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. Zarr "gold;" Mid.Pers. zarr;
Av. zaranya-, zarənu- "gold;" O.Pers. daraniya- "gold;"
cf. Skt. hiranya- "gold;" also Av. zaray-, zairi- "yellow, green;"
Mod.Pers. zard "yellow;" Skt. hari- "yellow, green;"
Gk. khloe literally "young green shoot;" L. helvus "yellowish, bay;"
Rus. zeltyj "yellow;" P.Gmc. *gelwaz; Du. geel;
Ger. gelb; E. yellow.

Goldbach's conjecture

هاشن ِ گلدباخ

hâšan-e Goldbach

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.

golden number

عدد ِ زرّین

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).
2) Same as → golden ratio.

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 φ^{2} - 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.

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.

Taylor-Goldstein equation

هموگش ِ تیلر-گلدشتاین

hamugeš-e Taylor-Goldstein

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.