title: Exponentiation

text: So, formula_118 can be used as an alternative definition of for any positive real . This agrees with the definition given above using rational exponents and continuity, with the advantage to extend straightforwardly to any complex exponent.


title: Exponentiation

text: If is a positive real number, exponentiation with base and complex exponent is defined by means of the exponential function with complex argument (see the end of , above) as


title: Exponentiation

text: formula_122 is not defined, since is not a real number. If a meaning is given to the exponentiation of a complex number (see , below), one has, in general,


title: Exponentiation

text: In the preceding sections, exponentiation with non-integer exponents has been defined for positive real bases only. For other bases, difficulties appear already with the apparently simple case of th roots, that is, of exponents formula_128 where is a positive integer. Although the general theory of exponentiation with non-integer exponents applies to th roots, this case deserves to be considered first, since it does not need to use complex logarithms, and is therefore easier to understand.


title: Exponentiation

text: where formula_130 is the absolute value of , and formula_131 is its argument. The argument is defined up to an integer multiple of ; this means that, if formula_131 is the argument of a complex number, then formula_133 is also an argument of the same complex number.


title: Exponentiation

text: The polar form of the product of two complex numbers is obtained by multiplying the absolute values and adding the arguments. It follows that the polar form of an th root of a complex number can be obtained by taking the th root of the absolute value and dividing its argument by :


title: Exponentiation

text: If formula_135 is added to formula_131, the complex number is not changed, but this adds formula_137 to the argument of the th root, and provides a new th root. This can be done times, and provides the th roots of the complex number.


title: Exponentiation

text: It is usual to choose one of the th root as the principal root. The common choice is to choose the th root for which formula_138 that is, the th root that has the largest real part, and, if they are two, the one with positive imaginary part. This makes the principal th root a continuous function in the whole complex plane, except for negative real values of the radicand. This function equals the usual th root for positive real radicands. For negative real radicands, and odd exponents, the principal th root is not real, although the usual th root is real. Analytic continuation shows that the principal th root is the unique complex differentiable function that extends the usual th root to the complex plane without the nonpositive real numbers.


title: Exponentiation

text: If the complex number is moved around zero by increasing its argument, after an increment of formula_139 the complex number comes back to its initial position, and its th roots are permuted circularly (they are multiplied by formula_140). This shows that it is not possible to define a th root function that is continuous in the whole complex plane.


title: Exponentiation

text: The th roots of unity are the complex numbers such that , where is a positive integer. They arise in various areas of mathematics, such as in discrete Fourier transform or algebraic solutions of algebraic equations (Lagrange resolvent).


title: Exponentiation

text: The th roots of unity are the first powers of formula_141, that is formula_142 The th roots of unity that have this generating property are called "primitive th roots of unity"; they have the form formula_143 with coprime with . The unique primitive square root of unity is formula_144 the primitive fourth roots of unity are formula_145 and formula_146


title: Exponentiation

text: The th roots of unity allow expressing all th roots of a complex number as the products of a given th roots of with a th root of unity.


title: Exponentiation

text: Geometrically, the th roots of unity lie on the unit circle of the complex plane at the vertices of a regular -gon with one vertex on the real number 1.


title: Exponentiation

text: As the number formula_147 is the primitive th root of unity with the smallest positive argument, it is called the "principal primitive th root of unity", sometimes shortened as "principal th root of unity", although this terminology can be confused with the principal value of formula_148 which is 1.


title: Exponentiation

text: Defining exponentiation with complex bases leads to difficulties that are similar to those described in the preceding section, except that there are, in general, infinitely many possible values for formula_149. So, either a principal value is defined, which is not continuous for the values of that are real and nonpositive, or formula_149 is defined as a multivalued function.


title: Exponentiation

text: where formula_152 is the variant of the complex logarithm that is used, which is, a function or a multivalued function such that


title: Exponentiation

text: The principal value of the complex logarithm is the unique function, commonly denoted formula_154 such that, for every nonzero complex number ,


title: Exponentiation

text: The principal value of the complex logarithm is not defined for formula_157 it is discontinuous at negative real values of , and it is holomorphic (that is, complex differentiable) elsewhere. If is real and positive, the principal value of the complex logarithm is the natural logarithm: formula_158


title: Exponentiation

text: The function formula_162 is holomorphic except in the neighbourhood of the points where is real and nonpositive.


title: Exponentiation

text: If is real and positive, the principal value of formula_159 equals its usual value defined above. If formula_164 where is an integer, this principal value is the same as the one defined above.


title: Exponentiation

text: In some contexts, there is a problem with the discontinuity of the principal values of formula_152 and formula_159 at the negative real values of . In this case, it is useful to consider these functions as multivalued functions.


title: Exponentiation

text: If formula_152 denotes one of the values of the multivalued logarithm (typically its principal value), the other values are formula_168 where is any integer. Similarly, if formula_159 is one value of the exponentiation, then the other values are given by


title: Exponentiation

text: Different values of give different values of formula_159 unless is a rational number, that is, there is an integer such that is an integer. This results from the periodicity of the exponential function, more specifically, that formula_172 if and only if formula_173 is an integer multiple of formula_174


title: Exponentiation

text: If formula_175 is a rational number with and coprime integers with formula_176 then formula_159 has exactly values. In the case formula_178 these values are the same as those described in § th roots of a complex number. If is an integer, there is only one value that agrees with that of .


title: Exponentiation

text: The multivalued exponentiation is holomorphic for formula_179 in the sense that its graph consists of several sheets that define each a holomorphic function in the neighborhood of every point. If varies continuously along a circle around , then, after a turn, the value of formula_159 has changed of sheet.


title: Exponentiation

text: The "canonical form" formula_181 of formula_159 can be computed from the canonical form of and . Although this can be described by a single formula, it is clearer to split the computation in several steps.


title: Exponentiation

text: In both examples, all values of formula_159 have the same argument. More generally, this is true if and only if the real part of is an integer.


title: Exponentiation

text: Some identities for powers and logarithms for positive real numbers will fail for complex numbers, no matter how complex powers and complex logarithms are defined "as single-valued functions". For example:


title: Exponentiation

text: If exponentiation is considered as a multivalued function then the possible values of are }. The identity holds, but saying } is wrong.


title: Exponentiation

text: The error is the following: by definition, formula_219 is a notation for formula_220 a true function, and formula_221 is a notation for formula_222 which is a multi-valued function. Thus the notation is ambiguous when . Here, before expanding the exponent, the second line should be


title: Exponentiation

text: Therefore, when expanding the exponent, one has implicitly supposed that formula_224 for complex values of , which is wrong, as the complex logarithm is multivalued. In other words, the wrong identity must be replaced by the identity


title: Exponentiation

text: If is a positive real algebraic number, and is a rational number, then is an algebraic number. This results from the theory of algebraic extensions. This remains true if is any algebraic number, in which case, all values of (as a multivalued function) are algebraic. If is irrational (that is, "not rational"), and both and are algebraic, Gelfond–Schneider theorem asserts that all values of are transcendental (that is, not algebraic), except if equals or .


title: Exponentiation

text: The definition of exponentiation with positive integer exponents as repeated multiplication may apply to any associative operation denoted as a multiplication. The definition of formula_227 requires further the existence of a multiplicative identity.


title: Exponentiation

text: An algebraic structure consisting of a set together with an associative operation denoted multiplicatively, and a multiplicative identity denoted by 1 is a monoid. In such a monoid, exponentiation of an element is defined inductively by


title: Exponentiation

text: If is a negative integer, formula_230 is defined only if has a multiplicative inverse. In this case, the inverse of is denoted formula_231 and formula_230 is defined as formula_233


title: Exponentiation

text: Exponentiation with integer exponents obeys the following laws, for and in the algebraic structure, and and integers:


title: Exponentiation

text: These definitions are widely used in many areas of mathematics, notably for groups, rings, fields, square matrices (which form a ring). They apply also to functions from a set to itself, which form a monoid under function composition. This includes, as specific instances, geometric transformations, and endomorphisms of any mathematical structure.


title: Exponentiation

text: When there are several operations that may be repeated, it is common to indicate the repeated operation by placing its symbol in the superscript, before the exponent. For example, if is a real function whose valued can be multiplied, formula_235 denotes the exponentiation with respect of multiplication, and formula_236 may denote exponentiation with respect of function composition. That is,


title: Exponentiation

text: A multiplicative group is a set with as associative operation denoted as multiplication, that has an identity element, and such that every element has an inverse.


title: Exponentiation

text: The set of all powers of an element of a group form a subgroup. A group (or subgroup) that consists of all powers of a specific element is the cyclic group generated by . If all the powers of are distinct, the group is isomorphic to the additive group formula_245 of the integers. Otherwise, the cyclic group is finite (it has a finite number of elements), and its number of elements is the order of . If the order of is , then formula_246 and the cyclic group generated by consists of the first powers of (starting indifferently from the exponent or ).


title: Exponentiation

text: Order of elements play a fundamental role in group theory. For example, the order of an element in a finite group is always a divisor of the number of elements of the group (the "order" of the group). The possible orders of group elements are important in the study of the structure of a group (see Sylow theorems), and in the classification of finite simple groups.


title: Exponentiation

text: Superscript notation is also used for conjugation; that is, , where "g" and "h" are elements of a group. This notation cannot be confused with exponentiation, since the superscript is not an integer. The motivation of this notation is that conjugation obeys some of the laws of exponentiation, namely formula_247 and formula_248


title: Exponentiation

text: In a ring, it may occur that some nonzero elements satisfy formula_249 for some integer . Such an element is said to be nilpotent. In a commutative ring, the nilpotent elements form an ideal, called the nilradical of the ring.


title: Exponentiation

text: If the nilradical is reduced to the zero ideal (that is, if formula_250 implies formula_251 for every positive integer ), the commutative ring is said reduced. Reduced rings important in algebraic geometry, since the coordinate ring of an affine algebraic set is always a reduced ring.


title: Exponentiation

text: More generally, given an ideal in a commutative ring , the set of the elements of that have a power in is an ideal, called the radical of . The nilradical is the radical of the zero ideal. A radical ideal is an ideal that equals its own radical. In a polynomial ring formula_252 over a field , an ideal is radical if and only if it is the set of all polynomials that are zero on an affine algebraic set (this is a consequence of Hilbert's Nullstellensatz).


