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The aorta is an elastic artery, and as such is quite distensible. The aorta consists of a heterogeneous mixture of smooth muscle, nerves, intimal cells, endothelial cells, immune cells, fibroblast-like cells, and a complex extracellular matrix. The vascular wall is subdivided into three layers known as the tunica externa, tunica media, and tunica intima. The aorta is covered by an extensive network of tiny blood vessels called vasa vasorum, which feed the tunica externa and tunica media, the outer layers of the aorta. The aortic arch contains baroreceptors and chemoreceptors that relay information concerning blood pressure and blood pH and carbon dioxide levels to the medulla oblongata of the brain. This information along with information from baroreceptors and chemoreceptors located elsewhere is processed by the brain and the autonomic nervous system mediates appropriate homeostatic responses.
Within the tunica media, smooth muscle and the extracellular matrix are quantitatively the largest components, these are arranged concentrically as musculoelastic layers (the elastic lamella) in mammals. The elastic lamella, which comprise smooth muscle and elastic matrix, can be considered as the fundamental structural unit of the aorta and consist of elastic fibers, collagens (predominately type III), proteoglycans, and glycoaminoglycans. The elastic matrix dominates the biomechanical properties of the aorta. The smooth muscle component, while contractile, does not substantially alter the diameter of the aorta, but rather serves to increase the stiffness and viscoelasticity of the aortic wall when activated.
Variation
Variations may occur in the location of the aorta, and the way in which arteries branch off the aorta. The aorta, normally on the left side of the body, may be found on the right in dextrocardia, in which the heart is found on the right, or situs inversus, in which the location of all organs are flipped.
Variations in the branching of individual arteries may also occur. For example, the left vertebral artery may arise from the aorta, instead of the left common carotid artery. | Aorta | Wikipedia | 480 | 2089 | https://en.wikipedia.org/wiki/Aorta | Biology and health sciences | Circulatory system | Biology |
In patent ductus arteriosus, a congenital disorder, the fetal ductus arteriosus fails to close, leaving an open vessel connecting the pulmonary artery to the proximal descending aorta.
Function
The aorta supplies all of the systemic circulation, which means that the entire body, except for the respiratory zone of the lung, receives its blood from the aorta. Broadly speaking, branches from the ascending aorta supply the heart; branches from the aortic arch supply the head, neck, and arms; branches from the thoracic descending aorta supply the chest (excluding the heart and the respiratory zone of the lung); and branches from the abdominal aorta supply the abdomen. The pelvis and legs get their blood from the common iliac arteries.
Blood flow and velocity
The contraction of the heart during systole is responsible for ejection and creates a (pulse) wave that is propagated down the aorta, into the arterial tree. The wave is reflected at sites of impedance mismatching, such as bifurcations, where reflected waves rebound to return to semilunar valves and the origin of the aorta. These return waves create the dicrotic notch displayed in the aortic pressure curve during the cardiac cycle as these reflected waves push on the aortic semilunar valve. With age, the aorta stiffens such that the pulse wave is propagated faster and reflected waves return to the heart faster before the semilunar valve closes, which raises the blood pressure. The stiffness of the aorta is associated with a number of diseases and pathologies, and noninvasive measures of the pulse wave velocity are an independent indicator of hypertension. Measuring the pulse wave velocity (invasively and non-invasively) is a means of determining arterial stiffness. Maximum aortic velocity may be noted as Vmax or less commonly as AoVmax. | Aorta | Wikipedia | 390 | 2089 | https://en.wikipedia.org/wiki/Aorta | Biology and health sciences | Circulatory system | Biology |
Mean arterial pressure (MAP) is highest in the aorta, and the MAP decreases across the circulation from aorta to arteries to arterioles to capillaries to veins back to atrium. The difference between aortic and right atrial pressure accounts for blood flow in the circulation. When the left ventricle contracts to force blood into the aorta, the aorta expands. This stretching gives the potential energy that will help maintain blood pressure during diastole, as during this time the aorta contracts passively. This Windkessel effect of the great elastic arteries has important biomechanical implications. The elastic recoil helps conserve the energy from the pumping heart and smooth out the pulsatile nature created by the heart. Aortic pressure is highest at the aorta and becomes less pulsatile and lower pressure as blood vessels divide into arteries, arterioles, and capillaries such that flow is slow and smooth for gases and nutrient exchange.
Clinical significance
Central aortic blood pressure has frequently been shown to have greater prognostic value and to show a more accurate response to antihypertensive drugs than has peripheral blood pressure.
Aortic aneurysm – mycotic, bacterial (e.g. syphilis), senile, genetic, associated with valvular heart disease
Aortic coarctation – pre-ductal, post-ductal
Aortic dissection
Aortic stenosis
Abdominal aortic aneurysm
Aortitis, inflammation of the aorta that can be seen in trauma, infections, and autoimmune disease
Atherosclerosis
Ehlers–Danlos syndrome
Marfan syndrome
Trauma, such as traumatic aortic rupture, most often thoracic and distal to the left subclavian artery and often quickly fatal
Transposition of the great vessels, see also dextro-Transposition of the great arteries and levo-Transposition of the great arteries
Other animals | Aorta | Wikipedia | 404 | 2089 | https://en.wikipedia.org/wiki/Aorta | Biology and health sciences | Circulatory system | Biology |
All amniotes have a broadly similar arrangement to that of humans, albeit with a number of individual variations. In fish, however, there are two separate vessels referred to as aortas. The ventral aorta carries de-oxygenated blood from the heart to the gills; part of this vessel forms the ascending aorta in tetrapods (the remainder forms the pulmonary artery). A second, dorsal aorta carries oxygenated blood from the gills to the rest of the body and is homologous with the descending aorta of tetrapods. The two aortas are connected by a number of vessels, one passing through each of the gills.
Amphibians also retain the fifth connecting vessel, so that the aorta has two parallel arches.
History
The word aorta stems from the Late Latin from Classical Greek aortē (), from aeirō, "I lift, raise" () This term was first applied by Aristotle when describing the aorta and describes accurately how it seems to be "suspended" above the heart.
The function of the aorta is documented in the Talmud, where it is noted as one of three major vessels entering or leaving the heart, and where perforation is linked to death. | Aorta | Wikipedia | 248 | 2089 | https://en.wikipedia.org/wiki/Aorta | Biology and health sciences | Circulatory system | Biology |
In mathematics, the axiom of regularity (also known as the axiom of foundation) is an axiom of Zermelo–Fraenkel set theory that states that every non-empty set A contains an element that is disjoint from A. In first-order logic, the axiom reads:
The axiom of regularity together with the axiom of pairing implies that no set is an element of itself, and that there is no infinite sequence (an) such that ai+1 is an element of ai for all i. With the axiom of dependent choice (which is a weakened form of the axiom of choice), this result can be reversed: if there are no such infinite sequences, then the axiom of regularity is true. Hence, in this context the axiom of regularity is equivalent to the sentence that there are no downward infinite membership chains.
The axiom was originally formulated by von Neumann; it was adopted in a formulation closer to the one found in contemporary textbooks by Zermelo. Virtually all results in the branches of mathematics based on set theory hold even in the absence of regularity. However, regularity makes some properties of ordinals easier to prove; and it not only allows induction to be done on well-ordered sets but also on proper classes that are well-founded relational structures such as the lexicographical ordering on
Given the other axioms of Zermelo–Fraenkel set theory, the axiom of regularity is equivalent to the axiom of induction. The axiom of induction tends to be used in place of the axiom of regularity in intuitionistic theories (ones that do not accept the law of the excluded middle), where the two axioms are not equivalent.
In addition to omitting the axiom of regularity, non-standard set theories have indeed postulated the existence of sets that are elements of themselves.
Elementary implications of regularity
No set is an element of itself
Let A be a set, and apply the axiom of regularity to {A}, which is a set by the axiom of pairing. We see that there must be an element of {A} which is disjoint from {A}. Since the only element of {A} is A, it must be that A is disjoint from {A}. So, since , we cannot have A the only element of A (by the definition of disjoint). | Axiom of regularity | Wikipedia | 505 | 2113 | https://en.wikipedia.org/wiki/Axiom%20of%20regularity | Mathematics | Axiomatic systems | null |
No infinite descending sequence of sets exists
Suppose, to the contrary, that there is a function, f, on the natural numbers with f(n+1) an element of f(n) for each n. Define S = {f(n): n a natural number}, the range of f, which can be seen to be a set from the axiom schema of replacement. Applying the axiom of regularity to S, let B be an element of S which is disjoint from S. By the definition of S, B must be f(k) for some natural number k. However, we are given that f(k) contains f(k+1) which is also an element of S. So f(k+1) is in the intersection of f(k) and S. This contradicts the fact that they are disjoint sets. Since our supposition led to a contradiction, there must not be any such function, f.
The nonexistence of a set containing itself can be seen as a special case where the sequence is infinite and constant.
Notice that this argument only applies to functions f that can be represented as sets as opposed to undefinable classes. The hereditarily finite sets, Vω, satisfy the axiom of regularity (and all other axioms of ZFC except the axiom of infinity). So if one forms a non-trivial ultrapower of Vω, then it will also satisfy the axiom of regularity. The resulting model will contain elements, called non-standard natural numbers, that satisfy the definition of natural numbers in that model but are not really natural numbers. They are "fake" natural numbers which are "larger" than any actual natural number. This model will contain infinite descending sequences of elements. For example, suppose n is a non-standard natural number, then and , and so on. For any actual natural number k, . This is an unending descending sequence of elements. But this sequence is not definable in the model and thus not a set. So no contradiction to regularity can be proved. | Axiom of regularity | Wikipedia | 438 | 2113 | https://en.wikipedia.org/wiki/Axiom%20of%20regularity | Mathematics | Axiomatic systems | null |
Simpler set-theoretic definition of the ordered pair
The axiom of regularity enables defining the ordered pair (a,b) as {a,{a,b}}; see ordered pair for specifics. This definition eliminates one pair of braces from the canonical Kuratowski definition (a,b) = {{a},{a,b}}.
Every set has an ordinal rank
This was actually the original form of the axiom in von Neumann's axiomatization.
Suppose x is any set. Let t be the transitive closure of {x}. Let u be the subset of t consisting of unranked sets. If u is empty, then x is ranked and we are done. Otherwise, apply the axiom of regularity to u to get an element w of u which is disjoint from u. Since w is in u, w is unranked. w is a subset of t by the definition of transitive closure. Since w is disjoint from u, every element of w is ranked. Applying the axioms of replacement and union to combine the ranks of the elements of w, we get an ordinal rank for w, to wit . This contradicts the conclusion that w is unranked. So the assumption that u was non-empty must be false and x must have rank.
For every two sets, only one can be an element of the other
Let X and Y be sets. Then apply the axiom of regularity to the set {X,Y} (which exists by the axiom of pairing). We see there must be an element of {X,Y} which is also disjoint from it. It must be either X or Y. By the definition of disjoint then, we must have either Y is not an element of X or vice versa.
The axiom of dependent choice and no infinite descending sequence of sets implies regularity
Let the non-empty set S be a counter-example to the axiom of regularity; that is, every element of S has a non-empty intersection with S. We define a binary relation R on S by , which is entire by assumption. Thus, by the axiom of dependent choice, there is some sequence (an) in S satisfying anRan+1 for all n in N. As this is an infinite descending chain, we arrive at a contradiction and so, no such S exists. | Axiom of regularity | Wikipedia | 508 | 2113 | https://en.wikipedia.org/wiki/Axiom%20of%20regularity | Mathematics | Axiomatic systems | null |
Regularity and the rest of ZF(C) axioms
Regularity was shown to be relatively consistent with the rest of ZF by Skolem and von Neumann, meaning that if ZF without regularity is consistent, then ZF (with regularity) is also consistent.
The axiom of regularity was also shown to be independent from the other axioms of ZFC, assuming they are consistent. The result was announced by Paul Bernays in 1941, although he did not publish a proof until 1954. The proof involves (and led to the study of) Rieger-Bernays permutation models (or method), which were used for other proofs of independence for non-well-founded systems.
Regularity and Russell's paradox
Naive set theory (the axiom schema of unrestricted comprehension and the axiom of extensionality) is inconsistent due to Russell's paradox. In early formalizations of sets, mathematicians and logicians have avoided that contradiction by replacing the axiom schema of comprehension with the much weaker axiom schema of separation. However, this step alone takes one to theories of sets which are considered too weak. So some of the power of comprehension was added back via the other existence axioms of ZF set theory (pairing, union, powerset, replacement, and infinity) which may be regarded as special cases of comprehension. So far, these axioms do not seem to lead to any contradiction. Subsequently, the axiom of choice and the axiom of regularity were added to exclude models with some undesirable properties. These two axioms are known to be relatively consistent.
In the presence of the axiom schema of separation, Russell's paradox becomes a proof that there is no set of all sets. The axiom of regularity together with the axiom of pairing also prohibit such a universal set. However, Russell's paradox yields a proof that there is no "set of all sets" using the axiom schema of separation alone, without any additional axioms. In particular, ZF without the axiom of regularity already prohibits such a universal set. | Axiom of regularity | Wikipedia | 435 | 2113 | https://en.wikipedia.org/wiki/Axiom%20of%20regularity | Mathematics | Axiomatic systems | null |
If a theory is extended by adding an axiom or axioms, then any (possibly undesirable) consequences of the original theory remain consequences of the extended theory. In particular, if ZF without regularity is extended by adding regularity to get ZF, then any contradiction (such as Russell's paradox) which followed from the original theory would still follow in the extended theory.
The existence of Quine atoms (sets that satisfy the formula equation x = {x}, i.e. have themselves as their only elements) is consistent with the theory obtained by removing the axiom of regularity from ZFC. Various non-wellfounded set theories allow "safe" circular sets, such as Quine atoms, without becoming inconsistent by means of Russell's paradox.
Regularity, the cumulative hierarchy, and types
In ZF it can be proven that the class , called the von Neumann universe, is equal to the class of all sets. This statement is even equivalent to the axiom of regularity (if we work in ZF with this axiom omitted). From any model which does not satisfy the axiom of regularity, a model which satisfies it can be constructed by taking only sets in .
Herbert Enderton wrote that "The idea of rank is a descendant of Russell's concept of type". Comparing ZF with type theory, Alasdair Urquhart wrote that "Zermelo's system has the notational advantage of not containing any explicitly typed variables, although in fact it can be seen as having an implicit type structure built into it, at least if the axiom of regularity is included.
Dana Scott went further and claimed that:
In the same paper, Scott shows that an axiomatic system based on the inherent properties of the cumulative hierarchy turns out to be equivalent to ZF, including regularity.
History
The concept of well-foundedness and rank of a set were both introduced by Dmitry Mirimanoff. Mirimanoff called a set x "regular" () if every descending chain x ∋ x1 ∋ x2 ∋ ... is finite. Mirimanoff however did not consider his notion of regularity (and well-foundedness) as an axiom to be observed by all sets; in later papers Mirimanoff also explored what are now called non-well-founded sets ( in Mirimanoff's terminology). | Axiom of regularity | Wikipedia | 489 | 2113 | https://en.wikipedia.org/wiki/Axiom%20of%20regularity | Mathematics | Axiomatic systems | null |
Skolem and von Neumann pointed out that non-well-founded sets are superfluous and in the same publication von Neumann gives an axiom which excludes some, but not all, non-well-founded sets. In a subsequent publication, von Neumann gave an equivalent but more complex version of the axiom of class foundation:
The contemporary and final form of the axiom is due to Zermelo.
Regularity in the presence of urelements
Urelements are objects that are not sets, but which can be elements of sets. In ZF set theory, there are no urelements, but in some other set theories such as ZFA, there are. In these theories, the axiom of regularity must be modified. The statement "" needs to be replaced with a statement that is not empty and is not an urelement. One suitable replacement is , which states that x is inhabited. | Axiom of regularity | Wikipedia | 187 | 2113 | https://en.wikipedia.org/wiki/Axiom%20of%20regularity | Mathematics | Axiomatic systems | null |
Apple II ("apple two") is a series of microcomputers manufactured by Apple Computer, Inc. from 1977 to 1993. The first Apple II model, that gave the series its name, was designed by Steve Wozniak, and was first sold on June 10, 1977. Its success led to it being followed by the Apple II Plus, Apple IIe, Apple IIc, and Apple IIc Plus, with the 1983 IIe being the most popular. The name is trademarked with square brackets as Apple ][, then, beginning with the IIe, as Apple //.
The Apple II was a major advancement over its predecessor, the Apple I, in terms of ease of use, features, and expandability. It became one of several recognizable and successful computers during the 1980s and early 1990s, although this was mainly limited to the US. It was aggressively marketed through volume discounts and manufacturing arrangements to educational institutions, which made it the first computer in widespread use in American secondary schools, displacing the early leader Commodore PET. The effort to develop educational and business software for the Apple II, including the 1979 release of the popular VisiCalc spreadsheet, made the computer especially popular with business users and families.
The Apple II computers are based on the 6502 8-bit processor and can display text and two resolutions of color graphics. A software-controlled speaker provides one channel of low-fidelity audio. A model with more advanced graphics and sound and a 16-bit processor, the Apple IIGS, was added in 1986. It remained compatible with earlier Apple II models, but the IIGS has more in common with mid-1980s systems like the Atari ST, Amiga, and Acorn Archimedes.
Despite the introduction of the Motorola 68000-based Macintosh in 1984, the Apple II series still reportedly accounted for 85% of the company's hardware sales in the first quarter of fiscal 1985. Apple continued to sell Apple II systems alongside the Macintosh until terminating the IIGS in December 1992 and the IIe in November 1993. The last II-series Apple in production, the IIe card for Macintoshes, was discontinued on October 15, 1993; having been one of the longest running mass-produced home computer series, the total Apple II sales of all of its models during its 16-year production run were about 6 million units (including about 1.25 million Apple IIGS models) with the peak occurring in 1983 when 1 million were sold.
Hardware | Apple II | Wikipedia | 504 | 2116 | https://en.wikipedia.org/wiki/Apple%20II | Technology | Early computers | null |
Unlike preceding home microcomputers, the Apple II was sold as a finished consumer appliance rather than as a kit (unassembled or preassembled). Apple marketed the Apple II as a durable product, including a 1981 ad in which an Apple II survived a fire started when a cat belonging to one early user knocked over a lamp.
All the machines in the series, except the IIc, share similar overall design elements. The plastic case was designed to look more like a home appliance than a piece of electronic equipment, and the case can be opened without the use of tools. All models in the Apple II series have a built-in keyboard, with the exception of the IIGS which has a separate keyboard.
Apple IIs have color and high-resolution graphics modes, sound capabilities and a built-in BASIC programming language. The motherboard holds eight expansion slots and an array of random access memory (RAM) sockets that can hold up to 48 kilobytes. Over the course of the Apple II series' life, an enormous amount of first- and third-party hardware was made available to extend the capabilities of the machine. The IIc was designed as a compact, portable unit, not intended to be disassembled, and cannot use most of the expansion hardware sold for the other machines in the series.
Software
The original Apple II has the operating system in ROM along with a BASIC variant called Integer BASIC. Apple eventually released Applesoft BASIC, a more advanced variant of the language which users can run instead of Integer BASIC. The Apple II series eventually supported over 1,500 software programs.
When the Disk II floppy disk drive was released in 1978, a new operating system, Apple DOS, was commissioned from Shepardson Microsystems and developed by Paul Laughton, adding support for the disk drive. The final and most popular version of this software was Apple DOS 3.3.
Apple DOS was superseded by ProDOS, which supported a hierarchical file system and larger storage devices. With an optional third-party Z80-based expansion card, the Apple II could boot into the CP/M operating system and run WordStar, dBase II, and other CP/M software. With the release of MousePaint in 1984 and the Apple IIGS in 1986, the platform took on the look of the Macintosh user interface, including a mouse. | Apple II | Wikipedia | 478 | 2116 | https://en.wikipedia.org/wiki/Apple%20II | Technology | Early computers | null |
Much commercial Apple II software shipped on self-booting disks and does not use standard DOS disk formats. This discouraged the copying or modifying of the software on the disks, and improved loading speed.
Models
Apple II
The first Apple II computers went on sale on June 10, 1977 with a MOS Technology 6502 (later Synertek) microprocessor running at 1.023 MHz, 4 KB of RAM, an audio cassette interface for loading programs and storing data, and the Integer BASIC programming language built into the ROMs. The video controller displayed 40 columns by 24 lines of monochrome, upper-case-only (the original character set matches ASCII characters 0x20 to 0x5F) text on the screen, with NTSC composite video output suitable for display on a TV monitor, or on a regular TV set by way of a separate RF modulator. The original retail price of the computer was (with 4 KB of RAM) and (with the maximum 48 KB of RAM). To reflect the computer's color graphics capability, the Apple logo on the casing was represented using rainbow stripes, which remained a part of Apple's corporate logo until early 1998. The earliest Apple IIs were assembled in Silicon Valley, and later in Texas; printed circuit boards were manufactured in Ireland and Singapore.
An external -inch floppy disk drive, the Disk II, attached via a controller card that plugged into one of the computer's expansion slots (usually slot 6), was used for data storage and retrieval to replace cassettes. The Disk II interface, created by Steve Wozniak, was regarded as an engineering masterpiece for its economy of electronic components.
