42,772 articles
Prometryn
Prometryn is a selective methylthio-s-triazine herbicide, first registered in 1964 by Ciba, that kills annual grasses and broadleaf weeds in cotton and celery by inhibiting photosynthesis.
Prompt-gamma neutron activation analysis
Prompt-gamma neutron activation analysis (PGNAA, also written PGAA) is a non-destructive technique that identifies and quantifies elements in a sample from gamma rays emitted as nuclei capture neutrons.
Pronic number
A pronic number, also known as an oblong or heteromecic number, is a number that is the product of two consecutive integers; the sequence begins 0, 2, 6, 12, 20.
Proof calculus
A proof calculus is a formal system of axioms and inference rules whose derivations establish the theorems of a logic; main forms include Hilbert systems, natural deduction, and sequent calculus.
Proof net
A proof net is a graph-based representation of a proof in linear logic, introduced by Jean-Yves Girard in 1987 to eliminate trivial rule permutations of sequent calculus derivations.
Proof that e is irrational
Proof that e is irrational: the demonstration, first given by Euler in the 1730s, that Euler's number e cannot be written as a ratio of two integers.
Proof that π is irrational
Proof that π is irrational, first given by Johann Heinrich Lambert in 1761, established that π cannot be written as a ratio of two integers.
Proof-theoretic semantics
Proof-theoretic semantics is an alternative to model-theoretic semantics that explains the meaning of logical constants in terms of the inference rules governing their behavior in proofs.
Proofs of convergence of random variables
Proofs of convergence of random variables presents the four modes of convergence in probability theory, the strict hierarchy among them, and proof tools such as Borel–Cantelli and uniform integrability.
Propafenone
Propafenone, sold as Rythmol, is a class 1C antiarrhythmic drug developed in Germany and marketed since 1977, used for atrial fibrillation in patients without structural heart disease.
Propagation of chaos
Propagation of chaos is a property of large systems of interacting random particles: as the number of particles tends to infinity, any fixed finite subset behaves as if independent.
Propagation of uncertainty
Propagation of uncertainty, also known as propagation of error, is the calculation of how the uncertainties of input quantities combine to give the uncertainty of a quantity derived from them through a measurement model.
Propagation-based phase-contrast imaging
Propagation-based phase-contrast imaging (PBI) is an X-ray imaging method where a wavefield travels in free space before the detector, converting phase shifts into visible intensity fringes; it is the most used phase-contrast setup at synchrotrons.
Propagator
A propagator, also called a causal Green's function, in quantum field theory is the two-point correlation function of a field, inverting the field's quadratic operator.
Propan-1-ol
Propan-1-ol, also known as n-propyl alcohol or 1-propanol, is a three-carbon primary alcohol that is a colorless liquid miscible with water, used mainly as an industrial solvent.
Propane
Propane (C3H8) is a three-carbon alkane gas, sold as liquefied petroleum gas and used mainly for heating, as an engine fuel, and as the refrigerant R-290.
Propargyl alcohol
Propargyl alcohol, also called prop-2-yn-1-ol, is the simplest acetylenic alcohol, a water-miscible liquid made as a coproduct of butynediol synthesis and used mainly to inhibit steel corrosion in hydrochloric acid.
Propargylic and homopropargylic alcohols
Propargylic and homopropargylic alcohols combine an alcohol with a carbon–carbon triple bond, one carbon apart, serving as bifunctional building blocks for pharmaceuticals and natural products.
Propargylic substitution
Propargylic substitution is a nucleophilic substitution reaction in organic synthesis in which a nucleophile replaces a leaving group at an alkyne's propargylic carbon, forming new carbon–carbon or carbon–heteroatom bonds.
Propensity score
A propensity score is the probability of receiving a treatment given observed covariates, used to reduce confounding in observational studies where treatment is not randomly assigned.
Propensity score matching
Propensity score matching, also known as propensity scoring, is a statistical technique that matches treated and untreated subjects with similar scores to mimic a randomized trial.
Propensity score weighting
Propensity score weighting is a statistical method for causal inference in observational studies that weights each subject by the inverse of the probability of the treatment received.
Proper acceleration
Proper acceleration is the acceleration experienced by an object in its own instantaneous rest frame, the quantity an accelerometer it carries measures, such as gravity at rest or zero in free fall.
Proper elements
Proper elements are quasi-constant orbital parameters of an asteroid, computed from its osculating elements by removing periodic planetary perturbations; stable over millions of years, they reveal clustered asteroid families.
Proper forcing
Proper forcing is a property of forcing notions in set theory, introduced by Saharon Shelah in 1980, that preserves ω₁ and is preserved under countable-support iterations.
Proper forcing axiom
The Proper Forcing Axiom (PFA) is a strengthening of Martin's Axiom in set theory, formulated by James Baumgartner in the early 1980s using Shelah's notion of properness.
Proper length
Proper length is the length of an object measured in its rest frame; observers who see it moving measure a contracted length along the direction of motion.
Proper morphism
In algebraic geometry, a proper morphism is a morphism of schemes that is separated, of finite type, and universally closed; projective space is proper, while affine space is not.
Proper orthogonal decomposition
The proper orthogonal decomposition (POD), also called the Karhunen–Loève decomposition, extracts orthogonal modes whose first few capture the most energy, a standard tool in fluid mechanics.
Proper time
Proper time is the time interval between two events measured by a clock present at both events, written Δτ, and it is the shortest measurable interval between them.