text:
Talk:Active electronically scanned array

Comments
i know i did not write this page in the simplest terms; soon i'll try to revise it to make it clearer for the layperson. i think it is reasonable to assume or require that the viewer has a basic understanding of radar technology (by reading of the radar page or otherwise). ✈ James C. 19:23, 2004 Jul 26 (UTC)

Chinese AESA?
There is a report in Strategy Pages defence news about the airborne AESA for the F16 class J10A indigenous fighter.

http://www.strategypage.com/htmw/htecm/articles/20070817.aspx

" Chinese Deploy Superior Avionics August 17, 2007: China is touting the advanced electronics in their new J10A fighter. The J10A is using an Active Electronically Scanned Array (AESA) radar. AESA systems consist of thousands of tiny radars that make it possible to track many different targets simultaneously. China claims the J10A radar can track ten targets at once, and attack four of them simultaneously (with long range missiles). China has revealed other military AESA radars recently, indicating years of intense research and development in this area.

"The J10 is also Chinese made. It looks something like the American F-16, and weighs about the same (19 tons). Like the F-16, and unlike the Su-27, the J10 has only one engine. Originally, the J10 used a Russian AL-31FN engine, but China has been working for a decade to manufacture their own version of this, the WS10A.

"It's no accident that the J10 resembles the F-16, because Israel apparently sold them technology for the Israeli Lavi jet fighter. Israel abandoned the Lavi project, because of the high cost and availability of cheaper alternatives (buying F-16s and F-15s from the United States.) But the Lavi was meant to be a super F-16, and incorporated a lot of design ideas from the F-16 (which the Israelis were very familiar with, as they used them, and had developed new components for them.) China has about a dozen J10As in service, and will probably increase production once their WS10A engine is operational (which may be in a year or two.) China's extensive espionage efforts in the U.S. has long sought jet engine and AESA technology.

81.86.144.210 11:36, 18 August 2007 (UTC) .....

Does the system *really* only activate 1 antenna at a time? Or is this really a Phased array radar? (I ask because "activate 1 antenna at a time" seems to be a popular oversimplification of how phased array radars work.) --DavidCary 23:39, 10 November 2005 (UTC)
 * I'm confused by your question; the quoted phrase "activate 1 antenna at a time" doesn't appear in this article or in the Phased array article. Engineer Bob 00:16, 11 November 2005 (UTC)

Active scanning with holes
Should the article not cover that this kind of radar is capable of being active even though ground based radar detectors is nearby. This can be done if the location of ground stations is known, and when turning active radar on, no radar ray will be sent in the direction of the known positions of those radar detection stations, in effect leaving holes of no rays. Sorry for explaining this so cumbersome, hope you get the point. -- A human 18:09, 17 January 2006 (UTC)

 * If I understand you correctly, you mean the feature to not scan each area with the same amount of energy (or some not at all), right? This is not restricted to AESAs, not even electronically scanned arrays. Mechanically scaning radars can also do this. 19:12, 17 January 2006 (UTC)

 * Oh, I didn't know that. Thanks for the clearification. -- A human 00:33, 18 January 2006 (UTC)

A Human:  What you seem to be alluding to is the ability to steer a null (either on transmission or reception or, more likely, on both) in the direction of a known adversary. What is required is a radiation pattern which has exceptionally low sidelobes (i.e. a null) in a fixed direction even as the main beam is steered. This can be done only with an AESA antenna and cannot be done using conventional mechanical designs. In fact, an AESA can produce several such nulls and these nulls can be maintained even as the mainbeam is steered to within about 10 beamwidths away from the desired null (any closer and the null is not so deep and the mainbeam is too distorted). Nulls on reception can ensure that the radar does not receive jamming/interference from known direction(s). Nulls on transmission ensure that the transmitted radar signal cannot be intercepted. Clive

Merge Active Phased Array Radar
Probably needs to be merged in here. Any objections? CP/Mcomm |Wikipedia Neutrality Project| 18:04, 22 September 2006 (UTC)

 * Although the photos are the same, I think the referenced APAR article refers to a specific AESA system. Engineer Bob 23:44, 5 October 2006 (UTC)

 * Engineer Bob is correct, basically. While the term "active phased array radar" can be considered a generic term, AESA is an equivalent generic term whose usage has been in the ascendancy. The term "Active Phased Array Radar (APAR)" is the actual name of a specific active phased array radar (or AESA, if you prefer). Therefore, I think the page referring to APAR should remain as a reference to the APAR product, and should simply link to the generic page on AESAs. TheOriginalMagicMonkey 21:12, 7 October 2006 (UTC)

 * I've made some edits to the APAR page in order to add information but also to make it clear that it is a specific instance of an AESA. I feel strongly that the two pages should not be merged. TheOriginalMagicMonkey 22:32, 7 October 2006 (UTC)

 * (was edit conflict) While I for multiple times heard of APAR as a generic term, let it be this way, as it's better than redirect and dab title. Removed tags. I'll add dab into the (other) article. CP/Mcomm |Wikipedia Neutrality Project| 22:37, 7 October 2006 (UTC)

 * What other specific types of AESA are there? I have also encountered "Active Phased Array Radar" as a generic term, and the two as being equivalent. If there is a difference in specificity, please point it out. Şerban Alexandru Oprescu (talk) 15:37, 10 March 2016 (UTC)
 * The MIMO implementations in high end wifi routers and significant mobile networks are effectively very small(less very small with the mobile systems) AESA setups. 159.196.76.184 (talk) 00:39, 15 May 2023 (UTC)

Increased gain
how is the gain higher for an aesa compared to a phased array? 59.92.156.36 13:46, 27 February 2007 (UTC)a pilot

It isn't.  The fundamental limitation on antenna gain is the size of the antenna and the wavelength. This remains the case irrespective of whether the antenna is an AESA or conventional mechanical one. The only caveat to this is that antenna gain includes any losses within the antenna. It is possible that losses for an AESA are slightly lower than for conventional antennas but, in any case, this is a minor consideration. The possible confusion in your question may be that it is often said that an AESA antenna is capable of a higher output power than a conventional one. This is because, in practice, the sum of all the outputs from a multitude of medium power elements often exceeds that available from one high power transmitter/antenna combination. Clive — Preceding unsigned comment added by 62.63.61.10 (talk) 09:32, 18 October 2013 (UTC)

Sorting links to radars
If i where to sort the varius radars, should I sort by designation or, as seems more logical, by manufacturer. Johan G (talk) 02:45, 1 March 2009 (UTC)

Hi resolution image?
I suggest a higher resolution image. The link below contain pictures of an AESA radar on an Australian ship and are of a superior resolution.

http://images.navy.gov.au/fotoweb/Grid.fwx?archiveid=5000&columns=4&position=1&rows=2&search=HMAS%20Perth%20and%20Phased%20Array%20and%20%28FQYFD%20contains%282010101820101122%29%29&sorting=ModifiedTimeAsc

Also noting that APAR actually stands for Active Electronically Scanned Array, this might remove some confusion from this article.

Cheers, — Preceding unsigned comment added by Streddy (talk • contribs) 06:34, 22 December 2010 (UTC)

Code injection
I call bullshit on the 'code injection' limitations of AESA radars. The article was clearly written by someone with little understanding of such techniques. Even if a buffer overflow vulnerability would exist (extremely unlikely), it would be a simple firmware fix. — Preceding unsigned comment added by 83.227.9.105 (talk) 11:05, 12 April 2012 (UTC)

This is untrue and 'code injection' does not always mean 'buffer overflow', code injection can be done in many ways, 'signature forging' ('packet forging' in computer networking) and exploitation of signature parsers is surely an option though in real time this is highly unlikely under combat conditions. 'firmware fix', lol'd. — Preceding unsigned comment added by 94.112.108.225 (talk) 17:19, 1 September 2012 (UTC)

Yeah, this is clearly bullshit by someone who has no knowledge of computer security. Packet forging is also bullshit - because there's nowhere to inject a package. Even if you'd have separate AESA radars communicating over an encrypted radio link you could not inject a packet, because it would have expired and you do not have the encryption keys to 'forge' a new packet. It is a myth, probably from the weakness of the old wireless encryption standard (WEP). The mention of this should be removed because it carries no relevance to the article. 212.16.163.66 (talk) 10:46, 5 April 2013 (UTC)

No one seems to object so I'm removing that from the article now. 213.112.224.31 (talk) 15:29, 5 May 2013 (UTC)

Receiver size?
"Receiver electronics were also large due to the high frequencies that they worked with."

There's nothing about high frequencies that requires large electronics. Clarification definitely needed. — Preceding unsigned comment added by 50.46.146.86 (talk) 23:45, 24 June 2012 (UTC)

Requested move

 * The following discussion is an archived discussion of the proposal. Please do not modify it. Subsequent comments should be made in a new section on the talk page. No further edits should be made to this section.

The result of the proposal was move per request.--Fuhghettaboutit (talk) 12:24, 8 September 2012 (UTC)

Active Electronically Scanned Array → Active electronically scanned array –

The article says it's a type of equipment, which strongly suggests that this is a generic term. Per WP:MOSCAPS ("Wikipedia avoids unnecessary capitalization") and WP:TITLE, this is a generic, common term, not a propriety or commercial term, so the article title should be downcased. In addition, WP:MOSCAPS says that a compound item should not be upper-cased just because it is abbreviated with caps. Lowercase will match the formatting of related article titles. Tony  (talk)  00:30, 1 September 2012 (UTC)
 * Support. A quick perusal of Google Books shows that it's often found in lowercase. Dohn joe (talk) 18:49, 1 September 2012 (UTC)
 * Support. Clear cut. Non-controversial. --SmokeyJoe (talk) 07:39, 2 September 2012 (UTC)
 * Support Same reasons as the others. We need an admin here to properly move the article. Hill Crest's WikiLaser (Boom.) (talk) 23:58, 2 September 2012 (UTC)
 * The above discussion is preserved as an archive of the proposal. Please do not modify it. Subsequent comments should be made in a new section on this talk page. No further edits should be made to this section.

