title: Hourglass figure

text: The hourglass figure is perhaps the most iconic of the four major body shapes, as reflected by the fashion industry. Such fashion designers as Christian Dior have designed clothes with the female hourglass body shape in mind. Fashion designers of today continue to design clothes to fit the hourglass body shape even though the body shapes of modern women are changing and becoming much more varied. Even now when plus-size is included in the fashion industry as well as being more commonly produced by various groups of clothing designers, the hourglass shape is a great influence on the design of plus-sized clothes. Models of plus size clothing retain the coveted hourglass figure, albeit larger than the models of regular clothing. Research conducted in Britain by the University College London and the London College of Fashion found that less than 10% of women had an hourglass body shape. The smooth and narrow waist continues to dominate in fashion designs meant to cater to plus-size women even when that particular body shape, the hourglass, is not commonly found.


title: Hourglass figure

text: Recent research indicates that men have a marked preference for women who have the hourglass figure. These studies found that this shape was even more highly preferred than breast size or facial features. While it is true that most men were initially drawn to a woman's cleavage, it was her hips and waist that were in fact what they found the most attractive. Scientists observed that the most desirable waist-to-hip ratio was 0.7- a waist that measures 70 percent of the circumference of the hips. Some examples of women who possess or have possessed the "perfect" body were Marilyn Monroe, Jessica Alba and Alessandra Ambrosio. A scientist on one of the studies speculated that the 0.7 ratio might signal female fertility. Recent studies have shown that only about 8 percent of women today have the sort of hourglass figure flaunted by curvaceous 1950s film stars such as Sophia Loren. Of the 6,000 women's body shapes analyzed in the study, 46 percent were described as rectangular, with the waist less than nine inches smaller than the hips or bust. Just over 20 percent of women were bottom-heavy "spoons", or pear shapes, with hips two inches larger than busts or more, while almost 14 percent were "inverted triangles" - women whose busts were three or more inches bigger than their hips.


title: Radio telescope

text: A radio telescope is a specialized antenna and radio receiver used to detect radio waves from astronomical radio sources in the sky. Radio telescopes are the main observing instrument used in radio astronomy, which studies the radio frequency portion of the electromagnetic spectrum emitted by astronomical objects, just as optical telescopes are the main observing instrument used in traditional optical astronomy which studies the light wave portion of the spectrum coming from astronomical objects. Unlike optical telescopes, radio telescopes can be used in the daytime as well as at night.


title: Radio telescope

text: Since astronomical radio sources such as planets, stars, nebulas and galaxies are very far away, the radio waves coming from them are extremely weak, so radio telescopes require very large antennas to collect enough radio energy to study them, and extremely sensitive receiving equipment. Radio telescopes are typically large parabolic ("dish") antennas similar to those employed in tracking and communicating with satellites and space probes. They may be used singly or linked together electronically in an array. Radio observatories are preferentially located far from major centers of population to avoid electromagnetic interference (EMI) from radio, television, radar, motor vehicles, and other man-made electronic devices.


title: Radio telescope

text: Radio waves from space were first detected by engineer Karl Guthe Jansky in 1932 at Bell Telephone Laboratories in Holmdel, New Jersey using an antenna built to study radio receiver noise. The first purpose-built radio telescope was a 9-meter parabolic dish constructed by radio amateur Grote Reber in his back yard in Wheaton, Illinois in 1937. The sky survey he performed is often considered the beginning of the field of radio astronomy.


title: Radio telescope

text: The first radio antenna used to identify an astronomical radio source was built by Karl Guthe Jansky, an engineer with Bell Telephone Laboratories, in 1932. Jansky was assigned the task of identifying sources of static that might interfere with radiotelephone service. Jansky's antenna was an array of dipoles and reflectors designed to receive short wave radio signals at a frequency of 20.5 MHz (wavelength about 14.6 meters). It was mounted on a turntable that allowed it to rotate in any direction, earning it the name "Jansky's merry-go-round." It had a diameter of approximately and stood tall. By rotating the antenna, the direction of the received interfering radio source (static) could be pinpointed. A small shed to the side of the antenna housed an analog pen-and-paper recording system. After recording signals from all directions for several months, Jansky eventually categorized them into three types of static: nearby thunderstorms, distant thunderstorms, and a faint steady hiss above shot noise, of unknown origin. Jansky finally determined that the "faint hiss" repeated on a cycle of 23 hours and 56 minutes. This period is the length of an astronomical sidereal day, the time it takes any "fixed" object located on the celestial sphere to come back to the same location in the sky. Thus Jansky suspected that the hiss originated outside of the Solar System, and by comparing his observations with optical astronomical maps, Jansky concluded that the radiation was coming from the Milky Way Galaxy and was strongest in the direction of the center of the galaxy, in the constellation of Sagittarius.


title: Radio telescope

text: An amateur radio operator, Grote Reber, was one of the pioneers of what became known as radio astronomy. He built the first parabolic "dish" radio telescope, in diameter, in his back yard in Wheaton, Illinois in 1937. He repeated Jansky's pioneering work, identifying the Milky Way as the first off-world radio source, and he went on to conduct the first sky survey at very high radio frequencies, discovering other radio sources. The rapid development of radar during World War II created technology which was applied to radio astronomy after the war, and radio astronomy became a branch of astronomy, with universities and research institutes constructing large radio telescopes.


title: Radio telescope

text: The range of frequencies in the electromagnetic spectrum that makes up the radio spectrum is very large. As a consequence, the types of antennas that are used as radio telescopes vary widely in design, size, and configuration. At wavelengths of 30 meters to 3 meters (10–100 MHz), they are generally either directional antenna arrays similar to "TV antennas" or large stationary reflectors with moveable focal points. Since the wavelengths being observed with these types of antennas are so long, the "reflector" surfaces can be constructed from coarse wire mesh such as chicken wire.


title: Radio telescope

text: The increasing use of radio frequencies for communication makes astronomical observations more and more difficult (see Open spectrum).


title: Radio telescope

text: Negotiations to defend the frequency allocation for parts of the spectrum most useful for observing the universe are coordinated in the Scientific Committee on Frequency Allocations for Radio Astronomy and Space Science.


title: Radio telescope

text: The world's largest filled-aperture (i.e. full dish) radio telescope is the Five-hundred-meter Aperture Spherical Telescope (FAST) completed in 2016 by China. The dish with an area as large as 30 football fields is built into a natural karst depression in the landscape in Guizhou province and cannot move; the feed antenna is in a cabin suspended above the dish on cables. The active dish is composed of 4,450 moveable panels controlled by a computer. By changing the shape of the dish and moving the feed cabin on its cables, the telescope can be steered to point to any region of the sky up to 40° from the zenith. Although the dish is 500 meters in diameter, only a 300-meter circular area on the dish is illuminated by the feed antenna at any given time, so the actual effective aperture is 300 meters. Construction was begun in 2007 and completed July 2016 and the telescope became operational September 25, 2016.


title: Radio telescope

text: The world's second largest filled-aperture telescope was the Arecibo radio telescope located in Arecibo, Puerto Rico, though it suffered catastrophic collapse on 1 December 2020. Arecibo was one of the world's few radio telescope also capable of active (i.e., transmitting) radar imaging of near-Earth objects (see: radar astronomy); most other telescopes employ passive detection, i.e., receiving only. Arecibo was another stationary dish telescope like FAST. Arecibo's dish was built into a natural depression in the landscape, the antenna was steerable within an angle of about 20° of the zenith by moving the suspended feed antenna, giving use of a 270-meter diameter portion of the dish for any individual observation.


title: Radio telescope

text: The largest individual radio telescope of any kind is the RATAN-600 located near Nizhny Arkhyz, Russia, which consists of a 576-meter circle of rectangular radio reflectors, each of which can be pointed towards a central conical receiver.


title: Radio telescope

text: The above stationary dishes are not fully "steerable"; they can only be aimed at points in an area of the sky near the zenith, and cannot receive from sources near the horizon. The largest fully steerable dish radio telescope is the 100 meter Green Bank Telescope in West Virginia, United States, constructed in 2000. The largest fully steerable radio telescope in Europe is the Effelsberg 100-m Radio Telescope near Bonn, Germany, operated by the Max Planck Institute for Radio Astronomy, which also was the world's largest fully steerable telescope for 30 years until the Green Bank antenna was constructed. The third-largest fully steerable radio telescope is the 76-meter Lovell Telescope at Jodrell Bank Observatory in Cheshire, England, completed in 1957. The fourth-largest fully steerable radio telescopes are six 70-meter dishes: three Russian RT-70, and three in the NASA Deep Space Network. The planned Qitai Radio Telescope, at a diameter of , is expected to become the world's largest fully steerable single-dish radio telescope when completed in 2023.


title: Radio telescope

text: A more typical radio telescope has a single antenna of about 25 meters diameter. Dozens of radio telescopes of about this size are operated in radio observatories all over the world.


title: Radio telescope

text: Since 1965, humans have launched three space-based radio telescopes. The first one, KRT-10, was attached to Salyut 6 orbital space station in 1979. In 1997, Japan sent the second, HALCA. The last one was sent by Russia in 2011 called Spektr-R.


title: Radio telescope

text: One of the most notable developments came in 1946 with the introduction of the technique called astronomical interferometry, which means combining the signals from multiple antennas so that they simulate a larger antenna, in order to achieve greater resolution. Astronomical radio interferometers usually consist either of arrays of parabolic dishes (e.g., the One-Mile Telescope), arrays of one-dimensional antennas (e.g., the Molonglo Observatory Synthesis Telescope) or two-dimensional arrays of omnidirectional dipoles (e.g., Tony Hewish's Pulsar Array). All of the telescopes in the array are widely separated and are usually connected using coaxial cable, waveguide, optical fiber, or other type of transmission line. Recent advances in the stability of electronic oscillators also now permit interferometry to be carried out by independent recording of the signals at the various antennas, and then later correlating the recordings at some central processing facility. This process is known as Very Long Baseline Interferometry (VLBI). Interferometry does increase the total signal collected, but its primary purpose is to vastly increase the resolution through a process called aperture synthesis. This technique works by superposing (interfering) the signal waves from the different telescopes on the principle that waves that coincide with the same phase will add to each other while two waves that have opposite phases will cancel each other out. This creates a combined telescope that is equivalent in resolution (though not in sensitivity) to a single antenna whose diameter is equal to the spacing of the antennas furthest apart in the array.


