42,772 articles
Impact-based warnings
Impact-based warnings describe the expected consequences of weather events and the actions people should take, rather than stating only hazard characteristics such as wind speed or rainfall depth.
Impedance matching
Impedance matching, also called a matching network, is a central RF and microwave design task that maximizes power transfer or minimizes signal reflection between a source and a load.
Impedance microscopy
Impedance microscopy is a family of scanning probe techniques that maps local electrical impedance, spanning low-frequency contact methods and microwave variants such as MIM and sMIM.
Impedance of free space
The impedance of free space, also called the vacuum impedance, is the ratio of electric to magnetic field strength in a wave traveling through vacuum, about 377 ohms.
Impedance tube
An impedance tube, also called a Kundt's tube or standing wave tube, is a rigid duct used to measure the normal-incidence sound absorption of small material specimens.
Impedimetric detection
Impedimetric detection is a label-free electrochemical sensing method that measures analyte binding as changes in electrode impedance, run in faradaic or non-faradaic modes and suited to low-cost point-of-care diagnostics.
Imperial units
Imperial units, also called the British Imperial System, are the weights and measures established by the British Weights and Measures Act 1824, replacing varied local measures across the British Empire.
Imperialist competitive algorithm
The imperialist competitive algorithm is a population-based metaheuristic for optimization, introduced in 2007, in which candidate solutions called countries form empires that compete and assimilate until one remains.
Implementation and software for sequential Monte Carlo
Implementation and software for sequential Monte Carlo covers the dominant per-particle costs, GPU and CPU parallel resampling, adaptive resampling criteria, and libraries such as SMCTC, LibBi, and particles.
Implementation of mathematics in set theory
The implementation of mathematics in set theory defines every mathematical object, such as numbers, functions, and ordered pairs, as a set, giving ZFC its foundational role in mathematics.
Implicate and explicate order
Implicate and explicate order are two levels of reality proposed by physicist David Bohm, introduced in 1971 and developed in his 1980 book Wholeness and the Implicate Order.
Implicational propositional calculus
The implicational propositional calculus is the fragment of propositional logic in which the only connective is material implication, with theorems derived from axiom schemas by modus ponens.
Implicit differentiation
Implicit differentiation is a calculus technique for finding the derivative of a function defined implicitly by an equation, treating y as a function of x via the chain rule.
Implicit function
An implicit function, or implicitly defined function, is a function defined by an equation F(x, y) = 0 rather than an explicit formula y = f(x).
Implicit function theorem
The implicit function theorem is a calculus result stating that an equation can locally be solved for one variable as a differentiable function of the others.
Implicit solvation
Implicit solvation is a computational method that treats the solvent around a solute as a continuous medium, folding its effect into a solvation free energy.
Implicit surface
An implicit surface is a surface in space defined as the set of points where a scalar function f takes a fixed value, conventionally f(x, y, z) = 0.
Implosion (mechanical process)
An implosion is the sudden inward collapse of a structure or body when external pressure exceeds its internal support, the mechanical opposite of an explosion; examples include crushed submarines, vacuum vessels, and collapsing stars.
Importance sampling
Importance sampling is a Monte Carlo variance-reduction technique that estimates expectations under a target distribution using samples from a proposal distribution, weighted to correct the change of measure.
Impossible early galaxies
Impossible early galaxies are galaxies seen so soon after the Big Bang that their mass seems impossible under standard cosmology, a problem named in 2015 and sharpened by JWST.
Imprecise probability
Imprecise probability is a family of mathematical models that represent uncertainty with sets of probability measures, interval probabilities, or lower and upper bounds, named in Peter Walley's 1991 book.
Impregnation (catalyst preparation)
Impregnation is a catalyst preparation method in which a porous support is contacted with a metal precursor solution, then dried and calcined; it is the oldest and most common route.
Improper ferroelectricity
Improper ferroelectricity is a form of ferroelectricity where polarization arises as a secondary effect of a non-polar distortion; it was formulated by Levanyuk and Sannikov in 1974 and is typified by hexagonal manganites such as YMnO₃.
Improper integral
An improper integral, or improper Riemann integral, extends the definite integral to unbounded intervals or unbounded integrands, defined as a limit that either converges or diverges.
Impulse (physics)
Impulse in physics is the product of a force and the time it acts, or the integral of a varying force, and it equals the object's change in momentum.
Impulse excitation technique
The impulse excitation technique (IET) is a nondestructive test, standardized as ASTM E1876, that measures a material's elastic moduli and damping by striking a specimen and analyzing its resonant vibrations.
Impulse response
The impulse response, also called the impulse response function, is the output of a system to a unit impulse; with convolution, it completely describes a linear time-invariant system.
Impulsive gravitational wave
An impulsive gravitational wave is an exact solution of general relativity where the entire gravitational radiation is concentrated on a single null hypersurface, with delta-function curvature.
Impurity radiation
Impurity radiation is the emission of light by non-fuel atoms and ions in a fusion plasma, cooling the core but deliberately used at the plasma edge to spread exhaust heat away from the divertor targets.
Impurity scattering
Impurity scattering is the elastic scattering of charge carriers by impurity atoms in a crystal, a principal limit on carrier mobility in doped semiconductors, especially at low temperature.