title: Vojislav Šešelj

text: The crimes in the indictment include, among others, that Šešelj, both individually and as part of a "joint criminal enterprise", engaged in "the permanent forcible removal, through the commission of crimes in violation of Articles 3 and 5 of the Statute of the Tribunal, of a majority of the Croat, Muslim and other non Serb populations from approximately one-third of the territory of the Republic of Croatia ("Croatia"), and large parts of Bosnia and Herzegovina, and from parts of Vojvodina, in the Republic of Serbia ("Serbia"), in order to make these areas part of a new Serb-dominated state".


title: Vojislav Šešelj

text: On 23 February 2003, following a "farewell meeting" held on Republic Square, Šešelj surrendered to the International Criminal Tribunal for the Former Yugoslavia (ICTY) on the indictment of "eight counts of crimes against humanity and six counts of violations of the laws or customs of war for his alleged participation in a joint criminal enterprise". He was transferred to the ICTY the following day.


title: Vojislav Šešelj

text: In 2005, Šešelj made headlines when he was asked to read a letter which he earlier sent to the ICTY that stated his contempt for the court. The letter was read in front of cameras by Šešelj and contained insults and expletives aimed at the top ICTY officials and judges. In his letter, Šešelj said the presiding judge has only "the right" (mocking the Hague's judges) to perform oral sex on him, and referred to Carla Del Ponte as "the prostitute".


title: Vojislav Šešelj

text: In custody, he wrote "Kriminalac i ratni zločinac Havijer Solana" ("Felon and War Criminal Javier Solana"), a criticism of the NATO Secretary General (and the current High Representative for the Common Foreign and Security Policy and the Secretary-General of the Council of the European Union and the Western European Union) who led the 1999 war in Kosovo.


title: Vojislav Šešelj

text: On 2 December 2006, around 40,000 people marched in the Serbian capital of Belgrade in support of Šešelj during his 28-day hunger strike in The Hague after the ICTY denied him the right to choose his own defence counsel. Speaking at the rally, Radical Party secretary Aleksandar Vučić said ""He's not fighting just for his life. But he's fighting for all of us who are gathered here. Vojislav Šešelj is fighting for Serbia!""


title: Vojislav Šešelj

text: Šešelj ended the hunger strike on 8 December after being allowed to present his own defence. While in custody in The Hague, Šešelj led his party's list of contenders for the January 2007 general election.


title: Vojislav Šešelj

text: Under the ICTY indictment, Šešelj was charged with 15 counts of crimes against humanity and violations of the laws or customs of war. The first of these charges is for persecution of Croats, Muslims and other non-Serbs in Vukovar, Šamac, Zvornik and Vojvodina. The other charges include murder, forced deportation, illegal imprisonment, torture and property destruction during the Yugoslav wars.


title: Vojislav Šešelj

text: Šešelj's aide, Ljubiša Petković, was found guilty by the ICTY's Trial Chamber III of contempt for refusing to appear as a Chamber's witness in Šešelj's trial. Petković was released on 26 September from the ICTY Detention Unit. He had been sentenced to four months' imprisonment, credit being given for the three months and 14 days already spent in the Detention Unit.


title: Vojislav Šešelj

text: On 11 February 2009, after 71 witnesses had been heard and with the expected conclusion of the prosecution's case seven hours away, the presiding judges suspended Šešelj's trial indefinitely at the request of prosecutors, who alleged that witnesses were being intimidated. Šešelj claimed the true motive of the prosecutors was that they were losing their case. He claimed the court had presented numerous false witnesses to avoid having to acquit him and said it should pay him damages for ""all the suffering and six years spent in detention"".


title: Vojislav Šešelj

text: One of the three judges voted against the suspension of the trial stating that it was "unfair to interrupt the trial of someone who has spent almost six years in detention". A contempt of court case against Šešelj was opened for having revealed, in a book he had written, the identities of three witnesses whose names had been ordered suppressed by the tribunal, and for which he was sentenced to 15 months imprisonment by the ICTY.


title: Vojislav Šešelj

text: On 24 July 2009, he was sentenced to 15 months in detention for disrespecting the court after publishing names of trial witnesses on his personal website.


title: Vojislav Šešelj

text: On 25 November 2009, it was announced that Šešelj's trial would resume on 12 January 2010. The trial resumed on schedule and continued until 17 March 2010.


title: Vojislav Šešelj

text: On 10 March 2010, the weekly ICTY press briefing announced that Šešelj was scheduled to appear in court on 20 April 2010 for contempt of court for allegedly disclosing court restricted information on 11 protected witnesses. This is the second time he was charged with contempt. In July 2009 he was found guilty of contempt on similar charges involving two protected witnesses and was sentenced to fifteen months in jail.


title: Vojislav Šešelj

text: On 17 March 2010, the weekly ICTY press briefing announced that "The trial of Vojislav Šešelj has been adjourned until further notice, pending checks on the health status of the remaining four Chamber witnesses". In the weekly ICTY briefing on 24 March stated "The trial of Vojislav Šešelj is expected to continue on Tuesday at 14:15 in Courtroom I with the testimony of one of the four remaining Trial Chamber witnesses". On 14 April 2010, the weekly ICTY press briefing announced that with only one witness still to be heard, on 30 March 2010 Šešelj trial was adjourned until further notice but was likely to resume in May 2010, after Šešelj's second contempt proceeding initiated against him by the Tribunal have ended.


title: Vojislav Šešelj

text: Prosecutors demanded a 28-year sentence against Šešelj for allegedly recruiting paramilitary groups and inciting them to commit atrocities during the Balkan wars of the early 1990s. In closing remarks at his war crimes trial on 14 March 2012, Šešelj said the Yugoslav tribunal empowered by the U.N. Security Council is actually a creation of Western intelligence agencies and it doesn't have jurisdiction in his case. He reportedly vowed "to make a mockery of his trial".


title: Vojislav Šešelj

text: In September 2011, the ICTY rejected Šešelj's bid to have his long-running trial discontinued. In his submission to the court, Šešelj had argued that his right to be tried in a reasonable amount of time has been violated, and called the situation "incomprehensible, scandalous and inappropriate". However, the bench ruled that "there is no predetermined threshold with regard to the time period beyond which a trial may be considered unfair on account of undue delay" and declared that Šešelj "failed to provide concrete proof of abuse of process".


title: Vojislav Šešelj

text: On 6 November 2014, the ICTY granted Šešelj provisional release. The decision was made on the basis of Šešelj's diagnosis of metastatic cancer and deteriorating health.


title: Vojislav Šešelj

text: Šešelj returned to Belgrade after spending more than 11 years on what proved to be an inconclusive trial at the Hague.


title: Vojislav Šešelj

text: On 31 March 2016, one week after the conviction of Bosnian Serb leader Radovan Karadžić, the ICTY found Šešelj not guilty on all charges, with a majority decision on eight counts and a unanimous decision on one.


title: Vojislav Šešelj

text: His acquittal was described by "The Economist" as "a victory for advocates of ethnic cleansing" which would have "broad ramifications for international justice." Aleksandar Vucic, who served as the PM at the time, commented that the case against Šešelj was inherently flawed and politicized from the beginning.


title: Vojislav Šešelj

text: The acquittal was appealed by prosecutors from the MICT, a United Nations Security Council agency which functions as oversight program of, and successor entity to, the ICTY. On 11 April 2018, the Appeals Chamber sentenced him to 10 years in prison under Counts 1, 10, and 11 of the indictment for instigating deportation, persecution (forcible displacement), and other inhumane acts (forcible transfer) as crimes against humanity due to his speech in Hrtkovci on 6 May 1992, in which he called for the expulsion of Croats from Vojvodina.


title: Vojislav Šešelj

text: Šešelj's wife, Jadranka Šešelj (Serbian Cyrillic: Јадранка Шешељ) was born in Podujevo on 11 October 1960. She participated in the President of Serbia elections in 2012 but failed to pass the first round gaining 3.78% of the votes. She is a member of the SRS.


title: Vojislav Šešelj

text: Šešelj was diagnosed with metastatic cancer and underwent surgery to remove a tumor from his colon on 19 December 2013, and later underwent chemotherapy.


title: Vojislav Šešelj

text: Šešelj authored 183 books, mostly in the form of (court) documents and transcripts from interviews and public appearances. Some of the book titles are formulated as insults to his opponents, ICTY judges and prosecutors, and domestic and foreign political figures.


title: Synovial fluid

text: Synovial fluid, also called synovia, is a viscous, non-Newtonian fluid found in the cavities of synovial joints. With its egg white–like consistency, the principal role of synovial fluid is to reduce friction between the articular cartilage of synovial joints during movement. Synovial fluid is a small component of the transcellular fluid component of extracellular fluid.


title: Synovial fluid

text: The inner membrane of synovial joints is called the synovial membrane and secretes synovial fluid into the joint cavity. Synovial fluid is an ultrafiltrate from plasma, and contains proteins derived from the blood plasma and proteins that are


title: Synovial fluid

text: produced by cells within the joint tissues. The fluid contains hyaluronan secreted by fibroblast-like cells in the synovial membrane, lubricin (proteoglycan 4; PRG4) secreted by the surface chondrocytes of the cartilage and interstitial fluid filtered from the blood plasma. This fluid forms a thin layer (roughly 50 μm) at the surface of cartilage and also seeps into microcavities and irregularities in the articular cartilage surface, filling all empty space. The fluid in articular cartilage effectively serves as a synovial fluid reserve. During movement, the synovial fluid held in the cartilage is squeezed out mechanically to maintain a layer of fluid on the cartilage surface (so-called "weeping lubrication").


