Eta
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Eta (
In the ancient Attic number system (Herodianic or acrophonic numbers), the number 100 was represented by "Η", because it was the initial of ΗΕΚΑΤΟΝ, the ancient spelling of ἑκατόν = "one hundred". In the later system of (Classical) Greek numerals eta represents 8.
Eta was derived from the
History
Consonant h
The letter shape 'H' was originally used in most Greek dialects to represent the
Other regional variants of the Greek alphabet (
Long e
In the East
Itacism
During the time of post-classical
Itacism is continued into Modern Greek, where the letter name is pronounced [ˈita] and represents the close front unrounded vowel, [i]. It shares this function with several other letters (ι, υ) and digraphs (ει, οι), which are all pronounced alike.
Cyrillic script
Eta was also borrowed with the sound value of [i] into the Cyrillic script, where it gave rise to the Cyrillic letter И.
Uses
Letter
In
Symbol
Upper case
The uppercase letter Η is used as a symbol in textual criticism for the Alexandrian text-type (from Hesychius, its once-supposed editor).
In chemistry, the letter H as symbol of enthalpy 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 Latin H for 'heat'.
In information theory the uppercase Greek letter Η is used to represent the concept of entropy of a discrete random variable.
Lower case
The lowercase letter η is used as a symbol in:
- Thermodynamics, the efficiency of a Carnot heat engine, or packing fraction.
- Aeronautics, the propulsive efficiency, or percentage of chemical energy converted to kinetic energy.
- coordination compound. For example, an allyl group can coordinate to palladiumin the η¹ mode (only one atom of an allyl group attached to palladium) or the η³ mode (3 atoms attached to palladium).
- electromagnetic impedance of a medium, or the quantum efficiencyof detectors.
- η mesons.
- Experimental particle physics, η stands for pseudorapidity.
- conformal time; dt = adη.
- Cosmology, baryon–photon ratio.
- Relativity and Quantum field theory (physics), η (with two subscripts) represents the metric tensor of Minkowski space (flat spacetime).
- Statistics, η2 is the "partial regression coefficient". η is the symbol for the linear predictor of a generalized linear model, and can also be used to denote the median of a population, or thresholding parameter in Sparse Partial Least Squares regression.
- Economics, η is the elasticity.
- Astronomy, the seventh-brightest (usually) star in a constellation. See Bayer designation.
- Mathematics, η-reduction in lambda calculus.
- Mathematics, the Weierstrass eta function.
- In category theory, the unit of an adjunction or monad is usually denoted η.
- eukaryotesand implicated in Translesion Synthesis.
- Neural network backpropagation, and stochastic gradient descent more generally, η stands for the learning rate.
- Telecommunications, η stands for efficiency
- bipolar 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.
- Power electronics, η stands for the efficiency of a power supply, defined as the output power divided by the input power.
- Atmospheric science, η represents absolute atmospheric vorticity.
- Rheology, η represents viscosity.
- Oceanography, η is the measurement (usually in metres) of sea-level height above or below the mean sea-level at that same location.
