42,772 articles
Rapid-quench flow
Rapid-quench flow (RQF), also called chemical quench-flow, is a laboratory kinetic technique that mixes reactants, ages the reaction for milliseconds, and chemically stops it to trap intermediates.
Rapidity
Rapidity is a quantity in special relativity and particle physics that describes motion relative to an axis, with successive boosts along the same axis simply adding.
Rapidly oscillating Ap star
A rapidly oscillating Ap (roAp) star is a magnetic, chemically peculiar A star pulsating in rapid, low-amplitude modes of 5 to 24 minutes, first described by Donald Kurtz in 1982.
Rare Earth hypothesis
The Rare Earth hypothesis, or Rare Earth theory, argues that complex extraterrestrial life is likely rare even if microbial life is common across the universe.
Rare event sampling
Rare event sampling is a family of Monte Carlo techniques, chiefly importance sampling and splitting, that estimate very low-probability events far more efficiently than naive simulation.
Rare event simulation
Rare event simulation is a class of Monte Carlo methods, including importance sampling and splitting, that estimates very low-probability events far more efficiently than naive sampling.
Rare-earth barium copper oxide
Rare-earth barium copper oxide (REBCO) is a family of high-temperature superconductors with a critical temperature of about 92 K, dominant in coated conductor tape used for compact fusion tokamak magnets.
Rare-earth element
The rare-earth elements, or rare earths, are a group of 17 chemically similar metals: the 15 lanthanides plus scandium and yttrium, used in magnets, phosphors, and catalysts.
Rare-earth hydroxides
Rare-earth hydroxides are the hydroxide and oxyhydroxide solid phases of scandium, yttrium, and the lanthanides, whose solubility varies smoothly across the 4f series, enabling classical fractional precipitation separation of the rare earths.
Rare-earth ion
A rare-earth ion (REI) is a charged lanthanide, scandium, or yttrium ion embedded in a host crystal, whose shielded 4f electrons give narrow, stable optical transitions used in quantum memories.
Rare-earth ion qubits
Rare-earth ion qubits are quantum bits formed from the spin states of rare-earth ions doped into crystals, valued for the longest coherence times in a solid-state system.
Rare-earth magnet
A rare-earth magnet is a permanent magnet made from a lanthanide alloy, in two families: neodymium iron boron, the strongest commercial magnets, and samarium cobalt.
Rare-earth quantum memory
A rare-earth quantum memory is a device that stores quantum states of light in rare-earth ions doped into crystals, developed mainly as the storage element of quantum repeaters for future quantum networks.
Rare-earth-doped crystal quantum memory
A rare-earth-doped crystal quantum memory is a solid-state device that stores quantum states of light in rare-earth ions embedded in crystals, developed for quantum repeaters and networks.
Rare-earth-doped quantum memories
Rare-earth-doped quantum memories store photons in rare-earth ions doped into crystals such as YSO at cryogenic temperatures, retrieving the quantum state after a controlled time.
Rarefaction (statistics)
Rarefaction is a statistical method that standardizes species richness by subsampling individuals or samples to a common count, introduced by Howard Sanders in 1968 for marine benthic ecology.
Rarefaction wave
A rarefaction wave, also called an expansion wave, is a disturbance in a compressible fluid across which pressure and density decrease, the smooth counterpart of a shock wave.
Rashba effect
The Rashba effect is a momentum-dependent splitting of electron energy bands into two spin states when inversion symmetry is broken, locking spin to momentum; it underlies the 1990 Datta–Das spin transistor.
Rashba–Edelstein effect
The Rashba–Edelstein effect converts electric current into spin polarization at interfaces lacking inversion symmetry, such as a two-dimensional electron gas, generating the spin-orbit torques used in spintronic devices.
Rashid Sunyaev
Rashid Sunyaev (Рашид Сюняев), born 1943 in Tashkent, is a Russian and German astrophysicist known for the Sunyaev–Zeldovich effect and the Shakura–Sunyaev accretion disk theory.
Rashid Zia
Rashid Zia is a nanophotonics researcher at Brown University who was Dean of the College from 2018 to 2025, studying light emission from quantum emitters.
Rasmus Fensholt
Rasmus Fensholt is a Danish remote-sensing scientist and professor of Geography at the University of Copenhagen, known for satellite-based mapping of individual trees and their carbon.
Raspberry ketone
Raspberry ketone is a phenolic compound that gives red raspberries their aroma, used as a flavoring, in perfumes, and since the 2010s in weight-loss supplements.
Rasputitsa
Rasputitsa (распу́тица), also bezdorozhye/bezdorizhzhia, is the twice-yearly spring-thaw and autumn-rain mud season of Russia, Belarus, and Ukraine, when unpaved roads become impassable; it shaped Napoleon's 1812 retreat and WWII Eastern Front operations.
Raster image correlation spectroscopy
Raster image correlation spectroscopy (RICS) is a fluorescence microscopy method introduced by Michelle Digman and colleagues in 2005 that measures molecular diffusion, concentration, and aggregation in living cells.
Rate equation
A rate equation, also called a rate law, relates the rate of a chemical reaction to reactant concentrations and is the central tool of chemical kinetics.
Rate-and-state friction
Rate-and-state friction is an empirical friction law for rock in which strength depends on slip velocity and a state variable, introduced by Dieterich in 1979.
Rate-determining step
The rate-determining step is the slowest elementary step in a multistep reaction mechanism, which limits the overall reaction rate like the narrowest funnel in a series.
Rate–distortion theory
Rate–distortion theory, also called distortion-rate theory, is the branch of information theory that gives the minimum rate for representing a source when a specified distortion is tolerated.
Rating curve
A rating curve is the empirical relation between water level and discharge at a stream gauging station, used to turn continuous stage records into continuous river discharge records.