title: Synovial fluid

text: Synovial tissue is sterile (meaning microorganisms are not typically found there) and composed of vascularized connective tissue that lacks a basement membrane. Two cell types (type A and type B) are present: Type A is derived from blood monocytes, and it removes the wear-and-tear debris from the synovial fluid. Type B produces hyaluronan. Synovial fluid is made of hyaluronic acid and lubricin, proteinases, and collagenases. Synovial fluid exhibits non-Newtonian flow characteristics; the viscosity coefficient is not a constant and the fluid is not linearly viscous. Synovial fluid has thixotropic characteristics; under conditions of sudden increase in pressure as in some kind of mechanical shock, its viscosity suddenly increases. Normal synovial fluid contains 3–4 mg/ml hyaluronan (hyaluronic acid), a polymer of disaccharides composed of D-glucuronic acid and D-N-acetylglucosamine joined by alternating beta-1,4 and beta-1,3 glycosidic bonds. Hyaluronan is synthesized by the synovial membrane and secreted into the joint cavity to increase the viscosity and elasticity of articular cartilages and to lubricate the surfaces between synovium and cartilage.


title: Synovial fluid

text: Synovial fluid contains lubricin (also known as PRG4) as a second lubricating component, secreted by synovial fibroblasts. Chiefly, it is responsible for so-called boundary-layer lubrication, which reduces friction between opposing surfaces of cartilage. There also is some evidence that it helps regulate synovial cell growth.


title: Synovial fluid

text: It also contains phagocytic cells that remove microbes and the debris that results from normal wear and tear in the joint.


title: Synovial fluid

text: Synovial fluid may be collected by syringe in a procedure termed arthrocentesis, also known as joint aspiration.


title: Synovial fluid

text: Synovial fluid may be classified into normal, noninflammatory, inflammatory, septic, and hemorrhagic:


title: Synovial fluid

text: The cytological and biochemical analysis of human synovial fluid began around 1940 using cadaver-derived fluid and comparing characteristics to those of, for instance, bovine synovial fluid.


title: Synovial fluid

text: The mucin clot test is a very old approach to determining if an inflammatory infiltrate is present. In this test, acetic acid is added to the synovial fluid specimen. In a normal specimen, this should lead to a congealing of the hyaluronic acid, forming a 'mucin clot.' If inflammation is present, a mucin clot is not formed (the hyaluronic acid is degraded).


title: Synovial fluid

text: Microscopic analysis of synovial fluid is performed to evaluate for cell count and crystals. Crystals include monosodium urate, calcium pyrophosphate, hydroxyapatite and corticosteroid crystals.


title: Synovial fluid

text: Monosodium urate crystals are seen in gout or gouty arthritis and appear as needle-shaped negatively birefringent crystals varying in length from 2 to 20 μm. With negative birefringence, the crystals appear yellow in parallel light and blue with perpendicular light.


title: Synovial fluid

text: Calcium pyrophosphate crystals are seen in pseudogout (also known as calcium pyrophosphate deposition disease or, CPPD). These crystals are rod-shaped or rhomboids varying in length from 2 to 20 μm and with positive birefringence (blue with parallel light, yellow with perpendicular light).


title: Synovial fluid

text: Hydroxyapatite crystals are small and negatively birefringent. They are usually only detectable with an Alizarin Red S stain.


title: Synovial fluid

text: Corticosteroid crystals may be seen following therapeutic corticosteroid injection into the joint space. They appear blunt, jagged, and show variable birefringence.


title: Synovial fluid

text: When the two articulating surfaces of a synovial joint are separated from one other, the volume within the joint capsule is increased and a negative pressure results. The volume of synovial fluid within the joint is insufficient to fill the expanding volume of the joint and gases dissolved in the synovial fluid (mostly carbon dioxide) are liberated and quickly fill the empty space, leading to the rapid formation of a bubble. This process is known as cavitation. Cavitation in synovial joints results in a high frequency 'cracking' sound.


title: Synovial fluid

text: The term "synovia" () came to English around 1640 (the anglicized form "synovial" is first recorded in the mid 18th century) from New Latin, where it was coined perhaps by Paracelsus from Greek "συν-" "with" and Latin "ovum" "egg" and "-ia" because it resembles egg white in consistency and external appearance.


title: Synovial fluid

text: The term "synovium" is a much more recent pseudo-Latin coinage for what is less confusingly called the synovial membrane. It is not recorded in general dictionaries, and medical dictionaries only explain its meaning, not its etymology, but it is apparently derived from the term "synovia", i.e. the obfuscated etymology of mixed Greek and Latin elements of the singular term "synovia" was misunderstood and the word was erroneously reinterpreted as the plural of the previously non-existent term "synovium" (perhaps in analogy to other plural terms for liquids such as "waters" for amniotic fluid). If one insists on using this pseudo-Latin term "synovium" for the synovial membrane, the non-Latinate plural "synoviums" is better and less confusing than "synovia".


title: Sheetz

text: Sheetz, Inc. is an American chain of convenience stores and coffee shops owned by the Sheetz family. The stores sell custom food, beverages and convenience store items, with all locations having offered 24/7 service since the 1980s. Nearly all of them sell gasoline; a few locations are full-scale truck stops, including showers and a laundromat. Sheetz's headquarters is in Altoona, Pennsylvania, with stores being located in Central and Western Pennsylvania, West Virginia, Maryland, Ohio, Virginia, and North Carolina, with plans to expand into Michigan.


title: Sheetz

text: Sheetz, Inc. was founded by G. Robert "Bob" Sheetz in 1952 when he purchased one of his father's five dairy stores located in Altoona. In 1961, Bob hired his brother Steve to work part-time.


title: Sheetz

text: In 1963, the second store was opened under the name "Sheetz Kwik Shopper." A third store followed in 1968. In 1969, Steve became general manager. The brothers planned to expand at the rate of one store per year with a target of seven stores by 1972. In 1972, the company expanded from seven to fourteen stores. One year later, Sheetz began selling gasoline, and opened the first self-serve gas pumps in central Pennsylvania.


title: Sheetz

text: In 1995, Stanton R. "Stan" Sheetz, Bob's son, became president and Steve assumed the position of chairman of the board. To this day, Sheetz maintains a family business with four family members serving on the executive committee.


title: Sheetz

text: During the mid-1990s, It! Cola, the chain's private-label brand of soft drinks was discontinued. It was available in cans, bottles, and as a fountain drink, which was replaced by Pepsi products. The chain now has both Pepsi and Coca-Cola products in its fountains.


title: Sheetz

text: In December 2004, Sheetz began offering their new MasterCard PayPass with RFID technology, and was one of the first retailers to accept such technology, ahead of McDonald's, Arby's, CVS, and rival 7-Eleven, all of which introduced it nationally in 2006.


title: Sheetz

text: On July 10, 2006, Sheetz became Pennsylvania's second retail chain to offer E85 ethanol-based fuel alternatives at select stations.


title: Sheetz

text: In 2008, Sheetz opened its first commissary, Sheetz Bros. Kitchen, to produce fresh sandwiches and bakery products that are sold at Sheetz locations.


title: Sheetz

text: In 2011, Sheetz gained national attention when it served as a major sponsor for Morgan Spurlock's film "". Sheetz actively promoted the film in stores, including selling collector cups, and Altoona even temporarily changed its name to "POM Wonderful Presents: The Greatest Movie Ever Sold, Pennsylvania" for $25,000. The name change was merely ceremonial, as it was not legally changed by the United States Board of Geographic Names, nor was it recognized by the United States Postal Service.


title: Sheetz

text: In October 2013, Stan Sheetz became chairman of the board of Sheetz, with his cousin Joseph S. "Joe" Sheetz becoming president and CEO.


title: Sheetz

text: Published in November 2013, Kenneth Womack's "Made to Order: The Sheetz Story" traces the company's history from its dairy-store origins through the present day.


title: Sheetz

text: In 2014, Sheetz opened its second distribution center and kitchen facility in Burlington, North Carolina.


title: Sheetz

text: On November 29, 2019, Sheetz announced an expansion into Columbus, Ohio starting in 2021. Currently, the major competitors in that area include Speedway, Circle K, GetGo, United Dairy Farmers, and the locally based Duchess Shoppe. Sheetz plans to open 60 locations in the Columbus area by 2025 (more than doubling its current store count in Ohio), with Sheetz COO Travis Sheetz telling "The Columbus Dispatch" that "we're not coming in lightly". Locations already confirmed will be located in Obetz (near Rickenbacker International Airport), four locations in Columbus proper (including one just outside of John Glenn Columbus International Airport near Gahanna, one in the Northland area of northeast Columbus, and another near Hollywood Casino Columbus and the former Westland Mall), Circleville, South Bloomfield, Polaris, Reynoldsburg, Newark, and two each in Delaware, New Albany and Hilliard; locations in Grove City & Lancaster (the latter due to its close proximity to an existing Sheetz location in Zanesville) are also expected. Another location was planned in Worthington but was shelved due to local resident opposition of the proposed site being next door to a water treatment plant. In January 2021, Sheetz launched a website to prepare for its Columbus launch, with accompanying digital billboards to hype its arrival, while also becoming a presenting sponsor for local CBS affiliate WBNS-TV's newscasts. Upon Sheetz's official arrival in the area with the opening of the first of two stores in Delaware in April 2021, Travis Sheetz said that the company had considered expanding into Columbus as early as the late 1990s when the company first expanded into Northeast Ohio, but decided to expand into North Carolina instead and only recently started expanding into Central Ohio due to many social media requests from transplants now living in the area asking for Sheetz.


title: Sheetz

text: On December 19, 2019, Sheetz celebrated the opening of its 600th store in Shaler Township, PA. Sheetz now has more than 600 locations across Pennsylvania, Maryland, Virginia, West Virginia, Ohio and North Carolina, and more than 21,000 employees. All Sheetz stores are company-owned-and-operated. The company has no plans to sell franchises. Sheetz is the dominant convenience store chain in much of Pennsylvania, holding a virtual monopoly in Altoona, although Rutter's moved into the Altoona area in 2017 and now has three locations in Blair County, and a commanding share in Pittsburgh (where it competes with 7-Eleven, Speedway, GetGo, and to a much lesser extent Circle K) and Harrisburg (where it primarily competes with Rutter's, as well as 7-Eleven and Speedway), but is noticeably absent from the Delaware Valley (including Philadelphia) due to the presence of Wawa, leading to a fierce "rivalry" between the two chains among Pennsylvanians, though the two companies themselves have a friendly relationship.


title: Sheetz

text: In 2020, Sheetz discontinued selling Faygo soft drinks and replaced them with their new private-label brand, Sheetz Pop!. This drink effectively replaces It! Cola 25 years after the latter product was discontinued.


