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🔗 Mathematics

A wallpaper group (or plane symmetry group or plane crystallographic group) is a mathematical classification of a two-dimensional repetitive pattern, based on the symmetries in the pattern. Such patterns occur frequently in architecture and decorative art, especially in textiles and tiles as well as wallpaper.

The simplest wallpaper group, Group p1, applies when there is no symmetry other than the fact that a pattern repeats over regular intervals in two dimensions, as shown in the section on p1 below.

Consider the following examples of patterns with more forms of symmetry:

Examples A and B have the same wallpaper group; it is called p4m in the IUC notation and *442 in the orbifold notation. Example C has a different wallpaper group, called p4g or 4*2 . The fact that A and B have the same wallpaper group means that they have the same symmetries, regardless of details of the designs, whereas C has a different set of symmetries despite any superficial similarities.

The number of symmetry groups depends on the number of dimensions in the patterns. Wallpaper groups apply to the two-dimensional case, intermediate in complexity between the simpler frieze groups and the three-dimensional space groups. Subtle differences may place similar patterns in different groups, while patterns that are very different in style, color, scale or orientation may belong to the same group.

A proof that there were only 17 distinct groups of such planar symmeries was first carried out by Evgraf Fedorov in 1891 and then derived independently by George Pólya in 1924. The proof that the list of wallpaper groups was complete only came after the much harder case of space groups had been done. The seventeen possible wallpaper groups are listed below in § The seventeen groups.

🔗 Environment 🔗 Books 🔗 Futures studies 🔗 Molecular Biology 🔗 Molecular Biology/Genetics

The Population Bomb is a 1968 book co-authored by former Stanford University professor Paul R. Ehrlich and former Stanford senior researcher in conservation biology Anne H. Ehrlich. From the opening page, it predicted worldwide famines due to overpopulation, as well as other major societal upheavals, and advocated immediate action to limit population growth. Fears of a "population explosion" existed in the mid-20th century baby boom years, but the book and its authors brought the idea to an even wider audience.

The book has been criticized since its publication for an alarmist tone, and over the subsequent decades, for inaccurate assertions and failed predictions. For instance, regional famines have occurred since the publication of the book, but not world famines. The Ehrlichs themselves still stand by the book despite the flaws identified by its critics, with Paul stating in 2009 that "perhaps the most serious flaw in The Bomb was that it was much too optimistic about the future," despite having predicted catastrophic global famines that never came to pass. They believe that it achieved their goals because "it alerted people to the importance of environmental issues and brought human numbers into the debate on the human future."

🔗 Japan

The Metropolitan Area Outer Underground Discharge Channel (Japanese: 首都圏外郭放水路, Hepburn: shutoken gaikaku hōsuiro), is an underground water infrastructure project in Kasukabe, Saitama, Japan. It is the world's largest underground flood water diversion facility, built to mitigate overflowing of the city's major waterways and rivers during rain and typhoon seasons. It is located between Showa in Tokyo and Kasukabe in Saitama prefecture, on the outskirts of the city of Tokyo in the Greater Tokyo Area, Japan.

Work on the project started in 1992 and was completed by early 2006. It consists of five concrete containment silos with heights of 65 m and diameters of 32 m, connected by 6.4 km of tunnels, 50 m beneath the surface, as well as a large water tank with a height of 25.4 m, with a length of 177m, with a width of 78m, and with 59 massive pillars connected to 78 10 MW (13,000 hp) pumps that can pump up to 200 tons of water into the Edo River per second.

"Ryukyukan" for Underground Exploration Museum of The Metropolitan Area Outer Underground Discharge Channel is also a tourist attraction and can be visited for 3.000 Yen; however, as the tours are conducted in Japanese, a Japanese speaker must be present in the group to act as a translator for non-Japanese speakers.

🔗 Chemical and Bio Engineering

In flow chemistry, a chemical reaction is run in a continuously flowing stream rather than in batch production. In other words, pumps move fluid into a tube, and where tubes join one another, the fluids contact one another. If these fluids are reactive, a reaction takes place. Flow chemistry is a well-established technique for use at a large scale when manufacturing large quantities of a given material. However, the term has only been coined recently for its application on a laboratory scale. Often, microreactors are used.

🔗 Philosophy 🔗 Philosophy/Logic

Bulverism is a term for a rhetorical fallacy that combines circular reasoning with presumption or condescenscion. The method of Bulverism is to "assume that your opponent is wrong, and explain his error." The Bulverist assumes a speaker's argument is invalid or false and then explains why the speaker came to make that mistake, even if the opponents's claim is actually right, attacking the speaker or the speaker's motive. The term Bulverism was coined by C. S. Lewis to poke fun at a very serious error in thinking that, he alleges, recurs often in a variety of religious, political, and philosophical debates.

Similar to Antony Flew's "subject/motive shift", Bulverism is a fallacy of irrelevance. One accuses an argument of being wrong on the basis of the arguer's identity or motive, but these are strictly speaking irrelevant to the argument's validity or truth.

🔗 Biography 🔗 Science Fiction 🔗 Literature 🔗 Poland 🔗 Biography/arts and entertainment

Stanisław Herman Lem (Polish: [staˈɲiswaf ˈlɛm] (listen); 12 or 13 September 1921 – 27 March 2006) was a Polish writer of science fiction, philosophy, and satire. Lem's books have been translated into 41 languages and have sold over 45 million copies. From the 1950s to 2000s, he published many books, both science fiction and philosophical/futurological. Worldwide, he is best known as the author of the 1961 novel Solaris, which has been made into a feature film three times. In 1976, Theodore Sturgeon wrote that Lem was the most widely read science fiction writer in the world. The total print of Lem's books is over 30 million copies.

Lem's works explore philosophical themes through speculation on technology, the nature of intelligence, the impossibility of communication with and understanding of alien intelligence, despair about human limitations, and humanity's place in the universe. They are sometimes presented as fiction, but others are in the form of essays or philosophical books.

Translating his works is difficult due to passages with elaborate word formation, idiomatic wordplay, alien or robotic poetry, and puns.

🔗 Human rights 🔗 Korea 🔗 Correction and Detention Facilities 🔗 Korea/North Korea

Hwasong concentration camp (Chosŏn'gŭl: 화성 제16호 관리소, also spelled Hwasŏng or Hwaseong) is a labor camp in North Korea for political prisoners. The official name is Kwan-li-so (Penal-labor colony) No. 16.

🔗 Aviation 🔗 Organized Labour

The Professional Air Traffic Controllers Organization or PATCO was a United States trade union that operated from 1968 until its decertification in 1981 following an illegal strike that was broken by the Reagan Administration. According to labor historian Joseph A. McCartin, the 1981 strike and defeat of PATCO was "one of the most important events in late twentieth century U.S. labor history".

🔗 Numbers

In number theory, a narcissistic number (also known as a pluperfect digital invariant (PPDI), an Armstrong number (after Michael F. Armstrong) or a plus perfect number) in a given number base ${\displaystyle b}$ is a number that is the sum of its own digits each raised to the power of the number of digits.

🔗 Computing 🔗 Computer Security 🔗 Computer Security/Computing 🔗 Computing/Software 🔗 Cryptography 🔗 Cryptography/Computer science

Pretty Good Privacy (PGP) is an encryption program that provides cryptographic privacy and authentication for data communication. PGP is used for signing, encrypting, and decrypting texts, e-mails, files, directories, and whole disk partitions and to increase the security of e-mail communications. Phil Zimmermann developed PGP in 1991.

PGP and similar software follow the OpenPGP, an open standard of PGP encryption software, standard (RFC 4880) for encrypting and decrypting data.