences of the simple replacement of a charged amino acid with a hydrophobic, neutral amino acid are far-ranging, Recent studies in West Africa suggest that the greatest impact of Hb S seems to be to protect against either death or severe disease—that is, profound anemia or cerebral malaria—while having less effect on infection per se. Children who are heterozygous for the sickle cell gene have only one-tenth the risk of death from falciparum as do those who are homozygous for the normal hemoglobin gene. Binding of parasitized sickle erythrocytes to endothelial cells and blood monocytes is significantly reduced due to an altered display of Plasmodium falciparum erythrocyte
|
{
"page_id": 24973826,
"source": null,
"title": "Human genetic resistance to malaria"
}
|
membrane protein 1 (PfEMP-1), the parasite's major cytoadherence ligand and virulence factor on the erythrocyte surface. Protection also derives from the instability of sickle hemoglobin, which clusters the predominant integral red cell membrane protein (called band 3) and triggers accelerated removal by phagocytic cells. Natural antibodies recognize these clusters on senescent erythrocytes. Protection by HbAS involves the enhancement of not only innate but also of acquired immunity to the parasite. Prematurely denatured sickle hemoglobin results in an upregulation of natural antibodies which control erythrocyte adhesion in both malaria and sickle cell disease. Targeting the stimuli that lead to endothelial activation will constitute a promising therapeutic strategy to inhibit sickle red cell adhesion and vaso-occlusion. This has led to the hypothesis that while homozygotes for the sickle cell gene suffer from disease, heterozygotes might be protected against malaria. Malaria remains a selective factor for the sickle cell trait. ==== Thalassemias ==== It has long been known that a kind of anemia, termed thalassemia, has a high frequency in some Mediterranean populations, including Greeks and southern Italians. The name is derived from the Greek words for sea (thalassa), meaning the Mediterranean Sea, and blood (haima). Vernon Ingram deserves the credit for explaining the genetic basis of different forms of thalassemia as an imbalance in the synthesis of the two polypeptide chains of hemoglobin. In the common Mediterranean variant, mutations decrease production of the β-chain (β-thalassemia). In α-thalassemia, which is relatively frequent in Africa and several other countries, production of the α-chain of hemoglobin is impaired, and there is relative over-production of the β-chain. Individuals homozygous for β-thalassemia have severe anemia and are unlikely to survive and reproduce, so selection against the gene is strong. Those homozygous for α-thalassemia also suffer from anemia and there is some degree of selection against the gene.
|
{
"page_id": 24973826,
"source": null,
"title": "Human genetic resistance to malaria"
}
|
The lower Himalayan foothills and Inner Terai or Doon Valleys of Nepal and India are highly malarial due to a warm climate and marshes sustained during the dry season by groundwater percolating down from the higher hills. Malarial forests were intentionally maintained by the rulers of Nepal as a defensive measure. Humans attempting to live in this zone suffered much higher mortality than at higher elevations or below on the drier Gangetic Plain. However, the Tharu people had lived in this zone long enough to evolve resistance via multiple genes. Medical studies among the Tharu and non-Tharu population of the Terai yielded the evidence that the prevalence of cases of residual malaria is nearly seven times lower among Tharus. The basis for resistance has been established to be homozygosity of α-Thalassemia gene within the local population. Endogamy along caste and ethnic lines appear to have prevented these genes from being more widespread in neighboring populations. ==== HbC and HbE erythroids ==== There is evidence that the persons with α-thalassemia, HbC and HbE have some degree of protection against the parasite. Hemoglobin C (HbC) is an abnormal hemoglobin with substitution of a lysine residue for glutamic acid residue of the β-globin chain, at exactly the same β-6 position as the HbS mutation. The "C" designation for HbC is from the name of the city where it was discovered—Christchurch, New Zealand. People who have this disease, particularly children, may have episodes of abdominal and joint pain, an enlarged spleen, and mild jaundice, but they do not have severe crises, as occur in sickle cell disease. Haemoglobin C is common in malarious areas of West Africa, especially in Burkina Faso. In a large case–control study performed in Burkina Faso on 4,348 Mossi subjects, that HbC was associated with a 29% reduction in risk