title: Sheetz

text: Following the chain's successful expansion into the Columbus market, in April 2022 Sheetz announced an expansion into the Dayton, Ohio market beginning in 2024. The move will put Sheetz up head-to-head with Casey's for the first time, while also competing with Speedway, Circle K, and UDF in the market. The move will also leave Cincinnati and Toledo as the only major Ohio markets without Sheetz.


title: Sheetz

text: On November 29, 2022, Sheetz announced it would expand into Michigan for the first time, beginning with Detroit in 2025.


title: Sheetz

text: In 1986, to boost lagging sales, Earl Springer, the manager of a Sheetz in Williamsport, Maryland, pursued a food concept that would become Sheetz's signature "Made To Order" (MTO) line. Beginning with only submarine sandwiches, customers would fill out a small slip of paper, designating the ingredients they wanted on their sandwich, and in what quantity. The order slip would be placed in a basket, and the kitchen staff would prepare the sub to the customer's order. Since that time, the menu expanded, and by the 1990s MTO was a sales leader for Sheetz. Beginning in 1996, the paper ordering system was phased out in favor of a picture-based touchscreen computer system. Now common at many restaurants and gas stations worldwide, Sheetz was the first company to implement this technology.


title: Sheetz

text: By 1999, Sheetz was selling 10,000 MTO units a day. Sheetz now trains employees to function as baristas for their newest brand of "Sheetz Bros. Coffeez", which are designed to be higher-grade coffee than typically found in convenience stores. With the introduction of the "Convenience Restaurant" concept, they have expanded their menu. Customers can purchase a wide variety of food items. The Espresso Bar, offering specialty coffees, is found at all locations. Sheetz regularly offers customers free coffee on Christmas Day and New Year's Day. During 2008–2009, Sheetz rolled out "MTGo!", a grab and go assortment of sandwiches, wraps and other small items for the hurried customer. Along with "MTGo!", Sheetz unveiled "Shweetz Bakery" items including donuts, fritters and muffins made and delivered daily from the "Sheetz Bros. Kitchen" in Claysburg, Pennsylvania.


title: Sheetz

text: In 2003, Sheetz opened a concept store in the food court of Hanes Mall in Winston-Salem, North Carolina. This location offered Sheetz's made-to-order foods and fountain beverages in a more traditional fast food layout. It did not function as a convenience store. The store has since closed.


title: Sheetz

text: In 2012, Sheetz again began contemplating "new concept", "fuel-free" locations. In 2014, a plan was announced to open such a location on the campus of West Virginia University, in Morgantown, West Virginia. The intent was to call it "Sheetz MTO Market", however, when opened, in February 2015, the store was named "Sheetz Café" (although outdoor signage is the same as all other stores).


title: Sheetz

text: In September 2015, another no-fuel café opened in State College, Pennsylvania, near the campus of Pennsylvania State University. In Indiana, Pennsylvania, on the border of the Indiana University of Pennsylvania campus, a Sheetz that previously carried gasoline was torn down, and replaced with a no-fuel café that opened in August 2016. A fourth such location opened in September 2017, in Charlottesville, Virginia, directly across the street from the campus of the University of Virginia.


title: Sheetz

text: In September 2019, Sheetz announced they would not renew their lease with WVU for that Morgantown location. The company offered no explanation for the closure.


title: Sheetz

text: Until June 8, 2016, Pennsylvania state law prohibited alcohol sales in convenience stores. Beer had to be sold at a beer distributor while liquor had to be sold at state-operated stores titled "Wines & Spirits". In 2007, Sheetz tried to find a loophole around this by classifying part of one of their prototype stores in Altoona as a restaurant, which would permit alcohol sales. The Malt Beverage Distributors Association of Pennsylvania protested and Sheetz was temporarily barred from selling beer. On appeal, Sheetz was awarded the license to sell beer and continues to do so today. On June 15, 2009, the Pennsylvania Supreme Court gave Sheetz permission to sell beer for takeout under the condition that it is also available to drink on site. Sheetz successfully led the effort to change alcohol sales laws in Pennsylvania to allow sales in convenience and grocery stores, which became law when Governor Tom Wolf signed Act 39 into law on June 8, 2016.


title: Sheetz

text: The Sheetz stores that sell gasoline offer three grades of gasoline (87, 89, and 93 Octane) and most offer diesel. An increasing number of stores also offer E85 and E15, and some also offer ethanol free gasoline. Some stores offer kerosene at separate pumps.


title: Sheetz

text: Sheetz is known for high fuel sales, mostly based on strong inside sales from their MTO's and other products that lead to sales at the pumps. In Pennsylvania, Sheetz is the market leader in all fuel sales at over 21%, ahead of all other competitor convenience store chains including those selling fuel from Big Oil brands such as Exxon, Sunoco, and BP, all of which have a major presence in Pennsylvania alongside Sheetz.


title: The Minority Report

text: "The Minority Report" is a 1956 science fiction novella by American writer Philip K. Dick, first published in "Fantastic Universe". In a future society, three mutants foresee all crime before it occurs. Plugged into a great machine, these "precogs" allow a division of the police called Precrime to arrest suspects before they can commit any actual crimes. When the head of Precrime, John Anderton, is himself predicted to murder a man whom he has never heard of, Anderton is convinced a great conspiracy is afoot.


title: The Minority Report

text: The story reflects many of Philip K. Dick's personal Cold War anxieties, particularly questioning the relationship between authoritarianism and individual autonomy. Like many stories dealing with knowledge of future events, "The Minority Report" questions the existence of free will. The title refers to the dissenting opinion of one of the precogs.


title: The Minority Report

text: In 2002, the story was adapted into a film directed by Steven Spielberg and starring Tom Cruise, Colin Farrell, Samantha Morton, and Max von Sydow. Spielberg's film was followed by a series of the same name, which debuted on the Fox Broadcasting Company on September 21, 2015.


title: The Minority Report

text: John Allison Anderton is the aging creator and head police commissioner of the Precrime Division, in which three mutants called "precogs" predict all crimes before they occur. While showing his new young second-in-command Ed Witwer around the premises, Anderton is shocked to receive a report that he, Anderton, is predicted to murder a man within the coming week. Believing Witwer has framed him in order to steal his job, Anderton tells his much younger wife, Lisa, another police official, though he soon suspects that she and Witwer may be joined in a conspiracy against him.


title: The Minority Report

text: Knowing that a copy of the report is automatically sent to the Army as a safeguard, Anderton rushes home, where he is suddenly abducted by armed men and brought before Leopold Kaplan: a retired general and Anderton's expected murder victim, although the two have never met. General Kaplan hears Anderton's plea, then hands him over to police custody. Along the way, a traffic accident allows Anderton to escape and then contact a friend at Precrime to inquire about a "minority report": a type of dissenting opinion, in which one of the three precogs' predictions conflicts with those of the other two. Indeed, a minority report exists, in which Anderton would refrain from murdering Kaplan, once he became aware of the prediction. Anderton is now in a catch-22 and must decide whether to remain silent and turn himself in or to speak up about the minority report thus revealing a flaw that could discredit the entire Precrime system. Lisa successfully convinces Anderton that no conspiracy is taking place and demands at gunpoint that Anderton turn himself in until an Army soldier attacks her. They subdue the attacker and discover that the military is trying to weaken Precrime's credibility; they even staged the earlier traffic accident to allow Anderton to escape.


title: The Minority Report

text: No longer certain whom to trust, Anderton carefully listens to each of the precog reports individually and then goes to an Army rally where General Kaplan is moments away from reading aloud Anderton's 'minority report' to the public, showing how countless people may have been wrongfully arrested through the Precrime system. Suddenly, Kaplan notices something that causes him to flee, but, surprisingly, Anderton draws his gun and shoots Kaplan dead.


title: The Minority Report

text: Anderton is arrested and both he and Lisa, as his accomplice, are scheduled for penal transportation to another planet. Before they leave Earth, Anderton explains to Ed Witwer his reasoning for shooting Kaplan. After obtaining the precog reports, he realized that all three were "minority reports" in a way because each described three entirely different situations, rather than a single situation with two possible outcomes. It dawned on Anderton that each report after the first was biased by him having knowledge of the prior reports. The first report suggested that he would kill Kaplan to prevent Precrime from being discredited and shut down. The second report suggested that, after reading the first report, he would decide not to shoot Kaplan in order to avoid arrest. The third report suggested that Kaplan was planning to discredit Precrime in order to enact a state of emergency and martial law, resulting in a military coup in which the Army would replace Precrime, leading Anderton to the decision that he had to assassinate Kaplan after all. Viewing this as the lesser of two evils, Anderton decided to follow the path predicted in that third report and kill Kaplan. The entire situation has thus become a self-fulfilling prophecy. As Anderton and Lisa are about to be transported, Anderton warns Ed Witwer, who has nervously inherited Anderton's job, that the same predicament could happen at any time to Witwer too.


title: The Minority Report

text: Precrime is a predictive policing system dedicated to apprehending and detaining people before they have the opportunity to commit a given crime. At the time of the story, it has been operating for thirty years. This method has replaced the traditional system of discovering a crime and its perpetrator after the crime has already been committed, then issuing punishment after the fact. As Witwer says early on in the story, "punishment was never much of a deterrent and could scarcely have afforded comfort to a victim already dead". Unlike the film adaptation, the story version of Precrime does not deal solely with cases of murder, but all crimes. As Commissioner John A. Anderton (the founder of Precrime) states, "Precrime has cut down felonies by 99.8%."


title: The Minority Report

text: Three mutants, known as "precogs", have precognitive abilities they can use to see up to two weeks into the future. The precogs are strapped into machines, nonsensically babbling as a computer listens and converts this gibberish into predictions of the future. This information is transcribed onto conventional punched cards that are ejected into various coded slots. These cards appear simultaneously at Precrime and the army headquarters to prevent systemic corruption.


