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

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.

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.

→ Raman effect; → scattering.

An effect that remains in a system for a while after the physical cause has been removed. For example the light remaining in a detector after elimination of the source, or the magnetic induction that remains in a material after removal of the magnetizing field.

From reman(ent), → remanent + -ence a noun suffix.

Noun of → pasmân.

Possessing → remanence.

M.E. from L. remanent- (stem of remanens), pr.p. of remanere "to remain, stay behind," from → re- "back" + manere "to stay, remain," cognate with Pers. mândan "to stay, remain," as below.

Pasmân, from pas- "behind," variant pošt "back; the back; behind" (Mid.Pers. pas "behind, before, after;" O.Pers. pasā "after;" Av. pasca "behind (of space); then, afterward (of time);" cf. Skt. paścā "behind, after, later;" L. post, as above; O.C.S. po "behind, after;" Lith. pas "at, by;" PIE *pos-, *posko-) + mân present stem of mândan "to remain, stay" (mân "house, home;" Mid.Pers. mândan "to remain, stay;" O.Pers. mān- "to remain, dwell;" Av. man- "to remain, dwell; to wait;" Gk. menein "to remain;" L. manere "to stay, abide" (Fr. maison, ménage; E. manor, mansion, permanent); PIE base *men- "to remain, wait for").

A 4th → rank tensor that characterizes the deviation of the geometry of space from the Euclidean type. The curvature tensor R^λ_μνκ is defined through the → Christoffel symbols Γ^λ_μν as follows: R^λ_μνκ = (∂Γ^λ_μκ)/(∂x^ν) - (∂Γ^λ_μν)/(∂x^κ) + Γ^η_μκΓ^λ_ην - Γ^η_μνΓ^λ_ηκ.

→ Riemannian geometry; → curvature; → tensor.

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) = u_l if x < 0, and u(x,0) = u_r if x > 0 .

→ Riemann's geometry; → problem.

Same as → Riemannian geometry.

→ Riemannian; → geometry.

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.

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.

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

→ Riemannian; → metric.

A positive-definite inner product, (.,.)_x, on T_x(M), the tangent space to a manifold M at x, for each x  ∈ M, which varies continually with x (Douglas N. Clark, Dictionary of Analysis, Calculus, and Differential Equations).

→ Riemannian; → metric.

Any of several → lunar calendars used by Romans before the advent of the → Julian calendar in 46 B.C. The original Roman calendar, which had 10 months and 304 days, went back to the Greek calendar, although Romulas, the ruler of Rome, is given credit for starting the Roman calendar. Originally, the Roman calendar started the year in March with the → vernal equinox. The Roman calendar went through several changes from 800 B.C. to the Julian calendar. The 800 B.C. calendar had 10 months and a winter period, with a year of 304 days. In this calendar, the first month, March, was followed by Aprilis, Maius, Junius, Quintilis, Sextilis, September, October, November, December, and Winter. The months starting with and following Quintilis all used the Latin numbers for names. Finally, for political reasons, the Romans made a change around 150 B.C. when they started using January as the beginning of their calendar year. Around 700 B.C. the 304 day calendar was expanded to 355 days by adding the months of February and January to the end of the year. Later in 450 B.C., January was moved in front of February. Finally, in 150 B.C. the Romans began to use January as the beginning of the calendar year. This calendar was replaced by the Julian calendar in 46 B.C.

From L. Romanus "of Rome, Roman," from Roma "Rome," of uncertain origin.

A → number system in which letters represent numbers, still used occasionally today. The cardinal numbers are expressed by the following seven letters: I (1), V (5), X (10), L (50), C (100), D (500), and M (1,000). If a numeral with smaller value is written on right of greater value then smaller value is added to the greater one. If it is preceded by one of lower value, the smaller numeral is subtracted from the greater. Thus VI = 6 (V + I), but IV = 4 (V - I). Other examples are XC (90), CL (150), XXII (22), XCVII (97), CCCXCV (395). If symbol is repeated then its value is added. The symbols I, X, C and M can be repeated maximum 3 times. A dash line over a numeral multiplies the value by 1,000. For example V^- = 5000, X^- = 10,000, C^- = 100,000, and DLIX^- = 559,000.

→ numeral; → system.

1) Of, pertaining to, or arising from the different meanings of words or other signs and symbols.
2) Of or pertaining to → semantics.

From Fr. sémantique, from Gk. semantikos "significant," from semainein "to show, signify, indicate by a sign," from sema "sign."

Cemârik, from cemâr, → meaning, + -ik, → -ic.

The study of the → meaning of signs or symbols, as opposed to their formal relations (→ syntactics).

→ semantic; → -ics.

An optical device, a modern version of the → Hartmann test, used for analyzing the wavefront of light. Theses sensors can be used to characterize the performance of optical systems. Moreover, they are increasingly used in real-time applications, such as → adaptive optics to remove the wavefront distortion before creating an image. It consists of a microlens array placed in front of a CCD array. A planar wavefront that is transmitted through a microlens array and imaged on the CCD array will form a regular pattern of bright spots. If, however, the wavefront is distorted, the light imaged on the CCD will consist of some regularly spaced spots mixed with displaced spots and missing spots. This information is used to calculate the shape of the wavefront that was incident on the microlens array.

Named after the German astronomer Johannes Hartmann (1865-1936), who first developed the method, and R. V. Shack, who in the late 1960s replaced the screen by a microlens array; → wavefront; → sensor.

A person who is experienced in the art of government or versed in the administration of government affairs (Dictionary.com).

From state's man, translation of Fr. homme d'Etat; → state; → man.

The constant of proportionality present in the → Stefan-Boltzmann law. It is equal to σ = 5.670 × 10^-8 W m^-2 K^-4 or 5.670 × 10^-5 erg cm^-2 s^-1 K^-4.

→ Stefan-Boltzmann law; → constant.

The flux of radiation from a blackbody is proportional to the fourth power of its absolute temperature: L = 4πR²σT⁴. Also known as Stefan's law.

Ludwig Eduard Boltzmann (1844-1906), an Austrian physicist, who made important contributions in the fields of statistical mechanics and statistical thermodynamics and Josef Stefan (1835-1893), an Austrian physicist; → law.

A person in charge of the configuration and administration of a multi-user computer system inside a network.

→ system; → manager.