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Ernst Stavro Blofeld
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Ernst Stavro Blofeld
James Bond character
Donald Pleasence as Blofeld in You Only Live Twice (1967).
Created by
Ian Fleming
Portrayed by
Anthony Dawson (uncredited)
Eric Pohlmann (voice, uncredited)
Donald Pleasence
Telly Savalas
Charles Gray
John Hollis (uncredited)
Robert Rietty (voice, uncredited)
Max von Sydow
Christoph Waltz
Information
Aliases
Franz Oberhauser
Affiliation
SPECTRE
Children
Nena Blofeld
Nationality
Polish
Classification
Supervillain
Henchmen
Rosa Klebb
Red Grant
Emilio Largo
Irma Bunt
Mr. Wint and Mr. Kidd
Le Chiffre
Mr. White
Dominic Greene
Raoul Silva
Mr. Hinx
Allies
Dr. Julius No
Ernst Stavro Blofeld is a fictional character and villain from the James Bond series of novels and films, created by Ian Fleming. A criminal mastermind with aspirations of world domination, he is the archenemy of the British Secret Service agent James Bond. Blofeld is head of the global criminal organisation SPECTRE and is commonly referred to by the codename Number 1 within this organisation. The character was originally written by Fleming as a physically massive and powerfully built man, standing around 6 ft 3 in (1.91 m) and weighing 21.6 stone (about 300 pounds (140 kg)), who had become flabby with a huge belly.[1]
Blofeld appears or is heard in three novels: Thunderball, On Her Majesty's Secret Service; and You Only Live Twice; as well as seven films from Eon Productions: From Russia with Love (1963); Thunderball (1965); You Only Live Twice (1967); On Her Majesty's Secret Service (1969); Diamonds Are Forever (1971); For Your Eyes Only (1981) (the pre-title sequence of which shows an unnamed character resembling him fall to his death); and Spectre (2015). He also appears in Never Say Never Again (1983), the non-Eon remake of Thunderball.
Blofeld has been played on screen by Donald Pleasence, Telly Savalas, Charles Gray, Max von Sydow, and Christoph Waltz, among others. It was initially a convention of the films not to show Blofeld's face, only a close-up of him stroking his white, blue-eyed Persian cat.
Many of Blofeld's characteristics have become tropes in popular fiction, representing the stock character of the supervillain, with the stroking of his white cat often retained as a parodic allusion to Blofeld's character, as seen in the Austin Powers film series with the character of Dr. Evil and his cat Mr. Bigglesworth, or in the cartoons Inspector Gadget with the character of Dr. Claw and Danger Mouse with the character of Baron Silas Greenback.
Contents
1 Character
2 In novels
3 In films
3.1 Table of film appearances
4 Video games
5 Homages
6 See also
7 References
Character[edit]
Ian Fleming includes information about Blofeld's background in his novel Thunderball. According to the novel, Blofeld was born on 28 May 1908 (which is also Fleming's birthday) in Gdingen, Imperial Germany (now Gdynia, Poland); his father Ernst George Blofeld was Polish, and his mother Maria Stavro Michelopoulos was Greek, hence the well-known Greek name Stavro.[2] After World War I, Blofeld became a Polish national. As a young man, he was well-versed in the social science disciplines, but also in the natural science and technology disciplines. He first graduated from the University of Warsaw with a degree in Political History and Economics, and then from the Warsaw University of Technology with a degree in Engineering and Radionics. He was then hired by the Polish Ministry of Posts and Telegraphs and appointed to a sensitive communication position, which he used for buying and selling stocks at the Warsaw Stock Exchange.[3]
Foreseeing World War II, Blofeld made copies of top-secret wires and sold them for cash to Nazi Germany. Before the German invasion of Poland in 1939, he destroyed all records of his existence, then moved first to Sweden, then to Turkey, where he worked for Turkish Radio and began to set up his own private intelligence organisation. During the war, he sold information to both sides. After the defeat of Erwin Rommel, he decided to back the Allied war effort, and was awarded numerous medals by the Allied powers after the war's end. Blofeld then moved temporarily to South America before founding SPECTRE.
In the John Gardner novel For Special Services, Blofeld is depicted as having had a daughter with a French mistress named Nena.
It is commonly believed that the name Blofeld was inspired by the English cricket commentator Henry Blofeld's father, with whom Fleming went to school.[4] Henry Blofeld offered on the BBC Radio 4 series Just a Minute that "Ian took my father's name as the name of the baddie."[5]
In novels[edit]
Blofeld has three appearances in Ian Fleming's novels. He first appears in a minor role as the leader of SPECTRE in the 1961 novel Thunderball. The plot that he formulates is carried out by his second-in-command Emilio Largo. Blofeld is described physically as a massive man, weighing roughly 20 stone (280 lb; 130 kg), who had previously been a champion amateur weightlifter in his youth before becoming obese in middle age; he has black crew-cut hair, black eyes (similar to those of Benito Mussolini), heavy eyelashes, a thin mouth, and long pointed hands and feet. He has violet-scented breath from chewing flavoured cachous (breath mints), a habit he adopts whenever he must deliver bad news. A meticulous planner of formidable intellect, he seems to be without conscience but not necessarily insane, and is motivated solely by financial gain. Blofeld's lifestyle is described in one chapter in Thunderball: "For the rest, he didn't smoke or drink and he had never been known to sleep with a member of either sex. He didn't even eat very much."
Blofeld is absent from the next novel, The Spy Who Loved Me, though its events take place while Bond is battling SPECTRE in North America. In On Her Majesty's Secret Service (1963), Bond learns that Blofeld has altered his appearance radically —he is now tall and thin; has reduced his weight to 12 stone (170 lb; 76 kg); sports long silver hair, a syphilitic infection on his nose, and no earlobes; he wears dark green tinted contact lenses to hide his distinctive eyes. Perhaps less calculating than previously, he is notably saddled with the exploitable weakness of snobbery about his assumed nobility, indicating that he is losing his sanity. He is hiding in Switzerland in the guise of the Comte Balthazar de Bleuchamp and Bond defeats his vindictive plans to destroy Britain's agricultural economy. In the final sequence of the novel, Blofeld gets revenge by murdering Bond's new wife, Tracy.
In You Only Live Twice, published in 1964, Blofeld returns and Bond finds him hiding in Japan under the alias Dr. Guntram Shatterhand. He has once again changed his appearance. He has put on some muscle, and has a gold-capped tooth, a fully healed nose, and a drooping grey mustache. Bond describes Blofeld on their confrontation as being "a big man, perhaps six foot three (190 cm), and powerfully built." It is indicated that Blofeld has by now gone completely insane, as he all but admits himself when Bond levels the accusation. Bond strangles him to death at the end of the novel. In both On Her Majesty's Secret Service and You Only Live Twice, Blofeld is aided in his schemes by Irma Bunt, who is clearly his lover in the latter, and posing as Shatterhand's wife. Bond incapacitates her in their Japanese castle base before it blows up, killing Bunt. The final mention of Blofeld is in the beginning of the next novel, The Man with the Golden Gun, published in 1965.