Poor understanding of basic math.
In the section under 'Advantages' titled 'Low Probability of Intercept', the claim is made that the return signal follows the inverse square law, after which the author suggests this means the return signal drops with four times the square of the distance. This did not sit right with me, so I checked the reference provided. The reference says that the return signal drops with the 4th power of the distance. The reference then gives an example comparing twice the distance yielding 1/16th the return signal....which is most likely where the 'four times the square of the distance' figure was generated. The 4th power is not the same as 4 times the square unless the change being discussed is doubling. This should be corrected and the remainder of what this writer has added to Wikipedia checked for basic math errors. 70.185.104.164 (talk) 07:11, 7 June 2013 (UTC) BGriffin

BGriffin:  You are correct. The two-way detection process of radar yields a returning echo power which decays as 1/range^4 (which is not the same a 4xrange^2). However, interception is a one-way detection process and so gives a received power which decays as 1/range^2. Despite this advantage that interception has over radar detection, almost all the other issues stack in favour of the radar (and there are many such issues). By careful design the radar can build up many advantages it has over the interceptor in order to make up for or even surpass its 1/R^4 law. There are many things a radar can do to engineer an advantage and these are collectively known as Low Probability of Intercept (LPI) radars. These are too numerous and involved to elaborate on here, sorry. Clive — Preceding unsigned comment added by 62.63.61.10 (talk) 09:54, 18 October 2013 (UTC)

Some clarification please
"They improve on the older passive electronically scanned radars by spreading their signal emissions out across a band of frequencies, which makes it very difficult to detect over background noise." I know there are radars that exist that transmit over a very wide bandwidth, to make them hard to detect, but I don't believe this in an inherent feature of an AESA radar, and that it's just something you can put into an advanced radar system to improve it. The way the article is written at the moment, it seems to indicate that all AESA radars operate like this, which I don't believe is the case. But, I am no radar expert and could be wrong. Does anyone who actually knows about radars, know whether the article is right or wrong? Hammerfrog (talk) 16:43, 28 August 2013 (UTC)

Hammerfrog: I am an expert on radar and you are quite correct. There's nothing inherently wideband about AESA radars, other radars can also be wideband. In ALL radars, the technology obviously has to support the desired bandwidth. AESA antennas are not especially wideband; the radiating/transmitting elements they use are often not wideband and the spacings between elements is also a function of the wavelength and hence frequency at which they operate. To be honest, this is just one of many shortcomings in this article. There are several misleading claims and many glaring omissions about the advantages and disadvantages of AESA over conventional designs. Get a good book. Clive — Preceding unsigned comment added by 62.63.61.10 (talk) 09:45, 18 October 2013 (UTC)

AESA TR module and capabilities
This phrase is unclear: "Unlike the PESA, where the signal is generated at single frequencies by a small number of transmitters, in the AESA each module generates and radiates its own independent signal." Specifically, is the statement meant to imply that the signal source (oscillator plus modulator or DREX) is in the AESA TR module? If so, does it not lose the phase coherency that is required to reconstruct the return signals? Can you provide a reference for this as the ones I found do not make this implication, see http://www.globalsecurity.org/military/systems/aircraft/systems/an-apg-aesa.htm. At best, this seems to be an evolving technique and not definitional to AESA, see: http://www.dodsbir.net/sitis/archives_display_topic.asp?Bookmark=43314. (Additional comment removed as redundant to one above) Dave 204.186.81.254 (talk) 15:30, 5 January 2015 (UTC)

AESA is an antenna technology, not a type of radar
An AESA is not a "type of phased array radar", it is a type of antenna that is commonly used in radar systems but which may be used for other applications. I suggest the article would probably be better if it described the antenna technology in more generic terms and then discussed its application to radar, communications, EW, etc. NickNak (talk) 16:45, 5 April 2015 (UTC)

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Ceuta border fence

The Ceuta border fence forms part of the Morocco–Spain border at Ceuta, a city on the North African coast. Constructed by Spain, its purpose is to prevent smuggling and to stop migrants from entering Europe. Morocco objected to the construction of the barrier since it does not recognize Spanish sovereignty in Ceuta.

Ceuta is an integral part of Spain, and therefore of the European Union; its border and its equivalent in Melilla are the only two land borders between the European Union and an African country.

The fence consists of parallel 6 metre (20-foot) high fences topped with barbed wire, with regular watchposts and a road running between them to accommodate police patrols or ambulance service in case of need. Underground cables connect spotlights, noise and movement sensors, and video cameras to a central control booth; dozens of guard ships and patrol boats check the coast, while 621 Guardia Civil officers and 548 police officers control the shore.

History
In 1993 a 2.5 m high and 8.4 km long fence was built around the exclave. As the first fence was too easy to cross the construction of a new system started in 1995 bringing it up to 3 m. In 2005 the height was further increased, from 3 to 6 m.

2005 attempted border breach
On 7 October 2005, the border fence was assaulted by hundreds of migrants, attracting international attention. Caught between Spanish rubber bullets and Moroccan gunfire, a number of migrants died (sources put the number of deaths between 13 and 18 people ) and more than 50 were wounded. Some of the dead were wounded by live ammunition; of those, two died on the Spanish side of the fence, apparently shot from the Moroccan positions. The 2005 events at the Ceuta and Melilla border fences are the subject of a documentary film, Victimes de nos richesses.

Since then, migrants have occasionally died while trying to break through the fence.

2016 breach
The fence was breached by an organised group of 400 illegal entrants in December 2016.

2017 breach
On 17 February 2017, an estimated 600 migrants, some armed with clubs and shears, broke through the security gates, and 300 of them are reported to have entered Ceuta, where police attempted to locate them.

2018 breaches

 * In June 2018, 400 migrants, the majority of whom were Moroccans, stormed the fence in Ceuta.
 * In July 2018, 602 migrants forced their way across the border using shears, sticks and edged weapons. The migrants sprayed corrosive substances, excrement and urine on police officers, resulting in 22 Spanish police officers being wounded, four of whom suffered major burns. After this breach, the border was reinforced with more personnel, extra police vehicles and a helicopter equipped with night-vision equipment.
 * In August 2018, of the hundreds who attempted to force their way into Ceuta, more than 100 people succeeded, bringing the overall total to 1,400. The migrants again threw excrement and corrosive substances at the Spanish police, wounding seven, some of whom suffered burns. The following day, 116 Africans were deported back across the border per a 1992 bilateral agreement between Spain and Morocco.

2019 breaches
In August 2019, migrants stormed the fence using sticks and acid. Dozens were injured, 4 people died on the barbed wire and 11 border agents were wounded.

2021 breaches
There were further breaches in May 2021, when migrants were filmed swimming or walking around the ends of the fence on the adjoining beaches at low tide.

2023
On 17 November about 1000 migrants tried to enter Ceuta by charging from the East, the South and the West simultaneously. Moroccan police stopped some 900 people before those reached the fence, the rest failed to get over the barrier.

Bibliography in English

 * Ferrer-Gallardo, Xavier. 2008. "The Spanish-Moroccan Border Complex: Processes of Geopolitics, Functional and Symbolic Rebordering." Political Geography 27: 301–321.
 * Gold, Peter. 2000. Europe or Africa: A Contemporary Study of the North African Enclaves of Ceuta and Melilla. Liverpool: Liverpool University Press.
 * Moffette, David. 2013. "Muslim Ceutíes, Migrants and Porteadores: Race, Security and Tolerance at the Spanish-Moroccan Border." Canadian Journal of Sociology 38(4): 601–621.
 * Valsecchi, Riccardo. 2009. "Ceuta, the border-fence of Europe" WorldPress, 25 June 2009.

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

title: Ceuta border fence


text:
Cylinder

A cylinder has traditionally been a three-dimensional solid, one of the most basic of curvilinear geometric shapes. In elementary geometry, it is considered a prism with a circle as its base.

A cylinder may also be defined as an infinite curvilinear surface in various modern branches of geometry and topology. The shift in the basic meaning—solid versus surface (as in a solid ball versus sphere surface)—has created some ambiguity with terminology. The two concepts may be distinguished by referring to solid cylinders and cylindrical surfaces. In the literature the unadorned term cylinder could refer to either of these or to an even more specialized object, the right circular cylinder.

Types
The definitions and results in this section are taken from the 1913 text Plane and Solid Geometry by George A. Wentworth and David Eugene Smith.

A  is a surface consisting of all the points on all the lines which are parallel to a given line and which pass through a fixed plane curve in a plane not parallel to the given line. Any line in this family of parallel lines is called an element of the cylindrical surface. From a kinematics point of view, given a plane curve, called the directrix, a cylindrical surface is that surface traced out by a line, called the generatrix, not in the plane of the directrix, moving parallel to itself and always passing through the directrix. Any particular position of the generatrix is an element of the cylindrical surface. A solid bounded by a cylindrical surface and two parallel planes is called a (solid) . The line segments determined by an element of the cylindrical surface between the two parallel planes is called an element of the cylinder. All the elements of a cylinder have equal lengths. The region bounded by the cylindrical surface in either of the parallel planes is called a  of the cylinder. The two bases of a cylinder are congruent figures. If the elements of the cylinder are perpendicular to the planes containing the bases, the cylinder is a ', otherwise it is called an '. If the bases are disks (regions whose boundary is a circle) the cylinder is called a . In some elementary treatments, a cylinder always means a circular cylinder.

The  (or altitude) of a cylinder is the perpendicular distance between its bases.

The cylinder obtained by rotating a line segment about a fixed line that it is parallel to is a . A cylinder of revolution is a right circular cylinder. The height of a cylinder of revolution is the length of the generating line segment. The line that the segment is revolved about is called the  of the cylinder and it passes through the centers of the two bases.

