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Diffusion
Diffusion is the net movement of a substance from regions of higher to lower concentration, driven by random particle motion without external energy, described by Fick's laws.
Diffusion chronometry
Diffusion chronometry is a geochemical method that converts chemical zoning profiles in minerals into durations of thermal events, most commonly the interval between magma recharge and eruption.
Diffusion encoding (NMR spectroscopy)
Diffusion encoding is an NMR technique that applies magnetic field gradients to measure molecular self-diffusion coefficients; its DOSY variant separates mixture spectra without physical separation.
Diffusion equation
The diffusion equation is a partial differential equation describing how heat or concentration spreads through a medium over time, first derived by Joseph Fourier in 1822 and identical to the heat equation.
Diffusion Monte Carlo
Diffusion Monte Carlo (DMC), also known as diffusion quantum Monte Carlo, is a stochastic quantum Monte Carlo method that projects a trial wave function onto the exact ground state.
Diffusion MRI
Diffusion MRI (dMRI), also known as diffusion-weighted MRI, is an MRI technique that measures water diffusion to reveal tissue microstructure, used for stroke diagnosis and white matter tractography.
Diffusion of innovations
Diffusion of innovations is a theory, formulated by Everett Rogers in 1962, explaining how new ideas, practices, and products spread through a social system, with adopters grouped into five categories.
Diffusion process (Markov process)
A diffusion process is a continuous-time Markov process with continuous sample paths, described locally by drift and diffusion coefficients; Brownian motion is the canonical example.
Diffusion pump
A diffusion pump is a high-vacuum pump with no moving parts that uses a high-speed jet of oil or mercury vapor to sweep gas molecules toward the exhaust.
Diffusion-limited aggregation
Diffusion-limited aggregation (DLA) is a computational growth model, introduced by Witten and Sander in 1981, in which randomly walking particles stick to a growing cluster, forming fractal aggregates.
Diffusion-ordered spectroscopy
Diffusion-ordered spectroscopy (DOSY), also called diffusion NMR, is an NMR method that separates the overlapping signals of molecules in a mixture by their diffusion coefficients.
Diffusiophoresis
Diffusiophoresis is the spontaneous migration of colloidal particles along or against a solute concentration gradient, driven not by external forces but by solute–surface interactions, first described by Derjaguin in 1947.
Diffusive gradients in thin films
Diffusive gradients in thin films (DGT) is an in-situ passive sampling technique, reported by Davison and Zhang in 1994, that measures labile solutes such as trace metals in waters, soils, and sediments.
Diffusive shock acceleration
Diffusive shock acceleration, also called first-order Fermi acceleration, is the process by which charged particles repeatedly cross shock waves, gaining energy until they form cosmic rays.
Difluoroalkylation
Difluoroalkylation is a set of organic synthesis methods for attaching a difluoroalkyl group, most often difluoromethyl (CF₂H), onto an organic molecule, valued in drug discovery.
Difluorocarbene chemistry
Difluorocarbene chemistry is the branch of organofluorine chemistry using the difluorocarbene (:CF2) reagent, first reported by Doering in 1954, to install CF2 and CF2H groups into organic molecules.
Difluorocarbene reagents for difluoromethylation
Difluorocarbene reagents for difluoromethylation are precursors that release difluorocarbene (:CF2) to install the difluoromethyl (CF2H) group on O, N, S, P, Se, or carbon nucleophiles.
Difluoromethylation
Difluoromethylation is the chemical introduction of a difluoromethyl group (–CF₂H) into an organic molecule, a group valued in medicinal chemistry as a hydrogen bond donor.
Digallyne
Digallyne is the doubly reduced gallium(I) dimer anion [R–GaGa–R]²⁻, trans-bent and originally described with a gallium–gallium triple bond, though later studies find it closer to a single bond.
Digamma function
The digamma function, written ψ(z) and also called the psi function, is the logarithmic derivative of the gamma function, first of the polygamma functions, with ψ(n+1) = Hn − γ.
Digby Johns McLaren
Digby Johns McLaren (1919–2004) was a Canadian geologist and paleontologist who was among the first to argue that a meteorite impact caused a mass extinction.
Digenite
Digenite is a copper sulfide mineral with formula Cu₉S₅ (Cu₁.₈S), an opaque blue to black ore mineral in primary and secondary copper deposits, named in 1844 and found at Sangerhausen, Germany, and Butte, Montana.
Digit (unit)
The digit is an ancient unit of length equal to a finger's breadth, the smallest subdivision of the cubit, palm, and foot in Egypt, Greece, and Rome.
Digital audio
Digital audio, also called digital sound, represents sound as a sequence of numbers, with quality fixed by sampling rate and bit depth, as in CD audio.
Digital camera
A digital camera, also known as a digicam or digital still camera, captures photographs electronically with an image sensor instead of film; the first was built by Steven Sasson at Kodak in 1975.
Digital clock
A digital clock is a clock that displays the time as numerals rather than by hands on a dial, whether driven by quartz, mains power, or a flip mechanism.
Digital elevation model
A digital elevation model (DEM) is a digital representation of the Earth's bare-ground topographic surface, excluding trees and buildings, used in flood modeling, road design, and topographic mapping.
Digital holographic microscopy
Digital holographic microscopy (DHM) is a label-free optical technique that numerically reconstructs holograms of microscopic samples into quantitative phase and amplitude images, notably of living cells.
Digital holography
Digital holography is an imaging technique in which a hologram is recorded on a digital sensor and reconstructed numerically, recovering both intensity and phase of the wavefield.
Digital photogrammetry
Digital photogrammetry is a measurement technique that derives 3D coordinates and surface models from overlapping digital photographs, producing point clouds, elevation models, and orthomosaics for mapping and engineering.