Physical world and mathematics

Radical relay C–H functionalization

Radical relay C–H functionalization is a synthetic chemistry strategy in which hydrogen-atom transfer generates a diffusible carbon radical that a second reagent or catalyst functionalizes.

Radical Smiles rearrangement

The radical Smiles rearrangement is a variant of the Smiles rearrangement in which a free radical triggers migration of an aryl group from sulfur to carbon.

Sep 29, 2026

Radical substitution

Radical substitution is an organic reaction in which a radical chain mechanism replaces an atom or group in a molecule, best known in the halogenation of alkanes.

Radical translocation is an organic chemistry process where a carbon-centered radical relocates within a molecule via intramolecular hydrogen atom transfer, enabling functionalization of remote, inert C–H bonds.

Radical-nucleophilic aromatic substitution

Radical-nucleophilic aromatic substitution, abbreviated SRN1 and known as the Bunnett reaction, is a radical chain mechanism, proposed by Bunnett in 1970, that replaces halides on unactivated aryl halides through electron transfer.

Radical-polar crossover

Radical-polar crossover is a strategy in organic synthesis in which a radical intermediate undergoes single-electron transfer to an ionic intermediate, combining radical and polar reactivity; the concept dates to 1993.

Oct 10, 2026

Radii Gurzhi

Radii Mykolayovych Gurzhi (1930–2011) was a Soviet and Ukrainian theoretical physicist at Kharkiv whose 1963 prediction of the Gurzhi effect, where a clean conductor conducts better as it warms, founded electron hydrodynamics.

Radio clock

A radio clock, also called a radio-controlled clock, is a quartz clock that keeps exact time by decoding a broadcast radio time signal, adjusting itself for daylight saving time.

Radio frequency

Radio frequency (RF) is the range of electromagnetic wave frequencies from 8.3 kHz to 3000 GHz, divided into bands for radio, television, mobile telephony, radar, and satellites.

Radio galaxy

A radio galaxy is a galaxy whose active nucleus, powered by a supermassive black hole, launches twin jets inflating vast magnetized lobes that emit strongly at radio wavelengths.

Radio halo

A radio halo is a diffuse region of synchrotron radio emission at the center of a galaxy cluster, produced by relativistic electrons in magnetic fields.

Sep 29, 2026

Radio interferometry

Radio interferometry is a radio astronomy technique that combines signals from separated antennas to synthesize high-resolution sky images, developed by Martin Ryle, who won the 1974 Nobel Prize in physics.

Radio mode feedback

Radio mode feedback is a mode of active galactic nucleus feedback in which the mechanical energy of radio jets heats gas in massive elliptical galaxies and suppresses cooling and star formation.

Radio Neutrino Observatory in Greenland

The Radio Neutrino Observatory in Greenland (RNO-G) is an in-ice radio detector under construction at Summit Station to detect ultra-high-energy neutrinos via the Askaryan effect in glacial ice.

Radio occultation

Radio occultation is a remote sensing technique in which a radio signal between two spacecraft is bent by a planetary atmosphere, yielding temperature, pressure, and electron density profiles.

Radio propagation

Radio propagation, also called radio-wave propagation, is the behavior of radio waves traveling from a transmitter to a receiver through the atmosphere, along the Earth's surface, or through space.

Radio pulsar

A radio pulsar is a rotation-powered neutron star emitting regular radio pulses at its spin period, ranging from 0.033 seconds for the Crab pulsar to 8.51 seconds.

Radio telescope

A radio telescope is an antenna and receiving system that collects and measures radio waves from celestial bodies; most are parabolic dishes, and the largest are interferometer arrays.

Radio transient

A radio transient is an astronomical source that appears at radio wavelengths where no quiescent counterpart is detected, arising from flaring stars, neutron stars, supernovae, and active galactic nuclei.

Radio wave

Radio waves, also called Hertzian waves, are electromagnetic waves with the longest wavelengths in the spectrum, generated by antennas to carry radio, TV, and wireless signals.

Radio-frequency cavity

A radio-frequency cavity is an evacuated metallic chamber that uses oscillating electromagnetic fields to accelerate charged particles in accelerators, from medical machines to the LHC.

Radio-frequency reflectometry

Radio-frequency reflectometry is a technique that measures microsecond-scale impedance changes in quantum devices by analyzing reflected radio waves, widely used for fast readout of spin qubits.

Radio-loud quasar

A radio-loud quasar is a quasar whose radio emission, powered by relativistic jets from its central black hole, is strong compared with its optical emission.

Radio-loudness parameter

The radio-loudness parameter R is the ratio of a quasar's radio to optical flux, classically 5 GHz to 4400 Å, dividing quasars into radio-loud and radio-quiet classes.

Radioactive contamination

Radioactive contamination, also called radiation or nuclear contamination, is the presence of radioactive material on surfaces, in the environment, or inside a person's body, distinct from radiation exposure.

Radioactive decay

Radioactive decay, also called nuclear decay, is the process in which an unstable atomic nucleus emits radiation and transforms into a daughter nucleus, following a characteristic half-life.

Radioactive tracer

A radioactive tracer, or radiotracer, is a compound containing a radioactive isotope, added in small amounts to follow physical, chemical, or biological processes by detecting its radiation.

Radiobiological dose modeling

Radiobiological dose modeling is the set of quantitative models linking radiation dose to biological effect, centered on the linear-quadratic model and its BED and EQD2 formalisms.

Radiobiology

Radiobiology, also called radiation biology or radiation biophysics, studies the biological effects of ionizing radiation on cells and tissues, underpinning radiation therapy, which about 50% of cancer patients receive.