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🔗 Mathematics

In number theory, a formula for primes is a formula generating the prime numbers, exactly and without exception. No such formula which is efficiently computable is known. A number of constraints are known, showing what such a "formula" can and cannot be.

🔗 Aviation 🔗 Military history 🔗 Military history/Military aviation 🔗 Aviation/Aviation accident 🔗 Wiltshire 🔗 Military history/European military history 🔗 Military history/British military history

On 22 July 1966 Walter "Taffy" Holden, an engineer in command of No. 33 Maintenance Unit RAF with limited experience flying small single-engine trainer aircraft, inadvertently engaged the afterburner of a Mach 2.0-capable English Electric Lightning during ground testing. Unable to disengage the afterburner, Holden ran down the runway, narrowly missing a crossing fuel bowser and a de Havilland Comet taking off, before taking off himself. Flying without a helmet or canopy, the ejection seat disabled, and the landing gear locked down, Holden aborted his first two landing attempts. He landed on his third approach, striking the runway with the aircraft's tail as he adopted in his flare the attitude of a taildragger aircraft. The aircraft returned to service, and was subsequently acquired by the Imperial War Museum Duxford.

🔗 Medicine 🔗 Medicine/Ophthalmology

The Purkinje effect or Purkinje phenomenon (Czech: [ˈpurkɪɲɛ] (listen); sometimes called the Purkinje shift, often incorrectly pronounced ) is the tendency for the peak luminance sensitivity of the eye to shift toward the blue end of the color spectrum at low illumination levels as part of dark adaptation. In consequence, reds will appear darker relative to other colors as light levels decrease. The effect is named after the Czech anatomist Jan Evangelista Purkyně. While the effect is often described from the perspective of the human eye, it is well established in a number of animals under the same name to describe the general shifting of spectral sensitivity due to pooling of rod and cone output signals as a part of dark/light adaptation.

This effect introduces a difference in color contrast under different levels of illumination. For instance, in bright sunlight, geranium flowers appear bright red against the dull green of their leaves, or adjacent blue flowers, but in the same scene viewed at dusk, the contrast is reversed, with the red petals appearing a dark red or black, and the leaves and blue petals appearing relatively bright.

The sensitivity to light in scotopic vision varies with wavelength, though the perception is essentially black-and-white. The Purkinje shift is the relation between the absorption maximum of rhodopsin, reaching a maximum at about 500 nanometres (2.0×10⁻⁵ in), and that of the opsins in the longer-wavelength cones that dominate in photopic vision, about 555 nanometres (2.19×10⁻⁵ in) (green).

In visual astronomy, the Purkinje shift can affect visual estimates of variable stars when using comparison stars of different colors, especially if one of the stars is red.

🔗 France 🔗 Military history 🔗 Military history/Military science, technology, and theory 🔗 Military history/Weaponry 🔗 Military history/World War I 🔗 Military history/French military history 🔗 Military history/Military land vehicles 🔗 Military history/European military history

The Boirault machine (French: Appareil Boirault), was an early French experimental landship, designed in 1914 and built in early 1915. It has been considered as "another interesting ancestor of the tank", and described as a "rhomboid-shaped skeleton tank without armour, with single overhead track". Ultimately, the machine was deemed impractical and was nicknamed Diplodocus militaris. It preceded the design and development of the English Little Willie tank by six months.

🔗 Mexico 🔗 Archaeology 🔗 Mesoamerica

The Great Pyramid of Cholula, also known as Tlachihualtepetl (Nahuatl for "made-by-hand mountain"), is a complex located in Cholula, Puebla, Mexico. It is the largest archaeological site of a pyramid (temple) in the New World, as well as the largest pyramid by volume known to exist in the world today. The adobe brick pyramid stands 25 metres (82 ft) above the surrounding plain, which is significantly shorter than the Great Pyramid of Giza's height of 146.6 metres (481 ft), but much wider, measuring 300 by 315 metres (984 by 1,033 ft) in its final form, compared to the Great Pyramid's base dimensions of 230.3 by 230.3 metres (756 by 756 ft). The pyramid is a temple that traditionally has been viewed as having been dedicated to the god Quetzalcoatl. The architectural style of the building was linked closely to that of Teotihuacan in the Valley of Mexico, although influence from the Gulf Coast is evident as well, especially from El Tajín.

🔗 Computing 🔗 Bulgaria

Pravetz (Правец in the original Cyrillic, series 8 and series 16) were Bulgarian computers, manufactured mainly in the town of Pravetz. Some components and software were produced in Stara Zagora, Plovdiv, and other Bulgarian cities.

🔗 Brands 🔗 Automobiles

The Isetta is an Italian-designed microcar built under license in a number of different countries, including Argentina, Spain, Belgium, France, Brazil, Germany, and the United Kingdom. Because of its egg shape and bubble-like windows, it became known as a bubble car, a name also given to other similar vehicles.

In 1955, the BMW Isetta became the world's first mass-production car to achieve a fuel consumption of 3 L/100 km (94 mpg_‑imp; 78 mpg_‑US). It was the top-selling single-cylinder car in the world, with 161,728 units sold.

Initially manufactured by the Italian firm Iso SpA, the name Isetta is the Italian diminutive form of Iso, meaning "little Iso".

🔗 Occupational Safety and Health

ISO 7010 is an International Organization for Standardization technical standard for graphical hazard symbols on hazard and safety signs, including those indicating emergency exits. It uses colours and principles set out in ISO 3864 for these symbols, and is intended to provide "safety information that relies as little as possible on the use of words to achieve understanding." It is distinct from the Globally Harmonized System of Classification and Labelling of Chemicals specified by the United Nations to standardise hazardous material classification and labelling.

As of August 2019, the latest version is ISO 7010:2019. This revision incorporates all previous corrigenda, as well as incorporates water safety signs and beach safety flags previously specified in (the now-withdrawn) ISO 20712.

🔗 Computing 🔗 Libraries

The memex (originally coined "at random", though sometimes said to be a portmanteau of "memory" and "index") is the name of the hypothetical proto-hypertext system that Vannevar Bush described in his 1945 The Atlantic Monthly article "As We May Think". Bush envisioned the memex as a device in which individuals would compress and store all of their books, records, and communications, "mechanized so that it may be consulted with exceeding speed and flexibility". The memex would provide an "enlarged intimate supplement to one's memory". The concept of the memex influenced the development of early hypertext systems (eventually leading to the creation of the World Wide Web) and personal knowledge base software. The hypothetical implementation depicted by Bush for the purpose of concrete illustration was based upon a document bookmark list of static microfilm pages and lacked a true hypertext system, where parts of pages would have internal structure beyond the common textual format. Early electronic hypertext systems were thus inspired by memex rather than modeled directly upon it.

🔗 Internet culture

The Valeriepieris circle is a South China Sea-centered circular region on the world map that is about 4,000 kilometers (2,500 mi) in radius and contains more than half the world’s population. It was named after the Reddit username of Ken Myers, a Texas ESL teacher who first drew attention to the phenomenon in 2013. The map became a meme and was featured in numerous forms of media.

In 2015, the circle was tested by Danny Quah, who verified the claim but moved the circle slightly to exclude most of Japan, and used a globe model rather than a map projection as well as more specific calculations. He calculated that, as of 2015, half of the world's population lived within a 3,300-kilometer (2,050 mi) radius of the city of Mong Khet in Myanmar.

The most common visual of the circle, originally used by Myers and also featured by io9 and Tech in Asia, used the Winkel tripel projection.