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

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory

   Homepage   
   


A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

<< < R a rad rad rad rad rad rad ran rap ray rea rea rec rec Red red ref ref reg rel rel rel rep res res res ret rev rho Rie rim roA Rom rot rot rul > >>

Number of Results: 715
rhombic
  لوزیک   
lowzik

Fr.: rhombique   

Shaped like a rhombus.

From rhomb, → rhombus, + → -ic.

rhombus
  لوزی   
lowzi (#)

Fr.: losange   

A quadrilateral having all sides equal and all angles oblique.

L.L. rhombus, from Gk. rhombos "rhombus, spinning top," from rhembesthai "to spin, whirl."

Lowzi, resembling a lowz "almond."

rhythm
  ریتم   
ritm (#)

Fr.: rythme   

1) An ordered recurrent alternation of strong and weak elements in the flow of sound and silence in speech; a particular example or form of rhythm.
2) The aspect of music comprising all the elements (as accent, meter, and tempo) that relate to forward movement.
3) A regularly recurrent quantitative change in a variable biological process (Merriam-Webster.com).

From L. rhythmus "movement in time," from Gk. rhythmos "measured flow or movement, rhythm; proportion, symmetry; arrangement," related to rhein "to flow," from PIE root *sreu- "to flow"

Ritm, loan from Fr.

Ricci scalar
  مرپلی ِ ریتچی   
marpeli-ye Ricci

Fr.: scalaire de Ricci   

The simplest curvature invariant for a → Riemannian manifold. It is derived from the → Ricci tensor Rμν ≡  Rαμαν by contracting indices. Taking the trace of the Ricci tensor gives the Ricci scalar: R ≡ Rμνgμnu; = Rμν = Rαμαμ. Also called → scalar curvature.

Ricci tensor; → scalar.

Ricci tensor
  تانسور ِ ریتچی   
tânsor-e Ricci

Fr.: tenseur de Ricci   

A → rank 2, → symmetric tensor Rμν that is a contraction of the → Riemann curvature tensor Rλμνλ. More specifically, Rμν ≡ Σ (λ) Rλμνκ = Rλμνκ. Closely related to the Ricci tensor is the → Einstein tensor, which plays an important role in the theory of → general relativity.

Named after the Italian mathematician Gregorio Ricci-Curbastro (1853-1925); → tensor.

rich
  پر-، پردار   
por-, pordâr

Fr.: riche   

Having large amounts of something specified. → metal-rich environment, → rich cluster; → enrich, → enrichment, → richness, → poor.

M.E., from O.E. rice "wealthy, powerful" (cf. Du. rijk, Ger. reich "rich"), from PIE base *reg- "move in a straight line," hence, "to direct, rule" (cf. Mod.Pers./Mid.Pers. râst "right, straight;" O.Pers. rāsta- "straight, true," rās- "to be right, straight, true;" Av. rāz- "to direct, put in line, set," razan- "order;" Skt. raj- "to direct, stretch," rjuyant- "walking straight;" Gk. orektos "stretched out;" L. regere "to lead straight, guide, rule," p.p. rectus "right, straight;" Ger. recht; E. right).

Por "full, much, very, too much" (Mid.Pers. purr "full;" O.Pers. paru- "much, many;" Av. parav-, pauru-, pouru-, from par- "to fill;" PIE base *pelu- "full," from *pel- "to be full;" cf. Skt. puru- "much, abundant;" Gk. polus "many," plethos "great number, multitude;" O.E. full); pordâr, literally "having much possession," from por + dâr "having, possessor," from dâštan "to have, to possess," → property.

rich cluster
  خوشه‌ی ِ پُردار   
xuše-ye pordâr

Fr.: amas riche   

A → galaxy cluster with a particularly large number of galaxies.

rich; → cluster.

Richardson cascade
  پی‌شار ِ ریچاردسون   
peyšâr-e Richardson

Fr.: cascade de Richarson   

Same as → energy cascade

Named after L. F. Richardson (1922), Weather Prediction by Numerical Process (Cambridge Univ. Press); → cascade.

Richardson criterion
  سنجیدار ِ ریچاردسون   
sanjidâr-e Richardson

Fr.: critère de Richardson   

A condition for the onset of → instability in multilayer fluids which compares the balance between the restoring force of → buoyancy and the destabilizing effect of the → shear.

Named after the British meteorologist Lewis Fry Richardson (1881-1953), who first arrived in 1920 to the dimensionless ratio now called → Richardson number. The first formal proof of the criterion, however, came four decades later for → incompressible flows (Miles, J. W. 1961, J. Fluid Mech., 10, 496; Howard, L. N., 1961, J. Fluid Mech., 10, 509). Its extension to → compressible flows was demonstrated subsequently (Chimonas 1970, J. Fluid Mech., 43, 833); → criterion.

