Have a deep view into what people are curious about.

🔗 Mathematics

A tautochrone or isochrone curve (from Greek prefixes tauto- meaning same or iso- equal, and chrono time) is the curve for which the time taken by an object sliding without friction in uniform gravity to its lowest point is independent of its starting point on the curve. The curve is a cycloid, and the time is equal to π times the square root of the radius (of the circle which generates the cycloid) over the acceleration of gravity. The tautochrone curve is related to the brachistochrone curve, which is also a cycloid.

🔗 Russia 🔗 Russia/technology and engineering in Russia 🔗 Military history 🔗 Military history/Military science, technology, and theory 🔗 Russia/Russian, Soviet, and CIS military history 🔗 Military history/Russian, Soviet and CIS military history

Dead Hand (Russian: Система «Периметр», Systema "Perimetr", lit. "Perimeter" System, with the GRAU Index 15E601, Cyrillic: 15Э601), also known as Perimeter, is a Cold War-era automatic nuclear weapons-control system (similar in concept to the American AN/DRC-8 Emergency Rocket Communications System) that was used by the Soviet Union. The system remains in use in the post-Soviet Russian Federation. An example of fail-deadly and mutual assured destruction deterrence, it can automatically initiate the launch of the Russian intercontinental ballistic missiles (ICBMs) by sending a pre-entered highest-authority order from the General Staff of the Armed Forces, Strategic Missile Force Management to command posts and individual silos if a nuclear strike is detected by seismic, light, radioactivity, and pressure sensors even with the commanding elements fully destroyed. By most accounts, it is normally switched off and is supposed to be activated during times of crisis; however, it is said to remain fully functional and able to serve its purpose whenever it may be needed.

🔗 Cryptography 🔗 Cryptography/Computer science

In cryptography, power analysis is a form of side channel attack in which the attacker studies the power consumption of a cryptographic hardware device (such as a smart card, tamper-resistant "black box", or integrated circuit). The attack can non-invasively extract cryptographic keys and other secret information from the device.

Simple power analysis (SPA) involves visually interpreting power traces, or graphs of electrical activity over time. Differential power analysis (DPA) is a more advanced form of power analysis, which can allow an attacker to compute the intermediate values within cryptographic computations through statistical analysis of data collected from multiple cryptographic operations. SPA and DPA were introduced to the open cryptology community in 1998 by Paul Kocher, Joshua Jaffe and Benjamin Jun.

🔗 Radio Stations

United Biscuits Network (UBN) was an internal radio station serving the factories of United Biscuits (UB) in Britain that operated from 1970 to 1979.

In 1970 the BBC had a monopoly on radio broadcasting in Britain, although there were a few offshore pirate radio broadcasters, such as Radio Caroline. At one time factories had sought to avoid unnecessary background sound, but during the Second World War psychologists found that light background music (muzak) increased productivity at times it was low, a trend that continued after the war. But as jobs became deskilled and ever more monotonous, muzak became less effective, and staff turnover increased. United Biscuits was affected by this trend; Hector Laing, the managing director in the 1960s, needed to reduce the costs of high staff turnover. Inspired by the success of the pirate stations, Laing hired suitable staff, bought state-of-the-art broadcasting equipment, and set up UBN at UB headquarters in Osterley, west London (later the headquarters of broadcaster Sky UK).

🔗 China 🔗 Novels 🔗 Novels/Science fiction 🔗 Science Fiction

The Dark Forest (Chinese: 黑暗森林) is a 2008 science fiction novel by the Chinese writer Liu Cixin. It is the sequel to the Hugo Award-winning novel The Three-Body Problem in the trilogy titled Remembrance of Earth's Past, but Chinese readers generally refer to the series by the title of the first novel. The English version, translated by Joel Martinsen, was published in 2015. The novel is about the dark forest hypothesis (which was named after the novel), a possible solution to the Fermi paradox, though similar theories have been described as early as 1983.

🔗 Mass surveillance 🔗 Computing 🔗 Korea 🔗 Korea/North Korea

Kwangmyong (literally “Bright Light”) is a North Korean "walled garden" national intranet service opened in 2000.

