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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.

🔗 Economics

"The Market for Lemons: Quality Uncertainty and the Market Mechanism" is a well-known 1970 paper by economist George Akerlof which examines how the quality of goods traded in a market can degrade in the presence of information asymmetry between buyers and sellers, leaving only "lemons" behind. In American slang, a lemon is a car that is found to be defective after it has been bought.

Suppose buyers cannot distinguish between a high-quality car (a "peach") and a "lemon". Then they are only willing to pay a fixed price for a car that averages the value of a "peach" and "lemon" together (p_avg). But sellers know whether they hold a peach or a lemon. Given the fixed price at which buyers will buy, sellers will sell only when they hold "lemons" (since p_lemon < p_avg) and they will leave the market when they hold "peaches" (since p_peach > p_avg). Eventually, as enough sellers of "peaches" leave the market, the average willingness-to-pay of buyers will decrease (since the average quality of cars on the market decreased), leading to even more sellers of high-quality cars to leave the market through a positive feedback loop.

Thus the uninformed buyer's price creates an adverse selection problem that drives the high-quality cars from the market. Adverse selection is a market mechanism that can lead to a market collapse.

Akerlof's paper shows how prices can determine the quality of goods traded on the market. Low prices drive away sellers of high-quality goods, leaving only lemons behind. In 2001, Akerlof, along with Michael Spence, and Joseph Stiglitz, jointly received the Nobel Memorial Prize in Economic Sciences, for their research on issues related to asymmetric information.

🔗 Military history 🔗 Poland 🔗 Military history/World War II 🔗 Scotland 🔗 Zoo

Wojtek (1942 – 2 December 1963; Polish pronunciation: [ˈvɔjtɛk]; in English, sometimes spelled Voytek and pronounced as such) was a Syrian brown bear (Ursus arctos syriacus) bought, as a young cub, at a railway station in Hamadan, Iran, by Polish II Corps soldiers who had been evacuated from the Soviet Union. In order to provide for his rations and transportation, he was eventually enlisted officially as a soldier with the rank of private, and was subsequently promoted to corporal.

He accompanied the bulk of the II Corps to Italy, serving with the 22nd Artillery Supply Company. During the Battle of Monte Cassino, in Italy in 1944, Wojtek helped move crates of ammunition and became a celebrity with visiting Allied generals and statesmen. After the war, mustered out of the Polish Army, he was billeted and lived out the rest of his life at the Edinburgh Zoo in Scotland.

🔗 Electronics

Resistor–transistor logic (RTL) (sometimes also transistor–resistor logic (TRL)) is a class of digital circuits built using resistors as the input network and bipolar junction transistors (BJTs) as switching devices. RTL is the earliest class of transistorized digital logic circuit; it was succeeded by diode–transistor logic (DTL) and transistor–transistor logic (TTL).

RTL circuits were first constructed with discrete components, but in 1961 it became the first digital logic family to be produced as a monolithic integrated circuit. RTL integrated circuits were used in the Apollo Guidance Computer, whose design begun in 1961 and which first flew in 1966.

🔗 Technology 🔗 Occupational Safety and Health 🔗 Brands 🔗 Typography 🔗 Netherlands

Velotype is the trademark for a type of keyboard for typing text known as a syllabic chord keyboard, an invention of the Dutchmen Nico Berkelmans and Marius den Outer.

🔗 Mathematics

In combinatorial mathematics, the ménage problem or problème des ménages asks for the number of different ways in which it is possible to seat a set of male-female couples at a round dining table so that men and women alternate and nobody sits next to his or her partner. This problem was formulated in 1891 by Édouard Lucas and independently, a few years earlier, by Peter Guthrie Tait in connection with knot theory. For a number of couples equal to 3, 4, 5, ... the number of seating arrangements is

12, 96, 3120, 115200, 5836320, 382072320, 31488549120, ... (sequence A059375 in the OEIS).

Mathematicians have developed formulas and recurrence equations for computing these numbers and related sequences of numbers. Along with their applications to etiquette and knot theory, these numbers also have a graph theoretic interpretation: they count the numbers of matchings and Hamiltonian cycles in certain families of graphs.

🔗 Spaceflight 🔗 Military history 🔗 Military history/Military aviation 🔗 Military history/North American military history 🔗 Military history/United States military history 🔗 Military history/Military science, technology, and theory 🔗 Cold War

The Manned Orbiting Laboratory (MOL), originally referred to as the Manned Orbital Laboratory, was a never-flown part of the United States Air Force's human spaceflight program, a successor to the canceled Boeing X-20 Dyna-Soar military reconnaissance space plane project. The project was developed from several early Air Force and NASA concepts of crewed space stations to be used for reconnaissance purposes. MOL evolved into a single-use laboratory, with which crews would be launched on 40-day missions and return to Earth using a Gemini B spacecraft, derived from NASA's Project Gemini.

The MOL program was announced to the public on 10 December 1963 as an inhabited platform to prove the utility of putting people in space for military missions. Astronauts selected for the program were later told of the reconnaissance mission for the program. The contractor for the MOL was the Douglas Aircraft Company. The Gemini B was externally similar to NASA's Gemini spacecraft, although it underwent several modifications, including the addition of a circular hatch through the heat shield, which allowed passage between the spacecraft and the laboratory.

MOL was canceled in 1969, during the height of the Apollo program, when it was shown that uncrewed reconnaissance satellites could achieve the same objectives much more cost-effectively. U.S. space station development was instead pursued with the civilian NASA Skylab (Apollo Applications Program) which flew in the mid-1970s.

In the 1970s, the Soviet Union launched three Almaz military space stations, similar in intent to the MOL, but cancelled the program in 1977 for the same reasons.

There is a MOL space suit on display at the Oklahoma City Science Museum, presumably never used.

🔗 Medicine 🔗 Science

The aesthetic–usability effect describes a paradox that people perceive more aesthetic designs as much more intuitive than those considered to be less aesthetically pleasing. The effect has been observed in several experiments and has significant implications regarding the acceptance, use, and performance of a design. Usability and aesthetics are the two most important factors in assessing the overall user experience for an application. Usability and aesthetics are judged by a user's reuse expectations, and then their post-use, or experienced, final judgement. A user's cognitive style can influence how they interact with and perceive an application, which in turn can influence their judgement of the application.

🔗 Technology 🔗 Military history 🔗 Military history/Military aviation 🔗 Military history/North American military history 🔗 Military history/Military science, technology, and theory 🔗 Military history/Weaponry 🔗 Canada 🔗 Architecture 🔗 United Kingdom 🔗 Military history/Maritime warfare 🔗 Military history/World War II 🔗 Engineering 🔗 Ships 🔗 Military history/Canadian military history 🔗 Military history/European military history 🔗 Military history/British military history

Project Habakkuk or Habbakuk (spelling varies) was a plan by the British during the Second World War to construct an aircraft carrier out of pykrete (a mixture of wood pulp and ice) for use against German U-boats in the mid-Atlantic, which were beyond the flight range of land-based planes at that time. The idea came from Geoffrey Pyke, who worked for Combined Operations Headquarters. After promising scale tests and the creation of a prototype on a lake (Patricia Lake, Jasper National Park) in Alberta, Canada, the project was shelved due to rising costs, added requirements, and the availability of longer-range aircraft and escort carriers which closed the Mid-Atlantic gap the project was intended to address.