42,772 articles
Properties of concrete
Properties of concrete are the measurable mechanical and durability characteristics of concrete, most often compressive strength, tensile strength, elastic modulus, creep, shrinkage, and resistance to chloride penetration.
Properties of metals, metalloids and nonmetals
Metals, metalloids, and nonmetals are the three broad classes of chemical elements: metals are shiny, malleable conductors, nonmetals are dull poor conductors, and metalloids are in-between semiconductors.
Properties of water
Water (H₂O), also called hydrogen oxide, is a polar molecule whose hydrogen bonding gives it unusually high melting and boiling points, heat capacity, and surface tension.
Property P (knot theory)
Property P is a property of knots in the 3-sphere, conjectured for every non-trivial knot and proved by Kronheimer and Mrowka in 2004 using gauge theory.
Property testing
Property testing is a subfield of algorithm theory in which a randomized procedure decides from a small sample whether an object has a property or is far from it.
Propionaldehyde
Propionaldehyde, also known as propanal, is the three-carbon saturated aldehyde, a clear, flammable liquid boiling at 49 °C and used industrially almost entirely as a reactive intermediate.
Propionic acid
Propionic acid, also called propanoic acid, is a three-carbon carboxylic acid, a colorless, oily liquid with a pungent odor produced industrially and used chiefly as a food and feed preservative.
Propionic anhydride
Propionic anhydride (propanoic anhydride) is the symmetrical acid anhydride of propionic acid, a colorless, water-reactive liquid used chiefly as an acylating agent to make cellulose propionate and other propionate esters.
Propionitrile
Propionitrile (propanenitrile, ethyl cyanide) is a colorless, flammable three-carbon nitrile used as a polar aprotic solvent and chemical intermediate; the body metabolizes it to release cyanide.
Propiophenone
Propiophenone, also called ethyl phenyl ketone or 1-phenyl-1-propanone, is a colorless aromatic ketone with a floral odor, used in perfumery and as a pharmaceutical intermediate.
Proportional counter
A proportional counter is a gas-filled radiation detector operated at a voltage where gas amplification keeps the collected charge proportional to the energy deposited by radiation.
Proportional hazards model
The proportional hazards model, usually called Cox regression or the Cox model, is a statistical regression model for time-to-event data proposed by David Cox in 1972.
Proportional meta-analysis
Proportional meta-analysis is a biostatistical evidence-synthesis method that pools a single proportion, such as disease prevalence or adverse event rates, from the proportions reported by multiple studies.
Proportionality (mathematics)
Proportionality is the mathematical relation between two varying quantities whose ratio or product is constant: a fixed ratio gives direct proportion and a fixed product gives inverse proportion.
Propositional calculus
A propositional calculus is a formal proof system for propositional logic, given by axioms and inference rules such as modus ponens; first axiomatized by Frege in 1879, it is sound and complete.
Propositional dynamic logic
Propositional dynamic logic (PDL) is a modal logic for reasoning about programs, in which [α]A means A holds after every execution of program α. Fischer and Ladner defined it in 1979.
Propositional logic
Propositional logic, also known as sentential logic or sentential calculus, studies reasoning with whole propositions that are true or false, joined by connectives like and, or, and if-then.
Propositional proof system
A propositional proof system is any polynomial-time computable function whose range is exactly the propositional tautologies, the abstract definition by Cook and Reckhow in 1979 that founded proof complexity.
Propyl acetate
Propyl acetate, or propyl ethanoate, is the acetate ester of acetic acid and propanol, a colorless liquid with a fruity odor used mainly as a solvent in inks and coatings.
Propylene
Propylene, also known as propene or methylethylene, is a colorless, flammable alkene gas (C₃H₆) produced from petroleum refining; about two thirds of it goes into polypropylene, a common plastic.
Propylene carbonate
Propylene carbonate is a clear, polar aprotic organic solvent, made from carbon dioxide and propylene oxide and widely used in lithium battery electrolytes and natural gas purification.
Propylene glycol
Propylene glycol, also called propane-1,2-diol, is a clear, water-absorbing synthetic liquid used as antifreeze and deicing fluid and as a safe solvent in foods, drugs, and cosmetics.
Propylene oxide
Propylene oxide, also known as methyloxirane, is a highly flammable three-carbon epoxide used mainly to make polyurethane polyols and propylene glycol, and detected in interstellar space in 2016.
Propylhexedrine
Propylhexedrine, sold under the brand name Benzedrex, is an over-the-counter nasal decongestant. It is a structural analog of amphetamine, and the FDA warned of abuse in 2020.
Propyliodone
Propyliodone (Dionosil) is a discontinued iodinated, non-water-soluble X-ray contrast medium, an iodopyridone ester introduced in 1952 for bronchography as 50% aqueous or 60% arachis-oil suspensions, absorbed within days.
Propyne
Propyne, also known as methylacetylene or allylene, is a colorless, extremely flammable gas of formula C₃H₄, used as a specialty fuel, calibration gas, and synthesis intermediate.
Prosper-René Blondlot
Prosper-René Blondlot (1849–1930) was a French physicist at the University of Nancy, respected for measuring electromagnetic waves and the Kerr effect, best known for the nonexistent N-rays.
Prosperite
Prosperite is a rare hydrated calcium zinc arsenate mineral, approved in 1978 and known only from the second oxidation zone of the Tsumeb Mine in Namibia, where it forms white prismatic crystals up to 10 mm.
Protactinium
Protactinium is a dense, silvery, highly radioactive actinide metal, atomic number 91, occurring naturally only as a decay product of uranium and among the rarest elements.
Protecting group
A protecting group is a group temporarily attached to a reactive functional group in a molecule, used in multistep organic synthesis to control where reactions occur.