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🔗 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.

🔗 Dogs 🔗 Psychology

Intelligent disobedience occurs where a service animal trained to help a disabled person goes directly against the owner's instructions in an effort to make a better decision. This behavior is a part of the dog's training and is central to a service animal's success on the job. The concept of intelligent disobedience has been in use and a common part of service animals' training since at least 1936.

🔗 Computing 🔗 Perl

Raku rules are the regular expression, string matching and general-purpose parsing facility of Raku, and are a core part of the language. Since Perl's pattern-matching constructs have exceeded the capabilities of formal regular expressions for some time, Raku documentation refers to them exclusively as regexes, distancing the term from the formal definition.

Raku provides a superset of Perl 5 features with respect to regexes, folding them into a larger framework called rules, which provide the capabilities of a parsing expression grammar, as well as acting as a closure with respect to their lexical scope. Rules are introduced with the rule keyword, which has a usage quite similar to subroutine definitions. Anonymous rules can be introduced with the regex (or rx) keyword, or simply be used inline as regexes were in Perl 5 via the m (matching) or s (substitution) operators.

🔗 Extinction 🔗 Birds 🔗 Scottish Islands

The great auk (Pinguinus impennis) is a species of flightless alcid that became extinct in the mid-19th century. It was the only modern species in the genus Pinguinus. It is not closely related to the birds now known as penguins, which were discovered later by Europeans and so named by sailors because of their physical resemblance to the great auk.

It bred on rocky, remote islands with easy access to the ocean and a plentiful food supply, a rarity in nature that provided only a few breeding sites for the great auks. When not breeding, they spent their time foraging in the waters of the North Atlantic, ranging as far south as northern Spain and along the coastlines of Canada, Greenland, Iceland, the Faroe Islands, Norway, Ireland, and Great Britain.

The great auk was 75 to 85 centimetres (30 to 33 inches) tall and weighed about 5 kilograms (11 pounds), making it the largest alcid to survive into the modern era, and the second-largest member of the alcid family overall (the prehistoric Miomancalla was larger). It had a black back and a white belly. The black beak was heavy and hooked, with grooves on its surface. During summer, great auk plumage showed a white patch over each eye. During winter, the great auk lost these patches, instead developing a white band stretching between the eyes. The wings were only 15 cm (6 in) long, rendering the bird flightless. Instead, the great auk was a powerful swimmer, a trait that it used in hunting. Its favourite prey were fish, including Atlantic menhaden and capelin, and crustaceans. Although agile in the water, it was clumsy on land. Great auk pairs mated for life. They nested in extremely dense and social colonies, laying one egg on bare rock. The egg was white with variable brown marbling. Both parents participated in the incubation of the egg for around 6 weeks before the young hatched. The young left the nest site after 2–3 weeks, although the parents continued to care for it.

The great auk was an important part of many Native American cultures, both as a food source and as a symbolic item. Many Maritime Archaic people were buried with great auk bones. One burial discovered included someone covered by more than 200 great auk beaks, which are presumed to be the remnants of a cloak made of great auks' skins. Early European explorers to the Americas used the great auk as a convenient food source or as fishing bait, reducing its numbers. The bird's down was in high demand in Europe, a factor that largely eliminated the European populations by the mid-16th century. Scientists soon began to realize that the great auk was disappearing and it became the beneficiary of many early environmental laws, but this proved ineffectual.

Its growing rarity increased interest from European museums and private collectors in obtaining skins and eggs of the bird. On 3 June 1844, the last two confirmed specimens were killed on Eldey, off the coast of Iceland, ending the last known breeding attempt. Later reports of roaming individuals being seen or caught are unconfirmed. A record of one great auk in 1852 is considered by some to be the last sighting of a member of the species. The great auk is mentioned in several novels, and the scientific journal of the American Ornithological Society was named The Auk (now Ornithology) in honour of the bird until 2021.

🔗 Biography

🔗 Color 🔗 Visual arts

Non-photo blue (or non-repro blue) is a common tool used in the graphic design and print industry.

🔗 Medicine

The choking game (also known as the fainting game and a wide variety of slang terms) refers to intentionally cutting off oxygen to the brain with the goal of inducing temporary loss of consciousness and euphoria.

