An Etymological Dictionary of Astronomy and Astrophysics
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فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory

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Number of Results: 31 Search : atom
atom
  اتم   
atom (#)

Fr.: atome   

The smallest stable unit forming the basic elements. An atom consists of positively charged → protons and → neutrons in the nucleus surrounded by negatively charged → electrons.

From L. atomus, from Gk. atomos "uncut," from → a- "not" + tomos "a cutting," from temnein "to cut."

atomic
  اتمی   
atomi (#)

Fr.: atomique   

Of or relating to an atom or atoms; of or employing nuclear energy.

Atomic, adj. from → atom + suffix → -ic

atomic clock
  ساعت ِ اتمی   
sâat-e atomi

Fr.: horloge atomique   

A modern clock, in which the characteristic frequencies of certain atoms (most commonly chosen cesium 133) are utilized for precision time measurement. → atomic fountain clock.

atomic; → clock.

atomic fountain
  فواره‌ی ِ اتمی   
favvâre-ye atomi

Fr.: fontaine atomique   

A gaseous ball of atoms, usually → cesium (133Cs), created by the → laser cooling technique and used in an → atomic fountain clock. The ball, typically a few millimeters in diameter and containing some 107 atoms, can be launched upward against gravity using a → laser beam. The launch velocity is chosen such that the atoms reach a height of about one meter before they turn back and fall down the same path they came up. The motion of the ball resembles that of the water in a pulsed fountain.

atomic; fountain, from M.E. fontayne from O.Fr. fontaine, from L.L. fontana, noun use of feminine of L. fontanus "of a spring," from fons "spring of water."

Favvâré, Pers. construction from Ar. faur "boiling, bubbling."

atomic fountain clock
  ساعت ِ فواره‌ی ِ اتمی   
sâ'at-e favvâre-ye atomi

Fr.: horloge à fontaine atomique   

An → atomic clock based on the principle of the → atomic fountain. A ball of atoms, usually → cesium (133Cs), created by the → laser cooling technique, is trapped in the intersection region of six laser beams. The ball is thrown upward by a laser beam and passes twice through a cavity where the atoms interact with the → microwave radiation generated by an → oscillator. The ball reaches the summit of its trajectory (about 1 m above the cooling zone) and then due to gravity falls through the same microwave cavity. The microwave radiation causes the electrons of the cesium atoms to move between two specific → energy states as they pass through the cavity. The clock is based on a → hyperfine transition (9.192631770 GHz) between two energy states in the electronic → ground state of the atom. The upper hyperfine state can in principle radiate to the lower state by → spontaneous emission, but the process takes a very long time -- thousands of years. Selection and detection of the hyperfine state is performed via → optical pumping and laser induced resonance fluorescence. In a carefully controlled setup, a relative uncertainty of 10 -16 can be reached for the cesium clock. This means an accuracy of 1 sec every 300 million years. This fluorescence is measured by a detector. The entire process is repeated until the maximum fluorescence of the cesium atoms is determined. This determination is used to lock the oscillator to the atomic frequency of cesium, which is used to define the SI → second. The first atomic fountain for metrological use was developed at the Paris Observatory (A. Clairon et al. 1996, Proc. 5th Symp. Frequency Standards and Metrology, p. 45).

atomic fountain; → clock.

atomic heat
  گرمای ِ اتمی   
garmâ-ye atomi

Fr.: chaleur atomique   

The → heat capacity of a → mole of a substance, expresses as: Ca = C.A , where C is the → specific heat and A the → atomic weight .

atomic; → heat.

atomic hydrogen
  هیدروژن ِ اتمی   
hidrožen-e atomi (#)

Fr.: hydrogène atomique   

Same as → neutral hydrogen or → H I.

atomic; → hydrogen.

atomic mass number (A-number)
  عدد ِ جرم ِ اتمی   
adad-e jerm-e atomi (#)

Fr.: nombre de masse atomique   

The total number of → protons and → neutrons in the → nucleus of an → atom (symbol A). For example, Oxygen-16 has a mass number of sixteen, because it has eight protons and eight neutrons.

atomic; → mass; → number.

