text stringlengths 26 3.6k | page_title stringlengths 1 71 | source stringclasses 1
value | token_count int64 10 512 | id stringlengths 2 8 | url stringlengths 31 117 | topic stringclasses 4
values | section stringlengths 4 49 ⌀ | sublist stringclasses 9
values |
|---|---|---|---|---|---|---|---|---|
Early computer-generated models of planetary formation predicted the existence of terrestrial planets around both Alpha Centauri A and B, but most recent numerical investigations have shown that the gravitational pull of the companion star renders the accretion of planets difficult. Despite these difficulties, given the similarities to the Sun in spectral types, star type, age and probable stability of the orbits, it has been suggested that this stellar system could hold one of the best possibilities for harbouring extraterrestrial life on a potential planet.
In the Solar System, it was once thought that Jupiter and Saturn were probably crucial in perturbing comets into the inner Solar System, providing the inner planets with a source of water and various other ices. However, since isotope measurements of the deuterium to hydrogen (D/H) ratio in comets Halley, Hyakutake, Hale–Bopp, 2002T7, and Tuttle yield values approximately twice that of Earth's oceanic water, more recent models and research predict that less than 10% of Earth's water was supplied from comets. In the system, Proxima Centauri may have influenced the planetary disk as the system was forming, enriching the area around Alpha Centauri with volatile materials. This would be discounted if, for example, happened to have gas giants orbiting (or vice versa), or if and B themselves were able to perturb comets into each other's inner systems, as Jupiter and Saturn presumably have done in the Solar System. Such icy bodies probably also reside in Oort clouds of other planetary systems. When they are influenced gravitationally by either the gas giants or disruptions by passing nearby stars, many of these icy bodies then travel star-wards. Such ideas also apply to the close approach of Alpha Centauri or other stars to the Solar system, when, in the distant future, the Oort Cloud might be disrupted enough to increase the number of active comets.
To be in the habitable zone, a planet around Alpha Centauri A would have an orbital radius of between about 1.2 and so as to have similar planetary temperatures and conditions for liquid water to exist. For the slightly less luminous and cooler , the habitable zone is between about 0.7 and . | Alpha Centauri | Wikipedia | 459 | 1979 | https://en.wikipedia.org/wiki/Alpha%20Centauri | Physical sciences | Notable stars | null |
With the goal of finding evidence of such planets, both Proxima Centauri and were among the listed "Tier-1" target stars for NASA's Space Interferometry Mission (S.I.M.). Detecting planets as small as three Earth-masses or smaller within two AU of a "Tier-1" target would have been possible with this new instrument. The S.I.M. mission, however, was cancelled due to financial issues in 2010.
Circumstellar discs
Based on observations between 2007 and 2012, a study found a slight excess of emissions in the 24 μm (mid/far-infrared) band surrounding , which may be interpreted as evidence for a sparse circumstellar disc or dense interplanetary dust. The total mass was estimated to be between to the mass of the Moon, or 10–100 times the mass of the Solar System's zodiacal cloud. If such a disc existed around both stars, disc would likely be stable to and would likely be stable to This would put A's disc entirely within the frost line, and a small part of B's outer disc just outside.
View from this system
The sky from would appear much as it does from the Earth, except that Centaurus's brightest star, being itself, would be absent from the constellation. The Sun would appear as a white star of apparent magnitude +0.5, roughly the same as the average brightness of Betelgeuse from Earth. It would be at the antipodal point of current right ascension and declination, at (2000), in eastern Cassiopeia, easily outshining all the rest of the stars in the constellation. With the placement of the Sun east of the magnitude 3.4 star Epsilon Cassiopeiae, nearly in front of the Heart Nebula, the "W" line of stars of Cassiopeia would have a "/W" shape.
Other nearby stars' placements may be affected somewhat drastically. Sirius, at 9.2 light years away from the system, would still be the brightest star in the night sky, with a magnitude of -1.2, but would be located in Orion less than a degree away from Betelgeuse. Procyon, which would also be at a slightly further distance than from the Sun, would move to outshine Pollux in the middle of Gemini. | Alpha Centauri | Wikipedia | 490 | 1979 | https://en.wikipedia.org/wiki/Alpha%20Centauri | Physical sciences | Notable stars | null |
A planet around either or B would see the other star as a very bright secondary. For example, an Earth-like planet at from (with a revolution period of 1.34 years) would get Sun-like illumination from its primary, and would appear 5.7–8.6 magnitudes dimmer (−21.0 to −18.2), 190–2,700 times dimmer than but still 150–2,100 times brighter than the full Moon. Conversely, an Earth-like planet at from (with a revolution period of 0.63 years) would get nearly Sun-like illumination from its primary, and would appear 4.6–7.3 magnitudes dimmer (−22.1 to −19.4), 70 to 840 times dimmer than but still 470–5,700 times brighter than the full Moon.
Proxima Centauri would appear dim as one of many stars, being magnitude 4.5 at its current distance, and magnitude 2.6 at periastron.
Future exploration
Alpha Centauri is a first target for crewed or robotic interstellar exploration. Using current spacecraft technologies, crossing the distance between the Sun and Alpha Centauri would take several millennia, though the possibility of nuclear pulse propulsion or laser light sail technology, as considered in the Breakthrough Starshot program, could make the journey to Alpha Centauri in 20 years. An objective of such a mission would be to make a fly-by of, and possibly photograph, planets that might exist in the system. The existence of Proxima Centauri b, announced by the European Southern Observatory (ESO) in August 2016, would be a target for the Starshot program.
NASA released a mission concept in 2017 that would send a spacecraft to Alpha Centauri in 2069, scheduled to coincide with the 100th anniversary of the first crewed lunar landing in 1969, Even at speed 10% of the speed of light (about 108 million km/h), which NASA experts say may be possible, it would take a spacecraft 44 years to reach the constellation, by the year 2113, and would take another 4 years for a signal, by the year 2117 to reach Earth. The concept received no further funding or development.
Historical distance estimates | Alpha Centauri | Wikipedia | 462 | 1979 | https://en.wikipedia.org/wiki/Alpha%20Centauri | Physical sciences | Notable stars | null |
{| class="wikitable sortable mw-collapsible"
|+ Alpha Centauri AB historical distance estimates
|-
! rowspan="2" | Source
! rowspan="2" |Year
! rowspan="2" |Subject!! rowspan="2" | Parallax (mas) !! colspan="3" | Distance !! rowspan="2" | | Alpha Centauri | Wikipedia | 91 | 1979 | https://en.wikipedia.org/wiki/Alpha%20Centauri | Physical sciences | Notable stars | null |
Amiga is a family of personal computers produced by Commodore from 1985 until the company's bankruptcy in 1994, with production by others afterward. The original model is one of a number of mid-1980s computers with 16-bit or 16/32-bit processors, 256 KB or more of RAM, mouse-based GUIs, and significantly improved graphics and audio compared to previous 8-bit systems. These include the Atari ST—released earlier the same year—as well as the Macintosh and Acorn Archimedes. The Amiga differs from its contemporaries through custom hardware to accelerate graphics and sound, including sprites, a blitter, and four channels of sample-based audio. It runs a pre-emptive multitasking operating system called AmigaOS.
The Amiga 1000, based on the Motorola 68000 microprocessor, was released in July 1985. Production problems kept it from becoming widely available until early 1986. While early advertisements cast the computer as an all-purpose business machine, especially with the Sidecar IBM PC compatibility add-on, the Amiga was most commercially successful as a home computer with a range of video games and creative software. The bestselling model, the Amiga 500, was introduced in 1987 along with the more expandable Amiga 2000. The 1990 Amiga 3000 includes a minor update to the graphics hardware via the Enhanced Chip Set, also used in subsequent models.
The Amiga established a niche in audio and multimedia. The first music tracker was written for the Amiga, and it became a popular platform music creation. The 3D rendering packages LightWave 3D, Imagine, and Traces (a predecessor to Blender) originated on the system. The 1990 third-party Video Toaster made the Amiga a comparatively low cost option for video production. In later years, the Amiga started losing market share to IBM PC compatibles and video game consoles, eventually leading to Commodore's bankruptcy in 1994 and then the end of Amiga. Commodore is estimated to have sold an 4.85 million Amigas. Various groups have since released spiritual successors. | Amiga | Wikipedia | 409 | 1980 | https://en.wikipedia.org/wiki/Amiga | Technology | Specific hardware | null |
Overview
The Amiga 1000, based on the Motorola 68000 microprocessor, was released in July 1985. Production problems kept it from becoming widely available until early 1986. While early advertisements cast the computer as an all-purpose business machine, especially when outfitted with the Sidecar IBM PC compatibility add-on, the Amiga was most commercially successful as a home computer with a wide range of video games and creative software. The best-selling model, the Amiga 500, was introduced in 1987 along with the more expandable Amiga 2000. The 1990 Amiga 3000 included a minor update to the graphics hardware via the Amiga Enhanced Chip Set. The ECS was included in the Amiga 500 Plus (1991) and Amiga 600 (March 1992), followed by the Amiga 1200 and Amiga 4000.
Poor marketing and the failure of later models to repeat the technological advances of the first systems resulted in Commodore quickly losing market share to the rapidly dropping prices of IBM PC compatibles (which gained 256 color graphics in 1987), as well as the fourth generation of video game consoles. Commodore went bankrupt in April 1994 after a version of the Amiga packaged as a game console, the CD32, failed in the marketplace. Escom of Germany, who acquired Commodore properties, continued developing the Amiga line for just under two more years until it also went bankrupt.
Since the demise of Commodore and Escom, various groups have marketed successors to the original Amiga line, including Eyetech, ACube Systems Srl and A-EON Technology who have produced AmigaOne computers since the 2000s. AmigaOS has influenced replacements, clones, and compatible software such as MorphOS and AROS. Currently Belgian company Hyperion Entertainment maintains and develops AmigaOS 4, which is an official and direct descendant of AmigaOS 3.1 – the last system made by Commodore for the original Amiga computers.
History
Concept and early development
Jay Miner joined Atari, Inc. in the 1970s and led development of the Atari Video Computer System's graphics and sound chip, the Television Interface Adaptor. When complete, the team began developing a much more sophisticated set of chips, CTIA, ANTIC and POKEY, that formed the basis of the Atari 8-bit computers. | Amiga | Wikipedia | 443 | 1980 | https://en.wikipedia.org/wiki/Amiga | Technology | Specific hardware | null |
With the 8-bit line's launch in 1979, the team once again started looking at a next generation chipset. Nolan Bushnell had sold the company to Warner Communications in 1978, and the new management was much more interested in the existing lines than development of new products that might cut into their sales. Miner wanted to start work with the new Motorola 68000, but management was only interested in another 6502 based system. Miner left the company, and, for a time, the industry.
In 1979, Larry Kaplan left Atari and founded Activision. In 1982, Kaplan was approached by a number of investors who wanted to develop a new game platform. Kaplan hired Miner to run the hardware side of the newly formed company, "Hi-Toro". The system was code-named "Lorraine" in keeping with Miner's policy of giving systems female names, in this case the company president's wife, Lorraine Morse. When Kaplan left the company late in 1982, Miner was promoted to head engineer and the company relaunched as Amiga Corporation.
The Amiga hardware was designed by Miner, RJ Mical, and Dale Luck. A breadboard prototype for testing and development was largely completed by late 1983, and shown at the January 1984 Consumer Electronics Show (CES). At the time, the operating system was not ready, so the machine was demonstrated with the "Boing Ball" demo, a real-time animation showing a red-and-white spinning ball bouncing and casting a shadow; this bouncing ball later became the official logo of Escom subsidiary Amiga Technologies. CES attendees had trouble believing the computer being demonstrated had the power to display such a demo and searched in vain for the "real" computer behind it.
A further developed version of the system was demonstrated at the June 1984 CES and shown to many companies in hopes of garnering further funding, but found little interest in a market that was in the final stages of the video game crash of 1983.
In March, Atari expressed a tepid interest in Lorraine for its potential use in a games console or home computer tentatively known as the . The talks were progressing slowly, and Amiga was running out of money. A temporary arrangement in June led to a $500,000 loan from Atari to Amiga to keep the company going. The terms required the loan to be repaid at the end of the month, otherwise Amiga would forfeit the Lorraine design to Atari. | Amiga | Wikipedia | 487 | 1980 | https://en.wikipedia.org/wiki/Amiga | Technology | Specific hardware | null |
Commodore
During 1983, Atari lost over a week due to the combined effects of the crash and the ongoing price war in the home computer market. By the end of the year, Warner was desperate to sell the company. In January 1984, Jack Tramiel resigned from Commodore due to internal battles over the future direction of the company. A number of Commodore employees followed him to his new company, Tramel Technology. This included a number of the senior technical staff, where they began development of a 68000-based machine of their own. In June, Tramiel arranged a no-cash deal to take over Atari, reforming Tramel Technology as Atari Corporation.
As many Commodore technical staff had moved to Atari, Commodore was left with no workable path to design their own next-generation computer. The company approached Amiga offering to fund development as a home computer system. They quickly arranged to repay the Atari loan, ending that threat. The two companies were initially arranging a license agreement before Commodore offered to purchase Amiga outright.
By late 1984, the prototype breadboard chipset had successfully been turned into integrated circuits, and the system hardware was being readied for production. At this time the operating system (OS) was not as ready, and led to a deal to port an OS known as TRIPOS to the platform. TRIPOS was a multitasking system that had been written in BCPL during the 1970s for the PDP-11 minicomputer, but later experimentally ported to the 68000. This early version was known as AmigaDOS and the GUI as Workbench. The BCPL parts were later rewritten in the C language, and the entire system became AmigaOS.
The system was enclosed in a pizza box form factor case; a late change was the introduction of vertical supports on either side of the case to provide a "garage" under the main section of the system where the keyboard could be stored. | Amiga | Wikipedia | 384 | 1980 | https://en.wikipedia.org/wiki/Amiga | Technology | Specific hardware | null |
Launch
The first model was announced in 1985 as simply "The Amiga from Commodore", later to be retroactively dubbed the Amiga 1000. They were first offered for sale in August, but by October only 50 had been built, all of which were used by Commodore. Machines only began to arrive in quantity in mid-November, meaning they missed the Christmas buying rush. By the end of the year, they had sold 35,000 machines, and severe cashflow problems made the company pull out of the January 1986 CES. Bad or entirely missing marketing, forcing the development team to move to the east coast, notorious stability problems and other blunders limited sales in early 1986 to between 10,000 and 15,000 units a month. 120,000 units were reported as having been sold from the machine's launch up to the end of 1986.
Later models
In late 1985, Thomas Rattigan was promoted to COO of Commodore, and then to CEO in February 1986. He immediately implemented an ambitious plan that covered almost all of the company's operations. Among these was the long-overdue cancellation of the now outdated PET and VIC-20 lines, as well as a variety of poorly selling Commodore 64 offshoots and the Commodore 900 workstation effort.
Another one of the changes was to split the Amiga into two products, a new high-end version of the Amiga aimed at the creative market, and a cost-reduced version that would take over for the Commodore 64 in the low-end market. These new designs were released in 1987 as the Amiga 2000 and Amiga 500, the latter of which went on to widespread success and became their best selling model.
Similar high-end/low-end models would make up the Amiga line for the rest of its history; follow-on designs included the Amiga 3000/Amiga 500 Plus/Amiga 600, and the Amiga 4000/Amiga 1200. These models incorporated a series of technical upgrades known as the ECS and AGA, which added higher resolution displays among many other improvements and simplifications. | Amiga | Wikipedia | 415 | 1980 | https://en.wikipedia.org/wiki/Amiga | Technology | Specific hardware | null |
The Amiga line sold an estimated 4,910,000 machines over its lifetime. The machines were most popular in the UK and Germany, with about 1.5 million sold in each country, and sales in the high hundreds of thousands in other European nations. The machine was less popular in North America, where an estimated 700,000 were sold. In the United States, the Amiga found a niche with enthusiasts and in vertical markets for video processing and editing. In Europe, it was more broadly popular as a home computer and often used for video games. Beginning in 1988 it overlapped with the 16-bit Mega Drive, then the Super Nintendo Entertainment System in the early 1990s. Commodore UK's Kelly Sumner did not see Sega or Nintendo as competitors, but instead credited their marketing campaigns which spent over or for promoting video games as a whole and thus helping to boost Amiga sales.
Bankruptcy and aftermath
In spite of his successes in making the company profitable and bringing the Amiga line to market, Rattigan was soon forced out in a power struggle with majority shareholder, Irving Gould. This is widely regarded as the turning point, as further improvements to the Amiga were eroded by rapid improvements in other platforms.
Commodore shut down the Amiga division on April 26, 1994, and filed for bankruptcy three days later. Commodore's assets were purchased by Escom, a German PC manufacturer, who created the subsidiary company Amiga Technologies. They re-released the A1200 and A4000T, and introduced a new 68060 version of the A4000T. Amiga Technologies researched and developed the Amiga Walker prototype. They presented the machine publicly at CeBit, but Escom went bankrupt in 1996. Some Amigas were still made afterwards for the North American market by QuikPak, a small Pennsylvania-based firm who was the manufacturer of Amigas for Escom.
After a reported sale to VisCorp fell through, a U.S. Wintel PC manufacturer, Gateway 2000, eventually purchased the Amiga branch and technology in 1997. QuickPak attempted but failed to license Amiga from Gateway and build new models. Gateway was then working on a brand new Amiga platform, likely encouraged by a desire to be independent of Microsoft and Intel. However this did not materialize and in 2000, Gateway sold the Amiga brand to Amiga, Inc., without having released any products. Amiga, Inc. licensed the rights to sell hardware using the AmigaOne brand to Eyetech Group and Hyperion Entertainment. In 2019, Amiga, Inc. sold its intellectual property to Amiga Corporation.
Hardware | Amiga | Wikipedia | 510 | 1980 | https://en.wikipedia.org/wiki/Amiga | Technology | Specific hardware | null |
The Amiga has a custom chipset consisting of several coprocessors which handle audio, video, and direct memory access independently of the central processing unit (CPU). This architecture gave the Amiga a performance edge over its competitors, particularly for graphics-intensive applications and games.
The architecture uses two distinct bus subsystems: the chipset bus and the CPU bus. The chipset bus allows the coprocessors and CPU to address "Chip RAM". The CPU bus provides addressing to conventional RAM, ROM and the Zorro II or Zorro III expansion subsystems. This enables independent operation of the subsystems. The CPU bus can be much faster than the chipset bus. CPU expansion boards may provide additional custom buses. Additionally, "busboards" or "bridgeboards" may provide ISA or PCI buses.
Central processing unit
The most popular models from Commodore, including the Amiga 1000, Amiga 500, and Amiga 2000, use the Motorola 68000 as the CPU. From a developer's point of view, the 68000 provides a full suite of 32-bit operations, but the chip can address only 16 MB of physical memory and is implemented using a 16-bit arithmetic logic unit and has a 16-bit external data bus, so 32-bit computations are transparently handled as multiple 16-bit values at a performance cost. The later Amiga 2500 and the Amiga 3000 models use fully 32-bit, 68000-compatible processors from Motorola with improved performance and larger addressing capability.
CPU upgrades were offered by both Commodore and third-party manufacturers. Most Amiga models can be upgraded either by direct CPU replacement or through expansion boards. Such boards often included faster and higher capacity memory interfaces and hard disk controllers.
Towards the end of Commodore's time in charge of Amiga development, there were suggestions that Commodore intended to move away from the 68000 series to higher performance RISC processors, such as the PA-RISC. Those ideas were never developed before Commodore filed for bankruptcy. Despite this, third-party manufacturers designed upgrades featuring a combination of 68000 series and PowerPC processors along with a PowerPC native microkernel and software. Later Amiga clones featured PowerPC processors only. | Amiga | Wikipedia | 442 | 1980 | https://en.wikipedia.org/wiki/Amiga | Technology | Specific hardware | null |
Custom chipset
The custom chipset at the core of the Amiga design appeared in three distinct generations, with a large degree of backward-compatibility. The Original Chip Set (OCS) appeared with the launch of the A1000 in 1985. OCS was eventually followed by the modestly improved Enhanced Chip Set (ECS) in 1990 and finally by the partly 32-bit Advanced Graphics Architecture (AGA) in 1992. Each chipset consists of several coprocessors that handle graphics acceleration, digital audio, direct memory access and communication between various peripherals (e.g., CPU, memory and floppy disks). In addition, some models featured auxiliary custom chips that performed tasks such as SCSI control and display de-interlacing.
Graphics
All Amiga systems can display full-screen animated planar graphics with 2, 4, 8, 16, 32, 64 (EHB Mode), or 4096 colors (HAM Mode). Models with the AGA chipset (A1200 and A4000) also have non-EHB 64, 128, 256, and 262144 (HAM8 Mode) color modes and a palette expanded from 4096 to 16.8 million colors.
The Amiga chipset can genlock, which is the ability to adjust its own screen refresh timing to match an incoming NTSC or PAL video signal. When combined with setting transparency, this allows an Amiga to overlay an external video source with graphics. This ability made the Amiga popular for many applications, and provides the ability to do character generation and CGI effects far more cheaply than earlier systems. This ability has been frequently utilized by wedding videographers, TV stations and their weather forecasting divisions (for weather graphics and radar), advertising channels, music video production, and desktop videographers. The NewTek Video Toaster was made possible by the genlock ability of the Amiga.
In 1988, the release of the Amiga A2024 fixed-frequency monochrome monitor with built-in framebuffer and flicker fixer hardware provided the Amiga with a choice of high-resolution graphic modes (1024×800 for NTSC and 1024×1024 for PAL).
