42,772 articles
False positives and false negatives
A false positive is a test result that incorrectly indicates a condition is present, and a false negative one that incorrectly indicates it is absent, measured by sensitivity and specificity.
False vacuum decay
False vacuum decay, also called vacuum decay, is the quantum tunneling of a metastable vacuum to a lower-energy true vacuum, with a theory developed by Sidney Coleman in 1977.
Falsifiability
Falsifiability, Popper's principle of falsification, holds that a theory counts as empirical science only if some conceivable observation could refute it; the US Supreme Court's Daubert standard cites it.
Falsification test
A falsification test is a statistical and econometric validation procedure that reruns a hypothesis test on placebo data where no true effect should exist, checking for spurious results.
Famciclovir
Famciclovir, sold as Famvir, is an oral antiviral prodrug of penciclovir, a nucleoside analog active against herpes simplex and varicella zoster viruses, first approved in the United States in 1994.
Family Portrait (Voyager)
The Family Portrait (Solar System Family Portrait) is a mosaic of 60 images taken by Voyager 1 in 1990, showing six planets and the Pale Blue Dot.
Fan Chung
Fan Chung, also known as Fan Chung Graham, is a Taiwanese-born American mathematician, born in 1949, known for spectral graph theory, quasirandom graphs, and random graph models of networks.
Fanaroff-Riley classification
The Fanaroff-Riley classification, introduced by Fanaroff and Riley in 1974, sorts extended radio galaxies into edge-darkened Class I and edge-brightened Class II sources by where their radio emission is brightest.
Fannes–Audenaert inequality
The Fannes–Audenaert inequality is a sharp upper bound on the difference between the von Neumann entropies of two quantum states in terms of their trace distance, refining Mark Fannes' 1973 inequality.
Fano factor
The Fano factor is a dimensionless measure of fluctuations in a counted quantity, the ratio of variance to mean, named after Ugo Fano's 1947 work on ionization statistics.
Fano plane
The Fano plane, or Fano configuration, is the smallest finite projective plane: 7 points and 7 lines, with 3 points on each line, constructed by Gino Fano in 1892.
Fano resonance
A Fano resonance is an asymmetric peak-and-dip line shape in scattering or absorption spectra, arising when a discrete state interferes with a continuum, described by Ugo Fano in 1935 and 1961.
Fano variety
A Fano variety is a smooth projective algebraic variety whose anticanonical divisor is ample, placing it at the positive-curvature end of the classification of algebraic varieties.
Fano's inequality
Fano's inequality is an information theory result lower-bounding the error probability of estimating a random variable X from an observation Y in terms of the conditional entropy.
Far-field superlens
A far-field superlens is a metamaterial-based optical device proposed in 2006 by Xiang Zhang's group that converts evanescent waves into propagating waves for imaging beyond the diffraction limit.
Farad
The farad, symbol F, is the SI derived unit of electrical capacitance, equal to one coulomb of charge per volt, named for the English scientist Michael Faraday.
Faraday cage
A Faraday cage, also called a Faraday shield, is an enclosure of conductive material that blocks external electric fields and electromagnetic waves, used in MRI rooms and aircraft.
Faraday constant
The Faraday constant (F), named for Michael Faraday, is the electric charge of one mole of electrons, about 96,485 C/mol, exact since the 2019 SI redefinition.
Faraday cup
A Faraday cup, also called a Faraday plate, measures charged particle beam intensity by stopping the beam on a metal collector and reading the deposited charge.
Faraday effect
The Faraday effect, or Faraday rotation, is the magnetic rotation of light's polarization, discovered by Michael Faraday in 1845 and used today in optical isolators.
Faraday paradox
The Faraday paradox is the puzzle that a conducting disk spinning in a static magnetic field develops an emf even though the flux through it never changes.
Faraday rotator
A Faraday rotator is a magneto-optical component that rotates the polarization of light non-reciprocally, serving as the key element in optical isolators and circulators that protect lasers from back reflections in optical networks.
Faraday wave
A Faraday wave is a standing wave forming on a liquid surface when its container is vibrated vertically, first described by Michael Faraday in 1831.
Faraday's law of induction
Faraday's law of induction is the physical law that a changing magnetic flux through a circuit induces an electromotive force, discovered by Michael Faraday in London in 1831.
Faraday's laws of electrolysis
Faraday's laws of electrolysis are two quantitative rules announced by Michael Faraday in 1834: the mass deposited at an electrode is proportional to the charge passed.
Farey sequence
The Farey sequence, or Farey series, is the ordered list of all reduced fractions between 0 and 1 with denominator at most n, a basic object of number theory.
Fariba Fahroo
Fariba Fahroo is an American applied mathematician who co-founded pseudospectral optimal control theory with I. Michael Ross and managed research programs at AFOSR and DARPA.
Farideh Firoozbakht
Farideh Firoozbakht (1962–2019) was an Iranian mathematician at the University of Isfahan known for Firoozbakht's conjecture, a 1982 unproven claim about the distribution of prime numbers.
Farmers' Almanac
The Farmers' Almanac is an American annual, first printed in 1818 in Morristown, New Jersey, known for long-range weather forecasts and planting calendars keyed to the Moon's phases.
Farnesene
Farnesene is a set of six acyclic sesquiterpene isomers, C₁₅H₂₄ hydrocarbons found in apple skins and aphid alarm signaling, produced commercially by fermentation since 2009.