Regulated river
A regulated river is one whose flow is largely controlled by major man-made structures such as dams and weirs, so water can be released from upstream storage on demand.
Regulation (EC) No 223/2009 on European statistics
Regulation (EC) No 223/2009 is the EU regulation establishing the legal framework for developing, producing, and disseminating European statistics, in force since 2009 and amended in 2024.
Regulus
Regulus, also known as Alpha Leonis, is the brightest star in the constellation Leo and the nearest B-type star to the Sun, about 79 light-years away in a four-star system.
Reheating (cosmology)
Reheating is the epoch at the end of cosmic inflation in which the energy of the inflaton field converts into particles and radiation, producing the hot Big Bang plasma.
Rei Kinjo
Rei Kinjo (金城 玲, born 1979) is a Japanese chemist at Nanyang Technological University in Singapore, known for his 2011 Science paper on tricoordinate organoboron compounds.
Reidemeister move
A Reidemeister move is one of three local changes to a knot diagram that do not change the knot, proved complete by Kurt Reidemeister in 1926.
Reimer–Tiemann reaction
The Reimer–Tiemann reaction, discovered by Karl Reimer and Ferdinand Tiemann in 1876, converts phenols into hydroxyaldehydes with chloroform and aqueous alkali, most famously making salicylaldehyde from phenol.
Reiner Anwander
Reiner Anwander is a German inorganic chemist and professor of chemistry at the University of Tübingen since 2008, working on organolanthanide chemistry and olefin polymerization catalysis.
Reinforcement learning tokamak control
This RL method commands magnetic coils to meet plasma targets, first demonstrated by DeepMind and the Swiss Plasma Center at EPFL on the TCV in 2022.
Reinhard Genzel
Reinhard Genzel is a German astrophysicist who shared the 2020 Nobel Prize in Physics for discovering the supermassive black hole at the Milky Way's center.
Reinhard Schinke
Reinhard Schinke is a German theoretical physicist who spent his career at Göttingen's Max Planck institutes, known for photodissociation dynamics, ozone theory, and the 1993 monograph Photodissociation Dynamics.
Reinhart Ahlrichs
Reinhart Ahlrichs (1940–2016) was a German theoretical chemist and professor at the Karlsruhe Institute of Technology, best known as the founder of the TURBOMOLE quantum chemistry program package.
Reinhold Baer
Reinhold Baer (1902–1979) was a German mathematician who worked in group theory, abelian groups, geometry, and topology, giving his name to Baer's criterion, Baer groups, and Baer rings.
Reinhold Blumel
Reinhold Blumel, also written Reinhold Blümel, is a physicist and the Charlotte Augusta Ayres Professor at Wesleyan University, awarded a 2000 PECASE for quantum chaos research.
Reinhold Remmert
Reinhold Remmert (1930–2016) was a German mathematician who helped found the modern theory of several complex variables, proved the proper mapping theorem, and wrote the Grauert–Remmert monographs on Stein spaces.
Reinout Willem van Bemmelen
Reinout Willem van Bemmelen, known as Rein van Bemmelen, was a Dutch geologist whose 1949 treatise The Geology of Indonesia became the standard work on Indonesian geology.
Reionization
Reionization is the process in cosmic history, between roughly 200 million and one billion years after the Big Bang, when ultraviolet light from the first stars and galaxies ionized the universe's neutral hydrogen.
Reissner–Nordström metric
The Reissner–Nordström (RN) metric is the exact Einstein–Maxwell solution for the spacetime outside a static, electrically charged, non-rotating mass, known since 1916; with charge below mass it has two horizons.
Reiwa era
Reiwa (令和) is the current Japanese era name, meaning "beautiful harmony," in use since May 1, 2019, when Emperor Naruhito acceded after Emperor Akihito abdicated.
Rejection sampling
Rejection sampling, also called the acceptance-rejection method, is a Monte Carlo method for drawing exact samples from a probability density, attributed to John von Neumann in 1951.
Rejuvenation of metallic glasses
Rejuvenation of metallic glasses is the induced return of an amorphous alloy to a higher-energy, less stable glassy state, reversing aging; methods include cryogenic thermal cycling and elastostatic loading.
Relation algebra
Relation algebra is an algebraic structure whose elements represent binary relations, equipped with Boolean operations, composition, and converse; Tarski axiomatized it in 1941, building on De Morgan, Peirce, and Schröder.
Relational quantum mechanics
Relational quantum mechanics is an interpretation of quantum mechanics proposed by Carlo Rovelli in 1996, according to which different observers can give different accounts of the same events.
Relationship between mathematics and physics
The relationship between mathematics and physics, also called the relation between physics and mathematics, is the use of mathematical structures to state physical laws and derive predictions.
Relationship between string theory and quantum field theory
The relationship between string theory and quantum field theory runs both ways: string theory was proposed to fix QFT's failure to describe quantum gravity, while AdS/CFT duality defines string theory itself through QFT.
Relative atomic mass
Relative atomic mass, formerly called atomic weight, is the dimensionless ratio of an element's average atomic mass to one twelfth of a carbon-12 atom's mass, about 35.45 for chlorine.
Relative biological effectiveness
Relative biological effectiveness (RBE) is a unitless quantity in radiobiology, defined as the ratio of reference-radiation dose to test-radiation dose producing the same biological effect.
Relative Citation Ratio
The Relative Citation Ratio (RCR) is a field- and time-normalized citation metric developed at the NIH, where 1.0 equals the median funded paper's citation rate.
Relative configuration
Relative configuration is the configuration of any stereogenic center with respect to another in the same molecule; a molecule and its mirror image share it.
Relative consistency
Relative consistency is a property of formal theories: a theory S is consistent relative to T when Con(T) implies Con(S), since strong theories like ZF cannot prove their own consistency.