In films[edit]
Blofeld in (clockwise from upper-left) You Only Live Twice (Donald Pleasence), On Her Majesty’s Secret Service (Telly Savalas), Never Say Never Again (Max von Sydow), Spectre (Christoph Waltz), and Diamonds Are Forever (Charles Gray)
In the film series, Blofeld first appears in From Russia with Love, then in Thunderball. In these two appearances, his face is not seen, and only his lower body is visible as he strokes his trademark white cat.
Czech actor Jan Werich was originally cast by producer Harry Saltzman to play Blofeld in You Only Live Twice. Upon his arrival at the Pinewood set, both producer Albert R. Broccoli and director Lewis Gilbert felt that he was a bad choice, resembling a "poor, benevolent Santa Claus." Nonetheless, in an attempt to make the casting work, Gilbert continued filming. After five days, both Gilbert and Broccoli determined that Werich was not menacing enough, and recast Donald Pleasence in the role – the official excuse being that Werich was ill.[6]
In the third, fourth, and fifth appearances – You Only Live Twice, On Her Majesty’s Secret Service and Diamonds Are Forever – he is the primary antagonist, meeting Bond face-to-face. During the opening sequence of Diamonds Are Forever, he reveals to Bond that some of his men have undergone plastic surgery to become his decoy duplicates.
In the film version of On Her Majesty's Secret Service, he is not Tracy Bond's actual killer. He drives the car from which Irma Bunt (Ilse Steppat) fires the fatal shots at Tracy, minutes after she married Bond.
In a sixth appearance – in the pre-credit sequence of For Your Eyes Only – he is an anonymous, bald, wheelchair-bound villain trying to kill Bond once again. Blofeld remains unnamed and unlisted in the film’s end credits. The only clues to his identity are the trademark white cat,[7] similar clothes to his previous onscreen appearances, the dialogue indicating that he and Bond have met before, and the fact that the scene begins with Bond paying his respects at Tracy's grave, often considered by the producers as a means of providing an "immediate continuity link" in the event of a new actor taking the part of Bond (although this was Roger Moore's fifth appearance as Bond).[8] The anonymity of the villain was due to the legal dispute between Kevin McClory and Eon Productions over the Thunderball copyrights.[9]
Blofeld's appearance and personality change according to the personifying actor and the production.[10] He has a full head of black hair in From Russia With Love and Thunderball; a bald head and a facial dueling scar in You Only Live Twice; a bald head with no scar or earlobes in On Her Majesty's Secret Service; and silver-grey hair in Diamonds Are Forever. This metamorphosing matches Fleming’s literary portrayal of a master criminal who will go to great lengths to preserve his anonymity, including the use of plastic surgery.[10] He often wears a jacket without lapels, based loosely either on the Nehru jacket or on the Mao suit, a feature which is used in spoofs like the Austin Powers series, though in his early two appearances on film he wore a black business suit.
By November 2013, MGM and the McClory estate had formally settled the issue with Danjaq and MGM and acquired the full copyright to the characters and concepts of Blofeld and SPECTRE.[11] Blofeld consequently reappeared in Spectre, played by Christoph Waltz, and with a new background. In this continuity, he was born Franz Oberhauser, the son of Hannes Oberhauser, Bond's legal guardian after he was orphaned at the age of 11, making him and Bond adoptive brothers. As a young man, he murdered his father, staged his own death, and took on the alias of Ernst Stavro Blofeld, using his mother's maiden name. He then assembled the global criminal organisation known as Spectre. He is revealed to have been trying for years to destroy Bond, whom he resents for having been his father's favourite; he is thus revealed to have been the power behind the villains of the previous three films, who were all Spectre agents. At the end of the film, Bond takes him into custody after foiling his plan to take control of the world's national security intelligence data. This incarnation of Blofeld again wears a jacket without lapels, has a full head of hair, and is disfigured in the course of the film, echoing the Pleasence version's duelling scar. He is also briefly shown holding a white Persian cat.
Table of film appearances[edit]
Year
Film
Actor and notes
Status after the film concludes
1963 From Russia with Love Anthony Dawson as actor (only hands and back of head are seen), Eric Pohlmann as voice actor; the end credits list a question mark instead of an actor's name in the "Blofeld" field (however, he is only referred to as "Number One" in the film). Active/indirect involvement in the field. Never has any contact with Bond.
1965 Thunderball Anthony Dawson as actor (only hands and back of head are seen), Eric Pohlmann as voice actor,[8] both uncredited; end credits do not list Blofeld (maybe due to the fact that he is only referred to as "Number One" in the film). Active/indirect involvement in the field. Never has any contact with Bond.
1967 You Only Live Twice Donald Pleasence. Actor Jan Werich was originally cast, and some clips show his hands petting cat, and tuft of hair can be seen just above back of chair. Pleasence, with a fake scar on his face, replaced Werich during filming when the latter was deemed unsuited for the role. Blofeld has a facial scar in this film. Injured in his right hand by a shuriken; escapes.
1969 On Her Majesty’s Secret Service Telly Savalas; appears with earlobes removed to back up claim to a noble title. Escapes; he was the driver in the drive-by murder of Tracy Bond.
1971 Diamonds Are Forever Charles Gray; appears also as doubles, all created via plastic surgery. He attempts to escape in his mini-sub, but Bond gains control of it and crashes it into the control room.
1981 For Your Eyes Only John Hollis as actor, Robert Rietty as voice actor;[12] Blofeld's face is not seen close-up and his name isn't used due to the legal battle with Kevin McClory revealed in the film's DVD commentary. Dropped down a very large chimney from his own helicopter.
1983 Never Say Never Again (non-Eon) Max von Sydow. Appears in a small number of scenes. Active/indirect involvement in the field. Never has any direct contact with Bond.
2015 Spectre Christoph Waltz; he, identified as being of Austrian ancestry, is initially known by his birth name as "Franz Oberhauser", but reveals that he began using his mother's maiden name, "Blofeld", after faking his own death. Later on in the film, Bond disfigures him with Q's explosive watch, leaving him with a milky eye and a facial scar reminiscent of Donald Pleasance's portrayal of the character. Captured and arrested by Bond and MI6.
Video games[edit]
Blofeld appears in the 2004 video game GoldenEye: Rogue Agent, with the likeness of Donald Pleasence, voiced by Gideon Emery.
Blofeld is a playable multiplayer character in the 2010 video game GoldenEye 007 for the Wii, with the likeness of Charles Gray.[13]
Blofeld is one of the main characters in the 2012 video game 007 Legends, featured in the mission based on On Her Majesty's Secret Service, in which the character is an amalgamation of the first three actors appearing in the official film series. Throughout the game, he is voiced by Glenn Wrage. Legends, released prior to Blofeld's appearance in Spectre, portrays a feud with 007 that is not related to the film.
Homages[edit]
Some of Blofeld's characteristics have become supervillain tropes in popular fiction and media, including the parodies Dr. Claw (and his pet, M.A.D. Cat) from the Inspector Gadget animated series (1983–86), Team Rocket leader Giovanni and his Persian cat from the Pokémon television series and Dr. Evil (and his cat Mr. Bigglesworth) from the Austin Powers film series (1997–2002).[14] The 1999 The Powerpuff Girls episode "Cat Man Do" also features a supervillain with a cat, though it is the feline that turns out to be the criminal mastermind.[15] In The Penguins of Madagascar, the recurring villain Dr. Blowhole is a parody homage to Blofeld.