ReTargetable Graphics | Amiga | Wikipedia | 452 | 1980 | https://en.wikipedia.org/wiki/Amiga | Technology | Specific hardware | null |
ReTargetable Graphics is an API for device drivers mainly used by 3rd party graphics hardware to interface with AmigaOS via a set of libraries. The software libraries may include software tools to adjust resolution, screen colors, pointers and screenmodes. The standard Intuition interface is limited to display depths of 8 bits, while RTG makes it possible to handle higher depths like 24-bits.
Sound
The sound chip, named Paula, supports four PCM sound channels (two for the left speaker and two for the right) with 8-bit resolution for each channel and a 6-bit volume control per channel. The analog output is connected to a low-pass filter, which filters out high-frequency aliasing when the Amiga is using a lower sampling rate (see Nyquist frequency). The brightness of the Amiga's power LED is used to indicate the status of the Amiga's low-pass filter. The filter is active when the LED is at normal brightness, and deactivated when dimmed (or off on older A500 Amigas). On Amiga 1000 (and first Amiga 500 and Amiga 2000 model), the power LED had no relation to the filter's status, and a wire needed to be manually soldered between pins on the sound chip to disable the filter. Paula can read arbitrary waveforms at arbitrary rates and amplitudes directly from the system's RAM, using direct memory access (DMA), making sound playback without CPU intervention possible.
Although the hardware is limited to four separate sound channels, software such as OctaMED uses software mixing to allow eight or more virtual channels, and it was possible for software to mix two hardware channels to achieve a single 14-bit resolution channel by playing with the volumes of the channels in such a way that one of the source channels contributes the most significant bits and the other the least.
The quality of the Amiga's sound output, and the fact that sound hardware is part of the standard chipset and easily addressed by software, were standout features of Amiga hardware unavailable on IBM PC compatibles for years. Third-party sound cards exist that provide DSP functions, multi-track direct-to-disk recording, multiple hardware sound channels and 16-bit and beyond resolutions. A retargetable sound API called AHI was developed allowing these cards to be used transparently by the OS and software.
Kickstart firmware | Amiga | Wikipedia | 485 | 1980 | https://en.wikipedia.org/wiki/Amiga | Technology | Specific hardware | null |
Kickstart is the firmware upon which AmigaOS is bootstrapped. Its purpose is to initialize the Amiga hardware and core components of AmigaOS and then attempt to boot from a bootable volume, such as a floppy disk or hard disk drive. Most models (excluding the Amiga 1000) come equipped with Kickstart on an embedded ROM-chip.
There are various editions of Kickstart ROMs starting with Kickstart v1.1 for the Amiga 1000, v1.2 and v1.3 for the A500, Kickstart v2.1 on A500+, Kickstart v2.2 for A600 and dual ROMs for Kickstart v3.0 and 3.1 for A1200 and A4000. After Commodore's demise there have been new Kickstart v3.1 ROMs made available for both the A500 and A600 Computers. Amiga Software is mostly backward compatible, but v2.1 ROMs and newer differ slightly, which can cause software glitches with earlier programs. To help address this and to get earlier programs to work with later Kickstart ROMs, some tools have been produced such as RELOKIK 1.4 and MAKE IT WORK! for the A600 and A1200. They revert the system to temporarily boot in Kickstart v1.3.
Keyboard and mouse
The keyboard on Amiga computers is similar to that found on a mid-80s IBM PC: Ten function keys, a numeric keypad, and four separate directional arrow keys. Caps Lock and Control share space to the left of A. Absent are Home, End, Page Up, and Page Down keys: These functions are accomplished on Amigas by pressing shift and the appropriate arrow key. The Amiga keyboard adds a Help key, which a function key usually acts as on PCs (usually F1). In addition to the Control and Alt modifier keys, the Amiga has 2 "Amiga" keys, rendered as "Open Amiga" and "Closed Amiga" similar to the Open/Closed Apple logo keys on Apple II keyboards. The left is used to manipulate the operating system (moving screens and the like) and the right delivers commands to the application. The absence of Num lock frees space for more mathematical symbols around the numeric pad. | Amiga | Wikipedia | 473 | 1980 | https://en.wikipedia.org/wiki/Amiga | Technology | Specific hardware | null |
Like IBM-compatible computers, the mouse has two buttons, but in AmigaOS, pressing and holding the right button replaces the system status line at the top of the screen with a Maclike menu bar. As with Apple's Mac OS prior to Mac OS 8, menu options are selected by releasing the button over that option, not by left clicking. Menu items that have a Boolean toggle state can be left clicked whilst the menu is kept open with the right button, which allows the user – for example – to set some selected text to bold, underline and italics in one visit to the menus.
The mouse plugs into one of two Atari joystick ports used for joysticks, game paddles, and graphics tablets. Although compatible with analog joysticks, Atari-style digital joysticks became standard. Unusually, two independent mice can be connected to the joystick ports; some games, such as Lemmings, were designed to take advantage of this.
Other peripherals and expansions
The Amiga was one of the first computers for which inexpensive sound sampling and video digitization accessories were available. As a result of this and the Amiga's audio and video capabilities, the Amiga became a popular system for editing and producing both music and video.
Many expansion boards were produced for Amiga computers to improve the performance and capability of the hardware, such as memory expansions, SCSI controllers, CPU boards, and graphics boards. Other upgrades include genlocks, network cards for Ethernet, modems, sound cards and samplers, video digitizers, extra serial ports, and IDE controllers. Additions after the demise of Commodore company are USB cards. The most popular upgrades were memory, SCSI controllers and CPU accelerator cards. These were sometimes combined into one device.
Early CPU accelerator cards used the full 32-bit CPUs of the 68000 family such as the Motorola 68020 and Motorola 68030, almost always with 32-bit memory and usually with FPUs and MMUs or the facility to add them. Later designs feature the Motorola 68040 or Motorola 68060. Both CPUs feature integrated FPUs and MMUs. Many CPU accelerator cards also had integrated SCSI controllers. | Amiga | Wikipedia | 444 | 1980 | https://en.wikipedia.org/wiki/Amiga | Technology | Specific hardware | null |
Phase5 designed the PowerUP boards (Blizzard PPC and CyberStorm PPC) featuring both a 68k (a 68040 or 68060) and a PowerPC (603 or 604) CPU, which are able to run the two CPUs at the same time and share the system memory. The PowerPC CPU on PowerUP boards is usually used as a coprocessor for heavy computations; a powerful CPU is needed to run MAME for example, but even decoding JPEG pictures and MP3 audio was considered heavy computation at the time. It is also possible to ignore the 68k CPU and run Linux on the PPC via project Linux APUS, but a PowerPC-native AmigaOS promised by Amiga Technologies GmbH was not available when the PowerUP boards first appeared.
24-bit graphics cards and video cards were also available. Graphics cards were designed primarily for 2D artwork production, workstation use, and later, gaming. Video cards are designed for inputting and outputting video signals, and processing and manipulating video.
In the North American market, the NewTek Video Toaster was a video effects board that turned the Amiga into an affordable video processing computer that found its way into many professional video environments. One well-known use was to create the special effects in early series of Babylon 5. Due to its NTSC-only design, it did not find a market in countries that used the PAL standard, such as in Europe. In those countries, the OpalVision card was popular, although less featured and supported than the Video Toaster. Low-cost time base correctors (TBC) specifically designed to work with the Toaster quickly came to market, most of which were designed as standard Amiga bus cards.
Various manufacturers started producing PCI busboards for the A1200, A3000 and A4000, allowing standard Amiga computers to use PCI cards such as graphics cards, Sound Blaster sound cards, 10/100 Ethernet cards, USB cards, and television tuner cards. Other manufacturers produced hybrid boards that contained an Intel x86 series chip, allowing the Amiga to emulate a PC.
PowerPC upgrades with Wide SCSI controllers, PCI busboards with Ethernet, sound and 3D graphics cards, and tower cases allowed the A1200 and A4000 to survive well into the late nineties. | Amiga | Wikipedia | 473 | 1980 | https://en.wikipedia.org/wiki/Amiga | Technology | Specific hardware | null |
Expansion boards were made by Richmond Sound Design that allow their show control and sound design software to communicate with their custom hardware frames either by ribbon cable or fiber optic cable for long distances, allowing the Amiga to control up to eight million digitally controlled external audio, lighting, automation, relay and voltage control channels spread around a large theme park, for example. See Amiga software for more information on these applications.
Other devices included the following:
Amiga 501 with 512 KB RAM and real-time clock
Trumpcard 500 Zorro-II SCSI interface
GVP A530 Turbo, accelerator, RAM expansion, PC emulator
A2091 / A590 SCSI hard disk controller + 2 MB RAM expansion
A3070 SCSI tape backup unit with a capacity of , OEM Archive Viper 1/4-inch
A2065 Ethernet Zorro-II interface – the first Ethernet interface for Amiga; uses the AMD Am7990 chip The same interface chip is used in DECstation as well.
Ariadne Zorro-II Ethernet interface using the AMD Am7990
A4066 Zorro II Ethernet interface using the SMC 91C90QF
X-Surf from Individual Computers using the Realtek 8019AS
A2060 Arcnet
A1010 floppy disk drive consisting of a 3.5-inch double density (DD), , drive unit connected via DB-23 connector; track-to-track delay is on the order of . The default capacity is . Many clone drives were available, and products such as the Catweasel and KryoFlux make it possible to read and write Amiga and other special disc formats on standard x86 PCs.
NE2000-compatible PCMCIA Ethernet cards for Amiga 600 and Amiga 1200
Serial ports
The Commodore A2232 board provides seven RS-232C serial ports in addition to the Amiga's built-in serial port. Each port can be driven independently at speeds of 50 to . There is, however, a driver available on Aminet that allows two of the serial ports to be driven at . The serial card used the 65CE02 CPU clocked at . This CPU was also part of the CSG 4510 CPU core that was used in the Commodore 65 computer. | Amiga | Wikipedia | 454 | 1980 | https://en.wikipedia.org/wiki/Amiga | Technology | Specific hardware | null |
Networking
Amiga has three networking interface APIs:
AS225: the official Commodore TCP/IP stack API with hard-coded drivers in revision 1 (AS225r1) for the A2065 Ethernet and the A2060 Arcnet interfaces. In revision 2, (AS225r2) the SANA-II interface was used.
SANA-II: a standardized API for hardware of network interfaces. It uses an inefficient buffer handling scheme, and lacks proper support for promiscuous and multicast modes.
Miami Network Interface (MNI): an API that doesn't have the problems that SANA-II suffers from. It requires AmigaOS v2.04 or higher.
Different network media were used:
Models and variants
The original Amiga models were produced from 1985 to 1996. They are, in order of production: 1000, 2000, 500, 1500, 2500, 3000, 3000UX, 3000T, CDTV, 500+, 600, 4000, 1200, CD32, and 4000T. The PowerPC-based AmigaOne computers were later marketed beginning in 2002. Several companies and private persons have also released Amiga clones and still do so today.
Commodore Amiga
The first Amiga model, the Amiga 1000, was launched in 1985. In 2006, PC World rated the Amiga 1000 as the seventh greatest PC of all time, stating "Years ahead of its time, the Amiga was the world's first multimedia, multitasking personal computer".
Commodore updated the desktop line of Amiga computers with the Amiga 2000 in 1987, the Amiga 3000 in 1990, and the Amiga 4000 in 1992, each offering improved capabilities and expansion options. The best-selling models were the budget models, however, particularly the highly successful Amiga 500 (1987) and the Amiga 1200 (1992). The Amiga 500+ (1991) was the shortest-lived model, replacing the Amiga 500 and lasting only six months until it was phased out and replaced with the Amiga 600 (1992). The A600 was only intended as a temporary gap filler until the A1200 was available for sale. The A600 was actually designed as a portable system, hence the lack of numeric Keypad, and it was originally to be named Amiga 300. Some early A600 models have retained the original A300 logo printed on the mainboard. The Amiga 600 was quickly replaced by the Amiga 1200. | Amiga | Wikipedia | 490 | 1980 | https://en.wikipedia.org/wiki/Amiga | Technology | Specific hardware | null |
The CDTV, launched in 1991, was a CD-ROM-based game console, Computer and multimedia appliance based on the Amiga A500 with the same v1.3 Kickstart ROM, several years before CD-ROM drives were common. The cost of CDTV media production and the CD-ROM drives at the time discouraged potential buyers and the system never achieved any real success. The CDTV was however one of the first ever CD-ROM-based machines that were mass produced. A CDTV legacy is the external A570 CD-ROM drive expansion for the A500 computer.
Commodore's last Amiga offering before filing for bankruptcy was the Amiga CD32 (1993), a 32-bit CD-ROM games console produced until mid 1994. Although discontinued after Commodore's demise it met with moderate commercial success in Europe. The CD32 was a next-generation CDTV, and it was designed and released by Commodore before the Playstation. It was Commodore's last attempt to enter the ever growing video-game console market.
Following purchase of Commodore's assets by Escom in 1995, the A1200 and A4000T continued to be sold in small quantities until 1996, though the ground lost since the initial launch and the prohibitive expense of these units meant that the Amiga line never regained any real popularity.
Several Amiga models contained references to songs by the rock band The B-52's. Early A500 units had the words "B52/ROCK LOBSTER" silk-screen printed onto their printed circuit board, a reference to the song "Rock Lobster" The Amiga 600 referenced "JUNE BUG" (after the song "Junebug") and the Amiga 1200 had "CHANNEL Z" (after "Channel Z"), and the CD-32 had "Spellbound."
AmigaOS 4 systems
AmigaOS 4 is designed for PowerPC Amiga systems. It is mainly based on AmigaOS 3.1 source code, with some parts of version 3.9. Currently runs on both Amigas equipped with CyberstormPPC or BlizzardPPC accelerator boards, on the Teron series based AmigaOne computers built by Eyetech under license by Amiga, Inc., on the Pegasos II from Genesi/bPlan GmbH, on the ACube Systems Srl Sam440ep / Sam460ex / AmigaOne 500 systems and on the A-EON AmigaOne X1000. | Amiga | Wikipedia | 493 | 1980 | https://en.wikipedia.org/wiki/Amiga | Technology | Specific hardware | null |
AmigaOS 4.0 had been available only in developer pre-releases for numerous years until it was officially released in December 2006. Due to the nature of some provisions of the contract between Amiga Inc. and Hyperion Entertainment (the Belgian company that is developing the OS), the commercial AmigaOS 4 had been available only to licensed buyers of AmigaOne motherboards.
AmigaOS 4.0 for Amigas equipped with PowerUP accelerator boards was released in November 2007. Version 4.1 was released in August 2008 for AmigaOne systems, and in May 2011 for Amigas equipped with PowerUP accelerator boards. The most recent release of AmigaOS for all supported platforms is 4.1 update 5. Starting with release 4.1 update 4 there is an Emulation drawer containing official AmigaOS 3.x ROMs (all classic Amiga models including CD32) and relative Workbench files.
Acube Systems entered an agreement with Hyperion under which it has ported AmigaOS 4 to its Sam440ep and Sam460ex line of PowerPC-based motherboards. In 2009 a version for Pegasos II was released in co-operation with Acube Systems. In 2012, A-EON Technology Ltd manufactured and released the AmigaOne X1000 to consumers through their partner, Amiga Kit who provided end-user support, assembly and worldwide distribution of the new system.
Amiga hardware clones
Long-time Amiga developer MacroSystem entered the Amiga-clone market with their DraCo non-linear video editing system. It appears in two versions, initially a tower model and later a cube. DraCo expanded upon and combined a number of earlier expansion cards developed for Amiga (VLabMotion, Toccata, WarpEngine, RetinaIII) into a true Amiga-clone powered by the Motorola 68060 processor. The DraCo can run AmigaOS 3.1 up through AmigaOS 3.9. It is the only Amiga-based system to support FireWire for video I/O. DraCo also offers an Amiga-compatible Zorro-II expansion bus and introduced a faster custom DraCoBus, capable of transfer rates (faster than Commodore's Zorro-III). The technology was later used in the Casablanca system, a set-top-box also designed for non-linear video editing. | Amiga | Wikipedia | 470 | 1980 | https://en.wikipedia.org/wiki/Amiga | Technology | Specific hardware | null |
In 1998, Index Information released the Access, an Amiga-clone similar to the Amiga 1200, but on a motherboard that could fit into a standard -inch drive bay. It features either a 68020 or 68030 CPU, with a AGA chipset, and runs AmigaOS 3.1.
In 1998, former Amiga employees (John Smith, Peter Kittel, Dave Haynie and Andy Finkel to mention few) formed a new company called PIOS. Their hardware platform, PIOS One, was aimed at Amiga, Atari and Macintosh users. The company was renamed to Met@box in 1999 until it folded.
The NatAmi (short for Native Amiga) hardware project began in 2005 with the aim of designing and building an Amiga clone motherboard that is enhanced with modern features. The NatAmi motherboard is a standard Mini-ITX-compatible form factor computer motherboard, powered by a Motorola/Freescale 68060 and its chipset. It is compatible with the original Amiga chipset, which has been inscribed on a programmable FPGA Altera chip on the board. The NatAmi is the second Amiga clone project after the Minimig motherboard, and its history is very similar to that of the C-One mainboard developed by Jeri Ellsworth and Jens Schönfeld. From a commercial point of view, Natami's circuitry and design are currently closed source. One goal of the NatAmi project is to design an Amiga-compatible motherboard that includes up-to-date features but that does not rely on emulation (as in WinUAE), modern PC Intel components, or a modern PowerPC mainboard. As such, NatAmi is not intended to become another evolutionary heir to classic Amigas, such as with AmigaOne or Pegasos computers. This "purist" philosophy essentially limits the resulting processor speed but puts the focus on bandwidth and low latencies. The developers also recreated the entire Amiga chipset, freeing it from legacy Amiga limitations such as two megabytes of audio and video graphics RAM as in the AGA chipset, and rebuilt this new chipset by programming a modern FPGA Altera Cyclone IV chip. Later, the developers decided to create from scratch a new software-form processor chip, codenamed "N68050" that resides in the physical Altera FPGA programmable chip. | Amiga | Wikipedia | 487 | 1980 | https://en.wikipedia.org/wiki/Amiga | Technology | Specific hardware | null |
In 2006, two new Amiga clones were announced, both using FPGA based hardware synthesis to replace the Amiga OCS custom chipset. The first, the Minimig, is a personal project of Dutch engineer Dennis van Weeren. Referred to as "new Amiga hardware", the original model was built on a Xilinx Spartan-3 development board, but soon a dedicated board was developed. The minimig uses the FPGA to reproduce the custom Denise, Agnus, Paula and Gary chips as well as both 8520 CIAs and implements a simple version of Amber. The rest of the chips are an actual 68000 CPU, ram chips, and a PIC microcontroller for BIOS control. The design for Minimig was released as open-source on July 25, 2007. In February 2008, an Italian company Acube Systems began selling Minimig boards. A third party upgrade replaces the PIC microcontroller with a more powerful ARM processor, providing more functionality such as write access and support for hard disk images. The Minimig core has been ported to the FPGArcade "Replay" board. The Replay uses an FPGA with about three times more capacity and that does support the AGA chipset and a 68020 soft core with 68030 capabilities. The Replay board is designed to implement many older computers and classic arcade machines.
The second is the Clone-A system announced by Individual Computers. As of mid-2007 it has been shown in its development form, with FPGA-based boards replacing the Amiga chipset and mounted on an Amiga 500 motherboard.
Operating systems
AmigaOS
AmigaOS is a single-user multitasking operating system. It was one of the first commercially available consumer operating systems for personal computers to implement preemptive multitasking. It was developed first by Commodore International and initially introduced in 1985 with the Amiga 1000. John C. Dvorak wrote in PC Magazine in 1996:
AmigaOS combines a command-line interface and graphical user interface. AmigaDOS is the disk operating system and command line portion of the OS and Workbench the native graphical windowing, graphical environment for file management and launching applications. AmigaDOS allows long filenames (up to 107 characters) with whitespace and does not require filename extensions. The windowing system and user interface engine that handles all input events is called Intuition. | Amiga | Wikipedia | 486 | 1980 | https://en.wikipedia.org/wiki/Amiga | Technology | Specific hardware | null |
The multi-tasking kernel is called Exec. It acts as a scheduler for tasks running on the system, providing pre-emptive multitasking with prioritised round-robin scheduling. It enabled true pre-emptive multitasking in as little as 256 KB of free memory.
AmigaOS does not implement memory protection; the 68000 CPU does not include a memory management unit. Although this speeds and eases inter-process communication because programs can communicate by simply passing a pointer back and forth, the lack of memory protection made the AmigaOS more vulnerable to crashes from badly behaving programs than other multitasking systems that did implement memory protection, and Amiga OS is fundamentally incapable of enforcing any form of security model since any program had full access to the system. A co-operational memory protection feature was implemented in AmigaOS 4 and could be retrofitted to old AmigaOS systems using Enforcer or CyberGuard tools.
The problem was somewhat exacerbated by Commodore's initial decision to release documentation relating not only to the OS's underlying software routines, but also to the hardware itself, enabling intrepid programmers who had developed their skills on the Commodore 64 to POKE the hardware directly, as was done on the older platform. While the decision to release the documentation was a popular one and allowed the creation of fast, sophisticated sound and graphics routines in games and demos, it also contributed to system instabilityas some programmers lacked the expertise to program at this level. For this reason, when the new AGA chipset was released, Commodore declined to release low-level documentation in an attempt to force developers into using the approved software routines.
