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

A → rootx₀ of function f(x), if f(x₀) = 0 and df/dx | x₀ = 0. See also → double root.

→ simple; → root.

A generalization of the simplest closed configuration that can be made from straight line segments. For example, a → triangle is a 2-simplex because it is in two → dimensions, and → tetrahedron is a 3-simplex because it is in three dimensions (Steven Schwartzman, An Etymological Dictionary of Mathematical Terms Used in English, 1994).

Simplex, literally "uncomplicated, → simple," from sim-, from PIE root *sem- "one, once, together" + plek- "to fold." "folded [only] once."

Taktâft, literally "folded once," from tak "→ single, alone," + tâft, contraction of tâfté "plated, twisted, fold," as in hamtâft, → complex.

An → algorithm for solving the classical → linear programming problem; developed by George B. Dantzig in 1947. The simplex method is an → iterative method, solving a system of → linear equations in each of its steps, and stopping when either the → optimum is reached, or the solution proves infeasible. The basic method remained pretty much the same over the years, though there were many refinements targeted at improving performance (e.g. using sparse matrix techniques), numerical accuracy and stability, as well as solving special classes of problems, such as mixed-integer programming (Free On-Line Dictionary of Computing, FOLDOC).

→ simplex; → method.

The act of simplifying, or the fact of being simplified.

Verbal noun of → simplify.

1) To make less complex or complicated.
2) Math.: Reduce an → expression by → algebraic manipulations.

→ simple + epenthesis -i- + → -fy.

Minute images or replicas of objects supposed by ancient atomist philosophers to be shed from any object and used in the explanation of vision. According to Democritus (c. 460-c. 370 BC) and Epicurus (341-270 BC), these replicas or effigies, called eidola, were perpetually peeled off the surfaces of things and caused vision by entering in the eye.

L. translation of eidola by Lucretius (1st Century BC), from L. simulacrum "likeness, image," from simulare "to → simulate."

To create a likeness or model of something (a situation, system, or the like).

M.E., from L. simulatus, p.p. of simulare "to imitate," from stem of similis "like;" cognate with Pers. ham "together, with; same, equally, even" (Mid.Pers. ham-, like L. com- and Gk. syn- with neither of which it is cognate. O.Pers./Av. ham-, Skt. sam-; also O.Pers./Av. hama- "one and the same," Skt. sama-, Gk. homos-; originally identical with PIE numeral *sam- "one," from *som-. The Av. ham- appears in various forms: han- (before gutturals, palatals, dentals) and also hem-, hen-).

Mânadidan verb from mânand "resembling, like," variant mânestan "to resemble;" Mid.Pers. mânag "like, resembling;" Av. man- "to resemble;" hamânad sâxtan, from hamânand, from ham-, as above, + mânad + sâxtan "to make, build."

The construction of a mathematical model to reproduce the characteristics of a phenomenon, system, or process, often using a computer, in order to infer information or solve problems.

Verbal noun of → simulate.

The property of events occurring → simultaneously.

Noun from → simultaneous; → -ity.

1) General: Happening, existing, or operating at the same time.
2) In a → space-time diagram, the points that have the same time values. Two events that are simultaneous in one → inertial frame are not, in general, simultaneous in another inertial reference frame moving relative to the first. → relativity of simultaneity. Compare → synchronous.

From L.L. simultaneus, from L. simul "at the same time" + -taneous, abstracted from → spontaneous.

Hamzamân, from ham-, → syn- + zamân, → time.

In trigonometry, the function of an acute angle of a right triangle represented by the ratio of the opposite side to the hypotenuse.

Greek mathematicians were not aware of the advantages of sine and instead used chord. The invention of this function is a great Indian contribution. It seems that Aryabhata (c. AD 500) was the first who coined a term in Skt. for this concept: árdha-jiyā- "half chord," which was later shortened to jiyā- "chord." This Skt. word was subsequently loaned in Ar. and corrupted to jayb (جیب). Later on Gerard of Cremona (1114-1187), who translated Ar. scientific texts in L., took the corrupted Skt. form jayb for Ar. jayb "pocket, bundle, bosom, fold," and translated it to L. sinus "pocket, fold, curve." The Skt. jiyā- "chord, bow-string;" is cognate with Av. jiiā- "bow-string;" Pers. zeh "chord, string;" → zij "astronomical table;" PIE base *g^whi- "thread, tendon" (from which derive also Gk. bios "bow;" L. filum "thread;" Russ. žca "thread").

Sinus loanword from Fr., as above.

A periodic oscillation that is defined by the function y = sin x.

→ sine; → wave.

Only one in number; one only; unique; sole.

M.E., from O.Fr. sengle "being one, separate," from L. singulus "one, individual, separate," from sim- (stem of simplus) + diminutive suffix, → -ule.

Tak"single, alone," related to tâq "odd, single," tâ, tâh "piece, part; fold, plait, ply;" Mid.Pers. tak "single," tâg, tâk, tâi "unit, piece."

A type of scattering where photons are scattered only once. Single scattering dominates in → optically thin media, since photons have a high probability of exiting the medium (e.g., a thin cloud) before being scattered again.

→ single; → scattering.

A radio astronomical observation which uses only one antenna, in contrast to interferometric observations.

→ single; → dish; → observation.

A → spectroscopic binary in which only one set of → spectral lines is detectable. The binary nature of the system is deduced from the fact that the spectral lines exhibit periodic → Doppler shifts due to orbital motions in the system. Same as → SB1 binary. See also: → double-lined binary.

→ single; → line; → binary.

A single unit; an unpaired or separate item. → doublet; → octet; → quadruplet.

From → single + -et diminutive suffix, M.E. from O.F. -et (masc.), -ette (fem.).

Taktâyé, literally "single-folded," from tak, → single, + -tâyé, from tâ- "fold, plait, ply; piece, part;" Mid.Pers. tâg "piece, part" + -yé nuance suffix.

In atomic physics, the electronic state of an atom or molecule for which the total → spin angular momentum is zero.

→ singlet; → state.

An atom that has lost one electron and has become a positive ion.

→ single; → ionized; → atom.

A carbon atom → singly ionized by a photon of energy 11.3 eV. The ion C⁺ emits a → fine-structure line (²P_3/2→ ²P_1/2) at 157.7 μm when excitation conditions are satisfied (critical density ~ 3 x 10³ cm^-3). In → photodissociation regions, [C II] 157.7 μm is a major cooling line for regions exposed to significant → far ultraviolet (FUV) photon fluxes. In Galactic → H II regions, as well as in the central regions of external galaxies, the luminosity of the [C II] line is typically ~ 0.05-0.5% of the FUV luminosity and correlates well with → carbon monoxide (CO) line intensities.

→ single; → ionized; → carbon.