title: Radio telescope

text: A high-quality image requires a large number of different separations between telescopes. Projected separation between any two telescopes, as seen from the radio source, is called a baseline. For example, the Very Large Array (VLA) near Socorro, New Mexico has 27 telescopes with 351 independent baselines at once, which achieves a resolution of 0.2 arc seconds at 3 cm wavelengths. Martin Ryle's group in Cambridge obtained a Nobel Prize for interferometry and aperture synthesis. The Lloyd's mirror interferometer was also developed independently in 1946 by Joseph Pawsey's group at the University of Sydney. In the early 1950s, the Cambridge Interferometer mapped the radio sky to produce the famous 2C and 3C surveys of radio sources. An example of a large physically connected radio telescope array is the Giant Metrewave Radio Telescope, located in Pune, India. The largest array, the Low-Frequency Array (LOFAR), finished in 2012, is located in western Europe and consists of about 81,000 small antennas in 48 stations distributed over an area several hundreds of kilometers in diameter and operates between 1.25 and 30 m wavelengths. VLBI systems using post-observation processing have been constructed with antennas thousands of miles apart. Radio interferometers have also been used to obtain detailed images of the anisotropies and the polarization of the Cosmic Microwave Background, like the CBI interferometer in 2004.


title: Radio telescope

text: The world's largest physically connected telescope, the Square Kilometre Array (SKA), is planned to start operations in 2025.


title: Radio telescope

text: Many astronomical objects are not only observable in visible light but also emit radiation at radio wavelengths. Besides observing energetic objects such as pulsars and quasars, radio telescopes are able to "image" most astronomical objects such as galaxies, nebulae, and even radio emissions from planets.


title: Highgate

text: Highgate ( ) is a suburban area of north London at the northeastern corner of Hampstead Heath, north-northwest of Charing Cross.


title: Highgate

text: Highgate is one of the most expensive London suburbs in which to live. It has two active conservation organisations, the "Highgate Society" and the "Highgate Neighbourhood Forum" to protect and enhance its character and amenities.


title: Highgate

text: Until late Victorian times it was a distinct village outside London, sitting astride the main road to the north. The area retains many green expanses including the eastern part of Hampstead Heath, three ancient woods, Waterlow Park and the eastern-facing slopes known as Highgate bowl.


title: Highgate

text: At its centre is Highgate village, largely a collection of Georgian shops, pubs, restaurants, residential streets, and the Sacred Spirits Distillery interspersed with diverse landmarks such as St Michael's Church and steeple, St. Joseph's Church and its green copper dome, Highgate School (1565), Jacksons Lane arts centre housed in a Grade II listed former church, the Gatehouse Inn dating from 1670 which houses the theatre Upstairs at the Gatehouse and Berthold Lubetkin's 1930s Highpoint buildings. Pond Square, behind the High Street, is a registered village green and is the centre of communal activities which take place in the elegant buildings of the Highgate Literary and Scientific Institution and Highgate Society facing the Square.


title: Highgate

text: Highgate is perhaps best known for the Victorian Highgate Cemetery in which the Communist philosopher Karl Marx and the novelist George Eliot are buried, along with many other notable people.


title: Highgate

text: The village is at the top of Highgate Hill, which provides views across central London. Highgate is above sea level at its highest point.


title: Highgate

text: The area is divided among three London boroughs: Haringey in the north, Camden in the south and west, and Islington in the south and east. The postal district is N6.


title: Highgate

text: Historically, Highgate adjoined the Bishop of London's hunting estate. Highgate gets its name from these hunting grounds, as there was a high, deer-proof hedge surrounding the estate: 'the gate in the hedge'.


title: Highgate

text: The bishop kept a toll-house where one of the main northward roads out of London entered his land. A number of pubs sprang up along the route, one of which, the Gatehouse, commemorates the toll-house.


title: Highgate

text: Hampstead Lane and Highgate Hill contain the red brick Victorian buildings of Highgate School and its adjacent Chapel of St Michael. The school has played a paramount role in the life of the village and has existed on its site since its founding was permitted by letters patent from Queen Elizabeth I in 1565.


title: Highgate

text: The area north of the High Street and Hampstead Lane was part of Hornsey parish and also later the Municipal Borough of Hornsey, and the seat of that borough's governing body for many years.


title: Highgate

text: Highgate Hill, the steep street linking Archway (traditionally called part of Upper Holloway) and Highgate village, was the route of the Highgate Hill Cable Tramway, the first cable car to be built in Europe. It operated between 1884 and 1909.


title: Highgate

text: Like much of London, Highgate suffered damage during World War II by German air raids. The local tube station was used as a bomb shelter.


title: Highgate

text: Highgate New Town is a post-war estate adjacent to the cemetery, designed by Camden Council with similarities to the Alexandra Road estate.


title: Highgate

text: Between 1983 and 2010 Highgate was part of the Hampstead and Highgate constituency. The Boundary Commission report of 2003 recommended removing the Camden part of Highgate from the remainder of that constituency and joining it with Kentish Town and Holborn to the south in order to form an enlarged Holborn and St Pancras constituency from the 2010 general election. Since 1983 the northern half of Highgate village has been part of the Hornsey and Wood Green constituency. The present MP for Holborn and St Pancras, elected in 2015, is Keir Starmer of the Labour Party.


title: Highgate

text: Highgate is known for its pubs which line the old high street and surrounding streets. Some notable favourites are the Angel, the Flask, the Duke's Head and the Wrestlers.


title: Highgate

text: The name of the village is commonly ; however, the London Underground in announcements at Highgate tube station uses the alternative pronunciation of , where the final syllable matches the last syllable in "frigate".


title: Highgate

text: The 2011 census showed that the Highgate ward of Haringey was 82% white (60% British, 19% Other, 3% Irish). 40.9% of the ward were Christian, 7% Jewish and 3.8% Muslim.


title: Highgate

text: The Highgate ward of Camden meanwhile was 80% white (61% British, 15% Other, 4% Irish), and 3% Black African. 37.5% of the ward were Christian, 4.2% Jewish, and 5.1% Muslim.


title: Highgate

text: Highgate's main Church of England parish church, St Michael's, is situated close to the summit of the hill, and is the highest church in Greater London. It was built as one of the Commissioners' churches in 1831 and consecrated and opened on 8 November 1832. The architect was Lewis Vulliamy, and in 1831 his original drawings for the church were exhibited at the Royal Academy of Arts.


title: Highgate

text: From the late 17th century until 1830 Ashhurst House, the home of former Lord Mayor of London Sir William Ashhurst, stood on the site of the church. The remains of the house's cellar now form part of the church's crypt.


title: Highgate

text: The church's spire, built of Bath stone, with a cross of Portland stone, is a landmark on London's northern skyline.


title: Highgate

text: Inside, the chancel and choir stalls were done by G. E. Street in 1880. The pulpit dates from 1848. The present bench pews date from 1879, replacing box pews. The present organ is by Hill and Davidson, and was installed in 1885, replacing an earlier instrument of 1842. It was overhauled in 1985.


title: Highgate

text: There is a monument to Samuel Taylor Coleridge and his family in the form of a slate slab in the middle of the church.


title: Highgate

text: The church was damaged in the Second World War by enemy air raids and the present stained glass window at the east end was installed in 1954, replacing a window broken in the Blitz. It is one of the last works by Evie Hone and depicts the Last Supper.


title: Highgate

text: Further down Highgate Hill is the town's Roman Catholic parish church, St Joseph's. It was designed by Albert Vickers, and built in 1888, replacing an earlier, smaller church of 1861. Although St Joseph's Church was opened in 1889 by the Bishop of Liverpool, it was not until 1932, when its debts were cleared, that it was officially consecrated.


title: Highgate

text: The church has a distinctive copper dome with a green patina, and the interior of the dome was painted by Nathaniel Westlake in 1891. The organ is by William Hill and Sons, and installed in 1945 as a memorial to the local victims of the Second World War.


title: Highgate

text: On Friday 26 August 1988, Michael Williams, a 43-year-old father from Highgate who worked for the Home Office in Pimlico, disappeared while travelling back home after an employee social. His body was found at Highgate Wood the next day. The case remains unsolved despite being featured heavily in the national press and on the BBC's TV programme "Crimewatch".


title: Highgate

text: Highgate Cemetery is the burial place of Communist philosopher Karl Marx, Michael Faraday, Douglas Adams, George Eliot, Jacob Bronowski, Sir Ralph Richardson, Dawn Foster, Christina Rossetti, Sir Sidney Nolan, Alexander Litvinenko, Malcolm McLaren, Radclyffe Hall, Joseph Wolf and singer-songwriter George Michael.


title: Highgate

text: Many notable alumni have passed through Highgate School, either Masters or indeed Old Cholmeleians, the name given to old boys of the school. These include T.S. Eliot, who taught the poet laureate John Betjeman there, Gerard Manley Hopkins the poet, the composers John Taverner and John Rutter, John Venn the inventor of Venn diagrams, actor Geoffrey Palmer, Anthony Crosland MP and Labour reformer, and the cabinet minister Charles Clarke.


title: Highgate

text: A blue plaque on a house at the top of North Hill notes that Charles Dickens stayed there in 1832, when he was 20 years old.


title: Highgate

text: Peter Sellers lived as a boy in a cottage in Muswell Hill Road, where his mother had moved in order to send him to the Catholic St Aloysius Boys' School in Hornsey Lane.


title: Highgate

text: In Victorian times St Mary Magdalene House of Charity in Highgate was a refuge for former prostitutes—"fallen women"—where Christina Rossetti was a volunteer from 1859 to 1870. It may have inspired her best-known poem, Goblin Market.


title: Highgate

text: In 1817 the poet, aesthetic philosopher and critic Samuel Taylor Coleridge came to live at 3, The Grove, Highgate, the home of Dr James Gillman, in order to rehabilitate from his opium addiction. After Dr Gillman built a special wing for the poet, Coleridge lived there for the rest of his life, becoming known as the sage of Highgate.


title: Highgate

text: While here some of his most famous poems, though written years earlier, were first published including "Kubla Khan". His literary autobiography, "Biographia Literaria", appeared in 1817. His home became a place of pilgrimage for figures such as Carlyle and Emerson. He died here on 25 July 1834 and is buried in the crypt of nearby St Michael's Church. The writer J. B. Priestley subsequently lived in the same house; a commemorative plaque marks the property.


