Physical world and mathematics

Prefix code

A prefix code, also called a prefix-free or instantaneous code, is a variable-length code in which no codeword is a prefix of another, allowing unambiguous decoding without separators.

Preformed Cooper pairs are bound electron pairs that form above the superconducting transition temperature Tc without phase coherence, a scenario proposed to explain the pseudogap in underdoped cuprate superconductors.

Pregeometry (model theory)

In model theory, a pregeometry, known in combinatorics as a matroid, is a set with a finitary closure operator satisfying the Steinitz exchange property, abstracting linear span and algebraic closure.

Prenex normal form

Prenex normal form (PNF), also called prenex form, is a standard form for first-order logic formulas in which all quantifiers are gathered at the front, before a quantifier-free matrix.

Preon

A preon, also called a prequark or subquark, is a hypothetical subatomic particle proposed as a building block of quarks and leptons; no experiment has found quark substructure.

Preorder

A preorder, also called a quasiorder, is a binary relation on a set that is reflexive and transitive, and a partial order if also antisymmetric.

Preparative chromatography

Preparative chromatography is a separation technique that isolates and collects purified quantities of compounds from mixtures, when the goal is the compound itself rather than information about it.

Prepreg

Prepreg, a contraction of pre-impregnated, is fiber reinforcement pre-impregnated with catalyzed but uncured resin, typically epoxy, ready for cure into composite laminates and most common in aerospace composites.

Preregistration (research)

Preregistration is the practice of posting a time-stamped, read-only version of a study's design, hypotheses, and analysis plan to a public repository before data are collected or analyzed.

Presaturation (NMR spectroscopy)

Presaturation is a solvent-suppression technique in NMR spectroscopy that saturates the solvent signal, typically water, with a low-power radiofrequency pulse, credited to Hoult in 1976.

Presburger arithmetic

Presburger arithmetic is the first-order theory of the integers with addition and order, omitting multiplication; Mojżesz Presburger proved it decidable in 1929, while adding multiplication yields undecidability.

Present

The present is the portion of time currently occurring, opposed to past and future: strictly a durationless boundary, experientially an interval of a few seconds.

Presheaf with transfers

A presheaf with transfers is a contravariant additive functor from smooth schemes with finite correspondences to abelian groups, used by Voevodsky to build motivic cohomology.

Presheath (plasma physics)

The presheath is the quasineutral transition layer of a plasma boundary that accelerates ions from near-thermal energies to the ion sound speed at the edge of the Debye sheath.

PRESS (MRI sequence)

PRESS (point resolved spectroscopy) is an MRI sequence that localizes magnetic resonance spectroscopy signal from a single rectangular volume of tissue using a 90° pulse and two 180° pulses.

Press–Schechter formalism

The Press–Schechter formalism is a 1974 analytic method in cosmology that predicts the abundance of dark matter halos, introduced by William H. Press and Paul Schechter.

Pressure

Pressure is the force applied perpendicular to a surface divided by the area, written p = F/A, measured in pascals and central to the physics of fluids.

Pressure broadening

Pressure broadening, also called collisional broadening, is the widening of a spectral line caused by collisions that shorten the lifetime of the emitting or absorbing state.

Pressure gap

The pressure gap is the difference in behavior between catalysts studied under ultra-high vacuum and the same materials at the high pressures and temperatures of industrial reactors.

Pressure head

Pressure head, also called static head, is the height of a fluid column that would produce a given pressure, equal to pressure divided by the fluid's weight density.

Pressure measurement

Pressure measurement is the determination of the force exerted by a fluid per unit area, measured in pascals with instruments from manometers and piston gauges to Bourdon tubes.

Pressure ridge (ice)

A pressure ridge is a wall of broken sea ice pushed up and down when ice floes compress, with a sail above water and a much larger keel below.

Pressure solution

Pressure solution is a geologic deformation process in which mineral grains dissolve where they touch under high stress, then reprecipitate on low-stress grain faces, reducing porosity.

Oct 21, 2026

Pressure Transducers

Pressure transducers convert applied pressure, usually via a deflecting diaphragm, into an electrical signal. Also called pressure sensors or transmitters; main types are piezoresistive, capacitive, piezoelectric, and triboelectric, used from industrial process control to invasive blood pressure monitoring.

Pressure-controlled scanning calorimetry

Pressure-controlled scanning calorimetry (PCSC) is a calorimetric technique in which pressure, rather than temperature, is scanned, revealing how pressure shifts phase transitions like fusion and lipid melting.

Pressure-induced amorphization of metal–organic frameworks

Pressure-induced amorphization of metal–organic frameworks (MOFs) is the abrupt loss of crystallinity when these porous solids are compressed, typically below 1 GPa, used to trap guest molecules and make amorphous MOFs.

Pressure-induced phase transitions in hybrid perovskites

Pressure-induced phase transitions in hybrid perovskites are structural transformations of soft organic–inorganic perovskites under hydrostatic pressure, often applied in diamond anvil cells, that tilt octahedra, reorder organic cations, and narrow bandgaps.