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🔗 Military history 🔗 Military history/North American military history 🔗 Military history/United States military history 🔗 Military history/Military science, technology, and theory 🔗 Military history/Weaponry 🔗 Military history/Cold War

The W54 (also known as the Mark 54 or B54) was a tactical nuclear warhead developed by the United States in the late 1950s. The weapon is notable for being the smallest nuclear weapon in both weight and yield to have entered US service. It was a compact implosion device containing plutonium-239 as its fissile material, and in its various versions and mods it had a yield of 10 to 1,000 tons of TNT (42 to 4,184 gigajoules).

The weapon had two distinct versions: a warhead used in the AIM-26 Falcon air-to-air missile and in the Davy Crockett recoilless gun, and another used in the Special Atomic Demolition Munition (SADM) system, along with several mods for each version. The two types are distinct in that much of the design between them was different, to the point that during the development of the SADM it was proposed that it be given its own unique mark designation.

A later development was the W72, which was a rebuilt W54 used with the AGM-62 Walleye guided bomb. The W72 was in service until 1979.

🔗 Chemicals 🔗 Palaeontology 🔗 Geology 🔗 Evolutionary biology 🔗 Limnology and Oceanography

The Great Oxidation Event (GOE), sometimes also called the Great Oxygenation Event, Oxygen Catastrophe, Oxygen Crisis, Oxygen Holocaust, or Oxygen Revolution, was a time period when the Earth's atmosphere and the shallow ocean experienced a rise in oxygen, approximately 2.4 billion years ago (2.4 Ga) to 2.1–2.0 Ga during the Paleoproterozoic era. Geological, isotopic, and chemical evidence suggests that biologically induced molecular oxygen (dioxygen, O₂) started to accumulate in Earth's atmosphere and changed Earth's atmosphere from a weakly reducing atmosphere to an oxidizing atmosphere, causing almost all life on Earth to go extinct. The cyanobacteria producing the oxygen caused the event which enabled the subsequent development of multicellular forms.

🔗 California 🔗 California/San Francisco Bay Area 🔗 Internet

The "PayPal Mafia" is a group of former PayPal employees and founders who have since founded and developed additional technology companies such as Tesla Motors, LinkedIn, Palantir Technologies, SpaceX, YouTube, Yelp, and Yammer. Most of the members attended Stanford University or University of Illinois at Urbana–Champaign at some point in their studies.

🔗 Computing 🔗 Trains 🔗 Trains/Rail transport modelling

The Tech Model Railroad Club (TMRC) is a student organization at the Massachusetts Institute of Technology (MIT). Historically it has been a wellspring of hacker culture and the oldest such hacking group in North America. Formed in 1946, its HO scale layout specializes in automated operation of model trains.

🔗 Computer science

In computer science, a succinct data structure is a data structure which uses an amount of space that is "close" to the information-theoretic lower bound, but (unlike other compressed representations) still allows for efficient query operations. The concept was originally introduced by Jacobson to encode bit vectors, (unlabeled) trees, and planar graphs. Unlike general lossless data compression algorithms, succinct data structures retain the ability to use them in-place, without decompressing them first. A related notion is that of a compressed data structure, in which the size of the data structure depends upon the particular data being represented.

Suppose that ${\displaystyle Z}$ is the information-theoretical optimal number of bits needed to store some data. A representation of this data is called:

• implicit if it takes ${\displaystyle Z+O(1)}$ bits of space,
• succinct if it takes ${\displaystyle Z+o(Z)}$ bits of space, and
• compact if it takes ${\displaystyle O(Z)}$ bits of space.

For example, a data structure that uses ${\displaystyle 2Z}$ bits of storage is compact, ${\displaystyle Z+{\sqrt {Z}}}$ bits is succinct, ${\displaystyle Z+\lg Z}$ bits is also succinct, and ${\displaystyle Z+3}$ bits is implicit.

Implicit structures are thus usually reduced to storing information using some permutation of the input data; the most well-known example of this is the heap.