title: Exponentiation

text: If "A" is a square matrix, then the product of "A" with itself "n" times is called the matrix power. Also formula_253 is defined to be the identity matrix, and if "A" is invertible, then formula_254.


title: Exponentiation

text: Matrix powers appear often in the context of discrete dynamical systems, where the matrix "A" expresses a transition from a state vector "x" of some system to the next state "Ax" of the system. This is the standard interpretation of a Markov chain, for example. Then formula_255 is the state of the system after two time steps, and so forth: formula_256 is the state of the system after "n" time steps. The matrix power formula_257 is the transition matrix between the state now and the state at a time "n" steps in the future. So computing matrix powers is equivalent to solving the evolution of the dynamical system. In many cases, matrix powers can be expediently computed by using eigenvalues and eigenvectors.


title: Exponentiation

text: Apart from matrices, more general linear operators can also be exponentiated. An example is the derivative operator of calculus, formula_258, which is a linear operator acting on functions formula_70 to give a new function formula_260. The "n"-th power of the differentiation operator is the "n"-th derivative:


title: Exponentiation

text: These examples are for discrete exponents of linear operators, but in many circumstances it is also desirable to define powers of such operators with continuous exponents. This is the starting point of the mathematical theory of semigroups. Just as computing matrix powers with discrete exponents solves discrete dynamical systems, so does computing matrix powers with continuous exponents solve systems with continuous dynamics. Examples include approaches to solving the heat equation, Schrödinger equation, wave equation, and other partial differential equations including a time evolution. The special case of exponentiating the derivative operator to a non-integer power is called the fractional derivative which, together with the fractional integral, is one of the basic operations of the fractional calculus.


title: Exponentiation

text: A field is an algebraic structure in which multiplication, addition, subtraction, and division are defined and satisfy the properties that multiplication is associative and every nonzero element has a multiplicative inverse. This implies that exponentiation with integer exponents is well-defined, except for nonpositive powers of . Common examples are the complex numbers and their subfields, the rational numbers and the real numbers, which have been considered earlier in this article, and are all infinite.


title: Exponentiation

text: A "finite field" is a field with a finite number of elements. This number of elements is either a prime number or a prime power; that is, it has the form formula_262 where is a prime number, and is a positive integer. For every such , there are fields with elements. The fields with elements are all isomorphic, which allows, in general, working as if there were only one field with elements, denoted formula_263


title: Exponentiation

text: A primitive element in formula_266 is an element such the set of the first powers of (that is, formula_267) equals the set of the nonzero elements of formula_263 There are formula_269 primitive elements in formula_270 where formula_271 is Euler's totient function.


title: Exponentiation

text: is linear over formula_270 and is a field automorphism, called the Frobenius automorphism. If formula_262 the field formula_266 has automorphisms, which are the first powers (under composition) of . In other words, the Galois group of formula_266 is cyclic of order , generated by the Frobenius automorphism.


title: Exponentiation

text: The Diffie–Hellman key exchange is an application of exponentiation in finite fields that is widely used for secure communications. It uses the fact that exponentiation is computationally inexpensive, whereas the inverse operation, the discrete logarithm, is computationally expensive. More precisely, if is a primitive element in formula_270 then formula_282 can be efficiently computed with exponentiation by squaring for any , even if is large, while there is no known algorithm allowing retrieving from formula_282 if is sufficiently large.


title: Exponentiation

text: The Cartesian product of two sets and is the set of the ordered pairs formula_284 such that formula_285 and formula_286 This operation is not properly commutative nor associative, but has these properties up to canonical isomorphisms, that allow identifying, for example, formula_287 formula_288 and formula_289


title: Exponentiation

text: This allows defining the th power formula_290 of a set as the set of all -tuples formula_291 of elements of .


title: Exponentiation

text: When is endowed with some structure, it is frequent that formula_290 is naturally endowed with a similar structure. In this case, the term "direct product" is generally used instead of "Cartesian product", and exponentiation denotes product structure. For example formula_293 (where formula_294 denotes the real numbers) denotes the Cartesian product of copies of formula_295 as well as their direct product as vector space, topological spaces, rings, etc.


title: Exponentiation

text: A -tuple formula_291 of elements of can be considered as a function from formula_297 This generalizes to the following notation.


title: Exponentiation

text: Given two sets and , the set of all functions from to is denoted formula_298. This exponential notation is justified by the following canonical isomorphisms (for the first one, see Currying):


title: Exponentiation

text: One can use sets as exponents for other operations on sets, typically for direct sums of abelian groups, vector spaces, or modules. For distinguishing direct sums from direct products, the exponent of a direct sum is placed between parentheses. For example, formula_303 denotes the vector space of the infinite sequences of real numbers, and formula_304 the vector space of those sequences that have a finite number of nonzero elements. The latter has a basis consisting of the sequences with exactly one nonzero element that equals , while the Hamel bases of the former cannot be explicitly described (because there existence involves Zorn's lemma).


title: Exponentiation

text: In this context, can represents the set formula_305 So, formula_306 denotes the power set of , that is the set of the functions from to formula_307 which can be identified with the set of the subsets of , by mapping each function to the inverse image of .


title: Exponentiation

text: This fits in with the exponentiation of cardinal numbers, in the sense that , where is the cardinality of .


title: Exponentiation

text: In the category of sets, the morphisms between sets and are the functions from to . It results that the set of the functions from to that is denoted formula_308 in the preceding section can also be denoted formula_309 The isomorphism formula_310 can be rewritten


title: Exponentiation

text: This means the functor "exponentiation to the power " is a right adjoint to the functor "direct product with ".


title: Exponentiation

text: This generalizes to the definition of exponentiation in a category in which finite direct products exist: in such a category, the functor formula_312 is, if it exists, a right adjoint to the functor formula_313 A category is called a "Cartesian closed category", if direct products exist, and the functor formula_314 has a right adjoint for every .


title: Exponentiation

text: Just as exponentiation of natural numbers is motivated by repeated multiplication, it is possible to define an operation based on repeated exponentiation; this operation is sometimes called hyper-4 or tetration. Iterating tetration leads to another operation, and so on, a concept named hyperoperation. This sequence of operations is expressed by the Ackermann function and Knuth's up-arrow notation. Just as exponentiation grows faster than multiplication, which is faster-growing than addition, tetration is faster-growing than exponentiation. Evaluated at , the functions addition, multiplication, exponentiation, and tetration yield 6, 9, 27, and () respectively.


title: Exponentiation

text: Zero to the power of zero gives a number of examples of limits that are of the indeterminate form 0. The limits in these examples exist, but have different values, showing that the two-variable function has no limit at the point . One may consider at what points this function does have a limit.


title: Exponentiation

text: More precisely, consider the function formula_315 defined on formula_316. Then can be viewed as a subset of (that is, the set of all pairs with , belonging to the extended real number line , endowed with the product topology), which will contain the points at which the function has a limit.


title: Exponentiation

text: In fact, has a limit at all accumulation points of , except for , , and . Accordingly, this allows one to define the powers by continuity whenever , , except for 0, (+∞), 1 and 1, which remain indeterminate forms.


title: Exponentiation

text: These powers are obtained by taking limits of for "positive" values of . This method does not permit a definition of when , since pairs with are not accumulation points of .


title: Exponentiation

text: On the other hand, when is an integer, the power is already meaningful for all values of , including negative ones. This may make the definition obtained above for negative problematic when is odd, since in this case as tends to through positive values, but not negative ones.


title: Exponentiation

text: Computing "b" using iterated multiplication requires multiplication operations, but it can be computed more efficiently than that, as illustrated by the following example. To compute 2, apply Horner's rule to the exponent 100 written in binary:


title: Exponentiation

text: In general, the number of multiplication operations required to compute can be reduced to formula_318 by using exponentiation by squaring, where formula_319 denotes the number of in the binary representation of . For some exponents (100 is not among them), the number of multiplications can be further reduced by computing and using the minimal addition-chain exponentiation. Finding the "minimal" sequence of multiplications (the minimal-length addition chain for the exponent) for is a difficult problem, for which no efficient algorithms are currently known (see Subset sum problem), but many reasonably efficient heuristic algorithms are available. However, in practical computations, exponentiation by squaring is efficient enough, and much more easy to implement.


title: Exponentiation

text: Function composition is a binary operation that is defined on functions such that the codomain of the function written on the right is included in the domain of the function written on the left. It is denoted formula_320 and defined as


title: Exponentiation

text: If the domain of a function equals its codomain, one may compose the function with itself an arbitrary number of time, and this defines the th power of the function under composition, commonly called the "th iterate" of the function. Thus formula_235 denotes generally the th iterate of ; for example, formula_323 means formula_324


title: Exponentiation

text: When a multiplication is defined on the codomain of the function, this defines a multiplication on functions, the pointwise multiplication, which induces another exponentiation. When using functional notation, the two kinds of exponentiation are generally distinguished by placing the exponent of the functional iteration "before" the parentheses enclosing the arguments of the function, and placing the exponent of pointwise multiplication "after" the parentheses. Thus formula_325 and formula_326 When functional notation is not used, disambiguation is often done by placing the composition symbol before the exponent; for example formula_327 and formula_328 For historical reasons, the exponent of a repeated multiplication is placed before the argument for some specific functions, typically the trigonometric functions. So, formula_329 and formula_330 both mean formula_331 and not formula_332 which, in any case, is rarely considered. Historically, several variants of these notations were used by different authors.


title: Exponentiation

text: In this context, the exponent formula_333 denotes always the inverse function, if it exists. So formula_334 For the multiplicative inverse fractions are generally used as in formula_335


title: Exponentiation

text: Programming languages generally express exponentiation either as an infix operator or as a function application, as they do not support superscripts. The most common operator symbol for exponentiation is the caret (codice_1). The original version of ASCII included an uparrow symbol (codice_2), intended for exponentiation, but this was replaced by the caret in 1967, so the caret became usual in programming languages.


title: Exponentiation

text: In most programming languages with an infix exponentiation operator, it is right-associative, that is, codice_11 is interpreted as codice_12. This is because codice_13 is equal to codice_14 and thus not as useful. In some languages, it is left-associative, notably in Algol, Matlab and the Microsoft Excel formula language.


