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Permutation notation
Permutation notation is the collection of mathematical symbols for denoting and counting permutations, including the factorial n!, the count nPr, and two-line and one-line notations.
Permutation polynomial
A permutation polynomial is a polynomial over a finite field, usually, that induces a bijection on the field's elements, with applications in cryptography, coding theory, and combinatorial design.
Permutation representation
A permutation representation is a way of realizing a group's elements as permutations of a set, equivalently a group action of the group on that set.
Permutation test
A permutation test is a nonparametric method of hypothesis testing in which the observed test statistic is compared against the distribution obtained by rearranging, or permuting, the data.
Permutohedron
The permutohedron is a convex polytope whose vertices are all permutations of a vector with distinct coordinates, a higher-dimensional generalization of the hexagon central to geometric combinatorics.
Perovskite
Perovskite is a calcium titanate mineral, CaTiO₃, found in the Ural Mountains in 1839 and named after Count Lev Perovski; the name also covers the ABX₃ crystal-structure family.
Perovskite (structure)
The perovskite structure is a crystal structure of formula ABX3 in which corner-sharing BX6 octahedra form a framework with larger A cations in the cavities between them.
Perovskite exsolution
Perovskite exsolution is a process in which metal cations in a perovskite oxide lattice migrate to the surface under reducing conditions and form anchored nanoparticles.
Perovskite LED
A perovskite LED (PeLED) is a light-emitting diode whose emissive layer is a metal halide perovskite, with high color purity and efficiencies nearing 30% since 2014.
Perovskite nanocrystal
A perovskite nanocrystal is a nanometer-sized crystal of a lead halide perovskite semiconductor, studied as a light-emitting and light-harvesting material for LEDs and solar cells.
Perovskite nanocrystal lasers
Perovskite nanocrystal lasers are lasers whose gain medium is colloidal or thin-film lead halide perovskite nanocrystals, chiefly CsPbX3, offering low thresholds, high gain, and visible-wavelength tunability.
Perovskite nanocrystal scintillator
A perovskite nanocrystal scintillator is a radiation detector material made of perovskite semiconductor nanocrystals, typically CsPbBr3, that converts X-rays and gamma rays into visible light, first reported in 2018.
Perovskite nanoplatelet
A perovskite nanoplatelet is an ultrathin, plate-shaped crystal of a metal-halide perovskite semiconductor, only a few monolayers thick, whose strong quantum confinement yields narrow emission tuned stepwise by thickness and used in LEDs, lasers, and photodetectors.
Perovskite nanowire laser
A perovskite nanowire laser is a miniature laser in which a single-crystal lead halide perovskite wire serves as gain medium and its own Fabry–Pérot cavity, lasing at room temperature.
Perovskite oxide electrocatalysts
Perovskite oxide electrocatalysts are low-cost, tunable ABO₃ crystalline oxides that speed up the oxygen evolution reaction in water splitting, metal-air batteries, and fuel cells, offering alternatives to noble-metal catalysts.
Perovskite photocatalysis
Perovskite photocatalysis is the use of perovskite-structured materials as light-absorbing catalysts driving reactions such as hydrogen evolution, carbon dioxide reduction, and pollutant degradation, constrained by instability and lead toxicity.
Perovskite quantum dots
Perovskite quantum dots (PQDs) are nanometer-scale crystals of metal halide perovskite semiconductors, typically 2 to 10 nm across, valued for size-tunable, narrow-band light emission in displays, LEDs, and solar cells.
Perovskite radiation detector
A perovskite radiation detector uses a metal halide perovskite semiconductor or scintillator to detect ionizing radiation, chiefly X-rays and gamma rays, by converting absorbed photons into charge or light.
Perovskite redox cycles for CO2 splitting
Perovskite redox cycles for CO2 splitting are two-step thermochemical processes that reduce a perovskite oxide at high temperature, then re-oxidize it with CO2 to yield carbon monoxide.
Perovskite scintillator
A perovskite scintillator is a radiation-detection material, typically a lead halide perovskite such as CsPbBr3, that converts X-rays and gamma rays into flashes of visible light for photodetectors to count.
Perovskite semiconductor detector
A perovskite semiconductor detector is a radiation or light sensor made from a metal halide perovskite such as CsPbBr3, used to detect X-rays, gamma rays, and visible light.
Peroxymonosulfate
Peroxymonosulfate is an inorganic sulfur oxoanion with formula O5S2−, containing a peroxide bond, best known in potassium salts sold as Oxone and used as an oxidant.
Peroxymonosulfate oxidation
Peroxymonosulfate oxidation is an advanced oxidation process that degrades organic pollutants in water by activating peroxymonosulfate to generate sulfate radicals, an approach introduced for remediation in the late 1990s.
Peroxynitrite
Peroxynitrite (ONOO⁻) is a short-lived, reactive biological oxidant formed by the rapid reaction of nitric oxide with superoxide, and it induces cell death in vascular disease, inflammation, and neurodegeneration.
Perpendicular
Perpendicular describes two lines, segments, rays, vectors, or planes that meet at a right angle of 90 degrees; in vector terms, perpendicular vectors have a dot product of zero.
Perpetua Resources
Perpetua Resources Corp., formerly Midas Gold until its 2021 renaming, is a mining company advancing the Stibnite Gold Project, a gold and antimony mine in central Idaho.
Perpetual calendar
A perpetual calendar is a table, mechanical instrument, or calculation method, such as Conway's Doomsday rule, that works for many years because the Gregorian calendar repeats every 400 years.
Perpetual motion
Perpetual motion, also known as a perpetual motion machine or free energy device, is the hypothetical operation of a machine indefinitely without energy input, impossible under the laws of thermodynamics.
Perron method (verification)
The Perron method is an existence proof technique for viscosity solutions of Hamilton–Jacobi PDEs, constructing a value function that encodes the set of states from which a system can be driven to a target.
Perron–Frobenius theorem
The Perron–Frobenius theorem is a linear algebra result stating that a matrix with positive entries, or an irreducible nonnegative one, has a dominant positive eigenvalue with a positive eigenvector.