title: The Minority Report

text: Precogs are mutants, identified talents further developed in a government-operated training school — for example, one precog was initially diagnosed as "a hydro-cephalic idiot" but the precog talent was found under layers of damaged brain tissue. The precogs are kept in rigid position by metal bands, clamps and wiring, strapping them into special high-backed chairs. Their physical needs are taken care of automatically and Anderton claims that they have no spiritual needs. Their physical appearance is distorted from an ordinary human, with enlarged heads and wasted bodies. Precogs are "deformed" and "retarded" as "the talent absorbs everything"; "the esp-lobe shrivels the balance of the frontal area". They do not understand their predictions; only through technological and mechanical aid can their nonsense be unraveled. The data produced does not always pertain to crime or murder, but this information is then passed on to other groups of people who use the precog necessities to create other future necessities.


title: The Minority Report

text: The reports of all the precogs are analyzed by a computer and, if these reports differ from one another, the computer identifies the two reports with the greatest overlap and produces a "majority report", taking this as the accurate prediction of the future. But the existence of majority reports implies the existence of a "minority report". In the story, Precrime Police Commissioner John A. Anderton believes that the prediction that he will commit a murder has been generated as a majority report. He sets out to find the minority report, which would give him an alternate future.


title: The Minority Report

text: However, as Anderton finds out, sometimes all three reports differ quite significantly, and there may be no majority report, even though two reports may have had enough in common for the computer to link them as such. In the storyline, all of the reports about Anderton differ because they predict events occurring sequentially, and thus each is a minority report. Anderton's situation is explained as unique, because he, as Police Commissioner, received notice of the precogs' predictions, allowing him to change his mind and invalidate earlier precog predictions.


title: The Minority Report

text: The existence of three apparent minority reports suggests the possibility of three future time paths, all existing simultaneously, any of which an individual could choose to follow or be sent along following an enticement (as in Anderton's being told he was going to murder an unknown man). In this way, the time-paths overlap, and the future of one is able to affect the past of another. It is in this way that the story weaves a complicated web of crossing time paths and makes a linear journey for Anderton harder to identify. This idea of multiple futures lets the precogs of Precrime be of benefit—because if only one time-path existed, the predictions of the precogs would be worthless since the future would be unalterable. Precrime is based on the notion that once one unpleasant future pathway is identified, an alternative, better one can be created with the arrest of the potential perpetrator.


title: The Minority Report

text: John A. Anderton is the protagonist of "The Minority Report". At first, he is highly insecure, suspicious of those closest to him - his wife, his assistant Witwer. He has complete faith in the Precrime system and its authority over individuals and their freedom of choice. The poor living condition of the precogs and the imprisonment of would-be criminals are necessary consequences for the greater good of a safe society. When his own autonomy comes under attack, Anderton retains this faith and convinces himself that the system has somehow been corrupted.


title: The Minority Report

text: Anderton struggles to find an appropriate balance between Precrime authority and individual liberty. Ultimately, Anderton decides to kill Leopold Kaplan to affirm the majority report and thereby preserve the validity of the Precrime system.


title: Benjamin Hoskins Paddock

text: Benjamin Hoskins Paddock Jr. (November 1, 1926 – January 18, 1998) was an American bank robber and con man who was on the FBI Ten Most Wanted Fugitives list from 1969 to 1977. He is the father of Stephen Paddock who committed the 2017 Las Vegas shooting that killed 60 people.


title: Benjamin Hoskins Paddock

text: Paddock was born at St. Nicholas Hospital in Sheboygan, Wisconsin on November 1, 1926, the son of Benjamin Hoskins Paddock Sr. and Olga Emelia Elizabeth Paddock (née Gunderson). He served in the United States Navy as an S2 (Seaman Second Class) during World War II.


title: Benjamin Hoskins Paddock

text: In the 1950s in Tucson, Arizona, he operated a service station where he sold used cars. He later sold garbage disposal units under the name of Arizona Disposer Company and was connected with the operation of a nightclub in Tucson. In the late 1950s, Paddock volunteered with the Pima County Juvenile Probation Department and in 1959 was named special deputy to handle cases of wayward youths.


title: Benjamin Hoskins Paddock

text: In 1946, Paddock was convicted of ten counts of auto larceny and five counts of confidence game and was confined at the Illinois State Penitentiary until July 1951. In 1953, he was convicted of conspiracy in connection with a bad check passing operation and was again held at the Illinois State Penitentiary until August 1956. In one of his early arrests, he was found with a concealed revolver.


title: Benjamin Hoskins Paddock

text: He was accused of robbing branches of the Valley National Bank of Arizona in Phoenix of $11,210 ($ in dollars) on February 19, 1959, and of $9,285 ($ in dollars) on January 29, 1960. He robbed another branch of $4,620 ($ in dollars) on July 26, 1960. He was captured and then convicted for the third robbery in federal court in January 1961. During his arrest, he attempted to run down an FBI agent with his car. He was sentenced to 20 years in prison. On December 30, 1968, Paddock escaped from the Federal Correctional Institution, La Tuna in Anthony, Texas. A warrant for his arrest relating to his escape was issued on February 3, 1969, and he was placed on the FBI Ten Most Wanted list.


title: Benjamin Hoskins Paddock

text: Most individuals who have been on the FBI Ten Most Wanted list are off the list in less than six months. Paddock was among those who were on the list the longest, being placed on the list on June 10, 1969, and removed on May 5, 1977. While on the most wanted list, he was described as being tall, weighing , having blond hair, but being balding and frequently shaved. He had green eyes and wore contact lenses or glasses. He also had a scar above his right eyebrow and on his right knee and had a birthmark on his left ankle. He was described as a smooth talker, as arrogant and egotistical, liking cigars, cigarettes, and steaks. He also played bridge, enjoyed gambling, and watching sports, particularly baseball, for which he also worked as an umpire. During his criminal career, Paddock had numerous aliases, including Perry Archer, Benjamin J. Butler, Leo Genstein, Pat Paddock, and Patrick Benjamin Paddock. His nicknames included "Chromedome", "Old Baldy", and "Big Daddy".


title: Benjamin Hoskins Paddock

text: After escaping prison in 1968, Paddock moved to Oregon where he took the name Bruce Warner Erickson. In Oregon, he worked as a contract trucker and in drug abuse rehabilitation. He was twice cited for traffic violations and in September 1977 he applied for and was granted a license to open a bingo parlor, but his identity was not uncovered. He then operated a bingo parlor for the Center for Education Reform, a non-profit organization based in Eugene, Oregon.


title: Benjamin Hoskins Paddock

text: He was captured and arrested in early September 1978 in Springfield, Oregon, and was eventually released on parole.


title: Benjamin Hoskins Paddock

text: In 1987, he was charged by the Oregon Attorney General with racketeering related to his bingo business and fraud for an illegal business he ran rolling back car odometers, but avoided a prison sentence by paying a $100,000 fine ($ in dollars). Later in life, his involvement in bingo earned him the nickname, Bingo Bruce. During the last decade of his life, he lived quietly in Texas where he co-owned a car shop with his girlfriend.


title: Benjamin Hoskins Paddock

text: Paddock married Dolores Irene Hudson (born January 10, 1928) in 1952, and they had four sons, Stephen (1953–2017), Patrick (born ), Bruce (1959), and Eric (born 1960).


title: Benjamin Hoskins Paddock

text: He died of a heart attack on January 18, 1998, in Arlington, Texas. He's buried at the Fort Gibson National Cemetery in Fort Gibson, Oklahoma.


title: Benjamin Hoskins Paddock

text: His eldest son Stephen was the perpetrator of the 2017 Las Vegas shooting, the deadliest mass shooting by a lone gunman in North American history. Stephen was seven at the time of his father's arrest in the summer of 1960. "We didn't grow up under his influence," said his brother Eric. Their mother told them at the time that their father was dead.<ref name="Kirby/Hartmann"></ref>


title: Benjamin Hoskins Paddock

text: Another son, Bruce, was arrested in North Hollywood on charges of possessing over 600 child pornography images. The charges were dropped in May 2018. On November 3, 2020, Bruce died due to health issues.


title: Heavy Metal 2000

text: Heavy Metal 2000 (also known as Heavy Metal: F.A.K.K.² outside North America) is a 2000 Canadian adult animated science fiction film produced by Jacques Pettigrew and Michel Lemire, and directed by Michael Coldewey and Lemire. Starring the voices of Michael Ironside, Julie Strain, and Billy Idol, the film is the follow-up to the 1981 animated cult film "Heavy Metal", which is based on the fantasy magazine of the same name. The story is based on the graphic novel, "The Melting Pot", written by Kevin Eastman, Simon Bisley and Eric Talbot. The film was made by CinéGroupe, a studio based in Montreal, Quebec.


title: Heavy Metal 2000

text: In ages past, the Arakacians, a malevolent race, discovered a place where space-time leaked a type of fluid. This fluid granted immortality to anyone who consumed it. The Arakacians built an empire and enslaved the known universe for centuries. They were finally vanquished after the fountain chamber (where they gathered the water of life) was sealed by freedom fighters. The key to the chamber, a glowing crystal that can lead the bearer back to the fountain and drives anyone who possessed it insane, was cast into space and lost among the stars.


title: Heavy Metal 2000

text: In a present-day asteroid excavation, space crewman Tyler and his colleague find the key by accident. Tyler touches the key and instantly goes insane. He kills his mining partner and takes over the ship, killing everyone but Dr. Schechter, and the pilots Lambert and Germain. His search for the planet with the fountain leads to Eden, a planet that is designated F.A.K.K.² (Federation-Assigned Ketogenic Killzone to the second level), but has inhabitants whose bodies carry the immortality fluid. Tyler invades Eden, and kills many of the Edenites, capturing some so he can extract the immortality fluids from their bodies. He also keeps the attractive Kerrie for his own sexual purposes. When Germain resists the idea, he is left on Eden.


title: Heavy Metal 2000

text: Kerrie's sister Julie survives the attack and teams up with Germain to follow Tyler. At a renegade space station, Julie finds Tyler and critically injures him. However, he ingests a vial with the immortality serum and heals instantly. In the ensuing gunfight, Tyler blows up the club. Escaping the explosion, Julie and Germain board a shuttlecraft that latches onto Tyler's ship before it jumps into hyperspace. Discovering them mid-travel, Tyler tries to shake them off, but the fight causes the two ships to crash.


