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Halogen bond
A halogen bond is a directional, noncovalent attraction in which a covalently bound halogen atom acts as a Lewis acid toward an electron-donor site, formally defined by IUPAC in 2013.
Halogen bonding catalysis
Halogen bonding catalysis is a branch of organocatalysis in which a catalyst activates a substrate through a halogen bond, a noncovalent interaction involving an electrophilic halogen atom.
Halogenation
Halogenation is a chemical reaction that introduces one or more halogen atoms (fluorine, chlorine, bromine, or iodine) into an organic molecule by substitution or addition.
Halomethane
A halomethane is a methane derivative in which one or more hydrogen atoms are replaced by fluorine, chlorine, bromine, or iodine, including chloroform and CFCs.
Halonitrophenols
Halonitrophenols are phenol compounds whose rings carry both a halogen atom and a nitro group, making them far more acidic than chlorophenols or nitrophenols alone.
Halorespiration
Halorespiration, now called organohalide respiration (OHR), is an anaerobic bacterial process in which halogenated compounds serve as terminal electron acceptors and are reductively dehalogenated, important in bioremediation.
Halting problem
The halting problem, also known as Turing's halting theorem, asks whether a program halts on a given input; Alan Turing proved in 1936 that no algorithm solves it.
Halvor Solberg
Halvor Solberg (1895–1974) was a Norwegian meteorologist who gave the Bergen School's cyclone model its mathematical form and identified the polar front, the boundary along which low-pressure systems form.
Ham sandwich theorem
The ham sandwich theorem, also called the Stone–Tukey theorem, states that n measurable sets in n-dimensional space can all be bisected at once by one hyperplane.
Hamaker constant
The Hamaker constant, A, is a material coefficient setting the strength of the van der Waals interaction between macroscopic bodies, introduced by H. C. Hamaker in 1937.
Hamilton–Jacobi equation
The Hamilton–Jacobi equation is a first-order partial differential equation of classical mechanics whose solution, Hamilton's principal function, solves the equations of motion by inversion; it was developed by Hamilton and Jacobi in the 1840s.
Hamilton–Jacobi–Bellman equation
The Hamilton–Jacobi–Bellman (HJB) equation is a nonlinear partial differential equation whose solution gives the minimum achievable cost in continuous-time optimal control, forming the basis of Bellman's 1957 dynamic programming method.
Hamilton's equations
Hamilton's equations, also called the canonical equations of motion, are a pair of first-order differential equations describing mechanical motion in terms of coordinates, momenta, and the Hamiltonian.
Hamiltonian (quantum mechanics)
In quantum mechanics, the Hamiltonian, also called the Hamilton operator, is the operator corresponding to a system's total energy, and it determines how the system's state changes in time.
Hamiltonian complexity
Hamiltonian complexity is the field of theoretical computer science and quantum physics studying the complexity of quantum Hamiltonian problems, above all the local Hamiltonian problem.
Hamiltonian constraint of loop quantum gravity
The Hamiltonian constraint of loop quantum gravity is the quantum operator encoding general relativity's local dynamics, first given a rigorous form by Thomas Thiemann, though ambiguities remain.
Hamiltonian cycle
A Hamiltonian cycle is a closed path in a graph that visits every vertex exactly once and returns to its start; it was posed as Hamilton's Icosian Game in 1857.
Hamiltonian interpolation and the adiabatic spectral gap
In adiabatic quantum computation, the interpolation from an easy initial Hamiltonian to a final one whose ground state encodes the answer, with the minimum spectral gap governing runtime.
Hamiltonian learning
Hamiltonian learning is a set of methods in quantum information science that infer the parameters, and sometimes the structure, of an unknown quantum Hamiltonian from measurement data.
Hamiltonian mechanics
Hamiltonian mechanics, also known as Hamiltonian dynamics, is a reformulation of classical mechanics introduced by William Rowan Hamilton in 1834 and 1835, describing motion by Hamilton's equations.
Hamiltonian Monte Carlo
Hamiltonian Monte Carlo, originally called Hybrid Monte Carlo, is a Markov chain Monte Carlo method introduced in 1987 that uses Hamiltonian dynamics for efficient sampling, later generalized by Radford Neal.
Hamiltonian neural networks
Hamiltonian neural networks, introduced at NeurIPS 2019 by Sam Greydanus, Misko Dzamba, and Jason Yosinski, learn a system's energy function from data so the learned dynamics conserve energy.
Hamiltonian simulation
Hamiltonian simulation is the quantum-computing task of implementing a Hamiltonian's time evolution as a quantum circuit of elementary gates, motivating quantum computers when Richard Feynman proposed the idea in 1982.
Hamiltonian truncation
Hamiltonian truncation is a non-perturbative numerical method for quantum field theories that restricts the Hamiltonian to a finite subspace of states below an energy cutoff, generalizing Rayleigh-Ritz to field theory.
Hamish Robertson
R. G. Hamish Robertson (born 1943) is a Canadian-born nuclear and neutrino physicist, emeritus professor at the University of Washington, known for the Los Alamos tritium experiments, SNO, and KATRIN.
Hammett equation
The Hammett equation, also known as Hammett analysis, is a linear free-energy relationship in physical organic chemistry relating reaction rates and equilibria to substituent electronic effects.
Hamming bound
The Hamming bound, also called the sphere-packing bound, is an upper limit on the size of an error-correcting code with given length and minimum distance.
Hamming distance
The Hamming distance between two equal-length strings is the number of positions where their symbols differ, named for Richard Hamming, who introduced it in 1950.
Han Htoon
Han Htoon is a Los Alamos National Laboratory staff scientist and Thrust Leader for Nanophotonics at the Center for Integrated Nanotechnologies, studying single-photon emitters in nanoscale materials.
Han Woong Yeom
Han Woong Yeom is a South Korean condensed matter physicist at POSTECH who studies atomic wires and directs an Institute for Basic Science center since 2013.