Have a deep view into what people are curious about.

🔗 Electronics

Wire wrap was invented to wire telephone crossbar switches, and later adapted to construct electronic circuit boards. Electronic components mounted on an insulating board are interconnected by lengths of insulated wire run between their terminals, with the connections made by wrapping several turns of uninsulated sections of the wire around a component lead or a socket pin.

Wires can be wrapped by hand or by machine, and can be hand-modified afterwards. It was popular for large-scale manufacturing in the 1960s and early 1970s, and continues today to be used for short runs and prototypes. The method eliminates the design and fabrication of a printed circuit board. Wire wrapping is unusual among other prototyping technologies since it allows for complex assemblies to be produced by automated equipment, but then easily repaired or modified by hand.

Wire wrap construction can produce assemblies which are more reliable than printed circuits: connections are less prone to fail due to vibration or physical stresses on the base board, and the lack of solder precludes soldering faults such as corrosion, cold joints and dry joints. The connections themselves are firmer and have lower electrical resistance due to cold welding of the wire to the terminal post at the corners.

Wire wrap was used for assembly of high frequency prototypes and small production runs, including gigahertz microwave circuits and supercomputers. It is unique among automated prototyping techniques in that wire lengths can be exactly controlled, and twisted pairs or magnetically shielded twisted quads can be routed together.

Wire wrap construction became popular around 1960 in circuit board manufacturing, and use has now sharply declined. Surface-mount technology has made the technique much less useful than in previous decades. Solder-less breadboards and the decreasing cost of professionally made PCBs have nearly eliminated this technology.

🔗 Military history/United States military history

🔗 Architecture 🔗 Japan 🔗 Japan/Tokyo

The X-Seed 4000 is a visionary skyscraper for what would be, if it was built, the tallest building in the world. The idea was initially created and developed by Peter Neville. Its proposed 4-kilometre (2.5 mi) height, 6-kilometre-wide (3.7 mi) sea-base, and 800-floor capacity could accommodate 500,000 to 1,000,000 inhabitants. This structure would be composed of over 3,000,000 tons of pure steel.

It was designed for Tokyo, Japan by the Taisei Corporation in 1995 as a futuristic environment combining ultra-modern living and interaction with nature. Methods of transportation within the X-seed would most likely include MagLev trains.

The X-Seed 4000 "is never meant to be built," says Georges Binder, managing director of Buildings & Data, a firm which compiles data banks on buildings worldwide. "The purpose of the plan was to earn some recognition for the firm, and it worked."

Unlike conventional skyscrapers, to remain habitable the (X-Seed 4000) would be forced to actively protect its occupants from considerable internal air pressure and external air pressure gradations and weather fluctuations that its massive elevation would cause. Its design calls for the use of solar power to maintain internal environmental conditions. As the proposed site for the structure is located in the Pacific Ring of Fire, the most active volcano range in the world, the X-Seed 4000 would be subject to earthquakes and tsunamis.

A sea-based location and a Mount Fuji shape are some of this building's other major design features—the real Mount Fuji is land-based and is 3,776 metres (12,388 ft) high so is 224 metres (735 ft) shorter than the X-Seed 4000.

The X-Seed 4000 is projected to be twice the height of the Shimizu Mega-City Pyramid at 2,004 metres (6,575 ft). The Shimizu Mega-City Pyramid (proposed in 2007, also planned for Tokyo, Japan) faces most of the same problems as the X-Seed. Other projects that may be in the top five man made structures are the Ultima Tower 3,218 metres (10,558 ft) in San Francisco, Dubai City Tower 2,400 metres (7,900 ft) and the Bionic Tower 1,228 metres (4,029 ft) in either Hong Kong or Shanghai.

🔗 Cryptography 🔗 Cryptography/Computer science

A physical unclonable function (sometimes also called physically unclonable function, which refers to a weaker security metric), or PUF, is a physical object that for a given input and conditions (challenge), provides a physically-defined "digital fingerprint" output (response) that serves as a unique identifier, most often for a semiconductor device such as a microprocessor. PUFs are most often based on unique physical variations which occur naturally during semiconductor manufacturing. A PUF is a physical entity embodied in a physical structure. Today, PUFs are usually implemented in integrated circuits and are typically used in applications with high security requirements, more specifically cryptography.