The 2022 United States House of Representatives elections in Colorado were held on November 8, 2022, to elect the eight U.S. representatives from the state of Colorado, one from each of the state's eight congressional districts. The elections coincided with the Colorado gubernatorial election, as well as other elections to the U.S. House of Representatives, elections to the U.S. Senate, and various state and local elections.


title: 2022 United States House of Representatives elections in Colorado

text: District boundaries were redrawn to ensure that the districts are apportioned based on data from the 2020 census, which added an eighth seat to Colorado's delegation.


text: The 1st district includes almost all of Denver, as well as the enclaves of Glendale and Holly Hills. The district is very similar to its predecessor before 2020 redistricting. The incumbent is Democrat Diana DeGette, who was re-elected with 73.6% of the vote in 2020. She is running for re-election.


text: The 2nd district is located in north-central Colorado, taking in Boulder, Fort Collins, and Longmont, as well as the surrounding mountain ski towns, including Vail, Grand Lake and Idaho Springs. The district was made slightly larger during redistricting, and it is now based in the north-central part of the state rather than just west of Denver. The incumbent is Democrat Joe Neguse, who was re-elected with 61.5% of the vote in 2020. He is running for re-election.


text: The 3rd district encompasses the Colorado Western Slope, including the cities of Montrose, Pueblo, and Grand Junction. Redistricting made the district slightly safer for the incumbent, Republican Lauren Boebert, who was elected with 51.4% of the vote in 2020. The district absorbs part of the old 4th district. She ran for re-election. Under the new district lines, the seat has a Cook PVI of R+7 and Donald Trump would have carried the district by 8 points. Despite this, Democrats very nearly flipped the seat, as Boebert defeated Frisch by a razor-thin margin of 546 votes.


text: Republican incumbent Lauren Boebert faced a strong challenge from former Aspen city councilman and businessman Adam Frisch who led on election day. Despite many prediction sites like The Cook Political Report giving the race a rating of "Solid R" up to election day, the race would prove to be one of the closest races of the cycle. Nate Silver of FiveThirtyEight gave Boebert a 97% chance of winning and most projections showed Boebert defeating Frisch by a margin of nearly 15%. However, on election night, Frisch led Boebert with over 90% of votes counted. Over time the vote would narrow, with at one point Frisch leading by only 60 votes. Boebert took the lead two days after the election, though confusion would start to grow as to how many outstanding votes would be left due to military absentee ballots among other errors with vote counting. Although the close margin triggered an automatic recount, Frisch conceded the race on November 17 after all overseas, military and provisional ballots were counted, as he acknowledged that a recount was very unlikely to overturn Boebert's lead. On December 12, Secretary of State Jena Griswold announced that the results of the recount showed minimal change, with Boebert losing 3 votes and Frisch gaining 1.


text: The 4th district encompasses rural eastern Colorado and the southern Denver exurbs, including Castle Rock and Parker. The district is smaller and less safe for the incumbent, Republican Ken Buck, who was re-elected with 60.1% of the vote in 2020. The old 4th district ceded parts to the new 3rd district. Buck is running for re-election.


text: The 5th district is based in Colorado Springs and its suburbs, including Fountain, Black Forest, and Ellicott after previously being spread out over central Colorado, The incumbent is Republican Doug Lamborn, who was re-elected with 57.6% of the vote in 2020. He is running for re-election.


text: The 6th district is based in the southern suburbs of the Denver metropolitan area including Aurora, Centennial, and Littleton. The incumbent is Democrat Jason Crow, who was re-elected with 57.1% of the vote in 2020.


text: The 7th district includes the western suburbs of Denver and central Colorado, including Arvada, Lakewood, Broomfield, and Cañon City, but also a large portion of central Colorado. The incumbent was Democrat Ed Perlmutter, who was re-elected with 59.1% of the vote in 2020. Perlmutter announced that he would retire at the end of his term, creating an open seat.


text: The 8th district is a new district created after the 2020 census. It includes the northern Front Range cities and surrounding Denver communities, including Thornton, Brighton, Johnstown, and Greeley.


title: Rafting

text: Rafting and whitewater rafting are recreational outdoor activities which use an inflatable raft to navigate a river or other body of water. This is often done on whitewater or different degrees of rough water. Dealing with risk is often a part of the experience.


title: Rafting

text: This activity as an adventure sport has become popular since the 1950s, if not earlier, evolving from individuals paddling to rafts with double-bladed paddles or oars to multi-person rafts propelled by single-bladed paddles and steered by a person at the stern, or by the use of oars.


title: Rafting

text: Rafting on certain sections of rivers is considered an extreme sport and can be fatal, while other sections are not so extreme or difficult. Rafting is also a competitive sport practiced around the world which culminates in a world rafting championship event between the participating nations. The International Rafting Federation, often referred to as the IRF, is the worldwide body which oversees all aspects of the sport.


title: Rafting

text: Rafting equipment has continuously evolved and developed significantly from old rubber WW II era military surplus rafts. Modern whitewater rafts are typically made with advanced nylon or Kevlar infused plastics like PVC or urethane; though many of the more entry-level low-cost manufacturers still use a glued rubber. Plastic is generally more durable, longer-lasting, and just as easy to repair compared to older rubber rafts.


title: Rafting

text: Paddles and oars are the typical means of propulsion for rafts and come in many sizes and varieties with specific river conditions in mind.


title: Rafting

text: Paddles are a combination of layered wood, plastic, aluminium, carbon fiber, or other advanced composites. There are many types and combinations of these materials with lower-end entry-level paddles being composed of cheap aluminum and plastic. Higher-end models are constructed of high-end composites and mostly utilized by professional rafting guides, raft racers, and expedition paddlers.


title: Rafting

text: Paddles are typically utilized by rafters in smaller and lower volume rivers where rocks and other hazards can damage larger oars. Paddles are typically used by guests on commercial trips as well since it is seen as a more engaging way to enjoy the river trip. When paddles are used in a raft it is referred to as "paddling" or "paddle guiding".


title: Rafting

text: Oars are commonly made from the same materials as paddles. Wood, plastic, aluminum, and carbon fiber. Oars are designed for several different rivers with sightly different blade shapes built to handle varying river conditions. Wooden oars are typically built as one solid piece to help retain strength and resilience of the oar while it is strained under a load. Composite or metallic oars typically are made in 3 parts:


title: Rafting

text: All of these parts are interchangeable and can be upgraded and altered in many ways to make rowing more enjoyable. Oars are generally used on wider flatter rivers of higher volume to facilitate moving more efficiently across long slow-moving pools, though anglers will often use shorter oars on smaller rafts in low volume rivers to help them maintain an advantageous upstream position while anglers cast from the raft. When a raft utilizes oars it is called "rowing" though many people typically incorrectly refer to this as "oaring" or "oar framing", however, these terms are incorrect and often suggest inexperience when used in conversation with members of the rafting community. Oars typically use one of 2 systems to attach to the boat, but in either case, they interface with the boat through a large metallic frame strapped to the boat called an "oar frame". Oars connect to the frame by either a pin and clip system or a system called oarlocks. Either system connects to the frame via oar towers on either side of the frame.


title: Rafting

text: Pins are referred to as "thole pins" or "oar pins". A large metal clip attaches to the oar and clips onto the pin. The top of the pin has a rubber or plastic stopper that prevents the oar from slipping over the top of the pin. The bottom of the pin connects to an oar tower designed to hold the pin in place. This system is an older system though it is useful for certain types of river running namely big, dangerous Class 5 rivers that require your oars to stay in place as much as possible.


title: Rafting

text: Oarlocks or locks are a more common form of attachment for oars as they allow the rower to "feather" the oar back and forth as they row making it easier on the person using the oars to continue downstream. Oarlocks look like a pin topped with a U-shaped metal flange. The oars slide into the gap between the U-shaped metal pieces and can be held in place with a plastic stopper called an oarlock. The oarlock allows the oar to maintain its position on the oar at a correct length for rowing.


title: Rafting

text: Whitewater rafting can be traced back to 1811 when the first recorded attempt to navigate the Snake River in Wyoming was planned. With no training, experience, or proper equipment, the river was found to be too difficult and dangerous. Hence, it was given the nickname "Mad River". On June 9, 1940, Clyde Smith lead a successful trip through the Snake River Canyon.


title: Rafting

text: Otherwise known as the International Scale of River Difficulty, below are the six grades of difficulty in white water rafting. They range from simple to very dangerous and potential death or serious injuries.


title: Rafting

text: Class 2: Some rough water, maybe some rocks, might require some maneuvering. (Skill level: Basic paddling skill)


title: Rafting

text: Class 3: Small waves, maybe a small drop, but no considerable danger. May require significant maneuvering. (Skill level: Some experience in rafting)


title: Rafting

text: Class 4: Whitewater, medium waves, maybe rocks, maybe a considerable drop, sharp maneuvers may be needed. (Skill level: Exceptional rafting experience)


title: Rafting

text: Class 5: Whitewater, large waves, large volume, possibility of large rocks and hazards, possibility of a large drop, requires precise maneuvering. (Skill level: Full mastery of rafting)


title: Rafting

text: Class 6: Class 6 rapids are considered to be so dangerous that they are effectively unnavigable on a reliably safe basis. Rafters can expect to encounter substantial whitewater, huge waves, huge rocks and hazards, and/or substantial drops that will impart severe impacts beyond the structural capacities and impact ratings of almost all rafting equipment. Traversing a Class 6 rapid has a dramatically increased likelihood of ending in serious injury or death compared to lesser classes. (Skill level: Full mastery of rafting, and even then it may not be safe)


title: Rafting

text: The overall risk level on a rafting trip using proper precautions is low. Thousands of people safely enjoy rafting trips every year.


