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Homopolar generator
The homopolar generator, also known as the Faraday disk, is a direct-current generator with a conductive disk spinning in a magnetic field, invented by Michael Faraday in 1831.
Homopolar motor
A homopolar motor is a direct-current electric motor whose fixed magnetic polarity needs no commutator; Faraday first demonstrated one in 1821 at the Royal Institution in London.
Homoserine
Homoserine, or L-homoserine, is a four-carbon amino acid central to bacterial and plant pathways. It is a platform chemical and precursor to signaling molecules used for quorum sensing.
Homothety
A homothety, also called a central dilatation, is a geometric transformation with a center O that sends each point M to a point on line OM at a scaled distance.
Homotopy
Homotopy is a continuous deformation of one map between topological spaces into another, introduced by Henri Poincaré in 1895 as a central idea of algebraic topology.
Homotopy analysis method
The homotopy analysis method, developed by Shi-Jun Liao of Shanghai Jiaotong University in 1992, is a semi-analytical technique giving convergent series solutions of strongly nonlinear differential equations.
Homotopy category
The homotopy category Ho(C) of a category with weak equivalences is obtained by universally forcing them to become isomorphisms, turning homotopy theory into equivalence classes of morphisms.
Homotopy equivalence
A homotopy equivalence is a continuous map between topological spaces with a homotopy inverse; homotopy equivalent spaces share invariants like the fundamental group and homology.
Homotopy group
A homotopy group is an algebraic invariant assigning to a space a group of homotopy classes of maps from the n-sphere, introduced by Witold Hurewicz in 1935–36.
Homotopy method
A homotopy method, also called a continuation method, solves a system of equations by deforming an easy problem with known solutions into the target problem and tracking the solution paths.
Homotopy perturbation method
The homotopy perturbation method (HPM) is an analytical technique introduced by Ji-Huan He in 1999 that solves nonlinear differential equations without needing a small parameter.
Homotopy type theory
Homotopy type theory, also known as homotopical type theory or HoTT, combines Martin-Löf type theory with homotopy theory, with Voevodsky's univalence axiom and higher inductive types at its core.
Homunculus
A homunculus (Latin for "little human") is an artificially made miniature human described in Renaissance alchemy, above all in Paracelsus's 1537 recipe in De natura rerum.
Homunculus Nebula
The Homunculus Nebula is a bipolar nebula of gas and dust around the star Eta Carinae, ejected during its Great Eruption of 1837 to 1858.
Hon Wai Lam
Hon Wai Lam (born 1976) is a British organic synthesis chemist who has held the GSK Chair of Sustainable Chemistry at the University of Nottingham since 2013.
Hondol
Hondol (Hondolen), village in Certeju de Sus, Hunedoara County, Romania, in the Metaliferi Mountains; Roman-era gold mine (RAN 89286.03) and the Coranda-Hondol Au-Ag deposit, about 4.8 Moz at 1.4 g/t Au, mined until 2006.
Honeycomb iridate
Honeycomb iridates are iridium oxides, such as Na₂IrO₃ and Li₂IrO₃, in which Ir ions form a honeycomb lattice and are studied as Kitaev spin-liquid candidates.
Hong Ding
Hong Ding (丁洪, born 1968) is a Chinese condensed matter physicist who studies high-temperature superconductors and topological materials using ARPES, discovering the cuprate pseudogap in 1996 and Weyl fermions in TaAs in 2015.
Hong Kong Observatory
The Hong Kong Observatory (HKO), established in 1883, is the government department of Hong Kong responsible for weather forecasting, tropical cyclone warning signals, radiation monitoring, and the Hong Kong time standard.
Hong Kong tropical cyclone warning signals
The Hong Kong tropical cyclone warning signals, known as typhoon signals, are numbered warnings from the Hong Kong Observatory using signals 1, 3, 8, 9, and 10.
Hong Qin
Hong Qin is a theoretical and computational plasma physicist known for structure-preserving geometric algorithms and topological plasma physics, and winner of the 2023 John Dawson Award.
Hong Wang (王虹)
Hong Wang (王虹), born 1991, is a Chinese mathematician at IHES near Paris known for the 2025 proof of the three-dimensional Kakeya conjecture and the 2026 Fields Medal.
Hong X. Tang
Hong X. Tang, also known as Hongxing Tang, is a physicist at Yale University who works on integrated photonic and optomechanical circuits and converting quantum signals between microwave and optical photons.
Hong-Cai "Joe" Zhou
Hong-Cai "Joe" Zhou (周宏才), born 1964, is an inorganic chemist and Robert A. Welch Chair professor at Texas A&M University, known for porous framework materials called metal–organic frameworks.
Hong‐Gyu Park
Hong-Gyu Park (박홍규) is a South Korean nanophotonics experimentalist and professor of physics at Seoul National University, known for nanolasers, photon-triggered nanowire transistors, and subwavelength optical devices.
Hong‐Jun Gao
Hong-Jun Gao (高鸿钧) is a Chinese condensed matter physicist and CAS academician at the Institute of Physics, known for observing Majorana zero modes in iron-based superconductors.
Hong–Ou–Mandel effect
The Hong–Ou–Mandel effect, or HOM effect, is a two-photon interference effect named after Hong, Ou, and Mandel, who first demonstrated it in 1987 at the University of Rochester.
Honggang Cui
Honggang Cui (崔宏刚) is a chemical and biomolecular engineer at Johns Hopkins University, known for developing self-assembling prodrugs in which anticancer drug molecules form their own delivery vehicles.
Hongkun Park
Hongkun Park is Mark Hyman Jr. Professor of Chemistry and Professor of Physics at Harvard University, working on quantum optoelectronics, quantum sensing, and nanoscale tools for studying living cells.
Hongliang Xin
Hongliang Xin is a chemical engineer and professor at Virginia Tech, where he leads the Xin Group applying machine learning to heterogeneous catalysis and electrocatalysis.