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Peano axioms
The Peano axioms, or Dedekind–Peano axioms, are axioms characterizing the natural numbers through zero, a successor operation, and induction, introduced by Giuseppe Peano in 1889.
Peano curve
The Peano curve is a continuous curve that passes through every point of a square, constructed by Giuseppe Peano in 1890 as the first known space-filling curve.
Pear-shaped nuclei
Pear-shaped nuclei are atomic nuclei with more of their mass at one end than the other, an octupole deformation observed mainly in unstable heavy nuclei such as radium-224 and radium-226.
Pearlite
Pearlite is a two-phase steel microstructure of alternating ferrite and cementite lamellae, named for its pearly appearance; finer spacing gives higher strength, as in pearlitic railway track steel.
Pearls in Graph Theory
Pearls in Graph Theory is an undergraduate graph theory textbook by Nora Hartsfield and Gerhard Ringel, first published by Academic Press in 1990 and reprinted by Dover in 2003.
Pearson correlation coefficient
The Pearson correlation coefficient, or Pearson's r, measures the linear relationship between two variables, ranging from −1 to +1, and is the most common correlation method in statistics.
Pearson correlation test
The Pearson correlation test is a statistical test of whether the population correlation between two continuous variables differs from zero, exact under bivariate normality and otherwise approximate.
Pearson's chi-squared test
Pearson's chi-squared test, also known as the Pearson chi square, is a significance test for categorical data comparing observed and expected counts, introduced by Karl Pearson in 1900.
Peat subsidence
Peat subsidence is the lowering of the land surface when drained peat soils shrink, consolidate, compact, and oxidize, typically at rates of millimeters to centimeters per year.
Peatland rewetting
Peatland rewetting is the cessation of drainage and restoration of high groundwater levels in degraded peatlands, typically by ditch blocking, to stop carbon dioxide emissions from dried-out peat soils.
Pebble
A pebble is a small rock fragment, 4 to 64 mm in diameter, rounded by stream or wave transport; its size and shape record how far it traveled.
Pebble accretion
Pebble accretion is a planet-formation mechanism in which planetary cores grow by capturing millimeter- to centimeter-sized pebbles, with gas drag boosting accretion rates far above planetesimal accretion.
PECAN resin
PECAN resin, short for PolyEster Covalently Adaptable Network, is a bio-derivable, recyclable thermoset resin developed at NREL as a drop-in replacement for epoxy in wind turbine blades.
Peccei–Quinn symmetry
Peccei–Quinn symmetry is a hypothetical chiral symmetry proposed by Roberto Peccei and Helen Quinn in 1977 to solve the strong CP problem, implying a light particle called the axion.
Pechini method
The Pechini method is a sol-gel synthesis route in which citric acid chelates metal cations and ethylene glycol forms a resin, calcined to give homogeneous mixed-metal oxides.
Péclet number
The Péclet number (Pe) is a dimensionless number comparing convective to diffusive transport in a fluid; small Pe means diffusion dominates, large Pe means advection.
Peculiar velocity
A peculiar velocity is a galaxy's velocity remaining after the Hubble flow from the universe's uniform expansion is subtracted, caused by gravitational tugs from surrounding matter concentrations.
Pedestal (plasma physics)
The pedestal is the narrow region of steep pressure gradient at the outer edge of a tokamak plasma, formed by the edge transport barrier in H-mode.
Pedometric mapping
Pedometric mapping, commonly known as digital soil mapping, uses mathematical and statistical methods to predict the distribution and properties of soils across space, producing raster maps with explicit uncertainty.
PEDOT:PSS
PEDOT:PSS, also known as Baytron P, is a water-processable conducting polymer blend of PEDOT and PSS, developed by Bayer in 1988, used in organic solar cells, thermoelectrics, and bioelectronics.
Pedotransfer functions
Pedotransfer functions are mathematical models, typically regressions or machine learning, that estimate hard-to-measure soil hydraulic properties from routinely available data like texture and bulk density.
Pedro M. Reis
Pedro M. Reis (Pedro Miguel Reis) is a physicist and mechanical engineer who studies the mechanics of slender structures and elastic instabilities, and is a Full Professor at EPFL in Switzerland.
Pedro Pérez (Spanish chemist)
Pedro J. Pérez, born 1965 in Aroche, Spain, is a Spanish organometallic chemist and professor of inorganic chemistry at the Universidad de Huelva, known for coinage-metal C–H activation catalysts.
PEDro scale
The PEDro scale is an 11-item checklist that rates the methodological quality of randomized controlled trials of physiotherapy interventions, with a 0 to 10 score ranking results in the Physiotherapy Evidence Database.
Peel testing
Peel testing is a mechanical test that separates one bonded layer from another at a controlled angle and rate, measuring the force required to quantify adhesion.
Pefloxacin
Pefloxacin is a fluoroquinolone antibiotic that inhibits bacterial DNA gyrase, developed by Rhône-Poulenc and introduced in France in 1985 but never approved in the United States.
Pegasus (Πήγασος) (constellation)
Pegasus (Πήγασος), the Winged Horse, is a large northern constellation known for the Great Square and the star 51 Pegasi, the first Sun-like star found with a planet.
Pegasus Dwarf Irregular Galaxy
The Pegasus Dwarf Irregular Galaxy (DDO 216, also called PegDIG) is a gas-poor dwarf irregular galaxy in the constellation Pegasus, a likely Local Group member about 760 kpc from the Milky Way.
PEGDA hydrogel
A PEGDA hydrogel is a synthetic, biocompatible polymer network formed by light-activated cross-linking of poly(ethylene glycol) diacrylate, used in tissue engineering, drug delivery, and soft robotic actuators.
Pegmatite
Pegmatite is a coarse-grained igneous rock composed largely of granite minerals such as quartz, feldspar, and muscovite, mined for rare elements like lithium and tantalum, and for gemstones.