title: Rafting

text: Like most outdoor sports, rafting, in general, has become safer over the years. Expertise in the sport has increased, and equipment has become more specialized and improved in quality. As a result, the difficulty rating of most river runs has changed. A classic example is the Colorado River in the Grand Canyon, which historically had a reputation far exceeding its actual safety statistics. Today the Grand Canyon sees hundreds of safe rafting trips by both do it yourself rafters and commercial river concessionaires.


title: Rafting

text: Rafting companies generally require customers to sign waiver forms indicating understanding and acceptance of potential serious risks. Both do-it-yourself and commercial rafting trips often begin with safety presentations to educate rafting participants about problems that may arise. Depending on the area, safety regulations covering rafting, both for the general do-it-yourself public as well as commercial operators, may exist in legislation. These range from the mandatory wearing of lifejackets, carrying certain equipment such as whistles and throwable flotation devices, to certification of commercial outfitters and their employees.


title: Rafting

text: It is generally advisable to discuss safety measures with a commercial rafting operator before signing on for that type of trip. The required equipment needed is essential information to be considered.


title: Rafting

text: Risks in white water rafting stem from both environmental dangers and from improper behavior. Certain features on rivers are inherently unsafe and have remained consistently so. These would include ‘keeper hydraulics’, ‘strainers’ (e.g. fallen trees), dams (especially low-head dams, which tend to produce river-wide keeper hydraulics), undercut rocks, and of course dangerously high waterfalls. Even in safe areas, moving water can always present risks—such as when a swimmer attempts to stand up on a rocky riverbed in strong current, risking foot entrapment. Irresponsible behavior related to rafting while intoxicated has also contributed to many accidents.


title: Rafting

text: Typical rafting injuries include trauma from striking an object, traumatic stress from the interaction of the paddler’s positioning and equipment and the force of the water, overuse injuries, submersion/environmental injuries, and non-environmental injuries due to undisclosed medical conditions (such as heart problems). Studies have shown that injury rates in rafting are relatively low, though they may be skewed due to a large number of unreported incidents. Fatalities are rare in both commercial and do-it-yourself rafting. Meta-analyses have calculated that fatalities ranged between 0.55 - 0.86 per 100,000 user days.


title: Rafting

text: Like all outdoor activities, rafting must balance its use of nature with the conservation of rivers as a natural resource and habitat. Because of these issues, some rivers now have regulations restricting the annual seasons and daily operating times or numbers of rafters.


title: Rafting

text: Conflicts have arisen when commercial rafting operators, often in co-operation with municipalities and tourism associations, alter the riverbed by dredging and/or blasting in order to eliminate safety hazards or create more interesting whitewater features in the river. Environmentalists argue that this may have negative impacts to riparian and aquatic ecosystems, while proponents claim these measures are usually only temporary since a riverbed is naturally subject to permanent changes during large floods and other events. Another conflict involves the distribution of scarce river permits to either the do-it-yourself public or commercial rafting companies.


title: Rafting

text: Rafting by do-it-yourself rafters and commercial rafting companies contributes to the economy of many regions which in turn may contribute to the protection of rivers from hydroelectric power generation, diversion for irrigation, and other development. Additionally, white water rafting trips can promote environmentalism. Multi-day rafting trips by do-it-yourself rafters and commercial rafting companies through the National Wild and Scenic Rivers System have the potential to develop environmental stewardship and general environmental behavior. Studies suggest that environmental efficacy increases when there is an increase in the length of the trip, daily immersion, and the amount of resource education by trip participants.


title: Mother's Mercy

text: "Mother's Mercy" is the fifth season finale episode of HBO's fantasy television series "Game of Thrones", and the 50th overall. The tenth and final episode of the fifth season, the episode was written by the series creators David Benioff and D. B. Weiss and directed by David Nutter.


title: Mother's Mercy

text: "Mother's Mercy" garnered critical acclaim, with critics lauding Lena Headey's performance, David Nutter's direction and the writing of Benioff and Weiss. Particular praise was directed to Cersei Lannister's walk of atonement, which involved a body double and the use of CGI. In the United States, the episode premiere achieved a viewership of 8.11 million, making it the show's most watched episode, until it was surpassed by the season six finale, "The Winds of Winter". The episode won Emmy Awards for Writing in a Drama Series and Directing in a Drama Series for Benioff, Weiss, and Nutter.


title: Mother's Mercy

text: This episode marks the final appearance for Stephen Dillane (Stannis Baratheon), Tara Fitzgerald (Selyse Baratheon), and Ian Beattie (Ser Meryn Trant).


title: Mother's Mercy

text: Arya kills Trant for the murder of Syrio Forel. Jaqen berates Arya for taking a life not meant for her to take, and declares that another life must be taken in order to appease the Many-Faced God before apparently committing suicide. The Waif, now wearing Jaqen's face, points out to Arya that "Jaqen" never existed and warns Arya that putting on a new face if one is not "No One" is like poison. As punishment, Arya is struck blind.


title: Mother's Mercy

text: Drogon brings Daenerys back to his lair. Daenerys wanders off on her own, spotting a Dothraki horde advancing in the distance. Daenerys drops a ring to the ground before being surrounded.


title: Mother's Mercy

text: Daario and Jorah leave Meereen to search for Daenerys. Tyrion is left to govern Meereen in Daenerys' absence, assisted by Missandei and Grey Worm. Varys arrives in Meereen and offers use of his spy network to aid Tyrion.


title: Mother's Mercy

text: Cersei confesses to committing adultery with Lancel to the High Sparrow, but denies mothering children to her brother Jaime. The High Sparrow allows Cersei to return to the Red Keep to await a formal trial, but she is forced to walk naked from the Great Sept of Baelor to the Red Keep while being jeered at and pelted with garbage by the angry crowd. Upon returning to the Red Keep, she is comforted by Maester Qyburn and the mutated, undead iteration of Gregor Clegane.


title: Mother's Mercy

text: Bidding farewell to Jaime and Myrcella, Ellaria kisses Myrcella on the lips. Myrcella reveals that she knows Jaime is her real father and that she is glad that he is her father. Myrcella suddenly collapses and dies in Jaime's arms, and it is revealed that Ellaria had secretly poisoned her with poisoned lipstick.


title: Mother's Mercy

text: In the wake of his sacrifice of his daughter, Shireen, Stannis is informed that half of his forces have deserted and his wife has hanged herself in grief. Stannis nonetheless orders his remaining troops to march on Winterfell. After a quick yet fierce battle, the Boltons emerge as the victors. Stannis survives the destruction of his army, but is severely wounded. Brienne arrives and executes Stannis for the murder of Renly Baratheon. Theon throws Myranda from the castle to her death just as the Bolton army returns to Winterfell. Theon and Sansa jump from the castle walls into the deep snow below in an attempt to escape.


title: Mother's Mercy

text: Jon sends Samwell with Gilly and her baby to Oldtown to become a maester. Olly and Thorne take Jon outside under the pretense of seeing a wildling who had recently seen his uncle Benjen Stark. Led outside, he realizes that he has been betrayed. Thorne, Marsh, Yarwyck, Olly, and the others take turns stabbing Jon, each uttering "For the Watch", before leaving him to die alone in the snow.


title: Mother's Mercy

text: "Mother's Mercy" was written by the series' creators David Benioff and D. B. Weiss. It primarily covers elements from George Martin's novels "A Feast for Crows", chapters "Samwell I" and "Cat of the Canals" and "A Dance with Dragons", chapters "Jon II", "Theon I", "Daenerys X", "Cersei I", "Cersei II" and "Jon XIII". It also contains material from Martin's upcoming sixth novel in the series, "The Winds of Winter", chapter "Mercy".


title: Mother's Mercy

text: "Mother's Mercy" was directed by David Nutter, He also directed the previous episode, "The Dance of Dragons". It was photographed by Robert McLachlan and was edited by Tim Porter, one of the show's main editors, under the supervision of Nutter.


title: Mother's Mercy

text: For Cersei Lannister's nude "walk of atonement" through King's Landing, HBO employed actress Rebecca Van Cleave as a body double for Lena Headey. While filming the scene on the Jesuit stairs in Dubrovnik, Croatia in October 2014, Van Cleave performed fully nude while Headey wore a simple beige shift. Both performances were then merged by the show's editing team, combining close-ups of Headey's facial expressions and long shots of Van Cleave's nude walk through the city. In some instances CGI was used to put Headey's face on Van Cleave's body.


title: Mother's Mercy

text: Headey says that the showrunners decided to cast a body double for "several reasons." Headey says she was glad to use a body double for the scene because she wanted to focus on the character's emotions. Another actor noted that Headey's "extensive tattoos" may have been another reason. Months later, Headey announced that she was pregnant with her second child, though it is unclear if she was pregnant when this scene had to be filmed. Sarah Buchanan of "Express" notes the strangeness of casting a much younger actress to play the middle-aged Cersei when the key outcome of the walk of atonement in "A Dance with Dragons" is that when the people see that Cersei's body is not beautiful, she loses a large part of her mystique. The 27-year-old Van Cleave did not show any of the specific signs of aging or past pregnancy for which the Cersei of the books was mocked by the crowd.


title: Mother's Mercy

text: When casting for the role, HBO received applications from more than actresses to act as Headey's body double for the scene. A selection of seven finalists, including Van Cleave, was then flown to Belfast, Northern Ireland to audition before the show's producers. Headey also opted out of the casting process, but director David Nutter said finding the right double was one of the most important parts of making the finale. "We needed somebody who could do The Walk of Shame physically, somebody who could match Lena's integrity, intensity, and sensibility. We found a tremendous actress in Rebecca; she was a godsend. The courage of this girl, who's never done anything like this in her life, who understood what was important about this...once I had her I felt like I could accomplish anything."


title: Mother's Mercy

text: Van Cleave herself described the scene as "one of the scariest, most wonderful, most gratifying experiences I could have imagined ... I never in a million years would have thought I would be in Dubrovnik surrounded by hundreds of extras and crew members throwing food at me, but it was amazing" and "I hope the next thing I do will have my head in it." She also praised Headey's willingness to help her, describing the two of them as a "tag-team"; Headey would walk behind Van Cleave during the shoot, coaching her on the character's responses.