atomic mass unit (amu)
  یکای ِ جرم ِ اتمی   
yekâ-ye jerm-e atomi (#)

Fr.: unité de masse atomique   

A unit of mass used for atoms and molecules, equal to 1/12 of the mass of an atom of carbon-12 (including orbital electrons). It is equal to 1.660 33 × 10-24 g.

atomic; → mass; → unit.

atomic nucleus
  هسته‌ی ِ اتم   
haste-ye atom (#)

Fr.: noyau atomique   

The central part of the → atom. It is made up of → protons and, in most cases, → neutrons. The nucleus is surrounded by a swarm of fast-moving → electrons. Almost all of the mass (more than 99%) of an atom is contained in the dense nucleus. The number of protons in the nucleus (called → atomic number) determines the type of → chemical element. Atoms that differ only in the number of neutrons in their nuclei are called → isotopes.

atomic; → nucleus.

atomic number
  عدد ِ اتمی   
adad-e atomi (#)

Fr.: nombre atomique   

The number of → protons in an → atomic nucleus (symbol Z). Same as → Z-number. The atomic number is written as a subscript to the left of the → chemical element name. For example, the most common isotope of oxygen is shown as 816O, which has 8 → protons and its → mass number (A) is 16.

atomic; → number.

atomic proposition
  گزاره‌ی ِ اتمی   
gozâre-ye atomi

Fr.: proposition atomique   

In → propositional logic, a → sentence without any → connectives. See also → molecular proposition.

atomic; → proposition.

atomic time
  زمان ِ اتمی   
zamân-e atomi (#)

Fr.: temps atomique   

Time measured using atomic clocks.

atomic; → number.

atomic transition
  گذرش ِ اتمی   
gozareš-e atomi

Fr.: transition atomique   

A change in the → energy level or → state of an → atom in which a → quantum of energy is either gained or lost. See also → forbidden transition; → permitted transition; → semiforbidden transition.

atomic; → transition.

atomic weight
  وزن ِ اتمی   
vazn-e atomi (#)

Fr.: poids atomique   

The mean atomic mass of a particular → chemical element in → atomic mass unit.

atomic; → weight.

atomic wff
   wff اتمی   
wff atomi

Fr.: FBF atomique   

i) If t1, t2, ..., tn are terms and P is a → predicate of arity n, then P(t1, t2, ..., tn) is an atomic wff.
ii) If t1 and t2 are terms, then (t1 = t2) is an atomic wff.

atomic; → wff.

Bohr atom
  اتم ِ بؤر   
atom-e Bohr

Fr.: atome de Bohr   

The simplest model of an atom according to which electrons move around the central nucleus in circular, but well-defined, orbits. For more details see → Bohr model.

Bohr; → atom.

diffuse atomic cloud
  ابر ِ اتمی ِ پخشیده   
abr-e atomi-ye paxšidé

Fr.: nuage atomique diffus   

A type of cloud in the → interstellar medium with low molecular content that is fully exposed to the → interstellar radiation field, and therefore nearly all its → molecules are quickly destroyed by → photodissociation. Hydrogen is mainly in → neutral atomic form (→ neutral hydrogen), and atoms with → ionization potentials less than that of hydrogen (most notably → carbon) are almost fully → ionized, providing abundant electrons. The paucity of molecules implies that very little chemistry occurs in such clouds. Many → sightlines with low → extinction seem to pass exclusively through → diffuse atomic gas. Such sightlines typically have a → column density, NH, less than about 5 × 1020 cm-2, and are sufficiently → optically thin to be observable by means of → visible and → ultraviolet → absorption line measurements. Diffuse atomic clouds typically have a fairly low → density (~ 10-100 cm-3), and → temperatures of 30-100 K (Snow & McCall, 2006, ARA&A 44, 367).

diffuse; → atomic; → gas.

excited atom
  اتم ِ بر‌انگیخته   
atom-e barangixté (#)

Fr.: atome excité   

An atom in which one or more of its bound electrons are at → energy levels higher than their normal level.

Excited p.p. of → excite; → atom.

interatomic
  اندر-اتومی   
andaratomi

Fr.: interatomique   

Between atoms; relating to the interaction of different atoms.

inter-; → atomic.

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