Physical world and mathematics

Protective belt

The protective belt is Imre Lakatos's term, from his 1970 methodology of scientific research programs, for the auxiliary hypotheses that absorb empirical tests on behalf of a research program's hard core.

Protein crystallography

Protein crystallography is a structural biology method that determines a protein's three-dimensional atomic structure from X-ray diffraction patterns of protein crystals, producing atomic coordinates deposited in the Protein Data Bank.

Protein folding

Protein folding is the process by which a linear chain of amino acids acquires its functional three-dimensional native state; Anfinsen showed the sequence holds all needed information, and AlphaFold later predicted structures with high accuracy.

Protein structure

Protein structure, also known as protein conformation, is the three-dimensional organization of a protein molecule across four levels, from amino acid sequence to assembled multi-chain complexes, and it determines function.

Protein–protein interaction prediction

Protein–protein interaction prediction is the use of computational methods, from genomic context and co-evolution to deep learning, to infer whether two proteins bind or otherwise associate.

Proteinogenic amino acid

A proteinogenic amino acid, also called a standard or encoded amino acid, is any amino acid incorporated into proteins during ribosomal translation, comprising 20 standard residues plus selenocysteine and pyrrolysine.

Proterozoic

The Proterozoic, or Proterozoic Eon, is the second of Earth's four geological eons, spanning 2,500 to 541 million years ago and forming most of the Precambrian.

ProteusONE

ProteusONE is a single-room, compact-gantry proton therapy system made by IBA of Louvain-la-Neuve, Belgium, first installed clinically at the Willis-Knighton Cancer Center in Shreveport, Louisiana, in 2014.

Protocatechuic acid

Protocatechuic acid, abbreviated PCA, is 3,4-dihydroxybenzoic acid, a naturally occurring phenolic acid in olives, chicory, and other plants, and a metabolite of anthocyanins in humans.

Protodeboronation

Protodeboronation is a chemical reaction in which an organoboron compound's carbon–boron bond is replaced with carbon–hydrogen, and it is the major side reaction in Suzuki–Miyaura cross-coupling.

ProtoDUNE

ProtoDUNE is the collective name for two large-scale liquid-argon time projection chamber prototypes at CERN, each holding about 750 tons of liquid argon, built to validate technologies for the DUNE far detectors.

Protolith

A protolith, also known as the parent rock or precursor, is the original unmetamorphosed rock that a metamorphic rock formed from; it may be igneous, sedimentary, or previously metamorphosed.

Proton

The proton is a stable subatomic particle with charge +1, made of two up quarks and one down quark, and forms the nucleus of ordinary hydrogen.

Proton affinity

Proton affinity (PA) is the negative of the enthalpy change when a molecule binds a proton in the gas phase; larger values mean stronger intrinsic bases, and values matter in mass spectrometry and interstellar chemistry.

Proton aurora

A proton aurora is an auroral emission from energetic protons striking a planetary atmosphere, first observed beyond Earth when MAVEN detected one at Mars in 2018.

Proton computed tomography

Proton computed tomography (pCT) is an imaging technique in which protons passing through an object at many angles reconstruct its relative stopping power, aimed at proton therapy treatment planning.

Proton conduction in hydrogen-bonded organic frameworks

Proton conduction in hydrogen-bonded organic frameworks (HOFs) is proton transport through the hydrogen-bond networks of crystalline porous organic materials, studied for fuel-cell membranes since 2016.

Proton conduction in metal–organic frameworks

Proton conduction in metal–organic frameworks (MOFs) is proton transport through the pores of these crystalline porous solids, studied for solid-state fuel-cell membranes, mostly via water-mediated Grotthuss hopping.

Proton decay

Proton decay is a hypothetical process, forbidden by the Standard Model, in which a proton decays into lighter particles such as a positron and a neutral pion.

Proton emission

Proton emission, also called proton radioactivity, is a radioactive decay mode in which a proton-rich atomic nucleus ejects one proton, or two protons simultaneously. First observed in 1963, it occurs beyond the proton drip line.

Proton Improvement Plan II

Proton Improvement Plan II (PIP-II) is a Fermilab project building an 800 MeV superconducting linear accelerator that will provide the world's most intense high-energy neutrino beam for DUNE.

Proton NMR

Proton NMR (¹H NMR) spectroscopy detects hydrogen nuclei in a magnetic field, reading chemical shifts, integrals, and multiplicities to identify and quantify compounds in solution.

Proton nuclear magnetic resonance spectroscopy

Proton nuclear magnetic resonance spectroscopy, or ¹H NMR, measures the radiofrequency resonance of hydrogen nuclei in a magnetic field to identify molecular structures and compositions.

Proton radiography

Proton radiography is an imaging method that passes short pulses of high-energy protons through an object or plasma, recording them to map areal density, electric fields, and magnetic fields.

Proton radius puzzle

The proton radius puzzle, also called the proton radius discrepancy, began in 2010 when muonic hydrogen measurements gave a proton charge radius about 4 percent smaller than accepted values.

Proton Synchrotron (CERN)

The Proton Synchrotron (PS) is a 628-meter-circumference synchrotron at CERN, its oldest operating machine, that first accelerated protons in 1959 and today feeds the Large Hadron Collider.

Proton synchrotron emission in relativistic jets

Proton synchrotron emission is synchrotron radiation from protons rather than electrons, proposed as a hadronic source of gamma rays in relativistic jets, though it demands protons of at least 10^19 eV.

Proton therapy

Proton therapy, also called proton beam therapy, is external radiation treatment using accelerated protons instead of X-rays, concentrating dose in the tumor with little exit dose.

Proton transport through graphene

Proton transport through graphene is the passage of hydrogen ions through one-atom-thick graphene, discovered in 2014. It underlies proposals for fuel-cell membranes and hydrogen isotope separation.