An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

A → chemical reaction on solid surfaces in which one atom or molecule is → adsorbed on the catalyst surface, and another reacts directly from the gas phase. This type of mechanism may occur preferentially on very small → dust grains, where transient heating events prevent weakly bound species from remaining and in larger grains at high temperatures. Compare with the → Langmuir-Hinshelwood mechanism.

Proposed in 1938 by D. D. Eley (1914-2015), a British chemist and Professor of Physical Chemistry and E. K. Rideal (1890-1974), an English physical chemist.

Of or pertaining to Euclid, or his postulates. → Euclidean division, → Euclidean geometry, → Euclidean space, → non-Euclidean geometry.

After the Gk. geometrician and educator at Alexandria, around 300 B.C., who applied the deductive principles of logic to geometry, thereby deriving statements from clearly defined axioms.

In arithmetic, the conventional process of division of two → integers. For a → real number a divided by b > 0, there exists a unique integer q and a real number r, 0 ≤ r <b, such that a = qb + r.

→ Euclidean; → division.

The geometry based on the postulates or descriptions of Euclid. One of the critical assumptions of the Euclidean geometry is given in his fifth postulate: through a point not on a line, one and only one line be drawn parallel to the given line. See also → non-Euclidean geometry.

→ Euclidean; → geometry.

A space in which the → distance between any two points is given by the → Pythagorean theorem: d² = (Δx)² + (Δy)² + (Δz)², where d is distance and Δx, Δy, and Δz are differential → Cartesian coordinates. Euclidean n-space Rⁿ is the set of all column vectors with n real entries.

→ Euclidean; → space.

A thought, conception, or notion existing in the mind as a result of mental understanding, awareness, or activity. See also → thought, → concept.

Idea, from L. idea "idea," pre-Platonic Gk. idea "form, semblance, nature, fashion," in Plato "a timeless, universal archetype of existents; ideal prototype," literally "look, form," from idein "to see," from PIE *wid-es-ya-, suffixed form of base *weid- "to know, to see;" cf. Pers. bin- "to see" (present stem of didan); Mid.Pers. wyn-; O.Pers. vain- "to see;" Av. vaēn- "to see;" Skt. veda "I know."

Miné "idea," related to Pers. maneš "disposition, temperament, greatness of soul," minu "heaven, paradise," also equivalent to Ger. Geist in recent philosophical translations, došman "enemy," pašimân "penitent, regretful," pežmân "sad, mournful," šâdmân "joyful, cheerful, pleased," ârmân "desire; → ideal;" dialectal (Šuštar) mana "(he) thinks, imagines," (Tarq-e Natanz) môna "to imagine, suppose;" Mid.Pers. mênidan "to think, consider," mên "thought, idea," mênišn "thought, thinking, mind, disposition," mênitâr "thinker," mênôg "spiritual, immaterial, heavenly," from Av. man- "to think," mainyeite "he thinks," manah- "mind, thinking, thought; purpose, intention," mainyu- "mind, mentality, mental force, inspiration," traditionally translated as "spirit," Angra Mainyu "hostile mentality" (Mod.Pers. Ahriman); O.Pers. maniyaiy "I think," Ardumaniš- (proper noun) "upright-minded," Haxāmaniš- (proper noun, Hellenized Achaemenes, founder of the Achaemenian dynasty) "having the mind of a friend;" cf. Sogdian mân "mind;" Skt. man- "to think," mánye "I think," manyate "he thinks," mánas- "intelligence, understanding, conscience;" Gk. mainomai "to be angry," mania "madness," mantis "one who divines, prophet;" L. mens "mind, understanding, reason," memini "I remember," mentio "remembrance;" Lith. mintis "thought, idea;" Goth. muns "thought," munan "to think;" Ger. Minne "love," originally "loving memory;" O.E. gemynd "memory, thinking, intention;" PIE base *men- "to think, mind; spiritual activity."

1) (n.) A standard of perfection, beauty, or excellence.
Math.: A subset of a ring that is closed under addition and multiplication by any element of the ring.
2) (adj.) Existing only in the imagination; not real or actual.
Conforming exactly to an ideal, law, or standard; perfect. → ideal gas.

M.E. ydeall, from L.L. idealis "existing in idea," from L. → idea.

Ârmân "ideal" in Mod.Pers., traditionally "desire; hope; grief," variants armân, urmân, prefixed from mân, "thought, mind," → idea. The first element may be related to Av. armaē- "in peace, still; quietly;" PIE base *er[ə]- "to be still" (cf. Skt. īrmā (adv.) "quiet, still, being in the same place;" Gk. erôé "calm, peace;" O.H.G. rouwa "rest"), as in Av. armaē.šad- "sitting quietly," armaē.štā- "standing still, stagnant." Therefore, Pers. ârmân may be related to Av. *armaē.manah- (PIE *ermen-) "thought in peace, quiet mind."
Mineyi, minevâr, adj. from miné, → idea.

An fluid which has no internal friction or → viscosity, and no → resistivity as well if the fluid is a plasma.

→ ideal; → fluid.

Theoretical gas assumed to consist of perfectly elastic molecules of negligible volume and mutual attraction force. Also called → perfect gas.

→ ideal; → gas.

An → equation of state that relates pressure (P), temperature (T), and volume (V) of an ideal or → perfect gas: PV = nRT, where n is the number of → moles of gas present and R is the → universal gas constant. Equivalently: PV = NkT, where N is the number of atoms of gas present and k is → Boltzmann's constant.

→ ideal; → gas; → law.

Magnetohydrodynamics of a → plasma with very large (infinite) → conductivity. In this condition, → Ohm's law reduces to E = -v × B, where E represents → electric field, B → magnetic field, and v the → fluid velocity. Ideal MHD is the simplest model to describe the dynamics of plasmas immersed in a magnetic field. It is concerned with → one-fluid magnetohydrodynamics and neglects → resistivity. This theory treats the plasma composed of many charged particles with locally neutral charge as a continuous single → fluid. Ideal MHD does not provide information on the velocity distribution and neglects the physics relating to wave-particle interactions, as does the two-fluid theory as well. It does have the advantage that the macroscopic dynamics of the → magnetized plasma can be analyzed in realistic three-dimensional geometries (K. Nishikawa & M. Wakatani, 2000, Plasma Physics, Springer). See also → non-ideal magnetohydrodynamics.

→ ideal; → magnetohydrodynamics.

Any one of a variety of systems of philosophical thought, which would make the ultimate reality of the Universe expressible or intangible only in terms of idea in mind, rather than in terms of matter in space.

From → ideal, see also → idea, + → -ism.

Any of several geometries which do not follow the postulates and results of Euclidean geometry. For example, in a non-Euclidean geometry through a point several lines can be drawn parallel to another line. Or, the sum of the interior angles of a triangle differs from 180 degrees. According to Einstein's general relativity theory, gravity distorts space into a non-Euclidean geometry.

→ non-; → Euclidean geometry.

A → magnetohydrodynamics approach dealing with → plasmas which is an improvement with respect to → ideal magnetohydrodynamics. Non-ideal magnetohydrodynamics allows for a drift between particles, redistributing the → magnetic flux and acting on both the → angular momentum and magnetic flux conservation issues.

→ non-→ ideal; → magnetohydrodynamics.

A real vector space of dimension n having a symmetric bilinear form (x, y) such that in some basis e₁, ..., e_n, the quadratic form (x²) takes the form x₁² + ... + x_{n - 1}² - x_n². Such bases are called orthonormal.

→ pseudo-; → Euclidean; → space.