Technology and the built world

RE100

RE100 (Renewable Energy 100) is a global corporate initiative led by the Climate Group with CDP, launched in 2014, asking companies to commit to 100 percent renewable electricity.

REA Group is an Australian multinational digital advertising company specializing in property, majority-owned by News Corp since floating in 1999, best known for realestate.com.au, Australia's largest residential property portal.

Rea Vaya

Rea Vaya is a bus rapid transit system in Johannesburg, South Africa, opened in August 2009 as the first full-feature BRT system on the African continent.

Reachability analysis

Reachability analysis is a formal verification method that computes the set of states a dynamical system can enter, certifying safety by checking that reachable states avoid unsafe regions.

Reachability map

A reachability map is a discretized voxel grid of a robot's workspace recording which end-effector positions and orientations are reachable, used for base placement, grasp planning, and workspace analysis.

Reachable set analysis

Reachable set analysis computes which states a dynamical system can enter from given initial states under all inputs, including which robot footsteps prevent a fall.

Reachy

Reachy is a family of open-source humanoid robots from Pollen Robotics, a Bordeaux company founded in 2016 that Hugging Face acquired in 2025, including Reachy 2 and Reachy Mini.

ReAct

ReAct is a 2022 prompting and agent-execution method in which a language model interleaves reasoning traces with actions such as tool calls, each action feeding the next thought.

React Native

React Native is an open-source framework created by Meta, first released in 2015, for building mobile apps with JavaScript and React that render real native views on iOS and Android.

ReAct prompting

ReAct prompting is a technique for large language models that interleaves reasoning traces with actions, introduced in a 2022 paper by Shunyu Yao and colleagues and presented at ICLR 2023.

React Router

React Router is a routing library for React that maps URLs to components and handles data loading, first released in 2014 by Ryan Florence and Michael Jackson.

Reaction bonding

Reaction bonding is a ceramic fabrication method that converts a shaped metal powder compact, usually silicon, into ceramic by reaction with nitrogen or another infiltrant.

Reaction control system

A reaction control system (RCS) is a set of small rocket thrusters on a spacecraft or aircraft, used for attitude control, small maneuvers, and station keeping, unlike main propulsion.

Oct 22, 2026

Reaction Mechanism Generator

Reaction Mechanism Generator (RMG) is a free, open-source software suite developed at MIT and Northeastern University that automatically builds detailed chemical kinetic models from elementary reaction steps.

Reaction wheel

A reaction wheel, also called a momentum wheel, is a flywheel spun by an electric motor to control a spacecraft's orientation; three or four wheels give precise three-axis pointing.

Reactive armour

Reactive armor, or explosive reactive armor (ERA), is add-on vehicle protection in which explosive-driven plates move into a projectile's path, reducing penetration by up to 75%.

Reactive extrusion

Reactive extrusion is a polymer processing method in which a twin-screw extruder acts as a continuous, solvent-free chemical reactor for polymerization, grafting, compatibilization, and controlled degradation of polymers.

Reactive grasping

Reactive grasping is a robotic grasping strategy where the robot adjusts its grasp during execution in response to real-time sensor feedback, most often tactile contact data, instead of executing a preplanned grasp open-loop.

Reactive power

Reactive power is the portion of AC electricity that sustains the electric and magnetic fields of equipment like motors and transformers, and it directly influences grid voltage.

Reactive power optimization

Reactive power optimization, also known as optimal reactive power dispatch or Volt/VAR optimization, adjusts generator voltages, transformer taps, and VAR sources to cut grid power losses.

Reactive programming

Reactive programming is a programming paradigm in which changes to values automatically propagate to dependent computations, essentially the spreadsheet's recalculation model embedded in programming languages.

Reactive sputter deposition

Reactive sputter deposition, also called reactive sputtering, is a physical vapor deposition method that makes compound films by sputtering a metal target in a reactive gas.

Reactive synthesis

Reactive synthesis is a formal methods technique that automatically constructs a controller, circuit, or transducer from a temporal logic specification, guaranteed correct no matter how its environment behaves.

Reactive-ion etching

Reactive-ion etching (RIE) is a dry etching method that combines plasma chemistry with ion bombardment to carve steep-sided, finely dimensioned features into semiconductor wafers during microfabrication.

Reactivity controlled compression ignition

Reactivity controlled compression ignition (RCCI) is a dual-fuel, low-temperature combustion strategy in which gasoline and similar fuels are ignited by injected diesel, giving high efficiency and low emissions.

Reactome

Reactome is a free, open-access, peer-reviewed knowledgebase describing human biology as a network of molecular pathways, founded in 2003 and led from the Ontario Institute for Cancer Research.

REACTOR (expert system)

REACTOR was an expert system developed by William R. Nelson at EG&G Idaho to help reactor operators diagnose and treat nuclear accidents, presented in 1982.

Reactor containment building

A reactor containment building is the air-tight, usually steel-reinforced concrete structure housing a nuclear reactor, acting as the primary barrier against radioactive release in an accident.

Reactor coolant pump

A reactor coolant pump is the large centrifugal pump that circulates primary coolant through a nuclear reactor core, with shaft seals that limit radioactive water leakage.