All articles starting with R
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Reforms of Urukagina
The Reforms of Urukagina, also called the Edicts of Urukagina, are royal decrees issued by Urukagina, king of the Sumerian city-state of Lagash, in the mid-24th century BCE.
Reformulated gasoline blendstock
Reformulated gasoline blendstock, or RBOB, is a low-volatility, low-octane petroleum blendstock shipped to fuel terminals, where ethanol is blended in to produce reformulated gasoline under the Clean Air Act.
Refracting telescope
A refracting telescope, or refractor, is an optical telescope that collects and focuses light with a front objective lens. It was the first type of telescope, made from 1608.
Refraction
Refraction is the change in direction of a wave, including light, sound, and water waves, when it crosses a boundary into a medium where its speed differs, following Snell's law.
Refraction of light in water
Refraction of light in water is the bending of light rays crossing the air–water interface, making a straight oar look bent and a pool bottom look closer.
Refractive error
A refractive error is a common eye condition where the eye's shape or length keeps light from focusing on the retina, causing blurred vision that eyeglasses correct.
Refractive index
The refractive index (symbol n), also called index of refraction, is the ratio of light's speed in vacuum to its speed in a material, determining how much light bends.
Refractive index detection
Refractive index detection (RID) is a liquid-chromatography detection method comparing the refractive index of column effluent with the mobile phase, used mainly for carbohydrates and polymers.
Refractive surgery
Refractive surgery, also called keratorefractive or corneal refractive surgery when corneal, is elective eye surgery reducing dependence on glasses or contacts. Includes LASIK, PRK, LASEK, SMILE, phakic IOLs, and refractive lens exchange; corrects myopia, hyperopia, and astigmatism but not presbyopia.
Refractometer
A refractometer is an optical instrument that measures refractive index, most often via the critical angle, doubling as a concentration meter for sugar solutions, urine, and gems.
Refractometry
Refractometry is an optical measurement technique that determines the refractive index of liquids, solids, or gases, used in chemistry, pharmacy, and food industries to assess purity and concentration.
Refractory
A refractory, or refractory material, is a non-metallic ceramic that withstands 1,000 °F or above, lining furnaces, kilns, and boilers, with about 70% of production used in steelmaking.
Refractory anemia
Refractory anemia is anemia unresponsive to hematinics such as iron, vitamin B12, or folate, a term coined in 1938 and now classified as myelodysplastic syndrome with low blasts.
Refractory anemia with excess blasts in transformation
Refractory anemia with excess blasts in transformation (RAEB-T), a historical FAB 1982 MDS subtype with 20-29% marrow blasts, >5% blood blasts, or Auer rods; eliminated by WHO 2001, now AML or MDS-IB2/MDS/AML.
Refractory anemia with ring sideroblasts
Refractory anemia with ring sideroblasts (RARS), now MDS-RS-SLD or MDS-SF3B1, is an acquired clonal sideroblastic anemia within MDS. SF3B1 mutations in ~80% of cases; median age 71; low AML risk; treated with ESAs, luspatercept, and iron chelation.
Refractory angina
Refractory angina is chronic angina lasting at least 3 months that cannot be controlled by medication, angioplasty, or coronary bypass surgery, affecting about 5–10% of patients with stable coronary artery disease.
Refractory celiac disease
Refractory celiac disease (RCD), types I and II, persistent malabsorption and villous atrophy despite a strict gluten-free diet; type II has aberrant clonal IELs, high EATL risk, 44% 5-year survival.
Refractory cytopenia of childhood
Refractory cytopenia of childhood (RCC), ICD-11 2A38, the most common childhood myelodysplastic neoplasm: persistent cytopenia, under 5% marrow and 2% blood blasts, often hypocellular marrow, monosomy 7 in 8–48%.
Refractory dissolved organic carbon
Refractory dissolved organic carbon, or rDOC, is the ocean's dissolved organic carbon that resists microbial degradation, persisting for millennia and totaling about 640 Pg C.
Refractory high-entropy alloys
A refractory high-entropy alloy (RHEA) is a high-entropy alloy of refractory metals such as niobium, tantalum, molybdenum, and tungsten, typically containing at least five elements, first designed in 2010.
Refractory hypertension
Refractory hypertension, or refractory hypertensive state, is blood pressure that remains uncontrolled despite five or more antihypertensive medications at maximal doses, a severe subgroup of resistant hypertension.
Refractory metals
Refractory metals, usually niobium, tantalum, molybdenum, tungsten, and rhenium, are metals with melting points above 2,000 °C and resistance to softening at high temperatures, though they oxidize poorly; tungsten melts at 3,422 °C.
Refractory period (physiology)
Refractory period (physiology): post-action-potential interval in neurons and muscle, with absolute phase (Na+ channel inactivation, no second spike) and relative phase (elevated K+ conductance, stronger stimulus needed); limits firing rate and ensures unidirectional conduction.
Refractory period (sex)
Sexual refractory period (post-ejaculation refractory time, PERT): the phase after male orgasm and ejaculation when erection and further ejaculation are inhibited, lasting minutes to days and lengthening with age; absent or controversial in females, with serotonin-related mechanisms proposed.
Refractory thrombocytopenia
Refractory thrombocytopenia (RT), ICD-11 2A32, a rare myelodysplastic syndrome subtype with isolated low platelets and ≥10% dysplastic megakaryocytes; formerly WHO 2008 RCUD, now MDS-SLD, distinguished from ITP.
Refrain
Refrain: a repeated line, phrase, or musical passage recurring at set points in poems and songs; from Old French refrain; distinct from a chorus and central to rondeau, rondo, and verse-chorus forms.
Reframe-IT+U trial
Reframe-IT+U trial (NCT07001202): a quasi-experimental pilot of a six-session blended CBT intervention for suicidal ideation in Chilean university students, adapted from Reframe-IT+ (schools) and Reframe-IT (Australia), assessing acceptability and feasibility.
Refresh rate
Refresh rate, also called vertical refresh rate or vertical scan rate, is the frequency in hertz at which a display redraws the entire screen image, typically about 60 times per second.
Refried beans
Refried beans, Spanish frijoles refritos ("well-fried beans"), are cooked pinto or black beans mashed and fried in lard or oil into a firm paste; a Mexican staple whose "refried" name is a mistranslation.
Refrigerant
A refrigerant, sometimes called refrigerant gas, is the working fluid in refrigeration, air-conditioning, and heat pump systems, absorbing heat by evaporation and rejecting it by condensation; HFCs are being phased down for their climate impact.