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Talk:Computer security

Article Cleanup
I am planning on fixing grammar and style issues and cleaning up the article in general. If you disagree with with any of the content removal, please let me know. Thanks. — Preceding unsigned comment added by 208.250.65.158 (talk • contribs) 13:13, July 17, 2007 (UTC) Can you be more specific about changes Tonymetz 💬  16:36, 1 April 2024 (UTC)
 * That's an IP post from 17 years ago... i just added a sig so it will archive. Meters (talk) 20:23, 1 April 2024 (UTC)

Information as unreliable
I feel Computer Security in using Wikipedia is unreliable. With a breach of IBM in Colorado healthcare due to some CLOP ransomware gang in Russia. Could be the Shadowcrew again involving hackers Russian and Cuban like Albert Gonzalez. People who developed database management and IBM software are being targeted as individuals as being the problem is wrong to do. INFORMATION gets proliferated more as a weapon of mass destruction. They have terrorists and serial killer Biographic data on wikipedia and this is why threats exist. Terrorists using Wikipedia as advantage. 65.163.112.196 (talk) 12:05, 19 October 2023 (UTC)

 * See Security through obscurity.
 * Everything on Wikipedia is (or at least should be) based on publicly available sources, available to anyone and everyone. Perhaps you are thinking of Wikileaks? (which has no connection with Wikipedia). 𝕁𝕄𝔽 (talk) 21:06, 19 October 2023 (UTC)

Create new article for cybersecurity
I suggest creating a new article to separate cybersecurity form computer security, the justification and explanation of why it is different is in the suggested article: https://en.wikipedia.org/wiki/Draft:Cybersecurity

But in summary, both concepts can be improved having separate articles for Computer Security and cybersecurity, because cybersecurity includes the protection of elements and processes which are not technology but depend on technology, as society depends more and more on technology. Pcoronaf (talk) 22:11, 14 November 2023 (UTC)

Changing order and prioritising the general public
Hi everyone. I've recently been contracted to do some editing work on Wikipedia articles, and this is one of the articles my employers would like improving.

(TLDR; I'm trying to make the article easier and more accessible for the general public to help improve their own computer security, so some topics may be moved around.)

I've recently completely some research for my master's degree on making Wikipedia more easy to understand and readable. The research includes surveying over 500 members of the general public on their responses to climate change articles on Wikipedia. The results suggest that both readability scores on Wikipedia are detrimental to people's understanding of the information, and in some cases can lead to people mistrusting the information. I'm looking to implement some of these findings into this article - in short, improve the readability of certain sections.

As well as readability, I also want to better prioritise information which suits the general public. Both the order of the article and the way advice is discussed on this article is slightly counterintuitive to aiding the general public on increasing their knowledge about computer security. Although computer security is a broad topic, topics that are within the realm of control or importance to the general public are mainly limited to protection and safety. This isn't prioritised in this article and is hidden amongst various subsections.

Over the next few weeks I will test moving some things around in the article with the goal of making the article more productive and easy to navigate for the general public. I hope to maintain the overall tone and information of the article, but simultaneously make it more helpful for the general public.

Please be free to comment on any of my edits if you believe it is changing the article in any way that you see unfit, and I would be more than happy to discuss your comments. Theobrad (talk) 11:49, 29 November 2023 (UTC)

Removal of 'Importance of Cyber Security' section
In the vein of condensing the article: keeping the information concise and in the right section, I believe this section (which is currently at the bottom of the article) may be slightly redundant following the rest of the information. With all respect to the author, as the section nicely summarises some of the points, unless it is placed high and condensed a bit as a kind of "summary" of issues, I don't think it should remain on its own at the bottom.

Would love to hear people's thoughts.

 * 1) As much of it is reiterated elsewhere, should it be removed?
 * 2) Or should it stay and be put higher up. I believe the article could do with more clear language (as this uses) and more straightforward explanations of things for the general public.

Theobrad (talk) 12:46, 29 November 2023 (UTC)

 * Remove that section. It violates Wikpedia's style guide in several ways and was added by a blocked user. —Dexxor (talk) 12:06, 2 December 2023 (UTC)
 * In that case, you might have removed yourself (as I have just done). See WP:BMB, revert all contributions by blocked editors, good or bad. (But, in response to, yes it was redundant.) --𝕁𝕄𝔽 (talk) 13:44, 2 December 2023 (UTC)
 * Thanks you all for your help! Please feel free to give input on any edits I make it the future! Theobrad (talk) 09:53, 4 December 2023 (UTC)
 * Well you can just WP:BEBOLD if you don't mind that it might be reverted and subjected to WP:Bold, revert, discuss cycle. My generally approach is only to use the talk page for proposals that might be controversial as it is usually easier to negotiate through a difficult issue there. But you often have to propose a draft anyway, just to be clear what the the proposal is. 𝕁𝕄𝔽 (talk) 13:38, 4 December 2023 (UTC)

title: Talk:Computer security


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Chris Cunningham

Chris Cunningham (born 15 October 1970) is a British video artist and music video director who directed music videos for electronic musicians such as Autechre, Squarepusher, and Aphex Twin on videos for "Windowlicker" and "Come to Daddy", and Björk's "All is Full of Love". All were used in Chris' chapter in Director's Label.

He has also created art installations and directed short movies. He was approached to direct a movie version of William Gibson's cyberpunk novel Neuromancer; the project has been in development hell for more than two decades. In the 2000s, Cunningham began doing music production work, and has also designed album artwork for a variety of musicians.

Early work
After seeing Cunningham's work on the 1995 film version of Judge Dredd, Stanley Kubrick head-hunted Cunningham to design and supervise animatronic tests of the central robot child character in his version of the film A.I. Artificial Intelligence. Cunningham worked for over a year on the film before leaving to pursue a career as a director.

Earlier work in film included model-making, prosthetic make-up and concept illustrations for Hardware and Dust Devil for director Richard Stanley, work on Nightbreed for Clive Barker, and on Alien3 for David Fincher. Between 1990 and 1992, he contributed the occasional cover painting and strip to Judge Dredd Megazine, working under the pseudonym "Chris Halls"; Halls is his stepfather's surname.

Music videos
Cunningham has had close ties to Warp Records since his first video for Autechre, "Second Bad Vilbel" in 1995 and Squarepusher's "Come On My Selector" in 1998, which received airplay on MTV's Amp and MTV's Chill Out Zone in Europe. Videos for Aphex Twin's "Come to Daddy" and "Windowlicker" are perhaps his best known. His video for Björk's "All Is Full of Love" won multiple awards, including an MTV music video award for Breakthrough Video and was nominated for a Grammy for Best Short Form Music Video. It was also the first ever music video to win a Gold Pencil at the D&AD Awards. It can still be seen at the Museum of Modern Art in New York. His video for Aphex Twin's "Windowlicker" was nominated for the "Best Video" award at the Brit Awards 2000. He also directed Madonna's "Frozen" video which became an international hit and won the award for Best Special Effects at the 1998 MTV Music Video Awards. Cunningham also came out of a seven-year hiatus from making music videos to direct the video for "Sheena Is a Parasite" by the Horrors.

Video art
His video installation Flex was first shown in 2000 at the Royal Academy of Arts, and subsequently at the Anthony d'Offay Gallery and other art galleries. Flex was commissioned by the Anthony d'Offay Gallery for the Apocalypse: Beauty & Horror in Contemporary Art exhibition curated by Norman Rosenthal and Max Wigram at the Royal Academy of Arts in 2000.

