42,772 articles
Ogive
An ogive is a pointed arch of two intersecting arcs, and by extension a Gothic vault rib, a bullet's curved nose profile, or a cumulative frequency curve.
Oh-My-God particle
The Oh-My-God particle (OMG particle) was an ultra-high-energy cosmic ray detected over Utah in 1991 with about 51 joules of energy, the most energetic ever observed.
Ohm
The ohm (symbol Ω) is the SI derived unit of electrical resistance, equal to one volt per ampere, named for Georg Simon Ohm, who published Ohm's law in 1827.
Ohm's law
Ohm's law, first published by German physicist Georg Simon Ohm in 1827, states that current through a conductor is directly proportional to voltage, written V = IR.
Ohmic contact
An ohmic contact is a metal-semiconductor junction that passes current in either direction with a linear, non-rectifying response, connecting devices to circuits; heavy doping makes carriers tunnel through the barrier.
Ohyun Kwon
Ohyun Kwon is an American-based organic chemist and UCLA professor known for deconstructive radical chemistry cleaving alkene C–C bonds, including hydrodealkenylation and aminodealkenylation published in Science.
Oil
Oil, in the industrial sense, is petroleum: a mixture of hydrocarbons formed underground over millions of years from marine organisms and refined into fuels and other products.
Oil and Gas Methane Partnership 2.0
The Oil and Gas Methane Partnership 2.0 is a UNEP framework, launched in 2020, under which oil and gas companies report methane emissions using measurement-based methods.
Oil bath (laboratory)
An oil bath is a laboratory setup that heats a reaction vessel in oil, usually mineral or silicone oil, for even heating up to 230 °C.
Oil drop experiment
The oil drop experiment, also known as Millikan's oil drop experiment, is a physics measurement that determined the elementary charge using charged oil droplets between charged plates.
Oil immersion
Oil immersion is a microscopy technique in which oil replaces the air gap between the objective and cover glass, raising resolution; it is standard for 100X objectives.
Oil sands
Oil sands, also known as tar sands, are geologic deposits of sand, clay, water, and bitumen so viscous it will not flow to a well, found chiefly in northern Alberta.
Oil shale
Oil shale, also known as kerogen shale or bituminous shale, is a sedimentary rock containing kerogen, a solid precursor of oil that converts to crude oil when heated.
Oil window
The oil window is the range of burial depth or thermal maturity within which a sedimentary source rock generates and expels liquid petroleum from kerogen.
OJ 287
OJ 287 is a blazar, a jet-pointed active galactic nucleus at redshift 0.306, and a leading binary black hole candidate whose optical outbursts recur about every 12 years.
Okadaic acid
Okadaic acid is a polyether toxin produced by dinoflagellates, first isolated from sponges in 1981, that causes diarrhetic shellfish poisoning and inhibits PP1 and PP2A.
Oklahoma Mesonet
The Oklahoma Mesonet is a network of 120 automated weather stations across Oklahoma, with at least one in each of its 77 counties, commissioned in 1994.
Okta
Okta, Inc. (Nasdaq: OKTA) is an American identity and access management company whose cloud platform authenticates users and governs their access to applications, serving organizations from small businesses to Fortune 500 companies.
Oku Volcanic Field
Oku Volcanic Field (Oku Volcanic Group), a volcanic field in northwest Cameroon on the Cameroon Volcanic Line; four stratovolcanoes culminating at Mt. Oku (3,011 m), activity 30 to <1 Ma, basanite-to-rhyolite lavas, and the Lake Nyos and Monoun CO2 disaster lakes.
Olaf Holtedahl
Olaf Holtedahl (1885–1975) was a Norwegian geologist, professor at Oslo, who led polar expeditions to Novaya Zemlya and Antarctica and first recognized the great Precambrian–Cambrian glaciation.
Olaf M. Magnussen
Olaf M. Magnussen is a professor of solid-state physics at the University of Kiel who studies electrode surfaces at the atomic scale, using video-STM and synchrotron X-ray scattering.
Olafs Daugulis
Olafs Daugulis is a Latvian-born chemist and Robert A. Welch Chair at the University of Houston, known for introducing the widely used 8-aminoquinoline directing group in 2005.
Olbers' paradox
Olbers' paradox, also called the dark night sky paradox, asks why the night sky is dark if the universe is infinite, eternal, and full of stars.
Olca-Paruma
Olca-Paruma, a 15-km-long east-west chain of stratovolcanoes on the Chile-Bolivia border in the Central Andean Volcanic Arc; summit 5,705 m, only reported historical eruption an unconfirmed flank event in 1865-1867, now fumarolic and seismically monitored.
Old New Year (Старый Новый год)
The Old New Year (Старый Новый год) is an informal holiday on January 14, corresponding to January 1 in the Julian calendar, celebrated in post-Soviet countries.
Old quantum theory
Old quantum theory, also called the Sommerfeld–Bohr theory, imposed quantum conditions on classical mechanics, dominating atomic physics from 1900 until Heisenberg's matrix mechanics of 1925.
Old Red Sandstone
The Old Red Sandstone is a unit of continental red beds of late Silurian to early Carboniferous age, best exposed in Britain, Ireland, and lands around the North Atlantic.
Old Style and New Style dates
Old Style and New Style dates are the labels historians use to distinguish Julian calendar dates from Gregorian ones, including the change of year start in 1752.
Older Dryas
The Older Dryas was a brief cold stadial about 14,000 years ago that interrupted the Bølling–Allerød warming at the end of the last ice age, named for Dryas octopetala leaves in Scandinavian lake clays.
Oldest Dryas
The Oldest Dryas was the oldest of the three cold Dryas stadials of the European late glacial, spanning roughly 19,000 to 14,700 years before present and preceding the Bølling warming.