A → water, → molecule with an additional hydrogen ion (H3O+). Also called hydronium ion. Hydronium is an abundant molecular ion in the interstellar diffuse and dense molecular clouds (→ Sagittarius B2, → Orion molecular cloud OMC-1) as well as the plasma tails of → comets (→ Halley, → Hale-Bopp).
From hydr-, → hydro- + -onium a suffix used in the names of complex cations, extrcated from ammonium "ionized ammonia" (NH4+).
A term denoting the water portion of the Earth's surface.
Of or pertaining to → hydrostatics.
Fr.: équation hydrostatique
The equation describing the → hydrostatic equilibrium in a star, expressed as: dP/dr = -GMρ/r2, where P and M are the mass and pressure of a spherical shell with thickness dr at some distance r around the center of the star, ρ is the density of the gas, and G the → gravitational constant.
Fr.: équilibre hydrostatique
1) The physical situation reached in a fluid when complete balance exists between
the internal pressure at any point and the weight of the material above the point.
Fr.: halo hydrostatique
A model of the → Milky Way galaxy in which the → Galactic halo (composed of → gas, → magnetic fields, and → cosmic rays) is assumed to be in → hydrostatic equilibrium. Parker (1966) presented the first study of stability considerations between gas, magnetic fields and cosmic rays in an equilibrium configuration. He found that it is difficult to maintain a stable configuration due to magnetohydrodynamic self-attraction (→ Parker instability). Subsequent works taking into account turbulent motions showed that turbulent pressure can mitigate the influence of Parker instabilities. This enabled new attempts to find conditions under which a stable equilibrium configuration of the Galaxy could exist.
Fr.: pression hydrodynamique
The term ρgz in the → Bernoulli equation. It is not pressure in a real sense, because its value depends on the reference level selected.
A branch of physics that deals with the characteristics of → fluids at rest and especially with the pressure in a fluid or exerted by a fluid on an immersed body.
Geology: Relating to or caused by high temperature underground water or gas heated by natural processes.
A diatomic ion containing one oxygen and one hydrogen atom with chemical formula OH-.
hydroxyl group (OH)
goruh-e hidroksil (#)
Fr.: groupe hydroxyle
The univalent radical or group consisting of one hydrogen and one oxygen atom, forming a part of a molecule of a compound.
From → hydro- + ox(y)- a combining form meaning "sharp, acute, pointed, acid," used in the formation of compound words, from Gk, oxys "sharp, keen, acid" + -yl a suffix used in the names of chemical radicals, from Fr. -yle, from Gk. hyle "matter, substance;" → group.
Fr.: Hydre mâle
The Male Water Snake. A minor constellation with three main stars, one of the 15 → circumpolar constellations in the southern hemisphere. It first appeared in Johann Bayer's Uranometria of 1603. It is often confused with → Hydra, the large constellation further north. It is also referred to as "male Hydra" or "little Hydra." Abbreviation: Hyi; genitive: Hydri.
From L., from Gk. hydros "water serpent."
Âbmâr "water snake," from âb "water" (Mid.Pers. âb "water;" O. Pers. ap- "water;" Av. ap- "water;" cf. Skt. áp- "water;" Hitt. happa- "water;" PIE āp-, ab- "water, river;" cf. Gk. Apidanos, proper noun, a river in Thessalia; L. amnis "stream, river" (from *abnis); O.Ir. ab "river," O.Prus. ape "stream," Lith. upé "stream;" Latv. upe "brook") + mâr "snake, serpent" (Mid.Pers. mâr "snake;" Av. mairya- "snake, serpent").
Hygro-, from Gk, combining form of hygros "wet, moist."
Nam "humidity, moisture" + -negâšt, → -gram. The first component nam, from Mid.Pers. nam, namb "moisture;" Av. napta- "moist," nabās-câ- "cloud," nabah- "sky;" cf. Skt. nábhas- "moisture, cloud, mist;" Gk. nephos "cloud, mass of clouds," nephele "cloud;" L. nebula "mist," nimbus "rainstorm, rain cloud;" O.H.G. nebul; Ger. Nebel "fog;" O.E. nifol "dark;" from PIE *nebh- "cloud, vapor, fog, moist, sky."
The graphical record made by a → hygrograph.
An instrument that records the hygrometer's measure of water vapor.
An instrument that measures the relative humidity of the air.
A member of a class of equations of state used in some models concerned with the evolution of a hypothetical supermassive star. The supermassive star is assumed to consist of a → convective core, which obeys a → polytropic law, and an envelope, which contains most of the whole mass, and follows the hylotropic → equation of state. This equation is expressed by P = A ρ4/3Mα, where A is a constant, ρ the density, M the mass, and α an index. First introduced by Mitchell C. Begelman (2010, MNRAS 402, 673).
Physical chemistry: Describing a substance that is capable of undergoing a change in phase (as from a liquid to a gas), with no change in chemical composition. If the substance is hylotropic over a limited range of pressure and temperatures, it is a pure chemical substance. If it is hylotropic over all pressure and temperatures except the most extreme ones, it is a → chemical element. See also → hylotrope.
First suggested by Wilhelm Ostwald (1904, in Annalen der Naturphilosophie 3, 355), from Gk. hylo-, combining form of hyle "matter; wood," because of the dependence on the composition, + → -tropic.
Physical chemistry: The fact or condition of being → hylotropic.
1) abar- (#); 2) hiper- (#)
From Gk. hyper, preposition and adverb, "over, beyond, overmuch, above;" cognate with L. super- and Pers. abar-, as below.
1) Mid.Pers. abar; O.Pers.
upariy "above; over, upon, according to;" Av. upairi "above, over,"
upairi.zəma- "located above the earth;" cf. Gk. hyper- "over, above;"
L. super-; O.H.G. ubir "over;" PIE base *uper "over."