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π Slow-Scan Television
Slow-scan television (SSTV) is a picture transmission method, used mainly by amateur radio operators, to transmit and receive static pictures via radio in monochrome or color.
A literal term for SSTV is narrowband television. Analog broadcast television requires at least 6Β MHz wide channels, because it transmits 25 or 30 picture frames per second (see ITU analog broadcast standards), but SSTV usually only takes up to a maximum of 3Β kHz of bandwidth. It is a much slower method of still picture transmission, usually taking from about eight seconds to a couple of minutes, depending on the mode used, to transmit one image frame.
Since SSTV systems operate on voice frequencies, amateurs use it on shortwave (also known as HF by amateur radio operators), VHF and UHF radio.
Discussed on
- "Slow-Scan Television" | 2023-11-13 | 117 Upvotes 24 Comments
π Vela Incident
The Vela incident, also known as the South Atlantic Flash, was an unidentified double flash of light detected by an American Vela Hotel satellite on 22 September 1979 near the Prince Edward Islands in the Indian Ocean.
The cause of the flash remains officially unknown, and some information about the event remains classified. While it has been suggested that the signal could have been caused by a meteoroid hitting the satellite, the previous 41 double flashes detected by the Vela satellites were caused by nuclear weapons tests. Today, most independent researchers believe that the 1979 flash was caused by a nuclear explosion β perhaps an undeclared nuclear test carried out by South Africa and Israel.
Discussed on
- "Vela incident (1979)" | 2023-11-13 | 87 Upvotes 54 Comments
- "Vela Incident" | 2022-04-06 | 10 Upvotes 1 Comments
- "Vela Incident" | 2022-03-11 | 19 Upvotes 1 Comments
- "Vela Incident" | 2019-09-22 | 117 Upvotes 58 Comments
π Geohash: text representation allows you to sort locations by proximity
Geohash is a public domain geocode system invented in 2008 by Gustavo Niemeyer and (similar work in 1966) G.M. Morton, which encodes a geographic location into a short string of letters and digits. It is a hierarchical spatial data structure which subdivides space into buckets of grid shape, which is one of the many applications of what is known as a Z-order curve, and generally space-filling curves.
Geohashes offer properties like arbitrary precision and the possibility of gradually removing characters from the end of the code to reduce its size (and gradually lose precision). As a consequence of the gradual precision degradation, nearby places will often (but not always) present similar prefixes. While in rare cases nearby places may have very short shared prefixes, the longer their shared prefix is, the closer two places are guaranteed to be.
Discussed on
- "Geohash" | 2023-11-12 | 44 Upvotes 15 Comments
- "Geohash: text representation allows you to sort locations by proximity" | 2014-08-23 | 39 Upvotes 8 Comments
π Inverted totalitarianism
The political philosopher Sheldon Wolin coined the term inverted totalitarianism in 2003 to describe what he saw as the emerging form of government of the United States. Wolin analysed the United States as increasingly turning into a managed democracy (similar to an illiberal democracy). He uses the term "inverted totalitarianism" to draw attention to the totalitarian aspects of the American political system while emphasizing its differences from proper totalitarianism, such as Nazi and Stalinist regimes.
The book Days of Destruction, Days of Revolt (2012) by Chris Hedges and Joe Sacco portrays inverted totalitarianism as a system where corporations have corrupted and subverted democracy and where economics bests politics. Every natural resource and living being is commodified and exploited by large corporations to the point of collapse as excess consumerism and sensationalism lull and manipulate the citizenry into surrendering their liberties and their participation in government.
Discussed on
- "Inverted Totalitarianism" | 2023-11-12 | 11 Upvotes 3 Comments
- "Inverted Totalitarianism" | 2021-08-26 | 33 Upvotes 3 Comments
- "Inverted totalitarianism" | 2013-12-14 | 240 Upvotes 158 Comments
- "Inverted Totalitarianism" | 2013-12-02 | 20 Upvotes 5 Comments
π Uncertainty Reduction Theory
The uncertainty reduction theory, also known as initial interaction theory, developed in 1975 by Charles Berger and Richard Calabrese, is a communication theory from the post-positivist tradition. It is one of the few communication theories that specifically looks into the initial interaction between people prior to the actual communication process. The theory asserts the notion that, when interacting, people need information about the other party in order to reduce their uncertainty. In gaining this information people are able to predict the other's behavior and resulting actions, all of which according to the theory is crucial in the development of any relationship.
Berger and Calabrese explain the connection between their central concept of uncertainty and seven key variables of relationship development with a series of axioms, and deduce a series of theorems accordingly. Within the theory two types of uncertainty are identified; cognitive uncertainty and behavioral uncertainty. There are three types of strategies which people may use to seek information about someone: passive, active, and interactive. Furthermore, the initial interaction of strangers can be broken down into individual stagesβthe entry stage, the personal stage, and the exit stage. According to the theory, people find uncertainty in interpersonal relationships unpleasant and are motivated to reduce it through interpersonal communication.
