18WuD2x

secular equilibrium • selective fading 615
is decaying as fast as the second substance is being
formed.
secular variation A slow change in the intensity of
the terrestrial magnetic field.
secure mode In a security system, the condition of
being fully activated.
securite In radiotelephony, a spoken word (pronounced
say-kyoor-ee-tay) identifying a transmission
concerning safety. Equivalent to TT in
radiotelegraphy.
security code 1. A set of alphanumeric characters
(letters and/or numbers) or switch settings that
activates or deactivates a security system. 2. See
PASSWORD.
security robot In a smart home, a robot that assists
in protection of a home or business, and its
occupants, from intrusion, burglary, or attack. If
an intruder enters the property, the security
robot might drive the offender away or detain the
offender until police arrive. The robot might employ
iris-print detection or facial feature detection
to identify an intruder from a distance. The robot
would be linked to the home computer via a
broad-bandwidth, high-speed wireless system.
Compare SENTRY ROBOT. Also see SMART
HOME OR BUSINESS.
security system A set of electronic (and sometimes
also electromechanical) devices designed to
do one or more of the following: restrict access to
a premises or computer system, detect abnormal
conditions, detect unauthorized entry, alert human
operators of abnormal conditions, alert owners
and/or authorities of unauthorized entry to a
premises, and (in some cases) provide physical
protection of property.
Seebeck effect The development of an electromotive
force in a junction of two dissimilar metals
(a thermocouple) when the temperature of the
junction is different from that of the rest of the
metal.
Seebeck emf The electromotive force resulting
from the Seebeck effect.
seed crystal A small single crystal from which a
larger single crystal (e.g., germanium or silicon) is
grown. Also see CZOCHRALSKI METHOD.
seeing-eye robot A robot that serves in the capacity
of a seeing-eye dog, to help visually impaired
people in their daily activities.
seek See SEARCH.
seek area An area of direct-access storage to which
are assigned specific records and from which the
records can be accessed quickly.
segment 1. The portion of a line or curve lying between
two points. 2. See PROGRAM SEGMENT.
segmental meter An expanded-scale meter (see
SCALE EXPANSION).
segmented encoding law An approximation of a
smooth encoding law, done by means of linear
partitions or segments. The greater the number of
segments, the more accurate the approximation.
segmenting See PARTITIONING.
segment mark A character indicating the division
between tape file sections.
segue (Pronounced SEG-way.) A smooth transition
from one sound or channel to another (e.g., between
musical selections in a radio broadcast).
The first selection decreases in volume as the second
selection increases. There is some overlap.
Seignette salt See ROCHELLE SALT.
seismic detector A vibration sensor used in some
types of intrusion-detection systems.
seismogram A record produced by a SEISMO-
GRAPH.
seismograph An instrument for detecting and
recording earth tremors. Indicates the direction,
magnitude, and time of a quake.
seismometer See SEISMOGRAPH.
seismoscope An instrument that shows the occurrence
and time of an earthquake. Compare SEIS-
MOGRAPH.
select To accept or separate a unit, quantity, or
course of action from all those available (in a
group, mixture, or series).
selectance 1. For a resonant circuit, the ratio
Er/Ex, where Er is the voltage at resonance, and
Ex is the voltage at a specified nonresonant frequency.
2. For a receiver, the figure S2/S1, where
S1 is the sensitivity of the receiver in a given frequency
channel, and S2 is the sensitivity in another
specified channel.
selected mode In an encoder, a mode in which one
output is read and the others are ignored.
selective Pertaining to a device or system, such as
a radio receiver, with a high degree of SELECTIV-
ITY.
selective absorption The attenuation or absorption
of some frequencies or bands of frequencies,
with little or no attenuation at other frequencies
or bands of frequencies.
selective amplifier An amplifier that can be
tuned, with the desired degree of sharpness, to a
single frequency or band of frequencies. Radiofrequency
amplifiers are generally tuned by
means of inductance-capacitance (LC) circuits;
audio-frequency amplifiers are usually tuned by
means of resistance-capacitance (RC) circuits.
selective calling The calling, alerting, or alarming
of a desired station without interfering with other
stations.
selective compliance assembly robot arm Abbreviation,
SCARA. An electromechanical device designed
especially for use in assembly lines. It
uses cylindrical coordinate geometry to allow precise,
programmable movements in three dimensions.
selective dump In computer operations, a dump
(see DUMP) affecting a small, specific memory
area.
selective fading Fading caused by propagation
conditions, whose effects differ at slightly different
frequencies. In an amplitude-modulated signal,
this effect causes the sidebands and carrier