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🔗 Mathematics 🔗 Physics

An amplituhedron is a geometric structure introduced in 2013 by Nima Arkani-Hamed and Jaroslav Trnka. It enables simplified calculation of particle interactions in some quantum field theories. In planar N = 4 supersymmetric Yang–Mills theory, also equivalent to the perturbative topological B model string theory in twistor space, an amplituhedron is defined as a mathematical space known as the positive Grassmannian.

Amplituhedron theory challenges the notion that spacetime locality and unitarity are necessary components of a model of particle interactions. Instead, they are treated as properties that emerge from an underlying phenomenon.

The connection between the amplituhedron and scattering amplitudes is at present a conjecture that has passed many non-trivial checks, including an understanding of how locality and unitarity arise as consequences of positivity. Research has been led by Nima Arkani-Hamed. Edward Witten described the work as "very unexpected" and said that "it is difficult to guess what will happen or what the lessons will turn out to be".

🔗 Occupational Safety and Health

A saddle chair uses the same principles in its design as an equestrian saddle. It is equipped with a chair base on casters and a gas cylinder for adjusting the correct sitting height. The casters enable moving around and reaching out for objects while sitting. Some saddle chairs have backrests, but most do not.

Riding-like sitting on a saddle chair differs from sitting on a conventional chair. Saddle chair users sit 20–30 cm higher, which puts the hips and the knees into a 135° angle, compared to the 90° angle typically associated with sitting on a traditional chair.

Because the saddle chair is higher than a normal office chair, the desk has to be higher as well. For this purpose there are desks that can be electronically or mechanically adjusted to fit the user. A saddle chair can also be used with a normal office desk, but then the desk has to be lifted up with height extension pieces.

The saddle chair seat is either solid or divided. A divided seat reduces pressure on the perineum and lowers the temperature in the genital area. A divided seat is thought to be healthier, especially for men, than a solid seat.

Some saddle chairs include not only height adjustments but also a tilt mechanism. There is also a divided saddle chair model on the market that has an adjustable gap between the two seat parts. Accessories, such as elbow and wrist supports, are available for saddle chairs to make different work tasks easier.

Adapting to a saddle chair takes time and requires a new kind of attitude towards sitting. The most common reason for using a saddle chair is that the users feel it is healthier for the back and legs than a standard chair. An intervention study on schoolchildren found that initially saddle chairs were liked better, but the difference leveled off over time.

🔗 Germany 🔗 Socialism 🔗 Germany/GDR

The East German coffee crisis refers to shortages of coffee in the late 1970s in East Germany caused by a poor harvest and unstable commodity prices, severely limiting the government's ability to buy coffee on the world markets. As a consequence, the East German government increased its engagement in Africa and Asia, exporting weapons and equipment to coffee-producing nations.

🔗 Physics 🔗 Physics/relativity

In physics, there is a speculative hypothesis that, if there were a black hole with the same mass, charge and angular momentum as an electron, it would share other properties of the electron. Most notably, Brandon Carter showed in 1968 that the magnetic moment of such an object would match that of an electron. This is interesting because calculations ignoring special relativity and treating the electron as a small rotating sphere of charge give a magnetic moment roughly half the experimental value (see Gyromagnetic ratio).

However, Carter's calculations also show that a would-be black hole with these parameters would be "super-extremal". Thus, unlike a true black hole, this object would display a naked singularity, meaning a singularity in spacetime not hidden behind an event horizon. It would also give rise to closed timelike curves.

Standard quantum electrodynamics (QED), currently the most comprehensive theory of particles, treats the electron as a point particle. There is no evidence that the electron is a black hole (or naked singularity) or not. Furthermore, since the electron is quantum-mechanical in nature, any description purely in terms of general relativity is paradoxical until a better model based on understanding of quantum nature of blackholes and gravitational behaviour of quantum particles is developed by research. Hence, the idea of a black hole electron remains strictly hypothetical.

🔗 Electronics

The term All American Five (abbreviated AA5) is a colloquial name for mass-produced, superheterodyne radio receivers that used five vacuum tubes in their design. These radio sets were designed to receive amplitude modulation (AM) broadcasts in the medium wave band, and were manufactured in the United States from the mid-1930s until the early 1960s. By eliminating a power transformer, cost of the units was kept low; the same principle was later applied to television receivers. Variations in the design for lower cost, shortwave bands, better performance or special power supplies existed, although many sets used an identical set of vacuum tubes.

🔗 Internet 🔗 Computing 🔗 Telecommunications 🔗 Computing/Software 🔗 Computing/Networking

Project Xanadu ( ZAN-ə-doo) was the first hypertext project, founded in 1960 by Ted Nelson. Administrators of Project Xanadu have declared it an improvement over the World Wide Web, with the mission statement: "Today's popular software simulates paper. The World Wide Web (another imitation of paper) trivialises our original hypertext model with one-way ever-breaking links and no management of version or contents."

Wired magazine published an article called "The Curse of Xanadu", calling Project Xanadu "the longest-running vaporware story in the history of the computer industry". The first attempt at implementation began in 1960, but it was not until 1998 that an incomplete implementation was released. A version described as "a working deliverable", OpenXanadu, was made available in 2014.

🔗 Telecommunications

A dark fibre or unlit fibre is an unused optical fibre, available for use in fibre-optic communication. Dark fibre may be leased from a network service provider.

Dark fibre originally referred to the potential network capacity of telecommunication infrastructure. Because the marginal cost of installing additional fibre optic cables is very low once a trench has been dug or conduit laid, a great excess of fibre was installed in the US during the telecom boom of the late 1990s and early 2000s. This excess capacity was later referred to as dark fibre following the dot-com crash of the early 2000s that briefly reduced demand for high-speed data transmission.

These unused fibre optic cables later created a new market for unique private services that could not be accommodated on lit fibre cables (i.e., cables used in traditional long-distance communication).

🔗 Spaceflight 🔗 Rocketry 🔗 Science 🔗 Photography

The V-2 No. 13 was a modified V-2 rocket that became the first object to take a photograph of the Earth from outer space. Launched on 24 October 1946, at the White Sands Missile Range in White Sands, New Mexico, the rocket reached a maximum altitude of 65 mi (105 km).

🔗 Computing 🔗 Computing/Software 🔗 Computing/Free and open-source software

Phantom OS is an operating system mostly made by Russian programmers. Phantom OS is based on a concept of persistent virtual memory, and is managed-code oriented. Phantom OS is one of a few OSes that are not based on classical concepts of Unix-like systems. Its primary goal is to achieve simplicity and effectiveness in both the operating system and applications at the same time.

Phantom is based on the principle that "Everything is an object", in contrast to the Unix-like approach of "Everything is a file".

🔗 Psychology

The need for cognition (NFC), in psychology, is a personality variable reflecting the extent to which individuals are inclined towards effortful cognitive activities.

Need for cognition has been variously defined as "a need to structure relevant situations in meaningful, integrated ways" and "a need to understand and make reasonable the experiential world". Higher NFC is associated with increased appreciation of debate, idea evaluation, and problem solving. Those with a high need for cognition may be inclined towards high elaboration. Those with a lower need for cognition may display opposite tendencies, and may process information more heuristically, often through low elaboration.

Need for cognition is closely related to the five factor model domain openness to experience, typical intellectual engagement, and epistemic curiosity (see below).