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π Long line (topology)
In topology, the long line (or Alexandroff line) is a topological space somewhat similar to the real line, but in a certain way "longer". It behaves locally just like the real line, but has different large-scale properties (e.g., it is neither LindelΓΆf nor separable). Therefore, it serves as one of the basic counterexamples of topology. Intuitively, the usual real-number line consists of a countable number of line segments [0,Β 1) laid end-to-end, whereas the long line is constructed from an uncountable number of such segments.
Discussed on
- "Long line (topology)" | 2015-05-02 | 46 Upvotes 21 Comments
π Lithops
Lithops is a genus of succulent plants in the ice plant family, Aizoaceae. Members of the genus are native to southern Africa. The name is derived from the Ancient Greek words Ξ»Ξ―ΞΈΞΏΟ (lΓthos), meaning "stone," and α½Ο (Γ³ps), meaning "face," referring to the stone-like appearance of the plants. They avoid being eaten by blending in with surrounding rocks and are often known as pebble plants or living stones. The formation of the name from the Ancient Greek "-ops" means that even a single plant is called a Lithops.
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- "Lithops" | 2022-02-24 | 91 Upvotes 18 Comments
π Deepstaria Enigmatica
Deepstaria enigmatica is a very rarely seen giant jellyfish of the family Ulmaridae first described in 1967 by F. S. Russell.
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- "Deepstaria Enigmatica" | 2025-10-11 | 21 Upvotes 2 Comments
π Nikon F-Mount
The Nikon F-mount is a type of interchangeable lens mount developed by Nikon for its 35mm format single-lens reflex cameras. The F-mount was first introduced on the Nikon F camera in 1959, and features a three-lug bayonet mount with a 44Β mm throat and a flange to focal plane distance of 46.5Β mm. The company continues, with the 2020 D6 model, to use variations of the same lens mount specification for its film and digital SLR cameras.
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- "Nikon F-Mount" | 2021-12-28 | 33 Upvotes 78 Comments
π Hindu units of time
Hindu texts describe units of Kala measurements, from microseconds to Trillions of years. According to these texts, time is cyclic, which repeats itself forever.
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- "Hindu units of time" | 2015-03-23 | 19 Upvotes 7 Comments
π Heilmeier's Catechism: questions for every startup, every project.
George Harry Heilmeier (May 22, 1936 β April 21, 2014) was an American engineer, manager, and a pioneering contributor to liquid crystal displays (LCDs), for which he was inducted into the National Inventors Hall of Fame. Heilmeier's work is an IEEE Milestone.
π Bangui Magnetic Anomaly
The Bangui magnetic anomaly is a local variation in the Earth's magnetic field centered at Bangui, the capital of Central African Republic. The magnetic anomaly is roughly elliptical, about 700Β km ΓΒ 1,000Β km (430Β mi ΓΒ 620Β mi), and covers most of the country, making it one of the "largest and most intense crustal magnetic anomalies on the African continent". The anomaly was discovered in the late 1950s, explored in the 1970s, and named in 1982. Its origin remains unclear.
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- "Bangui Magnetic Anomaly" | 2021-02-02 | 82 Upvotes 15 Comments
π The Market for Lemons
"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 (pavg). 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 plemonΒ <Β pavg) and they will leave the market when they hold "peaches" (since ppeach > pavg). 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.
Discussed on
- "The Market for Lemons" | 2019-01-13 | 82 Upvotes 44 Comments
π Salmonella-in-Eggs Controversy
The salmonella-in-eggs controversy was a political controversy in the United Kingdom caused by the Parliamentary Under-Secretary of State for Health, Edwina Currie's claims that "most of the egg production in this country, sadly, is now affected with salmonella" in 1988. These claims led to a 60 percent decline in egg sales over the next few weeks, and angered both politicians and those in the egg production industry. Currie's statement also resulted in the destruction of around 400 million eggs and the slaughter of around 4 million hens. The controversy dominated Currie's tenure as Parliamentary Under-Secretary of State for Health and resulted in her resignation two weeks later.
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- "Salmonella-in-Eggs Controversy" | 2023-02-22 | 55 Upvotes 73 Comments
π Holon
A holon (Greek: ὠλον, from ὠλοΟ, holos, 'whole' and -ΞΏΞ½, -on, 'part') is something that is simultaneously a whole in and of itself, as well as a part of a larger whole. In other words, holons can be understood as the constituent partβwholes of a hierarchy.
The holon represents a way to overcome the dichotomy between parts and wholes, as well as a way to account for both the self-assertive and the integrative tendencies of organisms. The term was coined by Arthur Koestler in The Ghost in the Machine (1967). In Koestler's formulations, a holon is something that has integrity and identity while simultaneously being a part of a larger system; it is a subsystem of a greater system.
Holons are sometimes discussed in the context of self-organizing holarchic open (SOHO) systems.