All articles starting with F

Fractional Chern insulator

A fractional Chern insulator is a fractionally filled topological band in a crystal whose interactions produce fractional quantized Hall conductance and anyonic excitations without a magnetic field.

Fractional crystallization is a stagewise chemical separation method that crystallizes mixture components in sequence using solid–liquid equilibria, reaching purities above 99% and historically used to separate rare-earth salts.

Fractional differential equation

A fractional differential equation is a differential equation in which the derivative is taken to a non-integer order, making it a tool for modeling systems with memory.

Fractional diffusion equation

A fractional diffusion equation is a partial differential equation that replaces an integer-order derivative with a fractional one to model anomalous diffusion in porous media, finance, biology, and hydrology.

Fractional distillation

Fractional distillation is a separation technique that boils a mixture of miscible liquids and repeatedly condenses and revaporizes the vapors in a fractionating column, enriching the distillate in the lower-boiling component.

Fractional exhaled nitric oxide testing

Fractional exhaled nitric oxide (FeNO) testing is a noninvasive breath test measuring eosinophilic airway inflammation in parts per billion at a standardized flow, used to support asthma diagnosis and guide corticosteroid therapy.

Fractional factorial design

A fractional factorial design is a designed experiment running only a selected fraction of a full factorial's treatment combinations, trading estimable effects for large run savings in industrial screening.

Fractional flow reserve

Fractional flow reserve (FFR) is an invasive coronary physiology index, the distal-to-aortic pressure ratio during maximal hyperemia, with FFR ≤0.80 guiding revascularization of intermediate stenoses; introduced by Pijls and De Bruyne in the early 1990s and validated by DEFER, FAME, and FAME 2 trials.

Fractional Fourier transform

The fractional Fourier transform (FrFT) is a linear integral operator generalizing the Fourier transform, rotating a signal's time-frequency representation through an arbitrary angle, used in signal processing and optics.

Fractional Josephson effect

The fractional Josephson effect is a variant of the ac Josephson effect where the supercurrent is 4π-periodic, oscillating at half the conventional frequency under voltage.

Fractional Laplacian

The fractional Laplacian is a nonlocal pseudo-differential operator, written (-Δ)^(α/2) for 0 < α < 2, that generalizes the Laplacian to fractional powers and appears in models of anomalous diffusion and stable Lévy processes.

Fractional laser treatment

Fractional laser treatment is a dermatologic laser procedure that creates microscopic thermal injury zones in the skin, sparing surrounding tissue, to stimulate collagen remodeling for scars, wrinkles, and pigmentation.

Fractional orbital bombardment system

A fractional orbital bombardment system (FOBS) is an orbital nuclear weapons delivery system developed by the Soviet Union in the 1960s, which deorbits a warhead before completing a full orbit.

Fractional programming

Fractional programming is the branch of optimization that maximizes or minimizes ratios of functions, such as signal-to-noise ratio or energy efficiency, solved with Dinkelbach's transform and the quadratic transform.

Fractional quantum anomalous Hall effect

The fractional quantum anomalous Hall effect is a fractional quantum Hall effect that appears at zero magnetic field in fractional Chern insulators, first observed in twisted MoTe₂ bilayers in 2023.

Fractional quantum anomalous Hall effect in moiré TMDs

The fractional quantum anomalous Hall effect is fractionally quantized Hall conductance at zero magnetic field in a moiré material, first demonstrated in twisted bilayer MoTe2 in 2023.

Fractional quantum Hall effect

The fractional quantum Hall effect (FQHE) quantizes Hall conductance at fractional values in a two-dimensional electron gas under a strong magnetic field, arising from strong electron-electron correlations.

Fractional quantum Hall effect in bilayer graphene

The fractional quantum Hall effect in bilayer graphene produces quantized Hall plateaus at fractional filling factors in two stacked graphene sheets in a strong magnetic field.

Fractional statistics

Fractional statistics is the quantum-mechanical behavior of identical particles in two dimensions whose exchange phase lies strictly between bosons (0) and fermions (π), yielding anyons.

Fractional-order model

A fractional-order model is a mathematical model whose derivatives or integrals appear at non-integer order, describing systems whose response depends on their entire past history.

Fractional-reserve banking

Fractional-reserve banking is the system in which banks hold only a fraction of deposits as reserves and lend the rest, creating most money in circulation.

Fractionalization

Fractionalization is the phenomenon in quantum many-body systems where excitations carry fractions of the constituents' quantum numbers, such as e/3 charges in the fractional quantum Hall effect.

Fractionally spaced equalization

Fractionally spaced equalization is an adaptive equalization technique whose filter taps are spaced at a fraction of the symbol period, sampling faster than the symbol rate.

Fractionally spaced equalizer

A fractionally spaced equalizer is an adaptive equalizer whose filter taps are spaced at a fraction of the symbol period, typically half, rather than a full symbol period.

Fractionated radiotherapy

Fractionated radiotherapy is a cancer treatment in which the total radiation dose is divided into smaller daily doses over weeks, allowing normal cells to repair.

Fractionated stereotactic radiation therapy

Fractionated stereotactic radiation therapy (FSRT) is a radiation oncology technique delivering precisely targeted, image-guided radiation to tumors over multiple sessions, usually intracranial, with a maximum of 12 fractions.

Fractionating column

A fractionating column, also called a distillation column, is a packed or trayed tube between flask and condenser that separates liquids with close boiling points by repeated vaporization-condensation cycles.

Fractographic analysis

Fractographic analysis is the examination of a fracture surface, typically by optical or electron microscopy, to determine how a component broke, identifying the failure mode, crack-initiation site, and often the loads involved.

Fractography

Fractography is the examination of fracture surfaces, by eye, light microscope, or scanning electron microscope, to determine where a crack started, how it grew, and why the component failed.