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Haldane model
The Haldane model, introduced by F. D. M. Haldane in 1988, is a honeycomb-lattice model whose complex hopping breaks time-reversal symmetry, giving a quantum Hall effect with no magnetic field.
Haldane phase
The Haldane phase is a gapped phase of one-dimensional integer-spin antiferromagnetic chains with hidden topological order and edge states, the first symmetry-protected topological phase discovered.
Hale cycle
The Hale cycle is the Sun's approximately 22-year magnetic cycle, named for George Ellery Hale, who discovered sunspot magnetic fields in 1908; its polarity reverses at each 11-year sunspot cycle.
Hale F. Trotter
Hale F. Trotter (Hale Freeman Trotter, 1931–2022) was a Canadian mathematician who spent his career at Princeton and is known for the Trotter product formula and the Johnson–Trotter algorithm.
Hale Telescope
The Hale Telescope, also known as the Hale reflector, is a 200-inch (5.1-meter) reflecting telescope at Palomar Observatory in San Diego County, California, owned and operated by Caltech.
Half-graben
A half-graben is an asymmetric area of subsidence controlled by hanging-wall subsidence above a single basin-margin normal fault, and is the most common structure in syn-rift settings, typically 25 to 100 km long.
Half-Heusler
Half-Heusler compounds are ternary intermetallics of composition XYZ with a non-centrosymmetric cubic structure, leading thermoelectric materials that convert waste heat into electricity at medium to high temperatures.
Half-life
Half-life is the time required for half of the atoms of a radioactive substance to decay, a concept also applied to drugs and chemicals in the environment.
Half-precision floating-point format
Half-precision floating-point format, also called FP16 or binary16, is a 16-bit IEEE 754 encoding that stores numbers in half the memory of single precision, widely used in graphics and machine learning.
Half-reaction
A half-reaction is the oxidation or reduction part of a redox reaction, written with electrons shown explicitly; balanced halves are added so electrons cancel, and tabulated half-reactions give electrode potentials.
Half-wave plate
A half-wave plate (λ/2 plate) is a birefringent optical retarder that introduces a 180-degree phase difference between polarization components, rotating linearly polarized light by twice the angle to its fast axis.
Halide
A halide, also called a halogenide, is the anion of a halogen like fluoride or chloride, or any compound containing a halogen, including metal halide salts and organohalides.
Halide perovskite nanocrystals
Halide perovskite nanocrystals are nanometer-scale semiconductor crystals with the perovskite structure ABX₃, first reported colloidally in 2015 and used in LEDs, solar cells, and quantum light sources.
Halide perovskite radiation detectors
Halide perovskite radiation detectors are X-ray and gamma-ray sensors using metal halide perovskite semiconductors like CsPbBr₃, first demonstrated in 2013 and studied as low-cost, solution-processable alternatives to cadmium zinc telluride.
Halite
Halite, commonly known as rock salt, is the water-soluble mineral form of sodium chloride that forms evaporite beds in saline lakes and marine basins, rising at depth into salt domes.
Hall effect
The Hall effect, or Hall's Law, is a transverse voltage that appears across a current-carrying conductor when a magnetic field is applied perpendicular to the current, discovered in 1879.
Hall effect current sensor
A Hall effect current sensor measures electric current by sensing the magnetic field it produces, using a Hall element, and can measure both DC and AC with galvanic isolation.
Hall's marriage theorem
Hall's marriage theorem, proved by Philip Hall in 1935, states that a bipartite graph has a matching covering one side if and only if every subset has enough neighbors.
Hallmark
A hallmark is an official mark certifying that an item of gold, silver, platinum, or palladium has been tested and meets legal standards of purity.
Halloysite
Halloysite is a naturally occurring aluminosilicate clay mineral of the kaolin group that most commonly occurs as hollow nanoscale tubes rather than the flat plates of kaolinite.
Halo (optical phenomenon)
A halo, also called an icebow, is an atmospheric optical phenomenon in which ice crystals in high clouds bend sunlight or moonlight into rings, arcs, or pillars.
Halo bias
Halo bias is the cosmological relation between the spatial distribution of dark matter haloes and the dark matter density field, quantifying how haloes cluster more strongly than matter itself.
Halo mass function
The halo mass function (HMF) is the comoving number density of dark matter halos per unit mass, a central prediction of structure formation models used to constrain cosmological parameters.
Halo nucleus
A halo nucleus is an atomic nucleus, usually near the neutron or proton drip line, in which weakly bound nucleons form an extended, dilute cloud around a compact core.
Halo occupation distribution
The halo occupation distribution (HOD) is a statistical model in cosmology giving the probability that a dark matter halo of a given mass contains a given number of galaxies.
Haloalkane
A haloalkane, also called an alkyl halide or halogenoalkane, is an organic compound in which one or more hydrogens of an alkane are replaced by halogens.
Haloanilines
Haloanilines are anilines with halogen atoms such as fluorine, chlorine, bromine, or iodine on the ring, used as pharmaceutical and agrochemical intermediates and found as disinfection byproducts in drinking water.
Halocline
A halocline is a layer of water where salinity changes rapidly with depth, separating fresher surface water from saltier water below and limiting vertical mixing.
Haloform reaction
The haloform reaction, also called the Lieben haloform reaction, treats methyl ketones with halogen and base to give carboxylates and haloforms such as iodoform and chloroform.
Halogen
The halogens, also called Group 17 elements, are the five highly reactive nonmetals fluorine, chlorine, bromine, iodine, and astatine, named in 1842 from Greek for salt-producing because they form salts with metals.