All articles starting with N
16,460 articles
Natural forest
Natural forest: forest of indigenous trees regenerated naturally, not planted, per FAO/FRA definitions; ranges from primary (undisturbed) forest to used stands; distinct from plantations.
Natural frequency
The natural frequency of a physical system is the frequency at which it oscillates freely, with no driving or damping force; it is also called the eigenfrequency.
Natural gas
Natural gas, also called fossil gas, is a naturally occurring gas mixture found underground, composed mostly of methane and commonly associated with petroleum, burned for electricity, heating, and industry.
Natural Gas Pipeline Company of America
Natural Gas Pipeline Company of America (NGPL), also called Natural, is an interstate natural gas pipeline company carrying gas from Texas to the upper Midwest, centered on Chicago.
Natural gas vehicle
A natural gas vehicle (NGV) is a vehicle that runs on compressed or liquefied natural gas instead of gasoline or diesel, powering some 23 million vehicles worldwide.
Natural gradient
The natural gradient is the steepest ascent direction of a function under the Fisher information metric, computed as the ordinary gradient multiplied by the inverse Fisher matrix.
Natural gradient descent
Natural gradient descent is an optimization method introduced by Shun-ichi Amari in 1998 that rescales the gradient by the inverse Fisher information matrix, following steepest descent on probability distributions.
Natural graphite
Natural graphite is graphite mined from metamorphic rock deposits rather than synthesized from hydrocarbons. It dominates lithium-ion battery anodes, offering low cost, abundance, and high theoretical capacity.
Natural hair movement
The natural hair movement is a cultural movement, mainly among Black women, embracing natural afro-textured hair, with waves in the 1960s to 1970s and from the late 2000s.
Natural hazard
A natural hazard is a naturally occurring process or event, such as an earthquake, flood, or tropical cyclone, that can cause deaths, injuries, property damage, or economic disruption.
Natural heritage
Natural heritage is the portion of the natural environment considered valuable enough to conserve and pass on to future generations, defined by Article 2 of UNESCO's World Heritage Convention.
Natural history
Natural history: the observational study of nature, past and present, by naturalists who observe, collect, and classify organisms and specimens; roots in Aristotle and Renaissance science, basis of ecology, conservation, and natural history museums.
Natural History (Pliny)
Pliny the Elder's Naturalis Historia (Latin Naturalis Historia) is a 37-book, c. 400,000-word Roman encyclopedia completed 77 CE, covering nature, geography, medicine, and art; first printed in Venice in 1469.
Natural history and clinical course of Duchenne muscular dystrophy
The natural history of Duchenne muscular dystrophy runs from symptoms at ages 2 to 3, loss of walking by 8 to 12 untreated, and death in the twenties.
Natural History Museum of Denmark
Natural History Museum of Denmark (Statens Naturhistoriske Museum): Denmark's national natural history museum at the Botanical Garden, Copenhagen; University of Copenhagen institute with 14 million objects; new 32,000 m2 building opens March 6, 2027.
Natural History Museum, London
The Natural History Museum in London is a national museum of life and earth science in South Kensington, holding more than 80 million specimens since opening in 1881.
Natural history study
A natural history study is a preplanned observational study that tracks a disease's course over time without assigning an intervention, informing rare-disease drug development and external controls.
Natural horn
The natural horn is the valveless ancestor of the modern French horn: a coiled brass tube with crooks for key changes, limited to its harmonic series, played chromatically via Hampel's 18th-century hand-stopping technique until valves arrived in 1814.
Natural inflation
Natural inflation is a model of cosmic inflation in which the inflaton is a pseudo Nambu-Goldstone boson with a cosine potential, proposed by Freese, Frieman, and Olinto in 1990.
Natural justice
Natural justice, also called procedural fairness, is the common law doctrine requiring a fair hearing (audi alteram partem) and an unbiased decision-maker (nemo iudex in causa sua) in administrative and quasi-judicial decisions, analogous to American procedural due process.
Natural killer cell
Natural killer (NK) cells are innate cytotoxic lymphocytes of the ILC family that kill virus-infected and tumor cells via missing-self recognition, perforin-granzyme lysis, and ADCC, and show adaptive features like CMV-driven clonal expansion.
Natural kinds
Natural kinds are groupings of things that reflect the structure of the natural world rather than human interests, with chemical elements like H₂O as paradigm examples.
Natural language generation
Natural language generation (NLG), also called language generation, is the area of natural language processing that produces readable text or speech from non-linguistic input like structured records.
Natural language inference
Natural language inference (NLI) is a natural language processing task in which a model decides whether a premise entails, contradicts, or neither implies a hypothesis.
Natural language processing
Natural language processing (NLP) is the field of computing that enables machines to recognize, understand, and generate human text and speech by combining computational linguistics with machine learning.
Natural law
Natural law (lex naturalis): Western ethical and legal tradition holding that moral and legal norms are rooted in human nature and knowable by reason. Key figures include Aquinas and Grotius; opposed to legal positivism; basis of international law theory.
Natural Law Party
Natural Law Party (NLP), US political party founded April 1992 in Fairfield, Iowa, tied to Maharishi Mahesh Yogi's Transcendental Meditation movement; ran John Hagelin for president in 1992, 1996, and 2000, peaked at 48-state ballot access, dissolved in many areas from 2004 but survived in Michigan.
Natural Law Party (United States)
Natural Law Party (US), founded April 1992 in Fairfield, Iowa, linked to Transcendental Meditation; ran quantum physicist John Hagelin for president in 1992, 1996, and 2000; reached 48-state ballot access in 1996; national headquarters closed April 30, 2004.
Natural linewidth
The natural linewidth is the irreducible width of a spectral line, caused by the finite lifetime of the atomic states involved and measured as the full width at half maximum.
Natural logarithm
The natural logarithm, also called the natural log, is the logarithm to the base e, written ln x; it is the inverse of the exponential function.