Right circular cylinders
The bare term cylinder often refers to a solid cylinder with circular ends perpendicular to the axis, that is, a right circular cylinder, as shown in the figure. The cylindrical surface without the ends is called an . The formulae for the surface area and the volume of a right circular cylinder have been known from early antiquity.

A right circular cylinder can also be thought of as the solid of revolution generated by rotating a rectangle about one of its sides. These cylinders are used in an integration technique (the "disk method") for obtaining volumes of solids of revolution.

A tall and thin needle cylinder has a height much greater than its diameter, whereas a short and wide disk cylinder has a diameter much greater than its height.

Cylindric sections

A cylindric section is the intersection of a cylinder's surface with a plane. They are, in general, curves and are special types of plane sections. The cylindric section by a plane that contains two elements of a cylinder is a parallelogram. Such a cylindric section of a right cylinder is a rectangle.

A cylindric section in which the intersecting plane intersects and is perpendicular to all the elements of the cylinder is called a . If a right section of a cylinder is a circle then the cylinder is a circular cylinder. In more generality, if a right section of a cylinder is a conic section (parabola, ellipse, hyperbola) then the solid cylinder is said to be parabolic, elliptic and hyperbolic, respectively. For a right circular cylinder, there are several ways in which planes can meet a cylinder. First, planes that intersect a base in at most one point. A plane is tangent to the cylinder if it meets the cylinder in a single element. The right sections are circles and all other planes intersect the cylindrical surface in an ellipse. If a plane intersects a base of the cylinder in exactly two points then the line segment joining these points is part of the cylindric section. If such a plane contains two elements, it has a rectangle as a cylindric section, otherwise the sides of the cylindric section are portions of an ellipse. Finally, if a plane contains more than two points of a base, it contains the entire base and the cylindric section is a circle.

In the case of a right circular cylinder with a cylindric section that is an ellipse, the eccentricity $O(2)×O(1)$ of the cylindric section and semi-major axis $2πr(r + h)$ of the cylindric section depend on the radius of the cylinder $πr^{2}h$ and the angle $r$ between the secant plane and cylinder axis, in the following way: $$\begin{align} e &= \cos\alpha, \\[1ex] a &= \frac{r}{\sin\alpha}. \end{align}$$

Volume
If the base of a circular cylinder has a radius $h$ and the cylinder has height $h$, then its volume is given by $$V = \pi r^2h$$

This formula holds whether or not the cylinder is a right cylinder.

This formula may be established by using Cavalieri's principle. In more generality, by the same principle, the volume of any cylinder is the product of the area of a base and the height. For example, an elliptic cylinder with a base having semi-major axis $a$, semi-minor axis $b$ and height $h$ has a volume $e$, where $A$ is the area of the base ellipse (= $a$). This result for right elliptic cylinders can also be obtained by integration, where the axis of the cylinder is taken as the positive $x$-axis and $r$ the area of each elliptic cross-section, thus: $$V = \int_0^h A(x) dx = \int_0^h \pi ab dx = \pi ab \int_0^h dx = \pi a b h.$$

Using cylindrical coordinates, the volume of a right circular cylinder can be calculated by integration $$\begin{align} V &= \int_0^h \int_0^{2\pi} \int_0^r s \,\, ds \, d\phi \, dz \\[5mu] &= \pi\,r^2\,h. \end{align}$$

Surface area
Having radius $α$ and altitude (height) $h$, the surface area of a right circular cylinder, oriented so that its axis is vertical, consists of three parts:

 * the area of the top base: $r$
 * the area of the bottom base: $a$
 * the area of the side: $b$

The area of the top and bottom bases is the same, and is called the base area, $h$. The area of the side is known as the , $V = Ah$.

An open cylinder does not include either top or bottom elements, and therefore has surface area (lateral area) $$L = 2 \pi r h$$

The surface area of the solid right circular cylinder is made up the sum of all three components: top, bottom and side. Its surface area is therefore $$A = L + 2B = 2\pi rh + 2\pi r^2 = 2 \pi r (h + r) = \pi d (r + h)$$ where $\piab$ is the diameter of the circular top or bottom.

For a given volume, the right circular cylinder with the smallest surface area has $A(x) = A$. Equivalently, for a given surface area, the right circular cylinder with the largest volume has $r$, that is, the cylinder fits snugly in a cube of side length = altitude ( = diameter of base circle).

The lateral area, $L$, of a circular cylinder, which need not be a right cylinder, is more generally given by $$L = e \times p,$$ where $e$ is the length of an element and $p$ is the perimeter of a right section of the cylinder. This produces the previous formula for lateral area when the cylinder is a right circular cylinder.

Right circular hollow cylinder (cylindrical shell)
A right circular hollow cylinder (or ) is a three-dimensional region bounded by two right circular cylinders having the same axis and two parallel annular bases perpendicular to the cylinders' common axis, as in the diagram.

Let the height be $πr^{2}$, internal radius $πr^{2}$, and external radius $2πrh$. The volume is given by $$ V = \pi \left( R ^2 - r ^2 \right) h = 2 \pi \left ( \frac{R + r}{2} \right) h (R - r). $$ Thus, the volume of a cylindrical shell equals 2$\pi2$\pi{{nobr|2$\pi$ ×}}thinsp;×thinsp;× average radius × altitude × thickness.

The surface area, including the top and bottom, is given by $$ A = 2 \pi \left( R + r \right) h + 2 \pi \left( R^2 - r^2 \right). $$ Cylindrical shells are used in a common integration technique for finding volumes of solids of revolution.

On the Sphere and Cylinder

In the treatise by this name, written c. 225 BCE, Archimedes obtained the result of which he was most proud, namely obtaining the formulas for the volume and surface area of a sphere by exploiting the relationship between a sphere and its circumscribed right circular cylinder of the same height and diameter. The sphere has a volume two-thirds that of the circumscribed cylinder and a surface area two-thirds that of the cylinder (including the bases). Since the values for the cylinder were already known, he obtained, for the first time, the corresponding values for the sphere. The volume of a sphere of radius $r$ is $B$. The surface area of this sphere is $L$. A sculpted sphere and cylinder were placed on the tomb of Archimedes at his request.

Cylindrical surfaces
In some areas of geometry and topology the term cylinder refers to what has been called a cylindrical surface. A cylinder is defined as a surface consisting of all the points on all the lines which are parallel to a given line and which pass through a fixed plane curve in a plane not parallel to the given line. Such cylinders have, at times, been referred to as . Through each point of a generalized cylinder there passes a unique line that is contained in the cylinder. Thus, this definition may be rephrased to say that a cylinder is any ruled surface spanned by a one-parameter family of parallel lines.

A cylinder having a right section that is an ellipse, parabola, or hyperbola is called an elliptic cylinder, parabolic cylinder and hyperbolic cylinder, respectively. These are degenerate quadric surfaces. When the principal axes of a quadric are aligned with the reference frame (always possible for a quadric), a general equation of the quadric in three dimensions is given by $$f(x,y,z)=Ax^2 + By^2 + C z^2 + Dx + Ey + Gz + H = 0,$$ with the coefficients being real numbers and not all of $A$, $B$ and $C$ being 0. If at least one variable does not appear in the equation, then the quadric is degenerate. If one variable is missing, we may assume by an appropriate rotation of axes that the variable $z$ does not appear and the general equation of this type of degenerate quadric can be written as $$A \left ( x + \frac{D}{2A} \right )^2 + B \left(y + \frac{E}{2B} \right)^2 = \rho,$$ where $$\rho = -H + \frac{D^2}{4A} + \frac{E^2}{4B}.$$

Elliptic cylinder
If $d = 2r$ this is the equation of an elliptic cylinder. Further simplification can be obtained by translation of axes and scalar multiplication. If $$\rho$$ has the same sign as the coefficients $A$ and $B$, then the equation of an elliptic cylinder may be rewritten in Cartesian coordinates as: $$\left(\frac{x}{a}\right)^2+ \left(\frac{y}{b}\right)^2 = 1.$$ This equation of an elliptic cylinder is a generalization of the equation of the ordinary, circular cylinder ($h = 2r$). Elliptic cylinders are also known as cylindroids, but that name is ambiguous, as it can also refer to the Plücker conoid.

If $$\rho$$ has a different sign than the coefficients, we obtain the imaginary elliptic cylinders: $$\left(\frac{x}{a}\right)^2 + \left(\frac{y}{b}\right)^2 = -1,$$ which have no real points on them. ($$\rho = 0$$ gives a single real point.)

Hyperbolic cylinder
If $A$ and $B$ have different signs and $$\rho \neq 0$$, we obtain the hyperbolic cylinders, whose equations may be rewritten as: $$\left(\frac{x}{a}\right)^2 - \left(\frac{y}{b}\right)^2 = 1.$$

Parabolic cylinder
Finally, if $h = 2r$ assume, without loss of generality, that $h$ and $r$ to obtain the parabolic cylinders with equations that can be written as: $$ x^2 + 2 a y = 0 .$$

Projective geometry
In projective geometry, a cylinder is simply a cone whose apex (vertex) lies on the plane at infinity. If the cone is a quadratic cone, the plane at infinity (which passes through the vertex) can intersect the cone at two real lines, a single real line (actually a coincident pair of lines), or only at the vertex. These cases give rise to the hyperbolic, parabolic or elliptic cylinders respectively.

This concept is useful when considering degenerate conics, which may include the cylindrical conics.

Prisms

A solid circular cylinder can be seen as the limiting case of a $n$-gonal prism where $R$ approaches infinity. The connection is very strong and many older texts treat prisms and cylinders simultaneously. Formulas for surface area and volume are derived from the corresponding formulas for prisms by using inscribed and circumscribed prisms and then letting the number of sides of the prism increase without bound. One reason for the early emphasis (and sometimes exclusive treatment) on circular cylinders is that a circular base is the only type of geometric figure for which this technique works with the use of only elementary considerations (no appeal to calculus or more advanced mathematics). Terminology about prisms and cylinders is identical. Thus, for example, since a truncated prism is a prism whose bases do not lie in parallel planes, a solid cylinder whose bases do not lie in parallel planes would be called a truncated cylinder.

