Mu (letter)

Names

Ancient Greek

In Greek, the name of the letter was written μῦ and pronounced .

Modern Greek

In Modern Greek, the letter is spelled μι and pronounced . In polytonic orthography, it is written with an acute accent: μί.

Use as symbol

The lowercase letter mu (μ) is used as a special symbol in many academic fields. Uppercase mu is not used, because it appears identical to Latin M.

Prefix for units of measurement

"μ" is used as a unit prefix denoting a factor of 10−6 (one millionth), in this context, the symbol's name is "micro".

• Metric prefix
• International System of Units prefix, also known as "SI prefix"
• The micrometre with a symbol of "μm" can also be referred to as the non-SI term "micron".

Mathematics

"μ" is conventionally used to denote certain things; however, any Greek letter or other symbol may be used freely as a variable name.

• a measure in measure theory
• minimalization in computability theory and Recursion theory
• the integrating factor in ordinary differential equations
• the degree of membership in a fuzzy set
• the Möbius function in number theory
• the population mean or expected value in probability and statistics
• the service or departure rate in queueing theory
• the Ramanujan–Soldner constant

Physics and engineering

In classical physics and engineering:

• the coefficient of friction (also used in aviation as braking coefficient (see Braking action))
• reduced mass in the two-body problem
• Standard gravitational parameter in celestial mechanics
• linear density, or mass per unit length, in strings and other one-dimensional objects
• permeability in electromagnetism
• the magnetic dipole moment of a current-carrying coil
• dynamic viscosity in fluid mechanics
• the amplification factor or voltage gain of a triode vacuum tube
• the electrical mobility of a charged particle
• the rotor advance ratio, the ratio of aircraft airspeed to rotor-tip speed in rotorcraft
• the pore water pressure in saturated soil
• the shear modulus in solid mechanics

In particle physics:

• elementary particles: muon and antimuon (, ), muon neutrino and antineutrino (, )
• the proton-to-electron mass ratio

In thermodynamics:

• the chemical potential of a system or component of a system

Computer science

In evolutionary algorithms:

• μ, population size from which in each generation λ offspring will generate (the terms μ and λ originate from evolution strategy notation)

In type theory:

• Used to introduce a recursive data type. For example, \text{list}(\tau) = \mu{}\alpha{}.1 + \tau{}\alpha is the type of lists with elements of type \tau (a type variable): a sum of unit, representing , with a pair of a \tau and another \text{list}(\tau) (represented by \alpha). In this notation, \mu is a binding form, where the variable (\alpha) introduced by \mu is bound within the following term (1 + \tau{}\alpha) to the term itself. Via substitution and arithmetic, the type expands to 1 + \tau + \tau^2 + \tau^3 + \cdots, an infinite sum of ever-increasing products of \tau (that is, a \tau{}\text{ list} is any k-tuple of values of type \tau for any k \ge 0). Another way to express the same type is \text{list}(\tau) = 1 + \tau{}\text{list}(\tau).

Chemistry

In chemistry:

• the prefix given in IUPAC nomenclature for a bridging ligand

Biology

In biology:

• the mutation rate in population genetics
• A class of Immunoglobulin heavy chain that defines IgM type Antibodies

Pharmacology

In pharmacology:

• an important opiate receptor

Orbital mechanics

In orbital mechanics:

• Standard gravitational parameter of a celestial body, the product of the gravitational constant G and the mass M
• planetary discriminant, represents an experimental measure of the actual degree of cleanliness of the orbital zone, a criterion for defining a planet. The value of μ is calculated by dividing the mass of the candidate body by the total mass of the other objects that share its orbital zone.

Music

• Mu chord
• Electronic musician Mike Paradinas runs the label Planet Mu which utilizes the letter as its logo, and releases music under the pseudonym μ-Ziq, pronounced "music"
• Used as the name of the school idol group μ's, pronounced "muse", consisting of nine singing idols in the anime Love Live! School Idol Project
• Official fandom name of Kpop group f(x), appearing as either MeU or 'μ'
• Hip-hop artist Muonboy has taken inspiration from the particle for his stage name and his first EP named Mu uses the letter as its title.

Cameras

The Olympus Corporation manufactures a series of digital cameras called Olympus μ (known as Olympus Stylus in North America).

Linguistics

In phonology:

• mora

In syntax:

• μP (mu phrase) can be used as the name for a functional projection.

In Celtic linguistics:

• /μ/ can represent an Old Irish nasalized labial fricative of uncertain articulation, the ancestor of the sound represented by Modern Irish mh.

Unicode

The lowercase mu (as "micro sign") appeared at in the 8-bit ISO-8859-1 encoding, from which Unicode and many other encodings inherited it. It was also at in the popular CP437 on the IBM PC. Unicode designates mu as is the compatibility equivalent of the micro sign.

References

References

1. (2003). "The Chambers Dictionary". Chambers.
2. {{OED. mu
3. Hadley, James. (1884). "A Greek Grammar for Schools and Colleges". American Book.
4. "Neoelliniki Grammatiki (Tis Dimotikis)".
5. "Grammatiki tis Dimotikis Glossas".
6. Chaira, Tamalika. (2019). "Fuzzy set and its extension: the intuitionistic fuzzy set". Wiley.
7. Weisstein, Eric W.. "Möbius Function".
8. "DLMF: §27.2 Functions ‣ Multiplicative Number Theory ‣ Chapter 27 Functions of Number Theory".
9. Weisstein, Eric W.. "Mean".
10. [https://www.stats.ox.ac.uk/~winkel/bs3a07l13-14.pdf M/M/1 queues and queueing networks], Oxford University lecture notes
11. Weisstein, Eric W.. "Soldner's Constant".
12. Dante, Roberto C.. (2016). "Handbook of friction materials and their applications". Woodhead Publishing.
13. Kulp, Christopher W.. (2021). "Classical mechanics: a computational approach with examples using mathematica and Python". CRC Press.
14. Dodd, Richard. (2012). "Using SI units in astronomy". Cambridge University Press.
15. Walker, Jearl. (2014). "Halliday & Resnick fundamentals of physics". Wiley.
16. Jiles, David. (2016). "Introduction to magnetism and magnetic materials". CRC Press, Taylor & Francis Group.
17. Braslavsky, S. E.. (2007-01-01). "Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006)". Pure and Applied Chemistry.
18. Ballou, Glen. (1987). "Handbook for Sound Engineers: The New Audio Cyclopedia". Howard W. Sams Co..
19. "[http://rotorcraft.arc.nasa.gov/tutorial/Nomenclature.htm#mu Nomenclature]" ''NASA''
20. "Definition".
21. MIT Aero]]'', February 2005. Accessed: December 2013. Size: 15MB and 114 pages
22. Thompson, Rodger I.. (2017). "Fundamental constants as monitors of the universe". WORLD SCIENTIFIC.
23. "Olympus History : μ[mju:] (Stylus) Series".
24. Johnson, Kyle. (1991). "Object Positions". Natural Language and Linguistic Theory.
25. Unicode Code Charts: [https://www.unicode.org/charts/PDF/U0370.pdf Greek and Coptic (Range: 0370-03FF)]