title: Audi A5

text: The Audi A5 is a series of compact executive coupe cars produced by the German automobile manufacturer Audi since June 2007. The A5 range additionally comprises the coupe, cabriolet, and "Sportback" (a five-door liftback with a fastback roofline) version of the Audi A4 saloon and estate models.


title: Audi A5

text: Under Audi's internal platform numbering convention, the A5 is a member of the "B-platform" series of vehicles, sharing its platform designation with the A4 saloon and "Avant". The first generation A5 ("Type 8T") is therefore a member of the "B8" family, whilst the second generation model ("Type 8W6") is based on the "B9". Both are derived from the Volkswagen MLB (Modular Longitudinal Matrix) architecture.


title: Audi A5

text: When presented at the March 2007 Geneva Motor Show, the A5 marked Audi's return to the compact executive coupé market since the (B3/B4) Audi 80 based coupé model ended production in 1996. On May 10, 2006, Audi confirmed that the A5 would go into production. The B6/B7 A4 spawned a convertible variant but not a coupé. For the fourth-generation A4 (B8), Audi decided to spin off the cabriolet, along with a new coupé and 4-door fastback sedan, into a nameplate of its own as the A5.


title: Audi A5

text: The A5 was the first of the B8 family of vehicles to be released (the others being the A4 and the Q5 crossover SUV), all based on the Audi MLP platform (Modular Longitudinal Platform) which underpin the next generation A6 and A8.


title: Audi A5

text: The A5 is the third coupé in Audi's line up, following the second generation TT and the R8. The A5 adopted design elements of the Nuvolari quattro concept car. The A5 debuted with the 3.2 litre FSI V6 engine delivering .


title: Audi A5

text: The design was based on the Nuvolari quattro concept car. The A5 and the S5 Coupé were unveiled simultaneously at the Salon International de l'Auto (Geneva) and Melbourne International Motor Shows on March 6, 2007.


title: Audi A5

text: Ordering of the A5 and S5 began on March 6, 2007 and the first deliveries were made in June 2007. Launch models included 3.2 FSI V6 engine multitronic and 3.0 TDI quattro 6-speed, with 1.8 TFSI available in autumn 2007.


title: Audi A5

text: Early U.S. models included the A5 3.2 FSI Quattro and the S5 coupé 4.2 FSI Quattro. Both included either a six-speed manual or six-speed Tiptronic automatic transmission. The S5 model went on sale in November 2007, equipped only with a manual transmission, while the A5 and the Tiptronic went on sale beginning of spring 2008.


title: Audi A5

text: The A5 went on sale in Canada in 2008, which included A5 3.2 FSI with choice of six speed manual or six speed Tiptronic transmission. Since 2011, only the 2.0 L Turbo engines are available for the A5 in Canada. In 2013 Audi introduced the new A5 Black Edition.


title: Audi A5

text: Both the Audi A5 and the S5 Cabriolet (convertible/cabriolet) production began in the beginning of 2009. The A5 Cabriolet included a fabric roof as opposed to a retractable hardtop as on the Volkswagen Eos. The engine ranges are same as contemporary A5 coupé models, but S5 Cabriolet came with a 3.0 TFSI V6 supercharged engine.


title: Audi A5

text: The A5 Cabriolet replaced the A4 Cabriolet. Delivery of A5 Cabriolet began in the second quarter of 2009. The vehicle was unveiled at the 2009 New York Auto Show.


title: Audi A5

text: The U.S. versions of A5 and S5 Cabriolet went on sale in September 2009 as a 2010 model. Early models included A5 2.0 I4 TFSI Multitronic, A5 2.0 Quattro Tiptronic, S5 Quattro S-Tronic.


title: Audi A5

text: The A5 Sportback has four frameless doors and a long, tapering fastback like roofline, giving it a "four door coupé like" appearance. While it shares many exterior cues with the A5 coupé, the Sportback's interior is similar to the A4 saloon; although all A5 models have same platform as the A4, the Sportback is closer in design to the A4 than the rest of the A5 family.


title: Audi A5

text: The Sportback has been described as "a saloon with the front end (including an identical S-line look) and taillights of the A5 coupé but the wheelbase of the A4", with the Sportback positioned more as the "designer's car" compared to the more conventional A4 saloon.


title: Audi A5

text: The Sportback model is available in Europe, Japan, South Korea, China, Australia, New Zealand, Middle East, Mexico, Argentina, and South Africa. Although not originally sold in the United States and Canada, the A5 Sportback entered the North American market as a 2018 model in the beginning of 2017.


title: Audi A5

text: Early production models included 2.0 TFSI quattro , 3.2 FSI quattro, 2.0 TDI with six speed manual gearbox and start/stop system, 2.7 TDI, 3.0 TDI quattro. Production versions went on sale in September 2009.


title: Audi A5

text: The Audi S5 was released in coupé form to the public at the same time as the A5. The Audi S5, in comparison to the A5, features a different fascia (as do most Audi S and RS models), including a string of LED daytime running lights around the bi-Xenon headlamps and a vertically striped chrome grille.


title: Audi A5

text: In many markets, the S5 includes as standard, 19-inch alloy wheels with a five parallel spoke design, bigger brakes, heated leather sport seats, and other convenience features, some of which are available only as an option on the A5. Changes for the 2010 model year include LED tail lamps, the introduction of Premium Plus and Prestige trim levels, and new optional equipment such as Leather/Alcantara seats.


title: Audi A5

text: Despite sharing the same nameplate, the powertrains were different between the coupé and the Cabriolet/Sportback for the 2010–12 model years. The 2010–12 Audi S5 coupé had a 4.2 litre fuel stratified injection (FSI) V8 engine that produces , while the S5 Cabriolet and Sportback have a supercharged 3.0 litre TFSI V6 engine producing which is shared with the 2010 Audi S4 3.0 TFSI quattro sedan and avant.


title: Audi A5

text: The coupé had a choice of either a six speed manual or six speed Tiptronic automatic, while the Cabriolet/Sportback has the seven speed S-tronic dual-clutch automatic transmission.


title: Audi A5

text: The Aluminium A5 Coupé is a prototype vehicle demonstrating the aluminum Audi Space Frame (ASF) concept. It is based on Audi A5 Coupé 2.0 TFSI with engine, but it uses the aluminum Audi Space Frame, aluminum and carbon fiber-reinforced plastics body. Punch riveting, bonding or laser-MIG hybrid welding replaced spot welding. The vehicle is lighter than the equivalent steel-bodied production model.


title: Audi A5

text: Available in coupé body, the RS5 features a 4.2 FSI engine rated at at 8250 rpm and at 4000-6000 rpm, coupled with a seven-speed S-Tronic transmission and quattro permanent all-wheel-drive with crown-gear centre differential and electronic torque vectoring. It has 19 inch alloy wheels in an exclusive five arm structure design with 275/35 tires (optional 19 inch winter wheels), diameter ventilated aluminum front brake discs (optional diameter carbon ceramic front brake discs), aluminum 8 piston brake calipers with RS logos in high-gloss black, electronic stabilization program with integrated sport mode, speed dependent servotronic steering, Audi drive select with three (4 with MMI navigation system) modes of operation (comfort, auto, and dynamic, optional custom), and optional dynamic steering.


title: Audi A5

text: Aesthetically, the RS5 features a single-frame grille with a shiny charcoal gray rhombus pattern grid, Xenon plus headlights with a sweeping strip of LED daytime running lights, redesigned bumper tapers downward into a splitter, flared fenders inspired by Audi Quattro, side sills with angular caps, trim strips with aluminum look on the single-frame grille and near the side windows and the outside mirrors; a choice of 8 body colours, two oval exhaust pipes integrated within the bumper, spoiler in the tailgate automatically extends at and retracts at , extensively clad underbody integrating air vents for the seven-speed S-Tronic and the front brakes.


title: Audi A5

text: In the cockpit, the model has electrically adjustable sports seats in leather/Alcantara combination upholstery with side sections and integrated head restraints (optional bucket seats with more prominent contours and folding backrests, ventilated and luxuriously upholstered climate-controlled comfort seats; optional seat upholstery featuring special leathers and colors as well as silver headlining), steering wheel upholstered in perforated leather, black gauges with white lettering and distinctive scaling, driver information system with integrated lap timer and an oil temperature gauge, black interior with decorative inlays made of carbon fiber (optional dark stainless-steel mesh, black piano finish or brushed aluminum inlay), instrument panel fascia in piano finish, pedals, footrests, optional MMI navigation systems' control buttons in aluminum; door handles with two slim strips, aluminum inserts at door sill trims and RS 5 logos, optional suede-covered controls and floor mats bearing RS 5 logos, sport exhaust system with a sound flap and black tailpipe trims.


title: Audi A5

text: A Carbon design package is available for the engine compartment and for the vehicle body. Styling packages include a black or matte aluminum look.


title: Audi A5

text: The RS5 weighs , with 56.3 percent at the front and 43.7 in the rear which makes it prone to understeer, however, Audi has added two electro-mechanical systems to counter its nose-heaviness. The stability-control system attempts to stop front-end plow before it happens by squeezing the brakes on the inside wheels which effectively drag those tires enough to pull the car into the corner.


title: Audi A5

text: The RS5 also has an active rear differential that can apportion power between the rear wheels to create a similar effect or even oversteer; in normal conditions, Quattro all-wheel-drive delivers 60% of the engine’s torque rearward and rising to as much as 85 percent depending on conditions.


title: Audi A5

text: According to Quattro GmbH chief Stephan Reil, the 4.2 FSI engine is based upon Audi's 5.2 FSI V10 engine (found in the D3 Audi S8 and Audi R8) with two cylinders removed.


title: Audi A5

text: The Ethanol E100 Coupé is a prototype designed for the Michelin Challenge Bibendum 2010 series. It includes a 2.0 TFSI engine rated and torque, six-gear manual quattro drivetrain. It accelerates from in 6.9 seconds with top speed of , and weighs . The car officially consumes when running on ethanol, but drivers managed on ethanol during the Michelin Challenge Bibendum Rallye.


title: Audi A5

text: The S5 Special Edition is a limited (125 units) version of the 2012 S5 4.2 FSI Quattro Coupé for the U.S. market, commemorating the end of Audi S5 4.2 FSI Quattro production. It included Prestige Package, Daytona Grey body color, 19-inch 5-spoke Rotor design wheels, a two-tone Polar Silver and Black S5 sport seats, silver contrast stitching on the seats, armrests, shifter and steering wheel; floor mats with a silver leather border, aluminum 'Audi exclusive' badges on door panels, carbon fiber beltline and a piano black instrument cluster.


