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Quinazoline
Quinazoline is an aromatic bicyclic organic compound, a fused benzene–pyrimidine ring system with formula C₈H₆N₂, first synthesized in 1895 and the scaffold of many drugs and about 150 natural alkaloids.
Quincke effect
The Quincke effect, also called Quincke rotation, is the spontaneous rotation of dielectric particles in a conducting liquid under a strong enough DC electric field.
Quincke roller
A Quincke roller is a dielectric colloidal particle that spontaneously rotates and rolls in a weakly conducting fluid above a threshold DC electric field, named for G. Quincke.
Quinic acid
Quinic acid, also called chinic acid, is a plant-derived carboxylic acid of the shikimate pathway, found in coffee, and a chiral building block for the influenza drug oseltamivir.
Quinoline
Quinoline, also known as benzopyridine, is a heterocyclic aromatic compound with fused benzene and pyridine rings, a colorless liquid used as a chemical intermediate in manufacturing.
Quinolinic acid
Quinolinic acid, also known as quinolinate, is a dicarboxylated pyridine formed from tryptophan in the kynurenine pathway, acting as an NMDA receptor agonist and neurotoxin linked to neurodegenerative disease.
Quinone
A quinone is an organic compound with a fully conjugated cyclic dione structure, derived from an aromatic compound; the simplest members, the benzoquinones, have the formula C₆H₄O₂.
Quinoxaline
Quinoxaline (1,4-benzodiazine, benzopyrazine) is a bicyclic aromatic heterocycle of fused benzene and pyrazine rings, first synthesized in 1884 and used as a scaffold in medicinal chemistry and organic electronics.
Quinten A. Akkerman
Quinten A. Akkerman is a Dutch nanomaterials chemist who has led the Quantum Dot Synthesis and Characterization group at LMU Munich since 2021, studying lead halide perovskite nanocrystals.
Quintessence (physics)
Quintessence is a hypothesized form of dark energy driven by a dynamic scalar field, not a constant cosmological constant, proposed by Ratra and Peebles in 1988.
Quintic equation
A quintic equation is a polynomial equation of degree five. Unlike lower-degree equations, the general quintic cannot be solved by radicals, as proved by Abel and Galois.
Quintuplet Cluster
The Quintuplet Cluster is a young, massive star cluster about 26,000 light years from Earth near the Milky Way's center, named for five bright infrared sources.
Quinuclidine
Quinuclidine, or 1-azabicyclo[2.2.2]octane, is a rigid bicyclic tertiary amine whose ring occurs in alkaloids such as quinine, and which serves as a laboratory reagent and catalyst.
Quinuclidine-catalyzed HAT arylation of C(sp3)–H bonds
Quinuclidine-catalyzed HAT arylation of C(sp3)–H bonds is a photoredox method in which a quinuclidine radical cation abstracts hydrogen atoms from strong aliphatic C–H bonds, forming new C–C bonds.
Quipu (cosmic structure)
Quipu, named for the Incan knotted cords, is a filamentary superstructure of galaxy clusters identified in 2025 as the largest found in its survey, about 1.3 billion light-years long with a mass of 200 quadrillion Suns.
Quorum-sensing active particles
Quorum-sensing active particles are self-propelled particles, biological or synthetic, whose motility depends on the local density of neighbors, adapting bacterial quorum sensing to active matter physics.
Quota sampling
Quota sampling is a non-probability survey method in which the sample is divided into quotas for demographic subpopulations, filled through non-random selection. George Gallup introduced it in 1936.
Quotient
A quotient is the result of dividing one number by another; in Euclidean division of 41 by 7, the quotient is 5 with remainder 6.
Quotient group
A quotient group, also called a factor group, is a group built from a group G and a normal subgroup N by treating the cosets of N as elements.
Quotient module
A quotient module, also called a factor module, is the module analog of a quotient group: the cosets M/N of a submodule N, with well-defined addition and scalar multiplication.
Quotient ring
A quotient ring, also called a factor ring or residue class ring, is a ring built from a ring R and an ideal I, generalizing modular arithmetic.
Quotient rule
The quotient rule is a differential calculus formula giving the derivative of a quotient of two differentiable functions, (f/g)' = (f'g − fg')/g², valid wherever the denominator g is nonzero.
Quotient set
A quotient set is the set of all equivalence classes of a set under an equivalence relation, so equivalence becomes equality, as in the integers modulo n.
Quotient space (linear algebra)
The quotient space V/W of a vector space V by a subspace W is the vector space of cosets v + W, formed by collapsing W to zero.
Quotient stack
A quotient stack, also called a quotient algebraic stack, is an algebraic stack of the form [X/G], recording orbits and stabilizers of a group action.
R (programming language)
R, also known as GNU S, is a free programming language for statistical computing and graphics, created by Ross Ihaka and Robert Gentleman in New Zealand.
R And
R Andromedae (R And) is a Mira variable star in Andromeda, varying from magnitude 5.0 to 15.2 over 409 days and notable for technetium in its spectrum.
R Aql
R Aquilae (R Aql) is a Mira variable red giant in Aquila whose pulsation period has declined from about 365 to about 275 days since 1850.
R Coronae Borealis
R Coronae Borealis (R CrB) is a hydrogen-deficient, carbon-rich supergiant in Corona Borealis and prototype of the RCB variables, which fade unpredictably when carbon dust clouds obscure the star.
R Coronae Borealis variable
An R Coronae Borealis variable (RCB star) is a rare hydrogen-deficient, carbon-rich supergiant that stays bright for long periods, then fades deeply, up to 8 magnitudes, as carbon dust clouds obscure it.