The Anthony d'Offay Gallery also commissioned Monkey Drummer, a 2½ minute piece intended for exhibition as a companion to Flex at the 2000 Apocalypse exhibition at the Royal Academy of Arts: however, the piece was not finished in time. In it an automaton with nine appendages and the head of a monkey plays the drums to "Mt Saint Michel + Saint Michaels Mount", the 10th track on Aphex Twin's 2001 album drukqs. Monkey Drummer debuted as part of Cunningham's installation at the 49th International Exhibition of Art at the 2001 Venice Biennale, which consisted of a loop of Monkey Drummer, Flex, and his video for Björk's "All Is Full of Love". In 2002 both Flex and Monkey Drummer were exhibited by 5th Gallery in Dublin, Ireland, in an exhibition curated by Artist/Curator Paul Murnaghan,

In 2007, an excerpt from Flex was shown in the Barbican's exhibition Seduced: Art and Sex from Antiquity to Now curated by Martin Kemp, Marina Wallace and Joanne Bernstein. alongside other pieces by Bacon, Klimt, Rembrandt, Rodin and Picasso.

Short films
In 2005, Cunningham released the short film Rubber Johnny as a DVD accompanied by a book of photographs and drawings. Rubber Johnny, a six-minute experimental short film cut to a soundtrack by Aphex Twin remixed by Cunningham, was shot between 2001 and 2004. Shot on DV night-vision, it was made in Cunningham's own time as a home movie of sorts, and took three and half years of weekends to complete. The Telegraph called it "like a Looney Tunes short for a generation raised on video nasties and rave music".

During this period Cunningham also made another short film for Warp Films, Spectral Musicians, which remains unreleased. The short film was set to Squarepusher's "My Fucking Sound" from his album Go Plastic; and to a piece called "Mutilation Colony" which was written especially for the short, and was released on the studio album Do You Know Squarepusher.

Commercials
Cunningham has directed a handful of commercials for companies and brands, including Gucci, Sony (PlayStation), Levi's, Telecom Italia, Nissan, and Orange.

Music production
In 2004/2005, Cunningham took a sabbatical from filmmaking to learn about music production and recording and to develop his own music projects. In December 2007 Cunningham produced two tracks, "Three Decades" and "Primary Colours", for Primary Colours, the second album by the Horrors. In the summer of 2008, due to scheduling conflicts with his feature film script writing he could not work on the rest of the album which was subsequently recorded by Geoff Barrow from Portishead.

In 2008, he produced and arranged a new version of 'I Feel Love' for the Gucci commercial that he also directed. He travelled to Nashville to work with Donna Summer to record a brand new vocal for it.

Chris Cunningham Live
In 2005, Cunningham played a 45-minute audio visual piece performed live in Tokyo and Osaka in front of 30,000+ fans over the two nights at the Japanese electronic music festival. These performances evolved into Chris Cunningham Live, a 55-minute long performance piece combining original and remixed music and film. It features remixed, unreleased and brand new videos and music dynamically edited together into a new live piece spread over three screens. The sound accompanying these images includes Cunningham's first publicly performed compositions interspersed with his remixes of other artist's work. Chris Cunningham Live debuted as one of the headline attractions at Warp 20 in Paris on 8 May 2009 with other performances scheduled at festivals in UK, and a number of European cities later in the year. Chris Cunningham Live continued in June 2011, with performances in London, Barcelona, and Sydney, Australia.

Photography
Cunningham has created photography and cover artwork for various people including Björk's "All Is Full of Love", Aphex Twin's "Windowlicker" and "Come to Daddy".

In 2008, Cunningham produced a fashion shoot for Dazed & Confused using Grace Jones as a model to create "Nubian versions" of Rubber Johnny. In an interview for BBC's "The Culture Show", it was suggested that the collaboration may expand into a video project. In regards to the collaboration, Cunningham stated "For me, Grace has the strongest iconography of any artist in music. She’s definitely the most inspiring person I’ve worked with so far".

In November 2008, Cunningham followed on with another photoshoot for Vice Magazine.

Neuromancer
In an August 1999 Spike Magazine interview, cyberpunk author William Gibson stated "He (Chris) was brought to my attention by someone else. We were told, third-hand, that he was extremely wary of the Hollywood process, and wouldn't return calls. But someone else told us that Neuromancer had been his The Wind in the Willows, that he'd read it when he was a kid. I went to London and we met." Gibson is also quoted in the article as saying "Chris is my own 100 percent personal choice...My only choice. The only person I've met who I thought might have a hope in hell of doing it right. I went back to see him in London just after he'd finished the Bjork video, and I sat on a couch beside this dead sex little Bjork robot, except it was wearing Aphex Twin's head. We talked."

In 2000, Cunningham and William Gibson began work on the script for Gibson's 1984 novel Neuromancer. However, because Neuromancer was due to be a big budget studio film, it is rumoured that Cunningham pulled out due to being a first time director without final cut approval. He also felt that too much of the original book's ideas had been cannibalised by other recent films.

On 18 November 2004, in the FAQ on the William Gibson Board, Gibson was asked:

"Q: Is it true there's a movie of Neuromancer in the works?

A: Perpetually, it seems, and going on a quarter of a century now. The most recently rumoured version, to have been directed by Chris Cunningham, is now definitely not happening."

Personal life
Cunningham was married to Warpaint's bassist Jenny Lee Lindberg. They are currently no longer together.

Videography
The video collection The Work of Director Chris Cunningham was released in November 2004 as part of the Directors Label set. This DVD includes selected highlights from 1995 to 2000.
 * "Second Bad Vilbel" (1996) video for Autechre
 * "Back with the Killer Again" (1996) video for the Auteurs
 * "Light Aircraft on Fire" (1996) video for the Auteurs
 * "Fighting Fit" (1996) video for Gene
 * "Another Day" (1996) video for Lodestar
 * "Space Junkie" (1996) video for Holy Barbarians
 * "36 Degrees" (1996) video for Placebo
 * "Personally" (1997) video for 12 Rounds
 * "Jesus Coming in for the Kill" (1997) video for Life's Addiction
 * "The Next Big Thing" (1997) video for Jesus Jones
 * "Tranquillizer" (1997) video for Geneva
 * "No More Talk" (1997) video for Dubstar
 * "Something to Say" (1997) video for Jocasta
 * "Come to Daddy" (1997) video for Aphex Twin
 * "Clip Clop" (1997) commercial for XFM London
 * "Sport is Free" (1997) – commercial for ITV
 * "Fetish" (1998) – commercial for NUS
 * "Only You" (1998) video for Portishead
 * "Frozen" (1998) video for Madonna
 * "Come on My Selector" (1998) video for Squarepusher
 * "Engine" (1999) commercial for Nissan. Featuring music by Boards of Canada
 * "All Is Full of Love" (1999) video for Björk
 * "Windowlicker" (1999) video for Aphex Twin
 * "Afrika Shox" (1999) video for Leftfield and Afrika Bambaataa
 * "Mental Wealth" (1999) commercial for Sony PlayStation
 * "Photocopier" (unreleased) commercial for Levi's
 * "Flex" (2000) video installation. Featuring music by Aphex Twin
 * "Quiet" (2000) – commercial for Telecom Italia. Featuring music by Boards of Canada
 * "Monkey Drummer" (2001) video installation. Featuring "Mt Saint Michel + Saint Michaels mount" from Aphex Twin's album Drukqs
 * "Up and Down" (2002) – commercial for Levi's
 * "Photo Messaging" (2003) commercial for Orange. Featuring music from Add N To (X).
 * "Rubber Johnny" (2005) featuring "Afx237 V7" from Aphex Twin's album Drukqs
 * "Sheena Is a Parasite" (2006) video for the Horrors
 * "Gucci Flora" (2009) commercial for Gucci Perfume
 * "New York Is Killing Me (Chris Cunningham Remix)" (2010) video for Gil Scott-Heron
 * "Jaqapparatus 1" (2012) robotic art installation performance for Audi City London.
 * "Love Is To Die" Multimedia documentary for the album release of Warpaint (2014).

