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Flamsteed designation
The Flamsteed designation, also called a Flamsteed number, is a star identifier combining a number with the Latin genitive of its constellation, such as 61 Cygni or 58 Orionis.
Flange focal distance
Flange focal distance, also called flange-to-film distance or registration distance, is the distance along the optical axis from a lens mount's flange to the film or sensor plane.
Flanging
Flanging is an audio effect produced by mixing a signal with a continuously varied delayed copy of itself, creating a sweeping comb filter heard as a jet-like whoosh.
Flare emission modeling in blazars and gamma-ray bursts
Flare emission modeling quantitatively describes sudden radiation increases from relativistic jets in blazars and gamma-ray bursts, testing whether electrons or protons produce the observed gamma rays.
Flare star
A flare star, or UV Ceti star, is a variable star, typically a red dwarf, that shows sudden, short-lived increases in brightness powered by magnetic energy.
Flash chromatography
Flash chromatography is a preparative column technique that purifies organic compounds by forcing solvent through fine silica gel under positive pressure instead of gravity flow.
Flash flood
A flash flood is a flood of short duration and high peak discharge that rises rapidly, usually within six hours of intense rainfall or a dam failure.
Flash flood warning
A flash flood warning is an official alert that flash flooding is in progress, imminent, or highly likely, issued in the United States by the National Weather Service.
Flash freezing
Flash freezing, also called shock freezing, rapidly freezes food so only small ice crystals form, preserving texture and flavor; Clarence Birdseye launched the industry in the 1920s.
Flash photolysis
Flash photolysis, also known as transient absorption spectroscopy, uses a short light pulse to trigger and monitor photochemical reactions, earning Norrish and Porter the 1967 Nobel Prize.
Flash pyrolysis
Flash pyrolysis is an analytical technique that heats microgram-scale samples at about 10,000 K/s in an inert atmosphere, identifying polymers, microplastics, and biomass by GC/MS.
Flash vacuum pyrolysis
Flash vacuum pyrolysis, also called flash vacuum thermolysis, is a technique that vaporizes a compound under high vacuum through a hot tube to generate reactive intermediates.
FlashCam
FlashCam is a fully digital Cherenkov camera for the medium-sized telescopes of the Cherenkov Telescope Array Observatory, assigned to its southern array site alongside NectarCAM.
Flashover
Flashover is the transition in a compartment fire where exposed surfaces ignite almost simultaneously and fire spreads rapidly, or, in electrical engineering, a conductive arc across an insulator surface or gas gap below bulk breakdown voltage.
Flat band
A flat band is an electronic energy band with little or no dispersion in momentum space, suppressing kinetic energy and enabling strongly correlated phases like superconductivity.
Flat dimension
Flat dimension, also called weak dimension, is a homological invariant of a module over a ring, the length of the shortest resolution of the module by flat modules.
Flat Earth
Flat Earth, also known as the flat Earth theory, is the disproven belief that Earth is a plane rather than a sphere about 12,742 km across.
Flat module
A flat module is one whose tensoring preserves exactness of sequences; Serre introduced flatness in his 1956 GAGA paper, and Grothendieck recognized its geometric significance.
Flat morphism
A flat morphism is a morphism of schemes whose local ring maps make every local ring of the source a flat module over the target.
Flat-band ferromagnetism
Flat-band ferromagnetism is a rigorously proven form of itinerant ferromagnetism in the Hubbard model on lattices with a completely flat lowest energy band, seen in Mielke, Lieb, and Tasaki models.
Flat-band superconductivity
Flat-band superconductivity is superconductivity arising in dispersionless electronic bands where quenched kinetic energy lets even weak interactions dominate, with transition temperatures scaling linearly with interaction strength rather than exponentially.
Flat-panel detector
A flat-panel detector is a large-area digital X-ray imaging device built on an active-matrix thin-film transistor array, introduced commercially in the late 1990s and now central to radiography, fluoroscopy, and mammography.
Flat-slab subduction
Flat-slab subduction is a style of subduction in which an oceanic plate flattens at about 100 km depth and runs nearly horizontally beneath the overriding plate.
Flat-spectrum radio quasar
A flat-spectrum radio quasar (FSRQ) is a blazar whose relativistic jet points near our line of sight, distinguished from BL Lac objects by strong, broad emission lines.
Flavin photocatalysis
Flavin photocatalysis is the use of flavin molecules such as vitamin B2 (riboflavin) as inexpensive, metal-free photocatalysts that absorb visible light to drive redox transformations in organic synthesis.
Flavone
Flavone, also known as 2-phenylchromone, is the simplest member of the flavone class, a plant polyketide natural product with formula C15H10O2, occurring in Primula exudates and tea.
Flavonol
Flavonol is a flavonoid compound: in chemistry, the specific molecule 3-hydroxyflavone, and in nutrition, a subclass including quercetin, kaempferol, myricetin, and isorhamnetin, abundant in onions, kale, and tea.
Flavor-changing neutral current
A flavor-changing neutral current is a rare particle interaction in which a quark changes flavor through a neutral boson, forbidden at tree level in the Standard Model.
Flavour (particle physics)
In particle physics, flavor is the label that distinguishes similar elementary particles, grouping six quarks and six leptons into three generations of the Standard Model.
Flavour quantum numbers
Flavour quantum numbers are integer labels that distinguish quarks and leptons of the same charge and color, conserved by strong interactions but violated by weak ones.