All articles starting with P
28,818 articles
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 heterojunction perovskite solar cells
A planar heterojunction perovskite solar cell is a photovoltaic device with a flat perovskite film between electron and hole transport layers, without a porous scaffold.
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.
Planar parallel manipulator
A planar parallel manipulator is a closed-loop mechanism that moves a platform in one plane with two translations and one rotation, three degrees of freedom at most.
Planar process
The planar process is a semiconductor manufacturing method, developed by Jean Hoerni at Fairchild Semiconductor between 1957 and 1959, that became the foundation of high-volume integrated circuit manufacturing.
Planar separator theorem
The planar separator theorem states that any n-vertex planar graph can be divided by at most 2√(2n) separator vertices, found in linear time by Lipton and Tarjan's 1979 algorithm.
Planar transformer
A planar transformer is a transformer whose primary and secondary windings are flat copper traces etched on a printed circuit board, used in compact, high-frequency power converters.
Planarian
Planarians (planarian worms, triclads) are free-living freshwater flatworms of the order Tricladida, best known for regenerating any missing body region, including heads, from small fragments.
Planarian regeneration
Planarian regeneration: flatworms regrow any missing body part within about a week using pluripotent neoblasts (25-30% of cells), blastema formation plus morphallaxis, and muscle-expressed position-control genes with Wnt, Bmp, and Slit patterning.
Planarian reproduction
Planarian reproduction takes two forms: asexual transverse fission, where torn pieces each regenerate into a complete worm, and sexual reproduction by cross-fertilizing hermaphrodites that lay egg capsules.
Planarity testing
Planarity testing, also called graph planarity, is the algorithmic problem of deciding whether a graph can be drawn without crossing edges, solvable in linear time since 1974.
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.
Planchette
A planchette is a small heart-shaped or triangular board on casters with a pencil, used for automatic writing and regarded by spiritualists as a means of spirit communication.
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.
Planck (lunar crater)
Planck is a 319.46-km-diameter impact crater on the Moon's far side at about 57°S, 135°E, inside the South Pole–Aitken basin, with IAU satellite craters Planck A, L, J, and Y.
Planck (spacecraft)
Planck was a European Space Agency satellite that surveyed the whole sky from 2009 to 2013 to map the cosmic microwave background, the relic radiation of the Big Bang.
Planck constant
The Planck constant (Planck's quantum of action) is a fundamental physical constant relating a photon's energy to its frequency, which has defined the kilogram since 2019.
Planck energy
The Planck energy is a natural unit of energy, about 1.22 × 10¹⁹ GeV, the scale where quantum gravity becomes important and far beyond any accelerator.
Planck epoch
The Planck epoch is the earliest period of the Universe, lasting from the Big Bang to one Planck time, about 5.39 × 10⁻⁴⁴ seconds, when gravity was as strong as the other forces.
Planck length
The Planck length is a natural unit of length built from fundamental physical constants, about 1.616 × 10⁻³⁵ meters, where quantum mechanics and general relativity both apply.
Planck mass
The Planck mass is a natural unit of mass formed from the constants of gravity, quantum mechanics, and light, equal to about 20 micrograms, roughly a flea egg.
Planck Sunyaev-Zel'dovich cluster catalogue
The Planck Sunyaev-Zel'dovich cluster catalogue lists galaxy clusters found by the Planck satellite through the Sunyaev-Zel'dovich effect, growing from 189 clusters in 2011 to 1653 detections in 2015.
Planck units
Planck units, sometimes called God's units, are natural units built from fundamental physical constants, proposed by Max Planck in 1899 and used in quantum gravity.
Planck's law
Planck's law, also called Planck's law of black-body radiation, gives the spectral radiance of radiation emitted by a blackbody, derived by Max Planck in 1900 through energy quantization.
Planckian dissipation
Planckian dissipation is a pattern in condensed matter physics where a metal's scattering rate is set by the Planckian time, h-bar over k-B times T, with order-one coefficient.
Planday
Planday is a Copenhagen-based software company selling a cloud workforce-management platform for shift-based businesses, covering scheduling, time tracking, and communication; Xero acquired it in 2021 for up to €183.5 million.