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

title: Chris Cunningham


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Centaur

A centaur (κένταυρος; centaurus), occasionally hippocentaur, also called Ixionidae (Ἰξιονίδαι), is a creature from Greek mythology with the upper body of a human and the lower body and legs of a horse that was said to live in the mountains of Thessaly. In one version of the myth, the centaurs were named after Centaurus, and, through his brother Lapithes, were kin to the legendary tribe of the Lapiths.

Centaurs are thought of in many Greek myths as being as wild as untamed horses, and were said to have inhabited the region of Magnesia and Mount Pelion in Thessaly, the Foloi oak forest in Elis, and the Malean peninsula in southern Laconia. Centaurs are subsequently featured in Roman mythology, and were familiar figures in the medieval bestiary. They remain a staple of modern fantastic literature.

Etymology
The Greek word kentauros is generally regarded as being of obscure origin. The etymology from ken + tauros, 'piercing bull', was a euhemerist suggestion in Palaephatus' rationalizing text on Greek mythology, On Incredible Tales (Περὶ ἀπίστων), which included mounted archers from a village called Nephele eliminating a herd of bulls that were the scourge of Ixion's kingdom. Another possible related etymology can be "bull-slayer".

Creation of centaurs
The centaurs were usually said to have been born of Ixion and Nephele. As the story goes, Nephele was a cloud made into the likeness of Hera in a plot to trick Ixion into revealing his lust for Hera to Zeus. Ixion seduced Nephele and from that relationship centaurs were created. Another version, however, makes them children of Centaurus, a man who mated with the Magnesian mares. Centaurus was either himself the son of Ixion and Nephele (inserting an additional generation) or of Apollo and the nymph Stilbe. In the latter version of the story, Centaurus's twin brother was Lapithes, ancestor of the Lapiths.

Another tribe of centaurs was said to have lived on Cyprus. According to Nonnus, the Cyprian Centaurs were fathered by Zeus, who, in frustration after Aphrodite had eluded him, spilled his seed on the ground of that land. Unlike those of mainland Greece, the Cyprian centaurs were ox-horned.

There were also the Lamian Pheres, twelve rustic daimones (spirits) of the Lamos river. They were set by Zeus to guard the infant Dionysos, protecting him from the machinations of Hera, but the enraged goddess transformed them into ox-horned Centaurs unrelated to the Cyprian Centaurs. The Lamian Pheres later accompanied Dionysos in his campaign against the Indians.

The centaur's half-human, half-horse composition has led many writers to treat them as liminal beings, caught between the two natures they embody in contrasting myths; they are both the embodiment of untamed nature, as in their battle with the Lapiths (their kin), and conversely, teachers like Chiron.

Centauromachy
The Centaurs are best known for their fight with the Lapiths who, according to one origin myth, would have been cousins to the centaurs. The battle, called the Centauromachy, was caused by the centaurs' attempt to carry off Hippodamia and the rest of the Lapith women on the day of Hippodamia's marriage to Pirithous, who was the king of the Lapithae and a son of Ixion. Theseus, a hero and founder of cities, who happened to be present, threw the balance in favour of the Lapiths by assisting Pirithous in the battle. The Centaurs were driven off or destroyed. Another Lapith hero, Caeneus, who was invulnerable to weapons, was beaten into the earth by Centaurs wielding rocks and the branches of trees. In her article "The Centaur: Its History and Meaning in Human Culture", Elizabeth Lawrence claims that the contests between the centaurs and the Lapiths typify the struggle between civilization and barbarism.

The Centauromachy is most famously portrayed in the metopes of the Parthenon by Phidias and in the Battle of the Centaurs, a relief by Michelangelo.