The latest version for the PPC Amigas is the AmigaOS 4.1 and for the 68k Amigas is the AmigaOS 3.2.2 | Amiga | Wikipedia | 367 | 1980 | https://en.wikipedia.org/wiki/Amiga | Technology | Specific hardware | null |
Influence on other operating systems
AmigaOS directly or indirectly inspired the development of various operating systems. MorphOS and AROS clearly inherit heavily from the structure of AmigaOS as explained directly in articles regarding these two operating systems. AmigaOS also influenced BeOS, which featured a centralized system of Datatypes, similar to that present in AmigaOS. Likewise, DragonFly BSD was also inspired by AmigaOS as stated by Dragonfly developer Matthew Dillon who is a former Amiga developer. WindowLab and amiwm are among several window managers for the X Window System seek to mimic the Workbench interface. IBM licensed the Amiga GUI from Commodore in exchange for the REXX language license. This allowed OS/2 to have the WPS (Workplace Shell) GUI shell for OS/2 2.0, a 32-bit operating system.
Unix and Unix-like systems
Commodore-Amiga produced Amiga Unix, informally known as Amix, based on AT&T SVR4. It supports the Amiga 2500 and Amiga 3000 and is included with the Amiga 3000UX. Among other unusual features of Amix is a hardware-accelerated windowing system that can scroll windows without copying data. Amix is not supported on the later Amiga systems based on 68040 or 68060 processors.
Other, still maintained, operating systems are available for the classic Amiga platform, including Linux and NetBSD. Both require a CPU with MMU such as the 68020 with 68851 or full versions of the 68030, 68040 or 68060. There is also a version of Linux for Amigas with PowerPC accelerator cards. Debian and Yellow Dog Linux can run on the AmigaOne.
There is an official, older version of OpenBSD. The last Amiga release is 3.2. MINIX 1.5.10 also runs on Amiga.
Emulating other systems
The Amiga Sidecar is a complete IBM PC XT compatible computer contained in an expansion card. It was released by Commodore in 1986 and promoted as a way to run business software on the Amiga 1000.
Amiga software
In the late 1980s and early 1990s the platform became particularly popular for gaming, demoscene activities and creative software uses. During this time commercial developers marketed a wide range of games and creative software, often developing titles simultaneously for the Atari ST due to the similar hardware architecture. Popular creative software included 3D rendering (ray-tracing) packages, bitmap graphics editors, desktop video software, software development packages and "tracker" music editors. | Amiga | Wikipedia | 501 | 1980 | https://en.wikipedia.org/wiki/Amiga | Technology | Specific hardware | null |
Until the late 1990s the Amiga remained a popular platform for non-commercial software, often developed by enthusiasts, and much of which was freely redistributable. An on-line archive, Aminet, was created in 1991 and until the late-1990s was the largest public archive of software, art and documents for any platform.
Marketing
The name Amiga was chosen by the developers from the Spanish word for a female friend, because they knew Spanish, and because it occurred before Apple and Atari alphabetically. It also conveyed the message that the Amiga computer line was "user friendly" as a pun or play on words.
The first official Amiga logo was a rainbow-colored double check mark. In later marketing material Commodore largely dropped the checkmark and used logos styled with various typefaces. Although it was never adopted as a trademark by Commodore, the "Boing Ball" has been synonymous with Amiga since its launch. It became an unofficial and enduring theme after a visually impressive animated demonstration at the 1984 Winter Consumer Electronics Show in January 1984 showing a checkered ball bouncing and rotating. Following Escom's purchase of Commodore in 1996, the Boing Ball theme was incorporated into a new logo.
Early Commodore advertisements attempted to cast the computer as an all-purpose business machine, though the Amiga was most commercially successful as a home computer. Throughout the 1980s and early 1990s Commodore primarily placed advertising in computer magazines and occasionally in national newspapers and on television.
Legacy
Since the demise of Commodore, various groups have marketed successors to the original Amiga line: | Amiga | Wikipedia | 307 | 1980 | https://en.wikipedia.org/wiki/Amiga | Technology | Specific hardware | null |
Genesi sold PowerPC based hardware under the Pegasos brand running AmigaOS and MorphOS;
Eyetech sold PowerPC based hardware under the AmigaOne brand from 2002 to 2005 running AmigaOS 4;
Amiga Kit distributes and sells PowerPC based hardware under the AmigaOne brand from 2010 to present day running AmigaOS 4;
ACube Systems sells the AmigaOS 3 compatible Minimig system with a Freescale MC68SEC000 CPU (Motorola 68000 compatible) and AmigaOS 4 compatible Sam440 / Sam460 / AmigaOne 500 systems with PowerPC processors;
A-EON Technology Ltd sells the AmigaOS 4 compatible AmigaOne X1000 system with P.A. Semi PWRficient PA6T-1682M processor, X5000 and A1222+ computers.
AmigaKit Ltd produce the A600GS and A1200NG computers systems. They also manufacture and sell a wide range of aftermarket components to refurbished classic systems.
ASB Computer Spain sell numerous items from aftermarket components to refurbished classic systems.
AmigaOS and MorphOS are commercial proprietary operating systems. AmigaOS 4, based on AmigaOS 3.1 source code with some parts of version 3.9, is developed by Hyperion Entertainment and runs on PowerPC based hardware. MorphOS, based on some parts of AROS source code, is developed by MorphOS Team and is continued on Apple and other PowerPC based hardware.
There is also AROS, a free and open source operating system (re-implementation of the AmigaOS 3.1 APIs), for Amiga 68k, x86 and ARM hardware (one version runs Linux-hosted on the Raspberry Pi). In particular, AROS for Amiga 68k hardware aims to create an open source Kickstart ROM replacement for emulation purpose and/or for use on real "classic" hardware.
Magazines
Amiga Format continued publication until 2000. Amiga Active was launched in 1999 and was published until 2001.
Several magazines are in publication today: Print magazine Amiga Addict started publication in 2020.Amiga Future, which is available in both English and German; Bitplane.it, a bimonthly magazine in Italian; and AmigaPower, a long-running French magazine.
Trade shows
The Amiga continues to be popular enough that fans to support conferences such as Amiga37 which had over 50 vendors. | Amiga | Wikipedia | 485 | 1980 | https://en.wikipedia.org/wiki/Amiga | Technology | Specific hardware | null |
Uses
The Amiga series of computers found a place in early computer graphic design and television presentation. Season 1 and part of season 2 of the television series Babylon 5 were rendered in LightWave 3D on Amigas. Other television series using Amigas for special effects included SeaQuest DSV and Max Headroom.
In addition, many celebrities and notable individuals have made use of the Amiga: | Amiga | Wikipedia | 75 | 1980 | https://en.wikipedia.org/wiki/Amiga | Technology | Specific hardware | null |
Andy Warhol was an early user of the Amiga and appeared at the launch, where he made a computer artwork of Debbie Harry. Warhol used the Amiga to create a new style of art made with computers, and was the author of a multimedia opera called You Are the One, which consists of an animated sequence featuring images of actress Marilyn Monroe assembled in a short movie with a soundtrack. The video was discovered on two old Amiga floppies in a drawer in Warhol's studio and repaired in 2006 by the Detroit Museum of New Art. The pop artist has been quoted as saying: "The thing I like most about doing this kind of work on the Amiga is that it looks like my work in other media".
Artist Jean "Moebius" Giraud credits the Amiga he bought for his son as a bridge to learning about "using paint box programs". He uploaded some of his early experiments to the file sharing forums on CompuServe.
Futurist and science fiction author Arthur C. Clarke used an Amiga computer to calculate and explore Mandelbrot sets in the 1988 documentary film God, the Universe and Everything Else.
The "Weird Al" Yankovic film UHF contains a computer-animated music video parody of the Dire Straits song "Money for Nothing", titled "Money for Nothing/Beverly Hillbillies*". According to the DVD commentary track, this spoof was created on an Amiga home computer.
Rolf Harris used an Amiga to digitize his hand-drawn art work for animation on his television series Rolf's Cartoon Club.
Debbie Harry appeared together with Andy Warhol (see above) at launch.
Todd Rundgren's video "Change Myself" was produced with Toaster and Lightwave.
Scottish pop artist Calvin Harris composed his 2007 debut album I Created Disco with an Amiga 1200.
Susumu Hirasawa, a Japanese progressive-electronic artist, is known for using Amigas to compose and perform music, aid his live shows and make his promotional videos. He has also been inspired by the Amiga, and has referenced it in his lyrics. His December 13, 1994 "Adios Jay" Interactive Live Show was dedicated to (then recently deceased) Jay Miner. He also used the Amiga to create the virtual drummer TAINACO, who was a CG rendered figure whose performance was made with Elan Performer and was projected with DCTV. He also composed and performed "Eastern-boot", the AmigaOS 4 boot jingle.
Electronic musician Max Tundra created his three albums with an Amiga 500. | Amiga | Wikipedia | 512 | 1980 | https://en.wikipedia.org/wiki/Amiga | Technology | Specific hardware | null |
Bob Casale, keyboardist and guitarist of the new wave band Devo, used Amiga computer graphics on the album cover to Devo's album Total Devo.
Most of Pokémon Gold and Silver's music was created on an Amiga computer, converted to MIDI, and then reconverted to the game's music format.
American professional skateboarder Tony Hawk used an Amiga 2000 during the late 1980s to early 1990s. NewTek sent him a Video Toaster for his Amiga in exchange for appearing in a promotional video alongside Wil Wheaton and Penn Jillette, which he later used for editing a promotional video for the TurboDuo game Lords of Thunder in 1993.
Veteran actor Dick Van Dyke also owned an Amiga equipped with a Video Toaster, where he is credited with the creation of 3D-rendered effects used on Diagnosis: Murder and The Dick Van Dyke Show Revisited. Van Dyke has displayed his computer-generated imagery work at SIGGRAPH, and continues to work with LightWave 3D.
A number of notable producers used OctaMED for composition and live performance of Drum and Bass, Jungle, and various other sub-genres of electronic dance music on Amiga systems, occasionally in conjunction with additional synthesizers. These include: Aphrodite, DJ Zinc, Omni Trio, and Paradox, among others. | Amiga | Wikipedia | 262 | 1980 | https://en.wikipedia.org/wiki/Amiga | Technology | Specific hardware | null |
Special purpose applications
Amigas were used in various NASA laboratories to keep track of low orbiting satellites until 2004. Amigas were used at Kennedy Space Center to run strip-chart recorders, to format and display data, and control stations of platforms for Delta rocket launches.
Palomar Observatory used Amigas to calibrate and control the charge-coupled devices in their telescopes, as well as to display and store the digitized images they collected.
London Transport Museum developed their own interactive multi-media software for the CD32 including a virtual tour of the museum.
Amiga 500 motherboards were used, in conjunction with a LaserDisc player and genlock device, in arcade games manufactured by American Laser Games.
A custom Amiga 4000T motherboard was used in the HDI 1000 medical ultrasound system built by Advanced Technology Labs.
, the Grand Rapids Public School district uses a Commodore Amiga 2000 with 1200 baud modem to automate its air conditioning and heating systems for the 19 schools covered by the GRPS district. The system has been operating day and night for decades.
The Weather Network used Amigas to display the weather on TV. | Amiga | Wikipedia | 225 | 1980 | https://en.wikipedia.org/wiki/Amiga | Technology | Specific hardware | null |
Algebraic geometry is a branch of mathematics which uses abstract algebraic techniques, mainly from commutative algebra, to solve geometrical problems. Classically, it studies zeros of multivariate polynomials; the modern approach generalizes this in a few different aspects.
The fundamental objects of study in algebraic geometry are algebraic varieties, which are geometric manifestations of solutions of systems of polynomial equations. Examples of the most studied classes of algebraic varieties are lines, circles, parabolas, ellipses, hyperbolas, cubic curves like elliptic curves, and quartic curves like lemniscates and Cassini ovals. These are plane algebraic curves. A point of the plane lies on an algebraic curve if its coordinates satisfy a given polynomial equation. Basic questions involve the study of points of special interest like singular points, inflection points and points at infinity. More advanced questions involve the topology of the curve and the relationship between curves defined by different equations.
Algebraic geometry occupies a central place in modern mathematics and has multiple conceptual connections with such diverse fields as complex analysis, topology and number theory. As a study of systems of polynomial equations in several variables, the subject of algebraic geometry begins with finding specific solutions via equation solving, and then proceeds to understand the intrinsic properties of the totality of solutions of a system of equations. This understanding requires both conceptual theory and computational technique.
In the 20th century, algebraic geometry split into several subareas.
The mainstream of algebraic geometry is devoted to the study of the complex points of the algebraic varieties and more generally to the points with coordinates in an algebraically closed field.
Real algebraic geometry is the study of the real algebraic varieties.
Diophantine geometry and, more generally, arithmetic geometry is the study of algebraic varieties over fields that are not algebraically closed and, specifically, over fields of interest in algebraic number theory, such as the field of rational numbers, number fields, finite fields, function fields, and p-adic fields.
A large part of singularity theory is devoted to the singularities of algebraic varieties.
Computational algebraic geometry is an area that has emerged at the intersection of algebraic geometry and computer algebra, with the rise of computers. It consists mainly of algorithm design and software development for the study of properties of explicitly given algebraic varieties. | Algebraic geometry | Wikipedia | 459 | 1997 | https://en.wikipedia.org/wiki/Algebraic%20geometry | Mathematics | Algebra | null |
Much of the development of the mainstream of algebraic geometry in the 20th century occurred within an abstract algebraic framework, with increasing emphasis being placed on "intrinsic" properties of algebraic varieties not dependent on any particular way of embedding the variety in an ambient coordinate space; this parallels developments in topology, differential and complex geometry. One key achievement of this abstract algebraic geometry is Grothendieck's scheme theory which allows one to use sheaf theory to study algebraic varieties in a way which is very similar to its use in the study of differential and analytic manifolds. This is obtained by extending the notion of point: In classical algebraic geometry, a point of an affine variety may be identified, through Hilbert's Nullstellensatz, with a maximal ideal of the coordinate ring, while the points of the corresponding affine scheme are all prime ideals of this ring. This means that a point of such a scheme may be either a usual point or a subvariety. This approach also enables a unification of the language and the tools of classical algebraic geometry, mainly concerned with complex points, and of algebraic number theory. Wiles' proof of the longstanding conjecture called Fermat's Last Theorem is an example of the power of this approach.
Basic notions
Zeros of simultaneous polynomials
In classical algebraic geometry, the main objects of interest are the vanishing sets of collections of polynomials, meaning the set of all points that simultaneously satisfy one or more polynomial equations. For instance, the two-dimensional sphere of radius 1 in three-dimensional Euclidean space R3 could be defined as the set of all points with
A "slanted" circle in R3 can be defined as the set of all points which satisfy the two polynomial equations
Affine varieties
First we start with a field k. In classical algebraic geometry, this field was always the complex numbers C, but many of the same results are true if we assume only that k is algebraically closed. We consider the affine space of dimension n over k, denoted An(k) (or more simply An, when k is clear from the context). When one fixes a coordinate system, one may identify An(k) with kn. The purpose of not working with kn is to emphasize that one "forgets" the vector space structure that kn carries. | Algebraic geometry | Wikipedia | 465 | 1997 | https://en.wikipedia.org/wiki/Algebraic%20geometry | Mathematics | Algebra | null |
A function f : An → A1 is said to be polynomial (or regular) if it can be written as a polynomial, that is, if there is a polynomial p in k[x1,...,xn] such that f(M) = p(t1,...,tn) for every point M with coordinates (t1,...,tn) in An. The property of a function to be polynomial (or regular) does not depend on the choice of a coordinate system in An.
When a coordinate system is chosen, the regular functions on the affine n-space may be identified with the ring of polynomial functions in n variables over k. Therefore, the set of the regular functions on An is a ring, which is denoted k[An].
We say that a polynomial vanishes at a point if evaluating it at that point gives zero. Let S be a set of polynomials in k[An]. The vanishing set of S (or vanishing locus or zero set) is the set V(S) of all points in An where every polynomial in S vanishes. Symbolically,
A subset of An which is V(S), for some S, is called an algebraic set. The V stands for variety (a specific type of algebraic set to be defined below).
Given a subset U of An, can one recover the set of polynomials which generate it? If U is any subset of An, define I(U) to be the set of all polynomials whose vanishing set contains U. The I stands for ideal: if two polynomials f and g both vanish on U, then f+g vanishes on U, and if h is any polynomial, then hf vanishes on U, so I(U) is always an ideal of the polynomial ring k[An].
Two natural questions to ask are:
Given a subset U of An, when is U = V(I(U))?
Given a set S of polynomials, when is S = I(V(S))? | Algebraic geometry | Wikipedia | 418 | 1997 | https://en.wikipedia.org/wiki/Algebraic%20geometry | Mathematics | Algebra | null |
The answer to the first question is provided by introducing the Zariski topology, a topology on An whose closed sets are the algebraic sets, and which directly reflects the algebraic structure of k[An]. Then U = V(I(U)) if and only if U is an algebraic set or equivalently a Zariski-closed set. The answer to the second question is given by Hilbert's Nullstellensatz. In one of its forms, it says that I(V(S)) is the radical of the ideal generated by S. In more abstract language, there is a Galois connection, giving rise to two closure operators; they can be identified, and naturally play a basic role in the theory; the example is elaborated at Galois connection.
For various reasons we may not always want to work with the entire ideal corresponding to an algebraic set U. Hilbert's basis theorem implies that ideals in k[An] are always finitely generated.
An algebraic set is called irreducible if it cannot be written as the union of two smaller algebraic sets. Any algebraic set is a finite union of irreducible algebraic sets and this decomposition is unique. Thus its elements are called the irreducible components of the algebraic set. An irreducible algebraic set is also called a variety. It turns out that an algebraic set is a variety if and only if it may be defined as the vanishing set of a prime ideal of the polynomial ring.
Some authors do not make a clear distinction between algebraic sets and varieties and use irreducible variety to make the distinction when needed.
Regular functions
Just as continuous functions are the natural maps on topological spaces and smooth functions are the natural maps on differentiable manifolds, there is a natural class of functions on an algebraic set, called regular functions or polynomial functions. A regular function on an algebraic set V contained in An is the restriction to V of a regular function on An. For an algebraic set defined on the field of the complex numbers, the regular functions are smooth and even analytic.
It may seem unnaturally restrictive to require that a regular function always extend to the ambient space, but it is very similar to the situation in a normal topological space, where the Tietze extension theorem guarantees that a continuous function on a closed subset always extends to the ambient topological space.
Just as with the regular functions on affine space, the regular functions on V form a ring, which we denote by k[V]. This ring is called the coordinate ring of V. | Algebraic geometry | Wikipedia | 508 | 1997 | https://en.wikipedia.org/wiki/Algebraic%20geometry | Mathematics | Algebra | null |
Since regular functions on V come from regular functions on An, there is a relationship between the coordinate rings. Specifically, if a regular function on V is the restriction of two functions f and g in k[An], then f − g is a polynomial function which is null on V and thus belongs to I(V). Thus k[V] may be identified with k[An]/I(V).
Morphism of affine varieties
Using regular functions from an affine variety to A1, we can define regular maps from one affine variety to another. First we will define a regular map from a variety into affine space: Let V be a variety contained in An. Choose m regular functions on V, and call them f1, ..., fm. We define a regular map f from V to Am by letting . In other words, each fi determines one coordinate of the range of f.
If V′ is a variety contained in Am, we say that f is a regular map from V to V′ if the range of f is contained in V′.
The definition of the regular maps apply also to algebraic sets.
The regular maps are also called morphisms, as they make the collection of all affine algebraic sets into a category, where the objects are the affine algebraic sets and the morphisms are the regular maps. The affine varieties is a subcategory of the category of the algebraic sets.
Given a regular map g from V to V′ and a regular function f of k[V′], then . The map is a ring homomorphism from k[V′] to k[V]. Conversely, every ring homomorphism from k[V′] to k[V] defines a regular map from V to V′. This defines an equivalence of categories between the category of algebraic sets and the opposite category of the finitely generated reduced k-algebras. This equivalence is one of the starting points of scheme theory.
Rational function and birational equivalence
In contrast to the preceding sections, this section concerns only varieties and not algebraic sets. On the other hand, the definitions extend naturally to projective varieties (next section), as an affine variety and its projective completion have the same field of functions. | Algebraic geometry | Wikipedia | 460 | 1997 | https://en.wikipedia.org/wiki/Algebraic%20geometry | Mathematics | Algebra | null |
If V is an affine variety, its coordinate ring is an integral domain and has thus a field of fractions which is denoted k(V) and called the field of the rational functions on V or, shortly, the function field of V. Its elements are the restrictions to V of the rational functions over the affine space containing V. The domain of a rational function f is not V but the complement of the subvariety (a hypersurface) where the denominator of f vanishes.
As with regular maps, one may define a rational map from a variety V to a variety V'. As with the regular maps, the rational maps from V to V' may be identified to the field homomorphisms from k(V') to k(V).
Two affine varieties are birationally equivalent if there are two rational functions between them which are inverse one to the other in the regions where both are defined. Equivalently, they are birationally equivalent if their function fields are isomorphic.
An affine variety is a rational variety if it is birationally equivalent to an affine space. This means that the variety admits a rational parameterization, that is a parametrization with rational functions. For example, the circle of equation is a rational curve, as it has the parametric equation
which may also be viewed as a rational map from the line to the circle.
The problem of resolution of singularities is to know if every algebraic variety is birationally equivalent to a variety whose projective completion is nonsingular (see also smooth completion). It was solved in the affirmative in characteristic 0 by Heisuke Hironaka in 1964 and is yet unsolved in finite characteristic.
