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PMMA depolymerization to monomer
PMMA depolymerization to monomer is the chemical recycling process that breaks poly(methyl methacrylate), the transparent plastic sold as Perspex and Plexiglass, back into its monomer, methyl methacrylate, for reuse.
PNAD
PNAD (Pesquisa Nacional por Amostra de Domicílios) is a Brazilian household sample survey run by the IBGE since 1967; its successor, the PNAD Contínua (2012), is Brazil's headline unemployment source.
Pnictogen
A pnictogen, also called a nitrogen group element, is one of the group 15 elements of the periodic table: nitrogen, phosphorus, arsenic, antimony, bismuth, and synthetic moscovium.
Pnictogen bond
A pnictogen bond is a directional noncovalent attraction between an electrophilic Group 15 atom (nitrogen through bismuth) and a nucleophile, used in crystal engineering, anion binding, and catalysis.
Po-Shen Loh
Po-Shen Loh is a mathematician at Carnegie Mellon University working in extremal combinatorics who coached the US IMO team to four first-place finishes and founded Expii.
Pochhammer symbol
The Pochhammer symbol, also called the shifted factorial, is the notation (a)n for the rising factorial a(a+1)(a+2)⋯(a+n-1); in combinatorics it can instead mean the falling factorial.
Pockels effect
The Pockels effect, also called the Pockels electro-optic effect, is the linear electro-optic effect in which a material's refractive index changes proportionally to an applied electric field.
Poco Mandasawu
Poco Mandasawu (Gunung Poco Mandasawu, Poco Likang) is a lava dome of the Ranakah volcanic complex in south-central Flores, Indonesia, near Ruteng; elevations 2,109-2,370 m are published, and the 1987 Anak Ranakah dome eruption ended 400 dormant years.
Pohang Light Source
The Pohang Light Source (PLS, 포항방사광가속기) is a synchrotron radiation facility in Pohang, South Korea, operated by PAL and POSTECH and upgraded to 3.0 GeV in 2012.
Pohang University of Science and Technology
Pohang University of Science and Technology, also known as POSTECH (포항공과대학교), is a small, STEM-focused private research university in Pohang, South Korea, founded by the steelmaker POSCO in 1986.
Pohela Boishakh (পহেলা বৈশাখ)
Pohela Boishakh (পহেলা বৈশাখ), also called Poila Baisakh, is the Bengali New Year, celebrated each 14 April in Bangladesh, where it is the largest secular festival.
Poincaré algebra
The Poincaré algebra is the ten-dimensional Lie algebra of the Poincaré group, the symmetry group of flat spacetime, named for Henri Poincaré, who studied the group in 1905.
Poincaré conjecture
The Poincaré conjecture, also called Smale's second problem, states that every closed, simply connected 3-dimensional manifold is the 3-sphere; Grigori Perelman proved it in 2002.
Poincaré disk model
The Poincaré disk model is a conformal model of hyperbolic geometry in which the hyperbolic plane is drawn as the interior of a circle, introduced by Eugenio Beltrami in 1868.
Poincaré duality
Poincaré duality is a theorem of algebraic topology stating that on a closed orientable n-manifold, the k-th cohomology group is isomorphic to the (n − k)-th homology group.
Poincaré group
The Poincaré group, or inhomogeneous Lorentz group, is the group of all symmetries of Minkowski spacetime in special relativity, combining Lorentz transformations with spacetime translations.
Poincaré half-plane model
The Poincaré half-plane model represents hyperbolic geometry on the upper half of the complex plane, where geodesics are vertical lines and semicircles meeting the real axis at right angles.
Poincaré homology sphere
The Poincaré homology sphere, also called the Poincaré dodecahedral space, is a closed 3-manifold with the same homology as the 3-sphere, whose nontrivial fundamental group disproved Poincaré's 1900 claim.
Poincaré inequality
The Poincaré inequality, a result in Sobolev space theory named after Henri Poincaré, bounds a function's size on a bounded domain by the size of its gradient.
Poincaré map
The Poincaré map, or first-return map, records where a continuous dynamical system's trajectories cross a transversal surface, reducing the flow to a lower-dimensional discrete map.
Poincaré plot
The Poincaré plot, also called a Lorenz plot, is a scatter plot of each value of a time series against the next, used in heart rate variability analysis.
Poincaré recurrence theorem
The Poincaré recurrence theorem, also called the Poincaré return theorem, states that in a finite measure-preserving dynamical system almost every point returns to its starting set infinitely often.
Poincaré sphere
The Poincaré sphere is a geometric representation mapping every polarization state of light to a point on or inside a unit sphere, introduced by Henri Poincaré in 1892.
Point (geometry)
A point in geometry is an object that marks a location and has no size, one of the primitive objects from which lines and figures are built.
Point at infinity
A point at infinity, also called an ideal point, is a point added to each family of parallel lines so that any two distinct lines meet in exactly one point.
Point bar
A point bar is a sediment deposit built on the inside of a river bend where slower water drops its load, a defining feature of meandering rivers.
Point charge
A point charge is an idealized electric charge concentrated at a single point in space, the simplest source in electrostatics, from whose fields more complicated charge distributions are built.
Point counting (stereology)
Point counting is a stereological method that estimates the volume or volume fraction of a structure by counting how many points of a regularly spaced grid fall on it in sections.
Point diffraction interferometer
The point diffraction interferometer (PDI), introduced by Smartt and Strong in 1972, is a common-path optical interferometer using a pinhole-diffracted reference wave to measure wavefronts with subnanometer accuracy.
Point group
A point group is a group of symmetry operations, such as rotations and reflections, that all leave one common point fixed; crystallography has exactly 32 such groups.