Rather than having a dedicated sound-synthesis chip, the Apple II had a toggle circuit that could only emit a click through a built-in speaker; all other sounds (including two, three and, eventually, four-voice music and playback of audio samples and speech synthesis) were generated entirely by software that clicked the speaker at just the right times. | Apple II | Wikipedia | 413 | 2116 | https://en.wikipedia.org/wiki/Apple%20II | Technology | Early computers | null |
The Apple II's multiple expansion slots permitted a wide variety of third-party devices, including Apple II peripheral cards such as serial controllers, display controllers, memory boards, hard disks, networking components, and real-time clocks. There were plug-in expansion cards – such as the Z-80 SoftCard – that permitted the Apple to use the Z80 processor and run a multitude of programs developed under the CP/M operating system, including the dBase II database and the WordStar word processor. There was also a third-party 6809 card that would allow OS-9 Level One to be run. Third-party sound cards greatly improved audio capabilities, allowing simple music synthesis and text-to-speech functions. Eventually, Apple II accelerator cards were created to double or quadruple the computer's speed.
Rod Holt designed the Apple II's power supply. He employed a switched-mode power supply design, which was far smaller and generated less unwanted heat than the linear power supply some other home computers used.
The original Apple II was discontinued at the start of 1981, superseded by the Apple II+.
Apple II Plus
The Apple II Plus, introduced in June 1979, included the Applesoft BASIC programming language in ROM. This Microsoft-authored dialect of BASIC, which was previously available as an upgrade, supported floating-point arithmetic, and became the standard BASIC dialect on the Apple II series (though it ran at a noticeably slower speed than Steve Wozniak's Integer BASIC).
Except for improved graphics and disk-booting support in the ROM, and the removal of the 2k 6502 assembler to make room for the floating point BASIC, the II+ was otherwise identical to the original II in terms of electronic functionality. There were small differences in the physical appearance and keyboard. RAM prices fell during 1980–81 and all II+ machines came from the factory with a full 48 KB of memory already installed.
Apple II Europlus and J-Plus
After the success of the first Apple II in the United States, Apple expanded its market to include Europe, Australia and the Far East in 1979, with the Apple II Europlus (Europe, Australia) and the Apple II J-Plus (Japan). In these models, Apple made the necessary hardware, software and firmware changes in order to comply to standards outside of the US.
Apple IIe | Apple II | Wikipedia | 479 | 2116 | https://en.wikipedia.org/wiki/Apple%20II | Technology | Early computers | null |
The Apple II Plus was followed in 1983 by the Apple IIe, a cost-reduced yet more powerful machine that used newer chips to reduce the component count and add new features, such as the display of upper and lowercase letters and a standard 64 KB of RAM.
The IIe RAM was configured as if it were a 48 KB Apple II Plus with a language card. The machine had no slot 0, but instead had an auxiliary slot that could accept a 1 KB memory card to enable the 80-column display. This card contained only RAM; the hardware and firmware for the 80-column display was built into the Apple IIe. An "extended 80-column card" with more memory increased the machine's RAM to 128 KB.
The Apple IIe was the most popular machine in the Apple II series. It has the distinction of being the longest-lived Apple computer of all time—it was manufactured and sold with only minor changes for nearly 11 years. The IIe was the last Apple II model to be sold, and was discontinued in November 1993.
During its lifespan two variations were introduced: the Apple IIe Enhanced (four replacement chips to give it some of the features of the later model Apple IIc) and the Apple IIe Platinum (a modernized case color to match other Apple products of the era, along with the addition of a numeric keypad).
Some of the feature of the IIe were carried over from the less successful Apple III, among them the ProDOS operating system.
Apple IIc
The Apple IIc was released in April 1984, billed as a portable Apple II because it could be easily carried due to its size and carrying handle, which could be flipped down to prop the machine up into a typing position. Unlike modern portables, it lacked a built-in display and battery. It was the first of three Apple II models to be made in the Snow White design language, and the only one that used its unique creamy off-white color.
The Apple IIc was the first Apple II to use the 65C02 low-power variant of the 6502 processor, and featured a built-in 5.25-inch floppy drive and 128 KB RAM, with a built-in disk controller that could control external drives, composite video (NTSC or PAL), serial interfaces for modem and printer, and a port usable by either a joystick or mouse. Unlike previous Apple II models, the IIc had no internal expansion slots at all. | Apple II | Wikipedia | 504 | 2116 | https://en.wikipedia.org/wiki/Apple%20II | Technology | Early computers | null |
Two different monochrome LC displays were sold for use with the IIc's video expansion port, although both were short-lived due to high cost and poor legibility. The IIc had an external power supply that converted AC power to 15 V DC, though the IIc itself will accept between 12 V and 17 V DC, allowing third parties to offer battery packs and automobile power adapters that connected in place of the supplied AC adapter.
Apple IIGS
The Apple IIGS, released on September 15, 1986, is the penultimate and most advanced model in the Apple II series, and a radical departure from prior models. It uses a 16-bit microprocessor, the 65C816 operating at 2.8 MHz with 24-bit addressing, allowing expansion up to 8 MB of RAM. The graphics are significantly improved, with 4096 colors and new modes with resolutions of 320×200 and 640×400. The audio capabilities are vastly improved, with a built-in music synthesizer that far exceeded any other home computer.
The Apple IIGS evolved the platform while still maintaining near-complete backward compatibility. Its Mega II chip contains the functional equivalent of an entire Apple IIe computer (sans processor). This, combined with the 65816's ability to execute 65C02 code directly, provides full support for legacy software, while also supporting 16-bit software running under a new OS.
The OS eventually included a Macintosh-like graphical Finder for managing disks and files and opening documents and applications, along with desk accessories. Later, the IIGS gained the ability to read and write Macintosh disks and, through third-party software, a multitasking Unix-like shell and TrueType font support.
The GS includes a 32-voice Ensoniq 5503 DOC sample-based sound synthesizer chip with 64 KB dedicated RAM, 256 KB (or later 1.125 MB) of standard RAM, built-in peripheral ports (switchable between IIe-style card slots and IIc-style onboard controllers for disk drives, mouse, RGB video, and serial devices) and, built-in AppleTalk networking.
Apple IIc Plus | Apple II | Wikipedia | 437 | 2116 | https://en.wikipedia.org/wiki/Apple%20II | Technology | Early computers | null |
The final Apple II model was the Apple IIc Plus introduced in 1988. It was the same size and shape as the IIc that came before it, but the 5.25-inch floppy drive had been replaced with a -inch drive, the power supply was moved inside the case, and the processor was a fast 4 MHz 65C02 processor that actually ran 8-bit Apple II software faster than the IIGS.
The IIc Plus also featured a new keyboard layout that matched the Platinum IIe and IIGS. Unlike the IIe IIc and IIGS, the IIc Plus came only in one version (American) and was not officially sold anywhere outside the US. The Apple IIc Plus ceased production in 1990, with its two-year production run being the shortest of all the Apple II computers.
Apple IIe Card
Although not an extension of the Apple II line, in 1990 the Apple IIe Card, an expansion card for the Macintosh LC, was released. Essentially a miniaturized Apple IIe computer on a card (using the Mega II chip from the Apple IIGS), it allowed the Macintosh to run 8-bit Apple IIe software through hardware emulation, with an option to run at roughly double the speed of the original IIe (about 1.8 MHz). However, the video output was emulated in software, and, depending on how much of the screen the currently running program was trying to update in a single frame, performance could be much slower compared to a real IIe. This is due to the fact that writes from the 65C02 on the IIe Card to video memory were caught by the additional hardware on the card, so the video emulation software running on the Macintosh side could process that write and update the video display. But, while the Macintosh was processing video updates, execution of Apple II code would be temporarily halted. | Apple II | Wikipedia | 382 | 2116 | https://en.wikipedia.org/wiki/Apple%20II | Technology | Early computers | null |
With a breakout cable which connected to the back of the card, the user could attach up to two UniDisk or Apple 5.25 Drives, up to one UniDisk 3.5 drive, and a DE-9 Apple II joystick. Many of the LC's built-in Macintosh peripherals could also be "borrowed" by the card when in Apple II mode, including extra RAM, the Mac's internal 3.5-inch floppy drives, AppleTalk networking, any ProDOS-formatted hard disk partitions, the serial ports, mouse, and real-time clock. The IIe card could not, however, run software intended for the 16-bit Apple IIGS.
Advertising, marketing, and packaging
Mike Markkula, a retired Intel marketing manager, provided the early critical funding for Apple Computer. From 1977 to 1981, Apple used the Regis McKenna agency for its advertisements and marketing. In 1981, Chiat-Day acquired Regis McKenna's advertising operations and Apple used Chiat-Day. At Regis McKenna Advertising, the team assigned to launch the Apple II consisted of Rob Janoff, art director, Chip Schafer, copywriter and Bill Kelley, account executive. Janoff came up with the Apple logo with a bite out of it. The design was originally an olive green with matching company logotype all in lowercase. Steve Jobs insisted on promoting the color capability of the Apple II by putting rainbow stripes on the Apple logo. In its letterhead and business card implementation, the rounded "a" of the logotype echoed the "bite" in the logo. This logo was developed simultaneously with an advertisement and a brochure; the latter being produced for distribution initially at the first West Coast Computer Faire.
Since the original Apple II, Apple has paid high attention to its quality of packaging, partly because of Steve Jobs' personal preferences and opinions on packaging and final product appearance. All of Apple's packaging for the Apple II series looked similar, featuring much clean white space and showing the Apple rainbow logo prominently. For several years up until the late 1980s, Apple used the Motter Tektura font for packaging, until changing to the Apple Garamond font. | Apple II | Wikipedia | 446 | 2116 | https://en.wikipedia.org/wiki/Apple%20II | Technology | Early computers | null |
Apple ran the first advertisement for the Apple II, a two-page spread ad titled "Introducing Apple II", in BYTE in July 1977. The first brochure, was entitled "Simplicity" and the copy in both the ad and brochure pioneered "demystifying" language intended to make the new idea of a home computer more "personal." The Apple II introduction ad was later run in the September 1977 issue of Scientific American.
Apple later aired eight television commercials for the Apple IIGS, emphasizing its benefits to education and students, along with some print ads.
Clones
The Apple II was frequently cloned, both in the United States and abroad, in a similar way to the IBM PC. According to some sources (see below), more than 190 different models of Apple II clones were manufactured. Most could not be legally imported into the United States. Apple sued and sought criminal charges against clone makers in more than a dozen countries.
Data storage
Cassette
Originally the Apple II used Compact Cassette tapes for program and data storage. A dedicated tape recorder along the lines of the Commodore Datasette was never produced; Apple recommended using the Panasonic RQ309 in some of its early printed documentation. The uses of common consumer cassette recorders and a standard video monitor or television set (with a third-party RF modulator) made the total cost of owning an Apple II less expensive and helped contribute to the Apple II's success.
Cassette storage may have been inexpensive, but it was also slow and unreliable. The Apple II's lack of a disk drive was "a glaring weakness" in what was otherwise intended to be a polished, professional product. Recognizing that the II needed a disk drive to be taken seriously, Apple set out to develop a disk drive and a DOS to run it. Wozniak spent the 1977 Christmas holidays designing a disk controller that reduced the number of chips used by a factor of 10 compared to existing controllers. Still lacking a DOS, and with Wozniak inexperienced in operating system design, Jobs approached Shepardson Microsystems with the project. On April 10, 1978, Apple signed a contract for $13,000 with Shepardson to develop the DOS. | Apple II | Wikipedia | 442 | 2116 | https://en.wikipedia.org/wiki/Apple%20II | Technology | Early computers | null |
Even after disk drives made the cassette tape interfaces obsolete they were still used by enthusiasts as simple one-bit audio input-output ports. Ham radio operators used the cassette input to receive slow scan TV (single frame images). A commercial speech recognition Blackjack program was available, after some user-specific voice training it would recognize simple commands (Hit, stand). Bob Bishop's "Music Kaleidoscope" was a simple program that monitored the cassette input port and based on zero-crossings created color patterns on the screen, a predecessor to current audio visualization plug-ins for media players. Music Kaleidoscope was especially popular on projection TV sets in dance halls.
The OS Disk
Apple and many third-party developers made software available on tape at first, but after the Disk II became available in 1978, tape-based Apple II software essentially disappeared from the market. The initial price of the Disk II drive and controller was US$595, although a $100 off coupon was available through the Apple newsletter "Contact". The controller could handle two drives and a second drive (without controller) retailed for $495.
The Disk II single-sided floppy drive used 5.25-inch floppy disks; double-sided disks could be used, one side at a time, by turning them over and notching a hole for the write protect sensor. The first disk operating systems for the were and DOS 3.2, which stored 113.75 KB on each disk, organized into 35 tracks of 13 256-byte sectors each. After about two years, DOS 3.3 was introduced, storing 140 KB thanks to a minor firmware change on the disk controller that allowed it to store 16 sectors per track. (This upgrade was user-installable as two PROMs on older controllers.) After the release of DOS 3.3, the user community discontinued use of except for running legacy software. Programs that required DOS 3.2 were fairly rare; however, as DOS 3.3 was not a major architectural change aside from the number of sectors per track, a program called MUFFIN was provided with DOS 3.3 to allow users to copy files from DOS 3.2 disks to DOS 3.3 disks. It was possible for software developers to create a DOS 3.2 disk which would also boot on a system with firmware. | Apple II | Wikipedia | 475 | 2116 | https://en.wikipedia.org/wiki/Apple%20II | Technology | Early computers | null |
Later, double-sided drives, with heads to read both sides of the disk, became available from third-party companies. (Apple only produced double-sided 5.25-inch disks for the Lisa 1 computer).
On a DOS 3.x disk, tracks 0, 1, and most of track 2 were reserved to store the operating system. (It was possible, with a special utility, to reclaim most of this space for data if a disk did not need to be bootable.) A short ROM program on the disk controller had the ability to seek to track zero which it did without regard for the read/write head's current position, resulting in the characteristic "chattering" sound of a Disk II boot, which was the read/write head hitting the rubber stop block at the end of the rail – and read and execute code from sector 0. The code contained in there would then pull in the rest of the operating system. DOS stored the disk's directory on track 17, smack in the middle of the 35-track disks, in order to reduce the average seek time to the frequently used directory track. The directory was fixed in size and could hold a maximum of 105 files. Subdirectories were not supported.
Most game publishers did not include DOS on their floppy disks, since they needed the memory it occupied more than its capabilities; instead, they often wrote their own boot loaders and read-only file systems. This also served to discourage "crackers" from snooping around in the game's copy-protection code, since the data on the disk was not in files that could be accessed easily.
Some third-party manufacturers produced floppy drives that could write 40 tracks to most 5.25-inch disks, yielding 160 KB of storage per disk, but the format did not catch on widely, and no known commercial software was published on 40-track media. Most drives, even Disk IIs, could write 36 tracks; a two byte modification to DOS to format the extra track was common. | Apple II | Wikipedia | 412 | 2116 | https://en.wikipedia.org/wiki/Apple%20II | Technology | Early computers | null |
The Apple Disk II stored 140 KB on single-sided, "single-density" floppy disks, but it was very common for Apple II users to extend the capacity of a single-sided floppy disk to 280 KB by cutting out a second write-protect notch on the side of the disk using a "disk notcher" or hole puncher and inserting the disk flipped over. Double-sided disks, with notches on both sides, were available at a higher price, but in practice the magnetic coating on the reverse of nominally single-sided disks was usually of good enough quality to be used (both sides were coated in the same way to prevent warping, although only one side was certified for use). Early on, diskette manufacturers routinely warned that this technique would damage the read/write head of the drives or wear out the disk faster, and these warnings were frequently repeated in magazines of the day. In practice, however, this method was an inexpensive way to store twice as much data for no extra cost, and was widely used for commercially released floppies as well.
Later, Apple IIs were able to use 3.5-inch disks with a total capacity of 800 KB and hard disks. did not support these drives natively; third-party software was required, and disks larger than about 400 KB had to be split up into multiple "virtual disk volumes."
DOS 3.3 was succeeded by ProDOS, a 1983 descendant of the Apple ///'s SOS. It added support for subdirectories and volumes up to 32 MB in size. ProDOS became the DOS of choice; AppleWorks and other newer programs required it.
Legacy
The Apple II series of computers had an enormous impact on the technology industry and expanded the role of microcomputers in society. The Apple II was the first personal computer many people ever saw. Its price was within the reach of many middle-class families, and a partnership with MECC helped make the Apple II popular in schools. By the end of 1980 Apple had already sold over 100,000 Apple IIs, and at the introduction of the IIGS, models in the range had been sold. However, in other markets, the range saw rather more limited adoption, with only 120,000 units selling in the UK over this nine-year period. | Apple II | Wikipedia | 471 | 2116 | https://en.wikipedia.org/wiki/Apple%20II | Technology | Early computers | null |
The Apple II's popularity bootstrapped the computer game and educational software markets and began the boom in the word processor and computer printer markets. The first spreadsheet application, VisiCalc, was initially released for the Apple II, and many businesses bought them just to run VisiCalc. Its success drove IBM in part to create the IBM PC, which many businesses purchased to run spreadsheet and word processing software, at first ported from Apple II versions.
The Apple II's slots, allowing any peripheral card to take control of the bus and directly access memory, enabled an independent industry of card manufacturers who together created a flood of hardware products that let users build systems that were far more powerful and useful (at a lower cost) than any competing system, most of which were not nearly as expandable and were universally proprietary. The first peripheral card was a blank prototyping card intended for electronics enthusiasts who wanted to design their own peripherals for the Apple II.
Specialty peripherals kept the Apple II in use in industry and education environments for many years after Apple Computer stopped supporting the Apple II. Well into the 1990s every clean-room (the super-clean facility where spacecraft are prepared for flight) at the Kennedy Space Center used an Apple II to monitor the environment and air quality. Most planetariums used Apple IIs to control their projectors and other equipment.
Even the game port was unusually powerful and could be used for digital and analog input and output. The early manuals included instructions for how to build a circuit with only four commonly available components (one transistor and three resistors) and a software routine to drive a common Teletype Model 33 machine. Don Lancaster used the game port I/O to drive a LaserWriter printer.
Modern use
Today, emulators for various Apple II models are available to run Apple II software on macOS, Linux, Microsoft Windows, homebrew enabled Nintendo DS and other operating systems. Numerous disk images of Apple II software are available free over the Internet for use with these emulators. AppleWin and MESS are among the best emulators compatible with most Apple II images. The MESS emulator supports recording and playing back of Apple II emulation sessions, as does Home Action Replay Page (a.k.a. HARP).
There is still a small annual convention, KansasFest, dedicated to the platform. | Apple II | Wikipedia | 481 | 2116 | https://en.wikipedia.org/wiki/Apple%20II | Technology | Early computers | null |
In 2017, the band 8 Bit Weapon released the world's first 100% Apple II-based music album entitled, "Class Apples". The album featured dance-oriented cover versions of classical music by Bach, Beethoven, and Mozart recorded directly off the Apple II motherboard. | Apple II | Wikipedia | 56 | 2116 | https://en.wikipedia.org/wiki/Apple%20II | Technology | Early computers | null |
In organic chemistry, hydrocarbons (compounds composed solely of carbon and hydrogen) are divided into two classes: aromatic compounds and aliphatic compounds (; G. aleiphar, fat, oil). Aliphatic compounds can be saturated (in which all the C-C bonds are single requiring the structure to be completed, or 'saturated', by hydrogen) like hexane, or unsaturated, like hexene and hexyne. Open-chain compounds, whether straight or branched, and which contain no rings of any type, are always aliphatic. Cyclic compounds can be aliphatic if they are not aromatic.
Structure
Aliphatic compounds can be saturated, joined by single bonds (alkanes), or unsaturated, with double bonds (alkenes) or triple bonds (alkynes). If other elements (heteroatoms) are bound to the carbon chain, the most common being oxygen, nitrogen, sulfur, and chlorine, it is no longer a hydrocarbon, and therefore no longer an aliphatic compound. However, such compounds may still be referred to as aliphatic if the hydrocarbon portion of the molecule is aliphatic, e.g. aliphatic amines, to differentiate them from aromatic amines.
The least complex aliphatic compound is methane (CH4).
Properties
Most aliphatic compounds are flammable, allowing the use of hydrocarbons as fuel, such as methane in natural gas for stoves or heating; butane in torches and lighters; various aliphatic (as well as aromatic) hydrocarbons in liquid transportation fuels like petrol/gasoline, diesel, and jet fuel; and other uses such as ethyne (acetylene) in welding.
Examples of aliphatic compounds
The most important aliphatic compounds are:
n-, iso- and cyclo-alkanes (saturated hydrocarbons)
n-, iso- and cyclo-alkenes and -alkynes (unsaturated hydrocarbons).
Important examples of low-molecular aliphatic compounds can be found in the list below (sorted by the number of carbon-atoms): | Aliphatic compound | Wikipedia | 457 | 2120 | https://en.wikipedia.org/wiki/Aliphatic%20compound | Physical sciences | Aliphatic hydrocarbons | Chemistry |
Armour (Commonwealth English) or armor (American English; see spelling differences) is a covering used to protect an object, individual, or vehicle from physical injury or damage, especially direct contact weapons or projectiles during combat, or from a potentially dangerous environment or activity (e.g. cycling, construction sites, etc.). Personal armour is used to protect soldiers and war animals. Vehicle armour is used on warships, armoured fighting vehicles, and some combat aircraft, mostly ground attack aircraft.
A second use of the term armour describes armoured forces, armoured weapons, and their role in combat. After the development of armoured warfare, tanks and mechanised infantry and their combat formations came to be referred to collectively as "armour".
Etymology
The word "armour" began to appear in the Middle Ages as a derivative of Old French. It is dated from 1297 as a "mail, defensive covering worn in combat". The word originates from the Old French , itself derived from the Latin meaning "arms and/or equipment", with the root meaning "arms or gear".
Personal
Armour has been used throughout recorded history. It has been made from a variety of materials, beginning with the use of leathers or fabrics as protection and evolving through chain mail and metal plate into today's modern composites. For much of military history the manufacture of metal personal armour has dominated the technology and employment of armour.
