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🔗 Mathematics

Hilbert's paradox of the Grand Hotel (colloquial: Infinite Hotel Paradox or Hilbert's Hotel) is a thought experiment which illustrates a counterintuitive property of infinite sets. It is demonstrated that a fully occupied hotel with infinitely many rooms may still accommodate additional guests, even infinitely many of them, and this process may be repeated infinitely often. The idea was introduced by David Hilbert in a 1924 lecture "Über das Unendliche", reprinted in (Hilbert 2013, p.730), and was popularized through George Gamow's 1947 book One Two Three... Infinity.

🔗 Mathematics

Modern Arabic mathematical notation is a mathematical notation based on the Arabic script, used especially at pre-university levels of education. Its form is mostly derived from Western notation, but has some notable features that set it apart from its Western counterpart. The most remarkable of those features is the fact that it is written from right to left following the normal direction of the Arabic script. Other differences include the replacement of the Greek and Latin alphabet letters for symbols with Arabic letters and the use of Arabic names for functions and relations.

🔗 Languages 🔗 Constructed languages

Ithkuil is an experimental constructed language created by John Quijada. It is designed to express deeper levels of human cognition briefly yet overtly and clearly, particularly with regard to human categorization. It is a cross between an a priori philosophical and a logical language. It tries to minimize the vagueness and semantic ambiguity found in natural human languages. Ithkuil is notable for its grammatical complexity and extensive phoneme inventory, the latter being simplified in an upcoming redesign. The name "Ithkuil" is an anglicized form of Iţkuîl, which in the original form roughly means "hypothetical representation of a language". Quijada states he did not create Ithkuil to be auxiliary or used in everyday conversations. He wanted the language to be used for more elaborate and profound fields where more insightful thoughts are expected, such as philosophy, arts, science and politics.

Meaningful phrases or sentences can usually be expressed in Ithkuil with fewer linguistic units than in natural languages. For example, the two-word Ithkuil sentence "Tram-mļöi hhâsmařpţuktôx" can be translated into English as "On the contrary, I think it may turn out that this rugged mountain range trails off at some point". Quijada deems his creation as too complex to have developed naturally, seeing it as an exercise in exploring how languages could function. No person, including Quijada himself, is known to be able to speak Ithkuil fluently. It was featured in the Language Creation Conference's 6th Conlang Relay.

Four versions of the language have been publicized: the initial version in 2004, a simplified version called Ilaksh in 2007, the current version in 2011, and as of 2017, various revisions of a new version of the language, named Ithkuil IV. In 2004—and again in 2009 with Ilaksh—Ithkuil was featured in the Russian-language popular science and IT magazine Computerra. In 2008, David Peterson awarded it the Smiley Award. In 2013, Bartłomiej Kamiński codified the language to be able to quickly parse complicated sentences. Julien Tavernier and anonymous others have followed suit. Since July 2015, Quijada has released several Ithkuil songs in a prog rock style as part of the album Kaduatán, which translates to "Wayfarers". Recently, online communities for the language have developed in English, Russian, Mandarin, and Japanese.

🔗 China/Chinese history 🔗 China 🔗 Toys 🔗 Project-independent assessment

The bamboo-copter, also known as the bamboo dragonfly or Chinese top (Chinese zhuqingting (竹蜻蜓), Japanese taketonbo 竹蜻蛉), is a toy helicopter rotor that flies up when its shaft is rapidly spun. This helicopter-like top originated in Jin dynasty China around 320 AD, and was the object of early experiments by English engineer George Cayley, the inventor of modern aeronautics.

In China, the earliest known flying toys consisted of feathers at the end of a stick, which was rapidly spun between the hands and released into flight. "While the Chinese top was no more than a toy, it is perhaps the first tangible device of what we may understand as a helicopter."

The Jin dynasty Daoist philosopher Ge Hong's (c. 317) book Baopuzi (抱樸子 "Master Who Embraces Simplicity") mentioned a flying vehicle in what Joseph Needham calls "truly an astonishing passage".

