talâ (#), zarr (#)
A yellow, → ductile → metal which occurs naturally in veins and alluvial deposits associated with → quartz or → pyrite; symbol Au (L. aurum "shining dawn"). → Atomic number 79; → atomic weight 196.9665; → melting point 1,064.43 °C; → boiling point 2,808 °C; → specific gravity 19.32 at 20 °C. Like other → chemical elements the gold found on Earth has an → interstellar origin. However, the new-born Earth was too hot and most of the molten gold, mixed with → iron, sank to its center to make the core during the first tens of millions of years. The removal of gold to the → Earth's core should have left the Earth's crust depleted of gold. Nevertheless, the precious metal is tens to thousands of times more abundant in the → Earth's mantle than predicted. One explanation for this over-abundance is the → Late Heavy Bombardment. Several hundred million years after the core formation a flux of → meteorites enriched the → Earth's crust with gold (Willbold et al., 2011, Nature 477, 195).
M.E., from O.E. gold, from P.Gmc. *gulth- (cf. O.H.G. gold, Ger. Gold, Du. goud, Dan. guld, Goth. gulþ), from PIE base *ghel-/*ghol- "yellow, green;" cf. Mod.Pers. zarr "gold," see below.
Talâ "gold," variants tala, tali.
Fr.: conjecture de Goldbach
Every number greater than 2 is the sum of two → prime numbers. Goldbach's number remains one of the most famous unsolved mathematical problems of today.
Named after the German mathematician Christian Goldbach (1690-1764); → conjecture.
adad-e zarrin (#)
Fr.: nombre d'or
1) The number giving the position of any year in the lunar or
→ Metonic cycle of about 19 years.
Each year has a golden number between 1 and 19. It is found by adding
1 to the given year and dividing by 19; the remainder in the division
is the golden number. If there is no remainder the golden number
is 19 (e.g., the golden number of 2007 is 13).
Fr.: nombre d'or
If a line segment is divided into a larger subsegment (a) and a smaller subsegment (b), when the larger subsegment is related to the smaller exactly as the whole segment is related to the larger segment, i.e. a/b = (a + b)/a. The golden ratio, a/b is usually represented by the Greek letter φ. It is also known as the divine ratio, the golden mean, the → golden number, and the golden section. It was believed by Greek mathematicians that a rectangle whose sides were in this proportion was the most pleasing to the eye. Similarly, the ratio of the radius to the side of a regular → decagon has this proportion. The numerical value of the golden ratio, given by the positive solution of the equation φ2 - φ - 1 = 0, is φ = (1/2)(1 + √5), approximately 1.618033989. The golden ratio is an → irrational number. It is closely related to the → Fibonacci sequence.
Fr.: classification de Goldschmidt
A → geochemical classification scheme in which → chemical elements on the → periodic table are divided into groups based on their → affinity to form various types of compounds: → lithophile, → chalcophile, → siderophile, and → atmophile. The classification takes into account the positions of the elements in the periodic table, the types of electronic structures of atoms and ions, the specifics of the appearance of an affinity for a particular → anion, and the position of a particular element on the → atomic volume curve.
Developed by Victor Goldschmidt (1888-1947); → classification.
Fr.: équation de Taylor-Goldstein
Fluid mechanics: A second order differential equation that governs the vertical structure of a perturbation in a stratified parallel flow.
Named after G. I. Taylor (Effect of variation in density on the stability of superposed streams of fluid, 1931, Proc. R. Soc. Lond. A, 132, 499), → Taylor number, and S. Goldstein (On the stability of superposed streams of fluids of different densities, 1931, Proc. R. Soc. Lond. A, 132, 524); → equation.