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Mossos d'Esquadra

The Mossos d'Esquadra ( Police Squad), also known as the Policia de la Generalitat de Catalunya and informally as Mossos, is the autonomous police force in Catalonia. They trace their origins back to squads formed in 1719.

History
On 21 July 1950 the Deputation of Barcelona was authorised to create a small security force using the historical title Mossos d'Esquadra. These new Mossos were a militarized corps having little similarity to the earlier incarnations, with limited powers and small numbers, which was in charge of protecting the government buildings of the Province of Barcelona. With the return of democracy to Spain, the Mossos d'Esquadra grew in number and powers. Since 25 October 1980 the force has been under the authority of the Generalitat de Catalunya (the Government of Catalonia).

Previous Catalan forces
The Escuadras de Paisanos, later known as the Esquadres de Catalunya, (and informally known as the Mossos d'Esquadra), were men-at-arms who had fought as irregulars in the War of the Spanish Succession, and were brought together by the mayor of the town of Valls near Tarragona between 1719 and 1721. The corps was constituted as a militia to provide security to trade routes and fairs. It was created as a complement to the regular troops of the Bourbon army, which opposed the Miquelets, who survived as rebel supporters of Archduke Charles.

The Mossos was manned by local people, who had to speak Catalan and be familiar with local paths, caves, and hiding places. It was eventually placed under military jurisdiction, but was less centralised than the Spanish police force (then known as the Intendencia General de Policía) formed in 1817, or the yet-to-be-established Guardia Civil. Throughout the centuries, control of the Mossos passed back and forth several times from Catalan authority to Spanish military command.

The Mossos were dissolved in 1868 by General Prim after the fall of Queen Isabella II of Spain, since the Mossos had always been royalists. They were reinstated in 1876 under the reign of Isabella's son king Alfonso XII of Spain, but only in the province of Barcelona. Under his son Alfonso XIII of Spain, the Mossos were not well regarded in Catalonia, especially by the Commonwealth of Catalonia, who paid them but had no control over them.

The Mossos flourished under Primo de Rivera's dictatorship.; despite this, when the Second Spanish Republic was proclaimed, the Mossos sided with the Generalitat de Catalunya. After the Spanish Civil War, the last Mossos left Catalonia with the President of the Generalitat, and the corps was dissolved by the Francoist authorities.

Current role
The Mossos d'Esquadra have now replaced the Guardia Civil and National Police within the territory of Catalonia. This process of substitution began in 1994 and was completed in 2008.

The Statute of Autonomy of Catalonia (Catalan: Estatut d'Autonomia de Catalunya) defines the scope of action of the Generalitat Police Force – Mossos d'Esquadra as the whole of the Catalan territory, and states that it exercises all the functions of a police force in the following fields:

 * Public safety and public order
 * Administrative policing, including that deriving from State regulations
 * Judicial policing and criminal investigation, including the various forms of organised crime and terrorism, in the terms established by law
 * Patrolling and ensuring the safety of highways within Catalonia

The Mossos d'Esquadra operate under the authority of the Generalitat de Catalunya within the territory of the autonomous community of Catalonia (through the Catalan Ministry of Home Affairs; Catalan: Departament d'Interior). The National Police and the Civil Guard, by contrast, are commanded directly by the Spanish Ministry of the Interior. The Mossos keep some officers in Catalonia to support anti-terrorism operations, handle identity documents, police immigration, and execute other limited responsibilities of the central government.

The sidearms officers can pick from are the Heckler & Koch USP or the Walther P99 both of which are chambered for 9×19mm. Regular Mossos can also use the Heckler & Koch UMP sub-machine gun, which used by the Mossos during the 2017 Barcelona attacks.

The Mossos are trained in the Institut de Seguretat Pública de Catalunya (Public Safety Institute of Catalonia), which also trains local police officers.

Special intervention group (GEI)
The Special Intervention Group (GEI; in Catalan: Grup Especial d'Intervenció) is a Mossos d'Esquadra body that specializes in situations with a high risk of armed violence such as terrorist detention, rescues of hostages, and VIP protection. This group is under the command of the Intervention Division.

This group was created in 1984 with the collaboration of Spezialeinsatzkommando (SEK) of Germany. It was kept secret in anticipation of the security challenges that would be posed with the holding of the Barcelona Olympic Games in 1992. Another rationale for its creation was to transfer responsibility for prisons to the Generalitat de Catalonia; this was felt to require a protocol to deal with riots or hostage-taking.

Armament
The force has a large quantity and variety of weapons. Each of the weapons is assigned only to one GEI.

Pistols
 * P30 Pistol – 9×19mm Parabellum.
 * HK USP – 9×19mm Parabellum.
 * FN Five-seveN– 5.7×28mm.
 * Walther P99 9×19mm

Submachine guns
 * MP-5 sub-machine gun – 9×19mm Parabellum.
 * FN P90– 5.7×28mm.
 * HK MP7 – 4.6×30mm.

Assault rifles
 * HK G-36 – 5.56×45mm NATO.
 * FN SCAR – 7.62×51mm NATO.
 * HK 417 – 7.62×51mm NATO.

Shotguns
 * Remington 870 – 12 gauge.

Sniper rifles In the most situations, each member is equipped with a sub-machine gun and two pistols.
 * Heckler & Koch PSG1 – 7.62×51mm NATO.
 * SAKO TRG-22 – 7.62×51mm NATO.
 * M110 Semi-Automatic Sniper System – 7.62×51mm NATO.
 * AMP DSR-1 – .338 Lapua Magnum.

Vehicles

 * Seat Ateca dels Mossos 01.jpg Mossos employs several makes of vehicles, for both patrol and undercover operations. These vehicles are high-powered SUVs, vans, motorbikes and 4x4 vehicles. They also operate helicopters and drones for aerial operations.

Controversies and legal cases
Controversies related to the Mossos d'Esquadra include:

 * In 2008, three Mossos were sentenced to six years of imprisonment for the torture and injury of an alleged delinquent who was later proven not guilty. In 2009, the Tribunal Supremo reduced the sentence. In 2012, the offending Mossos were paroled.
 * In 2016, six agents were detained for their involvement in a cardiac failure of a businessman in the Raval neighbourhood.
 * In 2017, the central government suspended the Chief of Police Major Trapero during the 2017–18 Spanish constitutional crisis, and also placed the force under investigation. The Mossos were eventually cleared of any wrongdoing and Trapero was reinstated.

title: Mossos d'Esquadra


text:
Twelve-string guitar

A twelve-string guitar (or 12-string guitar) is a steel-string guitar with 12 strings in six courses, which produces a thicker, more ringing tone than a standard six-string guitar. Typically, the strings of the lower four courses are tuned in octaves, with those of the upper two courses tuned in unison. The gap between the strings within each dual-string course is narrow, and the strings of each course are fretted and plucked as a single unit. The neck is wider, to accommodate the extra strings, and is similar to the width of a classical guitar neck. The sound, particularly on acoustic instruments, is fuller and more harmonically resonant than six-string instruments. The 12-string guitar can be played like a 6-string guitar as players still use the same notes, chords and guitar techniques like a standard 6-string guitar, but advanced techniques might be tough as players need to play or pluck two strings simultaneously.

Structurally, 12-string guitars, especially those built before 1970, differ from six-string guitars in the following ways:
 * The headstock is elongated to accommodate 12 tuning machines.
 * The added tension of the six additional strings necessitates stronger reinforcement of the neck.
 * The body is also reinforced, and built with a stronger structure, to withstand the higher tension.
 * The fretting scale is generally shorter to reduce the overall string tension.

Twelve-string guitars are made in both acoustic and electric forms. However, the acoustic type is more common.

"Chorus" effect
The double ranks of strings of the 12-string guitar produce a shimmering effect, because even the strings tuned in unison can never vibrate with precise simultaneity—that is, they vibrate out of phase. The result to the ear is a sound that seems to "shimmer", which some describe as resembling strings that are slightly detuned. The interference between the out-of-phase vibrations produces a phenomenon known as a beat that results in a periodic rise and fall of intensity which is, in music, often considered pleasing to the ear. Pete Seeger described the distinctive sound of the 12-string guitar as "the clanging of bells."

Origin and history
The origin of the modern 12-string guitar is not clear, but it arose in the closing years of the 19th century. The most likely ancestors using courses of doubled strings are some Mexican instruments of Spanish ancestry such as the bandolón, the guitarra séptima, the guitarra quinta huapanguera, and the bajo sexto. Pictures such as the 1901 Mexican Typical Orchestra at the Pan-American Exposition show a guitar with 12 strings. At the end of the 19th century, the archtop mandolin was one of the first instruments with courses of doubled strings designed in the United States.

In the 19th and early 20th centuries, 12-strings were regarded as "novelty" instruments. The 12-string guitar did not become a major part of blues and folk music till the 1920s and the 1930s, when their "larger than life" sound made them ideal as solo accompaniment for vocalists, especially Lead Belly and Blind Willie McTell. The 12-string guitar has since occupied roles in certain varieties of folk, rock, jazz, and popular music. In the 1930s, Mexican-American guitarist and singer Lydia Mendoza popularized the instrument. In the 1950s, Lead Belly's protégé, Fred Gerlach, brought the instrument into the American folk music world. Initially, it was primarily used for accompaniment, owing to the greater difficulty of picking or executing string "bends" on its double-strung courses. The Delta Blues guitar virtuoso Robert Lockwood Jr was presented a handcrafted acoustic 12-string guitar made by an outstanding Japanese luthier in the end of the sixties, and this became the instrument of choice for Lockwood thereafter. In the later 20th century, however, a number of players devoted themselves to producing solo performances on the 12-string guitar, including Leo Kottke, Peter Lang, John McLaughlin, Larry Coryell, Ralph Towner, Robbie Basho, Roger Whittaker, Jack Rose, and James Blackshaw.

Electric 12-string guitars
Electric 12-strings became a staple in pop and rock music in the 1960s. Early use of the instrument was pioneered by the guitarists of The Wrecking Crew; in 1963, Carol Kaye used a converted Guild six-string on The Crystals' hit "Then He Kissed Me," and on Jackie DeShannon's song "When You Walk in the Room," Glen Campbell played a well-known guitar figure, composed by DeShannon, on an electric 12-string.