See also[edit]
James Bond portal
List of recurring characters in the James Bond film series
List of James Bond villains
References[edit]
Jump up ^ Buckton, Oliver (8 October 2015). Espionage in British Fiction and Film since 1900: The Changing Enemy. Lanham, Maryland: Lexington Books. p. 244. ISBN 978-1-4985-0484-3. Yet this suggestion of femininity in Blofeld's face is belied by his massive girth, his body "weighed about twenty stone. It had once been all muscle ... but in the past ten years it had softened and he had a vast belly that he concealed behind roomy trousers.
Jump up ^ Griswold, John (2006). Ian Fleming's James Bond: Annotations and Chronologies for Ian Fleming's Bond Stories. Bloomington, Indiana: AuthorHouse. p. 34. ISBN 978-1425931001.
Jump up ^ "The Bond Film Informant: Ernst Stavro Blofeld". Mjnewton.demon.co.uk. 28 May 2008. Archived from the original on 8 November 2016. Retrieved 29 October 2015.
Jump up ^ "BBC Radio 4 – Desert Island Discs, Henry Blofeld". Bbc.co.uk. 5 December 2003. Retrieved 29 October 2015.
Jump up ^ "BBC Radio 4 – Just a Minute, Series 67, Episode 3". Bbc.co.uk. 2 September 2013. Retrieved 29 October 2015.
Jump up ^ Production Staff (2000). Inside You Only Live Twice: An Original Documentary (Television). MGM Home Entertainment Inc.
Jump up ^ Williams, Max (July 24, 2016). "For Your Eyes Only: The Last Good Roger Moore James Bond Movie". Den of Geek. London, England: Dennis Publishing. Retrieved June 26, 2018.
^ Jump up to: a b Lane, Andy; Simpson, Paul (1999). The Bond Files: An Unofficial Guide to the World's Greatest Secret Agent. London, England: Virgin Books. ISBN 978-0753507124.
Jump up ^ Smith, Jim; Lavington, Stephen (2002). Bond Films. London, England: Virgin Books. p. 178. ISBN 9780753507094.
^ Jump up to: a b Unger, Melissa (9 November 2015). "What James Bond Mythology Tells Us About Spectre". Screen Rant. Retrieved 22 May 2017.
Jump up ^ Vejvoda, Jim (15 November 2013). "MGM, Danjaq Settle James Bond Rights Dispute With McClory Estate". IGN. San Francisco, California: j2 Global. Retrieved 16 November 2013.
Jump up ^ Cork, John; Stutz, Collin (2007). James Bond Encyclopedia. New York: DK Pub. p. 40. ISBN 9780756631673.
Jump up ^ Franich, Darren (August 25, 2017). "What the James Bond movies can learn from the GoldenEye video game". Entertainment Weekly. New York City: Meredith Corporation. Retrieved June 26, 2018.
Jump up ^ Martens, Todd (March 28, 2015). "Spectre trailer reinvents a famous Bond rival". Los Angeles Times. Los Angeles, California: Tronc. Retrieved November 7, 2015.
Jump up ^ "Cat Man Do". The Powerpuff Girls. Season 1. Episode 10. January 27, 1999. Cartoon Network.
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Digestion
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For the industrial process, see anaerobic digestion. For the treatment of precipitates in analytical chemistry, see Precipitation (chemistry) § Digestion.
Digestive system
Details
Latin
systema digestorium
Anatomical terminology
[edit on Wikidata]
Digestion is the breakdown of large insoluble food molecules into small water-soluble food molecules so that they can be absorbed into the watery blood plasma. In certain organisms, these smaller substances are absorbed through the small intestine into the blood stream. Digestion is a form of catabolism that is often divided into two processes based on how food is broken down: mechanical and chemical digestion. The term mechanical digestion refers to the physical breakdown of large pieces of food into smaller pieces which can subsequently be accessed by digestive enzymes. In chemical digestion, enzymes break down food into the small molecules the body can use.
In the human digestive system, food enters the mouth and mechanical digestion of the food starts by the action of mastication (chewing), a form of mechanical digestion, and the wetting contact of saliva. Saliva, a liquid secreted by the salivary glands, contains salivary amylase, an enzyme which starts the digestion of starch in the food; the saliva also contains mucus, which lubricates the food, and hydrogen carbonate, which provides the ideal conditions of pH (alkaline) for amylase to work. After undergoing mastication and starch digestion, the food will be in the form of a small, round slurry mass called a bolus. It will then travel down the esophagus and into the stomach by the action of peristalsis. Gastric juice in the stomach starts protein digestion. Gastric juice mainly contains hydrochloric acid and pepsin. As these two chemicals may damage the stomach wall, mucus is secreted by the stomach, providing a slimy layer that acts as a shield against the damaging effects of the chemicals. At the same time protein digestion is occurring, mechanical mixing occurs by peristalsis, which is waves of muscular contractions that move along the stomach wall. This allows the mass of food to further mix with the digestive enzymes.
After some time (typically 1–2 hours in humans, 4–6 hours in dogs, 3–4 hours in house cats),[citation needed] the resulting thick liquid is called chyme. When the pyloric sphincter valve opens, chyme enters the duodenum where it mixes with digestive enzymes from the pancreas and bile juice from the liver and then passes through the small intestine, in which digestion continues. When the chyme is fully digested, it is absorbed into the blood. 95% of absorption of nutrients occurs in the small intestine. Water and minerals are reabsorbed back into the blood in the colon (large intestine) where the pH is slightly acidic about 5.6 ~ 6.9. Some vitamins, such as biotin and vitamin K (K2MK7) produced by bacteria in the colon are also absorbed into the blood in the colon. Waste material is eliminated from the rectum during defecation.[1]
Contents
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1 Digestive system
1.1 Secretion systems
1.1.1 Channel transport system
1.1.2 Molecular syringe
1.1.3 Conjugation machinery
1.1.4 Release of outer membrane vesicles
1.2 Gastrovascular cavity
1.3 Phagosome
1.4 Specialised organs and behaviours
1.4.1 Beaks
1.4.2 Tongue
1.4.3 Teeth
1.4.4 Crop
1.4.5 Abomasum
1.4.6 Specialised behaviours
1.5 In earthworms
2 Overview of vertebrate digestion
3 Human digestion process
3.1 Neural and biochemical control mechanisms
4 Breakdown into nutrients
4.1 Protein digestion
4.2 Fat digestion
4.3 Carbohydrate digestion
4.4 DNA and RNA digestion
5 Non-destructive digestion
6 Digestive hormones
7 Significance of pH
8 See also
9 References
10 External links
Digestive system
Digestive systems take many forms. There is a fundamental distinction between internal and external digestion. External digestion developed earlier in evolutionary history, and most fungi still rely on it.[2] In this process, enzymes are secreted into the environment surrounding the organism, where they break down an organic material, and some of the products diffuse back to the organism. Animals have a tube (gastrointestinal tract) in which internal digestion occurs, which is more efficient because more of the broken down products can be captured, and the internal chemical environment can be more efficiently controlled.[3]
Some organisms, including nearly all spiders, simply secrete biotoxins and digestive chemicals (e.g., enzymes) into the extracellular environment prior to ingestion of the consequent "soup". In others, once potential nutrients or food is inside the organism, digestion can be conducted to a vesicle or a sac-like structure, through a tube, or through several specialized organs aimed at making the absorption of nutrients more efficient.
