42,772 articles
Poynting–Robertson effect
The Poynting–Robertson effect, proposed by John Henry Poynting in 1903 and treated relativistically by Howard P. Robertson in 1937, is radiation drag that makes small orbiting dust particles lose momentum and spiral inward toward the Sun.
PP (complexity)
PP, or probabilistic polynomial time, is a complexity class of decision problems accepted by probabilistic polynomial-time machines with probability greater than 1/2, defined by John Gill in 1977.
Pp-wave spacetime
A pp-wave spacetime, or pp-wave metric, is a Lorentzian spacetime in general relativity with a covariantly constant null vector, describing massless radiation moving at light speed.
PPA (complexity)
PPA, short for Polynomial Parity Argument, is a complexity class of total search problems within TFNP, introduced by Christos Papadimitriou in 1994, whose totality rests on undirected parity.
PPM Star Catalog
The PPM Star Catalog (Catalogue of Positions and Proper Motions) is an all-sky astrometric catalog of 378,910 stars, compiled in Heidelberg and replacing the SAO Catalogue.
PPM Star Catalogue
The PPM Star Catalogue (Positions and Proper Motions) is an astrometric catalog of about 379,000 stars on the J2000/FK5 system, published from 1988 to 1993.
Pr1−xSrxNiO2
Pr1−xSrxNiO2, known as PSNO, is a strontium-doped praseodymium nickelate whose thin films superconduct at about 9 to 15 K, the second superconducting rare-earth nickelate after the Nd compound.
Practical number
A practical number is a positive integer such that every integer up to n is a sum of distinct divisors of n; 12 is the classic example.
Practolol
Practolol, sold as Eraldin, is a selective β1-adrenergic antagonist developed by Imperial Chemical Industries and introduced in 1970 as the first β1-selective beta blocker, withdrawn in 1976.
Pradeep R. Guduru
Pradeep R. Guduru is a Professor of Engineering at Brown University who studies adhesion and friction in soft materials and battery materials, and received a PECASE award in 2006.
Prafulla Chandra Ray (প্রফুল্ল চন্দ্র রায়)
Prafulla Chandra Ray (প্রফুল্ল চন্দ্র রায়), honored as Acharya Prafulla Chandra Ray, was an Indian chemist who discovered mercurous nitrite in 1896 and founded India's first pharmaceutical company.
Pranab K. Sen
Pranab Kumar Sen (1937–2023) was an Indian-born American statistician who spent five decades at UNC Chapel Hill and was known for nonparametric statistics, rank tests, and the Sen–Theil estimator.
Prandtl number
The Prandtl number (Pr) is a dimensionless fluid property, the ratio of momentum diffusivity to thermal diffusivity, named after Ludwig Prandtl and central to heat transfer.
Prasanta Chandra Mahalanobis
Prasanta Chandra Mahalanobis was an Indian statistician who founded the Indian Statistical Institute in Calcutta, introduced the Mahalanobis distance, and architectured India's statistical system and Second Five-Year Plan.
Praseodymium
Praseodymium is a soft, silvery lanthanide metal with atomic number 59, best known as a substitute for neodymium in magnets and as part of didymium glass.
Prashant K. Jain
Prashant K. Jain, also published as Prashant Jain, is a physical chemist who studies plasmonics and holds the G. L. Clark Professorship at the University of Illinois Urbana-Champaign.
Prashant Sonar
Prashant Sonar is an organic and printed electronics materials scientist at Queensland University of Technology in Brisbane, known for research on organic semiconductors, transistors, and solar cells.
Prashant V. Kamat
Prashant V. Kamat is a physical chemist at the University of Notre Dame known for quantum dot solar cells, perovskite photophysics, and founding editorship of ACS Energy Letters.
Prashanth W. Menezes
Prashanth W. Menezes is a materials chemist who heads the Department of Materials Chemistry for Catalysis at Helmholtz-Zentrum Berlin and studies electrocatalysts for splitting water into hydrogen and oxygen.
Pre-exponential factor
The pre-exponential factor, also called the frequency factor or Arrhenius A factor, is the constant A in the Arrhenius equation that represents the frequency of collisions between reactant molecules.
Pre-main-sequence star
A pre-main-sequence star is a young star that shines by gravitational contraction before hydrogen fusion begins in its core; low-mass examples are seen as T Tauri stars.
Pre-salt layer
The pre-salt layer is a sequence of Aptian-age rock salt off Brazil and West Africa, beneath which lie oil reservoirs supplying most of Brazil's oil.
Pre-sliding displacement
Pre-sliding displacement, also known as micro-slip or the Dahl effect, is the small tangential displacement in a contact before the whole body slides, showing hysteresis with non-local memory.
Pre-stack depth migration
Pre-stack depth migration, or PSDM, is a seismic imaging technique that migrates unstacked traces into a depth image using a velocity-depth model, correctly positioning reflectors under salt and complex structure.
Preamplifier
A preamplifier, or preamp, is an electronic amplifier that raises a weak signal to a noise-tolerant level, feeding a power amplifier and loudspeaker in an audio system.
Precalculus
Precalculus, also known as pre-calc or Advanced Algebra and Trigonometry, is the secondary and early college mathematics course covering algebra, trigonometry, and function theory, typically ending with limits, to prepare students for calculus.
Precambrian
The Precambrian is the supereon of geologic time from Earth's formation about 4.6 billion years ago to the start of the Cambrian, 538.8 million years ago.
Precedence effect
The precedence effect, also known as the Haas effect or law of the first wavefront, is an auditory phenomenon in which listeners localize a sound by its first-arriving wavefront, fusing echoes that follow within milliseconds.
Precession
Precession is the gradual change in the direction of a rotation axis, which sweeps around a second axis in a cone, as in spinning tops and gyroscopes.
Precession electron diffraction
Precession electron diffraction (PED) is a transmission electron microscopy technique, introduced by Vincent and Midgley in 1994, that makes diffraction intensities more suitable for crystal structure solution.