title: Audi A5

text: In 2009, Audi introduced the seven speed S-Tronic transmission option for A5 with 2.0 TFSI quattro (155 kW) for the UK market, which replaced the six speed Tiptronic in the United Kingdom and Germany.


title: Audi A5

text: Beginning with the 2011 model year, the A5 2.0 TFSI Quattro coupé and cabriolet includes 8 speed Tiptronic transmission option, replacing the 6-speed Tiptronic in the U.S. and Canada markets.


title: Audi A5

text: For the S5 3.0 TFSI quattro (245 kW), the manual transmission was discontinued for the European market.


title: Audi A5

text: The car was praised for its design, build quality, performance, and all-wheel drive system, and is favorably viewed by the majority of the motoring press. Appraised for a rarely seen example of an excellent all-round niche car. Walter de Silva has said that the Audi A5 coupe is "his most beautiful design ever".


title: Audi A5

text: The Ethanol E100 Coupé clinched overall victory in the Michelin Challenge Bibendum 2010 eco rally over a distance of 350 kilometers.


title: Audi A5

text: The facelift vehicles, covering A5 Coupé, Convertible, Sportback, S, and RS models, include updated front and rear lights, as well as a new front bumper design. The new front end includes pronounced air inlets, revamped grilles, and flat fog lights. The vehicle is longer overall than the predecessor.


title: Audi A5

text: Changes to S5 (available as Sportback, Coupé and Cabriolet) include the 3.0 TFSI (333PS) engines on all models, new lights, modified body details, new crystal effect paint finishes, Quattro drive with the crown-gear center differential, electromechanical power steering. special S sport suspension, standard 18-inch wheels.


title: Audi A5

text: Sales began in Europe in 2011 as 2012 model year vehicles. Early models include A5 1.8 TFSI, A5 2.0 TFSI, A5 3.0 TFSI, S5 3.0 TFSI, 2.0 TDI and 3.0 TDI. The base model is the Audi A5 Sportback 1.8 TFSI.


title: Audi A5

text: Changes to the RS5 Coupé for 2012 included upgraded dampers and springs on the suspension front, new electric power steering replacing engine-driven hydraulic power steering, exclusive retractable rear spoiler, red cam covers, and a carbon fiber intake manifold, optional piano black trim, twenty-inch graphite-colored wheels, a sport exhaust system with black finishers.


title: Audi A5

text: The RS5 Cabriolet was unveiled at the 2012 Paris Motor Show. Production of the RS5 ended permanently in June 2015. A race version of the S5, the RS5 has a valved exhaust whose note can be tuned to suit driving conditions and personal preference. The RS5 has a naturally aspirated 4.2 V8 that produces .


title: Audi A5

text: As part of the RS5 Cabriolet launch, Audi Land of Quattro Alpen Tour 2013 featured an RS5 Cabriolet starting on September 23, traveling across twelve driving stages in 6 countries (Klagenfurt – the capital of Carinthia, Austria, Monaco).


title: Audi A5

text: Codenamed R17, the Audi A5 DTM is a race car designed for the DTM beginning in year 2012, replacing the Audi A4 DTM. It includes a V8 engine rated at with a new 6-speed sequential semi-automatic transmission, pneumatically-operated suspension using paddle-shifters on the steering wheel, engine electronics (Bosch MS 5.1) and the central display from Audi R8 LMS, larger and wider tires from Hankook, safety fuel tank inside a carbon fiber cell, and a larger rear wing. The prototype was built by Audi Sport in Ingolstadt.


title: Audi A5

text: The vehicle was unveiled at the 2011 International Motor Show (IAA) in Frankfurt. The homologation of the A5 DTM was scheduled for 1 March 2012.


title: Audi A5

text: As part of the 2012 A5 launch in the United Kingdom, BBH London, Park Pictures, The Whitehouse and The Mill produced a television advert titled 'The Swan' (directed by Joachim Back), inspired by Hans Christian Andersen's tale of 'The Ugly Duckling'.


title: Audi A5

text: The commercial featured black and white shots of the rebodied 1920 Audi concept car designed by Audi engineer Paul Jaray, trawling the streets of a sleepy Bavarian village, the streamlined model gets shunned by disapproving locals not taking too well to the new aerodynamic design. After retiring in a nearby forest, the 'ugly' car transforms into the new Audi A5, metaphorically becoming the 'beautiful' white swan. The soundtrack features Danny Kaye singing the children's classic Ugly Duckling.


title: Audi A5

text: Changes to the Audi A5 Sportback include forced induction and direct injection on all engine models, standard start-stop-system; optional sport differential on the 3.0 TDI Quattro, and 3.0 TFSI Quattro, optional MMI navigation plus.


title: Audi A5

text: Changes to A5 Cabriolet include optional neck-level heating, special coating for optional leather seats.


title: Audi A5

text: Available in Sportback, Coupé, Cabriolet bodies, it includes 3.0 TFSI engine rated and , seven-speed S-Tronic transmission, S sport suspension, electronically controlled shock absorbers, dynamic steering, optional Audi drive select, 18-inch aluminum wheels.


title: Audi A5

text: Available in Coupé and Cabriolet bodies, it is a version of A5 with 4.2 FSI engine rated at and , seven-speed S-Tronic transmission, quattro permanent all-wheel drive system with crown-gear center differential and torque vectoring (optional quattro with sport differential rear axle), lower body, electromechanical power steering, exclusive 19-inch forged alloy wheels, optional carbon fiber-ceramic brake discs, Audi drive select dynamics system, optional RS sport suspension with Dynamic Ride Control (DRC).


title: Audi A5

text: Audi had problems with the oil consumption in the engines of the models between the years 2009 to 2011. More than 200 car owners in Switzerland were affected as well. In Switzerland, cars with less than and below five years old can have the hardware replaced and paid for by Audi. If the car is between and below five years, Audi fully pays the hardware but only half of the work.


title: Audi A5

text: The all-new A5 and S5 Coupé, based on the ninth generation of the Volkswagen Group MLB Platform, were unveiled in June 2016. Two petrol and two diesel engines are offered for the A5. The petrol engines are 2.0 litre TFSI with either or , and the diesel motors are 2.0 TDI and 3.0 TDI, with or . All the 2.0-liter powerplants can be paired with a 6-speed manual gearbox (in certain countries only), or a 7/8-speed S Tronic/Tiptronic, which is standard on the 3.0 TDI. Audi's latest coupé features the Virtual Cockpit instrument panel, an edge-to-edge display behind the steering wheel inspired by the airplane cockpit. The factory option for the A5 is the S line package which consists of a sportier front bumper with an aluminum line, diffuser on the rear bumper, and S line badges on the front fenders and side panel.


title: Audi A5

text: The Audi A5 and the S5 Sportback were unveiled in September 2016. They are powered by the same engines as the A5 and S5 Coupé respectively.


title: Audi A5

text: The S5 is powered by a turbocharged 3.0-litre TFSI engine that worked with an 8-speed automatic transmission. Inside the S5 has standard front bucket seats with diamond-shaped stitching, and a flat-bottom steering wheel with S badging.


title: Audi A5

text: The RS 5 Coupé is powered by a 2.9 liter TFSI V6 twin turbo engine producing and of torque that is also used in the Panamera 4S. It is lighter than its predecessor. Power is delivered to the quattro system with a 8-speed automatic transmission. The RS 5 accelerates from in 3.9 seconds, with a top speed of .


title: Audi A5

text: It also comes with a honeycomb grille, wider fenders, and aggressively-styled front bumper with bigger openings than the A5 and S5.


title: Audi A5

text: Further developments include a new chassis featuring a five-link front and rear suspension coupled to Audi Sport’s Dynamic Ride Control system offering variable damping control. Other options included with a carbon-fiber engine cover and ceramic front brakes.


title: Audi A5

text: Audi of America Product Planner, Anthony Garbis, has been credited for designing a limited run of 100 "Panther Edition" RS5s (75 Sportback and 25 Coupe) in late 2019. The Panther edition package retailed for $13,800 and included several exclusive options, most notably: Panther Black crystal effect paint, an Alcantara flat-bottom steering wheel, 20" 5-twin-spoke edge design wheels and Crescendo Red stitching on the seats, steering wheel and seat belts.


title: Diatom

text: A diatom (Neo-Latin "diatoma") is any member of a large group comprising several genera of algae, specifically microalgae, found in the oceans, waterways and soils of the world. Living diatoms make up a significant portion of the Earth's biomass: they generate about 20 to 50 percent of the oxygen produced on the planet each year, take in over 6.7 billion metric tons of silicon each year from the waters in which they live, and constitute nearly half of the organic material found in the oceans. The shells of dead diatoms can reach as much as a half-mile (800 m) deep on the ocean floor, and the entire Amazon basin is fertilized annually by 27 million tons of diatom shell dust transported by transatlantic winds from the African Sahara, much of it from the Bodélé Depression, which was once made up of a system of fresh-water lakes.


title: Diatom

text: Diatoms are unicellular organisms: they occur either as solitary cells or in colonies, which can take the shape of ribbons, fans, zigzags, or stars. Individual cells range in size from 2 to 200 micrometers. In the presence of adequate nutrients and sunlight, an assemblage of living diatoms doubles approximately every 24 hours by asexual multiple fission; the maximum life span of individual cells is about six days. Diatoms have two distinct shapes: a few ("centric diatoms") are "radially" symmetric, while most ("pennate diatoms") are broadly "bilaterally" symmetric. A unique feature of diatom anatomy is that they are surrounded by a cell wall made of silica (hydrated silicon dioxide), called a frustule. These frustules have structural coloration due to their photonic nanostructure, prompting them to be described as "jewels of the sea" and "living opals". Movement in diatoms primarily occurs passively as a result of both ocean currents and wind-induced water turbulence; however, male gametes of centric diatoms have flagella, permitting active movement to seek female gametes. Similar to plants, diatoms convert light energy to chemical energy by photosynthesis, but their chloroplasts were acquired in different ways.


