All articles starting with S
44,216 articles
Spherical cow
The spherical cow, or spherical cow in a vacuum, is a humorous metaphor from a physics joke for the highly simplified models scientists build from complex real-world problems.
Spherical Earth
Spherical Earth, also called the sphericity of the Earth, is the model of Earth's figure as a sphere, argued from antiquity and refined into an oblate spheroid.
Spherical harmonics
Spherical harmonics, also written Ylm, are eigenfunctions of the Laplace-Beltrami operator on the sphere, introduced by Laplace in 1782 as a spherical analog of Fourier series.
Spherical measure
Spherical measure is a mathematical term for either the surface measure on the unit sphere, used for spherical averages, or a ball-covering outer measure close to Hausdorff measure.
Spherical mirror
A spherical mirror is a mirror whose reflecting surface forms part of a sphere, either concave or convex, used in geometric optics to form images of objects.
Spherical model
The spherical model is an exactly solvable model of a ferromagnet in statistical mechanics, introduced by Berlin and Kac in 1952 as a continuous-spin generalization of the Ising model.
Spherical multipole moments
Spherical multipole moments are the coefficients of the expansion of a potential, such as an electric or magnetic field, in powers of distance and spherical harmonics.
Spherical nucleic acid
Spherical nucleic acid (SNA) nanoparticles are nanostructures with a nanoparticle core surrounded by a dense shell of radially oriented DNA or RNA strands, first synthesized in 1996.
Spherical robot (manipulator)
A spherical robot, also called a polar robot, is an industrial manipulator with two rotary joints and one linear joint, used for welding and die casting.
Spherical tokamak
The spherical tokamak, also known as the spherical torus, is a compact fusion device with a cored-apple plasma shape that operates at unusually high plasma pressure.
Spherical Tokamak for Energy Production
Spherical Tokamak for Energy Production (STEP) is a UK Atomic Energy Authority program to build a prototype fusion power plant at West Burton, Nottinghamshire, by the 2040s.
Spherical trigonometry
Spherical trigonometry, or spherical trig, is the branch of trigonometry that deals with triangles drawn on a sphere, the basis of great-circle and celestial navigation.
Spherical wave
A spherical wave is a wave whose surfaces of constant phase are concentric spheres expanding from a point source, its amplitude decaying as 1/r, following the inverse-square law.
Spherical wrist
A spherical wrist is a robot wrist mechanism whose three revolute joint axes intersect at a single point, the wrist center, as in the Stanford manipulator.
Sphero (toy)
Sphero is a smartphone-controlled spherical robot toy first launched in 2011 by Orbotix, a Boulder, Colorado company that later took the Sphero name and expanded into educational robotics.
Spherocytosis
Hereditary spherocytosis (Minkowski-Chauffard disease), congenital spherocytic hemolytic anemia: inherited red cell membrane protein defects (ANK1, spectrin, band 3) causing spherical fragile red cells, anemia, jaundice, splenomegaly; treated by splenectomy.
Spheroid
A spheroid, also called an ellipsoid of revolution, is a quadric surface made by rotating an ellipse, giving oblate or prolate shapes like Earth or a rugby ball.
Spheroid body myopathy
Spheroid body myopathy, a rare autosomal dominant myofibrillar myopathy (OMIM 609200, ORPHA 268129) caused by MYOT myotilin mutations, marked by proximal weakness and spheroid body inclusions on muscle biopsy.
Spheroidal carbonaceous particles
Spheroidal carbonaceous particles are carbon-rich fly-ash particles produced only by industrial coal and oil combustion, which accumulate in sediments as unambiguous markers of fossil-fuel pollution.
Spheroidal wave functions
Spheroidal wave functions are the special functions that arise when the wave equation is separated in spheroidal coordinates, reducing to Legendre functions when the spheroidal parameter vanishes.
Spheromak
A spheromak is a compact toroid of magnetized plasma that holds both poloidal and toroidal magnetic fields from internal currents, studied for compact magnetic confinement fusion.
Spheroplast
Spheroplasts: bacteria or yeast that have partially lost their cell wall and become round; wall-less Gram-negative forms retaining an outer membrane, used in patch clamp, imaging, transformation, and DNA delivery.
Spherulite
A spherulite is a spherically symmetric aggregate of fibrillar crystals that grow radially from a common nucleation center, formed when polymers and minerals crystallize from viscous melts at large undercooling.
Sphettos
Sphettos (Σφηττός, Sphettus), an inland Athenian deme of tribe Akamantis near modern Koropi in the Mesogaia; one of Theseus's twelve townships, with a theatre of Dionysos and the honorand Kallias of SEG 28.60.
Sphex pensylvanicus
Sphex pensylvanicus, the great black wasp or katydid hunter, is a 22–28 mm solitary digger wasp of North America (except the northwest) that nests in soft soil and provisions brood cells with 2–6 paralyzed katydids per cell.
Sphincter
A sphincter is a ring-shaped muscle that relaxes or tightens to open and close passages in the body, controlling the flow of food, urine, and stool.
Sphincterotomy
Sphincterotomy is an endoscopic procedure that cuts the biliary sphincter with high-frequency current, usually during ERCP, most often to treat gallstones lodged in the common bile duct.
Sphinganine
Sphinganine, also called dihydrosphingosine, is a saturated 18-carbon amino alcohol that is the first long-chain base made in de novo sphingolipid biosynthesis; its ratio to sphingosine is a biomarker of fumonisin mycotoxin exposure.
Sphingidae
Sphingidae, known as hawkmoths or sphinx moths, is a family of about 1,450 moth species found on every continent except Antarctica, whose hornworm caterpillars include major crop pests.
Sphingolipid
Sphingolipids: membrane and signaling lipids built on a sphingoid base backbone such as sphingosine, named by Thudichum in 1884. Key metabolites include ceramide and sphingosine-1-phosphate; dysregulation links to cardiovascular, metabolic, and neurodegenerative disease.