42,772 articles
Para-Methoxy-N-methylamphetamine
Para-methoxy-N-methylamphetamine (PMMA), also known as 4-methoxymethamphetamine, is a ring-substituted amphetamine derivative sold illicitly as ecstasy and known as "Death", substantially more toxic than MDMA and linked to fatal poisoning outbreaks worldwide.
Para-Methoxyamphetamine
Para-Methoxyamphetamine (PMA, 4-MA, 'death') is a toxic methoxylated amphetamine sold illicitly as fake ecstasy; a serotonin releaser and MAO-A inhibitor causing fatal hyperthermia, Schedule I under the 1971 UN Convention.
Para-selective C–H borylation
Para-selective C–H borylation is an iridium-catalyzed reaction that installs a boronate group at the arene position opposite the existing substituent, overriding the usual steric preference for meta.
Paraben
Parabens are a family of esters of para-hydroxybenzoic acid used widely as antimicrobial preservatives in cosmetics, pharmaceuticals, and food and beverage processing since the mid-1920s, with methylparaben, ethylparaben, propylparaben, and butylparaben the most common.
Parabola
A parabola is a plane curve of points equidistant from a fixed focus and a fixed line, the directrix; it is the conic section with eccentricity exactly 1.
Parabolic Anderson model
The parabolic Anderson model is the heat equation with a random potential, modeling electron conduction in defective crystals and known for intermittency, where mass concentrates on rare peaks.
Parabolic antenna
A parabolic antenna, also called a dish antenna, uses a parabolic reflector to focus radio waves, giving high gain for satellite, radar, and radio telescope use.
Parabolic reflector
A parabolic reflector, also called a parabolic mirror or parabolic dish, reflects parallel rays through a single focus, making it standard for satellite dishes, headlamps, and telescopes.
Parabolized stability equations
The parabolized stability equations (PSE), introduced by Thorwald Herbert and Fabio Bertolotti in the 1980s, compute the downstream growth of small disturbances in boundary-layer flows for transition prediction.
Paraboloid
A paraboloid is a quadric surface with two types, the bowl-shaped elliptic and the saddle-shaped hyperbolic, whose vertical cross sections are parabolas; elliptic paraboloids serve as reflecting antennas and telescopes.
Paracelsian
Paracelsian is a rare barium feldspar mineral, the dimorph of celsian, first described in 1905 from Candoglia, Italy, and best known from the Benallt Mine in Wales.
Parachute Creek
Parachute Creek is a stream in Garfield County, Colorado, whose name is attached to the Parachute Creek Member, the Green River Formation's oil shale unit, and Unocal's project there.
Paracompact space
A paracompact space is a topological space in which every open cover has a locally finite open refinement, a property introduced by Jean Dieudonné in 1944.
Paraconsistent logic
Paraconsistent logic is a family of formal logical systems in which a contradiction does not entail everything: explosion is invalid, so theories containing contradictions can remain non-trivial.
Paracrystalline diamond
Paracrystalline diamond (p-D) is a non-crystalline, fully sp3-bonded form of carbon made of sub-nanometre paracrystallites, first reported in Nature in 2021 and synthesized from C60 at 30 GPa and 1,600 K.
Paradata
Paradata is auxiliary data describing the process of collecting a dataset, usually a survey, covering records like call attempts, interview duration, keystroke logs, and interviewer observations of households.
Paradigm shift
A paradigm shift, also called a paradigm change, is a fundamental change in the framework of a science, a concept introduced by Thomas Kuhn in 1962.
Paradox
A paradox is seemingly sound reasoning from apparently true assumptions that still leads to a contradiction; the Liar dates to antiquity, and Russell's paradox arose in 1901.
Paradox of youth (astronomy)
The paradox of youth is the problem of why massive young stars exist near Sagittarius A, the Milky Way's central black hole, despite tidal forces that should prevent star formation there.
Paradoxes of set theory
The paradoxes of set theory are contradictions from naive comprehension, including Russell's paradox (1901), Burali-Forti's (1897), and Cantor's, which forced set theory onto axiomatic foundations.
Parafermion
A parafermion is a quasiparticle in condensed matter physics that generalizes the Majorana fermion; introduced by Fradkin and Kadanoff, it is pursued for topological quantum computation but remains experimentally unconfirmed.
Parafermion zero mode
A parafermion zero mode, also called a fractionalized Majorana mode, is a non-Abelian anyon excitation generalizing the Majorana zero mode to Zn symmetry in topological phases.
Paraformaldehyde
Paraformaldehyde is a low-molecular-weight linear polymer of formaldehyde with 8 to 100 units, a white solid used as a convenient formaldehyde source in industry and laboratories.
Parahydrogen-induced polarization
Parahydrogen-induced polarization (PHIP) is an NMR hyperpolarization technique that converts parahydrogen's singlet spin order into greatly enhanced magnetization for spectroscopy and MRI, first reported in 1987.
Paraldehyde
Paraldehyde is a cyclic trimer of acetaldehyde introduced into medicine in 1882 by Vincenzo Cervello; once a widely used hypnotic, it survives only against refractory status epilepticus.
Parallax
Parallax is the apparent shift of a nearby object against a distant background when viewed from different vantage points, used in astronomy to measure stellar distances.
Parallel (geometry)
In geometry, parallel lines are coplanar straight lines that never meet however far extended, staying a constant distance apart; Euclid's parallel postulate governs them, and denying it yields non-Euclidean geometries.
Parallel analysis
Parallel analysis is a statistical method for deciding how many factors or components to retain in factor analysis, comparing observed eigenvalues against those from random data of the same size.
Parallel and distributed graph algorithms
Parallel and distributed graph algorithms solve graph problems such as connectivity, shortest paths, and matching using many processors or machines, spanning shared-memory, cluster, and network settings.
Parallel axis theorem
The parallel axis theorem, also known as Steiner's theorem, states that the moment of inertia about any axis parallel to a center-of-mass axis equals I_cm + md².