Schematic drawing of bacterial conjugation. 1- Donor cell produces pilus. 2- Pilus attaches to recipient cell, bringing the two cells together. 3- The mobile plasmid is nicked and a single strand of DNA is transferred to the recipient cell. 4- Both cells recircularize their plasmids, synthesize second strands, and reproduce pili; both cells are now viable donors.
Secretion systems
Main article: Secretion § Secretion in Gram negative bacteria
Bacteria use several systems to obtain nutrients from other organisms in the environments.
Channel transport system
In a channel transupport system, several proteins form a contiguous channel traversing the inner and outer membranes of the bacteria. It is a simple system, which consists of only three protein subunits: the ABC protein, membrane fusion protein (MFP), and outer membrane protein (OMP)[specify]. This secretion system transports various molecules, from ions, drugs, to proteins of various sizes (20 – 900 kDa). The molecules secreted vary in size from the small Escherichia coli peptide colicin V, (10 kDa) to the Pseudomonas fluorescens cell adhesion protein LapA of 900 kDa.[4]
Molecular syringe
A type III secretion system means that a molecular syringe is used through which a bacterium (e.g. certain types of Salmonella, Shigella, Yersinia) can inject nutrients into protist cells. One such mechanism was first discovered in Y. pestis and showed that toxins could be injected directly from the bacterial cytoplasm into the cytoplasm of its host's cells rather than simply be secreted into the extracellular medium.[5]
Conjugation machinery
The conjugation machinery of some bacteria (and archaeal flagella) is capable of transporting both DNA and proteins. It was discovered in Agrobacterium tumefaciens, which uses this system to introduce the Ti plasmid and proteins into the host, which develops the crown gall (tumor).[6] The VirB complex of Agrobacterium tumefaciens is the prototypic system.[7]
The nitrogen fixing Rhizobia are an interesting case, wherein conjugative elements naturally engage in inter-kingdom conjugation. Such elements as the Agrobacterium Ti or Ri plasmids contain elements that can transfer to plant cells. Transferred genes enter the plant cell nucleus and effectively transform the plant cells into factories for the production of opines, which the bacteria use as carbon and energy sources. Infected plant cells form crown gall or root tumors. The Ti and Ri plasmids are thus endosymbionts of the bacteria, which are in turn endosymbionts (or parasites) of the infected plant.
The Ti and Ri plasmids are themselves conjugative. Ti and Ri transfer between bacteria uses an independent system (the tra, or transfer, operon) from that for inter-kingdom transfer (the vir, or virulence, operon). Such transfer creates virulent strains from previously avirulent Agrobacteria.
Release of outer membrane vesicles
In addition to the use of the multiprotein complexes listed above, Gram-negative bacteria possess another method for release of material: the formation of outer membrane vesicles.[8][9] Portions of the outer membrane pinch off, forming spherical structures made of a lipid bilayer enclosing periplasmic materials. Vesicles from a number of bacterial species have been found to contain virulence factors, some have immunomodulatory effects, and some can directly adhere to and intoxicate host cells. While release of vesicles has been demonstrated as a general response to stress conditions, the process of loading cargo proteins seems to be selective.[10]
Venus Flytrap (Dionaea muscipula) leaf
Gastrovascular cavity
The gastrovascular cavity functions as a stomach in both digestion and the distribution of nutrients to all parts of the body. Extracellular digestion takes place within this central cavity, which is lined with the gastrodermis, the internal layer of epithelium. This cavity has only one opening to the outside that functions as both a mouth and an anus: waste and undigested matter is excreted through the mouth/anus, which can be described as an incomplete gut.
In a plant such as the Venus Flytrap that can make its own food through photosynthesis, it does not eat and digest its prey for the traditional objectives of harvesting energy and carbon, but mines prey primarily for essential nutrients (nitrogen and phosphorus in particular) that are in short supply in its boggy, acidic habitat.[11]
Trophozoites of Entamoeba histolytica with ingested erythrocytes
Phagosome
A phagosome is a vacuole formed around a particle absorbed by phagocytosis. The vacuole is formed by the fusion of the cell membrane around the particle. A phagosome is a cellular compartment in which pathogenic microorganisms can be killed and digested. Phagosomes fuse with lysosomes in their maturation process, forming phagolysosomes. In humans, Entamoeba histolytica can phagocytose red blood cells.[12]
Specialised organs and behaviours
To aid in the digestion of their food animals evolved organs such as beaks, tongues, teeth, a crop, gizzard, and others.
A Catalina Macaw's seed-shearing beak
Squid beak with ruler for size comparison
Beaks
Birds have bony beaks that are specialised according to the bird's ecological niche. For example, macaws primarily eat seeds, nuts, and fruit, using their impressive beaks to open even the toughest seed. First they scratch a thin line with the sharp point of the beak, then they shear the seed open with the sides of the beak.
The mouth of the squid is equipped with a sharp horny beak mainly made of cross-linked proteins. It is used to kill and tear prey into manageable pieces. The beak is very robust, but does not contain any minerals, unlike the teeth and jaws of many other organisms, including marine species.[13] The beak is the only indigestible part of the squid.
Tongue
Main article: Tongue
The tongue is skeletal muscle on the floor of the mouth that manipulates food for chewing (mastication) and swallowing (deglutition). It is sensitive and kept moist by saliva. The underside of the tongue is covered with a smooth mucous membrane. The tongue also has a touch sense for locating and positioning food particles that require further chewing. The tongue is utilized to roll food particles into a bolus before being transported down the esophagus through peristalsis.
The sublingual region underneath the front of the tongue is a location where the oral mucosa is very thin, and underlain by a plexus of veins. This is an ideal location for introducing certain medications to the body. The sublingual route takes advantage of the highly vascular quality of the oral cavity, and allows for the speedy application of medication into the cardiovascular system, bypassing the gastrointestinal tract.
Teeth
Main article: Teeth
Teeth (singular tooth) are small whitish structures found in the jaws (or mouths) of many vertebrates that are used to tear, scrape, milk and chew food. Teeth are not made of bone, but rather of tissues of varying density and hardness, such as enamel, dentine and cementum. Human teeth have a blood and nerve supply which enables proprioception. This is the ability of sensation when chewing, for example if we were to bite into something too hard for our teeth, such as a chipped plate mixed in food, our teeth send a message to our brain and we realise that it cannot be chewed, so we stop trying.
The shapes, sizes and numbers of types of animals' teeth are related to their diets. For example, herbivores have a number of molars which are used to grind plant matter, which is difficult to digest. Carnivores have canine teeth which are used to kill and tear meat.
