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Extensional rheology
Extensional rheology, also called elongational rheology, is the study of how materials respond to stretching rather than shearing, measured through extensional viscosity, first examined by Trouton in 1906.
Extensional viscosity
Extensional viscosity, also called elongational viscosity or Trouton viscosity, is a fluid's resistance to stretching rather than shearing flow, introduced by Frederick Trouton in 1906.
Extensive air shower
An extensive air shower (EAS) is a cascade of secondary particles in the atmosphere produced when a high-energy cosmic ray collides with an air nucleus.
Extensive air showers at ultra-high energies
Extensive air showers are the particle cascades created when a cosmic ray above roughly 10^17 eV strikes the upper atmosphere, spreading billions of particles over the ground.
Exterior algebra
Exterior algebra, also called Grassmann algebra, is the algebra of a vector space in which vectors anticommute under the wedge product. It packages oriented volumes and determinants.
Exterior derivative
The exterior derivative, written d, is an operator of differential geometry that takes a k-form to a (k+1)-form, unifying the gradient, curl, and divergence into one coordinate-free operation.
Exterior power
The k-th exterior power ΛᵏV of a vector space or module V is built from the k-fold tensor power by forcing tensors with a repeated factor to vanish.
External ballistics
External ballistics, also called exterior ballistics, is the branch of ballistics covering a projectile's free-flight trajectory between launcher and target, governed by momentum, gravity, drag, and winds.
External validity
External validity is the extent to which a study's findings, especially its causal inferences, apply to populations, settings, and times beyond the study sample, complementing internal validity.
Extinction (astronomy)
Extinction, also called interstellar extinction, is the dimming of starlight by interstellar dust, which absorbs and scatters light and reddens stars. It was discovered by Robert Trumpler in 1930.
Extinction coefficient
The extinction coefficient is a per-path-length measure of how strongly a medium attenuates a wave through absorption and scattering, used in chemistry, atmospheric science, and optics.
Extinction probability of branching processes
The extinction probability of a branching process is the probability that a population dies out, equal to the smallest fixed point of the offspring generating function.
Extinction Rebellion
Extinction Rebellion (XR) is a decentralized international climate movement founded in the United Kingdom in 2018 that uses nonviolent mass civil disobedience to demand government action on climate change.
Extinction risk from climate change
Extinction risk from climate change, also known as species extinction from global warming, is the likelihood that a changing climate drives species or ecosystems extinct, projected to rise steeply with warming.
eXTP
eXTP (enhanced X-ray Timing and Polarimetry mission, 增强型X射线时变与偏振空间天文台) is a Chinese-led X-ray observatory with European partners, approved for launch in 2030 to study neutron stars and black holes.
Extra-large-pore zeolite
An extra-large-pore zeolite is a crystalline microporous framework with pore windows of more than 12 tetrahedral atoms and apertures above 7.5 Å, sought for converting bulky molecules.
Extra-low voltage
Extra-low voltage (ELV) is a voltage classification in electrical safety standards for supplies unlikely to cause hazardous electric shock, typically not exceeding 50 volts AC.
Extracellular electrophysiology
Extracellular electrophysiology is the measurement of electrical potentials from neurons, nerves, or muscles with electrodes outside the cells, capturing signals such as EEG, ECoG, and local field potentials.
Extraction (chemistry)
Extraction, also called chemical extraction, is a chemical separation technique that transfers a substance into a liquid in which it is more soluble, usually from water into an organic solvent.
Extraction chromatography
Extraction chromatography (EXC) is a chromatographic method for separating metal ions, in which a liquid extractant is adsorbed onto a porous solid support packed in a column.
Extractive distillation
Extractive distillation is a distillation technique in which a high-boiling selective solvent, the entrainer, changes relative volatility so close-boiling or azeotropic mixtures can be separated.
Extragalactic background light
The extragalactic background light (EBL) is the total diffuse light from all sources outside the Milky Way, second in energy only to the cosmic microwave background.
Extragalactic globular cluster systems
An extragalactic globular cluster system is the full population of globular clusters bound to a galaxy other than the Milky Way, serving as tracers of halo structure and accretion history.
Extragradient method
The extragradient method is an iterative algorithm for solving variational inequalities and saddle points, introduced by G. M. Korpelevich in 1976 for bilinear saddle-point problems.
Extrapolation
Extrapolation is a numerical and statistical technique for estimating a function or dataset at points outside the range of observed data, the complement of interpolation.
Extratropical cyclone
An extratropical cyclone, also called a mid-latitude or frontal cyclone, is a low-pressure storm system driven by horizontal temperature contrasts, and it brings most fall-to-spring weather in temperate zones.
Extratropical transition
Extratropical transition (ET) is the gradual process by which a tropical cyclone at higher latitudes becomes an extratropical cyclone, its energy shifting from latent heat to temperature contrasts, often while retaining strong winds.
Extremal black hole
An extremal black hole is a stationary black hole whose surface gravity and Hawking temperature are exactly zero, merging its event and Cauchy horizons into one.
Extremal combinatorics
Extremal combinatorics is the branch of combinatorics studying the maximum or minimum size of structures like graphs under prescribed properties, with classical results by Mantel and Turán.
Extremal graph theory
Extremal graph theory is the branch of combinatorics that studies how large a graph can be while avoiding a forbidden subgraph, with Turán's 1941 theorem as its prototype.