title: Diatom

text: Unusually for autotrophic organisms, diatoms possess a urea cycle, a feature that they share with animals, although this cycle is used to different metabolic ends in diatoms. The family "Rhopalodiaceae" also possess a cyanobacterial endosymbiont called a spheroid body. This endosymbiont has lost its photosynthetic properties, but has kept its ability to perform nitrogen fixation, allowing the diatom to fix atmospheric nitrogen. Other diatoms in symbiosis with nitrogen-fixing cyanobacteria are among the genera "Hemiaulus", "Rhizosolenia" and "Chaetoceros".


title: Diatom

text: Dinotoms are diatoms that have become endosymbionts inside dinoflagellates. Research on the dinoflagellates "Durinskia baltica" and "Glenodinium foliaceum" have shown that the endosymbiont event happened so recently, evolutionarily speaking, that their organelles and genome are still intact with minimum to no gene loss. The main difference between these and free living diatoms is that they have lost their cell wall of silica, making them the only known shell-less diatoms.


title: Diatom

text: The study of diatoms is a branch of phycology. Diatoms are classified as eukaryotes, organisms with a nuclear envelope-bound cell nucleus, that separates them from the prokaryotes archaea and bacteria. Diatoms are a type of plankton called phytoplankton, the most common of the plankton types. Diatoms also grow attached to benthic substrates, floating debris, and on macrophytes. They comprise an integral component of the periphyton community. Another classification divides plankton into eight types based on size: in this scheme, diatoms are classed as microalgae. Several systems for classifying the individual diatom species exist.


title: Diatom

text: Fossil evidence suggests that diatoms originated during or before the early Jurassic period, which was about 150 to 200 million years ago. The oldest fossil evidence for diatoms is a specimen of extant genus "Hemiaulus" in Late Jurassic aged amber from Thailand.


title: Diatom

text: Diatoms are used to monitor past and present environmental conditions, and are commonly used in studies of water quality. Diatomaceous earth (diatomite) is a collection of diatom shells found in the earth's crust. They are soft, silica-containing sedimentary rocks which are easily crumbled into a fine powder and typically have a particle size of 10 to 200 μm. Diatomaceous earth is used for a variety of purposes including for water filtration, as a mild abrasive, in cat litter, and as a dynamite stabilizer.


title: Diatom

text: Diatoms are protists that form massive annual spring and fall blooms in aquatic environments and are estimated to be responsible for about half of photosynthesis in the global oceans. This predictable annual bloom dynamic fuels higher trophic levels and initiates delivery of carbon into the deep ocean biome. Diatoms have complex life history strategies that are presumed to have contributed to their rapid genetic diversification into ~200,000 species that are distributed between the two major diatom groups: centrics and pennates.


title: Diatom

text: Diatoms are generally 2 to 200 micrometers in size, with a few larger species. Their yellowish-brown chloroplasts, the site of photosynthesis, are typical of heterokonts, having four cell membranes and containing pigments such as the carotenoid fucoxanthin. Individuals usually lack flagella, but they are present in male gametes of the centric diatoms and have the usual heterokont structure, including the hairs (mastigonemes) characteristic in other groups.


title: Diatom

text: Diatoms are often referred as "jewels of the sea" or "living opals" due to their optical properties. The biological function of this structural coloration is not clear, but it is speculated that it may be related to communication, camouflage, thermal exchange and/or UV protection.


title: Diatom

text: Diatoms build intricate hard but porous cell walls called frustules composed primarily of silica. This siliceous wall can be highly patterned with a variety of pores, ribs, minute spines, marginal ridges and elevations; all of which can be used to delineate genera and species.


title: Diatom

text: The cell itself consists of two halves, each containing an essentially flat plate, or valve, and marginal connecting, or girdle band. One half, the "hypotheca", is slightly smaller than the other half, the "epitheca". Diatom morphology varies. Although the shape of the cell is typically circular, some cells may be triangular, square, or elliptical. Their distinguishing feature is a hard mineral shell or frustule composed of opal (hydrated, polymerized silicic acid).


title: Diatom

text: Diatoms are divided into two groups that are distinguished by the shape of the frustule: the "centric diatoms" and the "pennate diatoms".


title: Diatom

text: Pennate diatoms are bilaterally symmetric. Each one of their valves have openings that are slits along the raphes and their shells are typically elongated parallel to these raphes. They generate cell movement through cytoplasm that streams along the raphes, always moving along solid surfaces.


title: Diatom

text: Centric diatoms are radially symmetric. They are composed of upper and lower valves – "epitheca" and "hypotheca" – each consisting of a valve and a girdle band that can easily slide underneath each other and expand to increase cell content over the diatoms progression. The cytoplasm of the centric diatom is located along the inner surface of the shell and provides a hollow lining around the large vacuole located in the center of the cell. This large, central vacuole is filled by a fluid known as "cell sap" which is similar to seawater but varies with specific ion content. The cytoplasmic layer is home to several organelles, like the chloroplasts and mitochondria. Before the centric diatom begins to expand, its nucleus is at the center of one of the valves and begins to move towards the center of the cytoplasmic layer before division is complete. Centric diatoms have a variety of shapes and sizes, depending on from which axis the shell extends, and if spines are present.


title: Diatom

text: Diatom cells are contained within a unique silica cell wall known as a frustule made up of two valves called thecae, that typically overlap one another. The biogenic silica composing the cell wall is synthesised intracellularly by the polymerisation of silicic acid monomers. This material is then extruded to the cell exterior and added to the wall. In most species, when a diatom divides to produce two daughter cells, each cell keeps one of the two-halves and grows a smaller half within it. As a result, after each division cycle, the average size of diatom cells in the population gets smaller. Once such cells reach a certain minimum size, rather than simply divide, they reverse this decline by forming an auxospore. This expands in size to give rise to a much larger cell, which then returns to size-diminishing divisions. Auxospore production is almost always linked to meiosis and sexual reproduction.


title: Diatom

text: The exact mechanism of transferring silica absorbed by the diatom to the cell wall is unknown. Much of the sequencing of diatom genes comes from the search for the mechanism of silica uptake and deposition in nano-scale patterns in the frustule. The most success in this area has come from two species, "Thalassiosira pseudonana", which has become the model species, as the whole genome was sequenced and methods for genetic control were established, and "Cylindrotheca fusiformis", in which the important silica deposition proteins silaffins were first discovered. Silaffins, sets of polycationic peptides, were found in "C. fusiformis" cell walls and can generate intricate silica structures. These structures demonstrated pores of sizes characteristic to diatom patterns. When "T. pseudonana" underwent genome analysis it was found that it encoded a urea cycle, including a higher number of polyamines than most genomes, as well as three distinct silica transport genes. In a phylogenetic study on silica transport genes from 8 diverse groups of diatoms, silica transport was found to generally group with species. This study also found structural differences between the silica transporters of pennate (bilateral symmetry) and centric (radial symmetry) diatoms. The sequences compared in this study were used to create a diverse background in order to identify residues that differentiate function in the silica deposition process. Additionally, the same study found that a number of the regions were conserved within species, likely the base structure of silica transport.


title: Diatom

text: These silica transport proteins are unique to diatoms, with no homologs found in other species, such as sponges or rice. The divergence of these silica transport genes is also indicative of the structure of the protein evolving from two repeated units composed of five membrane bound segments, which indicates either gene duplication or dimerization. The silica deposition that takes place from the membrane bound vesicle in diatoms has been hypothesized to be a result of the activity of silaffins and long chain polyamines. This Silica Deposition Vesicle (SDV) has been characterized as an acidic compartment fused with Golgi-derived vesicles. These two protein structures have been shown to create sheets of patterned silica in-vivo with irregular pores on the scale of diatom frustules. One hypothesis as to how these proteins work to create complex structure is that residues are conserved within the SDV's, which is unfortunately difficult to identify or observe due to the limited number of diverse sequences available. Though the exact mechanism of the highly uniform deposition of silica is as yet unknown, the "Thalassiosira pseudonana" genes linked to silaffins are being looked to as targets for genetic control of nanoscale silica deposition.


title: Diatom

text: The ability of diatoms to make silica-based cell walls has been the subject of fascination for centuries. It started with a microscopic observation by an anonymous English country nobleman in 1703, who observed an object that looked like a chain of regular parallelograms and debated whether it was just crystals of salt, or a plant. The viewer decided that it was a plant because the parallelograms didn't separate upon agitation, nor did they vary in appearance when dried or subjected to warm water (in an attempt to dissolve the "salt"). Unknowingly, the viewer's confusion captured the essence of diatoms—mineral utilizing plants. It is not clear when it was determined that diatom cell walls are made of silica, but in 1939 a seminal reference characterized the material as silicic acid in a "subcolloidal" state Identification of the main chemical component of the cell wall spurred investigations into how it was made. These investigations have involved, and been propelled by, diverse approaches including, microscopy, chemistry, biochemistry, material characterisation, molecular biology, 'omics, and transgenic approaches. The results from this work have given a better understanding of cell wall formation processes, establishing fundamental knowledge which can be used to create models that contextualise current findings and clarify how the process works.


title: Diatom

text: The process of building a mineral-based cell wall inside the cell, then exporting it outside, is a massive event that must involve large numbers of genes and their protein products. The act of building and exocytosing this large structural object in a short time period, synched with cell cycle progression, necessitates substantial physical movements within the cell as well as dedication of a significant proportion of the cell's biosynthetic capacities.


title: Diatom

text: The first characterisations of the biochemical processes and components involved in diatom silicification were made in the late 1990s. These were followed by insights into how higher order assembly of silica structures might occur. More recent reports describe the identification of novel components involved in higher order processes, the dynamics documented through real-time imaging, and the genetic manipulation of silica structure. The approaches established in these recent works provide practical avenues to not only identify the components involved in silica cell wall formation but to elucidate their interactions and spatio-temporal dynamics. This type of holistic understanding will be necessary to achieve a more complete understanding of cell wall synthesis.


title: Diatom

text: Most centric and araphid pennate diatoms are nonmotile, and their relatively dense cell walls cause them to readily sink. Planktonic forms in open water usually rely on turbulent mixing of the upper layers of the oceanic waters by the wind to keep them suspended in sunlit surface waters. Many planktonic diatoms have also evolved features that slow their sinking rate, such as spines or the ability to grow in colonial chains. These adaptations increase their surface area to volume ratio and drag, allowing them to stay suspended in the water column longer. Individual cells may regulate buoyancy via an ionic pump.


