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Extreme adaptive optics
Extreme adaptive optics (ExAO) is a class of telescope adaptive optics with far more actuators and faster control loops, built to directly image exoplanets next to bright stars.
Extreme Cold
Extreme cold: temperatures far below local historical averages that endanger people, animals, and infrastructure. Driven by polar vortex and cold air damming; causes hypothermia below 95°F and frostbite; higher mortality risk than extreme heat.
Extreme event attribution
Extreme event attribution, also called attribution science, is the field of climate science that quantifies how human-caused climate change altered the likelihood or intensity of specific extreme weather events.
Extreme Light Infrastructure
The Extreme Light Infrastructure (ELI) is a pan-European consortium of high-power laser facilities in the Czech Republic, Hungary, and Romania, offering researchers open access to some of the world's most intense lasers.
Extreme magnetoresistance
Extreme magnetoresistance, also called extremely large magnetoresistance (XMR), is a magnetotransport phenomenon in semimetals such as WTe₂, where resistance rises 10⁴ to 10⁷ percent in a magnetic field.
Extreme mass-ratio inspiral
An extreme mass-ratio inspiral (EMRI) is a binary system in which a stellar-mass compact object spirals into a much more massive black hole while emitting gravitational waves.
Extreme trans-Neptunian object
An extreme trans-Neptunian object orbits the Sun beyond Neptune with a semimajor axis of roughly 150 au or more, a class tied to the Planet Nine hypothesis.
Extreme ultraviolet frequency comb
An extreme ultraviolet frequency comb is an optical laser comb extended to wavelengths below 100 nm, first demonstrated in 2005, enabling precision spectroscopy and nuclear clocks.
Extreme value index
The extreme value index (EVI), written γ or ξ, is the shape parameter governing the tails of the generalized extreme value distribution, used to estimate high quantiles in finance, hydrology, and insurance.
Extreme value theorem
The extreme value theorem, also called the Weierstrass extreme value theorem, states that a continuous function on a closed, bounded interval attains an absolute maximum and minimum.
Extreme value theory
Extreme value theory is the branch of statistics concerned with the limiting behavior of unusually large or small observations, with applications in hydrology and finance.
Extreme weather
Extreme weather is weather that is rare at a particular place and time of year, including heat waves, cold snaps, droughts, heavy rainfall, and tropical cyclones. Climate change makes hot extremes more frequent.
Extreme-value copula
An extreme-value copula is a copula arising as the weak limit of componentwise maxima of independent samples, equivalently a max-stable copula applied in finance, insurance, and hydrology.
Extremely high frequency
Extremely high frequency, also known as the millimeter wave band, is the radio band from 30 to 300 GHz used for 5G, radar, and imaging.
Extremely Large Telescope
The Extremely Large Telescope (ELT) is a 39-meter optical and infrared telescope the European Southern Observatory is building in Chile, to become the world's largest.
Extrinsic curvature
Extrinsic curvature is the curvature a submanifold has because of how it sits inside an ambient space, unlike intrinsic curvature, which depends only on its own metric.
Extrinsic semiconductor
An extrinsic semiconductor is a semiconductor whose electrical properties have been changed by doping, the deliberate addition of impurity atoms that make it n-type (electron-rich) or p-type (hole-rich).
Eye (cyclone)
The eye of a cyclone is the calm, often clear center of a tropical cyclone, with light winds and the storm's lowest pressure, surrounded by the eyewall.
Eye relief
Eye relief is the distance from an eyepiece's outer lens surface to the eyepoint where the exit pupil forms; viewing from there shows the full field of view without vignetting.
Eyewall
The eyewall is the ring of cumulonimbus clouds surrounding the eye of a tropical cyclone, typically 5 to 25 nautical miles wide and containing the storm's strongest winds.
Eyewall replacement cycle
An eyewall replacement cycle, also called a concentric eyewall cycle, is when an outer ring of thunderstorms in an intense hurricane starves and replaces the original eyewall.
Eyring equation
The Eyring equation, or Eyring-Polanyi equation, gives a reaction's rate constant from temperature and the activation enthalpy and entropy, developed by Henry Eyring in 1935.
EZ Canis Majoris
EZ Canis Majoris, also known as EZ CMa or WR 6, is the 6th brightest Wolf-Rayet star, in Canis Major, varying every 3.77 days whether from a companion or its wind.
Ezio Rizzardo
Ezio Rizzardo, born 1943, is an Italian-Australian organic chemist who spent his career at CSIRO in Victoria and co-invented the NMP and RAFT polymerization methods.
F-algebra
An F-algebra, or algebra for an endofunctor, is a category-theory construction generalizing algebraic structure: a pair (A, α) with α : F(A) → A for an endofunctor F.
f-block
The f-block is the set of chemical elements in which the differentiating electron occupies an f orbital: the 15 lanthanides and 15 radioactive actinides, often shown below the periodic table.
F-center
An F-center, from the German Farbzentrum meaning color center, is a point defect in an ionic crystal where a single electron is trapped at an anion vacancy, coloring the crystal.
F-distribution
The F-distribution, also called Snedecor's F distribution, is a continuous probability distribution of the ratio of two independent chi-squared variables, used in the F-test and ANOVA.
F-number
The F-number, also called the stop or focal ratio, is the ratio of a lens's focal length to its entrance pupil diameter, defining light admission.
f-ratio (oceanography)
The f-ratio is a dimensionless index in biological oceanography, the fraction of phytoplankton production fueled by nitrate rather than recycled ammonium, introduced by Dugdale and Goering in 1967.