42,772 articles
Near-infrared spectroscopy
Near-infrared spectroscopy (NIRS) is a vibrational spectroscopy technique measuring absorption of near-infrared light, roughly 780–2500 nm, giving rapid, non-destructive chemical analysis in agriculture, food, pharmaceuticals, and medicine.
Near-ring
A near-ring is an algebraic structure with addition and multiplication in which addition forms a possibly nonabelian group and multiplication distributes over addition from one side only.
Nebula
A nebula, also called a gaseous nebula, is an interstellar cloud of gas and dust where new stars form and dying stars cast off glowing shells of gas.
Nebular continuum
The nebular continuum is smooth light emitted by ionized gas around hot young stars in galaxies, contributing 30–70% of optical and near-infrared emission in vigorously star-forming systems.
Nebular emission
Nebular emission is radiation produced by ionized gas around hot young stars or other ionizing sources, dominated by emission lines like Hα and [O III] that can contribute 20–60% of a young galaxy's broadband light.
Nebular hypothesis
The nebular hypothesis holds that stars and planets form from the gravitational collapse of a rotating cloud of gas and dust; planets accrete from the protoplanetary disk.
Necessary condition analysis
Necessary condition analysis (NCA) is a statistical method that identifies conditions that must be present for an outcome to occur and estimates how strongly each constrains it.
Necessity and sufficiency
Necessity and sufficiency, also called necessary and sufficient conditions, are concepts in logic and mathematics: a sufficient condition guarantees a statement, and a necessary condition must hold for it.
Necking (engineering)
Necking is a plastic instability in which tensile deformation of a ductile specimen localizes into a small region of reduced cross-section, starting at maximum load and ending in fracture.
Necklace (combinatorics)
A necklace in combinatorics is an equivalence class of fixed-length strings over a finite alphabet, where two strings count as the same if one is a cyclic rotation of the other.
Necklace splitting problem
The necklace splitting problem asks how to cut a multicolored necklace so several thieves each get an equal share of every color; Alon proved (k − 1) · t cuts always suffice.
Ned A. Porter
Ned A. Porter is an American organic chemist at Vanderbilt University known for working out how lipids oxidize by free radicals, linking the chemistry to disease.
Nedal Nassar
Nedal T. Nassar is an American mineral economist and criticality scientist who leads the Materials Flow Analysis Section at the U.S. Geological Survey's National Minerals Information Center.
nEDM@PSI
nEDM@PSI is a series of experiments at the Paul Scherrer Institute in Switzerland that search for a permanent electric dipole moment of the neutron using ultracold neutrons.
Nedocromil
Nedocromil is a synthetic cromone drug that stabilizes mast cells and reduces inflammation, developed by Fisons in the 1970s and sold as the asthma inhaler Tilade and eye drops Alocril.
Needham question
The Needham question, also called the Needham Puzzle or Grand Question, is Joseph Needham's problem of why modern science arose in Europe and not in China despite its technical achievements.
Needs assessment
A needs assessment is a systematic process for identifying gaps between a population's current and desired situation, used as a standard first step in program planning and resource allocation.
Néel spin-orbit torque
Néel spin-orbit torque (NSOT) is a current-induced torque that switches the Néel vector of collinear antiferromagnets, predicted by Jakub Železný and colleagues in 2014 and demonstrated in CuMnAs thin films in 2016.
Néel temperature
The Néel temperature, symbol TN, is the critical temperature below which an antiferromagnet develops antiparallel magnetic order; above it the material is paramagnetic, and the name honors Louis Néel.
NEEM (ice core)
NEEM (North Greenland Eemian Ice Drilling) was a Danish-led ice-core drilling project in northwest Greenland that recovered a 2,540 m core from 2008 to 2012.
Nefazodone
Nefazodone, sold as Serzone, is a phenylpiperazine antidepressant first marketed by Bristol-Myers Squibb in 1994 and withdrawn from many markets after sometimes fatal liver injury, though generic tablets remain available in the United States.
Negabinary
Negabinary is a positional numeral system with base −2, using digits 0 and 1, in which every positive and negative integer has a unique sign-free representation.
Negative binomial distribution
The negative binomial distribution, also called the Pascal distribution, is a discrete distribution counting failures before a fixed number of successes, widely used for overdispersed count data.
Negative binomial model
The negative binomial model is a statistical model that uses the negative binomial distribution for count data whose variance exceeds its mean, underlying count regression and RNA-seq differential expression tests.
Negative binomial regression
Negative binomial regression is a regression method for count outcomes whose variance exceeds their mean, derived as a Poisson–gamma mixture and widely used in econometrics and RNA-seq analysis.
Negative capacitance
Negative capacitance is a regime in which a device's effective capacitance is negative, so increasing charge lowers voltage, enabling voltage amplification; proposed by Salahuddin and Datta in 2008 for low-power ferroelectric transistors (NC-FETs).
Negative capacitance in ferroelectrics
Negative capacitance in ferroelectrics is an unstable regime where falling voltage means rising stored charge, stabilized by a series dielectric and proposed in 2008 for transistors switching below the 60 mV/decade limit.
Negative compressibility
Negative compressibility is a mechanical response in which a material expands rather than shrinks under increasing pressure, achieved in metamaterials and used in actuators and sensors.
Negative compressibility metamaterial
A metamaterial with negative compressibility is an architected solid that expands under hydrostatic pressure, the opposite of ordinary materials, through designed internal structure rather than composition.
Negative control
A negative control is a test condition in which a null result is expected, so any signal that appears must come from factors other than the effect under study.