|
{
"page_id": 24973826,
"source": null,
"title": "Human genetic resistance to malaria"
}
|
of clinical malaria in HbAC heterozygotes and of 93% in HbCC homozygotes. HbC represents a 'slow but gratis' genetic adaptation to malaria through a transient polymorphism, compared to the polycentric 'quick but costly' adaptation through balanced polymorphism of HbS. HbC modifies the quantity and distribution of the variant antigen P. falciparum erythrocyte membrane protein 1 (PfEMP1) on the infected red blood cell surface and the modified display of malaria surface proteins reduces parasite adhesiveness (thereby avoiding clearance by the spleen) and can reduce the risk of severe disease. Hemoglobin E is due to a single point mutation in the gene for the beta chain with a glutamate-to-lysine substitution at position 26. It is one of the most prevalent hemoglobinopathies with 30 million people affected. Hemoglobin E is very common in parts of Southeast Asia. HbE erythrocytes have an unidentified membrane abnormality that renders the majority of the RBC population relatively resistant to invasion by P falciparum. === Other erythrocyte mutations === Other genetic mutations besides hemoglobin abnormalities that confer resistance to Plasmodia infection involve alterations of the cellular surface antigenic proteins, cell membrane structural proteins, or enzymes involved in glycolysis. ==== Glucose-6-phosphate dehydrogenase deficiency ==== Glucose-6-phosphate dehydrogenase (G6PD) is an important enzyme in red cells, metabolizing glucose through the pentose phosphate pathway, an anabolic alternative to catabolic oxidation (glycolysis), while maintaining a reducing environment. G6PD is present in all human cells but is particularly important to red blood cells. Since mature red blood cells lack nuclei and cytoplasmic RNA, they cannot synthesize new enzyme molecules to replace genetically abnormal or ageing ones. All proteins, including enzymes, have to last for the entire lifetime of the red blood cell, which is normally 120 days. In 1956 Alving and colleagues showed that in some African Americans the antimalarial drug primaquine induces hemolytic
|
{
"page_id": 24973826,
"source": null,
"title": "Human genetic resistance to malaria"
}
|
anemia, and that those individuals have an inherited deficiency of G6PD in erythrocytes. G6PD deficiency is sex-linked, and common in Mediterranean, African and other populations. In Mediterranean countries such individuals can develop a hemolytic diathesis (favism) after consuming fava beans. G6PD deficient persons are also sensitive to several drugs in addition to primaquine. G6PD deficiency is the second most common enzyme deficiency in humans (after ALDH2 deficiency), estimated to affect some 400 million people. There are many mutations at this locus, two of which attain frequencies of 20% or greater in African and Mediterranean populations; these are termed the A- and Med mutations. Mutant varieties of G6PD can be more unstable than the naturally occurring enzyme, so that their activity declines more rapidly as red cells age. This question has been studied in isolated populations where antimalarial drugs were not used in Tanzania, East Africa and in the Republic of the Gambia, West Africa, following children during the period when they are most susceptible to falciparum malaria. In both cases parasite counts were significantly lower in G6PD-deficient persons than in those with normal red cell enzymes. The association has also been studied in individuals, which is possible because the enzyme deficiency is sex-linked and female heterozygotes are mosaics due to lyonization, where random inactivation of an X-chromosome in certain cells creates a population of G6PD deficient red blood cells coexisting with normal red blood cells. Malaria parasites were significantly more often observed in normal red cells than in enzyme-deficient cells. An evolutionary genetic analysis of malarial selection of G6PD deficiency genes has been published by Tishkoff and Verelli. The enzyme deficiency is common in many countries that are, or were formerly, malarious, but not elsewhere. ==== PK deficiency ==== Pyruvate kinase (PK) deficiency, also called erythrocyte pyruvate kinase deficiency, is
