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$100 hamburger ("hundred-dollar hamburger") is aviation slang for the excuse a general aviation pilot might use to fly.

John von Neumann's universal constructor is a self-replicating machine in a cellular automata (CA) environment. It was designed in the 1940s, without the use of a computer. The fundamental details of the machine were published in von Neumann's book Theory of Self-Reproducing Automata, completed in 1966 by Arthur W. Burks after von Neumann's death.

Von Neumann's goal was to specify an abstract machine which, when run, would replicate itself. In his design, the machine consists of three parts: a 'blueprint' for itself, a mechanism that can read any blueprint and construct the machine (sans blueprint) specified by that blueprint, and a 'copy machine' that can make copies of any blueprint. After the mechanism has been used to construct the machine specified by the blueprint, the copy machine is used to create a copy of that blueprint, and this copy is placed into the new machine, resulting in a working replication of the original machine. Some machines will do this backwards, copying the blueprint and then building a machine.

To define his machine in more detail, von Neumann invented the concept of a cellular automaton. The one he used consists of a two-dimensional grid of cells, each of which can be in one of 29 states at any point in time. At each timestep, each cell updates its state depending on the states of the surrounding cells at the prior timestep. The rules governing these updates are identical for all cells.

The universal constructor is a certain pattern of cell states in this cellular automaton. It contains one line of cells that serve as a 'tape', encoding a sequence of instructions that serve as a 'blueprint' for the machine. The machine reads these instructions one by one and performs the corresponding actions. The instructions direct the machine to use its 'construction arm' to build a copy of the machine, without tape, at some other location in the cell grid. The tape can't contain instructions to build an equally long tape, just as a container can't contain a container of the same size. Therefore, the machine contains a separate 'copy machine' which reads the tape and places a copy into the newly constructed machine. The resulting new machine and tape is identical to the old one, and it proceeds to replicate again.

The Cybernetic Culture Research Unit (CCRU) was an experimental cultural theorist collective formed in late 1995 at Warwick University, England and gradually separated from academia until it dissolved in 2003. It garnered reputation for its idiosyncratic and surreal "theory-fiction" which incorporated cyberpunk and Gothic horror, and its work has since had an online cult following related to the rise in popularity of accelerationism. Warwick University maintains that the CCRU was never a sanctioned academic project, with some faculty going so far as to assert that the CCRU "has never existed". The CCRU are strongly associated with their former leading members, Sadie Plant, Mark Fisher and Nick Land.

The blue field entoptic phenomenon is an entoptic phenomenon characterized by the appearance of tiny bright dots (nicknamed blue-sky sprites) moving quickly along undulating pathways in the visual field, especially when looking into bright blue light such as the sky. The dots are short-lived, visible for about one second or less, and traveling short distances along seemingly random, undulating paths. Some of them seem to follow the same path as other dots before them. The dots may appear elongated along the path, like tiny worms. The dots' rate of travel appears to vary in synchrony with the heartbeat: they briefly accelerate at each beat. The dots appear in the central field of view, within 15 degrees from the fixation point. The left and right eye see different, seemingly random, dot patterns; a person viewing through both eyes sees a combination of both left and right visual field disturbances. While seeing the phenomenon, lightly pressing inward on the sides of the eyeballs at the lateral canthus causes the movement to stop being fluid and the dots to move only when the heart beats.

Most people are able to see this phenomenon in the sky, although it is relatively weak in most instances; many will not notice it until asked to pay attention. The dots are highly conspicuous against any monochromatic blue background of a wavelength of around 430 nm in place of the sky. The phenomenon is also known as Scheerer's phenomenon, after the German ophthalmologist Richard Scheerer, who first drew clinical attention to it in 1924.

An emirp (prime spelled backwards) is a prime number that results in a different prime when its decimal digits are reversed. This definition excludes the related palindromic primes. The term reversible prime is used to mean the same as emirp, but may also, ambiguously, include the palindromic primes.

The sequence of emirps begins 13, 17, 31, 37, 71, 73, 79, 97, 107, 113, 149, 157, 167, 179, 199, 311, 337, 347, 359, 389, 701, 709, 733, 739, 743, 751, 761, 769, 907, 937, 941, 953, 967, 971, 983, 991, ... (sequence A006567 in the OEIS).

All non-palindromic permutable primes are emirps.

As of November 2009, the largest known emirp is 10¹⁰⁰⁰⁶+941992101×10⁴⁹⁹⁹+1, found by Jens Kruse Andersen in October 2007.

The term 'emirpimes' (singular) is used also in places to treat semiprimes in a similar way. That is, an emirpimes is a semiprime that is also a (distinct) semiprime upon reversing its digits.

The world's most livable cities is an informal name given to any list of cities as they rank on an annual survey of living conditions. In addition to providing clean water, clean air, adequate food and shelter, a ‘livable’ city must also generate a sense of community and offer hospitable settings for all, especially young people, to develop social skills, a sense of autonomy and identity.

Regions with cities commonly ranked in the top 50 include Australia, New Zealand, Canada and Europe. Three examples of such surveys are Monocle's "Most Liveable Cities Index", the Economist Intelligence Unit's "Global Liveability Ranking", and "Mercer Quality of Living Survey". Numbeo has the largest statistics and survey data based on cities and countries. Deutsche Bank's Liveability Survey is another ranking of cities by quality of life.