title: Diatom

text: Some pennate diatoms are capable of a type of locomotion called "gliding", which allows them to move across surfaces via adhesive mucilage secreted through a seamlike structure called the raphe. In order for a diatom cell to glide, it must have a solid substrate for the mucilage to adhere to.


title: Diatom

text: Cells are solitary or united into colonies of various kinds, which may be linked by siliceous structures; mucilage pads, stalks or tubes; amorphous masses of mucilage; or by threads of chitin (polysaccharide), which are secreted through strutted processes of the cell.


title: Diatom

text: Reproduction among these organisms is asexual by binary fission, during which the diatom divides into two parts, producing two "new" diatoms with identical genes. Each new organism receives one of the two frustules – one larger, the other smaller – possessed by the parent, which is now called the epitheca; and is used to construct a second, smaller frustule, the hypotheca. The diatom that received the larger frustule becomes the same size as its parent, but the diatom that received the smaller frustule remains smaller than its parent. This causes the average cell size of this diatom population to decrease. It has been observed, however, that certain taxa have the ability to divide without causing a reduction in cell size. Nonetheless, in order to restore the cell size of a diatom population for those that do endure size reduction, sexual reproduction and auxospore formation must occur.


title: Diatom

text: Vegetative cells of diatoms are diploid (2N) and so meiosis can take place, producing male and female gametes which then fuse to form the zygote. The zygote sheds its silica theca and grows into a large sphere covered by an organic membrane, the auxospore. A new diatom cell of maximum size, the initial cell, forms within the auxospore thus beginning a new generation. Resting spores may also be formed as a response to unfavourable environmental conditions with germination occurring when conditions improve.


title: Diatom

text: A defining characteristic of all diatoms is their restrictive and bipartite silica cell wall that causes them to progressively shrink during asexual cell division. At a critically small cell size and under certain conditions, auxosporulation restitutes cell size and prevents death. The entire lifecycles of only a few diatoms have been described and rarely have sexual events been captured in the environment.


title: Diatom

text: Diatoms are mostly non-motile; however, sperm found in some species can be flagellated, though motility is usually limited to a gliding motion. In centric diatoms, the small male gametes have one flagellum while the female gametes are large and non-motile (oogamous). Conversely, in pennate diatoms both gametes lack flagella (isogamous). Certain araphid species, that is pennate diatoms without a raphe (seam), have been documented as anisogamous and are, therefore, considered to represent a transitional stage between centric and raphid pennate diatoms, diatoms with a raphe.


title: Diatom

text: Certain species of bacteria in oceans and lakes can accelerate the rate of dissolution of silica in dead and living diatoms by using hydrolytic enzymes to break down the organic algal material.


title: Diatom

text: Diatoms are a widespread group and can be found in the oceans, in fresh water, in soils, and on damp surfaces. They are one of the dominant components of phytoplankton in nutrient-rich coastal waters and during oceanic spring blooms, since they can divide more rapidly than other groups of phytoplankton. Most live pelagically in open water, although some live as surface films at the water-sediment interface (benthic), or even under damp atmospheric conditions. They are especially important in oceans, where they contribute an estimated 45% of the total oceanic primary production of organic material. Spatial distribution of marine phytoplankton species is restricted both horizontally and vertically.


title: Diatom

text: Planktonic diatoms in freshwater and marine environments typically exhibit a "boom and bust" (or ""bloom" and bust") lifestyle. When conditions in the upper mixed layer (nutrients and light) are favourable (as at the spring), their competitive edge and rapid growth rate enables them to dominate phytoplankton communities ("boom" or "bloom"). As such they are often classed as opportunistic r-strategists ("i.e." those organisms whose ecology is defined by a high growth rate, "r").


title: Diatom

text: The freshwater diatom "Didymosphenia geminata", commonly known as "Didymo," causes severe environmental degradation in water-courses where it blooms, producing large quantities of a brown jelly-like material called "brown snot" or "rock snot". This diatom is native to Europe and is an invasive species both in the antipodes and in parts of North America. The problem is most frequently recorded from Australia and New Zealand.


title: Diatom

text: When conditions turn unfavourable, usually upon depletion of nutrients, diatom cells typically increase in sinking rate and exit the upper mixed layer ("bust"). This sinking is induced by either a loss of buoyancy control, the synthesis of mucilage that sticks diatoms cells together, or the production of heavy "resting spores". Sinking out of the upper mixed layer removes diatoms from conditions unfavourable to growth, including grazer populations and higher temperatures (which would otherwise increase cell metabolism). Cells reaching deeper water or the shallow seafloor can then rest until conditions become more favourable again. In the open ocean, many sinking cells are lost to the deep, but refuge populations can persist near the thermocline.


title: Diatom

text: Ultimately, diatom cells in these resting populations re-enter the upper mixed layer when vertical mixing entrains them. In most circumstances, this mixing also replenishes nutrients in the upper mixed layer, setting the scene for the next round of diatom blooms. In the open ocean (away from areas of continuous upwelling), this cycle of bloom, bust, then return to pre-bloom conditions typically occurs over an annual cycle, with diatoms only being prevalent during the spring and early summer. In some locations, however, an autumn bloom may occur, caused by the breakdown of summer stratification and the entrainment of nutrients while light levels are still sufficient for growth. Since vertical mixing is increasing, and light levels are falling as winter approaches, these blooms are smaller and shorter-lived than their spring equivalents.


title: Diatom

text: In the open ocean, the diatom (spring) bloom is typically ended by a shortage of silicon. Unlike other minerals, the requirement for silicon is unique to diatoms and it is not regenerated in the plankton ecosystem as efficiently as, for instance, nitrogen or phosphorus nutrients. This can be seen in maps of surface nutrient concentrations – as nutrients decline along gradients, silicon is usually the first to be exhausted (followed normally by nitrogen then phosphorus).


title: Diatom

text: Because of this bloom-and-bust cycle, diatoms are believed to play a disproportionately important role in the export of carbon from oceanic surface waters (see also the biological pump). Significantly, they also play a key role in the regulation of the biogeochemical cycle of silicon in the modern ocean.


title: Diatom

text: Diatoms are ecologically successful, and occur in virtually every environment that contains water – not only oceans, seas, lakes, and streams, but also soil and wetlands. The use of silicon by diatoms is believed by many researchers to be the key to this ecological success. Raven (1983) noted that, relative to organic cell walls, silica frustules require less energy to synthesize (approximately 8% of a comparable organic wall), potentially a significant saving on the overall cell energy budget. In a now classic study, Egge and Aksnes (1992) found that diatom dominance of mesocosm communities was directly related to the availability of silicic acid – when concentrations were greater than 2 μmol m, they found that diatoms typically represented more than 70% of the phytoplankton community. Other researchers have suggested that the biogenic silica in diatom cell walls acts as an effective pH buffering agent, facilitating the conversion of bicarbonate to dissolved CO (which is more readily assimilated). More generally, notwithstanding these possible advantages conferred by their use of silicon, diatoms typically have higher growth rates than other algae of the same corresponding size.


title: Diatom

text: Diatoms can be obtained from multiple sources. Marine diatoms can be collected by direct water sampling, and benthic forms can be secured by scraping barnacles, oyster and other shells. Diatoms are frequently present as a brown, slippery coating on submerged stones and sticks, and may be seen to "stream" with river current. The surface mud of a pond, ditch, or lagoon will almost always yield some diatoms. Living diatoms are often found clinging in great numbers to filamentous algae, or forming gelatinous masses on various submerged plants. "Cladophora" is frequently covered with "Cocconeis", an elliptically shaped diatom; "Vaucheria" is often covered with small forms. Since diatoms form an important part of the food of molluscs, tunicates, and fishes, the alimentary tracts of these animals often yield forms that are not easily secured in other ways. Diatoms can be made to emerge by filling a jar with water and mud, wrapping it in black paper and letting direct sunlight fall on the surface of the water. Within a day, the diatoms will come to the top in a scum and can be isolated.


title: Diatom

text: The diagram shows the major fluxes of silicon in the current ocean. Most biogenic silica in the ocean (silica produced by biological activity) comes from diatoms. Diatoms extract dissolved silicic acid from surface waters as they grow, and return it to the water column when they die. Inputs of silicon arrive from above via aeolian dust, from the coasts via rivers, and from below via seafloor sediment recycling, weathering, and hydrothermal activity.


title: Diatom

text: Although diatoms may have existed since the Triassic, the timing of their ascendancy and "take-over" of the silicon cycle occurred more recently. Prior to the Phanerozoic (before 544 Ma), it is believed that microbial or inorganic processes weakly regulated the ocean's silicon cycle. Subsequently, the cycle appears dominated (and more strongly regulated) by the radiolarians and siliceous sponges, the former as zooplankton, the latter as sedentary filter-feeders primarily on the continental shelves. Within the last 100 My, it is thought that the silicon cycle has come under even tighter control, and that this derives from the ecological ascendancy of the diatoms.


title: Diatom

text: However, the precise timing of the "take-over" remains unclear, and different authors have conflicting interpretations of the fossil record. Some evidence, such as the displacement of siliceous sponges from the shelves, suggests that this takeover began in the Cretaceous (146 Ma to 66 Ma), while evidence from radiolarians suggests "take-over" did not begin until the Cenozoic (66 Ma to present).


title: Diatom

text: The diagram depicts some mechanisms by which marine diatoms contribute to the biological carbon pump and influence the ocean carbon cycle. The anthropogenic CO emission to the atmosphere (mainly generated by fossil fuel burning and deforestation) is nearly 11 gigatonne carbon (GtC) per year, of which almost 2.5 GtC is taken up by the surface ocean. In surface seawater (pH 8.1–8.4), bicarbonate () and carbonate ions () constitute nearly 90 and <10% of dissolved inorganic carbon (DIC) respectively, while dissolved CO (CO aqueous) contributes <1%. Despite this low level of CO in the ocean and its slow diffusion rate in water, diatoms fix 10–20 GtC annually via photosynthesis thanks to their carbon dioxide concentrating mechanisms, allowing them to sustain marine food chains. In addition, 0.1–1% of this organic material produced in the euphotic layer sinks down as particles, thus transferring the surface carbon toward the deep ocean and sequestering atmospheric CO for thousands of years or longer. The remaining organic matter is remineralized through respiration. Thus, diatoms are one of the main players in this biological carbon pump, which is arguably the most important biological mechanism in the Earth System allowing CO to be removed from the carbon cycle for very long period.


