In the ancientAttic number system (Herodianic or acrophonic numbers), the number 100 was represented by "Η", because it was the initial ofΗΕΚΑΤΟΝ, the ancient spelling ofἑκατόν = "one hundred". In the later system of (Classical)Greek numerals eta represents 8.
Eta (heta) in the function of/h/ on theostrakon ofMegacles, son of Hippocrates, 487 BC. Inscription:ΜΕΓΑΚLES HIΠΠΟΚRATOS. On display in the Ancient Agora Museum in Athens, housed in theStoa of Attalus.Eta in the function of/h/ on an Atticred-figuredcalyx-krater, 515 BC. Amongst the depicted figures areHermes andHypnos. Inscriptions:ΗΕΡΜΕΣ –ΗΥΠΝΟΣ.
The letter shape 'H' was originally used in most Greek dialects to represent thevoiceless glottal fricative,[h]. In this function, it was borrowed in the 8th century BC by theEtruscan and other Old Italic alphabets, which were based on theEuboean form of the Greek alphabet. This also gave rise to the Latin alphabet with its letterH.
Other regional variants of the Greek alphabet (epichoric alphabets), in dialects that still preserved the sound[h], employed various glyph shapes for consonantalheta side by side with the new vocaliceta for some time. In the southern Italian colonies ofHeraclea andTarentum, the letter shape was reduced to a "half-heta" lacking the right vertical stem (Ͱ). From this sign later developed the sign forrough breathing orspiritus asper, which brought back the marking of the[h] sound into the standardized post-classical (polytonic) orthography.[2]Dionysius Thrax in the second century BC records that the letter name was still pronouncedheta (ἥτα), correctly explaining this irregularity by stating "in the old days the letter Η served to stand for the rough breathing, as it still does with the Romans."[3]
In the EastIonic dialect, however, the sound[h] disappeared by the sixth century BC, and the letter was re-used initially to represent a development of a longopen front unrounded vowel,[aː], which later merged in East Ionic with the longopen-mid front unrounded vowel,[ɛː] instead.[4] In 403 BC,Athens took over the Ionian spelling system and with it the vocalic use of H (even though it still also had the[h] sound itself at that time). This later became the standard orthography in all of Greece.
During the time of post-classicalKoiné Greek, the[ɛː] sound represented by eta wasraised and merged with several other formerly distinct vowels, a phenomenon callediotacism oritacism, after the new pronunciation of the letter name asita instead ofeta.
Itacism is continued intoModern Greek, where the letter name is pronounced[ˈita] and represents theclose front unrounded vowel,[i]. It shares this function with several other letters (ι,υ) anddigraphs (ει, οι, υι), which are all pronounced alike.
Inchemistry, the letter H as symbol ofenthalpy sometimes is said to be a Greek eta, but since enthalpy comes from ἐνθάλπος, which begins in a smooth breathing and epsilon, it is more likely a LatinH for 'heat'.
In information theory the uppercase Greek letter Η is used to represent the concept ofentropy of a discrete random variable.
Chemistry, thehapticity, or the number of atoms of a ligand attached to one coordination site of the metal in acoordination compound. For example, anallyl group can coordinate topalladium in the η¹ mode (only one atom of an allyl group attached to palladium) or the η³ mode (3 atoms attached to palladium).
Statistics,η2 is the "partial regression coefficient".η is the symbol for the linear predictor of ageneralized linear model, and can also be used to denote the median of a population, or thresholding parameter in Sparse Partial Least Squares regression.
