title: Romare Bearden

text: Bearden had struggled with two artistic sides of himself: his background as "a student of literature and of artistic traditions, and being a black human being involves very real experiences, figurative and concrete," which was at combat with the mid-twentieth century "exploration of abstraction". His frustration with abstraction won over, as he himself described his paintings' focus as coming to a plateau. Bearden then turned to a completely different medium at a very important time for the country.


title: Romare Bearden

text: During the civil rights movement, Bearden started to experiment again, this time with forms of collage. After helping to found an artists group in support of civil rights, Bearden expressed representational and more overtly socially conscious aspects in his work. He used clippings from magazines, which in and of itself was a new medium, as glossy magazines were fairly new. He used these glossy scraps to incorporate modernity in his works, trying to show how African-American rights were moving forward, and so was his socially conscious art. In 1964, he held an exhibition he called "Projections", where he introduced his new collage style. These works were very well received and are generally considered to be his best work.


title: Romare Bearden

text: Bearden had numerous museum shows of his work since then, including a 1971 show at the Museum of Modern Art entitled "Prevalence of Ritual", an exhibition of his prints, entitled "A Graphic Odyssey" showing the work of the last fifteen years of his life; and the 2005 National Gallery of Art retrospective entitled "The Art of Romare Bearden". In 2011, Michael Rosenfeld Gallery exhibited its second show of the artist's work, "Romare Bearden (1911–1988): Collage, A Centennial Celebration", an intimate grouping of 21 collages produced between 1964 and 1983.


title: Romare Bearden

text: One of his most famous series, "Prevalence of Ritual", concentrates mostly on southern African-American life. He used these collages to show his rejection of the Harmon Foundation's (a New York City arts organization) emphasis on the idea that African Americans must reproduce their culture in their art. Bearden found this approach to be a burden on African artists, because he saw the idea as creating an emphasis on reproduction of something that already exists in the world. He used this new series to speak out against this limitation on Black artists, and to emphasize modern art.


title: Romare Bearden

text: In this series, one of the pieces is entitled "Baptism". Bearden was influenced by Francisco de Zurbarán, and based "Baptism" on Zurbarán's painting "The Virgin Protectress of the Carthusians". Bearden wanted to show how the water that is about to be poured on the subject being baptized is always moving, giving the whole collage a feel and sense of temporal flux. He wanted to express how African Americans' rights were always changing, and society itself was in a temporal flux at the time. Bearden wanted to show that nothing is fixed, and expressed this idea throughout the image: not only is the subject about to have water poured from the top, but the subject is also to be submerged in water. Every aspect of the collage is moving and will never be the same more than once, which was congruent with society at the time.


title: Romare Bearden

text: In "The Art of Romare Bearden", Ruth Fine describes his themes as "universal". "A well-read man whose friends were other artists, writers, poets and jazz musicians, Bearden mined their worlds as well as his own for topics to explore. He took his imagery from both the everyday rituals of African American rural life in the south and urban life in the north, melding those American experiences with his personal experiences and with the themes of classical literature, religion, myth, music and daily human ritual."


title: Romare Bearden

text: In 2008 a 1984 mural by Romare Bearden in the Gateway Center subway station in Pittsburgh was estimated as worth $15 million, more than the cash-strapped transit agency expected. It raised questions about how it should be cared for once it is removed before the station is demolished.


title: Romare Bearden

text: "We did not expect it to be that much," Port Authority of Allegheny County spokeswoman Judi McNeil said. "We don't have the wherewithal to be a caretaker of such a valuable piece." It would cost the agency more than $100,000 a year to insure the tile mural, McNeil said. Bearden was paid $90,000 for the project, titled "Pittsburgh Recollections." It was installed in 1984.


title: Romare Bearden

text: Before his death, Bearden claimed the collage fragments aided him to usher the past into the present: "When I conjure these memories, they are of the present to me, because after all, the artist is a kind of enchanter in time."


title: Romare Bearden

text: "The Return of Odysseus", one of his collage works held by the Art Institute of Chicago, exemplifies Bearden's effort to represent African-American rights in a form of collage. This collage describes one of the scenes in Homer's epic "Odyssey", in which the hero Odysseus is returning home from his long journey. The viewer's eye is first captured by the main figure, Odysseus, situated at the center of the work and reaching his hand to his wife. All the figures are black, enlarging the context of the Greek legend. This is one of the ways in which Bearden works to represent African-American rights; by replacing white characters with blacks, he attempts to defeat the rigidity of historical roles and stereotypes and open up the possibilities and potential of blacks. "Bearden may have seen Odysseus as a strong mental model for the African-American community, which had endured its own adversities and setbacks." By portraying Odysseus as black, Bearden maximizes the potential for empathy by black audiences.


title: Romare Bearden

text: Bearden said that he used collage because "he felt that art portraying the lives of African Americans did not give full value to the individual. [...] In doing so he was able to combine abstract art with real images so that people of different cultures could grasp the subject matter of the African American culture: The people. This is why his theme always exemplified people of color." In addition, he said that collage's technique of gathering several pieces together to create one assembled work "symbolizes the coming together of tradition and communities."


title: Romare Bearden

text: In addition to painting, collage, and athletics, Bearden enjoyed music and even composed a number of songs.


title: Romare Bearden

text: In 1960, Loften Mitchell released the three act play, "Star of the Morning," for which he wrote the script and music, and Bearden and Clyde Fox wrote the lyrics.


title: Romare Bearden

text: A selection of them can be heard on the 2003 album "Romare Bearden Revealed," created by the Branford Marsalis Quartet.


title: Romare Bearden

text: Romare Bearden died in New York City on March 12, 1988, due to complications from bone cancer. The "New York Times" described Bearden in its obituary as "one of America's pre-eminent artists" and "the nation's foremost collagist."


title: Romare Bearden

text: Two years after his death, the Romare Bearden Foundation was founded. This non-profit organization not only serves as Bearden's official estate, but also helps "to preserve and perpetuate the legacy of this preeminent American artist." Recently, it has begun developing grant-giving programs aimed at funding and supporting children, young (emerging) artists, and scholars.


title: Romare Bearden

text: In Charlotte, a street was named after Bearden, intersecting West Boulevard, on the west side of the city. Romare Bearden Drive is lined by the West Boulevard Public Library and rows of townhouses.


title: Romare Bearden

text: Inside the Charlotte-Mecklenburg Main Library (310 N. Tryon Street) is Bearden's mosaic, "Before Dawn". After Bearden's death, his widow selected a collage by him to be recreated in smalti (glass tiles) by Crovatto Mosaics in Spilimbergo, Italy, for the grand reopening gala (June 18, 1989) of the "new" library. She was publicly honored at the ceremony for her contribution. The reinterpreted work is tall and wide.


title: Romare Bearden

text: Ground breaking for Romare Bearden Park in Charlotte took place on September 2, 2011, and the completed park opened in late August 2013. It is situated on a parcel located in Third Ward between Church and Mint streets. The artist lived near the new park for a time as a child, at the corner of what is now MLK Boulevard and Graham Street. The park design is based on work of public artist Norie Sato. Her concepts were inspired by Bearden's multimedia collages. Fittingly, the park serves as an entryway to a minor league baseball stadium, BB&T Charlotte Knights Ballpark.


title: Romare Bearden

text: DC Moore Gallery currently represents the estate of Romare Bearden. The first exhibition of his works at the gallery was in September 2008. In 2014-15, Columbia University hosted a major Smithsonian Institution travelling exhibition of Bearden's work and an accompanying series of lectures, readings, performances, and other events celebrating the artist. On display at the Miriam and Ira D. Wallach Gallery on Columbia's Morningside campus, and also at Columbia's Global Centers in Paris and Istanbul, "Romare Bearden: A Black Odyssey" focused on the cycle of collages and watercolors Bearden completed in 1977 based on Homer's epic poem, "The Odyssey".


title: Romare Bearden

text: In 2011, the U.S. Postal Service released a set of Forever stamps featuring four of Bearden's paintings during a first-day-of-issuance ceremony at the Schomburg Center for Research in Black Culture.


title: Romare Bearden

text: In 2017, the Virginia Museum of Fine Arts in Richmond announced acquisition of Romare Bearden's collage, "Three Folk Musicians", as part of the museum's permanent collection. The collage, which shows two guitar players and a banjo player, is often cited in art history books. It was shown at the VMFA for the first time in February 2017 in the museum's mid- to late 20th-century galleries.


title: Superman (comic book)

text: Superman is an ongoing American comic book series featuring the DC Comics superhero Superman as its main protagonist. Superman began as one of several anthology features in the National Periodical Publications comic book "Action Comics" #1 in June 1938. The strip proved so popular that National launched Superman into his own self-titled comic book, the first for any superhero, premiering with the cover date Summer 1939. Between 1986 and 2006 it was retitled, "The Adventures of Superman", while a new series used the title "Superman". In May 2006, it was returned to its original title and numbering. The title was canceled with issue #714 in 2011, and was relaunched with issue #1 the following month which ended its run in 2016. A fourth series was released in June 2016 and ended in April 2018, while the fifth series was launched in July 2018 and ended in June 2021. The series was replaced by "Superman: Son of Kal-El" in July 2021, featuring adventures of Superman's son, Jon Kent.


title: Superman (comic book)

text: Due to the Superman character's popularity after his premiere in "Action Comics" #1, National Allied Publications decided to launch an entirely new magazine featuring a single character, which at that time was unprecedented. "Superman" #1 appeared on the shelves in the summer of 1939. Superman now also had the distinction of being the first ever hero-character featured in more than one comic magazine. By issue #7, Superman was being hailed on the covers as the "World's Greatest Adventure Strip Character". Perry White, a supporting character who had originated on the Superman radio program was introduced into the comic book in issue #7 (October 1940). Editor Mort Weisinger began his long association with the title with issue #11 (July–August 1941). Jimmy Olsen first appeared as a named character in the story "Superman versus The Archer" in "Superman" #13 (Nov.–Dec. 1941). In the early 1940s, "Superman" was selling over a million copies per month. By 1942, artist Wayne Boring, who had previously been one of Shuster's assistants, had become a major artist on Superman. "Superman" #23 (July–August 1943) featured the first Superman comic book story written by someone other than Jerry Siegel. The story "America's Secret Weapon!" was written by Don Cameron despite bearing Siegel's signature. Siegel introduced Mister Mxyzptlk in issue #30 (September 1944). A more detailed origin story for Superman was presented in issue #53 (July 1948) to mark the character's tenth anniversary. Another part of the Superman mythos which had originated on the radio program made its way into the comic books when kryptonite was featured in a story by Bill Finger and Al Plastino.