One of the first mass-produced electric 12-strings was the Bellzouki. Introduced by Danelectro in 1961, from a design by session guitarist Vinnie Bell, it was initially considered a cross between an electric guitar and a bouzouki rather than an electric version of the traditional 12-string guitar. In the UK in 1963, JMI briefly produced the Vox Bouzouki, later produced in Italy as The Vox Tempest XII, which was used by Vic Flick on the Peter and Gordon hit single "A World Without Love" in 1964. In late 1963, Burns developed the Double Six, supplying a prototype to Hank Marvin of The Shadows, who used it on a number of songs for the soundtrack of the 1964 Cliff Richard movie Wonderful Life; the Double Six was also used on The Searchers' cover version of De Shannon's "When You Walk in the Room."

The electric 12-string gained prominence with the introduction in 1964 of the Rickenbacker 360, made famous through George Harrison's use of it on The Beatles' album A Hard Day's Night and many subsequent recordings. In 1965, inspired by Harrison, Roger McGuinn made the Rickenbacker 12-string central to The Byrds' folk rock sound, further popularising the instrument. By the mid-1960s, most major guitar manufacturers were producing competing instruments, including the Fender Electric XII (used by Roy Wood of The Move), and the Vox Phantom XII (used by Tony Hicks of The Hollies). Gretsch, Guild, and Gibson also produced electric 12-string models from the mid-Sixties and following decades, with Gretsch promoting theirs by supplying a number of custom made 12-strings for The Monkees guitarist Michael Nesmith, for use on The Monkees TV series.

Standard electric 12-strings became less popular with the end of the American folk rock scene in the late sixties; Fender and Gibson ceased production of the Electric XII and ES-335 12-string variant respectively, in 1969. However, from the 1970s, some progressive rock, hard rock, and jazz fusion guitarists, most notably Jimmy Page of Led Zeppelin, Don Felder of the Eagles, John McLaughlin of The Mahavishnu Orchestra and Alex Lifeson of Rush used double-necked guitars such as the Gibson EDS-1275, with six-string and 12-string necks, for live appearances, allowing easy transition between different sounds mid-song.

The post punk era of the late '70s and early '80s saw a resurgence of electric 12-string guitar use among '60s-influenced alternative rock, pop, and indie guitarists. Players such as Johnny Marr of The Smiths, Dave Gregory of XTC, Susanna Hoffs of The Bangles, Marty Willson-Piper of The Church, Peter Buck of R.E.M., and Tom Petty and Mike Campbell of Tom Petty and the Heartbreakers often chose 12-strings (particularly Rickenbackers) for many songs.

In the 1980s John C Hall, president of Rickenbacker, invited Roger McGuinn to participate in a limited-edition signature model. McGuinn was delighted. Roger McGuinn's signature model Rickenbacker 12-string was introduced in 1988 as the 370/12 RME1.

Design
The strings are placed in courses of two strings each that are usually played together. The two strings in each of the lower four courses are normally tuned an octave apart, while each pair of strings in the top two courses are tuned in unison. The strings are generally arranged such that the higher string of each pair is struck first on a downward strum. However, Rickenbacker usually reverses this arrangement on its electric 12-string guitars. The tuning of the second string in the third course (G) varies. Some players use a unison string, while most prefer the distinctive high-pitched, bell-like quality an octave string makes in this position. Another common variant is to tune the octave string in the sixth (lowest) course two octaves above the lower string, rather than one. Some players, either in search of distinctive tone or for ease of playing, remove some doubled strings. For example, removing the higher octave from the three bass courses simplifies playing running bass lines, but keeps the extra treble strings for the full strums. Some manufacturers have produced 9-string instruments based on this setup, in which either the lower three courses are singular, or the upper three courses are singular. Additionally; some players adapted more unconventional stringing: for example, Big Joe Williams used doubled strings on the 1st, 2nd and 4th courses of his guitars; at first adapted six-string instruments and into the sixties and later usually adapted 12-strings.

The extra tension placed on the instrument by the doubled strings is high, and because of this additional stress on their necks and soundboards, 12-string guitars long had a reputation for warping after a few years of use. (This is less of a problem in modern instruments, built after 1970.) Until the wide spread adoption by American makers of the truss rod after WWII, 12-string guitars were frequently tuned lower than the traditional EADGBE to reduce the stresses on the instrument. For example, Lead Belly often used a low-C tuning, but in some recordings, his tunings can be recognized as low-B and A tunings, partially due to the unusually long scale length (~26.5-27") of the particular models of guitar that he preferred in combination with the heavy strings that were commonly available (14-70). Some 12-string guitars have nontraditional structural supports to prevent or postpone warping, at the expense of appearance and tone. To additionally reduce string tension, 12-string guitars built prior to 1970 typically had shorter necks and scale lengths than six-string guitars, which made frets more closely spaced, with some notable exceptions such as the instruments made by the Oscar Schmidt company before their bankruptcy, which usually had scale lengths of around 26.5". Their bridges, especially in acoustic guitars, had a larger reinforcement plate for the same reason, and tailpiece and floating-bridge setups were far more common than on six string instruments as another way to combat the effect of the high tension.

Advances in materials, design, and construction in such guitars made after 1970 have eliminated most of these accommodations. Contemporary 12 string guitars are commonly built to the same dimensions and scale as their six-string counterparts, albeit still usually with heavier build and bracing.

Tuning
The most common tuning, considered standard today, is a variation on the standard six-string guitar tuning: E3•E2 A3•A2 D4•D3 G4•G3 B3•B3 E4•E4, moving from lowest (sixth) course to highest (first) course. Lead Belly and some other players have doubled the lowest course two octaves above instead of one, producing a third string in unison with the top course, and some stringing the third course in unison as well, and some others all courses except the top in octaves.

Some performers use open tunings and other non-standard guitar tunings on 12-string guitars. Some performers have experimented with tuning the two strings within a course to intervals other than octaves or unisons: jazz guitarists such as Ralph Towner (of Oregon), Larry Coryell, and Philip Catherine have tuned the bass courses of their 12-string guitars to the upper fifths and trebles to the lower fourths instead of octaves and unisons; Michael Gulezian tuned strings in the top two courses to whole-tone intervals (and possibly some of the other strings an octave lower) to achieve a very rich, complex sound. The greater number of strings offers almost endless possibilities.

Nashville tuning
Nashville Tuning is a way of simulating a 12-string guitar sound, using two six-string guitars playing in unison. This is achieved by replacing the lower four courses on one six-string with the higher octave strings for those four courses from a 12-string set, and tuning these four strings an octave higher than normal tuning for those courses on a six-string. Double-tracking this guitar with the standard-tuned six-string is commonly used in recording studios to achieve a "cleaner" 12-string effect.

Mexican 12-String tuning
Mexican 12-String, also known as requinto style or Sierreño style, are modified 12-string guitars that can approximate the sound of a bajo sexto or bajo quinto and play regional Mexican styles, such as norteño (music of Northern Mexico), Tejano (Tex-Mex), and conjunto (música mexicana-tejana). In a traditional 12-string setup, the lower four strings (E, A, D, and G) have octave pairs, while the top two (B and E) have unison pairs. However, for Regional Mexican styles, all strings are set up with identical unison pairs instead of the traditional octave courses. This configuration yields a resonant timbre reminiscent of the venerable bajo sexto, but adds significantly more tension on the bridge and neck. Furthermore, it usually requires the nut to be modified, the neck compensated, and the bridge to be reinforced.

Playing
The 12-string guitar's greater number of strings and higher cumulative string tension complicates playing, in both hands. Fretting chords requires greater force, and the width of the neck and the added string tension combine to make soloing and string-bending challenging. The gap between the dual-string courses is usually narrower than that between the single-string courses of a conventional six-string guitar, so more precision is required with the pick or fingertip when not simply strumming chords. Consequently, the instrument is most commonly used for accompaniment, though several players have taken the time to develop the 12-string guitar as a solo instrument. Flat-picking solos are more frequently seen with electric players, whereas a few acoustic players, such as Leo Kottke, have adapted fingerstyle techniques to the instrument; players such as Ralph Towner have applied classical playing techniques. Roger McGuinn developed his own style of playing a 12-string guitar. The neck of a Rickenbacker 360/12 12-string guitar is as wide as the 6-string guitar. Solos are therefore easier to play and he used his banjo techniques to play chords. In addition to applying a compressor, this determined the sound of The Byrds. Lead Belly adapted both the traditional, simple strum style and the finger-style method that was becoming popular at the time as well; Blind Willie McTell also played finger-style 12 string.

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

title: Twelve-string guitar


text:
Talk:Public key infrastructure

Example of Use
There should be a statement of use in the summary statement. It would be even better if there was an example of use given in the summary. Stephen Charles Thompson (talk) 00:33, 26 October 2008 (UTC)

should there be some examples of use outside strict computer-computer communication? - eg electronic passports are signed for verification purposes-- http://www.dfat.gov.au/dept/passports/ and the australian passport uses encryption in 2 ways, 1 to sign the info on there (so you know its a genuine passport) and the other is a written internal key which is needed to decode the rfid data from the chip in the card. 130.102.0.171 (talk) 02:01, 3 February 2009 (UTC)

Diagrams

 * Add some diagrams, maybe something like, , ?
 * If you wish, you may use the material at for this - we've tried to make it "non-sales" literature, and we can grant use of it to Wikipedia. - Ppatters 19:55, 31 December 2006 (UTC)
 * Ppatters, you have to release those materials to the public domain then upload it. Stephen Charles Thompson (talk) 00:36, 26 October 2008 (UTC)

It occurs to me that some vendor references might be pertinent, i.e., PKI Innovations Inc. (http://www.pk3i.com).