Some have made flying cars [feiche 飛車] with wood from the inner part of the jujube tree, using ox-leather (straps) fastened to returning blades so as to set the machine in motion [huan jian yi yin chiji 環劍以引其機]. Others have had the idea of making five snakes, six dragons and three oxen, to meet the "hard wind" [gangfeng 罡風] and ride on it, not stopping until they have risen to a height of forty li. That region is called [Taiqing 太清] (the purest of empty space). There the [qi] is extremely hard, so much so that it can overcome (the strength of) human beings. As the Teacher says: "The kite (bird) flies higher and higher spirally, and then only needs to stretch its two wings, beating the air no more, in order to go forward by itself. This is because it starts gliding (lit. riding) on the 'hard wind' [gangqi 罡炁]. Take dragons, for example; when they first rise they go up using the clouds as steps, and after they have attained a height of forty li then they rush forward effortlessly (lit. automatically) (gliding)." This account comes from the adepts [xianren 仙人], and is handed down to ordinary people, but they are not likely to understand it.

Needham concludes that Ge Hong was describing helicopter tops because "'returning (or revolving) blades' can hardly mean anything else, especially in close association with a belt or strap"; and suggests that "snakes", "dragons", and "oxen" refer to shapes of man-lifting kites. Other scholars interpret this Baopuzi passage mythologically instead of literally, based on its context's mentioning fantastic flights through chengqiao (乘蹻 "riding on tiptoe/stilts") and xian (仙 "immortal; adept") techniques. For instance, "If you can ride the arches of your feet, you will be able to wander anywhere in the world without hindrance from mountains or rivers … Whoever takes the correct amulet and gives serious thought to the process may travel a thousand miles by concentrating his thoughts for one double hour." Compare this translation.

Some build a flying vehicle from the pith of the jujube tree and have it drawn by a sword with a thong of buffalo hide at the end of its grip. Others let their thoughts dwell on the preparation of a joint rectangle from five serpents, six dragons, and three buffaloes, and mount in this for forty miles to the region known as Paradise.

This Chinese helicopter toy was introduced into Europe and "made its earliest appearances in Renaissance European paintings and in the drawings of Leonardo da Vinci." The toy helicopter appears in a c. 1460 French picture of the Madonna and Child at the Musée du Palais de Tesse’ in Mans depicting the Child holding a toy copter sitting in Mary’s lap next to St Benôit (unknown artist), and in a 16th-century stained glass panel at the Victoria and Albert Museum in London. A picture from c. 1560 by Pieter Breughel the Elder at the Kunsthistorisches Museum in Vienna, Children's Games, depicts a helicopter top with three airscrews.

"The helicopter top in China led to nothing but amusement and pleasure, but fourteen hundred years later it was to be one of the key elements in the birth of modern aeronautics in the West." Early Western scientists developed flying machines based upon the original Chinese model. The Russian polymath Mikhail Lomonosov developed a spring-driven coaxial rotor in 1743, and the French naturalist Christian de Launoy created a bow drill device with contra-rotating feather propellers.

In 1792, George Cayley began experimenting with helicopter tops, which he later called "rotary wafts" or "elevating fliers". His landmark (1809) article "On Aerial Navigation" pictured and described a flying model with two propellers (constructed from corks and feathers) powered by a whalebone bow drill. "In 1835 Cayley remarked that while the original toy would rise no more than about 20 or 25 feet (6 or 7.5 metres), his improved models would 'mount upward of 90 ft (27 metres) into the air'. This then was the direct ancestor of the helicopter rotor and the aircraft propeller."

Discussing the history of Chinese inventiveness, the British scientist, sinologist, and historian Joseph Needham wrote, "Some inventions seem to have arisen merely from a whimsical curiosity, such as the 'hot air balloons' made from eggshells which did not lead to any aeronautical use or aerodynamic discoveries, or the zoetrope which did not lead onto the kinematograph, or the helicopter top which did not lead to the helicopter."

🔗 Psychology 🔗 Education

Bloom's taxonomy is a set of three hierarchical models used to classify educational learning objectives into levels of complexity and specificity. The three lists cover the learning objectives in cognitive, affective and sensory domains. The cognitive domain list has been the primary focus of most traditional education and is frequently used to structure curriculum learning objectives, assessments and activities.

The models were named after Benjamin Bloom, who chaired the committee of educators that devised the taxonomy. He also edited the first volume of the standard text, Taxonomy of Educational Objectives: The Classification of Educational Goals.

