A physical quantity that describes the rate of change of temperature
with displacement in a given direction from a given reference point.
Same as → thermal gradient.

Meteo.: A reversal in the normal temperature decrease, the temperature
rising with increased elevation in the atmosphere instead of falling.
A layer in which temperature increases with altitude.

A temperature scale, measured in → kelvin (K),
that is related to the energy possessed by matter; it was formerly known as
→ absolute temperature.
The zero point on the scale (0 K) is absolute
zero. Thermodynamic temperature can be converted to temperature on
the → Celsius scale
by subtracting 273.15.

In celestial mechanics, a combination of orbital elements
commonly used to distinguish between comets and asteroids.
Objects whose Tisserand's parameter
value is smaller than 3 are considered to be dynamically cometary, and those with a value
larger than 3 asteroidal. Also called Tisserand's invariant.

Named after François Félix Tisserand (1845-1896), French astronomer, Director of the
Paris Observatory (1892).

tolerance

رواداری

ravâdâri (#)

Fr.: tolérance

The maximum permissible error or variation in a dimension of an object.

M.E., from O.Fr. tolerance, from L. tolerantia "endurance,"
from tolerans, pr.p. of tolerare "to bear, endure, tolerate."

Ravâdâri, noun from ravâdâr "consenter; judging right; lawful,"
from ravâ "admissible; allowable; tolerated" (from raftan
"to go, walk; to flow;"
Mid.Pers. raftan, raw-, Proto-Iranian *rab/f-
"to go; to attack" + -dâr
"having, possessor" (from dâštan "to have, to possess," Mid.Pers. dâštan,
O.Pers./Av. root dar- "to hold, keep back, maitain, keep in mind,"
Skt. dhr-, dharma- "law,"
Gk. thronos "elevated seat, throne,"
L. firmus "firm, stable," Lith. daryti
"to make," PIE *dher- "to hold, support").

trilateration

سهبربندی

sebarbandi

Fr.: trilatération

A geometrical method in land surveying for the determination of the relative
position of points. In contrast to → triangulation,
trilateration involves measuring the lengths of the three sides of
touching or overlapping triangles and not their angles.

A linear operator whose inverse is its → adjoint.
In addition to → Hermitian operators,
unitary operators constitute a
fundamentally important class of quantum-mechanical operators.

1) An act of uttering; a spoken word, statement, or vocal sound.
2) Something uttered; a word or words uttered; a cry, animal's call, or the like.
3) Linguistics: Any speech sequence consisting of one or more
words and preceded and followed by silence: it may be coextensive with
a sentence (Dictionary.com).

The mean temperature at which a gravitationally → bound system
would satisfy the → virial theorem.
For a system of mass M and radius R with constant density,
the gravitational energy per unit mass is W = GM/R. The kinetic energy per unit mass is
E = (3/2)kT_{vir}/μ, where k is
→ Boltzmann's constant and μ
the mean molecular weight. According to the virial theorem, E = W/2,
which leads to the virial temperature
T_{vir} = (1/3)(GM/kR).

One of the fundamental forces of nature that accounts for some particle
interaction, such as → beta decay
(→ radioactivity), the decay of free
→ neutrons, → neutrino
interactions, and so forth. It is short-ranged, dominating
at distances of 10^{-16} cm and occurs at a rate
slower than that of the → strong interaction
by a factor of about 10^{-13},
hence its name. Although the weak interaction also includes interactions in which
no neutrinos are emitted, neutrino emission accompanies all weak interactions of interest to
astrophysics. Weak interaction plays an important role in the evolution of the stars from
birth to death. For example, the → proton-proton reaction
is a weak interaction. Also called → weak force or
→ weak nuclear force.