atomic fountain clock
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).
Fr.: chaleur atomique
hidrožen-e atomi (#)
Fr.: hydrogène atomique
atomic mass number (A-number)
adad-e jerm-e atomi (#)
Fr.: nombre de masse atomique
atomic mass unit (amu)
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.
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.
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.
Fr.: proposition atomique
zamân-e atomi (#)
Fr.: temps atomique
Time measured using atomic clocks.
Fr.: transition atomique
vazn-e atomi (#)
Fr.: poids atomique
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.
To pay attention.
Âtânidan, from prefix â- + tân, from tan-, tanidan "to spin, twist, weave" (cf. tân "thread, warp of a web," variants târ "thread, warp, string," tâl "thread" (Borujerdi dialect), tur "fishing net, net, snare"); Mid.Pers. tanitan; Av. tan- to stretch, extend;" cf. Skt. tan- to stretch, extend;" tanoti "stretches," tantram "loom;" tántra- "warp; essence, main point;" Gk. teinein "to stretch, pull tight;" L. tendere "to stretch;" Lith. tiñklas "net, fishing net, snare;" PIE base *ten- "to stretch."
1) The act or faculty of attending, especially by directing the mind to an object.
1) Characterized by or giving attention; observant.
L. attenuatus, p.p. of attenuare "to make thin," from → ad- "to" + tenuare "make thin," from tenuis "thin;" cf. Gk. tanaos "thin, slender, elongated;" Skt. tanuka-, tanu- "thin;" Av. tan- "to stretch;" Pers. tonok "thin," as below; O.Ir. tanae "delicate, thin;" O.H.G. dunni "thin."
Tonokidan, from tonok "thin, slender, slight, tender, delicate" + -idan, infinitive suffix. Tonok, from Mid.Pers. tanuk, Av. root tan- "to stretch, extend," cognate with L. tenuis, as above.
The falling off of the energy density of radiation with distance from the source, or with passage through an absorbing or scattering medium.
Verbal noun of → attenuate.
Fr.: coefficient d'bsorption
The fraction of a beam of → X-rays or → gamma rays that is absorbed or scattered per unit thickness of the → absorber. The linear attenuation coefficient, denoted by the symbol μ, appears in the equation I(x) = I0e-μx, where I(x) is the intensity at depth of x cm and I0 is the original intensity.
Fr.: facteur d'atténuation
The ratio of the radiation intensity after traversing a layer of matter to its intensity before.
Position of a satellite with respect to the horizon or some other fixed reference plane.
Fr., from It. attitudine "disposition, posture," from L.L. aptitudo "faculty."
Ruykard, noun from ruy kardan "to turn the face toward,"
from ruy "face"
(Mid.Pers. rôy, rôdh "face," Av. raoδa-
"growth," in plural "appearance," from raod- "to grow, sprout, shoot,"
cf. Skt. róha- "rising, height") + kardan "to do, make, perform"
(Mid.Pers. kardan, O.Pers./Av. kar- "to do, make, build,"
Av. kərənaoiti "makes," cf. Skt. kr- "to do, to make,"
krnoti "makes," karma "act, deed;" PIE base kwer-
"to do, to make").