In an imaging system, the unvarying of the → point spread function over an extended field of view.
The condition in which the wavefronts arriving from different parts of a region of sky undergo almost identical phase perturbations. See also → isoplanatic patch.
A line on a map connecting points of equal value. For example the contour lines joining points of equal altitude on a topographic map. Some other examples of isopleths are: → isobar, → isoneph, and → isohel.
Izocand, from izo-, → iso-, + cand replacing candi (after prefix) "quantity," from Mid.Pers. candih "amount, quantity," from cand "how many, how much; so many, much;" O.Pers. yāvā "as long as;" Av. yauuant- [adj.] "how great?, how much?, how many?," yauuat [adv.] "as much as, as far as;" cf. Skt. yāvant- "how big, how much;" Gk. heos "as long as, until."
sebar-e do-pahlu-barâbar (#)
Fr.: triangle équilatéral
A triangle having two sides equal.
From L.L. isosceles, from Gk. isoskeles "with equal legs; that can be divided into two equal parts," from isos "equal, identical," → iso-, + skelos "leg."
A quantum number based on the assumption that the nucleon (proton and neutron) is a single entity having two states, like → spin. It is conserved by the strong interaction. Same as isotopic spin, isobaric spin.
Meteo.: A line on a map or graph joining points of equal temperature.
Isotherm, back formation from → isothermal.
1) Relating to or having a constant temperature.
Isothermal, from → iso- + therm, from Gk. therme "heat" thermos "warm;" cognate with Pers. garm "warm" (garmâ "heat, warmth," from Mid.Pers. garmâg; O.Pers./Av. garəma- "hot, warm;" cf. Skt. gharmah "heat;" L. formus "warm," fornax "oven;" P.Gmc. *warmaz; O.E. wearm; E. warm; O.H.G., Ger. warm; PIE *ghworm-/*ghwerm- "warm") + → -al; → process.
Fr.: processus isotherme
A → thermodynamic process that takes place at → constant → temperature. For the temperature of a system to remain strictly constant, the changes in other coordinates (pressure and volume) must be carried out slowly, and → heat must enter or leave the system to maintain a constant temperature. → polytropic process. Astrophysical examples include the → collapse of a → protostar down the → Hayashi track, and the collapse of a star at the end of its life to become a → white dwarf.
Fr.: vent isotherme
A → stellar wind in which the gas is subject to only two forces: the inward directed gravity and the outward directed gradient of the gas pressure.
One of several nuclides having the same number of neutrons in their nuclei but differing in the number of protons.
Isotone, from → iso- + tone, from Gk tonos "strain, tone, mode," literally, "a stretching," akin to teinein "to stretch," cognate with Pers. tanidan "to spin, twist, weave" (Mid.Pers. tanitan; Av. tan- "to stretch, extend;" cf. Skt. tan- to spin, stretch;" tanoti "stretches," tantram "loom;" Gk. teinein "to stretch, pull tight;" L. tendere "to stretch; PIE base *ten- "to stretch;" Pers. târ "string," tân "thread," tur "fishing net, net, snare," and tâl "thread" (Borujerdi dialect) belong to this family; variants tanta "cobweb," tanadu, tafen, kartané, kârtané, kâtené, Pashtu tanistah "cobweb;" cf. Skt. tantu- "cobweb, thread, string").
izotop (#), hamjâ (#)
One of two or more atoms having the same number of protons in its nucleus, but a different number of neutrons and, therefore, a different mass.
Isotope, from → iso- + -tope, from Gk. topos "place."
Izotop, loan from Fr., as above. hamjâ, from ham- "together" → com- + jâ "place" (from Mid.Pers. giyag "place;" O.Pers. ā-vahana- "place, village;" Av. vah- "to dwell, stay," vanhaiti "he dwells, stays;" Skt. vásati "he dwells;" Gk. aesa (nukta) "to pass (the night);" Ossetic wat "room; bed; place;" Tokharian B wäs- "to stay, wait;" PIE base ues- "to stay, live, spend the night").
Fr.: fractionnement isotopique
A slight difference between the → abundances of → isotopes of the same → chemical element owing to → physical or → chemical → processes. It results in the → enrichment or → depletion of an isotope. Same as → isotopic fractionation.
Fr.: décalage isotopique
A displacement in the spectral lines due to the different isotopes of an element.
Of or relating to an → isotope.
Fr.: fractionnement isotopique
Same as → isotope fractionation.
Fr.: nombre isotopique
The difference between the number of neutrons in an isotope and the number of protons. Neutron excess.
Fr.: rapport isotopique
The relative abundances of two isotopes of a given chemical element, such as D/H (deuterium/hydrogen), (carbon) 12C/13C, and (uranium) 235U/238U.
spin-e izotopi (#), izospin (#)
Fr.: spin isotopique
Same as → isospin.
Any of molecular entities which differ in their isotopic composition but retain the same → chemical elements, e.g. H2O and HDO.
Any of → isomers having the same number of each isotopic atom but differing in their positions. For example, CH3CHDCH3 and CH3CH2CH2D are a pair of isotopomers.
Short for isotopic isomers.