42,772 articles
Primene-type branched fatty amines
Primene-type branched fatty amines are long-chain primary amines whose nitrogen sits on a tertiary carbon of a branched chain, marketed by Dow as Primene 81-R and JM-T for fuel and lubricant uses.
Primitive equations
The primitive equations are the set of atmospheric and oceanic motion equations, simplified by the hydrostatic approximation, used in most numerical weather prediction and climate models.
Primitive permutation group
A primitive permutation group is a transitive permutation group preserving no nontrivial block system, equivalently one whose point stabilizers are maximal subgroups; these groups are the basic building blocks of all permutation groups.
Primitive recursive arithmetic
Primitive recursive arithmetic (PRA) is a quantifier-free formal theory of the natural numbers that serves in proof theory as the standard formalization of Hilbert's finitist reasoning about numbers.
Primitive recursive function
A primitive recursive function is a function on natural numbers built from basic functions by composition and primitive recursion, isolated by Kurt Gödel in 1931.
Primitive recursive functional
A primitive recursive functional is a functional of finite type definable by extending primitive recursion to higher types, introduced by Stephen Cole Kleene in 1959.
Primitive root modulo n
A primitive root modulo n is an integer whose powers generate all numbers coprime to n; primitive roots exist only for n = 1, 2, 4, p^k, and 2p^k.
Primordial black hole
A primordial black hole (PBH) is a hypothetical black hole formed within the first second after the Big Bang from collapsing dense regions, not from dying stars.
Primordial deuterium abundance
The primordial deuterium abundance is the deuterium-to-hydrogen ratio made by Big Bang nucleosynthesis in the universe's first minutes and preserved in gas that has never passed through stars.
Primordial gravitational waves
Primordial gravitational waves are ripples in spacetime generated during inflation, leaving a B-mode imprint in the cosmic microwave background polarization that experiments search for today.
Primordial magnetic fields
Primordial magnetic fields are magnetic fields generated in the early universe, during inflation or cosmological phase transitions. None has been directly detected; they are constrained through the cosmic microwave background, nucleosynthesis, and gamma-ray observations.
Primordial nuclide
A primordial nuclide, often called a primordial isotope, is a nuclide that existed on Earth when the planet formed, formed by nucleosynthesis before the solar system condensed.
Primordial power spectrum
The primordial power spectrum describes the amplitude of density and curvature fluctuations in the very early Universe as a function of scale, seeding CMB anisotropies and galaxy distribution.
Primorial
The primorial is the analog of the factorial for primes: the product of the first n primes, or all primes up to n, written n#.
Primus
PRIMUS (the PRIsm MUlti-object Survey) is an astronomical redshift survey of faint galaxies covering 9.1 square degrees of sky, the largest faint-galaxy redshift survey completed at the time.
Prince E. Rouse
Prince E. Rouse (1917–2003) was an American physical chemist and rheologist whose 1953 Rouse model of polymer chain dynamics remains the standard starting point for molecular rheology.
Prince Rupert's drop
Prince Rupert's drop, also called a Batavian tear or Rupert's ball, is a tadpole-shaped glass object whose head survives hammer blows yet shatters when its tail is snapped.
Principal axis factoring
Principal axis factoring, also called iterated principal factor analysis, is an extraction method in exploratory factor analysis that repeatedly estimates communalities to model shared rather than total variance.
Principal bundle
A principal bundle is a fiber bundle whose fibers carry a free and transitive right action of a group G, locally resembling the product of the base with G.
Principal component regression
Principal component regression (PCR) is a two-step regression method that applies PCA to the predictors and regresses the response on the component scores, reducing dimensionality and mitigating multicollinearity.
Principal curvature
Principal curvatures are the maximum and minimum values of the normal curvature of a surface at a point, occurring along perpendicular principal directions; their product gives the Gaussian curvature.
Principal ideal domain
A principal ideal domain (PID) is an integral domain in which every ideal is generated by a single element, examples including the integers and the Gaussian integers.
Principal ideal theorem
The principal ideal theorem, also called the Artin–Furtwängler theorem, states that every ideal of a number field becomes principal in its Hilbert class field, proved in 1930.
Principal quantum number
The principal quantum number, symbol n, labels the main energy shells of an electron in an atom, taking positive integer values 1, 2, 3, and so on.
Principal stratification
Principal stratification is a causal inference framework introduced by Constantine Frangakis and Donald Rubin in 2002 for comparing treatments while adjusting for a variable measured after treatment.
Principal stress
A principal stress is one of the three normal stresses acting on planes of zero shear stress at a point in a stressed body, found as eigenvalues of the stress tensor.
Principia Mathematica
Principia Mathematica is a three-volume work of formal logic by Alfred North Whitehead and Bertrand Russell, published by Cambridge University Press in 1910, 1912, and 1913, defending logicism.
Principle
Principle is a broad scientific statement describing a regularity in nature, which is not as universally established as a scientific law. Pascal's principle specifically describes confined fluids.
Principle of compositionality
The principle of compositionality, also called Frege's principle, is the thesis that an expression's meaning is determined by its structure and the meanings of its constituents.
Principle of explosion
The principle of explosion, also known as ex falso quodlibet or ex contradictione quodlibet, is the rule of inference that anything at all follows from a contradiction.