🔗 Biography 🔗 Medicine 🔗 Women's History 🔗 New York (state) 🔗 Medicine/Society and Medicine 🔗 New York (state)/Long Island 🔗 Northern Ireland

Mary Mallon (September 23, 1869 – November 11, 1938), also known as Typhoid Mary, was an Irish-born cook believed to have infected 53 people with typhoid fever, three of whom died, and the first person in the United States identified as an asymptomatic carrier of the disease, Salmonella typhi. Because she persisted in working as a cook, by which she exposed others to the disease, she was twice forcibly quarantined by authorities, eventually for the final two decades of her life. Mallon died after a total of nearly 30 years in isolation.

🔗 Military history 🔗 Military history/Military science, technology, and theory

The Kearny fallout meter, or KFM, is an expedient radiation meter. It is designed such that someone with a normal mechanical ability would be able to construct it before or during a nuclear attack, using common household items.

The Kearny fallout meter was developed by Cresson Kearny from research performed at Oak Ridge National Laboratory and published in the civil defense manual Nuclear War Survival Skills (ISBN 0-942487-01-X). The plans were originally released in Oak Ridge National Laboratory publication ORNL-5040, The KFM, A Homemade Yet Accurate and Dependable Fallout Meter and have been formatted in a newsprint-ready layout so that they may be quickly printed with accurate dimensions in local newspapers. It must be built from a correctly scaled copy of the plans; photocopies and printouts of digital copies may not be to scale.

🔗 Soviet Union 🔗 Russia 🔗 Russia/language and literature of Russia 🔗 Russia/history of Russia 🔗 Georgia (country)

Before he became a Bolshevik revolutionary and the leader of the Soviet Union, Joseph Stalin was a promising poet.

🔗 Chemicals

In organic chemistry, a Platonic hydrocarbon is a hydrocarbon whose structure matches one of the five Platonic solids, with carbon atoms replacing its vertices, carbon–carbon bonds replacing its edges, and hydrogen atoms as needed.

Not all Platonic solids have molecular hydrocarbon counterparts; those that do are the tetrahedron (tetrahedrane), the cube (cubane), and the dodecahedron (dodecahedrane). The possibility and existence of each platonic hydrocarbon is affected by the number of bonds to each carbon vertex and the angle strain between the bonds at each vertex.

🔗 Norway

Uniquely, the Norwegian archipelago of Svalbard, located in the High Arctic, is an entirely visa-free zone. However, travelers who have a visa requirement to enter mainland Norway/the Schengen area must have a Schengen visa if they travel via mainland Norway/the Schengen area. This must be a double-entry visa so they can return to mainland Norway/the Schengen area.

Those traveling to and from Svalbard must bring passports or national identity cards, as all are subject to identity check. Passports or national identity cards satisfy the Schengen regulatory requirements for identity verification. Due to a transitional arrangement, Norwegian citizens could also prove their identity with a document issued in Norway which included at least name, photo and date of birth, such as a Norwegian driving licence issued after 1998; the transitional period ended on 31 December 2021.

Everybody may live and work in Svalbard indefinitely regardless of country of citizenship. The Svalbard Treaty grants treaty nationals equal right of abode as Norwegian nationals. Non-treaty nationals may live and work indefinitely visa-free as well. Per Sefland, then Governor of Svalbard, said "It has been a chosen policy so far that we haven't made any difference between the treaty citizens and those from outside the treaty". "Regulations concerning rejection and expulsion from Svalbard" are enforced on a non-discriminatory basis. Grounds for exclusion include lack of means of support, and violation of laws or regulations.

Hans-Henrik Hartmann, then head of the legal unit at the Norwegian government's immigration department, said, "If an asylum seeker is refused residence in Norway he can settle in Svalbard so long as he can get there and is able to pay for himself." Svalbard has a high cost of living, but only a limited welfare system. Welfare and health care is available only for Norwegians and for workers employed by a Norwegian company.

The Norwegian Nationality Act applies to Svalbard, cf. Section 1. However, the Act does not provide any special rules for foreign nationals residing on Svalbard. Foreigners living on Svalbard must meet the conditions of the law to obtain Norwegian citizenship. In order to acquire Norwegian citizenship upon application, there is, according to the main rule, a requirement to fulfill the conditions for a permanent residence permit, and consequently a requirement for residence on the Norwegian mainland with a residence permit. Such permits are granted in accordance with the Norwegian Immigration Act. Because the Norwegian Immigration Act does not apply to Svalbard, cf. Section 6, residence on Svalbard does not qualify foreign nationals for residence permits on the Norwegian mainland.