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🔗 Toys

A pop-pop boat is a toy with a very simple steam engine without moving parts, typically powered by a candle or vegetable oil burner. The name comes from the noise made by some versions of the boats. Other names are putt-putt boat, crazy boat, flash-steamer, hot-air-boat, pulsating water engine boat. Around the world they may be called Can-Can-boot, Knatterboot, toc-toc, Puf-Puf boat, Poof Poof craft, Phut-Phut, or Pouet-Pouet.

🔗 Physics 🔗 New Zealand 🔗 Physics/History

The Beverly Clock is a clock situated in the 3rd floor lift foyer of the Department of Physics at the University of Otago, Dunedin, New Zealand. The clock is still running despite never having been manually wound since its construction in 1864 by Arthur Beverly.

🔗 Companies 🔗 Lists

This list of the oldest companies in the world includes brands and companies, excluding associations and educational, government, or religious organizations. To be listed, a brand or company name must remain operating, either in whole or in part, since inception. Note however that such claims are often open to question and should be researched further before citing them.

🔗 Languages 🔗 Constructed languages

Solresol (Solfège: Sol-Re-Sol) is a constructed language devised by François Sudre, beginning in 1827. His major book on it, Langue Musicale Universelle, was published after his death in 1866, though he had already been publicizing it for some years. Solresol enjoyed a brief spell of popularity, reaching its pinnacle with Boleslas Gajewski's 1902 publication of Grammaire du Solresol. An ISO 639-3 language code had been requested on 28 July 2017, but was rejected on 1 February 2018.

Today, there exist small communities of Solresol enthusiasts scattered across the world, able to communicate with one another thanks to the Internet.

🔗 Mathematics

Wang tiles (or Wang dominoes), first proposed by mathematician, logician, and philosopher Hao Wang in 1961, are a class of formal systems. They are modelled visually by square tiles with a color on each side. A set of such tiles is selected, and copies of the tiles are arranged side by side with matching colors, without rotating or reflecting them.

The basic question about a set of Wang tiles is whether it can tile the plane or not, i.e., whether an entire infinite plane can be filled this way. The next question is whether this can be done in a periodic pattern.

🔗 Australia 🔗 Buses 🔗 Australia/Adelaide

The O-Bahn Busway is a guided busway that is part of the bus rapid transit system servicing the northeastern suburbs of Adelaide, South Australia. The O-Bahn system was conceived by Daimler-Benz to enable buses to avoid traffic congestion by sharing tram tunnels in the German city of Essen.

Adelaide's O-Bahn was introduced in 1986 to service the city's rapidly expanding north-eastern suburbs, replacing an earlier plan for a tramway extension. The O-Bahn provides specially built track, combining elements of both bus and rail systems. Adelaide's track is 12 kilometres (7.5 mi) long and includes three interchanges at Klemzig, Paradise and Tea Tree Plaza. Interchanges allow buses to enter and exit the busway and to continue on suburban routes, avoiding the need for passengers to transfer to another bus to continue their journey. Buses can travel at a maximum speed of 100 km/h (60 mph), but are now restricted to 85 km/h (53 mph). As of 2015, the busway carries approximately 31,000 people per weekday. An additional section including a 670-metre (2,200 ft) tunnel opened in 2017 at the city end to reduce the number of congested intersections buses must traverse to enter the Adelaide city centre.

The development of the O-Bahn busway led to the development of the Torrens Linear Park from a run-down urban drain into an attractive public open space. It has also triggered urban development around the north-eastern terminus at Modbury.

🔗 Statistics

Berkson's paradox also known as Berkson's bias or Berkson's fallacy is a result in conditional probability and statistics which is often found to be counterintuitive, and hence a veridical paradox. It is a complicating factor arising in statistical tests of proportions. Specifically, it arises when there is an ascertainment bias inherent in a study design. The effect is related to the explaining away phenomenon in Bayesian networks, and conditioning on a collider in graphical models.

It is often described in the fields of medical statistics or biostatistics, as in the original description of the problem by Joseph Berkson.

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

Project A119, also known as A Study of Lunar Research Flights, was a top-secret plan developed in 1958 by the United States Air Force. The aim of the project was to detonate a nuclear bomb on the Moon, which would help in answering some of the mysteries in planetary astronomy and astrogeology. If the explosive device detonated on the surface, not in a lunar crater, the flash of explosive light would have been faintly visible to people on Earth with their naked eye, a show of force resulting in a possible boosting of domestic morale in the capabilities of the United States, a boost that was needed after the Soviet Union took an early lead in the Space Race and was also working on a similar project.

The project was never carried out, being cancelled primarily out of a fear of a negative public reaction, with the potential militarization of space that it would also have signified, and because a Moon landing would undoubtedly be a more popular achievement in the eyes of the American and international public alike. A similar project by the Soviet Union also never came to fruition.