The network uses domain names under the .kp top level domain that are not accessible from the global Internet. As of 2016 the network uses IPv4 addresses reserved for private networks in the 10.0.0.0/8 range. North Koreans often find it more convenient to access sites by their IP address rather than by URL using Latin characters. Like the global Internet, the network hosts content accessible with web browsers, and provides an internal web search engine. It also provides email services and news groups.

Only foreigners and a small number of government officials/scholars/elites are allowed to use the global Internet in North Korea, making Kwangmyong the only computer network available to most North Korean citizens. It is a free service for public use.

🔗 Aviation 🔗 Military history 🔗 Military history/Military aviation 🔗 Military history/North American military history 🔗 Military history/United States military history 🔗 Skepticism 🔗 Nevada 🔗 Paranormal 🔗 Aviation/airport

Area 51 is the common name of a highly classified United States Air Force (USAF) facility within the Nevada Test and Training Range. A remote detachment administered by Edwards Air Force Base, the facility is officially called Homey Airport (ICAO: KXTA, FAA LID: XTA) or Groom Lake (after the salt flat next to its airfield). Details of its operations are not made public, but the USAF says that it is an open training range, and it is commonly thought to support the development and testing of experimental aircraft and weapons systems. The USAF and CIA acquired the site in 1955, primarily for flight testing the Lockheed U-2 aircraft.

The intense secrecy surrounding the base has made it the frequent subject of conspiracy theories and a central component of unidentified flying object (UFO) folklore. It has never been declared a secret base, but all research and occurrences in Area 51 are Top Secret/Sensitive Compartmented Information (TS/SCI). The CIA publicly acknowledged the base's existence on 25 June 2013, following a Freedom of Information Act (FOIA) request filed in 2005 and declassified documents detailing its history and purpose.

Area 51 is located in the southern portion of Nevada, 83 miles (134 km) north-northwest of Las Vegas. The surrounding area is a popular tourist destination, including the small town of Rachel on the "Extraterrestrial Highway".

🔗 California 🔗 California/San Francisco Bay Area 🔗 Philosophy 🔗 Psychology 🔗 Philosophy/Social and political philosophy 🔗 Sociology

The Third Wave was an experimental social movement created by California high school history teacher Ron Jones in 1967 to explain how the German population could accept the actions of the Nazi regime during the Second World War. While he taught his students about Nazi Germany during his "Contemporary World History" class, Jones found it difficult to explain how the German people could accept the actions of the Nazis, and decided to create a social movement as a demonstration of the appeal of fascism. Over the course of five days, Jones – a member of the SDS, Cubberley United Student Movement sponsor and Black Panthers supporter – conducted a series of exercises in his classroom emphasizing discipline and community, intended to model certain characteristics of the Nazi movement. As the movement grew outside his class and began to number in the hundreds, Jones began to feel that the movement had spiraled out of control. He convinced the students to attend a rally where he claimed that the classroom project was part of a nationwide movement, and that the announcement of a Third Wave presidential candidate would be televised. Upon their arrival, the students were presented with a blank channel. Jones told his students of the true nature of the movement as an experiment in fascism, and presented to them a short film discussing the actions of Nazi Germany.

🔗 Computer science 🔗 Mathematics

In numerical analysis, the Kahan summation algorithm, also known as compensated summation, significantly reduces the numerical error in the total obtained by adding a sequence of finite-precision floating-point numbers, compared to the obvious approach. This is done by keeping a separate running compensation (a variable to accumulate small errors).

In particular, simply summing n numbers in sequence has a worst-case error that grows proportional to n, and a root mean square error that grows as ${\displaystyle {\sqrt {n}}}$ for random inputs (the roundoff errors form a random walk). With compensated summation, the worst-case error bound is effectively independent of n, so a large number of values can be summed with an error that only depends on the floating-point precision.

The algorithm is attributed to William Kahan. Similar, earlier techniques are, for example, Bresenham's line algorithm, keeping track of the accumulated error in integer operations (although first documented around the same time) and the delta-sigma modulation (integrating, not just summing the error).