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In mathematics, a combinatorial explosion is the rapid growth of the complexity of a problem due to how the combinatorics of the problem is affected by the input, constraints, and bounds of the problem. Combinatorial explosion is sometimes used to justify the intractability of certain problems. Examples of such problems include certain mathematical functions, the analysis of some puzzles and games, and some pathological examples which can be modelled as the Ackermann function.

Ark II is an American live-action science fiction television series, aimed at children, that aired on CBS from September 11 to December 18, 1976 (with reruns continuing through November 13, 1977) as part of its weekend line-up. It returned again in rerun from September 16, 1978 through August 25, 1979. Only 15 half-hour episodes were ever produced. The program's central characters were created by Martin Roth; Ted Post helped Roth develop its core format.

Janet, sometimes called Janet Airlines, is the unofficial name given to a highly classified fleet of passenger aircraft operated for the United States Department of the Air Force as an employee shuttle to transport military and contractor employees. The purpose is to pick up the employees at their home airport, and take them to their place of work. Then, in the afternoon, they take the employees back to their home airports. The airline mainly serves the Nevada National Security Site (most notably Area 51 and the Tonopah Test Range), from a private terminal at Las Vegas's McCarran International Airport.

The airline's aircraft are generally unmarked, but do have a red paint strip along the windows of the aircraft, which gives some sort of hint at Janet being the operator.

The computus (Latin for 'computation') is a calculation that determines the calendar date of Easter. Easter is traditionally celebrated on the first Sunday after the Paschal full moon, which is the first full moon on or after 21 March (an approximation of the March equinox). Determining this date in advance requires a correlation between the lunar months and the solar year, while also accounting for the month, date, and weekday of the calendar. The calculations produce different results depending on whether the Julian calendar or the Gregorian calendar is used.

In late antiquity, it was feasible for the entire Christian church to receive the date of Easter each year through an annual announcement from the Pope. By the early third century, however, communications had deteriorated to the point that the church put great value in a system that would allow the clergy to independently and consistently determine the date for themselves. Additionally, the church wished to eliminate dependencies on the Hebrew calendar, by deriving Easter directly from the vernal equinox.

In The Reckoning of Time (725), Bede uses computus as a general term for any sort of calculation, although he refers to the Easter cycles of Theophilus as a "Paschal computus." By the end of the 8th century, computus came to refer specifically to the calculation of time.

Utility fog (coined by Dr. John Storrs Hall in 1989) is a hypothetical collection of tiny robots that can replicate a physical structure. As such, it is a form of self-reconfiguring modular robotics.

The Lion-Eating Poet in the Stone Den (Chinese: 施氏食獅史; pinyin: Shī-shì shí shī shǐ) is a short narrative poem written in Classical Chinese that is composed of 92 characters in which every word is pronounced shi ([ʂɻ̩]) when read in present-day Standard Mandarin, with only the tones differing.

The poem was written in the 1930s by the Chinese linguist Yuen Ren Chao as a linguistic demonstration. The poem is coherent and grammatical in Classical Chinese, but the loss of older sound combinations in Chinese over the centuries has greatly increased the number of Chinese homophones, making Classical Chinese difficult to understand in oral speech. In Mandarin, the poem is incomprehensible when read aloud, since only four syllables cover the entire 92 words of the poem. The poem is less incomprehensible—but still not very intelligible—when read in other varieties of Chinese such as Cantonese, in which it has 22 different syllables, or Hokkien Chinese, in which it has 15 different syllables.

The poem is an example of a one-syllable article, a form of constrained writing possible in tonal languages such as Mandarin Chinese, where tonal contours expand the range of meaning for a single syllable.

Extreme learning machines are feedforward neural networks for classification, regression, clustering, sparse approximation, compression and feature learning with a single layer or multiple layers of hidden nodes, where the parameters of hidden nodes (not just the weights connecting inputs to hidden nodes) need not be tuned. These hidden nodes can be randomly assigned and never updated (i.e. they are random projection but with nonlinear transforms), or can be inherited from their ancestors without being changed. In most cases, the output weights of hidden nodes are usually learned in a single step, which essentially amounts to learning a linear model. The name "extreme learning machine" (ELM) was given to such models by its main inventor Guang-Bin Huang.

According to their creators, these models are able to produce good generalization performance and learn thousands of times faster than networks trained using backpropagation. In literature, it also shows that these models can outperform support vector machines (SVM) and SVM provides suboptimal solutions in both classification and regression applications.

Wake therapy is a form of sleep deprivation used as a treatment for depression. The subject stays awake all night, or is woken at 1AM and stays awake all morning, and the next full day. While sleepy, patients find that their depression vanishes, until they sleep again. Combining this with bright light therapy make the beneficial effects last longer than one day. Partial sleep deprivation in the second half of the night may be as effective as an all-night sleep deprivation session.

Wake therapy is a therapy that falls under chronotherapeutics. Chronotherapy (treatment scheduling) is a process to manipulate biological rhythms and sleep that can help to improve affective disorders quickly.

Wake therapy is beneficial for those experiencing major depression along with unipolar, bipolar, and melancholic types of depression. Wake therapy is best used to jump start the effects of the use of an antidepressant. Wake therapy is the use of prolonged times of wakefulness, along with periods of recovering sleep. It is a fast way to improve symptoms of depression. This therapy is best used with other chronotherapeutic techniques. Months of use of this therapy and other therapies can be quite effective to help prevent relapse of depression.

Polybius is an urban legend that emerged in early 2000. It has served as inspiration for several free and commercial games by the same name.

The legend describes the game as part of a government-run crowdsourced psychology experiment based in Portland, Oregon, during 1981. Gameplay supposedly produced intense psychoactive and addictive effects in the player. These few publicly staged arcade machines were said to have been visited periodically by men in black for the purpose of data-mining the machines and analyzing these effects. Eventually, all of these Polybius arcade machines allegedly disappeared from the arcade market.

Polybius is also the name of a Greek historian born in Arcadia, who was, coincidentally, known for his assertion that historians should never report what they cannot verify through interviews with witnesses.

Anthony Peter "Tony" Buzan (; 2 June 1942 – 13 April 2019) was an English author and educational consultant.

Buzan popularised the idea of mental literacy, radiant thinking, and a technique called mind mapping, inspired by techniques used by Leonardo da Vinci, Albert Einstein, and Joseph D. Novak's "concept mapping" techniques.