π Qanat
A qanat or kariz is a gently sloping underground channel to transport water from an aquifer or water well to surface for irrigation and drinking, acting as an underground aqueduct. This is an old system of water supply from a deep well with a series of vertical access shafts. The qanats still create a reliable supply of water for human settlements and irrigation in hot, arid, and semi-arid climates, but the value of this system is directly related to the quality, volume, and regularity of the water flow. Traditionally qanats are built by a group of skilled laborers, muqannΔ«s, with hand labor. The profession historically paid well and was typically handed down from father to son. According to most sources, the qanat technology was developed in ancient Iran by the Persian people sometime in the early 1st millennium BCE, and spread from there slowly westward and eastward. However, some other sources suggest a Southeast Arabian origin.
π A mathematical proof by an anonymous 4chan user
In combinatorial mathematics, a superpermutation on n symbols is a string that contains each permutation of n symbols as a substring. While trivial superpermutations can simply be made up of every permutation concatenated together, superpermutations can also be shorter (except for the trivial case of n = 1) because overlap is allowed. For instance, in the case of n = 2, the superpermutation 1221 contains all possible permutations (12 and 21), but the shorter string 121 also contains both permutations.
It has been shown that for 1 β€ n β€ 5, the smallest superpermutation on n symbols has length 1! + 2! + β¦ + n! (sequence A180632 in the OEIS). The first four smallest superpermutations have respective lengths 1, 3, 9, and 33, forming the strings 1, 121, 123121321, and 123412314231243121342132413214321. However, for n = 5, there are several smallest superpermutations having the length 153. One such superpermutation is shown below, while another of the same length can be obtained by switching all of the fours and fives in the second half of the string (after the bold 2):
12345123Β41523412Β53412354Β12314523Β14253142Β35142315Β42312453Β12435124Β31524312Β54312134Β52134251Β34215342Β13542132Β45132415Β32413524Β13254132Β14532143Β52143251Β432154321
For the cases of n > 5, a smallest superpermutation has not yet been proved nor a pattern to find them, but lower and upper bounds for them have been found.
π Leonard vs. Pepsico, Inc
Leonard v. Pepsico, Inc., 88 F. Supp. 2d 116, (S.D.N.Y. 1999), aff'd 210 F.3d 88 (2d Cir. 2000), more widely known as the Pepsi Points case, is an American contract law case regarding offer and acceptance. The case was brought in the United States District Court for the Southern District of New York in 1999; its judgment was written by Kimba Wood.
In 1996, PepsiCo began a promotional loyalty program, in which customers could earn Pepsi Points; these points could, in turn, be traded for physical items. A television commercial for the loyalty program displayed the commercial's protagonist flying a McDonnell Douglas AV-8B Harrier II vertical take off jet aircraft to school, valued at $37.4 million at the time, which could be redeemed for 7,000,000 Pepsi Points. The plaintiff, John Leonard, discovered a loophole in the promotion, allowing him to purchase Pepsi Points at 10Β’ per point. Leonard promptly delivered a check for $700,008.50 to PepsiCo, attempting to purchase the jet. PepsiCo initially refuted Leonard's offer, citing the humorous nature of the offer in the advertisement. Leonard then sued PepsiCo, Inc. in an effort to enforce the offer and acceptance perceived by Leonard to be made in the advertisement. In her judgment, Wood sided with PepsiCo, noting the frivolous and improbable nature of landing a fighter jet in a school zone that was portrayed by the protagonist. PepsiCo would re-release the advertisement, valuing the jet at 700,000,000 Pepsi Points.
Discussed on
- "Leonard vs. Pepsico, Inc" | 2023-11-10 | 81 Upvotes 60 Comments
π Eltanin Antenna
The Eltanin Antenna is an object photographed on the sea floor by the Antarctic oceanographic research ship USNS Eltanin in 1964, while photographing the sea bottom west of Cape Horn.
Due to its regular antenna-like structure and upright position on the seafloor at a depth of 3,904 metres (12,808Β ft), some proponents of fringe and UFO-related theories including Bruce Cathie have suggested that it might be an extraterrestrial artifact. Other authorities have suggested that the object photographed by the Eltanin was an unusual carnivorous sponge, Chondrocladia concrescens (formerly Cladorhiza concrescens).
Discussed on
- "Eltanin Antenna" | 2023-11-10 | 99 Upvotes 21 Comments
π Asterism (Typography)
In typography, an asterism, β, is a typographic symbol consisting of three asterisks placed in a triangle, which is used for a variety of purposes. The name originates from the astronomical term for a group of stars.
The asterism was originally used as a type of dinkus in typography, though increasingly rarely. It can also be used to mean "untitled" or author or title withheldΒ β as seen, for example, in some editions of Album for the Young by composer Robert Schumann (β 21, 26, and 30). In meteorology, an asterism in a station model indicates moderate snowfall.