title: Superman (comic book)

text: "Superman" was the first DC title with a letters column as a regular feature beginning with issue #124 (September 1958). In the view of comics historian Les Daniels, artist Curt Swan became the definitive artist of Superman in the early 1960s with a "new look" to the character that replaced Wayne Boring's version. Writer Jim Shooter and Swan crafted the story "Superman's Race With the Flash!" in "Superman" #199 (Aug. 1967) which featured the first race between the Flash and Superman, two characters known for their super-speed powers.


title: Superman (comic book)

text: Julius Schwartz became the title's editor with issue #233 (January 1971) and together with writer Denny O'Neil and artist Curt Swan streamlined the Superman mythos, starting with the elimination of Kryptonite. Elliot S. Maggin began his long association with the title with the story "Must There Be a Superman?" in issue #247 (Jan. 1972). Writer Cary Bates, in collaboration with Swan, introduced such characters as the supervillain Terra-Man in issue #249 (March 1972) and the superhero Vartox in issue #281 (Nov. 1974). Issues #272 (Feb. 1974), #278 (Aug. 1974), and #284 (Feb. 1975) of the series were in the 100 Page Super Spectacular format. "Superman" #300 (June 1976) featured an out-of-continuity story by Bates and Maggin which imagined the infant Superman landing on Earth in 1976 and becoming a superhero in 2001. The tale was an inspiration for Mark Millar's "" limited series published in 2003. DC's parent company Warner Communications reinstated the byline for Jerry Siegel and Joe Shuster which had been dropped decades earlier and the first issue with the restored credit was "Superman" #301 (August 1976). Martin Pasko and Swan created the Master Jailer character in issue #331 (January 1979). The bottle city of Kandor, which had been introduced in 1958, was restored to normal size in a story by Len Wein and Swan in "Superman" #338 (August 1979).


title: Superman (comic book)

text: The series reached issue #400 in October 1984. That issue featured work by several popular comics artists including the only major DC work by Jim Steranko as well as an introduction by noted science-fiction author Ray Bradbury. "Superman" ran uninterrupted until the mid-1980s, when DC Comics instituted a line-wide relaunch with the 1985 event maxi-series "Crisis on Infinite Earths". Folding their vast multiverse into a single shared universe, Superman and his supporting cast would receive a massive overhaul at the hands of writer/artist John Byrne. One last story, which also marked the end of Schwartz's tenure as editor of the series, was published to give a send-off to the former status quo: Alan Moore's "" The story's first part saw publication in "Superman" #423, which would be the last issue before the title was relaunched with its legacy numbering as "The Adventures of Superman". "Superman" was relaunched with a new #1 issue in a second volume in 1986, and was published concurrently with "The Adventures of Superman".


title: Superman (comic book)

text: The Adventures of Superman was numbered from issue #424 (January 1987) to issue #649 (April 2006), for a total of 228 monthly issues including issue #0 (October 1994) published between issues #516 and #517 as a tie-in to the "Zero Hour" limited series and issue #1,000,000 (November 1998) as a tie-in to the "DC One Million" limited series and nine Annuals published between 1987 and 1997.


title: Superman (comic book)

text: When the series was relaunched in late 1986 under its new title, the creative team initially was writer Marv Wolfman and artist Jerry Ordway. John Byrne replaced Wolfman with issue #436 (January 1988) and Ordway became both writer and artist with issue #445 (October 1988). Writer/artist Dan Jurgens worked on the title from 1989–1991. Hank Henshaw, a character who would later become the Cyborg Superman, first appeared in issue #466 (May 1990). By the late 1980s, the plots of the Superman books were often linked. To coordinate the storyline and sequence of event, from January 1991 to January 2002, "triangle numbers" (or "shield numbers") appeared on the cover of each Superman comic book. During these years, the Superman storylines ran with the story continuing through the titles "Superman", "Action Comics" and later in two further series, "" and "".


title: Superman (comic book)

text: Jerry Ordway returned as writer of the title with issue #480 (July 1991). Tom Grummett drew part of #480 and became the main artist on the series with the following issue. The series participated in the crossover storyline "Panic in the Sky" in 1992. During their run on "The Adventures of Superman", Grummett and Ordway (along with editor Mike Carlin and others) were the architects of "The Death of Superman" storyline, in which Superman died and was resurrected. It was during that storyline, that Grummett and writer Karl Kesel, created the new Superboy in "The Adventures of Superman" #500 (June 1993). Other crossovers the series participated in included "", "The Final Night", and "Infinite Crisis".


title: Superman (comic book)

text: As of the start of 2002, the integration between the Superman titles became less frequent, and the remaining issues of "The Adventures of Superman" commonly carried self-contained stories. Issue #600 (March 2002) was a double-sized special featuring Superman combating Lex Luthor. The final issue (#649) was part of a three-part crossover with "Superman" and "Action Comics", an homage to the Earth-2 Superman in the wake of events in the limited series "Infinite Crisis".


title: Superman (comic book)

text: For its last two years, "The Adventures of Superman" was written by Greg Rucka. His stories included the villain Ruin, the attempted assassination of Lois Lane and a number of Mister Mxyzptlk appearances.


title: Superman (comic book)

text: "Adventures of Superman" was relaunched on April 29, 2013. Unlike the previous volume, the new series is not set in the mainstream DC Universe continuity but instead features anthology style stories with rotating creative teams in the same format as the second "" series. It is released as a digital-first comic with print publication to follow. The first story was to have been written by Orson Scott Card and drawn by Chris Sprouse and Karl Story. Card's participation in the project became an issue. DC Comics responded to a petition about to be dropped with a statement that it supported freedom of expression and that the personal views of individuals associated with the company were not the views of the company. Illustrator Chris Sprouse left the project due to the media attention and some comic book stores announced a boycott. Card's Superman story was dropped and was replaced by a story written by Jeff Parker. The relaunched "Adventures of Superman" series came to an end with issue #17, released in September 2014.


title: Superman (comic book)

text: "Superman" volume 2 reached issue #226 (April 2006) and was then canceled as part of the linewide "Infinite Crisis" event. "The Adventures of Superman" was returned to its original title, "Superman", with issue #650 (May 2006), as a part of the "One Year Later" banner. "Superman" had a crossover with "Action Comics", titled "" co-written by Geoff Johns and Kurt Busiek with art by Pete Woods. This storyline told of Clark Kent attempting to protect Metropolis without his powers until eventually regaining them. Busiek became the sole writer of the series with issue #654 (September 2006) and Carlos Pacheco became the series' artist. The series participated in the weekly series "Countdown to Final Crisis", giving a different perspective on certain events shown in the weekly title, such as the events preceding the death of New God Lightray.


title: Superman (comic book)

text: Busiek and Pacheco developed an extended storyline featuring Arion coming into conflict with Superman. The plotline concluded in "Superman Annual" #13. Alex Ross painted the covers for issues #675 (June 2008) through #685 (April 2009).


title: Superman (comic book)

text: James Robinson replaced Busiek with issue #677 (August 2008). Robinson's run on the title began with "The Coming of Atlas" story arc and began a link between "Superman", "Action Comics", and "Supergirl" that started a long-form narrative with the "" event. The majority of Robinson's run featured Mon-El and the Guardian as the featured characters, while Superman himself had gone to live on the planet New Krypton. Robinson's last full issue was #699, tying into "", and he finished his run in a short story in issue #700 (August 2010) that returned Superman to Earth. "Superman" #700 also saw writer J. Michael Straczynski, a self-professed Superman fan who feels a personal connection to the character, take over writing duties with a short story in the issue, and his run on the title began with issue #701. Artist Eddy Barrows, a previous "Action Comics" artist and one of the artists on the "" event, was Straczynski's artistic collaborator. Straczynski and Barrows began a year-long story entitled "" that sees Superman begin a long walk across the United States to regain the connection with his adopted home that he feels he lost while away on New Krypton. The series ended with issue #714 (October 2011), prior to DC Comics' The New 52 company wide reboot and relaunch.


title: Superman (comic book)

text: DC Comics launched "Superman" volume 3 with issue #1 in September 2011 (cover dated November 2011), as part of The New 52. The first three issues saw George Pérez doing the scripting and breakdowns. Dan Jurgens began to co-write and draw "Superman" with Keith Giffen. Their first issue was #7 (May 2012). As of September 2012's issue #0, Scott Lobdell and Kenneth Rocafort became the creative team. John Romita Jr. draw the "Superman" series in collaboration with writer Geoff Johns in 2014. Romita Jr.'s "Superman" pencils were inked by Klaus Janson. Superman's secret identity as Clark Kent was revealed to the world in a storyline by writer Gene Luen Yang in 2015. This series ended its run with the release of issue #52 (July 2016).


title: Superman (comic book)

text: As part of the DC Rebirth relaunch, "Superman" Volume 4 began with issue #1 in June 2016 (cover dated August 2016), including a one-shot DC Rebirth special "Superman: Rebirth" #1. Peter J. Tomasi and Patrick Gleason are the creative team, with the "Superman" series shipping twice-monthly. This volume's 34th issue was also the 800th issue of the "Superman" series as a whole, with a variant cover done by Tony S. Daniel to commemorate the occasion. The series ended its run with issue #45 (April 2018).


title: Superman (comic book)

text: A fifth series under the direction of Brian Michael Bendis was released in July 2018 and ended its run in June 2021 with issue #32.


title: Superman (comic book)

text: "Superman: Son of Kal-El", written by Tom Taylor and art by John Timms, replaced the "Superman" title in July 2021. The monthly series conclude in December 2022, with 18 issues and one annual. The series follows the adventures of Jon Kent, the son of Superman and Lois Lane, as he is entrusted with the protection of Earth. Jon came out as bisexual in the fifth issue of the series, starting a relationship with his male reporter friend Jay Nakamura.


title: Superman (comic book)

text: A new ongoing "Superman" comic book series will launch in February 2023 from writer Joshua Williamson and artist Jamal Campbell.


