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Pululahua
Pululahua, a potentially active dacitic-andesitic lava dome complex 15 km north of Quito, Ecuador, with a ~3 km depression formed by VEI ~4 eruptions 2.6–2.3 ka; last eruption ~2.2 ka; inhabited crater and geobotanical reserve.
Pumice
Pumice is a light-colored, highly vesicular volcanic rock, a froth of silicic glass that forms in explosive eruptions; its sealed pores make most varieties float on water.
Pummerer rearrangement
The Pummerer rearrangement, or Pummerer reaction, converts a sulfoxide bearing an alpha-hydrogen into an alpha-substituted sulfide, an internal redox process first reported by Rudolf Pummerer in 1909.
Pump-and-treat
Pump-and-treat (P&T) is a groundwater remediation method that pumps contaminated water from wells to an above-ground treatment system; it has been used at over 800 US Superfund sites.
Pump–probe spectroscopy
Pump–probe spectroscopy, also called transient absorption spectroscopy, is a two-pulse optical technique in which a pump pulse excites a sample and a delayed probe pulse measures its time-dependent response.
Pumping lemma for context-free languages
The pumping lemma for context-free languages, also called the Bar-Hillel lemma, is a theorem proved by Bar-Hillel, Perles, and Shamir in 1961, used chiefly to prove languages are not context-free.
Pumping lemma for regular languages
The pumping lemma for regular languages, stated by Bar-Hillel, Perles, and Shamir in 1961, says long strings of a regular language can be pumped and stays used to prove non-regularity.
Pumping test
A pumping test pumps a well at a regulated rate while measuring water levels in observation wells to estimate aquifer properties such as transmissivity and storativity.
Punicalagin
Punicalagin is a water-soluble ellagitannin and the predominant polyphenol of the pomegranate, occurring in α and β forms and making up to 70% of the polyphenols in commercial pomegranate juice.
Punjabi calendar
The Punjabi calendar is the traditional timekeeping system of the Punjab region, built on twelve Desi months named in Sikh scripture, kept today in the lunisolar Bikrami form and the solar Nanakshahi calendar adopted in 2003.
Pupil function
The pupil function, also called the generalized or complex pupil function, is a complex-valued aperture function describing light transmission and phase shift at each point of an optical system's pupil.
Puppis
Puppis, abbreviation Pup, is a southern constellation representing the stern of the mythical ship Argo Navis, lying in the Milky Way between Vela and Canis Major.
Puppis A
Puppis A, cataloged G260.4−3.4, is an oxygen-rich shell supernova remnant in the southern constellation Puppis, roughly 4,000 years old and among the brightest in radio and X-ray light.
Purcell effect
The Purcell effect is the enhancement of a quantum emitter's spontaneous emission rate when it is placed in a resonant cavity, described by Edward Purcell in 1946.
Pure 4D N = 1 supergravity
Pure 4D N = 1 supergravity is the locally supersymmetric extension of general relativity in four dimensions, containing a graviton and one spin-3/2 gravitino and no matter multiplets.
Pure and mixed quantum states
A pure quantum state is described by a single state vector, while a mixed state is a statistical ensemble of pure states; the density matrix represents both.
Pure fusion weapon
A pure fusion weapon, also called a pure fusion bomb, is a hypothetical nuclear weapon deriving its explosive yield entirely from fusion, without a fission trigger or fissile material.
Pure mathematics
Pure mathematics is mathematics pursued for its own sake rather than immediate application, covering fields like algebra, number theory, and analysis, whose results often become applied later.
Pure state
A pure state is a quantum state completely specified by a single state vector, corresponding to a rank-one density operator, as opposed to a mixed state.
Pure-jump Lévy process
A pure-jump Lévy process is a Lévy process whose Gaussian (Brownian) component is absent, so all randomness enters through jumps; examples include the variance gamma, NIG, and CGMY processes.
Pure-shift NMR
Pure-shift NMR, also called broadband homonuclear decoupling, is a family of proton NMR experiments that removes J couplings so each multiplet becomes a single line, first demonstrated by Zangger and Sterk in 1997.
PUREX
PUREX (plutonium uranium extraction) is a liquid–liquid extraction process that separates uranium and plutonium from spent nuclear fuel using tributyl phosphate, accounting for over 95% of global commercial reprocessing capacity.
Purge and trap
Purge and trap, also called dynamic headspace extraction, is a sample-preparation technique invented in 1974 that concentrates volatile organic compounds for analysis by gas chromatography.
Purico Complex
Purico Complex, a Pleistocene pyroclastic shield volcano in northern Chile's Central Volcanic Zone at 23°S 67.75°W, 5,703 m high, formed by two ~1.3 Ma ignimbrite sheets with Holocene domes, the Macon stratovolcano, and the active Alitar maar.
Purine
Purine is a fused, double-ring organic compound occurring in nucleic acids; its ring system underlies the bases adenine and guanine in DNA and RNA, and caffeine.
Purnendu Κ. Dasgupta
Purnendu K. Dasgupta, known as Sandy, is an American analytical chemist at the University of Texas at Arlington, known for microdrop extraction and patented ion chromatography devices.
Purple
Purple is a nonspectral color seen when the eye receives both red and blue-violet light, so no single wavelength looks purple; Tyrian purple dyed ancient royalty.
PurpleAir
PurpleAir is a Draper, Utah manufacturer of low-cost air quality monitors that measure PM2.5 by laser light scattering and upload readings in real time to a public map, one of the largest crowdsourced air quality networks.
Purposive sampling
Purposive sampling, also called purposeful or judgment sampling, is a non-probability sampling method in which researchers deliberately select information-rich cases meeting criteria set out in advance.
Puru Jena
Puru Jena, full name Purusottam Jena, is a condensed matter physicist and Distinguished Professor at Virginia Commonwealth University, known for atomic clusters, hydrogen storage, and penta-graphene.