42,772 articles
Polish space
A Polish space, or Polish metric space, is a separable, completely metrizable topological space; examples include ℝⁿ, and the concept is central to descriptive set theory.
Pollard's rho algorithm for logarithms
Pollard's rho algorithm for logarithms is a probabilistic method for solving the discrete logarithm problem, found by John Pollard in 1974 and published in 1978, running in expected O(√n) operations.
Pollutant
A pollutant is any substance introduced into the environment that may harm human health or ecosystems, typically from human activities; some, like ground-level ozone, form in the air.
Pollution
Pollution is the introduction of contaminants, whether substances or energy, into the environment at rates that harm health, living systems, or air, water, and soil quality.
Polly Arnold
Polly L. Arnold is a British inorganic chemist known for her work on rare earth and actinide chemistry, and Professor of Chemistry at UC Berkeley since 2020.
Polonium
Polonium, atomic number 84, is a radioactive silvery-gray element discovered by Pierre and Marie Curie in 1898 and named after Poland; all its isotopes are unstable.
Polonium-210
Polonium-210, historically known as Radium F, is a radioactive isotope with a 138.4-day half-life, used in static eliminators and notorious as the poison that killed Alexander Litvinenko in 2006.
Poloxamer
Poloxamer, sold under names including Pluronic, is a family of synthetic triblock copolymer surfactants whose concentrated solutions gel near body temperature, making them the leading platform for in situ drug delivery gels.
Poly(carboxybetaine) nanoparticles
Poly(carboxybetaine) nanoparticles are drug-delivery and imaging particles coated with the zwitterionic polymer poly(carboxybetaine), a PEG alternative whose hydrated surface resists protein adsorption and immune clearance.
Poly(ionic liquid)s
Poly(ionic liquid)s, also called polymerized ionic liquids, are a subclass of polyelectrolytes combining ionic liquid properties with polymer robustness, used in batteries, CO2 capture, and catalysis.
Poly(lactic-co-glycolic acid)
Poly(lactic-co-glycolic acid) (PLGA) is a biodegradable copolymer of lactic and glycolic acids, FDA-approved since the 1970s and now the leading polymer carrier for controlled drug delivery and resorbable surgical implants.
Poly(p-phenylene oxide)
Poly(p-phenylene oxide), also known as polyphenylene oxide or PPO, is an amorphous engineering thermoplastic made by oxidative coupling of 2,6-dimethylphenol, first reported by Hay in 1959 and commercialized in 1965.
Pólya conjecture
The Pólya conjecture is a 1919 statement in number theory asserting the summatory Liouville function is never positive. Brian Haselgrove disproved it in 1958, and the smallest counterexample, 906,150,257, was found in 1980.
Pólya enumeration theorem
The Pólya enumeration theorem, or Pólya enumeration formula, is a combinatorics result counting distinct colorings and configurations up to a symmetry group, generalizing Burnside's lemma through weighted generating functions.
Pólya tree prior
The Pólya tree prior is a Bayesian nonparametric prior on distribution functions, built by recursive binary splitting with independent Beta branching probabilities, used in density estimation and survival analysis.
Pólya urn model
The Pólya urn model, or Pólya's urn, is a stochastic process where drawn balls are returned with extra balls of the same color, reinforcing frequent colors.
Polyacrylamide
Polyacrylamide, also known as linear polyacrylamide, is a water-soluble synthetic polymer of acrylamide monomers. It is used industrially as a flocculant in water treatment, a soil conditioner, and a friction reducer in hydraulic fracturing.
Polyacrylic acid
Polyacrylic acid (PAA), known in crosslinked grades as carbomers or Carbopols, is a synthetic water-soluble polymer whose sodium salt forms superabsorbent polymers in disposable diapers.
Polyacrylonitrile
Polyacrylonitrile (PAN) is a synthetic, semicrystalline polymer made by polymerizing acrylonitrile. First spun into fibers in 1938, it is the precursor for roughly 96% of the carbon fiber market.
Polyaddition
Polyaddition is a step polymerization in which monomers with two or more functional groups add together, forming polymer with no low-molar-mass by-product; polyurethane is the best-known example.
Polyakov action
The Polyakov action is the two-dimensional field-theory form of the bosonic string worldsheet action, introduced by Alexander Polyakov in 1981 and classically equivalent to the Nambu–Goto action.
Polyakov loop
The Polyakov loop is a Wilson loop winding around the thermal time direction of finite-temperature lattice gauge theory, measuring the free energy of an isolated static quark.
Polyamide
A polyamide is a polymer containing carboxamide groups as backbone linkages, a class that includes the aliphatic nylons such as PA6 and PA66 and the aromatic aramids like Kevlar.
Polyaryletherketone
Polyaryletherketone (PAEK) is a family of semicrystalline, high-temperature thermoplastics, including PEEK and PEKK, that combine chemical resistance and strength near 260 °C, making them valued in aerospace and medical implants.
Polyaspartic acid
Polyaspartic acid (PASP) is a synthetic, water-soluble, biodegradable polypeptide of aspartic acid units, produced industrially as a green alternative to polyacrylates and used as a mineral scale inhibitor.
Polyatomic ion
A polyatomic ion is an electrically charged molecule, a group of two or more covalently bonded atoms carrying a net charge and acting as a single unit in reactions and salts.
Polyborosiloxane
Polyborosiloxane (PBS) is a viscoelastic silicone polymer whose dynamic boron–oxygen bonds let it self-heal at room temperature; first made in 1947 as the main ingredient of Silly Putty.
Polybutadiene
Polybutadiene, also known as butadiene rubber, is a synthetic rubber made by polymerizing 1,3-butadiene; it is the second most produced rubber worldwide, used in tire treads and golf ball cores.
Polybutylene adipate terephthalate
Polybutylene adipate terephthalate (PBAT), formally poly(butylene adipate-co-terephthalate), is a biodegradable copolyester first commercialized by BASF in 1998 as ecoflex, used for compostable packaging and agricultural mulch films.
Polybutylene succinate
Polybutylene succinate, sometimes called poly(tetramethylene succinate), is a biodegradable thermoplastic aliphatic polyester made from succinic acid and 1,4-butanediol, used in compostable packaging and agricultural films.