42,772 articles
Ratio
A ratio is a comparison of two quantities expressing their relative size, written as a to b, a:b, or a/b; a 2:1 ratio means the first is twice the second.
Ratio distribution
A ratio distribution, also called a quotient distribution, is the probability distribution of a random variable formed as the quotient of two random variables, Z = X/Y.
Ratio estimation
Ratio estimation is a survey sampling method that estimates a population total or mean by scaling the sample ratio of two means by a known auxiliary total.
Ratio estimator
The ratio estimator is a survey-sampling estimator of a population total or mean that uses a known auxiliary total, such as cultivated area, to gain precision.
Ratio test
The ratio test, also known as d'Alembert's ratio test, is a convergence test for infinite series, giving absolute convergence when the limit of consecutive-term ratios is below 1.
Ratiometric fluorescence detection
Ratiometric fluorescence detection is an analytical method reporting analyte concentration as a ratio of two fluorescence bands, self-calibrating against dye concentration, illumination drift, and photobleaching.
Ratiometric imaging
Ratiometric imaging is a microscopy technique that measures ion concentrations or pH by taking the ratio of fluorescence signals at two wavelengths, canceling dye and illumination variations.
Rational function
A rational function, also called a fractional-rational function, is a function expressible as the ratio of two polynomials; such ratios form the field of rational functions F(x) in abstract algebra.
Rational interpolation
Rational interpolation approximates a function by a ratio of two polynomials forced through given data points, preferred over a single polynomial when the function has poles or nearly singular behavior.
Rational mapping
A rational mapping, or rational map, in algebraic geometry is a map between algebraic varieties given by rational functions, defined away from a closed subset.
Rational method (hydrology)
The rational method is an empirical hydrology formula, developed by Thomas Mulvany in 1850, that estimates peak runoff as the product of drainage area, runoff coefficient, and rainfall intensity.
Rational number
A rational number is a number that can be written as a fraction p/q of two integers, with q not zero; every integer and every terminating or repeating decimal is one.
Rational point
A rational point is a solution of an algebraic variety's defining equations whose coordinates are all rational numbers; finding them is the central problem of arithmetic geometry.
Rational reconstruction
Rational reconstruction is a computer algebra problem: recovering the rational number n/d from its residue a modulo m under size bounds, first solved by Paul S. Wang in 1981.
Rational representation
A rational representation of an algebraic group G is a linear representation on a finite-dimensional vector space given by a regular homomorphism G → GL(V).
Rational root theorem
The rational root theorem states that any rational root p/q of a polynomial with integer coefficients has p dividing the constant term and q dividing the leading coefficient.
Rational surface
A rational surface is a two-dimensional algebraic variety defined over an algebraically closed field and birationally isomorphic to the projective plane, the simplest class in the Enriques–Kodaira classification of algebraic surfaces.
Rattleback
The rattleback, also known as the wobblestone or Celtic stone, is a boat-shaped top that spins one way but rocks and reverses when spun the other way.
Raul Briceno
Raúl Briceño is a Venezuelan-born theoretical nuclear physicist and assistant professor at UC Berkeley and Lawrence Berkeley National Laboratory, awarded a 2025 PECASE for lattice QCD research.
Rauwolscine
Rauwolscine, also known as alpha-yohimbine or isoyohimbine, is an indole alkaloid found in Rauvolfia plants and a stereoisomer of yohimbine that acts as an alpha-2 adrenergic receptor antagonist.
Raven paradox
The raven paradox, also called Hempel's paradox, is a problem in confirmation theory posed by Carl Gustav Hempel in 1945, showing that observing a white shoe confirms that all ravens are black.
Raven's Progressive Matrices
Raven's Progressive Matrices, also known as Raven's Matrices, is a widely used nonverbal intelligence test of abstract reasoning, first published by British psychologist John C. Raven in 1938.
Ravi K. Sheth
Ravi K. Sheth is a cosmologist and professor of physics and astronomy at the University of Pennsylvania, known for the halo model and excursion-set theory of dark matter halo formation.
Ravi River
The Ravi River, known in Vedic Sanskrit as Parushni and to Greek writers as Hydraotes, is a transboundary river of the Indus basin and one of the five rivers of the Punjab.
Ravtansine
Ravtansine (DM4) is a synthetic maytansinoid, a derivative of the antimitotic natural product maytansine, used as the cytotoxic payload of antibody–drug conjugates in cancer therapy.
Ray (optics)
In optics, a ray is an idealized straight or curved path along which light travels when wavelengths are much smaller than the objects involved, the basis of geometric optics.
Ray class field
A ray class field is a finite abelian extension of a number field attached to a modulus, with Galois group the ray class group via the Artin map.
Ray F. Weiss
Ray F. Weiss is a chemical oceanographer and atmospheric scientist at Scripps Institution of Oceanography, UC San Diego, known for the first experimental proof of deep-sea hydrothermal vents.
Ray Freeman
Ray Freeman (Raymond Freeman, 1932–2022) was a British chemist who pioneered advances in liquid-state NMR spectroscopy, inventing widely used pulse sequences including INEPT, INADEQUATE, and DANTE, and training a generation of NMR leaders.
Ray J. Weymann
Ray J. Weymann is an American astronomer known for his work on quasar absorption lines, the Lyman-alpha forest, and mass ejection from active galactic nuclei.