All articles starting with R

Reaction–diffusion system

A reaction–diffusion system is a set of coupled partial differential equations describing substances spreading by diffusion while reacting, the standard mathematical model of spontaneous pattern formation.

Reactionary

Reactionary: a political label from the French Revolution era for those seeking to restore a pre-revolutionary order. Distinct from conservatism (status quo); includes neo-reaction (Yarvin, Land, Dark Enlightenment).

Reactionless drive

A reactionless drive, also called inertial propulsion, is a hypothetical propulsion device producing thrust without expelling reaction mass, conflicting with momentum conservation and never confirmed experimentally.

Reactions and applications of polyhydric phenols

Reactions and applications of polyhydric phenols covers benzene rings bearing two or more hydroxyl groups, whose adjacent hydroxyls drive oxidation, metal chelation, crosslinking, and industrial uses.

Reactions of benzylic alcohols

Reactions of benzylic alcohols covers the oxidation, substitution, and C–H functionalization chemistry of alcohols attached directly to benzene rings, whose resonance stabilization enables selective conversion to aldehydes, acids, and ketones.

Reactions to the 2026 Iran war

Reactions to the 2026 Iran war, the US-Israel war on Iran that killed Ali Khamenei: European refusal to join, Russian and Chinese UN vetoes, Gulf condemnations, Pakistani mediation, and US midterm backlash.

Reactions to the assassination of Ali Khamenei

Global reactions to the 28 February 2026 assassination of Iran's Supreme Leader Ali Khamenei in joint US-Israeli strikes: Iranian 40-day mourning, Mojtaba Khamenei's succession, Trump's celebration, Russian and Chinese condemnation, and protests in Iraq.

Reactions to the death of Pope Francis

Reactions to the death of Pope Francis: global response to the pope's death on 21 April 2025, Easter Monday, at the Domus Sanctae Marthae. Covers world tributes, the 26 April funeral with 160 delegations, national mourning, Russian disinformation, and Leo XIV's election.

Reactions to the September 11 attacks

Reactions to the September 11 attacks: American public, international, and institutional responses to the 2001 al-Qaeda attacks that killed nearly 3,000 people, including NATO's first Article 5 invocation, the rally-round-the-flag effect, and later reassessment.

Reactive airway disease

Reactive airway disease (RAD) is an informal, non-diagnostic placeholder term for asthma-like wheezing and cough of unknown cause, used mostly in young children; distinct from asthma, COPD, and reactive airways dysfunction syndrome (RADS).

Oct 21, 2026

Reactive angioendotheliomatosis

Reactive angioendotheliomatosis (RAE) is a rare, benign, self-limiting cutaneous vascular proliferation with endothelial hyperplasia inside and around dermal vessels, occurring with systemic diseases such as endocarditis, renal disease, and peripheral vascular disease.

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 arthritis

Reactive arthritis, formerly Reiter's syndrome, is inflammatory joint disease following gut or urogenital infection (Chlamydia, Salmonella, Shigella, Yersinia), HLA-B27-associated, usually resolving within 6 to 12 months.

Oct 20, 2026

Reactive arthropathies

Reactive arthropathies, or reactive arthritis (ReA), formerly Reiter's syndrome: sterile HLA-B27-associated spondyloarthritis after gastrointestinal or genitourinary infection with Salmonella, Yersinia, or Chlamydia; most remit within 6-12 months.

Reactive attachment disorder

Reactive attachment disorder (RAD), ICD-11 code 6B44, is a rare childhood diagnosis of emotionally withdrawn, inhibited attachment behavior after severe neglect; DSM-5 separates it from disinhibited social engagement disorder, and foster care intervention reduces its signs.

Reactive Black 5

Reactive Black 5, also sold as Remazol Black B, is a vinyl sulfone diazo reactive dye used to dye cellulosic fibers such as cotton in deep black shades.

Reactive Blue 19

Reactive Blue 19, sold as Remazol Brilliant Blue R, is an anthraquinone-based vinyl sulfone reactive dye that gives brilliant royal blue shades on cellulosic fibers such as cotton.

Reactive crystallization

Reactive crystallization is a crystallization method in which a chemical reaction between dissolved species generates a solid crystalline product, creating the supersaturation that drives nucleation and growth.

Reactive distillation

Reactive distillation is a chemical process method combining reaction and distillation in a single column, so products are removed as they form and equilibrium-limited reactions reach high conversion.

Reactive extraction

Reactive extraction is a liquid–liquid separation method in which a reactive extractant chemically complexes a solute, such as an acid or metal ion, into an organic phase.

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 hypoglycemia

Reactive hypoglycemia (postprandial hypoglycemia) is low blood sugar occurring 2–4 hours after a meal, distinct from fasting hypoglycemia. Causes include diabetes drugs, alcohol, and bariatric surgery; managed by diet and Whipple's triad diagnosis.

Reactive molecular dynamics

Reactive molecular dynamics is a molecular simulation method where chemical bonds break and form during the trajectory, so reaction pathways and intermediate species emerge directly.

Reactive oxygen species

Reactive oxygen species, also called reactive oxygen intermediates, are reactive oxygen-containing chemicals formed as oxygen is reduced to water, ranging from superoxide and hydrogen peroxide to the hydroxyl radical.

Oct 22, 2026

Reactive oxygen species generation by nanoparticles

Reactive oxygen species generation by nanoparticles is the production of reactive oxygen derivatives such as superoxide and hydroxyl radicals at nanoparticle surfaces, driving nanotoxicity and experimental cancer and antimicrobial therapies.

Oct 20, 2026

Reactive plasmacytic hyperplasia

Reactive plasmacytic hyperplasia (reactive plasmacytosis), ICD-11 2B32.1, is a benign polytypic plasma cell increase in blood, marrow, or nodes caused by infection, AITL, drugs, malignancy, or autoimmunity, distinct from plasmacytoma.

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.