Fr.: chauffage photoÃ©lectrique
A heating process occurring in → diffuse molecular clouds which is believed to be the main heating mechanism in cool → H I regions. Far-ultraviolet (FUV) photons, in the energy range 6 eV <hν < 13.6 eV, expel electrons from → interstellar dust grains and the excess → kinetic energy of the electrons is converted into gas → thermal energy through → collisions. The high energy limit corresponds to the cut-off in the → far-ultraviolet (FUV) radiation field caused by the hydrogen absorption (hν = 13.6 eV), while the low energy limit corresponds to the energy needed to free electrons from the grains (hν ~ 6 eV). In the cold neutral medium (Tkin≥ 200 K) photoelectric heating accounts for most of the heating, the → X-ray and → cosmic ray heating rates (→ cosmic-ray ionization) being more than an order of magnitude smaller. In a relatively dense neutral medium (nH≥ 100 cm-3), where a significant fraction of carbon is in the neutral form, carbon ionization becomes an important heating source, but it is still not comparable to the photoelectric effect. The heating rate cannot be directly measured, but it can be estimated through observations of the [C II] line emission, since this is believed to be the main → coolant in regions where the photoelectric heating is dominant (See, e.g., Juvela et al., 2003, arXiv:astro-ph/0302365).
Fr.: chauffage radiatif
The process by which temperature increases due to an excess of absorbed radiation over emitted radiation.
Scheat (β Peg)
The second-brightest star in the constellation → Pegasus. It is a giant star of spectral type M2.5 II-III whose magnitude varies between 2.3 and 2.7.
Scheat, from Ar. as-sâq "leg," erroneously taken from
the Ar. name of δ Aquarii as-sâq al-sâkib al-ma'
Asb-šâné, literally "the Horse's Shoulder," from asb→ horse + šâné "shoulder" (Lori šona, Kurd. šân, Gilaki cân, con), maybe related to Skt. skandhá- "shoulder, trunk of tree, bulk" (Pali khandha-, Ashkun kándä, Bashkarih kân, Tôrwâldi kan "shoulder"), from skand- "to jump, leap, spring out," skandati "he jumps;" cf. L. scandere "to climb."
Fr.: chaleur spécifique
1) The quantity of heat required to raise the temperature of 1 gm of
a substance through 1 °C. More generally, the → heat capacity
of a unit mass of a substance. For a homogeneous body it is expressed as:
C = dQ/M dT, where dQ is the quantity of heat transferred to a
mass of M to raise the temperature by dT. It is often convenient
to use the gram-mole as a unit of mass, → molar heat capacity.
Fr.: vapeur surchauffée
A vapor that has been heated above its boiling point temperature corresponding to the pressure.
The process in which a liquid is heated to a temperature higher than its boiling point, without boiling. Superheating is achieved by heating a homogeneous substance in a clean container, free of nucleation sites.
Fr.: chauffage par marées
The heating of the → interior of a → planet or → satellite due to the → friction caused by → tidal forces. For example, the huge tidal forces by → Jupiter heat its close satellite → Io, making it a seismically very active body.
Fr.: pont de Wheatstone
An device consisting of four → resistances in series, used to determine the value of an unknown electrical resistance when the other three resistances are known.
Named after Charles Wheatstone (1802-1875), British physicist, who extensively used the circuit (1843) but was not its inventor. Such an arrangement of four resistances was first used by Samuel Hunter Christie (1784-1865) in 1833; → bridge.