title: Mother's Mercy

text: When the showrunners first announced the plans of shooting a nude scene in Dubrovnik, the city's Catholic Church of St. Nicholas strongly opposed the idea, due to it being immoral to walk their sacred grounds in the nude. Eventually, both parties came to the agreement that the shooting could commence, provided no nude scenes would be filmed in a place of worship. During the three-day shoot, Headey walked Van Cleave through each shot, giving insight into all the emotions Cersei was feeling. The six-minute scene was filmed using 500 extras.


title: Mother's Mercy

text: D.B. Weiss discussed the decision to kill Jon Snow by saying that he felt the visual medium did not give him the freedom to leave Jon's fate open: "In a book, you can present that kind of ambiguity. In a show, everybody sees it for what it is. It's that rule: 'If we don't see the body then they’re not really dead.' Like when we cut Ned's head off, we didn't want a gory Monty Python geyser of blood, but we needed to see the blade enter his neck and cut out on the frame where the blade was mid-neck. [...] we needed Ned's death to be totally unambiguous." Actor Kit Harington said of the scene, "I loved it. I loved how they brought Olly in to be the person who kills me. I love how the storyline with Thorne was wrapped up."


title: Mother's Mercy

text: Although Weiss meant the scene to be unambiguous, the episode left many viewers uncertain as to whether Jon Snow had been killed or merely injured (his fate in the novels is left unconfirmed as of "A Dance with Dragons", with much debate about Martin's future intentions). Some of the confusion may be because, as reviewers have noted, Jon was killed in what can be seen as the middle of his story arc and his death does not have an obvious narrative purpose. For example, Nate Jones of "Vulture" notes, "[I]t's easy to see what [other characters'] deaths meant for the series' sprawling narrative: Ned's execution sent the Stark kids adrift in a universe where there was nobody looking out for them, while Robb's murder was the final death knell for the hopes that the saga would ever have a traditional 'happy' ending. What would be accomplished, narratively, by getting rid of Jon permanently right now?" Both before and after these announcements, viewers have speculated that Jon Snow might have survived his stabbing and there are many fan theories on how he might have accomplished this, including spiritually possessing his direwolf's body or being brought back to life by Melisandre. When jokingly asked during a panel if Kit Harington would ever get to play a warg (human who has possessed the body of an animal), Weiss replied with, "Two words for you: Season 6." In July 2015, photos of Kit Harington arriving in Belfast—where the series is primarily filmed and where other actors are arriving for the Season 6 script read-throughs—surfaced, fueling speculation of his survival. However, Joanna Robinson of "Vanity Fair" pointed out that Charles Dance was seen at Belfast the previous year, and his character Tywin Lannister only appeared in the first episode of the subsequent season and only as a corpse, although Dance himself confirmed the nature of his role shortly after the announcement. Another photo that showed Harington on set in Belfast in a costume that varied from the Night's Watch outfit was published on September 25, 2015.


title: Mother's Mercy

text: Various interviews with the producers, director and writers have indicated that it is a "safe bet" that Sansa Stark and Theon Greyjoy survive their fall, while Stannis and Myrcella were definitively killed after being beheaded and poisoned, respectively.


title: Mother's Mercy

text: "Mother's Mercy" was seen by an estimated 8.1 million viewers on its first airing. This is higher than any previous episode, exceeding the 8 million for "The Wars to Come". With Live+7 DVR viewing factored in, the episode had an overall rating of 10.43 million viewers, and a 5.4 in the 18–49 demographic, which was a series high in both viewership and 18–49 rating. In the United Kingdom, the episode was viewed by 2.437 million viewers, making it the highest-rated broadcast that week. It also received 0.121 million timeshift viewers.


title: Mother's Mercy

text: "Mother's Mercy" received critical acclaim. Review aggregation website Rotten Tomatoes assembled 31 reviews and gave "Mother's Mercy" a 97% score and an average rating of 9.1 out of 10. The site's consensus reads that the episode "wraps up a particularly dark "Game of Thrones" season with a finale that delivers strong character work and a handful of appropriately bleak cliffhangers." In his 9.0/10 review, Matt Fowler of "IGN" praised Jon Snow's death and Cersei's atonement, as well as Arya's and Dorne's storylines, but felt Sansa's storyline was too hurried. Sean T. Collins of "Rolling Stone" was positive too, writing, "Slaughter and shame made this the show's most upsetting season-ender yet."


title: Efe Ajagba

text: Efe Ajagba (born 22 April 1994) is a Nigerian professional boxer who holds the record for the fastest victory in boxing history after his opponent was disqualified for leaving the ring one second after the opening bell. As an amateur, he won a gold medal at the 2015 African Games and bronze at the 2014 Commonwealth Games.


title: Efe Ajagba

text: Ajagba took up the sport of boxing in 2011 after previously playing football for a club in Ughelli since 2005. He was coached by Anthony Konyegwachie.


title: Efe Ajagba

text: Ajagba was selected to compete for the Nigerian team at the 2014 Commonwealth Games held in Glasgow. Competing in the super heavyweight division he defeated Junior Fa of Tonga in the round of 16 and Paul Schafer of South Africa in the quarterfinals. He advanced to the semifinals where he was defeated by Joseph Goodall of Australia, meaning Ajagba won a bronze medal.


title: Efe Ajagba

text: At the 2015 African Games held in Brazzaville, Republic of the Congo, Ajagba was selected as the Nigerian entrant in the men's super heavyweight event. He won the gold medal, beating Keddy Angnes of the Seychelles by a score 3–0 in the final.


title: Efe Ajagba

text: In 2016 he won the gold medal in the super heavyweight event at the African Boxing Olympic Qualification Tournament held in Yaoundé, Cameroon. By doing so Ajagba qualified to represent Nigeria at the 2016 Summer Olympics to be held in Rio de Janeiro, Brazil. In the first round Ajagba beat Ugandan Michael Sekamembe on points, he defeated Tunisian boxer Aymen Trabelsi in the semifinal to secure his qualification, then in the final he beat Mohamed Arjaoui of Morocco. Ajagba was the only Nigerian boxer of the ten who competed to qualify for Rio through the tournament, leading to claims from Nigeria's coach Konyegwachie that judges had been bribed.


title: Efe Ajagba

text: After compiling a perfect record of 5–0, on 24 August 2018, Ajagba scored the fastest victory in boxing history in a match against Curtis Harper, winning in one second via disqualification after Harper walked out of the ring in protest over a pay dispute.


title: Efe Ajagba

text: After improving to 12–0, on 7 March 2020, Ajagba fought Razvan Cojanu. In a one-sided fight, Ajagba dismantled his opponent round by round, and managed to score knockdowns in both the eighth and ninth rounds. In the ninth, Cojanu took a knee with 2:25 left in the round, and the referee decided to stop the fight.


title: Efe Ajagba

text: In his next fight, Ajagba made his Top Rank debut and fought Jonathan Rice on 19 September 2020. The fight ended up being less entertaining than expected, especially because Ajagba was not throwing a lot of punches. He did however, still do enough to hurt Rice and earn a unanimous decision victory. Ajagba secured another victory in his 15th fight, knocking out Brian Howard in the third round on 10 April 2021.


title: Efe Ajagba

text: Ajagba faced off against undefeated Frank Sánchez on 9 October 2021 on the undercard of Tyson Fury vs. Deontay Wilder III. Ajagba was knocked down en route to a unanimous decision defeat, with scores of 98–91, 98–91 and 97–92 for Sánchez.


title: Craton

text: A craton (, , or ; from "strength") is an old and stable part of the continental lithosphere, which consists of Earth's two topmost layers, the crust and the uppermost mantle. Having often survived cycles of merging and rifting of continents, cratons are generally found in the interiors of tectonic plates; the exceptions occur where geologically recent rifting events have separated cratons and created passive margins along their edges. Cratons are characteristically composed of ancient crystalline basement rock, which may be covered by younger sedimentary rock. They have a thick crust and deep lithospheric roots that extend as much as several hundred kilometres into Earth's mantle.


title: Craton

text: The term "craton" is used to distinguish the stable portion of the continental crust from regions that are more geologically active and unstable. Cratons are composed of two layers: A continental "shield", in which the basement rock crops out at the surface, and a "platform" which overlays the shield in some areas with sedimentary rock.


title: Craton

text: The word "craton" was first proposed by the Austrian geologist Leopold Kober in 1921 as , referring to stable continental platforms, and "orogen" as a term for mountain or orogenic belts. Later Hans Stille shortened the former term to , from which "craton" derives.


title: Craton

text: Examples of cratons are the Dharwar Craton in India, North China Craton, the East European Craton, the Amazonian Craton in South America, the Kaapvaal Craton in South Africa, the North American Craton (also called the Laurentia Craton), and the Gawler Craton in South Australia.


title: Craton

text: Cratons have thick lithospheric roots. Mantle tomography shows that cratons are underlain by anomalously cold mantle corresponding to lithosphere more than twice the typical thickness of mature oceanic or non-cratonic, continental lithosphere. At that depth, craton roots extend into the asthenosphere, and the low-velocity zone seen elsewhere at these depths is weak or absent beneath stable cratons. Craton lithosphere is distinctly different from oceanic lithosphere because cratons have a neutral or positive buoyancy, and a low intrinsic density. This low density offsets density increases due to geothermal contraction and prevents the craton from sinking into the deep mantle. Cratonic lithosphere is much older than oceanic lithosphere—up to 4 billion years versus 180 million years.


title: Craton

text: Rock fragments (xenoliths) carried up from the mantle by magmas containing peridotite have been delivered to the surface as inclusions in subvolcanic pipes called kimberlites. These inclusions have densities consistent with craton composition and are composed of mantle material residual from high degrees of partial melt. Peridotite is strongly influenced by the inclusion of moisture. Craton peridotite moisture content is unusually low, which leads to much greater strength. It also contains high percentages of low-weight magnesium instead of higher-weight calcium and iron. Peridotites are important for understanding the deep composition and origin of cratons because peridotite nodules are pieces of mantle rock modified by partial melting. Harzburgite peridotites represent the crystalline residues after extraction of melts of compositions like basalt and komatiite.


