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🔗 Spaceflight 🔗 Astronomy 🔗 Engineering 🔗 Astronomy/Astronomical objects

A Dyson sphere is a hypothetical megastructure that completely encompasses a star and captures a large percentage of its power output. The concept is a thought experiment that attempts to explain how a spacefaring civilization would meet its energy requirements once those requirements exceed what can be generated from the home planet's resources alone. Only a tiny fraction of a star's energy emissions reach the surface of any orbiting planet. Building structures encircling a star would enable a civilization to harvest far more energy.

The first contemporary description of the structure was by Olaf Stapledon in his science fiction novel Star Maker (1937), in which he described "every solar system... surrounded by a gauze of light traps, which focused the escaping solar energy for intelligent use." The concept was later popularized by Freeman Dyson in his 1960 paper "Search for Artificial Stellar Sources of Infrared Radiation." Dyson speculated that such structures would be the logical consequence of the escalating energy needs of a technological civilization and would be a necessity for its long-term survival. He proposed that searching for such structures could lead to the detection of advanced, intelligent extraterrestrial life. Different types of Dyson spheres and their energy-harvesting ability would correspond to levels of technological advancement on the Kardashev scale.

Since then, other variant designs involving building an artificial structure or series of structures to encompass a star have been proposed in exploratory engineering or described in science fiction under the name "Dyson sphere". These later proposals have not been limited to solar-power stations, with many involving habitation or industrial elements. Most fictional depictions describe a solid shell of matter enclosing a star, which was considered by Dyson himself the least plausible variant of the idea. In May 2013, at the Starship Century Symposium in San Diego, Dyson repeated his comments that he wished the concept had not been named after him.

🔗 United States 🔗 Mathematics 🔗 Education 🔗 United States/Massachusetts 🔗 Higher Education

Math 55 is a two-semester long first-year undergraduate mathematics course at Harvard University, founded by Lynn Loomis and Shlomo Sternberg. The official titles of the course are Honors Abstract Algebra (Math 55a) and Honors Real and Complex Analysis (Math 55b). Previously, the official title was Honors Advanced Calculus and Linear Algebra.

🔗 Soviet Union 🔗 Russia 🔗 Law 🔗 Politics 🔗 Cities 🔗 Russia/Russian, Soviet, and CIS military history 🔗 Russia/politics and law of Russia 🔗 Russia/human geography of Russia

A closed city or closed town is a settlement where travel or residency restrictions are applied so that specific authorization is required to visit or remain overnight. They may be sensitive military establishments or secret research installations that require much more space or freedom than is available in a conventional military base. There may also be a wider variety of permanent residents including close family members of workers or trusted traders who are not directly connected with its clandestine purposes.

Many closed cities existed in the Soviet Union until its collapse in 1991. After 1991, a number of them still existed in the CIS countries, especially Russia. In modern Russia, such places are officially known as "closed administrative-territorial formations" (закрытые административно-территориальные образования, zakrytye administrativno-territorial'nye obrazovaniya, or ЗАТО ZATO for short).

🔗 Aviation

Bitching Betty is a slang term used by some pilots and aircrew (mainly North American), when referring to the voices used by some aircraft warning systems.

The enunciating voice, in at least some aircraft systems, may be either male or female and in some cases this may be selected according to pilot preference. If the voice is female, it may be referred to as Bitching Betty; if the voice is male, it may be referred to as Barking Bob. A female voice is heard on military aircraft such as the F-16 Fighting Falcon, the Eurofighter Typhoon and the Mikoyan MiG-29. A male voice is heard on Boeing commercial airliners and is also used in the BAE Hawk.

In the United Kingdom the term Nagging Nora is sometimes used, and in New Zealand the term used for Boeing aircraft is Hank the Yank. The voice warning system used on London Underground trains, which also uses a female voice, is known to some staff as Sonya, as it "gets on ya nerves".