Richardson number
  عدد ِ ریچاردسون   
adad-e Richardson

Fr.: nombre de Richardson   

A dimensionless number which is used according to the → Richardson criterion to describe the condition for the → stability of a flow in the presence of vertical density stratification. If the → shear flow is characterized by linear variation of velocity and density, with velocities and densities ranging from U1 to U2 and ρ1 to ρ2 (ρ2>ρ1), respectively, over a depth H, then the Richardson number is expressed as: Ri = (ρ2 - ρ1) gH / ρ0 (U1 - U2)2. If Ri < 0.25, somewhere in the flow turbulence is likely to occur. For Ri > 0.25 the flow is stable.

Richardson criterion; → number.

richness
  پرداری   
pordâri

Fr.: richesse   

The property of being very abundant.

rich; → -ness.

richness class
  رده‌ی ِ پرداری   
rade-ye pordâri

Fr.: classe de richesse   

A classification of → galaxy clusters into six groups (0 to 5), as in the → Abell catalog. It depends on the number of galaxies in a given cluster that lie within a → magnitude range m3 to m3+2, where m3 is the magnitude of the 3rd brightest member of the cluster. The first group contains 30-49 galaxies and the last group more than 299 galaxies.

richness; → group.

riddle
  کروس   
kervas (#)

Fr.: énigme, devinette   

1) A question or statement so framed as to exercise one's ingenuity in answering it or discovering its meaning; conundrum.
2) A puzzling question, problem, or matter (Dictionary.com).

M.E. redel, redels, from O.E. rædels "riddle; counsel; conjecture; imagination;" cf. O.Fr. riedsal "riddle," O.Sax. radisli, M.Du. raetsel, Du. raadsel, O.H.G. radisle, Ger. Rätsel "riddle."

Kervas "riddle, puzzle" [Dehxodâ], Kurd. karvâs "riddle," of unknown origin.

ridge
  روک   
ruk

Fr.: faîte, dorsale   

A long, narrow elevation of the Earth's surface, generally sharp crested with steep sides, either independently or as part of a larger mountain or hill. See also: → submarine ridge, → wrinkle ridge, → mid-Atlantic ridge.

M.E. rigge; O.E. hrycg "spine, back of a man or beast" (cf. O.Fris. hregg, Du. rug, O.H.G. hrukki, Ger. Rücken "the back").

Ruk, from dialectal Tabari ruk "mountain, ridge;" cf. (Dehxodâ) raš "hill."

Riemann curvature tensor
  تانسور ِ خمیدگی ِ ریمان   
tânsor-e xamidegi-ye Riemann

Fr.: tenseur de courbure de Riemann   

A 4th → rank tensor that characterizes the deviation of the geometry of space from the Euclidean type. The curvature tensor Rλμνκ is defined through the → Christoffel symbols Γλμν as follows: Rλμνκ = (∂Γλμκ)/(∂xν) - (∂Γλμν)/(∂xκ) + ΓημκΓλην - ΓημνΓληκ.

Riemannian geometry; → curvature; → tensor.

Riemann problem
  پراسه‌ی ِ ریمان   
parâse-ye Riemann

Fr.: problème de Riemann   

The combination of a → partial differential equation and a → piecewise constant → initial condition. The Riemann problem is a basic tool in a number of numerical methods for wave propagation problems. The canonical form of the Riemann problem is: ∂u/∂t + ∂f(u)/∂x = 0, x ∈ R, t > 0, u(x,0) = ul if x < 0, and u(x,0) = ur if x > 0 .

Riemann's geometry; → problem.

Riemann's geometry
  هندسه‌ی ِ ریمان   
hendese-ye Riemann

Fr.: géométrie de Riemann   

Same as → Riemannian geometry.

Riemannian; → geometry.

Riemannian
  ریمانی   
Riemanni (#)

Fr.: riemannien   

Of or pertaining to Georg Friedrich Bernhard Riemann (1826-1866) or his mathematics findings. → Riemannian geometry, → Riemannian manifold, → Riemannian metric, → Riemann problem, → Riemann curvature tensor.

After the German mathematician Georg Friedrich Bernhard Riemann (1826-1866), the inventor of the elliptic form of → non-Euclidean geometry, who made important contributions to analysis and differential geometry, some of them paving the way for the later development of → general relativity.

Riemannian geometry
  هندسه‌ی ِ ریمانی   
hendese-ye Riemanni

Fr.: géométrie riemannienne   

A → non-Euclidean geometry in which there are no → parallel lines, and the sum of the → angles of a → triangle is always greater than 180°. Riemannian figures can be thought of as figures constructed on a curved surface. The geometry is called elliptic because the section formed by a plane that cuts the curved surface is an ellipse.

Riemannian; → geometry.

Riemannian manifold
  بسلای ِ ریمانی   
baslâ-ye Riemanni

Fr.: variété riemannienne   

A → manifold on which there is a defined → Riemannian metric (Douglas N. Clark, 2000, Dictionary of Analysis, Calculus, and Differential Equations).

Riemannian; → metric.

<< < R a rad rad rad rad rad rad ran rap ray rea rea rec rec Red red ref ref reg rel rel rel rep res res res ret rev rho Rie rim roA Rom rot rot rul > >>