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Epsilon Ursae Majoris
Epsilon Ursae Majoris, better known as Alioth, is the brightest star in the constellation Ursa Major, a chemically peculiar A-type variable star about 82.5 light-years away.
Epsilon Virginis
Epsilon Virginis, better known as Vindemiatrix, is a yellow giant star in the constellation Virgo, its third-brightest star, lying about 102 light years from the Sun.
Epsilon-near-zero enhanced nonlinear optics
Epsilon-near-zero enhanced nonlinear optics is the strengthening of nonlinear optical effects, like harmonic generation and all-optical switching, in materials whose electric permittivity approaches zero at a particular wavelength.
Epsilon-near-zero material
An epsilon-near-zero (ENZ) material is an electromagnetic material whose electric permittivity approaches zero at some frequency, enabling field squeezing, perfect absorption, and ultrafast optical switching.
Epsilon-near-zero metasurfaces
Epsilon-near-zero metasurfaces are optical surfaces built from subwavelength nanostructures on materials, typically transparent conducting oxides like indium tin oxide, whose permittivity nears zero, enabling ultrafast switching and beam steering.
Epsilon-near-zero nonlinearity
Epsilon-near-zero (ENZ) nonlinearity is the strong nonlinear optical response of materials with near-zero permittivity, typically transparent conducting oxides like ITO, enabling ultrafast all-optical switching, enhanced harmonic generation, and unity-order refractive index changes in nanometer-thin films.
Epsilon-near-zero photonics
Epsilon-near-zero (ENZ) photonics is the study of light–matter interactions in materials whose permittivity approaches zero, producing strong field confinement, slow light, and enhanced nonlinear effects over sub-wavelength distances.
Epsilon-near-zero response
The epsilon-near-zero (ENZ) response is the electromagnetic behavior of a material whose electric permittivity approaches zero at a particular frequency, producing extreme light-matter interactions, field enhancement, and ultrafast optical nonlinearities.
Epsomite
Epsomite, also known as Epsom salt or magnesium sulfate heptahydrate, is a soft, highly soluble magnesium sulfate mineral named in 1806 for Epsom, Surrey, England, where it occurred as crusts from thermal springs.
Equal-loudness contour
Equal-loudness contours, also called Fletcher-Munson curves, are curves connecting pure tones judged equally loud despite differing in frequency and level; first measured in 1933, they underpin A-weighting.
Equalization (audio)
Equalization (EQ), or audio equalizer, adjusts the balance of frequencies in an audio signal using filters that boost or cut parts of the spectrum, in recording, mixing, and broadcast.
Equals sign
The equals sign, also called the equality sign, is a mathematical symbol stating that two expressions have the same value, introduced by Robert Recorde in 1557.
Equation
An equation is a mathematical statement that two expressions are equal, written with an equals sign; identities hold for all values, conditional equations for some, and contradictions for none.
Equation of motion coupled cluster
Equation-of-motion coupled cluster (EOM-CC) is a family of quantum-chemistry methods that computes excited, ionized, electron-attached, and spin-flip states of molecules from a coupled-cluster ground state.
Equation of state
An equation of state, also called a state equation, relates the pressure, volume, and temperature of a thermodynamic system, as in the ideal gas law PV = nRT.
Equation of state of quark–gluon plasma
The equation of state of quark–gluon plasma relates energy density, pressure, entropy density, and temperature of deconfined QCD matter, computed by lattice QCD and used in heavy-ion collision modeling.
Equation of state parameter w
In cosmology, the equation of state parameter w is the dimensionless ratio of pressure to energy density of a cosmic component, the standard way of characterizing dark energy.
Equation of time
The equation of time is the difference between apparent solar time on a sundial and mean clock time, reaching 16 minutes over the year due to Earth's axial tilt and elliptical orbit.
Equation solving
Equation solving, also called solving an equation, is the task of finding values of unknowns that make equations true, either exactly in symbols or approximately by numerical methods.
Equational logic
Equational logic is the formal logic whose only formulas are identities s = t between terms, underlying universal algebra and term rewriting; Birkhoff proved it sound and complete in 1935.
Equations for a falling body
The equations for a falling body, or law of falling bodies, give the position and velocity of an object falling under gravity with constant acceleration.
Equations of motion
An equation of motion is a differential equation that determines a physical system's state at later times from its initial state, as in F = ma.
Equator
The Equator is the imaginary line at 0 degrees latitude halfway between the poles, dividing Earth into two hemispheres and measuring about 40,075 km around.
Equatorial coordinate system
The equatorial coordinate system is the astronomical system that specifies positions on the celestial sphere by right ascension and declination, used in star charts, telescope pointing, and most astronomical catalogs.
Equatorial spread F
Equatorial spread F (ESF) is the spreading of ionogram echo traces caused by plasma density irregularities in the nighttime equatorial F region, disrupting satellite navigation signals.
Equatorial undercurrent
The equatorial undercurrent is a narrow subsurface ocean current flowing eastward along the Equator in the Pacific, Atlantic, and Indian Oceans, against the trade winds, about 100 meters deep in the Pacific.
Equatorial upwelling
Equatorial upwelling is the rising of cold, nutrient-rich subsurface water to the ocean surface along the equator, driven by trade winds through Ekman transport and supporting major fisheries.
Equiconsistency
Equiconsistency is a relation between formal theories in which each is consistent if and only if the other is; it underlies the consistency strength hierarchy comparing theories like ZFC.
Equilateral triangle
An equilateral triangle, also known as an equiangular triangle, is a triangle with all three sides of equal length and three interior angles of 60 degrees, the simplest regular polygon.
Equilibrium constant
The equilibrium constant, also known as Keq, is a dimensionless number characterizing a chemical reaction's equilibrium, defined as the quotient of equilibrium activities of products over reactants, each raised to its stoichiometric coefficient.