title: Heavy Metal 2000

text: Julie wakes up on Oroboris, a desert planet, and meets Odin, a mysterious cloaked sage, and his assistant, Zeek, a rock-like creature. The two are guardians of the ancient fountain. With his ship destroyed and most of his crew dead, Tyler orders Dr. Schechter to extract Kerrie's fluids. While exploring the planet, he finds a race of reptilian beings and conquers them by defeating their champion and their leader in a death match. Julie enters the reptilian city in disguise as a woman that the reptiles found for Tyler. That night, she seduces Tyler and tries to kill him, but Zeek stops the attempt and captures her, taking her back to Odin. Julie then infiltrates Tyler's ship and discovers Kerrie is still alive. She takes out Dr. Schechter, frees Kerrie, and escapes as the complex explodes. As a result, Tyler vows to make Julie immortal so he can "screw her and kill her every hour of every day for all eternity." With only three vials of serum, he orders his troops to storm the citadel where the immortality fountain is located.


title: Heavy Metal 2000

text: At the citadel, Julie undergoes a ritual where armor is bestowed upon her. She, Kerrie, and Germain help the fountain's guardians defend against Tyler's army. In the fighting, Lambert suffers a near-fatal injury and knocks Tyler's last vial of immortality serum loose, breaking it on the ground. Tyler, enraged, kills Lambert for the blunder and walks to the pit of immortality. He is about to put the crystal into the fountain's final lock but is stopped by Julie, who stabs him in the left eye. A fight ensues in which, with Odin's help, Julie finally kills Tyler. Odin then throws off his cloak, revealing himself to be the last of the Arakacians. He has been in hiding all these centuries, waiting for someone to find the chamber key and be drawn to the fountain. He intends to claim it as his own and reestablish the Arakacian empire. However, Zeek pulls the crystal key from the pedestal, locking Odin inside the fountain chamber forever, and flies into outer space. As Germain and Kerrie help Julie to her feet, Zeek envelops the crystal into himself and becomes a new asteroid to hide the key for all time.


title: Heavy Metal 2000

text: "Heavy Metal 2000" was panned by critics. On review aggregator website Rotten Tomatoes, the film holds a 17% rating based on reviews from 12 critics.


title: Heavy Metal 2000

text: The film had a video game about the events after "Heavy Metal 2000", titled "", in which the player assumes the role of Julie as she fights to save Eden from an evil entity called "GITH". The game is set some time after the film and features cameo appearances of several characters, for example, Julie's sister Kerrie, the pilot Germaine (now married to Kerrie), and a resurrected Tyler.


title: Heavy Metal 2000

text: After the release of "2000", a third film has been in various stages of development since then. During 2008 and into 2009, reports circulated that David Fincher and James Cameron would executive produce, and each direct one of the eight to nine segments for a new film based on "Heavy Metal". Eastman would also direct a segment, as well as animator Tim Miller, with Zack Snyder, Gore Verbinski, and Guillermo del Toro attached to direct segments. However, Paramount Pictures decided to stop funding the film by August 2009 and no distributor or production company has shown interest in the second sequel since. Fincher and Miller subsequently developed their plans into Love, Death & Robots, an original animated series for Netflix initially released in 2019.


title: Heavy Metal 2000

text: In 2011, filmmaker Robert Rodriguez announced at Comic-Con that he had purchased the film rights to "Heavy Metal" and planned to develop a new animated film at the new Quick Draw Studios. However, on March 11, 2014, with the formation of his very own television network, El Rey, Rodriguez considered switching gears and bringing it to TV.


title: Heavy Metal 2000

text: The Heavy Metal 2000 Original Soundtrack is the 2000 soundtrack album to the film of the same name. In his AllMusic review, Greg Prato said that the album was a "truer heavy metal soundtrack" than that of the first film, featuring a combination of established bands such as Pantera, Monster Magnet, and Machine Head; then-newer bands such as Queens of the Stone Age, System of a Down, Hate Dept., Puya, and Coal Chamber; and a few non-metal artists such as Billy Idol, Insane Clown Posse, Twiztid, and Bauhaus. The vast majority of the tracks were either specifically recorded for the soundtrack or were previously unreleased up to that point. One month after its release in the U.S., the soundtrack peaked at No. 101 on the "Billboard" 200 chart.


title: Quasi-experiment

text: A quasi-experiment is an empirical interventional study used to estimate the causal impact of an intervention on target population without random assignment. Quasi-experimental research shares similarities with the traditional experimental design or randomized controlled trial, but it specifically lacks the element of random assignment to treatment or control. Instead, quasi-experimental designs typically allow the researcher to control the assignment to the treatment condition, but using some criterion other than random assignment (e.g., an eligibility cutoff mark).


title: Quasi-experiment

text: Quasi-experiments are subject to concerns regarding internal validity, because the treatment and control groups may not be comparable at baseline. In other words, it may not be possible to convincingly demonstrate a causal link between the treatment condition and observed outcomes. This is particularly true if there are confounding variables that cannot be controlled or accounted for.


title: Quasi-experiment

text: With random assignment, study participants have the same chance of being assigned to the intervention group or the comparison group. As a result, differences between groups on both observed and unobserved characteristics would be due to chance, rather than to a systematic factor related to treatment (e.g., illness severity). Randomization itself does not guarantee that groups will be equivalent at baseline. Any change in characteristics post-intervention is likely attributable to the intervention.


title: Quasi-experiment

text: The first part of creating a quasi-experimental design is to identify the variables. The quasi-independent variable will be the x-variable, the variable that is manipulated in order to affect a dependent variable. "X" is generally a grouping variable with different levels. Grouping means two or more groups, such as two groups receiving alternative treatments, or a treatment group and a no-treatment group (which may be given a placebo – placebos are more frequently used in medical or physiological experiments). The predicted outcome is the dependent variable, which is the y-variable. In a time series analysis, the dependent variable is observed over time for any changes that may take place. Once the variables have been identified and defined, a procedure should then be implemented and group differences should be examined.


title: Quasi-experiment

text: In an experiment with random assignment, study units have the same chance of being assigned to a given treatment condition. As such, random assignment ensures that both the experimental and control groups are equivalent. In a quasi-experimental design, assignment to a given treatment condition is based on something other than random assignment. Depending on the type of quasi-experimental design, the researcher might have control over assignment to the treatment condition but use some criteria other than random assignment (e.g., a cutoff score) to determine which participants receive the treatment, or the researcher may have no control over the treatment condition assignment and the criteria used for assignment may be unknown. Factors such as cost, feasibility, political concerns, or convenience may influence how or if participants are assigned to a given treatment conditions, and as such, quasi-experiments are subject to concerns regarding internal validity (i.e., can the results of the experiment be used to make a causal inference?).


title: Quasi-experiment

text: Quasi-experiments are also effective because they use the "pre-post testing". This means that there are tests done before any data are collected to see if there are any person confounds or if any participants have certain tendencies. Then the actual experiment is done with post test results recorded. This data can be compared as part of the study or the pre-test data can be included in an explanation for the actual experimental data. Quasi experiments have independent variables that already exist such as age, gender, eye color. These variables can either be continuous (age) or they can be categorical (gender). In short, naturally occurring variables are measured within quasi experiments.


title: Quasi-experiment

text: There are several types of quasi-experimental designs, each with different strengths, weaknesses and applications. These designs include (but are not limited to):


title: Quasi-experiment

text: Of all of these designs, the regression discontinuity design comes the closest to the experimental design, as the experimenter maintains control of the treatment assignment and it is known to "yield an unbiased estimate of the treatment effects". It does, however, require large numbers of study participants and precise modeling of the functional form between the assignment and the outcome variable, in order to yield the same power as a traditional experimental design.


title: Quasi-experiment

text: Though quasi-experiments are sometimes shunned by those who consider themselves to be experimental purists (leading Donald T. Campbell to coin the term “queasy experiments” for them), they are exceptionally useful in areas where it is not feasible or desirable to conduct an experiment or randomized control trial. Such instances include evaluating the impact of public policy changes, educational interventions or large scale health interventions. The primary drawback of quasi-experimental designs is that they cannot eliminate the possibility of confounding bias, which can hinder one's ability to draw causal inferences. This drawback is often used to discount quasi-experimental results. However, such bias can be controlled for using various statistical techniques such as multiple regression, if one can identify and measure the confounding variable(s). Such techniques can be used to model and partial out the effects of confounding variables techniques, thereby improving the accuracy of the results obtained from quasi-experiments. Moreover, the developing use of propensity score matching to match participants on variables important to the treatment selection process can also improve the accuracy of quasi-experimental results.


title: Quasi-experiment

text: In fact, data derived from quasi-experimental analyses has been shown to closely match experimental data in certain cases, even when different criteria were used. In sum, quasi-experiments are a valuable tool, especially for the applied researcher. On their own, quasi-experimental designs do not allow one to make definitive causal inferences; however, they provide necessary and valuable information that cannot be obtained by experimental methods alone. Researchers, especially those interested in investigating applied research questions, should move beyond the traditional experimental design and avail themselves of the possibilities inherent in quasi-experimental designs.


title: Quasi-experiment

text: A true experiment would, for example, randomly assign children to a scholarship, in order to control for all other variables. Quasi-experiments are commonly used in social sciences, public health, education, and policy analysis, especially when it is not practical or reasonable to randomize study participants to the treatment condition.


title: Quasi-experiment

text: As an example, suppose we divide households into two categories: Households in which the parents spank their children, and households in which the parents do not spank their children. We can run a linear regression to determine if there is a positive correlation between parents' spanking and their children's aggressive behavior. However, to simply randomize parents to spank or to not spank their children may not be practical or ethical, because some parents may believe it is morally wrong to spank their children and refuse to participate.


title: Quasi-experiment

text: Some authors distinguish between a natural experiment and a "quasi-experiment". The difference is that in a quasi-experiment the criterion for assignment is selected by the researcher, while in a natural experiment the assignment occurs 'naturally,' without the researcher's intervention.