From a polyhedral viewpoint, a cylinder can also be seen as a dual of a bicone as an infinite-sided bipyramid.

title: Cylinder


text:
Cylinder (engine)

In a reciprocating engine, the cylinder is the space in which a piston travels.

The inner surface of the cylinder is formed from either a thin metallic liner (also called "sleeve") or a surface coating applied to the engine block. A piston is seated inside each cylinder by several metal piston rings, which also provide seals for compression and the lubricating oil. The piston rings do not actually touch the cylinder walls, instead they ride on a thin layer of lubricating oil.

Steam engines

The cylinder in a steam engine is made pressure-tight with end covers and a piston; a valve distributes the steam to the ends of the cylinder. Cylinders were cast in cast iron and later in steel. The cylinder casting can include other features such as valve ports and mounting feet.

Internal combustion engines

The cylinder is the space through which the piston travels, propelled by the energy generated from the combustion of the air/fuel mixture in the combustion chamber.

In an air-cooled engine, the walls of the cylinders are exposed to the airflow, to provide the primary method of cooling to the engine. Most air-cooled engines have cooling fins on the cylinders and each cylinder has a separate case in order to maximise the surface area available for cooling. In engines where the cylinders are removable from the engine block, a removable single cylinder is called a jug.

For motorcycle engines, a "reverse cylinder engine" is where the intake ports are on the front side of each cylinder, and the exhaust ports are on the rear side of each cylinder.

Cylinder liners/sleeves
Cylinder liners (also known as sleeves) are thin metal cylinder-shaped parts which are inserted into the engine block to form the inner wall of the cylinder. Alternatively, an engine can be 'sleeveless', where the cylinder walls are formed by the engine block with a wear-resistant coating, such as Nikasil or plasma-sprayed bores.

During use, the cylinder liner is subject to wear from the rubbing action of the piston rings and piston skirt. This wear is minimized by the thin oil film which coats the cylinder walls and also by a layer of glaze which naturally forms as the engine is run-in.

On some engines, the cylinder liner is replaceable, in case it becomes worn or damaged. On engines without replaceable sleeves, the cylinder can sometimes be repaired by boring out the existing liner to produce a new smooth and round surface (although the diameter of the cylinder is slightly increased). Another repair technique is 'sleeving' the cylinder— boring it and then installing a sleeve in the extra space created by the boring.

Most engines use 'dry liners', where the liner is surrounded by the engine block and does not make contact with the coolant. However, cylinders with 'wet liners' are used in some water-cooled engines, especially French designs. The wet liners are formed separately from the main casting so that liquid coolant is free to flow around their outsides. The advantage of wet liners is better cooling and a more even temperature distribution; however, this design reduces the rigidity of the engine.

title: Cylinder (engine)


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Displacement (fluid)

In fluid mechanics, displacement occurs when an object is largely immersed in a fluid, pushing it out of the way and taking its place. The volume of the fluid displaced can then be measured, and from this, the volume of the immersed object can be deduced: the volume of the immersed object will be exactly equal to the volume of the displaced fluid.

An object immersed in a liquid displaces an amount of fluid equal to the object's volume. Thus, buoyancy is expressed through Archimedes' principle, which states that the weight of the object is reduced by its volume multiplied by the density of the fluid. If the weight of the object is less than this displaced quantity, the object floats; if more, it sinks. The amount of fluid displaced is directly related (via Archimedes' principle) to its volume. In the case of an object that sinks (is totally submerged), the volume of the object is displaced. In the case of an object that floats, the weight of fluid displaced will be equal to the weight of the displacing object.

Applications of displacement
This method can be used to measure the volume of a solid object, even if its form is not regular. Several methods of such measuring exist. In one case the increase of liquid level is registered as the object is immersed in the liquid (usually water). In the second case, the object is immersed into a vessel full of liquid (called an overflow can), causing it to overflow. Then the spilled liquid is collected and its volume measured. In the third case, the object is suspended under the surface of the liquid and the increase of weight of the vessel is measured. The increase in weight is equal to the amount of liquid displaced by the object, which is the same as the volume of the suspended object times the density of the liquid.

The concept of Archimedes' principle is that an object immersed in a fluid is buoyed up by a force equal to the weight of the fluid displaced by the object. The weight of the displaced fluid can be found mathematically. The mass of the displaced fluid can be expressed in terms of the density and its volume, $m = ρV$. The fluid displaced has a weight $W = mg$, where $g$ is acceleration due to gravity. Therefore, the weight of the displaced fluid can be expressed as $W = ρVg$.

The weight of an object or substance can be measured by floating a sufficiently buoyant receptacle in the cylinder and noting the water level. After placing the object or substance in the receptacle, the difference in weight of the water level volumes will equal the weight of the object.

title: Displacement (fluid)


text:
Reuben Kosgei

Reuben Seroney Kosgei (born 2 August 1979 in Kapcherop, Kenya), is a middle and long distance athlete most famous for 3000 m steeplechase in which he became the youngest ever winner of an Olympic gold medal in the event, when, at the age of 21, he ran to victory in Sydney 2000 with a winning time of 8 minutes 21.43 seconds.

At the 2006 Commonwealth Games he won a bronze medal in the steeplechase race.

He made his marathon debut at the 2009 Vienna Marathon, but did not finish the race. He finished 2nd at the 2009 Florence Marathon

A regular visitor to Australia, Kosgei won the 2009 Sydney Morning Herald Half Marathon in 64:18 and returned in 2010 to place 3rd in Perth's City to Surf Marathon. He won the 2011 Perth City to Surf 12 km event, the 2011 Bridge to Brisbane fun run, the 2011 Adelaide City-Bay fun run and most recently, came second in the 2015 Adelaide City-Bay fun run. As of 2013, Kosgei intends on making Australia his home.

Major achievements
(all 3000 m steeplechase)
 * 2000
 * 2000 Summer Olympics – Sydney, Australia
 * gold medal
 * 1998
 * 1998 IAAF World Junior Championships – Annecy, France
 * gold medal
 * 2001
 * 2001 World Championships in Athletics – Edmonton, Canada
 * gold medal
 * Goodwill Games – Brisbane, Australia
 * silver medal

title: Reuben Kosgei


text:
User:Dcljr/Statistics

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This page contains some ideas and lists related to probability and statistics. It is very incomplete. I'll continue to work on this page until portions of it become suitable for moving to other places in the wikiverse...

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Definitions
Some textbook definitions of statistics and related terms (italics added):

 * Stephen Bernstein and Ruth Bernstein, Schaum's Outline of Elements of Statistics II: Inferential Statistics (1999)
 * Statistics is the science that deals with the collection, analysis, and interpretation of numerical information.

 * In descriptive statistics, techniques are provided for collecting, organizing, summarizing, describing, and representing numerical information.

 * [Inferential statistics provides] techniques.... for making generalizations and decisions about the entire population from limited and uncertain sample information.

 * Donald A. Berry, Statistics: A Bayesian Perspective (1996)
 * Statistical inferences have two characteristics:
 * Experimental or observational evidence is available or can be gathered.
 * Conclusions are uncertain.

 * John E. Freund, Mathematical Statistics, 2nd edition (1971)
 * Statistics no longer consists merely of the collection of data and their representation in charts and tables — it is now considered to encompass not only the science of basing inferences on observed data, but the entire problem of making decisions in the face of uncertainty.

 * Gouri K. Bhattacharyya and Richard A. Johnson, Statistical Concepts and Methods (1977)
 * Statistics is a body of concepts and methods used to collect and interpret data concerning a particular area of investigation and to draw conclusions in situations where uncertainty and variation are present.

 * E. L. Lehmann, Theory of Point Estimation (1983)
 * Statistics is concerned with the collection of data and with their analysis and interpretation.

 * William H. Beyer (editor), CRC Standard Probability and Statistics Tables and Formulae (1991)
 * The pursuit of knowledge frequently involves data collection; and those responsible for the collection must appreciate the need for analyzing the data to recover and interpret the information therein. Today, statistics are being accepted as the universal language for the results of experimentation and research and the dissemination of information.

 * Oscar Kempthorne, The Design and Analysis of Eperiments, reprint edition (1973)
 * Statistics enters [the scientific method] at two places:
 * The taking of observations
 * The comparison of the observations with the predictions from... theory.

 * Marvin Lentner and Thomas Bishop, Experimental Design and Analysis (1986)
 * The information obtained from planned experiments is used inductively. That is, generalizations are made about a population from information contained in a random sample of that particular population. ... [Such] inferences and decisions... are sometimes erroneous. Proper statistical analyses provide the tools for quantifying the chances of obtaining erroneous results.

 * Robert L. Mason, Richard F. Gunst and James L. Hess, Statistical Design and Analysis of Experiments (1989)
 * Statistics is the science of problem-solving in the presence of variability.

 * Statistics is a scientific discipline devoted to the drawing of valid inferences from experimental or observational data.

 * Stephen K. Campbell, Flaws and Fallacies in Statistical Thinking (1974)
 * Statistics... is a set of methods for obtaining, organizing, summarizing, presenting, and analyzing numerical facts. Usually these numerical facts represent partial rather than complete knowledge about a situation, as is the case when a sample is used in lieu of a complete census.