Projective variety
Just as the formulas for the roots of second, third, and fourth degree polynomials suggest extending real numbers to the more algebraically complete setting of the complex numbers, many properties of algebraic varieties suggest extending affine space to a more geometrically complete projective space. Whereas the complex numbers are obtained by adding the number i, a root of the polynomial , projective space is obtained by adding in appropriate points "at infinity", points where parallel lines may meet. | Algebraic geometry | Wikipedia | 442 | 1997 | https://en.wikipedia.org/wiki/Algebraic%20geometry | Mathematics | Algebra | null |
To see how this might come about, consider the variety . If we draw it, we get a parabola. As x goes to positive infinity, the slope of the line from the origin to the point (x, x2) also goes to positive infinity. As x goes to negative infinity, the slope of the same line goes to negative infinity.
Compare this to the variety V(y − x3). This is a cubic curve. As x goes to positive infinity, the slope of the line from the origin to the point (x, x3) goes to positive infinity just as before. But unlike before, as x goes to negative infinity, the slope of the same line goes to positive infinity as well; the exact opposite of the parabola. So the behavior "at infinity" of V(y − x3) is different from the behavior "at infinity" of V(y − x2).
The consideration of the projective completion of the two curves, which is their prolongation "at infinity" in the projective plane, allows us to quantify this difference: the point at infinity of the parabola is a regular point, whose tangent is the line at infinity, while the point at infinity of the cubic curve is a cusp. Also, both curves are rational, as they are parameterized by x, and the Riemann-Roch theorem implies that the cubic curve must have a singularity, which must be at infinity, as all its points in the affine space are regular.
Thus many of the properties of algebraic varieties, including birational equivalence and all the topological properties, depend on the behavior "at infinity" and so it is natural to study the varieties in projective space. Furthermore, the introduction of projective techniques made many theorems in algebraic geometry simpler and sharper: For example, Bézout's theorem on the number of intersection points between two varieties can be stated in its sharpest form only in projective space. For these reasons, projective space plays a fundamental role in algebraic geometry. | Algebraic geometry | Wikipedia | 413 | 1997 | https://en.wikipedia.org/wiki/Algebraic%20geometry | Mathematics | Algebra | null |
Nowadays, the projective space Pn of dimension n is usually defined as the set of the lines passing through a point, considered as the origin, in the affine space of dimension , or equivalently to the set of the vector lines in a vector space of dimension . When a coordinate system has been chosen in the space of dimension , all the points of a line have the same set of coordinates, up to the multiplication by an element of k. This defines the homogeneous coordinates of a point of Pn as a sequence of elements of the base field k, defined up to the multiplication by a nonzero element of k (the same for the whole sequence).
A polynomial in variables vanishes at all points of a line passing through the origin if and only if it is homogeneous. In this case, one says that the polynomial vanishes at the corresponding point of Pn. This allows us to define a projective algebraic set in Pn as the set , where a finite set of homogeneous polynomials vanishes. Like for affine algebraic sets, there is a bijection between the projective algebraic sets and the reduced homogeneous ideals which define them. The projective varieties are the projective algebraic sets whose defining ideal is prime. In other words, a projective variety is a projective algebraic set, whose homogeneous coordinate ring is an integral domain, the projective coordinates ring being defined as the quotient of the graded ring or the polynomials in variables by the homogeneous (reduced) ideal defining the variety. Every projective algebraic set may be uniquely decomposed into a finite union of projective varieties.
The only regular functions which may be defined properly on a projective variety are the constant functions. Thus this notion is not used in projective situations. On the other hand, the field of the rational functions or function field is a useful notion, which, similarly to the affine case, is defined as the set of the quotients of two homogeneous elements of the same degree in the homogeneous coordinate ring.
Real algebraic geometry
Real algebraic geometry is the study of real algebraic varieties.
The fact that the field of the real numbers is an ordered field cannot be ignored in such a study. For example, the curve of equation is a circle if , but has no real points if . Real algebraic geometry also investigates, more broadly, semi-algebraic sets, which are the solutions of systems of polynomial inequalities. For example, neither branch of the hyperbola of equation is a real algebraic variety. However, the branch in the first quadrant is a semi-algebraic set defined by and . | Algebraic geometry | Wikipedia | 511 | 1997 | https://en.wikipedia.org/wiki/Algebraic%20geometry | Mathematics | Algebra | null |
One open problem in real algebraic geometry is the following part of Hilbert's sixteenth problem: Decide which respective positions are possible for the ovals of a nonsingular plane curve of degree 8.
Computational algebraic geometry
One may date the origin of computational algebraic geometry to meeting EUROSAM'79 (International Symposium on Symbolic and Algebraic Manipulation) held at Marseille, France, in June 1979. At this meeting,
Dennis S. Arnon showed that George E. Collins's Cylindrical algebraic decomposition (CAD) allows the computation of the topology of semi-algebraic sets,
Bruno Buchberger presented Gröbner bases and his algorithm to compute them,
Daniel Lazard presented a new algorithm for solving systems of homogeneous polynomial equations with a computational complexity which is essentially polynomial in the expected number of solutions and thus simply exponential in the number of the unknowns. This algorithm is strongly related with Macaulay's multivariate resultant.
Since then, most results in this area are related to one or several of these items either by using or improving one of these algorithms, or by finding algorithms whose complexity is simply exponential in the number of the variables.
A body of mathematical theory complementary to symbolic methods called numerical algebraic geometry has been developed over the last several decades. The main computational method is homotopy continuation. This supports, for example, a model of floating point computation for solving problems of algebraic geometry.
Gröbner basis
A Gröbner basis is a system of generators of a polynomial ideal whose computation allows the deduction of many properties of the affine algebraic variety defined by the ideal. | Algebraic geometry | Wikipedia | 314 | 1997 | https://en.wikipedia.org/wiki/Algebraic%20geometry | Mathematics | Algebra | null |
Given an ideal I defining an algebraic set V:
V is empty (over an algebraically closed extension of the basis field), if and only if the Gröbner basis for any monomial ordering is reduced to {1}.
By means of the Hilbert series one may compute the dimension and the degree of V from any Gröbner basis of I for a monomial ordering refining the total degree.
If the dimension of V is 0, one may compute the points (finite in number) of V from any Gröbner basis of I (see Systems of polynomial equations).
A Gröbner basis computation allows one to remove from V all irreducible components which are contained in a given hypersurface.
A Gröbner basis computation allows one to compute the Zariski closure of the image of V by the projection on the k first coordinates, and the subset of the image where the projection is not proper.
More generally Gröbner basis computations allow one to compute the Zariski closure of the image and the critical points of a rational function of V into another affine variety.
Gröbner basis computations do not allow one to compute directly the primary decomposition of I nor the prime ideals defining the irreducible components of V, but most algorithms for this involve Gröbner basis computation. The algorithms which are not based on Gröbner bases use regular chains but may need Gröbner bases in some exceptional situations.
Gröbner bases are deemed to be difficult to compute. In fact they may contain, in the worst case, polynomials whose degree is doubly exponential in the number of variables and a number of polynomials which is also doubly exponential. However, this is only a worst case complexity, and the complexity bound of Lazard's algorithm of 1979 may frequently apply. Faugère F5 algorithm realizes this complexity, as it may be viewed as an improvement of Lazard's 1979 algorithm. It follows that the best implementations allow one to compute almost routinely with algebraic sets of degree more than 100. This means that, presently, the difficulty of computing a Gröbner basis is strongly related to the intrinsic difficulty of the problem.
Cylindrical algebraic decomposition (CAD)
CAD is an algorithm which was introduced in 1973 by G. Collins to implement with an acceptable complexity the Tarski–Seidenberg theorem on quantifier elimination over the real numbers. | Algebraic geometry | Wikipedia | 485 | 1997 | https://en.wikipedia.org/wiki/Algebraic%20geometry | Mathematics | Algebra | null |
This theorem concerns the formulas of the first-order logic whose atomic formulas are polynomial equalities or inequalities between polynomials with real coefficients. These formulas are thus the formulas which may be constructed from the atomic formulas by the logical operators and (∧), or (∨), not (¬), for all (∀) and exists (∃). Tarski's theorem asserts that, from such a formula, one may compute an equivalent formula without quantifier (∀, ∃).
The complexity of CAD is doubly exponential in the number of variables. This means that CAD allows, in theory, to solve every problem of real algebraic geometry which may be expressed by such a formula, that is almost every problem concerning explicitly given varieties and semi-algebraic sets.
While Gröbner basis computation has doubly exponential complexity only in rare cases, CAD has almost always this high complexity. This implies that, unless if most polynomials appearing in the input are linear, it may not solve problems with more than four variables.
Since 1973, most of the research on this subject is devoted either to improving CAD or finding alternative algorithms in special cases of general interest.
As an example of the state of art, there are efficient algorithms to find at least a point in every connected component of a semi-algebraic set, and thus to test if a semi-algebraic set is empty. On the other hand, CAD is yet, in practice, the best algorithm to count the number of connected components.
Asymptotic complexity vs. practical efficiency
The basic general algorithms of computational geometry have a double exponential worst case complexity. More precisely, if d is the maximal degree of the input polynomials and n the number of variables, their complexity is at most for some constant c, and, for some inputs, the complexity is at least for another constant c′.
During the last 20 years of the 20th century, various algorithms have been introduced to solve specific subproblems with a better complexity. Most of these algorithms have a complexity . | Algebraic geometry | Wikipedia | 409 | 1997 | https://en.wikipedia.org/wiki/Algebraic%20geometry | Mathematics | Algebra | null |
Among these algorithms which solve a sub problem of the problems solved by Gröbner bases, one may cite testing if an affine variety is empty and solving nonhomogeneous polynomial systems which have a finite number of solutions. Such algorithms are rarely implemented because, on most entries Faugère's F4 and F5 algorithms have a better practical efficiency and probably a similar or better complexity (probably because the evaluation of the complexity of Gröbner basis algorithms on a particular class of entries is a difficult task which has been done only in a few special cases).
The main algorithms of real algebraic geometry which solve a problem solved by CAD are related to the topology of semi-algebraic sets. One may cite counting the number of connected components, testing if two points are in the same components or computing a Whitney stratification of a real algebraic set. They have a complexity of
, but the constant involved by O notation is so high that using them to solve any nontrivial problem effectively solved by CAD, is impossible even if one could use all the existing computing power in the world. Therefore, these algorithms have never been implemented and this is an active research area to search for algorithms with have together a good asymptotic complexity and a good practical efficiency.
Abstract modern viewpoint
The modern approaches to algebraic geometry redefine and effectively extend the range of basic objects in various levels of generality to schemes, formal schemes, ind-schemes, algebraic spaces, algebraic stacks and so on. The need for this arises already from the useful ideas within theory of varieties, e.g. the formal functions of Zariski can be accommodated by introducing nilpotent elements in structure rings; considering spaces of loops and arcs, constructing quotients by group actions and developing formal grounds for natural intersection theory and deformation theory lead to some of the further extensions. | Algebraic geometry | Wikipedia | 371 | 1997 | https://en.wikipedia.org/wiki/Algebraic%20geometry | Mathematics | Algebra | null |
Most remarkably, in the early 1960s, algebraic varieties were subsumed into Alexander Grothendieck's concept of a scheme. Their local objects are affine schemes or prime spectra which are locally ringed spaces which form a category which is antiequivalent to the category of commutative unital rings, extending the duality between the category of affine algebraic varieties over a field k, and the category of finitely generated reduced k-algebras. The gluing is along Zariski topology; one can glue within the category of locally ringed spaces, but also, using the Yoneda embedding, within the more abstract category of presheaves of sets over the category of affine schemes. The Zariski topology in the set theoretic sense is then replaced by a Grothendieck topology. Grothendieck introduced Grothendieck topologies having in mind more exotic but geometrically finer and more sensitive examples than the crude Zariski topology, namely the étale topology, and the two flat Grothendieck topologies: fppf and fpqc; nowadays some other examples became prominent including Nisnevich topology. Sheaves can be furthermore generalized to stacks in the sense of Grothendieck, usually with some additional representability conditions leading to Artin stacks and, even finer, Deligne–Mumford stacks, both often called algebraic stacks.
Sometimes other algebraic sites replace the category of affine schemes. For example, Nikolai Durov has introduced commutative algebraic monads as a generalization of local objects in a generalized algebraic geometry. Versions of a tropical geometry, of an absolute geometry over a field of one element and an algebraic analogue of Arakelov's geometry were realized in this setup.
Another formal generalization is possible to universal algebraic geometry in which every variety of algebras has its own algebraic geometry. The term variety of algebras should not be confused with algebraic variety.
The language of schemes, stacks and generalizations has proved to be a valuable way of dealing with geometric concepts and became cornerstones of modern algebraic geometry. | Algebraic geometry | Wikipedia | 436 | 1997 | https://en.wikipedia.org/wiki/Algebraic%20geometry | Mathematics | Algebra | null |
Algebraic stacks can be further generalized and for many practical questions like deformation theory and intersection theory, this is often the most natural approach. One can extend the Grothendieck site of affine schemes to a higher categorical site of derived affine schemes, by replacing the commutative rings with an infinity category of differential graded commutative algebras, or of simplicial commutative rings or a similar category with an appropriate variant of a Grothendieck topology. One can also replace presheaves of sets by presheaves of simplicial sets (or of infinity groupoids). Then, in presence of an appropriate homotopic machinery one can develop a notion of derived stack as such a presheaf on the infinity category of derived affine schemes, which is satisfying certain infinite categorical version of a sheaf axiom (and to be algebraic, inductively a sequence of representability conditions). Quillen model categories, Segal categories and quasicategories are some of the most often used tools to formalize this yielding the derived algebraic geometry, introduced by the school of Carlos Simpson, including Andre Hirschowitz, Bertrand Toën, Gabrielle Vezzosi, Michel Vaquié and others; and developed further by Jacob Lurie, Bertrand Toën, and Gabriele Vezzosi. Another (noncommutative) version of derived algebraic geometry, using A-infinity categories has been developed from the early 1990s by Maxim Kontsevich and followers.
History | Algebraic geometry | Wikipedia | 309 | 1997 | https://en.wikipedia.org/wiki/Algebraic%20geometry | Mathematics | Algebra | null |
Before the 16th century
Some of the roots of algebraic geometry date back to the work of the Hellenistic Greeks from the 5th century BC. The Delian problem, for instance, was to construct a length x so that the cube of side x contained the same volume as the rectangular box a2b for given sides a and b. Menaechmus () considered the problem geometrically by intersecting the pair of plane conics ay = x2 and xy = ab. In the 3rd century BC, Archimedes and Apollonius systematically studied additional problems on conic sections using coordinates. Apollonius in the Conics further developed a method that is so similar to analytic geometry that his work is sometimes thought to have anticipated the work of Descartes by some 1800 years. His application of reference lines, a diameter and a tangent is essentially no different from our modern use of a coordinate frame, where the distances measured along the diameter from the point of tangency are the abscissas, and the segments parallel to the tangent and intercepted between the axis and the curve are the ordinates. He further developed relations between the abscissas and the corresponding coordinates using geometric methods like using parabolas and curves. Medieval mathematicians, including Omar Khayyam, Leonardo of Pisa, Gersonides and Nicole Oresme in the Medieval Period, solved certain cubic and quadratic equations by purely algebraic means and then interpreted the results geometrically. The Persian mathematician Omar Khayyám (born 1048 AD) believed that there was a relationship between arithmetic, algebra and geometry. This was criticized by Jeffrey Oaks, who claims that the study of curves by means of equations originated with Descartes in the seventeenth century.
Renaissance | Algebraic geometry | Wikipedia | 342 | 1997 | https://en.wikipedia.org/wiki/Algebraic%20geometry | Mathematics | Algebra | null |
Such techniques of applying geometrical constructions to algebraic problems were also adopted by a number of Renaissance mathematicians such as Gerolamo Cardano and Niccolò Fontana "Tartaglia" on their studies of the cubic equation. The geometrical approach to construction problems, rather than the algebraic one, was favored by most 16th and 17th century mathematicians, notably Blaise Pascal who argued against the use of algebraic and analytical methods in geometry. The French mathematicians Franciscus Vieta and later René Descartes and Pierre de Fermat revolutionized the conventional way of thinking about construction problems through the introduction of coordinate geometry. They were interested primarily in the properties of algebraic curves, such as those defined by Diophantine equations (in the case of Fermat), and the algebraic reformulation of the classical Greek works on conics and cubics (in the case of Descartes).
During the same period, Blaise Pascal and Gérard Desargues approached geometry from a different perspective, developing the synthetic notions of projective geometry. Pascal and Desargues also studied curves, but from the purely geometrical point of view: the analog of the Greek ruler and compass construction. Ultimately, the analytic geometry of Descartes and Fermat won out, for it supplied the 18th century mathematicians with concrete quantitative tools needed to study physical problems using the new calculus of Newton and Leibniz. However, by the end of the 18th century, most of the algebraic character of coordinate geometry was subsumed by the calculus of infinitesimals of Lagrange and Euler. | Algebraic geometry | Wikipedia | 314 | 1997 | https://en.wikipedia.org/wiki/Algebraic%20geometry | Mathematics | Algebra | null |
19th and early 20th century
It took the simultaneous 19th century developments of non-Euclidean geometry and Abelian integrals in order to bring the old algebraic ideas back into the geometrical fold. The first of these new developments was seized up by Edmond Laguerre and Arthur Cayley, who attempted to ascertain the generalized metric properties of projective space. Cayley introduced the idea of homogeneous polynomial forms, and more specifically quadratic forms, on projective space. Subsequently, Felix Klein studied projective geometry (along with other types of geometry) from the viewpoint that the geometry on a space is encoded in a certain class of transformations on the space. By the end of the 19th century, projective geometers were studying more general kinds of transformations on figures in projective space. Rather than the projective linear transformations which were normally regarded as giving the fundamental Kleinian geometry on projective space, they concerned themselves also with the higher degree birational transformations. This weaker notion of congruence would later lead members of the 20th century Italian school of algebraic geometry to classify algebraic surfaces up to birational isomorphism.
The second early 19th century development, that of Abelian integrals, would lead Bernhard Riemann to the development of Riemann surfaces.
In the same period began the algebraization of the algebraic geometry through commutative algebra. The prominent results in this direction are Hilbert's basis theorem and Hilbert's Nullstellensatz, which are the basis of the connection between algebraic geometry and commutative algebra, and Macaulay's multivariate resultant, which is the basis of elimination theory. Probably because of the size of the computation which is implied by multivariate resultants, elimination theory was forgotten during the middle of the 20th century until it was renewed by singularity theory and computational algebraic geometry.
20th century
B. L. van der Waerden, Oscar Zariski and André Weil developed a foundation for algebraic geometry based on contemporary commutative algebra, including valuation theory and the theory of ideals. One of the goals was to give a rigorous framework for proving the results of the Italian school of algebraic geometry. In particular, this school used systematically the notion of generic point without any precise definition, which was first given by these authors during the 1930s. | Algebraic geometry | Wikipedia | 456 | 1997 | https://en.wikipedia.org/wiki/Algebraic%20geometry | Mathematics | Algebra | null |
In the 1950s and 1960s, Jean-Pierre Serre and Alexander Grothendieck recast the foundations making use of sheaf theory. Later, from about 1960, and largely led by Grothendieck, the idea of schemes was worked out, in conjunction with a very refined apparatus of homological techniques. After a decade of rapid development the field stabilized in the 1970s, and new applications were made, both to number theory and to more classical geometric questions on algebraic varieties, singularities, moduli, and formal moduli.
An important class of varieties, not easily understood directly from their defining equations, are the abelian varieties, which are the projective varieties whose points form an abelian group. The prototypical examples are the elliptic curves, which have a rich theory. They were instrumental in the proof of Fermat's Last Theorem and are also used in elliptic-curve cryptography.
In parallel with the abstract trend of the algebraic geometry, which is concerned with general statements about varieties, methods for effective computation with concretely-given varieties have also been developed, which lead to the new area of computational algebraic geometry. One of the founding methods of this area is the theory of Gröbner bases, introduced by Bruno Buchberger in 1965. Another founding method, more specially devoted to real algebraic geometry, is the cylindrical algebraic decomposition, introduced by George E. Collins in 1973. | Algebraic geometry | Wikipedia | 282 | 1997 | https://en.wikipedia.org/wiki/Algebraic%20geometry | Mathematics | Algebra | null |
Avionics (a portmanteau of aviation and electronics) are the electronic systems used on aircraft. Avionic systems include communications, navigation, the display and management of multiple systems, and the hundreds of systems that are fitted to aircraft to perform individual functions. These can be as simple as a searchlight for a police helicopter or as complicated as the tactical system for an airborne early warning platform.
History
The term "avionics" was coined in 1949 by Philip J. Klass, senior editor at Aviation Week & Space Technology magazine as a portmanteau of "aviation electronics".
Radio communication was first used in aircraft just prior to World War I. The first airborne radios were in zeppelins, but the military sparked development of light radio sets that could be carried by heavier-than-air craft, so that aerial reconnaissance biplanes could report their observations immediately in case they were shot down. The first experimental radio transmission from an airplane was conducted by the U.S. Navy in August 1910. The first aircraft radios transmitted by radiotelegraphy. They required a two-seat aircraft with a second crewman who operated a telegraph key to spell out messages in Morse code. During World War I, AM voice two way radio sets were made possible in 1917 (see TM (triode)) by the development of the triode vacuum tube, which were simple enough that the pilot in a single seat aircraft could use it while flying.
