Operation Sigma Sigma
The Sigma is an experimental glider developed in Britain from 1966 by a team led by Nicholas Goodhart. After disappointing performance during flight testing the Sigma was passed on to a Canadian group which carried out modifications, making the Sigma more competitive.
Design and development
Designed to compete in the 1970 World Championships, the team aimed to develop a wing that would climb well through a high lift coefficient and a large wing area, but equally had the "maximum possible reduction of area for cruise at low lift coefficients". At the same time for the minimum possible drag they aimed for "extensive" laminar flow. To achieve this they employed flaps that would alter both wing area and wing camber. Based on analysis of the nature of thermals encountered in cross-country flying, they reasoned that by having a slow turning circle, their sailplane could stay close to the central (and strongest) part of the thermal and gain maximum benefit.
Its unusual feature is its ability to vary its wing area using Fowler flaps. It had been tried before by the Hannover Akaflieg in 1938 with their AFH-4, the South African Beatty-Johl BJ-2 Assegai and the SZD Zefir gliders.
Sigma (cosmology)
Sigma in cosmology was a property of galaxies used when trying to work out the mystery of galaxies and their supermassive black holes.
History
In the late 1990s the NUKER experts had made observations with a spectroscope of two galaxies, one of an active galaxy with an active galactic nucleus called NGC10-68 and a dormant galaxy next door to us named Andromeda.
The observations are shown. The light from the centre in Andromeda galaxy was distorted proving the existence of super-massive black holes.
Other observations proved most galaxies had a similar centre whether it be active or dormant.
They then realised that the black holes must have something to do with a galaxy's formation, so they turned to something they thought was useless: the speed of the stars around the edge of the galaxy. This was Sigma, the speed of the stars at the edge of the galaxy supposedly unaffected by the mass of the black hole at the centre.
Usage In Cosmology
The NUKER team calculated the sigma of several stars in different galaxies and the mass of the black hole at the (nucleus) centre. They expected no correlation what so ever. But when plotting their results on a Scatter diagram and drawing a line of best fit they ended up with a positive correlation. It appeared that the heavier the black hole at the centre was the faster the stars within the galaxy travelled.
Sigma (duo)
Sigma is an English drum and bass duo consisting of Cameron Edwards and Joe Lenzie. They met at Leeds University at drum and bass nights. Their 2010 collaboration with DJ Fresh, "Lassitude", peaked at number 98 on the UK Singles Chart. Their single "Nobody to Love" topped the UK Singles Chart, becoming their first UK number one. Follow-up single "Changing", featuring Paloma Faith, also got to number one.
Career
Formation
Lenzie and Edwards met in 2006 at Leeds University; Cameron was working in local record store Tribe Records and with Echo Location's Obi running local night Event Horizon, while Lenzie was DJing hip-hop and warming up Event Horizon for such acts as Rahzel and Grandmaster Flash. Once they had finished in Leeds, they relocated to London and became a three-piece with Edwards' school friend Ben Mauerhoff, being signed under DJ Fresh's Breakbeat Kaos. After a while, long distances took their toll – Edwards and Mauerhoff were based in Surrey, whereas Lenzie was based in Harpenden, Hertfordshire and they couldn't get three people into the Harpenden studio – and Mauerhoff left. In December 2008 they formed their own record label, Life Recordings (so called because, according to Lenzie, the industry demanded that it be their life). Its inaugural release was a VIP mix of their early Bingo Beats single "El Presidente".
Arrow
An arrow is a shafted projectile that is shot with a bow. It predates recorded history and is common to most cultures. An arrow usually consists of a shaft with an arrowhead attached to the front end, with fletchings and a nock at the other.
History
The oldest evidence of stone-tipped projectiles, which may or may not have been propelled by a bow (c.f. atlatl), dating to c. 64,000 years ago, were found in Sibudu Cave, South Africa. The oldest evidence of the use of bows to shoot arrows dates to about 10,000 years ago; it is based on pinewood arrows found in the Ahrensburg valley north of Hamburg. They had shallow grooves on the base, indicating that they were shot from a bow. The oldest bow so far recovered is about 8,000 years old, found in the Holmegård swamp in Denmark. Archery seems to have arrived in the Americas with the Arctic small tool tradition, about 4,500 years ago.
Size
Arrow sizes vary greatly across cultures, ranging from eighteen inches to five feet (45 cm to 150 cm). However, most modern arrows are 75 centimetres (30 in) to 96 centimetres (38 in); most war arrows from an English ship sunk in 1545 were 76 centimetres (30 in). Very short arrows have been used, shot through a guide attached either to the bow (an "overdraw") or to the archer's wrist (the Turkish "siper"). These may fly farther than heavier arrows, and an enemy without suitable equipment may find himself unable to return them.
Arrows (Unicode block)
Arrows is a Unicode block containing line, curve, and semicircle symbols terminating in barbs or arrows.
The Arrows block contains eight emoji: U+2194–U+2199 and U+21A9–U+21AA.
The block has sixteen standardized variants defined to specify emoji-style (U+FE0F VS16) or text presentation (U+FE0E VS15) for the eight emoji, all of which default to a text presentation.
See also
References
Arrow (computer science)
In computer science, arrows are a type class used in programming to describe computations in a pure and declarative fashion. First proposed by computer scientist John Hughes as a generalization of monads, arrows provide a referentially transparent way of expressing relationships between logical steps in a computation. Unlike monads, arrows don't limit steps to having one and only one input. As a result, they have found use in functional reactive programming, point-free programming, and parsers among other applications.
Motivation and history
While arrows were in use before being recognized as a distinct class, Hughes would publish their first definition in 2000. Until then, monads had proven sufficient for most problems requiring the combination of program logic in pure code. However, some useful libraries, such as the Fudgets library for graphical user interfaces and certain efficient parsers, defied rewriting in a monadic form.
The formal concept of arrows was developed to explain these exceptions to monadic code, and in the process, monads themselves turned out to be a subset of arrows. Since then, arrows have been an active area of research. Their underlying laws and operations have been refined several times, with recent formulations such as arrow calculus requiring only five laws.