Statistical practice and methods

 * Data collection
 * Statistical planning
 * Sampling
 * Probability sampling
 * Simple random sampling
 * Systematic sampling
 * Stratified sampling
 * Cluster sampling
 * Multistage sampling
 * Non-probability sampling
 * Convenience sampling
 * Self-selective sampling (or Self selection)
 * Experimental design
 * Controlled experiment
 * Double-blind experiment
 * Data analysis
 * Descriptive statistics
 * Categorical data (or Qualitative data)
 * Univariate data
 * Pie chart
 * Bar chart
 * Pareto chart
 * Bivariate or Multivariate data
 * Contingency table (or Cross-tabulation)
 * Time series
 * Line chart (or Time series plot)
 * Numerical data (or Quantitative data)
 * Dot plot
 * Frequency table
 * Relative frequency table
 * Grouped frequency table
 * Histogram
 * Box plot
 * Statistical inference
 * Statistical estimation
 * Point estimation
 * Interval estimation
 * Hypothesis testing
 * z test
 * t test
 * F test
 * Analysis of variance (ANOVA)
 * Chi-squared test
 * Statistical modeling
 * Simple linear regression
 * Multiple regression
 * Curvilinear regression
 * Drawing conclusions

Typical course in mathematical probability
Below are the topics typically (?) covered in a one-year course introducing the mathematical theory of probability to undergraduate students in mathematics and statistics. (Actually, this list contains much more material than is typically covered in one year.)

Topics of a more advanced nature are italicized, including those typically only covered in mathematical statistics or graduate-level probability theory courses (e.g., topics requiring measure theory). See also the below.

 * Interpretation of probability
 * Frequency interpretation of probability
 * Classical interpretation of probability
 * Subjective interpretation of probability
 * Random experiments
 * Outcomes (or Simple event)
 * Sample space
 * Events
 * Set theory
 * Universal set
 * Empty set
 * Union
 * Intersection
 * Complement
 * Mutually exclusive events (or Disjoint events)
 * Measure theory
 * Measure space
 * Borel sets
 * Sequence of sets
 * Countable union
 * Countable intersection
 * Nested sets
 * Measure
 * Definition of probability (or Probability measure)
 * Axioms of probability (or Probability axioms, or Probability axiom)
 * Properties of probability
 * General addition rule
 * Equally likely outcomes
 * Counting methods
 * Multiplication principle
 * Factorial
 * Permutation
 * Combination
 * Binomial coefficients
 * Pascal's triangle
 * Multinomial coefficients
 * Independent events
 * Joint probability
 * Marginal probability
 * Conditional probability
 * General multiplication rule
 * Law of total probability
 * Bayes' theorem
 * Prior probability
 * Posterior probability
 * Markov chain
 * Transition matrix
 * Famous problems in probability
 * Birthday problem
 * False-positive problem (or False-Positive problem?)
 * Sensitivity vs. Selectivity
 * Gambler's Ruin problem
 * Matching problem
 * Monty Hall problem
 * Prisoner's Dilemma
 * Optimal Stopping problem
 * Random variable
 * Probability distribution
 * Probability function (pf)
 * Support of a probability function
 * Discrete random variable
 * Probability mass function (pmf)
 * Continuous random variable
 * Probability density function (pdf)
 * Cumulative distribution function (cdf) (Note: Distribution function is now about physics -- df)
 * Mixed probability distribution (i.e., discrete and continuous parts — name??)
 * Distribution of a function of a random variable
 * Direct method for deriving the pdf of a function of a random variable
 * Probability integral transform (or Probability integral transformation)
 * Expectation
 * Expected value or Mean
 * Variance
 * Standard Deviation
 * Moment
 * Central moment
 * Absolute moment
 * Moment generating function (mgf)
 * Non-uniqueness of moments
 * Characteristic function (cf)
 * ...
 * Joint distribution (Joint probability distribution)
 * Joint probability mass function (Joint pmf)
 * Joint probability density function (Joint pdf)
 * Joint distribution function (Joint cdf)
 * Marginal distribution (Marginal probability distribution, Marginal density, Marginal density function, Marginal probability density function, Marginal probability mass function, Marginal distribution function, Marginal probability distribution function)
 * Independent random variables
 * Independent identically-distributed random variables (iid)
 * Random sample
 * Order statistics
 * Distribution of the sample range
 * Conditional distribution (Conditional probability distribution, Conditional density, Conditional density function, Conditional probability density function, Conditional probability mass function, Conditional distribution function, Conditional probability distribution function)
 * Hierarchical probability model
 * Borel-Kolmogorov paradox
 * Bivariate distribution
 * Multivariate distribution
 * Distribution of a function of two or more random variables
 * Jacobian
 * Distribution of a linear transformation of random variables
 * Convolution

 * List of probability distributions (or Table of probability distributions)
 * Discrete probability distributions
 * Discrete uniform distribution (Discrete-uniform distribution?)
 * Bernoulli distribution
 * Binomial distribution
 * Geometric distribution
 * Negative binomial distribution (or Pascal negative binomial distribution, Negative-binomial distribution, Pascal negative-binomial distribution)
 * Hypergeometric distribution
 * Poisson distribution
 * Zeta distribution (or Zipf distribution)
 * Continuous probability distributions (see also Sampling distributions below)
 * Uniform distribution (or Rectangular distribution)
 * Triangular distribution
 * Beta distribution
 * Exponential distribution
 * Double exponential distribution (or Double-exponential distribution, Laplace distribution)
 * Gamma distribution
 * Erlang distribution
 * Maxwell distribution
 * Weibull distribution
 * Rayleigh distribution
 * Gumbel distribution
 * Inverted gamma distribution (or Inverted-gamma distribution)
 * Normal distribution (or Gaussian distribution)
 * Standard normal distribution (or Z distribution, Z-distribution, Standard-normal distribution)
 * Lognormal distribution
 * Half-normal distribution (Half normal distribution?)
 * Cauchy distribution
 * Pareto distribution
 * Logistic distribution
 * Hyperbolic secant distribution (Hyperbolic-secant distribution)
 * Slash distribution
 * Mixture distributions (Hierarchical probability distribution?)
 * Beta-binomial distribution
 * ...

order?

 * Probability tables (e.g., Z table)
 * Upper-tail probability
 * Critical value

 * Relationships among probability distributions (List or Table...)
 * Special cases
 * ...
 * Limit relationships
 * Approximation of one distribution by another
 * Poisson approximation to the binomial
 * Normal approximation to the binomial

 * Other Properties of the cumulative distribution function
 * Memory (or Memoryless property, or whatever)
 * Hazard function
 * Stochastic order or Stochastic ordering (Stochastically greater, Stochastically smaller, Stochastically increasing, Stochastically descreasing)

 * Sampling distributions
 * Sampling distribution of the sample mean
 * Central Limit Theorem
 * t distribution (or t-distribution, Student's t distribution, Student's t-distribution)
 * Degrees of freedom (Degree of freedom)
 * Sampling distribution of the sample variance
 * Chi-squared distribution (Chi-square distribution, Chi squared distribution)
 * F distribution (F-distribution)

 * Family of probability distributions (or Probability distribution family, Distribution family, etc.?)
 * Location-scale family
 * Exponential family
 * Exponential power family
 * Simulation (Generating random numbers with a given distribution, Generating random observations, Generating random numbers, Generating observations from a probability distribution, Generating observations on a random variable, etc. — "pseudo-random" on all these, too)
 * Pseudorandom numbers (see Pseudorandom, Pseudo-random number, Pseudo-random)
 * Random number table (and Table of random digits — former is how to use, latter an actual table)
 * Pseudorandom variables (Pseudo-random variable)

 * ...

 * And so on, and so forth...

Typical course in mathematical statistics
Would cover many of the topics from the outlined above, plus...

 * ...

 * And so on, and so forth...

Typical course in applied statistics
Less theoretical than the outlined above. (Sometimes portions of the following form the basis of a second statistics course for mathematics majors — third in the sequence if probability is the first course).

 * Statistical charts
 * Frequency distribution (Relative..., Cumulative..., Grouped...)
 * Stem-and-leaf display (Stem and leaf display, Stem-and-leaf diagram, Stem and leaf diagram, Stem and leaf)
 * Contingency table
 * Statistical plots (Statistical graphs)
 * Bar chart
 * Pareto plot
 * Pie chart (Pie graph)
 * Line plot (Line graph)
 * Time plot
 * Frequency polygon
 * Ogive
 * Histogram
 * Box plot (Box-and-whisker plot, Box and whisker plot)
 * Quantile-quantile plot (Q-Q plot, Q-q plot)
 * Chernoff face

 * ...

 * List of experimental designs
 * Completely randomized design (CR design, CR)
 * Randomized block design (RB design, RB)
 * Randomized complete block design (RCB design, RCB)
 * Latin square design (LS design, LS)
 * Graeco-Latin square design
 * Crossover design
 * Repeated Latin square design (RLS design, RLS)
 * Factorial design
 * Knut Vik square design
 * Hierarchically nested design
 * Split-plot design (SP design, SP)
 * Split-block design
 * Split-split-plot design
 * Quasifactorial design
 * Lattice design
 * Incomplete block design (IB design, IB)
 * Fractional factorial design
 * Fractional-replication design
 * Half replicate design
 * Half fraction of a factorial design
 * Completely balanced lattice design
 * Rectangular lattice design
 * Triple rectangular lattice design
 * Balanced incomplete block design (BIB design, BIB)
 * Cyclic design
 * Alpha-design ("α-design")
 * Incomplete Latin square design
 * Youden square design
 * Partially balanced incomplete block design (PBIB design, PBIB)
 * Repeated measures design

 * ...

 * And so on, and so forth...

Bayesian anaylsis
Hmm...

Terms from categorical data analysis
(By chapter: Agresti, 1990.)