title: Quasi-experiment

text: Quasi-experiments have outcome measures, treatments, and experimental units, but do not use random assignment. Quasi-experiments are often the design that most people choose over true experiments. It is usually easily conducted as opposed to true experiments, because they bring in features from both experimental and non-experimental designs. Measured variables can be brought in, as well as manipulated variables. Usually quasi-experiments are chosen by experimenters because they maximize internal and external validity.


title: Quasi-experiment

text: Since quasi-experimental designs are used when randomization is impractical and/or unethical, they are typically easier to set up than true experimental designs, which require random assignment of subjects. Additionally, utilizing quasi-experimental designs minimizes threats to ecological validity as natural environments do not suffer the same problems of artificiality as compared to a well-controlled laboratory setting. Since quasi-experiments are natural experiments, findings in one may be applied to other subjects and settings, allowing for some generalizations to be made about population. Also, this experimentation method is efficient in longitudinal research that involves longer time periods which can be followed up in different environments.


title: Quasi-experiment

text: Other advantages of quasi experiments include the idea of having any manipulations the experimenter so chooses. In natural experiments, the researchers have to let manipulations occur on their own and have no control over them whatsoever. Also, using self selected groups in quasi experiments also takes away to chance of ethical, conditional, etc. concerns while conducting the study.


title: Quasi-experiment

text: Quasi-experimental estimates of impact are subject to contamination by confounding variables. In the example above, a variation in the children's response to spanking is plausibly influenced by factors that cannot be easily measured and controlled, for example the child's intrinsic wildness or the parent's irritability. The lack of random assignment in the quasi-experimental design method may allow studies to be more feasible, but this also poses many challenges for the investigator in terms of internal validity. This deficiency in randomization makes it harder to rule out confounding variables and introduces new threats to internal validity. Because randomization is absent, some knowledge about the data can be approximated, but conclusions of causal relationships are difficult to determine due to a variety of extraneous and confounding variables that exist in a social environment. Moreover, even if these threats to internal validity are assessed, causation still cannot be fully established because the experimenter does not have total control over extraneous variables.


title: Quasi-experiment

text: Disadvantages also include the study groups may provide weaker evidence because of the lack of randomness. Randomness brings a lot of useful information to a study because it broadens results and therefore gives a better representation of the population as a whole. Using unequal groups can also be a threat to internal validity. If groups are not equal, which is sometimes the case in quasi experiments, then the experimenter might not be positive what the causes are for the results.


title: Quasi-experiment

text: Internal validity is the approximate truth about inferences regarding cause-effect or causal relationships. This is why validity is important for quasi experiments because they are all about causal relationships. It occurs when the experimenter tries to control all variables that could affect the results of the experiment. Statistical regression, history and the participants are all possible threats to internal validity. The question you would want to ask while trying to keep internal validity high is "Are there any other possible reasons for the outcome besides the reason I want it to be?" If so, then internal validity might not be as strong.


title: Quasi-experiment

text: External validity is the extent to which results obtained from a study sample can be generalized "to" some well-specified population of interest, and "across" subpopulations of people, times, contexts, and methods of study. Lynch has argued that generalizing "to" a population is almost never possible because the populations to which we would like to project are measures of future behavior, which by definition cannot be sampled. Therefore, the more relevant question is whether treatment effects generalize "across" subpopulations that vary on background factors that might not be salient to the researcher. External validity depends on whether the treatments studies have homogeneous effects across different subsets of people, times, contexts, and methods of study or whether the sign and magnitude of any treatment effects changes across subsets in ways that may not be acknowledged or understood by the researchers. Athey and Imbens and Athey and Wager have pioneered machine learning techniques for inductive understanding of heterogeneous treatment effects.


title: Quasi-experiment

text: "Person-by-treatment" designs are the most common type of quasi experiment design. In this design, the experimenter measures at least one independent variable. Along with measuring one variable, the experimenter will also manipulate a different independent variable. Because there is manipulating and measuring of different independent variables, the research is mostly done in laboratories. An important factor in dealing with person-by-treatment designs are that random assignment will need to be used in order to make sure that the experimenter has complete control over the manipulations that are being done to the study.


title: Quasi-experiment

text: An example of this type of design was performed at the University of Notre Dame. The study was conducted to see if being mentored for your job led to increased job satisfaction. The results showed that many people who did have a mentor showed very high job satisfaction. However, the study also showed that those who did not receive the mentor also had a high number of satisfied employees. Seibert concluded that although the workers who had mentors were happy, he could not assume that the reason for it was the mentors themselves because of the numbers of the high number of non-mentored employees that said they were satisfied. This is why prescreening is very important so that you can minimize any flaws in the study before they are seen.


title: Quasi-experiment

text: "Natural experiments" are a different type of quasi-experiment design used by researchers. It differs from person-by-treatment in a way that there is not a variable that is being manipulated by the experimenter. Instead of controlling at least one variable like the person-by-treatment design, experimenters do not use random assignment and leave the experimental control up to chance. This is where the name ""natural"" experiment comes from. The manipulations occur naturally, and although this may seem like an inaccurate technique, it has actually proven to be useful in many cases. These are the studies done to people who had something sudden happen to them. This could mean good or bad, traumatic or euphoric. An example of this could be studies done on those who have been in a car accident and those who have not. Car accidents occur naturally, so it would not be ethical to stage experiments to traumatize subjects in the study. These naturally occurring events have proven to be useful for studying posttraumatic stress disorder cases.


title: Variable (mathematics)

text: In mathematics, a variable (from Latin "variabilis", "changeable") is a symbol and placeholder for any mathematical object. In particular, a variable may represent a number, a vector, a matrix, a function, the argument of a function, a set, or an element of a set.


title: Variable (mathematics)

text: Algebraic computations with variables as if they were explicit numbers solve a range of problems in a single computation. For example, the quadratic formula solves any quadratic equation by substituting the numeric values of the coefficients of that equation for the variables that represent them in the quadratic formula. In mathematical logic, a "variable" is either a symbol representing an unspecified term of the theory (a meta-variable), or a basic object of the theory that is manipulated without referring to its possible intuitive interpretation.


title: Variable (mathematics)

text: In ancient works such as Euclid's "Elements", single letters refer to geometric points and shapes. In the 7th century, Brahmagupta used different colours to represent the unknowns in algebraic equations in the "Brāhmasphuṭasiddhānta". One section of this book is called "Equations of Several Colours".


title: Variable (mathematics)

text: At the end of the 16th century, François Viète introduced the idea of representing known and unknown numbers by letters, nowadays called variables, and the idea of computing with them as if they were numbers—in order to obtain the result by a simple replacement. Viète's convention was to use consonants for known values, and vowels for unknowns.


title: Variable (mathematics)

text: In 1637, René Descartes "invented the convention of representing unknowns in equations by "x", "y", and "z", and knowns by "a", "b", and "c"". Contrarily to Viète's convention, Descartes' is still commonly in use. The history of the letter x in math was discussed in a 1887 Scientific American article.


title: Variable (mathematics)

text: Starting in the 1660s, Isaac Newton and Gottfried Wilhelm Leibniz independently developed the infinitesimal calculus, which essentially consists of studying how an infinitesimal variation of a "variable quantity" induces a corresponding variation of another quantity which is a "function" of the first variable. Almost a century later, Leonhard Euler fixed the terminology of infinitesimal calculus, and introduced the notation for a function , its variable and its value . Until the end of the 19th century, the word "variable" referred almost exclusively to the arguments and the values of functions.


title: Variable (mathematics)

text: In the second half of the 19th century, it appeared that the foundation of infinitesimal calculus was not formalized enough to deal with apparent paradoxes such as a nowhere differentiable continuous function. To solve this problem, Karl Weierstrass introduced a new formalism consisting of replacing the intuitive notion of limit by a formal definition. The older notion of limit was "when the "variable" varies and tends toward , then tends toward ", without any accurate definition of "tends". Weierstrass replaced this sentence by the formula


title: Variable (mathematics)

text: This static formulation led to the modern notion of variable, which is simply a symbol representing a mathematical object that either is unknown, or may be replaced by any element of a given set (e.g., the set of real numbers).


title: Variable (mathematics)

text: Variables are generally denoted by a single letter, most often from the Latin alphabet and less often from the Greek, which may be lowercase or capitalized. The letter may be followed by a subscript: a number (as in ), another variable (), a word or abbreviation of a word () or a mathematical expression (). Under the influence of computer science, some variable names in pure mathematics consist of several letters and digits. Following René Descartes (1596–1650), letters at the beginning of the alphabet such as "a", "b", "c" are commonly used for known values and parameters, and letters at the end of the alphabet such as ("x", "y", "z") are commonly used for unknowns and variables of functions. In printed mathematics, the norm is to set variables and constants in an italic typeface.


title: Variable (mathematics)

text: For example, a general quadratic function is conventionally written as formula_2, where "a", "b" and "c" are parameters (also called constants, because they are constant functions), while "x" is the variable of the function. A more explicit way to denote this function is formula_3, which clarifies the function-argument status of "x" and the constant status of "a", "b" and "c". Since "c" occurs in a term that is a constant function of "x", it is called the constant term.


title: Variable (mathematics)

text: Specific branches and applications of mathematics have specific naming conventions for variables. Variables with similar roles or meanings are often assigned consecutive letters or the same letter with different subscripts. For example, the three axes in 3D coordinate space are conventionally called "x", "y", and "z". In physics, the names of variables are largely determined by the physical quantity they describe, but various naming conventions exist. A convention often followed in probability and statistics is to use "X", "Y", "Z" for the names of random variables, keeping "x", "y", "z" for variables representing corresponding better-defined values.


title: Variable (mathematics)

text: It is common for variables to play different roles in the same mathematical formula, and names or qualifiers have been introduced to distinguish them. For example, the general cubic equation


title: Variable (mathematics)

text: is interpreted as having five variables: four, , which are taken to be given numbers and the fifth variable, is understood to be an "unknown" number. To distinguish them, the variable is called "an unknown", and the other variables are called "parameters" or "coefficients", or sometimes "constants", although this last terminology is incorrect for an equation, and should be reserved for the function defined by the left-hand side of this equation.


title: Variable (mathematics)

text: In the context of functions, the term "variable" refers commonly to the arguments of the functions. This is typically the case in sentences like "function of a real variable", " is the variable of the function ", " is a function of the variable " (meaning that the argument of the function is referred to by the variable ).