Armour drove the development of many important technologies of the Ancient World, including wood lamination, mining, metal refining, vehicle manufacture, leather processing, and later decorative metal working. Its production was influential in the Industrial Revolution, and furthered commercial development of metallurgy and engineering. Armour was also an important factor in the development of firearms, which in turn revolutionised warfare.
History
Significant factors in the development of armour include the economic and technological necessities of its production. For instance, plate armour first appeared in Medieval Europe when water-powered trip hammers made the formation of plates faster and cheaper. At times the development of armour has paralleled the development of increasingly effective weaponry on the battlefield, with armourers seeking to create better protection without sacrificing mobility. | Armour | Wikipedia | 437 | 2147 | https://en.wikipedia.org/wiki/Armour | Technology | Weapons | null |
Well-known armour types in European history include the lorica hamata, lorica squamata, and the lorica segmentata of the Roman legions, the mail hauberk of the early medieval age, and the full steel plate harness worn by later medieval and renaissance knights, and breast and back plates worn by heavy cavalry in several European countries until the first year of World War I (1914–1915). The samurai warriors of Feudal Japan utilised many types of armour for hundreds of years up to the 19th century.
Early
The first record of body armor in history was found on the Stele of Vultures in ancient Sumer in today's south Iraq, and various forms of scale mail can be seen in surviving records from the New Kingdom of Egypt, Zhou dynasty China, and dynastic India. Cuirasses and helmets were manufactured in Japan as early as the 4th century. Tankō, worn by foot soldiers and keikō, worn by horsemen were both pre-samurai types of early Japanese armour constructed from iron plates connected together by leather thongs. Japanese lamellar armour (keiko) passed through Korea and reached Japan around the 5th century. These early Japanese lamellar armours took the form of a sleeveless jacket, leggings and a helmet.
Armour did not always cover all of the body; sometimes no more than a helmet and leg plates were worn. The rest of the body was generally protected by means of a large shield. Examples of armies equipping their troops in this fashion were the Aztecs (13th to 15th century CE).
In East Asia, many types of armour were commonly used at different times by various cultures, including scale armour, lamellar armour, laminar armour, plated mail, mail, plate armour, and brigandine. Around the dynastic Tang, Song, and early Ming Period, cuirasses and plates (mingguangjia) were also used, with more elaborate versions for officers in war. The Chinese, during that time used partial plates for "important" body parts instead of covering their whole body since too much plate armour hinders their martial arts movement. The other body parts were covered in cloth, leather, lamellar, or mountain pattern armor. In pre-Qin dynasty times, leather armour was made out of various animals, with more exotic ones such as the rhinoceros. | Armour | Wikipedia | 481 | 2147 | https://en.wikipedia.org/wiki/Armour | Technology | Weapons | null |
Mail, sometimes called "chainmail", made of interlocking iron rings is believed to have first appeared some time after 300 BC. Its invention is credited to the Celts; the Romans are thought to have adopted their design.
Gradually, small additional plates or discs of iron were added to the mail to protect vulnerable areas. Hardened leather and splinted construction were used for arm and leg pieces. The coat of plates was developed, an armour made of large plates sewn inside a textile or leather coat.
13th to 18th century Europe
Early plate in Italy, and elsewhere in the 13th–15th century, were made of iron. Iron armour could be carburised or case hardened to give a surface of harder steel. Plate armour became cheaper than mail by the 15th century as it required much less labour and labour had become much more expensive after the Black Death, though it did require larger furnaces to produce larger blooms. Mail continued to be used to protect those joints which could not be adequately protected by plate, such as the armpit, crook of the elbow and groin. Another advantage of plate was that a lance rest could be fitted to the breast plate.
The small skull cap evolved into a bigger true helmet, the bascinet, as it was lengthened downward to protect the back of the neck and the sides of the head. Additionally, several new forms of fully enclosed helmets were introduced in the late 14th century.
Probably the most recognised style of armour in the world became the plate armour associated with the knights of the European Late Middle Ages, but continuing to the early 17th century Age of Enlightenment in all European countries.
By 1400, the full harness of plate armour had been developed in armouries of Lombardy. Heavy cavalry dominated the battlefield for centuries in part because of their armour.
In the early 15th century, advances in weaponry allowed infantry to defeat armoured knights on the battlefield. The quality of the metal used in armour deteriorated as armies became bigger and armour was made thicker, necessitating breeding of larger cavalry horses. If during the 14–15th centuries armour seldom weighed more than 15 kg, then by the late 16th century it weighed 25 kg. The increasing weight and thickness of late 16th century armour therefore gave substantial resistance. | Armour | Wikipedia | 447 | 2147 | https://en.wikipedia.org/wiki/Armour | Technology | Weapons | null |
In the early years of low velocity firearms, full suits of armour, or breast plates actually stopped bullets fired from a modest distance. Crossbow bolts, if still in use, would seldom penetrate good plate, nor would any bullet unless fired from close range. In effect, rather than making plate armour obsolete, the use of firearms stimulated the development of plate armour into its later stages. For most of that period, it allowed horsemen to fight while being the targets of defending arquebusiers without being easily killed. Full suits of armour were actually worn by generals and princely commanders right up to the second decade of the 18th century. It was the only way they could be mounted and survey the overall battlefield with safety from distant musket fire.
The horse was afforded protection from lances and infantry weapons by steel plate barding. This gave the horse protection and enhanced the visual impression of a mounted knight. Late in the era, elaborate barding was used in parade armour.
Later
Gradually, starting in the mid-16th century, one plate element after another was discarded to save weight for foot soldiers.
Back and breast plates continued to be used throughout the entire period of the 18th century and through Napoleonic times, in many European heavy cavalry units, until the early 20th century. From their introduction, muskets could pierce plate armour, so cavalry had to be far more mindful of the fire. In Japan, armour continued to be used until the late 19th century, with the last major fighting in which armour was used, this occurred in 1868. Samurai armour had one last short lived use in 1877 during the Satsuma Rebellion.
Though the age of the knight was over, armour continued to be used in many capacities. Soldiers in the American Civil War bought iron and steel vests from peddlers (both sides had considered but rejected body armour for standard issue). The effectiveness of the vests varied widely, some successfully deflected bullets and saved lives, but others were poorly made and resulted in tragedy for the soldiers. In any case the vests were abandoned by many soldiers due to their increased weight on long marches, as well as the stigma they got for being cowards from their fellow troops. | Armour | Wikipedia | 440 | 2147 | https://en.wikipedia.org/wiki/Armour | Technology | Weapons | null |
At the start of World War I, thousands of the French Cuirassiers rode out to engage the German Cavalry. By that period, the shiny metallic cuirass was covered in a dark paint and a canvas wrap covered their elaborate Napoleonic style helmets, to help mitigate the sunlight being reflected off the surfaces, thereby alerting the enemy of their location. Their armour was only meant for protection against edged weapons such as bayonets, sabres, and lances. Cavalry had to be wary of repeating rifles, machine guns, and artillery, unlike the foot soldiers, who at least had a trench to give them some protection.
Present
Today, ballistic vests, also known as flak jackets, made of ballistic cloth (e.g. kevlar, dyneema, twaron, spectra etc.) and ceramic or metal plates are common among police officers, security guards, corrections officers and some branches of the military.
The US Army has adopted Interceptor body armour, which uses Enhanced Small Arms Protective Inserts (ESAPIs) in the chest, sides, and back of the armour. Each plate is rated to stop a range of ammunition including 3 hits from a 7.62×51 NATO AP round at a range of . Dragon Skin is another ballistic vest which is currently in testing with mixed results. As of 2019, it has been deemed too heavy, expensive, and unreliable, in comparison to more traditional plates, and it is outdated in protection compared to modern US IOTV armour, and even in testing was deemed a downgrade from the IBA.
The British Armed Forces also have their own armour, known as Osprey. It is rated to the same general equivalent standard as the US counterpart, the Improved Outer Tactical Vest, and now the Soldier Plate Carrier System and Modular Tactical Vest.
The Russian Armed Forces also have armour, known as the 6B43, all the way to 6B45, depending on variant. Their armour runs on the GOST system, which, due to regional conditions, has resulted in a technically higher protective level overall.
Vehicle
The first modern production technology for armour plating was used by navies in the construction of the ironclad warship, reaching its pinnacle of development with the battleship. The first tanks were produced during World War I. Aerial armour has been used to protect pilots and aircraft systems since the First World War. | Armour | Wikipedia | 477 | 2147 | https://en.wikipedia.org/wiki/Armour | Technology | Weapons | null |
In modern ground forces' usage, the meaning of armour has expanded to include the role of troops in combat. After the evolution of armoured warfare, mechanised infantry were mounted in armoured fighting vehicles and replaced light infantry in many situations. In modern armoured warfare, armoured units equipped with tanks and infantry fighting vehicles serve the historic role of heavy cavalry, light cavalry, and dragoons, and belong to the armoured branch of warfare.
History
Ships
The first ironclad battleship, with iron armour over a wooden hull, , was launched by the French Navy in 1859 prompting the British Royal Navy to build a counter. The following year they launched , which was twice the size and had iron armour over an iron hull. After the first battle between two ironclads took place in 1862 during the American Civil War, it became clear that the ironclad had replaced the unarmoured line-of-battle ship as the most powerful warship afloat.
Ironclads were designed for several roles, including as high seas battleships, coastal defence ships, and long-range cruisers. The rapid evolution of warship design in the late 19th century transformed the ironclad from a wooden-hulled vessel which carried sails to supplement its steam engines into the steel-built, turreted battleships and cruisers familiar in the 20th century. This change was pushed forward by the development of heavier naval guns (the ironclads of the 1880s carried some of the heaviest guns ever mounted at sea), more sophisticated steam engines, and advances in metallurgy which made steel shipbuilding possible.
The rapid pace of change in the ironclad period meant that many ships were obsolete as soon as they were complete, and that naval tactics were in a state of flux. Many ironclads were built to make use of the ram or the torpedo, which a number of naval designers considered the crucial weapons of naval combat. There is no clear end to the ironclad period, but towards the end of the 1890s the term ironclad dropped out of use. New ships were increasingly constructed to a standard pattern and designated battleships or armoured cruisers.
Trains | Armour | Wikipedia | 420 | 2147 | https://en.wikipedia.org/wiki/Armour | Technology | Weapons | null |
Armoured trains saw use from the mid-19th to the mid-20th century, including the American Civil War (1861–1865), the Franco-Prussian War (1870–1871), the First and Second Boer Wars (1880–81 and 1899–1902), the Polish–Soviet War (1919–1921), the First (1914–1918) and Second World Wars (1939–1945) and the First Indochina War (1946–1954). The most intensive use of armoured trains was during the Russian Civil War (1918–1920).
Armoured fighting vehicles
Ancient siege engines were usually protected by wooden armour, often covered with wet hides or thin metal to prevent being easily burned.
Medieval war wagons were horse-drawn wagons that were similarly armoured. These contained guns or crossbowmen that could fire through gun-slits.
The first modern armoured fighting vehicles were armoured cars, developed . These started as ordinary wheeled motor-cars protected by iron shields, typically mounting a machine gun.
During the First World War, the stalemate of trench warfare during on the Western Front spurred the development of the tank. It was envisioned as an armoured machine that could advance under fire from enemy rifles and machine guns, and respond with its own heavy guns. It used caterpillar tracks to cross ground broken up by shellfire and trenches.
Aircraft
With the development of effective anti-aircraft artillery in the period before the Second World War, military pilots, once the "knights of the air" during the First World War, became far more vulnerable to ground fire. As a response, armour plating was added to aircraft to protect aircrew and vulnerable areas such as engines and fuel tanks. Self-sealing fuel tanks functioned like armour in that they added protection but also increased weight and cost.
Present
Tank armour has progressed from the Second World War armour forms, now incorporating not only harder composites, but also reactive armour designed to defeat shaped charges. As a result of this, the main battle tank (MBT) conceived in the Cold War era can survive multiple rocket-propelled grenade strikes with minimal effect on the crew or the operation of the vehicle. The light tanks that were the last descendants of the light cavalry during the Second World War have almost completely disappeared from the world's militaries due to increased lethality of the weapons available to the vehicle-mounted infantry. | Armour | Wikipedia | 471 | 2147 | https://en.wikipedia.org/wiki/Armour | Technology | Weapons | null |
The armoured personnel carrier (APC) was devised during the First World War. It allows the safe and rapid movement of infantry in a combat zone, minimising casualties and maximising mobility. APCs are fundamentally different from the previously used armoured half-tracks in that they offer a higher level of protection from artillery burst fragments, and greater mobility in more terrain types. The basic APC design was substantially expanded to an infantry fighting vehicle (IFV) when properties of an APC and a light tank were combined in one vehicle.
Naval armour has fundamentally changed from the Second World War doctrine of thicker plating to defend against shells, bombs and torpedoes. Passive defence naval armour is limited to kevlar or steel (either single layer or as spaced armour) protecting particularly vital areas from the effects of nearby impacts. Since ships cannot carry enough armour to completely protect against anti-ship missiles, they depend more on defensive weapons destroying incoming missiles, or causing them to miss by confusing their guidance systems with electronic warfare.
Although the role of the ground attack aircraft significantly diminished after the Korean War, it re-emerged during the Vietnam War, and in the recognition of this, the US Air Force authorised the design and production of what became the A-10 dedicated anti-armour and ground-attack aircraft that first saw action in the Gulf War.
High-voltage transformer fire barriers are often required to defeat ballistics from small arms as well as projectiles from transformer bushings and lightning arresters, which form part of large electrical transformers, per NFPA 850. Such fire barriers may be designed to inherently function as armour, or may be passive fire protection materials augmented by armour, where care must be taken to ensure that the armour's reaction to fire does not cause issues with regards to the fire barrier being armoured to defeat explosions and projectiles in addition to fire, especially since both functions must be provided simultaneously, meaning they must be fire-tested together to provide realistic evidence of fitness for purpose.
Combat drones use little to no vehicular armour as they are not crewed vessels, this results in them being lightweight and small in size.
Animal armour
Horse armour | Armour | Wikipedia | 433 | 2147 | https://en.wikipedia.org/wiki/Armour | Technology | Weapons | null |
Body armour for war horses has been used since at least 2000 BC. Cloth, leather, and metal protection covered cavalry horses in ancient civilisations, including ancient Egypt, Assyria, Persia, and Rome. Some formed heavy cavalry units of armoured horses and riders used to attack infantry and mounted archers. Armour for horses is called barding (also spelled bard or barb) especially when used by European knights.
During the late Middle Ages as armour protection for knights became more effective, their mounts became targets. This vulnerability was exploited by the Scots at the Battle of Bannockburn in the 14th century, when horses were killed by the infantry, and for the English at the Battle of Crécy in the same century where longbowmen shot horses and the then dismounted French knights were killed by heavy infantry. Barding developed as a response to such events.
Examples of armour for horses could be found as far back as classical antiquity. Cataphracts, with scale armour for both rider and horse, are believed by many historians to have influenced the later European knights, via contact with the Byzantine Empire.
Surviving period examples of barding are rare; however, complete sets are on display at the Philadelphia Museum of Art, the Wallace Collection in London, the Royal Armouries in Leeds, and the Metropolitan Museum of Art in New York City. Horse armour could be made in whole or in part of cuir bouilli (hardened leather), but surviving examples of this are especially rare.
Elephant armour
War elephants were first used in ancient times without armour, but armour was introduced because elephants injured by enemy weapons would often flee the battlefield. Elephant armour was often made from hardened leather, which was fitted onto an individual elephant while moist, then dried to create a hardened shell. Alternatively, metal armour pieces were sometimes sewn into heavy cloth. Later lamellar armour (small overlapping metal plates) was introduced. Full plate armour was not typically used due to its expense and the danger of the animal overheating. | Armour | Wikipedia | 400 | 2147 | https://en.wikipedia.org/wiki/Armour | Technology | Weapons | null |
Armadillos () are New World placental mammals in the order Cingulata. They form part of the superorder Xenarthra, along with the anteaters and sloths. 21 extant species of armadillo have been described, some of which are distinguished by the number of bands on their armor. All species are native to the Americas, where they inhabit a variety of different environments.
Living armadillos are characterized by a leathery armor shell and long, sharp claws for digging. They have short legs, but can move quite quickly. The average length of an armadillo is about , including its tail. The giant armadillo grows up to and weighs up to , while the pink fairy armadillo has a length of only . When threatened by a predator, Tolypeutes species frequently roll up into a ball; they are the only species of armadillo capable of this.
Recent genetic research has shown that the megafaunal glyptodonts (up to tall with maximum body masses of around 2 tonnes), which became extinct around 12,000 years ago are true armadillos more closely related to all other living armadillos than to Dasypus (the long-nosed or naked-tailed armadillos). Armadillos are currently classified into two families, Dasypodidae, with Dasypus as the only living genus, and Chlamyphoridae, which contains all other living armadillos as well as the glyptodonts.
Etymology
The word means in Spanish; it is derived from , with the diminutive suffix attached. While the phrase little armored one would translate to normally, the suffix can be used in place of when the diminutive is used in an approximative tense. The Aztecs called them , Nahuatl for : and . The Portuguese word for is which is derived from the Tupi language and ; and used in Argentina, Bolivia, Brazil, Paraguay and Uruguay; similar names are also found in other, especially European, languages.
Other various vernacular names given are: | Armadillo | Wikipedia | 431 | 2186 | https://en.wikipedia.org/wiki/Armadillo | Biology and health sciences | Mammals | null |
(from ) in Argentina, Bolivia, Chile, Colombia and Peru;
(from Nahuatl) in Costa Rica, El Salvador, Honduras and Nicaragua;
in Argentina and Uruguay;
in Argentina, Chile, Colombia and Uruguay;
in Argentina, Brazil, Chile, Colombia and Paraguay;
in Colombia and Venezuela
in Tolima, Caldas and Antioquia, Colombia;
in Caribbean Colombia;
in southeast Mexico;
in the state of Veracruz, Mexico;
in Perú.
Classification
Family Dasypodidae
Subfamily Dasypodinae
Genus Dasypus
Nine-banded armadillo or long-nosed armadillo, Dasypus novemcinctus
Seven-banded armadillo, Dasypus septemcinctus
Southern long-nosed armadillo, Dasypus hybridus
Llanos long-nosed armadillo, Dasypus sabanicola
Greater long-nosed armadillo, Dasypus kappleri
Hairy long-nosed armadillo, Dasypus pilosus
Yepes's mulita, Dasypus yepesi
†Beautiful armadillo, Dasypus bellus
†Dasypus neogaeus
Genus †Stegotherium | Armadillo | Wikipedia | 240 | 2186 | https://en.wikipedia.org/wiki/Armadillo | Biology and health sciences | Mammals | null |
Family Chlamyphoridae
Subfamily Chlamyphorinae
Genus Calyptophractus
Greater fairy armadillo, Calyptophractus retusus
Genus Chlamyphorus
Pink fairy armadillo, Chlamyphorus truncatus
Subfamily Euphractinae
Genus Chaetophractus
Screaming hairy armadillo, Chaetophractus vellerosus
Big hairy armadillo, Chaetophractus villosus
Andean hairy armadillo, Chaetophractus nationi
Genus †Macroeuphractus
Genus †Paleuphractus
Genus †Proeuphractus
Genus †Doellotatus
Genus †Peltephilus
†Horned armadillo, Peltephilus ferox
Genus Euphractus
Six-banded armadillo, Euphractus sexcinctus
Genus Zaedyus
Pichi, Zaedyus pichiy
Subfamily Tolypeutinae
Genus †Kuntinaru
Genus Cabassous
Northern naked-tailed armadillo, Cabassous centralis
Chacoan naked-tailed armadillo, Cabassous chacoensis
Southern naked-tailed armadillo, Cabassous unicinctus
Greater naked-tailed armadillo, Cabassous tatouay
Genus Priodontes
Giant armadillo, Priodontes maximus
Genus Tolypeutes
Southern three-banded armadillo, Tolypeutes matacus
Brazilian three-banded armadillo, Tolypeutes tricinctus
† indicates extinct taxon
Phylogeny
Below is a recent simplified phylogeny of the xenarthran families, which includes armadillos. The dagger symbol, "†", denotes extinct groups.
Evolution
Recent genetic research suggests that an extinct group of giant armored mammals, the glyptodonts, should be included within the lineage of armadillos, having diverged some 35 million years ago, more recently than previously assumed. | Armadillo | Wikipedia | 404 | 2186 | https://en.wikipedia.org/wiki/Armadillo | Biology and health sciences | Mammals | null |
Distribution
Like all of the Xenarthra lineages, armadillos originated in South America. Due to the continent's former isolation, they were confined there for most of the Cenozoic. The recent formation of the Isthmus of Panama allowed a few members of the family to migrate northward into southern North America by the early Pleistocene, as part of the Great American Interchange. (Some of their much larger cingulate relatives, the pampatheres and chlamyphorid glyptodonts, made the same journey.)
Today, all extant armadillo species are still present in South America. They are particularly diverse in Paraguay (where 11 species exist) and surrounding areas. Many species are endangered. Some, including four species of Dasypus, are widely distributed over the Americas, whereas others, such as Yepes's mulita, are restricted to small ranges. Two species, the northern naked-tailed armadillo and nine-banded armadillo, are found in Central America; the latter has also reached the United States, primarily in the south-central states (notably Texas), but with a range that extends as far east as North Carolina and Florida, and as far north as southern Nebraska and southern Indiana. Their range has consistently expanded in North America over the last century due to a lack of natural predators. Armadillos are increasingly documented in southern Illinois and are tracking northwards due to climate change.
Characteristics
Size
The smallest species of armadillo, the pink fairy armadillo, weighs around and is in total length. The largest species, the giant armadillo, can weigh up to , and can be long.