Electronics, η stands for theideality factor of abipolar transistor, and has a value close to 1.000. It appears in contexts where the transistor is used as a temperature sensing device, e.g. the thermal "diode" transistor that is embedded within a computer's microprocessor.[16]
U+03B7ηGREEK SMALL LETTER ETA (η) (\eta in TeX)
U+2C8EⲎCOPTIC CAPITAL LETTER HATE
U+2C8FⲏCOPTIC SMALL LETTER HATE
These characters are used only as mathematical symbols. Stylized Greek text should be encoded using the normal Greek letters, with markup and formatting to indicate text style:
U+1D6AE𝚮MATHEMATICAL BOLD CAPITAL ETA
U+1D6C8𝛈MATHEMATICAL BOLD SMALL ETA
U+1D6E8𝛨MATHEMATICAL ITALIC CAPITAL ETA
U+1D702𝜂MATHEMATICAL ITALIC SMALL ETA
U+1D722𝜢MATHEMATICAL BOLD ITALIC CAPITAL ETA
U+1D73C𝜼MATHEMATICAL BOLD ITALIC SMALL ETA
U+1D75C𝝜MATHEMATICAL SANS-SERIF BOLD CAPITAL ETA
U+1D776𝝶MATHEMATICAL SANS-SERIF BOLD SMALL ETA
U+1D796𝞖MATHEMATICAL SANS-SERIF BOLD ITALIC CAPITAL ETA
U+1D7B0𝞰MATHEMATICAL SANS-SERIF BOLD ITALIC SMALL ETA
^Feidt, Michel, ed. (2020).Carnot Cycle and Heat Engine Fundamentals and Applications. Basel, Switzerland: MDPI - Multidisciplinary Digital Publishing Institute. p. 3.ISBN978-3-03928-845-8.Without any doubt, the main result was the so-called CA-efficiencyη =…
^Hansen, Jean-Pierre; McDonald, Ian Ranald (2013).Theory of simple liquids: with applications to soft matter (4th ed.). Amstersdam: Elsevier/AP. p. 102.ISBN978-0-12-387032-2.… and the system reduces to that of two, identical, pure fluids confined to the same volume at a packing fractionη.
^Larkoski, Andrew J. (2019).Elementary particle physics: an intuitive introduction. Cambridge New York: Cambridge university press. p. 118.ISBN978-1-108-49698-8.Pseudorapidityη is zero for central collisions, directly perpendicular to the beam at the interaction point.
^Huterer, Dragan (2023).A course in cosmology: from theory to practice. Cambridge: Cambridge university press. p. 28.ISBN978-1-316-51359-0.A very closely related quantity isconformal timeη (sometimes labeled asτ, and sometimes called coordinate time),...
^Grupen, Claus (2020).Astroparticle physics. Undergraduate texts in physics. Tilo Stroh (Second ed.). Cham: Springer. p. 209.ISBN978-3-030-27341-5.Further, the baryon-number-to-photon ratio can be defined: η =...
^Rybicki, George B.; Lightman, Alan P. (1979).Radiative processes in astrophysics. A Wiley-Interscience publication. New York: Wiley. p. 123.ISBN978-0-471-04815-2.
^Bronshtein, I.; Bronshtein, I. N. (2015).Handbook of Mathematics. Berlin: Springer Berlin Heidelberg. p. 589.ISBN978-3-662-46220-1.Weierstrass eta-function
^Böhm, Gabriella (2019).Hopf algebras and their generalizations from a category theoretical point of view. Lecture notes in mathematics (Corrected publication ed.). Cham, Switzerland: Springer. p. 18.ISBN978-3-319-98136-9.Consider a monadt on a categoryA with unitη and multiplicationμ.
^Haber, Peter; Lampoltshammer, Thomas; Leopold, Helmut; Mayr, Manfred, eds. (2022).Data Science – Analytics and Applications: Proceedings of the 4th International Data Science Conference – iDSC2021. Springer eBook Collection (1st ed. 2022 ed.). Wiesbaden: Springer Fachmedien Wiesbaden. p. 28.ISBN978-3-658-36294-2.We searched for the learning rate η with fixed fraction of participating clients C,…
^Shur, Michael; World Scientific (Firm), eds. (1996).Compound semiconductor electronics: the age of maturity. Selected topics in electronics and systems. Singapore River Edge, N.J: World Scientific Pub. Co. p. 115.ISBN978-981-02-2325-0.The ideality factor of the base current, ηB,
^Papaēliu, Kōstas, ed. (2021).Springer Handbook of Power Systems. Singapore: Springer. p. 126.ISBN978-981-329-937-5.
^Riegel, Christopher A. (1992).Fundamentals of atmospheric dynamics and thermodynamics. Singapore: World Scientific. p. 359.ISBN978-9971-978-86-0.The vertical component of the absolute curl, which we shall simply call theabsolute vorticity, is η =...
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