List of centaurs

 * Abas, attended Pirithous' wedding, fought against the Lapiths and fled.
 * Agrius, repelled by Heracles in a fight.
 * Amphion, tried to plunder Pholus of his wine and was killed by Heracles.
 * Amycus, son of Ophion. He attended Pirithous' wedding and fought against the Lapiths. Amycus was killed by Pelates.
 * Anchius, repelled by Heracles when he tried to steal the wine of Pholus.
 * Antimachus, attended Pirithous' wedding, fought in the battle against the Lapiths and was killed by Caeneus.
 * Aphareus, killed by Theseus in the fight at Pirithous' wedding.
 * Aphidas, killed by Phorbas in the fight at Pirithous' wedding.
 * Arctus, attended Pirithous' wedding and fought against the Lapiths.
 * Areos, attended Pirithous' wedding and fought against the Lapiths.
 * Argius, killed by Heracles when he tried to steal the wine of Pholus.
 * Asbolus, an augur who had attempted in vain to dissuade his friends from engaging in battle against the Lapiths at Pirithous' wedding.
 * Bienor, attended Pirithous' wedding, fought in the battle against the Lapiths and was killed by Theseus.
 * Bromus, attended Pirithous' wedding, fought in the battle against the Lapiths and was killed by Caeneus.
 * Chiron, the son of Cronus and Philyra.
 * Chromis, attended Pirithous' wedding, fought in the battle against the Lapiths and was killed by Pirithous.
 * Chthonius, attended Pirithous' wedding, fought in the battle against the Lapiths and was killed by Nestor.
 * Clanis, attended Pirithous' wedding, fought in the battle against the Lapiths and was killed by Peleus.
 * Crenaeus, attended Pirithous' wedding, fought in the battle against the Lapiths and was killed by Dryas.
 * Cyllarus, attended Pirithous' wedding, fought in the battle against the Lapiths. Killed by a javelin thrown from an unknown hand. He was married to Hylonome.
 * Daphnis, tried to plunder Pholus of his wine and was killed by Heracles.
 * Demoleon, attended Pirithous' wedding, fought in the battle against the Lapiths and was killed by Peleus.
 * Dictys, attended Pirithous' wedding, fought in the battle against the Lapiths and was killed by Pirithous.
 * Dorylas, attended Pirithous' wedding, fought in the battle against the Lapiths and was killed by Peleus.
 * Doupon, tried to plunder Pholus of his wine and was killed by Heracles.
 * Dryalus, son of Peuceus who attended Pirithous' wedding and fought against the Lapiths.
 * Echeclus, attended Pirithous' wedding, fought in the battle against the Lapiths and was killed by Ampyx.
 * Elatus, tried to plunder Pholus of his wine. Heracles shot an arrow at him, which, passing through his arm, stuck in the knee of Chiron.
 * Elymus, attended Pirithous' wedding, fought in the battle against the Lapiths and was killed by Caeneus.
 * Eurynomus, fought against the Lapiths at Pirithous' wedding. Killed by Dryas. Sebastiano Ricci 045.jpg, of centaurs at the marriage of Pirithous, king of the Lapithae|296x296px]]
 * Eurytion, acted in an insulting manner towards Hippolyte when she was being joined in marriage to Azan in the house of Pirithous. He was killed by Heracles.
 * Eurytus, the wildest of the wild Centaurs. He started the fight at Pirithous' wedding and was killed by Theseus.
 * Gryneus, fought against the Lapiths at Pirithous' wedding and was killed by Exadius.
 * Helops, attended Pirithous' wedding and fought in the battle against the Lapiths. While fleeing from Pirithous, he fell from a precipice into the top of a tree and impaled his body.
 * Hippasus, fought against the Lapiths at Pirithous' wedding. Killed by Theseus.
 * Hippotion, another Centaur, killed by Heracles when he tried to steal the wine of Pholus.
 * Hodites, fought against the Lapiths at Pirithous' wedding. Killed by Mopsus.
 * Homadus, tried to plunder Pholus of his wine. Some time after he attempted to rape Alcyone, a granddaughter of Perseus. He got killed in Arcadia.
 * Hylaeus, tried to rape Atalanta but was shot by her (same thing happened to Rhoecus).
 * Hylaeus, killed by Heracles under unknown circumstances.
 * Hylaeus, followed Dionysus in his Indian campaign and was killed by Orontes, an Indian General.
 * Hyles, attended Pirithous' wedding, fought in the battle against the Lapiths and was killed by Peleus.
 * Hylonome, attended Pirithous' wedding together with her lover Cyllarus. Having seen the latter dead, she threw herself upon the spear which had killed him.
 * Imbreus, fought against the Lapiths at Pirithous' wedding and was killed by Dryas.
 * Iphinous, fought against the Lapiths at Pirithous' wedding and was killed by Peleus.
 * Isoples, killed by Heracles when he tried to steal the wine of Pholus.
 * Latreus, fought against the Lapiths at Pirithous' wedding and was killed by Caeneus.
 * Lycabas, attended Pirithous' wedding, fought against the Lapiths and fled.
 * Lycidas, fought against the Lapiths at Pirithous' wedding and was killed by Dryas.
 * Lycopes, fought against the Lapiths at Pirithous' wedding and was killed by Theseus.
 * Lycus, fought against the Lapiths at Pirithous' wedding was killed by Pirithous.
 * Medon, attended Pirithous' wedding, fought against the Lapiths and fled.
 * Melanchaetes, killed by Heracles when he tried to steal the wine of Pholus.
 * Melaneus, attended Pirithous' wedding, fought against the Lapiths and fled.
 * Mermerus, wounded by the Lapiths at Pirithous' wedding and fled.
 * Mimas, attended Pirithous' wedding and fought against the Lapiths.
 * Monychus, attended Pirithous' wedding and fought in the battle against the Lapiths. He was conquered by Nestor, mounted on his unwilling back.
 * Nedymnus, fought against the Lapiths at Pirithous' wedding. Killed by Theseus.
 * Nessus, fled during the fight with the Lapiths at Pirithous' wedding. Later he attempted to rape Deianira and before dying gave her a charm which resulted in the death of Heracles. He was killed by the latter.
 * Ophion, father of Amycus.
 * Oreius, killed by Heracles when he tried to steal the wine of Pholus.
 * Orneus, attended Pirithous' wedding fought against the Lapiths and fled.
 * Perimedes, son of Peuceus and attended Pirithous' wedding and fought against the Lapiths.
 * Petraeus, fought against the Lapiths at Pirithous' wedding and was killed by Pirithous.
 * Peuceus, father of Perimedes and Dryalus.
 * Phaecomes, fought against the Lapiths at Pirithous' wedding and was killed by Nestor.
 * Phlegraeus, fought against the Lapiths at Pirithous' wedding and was killed by Peleus.
 * Pholus Achilleus Lyra.jpg teaching Achilles how to play the lyre, a Roman fresco from Herculaneum, 1st century AD.|305x305px]]
 * Phrixus, killed by Heracles when he tried to steal the wine of Pholus.
 * Pisenor, attended Pirithous' wedding, fought against the Lapiths and fled.
 * Pylenor, having been wounded by Heracles washed himself in the river Anigrus, thus providing the river with a peculiar odor.
 * Pyracmus, fought against the Lapiths at Pirithous' wedding and was killed by Caeneus.
 * Pyraethus, fought against the Lapiths at Pirithous' wedding and was killed by Periphas.
 * Rhoecus, He also tried to rape Atalanta and was killed by her.
 * Rhoetus, fought against the Lapiths at Pirithous' wedding and was killed by Dryas.
 * Ripheus, fought against the Lapiths at Pirithous' wedding and was killed by Theseus.
 * Styphelus, fought against the Lapiths at Pirithous' wedding and was killed by Caeneus.
 * Teleboas, fought against the Lapiths at Pirithous' wedding and was killed by Nestor.
 * Thaumas, attended Pirithous' wedding, fought against the Lapiths and fled.
 * Thereus, this Centaur used to catch bears and carry them home alive and struggling. Attended Pirithous' wedding and fought in the battle against the Lapiths. Killed by Theseus.
 * Thereus, killed by Heracles when he tried to steal the wine of Pholus.
 * Ureus, attended Pirithous' wedding and fought against the Lapiths.

Origin of the myth
The most common theory holds that the idea of centaurs came from the first reaction of a non-riding culture, as in the Minoan Aegean world, to nomads who were mounted on horses. The theory suggests that such riders would appear as half-man, half-animal. Bernal Díaz del Castillo reported that the Aztecs also had this misapprehension about Spanish cavalrymen. The Lapith tribe of Thessaly, who were the kinsmen of the Centaurs in myth, were described as the inventors of horse-riding by Greek writers. The Thessalian tribes also claimed their horse breeds were descended from the centaurs.

Robert Graves (relying on the work of Georges Dumézil, who argued for tracing the centaurs back to the Indian Gandharva), speculated that the centaurs were a dimly remembered, pre-Hellenic fraternal earth cult who had the horse as a totem. A similar theory was incorporated into Mary Renault's The Bull from the Sea.

Female centaurs
Though female centaurs, called centaurides or centauresses, are not mentioned in early Greek literature and art, they do appear occasionally in later antiquity. A Macedonian mosaic of the 4th century BC is one of the earliest examples of the centauress in art. Ovid also mentions a centauress named Hylonome who committed suicide when her husband Cyllarus was killed in the war with the Lapiths.

India
The Kalibangan cylinder seal, dated to be around 2600–1900 BC, found at the site of Indus-Valley civilization shows a battle between men in the presence of centaur-like creatures. Other sources claim the creatures represented are actually half human and half tigers, later evolving into the Hindu Goddess of War. These seals are also evidence of Indus-Mesopotamia relations in the 3rd millennium BC.

In a popular legend associated with Pazhaya Sreekanteswaram Temple in Thiruvananthapuram, the curse of a saintly Brahmin transformed a handsome Yadava prince into a creature having a horse's body and the prince's head, arms, and torso in place of the head and neck of the horse.

Kinnaras, another half-man, half-horse mythical creature from Indian mythology, appeared in various ancient texts, arts, and sculptures from all around India. It is shown as a horse with the torso of a man where the horse's head would be, and is similar to a Greek centaur.

Russia
A centaur-like half-human, half-equine creature called Polkan appeared in Russian folk art and lubok prints of the 17th–19th centuries. Polkan is originally based on Pulicane, a half-dog from Andrea da Barberino's poem I Reali di Francia, which was once popular in the Slavonic world in prosaic translations.