Radar, the central technology used today in aircraft navigation and air traffic control, was developed by several nations, mainly in secret, as an air defense system in the 1930s during the runup to World War II. Many modern avionics have their origins in World War II wartime developments. For example, autopilot systems that are commonplace today began as specialized systems to help bomber planes fly steadily enough to hit precision targets from high altitudes. Britain's 1940 decision to share its radar technology with its U.S. ally, particularly the magnetron vacuum tube, in the famous Tizard Mission, significantly shortened the war. Modern avionics is a substantial portion of military aircraft spending. Aircraft like the F-15E and the now retired F-14 have roughly 20 percent of their budget spent on avionics. Most modern helicopters now have budget splits of 60/40 in favour of avionics. | Avionics | Wikipedia | 475 | 2039 | https://en.wikipedia.org/wiki/Avionics | Technology | Aircraft components | null |
The civilian market has also seen a growth in cost of avionics. Flight control systems (fly-by-wire) and new navigation needs brought on by tighter airspaces, have pushed up development costs. The major change has been the recent boom in consumer flying. As more people begin to use planes as their primary method of transportation, more elaborate methods of controlling aircraft safely in these high restrictive airspaces have been invented.
Modern avionics
Avionics plays a heavy role in modernization initiatives like the Federal Aviation Administration's (FAA) Next Generation Air Transportation System project in the United States and the Single European Sky ATM Research (SESAR) initiative in Europe. The Joint Planning and Development Office put forth a roadmap for avionics in six areas:
Published Routes and Procedures – Improved navigation and routing
Negotiated Trajectories – Adding data communications to create preferred routes dynamically
Delegated Separation – Enhanced situational awareness in the air and on the ground
LowVisibility/CeilingApproach/Departure – Allowing operations with weather constraints with less ground infrastructure
Surface Operations – To increase safety in approach and departure
ATM Efficiencies – Improving the air traffic management (ATM) process
Market
The Aircraft Electronics Association reports $1.73 billion avionics sales for the first three quarters of 2017 in business and general aviation, a 4.1% yearly improvement: 73.5% came from North America, forward-fit represented 42.3% while 57.7% were retrofits as the U.S. deadline of January 1, 2020 for mandatory ADS-B out approach. | Avionics | Wikipedia | 320 | 2039 | https://en.wikipedia.org/wiki/Avionics | Technology | Aircraft components | null |
Aircraft avionics
The cockpit or, in larger aircraft, under the cockpit of an aircraft or in a movable nosecone, is a typical location for avionic bay equipment, including control, monitoring, communication, navigation, weather, and anti-collision systems. The majority of aircraft power their avionics using 14- or 28‑volt DC electrical systems; however, larger, more sophisticated aircraft (such as airliners or military combat aircraft) have AC systems operating at 115 volts 400 Hz, AC. There are several major vendors of flight avionics, including The Boeing Company, Panasonic Avionics Corporation, Honeywell (which now owns Bendix/King), Universal Avionics Systems Corporation, Rockwell Collins (now Collins Aerospace), Thales Group, GE Aviation Systems, Garmin, Raytheon, Parker Hannifin, UTC Aerospace Systems (now Collins Aerospace), Selex ES (now Leonardo), Shadin Avionics, and Avidyne Corporation.
International standards for avionics equipment are prepared by the Airlines Electronic Engineering Committee (AEEC) and published by ARINC.
Avionics Installation
Avionics installation is a critical aspect of modern aviation, ensuring that aircraft are equipped with the necessary electronic systems for safe and efficient operation. These systems encompass a wide range of functions, including communication, navigation, monitoring, flight control, and weather detection. Avionics installations are performed on all types of aircraft, from small general aviation planes to large commercial jets and military aircraft. | Avionics | Wikipedia | 311 | 2039 | https://en.wikipedia.org/wiki/Avionics | Technology | Aircraft components | null |
Installation Process
The installation of avionics requires a combination of technical expertise, precision, and adherence to stringent regulatory standards. The process typically involves:
Planning and Design: Before installation, the avionics shop works closely with the aircraft owner to determine the required systems based on the aircraft type, intended use, and regulatory requirements. Custom instrument panels are often designed to accommodate the new systems.
Wiring and Integration: Avionics systems are integrated into the aircraft’s electrical and control systems, with wiring often requiring laser marking for durability and identification. Shops use detailed schematics to ensure correct installation.
Testing and Calibration: After installation, each system must be thoroughly tested and calibrated to ensure proper function. This includes ground testing, flight testing, and system alignment with regulatory standards such as those set by the FAA.
Certification: Once the systems are installed and tested, the avionics shop completes the necessary certifications. In the U.S., this often involves compliance with FAA Part 91.411 and 91.413 for IFR (Instrument Flight Rules) operations, as well as RVSM (Reduced Vertical Separation Minimum) certification.
Regulatory Standards
Avionics installation is governed by strict regulatory frameworks to ensure the safety and reliability of aircraft systems. In the United States, the Federal Aviation Administration (FAA) sets the standards for avionics installations. These include guidelines for:
System Performance: Avionics systems must meet performance benchmarks as defined by the FAA, ensuring they function correctly in all phases of flight.
Certification: Shops performing installations must be FAA-certified, and their technicians often hold certifications such as the General Radiotelephone Operator License (GROL).
Inspections: Aircraft equipped with newly installed avionics systems must undergo rigorous inspections before being cleared for flight, including both ground and flight tests.
Advancements in Avionics Technology
The field of avionics has seen rapid technological advancements in recent years, leading to more integrated and automated systems. Key trends include:
Glass Cockpits: Traditional analog gauges are being replaced by fully integrated glass cockpit displays, providing pilots with a centralized view of all flight parameters.
NextGen Technologies: ADS-B and satellite-based navigation are part of the FAA’s NextGen initiative, aimed at modernizing air traffic control and improving the efficiency of the national airspace.
Autonomous Systems: Advances in artificial intelligence and machine learning are paving the way for more autonomous aircraft systems, enhancing safety and reducing pilot workload.
Communications | Avionics | Wikipedia | 504 | 2039 | https://en.wikipedia.org/wiki/Avionics | Technology | Aircraft components | null |
Communications connect the flight deck to the ground and the flight deck to the passengers. On‑board communications are provided by public-address systems and aircraft intercoms.
The VHF aviation communication system works on the airband of 118.000 MHz to 136.975 MHz. Each channel is spaced from the adjacent ones by 8.33 kHz in Europe, 25 kHz elsewhere. VHF is also used for line of sight communication such as aircraft-to-aircraft and aircraft-to-ATC. Amplitude modulation (AM) is used, and the conversation is performed in simplex mode. Aircraft communication can also take place using HF (especially for trans-oceanic flights) or satellite communication.
Navigation
Air navigation is the determination of position and direction on or above the surface of the Earth. Avionics can use satellite navigation systems (such as GPS and WAAS), inertial navigation system (INS), ground-based radio navigation systems (such as VOR or LORAN), or any combination thereof. Some navigation systems such as GPS calculate the position automatically and display it to the flight crew on moving map displays. Older ground-based Navigation systems such as VOR or LORAN requires a pilot or navigator to plot the intersection of signals on a paper map to determine an aircraft's location; modern systems calculate the position automatically and display it to the flight crew on moving map displays.
Monitoring
The first hints of glass cockpits emerged in the 1970s when flight-worthy cathode-ray tube (CRT) screens began to replace electromechanical displays, gauges and instruments. A "glass" cockpit refers to the use of computer monitors instead of gauges and other analog displays. Aircraft were getting progressively more displays, dials and information dashboards that eventually competed for space and pilot attention. In the 1970s, the average aircraft had more than 100 cockpit instruments and controls.
Glass cockpits started to come into being with the Gulfstream G‑IV private jet in 1985. One of the key challenges in glass cockpits is to balance how much control is automated and how much the pilot should do manually. Generally they try to automate flight operations while keeping the pilot constantly informed.
Aircraft flight-control system | Avionics | Wikipedia | 446 | 2039 | https://en.wikipedia.org/wiki/Avionics | Technology | Aircraft components | null |
Aircraft have means of automatically controlling flight. Autopilot was first invented by Lawrence Sperry during World War I to fly bomber planes steady enough to hit accurate targets from 25,000 feet. When it was first adopted by the U.S. military, a Honeywell engineer sat in the back seat with bolt cutters to disconnect the autopilot in case of emergency. Nowadays most commercial planes are equipped with aircraft flight control systems in order to reduce pilot error and workload at landing or takeoff.
The first simple commercial auto-pilots were used to control heading and altitude and had limited authority on things like thrust and flight control surfaces. In helicopters, auto-stabilization was used in a similar way. The first systems were electromechanical. The advent of fly-by-wire and electro-actuated flight surfaces (rather than the traditional hydraulic) has increased safety. As with displays and instruments, critical devices that were electro-mechanical had a finite life. With safety critical systems, the software is very strictly tested.
Fuel Systems
Fuel Quantity Indication System (FQIS) monitors the amount of fuel aboard. Using various sensors, such as capacitance tubes, temperature sensors, densitometers & level sensors, the FQIS computer calculates the mass of fuel remaining on board.
Fuel Control and Monitoring System (FCMS) reports fuel remaining on board in a similar manner, but, by controlling pumps & valves, also manages fuel transfers around various tanks.
Refuelling control to upload to a certain total mass of fuel and distribute it automatically.
Transfers during flight to the tanks that feed the engines. E.G. from fuselage to wing tanks
Centre of gravity control transfers from the tail (trim) tanks forward to the wings as fuel is expended
Maintaining fuel in the wing tips (to alleviate wing bending due to lift in flight) & transferring to the main tanks after landing
Controlling fuel jettison during an emergency to reduce the aircraft weight.
Collision-avoidance systems
To supplement air traffic control, most large transport aircraft and many smaller ones use a traffic alert and collision avoidance system (TCAS), which can detect the location of nearby aircraft, and provide instructions for avoiding a midair collision. Smaller aircraft may use simpler traffic alerting systems such as TPAS, which are passive (they do not actively interrogate the transponders of other aircraft) and do not provide advisories for conflict resolution. | Avionics | Wikipedia | 489 | 2039 | https://en.wikipedia.org/wiki/Avionics | Technology | Aircraft components | null |
To help avoid controlled flight into terrain (CFIT), aircraft use systems such as ground-proximity warning systems (GPWS), which use radar altimeters as a key element. One of the major weaknesses of GPWS is the lack of "look-ahead" information, because it only provides altitude above terrain "look-down". In order to overcome this weakness, modern aircraft use a terrain awareness warning system (TAWS).
Flight recorders
Commercial aircraft cockpit data recorders, commonly known as "black boxes", store flight information and audio from the cockpit. They are often recovered from an aircraft after a crash to determine control settings and other parameters during the incident.
Weather systems
Weather systems such as weather radar (typically Arinc 708 on commercial aircraft) and lightning detectors are important for aircraft flying at night or in instrument meteorological conditions, where it is not possible for pilots to see the weather ahead. Heavy precipitation (as sensed by radar) or severe turbulence (as sensed by lightning activity) are both indications of strong convective activity and severe turbulence, and weather systems allow pilots to deviate around these areas.
Lightning detectors like the Stormscope or Strikefinder have become inexpensive enough that they are practical for light aircraft. In addition to radar and lightning detection, observations and extended radar pictures (such as NEXRAD) are now available through satellite data connections, allowing pilots to see weather conditions far beyond the range of their own in-flight systems. Modern displays allow weather information to be integrated with moving maps, terrain, and traffic onto a single screen, greatly simplifying navigation.
Modern weather systems also include wind shear and turbulence detection and terrain and traffic warning systems. In‑plane weather avionics are especially popular in Africa, India, and other countries where air-travel is a growing market, but ground support is not as well developed.
Aircraft management systems
There has been a progression towards centralized control of the multiple complex systems fitted to aircraft, including engine monitoring and management. Health and usage monitoring systems (HUMS) are integrated with aircraft management computers to give maintainers early warnings of parts that will need replacement.
The integrated modular avionics concept proposes an integrated architecture with application software portable across an assembly of common hardware modules. It has been used in fourth generation jet fighters and the latest generation of airliners. | Avionics | Wikipedia | 468 | 2039 | https://en.wikipedia.org/wiki/Avionics | Technology | Aircraft components | null |
Mission or tactical avionics
Military aircraft have been designed either to deliver a weapon or to be the eyes and ears of other weapon systems. The vast array of sensors available to the military is used for whatever tactical means required. As with aircraft management, the bigger sensor platforms (like the E‑3D, JSTARS, ASTOR, Nimrod MRA4, Merlin HM Mk 1) have mission-management computers.
Police and EMS aircraft also carry sophisticated tactical sensors.
Military communications
While aircraft communications provide the backbone for safe flight, the tactical systems are designed to withstand the rigors of the battle field. UHF, VHF Tactical (30–88 MHz) and SatCom systems combined with ECCM methods, and cryptography secure the communications. Data links such as Link 11, 16, 22 and BOWMAN, JTRS and even TETRA provide the means of transmitting data (such as images, targeting information etc.).
Radar
Airborne radar was one of the first tactical sensors. The benefit of altitude providing range has meant a significant focus on airborne radar technologies. Radars include airborne early warning (AEW), anti-submarine warfare (ASW), and even weather radar (Arinc 708) and ground tracking/proximity radar.
The military uses radar in fast jets to help pilots fly at low levels. While the civil market has had weather radar for a while, there are strict rules about using it to navigate the aircraft.
Sonar
Dipping sonar fitted to a range of military helicopters allows the helicopter to protect shipping assets from submarines or surface threats. Maritime support aircraft can drop active and passive sonar devices (sonobuoys) and these are also used to determine the location of enemy submarines.
Electro-optics
Electro-optic systems include devices such as the head-up display (HUD), forward looking infrared (FLIR), infrared search and track and other passive infrared devices (Passive infrared sensor). These are all used to provide imagery and information to the flight crew. This imagery is used for everything from search and rescue to navigational aids and target acquisition.
ESM/DAS
Electronic support measures and defensive aids systems are used extensively to gather information about threats or possible threats. They can be used to launch devices (in some cases automatically) to counter direct threats against the aircraft. They are also used to determine the state of a threat and identify it. | Avionics | Wikipedia | 476 | 2039 | https://en.wikipedia.org/wiki/Avionics | Technology | Aircraft components | null |
Aircraft networks
The avionics systems in military, commercial and advanced models of civilian aircraft are interconnected using an avionics databus. Common avionics databus protocols, with their primary application, include:
Aircraft Data Network (ADN): Ethernet derivative for Commercial Aircraft
Avionics Full-Duplex Switched Ethernet (AFDX): Specific implementation of ARINC 664 (ADN) for Commercial Aircraft
ARINC 429: Generic Medium-Speed Data Sharing for Private and Commercial Aircraft
ARINC 664: See ADN above
ARINC 629: Commercial Aircraft (Boeing 777)
ARINC 708: Weather Radar for Commercial Aircraft
ARINC 717: Flight Data Recorder for Commercial Aircraft
ARINC 825: CAN bus for commercial aircraft (for example Boeing 787 and Airbus A350)
Commercial Standard Digital Bus
IEEE 1394b: Military Aircraft
MIL-STD-1553: Military Aircraft
MIL-STD-1760: Military Aircraft
TTP – Time-Triggered Protocol: Boeing 787, Airbus A380, Fly-By-Wire Actuation Platforms from Parker Aerospace | Avionics | Wikipedia | 223 | 2039 | https://en.wikipedia.org/wiki/Avionics | Technology | Aircraft components | null |
In computer science, an array is a data structure consisting of a collection of elements (values or variables), of same memory size, each identified by at least one array index or key. An array is stored such that the position of each element can be computed from its index tuple by a mathematical formula. The simplest type of data structure is a linear array, also called a one-dimensional array.
For example, an array of ten 32-bit (4-byte) integer variables, with indices 0 through 9, may be stored as ten words at memory addresses 2000, 2004, 2008, ..., 2036, (in hexadecimal: 0x7D0, 0x7D4, 0x7D8, ..., 0x7F4) so that the element with index i has the address 2000 + (i × 4).
The memory address of the first element of an array is called first address, foundation address, or base address.
Because the mathematical concept of a matrix can be represented as a two-dimensional grid, two-dimensional arrays are also sometimes called "matrices". In some cases the term "vector" is used in computing to refer to an array, although tuples rather than vectors are the more mathematically correct equivalent. Tables are often implemented in the form of arrays, especially lookup tables; the word "table" is sometimes used as a synonym of array.
Arrays are among the oldest and most important data structures, and are used by almost every program. They are also used to implement many other data structures, such as lists and strings. They effectively exploit the addressing logic of computers. In most modern computers and many external storage devices, the memory is a one-dimensional array of words, whose indices are their addresses. Processors, especially vector processors, are often optimized for array operations.
Arrays are useful mostly because the element indices can be computed at run time. Among other things, this feature allows a single iterative statement to process arbitrarily many elements of an array. For that reason, the elements of an array data structure are required to have the same size and should use the same data representation. The set of valid index tuples and the addresses of the elements (and hence the element addressing formula) are usually, but not always, fixed while the array is in use. | Array (data structure) | Wikipedia | 481 | 2052 | https://en.wikipedia.org/wiki/Array%20%28data%20structure%29 | Mathematics | Data structures and types | null |
The term "array" may also refer to an array data type, a kind of data type provided by most high-level programming languages that consists of a collection of values or variables that can be selected by one or more indices computed at run-time. Array types are often implemented by array structures; however, in some languages they may be implemented by hash tables, linked lists, search trees, or other data structures.
The term is also used, especially in the description of algorithms, to mean associative array or "abstract array", a theoretical computer science model (an abstract data type or ADT) intended to capture the essential properties of arrays.
History
The first digital computers used machine-language programming to set up and access array structures for data tables, vector and matrix computations, and for many other purposes. John von Neumann wrote the first array-sorting program (merge sort) in 1945, during the building of the first stored-program computer. Array indexing was originally done by self-modifying code, and later using index registers and indirect addressing. Some mainframes designed in the 1960s, such as the Burroughs B5000 and its successors, used memory segmentation to perform index-bounds checking in hardware.
Assembly languages generally have no special support for arrays, other than what the machine itself provides. The earliest high-level programming languages, including FORTRAN (1957), Lisp (1958), COBOL (1960), and ALGOL 60 (1960), had support for multi-dimensional arrays, and so has C (1972). In C++ (1983), class templates exist for multi-dimensional arrays whose dimension is fixed at runtime as well as for runtime-flexible arrays.
Applications
Arrays are used to implement mathematical vectors and matrices, as well as other kinds of rectangular tables. Many databases, small and large, consist of (or include) one-dimensional arrays whose elements are records.
Arrays are used to implement other data structures, such as lists, heaps, hash tables, deques, queues, stacks, strings, and VLists. Array-based implementations of other data structures are frequently simple and space-efficient (implicit data structures), requiring little space overhead, but may have poor space complexity, particularly when modified, compared to tree-based data structures (compare a sorted array to a search tree). | Array (data structure) | Wikipedia | 481 | 2052 | https://en.wikipedia.org/wiki/Array%20%28data%20structure%29 | Mathematics | Data structures and types | null |
One or more large arrays are sometimes used to emulate in-program dynamic memory allocation, particularly memory pool allocation. Historically, this has sometimes been the only way to allocate "dynamic memory" portably.
Arrays can be used to determine partial or complete control flow in programs, as a compact alternative to (otherwise repetitive) multiple IF statements. They are known in this context as control tables and are used in conjunction with a purpose-built interpreter whose control flow is altered according to values contained in the array. The array may contain subroutine pointers (or relative subroutine numbers that can be acted upon by SWITCH statements) that direct the path of the execution.
Element identifier and addressing formulas
When data objects are stored in an array, individual objects are selected by an index that is usually a non-negative scalar integer. Indexes are also called subscripts. An index maps the array value to a stored object.
There are three ways in which the elements of an array can be indexed:
0 (zero-based indexing) The first element of the array is indexed by subscript of 0.
1 (one-based indexing) The first element of the array is indexed by subscript of 1.
n (n-based indexing) The base index of an array can be freely chosen. Usually programming languages allowing n-based indexing also allow negative index values and other scalar data types like enumerations, or characters may be used as an array index.
Using zero based indexing is the design choice of many influential programming languages, including C, Java and Lisp. This leads to simpler implementation where the subscript refers to an offset from the starting position of an array, so the first element has an offset of zero.
Arrays can have multiple dimensions, thus it is not uncommon to access an array using multiple indices. For example, a two-dimensional array A with three rows and four columns might provide access to the element at the 2nd row and 4th column by the expression A[1][3] in the case of a zero-based indexing system. Thus two indices are used for a two-dimensional array, three for a three-dimensional array, and n for an n-dimensional array.
The number of indices needed to specify an element is called the dimension, dimensionality, or rank of the array. | Array (data structure) | Wikipedia | 478 | 2052 | https://en.wikipedia.org/wiki/Array%20%28data%20structure%29 | Mathematics | Data structures and types | null |
In standard arrays, each index is restricted to a certain range of consecutive integers (or consecutive values of some enumerated type), and the address of an element is computed by a "linear" formula on the indices.
One-dimensional arrays
A one-dimensional array (or single dimension array) is a type of linear array. Accessing its elements involves a single subscript which can either represent a row or column index.
As an example consider the C declaration int anArrayName[10]; which declares a one-dimensional array of ten integers. Here, the array can store ten elements of type int . This array has indices starting from zero through nine. For example, the expressions anArrayName[0] and anArrayName[9] are the first and last elements respectively.
For a vector with linear addressing, the element with index i is located at the address , where B is a fixed base address and c a fixed constant, sometimes called the address increment or stride.
If the valid element indices begin at 0, the constant B is simply the address of the first element of the array. For this reason, the C programming language specifies that array indices always begin at 0; and many programmers will call that element "zeroth" rather than "first".