title: Variable (mathematics)

text: In the same context, variables that are independent of define constant functions and are therefore called "constant". For example, a "constant of integration" is an arbitrary constant function that is added to a particular antiderivative to obtain the other antiderivatives. Because the strong relationship between polynomials and polynomial function, the term "constant" is often used to denote the coefficients of a polynomial, which are constant functions of the indeterminates.


title: Variable (mathematics)

text: This use of "constant" as an abbreviation of "constant function" must be distinguished from the normal meaning of the word in mathematics. A constant, or mathematical constant is a well and unambiguously defined number or other mathematical object, as, for example, the numbers 0, 1, and the identity element of a group. Since a variable may represent any mathematical object, a letter that represents a constant is often called a variable. This is, in particular, the case of and , even when they represents Euler's number and


title: Variable (mathematics)

text: All these denominations of variables are of semantic nature, and the way of computing with them (syntax) is the same for all.


title: Variable (mathematics)

text: In calculus and its application to physics and other sciences, it is rather common to consider a variable, say , whose possible values depend on the value of another variable, say . In mathematical terms, the "dependent" variable represents the value of a function of . To simplify formulas, it is often useful to use the same symbol for the dependent variable and the function mapping onto . For example, the state of a physical system depends on measurable quantities such as the pressure, the temperature, the spatial position, ..., and all these quantities vary when the system evolves, that is, they are function of the time. In the formulas describing the system, these quantities are represented by variables which are dependent on the time, and thus considered implicitly as functions of the time.


title: Variable (mathematics)

text: Therefore, in a formula, a dependent variable is a variable that is implicitly a function of another (or several other) variables. An independent variable is a variable that is not dependent.


title: Variable (mathematics)

text: The property of a variable to be dependent or independent depends often of the point of view and is not intrinsic. For example, in the notation , the three variables may be all independent and the notation represents a function of three variables. On the other hand, if and depend on (are "dependent variables") then the notation represents a function of the single "independent variable" .


title: Variable (mathematics)

text: then "x" is a variable standing for the argument of the function being defined, which can be any real number.


title: Variable (mathematics)

text: the variable "i" is a summation variable which designates in turn each of the integers 1, 2, ..., "n" (it is also called index because its variation is over a discrete set of values) while "n" is a parameter (it does not vary within the formula).


title: Variable (mathematics)

text: In the theory of polynomials, a polynomial of degree 2 is generally denoted as "ax" + "bx" + "c", where "a", "b" and "c" are called coefficients (they are assumed to be fixed, i.e., parameters of the problem considered) while "x" is called a variable. When studying this polynomial for its polynomial function this "x" stands for the function argument. When studying the polynomial as an object in itself, "x" is taken to be an indeterminate, and would often be written with a capital letter instead to indicate this status.


title: Variable (mathematics)

text: This equation would generally be interpreted to have four variables, and one constant. The constant is formula_8, the Boltzmann constant. One of the variables, formula_9, the number of particles, is a positive integer (and therefore a discrete variable), while the other three, formula_10 and formula_11, for pressure, volume and temperature, are continuous variables.


title: Variable (mathematics)

text: Then formula_12, as a function of the other variables, is the dependent variable, while its arguments, formula_15 and formula_11, are independent variables. One could approach this function more formally and think about its domain and range: in function notation, here formula_12 is a function formula_18.


title: Variable (mathematics)

text: However, in an experiment, in order to determine the dependence of pressure on a single one of the independent variables, it is necessary to fix all but one of the variables, say formula_11. This gives a function


title: Variable (mathematics)

text: where now formula_9 and formula_22 are also regarded as constants. Mathematically, this constitutes a partial application of the earlier function formula_12.


title: Variable (mathematics)

text: This illustrates how independent variables and constants are largely dependent on the point of view taken. One could even regard formula_8 as a variable to obtain a function


title: Variable (mathematics)

text: Considering constants and variables can lead to the concept of moduli spaces. For illustration, consider the equation for a parabola,


title: Variable (mathematics)

text: where formula_27 and formula_28 are all considered to be real. The set of points formula_29 in the 2D plane satisfying this equation trace out the graph of a parabola. Here, formula_30 and formula_31 are regarded as constants, which specify the parabola, while formula_32 and formula_28 are variables.


title: Variable (mathematics)

text: Then instead regarding formula_30 and formula_31 as variables, we observe that each set of 3-tuples formula_36 corresponds to a different parabola. That is, they specify coordinates on the 'space of parabolas': this is known as a moduli space of parabolas.


title: Active galactic nucleus

text: An active galactic nucleus (AGN) is a compact region at the center of a galaxy that has a much-higher-than-normal luminosity over at least some portion of the electromagnetic spectrum with characteristics indicating that the luminosity is not produced by stars. Such excess non-stellar emission has been observed in the radio, microwave, infrared, optical, ultra-violet, X-ray and gamma ray wavebands. A galaxy hosting an AGN is called an "active galaxy". The non-stellar radiation from an AGN is theorized to result from the accretion of matter by a supermassive black hole at the center of its host galaxy.


title: Active galactic nucleus

text: Active galactic nuclei are the most luminous persistent sources of electromagnetic radiation in the universe, and as such can be used as a means of discovering distant objects; their evolution as a function of cosmic time also puts constraints on models of the cosmos.


title: Active galactic nucleus

text: The observed characteristics of an AGN depend on several properties such as the mass of the central black hole, the rate of gas accretion onto the black hole, the orientation of the accretion disk, the degree of obscuration of the nucleus by dust, and presence or absence of jets.


title: Active galactic nucleus

text: Numerous subclasses of AGN have been defined based on their observed characteristics; the most powerful AGN are classified as quasars. A blazar is an AGN with a jet pointed toward the Earth, in which radiation from the jet is enhanced by relativistic beaming.


title: Active galactic nucleus

text: During the first half of the 20th century, photographic observations of nearby galaxies detected some characteristic signatures of AGN emission, although there was not yet a physical understanding of the nature of the AGN phenomenon. Some early observations included the first spectroscopic detection of emission lines from the nuclei of NGC 1068 and Messier 81 by Edward Fath (published in 1909), and the discovery of the jet in Messier 87 by Heber Curtis (published in 1918). Further spectroscopic studies by astronomers including Vesto Slipher, Milton Humason, and Nicholas Mayall noted the presence of unusual emission lines in some galaxy nuclei. In 1943, Carl Seyfert published a paper in which he described observations of nearby galaxies having bright nuclei that were sources of unusually broad emission lines. Galaxies observed as part of this study included NGC 1068, NGC 4151, NGC 3516, and NGC 7469. Active galaxies such as these are known as Seyfert galaxies in honor of Seyfert's pioneering work.


title: Active galactic nucleus

text: The development of radio astronomy was a major catalyst to understanding AGN. Some of the earliest detected radio sources are nearby active elliptical galaxies such as Messier 87 and Centaurus A. Another radio source, Cygnus A, was identified by Walter Baade and Rudolph Minkowski as a tidally distorted galaxy with an unusual emission-line spectrum, having a recessional velocity of 16,700 kilometers per second. The 3C radio survey led to further progress in discovery of new radio sources as well as identifying the visible-light sources associated with the radio emission. In photographic images, some of these objects were nearly point-like or quasi-stellar in appearance, and were classified as quasi-stellar radio sources (later abbreviated as "quasars").


title: Active galactic nucleus

text: Soviet Armenian astrophysicist Viktor Ambartsumian introduced Active Galactic Nuclei in the early 1950s. At the Solvay Conference on Physics in 1958, Ambartsumian presented a report arguing that "explosions in galactic nuclei cause large amounts of mass to be expelled. For these explosions to occur, galactic nuclei must contain bodies of huge mass and unknown nature. From this point forward Active Galactic Nuclei (AGN) became a key component in theories of galactic evolution." His idea was initially accepted skeptically.


title: Active galactic nucleus

text: A major breakthrough was the measurement of the redshift of the quasar 3C 273 by Maarten Schmidt, published in 1963. Schmidt noted that if this object was extragalactic (outside the Milky Way, at a cosmological distance) then its large redshift of 0.158 implied that it was the nuclear region of a galaxy about 100 times more powerful than other radio galaxies that had been identified. Shortly afterward, optical spectra were used to measure the redshifts of a growing number of quasars including 3C 48, even more distant at redshift 0.37.


title: Active galactic nucleus

text: The enormous luminosities of these quasars as well as their unusual spectral properties indicated that their power source could not be ordinary stars. Accretion of gas onto a supermassive black hole was suggested as the source of quasars' power in papers by Edwin Salpeter and Yakov Zeldovich in 1964. In 1969 Donald Lynden-Bell proposed that nearby galaxies contain supermassive black holes at their centers as relics of "dead" quasars, and that black hole accretion was the power source for the non-stellar emission in nearby Seyfert galaxies. In the 1960s and 1970s, early X-ray astronomy observations demonstrated that Seyfert galaxies and quasars are powerful sources of X-ray emission, which originates from the inner regions of black hole accretion disks.


title: Active galactic nucleus

text: Today, AGN are a major topic of astrophysical research, both observational and theoretical. AGN research encompasses observational surveys to find AGN over broad ranges of luminosity and redshift, examination of the cosmic evolution and growth of black holes, studies of the physics of black hole accretion and the emission of electromagnetic radiation from AGN, examination of the properties of jets and outflows of matter from AGN, and the impact of black hole accretion and quasar activity on galaxy evolution.


title: Active galactic nucleus

text: For a long time it has been argued that an AGN must be powered by accretion of mass onto massive black holes (10 to 10 times the Solar mass). AGN are both compact and persistently extremely luminous. Accretion can potentially give very efficient conversion of potential and kinetic energy to radiation, and a massive black hole has a high Eddington luminosity, and as a result, it can provide the observed high persistent luminosity. Supermassive black holes are now believed to exist in the centres of most if not all massive galaxies since the mass of the black hole correlates well with the velocity dispersion of the galactic bulge (the M–sigma relation) or with bulge luminosity. Thus AGN-like characteristics are expected whenever a supply of material for accretion comes within the sphere of influence of the central black hole.