---

Matt, The use of computing that you cut was the result of some cogitation. I was trying to make clear in the wording that there are multiple uses, not merely in overt crypto or overt computer security. PKIs are hidden from view in many contexts and not all of them are either. For instance, copyright protection is commercial and would use squirrels if there were any prospect of it working. That it uses (or misuses, misapplies, goofs badly, ...) crypto, and claims to be a computer security issue is another thing altogether. The point was worth making, though perhaps it was made too covertly. Have you a suggestion? ww 19:50, 14 Jul 2004 (UTC)
 * The real purpose of putting "In field F, ..." at the start of articles is to provide the reader with some context about what general domain he's reading about. If the clause is too wordy, then I think it lessens the usefulness. — Matt 20:04, 14 Jul 2004 (UTC)

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If PKIX is to be merged with anything, it needs to be merged with X.509 not Public_key_infrastructure, because X.509 is a subset of Public_key_infrastructure and PKIX is related entirely to the subset rather than the set. Stuartyeates 07:10, 30 May 2006 (UTC)

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added external link
I added a link to a FAQ at Entrust website, which presents a useful overview of a PKI. At least I appreciated it as an engineering student, it doesn't have the purpose of advertise a company instead of one another (by the way, I know nothing about their products). carlo —Preceding unsigned comment added by 83.184.183.81 (talk • contribs) 08:24, 26 June 2006

diagram
Diagram has no description, RA and VA are not referenced in the article. Also the order of arrows would be unclear to novice reader. Maybe someone could help? Gryszkalis 11:21, 20 October 2007 (UTC)
 * Here is a german version of the diagram with editable texts. --Bananenfalter (talk) 19:18, 15 June 2012 (UTC)

Plagiarism?
Do slides 14-17 from the following URL seem awfully familiar when reading the "PKI Software" section of this article?

http://ocw.kfupm.edu.sa/user062/CSE55101/KeyM.pdf

What is the usual course of action in this case?

Also, I think some of these products do not exist anymore (e.g. CyberTrust TrustedCA)...or never existed.

Karl Wiegand (talk) 00:56, 27 December 2007 (UTC)

 * Well, it's not clear which cis original. I would suspect the slides are preped from the wikipedia page though, as the section was added 1st March 2007, nearly 3 months before the slides are dated. RobbieAB (talk) 02:51, 2 April 2008 (UTC)aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa

"bind" should be more prominent.
Over the past year, when trying to explain digital security and digital certificates, I've found people stumble until they grasp the concept of BINDING a digital certificate to a person's identity. This article makes the point very early, which is good, but I think you should make it much more emphatically. ie bold, linked to a detailed explanation, etc.

Richard. —Preceding unsigned comment added by Richardh9935 (talk • contribs) 01:41, 2 July 2008 (UTC)

'VA' ?
In the diagram on the page is an object called 'VA', but this term is not explained or referenced to in the main text. 77.63.71.8 (talk) 10:52, 20 October 2008 (UTC)

--

It probably stands for Validation Authority AH, S+

A Question
Hi. Do you know any free, gpl or open source software, for Windows XP or platform-independent, that shows me all the certificates installed on my machine, in something like a "who-certificates-whom" (certificate dependencies) graphical tree?

(Or, in case you don't know any software like this, do you know any good source or site where I could ask?)

Thank you very much. --Faustnh (talk) 16:16, 28 March 2009 (UTC)

Simplified Intro
As a result of feedback from Skippydo I have simplified the opening (introductory) section. It now contains only a statement of the problem and an un-jargon-ized context statement. I think this goes some way toward reducing the problem of examples of use, since the goal of any encyclopedia article is to reach a wide audience, which I take to be the real reason for examples.

Diagrams likewise. I've left the dia in, even though it's not well integrated, since it helps a wide audience. You don't have to understand a dia completely to get some help from it.

I've removed the word 'bind' although not the idea. 'Bind' is in vogue right now, and therefore, it has acquired a variety of metaphorical meanings: map, instantiate, allocate, control. I thought it better to explain in plain English.

I created a section for the CA approach to authentication. Hopefully, new material on that topic will be put there. Akurn (talk) 21:32, 16 October 2009 (UTC)

 * In my opinion, you have completely trashed the intro. PK cryptography enables secure communication between systems as well as individuals; it provides security without regard to whether there is actually an attacker or not.  NO SUPPORT IS NEEDED???  Please explain how you expect to revoke a compromised key?  The article title is 'Public Key Infrastructure' and should talk about the infrastructure.  The intro was fine like it was.  Please fix these deficiencies or revert.Jarhed (talk) 08:09, 30 October 2009 (UTC)

Not only for users
Clark Gabler / March 2011 —Preceding unsigned comment added by 212.23.234.250 (talk) 15:08, 4 March 2011 (UTC)
 * Reading your introduction gives the feeling that a user identity refers only to a person as digital certificates are meant for wider usage.
 * The Validation Authority (VA) is still not referred

 * If a digital cert can be issued to a corporate entity, that needs to be described in the article.Jarhed (talk) 23:00, 15 June 2011 (UTC)

File:Public-Key-Infrastructure.svg needs a do-over
Can we please get something a little less hokey? 209.217.100.70 (talk) 17:26, 23 April 2012 (UTC)

Maybe something from the Bananenfalter (who did such excellent work as commons:Category:Orange_blue_cryptography_diagrams 209.217.100.70 (talk) 17:29, 23 April 2012 (UTC)
 * Took me some time, but now it’s done. See the category mentioned above. --Bananenfalter (talk) 19:20, 15 June 2012 (UTC)

PKA redirects here and I believe that's incorrect
PKA (Public Key Authentication) is related to PKI, but lacks certificates or an Infrastructure for validating certificates. I see that PKA can also be an acronym for Public Key Authority, which may be another name for PKI, but that should be made clear on the disambiguation page.

I'm not bold enough to edit the articles at this point, because I admit I might be right about some of these issues. JordanHenderson (talk) 14:00, 17 September 2012 (UTC)
 * You mean PKA? If so, add as many additional entries as you feel is necessary. What you say makes sense and I don't see that anyone would object. Skippydo (talk) 04:33, 18 September 2012 (UTC)
 * I've changed the disambiguation link target to the more appropriate public-key cryptography, within which the concept Public Key Authentication lives more comfortably. I'm not convinced that the term Public Key Authority is notable. — Quondum 06:38, 18 September 2012 (UTC)

[Citation needed]
While reading this article I got crazy by all the templates "citation needed". The footnotes distract terribly from the text and are completely useless for the reader. What is the reader supposed to do the with this info? Not believe the marked paragraph? But why would (s)he bother to read it then? The templates should be used sparingly: only when a surprising statement without proper foundation is made. Also, the template text should be much less obtrusive. --P.wormer (talk) 08:29, 3 January 2014 (UTC)
 * The article contains many claims which need in-line citations of reliable sources. Could you please help by adding a few? For the History section, I replaced all distracting citation needed templates with an section to reduce distraction. I also moved refimprove from the references section to the top of the article. The Yeti 09:10, 3 January 2014 (UTC)

Market Share
Is a section on market share really relevant to this topic? Sounds more like advertising for Symantec.

Interestingly, almost the same paragraph appears here: https://en.wikipedia.org/wiki/Transport_Layer_Security#Certificate_Authorities, where it is equally questionable.

External links modified (January 2018)
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Question Relating to Criticism Section
I'm not quite sure I understand this statement, from the Criticism section of the article: "Current web browsers carry pre-installed intermediary certificates issued and signed by a Certificate Authority. This means browsers need to carry a large number of different certificate providers, increasing the risk of a key compromise."

Web browsers carry many certificates signed by many CAs. They don't carry the (private) keys with which the certificates are signed, so I don't know how those keys would risk being compromised. — Preceding unsigned comment added by Scottnch (talk • contribs) 17:42, 12 October 2018 (UTC)

 * One possible interpretation is that a certificate authority could be compromised, on a small or large scale. Their secret keys could be leaked by an insider (one hopes a CA would use hardware that prevents even insiders from seeing the actual values of the secret keys, but who knows)? Or, a government could force a CA to issue illegitimate certificates. Or, a CA could be careless in verifying the identity of those who apply for certificates. Jc3s5h (talk) 18:05, 12 October 2018 (UTC)

*the* PKI?
It seems to me that this article should be about the PKI using CA's etc. Does this have a name? is it OK to call it "*the* PKI"?. If that is the case, then I think that "Web of trust", "Simple public key infrastructure" and "Blockchain-based PKI" need to go under an "Alternatives" section.

Thoughts? - Snori (talk) 22:03, 26 December 2018 (UTC)

Blockchain
The blockchain section looks like a marketing page. The claim that blockchain is suited for public key distribution does not make sense. In theory a Public key can be broadcast on a billboard or the Internet, and technically it is almost the very first thing you get when you visit any https site (these days any site!). The fact that there are no references to this claim should flag it for removal. Or at least reword it to "Blockchain solutions have attempted to provide infrastructure to distribute public keys". Either way the world wide web has done a better job at distribution of public keys. Supcmd (talk) 13:04, 14 April 2020 (UTC)

Capabilities
The capabilities section regards capabilities of public key cryptography and not public key infrastructure. PKI is eventually about certification (and related topics, e.g., revocation). I propose removing this section. رهبرمعظم (talk) 14:23, 2 January 2024 (UTC)

title: Talk:Public key infrastructure


text:
Rebreather

A rebreather is a breathing apparatus that absorbs the carbon dioxide of a user's exhaled breath to permit the rebreathing (recycling) of the substantially unused oxygen content, and unused inert content when present, of each breath. Oxygen is added to replenish the amount metabolised by the user. This differs from open-circuit breathing apparatus, where the exhaled gas is discharged directly into the environment. The purpose is to extend the breathing endurance of a limited gas supply, while also eliminating the bubbles otherwise produced by an open circuit system. The latter advantage over other systems is useful for covert military operations by frogmen, as well as for undisturbed observation of underwater wildlife. A rebreather is generally understood to be a portable apparatus carried by the user. The same technology on a vehicle or non-mobile installation is more likely to be referred to as a life-support system.