title: Superman (comic book)

text: The "Superman" series had "Annuals" published since 1960. Eight issues of "Superman Annual" were published starting in winter 1960. An additional four issues were published from 1983 to 1986 and the numbering continued from the 1960 series. "Superman Annual" #11 (1985) featured the story "For the Man Who Has Everything" by Alan Moore and Dave Gibbons. When the original "Superman" series was retitled as "The Adventures of Superman", both it and "Superman" (vol. 2) received "Annuals" relaunched with #1 issues. "The Adventures of Superman Annual" ran for nine issues from 1987 to 1997. After "The Adventures of Superman" was restored to its original title as "Superman", its "Annuals" continued the (vol. 2) "Annuals".


title: TC Energy

text: TC Energy Corporation (formerly TransCanada Corporation) is a major North American energy company, based in the TC Energy Tower building in Calgary, Alberta, Canada, that develops and operates energy infrastructure in Canada, the United States, and Mexico. The company operates three core businesses: Natural Gas Pipelines, Liquids Pipelines and Energy.


title: TC Energy

text: The Natural Gas Pipeline network includes of gas pipeline, which transports more than 25% of North American natural gas demand. The Liquids Pipelines division includes of oil pipeline, which ships 590,000 barrels of crude oil per day, which is about 20% of Western Canadian exports. The Energy division owns or has interests in 11 power generation facilities with combined capacity of 6,600 megawatts (MW). These power sources include nuclear and natural gas fired. The company is expanding its energy division to include more renewable sources including pumped storage, wind, and solar generation.


title: TC Energy

text: The company was founded in 1951 in Calgary. The company's US headquarters is located in the TC Energy Center skyscraper in Houston, Texas.


title: TC Energy

text: The company was incorporated in 1951 by a Special Act of Parliament as Trans-Canada Pipe Lines Limited. The purpose of the company was to develop the TransCanada pipeline (now known as the Canadian Mainline) to supply eastern Canadian markets with natural gas produced in the west.


title: TC Energy

text: In 1998, TransCanada Pipelines merged with NOVA Corporation's pipeline business, keeping the TransCanada name and becoming "the fourth largest energy services company in North America".


title: TC Energy

text: Seeking to expand its presence in the United States, in 2016, TransCanada acquired Columbia Pipeline Group (CPG) for US$13 billion from NiSource's Shareholders. The CPG acquisition added a pipeline network in Pennsylvania and surrounding states, where the Marcellus and Utica shale gas formations are located.


title: TC Energy

text: In May 2019, the company changed its name from TransCanada Corporation to TC Energy Corporation to better reflect the company's business, which includes pipelines, power generation and energy storage operations in Canada, the United States and Mexico.


title: TC Energy

text: In October 2019, the iconic 56-story Bank of America Center skyscraper in Houston, Texas was renamed as TC Energy Center and serves as the company's US headquarters.


title: TC Energy

text: TC Energy's natural gas pipelines business builds, owns and operates a network of natural gas pipelines across North America that connects gas production to interconnects and end use markets. The company transports over 25% of continental daily natural gas demand through 91,900 km (57,100 mi) of pipelines. In addition, the company owns 535 Bcf of natural gas storage facilities, making TC Energy one of the largest natural gas storage providers in North America. This segment is TC Energy's largest segment, generating approximately two-thirds of the company's EBITDA in 2017. The Natural Gas Pipelines business is split into three operating segments: Canadian Natural Gas Pipelines, U.S. Natural Gas Pipelines, and Mexico Natural Gas Pipelines.


title: TC Energy

text: Coastal GasLink Pipeline Project – In June 2012 it was announced that TransCanada was selected by Shell and LNG Canada partners Korea Gas Corporation, Mitsubishi Corporation and PetroChina Company Limited (to which Petronas of Malaysia was added in 2018) to design, build, own and operate the Coastal GasLink pipeline between northeastern B.C. gas fields near Dawson Creek, British Columbia, and the LNG Canada LNG liquefaction, storage and export facility in the port of Kitimat, on the Douglas Channel.


title: TC Energy

text: The investment and construction decisions for the LNG Canada and Coastal GasLink Pipeline Project were officially confirmed early October 2018, for completion by 2024–2025. However, hereditary chiefs of the Wetʼsuwetʼen have denied consent to construct the pipeline on the company's preferred route through culturally and ecologically sensitive lands in their unceded territory, leading to nationwide protests.


title: TC Energy

text: Prince Rupert Gas Transmission project – In January 2013 it was announced that TransCanada was selected by Petronas to design, build, own, and operate the Prince Rupert Gas Transmission project, a gas pipeline that would transport natural gas from the Montney region near Fort St. John, British Columbia to a LNG terminal planned by Progress Energy Canada Ltd. in Port Edward, British Columbia on Lelu Island near Prince Rupert, British Columbia. The project faced opposition from the Gitxsan first nation due to concerns about the impact it would have on salmon in the Skeena River. On July 25, 2017, Petronas announced they were abandoning the Pacific NorthWest LNG proposal and TransCanada said they were "reviewing our options related to our proposed Prince Rupert Gas Transmission (PRGT) project".


title: TC Energy

text: Two TC Energy's Liquids pipelines connect Alberta crude oil supplies to U.S. refining markets., the Keystone Pipeline System and the Grand Rapids pipelines. The 460 km-Grand Rapids pipeline transports crude oil from the producing area northwest of Fort McMurray, Alberta, to the Edmonton/Heartland, Alberta market region. In October 2012, TransCanada formed a 50–50 CAD$3bn joint-venture with Phoenix Energy Holdings Ltd. (the Canadian subsidiary of PetroChina) to develop the 500 km Grand Rapids Pipeline.


title: TC Energy

text: The 4,324 km-Keystone Pipeline System transports crude oil from Hardisty, Alberta, to U.S. markets at Wood River and Patoka, Illinois, Cushing, Oklahoma, and the U.S. Gulf Coast. The Keystone System transports approximately 20% of Western Canadian crude oil to export markets. The Keystone Pipeline has had three significant leaks since it opened in 2010. It has leaked approximately 400 barrels in North Dakota in 2011 and South Dakota in 2016, and approximately 5000 barrels in South Dakota in 2017.


title: TC Energy

text: A third pipeline, the 1,906 km-long Keystone XL Pipeline—which is an expansion of the Keystone Pipeline System—began construction in 2020. When completed, the Keystone XL Pipeline will transport 830,000 barrels of Athabasca oil sands crude oil per day from the Hardisty, Alberta to Steele City, Nebraska.


title: TC Energy

text: TC Energy had first proposed the Keystone XL pipeline in 2008. The proposal faced widespread grassroots opposition with tactics including tree sits in the path of the pipeline and civil disobedience by celebrities. Critics state that by developing the oil sands, fossil fuels will be readily available and the trend toward warming of the atmosphere won't be curbed. The fate of the pipeline is therefore held up as symbolic of America's energy future. Critics have raised concerns about the risks of spillage, as the Sandhills region of Nebraska is a fragile ecosystem.


title: TC Energy

text: In October 2011, TransCanada was involved in up to 56 separate eminent domain actions against landowners in Texas and South Dakota who refused to give permission to the company to build the Keystone Pipeline through their land. However, on August 23, 2012, Texas Judge Bill Harris ruled that TransCanada had the right of eminent domain and could lease or purchase land from owners who refused to sign an agreement with the company for a public right of way for the pipeline. The landowners had said that the pipeline was not open to other companies, and so did not meet the criteria for eminent domain.


title: TC Energy

text: Early in his tenure in 2017, President Donald Trump signed presidential memoranda to revive both Keystone XL and Dakota Access pipelines. The order would expedite the environmental review that Trump described as an "incredibly cumbersome, long, horrible permitting process".


title: TC Energy

text: In 2017, Trump signed a U.S. Presidential Permit to allow TransCanada to build the Nebraska pipeline route of the Keystone XL. TransCanada secured sufficient commercial support to commence construction preparation.


title: TC Energy

text: In March 2020, Premier Jason Kenney of Alberta, agreed to help finance the construction of TC Energy's Keystone XL oil sands pipeline in southern Alberta, Montana, South Dakota and Nebraska with a CA$7.5 billion (US$5.3 billion) financing agreement. According to "The New York Times" , despite the coronavirus pandemic, a down turn in the global economy, and "plunging oil prices", Premier Kenney said that Alberta could not afford "for Keystone XL to be delayed." With this financial agreement, the Alberta government gained a US$1.1-billion ownership stake in the 1,947-kilometre pipeline which will "575,000 barrels of oil daily". The province intends to sell its shares to TC Energy "after commercial operations begin." Alberta also gave a full guarantee on a US$4.2-billion project loan. The $USD1.1 billion equity covers construction costs from April through December 2020. TC Energy will also invest CA$.7 billion. The Alberta government are also providing a fully guaranteed CA$4.2 billion loan for the project. The premier also said that over the next twenty years, the financial benefits to Alberta through tax and royalty revenue would be approximately CA$30 billion. In response to Alberta's financial support, in March, TC Energy "approved construction of the US$8-billion project to transport up to 830,000 barrels per day of oil." According to a Canadian Press March 31, 2020 article Premier Kenney estimated that "1,400 direct and 5,400 indirect jobs" would be created in Alberta during construction. In September 2020, TC Energy announced that it would be restructuring some of its gas pipeline operations in Alberta.


title: TC Energy

text: In April, shortly after construction on Keystone XL began, Judge Brian M. Morris of the Federal District Court in Montana suspended the United States Army Corps of Engineers (USACE)'s program allowing permits for pipelines to cross waterways, in spite of the Clean Water Act (CWA). Judge Morris said that the USACE pipeline permits "posed a threat to endangered species" and its reauthorization in 2017, had been improper. In July 2020, the Supreme Court of the United States declined to block Judge Morris' ruling, effectively halting all construction on the XL Pipeline.


title: TC Energy

text: In September 2020, the Nekaneet Cree Nation in Saskatchewan, the Ermineskin Cree Nation, Montana First Nation, Louis Bull Tribe, and Saddle Lake Cree Nation in Alberta signed a memoranda of understanding (MOU) for an ownership stake in Keystone XL.


title: TC Energy

text: In a Canadian Press article Calgary energy reporter, Dan Healing, wrote that Keystone XL's future was "still in doubt"—if Presidential candidate Joe Biden wins the November 3, 2020 United States presidential election, he would fulfill his promise to cancel the pipeline's "vital presidential permit."