Diet and predation
The diets of different armadillo species vary, but consist mainly of insects, grubs, and other invertebrates. Some species, however, feed almost entirely on ants and termites.
They are prolific diggers. Many species use their sharp claws to dig for food, such as grubs, and to dig dens. The nine-banded armadillo prefers to build burrows in moist soil near the creeks, streams, and arroyos around which it lives and feeds. | Armadillo | Wikipedia | 442 | 2186 | https://en.wikipedia.org/wiki/Armadillo | Biology and health sciences | Mammals | null |
Armadillos have very poor eyesight, and use their keen sense of smell to hunt for food. They use their claws not only for digging and finding food but also for digging burrows for their dwellings, each of which is a single corridor the width of the animal's body. They have five clawed toes on their hind feet, and three to five toes with heavy digging claws on their fore feet. Armadillos have numerous cheek teeth which are not divided into premolars and molars, but usually have no incisors or canines. The dentition of the nine-banded armadillo is P 7/7, M 1/1 = 32.
Body temperature
In common with other xenarthrans, armadillos, in general, have low body temperatures of and low basal metabolic rates (40–60% of that expected in placental mammals of their mass). This is particularly true of types that specialize in using termites as their primary food source (for example, Priodontes and Tolypeutes).
Skin
The armor is formed by plates of dermal bone covered in relatively small overlapping epidermal scales called "scutes" which are composed of keratin. The skin of an armadillo can glow under ultraviolet light.
Most species have rigid shields over the shoulders and hips, with a number of bands separated by flexible skin covering the back and flanks. Additional armor covers the top of the head, the upper parts of the limbs, and the tail. The underside of the animal is never armored and is simply covered with soft skin and fur. This armor-like skin appears to be an important defense for many armadillos, although most escape predators by fleeing (often into thorny patches, from which their armor protects them) or digging to safety. Only the South American three-banded armadillos (Tolypeutes) rely heavily on their armor for protection.
Defensive behavior
When threatened by a predator, Tolypeutes species frequently roll up into a ball. Other armadillo species cannot roll up because they have too many plates. When surprised, the North American nine-banded armadillo tends to jump straight in the air, which can lead to a fatal collision with the undercarriage or fenders of passing vehicles. | Armadillo | Wikipedia | 471 | 2186 | https://en.wikipedia.org/wiki/Armadillo | Biology and health sciences | Mammals | null |
Movement
Armadillos have short legs, but can move quite quickly. The nine-banded armadillo is noted for its movement through water, which is accomplished via two different methods: it can walk underwater for short distances, holding its breath for as long as six minutes; or, to cross larger bodies of water, it can increase its buoyancy by swallowing air to inflate its stomach and intestines.
Reproduction
Gestation lasts from 60 to 120 days, depending on species, although the nine-banded armadillo also exhibits delayed implantation, so the young are not typically born for eight months after mating. Most members of the genus Dasypus give birth to four monozygotic young (that is, identical quadruplets), but other species may have typical litter sizes that range from one to eight. The young are born with soft, leathery skin which hardens within a few weeks. They reach sexual maturity in three to twelve months, depending on the species. Armadillos are solitary animals that do not share their burrows with other adults.
Armadillos and humans
Science and education
Armadillos are often used in the study of leprosy, since they, along with mangabey monkeys, rabbits, and mice (on their footpads), are among the few known species that can contract the disease systemically. They are particularly susceptible due to their unusually low body temperature, which is hospitable to the leprosy bacterium, Mycobacterium leprae. (The leprosy bacterium is difficult to culture and armadillos have a body temperature of , similar to human skin.) Humans can acquire a leprosy infection from armadillos by handling them or consuming armadillo meat. Armadillos are a presumed vector and natural reservoir for the disease in Texas, Louisiana and Florida. Prior to the arrival of Europeans in the late 15th century, leprosy was unknown in the New World. Given that armadillos are native to the New World, at some point they must have acquired the disease from old-world humans.
The armadillo is also a natural reservoir for Chagas disease. | Armadillo | Wikipedia | 447 | 2186 | https://en.wikipedia.org/wiki/Armadillo | Biology and health sciences | Mammals | null |
The nine-banded armadillo also serves science through its unusual reproductive system, in which four genetically identical offspring are born, the result of one original egg. Because they are always genetically identical, the group of four young provides a good subject for scientific, behavioral, or medical tests that need consistent biological and genetic makeup in the test subjects. This is the only reliable manifestation of polyembryony in the class Mammalia, and exists only within the genus Dasypus and not in all armadillos, as is commonly believed. Other species that display this trait include parasitoid wasps, certain flatworms, and various aquatic invertebrates.
Even though they have a leathery, tough shell, armadillos, (mainly Dasypus) are common roadkill due to their habit of jumping 3–4 ft vertically when startled, which puts them into collision with the underside of vehicles. Wildlife enthusiasts are using the northward march of the armadillo as an opportunity to educate others about the animals, which can be a burrowing nuisance to property owners and managers.
Culture
Armadillo shells have traditionally been used to make the back of the charango, an Andean lute instrument.
In certain parts of Central and South America, armadillo meat is eaten; it is a popular ingredient in Oaxaca, Mexico. During the Great Depression, Americans were known to eat armadillo, known begrudgingly as "Hoover hogs", a nod to the belief that President Herbert Hoover was responsible for the economic despair facing the nation at that time.
A whimsical account of The Beginning of the Armadillos is one of the chapters of Rudyard Kipling's Just So Stories 1902 children's book. The vocal and piano duo Flanders and Swann recorded a humorous song called "The Armadillo".
Shel Silverstein wrote a two-line poem called "Instructions" on how to bathe an armadillo in his collection A Light in the Attic. The reference was "use one bar of soap, a whole lot of hope, and 72 pads of Brillo." | Armadillo | Wikipedia | 428 | 2186 | https://en.wikipedia.org/wiki/Armadillo | Biology and health sciences | Mammals | null |
In mathematics, analytic geometry, also known as coordinate geometry or Cartesian geometry, is the study of geometry using a coordinate system. This contrasts with synthetic geometry.
Analytic geometry is used in physics and engineering, and also in aviation, rocketry, space science, and spaceflight. It is the foundation of most modern fields of geometry, including algebraic, differential, discrete and computational geometry.
Usually the Cartesian coordinate system is applied to manipulate equations for planes, straight lines, and circles, often in two and sometimes three dimensions. Geometrically, one studies the Euclidean plane (two dimensions) and Euclidean space. As taught in school books, analytic geometry can be explained more simply: it is concerned with defining and representing geometric shapes in a numerical way and extracting numerical information from shapes' numerical definitions and representations. That the algebra of the real numbers can be employed to yield results about the linear continuum of geometry relies on the Cantor–Dedekind axiom.
History
Ancient Greece
The Greek mathematician Menaechmus solved problems and proved theorems by using a method that had a strong resemblance to the use of coordinates and it has sometimes been maintained that he had introduced analytic geometry.
Apollonius of Perga, in On Determinate Section, dealt with problems in a manner that may be called an analytic geometry of one dimension; with the question of finding points on a line that were in a ratio to the others. Apollonius in the Conics further developed a method that is so similar to analytic geometry that his work is sometimes thought to have anticipated the work of Descartes by some 1800 years. His application of reference lines, a diameter and a tangent is essentially no different from our modern use of a coordinate frame, where the distances measured along the diameter from the point of tangency are the abscissas, and the segments parallel to the tangent and intercepted between the axis and the curve are the ordinates. He further developed relations between the abscissas and the corresponding ordinates that are equivalent to rhetorical equations (expressed in words) of curves. However, although Apollonius came close to developing analytic geometry, he did not manage to do so since he did not take into account negative magnitudes and in every case the coordinate system was superimposed upon a given curve a posteriori instead of a priori. That is, equations were determined by curves, but curves were not determined by equations. Coordinates, variables, and equations were subsidiary notions applied to a specific geometric situation. | Analytic geometry | Wikipedia | 498 | 2202 | https://en.wikipedia.org/wiki/Analytic%20geometry | Mathematics | Geometry | null |
Persia
The 11th-century Persian mathematician Omar Khayyam saw a strong relationship between geometry and algebra and was moving in the right direction when he helped close the gap between numerical and geometric algebra with his geometric solution of the general cubic equations, but the decisive step came later with Descartes. Omar Khayyam is credited with identifying the foundations of algebraic geometry, and his book Treatise on Demonstrations of Problems of Algebra (1070), which laid down the principles of analytic geometry, is part of the body of Persian mathematics that was eventually transmitted to Europe. Because of his thoroughgoing geometrical approach to algebraic equations, Khayyam can be considered a precursor to Descartes in the invention of analytic geometry.
Western Europe
Analytic geometry was independently invented by René Descartes and Pierre de Fermat, although Descartes is sometimes given sole credit. Cartesian geometry, the alternative term used for analytic geometry, is named after Descartes.
Descartes made significant progress with the methods in an essay titled La Géométrie (Geometry), one of the three accompanying essays (appendices) published in 1637 together with his Discourse on the Method for Rightly Directing One's Reason and Searching for Truth in the Sciences, commonly referred to as Discourse on Method.
La Geometrie, written in his native French tongue, and its philosophical principles, provided a foundation for calculus in Europe. Initially the work was not well received, due, in part, to the many gaps in arguments and complicated equations. Only after the translation into Latin and the addition of commentary by van Schooten in 1649 (and further work thereafter) did Descartes's masterpiece receive due recognition. | Analytic geometry | Wikipedia | 340 | 2202 | https://en.wikipedia.org/wiki/Analytic%20geometry | Mathematics | Geometry | null |
Pierre de Fermat also pioneered the development of analytic geometry. Although not published in his lifetime, a manuscript form of Ad locos planos et solidos isagoge (Introduction to Plane and Solid Loci) was circulating in Paris in 1637, just prior to the publication of Descartes' Discourse. Clearly written and well received, the Introduction also laid the groundwork for analytical geometry. The key difference between Fermat's and Descartes' treatments is a matter of viewpoint: Fermat always started with an algebraic equation and then described the geometric curve that satisfied it, whereas Descartes started with geometric curves and produced their equations as one of several properties of the curves. As a consequence of this approach, Descartes had to deal with more complicated equations and he had to develop the methods to work with polynomial equations of higher degree. It was Leonhard Euler who first applied the coordinate method in a systematic study of space curves and surfaces.
Coordinates
In analytic geometry, the plane is given a coordinate system, by which every point has a pair of real number coordinates. Similarly, Euclidean space is given coordinates where every point has three coordinates. The value of the coordinates depends on the choice of the initial point of origin. There are a variety of coordinate systems used, but the most common are the following:
Cartesian coordinates (in a plane or space)
The most common coordinate system to use is the Cartesian coordinate system, where each point has an x-coordinate representing its horizontal position, and a y-coordinate representing its vertical position. These are typically written as an ordered pair (x, y). This system can also be used for three-dimensional geometry, where every point in Euclidean space is represented by an ordered triple of coordinates (x, y, z).
Polar coordinates (in a plane)
In polar coordinates, every point of the plane is represented by its distance r from the origin and its angle θ, with θ normally measured counterclockwise from the positive x-axis. Using this notation, points are typically written as an ordered pair (r, θ). One may transform back and forth between two-dimensional Cartesian and polar coordinates by using these formulae: This system may be generalized to three-dimensional space through the use of cylindrical or spherical coordinates.
Cylindrical coordinates (in a space) | Analytic geometry | Wikipedia | 474 | 2202 | https://en.wikipedia.org/wiki/Analytic%20geometry | Mathematics | Geometry | null |
In cylindrical coordinates, every point of space is represented by its height z, its radius r from the z-axis and the angle θ its projection on the xy-plane makes with respect to the horizontal axis.
Spherical coordinates (in a space)
In spherical coordinates, every point in space is represented by its distance ρ from the origin, the angle θ its projection on the xy-plane makes with respect to the horizontal axis, and the angle φ that it makes with respect to the z-axis. The names of the angles are often reversed in physics.
Equations and curves
In analytic geometry, any equation involving the coordinates specifies a subset of the plane, namely the solution set for the equation, or locus. For example, the equation y = x corresponds to the set of all the points on the plane whose x-coordinate and y-coordinate are equal. These points form a line, and y = x is said to be the equation for this line. In general, linear equations involving x and y specify lines, quadratic equations specify conic sections, and more complicated equations describe more complicated figures.
Usually, a single equation corresponds to a curve on the plane. This is not always the case: the trivial equation x = x specifies the entire plane, and the equation x2 + y2 = 0 specifies only the single point (0, 0). In three dimensions, a single equation usually gives a surface, and a curve must be specified as the intersection of two surfaces (see below), or as a system of parametric equations. The equation x2 + y2 = r2 is the equation for any circle centered at the origin (0, 0) with a radius of r.
Lines and planes
Lines in a Cartesian plane, or more generally, in affine coordinates, can be described algebraically by linear equations. In two dimensions, the equation for non-vertical lines is often given in the slope-intercept form:
where:
m is the slope or gradient of the line.
b is the y-intercept of the line.
x is the independent variable of the function y = f(x).
In a manner analogous to the way lines in a two-dimensional space are described using a point-slope form for their equations, planes in a three dimensional space have a natural description using a point in the plane and a vector orthogonal to it (the normal vector) to indicate its "inclination". | Analytic geometry | Wikipedia | 489 | 2202 | https://en.wikipedia.org/wiki/Analytic%20geometry | Mathematics | Geometry | null |
Specifically, let be the position vector of some point , and let be a nonzero vector. The plane determined by this point and vector consists of those points , with position vector , such that the vector drawn from to is perpendicular to . Recalling that two vectors are perpendicular if and only if their dot product is zero, it follows that the desired plane can be described as the set of all points such that
(The dot here means a dot product, not scalar multiplication.)
Expanded this becomes
This is just a linear equation:
Conversely, it is easily shown that if a, b, c and d are constants and a, b, and c are not all zero, then the graph of the equation
This familiar equation for a plane is called the general form of the equation of the plane.
In three dimensions, lines can not be described by a single linear equation, so they are frequently described by parametric equations:
where:
x, y, and z are all functions of the independent variable t which ranges over the real numbers.
(x0, y0, z0) is any point on the line.
a, b, and c are related to the slope of the line, such that the vector (a, b, c) is parallel to the line.
Conic sections
In the Cartesian coordinate system, the graph of a quadratic equation in two variables is always a conic section – though it may be degenerate, and all conic sections arise in this way. The equation will be of the form
As scaling all six constants yields the same locus of zeros, one can consider conics as points in the five-dimensional projective space
The conic sections described by this equation can be classified using the discriminant
If the conic is non-degenerate, then:
if , the equation represents an ellipse;
if and , the equation represents a circle, which is a special case of an ellipse;
if , the equation represents a parabola;
if , the equation represents a hyperbola;
if we also have , the equation represents a rectangular hyperbola.
Quadric surfaces
A quadric, or quadric surface, is a 2-dimensional surface in 3-dimensional space defined as the locus of zeros of a quadratic polynomial. In coordinates , the general quadric is defined by the algebraic equation
Quadric surfaces include ellipsoids (including the sphere), paraboloids, hyperboloids, cylinders, cones, and planes.
Distance and angle | Analytic geometry | Wikipedia | 509 | 2202 | https://en.wikipedia.org/wiki/Analytic%20geometry | Mathematics | Geometry | null |
In analytic geometry, geometric notions such as distance and angle measure are defined using formulas. These definitions are designed to be consistent with the underlying Euclidean geometry. For example, using Cartesian coordinates on the plane, the distance between two points (x1, y1) and (x2, y2) is defined by the formula
which can be viewed as a version of the Pythagorean theorem. Similarly, the angle that a line makes with the horizontal can be defined by the formula
where m is the slope of the line.
In three dimensions, distance is given by the generalization of the Pythagorean theorem:
while the angle between two vectors is given by the dot product. The dot product of two Euclidean vectors A and B is defined by
where θ is the angle between A and B.
Transformations
Transformations are applied to a parent function to turn it into a new function with similar characteristics.
The graph of is changed by standard transformations as follows:
Changing to moves the graph to the right units.
Changing to moves the graph up units.
Changing to stretches the graph horizontally by a factor of . (think of the as being dilated)
Changing to stretches the graph vertically.
Changing to and changing to rotates the graph by an angle .
There are other standard transformation not typically studied in elementary analytic geometry because the transformations change the shape of objects in ways not usually considered. Skewing is an example of a transformation not usually considered.
For more information, consult the Wikipedia article on affine transformations.
For example, the parent function has a horizontal and a vertical asymptote, and occupies the first and third quadrant, and all of its transformed forms have one horizontal and vertical asymptote, and occupies either the 1st and 3rd or 2nd and 4th quadrant. In general, if , then it can be transformed into . In the new transformed function, is the factor that vertically stretches the function if it is greater than 1 or vertically compresses the function if it is less than 1, and for negative values, the function is reflected in the -axis. The value compresses the graph of the function horizontally if greater than 1 and stretches the function horizontally if less than 1, and like , reflects the function in the -axis when it is negative. The and values introduce translations, , vertical, and horizontal. Positive and values mean the function is translated to the positive end of its axis and negative meaning translation towards the negative end. | Analytic geometry | Wikipedia | 494 | 2202 | https://en.wikipedia.org/wiki/Analytic%20geometry | Mathematics | Geometry | null |
Transformations can be applied to any geometric equation whether or not the equation represents a function.
Transformations can be considered as individual transactions or in combinations.
Suppose that is a relation in the plane. For example,
is the relation that describes the unit circle.
Finding intersections of geometric objects
For two geometric objects P and Q represented by the relations and the intersection is the collection of all points which are in both relations.
For example, might be the circle with radius 1 and center : and might be the circle with radius 1 and center . The intersection of these two circles is the collection of points which make both equations true. Does the point make both equations true? Using for , the equation for becomes or which is true, so is in the relation . On the other hand, still using for the equation for becomes or which is false. is not in so it is not in the intersection.
The intersection of and can be found by solving the simultaneous equations:
Traditional methods for finding intersections include substitution and elimination.
Substitution: Solve the first equation for in terms of and then substitute the expression for into the second equation:
We then substitute this value for into the other equation and proceed to solve for :
Next, we place this value of in either of the original equations and solve for :
So our intersection has two points:
Elimination: Add (or subtract) a multiple of one equation to the other equation so that one of the variables is eliminated. For our current example, if we subtract the first equation from the second we get . The in the first equation is subtracted from the in the second equation leaving no term. The variable has been eliminated. We then solve the remaining equation for , in the same way as in the substitution method:
We then place this value of in either of the original equations and solve for :
So our intersection has two points:
For conic sections, as many as 4 points might be in the intersection.
Finding intercepts
One type of intersection which is widely studied is the intersection of a geometric object with the and coordinate axes.
The intersection of a geometric object and the -axis is called the -intercept of the object.
The intersection of a geometric object and the -axis is called the -intercept of the object.
For the line , the parameter specifies the point where the line crosses the axis. Depending on the context, either or the point is called the -intercept.
Geometric axis
Axis in geometry is the perpendicular line to any line, object or a surface. | Analytic geometry | Wikipedia | 497 | 2202 | https://en.wikipedia.org/wiki/Analytic%20geometry | Mathematics | Geometry | null |
Also for this may be used the common language use as a: normal (perpendicular) line, otherwise in engineering as axial line.
In geometry, a normal is an object such as a line or vector that is perpendicular to a given object. For example, in the two-dimensional case, the normal line to a curve at a given point is the line perpendicular to the tangent line to the curve at the point.
In the three-dimensional case a surface normal, or simply normal, to a surface at a point P is a vector that is perpendicular to the tangent plane to that surface at P. The word "normal" is also used as an adjective: a line normal to a plane, the normal component of a force, the normal vector, etc. The concept of normality generalizes to orthogonality.
Spherical and nonlinear planes and their tangents
Tangent is the linear approximation of a spherical or other curved or twisted line of a function.
Tangent lines and planes
In geometry, the tangent line (or simply tangent) to a plane curve at a given point is the straight line that "just touches" the curve at that point. Informally, it is a line through a pair of infinitely close points on the curve. More precisely, a straight line is said to be a tangent of a curve at a point on the curve if the line passes through the point on the curve and has slope where f is the derivative of f. A similar definition applies to space curves and curves in n-dimensional Euclidean space.
As it passes through the point where the tangent line and the curve meet, called the point of tangency, the tangent line is "going in the same direction" as the curve, and is thus the best straight-line approximation to the curve at that point.
Similarly, the tangent plane to a surface at a given point is the plane that "just touches" the surface at that point. The concept of a tangent is one of the most fundamental notions in differential geometry and has been extensively generalized; see Tangent space. | Analytic geometry | Wikipedia | 406 | 2202 | https://en.wikipedia.org/wiki/Analytic%20geometry | Mathematics | Geometry | null |
The Arctic fox (Vulpes lagopus), also known as the white fox, polar fox, or snow fox, is a small species of fox native to the Arctic regions of the Northern Hemisphere and common throughout the Arctic tundra biome. It is well adapted to living in cold environments, and is best known for its thick, warm fur that is also used as camouflage. It has a large and very fluffy tail. In the wild, most individuals do not live past their first year but some exceptional ones survive up to 11 years. Its body length ranges from , with a generally rounded body shape to minimize the escape of body heat.
The Arctic fox preys on many small creatures such as lemmings, voles, ringed seal pups, fish, waterfowl, and seabirds. It also eats carrion, berries, seaweed, and insects and other small invertebrates. Arctic foxes form monogamous pairs during the breeding season and they stay together to raise their young in complex underground dens. Occasionally, other family members may assist in raising their young. Natural predators of the Arctic fox are golden eagles, Arctic wolves, polar bears, wolverines, red foxes, and grizzly bears.