 * 1) (none)
 * 2) contingency table, two-way table, two-way contingency table, cross-classification table, cross-tabulation, relative risk, odds ratio, concordant pair, discordant pair, gamma, Yule's Q, Goodman and Kruskal's tau, concentration coefficient, Kendall's tau-b, Sommer's d, proportional prediction, proportional prediction rule, uncertainty coefficient, Gini concentration, entropy (variation measure), tetrachoric correlation, contingency coefficient, Pearson's contingency coefficient, log odds ratio, cumulative odds ratio, Goodman and Kruskal's lambda, observed frequency
 * 3) expected frequency, independent multinomial sampling, product multinomial sampling, overdispersion, chi-squared goodness-of-fit test, goodness-of-fit test, Pearson's chi-squared statistic, likelihood-ratio chi-squared statistic, partitioning chi-squared, Fisher's exact test, multiple hypergeometric distribution, Freeman-Halton p-value, phi-squared, power divergence statistic, minimum discrimination information statistic, Neyman modified chi-squared, Freeman-Tukey statistic, ...

And...

 * Berger, James O. (1985). Statistical Decision Theory and Bayesian Analysis (2nd ed.). NY: Springer-Verlag. ISBN 0-387-96098-8. (Also, Berlin: ISBN 3-540-96098-8.)
 * Berry, Donald A. (1996). Statistics: A Bayesian Perspective. Belmont, CA: Duxbury Press. ISBN 0-534-23472-0.
 * Feller, William (1950). An Introduction to Probability Theory and Its Applications, Vol. 1. NY: John Wiley & Sons. ISBN unknown. (Current: 3rd ed., 1968, NY: John Wiley & Sons, ISBN 0-471-25708-7.)
 * Feller, William (1971). An Introduction to Probability Theory and Its Applications, Vol. 2 (2nd ed.). NY: John Wiley & Sons. ISBN 0-471-25709-5.
 * Lehmann E. L. [Eric Leo] (1991). Theory of Point Estimation. Pacific Grove, CA: Wadsworth & Brooks/Cole. ISBN 0-534-15978-8. (Orig. 1983, NY: John Wiley & Sons.)
 * Lehmann E. L. [Eric Leo] (1994). Testing Statistical Hypotheses (2nd ed.). NY: Chapman & Hall. ISBN 0-412-05321-7. (Orig. 2nd ed., 1986, NY: John Wiley & Sons.)

'''Please do not edit this page. Comments should be placed on my talk page. Thanks.'''

title: User:Dcljr/Statistics


text:
Talk:Attacker

Untitled
Matt, I appreciate your tidying up instincts, but must note that the sense you have condensed to a dab pointer has now been lost. Adversary speaks only of crypto usage, not computer security usage. As I review this in my mind, I don't think I've ever heard adversary used in computer security -- it's almost always attacker (or cracker, or hacker amongst the psuedo informed and law enforcement types). Although I do recall one use of 'enemy' (spoken, so I can't testify as to uc or lc).

I think this change has lost information for our Reader. ww 19:30, 26 Jul 2004 (UTC)
 * The information can be found at the Adversary page, which the disambiguation header links to. — Matt 16:52, 27 Jul 2004 (UTC)

Football context
I don't think attacker and striker are synonyms, as this article implies. Attacking midfielders and wingers might also be classed as attackers (as might a marauding defender in a particular situation). Forward is closer in meaning, but still not perfect. Dave.Dunford 17:59, 13 May 2006 (UTC)

Scoring Table
Is it really relevant to have this table in this article, which is about forwards in general, and not merely association football attackers? It's not sourced, and a non–registered user keeps changing the formatting so that it doesn't conform to wiki standards, and I don't think it's relevant; if anything it could be added to the article on strikers with 500 or more goals. I removed it but my edit was reverted. Could the page be protected? Thanks, Messirulez (talk) 23:37, 19 May 2021 (UTC)

title: Talk:Attacker


text:
Talk:Congressional Space Medal of Honor

Columbia
156.33.18.43, are your sure that the Columbia crew were awarded the CSMH? I see that the Challenger crew were so awarded a few days ago, but I can't find any announcement anywhere that the Columbia also received the award this year. 169.154.204.2 19:31, 26 Jul 2004 (UTC)

 * Never mind my above comment. I have run across evidence that the crew of Columbia was awarded the medal on the anniversary of their deaths. For example, the official astronaut biographies now cite the award. 169.154.204.2 21:18, 11 Aug 2004 (UTC)

Font?
Is there a reason that the award info after the awardee's name is in subscript? Makes if harder to read, and is non-standard on WP. I'd like to change it, if there's no objections. Akradecki 05:23, 2 September 2006 (UTC)

Gemini 4 ???
The description at an astronauts name is describing why the individual received the Congressional Space Medal of Honor. Edward White didn't received the medal just because he flew on Gemini 4, else James McDivitt would have one too! Please stop posting irrelevant information. Necessary Evil 20:09, 28 March 2007 (UTC)

The † symbol
In the Recipients table, the † symbol indicates a posthumous award. I was wondering whether this symbol is the most appropriate symbol, since it is a christian sign and not all astronauts who have been honored with the award are christians. I saw that the entries in other languages use * or explicitly mention "posthumous" (expect the russian version, that currently also uses the †).

I don't know about all astronauts, but Ilan Ramon was jew for sure. Not only he was jew, he also tried to express it in many ways during the mission he was killed in (he took a Torah with him, asked for Kosher food, carried a Mezuzah etc.). Personally I believe that after trying to emphasize he's being Jew, adding a cross next to his name is not as sensitive as expected. (There are also other solutions but using * or explicit mentioning, like using the relevant symbol for each astronaut - for example - Star of david next to Ilan Ramon). —Preceding unsigned comment added by 79.176.0.154 (talk) 23:42, 10 July 2009 (UTC)
 * See Dagger (typography). Reywas92 Talk  00:19, 12 July 2009 (UTC)

Hi, Thank you for the respond. As you suggested, I looked at Dagger (typography), yet it seems to me only as a strengthening to my argument since it says there: "The religious connotations of the symbol can also make this usage (adding the symbol after the name of a deceased person) inappropriate for persons from non-Christian cultures.[1]" - the cite note redirects Oxford Manual of Style. (p.s - Please ignore language mistakes as I am not a native English speaker). If nobody objects, I am now willing to change that. —Preceding unsigned comment added by 79.176.0.154 (talk) 15:52, 12 July 2009 (UTC)

Highest Medal?
This page states that this is the highest honour NASA can bestow. So does the page for the NASA Distinguished Service Medal, which states that the DSM is "the highest award which may be bestowed by the National Aeronautics and Space Administration of the United States. "

Which is it then, & can someone fix this? zarathustra (talk) 17:38, 29 January 2019 (UTC)
 * Obviously the phrase on this page, unverified by citation, is in error. Though it is obviously a higher honor than the NASA DSM, it is not "bestowed by NASA", but by the President by the will of Congress. Easy enough to fix. JustinTime55 (talk) 18:43, 29 January 2019 (UTC)

title: Talk:Congressional Space Medal of Honor


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Displacement (psychology)

In psychology, displacement (Verschiebung) is an unconscious defence mechanism whereby the mind substitutes either a new aim or a new object for things felt in their original form to be dangerous or unacceptable.

Freud
The concept of displacement originated with Sigmund Freud. Initially he saw it as a means of dream-distortion, involving a shift of emphasis from important to unimportant elements, or the replacement of something by a mere illusion. Freud called this “displacement of accent.”

Displacement of object: Feelings that are connected with one person are displaced onto another person. A man who has had a bad day at the office, comes home and yells at his wife and children, is displacing his anger from the workplace onto his family. Freud thought that when children have animal phobias, they may be displacing fears of their parents onto an animal.

Displacement of attribution: A characteristic that one perceives in oneself but seems unacceptable is instead attributed to another person. This is essentially the mechanism of psychological projection; an aspect of the self is projected (displaced) onto someone else. Freud wrote that people commonly displace their own desires onto God’s will.

Bodily displacements: A genital sensation may be experienced in the mouth (displacement upward) or an oral sensation may be experienced in the genitals (displacement downward). Novelist John Cleland in ‘’Fanny Hill’’ referred to the vagina as “the nethermouth.” Sexual attraction toward a human body can be displaced in sexual fetishism, sometimes onto a particular body part like the foot, or at other times onto an inanimate fetish object.

Freud also saw displacement as occurring in jokes, as well as in neuroses – the obsessional neurotic being especially prone to the technique of displacement onto the minute. When two or more displacements occurs towards the same idea, the phenomenon is called condensation (from the German Verdichtung).

Phobia displacement or repression: Humans were able to express specific unconscious needs through phobias. These needs that were suppressed deep within themselves created anxiety and tension. The stress, fear, and anxiety that characterize a phobic disorder were the discharge.

Reaction Formation: Cognizant practices are embraced to overcompensate for the nervousness an individual feels in regards to their socially inadmissible oblivious considerations or feelings. Typically, a response arrangement is set apart by misrepresented conduct, like garishness and urgency. An illustration of reaction formation incorporates the loyal little girl who adores her mom is responding to her Oedipus scorn of her mom.

The psychoanalytic mainstream
Among Freud's mainstream followers, Otto Fenichel highlighted the displacement of affect, either through postponement or by redirection, or both. More broadly, he considered that "in part the paths of displacement depend on the nature of the drives that are warded off". Freud's daughter, Anna Freud, also played an important role in the upbringing of these defense mechanisms by the twentieth century. She introduced and analyzed ten of her own defense mechanisms and her work has been used and increased through the years by newer psychoanalysts.

Eric Berne in his first, psychoanalytic work, maintained that "some of the most interesting and socially useful displacements of libido occur when both the aim and the object are partial substitutions for the biological aim and object...sublimation".

Lacan
In 1957, psychoanalyst Jacques Lacan, inspired by an article by linguist Roman Jakobson on metaphor and metonymy, argued that the unconscious has the structure of a language, linking displacement to the poetic function of metonymy, and condensation to that of metaphor.

As Lacan put it, "in the case of Verschiebung, 'displacement', the German term is closer to the idea of that veering off of signification that we see in metonymy, and which from its first appearance in Freud is represented as the most appropriate means used by the unconscious to foil censorship".

