42,772 articles
Recruitment and retention of women in physics education
Recruitment and retention of women in physics education covers the school-to-undergraduate pipeline, where girls are about half of US high school physics students but only 20% of college majors.
Recrystallization (chemistry)
Recrystallization is a laboratory technique for purifying solid compounds by dissolving them in a minimum of hot solvent and cooling slowly, so the compound crystallizes while impurities stay dissolved.
Rectangle
A rectangle is a quadrilateral with four right angles, a special parallelogram with equal, parallel opposite sides and equal diagonals; its area is length times width.
Rectangular function
The rectangular function, also called the rect or gate function, equals 1 on an interval centered at zero and 0 elsewhere; its Fourier transform is the sinc function.
Rectangular hyperbola
A rectangular hyperbola, also called an equilateral or right hyperbola, is a hyperbola whose two asymptotes are perpendicular, equivalent to equal semi-axes (a = b) and giving it the fixed eccentricity √2.
Rectangular potential barrier
The rectangular potential barrier, also called the finite potential barrier, is a standard quantum mechanics model used to describe tunneling through a region of constant potential.
Rectification (chemistry)
Rectification is a distillation method in which a liquid mixture is repeatedly vaporized and condensed inside a column, used for high-purity separations such as crude-oil refining and alcohol purification.
Rectilinear locomotion
Rectilinear locomotion is one of the four traditional modes of snake locomotion, in which a snake moves straight ahead by alternately shortening and lengthening its belly skin.
Recurrence plot
A recurrence plot is a graphical tool from nonlinear time-series analysis that shows when a dynamical system returns to earlier states, introduced by Eckmann, Oliffson Kamphorst, and Ruelle in 1987.
Recurrence quantification analysis
Recurrence quantification analysis (RQA) is a nonlinear time-series method that quantifies a recurrence plot into measures such as determinism, laminarity, and entropy, introduced in the 1990s.
Recurrence relation
A recurrence relation, also called a recurrence equation, defines each term of a sequence as a function of earlier ones; with initial values, like the Fibonacci recurrence, it determines the sequence uniquely.
Recurrent neural network wave functions
Recurrent neural network wave functions are variational ansatz representing quantum many-body wave functions with recurrent neural networks, introduced in 2020 and optimized by variational Monte Carlo to find ground states.
Recurrent nova
A recurrent nova is a cataclysmic binary system containing a white dwarf that undergoes nova eruptions more than once, with recurrence times of about 1 to 100 years.
Recursion
Recursion, also called recursivity, is the process of defining or solving something in terms of smaller instances of itself, as when a function invokes itself on simpler sub-problems.
Recursion theorem (Dedekind)
The Dedekind recursion theorem, proved by Richard Dedekind in 1888, guarantees that a function defined by recursion on the natural numbers exists and is unique.
Recursion theorem fixed point
In computability theory, a recursion theorem fixed point is a program index n with the same partial function as its transform, φn = φf(n), guaranteed by Kleene's second recursion theorem.
Recursive Bayesian estimation
Recursive Bayesian estimation, also known as Bayesian or Bayes filtering, sequentially estimates a system's hidden state through prediction and update steps, with the Kalman and particle filters as best-known forms.
Recursive language
A recursive language, also known as a decidable or Turing-decidable language, is a formal language decidable by a Turing machine that halts on every input, finite or not.
Recursive largest first algorithm
The recursive largest first algorithm is a greedy graph coloring heuristic, introduced by Frank Leighton in 1979, that builds each color class as an independent set.
Recursive least squares filter
The recursive least squares (RLS) filter, or RLS algorithm, is an adaptive filter that recursively minimizes weighted squared error, converging faster than LMS at higher computational cost per step.
Recursive partitioning
Recursive partitioning is a statistical method that builds classification and regression models by repeatedly splitting a dataset into smaller subgroups, producing a binary tree whose leaves carry predictions.
Recursively enumerable language
A recursively enumerable language, also called a Turing-recognizable language, is a formal language accepted by some Turing machine, which may run forever on strings outside it.
Recycled polyethylene terephthalate
Recycled polyethylene terephthalate (rPET) is PET plastic, chiefly from post-consumer bottles, reprocessed mainly by mechanical recycling into flakes, pellets, fiber, or new bottles, with polyester fiber its largest end use.
RecycleUnits
RecycleUnits, also written Recycle-Units, is a linear-time algorithm that shrinks SAT solvers' resolution proofs and their unsatisfiable cores, introduced by IBM Haifa and Technion researchers in 2008.
Red
Red is the color of visible light with the longest wavelengths, around 700 nanometers, at one end of the spectrum opposite violet and bordering infrared.
Red Chris mine
Red Chris is a copper and gold mine in the Golden Triangle of northwest British Columbia, Canada, which began production in 2015 and is operated by Newmont.
Red clump
The red clump is a concentration of low-mass stars burning helium in their cores, a sharp feature in color-magnitude diagrams used as a standard candle for distances.
Red Dog Mine
The Red Dog Mine is one of the world's largest zinc mines, an open-pit operation in the De Long Mountains of northwest Alaska producing zinc and lead since 1989.
Red dwarf
A red dwarf, or M dwarf, is a small, cool, low-mass star and the most common type, making up about 75% of the galaxy's stars.
Red flag warning
A red flag warning is a National Weather Service alert that critical fire weather conditions, such as strong wind and very low humidity, are occurring or expected within about a day.