Crop
A crop, or croup, is a thin-walled expanded portion of the alimentary tract used for the storage of food prior to digestion. In some birds it is an expanded, muscular pouch near the gullet or throat. In adult doves and pigeons, the crop can produce crop milk to feed newly hatched birds.[14]
Certain insects may have a crop or enlarged esophagus.
Rough illustration of a ruminant digestive system
Abomasum
Main article: Abomasum
Herbivores have evolved cecums (or an abomasum in the case of ruminants). Ruminants have a fore-stomach with four chambers. These are the rumen, reticulum, omasum, and abomasum. In the first two chambers, the rumen and the reticulum, the food is mixed with saliva and separates into layers of solid and liquid material. Solids clump together to form the cud (or bolus). The cud is then regurgitated, chewed slowly to completely mix it with saliva and to break down the particle size.
Fibre, especially cellulose and hemi-cellulose, is primarily broken down into the volatile fatty acids, acetic acid, propionic acid and butyric acid in these chambers (the reticulo-rumen) by microbes: (bacteria, protozoa, and fungi). In the omasum, water and many of the inorganic mineral elements are absorbed into the blood stream.
The abomasum is the fourth and final stomach compartment in ruminants. It is a close equivalent of a monogastric stomach (e.g., those in humans or pigs), and digesta is processed here in much the same way. It serves primarily as a site for acid hydrolysis of microbial and dietary protein, preparing these protein sources for further digestion and absorption in the small intestine. Digesta is finally moved into the small intestine, where the digestion and absorption of nutrients occurs. Microbes produced in the reticulo-rumen are also digested in the small intestine.
A flesh fly "blowing a bubble", possibly to concentrate its food by evaporating water
Specialised behaviours
Regurgitation has been mentioned above under abomasum and crop, referring to crop milk, a secretion from the lining of the crop of pigeons and doves with which the parents feed their young by regurgitation.[15]
Many sharks have the ability to turn their stomachs inside out and evert it out of their mouths in order to get rid of unwanted contents (perhaps developed as a way to reduce exposure to toxins).
Other animals, such as rabbits and rodents, practise coprophagia behaviours – eating specialised faeces in order to re-digest food, especially in the case of roughage. Capybara, rabbits, hamsters and other related species do not have a complex digestive system as do, for example, ruminants. Instead they extract more nutrition from grass by giving their food a second pass through the gut. Soft faecal pellets of partially digested food are excreted and generally consumed immediately. They also produce normal droppings, which are not eaten.
Young elephants, pandas, koalas, and hippos eat the faeces of their mother, probably to obtain the bacteria required to properly digest vegetation. When they are born, their intestines do not contain these bacteria (they are completely sterile). Without them, they would be unable to get any nutritional value from many plant components.
In earthworms
An earthworm's digestive system consists of a mouth, pharynx, esophagus, crop, gizzard, and intestine. The mouth is surrounded by strong lips, which act like a hand to grab pieces of dead grass, leaves, and weeds, with bits of soil to help chew. The lips break the food down into smaller pieces. In the pharynx, the food is lubricated by mucus secretions for easier passage. The esophagus adds calcium carbonate to neutralize the acids formed by food matter decay. Temporary storage occurs in the crop where food and calcium carbonate are mixed. The powerful muscles of the gizzard churn and mix the mass of food and dirt. When the churning is complete, the glands in the walls of the gizzard add enzymes to the thick paste, which helps chemically breakdown the organic matter. By peristalsis, the mixture is sent to the intestine where friendly bacteria continue chemical breakdown. This releases carbohydrates, protein, fat, and various vitamins and minerals for absorption into the body.
Overview of vertebrate digestion
In most vertebrates, digestion is a multistage process in the digestive system, starting from ingestion of raw materials, most often other organisms. Ingestion usually involves some type of mechanical and chemical processing. Digestion is separated into four steps:
Ingestion: placing food into the mouth (entry of food in the digestive system),
Mechanical and chemical breakdown: mastication and the mixing of the resulting bolus with water, acids, bile and enzymes in the stomach and intestine to break down complex molecules into simple structures,
Absorption: of nutrients from the digestive system to the circulatory and lymphatic capillaries through osmosis, active transport, and diffusion, and
Egestion (Excretion): Removal of undigested materials from the digestive tract through defecation.
Underlying the process is muscle movement throughout the system through swallowing and peristalsis. Each step in digestion requires energy, and thus imposes an "overhead charge" on the energy made available from absorbed substances. Differences in that overhead cost are important influences on lifestyle, behavior, and even physical structures. Examples may be seen in humans, who differ considerably from other hominids (lack of hair, smaller jaws and musculature, different dentition, length of intestines, cooking, etc.).
The major part of digestion takes place in the small intestine. The large intestine primarily serves as a site for fermentation of indigestible matter by gut bacteria and for resorption of water from digests before excretion.
In mammals, preparation for digestion begins with the cephalic phase in which saliva is produced in the mouth and digestive enzymes are produced in the stomach. Mechanical and chemical digestion begin in the mouth where food is chewed, and mixed with saliva to begin enzymatic processing of starches. The stomach continues to break food down mechanically and chemically through churning and mixing with both acids and enzymes. Absorption occurs in the stomach and gastrointestinal tract, and the process finishes with defecation.[1]
Human digestion process
Main article: Human digestive system
Upper and lower human gastrointestinal tract
The human gastrointestinal tract is around 9 meters long. Food digestion physiology varies between individuals and upon other factors such as the characteristics of the food and size of the meal, and the process of digestion normally takes between 24 and 72 hours.[16]
Digestion begins in the mouth with the secretion of saliva and its digestive enzymes. Food is formed into a bolus by the mechanical mastication and swallowed into the esophagus from where it enters the stomach through the action of peristalsis. Gastric juice contains hydrochloric acid and pepsin which would damage the walls of the stomach and mucus is secreted for protection. In the stomach further release of enzymes break down the food further and this is combined with the churning action of the stomach. The partially digested food enters the duodenum as a thick semi-liquid chyme. In the small intestine, the larger part of digestion takes place and this is helped by the secretions of bile, pancreatic juice and intestinal juice. The intestinal walls are lined with villi, and their epithelial cells is covered with numerous microvilli to improve the absorption of nutrients by increasing the surface area of the intestine.
In the large intestine the passage of food is slower to enable fermentation by the gut flora to take place. Here water is absorbed and waste material stored as feces to be removed by defecation via the anal canal and anus.
Neural and biochemical control mechanisms
Different phases of digestion take place including: the cephalic phase, gastric phase, and intestinal phase.
The cephalic phase occurs at the sight, thought and smell of food, which stimulate the cerebral cortex. Taste and smell stimuli are sent to the hypothalamus and medulla oblongata. After this it is routed through the vagus nerve and release of acetylcholine. Gastric secretion at this phase rises to 40% of maximum rate. Acidity in the stomach is not buffered by food at this point and thus acts to inhibit parietal (secretes acid) and G cell (secretes gastrin) activity via D cell secretion of somatostatin.