However, one can choose the index of the first element by an appropriate choice of the base address B. For example, if the array has five elements, indexed 1 through 5, and the base address B is replaced by , then the indices of those same elements will be 31 to 35. If the numbering does not start at 0, the constant B may not be the address of any element.
Multidimensional arrays
For a multidimensional array, the element with indices i,j would have address B + c · i + d · j, where the coefficients c and d are the row and column address increments, respectively.
More generally, in a k-dimensional array, the address of an element with indices i1, i2, ..., ik is
B + c1 · i1 + c2 · i2 + … + ck · ik.
For example: int a[2][3]; | Array (data structure) | Wikipedia | 451 | 2052 | https://en.wikipedia.org/wiki/Array%20%28data%20structure%29 | Mathematics | Data structures and types | null |
This means that array a has 2 rows and 3 columns, and the array is of integer type. Here we can store 6 elements they will be stored linearly but starting from first row linear then continuing with second row. The above array will be stored as a11, a12, a13, a21, a22, a23.
This formula requires only k multiplications and k additions, for any array that can fit in memory. Moreover, if any coefficient is a fixed power of 2, the multiplication can be replaced by bit shifting.
The coefficients ck must be chosen so that every valid index tuple maps to the address of a distinct element.
If the minimum legal value for every index is 0, then B is the address of the element whose indices are all zero. As in the one-dimensional case, the element indices may be changed by changing the base address B. Thus, if a two-dimensional array has rows and columns indexed from 1 to 10 and 1 to 20, respectively, then replacing B by will cause them to be renumbered from 0 through 9 and 4 through 23, respectively. Taking advantage of this feature, some languages (like FORTRAN 77) specify that array indices begin at 1, as in mathematical tradition while other languages (like Fortran 90, Pascal and Algol) let the user choose the minimum value for each index.
Dope vectors
The addressing formula is completely defined by the dimension d, the base address B, and the increments c1, c2, ..., ck. It is often useful to pack these parameters into a record called the array's descriptor, stride vector, or dope vector. The size of each element, and the minimum and maximum values allowed for each index may also be included in the dope vector. The dope vector is a complete handle for the array, and is a convenient way to pass arrays as arguments to procedures. Many useful array slicing operations (such as selecting a sub-array, swapping indices, or reversing the direction of the indices) can be performed very efficiently by manipulating the dope vector.
Compact layouts
Often the coefficients are chosen so that the elements occupy a contiguous area of memory. However, that is not necessary. Even if arrays are always created with contiguous elements, some array slicing operations may create non-contiguous sub-arrays from them.
There are two systematic compact layouts for a two-dimensional array. For example, consider the matrix | Array (data structure) | Wikipedia | 498 | 2052 | https://en.wikipedia.org/wiki/Array%20%28data%20structure%29 | Mathematics | Data structures and types | null |
In the row-major order layout (adopted by C for statically declared arrays), the elements in each row are stored in consecutive positions and all of the elements of a row have a lower address than any of the elements of a consecutive row:
{| class="wikitable"
|-
| 1 || 2 || 3 || 4 || 5 || 6 || 7 || 8 || 9
|}
In column-major order (traditionally used by Fortran), the elements in each column are consecutive in memory and all of the elements of a column have a lower address than any of the elements of a consecutive column:
{| class="wikitable"
|-
| 1 || 4 || 7 || 2 || 5 || 8 || 3 || 6 || 9
|}
For arrays with three or more indices, "row major order" puts in consecutive positions any two elements whose index tuples differ only by one in the last index. "Column major order" is analogous with respect to the first index.
In systems which use processor cache or virtual memory, scanning an array is much faster if successive elements are stored in consecutive positions in memory, rather than sparsely scattered. This is known as spatial locality, which is a type of locality of reference. Many algorithms that use multidimensional arrays will scan them in a predictable order. A programmer (or a sophisticated compiler) may use this information to choose between row- or column-major layout for each array. For example, when computing the product A·B of two matrices, it would be best to have A stored in row-major order, and B in column-major order.
Resizing
Static arrays have a size that is fixed when they are created and consequently do not allow elements to be inserted or removed. However, by allocating a new array and copying the contents of the old array to it, it is possible to effectively implement a dynamic version of an array; see dynamic array. If this operation is done infrequently, insertions at the end of the array require only amortized constant time.
Some array data structures do not reallocate storage, but do store a count of the number of elements of the array in use, called the count or size. This effectively makes the array a dynamic array with a fixed maximum size or capacity; Pascal strings are examples of this. | Array (data structure) | Wikipedia | 490 | 2052 | https://en.wikipedia.org/wiki/Array%20%28data%20structure%29 | Mathematics | Data structures and types | null |
Non-linear formulas
More complicated (non-linear) formulas are occasionally used. For a compact two-dimensional triangular array, for instance, the addressing formula is a polynomial of degree 2.
Efficiency
Both store and select take (deterministic worst case) constant time. Arrays take linear (O(n)) space in the number of elements n that they hold.
In an array with element size k and on a machine with a cache line size of B bytes, iterating through an array of n elements requires the minimum of ceiling(nk/B) cache misses, because its elements occupy contiguous memory locations. This is roughly a factor of B/k better than the number of cache misses needed to access n elements at random memory locations. As a consequence, sequential iteration over an array is noticeably faster in practice than iteration over many other data structures, a property called locality of reference (this does not mean however, that using a perfect hash or trivial hash within the same (local) array, will not be even faster - and achievable in constant time). Libraries provide low-level optimized facilities for copying ranges of memory (such as memcpy) which can be used to move contiguous blocks of array elements significantly faster than can be achieved through individual element access. The speedup of such optimized routines varies by array element size, architecture, and implementation.
Memory-wise, arrays are compact data structures with no per-element overhead. There may be a per-array overhead (e.g., to store index bounds) but this is language-dependent. It can also happen that elements stored in an array require less memory than the same elements stored in individual variables, because several array elements can be stored in a single word; such arrays are often called packed arrays. An extreme (but commonly used) case is the bit array, where every bit represents a single element. A single octet can thus hold up to 256 different combinations of up to 8 different conditions, in the most compact form.
Array accesses with statically predictable access patterns are a major source of data parallelism.
Comparison with other data structures
Dynamic arrays or growable arrays are similar to arrays but add the ability to insert and delete elements; adding and deleting at the end is particularly efficient. However, they reserve linear (Θ(n)) additional storage, whereas arrays do not reserve additional storage. | Array (data structure) | Wikipedia | 488 | 2052 | https://en.wikipedia.org/wiki/Array%20%28data%20structure%29 | Mathematics | Data structures and types | null |
Associative arrays provide a mechanism for array-like functionality without huge storage overheads when the index values are sparse. For example, an array that contains values only at indexes 1 and 2 billion may benefit from using such a structure. Specialized associative arrays with integer keys include Patricia tries, Judy arrays, and van Emde Boas trees.
Balanced trees require O(log n) time for indexed access, but also permit inserting or deleting elements in O(log n) time, whereas growable arrays require linear (Θ(n)) time to insert or delete elements at an arbitrary position.
Linked lists allow constant time removal and insertion in the middle but take linear time for indexed access. Their memory use is typically worse than arrays, but is still linear.
An Iliffe vector is an alternative to a multidimensional array structure. It uses a one-dimensional array of references to arrays of one dimension less. For two dimensions, in particular, this alternative structure would be a vector of pointers to vectors, one for each row(pointer on c or c++). Thus an element in row i and column j of an array A would be accessed by double indexing (A[i][j] in typical notation). This alternative structure allows jagged arrays, where each row may have a different size—or, in general, where the valid range of each index depends on the values of all preceding indices. It also saves one multiplication (by the column address increment) replacing it by a bit shift (to index the vector of row pointers) and one extra memory access (fetching the row address), which may be worthwhile in some architectures.
Dimension
The dimension of an array is the number of indices needed to select an element. Thus, if the array is seen as a function on a set of possible index combinations, it is the dimension of the space of which its domain is a discrete subset. Thus a one-dimensional array is a list of data, a two-dimensional array is a rectangle of data, a three-dimensional array a block of data, etc. | Array (data structure) | Wikipedia | 438 | 2052 | https://en.wikipedia.org/wiki/Array%20%28data%20structure%29 | Mathematics | Data structures and types | null |
This should not be confused with the dimension of the set of all matrices with a given domain, that is, the number of elements in the array. For example, an array with 5 rows and 4 columns is two-dimensional, but such matrices form a 20-dimensional space. Similarly, a three-dimensional vector can be represented by a one-dimensional array of size three. | Array (data structure) | Wikipedia | 76 | 2052 | https://en.wikipedia.org/wiki/Array%20%28data%20structure%29 | Mathematics | Data structures and types | null |
Aeronautics is the science or art involved with the study, design, and manufacturing of air flight-capable machines, and the techniques of operating aircraft and rockets within the atmosphere.
While the term originally referred solely to operating the aircraft, it has since been expanded to include technology, business, and other aspects related to aircraft.
The term "aviation" is sometimes used interchangeably with aeronautics, although "aeronautics" includes lighter-than-air craft such as airships, and includes ballistic vehicles while "aviation" technically does not.
A significant part of aeronautical science is a branch of dynamics called aerodynamics, which deals with the motion of air and the way that it interacts with objects in motion, such as an aircraft.
History
Early ideas
Attempts to fly without any real aeronautical understanding have been made from the earliest times, typically by constructing wings and jumping from a tower with crippling or lethal results.
Wiser investigators sought to gain some rational understanding through the study of bird flight. Medieval Islamic Golden Age scientists such as Abbas ibn Firnas also made such studies. The founders of modern aeronautics, Leonardo da Vinci in the Renaissance and Cayley in 1799, both began their investigations with studies of bird flight.
Man-carrying kites are believed to have been used extensively in ancient China. In 1282 the Italian explorer Marco Polo described the Chinese techniques then current. The Chinese also constructed small hot air balloons, or lanterns, and rotary-wing toys.
An early European to provide any scientific discussion of flight was Roger Bacon, who described principles of operation for the lighter-than-air balloon and the flapping-wing ornithopter, which he envisaged would be constructed in the future. The lifting medium for his balloon would be an "aether" whose composition he did not know. | Aeronautics | Wikipedia | 360 | 2082 | https://en.wikipedia.org/wiki/Aeronautics | Technology | Concepts of aviation | null |
In the late fifteenth century, Leonardo da Vinci followed up his study of birds with designs for some of the earliest flying machines, including the flapping-wing ornithopter and the rotating-wing helicopter. Although his designs were rational, they were not based on particularly good science. Many of his designs, such as a four-person screw-type helicopter, have severe flaws. He did at least understand that "An object offers as much resistance to the air as the air does to the object." (Newton would not publish the Third law of motion until 1687.) His analysis led to the realisation that manpower alone was not sufficient for sustained flight, and his later designs included a mechanical power source such as a spring. Da Vinci's work was lost after his death and did not reappear until it had been overtaken by the work of George Cayley.
Balloon flight
The modern era of lighter-than-air flight began early in the 17th century with Galileo's experiments in which he showed that air has weight. Around 1650 Cyrano de Bergerac wrote some fantasy novels in which he described the principle of ascent using a substance (dew) he supposed to be lighter than air, and descending by releasing a controlled amount of the substance. Francesco Lana de Terzi measured the pressure of air at sea level and in 1670 proposed the first scientifically credible lifting medium in the form of hollow metal spheres from which all the air had been pumped out. These would be lighter than the displaced air and able to lift an airship. His proposed methods of controlling height are still in use today; by carrying ballast which may be dropped overboard to gain height, and by venting the lifting containers to lose height. In practice de Terzi's spheres would have collapsed under air pressure, and further developments had to wait for more practicable lifting gases.
From the mid-18th century the Montgolfier brothers in France began experimenting with balloons. Their balloons were made of paper, and early experiments using steam as the lifting gas were short-lived due to its effect on the paper as it condensed. Mistaking smoke for a kind of steam, they began filling their balloons with hot smoky air which they called "electric smoke" and, despite not fully understanding the principles at work, made some successful launches and in 1783 were invited to give a demonstration to the French Académie des Sciences. | Aeronautics | Wikipedia | 482 | 2082 | https://en.wikipedia.org/wiki/Aeronautics | Technology | Concepts of aviation | null |
Meanwhile, the discovery of hydrogen led Joseph Black in to propose its use as a lifting gas, though practical demonstration awaited a gas-tight balloon material. On hearing of the Montgolfier Brothers' invitation, the French Academy member Jacques Charles offered a similar demonstration of a hydrogen balloon. Charles and two craftsmen, the Robert brothers, developed a gas-tight material of rubberised silk for the envelope. The hydrogen gas was to be generated by chemical reaction during the filling process.
The Montgolfier designs had several shortcomings, not least the need for dry weather and a tendency for sparks from the fire to set light to the paper balloon. The manned design had a gallery around the base of the balloon rather than the hanging basket of the first, unmanned design, which brought the paper closer to the fire. On their free flight, De Rozier and d'Arlandes took buckets of water and sponges to douse these fires as they arose. On the other hand, the manned design of Charles was essentially modern. As a result of these exploits, the hot air balloon became known as the Montgolfière type and the gas balloon the Charlière.
Charles and the Robert brothers' next balloon, La Caroline, was a Charlière that followed Jean Baptiste Meusnier's proposals for an elongated dirigible balloon, and was notable for having an outer envelope with the gas contained in a second, inner ballonet. On 19 September 1784, it completed the first flight of over 100 km, between Paris and Beuvry, despite the man-powered propulsive devices proving useless.
In an attempt the next year to provide both endurance and controllability, de Rozier developed a balloon having both hot air and hydrogen gas bags, a design which was soon named after him as the Rozière. The principle was to use the hydrogen section for constant lift and to navigate vertically by heating and allowing to cool the hot air section, in order to catch the most favourable wind at whatever altitude it was blowing. The balloon envelope was made of goldbeater's skin. The first flight ended in disaster and the approach has seldom been used since. | Aeronautics | Wikipedia | 438 | 2082 | https://en.wikipedia.org/wiki/Aeronautics | Technology | Concepts of aviation | null |
Cayley and the foundation of modern aeronautics
Sir George Cayley (1773–1857) is widely acknowledged as the founder of modern aeronautics. He was first called the "father of the aeroplane" in 1846 and Henson called him the "father of aerial navigation." He was the first true scientific aerial investigator to publish his work, which included for the first time the underlying principles and forces of flight.
In 1809 he began the publication of a landmark three-part treatise titled "On Aerial Navigation" (1809–1810). In it he wrote the first scientific statement of the problem, "The whole problem is confined within these limits, viz. to make a surface support a given weight by the application of power to the resistance of air." He identified the four vector forces that influence an aircraft: thrust, lift, drag and weight and distinguished stability and control in his designs.
He developed the modern conventional form of the fixed-wing aeroplane having a stabilising tail with both horizontal and vertical surfaces, flying gliders both unmanned and manned.
He introduced the use of the whirling arm test rig to investigate the aerodynamics of flight, using it to discover the benefits of the curved or cambered aerofoil over the flat wing he had used for his first glider. He also identified and described the importance of dihedral, diagonal bracing and drag reduction, and contributed to the understanding and design of ornithopters and parachutes.
Another significant invention was the tension-spoked wheel, which he devised in order to create a light, strong wheel for aircraft undercarriage.
The 19th century: Otto Lilienthal and the first human flights
During the 19th century Cayley's ideas were refined, proved and expanded on, culminating in the works of Otto Lilienthal.
Lilienthal was a German engineer and businessman who became known as the "flying man". He was the first person to make well-documented, repeated, successful flights with gliders, therefore making the idea of "heavier than air" a reality. Newspapers and magazines published photographs of Lilienthal gliding, favourably influencing public and scientific opinion about the possibility of flying machines becoming practical. | Aeronautics | Wikipedia | 439 | 2082 | https://en.wikipedia.org/wiki/Aeronautics | Technology | Concepts of aviation | null |
His work lead to him developing the concept of the modern wing. His flight attempts in Berlin in the year 1891 are seen as the beginning of human flight and the "Lilienthal Normalsegelapparat" is considered to be the first air plane in series production, making the Maschinenfabrik Otto Lilienthal in Berlin the first air plane production company in the world.
Otto Lilienthal is often referred to as either the "father of aviation" or "father of flight".
Other important investigators included Horatio Phillips.
Branches
Aeronautics may be divided into three main branches, Aviation, Aeronautical science and Aeronautical engineering.
Aviation
Aviation is the art or practice of aeronautics. Historically aviation meant only heavier-than-air flight, but nowadays it includes flying in balloons and airships.
Aeronautical engineering
Aeronautical engineering covers the design and construction of aircraft, including how they are powered, how they are used and how they are controlled for safe operation.
A major part of aeronautical engineering is aerodynamics, the science of passing through the air.
With the increasing activity in space flight, nowadays aeronautics and astronautics are often combined as aerospace engineering.
Aerodynamics
The science of aerodynamics deals with the motion of air and the way that it interacts with objects in motion, such as an aircraft.
The study of aerodynamics falls broadly into three areas:
Incompressible flow occurs where the air simply moves to avoid objects, typically at subsonic speeds below that of sound (Mach 1).
Compressible flow occurs where shock waves appear at points where the air becomes compressed, typically at speeds above Mach 1.
Transonic flow occurs in the intermediate speed range around Mach 1, where the airflow over an object may be locally subsonic at one point and locally supersonic at another.
Rocketry
A rocket or rocket vehicle is a missile, spacecraft, aircraft or other vehicle which obtains thrust from a rocket engine. In all rockets, the exhaust is formed entirely from propellants carried within the rocket before use. Rocket engines work by action and reaction. Rocket engines push rockets forwards simply by throwing their exhaust backwards extremely fast.
Rockets for military and recreational uses date back to at least 13th-century China. Significant scientific, interplanetary and industrial use did not occur until the 20th century, when rocketry was the enabling technology of the Space Age, including setting foot on the Moon. | Aeronautics | Wikipedia | 476 | 2082 | https://en.wikipedia.org/wiki/Aeronautics | Technology | Concepts of aviation | null |
Rockets are used for fireworks, weaponry, ejection seats, launch vehicles for artificial satellites, human spaceflight and exploration of other planets. While comparatively inefficient for low speed use, they are very lightweight and powerful, capable of generating large accelerations and of attaining extremely high speeds with reasonable efficiency.
Chemical rockets are the most common type of rocket and they typically create their exhaust by the combustion of rocket propellant. Chemical rockets store a large amount of energy in an easily released form, and can be very dangerous. However, careful design, testing, construction and use minimizes risks. | Aeronautics | Wikipedia | 120 | 2082 | https://en.wikipedia.org/wiki/Aeronautics | Technology | Concepts of aviation | null |
Aphasia, also known as dysphasia, is an impairment in a person’s ability to comprehend or formulate language because of damage to specific brain regions. The major causes are stroke and head trauma; prevalence is hard to determine, but aphasia due to stroke is estimated to be 0.1–0.4% in developed countries. Aphasia can also be the result of brain tumors, epilepsy, autoimmune neurological diseases, brain infections, or neurodegenerative diseases (such as dementias).
To be diagnosed with aphasia, a person's language must be significantly impaired in one or more of the four aspects of communication. In the case of progressive aphasia, a noticeable decline in language abilities over a short period of time is required. The four aspects of communication include spoken language production and comprehension, written language production and comprehension. Impairments in any of these aspects can impact functional communication.
The difficulties of people with aphasia can range from occasional trouble finding words, to losing the ability to speak, read, or write; intelligence, however, is unaffected. Expressive language and receptive language can both be affected as well. Aphasia also affects visual language such as sign language. In contrast, the use of formulaic expressions in everyday communication is often preserved. For example, while a person with aphasia, particularly expressive aphasia (Broca's aphasia), may not be able to ask a loved one when their birthday is, they may still be able to sing "Happy Birthday". One prevalent deficit in all aphasias is anomia, which is a difficulty in finding the correct word. | Aphasia | Wikipedia | 346 | 2088 | https://en.wikipedia.org/wiki/Aphasia | Biology and health sciences | Disabilities | Health |
With aphasia, one or more modes of communication in the brain have been damaged and are therefore functioning incorrectly. Aphasia is not caused by damage to the brain resulting in motor or sensory deficits, thus producing abnormal speech — that is, aphasia is not related to the mechanics of speech, but rather the individual's language cognition. However, it is possible for a person to have both problems, e.g. in the case of a hemorrhage damaging a large area of the brain. An individual's language abilities incorporate the socially shared set of rules, as well as the thought processes that go behind communication (as it affects both verbal and nonverbal language). Aphasia is not a result of other peripheral motor or sensory difficulty, such as paralysis affecting the speech muscles, or a general hearing impairment.
Neurodevelopmental forms of auditory processing disorder (APD) are differentiable from aphasia in that aphasia is by definition caused by acquired brain injury, but acquired epileptic aphasia has been viewed as a form of APD.
Signs and symptoms
People with aphasia may experience any of the following behaviors due to an acquired brain injury, although some of these symptoms may be due to related or concomitant problems, such as dysarthria or apraxia, and not primarily due to aphasia. Aphasia symptoms can vary based on the location of damage in the brain. Signs and symptoms may or may not be present in individuals with aphasia and may vary in severity and level of disruption to communication. Often those with aphasia may have a difficulty with naming objects, so they might use words such as thing or point at the objects. When asked to name a pencil they may say it is a "thing used to write".
Inability to comprehend language
Inability to pronounce, not due to muscle paralysis or weakness
Inability to form words
Inability to recall words (anomia)
Poor enunciation
Excessive creation and use of protologisms
Inability to repeat a phrase
Persistent repetition of one syllable, word, or phrase (stereotypies, recurrent/recurring utterances/speech automatism) also known as perseveration.