Behavior
Arctic foxes must endure a temperature difference of up to between the external environment and their internal core temperature. To prevent heat loss, the Arctic fox curls up tightly tucking its legs and head under its body and behind its furry tail. This position gives the fox the smallest surface area to volume ratio and protects the least insulated areas. Arctic foxes also stay warm by getting out of the wind and residing in their dens. Although the Arctic foxes are active year-round and do not hibernate, they attempt to preserve fat by reducing their locomotor activity. They build up their fat reserves in the autumn, sometimes increasing their body weight by more than 50%. This provides greater insulation during the winter and a source of energy when food is scarce.
Reproduction
In the spring, the Arctic fox's attention switches to reproduction and a home for their potential offspring. They live in large dens in frost-free, slightly raised ground. These are complex systems of tunnels covering as much as and are often in eskers, long ridges of sedimentary material deposited in formerly glaciated regions. These dens may be in existence for many decades and are used by many generations of foxes. | Arctic fox | Wikipedia | 484 | 2208 | https://en.wikipedia.org/wiki/Arctic%20fox | Biology and health sciences | Canines | Animals |
Arctic foxes tend to select dens that are easily accessible with many entrances, and that are clear from snow and ice making it easier to burrow in. The Arctic fox builds and chooses dens that face southward towards the sun, which makes the den warmer. Arctic foxes prefer large, maze-like dens for predator evasion and a quick escape especially when red foxes are in the area. Natal dens are typically found in rugged terrain, which may provide more protection for the pups. But, the parents will also relocate litters to nearby dens to avoid predators. When red foxes are not in the region, Arctic foxes will use dens that the red fox previously occupied. Shelter quality is more important to the Arctic fox than the proximity of spring prey to a den.
The main prey of the Arctic fox in the tundra are lemmings, which is why the white fox is often called the "lemming fox". The white fox's reproduction rates reflect the lemming population density, which cyclically fluctuates every 3–5 years. When lemmings are abundant, the white fox can give birth to 18 pups, but they often do not reproduce when food is scarce. The "coastal fox" or blue fox lives in an environment where food availability is relatively consistent, and they will have up to 5 pups every year.
Breeding usually takes place in April and May, and the gestation period is about 52 days. Litters may contain as many as 25 (the largest litter size in the order Carnivora). The young emerge from the den when 3 to 4 weeks old and are weaned by 9 weeks of age. | Arctic fox | Wikipedia | 340 | 2208 | https://en.wikipedia.org/wiki/Arctic%20fox | Biology and health sciences | Canines | Animals |
Arctic foxes are primarily monogamous and both parents will care for the offspring. When predators and prey are abundant, Arctic foxes are more likely to be promiscuous (exhibited in both males and females) and display more complex social structures. Larger packs of foxes consisting of breeding or non-breeding males or females can guard a single territory more proficiently to increase pup survival. When resources are scarce, competition increases and the number of foxes in a territory decreases. On the coasts of Svalbard, the frequency of complex social structures is larger than inland foxes that remain monogamous due to food availability. In Scandinavia, there are more complex social structures compared to other populations due to the presence of the red fox. Also, conservationists are supplying the declining population with supplemental food. One unique case, however, is Iceland where monogamy is the most prevalent. The older offspring (1-year-olds) often remain within their parent's territory even though predators are absent and there are fewer resources, which may indicate kin selection in the fox.
Diet
Arctic foxes generally eat any small animal they can find, including lemmings, voles, other rodents, hares, birds, eggs, fish, and carrion. They scavenge on carcasses left by larger predators such as wolves and polar bears, and in times of scarcity also eat their feces. In areas where they are present, lemmings are their most common prey, and a family of foxes can eat dozens of lemmings each day. In some locations in northern Canada, a high seasonal abundance of migrating birds that breed in the area may provide an important food source. On the coast of Iceland and other islands, their diet consists predominantly of birds. During April and May, the Arctic fox also preys on ringed seal pups when the young animals are confined to a snow den and are relatively helpless. They also consume berries and seaweed, so they may be considered omnivores. This fox is a significant bird-egg predator, consuming eggs of all except the largest tundra bird species. | Arctic fox | Wikipedia | 424 | 2208 | https://en.wikipedia.org/wiki/Arctic%20fox | Biology and health sciences | Canines | Animals |
Arctic foxes survive harsh winters and food scarcity by either hoarding food or storing body fat subcutaneously and viscerally. At the beginning of winter, one Arctic fox has approximately 14740 kJ of energy storage from fat alone. Using the lowest BMR value measured in Arctic foxes, an average sized fox of would need 471 kJ/day during the winter to survive. In Canada, Arctic foxes acquire from snow goose eggs at a rate of 2.7–7.3 eggs/h and store 80–97% of them. Scats provide evidence that they eat the eggs during the winter after caching. Isotope analysis shows that eggs can still be eaten after a year, and the metabolizable energy of a stored goose egg only decreases by 11% after 60 days; a fresh egg has about 816 kJ. Eggs stored in the summer are accessed the following spring prior to reproduction.
Adaptations
The Arctic fox lives in some of the most frigid extremes on the planet, but they do not start to shiver until the temperature drops to . Among its adaptations for survival in the cold is its dense, multilayered pelage, which provides excellent insulation. Additionally, the Arctic fox is the only canid whose foot pads are covered in fur. There are two genetically distinct coat color morphs: white and blue. The white morph has seasonal camouflage, white in winter and brown along the back with light grey around the abdomen in summer. The blue morph is often a dark blue, brown, or grey color year-round. Although the blue allele is dominant over the white allele, 99% of the Arctic fox population is the white morph. Two similar mutations to MC1R cause the blue color and the lack of seasonal color change. The fur of the Arctic fox provides the best insulation of any mammal.
The Arctic fox has a low surface area to volume ratio, as evidenced by its generally compact body shape, short muzzle and legs, and short, thick ears. Since less of its surface area is exposed to the Arctic cold, less heat escapes from its body. | Arctic fox | Wikipedia | 428 | 2208 | https://en.wikipedia.org/wiki/Arctic%20fox | Biology and health sciences | Canines | Animals |
Sensory modalities
The Arctic fox has a functional hearing range between 125 Hz–16 kHz with a sensitivity that is ≤ 60 dB in air, and an average peak sensitivity of 24 dB at 4 kHz. Overall, the Arctic foxes hearing is less sensitive than the dog and the kit fox. The Arctic fox and the kit fox have a low upper-frequency limit compared to the domestic dog and other carnivores. The Arctic fox can easily hear lemmings burrowing under 4-5 inches of snow. When it has located its prey, it pounces and punches through the snow to catch its prey.
The Arctic fox also has a keen sense of smell. They can smell carcasses that are often left by polar bears anywhere from . It is possible that they use their sense of smell to also track down polar bears. Additionally, Arctic foxes can smell and find frozen lemmings under of snow, and can detect a subnivean seal lair under of snow.
Physiology
The Arctic fox contains advantageous genes to overcome extreme cold and starvation periods. Transcriptome sequencing has identified two genes that are under positive selection: Glycolipid transfer protein domain containing 1 (GLTPD1) and V-akt murine thymoma viral oncogene homolog 2 (AKT2). GLTPD1 is involved in the fatty acid metabolism, while AKT2 pertains to the glucose metabolism and insulin signaling.
The average mass specific BMR and total BMR are 37% and 27% lower in the winter than the summer. The Arctic fox decreases its BMR via metabolic depression in the winter to conserve fat storage and minimize energy requirements. According to the most recent data, the lower critical temperature of the Arctic fox is at in the winter and in the summer. It was commonly believed that the Arctic fox had a lower critical temperature below . However, some scientists have concluded that this statistic is not accurate since it was never tested using the proper equipment. | Arctic fox | Wikipedia | 406 | 2208 | https://en.wikipedia.org/wiki/Arctic%20fox | Biology and health sciences | Canines | Animals |
About 22% of the total body surface area of the Arctic fox dissipates heat readily compared to red foxes at 33%. The regions that have the greatest heat loss are the nose, ears, legs, and feet, which is useful in the summer for thermal heat regulation. Also, the Arctic fox has a beneficial mechanism in their nose for evaporative cooling like dogs, which keeps the brain cool during the summer and exercise. The thermal conductivity of Arctic fox fur in the summer and winter is the same; however, the thermal conductance of the Arctic fox in the winter is lower than the summer since fur thickness increases by 140%. In the summer, the thermal conductance of the Arctic foxes body is 114% higher than the winter, but their body core temperature is constant year-round.
One way that Arctic foxes regulate their body temperature is by utilizing a countercurrent heat exchange in the blood of their legs. Arctic foxes can constantly keep their feet above the tissue freezing point () when standing on cold substrates without losing mobility or feeling pain. They do this by increasing vasodilation and blood flow to a capillary rete in the pad surface, which is in direct contact with the snow rather than the entire foot. They selectively vasoconstrict blood vessels in the center of the foot pad, which conserves energy and minimizes heat loss. Arctic foxes maintain the temperature in their paws independently from the core temperature. If the core temperature drops, the pad of the foot will remain constantly above the tissue freezing point.
Size
The average head-and-body length of the male is , with a range of , while the female averages with a range of . In some regions, no difference in size is seen between males and females. The tail is about long in both sexes. The height at the shoulder is . On average males weigh , with a range of , while females average , with a range of .
Taxonomy
Vulpes lagopus is a 'true fox' belonging to the genus Vulpes of the fox tribe Vulpini, which consists of 12 extant species. It is classified under the subfamily Caninae of the canid family Canidae. Although it has previously been assigned to its own monotypic genus Alopex, recent genetic evidence now places it in the genus Vulpes along with the majority of other foxes. | Arctic fox | Wikipedia | 481 | 2208 | https://en.wikipedia.org/wiki/Arctic%20fox | Biology and health sciences | Canines | Animals |
It was originally described by Carl Linnaeus in the 10th edition of Systema Naturae in 1758 as Canis lagopus. The type specimen was recovered from Lapland, Sweden. The generic name vulpes is Latin for "fox". The specific name lagopus is derived from Ancient Greek λαγώς (lagōs, "hare") and πούς (pous, "foot"), referring to the hair on its feet similar to those found in cold-climate species of hares.
Looking at the most recent phylogeny, the Arctic fox and the red fox (Vulpes vulpes) diverged approximately 3.17MYA. Additionally, the Arctic fox diverged from its sister group, the kit fox (Vulpes macrotis), at about 0.9MYA.
Origins
The origins of the Arctic fox have been described by the "out of Tibet" hypothesis. On the Tibetan Plateau, fossils of the extinct ancestral Arctic fox (Vulpes qiuzhudingi) from the early Pliocene (5.08–3.6 MYA) were found along with many other precursors of modern mammals that evolved during the Pliocene (5.3–2.6 MYA). It is believed that this ancient fox is the ancestor of the modern Arctic fox. Globally, the Pliocene was about 2–3 °C warmer than today, and the Arctic during the summer in the mid-Pliocene was 8 °C warmer. By using stable carbon and oxygen isotope analysis of fossils, researchers claim that the Tibetan Plateau experienced tundra-like conditions during the Pliocene and harbored cold-adapted mammals that later spread to North America and Eurasia during the Pleistocene Epoch (2.6 million-11,700 years ago).
Subspecies
Besides the nominate subspecies, the common Arctic fox, V. l. lagopus, four other subspecies of this fox have been described:
Bering Islands Arctic fox, V. l. beringensis
Greenland Arctic fox, V. l. foragoapusis
Iceland Arctic fox, V. l. fuliginosus
Pribilof Islands Arctic fox, V. l. pribilofensis
Distribution and habitat | Arctic fox | Wikipedia | 456 | 2208 | https://en.wikipedia.org/wiki/Arctic%20fox | Biology and health sciences | Canines | Animals |
The Arctic fox has a circumpolar distribution and occurs in Arctic tundra habitats in northern Europe, northern Asia, and North America. Its range includes Greenland, Iceland, Fennoscandia, Svalbard, Jan Mayen (where it was hunted to extinction) and other islands in the Barents Sea, northern Russia, islands in the Bering Sea, Alaska, and Canada as far south as Hudson Bay. In the late 19th century, it was introduced into the Aleutian Islands southwest of Alaska. However, the population on the Aleutian Islands is currently being eradicated in conservation efforts to preserve the local bird population. It mostly inhabits tundra and pack ice, but is also present in Canadian boreal forests (northeastern Alberta, northern Saskatchewan, northern Manitoba, Northern Ontario, Northern Quebec, and Newfoundland and Labrador) and the Kenai Peninsula in Alaska. They are found at elevations up to above sea level and have been seen on sea ice close to the North Pole.
The Arctic fox is the only land mammal native to Iceland. It came to the isolated North Atlantic island at the end of the last ice age, walking over the frozen sea. The Arctic Fox Center in Súðavík contains an exhibition on the Arctic fox and conducts studies on the influence of tourism on the population. Its range during the last ice age was much more extensive than it is now, and fossil remains of the Arctic fox have been found over much of northern Europe and Siberia.
The color of the fox's coat also determines where they are most likely to be found. The white morph mainly lives inland and blends in with the snowy tundra, while the blue morph occupies the coasts because its dark color blends in with the cliffs and rocks.
Migrations and travel
During the winter, 95.5% of Arctic foxes utilize commuting trips, which remain within the fox's home range. Commuting trips in Arctic foxes last less than 3 days and occur between 0–2.9 times a month. Nomadism is found in 3.4% of the foxes, and loop migrations (where the fox travels to a new range, then returns to its home range) are the least common at 1.1%. Arctic foxes in Canada that undergo nomadism and migrations voyage from the Canadian archipelago to Greenland and northwestern Canada. The duration and distance traveled between males and females is not significantly different. | Arctic fox | Wikipedia | 491 | 2208 | https://en.wikipedia.org/wiki/Arctic%20fox | Biology and health sciences | Canines | Animals |
Arctic foxes closer to goose colonies (located at the coasts) are less likely to migrate. Meanwhile, foxes experiencing low-density lemming populations are more likely to make sea ice trips. Residency is common in the Arctic fox population so that they can maintain their territories. Migratory foxes have a mortality rate >3 times higher than resident foxes. Nomadic behavior becomes more common as the foxes age.
In July 2019, the Norwegian Polar Institute reported the story of a yearling female which was fitted with a GPS tracking device and then released by their researchers on the east coast of Spitsbergen in the Svalbard group of islands. The young fox crossed the polar ice from the islands to Greenland in 21 days, a distance of . She then moved on to Ellesmere Island in northern Canada, covering a total recorded distance of in 76 days, before her GPS tracker stopped working. She averaged just over a day, and managed as much as in a single day.
Conservation status
The Arctic fox has been assessed as least concern on the IUCN Red List since 2004. However, the Scandinavian mainland population is acutely endangered, despite being legally protected from hunting and persecution for several decades. The estimate of the adult population in all of Norway, Sweden, and Finland is fewer than 200 individuals. Of these, especially in Finland, the Arctic fox is even classified as critically endangered, because even though the animal was declared a protected species in Finland in 1940, the population has not recovered despite that. As a result, the populations of Arctic fox have been carefully studied and inventoried in places such as the Vindelfjällens Nature Reserve (Sweden), which has the Arctic fox as its symbol.
The abundance of the Arctic fox tends to fluctuate in a cycle along with the population of lemmings and voles (a 3- to 4-year cycle). The populations are especially vulnerable during the years when the prey population crashes, and uncontrolled trapping has almost eradicated two subpopulations.
The pelts of Arctic foxes with a slate-blue coloration were especially valuable. They were transported to various previously fox-free Aleutian Islands during the 1920s. The program was successful in terms of increasing the population of blue foxes, but their predation of Aleutian Canada geese conflicted with the goal of preserving that species. | Arctic fox | Wikipedia | 469 | 2208 | https://en.wikipedia.org/wiki/Arctic%20fox | Biology and health sciences | Canines | Animals |
The Arctic fox is losing ground to the larger red fox. This has been attributed to climate change—the camouflage value of its lighter coat decreases with less snow cover. Red foxes dominate where their ranges begin to overlap by killing Arctic foxes and their kits. An alternative explanation of the red fox's gains involves the gray wolf. Historically, it has kept red fox numbers down, but as the wolf has been hunted to near extinction in much of its former range, the red fox population has grown larger, and it has taken over the niche of top predator. In areas of northern Europe, programs are in place that allow the hunting of red foxes in the Arctic fox's previous range.
As with many other game species, the best sources of historical and large-scale population data are hunting bag records and questionnaires. Several potential sources of error occur in such data collections. In addition, numbers vary widely between years due to the large population fluctuations. However, the total population of the Arctic fox must be in the order of several hundred thousand animals.
The world population of Arctic foxes is thus not endangered, but two Arctic fox subpopulations are. One is on Medny Island (Commander Islands, Russia), which was reduced by some 85–90%, to around 90 animals, as a result of mange caused by an ear tick introduced by dogs in the 1970s. The population is currently under treatment with antiparasitic drugs, but the result is still uncertain.
The other threatened population is the one in Fennoscandia (Norway, Sweden, Finland, and Kola Peninsula). This population decreased drastically around the start of the 20th century as a result of extreme fur prices, which caused severe hunting also during population lows. The population has remained at a low density for more than 90 years, with additional reductions during the last decade. The total population estimate for 1997 is around 60 adults in Sweden, 11 adults in Finland, and 50 in Norway. From Kola, there are indications of a similar situation, suggesting a population of around 20 adults. The Fennoscandian population thus numbers around 140 breeding adults. Even after local lemming peaks, the Arctic fox population tends to collapse back to levels dangerously close to nonviability.
The Arctic fox is classed as a "prohibited new organism" under New Zealand's Hazardous Substances and New Organisms Act 1996, preventing it from being imported into the country. | Arctic fox | Wikipedia | 487 | 2208 | https://en.wikipedia.org/wiki/Arctic%20fox | Biology and health sciences | Canines | Animals |
The Apicomplexa (also called Apicomplexia; single: apicomplexan) are organisms of a large phylum of mainly parasitic alveolates. Most possess a unique form of organelle structure that comprises a type of non-photosynthetic plastid called an apicoplastwith an apical complex membrane. The organelle's apical shape (e.g., see Ceratium furca) is an adaptation that the apicomplexan applies in penetrating a host cell.
The Apicomplexa are unicellular and spore-forming. Most are obligate endoparasites of animals, except Nephromyces, a symbiont in marine animals, originally classified as a chytrid fungus, and the Chromerida, some of which are photosynthetic partners of corals. Motile structures such as flagella or pseudopods are present only in certain gamete stages.
The Apicomplexa are a diverse group that includes organisms such as the coccidia, gregarines, piroplasms, haemogregarines, and plasmodia.
Diseases caused by Apicomplexa include:
Babesiosis (Babesia)
Malaria (Plasmodium)
Cryptosporidiosis (Cryptosporidium parvum)
Cyclosporiasis (Cyclospora cayetanensis)
Cystoisosporiasis (Cystoisospora belli)
Toxoplasmosis (Toxoplasma gondii)
The name Apicomplexa derives from two Latin words—apex (top) and complexus (infolds)—for the set of organelles in the sporozoite. The Apicomplexa comprise the bulk of what used to be called the Sporozoa, a group of parasitic protozoans, in general without flagella, cilia, or pseudopods. Most of the Apicomplexa are motile, however, with a gliding mechanism that uses adhesions and small static myosin motors. The other main lines of this obsolete grouping were the Ascetosporea (a group of Rhizaria), the Myxozoa (highly derived cnidarian animals), and the Microsporidia (derived from fungi). Sometimes, the name Sporozoa is taken as a synonym for the Apicomplexa, or occasionally as a subset.
Description | Apicomplexa | Wikipedia | 511 | 2221 | https://en.wikipedia.org/wiki/Apicomplexa | Biology and health sciences | SAR supergroup | Plants |
The phylum Apicomplexa contains all eukaryotes with a group of structures and organelles collectively termed the apical complex. This complex consists of structural components and secretory organelles required for invasion of host cells during the parasitic stages of the Apicomplexan life cycle. Apicomplexa have complex life cycles, involving several stages and typically undergoing both asexual and sexual replication. All Apicomplexa are obligate parasites for some portion of their life cycle, with some parasitizing two separate hosts for their asexual and sexual stages.
Besides the conserved apical complex, Apicomplexa are morphologically diverse. Different organisms within Apicomplexa, as well as different life stages for a given apicomplexan, can vary substantially in size, shape, and subcellular structure. Like other eukaryotes, Apicomplexa have a nucleus, endoplasmic reticulum and Golgi complex. Apicomplexa generally have a single mitochondrion, as well as another endosymbiont-derived organelle called the apicoplast which maintains a separate 35 kilobase circular genome (with the exception of Cryptosporidium species and Gregarina niphandrodes which lack an apicoplast). | Apicomplexa | Wikipedia | 263 | 2221 | https://en.wikipedia.org/wiki/Apicomplexa | Biology and health sciences | SAR supergroup | Plants |
All members of this phylum have an infectious stage—the sporozoite—which possesses three distinct structures in an apical complex. The apical complex consists of a set of spirally arranged microtubules (the conoid), a secretory body (the rhoptry) and one or more polar rings. Additional slender electron-dense secretory bodies (micronemes) surrounded by one or two polar rings may also be present. This structure gives the phylum its name. A further group of spherical organelles is distributed throughout the cell rather than being localized at the apical complex and are known as the dense granules. These typically have a mean diameter around 0.7 μm. Secretion of the dense-granule content takes place after parasite invasion and localization within the parasitophorous vacuole and persists for several minutes.
Flagella are found only in the motile gamete. These are posteriorly directed and vary in number (usually one to three).
Basal bodies are present. Although hemosporidians and piroplasmids have normal triplets of microtubules in their basal bodies, coccidians and gregarines have nine singlets.