Rebreather technology may be used where breathing gas supply is limited, such as underwater, in space, where the environment is toxic or hypoxic (as in firefighting), mine rescue, high-altitude operations, or where the breathing gas is specially enriched or contains expensive components, such as helium diluent or anaesthetic gases.

Rebreathers are used in many environments: underwater, diving rebreathers are a type of self-contained underwater breathing apparatus which have provisions for both a primary and emergency gas supply. On land they are used in industrial applications where poisonous gases may be present or oxygen may be absent, firefighting, where firefighters may be required to operate in an atmosphere immediately dangerous to life and health for extended periods, in hospital anaesthesia breathing systems to supply controlled concentrations of anaesthetic gases to patients without contaminating the air that the staff breathe, and at high altitude, where the partial pressure of oxygen is low, for high altitude mountaineering. In aerospace there are applications in unpressurised aircraft and for high altitude parachute drops, and above the Earth's atmosphere, in space suits for extra-vehicular activity. Similar technology is used in life-support systems in submarines, submersibles, atmospheric diving suits, underwater and surface saturation habitats, spacecraft, and space stations, and in gas reclaim systems used to recover the large volumes of helium used in saturation diving.

The recycling of breathing gas comes at the cost of technological complexity and specific hazards, some of which depend on the application and type of rebreather used. Mass and bulk may be greater or less than open circuit depending on circumstances. Electronically controlled diving rebreathers may automatically maintain a partial pressure of oxygen between programmable upper and lower limits, or set points, and be integrated with decompression computers to monitor the decompression status of the diver and record the dive profile.

General concept
As a person breathes, the body consumes oxygen and produces carbon dioxide. Base metabolism requires about 0.25 L/min of oxygen from a breathing rate of about 6 L/min, and a fit person working hard may ventilate at a rate of 95 L/min but will only metabolise about 4 L/min of oxygen. The oxygen metabolised is generally about 4% to 5% of the inspired volume at normal atmospheric pressure, or about 20% of the available oxygen in the air at sea level. Exhaled air at sea level contains roughly 13.5% to 16% oxygen.

The situation is even more wasteful of oxygen when the oxygen fraction of the breathing gas is higher, and in underwater diving, the compression of breathing gas due to depth makes the recirculation of exhaled gas even more desirable, as an even larger proportion of open circuit gas is wasted. Continued rebreathing of the same gas will deplete the oxygen to a level which will no longer support consciousness, and eventually life, so gas containing oxygen must be added to the breathing gas to maintain the required concentration of oxygen.

However, if this is done without removing the carbon dioxide, it will rapidly build up in the recycled gas, resulting almost immediately in mild respiratory distress, and rapidly developing into further stages of hypercapnia, or carbon dioxide toxicity. A high ventilation rate is usually necessary to eliminate the metabolic product carbon dioxide (CO2). The breathing reflex is triggered by CO2 concentration in the blood, not by the oxygen concentration, so even a small buildup of CO2 in the inhaled gas quickly becomes intolerable; if a person tries to directly rebreathe their exhaled breathing gas, they will soon feel an acute sense of suffocation, so rebreathers must remove the CO2 in a component known as a carbon dioxide scrubber.

By adding sufficient oxygen to compensate for the metabolic usage, removing the carbon dioxide, and rebreathing the gas, most of the volume is conserved.

Endurance
The endurance of a rebreather, the duration for which it can be safely and comfortably used, is dependent on the oxygen supply at the oxygen consumption rate of the user, and the capacity of the scrubber to remove carbon dioxide at the rate it is produced by the user. These variables are closely linked, as the carbon dioxide is a product of metabolic oxygen consumption, though not the only product. This is independent of depth, except for work of breathing increase due to gas density increase.

Architecture
[[File:Rebreather architecture.png|thumb|upright=1.3|Comparison of pendulum and loop rebreather architecture1 Mouthpiece with dive/surface valve

2 Two way breathing hose

2a Exhalation hose with non-return valve

2b Inhalation hose with non-return valve

3 Scrubber

4 Counterlung

5 Automatic make-up valve

6 Manual bypass valve

7 Breathing gas storage cylinder

8 Cylinder valve

9 Regulator first stage

10 Cylinder pressure gauge

11 Over-pressure valve]] There are two basic arrangements controlling the flow of breathing gas inside the rebreather, known as the pendulum and loop systems.

Pendulum
In the pendulum configuration, the user inhales gas from the counterlung through a breathing hose, and exhaled gas returns to the counter lung by flowing back through the same hose. The scrubber is usually between the breathing hose and the counterlung bag, and gas flow is bi-directional. All of the flow passages between the user and the active absorbent in the scrubber are dead space – volume containing gas which is rebreathed without modification by the rebreather. The dead space increases as the absorbent is depleted. Breathing hose volume must be minimised to limit dead space.

Loop
In the loop configuration, the user inhales gas through one hose, and exhales through a second hose. Exhaled gas flows into the scrubber from one side, and exits at the other side. There may be one large counterlung, on either side of the scrubber, or two smaller counterlungs, one on each side of the scrubber. Flow is in one direction, enforced by non-return valves, which are usually in the breathing hoses where they join the mouthpiece. Only the flow passage in the mouthpiece before the split between inhalation and exhalation hoses is dead space, and this is not affected by hose volume.

Components
There are some components that are common to almost all personal portable rebreathers. These include the ambient pressure breathing volume components, usually called the breathing loop in a circulating flow rebreather, and the make-up gas supply and control system.

Counterlung
The counterlung is an airtight bag of strong flexible material that holds the volume of the exhaled gas until it is inhaled again. There may be a single counterlung, or one on each side of the scrubber, which allows a more even flow rate of gas through the scrubber, which can reduce work of breathing and improve scrubber efficiency by a more consistent.

Scrubber
The scrubber is a container filled with carbon dioxide absorbent material, mostly strong bases, through which the exhaled gas passes to remove the carbon dioxide. The absorbent may be granular or in the form of a moulded cartridge. Granular sorb may be manufactured by breaking up lumps of lime and sorting the granules by size, or by moulding granules at a consistent size and shape. Gas flow through the scrubber may be in one direction in a loop rebreather, or both ways in a pendulum rebreather. The scrubber canister generally has an inlet on one side and an outlet on the other side.

A typical absorbent is Sodalime, which is made up of calcium hydroxide Ca(OH)2, and potassium hydroxide KOH, or sodium hydroxide NaOH (Either or both of these may be present). The main component of soda lime is calcium hydroxide, which is relatively cheap and easily available. Other components may be present in the absorbent. Sodium hydroxide is added to accelerate the reaction with carbon dioxide. Other chemicals may be added to prevent unwanted decomposition products when used with standard halogenated inhalation anaesthetics. An indicator may be included to show when carbon dioxide has dissolved in the water of the soda lime and formed carbonic acid, changing the pH from basic to acid, as the change of colour shows that the absorbent has reached saturation with carbon dioxide and must be changed.

The carbon dioxide combines with water or water vapor to produce a weak carbonic acid: CO2 + H2O –> H2CO3. This reacts with the hydroxides to produce carbonates and water in an exothermic reaction: In the intermediate reaction, the carbonic acid reacts exothermically with sodium hydroxide to form sodium carbonate and water: H2CO3 + 2NaOH –> Na2CO3 + 2H2O + heat. In the final reaction, the sodium carbonate reacts with the slaked lime (calcium hydroxide) to form calcium carbonate and sodium hydroxide: Na2CO3 + Ca(OH)2 –> CaCO3 + 2NaOH. The sodium hydroxide is then available again to react with more carbonic acid. 100 g of this absorbent can remove about 15 to 25 L of carbon dioxide at standard atmospheric pressure This process also heats and humidifies the air, which is desirable for diving in cold water, or climbing at high altitudes, but not for working in hot environments.

Other reactions may be used in special circumstances. Lithium hydroxide and particularly lithium peroxide may be used where low mass is important, such as in space stations and space suits. Lithium peroxide also replenishes the oxygen during the scrubbing reaction.

Another method of carbon dioxide removal occasionally used in portable rebreathers is to freeze it out, which is possible in a cryogenic rebreather which uses liquid oxygen. The liquid oxygen absorbs heat from the carbon dioxide in a heat exchanger to convert the oxygen to gas, which is sufficient to freeze the carbon dioxide. This process also chills the gas, which is sometimes, but not always, desirable.

Breathing hoses
A breathing hose or sometimes breathing tube on a rebreather is a flexible tube for breathing gas to pass through at ambient pressure. They are distinguished from the low-, intermediate-, and high-pressure hoses which may also be parts of rebreather apparatus. They have a wide enough bore to minimise flow resistance at the ambient pressure in the operational range for the equipment, are usually circular in cross section, and may be corrugated to let the user's head move about without the tube collapsing at kinks.

Each end has an airtight connection to the adjacent component, and they may contain a one-way valve to keep the gas circulating the right way in a loop system. Depending on the service, they may be made of a flexible polymer, an elastomer, a fibre or cloth reinforced elastomer, or elastomer covered with a woven fabric for reinforcement or abrasion resistance. If the woven layer is bonded to the outside surface it protects the rubber from damage from scrapes but makes it more difficult to wash off contaminants.

Breathing hoses are usually long enough to connect the apparatus to the user's head in all attitudes of their head, but should not be unnecessarily long, which will cause additional weight, hydrodynamic drag, risk snagging on things, or contain excess dead space in a pendulum rebreather. Breathing hoses can be tethered down to a diver's shoulders or ballasted for neutral buoyancy to minimise loads on the mouthpiece.

Mouthpiece or facemask
A mouthpiece with bite-grip, an oro-nasal mask, a full-face mask, or a sealed helmet is provided so that the user can breathe from the unit hands-free.

Oxygen supply
A store of oxygen, usually as compressed gas in a high pressure cylinder, but sometimes as liquid oxygen, that feeds gaseous oxygen into the ambient pressure breathing volume, either continuously, or when the user operates the oxygen addition valve, or via a demand valve in an oxygen rebreather, when the volume of gas in the breathing circuit becomes low and the pressure drops, or in an electronically controlled mixed gas rebreather, after a sensor has detected insufficient oxygen partial pressure, and activates a solenoid valve.