Pentaborane(9) is an inorganic compound with the formula B₅H₉. It is one of the most common boron hydride clusters, although it is a highly reactive compound. Because of its high reactivity with oxygen, it was once evaluated as rocket or jet fuel. Like many of the smaller boron hydrides, pentaborane is colourless, diamagnetic, and volatile. It is related to pentaborane(11) (B₅H₁₁).

The Tulsa race massacre (also called the Tulsa race riot, the Greenwood Massacre, or the Black Wall Street Massacre) of 1921 took place on May 31 and June 1, 1921, when mobs of white residents attacked black residents and businesses of the Greenwood District in Tulsa, Oklahoma. It has been called "the single worst incident of racial violence in American history." The attack, carried out on the ground and from private aircraft, destroyed more than 35 square blocks of the district – at that time the wealthiest black community in the United States, known as "Black Wall Street".

More than 800 people were admitted to hospitals and as many as 6,000 black residents were interned at large facilities, many for several days. The Oklahoma Bureau of Vital Statistics officially recorded 36 dead, but the American Red Cross declined to provide an estimate. A 2001 state commission examination of events was able to confirm 39 dead, 26 black and 13 white, based on contemporary autopsy reports, death certificates and other records. The commission gave overall estimates from 75–100 to 150–300 dead.

The massacre began over Memorial Day weekend after 19-year-old Dick Rowland, a black shoeshiner, was accused of assaulting Sarah Page, the 17-year-old white elevator operator of the nearby Drexel Building. He was taken into custody. A subsequent gathering of angry local whites outside the courthouse where Rowland was being held, and the spread of rumors he had been lynched, alarmed the local black population, some of whom arrived at the courthouse armed. Shots were fired and twelve people were killed: ten white and two black. As news of these deaths spread throughout the city, mob violence exploded. White rioters rampaged through the black neighborhood that night and morning killing men and burning and looting stores and homes, and only around noon the next day Oklahoma National Guard troops managed to get control of the situation by declaring martial law. About 10,000 black people were left homeless, and property damage amounted to more than $1.5 million in real estate and $750,000 in personal property (equivalent to $32.25 million in 2019).

Many survivors left Tulsa. Black and white residents who stayed in the city were silent for decades about the terror, violence, and losses of this event. The massacre was largely omitted from local, state, and national histories.

In 1996, seventy-five years after the massacre, a bipartisan group in the state legislature authorized formation of the Oklahoma Commission to Study the Tulsa Race Riot of 1921 (renamed Oklahoma Commission to Study the Tulsa Race Massacre, in November 2018). Members were appointed to investigate events, interview survivors, hear testimony from the public, and prepare a report of events. There was an effort toward public education about these events through the process. The Commission's final report, published in 2001, said that the city had conspired with the mob of white citizens against black citizens; it recommended a program of reparations to survivors and their descendants. The state passed legislation to establish some scholarships for descendants of survivors, encourage economic development of Greenwood, and develop a memorial park in Tulsa to the massacre victims. The park was dedicated in 2010. In 2020, the massacre became part of the Oklahoma school curriculum.

A payphone (alternative spelling: pay phone) is typically a coin-operated public telephone, often located in a telephone booth or in high-traffic outdoor areas, with pre-payment by inserting money (usually coins) or by billing a credit or debit card, or a telephone card. Prepaid calling cards also facilitate establishing a call by first calling the provided toll-free telephone number, entering the card account number and PIN, then the desired telephone number. An equipment usage fee may be charged as additional units, minutes or tariff fee to the collect/third-party, debit, credit, telephone or prepaid calling card when used at payphones. By agreement with the landlord, either the phone company pays rent for the location and keeps the revenue, or the landlord pays rent for the phone and shares the revenue.

Payphones are often found in public places to contribute to the notion of universal access to basic communication services. One thesis, written as early as 2003, recognised this as a digital divide problem.

In the 20th century, payphones in some countries, such as Spain, used token coins, available for sale at a local retailer, to activate pay phones, instead of legal tender coins. In some cases, these were upgraded to use magnetic cards or credit card readers over the years.

In the past, payphones were ubiquitous worldwide, but their prevalence has decreased significantly over the years due to the increasing availability of mobile phones, even though cell phone service is not always available in emergencies.

Mummy brown, also known as Egyptian brown or Caput Mortuum,^: 254 is a rich brown bituminous pigment with good transparency, sitting between burnt umber and raw umber in tint. The pigment was made from the flesh of mummies mixed with white pitch and myrrh. Mummy brown was extremely popular from the mid-eighteenth to the nineteenth centuries. However, fresh supplies of mummies diminished, and artists were less satisfied with the pigment's permanency and finish. By 1915, demand had significantly declined. Suppliers ceased to offer it by the middle of the twentieth century.^: 82

Mummy brown was one of the favourite colours of the Pre-Raphaelites. It was used by many artists, including Eugene Delacroix, William Beechey, Edward Burne-Jones, Lawrence Alma-Tadema, and Martin Drolling.