title: Craton

text: The process by which cratons were formed is called cratonization. There is much about this process that remains uncertain. However, the first cratonic landmasses likely formed during the Archean Eon. This is indicated by the age of diamonds, which originate in the roots of cratons, and which are almost always over 2 billion years and often over 3 billion years in age. Rock of Archean age makes up only 7% of the world's current cratons; even allowing for erosion and destruction of past formations, this suggests that only 5 to 40 percent of the present continental crust formed during the Archean. Cratonization likely was completed during the Proterozoic. Subsequent growth of continents was by accretion at continental margins.


title: Craton

text: The origin of the roots of cratons is still debated. However, the present understanding of cratonization began with the publication in 1978 of a paper by Thomas H. Jordan in "Nature". Jordan proposed that cratons formed from a high degree of partial melting of the upper mantle, with 30 to 40 percent of the source rock entering the melt. Such a high degree of melting was possible because of the high mantle temperatures of the Archean. The extraction of so much magma left behind a solid peridotite residue that was enriched in lightweight magnesium, and thus lower in chemical density than undepleted mantle. This lower chemical density compensated for the effects of thermal contraction as the craton and its roots cooled, so that the physical density of the cratonic roots matched that of the surrounding hotter, but more chemically dense, mantle. In addition to cooling the craton roots and lowering their chemical density, the extraction of magma also increased the viscosity and melting temperature of the craton roots and prevented mixing with the surrounding undepleted mantle. The resulting mantle roots have remained stable for billions of years. Jordan suggested that depletion occurred primarily in subduction zones and secondarily as flood basalts.


title: Craton

text: This model of melt extraction from the upper mantle has held up well with subsequent observations. The properties of mantle xenoliths confirm that the geothermal gradient is much lower beneath continents than oceans. The olivine of craton root xenoliths is extremely dry, which would give the roots a very high viscosity. Rhenium–osmium dating of xenoliths indicates that the oldest melting events took place in the early to middle Archean. Significant cratonization continued into the late Archean, accompanied by voluminous mafic magmatism. However, melt extraction alone cannot explain all the properties of craton roots. Jordan noted in his original paper that this mechanism could be effective for constructing craton roots only down to a depth of . The great depths of craton roots required further explanation. The 30 to 40 percent partial melting of mantle rock at 4 to 10 GPa pressure produces komatiite magma and a solid residue very close in composition to Archean lithospheric mantle, but continental shields do not contain enough komatiite to match the expected depletion. Either much of the komatiite never reached the surface, or other processes aided craton root formation.


title: Craton

text: There are at least three hypotheses of how cratons have been formed. Jordan's suggestion was that further cratonization was a result of repeated continental collisions. The thickening of the crust associated with these collusions must have been balanced by craton root thickening according to the principle of isostacy. Jordan likened this model to "kneading" of the cratons, allowing low density material to move up and higher density to move down, creating stable cratonic roots as deep as . A second model suggests that the surface crust was thickened by a rising plume of molten material from the deep mantle. This would have built up a thick layer of depleted mantle underneath the cratons. The third model suggests that successive slabs of subducting oceanic lithosphere became lodged beneath a proto-craton, underplating the craton with chemically depleted rock.


title: Craton

text: The chemistry of xenoliths and seismic tomography both favor the two accretional models over the plume model. However, other geochemical evidence favors mantle plumes. Tomography shows two layers in the craton roots beneath North America. One is found at depths shallower than and may be Archean, while the second is found at depths from and may be younger. The second layer may be a less depleted thermal boundary layer that stagnated against the depleted "lid" formed by the first layer.


title: Craton

text: All these proposed mechanisms rely on buoyant, viscous material separating from a denser residue due to mantle flow, and it is possible that more than one mechanism contributed to craton root formation.


title: Craton

text: The long-term erosion of cratons has been labelled the "cratonic regime". It involves processes of pediplanation and etchplanation that lead to the formation of flattish surfaces known as peneplains. While the process of etchplanation is associated to humid climate and pediplanation with arid and semi-arid climate, shifting climate over geological time leads to the formation of so-called polygenetic peneplains of mixed origin. Another result of the longevity of cratons is that they may alternate between periods of high and low relative sea levels. High relative sea level leads to increased oceanicity, while the opposite leads to increased inland conditions.


title: Craton

text: Many cratons have had subdued topographies since Precambrian times. For example, the Yilgarn Craton of Western Australia was flattish already by Middle Proterozoic times and the Baltic Shield had been eroded into a subdued terrain already during the Late Mesoproterozoic when the rapakivi granites intruded.


title: Samford University

text: Samford University is a private Christian university in Homewood, Alabama. In 1841, the university was founded as Howard College by Baptists. Samford University describes itself as the 87th oldest institution of higher learning in the United States. The university enrolls 5,683 students from 47 states, 2 U.S. territories, and 19 countries.


title: Samford University

text: In 1841, Samford University was founded as Howard College in Marion, Alabama. Some of the land was donated by Reverend James H. DeVotie, who served on the Samford Board of Trustees for fifteen years and as its president for two years. The first financial gift, $4,000, was given by Julia Tarrant Barron and both she and her son also gave land to establish the college. The university was established after the Alabama Baptist State Convention decided to build a school for men in Perry County, Alabama. The college's first nine students began studies in January 1842 with a traditional curriculum of language, literature and sciences. In those early years the graduation addresses of several distinguished speakers were published, including those by Thomas G. Keen of Mobile, Joseph Walters Taylor, Noah K. Davis and Samuel Sterling Sherman. In October 1854, a fire destroyed all of the college's property, including its only building. While the college recovered from the fire, the Civil War began. Howard College was converted to a military hospital by the Confederate government in 1863. During this time, the college's remaining faculty offered basic instruction to soldiers recovering at the hospital. For a short period after the war, federal troops occupied the college and sheltered freed slaves on its campus.


title: Samford University

text: In 1865 the college reopened. Jabez Lamar Monroe Curry, an attorney, former US Congressman and Confederate military officer, served as president from 1865 to 1868. He was committed to the cause of broader education, and supported expansion of normal school training.


title: Samford University

text: In 1887 Howard College's board of trustees accepted real estate and funding from the city of Birmingham, Alabama, and moved the institution there. Faculty who remained in Marion formed Marion Military Institute (MMI) on the old campus. MMI continues to operate in Marion.


title: Samford University

text: In 1913, the college became fully and permanently coeducational. Howard College added its School of Music in 1914 and School of Education and Journalism the following year. The college introduced its Department of Pharmacy in 1927. At the time, it was the only program of its kind in the Southeastern United States. During World War II, Howard College hosted a V-12 Navy College Training Program, allowing enlisted sailors to earn college degrees while receiving military training.


title: Samford University

text: After the war, the number of veterans attending the college under the GI Bill boosted enrollment beyond capacity. The college moved to the Shades Valley in Homewood, Alabama. The new campus was built in 1955 and opened in 1957. In 1961, the college acquired Cumberland School of Law, one of the nation's oldest law schools.


title: Samford University

text: In addition to the law school, Howard College added a new school of business, and reorganized to achieve university status in 1965. Since the name "Howard University" was already in use, Howard College was renamed as Samford University in honor of Frank Park Samford, a longtime trustee of the school. In 1973, the university acquired Ida V. Moffett School of Nursing. Samford University established a study center in 1984 for students to study abroad in Kensington, England. On September 21, 1989, a Samford University professor, William Lee Slagle, fatally stabbed one of his debating team students and escaped. Slagle was finally captured six months later.


title: Samford University

text: In 1994, Samford's board of trustees voted to allow the board to elect its own members. This gave the university formal independence from the Alabama Baptist State Convention, but until 2017 convention leaders retained ex officio seats on the board, were consulted on trustee selection, and the new trustees were presented to the convention for affirmation.


title: Samford University

text: As a private, segregated institution, Samford University was to some degree insulated from the activities of leaders and protesters of the Civil Rights Movement in the 1950s and early 1960s. The officers of the Samford Student Government Association challenged a segregated concert held on campus by the Birmingham Symphony by inviting as guests the student government officers of nearby Miles College, a historically black school.


title: Samford University

text: Segregation by private universities was ended by the passage of the 1964 Civil Rights Act by the US Congress. Initially, the school's leaders declined to express their commitment to desegregation. For example, the university declined to apply for the NDEA Student Loan Program for 1965-66 because it would have to affirm desegregation. Cumberland School of Law faced the greatest immediate risk of losing accreditation. In 1967, it admitted Samford's first black student, Audrey Lattimore Gaston. The entire university proceeded with desegregation. In the fall of 1969 Elizabeth Sloan Ragland became the first African American student to live on campus. On June 1, 2020, the university announced the installation of a memorial honoring "the sacrifices of many African Americans for the mission and vision of Samford University even in days when their efforts were invisible or barely acknowledged" it specifically remembered Gaston and an enslaved servant named "Harry" who died while saving students from the 1854 fire. A few weeks later, as a result of campus conversations in the wake of the murder of George Floyd, Westmoreland created a university task force on racial justice. The final version of this task force's report was approved by the university's board of trustees on April 26, 2021 and released to the public the next day. A "diversity action plan" was released the following year.


title: Samford University

text: Andrew Westmoreland was appointed president of the university in 2006. That year, the Jane Hollock Brock Recital Hall was dedicated as part of the university’s fine arts complex. A new soccer and track facility opened in 2011, part of a decade-long expansion of new athletics facilities that included a tennis center, a basketball arena, a football field house and a softball stadium. For the 2016–17 academic year, the economic and fiscal impacts of the university on Alabama were $424.8 million, 2,424 jobs, $16.1 million in state income and sales taxes, and $6 million in local sales tax. In 2013, the university established a new College of Health Sciences, including Ida V. Moffett School of Nursing, McWhorter School of Pharmacy, the School of Health Professions and the School of Public Health. The dean of the nursing school, Nena Sanders, was named vice-provost of the new college, and after her retirement in 2020 the nursing school was renamed the Moffett & Sanders School of Nursing. In 2013, the university announced the construction of a new facility to house Brock School of Business. In 2014, the West Village residence complex opened. That December, the university purchased the adjacent headquarters of Southern Progress, a subsidiary of Time, Inc., that houses the College of Health Sciences.