The existence of the US project was revealed in 2000 by a former executive at the National Aeronautics and Space Administration (NASA), Leonard Reiffel, who led the project in 1958. A young Carl Sagan was part of the team responsible for predicting the effects of a nuclear explosion in vacuum and low gravity and in evaluating the scientific value of the project. The project documents remained secret for nearly 45 years, and despite Reiffel's revelations, the United States government has never officially recognized its involvement in the study.

🔗 Mathematics

The shoelace formula or shoelace algorithm (also known as Gauss's area formula and the surveyor's formula) is a mathematical algorithm to determine the area of a simple polygon whose vertices are described by their Cartesian coordinates in the plane. The user cross-multiplies corresponding coordinates to find the area encompassing the polygon, and subtracts it from the surrounding polygon to find the area of the polygon within. It is called the shoelace formula because of the constant cross-multiplying for the coordinates making up the polygon, like tying shoelaces. It is also sometimes called the shoelace method. It has applications in surveying and forestry, among other areas.

The formula was described by Meister (1724–1788) in 1769 and by Gauss in 1795. It can be verified by dividing the polygon into triangles, and can be considered to be a special case of Green's theorem.

The area formula is derived by taking each edge AB, and calculating the area of triangle ABO with a vertex at the origin O, by taking the cross-product (which gives the area of a parallelogram) and dividing by 2. As one wraps around the polygon, these triangles with positive and negative area will overlap, and the areas between the origin and the polygon will be cancelled out and sum to 0, while only the area inside the reference triangle remains. This is why the formula is called the surveyor's formula, since the "surveyor" is at the origin; if going counterclockwise, positive area is added when going from left to right and negative area is added when going from right to left, from the perspective of the origin.

The area formula can also be applied to self-overlapping polygons since the meaning of area is still clear even though self-overlapping polygons are not generally simple. Furthermore, a self-overlapping polygon can have multiple "interpretations" but the Shoelace formula can be used to show that the polygon's area is the same regardless of the interpretation.

🔗 Switzerland 🔗 Countries

Switzerland, officially the Swiss Confederation, is a country situated in the confluence of Western, Central, and Southern Europe. It is a federal republic composed of 26 cantons, with federal authorities seated in Bern. Switzerland is a landlocked country bordered by Italy to the south, France to the west, Germany to the north, and Austria and Liechtenstein to the east. It is geographically divided among the Swiss Plateau, the Alps, and the Jura, spanning a total area of 41,285 km² (15,940 sq mi), and land area of 39,997 km² (15,443 sq mi). While the Alps occupy the greater part of the territory, the Swiss population of approximately 8.5 million is concentrated mostly on the plateau, where the largest cities are located, among them the two global cities and economic centres of Zürich and Geneva.

The establishment of the Old Swiss Confederacy dates to the late medieval period, resulting from a series of military successes against Austria and Burgundy. Swiss independence from the Holy Roman Empire was formally recognized in the Peace of Westphalia in 1648. The Federal Charter of 1291 is considered the founding document of Switzerland which is celebrated on Swiss National Day. Since the Reformation of the 16th century, Switzerland has maintained a strong policy of armed neutrality; it has not fought an international war since 1815 and did not join the United Nations until 2002. Nevertheless, it pursues an active foreign policy and is frequently involved in peace-building processes around the world. Switzerland is the birthplace of the Red Cross, one of the world's oldest and best known humanitarian organisations, and is home to numerous international organisations, including the second largest UN office. It is a founding member of the European Free Trade Association, but notably not part of the European Union, the European Economic Area or the Eurozone. However, it participates in the Schengen Area and the European Single Market through bilateral treaties.

Switzerland occupies the crossroads of Germanic and Romance Europe, as reflected in its four main linguistic and cultural regions: German, French, Italian and Romansh. Although the majority of the population are German-speaking, Swiss national identity is rooted in a common historical background, shared values such as federalism and direct democracy, and Alpine symbolism. Due to its linguistic diversity, Switzerland is known by a variety of native names: Schweiz [ˈʃvaɪts] (German); Suisse [sɥis(ə)] (French); Svizzera [ˈzvittsera] (Italian); and Svizra [ˈʒviːtsrɐ, ˈʒviːtsʁɐ] (Romansh). On coins and stamps, the Latin name, Confoederatio Helvetica – frequently shortened to "Helvetia" – is used instead of the four national languages.

The sovereign state is one of the most developed countries in the world, with the highest nominal wealth per adult and the eighth-highest per capita gross domestic product. It ranks at or near the top in several international metrics, including economic competitiveness and human development. Zürich, Geneva and Basel have been ranked among the top ten cities in the world in terms of quality of life, with Zürich ranked second globally. In 2019, IMD placed Switzerland first in the world in attracting skilled workers. World Economic Forum ranks it the 5th most competitive country globally.