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Pyrrole
Pyrrole is a colorless, aromatic five-membered heterocycle with formula C₄H₅N, detected in coal tar in 1834 and parent of the ring in heme, chlorophyll, and cobalamin.
Pyrrole-, furan- and thiophene-carboxylic acids
Pyrrole-, furan- and thiophene-carboxylic acids are carboxylic acids on five-membered heteroaromatic rings, ranging in acidity from pKa 3.15 to 5.0; furan acids are made from biomass and FDCA is a monomer of the polyester PEF.
Pyrrolidine
Pyrrolidine, also known as tetrahydropyrrole or azacyclopentane, is a colorless, strongly basic five-membered cyclic secondary amine (C₄H₉N) used industrially and found in drugs and tobacco.
Pyruvic acid
Pyruvic acid, also called acetylformic acid, is the simplest alpha-keto carboxylic acid; at neutral pH it is pyruvate, the junction of glycolysis and the citric acid cycle.
Pythagorean cup
The Pythagorean cup, also called the greedy cup or Tantalus cup, is a drinking cup with a hidden siphon that drains all its contents when filled above a set level.
Pythagorean theorem
The Pythagorean theorem, also known as Pythagoras's theorem, states that in a right triangle with legs a and b and hypotenuse c, a² + b² = c².
Pythagorean triple
A Pythagorean triple is a set of three positive integers (a, b, c) with a² + b² = c², such as (3, 4, 5), the side lengths of a right triangle.
Pyxis
Pyxis is a small southern constellation, the mariner's compass, created by French astronomer Nicolas-Louis de Lacaille in the 18th century and now one of the 88 official constellations.
PZ Tel
PZ Tel, also cataloged as HD 174429, is a young G9 pre-main-sequence star in Telescopium, about 51.5 parsecs away, hosting the directly imaged brown dwarf PZ Tel B.
Q (number format)
Q is a notation for fixed-point binary numbers, devised by Texas Instruments, in which Qm.n names m integer bits and n fractional bits, fixing an implicit scaling factor.
Q factor
The Q factor (quality factor) is a dimensionless parameter measuring how weakly damped a resonator is: the ratio of stored energy to energy dissipated per cycle, or resonance frequency divided by bandwidth.
Q value (nuclear science)
The Q value in nuclear science is the energy released or absorbed in a nuclear reaction or decay, positive for exothermic processes and negative for endothermic ones.
Q-analog
A q-analog, also called a q-analog or q-deformation, is a mathematical expression or identity parameterized by q that reduces to a known classical object when q is set to 1.
Q-Pochhammer symbol
The q-Pochhammer symbol (a;q)n, also called the q-shifted factorial, is the q-analog of the Pochhammer symbol, a finite product that becomes an infinite product building block of q-series and partition generating functions.
Q-sort
A Q-sort is a research procedure in which participants rank-order a shared set of statements on cards from agreement to disagreement, the data-collection step of Q methodology for studying subjectivity.
q-value (statistics)
John D. Storey introduced the q-value (statistics) in 2002, a measure of significance that defines the minimum false discovery rate at which a test would be called significant.
Q-vector
A Q-vector is a horizontal vector used in quasigeostrophic meteorology whose divergence appears in the omega equation, forcing synoptic-scale vertical velocity; Q-vector convergence implies ascent.
Q–Q plot
A Q–Q plot (quantile–quantile plot) is a statistical graphic comparing two probability distributions by plotting their quantiles against each other; points off the 45-degree reference line reveal differences in location, scale, or tails.
Q. Daniel Wang
Q. Daniel Wang is an astrophysicist and professor of astronomy at the University of Massachusetts Amherst, known for X-ray studies of hot plasma in and around galaxies.
Q.E.D.
Q.E.D., short for the Latin quod erat demonstrandum ("which was to be demonstrated"), is written at the end of a mathematical proof to signal completion.
QAM (complexity class)
QAM, or quantum Arthur-Merlin, is a quantum complexity class of decision problems with two-message public-coin quantum interactive proofs, where Arthur sends random bits, Merlin replies with a quantum state, and it sits between QMA and QIP.
QCD critical point
The QCD critical point is a hypothesized point in the quantum chromodynamics phase diagram where the first-order transition between quark-gluon plasma and hadronic matter ends, sought at RHIC.
QCD factorization
QCD factorization is a particle physics framework separating hard hadronic processes into short-distance parts calculable in perturbation theory and universal nonperturbative functions such as parton distribution functions.
QCD matter
QCD matter, also called quark matter, is matter whose behavior follows quantum chromodynamics, including the hot quark-gluon plasma and cold dense quark matter in neutron stars.
QCD sum rules
QCD sum rules are a theoretical physics method relating hadron properties, such as masses and decay constants, to the fundamental parameters of quantum chromodynamics (QCD).
Qi Jie Wang
Qi Jie Wang (Wang Qijie) is a Singapore-based optoelectronics researcher and President's Chair Professor at Nanyang Technological University, known for demonstrating the first electrically pumped topological laser in 2020.
Qian Chen
Qian Chen is a materials chemist and professor at the University of Illinois Urbana-Champaign known for electron videography, using liquid-phase electron microscopy to film nanoparticles and proteins as they self-assemble.
Qian Niu
Qian Niu (牛谦) is a Chinese condensed matter theorist known for work on the Berry phase and semiclassical electron dynamics in crystals, including the anomalous velocity of Bloch electrons.
Qiang Fu (environmental scientist)
Qiang Fu is an atmospheric scientist at the University of Washington known for correcting satellite temperature records and elected to the National Academy of Sciences in 2024.
Qiang Lin
Qiang Lin is an American-based physicist at the University of Rochester working on integrated quantum photonics and lithium niobate photonics, who received a 2015 PECASE award.