title: Diatom

text: A feature of diatoms is the urea cycle, which links them evolutionarily to animals. In 2011, Allen et al. established that diatoms have a functioning urea cycle. This result was significant, since prior to this, the urea cycle was thought to have originated with the metazoans which appeared several hundreds of millions of years before the diatoms. Their study demonstrated that while diatoms and animals use the urea cycle for different ends, they are seen to be evolutionarily linked in such a way that animals and plants are not.


title: Diatom

text: While often overlooked in photosynthetic organisms, the mitochondria also play critical roles in energy balance. Two nitrogen-related pathways are relevant and they may also change under ammonium () nutrition compared with nitrate () nutrition. First, in diatoms, and likely some other algae, there is a urea cycle. The long-known function of the urea cycle in animals is to excrete excess nitrogen produced by amino acid catabolism; like photorespiration, the urea cycle had long been considered a waste pathway. However, in diatoms the urea cycle appears to play a role in exchange of nutrients between the mitochondria and the cytoplasm, and potentially the plastid and may help to regulate ammonium metabolism. Because of this cycle, marine diatoms, in contrast to chlorophytes, also have acquired a mitochondrial urea transporter and, in fact, based on bioinformatics, a complete mitochondrial GS-GOGAT cycle has been hypothesised.


title: Diatom

text: Diatoms are mainly photosynthetic; however a few are obligate heterotrophs and can live in the absence of light provided an appropriate organic carbon source is available.


title: Diatom

text: Photosynthetic diatoms that find themselves in an environment absent of oxygen and/or sunlight can switch to anaerobic respiration known as nitrate respiration (DNRA), and stay dormant for up till months and decades.


title: Diatom

text: Major pigments of diatoms are chlorophylls a and c, beta-carotene, fucoxanthin, diatoxanthin and diadinoxanthin.


title: Diatom

text: Diatoms belong to a large group of protists, many of which contain plastids rich in chlorophylls a and c. The group has been variously referred to as heterokonts, chrysophytes, chromists or stramenopiles. Many are autotrophs such as golden algae and kelp; and heterotrophs such as water moulds, opalinids, and actinophryid heliozoa. The classification of this area of protists is still unsettled. In terms of rank, they have been treated as a division, phylum, kingdom, or something intermediate to those. Consequently, diatoms are ranked anywhere from a class, usually called Diatomophyceae or Bacillariophyceae, to a division (=phylum), usually called Bacillariophyta, with corresponding changes in the ranks of their subgroups.


title: Diatom

text: An estimated 20,000 extant diatom species are believed to exist, of which around 12,000 have been named to date according to Guiry, 2012 (other sources give a wider range of estimates). Around 1,000–1,300 diatom genera have been described, both extant and fossil, of which some 250–300 exist only as fossils.


title: Diatom

text: For many years the diatoms—treated either as a class (Bacillariophyceae) or a phylum (Bacillariophyta)—were divided into just 2 orders, corresponding to the centric and the pennate diatoms (Centrales and Pennales). This classification was extensively overhauled by Round, Crawford and Mann in 1990 who treated the diatoms at a higher rank (division, corresponding to phylum in zoological classification), and promoted the major classification units to classes, maintaining the centric diatoms as a single class Coscinodiscophyceae, but splitting the former pennate diatoms into 2 separate classes, Fragilariophyceae and Bacillariophyceae (the latter older name retained but with an emended definition), between them encompassing 45 orders, the majority of them new.


title: Diatom

text: Today (writing at mid 2020) it is recognised that the 1990 system of Round et al. is in need of revision with the advent of newer molecular work, however the best system to replace it is unclear, and current systems in widespread use such as AlgaeBase, the World Register of Marine Species and its contributing database DiatomBase, and the system for "all life" represented in Ruggiero et al., 2015, all retain the Round et al. treatment as their basis, albeit with diatoms as a whole treated as a class rather than division/phylum, and Round et al.'s classes reduced to subclasses, for better agreement with the treatment of phylogenetically adjacent groups and their containing taxa. (For references refer the individual sections below).


title: Diatom

text: One proposal, by Linda Medlin and co-workers commencing in 2004, is for some of the centric diatom orders considered more closely related to the pennates to be split off as a new class, Mediophyceae, itself more closely aligned with the pennate diatoms than the remaining centrics. This hypothesis—later designated the Coscinodiscophyceae-Mediophyceae-Bacillariophyceae, or Coscinodiscophyceae+(Mediophyceae+Bacillariophyceae) (CMB) hypothesis—has been accepted by D.G. Mann among others, who uses it as the basis for the classification of diatoms as presented in Adl. et al.'s series of syntheses (2005, 2012, 2019), and also in the Bacillariophyta chapter of the 2017 "Handbook of the Protists" edited by Archibald et al., with some modifications reflecting the apparent non-monophyly of Medlin et al. original "Coscinodiscophyceae". Meanwhile, a group led by E.C. Theriot favours a different hypothesis of phylogeny, which has been termed the structural gradation hypothesis (SGH) and does not recognise the Mediophyceae as a monophyletic group, while another analysis, that of Parks et al., 2018, finds that the radial centric diatoms (Medlin et al.'s Coscinodiscophyceae) are not monophyletic, but supports the monophyly of Mediophyceae minus "Attheya", which is an anomalous genus. Discussion of the relative merits of these conflicting schemes continues by the various parties involved.


title: Diatom

text: In 2019, Adl "et al." presented the following classification of diatoms, while noting: "This revision reflects numerous advances in the phylogeny of the diatoms over the last decade. Due to our poor taxon sampling outside of the Mediophyceae and pennate diatoms, and the known and anticipated diversity of all diatoms, many clades appear at a high classification level (and the higher level classification is rather flat)." This classification treats diatoms as a phylum (Diatomeae/Bacillariophyta), accepts the class Mediophyceae of Medlin and co-workers, introduces new subphyla and classes for a number of otherwise isolated genera, and re-ranks a number of previously established taxa as subclasses, but does not list orders or families. Inferred ranks have been added for clarity (Adl. et al. do not use ranks, but the intended ones in this portion of the classification are apparent from the choice of endings used, within the system of botanical nomenclature employed).


title: Diatom

text: Three diatom species were sent to the International Space Station, including the huge (6 mm length) diatoms of Antarctica and the exclusive colonial diatom, "Bacillaria paradoxa". The cells of "Bacillaria" moved next to each other in partial but opposite synchrony by a microfluidics method.


title: Diatom

text: Heterokont chloroplasts appear to derive from those of red algae, rather than directly from prokaryotes as occurred in plants. This suggests they had a more recent origin than many other algae. However, fossil evidence is scant, and only with the evolution of the diatoms themselves do the heterokonts make a serious impression on the fossil record.


title: Diatom

text: The earliest known fossil diatoms date from the early Jurassic (~185 Ma ago), although the molecular clock and sedimentary evidence suggests an earlier origin. It has been suggested that their origin may be related to the end-Permian mass extinction (~250 Ma), after which many marine niches were opened. The gap between this event and the time that fossil diatoms first appear may indicate a period when diatoms were unsilicified and their evolution was cryptic. Since the advent of silicification, diatoms have made a significant impression on the fossil record, with major fossil deposits found as far back as the early Cretaceous, and with some rocks such as diatomaceous earth, being composed almost entirely of them.


title: Diatom

text: The expansion of grassland biomes and the evolutionary radiation of grasses during the Miocene is believed to have increased the flux of soluble silicon to the oceans, and it has been argued that this promoted the diatoms during the Cenozoic era. Recent work suggests that diatom success is decoupled from the evolution of grasses, although both diatom and grassland diversity increased strongly from the middle Miocene.


title: Diatom

text: Diatom diversity over the Cenozoic has been very sensitive to global temperature, particularly to the equator-pole temperature gradient. Warmer oceans, particularly warmer polar regions, have in the past been shown to have had substantially lower diatom diversity. Future warm oceans with enhanced polar warming, as projected in global-warming scenarios, could thus in theory result in a significant loss of diatom diversity, although from current knowledge it is impossible to say if this would occur rapidly or only over many tens of thousands of years.


title: Diatom

text: The fossil record of diatoms has largely been established through the recovery of their siliceous frustules in marine and non-marine sediments. Although diatoms have both a marine and non-marine stratigraphic record, diatom biostratigraphy, which is based on time-constrained evolutionary originations and extinctions of unique taxa, is only well developed and widely applicable in marine systems. The duration of diatom species ranges have been documented through the study of ocean cores and rock sequences exposed on land. Where diatom biozones are well established and calibrated to the geomagnetic polarity time scale (e.g., Southern Ocean, North Pacific, eastern equatorial Pacific), diatom-based age estimates may be resolved to within <100,000 years, although typical age resolution for Cenozoic diatom assemblages is several hundred thousand years.


title: Diatom

text: Diatoms preserved in lake sediments are widely used for paleoenvironmental reconstructions of Quaternary climate, especially for closed-basin lakes which experience fluctuations in water depth and salinity.


title: Diatom

text: When diatoms die their shells (frustules) can settle on the seafloor and become microfossils. Over time, these microfossils become buried as opal deposits in the marine sediment. Paleoclimatology is the study of past climates. Proxy data is used in order to relate elements collected in modern-day sedimentary samples to climatic and oceanic conditions in the past. Paleoclimate proxies refer to preserved or fossilized physical markers which serve as substitutes for direct meteorological or ocean measurements. An example of proxies is the use of diatom isotope records of δ13C, δ18O, δ30Si (δ13C, δ18O, and δ30Si). In 2015, Swann and Snelling used these isotope records to document historic changes in the photic zone conditions of the north-west Pacific Ocean, including nutrient supply and the efficiency of the soft-tissue biological pump, from the modern day back to marine isotope stage 5e, which coincides with the last interglacial period. Peaks in opal productivity in the marine isotope stage are associated with the breakdown of the regional halocline stratification and increased nutrient supply to the photic zone.