Paraphasia (substituting letters, syllables or words)
Agrammatism (inability to speak in a grammatically correct fashion)
speaking in incomplete sentences
Inability to read
Inability to write
Limited verbal output
Difficulty in naming
Speech disorder
Speaking gibberish
Inability to follow or understand simple requests | Aphasia | Wikipedia | 510 | 2088 | https://en.wikipedia.org/wiki/Aphasia | Biology and health sciences | Disabilities | Health |
Related behaviors
Given the previously stated signs and symptoms, the following behaviors are often seen in people with aphasia as a result of attempted compensation for incurred speech and language deficits:
Self-repairs: Further disruptions in fluent speech as a result of mis-attempts to repair erred speech production.
Struggle in non-fluent aphasias: A severe increase in expelled effort to speak after a life where talking and communicating was an ability that came so easily can cause visible frustration.
Preserved and automatic language: A behavior in which some language or language sequences that were used frequently prior to onset are still produced with more ease than other language post onset.
Subcortical
Subcortical aphasia's characteristics and symptoms depend upon the site and size of subcortical lesion. Possible sites of lesions include the thalamus, internal capsule, and basal ganglia.
Cognitive deficits
While aphasia has traditionally been described in terms of language deficits, there is increasing evidence that many people with aphasia commonly experience co-occurring non-linguistic cognitive deficits in areas such as attention, memory, executive functions and learning. By some accounts, cognitive deficits, such as attention and working memory constitute the underlying cause of language impairment in people with aphasia. Others suggest that cognitive deficits often co-occur, but are comparable to cognitive deficits in stroke patients without aphasia and reflect general brain dysfunction following injury. Whilst it has been shown that cognitive neural networks support language reorganisation after stroke,
The degree to which deficits in attention and other cognitive domains underlie language deficits in aphasia is still unclear.
In particular, people with aphasia often demonstrate short-term and working memory deficits. These deficits can occur in both the verbal domain as well as the visuospatial domain. Furthermore, these deficits are often associated with performance on language specific tasks such as naming, lexical processing, and sentence comprehension, and discourse production. Other studies have found that most, but not all people with aphasia demonstrate performance deficits on tasks of attention, and their performance on these tasks correlate with language performance and cognitive ability in other domains. Even patients with mild aphasia, who score near the ceiling on tests of language often demonstrate slower response times and interference effects in non-verbal attention abilities. | Aphasia | Wikipedia | 473 | 2088 | https://en.wikipedia.org/wiki/Aphasia | Biology and health sciences | Disabilities | Health |
In addition to deficits in short-term memory, working memory, and attention, people with aphasia can also demonstrate deficits in executive function. For instance, people with aphasia may demonstrate deficits in initiation, planning, self-monitoring, and cognitive flexibility. Other studies have found that people with aphasia demonstrate reduced speed and efficiency during completion of executive function assessments.
Regardless of their role in the underlying nature of aphasia, cognitive deficits have a clear role in the study and rehabilitation of aphasia. For instance, the severity of cognitive deficits in people with aphasia has been associated with lower quality of life, even more so than the severity of language deficits. Furthermore, cognitive deficits may influence the learning process of rehabilitation and language treatment outcomes in aphasia. Non-linguistic cognitive deficits have also been the target of interventions directed at improving language ability, though outcomes are not definitive. While some studies have demonstrated language improvement secondary to cognitively-focused treatment, others have found little evidence that the treatment of cognitive deficits in people with aphasia has an influence on language outcomes.
One important caveat in the measurement and treatment of cognitive deficits in people with aphasia is the degree to which assessments of cognition rely on language abilities for successful performance. Most studies have attempted to circumvent this challenge by utilizing non-verbal cognitive assessments to evaluate cognitive ability in people with aphasia. However, the degree to which these tasks are truly "non-verbal" and not mediated by language is unclear. For instance, Wall et al. found that language and non-linguistic performance was related, except when non-linguistic performance was measured by "real life" cognitive tasks.
Causes
Aphasia is most often caused by stroke, where about a quarter of patients who experience an acute stroke develop aphasia. However, any disease or damage to the parts of the brain that control language can cause aphasia. Some of these can include brain tumors, traumatic brain injury, epilepsy and progressive neurological disorders. In rare cases, aphasia may also result from herpesviral encephalitis. The herpes simplex virus affects the frontal and temporal lobes, subcortical structures, and the hippocampal tissue, which can trigger aphasia. In acute disorders, such as head injury or stroke, aphasia usually develops quickly. When caused by brain tumor, infection, or dementia, it develops more slowly. | Aphasia | Wikipedia | 506 | 2088 | https://en.wikipedia.org/wiki/Aphasia | Biology and health sciences | Disabilities | Health |
Substantial damage to tissue anywhere within the region shown in blue (on the figure in the infobox above) can potentially result in aphasia. Aphasia can also sometimes be caused by damage to subcortical structures deep within the left hemisphere, including the thalamus, the internal and external capsules, and the caudate nucleus of the basal ganglia. The area and extent of brain damage or atrophy will determine the type of aphasia and its symptoms. A very small number of people can experience aphasia after damage to the right hemisphere only. It has been suggested that these individuals may have had an unusual brain organization prior to their illness or injury, with perhaps greater overall reliance on the right hemisphere for language skills than in the general population.
Primary progressive aphasia (PPA), while its name can be misleading, is actually a form of dementia that has some symptoms closely related to several forms of aphasia. It is characterized by a gradual loss in language functioning while other cognitive domains are mostly preserved, such as memory and personality. PPA usually initiates with sudden word-finding difficulties in an individual and progresses to a reduced ability to formulate grammatically correct sentences (syntax) and impaired comprehension. The etiology of PPA is not due to a stroke, traumatic brain injury (TBI), or infectious disease; it is still uncertain what initiates the onset of PPA in those affected by it.
Epilepsy can also include transient aphasia as a prodromal or episodic symptom. However, the repeated seizure activity within language regions may also lead to chronic, and progressive aphasia. Aphasia is also listed as a rare side-effect of the fentanyl patch, an opioid used to control chronic pain.
Diagnosis
Neuroimaging methods
Magnetic resonance imaging (MRI) and functional magnetic resonance imaging (fMRI) are the most common neuroimaging tools used in identifying aphasia and studying the extent of damage in the loss of language abilities. This is done by doing MRI scans and locating the extent of lesions or damage within brain tissue, particularly within areas of the left frontal and temporal regions- where a lot of language related areas lie. In fMRI studies a language related task is often completed and then the BOLD image is analyzed. If there are lower than normal BOLD responses that indicate a lessening of blood flow to the affected area and can show quantitatively that the cognitive task is not being completed. | Aphasia | Wikipedia | 508 | 2088 | https://en.wikipedia.org/wiki/Aphasia | Biology and health sciences | Disabilities | Health |
There are limitations to the use of fMRI in aphasic patients particularly. Because a high percentage of aphasic patients develop it because of stroke there can be infarct present which is the total loss of blood flow. This can be due to the thinning of blood vessels or the complete blockage of it. This is important in fMRI as it relies on the BOLD response (the oxygen levels of the blood vessels), and this can create a false hyporesponse upon fMRI study. Due to the limitations of fMRI such as a lower spatial resolution, it can show that some areas of the brain are not active during a task when they in reality are. Additionally, with stroke being the cause of many cases of aphasia the extent of damage to brain tissue can be difficult to quantify therefore the effects of stroke brain damage on the functionality of the patient can vary.
Neural substrates of aphasia subtypes
MRI is often used to predict or confirm the subtype of aphasia present. Researchers compared three subtypes of aphasia — nonfluent-variant primary progressive aphasia (nfPPA), logopenic-variant primary progressive aphasia (lvPPA), and semantic-variant primary progressive aphasia (svPPA), with primary progressive aphasia (PPA) and Alzheimer's disease. This was done by analyzing the MRIs of patients with each of the subsets of PPA. Images which compare subtypes of aphasia as well as for finding the extent of lesions are generated by overlapping images of different participant's brains (if applicable) and isolating areas of lesions or damage using third-party software such as MRIcron. MRI has also been used to study the relationship between the type of aphasia developed and the age of the person with aphasia. It was found that patients with fluent aphasia are on average older than people with non-fluent aphasia. It was also found that among patients with lesions confined to the anterior portion of the brain an unexpected portion of them presented with fluent aphasia and were remarkably older than those with non-fluent aphasia. This effect was not found when the posterior portion of the brain was studied. | Aphasia | Wikipedia | 464 | 2088 | https://en.wikipedia.org/wiki/Aphasia | Biology and health sciences | Disabilities | Health |
Associated conditions
In a study on the features associated with different disease trajectories in Alzheimer's disease (AD)-related primary progressive aphasia (PPA), it was found that metabolic patterns via PET SPM analysis can help predict progression of total loss of speech and functional autonomy in AD and PPA patients. This was done by comparing an MRI or CT image of the brain and presence of a radioactive biomarker with normal levels in patients without Alzheimer's Disease. Apraxia is another disorder often correlated with aphasia. This is due to a subset of apraxia which affects speech. Specifically, this subset affects the movement of muscles associated with speech production, apraxia and aphasia are often correlated due to the proximity of neural substrates associated with each of the disorders. Researchers concluded that there were 2 areas of lesion overlap between patients with apraxia and aphasia, the anterior temporal lobe and the left inferior parietal lobe.
Treatment and neuroimaging
Evidence for positive treatment outcomes can also be quantified using neuroimaging tools. The use of fMRI and an automatic classifier can help predict language recovery outcomes in stroke patients with 86% accuracy when coupled with age and language test scores. The stimuli tested were sentences both correct and incorrect and the subject had to press a button whenever the sentence was incorrect. The fMRI data collected focused on responses in regions of interest identified by healthy subjects. Recovery from aphasia can also be quantified using diffusion tensor imaging. The accurate fasciculus (AF) connects the right and left superior temporal lobe, premotor regions/posterior inferior frontal gyrus. and the primary motor cortex. In a study which enrolled patients in a speech therapy program, an increase in AF fibers and volume was found in patients after 6-weeks in the program which correlated with long-term improvement in those patients. The results of the experiment are pictured in Figure 2. This implies that DTI can be used to quantify the improvement in patients after speech and language treatment programs are applied. | Aphasia | Wikipedia | 422 | 2088 | https://en.wikipedia.org/wiki/Aphasia | Biology and health sciences | Disabilities | Health |
Classification
Aphasia is best thought of as a collection of different disorders, rather than a single problem. Each individual with aphasia will present with their own particular combination of language strengths and weaknesses. Consequently, it is a major challenge just to document the various difficulties that can occur in different people, let alone decide how they might best be treated. Most classifications of the aphasias tend to divide the various symptoms into broad classes. A common approach is to distinguish between the fluent aphasias (where speech remains fluent, but content may be lacking, and the person may have difficulties understanding others), and the nonfluent aphasias (where speech is very halting and effortful, and may consist of just one or two words at a time).
However, no such broad-based grouping has proven fully adequate, or reliable. There is wide variation among people even within the same broad grouping, and aphasias can be highly selective. For instance, people with naming deficits (anomic aphasia) might show an inability only for naming buildings, or people, or colors. Unfortunately, assessments that characterize aphasia in these groupings have persisted. This is not helpful to people living with aphasia, and provides inaccurate descriptions of an individual pattern of difficulties.
There are typical difficulties with speech and language that come with normal aging as well. As we age, language can become more difficult to process, resulting in a slowing of verbal comprehension, reading abilities and more likely word finding difficulties. With each of these, though, unlike some aphasias, functionality within daily life remains intact.
Boston classification | Aphasia | Wikipedia | 329 | 2088 | https://en.wikipedia.org/wiki/Aphasia | Biology and health sciences | Disabilities | Health |
Individuals with receptive aphasia (Wernicke's aphasia), also referred to as fluent aphasia, may speak in long sentences that have no meaning, add unnecessary words, and even create new "words" (neologisms). For example, someone with receptive aphasia may say, "delicious taco", meaning "The dog needs to go out so I will take him for a walk". They have poor auditory and reading comprehension, and fluent, but nonsensical, oral and written expression. Individuals with receptive aphasia usually have great difficulty understanding the speech of both themselves and others and are, therefore, often unaware of their mistakes. Receptive language deficits usually arise from lesions in the posterior portion of the left hemisphere at or near Wernicke's area. It is often the result of trauma to the temporal region of the brain, specifically damage to Wernicke's area. Trauma can be the result from an array of problems, however it is most commonly seen as a result of stroke | Aphasia | Wikipedia | 220 | 2088 | https://en.wikipedia.org/wiki/Aphasia | Biology and health sciences | Disabilities | Health |
Individuals with expressive aphasia (Broca's aphasia) frequently speak short, meaningful phrases that are produced with great effort. It is thus characterized as a nonfluent aphasia. Affected people often omit small words such as "is", "and", and "the". For example, a person with expressive aphasia may say, "walk dog", which could mean "I will take the dog for a walk", "you take the dog for a walk" or even "the dog walked out of the yard." Individuals with expressive aphasia are able to understand the speech of others to varying degrees. Because of this, they are often aware of their difficulties and can become easily frustrated by their speaking problems. While Broca's aphasia may appear to be solely an issue with language production, evidence suggests that it may be rooted in an inability to process syntactical information. Individuals with expressive aphasia may have a speech automatism (also called recurring or recurrent utterance). These speech automatisms can be repeated lexical speech automatisms; e.g., modalisations ('I can't ..., I can't ...'), expletives/swearwords, numbers ('one two, one two') or non-lexical utterances made up of repeated, legal, but meaningless, consonant-vowel syllables (e.g.., /tan tan/, /bi bi/). In severe cases, the individual may be able to utter only the same speech automatism each time they attempt speech.
Individuals with anomic aphasia have difficulty with naming. People with this aphasia may have difficulties naming certain words, linked by their grammatical type (e.g., difficulty naming verbs and not nouns) or by their semantic category (e.g., difficulty naming words relating to photography, but nothing else) or a more general naming difficulty. People tend to produce grammatic, yet empty, speech. Auditory comprehension tends to be preserved. Anomic aphasia is the aphasial presentation of tumors in the language zone; it is the aphasial presentation of Alzheimer's disease. Anomic aphasia is the mildest form of aphasia, indicating a likely possibility for better recovery. | Aphasia | Wikipedia | 486 | 2088 | https://en.wikipedia.org/wiki/Aphasia | Biology and health sciences | Disabilities | Health |
Individuals with transcortical sensory aphasia, in principle the most general and potentially among the most complex forms of aphasia, may have similar deficits as in receptive aphasia, but their repetition ability may remain intact.
Global aphasia is considered a severe impairment in many language aspects since it impacts expressive and receptive language, reading, and writing. Despite these many deficits, there is evidence that has shown individuals benefited from speech language therapy. Even though individuals with global aphasia will not become competent speakers, listeners, writers, or readers, goals can be created to improve the individual's quality of life. Individuals with global aphasia usually respond well to treatment that includes personally relevant information, which is also important to consider for therapy.
Individuals with conduction aphasia have deficits in the connections between the speech-comprehension and speech-production areas. This might be caused by damage to the arcuate fasciculus, the structure that transmits information between Wernicke's area and Broca's area. Similar symptoms, however, can be present after damage to the insula or to the auditory cortex. Auditory comprehension is near normal, and oral expression is fluent with occasional paraphasic errors. Paraphasic errors include phonemic/literal or semantic/verbal. Repetition ability is poor. Conduction and transcortical aphasias are caused by damage to the white matter tracts. These aphasias spare the cortex of the language centers, but instead create a disconnection between them. Conduction aphasia is caused by damage to the arcuate fasciculus. The arcuate fasciculus is a white matter tract that connects Broca's and Wernicke's areas. People with conduction aphasia typically have good language comprehension, but poor speech repetition and mild difficulty with word retrieval and speech production. People with conduction aphasia are typically aware of their errors. Two forms of conduction aphasia have been described: reproduction conduction aphasia (repetition of a single relatively unfamiliar multisyllabic word) and repetition conduction aphasia (repetition of unconnected short familiar words. | Aphasia | Wikipedia | 446 | 2088 | https://en.wikipedia.org/wiki/Aphasia | Biology and health sciences | Disabilities | Health |
Transcortical aphasias include transcortical motor aphasia, transcortical sensory aphasia, and mixed transcortical aphasia. People with transcortical motor aphasia typically have intact comprehension and awareness of their errors, but poor word finding and speech production. People with transcortical sensory and mixed transcortical aphasia have poor comprehension and unawareness of their errors. Despite poor comprehension and more severe deficits in some transcortical aphasias, small studies have indicated that full recovery is possible for all types of transcortical aphasia. | Aphasia | Wikipedia | 120 | 2088 | https://en.wikipedia.org/wiki/Aphasia | Biology and health sciences | Disabilities | Health |
Classical-localizationist approaches
Localizationist approaches aim to classify the aphasias according to their major presenting characteristics and the regions of the brain that most probably gave rise to them. Inspired by the early work of nineteenth-century neurologists Paul Broca and Carl Wernicke, these approaches identify two major subtypes of aphasia and several more minor subtypes:
Expressive aphasia (also known as "motor aphasia" or "Broca's aphasia"), which is characterized by halted, fragmented, effortful speech, but well-preserved comprehension relative to expression. Damage is typically in the anterior portion of the left hemisphere, most notably Broca's area. Individuals with Broca's aphasia often have right-sided weakness or paralysis of the arm and leg, because the left frontal lobe is also important for body movement, particularly on the right side.
Receptive aphasia (also known as "sensory aphasia" or "Wernicke's aphasia"), which is characterized by fluent speech, but marked difficulties understanding words and sentences. Although fluent, the speech may lack in key substantive words (nouns, verbs, adjectives), and may contain incorrect words or even nonsense words. This subtype has been associated with damage to the posterior left temporal cortex, most notably Wernicke's area. These individuals usually have no body weakness, because their brain injury is not near the parts of the brain that control movement.
Conduction aphasia, where speech remains fluent, and comprehension is preserved, but the person may have disproportionate difficulty repeating words or sentences. Damage typically involves the arcuate fasciculus and the left parietal region.
Transcortical motor aphasia and transcortical sensory aphasia, which are similar to Broca's and Wernicke's aphasia respectively, but the ability to repeat words and sentences is disproportionately preserved. | Aphasia | Wikipedia | 414 | 2088 | https://en.wikipedia.org/wiki/Aphasia | Biology and health sciences | Disabilities | Health |
Recent classification schemes adopting this approach, such as the Boston-Neoclassical Model, also group these classical aphasia subtypes into two larger classes: the nonfluent aphasias (which encompasses Broca's aphasia and transcortical motor aphasia) and the fluent aphasias (which encompasses Wernicke's aphasia, conduction aphasia and transcortical sensory aphasia). These schemes also identify several further aphasia subtypes, including: anomic aphasia, which is characterized by a selective difficulty finding the names for things; and global aphasia, where both expression and comprehension of speech are severely compromised.
Many localizationist approaches also recognize the existence of additional, more "pure" forms of language disorder that may affect only a single language skill. For example, in pure alexia, a person may be able to write, but not read, and in pure word deafness, they may be able to produce speech and to read, but not understand speech when it is spoken to them.
Cognitive neuropsychological approaches
Although localizationist approaches provide a useful way of classifying the different patterns of language difficulty into broad groups, one problem is that most individuals do not fit neatly into one category or another. Another problem is that the categories, particularly the major ones such as Broca's and Wernicke's aphasia, still remain quite broad and do not meaningfully reflect a person's difficulties. Consequently, even amongst those who meet the criteria for classification into a subtype, there can be enormous variability in the types of difficulties they experience. | Aphasia | Wikipedia | 337 | 2088 | https://en.wikipedia.org/wiki/Aphasia | Biology and health sciences | Disabilities | Health |
Instead of categorizing every individual into a specific subtype, cognitive neuropsychological approaches aim to identify the key language skills or "modules" that are not functioning properly in each individual. A person could potentially have difficulty with just one module, or with a number of modules. This type of approach requires a framework or theory as to what skills/modules are needed to perform different kinds of language tasks. For example, the model of Max Coltheart identifies a module that recognizes phonemes as they are spoken, which is essential for any task involving recognition of words. Similarly, there is a module that stores phonemes that the person is planning to produce in speech, and this module is critical for any task involving the production of long words or long strings of speech. Once a theoretical framework has been established, the functioning of each module can then be assessed using a specific test or set of tests. In the clinical setting, use of this model usually involves conducting a battery of assessments, each of which tests one or a number of these modules. Once a diagnosis is reached as to the skills/modules where the most significant impairment lies, therapy can proceed to treat these skills.
