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🔗 Philately

Rocket mail is the delivery of mail by rocket or missile. The rocket lands by deploying an internal parachute upon arrival. It has been attempted by various organizations in many different countries, with varying levels of success. It has never become widely seen as being a viable option for delivering mail, due to the cost of the schemes and numerous failures.

The collection of philatelic material ("stamps") used for (and depicting) rocket mail is part of a specialist branch of aerophilately known as astrophilately.

🔗 Telecommunications 🔗 Brands

The IBM Simon Personal Communicator (simply known as IBM Simon) is a handheld, touchscreen PDA designed by International Business Machines (IBM), and manufactured by Mitsubishi Electric. BellSouth Cellular Corp. distributed the Simon Personal Communicator in the United States between August 1994 and February 1995, selling 50,000 units. The Simon Personal Communicator was the first personal digital assistant or PDA to include telephony features. The battery lasted only an hour, and flip phones became increasingly slim which led to its demise.

🔗 United States/U.S. Government 🔗 United States 🔗 Medicine 🔗 Economics 🔗 Politics 🔗 Geography

Universal healthcare (also called universal health coverage, universal coverage, or universal care) is a health care system in which all residents of a particular country or region are assured access to health care. It is generally organized around providing either all residents or only those who cannot afford on their own, with either health services or the means to acquire them, with the end goal of improving health outcomes.

Universal healthcare does not imply coverage for all cases and for all people – only that all people have access to healthcare when and where needed without financial hardship. Some universal healthcare systems are government-funded, while others are based on a requirement that all citizens purchase private health insurance. Universal healthcare can be determined by three critical dimensions: who is covered, what services are covered, and how much of the cost is covered. It is described by the World Health Organization as a situation where citizens can access health services without incurring financial hardship. The Director General of WHO describes universal health coverage as the “single most powerful concept that public health has to offer” since it unifies “services and delivers them in a comprehensive and integrated way”. One of the goals with universal healthcare is to create a system of protection which provides equality of opportunity for people to enjoy the highest possible level of health.

As part of Sustainable Development Goals, United Nations member states have agreed to work toward worldwide universal health coverage by 2030.

🔗 Russia 🔗 Military history 🔗 Military history/Military science, technology, and theory 🔗 Military history/Weaponry 🔗 Dogs 🔗 Military history/World War II 🔗 Military history/German military history 🔗 Military history/Military land vehicles 🔗 Russia/Russian, Soviet, and CIS military history 🔗 Military history/Russian, Soviet and CIS military history 🔗 Russia/history of Russia 🔗 Military history/European military history

Anti-tank dogs (Russian: собаки-истребители танков sobaki-istrebiteli tankov or противотанковые собаки protivotankovye sobaki; German: Panzerabwehrhunde or Hundeminen, "dog-mines") were dogs taught to carry explosives to tanks, armored vehicles and other military targets. They were intensively trained by the Soviet and Russian military forces between 1930 and 1996, and used from 1941 to 1943, against German tanks in World War II. Initially dogs were trained to leave a timer-detonated bomb and retreat, but this routine was replaced by an impact-detonation procedure which killed the dog in the process. The U.S. military started training anti-tank dogs in 1943 in the same way the Russians used them, but this training exposed several problems and the program was discontinued.

🔗 Science Fiction

"Computers Don't Argue" is a 1965 science fiction short story by American writer Gordon R. Dickson, about the dangers of relying too strongly upon computers. It was nominated for a Nebula Award in 1966.

🔗 Finance & Investment 🔗 Economics

In finance, the greater fool theory suggests that one can sometimes make money through the purchase of overvalued assets — items with a purchase price drastically exceeding the intrinsic value — if those assets can later be resold at an even higher price.

In this context, one "fool" might pay for an overpriced asset, on the assumption that he can probably sell it to an even "greater fool" and make a profit. This only works as long as there are new "greater fools" willing to pay higher and higher prices for the asset. Eventually, investors can no longer deny that the price is out of touch with reality, at which point a sell-off can cause the price to drop significantly until it is closer to its fair value.