Valves
Valves are needed to control gas flow in the breathing volume, and gas feed from the storage container. They include:
 * Non-return valves in the breathing loop of loop rebreathers, which enforce one-directional flow to minimise dead space,
 * Dive/surface valves on diving rebreathers, which prevent water from entering the breathing volume when the mouthpiece is removed, or the user elects to breathe ambient air at the surface.
 * Gas supply valves, including a cylinder valve, to allow high pressure gas to flow from the cylinder. This may be manually operated by the user to directly supply make-up gas, or may provide the gas to a pressure regulator which reduces the pressure to a few bar above ambient pressure, and supplies this intermediate pressure gas to the gas feed system, which may contain one or more of:
 * Manually operated feed valve,
 * Constant mass flow orifice or needle valve, to provide a continuous feed,
 * Demand valve which automatically adds gas when the volume of the counterlung(s) is too low, and pressure in the breathing volume drops below ambient pressure.
 * Overpressure valve, to release excess gas. This is mainly used in diving rebreathers to compensate for expansion during ascent. Excess gas may also be vented past the skirt seal of a full-face mask, or through the nose when a mouthpiece is used.

Oxygen sensors
Oxygen sensors may be used to monitor partial pressure of oxygen in mixed gas rebreathers to ensure that it does not fall outside the safe limits, but are generally not used on oxygen rebreathers, as the oxygen content is fixed at 100%, and its partial pressure varies only with the ambient pressure.

System variants
Rebreathers can be primarily categorised as diving rebreathers, intended for hyperbaric use, and other rebreathers used at pressures from slightly more than normal atmospheric pressure at sea level to significantly lower ambient pressure at high altitudes and in space. Diving rebreathers must often deal with the complications of avoiding hyperbaric oxygen toxicity, while normobaric and hypobaric applications can use the relatively trivially simple oxygen rebreather technology, where there is no requirement to monitor oxygen partial pressure during use providing the ambient pressure is sufficient.

Rebreathers can also be subdivided by functional principle as closed circuit and semi-closed circuit rebreathers.
 * : A closed circuit rebreather adds oxygen to the loop gas to make up for oxygen used by metabolic processes. These processes do not use diluent gas, so none is added unless the volume of the loop is reduced for other reasons, such as intentional dumping, flushing, or an ambient pressure change. Gas is dumped from the loop when it expands during a pressure reduction, or too much is added.
 *  also known as a gas extender: A semi-closed circuit rebreather either dumps some loop gas nearly constantly or constantly adds gas to the loop, and consequently needs an inflow of both diluent and oxygen to make up the volume. Changes in ambient pressure also require changes in the amount (mass) of gas in the loop to maintain the working volume.

Oxygen rebreathers

This is the earliest type of rebreather and was commonly used by navies for submarine escape and shallow water diving work, for mine rescue, high altitude mountaineering and flight, and in industrial applications from the early twentieth century. Oxygen rebreathers can be remarkably simple and mechanically reliable, and they were invented before open-circuit scuba. They only supply oxygen, so there is no requirement to control the gas composition other than removing the carbon dioxide.

Oxygen feed options
In some rebreathers the oxygen cylinder has oxygen supply mechanisms in parallel. One is constant flow; the other is a manual on-off valve called a bypass valve; both feed into the same hose which feeds the counterlung. Others are supplied via a demand valve on the counterlung. This will add gas at any time that the counterlung is emptied and the diver continues to inhale. Oxygen can also be added manually by a button which activates the demand valve. Some simple oxygen rebreathers had no automatic supply system, but only the manual feed valve, and the diver had to operate the valve at intervals to refill the breathing bag as the volume of oxygen decreased below a comfortable level.

Mixed gas rebreathers
All rebreathers other than oxygen rebreathers may be considered mixed gas rebreathers, as the breathing gas is a mixture of oxygen and metabolically inactive diluent gas. These can be divided into semi-closed circuit, where the supply gas is a breathable mixture containing oxygen and inert diluents, usually nitrogen and helium, and which is replenished by adding more of the mixture as the oxygen is used up, sufficient to maintain a breathable partial pressure of oxygen in the loop, and closed circuit rebreathers, where two parallel gas supplies are used: the diluent, to provide the bulk of the gas, and which is recycled, and oxygen, which is metabolically expended. Carbon dioxide is considered a waste product, and in a correctly functioning rebreather, is effectively removed when the gas passes through the scrubber.

Rebreathers using an absorbent that releases oxygen

There have been a few rebreather designs (e.g. the Oxylite) which use potassium superoxide, which gives off oxygen as it absorbs carbon dioxide, as the carbon dioxide absorbent: 4KO2 + 2CO2 = 2K2CO3 + 3O2. A small volume oxygen cylinder is needed to fill and purge the loop at the start of use. This technology may be applied to both oxygen and mixed gas rebreathers, and can be used for diving and other applications. Potassium superoxide reacts vigorously with liquid water, releasing considerable heat and oxygen, and causing a fire hazard, so the more successful applications have been for space-suits, fire-fighting and mine rescue.

Rebreathers which use liquid oxygen
A liquid oxygen supply can be used for oxygen or mixed gas rebreathers. If used underwater, the liquid-oxygen container must be well insulated against heat transfer from the water. Industrial sets of this type may not be suitable for diving, and diving sets of this type may not be suitable for use out of water due to conflicting heat transfer requirements. The set's liquid oxygen tank must be filled immediately before use. Examples of the type include:
 * Blackett's Aerophor
 * Aerorlox

Cryogenic rebreather
A cryogenic rebreather removes the carbon dioxide by freezing it out in a "snow box" by the low temperature produced as liquid oxygen evaporates to replace the oxygen used.

Fields of application

 * Underwater – as a self-contained breathing apparatus, where it is sometimes known as "closed circuit scuba" as opposed to "open circuit scuba" where the diver exhales breathing gas into the surrounding water. Surface-supplied diving equipment may incorporate rebreather technology either as a gas reclaim system, where the surface-supplied breathing gas is returned and scrubbed at the surface, or as a carried by the diver.  Rebreathers may also be used as self-contained diver bailout systems for either scuba or surface-supplied diving.
 * Mine rescue and other industrial applications – where poisonous gases may be present or oxygen may be absent.
 * Fire fighting, where personnel may be required to operate in an atmosphere immediately dangerous to life and health for longer periods than open-circuit Self-contained breathing apparatus (SCBA) can provide air.
 * Crewed spacecraft and space suits – outer space is, effectively, a vacuum without oxygen to support life.
 * Himalayan or high-altitude mountaineering. High altitude reduces the partial pressure of oxygen in the ambient air, which reduces the ability of the climber to function effectively. Mountaineering rebreathers are closed-circuit oxygen sets that provide a higher partial pressure of oxygen to the climber than the ambient air.
 * Medical anaesthesia breathing systems – to supply controlled concentrations of anaesthetic gases to patients without contaminating the air that the staff breathe, and to conserve anaesthetic gas.
 * Life-support systems of submarines, underwater habitats, and saturation diving systems use a scrubber system working on the same principles as a rebreather.

This may be compared with some applications of open-circuit breathing apparatus:
 * The oxygen enrichment systems primarily used by medical patients, high altitude mountaineers and commercial aircraft emergency systems, in which the user breathes ambient air which is enriched by the addition of pure oxygen,
 * Open circuit breathing apparatus used by firefighters, underwater divers and some mountaineers, which supplies fresh gas for each breath, which is then discharged into the environment.
 * Gas masks and respirators which filter contaminants from ambient air which is then breathed.

Diving rebreathers

The widest variety of rebreather types is used in diving, as the consequences of breathing under pressure complicate the requirements, and a large range of options are available depending on the specific application and available budget. A diving rebreather is safety-critical life-support equipment – some modes of failure can kill the diver without warning, others can require immediate appropriate response for survival.

Surface supplied diving gas reclaim systems
A helium reclaim system (or push-pull system) is used to recover helium based breathing gas after use by the diver when this is more economical than losing it to the environment in open circuit systems. The recovered gas is passed through a scrubber system to remove carbon dioxide, filtered to remove odours, and pressurised into storage containers, where it may be mixed with oxygen to the required composition for re-use, either immediately, or at a later date.

Saturation diving life-support systems
The life support system provides breathing gas and other services to support life for the personnel under pressure in the accommodation chambers and closed diving bell. It includes the following components:
 * Breathing gas supply, distribution and recycling equipment: scrubbers, filters, boosters, compressors, mixing, monitoring, and storage facilities
 * Chamber climate control system - control of temperature and humidity, and filtration of gas
 * Instrumentation, control, monitoring and communications equipment
 * Fire suppression systems
 * Sanitation systems

The life support system for the bell provides and monitors the main supply of breathing gas, and the control station monitors the deployment and communications with the divers. Primary gas supply, power and communications to the bell are through a bell umbilical, made up from a number of hoses and electrical cables twisted together and deployed as a unit. This is extended to the divers through the diver umbilicals.

The accommodation life support system maintains the chamber environment within the acceptable range for health and comfort of the occupants. Temperature, humidity, breathing gas quality, sanitation systems, and equipment function are monitored and controlled.

Atmospheric diving suits

An atmospheric diving suit is a small one-man articulated submersible of roughly anthropomorphic form, with limb joints which allow articulation under external pressure while maintaining an internal pressure of one atmosphere. Breathing gas supply may be surface supplied by umbilical, or from a rebreather carried on the suit. An emergency gas supply rebreather may also be fitted to a suit with either surface supply or rebreather for primary breathing gas. As the internal pressure is maintained at one atmosphere, there is no risk of acute oxygen toxicity. This is an underwater diving application, but has more in common with industrial applications than with ambient pressure scuba rebreathers.