The mitochondria have tubular cristae.
Centrioles, chloroplasts, ejectile organelles, and inclusions are absent.
The cell is surrounded by a pellicle of three membrane layers (the alveolar structure) penetrated by micropores.
Replication:
Mitosis is usually closed, with an intranuclear spindle; in some species, it is open at the poles.
Cell division is usually by schizogony.
Meiosis occurs in the zygote.
Mobility:
Apicomplexans have a unique gliding capability which enables them to cross through tissues and enter and leave their host cells. This gliding ability is made possible by the use of adhesions and small static myosin motors.
Other features common to this phylum are a lack of cilia, sexual reproduction, use of micropores for feeding, and the production of oocysts containing sporozoites as the infective form.
Transposons appear to be rare in this phylum, but have been identified in the genera Ascogregarina and Eimeria.
Life cycle | Apicomplexa | Wikipedia | 479 | 2221 | https://en.wikipedia.org/wiki/Apicomplexa | Biology and health sciences | SAR supergroup | Plants |
Most members have a complex lifecycle, involving both asexual and sexual reproduction. Typically, a host is infected via an active invasion by the parasites (similar to entosis), which divide to produce sporozoites that enter its cells. Eventually, the cells burst, releasing merozoites, which infect new cells. This may occur several times, until gamonts are produced, forming gametes that fuse to create new cysts. Many variations occur on this basic pattern, however, and many Apicomplexa have more than one host.
The apical complex includes vesicles called rhoptries and micronemes, which open at the anterior of the cell. These secrete enzymes that allow the parasite to enter other cells. The tip is surrounded by a band of microtubules, called the polar ring, and among the Conoidasida is also a funnel of tubulin proteins called the conoid. Over the rest of the cell, except for a diminished mouth called the micropore, the membrane is supported by vesicles called alveoli, forming a semirigid pellicle.
The presence of alveoli and other traits place the Apicomplexa among a group called the alveolates. Several related flagellates, such as Perkinsus and Colpodella, have structures similar to the polar ring and were formerly included here, but most appear to be closer relatives of the dinoflagellates. They are probably similar to the common ancestor of the two groups.
Another similarity is that many apicomplexan cells contain a single plastid, called the apicoplast, surrounded by either three or four membranes. Its functions are thought to include tasks such as lipid and heme biosynthesis, and it appears to be necessary for survival. In general, plastids are considered to have a common origin with the chloroplasts of dinoflagellates, and evidence points to an origin from red algae rather than green.
Subgroups
Within this phylum are four groups — coccidians, gregarines, haemosporidians (or haematozoans, including in addition piroplasms), and marosporidians. The coccidians and haematozoans appear to be relatively closely related.
Perkinsus , while once considered a member of the Apicomplexa, has been moved to a new phylum — Perkinsozoa.
Gregarines | Apicomplexa | Wikipedia | 510 | 2221 | https://en.wikipedia.org/wiki/Apicomplexa | Biology and health sciences | SAR supergroup | Plants |
The gregarines are generally parasites of annelids, arthropods, and molluscs. They are often found in the guts of their hosts, but may invade the other tissues. In the typical gregarine lifecycle, a trophozoite develops within a host cell into a schizont. This then divides into a number of merozoites by schizogony. The merozoites are released by lysing the host cell, which in turn invade other cells. At some point in the apicomplexan lifecycle, gametocytes are formed. These are released by lysis of the host cells, which group together. Each gametocyte forms multiple gametes. The gametes fuse with another to form oocysts. The oocysts leave the host to be taken up by a new host.
Coccidians
In general, coccidians are parasites of vertebrates. Like gregarines, they are commonly parasites of the epithelial cells of the gut, but may infect other tissues.
The coccidian lifecycle involves merogony, gametogony, and sporogony. While similar to that of the gregarines it differs in zygote formation. Some trophozoites enlarge and become macrogamete, whereas others divide repeatedly to form microgametes (anisogamy). The microgametes are motile and must reach the macrogamete to fertilize it. The fertilized macrogamete forms a zygote that in its turn forms an oocyst that is normally released from the body. Syzygy, when it occurs, involves markedly anisogamous gametes. The lifecycle is typically haploid, with the only diploid stage occurring in the zygote, which is normally short-lived. | Apicomplexa | Wikipedia | 392 | 2221 | https://en.wikipedia.org/wiki/Apicomplexa | Biology and health sciences | SAR supergroup | Plants |
The main difference between the coccidians and the gregarines is in the gamonts. In the coccidia, these are small, intracellular, and without epimerites or mucrons. In the gregarines, these are large, extracellular, and possess epimerites or mucrons. A second difference between the coccidia and the gregarines also lies in the gamonts. In the coccidians, a single gamont becomes a macrogametocyte, whereas in the gregarines, the gamonts give rise to multiple gametocytes.
Haemosporidia
The Haemosporidia have more complex lifecycles that alternate between an arthropod and a vertebrate host. The trophozoite parasitises erythrocytes or other tissues in the vertebrate host. Microgametes and macrogametes are always found in the blood. The gametes are taken up by the insect vector during a blood meal. The microgametes migrate within the gut of the insect vector and fuse with the macrogametes. The fertilized macrogamete now becomes an ookinete, which penetrates the body of the vector. The ookinete then transforms into an oocyst and divides initially by meiosis and then by mitosis (haplontic lifecycle) to give rise to the sporozoites. The sporozoites escape from the oocyst and migrate within the body of the vector to the salivary glands where they are injected into the new vertebrate host when the insect vector feeds again. | Apicomplexa | Wikipedia | 337 | 2221 | https://en.wikipedia.org/wiki/Apicomplexa | Biology and health sciences | SAR supergroup | Plants |
Marosporida
The class Marosporida Mathur, Kristmundsson, Gestal, Freeman, and Keeling 2020 is a newly recognized lineage of apicomplexans that is sister to the Coccidia and Hematozoa. It is defined as a phylogenetic clade containing Aggregata octopiana Frenzel 1885, Merocystis kathae Dakin, 1911 (both Aggregatidae, originally coccidians), Rhytidocystis sp. 1 and Rhytidocystis sp. 2 Janouškovec et al. 2019 (Rhytidocystidae Levine, 1979, originally coccidians, Agamococcidiorida), and Margolisiella islandica Kristmundsson et al. 2011 (closely related to Rhytidocystidae). Marosporida infect marine invertebrates. Members of this clade retain plastid genomes and the canonical apicomplexan plastid metabolism. However, marosporidians have the most reduced apicoplast genomes sequenced to date, lack canonical plastidial RNA polymerase and so provide new insights into reductive organelle evolution.
Ecology and distribution | Apicomplexa | Wikipedia | 255 | 2221 | https://en.wikipedia.org/wiki/Apicomplexa | Biology and health sciences | SAR supergroup | Plants |
Many of the apicomplexan parasites are important pathogens of humans and domestic animals. In contrast to bacterial pathogens, these apicomplexan parasites are eukaryotic and share many metabolic pathways with their animal hosts. This makes therapeutic target development extremely difficult – a drug that harms an apicomplexan parasite is also likely to harm its human host. At present, no effective vaccines are available for most diseases caused by these parasites. Biomedical research on these parasites is challenging because it is often difficult, if not impossible, to maintain live parasite cultures in the laboratory and to genetically manipulate these organisms. In recent years, several of the apicomplexan species have been selected for genome sequencing. The availability of genome sequences provides a new opportunity for scientists to learn more about the evolution and biochemical capacity of these parasites. The predominant source of this genomic information is the EuPathDB family of websites, which currently provides specialised services for Plasmodium species (PlasmoDB), coccidians (ToxoDB), piroplasms (PiroplasmaDB), and Cryptosporidium species (CryptoDB). One possible target for drugs is the plastid, and in fact existing drugs such as tetracyclines, which are effective against apicomplexans, seem to operate against the plastid.
Many Coccidiomorpha have an intermediate host, as well as a primary host, and the evolution of hosts proceeded in different ways and at different times in these groups. For some coccidiomorphs, the original host has become the intermediate host, whereas in others it has become the definitive host. In the genera Aggregata, Atoxoplasma, Cystoisospora, Schellackia, and Toxoplasma, the original is now definitive, whereas in Akiba, Babesiosoma, Babesia, Haemogregarina, Haemoproteus, Hepatozoon, Karyolysus, Leucocytozoon, Plasmodium, Sarcocystis, and Theileria, the original hosts are now intermediate. | Apicomplexa | Wikipedia | 446 | 2221 | https://en.wikipedia.org/wiki/Apicomplexa | Biology and health sciences | SAR supergroup | Plants |
Similar strategies to increase the likelihood of transmission have evolved in multiple genera. Polyenergid oocysts and tissue cysts are found in representatives of the orders Protococcidiorida and Eimeriida. Hypnozoites are found in Karyolysus lacerate and most species of Plasmodium; transovarial transmission of parasites occurs in lifecycles of Karyolysus and Babesia.
Horizontal gene transfer appears to have occurred early on in this phylum's evolution with the transfer of a histone H4 lysine 20 (H4K20) modifier, KMT5A (Set8), from an animal host to the ancestor of apicomplexans. A second gene—H3K36 methyltransferase (Ashr3 in plants)—may have also been horizontally transferred.
Blood-borne genera
Within the Apicomplexa are three suborders of parasites:
suborder Adeleorina—eight genera
suborder Laveraniina (formerly Haemosporina)—all genera in this suborder
suborder Eimeriorina—two genera (Lankesterella and Schellackia)
Within the Adelorina are species that infect invertebrates and others that infect vertebrates. The Eimeriorina—the largest suborder in this phylum—the lifecycle involves both sexual and asexual stages. The asexual stages reproduce by schizogony. The male gametocyte produces a large number of gametes and the zygote gives rise to an oocyst, which is the infective stage. The majority are monoxenous (infect one host only), but a few are heteroxenous (lifecycle involves two or more hosts).
The number of families in this later suborder is debated, with the number of families being between one and 20 depending on the authority and the number of genera being between 19 and 25.
Taxonomy | Apicomplexa | Wikipedia | 419 | 2221 | https://en.wikipedia.org/wiki/Apicomplexa | Biology and health sciences | SAR supergroup | Plants |
History
The first Apicomplexa protozoan was seen by Antonie van Leeuwenhoek, who in 1674 saw probably oocysts of Eimeria stiedae in the gall bladder of a rabbit. The first species of the phylum to be described, Gregarina ovata, in earwigs' intestines, was named by Dufour in 1828. He thought that they were a peculiar group related to the trematodes, at that time included in Vermes. Since then, many more have been identified and named. During 1826–1850, 41 species and six genera of Apicomplexa were named. In 1951–1975, 1873 new species and 83 new genera were added.
The older taxon Sporozoa, included in Protozoa, was created by Leuckart in 1879 and adopted by Bütschli in 1880. Through history, it grouped with the current Apicomplexa many unrelated groups. For example, Kudo (1954) included in the Sporozoa species of the Ascetosporea (Rhizaria), Microsporidia (Fungi), Myxozoa (Animalia), and Helicosporidium (Chlorophyta), while Zierdt (1978) included the genus Blastocystis (Stramenopiles). Dermocystidium was also thought to be sporozoan. Not all of these groups had spores, but all were parasitic. However, other parasitic or symbiotic unicellular organisms were included too in protozoan groups outside Sporozoa (Flagellata, Ciliophora and Sarcodina), if they had flagella (e.g., many Kinetoplastida, Retortamonadida, Diplomonadida, Trichomonadida, Hypermastigida), cilia (e.g., Balantidium) or pseudopods (e.g., Entamoeba, Acanthamoeba, Naegleria). If they had cell walls, they also could be included in plant kingdom between bacteria or yeasts. | Apicomplexa | Wikipedia | 452 | 2221 | https://en.wikipedia.org/wiki/Apicomplexa | Biology and health sciences | SAR supergroup | Plants |
Sporozoa is no longer regarded as biologically valid and its use is discouraged, although some authors still use it as a synonym for the Apicomplexa. More recently, other groups were excluded from Apicomplexa, e.g., Perkinsus and Colpodella (now in Protalveolata).
The field of classifying Apicomplexa is in flux and classification has changed throughout the years since it was formally named in 1970.
By 1987, a comprehensive survey of the phylum was completed: in all, 4516 species and 339 genera had been named. They consisted of:
Class Conoidasida
Subclass Gregarinasina p.p.
Order Eugregarinorida, with 1624 named species and 231 named genera
Subclass Coccidiasina p.p
Order Eucoccidiorida p.p
Suborder Adeleorina p.p
Group Hemogregarines, with 399 species and four genera
Suborder Eimeriorina, with 1771 species and 43 genera
Class Aconoidasida
Order Haemospororida, with 444 species and nine genera
Order Piroplasmorida, with 173 species and 20 genera
Other minor groups omitted above, with 105 species and 32 genera
Although considerable revision of this phylum has been done (the order Haemosporidia now has 17 genera rather than 9), these numbers are probably still approximately correct.
Jacques Euzéby (1988)
Jacques Euzéby in 1988 created a new class Haemosporidiasina by merging subclass Piroplasmasina and suborder Haemospororina.
Subclass Gregarinasina (the gregarines)
Subclass Coccidiasina
Suborder Adeleorina (the adeleorins)
Suborder Eimeriorina (the eimeriorins)
Subclass Haemosporidiasina
Order Achromatorida
Order Chromatorida
The division into Achromatorida and Chromatorida, although proposed on morphological grounds, may have a biological basis, as the ability to store haemozoin appears to have evolved only once. | Apicomplexa | Wikipedia | 448 | 2221 | https://en.wikipedia.org/wiki/Apicomplexa | Biology and health sciences | SAR supergroup | Plants |
Roberts and Janovy (1996)
Roberts and Janovy in 1996 divided the phylum into the following subclasses and suborders (omitting classes and orders):
Subclass Gregarinasina (the gregarines)
Subclass Coccidiasina
Suborder Adeleorina (the adeleorins)
Suborder Eimeriorina (the eimeriorins)
Suborder Haemospororina (the haemospororins)
Subclass Piroplasmasina (the piroplasms)
These form the following five taxonomic groups:
The gregarines are, in general, one-host parasites of invertebrates.
The adeleorins are one-host parasites of invertebrates or vertebrates, or two-host parasites that alternately infect haematophagous (blood-feeding) invertebrates and the blood of vertebrates.
The eimeriorins are a diverse group that includes one host species of invertebrates, two-host species of invertebrates, one-host species of vertebrates and two-host species of vertebrates. The eimeriorins are frequently called the coccidia. This term is often used to include the adeleorins.
Haemospororins, often known as the malaria parasites, are two-host Apicomplexa that parasitize blood-feeding dipteran flies and the blood of various tetrapod vertebrates.
Piroplasms where all the species included are two-host parasites infecting ticks and vertebrates.
Perkins (2000) | Apicomplexa | Wikipedia | 328 | 2221 | https://en.wikipedia.org/wiki/Apicomplexa | Biology and health sciences | SAR supergroup | Plants |
Perkins et al. proposed the following scheme. It is outdated as the Perkinsidae have since been recognised as a sister group to the dinoflagellates rather that the Apicomplexia:
Class Aconoidasida
Conoid present only in the ookinete of some species
Order Haemospororida
Macrogamete and microgamete develop separately. Syzygy does not occur. Ookinete has a conoid. Sporozoites have three walls. Heteroxenous: alternates between vertebrate host (in which merogony occurs) and invertebrate host (in which sporogony occurs). Usually blood parasites, transmitted by blood-sucking insects.
Order Piroplasmorida
Class Conoidasida
Subclass Gregarinasina
Order Archigregarinorida
Order Eugregarinorida
Suborder Adeleorina
Suborder Eimeriorina
Order Neogregarinorida
Subclass Coccidiasina
Order Agamococcidiorida
Order Eucoccidiorida
Order Ixorheorida
Order Protococcidiorida
Class Perkinsasida
Order Perkinsorida
Family Perkinsidae
The name Protospiromonadida has been proposed for the common ancestor of the Gregarinomorpha and Coccidiomorpha.
Another group of organisms that belong in this taxon are the corallicolids. These are found in coral reef gastric cavities. Their relationship to the others in this phylum has yet to be established.
Another genus has been identified - Nephromyces - which appears to be a sister taxon to the Hematozoa. This genus is found in the renal sac of molgulid ascidian tunicates.
Evolution
Members of this phylum, except for the photosynthetic chromerids, are parasitic and evolved from a free-living ancestor. This lifestyle is presumed to have evolved at the time of the divergence of dinoflagellates and apicomplexans. Further evolution of this phylum has been estimated to have occurred about . The oldest extant clade is thought to be the archigregarines. | Apicomplexa | Wikipedia | 451 | 2221 | https://en.wikipedia.org/wiki/Apicomplexa | Biology and health sciences | SAR supergroup | Plants |
These phylogenetic relations have rarely been studied at the subclass level. The Haemosporidia are related to the gregarines, and the piroplasms and coccidians are sister groups. The Haemosporidia and the Piroplasma appear to be sister clades, and are more closely related to the coccidians than to the gregarines. Marosporida is a sister group to Coccidiomorphea.
Janouškovec et al. 2015 presents a somewhat different phylogeny, supporting the work of others showing multiple events of plastids losing photosynthesis. More importantly this work provides the first phylogenetic evidence that there have also been multiple events of plastids becoming genome-free. | Apicomplexa | Wikipedia | 154 | 2221 | https://en.wikipedia.org/wiki/Apicomplexa | Biology and health sciences | SAR supergroup | Plants |
In computer science, the analysis of algorithms is the process of finding the computational complexity of algorithms—the amount of time, storage, or other resources needed to execute them. Usually, this involves determining a function that relates the size of an algorithm's input to the number of steps it takes (its time complexity) or the number of storage locations it uses (its space complexity). An algorithm is said to be efficient when this function's values are small, or grow slowly compared to a growth in the size of the input. Different inputs of the same size may cause the algorithm to have different behavior, so best, worst and average case descriptions might all be of practical interest. When not otherwise specified, the function describing the performance of an algorithm is usually an upper bound, determined from the worst case inputs to the algorithm.
The term "analysis of algorithms" was coined by Donald Knuth. Algorithm analysis is an important part of a broader computational complexity theory, which provides theoretical estimates for the resources needed by any algorithm which solves a given computational problem. These estimates provide an insight into reasonable directions of search for efficient algorithms.
In theoretical analysis of algorithms it is common to estimate their complexity in the asymptotic sense, i.e., to estimate the complexity function for arbitrarily large input. Big O notation, Big-omega notation and Big-theta notation are used to this end. For instance, binary search is said to run in a number of steps proportional to the logarithm of the size of the sorted list being searched, or in , colloquially "in logarithmic time". Usually asymptotic estimates are used because different implementations of the same algorithm may differ in efficiency. However the efficiencies of any two "reasonable" implementations of a given algorithm are related by a constant multiplicative factor called a hidden constant.
Exact (not asymptotic) measures of efficiency can sometimes be computed but they usually require certain assumptions concerning the particular implementation of the algorithm, called a model of computation. A model of computation may be defined in terms of an abstract computer, e.g. Turing machine, and/or by postulating that certain operations are executed in unit time.
For example, if the sorted list to which we apply binary search has elements, and we can guarantee that each lookup of an element in the list can be done in unit time, then at most time units are needed to return an answer. | Analysis of algorithms | Wikipedia | 498 | 2230 | https://en.wikipedia.org/wiki/Analysis%20of%20algorithms | Mathematics | Algorithms | null |
Cost models
Time efficiency estimates depend on what we define to be a step. For the analysis to correspond usefully to the actual run-time, the time required to perform a step must be guaranteed to be bounded above by a constant. One must be careful here; for instance, some analyses count an addition of two numbers as one step. This assumption may not be warranted in certain contexts. For example, if the numbers involved in a computation may be arbitrarily large, the time required by a single addition can no longer be assumed to be constant.
Two cost models are generally used:
the uniform cost model, also called unit-cost model (and similar variations), assigns a constant cost to every machine operation, regardless of the size of the numbers involved
the logarithmic cost model, also called logarithmic-cost measurement (and similar variations), assigns a cost to every machine operation proportional to the number of bits involved
The latter is more cumbersome to use, so it is only employed when necessary, for example in the analysis of arbitrary-precision arithmetic algorithms, like those used in cryptography.
A key point which is often overlooked is that published lower bounds for problems are often given for a model of computation that is more restricted than the set of operations that you could use in practice and therefore there are algorithms that are faster than what would naively be thought possible.
Run-time analysis
Run-time analysis is a theoretical classification that estimates and anticipates the increase in running time (or run-time or execution time) of an algorithm as its input size (usually denoted as ) increases. Run-time efficiency is a topic of great interest in computer science: A program can take seconds, hours, or even years to finish executing, depending on which algorithm it implements. While software profiling techniques can be used to measure an algorithm's run-time in practice, they cannot provide timing data for all infinitely many possible inputs; the latter can only be achieved by the theoretical methods of run-time analysis.
Shortcomings of empirical metrics
Since algorithms are platform-independent (i.e. a given algorithm can be implemented in an arbitrary programming language on an arbitrary computer running an arbitrary operating system), there are additional significant drawbacks to using an empirical approach to gauge the comparative performance of a given set of algorithms. | Analysis of algorithms | Wikipedia | 476 | 2230 | https://en.wikipedia.org/wiki/Analysis%20of%20algorithms | Mathematics | Algorithms | null |
Take as an example a program that looks up a specific entry in a sorted list of size n. Suppose this program were implemented on Computer A, a state-of-the-art machine, using a linear search algorithm, and on Computer B, a much slower machine, using a binary search algorithm. Benchmark testing on the two computers running their respective programs might look something like the following:
Based on these metrics, it would be easy to jump to the conclusion that Computer A is running an algorithm that is far superior in efficiency to that of Computer B. However, if the size of the input-list is increased to a sufficient number, that conclusion is dramatically demonstrated to be in error:
Computer A, running the linear search program, exhibits a linear growth rate. The program's run-time is directly proportional to its input size. Doubling the input size doubles the run-time, quadrupling the input size quadruples the run-time, and so forth. On the other hand, Computer B, running the binary search program, exhibits a logarithmic growth rate. Quadrupling the input size only increases the run-time by a constant amount (in this example, 50,000 ns). Even though Computer A is ostensibly a faster machine, Computer B will inevitably surpass Computer A in run-time because it is running an algorithm with a much slower growth rate.