🔗 Classical Greece and Rome 🔗 Greece 🔗 Trains 🔗 Archaeology

The Diolkos (Δίολκος, from the Greek διά, dia "across" and ὁλκός, holkos "portage machine") was a paved trackway near Corinth in Ancient Greece which enabled boats to be moved overland across the Isthmus of Corinth. The shortcut allowed ancient vessels to avoid the long and dangerous circumnavigation of the Peloponnese peninsula. The phrase "as fast as a Corinthian", penned by the comic playwright Aristophanes, indicates that the trackway was common knowledge and had acquired a reputation for swiftness.

The main function of the Diolkos was the transfer of goods, although in times of war it also became a preferred means of speeding up naval campaigns. The 6 km (3.7 mi) to 8.5 km (5.3 mi) long roadway was a rudimentary form of railway, and operated from c. 600 BC until the middle of the 1st century AD. The scale on which the Diolkos combined the two principles of the railway and the overland transport of ships remained unique in antiquity.

🔗 Business 🔗 Urban studies and planning 🔗 Cities

A company town is a place where practically all stores and housing are owned by the one company that is also the main employer. Company towns are often planned with a suite of amenities such as stores, houses of worship, schools, markets and recreation facilities. They are usually bigger than a model village ("model" in the sense of an ideal to be emulated).

Some company towns have had high ideals, but many have been regarded as controlling and/or exploitative. Others developed more or less in unplanned fashion, such as Summit Hill, Pennsylvania, United States, one of the oldest, which began as an LC&N Co. mining camp and mine site nine miles (14.5 km) from the nearest outside road.

🔗 Physics

Flux pinning is the phenomenon where a superconductor is pinned in space above a magnet. The superconductor must be a type-II superconductor because type-I superconductors cannot be penetrated by magnetic fields. The act of magnetic penetration is what makes flux pinning possible. At higher magnetic fields (above Hc1 and below Hc2) the superconductor allows magnetic flux to enter in quantized packets surrounded by a superconducting current vortex (see Quantum vortex). These sites of penetration are known as flux tubes. The number of flux tubes per unit area is proportional to the magnetic field with a constant of proportionality equal to the magnetic flux quantum. On a simple 76 millimeter diameter, 1-micrometer thick disk, next to a magnetic field of 28 kA/m, there are approximately 100 billion flux tubes that hold 70,000 times the superconductor's weight. At lower temperatures the flux tubes are pinned in place and cannot move. This pinning is what holds the superconductor in place thereby allowing it to levitate. This phenomenon is closely related to the Meissner effect, though with one crucial difference — the Meissner effect shields the superconductor from all magnetic fields causing repulsion, unlike the pinned state of the superconductor disk which pins flux, and the superconductor in place.

🔗 Computing 🔗 Computing/Computer hardware 🔗 Computing/Computer Security

A Kensington Security Slot (also called a K-Slot or Kensington lock) is part of an anti-theft system designed in the early 1990s and patented by Kryptonite in 1999–2000, assigned to Schlage in 2002, and since 2005 owned and marketed by Kensington Computer Products Group, a division of ACCO Brands.

🔗 Russia 🔗 Russia/technology and engineering in Russia 🔗 Russia/mass media in Russia 🔗 Military history 🔗 Military history/Military science, technology, and theory 🔗 Military history/Intelligence 🔗 Military history/Russian, Soviet and CIS military history 🔗 Radio Stations

UVB-76, also known as "The Buzzer", is a nickname given by radio listeners to a shortwave radio station that broadcasts on the frequencies 4625 and 4810 kHz. It broadcasts a short, monotonous buzz tone , repeating at a rate of approximately 25 tones per minute, 24 hours per day. Sometimes, the buzzer signal is interrupted and a voice transmission in Russian takes place. The first reports were made of a station on this frequency in 1973.

🔗 Environment 🔗 Disaster management 🔗 Mexico 🔗 Occupational Safety and Health 🔗 Energy 🔗 Caribbean 🔗 Fisheries and Fishing

Ixtoc I was an exploratory oil well being drilled by the semi-submersible drilling rig Sedco 135 in the Bay of Campeche of the Gulf of Mexico, about 100 km (62 mi) northwest of Ciudad del Carmen, Campeche in waters 50 m (160 ft) deep. On 3 June 1979, the well suffered a blowout resulting in one of the largest oil spills in history.