Physical world and mathematics

Phosphorus donor qubit in silicon

A phosphorus donor qubit in silicon is a quantum bit formed from a single phosphorus-31 atom in silicon, encoding information in its electron or nuclear spin.

Phosphorus limitation

Phosphorus limitation is the control of biological production by phosphorus supply, the principle that phosphorus, not nitrogen or carbon, governs algal blooms and eutrophication in lakes.

Phosphorus loading

Phosphorus loading is the quantity of phosphorus delivered to a water body per unit time, either from the watershed and atmosphere or released from lake sediments.

Phosphorus nitride refers to binary compounds of phosphorus and nitrogen, chiefly the diatomic PN molecule, first detected in interstellar space, and solid phosphorus(V) nitride, P3N5, first obtained in 1862.

Phosphorus pentachloride

Phosphorus pentachloride (PCl₅) is a pale-yellow, fuming solid of phosphorus and chlorine used as a chlorinating agent, existing as trigonal bipyramidal molecules in gas and an ionic lattice in the solid.

Phosphorus pentoxide

Phosphorus pentoxide, also known as phosphoric anhydride, is a white, hygroscopic oxide of phosphorus with the molecular formula P4O10, made by burning phosphorus in dry air and used as a powerful drying and dehydrating agent.

Phosphorus sorption

Phosphorus sorption is the attachment of dissolved phosphate to sediment and soil particle surfaces, a process that buffers phosphorus concentrations in streams, lakes, and estuaries and drives eutrophication.

Phosphorus trichloride

Phosphorus trichloride, also known as PCl3 or trichlorophosphine, is a colorless fuming liquid used industrially as a reactive chlorinating agent that reacts violently with water.

Phosphorus-32

Phosphorus-32 is a radioactive isotope of phosphorus with a half-life of about 14.3 days that decays by beta emission, used to label DNA and proteins in research.

Phosphoryl chloride

Phosphoryl chloride, also called phosphorus oxychloride, is a colorless fuming liquid with the formula POCl₃, used as a chlorinating agent and to dope silicon solar cells.

Phosphorylcholine

Phosphorylcholine, also called phosphocholine, is a small zwitterionic molecule that serves as the polar head group of phosphatidylcholine and an intermediate in its biosynthesis via the Kennedy pathway.

Phosphothreonine

Phosphothreonine, or O-phospho-L-threonine, is the phosphorylated derivative of the amino acid L-threonine, first isolated from bovine casein in 1953 and the second most abundant protein phosphorylation.

Phosphotungstic acid

Phosphotungstic acid, also called 12-tungstophosphoric acid, is a heteropoly acid (H3PW12O40) used as a strong acid catalyst and as a negative stain in electron microscopy.

Photo 51

Photo 51 is the clearest X-ray diffraction photograph of B-form DNA, taken in May 1952 under Rosalind Franklin at King's College London, informing the 1953 double-helix model.

Photo-elicitation

Photo-elicitation is a qualitative interview technique in which photographs are shown to participants to evoke memories, emotions, and narratives that purely verbal interviews may miss.

Photo-Fenton reaction

The photo-Fenton reaction is a light-assisted advanced oxidation process in which irradiating an iron–hydrogen peroxide mixture generates hydroxyl radicals that degrade organic pollutants and inactivate microorganisms in water.

Photo-induced hidden phase in 1T-TaS2

The photo-induced hidden phase in 1T-TaS2 is a long-lived metallic state of tantalum disulfide reached by striking its insulating ground state with a single femtosecond laser pulse.

Photo-induced superconductivity in K3C60

Photo-induced superconductivity in K3C60 is a claimed state where mid-infrared pulses make the fulleride superconductor behave superconductingly at up to room temperature, well above its 20 K transition temperature.

Photoacoustic detection

Photoacoustic detection is a spectroscopy method in which modulated light absorbed by a sample is converted into sound, enabling trace-gas measurements at parts-per-billion to parts-per-trillion levels.

Photoacoustic effect

The photoacoustic effect is the generation of sound or ultrasound waves when a material absorbs light energy, discovered by Alexander Graham Bell in 1880 and used in biomedical imaging.

Photoacoustic imaging

Photoacoustic imaging (PAI) is a hybrid biomedical imaging method that uses pulsed light to generate ultrasound in tissue, combining optical-absorption contrast with ultrasound-like resolution beyond the optical diffusion limit.

Photoacoustic microscopy

Photoacoustic microscopy (PAM) is a label-free biomedical imaging technique that maps optical absorption in tissue using pulsed laser light and ultrasound, including OR-PAM and AR-PAM forms.

Photoacoustic spectroscopy

Photoacoustic spectroscopy (PAS) determines the absorption spectrum of gases, liquids, or solids by detecting sound from absorbed modulated light, enabling trace-gas sensing and analysis of opaque samples.

Photoassociation

Photoassociation is a process in which two colliding laser-cooled atoms below 1 millikelvin absorb a photon and form an electronically excited molecule, probing molecular states near the dissociation limit.

Photobiocatalysis with excited flavins and Ru complexes

Photobiocatalysis with excited flavins and Ru complexes is a branch of biocatalysis in which light promotes a flavin cofactor or a ruthenium complex into an excited state that forms radicals the enzyme steers with high stereoselectivity.

Photobiocatalytic radical C–H functionalization

Photobiocatalytic radical C–H functionalization is a synthetic strategy combining light-driven photoredox generation of radicals from C–H bonds with enzyme catalysis, using engineered thiamine diphosphate enzymes to control stereochemistry.

Photocaging

Photocaging is a chemical technique that inactivates a bioactive molecule by attaching a photoremovable protecting group, restoring its activity on demand by irradiation, first applied in 1978 to caged ATP.

Photocatalysis

Photocatalysis is a catalytic method in which a light-activated semiconductor particle absorbs photons and uses excited electrons and holes to drive redox reactions, underpinning solar fuel production, environmental remediation, and organic synthesis.

Photocatalytic [2+2] cycloaddition

Photocatalytic [2+2] cycloaddition is a light-driven reaction where a photocatalyst converts two alkene π bonds into a cyclobutane ring, a route thermally forbidden by orbital symmetry.