All articles starting with O
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Orogenic gold deposit
An orogenic gold deposit is gold mineralization deposited from low-salinity, aqueous-carbonic fluids rising along crustal faults during mountain building, supplying an estimated 75% of all gold extracted by humans.
Orogeny
Orogeny is the process by which mountain belts form, typically when tectonic plates collide or converge, folding and thickening the crust; examples include the Alps, Himalayas, and Appalachians.
Orographic lift
Orographic lift is the forced upward movement of air over rising terrain such as a mountain, cooling it and producing clouds and precipitation on the windward side.
Orography
Orography, also called orology, is the study and mapping of mountains and elevated terrain. It underlies orographic precipitation (windward enhancement, rain shadows), mountain meteorology, and the representation of terrain and orographic drag in weather and climate models.
Oromandibular dystonia
Oromandibular dystonia is a focal dystonia in which involuntary contractions of the jaw, tongue, and facial muscles disrupt chewing, speaking, and swallowing, typically beginning in the 50s.
Oromia
Oromia (Oromiyaa) is Ethiopia's largest and most populous regional state, created in July 1992, capital Finfinne (Addis Ababa), producing most of Ethiopia's coffee and grain, and affected by ongoing OLA insurgency conflict.
Oromo Federalist Congress
Oromo Federalist Congress (OFC), Ethiopian opposition party formed by the 2012 merger of OPC and OFDM, led by Merera Gudina; advocates genuine federalism and Oromo self-government, member of Medrek, boycotted the 2021 and 2026 elections.
Oromo Federalist Democratic Movement
The Oromo Federalist Democratic Movement (OFDM) was an Ethiopian opposition party, active from 2004, that drew support from western Oromia and won 11 seats in the 2005 elections.
Oromo language
Oromo (Afaan Oromoo), a Lowland East Cushitic language of Ethiopia and Kenya, spoken by tens of millions; Latin-based Qubee script adopted 1991 after decades of suppression; SOV grammar, marked nominative, dialects, and growing NLP resources.
Oromo Liberation Front
The Oromo Liberation Front (OLF; Oromo: Adda Bilisummaa Oromoo) is an Oromo nationalist organization founded in eastern Ethiopia in 1973 to pursue Oromo self-determination, first through armed struggle and now as a registered political party.
Oromo migrations
The Oromo migrations were successive movements of pastoral Oromo from southern Ethiopia into the Ethiopian highlands beginning in the sixteenth century, after the Muslim-Christian wars of 1529 to 1559.
Oromo people
The Oromo people are Ethiopia's largest ethnic group, Cushitic-speaking (Afaan Oromo), known for the Gada governance system, the 16th-century Oromo expansion, and the Irreecha festival.
Oromo sack of Harar
The Oromo sack of Harar was a 16th-century Oromo attack on Harar, capital of the Adal Sultanate, which the sultanate abandoned for Aussa in 1577.
Orontes
Orontes (Nahr al-Assi, Asi River), a Middle East river rising in Lebanon and flowing through Syria and Turkey to the Mediterranean; also the name of Achaemenid satraps of Armenia and the Orontid dynasty.
Orontid dynasty
The Orontid dynasty (Երվանդունի), an Iranian-origin family claiming descent from Hydarnes, ruled Armenia as satraps of the Median and Achaemenid empires and later as semi-independent dynasts under the Seleucids, ending around 200 BCE.
Orontid dynasty of Commagene
The Orontid dynasty of Commagene (Yervanduni) was a royal house founded by Ptolemaeus that ruled Commagene from 163 BC until Vespasian abolished it in AD 72.
Orontius (lunar crater)
Orontius is a 121-km lunar impact crater in the southern highlands at 40.4°S, 4.0°W, named for French mathematician-cartographer Oronce Fine. It is the oldest of a crater chain overlain by Huggins and Nasireddin.
Oroonoko
Oroonoko: or, The Royal Slave (1688) is Aphra Behn's short prose fiction about an African prince tricked into slavery in Surinam, an early English novel and early anti-slavery narrative.
Oropharyngeal cancer
Oropharyngeal cancer, or oropharyngeal squamous cell carcinoma (OPSCC), is throat cancer of the tonsils, tongue base, and soft palate, increasingly caused by HPV-16 and divided into HPV-positive and HPV-negative forms with different prognosis and treatment.
Oropouche fever
Oropouche fever, also called sloth fever, is a febrile illness caused by Oropouche virus, spread mainly by Culicoides paraensis biting midges in South America, Central America, and the Caribbean; no vaccine or specific treatment exists.
Oros Ossa (Kissavos)
Oros Ossa (Kissavos, Όσσα/Κίσσαβος) is a 1,978 m mountain in eastern Thessaly, Greece, between Olympus and Pelion, divided from Olympus by the Tempe gorge; Natura 2000 Aesthetic Forest, giants' mythology, blueschist geology.
Orot Rabin power station
Orot Rabin (אורות רבין) is a power station on the Mediterranean coast at Hadera, Israel, owned by the Israel Electric Corporation and converting from coal to natural gas.
Orotate phosphoribosyltransferase
Orotate phosphoribosyltransferase (OPRT, EC 2.4.2.10) catalyzes orotate plus PRPP to orotidine 5'-monophosphate in pyrimidine biosynthesis; in humans it is the N-terminal domain of bifunctional UMPS, whose loss causes hereditary orotic aciduria.
Orotic acid
Orotic acid is a pyrimidine carboxylic acid intermediate in de novo pyrimidine nucleotide synthesis, once called vitamin B13 and now known not to be a vitamin.
Orotic aciduria
Hereditary orotic aciduria (UMPS deficiency, uridine monophosphate synthase deficiency) is a rare autosomal recessive pyrimidine metabolism disorder causing megaloblastic anemia without hyperammonemia, growth failure, and massive urinary orotic acid; treated with uridine or uridine triacetate, distinct from OTC deficiency.
Orotidine 5'-phosphate decarboxylase
Orotidine 5'-phosphate decarboxylase (ODCase), also called OMP decarboxylase, is the enzyme that catalyzes OMP to UMP, the final step of pyrimidine biosynthesis, accelerating a reaction with a 78-million-year half-time to 18 ms.
Orotracheal intubation
Orotracheal intubation is the insertion of a cuffed tube through the mouth into the trachea to secure the airway and enable mechanical ventilation, performed in about 1.6 million US patients yearly.
Oroville Dam
Oroville Dam is an earthfill dam on the Feather River in Butte County, California. At 770 feet (235 m) high, it is the tallest dam in the United States.
Oroville Dam crisis
The Oroville Dam crisis was a February 2017 emergency at Oroville Dam on the Feather River in California, in which spillway failures prompted the evacuation of about 188,000 people.
Oroville, California
Oroville, formerly Ophir City, is the county seat of Butte County, California, on the Feather River, best known for Oroville Dam, the tallest dam in the country.