🔗 Technology 🔗 Military history 🔗 Military history/North American military history 🔗 Military history/Military science, technology, and theory 🔗 Architecture 🔗 United Kingdom 🔗 Transport 🔗 Military history/Maritime warfare 🔗 Military history/World War II 🔗 Civil engineering 🔗 Engineering 🔗 Transport/Maritime 🔗 Military history/Canadian military history 🔗 Military history/European military history 🔗 Military history/British military history

Pykrete is a frozen ice alloy , originally made of approximately 14 percent sawdust or some other form of wood pulp (such as paper) and 86 percent ice by weight (6 to 1 by weight). During World War II, Geoffrey Pyke proposed it as a candidate material for a supersized aircraft carrier for the British Royal Navy. Pykrete features unusual properties, including a relatively slow melting rate due to its low thermal conductivity, as well as a vastly improved strength and toughness compared to ordinary ice. These physical properties can make the material comparable to concrete, as long as the material is kept frozen.

Pykrete is slightly more difficult to form than concrete, as it expands during the freezing process. However, it can be repaired and maintained using seawater as a raw material. The mixture can be moulded into any shape and frozen, and it will be tough and durable, as long as it is kept at or below freezing temperature. Resistance to gradual creep or sagging is improved by lowering the temperature further, to −15 °C (5 °F).

🔗 Ancient Near East 🔗 Assyria 🔗 Mythology 🔗 Project-independent assessment 🔗 Intertranswiki/OKA

The Descent of Inanna into the Underworld (or, in its Akkadian version, Descent of Ishtar into the Underworld) or Angalta ("From the Great Sky") is a Sumerian myth that narrates the descent of the goddess Inanna (Ishtar in Akkadian) into the Underworld to overthrow its ruler, her sister Ereshkigal, the "Queen of the Dead." But following the removal of her adornments, she perishes and her corpse is suspended on a nail. The god Enki intervenes indirectly, restoring Inanna to life. However, on her return journey, Inanna is required to deliver another living human in exchange for her freedom. She selects Dumuzi, her spouse, who is abruptly transported to the Underworld. In response to the pleas of Dumuzi's sister, Geshtinanna, his circumstances are somewhat ameliorated: he is permitted to remain in the Underworld for only a portion of the year, with his sister assuming his role for the remaining duration.

The myth exists in two main versions: one in Sumerian and the other in Akkadian. The Akkadian version was first discovered and translated in the 1860s. The existence of the longer and older Sumerian version was first established in the early 20th century, but it required approximately fifty years for epigraphists to fully reconstruct and translate it.

The story of Descent of Inanna into the Underworld offers insights into Mesopotamian culture through its numerous characters and developed plot. The influence of this culture on subsequent civilizations is evident in the traces of Mesopotamian elements found in Greece, Phoenicia, and the Old Testament. In the 20th century, the story was used by some psychoanalysis theorists to illustrate psychic mechanisms.

🔗 Constructed languages 🔗 Graphic design

Isotype (International System of Typographic Picture Education) is a method of showing social, technological, biological, and historical connections in pictorial form. It consists of a set of standardized and abstracted pictorial symbols to represent social-scientific data with specific guidelines on how to combine the identical figures using serial repetition. It was first known as the Vienna Method of Pictorial Statistics (Wiener Methode der Bildstatistik), due to its having been developed at the Gesellschafts- und Wirtschaftsmuseum in Wien (Social and Economic Museum of Vienna) between 1925 and 1934. The founding director of this museum, Otto Neurath, was the initiator and chief theorist of the Vienna Method. Gerd Arntz was the artist responsible for realising the graphics. The term Isotype was applied to the method around 1935, after its key practitioners were forced to leave Vienna by the rise of Austrian fascism.

🔗 Germany 🔗 Anthroponymy

In German, Kevinismus ("Kevinism") is the negative preconception German people have of Germans with trendy, exotic-sounding first names considered to be an indicator of a low social class. The protypical example is Kevin, which like most such names came to Germany from Anglo-American culture. Sometimes Chantalismus ("Chantalism") is used as a female equivalent, from the French name Chantal.

🔗 Computing 🔗 Telecommunications 🔗 Lists

This list ranks the countries of the world by the number of mobile phone numbers in use. Note that it is not the number of phone devices that are being given here, but the number of phone numbers in a country. In some countries, one person might have two mobile phones. Also, some mobile phone numbers may be used by machines as a modem (examples: intrusion detection systems, home automation, leak detection).