Character encodings
Greek Eta, Coptic Ayta
Preview | Η | η | Ͱ | ͱ | Ⲏ | ⲏ | ||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
Unicode name | GREEK CAPITAL LETTER ETA | GREEK SMALL LETTER ETA | GREEK CAPITAL LETTER HETA | GREEK SMALL LETTER HETA | COPTIC CAPITAL LETTER AYTA | COPTIC SMALL LETTER AYTA | ||||||
Encodings | decimal | hex | dec | hex | dec | hex | dec | hex | dec | hex | dec | hex |
Unicode | 919 | U+0397 | 951 | U+03B7 | 880 | U+0370 | 881 | U+0371 | 11406 | U+2C8E | 11407 | U+2C8F |
UTF-8 | 206 151 | CE 97 | 206 183 | CE B7 | 205 176 | CD B0 | 205 177 | CD B1 | 226 178 142 | E2 B2 8E | 226 178 143 | E2 B2 8F |
Numeric character reference | Η |
Η |
η |
η |
Ͱ |
Ͱ |
ͱ |
ͱ |
Ⲏ |
Ⲏ |
ⲏ |
ⲏ |
Named character reference | Η | η | ||||||||||
DOS Greek | 134 | 86 | 158 | 9E | ||||||||
DOS Greek-2 | 170 | AA | 225 | E1 | ||||||||
Windows 1253 | 199 | C7 | 231 | E7 | ||||||||
TeX | \eta |
Mathematical Eta
Preview | 𝚮 | 𝛈 | 𝛨 | 𝜂 | 𝜢 | 𝜼 | ||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
Unicode name | MATHEMATICAL BOLD CAPITAL ETA |
MATHEMATICAL BOLD SMALL ETA |
MATHEMATICAL ITALIC CAPITAL ETA |
MATHEMATICAL ITALIC SMALL ETA |
MATHEMATICAL BOLD ITALIC CAPITAL ETA |
MATHEMATICAL BOLD ITALIC SMALL ETA | ||||||
Encodings | decimal | hex | dec | hex | dec | hex | dec | hex | dec | hex | dec | hex |
Unicode | 120494 | U+1D6AE | 120520 | U+1D6C8 | 120552 | U+1D6E8 | 120578 | U+1D702 | 120610 | U+1D722 | 120636 | U+1D73C |
UTF-8 | 240 157 154 174 | F0 9D 9A AE | 240 157 155 136 | F0 9D 9B 88 | 240 157 155 168 | F0 9D 9B A8 | 240 157 156 130 | F0 9D 9C 82 | 240 157 156 162 | F0 9D 9C A2 | 240 157 156 188 | F0 9D 9C BC |
UTF-16 | 55349 57006 | D835 DEAE | 55349 57032 | D835 DEC8 | 55349 57064 | D835 DEE8 | 55349 57090 | D835 DF02 | 55349 57122 | D835 DF22 | 55349 57148 | D835 DF3C |
Numeric character reference | 𝚮 |
𝚮 |
𝛈 |
𝛈 |
𝛨 |
𝛨 |
𝜂 |
𝜂 |
𝜢 |
𝜢 |
𝜼 |
𝜼 |
Preview | 𝝜 | 𝝶 | 𝞖 | 𝞰 | ||||
---|---|---|---|---|---|---|---|---|
Unicode name | MATHEMATICAL SANS-SERIF BOLD CAPITAL ETA |
MATHEMATICAL SANS-SERIF BOLD SMALL ETA |
MATHEMATICAL SANS-SERIF BOLD ITALIC CAPITAL ETA |
MATHEMATICAL SANS-SERIF BOLD ITALIC SMALL ETA | ||||
Encodings | decimal | hex | dec | hex | dec | hex | dec | hex |
Unicode | 120668 | U+1D75C | 120694 | U+1D776 | 120726 | U+1D796 | 120752 | U+1D7B0 |
UTF-8 | 240 157 157 156 | F0 9D 9D 9C | 240 157 157 182 | F0 9D 9D B6 | 240 157 158 150 | F0 9D 9E 96 | 240 157 158 176 | F0 9D 9E B0 |
UTF-16 | 55349 57180 | D835 DF5C | 55349 57206 | D835 DF76 | 55349 57238 | D835 DF96 | 55349 57264 | D835 DFB0 |
Numeric character reference | 𝝜 |
𝝜 |
𝝶 |
𝝶 |
𝞖 |
𝞖 |
𝞰 |
𝞰 |
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.
See also
References
- ^ "eta". Oxford English Dictionary (Online ed.). Oxford University Press. (Subscription or participating institution membership required.)
- ^ Nick Nicholas (2003), "Greek /h/" Archived 2013-09-01 at archive.today
- ^ παρὰ τοῖς ἀρχαίοις ὁ τύπος τοῦ Η ἐν τύπῳ δασείας ἔκειτο, ὥσπερ καὶ νῦν <παρὰ> τοῖς Ῥωμαίοις Alfredus Hilgard (ed), "In artis Dionysianae §6" in Grammatici Graeci. Scholia in Dionysii Thracis Artem Grammaticam (1901), p. 486.
- ^
Sihler, Andrew L. (1995). New Comparative Grammar of Greek and Latin (illustrated ed.). New York: Oxford University Press. pp. 10–20. ISBN 0-19-508345-8.