title: TC Energy

text: On November 16, 2017, oil leaked from the pipeline in Marshall County, South Dakota, for 15 minutes before the flow of oil could be stopped. The company reported the amount as over 210,000 gallons. TransCanada reported it discovered the leak in Amherst, South Dakota, at 6 am on Thursday after systems detected a drop in pressure in the northern leg of the pipeline. The leak was discovered about 35 miles south of the Ludden pump station.


title: TC Energy

text: In April 2018, a federal investigation showed that the spill was almost twice as large as TransCanada had claimed in November, and that it was the seventh-largest onshore oil spill since 2002. The study showed that 407,000 gallons, not 210,000 gallons, had spilled. Also in April 2018, "Reuters" reviewed documents that showed that Keystone had "leaked substantially more oil, and more often, in the United States than the company indicated to regulators in risk assessments before operations began in 2010".


title: TC Energy

text: TC Energy's Energy division consists of power generation and unregulated natural gas storage assets. The power business consists of approximately 7,000 megawatts (MW) of generation capacity owned or under development. These assets are located primarily in Canada and are powered by natural gas, nuclear, and wind.


title: TC Energy

text: TC Energy has proposed two pumped storage projects and one solar project to store and supply clean energy. The Ontario Pumped Storage Project near Meaford, Ontario would provide 1000 MW of clean energy and the proposed Canyon Creek Pumped Storage Project near Hinton, Alberta would provide 75 MW of clean energy. The proposed Saddlebrook Solar + Storage project in Aldersyde, Alberta would consist of 102.5 MW of solar generation with utility-scale energy storage.


title: TC Energy

text: As of February 2020, the bulk of the share capital of TC Energy is owned by 488 institutional investors, who compose 62% of the stock. The dominant shareholder is the Royal Bank of Canada, which owns a fraction over 8% of the company. The Big Five (banks) together own more than 17% of the outstanding share capital. Significant holdings accrue to the Caisse de dépôt et placement du Québec and the OMERS.


title: TC Energy

text: In 2019 TransCanada aided the drafting of anti-protest legislation in South Dakota. The legislation, which Governor Kristi Noem signed into law in March 2019, created a fund to cover the costs of policing pipeline protests, and was accompanied by another law which sought to raise revenue for the fund by creating civil penalties for advising, directing, or encouraging persons participating in rioting. In response to the law Noem was sued by the Indigenous Environmental Network, Sierra Club, and other groups, who argued the laws violate First Amendment rights by incentivizing the state to sue protesters.


"England expects that every man will do his duty" was a signal sent by Vice-Admiral of the Royal Navy Horatio Nelson, 1st Viscount Nelson from his flagship as the Battle of Trafalgar was about to commence on 21 October 1805.


title: England expects that every man will do his duty

text: During the battle, as Nelson's fleet closed in on the allied fleet, he ordered Lieutenant John Pasco to signal the British fleet as soon as possible. After Pasco suggested some changes, and Nelson agreeing to them, the signal was sent at around 11:45 am on October 21, 1805, and relayed using a numeric flag code known as the "Telegraphic Signals of Marine Vocabulary".


text: Although there was much confusion surrounding the precise wording of the signal in the aftermath of the battle, the significance of the victory and Nelson's death during the battle led to the phrase becoming a standard representation of a militant English spirit of courage and virtue in the face of conflict. It has been regularly quoted, paraphrased and referenced up to the modern day.


text: During the Napoleonic Wars, Napoleon planned to invade Britain. To do so, he ordered both the French and Spanish navies to take control of the English Channel in order to ensure a safe passage for the Grande Armée. Commanded by Admiral Villeneuve, the allied navy went down to Cape Trafalgar, where they encountered a British Fleet commanded by Horatio Nelson.


text: On October 21, 1805, the Battle of Trafalgar began, with Nelson's fleet of 27 ships pitted against the combined Spanish and French fleet of 33. In order to secure victory, Nelson sailed his fleet towards the flank of the allied fleet in order to break it into pieces. The naval battle resulted in 22 allied ships being lost, while the British lost none. As a result, the British were victorious, ensuring their control of the sea and removing the possibility of a French invasion of Britain.


text: As the British fleet closed with the opposing combined fleets of France and Spain, Lord Nelson signalled all the necessary battle instructions to his ships. Aware of the momentousness of events to come, Lord Nelson felt that something extra was required. He instructed his signal officer, Lieutenant John Pasco, to signal to the fleet, as quickly as possible, the message "England confides [i.e. is confident] that every man will do his duty." Pasco suggested to Nelson that "expects" be substituted for "confides", since the former word was in the signal book, whereas "confides" would have to be spelt out letter-by-letter. Nelson agreed to the change (even though it produced a less trusting impression):


text: Thus, at around 11:45 a.m. on 21 October 1805, the signal was sent. The exact time the signal was sent is not known (one account puts it as early as 10:30), as the message was repeated throughout the fleet, but Pasco puts it at "about a quarter to noon" and logs from other ships of the line also put it close to this time.


text: The signal was relayed using the numeric flag code known as the "Telegraphic Signals of Marine Vocabulary", devised in 1800 by Rear Admiral Sir Home Popham, and based on the signal books created earlier by Admiral Lord Howe. This code assigned the digits 0 to 9 to ten signal flags, which were used in combination. Code numbers 1–25 represented letters of the alphabet (omitting J and with V=20 before U=21); higher numbers were assigned meanings by a code book.


text: The code numbers are believed to have been hoisted on the mizzenmast, one after another, with the "telegraphic flag" (a red-over-white diagonally-split flag) also being flown to show that the signals employed Popham's code. As well as digit flags, the code used "repeat" flags so that only one set of digits was needed; thus the word "do", coded as "220", used a "2" flag, a "first repeat" flag here serving as a second 2, and a "0" flag. The word "duty" was not in the codebook (and was not replaced as "confides" had been), so had to be spelt out, and the whole message required twelve "lifts". It is believed that it would have taken about four minutes, with the end of the message indicated by an "end of code" flag (blue over yellow diagonally split). A team of four to six men, led by Lt. Pasco, would have prepared and hoisted the flags onboard Lord Nelson's flagship . The message shows one of the shortcomings of Popham's code—even the two-letter "do" required three flags hoisted for the signal. It is reported that a great cheer went up as the signal was hoisted and repeated throughout the fleet.


text: It is said that, as he saw the flags going up, Collingwood remarked half-peevishly to his flag-lieutenant, "I wish Nelson would make no more signals; we all understand what we have to do." When, however, the signal was reported, he was delighted, and ordered it to be announced to the ship's company, by whom it was received with the greatest enthusiasm.


text: The message "engage the enemy more closely" was Nelson's final signal to the fleet, sent at 12:15 p.m., before a single British cannon had been fired at the enemy. This message was signalled using the telegraphic flag and flags 1 and 6. Nelson ordered this signal hauled up and kept aloft.


text: Almost immediately, the signal began to be misquoted. A number of ships in the fleet recorded the signal as "England expects every man "to" do his duty" (omitting "that" and replacing "will" with "to"). This version became so prevalent that it is recorded on Nelson's tomb in St. Paul's Cathedral. The word "that" is also omitted on the version around the base of Nelson's Column, as seen in the photo above. However, the "Victory"s log and the accounts of signal officer John Pasco and Henry Blackwood (captain of the frigate "Euryalus"), both present at the preparation of the signal, agree on the form given here. On 26 December 1805, "The Times" newspaper in London reported the signal as; "England expects every officer and man to do his duty this day". In 1811, the tenor John Braham composed a song, "The Death of Nelson", including the words of the signal. The song became popular almost immediately and was performed throughout the British Empire during the 19th century. To make the words fit the metre, they were altered to "England expects that every man this day will do his duty". This version of the wording is also persistent.


text: Between 1885 and 1908 it was believed that the signal had been sent using the 1799 code book, as in 1885 it was pointed out that this had not been replaced until 1808. In 1908 it was discovered that the Admiralty had, in fact, changed the signal code in November 1803, after the 1799 version had been captured by the French, and new code books had been issued to Nelson's fleet at Cadiz in September 1805. As a result, books published between these two dates show the signal using the wrong flags.


text: The signal is still hoisted on the "Victory" at her dry dock in Portsmouth on Trafalgar Day (21 October) every year, although the signal flags are displayed all at once, running from fore to aft, rather than hoisted sequentially from the mizzenmast.


text: The signal has been imitated in other navies of the world. Napoleon ordered the French equivalent, "", to be displayed on French vessels. At the opening of the Battle of Plattsburgh in September 1814, Commodore Thomas MacDonough of the United States Navy flew the signal "Impressed seamen call on every man to do his duty", referring to the fact that impressment of sailors had been a U.S. casus belli of the War of 1812.


text: A similar signal was used by the Imperial Japanese Navy during the Russo-Japanese War. At the Battle of Tsushima on 27 May 1905, Admiral Tōgō Heihachirō – who had studied naval tactics in Britain from 1871 to 1878, and was known as the "Nelson of the East" – signalled to his fleet: "The fate of the Empire depends upon today's battle: let every man do his utmost".


text: In Ogden Nash's collection of poems "I'm a Stranger Here Myself" (1938) there is a short poem "England Expects".


text: During the Second World War, an Admiralty propaganda poster intended to increase industrial production on the home front, carried the slogan; "Britain expects that you too, this day, will do your duty". Nelson's flag signal was hoisted by the Royal Navy monitor HMS "Erebus" at the start of the bombardment for the Normandy landings on 6 June 1944.


text: It was also referenced by Margaret Thatcher during her crucial speech to the cabinet which finally persuaded them to rally behind her over the divisive issue of the poll tax. Further afield, it has been adapted by James Joyce in his novel, "Ulysses", such as "Ireland expects that every man this day will do his duty".


text: Today "England expects..." is often adapted for use in the media, especially in relation to the expectations for the victory of English sporting teams. Such is the sentence's connotation with sport that a book on the history of the England national football team by James Corbett was entitled "England Expects". A BBC Scotland television drama also bears its name.


title: 200 Cigarettes

text: 200 Cigarettes is a 1999 American comedy film directed by Risa Bramon Garcia and written by Shana Larsen. The film follows multiple characters in New York City on New Year's Eve 1981. The film features an ensemble cast consisting of brothers Ben and Casey Affleck, Dave Chappelle, Guillermo Díaz, Angela Featherstone, Janeane Garofalo, Gaby Hoffmann, Kate Hudson, Courtney Love, Jay Mohr, Nicole Ari Parker, Martha Plimpton, Christina Ricci and Paul Rudd, with a cameo by Elvis Costello, as well as paintings by Sally Davies.


