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Pitch (resin)
Pitch is a thick, dark-colored bituminous substance, the heavy residue left when tar or petroleum is distilled. Solid at room temperature, it binds carbon electrodes for aluminum smelting and serves as a precursor for carbon fiber.
Pitch angle scattering
Pitch angle scattering is the random change of a charged particle's angle to the magnetic field, controlling how energetic particles diffuse and precipitate in magnetized plasmas.
Pitch drop experiment
The pitch drop experiment is a demonstration at the University of Queensland, running since 1927, in which pitch drips from a funnel about once a decade.
Pitman–Yor process
The Pitman–Yor process, also known as the two-parameter Poisson–Dirichlet process, is a Bayesian nonparametric prior over probability measures that generalizes the Dirichlet process by adding a discount parameter, producing power-law behavior useful in language modeling.
Pitru Paksha (पितृ पक्ष)
Pitru Paksha, also known as Pitri Paksha, is a sixteen-day Hindu lunar observance around September–October for honoring ancestors through Shraddha, Tarpan, and Pind Daan rites.
Pitting (contact fatigue)
Pitting, a surface-damage process in contact fatigue, occurs when repeated rolling or rolling-sliding contact removes small pieces of material from bearings, gear teeth, cams, and rails.
Pituitary adenylate cyclase-activating peptide
Pituitary adenylate cyclase-activating peptide (PACAP), also called pituitary adenylate cyclase-activating polypeptide, is a neuropeptide isolated from sheep hypothalamus in 1989 and implicated in migraine and stress responses.
Pityusa Patera
Pityusa Patera, a large volcanic depression in Malea Planum, southern Mars near Hellas basin; IAU diameter 196.51 km, formed 3.9–3.8 Ga; interpreted as a giant caldera above a crust-mantle-boundary magma chamber.
Pivalic acid
Pivalic acid, also called neopentanoic acid or trimethylacetic acid, is a branched five-carbon carboxylic acid, solid at room temperature, known for its sterically hindered neoacid structure and pivalate esters that resist hydrolysis.
Pivot element
A pivot element, central to complete pivoting and other pivoting strategies, is the entry by which Gaussian elimination divides rows below it to create zero multipliers.
Pixel binning
Pixel binning is an image-sensor technique that combines signals from adjacent pixels into one larger pixel, trading resolution for a better signal-to-noise ratio; it is a key solution to the limits of small smartphone camera sensors.
PK 11195
PK 11195 is an isoquinoline carboxamide ligand for the translocator protein (TSPO), synthesized in 1983; radiolabeled with carbon-11, it became the first PET tracer for imaging TSPO in humans.
PKS 1510-089
PKS 1510-089 is a flat-spectrum radio quasar, a blazar whose jet points almost at Earth, about 6 billion light-years away and known for dramatic variability.
PKS 2155-304
PKS 2155-304 is a bright high-frequency-peaked BL Lac object at redshift 0.116, detected at TeV energies by H.E.S.S. and famous for its extreme 2006 gamma-ray outburst.
Place-exchange mechanism in Pt oxide formation
The place-exchange mechanism is an atomic-scale model of platinum surface oxide formation, first proposed in the 1960s, in which an adsorbed oxygen atom and a surface platinum atom exchange positions.
Placebo control
A placebo control is an inactive comparison group in a clinical trial, used with randomization and blinding to distinguish a drug's effect from the placebo effect.
Placer mining
Placer mining extracts valuable minerals, mostly gold, from loose sediment like stream gravel and beach sand using water and gravity, supplying two-thirds of the world's gold.
Placidus Plattner
Placidus Andreas Plattner (1904–1975) was a Swiss organic chemist who taught at ETH Zurich and later directed pharmaceutical research at Ciba Geigy and Hoffmann-La Roche.
Plackett–Burman design
A Plackett–Burman design is a two-level screening design of experiments, introduced by Plackett and Burman in 1946, that estimates the main effects of many factors in few runs.
Plactic monoid
The plactic monoid, or tableau algebra, is the monoid of semistandard Young tableaux with multiplication by insertion; two words are equal exactly when Schensted's algorithm gives the same tableau.
Plagioclase
Plagioclase, or plagioclase feldspar, is a group of rock-forming feldspar minerals forming a continuous solid solution between the sodium end-member albite and calcium end-member anorthite.
Plamen Atanassov
Plamen Atanassov is a Bulgarian-trained American electrochemist and Chancellor's Professor at UC Irvine, known for iron–nitrogen–carbon fuel cell catalysts and elected president-elect of the International Society of Electrochemistry in 2025.
Planar algebra
A planar algebra is an algebraic structure of vector spaces acted on by planar diagrams, introduced by Vaughan Jones in 1999 to axiomatize subfactor invariants.
Planar chirality
Planar chirality is a form of stereoisomerism in which out-of-plane groups destroy the symmetry of a chirality plane, so the molecule is chiral with no stereogenic center, as in (E)-cyclooctene and paracyclophanes.
Planar chromatography
Planar chromatography is a separation technique in analytical chemistry in which the stationary phase is a plane, including paper chromatography and thin-layer chromatography, with components separated by capillary flow.
Planar graph
A planar graph is a graph that can be drawn in the plane with no edge crossings. Planarity is a property of the graph itself, not of one drawing.
Planar Hall effect
The planar Hall effect is a transverse voltage in the same plane as the applied current and magnetic field, arising from anisotropic magnetoresistance rather than the Lorentz force.
Planar laser-induced fluorescence
Planar laser-induced fluorescence (PLIF) is an optical diagnostic that uses a laser sheet to produce instantaneous 2D images of species concentration, temperature, and velocity in flows and flames.
Planarization
Planarization is the process of turning a non-planar graph into a planar one by removing edges or replacing crossings with vertices, used in graph drawing and circuit design.
Planchon-Peteroa
Planchon-Peteroa, a complex of Azufre, Planchon, and Peteroa stratovolcanoes with overlapping calderas on the Chile-Argentina border, 3,977 m, frequently erupting ash; largest historical eruption VEI 4 in 1762; binational monitoring.