Aggression
Within the Freudian psychoanalytic framework, the aggressive drives may be displaced in a similar manner to the libidinal drives. Business or athletic competition, or hunting, for instance, may offer opportunities for the expression of displaced aggression. In such scapegoating behavior, aggression may be displaced onto items or people with little to no connection to the cause of the aggressors frustration.

Displacement can also act in what looks like a 'chain-reaction,' with people unwittingly becoming both victims and perpetrators of displacement. For example, a man is angry with his boss, but he cannot express this properly, so he hits his wife. The wife, in turn, hits one of the children, possibly disguising this as a "punishment." (rationalization)

Ego psychology sought to use displacement in child rearing, a dummy being used as a displaced target for toddler sibling rivalry. With a purpose to apprehend how the ego uses defense mechanisms, it is important to apprehend the defense mechanisms themselves and the way they function. A few defense mechanisms are visible as protecting us from the internal impulses (e.g., repression); other defense mechanism guard us from external threats (e.g., denial).

Transferential displacement
The displacement of feelings and attitudes from past significant others onto the present-day ones constitutes a central aspect of the transference, particularly in the case of the neurotic.

A subsidiary form of displacement within the transference occurs when the patient disguises transference references by applying them to an apparent third party or to themself.

As of now encoded in subcortical neural pathways, material from our oblivious brain is pushed into our cognizant psyche as we attempt to manage mental wonders – typically agonizing – that we are encountering. With the "help" of mind movement, we unknowingly re-surface and re-order struggle ridden encounters as though the past were the present and one setting were another. We move contemplations, sentiments, and perspectives, particularly about individuals who take after others. We allocate them jobs once played by others. We take on old jobs ourselves. All unwittingly.

Criticism
Later writers have objected that whereas Freud only described the displacement of sex into culture, for example, the converse – social conflict being displaced into sexuality – is also true.

Freud's hypothesis is acceptable at clarifying however not at anticipating conduct. Therefore, Freud's hypothesis is unfalsifiable - it cannot be demonstrated valid or invalidated. Freud may likewise have shown research predisposition in his understandings - he may just focused on data which upheld his hypotheses, and overlooked data and different clarifications that didn't fit them.

title: Displacement (psychology)


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Displacement (fencing)

In fencing, displacement is a movement that avoids or dodges an attack.

Fencers commonly use displacement when attacking while not having priority. Attacking into the opponent's right-of-way is known as a counter-attack. If both fencers land, the fencer with priority, the attacker, is awarded the touch; therefore, the goal of the displacement is to hit the opponent while avoiding being hit in return. Displacement can take the form of retreating, advancing past the enemy's blade, utilising a flèche, ducking, or even stepping off the piste.

title: Displacement (fencing)


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User:Temoo

Welcome!

title: User:Temoo


text: Category:Integral geometry

title: Category:Integral geometry


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Northstar engine series

The Northstar engine is a family of high-performance 90° V engines produced by General Motors between 1993 and 2011. Regarded as GM's most technically complex engine, the original double overhead cam, four valve per cylinder, aluminum block/aluminum head V8 design was developed by Oldsmobile R&D, but is most associated with Cadillac's Northstar series.

Displacing 4565 cc in its basic form, the direct family line transitioned to longitudinal and 4371 cc supercharged versions. Variants were used at Oldsmobile (as the Aurora L47 V8 and "Shortstar" LX5 V6), as well as in several top-end 2000s Pontiacs and Buicks.

The related Northstar System was Cadillac's trademarked name for a package of performance features introduced in mid-1992 that coupled the 4T80E transmission, a 100,000 mile service interval, road sensing suspension, variable power steering, and 4-wheel disc brakes to the Division's high-output and high-torque Northstar engines.

GM ceased production of the Northstar in 2011. The final cars to receive it, the Cadillac DTS, Buick Lucerne, and Cadillac STS, rolled off the line in 2011. It was replaced by the GM LS small-block OHV engine, used in newer Cadillac V8 models like the CTS-V, marking a step back to a simpler, more reliable pushrod engine design. These LS V8 engines were the only V8 engines used by Cadillac for the next eight years, until the clean sheet Blackwing V8 was introduced in 2018 in the 2019 Cadillac CT6-V. A Cadillac-exclusive, it was discontinued after just two years in early 2020.

Development and features
GM initiated what ultimately became the Northstar's design at Oldsmobile R&D some time in 1984 in anticipation of the advanced dual overhead cam V8 engines to be introduced by European and Japanese competitors later in the decade. At that time, Cadillac was using the aluminum HT Overhead Valve (OHV) V8 which GM pushed hastily into production because the CAFE standards for 1982 would preempt using 1981's V8-6-4. At the time it was GM's corporate policy not to pass the gas guzzler tax on to the consumer.

Cadillac was developing new models which they hoped would compete against the best luxury cars from BMW, Mercedes-Benz, and Asian rivals like Lexus, Acura, and Infiniti. GM developed a laundry list of items to be included in the Allanté and updated Eldorado and Seville STS, including sophisticated steering, braking, and suspension technologies, and an engine exclusive to "Cadillac" the Division's dealers were clamoring for. This group of features became known as the Northstar System. Central to it was a high-tech V8 with the performance and sophistication to compete with an ever-expanding list of imported challengers.

Capable of producing 300 hp out of its 4565 cc displacement, the Northstar featured a cast aluminum 90° V8 block with 4 in bore spacing split into unitary upper and lower halves. The lower crankcase assembly supported the crankshaft without conventional main bearing caps. An oil manifold plate with an integrated silicone gasket forms the oil gallery under this. A typical oil change used 7.5–8 USqt of oil.

GM specified cast-iron cylinder liners and the cast aluminum pistons included valve clearance. Northstar is an interference engine: the valves will strike the pistons if they lose timing. It has bronze piston pin bushings and free-floating piston pins. GM used cast aluminum cylinder heads featuring 4 valves per cylinder. The heads used dual overhead cams driven through the "maintenance-free" cam-drive chain case. The cams act directly on hydraulic lifters on the ends of the valves and are fed with a lubrication passage drilled through the cylinder head lengthwise. The intake valves are inclined at 25°, while the exhaust valves are canted to 7° with center-mounted platinum-tipped spark plugs. The cam covers are magnesium for light weight and sound damping.

Sequential fuel injection was delivered via eight thermoplastic tubes. Ignition was distributorless, with a waste spark setup. The powertrain control module (PCM) controlled spark and fuel injection timing as well as the shift points for the new four-speed, transverse GM 4T80 transmission. All engines of this family share the same Northstar bellhousing pattern.

One notable feature advertised at the time was the "limp home" fail-safe mode, which allowed the engine to continue running for a limited time without any coolant. Supplying fuel to only one cylinder bank in turn, the engine would "air cool" the inactive bank. This technique, combined with its all-aluminum construction and large oil capacity, allows the engine to maintain safe temperatures, allowing a Northstar-equipped car to be driven with no coolant for about 100 mi without damage. Another unusual feature of some heavily electronic-laden Northstar-equipped cars such as the Seville, DeVille, and Eldorado is a liquid-cooled alternator. Although this was intended to prolong alternator life, GM reverted to a traditional air-cooled setup for 2001 to eliminate potential leak points and extraneous tubing.

Later developments included direct coil-on-plug ignition, roller lifters, and variable valve timing, which can vary intake by up to 40° and the exhaust by up to 50°. VVT was devised for the longitudinal LH2 version, and was not used on the transverse front wheel drive engines due to packaging considerations.

Northstar series
The engine was introduced in mid-1992 in the 1993 Cadillac Allanté; in 1996 the Northstar became the standard engine on all Cadillacs except the Fleetwood, but is now phased out of all Cadillac models. The 275 hp Northstar engine was used on all Northstar equipped Cadillacs while the Deville Concours, Eldorado ETC, Seville STS, and in 2000 the Deville DTS, were fitted with the 300 hp version. The original Northstar Allanté also introduced the Northstar System which included traction control, adaptive suspension, and antilock brakes. Early Northstar required premium grade gasoline to run safely.

The Northstar was sold exclusively by that name by Cadillac for over a decade before being introduced in the 2004-2005 Pontiac Bonneville and 2006 Buick Lucerne. However, the 3995 cc L47 V8 Northstar variant was used in the Oldsmobile Aurora the 3.5L LX5 V6 in the Oldsmobile Intrigue and Oldsmobile Shelby Series 1. The LH2 engine variant received a forged steel crankshaft in October 2003. The LD8 and L37 variants received a forged crankshaft for the 2006 model year. Cadillac had planned to introduce a V12 Northstar this decade, likely for use in the Escalade, but economics and new CAFE standards killed the idea.

Most Northstar engines produce 275 to 300 hp, with power reaching as high as 469 hp in the supercharged LC3. The engines were revised for 2000 with coil-on-plug ignition and roller follower valvegear for improved fuel economy and reduced emissions. Though power output did not change, this update made premium fuel merely recommended, rather than required.

All but the supercharged Northstars displaced 4565 cc with a 93x84 mm bore and stroke. For better head gasket sealing between cylinders, the supercharged version is de-bored to 91 mm for a total displacement of 4371 cc. The block is believed to be capable of expansion up to 5.4 L, though no such engine has been produced.

The Northstar was on the Ward's 10 Best Engines list for 1995, 1996, and 1997.

The 4.6L V8 engine found in models from 1995-2005 were notorious for failure due to a design flaw involving the use of torque-to-yield bolts in the head gasket. Essentially, these type of bolts are stretched beyond their elasticity upon installation, ultimately increasing wear and fatigue on the bolt and decreasing its service life. The high load of the engine would eventually cause these bolts to weaken and loosen in their threads, rupturing the seal and in turn blowing the head gasket.