Progressive aphasias
Primary progressive aphasia (PPA) is a neurodegenerative focal dementia that can be associated with progressive illnesses or dementia, such as frontotemporal dementia / Pick Complex Motor neuron disease, Progressive supranuclear palsy, and Alzheimer's disease, which is the gradual process of progressively losing the ability to think. Gradual loss of language function occurs in the context of relatively well-preserved memory, visual processing, and personality until the advanced stages. Symptoms usually begin with word-finding problems (naming) and progress to impaired grammar (syntax) and comprehension (sentence processing and semantics). The loss of language before the loss of memory differentiates PPA from typical dementias. People with PPA may have difficulties comprehending what others are saying. They can also have difficulty trying to find the right words to make a sentence. There are three classifications of Primary Progressive Aphasia : Progressive nonfluent aphasia (PNFA), Semantic Dementia (SD), and Logopenic progressive aphasia (LPA). | Aphasia | Wikipedia | 459 | 2088 | https://en.wikipedia.org/wiki/Aphasia | Biology and health sciences | Disabilities | Health |
Progressive Jargon Aphasia is a fluent or receptive aphasia in which the person's speech is incomprehensible, but appears to make sense to them. Speech is fluent and effortless with intact syntax and grammar, but the person has problems with the selection of nouns. Either they will replace the desired word with another that sounds or looks like the original one or has some other connection or they will replace it with sounds. As such, people with jargon aphasia often use neologisms, and may perseverate if they try to replace the words they cannot find with sounds. Substitutions commonly involve picking another (actual) word starting with the same sound (e.g., clocktower – colander), picking another semantically related to the first (e.g., letter – scroll), or picking one phonetically similar to the intended one (e.g., lane – late). | Aphasia | Wikipedia | 193 | 2088 | https://en.wikipedia.org/wiki/Aphasia | Biology and health sciences | Disabilities | Health |
Deaf aphasia
There have been many instances showing that there is a form of aphasia among deaf individuals. Sign languages are, after all, forms of language that have been shown to use the same areas of the brain as verbal forms of language. Mirror neurons become activated when an animal is acting in a particular way or watching another individual act in the same manner. These mirror neurons are important in giving an individual the ability to mimic movements of hands. Broca's area of speech production has been shown to contain several of these mirror neurons resulting in significant similarities of brain activity between sign language and vocal speech communication. People use facial movements to create, what other people perceive, to be faces of emotions. While combining these facial movements with speech, a more full form of language is created which enables the species to interact with a much more complex and detailed form of communication. Sign language also uses these facial movements and emotions along with the primary hand movement way of communicating. These facial movement forms of communication come from the same areas of the brain. When dealing with damages to certain areas of the brain, vocal forms of communication are in jeopardy of severe forms of aphasia. Since these same areas of the brain are being used for sign language, these same, at least very similar, forms of aphasia can show in the Deaf community. Individuals can show a form of Wernicke's aphasia with sign language and they show deficits in their abilities in being able to produce any form of expressions. Broca's aphasia shows up in some people, as well. These individuals find tremendous difficulty in being able to actually sign the linguistic concepts they are trying to express. | Aphasia | Wikipedia | 341 | 2088 | https://en.wikipedia.org/wiki/Aphasia | Biology and health sciences | Disabilities | Health |
Severity
The severity of the type of aphasia varies depending on the size of the stroke. However, there is much variance between how often one type of severity occurs in certain types of aphasia. For instance, any type of aphasia can range from mild to profound. Regardless of the severity of aphasia, people can make improvements due to spontaneous recovery and treatment in the acute stages of recovery. Additionally, while most studies propose that the greatest outcomes occur in people with severe aphasia when treatment is provided in the acute stages of recovery, Robey (1998) also found that those with severe aphasia are capable of making strong language gains in the chronic stage of recovery as well. This finding implies that persons with aphasia have the potential to have functional outcomes regardless of how severe their aphasia may be. While there is no distinct pattern of the outcomes of aphasia based on severity alone, global aphasia typically makes functional language gains, but may be gradual since global aphasia affects many language areas.
Prevention
Aphasia is largely caused by unavoidable instances. However, some precautions can be taken to decrease risk for experiencing one of the two major causes of aphasia: stroke and traumatic brain injury (TBI). To decrease the probability of having an ischemic or hemorrhagic stroke, one should take the following precautions:
Exercising regularly
Eating a healthy diet, avoiding cholesterol in particular
Keeping alcohol consumption low and avoiding tobacco use
Controlling blood pressure
Going to the emergency room immediately if you begin to experience unilateral extremity (especially leg) swelling, warmth, redness, and/or tenderness as these are symptoms of a deep vein thrombosis which can lead to a stroke | Aphasia | Wikipedia | 358 | 2088 | https://en.wikipedia.org/wiki/Aphasia | Biology and health sciences | Disabilities | Health |
To prevent aphasia due to traumatic injury, one should take precautionary measures when engaging in dangerous activities such as:
Wearing a helmet when operating a bicycle, motor cycle, ATV, or any other moving vehicle that could potentially be involved in an accident
Wearing a seatbelt when driving or riding in a car
Wearing proper protective gear when playing contact sports, especially American football, rugby, and hockey, or refraining from such activities
Minimizing anticoagulant use (including aspirin) if at all possible as they increase the risk of hemorrhage after a head injury
Additionally, one should always seek medical attention after sustaining head trauma due to a fall or accident. The sooner that one receives medical attention for a traumatic brain injury, the less likely one is to experience long-term or severe effects.
Management
Most acute cases of aphasia recover some or most skills by participating in speech and language therapy. Recovery and improvement can continue for years after the stroke. After the onset of aphasia, there is approximately a six-month period of spontaneous recovery; during this time, the brain is attempting to recover and repair the damaged neurons. Improvement varies widely, depending on the aphasia's cause, type, and severity. Recovery also depends on the person's age, health, motivation, handedness, and educational level.
Speech and language therapy that is higher intensity, higher dose or provided over a long duration of time leads to significantly better functional communication, but people might be more likely to drop out of high intensity treatment (up to 15 hours per week). A total of 20–50 hours of speech and language therapy is necessary for the best recovery. The most improvement happens when 2–5 hours of therapy is provided each week over 4–5 days. Recovery is further improved when besides the therapy people practice tasks at home. Speech and language therapy is also effective if it is delivered online through video or by a family member who has been trained by a professional therapist.
Recovery with therapy is also dependent on the recency of stroke and the age of the person. Receiving therapy within a month after the stroke leads to the greatest improvements. Three or six months after the stroke more therapy will be needed, but symptoms can still be improved. People with aphasia who are younger than 55 years are the most likely to improve, but people older than 75 years can still get better with therapy. | Aphasia | Wikipedia | 488 | 2088 | https://en.wikipedia.org/wiki/Aphasia | Biology and health sciences | Disabilities | Health |
There is no one treatment proven to be effective for all types of aphasias. The reason that there is no universal treatment for aphasia is because of the nature of the disorder and the various ways it is presented. Aphasia is rarely exhibited identically, implying that treatment needs to be catered specifically to the individual. Studies have shown that, although there is no consistency on treatment methodology in literature, there is a strong indication that treatment, in general, has positive outcomes. Therapy for aphasia ranges from increasing functional communication to improving speech accuracy, depending on the person's severity, needs and support of family and friends. Group therapy allows individuals to work on their pragmatic and communication skills with other individuals with aphasia, which are skills that may not often be addressed in individual one-on-one therapy sessions. It can also help increase confidence and social skills in a comfortable setting.
Evidence does not support the use of transcranial direct current stimulation (tDCS) for improving aphasia after stroke. Moderate quality evidence does indicate naming performance improvements for nouns, but not verbs using tDCS
Specific treatment techniques include the following:
Copy and recall therapy (CART) – repetition and recall of targeted words within therapy may strengthen orthographic representations and improve single word reading, writing, and naming
Visual communication therapy (VIC) – the use of index cards with symbols to represent various components of speech
Visual action therapy (VAT) – typically treats individuals with global aphasia to train the use of hand gestures for specific items
Functional communication treatment (FCT) – focuses on improving activities specific to functional tasks, social interaction, and self-expression
Promoting aphasic's communicative effectiveness (PACE) – a means of encouraging normal interaction between people with aphasia and clinicians. In this kind of therapy, the focus is on pragmatic communication rather than treatment itself. People are asked to communicate a given message to their therapists by means of drawing, making hand gestures or even pointing to an object
Melodic intonation therapy (MIT) – aims to use the intact melodic/prosodic processing skills of the right hemisphere to help cue retrieval of words and expressive language
Centeredness Theory Interview (CTI) - Uses client centered goal formation into the nature of current patient interactions as well as future / desired interactions to improve subjective well-being, cognition and communication.
Other – i.e., drawing as a way of communicating, trained conversation partners | Aphasia | Wikipedia | 499 | 2088 | https://en.wikipedia.org/wiki/Aphasia | Biology and health sciences | Disabilities | Health |
Semantic feature analysis (SFA) — a type of aphasia treatment that targets word-finding deficits — is based on the theory that neural connections can be strengthened by using related words and phrases that are similar to the target word, to eventually activate the target word in the brain. SFA can be implemented in multiple forms such as verbally, written, using picture cards, etc. The SLP provides prompting questions to the individual with aphasia in order for the person to name the picture provided. Studies show that SFA is an effective intervention for improving confrontational naming.
Melodic intonation therapy is used to treat non-fluent aphasia and has proved to be effective in some cases. However, there is still no evidence from randomized controlled trials confirming the efficacy of MIT in chronic aphasia. MIT is used to help people with aphasia vocalize themselves through speech song, which is then transferred as a spoken word. Good candidates for this therapy include people who have had left hemisphere strokes, non-fluent aphasias such as Broca's, good auditory comprehension, poor repetition and articulation, and good emotional stability and memory. An alternative explanation is that the efficacy of MIT depends on neural circuits involved in the processing of rhythmicity and formulaic expressions (examples taken from the MIT manual: "I am fine," "how are you?" or "thank you"); while rhythmic features associated with melodic intonation may engage primarily left-hemisphere subcortical areas of the brain, the use of formulaic expressions is known to be supported by right-hemisphere cortical and bilateral subcortical neural networks.
Systematic reviews support the effectiveness and importance of partner training. According to the National Institute on Deafness and Other Communication Disorders (NIDCD), involving family with the treatment of an aphasic loved one is ideal for all involved, because while it will no doubt assist in their recovery, it will also make it easier for members of the family to learn how best to communicate with them.
When a person's speech is insufficient, different kinds of augmentative and alternative communication could be considered such as alphabet boards, pictorial communication books, specialized software for computers or apps for tablets or smartphones. | Aphasia | Wikipedia | 455 | 2088 | https://en.wikipedia.org/wiki/Aphasia | Biology and health sciences | Disabilities | Health |
When addressing Wernicke's aphasia, according to Bakheit et al. (2007), the lack of awareness of the language impairments, a common characteristic of Wernicke's aphasia, may affect the rate and extent of therapy outcomes. Robey (1998) determined that at least 2 hours of treatment per week is recommended for making significant language gains. Spontaneous recovery may cause some language gains, but without speech-language therapy, the outcomes can be half as strong as those with therapy.
When addressing Broca's aphasia, better outcomes occur when the person participates in therapy, and treatment is more effective than no treatment for people in the acute period. Two or more hours of therapy per week in acute and post-acute stages produced the greatest results. High-intensity therapy was most effective, and low-intensity therapy was almost equivalent to no therapy.
People with global aphasia are sometimes referred to as having irreversible aphasic syndrome, often making limited gains in auditory comprehension, and recovering no functional language modality with therapy. With this said, people with global aphasia may retain gestural communication skills that may enable success when communicating with conversational partners within familiar conditions. Process-oriented treatment options are limited, and people may not become competent language users as readers, listeners, writers, or speakers no matter how extensive therapy is. However, people's daily routines and quality of life can be enhanced with reasonable and modest goals. After the first month, there is limited to no healing to language abilities of most people. There is a grim prognosis, leaving 83% who were globally aphasic after the first month that will remain globally aphasic at the first year. Some people are so severely impaired that their existing process-oriented treatment approaches offer no signs of progress, and therefore cannot justify the cost of therapy.
Perhaps due to the relative rareness of conduction aphasia, few studies have specifically studied the effectiveness of therapy for people with this type of aphasia. From the studies performed, results showed that therapy can help to improve specific language outcomes. One intervention that has had positive results is auditory repetition training. Kohn et al. (1990) reported that drilled auditory repetition training related to improvements in spontaneous speech, Francis et al. (2003) reported improvements in sentence comprehension, and Kalinyak-Fliszar et al. (2011) reported improvements in auditory-visual short-term memory. | Aphasia | Wikipedia | 506 | 2088 | https://en.wikipedia.org/wiki/Aphasia | Biology and health sciences | Disabilities | Health |
Individualized service delivery
Intensity of treatment should be individualized based on the recency of stroke, therapy goals, and other specific characteristics such as age, size of lesion, overall health status, and motivation. Each individual reacts differently to treatment intensity and is able to tolerate treatment at different times post-stroke. Intensity of treatment after a stroke should be dependent on the person's motivation, stamina, and tolerance for therapy.
Outcomes
If the symptoms of aphasia last longer than two or three months after a stroke, a complete recovery is unlikely. However, it is important to note that some people continue to improve over a period of years and even decades. Improvement is a slow process that usually involves both helping the individual and family understand the nature of aphasia and learning compensatory strategies for communicating.
After a traumatic brain injury (TBI) or cerebrovascular accident (CVA), the brain undergoes several healing and re-organization processes, which may result in improved language function. This is referred to as spontaneous recovery. Spontaneous recovery is the natural recovery the brain makes without treatment, and the brain begins to reorganize and change in order to recover. There are several factors that contribute to a person's chance of recovery caused by stroke, including stroke size and location. Age, sex, and education have not been found to be very predictive. There is also research pointing to damage in the left hemisphere healing more effectively than the right.
Specific to aphasia, spontaneous recovery varies among affected people and may not look the same in everyone, making it difficult to predict recovery.
Though some cases of Wernicke's aphasia have shown greater improvements than more mild forms of aphasia, people with Wernicke's aphasia may not reach as high a level of speech abilities as those with mild forms of aphasia. | Aphasia | Wikipedia | 383 | 2088 | https://en.wikipedia.org/wiki/Aphasia | Biology and health sciences | Disabilities | Health |
Prevalence
Aphasia affects about two million people in the U.S. and 250,000 people in Great Britain. Nearly 180,000 people acquire the disorder every year in the U.S., 170,000 due to stroke. Any person of any age can develop aphasia, given that it is often caused by a traumatic injury. However, people who are middle aged and older are the most likely to acquire aphasia, as the other etiologies are more likely at older ages. For example, approximately 75% of all strokes occur in individuals over the age of 65. Strokes account for most documented cases of aphasia: 25% to 40% of people who survive a stroke develop aphasia as a result of damage to the language-processing regions of the brain.
History
The first recorded case of aphasia is from an Egyptian papyrus, the Edwin Smith Papyrus, which details speech problems in a person with a traumatic brain injury to the temporal lobe.
During the second half of the 19th century, aphasia was a major focus for scientists and philosophers who were working in the beginning stages of the field of psychology.
In medical research, speechlessness was described as an incorrect prognosis, and there was no assumption that underlying language complications existed. Broca and his colleagues were some of the first to write about aphasia, but Wernicke was the first credited to have written extensively about aphasia being a disorder that contained comprehension difficulties. Despite claims of who reported on aphasia first, it was F.J. Gall that gave the first full description of aphasia after studying wounds to the brain, as well as his observation of speech difficulties resulting from vascular lesions. A recent book on the entire history of aphasia is available (Reference: Tesak, J. & Code, C. (2008) Milestones in the History of Aphasia: Theories and Protagonists. Hove, East Sussex: Psychology Press).
Etymology
Aphasia is from Greek a- ("without", negative prefix) + phásis (φάσις, "speech").
The word aphasia comes from the word ἀφασία aphasia, in Ancient Greek, which means "speechlessness", derived from ἄφατος aphatos, "speechless" from ἀ- a-, "not, un" and φημί phemi, "I speak". | Aphasia | Wikipedia | 501 | 2088 | https://en.wikipedia.org/wiki/Aphasia | Biology and health sciences | Disabilities | Health |
Further research
Research is currently being done using functional magnetic resonance imaging (fMRI) to witness the difference in how language is processed in normal brains vs aphasic brains. This will help researchers to understand exactly what the brain must go through in order to recover from Traumatic Brain Injury (TBI) and how different areas of the brain respond after such an injury.
Another intriguing approach being tested is that of drug therapy. Research is in progress that will hopefully uncover whether or not certain drugs might be used in addition to speech-language therapy in order to facilitate recovery of proper language function. It's possible that the best treatment for Aphasia might involve combining drug treatment with therapy, instead of relying on one over the other.
One other method being researched as a potential therapeutic combination with speech-language therapy is brain stimulation. One particular method, Transcranial Magnetic Stimulation (TMS), alters brain activity in whatever area it happens to stimulate, which has recently led scientists to wonder if this shift in brain function caused by TMS might help people re-learn language. Another type of external brain stimulation is transcranial Direct Current Stimulation (tDCS), but existing research has not shown it to be useful for improving aphasia after a stroke. | Aphasia | Wikipedia | 252 | 2088 | https://en.wikipedia.org/wiki/Aphasia | Biology and health sciences | Disabilities | Health |
The aorta ( ; : aortas or aortae) is the main and largest artery in the human body, originating from the left ventricle of the heart, branching upwards immediately after, and extending down to the abdomen, where it splits at the aortic bifurcation into two smaller arteries (the common iliac arteries). The aorta distributes oxygenated blood to all parts of the body through the systemic circulation.
Structure
Sections
In anatomical sources, the aorta is usually divided into sections.
One way of classifying a part of the aorta is by anatomical compartment, where the thoracic aorta (or thoracic portion of the aorta) runs from the heart to the diaphragm. The aorta then continues downward as the abdominal aorta (or abdominal portion of the aorta) from the diaphragm to the aortic bifurcation.
Another system divides the aorta with respect to its course and the direction of blood flow. In this system, the aorta starts as the ascending aorta, travels superiorly from the heart, and then makes a hairpin turn known as the aortic arch. Following the aortic arch, the aorta then travels inferiorly as the descending aorta. The descending aorta has two parts. The aorta begins to descend in the thoracic cavity and is consequently known as the thoracic aorta. After the aorta passes through the diaphragm, it is known as the abdominal aorta. The aorta ends by dividing into two major blood vessels, the common iliac arteries and a smaller midline vessel, the median sacral artery.
Ascending aorta
The ascending aorta begins at the opening of the aortic valve in the left ventricle of the heart. It runs through a common pericardial sheath with the pulmonary trunk. These two blood vessels twist around each other, causing the aorta to start out posterior to the pulmonary trunk, but end by twisting to its right and anterior side.
The transition from ascending aorta to aortic arch is at the pericardial reflection on the aorta. | Aorta | Wikipedia | 439 | 2089 | https://en.wikipedia.org/wiki/Aorta | Biology and health sciences | Circulatory system | Biology |
At the root of the ascending aorta, the lumen has small pockets between the cusps of the aortic valve and the wall of the aorta, which are called the aortic sinuses or the sinuses of Valsalva. The left aortic sinus contains the origin of the left coronary artery and the right aortic sinus likewise gives rise to the right coronary artery. Together, these two arteries supply the heart. The posterior aortic sinus does not give rise to a coronary artery. For this reason the left, right and posterior aortic sinuses are also called left-coronary, right-coronary and non-coronary sinuses.
Aortic arch
The aortic arch loops over the left pulmonary artery and the bifurcation of the pulmonary trunk, to which it remains connected by the ligamentum arteriosum, a remnant of the fetal circulation that is obliterated a few days after birth. In addition to these blood vessels, the aortic arch crosses the left main bronchus. Between the aortic arch and the pulmonary trunk is a network of autonomic nerve fibers, the cardiac plexus or aortic plexus. The left vagus nerve, which passes anterior to the aortic arch, gives off a major branch, the recurrent laryngeal nerve, which loops under the aortic arch just lateral to the ligamentum arteriosum. It then runs back to the neck.
The aortic arch has three major branches: from proximal to distal, they are the brachiocephalic trunk, the left common carotid artery, and the left subclavian artery. The brachiocephalic trunk supplies the right side of the head and neck as well as the right arm and chest wall, while the latter two together supply the left side of the same regions.
The aortic arch ends, and the descending aorta begins at the level of the intervertebral disc between the fourth and fifth thoracic vertebrae.
Thoracic aorta | Aorta | Wikipedia | 432 | 2089 | https://en.wikipedia.org/wiki/Aorta | Biology and health sciences | Circulatory system | Biology |
The thoracic aorta gives rise to the intercostal and subcostal arteries, as well as to the superior and inferior left bronchial arteries and variable branches to the esophagus, mediastinum, and pericardium. Its lowest pair of branches are the superior phrenic arteries, which supply the diaphragm, and the subcostal arteries for the twelfth rib.
Abdominal aorta
The abdominal aorta begins at the aortic hiatus of the diaphragm at the level of the twelfth thoracic vertebra. It gives rise to lumbar and musculophrenic arteries, renal and middle suprarenal arteries, and visceral arteries (the celiac trunk, the superior mesenteric artery and the inferior mesenteric artery). It ends in a bifurcation into the left and right common iliac arteries. At the point of the bifurcation, there also springs a smaller branch, the median sacral artery.
Development
The ascending aorta develops from the outflow tract, which initially starts as a single tube connecting the heart with the aortic arches (which will form the great arteries) in early development but is then separated into the aorta and the pulmonary trunk.
The aortic arches start as five pairs of symmetrical arteries connecting the heart with the dorsal aorta, and then undergo a significant remodelling to form the final asymmetrical structure of the great arteries, with the 3rd pair of arteries contributing to the common carotids, the right 4th forming the base and middle part of the right subclavian artery and the left 4th being the central part of the aortic arch. The smooth muscle of the great arteries and the population of cells that form the aorticopulmonary septum that separates the aorta and pulmonary artery is derived from cardiac neural crest. This contribution of the neural crest to the great artery smooth muscle is unusual as most smooth muscle is derived from mesoderm. In fact the smooth muscle within the abdominal aorta is derived from mesoderm, and the coronary arteries, which arise just above the semilunar valves, possess smooth muscle of mesodermal origin. A failure of the aorticopulmonary septum to divide the great vessels results in persistent truncus arteriosus.
Microanatomy | Aorta | Wikipedia | 491 | 2089 | https://en.wikipedia.org/wiki/Aorta | Biology and health sciences | Circulatory system | Biology |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.