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Return to Terminology
U
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- Ullage
- The empty volume of a propellant tank which is not occupied by
fuel or oxidizer.
- Ultrasonics
- Ultrasonics is the study and application of Sound Waves with
frequencies greater than 20,000 cycles per second, i.e., beyond the range of human
hearing. Ultrasounds are commonly produced by piezoelectric transducers. They are used for
nondestructive testing, and for the cleaning of fine machine parts and surgical
instruments. In medicine, Ultrasound devices are used to examine internal organs without
surgery. Ultrasonic whistles are audible to dogs and are used to summon them.
- Ultrasound
- Ultrasound, in medicine, a technique that uses sound waves to
study hard-to-reach body areas. In scanning with ultrasound, high-frequency sound waves
are transmitted to the area of interest and the returning echoes recorded. First developed
in World War II to locate submerged objects, the technique is now widely used in virtually
every branch of medicine, e.g., in obstetrics to study the fetus, in cardiology to detect
heart damage, in ophthalmology to detect retinal problems. It is noninvasive, involves no
radiation, and avoids the possible hazards—such as bleeding, infection, or reactions
to chemicals—of other diagnostic methods.
- Ultraviolet Radiation
- Ultraviolet radiation is invisible Electromagnetic Radiation
with frequencies (about 1015 to 1018 Hz) between that of visible violet light and X rays;
it ranges in wavelength from about 400 to 4 nanometers. Ultraviolet (UV) radiation can be
detected by the Fluorescence it induces in certain substances and by its blackening of
photographic film. Most of the UV component of sunlight is absorbed by the Ozone layer of
the atmosphere. UV radiation can also be produced artificially in arc lamps. Vitamin D in
humans is produced by the action of UV radiation on ergosterol, a substance present in the
human skin.
- Unconfined Detonation Velocity
- The detonation velocity of an explosive material without
confinement, for example, a charge fired in the open.
- Underwriters Laboratory, Inc. (UL)
- A nationally recognized incorporated testing laboratory
qualified and equipped to conduct the necessary tests to determine compliance with
appropriate standards and the satisfactory performance of materials or equipment in actual
usage.
- Uranium
- uranium (y-rä´në-m) (U), radioactive metallic
element, discovered in oxide form in Pitchblende by M.H. Klaproth in 1789. A silver-white,
hard, dense, malleable, ductile, highly reactive metal in the Actinide
series it occurs naturally as a mixture of three Isotopes. Because of a constant decay
rate, the age of uranium samples can be estimated (v Dating).
The rare uranium-235 isotope is the only naturally occurring fission fuel for Nuclear
Energy. Breeder reactors convert the abundant but nonfissionable uranium-238 into
fissionable plutonium-239. Uranium-235 and plutonium-239 are also practicable fissionable
nuclei for Atomic Bombs. Element;
Nuclear Reactor; Periodic Table; Radioactivity.
- U.S. Bureau of Mines (USBM)
- A bureau of the Department of Interior active in promoting
safety in coal mines and in carrying out broad programs in mining and related fields.
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