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🔗 Time 🔗 Christianity

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.

🔗 China

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.

🔗 Statistics

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.

🔗 Medicine

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.

🔗 Video games

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.

🔗 Australia 🔗 Military history 🔗 Military history/North American military history 🔗 Military history/United States military history 🔗 Military history/Intelligence 🔗 Australia/Australia, New Zealand and South Pacific military history 🔗 Military history/Australia, New Zealand and South Pacific military history 🔗 Australia/Northern Territory

Pine Gap is the commonly used name for a US satellite surveillance base and Australian Earth station approximately 18 kilometres (11 mi) south-west of the town of Alice Springs, Northern Territory in the centre of Australia which is jointly operated by Australia and the United States. Since 1988, it has been officially called the Joint Defence Facility Pine Gap (JDFPG); previously, it was misleadingly known as Joint Defence Space Research Facility.

The station is partly run by the US Central Intelligence Agency (CIA), US National Security Agency (NSA), and US National Reconnaissance Office (NRO) and is a key contributor to the NSA's global interception effort, which included the ECHELON program. The classified NRO name of the Pine Gap base is Australian Mission Ground Station (AMGS), while the unclassified cover term for the NSA function of the facility is RAINFALL.

🔗 Mathematics 🔗 Geography

The haversine formula determines the great-circle distance between two points on a sphere given their longitudes and latitudes. Important in navigation, it is a special case of a more general formula in spherical trigonometry, the law of haversines, that relates the sides and angles of spherical triangles.

The first table of haversines in English was published by James Andrew in 1805, but Florian Cajori credits an earlier use by José de Mendoza y Ríos in 1801. The term haversine was coined in 1835 by James Inman.

These names follow from the fact that they are customarily written in terms of the haversine function, given by hav(θ) = sin²(θ/2). The formulas could equally be written in terms of any multiple of the haversine, such as the older versine function (twice the haversine). Prior to the advent of computers, the elimination of division and multiplication by factors of two proved convenient enough that tables of haversine values and logarithms were included in nineteenth and early twentieth century navigation and trigonometric texts. These days, the haversine form is also convenient in that it has no coefficient in front of the sin² function.

🔗 United States 🔗 Biography 🔗 Biography/science and academia 🔗 United States/Ohio 🔗 University of California

Elwyn Ralph Berlekamp (September 6, 1940 – April 9, 2019) was an American mathematician known for his work in computer science, coding theory and combinatorial game theory. He was a professor emeritus of mathematics and EECS at the University of California, Berkeley.

Berlekamp was the inventor of an algorithm to factor polynomials, and was one of the inventors of the Berlekamp–Welch algorithm and the Berlekamp–Massey algorithms, which are used to implement Reed–Solomon error correction.

Berlekamp had also been active in money management. In 1986, he began information-theoretic studies of commodity and financial futures.

🔗 Mathematics

In mathematics, the seven-dimensional cross product is a bilinear operation on vectors in seven-dimensional Euclidean space. It assigns to any two vectors a, b in R⁷ a vector a × b also in R⁷. Like the cross product in three dimensions, the seven-dimensional product is anticommutative and a × b is orthogonal both to a and to b. Unlike in three dimensions, it does not satisfy the Jacobi identity, and while the three-dimensional cross product is unique up to a sign, there are many seven-dimensional cross products. The seven-dimensional cross product has the same relationship to the octonions as the three-dimensional product does to the quaternions.

The seven-dimensional cross product is one way of generalising the cross product to other than three dimensions, and it is the only other bilinear product of two vectors that is vector-valued, orthogonal, and has the same magnitude as in the 3D case. In other dimensions there are vector-valued products of three or more vectors that satisfy these conditions, and binary products with bivector results.

🔗 Politics of the United Kingdom 🔗 Scotland 🔗 Central America

The Darien scheme was an unsuccessful attempt at establishing a Scottish colony on the Isthmus of Panama on the Gulf of Darién in the late 1690s. The aim was for the colony to have an overland route that connected the Pacific and Atlantic oceans. From its contemporary time to the present day, claims have been made that the undertaking was beset by poor planning and provisioning, divided leadership, a lack of demand for trade goods particularly caused by an English trade blockade, devastating epidemics of disease, collusion between the English East India Company and the English government to frustrate it, and a failure to anticipate the Spanish Empire's military response. It was finally abandoned in March 1700 after a siege by Spanish forces, which also blockaded the harbour.

As the Company of Scotland was backed by approximately 20% of all the money circulating in Scotland, its failure left the entire Lowlands in substantial financial ruin and was an important factor in weakening their resistance to the Act of Union (completed in 1707). The land where the Darien colony was built, in the modern province of Guna Yala, is virtually uninhabited today.