Classical art
The extensive Mycenaean pottery found at Ugarit included two fragmentary Mycenaean terracotta figures which have been tentatively identified as centaurs. This finding suggests a Bronze Age origin for these creatures of myth. A painted terracotta centaur was found in the "Hero's tomb" at Lefkandi, and by the Geometric period, centaurs figure among the first representational figures painted on Greek pottery. An often-published Geometric period bronze of a warrior face-to-face with a centaur is at the Metropolitan Museum of Art.

In Greek art of the Archaic period, centaurs are depicted in three different forms.

 * Some centaurs are depicted with a human torso attached to the body of a horse at the withers, where the horse's neck would be; this form, designated "Class A" by Professor Paul Baur, later became standard.
 * "Class B" centaurs are depicted with a human body and legs joined at the waist to the hindquarters of a horse; in some cases centaurs of both Class A and Class B appear together.
 * A third type, designated "Class C", depicts centaurs with human forelegs terminating in hooves. Baur describes this as an apparent development of Aeolic art, which never became particularly widespread.

There are also paintings and motifs on amphorae and Dipylon cups which depict winged centaurs.

Centaurs were also frequently depicted in Roman art. One example is the pair of centaurs drawing the chariot of Constantine the Great and his family in the Great Cameo of Constantine (circa AD 314–16), which embodies wholly pagan imagery, and contrasts sharply with the popular image of Constantine as the patron of early Christianity.

Medieval art

Centaurs preserved a Dionysian connection in the 12th-century Romanesque carved capitals of Mozac Abbey in the Auvergne. Other similar capitals depict harvesters, boys riding goats (a further Dionysiac theme), and griffins guarding the chalice that held the wine. Centaurs are also shown on a number of Pictish carved stones from north-east Scotland erected in the 8th–9th centuries AD (e.g., at Meigle, Perthshire). Though outside the limits of the Roman Empire, these depictions appear to be derived from Classical prototypes.

Modern art
The John C. Hodges library at The University of Tennessee hosts a permanent exhibit of a "Centaur from Volos" in its library. The exhibit, made by sculptor Bill Willers by combining a study human skeleton with the skeleton of a Shetland pony, is entitled "Do you believe in Centaurs?". According to the exhibitors, it was meant to mislead students in order to make them more critically aware.

Cartography
Depictions of centaurs in a mythical land located south beyond the world's known continents appear on a map by Urbano Monti from 1587, sometimes called Monti's Planisphere.

In heraldry
Centaurs are common in European heraldry, although more frequent in continental than in British arms. A centaur holding a bow is referred to as a sagittarius.

Classical literature
Jerome's version of the Life of St Anthony the Great, written by Athanasius of Alexandria about the hermit monk of Egypt, was widely disseminated in the Middle Ages; it relates Anthony's encounter with a centaur who challenged the saint, but was forced to admit that the old gods had been overthrown. The episode was often depicted in The Meeting of St Anthony Abbot and St Paul the Hermit by the painter Stefano di Giovanni, who was known as "Sassetta". Of the two episodic depictions of the hermit Anthony's travel to greet the hermit Paul, one is his encounter with the demonic figure of a centaur along the pathway in a wood.

Lucretius, in his first-century BC philosophical poem On the Nature of Things, denied the existence of centaurs, based on the differing rates of growth of human and equine anatomies. Specifically, he states that at the age of three years, horses are in the prime of their life while humans at the same age are still little more than babies, making hybrid animals impossible.

Medieval literature
Centaurs are among the creatures which 14th-century Italian poet Dante placed as guardians in his Inferno. In Canto XII, Dante and his guide Virgil meet a band led by Chiron and Pholus, guarding the bank of Phlegethon in the seventh circle of Hell, a river of boiling blood in which the violent against their neighbours are immersed, shooting arrows into any who move to a shallower spot than their allotted station. The two poets are treated with courtesy, and Nessus guides them to a ford. In Canto XXIV, in the eighth circle, in Bolgia 7, a ditch where thieves are confined, they meet but do not converse with Cacus (who is a giant in the ancient sources), wreathed in serpents and with a fire-breathing dragon on his shoulders, arriving to punish a sinner who has just cursed God. In his Purgatorio, an unseen spirit on the sixth terrace cites the centaurs ("the drunken double-breasted ones who fought Theseus") as examples of the sin of gluttony.

Modern day literature
C.S. Lewis' The Chronicles of Narnia series depicts centaurs as the wisest and noblest of creatures. Narnian Centaurs are gifted at stargazing, prophecy, healing, and warfare; a fierce and valiant race always faithful to the High King Aslan the Lion.

In J.K. Rowling's Harry Potter series, centaurs live in the Forbidden Forest close to Hogwarts, preferring to avoid contact with humans. They live in societies called herds and are skilled at archery, healing, and astrology, but like in the original myths, they are known to have some wild and barbarous tendencies.

With the exception of Chiron, the centaurs in Rick Riordan's Percy Jackson & the Olympians are seen as wild party-goers who use a lot of American slang. Chiron retains his mythological role as a trainer of heroes and is skilled in archery. In Riordan's subsequent series, Heroes of Olympus, another group of centaurs are depicted with more animalistic features (such as horns) and appear as villains, serving the Gigantes.

Philip Jose Farmer's World of Tiers series (1965) includes centaurs, called Half-Horses or Hoi Kentauroi. His creations address several of the metabolic problems of such creatures—how could the human mouth and nose intake sufficient air to sustain both itself and the horse body and, similarly, how could the human ingest sufficient food to sustain both parts.

Brandon Mull's Fablehaven series features centaurs that live in an area called Grunhold. The centaurs are portrayed as a proud, elitist group of beings that consider themselves superior to all other creatures. The fourth book also has a variation on the species called an Alcetaur, which is part man, part moose.

The myth of the centaur appears in John Updike's novel The Centaur. The author depicts a rural Pennsylvanian town as seen through the optics of the myth of the centaur. An unknown and marginalized local school teacher, just like the mythological Chiron did for Prometheus, gave up his life for the future of his son who had chosen to be an independent artist in New York.

title: Centaur


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Chemotaxis

Chemotaxis (from chemo- + taxis) is the movement of an organism or entity in response to a chemical stimulus. Somatic cells, bacteria, and other single-cell or multicellular organisms direct their movements according to certain chemicals in their environment. This is important for bacteria to find food (e.g., glucose) by swimming toward the highest concentration of food molecules, or to flee from poisons (e.g., phenol). In multicellular organisms, chemotaxis is critical to early development (e.g., movement of sperm towards the egg during fertilization) and development (e.g., migration of neurons or lymphocytes) as well as in normal function and health (e.g., migration of leukocytes during injury or infection). In addition, it has been recognized that mechanisms that allow chemotaxis in animals can be subverted during cancer metastasis, and the aberrant change of the overall property of these networks, which control chemotaxis, can lead to carcinogenesis. The aberrant chemotaxis of leukocytes and lymphocytes also contribute to inflammatory diseases such as atherosclerosis, asthma, and arthritis. Sub-cellular components, such as the polarity patch generated by mating yeast, may also display chemotactic behavior.

Positive chemotaxis occurs if the movement is toward a higher concentration of the chemical in question; negative chemotaxis if the movement is in the opposite direction. Chemically prompted kinesis (randomly directed or nondirectional) can be called chemokinesis.