🔗 Computer Security 🔗 Computer Security/Computing 🔗 Microsoft Windows 🔗 Microsoft Windows/Computing 🔗 Cryptography 🔗 Cryptography/Computer science

_NSAKEY was a variable name discovered in an operating system from Microsoft in 1999. The variable contained a 1024-bit public key; such keys are used in cryptography for encryption and authentication. Due to the name it was speculated that the key was owned by the United States National Security Agency (the NSA) which would allow the intelligence agency to subvert any Windows user's security. Microsoft denied the speculation and said that the key's name came from the NSA being the technical review authority for U.S. cryptography export controls.

The key was discovered in a Windows NT 4 Service Pack 5 (which had been released unstripped of its symbolic debugging data) in August 1999 by Andrew D. Fernandes of Cryptonym Corporation.

🔗 Astronomy 🔗 Astronomy/Astronomical objects

Tabby's Star (also known as Boyajian's Star and WTF Star, and designated KIC 8462852 in the Kepler Input Catalog) is an F-type main-sequence star in the constellation Cygnus approximately 1,470 light-years (450 pc) from Earth. Unusual light fluctuations of the star, including up to a 22% dimming in brightness, were discovered by citizen scientists as part of the Planet Hunters project. In September 2015, astronomers and citizen scientists associated with the project posted a preprint of an article describing the data and possible interpretations. The discovery was made from data collected by the Kepler space telescope, which observed changes in the brightness of distant stars to detect exoplanets.

Several hypotheses have been proposed to explain the star's large irregular changes in brightness as measured by its light curve, but none to date fully explain all aspects of the curve. One explanation is that an "uneven ring of dust" orbits Tabby's Star. In another explanation, the star's luminosity is modulated by changes in the efficiency of heat transport to its photosphere, so no external obscuration is required. A third hypothesis, based on a lack of observed infrared light, posits a swarm of cold, dusty comet fragments in a highly eccentric orbit; however, the notion that disturbed comets from such a cloud could exist in high enough numbers to obscure 22% of the star's observed luminosity has been doubted. Another hypothesis is that a large number of small masses in "tight formation" are orbiting the star. Furthermore, spectroscopic study of the system has found no evidence for coalescing material or hot close-in dust or circumstellar matter from an evaporating or exploding planet within a few astronomical units of the mature central star. It has also been hypothesized that the changes in brightness could be signs of activity associated with intelligent extraterrestrial life constructing a Dyson swarm; however, further analysis based on data through the end of 2017 showed wavelength-dependent dimming consistent with dust but not an opaque object such as an alien megastructure, which would block all wavelengths of light equally.

Tabby's Star is not the only star that has large irregular dimmings, but other such stars include young stellar objects called YSO dippers, which have different dimming patterns. An example of such an object is EPIC 204278916.

New fluctuations ran from mid-May 2017 until July 2018, assuming their continuance in late-December 2017 to mid-February 2018 when obscured by the Sun.

In September 2019, astronomers reported that the observed dimmings of Tabby's Star may have been produced by fragments resulting from the disruption of an orphaned exomoon. An overall study of other similar stars has been presented. In January 2021, a distant stellar-mass companion was reported, making Tabby's Star a binary stellar system.

🔗 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.

🔗 Energy 🔗 Mining

Uranium mining is the process of extraction of uranium ore from the ground. The worldwide production of uranium in 2019 amounted to 53,656 tonnes. Kazakhstan, Canada, and Australia were the top three uranium producers, respectively, and together account for 68% of world production. Other countries producing more than 1,000 tonnes per year included Namibia, Niger, Russia, Uzbekistan, the United States, and China. Nearly all of the world's mined uranium is used to power nuclear power plants.

Uranium is mined by in-situ leaching (57% of world production) or by conventional underground or open-pit mining of ores (43% of production). During in-situ mining, a leaching solution is pumped down drill holes into the uranium ore deposit where it dissolves the ore minerals. The uranium-rich fluid is then pumped back to the surface and processed to extract the uranium compounds from solution. In conventional mining, ores are processed by grinding the ore materials to a uniform particle size and then treating the ore to extract the uranium by chemical leaching. The milling process commonly yields dry powder-form material consisting of natural uranium, "yellowcake," which is sold on the uranium market as U₃O₈.