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All articles starting with H

20,046 articles

Harmine

Harmine is a β-carboline alkaloid first isolated in 1847 from Syrian rue, the principal active alkaloid of ayahuasca, now under study for regenerating insulin-producing beta cells in diabetes.

Harmit Malik

Harmit Malik is an evolutionary biologist who studies genetic conflict at Fred Hutchinson Cancer Center in Seattle, where he is a professor and Howard Hughes Medical Institute Investigator.

Harmon Craig

Harmon Craig (1926–2003) was an American isotope geochemist who spent his career at Scripps Institution of Oceanography, pioneering carbon isotope and radiocarbon studies of the global carbon cycle.

Harmon Killebrew

Harmon Killebrew (Harmon Clayton Killebrew, 1936–2011), nicknamed "Killer", was an American baseball player who hit 573 home runs and entered the Hall of Fame in 1984.

Harmon Northrop Morse

Harmon Northrop Morse (1848–1920) was an American chemist at Johns Hopkins University whose fifteen-year osmotic-pressure campaign supplied experimental support for van 't Hoff's theory of solutions.

Harmon Trophy

The Harmon Trophy, or Harmon International Trophy, is a set of annual aviation awards founded by Clifford B. Harmon in 1926 for outstanding achievement in aeronautics.

Harmonia axyridis

Harmonia axyridis, the harlequin ladybird or multicolored Asian lady beetle, is an aphid-eating ladybird native to Asia, introduced worldwide for biocontrol since 1916, now invasive and harmful to native ladybirds through competition and intraguild predation.

Harmonia Linea

Harmonia Linea, a linea on Jupiter's moon Europa, IAU feature ID 2368, about 1,154 km across near 28°N, 171.7°W, approved 1997 and named for Cadmus's mythological wife.

Harmonic

A harmonic, also called a flageolet tone or harmonic partial, is a component of a periodic sound at a whole-number multiple of the fundamental, and the pattern of harmonics gives a note its timbre.

Harmonic analysis

Harmonic analysis is the branch of mathematics that decomposes functions and signals into sine and cosine waves, the idea behind Fourier series and the Fourier transform.

Harmonic balance

Harmonic balance, or the harmonic balance method, is a frequency-domain numerical method for the periodic steady-state response of nonlinear circuits, used for amplifiers, mixers, and oscillators.

Harmonic coordinate condition

The harmonic coordinate condition, also called the harmonic gauge or De Donder gauge, is a gauge choice in general relativity requiring each coordinate function to satisfy the wave equation.

Harmonic coordinates

Harmonic coordinates, also known as the harmonic coordinate system or wave coordinates, are a coordinate system in general relativity where each coordinate satisfies the wave equation.

Harmonic Drive

Harmonic Drive is a brand of strain wave gear, a compact, backlash-free speed reducer used in industrial and humanoid robots, invented by C. Walton Musser in 1957.

Harmonic filter

A harmonic filter is electrical equipment that reduces harmonic distortion in power systems by diverting or canceling harmonic currents from nonlinear loads such as variable frequency drives, rectifiers, and arc furnaces.

Harmonic form

A harmonic form is a differential form on a Riemannian manifold lying in the kernel of the Hodge Laplacian, central to Hodge theory, which links analysis and topology.

Harmonic function

A harmonic function is a twice continuously differentiable function satisfying the Laplace equation, describing steady-state temperatures, electrostatic potentials, and ideal fluid flows; it obeys the mean value property.

Harmonic imaging

Harmonic imaging is an ultrasound method that forms diagnostic images from harmonic frequencies generated as the pulse travels through tissue, giving less noise and better contrast.

Harmonic map

A harmonic map is a mapping between Riemannian manifolds that is a critical point of a natural energy integral, generalizing Dirichlet's integral; the theory was begun systematically by Eells and Sampson in 1964.

Harmonic mean

The harmonic mean is a type of average, one of the three Pythagorean means, calculated as the number of values divided by the sum of their reciprocals.

Harmonic measure

Harmonic measure is a probability measure on a domain's boundary giving where Brownian motion from an interior point first exits, equivalently how boundary values determine solutions of the Dirichlet problem.

Harmonic mixer

A harmonic mixer is a frequency converter that mixes a harmonic of the local oscillator with an incoming radio frequency signal, chiefly used to down-convert millimeter-wave and terahertz signals.

Harmonic motion imaging

Harmonic motion imaging (HMI) is an ultrasound-based elasticity imaging technique that assesses tissue stiffness by inducing oscillations with a focused ultrasound transducer and tracking the resulting displacement.

Harmonic number

A harmonic number is the sum of the reciprocals of the first n positive integers, a partial sum of the divergent harmonic series that grows like the natural logarithm.

Harmonic oscillator

A harmonic oscillator is any physical system in which a restoring force proportional to displacement from equilibrium produces oscillation, exemplified by a mass on a spring obeying Hooke's law.

Harmonic oscillator model of aromaticity

The harmonic oscillator model of aromaticity (HOMA) is a geometric index, introduced in 1972 by Kruszewski and Krygowski, that measures the aromaticity of cyclic molecules from bond lengths.

Harmonic resonance

Harmonic resonance in power systems occurs when the system's natural frequency, set by inductance and capacitor banks, matches a harmonic source like a variable-frequency drive, amplifying harmonic voltages far above normal levels and damaging equipment.

Harmonic restraint

Harmonic restraint is a technique in transformer differential protection that uses the harmonic content of inrush current, especially the second harmonic, to prevent relay tripping.

Harmonic series (mathematics)

The harmonic series is the infinite sum of 1 + 1/2 + 1/3 + 1/4 + …, which diverges even though its terms tend to zero.

Harmonic series (music)

Harmonic series (music): the whole-number multiples f, 2f, 3f of a fundamental frequency, also called the overtone series. It underlies timbre, brass playing, just intonation, and consonance, with real instruments showing inharmonicity.