title: Active galactic nucleus

text: In the standard model of AGN, cold material close to a black hole forms an accretion disc. Dissipative processes in the accretion disc transport matter inwards and angular momentum outwards, while causing the accretion disc to heat up. The expected spectrum of an accretion disc peaks in the optical-ultraviolet waveband; in addition, a corona of hot material forms above the accretion disc and can inverse-Compton scatter photons up to X-ray energies. The radiation from the accretion disc excites cold atomic material close to the black hole and this in turn radiates at particular emission lines. A large fraction of the AGN's radiation may be obscured by interstellar gas and dust close to the accretion disc, but (in a steady-state situation) this will be re-radiated at some other waveband, most likely the infrared.


title: Active galactic nucleus

text: Some accretion discs produce jets of twin, highly collimated, and fast outflows that emerge in opposite directions from close to the disc. The direction of the jet ejection is determined either by the angular momentum axis of the accretion disc or the spin axis of the black hole. The jet production mechanism and indeed the jet composition on very small scales are not understood at present due to the resolution of astronomical instruments being too low. The jets have their most obvious observational effects in the radio waveband, where very-long-baseline interferometry can be used to study the synchrotron radiation they emit at resolutions of sub-parsec scales. However, they radiate in all wavebands from the radio through to the gamma-ray range via the synchrotron and the inverse-Compton scattering process, and so AGN jets are a second potential source of any observed continuum radiation.


title: Active galactic nucleus

text: There exists a class of "radiatively inefficient" solutions to the equations that govern accretion. Several theories exist, but the most widely known of these is the Advection Dominated Accretion Flow (ADAF). In this type of accretion, which is important for accretion rates well below the Eddington limit, the accreting matter does not form a thin disc and consequently does not efficiently radiate away the energy that it acquired as it moved close to the black hole. Radiatively inefficient accretion has been used to explain the lack of strong AGN-type radiation from massive black holes at the centres of elliptical galaxies in clusters, where otherwise we might expect high accretion rates and correspondingly high luminosities. Radiatively inefficient AGN would be expected to lack many of the characteristic features of standard AGN with an accretion disc.


title: Active galactic nucleus

text: AGN are a candidate source of high and ultra-high energy cosmic rays "(see also Centrifugal mechanism of acceleration)".


title: Active galactic nucleus

text: There is no single observational signature of an AGN. The list below covers some of the features that have allowed systems to be identified as AGN.


title: Active galactic nucleus

text: It is convenient to divide AGN into two classes, conventionally called radio-quiet and radio-loud. Radio-loud objects have emission contributions from both the jet(s) and the lobes that the jets inflate. These emission contributions dominate the luminosity of the AGN at radio wavelengths and possibly at some or all other wavelengths. Radio-quiet objects are simpler since jet and any jet-related emission can be neglected at all wavelengths.


title: Active galactic nucleus

text: AGN terminology is often confusing, since the distinctions between different types of AGN sometimes reflect historical differences in how the objects were discovered or initially classified, rather than real physical differences.


title: Active galactic nucleus

text: See main article Radio galaxy for a discussion of the large-scale behaviour of the jets. Here, only the active nuclei are discussed.


title: Active galactic nucleus

text: Unified models propose that different observational classes of AGN are a single type of physical object observed under different conditions. The currently favoured unified models are 'orientation-based unified models' meaning that they propose that the apparent differences between different types of objects arise simply because of their different orientations to the observer. However, they are debated (see below).


title: Active galactic nucleus

text: At low luminosities, the objects to be unified are Seyfert galaxies. The unification models propose that in Seyfert 1s the observer has a direct view of the active nucleus. In Seyfert 2s the nucleus is observed through an obscuring structure which prevents a direct view of the optical continuum, broad-line region or (soft) X-ray emission. The key insight of orientation-dependent accretion models is that the two types of object can be the same if only certain angles to the line of sight are observed. The standard picture is of a torus of obscuring material surrounding the accretion disc. It must be large enough to obscure the broad-line region but not large enough to obscure the narrow-line region, which is seen in both classes of object. Seyfert 2s are seen through the torus. Outside the torus there is material that can scatter some of the nuclear emission into our line of sight, allowing us to see some optical and X-ray continuum and, in some cases, broad emission lines—which are strongly polarized, showing that they have been scattered and proving that some Seyfert 2s really do contain hidden Seyfert 1s. Infrared observations of the nuclei of Seyfert 2s also support this picture.


title: Active galactic nucleus

text: At higher luminosities, quasars take the place of Seyfert 1s, but, as already mentioned, the corresponding 'quasar 2s' are elusive at present. If they do not have the scattering component of Seyfert 2s they would be hard to detect except through their luminous narrow-line and hard X-ray emission.


title: Active galactic nucleus

text: Historically, work on radio-loud unification has concentrated on high-luminosity radio-loud quasars. These can be unified with narrow-line radio galaxies in a manner directly analogous to the Seyfert 1/2 unification (but without the complication of much in the way of a reflection component: narrow-line radio galaxies show no nuclear optical continuum or reflected X-ray component, although they do occasionally show polarized broad-line emission). The large-scale radio structures of these objects provide compelling evidence that the orientation-based unified models really are true. X-ray evidence, where available, supports the unified picture: radio galaxies show evidence of obscuration from a torus, while quasars do not, although care must be taken since radio-loud objects also have a soft unabsorbed jet-related component, and high resolution is necessary to separate out thermal emission from the sources' large-scale hot-gas environment. At very small angles to the line of sight, relativistic beaming dominates, and we see a blazar of some variety.


title: Active galactic nucleus

text: However, the population of radio galaxies is completely dominated by low-luminosity, low-excitation objects. These do not show strong nuclear emission lines—broad or narrow—they have optical continua which appear to be entirely jet-related, and their X-ray emission is also consistent with coming purely from a jet, with no heavily absorbed nuclear component in general. These objects cannot be unified with quasars, even though they include some high-luminosity objects when looking at radio emission, since the torus can never hide the narrow-line region to the required extent, and since infrared studies show that they have no hidden nuclear component: in fact there is no evidence for a torus in these objects at all. Most likely, they form a separate class in which only jet-related emission is important. At small angles to the line of sight, they will appear as BL Lac objects.


title: Active galactic nucleus

text: In the recent literature on AGN, being subject to an intense debate, an increasing set of observations appear to be in conflict with some of the key predictions of the Unified Model, e.g. that each Seyfert 2 has an obscured Seyfert 1 nucleus (a hidden broad-line region).


title: Active galactic nucleus

text: Therefore, one cannot know whether the gas in all Seyfert 2 galaxies is ionized due to photoionization from a single, non-stellar continuum source in the center or due to shock-ionization from e.g. intense, nuclear starbursts. Spectropolarimetric studies reveal that only 50% of Seyfert 2s show a hidden broad-line region and thus split Seyfert 2 galaxies into two populations. The two classes of populations appear to differ by their luminosity, where the Seyfert 2s without a hidden broad-line region are generally less luminous. This suggests absence of broad-line region is connected to low Eddington ratio, and not to obscuration.


title: Active galactic nucleus

text: The covering factor of the torus might play an important role. Some torus models predict how Seyfert 1s and Seyfert 2s can obtain different covering factors from a luminosity- and accretion rate- dependence of the torus covering factor, something supported by studies in the x-ray of AGN. The models also suggest an accretion-rate dependence of the broad-line region and provide a natural evolution from more active engines in Seyfert 1s to more “dead” Seyfert 2s and can explain the observed break-down of the unified model at low luminosities and the evolution of the broad-line region.


title: Active galactic nucleus

text: While studies of single AGN show important deviations from the expectations of the unified model, results from statistical tests have been contradictory. The most important short-coming of statistical tests by direct comparisons of statistical samples of Seyfert 1s and Seyfert 2s is the introduction of selection biases due to anisotropic selection criteria.


title: Active galactic nucleus

text: Studying neighbour galaxies rather than the AGN themselves first suggested the numbers of neighbours were larger for Seyfert 2s than for Seyfert 1s, in contradiction with the Unified Model. Today, having overcome the previous limitations of small sample sizes and anisotropic selection, studies of neighbours of hundreds to thousands of AGN have shown that the neighbours of Seyfert 2s are intrinsically dustier and more star-forming than Seyfert 1s and a connection between AGN type, host galaxy morphology and collision history. Moreover, angular clustering studies of the two AGN types confirm that they reside in different environments and show that they reside within dark matter halos of different masses. The AGN environment studies are in line with evolution-based unification models where Seyfert 2s transform into Seyfert 1s during merger, supporting earlier models of merger-driven activation of Seyfert 1 nuclei.


title: Active galactic nucleus

text: While controversy about the soundness of each individual study still prevails, they all agree on that the simplest viewing-angle based models of AGN Unification are incomplete. Seyfert-1 and Seyfert-2 seem to differ in star formation and AGN engine power.


title: Active galactic nucleus

text: While it still might be valid that an obscured Seyfert 1 can appear as a Seyfert 2, not all Seyfert 2s must host an obscured Seyfert 1. Understanding whether it is the same engine driving all Seyfert 2s, the connection to radio-loud AGN, the mechanisms of the variability of some AGN that vary between the two types at very short time scales, and the connection of the AGN type to small- and large-scale environment remain important issues to incorporate into any unified model of active galactic nuclei.


title: Active galactic nucleus

text: For a long time, active galaxies held all the records for the highest-redshift objects known either in the optical or the radio spectrum, because of their high luminosity. They still have a role to play in studies of the early universe, but it is now recognised that an AGN gives a highly biased picture of the "typical" high-redshift galaxy.


title: Active galactic nucleus

text: Most luminous classes of AGN (radio-loud and radio-quiet) seem to have been much more numerous in the early universe. This suggests that massive black holes formed early on and that the conditions for the formation of luminous AGN were more common in the early universe, such as a much higher availability of cold gas near the centre of galaxies than at present. It also implies that many objects that were once luminous quasars are now much less luminous, or entirely quiescent. The evolution of the low-luminosity AGN population is much less well understood due to the difficulty of observing these objects at high redshifts.