title: 200 Cigarettes

text: The film follows various plot arcs all occurring on New Year's Eve of 1981. Monica is throwing a big party and is desperately afraid no one will attend. Early on, the only arrival is her friend Hillary. As Monica tries to convince Hillary to stay, various other groupings are shown making their way to the celebration.


title: 200 Cigarettes

text: The plot follows these several characters as they spend New Year's Eve in New York City before eventually turning up at Monica's party. The party guests are:


title: 200 Cigarettes

text: Eventually, everyone finds their way to the party, although Monica has passed out after drowning her sorrows in alcohol. She wakes the next morning to find unrecognizable people on her floor, including Stephie, who tells her what a big hit her party was. Monica is thrilled, even though she missed it all, especially when she finds out that Elvis Costello showed up.


title: 200 Cigarettes

text: The final montage shows Polaroids of the party, narrated by the disco cabbie, mostly featuring the unlikely romances from the night and the unconscious Monica being propped up by her guests.


title: 200 Cigarettes

text: On Rotten Tomatoes the film has an approval rating of 30% based on 63 reviews, with an average rating of 4.4/10 and the consensus that it is "[a] clumsy and scattered comedy with a poorly executed script". On Metacritic the film has a score of 33% based on reviews from 26 critics, indicating "Generally unfavorable reviews."


title: 200 Cigarettes

text: Todd McCarthy of "Variety magazine" called the film "dismally unfunny" and questions "if any director could have surmounted the script’s limitations" and of the acting performances he says "only Garofalo and Ben Affleck manage to project any wit that cracks through the prevailing humorlessness."


title: 200 Cigarettes

text: Mick LaSalle of the "San Francisco Chronicle" gave it a positive review, saying "200 Cigarettes doesn't have a bad scene or a false note. The picture is a succession of pointed little moments, nicely written by Shana Larsen and acted with comic assurance and sensitivity."


title: Lupus anticoagulant

text: Lupus anticoagulant is an immunoglobulin that binds to phospholipids and proteins associated with the cell membrane. Its name is a partial misnomer, as it is actually a prothrombotic antibody "in vivo". Lupus anticoagulant in living systems causes a decrease in clotting time. The name derives from their properties "in vitro", as these antibodies increase coagulation times in laboratory tests such as the activated partial thromboplastin time (aPTT). Investigators speculate that the antibodies interfere with phospholipids used to induce in vitro coagulation. In vivo, the antibodies are thought to interact with platelet membrane phospholipids, increasing adhesion and aggregation of platelets, which accounts for the in vivo prothrombotic characteristics.


title: Lupus anticoagulant

text: The main indication for testing for lupus anticoagulant is a suspected antiphospholipid syndrome, whose main manifestations are blood clots (thrombosis) in both arteries and veins as well as pregnancy-related complications such as miscarriage, stillbirth, preterm delivery, and severe preeclampsia.


title: Lupus anticoagulant

text: In a suspected antiphospholipid syndrome, lupus anticoagulant is generally tested in conjunction with anti-apolipoprotein antibodies and anti-cardiolipin antibodies, and diagnostic criteria require one clinical event (i.e. thrombosis or pregnancy complication) and two positive blood test results spaced at least three months apart that detect at least one of the three types of antibodies.


title: Lupus anticoagulant

text: An aPTT is generally included in a differential diagnosis in vague symptoms, and is a non-specific test of coagulation. In contrast, the prothrombin time (PT), another non-specific coagulation test, is normally unaffected by lupus anticoagulant. Nevertheless, falsely increased PT has been reported, likely by lupus anticoagulant interfering with the phospholipid component of the PT reagent, particularly when using recombinant tissue factor and purified phospholipids.


title: Lupus anticoagulant

text: A mixing test is generally in the initial workup of a prolonged aPTT. In a mixing test, patient plasma is mixed with normal pooled plasma and the clotting is reassessed. If a clotting inhibitor such as a lupus anticoagulant is present, the inhibitor will interact with the normal pooled plasma and the clotting time will generally remain abnormal. However, if the clotting time of the mixed plasma corrects towards normal, the presence of an inhibitor such as the lupus anticoagulant is less likely, instead indicating a deficient quantity of clotting factor (that is replenished by the normal plasma). In case of a corrected mixing test, a lower dose of normal pooled plasma is often used, such as a 4:1 mix (4 times as much patient plasma than normal pooled plasma), as some studies suggest that this method is more sensitive for the detection of a weak lupus anticoagulant that is not enough prevalent or potent to affect a 1:1 mix.


title: Lupus anticoagulant

text: However, only about 60 per cent of patients with lupus anticoagulants have a both a prolonged APTT and APTT mix, making it unsuitable as the only test in case of a high suspicion of the antiphospholipid syndrome. Thus, one or more of the following tests are generally performed to detect lupus anticoagulant if a high suspicion remains, and/or specify lupus anticoagulant as the cause of an abnormal mixing test:


title: Lupus anticoagulant

text: Treatment for a lupus anticoagulant is usually undertaken in the context of documented thrombosis, such as extremity phlebitis or dural sinus vein thrombosis. Patients with a well-documented (i.e., present at least twice) lupus anticoagulant and a history of thrombosis should be considered candidates for indefinite treatment with anticoagulants. Patients with no history of thrombosis and a lupus anticoagulant should probably be observed. Current evidence suggests that the risk of recurrent thrombosis in patients with an antiphospholipid antibody is enhanced whether that antibody is measured on serological testing or functional testing. The Sapporo criteria specify that both serological and functional tests must be positive to diagnose the antiphospholipid antibody syndrome.


title: Lupus anticoagulant

text: Miscarriages may be more prevalent in patients with a lupus anticoagulant. Some of these miscarriages may "potentially" be prevented with the administration of aspirin and unfractionated heparin. The Cochrane Database of Systematic Reviews provide a deeper understanding on the subject.


title: Galaxy formation and evolution

text: The study of galaxy formation and evolution is concerned with the processes that formed a heterogeneous universe from a homogeneous beginning, the formation of the first galaxies, the way galaxies change over time, and the processes that have generated the variety of structures observed in nearby galaxies. Galaxy formation is hypothesized to occur from structure formation theories, as a result of tiny quantum fluctuations in the aftermath of the Big Bang. The simplest model in general agreement with observed phenomena is the Lambda-CDM model—that is, that clustering and merging allows galaxies to accumulate mass, determining both their shape and structure.


title: Galaxy formation and evolution

text: Because of the inability to conduct experiments in outer space, the only way to “test” theories and models of galaxy evolution is to compare them with observations. Explanations for how galaxies formed and evolved must be able to predict the observed properties and types of galaxies.


title: Galaxy formation and evolution

text: Edwin Hubble created the first galaxy classification scheme known as the Hubble tuning-fork diagram. It partitioned galaxies into ellipticals, normal spirals, barred spirals (such as the Milky Way), and irregulars. These galaxy types exhibit the following properties which can be explained by current galaxy evolution theories:


title: Galaxy formation and evolution

text: There is a common misconception that Hubble believed incorrectly that the tuning fork diagram described an evolutionary sequence for galaxies, from elliptical galaxies through lenticulars to spiral galaxies. This is not the case; instead, the tuning fork diagram shows an evolution from simple to complex with no temporal connotations intended. Astronomers now believe that disk galaxies likely formed first, then evolved into elliptical galaxies through galaxy mergers.


title: Galaxy formation and evolution

text: Current models also predict that the majority of mass in galaxies is made up of dark matter, a substance which is not directly observable, and might not interact through any means except gravity. This observation arises because galaxies could not have formed as they have, or rotate as they are seen to, unless they contain far more mass than can be directly observed.


title: Galaxy formation and evolution

text: The earliest stage in the evolution of galaxies is their formation. When a galaxy forms, it has a disk shape and is called a spiral galaxy due to spiral-like "arm" structures located on the disk. There are different theories on how these disk-like distributions of stars develop from a cloud of matter: however, at present, none of them exactly predicts the results of observation.


title: Galaxy formation and evolution

text: Olin Eggen, Donald Lynden-Bell, and Allan Sandage in 1962, proposed a theory that disk galaxies form through a monolithic collapse of a large gas cloud. The distribution of matter in the early universe was in clumps that consisted mostly of dark matter. These clumps interacted gravitationally, putting tidal torques on each other that acted to give them some angular momentum. As the baryonic matter cooled, it dissipated some energy and contracted toward the center. With angular momentum conserved, the matter near the center speeds up its rotation. Then, like a spinning ball of pizza dough, the matter forms into a tight disk. Once the disk cools, the gas is not gravitationally stable, so it cannot remain a singular homogeneous cloud. It breaks, and these smaller clouds of gas form stars. Since the dark matter does not dissipate as it only interacts gravitationally, it remains distributed outside the disk in what is known as the dark halo. Observations show that there are stars located outside the disk, which does not quite fit the "pizza dough" model. It was first proposed by Leonard Searle and Robert Zinn that galaxies form by the coalescence of smaller progenitors. Known as a top-down formation scenario, this theory is quite simple yet no longer widely accepted.


title: Galaxy formation and evolution

text: More recent theories include the clustering of dark matter halos in the bottom-up process. Instead of large gas clouds collapsing to form a galaxy in which the gas breaks up into smaller clouds, it is proposed that matter started out in these “smaller” clumps (mass on the order of globular clusters), and then many of these clumps merged to form galaxies, which then were drawn by gravitation to form galaxy clusters. This still results in disk-like distributions of baryonic matter with dark matter forming the halo for all the same reasons as in the top-down theory. Models using this sort of process predict more small galaxies than large ones, which matches observations.


title: Galaxy formation and evolution

text: Astronomers do not currently know what process stops the contraction. In fact, theories of disk galaxy formation are not successful at producing the rotation speed and size of disk galaxies. It has been suggested that the radiation from bright newly formed stars, or from an active galactic nucleus can slow the contraction of a forming disk. It has also been suggested that the dark matter halo can pull the galaxy, thus stopping disk contraction.


