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π The moving sofa problem
The moving sofa problem or sofa problem is a two-dimensional idealisation of real-life furniture-moving problems and asks for the rigid two-dimensional shape of largest area A that can be maneuvered through an L-shaped planar region with legs of unit width. The area A thus obtained is referred to as the sofa constant. The exact value of the sofa constant is an open problem.
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- "The moving sofa problem" | 2018-07-13 | 215 Upvotes 51 Comments
- "Moving sofa problem" | 2016-12-28 | 38 Upvotes 5 Comments
π Mumps (Programming Language)
MUMPS ("Massachusetts General Hospital Utility Multi-Programming System"), or M, is an imperative, high-level programming language with an integrated transaction processing keyβvalue database. It was originally developed at Massachusetts General Hospital for managing patient medical records and hospital laboratory information systems.
MUMPS technology has since expanded as the predominant database for health information systems and electronic health records in the United States. MUMPS-based information systems, such as Epic Systems', provide health information services for over 78% of patients across the U.S.
A unique feature of the MUMPS technology is its integrated database language, allowing direct, high-speed read-write access to permanent disk storage.
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- "Mumps (Programming Language)" | 2025-06-13 | 103 Upvotes 71 Comments
π Cecilia Payne-Gaposchkin
Cecilia Helena Payne-Gaposchkin (nΓ©e Payne; (1900-05-10)May 10, 1900 β (1979-12-07)December 7, 1979) was a British-born American astronomer and astrophysicist who proposed in her 1925 doctoral thesis that stars were composed primarily of hydrogen and helium. Her groundbreaking conclusion was initially rejected because it contradicted the scientific wisdom of the time, which held that there were no significant elemental differences between the Sun and Earth. Independent observations eventually proved she was actually correct
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- "Cecilia Payne-Gaposchkin" | 2023-10-16 | 225 Upvotes 98 Comments
- "Cecilia Payne-Gaposchkin" | 2013-08-11 | 38 Upvotes 55 Comments
π Fifth Generation Computer
The Fifth Generation Computer Systems (FGCS) was an initiative by Japan's Ministry of International Trade and Industry (MITI), begun in 1982, to create computers using massively parallel computing and logic programming. It was to be the result of a massive government/industry research project in Japan during the 1980s. It aimed to create an "epoch-making computer" with supercomputer-like performance and to provide a platform for future developments in artificial intelligence. There was also an unrelated Russian project also named as a fifth-generation computer (see Kronos (computer)).
Prof. Ehud Shapiro, in his "Trip Report" paper (which focused the FGCS project on concurrent logic programming as the software foundation for the project), captured the rationale and motivations driving this huge project:
"As part of Japan's effort to become a leader in the computer industry, the Institute for New Generation Computer Technology has launched a revolutionary ten-year plan for the development of large computer systems which will be applicable to knowledge information processing systems. These Fifth Generation computers will be built around the concepts of logic programming. In order to refute the accusation that Japan exploits knowledge from abroad without contributing any of its own, this project will stimulate original research and will make its results available to the international research community."
The term "fifth generation" was intended to convey the system as being a leap beyond existing machines. In the history of computing hardware, computers using vacuum tubes were called the first generation; transistors and diodes, the second; integrated circuits, the third; and those using microprocessors, the fourth. Whereas previous computer generations had focused on increasing the number of logic elements in a single CPU, the fifth generation, it was widely believed at the time, would instead turn to massive numbers of CPUs for added performance.
The project was to create the computer over a ten-year period, after which it was considered ended and investment in a new "sixth generation" project would begin. Opinions about its outcome are divided: either it was a failure, or it was ahead of its time.
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- "Fifth Generation Computer" | 2019-08-06 | 12 Upvotes 3 Comments
π East Germany balloon escape
On 16 September 1979, eight people from two families escaped from East Germany by crossing the border into West Germany at night in a homemade hot air balloon. The unique feat was the result of over a year and a half of preparations involving three different balloons, various modifications, and a first, unsuccessful attempt. The failed attempt alerted the East German authorities to the plot, but the police were unable to identify the escapees before their second, successful flight two months later.
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- "East Germany balloon escape" | 2026-01-16 | 724 Upvotes 301 Comments
π Wikipedia: List of Citogenesis Incidents
In 2011, Randall Munroe in his comic xkcd coined the term "citogenesis" to describe the creation of "reliable" sources through circular reporting. This is a list of some well-documented cases where Wikipedia has been the source.
