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🔗 Birds

Wrens are a family, Troglodytidae, of small brown passerine birds. The family includes 96 species and is divided into 19 genera. All species are restricted to the New World except for the Eurasian wren that is widely distributed in the Old World. In Anglophone regions, the Eurasian wren is commonly known simply as the "wren", as it is the originator of the name. The name wren has been applied to other, unrelated birds, particularly the New Zealand wrens (Acanthisittidae) and the Australian wrens (Maluridae).

Most wrens are visually inconspicuous though they have loud and often complex songs. Exceptions include the relatively large members of the genus Campylorhynchus, which can be quite bold in their behaviour. Wrens have short wings that are barred in most species, and they often hold their tails upright. Wrens are primarily insectivorous, eating insects, spiders and other small invertebrates, but many species also eat vegetable matter and some eat small frogs and lizards.

🔗 Mathematics

The Ulam spiral or prime spiral is a graphical depiction of the set of prime numbers, devised by mathematician Stanisław Ulam in 1963 and popularized in Martin Gardner's Mathematical Games column in Scientific American a short time later. It is constructed by writing the positive integers in a square spiral and specially marking the prime numbers.

Ulam and Gardner emphasized the striking appearance in the spiral of prominent diagonal, horizontal, and vertical lines containing large numbers of primes. Both Ulam and Gardner noted that the existence of such prominent lines is not unexpected, as lines in the spiral correspond to quadratic polynomials, and certain such polynomials, such as Euler's prime-generating polynomial x² − x + 41, are believed to produce a high density of prime numbers. Nevertheless, the Ulam spiral is connected with major unsolved problems in number theory such as Landau's problems. In particular, no quadratic polynomial has ever been proved to generate infinitely many primes, much less to have a high asymptotic density of them, although there is a well-supported conjecture as to what that asymptotic density should be.

In 1932, more than thirty years prior to Ulam's discovery, the herpetologist Laurence Klauber constructed a triangular, non-spiral array containing vertical and diagonal lines exhibiting a similar concentration of prime numbers. Like Ulam, Klauber noted the connection with prime-generating polynomials, such as Euler's.

🔗 Computing 🔗 Computer science 🔗 Computing/Software

A Turing tarpit (or Turing tar-pit) is any programming language or computer interface that allows for flexibility in function but is difficult to learn and use because it offers little or no support for common tasks. The phrase was coined in 1982 by Alan Perlis in the Epigrams on Programming:

54. Beware of the Turing tar-pit in which everything is possible but nothing of interest is easy.

In any Turing complete language, it is possible to write any computer program, so in a very rigorous sense nearly all programming languages are equally capable. Showing that theoretical ability is not the same as usefulness in practice, Turing tarpits are characterized by having a simple abstract machine that requires the user to deal with many details in the solution of a problem. At the extreme opposite are interfaces that can perform very complex tasks with little human intervention but become obsolete if requirements change slightly.

Some esoteric programming languages, such as Brainfuck, are specifically referred to as "Turing tarpits" because they deliberately implement the minimum functionality necessary to be classified as Turing complete languages. Using such languages is a form of mathematical recreation: programmers can work out how to achieve basic programming constructs in an extremely difficult but mathematically Turing-equivalent language.

🔗 Evolutionary biology 🔗 Ecology

Motion camouflage is camouflage which provides a degree of concealment for a moving object, given that motion makes objects easy to detect however well their coloration matches their background or breaks up their outlines.

The principal form of motion camouflage, and the type generally meant by the term, involves an attacker's mimicking the optic flow of the background as seen by its target. This enables the attacker to approach the target while appearing to remain stationary from the target's perspective, unlike in classical pursuit (where the attacker moves straight towards the target at all times, and often appears to the target to move sideways). The attacker chooses its flight path so as to remain on the line between the target and some landmark point. The target therefore does not see the attacker move from the landmark point. The only visible evidence that the attacker is moving is its looming, the change in size as the attacker approaches.

Camouflage is sometimes facilitated by motion, as in the leafy sea dragon and some stick insects. These animals complement their passive camouflage by swaying like plants in the wind or ocean currents, delaying their recognition by predators.

First discovered in hoverflies in 1995, motion camouflage by minimizing optic flow has been demonstrated in another insect order, dragonflies, as well as in two groups of vertebrates, falcons and echolocating bats. Since bats hunt at night, they cannot use camouflage. Instead they use an efficient homing strategy called constant absolute target direction. It has been suggested that anti-aircraft missiles could benefit from similar techniques.

🔗 Video games 🔗 Law

Bleem! (styled as bleem!) is a commercial PlayStation emulator released by the Bleem! Company in 1999 for IBM-compatible PCs and Dreamcast. It is notable for being one of the few commercial software emulators to be aggressively marketed during the emulated console's lifetime, and was the center of multiple controversial lawsuits.

🔗 Computing

In computing, the Two Generals' Problem is a thought experiment meant to illustrate the pitfalls and design challenges of attempting to coordinate an action by communicating over an unreliable link. In the experiment, two generals are only able to communicate with one another by sending a messenger through enemy territory. The experiment asks how they might reach an agreement on the time to launch an attack, while knowing that any messenger they send could be captured.

It is related to the more general Byzantine Generals Problem and appears often in introductory classes about computer networking (particularly with regard to the Transmission Control Protocol, where it shows that TCP can't guarantee state consistency between endpoints and why this is the case), though it applies to any type of two-party communication where failures of communication are possible. A key concept in epistemic logic, this problem highlights the importance of common knowledge. Some authors also refer to this as the Two Generals' Paradox, the Two Armies Problem, or the Coordinated Attack Problem. The Two Generals' Problem was the first computer communication problem to be proved to be unsolvable. An important consequence of this proof is that generalizations like the Byzantine Generals problem are also unsolvable in the face of arbitrary communication failures, thus providing a base of realistic expectations for any distributed consistency protocols.

