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

1) The act or process of transmitting. The fact of being transmitted.
2) The broadcasting of electromagnetic waves from one location to another, as from a transmitter to a receiver.

Verbal noun of → transmit.

The frequency range above the cutoff frequency in a waveguide or transmission line.

→ transmission; → band.

The ratio given by the → amplitude (or energy) of a transmitted wave divided by the amplitude (or energy) of the incident wave.

→ transmission; → coefficient.

A diffraction grating that has grooves ruled onto a transparent material so that a beam of light passed through the grating is partly split into spectral orders.

→ transmission; → grating.

A decrease in power in transmission from one point to another.

→ transmission; → loss.

An assembly of elements which are capable of functioning together to transmit power or signals.

→ transmission; → system.

The simultaneous emission of two photons whose sum of energies is equal to that of a single electron transition. The energy of each individual photon of the pair is not fixed, so that the spectrum of two-photon emission is continuous from the wavelength of that transition to infinity. In practice, there is a peak in wavelength distribution of the emitted photons. Two-photon emission is studied atomic physics with application in astrophysics, as it contributes to the continuum radiation from → planetary nebulae. It was recently observed in condensed matter and specifically in → semiconductors.

→ two; → photon; → emission.

A member of a class of cntral stars of planetary nebula, → CSPN, which have weaker and narrower emission lines than → Wolf-Rayet-like CSPNe (Tylenda et al. 1993, A&AS 102, 595).

→ weak; → emission; → line.