The gastric phase takes 3 to 4 hours. It is stimulated by distension of the stomach, presence of food in stomach and decrease in pH. Distention activates long and myenteric reflexes. This activates the release of acetylcholine, which stimulates the release of more gastric juices. As protein enters the stomach, it binds to hydrogen ions, which raises the pH of the stomach. Inhibition of gastrin and gastric acid secretion is lifted. This triggers G cells to release gastrin, which in turn stimulates parietal cells to secrete gastric acid. Gastric acid is about 0.5% hydrochloric acid (HCl), which lowers the pH to the desired pH of 1-3. Acid release is also triggered by acetylcholine and histamine.
The intestinal phase has two parts, the excitatory and the inhibitory. Partially digested food fills the duodenum. This triggers intestinal gastrin to be released. Enterogastric reflex inhibits vagal nuclei, activating sympathetic fibers causing the pyloric sphincter to tighten to prevent more food from entering, and inhibits local reflexes.
Breakdown into nutrients
This section needs expansion with: digestion of other substances. You can help by adding to it. (August 2011)
Protein digestion
Protein digestion occurs in the stomach and duodenum in which 3 main enzymes, pepsin secreted by the stomach and trypsin and chymotrypsin secreted by the pancreas, break down food proteins into polypeptides that are then broken down by various exopeptidases and dipeptidases into amino acids. The digestive enzymes however are mostly secreted as their inactive precursors, the zymogens. For example, trypsin is secreted by pancreas in the form of trypsinogen, which is activated in the duodenum by enterokinase to form trypsin. Trypsin then cleaves proteins to smaller polypeptides.
Fat digestion
Main article: Fatty acid metabolism § Dietary sources of fatty acids, their digestion, absorption, transport in the blood and storage
Digestion of some fats can begin in the mouth where lingual lipase breaks down some short chain lipids into diglycerides. However fats are mainly digested in the small intestine.[17] The presence of fat in the small intestine produces hormones that stimulate the release of pancreatic lipase from the pancreas and bile from the liver which helps in the emulsification of fats for absorption of fatty acids.[17] Complete digestion of one molecule of fat (a triglyceride) results a mixture of fatty acids, mono- and di-glycerides, as well as some undigested triglycerides, but no free glycerol molecules.[17]
Carbohydrate digestion
In humans, dietary starches are composed of glucose units arranged in long chains called amylose, a polysaccharide. During digestion, bonds between glucose molecules are broken by salivary and pancreatic amylase, resulting in progressively smaller chains of glucose. This results in simple sugars glucose and maltose (2 glucose molecules) that can be absorbed by the small intestine.
Lactase is an enzyme that breaks down the disaccharide lactose to its component parts, glucose and galactose. Glucose and galactose can be absorbed by the small intestine. Approximately 65 percent of the adult population produce only small amounts of lactase and are unable to eat unfermented milk-based foods. This is commonly known as lactose intolerance. Lactose intolerance varies widely by ethnic heritage; more than 90 percent of peoples of east Asian descent are lactose intolerant, in contrast to about 5 percent of people of northern European descent.[18]
Sucrase is an enzyme that breaks down the disaccharide sucrose, commonly known as table sugar, cane sugar, or beet sugar. Sucrose digestion yields the sugars fructose and glucose which are readily absorbed by the small intestine.
DNA and RNA digestion
DNA and RNA are broken down into mononucleotides by the nucleases deoxyribonuclease and ribonuclease (DNase and RNase) from the pancreas.
Non-destructive digestion
Some nutrients are complex molecules (for example vitamin B12) which would be destroyed if they were broken down into their functional groups. To digest vitamin B12 non-destructively, haptocorrin in saliva strongly binds and protects the B12 molecules from stomach acid as they enter the stomach and are cleaved from their protein complexes.[19]
After the B12-haptocorrin complexes pass from the stomach via the pylorus to the duodenum, pancreatic proteases cleave haptocorrin from the B12 molecules which rebind to intrinsic factor (IF). These B12-IF complexes travel to the ileum portion of the small intestine where cubilin receptors enable assimilation and circulation of B12-IF complexes in the blood.[20]
Digestive hormones
Action of the major digestive hormones
There are at least five hormones that aid and regulate the digestive system in mammals. There are variations across the vertebrates, as for instance in birds. Arrangements are complex and additional details are regularly discovered. For instance, more connections to metabolic control (largely the glucose-insulin system) have been uncovered in recent years.
Gastrin – is in the stomach and stimulates the gastric glands to secrete pepsinogen (an inactive form of the enzyme pepsin) and hydrochloric acid. Secretion of gastrin is stimulated by food arriving in stomach. The secretion is inhibited by low pH.
Secretin – is in the duodenum and signals the secretion of sodium bicarbonate in the pancreas and it stimulates the bile secretion in the liver. This hormone responds to the acidity of the chyme.
Cholecystokinin (CCK) – is in the duodenum and stimulates the release of digestive enzymes in the pancreas and stimulates the emptying of bile in the gall bladder. This hormone is secreted in response to fat in chyme.
Gastric inhibitory peptide (GIP) – is in the duodenum and decreases the stomach churning in turn slowing the emptying in the stomach. Another function is to induce insulin secretion.
Motilin – is in the duodenum and increases the migrating myoelectric complex component of gastrointestinal motility and stimulates the production of pepsin.
Significance of pH
Digestion is a complex process controlled by several factors. pH plays a crucial role in a normally functioning digestive tract. In the mouth, pharynx and esophagus, pH is typically about 6.8, very weakly acidic. Saliva controls pH in this region of the digestive tract. Salivary amylase is contained in saliva and starts the breakdown of carbohydrates into monosaccharides. Most digestive enzymes are sensitive to pH and will denature in a high or low pH environment.
The stomach's high acidity inhibits the breakdown of carbohydrates within it. This acidity confers two benefits: it denatures proteins for further digestion in the small intestines, and provides non-specific immunity, damaging or eliminating various pathogens.[citation needed]
In the small intestines, the duodenum provides critical pH balancing to activate digestive enzymes. The liver secretes bile into the duodenum to neutralize the acidic conditions from the stomach, and the pancreatic duct empties into the duodenum, adding bicarbonate to neutralize the acidic chyme, thus creating a neutral environment. The mucosal tissue of the small intestines is alkaline with a pH of about 8.5.[citation needed]
See also
Digestive system of gastropods
Digestive system of humpback whales
Erepsin
Gastroesophageal reflux disease
Discovery and development of proton pump inhibitors
References
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Jump up ^ Cascales E, Christie PJ (2003). "The versatile Type IV secretion systems". Nature Reviews Microbiology. 1 (2): 137–149. doi:10.1038/nrmicro753. PMC 3873781  . PMID 15035043.
Jump up ^ Christie PJ; Atmakuri K; Jabubowski S; Krishnamoorthy V; Cascales E. (2005). "Biogenesis, architecture, and function of bacterial Type IV secretion systems". Annu Rev Microbiol. 59: 451–485. doi:10.1146/annurev.micro.58.030603.123630. PMC 3872966  . PMID 16153176.
Jump up ^ Chatterjee, S. N.; Das, J (1967). "Electron microscopic observations on the excretion of cell-wall material by Vibrio cholerae". Journal of General Microbiology. 49 (1): 1–11. doi:10.1099/00221287-49-1-1. PMID 4168882.