Orders of growth
Informally, an algorithm can be said to exhibit a growth rate on the order of a mathematical function if beyond a certain input size , the function times a positive constant provides an upper bound or limit for the run-time of that algorithm. In other words, for a given input size greater than some 0 and a constant , the run-time of that algorithm will never be larger than . This concept is frequently expressed using Big O notation. For example, since the run-time of insertion sort grows quadratically as its input size increases, insertion sort can be said to be of order .
Big O notation is a convenient way to express the worst-case scenario for a given algorithm, although it can also be used to express the average-case — for example, the worst-case scenario for quicksort is , but the average-case run-time is . | Analysis of algorithms | Wikipedia | 460 | 2230 | https://en.wikipedia.org/wiki/Analysis%20of%20algorithms | Mathematics | Algorithms | null |
Empirical orders of growth
Assuming the run-time follows power rule, , the coefficient can be found by taking empirical measurements of run-time } at some problem-size points }, and calculating so that . In other words, this measures the slope of the empirical line on the log–log plot of run-time vs. input size, at some size point. If the order of growth indeed follows the power rule (and so the line on the log–log plot is indeed a straight line), the empirical value of will stay constant at different ranges, and if not, it will change (and the line is a curved line)—but still could serve for comparison of any two given algorithms as to their empirical local orders of growth behaviour. Applied to the above table:
It is clearly seen that the first algorithm exhibits a linear order of growth indeed following the power rule. The empirical values for the second one are diminishing rapidly, suggesting it follows another rule of growth and in any case has much lower local orders of growth (and improving further still), empirically, than the first one.
Evaluating run-time complexity
The run-time complexity for the worst-case scenario of a given algorithm can sometimes be evaluated by examining the structure of the algorithm and making some simplifying assumptions. Consider the following pseudocode:
1 get a positive integer n from input
2 if n > 10
3 print "This might take a while..."
4 for i = 1 to n
5 for j = 1 to i
6 print i * j
7 print "Done!"
A given computer will take a discrete amount of time to execute each of the instructions involved with carrying out this algorithm. Say that the actions carried out in step 1 are considered to consume time at most T1, step 2 uses time at most T2, and so forth.
In the algorithm above, steps 1, 2 and 7 will only be run once. For a worst-case evaluation, it should be assumed that step 3 will be run as well. Thus the total amount of time to run steps 1-3 and step 7 is: | Analysis of algorithms | Wikipedia | 426 | 2230 | https://en.wikipedia.org/wiki/Analysis%20of%20algorithms | Mathematics | Algorithms | null |
The loops in steps 4, 5 and 6 are trickier to evaluate. The outer loop test in step 4 will execute ( n + 1 )
times, which will consume T4( n + 1 ) time. The inner loop, on the other hand, is governed by the value of j, which iterates from 1 to i. On the first pass through the outer loop, j iterates from 1 to 1: The inner loop makes one pass, so running the inner loop body (step 6) consumes T6 time, and the inner loop test (step 5) consumes 2T5 time. During the next pass through the outer loop, j iterates from 1 to 2: the inner loop makes two passes, so running the inner loop body (step 6) consumes 2T6 time, and the inner loop test (step 5) consumes 3T5 time.
Altogether, the total time required to run the inner loop body can be expressed as an arithmetic progression:
which can be factored as
The total time required to run the inner loop test can be evaluated similarly:
which can be factored as
Therefore, the total run-time for this algorithm is:
which reduces to
As a rule-of-thumb, one can assume that the highest-order term in any given function dominates its rate of growth and thus defines its run-time order. In this example, n2 is the highest-order term, so one can conclude that . Formally this can be proven as follows:
A more elegant approach to analyzing this algorithm would be to declare that [T1..T7] are all equal to one unit of time, in a system of units chosen so that one unit is greater than or equal to the actual times for these steps. This would mean that the algorithm's run-time breaks down as follows:
Growth rate analysis of other resources
The methodology of run-time analysis can also be utilized for predicting other growth rates, such as consumption of memory space. As an example, consider the following pseudocode which manages and reallocates memory usage by a program based on the size of a file which that program manages:
while file is still open:
let n = size of file
for every 100,000 kilobytes of increase in file size
double the amount of memory reserved | Analysis of algorithms | Wikipedia | 472 | 2230 | https://en.wikipedia.org/wiki/Analysis%20of%20algorithms | Mathematics | Algorithms | null |
In this instance, as the file size n increases, memory will be consumed at an exponential growth rate, which is order . This is an extremely rapid and most likely unmanageable growth rate for consumption of memory resources.
Relevance
Algorithm analysis is important in practice because the accidental or unintentional use of an inefficient algorithm can significantly impact system performance. In time-sensitive applications, an algorithm taking too long to run can render its results outdated or useless. An inefficient algorithm can also end up requiring an uneconomical amount of computing power or storage in order to run, again rendering it practically useless.
Constant factors
Analysis of algorithms typically focuses on the asymptotic performance, particularly at the elementary level, but in practical applications constant factors are important, and real-world data is in practice always limited in size. The limit is typically the size of addressable memory, so on 32-bit machines 232 = 4 GiB (greater if segmented memory is used) and on 64-bit machines 264 = 16 EiB. Thus given a limited size, an order of growth (time or space) can be replaced by a constant factor, and in this sense all practical algorithms are for a large enough constant, or for small enough data.
This interpretation is primarily useful for functions that grow extremely slowly: (binary) iterated logarithm (log*) is less than 5 for all practical data (265536 bits); (binary) log-log (log log n) is less than 6 for virtually all practical data (264 bits); and binary log (log n) is less than 64 for virtually all practical data (264 bits). An algorithm with non-constant complexity may nonetheless be more efficient than an algorithm with constant complexity on practical data if the overhead of the constant time algorithm results in a larger constant factor, e.g., one may have so long as and .
For large data linear or quadratic factors cannot be ignored, but for small data an asymptotically inefficient algorithm may be more efficient. This is particularly used in hybrid algorithms, like Timsort, which use an asymptotically efficient algorithm (here merge sort, with time complexity ), but switch to an asymptotically inefficient algorithm (here insertion sort, with time complexity ) for small data, as the simpler algorithm is faster on small data. | Analysis of algorithms | Wikipedia | 498 | 2230 | https://en.wikipedia.org/wiki/Analysis%20of%20algorithms | Mathematics | Algorithms | null |
An analgesic drug, also called simply an analgesic, antalgic, pain reliever, or painkiller, is any member of the group of drugs used for pain management. Analgesics are conceptually distinct from anesthetics, which temporarily reduce, and in some instances eliminate, sensation, although analgesia and anesthesia are neurophysiologically overlapping and thus various drugs have both analgesic and anesthetic effects.
Analgesic choice is also determined by the type of pain: For neuropathic pain, recent research has suggested that classes of drugs that are not normally considered analgesics, such as tricyclic antidepressants and anticonvulsants may be considered as an alternative.
Various analgesics, such as many NSAIDs, are available over the counter in most countries, whereas various others are prescription drugs owing to the substantial risks and high chances of overdose, misuse, and addiction in the absence of medical supervision.
Etymology
The word analgesic derives from Greek an- (, "without"), álgos (, "pain"), and -ikos (, forming adjectives). Such drugs were usually known as "anodynes" before the 20th century.
Classification
Analgesics are typically classified based on their mechanism of action.
Paracetamol (acetaminophen)
Paracetamol, also known as acetaminophen or APAP, is a medication used to treat pain and fever. It is typically used for mild to moderate pain. In combination with opioid pain medication, paracetamol is now used for more severe pain such as cancer pain and after surgery. It is typically used either by mouth or rectally but is also available intravenously. Effects last between two and four hours. Paracetamol is classified as a mild analgesic. Paracetamol is generally safe at recommended doses.
NSAIDs
Nonsteroidal anti-inflammatory drugs (usually abbreviated to NSAIDs), are a drug class that groups together drugs that decrease pain and lower fever, and, in higher doses, decrease inflammation. The most prominent members of this group of drugs—aspirin, ibuprofen and naproxen, and Diclofenac—are all available over the counter in most countries.
COX-2 inhibitors | Analgesic | Wikipedia | 486 | 2246 | https://en.wikipedia.org/wiki/Analgesic | Biology and health sciences | Drugs and pharmacology | null |
These drugs have been derived from NSAIDs. The cyclooxygenase enzyme inhibited by NSAIDs was discovered to have at least two different versions: COX1 and COX2. Research suggested most of the adverse effects of NSAIDs to be mediated by blocking the COX1 (constitutive) enzyme, with the analgesic effects being mediated by the COX2 (inducible) enzyme. Thus, the COX2 inhibitors were developed to inhibit only the COX2 enzyme (traditional NSAIDs block both versions in general). These drugs (such as rofecoxib, celecoxib, and etoricoxib) are equally effective analgesics when compared with NSAIDs, but cause less gastrointestinal hemorrhage in particular.
After widespread adoption of the COX-2 inhibitors, it was discovered that most of the drugs in this class increase the risk of cardiovascular events by 40% on average. This led to the withdrawal of rofecoxib and valdecoxib, and warnings on others. Etoricoxib seems relatively safe, with the risk of thrombotic events similar to that of non-coxib NSAID diclofenac.
Opioids | Analgesic | Wikipedia | 248 | 2246 | https://en.wikipedia.org/wiki/Analgesic | Biology and health sciences | Drugs and pharmacology | null |
Morphine, the archetypal opioid, and other opioids (e.g., codeine, oxycodone, hydrocodone, dihydromorphine, pethidine) all exert a similar influence on the cerebral opioid receptor system. Buprenorphine is a partial agonist of the μ-opioid receptor, and tramadol is a serotonin norepinephrine reuptake inhibitor (SNRI) with weak μ-opioid receptor agonist properties. Tramadol is structurally closer to venlafaxine than to codeine and delivers analgesia by not only delivering "opioid-like" effects (through mild agonism of the mu receptor) but also by acting as a weak but fast-acting serotonin releasing agent and norepinephrine reuptake inhibitor. Tapentadol, with some structural similarities to tramadol, presents what is believed to be a novel drug working through two (and possibly three) different modes of action in the fashion of both a traditional opioid and as an SNRI. The effects of serotonin and norepinephrine on pain, while not completely understood, have had causal links established and drugs in the SNRI class are commonly used in conjunction with opioids (especially tapentadol and tramadol) with greater success in pain relief.
Dosing of all opioids may be limited by opioid toxicity (confusion, respiratory depression, myoclonic jerks and pinpoint pupils), seizures (tramadol), but opioid-tolerant individuals usually have higher dose ceilings than patients without tolerance.
Opioids, while very effective analgesics, may have some unpleasant side-effects. Patients starting morphine may experience nausea and vomiting (generally relieved by a short course of antiemetics such as phenergan). Pruritus (itching) may require switching to a different opioid. Constipation occurs in almost all patients on opioids, and laxatives (lactulose, macrogol-containing or co-danthramer) are typically co-prescribed. | Analgesic | Wikipedia | 459 | 2246 | https://en.wikipedia.org/wiki/Analgesic | Biology and health sciences | Drugs and pharmacology | null |
When used appropriately, opioids and other central analgesics are safe and effective; however, risks such as addiction and the body's becoming used to the drug (tolerance) can occur. The effect of tolerance means that frequent use of the drug may result in its diminished effect. When safe to do so, the dosage may need to be increased to maintain effectiveness against tolerance, which may be of particular concern regarding patients with chronic pain and requiring an analgesic over long periods. Opioid tolerance is often addressed with opioid rotation therapy in which a patient is routinely switched between two or more non-cross-tolerant opioid medications in order to prevent exceeding safe dosages in the attempt to achieve an adequate analgesic effect.
Opioid tolerance should not be confused with opioid-induced hyperalgesia. The symptoms of these two conditions can appear very similar but the mechanism of action is different. Opioid-induced hyperalgesia is when exposure to opioids increases the sensation of pain (hyperalgesia) and can even make non-painful stimuli painful (allodynia).
Alcohol
Alcohol has biological, mental, and social effects which influence the consequences of using alcohol for pain. Moderate use of alcohol can lessen certain types of pain in certain circumstances.
The majority of its analgesic effects come from antagonizing NMDA receptors, similarly to ketamine, thus decreasing the activity of the primary excitatory (signal boosting) neurotransmitter, glutamate. It also functions as an analgesic to a lesser degree by increasing the activity of the primary inhibitory (signal reducing) neurotransmitter, GABA.
Attempting to use alcohol to treat pain has also been observed to lead to negative outcomes including excessive drinking and alcohol use disorder.
Cannabis
Medical cannabis, or medical marijuana, refers to cannabis or its cannabinoids used to treat disease or improve symptoms. There is evidence suggesting that cannabis can be used to treat chronic pain and muscle spasms, with some trials indicating improved relief of neuropathic pain over opioids.
Combinations
Analgesics are frequently used in combination, such as the paracetamol and codeine preparations found in many non-prescription pain relievers. They can also be found in combination with vasoconstrictor drugs such as pseudoephedrine for sinus-related preparations, or with antihistamine drugs for people with allergies. | Analgesic | Wikipedia | 509 | 2246 | https://en.wikipedia.org/wiki/Analgesic | Biology and health sciences | Drugs and pharmacology | null |
While the use of paracetamol, aspirin, ibuprofen, naproxen, and other NSAIDS concurrently with weak to mid-range opiates (up to about the hydrocodone level) has been said to show beneficial synergistic effects by combating pain at multiple sites of action, several combination analgesic products have been shown to have few efficacy benefits when compared to similar doses of their individual components. Moreover, these combination analgesics can often result in significant adverse events, including accidental overdoses, most often due to confusion that arises from the multiple (and often non-acting) components of these combinations.
Alternative medicine
There is some evidence that some treatments using alternative medicine can relieve some types of pain more effectively than placebo. The available research concludes that more research would be necessary to better understand the use of alternative medicine.
Other drugs
Nefopam—a monoamine reuptake inhibitor, and calcium and sodium channel modulator—is also approved for the treatment of moderate to severe pain in some countries.
Flupirtine is a centrally acting K+ channel opener with weak NMDA antagonist properties. It was used in Europe for moderate to strong pain, as well as its migraine-treating and muscle-relaxant properties. It has no significant anticholinergic properties, and is believed to be devoid of any activity on dopamine, serotonin, or histamine receptors. It is not addictive, and tolerance usually does not develop. However, tolerance may develop in some cases.
Ziconotide, a blocker of potent N-type voltage-gated calcium channels, is administered intrathecally for the relief of severe, usually cancer-related pain.
Adjuvants
Certain drugs that have been introduced for uses other than analgesics are also used in pain management. Both first-generation (such as amitriptyline) and newer antidepressants (such as duloxetine) are used alongside NSAIDs and opioids for pain involving nerve damage and similar problems. Other agents directly potentiate the effects of analgesics, such as using hydroxyzine, promethazine, carisoprodol, or tripelennamine to increase the pain-killing ability of a given dose of opioid analgesic. | Analgesic | Wikipedia | 477 | 2246 | https://en.wikipedia.org/wiki/Analgesic | Biology and health sciences | Drugs and pharmacology | null |
Adjuvant analgesics, also called atypical analgesics, include orphenadrine, mexiletine, pregabalin, gabapentin, cyclobenzaprine, hyoscine (scopolamine), and other drugs possessing anticonvulsant, anticholinergic, and/or antispasmodic properties, as well as many other drugs with CNS actions. These drugs are used along with analgesics to modulate and/or modify the action of opioids when used against pain, especially of neuropathic origin.
Dextromethorphan has been noted to slow the development of and reverse tolerance to opioids, as well as to exert additional analgesia by acting upon NMDA receptors, as does ketamine. Some analgesics such as methadone and ketobemidone and perhaps piritramide have intrinsic NMDA action.
The anticonvulsant carbamazepine is used to treat neuropathic pain. Similarly, the gabapentinoids gabapentin and pregabalin are prescribed for neuropathic pain, and phenibut is available without prescription. Gabapentinoids work as α2δ-subunit blockers of voltage-gated calcium channels, and tend to have other mechanisms of action as well. Gabapentinoids are all anticonvulsants, which are most commonly used for neuropathic pain, as their mechanism of action tends to inhibit pain sensation originating from the nervous system.
Other uses | Analgesic | Wikipedia | 329 | 2246 | https://en.wikipedia.org/wiki/Analgesic | Biology and health sciences | Drugs and pharmacology | null |
Topical analgesia is generally recommended to avoid systemic side-effects. Painful joints, for example, may be treated with an ibuprofen- or diclofenac-containing gel (The labeling for topical diclofenac has been updated to warn about drug-induced hepatotoxicity.); capsaicin also is used topically. Lidocaine, an anesthetic, and steroids may be injected into joints for longer-term pain relief. Lidocaine is also used for painful mouth sores and to numb areas for dental work and minor medical procedures. In February 2007 the FDA notified consumers and healthcare professionals of the potential hazards of topical anesthetics entering the bloodstream when applied in large doses to the skin without medical supervision. These topical anesthetics contain anesthetic drugs such as lidocaine, tetracaine, benzocaine, and prilocaine in a cream, ointment, or gel.
Uses
Topical nonsteroidal anti-inflammatory drugs provide pain relief in common conditions such as muscle sprains and overuse injuries. Since the side effects are also lesser, topical preparations could be preferred over oral medications in these conditions.
List of drugs with comparison
Research
Some novel and investigational analgesics include subtype-selective voltage-gated sodium channel blockers such as funapide and raxatrigine, as well as multimodal agents such as ralfinamide. | Analgesic | Wikipedia | 301 | 2246 | https://en.wikipedia.org/wiki/Analgesic | Biology and health sciences | Drugs and pharmacology | null |
The adrenal glands (also known as suprarenal glands) are endocrine glands that produce a variety of hormones including adrenaline and the steroids aldosterone and cortisol. They are found above the kidneys. Each gland has an outer cortex which produces steroid hormones and an inner medulla. The adrenal cortex itself is divided into three main zones: the zona glomerulosa, the zona fasciculata and the zona reticularis.
The adrenal cortex produces three main types of steroid hormones: mineralocorticoids, glucocorticoids, and androgens. Mineralocorticoids (such as aldosterone) produced in the zona glomerulosa help in the regulation of blood pressure and electrolyte balance. The glucocorticoids cortisol and cortisone are synthesized in the zona fasciculata; their functions include the regulation of metabolism and immune system suppression. The innermost layer of the cortex, the zona reticularis, produces androgens that are converted to fully functional sex hormones in the gonads and other target organs. The production of steroid hormones is called steroidogenesis, and involves a number of reactions and processes that take place in cortical cells. The medulla produces the catecholamines, which function to produce a rapid response throughout the body in stress situations.
A number of endocrine diseases involve dysfunctions of the adrenal gland. Overproduction of cortisol leads to Cushing's syndrome, whereas insufficient production is associated with Addison's disease. Congenital adrenal hyperplasia is a genetic disease produced by dysregulation of endocrine control mechanisms. A variety of tumors can arise from adrenal tissue and are commonly found in medical imaging when searching for other diseases.
Structure
The adrenal glands are located on both sides of the body in the retroperitoneum, above and slightly medial to the kidneys. In humans, the right adrenal gland is pyramidal in shape, whereas the left is semilunar or crescent shaped and somewhat larger. The adrenal glands measure approximately 5 cm in length, 3 cm in width, and up to 1 cm in thickness. Their combined weight in an adult human ranges from 7 to 10 grams. The glands are yellowish in colour. | Adrenal gland | Wikipedia | 499 | 2296 | https://en.wikipedia.org/wiki/Adrenal%20gland | Biology and health sciences | Animal: General | null |
The adrenal glands are surrounded by a fatty capsule and lie within the renal fascia, which also surrounds the kidneys. A weak septum (wall) of connective tissue separates the glands from the kidneys. The adrenal glands are directly below the diaphragm, and are attached to the crura of the diaphragm by the renal fascia.
Each adrenal gland has two distinct parts, each with a unique function, the outer adrenal cortex and the inner medulla, both of which produce hormones.
Adrenal cortex
The adrenal cortex is the outer region and also the largest part of an adrenal gland. It is divided into three separate zones: zona glomerulosa, zona fasciculata and zona reticularis. Each zone is responsible for producing specific hormones.
The adrenal cortex is the outermost layer of the adrenal gland. Within the cortex are three layers, called "zones". When viewed under a microscope each layer has a distinct appearance, and each has a different function. The adrenal cortex is devoted to production of hormones, namely aldosterone, cortisol, and androgens.
Zona glomerulosa
The outermost zone of the adrenal cortex is the zona glomerulosa. It lies immediately under the fibrous capsule of the gland. Cells in this layer form oval groups, separated by thin strands of connective tissue from the fibrous capsule of the gland and carry wide capillaries.
This layer is the main site for production of aldosterone, a mineralocorticoid, by the action of the enzyme aldosterone synthase. Aldosterone plays an important role in the long-term regulation of blood pressure.