title: Samford University

text: The university's long financial connection with the Alabama Baptist State Convention was ended by the university in July 2017 when the trustees announced they would no longer accept funds from the convention. Later that year Samford and the state convention agreed that Samford would no longer present its slate of trustees to the convention for affirmation and that convention officers would no longer have an "ex officio" position on the board. This ended key aspects of Samford's formal connection to the state convention that had existed for decades. Still, by the trustees’ own rule, all trustees must be members of Baptist churches and 75% from Alabama. Samford is a collaborative partner of the Council for Christian Colleges and Universities. In August 2020, Westmoreland announced he would retire on June 30, 2021. On March 10, 2021, it was announced that he will be succeeded by Whitworth University president Beck A. Taylor. Taylor took office on July 1, 2021.


title: Samford University

text: In May 2022, the university received a $100 million gift from the estate of alumnus Marvin Mann, making it the largest single-donor gift ever made to a higher education institution in Alabama.


title: Samford University

text: Samford has been involved in several well publicized incidents in which the university rejected LGBTQ+ students' requests to form student organizations or refused to work with Christian groups that were LGBTQ+ affirming. In 2017, President Westmoreland rejected Samford Together, a organization that sought to create a space for students to discuss topics related to sexual orientation and gender identity “in an open-minded and accepting environment,” even though the organization had been approved by both the Student Government Association and the faculty


title: Samford University

text: Similar actions occurred again in 2022. In late August, Samford administration “uninvited” representatives of Episcopalian and Presbyterian campus ministries from a campus event because these ministries were affirming of LGBTQ+ individuals. In justifying the move, Vice President of Student Affairs Phil Kimrey stated, “Throughout its history, the university has consistently subscribed to and practiced biblically orthodox beliefs," and "the university has a responsibility to formally partner with ministry organizations that share our beliefs.” On September 30, President Beck Taylor stated more explicitly in a video message that "we decided to limit Samford’s formal ministry partnerships to churches and to organizations that support Samford’s traditional view of human sexuality and marriage." In October, Taylor declined university recognition to a chapter of OUTLaw in Samford's Cumberland School of Law. OUTLaw is a national organization supporting LGBTQ+ law students.


title: Samford University

text: Samford, a Christian university, offers undergraduate and graduate degree programs, with 170 undergraduate majors, minors and concentrations. The university is divided into the School of the Arts, Howard College of Arts and Sciences, Brock School of Business, Beeson Divinity School, Orlean Beeson School of Education, Cumberland School of Law, Moffett & Sanders School of Nursing, McWhorter School of Pharmacy, School of Health Professions, and School of Public Health. The faculty-to-student ratio at Samford University is 1:13. Approximately two-thirds of the university's classes have fewer than 20 students.


title: Samford University

text: Samford has moved four times during its history. Originally, Howard College was located in Marion, Alabama, a black-belt town between Selma and Tuscaloosa; it was the birthplace of Coretta Scott King. The college moved twice in the town. Its second campus is now the home of Marion Military Institute. In 1887, the college moved to the East Lake community in Birmingham. The university is now located approximately south of downtown Birmingham in Homewood, Alabama's Shades Valley along Lakeshore Drive in Homewood, just from Interstate 65. It is built in the Georgian Colonial style based on Colonial Williamsburg as envisioned by Lena Vail Davis, wife of then President Harwell Davis when the campus was moved to the Shades Valley area of Jefferson County in 1953-57. {https://www.samford.edu/about/history} The campus was designed by the Birmingham architectural firm Van Keuren & Davis, and most later buildings have also been designed by the same firm, known as Davis Architects since 1986.


title: Samford University

text: In 1983 the university established a study center in London, England, to facilitate students studying abroad. Named The Daniel House, the center is located at 12 Ashburn Gardens in South Kensington and hosts over 20 students most semesters.


title: Samford University

text: In 2014 the university purchased the campus of the Southern Progress Corporation which borders its main campus to the east. (The land had originally been part of Samford's undeveloped campus and was previously sold by Samford to Southern Progress.) The three huge buildings on the former Southern Progress campus are strikingly modern in their architecture and nestled among trees. This contrasts with the Georgian Colonial classicism of the central campus.


title: Samford University

text: In 2020, Samford University enrolled 3,576 undergraduate and 2,153 graduate and professional students. Students from 47 states and 30 countries attend Samford, with 66 percent of the undergraduate student body coming from outside the state of Alabama. 97 percent of all May 2019 undergraduate alumni were employed or enrolled in graduate school or in internships within six months of graduation. 81 percent of May 2015 graduates completed an internship during their time at Samford. During 2015, Samford students completed 716,902 hours of community service.


title: Samford University

text: The university fields 17 varsity sports and participates in the NCAA at the Division I level as a member of the Southern Conference. Men's sports include baseball, basketball, cross country, football, golf, tennis and indoor and outdoor track and field. Women's sports include basketball, cross country, golf, soccer, softball, tennis, indoor and outdoor track and field and volleyball.


title: Samford University

text: In the NCAA's 2013 report, Samford student-athletes achieved an average Academic Progress Rate of 990, the highest in Alabama. It marked the eighth consecutive year that Samford has been a leader in APR measures, beginning in 2005 when it placed 7th in the nation in the inaugural ranking. The university is one of only 61 schools to have received an NCAA Public Recognition Award for academic excellence in the past eight years.


title: Samford University

text: In 2019, Samford's athletics teams were ranked first in Alabama and the Southern Conference and 18th in the country among all NCAA Division 1 schools for Graduation Success Rate by the NCAA with an average score of 97%. Nine teams posted perfect scores. Samford is first among Division I schools in Alabama and in the Southern Conference.


title: Samford University

text: The Bulldogs have won 57 conference championships since joining the Southern Conference in 2008. In the last 20 years, 28 Samford baseball players have been selected in the Major League Baseball Draft, and 19 Bulldog football players have been chosen in the National Football League Draft. Past student-athletes include national-championship football coaches Bobby Bowden and Jimbo Fisher All-Pro defensive back Cortland Finnegan, NFL standouts include James Bradberry (Carolina Panthers), Michael Pierce (Baltimore Ravens) and Jaquiski Tartt (San Francisco 49ers), and baseball’s Phillip Ervin, who has had success with the Cincinnati Reds.


title: Samford University

text: The university has more than 52,000 alumni, including U.S. congressmen, seven state governors, two U.S. Supreme Court justices, four Rhodes Scholars, multiple Emmy and Grammy award-winning artists, two national championship football coaches, and recipients of the Pulitzer and Nobel Peace prizes. Some notable alumni include:


title: AdS/CFT correspondence

text: In theoretical physics, the anti-de Sitter/conformal field theory correspondence, sometimes called Maldacena duality or gauge/gravity duality, is a conjectured relationship between two kinds of physical theories. On one side are anti-de Sitter spaces (AdS) which are used in theories of quantum gravity, formulated in terms of string theory or M-theory. On the other side of the correspondence are conformal field theories (CFT) which are quantum field theories, including theories similar to the Yang–Mills theories that describe elementary particles.


title: AdS/CFT correspondence

text: The duality represents a major advance in the understanding of string theory and quantum gravity. This is because it provides a non-perturbative formulation of string theory with certain boundary conditions and because it is the most successful realization of the holographic principle, an idea in quantum gravity originally proposed by Gerard 't Hooft and promoted by Leonard Susskind.


title: AdS/CFT correspondence

text: It also provides a powerful toolkit for studying strongly coupled quantum field theories. Much of the usefulness of the duality results from the fact that it is a strong–weak duality: when the fields of the quantum field theory are strongly interacting, the ones in the gravitational theory are weakly interacting and thus more mathematically tractable. This fact has been used to study many aspects of nuclear and condensed matter physics by translating problems in those subjects into more mathematically tractable problems in string theory.


title: AdS/CFT correspondence

text: The AdS/CFT correspondence was first proposed by Juan Maldacena in late 1997. Important aspects of the correspondence were soon elaborated in two articles, one by Steven Gubser, Igor Klebanov and Alexander Polyakov, and another by Edward Witten. By 2015, Maldacena's article had over 10,000 citations, becoming the most highly cited article in the field of high energy physics, reaching over 20,000 citations in 2020.


title: AdS/CFT correspondence

text: Current understanding of gravity is based on Albert Einstein's general theory of relativity. Formulated in 1915, general relativity explains gravity in terms of the geometry of space and time, or spacetime. It is formulated in the language of classical physics developed by physicists such as Isaac Newton and James Clerk Maxwell. The other nongravitational forces are explained in the framework of quantum mechanics. Developed in the first half of the twentieth century by a number of different physicists, quantum mechanics provides a radically different way of describing physical phenomena based on probability.


title: AdS/CFT correspondence

text: Quantum gravity is the branch of physics that seeks to describe gravity using the principles of quantum mechanics. Currently, a popular approach to quantum gravity is string theory, which models elementary particles not as zero-dimensional points but as one-dimensional objects called strings. In the AdS/CFT correspondence, one typically considers theories of quantum gravity derived from string theory or its modern extension, M-theory.


title: AdS/CFT correspondence

text: In everyday life, there are three familiar dimensions of space (up/down, left/right, and forward/backward), and there is one dimension of time. Thus, in the language of modern physics, one says that spacetime is four-dimensional. One peculiar feature of string theory and M-theory is that these theories require extra dimensions of spacetime for their mathematical consistency: in string theory spacetime is ten-dimensional, while in M-theory it is eleven-dimensional. The quantum gravity theories appearing in the AdS/CFT correspondence are typically obtained from string and M-theory by a process known as compactification. This produces a theory in which spacetime has effectively a lower number of dimensions and the extra dimensions are "curled up" into circles.


title: AdS/CFT correspondence

text: A standard analogy for compactification is to consider a multidimensional object such as a garden hose. If the hose is viewed from a sufficient distance, it appears to have only one dimension, its length, but as one approaches the hose, one discovers that it contains a second dimension, its circumference. Thus, an ant crawling inside it would move in two dimensions.


title: AdS/CFT correspondence

text: The application of quantum mechanics to physical objects such as the electromagnetic field, which are extended in space and time, is known as quantum field theory. In particle physics, quantum field theories form the basis for our understanding of elementary particles, which are modeled as excitations in the fundamental fields. Quantum field theories are also used throughout condensed matter physics to model particle-like objects called quasiparticles.