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Jump up ^ McBroom, A. J.; Kuehn, M. J. (2007). "Release of outer membrane vesicles by Gram-negative bacteria is a novel envelope stress response". Molecular Microbiology. 63 (2): 545–558. doi:10.1111/j.1365-2958.2006.05522.x. PMC 1868505  . PMID 17163978.
Jump up ^ Leege, Lissa. "How does the Venus flytrap digest flies?". Scientific American. Retrieved 2008-08-20.
Jump up ^ Boettner, D. R.; Huston, C. D.; Linford, A. S.; Buss, S. N.; Houpt, E.; Sherman, N. E.; Petri, W. A. (2008). "Entamoeba histolytica Phagocytosis of Human Erythrocytes Involves PATMK, a Member of the Transmembrane Kinase Family". PLoS Pathogens. 4 (1): e8. doi:10.1371/journal.ppat.0040008. PMC 2211552  . PMID 18208324.
Jump up ^ Miserez, A; Li, Y; Waite, H; Zok, F (2007). "Jumbo squid beaks: Inspiration for design of robust organic composites". Acta Biomaterialia. 3 (1): 139–149. doi:10.1016/j.actbio.2006.09.004. PMID 17113369.
Jump up ^ Gordon John Larkman Ramel (2008-09-29). "The Alimentary Canal in Birds". Retrieved 2008-12-16.
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^ Jump up to: a b c Digestion of fats (triacylglycerols)
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Latency (engineering)
From Wikipedia, the free encyclopedia
Jump to: navigation, search
This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (April 2011) (Learn how and when to remove this template message)
Latency is a time interval between the stimulation and response, or, from a more general point of view, a time delay between the cause and the effect of some physical change in the system being observed.[1] Latency is physically a consequence of the limited velocity with which any physical interaction can propagate. The magnitude of this velocity is always less than or equal to the speed of light. Therefore, every physical system will experience some sort of latency, regardless of the nature of stimulation that it has been exposed to.
The precise definition of latency depends on the system being observed and the nature of stimulation. In communications, the lower limit of latency is determined by the medium being used for communications. In reliable two-way communication systems, latency limits the maximum rate that information can be transmitted, as there is often a limit on the amount of information that is "in-flight" at any one moment. In the field of human–machine interaction, perceptible latency has a strong effect on user satisfaction and usability.
Contents
[hide]
1 Communication latency
1.1 Packet-switched networks
1.2 Fiber optics
1.3 Satellite transmission
2 Audio latency
3 Operational latency
3.1 Consumer view
3.2 Producer view
4 Mechanical latency
5 Computer hardware and operating system latency
6 In simulators and simulation
7 See also
8 References
9 External links
Communication latency[edit]
Online games are sensitive to latency since fast response times to new events occurring during a game session are rewarded while slow response times may carry penalties. Lag is the term used to describe latency in gaming. Due to a delay in transmission of game events, a player with a high latency internet connection may show slow responses in spite of appropriate reaction time. This gives players with low latency connections a technical advantage.
Minimizing latency is of interest in the capital markets,[2] particularly where algorithmic trading is used to process market updates and turn around orders within milliseconds. Low-latency trading occurs on the networks used by financial institutions to connect to stock exchanges and electronic communication networks (ECNs) to execute financial transactions.[3] Joel Hasbrouck and Gideon Saar (2011) measure latency based on three components: the time it takes for information to reach the trader, execution of the trader’s algorithms to analyze the information and decide a course of action, and the generated action to reach the exchange and get implemented. Hasbrouck and Saar contrast this with the way in which latencies are measured by many trading venues who use much more narrow definitions, such as, the processing delay measured from the entry of the order (at the vendor’s computer) to the transmission of an acknowledgement (from the vendor’s computer).[4] Electronic trading now makes up 60% to 70% of the daily volume on the NYSE and algorithmic trading close to 35%.[5] Trading using computers has developed to the point where millisecond improvements in network speeds offer a competitive advantage for financial institutions.[6]
Packet-switched networks[edit]
See also: Bandwidth-delay product and Network delay
Network latency in a packet-switched network is measured either one-way (the time from the source sending a packet to the destination receiving it), or round-trip delay time (the one-way latency from source to destination plus the one-way latency from the destination back to the source). Round-trip latency is more often quoted, because it can be measured from a single point. Note that round trip latency excludes the amount of time that a destination system spends processing the packet. Many software platforms provide a service called ping that can be used to measure round-trip latency. Ping performs no packet processing; it merely sends a response back when it receives a packet (i.e. performs a no-op), thus it is a first rough way of measuring latency. Ping cannot perform accurate measurements,[7] principally because it uses the ICMP protocol that is used only for diagnostic or control purposes, and differs from real communication protocols such as TCP. Furthermore, routers and ISP's might apply different traffic shaping policies to different protocols.[8][9]
For more accurate measurements it is better to use specific software (for example: lft, paketto, hping, superping.d, NetPerf, IPerf)
However, in a non-trivial network, a typical packet will be forwarded over many links via many gateways, each of which will not begin to forward the packet until it has been completely received. In such a network, the minimal latency is the sum of the minimum latency of each link, plus the transmission delay of each link except the final one, plus the forwarding latency of each gateway. In practice, this minimal latency is further augmented by queuing and processing delays. Queuing delay occurs when a gateway receives multiple packets from different sources heading towards the same destination. Since typically only one packet can be transmitted at a time, some of the packets must queue for transmission, incurring additional delay. Processing delays are incurred while a gateway determines what to do with a newly received packet. A new and emergent behavior called bufferbloat can also cause increased latency that is an order of magnitude or more. The combination of propagation, serialization, queuing, and processing delays often produces a complex and variable network latency profile.
Latency limits total throughput in reliable two-way communication systems as described by the bandwidth-delay product.
Fiber optics[edit]
Latency is largely a function of the speed of light, which is 299,792,458 meters/second in vacuum. This would equate to a latency of 3.33 µs for every kilometer of path length. The index of refraction of most fibre optic cables is about 1.5, meaning that light travels about 1.5 times as fast in a vacuum as it does in the cable. This works out to about 5.0 µs of latency for every kilometer. In shorter metro networks, the latency performance rises a bit more due to building risers and cross-connects and can push the latency over 5 µs per kilometer.
It follows that to calculate latency of a connection, one has to know the distance traveled by the fibre, which is rarely a straight line, since it has to traverse geographic contours and obstacles, such as roads and railway tracks, as well as other rights-of-way. Due to imperfections in the fibre, light degrades as it is transmitted through it. For distances of greater than 100 kilometers, either amplifiers or regenerators need to be deployed. Passive amplifiers typically add less latency than regenerators, at the cost of compounding attenuation, though in both cases it can be highly variable, and so needs to be taken into account. In particular, legacy spans are more likely to make use of higher latency regenerators.
Satellite transmission[edit]
This is illustrated when a news presenter in a studio talks with a reporter in a distant place via a geostationary communication satellite. The signal travels from the newsreader up to and down from the satellite to the reporter and then the reply from the reporter does the same, resulting in four satellite hops incurring a latency on the order of a half second, not including the typically smaller latencies inside the communications equipment.