title: Galaxy formation and evolution

text: The Lambda-CDM model is a cosmological model that explains the formation of the universe after the Big Bang. It is a relatively simple model that predicts many properties observed in the universe, including the relative frequency of different galaxy types; however, it underestimates the number of thin disk galaxies in the universe. The reason is that these galaxy formation models predict a large number of mergers. If disk galaxies merge with another galaxy of comparable mass (at least 15 percent of its mass) the merger will likely destroy, or at a minimum greatly disrupt the disk, and the resulting galaxy is not expected to be a disk galaxy (see next section). While this remains an unsolved problem for astronomers, it does not necessarily mean that the Lambda-CDM model is completely wrong, but rather that it requires further refinement to accurately reproduce the population of galaxies in the universe.


title: Galaxy formation and evolution

text: Elliptical galaxies (most notably supergiant ellipticals, such as ESO 306-17) are among some of the largest known thus far. Their stars are on orbits that are randomly oriented within the galaxy (i.e. they are not rotating like disk galaxies). A distinguishing feature of elliptical galaxies is that the velocity of the stars does not necessarily contribute to flattening of the galaxy, such as in spiral galaxies. Elliptical galaxies have central supermassive black holes, and the masses of these black holes correlate with the galaxy's mass.


title: Galaxy formation and evolution

text: Elliptical galaxies have two main stages of evolution. The first is due to the supermassive black hole growing by accreting cooling gas. The second stage is marked by the black hole stabilizing by suppressing gas cooling, thus leaving the elliptical galaxy in a stable state. The mass of the black hole is also correlated to a property called sigma which is the dispersion of the velocities of stars in their orbits. This relationship, known as the M-sigma relation, was discovered in 2000. Elliptical galaxies mostly lack disks, although some bulges of disk galaxies resemble elliptical galaxies. Elliptical galaxies are more likely found in crowded regions of the universe (such as galaxy clusters).


title: Galaxy formation and evolution

text: Astronomers now see elliptical galaxies as some of the most evolved systems in the universe. It is widely accepted that the main driving force for the evolution of elliptical galaxies is mergers of smaller galaxies. Many galaxies in the universe are gravitationally bound to other galaxies, which means that they will never escape their mutual pull. If the galaxies are of similar size, the resultant galaxy will appear similar to neither of the progenitors, but will instead be elliptical. There are many types of galaxy mergers, which do not necessarily result in elliptical galaxies, but result in a structural change. For example, a minor merger event is thought to be occurring between the Milky Way and the Magellanic Clouds.


title: Galaxy formation and evolution

text: Mergers between such large galaxies are regarded as violent, and the frictional interaction of the gas between the two galaxies can cause gravitational shock waves, which are capable of forming new stars in the new elliptical galaxy. By sequencing several images of different galactic collisions, one can observe the timeline of two spiral galaxies merging into a single elliptical galaxy.


title: Galaxy formation and evolution

text: In the Local Group, the Milky Way and the Andromeda Galaxy are gravitationally bound, and currently approaching each other at high speed. Simulations show that the Milky Way and Andromeda are on a collision course, and are expected to collide in less than five billion years. During this collision, it is expected that the Sun and the rest of the Solar System will be ejected from its current path around the Milky Way. The remnant could be a giant elliptical galaxy.


title: Galaxy formation and evolution

text: One observation (see above) that must be explained by a successful theory of galaxy evolution is the existence of two different populations of galaxies on the galaxy color-magnitude diagram. Most galaxies tend to fall into two separate locations on this diagram: a "red sequence" and a "blue cloud". Red sequence galaxies are generally non-star-forming elliptical galaxies with little gas and dust, while blue cloud galaxies tend to be dusty star-forming spiral galaxies.


title: Galaxy formation and evolution

text: As described in previous sections, galaxies tend to evolve from spiral to elliptical structure via mergers. However, the current rate of galaxy mergers does not explain how all galaxies move from the "blue cloud" to the "red sequence". It also does not explain how star formation ceases in galaxies. Theories of galaxy evolution must therefore be able to explain how star formation turns off in galaxies. This phenomenon is called galaxy "quenching".


title: Galaxy formation and evolution

text: Stars form out of cold gas (see also the Kennicutt–Schmidt law), so a galaxy is quenched when it has no more cold gas. However, it is thought that quenching occurs relatively quickly (within 1 billion years), which is much shorter than the time it would take for a galaxy to simply use up its reservoir of cold gas. Galaxy evolution models explain this by hypothesizing other physical mechanisms that remove or shut off the supply of cold gas in a galaxy. These mechanisms can be broadly classified into two categories: (1) preventive feedback mechanisms that stop cold gas from entering a galaxy or stop it from producing stars, and (2) ejective feedback mechanisms that remove gas so that it cannot form stars.


title: Galaxy formation and evolution

text: One theorized preventive mechanism called “strangulation” keeps cold gas from entering the galaxy. Strangulation is likely the main mechanism for quenching star formation in nearby low-mass galaxies. The exact physical explanation for strangulation is still unknown, but it may have to do with a galaxy's interactions with other galaxies. As a galaxy falls into a galaxy cluster, gravitational interactions with other galaxies can strangle it by preventing it from accreting more gas. For galaxies with massive dark matter halos, another preventive mechanism called “virial shock heating” may also prevent gas from becoming cool enough to form stars.


title: Galaxy formation and evolution

text: Ejective processes, which expel cold gas from galaxies, may explain how more massive galaxies are quenched. One ejective mechanism is caused by supermassive black holes found in the centers of galaxies. Simulations have shown that gas accreting onto supermassive black holes in galactic centers produces high-energy jets; the released energy can expel enough cold gas to quench star formation.


title: Galaxy formation and evolution

text: Our own Milky Way and the nearby Andromeda Galaxy currently appear to be undergoing the quenching transition from star-forming blue galaxies to passive red galaxies.


title: Amusement arcade

text: An amusement arcade (often referred to as a video arcade, amusements or simply arcade) is a venue where people play arcade games, including arcade video games, pinball machines, electro-mechanical games, redemption games, merchandisers (such as claw cranes), or coin-operated billiards or air hockey tables. In some countries, some types of arcades are also legally permitted to provide gambling machines such as slot machines or "pachinko" machines. Games are usually housed in cabinets. The term used for ancestors of these venues in the beginning of the 20th century was penny arcades.


title: Amusement arcade

text: Video games were introduced in amusement arcades in the late 1970s and were most popular during the golden age of arcade video games, the early 1980s. Arcades became popular with children and particularly adolescents, which led parents to be concerned that video game playing might cause them to skip school.


title: Amusement arcade

text: A penny arcade can be any type of venue for coin-operated devices, usually for entertainment. The term came into use about 1905–1910. The name derives from the penny, once a staple coin for the machines. The machines used included:


title: Amusement arcade

text: Between the 1940s and 1960s, mechanical arcade games evolved into electro-mechanical games (EM games). Popular examples of EM games in the 1960s included shooters such as Sega's "Periscope" (1965) and "Rifleman" (1967), and racing games such as Kasco's "Indy 500" (1968) and Chicago Coin's "Speedway" (1969). Penny arcades later led to the creation of video arcades in the 1970s.


title: Amusement arcade

text: Video game arcades began to gain momentum in the late 1970s with games such as "Space Invaders" (1978) and "Galaxian" (1979) and became widespread in 1980 with "Pac-Man," "Centipede" and others. The central processing unit in these games allowed for more complexity than earlier discrete-circuitry games such as Atari's "Pong" (1972).


title: Amusement arcade

text: During the late 1970s video-arcade game technology had become sophisticated enough to offer good-quality graphics and sounds, but it remained fairly basic (realistic images and full motion video were not yet available, and only a few games used spoken voice) and so the success of a game had to rely on simple and fun gameplay. This emphasis on the gameplay explains why many of these games continue to be enjoyed today, despite the progress made by modern computing technology.


title: Amusement arcade

text: The golden age of arcade video games in the 1980s became a peak era of video arcade game popularity, innovation, and earnings. Color arcade games became more prevalent and video arcades themselves started appearing outside their traditional bowling-alley and bar locales. Designers experimented with a wide variety of game genres, while developers still had to work within strict limits of available processor-power and memory. The era saw the rapid spread of video arcades across North America, Western Europe and Japan. The number of video-game arcades in North America, for example, more than doubled between 1980 and 1982, reaching a peak of 13,000 video game arcades across the region (compared to 4,000 today). Beginning with "Space Invaders", video arcade games also started to appear in supermarkets, restaurants, liquor stores, gas stations and many other retail establishments looking for extra income. This boom came to an end in the mid-1980s, in what has been referred to as "the great coin-op video crash of 1983".


title: Amusement arcade

text: On November 30, 1982, Jerry Parker, the Mayor of Ottumwa, Iowa, declared his city the "Video Game Capital of the World". This initiative resulted in many firsts in video game history. Playing a central role in arcade history, Ottumwa saw the birth of the Twin Galaxies Intergalactic Scoreboard and the U.S. National Video Game Team, two organizations that still exist today. Other firsts that happened in the Video Game Capital of the World included:


title: Amusement arcade

text: High game-turnover in Japanese arcades required quick game-design, leading to the adoption of standardized systems like JAMMA, Neo-Geo and CPS-2. These systems essentially provided arcade-only consoles where the video game ROM could be swapped easily to replace a game. This allowed easier development and replacement of games, but it also discouraged the hardware innovation necessary to stay ahead of the technology curve.


title: Amusement arcade

text: Most US arcades didn't see the intended benefit of this practice since many games weren't exported to the US, and if they were, distributors generally refused to release them as simply a ROM, preferring to sell the entire ROM, console, and sometimes the cabinet as a package. In fact, several arcade systems such as Sega's NAOMI board are arcade versions of home systems.


title: Amusement arcade

text: Other problems were that many arcades focused on quantity more than quality, and that games showed a rising difficulty curve, making them increasingly inaccessible to casual players and more expensive for the skilled players.


title: Amusement arcade

text: The rise of the fighting game genre with games such as "Street Fighter II" and "Mortal Kombat", combined with the release of popular sports titles such as "NBA Jam" and "NFL Blitz", led to a brief resurgence in the popularity of video arcades, with new locations opening in shopping malls and strip malls throughout the country in the early 90s.


title: Amusement arcade

text: The arcade industry entered a major slump in mid-1994. Arcade attendance and per-visit spending, though not as poor as during the 1983 crash, declined to the point where several of the largest arcade chains either were put up for sale or declared bankruptcy, while many large arcade machine manufacturers likewise moved to get out of the business. In the second quarter of 1996, video game factories reported 90,000 arcade cabinets sold, as compared to 150,000 cabinets sold in 1990.