History of chemotaxis research
Although migration of cells was detected from the early days of the development of microscopy by Leeuwenhoek, a Caltech lecture regarding chemotaxis propounds that 'erudite description of chemotaxis was only first made by T. W. Engelmann (1881) and W. F. Pfeffer (1884) in bacteria, and H. S. Jennings (1906) in ciliates'. The Nobel Prize laureate I. Metchnikoff also contributed to the study of the field during 1882 to 1886, with investigations of the process as an initial step of phagocytosis. The significance of chemotaxis in biology and clinical pathology was widely accepted in the 1930s, and the most fundamental definitions underlying the phenomenon were drafted by this time. The most important aspects in quality control of chemotaxis assays were described by H. Harris in the 1950s. In the 1960s and 1970s, the revolution of modern cell biology and biochemistry provided a series of novel techniques that became available to investigate the migratory responder cells and subcellular fractions responsible for chemotactic activity. The availability of this technology led to the discovery of C5a, a major chemotactic factor involved in acute inflammation. The pioneering works of J. Adler modernized Pfeffer's capillary assay and represented a significant turning point in understanding the whole process of intracellular signal transduction of bacteria.

Bacterial chemotaxis—general characteristics
Some bacteria, such as E. coli, have several flagella per cell (4–10 typically). These can rotate in two ways: The directions of rotation are given for an observer outside the cell looking down the flagella toward the cell.
 * 1) Counter-clockwise rotation aligns the flagella into a single rotating bundle, causing the bacterium to swim in a straight line; and
 * 2) Clockwise rotation breaks the flagella bundle apart such that each flagellum points in a different direction, causing the bacterium to tumble in place.

Behavior
The overall movement of a bacterium is the result of alternating tumble and swim phases, called run-and-tumble motion. As a result, the trajectory of a bacterium swimming in a uniform environment will form a random walk with relatively straight swims interrupted by random tumbles that reorient the bacterium. Bacteria such as E. coli are unable to choose the direction in which they swim, and are unable to swim in a straight line for more than a few seconds due to rotational diffusion; in other words, bacteria "forget" the direction in which they are going. By repeatedly evaluating their course, and adjusting if they are moving in the wrong direction, bacteria can direct their random walk motion toward favorable locations.

In the presence of a chemical gradient bacteria will chemotax, or direct their overall motion based on the gradient. If the bacterium senses that it is moving in the correct direction (toward attractant/away from repellent), it will keep swimming in a straight line for a longer time before tumbling; however, if it is moving in the wrong direction, it will tumble sooner. Bacteria like E. coli use temporal sensing to decide whether their situation is improving or not, and in this way, find the location with the highest concentration of attractant, detecting even small differences in concentration.

This biased random walk is a result of simply choosing between two methods of random movement; namely tumbling and straight swimming. The helical nature of the individual flagellar filament is critical for this movement to occur. The protein structure that makes up the flagellar filament, flagellin, is conserved among all flagellated bacteria. Vertebrates seem to have taken advantage of this fact by possessing an immune receptor (TLR5) designed to recognize this conserved protein.

As in many instances in biology, there are bacteria that do not follow this rule. Many bacteria, such as Vibrio, are monoflagellated and have a single flagellum at one pole of the cell. Their method of chemotaxis is different. Others possess a single flagellum that is kept inside the cell wall. These bacteria move by spinning the whole cell, which is shaped like a corkscrew.

Signal transduction
Chemical gradients are sensed through multiple transmembrane receptors, called methyl-accepting chemotaxis proteins (MCPs), which vary in the molecules that they detect. Thousands of MCP receptors are known to be encoded across the bacterial kingdom. These receptors may bind attractants or repellents directly or indirectly through interaction with proteins of periplasmatic space. The signals from these receptors are transmitted across the plasma membrane into the cytosol, where Che proteins are activated. The Che proteins alter the tumbling frequency, and alter the receptors.

Flagellum regulation
The proteins CheW and CheA bind to the receptor. The absence of receptor activation results in autophosphorylation in the histidine kinase, CheA, at a single highly conserved histidine residue. CheA, in turn, transfers phosphoryl groups to conserved aspartate residues in the response regulators CheB and CheY; CheA is a histidine kinase and it does not actively transfer the phosphoryl group, rather, the response regulator CheB takes the phosphoryl group from CheA. This mechanism of signal transduction is called a two-component system, and it is a common form of signal transduction in bacteria. CheY induces tumbling by interacting with the flagellar switch protein FliM, inducing a change from counter-clockwise to clockwise rotation of the flagellum. Change in the rotation state of a single flagellum can disrupt the entire flagella bundle and cause a tumble.

Receptor regulation
CheB, when activated by CheA, acts as a methylesterase, removing methyl groups from glutamate residues on the cytosolic side of the receptor; it works antagonistically with CheR, a methyltransferase, which adds methyl residues to the same glutamate residues. If the level of an attractant remains high, the level of phosphorylation of CheA (and, therefore, CheY and CheB) will remain low, the cell will swim smoothly, and the level of methylation of the MCPs will increase (because CheB-P is not present to demethylate). The MCPs no longer respond to the attractant when they are fully methylated; therefore, even though the level of attractant might remain high, the level of CheA-P (and CheB-P) increases and the cell begins to tumble. The MCPs can be demethylated by CheB-P, and, when this happens, the receptors can once again respond to attractants. The situation is the opposite with regard to repellents: fully methylated MCPs respond best to repellents, while least-methylated MCPs respond worst to repellents. This regulation allows the bacterium to 'remember' chemical concentrations from the recent past, a few seconds, and compare them to those it is currently experiencing, thus 'know' whether it is traveling up or down a gradient. that bacteria have to chemical gradients, other mechanisms are involved in increasing the absolute value of the sensitivity on a given background. Well-established examples are the ultra-sensitive response of the motor to the CheY-P signal, and the clustering of chemoreceptors.

Chemoattractants and chemorepellents
Chemoattractants and chemorepellents are inorganic or organic substances possessing chemotaxis-inducer effect in motile cells. These chemotactic ligands create chemical concentration gradients that organisms, prokaryotic and eukaryotic, move toward or away from, respectively. Effects of chemoattractants are elicited via chemoreceptors such as methyl-accepting chemotaxis proteins (MCP). MCPs in E.coli include Tar, Tsr, Trg and Tap. Chemoattracttants to Trg include ribose and galactose with phenol as a chemorepellent. Tap and Tsr recognize dipeptides and serine as chemoattractants, respectively.

Chemoattractants or chemorepellents bind MCPs at its extracellular domain; an intracellular signaling domain relays the changes in concentration of these chemotactic ligands to downstream proteins like that of CheA which then relays this signal to flagellar motors via phosphorylated CheY (CheY-P). CheY-P can then control flagellar rotation influencing the direction of cell motility.

For E.coli, S. meliloti, and R. spheroides, the binding of chemoattractants to MCPs inhibit CheA and therefore CheY-P activity, resulting in smooth runs, but for B. substilis, CheA activity increases. Methylation events in E.coli cause MCPs to have lower affinity to chemoattractants which causes increased activity of CheA and CheY-P resulting in tumbles. In this way cells are able to adapt to the immediate chemoattractant concentration and detect further changes to modulate cell motility.

Chemoattractants in eukaryotes are well characterized for immune cells. Formyl peptides, such as fMLF, attract leukocytes such as neutrophils and macrophages, causing movement toward infection sites. Non-acylated methioninyl peptides do not act as chemoattractants to neutrophils and macrophages. Leukocytes also move toward chemoattractants C5a, a complement component, and pathogen-specific ligands on bacteria.