|
{
"page_id": 24973826,
"source": null,
"title": "Human genetic resistance to malaria"
}
|
an inherited metabolic disorder of the enzyme pyruvate kinase. In this condition, a lack of pyruvate kinase slows down the process of glycolysis. This effect is especially devastating in cells that lack mitochondria because these cells must use anaerobic glycolysis as their sole source of energy because the TCA cycle is not available. One example is red blood cells, which in a state of pyruvate kinase deficiency rapidly become deficient in ATP and can undergo hemolysis. Therefore, pyruvate kinase deficiency can cause hemolytic anemia. There is a significant correlation between severity of PK deficiency and extent of protection against malaria. ==== Elliptocytosis ==== Elliptocytosis, a blood disorder in which an abnormally large number of the patient's erythrocytes are elliptical. There is much genetic variability amongst those affected. There are three major forms of hereditary elliptocytosis: common hereditary elliptocytosis, spherocytic elliptocytosis and southeast Asian ovalocytosis. ==== Southeast Asian ovalocytosis ==== Ovalocytosis is a subtype of elliptocytosis, and is an inherited condition in which erythrocytes have an oval instead of a round shape. In most populations ovalocytosis is rare, but South-East Asian ovalocytosis (SAO) occurs in as many as 15% of the indigenous people of Malaysia and of Papua New Guinea. Several abnormalities of SAO erythrocytes have been reported, including increased red cell rigidity and reduced expression of some red cell antigens. SAO is caused by a mutation in the gene encoding the erythrocyte band 3 protein. There is a deletion of codons 400–408 in the gene, leading to a deletion of 9 amino-acids at the boundary between the cytoplasmic and transmembrane domains of band 3 protein. Band 3 serves as the principal binding site for the membrane skeleton, a submembrane protein network composed of ankyrin, spectrin, actin, and band 4.1. Ovalocyte band 3 binds more tightly than normal band 3 to
|
{
"page_id": 24973826,
"source": null,
"title": "Human genetic resistance to malaria"
}
|
ankyrin, which connects the membrane skeleton to the band 3 anion transporter. These qualitative defects create a red blood cell membrane that is less tolerant of shear stress and more susceptible to permanent deformation. SAO is associated with protection against cerebral malaria in children because it reduces sequestration of erythrocytes parasitized by P. falciparum in the brain microvasculature. Adhesion of P. falciparum-infected red blood cells to CD36 is enhanced by the cerebral malaria-protective SAO trait . Higher efficiency of sequestration via CD36 in SAO individuals could determine a different organ distribution of sequestered infected red blood cells. These provide a possible explanation for the selective advantage conferred by SAO against cerebral malaria. ==== Duffy antigen receptor negativity ==== Plasmodium vivax has a wide distribution in tropical countries, but is absent or rare in a large region in West and Central Africa, as recently confirmed by PCR species typing. This gap in distribution has been attributed to the lack of expression of the Duffy antigen receptor for chemokines (DARC) on the red cells of many sub-Saharan Africans. Duffy negative individuals are homozygous for a DARC allele, carrying a single nucleotide mutation (DARC 46 T → C), which impairs promoter activity by disrupting a binding site for the hGATA1 erythroid lineage transcription factor. In widely cited in vitro and in vivo studies, Miller et al. reported that the Duffy blood group is the receptor for P. vivax and that the absence of the Duffy blood group on red cells is the resistance factor to P. vivax in persons of African descent. This has become a well-known example of innate resistance to an infectious agent because of the absence of a receptor for the agent on target cells. However, observations have accumulated showing that the original Miller report needs qualification. In human studies
|
{
"page_id": 24973826,
"source": null,
"title": "Human genetic resistance to malaria"
}
|
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