title: AdS/CFT correspondence

text: In the AdS/CFT correspondence, one considers, in addition to a theory of quantum gravity, a certain kind of quantum field theory called a conformal field theory. This is a particularly symmetric and mathematically well behaved type of quantum field theory. Such theories are often studied in the context of string theory, where they are associated with the surface swept out by a string propagating through spacetime, and in statistical mechanics, where they model systems at a thermodynamic critical point.


title: AdS/CFT correspondence

text: In the AdS/CFT correspondence, one considers string theory or M-theory on an anti-de Sitter background. This means that the geometry of spacetime is described in terms of a certain vacuum solution of Einstein's equation called anti-de Sitter space.


title: AdS/CFT correspondence

text: In very elementary terms, anti-de Sitter space is a mathematical model of spacetime in which the notion of distance between points (the metric) is different from the notion of distance in ordinary Euclidean geometry. It is closely related to hyperbolic space, which can be viewed as a disk as illustrated on the right. This image shows a tessellation of a disk by triangles and squares. One can define the distance between points of this disk in such a way that all the triangles and squares are the same size and the circular outer boundary is infinitely far from any point in the interior.


title: AdS/CFT correspondence

text: Now imagine a stack of hyperbolic disks where each disk represents the state of the universe at a given time. The resulting geometric object is three-dimensional anti-de Sitter space. It looks like a solid cylinder in which any cross section is a copy of the hyperbolic disk. Time runs along the vertical direction in this picture. The surface of this cylinder plays an important role in the AdS/CFT correspondence. As with the hyperbolic plane, anti-de Sitter space is curved in such a way that any point in the interior is actually infinitely far from this boundary surface.


title: AdS/CFT correspondence

text: This construction describes a hypothetical universe with only two space and one time dimension, but it can be generalized to any number of dimensions. Indeed, hyperbolic space can have more than two dimensions and one can "stack up" copies of hyperbolic space to get higher-dimensional models of anti-de Sitter space.


title: AdS/CFT correspondence

text: An important feature of anti-de Sitter space is its boundary (which looks like a cylinder in the case of three-dimensional anti-de Sitter space). One property of this boundary is that, locally around any point, it looks just like Minkowski space, the model of spacetime used in nongravitational physics.


title: AdS/CFT correspondence

text: One can therefore consider an auxiliary theory in which "spacetime" is given by the boundary of anti-de Sitter space. This observation is the starting point for AdS/CFT correspondence, which states that the boundary of anti-de Sitter space can be regarded as the "spacetime" for a conformal field theory. The claim is that this conformal field theory is equivalent to the gravitational theory on the bulk anti-de Sitter space in the sense that there is a "dictionary" for translating calculations in one theory into calculations in the other. Every entity in one theory has a counterpart in the other theory. For example, a single particle in the gravitational theory might correspond to some collection of particles in the boundary theory. In addition, the predictions in the two theories are quantitatively identical so that if two particles have a 40 percent chance of colliding in the gravitational theory, then the corresponding collections in the boundary theory would also have a 40 percent chance of colliding.


title: AdS/CFT correspondence

text: Notice that the boundary of anti-de Sitter space has fewer dimensions than anti-de Sitter space itself. For instance, in the three-dimensional example illustrated above, the boundary is a two-dimensional surface. The AdS/CFT correspondence is often described as a "holographic duality" because this relationship between the two theories is similar to the relationship between a three-dimensional object and its image as a hologram. Although a hologram is two-dimensional, it encodes information about all three dimensions of the object it represents. In the same way, theories which are related by the AdS/CFT correspondence are conjectured to be "exactly" equivalent, despite living in different numbers of dimensions. The conformal field theory is like a hologram which captures information about the higher-dimensional quantum gravity theory.


title: AdS/CFT correspondence

text: Following Maldacena's insight in 1997, theorists have discovered many different realizations of the AdS/CFT correspondence. These relate various conformal field theories to compactifications of string theory and M-theory in various numbers of dimensions. The theories involved are generally not viable models of the real world, but they have certain features, such as their particle content or high degree of symmetry, which make them useful for solving problems in quantum field theory and quantum gravity.


title: AdS/CFT correspondence

text: The most famous example of the AdS/CFT correspondence states that type IIB string theory on the product space formula_1 is equivalent to "N" = 4 supersymmetric Yang–Mills theory on the four-dimensional boundary. In this example, the spacetime on which the gravitational theory lives is effectively five-dimensional (hence the notation formula_2), and there are five additional compact dimensions (encoded by the formula_3 factor). In the real world, spacetime is four-dimensional, at least macroscopically, so this version of the correspondence does not provide a realistic model of gravity. Likewise, the dual theory is not a viable model of any real-world system as it assumes a large amount of supersymmetry. Nevertheless, as explained below, this boundary theory shares some features in common with quantum chromodynamics, the fundamental theory of the strong force. It describes particles similar to the gluons of quantum chromodynamics together with certain fermions. As a result, it has found applications in nuclear physics, particularly in the study of the quark–gluon plasma.


title: AdS/CFT correspondence

text: Another realization of the correspondence states that M-theory on formula_4 is equivalent to the so-called (2,0)-theory in six dimensions. In this example, the spacetime of the gravitational theory is effectively seven-dimensional. The existence of the (2,0)-theory that appears on one side of the duality is predicted by the classification of superconformal field theories. It is still poorly understood because it is a quantum mechanical theory without a classical limit. Despite the inherent difficulty in studying this theory, it is considered to be an interesting object for a variety of reasons, both physical and mathematical.


title: AdS/CFT correspondence

text: Yet another realization of the correspondence states that M-theory on formula_5 is equivalent to the ABJM superconformal field theory in three dimensions. Here the gravitational theory has four noncompact dimensions, so this version of the correspondence provides a somewhat more realistic description of gravity.


title: AdS/CFT correspondence

text: In quantum field theory, one typically computes the probabilities of various physical events using the techniques of perturbation theory. Developed by Richard Feynman and others in the first half of the twentieth century, perturbative quantum field theory uses special diagrams called Feynman diagrams to organize computations. One imagines that these diagrams depict the paths of point-like particles and their interactions. Although this formalism is extremely useful for making predictions, these predictions are only possible when the strength of the interactions, the coupling constant, is small enough to reliably describe the theory as being close to a theory without interactions.


title: AdS/CFT correspondence

text: The starting point for string theory is the idea that the point-like particles of quantum field theory can also be modeled as one-dimensional objects called strings. The interaction of strings is most straightforwardly defined by generalizing the perturbation theory used in ordinary quantum field theory. At the level of Feynman diagrams, this means replacing the one-dimensional diagram representing the path of a point particle by a two-dimensional surface representing the motion of a string. Unlike in quantum field theory, string theory does not yet have a full non-perturbative definition, so many of the theoretical questions that physicists would like to answer remain out of reach.


title: AdS/CFT correspondence

text: The problem of developing a non-perturbative formulation of string theory was one of the original motivations for studying the AdS/CFT correspondence. As explained above, the correspondence provides several examples of quantum field theories which are equivalent to string theory on anti-de Sitter space. One can alternatively view this correspondence as providing a "definition" of string theory in the special case where the gravitational field is asymptotically anti-de Sitter (that is, when the gravitational field resembles that of anti-de Sitter space at spatial infinity). Physically interesting quantities in string theory are defined in terms of quantities in the dual quantum field theory.


title: AdS/CFT correspondence

text: In 1975, Stephen Hawking published a calculation which suggested that black holes are not completely black but emit a dim radiation due to quantum effects near the event horizon. At first, Hawking's result posed a problem for theorists because it suggested that black holes destroy information. More precisely, Hawking's calculation seemed to conflict with one of the basic postulates of quantum mechanics, which states that physical systems evolve in time according to the Schrödinger equation. This property is usually referred to as unitarity of time evolution. The apparent contradiction between Hawking's calculation and the unitarity postulate of quantum mechanics came to be known as the black hole information paradox.


title: AdS/CFT correspondence

text: The AdS/CFT correspondence resolves the black hole information paradox, at least to some extent, because it shows how a black hole can evolve in a manner consistent with quantum mechanics in some contexts. Indeed, one can consider black holes in the context of the AdS/CFT correspondence, and any such black hole corresponds to a configuration of particles on the boundary of anti-de Sitter space. These particles obey the usual rules of quantum mechanics and in particular evolve in a unitary fashion, so the black hole must also evolve in a unitary fashion, respecting the principles of quantum mechanics. In 2005, Hawking announced that the paradox had been settled in favor of information conservation by the AdS/CFT correspondence, and he suggested a concrete mechanism by which black holes might preserve information.


title: AdS/CFT correspondence

text: One physical system which has been studied using the AdS/CFT correspondence is the quark–gluon plasma, an exotic state of matter produced in particle accelerators. This state of matter arises for brief instants when heavy ions such as gold or lead nuclei are collided at high energies. Such collisions cause the quarks that make up atomic nuclei to deconfine at temperatures of approximately two trillion kelvins, conditions similar to those present at around 10 seconds after the Big Bang.


title: AdS/CFT correspondence

text: The physics of the quark–gluon plasma is governed by quantum chromodynamics, but this theory is mathematically intractable in problems involving the quark–gluon plasma. In an article appearing in 2005, Đàm Thanh Sơn and his collaborators showed that the AdS/CFT correspondence could be used to understand some aspects of the quark–gluon plasma by describing it in the language of string theory. By applying the AdS/CFT correspondence, Sơn and his collaborators were able to describe the quark gluon plasma in terms of black holes in five-dimensional spacetime. The calculation showed that the ratio of two quantities associated with the quark–gluon plasma, the shear viscosity formula_6 and volume density of entropy formula_7, should be approximately equal to a certain universal constant:


title: AdS/CFT correspondence

text: where formula_9 denotes the reduced Planck constant and formula_10 is the Boltzmann constant. In addition, the authors conjectured that this universal constant provides a lower bound for formula_11 in a large class of systems. In 2008, the predicted value of this ratio for the quark–gluon plasma was confirmed at the Relativistic Heavy Ion Collider at Brookhaven National Laboratory.