Page 105 - Electrical Engineering Dictionary

brightness adaptation the ability of the broadband a service or system requiring
human visual system (HVS) to shift the nar- transmission channels capable of supporting
row range in which it can distinguish differ- bit rates greater than 2 Mbit/s.
ent light intensities over a large span of lumi-
nances. This permits the overall sensitivity broadband antenna an antenna whose
of the HVS to gray levels to be very large characteristics (such as input impedance,
even though the number of gray levels that gain, and pattern) remain almost constant
it can simultaneously differentiate is fairly over a wide frequency band. Two such types
small. See also gray level, human visual of antennas are the log periodic and the bi-
system (HVS), luminance. conical.

brightness constancy the perception that broadband emission an emission having
an object has the same brightness despite a spectral distribution sufficiently broad in
large changes in its illumination. Thus a comparison to the response of a measuring
piece of paper appears to be approximately receiver.
as white in moonlight as in sunlight, even
though the illumination from the sun may broadband integrated services digital net-
be one million times greater than that from work (B-ISDN) a generic term that gen-
the moon. See also brightness, human visual erally refers to the future network infrastruc-
system (HVS), illumination, simultaneous ture that will provide ubiquitous availability
contrast. of integrated voice, data, imagery, and video
services.
Brillouin flow a stream of electron beam
emitted from an electron gun that is not ex- broadband system a broadband commu-
posed to a focusing magnetic field. nication system is one that employs a high
data transmission rate. In radio terminology
it implies that the system occupies a wide ra-
Brillouin frequency shift the frequency dio bandwidth.
shift that a wave experiences in undergoing
Brillouin scattering. The shift can be to either
broadcast (1)thetransferofdatatomulti-
lower or higher frequency, and typically has
ple receiver units simultaneously rather than
a value in the range 0.1 to 10 GHz. See also
to just one other subsystem.
Stokes scattering, anti-Stokes scattering.
(2) a bus-write operation intended to be
recognized by more than one attached device.
Brillouin laser acoustic maser in which
the amplification mechanism is considered to
broadcast channel a single transmit-
be Brillouin scattering.
ter, multiple receiver system in which iden-
tical information is transmitted to each re-
Brillouin scattering the scattering of ceiver, possibly over different channels. See
light from sound waves. Typically in Bril- also interference channel, multiple access
louin scattering the sound waves have fre- channel.
quencies in the range 0.1 to 10 GHz, whereas
in acousto-optics the sound waves have fre- broadcast channel allocations a fre-
quencies <0.1 GHz. Brillouin scattering can quency of a width prescribed by a nation’s
be either spontaneous or stimulated. See communications governing agency that are
also acousto-optic effect, spontaneous light standardized throughout the country for use
scattering, stimulated light scattering. in one-way electronic communication.

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2000 by CRC Press LLC