title: Amusement arcade

text: The main reason for the slump was increasing competition from console ports. During the 1980s it typically took several years for an arcade game to be released on a home console, and the port usually differed greatly from the arcade version; during the mid-1990s it became common for a game publisher to release a highly accurate port of an arcade game that had yet to peak in popularity, thus severely cutting into arcade owners' profits.


title: Amusement arcade

text: In the late 1990s, a bar opened in the new Crown Casino complex in Melbourne, Australia named "Barcode". Barcode was a 'games bar' with the latest arcade games, the classics, pool tables, air hockey and pinball machines which players could play while consuming alcohol. The bar was very popular with other bars later opening in the early 2000s in King Street alongside the strip clubs and at the shopping centre Melbourne Central. A Barcode opened in Times Square, New York in May 2000 and was very popular, with the launch featuring on an episode of TV series "Sex and the City". Barcode Times Square closed in March 2003. Barcode Crown Casino closed in 2006, followed later by King Street and Melbourne Central.


title: Amusement arcade

text: In the mid-2000s, Madrid businessman Enrique Martínez updated the video arcade for the new generation by creating a "hybrid movie theater with...fog, black light, flashing green lasers, high-definition digital projectors, vibrating seats, game pads and dozens of 17-inch screens attached to individual chairs." At the Yelmo Cineplex in Spain, $390,000 was spent refitting a theater into a "high-tech video gaming hall seating about 50 people." In Germany, the CinemaxX movie theater company was in 2007 also considering this approach. It conducted a four-month trial with video games to test the level of demand for video gaming in a theater setting.


title: Amusement arcade

text: Manufacturers started adding innovative features to games in the 2000s. Konami used motion and position sensing of the player in "Police 911" in 2000 and "Mocap Boxing" in 2001. Sega started using "Tuning cards" in games such as the "Initial D" series of games allowing the customer to save game data on a card vended from the game; Namco copied the idea with the "Maximum Tune" series. Arcade games continued to use a variety of games with enhanced features to attract clients, such as motorized seating areas, interconnected games, and surround sound systems. Redemption and merchandiser games are also a staple of arcades in the 2000s. One of the most popular redemption games, "Deal or No Deal" by ICE, simulates the popular television game show. Merchandiser games such as Stacker by LAI Games gives the player the chance to win high end prizes like iPods and video game consoles.


title: Amusement arcade

text: At the same time as these innovations, a small resurgence in the interest of classic video games and arcades grew with the opening of Barcade in Brooklyn, New York in 2004. Barcade combined a video arcade and a full bar, with a strict focus on classic machines from the 1970s and 1980s, known as the golden age of arcade video games. The idea proved popular and Barcade received recognition as a good place to play classic video game cabinets, because it is "one of the few places where classic arcade games can still be found in public, and in good working order." Barcade's success influenced other similarly themed businesses which opened across the country. Other arcades, like Ground Kontrol in Portland, Oregon, began including full bars in their arcades. Even regular bars added classic arcade games to their venues.


title: Amusement arcade

text: As the trend grew, the industry and press looked for ways to classify these arcade bar hybrids, with the DNA Association branding them "social-tainment" and also referring to them as "game bars". Many of these newer game bars proved to be popular and expansion continued.


title: Amusement arcade

text: In the UK, classic arcades such as Casino and Trocadero, both located in London, closed, with some of the games from Trocadero finding their way to a new arcade, Heart of Gaming in North Acton. The newer Loading Soho Gaming Cafe features arcade machines manufactured by Bespoke Arcades for its customers to use. The UK is also home to the largest arcade in Europe, Arcade Club, located in Bury, Greater Manchester. Home to over 400 original arcade machines, it is recognised as the largest collection in Europe. In May 2019 Arcade Club opened a second venue in Leeds with a third announced for Blackpool opening in 2020.


title: Amusement arcade

text: The video games are typically in arcade cabinets. The most common kind are "uprights", tall boxes with a monitor and controls in front. Customers insert coins or tokens into the machines (or, in newer models, use credit cards or mobile devices) and stand in front of them to play the game. These traditionally were the most popular arcade format, although presently American arcades make much more money from deluxe driving games and ticket redemption games. However, Japanese arcades, while also heavily featuring deluxe games, continue to do well with traditional JAMMA arcade video games.


title: Amusement arcade

text: Some machines, such as "Ms. Pac-Man" and "Joust", are occasionally in smaller boxes with a flat, clear glass or acrylic glass top; the player sits at the machine playing it, looking down. This style of arcade game is known as a "cocktail-style arcade game table" or tabletop arcade machine, since they were first popularized in bars and pubs. For two player games on this type of machine, the players sit on opposite sides with the screen flipped upside down for each player. A few cocktail-style games had players sitting next to rather than across from one another. Both "Joust" and "Gun Fight" had these type of tables.


title: Amusement arcade

text: Some arcade games, such as racing games, are designed to be sat in or on. These types of games are sometimes referred to as "sit-down" games. Sega and Namco are two of the largest manufacturers of these types of arcade games.


title: Amusement arcade

text: Other games include pinball machines, redemption games and merchandiser games. Pinball machines have a tilted, glass-covered play area in which the player uses mechanical flippers to direct a heavy metal ball towards lighted targets. Redemption games reward winners with tickets that can be redeemed for prizes such as toys or novelty items. The prizes are usually displayed behind a counter or in a glass showcase, and an arcade employee gives the items to players after counting their tickets. Merchandiser games reward winners with prizes such as stuffed toys, CDs, DVDs, or candy which are dispensed directly from the machine.


title: Amusement arcade

text: In some countries, some types of video arcades are legally allowed to provide gambling machines such as slot machines and pachinko machines. Large arcades may also have small coin-operated ride-on toys for small children. Some businesses, such as Dave & Buster's, combine a bar and restaurant with a video arcade. The ROUND1 entertainment chain combines a large arcade with a full-service bowling alley, along with billiards and karaoke.


title: Amusement arcade

text: Arcades typically have change machines to dispense tokens or quarters when bills are inserted, although larger chain arcades, such as Dave and Busters and Chuck E. Cheese are deviating towards a refillable card system. Arcades may also have vending machines which sell soft drinks, candy, and chips. Arcades may play recorded music or a radio station over a public address system. Video arcades typically have subdued lighting to inhibit glare on the screen and enhance the viewing of the games' video displays, as well as of any decorative lighting on the cabinets.


title: Scintillator

text: A scintillator is a material that exhibits scintillation, the property of luminescence, when excited by ionizing radiation. Luminescent materials, when struck by an incoming particle, absorb its energy and scintillate (i.e. re-emit the absorbed energy in the form of light). Sometimes, the excited state is metastable, so the relaxation back down from the excited state to lower states is delayed (necessitating anywhere from a few nanoseconds to hours depending on the material). The process then corresponds to one of two phenomena: delayed fluorescence or phosphorescence. The correspondence depends on the type of transition and hence the wavelength of the emitted optical photon.


title: Scintillator

text: A scintillation detector or scintillation counter is obtained when a scintillator is coupled to an electronic light sensor such as a photomultiplier tube (PMT), photodiode, or silicon photomultiplier. PMTs absorb the light emitted by the scintillator and re-emit it in the form of electrons via the photoelectric effect. The subsequent multiplication of those electrons (sometimes called photo-electrons) results in an electrical pulse which can then be analyzed and yield meaningful information about the particle that originally struck the scintillator. Vacuum photodiodes are similar but do not amplify the signal while silicon photodiodes, on the other hand, detect incoming photons by the excitation of charge carriers directly in the silicon. Silicon photomultipliers consist of an array of photodiodes which are reverse-biased with sufficient voltage to operate in avalanche mode, enabling each pixel of the array to be sensitive to single photons.


title: Scintillator

text: The first device which used a scintillator was built in 1903 by Sir William Crookes and used a ZnS screen. The scintillations produced by the screen were visible to the naked eye if viewed by a microscope in a darkened room; the device was known as a spinthariscope. The technique led to a number of important discoveries but was obviously tedious. Scintillators gained additional attention in 1944, when Curran and Baker replaced the naked eye measurement with the newly developed PMT. This was the birth of the modern scintillation detector.


title: Scintillator

text: Scintillators are used by the American government as Homeland Security radiation detectors. Scintillators can also be used in particle detectors, new energy resource exploration, X-ray security, nuclear cameras, computed tomography and gas exploration. Other applications of scintillators include CT scanners and gamma cameras in medical diagnostics, and screens in older style CRT computer monitors and television sets. Scintillators have also been proposed as part of theoretical models for the harnessing of gamma-ray energy through the photovoltaic effect, for example in a nuclear battery.


title: Scintillator

text: The use of a scintillator in conjunction with a photomultiplier tube finds wide use in hand-held survey meters used for detecting and measuring radioactive contamination and monitoring nuclear material. Scintillators generate light in fluorescent tubes, to convert the ultra-violet of the discharge into visible light. Scintillation detectors are also used in the petroleum industry as detectors for Gamma Ray logs.


title: Scintillator

text: There are many desired properties of scintillators, such as high density, fast operation speed, low cost, radiation hardness, production capability and durability of operational parameters.


title: Scintillator

text: High density reduces the material size of showers for high-energy γ-quanta and electrons. The range of Compton scattered photons for lower energy γ-rays is also decreased via high density materials. This results in high segmentation of the detector and leads to better spatial resolution. Usually high density materials have heavy ions in the lattice (e.g., lead, cadmium), significantly increasing the contribution of photoelectric effect (~Z). The increased photo-fraction is important for some applications such as positron emission tomography. High stopping power for electromagnetic component of the ionizing radiation needs greater photo-fraction; this allows for a compact detector.


title: Scintillator

text: High operating speed is needed for good resolution of spectra. Precision of time measurement with a scintillation detector is proportional to . Short decay times are important for the measurement of time intervals and for the operation in fast coincidence circuits. High density and fast response time can allow detection of rare events in particle physics.


title: Scintillator

text: Particle energy deposited in the material of a scintillator is proportional to the scintillator's response. Charged particles, γ-quanta and ions have different slopes when their response is measured. Thus, scintillators could be used to identify various types of γ-quanta and particles in fluxes of mixed radiation.