🔗 Computer science 🔗 Mathematics

In combinatory logic for computer science, a fixed-point combinator (or fixpoint combinator),^: p.26 is a higher-order function (i.e. a function which takes a function as argument) that returns some fixed point (a value that is mapped to itself) of its argument function, if one exists.

Formally, if ${\displaystyle {\textsf {fix}}}$ is a fixed-point combinator and the function ${\displaystyle f}$ has one or more fixed points, then ${\displaystyle {\textsf {fix}}\ f}$ is one of these fixed points, i.e.

${\displaystyle f\ ({\textsf {fix}}\ f)={\textsf {fix}}\ f\ .}$

Fixed-point combinators can be defined in the lambda calculus and in functional programming languages and provide a means to allow for recursive definitions.

🔗 Video games

Game Oriented Assembly Lisp (GOAL) is a programming language, a dialect of the language Lisp, made for video games developed by Andy Gavin and the Jak and Daxter team at the company Naughty Dog.

It was written using Allegro Common Lisp and used in the development of the entire Jak and Daxter series of games.

🔗 Spaceflight 🔗 Rocketry

Black Arrow, officially capitalised BLACK ARROW, was a British satellite carrier rocket. Developed during the 1960s, it was used for four launches between 1969 and 1971. Its final flight was the first and only successful orbital launch to be conducted by the United Kingdom, and placed the Prospero satellite into low Earth orbit.

Black Arrow originated from studies by the Royal Aircraft Establishment for carrier rockets based on the Black Knight rocket, with the project being authorised in 1964. It was initially developed by Saunders-Roe, and later Westland Aircraft as the result of a merger.

Black Arrow was a three-stage rocket, fuelled by RP-1 paraffin (kerosene) and high test peroxide, a concentrated form of hydrogen peroxide (85% hydrogen peroxide + 15% water). It was retired after only four launches in favour of using American Scout rockets, which the Ministry of Defence calculated to be cheaper than maintaining the Black Arrow programme.

🔗 History of Science 🔗 Tree of Life

The species problem is the set of questions that arises when biologists attempt to define what a species is. Such a definition is called a species concept; there are at least 26 recognized species concepts. A species concept that works well for sexually reproducing organisms such as birds is useless for species that reproduce asexually, such as bacteria. The scientific study of the species problem has been called microtaxonomy.

One common, but sometimes difficult, question is how best to decide which species an organism belongs to, because reproductively isolated groups may not be readily recognizable, and cryptic species may be present. There is a continuum from reproductive isolation with no interbreeding, to panmixis, unlimited interbreeding. Populations can move forward or backwards along this continuum, at any point meeting the criteria for one or another species concept, and failing others.

Many of the debates on species touch on philosophical issues, such as nominalism and realism, and on issues of language and cognition.

The current meaning of the phrase "species problem" is quite different from what Charles Darwin and others meant by it during the 19th and early 20th centuries. For Darwin, the species problem was the question of how new species arose. Darwin was however one of the first people to question how well-defined species are, given that they constantly change.

🔗 Aviation 🔗 Aviation/aircraft

A ram air turbine (RAT) is a small wind turbine that is connected to a hydraulic pump, or electrical generator, installed in an aircraft and used as a power source. The RAT generates power from the airstream by ram pressure due to the speed of the aircraft.

🔗 Military history 🔗 Military history/Military aviation 🔗 Military history/World War II 🔗 Military history/German military history 🔗 Military history/European military history 🔗 Military history/British military history

The Charlie Brown and Franz Stigler incident occurred on 20 December 1943, when, after a successful bomb run on Bremen, 2nd Lt Charles "Charlie" Brown's B-17 Flying Fortress (named "Ye Olde Pub") was severely damaged by German fighters. Luftwaffe pilot Franz Stigler had the opportunity to shoot down the crippled bomber but did not do so. After an extensive search by Brown, the two pilots met each other 50 years later and developed a friendship that lasted until Stigler's death in March 2008.