Mechanisms concerning chemorepellents are less known than chemoattractants. Although chemorepellents work to confer an avoidance response in organisms, Tetrahymena thermophila adapt to a chemorepellent, Netrin-1 peptide, within 10 minutes of exposure; however, exposure to chemorepellents such as GTP, PACAP-38, and nociceptin show no such adaptations. GTP and ATP are chemorepellents in micro-molar concentrations to both Tetrahymena and Paramecium. These organisms avoid these molecules by producing avoiding reactions to re-orient themselves away from the gradient.

Eukaryotic chemotaxis
The mechanism of chemotaxis that eukaryotic cells employ is quite different from that in the bacteria E. coli; however, sensing of chemical gradients is still a crucial step in the process. Due to their small size and other biophysical constraints, E. coli cannot directly detect a concentration gradient. Instead, they employ temporal gradient sensing, where they move over larger distances several times their own width and measure the rate at which perceived chemical concentration changes.

Eukaryotic cells are much larger than prokaryotes and have receptors embedded uniformly throughout the cell membrane. Eukaryotic chemotaxis involves detecting a concentration gradient spatially by comparing the asymmetric activation of these receptors at the different ends of the cell. Activation of these receptors results in migration towards chemoattractants, or away from chemorepellants. In mating yeast, which are non-motile, patches of polarity proteins on the cell cortex can relocate in a chemotactic fashion up pheromone gradients.

It has also been shown that both prokaryotic and eukaryotic cells are capable of chemotactic memory. In prokaryotes, this mechanism involves the methylation of receptors called methyl-accepting chemotaxis proteins (MCPs). This results in their desensitization and allows prokaryotes to "remember" and adapt to a chemical gradient. In contrast, chemotactic memory in eukaryotes can be explained by the Local Excitation Global Inhibition (LEGI) model. LEGI involves the balance between a fast excitation and delayed inhibition which controls downstream signaling such as Ras activation and PIP3 production.

Levels of receptors, intracellular signalling pathways and the effector mechanisms all represent diverse, eukaryotic-type components. In eukaryotic unicellular cells, amoeboid movement and cilium or the eukaryotic flagellum are the main effectors (e.g., Amoeba or Tetrahymena). Some eukaryotic cells of higher vertebrate origin, such as immune cells also move to where they need to be. Besides immune competent cells (granulocyte, monocyte, lymphocyte) a large group of cells—considered previously to be fixed into tissues—are also motile in special physiological (e.g., mast cell, fibroblast, endothelial cells) or pathological conditions (e.g., metastases). Chemotaxis has high significance in the early phases of embryogenesis as development of germ layers is guided by gradients of signal molecules.

Motility
Unlike motility in bacterial chemotaxis, the mechanism by which eukaryotic cells physically move is unclear. There appear to be mechanisms by which an external chemotactic gradient is sensed and turned into an intracellular Ras and PIP3 gradients, which results in a gradient and the activation of a signaling pathway, culminating in the polymerisation of actin filaments. The growing distal end of actin filaments develops connections with the internal surface of the plasma membrane via different sets of peptides and results in the formation of anterior pseudopods and posterior uropods. Cilia of eukaryotic cells can also produce chemotaxis; in this case, it is mainly a Ca2+-dependent induction of the microtubular system of the basal body and the beat of the 9 + 2 microtubules within cilia. The orchestrated beating of hundreds of cilia is synchronized by a submembranous system built between basal bodies. The details of the signaling pathways are still not totally clear.

Chemotaxis-related migratory responses
Chemotaxis refers to the directional migration of cells in response to chemical gradients; several variations of chemical-induced migration exist as listed below.
 * Chemokinesis refers to an increase in cellular motility in response to chemicals in the surrounding environment. Unlike chemotaxis, the migration stimulated by chemokinesis lacks directionality, and instead increases environmental scanning behaviors.
 * In haptotaxis the gradient of the chemoattractant is expressed or bound on a surface, in contrast to the classical model of chemotaxis, in which the gradient develops in a soluble fluid. The most common biologically active haptotactic surface is the extracellular matrix (ECM); the presence of bound ligands is responsible for induction of transendothelial migration and angiogenesis.
 * Necrotaxis embodies a special type of chemotaxis when the chemoattractant molecules are released from necrotic or apoptotic cells. Depending on the chemical character of released substances, necrotaxis can accumulate or repel cells, which underlines the pathophysiological significance of this phenomenon.

Receptors
In general, eukaryotic cells sense the presence of chemotactic stimuli through the use of 7-transmembrane (or serpentine) heterotrimeric G-protein-coupled receptors, a class representing a significant portion of the genome. Some members of this gene superfamily are used in eyesight (rhodopsins) as well as in olfaction (smelling). The main classes of chemotaxis receptors are triggered by: However, induction of a wide set of membrane receptors (e.g., cyclic nucleotides, amino acids, insulin, vasoactive peptides) also elicit migration of the cell.
 * Formyl peptides - formyl peptide receptors (FPR),
 * Chemokines - chemokine receptors (CCR or CXCR), and
 * Leukotrienes - leukotriene receptors (BLT).

Chemotactic selection
While some chemotaxis receptors are expressed in the surface membrane with long-term characteristics, as they are determined genetically, others have short-term dynamics, as they are assembled ad hoc in the presence of the ligand. The diverse features of the chemotaxis receptors and ligands allows for the possibility of selecting chemotactic responder cells with a simple chemotaxis assay By chemotactic selection, we can determine whether a still-uncharacterized molecule acts via the long- or the short-term receptor pathway. The term chemotactic selection is also used to designate a technique that separates eukaryotic or prokaryotic cells according to their chemotactic responsiveness to selector ligands.