Zona fasciculata
The zona fasciculata is situated between the zona glomerulosa and zona reticularis. Cells in this layer are responsible for producing glucocorticoids such as cortisol. It is the largest of the three layers, accounting for nearly 80% of the volume of the cortex. In the zona fasciculata, cells are arranged in columns radially oriented towards the medulla. Cells contain numerous lipid droplets, abundant mitochondria and a complex smooth endoplasmic reticulum. | Adrenal gland | Wikipedia | 490 | 2296 | https://en.wikipedia.org/wiki/Adrenal%20gland | Biology and health sciences | Animal: General | null |
Zona reticularis
The innermost cortical layer, the zona reticularis, lies directly adjacent to the medulla. It produces androgens, mainly dehydroepiandrosterone (DHEA), DHEA sulfate (DHEA-S), and androstenedione (the precursor to testosterone) in humans. Its small cells form irregular cords and clusters, separated by capillaries and connective tissue. The cells contain relatively small quantities of cytoplasm and lipid droplets, and sometimes display brown lipofuscin pigment.
Medulla
The adrenal medulla is at the centre of each adrenal gland, and is surrounded by the adrenal cortex. The chromaffin cells of the medulla are the body's main source of the catecholamines, such as adrenaline and noradrenaline, released by the medulla. Approximately 20% noradrenaline (norepinephrine) and 80% adrenaline (epinephrine) are secreted here.
The adrenal medulla is driven by the sympathetic nervous system via preganglionic fibers originating in the thoracic spinal cord, from vertebrae T5–T11. Because it is innervated by preganglionic nerve fibers, the adrenal medulla can be considered as a specialized sympathetic ganglion. Unlike other sympathetic ganglia, however, the adrenal medulla lacks distinct synapses and releases its secretions directly into the blood.
Blood supply
The adrenal glands have one of the greatest blood supply rates per gram of tissue of any organ: up to 60 small arteries may enter each gland. Three arteries usually supply each adrenal gland:
The superior suprarenal artery, a branch of the inferior phrenic artery
The middle suprarenal artery, a direct branch of the abdominal aorta
The inferior suprarenal artery, a branch of the renal artery
These blood vessels supply a network of small arteries within the capsule of the adrenal glands. Thin strands of the capsule enter the glands, carrying blood to them.
Venous blood is drained from the glands by the suprarenal veins, usually one for each gland:
The right suprarenal vein drains into the inferior vena cava.
The left suprarenal vein drains into the left renal vein or the left inferior phrenic vein. | Adrenal gland | Wikipedia | 497 | 2296 | https://en.wikipedia.org/wiki/Adrenal%20gland | Biology and health sciences | Animal: General | null |
The central adrenomedullary vein, in the adrenal medulla, is an unusual type of blood vessel. Its structure is different from the other veins in that the smooth muscle in its tunica media (the middle layer of the vessel) is arranged in conspicuous, longitudinally oriented bundles.
Variability
The adrenal glands may not develop at all, or may be fused in the midline behind the aorta. These are associated with other congenital abnormalities, such as failure of the kidneys to develop, or fused kidneys. The gland may develop with a partial or complete absence of the cortex, or may develop in an unusual location.
Function
The adrenal gland secretes a number of different hormones which are metabolised by enzymes either within the gland or in other parts of the body. These hormones are involved in a number of essential biological functions.
Corticosteroids
Corticosteroids are a group of steroid hormones produced from the cortex of the adrenal gland, from which they are named.
Mineralocorticoids such as aldosterone regulate salt ("mineral") balance and blood pressure
Glucocorticoids such as cortisol influence metabolism rates of proteins, fats and sugars ("glucose").
Androgens such as dehydroepiandrosterone.
Mineralocorticoids
The adrenal gland produces aldosterone, a mineralocorticoid, which is important in the regulation of salt ("mineral") balance and blood volume. In the kidneys, aldosterone acts on the distal convoluted tubules and the collecting ducts by increasing the reabsorption of sodium and the excretion of both potassium and hydrogen ions. Aldosterone is responsible for the reabsorption of about 2% of filtered glomerular filtrate. Sodium retention is also a response of the distal colon and sweat glands to aldosterone receptor stimulation. Angiotensin II and extracellular potassium are the two main regulators of aldosterone production. The amount of sodium present in the body affects the extracellular volume, which in turn influences blood pressure. Therefore, the effects of aldosterone in sodium retention are important for the regulation of blood pressure. | Adrenal gland | Wikipedia | 462 | 2296 | https://en.wikipedia.org/wiki/Adrenal%20gland | Biology and health sciences | Animal: General | null |
Glucocorticoids
Cortisol is the main glucocorticoid in humans. In species that do not create cortisol, this role is played by corticosterone instead. Glucocorticoids have many effects on metabolism. As their name suggests, they increase the circulating level of glucose. This is the result of an increase in the mobilization of amino acids from protein and the stimulation of synthesis of glucose from these amino acids in the liver. In addition, they increase the levels of free fatty acids, which cells can use as an alternative to glucose to obtain energy. Glucocorticoids also have effects unrelated to the regulation of blood sugar levels, including the suppression of the immune system and a potent anti-inflammatory effect. Cortisol reduces the capacity of osteoblasts to produce new bone tissue and decreases the absorption of calcium in the gastrointestinal tract.
The adrenal gland secretes a basal level of cortisol but can also produce bursts of the hormone in response to adrenocorticotropic hormone (ACTH) from the anterior pituitary. Cortisol is not evenly released during the day – its concentrations in the blood are highest in the early morning and lowest in the evening as a result of the circadian rhythm of ACTH secretion. Cortisone is an inactive product of the action of the enzyme 11β-HSD on cortisol. The reaction catalyzed by 11β-HSD is reversible, which means that it can turn administered cortisone into cortisol, the biologically active hormone.
Formation
All corticosteroid hormones share cholesterol as a common precursor. Therefore, the first step in steroidogenesis is cholesterol uptake or synthesis. Cells that produce steroid hormones can acquire cholesterol through two paths. The main source is through dietary cholesterol transported via the blood as cholesterol esters within low density lipoproteins (LDL). LDL enters the cells through receptor-mediated endocytosis. The other source of cholesterol is synthesis in the cell's endoplasmic reticulum. Synthesis can compensate when LDL levels are abnormally low. In the lysosome, cholesterol esters are converted to free cholesterol, which is then used for steroidogenesis or stored in the cell. | Adrenal gland | Wikipedia | 500 | 2296 | https://en.wikipedia.org/wiki/Adrenal%20gland | Biology and health sciences | Animal: General | null |
The initial part of conversion of cholesterol into steroid hormones involves a number of enzymes of the cytochrome P450 family that are located in the inner membrane of mitochondria. Transport of cholesterol from the outer to the inner membrane is facilitated by steroidogenic acute regulatory protein and is the rate-limiting step of steroid synthesis.
The layers of the adrenal gland differ by function, with each layer having distinct enzymes that produce different hormones from a common precursor. The first enzymatic step in the production of all steroid hormones is cleavage of the cholesterol side chain, a reaction that forms pregnenolone as a product and is catalyzed by the enzyme P450scc, also known as cholesterol desmolase. After the production of pregnenolone, specific enzymes of each cortical layer further modify it. Enzymes involved in this process include both mitochondrial and microsomal P450s and hydroxysteroid dehydrogenases. Usually a number of intermediate steps in which pregnenolone is modified several times are required to form the functional hormones. Enzymes that catalyze reactions in these metabolic pathways are involved in a number of endocrine diseases. For example, the most common form of congenital adrenal hyperplasia develops as a result of deficiency of 21-hydroxylase, an enzyme involved in an intermediate step of cortisol production.
Regulation
Glucocorticoids are under the regulatory influence of the hypothalamic–pituitary–adrenal axis (HPA) axis. Glucocorticoid synthesis is stimulated by adrenocorticotropic hormone (ACTH), a hormone released into the bloodstream by the anterior pituitary. In turn, production of ACTH is stimulated by the presence of corticotropin-releasing hormone (CRH), which is released by neurons of the hypothalamus. ACTH acts on the adrenal cells first by increasing the levels of StAR within the cells, and then of all steroidogenic P450 enzymes. The HPA axis is an example of a negative feedback system, in which cortisol itself acts as a direct inhibitor of both CRH and ACTH synthesis. The HPA axis also interacts with the immune system through increased secretion of ACTH at the presence of certain molecules of the inflammatory response. | Adrenal gland | Wikipedia | 495 | 2296 | https://en.wikipedia.org/wiki/Adrenal%20gland | Biology and health sciences | Animal: General | null |
Mineralocorticoid secretion is regulated mainly by the renin–angiotensin–aldosterone system (RAAS), the concentration of potassium, and to a lesser extent the concentration of ACTH. Sensors of blood pressure in the juxtaglomerular apparatus of the kidneys release the enzyme renin into the blood, which starts a cascade of reactions that lead to formation of angiotensin II. Angiotensin receptors in cells of the zona glomerulosa recognize the substance, and upon binding they stimulate the release of aldosterone.
Androgens
Cells in zona reticularis of the adrenal glands produce male sex hormones, or androgens, the most important of which is DHEA. In general, these hormones do not have an overall effect in the male body, and are converted to more potent androgens such as testosterone and DHT or to estrogens (female sex hormones) in the gonads, acting in this way as a metabolic intermediate.
Catecholamines
Primarily referred to in the United States as epinephrine and norepinephrine, adrenaline and noradrenaline are catecholamines, water-soluble compounds that have a structure made of a catechol group and an amine group. The adrenal glands are responsible for most of the adrenaline that circulates in the body, but only for a small amount of circulating noradrenaline. These hormones are released by the adrenal medulla, which contains a dense network of blood vessels. Adrenaline and noradrenaline act by interacting with adrenoreceptors throughout the body, with effects that include an increase in blood pressure and heart rate. Actions of adrenaline and noradrenaline are responsible for the fight or flight response, characterised by a quickening of breathing and heart rate, an increase in blood pressure, and constriction of blood vessels in many parts of the body. | Adrenal gland | Wikipedia | 406 | 2296 | https://en.wikipedia.org/wiki/Adrenal%20gland | Biology and health sciences | Animal: General | null |
Formation
Catecholamines are produced in chromaffin cells in the medulla of the adrenal gland, from tyrosine, a non-essential amino acid derived from food or produced from phenylalanine in the liver. The enzyme tyrosine hydroxylase converts tyrosine to L-DOPA in the first step of catecholamine synthesis. L-DOPA is then converted to dopamine before it can be turned into noradrenaline. In the cytosol, noradrenaline is converted to epinephrine by the enzyme phenylethanolamine N-methyltransferase (PNMT) and stored in granules. Glucocorticoids produced in the adrenal cortex stimulate the synthesis of catecholamines by increasing the levels of tyrosine hydroxylase and PNMT.
Catecholamine release is stimulated by the activation of the sympathetic nervous system. Splanchnic nerves of the sympathetic nervous system innervate the medulla of the adrenal gland. When activated, it evokes the release of catecholamines from the storage granules by stimulating the opening of calcium channels in the cell membrane.
Gene and protein expression
The human genome includes approximately 20,000 protein coding genes and 70% of these genes are expressed in the normal adult adrenal glands. Only some 250 genes are more specifically expressed in the adrenal glands compared to other organs and tissues. The adrenal-gland-specific genes with the highest level of expression include members of the cytochrome P450 superfamily of enzymes. Corresponding proteins are expressed in the different compartments of the adrenal gland, such as CYP11A1, HSD3B2 and FDX1 involved in steroid hormone synthesis and expressed in cortical cell layers, and PNMT and DBH involved in noradrenaline and adrenaline synthesis and expressed in the medulla. | Adrenal gland | Wikipedia | 405 | 2296 | https://en.wikipedia.org/wiki/Adrenal%20gland | Biology and health sciences | Animal: General | null |
Development
The adrenal glands are composed of two heterogenous types of tissue. In the center is the adrenal medulla, which produces adrenaline and noradrenaline and releases them into the bloodstream, as part of the sympathetic nervous system. Surrounding the medulla is the cortex, which produces a variety of steroid hormones. These tissues come from different embryological precursors and have distinct prenatal development paths. The cortex of the adrenal gland is derived from mesoderm, whereas the medulla is derived from the neural crest, which is of ectodermal origin.
The adrenal glands in a newborn baby are much larger as a proportion of the body size than in an adult. For example, at age three months the glands are four times the size of the kidneys. The size of the glands decreases relatively after birth, mainly because of shrinkage of the cortex. The cortex, which almost completely disappears by age 1, develops again from age 4–5. The glands weigh about at birth and develop to an adult weight of about each. In a fetus the glands are first detectable after the sixth week of development. | Adrenal gland | Wikipedia | 238 | 2296 | https://en.wikipedia.org/wiki/Adrenal%20gland | Biology and health sciences | Animal: General | null |
Cortex
Adrenal cortex tissue is derived from the intermediate mesoderm. It first appears 33 days after fertilisation, shows steroid hormone production capabilities by the eighth week and undergoes rapid growth during the first trimester of pregnancy. The fetal adrenal cortex is different from its adult counterpart, as it is composed of two distinct zones: the inner "fetal" zone, which carries most of the hormone-producing activity, and the outer "definitive" zone, which is in a proliferative phase. The fetal zone produces large amounts of adrenal androgens (male sex hormones) that are used by the placenta for estrogen biosynthesis. Cortical development of the adrenal gland is regulated mostly by ACTH, a hormone produced by the pituitary gland that stimulates cortisol synthesis. During midgestation, the fetal zone occupies most of the cortical volume and produces 100–200 mg/day of DHEA-S, an androgen and precursor of both androgens and estrogens (female sex hormones). Adrenal hormones, especially glucocorticoids such as cortisol, are essential for prenatal development of organs, particularly for the maturation of the lungs. The adrenal gland decreases in size after birth because of the rapid disappearance of the fetal zone, with a corresponding decrease in androgen secretion.
Adrenarche
During early childhood androgen synthesis and secretion remain low, but several years before puberty (from 6–8 years of age) changes occur in both anatomical and functional aspects of cortical androgen production that lead to increased secretion of the steroids DHEA and DHEA-S. These changes are part of a process called adrenarche, which has only been described in humans and some other primates. Adrenarche is independent of ACTH or gonadotropins and correlates with a progressive thickening of the zona reticularis layer of the cortex. Functionally, adrenarche provides a source of androgens for the development of axillary and pubic hair before the beginning of puberty. | Adrenal gland | Wikipedia | 448 | 2296 | https://en.wikipedia.org/wiki/Adrenal%20gland | Biology and health sciences | Animal: General | null |
Medulla
The adrenal medulla is derived from neural crest cells, which come from the ectoderm layer of the embryo. These cells migrate from their initial position and aggregate in the vicinity of the dorsal aorta, a primitive blood vessel, which activates the differentiation of these cells through the release of proteins known as BMPs. These cells then undergo a second migration from the dorsal aorta to form the adrenal medulla and other organs of the sympathetic nervous system. Cells of the adrenal medulla are called chromaffin cells because they contain granules that stain with chromium salts, a characteristic not present in all sympathetic organs. Glucocorticoids produced in the adrenal cortex were once thought to be responsible for the differentiation of chromaffin cells. More recent research suggests that BMP-4 secreted in adrenal tissue is the main responsible for this, and that glucocorticoids only play a role in the subsequent development of the cells.
Clinical significance
The normal function of the adrenal gland may be impaired by conditions such as infections, tumors, genetic disorders and autoimmune diseases, or as a side effect of medical therapy. These disorders affect the gland either directly (as with infections or autoimmune diseases) or as a result of the dysregulation of hormone production (as in some types of Cushing's syndrome) leading to an excess or insufficiency of adrenal hormones and the related symptoms.
Corticosteroid overproduction
Cushing's syndrome
Cushing's syndrome is the manifestation of glucocorticoid excess. It can be the result of a prolonged treatment with glucocorticoids or be caused by an underlying disease which produces alterations in the HPA axis or the production of cortisol. Causes can be further classified into ACTH-dependent or ACTH-independent. The most common cause of endogenous Cushing's syndrome is a pituitary adenoma which causes an excessive production of ACTH. The disease produces a wide variety of signs and symptoms which include obesity, diabetes, increased blood pressure, excessive body hair (hirsutism), osteoporosis, depression, and most distinctively, stretch marks in the skin, caused by its progressive thinning. | Adrenal gland | Wikipedia | 480 | 2296 | https://en.wikipedia.org/wiki/Adrenal%20gland | Biology and health sciences | Animal: General | null |
Primary aldosteronism
When the zona glomerulosa produces excess aldosterone, the result is primary aldosteronism. Causes for this condition are bilateral hyperplasia (excessive tissue growth) of the glands, or aldosterone-producing adenomas (a condition called Conn's syndrome). Primary aldosteronism produces hypertension and electrolyte imbalance, increasing potassium depletion sodium retention.
Adrenal insufficiency
Adrenal insufficiency (the deficiency of glucocorticoids) occurs in about 5 in 10,000 in the general population. Diseases classified as primary adrenal insufficiency (including Addison's disease and genetic causes) directly affect the adrenal cortex. If a problem that affects the hypothalamic–pituitary–adrenal axis arises outside the gland, it is a secondary adrenal insufficiency.
Addison's disease
Addison's disease refers to primary hypoadrenalism, which is a deficiency in glucocorticoid and mineralocorticoid production by the adrenal gland. In the Western world, Addison's disease is most commonly an autoimmune condition, in which the body produces antibodies against cells of the adrenal cortex. Worldwide, the disease is more frequently caused by infection, especially from tuberculosis. A distinctive feature of Addison's disease is hyperpigmentation of the skin, which presents with other nonspecific symptoms such as fatigue.
A complication seen in untreated Addison's disease and other types of primary adrenal insufficiency is the adrenal crisis, a medical emergency in which low glucocorticoid and mineralocorticoid levels result in hypovolemic shock and symptoms such as vomiting and fever. An adrenal crisis can progressively lead to stupor and coma. The management of adrenal crises includes the application of hydrocortisone injections. | Adrenal gland | Wikipedia | 414 | 2296 | https://en.wikipedia.org/wiki/Adrenal%20gland | Biology and health sciences | Animal: General | null |
Secondary adrenal insufficiency
In secondary adrenal insufficiency, a dysfunction of the hypothalamic–pituitary–adrenal axis leads to decreased stimulation of the adrenal cortex. Apart from suppression of the axis by glucocorticoid therapy, the most common cause of secondary adrenal insufficiency are tumors that affect the production of adrenocorticotropic hormone (ACTH) by the pituitary gland. This type of adrenal insufficiency usually does not affect the production of mineralocorticoids, which are under regulation of the renin–angiotensin system instead.
Congenital adrenal hyperplasia
Congenital adrenal hyperplasia is a family of congenital diseases in which mutations of enzymes that produce steroid hormones result in a glucocorticoid deficiency and malfunction of the negative feedback loop of the HPA axis. In the HPA axis, cortisol (a glucocorticoid) inhibits the release of CRH and ACTH, hormones that in turn stimulate corticosteroid synthesis. As cortisol cannot be synthesized, these hormones are released in high quantities and stimulate production of other adrenal steroids instead. The most common form of congenital adrenal hyperplasia is due to 21-hydroxylase deficiency. 21-hydroxylase is necessary for production of both mineralocorticoids and glucocorticoids, but not androgens. Therefore, ACTH stimulation of the adrenal cortex induces the release of excessive amounts of adrenal androgens, which can lead to the development of ambiguous genitalia and secondary sex characteristics.
Adrenal tumors
Adrenal tumors are commonly found as incidentalomas, unexpected asymptomatic tumors found during medical imaging. They are seen in around 3.4% of CT scans, and in most cases they are benign adenomas. Adrenal carcinomas are very rare, with an incidence of 1 case per million per year. | Adrenal gland | Wikipedia | 430 | 2296 | https://en.wikipedia.org/wiki/Adrenal%20gland | Biology and health sciences | Animal: General | null |
Pheochromocytomas are tumors of the adrenal medulla that arise from chromaffin cells. They can produce a variety of nonspecific symptoms, which include headaches, sweating, anxiety and palpitations. Common signs include hypertension and tachycardia. Surgery, especially adrenal laparoscopy, is the most common treatment for small pheochromocytomas.
History
Bartolomeo Eustachi, an Italian anatomist, is credited with the first description of the adrenal glands in 1563–4. However, these publications were part of the papal library and did not receive public attention, which was first received with Caspar Bartholin the Elder's illustrations in 1611.
The adrenal glands are named for their location relative to the kidneys. The term "adrenal" comes from Latin ad, "near", and ren, "kidney". Similarly, "suprarenal", as termed by Jean Riolan the Younger in 1629, is derived from the Latin supra, "above", and ren, "kidney", as well. The suprarenal nature of the glands was not truly accepted until the 19th century, as anatomists clarified the ductless nature of the glands and their likely secretory role – prior to this, there was some debate as to whether the glands were indeed suprarenal or part of the kidney.
One of the most recognized works on the adrenal glands came in 1855 with the publication of On the Constitutional and Local Effects of Disease of the Suprarenal Capsule, by the English physician Thomas Addison. In his monography, Addison described what the French physician George Trousseau would later name Addison's disease, an eponym still used today for a condition of adrenal insufficiency and its related clinical manifestations. In 1894, English physiologists George Oliver and Edward Schafer studied the action of adrenal extracts and observed their pressor effects. In the following decades several physicians experimented with extracts from the adrenal cortex to treat Addison's disease. Edward Calvin Kendall, Philip Hench and Tadeusz Reichstein were then awarded the 1950 Nobel Prize in Physiology or Medicine for their discoveries on the structure and effects of the adrenal hormones. | Adrenal gland | Wikipedia | 483 | 2296 | https://en.wikipedia.org/wiki/Adrenal%20gland | Biology and health sciences | Animal: General | null |
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