🔗 Computer science 🔗 Philosophy 🔗 Psychology 🔗 Philosophy/Social and political philosophy 🔗 Philosophy/Philosophy of science 🔗 Philosophy/Contemporary philosophy 🔗 Philosophy/Philosophy of mind 🔗 Sociology 🔗 Cultural Evolution

Memetics is a theory of the evolution of culture based on Darwinian principles with the meme as the unit of culture. The term "meme" was coined by biologist Richard Dawkins in his 1976 book The Selfish Gene, to illustrate the principle that he later called "Universal Darwinism". All evolutionary processes depend on information being copied, varied, and selected, a process also known as variation with selective retention. The information that is copied is called the replicator, and genes are the replicator for biological evolution. Dawkins proposed that the same process drives cultural evolution, and he called this second replicator the "meme". He gave as examples, tunes, catchphrases, fashions, and technologies. Like genes, memes are selfish replicators and have causal efficacy; in other words, their properties influence their chances of being copied and passed on. Some succeed because they are valuable or useful to their human hosts while others are more like viruses.

Just as genes can work together to form co-adapted gene complexes, so groups of memes acting together form co-adapted meme complexes or memeplexes. Memeplexes include (among many other things) languages, traditions, scientific theories, financial institutions, and religions. Dawkins famously referred to religions as "viruses of the mind".

Among proponents of memetics are psychologist Susan Blackmore, author of The Meme Machine, who argues that when our ancestors began imitating behaviours, they let loose a second replicator and co-evolved to become the "meme machines" that copy, vary, and select memes in culture. Philosopher Daniel Dennett develops memetics extensively, notably in his books Darwin's Dangerous Idea, and From Bacteria to Bach and Back. He describes the units of memes as "the smallest elements that replicate themselves with reliability and fecundity." and claims that "Human consciousness is itself a huge complex of memes." In The Beginning of Infinity, physicist David Deutsch contrasts static societies that depend on anti-rational memes suppressing innovation and creativity, with dynamic societies based on rational memes that encourage enlightenment values, scientific curiosity, and progress.

Criticisms of memetics include claims that memes do not exist, that the analogy with genes is false, that the units cannot be specified, that culture does not evolve through imitation, and that the sources of variation are intelligently designed rather than random. Critics of memetics include biologist Stephen Jay Gould who calls memetics a "meaningless metaphor". Philosopher Dan Sperber argues against memetics as a viable approach to cultural evolution because cultural items are not directly copied or imitated but are reproduced. Anthropologist Robert Boyd and biologist Peter Richerson work within the alternative, and more mainstream, field of cultural evolution theory and gene-culture coevolution. Dual inheritance theory has much in common with memetics but rejects the idea that memes are replicators. From this perspective, memetics is seen as just one of several approaches to cultural evolution and one that is generally considered less useful than the alternatives of gene-culture coevolution or dual inheritance theory. The main difference is that dual inheritance theory ultimately depends on biological advantage to genes, whereas memetics treats memes as a second replicator in its own right. Memetics also extends to the analysis of Internet culture and Internet memes.

🔗 Mathematics

This is a list of mathematical symbols used in all branches of mathematics to express a formula or to represent a constant.

A mathematical concept is independent of the symbol chosen to represent it. For many of the symbols below, the symbol is usually synonymous with the corresponding concept (ultimately an arbitrary choice made as a result of the cumulative history of mathematics), but in some situations, a different convention may be used. For example, depending on context, the triple bar "≡" may represent congruence or a definition. However, in mathematical logic, numerical equality is sometimes represented by "≡" instead of "=", with the latter representing equality of well-formed formulas. In short, convention dictates the meaning.

Each symbol is shown both in HTML, whose display depends on the browser's access to an appropriate font installed on the particular device, and typeset as an image using TeX.

🔗 Astronomy 🔗 Astronomy/Astronomical objects

PSR J1748−2446ad is the fastest-spinning pulsar known, at 716 Hz, or 716 times per second. This pulsar was discovered by Jason W. T. Hessels of McGill University on November 10, 2004 and confirmed on January 8, 2005.

If the neutron star is assumed to contain less than two times the mass of the Sun, within the typical range of neutron stars, its radius is constrained to be less than 16 km. At its equator it is spinning at approximately 24% of the speed of light, or over 70,000 km per second.

The pulsar is located in a globular cluster of stars called Terzan 5, located approximately 18,000 light-years from Earth in the constellation Sagittarius. It is part of a binary system and undergoes regular eclipses with an eclipse magnitude of about 40%. Its orbit is highly circular with a 26-hour period. The other object is at least 0.14 solar masses, with a radius of 5–6 solar radii. Hessels et al. state that the companion may be a "bloated main-sequence star, possibly still filling its Roche Lobe". Hessels et al. go on to speculate that gravitational radiation from the pulsar might be detectable by LIGO.