title: Diatom

text: The initial development of the halocline and stratified water column has been attributed to the onset of major Northern Hemisphere glaciation at 2.73 Ma, which increased the flux of freshwater to the region, via increased monsoonal rainfall and/or glacial meltwater, and sea surface temperatures. The decrease of abyssal water upwelling associated with this may have contributed to the establishment of globally cooler conditions and the expansion of glaciers across the Northern Hemisphere from 2.73 Ma. While the halocline appears to have prevailed through the late Pliocene and early Quaternary glacial–interglacial cycles, other studies have shown that the stratification boundary may have broken down in the late Quaternary at glacial terminations and during the early part of interglacials.


title: Diatom

text: The Cretaceous record of diatoms is limited, but recent studies reveal a progressive diversification of diatom types. The Cretaceous–Paleogene extinction event, which in the oceans dramatically affected organisms with calcareous skeletons, appears to have had relatively little impact on diatom evolution.


title: Diatom

text: Although no mass extinctions of marine diatoms have been observed during the Cenozoic, times of relatively rapid evolutionary turnover in marine diatom species assemblages occurred near the Paleocene–Eocene boundary, and at the Eocene–Oligocene boundary. Further turnover of assemblages took place at various times between the middle Miocene and late Pliocene, in response to progressive cooling of polar regions and the development of more endemic diatom assemblages.


title: Diatom

text: A global trend toward more delicate diatom frustules has been noted from the Oligocene to the Quaternary. This coincides with an increasingly more vigorous circulation of the ocean's surface and deep waters brought about by increasing latitudinal thermal gradients at the onset of major ice sheet expansion on Antarctica and progressive cooling through the Neogene and Quaternary towards a bipolar glaciated world. This caused diatoms to take in less silica for the formation of their frustules. Increased mixing of the oceans renews silica and other nutrients necessary for diatom growth in surface waters, especially in regions of coastal and oceanic upwelling.


title: Diatom

text: In 2002, the first insights into the properties of the "Phaeodactylum tricornutum" gene repertoire were described using 1,000 expressed sequence tags (ESTs). Subsequently, the number of ESTs was extended to 12,000 and the diatom EST database was constructed for functional analyses. These sequences have been used to make a comparative analysis between "P. tricornutum" and the putative complete proteomes from the green alga "Chlamydomonas reinhardtii", the red alga "Cyanidioschyzon merolae", and the diatom "Thalassiosira pseudonana". The diatom EST database now consists of over 200,000 ESTs from "P. tricornutum" (16 libraries) and "T. pseudonana" (7 libraries) cells grown in a range of different conditions, many of which correspond to different abiotic stresses.


title: Diatom

text: In 2004, the entire genome of the centric diatom, "Thalassiosira pseudonana" (32.4 Mb) was sequenced, followed in 2008 with the sequencing of the pennate diatom, "Phaeodactylum tricornutum" (27.4 Mb). Comparisons of the two reveal that the "P. tricornutum" genome includes fewer genes (10,402 opposed to 11,776) than "T. pseudonana"; no major synteny (gene order) could be detected between the two genomes. "T. pseudonana" genes show an average of ~1.52 introns per gene as opposed to 0.79 in "P. tricornutum", suggesting recent widespread intron gain in the centric diatom. Despite relatively recent evolutionary divergence (90 million years), the extent of molecular divergence between centrics and pennates indicates rapid evolutionary rates within the Bacillariophyceae compared to other eukaryotic groups. Comparative genomics also established that a specific class of transposable elements, the Diatom Copia-like retrotransposons (or CoDis), has been significantly amplified in the "P. tricornutum" genome with respect to "T. pseudonana", constituting 5.8 and 1% of the respective genomes.


title: Diatom

text: Diatom genomics brought much information about the extent and dynamics of the endosymbiotic gene transfer (EGT) process. Comparison of the "T. pseudonana" proteins with homologs in other organisms suggested that hundreds have their closest homologs in the Plantae lineage. EGT towards diatom genomes can be illustrated by the fact that the "T. pseudonana" genome encodes six proteins which are most closely related to genes encoded by the "Guillardia theta" (cryptomonad) nucleomorph genome. Four of these genes are also found in red algal plastid genomes, thus demonstrating successive EGT from red algal plastid to red algal nucleus (nucleomorph) to heterokont host nucleus. More recent phylogenomic analyses of diatom proteomes provided evidence for a prasinophyte-like endosymbiont in the common ancestor of chromalveolates as supported by the fact the 70% of diatom genes of Plantae origin are of green lineage provenance and that such genes are also found in the genome of other stramenopiles. Therefore, it was proposed that chromalveolates are the product of serial secondary endosymbiosis first with a green algae, followed by a second one with a red algae that conserved the genomic footprints of the previous but displaced the green plastid. However, phylogenomic analyses of diatom proteomes and chromalveolate evolutionary history will likely take advantage of complementary genomic data from under-sequenced lineages such as red algae.


title: Diatom

text: In addition to EGT, horizontal gene transfer (HGT) can occur independently of an endosymbiotic event. The publication of the "P. tricornutum" genome reported that at least 587 "P. tricornutum" genes appear to be most closely related to bacterial genes, accounting for more than 5% of the "P. tricornutum" proteome. About half of these are also found in the "T. pseudonana" genome, attesting their ancient incorporation in the diatom lineage.


title: Diatom

text: To understand the biological mechanisms which underlie the great importance of diatoms in geochemical cycles, scientists have used the "Phaeodactylum tricornutum" and "Thalassiosira spp." species as model organisms since the 90's.


title: Diatom

text: Few molecular biology tools are currently available to generate mutants or transgenic lines : plasmids containing transgenes are inserted into the cells using the biolistic method or transkingdom bacterial conjugation (with 10 and 10 yield respectively), and other classical transfection methods such as electroporation or use of PEG have been reported to provide results with lower efficiencies.


title: Diatom

text: Transfected plasmids can be either randomly integrated into the diatom's chromosomes or maintained as stable circular episomes (thanks to the CEN6-ARSH4-HIS3 yeast centromeric sequence). The phleomycin/zeocin resistance gene Sh Ble is commonly used as a selection marker, and various transgenes have been successfully introduced and expressed in diatoms with stable transmissions through generations, or with the possibility to remove it.


title: Diatom

text: Furthermore, these systems now allow the use of the CRISPR-Cas genome edition tool, leading to a fast production of functional knock-out mutants and a more accurate comprehension of the diatoms' cellular processes.


title: Diatom

text: Decomposition and decay of diatoms leads to organic and inorganic (in the form of silicates) sediment, the inorganic component of which can lead to a method of analyzing past marine environments by corings of ocean floors or bay muds, since the inorganic matter is embedded in deposition of clays and silts and forms a permanent geological record of such marine strata (see siliceous ooze).


title: Diatom

text: Diatoms, and their shells (frustules) as diatomite or diatomaceous earth, are important industrial resources used for fine polishing and liquid filtration. The complex structure of their microscopic shells has been proposed as a material for nanotechnology.


title: Diatom

text: Diatomite is considered to be a natural nano material and has many uses and applications such as: production of various ceramic products, construction ceramics, refractory ceramics, special oxide ceramics, for production of humidity control materials, used as filtration material, material in the cement production industry, initial material for production of prolonged-release drug carriers, absorption material in an industrial scale, production of porous ceramics, glass industry, used as catalyst support, as a filler in plastics and paints, purification of industrial waters, pesticide holder, as well as for improving the physical and chemical characteristics of certain soils, and other uses.


title: Diatom

text: The deposition of silica by diatoms may also prove to be of utility to nanotechnology. Diatom cells repeatedly and reliably manufacture valves of various shapes and sizes, potentially allowing diatoms to manufacture micro- or nano-scale structures which may be of use in a range of devices, including: optical systems; semiconductor nanolithography; and even vehicles for drug delivery. With an appropriate artificial selection procedure, diatoms that produce valves of particular shapes and sizes might be evolved for cultivation in chemostat cultures to mass-produce nanoscale components. It has also been proposed that diatoms could be used as a component of solar cells by substituting photosensitive titanium dioxide for the silicon dioxide that diatoms normally use to create their cell walls. Diatom biofuel producing solar panels have also been proposed.


title: Diatom

text: The main goal of diatom analysis in forensics is to differentiate a death by submersion from a post-mortem immersion of a body in water. Laboratory tests may reveal the presence of diatoms in the body. Since the silica-based skeletons of diatoms do not readily decay, they can sometimes be detected even in heavily decomposed bodies. As they do not occur naturally in the body, if laboratory tests show diatoms in the corpse that are of the same species found in the water where the body was recovered, then it may be good evidence of drowning as the cause of death. The blend of diatom species found in a corpse may be the same or different from the surrounding water, indicating whether the victim drowned in the same site in which the body was found.


title: Diatom

text: The first illustrations of diatoms are found in an article from 1703 in Transactions of the Royal Society showing unmistakable drawings of "Tabellaria". Although the publication was authored by an unnamed English gentleman, there is recent evidence that he was Charles King of Staffordshire. It is only 80 years later that we find the first formally identified diatom, the colonial "Bacillaria paxillifera", discovered and described in 1783 by Danish naturalist Otto Friedrich Müller. Like many others after him, he wrongly thought that it was an animal due to its ability to move. Even Charles Darwin saw diatom remains in dust whilst in the Cape Verde Islands, although he was not sure what they were. It was only later that they were identified for him as siliceous polygastrics. The infusoria that Darwin later noted in the face paint of Fueguinos, native inhabitants of Tierra del Fuego in the southern end of South America, were later identified in the same way. During his lifetime, the siliceous polygastrics were clarified as belonging to the "Diatomaceae", and Darwin struggled to understand the reasons underpinning their beauty. He exchanged opinions with the noted cryptogamist G. H. K. Thwaites on the topic. In the fourth edition of On the Origin of Species he stated that ""Few objects are more beautiful than the minute siliceous cases of the diatomaceae: were these created that they might be examined and admired under the high powers of the microscope""? and reasoned that their exquisite morphologies must have functional underpinnings rather than having been created purely for humans to admire.


title: Looking for Alaska

text: Looking for Alaska is American author John Green‘s debut novel, published in March 2005 by Dutton Juvenile. Based on his time at Indian Springs School, Green wrote the novel as a result of his desire to create meaningful young adult fiction. The characters and events of the plot are grounded in Green's life, while the story itself is fictional.