42,772 articles
Operator space theory
Operator space theory studies Banach spaces embedded in C-algebras, where matrix-level norms distinguish spaces that look identical as Banach spaces, merging C-algebra and Banach space theory.
Operator splitting
Operator splitting is a numerical time-integration method for ODEs and PDEs that applies sub-operators one after another, exact when they commute and otherwise carrying a splitting error.
Operator theory
Operator theory is the branch of functional analysis that studies linear operators, especially bounded linear maps between Hilbert and Banach spaces, and underlies the mathematics of quantum mechanics.
Oph 11
Oph 11 (Oph 162225-240515, Oph 1622) is a wide ~240 AU binary of young brown dwarfs in Scorpius, discovered in 2006 by Jayawardhana and Ivanov; later spectra revised its masses above the planetary range.
Ophiolite
An ophiolite is a fragment of oceanic crust and underlying upper mantle thrust, or obducted, onto continental crust, occurring in all Phanerozoic mountain systems as fossil oceanic lithosphere.
Ophiuchus (astrology)
Ophiuchus, the Serpent Bearer, is an equatorial constellation the Sun passes in front of from about November 30 to December 17, often called a "thirteenth zodiac sign."
Ophiuchus (Ὀφιοῦχος)
Ophiuchus (Ὀφιοῦχος), the serpent bearer, is one of the 88 IAU constellations, an equatorial constellation between Scorpius and Sagittarius representing Asclepius; the Sun crosses it each November, though it was never a classical zodiac sign.
Ophiuchus Supercluster
The Ophiuchus Supercluster is a large concentration of galaxies behind the Galactic Bulge, centered on the Ophiuchus galaxy cluster about 390 million light-years away, known for the most powerful AGN outburst recorded in any cluster.
Opiate
Opiate: natural alkaloids of opium from Papaver somniferum, chiefly morphine, codeine, and thebaine; distinct from the broader term opioid. Isolated by Sertürner in 1803/1805; act at mu, delta, and kappa receptors.
Opinion dynamics
Opinion dynamics is the statistical-physics study of how interacting agents' opinions evolve under simple local rules into consensus, polarization, or fragmentation, a field dating to Weidlich's 1971 sociodynamics model.
Opinion poll
An opinion poll is a survey of a sample of people, designed to measure what a population thinks or intends, most visibly how it plans to vote.
OPLS3
OPLS3 is an all-atom molecular mechanics force field for drug-like small molecules and proteins, published in 2016 by Edward Harder and colleagues at Schrödinger with Jorgensen and Friesner.
Oppenauer oxidation
The Oppenauer oxidation is the aluminum alkoxide-catalyzed oxidation of secondary alcohols to ketones using excess acetone, reported by R. V. Oppenauer in 1937 and long central to steroid chemistry.
Oppenheimer–Snyder collapse
The Oppenheimer–Snyder collapse is an exact solution of the Einstein field equations describing the gravitational collapse of a pressureless spherical star into a black hole, published in 1939.
Opportunistic sampling
Opportunistic sampling is a form of nonprobability sampling that collects data from readily available sources, such as citizen-science records and museum specimens, rather than by a known random mechanism.
Optic axis of a crystal
The optic axis of a crystal, or extraordinary axis, is the direction along which light travels without double refraction; uniaxial crystals have one, biaxial two.
Optica (society)
Optica, formerly the Optical Society of America, is an international optics and photonics society founded in 1916, headquartered in Washington, DC, with more than 24,000 members.
Optical aberration
Optical aberration, also called lens aberration, is a departure of a real optical system's image from the ideal of simple lens theory, arising as monochromatic or chromatic types.
Optical activity
Optical activity is the rotation of the plane of polarized light as it passes through a chiral material such as quartz or sugar, a phenomenon discovered by François Arago in 1811.
Optical antenna
An optical antenna, also called a nanoantenna, is a nanoscale metallic or dielectric structure that converts light into localized energy and back, beating the diffraction limit.
Optical axis
The optical axis is the line of rotational symmetry of an optical system: a ray traveling along it meets each surface at normal incidence and leaves undeviated.
Optical binding
Optical binding is a laser-induced inter-particle force between particles illuminated by off-resonant light, first predicted in 1980 and able to self-organize particles into optical matter.
Optical bistability
Optical bistability is a nonlinear optical effect where a device has two stable output states for the same input light intensity, enabling all-optical switching and memory.
Optical black hole
An optical black hole is a laboratory structure reproducing a black hole's event horizon or omnidirectional light absorption, built to study Hawking radiation in the lab.
Optical breakdown
Optical breakdown is the rapid ionization of a medium by an intense laser pulse, first observed in 1964, which forms a luminous plasma that limits light transmission through transparent materials.
Optical cavity
An optical cavity, also called an optical resonator or laser resonator, is an arrangement of mirrors in which light circulates repeatedly, selecting laser frequencies and enhancing light-matter interactions.
Optical center (optics)
The optical center of a lens is the point where light passes through without deviation, with zero prismatic effect; in a thin lens it lies on the optical axis.
Optical clock
An optical clock is an atomic clock that keeps time using an optical transition in trapped ions or atoms, outperforming caesium clocks by about a factor of 100.
Optical clock network
An optical clock network links optical atomic clocks at separate laboratories by phase-stabilized fiber, comparing frequencies remotely at uncertainties approaching the clocks' own, chiefly in Europe.
Optical clock tests of general relativity
Optical clock tests of general relativity measure gravitational redshift, the prediction that clocks tick faster at higher gravitational potential, using optical atomic clocks accurate to about 10⁻¹⁸.