Industrial and rescue self-contained rebreathers
Different design criteria apply to SCBA rebreathers for use only out of the water:
 * There is no variation in ambient pressure on the components. The counterlung may be placed for comfort and convenience.
 * Cooling of the gas in the breathing loop may be desirable, as the absorbent produces heat as it reacts with carbon dioxide, and the warming of the gas is not welcome in hot industrial situations such as firefighting and deep mines.
 * Absorbent containers may in some cases rely on gravity for preventing channeling.
 * If a full-face mask is used, it may have viewports designed for convenience or improved field of vision, and they do not need to be flat and parallel to prevent visual distortion as when underwater.
 * In firefighting rebreathers, consideration must be given to making the set reasonably flame-proof and protecting it from heat and debris impacts.
 * The need to ditch the set quickly may not arise, and harness straps may not need a quick-release.
 * Buoyancy is not a consideration, but weight may be critical. Good ergonomic design for ease of carrying, comfort, and balance are important where the unit may be worn in confined spaces, while climbing and crawling through small gaps.
 * A spring loaded counterlung pressurisation system may be used to provide slight positive pressure in the breathing loop, to prevent noxious gas entry if the mask seal is not perfect.
 * There are no constraints due to the physiological effects of breathing under pressure. Complex gas mixtures are unnecessary. Oxygen rebreathers can usually be used, which makes the design considerably simpler, and the mechanism more reliable.
 * A system allowing the user to access drinking water from a bag may be fitted, A bite operated valve van be used to control flow.
 * Radio voice communications may be fitted.
 * A constant mass flow systen may be used to ensure a minimum fresh gas supply, with a demand valve to add gas if the loop is emptied.
 * Gas supply and absorbent duratio would usually be matched for efficiency
 * Insulation may be needed for the breathing loop for use in sub-zero temperatures where freezing of the absorbent would reduce its effectiveness.
 * A water trap may be provided to collect condensed water from the absorbent reaction and from metabolic product.
 * Monitoring functions may include:
 * Cylinder pressure (analog and digital)
 * Estimated remaining duration of use until residual low pressure warning is activated
 * Temperature indication
 * Automatic recording of warning signals
 * Optical and/or acoustic warning signals may be provided for:
 * Low gas pressure in the cylinder
 * Alarm triggered by lack of user movement
 * Manually triggered alarm.

Mountaineering rebreathers
Mountaineering rebreathers provide oxygen at a higher concentration than available from atmospheric air in a naturally hypoxic environment. They need to be lightweight and to be reliable in severe cold including not getting choked with deposited frost. A high rate of system failures due to extreme cold has not been solved. Breathing pure oxygen results in an elevated partial pressure of oxygen in the blood: a climber breathing pure oxygen at the summit of Mount Everest has a greater oxygen partial pressure than breathing air at sea level. This results in being able to exert greater physical effort at altitude. The exothermic reaction helps keep the scrubber contents from freezing, and helps reduce heat loss from the user.

Both chemical and compressed gas oxygen have been used in experimental closed-circuit oxygen systems – the first on Mount Everest in 1938. The 1953 expedition used closed-circuit oxygen equipment developed by Tom Bourdillon and his father for the first assault team of Bourdillon and Evans; with one "dural" 800l compressed oxygen cylinder and soda lime canister (the second (successful) assault team of Hillary and Tenzing used open-circuit equipment).

Rebreathers for unpressurised aircraft and high altitude parachuting
Similar requirement and working environment to mountaineering, but weight is less of a problem. The Soviet IDA71 rebreather was also manufactured in a high altitude version, which was operated as an oxygen rebreather.

Anaesthesia systems
Anaesthetic machines can be configured as rebreathers to provide oxygen and anaesthetic gases to a patient during surgery or other procedures that require sedation. An absorbent is present in the machine to remove the carbon dioxide from the loop.

Both semi-closed and fully closed circuit systems may be used for anaesthetic machines, and both push-pull (pendulum) two directional flow and one directional loop systems are used. The breathing circuit of a loop configured machine has two unidirectional valves so that only scrubbed gas flows to the patient while expired gas goes back to the machine.

The anaesthetic machine can also provide gas to ventilated patients who cannot breathe on their own. A waste gas scavenging system removes any gasses from the operating room to avoid environmental contamination.

Space suits

One of the functions of a space suit is to provide the wearer with breathing gas. This can be done via an umbilical from the life-support systems of the spacecraft or habitat, or from a primary life support system carried on the suit. Both of these systems involve rebreather technology as they both remove carbon dioxide from the breathing gas and add oxygen to compensate for oxygen used by the wearer. Space suits usually use oxygen rebreathers as this allows a lower pressure in the suit which gives the wearer better freedom of movement.

Habitat life-support systems
Submarines, underwater habitats, bomb shelters, space stations, and other living spaces occupied by several people over medium to long periods on a limited gas supply, are equivalent to closed circuit rebreathers in principle, but generally rely on mechanical circulation of breathing gas through the scrubbers.

Safety
There are several safety issues with rebreather equipment, and these tend to be more severe in diving rebreathers.

Hazards
Some of the hazards are due to the way the equipment works, while others are related to the environment in which the equipment is used, as rebreathers are usually used where no breathable ambient atmosphere is available.

Hypoxia
Hypoxia can occur in any rebreather which contains enough inert gas to allow breathing without triggering automatic gas addition.

In an oxygen rebreather this can occur if the loop is not sufficiently purged at the start of use. Purging is the replacement of the original gas content by fresh gas, and may have to be repeated to completely remove inert gas. Purging should be done while breathing off the unit so that the inert gas in the user's lungs and body tissues that finds its way into the loop is also removed from the system.

Carbon dioxide buildup
Carbon dioxide buildup will occur if the scrubber medium is absent, badly packed, inadequate or exhausted. The normal human body is fairly sensitive to carbon dioxide partial pressure, and a buildup will be noticed by the user. However, there is not often much that can be done to rectify the problem except changing to another breathing gas supply until the scrubber can be repacked. Continued use of a rebreather with an ineffective scrubber is not possible for very long, as the levels will become toxic and the user will experience extreme respiratory distress, ultimately leading to loss of consciousness and death. The rate at which these problems develop depends on the volume of the circuit and the metabolic rate of the user at the time.

Carbon dioxide buildup can also occur when a combination of exertion and work of breathing exceeds the capacity of the user. If this occurs where the user cannot reduce exertion sufficiently, it may be impossible to correct. This problem is more likely to occur with diving rebreathers at depths where the density of the breathing gas is severely elevated. The only recourse is to vent the expelled breath outside the closed system, therefore not reusing the oxygen, and thereby increasing use of the gas mixture, but this is not an option in every field of application.

Leakage of toxic gases into the breathing loop
Industrial rebreathers are often used where the ambient air is contaminated and may be toxic. Parts of the loop will be at a slightly lower than external ambient pressure during inhalation, and if the circuit is not airtight external gases may leak in. This is a particular issue around the edge of a full-face mask, where the rubber mask skirt must seal against the user's face.

Fire hazards of high concentration of oxygen
High partial pressures of oxygen greatly increase fire hazard, and many materials which are self-extinguishing in atmospheric air will burn continuously in a high oxygen concentration. This is more of a hazard for terrestrial applications such as rescue and firefighting than for diving, where the ignition risk is relatively low.

Caustic cocktail
Caused by a loop flood reaching the absorbent canister, so only applicable in immersed applications.

Scrubber failure
The term "break-through" means the failure of the scrubber to continue removing sufficient carbon dioxide from the gas circulating in the loop. This will inevitably happen if the scrubber is used too long, but can happen prematurely in some circumstances. There are several ways that the scrubber may fail or become less efficient:
 * Complete consumption of the active ingredient in a "general break through". Depending on scrubber design and user workload, this may be gradual, allowing the user to become aware of the problem in time to make a controlled exit or bailout to open circuit, or relatively sudden, triggering an urgent or emergency response.
 * Bypassing the absorbent. The absorbent granules must be packed closely so that all exhaled gas comes into contact with the surface of soda lime and the canister is designed to avoid any large spaces or gaps between the absorbent granules or between the granules and the canister walls that would let gas bypass contact with the absorbent. If any of the seals, such as O-rings, or spacers that prevent bypassing of the scrubber, are not present or not fitted properly, or if the scrubber canister has been incorrectly packed or fitted, it may allow the exhaled gas to bypass the absorbent, and the scrubber will be less effective. This failure mode is also called "tunneling" when absorbent settles to form void spaces inside the canister. Bypass will cause an unexpected early break-through.
 * When the gas mix is under pressure at depth, the gas molecules are more densely packed, and the carbon dioxide molecules' mean path between collisions is shorter, so they are not so free to move around to reach the absorbent surface, and require a longer dwell time. Because of this effect, the scrubber must be bigger for deep diving than is needed for a shallow-water, industrial or high altitude rebreather.
 * Carbon dioxide absorbent can be caustic and can cause burns to the eyes, mucous membranes and skin. A mixture of water and absorbent occurs when the scrubber floods and depending on the chemicals used, can produce a chalky taste or a burning sensation if the contaminated water reaches the mouthpiece, which should prompt the diver to switch to an alternative source of breathing gas and rinse their mouth out with water. This is known to rebreather divers as a caustic cocktail. The excessive wetting of the absorbent also reduces the rate of carbon dioxide removal and can cause premature break-through even if no caustic liquid reaches the diver. Work of breathing may also increase. Many modern diving rebreather absorbents are designed not to produce this caustic fluid if they get wet.
 * In below-freezing operation (primarily mountain climbing), wet scrubber chemicals can freeze when oxygen bottles are changed, while there is a pause in the exothermic reaction of taking up the carbon dioxide, thus preventing carbon dioxide from reaching the scrubber material, and slowing the reaction when used again.

Other failure modes

 * Flooding of the ambient pressure volume can occur in diving rebreathers.
 * Gas leakage to or from the ambient pressure volume can occur. Since the volume of gas lost or gained is likely to be very small, it is most relevant when the surroundings contain toxic gases or fumes.
 * Oxygen monitoring failure can lead to incorrect partial pressure of oxygen in the breathing gas. This is only relevant in mixed gas rebreathers used for diving.
 * Gas injection system failure is also mainly a problem of mixed gas diving rebreathers. Oxygen rebreathers gas injection systems are generally robust and reliable and can be manually overridden if they fail, and this form of failure is identifiable by an inappropriate volume of gas in the ambient pressure volume of the rebreather.

