Relativistic mechanics
Relativistic mechanics describes the motion of bodies whose speeds are a significant fraction of the speed of light, replacing Newtonian momentum and energy with Lorentz-invariant quantities built from rest mass.
Relativistic momentum
Relativistic momentum is the momentum of a particle in special relativity, p = γmu, which replaces the classical expression so that momentum conservation holds in every inertial frame.
Relativistic polytrope
A relativistic polytrope is a general-relativistic model of a self-gravitating fluid star whose pressure follows a polytropic law, introduced by Robert Tooper in 1964 as a compact-object extension of the Newtonian polytrope.
Relativistic shock waves
Relativistic shock waves are discontinuities in fluid flows moving at nearly the speed of light, pioneered by Abraham Taub in 1948 and applied to gamma-ray bursts and jets.
Relativistic thermodynamics
Relativistic thermodynamics studies how temperature, heat, and entropy behave for bodies moving near light speed; whether a moving body appears cooler, hotter, or unchanged is still debated over 110 years.
Relativistic time scales (TCB, TCG, TT)
Relativistic time scales (TCB, TCG, TT) are coordinate time scales defined by the IAU for general-relativistic modeling of the solar system, because clocks at different gravitational potentials run at different rates.
Relativistic viscous hydrodynamics
Relativistic viscous hydrodynamics is the extension of fluid dynamics to near-light-speed fluids including shear viscosity, bulk viscosity, and diffusion, the standard model of the quark-gluon plasma at RHIC and the LHC.
Relativity of simultaneity
The relativity of simultaneity is the principle in special relativity that events simultaneous in one inertial frame are not simultaneous in another moving relative to it.
Relativity priority dispute
The relativity priority dispute is the controversy over who discovered relativity: Einstein and Poincaré in 1905 on special relativity, and Einstein and Hilbert in 1915 on general relativity.
Relaxation (NMR)
Relaxation (NMR relaxation) is the process by which nuclear magnetization perturbed by a radiofrequency pulse returns to thermal equilibrium, characterized by the time constants T1 and T2.
Relaxation kinetics
Relaxation kinetics, or chemical relaxation, is the chemical kinetics technique of suddenly perturbing a system at equilibrium, by temperature, pressure, or electric field, developed by Manfred Eigen in the 1950s.
Relaxation method
A relaxation method measures rates of fast chemical reactions by suddenly perturbing a system at equilibrium, developed by Manfred Eigen, who won the 1967 Nobel Prize in Chemistry.
Relaxation oscillation
A relaxation oscillation is a non-sinusoidal periodic oscillation produced by nonlinear systems alternating slow and fast phases, a term coined by Balthasar van der Pol in 1926.
Relaxation time approximation
The relaxation time approximation (RTA) replaces the collision term of the Boltzmann transport equation with a single relaxation time, so a disturbed distribution decays exponentially back to equilibrium.
Relevance logic
Relevance logic, also known as relevant logic, is a family of non-classical logics developed to avoid the paradoxes of material and strict implication by requiring content connection.
Relevant type theory
Relevant type theory is the substructural type system with exchange and contraction but no weakening, so every variable is used at least once; it corresponds to relevant logic and the λI-calculus.
Reliability (statistics)
Reliability in statistics and psychometrics is the consistency of test scores across replications of a testing procedure, estimated through coefficients such as test-retest, alternate-forms, and internal consistency measures.
Reliability engineering
Reliability engineering, also called systems reliability, is a branch of systems engineering that ensures products perform their intended functions without failure, using probability, statistics, and testing across the product lifecycle.
Remainder
A remainder is the integer left over when one integer is divided by another and only whole multiples are subtracted; dividing 14 by 3 leaves a remainder of 2.
Remaining carbon budget
The remaining carbon budget is the net CO2 humans can still emit while keeping warming below a temperature limit with a stated probability, key to Paris Agreement goals.
Remaining useful life prediction
Remaining useful life (RUL) prediction estimates how much longer a system can perform before its health crosses a failure threshold, a core prognostics and health management technology using model-based, statistical, data-driven, and hybrid methods.
Remanence
Remanence, also called remanent magnetization or residual magnetism, is the magnetization remaining in a ferromagnetic material after an applied field is removed, measured in teslas.
Remifentanil
Remifentanil, marketed as Ultiva, is an ultra-short-acting synthetic opioid of the fentanyl family, synthesized in 1990 and marketed in 1996, used intravenously for anesthesia and intensive care sedation.
Remote C–H borylation
Remote C–H borylation converts carbon–hydrogen bonds at positions distant from any directing group, typically meta or para on arenes, into versatile carbon–boron bonds using templates and ligand design.
Remote C–H functionalization
Remote C–H functionalization is the chemical conversion of a carbon–hydrogen bond located far from any reactive functional group, using strategies like chain-walking, templates, and radical hydrogen atom transfer.
Remote C–H functionalization via 1,5-HAT
Remote C–H functionalization via 1,5-HAT is a radical strategy in organic synthesis in which an intramolecular 1,5-hydrogen atom transfer moves a radical to a distant C–H bond for functionalization.
Remote C–H functionalization via radical relay
Remote C–H functionalization via radical relay is an organic synthesis strategy in which hydrogen-atom transfer forms a diffusible carbon radical that a separate reagent then functionalizes.
Remote state preparation
Remote state preparation is a quantum communication protocol where a sender who knows the target state uses shared entanglement and classical communication to prepare it remotely.
Remotely operated underwater vehicle
A remotely operated underwater vehicle, or ROV, is a tethered underwater robot piloted in real time from a surface ship, first developed by the U.S. Navy in the 1960s.
Ren‐Gen Xiong
Ren-Gen Xiong (熊仁根, born 1961) is a Chinese chemist at Southeast University who founded ferroelectrochemistry and was elected a Chinese Academy of Sciences academician in 2023.