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- "Wikipedia: List of Citogenesis Incidents" | 2023-04-12 | 169 Upvotes 92 Comments
π Cyclorotor
A cyclorotor, cycloidal rotor, cycloidal propeller or cyclogiro, is a fluid propulsion device that converts shaft power into the acceleration of a fluid using a rotating axis perpendicular to the direction of fluid motion. It uses several blades with a spanwise axis parallel to the axis of rotation and perpendicular to the direction of fluid motion. These blades are cyclically pitched twice per revolution to produce force (thrust or lift) in any direction normal to the axis of rotation. Cyclorotors are used for propulsion, lift, and control on air and water vehicles. An aircraft using cyclorotors as the primary source of lift, propulsion, and control is known as a cyclogyro or cyclocopter. A unique aspect is that it can change the magnitude and direction of thrust without the need of tilting any aircraft structures. The patented application, used on ships with particular actuation mechanisms both mechanical or hydraulic, is named after German company Voith Turbo.
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- "Cyclorotor" | 2023-07-02 | 26 Upvotes 1 Comments
π List of multiple discoveries
Historians and sociologists have remarked the occurrence, in science, of "multiple independent discovery". Robert K. Merton defined such "multiples" as instances in which similar discoveries are made by scientists working independently of each other. "Sometimes," writes Merton, "the discoveries are simultaneous or almost so; sometimes a scientist will make a new discovery which, unknown to him, somebody else has made years before."
Commonly cited examples of multiple independent discovery are the 17th-century independent formulation of calculus by Isaac Newton, Gottfried Wilhelm Leibniz and others, described by A. Rupert Hall; the 18th-century discovery of oxygen by Carl Wilhelm Scheele, Joseph Priestley, Antoine Lavoisier and others; and the theory of the evolution of species, independently advanced in the 19th century by Charles Darwin and Alfred Russel Wallace.
Multiple independent discovery, however, is not limited to such famous historic instances. Merton believed that it is multiple discoveries, rather than unique ones, that represent the common pattern in science.
Merton contrasted a "multiple" with a "singleton"βa discovery that has been made uniquely by a single scientist or group of scientists working together.
A distinction is drawn between a discovery and an invention, as discussed for example by BolesΕaw Prus. However, discoveries and inventions are inextricably related, in that discoveries lead to inventions, and inventions facilitate discoveries; and since the same phenomenon of multiplicity occurs in relation to both discoveries and inventions, this article lists both multiple discoveries and multiple inventions.
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- "List of multiple discoveries" | 2015-09-08 | 12 Upvotes 2 Comments
- "List of Multiple Discoveries" | 2014-07-06 | 25 Upvotes 2 Comments
π Moon Illusion
The Moon illusion is an optical illusion which causes the Moon to appear larger near the horizon than it does higher up in the sky. It has been known since ancient times and recorded by various cultures. The explanation of this illusion is still debated.
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- "Moon Illusion" | 2022-06-12 | 129 Upvotes 71 Comments
π The Albanian Civil War in 1997 was sparked by pyramid scheme failures
The Albanian Civil War was a period of civil disorder in Albania in 1997, sparked by pyramid scheme failures. The government was toppled and more than 2,000 people were killed. It is considered to be either a rebellion, a civil war, or a rebellion that escalated into a civil war.
By January 1997, Albanian citizens, who had lost a total of $1.2 billion (an average of $400 per person countrywide) took their protest to the streets. Beginning in February, thousands of citizens launched daily protests demanding reimbursement by the government, which they believed was profiting from the schemes. On 1 March, Prime Minister AleksandΓ«r Meksi resigned and on 2 March, President Sali Berisha declared a state of emergency. On 11 March the Socialist Party of Albania won a major victory when its leader, Bashkim Fino, was appointed prime minister. However, the transfer of power did not halt the unrest, and protests spread to northern Albania. Although the government quelled revolts in the north, the ability of the government and military to maintain order began to collapse, especially in the southern half of Albania, which fell under the control of rebels and criminal gangs.
All major population centres were engulfed in demonstrations by 13 March and foreign countries began to evacuate their citizens. These evacuations included Operation Libelle, Operation Silver Wake and Operation Kosmas.. The United Nations Security Council, in Resolution 1101, authorised a force of 7,000 troops on 28 March to direct relief efforts and restore order in Albania. The UN feared the unrest would spread beyond Albania's borders and send refugees throughout Europe. On 15 April, Operation Alba was launched and helped restore rule of law in the country. After the unrest, looted weapons were made available to the Kosovo Liberation Army, many making their way to the Kosovo War (1998β99).
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- "The Albanian Civil War in 1997 was sparked by pyramid scheme failures" | 2020-08-30 | 68 Upvotes 60 Comments