title: Scintillator

text: Another consideration of scintillators is the cost of producing them. Most crystal scintillators require high-purity chemicals and sometimes rare-earth metals that are fairly expensive. Not only are the materials an expenditure, but many crystals require expensive furnaces and almost six months of growth and analyzing time. Currently, other scintillators are being researched for reduced production cost.


title: Scintillator

text: Several other properties are also desirable in a good detector scintillator: a low gamma output (i.e., a high efficiency for converting the energy of incident radiation into scintillation photons), transparency to its own scintillation light (for good light collection), efficient detection of the radiation being studied, a high stopping power, good linearity over a wide range of energy, a short rise time for fast timing applications (e.g., coincidence measurements), a short decay time to reduce detector dead-time and accommodate high event rates, emission in a spectral range matching the spectral sensitivity of existing PMTs (although wavelength shifters can sometimes be used), an index of refraction near that of glass (≈1.5) to allow optimum coupling to the PMT window. Ruggedness and good behavior under high temperature may be desirable where resistance to vibration and high temperature is necessary (e.g., oil exploration). The practical choice of a scintillator material is usually a compromise among those properties to best fit a given application.


title: Scintillator

text: Among the properties listed above, the light output is the most important, as it affects both the efficiency and the resolution of the detector (the efficiency is the ratio of detected particles to the total number of particles impinging upon the detector; the energy resolution is the ratio of the full width at half maximum of a given energy peak to the peak position, usually expressed in %). The light output is a strong function of the type of incident particle or photon and of its energy, which therefore strongly influences the type of scintillation material to be used for a particular application. The presence of quenching effects results in reduced light output (i.e., reduced scintillation efficiency). Quenching refers to all radiationless deexcitation processes in which the excitation is degraded mainly to heat. The overall signal production efficiency of the detector, however, also depends on the quantum efficiency of the PMT (typically ~30% at peak), and on the efficiency of light transmission and collection (which depends on the type of reflector material covering the scintillator and light guides, the length/shape of the light guides, any light absorption, etc.). The light output is often quantified as a number of scintillation photons produced per keV of deposited energy. Typical numbers are (when the incident particle is an electron): ≈40 photons/keV for , ~10 photons/keV for plastic scintillators, and ~8 photons/keV for bismuth germanate ().


title: Scintillator

text: Scintillation detectors are generally assumed to be linear. This assumption is based on two requirements: (1) that the light output of the scintillator is proportional to the energy of the incident radiation; (2) that the electrical pulse produced by the photomultiplier tube is proportional to the emitted scintillation light. The linearity assumption is usually a good rough approximation, although deviations can occur (especially pronounced for particles heavier than the proton at low energies).


title: Scintillator

text: Resistance and good behavior under high-temperature, high-vibration environments is especially important for applications such as oil exploration (wireline logging, measurement while drilling). For most scintillators, light output and scintillation decay time depends on the temperature. This dependence can largely be ignored for room-temperature applications since it is usually weak. The dependence on the temperature is also weaker for organic scintillators than it is for inorganic crystals, such as NaI-Tl or BGO. Strong dependence of decay time on the temperature in BGO scintillator is used for remote monitoring of temperature in vacuum environment. The coupled PMTs also exhibit temperature sensitivity, and can be damaged if submitted to mechanical shock. Hence, high temperature rugged PMTs should be used for high-temperature, high-vibration applications.


title: Scintillator

text: The time evolution of the number of emitted scintillation photons "N" in a single scintillation event can often be described by linear superposition of one or two exponential decays. For two decays, we have the form:


title: Scintillator

text: Many scintillators are characterized by 2 time components: one fast (or prompt), the other slow (or delayed). While the fast component usually dominates, the relative amplitude "A" and "B" of the two components depend on the scintillating material. Both of these components can also be a function of the energy loss "dE"/"dx". In cases where this energy loss dependence is strong, the overall decay time constant varies with the type of incident particle. Such scintillators enable pulse shape discrimination, i.e., particle identification based on the decay characteristics of the PMT electric pulse. For instance, when BaF is used, γ rays typically excite the fast component, while α particles excite the slow component: it is thus possible to identify them based on the decay time of the PMT signal.


title: Scintillator

text: Organic scintillators are aromatic hydrocarbon compounds which contain benzene ring structures interlinked in various ways. Their luminescence typically decays within a few nanoseconds.


title: Scintillator

text: Some organic scintillators are pure crystals. The most common types are anthracene (, decay time ≈30 ns), stilbene (, 4.5 ns decay time), and naphthalene (, few ns decay time). They are very durable, but their response is anisotropic (which spoils energy resolution when the source is not collimated), and they cannot be easily machined, nor can they be grown in large sizes; hence they are not very often used. Anthracene has the highest light output of all organic scintillators and is therefore chosen as a reference: the light outputs of other scintillators are sometimes expressed as a percent of anthracene light.


title: Scintillator

text: These are liquid solutions of one or more organic scintillators in an organic solvent. The typical solutes are fluors such as "p"-terphenyl (), PBD (), butyl PBD (), PPO (), and wavelength shifter such as POPOP (). The most widely used solvents are toluene, xylene, benzene, phenylcyclohexane, triethylbenzene, and decalin. Liquid scintillators are easily loaded with other additives such as wavelength shifters to match the spectral sensitivity range of a particular PMT, or B to increase the neutron detection efficiency of the scintillation counter itself (since B has a high interaction cross section with thermal neutrons). For many liquids, dissolved oxygen can act as a quenching agent and lead to reduced light output, hence the necessity to seal the solution in an oxygen-free, airtight enclosure.


title: Scintillator

text: The term "plastic scintillator" typically refers to a scintillating material in which the primary fluorescent emitter, called a fluor, is suspended in the base, a solid polymer matrix. While this combination is typically accomplished through the dissolution of the fluor prior to bulk polymerization, the fluor is sometimes associated with the polymer directly, either covalently or through coordination, as is the case with many Li6 plastic scintillators. Polyethylene naphthalate has been found to exhibit scintillation by itself without any additives and is expected to replace existing plastic scintillators due to higher performance and lower price. The advantages of plastic scintillators include fairly high light output and a relatively quick signal, with a decay time of 2–4 nanoseconds, but perhaps the biggest advantage of plastic scintillators is their ability to be shaped, through the use of molds or other means, into almost any desired form with what is often a high degree of durability. Plastic scintillators are known to show light output saturation when the energy density is large (Birks' Law).


title: Scintillator

text: The most common bases used in plastic scintillators are the aromatic plastics, polymers with aromatic rings as pendant groups along the polymer backbone, amongst which polyvinyltoluene (PVT) and polystyrene (PS) are the most prominent. While the base does fluoresce in the presence of ionizing radiation, its low yield and negligible transparency to its own emission make the use of fluors necessary in the construction of a practical scintillator. Aside from the aromatic plastics, the most common base is polymethylmethacrylate (PMMA), which carries two advantages over many other bases: high ultraviolet and visible light transparency and mechanical properties and higher durability with respect to brittleness. The lack of fluorescence associated with PMMA is often compensated through the addition of an aromatic co-solvent, usually naphthalene. A plastic scintillator based on PMMA in this way boasts transparency to its own radiation, helping to ensure uniform collection of light.


title: Scintillator

text: Other common bases include polyvinyl xylene (PVX) polymethyl, 2,4-dimethyl, 2,4,5-trimethyl styrenes, polyvinyl diphenyl, polyvinyl naphthalene, polyvinyl tetrahydronaphthalene, and copolymers of these and other bases.


title: Scintillator

text: Also known as luminophors, these compounds absorb the scintillation of the base and then emit at larger wavelength, effectively converting the ultraviolet radiation of the base into the more easily transferred visible light. Further increasing the attenuation length can be accomplished through the addition of a second fluor, referred to as a spectrum shifter or converter, often resulting in the emission of blue or green light.


title: Scintillator

text: Common fluors include polyphenyl hydrocarbons, oxazole and oxadiazole aryls, especially, n-terphenyl (PPP), 2,5-diphenyloxazole (PPO), 1,4-di-(5-phenyl-2-oxazolyl)-benzene (POPOP), 2-phenyl-5-(4-biphenylyl)-1,3,4-oxadiazole (PBD), and 2-(4’-tert-butylphenyl)-5-(4’’-biphenylyl)-1,3,4-oxadiazole (B-PBD).


title: Scintillator

text: Inorganic scintillators are usually crystals grown in high temperature furnaces, for example, alkali metal halides, often with a small amount of activator impurity. The most widely used is (thallium-doped sodium iodide); its scintillation light is blue. Other inorganic alkali halide crystals are: , , (pure), , , . Some non-alkali crystals include: BGO, , , , , , (), , . (For more examples, see also phosphors).


title: Scintillator

text: Newly developed products include , lanthanum chloride doped with cerium, as well as a cerium-doped lanthanum bromide, . They are both very hygroscopic (i.e., damaged when exposed to moisture in the air) but offer excellent light output and energy resolution (63 photons/keV γ for versus 38 photons/keV γ for ), a fast response (16 ns for versus 230 ns for ), excellent linearity, and a very stable light output over a wide range of temperatures. In addition LaBr(Ce) offers a higher stopping power for γ rays (density of 5.08 g/cm versus 3.67 g/cm for ). LYSO () has an even higher density (7.1 g/cm, comparable to ), is non-hygroscopic, and has a higher light output than (32 photons/keV γ), in addition to being rather fast (41 ns decay time versus 300 ns for ).


title: Scintillator

text: A disadvantage of some inorganic crystals, e.g., NaI, is their hygroscopicity, a property which requires them to be housed in an airtight container to protect them from moisture. and BaF are only slightly hygroscopic and do not usually need protection. CsF, , , are hygroscopic, while , , , and are not.


title: Scintillator

text: Inorganic crystals can be cut to small sizes and arranged in an array configuration so as to provide position sensitivity. Such arrays are often used in medical physics or security applications to detect X-rays or γ rays: high-"Z", high density materials (e.g. LYSO, BGO) are typically preferred for this type of applications.


title: Scintillator

text: Scintillation in inorganic crystals is typically slower than in organic ones, ranging typically from 1.48 ns for to 9000 ns for . Exceptions are (~5 ns), fast (0.7 ns; the slow component is at 630 ns), as well as the newer products (, 28 ns; , 16 ns; , 41 ns).