42,772 articles
Non-linear least squares
Non-linear least squares is a parameter estimation method that fits models nonlinear in their parameters by minimizing squared residuals, typically with the Gauss-Newton or Levenberg-Marquardt algorithm.
Non-local thermodynamic equilibrium
Non-local thermodynamic equilibrium (non-LTE, or NLTE) is the condition of a gas or plasma in which radiative processes, not local collisions, set atomic energy-state populations.
Non-metric multidimensional scaling
Non-metric multidimensional scaling (NMDS) is a statistical technique that represents objects as points in low-dimensional space, preserving only the rank order of observed dissimilarities, not their numerical values.
Non-negative least squares
Non-negative least squares (NNLS) is a constrained regression method fitting a linear least squares model with every coefficient zero or positive, used in deconvolution and unmixing.
Non-negative matrix factorization
Non-negative matrix factorization (NMF) is a family of algorithms approximating a nonnegative matrix as a product of two lower-rank nonnegative matrices, giving additive, parts-based representations of data.
Non-Nernstian pH dependence of ORR/HOR kinetics
Non-Nernstian pH dependence of ORR/HOR kinetics is the deviation of oxygen and hydrogen electrode reaction rates from the pH shift predicted by the Nernst equation.
Non-Newtonian fluid
A non-Newtonian fluid is a fluid whose viscosity changes with shear rate rather than staying constant; ketchup, paint, blood, and cornstarch-water mixtures are common examples.
Non-normal modal logic
A non-normal modal logic is a modal logic weaker than the smallest normal logic K, lacking necessitation or the K axiom, and interpreted over neighborhood (Scott–Montague) models.
Non-oscillatory scheme
A non-oscillatory scheme is a numerical method for hyperbolic partial differential equations that suppresses spurious oscillations near shocks and discontinuities while keeping high-order accuracy in smooth regions.
Non-phenolic aryl alkyl ethers
Non-phenolic aryl alkyl ethers are ethers in which an alkyl group bonds through oxygen to a benzenoid or polycyclic aromatic ring, as in methoxyarenes and naphthyl methyl ethers.
Non-probability sampling
Non-probability sampling is a survey sampling approach in which units are chosen non-randomly, by convenience, judgment, or quotas, making selection probabilities unknown and inference dependent on untestable models.
Non-reciprocal active matter
Non-reciprocal active matter is a branch of active-matter physics studying self-driven entities whose interactions are asymmetric, evading Newton's third law and giving rise to traveling waves, oscillations, and nonreciprocal phase transitions.
Non-reciprocal phase transitions
Non-reciprocal phase transitions are phase transitions in many-body systems whose interactions are asymmetric, so equilibrium theory fails and new time-dependent phases with dynamically restored symmetries appear.
Non-relativistic gravitational fields
Non-relativistic gravitational fields are descriptions of gravity where the speed of light plays no operational role, ranging from the Newtonian limit of general relativity to Newton–Cartan geometry and broader non-relativistic gravity theories.
Non-renewable resource
A non-renewable resource, also called non-renewable energy, is a natural resource, such as coal, petroleum, natural gas, uranium, and metals, that cannot be replaced within a human timescale, so using it depletes the supply.
Non-SI units mentioned in the SI
Non-SI units mentioned in the SI are units like the minute, hour, liter, tonne, and electronvolt that the SI Brochure accepts for use alongside SI units.
Non-standard model
A non-standard model is a mathematical structure satisfying the same first-order axioms as a standard structure like the natural numbers, yet containing extra elements such as infinite integers.
Non-standard model of arithmetic
The non-standard model of arithmetic, or non-standard arithmetic, is a model of Peano Arithmetic not isomorphic to the natural numbers, containing infinite integers, first constructed by Thoralf Skolem in 1934.
Non-stoichiometric compound
A non-stoichiometric compound, also called a berthollide, is a chemical compound whose composition violates the law of definite proportions, caused by crystal defects such as vacancies.
Non-target screening
Non-target screening (NTS) is an analytical chemistry method that uses high-resolution mass spectrometry to detect and tentatively identify unknown chemical contaminants in environmental or biological samples without preselecting which compounds to look for.
Non-targeted analysis
Non-targeted analysis (NTA), also called non-target screening, is an analytical chemistry approach that detects and identifies chemicals in a sample without a predefined target list, typically using chromatography coupled to high-resolution mass spectrometry.
Non-uniform rational B-spline
A non-uniform rational B-spline, or NURBS, is a mathematical representation of curves and surfaces built from control points, weights, and a knot vector, created for computer 3D modeling.
Non-uniform sampling (statistics)
Non-uniform sampling in statistics is a sampling design that selects population units with unequal probabilities, concentrating effort where measured quantities are largest or most variable.
Non-unique factorization
Non-unique factorization is the phenomenon in rings of algebraic integers and factorization monoids where an element has essentially different irreducible factorizations, classically 6 = 2·3 = (1+√−5)(1−√−5) in Z[√−5], measured by invariants like elasticity.
Nonadiabatic coupling
Nonadiabatic coupling is the set of terms in the molecular Schrödinger equation that couple different electronic states, arising from the nuclear kinetic energy operator and driving transitions between adiabatic potential energy surfaces.
Nonadiabatic dynamics simulation
Nonadiabatic dynamics simulation is a computational method in theoretical chemistry that models coupled nuclear-electron motion on excited-state potential energy surfaces, chiefly by trajectory surface hopping.
Nonagon
A nonagon, also called an enneagon or 9-gon, is a polygon with nine sides and nine angles totaling 1260°; the regular form cannot be constructed with compass and straightedge.
Nonanal
Nonanal, also called pelargonaldehyde or nonanaldehyde, is a nine-carbon fatty aldehyde with a rose-orange odor, found in rose and citrus oils and used as a flavoring agent.
Nonane
Nonane, also known as n-nonane, is a straight-chain alkane with the formula C₉H₂₀, a colorless, flammable liquid in the gasoline and kerosene fraction of crude oil.
Noncentrosymmetric superconductivity
Noncentrosymmetric superconductivity is superconductivity in a crystal that lacks inversion symmetry, allowing antisymmetric spin-orbit coupling to mix spin-singlet and spin-triplet pairing, as studied in the heavy-fermion compound CeRh2As2.