All articles starting with U
6,146 articles
Ultrafast ferroelectric switching
Ultrafast ferroelectric switching is the reversal of a ferroelectric material's electric polarization on picosecond or faster timescales, driven by intense terahertz or ultrashort optical pulses instead of slow electrical fields.
Ultrafast high-temperature sintering
Ultrafast high-temperature sintering (UHS) is a pressureless ceramic processing technique introduced in 2020 at the University of Maryland, which sinters ceramics in seconds at temperatures up to about 3000 °C.
Ultrafast laser
An ultrafast laser is a laser that emits pulses lasting picoseconds to femtoseconds, typically produced by mode locking, and used in eye surgery, micromachining, spectroscopy, and frequency metrology.
Ultrafast laser spectroscopy
Ultrafast laser spectroscopy uses femtosecond laser pulses to observe molecular vibrations and chemical bond breaking, a field established by Ahmed H. Zewail, who won the 1999 Nobel Prize in Chemistry.
Ultrafast laser-driven magnetization reversal via inverse Faraday effect
Ultrafast laser-driven magnetization reversal via the inverse Faraday effect (IFE) reverses a material's magnetization with circularly polarized femtosecond laser pulses, enabling all-optical magnetic bit writing.
Ultrafast Lorentz microscopy
Ultrafast Lorentz microscopy is a time-resolved form of Lorentz transmission electron microscopy that uses a pulsed electron beam, synchronized with a pump pulse, to image nanoscale magnetic textures.
Ultrafast magnetism
Ultrafast magnetism, also called femtomagnetism, is the field of physics studying magnetization dynamics on femtosecond and picosecond timescales, pioneered by a 1996 laser experiment on nickel.
Ultrafast MRI
Ultrafast MRI is a magnetic resonance imaging technique that acquires images in tens of milliseconds to a few minutes, enabling sedation-free pediatric scans and stroke triage.
Ultrafast scanning transmission electron microscopy
Ultrafast scanning transmission electron microscopy (USTEM), also called ultrafast 4D STEM, is a pump-probe technique that films nanoscale dynamics with femtosecond time and nanometer spatial resolution.
Ultrafast ultrasound imaging
Ultrafast ultrasound imaging is an ultrasound method that forms each frame with one unfocused transmission instead of line-by-line scanning, reaching 1,000 to 20,000 frames per second and enabling shear wave tracking and functional brain imaging.
Ultrafast X-ray diffraction
Ultrafast X-ray diffraction is a pump–probe technique that uses short X-ray pulses to record diffraction patterns at set delays after a sample is excited, capturing femtosecond-scale structural changes.
Ultrafast X-ray imaging
Ultrafast X-ray imaging is the use of intense synchrotron X-ray beams, at frame rates of tens of kilohertz, to observe melt pool dynamics and defect formation in laser-based metal additive manufacturing.
Ultrafast X-ray magnetic imaging
Ultrafast X-ray magnetic imaging is a set of techniques recording nanoscale maps of magnetization on femtosecond-to-picosecond timescales, using short X-ray pulses from synchrotrons and free-electron lasers.
UltraFeedback
UltraFeedback is a large-scale preference dataset for language-model alignment, released in October 2023, in which GPT-4 scored answers to about 64,000 prompts for training reward models and DPO.
Ultrafilter
An ultrafilter is a maximal filter on a set: for every subset, exactly one of it and its complement belongs. It connects logic through ultraproducts and topology through compactification.
Ultrafiltration
Ultrafiltration (UF) is a pressure-driven membrane separation process with pores of 0.001 to 0.1 µm that retains macromolecules and colloids while water and small solutes pass through.
Ultrafine-grained materials
Ultrafine-grained materials are metals and alloys with grains below about 1 micrometer, giving high strength at room temperature and superplasticity when heated; they are made mainly by severe plastic deformation.
Ultraflight Lazair
The Ultraflight Lazair, or Lazair, is a Canadian single-seat, twin-engine ultralight aircraft designed by Dale Kramer in 1978. Sold in kit form from 1979, over 1,200 were built.
Ultrahigh vacuum
Ultrahigh vacuum (UHV) is the vacuum regime below 1 × 10⁻⁶ Pa per ISO 3529-1, requiring metal seals, bake-out, and ionization gauges, used for surface science.
Ultrahigh-Q silicon nitride microresonators
Ultrahigh-Q silicon nitride microresonators are photonic-chip optical resonators in silicon nitride with quality factors in the hundreds of millions, enabling chip-scale frequency combs, narrow-linewidth lasers, and microwave photonics.
Ultraism
Ultraism (Spanish: ultraísmo) was a Spanish vanguardist poetic movement of the late 1910s and early 1920s that reduced poetry to the pure image and autonomous metaphor.
Ultrakill
Ultrakill (ULTRAKILL) is a fast-paced retro-style FPS by Arsi "Hakita" Patala and New Blood Interactive, in Steam early access since September 3, 2020. A Dante's Inferno-inspired movement shooter with blood-fueled healing, style ranks up to ULTRAKILL, and 97% positive Steam reviews.
Ultraleap
Ultraleap, formerly Ultrahaptics, is a British company founded by Tom Carter in 2013 as a University of Bristol spin-out, making mid-air haptics and hand tracking.
Ultraliberalism
Ultraliberalism (ultraliberal) is a pejorative political label for an extreme form of liberalism; American usage marks the far left, French usage (ultralibéralisme) marks radical laissez-faire economics, as applied to Javier Milei.
Ultralife Corporation
Ultralife Corporation (NASDAQ: ULBI) is an American manufacturer of lithium primary batteries, rechargeable battery packs, charging systems, and communications equipment, headquartered in Newark, New York and founded in 1990.
Ultralight aircraft engines
Ultralight aircraft engines are lightweight, usually non-certified piston engines that power ultralights, traditionally two-strokes like the Rotax 503 and 582, now shifting toward four-strokes such as the Rotax 912.
Ultralight aviation
Ultralight aviation, known as microlight aviation in Britain and ULM in France, is sport aviation using very light aircraft flown under far lighter rules than certificated aircraft.
Ultralight dark matter
Ultralight dark matter, also called fuzzy or scalar field dark matter, is a class of models where dark matter is bosons so light they behave as coherent waves.
Ultralight mechanical metamaterials
Ultralight mechanical metamaterials are architected materials whose extremely low density, high stiffness, and energy absorption come from engineered periodic lattices rather than chemical composition, exemplified by HRL's 2011 metallic microlattice.
Ultralight metallic microlattice
An ultralight metallic microlattice is a cellular material of hollow metal tubes, developed at HRL Laboratories and reported in 2011, with densities as low as 0.9 mg/cm³.