🔗 Computer Security 🔗 Computer Security/Computing

Slopsquatting is a type of cybersquatting. It is the practice of registering a non-existent software package name that a large language model (LLM) may hallucinate in its output, whereby someone unknowingly may copy-paste and install the software package without realizing it is fake. Attempting to install a non-existent package should result in an error, but some have exploited this for their gain in the form of typosquatting.

The name is a portmanteau of "slop" and "typosquatting".

🔗 Soviet Union 🔗 Military history 🔗 Military history/Military science, technology, and theory 🔗 Military history/World War II 🔗 Military history/Russian, Soviet and CIS military history

Deep operation (Russian: Глубокая операция, glubokaya operatsiya), also known as Soviet Deep Battle, was a military theory developed by the Soviet Union for its armed forces during the 1920s and 1930s. It was a tenet that emphasized destroying, suppressing or disorganizing enemy forces not only at the line of contact, but throughout the depth of the battlefield.

The term comes from Vladimir Triandafillov, an influential military writer, who worked with others to create a military strategy with its own specialized operational art and tactics. The concept of deep operations was a national strategy, tailored to the economic, cultural and geopolitical position of the Soviet Union. In the aftermath of several failures or defeats in the Russo-Japanese War, First World War and Polish–Soviet War, the Soviet High Command (Stavka) focused on developing new methods for the conduct of war. This new approach considered military strategy and tactics, but also introduced a new intermediate level of military art: operations. The Soviet Union was the first country to officially distinguish the third level of military thinking which occupied the position between strategy and tactics.

Using these templates, the Soviets developed the concept of deep battle and by 1936 it had become part of the Red Army Field Regulations. Deep operations had two phases: the tactical deep battle, followed by the exploitation of tactical success, known as the conduct of deep battle operations. Deep battle envisaged the breaking of the enemy's forward defenses, or tactical zones, through combined arms assaults, which would be followed up by fresh uncommitted mobile operational reserves sent to exploit the strategic depth of an enemy front. The goal of a deep operation was to inflict a decisive strategic defeat on the enemy's logistical abilities and render the defence of their front more difficult, impossible—or, indeed, irrelevant. Unlike most other doctrines, deep battle stressed combined arms cooperation at all levels: strategic, operational, and tactical.

🔗 Korea 🔗 China 🔗 East Asia 🔗 Writing systems 🔗 Japan 🔗 Japan/History 🔗 Japan/Culture 🔗 Korea/one or more inactive working groups 🔗 Japan/Education

The Thousand Character Classic (Chinese: 千字文; pinyin: Qiānzì Wén), also known as the Thousand Character Text, is a Chinese poem that has been used as a primer for teaching Chinese characters to children from the sixth century onward. It contains exactly one thousand characters, each used only once, arranged into 250 lines of four characters apiece and grouped into four line rhyming stanzas to make it easy to memorize. It is sung, much as children learning the Latin alphabet sing an "alphabet song." Along with the Three Character Classic and the Hundred Family Surnames, it has formed the basis of literacy training in traditional China.

The first line is Tian di xuan huang (traditional Chinese: 天地玄黃; simplified Chinese: 天地玄黄; pinyin: Tiāndì xuán huáng; Jyutping: tin1 dei6 jyun4 wong4; lit. 'Heaven and Earth Dark and Yellow') and the last line, Yan zai hu ye (焉哉乎也; Yān zāi hū yě; yin1 zoi1 fu4 jaa5) explains the use of the grammatical particles "yan", "zai", "hu", and "ye".

🔗 Trains 🔗 Trains/Operations

Signalling block systems enable the safe and efficient operation of railways by preventing collisions between trains. The basic principle is that a route is broken up into a series of sections or "blocks". Only one train may occupy a block at a time, and the blocks are sized to allow a train to stop within them. That ensures that a train always has time to stop before getting dangerously close to another train on the same line. The block system is referred to in the UK as the method of working, in the US as the method of operation, and in Australia as safeworking.

In most situations, a system of signals is used to control the passage of trains between the blocks. When a train enters a block, signals at both ends change to indicate that the block is occupied, typically using red lamps or indicator flags. When a train first enters a block, the rear of the same train has not yet left the previous block, so both blocks are marked as occupied. That ensures there is slightly less than one block length on either end of the train that is marked as occupied, so any other train approaching that section will have enough room to stop in time, even if the first train has stopped dead on the tracks. The previously-occupied block will only be marked unoccupied when the end of the train has entirely left it, leaving the entire block clear.

Block systems have the disadvantage that they limit the number of trains on a particular route to something fewer than the number of blocks. Since the route has a fixed length, increasing the number of trains requires the creation of more blocks, which means the blocks are shorter and trains have to operate at lower speeds in order to stop safely. As a result, the number and size of blocks are closely related to the overall route capacity, and cannot be changed easily because expensive alterations to the signals along the line would be required.

Block systems are used to control trains between stations and yards, but not normally within the yards, where some other method is used. Any block system is defined by its associated physical equipment and by the application of a relevant set of rules. Some systems involve the use of signals while others do not. Some systems are specifically designed for single track railways, on which there is a danger of both head-on and rear-end collision, as opposed to double track, on which the main danger is rear-end collisions.