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magnetized, all the magnetic domains are aligned, or oriented in the same direction. When it is
demagnetized, the magnetic domains are knocked out of alignment, and their magnetic fields cancel so
there is no overall magnetic field.
demand oxygen system (breathing oxygen system). An oxygen system installed in an aircraft and used
by the flight crew when flying at high altitude. The demand system meters oxygen from the regulator to the
mask only when the user inhales, and the flow of oxygen is shut off during exhale.
A demand oxygen system is much more economical of the oxygen supply than a continuous-flow
system.
demodulate (telecommunications). To remove the modulation from a telecommunicated signal.
When computer data is transmitted by telecommunications, it is changed into audible tones, or
modulated, so it will pass it over the telephone lines. At the receiving computer, the data is demodulated
(the modulation is removed), and the data is changed back into its digital form.
demodulation (radio signal). The production inside a radio receiver of an audio-frequency AC signal that
follows the modulation on a radio-frequency carrier. Audio-frequency information or music is used to
change the amplitude or frequency of the RF carrier wave in the radio transmitter.
When the modulated carrier is picked up by the receiver, it is demodulated. Changes in the
amplitude or frequency of the carrier produce an audio-frequency AC that follows these changes.
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Page 182
demulsibility. The ability of an oil-water emulsion to separate into its components of water and oil.
demulsifier. A chemical, physical, or electrical system that either breaks down a liquid-in-liquid emulsion
or keeps such an emulsion from forming.
denatured alcohol. Ethyl, or grain, alcohol that has been treated with some type of additive to make it unfit
for humans to drink.
denier. A measure of the fineness of the yarns in a fabric.
denim. A tough, heavy-duty fabric used for making work clothing. Denim is woven with colored threads
for the warp (the threads that run the length of the fabric) and white threads for the fill (the threads that run
across the fabric).
denominate number. A number that has a unit of measurement with it. Three inches, six minutes, and 360
degrees are all denominate numbers.
denominator (mathematical term). The part of a common fraction below the line. The denominator
shows the number of parts the whole unit is divided into. In the common fraction 9/16, the denominator is
16. The whole unit is divided into 16 equal parts, and this fraction uses only nine of them.
density. A measure of the amount of mass in a unit volume. An example is the amount of mass in a cubic
foot, cubic inch, or cubic centimeter. Density is usually expressed in such units as pounds per cubic foot or
grams per cubic centimeter.
density altitude. The altitude in standard air at which the density is the same as that of the existing air.
Density altitude is found by using a computer or chart to correct pressure altitude for nonstandard air
temperature. Density altitude is used for computing the performance of an aircraft and its engines.
density ratio (σ). The ratio of the density of the air at a given altitude to the density of the air at sea level
under standard conditions.
dent. A depression (usually smooth) in the surface of a material caused by the part being struck or pressed
on by some outside object. A dent, unlike a gouge, removes none of the material.
departure center (air traffic control). The ARTCC having jurisdiction for the airspace that generates a
flight to the impacted airport.
departure control (air traffic control). The function of an approach control facility that provides air
traffic control service for departing IFR and, under certain conditions, VFR aircraft.
departure sequencing program (air traffic control). A program designed to assist in achieving a
specified interval over a common point for departures.
depletion area (semiconductor term). The area on either side of the junction in a semiconductor device in
which the majority carriers have been pulled away and ionic charges left.
When the junction is forward-biased, the depletion area is very small. But when the junction is
reverse-biased, the depletion area is large.
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
Page 183
depolarization (electrochemical cell condition). Removal of the hydrogen gas which forms on the
positive material inside an electrochemical cell by absorbing it into one of the materials mixed with the
electrolyte.
If the cell is not depolarized, the hydrogen gas will form an insulation on the positive material and
　
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