Low-Earth orbit is sometimes used to cut this delay, at the expense of more complicated satellite tracking on the ground and requiring more satellites in the satellite constellation to ensure continuous coverage.
Audio latency[edit]
Main article: Latency (audio)
Audio latency is the delay between when an audio signal enters and when it emerges from a system. Potential contributors to latency in an audio system include analog-to-digital conversion, buffering, digital signal processing, transmission time, digital-to-analog conversion and the speed of sound in air.
Operational latency[edit]
Any individual workflow within a system of workflows can be subject to some type of operational latency. It may even be the case that an individual system may have more than one type of latency, depending on the type of participant or goal-seeking behavior. This is best illustrated by the following two examples involving air travel.
Consumer view[edit]
From the point of view of a passenger, latency can be described as follows. Suppose John Doe flies from London to New York. The latency of his trip is the time it takes him to go from his house in England to the hotel he is staying at in New York. This is independent of the throughput of the London-New York air link – whether there were 100 passengers a day making the trip or 10000, the latency of the trip would remain the same.
Producer view[edit]
From the point of view of flight operations personnel, latency can be entirely different. Consider the staff at the London and New York airports. Only a limited number of planes are able to make the transatlantic journey, so when one lands they must prepare it for the return trip as quickly as possible. It might take, for example:
35 minutes to clean a plane
15 minutes to refuel a plane
10 minutes to load the passengers
30 minutes to load the cargo
Assuming the above are done one after another, minimum plane turnaround time is:
35 + 15 + 10 + 30 = 90
However, cleaning, refueling and loading the cargo can be done at the same time. Passengers can be loaded after cleaning is complete. The reduced latency, then, is:
35 + 10 = 45
15
30
Minimum latency = 45
The people involved in the turnaround are interested only in the time it takes for their individual tasks. When all of the tasks are done at the same time, however, it is possible to reduce the latency to the length of the longest task. If some steps have prerequisites, it becomes more difficult to perform all steps in parallel. In the example above, the requirement to clean the plane before loading passengers results in a minimum latency longer than any single task.
Mechanical latency[edit]
Any mechanical process encounters limitations modeled by Newtonian physics. The behavior of disk drives provides an example of mechanical latency. Here, it is the time needed for the data encoded on a platter to rotate from its current position to a position adjacent to the read-write head as well as the seek time required for the actuator arm for the read-write head to be positioned above the appropriate track. This is also known as rotational latency and seek time since the basic term latency is also applied to the time required by a computer's electronics and software to perform polling, interrupts, and direct memory access.
Computer hardware and operating system latency[edit]
Further information: Access time
Computers run sets of instructions called a process. In operating systems, the execution of the process can be postponed if other processes are also executing. In addition, the operating system can schedule when to perform the action that the process is commanding. For example, suppose a process commands that a computer card's voltage output be set high-low-high-low and so on at a rate of 1000 Hz. The operating system may choose to adjust the scheduling of each transition (high-low or low-high) based on an internal clock. The latency is the delay between the process instruction commanding the transition and the hardware actually transitioning the voltage from high to low or low to high.
On Microsoft Windows, it appears[original research?] that the timing of commands to hardware is not exact. Empirical data suggest that Windows (using the Windows sleep timer which accepts millisecond sleep times) will schedule on a 1024 Hz clock and will delay 24 of 1024 transitions per second to make an average of 1000 Hz for the update rate.[citation needed] This can have serious ramifications for discrete-time algorithms that rely on fairly consistent timing between updates such as those found in control theory. The sleep function or similar windows API were at no point designed for accurate timing purposes. Certain multimedia-oriented API routines like timeGetTime() and its siblings provide better timing consistency. However, consumer- and server-grade Windows (as of 2011[update] those based on NT kernel) were not to be real-time operating systems. Drastically more accurate timings could be achieved by using dedicated hardware extensions and control-loop cards.
Linux may have the same problems with scheduling of hardware I/O.[citation needed] The problem in Linux is mitigated by support for posix real-time extensions, and the possibility of using a kernel with the PREEMPT_RT patch applied.
On embedded systems, the real-time execution of instructions is often supported by the low-level embedded operating system.
In simulators and simulation[edit]
In simulation applications, 'latency' refers to the time delay, normally measured in milliseconds (1/1,000 sec), between initial input and an output clearly discernible to the simulator trainee or simulator subject. Latency is sometimes also called transport delay.
Some authorities distinguish between latency and transport delay by using the term 'latency' in the sense of the extra time delay of a system over and above the reaction time of the vehicle being simulated, but this requires a detailed knowledge of the vehicle dynamics and can be controversial.
Importance of Motion and Visual Latencies. In simulators with both visual and motion systems, it is particularly important that the latency of the motion system not be greater than of the visual system, or symptoms of simulator sickness may result. This is because in the real world, motion cues are those of acceleration and are quickly transmitted to the brain, typically in less than 50 milliseconds; this is followed some milliseconds later by a perception of change in the visual scene. The visual scene change is essentially one of change of perspective and/or displacement of objects such as the horizon, which takes some time to build up to discernible amounts after the initial acceleration which caused the displacement. A simulator should therefore reflect the real-world situation by ensuring that the motion latency is equal to or less than that of the visual system and not the other way round.
See also[edit]
Comparison of latency and bandwidth
Feedback
Interrupt latency
Jitter
Lead time
Memory latency
Performance engineering
Response time (technology)
Responsiveness
Throughput
References[edit]
Jump up ^ "What is Latency?" / "Latency" Retrieved 2015-02-22.
Jump up ^ TABB (2009). High Frequency Trading Technology: a TABB Anthology.
Jump up ^ Mackenzie, Michael; Grant, Jeremy (2009). "The dash to flash" (PDF). Financial Times. Retrieved 18 July 2011. extracting tiny slices of profit from trading small numbers of shares in companies, often between different trading platforms, with success relying on minimal variations in speed - or "latency", in the trading vernacular.
Jump up ^ Hasbrouck, Joel; Saar, Gideon. "Low-Latency Trading" (PDF). p. 1. Retrieved 18 July 2011.
Jump up ^ Heires, Katherine (July 2009). "Code Green: Goldman Sachs & UBS Cases Heighten Need to Keep Valuable Digital Assets From Walking Out The Door. Millions in Trading Profits May Depend On It" (PDF). Securities Industry News. Retrieved 18 July 2011.
Jump up ^ "High-frequency trading: when milliseconds mean millions". The Telegraph. Retrieved 2018-03-25.
Jump up ^ "Don't misuse ping!". Retrieved 29 April 2015.
Jump up ^ Shane Chen (2005). "Network Protocols Discussion / Traffic Shaping Strategies". knowplace.org. Archived from the original on 2007-01-09.
Jump up ^ "Basic QoS part 1 – Traffic Policing and Shaping on Cisco IOS Router". The CCIE R&S. Retrieved 29 April 2015.
M. Brian Blake (December 2003). "Coordinating Multiple Agents for Workflow-Oriented Process Orchestration" (PDF). Information Systems and e-Business Management Journal. Springer-Verlag. Archived from the original (PDF) on 2006-09-01.
External links[edit]
Simulating network link latency under Linux
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