Early history
Around 1620, Cornelius Drebbel discovered that heating saltpetre (potassium nitrate) would generate oxygen.

The first basic rebreather based on carbon dioxide absorption was patented in France in 1808 by Pierre-Marie Touboulic from Brest, a mechanic in Napoleon's Imperial Navy. This early rebreather design worked with an oxygen reservoir, the oxygen being delivered progressively by the diver and circulating in a closed circuit through a sponge soaked in limewater, a solution of calcium hydroxide in water. Touboulic called his invention Ichtioandre (Greek for 'fish-man'). There is no evidence of a prototype having been manufactured.

A prototype rebreather was built in 1849 by Pierre Aimable De Saint Simon Sicard,

In 1853 Professor T. Schwann presented a rebreather at the Belgian Academy of Science. It had a large back mounted oxygen tank with working pressure of about 13.3 bar, and two scrubbers containing sponges soaked in a caustic soda solution.

Working rebreathers

The first commercially practical closed-circuit scuba was designed and built by the diving engineer Henry Fleuss in 1878, while working for Siebe Gorman in London. His self-contained breathing apparatus consisted of a rubber mask connected to a breathing bag, with (estimated) 50–60% O2 supplied from a copper tank and CO2 scrubbed by rope yarn soaked in a solution of caustic potash; the system giving a duration of about three hours. Fleuss tested his device in 1879 by spending an hour submerged in a water tank, then one week later by diving to a depth of 5.5 m in open water, upon which occasion he was slightly injured when his assistants abruptly pulled him to the surface.

His apparatus was first used under operational conditions in 1880 by Alexander Lambert, the lead diver on the Severn Tunnel construction project, who was able to travel 1000 feet in the darkness to close several submerged sluice doors in the tunnel; this had defeated his best efforts with standard diving dress due to the danger of the air supply hose becoming fouled on submerged debris, and the strong water currents in the workings. In 1880 Fleuss, used a rebreather to inspect Seaham Colliery in the UK after a gas explosion.

Fleuss and Siebe Gorban developed the Proto breathing apparatus for mine rescue in 1911.

Fleuss continually improved his apparatus, adding a demand regulator and tanks capable of holding greater amounts of oxygen at higher pressure. Sir Robert Davis, head of Siebe Gorman, improved the oxygen rebreather in 1910 with his invention of the Davis Submerged Escape Apparatus, the first practical rebreather to be made in quantity. While intended primarily as an emergency escape apparatus for submarine crews, it was soon also used for diving, being a handy shallow water diving apparatus with a thirty-minute endurance, and as an industrial breathing set.

The rig comprised a rubber breathing/buoyancy bag containing a canister of barium hydroxide to scrub exhaled CO2 and, in a pocket at the lower end of the bag, a steel pressure cylinder holding approximately 56 litres of oxygen at a pressure of 120 bar. The cylinder was equipped with a control valve and was connected to the breathing bag. Opening the cylinder's valve admitted oxygen to the bag and charged it to the pressure of the surrounding water. The rig also included an emergency buoyancy bag on the front of to help keep the wearer afloat. The DSEA was adopted by the Royal Navy after further development by Davis in 1927. Various industrial oxygen rebreathers such as the Siebe Gorman Salvus and the Siebe Gorman Proto, both invented in the early 1900s, were derived from it.

Professor Georges Jaubert invented the chemical compound Oxylithe in 1907. It was a form of sodium peroxide (Na2O2) or sodium superoxide (NaO2). As it absorbs carbon dioxide in a rebreather's scrubber it emits oxygen. This compound was first incorporated into a rebreather design by Captain S.S. Hall and Dr. O. Rees of the Royal Navy in 1909. Although intended for use as a submarine escape apparatus, it was never accepted by the Royal Navy and was instead used for shallow water diving.

In 1912 the German firm Dräger began mass production of their own version of standard diving dress with the air supply from a rebreather. The apparatus had been invented some years earlier by Hermann Stelzner, an engineer at the Dräger company, for mine rescue.

In the 1930s, after some tragic accidents in the 1920s, the United States Navy began to equip Porpoise- and Salmon-class submarines with primitive rebreathers called Momsen lungs, which were in use until the 1960s.

Rebreathers during World War II

In the 1930s, Italian sport spearfishers began to use the Davis rebreather; Italian manufacturers received a licence from the English patent holders to produce it. This practice soon came to the attention of the Italian Navy, which developed an extensively upgraded model designed by Teseo Tesei and Angelo Belloni that was used by its frogman unit Decima Flottiglia MAS with good results during World War II.

During the Second World War, captured Italian frogmen's rebreathers influenced improved designs for British rebreathers. Many British frogmen's breathing sets used aircrew breathing oxygen cylinders salvaged from shot-down German Luftwaffe aircraft. The earliest of these breathing sets may have been modified Davis Submerged Escape Apparatus; their fullface masks were the type intended for the Siebe Gorman Salvus, but in later operations different designs were used, leading to a fullface mask with one big face window, at first circular or oval and later rectangular (mostly flat, but the sides curved back to allow better vision sideways). Early British frogman's rebreathers had rectangular counterlungs on the chest like Italian frogman's rebreathers, but later designs had a square recess in the top of the counterlung so it could extend further up toward the shoulders. In front they had a rubber collar that was clamped around the absorbent canister. Some British armed forces divers used bulky thick diving suits called Sladen suits; one version of it had a flip-up single faceplate for both eyes to let the user get binoculars to his eyes when on the surface.

The Dräger rebreathers, especially the DM20 and DM40 model series, were used by the German helmet divers and German frogmen during World War II. Rebreathers for the US Navy were developed by Dr. Christian J. Lambertsen for underwater warfare. Lambertsen held the first closed-circuit oxygen rebreather course in the United States for the Office of Strategic Services maritime unit at the Naval Academy on 17 May 1943.

During and after WWII, needs arose in the armed forces to dive deeper than allowed by pure oxygen. That prompted, at least in Britain, design of simple constant-flow "mixture rebreather" variants of some of their diving oxygen rebreathers (= what is now called "nitrox"): SCMBA from the SCBA (Swimmer Canoeist's Breathing Apparatus), and CDMBA from the Siebe Gorman CDBA, by adding an extra gas supply cylinder. Before a dive with such a set, the diver had to know the maximum or working depth of his dive, and how fast his body used his oxygen supply, and from those to calculate what to set his rebreather's gas flow rate to.

Post-WWII
The diving pioneer Hans Hass used Dräger oxygen rebreathers in the early 1940s for underwater cinematography.

Due to the military importance of the rebreather, amply demonstrated during the naval campaigns of the Second World War, most governments were reluctant to issue the technology into the public domain. In Britain rebreather use for civilians was negligible, and the BSAC formally prohibited rebreather use by its members. The Italian firms Pirelli and Cressi-Sub at first each sold a model of sport diving rebreather, but after a while discontinued those models. Some home made rebreathers were used by cave divers to penetrate cave sumps.

Most high-altitude mountaineers use open-circuit oxygen equipment; the 1953 Everest expedition used both closed-circuit and open-circuit oxygen equipment: see bottled oxygen.

Eventually the Cold War ended, and in 1989 the Communist Bloc collapsed, and as a result the perceived risk of sabotage attacks by combat divers dwindled, and Western armed forces had less reason to requisition civilian rebreather patents, and automatic and semi-automatic recreational diving rebreathers with oxygen partial pressure sensors started to appear.

Manufacturers and models
Industrial/rescue:
 * made in England from 1910 onwards for use in mine rescue and other industrial uses.
 * SEFA (Selected Elevated Flow Apparatus) – an industrial oxygen rebreather formerly made by Sabre Safety with 2 hours duration on a filling.
 * The Savox was an oxygen rebreather with a use duration of 45 minutes. It had no hard casing and was worn in front of the body.
 * The Savox was an oxygen rebreather with a use duration of 45 minutes. It had no hard casing and was worn in front of the body.
 * The Savox was an oxygen rebreather with a use duration of 45 minutes. It had no hard casing and was worn in front of the body.

Others:

title: Rebreather


text:
Grains of paradise

Grains of paradise (Aframomum melegueta) is a species in the ginger family, Zingiberaceae, and closely related to cardamom. Its seeds are used as a spice (ground or whole); it imparts a pungent, black-pepper-like flavor with hints of citrus. It is also known as melegueta pepper, Guinea grains, ossame, or fom wisa, and is sometimes confused with alligator pepper. The terms African pepper and Guinea pepper have also been used, but are ambiguous as they can apply to other spices such as grains of Selim (Xylopia aethiopica).

It is native to West Africa, which is sometimes named the Pepper Coast (or Grain Coast) because of this commodity. It is also an important cash crop in the Basketo district of southern Ethiopia.

Characteristics
Aframomum melegueta is an herbaceous perennial plant native to swampy habitats along the West African coast. Its trumpet-shaped, purple flowers develop into pods 5 – long, containing numerous small, reddish-brown seeds.

The pungent, peppery taste of the seeds is caused by aromatic ketones, such as (6)-paradol (systematic name: 1-(4-hydroxy-3-methoxyphenyl)-decan-3-one). Essential oils, which are the dominating flavor components in the closely related cardamom, occur only in traces.

The stem at times can be short, and usually shows signs of scars and dropped leaves. The leaves are narrow and similar to those of bamboo, with a well-structured vascular system. The flowers of the herbaceous plant are aromatic, with an orange-colored lip and rich pinkish-orange upper part. The fruits contain numerous, small, golden red-brown seeds.

Ecology
Melegueta is a major component in the diet of Western Lowland gorilla—around 80 to 90 percent. The gorillas eat the entire fruit and act as a source of seed dispersal for meleguetta. In addition to food, the plant is also the most common material used to make nests and beds.

