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🔗 Biography 🔗 Aviation 🔗 Soviet Union 🔗 Russia 🔗 Russia/technology and engineering in Russia 🔗 Spaceflight 🔗 Military history 🔗 Military history/Military aviation 🔗 Biography/science and academia 🔗 Military history/Military biography 🔗 Biography/military biography 🔗 Aviation/aerospace biography 🔗 Military history/Cold War 🔗 Biography/sports and games 🔗 Russia/Russian, Soviet, and CIS military history 🔗 Military history/Russian, Soviet and CIS military history 🔗 Russia/history of Russia

Yuri Alekseyevich Gagarin  (9 March 1934 – 27 March 1968) was a Soviet Air Forces pilot and cosmonaut who became the first human to journey into outer space, achieving a major milestone in the Space Race; his capsule Vostok 1 completed one orbit of Earth on 12 April 1961. Gagarin became an international celebrity and was awarded many medals and titles, including Hero of the Soviet Union, his nation's highest honour.

Born in the village of Klushino near Gzhatsk (a town later renamed after him), in his youth Gagarin was a foundryman at a steel plant in Lyubertsy. He later joined the Soviet Air Forces as a pilot and was stationed at the Luostari Air Base, near the Norwegian border, before his selection for the Soviet space programme with five other cosmonauts. Following his spaceflight, Gagarin became deputy training director of the Cosmonaut Training Centre, which was later named after him. He was also elected as a deputy of the Soviet of the Union in 1962 and then to the Soviet of Nationalities, respectively the lower and upper chambers of the Supreme Soviet.

Vostok 1 was Gagarin's only spaceflight but he served as the backup crew to the Soyuz 1 mission, which ended in a fatal crash, killing his friend and fellow cosmonaut Vladimir Komarov. Fearing for his life, Soviet officials permanently banned Gagarin from further spaceflights. After completing training at the Zhukovsky Air Force Engineering Academy on 17 February 1968, he was allowed to fly regular aircraft. Gagarin died five weeks later when the MiG-15 training jet he was piloting with his flight instructor Vladimir Seryogin crashed near the town of Kirzhach.

🔗 Mathematics

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.

🔗 Toys

A pantograph (Greek roots παντ- "all, every" and γραφ- "to write", from their original use for copying writing) is a mechanical linkage connected in a manner based on parallelograms so that the movement of one pen, in tracing an image, produces identical movements in a second pen. If a line drawing is traced by the first point, an identical, enlarged, or miniaturized copy will be drawn by a pen fixed to the other. Using the same principle, different kinds of pantographs are used for other forms of duplication in areas such as sculpture, minting, engraving, and milling.

Because of the shape of the original device, a pantograph also refers to a kind of structure that can compress or extend like an accordion, forming a characteristic rhomboidal pattern. This can be found in extension arms for wall-mounted mirrors, temporary fences, scissor lifts, and other scissor mechanisms such as the pantograph used on electric locomotives and trams.

🔗 Computing

The Olivetti Programma 101, also known as Perottina or P101, is one of the first "all in one" commercial programmable desktop calculators, although not the first. Produced by Italian manufacturer Olivetti, based in Ivrea, Piedmont, and invented by the Italian engineer Pier Giorgio Perotto, the P101 has the main features of large computers of that period. It was launched at the 1964 New York World's Fair; volume production started in 1965. A futuristic design for its time, the Programma 101 was priced at $3,200 (equivalent to $26,000 in 2019). About 44,000 units were sold, primarily in the US.

It is usually called a printing programmable calculator or desktop calculator because its arithmetic instructions correspond to calculator operations.

🔗 Archaeology 🔗 Museums 🔗 Merseyside

The Williamson Tunnels are a series of extensive subterranean excavations, of unknown purpose, in the Edge Hill area of Liverpool, England. They are thought to have been created under the direction of tobacco merchant, landowner and philanthropist Joseph Williamson between 1810 and 1840. Although popularly described as "tunnels", the majority comprise brick or stone vaulting over excavations in the underlying sandstone. The purpose of the works remains unclear and remains a subject of heavy speculation; suggestions include commercial quarrying, a philanthropic desire to provide employment, and Williamson's own eccentric interests.

