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Antennae Galaxies
The Antennae Galaxies, NGC 4038 and NGC 4039, are a pair of colliding spiral galaxies in Corvus, discovered by William Herschel in 1785 and named for their insect-like tidal tails.
Antennae search algorithm
The antennae search algorithm, usually called beetle antennae search (BAS), is a beetle-inspired metaheuristic for continuous optimization that iterates a single candidate solution, reported by Jiang and Li in 2018.
Antennagate
Antennagate was the 2010 controversy over the iPhone 4 losing reception when gripped at its lower-left corner, which Apple answered with a free case for every buyer.
Antennaria
Antennaria (pussytoes) is a genus of about 45 accepted species of dioecious perennial herbs in Asteraceae, tribe Gnaphalieae, native from subarctic and temperate Northern Hemisphere to Mexico and southern South America, known for apomixis and polyploid complexes.
Antenor (crater on Dione)
Antenor is an 81-km impact crater on Saturn's moon Dione at 7.00 S, 11.54 W, named in 1982 after Priam's nephew who founded Padua; Dione craters follow Trojan and Aeneid naming themes.
Anténor Firmin
Anténor Firmin (Joseph Auguste Anténor Firmin, 1850–1911) was a Haitian anthropologist, journalist, and politician whose 1885 book De l'égalité des races humaines rebutted racial hierarchy theories.
Antenora Mons
Antenora Mons is a 122 km mountain feature on Jupiter's moon Io near the north pole, approved by the IAU on January 29, 2025 and named after Antenora, the second ring of Cocytus in Dante's Inferno.
Anteon
Anteon Jurine, 1807 is a cosmopolitan genus of dryinid parasitoid wasps attacking leafhoppers; largest Anteoninae genus with 464 species, extreme sexual dimorphism, and DNA barcoding used to link sexes and delimit species.
Antepartum fetal death
Antepartum fetal death (ICD-11 KD3B.0) is fetal death before the onset of labor, distinct from intrapartum death; maceration suggests antepartum timing, and it accounts for over half of stillbirths.
Antepartum haemorrhage
Antepartum haemorrhage (APH, ICD-11 JA41) is genital tract bleeding in late pregnancy before labour, complicating 2–5% of pregnancies; main causes are placental abruption and placenta praevia, with vasa previa and uterine rupture rarer.
Antera Duke
Antera Duke (ca. 1735–ca. 1809) was an Efik slave-trading chief of Duke Town, Old Calabar, Nigeria, known for his pidgin-English diary of 1785 to 1788.
Anterior cerebral artery
Anterior cerebral artery (ACA), artery of the circle of Willis supplying medial frontal and parietal cortex and corpus callosum; segments A1-A5, variants include azygous ACA and persistent primitive olfactory artery, associated with aneurysms.
Anterior cerebral artery syndrome
Anterior cerebral artery syndrome: stroke deficits from infarction in ACA territory, also called ACA infarction syndrome. Rare (0.3–4.4% of strokes), cardioembolic in origin, with leg-predominant weakness, abulia, alien hand, and akinetic mutism.
Anterior cervical discectomy and fusion
Anterior cervical discectomy and fusion (ACDF) is a spine operation that removes a herniated or degenerative neck disc through the front of the neck and fuses the adjacent vertebrae.
Anterior chamber paracentesis
Anterior chamber paracentesis (ACP) is an ophthalmologic procedure using a fine needle through the cornea to withdraw aqueous humor for diagnostic testing or to lower intraocular pressure.
Anterior cingulate cortex
Anterior cingulate cortex (ACC), including subgenual, pregenual, and anterior midcingulate subregions: medial frontal cortex around the corpus callosum involved in pain affect, conflict monitoring, motor control, and decision-making, targeted by cingulotomy and neuromodulation.
Anterior cruciate ligament
The anterior cruciate ligament (ACL) is one of two cruciate ligaments of the knee, joining femur to tibia and stabilizing the joint against excessive movement.
Anterior cruciate ligament injury
Anterior cruciate ligament (ACL) injury: rupture of the knee ligament preventing tibial forward slide. Over 200,000 US cases yearly, 70% noncontact, females 2-8x higher risk; surgery versus rehabilitation compared in KANON, COMPARE, and ACL SNNAP trials.
Anterior cruciate ligament reconstruction
Anterior cruciate ligament reconstruction (ACLR) is an orthopedic surgical procedure that replaces a torn knee ligament with a tendon graft routed through bone tunnels, restoring knee stability.
Anterior cruciate ligament repair
Anterior cruciate ligament repair is a knee operation that reattaches a patient's own torn ACL rather than replacing it with a graft, as ACL reconstruction does.
Anterior cutaneous nerve entrapment syndrome
Anterior cutaneous nerve entrapment syndrome (ACNES), also called abdominal cutaneous nerve entrapment syndrome or intercostal neuralgia, is entrapment of T7-T12 intercostal nerve branches at the rectus abdominis border, causing chronic localized abdominal wall pain diagnosed by Carnett test and treated with injections or neurectomy.
Anterior horn motor neuron
Anterior horn motor neuron (anterior horn cell, ventral horn motor neuron): a lower motor neuron of the spinal cord's anterior horn, in Rexed lamina IX, with alpha and gamma types, that innervates skeletal muscle via acetylcholine at the neuromuscular junction as the final common pathway; targeted in ALS, SMA, and polio.
Anterior ischemic optic neuropathy
Anterior ischemic optic neuropathy (AION), also called NAION or AAION, is sudden infarction of the optic nerve head from posterior ciliary artery occlusion; the nonarteritic form is the most common acute optic neuropathy over age 50, while the arteritic form signals giant cell arteritis and is a steroid emergency.
Anterior pituitary
Anterior pituitary (adenohypophysis): front lobe of the pituitary gland in the sella turcica; five cell types secrete GH, prolactin, ACTH, TSH, FSH, and LH under hypothalamic portal control.
Anterior spinal artery syndrome
Anterior spinal artery syndrome (anterior cord syndrome) is infarction of the anterior two-thirds of the spinal cord, causing paralysis and pain-temperature loss with preserved vibration sense, most often after aortic surgery or atherosclerosis.
Anterior Temporal Lobectomy
Anterior temporal lobectomy (ATL), a neurosurgical resection of the anterior temporal lobe including amygdala, hippocampus, and parahippocampal gyrus, treats drug-resistant temporal lobe epilepsy; pioneered by Penfield and Falconer, it yields roughly 64% seizure freedom with visual field and memory risks.
Anterior urethral valve
Anterior urethral valve (AUV): a rare congenital semilunar fold on the ventral male urethra causing lower urinary tract obstruction in boys; diagnosed by VCUG, treated by endoscopic ablation, sometimes with posterior urethral valves.
Anterix
Anterix is an American wireless communications company holding the largest share of licensed 900 MHz spectrum in the United States, which it leases to utilities for private broadband networks.
Antero de Quental
Antero de Quental (1842–1891) was a Portuguese poet and philosopher from Ponta Delgada, Azores, the leading figure of the Generation of 70 and a cofounder of Portugal's socialist movement.
Antero Midstream Corp
Antero Midstream Corp is a Denver, Colorado-based midstream energy company providing gathering, compression, and water handling services to Antero Resources' natural gas production in West Virginia and Ohio.