Uses

Melegueta pepper is commonly used in the cuisines of West and North Africa, from where it has been traditionally transported by camel caravan routes through the Sahara desert and distributed to Sicily and the rest of Italy. Mentioned by Pliny as "African pepper" but subsequently forgotten in Europe, they were renamed "grains of paradise" and became a popular substitute for black pepper in Europe in the 14th and 15th centuries. The Ménagier de Paris recommends it for improving wine that "smells stale". Through the Middle Ages and into the early modern period, the theory of the four humors governed theories about nourishment on the part of doctors, herbalists, and druggists. In this context, John Russell characterized grains of paradise in The Boke of Nurture as "hot and moist".

In 1469, King Afonso V of Portugal granted the monopoly of trade in the Gulf of Guinea to Lisbon merchant Fernão Gomes. This included the exclusivity in trade of Aframomum melegueta, then called malagueta pepper. The grant came at the cost of 100,000 real annually and agreement to explore 100 mi of the coast of Africa per year for five years; this gives some indication of the European value of the spice. After Christopher Columbus reached the New World in 1492 and brought the first samples of the chili pepper (Capsicum frutescens) back with him to Europe, the name malagueta, and Spanish and Portuguese spelling, was then applied to the new chili "pepper" because its piquancy was reminiscent of grains of paradise. Malagueta, thanks to its low price, remained popular in Europe even after the Portuguese opened the direct maritime route to the Spice Islands around 1500. This namesake, the malagueta chili, remains popular in Brazil, the Caribbean, Portugal, and Mozambique.

The importance of the A. melegueta spice is shown by the designation of the area from the St. John River (near present-day Buchanan) to Harper in Liberia as the Grain Coast or Pepper Coast in honor of the availability of grains of paradise. Later, the craze for the spice waned, and its uses were reduced to a flavoring for sausages and beer. In the 18th century, its importation to Great Britain collapsed after an act of Parliament during the reign of George III forbade its use in alcoholic beverages. In 1855, England imported about 15000 to 19,000 lb per year legally (duty paid). By 1880, the 9th edition of the Encyclopædia Britannica reported: "Grains of paradise are to some extent used in veterinary practice, but for the most part illegally to give a fictitious strength to malt liquors, gin, and cordials".

The presence of the seeds in the diets of lowland gorillas in the wild seems to have some sort of beneficial effect on their cardiovascular health. They also eat the leaves, and use them for bedding material. The absence of the seeds in the diets of captive lowland gorillas may contribute to their occasionally poor cardiovascular health in zoos.

Today the condiment is sometimes used in gourmet cuisine as a replacement for pepper, and to give unique flavor in some craft beers, gins, and Norwegian akvavit. Grains of paradise are starting to enjoy a slight resurgence in popularity in North America due to their use by some well-known chefs. Alton Brown is a fan of the condiment, and he uses it in okra stew and his apple-pie recipe on an episode of the TV cooking show Good Eats. Grains of paradise are also used by people on certain diets, such as a raw food diet, because they are considered less irritating to digestion than black pepper.

Folk medicine and ritual uses
In West African folk medicine, grains of paradise are valued for their warming and digestive properties, and among the Efik people in Nigeria have been used for divination and ordeals determining guilt. A. melegueta has been introduced to the Caribbean and Latin America, where it is used in Voodoo religious rites. It is also found widely among Protestant Christian practitioners of African-American hoodoo and rootwork, where the seeds are employed in luck-bringing and may be held in the mouth or chewed to prove sincerity.

title: Grains of paradise


text:
Pike (cipher)

The Pike stream cipher was invented by Ross Anderson to be a "leaner and meaner" version of FISH after he broke FISH in 1994. Its name is supposed to be a humorous allusion to the pike fish.

The cipher combines ideas from A5 with the lagged Fibonacci generators used in FISH. It is about 10% faster than FISH, yet believed to be much stronger. It potentially has a huge key length, and no attacks have been published.

Inner workings
Pike consists of three lagged Fibonacci generators with relations $$ \begin{align} a_i = a_{i-55} + a_{i-24} \ (mod \ 2^{32}) \\[] b_i = b_{i-57} + b_{i-7} \ (mod \ 2^{32}) \\[] c_i = c_{i-58} + c_{i-19} \ (mod \ 2^{32}) \end{align} $$

The clock control is based on the carry bits. If all carry bits agree we step all three LFG's, otherwise we step the two who do agree.

This control will be delayed 8 cycles. The final output is the XOR of the least significant words of all three generators.

title: Pike (cipher)


text:
Jill de Jong

Jill de Jong, also known as Jildou de Jong (born 17 February 1982) is a Dutch fitness trainer, health coach, podcast host and former model and actress. Born in Hoogeveen, Drenthe, Netherlands, on 21 March 2002 she was selected by Eidos Interactive as the Lara Croft character model for the Tomb Raider video game series.

She began her career as a model at the age of fifteen after winning a modeling contest in the Netherlands. She went on to become a respected and successful top model, shooting TV and print campaigns for big brand names such as, Ralph Lauren, Escada, Redken, Izod, St. Yves, Fa shower gel, Calvin Klein, Dolce & Gabbana and L'Oréal in Europe and the United States.

In 2019, she published a cookbook titled Models Do Eat. De Jong lives and works in Los Angeles, California.

title: Jill de Jong


text:
Avinash Kak

Avinash C. Kak (born 1944) is a professor of Electrical and Computer Engineering at Purdue University who has conducted pioneering research in several areas of information processing. His most noteworthy contributions deal with algorithms, languages, and systems related to networks (including sensor networks), robotics, and computer vision. Born in Srinagar, Kashmir, he did his Bachelors in BE at University of Madras and Phd in Indian Institute of Technology Delhi. He joined the faculty of Purdue University in 1971.

His brother is the computer scientist Subhash Kak and sister the literary theorist Jaishree Odin.

Robotics and computer vision
His contributions include the 3D-POLY, which is the fastest algorithm for recognizing 3D objects in depth maps In 1992, Kosaka and Kak published FINALE, which is considered to be a computationally efficient and highly robust approach to vision-based navigation by indoor mobile robots. In 2003, a group of researchers that included Kak developed a tool for content-based image retrieval that was demonstrated by clinical trials to improve the performance of radiologists. This remains the only clinically evaluated system for content-based image retrieval for radiologists. His book Digital Picture Processing, co-authored with Azriel Rosenfeld, is also considered a classic and has been one of the most widely referenced sources in literature dealing with digital image processing and computer vision.

Kak is not a believer in Strong AI as evidenced by his provocative/amusing essay Why Robots Will Never Have Sex. This essay a rejoinder to those who believe that robots/computers will someday take over the world.

Image reconstruction algorithms
The SART algorithm (Simultaneous Algebraic Reconstruction Technique) proposed by Andersen and Kak in 1984 has had a major impact in CT imaging applications where the projection data is limited. As a measure of its popularity, researchers have proposed various extensions to SART: OS-SART, FA-SART, VW-OS-SART, SARTF, etc. Researchers have also studied how SART can best be implemented on different parallel processing architectures. SART and its proposed extensions are used in emission CT in nuclear medicine, dynamic CT, and holographic tomography, and other reconstruction applications. Convergence of the SART algorithm was theoretically established in 2004 by Jiang and Wang. His book Principles of Computerized Tomographic Imaging, now re-published as a classic in applied mathematics by SIAM (Society of Industrial and Applied Mathematics), is widely used in courses dealing with modern medical imaging. It is one of the most frequently cited books in the literature on image reconstruction.

Software engineering and open source
The three books written by Kak in the course of his 17-year-long Objects Trilogy Project cover object-oriented programming, object-oriented scripting, and object-oriented design. The first of these, Programming with Objects, presents a comparative approach to the teaching and learning of two large object-oriented languages, C++ and Java. This book is now used in several universities for teaching object-oriented programming with C++ and Java simultaneously. The second book, Scripting with Objects does the same with Perl and Python. The last book of the trilogy is Designing with Objects. Regarding the teaching of programming languages in universities, Kak is critical of programs that start the students off with relatively easier-to-learn languages like Java. and

Over the years, Kak has also contributed to several open-source projects. The software modules developed through these projects are widely used for data analytics and computer security. In addition, during the last decade, Kak has collaborated with people in industry and developed metrics for measuring the quality of large software systems and the usability of APIs (Application Programming Interfaces).

Computer and network security
In computer security research, together with Padmini Jaikumar he has presented a robust solution to the difficult problem of botnet detection in computer networks. He has authored popular online lecture notes that are updated regularly. These notes provide comprehensive overview of computer and network security.

title: Avinash Kak


text:
Whitton

Whitton may refer to:

People

 * Whitton (singer-songwriter), American singer-songwriter
 * Whitton (EP), 2010
 * Charlotte Whitton (1896–1975), Canadian feminist and Mayor of Ottawa
 * David Whitton (born 1952), Scottish politician
 * Donald Whitton (born 1923), Canadian cellist, and teacher
 * Evan Whitton, (1928–2018) Australian journalist
 * Geoff Whitton (born 1942), Australian rules footballer
 * Ivo Whitton (1893–1967), Australian golfer
 * John Whitton (1820–1898), Australian rail engineer
 * Margaret Whitton (1949–2016), American actress
 * Mary Whitton, American computer graphics researcher
 * Michael Whitton, American film director
 * Nicola Whitton (born 1972), British academic and author
 * Steve Whitton (born 1960), English footballer
 * Tiffany Whitton, (born 1987), American woman missing since 2013

Australia

 * Whitton, New South Wales

United Kingdom

 * Whitton, Scottish Borders, a location in Scotland

England

 * Whitton, County Durham
 * Whitton, Herefordshire, a location
 * Whitton, Lincolnshire
 * Whitton, London
 * Whitton, Northumberland, a location
 * Whitton, Shropshire
 * Whitton, Ipswich, Suffolk, a suburb
 * Whitton, Mid Suffolk, Suffolk, a civil parish
 * Whitton, Lowestoft, an estate of Lowestoft, Suffolk

Wales

 * Whitton, Powys

United States

 * Whitton, Arkansas, an unincorporated community
 * Whitton, California, name prior to 1911 of Planada, California
 * Whitton, Illinois, an unincorporated community
 * Whitton, Texas, an unincorporated community

title: Whitton