Northstar System
The Northstar System was Cadillac's trademarked name for a package of automobile performance features introduced in mid-1992 on the 1993 Cadillac Allanté and later on the 1993 Seville and Eldorado.

The Northstar System included the following components:
 * L37 high-output 300 hp and 295 lbft
 * LD8 high-torque 275 hp and 300 lbft
 * Variable valve timing (VVT), a continuously variable system throughout the rpm range, increasing fuel economy.
 * GM engines use the double overhead cam, varying both intake and exhaust for better performance.

 * GM 4T80-E 4-speed automatic transmission
 * Road Sensing Suspension (RSS), which monitored damping rates of the shock absorbers every 15 milliseconds, selecting between two settings.
 * RSS was available in both standard and CV-RSS (continuously-variable) systems.

 * 4-wheel disc brakes with Bosch antilock brakes
 * Magnasteer speed-variable power steering, which combines conventional hydraulic power steering and magnetized "doughnuts" mounted around the output shaft, which stiffen the steering as vehicle speed increases.

Later versions of the Northstar engine included the 4.6L 320 hp and 315 lbft LH2 which began in 2004, and supercharged 4.4L 469 hp LC3 created for the STS-V which are detailed below.

L37
The 4565 cc L37 (VIN "9") was the original Northstar. It is tuned for responsiveness and power, while the later LD8 is designed for more sedate use. The L37 code had been used on all high-output transverse Northstars, even as the exact engine specifications evolved. The compression ratio for the L37 is 10.3:1 for engines built prior to 2000, and 10.0:1 afterwards.

The original L37 was specified at 290 hp, but 1993 production examples were rated at 295 hp. The engine topped out at 300 hp from 1996 through 2004 on the STS, DTS and ETC models, making these some of the most powerful domestic front wheel drive cars ever built. For 2005 the high output Northstar became Northstar NHP, and was downrated to 290 hp under the new SAE certified horsepower rating system. In 2006, the updated DTS "Performance Package" model got a slight bump to 292 hp. Vehicles using the L37 include:

LD8
The 4565 cc LD8 (VIN "Y") is a transverse V8 for front-wheel drive cars. Introduced in 1994, it is designed to provide more torque than the high-revving L37. The LD8 code had been used on all torque-tuned transverse Northstars, even as the exact engine specifications evolved. Compression ratio is 10.3:1 for engines built prior to model year 2000, and 10.0:1 for those built afterwards. The 1998 revision is quieter than previous Northstar engines, due to hydraulic engine mounts, and performs better due to a tuned intake system.

Most LD8 Northstars are rated at 275 hp and 300 lbft.

LH2 (VIN "A")
The 4565 cc Northstar was designed originally for transverse front-wheel drive applications. It was modified substantially in 2004 for longitudinal rear- and all-wheel drive use in the STS, SRX, and XLR, as well as receiving continuously variable valve timing on both intake and exhaust sides. The RWD (LH2) Northstar produces 320 hp and 315 lbft. The addition of variable valve timing enables most of the increase in power from the L37 and LD8 Northstars.

LC3
A 4371 cc supercharged Northstar was used in the 2006 Cadillac STS-V and Cadillac XLR-V. The bore was reduced for increased strength and improved head gasket sealing. Variable valve timing is used on both the intake and exhaust sides. The STS-V engine produces 469 hp at 6400 rpm and 439 lbft at 3900 rpm with 9.0:1 compression and the XLR-V engine produces 443 hp at 6400 rpm and 414 lbft at 3900 rpm.

L47
The L47 Aurora engine was a special V8 designed for the Oldsmobile Aurora, based on the Northstar engine, used during the 1995-1999 and 2001-2003 model years. It is a DOHC 3995 cc V8 which produced 250 hp and 260 lbft of torque. The bore and stroke was 87x84 mm. The L47 had a 10.3:1 compression ratio and used premium fuel.

Although most of the Northstar's features, including the coolant loss system, remained intact, the decreased bore increased weight unacceptably. To reduce it, Oldsmobile used a one-piece glass-filled thermoplastic intake manifold and simplified AC Rochester sequential fuel injection. A new die-cast structural aluminum oil pan incorporated baffling to reduce oil starvation in hard driving. A starter interlock prevented the starter from engaging if the quiet L47 was already running.

An early version or prototype of this engine was used in the 2nd generation Oldsmobile Aerotech. A highly modified 650 hp version of this engine was used by General Motors racing division initially for IMSA sports car competition in an Oldsmobile Aurora GTS-1 and Riley&Scott LMP prototypes in 1995, Indy Racing League competition starting in 1997, then was later used in the Cadillac Northstar LMP program in 2000. Both engines retained the 4.0 L displacement, but the Northstar LMP version was twin-turbocharged. The Aurora was also used in the Shelby Series 1 car. In the inaugural DTM season, Opel would debut their Astra with a V8 derived from the L47.

The Aurora engine was introduced in 1994 for the 1995 model year, and General Motors has not used this engine since the retirement of Oldsmobile in 2004.

LX5 (Shortstar)
The LX5 is a DOHC V6 from Oldsmobile, introduced in 1999 with the Intrigue. It was produced by the Premium engine group at GM and was thus called the Premium V6, or PV6, while it was being developed. It is based on the L47 Aurora V8, which is itself based on the Northstar engine, so engineers called it the Short North, though Oldsmobile fans have taken to calling it the Shortstar.

Although it has a 90° V-angle like the Northstar, the engine block was engineered from scratch, so bore centers are different. It has chain-driven dual overhead cams and four valves per cylinder, but is an even-firing design with a split-pin crankshaft similar to the Buick 3800 engine. The LX5 displaced 3473 cc and produced 215 hp at 5,600 rpm and 234 lbft at 4,400 rpm. Bore and stroke is 89.5x92 mm. It was also one of GM's first engines to use coil-on-plug ignition. Compression ratio is 9.3:1.

The cost of building this engine was high, and it was not used in many vehicles. It was said at the time that a family of premium V6s would follow, with displacements ranging from 3.3 L to 3.7 L, but only the LX5 was ever produced before GM discontinued the Shortstar in favor of their current flagship V6, the High Feature engine, in 2004.

The LX5 was entirely different from any other V6 in the GM inventory - the only other DOHC V6 engines ever offered by GM included the Chevrolet Twin Dual Cam produced from 1991-1997, which was made by modifying the traditional Chevy 60-degree OHV block V6 for the dual overhead cams rather than building a DOHC engine from the ground up, and the Cadillac/Holden HFV6 available from 2004 to the present day. These three designs are completely unrelated and leave two gaps in 1998 and 2003 where no DOHC V6 was available from GM (except for the 54 degree Opel V6 used most notably in the first generation Cadillac CTS at launch as well as the Saturn L Series and Catera). This contrasts starkly with competitors practices of evolving engineering over multiple, continuously improving designs. As with the Aurora V8, production stopped with the demise of Oldsmobile.

The 3.5L LX5 was on the Ward's 10 Best Engines list for 1999 and 2000.

title: Northstar engine series


text:
Thymallus thymallus

Thymallus thymallus, the grayling or European grayling, is a species of freshwater fish in the salmon family Salmonidae. It is the only species of the genus Thymallus (the graylings) native to Europe, where it is widespread from the United Kingdom and France to the Ural Mountains in Russia, and Balkans on the south-east, but does not occur in the southern parts of the continent. It was introduced to Morocco in 1948, but it does not appear to have become established there.

Description
The grayling grows to a maximum recorded length of 60 cm and a maximum recorded weight of 6.7 kg. Of typical Thymallus appearance, the grayling proper is distinguished from the similar Arctic grayling (T. arcticus arcticus) by the presence of 5–8 dorsal and 3–4 anal spines, which are absent in the other species; T. thymallus also has a smaller number of soft rays in these fins. Individuals of the species have been recorded as reaching an age of 14 years.

The grayling prefers cold, clean, running riverine waters, but also occurs in lakes and, exceptionally, in brackish waters around the Baltic Sea. Omnivorous, the fish feeds on vegetable matter, as well as crustaceans, insects and spiders, mollusks, zooplankton, and smaller fishes, such as Eurasian minnows. Grayling are also prey for larger fish, including the huchen (Hucho hucho).

With the Arctic grayling, T. thymallus is one of the economically important Thymallus species, being raised commercially and fished for sport.

The grayling is a protected species listed in Appendix III of the Bern Convention. It has become critically endangered in the Baltic Sea.

The term "grayling" is often used to refer generically to the Thymallus species, and T. thymallus is sometimes called the European grayling for clarity. There are many obsolete synonyms for the species.

Thymallus thymallus is the type species of its genus.

Angling
The grayling is known as the 'lady of the stream'. In Europe, they used to be persecuted by anglers for the false perception that they stopped trout colonizing stretches of rivers and streams. However, research has shown that grayling and trout feed on different prey items and generally prefer different microhabitats within rivers and streams but do occupy similar niches to smaller, less-predatory trout.

In England and Wales, they can be fished throughout the coarse fishing season (16 June to 14 March), providing thrilling sport on the fly when the trout season is closed. There is no closed season for grayling in Scotland; where they have been introduced. There are no grayling in Ireland. Well-known grayling flies include the grayling witch, klinkhamers, various nymphs and 'red tags', along with other trout patterns. Flies tied to resemble small pink shrimps have also been found to be useful. A method known as 'Czech-nymphing' has been known to be helpful to anglers where grayling shoal up in colder periods. The method involves moving a series of Czech nymphs under the tip of the fly rod with the flow of the river and the nymphs should entice the grayling to take one. Fly-anglers may wade in the river to perform this method where they can access deeper water. Wading does not necessarily spook the grayling as they are generally less cautious than trout and are not as easily put off by human presence.

In France, too, the season is limited depending upon several factors. The Allier is one of the rare places in Southern Europe where the common grayling occurs in a natural habitat.

title: Thymallus thymallus