General: Any of a set of physical properties whose values determine the
characteristics or behavior of something. → impact parameter;
→ ionization parameter.
Parâmun, from parâ-, → para-, + mun/mân "measure," as in Pers. terms pirâmun "perimeter," âzmun "test, trial," peymân "measuring, agreement," peymâné "a measure; a cup, bowl," from O.Pers./Av. mā(y)- "to measure;" cf. Skt. mati "measures," matra- "measure;" Gk. metron "measure;" L. metrum; PIE base *me- "to measure."
Fr.: équation paramétrique
Any of a set of equations that defines the coordinates of the dependent variables of a curve or surface in terms of one or more independent variables or parameters.
nemudâr-e Penrose-Carter (#)
Fr.: diagramme de Penrose-Carter
A diagram involving → formal compactification of → space-time used in → general relativity to describe the causal properties of the space-time. Only two of the space dimensions are shown and horizontal lines represent space, while vertical lines belong to time. The → null geodesicss are at 45Â°, which facilitates the visualization of → light cones. The major feature of Penrose-Carter diagram is representing the whole space-time on a finite surface, while putting → spacelike and → timelike infinities at finite distance.
Named for Roger Penrose (1931-) and Brandon Carter (1942-) who introduced it independently; → diagram.
A plot for examining frequency-domain data in an equi-spaced → time series. The periodogram is the → Fourier transform of the → autocovariance function. The periodogram method relies on the definition of the → power spectral density .
Fr.: diagramme de phases
A graph showing the equilibrium relationships between phases (such as vapor-liquid, liquid-solid) of a chemical compound, mixture of compounds, or solution.
Fr.: paramètre physique
A plan or schedule of activities, procedures, etc., to be followed.
From L.L. programma "proclamation, edict," from Gk. programma "a written public notice," from the stem of prographein "to write publicly," from → pro- "forth" + graphein "to write."
Barnâmé, originally "model, examplar; acount-book," from bar- "on; up; upon; in; into; at; forth; with; near; before; according to" (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") + nâmé "letter; book" (Mid.Pers. nâmak "inscription; letter; book," related to nâm "name;" Mid.Pers. nâm; O.Pers./Av. nâman-; cf. Skt. nama-; Gk. onoma, onuma; L. nomen; PIE *nomen-).
Fr.: étoiles du programme
Stars for the observation of which telescope time has been awarded.
barnâme sâz (#)
A computer expert who carries out → programming.
Agent noun of the verb → program.
The process of writing, testing, debugging/troubleshooting, and maintaining the source code of computer programs.
Verbal noun of → program.
Barnâme-sâzi, from barnâmé, → program, + sâzi verbal noun of sâxtan, sâzidan "to build, make, fashion; to adapt, adjust, be fit" (from Mid.Pers. sâxtan, sâz-, Manichean Parthian s'c'dn "to prepare, to form;" Av. sak- "to understand, to mark," sācaya- (causative) "to teach").
Graphic display of measurements by a → radar of mineral deposits on a planetary surface.
1) quc, garând; 2) qucvâr
M.E. ram, from O.E. ramm "male sheep," also "battering ram," earlier rom "male sheep," a W.Gmc. word of unknown origin (cf. M.L.G., M.Du., Du., O.H.G. ram). The verb meaning "to beat with a heavy implement" is first recorded c.1330.
Quc "ram, horned male sheep," loan from Turkish.
Fr.: pression dynamique
The pressure exerted on a body moving through a → fluid medium. For example, a → meteor traveling through the Earth's atmosphere produces a → shock wave generated by the extremely rapid → compression of air in front of the → meteoroid. It is primarily this ram pressure (rather than → friction) that heats the air which in turn heats the meteoroid as it flows around the meteoroid. The ram pressure increases with → velocity according to the relation P = (1/2)ρv2, where ρ is the density of the medium and v the relative velocity between the body and the medium. Similarly, → ram pressure stripping produces → jellyfish galaxies. Same as → dynamic pressure.
ram pressure stripping
loxtâneš bâ fešâr-e qucvâr
Fr.: balayage par la pression dynamique
A process proposed to explain the observed absence of gas-rich galaxies in → galaxy clusters whereby a galaxy loses its gas when it falls into a cluster. There is a tremendous amount of hot (~ 107 K) and tenuous (~ 10-4 cm-3) gas (several 1013 → solar masses) in the → intracluster medium (ICM). Ram pressure stripping was first proposed by Gunn & Gott (1972) who noted that galaxies falling into clusters feel an ICM wind. If this wind can overcome the → gravitational attraction between the stellar and gas disks, then the gas disk will be blown away. The mapping of the gas content of spiral galaxies in the → Virgo cluster showed that the → neutral hydrogen (H I) disks of cluster spiral galaxies are disturbed and considerably reduced. Their molecular gas, more bound to the galaxy, is less perturbed, but still may be swept out in case of very strong ram pressure. These observational results indicate that the gas removal due to the rapid motion of the galaxy within the intracluster medium is responsible for the H I deficiency and the disturbed gas disks of the cluster spirals (e.g., J. A. Hester, 2006, ApJ 647:910).
Fr.: effet Raman
Same as → Raman scattering.
Named after the Indian physicist Sir Chandrasekhara Venkata Raman (1888-1970), who discovered the effect; recipient of the 1930 Nobel Prize in Physics; → effect.
parâkaneš-e Raman (#)
Fr.: diffusion Raman
The scattering of monochromatic light (visible or ultraviolet) by molecules in which the scattered light differs in wavelength from the incident light. It is caused by the light's interaction with the vibrational or rotational energy of the medium's scattering molecules.
gerde-ye Ramsden, disk-e ~ (#)
Fr.: disque de Ramsden
The small circular patch of light visible in the back focal plane of an eyepiece.
Named after Jesse Ramsden (1735-1800), English maker of astronomical instruments; → disk.
cešmi-ye Ramsden (#)
Fr.: oculaire de Ramsden
An eyepiece consisting of two planoconvex lenses of the same focal length, placed with the convex sides facing each other and with a separation between the lenses of about two-thirds of the focal length of each.
Named after Jesse Ramsden (1735-1800), English maker of astronomical instruments; → eyepiece.
random access memory (RAM)
barm bâ dastrasi-ye kâtruré
Fr.: mémoire à accès aléatoire
In computer technique, a configuration of memory cells that hold data for processing by a central processing unit (CPU). The term random derives from the fact that the CPU can retrieve data from any individual location, or address, within RAM.
Fr.: paramètre de rougissement
A dimensionless quantity characterizing the → interstellar extinction, defined by the total-to-selective extinction ratio: RV = AV/E(B-V). The typical value found for the reddening parameter in the Milky Way is RV ~ 3.1, but it is known to vary from one line of sight to another, from values as 2 to as large as 6. Very large → dust grains would produce extinction with RV → ∞.