After being gradually infilled with rubble and spoil during the late 19th and early 20th centuries, they remained largely inaccessible until archaeological investigations were carried out in 1995. Since then volunteers have rediscovered and excavated an extensive network of tunnels, chambers and voids across several sites, with sections open to the public. Guided tours are available at the Williamson Tunnels Heritage Centre and the Friends Of Williamson's Tunnels, and excavation continues as volunteers continue to uncover new sections.

🔗 Mathematics 🔗 Statistics

In statistics, the 68–95–99.7 rule, also known as the empirical rule, is a shorthand used to remember the percentage of values that lie within an interval estimate in a normal distribution: 68%, 95%, and 99.7% of the values lie within one, two, and three standard deviations of the mean, respectively.

In mathematical notation, these facts can be expressed as follows, where Pr() is the probability function, Χ is an observation from a normally distributed random variable, μ (mu) is the mean of the distribution, and σ (sigma) is its standard deviation:

${\displaystyle {\begin{aligned}\Pr(\mu -1\sigma \leq X\leq \mu +1\sigma )&\approx 68.27\%\\\Pr(\mu -2\sigma \leq X\leq \mu +2\sigma )&\approx 95.45\%\\\Pr(\mu -3\sigma \leq X\leq \mu +3\sigma )&\approx 99.73\%\end{aligned}}}$

The usefulness of this heuristic especially depends on the question under consideration.

In the empirical sciences, the so-called three-sigma rule of thumb (or 3σ rule) expresses a conventional heuristic that nearly all values are taken to lie within three standard deviations of the mean, and thus it is empirically useful to treat 99.7% probability as near certainty.

In the social sciences, a result may be considered "significant" if its confidence level is of the order of a two-sigma effect (95%), while in particle physics, there is a convention of a five-sigma effect (99.99994% confidence) being required to qualify as a discovery.

A weaker three-sigma rule can be derived from Chebyshev's inequality, stating that even for non-normally distributed variables, at least 88.8% of cases should fall within properly calculated three-sigma intervals. For unimodal distributions, the probability of being within the interval is at least 95% by the Vysochanskij–Petunin inequality. There may be certain assumptions for a distribution that force this probability to be at least 98%.

🔗 Philosophy 🔗 Philosophy/Philosophy of religion

The self-referencing doomsday argument rebuttal is an attempt to refute the doomsday argument (that there is a credible link between the brevity of the human race's existence and its expected extinction) by applying the same reasoning to the lifetime of the doomsday argument itself.

The first researchers to write about this were P. T. Landsberg and J. N. Dewynne in 1997; they applied belief in the doomsday argument to itself, and claimed that a paradox results.

🔗 Birds

Wrens are a family, Troglodytidae, of small brown passerine birds. The family includes 96 species and is divided into 19 genera. All species are restricted to the New World except for the Eurasian wren that is widely distributed in the Old World. In Anglophone regions, the Eurasian wren is commonly known simply as the "wren", as it is the originator of the name. The name wren has been applied to other, unrelated birds, particularly the New Zealand wrens (Acanthisittidae) and the Australian wrens (Maluridae).

Most wrens are visually inconspicuous though they have loud and often complex songs. Exceptions include the relatively large members of the genus Campylorhynchus, which can be quite bold in their behaviour. Wrens have short wings that are barred in most species, and they often hold their tails upright. Wrens are primarily insectivorous, eating insects, spiders and other small invertebrates, but many species also eat vegetable matter and some eat small frogs and lizards.

🔗 Medicine 🔗 Biology

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.

🔗 Horse racing

Potoooooooo or variations of Pot-8-Os (1773 – November 1800) was an 18th-century thoroughbred racehorse who won over 30 races and defeated some of the greatest racehorses of the time. He went on to be a sire. He is now best known for the unusual spelling of his name, pronounced 'Potatoes'.