Chemotactic ligands
The number of molecules capable of eliciting chemotactic responses is relatively high, and we can distinguish primary and secondary chemotactic molecules. The main groups of the primary ligands are as follows:
 * Formyl peptides are di-, tri-, tetrapeptides of bacterial origin, formylated on the N-terminus of the peptide. They are released from bacteria in vivo or after decomposition of the cell[ a typical member of this group is the N-formylmethionyl-leucyl-phenylalanine (abbreviated fMLF or fMLP). Bacterial fMLF is a key component of inflammation has characteristic chemoattractant effects in neutrophil granulocytes and monocytes. The chemotactic factor ligands and receptors related to formyl peptides are summarized in the related article, Formyl peptide receptors.
 * Complement 3a (C3a) and complement 5a (C5a) are intermediate products of the complement cascade. Their synthesis is joined to the three alternative pathways (classical, lectin-dependent, and alternative) of complement activation by a convertase enzyme. The main target cells of these derivatives are neutrophil granulocytes and monocytes as well.
 * Chemokines belong to a special class of cytokines; not only do their groups (C, CC, CXC, CX3C chemokines) represent structurally related molecules with a special arrangement of disulfide bridges but also their target cell specificity is diverse. CC chemokines act on monocytes (e.g., RANTES), and CXC chemokines are neutrophil granulocyte-specific (e.g., IL-8). Investigations of the three-dimensional structures of chemokines provided evidence that a characteristic composition of beta-sheets and an alpha helix provides expression of sequences required for interaction with the chemokine receptors. Formation of dimers and their increased biological activity was demonstrated by crystallography of several chemokines, e.g. IL-8.
 * Metabolites of polyunsaturated fatty acids
 * Leukotrienes are eicosanoid lipid mediators made by the metabolism of arachidonic acid by ALOX5 (also termed 5-lipoxygenase). Their most prominent member with chemotactic factor activity is leukotriene B4, which elicits adhesion, chemotaxis, and aggregation of leukocytes. The chemoattractant action of LTB4 is induced via either of two G protein–coupled receptors, BLT1 and BLT2, which are highly expressed in cells involved in inflammation and allergy.
 * The family of 5-Hydroxyicosatetraenoic acid eicosanoids are arachidonic acid metabolites also formed by ALOX5. Three members of the family form naturally and have prominent chemotactic activity. These, listed in order of decreasing potency, are: 5-oxo-eicosatetraenoic acid, 5-oxo-15-hydroxy-eicosatetraenoic acid, and 5-Hydroxyeicosatetraenoic acid. This family of agonists stimulates chemotactic responses in human eosinophils, neutrophils, and monocytes by binding to the Oxoeicosanoid receptor 1, which like the receptors for leukotriene B4, is a G protein-coupled receptor. Aside from the skin, neutrophils are the body's first line of defense against bacterial infections. After leaving nearby blood vessels, these cells recognize chemicals produced by bacteria in a cut or scratch and migrate "toward the smell".
 * 5-hydroxyeicosatrienoic acid and 5-oxoeicosatrienoic acid are metabolites of Mead acid (5Z,8Z,11Z-eicosatrirenoid acid); they stimulate leukocyte chemotaxis through the oxoeicosanoid receptor 1 with 5-oxoeicosatrienoic acid being as potent as its arachidonic acid-derived analog, 5-oxo-eicosatetraenoic acid, in stimulating human blood eosinophil and neutrophil chemotaxis.
 * 12-Hydroxyeicosatetraenoic acid is an eicosanoid metabolite of arachidonic acid made by ALOX12 which stimulates leukocyte chemotaxis through the leukotriene B4 receptor, BLT2.
 * Prostaglandin D2 is an eicosanoid metabolite of arachidononic acid made by cyclooxygenase 1 or cyclooxygenase 2 that stimulates chemotaxis through the Prostaglandin DP2 receptor. It elicits chemotactic responses in eosinophils, basophils, and T helper cells of the Th2 subtype.
 * 12-Hydroxyheptadecatrienoic acid is a non-eicosanoid metabolite of arachidonic acid made by cyclooxygenase 1 or cyclooxygenase 2 that stimulates leukocyte chemotaxis though the leukotriene B4 receptor, BLT2.
 * 15-oxo-eicosatetraenoic acid is an eicosanoid metabolite of arachidonic acid made my ALOX15; it has weak chemotactic activity for human monocytes (sees 15-Hydroxyeicosatetraenoic acid). The receptor or other mechanism by which this metabolite stimulates chemotaxis has not been elucidated.

Chemotactic range fitting
Chemotactic responses elicited by ligand-receptor interactions vary with the concentration of the ligand. Investigations of ligand families (e.g. amino acids or oligopeptides) demonstrates that chemoattractant activity occurs over a wide range, while chemorepellent activities have narrow ranges.

Clinical significance
A changed migratory potential of cells has relatively high importance in the development of several clinical symptoms and syndromes. Altered chemotactic activity of extracellular (e.g., Escherichia coli) or intracellular (e.g., Listeria monocytogenes) pathogens itself represents a significant clinical target. Modification of endogenous chemotactic ability of these microorganisms by pharmaceutical agents can decrease or inhibit the ratio of infections or spreading of infectious diseases. Apart from infections, there are some other diseases wherein impaired chemotaxis is the primary etiological factor, as in Chédiak–Higashi syndrome, where giant intracellular vesicles inhibit normal migration of cells.

Mathematical models
Several mathematical models of chemotaxis were developed depending on the type of
 * Migration (e.g., basic differences of bacterial swimming, movement of unicellular eukaryotes with cilia/flagellum and amoeboid migration)
 * Physico-chemical characteristics of the chemicals (e.g., diffusion) working as ligands
 * Biological characteristics of the ligands (attractant, neutral, and repellent molecules)
 * Assay systems applied to evaluate chemotaxis (see incubation times, development, and stability of concentration gradients)
 * Other environmental effects possessing direct or indirect influence on the migration (lighting, temperature, magnetic fields, etc.)

Although interactions of the factors listed above make the behavior of the solutions of mathematical models of chemotaxis rather complex, it is possible to describe the basic phenomenon of chemotaxis-driven motion in a straightforward way. Indeed, let us denote with $$ \varphi$$ the spatially non-uniform concentration of the chemo-attractant and $$\nabla \varphi$$ as its gradient. Then the chemotactic cellular flow (also called current) $$ {\bf J} $$ that is generated by the chemotaxis is linked to the above gradient by the law: $$where $$ C $$ is the spatial density of the cells and $$ \chi $$ is the so-called 'Chemotactic coefficient' - $$\chi$$ is often not constant, but a decreasing function of the chemo-attractant. For some quantity $$\rho$$ that is subject to total flux $${\bf J}$$ and generation/destruction term $$S$$, it is possible to formulate a continuity equation:

 * $$ {\partial \rho\over{\partial t}} + \nabla \cdot {\bf J} = S $$

where $$\nabla \cdot $$ is the divergence. This general equation applies to both the cell density and the chemo-attractant. Therefore, incorporating a diffusion flux into the total flux term, the interactions between these quantities are governed by a set of coupled reaction-diffusion partial differential equations describing the change in $$C$$ and $$\varphi$$: $$where $$f(C)$$ describes the growth in cell density, $$g(\varphi,C)$$ is the kinetics/source term for the chemo-attractant, and the diffusion coefficients for cell density and the chemo-attractant are respectively $$D_{C}$$ and $$D_{\varphi}$$.

Spatial ecology of soil microorganisms is a function of their chemotactic sensitivities towards substrate and fellow organisms. The chemotactic behavior of the bacteria was proven to lead to non-trivial population patterns even in the absence of environmental heterogeneities. The presence of structural pore scale heterogeneities has an extra impact on the emerging bacterial patterns.

Measurement of chemotaxis
A wide range of techniques is available to evaluate chemotactic activity of cells or the chemoattractant and chemorepellent character of ligands. The basic requirements of the measurement are as follows:
 * Concentration gradients can develop relatively quickly and persist for a long time in the system
 * Chemotactic and chemokinetic activities are distinguished
 * Migration of cells is free toward and away on the axis of the concentration gradient
 * Detected responses are the results of active migration of cells

Despite the fact that an ideal chemotaxis assay is still not available, there are several protocols and pieces of equipment that offer good correspondence with the conditions described above. The most commonly used are summarised in the table below:

Artificial chemotactic systems
Chemical robots that use artificial chemotaxis to navigate autonomously have been designed. Applications include targeted delivery of drugs in the body. More recently, enzyme molecules have also shown positive chemotactic behavior in the gradient of their substrates. The thermodynamically-favorable binding of enzymes to their specific substrates is recognized as the origin of enzymatic chemotaxis. Additionally, enzymes in cascades have also shown substrate-driven chemotactic aggregation.

Apart from active enzymes, non-reacting molecules also show chemotactic behavior. This has been demonstrated by using dye molecules that move directionally in gradients of polymer solution through favorable hydrophobic interactions.

title: Chemotaxis